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Communication Systems/Wired Transmission

This page will discuss the topic of signal propagation through physical mediums, such as wires.

Transmission Line Equation
Many kinds of communication systems require signals at some point to be conveyed over copper wires.

The following analysis requires two assumptions:

 * • A transmission line can be decomposed into small, distributed passive electrical elements
 * • These elements are independent of frequency (i.e. although reactance is a function of frequency, resistance, capacitance and inductance are not)

These two assumptions limit the following analysis to frequencies up to the low MHz region. The second assumption is particularly difficult to defend since it is well known that the resistance of a wire increases with frequency because the conduction cross-section decreases. This phenomenon is known as the skin effect and is not easy to evaluate.

 * [[Image:transmission_line.gif]]

The purpose behind the following mathematical manipulation is to obtain an expression that defines the voltage (or current) at any time (t) along any portion (x) of the transmission line. Later, this analysis will be extended to include the frequency domain.

Recall the characteristic equations for inductors and capacitors:

 * $$ v = L\frac$$   and    $$ i = C\frac$$

Kirchoff's Voltage Law
Kirchoff's voltage law (KVL) simply states that the sum of all voltage potentials around a closed loop equal zero. Or in other words, if you walked up a hill and back down, the net altitude change would be zero.

 * Applying KVL in the above circuit, we obtain:

 * $$ v\left( {x,t} \right) = R\Delta xi\left( {x,t} \right) + L\Delta x\frac\left( {x,t} \right) + v\left( {x + \Delta x,t} \right)$$

 * Rearranging:

 * $$ v\left( {x,t} \right) - v\left( {x + \Delta x,t} \right) = R\Delta xi\left( {x,t} \right) + L\Delta x\frac\left( {x,t} \right)$$

 * But the LHS (left hand side) of the above equation, represents the voltage drop across the cable element $$\Delta v$$, therefor:

 * $$\Delta v = R\Delta xi\left( {x,t} \right) + L\Delta x\frac\left( {x,t} \right)$$

 * Dividing through by $$\Delta x$$, we obtain:

 * $$\frac = Ri\left( {x,t} \right) + L\frac\left( {x,t} \right)$$

 * The LHS is easily recognized as a derivative. Simplifying the notation:

 * $$\frac = Ri + L\frac$$

This expression has both current and voltage in it. It would be convenient to write the equation in terms of current or voltage as a function of distance or time.

Simplifying the Equation (trust me)
The first step in separating voltage and current is to take the derivative with respect to the position x (Equation 1):

 * $$\frac = R\frac + L\frac$$

 * The next step is to eliminate the current terms, leaving an expression with voltage only. The change in current along the line is equal to the current being shunted across the line through the capacitance C and conductance G. By applying KCL in the circuit, we obtain the necessary information (Equation 2):

 * $$\frac = Gv + C\frac$$

 * Taking the derivative with respect to time, we obtain (Equation 3):

 * $$\frac = G\frac + C\frac$$

 * Substituting (Equation 2) and (Equation 3) into (Equation 1), we obtain the desired simplification:

 * $$\frac = R\left[ {Gv + C\frac} \right] + L\left[ {G\frac + C\frac} \right]$$

 * Collecting the terms, we obtain:

 * The Transmission Line Equation for Voltage

 * $$\frac = RGv + \left( {RC + LG} \right)\frac + LC\frac$$

This equation is known as the transmission line equation. Note that it has voltage at any particular location x as a function of time t.

 * Similarly for current, we obtain:

 * The Transmission Line Equation for Current

 * $$\frac = RGi + \left( {RC + LG} \right)\frac + LC\frac$$

But we're not quite done yet.

Solving the Transmission Line Equation
Historically, a mathematician would solve the transmission line equation for v by assuming a solution for v, substituting it into the equation, and observing whether the result made any sense. An engineer would follow a similar procedure by making an “educated guess” based on some laboratory experiments, as to what the solution might be. Today there are more sophisticated techniques used to find solutions. In this respect, the engineer may lag behind the mathematician by several centuries in finding applications for mathematical tools.

To solve the transmission line equation, we shall guess that the solution for the voltage function is of the form:

 * $$ v\left( t \right) = e^{j\omega t} e^{ - \gamma x} $$

The first term represents a unity vector rotating at an angular velocity of $$\omega$$ radians per second, in other words, a sine wave of some frequency. The second term denotes the sinusoid being modified by the transmission line, namely its amplitude decaying exponentially with distance. If we let $$\gamma$$ be a complex quantity, we can also include any phase changes which occur as the signal travels down the line.

 * The sine wave is used as a signal source because it is easy to generate, and manipulate mathematically. Euler’s Identity shows the relationship between exponential notation and trigonometric functions:

 * Euler's Identity

 * $$ e^{j\omega t} = \cos \left( {\omega t} \right) + j\sin \left( {\omega t} \right)$$

 * Going back to our educated guess, we will let $$\gamma = \alpha  + j\beta$$, therefore:

 * $$ v\left( t \right) = e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x}  = e^{ - \alpha x} e^{\left( {\omega t - \beta x} \right)j} $$

 * The term $$ e^{ - \alpha x} $$ represents the exponential amplitude decay as this signal travels down the line. $$\alpha$$ is known as the attenuation coefficient and is expressed in Nepers per meter.

 * The term $$ e^{\left( {\omega t - \beta x} \right)j} $$ represents the frequency of the signal at any point along the line. $$\beta$$ component is known as the phase shift coefficient, and is expressed in radians per meter.

 * Substituting our educated guess

 * $$ v\left( t \right) = e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x}  $$

 * into the transmission line equation for voltage, we obtain:

 * $$\frac\left[ {e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} } \right] = RG\left[ {e^{j\omega t} e^{ - \left( {\alpha  + j\beta } \right)x} } \right] + \left( {RC + LG} \right)\frac{\partial }\left[ {e^{j\omega t} e^{ - \left( {\alpha  + j\beta } \right)x} } \right] + LC\frac\left[ {e^{j\omega t} e^{ - \left( {\alpha  + j\beta } \right)x} } \right]$$

This looks pretty intimidating, but if you can do basic differentials and algebra, you can do this!

Simplifying the Equation (trust me)
The idea now is to work through the math to see if we come up with a reasonable solution. If we arrive at a contradiction or an unreasonable result, it means that our educated guess was wrong and we have to do more experimenting and come up with a better guess as to how voltage and current travel down a transmission line.

Let's look at this equation one term at a time:

 * LHS = RHS Term 1 + RHS Term 2 + RHS Term 3

 * Starting with the left hand side (LHS) we get the following simplification:

 * $$\frac\left[ {e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} } \right] = \frac{\partial }\left[ { - \left( {\alpha  + j\beta } \right)e^{j\omega t} e^{ - \left( {\alpha  + j\beta } \right)x} } \right] = \left( {\alpha  + j\beta } \right)^2 e^{j\omega t} e^{ - \left( {\alpha  + j\beta } \right)x} $$

 * Believe it or not, the RHS Term 1 does not need simplifying.

 * Simplifying the RHS Term 2, we obtain:

 * $$\left( {RC + LG} \right)\frac{\partial }\left[ {e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} } \right] = \left( {RC + LG} \right)j\omega \left( {e^{j\omega t} e^{ - \left( {\alpha  + j\beta } \right)x} } \right)$$

 * Simplifying the RHS Term 3, we obtain:

 * $$ LC\frac\left[ {e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} } \right] = LC\frac{\partial }\left[ {j\omega e^{j\omega t} e^{ - \left( {\alpha  + j\beta } \right)x} } \right] =  - LC\omega ^2 e^{j\omega t} e^{ - \left( {\alpha  + j\beta } \right)x} $$

 * Let's put it all back together:

 * $$\left( {\alpha + j\beta } \right)^2 e^{j\omega t} e^{ - \left( {\alpha  + j\beta } \right)x}  = RG\left( {e^{j\omega t} e^{ - \left( {\alpha  + j\beta } \right)x} } \right) + \left( {RC + LG} \right)j\omega \left( {e^{j\omega t} e^{ - \left( {\alpha  + j\beta } \right)x} } \right) - LC\omega ^2 \left( {e^{j\omega t} e^{ - \left( {\alpha  + j\beta } \right)x} } \right)$$

 * Note that each of the four terms contain the expression $$ e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} $$.

 * Therefore we end up with:

 * $$\left( {\alpha + j\beta } \right)^2  = RG + \left( {RC + LG} \right)j\omega  - LC\omega ^2 $$

 * And this can be further simplified to:

 * Attenuation and Phase Shift Coefficients

 * $$\alpha + j\beta  = \gamma  = \sqrt {\left( {R + j\omega L} \right)\left( {G + j\omega C} \right)} $$

This result is not self contradictory or unreasonable. Therefore we conclude that our educated guess was right and we have successfully found an expression for attenuation and phase shift on a transmission line as a function of its distributed electrical components and frequency.

Lossless Transmission Line
Signal loss occurs by two basic mechanisms: signal power can be dissipated in a resistor [or conductance] or signal currents may be shunted to an AC ground via a reactance. In transmission line theory, a lossless transmission line does not dissipate power. Signals, will still gradually diminish however, as shunt reactances return the current to the source via the ground path. For the power loss to equal zero, R = G = 0. This condition occurs when the transmission line is very short. An oscilloscope probe is an example of a very short transmission line. The transmission line equation reduces to the voltage equation:

 * $$\frac = LC\frac$$

 * and the current equation:

 * $$\frac = LC\frac$$

To determine how sinusoidal signals are affected by this type of line, we simply substitute a sinusoidal voltage or current into the above expressions and solve as before, or we could take a much simpler approach. We could start with the solution for the general case:

 * $$\alpha + j\beta  = \gamma  = \sqrt {\left( {R + j\omega L} \right)\left( {G + j\omega C} \right)} $$

 * Let R = G = 0, and simplify:

 * $$\alpha + j\beta  = \sqrt {\left( {j\omega L} \right)\left( {j\omega C} \right)}  = \omega \left( {LC} \right)^2 j$$

 * Equating the real and imaginary parts:

 * $$\alpha = 0$$
 * $$\beta = \omega \sqrt {LC} $$

This expression tells us that a signal travelling down a lossless transmission line, experiences a phase shift directly proportional to its frequency.

Phase Velocity
A new parameter, known as phase velocity, can be extracted from these variables:

 * $$ V_p = \frac{1} = \frac{\omega }{\beta }$$ meters per second

Phase velocity is the speed at which a fixed point on a wavefront, appears to move. In the case of wire transmission lines, it is also the velocity of propagation., typically: 0.24c < Vp < 0.9c.

The distance between two identical points on a wavefront is its wavelength ($$\lambda$$) and since one cycle is defined as 2$$\pi$$ radians:

 * $$\lambda = \frac{\beta }$$ and $$ \omega  = 2\pi f$$

 * therefore:

 * $$ V_p = \lambda f$$

In free space, the phase velocity is 3 x 108 meters/sec, the speed of light. In a cable, the phase velocity is somewhat lower because the signal is carried by electrons. In a waveguide transmission line, the phase velocity exceeds the speed of light.

Distortionless Transmission Line
A distortionless line does not distort the signal phase, but does introduce a signal loss. Since common transmission lines are not super conductors, the signal will decrease in amplitude but retain the same shape as the input. This characteristic is essential for long cable systems.

Phase distortion does not occur if the phase velocity Vp is constant at all frequencies.

By definition, a phase shift of 2$$\pi$$ radians occurs over one wavelength $$\lambda$$.

 * Since

 * $$V_p = \lambda f\quad \quad \lambda  = \frac{\beta }\quad \quad f = \frac{\omega }$$

 * Then:

 * $$V_p = \frac{\beta } \times \frac{\omega } = \frac{\omega }{\beta }$$

This tells us that in order for phase velocity Vp to be constant, the phase shift coefficient $$\beta$$, must vary directly with frequency $$\omega$$.

 * Recall

 * $$\gamma = \sqrt {\left( {R + j\omega L} \right)\left( {G + j\omega C} \right)}  = \alpha  + j\beta $$

The problem now is to find $$\beta$$. This can be done as follows:

 * $$\gamma = \sqrt {\left( {\frac} \right)\left( {j\omega L} \right)\left( {\frac} \right)\left( {j\omega C} \right)}  = j\omega \sqrt {LC} \sqrt {1 + \frac{R}} \sqrt {1 + \frac{G}} $$

It may seem that we have lost $$\beta$$, but do not give up. The 2nd and 3rd roots can be expanded by means of the Binomial Expansion.

 * Recall:

 * $$\left( {1 + x} \right)^n = 1 + nx + \fracx^2  + \fracx^3  +  \cdots $$

 * In this instance n = 1/2. Since the contribution of successive terms diminishes rapidly, $$\gamma$$ is expanded to only 3 terms:

 * $$\gamma \approx j\omega \sqrt {LC} \left( {1 + \frac{1}{2}\frac{R} - \frac{1}{8}\left( {\frac{R}} \right)^2 } \right)\left( {1 + \frac{1}{2}\frac{G} - \frac{1}{8}\left( {\frac{G}} \right)^2 } \right)$$

This may seem complex, but remember it is only algebra and it will reduce down to simple elegance. Expanding the terms we obtain:

 * $$\gamma \approx j\omega \sqrt {LC} \left\{ \begin{array}{l}

1 + \frac{1}{2}\frac{G} - \frac{1}{8}\left( {\frac{G}} \right)^2 + \frac{1}{2}\frac{R} - \frac{1}{4}\frac \\ - \frac{1}\frac{R}\left( {\frac{G}} \right)^2 - \frac{1}{8}\left( {\frac{R}} \right)^2  \\ - \frac{1}\left( {\frac{R}} \right)^2 \frac{G} + \frac{1}\left( {\frac{R}} \right)^2 \left( {\frac{G}} \right)^2 \\ \end{array} \right\}$$

 * Since $$\gamma = \alpha  + j\beta $$, we merely have to equate the real and imaginary terms to find $$\beta$$.

 * $$\beta \approx \omega \sqrt {LC} \left\{ {1 + \underbrace {\frac{1}{8}\left( {\frac{G}} \right)^2  - \frac{1}{4}\frac + \frac{1}{8}\left( {\frac{R}} \right)^2 }_{{\rm{Difference}}\;{\rm{of}}\;{\rm{squares}}} + \underbrace {\frac{1}\left( {\frac{R}} \right)^2 \left( {\frac{G}} \right)^2 }_{{\rm{Very}}\;{\rm{small}}}} \right\}$$

 * Or

 * $$\beta \approx \omega \sqrt {LC} \left\{ {1 + \frac{1}{8}\left( {\frac{R} - \frac{G}} \right)^2 } \right\}$$

 * Note that if $$\frac{R} = \frac{G}$$ then $$\beta \approx \omega \sqrt {LC} $$

From this we observe that $$\beta$$ is directly proportional to $$\omega$$.

 * Therefore the requirement for distortionless transmission is:

 * RC = LG

 * This is one of the essential design characteristics for a broadband coax cable network.

If we equate the real terms, we obtain:

 * $$\alpha \approx \sqrt {RG} $$

So there is a reason to study algebra after all!

The Frequency Domain
Signal analysis is often performed in the frequency domain. This tells us how the transmission line affects the spectral content of the signals they are carrying.

To determine this, it is necessary to find the Fourier Transform of the transmission line equation. Recall:

 * $$\frac = RGv + \left( {RC + LG} \right)\frac + LC\frac$$

and recall (hopefully) the Fourier Transform (which converts the time domain to the frequency domain):

 * $$\mathbb{F}\left\{ {f\left( t \right)} \right\} = F\left( \omega \right) = \int\limits_{ - \infty }^\infty  {e^{ - j\omega t} f\left( t \right)dt}$$

To prevent this analysis from ‘blowing up’, we must put a stipulation on the voltage function namely, that it vanishes to zero at an infinite distance down the line. This comprises a basic boundary condition.

 * $${\text{let}}\quad v \to 0\quad {\text{as}}\quad x \to \infty$$

This stipulation is in agreement with actual laboratory experiments. It is well known that the signal magnitude diminishes as the path lengthens.

Likewise, a time boundary condition, that the signal was zero at some time in the distant past and will be zero at some time in the distant future, must be imposed.

 * $${\text{let}}\quad v \to 0\quad {\text{as}}\quad t \to \infty $$

Although engineers have no difficulty imposing these restrictions, mathematical purists, are somewhat offended. For this and other reasons, other less restrictive transforms have been developed. The most notable in this context, is the Laplace transform, which does not have the same boundary conditions.

Having made the necessary concessions in order to continue our analysis, we must find the Fourier Transform corresponding to the following terms:

 * $$\mathbb{F}\left\{ v \right\}\quad \quad \quad \mathbb{F}\left\{ {\frac

} \right\}\quad \quad \quad \mathbb{F}\left\{ {\frac } \right\}$$

 * $${\text{Let:}}\quad \quad \quad \mathbb{F}\left\{ v \right\} = V$$

 * Then applying the transform on the derivative, we obtain:

 * $$\mathbb{F}\left\{ {\frac

} \right\} = \int\limits_{ - \infty }^\infty {e^{ - j\omega t} \frac dt} $$

This equation can be solved by using integration by parts:

 * $$\int {u\,dv} = uv - \int {v\,du} $$

 * $${\text{let}}\quad u = e^{ - j\omega t} \quad \quad \quad \therefore du = - j\omega e^{ - j\omega t} $$

 * $${\text{and}}\quad dv = \frac\quad \quad \quad \therefore v = v$$

 * $$\therefore \mathbb{F}\left\{ {\frac

} \right\} = e^{ - j\omega t} \left. v \right|_{ - \infty }^\infty  - \int\limits_{ - \infty }^\infty  {v\left( { - j\omega e^{ - j\omega t} } \right)dt} $$

Applying the boundary conditions when t goes to infinity makes the 1st term disappear.

 * $$\therefore \mathbb{F}\left\{ {\frac

} \right\} = j\omega \int\limits_{ - \infty }^\infty {e^{ - j\omega t} v\,dt} $$

Note that the resulting integral is simply the Fourier Transform. In other words:

 * $$\mathbb{F}\left\{ {\frac

} \right\} = j\omega \mathbb{F}\left\{ v \right\} = j\omega V$$

 * similarly:

 * $$\mathbb{F}\left\{ {\frac

} \right\} = \left( {j\omega } \right)^2 \mathbb{F}\left\{ v \right\} = \left( {j\omega } \right)^2 V$$

We can now write the transmission line equation in the frequency domain:

 * $$\frac

= RGV + \left( {RC + LG} \right)j\omega V + LC\left( {j\omega } \right)^2 V$$

 * where:

 * $$V = V\left( \omega \right) = \mathbb{F}\left\{ {v\left( t \right)} \right\}$$

 * Rearranging the terms, we obtain:

 * $$\frac

= \left[ {RG + \left( {RC + LG} \right)j\omega + \left( {j\omega L} \right)\left( {j\omega C} \right)} \right]V$$

 * or

 * $$\frac

= \left[ {\left( {R + j\omega L} \right)\left( {G + j\omega C} \right)} \right]V$$

 * since:

 * $$\sqrt {\left( {R + j\omega L} \right)\left( {G + j\omega C} \right)} = \alpha  + j\beta  = \gamma $$

 * then

 * $$\frac = \gamma ^2 V$$

 * or

 * $$\frac - \gamma ^2 V = 0$$

This represents the most general form of the transmission line equation in the frequency domain. This equation must now be solved for V to observe how voltage (or current) varies with distance and frequency. This can be done by assuming a solution of the form:

 * $$V = \underbrace {Ae^{ - \gamma x} }_{{\text{forward}}\;{\text{wave}}} + \underbrace {Be^{\gamma x} }_{{\text{reverse}}\;{\text{wave}}}$$

These terms represent an exponential decay as the signal travels down the transmission line. If we ignore any reflections, assuming that the cable is infinitely long or properly terminated, this simplifies to:

 * $$V = V_0 e^{ - \gamma x} $$

To verify whether this assumption is correct, substitute it into the equation, and see if a contradiction occurs. If there is no contradiction, then our assumption constitutes a valid solution.

 * $$\fracV_0 e^{ - \gamma x} - \gamma ^2 V_0 e^{ - \gamma x}  = 0$$

 * $$\frac{\partial }\left( { - \gamma ^2 V_0 e^{ - \gamma x} } \right) - \gamma ^2 V_0 e^{ - \gamma x} = 0$$

 * $$\gamma ^2 V_0 e^{ - \gamma x} - \gamma ^2 V_0 e^{ - \gamma x}  = 0$$

 * $$0 = 0$$

Thus we validate the assumed solution. This tells us that in the frequency domain, the voltage or current on a transmission line decays exponentially:

 * $$V = V_0 e^{ - \gamma x} $$

 * where:

 * $$\gamma = \sqrt {\left( {R + j\omega } \right)\left( {G + j\omega } \right)}  = \left| \gamma  \right|\angle \varphi  = \alpha  + j\beta $$

 * $$\gamma = {\text{ propagation}}\;{\text{constant}}$$

 * $$\alpha = {\text{ attenuation}}\;{\text{coeficient}}$$

 * $$\beta = {\text{phase}}\;{\text{coefficient}}$$

In exponential notation, a sinusoid may be represented by a rotating unity vector, of some frequency:

 * $$e^{j\omega t} = \cos \omega t + j\sin \omega t$$

Note that the magnitude of this function is 1, but the phase angle is changing as a function of t.

 * If we let: $$V_0 = e^{j\omega t} $$

 * Then: $$V_0 = e^{j\omega t} e^{ - \gamma x}  = e^{j\omega t} e^{ - \left( {\alpha  + j\beta } \right)x}  = \underbrace {e^{ - \alpha x} }_{{\text{attenuation}}\;vs.\;x}\overbrace {e^{j\left( {\omega t - \beta x} \right)} }^{{\text{phase}}\;vs{\text{.}}\;t\;{\text{and}}\;x}$$

This result is quite interesting because it is the same solution for the transmission line equation in the time domain. The term $${e^{ - \alpha x} }$$ represents an exponential decay. The signal is attenuated as length x increases. The amount of attenuation is defined as:

 * Attenuation in Nepers: $$N = \left| {\ln e^{ - \alpha x} } \right| = \alpha x$$

 * Attenuation in dB: $$ = 20\log e^{ - \alpha x} \approx 8.68589\alpha x$$

This allows us to determine the attenuation at any frequency at any point in a transmission line, if we are given the basic line parameters of R, L, G, & C.

The term $${e^{j\left( {\omega t - \beta x} \right)} }$$ represents a rotating unity vector since:

 * $$e^{j\left( {\omega t - \beta x} \right)} = \cos \left( {\omega t - \beta x} \right) + j\sin \left( {\omega t - \beta x} \right)$$

The phase angle of this vector is $${\beta x}$$ radians.

Characteristic Impedance
The characteristic impedance of a transmission line is also known as its surge impedance, and should not be confused with its resistance. If a line is infinitely long, electrical signals will still propagate down it, even though the resistance approaches infinity. The characteristic impedance is determined from its AC attributes, not its DC ones.

Recall from our earlier analysis:


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Communication Systems/Wireless Transmission

This page will discuss Wireless EM wave propagation, and some basics about antennas.

Isotropic Antennas
An isotropic antenna radiates it's transmitted power equally in all directions. This is an ideal model; all real antennas have at least some directionality associated with them. However, it is mathematically convenient, and good enough for most purposes.

Power Flux Density
If the transmitted power is spread evenly across a sphere of radius R from the antenna, we can find the power per unit area of that sphere, called the Power Flux Density using the Greek letter Φ (capital phi) and the following formula:

 * $$\Phi = \frac{P_T}{4 \pi R^2}$$

Where $$P_T$$ is the total transmitted power of the signal.

Effective Area
The effective area of an antenna is the equivalent amount of area of transmission power, from a non-ideal isotropic antenna that appears to be the area from an ideal antenna. For instance, if our antenna is non-ideal, and 1 meter squared of area can effectively be modeled as .5 meters squared from an ideal antenna, then we can use the ideal number in our antenna. We can relate the actual area and the effective area of our antenna using the antenna efficiency number, as follows:

 * $$\eta = \frac{A_e}{A}$$

The area of an ideal isotropic antenna can be calculated using the wavelength of the transmitted signal as follows:

 * $$A = \frac{\lambda^2}{4 \pi}$$

Received Power
The amount of power that is actually received by a receiver placed at distance R from the isotropic antenna is denoted $$P_R$$, and can be found with the following equation:

 * $$P_R = \Phi_R A_e $$

Where $$\Phi_R$$ is the power flux density at the distance R. If we plug in the formula for the effective area of an ideal isotropic antenna into this equation, we get the following result:

 * $$P_R = \frac{P_T}{(4 \pi R / \lambda)^2} = \frac{P_T}{L_P}$$

Where $$L_P$$ is the path-loss, and is defined as:

 * $$L_P = \left( \frac{4 \pi R}{\lambda} \right)^2$$

The amount of power lost across freespace between two isotropic antenna (a transmitter and a receiver) depends on the wavelength of the transmitted signal.

Directional Antennas
A directional antenna, such as a parabolic antenna, attempts to radiate most of its power in the direction of a known receiver.

Here are some definitions that we need to know before we proceed:

 * Azimuth Angle:The Azimuth angle, often denoted with a θ (Greek lower-case Theta), is the angle that the direct transmission makes with respect to a given reference angle (often the angle of the target receiver) when looking down on the antenna from above.
 * Elevation Angle:The elevation angle is the angle that the transmission direction makes with the ground. Elevation angle is denoted with a φ (Greek lower-case phi)

Directivity
Given the above definitions, we can define the transmission gain of a directional antenna as a function of θ and φ, assuming the same transmission power:

 * $$G_T(\theta, \phi) = \frac{\Phi_{\theta,\ \phi}}{\Phi_{isotropic}}$$

Effective Area
The effective area of a parabolic antenna is given as such:

 * $$A_e = \eta \frac{\pi D^2}{4}$$

Transmit Gain

 * $$G_{max} = \frac{4 \pi A_e}{\lambda^2}$$

If we are at the transmit antenna, and looking at the receiver, the angle that the transmission differs from the direction that we are looking is known as Ψ (Greek upper-case Psi), and we can find the transmission gain as a function of this angle as follows:

 * $$G(\Psi) = \left( \frac{2J_1((\pi D / \lambda) sin(\Psi))}{sin(\Psi)} \right)^2 \left( \frac{\lambda}{\pi D} \right)^2$$

Where $$J_1(\ )$$ denotes the first-order bessel function.

Friis Equation
The Friis Equation is used to relate several values together when using directional antennas:

 * $$P_R = \frac{P_T G_T G_R}{L_P}$$

The Friis Equation is the fundamental basis for link-budget analysis.

Link-Budget Analysis
If we express all quantities from the Friis Equation in decibels, and divide both sides by the noise-density of the transmission medium, N0, we get the following equation:

 * $$C/N_0 = EIRP - L_P + (G_R/T_e) - k$$

Where C/N0 is the received carrier-to-noise ratio, and we can decompose N0 as follows:

 * $$N_0 = kTe$$

k is Boltzmann's constant, (-228.6dBW) and Te is the effective temperature of the noise signal (in degrees Kelvin). EIRP is the "Equivalent Isotropic Radiated Power", and is defined as:

 * $$EIRP = G_T P_T$$

To perform a link-budget analysis, we add all the transmission gain terms from the transmitter, we add the receive gain divided by the effective temperature, and we subtract Boltzmann's constant and all the path losses of the transmission.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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Communication Systems/Noncoherent Receivers

This page will discuss the mathematical basis, and the design of noncoherent receivers.


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Talk:Electric Vehicle Conversion/Powertrain

I am starting a website www.virtualelectriccar.com that we will build a usable electric car. We will have a panel of experts in many fields such as, solar, electric, inverters, wind, electric motors, and many more. Plus, we will encourage the general public to give their input. Each week or so we will add a new part to the electric car. The car is based on exchange, not storage. It will be interesting.

Sincerely, Carl Peterson, President Mega 1 Marketing Group, Inc. E-Mail: mega-1@hotmail.com


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User talk:Sbower~enwikibooks

Votes for undeletion
The BDSM book that you started is presently in the "Votes for undeletion" process. It was originally deleted by an administrator, and we have temporarily undeleted it again while the Wikibooks community at large discusses whether to restore the book.

The main concern seems to be that BDSM is somehow "original research". However I checked; BDSM does not seem to be a new invention. My own concern is that I do not want how-to guides about a practice as dangerous as BDSM, even guides oriented toward making it safer.

Once Wikibooks had a "Manual of Crime", all about arson, carjacking, rape, and such. We deleted it. Then we had "How to cheat on tests and examinations", about how to be academically dishonest. We deleted it. We had a page about how to be an Internet troll. We deleted it. BDSM (which was unknown to me before it appeared on Wikibooks) does not have the same problem, but it is risky and dangerous, with entertainment as its only goal.

Further, if the intent is to write mostly for Wikipedia (in BDSM and linked articles), and only submit leftovers to Wikibooks, then the BDSM book would not have fared well here. What I suggest you do, if you want to write BDSM content on a wiki other than Wikipedia, is to try either of the two wikis linked from the bottom of the BDSM page. --Kernigh 23:16, 3 May 2006 (UTC)

Your account will be renamed
Hello,

The developer team at Wikimedia is making some changes to how accounts work, as part of our on-going efforts to provide new and better tools for our users like cross-wiki notifications. These changes will mean you have the same account name everywhere. This will let us give you new features that will help you edit and discuss better, and allow more flexible user permissions for tools. One of the side-effects of this is that user accounts will now have to be unique across all 900 Wikimedia wikis. See the announcement for more information.

Unfortunately, your account clashes with another account also called Sbower. To make sure that both of you can use all Wikimedia projects in future, we have reserved the name Sbower~enwikibooks that only you will have. If you like it, you don't have to do anything. If you do not like it, you can pick out a different name.

Your account will still work as before, and you will be credited for all your edits made so far, but you will have to use the new account name when you log in.

Sorry for the inconvenience.

Yours, Keegan Peterzell Community Liaison, Wikimedia Foundation 23:43, 17 March 2015 (UTC)

Renamed
 This account has been renamed as part of single-user login finalisation. If you own this account you can |log in using your previous username and password for more information. If you do not like this account's new name, you can choose your own using this form after logging in: . -- Keegan (WMF) (talk) 05:28, 19 April 2015 (UTC)

title: User talk:Sbower~enwikibooks


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Template:GNU C Compiler Internals/GEM Framework

Hooks
GEM framework is designed to facilitate development of compiler extensions. The idea of GEM is similar to the idea of Linux Security Modules (LSM), a project that defines hooks throughout Linux kernel that allow one to enforce a security policy.

GEM defines a number of hooks throughout GCC's source code. It is implemented as a patch to GCC. With GEM, a compiler extension is developed as a stand-alone program. It is compiled into a dynamically-linked module which is specified as the command line argument when GCC is invoked. GCC loads the module and calls its initialization function. The module then registers its hooks that are call-back functions in GCC.

In addition to the compiler hooks, GEM provides macros and functions that simplify extension development. In this chapter we will first introduce the hooks that GEM framework adds to GCC. Then we describe the typical issues in extension programming.

The project home page is at http://research.alexeysmirnov.name/gem

GEM adds several hooks throughout GCC source code. New hooks are added to GEM as necessary.

 * Hook gem_handle_option to function handle_option which processes each command line option. The hook takes the current option as its argument. If the hook returns value GEM_RETURN then GCC ignores the option.

 * Hook gem_c_common_nodes_and_builtins which is called after all standard types are created. The GCC extension can create additional types.

 * Hook gem_macro_name allows one to save the name of the macro being defined. Another GEM hook gem_macro_def is called when the macro definition is parsed. Using the macro name of the new macro definition it is possible to re-define the macro. This hook is added to function create_iso_definition.

 * Hooks gem_start_decl and gem_start_function are called when a function or variable declaration/definition starts.

 * Hook gem_build_function_call allows one to modify the name and the arguments of a function call.

 * Hook gem_finish_function is inserted to finish_function which is called from from grammar file. The compiler extension receives the function body of the function before it is translated into RTL.

 * Hooks gem_output_asm_insn and gem_final_start_function are added to function output_asm_insn which is called for each instruction of the assembly code and function final_start_function called when the assembly code is written to the file, respectively. The former hook receives the text that is written to the file which allows it to modify the output. The latter hook can modify function's prolog.

Traversing an AST
When the function's AST is constructed one can instrument it. GEM's gem_finish_function hook receives the AST of a function. The idea is to traverse the AST and instrument the AST nodes as necessary. Function walk_tree takes the AST, the callback function, the optional data, NULL by default, and the walk_subtrees parameter, NULL by default. The callback function is called for each node of the AST before the operands are traversed. If the callback function modifies the walk_subtree variable then the operands are not processed.

The following code demonstrates the idea:

static tree walk_tree_callback(tree *tp, int *walk_subtrees, void *data) { tree t=*tp; enum tree_code code = TREE_CODE(t); switch (code) { case CALL_EXPR: instrument_call_expr(t); break; case MODIFY_EXPR: instrument_modify_expr(t); break; }  }   walk_tree(&t_body, walk_tree_callback, NULL, NULL);

Instrumenting an AST
In this section we describe functions that create new tree nodes and how to add the new nodes to an AST.

When to Instrument
In this section we will describe when each of GEM hooks is used.

Function Prolog/Epilog
The assembly instructions are written to the assembly file:

#define OUTPUT_ASM_INST(inst) \ p=inst;                    \ putc('\t', asm_out_file);  \ while (*p++) putc(p, asm_out_file); \ putc('\n', asm_out_file); OUTPUT_ASM_INST("pushl %%eax"); OUTPUT_ASM_INST("popl %%eax");


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Template:GNU C Compiler Internals/Instrumenting an AST 3 4

The walk_tree callback function can instrument the AST. Functions build1 and build construct new tree nodes. The former function takes one operand, the latter one takes more then one operand. The following code computes the address of the operand, same as '&' C operator:

t = build1(ADDR_EXPR, TREE_TYPE(t), t);

The following example refers to an array element arr[0]:

t = build(ARRAY_REF, integer_type_node, arr, integer_zero_node);

The following example builds an integer constant:

t = build_int_2(value, 0);

Building string constant is more difficult. The following example demonstrates the idea:

tree gem_build_string_literal(int len, const char *str) { tree t, elem, index, type; t = build_string (len, str); elem = build_type_variant (char_type_node, 1, 0); index = build_index_type (build_int_2(len-1, 0)); type = build_array_type (elem, index); T_T(t) = type; TREE_READONLY(t)=1; TREE_STATIC(t)=1; TREE_CONSTANT(t)=1; type=build_pointer_type (type); t = build1 (ADDR_EXPR, type, t); t = build1 (NOP_EXPR, build_pointer_type(char_type_node), t); return t;  }

To build a function call one needs to build the list of arguments. Then the CALL_EXPR is constructed:

t_arg1 = build_tree_list(NULL_TREE, arg1); t_arg2 = build_tree_list(NULL_TREE, arg2); ...  TREE_CHAIN(t_arg1)=t_arg2; ...  TREE_CHAIN(t_argn)=NULL_TREE; t_call = build_function_call(t_func_decl, t_arg1);

The constructed tree node is added to the AST as a statement or as an expression. A statement is added to the linked list of statements using TREE_CHAIN:

t_stmt=build_stmt (EXPR_STMT, t_call); TREE_CHAIN(t_cur)=t_stmt;

Adding a tree node as an expression is the same as using '' C operator. The new expression is added as the first argument of the operator. The result of the operator is the result of its second argument:

t_res = build(COMPOUND_EXPR, TREE_TYPE(t), t_call, t);

If you want to add the call after t then you need to build a compound statement. This is equivalent to using curly brackets in C:

static tree gen_start_scope { t_hdr = build_stmt (COMPOUND_STMT, NULL_TREE); ss = build_stmt (SCOPE_STMT, NULL_TREE); SCOPE_BEGIN_P(ss)=1; SCOPE_PARTIAL_P(ss)=0; TREE_CHAIN(t_hdr)=NULL_TREE; TREE_OPERAND(t_hdr, 0)=ss; return t_hdr; }

static tree gen_end_scope { ss = build_stmt (SCOPE_STMT, NULL_TREE); SCOPE_BEGIN_P(ss)=0; SCOPE_PARTIAL_P(ss)=0; return ss; }

static tree scope_stmt(tree t) { t_res=gen_start_scope; TREE_CHAIN(TREE_OPERAND(t_res, 0)) = t;    while (TREE_CHAIN(t)) t = TREE_CHAIN(t); TREE_CHAIN(t)=gen_end_scope; return t_res; }


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Template:GNU C Compiler Internals/Instrumenting an AST 4 1

Lookup of a Declaration in the Symbol Table
void gem_find_symtab(tree *t_var, char *name) { tree t_ident = get_identifier(name); if (t_ident) *t_var = lookup_name(t_ident); else *t_var=NULL_TREE; }

Building Tree Nodes
The walk_tree callback function can instrument the AST. Functions build1 and build construct new tree nodes. The former function takes one operand, the latter one takes more then one operand. The following code computes the address of the operand, same as '&' C operator:

t = build1(ADDR_EXPR, TREE_TYPE(t), t);

The following example refers to an array element arr[0]:

t = build(ARRAY_REF, integer_type_node, arr, integer_zero_node);

The following example builds an integer constant:

t = build_int_cst(NULL_TREE, 123);

Building a string constant is more difficult. The following example demonstrates the idea:

tree gem_build_string_literal(int len, const char *str) { tree t, elem, index, type; t = build_string (len, str); elem = build_type_variant (char_type_node, 1, 0); index = build_index_type (build_int_2(len-1, 0)); type = build_array_type (elem, index); T_T(t) = type; TREE_READONLY(t)=1; TREE_STATIC(t)=1; TREE_CONSTANT(t)=1; type=build_pointer_type (type); t = build1 (ADDR_EXPR, type, t); t = build1 (NOP_EXPR, build_pointer_type(char_type_node), t); return t;  }

To build a function call one needs to find the function's declaration and build the list of arguments. Then the CALL_EXPR is constructed:

gem_find_symtab(&t_func_decl, "func"); t_arg1 = build_tree_list(NULL_TREE, arg1); t_arg2 = build_tree_list(NULL_TREE, arg2); ...  TREE_CHAIN(t_arg1)=t_arg2; ...  TREE_CHAIN(t_argn)=NULL_TREE; t_call = build_function_call(t_func_decl, t_arg1);

If you want to build a list of statements { stmt1; stmt2; ... }, then you need to use function append_to_statement_list:

tree list=NULL_TREE; for (i=0; i<num_stmt; i++) { BUILD_FUNC_CALL1(t_call, t_send, t_arr[i], NULL_TREE); append_to_statement_list(t_call, &list); }

Adding Nodes to a Tree
GCC 4.1 has an interface that allows one to add a chain of nodes into another chain of nodes implemented in file tree-iterator.c. Functions tsi_start and tsi_last create a tree statement iterator and assigns it to the first or the last tree in the list, respectively. Functions tsi_link_before and tsi_link_after link a statement using the iterator either before or after the current statement. There is also function append_to_statement_list that adds a node to a list. If the specified list argument is NULL_TREE then a new statement list is allocated.

Building Function and Variable Declarations
A global declaration is added in hook gem_c_common_nodes_and_builtins. In this following example we build a structure type and create a global variable of this type. The structure has a field of type unsigned int and a function pointer field.

t_log = make_node(RECORD_TYPE); decl_chain = NULL_TREE; field_decl = build_decl(FIELD_DECL, get_identifier("addr"), unsigned_type_node); TREE_CHAIN(field_decl)=decl_chain; decl_chain=field_decl; DECL_FIELD_CONTEXT(decl_chain) = t_log; ...  t_func_type = build_function_type_list(void_type_node, unsigned_type_node, NULL_TREE); field_decl = build_decl(FIELD_DECL, get_identifier("add_addr"), build_pointer_type(t_func_type);  TREE_CHAIN(field_decl)=decl_chain;   decl_chain=field_decl;   DECL_FIELD_CONTEXT(decl_chain) = t_log;   ...   TYPE_FIELDS(t_log) = nreverse(decl_chain);   layout_type(t_log);   pushdecl(build_decl(TYPE_DECL, get_identifier("log_t"), t_log));   decl = build_decl(VAR_DECL, get_identifier("log"), build_pointer_type(t_log));   DECL_EXTERNAL(decl)=1;   pushdecl(decl);


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Cookbook:Cheese and Bacon Rolls

Procedure

 * 1) Lightly grease an oven tray.
 * 2) Combine dried yeast, sugar and warm water. Stir together and leave covered to stand for 5 minutes (or until frothy).
 * 3) Mix together the bakers flour, bread improver and salt in a large bowl. Add the wet ingredients and mix until the dough is smooth and stretches well (usually about three minutes).
 * 4) Turn out onto a lightly floured surface and knead the dough for two to three minutes.
 * 5) Return the dough to a mixing bowl. Cover and store in a warm place until the mixture has doubled in size.
 * 6) Turn oven on to 200 C
 * 7) Turn out dough onto lightly floured surface and gently deflate mixture. Cut mixture into eight roughly even pieces, and sprinkle cheese and bacon pieces over the bread rolls.
 * 8) Place rolls in oven on the lightly greased tray, and leave for 10–15 minutes (or until golden brown).

title: Cookbook:Cheese and Bacon Rolls


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European History/Europe: 1918 to 1945

The end of World War I saw the European combatant nations exhausted, an entire generation of young men dead on the battlefield, and political conditions vastly changed from those before the war. The German, Austrian and Russian monarchies had been driven from power and replaced with democratic or revolutionary governments, and many European ethnic groups which had been subject to these three states seized the chance to obtain independence. It was against this background that the victorious powers attempted to bring permanent peace to Europe. The victors of the war were quick to blame Germany for starting the war and resolved to punish her, and this is exactly what took place at the Treaty of Versailles on June 28 1919. the treaty was so harsh on Germany mostly because France and Italy were angry with them.

The Treaty of Versailles of 1919

At the Peace of Paris or Treaty of Versailles, the "Big Four" convened to discuss what the result of the end of the war should be. The big four consisted of the United States, represented by President Woodrow Wilson; Britain, represented by Prime Minister Lloyd-George; France, represented by Clemenceau, who wanted most of all to get revenge against Germany; and Orlando of Italy. Germany and Russia were not invited, as Germany was defeated, and Russia had made a separate peace with Germany in 1917, and was feared because of the rise of the revolutionary Bolsheviks there.

At the discussions, many taking part looked to President Wilson for leadership, as the United States was the least damaged and seemingly the most neutral victor, and because the members saw Wilson's 14 Points plan provide an idealistic road map to a new future.

Wilson's Fourteen Points
Wilson's Fourteen Points were democratic, liberal, enlightened, and progressive - a new type of treaty designed to make peace forever secure. The key aspects of his propositions were to disallow secret treaties in the future, allow freedom of the seas, provide for arms reduction, allow the self-determination of nations, and to establish the League of Nations, which Wilson saw as a key instrument to prevent future war.

The Treaty's Treatment of Germany
In contrast to Wilson's idealism, the Treaty of Versailles was harsh, brutal, punitive, and retributive, especially because France still had lingering anger over the Franco-Prussian war. The aspects of the Treaty were designed to attempt to prevent Germany's ability to wage war in the future. It ordered that France would control the Saar valley, rich in coal and iron, for 15 years, and that France would have Alsace-Lorraine returned. The Rhineland between France and Germany would be demilitarized as a buffer zone between the two nations. Germany's colonies were divided between France and Britain, and Germany itself lost all together 13.5% of land and 12.5% of her population. The German navy was confiscated and the German army was limited to 100,000 members, and no submarines, planes, or artillery were permitted. Germany was forced to pay brutal war reparations in the amount of 132 billion gold marks. Finally, Article 231, or the War Guilt Clause, was a strictly retributive measure, ordering Germany and her allies to bear full responsibility for the war.

Problems of Germany After World War I
Germany's new democratic government, the so-called Weimar Republic, faced serious problems following the Treaty of Versailles. Though Kaiser Wilhelm II had abdicated and the wartime military leadership had lost its authority, Germans widely refused to admit that their army had lost the war. A significant number believed that Germany could have continued to fight and eventually gotten the upper hand, and that surrender was a "stab in the back" of an army capable of winning the war.

While this severely undermined the credibility of the new republic, the notion that the German army could have continued the war and eventually won is rejected by most historians, due to the introduction of fresh U.S. forces and Germany's weakness after four years of battle. In fact, in late 1918 the German High Command, facing a powerful Allied offensive toward German soil and exhaustion of their own troops, turned in desperation to Germany's democratic politicians and asked them to form a government which the Allies would find acceptable for negotiations.

Immediately after the war, the Weimar Republic encountered severe economic problems. Millions of demobilized soldiers arrived home to find little or no work. Hunger was widespread. In addition, France and Britain owed war debts to the United States, and in order to pay them demanded reparation from Germany. Germany was unable to pay, so France seized the industrial towns of the Ruhr valley. The German response was to print money to pay the unemployed workers of the Ruhr, which resulted in massive hyperinflation in Germany.

Politically, there was near-chaos for several years, as fringe political groups on both the left and the right openly and violently battled each other and the central government. The Spartacists, or communists, staged uprisings in Berlin and other cities and briefly seized power in Bavaria. The Freikorps, various bands of demobilized soldiers who did not want to lay down their arms, crushed the Bavarian coup d'état. However, the Freikorps also sought to overthrow the Weimar Republic's government with a coup of their own in 1920, which failed when German workers responded with a general strike.

This was the atmosphere in 1919 when a small right-wing party in Munich took in a new member, an army corporal named Adolf Hitler. A skilled orator and politician, Hitler rapidly rose to head the National Socialist German Worker's Party, known as the Nazis.

German Prosperity Returns
In the late 1920s, prosperity returned to Germany, primarily as a result of U.S. efforts through the Dawes Plan of 1924 and the Young Plan of 1929. These plans provided loans to the Weimar Republic and gave the Republic a realistic plan for reparation payments, helping to restore economic stability.

This prosperity had a diminishing effect on the radical groups of the right and left. The appeal of these groups was reduced as a result of a prosperous Germany.

The Rise of Pacifism and Isolation in the 1920s
During the 1920s, the prevailing attitudes of most citizens and nations was that of pacifism and isolation. After seeing the horrors and atrocities of war during World War I, nations desired to avoid such a situation again in the future. Thus, Europe took a number of steps to ensure peace during the 1920s.

At the Washington Naval Conference in 1921, the United States, Great Britain, France, Japan, and Italy agreed to build no new battleships for ten years and to reduce the current size of their navies.

During the Locarno Treaties of 1925, Germany unconditionally guaranteed the borders of France and Belgium and pledged to never violate the borders of Czechoslovakia and Poland.

In 1926, Germany joined the League of Nations. The League was one of the major means that Europeans ensured peace during the time.

In 1928, 65 nations signed the Kellogg Briand Pact, rejecting war as a means of policy. In 1934, Russia joined the League of Nations.

Democracies in Europe from 1919 through 1939
While fascism rose in Europe, the liberal democracies in the Britain and France were encountering isolationism and pacifism, as explained above, as well as problems with unemployment and colonial struggles. As a result of the Great Depression of the 1930s, the concept that government is responsible for meeting the social needs of its citizens became increasingly popular.

Britain
Before WW1 The Old-Age Pensions Act 1908 of the United Kingdom, passed in 1908 is often regarded as one of the foundations of modern social welfare in the United Kingdom and forms part of the wider social welfare reforms of the Liberal Government of 1906–1914.

The Act provided for a non-contributory old age pension for persons over the age of 70. It was enacted in January 1909 and paid a weekly pension of 5s a week (7s 6d for married couples) to half a million who were eligible. The level of benefit was deliberately set low to encourage workers to also make their own provision for retirement. In order to be eligible, they had to be earning less than £31. 10s. per year, and had to pass a 'character test'; only those with a 'good character' could receive the pensions. You also had to have been a UK resident for at least 20 years to be eligible and people who hadn't worked their whole life were also not eligible.

Also excluded were those in receipt of poor relief, 'lunatics' in asylums, persons sentenced to prison for ten years after their release, persons convicted of drunkenness (at the discretion of the court), and any person who was guilty of ‘habitual failure to work’ according to one’s ability.

After World War I, Britain faced a number of problems. One of the most serious was unemployment, with approximately 2 million people on the "dole," or Britain's welfare system. This resulted in the rise of the Labour party. The Labour party created a modern welfare state in Britain, creating an old age pension, medical care, public housing, and unemployment relief.

The British industries, now antiquated and falling behind, were selling less as the United States stepped up to the industrial plate.

Members of British colonies, such as Ireland, Egypt, India, and Palestine, were finding the ideals of the Enlightenment appealing and were beginning to resist British rule.

Finally, the Great Depression caused massive problems in Britain.

Prime Minister Ramsay MacDonald, a member of the Labour Party, enacted a policy of "retrenchment," which cut social spending, disallowed employment for women, and installed 100% tariffs on foreign goods. He enacted the ideas of Keynesian Economics, authored by J.M. Keynes, which advocated increased government spending during a depression in order to put money into the economy.

France
The Third Republic of France was the governing body from 1870 until 1940. Although it was widely disliked for its political instability and corruption, it did manage to deliver a golden age, what became known as the belle epoque, for Paris. The city acquired many distinctive new monuments and public buildings, foremost among them the Eiffel Tower, constructed for the World Exhibition of 1889. It was renowned as a centre for the arts, with the Impressionists taking their inspiration from its new vistas. At the same time, Paris acquired a less savoury reputation as the "sin capital of Europe", with hundreds of brothels, revues and risqué cabarets such as the famous Moulin Rouge. The city also acquired its metro system, opened in 1900.

In 1877, President MacMahon tried to dissolve parliament out of disgust with the premier and to seize more power. However, the French people elected the same deputies to Parliament. The French people clearly wanted to prevent another dictator from taking power.

In 1886-1889, General Boulanger came close to overthrowing the government. He gained large support among monarchists, aristocrats, and workers, pleading to fight Germany. However, he lost his courage at the moment of the coup, and he fled to Belgium and committed suicide.

In 1894, a French Jewish army officer named Alfred Dreyfus was falsely accused of treason in what became known as the "Dreyfus Affair," showing that anti-Semitism was still strong in France, especially in the army and the Catholic Church. Émile Zola wrote the famous letter "J'Accuse!" which helped raised support for Dreyfus, who was eventually pardoned and restored to rank. Thus, in 1905 France enacted the separation of church and state.

After World War I, France encountered a number of problems. They had difficulty with the cost and burden of rebuilding the nation, and they lost all of their investments in Russia as a result of the Russian Revolution. The reparations were not paid by Germany as expected. Additionally, tax evasion was common in France at the time.

By the late 1920s, prosperity had been restored. However, the Great Depression of the 1930s triggered political unrest and social turmoil. In 1934, the socialists and communists fought the fascists in the Chamber of Deputies, one of the houses of parliament, and threw ink at each other. As a result of the unrest, the people elected a "Popular Front," a coalition of socialists, liberals, and communists, to govern. The leader of the Popular Front was Leon Blum, who during his tenure enacted family subsidies, welfare benefits, two weeks of vacation, a forty hour work week, and collective bargaining. Léon Blum was replaced in 1938 by Eduard Daladier.

Challenges to Democracy in the 1930s
As a result of the Great Depression, fringe groups such as fascists and communists became more appealing to the general populace of Europe.

Causes of the Great Depression
The Great Depression occurred because of a number of reasons. Low wages at the time resulted in less purchasing power. An agricultural depression and falling prices resulted in increased agricultural output but decreased demand. Overproduction in the factories, and overexpansion of credit, as well as the U.S. stock market crash of 1929 also contributed greatly. Actions pursued when the Great Depression was still in its infancy involved the Fed's untimely raise in interest rates (in hopes to lure foreign investment), and later on, the Smoot–Hawley Tariff created immediate tariff backlash across the world and collapsed a great majority of world trade.

Effects on the Colonies
These changes in Europe resulted in more calls for autonomy in the colonies, and the influence of Woodrow Wilson's proposed "self-determination" of nations grew.

In 1931, the Statute of Westminister created the "Commonwealth of Nations" consisting of Canada, New Zealand, Australia, the Irish Free State, and South Africa. These nations were given autonomy but were linked to Britain through trade.

In the 1930s, India began yearning for autonomy. The Muslim League and the Indian National Congress called for a greater role of Indians in their government. Gandhi's "civil disobedience" led to an end to British rule, and in 1935 the Government of India Act provided India with an internal self-government. In 1947 India gained its independence and split with Pakistan.

In 1908, "Young Turks" overthrew Abdul Hamid II of Turkey and ruled the nation until 1918. After World War I, Kemal Atatürk took the leadership of Turkey. In 1923 he moved the capital from Istanbul to Ankara, beginning the Republic of Turkey. Atatürk established western dress, the Latin alphabet, and banned polygamy from Turkey. In 1936, women were given suffrage and were allowed to serve in parliament.

Fascism in Germany and Italy
Italy experienced a turn to fascism after World War I, and Benito Mussolini took control as dictator of the nation. Soon afterward, Germany under Hitler took the same turn. Fascism was a new form of government, initiated by Mussolini, that promoted extreme nationalism and national unity; an emphasis on masculinity, youth, aggression, and violence; racial superiority; one supreme leader with superhuman abilities; the rejection of individual rights; the use of secret police, censorship, and propaganda; a militaristic and aggressive foreign policy; strict central control of the economy; and the holding of the individual as subordinate to the needs of society as a whole.

The Italian Fascist Regime

The liberal establishment of Italy, fearing a socialist revolution inspired by the ideas of the Russian Revolution, endorsed the small National Fascist Party, led by Benito Mussolini. After several years of struggle, in October 1922 the fascists attempted a coup (the "Marcia su Roma", i.e. March on Rome); the fascist forces were largely inferior, but the king ordered the army not to intervene, formed an alliance with Mussolini, and convinced the liberal party to endorse a fascist-led government. Over the next few years, Mussolini (who became known as "Il Duce", the leader) eliminated all political parties (including the liberals) and curtailed personal liberties under the pretext of preventing revolution.

The Rise of Fascism and Hitler in Germany

At the beginning of the 1930s, Germany was not far from a civil war. Paramilitary troops, which were set up by several parties, intimidated voters and seeded violence and anger among the public, who suffered from high unemployment and poverty. Meanwhile, elitists in influential positions, alarmed by the rise of anti-governmental parties, fought amongst themselves and exploited the emergency authority provided in the Weimar Constitution to rule undemocratically by presidential decree.

After a succession of unsuccessful cabinets, on January 29, 1933, President von Hindenburg, seeing little alternative and pushed by advisors, appointed Adolf Hitler Chancellor of Germany.

On 27 February, the Reichstag was set on fire. Basic rights were abrogated under an emergency decree. An Enabling Act gave Hitler's government full legislative power. A centralised totalitarian state was established, no longer based on the rule of democratic law, a policy that Hitler had outlined in his biography 'Mein Kampf.' The new regime made Germany a one-party state by outlawing all oppositional parties and repressing the different-minded parts of the public with the party's own organisations SA and SS, as well as the newly founded state security police Gestapo.

Industry was closely regulated with quotas and requirements in order to shift the economy towards a war production base. Massive public work projects and extensive deficit spending by the state helped to significantly lower the high unemployment rate. This and large welfare programmes are said to be the main factors that kept support of the public even late in the war.

In 1936, German troops entered the demilitarised Rhineland in an attempt to rebuild national self-esteem. Emboldened, Hitler followed from 1938 onwards a policy of expansionism to establish Greater Germany, that is, one German nation state, starting with the unification with Austria (called "Anschluss") and the annexation of the Sudetes region in Bohemia from Czechoslovakia. The British Prime Minister realized that his policies of appeasement towards Germany were being taken advantage of. To avoid a two-front war, Hitler concluded the Molotov-Ribbentrop Pact, a treaty of non-aggression, with the Soviet Union.

The Spanish Civil War 1936–1939
In 1923, a coup led by General Miguel Primo de Rivera formed a new government in alliance with King Alfonso XIII Bourbon. In 1930, opposition to Primo de Rivera's right wing government led to his resignation. Out of a desire for democracy and socialism by the populace of Spain, Alfonso was overthrown in 1931 and a republic declared. In 1936, a Popular Front of leftists forces was elected to Parliament and took control of the government. Anticlerical actions of leftists and their direct attacks on Catholic churches and monasteries angered all conservative Spaniards. Left and right-wing political militants clashed on the streets. In July 1936, rebellion broke out among a big part of army units. It was supported by conservative forces of all kinds of social background and the fighting began.

The nation broke into two factions. The Republicans, or "Loyalists," consisted of communists, socialists, anarchists, and liberals, and received some international support as well as big military and financial aid from Stalin. The "Nationalists" consisted of monarchists, angered Catholic believers, landowners, the army, members of the "Falange" party, traditionalists and received a great deal of direct aid from Italy and Germany.

In 1936, Great Britain, France, and the United States signed a non-intervention pact regarding the civil war. In 1937, the town of Guernica, a civilian town, was attacked and bombed by the German airforce. In 1939, nationalists took Barcelona and Madrid, and General Francisco Franco announced the end of the Civil War. From 1939 until 1975 Franco would rule as dictator in Spain.

Again to War, the Outbreak of World War II
The Treaty of Versailles produced so-called "revisionist" powers. Germany, who was the loser of the war, had harsh reparations imposed against them. Italy got nothing out of the Peace of Paris. Hungary lost two thirds of her territory and each third ethnic Hungarian was placed under foreign rule. Japan didn't receive the racial equality clause they desired, even after defeating the Russians in the Russo-Japanese War. The Soviet Union was snubbed at the Peace of Paris as well, as it was not invited to attend.

Aggressive Actions by the Axis Powers and Western Response
In 1933, Germany left the League of Nations. In 1934, Germany attempted to annex Austria. In 1935, Italy invaded Ethiopia while Germany reoccupied the Saar valley and began conscription and open rearmament. In 1936, Germany remilitarized the Rhineland. In 1938, Germany annexed Austria and the Sudetenland.

The prevalence of pacificism in the 1920s in Europe meant that European nations were reluctant to interfere in the actions of the revisionist powers. In addition, the nations of the Treaty of Versailles began to feel guilt for their treatment of Germany, and believed that they had wronged Germany. Moreover, the areas that Germany initially invaded were all of German heritage, and the leaders of the nations wondered if perhaps Germany should be allowed to take those territories. The leaders met at the Munich Conference in 1938, and Hitler promised to take no more aggressive actions.

In 1939, however, Germany seized the rest of Czechoslovakia, showing that war was inevitable and that appeasement had failed. Poland and Hungary also participated, taking sections of Czech and Slovak territory adjacent to their borders. During the same year, Italy and Germany signed the "Pact of Steel" alliance.

British Prime Minister Neville Chamberlain responded to the occupation of Czechoslovakia by giving a guarantee to Poland that Britain would go to war against Germany if Germany attacked Poland. The Polish government had not requested this alliance. Many historians have seen the guarantee as Chamberlain opening his eyes to Hitler's aggressive plans, but some others hold that it foolishly made war much more likely, by encouraging Poland to defy Germany in any negotiations over the Polish Corridor and the city of Danzig.

Possibly in response to Chamberlain's action, Germany and the Soviet Union shocked the Western powers by signing a non-aggression pact. This pact showed that war was imminent because two systems mutually pledged for the other's destruction came to agreement.

On September 1, 1939, Germany invaded Poland with its new war machine using what was called lightning warfare or Blitzkrieg. As a result, on September 3, 1939, Great Britain and France declared war on Germany. On September 17, 1939, the U.S.S.R. invaded Poland. In 1940, Germany, Italy, and Japan signed the Tripartite Treaty, forming the Axis powers.

The Second World War
After the invasion of Poland on September 1, 1939, between the fall of 1939 and the spring of 1940 the Allies did not directly attack Germany in the west, but rather they engaged in harassing operations which had become known as the "phony war." This allowed Germany to finish the mobilization of its forces. In April 1940, Germany invaded Denmark and Norway. The next month Belgium, the Netherlands, and France were attacked. Within six weeks, France had surrendered.

Winston Churchill became Prime Minister of Britain in May 1940. Churchill was dedicated to the destruction of Hitler, whatever the cost and using any means necessary. Churchill opened a new era in warfare by launching an unprecedented bombing campaign against civilian targets in Germany. The Germans retaliated, and the heroic British defense became what is known as the Battle of Britain. London and many other cities in England were hard-hit with large civilian casualties.

In 1941, Germany invaded Russia in an attempt to destroy communism, enslave the Russians, and get oil that was desperately needed to power the German war machine. However, the invasion failed, and winter hit Russia, causing massive death and destruction among Germany's army.

In 1942, Germany attempted to siege the Russian city of Stalingrad, but the attack ultimately ended in Soviet victory and the defeat of the Germans. Also during 1942, the British and the United States defeated German forces in North Africa.

By 1943, the Allies had landed in Italy and were beating back Mussolini's forces. During 1943, the Battle of Kursk, the largest armored engagement of all time, also took place on the Eastern Front. Again, the Soviets were highly victorious against German forces. On September 8, 1943, Italy surrendered to the allies.

By 1943, an immense bombing campaign by the U.S. and Britain was under way to break Germany's will to fight by destroying her cities and making her population homeless. Almost every major city was devastated with huge loss of life, but postwar studies showed that the bombing had little effect on industrial production, and may have strengthened Germans' will to fight.

On June 6, 1944, Allied forces landed on the beaches of Normandy on what has become known as D-Day. The offensive was successful for the Allies, and the Allies suffered far fewer casualties than expected. This marked the beginning of the end of the war. In December 1944, the Battle of the Bulge, the German's last major offensive in Western Europe, took place in Belgium. The result of this battle was a victory for the Allies and the crushing of much of the remainder of Germany's forces. On May 8, 1945, Victory in Europe Day occurred as the Russians took Berlin.

Conclusion of the War
As the war neared the end, two major conferences took place to discuss how to most effectively terminate the war.

The Yalta Conference
The Yalta Conference began on February 11, 1945. In attendance were U.S. President Franklin D. Roosevelt, British Prime Minister Winston Churchill, and the Soviet leader Joseph Stalin. Yalta resulted in a number of essential provisions.

The first was the establishment of the United Nations, an international organization that describes itself as a "global association of governments facilitating cooperation in international law, international security, economic development, and social equity." The United Nations replaced the League of Nations, and was given the capacity to enforce itself militarily.

Yalta called for a four part dismemberment of Germany, with a portion going to each the United Kingdom, France, the United States, and Russia. This was based upon the fact that while Germany was not unified it did not present nearly the threat that it did as a unified nation.

War criminals were tried at Nuremberg, marking the first time that members of an army were held to international standards.

Poland was reconstituted, albeit with large territorial changes and placement in the Soviet sphere of influence. Reparations were enforced against Germany, and it was agreed that Russia would enter the war against Japan after the defeat with Germany.

Finally, the parties agreed to the Declaration of Liberated Europe. This provided that liberated countries would be given the right to hold free elections and choose their own government. This was an attempt to keep Stalin from annexing eastern Europe, but this attempt obviously failed.

The Potsdam Conference
The Potsdam Conference took place from July to August 1945. In attendance were President Harry S. Truman, replacing President Roosevelt as a result of Roosevelt's death, British Prime Minister Attlee of the Labour party, who represented Britain after Churchill's Conservative Party's defeat in Britain, and Joseph Stalin. The Conference provided for German disarmament, demilitarization, and denazification. Poland was shifted to the west to reward the Soviet Union and to punish Germany, and as a result there was a massive post-war migration.

Finally, Japan was threatened with destruction by a "powerful new weapon" which turned out to be the atomic bomb.

Lịch sử châu Âu/Châu Âu từ 1918 đến 1945

title: European History/Europe: 1918 to 1945


text:
European History/Bibliography

The below list represents all of the references used for the writing of this wikibook.

 * Baugh, Albert C. A History of the English Language. 2nd ed. New York: Appleton-Century-Crofts, Inc., 1963.
 * Fine Jr., John V.A. The early medieval Balkans a critical survey from the sixth to the late twelfth century University of Michigan Press, 1983.
 * Fine Jr., John V.A. The late medieval Balkans a critical survey from the late twelfth century to the Ottoman Conquest. 1st paperback ed. University of Michigan Press 1994.
 * Durant, William. The Story of Civilization. 11 vols. New York: Simon & Schuster, 1950.
 * Gardner, Helen. Art Through the Ages. 5th ed. New York: Harcourt, Brace & World, Inc., 1970.
 * Gustavson, Carl G. A Preface to History. McGraw-Hill, 1955.
 * Heilbroner, Robert L. The Wordly Philosophers: the Lives, Times, and Ideas of the Great Economic Thinkers. 4th ed. New York: Simon & Schuster, 1972.
 * Hunt, Lynn, Thomas R. Martin, Barbara H. Rosenwein, R. Po-Chia Hsia, and Bonnie G. Smith. The Making of the West: People and Cultures. Vol. B. New York: Bedford/St. Martins, 2001.
 * Hunt, Lynn, Thomas R. Martin, Barbara H. Rosenwein, R. Po-Chia Hsia, and Bonnie G. Smith. The Making of the West: People and Cultures. Vol. C. New York: Bedford/St. Martins, 2001.
 * Turner, William. Catholic Encyclopedia. 11 pp. Online. Internet. 29 May 2004
 * Wikipedia: The Free Encyclopedia. 23 Oct. 2005. Wikimedia Foundation. 23 Oct. 2005 .

title: European History/Bibliography


text:
European History/Europe: 1945 to Present

Introduction
As Europe enters a new era, with two world wars still residing in the collective memory, peace and prosperity seems likely to continue. The Soviet Union was dissolved in 1991, resulting in a Europe whose countries and borders have returned to their pre-WW2 state. Its nations, however, are faced with aging populations and falling birthrates, making it increasingly challenging to sustain expensive programs of social services. As the 21st century began, the continent is redefining itself with multiculturalism, a strengthening of Europe's common economic policies and the formation of a European parliament. The Europe of Nations, whose nationalistic sentiments led to two world wars during the last century, is viewing the federalism of the USA as a possible solution to forging a United Europe.

Western Europe 1945-Present
After World War II the countries of Europe were faced with finding ways to reconstruct their economies. Sweden, Switzerland, Ireland and Spain who had all remained neutral during the war fared slightly better. Sweden and Switzerland had provided banking and materials for the Nazi war effort and this meant that both countries had come out of the war relatively unscathed. Neutrality has its benefits but for those countries who were at the vanguard of military action the situation was far worse. Britain's industries had been almost exclusively dedicated to the war effort and coupled with the loss of economic and political influence amongst its former colonies the outlook for a quick recovery seemed unlikely. The countries that had been occupied by Germany had seen their industrial output directed to the German war effort and the influx of money and goods from occupied countries into the German economy meant that the shortages and austerity of war were not felt by the German population until the last year of the war. All over Europe the expectations was one of a return to normality and economic strength though it soon became obvious that this could only be achieved with American aid. In a speech given at Havard in 1947 by George C. Marshall, the American Secretary of State, proposed that the rebuilding of europe's economies including Germany's should in part be funded by American grants.

"'The truth of the matter is that Europe's requirements for the next three or four years of foreign food and other essential products - principally from America - are so much greater than her present ability to pay that she must have substantial additional help or face economic, social, and political deterioration of a very grave character.'" Excerpt from the Havard Speech given by George C. Marshall.

The Marshall Plan was passed into law by President Truman in April 1948 under the formal name of the "European Recovery Program". The Marshall Plan was to apply to all the areas of Europe that had been ravaged by war regardless of whether the recipient had been an Ally or member of the Axis. Stalin rejected the plan therefore ensuring that East Germany, Poland, Romania, Yugoslavia and other countries then under post-war Soviet occupation or influence were excluded.

Britain

Britain after the war was heavily in debt. The bombing of major urban centers and exhaustion of manpower due to war casualties further added to the financial difficulties. The damage to the economy led to rationing being extended into the next decade. From 1945 until 1951, the Labour Party and Prime Minister Attlee replaced the Conservative Party. Winston Churchill was considered by the general populace to be a "War Prime Minister" and though having lost the first post-war election did serve a further term as Prime Minister from 1951 to 1955. In August 1947, India became independent of Britain. From 1950 to 1980 Britain, now without the full economic benefit of its colonies, embraced the free-market capitalism advanced by the USA though more emphasis was given to social programs and state ownership of major utilities. In many respects America's involvement in the war had been conditional on Britain dismantling its colonial power base with the USA viewing it as an obstacle to their own ideas of trade and free-market capitalism. This had first been proposed by Roosevelt to Churchill at the August 1941 meeting where the future of post-war europe was being discussed. America had viewed Britain's colonial trade as monopolistic and though it was Pearl Harbour and Japanese aggression that led to the USA entering the war; the agenda for colonial independence remained. America the Colony who had fought a war against the English for independence was pre-disposed culturally and economically to make this request.

Margaret Thatcher, leader of the Conservative Party, became Prime Minister from 1979 until 1990. She was the first Western female leader of the modern era, and was faced with depression and "stagflation" - high unemployment and inflation resulting from high oil prices. Thatcher was closely allied with U.S. President Ronald Reagan and employed "trickle-down" supply-side economics, cutting taxes on the wealthy in hopes that they would spend the additional money to hire new workers and endorsing privatization and deregulation. Thatcher cut many other social programs including education, health care, and welfare, and sold off nationalized industries such as BritOil and British Airways. She also broke the power of the unions in Britain.

Thatcher also deployed a taskforce to regain control of the Falkland Islands (Malvinas) after the invasion of the islands by Argentina in 1982.

John Major was the Conservative Prime Minister from 1990 until 1997. Tony Blair was the New Labour Prime Minister from 1997 until 2007. The Iraq invasion and Afghanistan conflicts. Gordon Brown was briefly the Prime Minister. After the general election of 2010 no political party had an overall majority in the House of Commons and a coalition was formed between the Conservatives and Liberal Democrats, with David Cameron as Prime Minister and Nick Clegg as Deputy Prime Minister. By the next general election in 2015, however, the popularity of the Liberal Democrats had fallen significantly, many would argue as a result of decisions taken within the coalition government, and the Conservative party gained a small and unexpected majority with the Labour party making no significant gains, in fact losing some representation. David Cameron would continue as Prime Minister of the majority Conservative government until the referendum of leaving the European Union when he resigned after failing to secure a remain vote, he was then swiftly replaced by Theresa May.

France
The Vichy regime installed by the Nazis after their invasion of France during World War II was replaced in 1946 by the Fourth Republic, which lasted until 1958. The Fourth Republic consisted of a strong Parliament with a Premier chosen by the majority party. There was also a weak ceremonial President. Charles De Gaulle, who led the Free French Resistance movement against the Nazis during their occupation of France in World War II, was elected but refused to participate and thus resigned. After World War II, France decolonized Indochina, Morocco, Tunisia, and the rest of West Africa. The Fourth Republic also allowed women's suffrage.

Violent conflict arose in Algeria, still a french colony. Bombings, terrorism, and the death of nearly one million people during anti-french actions led to this conflict taking center stage in French politics. When senior officers of the French military in Algeria rebelled in May 1958 and fears of a coup d'état spread among the members of the government, the latter called upon Charles De Gaulle to resolve the problem. De Gaulle refused to take power unless the government would allow for a stronger Presidential position.

The people of France conceded, and in 1958 the Fifth Republic was formed with a strong authoritarian President. However, De Gaulle's solution to the problem was to simply free Algeria. In 1968, university students protest over their conditions, leading to a mass working-class strike. After the failed "régionalisation" referendum, De Gaulle resigned in 1969. He was followed by two right wing presidents: Georges Pompidou (elected in 1969 and deceased in 1974), and Valéry Giscard d'Estaing (elected in 1974). Abortion became legal under Giscard's rule.

From 1981 until 1995, François Mitterand served as President of France. He was a Socialist, and implemented numerous social programs. He abolished the death penalty. He instituted nationalized banks, insurance industries, and defense industries. Workers' wages increased during his tenure and working hours were reduced. However, when the French economy lagged, he abandoned socialism in 1984 and the French economy revived. In 1986, the right won the parliamentary elections, leading to the first "cohabitation" period, where the president and prime minister were not from the same political side. Jacques Chirac, mayor of Paris and founder of the RPR Gullist party, was chosen as prime minister. Mitterrand was re-elected in 1988, but had to face a second "cohabitation" from 1993 to 1995, with Édouard Balladur as a prime minister.

In 1995, Jacques Chirac, became President. He also had to face the third "cohabitation", with the socialist Lionel Jospin as prime minister from 1997 to 2002. Chirac was easily re-elected in 2002 against the extreme-right candidate Jean-Marie Le Pen, who had unexpectedly reached the runoff, eliminating Lionel Jospin at the first round. Jacques Chirac then founded a new party, the UMP, uniting the majority of the right wing. Jacques Chirac was followed by Nicolas Sarkozy, president of the UMP in 2007.

In 2012, Nicolas Sarkozy, very unpopular and having to deal with the economic crisis, was defeated by a socialist candidate, François Hollande.

Germany

After World War II, Germany was divided into zones according to agreements reached between the ally powers. Western zones were placed under American and Western European control, while the eastern zones came under the control of the Soviet Union. Germany was to be occupied by the allies until some point in the future; how this was to be achieved itself became a source of conflict between the allies. This division of Germany also mirrored the presence of Allied troops in the now liberated countries of Europe. The Soviet army maintained a military presence in Poland, Romania and other eastern european states. American troops were still stationed in many western european states. With the war at an end the concord between the USA and Russia was now faltering and Germany and many of its neighbours were soon to become the center stage for an ideological battle between these once allies. The division of Berlin was a precursor to the Cold War; the first post-war arena for the entrenched differences between Russia and the USA and an ominous sign for the later conflicts of Vietnam and Korea.

In 1948, the Berlin Airlift took place. Berlin was in the eastern part of Germany administered by the Soviets though the city itself was administered by France, America, Britain and the Soviets. The western Allies had merged the three occupation zones they possessed after the end of World War II. The prelude to the blockade involved a gradual escalation of tension. At first the Soviets moved troops to borders and this itself prompted American intelligence to consider that the Soviets may be seeking further territorial expansion. The Russians then issued orders to General Dratvin (Russian command in Berlin) that all trains entering Berlin would now need to be inspected and the appropiate paperwork must be present. This was relayed to General Clay (US command in Berlin) who cabled the letter to Washington. The Washington administration came to the conclusion that imminent invasion of West Germany was highly unlikely and that the purpose of the recent Russian movement was aimed at removing the Allied powers from Berlin itself. The Russians increased the pressure with new inspection posts on roads and canals into Berlin. In March 1948 nine British registered barges were held at Buchhorst and in April British and American military trains were detained at Marienborn on the basis that the Russians had not been allowed to inspect them. The autobahns also came under pressure with the Russians insisting that Britain evacuate two Emergency Aid stations on the Belin to Helmstedt autobahn. On the 18th June 1948 the Allies issued a new currency called the Deutsche Mark which replaced the Reichsmark and on the same day Russia suspends all road and train travel to and from Berlin. On the 4th August the Allies officially started the airlift to supply Berlin.

In 1949, the two areas were formally split into the Federal Republic in the West and the German Democratic Republic (GDR) in the East. In addition, the Basic Law, Germany's constitution, came into effect in 1949.

From 1949 until 1963, Chancellor Konrad Adenauer, a member of the Christian Democrat Party (CDU), came to power in West Germany and pursued a policy of integration with NATO and the US led Western alliance. Adenauer successfully resisted domestic political pressures for Germany to adopt a policy of neutrality between the Cold War blocs as a path to reunification. Under him West Germany encountered the Wirtschaftswunder, or Economic Miracle, with great recovery throughout the nation. The country underwent denazification which involved censoring of fascist ideas and the showing of films taken at Dachau and other concentration camps to German cinema audiences. The education system in Germany was also subject to denazification with text books discarded due to their inclusion of Nazi propaganda. The Nuremberg Trials is the most visible example of denazification during this period since it involved the highest Nazi party members though thousands were tried at a local level by the Allies. One of the problems the Allies faced with denazification was that to remove all Nazis would have left a Germany struggling to reconstruct itself. In many respects Germans who had been complicit in Hitler's pogroms had escaped retribution because either they hadn't come to the attention of the Allies or they were part of the balancing act of German reconstruction.

In 1961, East German authorities, with Soviet backing, erected the Berlin Wall to stop the flood of refugees escaping to the west. Both Adenauer and his parliamentary opponents, the Social Democrats, considered the GDR to be an occupied part of a legally unified German nation, but were not in a position to change these circumstances because of the Cold War confrontation between the US and USSR. Berlin's importance as the first arena of the Cold War is reflected in the 1962 Cuban Missile Crisis. Released classified documents about the Cuban Crisis show an American administration worried that any sign of weakness during the Cuban Crisis may lead to Soviet aggression in Berlin. The zones of 1945 had become a border by 1962 and Berlin had a wall of concrete and barbwire. This is where the Cold War started and this is where it would have to end.

From 1963 until 1966, Chancellor Ludwig Erhard of the CDU served, followed by Kurt Georg Kiesinger.

From 1969 until 1974, Chancellor Willy Brandt, of the Social Democrats (SPD) came to power. He enacted Ostpolitik, a policy of economic friendship and trade with the eastern bloc and East Germany. Though he supported the NATO alliance, Brandt's overtures to the east earned him suspicion in some Western circles that he might trade off the alliance for German unification. Ironically, Brandt's government fell in a scandal over an East German spy within his office. His successor as chancellor, Helmut Schmidt, was also from the SPD (1974–1982).

From 1982 through 1998, Chancellor Helmut Kohl of the CDU served. In 1989 he was in office when the Berlin Wall fell, as Gorbachev abandoned the Brezhnev Doctrine of Soviet protection for other communist regimes. In 1990 the two portions of Germany reunified, but the East German economy lags far behind that of West Germany, even today. Chancellor Kohl, styling himself a conservative in a similar mold to Ronald Reagan and Margaret Thatcher, cut welfare spending and taxes, helping the economy.

From 1998 through 2006, Chancellor Gerhard Schroeder of the SPD served. He is most prominently known for his adamant opposition to the US led invasion of Iraq as well as for largely abolishing unemployment insurance benefits in the so-called Hartz reforms.

After elections in 2006, Angela Merkel became Chancellor and is a member of the CDU.

The European Union

The Franco-Prussian War, World War I, and World War II have left an indelible mark on modern Europe. The ferocity and destruction of these wars has led to a concerted effort by European leaders to secure a lasting peace in Europe. At a political level it was agreed that the best method would be to unite the nations economically and politically. Thus began the European Union (EU).

Members
There are currently 28 members of the European Union. The original six members were France, (West) Germany, Italy, Luxembourg, Belgium, and the Netherlands. Between 1973 and 1986, Denmark, Ireland, Britain, Greece, Portugal, and Spain joined the EU. The emblem of the European Union is a blue flag with twelve gold stars on it. In 1995, Austria, Finland, and Sweden joined the EU. Nine years later ten countries were admitted - Poland, Czech Republic, Slovak Republic, Lithuania, Latvia, Estonia, Hungary, Slovenia, Malta and Cyprus. The number of EU members rose again in January 2007 with the addition of Romania and Bulgaria and in July 2013 when Croatia joined. Macedonia, Montenegro, Serbia, and Turkey are currently in talks about future possible membership of the EU.

Background
In 1944 the Bretton Woods agreement created the World Trade Organization (WTO) that fights to eliminate tariffs and promote free trade. It established the World Bank, which provides loans to less-developed countries, and the International Monetary Fund (IMF), which provides loans to countries in economic crisis to prevent the collapse of their government. The agreement also fixed exchange rates for currencies, which became floating exchange rates in 1971.

In 1945 the United Nations was established.

In 1951, the European Coal and Steel Community (ECSC) was established with Belgium, West Germany, Luxembourg, France, Italy, and the Netherlands as members.

In 1957, the Treaties of Rome established the European Atomic Energy Community (EURATOM) and the European Economic Community (EEC). The members removed trade barriers between themselves and formed a "Common Market."

In 1992, the Treaty of Maastricht provided for cooperation in law enforcement, criminal justice, civil judicial matters, and asylum and immigration.

In 2004, Estonia, Latvia, Lithuania, Poland, the Czech Republic, Hungary, Slovakia, Slovenia, Malta, and Cyprus were admitted into the EU.

In 2007, Romania and Bulgaria were admitted as members of the EU.

In 2013, Croatia was admitted as a member of the EU.

In 2016, it was announced that the United Kingdom, also known as UK or the Great Britain, would be withdrawing and leaving the EU in 2020, therefore, making it the first country in Europe to leave the European Union. The vote was in favour of leaving the EU by a margin of 51.9% in favour to 48.1% against. Contributing factors included a desire for independent sovereignty, immigration issues, the economy, and anti-establishment politics.

The Soviet Union
The Soviet Union after the war found itself in a position to secure its borders and to advance its own economic and political ideology into neighbouring states. They rejected the Marshall Plan and set up an alternative solution known as the Cominform. Russian troops had been first to enter Berlin and Stalin for all his faults was an astute politician who saw in this situation the chance to turn Russia into a world power. The Red Army was to maintain a presence in many of the countries it had liberated. The Americans who had wanted to extricate themselves from Europe's arena now found themselves drawn further into the tangled borders of Europe. The Cold War had started.

Nikita Khrushchev 1953-1964
Khrushchev reversed many of Stalin's policies through a process which became known as "Destalinization". This time period is known as "The Thaw", since tensions between the US and the USSR became more relaxed. The theory of peaceful coexistence, which believed that the communist nations could live in peace with the democracies of the West, was spread throughout the Soviet Union by Khrushchev, who attended peace summits in Geneva and Camp David. In addition, Khrushchev attempted to modernize Russia and to give its citizens more freedom. He rid the USSR. of purges and eliminated show trials, replacing them with actual court systems. He gave more latitude to the 6 Eastern European states, and also allowed more freedom of speech and criticism of Stalin. At the 1956 XX Party Congress, Khrushchev announced that Stalin had indeed made many mistakes during his reign.

Khrushchev tried to reform collectivized agriculture and to shake up the Communist Party in order to remove inefficiency, so the Party forced him out in 1964.

The West regards Khrushchev as generally unpredictable, especially considering his actions in the Cuban Missile Crisis of 1962.

Leonid Brezhnev (1964-1982)
After Khrushchev's removal from office, Leonid Brezhnev came to power. He was widely seen as humorless, colorless, and unimaginative. He brought an end to destalinization and is blamed for bringing an era of stagnation to the Soviet Union.

Brezhnev is well known for his Brezhnev Doctrine, which promised to intervene if a socialist regime was threatened. During Brezhnev's reign, in 1968, there was revolution in Czechoslovakia. Alexander Dubček was elected leader of the communist party, and he called for free press, democracy, and other parties. In this sense he curbed repression, and he advocated "Socialism with a Human Face" in what has become known as the "Prague Spring" - that is, more rights, more consumer goods, and more freedom. However, the Soviets invaded the country and crushed this new government in August 1968.

Under Brezhnev, the United States and the Soviet Union underwent Détente, which was in essence a relaxation of tensions between the two nations. This occurred primarily because both countries recognized the concept of Mutually Assured Destruction, which stems from a realisation that the proliferation of nuclear arms had ensured that each nation had enough warheads to guarantee each other's destruction. It was during this period that many countries witnessed the rise of campaigns for nuclear disarmament by the general public. These campaigns formed a defining social phenomena during the decades of the 60s and 70s, especially within the NATO countries, and in some part must have helped in the "thaw" of the Cold War.

In 1975 both NATO and Warsaw Pact members signed the Helsinki Accords. In these, the West recognized the Soviet occupation of Eastern Europe, and the Soviets promised to respect the civil rights of people living in the occupied territories.

Brezhnev had a great deal of trouble during his rule. In 1977 Czech dissidents, led by writer Václav Havel, signed a manifesto called the Charter 77 that demanded human rights, free expression, freedom of religion, and the right to organize. Then, from 1980 until 1989, the Soviet Union was engaged in military action in Afghanistan in support of the communist government who were fighting a war with Muslim anti-communists. The USSR eventually withdrew their troops after a stale-mate was reached and russian casualties had mounted.

Brezhnev presided over the USSR for longer than any other but Stalin, and there was never a plot to take his position. He was allowed to grow old in office, and died on November 10, 1982 at the age of 75. He was succeeded by Yuri Andropov, then Konstantin Chernenko, both of whom ruled for only around a year, and had little real impact on the Soviet Union. Both were very physically unhealthy, died soon after being in office, and Chernenko was succeeded by the reformist Mikhail Gorbachev.

Mikhail Gorbachev (1985-1991)

With the Soviet Union on the verge of economic collapse, a young, vigorous, and creative General Secretary, Mikhail Gorbachev, came to power. Gorbachev created the policy of Glasnost, or "Openness," which allowed criticism (albeit limited) of the system, examination of past mistakes, rehabilitated victims of the purge, and changed textbooks in the nation.

He also implemented Perestroika, or "Economic Restructuring." He decentralized the economy, offered incentives to managers for increased production and quality and allowed them to make more decisions, introduced elements of "working place democracy", and allowed peasants to lease their own land.

However, these economic policies actually failed, and the situation became increasingly worse. The Soviet Union encountered massive problems in the 1990s, including alcoholism, divorce, a high abortion rate, low life expectancy, and no consumer goods.

Revolutions of 1988-1990
In 1988 Lithuanian liberation movement - Sajudis, Latvian - Tautas fronte, Estonian - Rahvarinne were created and soon they started struggle for independence of the Baltic states.

In 1989, a number of Eastern bloc states began to revolt against Soviet authority.

The spark of it all occurred in 1989, when declining conditions in Poland forced Poland to legalize Lech Walesa's "Solidarity" Party. The party won control of the government in a landslide election. Gorbachev then told the Eastern Bloc satellite states that he cannot enforce the Brezhnev Doctrine. As a result, other nations followed Poland's lead. Hungary held elections, relaxed economic controls, and opened its door to the West. The Czechoslovakian and Bulgarian communist governments collapsed without bloodshed in what has become known as the "Velvet Revolution." In East Germany, Germans flooded to Hungary and then to the West. The Communist leader of East Germany, Honecker, was forced to step down, and the Berlin wall was torn down on November 9, 1989. In Romania, Nicolae Ceauşescu, a brutal Stalinist dictator, was executed on December 25, 1989. Ceauşescu was the only leader to be executed during the Eastern Bloc uprising and Romania itself the only country to violently overthrow its Communist regime.

The Break Up Of The Soviet Union
The failure of Glasnost and Perestroika to revive the situation in the Soviet Union resulted in its demise.

In 1989, the first competitive elections since 1917 were held for the Soviet Congress of People's Deputies. Boris Yeltsin was elected and became a leader of the opposition in the U.S.S.R. In 1990, other parties became officially tolerated, and in June 1991 Yeltsin was elected President of Russia. On August 19–21, 1991, a coup of communist hard-liners occurred while Gorbachev was in the Crimea. Yeltsin led non-violent resistance to the coup, which ultimately prevailed and saw all the coup leaders arrested or commit suicide. On August 24, 1991, the Communist Party was banned in Russia. December 31, 1991, the Soviet Union officially ceased to exist and was replaced with 15 independent states.

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