Monday, September 27, 2021

09-27-2021-0021 - COVID-19 Death

Party Lights Disco Ball on Black Background by KinoMaster on Envato Elements

Cases

219,000,000

Deaths

4,550,000

Location	Cases	Deaths
United States	42,900,000 +51,575	688,000 +629
India	33,700,000	447,000
Brazil	21,300,000	594,000
United Kingdom	7,630,000	136,000
Russia	7,290,000

https://en.wikipedia.org/wiki/Template:COVID-19_pandemic_data

https://www.militarytimes.com/news/your-air-force/2021/09/20/nearly-all-new-air-force-trainees-are-vaccinated-against-covid-19-training-boss-says/

fixed (plate, slab, slatted, etc.) graphite reactor - nlab 1900s et bf.

marburg II [21] - nlab 19

COVID-19 death toll spikes due to backlog of data

Health officials struggle to keep up with coronavirus tracking.

By Camille Botello
Saturday, September 25, 2021 9:50pm

https://www.peninsulaclarion.com/news/covid-19-death-toll-spikes-due-to-backlog-of-data/

Ludacris blueberry yum yum

Cast iron is a group of iron-carbon alloys with a carbon content more than 2%.^[1] Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its colour when fractured: white cast iron has carbide impurities which allow cracks to pass straight through, grey cast iron has graphite flakes which deflect a passing crack and initiate countless new cracks as the material breaks, and ductile cast iron has spherical graphite "nodules" which stop the crack from further progressing.

Carbon (C) ranging from 1.8 to 4 wt%, and silicon (Si) 1–3 wt%, are the main alloying elements of cast iron. Iron alloys with lower carbon content are known as steel.

Cast iron tends to be brittle, except for malleable cast irons. With its relatively low melting point, good fluidity, castability, excellent machinability, resistance to deformation and wear resistance, cast irons have become an engineering material with a wide range of applications and are used in pipes, machines and automotive industryparts, such as cylinder heads, cylinder blocks and gearbox cases. It is resistant to damage by oxidation but is difficult to weld.

The earliest cast-iron artefacts date to the 5th century BC, and were discovered by archaeologists in what is now Jiangsu in China. Cast iron was used in ancient China for warfare, agriculture, and architecture.^[2] During the 15th century, cast iron became utilized for cannon in Burgundy, France, and in England during the Reformation. The amounts of cast iron used for cannon required large scale production.^[3] The first cast-iron bridge was built during the 1770s by Abraham Darby III, and is known as The Iron Bridge in Shropshire, England. Cast iron was also used in the construction of buildings.

https://en.wikipedia.org/wiki/Cast_iron

The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term temperature is used, since hot, thermal and cold neutrons are moderated in a medium with a certain temperature. The neutron energy distribution is then adapted to the Maxwellian distribution known for thermal motion. Qualitatively, the higher the temperature, the higher the kinetic energy of the free neutrons. The momentum and wavelength of the neutron are related through the de Broglie relation. The large wavelength of slow neutrons allows for the large cross section.^[1]

Neutron energy distribution ranges[edit]

Neutron energy range names^[2]^[3]
Neutron energy	Energy range
0.0–0.025 eV	Cold neutrons
0.025 eV	Thermal neutrons
0.025–0.4 eV	Epithermal neutrons
0.4–0.5 eV	Cadmium neutrons
0.5–1 eV	EpiCadmium neutrons
1–10 eV	Slow neutrons
10–300 eV	Resonance neutrons
300 eV–1 MeV	Intermediate neutrons
1–20 MeV	Fast neutrons
> 20 MeV	Ultrafast neutrons

But different ranges with different names are observed in other sources.^[4]

The following is a detailed classification:

Thermal[edit]

A thermal neutron is a free neutron with a kinetic energy of about 0.025 eV (about 4.0×10⁻²¹ J or 2.4 MJ/kg, hence a speed of 2.19 km/s), which is the energy corresponding to the most probable speed at a temperature of 290 K (17 °C or 62 °F), the mode of the Maxwell–Boltzmann distribution for this temperature.

After a number of collisions with nuclei (scattering) in a medium (neutron moderator) at this temperature, those neutrons which are not absorbed reach about this energy level.

Thermal neutrons have a different and sometimes much larger effective neutron absorption cross-section for a given nuclide than fast neutrons, and can therefore often be absorbed more easily by an atomic nucleus, creating a heavier, often unstable isotope of the chemical element as a result. This event is called neutron activation.

Epithermal[edit]

^{[example needed]}

Neutrons of energy greater than thermal
Greater than 0.025 eV

Cadmium[edit]

^{[example needed]}

Neutrons which are strongly absorbed by cadmium
Less than 0.5 eV.

Epicadmium[edit]

^{[example needed]}

Neutrons which are not strongly absorbed by cadmium
Greater than 0.5 eV.

Slow[edit]

^{[example needed]}

Neutrons of energy slightly greater than epicadmium neutrons.
Less than 1 to 10 eV.

Resonance[edit]

^{[example needed]}

Refers to neutrons which are strongly susceptible to non-fission capture by U-238.
1 eV to 300 eV

Intermediate[edit]

^{[example needed]}

Neutrons that are between slow and fast
Few hundred eV to 0.5 MeV.

Fast[edit]

A fast neutron is a free neutron with a kinetic energy level close to 1 M eV (100 T J/kg), hence a speed of 14,000 km/s, or higher. They are named fast neutrons to distinguish them from lower-energy thermal neutrons, and high-energy neutrons produced in cosmic showers or accelerators.

Fast neutrons are produced by nuclear processes:

Nuclear fission produces neutrons with a mean energy of 2 MeV (200 TJ/kg, i.e. 20,000 km/s), which qualifies as "fast". However the range of neutrons from fission follows a Maxwell–Boltzmann distribution from 0 to about 14 MeV in the center of momentum frame of the disintegration, and the mode of the energy is only 0.75 MeV, meaning that fewer than half of fission neutrons qualify as "fast" even by the 1 MeV criterion.^[5]
Spontaneous fission is a type of radioactive decay that some heavy elements undergo. Examples include plutonium-240 and californium-252.
Nuclear fusion: deuterium–tritium fusion produces neutrons of 14.1 MeV (1400 TJ/kg, i.e. 52,000 km/s, 17.3% of the speed of light) that can easily fission uranium-238 and other non-fissile actinides.
Neutron emission occurs in situations in which a nucleus contains enough excess neutrons that the separation energy of one or more neutrons becomes negative (i.e. excess neutrons "drip" out of the nucleus). Unstable nuclei of this sort will often decay in less than one second.

Fast neutrons are usually undesirable in a steady-state nuclear reactor because most fissile fuel has a higher reaction rate with thermal neutrons. Fast neutrons can be rapidly changed into thermal neutrons via a process called moderation. This is done through numerous collisions with (in general) slower-moving and thus lower-temperature particles like atomic nuclei and other neutrons. These collisions will generally speed up the other particle and slow down the neutron and scatter it. Ideally, a room temperature neutron moderator is used for this process. In reactors, heavy water, light water, or graphite are typically used to moderate neutrons.

See caption for explanation. Lighter noble gases (helium and neon depicted) have a much higher probability density peak at low speeds than heavier noble gases, but have a probability density of 0 at most higher speeds. Heavier noble gases (argon and xenon depicted) have lower probability density peaks, but have non-zero densities over much larger ranges of speeds.

A chart displaying the speed probability density functions of the speeds of a few noble gases at a temperature of 298.15 K (25 C). An explanation of the vertical axis label appears on the image page (click to see). Similar speed distributions are obtained for neutrons upon moderation.

Ultrafast[edit]

^{[example needed]}

Relativistic
Greater than 20 MeV

Other classifications[edit]

Pile

Neutrons of all energies present in nuclear reactors
0.001 eV to 15 MeV.

Ultracold

Neutrons with sufficiently low energy to be reflected and trapped
Upper bound of 335 neV

Fast-neutron reactor and thermal-neutron reactor compared[edit]

Most fission reactors are thermal-neutron reactors that use a neutron moderator to slow down ("thermalize") the neutrons produced by nuclear fission. Moderation substantially increases the fission cross section for fissile nuclei such as uranium-235 or plutonium-239. In addition, uranium-238 has a much lower capture cross section for thermal neutrons, allowing more neutrons to cause fission of fissile nuclei and propagate the chain reaction, rather than being captured by ²³⁸U. The combination of these effects allows light water reactors to use low-enriched uranium. Heavy water reactors and graphite-moderated reactors can even use natural uranium as these moderators have much lower neutron capture cross sections than light water.^[6]

An increase in fuel temperature also raises U-238's thermal neutron absorption by Doppler broadening, providing negative feedback to help control the reactor. When the coolant is a liquid that also contributes to moderation and absorption (light water or heavy water), boiling of the coolant will reduce the moderator density, which can provide positive or negative feedback (a positive or negative void coefficient), depending on whether the reactor is under- or over-moderated.

Intermediate-energy neutrons have poorer fission/capture ratios than either fast or thermal neutrons for most fuels. An exception is the uranium-233 of the thorium cycle, which has a good fission/capture ratio at all neutron energies.

Fast-neutron reactors use unmoderated fast neutrons to sustain the reaction and require the fuel to contain a higher concentration of fissile material relative to fertile materialU-238. However, fast neutrons have a better fission/capture ratio for many nuclides, and each fast fission releases a larger number of neutrons, so a fast breeder reactor can potentially "breed" more fissile fuel than it consumes.

Fast reactor control cannot depend solely on Doppler broadening or on negative void coefficient from a moderator. However, thermal expansion of the fuel itself can provide quick negative feedback. Perennially expected to be the wave of the future, fast reactor development has been nearly dormant with only a handful of reactors built in the decades since the Chernobyl accident due to low prices in the uranium market, although there is now a revival with several Asian countries planning to complete larger prototype fast reactors in the next few years.

Nuclear reactors[edit]

In a uranium graphite chain reacting pile, the critical size may be considerably reduced by surrounding the pile with a layer of graphite, since such an envelope reflects many neutrons back into the pile.

To obtain a 30-year life span, the SSTAR nuclear reactor design calls for a moveable neutron reflector to be placed over the column of fuel. The reflector's slow downward travel over the column would cause the fuel to be burned from the top of the column to the bottom.

A reflector made of a light material like graphite or beryllium will also serve as a neutron moderator reducing neutron kinetic energy, while a heavy material like lead or lead-bismuth eutectic will have less effect on neutron velocity.

In power reactors, a neutron reflector reduces the non-uniformity of the power distribution in the peripheral fuel assemblies, reduces neutron leakage and reduces a coolant flow bypass of the core. By reducing neutron leakage, the reflector increases reactivity of the core and reduces the amount of fuel necessary to maintain the reactor critical for a long period. In light-water reactors, the neutron reflector is installed for following purposes:

The neutron flux distribution is “flattened“, i.e., the ratio of the average flux to the maximum flux is increased. Therefore reflectors reduce the non-uniformity of the power distribution.
By increasing the neutron flux at the edge of the core, there is much better utilization in the peripheral fuel assemblies. This fuel, in the outer regions of the core, now contributes much more to the total power production.
The neutron reflector scatters back (or reflects) into the core many neutrons that would otherwise escape. The neutrons reflected back into the core are available for chain reaction. This means that the minimum critical size of the reactor is reduced. Alternatively, if the core size is maintained, the reflector makes additional reactivity available for higher fuel burnup. The decrease in the critical size of core required is known as the reflector savings.
Neutron reflectors reduce neutron leakage i.e. to reduce the neutron fluence on a reactor pressure vessel.
Neutron reflectors reduce a coolant flow bypass of a core.
Neutron reflectors serve as a thermal and radiation shield of a reactor core.

References[edit]

^ Chupp, T. "Neutron Optics and Polarization" (PDF). Retrieved 16 April 2019.
^ Mezei, F (1976). "Novel polarized neutron devices: supermirror and spin component amplifier". Communications on Physics (London). 1 (3): 81–85.
^ Hayter, J. B.; Mook, H. A. (1989). "Discrete Thin-Film Multilayer Design for X-ray and Neutron Supermirrors". J. Appl. Cryst. 22: 35–41. doi:10.1107/S0021889888010003.
^ Bentley, PM (2020). "Instrument suite cost optimisation in a science megaproject". Journal of Physics Communications. 4 (4): 045014. doi:10.1088/2399-6528/ab8a06.

https://en.wikipedia.org/wiki/Neutron_supermirror

Subcategories

This category has the following 7 subcategories, out of 7 total.

A

Anisotropic optical materials‎ (1 P)

G

Glass‎ (11 C, 29 P)
Glass-ceramics‎ (14 P)

L

Laser gain media‎ (28 P)

M

Metamaterials‎ (2 C, 43 P)

N

Nonlinear optical materials‎ (2 C, 25 P)

P

Phosphors and scintillators‎ (1 C, 35 P)

Pages in category "Optical materials"

The following 64 pages are in this category, out of 64 total. This list may not reflect recent changes (learn more).

List of refractive indices

A

B

Barium fluoride

C

G

H

I

L

M

N

P

R

S

U

Uniformity tape

W

Optical properties of water and ice

Y

Z

https://en.wikipedia.org/wiki/Category:Optical_materials

Categories:

Neutron reflectometry is a neutron diffraction technique for measuring the structure of thin films, similar to the often complementary techniques of X-ray reflectivity and ellipsometry. The technique provides valuable information over a wide variety of scientific and technological applications including chemical aggregation, polymer and surfactant adsorption, structure of thin film magnetic systems, biological membranes, etc.

History[edit]

Neutron reflectometery emerged as a new field in the 1980s, after the discovery of giant magnetoresistance in antiferromagnetically-coupled multilayered films.^[1]

Technique[edit]

The technique involves shining a highly collimated beam of neutrons onto an extremely flat surface and measuring the intensity of reflected radiation as a function of angle or neutron wavelength. The exact shape of the reflectivity profile provides detailed information about the structure of the surface, including the thickness, density, and roughness of any thin films layered on the substrate.

Neutron reflectometry is most often made in specular reflection mode, where the angle of the incident beam is equal to the angle of the reflected beam. The reflection is usually described in terms of a momentum transfer vector, denoted $q_{z}$ , which describes the change in momentum of a neutron after reflecting from the material. Conventionally the $z$ direction is defined to be the direction normal to the surface, and for specular reflection, the scattering vector has only a $z$ -component. A typical neutron reflectometry plot displays the reflected intensity (relative to the incident beam) as a function of the scattering vector:

q_{z}={\frac {4\pi }{\lambda }}\sin(\theta )

where $\lambda$ is the neutron wavelength, and $\theta$ is the angle of incidence. The Abeles matrix formalism or the Parratt recursion can be used to calculate the specular signal arising from the interface.

Off-specular reflectometry gives rise to diffuse scattering and involves momentum transfer within the layer, and is used to determine lateral correlations within the layers, such as those arising from magnetic domains or in-plane correlated roughness.

The wavelength of the neutrons used for reflectivity are typically on the order of 0.2 to 1 nm (2 to 10 Å). This technique requires a neutron source, which may be either a research reactor or a spallation source (based on a particle accelerator). Like all neutron scattering techniques, neutron reflectometry is sensitive to contrast arising from different nuclei (as compared to electron density, which is measured in x-ray scattering). This allows the technique to differentiate between various isotopes of elements. Neutron reflectometry measures the neutron scattering length density (SLD) and can be used to accurately calculate material density if the atomic composition is known.

Comparison to other reflectometry techniques[edit]

Although other reflectivity techniques (in particular optical reflectivity, x-ray reflectometry) operate using the same general principles, neutron measurements are advantageous in a few significant ways. Most notably, since the technique probes nuclear contrast, rather than electron density, it is more sensitive for measuring some elements, especially lighter elements (hydrogen, carbon, nitrogen, oxygen, etc.). Sensitivity to isotopes also allows contrast to be greatly (and selectively) enhanced for some systems of interest using isotopic substitution, and multiple experiments that differ only by isotopic substitution can be used to resolve the phase problem that is general to scattering techniques. Finally, neutrons are highly penetrating and typically non-perturbing: which allows for great flexibility in sample environments, and the use of delicate sample materials (e.g., biological specimens). By contrast x-ray exposure may damage some materials, and laser light can modify some materials (e.g. photoresists). Also, optical techniques may include ambiguity due to optical anisotropy (birefringence), which complementary neutron measurements can resolve. Dual polarisation interferometry is one optical method which provides analogous results to neutron reflectometry at comparable resolution although the underpinning mathematical model is somewhat simpler, i.e. it can only derive a thickness (or birefringence) for a uniform layer density.

Disadvantages of neutron reflectometry include the higher cost of the required infrastructure, the fact that some materials may become radioactive upon exposure to the beam, and insensitivity to the chemical state of constituent atoms. Moreover, the relatively lower flux and higher background of the technique (when compared to x-ray reflectivity) limit the maximum value of $q_{z}$ that can be probed (and hence the measurement resolution).

References[edit]

^ Dalliant, Jean; Gibaud, Alain, eds. (2009). X-ray and Neutron Reflectivity. Lecture Notes in Physics. 770. Berlin Heidelberg: Springer. p. 183. ISBN 9783540885870.

https://en.wikipedia.org/wiki/Neutron_reflectometry

A plain bearing, or more commonly sliding contact bearing and slide bearing (in railroading sometimes called a solid bearing, journal bearing, or friction bearing^[1]), is the simplest type of bearing, comprising just a bearing surface and no rolling elements. Therefore, the journal (i.e., the part of the shaft in contact with the bearing) slides over the bearing surface. The simplest example of a plain bearing is a shaft rotating in a hole. A simple linear bearing can be a pair of flat surfaces designed to allow motion; e.g., a drawer and the slides it rests on^[2] or the ways on the bed of a lathe.

Plain bearings, in general, are the least expensive type of bearing. They are also compact and lightweight, and they have a high load-carrying capacity.^[3]

https://en.wikipedia.org/wiki/Plain_bearing

Giant magnetoresistance (GMR) is a quantum mechanical magnetoresistance effect observed in multilayers composed of alternating ferromagnetic and non-magnetic conductive layers. The 2007 Nobel Prize in Physics was awarded to Albert Fert and Peter Grünberg for the discovery of GMR.

The effect is observed as a significant change in the electrical resistance depending on whether the magnetization of adjacent ferromagnetic layers are in a parallel or an antiparallel alignment. The overall resistance is relatively low for parallel alignment and relatively high for antiparallel alignment. The magnetization direction can be controlled, for example, by applying an external magnetic field. The effect is based on the dependence of electron scattering on spin orientation.

The main application of GMR is in magnetic field sensors, which are used to read data in hard disk drives, biosensors, microelectromechanical systems (MEMS) and other devices.^[1] GMR multilayer structures are also used in magnetoresistive random-access memory (MRAM) as cells that store one bit of information.

In literature, the term giant magnetoresistance is sometimes confused with colossal magnetoresistance of ferromagnetic and antiferromagnetic semiconductors, which is not related to a multilayer structure.^[2]^[3]

https://en.wikipedia.org/wiki/Giant_magnetoresistance