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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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Acceptance Test–Driven Development
Acceptance test–driven development (ATDD) is a development methodology based on communication between the business customers, the developers, and the testers. ATDD encompasses many of the same practices as specification by example (SBE), behavior-driven development (BDD), example-driven development (EDD), and support-driven development also called story test–driven development (SDD). All these processes aid developers and testers in understanding the customer's needs prior to implementation and allow customers to be able to converse in their own domain language. ATDD is closely related to test-driven development (TDD). It differs by the emphasis on developer-tester-business customer collaboration. ATDD encompasses acceptance testing, but highlights writing acceptance tests before developers begin coding.
  • 1.2K
  • 16 Nov 2022
Topic Review
Head Direction Cells
Head direction cells are type of neuron involved in spatial processing. Head direction (HD) cells are neurons found in a number of brain regions that increase their firing rates above baseline levels only when the animal's head points in a specific direction. They have been reported in rats, monkeys, mice, chinchillas and bats, but are thought to be common to all mammals, perhaps all vertebrates and perhaps even some invertebrates, and to underlie the "sense of direction". When the animal's head is facing in the cell's "preferred firing direction" these neurons fire at a steady rate (i.e., they do not show adaptation), but firing decreases back to baseline rates as the animal's head turns away from the preferred direction (usually about 45° away from this direction). HD cells are found in many brain areas, including the cortical regions of postsubiculum (also known as the dorsal presubiculum), retrosplenial cortex, and entorhinal cortex, and subcortical regions including the thalamus (the anterior dorsal and the lateral dorsal thalamic nuclei), lateral mammillary nucleus, dorsal tegmental nucleus and striatum. It is thought that the cortical head direction cells process information about the environment, while the subcortical ones process information about angular head movements. A striking characteristic of HD cells is that in most brain regions they maintain the same relative preferred firing directions, even if the animal is moved to a different room, or if landmarks are moved. This has suggested that the cells interact so as to maintain a unitary stable heading signal (see "Theoretical models"). Recently, however, a subpopulation of HD neurons has been found in the dysgranular part of retrosplenial cortex that can operate independently of the rest of the network, and which seems more responsive to environmental cues. The system is related to the place cell system, located in the hippocampus, which is mostly orientation-invariant and location-specific, whereas HD cells are mostly orientation-specific and location-invariant. However, HD cells do not require a functional hippocampus to express their head direction specificity. They depend on the vestibular system, and the firing is independent of the position of the animal's body relative to its head. Some HD cells exhibit anticipatory behaviour: the best match between HD activity and the animal's actual head direction has been found to be up to 95 ms in future. That is, activity of head direction cells predicts, 95 ms in advance, what the animal's head direction will be. This possibly reflects inputs from the motor system ("motor efference copy") preparing the network for an impending head turn. HD cells continue to fire in an organized manner during sleep, as if animals were awake. However, instead of always pointing toward the same direction—the animals are asleep and thus immobile—the neuronal "compass needle" moves constantly. In particular, during rapid eye movement sleep, a brain state rich in dreaming activity in humans and whose electrical activity is virtually indistinguishable from the waking brain, this directional signal moves as if the animal is awake: that is, HD neurons are sequentially activated, and the individual neurons representing a common direction during wake are still active, or silent, at the same time.
  • 1.4K
  • 16 Nov 2022
Topic Review
Life Annuity
A life annuity is an annuity, or series of payments at fixed intervals, paid while the purchaser (or annuitant) is alive. The majority of life annuities are insurance products sold or issued by life insurance companies however substantial case law indicates that annuity products are not necessarily insurance products. Annuities can be purchased to provide an income during retirement, or originate from a structured settlement of a personal injury lawsuit. Life annuities may be sold in exchange for the immediate payment of a lump sum (single-payment annuity) or a series of regular payments (flexible payment annuity), prior to the onset of the annuity. The payment stream from the issuer to the annuitant has an unknown duration based principally upon the date of death of the annuitant. At this point the contract will terminate and the remainder of the fund accumulated is forfeited unless there are other annuitants or beneficiaries in the contract. Thus a life annuity is a form of longevity insurance, where the uncertainty of an individual's lifespan is transferred from the individual to the insurer, which reduces its own uncertainty by pooling many clients.
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  • 10 Nov 2022
Topic Review
English Conditional Sentences
Prototypical conditional sentences in English are those of the form "If X, then Y". The clause X is referred to as the antecedent (or protasis), while the clause Y is called the consequent (or apodosis). A conditional is understood as expressing its consequent under the temporary hypothetical assumption of its antecedent. Conditional sentences can take numerous forms. The consequent can precede the "if"-clause and the word "if" itself may be omitted or replaced with a different complementizer. The consequent can be a declarative, an interrogative, or an imperative. Special tense morphology can be used to form a counterfactual conditional. Some linguists have argued that other superficially distinct grammatical structures such as wish reports have the same underlying structure as conditionals. Conditionals are one of the most widely studied phenomena in formal semantics, and have also been discussed widely in philosophy of language, computer science, decision theory, among other fields.
  • 2.4K
  • 10 Nov 2022
Topic Review
Click Fraud
Click fraud is a type of fraud that occurs on the Internet in pay-per-click (PPC) online advertising. In this type of advertising, the owners of websites that post the ads are paid an amount of money determined by how many visitors to the sites click on the ads. Fraud occurs when a person, automated script or computer program imitates a legitimate user of a web browser, clicking on such an ad without having an actual interest in the target of the ad's link. Click fraud is the subject of some controversy and increasing litigation due to the advertising networks being a key beneficiary of the fraud. Media entrepreneur and journalist John Battelle describes click fraud as the intentionally malicious, "decidedly black hat" practice of publishers illegitimately gaming paid search advertising by employing robots or low-wage workers to repeatedly click on each AdSense ad on their sites, thereby generating money to be paid by the advertiser to the publisher and to Google.
  • 1.2K
  • 10 Nov 2022
Topic Review
Learning Disability
Learning disability, learning disorder, or learning difficulty (British English) is a condition in the brain that causes difficulties comprehending or processing information and can be caused by several different factors. Given the "difficulty learning in a typical manner", this does not exclude the ability to learn in a different manner. Therefore, some people can be more accurately described as having a "learning difference", thus avoiding any misconception of being disabled with a lack of ability to learn and possible negative stereotyping. In the United Kingdom, the term "learning disability" generally refers to an intellectual disability, while difficulties such as dyslexia and dyspraxia are usually referred to as "learning difficulties". While learning disability and learning disorder are often used interchangeably, they differ in many ways. Disorder refers to significant learning problems in an academic area. These problems, however, are not enough to warrant an official diagnosis. Learning disability, on the other hand, is an official clinical diagnosis, whereby the individual meets certain criteria, as determined by a professional (such as a psychologist, psychiatrist, speech language pathologist, or pediatrician). The difference is in degree, frequency, and intensity of reported symptoms and problems, and thus the two should not be confused. When the term "learning disorder" is used, it describes a group of disorders characterized by inadequate development of specific academic, language, and speech skills. Types of learning disorders include reading (dyslexia), arithmetic (dyscalculia) and writing (dysgraphia). The unknown factor is the disorder that affects the brain's ability to receive and process information. This disorder can make it problematic for a person to learn as quickly or in the same way as someone who is not affected by a learning disability. People with a learning disability have trouble performing specific types of skills or completing tasks if left to figure things out by themselves or if taught in conventional ways. Individuals with learning disabilities can face unique challenges that are often pervasive throughout the lifespan. Depending on the type and severity of the disability, interventions, and current technologies may be used to help the individual learn strategies that will foster future success. Some interventions can be quite simplistic, while others are intricate and complex. Current technologies may require student training to be effective classroom supports. Teachers, parents, and schools can create plans together that tailor intervention and accommodations to aid the individuals in successfully becoming independent learners. A multi-disciplinary team frequently helps to design the intervention and to coordinate the execution of the intervention with teachers and parents. This team frequently includes school psychologists, special educators, speech therapists (pathologists), occupational therapists, psychologists, ESL teachers, literacy coaches, and/or reading specialists.
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  • 10 Nov 2022
Topic Review
Data Transmission
Data transmission (also data communication or digital communications) is the transfer of data (a digital bitstream or a digitized analog signal) over a point-to-point or point-to-multipoint communication channel. Examples of such channels are copper wires, optical fibers, wireless communication channels, storage media and computer buses. The data are represented as an electromagnetic signal, such as an electrical voltage, radiowave, microwave, or infrared signal. Analog or analogue transmission is a transmission method of conveying voice, data, image, signal or video information using a continuous signal which varies in amplitude, phase, or some other property in proportion to that of a variable. The messages are either represented by a sequence of pulses by means of a line code (baseband transmission), or by a limited set of continuously varying waveforms (passband transmission), using a digital modulation method. The passband modulation and corresponding demodulation (also known as detection) is carried out by modem equipment. According to the most common definition of digital signal, both baseband and passband signals representing bit-streams are considered as digital transmission, while an alternative definition only considers the baseband signal as digital, and passband transmission of digital data as a form of digital-to-analog conversion. Data transmitted may be digital messages originating from a data source, for example a computer or a keyboard. It may also be an analog signal such as a phone call or a video signal, digitized into a bit-stream, for example, using pulse-code modulation (PCM) or more advanced source coding (analog-to-digital conversion and data compression) schemes. This source coding and decoding is carried out by codec equipment.
  • 2.2K
  • 10 Nov 2022
Topic Review
Stall (Fluid Mechanics)
In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded. The critical angle of attack is typically about 15 degrees, but it may vary significantly depending on the fluid, foil, and Reynolds number. Stalls in fixed-wing flight are often experienced as a sudden reduction in lift as the pilot increases the wing's angle of attack and exceeds its critical angle of attack (which may be due to slowing down below stall speed in level flight). A stall does not mean that the engine(s) have stopped working, or that the aircraft has stopped moving—the effect is the same even in an unpowered glider aircraft. Vectored thrust in manned and unmanned aircraft is used to surpass the stall limit, thereby giving rise to post-stall technology. Because stalls are most commonly discussed in connection with aviation, this article discusses stalls as they relate mainly to aircraft, in particular fixed-wing aircraft. The principles of stall discussed here translate to foils in other fluids as well.
  • 8.7K
  • 16 Nov 2022
Topic Review
Consumerization of Information Technology
Consumerization is the reorientation of product and service designs to focus on (and market to) the end user as an individual consumer, in contrast with an earlier era of only organization-oriented offerings (designed solely for business-to-business or business-to-government sales). Technologies whose first commercialization was at the inter-organization level thus have potential for later consumerization. The emergence of the individual consumer as the primary driver of product and service design is most commonly associated with the IT industry, as large business and government organizations dominated the early decades of computer usage and development. Thus the microcomputer revolution, in which electronic computing moved from exclusively enterprise and government use to include personal computing, is a cardinal example of consumerization. But many technology-based products, such as calculators and mobile phones, have also had their origins in business markets, and only over time did they become dominated by high-volume consumer usage, as these products commoditized and prices fell. An example of enterprise software that became consumer software is optical character recognition software, which originated with banks and postal systems (to automate cheque clearing and mail sorting) but eventually became personal productivity software. In a different sense, consumerization of IT is the proliferation of personally owned IT at the workplace (in addition to, or even instead of, company-owned IT), which originates in the consumer market, to be used for professional purposes. This bring your own device trend has significantly changed corporate IT policies, as employees now often use their own laptops, netbooks, tablets, and smartphones on the hardware side, and social media, web conferencing, cloud storage, and software as a service on the software side.
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  • 10 Nov 2022
Topic Review
Mount Tai
Mount Tai (Chinese: 泰山; pinyin: Tài Shān) is a mountain of historical and cultural significance located north of the city of Tai'an, it is the highest point in Shandong province, China. The tallest peak is the Jade Emperor Peak (simplified Chinese: 玉皇顶; traditional Chinese: 玉皇頂; pinyin: Yùhuáng Dǐng), which is commonly reported as being 1,545 meters (5,069 ft) tall, but is officially described by the PRC government as 1,532.7 meters (5,029 ft) tall. Mount Tai is known as the eastern mountain of the Sacred Mountains of China. It is associated with sunrise, birth, and renewal, and is often regarded the foremost of the five. Mount Tai has been a place of worship for at least 3,000 years and served as one of the most important ceremonial centers of China during large portions of this period. Because of its sacred importance and dramatic landscape, Promulgated by UNESCO as a Mixed Cultural and Natural Heritage in 1987. And it meets 7 of the 10 evaluation standards of World Heritage, and is listed as the World Heritage that meets the most standards along with the Tasmanian Wilderness World Heritage Area in Australia. An Earthquake or thunderstorm occurred in Mount Tai in 1831 BC or 1652 BC, also known as Mount Tai earthquake. First seen in "Bamboo Annals". At present, it is recognized by most scholars as the first recorded earthquake in Chinese history.
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  • 10 Nov 2022
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