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Reflection (physics)

Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves. The law of reflection says that for specular reflection (for example at a mirror) the angle at which the wave is incident on the surface equals the angle at which it is reflected.

In acoustics, reflection causes echoes and is used in sonar. In geology, it is important in the study of seismic waves. Reflection is observed with surface waves in bodies of water. Reflection is observed with many types of electromagnetic wave, besides visible light. Reflection of VHF and higher frequencies is important for radio transmission and for radar. Even hard X-rays and gamma rays can be reflected at shallow angles with special "grazing" mirrors.

Reflection of light
Reflection of light is either specular (mirror-like) or diffuse (retaining the energy, but losing the image) depending on the nature of the interface. In specular reflection the phase of the reflected waves depends on the choice of the origin of coordinates, but the relative phase between s and p (TE and TM) polarizations is fixed by the properties of the media and of the interface between them.

A mirror provides the most common model for specular light reflection, and typically consists of a glass sheet with a metallic coating where the significant reflection occurs. Reflection is enhanced in metals by suppression of wave propagation beyond their skin depths. Reflection also occurs at the surface of transparent media, such as water or glass.

In the diagram, a light ray PO strikes a vertical mirror at point O, and the reflected ray is OQ. By projecting an imaginary line through point O perpendicular to the mirror, known as the normal, we can measure the angle of incidence, θi and the angle of reflection, θr. The law of reflection states that θi = θ''r, or in other words, the angle of incidence equals the angle of reflection.

In fact, reflection of light may occur whenever light travels from a medium of a given refractive index into a medium with a different refractive index. In the most general case, a certain fraction of the light is reflected from the interface, and the remainder is refracted. Solving Maxwell's equations for a light ray striking a boundary allows the derivation of the Fresnel equations, which can be used to predict how much of the light is reflected, and how much is refracted in a given situation. This is analogous to the way impedance mismatch in an electric circuit causes reflection of signals. Total internal reflection of light from a denser medium occurs if the angle of incidence is greater than the critical angle.

Total internal reflection is used as a means of focusing waves that cannot effectively be reflected by common means. X-ray telescopes are constructed by creating a converging "tunnel" for the waves. As the waves interact at low angle with the surface of this tunnel they are reflected toward the focus point (or toward another interaction with the tunnel surface, eventually being directed to the detector at the focus). A conventional reflector would be useless as the X-rays would simply pass through the intended reflector.

When light reflects off of a material with higher refractive index than the medium in which is traveling, it undergoes a 180° phase shift. In contrast, when light reflects off of a material with lower refractive index the reflected light is in phase with the incident light. This is an important principle in the field of thin-film optics.

Specular reflection forms images. Reflection from a flat surface forms a mirror image, which appears to be reversed from left to right because we compare the image we see to what we would see if we were rotated into the position of the image. Specular reflection at a curved surface forms an image which may be magnified or demagnified; curved mirrors have optical power. Such mirrors may have surfaces that are spherical or parabolic.

Laws of reflection

If the reflecting surface is very smooth, the reflection of light that occurs is called specular or regular reflection. The laws of reflection are as follows:
 * 1) The incident ray, the reflected ray and the normal to the reflection surface at the point of the incidence lie in the same plane.
 * 2) The angle which the incident ray makes with the normal is equal to the angle which the reflected ray makes to the same normal.
 * 3) The reflected ray and the incident ray are on the opposite sides of the normal.

These three laws can all be derived from the Fresnel equations.

Mechanism

In classical electrodynamics, light is considered as an electromagnetic wave, which is described by Maxwell's equations. Light waves incident on a material induce small oscillations of polarisation in the individual atoms (or oscillation of electrons, in metals), causing each particle to radiate a small secondary wave in all directions, like a dipole antenna. All these waves add up to give specular reflection and refraction, according to the Huygens–Fresnel principle.

In the case of dielectrics such as glass, the electric field of the light acts on the electrons in the material, and the moving electrons generate fields and become new radiators. The refracted light in the glass is the combination of the forward radiation of the electrons and the incident light. The reflected light is the combination of the backward radiation of all of the electrons.

In metals, electrons with no binding energy are called free electrons. When these electrons oscillate with the incident light, the phase difference between their radiation field and the incident field is π (180°), so the forward radiation cancels the incident light, and backward radiation is just the reflected light.

Light–matter interaction in terms of photons is a topic of quantum electrodynamics, and is described in detail by Richard Feynman in his popular book QED: The Strange Theory of Light and Matter.

Diffuse reflection

When light strikes the surface of a (non-metallic) material it bounces off in all directions due to multiple reflections by the microscopic irregularities inside the material (e.g. the grain boundaries of a polycrystalline material, or the cell or fiber boundaries of an organic material) and by its surface, if it is rough. Thus, an 'image' is not formed. This is called diffuse reflection. The exact form of the reflection depends on the structure of the material. One common model for diffuse reflection is Lambertian reflectance, in which the light is reflected with equal luminance (in photometry) or radiance (in radiometry) in all directions, as defined by Lambert's cosine law.

The light sent to our eyes by most of the objects we see is due to diffuse reflection from their surface, so that this is our primary mechanism of physical observation.

Retroreflection

Some surfaces exhibit retroreflection. The structure of these surfaces is such that light is returned in the direction from which it came.

When flying over clouds illuminated by sunlight the region seen around the aircraft's shadow will appear brighter, and a similar effect may be seen from dew on grass. This partial retro-reflection is created by the refractive properties of the curved droplet's surface and reflective properties at the backside of the droplet.

Some animals' retinas act as retroreflectors (see tapetum lucidum for more detail), as this effectively improves the animals' night vision. Since the lenses of their eyes modify reciprocally the paths of the incoming and outgoing light the effect is that the eyes act as a strong retroreflector, sometimes seen at night when walking in wildlands with a flashlight.

A simple retroreflector can be made by placing three ordinary mirrors mutually perpendicular to one another (a corner reflector). The image produced is the inverse of one produced by a single mirror. A surface can be made partially retroreflective by depositing a layer of tiny refractive spheres on it or by creating small pyramid like structures. In both cases internal reflection causes the light to be reflected back to where it originated. This is used to make traffic signs and automobile license plates reflect light mostly back in the direction from which it came. In this application perfect retroreflection is not desired, since the light would then be directed back into the headlights of an oncoming car rather than to the driver's eyes.

Multiple reflections
When light reflects off a mirror, one image appears. Two mirrors placed exactly face to face give the appearance of an infinite number of images along a straight line. The multiple images seen between two mirrors that sit at an angle to each other lie over a circle. The center of that circle is located at the imaginary intersection of the mirrors. A square of four mirrors placed face to face give the appearance of an infinite number of images arranged in a plane. The multiple images seen between four mirrors assembling a pyramid, in which each pair of mirrors sits an angle to each other, lie over a sphere. If the base of the pyramid is rectangle shaped, the images spread over a section of a torus.

Note that these are theoretical ideals, requiring perfect alignment of perfectly smooth, perfectly flat perfect reflectors that absorb none of the light. In practice, these situations can only be approached but not achieved because the effects of any surface imperfections in the reflectors propagate and magnify, absorption gradually extinguishes the image, and any observing equipment (biological or technological) will interfere.

Complex conjugate reflection
In this process (which is also known as phase conjugation), light bounces exactly back in the direction from which it came due to a nonlinear optical process. Not only the direction of the light is reversed, but the actual wavefronts are reversed as well. A conjugate reflector can be used to remove aberrations from a beam by reflecting it and then passing the reflection through the aberrating optics a second time. If one were to look into a complex conjugating mirror, it would be black because only the photons which left the pupil would reach the pupil.

Neutron reflection
Materials that reflect neutrons, for example beryllium, are used in nuclear reactors and nuclear weapons. In the physical and biological sciences, the reflection of neutrons off of atoms within a material is commonly used to determine the material's internal structure.

Sound reflection

When a longitudinal sound wave strikes a flat surface, sound is reflected in a coherent manner provided that the dimension of the reflective surface is large compared to the wavelength of the sound. Note that audible sound has a very wide frequency range (from 20 to about 17000 Hz), and thus a very wide range of wavelengths (from about 20 mm to 17 m). As a result, the overall nature of the reflection varies according to the texture and structure of the surface. For example, porous materials will absorb some energy, and rough materials (where rough is relative to the wavelength) tend to reflect in many directions—to scatter the energy, rather than to reflect it coherently. This leads into the field of architectural acoustics, because the nature of these reflections is critical to the auditory feel of a space. In the theory of exterior noise mitigation, reflective surface size mildly detracts from the concept of a noise barrier by reflecting some of the sound into the opposite direction. Sound reflection can affect the acoustic space.

Seismic reflection
Seismic waves produced by earthquakes or other sources (such as explosions) may be reflected by layers within the Earth. Study of the deep reflections of waves generated by earthquakes has allowed seismologists to determine the layered structure of the Earth. Shallower reflections are used in reflection seismology to study the Earth's crust generally, and in particular to prospect for petroleum and natural gas deposits.

title: Reflection (physics)


text:
User:LiYan~enwiki

I am living in Shanghai.

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

title: User:LiYan~enwiki


text:
Pin the tail on the donkey

Pin the tail on the donkey is a game played by groups of children. The earliest version listed in a catalog of American games compiled by the American Game Collectors Association in 1998, is dated 1899, and attributed to Kate Hunt.

It is common at birthday parties and other gatherings. A picture of a donkey with a missing tail is tacked to a wall within easy reach of children. One at a time, each child is blindfolded and handed a paper "tail" with a push pin or thumbtack poked through it. The blindfolded child is then spun around until disoriented. The child gropes around and tries to pin the tail on the donkey. The player who pins their tail closest to the target, the donkey's rear, wins. The game, a group activity, is generally not competitive; "winning" is only of marginal importance. It is often seen as more entertaining, seeing the children stumble around and try to put their tail at the right place.

The game is also used in child development research.

The game can also be played by teenagers and adults, especially if the "donkey" is replaced with depictions of something or someone else. As a drinking game, the person with the worst tail pinning is awarded one shot of a selected alcohol, to be determined by house rules or the loser in a friendly environment.

Idiomatically, the term can be used derisively for any assigned activity which is pointless or for which a person has been handicapped (blindfolded).

title: Pin the tail on the donkey


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Karambit

The karambit or kerambit (as used in Indonesian), kurambik or karambiak (both from the Minangkabau language) is a small Indonesian curved knife resembling a claw, associated with the Minangkabau people of West Sumatra. The karambit is one of the weapons commonly used in pencak silat and Filipino martial arts.

Origin

The karambit was originally an agricultural implement designed to rake roots, gather threshing and plant rice in most of island Southeast Asia. It's a smaller variant of the Southeast Asian sickles (Filipino garab and karit; Indonesian celurit, arit, or sabit; and Malaysian sabit). It still possesses many efficient uses for the modern laborer, allowing use of the blade for utility work, with the finger ring eliminating the need to put the knife down between operations, if use of the fingers to manipulate the object to be worked on is required (such as the action of cutting and opening a shipping box, or removing plastic wrap from shipments, in two very basic examples). The finger ring also provides an added degree of protection against dropping the knife during use, which is particularly essential in work environments that include heavy machinery, into which dropping a handheld, metal tool of any kind can cause massive damage to the equipment and those around it, especially if the tool is ejected at high velocity from rotating components. The karambit is believed to have originally been weaponized among the Minangkabau people of West Sumatra where, according to folklore, it was inspired by the claws of a tiger. As it was weaponised, the blade became more curved to maximise cutting potential. Through Indonesia's trade network and close contact with neighbouring countries, the weaponization of the karambit was eventually dispersed through what are now Thailand, Cambodia, Laos, Myanmar and the Philippines.

European accounts tell that soldiers in Indonesia were armed with a kris at their waist or back and a spear in their hands, while the karambit was used as a last resort when the fighter's other weapons were lost in battle. The renowned Bugis warriors of Sulawesi were famous for their embrace of the karambit. Today it is one of the main weapons of silat and is commonly used in Filipino martial arts as well.

Superficially, the karambit resembles the jambiyah, although there is no connection. The jambiyah was always designed as a weapon and serves as a status marker, often made by skilled artisans and jewelers using precious stones and metals, whereas the karambit was and still remains an unadorned farmer's implement and utility knife.

Technique
The karambit is held with the blade pointing downward from the bottom of the fist, usually curving forwards. While it is primarily used in a slashing or hooking motion, karambit with a finger ring are also used in a punching motion hitting the opponent with the finger ring. Some karambit are designed to be used in a hammering motion. This flexibility of striking methods is what makes it useful in self-defense situations. The finger guard makes it difficult to disarm and allows the knife to be maneuvered in the fingers without losing one's grip.

The short Filipino karambit has found some favor in the West because such proponents allege the biomechanics of the weapon allow for more powerful cutting strokes and painful "ripping" wounds, and because its usability is hypothesized as more intuitive, but more difficult to master than a classic knife.

Variations
There are many regional variants of karambit. The length of the blade, for example, could vary from one village or blacksmith to another. Some have no finger guard and some feature two blades, one on each side of the handle. Traditional types include:
 * Kuku Bima: Bhima's claw from West Java
 * Kuku Hanuman: Hanuman's claw from West Java
 * Kuku Macan: tiger's claw, endemic to Sumatra, Central Java and Madura
 * Kerambit Sumbawa: larger, sturdier kerambit made specially for battle. From the Sumba Islands
 * Kerambit Lombok: larger, sturdier kerambit made specially for battle. From Lombok
 * Lawi Ayam: chicken's claw, created by the Minang community

Additionally, modern karambit may have spikes or spurs on the front or rear ricasso, which may be intended for gripping clothing or horse tack, tearing flesh or for injecting a poison, such as the upas.

Modern forms
The modern Western interpretation of the karambit is far removed from the original agricultural tool. They may have folding blades, are finished to a high standard, made from expensive materials as opposed to being rudimentary and makeshift and are generally larger to accommodate larger hands giving it pure shape.

title: Karambit


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Bel Riose

Bel Riose is a fictional character in the Foundation series by Isaac Asimov. In the 1945 novella "Dead Hand", he is the last great general of the declining Galactic Empire. He targets the Foundation both as a perceived threat to the Empire and to further his own ambitions, but is outmaneuvered by its agents.

Riose is voiced by Dinsdale Landen in the 1973 BBC Radio 4 adaptation The Foundation Trilogy. He is portrayed by Ben Daniels in season two of the 2021 Apple TV+ television series adaptation Foundation.

Literature
Bel Riose appears in the novella "Dead Hand", published in the April 1945 issue of Astounding Science Fiction. It was later retitled "The General" and paired with the November/December 1945 novella "The Mule", and published as Foundation and Empire in 1952.

Description
Riose is loosely based on Belisarius, a great general of the Roman Empire who served Justinian I during the 6th century AD.  Josh Wimmer and Alasdair Wilkins of Gizmodo wrote: "Bel Riose might be the best example I've seen of an anti-villain—his goal is the destruction of the Foundation and the defeat of the Seldon Plan, and he can be quite brutal in his means, but he's fundamentally honorable, honest, and really rather brilliant. You might even call him the tragic hero of the Foundation series, struggling in vain against the forces of history for no greater reason than to prove that he can. He certainly gets an appropriately tragic ending."

James E. Gunn saw Riose as "the only character who stares in the face of determinism". While his failure against the forces of historic necessity might seem depressing, the fact that he is not the viewpoint character changes the impact of the story: The reader sympathizes with the Foundation. Riose's failure is depicted as desirable, as it ensures the Foundation's survival.

Plot
In "Dead Hand", Imperial General Bel Riose governs the planet Siwenna. He investigates the Foundation and is soon determined to destroy it, both as a perceived threat to the Empire and to further his own ambitions. Foundation trader Lathan Devers lets himself be captured by Riose to disrupt his overtures against the Foundation from the inside. With Emperor Cleon II's Privy Secretary Ammel Brodrig present to observe Riose, Devers attempts to implicate Riose in a nonexistent attempt to overthrow Cleon. His machinations are exposed, but Ducem Barr, a Foundation sympathizer forced to aid Riose, helps him escape further interrogation by knocking Riose unconscious and fleeing the planet with Devers in tow. They travel to the Imperial capital planet, Trantor, and plot to influence Cleon directly with Devers' invented conspiracy, implicating both Riose and Brodrig. Though they are caught by the Secret Police, they escape and later learn that Riose and Brodrig have been arrested for treason and executed. Asimov later explains the political dynamics of why Riose would never have been able to defeat the Foundation: a strong emperor's sense of self-preservation would never allow him to tolerate a subordinate who develops potentially threatening power.

Radio
Riose is voiced by Dinsdale Landen in episode four "The General" of the 1973 BBC Radio 4 adaptation The Foundation Trilogy.

Television
Riose is portrayed by Ben Daniels in season two of the 2021 Apple TV+ television series adaptation Foundation. He is the last great general of the Superliminal Fleet, imprisoned by Emperor Cleon for breaking orders to save troops, despite still achieving a victory. Riose is described as "noble to a fault, but his fealty to the Galactic Empire is waning." The Empire has learned that the Foundation has not been destroyed as had been previously believed, and is in fact flourishing and amassing influence. Riose, known to be ruthless and unpredictable, seems the perfect military leader to set upon the Foundation, but he is also bitter toward the Empire. Sean T. Collins of Decider wrote, "I enjoyed Bel Riose's case for rejoining the government that destroyed him even though Empire clearly fears his strength: As the only human whom Cleon does not see as dispensable, it's his responsibility to protect the citizens of the Empire, since Empire himself cannot and will not."

Storyline
In the 2023 episode "King and Commoner", Cleon's emissary Lady Demerzel visits Riose at the Lepsis penal colony, offering him his freedom to investigate the Foundation on behalf of the Empire. He is also reunited with his husband and former second-in-command, Glawen Curr, both men having been previously told that the other was executed. In "Where the Stars are Scattered Thinly", Riose and Curr visit Imperial informant Ducem Barr on Siwenna and learn that the Foundation, and by extension their propagandists the Church of the Galactic Spirit, possess auras, protective force shield technology forbidden to everyone except the Emperors, and whisper-ships, a Foundation-created type of jumpship which can perform faster-than-light travel without requiring an enhanced human Spacer to navigate. As Riose and Curr flee an anti-Imperial mob, Riose mercy kills Barr at his request. Riose and Curr debate their options for turning against Empire in "A Necessary Death", but Riose ultimately declares any such action to be too great a risk.

The Imperial fleet faces off against the Foundation in "Long Ago, Not Far Away", and Riose believes he can end the conflict without violence. But the Emperor clone Brother Day, baited by Hari Seldon, orders Riose to crash the Invictus, an ancient Imperial warship commandeered by the Foundation, into Terminus to devastate the planet and destroy the Foundation. Riose reluctantly does so, even though he knows Curr is on the surface. In the season two finale "Creation Myths", She-Bends-Light, a Spacer on Riose's flagship Shining Destiny, uses a jump sequence smuggled onboard by con man Hober Mallow to program the fleet's warships to jump into one another, which will inevitably consume the entire fleet and free the remaining Spacers from Empire. Riose battles Day in hand-to-hand combat, and uses Mallow's castling device to switch places with Day via teleportation, venting the Emperor into space and killing him. Trapped on the doomed flagship, Riose and Mallow share a toast as the Shining Destiny explodes. Meanwhile, Curr and the population of Terminus have escaped the planet's destruction via Seldon's Vault.

Reception
Collins wrote, "Ben Daniels, who goes from a hermit of the wastes to one of the handsomest men on TV with a shave and a haircut, has a great deal of screen presence as Bel". Series executive producer David S. Goyer called Riose his favorite Foundation character. He said that the deaths of Riose and Mallow were always planned for season two, adding that "I like that they meet their fates twinned together". Gary Grimes of Attitude described the emotional reunion of Riose and Curr as "a cornerstone moment in the high-octane series." The series depicts their homosexuality as a non-issue. Curr's portrayer, Dino Fetscher, said "It was so refreshing that our characters' sexualities were just incidental ... In this world, sexuality is very different. It's just the same as you have blue eyes and I have brown eyes. In lots of ways, it's really inspiring because it's not so far in the future."

title: Bel Riose


text:
User:Nul~enwiki

de:Benutzer:Nul es:Usuario:Nul fr:Utilisateur:Nul it:Utente:Nul &

title: User:Nul~enwiki


text:
Critical infrastructure

Critical infrastructure, or critical national infrastructure (CNI) in the UK, describes infrastructure considered essential by governments for the functioning of a society and economy and deserving of special protection for national security. Critical infrastructure has traditionally been viewed as under the scope of government due to its strategic importance, yet there's an observable trend towards its privatization, raising discussions about how the private sector can contribute to these essential services.

Items
Most commonly associated with the term are assets and facilities for:
 * Shelter; Heating (e.g. natural gas, fuel oil, district heating);
 * Agriculture, food production and distribution;
 * Education, skills development and technology transfer / basic subsistence and unemployment rate statistics;
 * Water supply (drinking water, waste water/sewage, stemming of surface water (e.g. dikes and sluices));
 * Public health (hospitals, ambulances);
 * Transportation systems (fuel supply, railway network, airports, harbours, inland shipping);
 * Security services (police, military).
 * Electricity generation, transmission and distribution; (e.g. natural gas, fuel oil, coal, nuclear power)
 * Renewable energy, which are naturally replenished on a human timescale, such as sunlight, wind, rain, tides, waves, and geothermal heat.
 * Telecommunication; coordination for successful operations
 * Economic sector; Goods and services and financial services (banking, clearing);

Canada
The Canadian Federal Government identifies the following 10 Critical Infrastructure Sectors as a way to classify essential assets.
 * 1) Energy & Utilities: Electricity providers; off-shore/on-shore oil & gas; coal supplies, natural gas providers; home fuel oil; gas station supplies; alternative energy suppliers (wind, solar, other)
 * 2) Information and Communication Technology: Broadcast Media; telecommunication providers (landlines, cell phones, internet, wifi); Postal services;
 * 3) Finance: Banking services, government finance/aid departments; taxation
 * 4) Health: Public health & wellness programs, hospital/clinic facilities; blood & blood products
 * 5) Food: Food supply chains; food inspectors; import/export programs; grocery stores; Agri & Acqua culture; farmers markets
 * 6) Water: Water supply & protection; wastewater management; fisheries & ocean protection programs
 * 7) Transportation: Roads, bridges, railways, aviation/airports; shipping & ports; transit
 * 8) Safety: Emergency responders; public safety programs
 * 9) Government: Military; Continuity of governance
 * 10) Manufacturing: Industry, economic development

European Union
European Programme for Critical Infrastructure Protection (EPCIP) refers to the doctrine or specific programs created as a result of the European Commission's directive EU COM(2006) 786 which designates European critical infrastructure that, in case of fault, incident, or attack, could impact both the country where it is hosted and at least one other European Member State. Member states are obliged to adopt the 2006 directive into their national statutes.

It has proposed a list of European critical infrastructures based upon inputs by its member states. Each designated European Critical Infrastructures (ECI) will have to have an Operator Security Plan (OSP) covering the identification of important assets, a risk analysis based on major threat scenarios and the vulnerability of each asset, and the identification, selection and prioritisation of counter-measures and procedures.

Germany
The German critical-infrastructure protection programme KRITIS is coordinated by the Federal Ministry of the Interior. Some of its special agencies like the German Federal Office for Information Security or the Federal Office of Civil Protection and Disaster Assistance BBK deliver the respective content, e.g., about IT systems.

Singapore
In Singapore, critical infrastructures are mandated under the Protected Areas and Protected Places Act. In 2017, the Infrastructure Protection Act was passed in Parliament, which provides for the protection of certain areas, places and other premises in Singapore against security risks. It came into force in 2018.

United Kingdom
In the UK, the National Protective Security Authority (NPSA) provides information, personnel and physical security advice to the businesses and organizations which make up the UK's national infrastructure, helping to reduce its vulnerability to terrorism and other threats.

It can call on resources from other government departments and agencies, including MI5, the National Cyber Security Centre (NCSC) and other government departments responsible for national infrastructure sectors.

United States
The U.S. has had a wide-reaching critical infrastructure protection program in place since 1996. Its Patriot Act of 2001 defined critical infrastructure as those "systems and assets, whether physical or virtual, so vital to the United States that the incapacity or destruction of such systems and assets would have a debilitating impact on security, national economic security, national public health or safety, or any combination of those matters."

In 2014 the NIST Cybersecurity Framework was published, and quickly became a popular set of guidelines, despite the significant costs of full compliance.

These have identified a number of critical infrastructures and responsible agencies:

 * 1) Agriculture and food – Departments of Agriculture and Health and Human Services
 * 2) Water – Environmental Protection Agency
 * 3) Public Health – Department of Health and Human Services
 * 4) Emergency Services – Department of Homeland Security
 * 5) Government – Department of Homeland Security
 * 6) Defense Industrial Base – Department of Defense
 * 7) Information and Telecommunications – Department of Commerce
 * 8) Energy – Department of Energy
 * 9) Transportation and Shipping – Department of Transportation
 * 10) Banking and Finance – Department of the Treasury
 * 11) Chemical Industry and Hazardous Materials – Department of Homeland Security
 * 12) Post  – Department of Homeland Security
 * 13) National monuments and icons - Department of the Interior
 * 14) Critical manufacturing - Department of Homeland Security (14th sector announced March 3, 2008; recorded April 30, 2008)

National Infrastructure Protection Plan
The National Infrastructure Protection Plan (NIPP) defines critical infrastructure sector in the US. Presidential Policy Directive 21 (PPD-21), issued in February 2013 entitled Critical Infrastructure Security and Resilience mandated an update to the NIPP. This revision of the plan established the following 16 critical infrastructure sectors:

 * 1) Chemical
 * 2) Commercial facilities
 * 3) Communications
 * 4) Critical manufacturing
 * 5) Dams
 * 6) Defense industrial base
 * 7) Emergency services
 * 8) Energy
 * 9) Financial services
 * 10) Food and agriculture
 * 11) Government facilities
 * 12) Healthcare and public health
 * 13) Information technology
 * 14) Nuclear reactors, materials, and waste
 * 15) Transportation systems
 * 16) Water and wastewater systems

National Monuments and Icons along with the postal and shipping sector were removed in 2013 update to the NIPP. The 2013 version of the NIPP has faced criticism for lacking viable risk measures. The plan assigns the following agencies sector-specific coordination responsibilities:

 * Department of Homeland Security
 * Chemical
 * Commercial facilities
 * Communications
 * Critical manufacturing
 * Dams
 * Emergency services
 * Government facilities (jointly with General Services Administration)
 * Information technology
 * Nuclear reactors, materials, and waste
 * Transportation systems (jointly with Department of Transportation)

 * Department of Defense
 * Defense industrial base

 * Department of Energy
 * Energy

 * Department of the Treasury
 * Financial services

 * Department of Agriculture
 * Food and agriculture

 * General Services Administration
 * Government facilities (jointly with Department of Homeland Security)

 * Department of Health and Human Services
 * Healthcare and Public Health

 * Department of Transportation
 * Transportation systems (jointly with Department of Homeland Security)

 * Environmental Protection Agency
 * Water and wastewater systems

State-level legislation
Several U.S. states have passed "critical infrastructure" bills, promoted by the American Legislative Exchange Council (ALEC), to criminalize protests against the fossil fuel industry. In May 2017, Oklahoma passed legislation which created felony penalties for trespassing on land considered critical infrastructure, including oil and gas pipelines, or conspiring to do so; ALEC introduced a version of the bill as a model act and encouraged other states to adopt it. In June 2020, West Virginia passed the Critical Infrastructure Protection Act, which created felony penalties for protests against oil and gas facilities.

Stress testing
Critical infrastructure (CI) such as highways, railways, electric power networks, dams, port facilities, major gas pipelines or oil refineries are exposed to multiple natural and human-induced hazards and stressors, including earthquakes, landslides, floods, tsunami, wildfires, climate change effects or explosions. These stressors and abrupt events can cause failures and losses, and hence, can interrupt essential services for the society and the economy. Therefore, CI owners and operators need to identify and quantify the risks posed by the CIs due to different stressors, in order to define mitigation strategies and improve the resilience of the CIs. Stress tests are advanced and standardised tools for hazard and risk assessment of CIs, that include both low-probability high-consequence (LP-HC) events and so-called extreme or rare events, as well as the systematic application of these new tools to classes of CI.

Stress testing is the process of assessing the ability of a CI to maintain a certain level of functionality under unfavourable conditions, while stress tests consider LP-HC events, which are not always accounted for in the design and risk assessment procedures, commonly adopted by public authorities or industrial stakeholders. A multilevel stress test methodology for CI has been developed in the framework of the European research project STREST, consisting of four phases:

Phase 1: Preassessment, during which the data available on the CI (risk context) and on the phenomena of interest (hazard context) are collected. The goal and objectives, the time frame, the stress test level and the total costs of the stress test are defined.

Phase 2: Assessment, during which the stress test at the component and the system scope is performed, including fragility and risk analysis of the CIs for the stressors defined in Phase 1. The stress test can result in three outcomes: Pass, Partly Pass and Fail, based on the comparison of the quantified risks to acceptable risk exposure levels and a penalty system.

Phase 3: Decision, during which the results of the stress test are analyzed according to the goal and objectives defined in Phase 1. Critical events (events that most likely cause the exceedance of a given level of loss) and risk mitigation strategies are identified.

Phase 4: Report, during which the stress test outcome and risk mitigation guidelines based on the findings established in Phase 3 are formulated and presented to the stakeholders.

This stress-testing methodology has been demonstrated to six CIs in Europe at component and system level: an oil refinery and petrochemical plant in Milazzo, Italy; a conceptual alpine earth-fill dam in Switzerland; the Baku–Tbilisi–Ceyhan pipeline in Turkey; part of the Gasunie national gas storage and distribution network in the Netherlands; the port infrastructure of Thessaloniki, Greece; and an industrial district in the region of Tuscany, Italy. The outcome of the stress testing included the definition of critical components and events and risk mitigation strategies, which are formulated and reported to stakeholders.

title: Critical infrastructure


text:
User:Ian Maxwell

I am none of these Ian Maxwells.

Wow, I haven't looked at this in a while! Just about everything I had here before is no longer true. What's in the infobox over there... that's pretty much true.

title: User:Ian Maxwell


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Trbovlje

Trbovlje (Trifail ) is Slovenia's tenth-largest town, and the seat of the Municipality of Trbovlje. It is located in the valley of a minor left tributary of the Sava River in the Central Sava Valley in central-eastern Slovenia.

Name
Trbovlje was attested in written sources in 1220–30 as Trefeul (and as Trevůl and Trevol in 1265–67, Triuella in 1302, Trifeul in 1325, Triueal in 1330, and Triuel in 1424). The name is a feminine plural noun in standard Slovene, but in the local dialect it is declined as a neuter singular adjective. This indicates that the name is derived from *Trěbovľe selo (literally, 'Trěbo's village'), referring to an early inhabitant of the place. In the past the German name was Trifail.

History
Coal mining began at Beech Mountain (Bukova gora, 547 m) south of the town in 1804. The town was connected to the Austrian Southern Railway in 1849, which contributed to its further development. During the 19th century, a cement plant, mechanical separator, sawmill, and power plant were built in Trbovlje.

Poor social conditions in Trbovlje led to several strikes by mine workers, and the town became a center of the leftist movement and communist agitation. On June 1, 1924, there was a clash between workers and members of the Organization of Yugoslav Nationalists that resulted in several fatalities on both sides. In 1934, miners staged a sitdown strike at the mine.

Second World War
During the Second World War, Trbovlje, along with the rest of Lower Styria, was annexed to the Third Reich. The coal mine and other industries of Trbovlje were especially important to the German authorities, and they initially lowered unemployment in the town and increased wages, increasing satisfaction with the new regime. However, the arrest and exile of Slovenes in August 1941 created disaffection. This and other repressive measures resulted in an estimated 90% of the population opposing the Germans by the summer of 1944.

Mass grave
The Abandoned Cemetery Mass Grave (Grobišče na opuščenem pokopališču) site, associated with World War II, is located in the former cemetery in the northern part of the town, between the fence and Trboveljščica Creek. It is also known as the Town Park Mass Grave (Grobišče Mestni park), and it contains the remains of about 30 German soldiers.

Culture
The Trbovlje Museum (Zasavski Muzej Trbovlje) has a large section dedicated to the history of mining.

The Slovenian industrial band Laibach also originated in Trbovlje.

The Trbovlje Student Club organization (Klub trboveljskih študentov) holds various events.

Economy
Trbovlje is known for its long coal mining history. Trbovlje is also known for Trbovlje Power Station, which is the location of European Union's tallest chimney at 360 meters. In the past there were companies like respected Strojna Tovarna Trbovlje - STT, well known Iskra, Mehanika, Cementarna Trbovlje, et cetera that have employed many high skilled people and contributed to the economy. Due to their size this was not felt only locally but nationally.

Parishes and churches
Two Roman Catholic parishes have their seat in Trbovlje: the Parish of Trbovlje–St. Martin and the Parish of Trbovlje–St. Mary. Both belong to the Diocese of Celje.

The Parish Church of St Martin was originally a Romanesque church, of which part of the nave survives. The sanctuary is Gothic and in the 18th century a Baroque belfry and chapel were added. In the 19th century the nave was extended. A second church of the Parish of Trbovlje–St. Martin in the western end of town is dedicated to Saint Nicholas and was built in the 18th century.

The Parish of Trbovlje–St Mary in the southern part of the town was established in 2000. Its parish church is dedicated to the Virgin Mary, Mother of the Church. It was built from 1998 to 2000 according to plans by the architect Jože Marinko. Stained glasses, paintings, and the Stations of the Cross were created by the academy-trained painter Lojze Čemažar. The church was blessed in August 2000 and consecrated in October 2007.

A significant portion of Trbovlje's populace today describe themselves as atheists, in third place behind Catholic and "no response."

Twin places

 * 🇫🇷 Sallaumines, northern France since 1964. There is a street in Sallaumines named Trbovlje, and a street in Trbovlje named Sallaumines. There are also regular short-term exchanges of schoolchildren.

title: Trbovlje


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User:Matt Crypto/Simplified Cryptography

Cryptography (from Greek kryptós, "hidden", and gráphein, "to write") is, traditionally, the practice of rendering information in an obscured form in order to prevent others from understanding it. In recent decades, cryptography has expanded its remit and now provides mechanisms for a wide range of security goals, in addition to the ever-important task of ensuring secrecy in communications. Cryptography is an interdisciplinary subject, drawing from several fields: it can be viewed as an application of information theory, and yet it makes extensive use of other areas of mathematics too, notably number theory. It is also a branch of engineering, but an unusual one as it must deal with active, intelligent and malevolent opposition (see cryptographic engineering and security engineering).

Closely related fields are steganography, which is distinguished from cryptography as the study of ways of obscuring the very existence of a message, and not the contents of the message itself; and traffic analysis, which is the analysis of patterns of communication in order to gain knowledge.

Terminology
The original information which is to be protected by cryptography is called the plaintext. Encryption is the process of converting plaintext into an unreadable form, termed ciphertext, or, occasionally, a cryptogram. Decryption is the reverse process, recovering the plaintext back from the ciphertext. Enciphering and deciphering are alternative terms. A cipher is an algorithm for encryption and decryption. The exact operation of a cipher is almost always controlled by one or more keys &mdash pieces of information that customise the encryption and decryption. Protocols specify the details of how ciphers (and other cryptographic primitives) are to be used to achieve specific tasks. Protocols, cryptographic algorithms, prescribed actions and other specifics are combined together and implemented in a cryptosystem.

In ordinary parlance, a (secret) "code" is synonymous with "cipher". In cryptography, however, the term has a specialised, technical meaning, and should be avoided unless this is intended.

The study of how to circumvent the use of cryptography is called cryptanalysis; an attack is a specific attempt at or method for cryptanalysis. Cryptography and cryptanalysis are sometimes linked together under the umbrella term "cryptology", though "cryptography" also has this wider meaning, and both are acceptable terms for the entire field. "Crypto" is a common informal abbreviation for cryptography

"Cipher" is alternatively spelt "cypher"; similarly "ciphertext" and "cyphertext", and so forth. Although both spellings have long histories in English, there is occasional tension between their adherents.

Cryptanalysis
Main article: Cryptanalysis

A cryptanalyst might appear to be the natural adversary of a cryptographer, and to an extent this is true: one can view this contest all through the history of cryptography. However, it is also possible to interpret the two roles as complementary: a thorough understanding of cryptanalysis is necessary to create secure cryptography.

A variety of different assumptions are considered regarding what an attacker can know and do in order to learn secret information. One important distinction is whether the cryptanalyst has access only to ciphertext, whether he also knows or can guess some corresponding plaintexts, or even if he can choose plaintexts to be encrypted; (see ciphertext only, known plaintext and chosen plaintext). These scenarios all view the cipher as a black box. Some attacks, however, are based on the implementation of the cipher. If a cryptanalyst has access to, for example, timing or power consumption, he may be able to deduce secret information.

Notable methods of cryptanalysis include exhaustive search for the key, which is a risk for all ciphers. Linear cryptanalysis and differential cryptanalysis are general methods for symmetric key cryptography. When cryptography relies on hard mathematical problems, as is usually the case in asymmetric cryptography, algorithms for tasks such as factoring become potential tools for cryptanalysis.

History of cryptography
Main article: History of cryptography

Cryptography has had a long and colourful history. The earliest forms of secret writing required only pen and paper, and are now collectively termed classical cryptography. The two main categories are transposition ciphers, which rearrange the order of letters in a message, and substitution ciphers, which systematically replace groups of letters with others. Classical ciphers tend to leak varying amounts of information about the statistics of the plaintext, and because of this they are easily broken, for example by frequency analysis. Classical ciphers still enjoy popularity today, though mostly as puzzles (see cryptogram).

Early in the 20th century, several mechanical devices were invented for performing encryption, including rotor machines &mdash most famously the Enigma cipher used in World War II. The ciphers implemented by these machines brought about a significant increase in the complexity of cryptanalysis. The various attacks on Enigma, for example, succeeded only after considerable effort.

With the advent of digital computers and electronics, very complex ciphers could be implemented. A characteristic of computer ciphers is that they operate on binary strings unlike classical and mechanical schemes, which use an alphabet of around 26 letters, depending on the language. Computer ciphers are also much more resistant to cryptanalysis; few are susceptible to a ciphertext-only attack.

Extensive academic research into modern cryptography is relatively recent &mdash it only began in the open community during the 1970s with the specification of DES and the invention of RSA. It is well that much progress has been made in a short time; popular applications such as the Internet and mobile phones have repositioned cryptography, historically the sole province of a few groups with exceptional needs for secrecy, into a mainstream technology on which millions rely.

As well as noting lessons from its history, cryptographers are also careful to consider the future. Moore's law is routinely taken into account when specifying key-lengths, and the potential effects of quantum computing have already been considered. Note also quantum cryptography.

Secure communications
See also: Information security

Cryptography is commonly used for securing communications. Four desirable properties are:

 * 1) confidentiality, also known as secrecy: only an authorised recipient should be able to extract the contents of the message from its encrypted form. Otherwise, it should not be possible to obtain any significant information about the message contents.
 * 2) integrity: the recipient should be able to determine if the message has been altered during transmission.
 * 3) authentication: the recipient should be able to identify the sender, and verify that the purported sender actually did send the message.
 * 4) non-repudiation: the sender should not be able to deny sending the message.

Cryptography can provide mechanisms to help achieve all of the above. However, some goals aren't always necessary, practical or even desirable in some contexts. For example, the sender of a message may wish to remain anonymous; clearly non-repudiation would be inappropriate.

Symmetric key cryptography
Main article: Symmetric key algorithm

Symmetric key ciphers use the same key for encryption and decryption, or a little more precisely, the key used for decryption is "easy" to calculate from the key used for encryption. Other terms include "private-key", "one-key" and "single-key" cryptography.

Symmetric key ciphers can be broadly grouped into block ciphers and stream ciphers. Stream ciphers encrypt one bit at a time, in contrast to a block cipher, which operates on a group of bits (a "block") of a certain length all in one go. The block ciphers DES, IDEA and AES, and the stream cipher RC4, are among the most well-known symmetric key ciphers.

Other cryptographic primitives are sometimes classified as symmetric cryptography:
 * Cryptographic hash functions produce a hash of a message. While it should be easy to compute, it must be very difficult to invert (one-way-ness, though other properties are usually needed as well). MD5 and SHA-1 are well-known hash functions.
 * Message authentication codes (MACs), also known as keyed-hash functions, are similar to hash functions, except that a key is needed to compute the hash. As the name suggests, they are commonly used for message authentication. They are often constructed from other primitives, such as block ciphers, unkeyed-hash functions or stream ciphers.

Public key cryptography
Main article: Public key cryptography / Asymmetric key algorithm

Symmetric key encryption has a troublesome drawback &mdash two people who wish to exchange confidential messages must share a secret key. The key must be exchanged in a secure way, and not by the means they would normally communicate. This is usually inconvenient, and public-key (or aysmmetric) cryptography provides an alternative. In public key encryption there are two keys used, a public and a private key, for encryption and decryption respectively. It must be "difficult" to derive the private key from the public key. This means that someone can freely send their public key out over an insecure channel and yet be sure that only they can decrypt messages encrypted with it.

Public key algorithms are usually based on hard mathematical problems. RSA, for example, relies on the (conjectured) difficulty of factorisation. For efficiency reasons, hybrid encryption systems are usually used in practice; a key is exchanged using a public-key cipher, and the rest of the communication is encrypted using a symmetric-key algorithm (which is typically much faster). Elliptic curve cryptography is a type of public-key algorithm that may offer efficiency gains over other schemes.

Assymetric cryptography also provides mechanisms for digital signatures, which are a digital equivalent of physical signatures for paper documents, for example DSA and ElGamal.

Other Topics
See also: Topics in cryptography

The security of all practical encryption schemes remains unproven, both for symmetric and asymmetric schemes. For symmetric ciphers, confidence gained in an algorithm is usually anecdotal &mdash e.g. no successful attack has been reported on an algorithm for several years despite intensive analysis. Such a cipher might also have provable security against a limited class of attacks. For asymmetric schemes, it is common to rely on the difficulty of the associated mathematical problem, but this, too, is not provably secure.

Surprisingly, cryptography does have provably secure ciphers &mdash the one time pad, for example. However, such schemes require keys as long as the plaintext, so are almost always too cumbersome to use.

When the security of a system fails, it is rare that a weakness in the cryptographic algorithms is exploited. More often, it is a mistake in the implementation, the protocols used or some other human error. The study of how best to implement and integrate cryptography is a field in itself, see: cryptographic engineering, security engineering and cryptosystem.

Cryptography can be used to implement some remarkable protocols: zero-knowledge proof, secure multiparty computation and secret sharing, for example.

Warnings
Myths and misunderstandings about cryptography are widespread, and there is an abundance of insecure cryptographic software on the market, sometimes referred to (perjoratively) as snake oil. Readers, buyers, and users should therefore exercise substantial caution when selecting books and products; self-education is advised.