Topic Review
Application of Two-Dimensional Materials towards CMOS-Integrated Gas Sensors
The semiconductor metal oxide (SMO)-based gas sensor, considered the current workhorse of semiconductor-based chemiresistive gas sensor technologies, requires high temperatures to initiate the surface reactions which result in the sensing response, making it difficult to fabricate and prone to high mechanical instability. Therefore, alternatives at lower temperatures are desired, where 2D materials seem to hold the most promise. Even at ambient temperature, their sensitivity is extraordinarily large due to their extremely high surface-to-volume ratio. However, some ongoing issues still need to be resolved before gas sensors based on 2D materials can be widely used and commercialized. The alternative room temperature solutions involve optical signals, either by designing an nondispersive infrared (NDIR) sensor based on the Beer-Lambert law or by introducing an additional UV illumination to SMO sensors. In both cases, complementary metal oxide semiconductor (CMOS) integration is not feasible, which is why continued interest in 2D-material-based gas sensors persists.
  • 41
  • 02 Dec 2022
Topic Review
Transit of Venus, 1639
The first known observations and recording of a transit of Venus were made in 1639 by the English astronomers Jeremiah Horrocks and his friend and correspondent William Crabtree. The pair made their observations independently on 4 December that year (24 November under the Julian calendar then used in England); Horrocks from Carr House, then in the village of Much Hoole, Lancashire, and Crabtree from his home in Broughton, near Manchester. The friends, followers of the new astronomy of Johannes Kepler, were self-taught mathematical astronomers who had worked methodically to correct and improve Kepler's Rudolphine tables by observation and measurement. In 1639, Horrocks was the only astronomer to realise that a transit of Venus was imminent; others became aware of it only after the event when Horrocks's report of it was circulated. Although the friends both died within five years of making their observations, their ground-breaking work was influential in establishing the size of the Solar System; for this and their other achievements Horrocks and Crabtree, along with their correspondent William Gascoigne, are considered to be the founding fathers of British research astronomy.
  • 3
  • 02 Dec 2022
Topic Review
(225088) 2007 OR10
(225088) 2007 OR10, proposed to be named Gonggong, is a likely dwarf planet in the Solar System beyond Neptune, and is a member of the scattered disc. It has a highly eccentric and inclined orbit during which it ranges from 33–101 astronomical units (4.9–15.1 billion kilometers) from the Sun. (As of 2019), its distance from the Sun is 88 AU (1.32×1010 km; 8.2×109 mi), and it is the sixth-farthest known Solar System object. 2007 OR10 is in a 3:10 orbital resonance with Neptune, in which it completes three orbits around the Sun for every ten orbits completed by Neptune. 2007 OR10 was discovered in July 2007 by American astronomers Megan Schwamb, Michael Brown, and David Rabinowitz at the Palomar Observatory, and the discovery was announced in January 2009. At 1,230 km (760 mi) in diameter, 2007 OR10 is approximately the size of Pluto's moon Charon, and is the fifth-largest known trans-Neptunian object in the Solar System. It is sufficiently massive to be gravitationally rounded, thereby qualifying for dwarf planet status. Its large mass also makes retention of a tenuous atmosphere of methane just possible, though such an atmosphere would slowly escape into space. 2007 OR10 is currently the largest known body in the Solar System without an official name, but in 2019, the discoverers hosted an online poll for the general public to help choose a name for the object, and the name Gonggong won. The winning name is derived from Gonggong, a Chinese water god responsible for chaos, floods and the tilt of the Earth. 2007 OR10 is red in color, likely due to the presence of organic compounds called tholins on its surface. Water ice is also present on its surface, which hints at a brief period of cryovolcanic activity in the distant past. 2007 OR10 rotates slowly compared to other trans-Neptunian objects, which typically have rotation periods less than 12 hours, which may be due to its natural satellite, provisionally designated S/2010 (225088) 1.
  • 6
  • 02 Dec 2022
Topic Review
Protein Film Voltammetry
In electrochemistry, protein film voltammetry (or protein film electrochemistry, or direct electrochemistry of proteins) is a technique for examining the behavior of proteins immobilized (either adsorbed or covalently attached) on an electrode. The technique is applicable to proteins and enzymes that engage in electron transfer reactions and it is part of the methods available to study enzyme kinetics. Provided that it makes suitable contact with the electrode surface (electron transfer between the electrode and the protein is direct) and provided that it is not denatured, the protein can be fruitfully interrogated by monitoring current as a function of electrode potential and other experimental parameters. Various electrode materials can be used. Special electrode designs are required to address membrane-bound proteins.
  • 7
  • 02 Dec 2022
Topic Review
Convection
Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convection is unspecified, convection due to the effects of thermal expansion and buoyancy can be assumed. Convection may also take place in soft solids or mixtures where particles can flow. Convective flow may be transient (such as when a multiphase mixture of oil and water separates) or steady state (see Convection cell). The convection may be due to gravitational, electromagnetic or fictitious body forces. Heat transfer by natural convection plays a role in the structure of Earth's atmosphere, its oceans, and its mantle. Discrete convective cells in the atmosphere can be identified by clouds, with stronger convection resulting in thunderstorms. Natural convection also plays a role in stellar physics. Convection is often categorised or described by the main effect causing the convective flow, e.g. Thermal convection. Convection cannot take place in most solids because neither bulk current flows nor significant diffusion of matter can take place.
  • 2
  • 02 Dec 2022
Topic Review
Equinox (Celestial Coordinates)
In astronomy, an equinox is either of two places on the celestial sphere at which the ecliptic intersects the celestial equator. Although there are two intersections of the ecliptic with the celestial equator, by convention, the equinox associated with the Sun's ascending node is used as the origin of celestial coordinate systems and referred to simply as "the equinox". In contrast to the common usage of spring/vernal and autumnal equinoxes, the celestial coordinate system equinox is a direction in space rather than a moment in time. In a cycle of about 25,800 years, the equinox moves westward with respect to the celestial sphere because of perturbing forces; therefore, in order to define a coordinate system, it is necessary to specify the date for which the equinox is chosen. This date should not be confused with the epoch. Astronomical objects show real movements such as orbital and proper motions, and the epoch defines the date for which the position of an object applies. Therefore, a complete specification of the coordinates for an astronomical object requires both the date of the equinox and of the epoch. The currently used standard equinox and epoch is J2000.0, which is January 1, 2000 at 12:00 TT. The prefix "J" indicates that it is a Julian epoch. The previous standard equinox and epoch was B1950.0, with the prefix "B" indicating it was a Besselian epoch. Before 1984 Besselian equinoxes and epochs were used. Since that time Julian equinoxes and epochs have been used.
  • 2
  • 02 Dec 2022
Topic Review
Video Feedback
Video feedback is the process that starts and continues when a video camera is pointed at its own playback video monitor. The loop delay from camera to display back to camera is at least one video frame time, due to the input and output scanning processes; it can be more if there is more processing in the loop.
  • 2
  • 02 Dec 2022
Topic Review
Strangeness Production
Strangeness production is a signature and a diagnostic tool of quark–gluon plasma (or QGP) formation and properties. Unlike up and down quarks, from which everyday matter is made, strange quarks are formed in pair-production processes in collisions between constituents of the plasma. The dominant mechanism of production involves gluons only present when matter has become a quark–gluon plasma. When quark–gluon plasma disassembles into hadrons in a breakup process, the high availability of strange antiquarks helps to produce antimatter containing multiple strange quarks, which is otherwise rarely made. Similar considerations are at present made for the heavier charm flavor, which is made at the beginning of the collision process in the first interactions and is only abundant in the high-energy environments of CERN's Large Hadron Collider.
  • 6
  • 02 Dec 2022
Topic Review
Transit
File:Moon transit of sun large.ogv In astronomy, a transit (or astronomical transit) is a phenomenon when a celestial body passes directly between a larger body and the observer. As viewed from a particular vantage point, the transiting body appears to move across the face of the larger body, covering a small portion of it. The word "transit" refers to cases where the nearer object appears smaller than the more distant object. Cases where the nearer object appears larger and completely hides the more distant object are known as occultations. However, the probability of seeing a transiting planet is low because it is dependent on the alignment of the three objects in a nearly perfectly straight line. Many parameters of a planet and its parent star can be determined based on the transit.
  • 2
  • 02 Dec 2022
Topic Review
Strain Rate Tensor
In continuum mechanics, the strain rate tensor is a physical quantity that describes the rate of change of the deformation of a material in the neighborhood of a certain point, at a certain moment of time. It can be defined as the derivative of the strain tensor with respect to time, or as the symmetric component of the gradient (derivative with respect to position) of the flow velocity. The strain rate tensor is a purely kinematic concept that describes the macroscopic motion of the material. Therefore, it does not depend on the nature of the material, or on the forces and stresses that may be acting on it; and it applies to any continuous medium, whether solid, liquid or gas. On the other hand, for any fluid except superfluids, any gradual change in its deformation (i.e. a non-zero strain rate tensor) gives rise to viscous forces in its interior, due to friction between adjacent fluid elements, that tend to oppose that change. At any point in the fluid, these stresses can be described by a viscous stress tensor that is, almost always, completely determined by the strain rate tensor and by certain intrinsic properties of the fluid at that point. Viscous stress also occur in solids, in addition to the elastic stress observed in static deformation; when it is too large to be ignored, the material is said to be viscoelastic.
  • 5
  • 02 Dec 2022
  • Page
  • of
  • 100
Top
Feedback