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Basic Physics of Nuclear Medicine/Dual-Energy Absorptiometry

Introduction
This is a developing chapter of a wikibook entitled Basic Physics of Nuclear Medicine.

Dual-energy radiography is an imaging technique which can be used to eliminate bone information in an radiograph, so that an image displaying tissues only can be displayed. Alternatively, the technique can be used to generate the reverse effect where tissue information is eliminated and an image displaying bone only is generated. This latter option ideally allows indicators of bone density to be assessed. A theoretical background to this technique will first be developed below with the discussion leading towards Dual-Energy X-Ray Absorptiometry (DEXA).

Dual-Energy Radiography
Dual-energy imaging is based on exploiting the difference in the attenuation of tissue and bone at different X- ray energies – see the following figure:

It generally involves acquiring images at two X-ray energies and processing these images to suppress either the bone or the tissue information. A simple mathematical model assumes that monoenergetic radiation is used and no scattered radiation is detected, so that the transmitted radiation intensity through a region of bone and tissue, acquired at a low X-ray energy and following logarithmic transformation, is given by:

Ilo = μtlo xt + μblo xb ,

where:
 * μtlo is the linear attenuation coefficient of tissue at the low X-ray energy;
 * xt is the tissue thickness;
 * μblo is the linear attenuation coefficient of bone at the low X-ray energy; and
 * xb is the bone thickness.

Similarly, the transmitted radiation intensity for the same region of an image acquired at a higher X-ray energy is given by:

Ihi = μthi xt + μbhi xb ,

where:
 * μthi is the linear attenuation coefficient of tissue at the higher X-ray energy; and
 * μbhi is the linear attenuation coefficient of bone at the higher X-ray energy.

When these images are multiplied by separate weighting factors, klo and khi, and the result combined to form a composite image, the output image is given by:

I = klo Ilo + khi Ihi.

Therefore:

I = (klo μtlo + khi μthi) xt + (klo μblo + khi μbhi) xb,               (1)

which indicates that tissue cancellation can be achieved by setting the coefficient of xt equal to zero, i.e.

klo μtlo + khi μthi = 0.

Thus,

klo μtlo = - khi μthi ,

and

$$\frac{k_{hi}}{k_{lo}} = -\frac{\mu_{tlo}}{\mu_{thi}}$$

which indicates that tissue can be eliminated from the composite image when the ratio of weighting factors in equation (1) above is chosen to equal the negative of the ratio of the attenuation coefficients of tissue at the two X-ray energies. A similar approach can be used to cause bone cancellation by setting the coefficient of xb in equation (1) to zero.

This form of image data processing is illustrated in the following figure:

A chest radiograph acquired at 56 kVp is shown in the top left panel of the figure. This is referred to as a low energy image. In the top right panel is a radiograph of the same patient's chest acquired at a high energy – 120 kVp, with 1 mm copper filtration. Results of the dual-energy processing are shown on the bottom row. The bone-subtracted image is shown in the bottom left panel and the tissue-subtracted image in the bottom right panel. Notice that the tissue-subtracted image demonstrates that the lesion in the patient's left lung is a calcified nodule, since it doesn't appear in the bone-subtracted image.

Radiographic Image Receptors
There are at least three new technologies used in radiography which offer numerous advantages over the traditional screen/film image receptors. An overview of these technologies is provided below to support our treatment of dual-energy imaging – and also our consideration of the registration and fusion of planar images in another chapter of this wikibook.

 * Computed Radiography (CR)
 * This method of recording a projection radiograph is based on exploiting the photostimulable luminescent properties of barium fluorohalide compounds. The phosphor is layered on an imaging plate which when mounted in a cassette is used in place of the film/screen cassette used traditionally in radiography. The imaging plate is sometimes referred to as a storage phosphor because it stores a latent image following the radiation exposure which can be scanned afterwards using a readout device – as illustrated in the following figure:

 * The figure shows the radiation exposure in the top left where the cassette is placed anterior to the patient to record the projected image. The cassette is then placed in a readout device (follow the blue downward arrow!), where it is scanned by a laser beam to digitize the latent image.  The cassette can then be prepared for re-use by exposing it to intense incandescent light to erase any residual latent image information (top right in the figure above).

 * The readout stage is shown in more detail in our next figure:

 * The figure illustrates one mechanism used to scan the imaging plate where a narrow laser beam strikes a rotating mirror causing it to scan a single line across the plate. The plate is then moved so that the scanning laser beam can read the next line of the latent image information.

 * The latent image is formed through radiation absorption processes in the photostimulable phosphor where electrons are knocked into higher energy states where they remain until they're later stimulated to return to their ground states using the red laser beam – a process similar to thermoluminescence where light is used instead of heat. The electrons emit blue light – called a photostimulable luminescence (PSL) – as they return to their ground states with the amount of light being proprotional to the radiation exposure.

 * The emitted light is guided by a light guide, as shown in the figure above, so that its intensity can be measured using a photomultiplier tube (PMT). The output of the PMT is digitized using an analogue-to-digital converter (ADC) before computer processing is applied.

 * One major advantage of computed radiography (CR) over traditional methods is its excellent linearity and dynamic range, as illustrated by the graph. The vertical axis on the left of the graph refers to the response of a CR plate, while the one on the right refers to a film/screen system. Its seen that the film/screen response (red curve) contains regions which can generate under- and over-exposures of the radiographic film.  The linear region between these two is ideally used for recording a patient's image.  Notice that the range of exposures equivalent to this linear region is substantially smaller than that provided by CR technology, i.e. its got a smaller dynamic range (also called exposure latitude in photography).

 * The important point to appreciate here is that CR images present data which is a superior record of the radiation exposure pattern incident on the cassette. They do not contain regions of over- and/or under-exposure, as is common is film/screen radiography. An improved ability to discriminate within regions of high (or indeed low) transmission results, so that, for example, a renal calculus can be readily depicted within a contrast filled renal pelvis in an IVP.  Note that the dynamic range of CR is rather broad and that contrast enhancement techniques are typically applied in a post-processing mode to window through the image data so that particular features of interest can be discerned.  Example CR images are shown below:

 * This linear, wide dynamic range characteristic is also shared by digital radiographic image receptors.

 * Digital Radiography (DR)
 * Considerable research has been conducted in recent years into the development of flat panel image receptors for digital radiography. This research has extended from the development of active-matrix liquid-crystal flat panel displays (AMLCDs) for application in, for example, portable computers.  The underlying technology of AMLCDs is a large area integrated circuit called an active matrix array which consists of many millions of identical semiconductor elements deposited on a substrate material.  An intensifying screen or a photoconductor coupled to such an active matrix array forms the basis of flat panel X-ray image receptors.

 * Such a receptor is illustrated in the following figure, where the active matrix array and associated electronic circuitry is mounted in a device which replaces the X-ray cassette in screen-film radiography:

 * Array sizes of up to 43 cm x 43 cm have been constructed with more than 9 million pixels (pixel size ~150 μm). Operation of the array is controlled by a digital image processor which also stores and displays the resultant images.

 * The operation is illustrated in more detail in the right panel of the above figure. Each pixel of the array has a switch (typically made from a thin film transistor) which is connected to switching control circuitry in a manner which allows all switches in a row of the array to be operated simultaneously.  The output from each pixel is connected in columns with individual pre-amplifiers.

 * All switches are kept in the off position during the X-ray exposure. Following the exposure, the switches in the first row are turned on and the signal from each pixel is amplified by the pre-amplifiers, digitised in an analogue-to-digital converter (ADC) and stored in the image memory of the digital image processor.  These switches are then turned off and the switches in the second row are turned on to acquire signals from the second row of pixels. This process is repeated for the whole array so that an image is acquired in a sequential, line-by-line manner.

 * Research developments have resulted in two distinct types of digital receptor:

 * Indirect Image Receptors
 * Indirect receptors are based on coupling an fluorescent screen to the active matrix array. Phosphors such as Gd2O2S:Tb and CsI:Tl have been used, and the light produced following X-ray interaction is detected by an array of pixels consisting of photodetectors – see the following figure:

 * Each photodetector generates an electric charge that is proportional to the amount of light striking it, and this charge is stored until it is read-out by the switching control circuitry. The detection process is referred to as indirect since the detected X-rays are first converted to  light, which is subsequently converted to electric charge.

 * Direct Image Receptors
 * Direct receptors are based on coupling a photoconductor to the active matrix array. Photoconductors such as amorphous selenium (a-Se) have been used, and the electric charge produced following X-ray interaction is detected by an array of pixels each consisting of an electrode and a capacitor – see the following figure:

 * This charge is stored in each capacitor until it is read-out by the electronic switching circuitry. The photoconductor requires a voltage of the order of 5,000 V to be applied, using a surface electrode, so that the charge produced can be attracted to the pixel electrodes.  Other photoconductors under investigation for this application include PbI2, PbO, TlBr and CdTe.

 * The photoconductive properties of amorphous selenium (a-Se) have been known for many years and have been widely applied in photocopier, facsimile and laser printer devices. This direct imaging technique has evolved from xeroradiography, which was a popular medical imaging technique many years ago mainly for soft tissue imaging.  Here, X-ray absorption in the photoconductor results in changes in the distribution of the electric charge reflecting local X-ray absorption, i.e. a latent image is recorded in terms of the distribution of electric charge on the surface of an a-Se plate.  Methods of rendering the latent image visible include:
 * spraying charged toner particles onto the plate and transferring this image to paper;
 * scanning the plate with electric charge transducers (e.g. electrometers) and digitising the output for storage in computer memory.
 * The toner approach was that adopted in the original xeroradiography systems and is no longer in widespread clinical use, mainly due to developments in film-screen technology. The scanning electrometer approach has been applied to the clinical imaging of chests with the Philips Thoravision system.  This involves use of an a-Se layer deposited on a cylinder.  The latent image is recorded on the surface of the layer and the drum is subsequently rotated past a linear array of tiny electrometers.  In comparison, the direct image receptors use an a-Se layer in intimate contact with a two-dimensional array of pixel-sized electrodes, as we have seen above.

 * Important design features of flat panel image receptors include the pixel size and the fill factor. Pixel size undoubtedly affects spatial resolution and sizes of the order of 100 – 200 μm are typical.  The fill factor is the percentage of a pixel area which is sensitive to the image signal – be it electric charge or light photons.  It is never 100%, given the need to accommodate conductors (~10 μm wide) which input switching signals and which output image signals, as well as the thin film transistor in each pixel.

 * Digital image processing techniques are typically applied to acquired images before they are displayed. These include logarithmic transformation, to correct for exponential X-ray attenuation, and contrast enhancement, to optimise the displayed gray values.  Other digital processing techniques are also necessary to overcome limitations associated with the manufacturing process for individual image receptors.  These include flat field (i.e. uniformity) corrections, to overcome spatial sensitivity variations, and median filtering, to remove the effects of defective pixels.

 * Advantages of the indirect and direct image receptors purport to include a large, linear dynamic range, similar to photostimulable phosphors, and superior modulation transfer function (MTF) and detective quantum efficiency (DQE) compared with both film-screen and photostimulable phosphor systems. Such receptors are currently (i.e. in 2006) being introduced by major medical imaging companies and it is likely that their clinical application will become a significant feature in coming years.

A final point to note is that both CR and DR receptors can be used for dual-energy radiography in either of the following configurations:

 * Two exposures: where two separate exposures are used in applications where patient movement isn't an issue; and

 * Single exposure: where two imaging plates separated by a filter are mounted in a dual-energy cassette to record the low energy image on the anterior plate and the high energy image on the other.

Dual-Energy X-Ray Absorptiometry (DEXA)
This technique has its origin in a nuclear medicine procedure where transmission for two gamma ray energies was used to determine bone mineral density. The procedure is referred to as Dual Photon Absorptiometry and typically used the isotope 153Gd, which emits gamma rays at 44 and 100 keV. As a result of limitations in photon flux and practical considerations, the radioactive source has been replaced by an X-ray tube (XRT) in the DEXA technique – just like scanning radioisotope sources have been replaced by XRTs for attenuation correction in SPECT imaging. This method has found widespread clinical application for the assessment and monitoring of osteoporosis and has surpassed the main alternative technique, Quantitative Computed Tomography (QCT) in terms of accuracy, precision and radiation dose.

Two general approaches to generating the appropriate X-ray energies have been developed. In one approach, the kilovoltage and filtration are switched rapidly during image acquisition, e.g. from 70 kVp and 4 mm Al filtration to 140 kVp with an additional 3 mm Cu filter. In the second approach, a single X-ray energy with two different filters is used, e.g. 80 kVp with alternatively no added filtration and a cerium or samarium filter. Cerium has a K absorption edge at 40.4 keV, and samarium at 46.8 keV, and both materials generate a hardened beam compared with the unfiltered spectrum.

The DEXA technique typically involves an X-ray tube and scintillation detector mounted on a C-arm (see the figure below) so that the patient is exposed to a pencil X-ray beam scanning in a rectilinear fashion.

The pencil beam is used to reduce the detection of scattered radiation and the scintillation detector typically consists of a CdWO4 or NaI(Tl) scintillator coupled to a photomultiplier tube. The filter assembly is used to switch filters and calibration standards into and out of the pencil beam at appropriate intervals. Scan times with this approach are of the order of 2 to 5 minutes, depending on the examination, which are reduced in second generation instruments where a fan X-ray beam and a detector array are used. By rotating the C-arm around the patient during the scan in the second generation devices, a CT image can be formed. The output of the scintillation detector is fed to a computer for dual-energy data processing and image display. A host of body composition parameters can be derived from the image data, e.g. bone mineral density and soft tissue composition.


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Technologies for Rural Development/Creating energy

Creating Energy

Energy is used for many purposes, as a culture becomes more complex the uses for energy diversify.

Basic energy uses
The prime need for energy use in all parts of the world is for food preparation, preservation in hot climes & cooking. In cold climates it is essential for heating living spaces.

Energy Sources

 * Firewood
 * Solar energy
 * Solar Energy for cooking
 * Solar energy for water heating
 * Solar energy for creating electricity
 * Hydroelectricity
 * Hydromechanical
 * Wind energy
 * Connection to the network

Firewood
Firewood is the oldest and often most accessible energy source. An open wood fire can be used to cook food. There are many types of stoves and ovens that use wood to create heat for cooking and for heating of living spaces.

It is important to consider the source of the firewood; in many areas in the world people have cut all the trees down in an area to supply firewood or building material leaving no trees for future generations. As a general rule for every tree that is cut down 3 new ones should planted.

Solar Energy
The energy from the sun can be used to heat water or even cook food; this is the best way to do this from an environmental point of view. It creates no pollution and uses no resources apart from those used for its fabrication.

Solar Cooking

Solar cooking has been used for centuries by explorers travelling in areas without access to wood to create fire. Since the 1970´s general interest has increased because of the energy it saves.

The simplest design is called the CooKit designed by Frenchman Roger Bernard en the early 1990´s; it is made from cardboard tinfoil a heat resistant plastic bag and a dark coloured pot.

See links below for more information.

Solar for Heating Water
Solar water heating systems are very efficient. In developed countries where it is common to heat water with electricity or gas from a centralized system, the cost of the installation can be paid back from saving in energy costs.

For rural development simple solar heating systems can be used to heat water even in areas the electricity or gas network has not yet reached.

Solar heating of the water is also called solar pasteurization; by heating the water many viruses and bacteria that cause diseases are killed. Hot water can also be used to clean living spaces and cooking and eating utensils more effectively.

Solar for Generating Electricity
Using solar energy for creating electricity is an environmentally friendly process but is unfortunately not very efficient, primarily because of the cost of fabrication of the solar panels. It is a very good technology when small amounts of energy are needed; to supply power for school computers etc.

If electricity is needed at night then a battery system must be added to store the energy.

Hydroelectricity
If there are waterways nearby, dams are a very easy way to create energy in mechanical form; this can be turned into electricity with a turbine and generator.

The main problem with damming waterways to create energy is the change in ecosystem it creates, and the negative effect is has on the movement of silt downstream, the probability of the dam silting up, & the migration of fish up and downstream.

It is very important to create fish passes (ladders) so that the natural migration of fish can continue.

Small scale hydroelectric sets can be placed directly in streams with little or no civil engineering needed other than to anchor the set.

Hydromechanical
This is a very old technology, & is simply extracting energy as torque, via a paddle-wheel of some sort, & applying it to a set of grinding wheels, hammers

Wind Energy
Wind energy was first harnessed in Persia around 200BC to grind grain, shortly after the technology was copied by the Romans and consequently spreads across Europe where it has been used for pumping water and grinding grain until the early 20th century.

The first wind-,turbine used to create electricity was constructed in the United States in 1888, since then they have been used for pumping water or generating electricity in isolated areas around the world primarily on farms.

Wind turbines range in size from small 30 cm diameter models used to generate small amounts of electricity, to 10m high 2m diameter wind-turbine that typically has many blades, to giant 100m high 120m diameter wind-turbine that produce up to 5MW of energy.

In rural areas where it is not possible to connect to the electrical network, wind-turbines can installed to pump water and generate electricity.

Energy Storage
Electrical energy can be stored mechanically or chemically. The most common mechanical storage is by damming water; this can be done by waiting for it to flow into a dam or by pumping it up into a dam using excess electricity in a network. Batteries use a chemical process to store electricity. This process is not very efficient, batteries are expensive to make & dispose of, and even rechargeable ones have quite short life spans. Therefore it is best to try and avoid storing electricity and only create it when it is needed. That is why developed countries have large electrical networks to supply the electricity as it is generated.

Connecting to the Electrical Network
The first electrical network was connected in New York in 1883 by Thomas Edison the American inventor at the worlds first Research & Development centre. Since then the network has grown across the globe with most most developed countries in the world having centralized networks by mid 20th century.

Because alternative energy sources are only available when there is wind or sunshine, having a village connected to the electrical network means that excess energy produced from generation installations can be sold and when there is no wind or sunshine needed energy can be purchased. This is more efficient and environmentally friendly than using batteries.

Environmental Considerations
Energy creating generally uses up resources, which should be replaced if possible; trees cut down for firewood should be replaced with 3 trees planted.

Energy creating also produces Carbon Dioxide and other gases which pollute the air. CO2 (Carbon Dioxide) is one of the known Greenhouse gases, which may be linked to Global warming.

Whenever possible it is best to use renewable energy sources like solar or wind energy, and also try and be inventive about the way of using energy to minimize the amount that is used.

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


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Speedy delete
Hi - I've removed the speedy tag on Cookbook:Calamari as it is a valid redirect - if someone types in Calamari - they get the right page - cheers -- Herby talk thyme 16:58, 11 November 2006 (UTC)

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title: User talk:Sugarpine~enwikibooks


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Talk:Organic Chemistry/Introduction to reactions/Nucleophilic Substitution Reactions

I've made quite a few changes (mostly additions) to this page. I think the hyperconjugation stuff needs to be moved. In fact, I think we need a page that specifically discusses carbocations, since they have application to a lot more than just SN1 and SN2 reactions. Pete 21:45, 11 November 2006 (UTC)


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General Astronomy/Mass

The mass of a star - along with its chemical composition - are key to its behavior. Once these two features of a star are determined, one can calculate the temperature of the star's core and the pressures of its gases as well as the strength of the gravitational force acting within the star itself. The star's mass and composition can, therefore, determine the star's size and luminosity.

How, then, do we begin to calculate a star's mass? Binary stars can help us determine the mass of stars.

Binary systems are composed of two stars that orbit each other. Mizar and Alcor, for instance, are two stars that are apparent (not actual) binaries; they appear to be very close together in the sky, they are actually distant from each other. Mizar, however, is a true binary, made up of Mizar A and Mizar B, with a period of 10,000 years.

Because binary stars' orbits depend on their gravitational attraction to each other, the measurement of their orbital distance and the length of time it takes them to complete one orbit can be used to calculate the summation of the stars' masses. Hence, the following equation can be used:

$$(M_1 + M_2)P^2 = (D_1 + D_2)^3 = R^3$$

where $$M_1$$ and $$M_2$$ are the masses of the two stars, $$P$$ is the period of the orbit, $$D_1$$ and $$D_2$$ are the distances from the center of each star to the center of mass of the binary system, and $$R$$ is the total separation between the centers of the two stars, or $$(D_1 + D_2)$$.

Astronomers usually express the masses of astronomical objects in terms of our Sun's mass, where one solar mass is approximately equal to 1.99 x 1030 kilograms, or about 4.39 x 1030 pounds.

An astrometric binary is found by observing a star's proper motion. If it is wavy, that indicates the presence of a binary; non-binary stars have a straight line proper motion.

An eclipsing binary is detected by observing a star as it becomes occluded by its twin. An example of this is Algol (Beta Persei in Perseus).

There are three different types of binary systems of stars which provide information about the masses of those stars. Visual binaries refer to those stars which can each be visibly seen by astronomers through telescopes. The masses of these types of stars can be calculated when they are near enough to the Earth for astronomers to determine the size and tilt of the two stars' orbits about each other.

Another type of binary system that provides information about stellar masses is known as the spectroscopic binary. Using spectroscopic observations of the two stars, the doppler shifts of the two stars as they orbit each other can be measured and astronomers can collect sufficient data in order to find estimates for the masses of those binary stars. In this type of binary, astronomers are only able to conclude upon a lower limit of the masses because they must first know the orientation of the stars in their orbits. If the two stars do not form an eclipsing binary, then one of the stars never passes in front of the other, so astronomers are unable to calculate the orbit's orientation.

As stated previously, the use of binary systems to calculate star masses often leads to limited information. The above method of determining mass is very useful given that the other values are known, but obtaining these needed values can prove to be troublesome. When observing an astrometric binary, for example, we are unable to see the exact orbits. Moreover, even mapped orbits are problematic because they are two-dimensional representations of a truly three-dimensional motion of two stars. In either case, additional information is needed to calculate the orbits and masses of the stars more accurately. As a result, it is oftentimes easier to calculate the total mass of the binary system.

Astronomers have calculated that all stars that have been measured to date have masses that range from $$\frac {1}{50}$$ to 50 solar masses.

The mass of a star can then be used to determine its escape velocity: the velocity necessary for an object to escape the star's gravitational force. The escape velocity becomes greater as a star is more massive but decreases with the star's radius. The formula for calculating escape velocity is

$$\sqrt{\frac {2GM}{R}} $$

where $$M$$ is mass, and $$R$$ is radius.

Elements
Besides providing light, stars have another important role in the development of life: creation of elements! Stars produce many elements during their life cycles, which are thrown off through their solar wind, when they blow off their outer atmosphere and form planetary nebulae and most spectacularly, when they go supernova. Indeed, all elements, except for hydrogen and helium, were produced by stars. This means that the material making up plants, animals, even you, was at one time manufactured by a star! The famous astronomer Carl Sagan once observed, "We are made of star-stuff."

Main sequence stars are made up of hydrogen (H) and helium (He). Red giants are made of elements heavier than helium, up to and including iron (Fe). Iron is the most stable element, meaning that it's the hardest to transmute. Supernovas produce all elements heavier than iron, up to and including Californium (Cf).

title: General Astronomy/Mass


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General Astronomy/The Terrestrial Planets

The Solar System consists of eight planets orbiting a star - the Sun. The eight planets fall into two distinct groups. The four innermost planets are very close to the sun, are formed of rocky materials, and are relatively small. The four outermost planets are far from the Sun, are formed of gasses, and are relatively large. The Earth is one of the four innermost planets, so they are called the terrestrial planets (Terra is latin for earth, so terrestrial means "earth-like". The four outer planets are called the Jovian (Jupiter-like) planets.

The terrestrial planets are, in order of distance from the Sun, Mercury, Venus, Earth and Mars. All of these planets are made of rocky substances, primarily nickel, iron, and silicon. The Jovians are composed mostly of hydrogen and helium gas. The terrestrials orbit the Sun at distances between approximately 0.3 and 1.5 Astronomical Units from the Sun (an Astronomical Unit or AU is defined as the average distance between the Earth and the Sun, so the Earth is 1 A. U. from the Sun). In contrast, the Jovian planets spread from 5AU to 30 AU. The terrestrials are fairly small; the Earth is the largest of the four, and Mercury is only about 1/4 the diameter of the Earth. The Jovians are relatively large, from 4 to 11 times the size of the Earth.

All of the terrestrial planets are presumed to have formed through the same process, so all should share common properties. The terrestrial planets are different than the Jovians because a planet close to a star forms under different conditions than if it is far from the star. The terrestrial planets formed separately in different orbits, so there are significant differences between the four. The four terrestrials have many things in common, but each one is unique in its particular size, atmosphere, orbit, and so on.

Mercury
General Information

Mercury is the closest planet to the Sun. Its orbit is a mere 88 Earth-days, meaning that in the time it takes for the Earth to make one full revolution around the Sun, Mercury makes a little over four revolutions.

Solar days on Mercury are extremely long. It takes two orbits about the Sun for Mercury to complete one full rotation around its axis relative to the sun, so most points on the planet experience direct sunlight for a (Mercurial) year at a time.

Mercury has a highly elliptical orbit, finding itself a mere 0.313 AU from the sun at Perihelion (closest point to the Sun) and at 0.459 AU at Aphelion (farthest point from the Sun). This stretched orbit, combined with a thin and nebulous atmosphere, result in Mercury having wild temperature swings: temperatures during the day tend to exceed 430 degrees °C, while temperatures during Mercurial night tend to drop to a frigid -180 °C.

Mercury has a mantle far thinner than its core, so it is the second-densest planet and has surface gravity as strong as that of Mars.

Venus
Venus is the second planet from the sun, and the only terrestrial planet to rotate in a retrograde manner. Venus has a sidereal day (rotation period relative to the distant stars) lasting about 243.0 Earth-days, or about 1.08 times its orbital period of 224.7 Earth-days. Because of its retrograde rotation, its solar day is "only" about 116.8 Earth-days, and it has about 1.9 solar days per orbital period.

The surface temperature of Venus is highly uniform, about 462 °C (about 736 K/864 °F). The surface of Venus is thought to have been completely resurfaced by volcanic activity 300 to 500 million years ago.

Normal telescopes cannot penetrate the thick clouds of sulfuric acid droplets, but radar can be used to map out the topography of the land.

Earth
The planet Earth is the planet on which all known life in the universe lives. It is the third planet from the sun and the largest terrestrial planet.

Life on Earth is made possible by its massive reserves of liquid water. No other body in the solar system is known to have massive quantities of liquid water, though several Jovian moons are suspected to have oceans under their crust.

The Earth's only natural satellite, the Moon, is the largest satellite in the solar system relative to its planet. This means that the Moon and Earth are sometimes considered to be a double planet. The Moon is also the only celestial body aside from the Earth that has been set foot upon by humans.

Mars
The highest mountain on Mars is Olympus Mons. The northern hemisphere is dominated by volcanic plains; the south by heavily-cratered highlands. The surface is very dusty, and covered with dunes. The sky is a pinkish-orange, from dust storms.

Mars has a chaotic terrain. Astronomers believe it was created when magma melted underground permafrost, causing the ground to collapse. Valley networks are believed to have been caused by rain, and water flowing under ice.

Dried lake beds indicate the presence of water in Mars' past. Another indicator is calcium carbonate, found in a Martian meteor in 1996. Yet another is the presence of outflow channels (believed to have been caused by underground permafrost melted by magma) and alluvial fans. Evidence of seepage flows have also been found. These occur when water breaks through ice and cascades down a cliff.

Martian craters are different from the craters found on the Moon, Venus, or Earth. They're surrounded by mud flows.

The first to map the surface of Mars was Italian astronomer Giovanni Schiaperelli in 1877. He observed a series of lines crisscrossing the Martian landscape, which he called canali (channels). Some astronomers translated canali as canal, implying that they had been built by intelligent beings. This idea was advanced by Percival Lowell in his books Mars and Its Waterways (1903) and Mars as the Abode of Life (1908). It was later discovered that the Martian canals don't actually exist, and were very likely an optical illusion.


text:
General Astronomy/Star Clusters as Cosmic Laboratories

It is estimated that the number of the stars in the universe is around $$10^{20}$$. This is calculated based on the fact that there are about $$10^9$$ galaxies in the universe, each of which is composed of an average of $$10^{11}$$ stars each.

A nebula is a cloudlike object. Scientists can determine what type of nebula they are observing by examing its spectrum: an emission spectrum indicates glowing gas, while an absorption spectrum indicates a mass of stars. The Pleiades, for instance, has absorption spectrum.

Two kinds of nebulae are open clusters (loose groups of a few hundred stars; e.g. Pleiades, Hyades, Ursa Major) and globular clusters (spherical nebulae with hundreds of thousands of stars, such as M13 in Hercules and M3 in Canes Venatici). Most nebulae appear as a hazy patch when viewed with a small telescope. Dark nebulae are gaseous clouds that block light. This is where stars form.

Stars are created when gravity collapses dust and gasses together.


text:
User talk:Pdavis68

Hello and welcome to Wikibooks!

Here are some tips to help you get started:
 * You can sign your name on Talk and vote pages using four tildes, like this: ~~~~.
 * Remember to conduct any editing experiments in the sandbox.
 * If you're a Wikipedian, see Wikibooks for Wikipedians for a primer on how things work here (it's a little different).
 * If you want to base your work here on materials from Wikipedia, please use WB:RFI to bring the material over in compliance with the GFDL.
 * If you're an instructor and plan on using wikibooks for a class project, see Guidelines for class projects
 * Please say hello at the Staff Lounge with any questions or ideas.
 * Eventually, you might want to read the Manual of Style and Policies and Guidelines.
 * Please take a look at Naming policy before starting a new book.
 * Remember to maintain a Neutral point of view.
 * Explore, be bold in editing pages, and have fun!

You will find more resources in Community Portal. If you want to ask a question, visit the Study help desk, the Staff lounge, IRC channel or ask me personally on my talk page.

Good luck! -- Herby talk thyme 18:10, 11 November 2006 (UTC)

 * Thanks for the welcome. I'm trying to "be bold" without being "too bold". I'm trying to keep an eye on existing styles and guidelines and using other pages within the book for examples on layout and coidng. Been to a bunch of the pages you have mentioned. Thanks again for the welcome.

Pete 18:46, 11 November 2006 (UTC)

 * Feel free to get in touch if you need any help - -- Herby talk thyme 09:56, 12 November 2006 (UTC)

Questions!
Hi Pete - good to hear from you. You gets loads of brownie points from me for user the "edit summary" apart from anything else - a rarity here!

So some answers (accurately my thoughts - answers will be yours!). Quite a lot of wikibooks seems to have been created enthusiatically and then abandoned (I've only been here a couple of weeks myself but I was and still am on Wikipedia too).

Take a look at the history of the page you are interested in. When was the last consistent contribution by a named editor (IP's kinda don't count)? Go to that editors user page and look at "user contributions" - that will give you an idea of whether they are still active but on other books maybe. If they are a message on their talk page should get you some answers. Frankly if they aren't active make it your way (any changes are always reversible effectively).

Until I got here I'd not done much page moving but it doesn't hurt . As to the effect on links you can always look at the "What links here" in the toolbox but in practice you can check out "Module cleanup" (under "Tools") and the look at "Redirects" there. Anything is fixable! I'll happily help if needed. Consider posting in the "Staff lounge" too. A very small but friendly bunch and that applies to the very few active admins too.

Feel free to get back to me if I can help at all and best of luck with the change in direction - I've done a bit of "late learning" too but not as ambitious as yours. You know where I am - all the best -- Herby talk thyme 16:03, 12 November 2006 (UTC)

PS - most of my "best" ideas came from looking at pages I like and copying the layout, wikitext, whatever! - H

 * Thanks Herby. I'm certainly familiar with the "start and abandon" thing. I've done it on a number of software projects myself. Fortunately, for a project like this, people can step in at any time and continue the work, which is nice. I'm very busy these days, but I'm taking organic chemistry right now and I'm finding that if I have to write about it, then I have to know it well enough to write about it and that's helping me learn more. I also tend to remember the stuff I write myself better than what I read, so part of it is just an exercise in studying for me.

 * As for the edit summaries, I set my preferences to remind me. As a software engineer, we use software for keeping track of code changes and it's REALLY, REALLY valuable, especially when you wonder, "Why did I do that?" So, unless I'm simply fixing some spelling or formatting, I'll generally leave comments as to why I made the change I made.

 * Thanks for the tips on how to maintain the links and tracking down active authors. Those will be really helpful (well, the first will. The second will only be helpful if there are any active authors...) Thanks again. Pete 16:19, 12 November 2006 (UTC)

 * I understand the idea of it helping the study - had such a thing existed when I did mine it probably would have helped a lot. I'll help if I can (but the chemistry knowledge is VERY out of date!) -- Herby  talk thyme 16:31, 12 November 2006 (UTC)

 * I'm not too concerned with the "knowledge" aspect. I have a lot of resources. 4 organic chemistry textbooks, a fantastic professor, and the web. In making sure that what I write is accurate, it really reinforces all the information in my head. Once I'm done with organic chemistry, I may end up contributing to other books (biochemistry, anatomy, physiology, etc) as I take the classes, since it's clearly helping me to learn the stuff better.

Importing from Wikipedia
Hi Pete, sorry I misunderstodd the question on the staff lounge :). If you've been gone for a while and arte now returned, you might not know about the Special:Import function we have now. If you want to "harvest" wikipedia atricles for making chapters of the book, just request them on WB:RFI... this imports all revisions of the wikipedia article, so (a) you don't have to start every chapter from scratch, and (b) it's all good with the copyrights.

We can import templates as well as articles, of course :). -- SB_Johnny | talk 17:59, 12 November 2006 (UTC)

 * Hi Pete - told you they were nice folk (mostly )! -- Herby talk thyme 18:03, 12 November 2006 (UTC)
 * BTW the "undelete" request could be addressed to Johnny too (or another admin or staff lounge) - not sure the page you put it on gets much attention! -- Herby talk thyme 18:06, 12 November 2006 (UTC)

 * Thanks for the help guys. The undelete request went to the undelete request page. That's where the image cleanup said to put it. I can send it straigth to Johnny, though. I still have a lot of work to do on the organic chemistry book. There's a lot of cleanup, some reorganization to make things flow a little better, and so forth. Once that stuff is done, I'll probably want to import some templates from Wikipedia to add to the articles. In As an example, the reactions are all done as an appendix, which is really fine, but when talking about structure, generally, there are reactions that are specific to certain structures, so having links to those from the structure pages would be useful, and I think the template that I specified in the staff lounge is appropriate for that. —The preceding unsigned comment was added by Pdavis68 (talk • contribs) 18:11, 12 Nov 2006  (UTC)

 * The structure here is a bit "loose" - if in doubt - staff lounge/user talk page will probably get the quickest response. In passing, a reminder to sign talk page stuff stuff tho I can't talk cos I just missed one on Johnny's!.  Also "Recent Changes" can help you see what is going on and where activity is. -- Herby  talk thyme 18:18, 12 November 2006 (UTC)

Org chem
Hi Pete I've merely removed the link. The page is still there but I've asked for it to be deleted.

I tinker with Org Chem from time to time but mostly I'm doing the A-level Applied Science book. The two overlap a bit, mind. Anything you think I could tackle in Org Chem? Ewen 16:34, 13 November 2006 (UTC)

 * Honestly Ewen, the Org. Chem book needs so much work, you could pick almost any page and find a good bit of stuff that needs to be added, fixed, or whatever. I don't want to drag you away from the A-level Applied Science, unless you feel a strong motivation to get into the organic chem. For myself, I see it like this: I'm currently learning organic chem and working on this book is simply my way of studying. As a writer, I try to make sure what I write is correct, and that means I need to really understand it well. Since I have a long way to go, I'm just looking at the book as a long-term studying aid and will devote as much time as I can in an effort to better understand it all. So I'm in no particular rush to have anything done to it, but I'm certainly not opposed to help. I guess, more importantly, it would be nice to have someone I could bounce ideas off of and get recommendations. -- Pete 16:44, 13 November 2006 (UTC)

Navigation popups
Could check this out if you want - hover mouse over link and voila - preview! Just don't tell eveyone . There are other useful bits around too - cheers -- Herby talk thyme 18:22, 13 November 2006 (UTC)

 * Herby, I'll check it out. Relly, what I'd find more useful (and I may try to code this myself), is to have the preview pop up in a separate browser window. I have two monitors and what I usually do, particularly when editing an existing document, is show the original in one browser on one screen, and edit it in another browser on the other screen. So being able to popup the preview in a separate window and place that in the other screen would be nice. I might be able to take that script and modify it to do that. -- Pete 18:47, 13 November 2006 (UTC)

Not trying to bug you but
you are obviously a useful editor - could I ask you to look at this Staff_lounge and see if you feel like helping a bit. I do realise you have your own "thing" to do and won't be offended if it's no - cheers -- Herby talk thyme 19:35, 13 November 2006 (UTC)

 * Herby, no bother at all. I chimed in on the topic. My issue, really, is simply time. I have a tendency to want to jump into things with grandiose plans and other priorities destroy my plans. So I'm taking my contributions here, one step at a time. I'm going to contribue to the book as it's convenient for me and as it serves my own selfish purposes. I'll help out in other areas when asked and if I have the time to spare, but work and school are absolute priorities to me right now. I'm considering very seriously going to med school and to keep that option open, because of grades when I was younger, I need to get pretty close to straight As, which means I devote extra time to school to make sure that happens. Anyway, just wanted to make my position clear. Happy to help where I can, but my time is limited.

 * I guess I was looking to confirm a suspicion that you could be interested in the project as a whole rather than a particular area. Time is always an issue - here is voluntary! -- Herby  talk thyme 10:33, 15 November 2006 (UTC)

 * Herby, I am interested in the project as a whole, and to be honest, I think that time would best be spent trying to get the site better known. I've been using Wikipedia for a couple years now but I came across wikibooks by complete accident. I'm not completely out of touch with what's going on on the internet. I'm a regular Slashdot reader, and maybe it's been mentioned on Slashdot.
 * My honest opinion is that the site should make the books that are complete (or more so than say, organic chem) very visible and books that aren't so complete (like organic) less visible. I'm not really sure how you do that. But here's my thinking. When new people come to the site, you want them to see mostly finished products. You want them to look around and say, "Wow, they're really producing something here." And if they want to get involved and dig a little deeper, they'll find there are other books that need lots of work. But, as they say, you never get a second chance to make a first impression, and the first impression people get of the site shouldn't be, "Wow, they have a long way to go..."
 * I think this would drive more interest in the site as a whole and probably get a lot more people editing. For books that are complete, people ought to be getting out there on other web sites and recommending and linking to the books. There ought to be tons of incoming links to those books. I think it's going to be the only way to drive up the editorship significantly.
 * Anyway, just my opinion. -- Pete 13:55, 15 November 2006 (UTC)

 * Got a feeling that it is A - a very good point & B - should be posted in the staff lounge. I got to here thro a random edit on a page I was watching on wikip. Looked at the editor, found this on his page and realised there was quite a bit to do and not many people, ho hum - I'll find the way out one day.  All the best -- Herby  talk thyme 14:49, 15 November 2006 (UTC)

E-Z notation of Alkenes
Ewan, I noticed you've been doing some work in the Stereochemistry section. Something that seems really out of place to me is that the E-Z notation for Alkenes is discussed in both Chirality/R-S_notational_system and Chirality/Diastereomers. Where it isn't discussed is in the Alkenes/Naming_alkenes section. I think both of those sections ought to be collapsed into one section and moved to Alkenes/Naming_alkenes. I also think the cis-trans naming stuff should be moved Alkanes/Naming_alkanes. Do you agree? If so, I'll be happy to do it if you want, but I just didn't want to step on anything you're currently working on.

Pete, I'd like to have a single section for stereochemistry with quick summaries where relevant on the alkanes, alkenes, etc pages. Cis/trans isomers are not limited to alkenes (1,2-dichlorocyclohexane, for example) so although the alkene section should have a brief account of cis/trans isomerism I think it would be best to have the main discussion of these isomers in a stand-alone section. Ewen 14:53, 14 November 2006 (UTC)
 * I've centralised the stereoisomerism section by cutting and pasting material from the large sections under 'Enantiomers' and 'Naming alkanes'. I'm not sure 'Enantiomers' should be retained - enantiomers are simply chiral molecules so the 'Chirality' section is the one I've used to stash all the relevant material with 'Enantiomers' reduced to a stub.

 * Under naming alkanes, naming alkenes and cycloalkanes I've referenced the stereochemistry area and edited the discussion to a few lines pertinent to alkanes, alkenes or cycloalkanes respectively.

 * Ewen 15:39, 14 November 2006 (UTC)

 * I think you misunderstood my original note. I suggested moving E-Z to alkenes (to which it's specific) and cis-trans to alkanes since cis-trans applies to cycloalkanes and they're covered in the alkanes section. Alkanes always comes before alkenes in the learning, so there's no point in rehashing it there, but to me, these issues have more to do with naming and less to do with stereochemistry. They're simply naming conventions. Stereochemistry, on the other hand, is about structure and geometry. The only naming specific stuff that I think should really be there is the R/S, d/l, and (+)(-) stuff which is directly related to stereochemistry. Anyway, that's just my personal opinion, and I'm flexible, but that's the way all 4 of my organic chemistry books organize it and it simply makes sense to me. -- Pete 17:12, 14 November 2006 (UTC)

 * I'm not sure that's the way to do it, but who am I to judge? On the one hand, following the standard textbook organisation makes sense. On the other hand, this is an online book with hyperlinks - a traditional linear structure is not necessary.

 * E-Z is not specific to alkenes; cycloalkanes can/should be named using E-Z notation. Putting cycloalkanes before alkenes (if we follow a linear sequence) creates a problem: A reader might expect cis/trans E/Z to be under alkenes, but we're putting it under cycloalkanes because they come first. Hmm. I've been trying to make brief notes on these topics in the cycloalkane and alkene sections with a reference to the main chapter on stereochemistry with the technical discussion of how to use CIP priority rules, etc. I'm sure that merging the various pieces into a single main section and little referring sections has been beneficial; but where to put the main section?

 * BTW: Let's post everything here. I'll put your Talk page on my watchlist and then I won't miss your replies. I should have thought of that sooner. Duh! I'm not the most experienced here myself... Of course, if it's one particular page we're discussing, each page has its discussion page...

 * Ewen 20:12, 14 November 2006 (UTC)

 * "Of course, if it's one particular page we're discussing, each page has its discussion page..."

 * This is true, however the discussion is in regards to which page it all belongs. You're right, we might be better served discussing it somewhere in the book, though I don't think there are any other people working on the book right now.

 * Although the IUPAC specifications don't use the word "alkene", they use the term double-bonded atoms. The E-Z is used because the cis-trans system is inadequate for tri- and tetra-substituted alkenes. I suppose you could end up with double-bonded sulphers or phosphates other atoms capable of 4+ bonding pairs that might appropriately use E-Z, though I cannot think of a single example where this isn't handled by functional group namings. Can you provide an example of a non-alkene using the E-Z system? I have no recollection of ever seeing it associated with a non-alkene and can't find anything in the IUPAC specs that lead me to believe that it can be. I could very well be wrong, though.

 * The truth is, as long as the stereochemistry stuff comes before the alkene section, I suppose it's fine. I'd be more concerned if it came after the alkene section. For now, I guess we can just leave it the way it is and worry about it if there's ever a major re-ordering of chapters. -- Pete 21:02, 14 November 2006 (UTC)

 * I forgot to address your comment: "Putting cycloalkanes before alkenes (if we follow a linear sequence) creates a problem". I completely agree and that's something that ought to be fixed. Currently Cycloalkanes and alkanes are handled together and that needs to be fixed. -- Pete 21:03, 14 November 2006 (UTC)

 * The firstsite that I used for the IUPAC rules isn't an actual IUPACsite,butgenerally has easier to follow interpretations of the rules.But I just checked the  [|IUPAC Gold Book] and it very specifically says alkenes and  "related systems" and lists a few examples, all double-bonded. -- Pete 21:24, 14 November 2006 (UTC)

 * Oh, you found that site too! It's worth listing as a link for the book. You're dead right: E/Z notation is not for cycloalkanes; R/S notation does the trick. Ewen 21:36, 14 November 2006 (UTC)

 * Good point to link to the site in the book. IUPAC can get extremely overbearing, particularly with large molecules. Thank God for software that can name stuff from the models!!!! -- Pete 23:58, 14 November 2006 (UTC)

Image deletions
Hi Pete... your best bet it to just mark them for speedy deletion... use delete to do that.

BTW: have you considered uploading to Commons rather than to here? This allows any wikimedia project to link to the image without having to reload it on that project (for example, if the book you're working on was translated into another language, they would have the images ready to go). -- SB_Johnny | talk 10:25, 15 November 2006 (UTC)

Double redirects
Hi Pete - you've been around long enough to sort your own out  -. Quite a few are yours I think but do let me know if you want a hand (one of those things I look at from time to time) cheers -- Herby talk thyme 16:18, 22 November 2006 (UTC)

 * Herby, thanks for pointing it out. Could be either me or Ewen. We've both been reorganizing that section a lot the past week... I'll get it cleaned up. -- Pete 16:27, 22 November 2006 (UTC)
 *  - thanks -- Herby talk thyme 16:30, 22 November 2006 (UTC)
 * Okie dokie, I think we're good... I'll try to keep an eye on those in the future. -- Pete 16:38, 22 November 2006 (UTC)
 * No worries - it's just an easy one to keep an eye on. Just moved a bunch of pages myself so in a day or two they may show.  Case of checking back from time to time - regards -- Herby  talk thyme 17:06, 22 November 2006 (UTC)

Votes_for_deletion VfD
(cross posted to Swift & Pete)

Could you just confirm that you are happy with Ewen's comments at the bottom of this debate. My sense of tidiness (among other things) makes me want to close and archive this but I would not wish to do so without your approval. Then I'll close it and archive it unless anyone else wants to with "doom" on Organic Chemistry/Acetone peroxide synthesis. I'm guessing if the staff chemistry experts are happy with it the rest of us will be fine -- Herby talk thyme 18:21, 25 November 2006 (UTC)
 * Thanks Pete - hopefully I can finish this one off quite quickly -- Herby talk thyme 18:59, 25 November 2006 (UTC)

Referencing
Pete

I found good referencing trick for citing the same reference serveral times. First time, use ref name=whatever (and /ref as usual). Subsequently, use ref name=whatever/. I edited the Organic Chemistry/Alkenes page to include this system. Ewen 15:57, 26 November 2006 (UTC)
 * Thanks Ewen. I was wondering about that. Seemed kind of redundant to have it twice down there, but didn't know how to fix it.
 * On another topic, do you know where (if anywhere) organic chemistry students hang out on the internet? I mean, are there forums and stuff where chemists ask each other questions? Not just kids trying to blow stuff up, I mean... I saw a posting on Usenet where a guy wanted to synthesis 2R-2-hydroxypropionamidine. This is quite a ways out of my league, but I gave it my best shot (13-step synthesis). But I would have liked to have a place to ask questions of other chemists. I pepper my professors with so many, I'd like to take some of the weight of my many, many questions, off of them. -- Pete 00:48, 27 November 2006 (UTC)

Deleted pages from Organic chemistry
Cross posted to User talk:Ewen --Swift 02:55, 10 December 2006 (UTC)

I just deleted a bunch of pages marked by you and User:Ewen with delete. A few of these were linked to from Organic Chemistry/Book outline. I thought I'd give you the heads-up so you could update that to fit your new outline or delete it as well. Thanks for your hard work, --Swift 02:55, 10 December 2006 (UTC)

Reorganisation?
Talk:Organic_Chemistry

A bit of constructive criticism to consider! Ewen 19:41, 30 January 2007 (UTC)

title: User talk:Pdavis68


text:
General Astronomy/The Search for Extraterrestrial Intelligence

There is intelligent life other than us humans in the universe: whales, dolphins, elephants, pigs, seals, great apes, and surprisingly octopuses. But none of these is ever likely to build spaceships or transmit signals into space, and we have difficulty understanding the other intelligent species on our planet.

We have an intense curiosity: are we alone in the universe as a technological civilization? Some people would like to believe that other civilizations, perhaps with creatures even more different from us than elephants or even octopuses are far away in space, and that those creatures have something that we can learn.

To find such intelligent civilizations deep in space we need first to find signals from deep in space. That won't be easy; even radio has been broadcast for a short time (about 85 years as of 2008), a short time compared to human existence. We might also look for planets that have conditions similar to those of Earth—similar in size and temperature. Extraterrestrial civilizations are unlikely to be found on a gas giant planet or a planet of the Moon's size. We also have to be lucky enough to find a congenial planet with a civilization that has been sending signals of its own sophistication for a long enough time to reach us. If some sophisticated civilization has been sending signals to us for forty years but is fifty light-years away from us, then we on Earth will not get them for another ten years, and then only if we are tuned in. A civilization so sophisticated as ours was in 1875 would have given no evidence of its existence (such as electric lighting) visible even from the Moon—even if we then had some fine art, literature, and music.

What about alien visitors? Some people believe that some UFOs, or Unidentified Flying Objects are visitors from space. Almost all prove to have simpler explanations such as mirages, optical illusions, aircraft, and weather balloons. Even the planet Venus, bright enough to be visible by day is often seen as a UFO. Most scientists discount stories of visitors from outer space even if they think visits from distant space possible. Not until we actually see a creature like "ET" or, worse, the alien visitors of the movie Independence Day can we claim to have met alien visitors. Space travel is difficult and time-consuming. Species with lifespans similar to ours are unlikely to travel to and from "promising" planets such as their and ours.


text:
General Astronomy/The Doppler Effect

The Doppler effect or Doppler shift describes a phenomenon in which the wavelength of radiated energy from a body approaching the observer is shifted toward shorter wavelengths, whereas the wavelengths are shifted to longer values when the emitting object is receding from the observer. This happens with any form of any energy emitted in waves, including sound and light. Sound propagates in a different manner from electromagnetic energy, but the effect is analogous.

With the sound of a moving object, like with a train, the wavelength of the approaching train horn will sound like a buzzing noise at first getting louder intill it passes you and then fades away at a lower tone. That is because the wavelengths that you are hearing is being squished in the front of the train and then stretched out as it passes by. When the wavelength is shorter (coming closer to you) the frequency of the wavelength is going to be bigger, with a higher pitch. The opposite happens when the wavelength is longer; the frequency will be smaller, which is an effect that rapidly changes to a lower pitch as the train passes, going away from you. This works with light waves as well, in terms of visible light. Approaching objects shift toward shorter wavelengths are called blue shifted. Where as the light of receding objects have longer wavelengths, those wavelengths are known as red shifted. As shown in the diagram below if you’re looking outward from the telescope, you can see the red shift going out toward an object, or in this case an unseen planet. Then there are the blue shifted wavelengths that are coming back towards the telescope from the unseen planet.

The relative speed of stars moving toward or away from the Sun, as detected through the doppler effect, gives clues to the Sun's motion through the Milky Way Galaxy as well as other information about the motion of stars, star clusters and gas clouds in space. The relative motions of binary stars (two stars orbiting around a common center of gravity) can be detected in the variations of their light, and in fact even some binary stars have been detected that cannot be seen as separate stars, but whose binary nature is known from the variations in their combined spectra.

Since both sound and light waves have red and blue shifts, Edwin Hubble was able to use the doppler effect to discover that our neighboring galaxies are receding from the Milky Way. This lead to his conclusion that the universe was expanding. The red shift or more specifically known as the Cosmological Red Shift because of its implications for cosmology; the study of origin and evolution of the universe. Scientist could even go further into discovering more of the universe when they realized they could add velocity to Hubble's equation. Using the shift spectrum they now can find the distances based off of those observations.

title: General Astronomy/The Doppler Effect


text:
General Astronomy/Asteroids

Asteroids are rocky or metallic solar system objects smaller than planets, whose orbits usually lie between Mars and Jupiter, although some venture close to the Sun and even pass dangerously close to Earth. They range in size from a maximum of several hundred kilometers, to an undetermined small size that merges into the category of meteoroids. Some meteoroids are unquestionably of the same composition, origin and structure as asteroids, just smaller. The age of asteroids is derived from that of meteorites, are thought to date from the very early periods of the Solar System, and to have been little changed since then.

There are tens of thousands of asteroids large enough to track, and perhaps hundreds of thousands of smaller size that range into the meteoroids. More than 1000 asteroids of 100 meters or larger (about the length of a city block) that pass close enough to the Earth to be of concern are being tracked.

In October, 2008, a small asteroid roughly the size of an SUV was discovered on a collision course with Earth, only about 20 hours before it impacted the upper atmosphere. The impact produced a fireball explosion approximately one kiloton of TNT in strength, or about one twentieth of the strength of the WWII atomic bombs dropped on Japan. However, this produced no dangerous radiation and occurred harmlessly far above the Earth's surface. Fragments survived and fell over Africa, about 5 kg of which were recovered in the Nubian Desert of Sudan, making this the first time an object had been tracked before impacting Earth, and fragments later recovered. Preliminary investigations are confirming the nature of the asteroidal/meteoroidal connection.

The first asteroid was discovered on the first day of 1800, by Italian astronomer Giuseppe Piazzi, who was part of a larger group of astronomers informally known as the "Celestial Police." The group had been convinced of the existence of a previously unknown planet between Mars and Jupiter, as apparently predicted by a mathematical relationship called Bode's Law (or the Titus-Bode Law). Soon after Piazzi's discovery, which he named Ceres for the Roman Goddess of Grain, others were discovered and their relatively small size deduced. Too small for full planets, they became known as asteroids, or "starlike bodies," or somewhat more appropriately, "minor planets." Ceres, was not only the first but the largest, at 950 km in diameter. It is so large that recently it has been designated as "dwarf planet" rather than an asteroid.

The asteroids are thought to have been small bodies left over at the formation of the Solar System, which were prevented from forming into a larger planet by the overpowering gravitational influence of "nearby" Jupiter. It is likely that some of the original asteroidal bodies collided and broke apart, resulting in the many fragments found today.

title: General Astronomy/Asteroids


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General Astronomy/Meteors and Meteorites

There are different terms for the same object, depending on where it is observed. In space, it is a meteoroid. A meteor is a meteroid that has been captured by some object's gravitational field (e.g., the Earth), and is falling toward it. Meteorites are meteors that have landed.

There are three kinds of meteors: irons, stones, and stony-irons. They usually come from asteroids or the Oort Cloud.
 * Irons are composed of mainly iron.
 * Stones are rocky, and are composed of silicate minerals.
 * Stony-irons are composed of silicate and nickel-iron minerals.


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General Astronomy/Comets

Comets were previously thought of as a, “dirty snowball” but due to the fact that a comet has more dust than ice, they are now referred to as an, “icy dirt ball.” The nucleus is mainly made up of H2O (water), with some parts NH3 (ammonia), CH4 (methane), and CO2 (carbon dioxide). When the Big Bang happened over 4.6 billion years ago, the hydrogen and helium accreted into the first generation of stars, which quickly became supernovae. During which, the heavier elements (collectively called metals) were produced, which once again condensed with hydrogen and helium to form the second generation of stars. Much of the "metals" condensed at that time to form the terrestrial planets, and some of the material became small lumps of frozen gas and dust. These lumps are located in the outer region of the solar system, where temperatures are cold enough to produce ice, thus keeping the lumps frozen. The outer region is called, the Oort Cloud or the Kuiper Belt.  The Oort Cloud is estimated to contain 1011 (one hundred billion) comets.

As the comets orbit our sun, they may be disturbed by close encounters with other objects and some of those move out of the Oort Cloud and toward the sun. As they approach, their frozen gases become vaporized, dust is ejected, and they form streamers called tails. The tails tend to flow behind the nucleus of the comet. The gases and dust are easily influenced by the forces applied to them; which in turn is the sun's photons of light bouncing off of them, and the electromagnetic field that acts on the charged particles. Comets have two tails: the ion tail (blue, composed of gas), and the dust tail (yellow). Meteor showers, like the Perseid or Leonids, occur when the Earth travels through a comet's dust tail.

One of the most famous comets is Halley's Comet, which was discovered by Edmond Halley in 1705. The comet was last seen in 1682; Halley predicted it would return in 1758. Unfortunately, he died in 1742, so he was unable to see his prediction come true. The comet was subsequently named after him.

Halley's Comet has a period of about 76 years. It came by the Earth last in 1986, and will return in 2061.

Chemical Diversity in Comets
It has been postulated that the chemical diversity observed in the population of comets found in the Kuiper Belt (region extended after Neptune orbit) as well as Oort cloud (spherical cloud lie roughly 50,000 AU from the Sun) is primordial.

The chemical abundances were observed in both classes of comets: Oort cloud comets and the Jupiter-Family of comets whose population consisting of short-period comets formed in the Kuiper belt Differences were noted between the two groups. This can be attributed to several factors including differences in the chemical and physical environments in comet-forming regions, chemical evolution during their long storage in the Oort cloud and Kuiper belt, and thermal processing by the Sun when entering the inner Solar System. The chemical composition of comets is investigated by remote sensing using spectroscopy. This investigation is indirect, since only the gas and dust of the coma can be observed after the nucleus ices have sublimated from the nucleus.

Observations were made at millimeter/sub-millimeter wavelengths with the IRAM 30-m, JCMT, CSO and SEST radio telescopes. Six Jupiter-family, three Halley-family, and fifteen long-period comets were observed from 1986 to 2001. The eight molecular species were HCN, HNC, CH3CN, CH3OH, H2CO, CO, CS, and H2S. HCN were detected in all comets, while at least two types of molecules were detected in nineteen comets. It was inferred that the HCN abundance relative to water varies from 0.08% to 0.25% from the sub-sample of comets for which contemporary H2O production rates are available. HCN is the molecule which exhibits the lowest abundance variation from comet to comet with respect to other species and was found in all the 24 Comets. HCN was found only in the four Comets and low CO abundances was measured in Jupiter-family comets, while several Oort cloud comets exhibit high CO abundances. According to the observation 23% of CO molecule with respect to water was observed in 5 comets. While 0.035% of HNC relative to water was observed in 5 comets. Fifteen comets exhibited CH3CN up to maximum 6.2%. And H2CO, H2S and CS was found in 13,11,9 comets respectively. They were found at a concentration maximum up to 1.3%, 1.5% and 0.17% respectively relative to water.

Comet C/2001 Q4 (NEAT)

Comet C/2001 Q4 NEAT was discovered in August 2001 in the course of the Near Earth Asteroid Tracking (NEAT) program. The comet was found on Charged Coupled Device (CCD) images and the astronomers were able to confirm the discovery on August 24. The comet was described as a round nebulosity measuring about 8 arc seconds across at the distance of 10.1 AU from the Sun. The total visual magnitude was 20.0. Its perihelion date was 2004 May 26 and perihelion distance was 1.00 AU. It has an unusual, almost perpendicular retrograde orbit which brings it into the inner solar system by a deeply southward path. It initially emerged from its remote home where it spent most of its time near the south celestial pole. The comet brightened slowly during the remainder of 2001 and throughout 2002. It appeared fainter than magnitude 15 at the beginning of the 2003, but it steadily brightened as the year progressed, to magnitude 12 around mid-September. In September amateur astronomers could easily mark the time of comet in the Southern Hemisphere began supplying regular visual observations of this comet, at which time the diameter of the coma was typically measured as 0.6 to 1.2 arc minutes. In CCD images amateurs began observing a short fan-shaped tail pointing northward in July as on its approached to the Sun. In late September, the tail extended about 0.8 arc minutes toward the northwest. As 2003 came to an end, the comet became slightly brighter than magnitude 10, with a coma diameter of about 2 arc minutes. A faint, fan-shaped tail extended about 4 arc minutes toward the east. Finally, Comet C/2001 Q4 (NEAT) entered the inner solar system in 2004, reaching perihelion of 1 AU. It's peak magnitude of 3.3 rendered it clearly visible to the naked eye. C/2001 Q4 is referred to as an Oort cloud comet as it originated from Oort cloud. It is composed of HCN, CO, CH3OH, H2S and other species.

We know how a comet is formed because of the recent discoveries made in 2009 by NASA’s Deep Impact which impacted Comet Tempel 1 in 2005 that revealed what exactly a comet’s nucleus is made of and its structure.

title: General Astronomy/Comets


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User talk:Gopalpaliwal

Image copyright problem with Image:Tcp udp1.jpg
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Please signify the copyright information on any other images you have uploaded or will upload. Remember that images without this important information or giving false information can be deleted by an administrator. If you have any questions, feel free to contact me, or ask them at the Study help desk. Thank you. -- Herby talk thyme 19:39, 11 November 2006 (UTC)

title: User talk:Gopalpaliwal


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User:Herbythyme/eyeball

Stuff to keep an eye on

Stuff stuff
w:Category:Wikipedia_sockpuppets_of_Johnny_the_Vandal

Pages

 * Scienceshow/Cryogenics - speedy but was wotk in progress - Oct 06, nothing happened so far
 * International Relations/The Making of Foreign Policy
 * Mechatronics - ditto
 * USMLE Step One Review - attention
 * Test Prep for USMLE Step 2 - ditto
 * Emotions - in need of treatment
 * Getting a girl (for guys)/Losing fear - yuk
 * Force in motion - in need of something
 * Stock
 * Remote Viewing - gotta go really
 * Prentice Hall Chemistry - copyvio/large stub????

title: User:Herbythyme/eyeball


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User talk:59.176.6.195

Thank you for experimenting with Wikibooks. Your test worked, and the pages that you created has been or soon will be deleted. Please use the sandbox for any other tests you want to do. Take a look at the welcome page if you would like to learn more about contributing.--Az1568 21:30, 11 November 2006 (UTC)

title: User talk:59.176.6.195


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Talk:Guide to X11/Configuring

Recovery
I think this needs a bit of information on recovering if you've totally b0rked a system by mashing your xorg.conf file. Most of the time you can get to a terminal, which is fine (you can edit, restore a backup or dpkg-reconfigure. But once I completely mashed it - I couldn't Ctrl+Alt+F2 or Ctrl+Alt+Backspace. And of course, restarting automatically started X, so back to the Black Screen of Death I went. I had to start from a live CD and edit the file from there. --H2g2bob 22:25, 11 November 2006 (UTC)

title: Talk:Guide to X11/Configuring


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Template:MATLAB Programming/Nav

 [MATLAB Programming\|/MATLAB Programming]m]

Chapter 1: MATLAB ._. Introductions .
 * Fundamentals of MATLAB
 * MATLAB Workspace
 * MATLAB Variables
 * *.mat files

Chapter 2: MATLAB Concepts
 * MATLAB operator
 * Data File I/O

Chapter 3: Variable Manipulation
 * Numbers and Booleans
 * Strings
 * Portable Functions
 * Complex Numbers

Chapter 4: Vector and matrices
 * Vector and Matrices
 * Special Matrices
 * Operation on Vectors
 * Operation on Matrices
 * Sparse Matrices

Chapter 5: Array
 * Arrays
 * Introduction to array operations
 * Vectors and Basic Vector Operations
 * Mathematics with Vectors and Matrices
 * Struct Arrays
 * Cell Arrays

Chapter 6: Graphical Plotting
 * Basic Graphics Commands
 * Plot
 * Polar Plot
 * Semilogx or Semilogy
 * Loglog
 * Bode Plot
 * Nichols Plot
 * Nyquist Plot

Chapter 7: M File Programming
 * Scripts
 * Comments
 * The Input Function
 * Control Flow
 * Loops and Branches
 * Error Messages

 * Debugging M Files

Chapter 8: Advanced Topics
 * Numerical Manipulation
 * Advanced File I/O
 * Object Oriented Programming
 * Applications and Examples
 * Toolboxes and Extensions

Chapter 9: Bonus chapters
 * MATLAB Benefits and Caveats
 * Alternatives to MATLAB
 * [MATLAB_Programming/GNU_Octave|What is Octave= (8) hsrmonic functions]
 * Octave/MATLAB differences

edit this box

title: Template:MATLAB Programming/Nav


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Cookbook talk:Caramel

Could the author of this book please indicate in the recipe whether they are referring to temperatue in celcius or fahrenheit? 240 and 180 doesn't really help but I'd assume that it's celcius. Xania 23:50, 11 November 2006 (UTC)

Sorry! All temperatures are fahrenheit. I added this to the directions section. thank you.

Request/Question
When I was younger, my grandma made Pecan Turtles using homemade caramel made from sweetened condensed milk. She would boil the unopened cans in a large pot of water until they were solid, but still soft and slightly runny. It was solid enough to spoon onto the turtles but not especially runny. Unfortunately I don't have her recipe, so I don't know how long to boil the cans. Has anyone ever heard of making caramel this way and know how long to boil the cans? I think it'd make an interesting addition to the article as a simpler way to make caramel. 75.206.209.156 07:01, 20 October 2007 (UTC)

Boiling (in water) restricts the heat to 212°F/100°C, which is way too low to cause changes in the sugar required for true caramel. OTOH, heating unopened cans past the canning temperature (near boiling) is dangerous! It's likely that some other (non-candy) process was thickening the 'milk'. Why not try it (boiling them) and see? A little experimentation at that point might get you close enough. Dmforcier (talk) 18:57, 23 January 2008 (UTC)

Notwithstanding the caution above, folks in Latin countries have been making ‘caramel’ by heating sweetened condensed milk in a closed can in a boiling water bath for decades. I was told two hours. Keep an eye on water level so can remains completely immersed in boiling water. Just keep water barely boiling. Keep pan covered. Check water level frequently. Remove paper label from can before cooking. Allow cooked can to cool completely before opening the can. Wordplay7 (discuss • contribs) 11:10, 24 January 2022 (UTC)

Taste.com.au has a recipe for it. Search for ‘Caramel from condensed milk’. Dulce de levhe is Spanish name. Describes in more detail. Note comments. Don’t use cans that have pull-tab top. Wordplay7 (discuss • contribs) 11:26, 24 January 2022 (UTC)

 * dulce de leche Wordplay7 (discuss • contribs) 11:28, 24 January 2022 (UTC)

title: Cookbook talk:Caramel


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User talk:Melllic~enwikibooks

Welcome
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title: User talk:Melllic~enwikibooks


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User talk:Mathics~enwikibooks

Please stop. If you continue to use Wikibooks for advertising, you will be temporarily blocked from editing.--Az1568 00:08, 12 November 2006 (UTC)

This is your last warning. The next time you insert a commercial link you will be blocked from editing Wikibooks.--Az1568 00:10, 12 November 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 Mathics. To make sure that both of you can use all Wikimedia projects in future, we have reserved the name Mathics~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.

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Yours, Keegan Peterzell Community Liaison, Wikimedia Foundation 23:26, 17 March 2015 (UTC)

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title: User talk:Mathics~enwikibooks


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User talk:206.116.76.133

Your change was determined to be unhelpful and has been reverted or removed. Please use the sandbox for any tests you want to do. Take a look at the welcome page if you would like to learn more about contributing. Thanks.--Az1568 01:23, 12 November 2006 (UTC)

title: User talk:206.116.76.133


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Trigonometry/Trigonometric identities

What is an identity?
An identity is an equation that holds true for all values of the variables appearing in it, because it either is a definition or is the logical consequence of a definition. An example of a definitional identity is $$\tan(x)=\frac{\sin(x)}{\cos(x)}.$$  An example of an identity that can logically be proven to hold for all values of its variable is the Pythagorean identity expressed in trigonometric form:  $$sin^2(x)+cos^2(x)=1.$$

Next Page: Graphs of Sine and Cosine Functions

Previous Page: Right Angle Trigonometry

Home: Trigonometry

title: Trigonometry/Trigonometric identities


text:
Talk:Trigonometry/Trigonometric identities

Try to transfer the idenities in right angle trig over to here.

Misleading page name
I agree with the implication of the above comment. The page title implies that if you click on the page you will find a list of trig identities. Instead there is just a definition of identity along with two examples to illustrate the definition. At least some basic identities should be put into this page. But then we need to decide what to do with the pages that the identities are transferred from. Douglas W. Mitchell (talk) 15:55, 27 August 2010 (UTC)


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Adventist Youth Honors Answer Book/Nature/Orchids

1. Define the characteristics of an orchid.
Orchids are monocot plants characterised by the presence of three sepals, two petals and the third petal modified as a lip.

2. What are the two main groupings of orchids? Name and show examples of each from a live plant or picture.
There are five identified groupings of orchids. (Also see Taxonomy of the Orchid family)

The last two, Epidendroideae and Orchidoideae are the largest subfamilies (main groupings).
 * Apostasioideae: 2 group(s) in this sub-family and 16 species, south-western Asia
 * Cypripedioideae: 5 group(s) in this sub-family and 130 species, mostly from the temperate regions of the world, some in tropical America
 * Vanilloideae: 15 group(s) in this sub-family and 180 species, humid tropical and subtropical regions, eastern North America
 * Epidendroideae: more than 500 group(s) in this sub-family and more or less 20 000 species, cosmopolitan
 * Orchidoideae: 208 group(s) in this sub-family and 3,630 species, cosmopolitan

Epiphytic
An epiphytic is an organism that grows upon or attached to a living plant.

Parasitic
Parasitic is symbiosis or "living together", a phenomenon in which two organisms which are unrelated co-exist over a long period of time, usually the lifetime of one of the individuals. A parasitic relationship does not benefit the host and can, in fact, be detrimental to it.

Saprophytic
A saprotroph (or saprobe) is an organism that obtains its nutrients from non-living organic matter, usually dead and decaying plant or animal matter, by absorbing soluble organic compounds. They cannot make food for themselves.

Distribution
Orchids are cosmopolitan, occurring in almost every habitat. The great majority are to be found in the tropics, mostly Asia, South America and Central America. They are found above the Arctic Circle, in southern Patagonia and even on Macquarie Island, close to Antarctica.

The following list gives a rough overview of their distribution:
 * tropical America: 300 to 350 genera
 * tropical Asia: 250 to 300 genera
 * tropical Africa: 125 to 150 genera
 * Oceania: 50 to 70 genera
 * Europe and temperate Asia: 40 to 60 genera
 * North America: 20 to 30 genera

5. Name the main cultivated genera of orchids. Identify three from plants or picture. What is cultivar?
Most cultivated orchids are tropical or subtropical, but quite a few which grow in colder climates can be found on the market.

Temperate species available at nurseries include:
 * Ophrys apifera (bee orchid),
 * Gymnadenia conopsea (fragrant orchid),
 * Anacamptis pyramidalis (pyramidal orchid) and
 * Dactylorhiza fuchsii (common spotted orchid).

The main cultivated genera of orchids is Epidendroideae.

6. Discuss the main essentials to observe in the cultivation of orchids. Grow at least one orchid for at least six months.

 * Light - is important in all living things.
 * Temperature - mature plants need a 15-20 degree F temperature difference between day and night.
 * Water - seedlings need more moisture, mature plants must dry out between watering.
 * Humidity -
 * Fertilizer - remember that these are usually parasitic plants.
 * Potting - plant in material that allows good aeration and drainage.

The Wikipedia article Hippeastrum has detailed instructions for growing this orchid throughout the year. Another common houseplant orchid is the Cymbidium.

Another option is to grow your orchids using hydroponics, which satisfies a requirement of the Voyager curriculum. Again Wikipedia has an article called "Hydroponics for orchid cultivation" which is filled with important details.

Have a fun time growing your orchid(s).

Main Uses of Orchids

 * The underground tubers of terrestrial orchids (mainly Orchis mascula) are ground to a powder and used for cooking, such as in the hot beverage salep or the so-called "fox-testicle ice cream" salepi dondurma.
 * The scent of orchids is frequently analysed by perfumists (using Gas-liquid chromatography) to identify potential fragrance chemicals.
 * The other important use of orchids is their cultivation for the enjoyment of the flowers.

What orchid is used commercially?

 * Vanilla is a flavoring derived from orchids in the genus Vanilla native to Mexico. The name came from the Spanish word vainilla, meaning little pod.

Navasota Ladies'-Tresses
The Navasota Ladies'-Tresses (Spiranthes parksii) is on the Federal endangered species list Reason for Concern: Navasota ladies-tresses is endemic to the Oak Woodlands and Prairies region of east-central Texas. Once thought to be extremely rare, it is now known to be locally common in parts of its range. However, many of the sites are near an active coal stripmining operation. Other sites are within the area of Bryan-College Station and are threatened by the rapid development of this metroplex.
 * http://www.tpwd.state.tx.us/huntwild/wild/species/endang/plants/navasolt.phtml

 * How YOU Can Help to Protect Wild Orchids

Pink Lady's Slipper
Cypripedium acaule, or Pink Lady's Slipper, is endangered in Nova Scotia, Canada, and in the U.S. States of Georgia, Tennessee, Illinois, and New York. Because of a fungus association needed for growth, and the high acid this plant needs, C. acaule is very difficult to grow in the average garden and is unlikely to survive any attempts at transplantation. It should not be removed or disturbed if found in nature.

Showy Lady's Slipper
Cypripedium reginae, or Showy Lady's Slipper is endangered (or extirpated) in the U.S. States of Arkansas, Connecticut, Illinois, Iowa, Kentucky, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, and Tennessee.


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User:Pdavis68

A Bit About Me
My name is Pete Davis. I've been a software engineer, professionally, for roughly 30 years. I currently live in Fayetteville, Arkansas, USA.

I love most areas of science.

My Contributions
Contributed to the Organic Chemistry textbook years ago.

To date, my primary contributions to the Organic Chemistry text have been in:

 * Alkenes
 * Cycloalkanes
 * Visualization

I'm personally of the opinion that the Organic Chemistry text still needs a great deal of work to become a usable textbook. That's not to say that there aren't some good and complete sections, but it is far from complete enough to teach a class from. I hope to see it get to that point some day, however.

I'm currently working on the Electronics textbook, specifically the vacuum tube section.

title: User:Pdavis68