Subject:
All Disciplines Arts & Humanities Biology & Life Sciences Business & Economics Chemistry & Materials Science Computer Science & Mathematics Engineering Environmental & Earth Sciences Medicine & Pharmacology Physical Sciences Public Health & Healthcare Social Sciences
Sort:
Hottest Latest Alphabetical (A-Z) Alphabetical (Z-A)
Type:
All Topic Review Biography
Topic Review
Lyra
Lyra is a constellation in the northern celestial hemisphere known for its prominent star Vega, one of the brightest stars in the sky. Represented as a lyre, a musical instrument from Greek mythology, Lyra is rich in celestial objects. Lyra is bordered by Vulpecula to the south, Hercules to the west, Draco to the north, and Cygnus to the east.
  • 362
  • 15 Mar 2024
Topic Review
Machine-Learning-Based Methods for Acoustic Emission Testing
Acoustic emission (AE) testing has obvious limitations regarding its reproducibility: as it was said, this type of test involves the formation or progression of cracks in the material. Even when referring to specimens of the same material, of the same dimensions, and subjected to the same load cycle, they do not necessarily produce the same results. This is especially true in the case of anisotropic and heterogeneous materials. Moreover, since the signals used by precursors are of modest entity, to be able to detect possible forms of energy in the material, it is necessary to use particularly sensitive sensors. Further problems arise due to the attenuation phenomena of the acoustic stress wave that is dispersed in the material as it propagates: just as the noise due to sources independent of the possible structural defect can disturb the detection methodology. To overcome these limitations, researchers adopted alternative methodologies to improve the results of the structural damage identification procedures. The capabilities demonstrated by the technologies based on ML in detecting patterns were immediately noticed by AE researchers. To make this nondestructive testing method even more effective, all the methodologies based on ML for the recognition of the stress wave can be applied during the detection phase of the acoustic emission generated by the source. In this way, it is possible to carry out a test that is robust regarding noise and effective in detecting waves of modest entity. The most common methodologies based on ML applied in the field of AE are presented below. ML is a branch of artificial intelligence whose goal is to allow machines to automatically learn something from experience, without the need for them to be programmed in advance. Experience is a collection of data, which can be fixed and immutable, or even expand over time. Learning can be carried out through two main approaches: supervised and unsupervised.
  • 644
  • 03 Nov 2022
Topic Review
Magic Number
In nuclear physics, a magic number is a number of nucleons (either protons or neutrons, separately) such that they are arranged into complete shells within the atomic nucleus. As a result, atomic nuclei with a 'magic' number of protons or neutrons are much more stable than other nuclei. The seven most widely recognized magic numbers as of 2019 are 2, 8, 20, 28, 50, 82, and 126 (sequence A018226 in the OEIS). For protons, this corresponds to the elements helium, oxygen, calcium, nickel, tin, lead and the hypothetical unbihexium, although 126 is so far only known to be a magic number for neutrons. Atomic nuclei consisting of such a magic number of nucleons have a higher average binding energy per nucleon than one would expect based upon predictions such as the semi-empirical mass formula and are hence more stable against nuclear decay. The unusual stability of isotopes having magic numbers means that transuranium elements could theoretically be created with extremely large nuclei and yet not be subject to the extremely rapid radioactive decay normally associated with high atomic numbers. Large isotopes with magic numbers of nucleons are said to exist in an island of stability. Unlike the magic numbers 2–126, which are realized in spherical nuclei, theoretical calculations predict that nuclei in the island of stability are deformed. Before this was realized, higher magic numbers, such as 184, 258, 350, and 462 (sequence A033547 in the OEIS), were predicted based on simple calculations that assumed spherical shapes: these are generated by the formula [math]\displaystyle{ 2(\tbinom n1+ \tbinom n2+\tbinom n3) }[/math] (see Binomial coefficient). It is now believed that the sequence of spherical magic numbers cannot be extended in this way. Further predicted magic numbers are 114, 122, 124, and 164 for protons as well as 184, 196, 236, and 318 for neutrons. However, more modern calculations predict 228 and 308 for neutrons, along with 184 and 196.
  • 897
  • 03 Nov 2022
Topic Review
Magnetic Ag-Integrated Photocatalysts in Water Treatment
One of the great dangers facing humanity is the depletion of natural resources. For water specifically, the problem of shortage is all but gone. In 1960, only 9% of the world’s population was facing chronic water shortage issues, while nearly 50% of the global population has to manage moderate shortage, with around 10% of that population facing almost complete lack of water. Many measures have been employed to balance this ever-increasing threat, such as irrigated areas, groundwater utilization and reservoir storage, as this increase in water shortage does not only affect agriculture but human health itself as well and can even increase risks of diseases. The need for low-cost water treatment is especially evident in countries such as Pakistan, where the increased dependency on severely threatening contaminated water (by ~80% of the population) necessitates methods such as low-cost water filters for increased availability of affordable drinking water throughout the country. A magnetic/silver composite combines the advantages of magnetic properties with those of plasmonic nanoparticles, and these composites are able to perform well under UV and visible light, are effective against pollutants and pathogenic bacteria and can be easily separated from a solution with a simple magnet.
  • 539
  • 19 Jul 2022
Topic Review
Magnetic Fluids
Magnetic fluids were historically the first active nano-dispersion material. Despite over half a century of research, interest in these nano-objects continues to grow every year. This is due to the impressive development of nanotechnology, the synthesis of nanoscale structures, and surface-active systems.
  • 227
  • 25 Jan 2024
Topic Review
Magnetic Force Microscopy on Nanofibers
Magnetic force microscopy is a magnetic characterization method of samples usually with a maximum of a few ten nanometers surface roughness. It works by measuring an atomic force microscopy (AFM) image of the surface topography of a sample, followed by lifting the probe to avoid short-range van der Waals interactions between the tip and sample and instead measuring the long-range magnetic interactions. In addition to this simplest form of magnetic force microscopy (MFM), there are more sophisticated ones, including frequency-modulated Kelvin probe force MFM, dynamic magneto-electric force microscopy, phase-locked loop methods, and even measurements in different environments, e.g., in liquids, that have been shown.
  • 493
  • 10 Nov 2021
Topic Review
Magnetic Guiding
Magnetic guidance is understood as a remote, untethered and contact-free control of the movements of an object via magnetic interactions. The movements should happen on arbitrary trajectories inside a container caused by an external device. The concept of remote magnetic guiding is developed from the underlying physics for bijective force generation over the inner volume of magnet systems. This concept can equally be implemented by electro- or permanent magnets. 
  • 866
  • 07 Dec 2021
Topic Review
Magnetic Potential
The term magnetic potential can be used for either of two quantities in classical electromagnetism: the magnetic vector potential, or simply vector potential, A; and the magnetic scalar potential ψ. Both quantities can be used in certain circumstances to calculate the magnetic field B. The more frequently used magnetic vector potential is defined so that its curl is equal to the magnetic field: [math]\displaystyle{ \nabla \times \mathbf{A}=\mathbf{B}\, }[/math]. Together with the electric potential φ, the magnetic vector potential can be used to specify the electric field E as well. Therefore, many equations of electromagnetism can be written either in terms of the fields E and B, or equivalently in terms of the potentials φ and A. In more advanced theories such as quantum mechanics, most equations use potentials rather than fields. The magnetic scalar potential ψ is sometimes used to specify the magnetic H-field in cases when there are no free currents, in a manner analogous to using the electric potential to determine the electric field in electrostatics. One important use of ψ is to determine the magnetic field due to permanent magnets when their magnetization is known. With some care the scalar potential can be extended to include free currents as well. Historically, Lord Kelvin first introduced vector potential in 1851, along with the formula relating it to the magnetic field.
  • 6.6K
  • 29 Sep 2022
Topic Review
Magnetic Properties and Magnetocaloric Effect of Pr2Co7 Compound
The Pr2Co7 compound has interesting magnetic properties, such as a high Curie temperature TC and uniaxial magnetocrystalline anisotropy. It crystallizes in a hexagonal structure (2:7 H) of the Ce2Ni7 type and is stable at relatively low temperatures (Ta ≤ 1023 K), or it has a rhombohedral structure (2:7 R) of the Gd2Co7 type and is stable at high temperatures (Ta ≥ 1223 K). Studies of the magnetocaloric properties of the nanocrystalline Pr2Co7 compound have shown the existence of a large reversible magnetic entropy change (ΔSM) with a second-order magnetic transition. 
  • 567
  • 15 Jun 2023
Topic Review
Magnetoelectric Magnetic Field Sensors
One of the new materials that have attracted wide attention of researchers are magnetoelectric (ME) composites. Great interest in these materials is due to their properties associated with the transformation of electric polarization/magnetization under the influence of external magnetic/electric fields and the possibility of their use to create new devices. ME magnetic field sensors based on the widely used structures Terfenol—PZT/PMN-PT,Metglas—PZT/PMN-PT, and Metglas—Lithium niobate, among others, are considered as the first applications of the ME effect in technology. Estimates of the parameters of ME sensors are given, and comparative characteristics of magnetic field sensors are presented. Taking into account the high sensitivity of ME magnetic field sensors, comparable to superconducting quantum interferencedevices (SQUIDs), this entry discuss the areas of their application.
  • 487
  • 08 Feb 2023
  • Page
  • of
  • 118
Featured Entry Collections
>>

Featured Books

>>
Encyclopedia of Social Sciences
Encyclopedia of COVID-19
Encyclopedia of Fungi
Encyclopedia of Digital Society, Industry 5.0 and Smart City
Video Production Service
Feedback