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HandWiki is the world's largest wiki-style encyclopedia dedicated to science, technology and computing. It allows you to create and edit articles as long as you have external citations and login account. In addition, this is a content management environment that can be used for collaborative editing of original scholarly content, such as books, manuals, monographs and tutorials.

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Switchgear
In an electric power system, switchgear is the combination of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream. This type of equipment is directly linked to the reliability of the electricity supply. The earliest central power stations used simple open knife switches, mounted on insulating panels of marble or asbestos. Power levels and voltages rapidly escalated, making opening manually operated switches too dangerous for anything other than isolation of a de-energized circuit. Oil-filled equipment allowed arc energy to be contained and safely controlled. By the early 20th century, a switchgear line-up would be a metal-enclosed structure with electrically operated switching elements, using oil circuit breakers. Today, oil-filled equipment has largely been replaced by air-blast, vacuum, or SF6 equipment, allowing large currents and power levels to be safely controlled by automatic equipment. High-voltage switchgear was invented at the end of the 19th century for operating motors and other electric machines. The technology has been improved over time and can now be used with voltages up to 1,100 kV. Typically, switchgear in substations are located on both the high- and low-voltage sides of large power transformers. The switchgear on the low-voltage side of the transformers may be located in a building, with medium-voltage circuit breakers for distribution circuits, along with metering, control, and protection equipment. For industrial applications, a transformer and switchgear line-up may be combined in one housing, called a unitized substation (USS).
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  • 21 Nov 2022
Topic Review
Plant Embryogenesis
Plant embryogenesis is a process that occurs after the fertilization of an ovule to produce a fully developed plant embryo. This is a pertinent stage in the plant life cycle that is followed by dormancy and germination. The zygote produced after fertilization must undergo various cellular divisions and differentiations to become a mature embryo. An end stage embryo has five major components including the shoot apical meristem, hypocotyl, root meristem, root cap, and cotyledons. Unlike animal embryogenesis, plant embryogenesis results in an immature form of the plant, lacking most structures like leaves, stems, and reproductive structures. However, both plants and animals pass through a phylotypic stage that evolved independently and that causes a developmental constraint limiting morphological diversification.
  • 17.3K
  • 28 Apr 2023
Topic Review
Sonic Hedgehog
Sonic hedgehog is a protein encoded for by the SHH gene. The protein is named after the character Sonic the Hedgehog. This signaling molecule is key in regulating embryonic morphogenesis in all different types of animals. SHH controls organogenesis and the organization of the central nervous system, limbs, digits and many other parts of the body. Sonic hedgehog is a morphogen that patterns the developing embryo using a concentration gradient characterized by the French Flag model. This model has a non-uniform distribution of SHH molecules which governs different cell fates according to concentration. Mutations in this gene can cause holoprosencephaly, a failure of splitting in the cerebral hemispheres, as demonstrated in an experiment using SHH knock-out mice in which the forebrain midline failed to develop and instead only a single fused telencephalic vesicle resulted. Sonic hedgehog still plays a role in differentiation, proliferation, and maintenance of adult tissues. Abnormal activation of SHH signaling in adult tissues has been implicated in various types of cancers including breast, skin, brain, liver, gallbladder and many more.
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  • 21 Nov 2022
Topic Review
Visna Virus
Visna virus (also known as visna-maedi virus, maedi-visna virus and ovine lentivirus) from the genus Lentivirus and subfamily Orthoretrovirinae, is a "prototype" retrovirus that causes encephalitis and chronic pneumonitis in sheep. It is known as visna when found in the brain, and maedi when infecting the lungs. Lifelong, persistent infections in sheep occur in the lungs, lymph nodes, spleen, joints, central nervous system, and mammary glands; The condition is sometimes known as "ovine progressive pneumonia" (OPP), particularly in the United States , or "Montana sheep disease". White blood cells of the monocyte/macrophage lineage are the main target of visna virus.
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  • 21 Nov 2022
Topic Review
Timeline of Physical Chemistry
The timeline of physical chemistry lists the sequence of physical chemistry theories and discoveries in chronological order.
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  • 21 Nov 2022
Topic Review
The Occult World
The Occult World is a book originally published in 1881 in London; it was compiled by a member of the Theosophical Society A. P. Sinnett. It was the first theosophical work by the author; according to Goodrick-Clarke, this book "gave sensational publicity to Blavatsky's phenomena" and the letters from the mahatmas, and drew the attention of the London Society for Psychical Research.
  • 1.3K
  • 22 Nov 2022
Topic Review
Triacontanol
1-Triacontanol is a fatty alcohol of the general formula C30H62O, also known as melissyl alcohol or myricyl alcohol. It is found in plant cuticle waxes and in beeswax. Triacontanol is a growth stimulant for many plants, most notably roses, in which it rapidly increases the number of basal breaks. 1-Triacontanol or n-triacontanol is a natural plant growth regulator. It has been widely used to enhance the yield of various crops around the world, mainly in Asia. . Triacontanol has been reported to increase the growth of plants by enhancing the rates of photosynthesis, protein biosynthesis, the transport of nutrients in a plant and enzyme activity, reducing complex carbohydrates among many other purposes. The fatty alcohol appears to increase the physiological efficiency of plant cells and boost the potential of the cells responsible for the growth and maturity of a plant.
  • 1.1K
  • 21 Nov 2022
Topic Review
Plutoid
A plutoid or ice dwarf is a trans-Neptunian dwarf planet, i.e. a body orbiting beyond Neptune that is massive enough to be rounded in shape. The term plutoid was adopted by the International Astronomical Union (IAU) working group Committee on Small Bodies Nomenclature, but was rejected by the IAU working group Planetary System Nomenclature. The term plutoid is not widely used by astronomers, though ice dwarf is not uncommon. There are thought to be thousands of plutoids in the Solar System, although only four have been formally designated as such by the IAU. The IAU developed this category of astronomical objects as a consequence of its 2006 resolution defining the word "planet". The IAU's formal definition of "plutoid", announced 11 June 2008, is: In light of the difficulty of remotely ascertaining hydrostasis, the IAU only formally confers "dwarf planet" (and by extension, "plutoid") status to those bodies whose minimum estimated size is substantially greater than what is generally thought necessary to guarantee hydrostatic equilibrium. (As of 2009), Pluto, Eris, Haumea, and Makemake are the only objects officially recognized as plutoids, while upwards of seventy more bodies that currently lack formal recognition are thought likely to meet the definition, and can expect formal recognition at some time in the future. Alan Stern of the Southwest Research Institute believes the outer planets show signs of collisions with plutoids 1,000 to 2,000 kilometers in diameter: Uranus could have been tipped off its axis by a plutoid, and Triton, the largest moon of Neptune, is probably a captured plutoid from the Kuiper belt.
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  • 21 Nov 2022
Topic Review
Stunting (Broadcasting)
In radio broadcasting, stunting occurs when a station abruptly airs content that is seemingly uncharacteristic compared to what they normally play. The tactic is commonly used when a station is about to undergo a major change (such as a change in format, branding, frequency, ownership or management, or even the acquisition of a high-profile program or personality), or simply as a prank on listeners and rival broadcasters. Either way, stunting is intended as a way to generate a greater amount of media publicity and audience attention to the station, by virtue of its shock value, than a straightforward format change could provide. Depending on the station's situation and its management's preference, stunt formats can last anywhere from a few minutes to several weeks before the permanent change is launched.
  • 1.6K
  • 21 Nov 2022
Topic Review
Positive Stereotype
In social psychology, a positive stereotype refers to a subjectively favorable belief held about a social group. Common examples of positive stereotypes are Asians with better math ability, African Americans with greater athletic ability, and women with being more warm and communal. As opposed to negative stereotypes, positive stereotypes represent a "positive" evaluation of a group that typically signals an advantage over another group. As such, positive stereotypes may be considered a form of compliment or praise. However, positive stereotypes can have a positive or negative effect on targets of positive stereotypes. The positive or negative influence of positive stereotypes on targets depends on three factors: (1) how the positive stereotype is stated, (2) who is stating the positive stereotype, (3) in what culture the positive stereotype is presented (e.g., Western contexts vs. East Asian contexts).
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  • 21 Nov 2022
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