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ATOM Program System
The ATOM computer system is designed to study the structure of atoms and the physical processes occurring with their participation. 
  • 590
  • 07 Jun 2022
Topic Review
Atomic Mass Unit
The dalton or unified atomic mass unit (SI symbols: Da or u) is a unit of mass widely used in physics and chemistry. . It is approximately the mass of one nucleon (either a proton or neutron). A mass of 1 Da is also referred to as the atomic mass constant and denoted by mu. Several definitions of this unit have been used, implying slightly different values. The current IUPAC endorsed definition is the unified atomic mass unit, denoted by the symbol u. As of 2019, the International System of Units (SI) lists the dalton, symbol Da, as a unit acceptable for use with the SI unit system and secondarily notes that the dalton (Da) and the unified atomic mass unit (u) are alternative names (and symbols) for the same unit. The symbol Da is more widely used in most fields. It is defined precisely as 1/12 of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest. Despite being an official abbreviation for a related obsolete unit and not widely used in the scientific literature, the abbreviation "amu" now often refers to the modern unit (Da or u) in many preparatory texts. As of June 2019, the value recommended by the Committee on Data for Science and Technology (CODATA) is 1.66053906660(50)×10−27 kg, or approximately 1.66 yoctograms. This unit is commonly used in physics and chemistry to express the mass of atomic-scale objects, such as atoms, molecules, and elementary particles. For example, an atom of helium has a mass of about 4 Da, and a molecule of acetylsalicylic acid (aspirin), C9H8O4, has a mass of about 180.16 Da. In general, the standard atomic weight of an element is the average weight of its atom as it occurs in nature, expressed in daltons. The molecular masses of proteins, nucleic acids, and other large polymers are often expressed with the units kilodalton (kDa), equal to 1000 daltons, megadalton (MDa), one million daltons, etc. Titin, one of the largest known proteins, has an atomic mass of between 3 and 3.7 megadaltons. The DNA of chromosome 1 in the human genome has about 249 million base pairs, each with an average mass of about 650 Da, or 156 GDa total. The mole is a unit of amount of substance, widely used in chemistry and physics, which was originally defined so that the mass of one mole of a substance, measured in grams, would be numerically equal to the average mass of one of its constituent particles, measured in daltons. That is, the molar mass of a chemical compound was meant to be numerically equal to its average molecular mass. For example, the average mass of one molecule of water is about 18.0153 daltons, and one mole of water is about 18.0153 grams. A protein whose molecule has an average mass of 64 kDa would have a molar mass of 64 kg/mol. However, while this equality can be assumed for almost all practical purposes, it is now only approximate, because of the way the mole was redefined on 20 May 2019. The mass in daltons of an atom is numerically very close to the number of nucleons A in its atomic nucleus. It follows that the molar mass of a compound (grams per mole) is also numerically close to the average number of nucleons per molecule. However, the mass of an atomic-scale object is affected by the binding energy of the nucleons in its atomic nuclei, as well as the mass and binding energy of the electrons. Therefore, this equality holds only for the carbon-12 atom in the stated conditions, and will vary for other substances. For example, the mass of one unbound atom of the common hydrogen isotope (hydrogen-1, protium) is 1.007825032241(94) Da, the mass of one free neutron is 1.008664915823(491) Da, and the mass of one hydrogen-2 (deuterium) atom is 2.014101778114(122) Da. In general, the difference (mass defect) is less than 0.1%; except for hydrogen (about 0.8%), helium-3 (0.5%), lithium (0.25%) and beryllium (0.15%). The atomic mass unit should not be confused with unit of mass in the atomic units systems, which is instead the electron rest mass (me).
  • 3.6K
  • 31 Oct 2022
Topic Review
Atomic Units
Atomic units (au or a.u.) form a system of natural units which is especially convenient for atomic physics calculations. There are two different kinds of atomic units, Hartree atomic units and Rydberg atomic units, which differ in the choice of the unit of mass and charge. This article deals with Hartree atomic units, where the numerical values of the following four fundamental physical constants are all unity by definition: In Hartree units, the speed of light is approximately [math]\displaystyle{ 137 }[/math]. Atomic units are often abbreviated "a.u." or "au", not to be confused with the same abbreviation used also for astronomical units, arbitrary units, and absorbance units in different contexts.
  • 5.6K
  • 10 Nov 2022
Topic Review
Auger Electron Spectroscopy
thumb|A Hanford scientist uses an Auger electron spectrometer to determine the elemental composition of surfaces. Auger electron spectroscopy (AES; pronounced [oʒe] in French) is a common analytical technique used specifically in the study of surfaces and, more generally, in the area of materials science. Underlying the spectroscopic technique is the Auger effect, as it has come to be called, which is based on the analysis of energetic electrons emitted from an excited atom after a series of internal relaxation events. The Auger effect was discovered independently by both Lise Meitner and Pierre Auger in the 1920s. Though the discovery was made by Meitner and initially reported in the journal Zeitschrift für Physik in 1922, Auger is credited with the discovery in most of the scientific community. Until the early 1950s Auger transitions were considered nuisance effects by spectroscopists, not containing much relevant material information, but studied so as to explain anomalies in X-ray spectroscopy data. Since 1953 however, AES has become a practical and straightforward characterization technique for probing chemical and compositional surface environments and has found applications in metallurgy, gas-phase chemistry, and throughout the microelectronics industry.
  • 920
  • 01 Nov 2022
Topic Review
Augmented Reality in K-12 Education
Augmented Reality (AR) could provide key benefits in education and create a richer user experience by increasing the motivation and engagement of the students. Initially, AR was used as a science-oriented tool, but after its acceptance by students and teachers, it evolved into a modern pedagogical tool that was adopted into the classroom to enhance the educational process. In summary, AR-based technology has become a popular topic in educational fields in the last decade as well as in educational research [26]. Taking into consideration various modern educational disciplines, technologies such as AR must be included in the learning environment in science education; otherwise, the absence of them could possibly negatively affect productivity and learning achievements [27]. However, the educational values of AR in the domain of physical science are not exclusively based on the use of AR technologies themselves. These educational values are more likely connected to how AR is designed, implemented and integrated into formal and informal learning settings [28].
  • 760
  • 11 Aug 2022
Topic Review
Auriga
Auriga, an IAU-recognized constellation, lies in the northern celestial hemisphere. Notable for its pentagonal shape, it encompasses several bright stars, including Capella. This constellation is visible during winter and contains various deep-sky objects like star clusters and nebulae.
  • 239
  • 29 Feb 2024
Topic Review
Autostereoscopic Displays Based on Various Display Technologies
The autostereoscopic display is a promising way towards three-dimensional-display technology since it allows humans to perceive stereoscopic images with naked eyes. However, it faces great challenges from low resolution, narrow viewing angle, ghost images, eye strain, and fatigue. Nowadays, the prevalent liquid crystal display (LCD), the organic light-emitting diode (OLED), and the emerging micro light-emitting diode (Micro-LED) offer more powerful tools to tackle these challenges. 
  • 1.9K
  • 21 Feb 2022
Topic Review
Avalanche Photodiodes and Silicon Photomultipliers of Non-Planar Designs
Conventional designs of an avalanche photodiode (APD) have been based on a planar p–n junction since the 1960s. APD developments have been driven by the necessity to provide a uniform electric field over the active junction area and to prevent edge breakdown by special measures. Most modern silicon photomultipliers (SiPM) are designed as an array of Geiger-mode APD cells based on planar p–n junctions. Modern Silicon Photomultipliers (SiPM) are designed as an array of Geiger-mode APD cells based on planar p-n junctions. However, the planar design faces an inherent trade-off between photon detection efficiency and dynamic range due to loss of an active area at the cell edges. Non-planar designs of APDs and SiPMs have also been known since the development of spherical APD (1968), Metal-Resistor-Semiconductor APD (1989), and Micro-well APD (2005). Recent development of Tip Avalanche Photodiode (2020) based on the spherical p-n junction eliminates the trade-off, outperforms the planar SiPMs in the photon detection efficiency, and opens new opportunities for SiPM improvements. Moreover, the latest developments of APDs based on electric field-line crowding and charge-focusing topology with quasi-spherical p-n junctions (2019–2023) show promising functionality in linear and Geiger operating modes.
  • 636
  • 27 Jun 2023
Topic Review
Azulene Moiety as Electron Reservoir
The nonalternant aromatic azulene, an isomer of alternant naphthalene, differs from the latter in peculiar properties. The large polarization of the π-electron system over the seven and five rings gives to azulene electrophile property a pronounced tendency to donate electrons to an acceptor, substituted at azulene 1 position. This paper presents cases in which azulene transfers electrons to a suitable acceptor as methylium ions, positive charged heteroaromatics and examples of neutral molecules that can accept electrons. 
  • 1.2K
  • 18 May 2021
Topic Review
Baltimore–Washington Superconducting Maglev Project
The Baltimore–Washington Superconducting Maglev Project (SCMAGLEV) is a proposed project connecting the United States cities of Baltimore, Maryland, and Washington, D.C., with a 40 mi (64 km) maglev train system between their respective central business districts. It is the first segment of the planned Washington-New York Northeast Maglev project. The maglev proposal is not related to the Baltimore–Washington hyperloop proposed by the Boring Company.
  • 553
  • 18 Oct 2022
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