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Topic Review
Guru Purnima
Guru Purnima (Poornima) is an eastern spiritual tradition dedicated to spiritual and academic teachers, who are evolved or enlightened humans, ready to share their wisdom, with very little or no monetary expectation, based on Karma Yoga. It is celebrated as a festival in Nepal by the Nepalese Hindus and Buddhists. This festival is traditionally observed by Hindus, Buddhists and Jains to revere their chosen spiritual teachers / leaders and express their gratitude. The festival is celebrated on the full moon day (Purnima) in the Hindu month of Ashadha (June–July) as it is known in the Hindu calendar of India and Nepal. This day marks the first peak of the lunar cycle after the peak of the solar cycle.
  • 238
  • 17 Oct 2022
Topic Review
Gyrotrons
Gyrotrons are among the most powerful sources of coherent radiation that operate in CW and long pulse regimes in the sub-THz and the THz frequency ranges of the electromagnetic spectrum, i.e. between 0.3 THz and 3.0 THz (corresponding to wavelengths from 1.0 to 0.1 mm). This region, which spans between the frequency bands occupied by various electronic and photonic devices, respectively, is habitually called a THz power gap. The underlying mechanism of the operation of the gyrotron involves a formation of bunches of electrons gyrating in a helical electron beam and their synchronous interaction with a fast (i.e. having a superluminal phase velocity) electromagnetic wave, producing a bremsstrahlung radiation. In contrast to the slow-wave tubes, which utilize tiny structures with dimensions comparable to the wavelength of the radiation, the gyrotrons have a simpler resonant system (cavity resonator) with dimensions that are much greater than the wavelength. This allows much more powerful electron beams to be used and thus higher output powers to be achieved. Although in comparison with the classical microwave tubes the gyrotrons are characterized by greater volume and weight due to the presence of bulky parts (such as superconducting magnets and massive collectors where the energy of the spent electron beam is dissipated) they are much more compact and can easily be embedded in a sophisticated laboratory equipment (e.g. spectrometers, technological systems, etc.) than other devices such as free-electron lasers (FEL) and radiation sources based on electron accelerators. Nowadays, the gyrotrons are used as powerful sources of coherent radiation in the wide fields of high-power sub-THz and THz science and technologies [1][2][3].
  • 1.8K
  • 29 Oct 2020
Topic Review
Half-Reaction
A half reaction (or half-cell reaction) is either the oxidation or reduction reaction component of a redox reaction. A half reaction is obtained by considering the change in oxidation states of individual substances involved in the redox reaction. Often, the concept of half reactions is used to describe what occurs in an electrochemical cell, such as a Galvanic cell battery. Half reactions can be written to describe both the metal undergoing oxidation (known as the anode) and the metal undergoing reduction (known as the cathode). Half reactions are often used as a method of balancing redox reactions. For oxidation-reduction reactions in acidic conditions, after balancing the atoms and oxidation numbers, one will need to add H+ ions to balance the hydrogen ions in the half reaction. For oxidation-reduction reactions in basic conditions, after balancing the atoms and oxidation numbers, first treat it as an acidic solution and then add OH− ions to balance the H+ ions in the half reactions (which would give H2O).
  • 3.1K
  • 28 Nov 2022
Topic Review
Halide Perovskites Films for Ionizing Radiation Detection
Halide perovskites are a novel class of semiconductors that have attracted great interest due to their peculiar properties of interest for optoelectronics. In fact, their use ranges from the field of sensors and light emitters to ionizing radiation detectors. Since 2015, ionizing radiation detectors exploiting perovskite films as active media have been developed. 
  • 282
  • 15 Jun 2023
Topic Review
Heat Modulation of Intrinsic MR Contrasts
Multi-parametric magnetic resonance imaging (MRI) is a paradigm that combines several MR imaging contrast types to provide added layers of information for the characterization of tissue types, including benign and malignant tumors. 
  • 320
  • 28 Feb 2022
Topic Review
Heliophysics NASA Science
Heliophysics is an aspect of NASA science that enables understanding the Sun, heliosphere, and planetary environments as a single connected system. In addition to solar processes, this domain of study includes the interaction of solar plasma and solar radiation with Earth, the other planets, and the galaxy. By analyzing the connections between the Sun, solar wind, and planetary space environments, the fundamental physical processes that occur throughout the universe are uncovered. Understanding the connections between the Sun and its planets will allow for predicting the impacts of solar interaction on humans, technological systems, and even the presence of life itself. This is also the stated goal of Science Mission Directorate's Heliophysics Research.
  • 244
  • 25 Oct 2022
Topic Review
Hercules
Hercules is a prominent constellation in the northern celestial hemisphere, named after the legendary hero from Greek mythology known for his incredible strength and courage. It is the fifth-largest of the 88 modern constellations.
  • 385
  • 15 Mar 2024
Topic Review
Hidden Jahn-Teller and Pseudo-Jahn-Teller effects
The source of spontaneous symmetry breaking (SSB) in polyatomic systems, attributed to the Jahn-Teller effect (in electronic degenerate states) or to the pseudo-Jahn-Teller effect (under the condition of pseudodegeneracy), is complemented with the notions of hidden Jahn-Teller effect (h-JTE) and hidden pseudo-Jahn-Teller effect (h-PJTE) to stand for the cases when neither electronic degeneracy, nor pseudodegeneracy is present, but the system is still spontaneously distorted. The h-JTE and h-PJTE occur due to, respectively, the JTE and PJTE in the excited states of the undistorted system, but being strong enough, they penetrate its ground state forming a stable configuration with lower symmetry and (possibly) different spin.
  • 1.5K
  • 11 Dec 2020
Topic Review
Hidden-Measurements Interpretation
The hidden-measurements interpretation (HMI), also known as the hidden-measurements approach, is a realistic interpretation of quantum mechanics. The basis of the hidden-measurements interpretation (HMI) is the hypothesis that a quantum measurement involves a certain amount of unavoidable fluctuations in the way the measuring system interacts with the measured entity. As a consequence, the interaction is not a priori given in a quantum measurement, but is each time selected (that is, actualized, through a weighted symmetry breaking processes) when the experiment is executed; and since different measurement-interactions can produce different outcomes, this can explain why the output of a quantum measurement can only be predicted in probabilistic terms. (One should not think however of these hidden measurement-interactions to be something similar to, or to be describable in the same way as, the fundamental interactions (fundamental forces) of the standard model of particle physics, mediated by bosonic elementary entities).
  • 705
  • 03 Nov 2022
Topic Review
Hierarchical Nanobiosensors
Nanostructures have played a key role in the development of different techniques to attack severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Some applications include masks, vaccines, and biosensors. The latter are of great interest for detecting diseases since some of their features allowed us to find specific markers in secretion samples such as saliva, blood, and even tears.
  • 145
  • 21 Feb 2024
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