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Relative Hour (Jewish Law)
Relative hour (Hebrew singular: shaʿah zǝmanit / שעה זמנית; plural: shaʿot - zǝmaniyot / שעות זמניות), sometimes called halachic hour, seasonal hour and variable hour, is a term used in rabbinic Jewish law that assigns 12 hours to each day and 12 hours to each night, all throughout the year. A relative hour has no fixed radical, but changes with the length of each day - depending on summer (when the days are long and the nights are short), and on winter (when the days are short and the nights are long). Even so, in all seasons a day is always divided into 12 hours, and a night is always divided into 12 hours, which inevitably makes for a longer hour or a shorter hour. All of the hours mentioned by the Sages in either the Mishnah or Talmud, or in other rabbinic writings, refer strictly to relative hours. Another feature of this ancient practice is that, unlike the standard modern 12-hour clock that assigns 12 o'clock pm for noon time, in the ancient Jewish tradition noon time was always the sixth hour of the day, whereas the first hour began with the break of dawn, by most exponents of Jewish law, and with sunrise by the Vilna Gaon and Rabbi Hai Gaon. 12:o'clock am (midnight) was also the sixth hour of the night, whereas the first hour of the night began when the first three stars appeared in the night sky.
  • 16.9K
  • 19 Oct 2022
Topic Review
Osmium-186
Osmium (76Os) has seven naturally occurring isotopes, five of which are stable: 187Os, 188Os, 189Os, 190Os, and (most abundant) 192Os. The other natural isotopes, 184Os, and 186Os, have extremely long half-life (1.12×1013 years and 2×1015 years, respectively) and for practical purposes can be considered to be stable as well. 187Os is the daughter of 187Re (half-life 4.56×1010 years) and is most often measured in an 187Os/188Os ratio. This ratio, as well as the 187Re/188Os ratio, have been used extensively in dating terrestrial as well as meteoric rocks. It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons. However, the most notable application of Os in dating has been in conjunction with iridium, to analyze the layer of shocked quartz along the Cretaceous–Paleogene boundary that marks the extinction of the dinosaurs 66 million years ago. There are also 30 artificial radioisotopes, the longest-lived of which is 194Os with a half-life of six years; all others have half-lives under 94 days. There are also nine known nuclear isomers, the longest-lived of which is 191mOs with a half-life of 13.10 hours. All isotopes and nuclear isomers of osmium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.
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  • 19 Oct 2022
Topic Review
The World (Descartes)
The World, also called Treatise on the Light (French title: Traité du monde et de la lumière), is a book by René Descartes (1596–1650). Written between 1629 and 1633, it contains a nearly complete version of his philosophy, from method, to metaphysics, to physics and biology. Descartes espoused mechanical philosophy, a form of natural philosophy popular in the 17th century. He thought everything physical in the universe to be made of tiny "corpuscles" of matter. Corpuscularianism is closely related to atomism. The main difference was that Descartes maintained that there could be no vacuum, and all matter was constantly swirling to prevent a void as corpuscles moved through other matter. The World presents a corpuscularian cosmology in which swirling vortices explain, among other phenomena, the creation of the Solar System and the circular motion of planets around the Sun. The World rests on the heliocentric view, first explicated in Western Europe by Copernicus. Descartes delayed the book's release upon news of the Roman Inquisition's conviction of Galileo for "suspicion of heresy" and sentencing to house arrest. Descartes discussed his work on the book, and his decision not to release it, in letters with another philosopher, Marin Mersenne. Some material from The World was revised for publication as Principia philosophiae or Principles of Philosophy (1644), a Latin textbook at first intended by Descartes to replace the Aristotelian textbooks then used in universities. In the Principles the heliocentric tone was softened slightly with a relativist frame of reference. The last chapter of The World was published separately as De Homine (On Man) in 1662. The rest of The World was finally published in 1664, and the entire text in 1677.
  • 1.1K
  • 19 Oct 2022
Topic Review
Neural Circuit
A neural circuit, is a population of neurons interconnected by synapses to carry out a specific function when activated. Neural circuits interconnect to one another to form large scale brain networks. Biological neural networks have inspired the design of artificial neural networks.
  • 1.5K
  • 19 Oct 2022
Topic Review
Boston Computer Society
The Boston Computer Society (BCS) was an organization of personal computer users, based in Boston, Massachusetts, United States , that ran from 1977 to 1996. At one point, it was the largest such group in the world, with regular user group meetings, many publications, permanent offices in Boston, and hosting major product announcements, including the East Coast release of the Apple Macintosh in 1984.
  • 566
  • 19 Oct 2022
Topic Review
Ontological Turn
The ontological turn broadly relates to a development in a number of philosophical and academic disciplines that led to an increased focus on being. The ontological turn in anthropology is not concerned with anthropological notions of culture, epistemology, nor world views. Instead, the ontological turn generates interest in being in the world and accepts that different world views are not simply different representations of the same world. Rather, people have different perspectives and people see the world in different ways, but the world is still the world. Therefore, the ontological turn refers to a change in perspective that suggests that difference can be understood, not in terms of a difference in world views, but a differences in worlds and all of these worlds are of equal validity.
  • 3.5K
  • 19 Oct 2022
Topic Review
Verrucomicrobia
Verrucomicrobia is a phylum of Gram-negative bacteria that contains only a few described species. The species identified have been isolated from fresh water, marine and soil environments and human faeces. A number of as-yet uncultivated species have been identified in association with eukaryotic hosts including extrusive explosive ectosymbionts of protists and endosymbionts of nematodes residing in their gametes. Verrucomicrobia are abundant within the environment, though relatively inactive. This phylum is considered to have two sister phyla: Chlamydiae and Lentisphaerae within the PVC group. The Verrucomicrobia phylum can be distinguished from neighbouring phyla within the PVC group by the presence of several conserved signature indels (CSIs). These CSIs represent unique, synapomorphic characteristics that suggest common ancestry within Verrucomicrobia and an independent lineage amidst other bacteria. CSIs have also been found that are shared by Verrucomicrobia and Chlamydiae exclusively of all other bacteria. These CSIs provide evidence that Chlamydiae is the closest relative to Verrucomicrobia, and that they are more closely related to one another than to the Planctomycetales. Verrucomicrobia might belong in the clade Planctobacteria in the larger clade Gracilicutes. In 2008, the whole genome of Methylacidiphilum infernorum (2.3 Mbp) was published. On the single circular chromosome, 2473 predicted proteins were found, 731 of which had no detectable homologs. These analyses also revealed many possible homologies with Proteobacteria.
  • 2.3K
  • 21 Oct 2022
Topic Review
Echoic Memory
Echoic memory is the sensory memory that registers specific to auditory information (sounds). Once an auditory stimulus is heard, it is stored in memory so that it can be processed and understood. Unlike visual memory, in which our eyes can scan the stimuli over and over, the auditory stimuli cannot be scanned over and over. Since echoic memories are heard once, they are stored for slightly longer periods of time than iconic memories (visual memories). Auditory stimuli are received by the ear one at a time before they can be processed and understood. For instance, hearing the radio is very different from reading a magazine. A person can only hear the radio once at a given time, while the magazine can be read over and over again. It can be said that the echoic memory is like a "holding tank" concept, because a sound is unprocessed (or held back) until the following sound is heard, and only then can it be made meaningful. This particular sensory store is capable of storing large amounts of auditory information that is only retained for a short period of time (3–4 seconds). This echoic sound resonates in the mind and is replayed for this brief amount of time shortly after being heard. Echoic memory encodes only moderately primitive aspects of the stimuli, for example pitch, which specifies localization to the non-association brain regions.
  • 2.9K
  • 21 Oct 2022
Topic Review
FYAT Multirotor
FYAT multirotors are Chinese UAVs developed by Linyi Feng-Yun (meaning Wind Cloud) Aviation Technology Co., Ltd. (FYAT, 临沂风云航空科技有限公司), some of which have entered service with Chinese law enforcement and other governmental establishments.
  • 550
  • 19 Oct 2022
Topic Review
Single-Letter Second-Level Domain
Single-letter second-level domains are domain names in which the second-level domain consists of only one letter, such as x.com. In 1993, the Internet Assigned Numbers Authority (IANA) explicitly reserved all single-letter and single-digit second-level domain names in the top-level domains com, net, and org, and grandfathered those that had already been assigned. In December 2005, ICANN considered auctioning these domains.
  • 6.3K
  • 03 Nov 2022
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