Summary

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.

Expand All
Entries
Topic Review
Ground Level Ozone
Ground level ozone (O3), also known as tropospheric ozone, is a trace gas of the troposphere (the lowest level of the Earth's atmosphere), with an average concentration of 20–30 parts per billion by volume (ppbv), with close to 100 ppbv in polluted areas. Ozone is also an important constituent of the stratosphere, where the ozone layer exists which is located between 10 and 50 kilometers above the Earth's surface. The troposphere extends from the ground up to a variable height of approximately 14 kilometers above sea level. Ozone is least concentrated in the ground layer (or planetary boundary layer) of the troposphere. Ground level or tropospheric ozone is created by chemical reactions between oxides of nitrogen (NOx gases) and volatile organic compounds (VOCs). The combination of these chemicals in the presence of sunlight form ozone. Its concentration increases as height above sea level increases, with a maximum concentration at the tropopause. About 90% of total ozone in the atmosphere is in the stratosphere, and 10% is in the troposphere. Although tropospheric ozone is less concentrated than stratospheric ozone, it is of concern because of its health effects. Ozone in the troposphere is considered a greenhouse gas, and may contribute to global warming. Photochemical and chemical reactions involving ozone drive many of the chemical processes that occur in the troposphere by day and by night. At abnormally high concentrations (the largest source being emissions from combustion of fossil fuels), it is a pollutant, and a constituent of smog. Its levels have increased significantly since the industrial revolution, as NOx gasses and VOCs are some of the byproducts of combustion. With more heat and sunlight in the summer months, more ozone is formed which is why regions often experience higher levels of pollution in the summer months. Although the same molecule, ground level ozone can be harmful to our health, unlike stratospheric ozone that protects the earth from excess UV radiation. Photolysis of ozone occurs at wavelengths below approximately 310–320 nanometres. This reaction initiates the chain of chemical reactions that remove carbon monoxide, methane, and other hydrocarbons from the atmosphere via oxidation. Therefore, the concentration of tropospheric ozone affects how long these compounds remain in the air. If the oxidation of carbon monoxide or methane occur in the presence of nitrogen monoxide (NO), this chain of reactions has a net product of ozone added to the system.
  • 1.1K
  • 28 Sep 2022
Topic Review
Exploration Mission-1
Exploration Mission-1 or EM-1 (previously known as Space Launch System 1 or SLS-1) is the uncrewed first planned flight of the Space Launch System and the second flight of the Orion Multi-Purpose Crew Vehicle. The launch is planned for June 2020 from Launch Complex 39B at the Kennedy Space Center. The Orion spacecraft will spend approximately 3 weeks in space, including 6 days in a retrograde orbit around the Moon. It is planned to be followed by Exploration Mission 2 in 2023.
  • 1.3K
  • 28 Sep 2022
Topic Review
Magnitude
In astronomy, magnitude is a unitless measure of the brightness of an object in a defined passband, often in the visible or infrared spectrum, but sometimes across all wavelengths. An imprecise but systematic determination of the magnitude of objects was introduced in ancient times by Hipparchus. The scale is logarithmic and defined such that a magnitude 1 star is exactly 100 times brighter than a magnitude 6 star. Thus each step of one magnitude is [math]\displaystyle{ \sqrt{100} \approx 2.512 }[/math] times brighter than the next faintest. The brighter an object appears, the lower the value of its magnitude, with the brightest objects reaching negative values. Astronomers use two different definitions of magnitude: apparent magnitude and absolute magnitude. The apparent magnitude (m) is the brightness of an object as it appears in the night sky from Earth. Apparent magnitude depends on an object's intrinsic luminosity, its distance, and the extinction reducing its brightness. The absolute magnitude (M) describes the intrinsic luminosity emitted by an object and is defined to be equal to the apparent magnitude that the object would have if it were placed at a certain distance from Earth, 10 parsecs for stars. A more complex definition of absolute magnitude is used for planets and small Solar System bodies, based on its brightness at one astronomical unit from the observer and the Sun. The Sun has an apparent magnitude of −27 and Sirius, the brightest visible star in the night sky, −1.46. Venus at its brightest is -5. The International Space Station (ISS) sometimes reaches a magnitude of −6.
  • 3.4K
  • 28 Sep 2022
Topic Review
Quad Flat No-leads Package
Flat no-leads packages such as quad-flat no-leads (QFN) and dual-flat no-leads (DFN) physically and electrically connect integrated circuits to printed circuit boards. Flat no-leads, also known as micro leadframe (MLF) and SON (small-outline no leads), is a surface-mount technology, one of several package technologies that connect ICs to the surfaces of PCBs without through-holes. Flat no-lead is a near chip scale plastic encapsulated package made with a planar copper lead frame substrate. Perimeter lands on the package bottom provide electrical connections to the PCB. Flat no-lead packages include an exposed thermal pad to improve heat transfer out of the IC (into the PCB). Heat transfer can be further facilitated by metal vias in the thermal pad. The QFN package is similar to the quad-flat package (QFP), and a ball grid array (BGA).
  • 1.8K
  • 11 Nov 2022
Topic Review
NetApp Filer
In computer storage, a so called NetApp "filer" was referring to the storage systems product by NetApp, before block protocols were supported. It can serve storage over a network using file-based protocols such as NFS, SMB, FTP, TFTP, and HTTP. But the so-called "Filers" can also serve data over block-based protocol, such as the SCSI command protocol over the Fibre Channel Protocol on a Fibre Channel network, Fibre Channel over Ethernet (FCoE), FC-NVMe or iSCSI transport layer. The product is also known as NetApp Fabric-Attached Storage (FAS) and NetApp All Flash FAS (AFF) NetApp Filers implement their physical storage in large disk arrays. While most large-storage filers are implemented with commodity computers with an operating system such as Microsoft Windows Server, VxWorks or tuned Linux, NetApp filers use highly customized hardware and the proprietary Data ONTAP operating system with WAFL file system, all originally designed by NetApp founders David Hitz and James Lau specifically for storage-serving purposes. Data ONTAP is NetApp's internal operating system, specially optimised for storage functions at high and low level. It boots from FreeBSD as a stand-alone kernel-space module and uses some functions of FreeBSD (command interpreter and drivers stack, for example). All filers have battery-backed non-volatile random access memory or NVDIMM, referred to as NVRAM or NVDIMM, which allows them to commit writes to stable storage more quickly than traditional systems with only volatile memory. Early filers connected to external disk enclosures via parallel SCSI, while modern models ((As of 2009 )) use fibre channel and SAS (Serial Attach SCSI) SCSI transport protocols. The disk enclosures (shelves) use fibre channel hard disk drives, as well as parallel ATA, serial ATA and Serial attached SCSI. Starting with AFF A800 NVRAM PCI card no longer used for NVLOGs, it was replaced with NVDIMM memory directly connected to memory bus. Implementers often organize two filers in a high-availability cluster with a private high-speed link, either Fibre Channel, InfiniBand, 10 Gigabit Ethernet, 40 Gigabit Ethernet or 100 Gigabit Ethernet. One can additionally group such clusters together under a single namespace when running in the "cluster mode" of the Data ONTAP 8 operating system.
  • 1.2K
  • 28 Sep 2022
Topic Review
SLC7A11
An Error has occurred retrieving Wikidata item for infobox Cystine/glutamate transporter is an antiporter that in humans is encoded by the SLC7A11 gene. The SLC7A11 gene codes for a sodium-independent cystine-glutamate antiporter that is chloride dependent, known as system Xc- or xCT. It regulates synaptic activity by stimulating extrasynaptic receptors and performs nonvesicular glutamate release. This gene is highly expressed by astrocytes and couples the uptake of one molecule of cystine with the release of one molecule of glutamate. The dimer cystine gets taken up by glial cells and the monomer of cystine, cysteine, is taken up by neurons. The expression of Xc- was detected throughout the brain with higher expression found in the basolateral amygdala and the prefrontal cortex. The inhibition of system Xc- has been found to alter a number of behaviors, which suggests that it plays a key role in excitatory signaling.
  • 1.0K
  • 28 Sep 2022
Topic Review
Google Street View
Google Street View is a technology featured in Google Maps and Google Earth that provides interactive panoramas from positions along many streets in the world. It was launched in 2007 in several cities in the United States, and has since expanded to include cities and rural areas worldwide. Streets with Street View imagery available are shown as blue lines on Google Maps. Google Street View displays interactively panoramas of stitched VR photographs. Most photography is done by car, but some is done by tricycle, camel, boat, snowmobile, underwater apparatus, and on foot.
  • 5.4K
  • 28 Sep 2022
Topic Review
Proto-Finnic
Proto-Finnic or Proto-Baltic-Finnic is the common ancestor of the Finnic languages, which include the national languages Finnish and Estonian. Proto-Finnic is not attested in any texts, but has been reconstructed by linguists. Proto-Finnic is itself descended ultimately from Proto-Uralic.
  • 1.3K
  • 28 Sep 2022
Topic Review
News Analytics
In trading strategy, news analysis refers to the measurement of the various qualitative and quantitative attributes of textual (unstructured data) news stories. Some of these attributes are: sentiment, relevance, and novelty. Expressing news stories as numbers and metadata permits the manipulation of everyday information in a mathematical and statistical way. This data is often used in financial markets as part of a trading strategy or by businesses to judge market sentiment and make better business decisions. News analytics are usually derived through automated text analysis and applied to digital texts using elements from natural language processing and machine learning such as latent semantic analysis, support vector machines, "bag of words" among other techniques.
  • 692
  • 28 Sep 2022
Topic Review
McClure Arctic Expedition
The McClure Arctic Expedition of 1850, among numerous British search efforts to determine the fate of the Franklin's lost expedition, is distinguished as the voyage during which Robert McClure became the first person to confirm and transit the Northwest Passage by a combination of sea travel and sledging. McClure and his crew spent three years locked in the pack ice aboard HMS Investigator before abandoning it and making their escape across the ice. Rescued by HMS Resolute, which was itself later lost to the ice, McClure returned to England in 1854, where he was knighted and rewarded for completing the passage.
  • 866
  • 28 Sep 2022
  • Page
  • of
  • 863

Other Entry Collections

>>