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Topic Review
Zeta Ursae Majoris
Mizar is a 2nd magnitude star in the handle of the Big Dipper asterism in the constellation of Ursa Major. It has the Bayer designation ζ Ursae Majoris (Latinised as Zeta Ursae Majoris). It forms a well-known naked eye double star with the fainter star Alcor, and is itself a quadruple star system. The whole system lies about 83 light-years away from the Sun, as measured by the Hipparcos astrometry satellite, and is part of the Ursa Major Moving Group.
  • 799
  • 29 Sep 2022
Topic Review
ADM Formalism
The ADM formalism (named for its authors Richard Arnowitt, Stanley Deser and Charles W. Misner) is a Hamiltonian formulation of general relativity that plays an important role in canonical quantum gravity and numerical relativity. It was first published in 1959. The comprehensive review of the formalism that the authors published in 1962 has been reprinted in the journal General Relativity and Gravitation, while the original papers can be found in the archives of Physical Review.
  • 798
  • 01 Nov 2022
Topic Review
Ceramics, Glass and Glass-Ceramics for Personal Radiation Detectors
Different types of ceramics and glass have been extensively investigated due to their application in brachytherapy, radiotherapy, nuclear medicine diagnosis, radioisotope power systems, radiation processing of food, geological and archaeological dating methods. The comparison of the physico-chemical properties shows that glassy materials could be a promising alternative for dosimetry purposes.
  • 796
  • 27 Oct 2021
Topic Review
Introduction to the Mathematics of General Relativity
The mathematics of general relativity is complex. In Newton's theories of motion, an object's length and the rate at which time passes remain constant while the object accelerates, meaning that many problems in Newtonian mechanics may be solved by algebra alone. In relativity, however, an object's length and the rate at which time passes both change appreciably as the object's speed approaches the speed of light, meaning that more variables and more complicated mathematics are required to calculate the object's motion. As a result, relativity requires the use of concepts such as vectors, tensors, pseudotensors and curvilinear coordinates. For an introduction based on the example of particles following circular orbits about a large mass, nonrelativistic and relativistic treatments are given in, respectively, Newtonian motivations for general relativity and Theoretical motivation for general relativity.
  • 795
  • 01 Dec 2022
Topic Review
Bya (Unit)
A year is the orbital period of a planetary body, for example, the Earth, moving in its orbit around the Sun. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by change in weather, the hours of daylight, and, consequently, vegetation and soil fertility. In temperate and subpolar regions around the planet, four seasons are generally recognized: spring, summer, autumn and winter. In tropical and subtropical regions, several geographical sectors do not present defined seasons; but in the seasonal tropics, the annual wet and dry seasons are recognized and tracked. A calendar year is an approximation of the number of days of the Earth's orbital period, as counted in a given calendar. The Gregorian calendar, or modern calendar, presents its calendar year to be either a common year of 365 days or a leap year of 366 days, as do the Julian calendars; see below. For the Gregorian calendar, the average length of the calendar year (the mean year) across the complete leap cycle of 400 years is 365.2425 days. The ISO standard ISO 80000-3, Annex C, supports the symbol a (for Latin annus) to represent a year of either 365 or 366 days. In English, the abbreviations y and yr are commonly used. In astronomy, the Julian year is a unit of time; it is defined as 365.25 days of exactly 86,400 seconds (SI base unit), totalling exactly 31,557,600 seconds in the Julian astronomical year. The word year is also used for periods loosely associated with, but not identical to, the calendar or astronomical year, such as the seasonal year, the fiscal year, the academic year, etc. Similarly, year can mean the orbital period of any planet; for example, a Martian year and a Venusian year are examples of the time a planet takes to transit one complete orbit. The term can also be used in reference to any long period or cycle, such as the Great Year.
  • 793
  • 01 Dec 2022
Topic Review
Left-Right Asymmetry
Left-right asymmetry (LR asymmetry) refers to differences in structure (symmetry breaking) across the mediolateral (left and right) plane in animals. This plane is defined with respect to the anteroposterior and dorsoventral axes and is perpendicular to both. Because the left-right plane is not strictly an axis (as it is not established through a morphogen gradient), to create asymmetry, the left and right sides need to be patterned separately. LR asymmetry is pervasive throughout metazoans and present throughout every major lineage. Notable examples include the large and small claws of the fiddler crab, the left offset of the vertebrate heart, asymmetrical gut coiling in Drosophila melanogaster, and dextral (clockwise) and sinistral (counterclockwise) coiling of gastropods. This asymmetry can be restricted to a specific organ or feature, as in the crab claws, or be expressed throughout the entire body as in snails.
  • 793
  • 02 Nov 2022
Topic Review
Nebra Sky Disk
The Nebra sky disk is a bronze disk of around 30 centimetres (11 3⁄4 in) diameter and a weight of 2.2 kilograms (4.9 lb), having a blue-green patina and inlaid with gold symbols. These symbols are interpreted generally as the Sun or full moon, a lunar crescent, and stars (including a cluster of seven stars interpreted as the Pleiades). Two golden arcs along the sides, interpreted to mark the angle between the solstices, were added later. A final addition was another arc at the bottom surrounded with multiple strokes (of uncertain meaning, variously interpreted as a solar barge with numerous oars, the Milky Way, or a rainbow). The disk has been attributed to a site in present-day Germany near Nebra, Saxony-Anhalt, and was originally dated by archaeologists to c. 1600 BCE. Researchers initially suggested the disk is an artifact of the Bronze Age Unetice culture, although a later dating to the Iron Age has been proposed as well. If its Bronze Age dating is accurate, the Nebra sky disk features the oldest concrete depiction of the cosmos yet known from anywhere in the world. In June 2013 it was included in the UNESCO Memory of the World Register and termed "one of the most important archaeological finds of the twentieth century."
  • 790
  • 23 Nov 2022
Topic Review
Water Hammer Modelling
Water Hammer is a physical phenomenon that occurs due to sudden stopping of flow in a pipeline system which causes a sudden large pressure rise mimicking the hammering effect. It is considered one of the worst nightmare for hydraulic engineers due to its potential of causing widespread damage to property and lives. Therefore, numerical estimation of water hammer pressure is crucial for the design, operation, and risk analysis of pipeline systems. Generally, the traditional Method of Characteristics (MOC) is preferred by modellers worldwide due to its simplicity and usability. However, due to high shock generation during large water hammer event in pipeline, Finite Volume Method (FVM) has a clear advantage because of its desirable attribute of conserving mass, momentum compared to traditional MOC Schemes. Further, modelling of the water hammer phenomenon for dynamic characteristics within a turbine is impossible using the classical 1D MOC or 1D FVM schemes, and such applications require more extensive 3D grids and turbulence models. Several commercial pieces of software for turbulence modelling available today can be effectively used for this type of study. Some well-known and well-applied turbulence models currently in use are FLUENT and CFX (https://www.ansys.com(accessed on 1 June 2021)).
  • 788
  • 24 Jun 2021
Topic Review
The BIANCA Biophysical Model
Cancer ion therapy is constantly growing, thanks to its increased precision and, for heavy ions, its increased biological effectiveness (RBE) with respect to conventional photon therapy. The complex dependence of RBE on many factors demands for biophysical modelling. Up to now only the Local Effect Model (LEM), the Microdosimetric Kinetic Model (MKM) and the “mixed-beam” model are used in clinics. In this work the BIANCA biophysical model, after extensive benchmarking in vitro, was applied to develop a database predicting cell survival for different ions, energies and doses. Following interface with the FLUKA Monte Carlo transport code, for the first time BIANCA was benchmarked against in vivo data obtained by C-ion or proton irradiation of the rat spinal cord. The latter is a well-established model for CNS (Central Nervous System) late effects, which in turn are the main dose-limiting factor for head-and-neck tumors. Furthermore, these data have been considered to validate the LEM version applied in clinics. Although further benchmarking is desirable, the agreement between simulations and data suggests that BIANCA can predict RBE for C-ion or proton treatment of head-and-neck tumors. In particular, the agreement with proton data may be relevant if the current assumption of a constant proton RBE of 1.1 is revised. This work provides the bases for future benchmarking against patient data, as well as the development of other databases for specific tumor types and/or normal tissues.
  • 786
  • 02 Nov 2020
Topic Review
V-HOE Based Solar Concentrators
The fundamental advantages of volume holographic optical elements are very appealing for lightweight and cheap solar concentrators applications and can become a valuable asset that can be integrated into solar panels. 
  • 783
  • 10 Jun 2021
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