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Topic Review
Levitated Dipole Experiment
The Levitated Dipole Experiment (LDX) was an experiment investigating the generation of fusion power using the concept of a levitated dipole. The device was the first of its kind to test the levitated dipole concept and was funded by the US Department of Energy. The machine was also part of a collaboration between the MIT Plasma Science and Fusion Center and Columbia University, where another levitated dipole experiment, the Collisionless Terrella Experiment (CTX), was located. LDX ceased operations in November 2011 when its funding from the Department of Energy ended as resources were being diverted to tokamak research.
  • 688
  • 22 Nov 2022
Topic Review
Old Quantum Theory
The old quantum theory is a collection of results from the years 1900–1925 which predate modern quantum mechanics. The theory was never complete or self-consistent, but was rather a set of heuristic corrections to classical mechanics. The theory is now understood as the semi-classical approximation to modern quantum mechanics. The main and final accomplishments of the old quantum theory were the determination of the modern form of the periodic table by Edmund Stoner and the Pauli Exclusion Principle which were both premised on the Arnold Sommerfeld enhancements to the Bohr model of the atom. The main tool of the old quantum theory was the Bohr–Sommerfeld quantization condition, a procedure for selecting out certain states of a classical system as allowed states: the system can then only exist in one of the allowed states and not in any other state.
  • 854
  • 22 Nov 2022
Topic Review
Biogas
Biogas refers to a mixture of different gases produced by the breakdown of organic matter in the absence of oxygen. Biogas can be produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste or food waste. Biogas is a renewable energy source. Biogas can be produced by anaerobic digestion with methanogen or anaerobic organisms, which digest material inside a closed system, or fermentation of biodegradable materials. This closed system is called an anaerobic digester, biodigester or a bioreactor. Biogas is primarily methane (CH4) and carbon dioxide (CO2) and may have small amounts of hydrogen sulphide (H2S), moisture and siloxanes. The gases methane, hydrogen, and carbon monoxide (CO) can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel; it can be used for any heating purpose, such as cooking. It can also be used in a gas engine to convert the energy in the gas into electricity and heat. Biogas can be compressed, the same way as natural gas is compressed to CNG, and used to power motor vehicles. In the United Kingdom , for example, biogas is estimated to have the potential to replace around 17% of vehicle fuel. It qualifies for renewable energy subsidies in some parts of the world. Biogas can be cleaned and upgraded to natural gas standards, when it becomes bio-methane. Biogas is considered to be a renewable resource because its production-and-use cycle is continuous, and it generates no net carbon dioxide. As the organic material grows, it is converted and used. It then regrows in a continually repeating cycle. From a carbon perspective, as much carbon dioxide is absorbed from the atmosphere in the growth of the primary bio-resource as is released, when the material is ultimately converted to energy.
  • 2.1K
  • 22 Nov 2022
Topic Review
Epoch
In astronomy, an epoch or reference epoch is a moment in time used as a reference point for some time-varying astronomical quantity. It is useful for the celestial coordinates or orbital elements of a celestial body, as they are subject to perturbations and vary with time. These time-varying astronomical quantities might include, for example, the mean longitude or mean anomaly of a body, the node of its orbit relative to a reference plane, the direction of the apogee or aphelion of its orbit, or the size of the major axis of its orbit. The main use of astronomical quantities specified in this way is to calculate other relevant parameters of motion, in order to predict future positions and velocities. The applied tools of the disciplines of celestial mechanics or its subfield orbital mechanics (for predicting orbital paths and positions for bodies in motion under the gravitational effects of other bodies) can be used to generate an ephemeris, a table of values giving the positions and velocities of astronomical objects in the sky at a given time or times. Astronomical quantities can be specified in any of several ways, for example, as a polynomial function of the time-interval, with an epoch as a temporal point of origin (this is a common current way of using an epoch). Alternatively, the time-varying astronomical quantity can be expressed as a constant, equal to the measure that it had at the epoch, leaving its variation over time to be specified in some other way—for example, by a table, as was common during the 17th and 18th centuries. The word epoch was often used in a different way in older astronomical literature, e.g. during the 18th century, in connection with astronomical tables. At that time, it was customary to denote as "epochs", not the standard date and time of origin for time-varying astronomical quantities, but rather the values at that date and time of those time-varying quantities themselves. In accordance with that alternative historical usage, an expression such as 'correcting the epochs' would refer to the adjustment, usually by a small amount, of the values of the tabulated astronomical quantities applicable to a fixed standard date and time of reference (and not, as might be expected from current usage, to a change from one date and time of reference to a different date and time).
  • 589
  • 22 Nov 2022
Topic Review
Broken/Astronomy
Astronomy (from Greek: ἀστρονομία) is a natural science that studies celestial objects and phenomena. It applies mathematics, physics, and chemistry in an effort to explain the origin of those objects and phenomena and their evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, and comets; the phenomena also includes supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, all phenomena that originate outside Earth's atmosphere are within the purview of astronomy. A branch of astronomy called cosmology is the study of the Universe as a whole. Astronomy is one of the oldest of the natural sciences. The early civilizations in recorded history, such as the Babylonians, Greeks, Indians, Egyptians, Nubians, Iranians, Chinese, Maya, and many ancient indigenous peoples of the Americas, performed methodical observations of the night sky. Historically, astronomy has included disciplines as diverse as astrometry, celestial navigation, observational astronomy, and the making of calendars, but professional astronomy is now often considered to be synonymous with astrophysics. Professional astronomy is split into observational and theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects, which is then analyzed using basic principles of physics. Theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. The two fields complement each other, with theoretical astronomy seeking to explain observational results and observations being used to confirm theoretical results. Astronomy is one of the few sciences in which amateurs still play an active role, especially in the discovery and observation of transient events. Amateur astronomers have made and contributed to many important astronomical discoveries, such as finding new comets.
  • 681
  • 22 Nov 2022
Topic Review
Thermodynamics and an Introduction to Thermostatistics
Thermodynamics and an Introduction to Thermostatistics is a textbook written by Herbert Callen that explains the basics of classical thermodynamics and discusses advanced topics in both classical and quantum frameworks. The textbook contains three parts, each building upon the previous. The first edition was published in 1960 and a second followed in 1985.
  • 320
  • 22 Nov 2022
Topic Review
Solar Chemical
Solar chemical refers to a number of possible processes that harness solar energy by absorbing sunlight in a chemical reaction. The idea is conceptually similar to photosynthesis in plants, which converts solar energy into the chemical bonds of glucose molecules, but without using living organisms, which is why it is also called artificial photosynthesis. A promising approach is to use focused sunlight to provide the energy needed to split water into its constituent hydrogen and oxygen in the presence of a metallic catalyst such as zinc. This is normally done in a two-step process so that hydrogen and oxygen are not produced in the same chamber, which creates an explosion hazard. Another approach involves taking the hydrogen created in this process and combining it with carbon dioxide to create methane. The benefit of this approach is that there is an established infrastructure for transporting and burning methane for power generation, which is not true for hydrogen. One main drawback to both of these approaches is common to most methods of energy storage: adding an extra step between energy collection and electricity production drastically decreases the efficiency of the overall process.
  • 460
  • 22 Nov 2022
Topic Review
Moberly–Jourdain Incident
The Moberly–Jourdain incident (also the Ghosts of Petit Trianon or Versailles, French: les fantômes du Trianon / les fantômes de Versailles) is a claim of time travel and hauntings made by Charlotte Anne Moberly (1846–1937) and Eleanor Jourdain (1863–1924). In 1911, Moberly and Jourdain published a book entitled An Adventure under the names of "Elizabeth Morison" and "Frances Lamont". Their book describes a visit they made to the Petit Trianon, a small château in the grounds of the Palace of Versailles where they claimed to have seen the gardens as they had been in the late eighteenth century as well as ghosts, including Marie Antoinette and others. Their story caused a sensation and was subject to much ridicule.
  • 361
  • 22 Nov 2022
Topic Review
Drag
In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers (or surfaces) or between a fluid and a solid surface. Unlike other resistive forces, such as dry friction, which are nearly independent of velocity, the drag force depends on velocity. Drag force is proportional to the velocity for low-speed flow and the squared velocity for high speed flow, where the distinction between low and high speed is measured by the Reynolds number. Even though the ultimate cause of drag is viscous friction, turbulent drag is independent of viscosity. Drag forces always tend to decrease fluid velocity relative to the solid object in the fluid's path.
  • 1.2K
  • 22 Nov 2022
Topic Review
Effective Atomic Number
Effective atomic number has two different meanings: one that is the effective nuclear charge of an atom, and one that calculates the average atomic number for a compound or mixture of materials. Both are abbreviated Zeff.
  • 2.0K
  • 22 Nov 2022
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