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Topic Review
Biography
Topic Review
High Energy Nuclear Physics
High-energy nuclear physics studies the behaviour of nuclear matter in energy regimes typical of high energy physics. The primary focus of this field is the study of heavy-ion collisions, as compared to lower atomic mass atoms in other particle accelerators. At sufficient collision energies, these types of collisions are theorized to produce the quark–gluon plasma. In peripheral nuclear collisions at high energies one expects to obtain information on the electromagnetic production of leptons and mesons which are not accessible in electron-positron colliders due to their much smaller luminosities. Previous high-energy nuclear accelerator experiments have studied heavy-ion collisions using projectile energies of 1 GeV/nucleon up to 158 GeV/nucleon. Experiments of this type, called "fixed target" experiments, primarily accelerate a "bunch" of ions (typically around [math]\displaystyle{ 10^6 }[/math] to [math]\displaystyle{ 10^8 }[/math] ions per bunch) to speeds approaching the speed of light (0.999c) and smash them into a target of similar heavy ions. While all collision systems are interesting, great focus was applied in the late 1990s to symmetric collision systems of gold beams on gold targets at Brookhaven National Laboratory's Alternating Gradient Synchrotron (AGS) and uranium beams on uranium targets at CERN's Super Proton Synchrotron. Currently, high-energy nuclear physics experiments are being conducted at Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC) and in CERN's new Large Hadron Collider. The four primary experiments at RHIC (PHENIX, STAR, PHOBOS, and BRAHMS) study collisions of highly relativistic nuclei. Unlike fixed target experiments, collider experiments steer two accelerated beams of ions toward each other at (in the case of RHIC) six interaction regions. At RHIC, ions can be accelerated (depending on the ion size) from 100 GeV/nucleon to 250GeV/nucleon. Since each colliding ion possesses this energy moving in opposite directions, the maximum energy of the collisions can achieve a center of mass collision energy of 200GeV/nucleon for gold and 500GeV/nucleon for protons. The ALICE (A Large Ion Collider Experiment) detector at the LHC at CERN is specialized in studying Pb-Pb nuclei collisions at a centre of mass energy of 2.76 TeV per nucleon pair. Other LHC detectors like CMS, ATLAS, and LHCb also have heavy ion programs.
311
20 Oct 2022
Topic Review
Osmium-162
Osmium (76Os) has seven naturally occurring isotopes, five of which are stable: 187Os, 188Os, 189Os, 190Os, and (most abundant) 192Os. The other natural isotopes, 184Os, and 186Os, have extremely long half-life (1.12×1013 years and 2×1015 years, respectively) and for practical purposes can be considered to be stable as well. 187Os is the daughter of 187Re (half-life 4.56×1010 years) and is most often measured in an 187Os/188Os ratio. This ratio, as well as the 187Re/188Os ratio, have been used extensively in dating terrestrial as well as meteoric rocks. It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons. However, the most notable application of Os in dating has been in conjunction with iridium, to analyze the layer of shocked quartz along the Cretaceous–Paleogene boundary that marks the extinction of the dinosaurs 66 million years ago. There are also 30 artificial radioisotopes, the longest-lived of which is 194Os with a half-life of six years; all others have half-lives under 94 days. There are also nine known nuclear isomers, the longest-lived of which is 191mOs with a half-life of 13.10 hours. All isotopes and nuclear isomers of osmium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.
381
20 Oct 2022
Topic Review
NanoPutian
NanoPutians are a series of organic molecules whose structural formulae resemble human forms. James Tour et al. (Rice University) designed and synthesized these compounds in 2003 as a part of a sequence on chemical education for young students. The compounds consist of two benzene rings connected via a few carbon atoms as the body, four acetylene units each carrying an alkyl group at their ends which represents the hands and legs, and a 1,3-dioxolane ring as the head. Tour and his team at Rice University used the NanoPutians in their NanoKids educational outreach program. The goal of this program was to educate children in the sciences in an effective and enjoyable manner. They have made several videos featuring the NanoPutians as anthropomorphic animated characters. Construction of the structures depends on Sonogashira coupling and other synthetic techniques. By replacing the 1,3-dioxolane group with an appropriate ring structure, various other types of putians have been synthesized, e.g. NanoAthlete, NanoPilgrim, and NanoGreenBeret. Placing thiol (R-SH) functional groups at the end of the legs enables them to "stand" on a gold surface. "NanoPutian" is a portmanteau of nanometer, a unit of length commonly used to measure chemical compounds, and lilliputian, a fictional race of humans in the novel Gulliver's Travels by Jonathan Swift.
881
20 Oct 2022
Topic Review
Double-Blind FROG
Double-Blind FROG is a method for simultaneously measuring two unknown ultrashort laser pulses. Well established ultrafast measurement techniques like Frequency-Resolved Optical Gating (FROG) and its simplified version GRENOUILLE can only measure one unknown ultrashort laser pulse at a time. Another version of FROG, called cross-correlation FROG (XFROG), also measures only one pulse, but it involves two pulses: a known reference pulse and the unknown pulse to be measured. In modern optics experiments, ultrashort laser pulses have been used in a great variety of engineering application and scientific research, for example, biomedical engineering, material science, nonlinear spectroscopy, ultrafast chemistry, etc. Often, these experiments involve using two potentially different input laser pulses, for example, Raman spectroscopy, two-color pump-probe experiments, and non-degenerate four-wave mixing. In many situations, an output pulse is generated by a nonlinear optical process, such as harmonic generation, continuum generation, or optical parametric oscillation. In all such cases, measuring more than one pulse simultaneously is required to completely characterize the experiment and understand its results in order to eventually understand the underlying science of the process under study. Thus a measurement device capable of measuring two pulses simultaneously is highly desired.
582
20 Oct 2022
Topic Review
Timoshenko-Ehrenfest Beam Theory
The Timoshenko-Ehrenfest beam theory was developed by Stephen Timoshenko and Paul Ehrenfest early in the 20th century. The model takes into account shear deformation and rotational bending effects, making it suitable for describing the behaviour of thick beams, sandwich composite beams, or beams subject to high-frequency excitation when the wavelength approaches the thickness of the beam. The resulting equation is of 4th order but, unlike Euler–Bernoulli beam theory, there is also a second-order partial derivative present. Physically, taking into account the added mechanisms of deformation effectively lowers the stiffness of the beam, while the result is a larger deflection under a static load and lower predicted eigenfrequencies for a given set of boundary conditions. The latter effect is more noticeable for higher frequencies as the wavelength becomes shorter (in principle comparable to the height of the beam or shorter), and thus the distance between opposing shear forces decreases. Rotary inertia effect was introduced by Bresse and Rayleigh. If the shear modulus of the beam material approaches infinity—and thus the beam becomes rigid in shear—and if rotational inertia effects are neglected, Timoshenko beam theory converges towards ordinary beam theory.
13.3K
20 Oct 2022
Topic Review
Solar Power
Solar power is the conversion of renewable energy from sunlight into electricity, either directly using photovoltaics (PV), indirectly using concentrated solar power, or a combination. Photovoltaic cells convert light into an electric current using the photovoltaic effect. Concentrated solar power systems use lenses or mirrors and solar tracking systems to focus a large area of sunlight to a hot spot, often to drive a steam turbine. Photovoltaics were initially solely used as a source of electricity for small and medium-sized applications, from the calculator powered by a single solar cell to remote homes powered by an off-grid rooftop PV system. Commercial concentrated solar power plants were first developed in the 1980s. Since then, as the cost of solar electricity has fallen, grid-connected solar PV systems have grown more or less exponentially. Millions of installations and gigawatt-scale photovoltaic power stations have been and are being built. Solar PV has rapidly become a viable low-carbon technology, and as of 2020, provides the cheapest source of electricity in history. As of 2021, solar generates 4% of the world's electricity, compared to 1% in 2015 when the Paris Agreement to limit climate change was signed. Along with onshore wind, the cheapest levelised cost of electricity is utility-scale solar. The International Energy Agency said in 2021 that under its "Net Zero by 2050" scenario solar power would contribute about 20% of worldwide energy consumption, and solar would be the world's largest source of electricity.
2.2K
20 Oct 2022
Topic Review
Micro-Imaging Dust Analysis System
The Micro-Imaging Dust Analysis System (MIDAS) is one of several instruments on the European Space Agency's Rosetta mission which studied in-situ the environment around the active comet 67P/Churyumov–Gerasimenko as it flew into the inner Solar System. MIDAS is an atomic force microscope (AFM) designed to collect dust particles emitted from the comet, and then scan them with a very sharp needle-like tip to determine their 3D structure, size and texture with very high resolution (4 nanometers).
273
20 Oct 2022
Topic Review
Solid Oxide Electrolysis Cells and SOFCs Components
Solid oxide electrolysis cells (SOECs) and solid oxide fuel cells (SOFCs) are the leading high-temperature devices to realize the global “Hydrogen Economy”. These devices are inherently multi-material (ceramic and cermets). They have multi-scale, multilayer configurations (a few microns to hundreds of microns) and different morphology (porosity and densification) requirements for each layer. Adjacent layers should exhibit chemical and thermal compatibility and high-temperature mechanical stability.
1.5K
20 Oct 2022
Topic Review
Deformation (Mechanics)
Deformation in continuum mechanics is the transformation of a body from a reference configuration to a current configuration. A configuration is a set containing the positions of all particles of the body. A deformation may be caused by external loads, body forces (such as gravity or electromagnetic forces), or changes in temperature, moisture content, or chemical reactions, etc. Strain is a description of deformation in terms of relative displacement of particles in the body that excludes rigid-body motions. Different equivalent choices may be made for the expression of a strain field depending on whether it is defined with respect to the initial or the final configuration of the body and on whether the metric tensor or its dual is considered. In a continuous body, a deformation field results from a stress field induced by applied forces or is due to changes in the temperature field inside the body. The relation between stresses and induced strains is expressed by constitutive equations, e.g., Hooke's law for linear elastic materials. Deformations which are recovered after the stress field has been removed are called elastic deformations. In this case, the continuum completely recovers its original configuration. On the other hand, irreversible deformations remain even after stresses have been removed. One type of irreversible deformation is plastic deformation, which occurs in material bodies after stresses have attained a certain threshold value known as the elastic limit or yield stress, and are the result of slip, or dislocation mechanisms at the atomic level. Another type of irreversible deformation is viscous deformation, which is the irreversible part of viscoelastic deformation. In the case of elastic deformations, the response function linking strain to the deforming stress is the compliance tensor of the material.
951
20 Oct 2022
Topic Review
Diffraction Formalism
Diffraction processes affecting waves are amenable to quantitative description and analysis. Such treatments are applied to a wave passing through one or more slits whose width is specified as a proportion of the wavelength. Numerical approximations may be used, including the Fresnel and Fraunhofer approximations.
320
20 Oct 2022
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