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Cassiopeia
Cassiopeia, named after the queen in Greek mythology, is a prominent constellation in the northern celestial hemisphere. Known for its distinctive "W" or "M" shape, depending on its orientation in the sky, Cassiopeia is easily recognizable and has been a subject of fascination for astronomers and stargazers throughout history.
  • 332
  • 29 Feb 2024
Topic Review
Chemical Force Microscopy
In materials science, chemical force microscopy (CFM) is a variation of atomic force microscopy (AFM) which has become a versatile tool for characterization of materials surfaces. With AFM, structural morphology is probed using simple tapping or contact modes that utilize van der Waals interactions between tip and sample to maintain a constant probe deflection amplitude (constant force mode) or maintain height while measuring tip deflection (constant height mode). CFM, on the other hand, uses chemical interactions between functionalized probe tip and sample. Choice chemistry is typically gold-coated tip and surface with R–SH thiols attached, R being the functional groups of interest. CFM enables the ability to determine the chemical nature of surfaces, irrespective of their specific morphology, and facilitates studies of basic chemical bonding enthalpy and surface energy. Typically, CFM is limited by thermal vibrations within the cantilever holding the probe. This limits force measurement resolution to ~1 pN which is still very suitable considering weak COOH/CH3 interactions are ~20 pN per pair. Hydrophobicity is used as the primary example throughout this consideration of CFM, but certainly any type of bonding can be probed with this method.
  • 332
  • 23 Nov 2022
Topic Review
Dirac Equation in the Algebra of Physical Space
The Dirac equation, as the relativistic equation that describes spin 1/2 particles in quantum mechanics, can be written in terms of the Algebra of physical space (APS), which is a case of a Clifford algebra or geometric algebra that is based on the use of paravectors. The Dirac equation in APS, including the electromagnetic interaction, reads Another form of the Dirac equation in terms of the Space time algebra was given earlier by David Hestenes. In general, the Dirac equation in the formalism of geometric algebra has the advantage of providing a direct geometric interpretation.
  • 331
  • 17 Oct 2022
Topic Review
Biology Monte Carlo Method
Biology Monte Carlo methods (BioMOCA) have been developed at the University of Illinois at Urbana-Champaign to simulate ion transport in an electrolyte environment through ion channels or nano-pores embedded in membranes. It is a 3-D particle-based Monte Carlo simulator for analyzing and studying the ion transport problem in ion channel systems or similar nanopores in wet/biological environments. The system simulated consists of a protein forming an ion channel (or an artificial nanopores like a Carbon Nano Tube, CNT), with a membrane (i.e. lipid bilayer) that separates two ion baths on either side. BioMOCA is based on two methodologies, namely the Boltzmann transport Monte Carlo (BTMC) and particle-particle-particle-mesh (P3M). The first one uses Monte Carlo method to solve the Boltzmann equation, while the later splits the electrostatic forces into short-range and long-range components.
  • 330
  • 04 Nov 2022
Topic Review
Boötes
Boötes, recognized by the International Astronomical Union (IAU), is a constellation in the northern celestial hemisphere. It is known for its prominent shape resembling a kite or an ice cream cone, with its brightest star, Arcturus, marking one corner.
  • 328
  • 29 Feb 2024
Topic Review
Pictor
Pictor, a relatively faint constellation in the southern celestial hemisphere, is named after the easel used by artists to hold their canvases. It is located between the star Canopus and the Large Magellanic Cloud.
  • 328
  • 15 Mar 2024
Topic Review
Broken/Asymptotic Safety in Quantum Gravity
Asymptotic safety (sometimes also referred to as nonperturbative renormalizability) is a concept in quantum field theory which aims at finding a consistent and predictive quantum theory of the gravitational field. Its key ingredient is a nontrivial fixed point of the theory's renormalization group flow which controls the behavior of the coupling constants in the ultraviolet (UV) regime and renders physical quantities safe from divergences. Although originally proposed by Steven Weinberg to find a theory of quantum gravity, the idea of a nontrivial fixed point providing a possible UV completion can be applied also to other field theories, in particular to perturbatively nonrenormalizable ones. In this respect, it is similar to quantum triviality. The essence of asymptotic safety is the observation that nontrivial renormalization group fixed points can be used to generalize the procedure of perturbative renormalization. In an asymptotically safe theory the couplings do not need to be small or tend to zero in the high energy limit but rather tend to finite values: they approach a nontrivial UV fixed point. The running of the coupling constants, i.e. their scale dependence described by the renormalization group (RG), is thus special in its UV limit in the sense that all their dimensionless combinations remain finite. This suffices to avoid unphysical divergences, e.g. in scattering amplitudes. The requirement of a UV fixed point restricts the form of the bare action and the values of the bare coupling constants, which become predictions of the asymptotic safety program rather than inputs. As for gravity, the standard procedure of perturbative renormalization fails since Newton's constant, the relevant expansion parameter, has negative mass dimension rendering general relativity perturbatively nonrenormalizable. This has driven the search for nonperturbative frameworks describing quantum gravity, including asymptotic safety which — in contrast to other approaches—is characterized by its use of quantum field theory methods, without depending on perturbative techniques, however. At the present time, there is accumulating evidence for a fixed point suitable for asymptotic safety, while a rigorous proof of its existence is still lacking.
  • 328
  • 19 Oct 2022
Topic Review
Thin Films of Sn Perovskites
Compared to Pb-based perovskites solar cells (PSCs), tin-based perovskite solar cells (TPSCs) exhibit a much lower power conversion energy (PCE), mainly due to the poor film quality, correlated degradation, and detrimental effects. Perovskite films are often fabricated from solutions due to ease of fabrication. In order to create a high-performance tin-based PSC, it is imperative to form dense, compact, well-crystalline perovskite films. Many ways have been proposed to resolve the instabilities of tin-based perovskites. The first step to enhance the stability of the device is to gain a deeper understanding of the degradation mechanisms. Earlier, the researchers briefly pointed out the effects of moisture, oxygen, illumination, ion migration, and chemical reactions which are the most common causes of degradation in perovskite halides.
  • 326
  • 20 Apr 2023
Topic Review
Stellar Magnetic Field
A stellar magnetic field is a magnetic field generated by the motion of conductive plasma inside a star. This motion is created through convection, which is a form of energy transport involving the physical movement of material. A localized magnetic field exerts a force on the plasma, effectively increasing the pressure without a comparable gain in density. As a result, the magnetized region rises relative to the remainder of the plasma, until it reaches the star's photosphere. This creates starspots on the surface, and the related phenomenon of coronal loops.
  • 326
  • 08 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.
  • 324
  • 20 Oct 2022
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