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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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Jet Engine Thrust
The familiar explanation for jet thrust is a "black box" description which only looks at what goes into the jet engine, air and fuel, and what comes out, exhaust gas and an unbalanced force. This force, called thrust, is the sum of the momentum difference between entry and exit and any unbalanced pressure force between entry and exit, as explained in "Thrust calculation". As an example, an early turbojet, the Bristol Olympus Mk. 101, had a momentum thrust of 9300 lb. and a pressure thrust of 1800 lb. giving a total of 11,100 lb. Looking inside the "black box" shows that the thrust results from all the unbalanced momentum and pressure forces created within the engine itself. These forces, some forwards and some rearwards, are across all the internal parts, both stationary and rotating, such as ducts, compressors, etc., which are in the primary gas flow which flows through the engine from front to rear. The algebraic sum of all these forces is delivered to the airframe for propulsion. "Flight" gives examples of these internal forces for two early jet engines, the Rolls-Royce Avon Ra.14 and the de Havilland Goblin
  • 16.0K
  • 23 Nov 2022
Topic Review
Coronagraph
A coronagraph is a telescopic attachment designed to block out the direct light from a star so that nearby objects – which otherwise would be hidden in the star's bright glare – can be resolved. Most coronagraphs are intended to view the corona of the Sun, but a new class of conceptually similar instruments (called stellar coronagraphs to distinguish them from solar coronagraphs) are being used to find extrasolar planets and circumstellar disks around nearby stars as well as host galaxies in quasars and other similar objects with active galactic nuclei (AGN).
  • 1.3K
  • 23 Nov 2022
Topic Review
BFR Tanker
The Big Falcon Rocket (officially shortened to BFR) is a privately funded fully reusable launch vehicle and spacecraft system in development by SpaceX. The overall space vehicle architecture includes both launch vehicles and spacecraft, as well as ground infrastructure for rapid launch and relaunch, and zero-gravity propellant transfer technology to be deployed in low Earth orbit (LEO). The payload capacity to Earth orbit of at least 100,000 kg (220,000 lb) makes BFR a super heavy-lift launch vehicle. The first orbital flight is tentatively planned for 2020. SpaceX has been developing a super heavy-lift launch vehicle for many years, with the exact design and nomenclature of the vehicle undergoing multiple revisions over time. Before 2016, the vehicle was referred to as the Mars Colonial Transporter (MCT), though very few details about the design of the MCT were ever made public. Starting from 2016, SpaceX began sharing annual updates with the public, detailing the designs and uses of their upcoming new launch vehicle. In 2016, SpaceX CEO Elon Musk presented the vehicle at the International Astronautical Congress as the ITS launch vehicle, forming a core part of Musk's comprehensive vision for an Interplanetary Transport System (ITS). The ITS vehicle had a 12-meter (39 ft) core diameter, but was only intended for interplanetary travel. In September 2017, the design (now known as the BFR) was scaled down to 9 meters (30 ft) While the ITS had been solely aimed at Mars transit and other interplanetary uses, SpaceX pivoted to a plan that would support all SpaceX launch service provider capabilities with a single set of 9-meter vehicles: Earth orbit, lunar orbit, Interplanetary spaceflight, and potentially, even intercontinental passenger transport on Earth. In September 2018, a redesign of the second stage was announced, adding steerable canards, two radially adjustable fins also acting as landing legs, and a third leg that looks like a vertical stabilizer but has no aerodynamic function due to the special re-entry profile of the spacecraft. The launch vehicle design is dependent on the concurrent development work on the Raptor rocket engines, which are cryogenic methalox-fueled engines to be used for both stages of the BFR launch vehicle. Development on the Raptor began in 2012, leading to engine testing which began in 2016. The BFR system is intended to completely replace all of SpaceX's existing space hardware (the Falcon 9 and Falcon Heavy launch vehicles, and the Dragon spacecraft), initially aiming at the Earth-orbit launch market, but explicitly adding substantial capability to support long-duration spaceflight in the cislunar and Mars transport flight environments.
  • 1.1K
  • 23 Nov 2022
Topic Review
Pipe and Filter Architecture
In software engineering, a pipeline consists of a chain of processing elements (processes, threads, coroutines, functions, etc.), arranged so that the output of each element is the input of the next; the name is by analogy to a physical pipeline. Usually some amount of buffering is provided between consecutive elements. The information that flows in these pipelines is often a stream of records, bytes, or bits, and the elements of a pipeline may be called filters; this is also called the pipes and filters design pattern. Connecting elements into a pipeline is analogous to function composition. Narrowly speaking, a pipeline is linear and one-directional, though sometimes the term is applied to more general flows. For example, a primarily one-directional pipeline may have some communication in the other direction, known as a return channel or backchannel, as in the lexer hack, or a pipeline may be fully bi-directional. Flows with one-directional tree and directed acyclic graph topologies behave similarly to (linear) pipelines – the lack of cycles makes them simple – and thus may be loosely referred to as "pipelines".
  • 1.4K
  • 23 Nov 2022
Topic Review
Stuttering
Stuttering, also known as stammering, is a speech disorder in which the flow of speech is disrupted by involuntary repetitions and prolongations of sounds, syllables, words, or phrases as well as involuntary silent pauses or blocks in which the person who stutters is unable to produce sounds. The term stuttering is most commonly associated with involuntary sound repetition, but it also encompasses the abnormal hesitation or pausing before speech, referred to by people who stutter as blocks, and the prolongation of certain sounds, usually vowels or semivowels. According to Watkins et al., stuttering is a disorder of "selection, initiation, and execution of motor sequences necessary for fluent speech production". For many people who stutter, repetition is the main concern. The term "stuttering" covers a wide range of severity, from barely perceptible impediments that are largely cosmetic to severe symptoms that effectively prevent oral communication. Almost 70 million people worldwide stutter, about 1% of the world's population. The impact of stuttering on a person's functioning and emotional state can be severe. This may include fears of having to enunciate specific vowels or consonants, fears of being caught stuttering in social situations, self-imposed isolation, anxiety, stress, shame, low self-esteem, being a possible target of bullying (especially in children), having to use word substitution and rearrange words in a sentence to hide stuttering, or a feeling of "loss of control" during speech. Stuttering is sometimes popularly seen as a symptom of anxiety, but there is no direct correlation in that direction. Stuttering is generally not a problem with the physical production of speech sounds or putting thoughts into words. Acute nervousness and stress are not thought to cause stuttering, but they can trigger stuttering in people who have the speech disorder, and living with a stigmatized disability can result in anxiety and high allostatic stress load (chronic nervousness and stress) that reduce the amount of acute stress necessary to trigger stuttering in any given person who stutters, worsening the situation in the manner of a positive feedback system; the name 'stuttered speech syndrome' has been proposed for this condition. Neither acute nor chronic stress, however, itself creates any predisposition to stuttering. The disorder is also variable, which means that in certain situations, such as talking on the telephone or in a large group, the stuttering might be more severe or less, depending on whether or not the person who stutters is self-conscious about their stuttering. People who stutter often find that their stuttering fluctuates and that they have "good" days, "bad" days and "stutter-free" days. The times in which their stuttering fluctuates can be random. Although the exact etiology, or cause, of stuttering is unknown, both genetics and neurophysiology are thought to contribute. There are many treatments and speech therapy techniques available that may help decrease speech disfluency in some people who stutter to the point where an untrained ear cannot identify a problem; however, there is essentially no cure for the disorder at present. The severity of the person's stuttering would correspond to the amount of speech therapy needed to decrease disfluency. For severe stuttering, long-term therapy and hard work is required to decrease disfluency.
  • 4.1K
  • 23 Nov 2022
Topic Review
Attachment Behaviour in Wolves
Attachment behaviour is a behaviour which is observed when an animal forms a strong bond to either a human or another animal. The behaviour of the animal that is seeking to be close to its either a human or another animal is characterized as attachment behaviour. Bowlby and Ainsworth were the first to describe attachment behaviour in humans. Since then the theory has been applied to other animals and their caregivers and to animal relationships with each other. This bond is often formed as the caregiver provides the essentials for life, such as food and security. Many studies have shown that dogs show attachment behaviour to their human caregivers. Wolves are highly social animals and their social interactions in their packs fit the criteria of attachment behaviour. As dogs are closely related to wolves many investigators have studied wolf attachment behaviour to humans. Wolves that were raised for 3–7 weeks showed attachment behaviour to their human caregivers. This attachment behaviour was characterized by preferring to be close to their human caregiver, by seeking contact, and by greeting the caregiver more frequently compared to a stranger. As the wolf is a non-domesticated animal this is an example of attachment behaviour without domestication. Another study showed that wolves that were hand-reared for 16 weeks of their lives by human caregivers showed attachment behaviour to a stranger rather than their caregiver.
  • 1.1K
  • 23 Nov 2022
Topic Review
Electric Outboard Motor
Electric outboard motors are self contained propulsory units for boats, first invented in 1973 by Morton Ray of Ray Electric Outboards. These are not to be confused with trolling motors, which are not designed as a primary source of power. Most electric outboard motors have 0.5 to 4 kW direct current (DC) electric motors, operated at 12 to 60 volts DC. Recently developed outboard motors are powered with an alternating current (AC) or DC electric motor in the power head like a conventional petrol engine. With this setup, a motor can produce 10 kW output or more and is able to replace a petrol engine of 15 HP or more. The advantage of the induction or asynchronous motor is the power transfer to the rotor by means of electromagnetic induction. As these engines do not use permanent magnets, they require less maintenance and develop more torque at lower RPM.
  • 2.2K
  • 23 Nov 2022
Topic Review
Dissociation (Neuropsychology)
In neuropsychology, dissociation involves identifying the neural substrate of a particular brain function through identification of case studies, neuroimaging, or neuropsychological testing.
  • 2.3K
  • 23 Nov 2022
Topic Review
Bad Breath
Bad breath, also known as halitosis, is a symptom in which a noticeably unpleasant breath odour is present. It can result in anxiety among those affected. It is also associated with depression and symptoms of obsessive compulsive disorder. The concerns of bad breath may be divided into genuine and non-genuine cases. Of those who have genuine bad breath, about 85% of cases come from inside the mouth. The remaining cases are believed to be due to disorders in the nose, sinuses, throat, lungs, esophagus, or stomach. Rarely, bad breath can be due to an underlying medical condition such as liver failure or ketoacidosis. Non-genuine cases occur when someone feels they have bad breath but someone else cannot detect it. This is estimated to make up between 5% and 72% of cases. The treatment depends on the underlying cause. Initial efforts may include tongue cleaning, mouthwash, and flossing. Tentative evidence supports the use of mouthwash containing chlorhexidine or cetylpyridinium chloride. While there is tentative evidence of benefit from the use of a tongue cleaner it is insufficient to draw clear conclusions. Treating underlying disease such as gum disease, tooth decay, or gastroesophageal reflux disease may help. Counselling may be useful in those who falsely believe that they have bad breath. Estimated rates of bad breath vary from 6% to 50% of the population. Concern about bad breath is the third most common reason people seek dental care, after tooth decay and gum disease. It is believed to become more common as people age. Bad breath is viewed as a social taboo and those affected may be stigmatized. People in the United States spend more than $1 billion per year on mouthwash to treat the condition.
  • 1.6K
  • 23 Nov 2022
Topic Review
Epidemiology of Diabetes Mellitus
Globally, an estimated 422 million adults are living with diabetes mellitus, according to the latest 2016 data from the World Health Organization (WHO). Diabetes prevalence is increasing rapidly; previous 2013 estimates from the International Diabetes Federation put the number at 381 million people having diabetes. The number is projected to almost double by 2030. Type 2 diabetes makes up about 85-90% of all cases. Increases in the overall diabetes prevalence rates largely reflect an increase in risk factors for type 2, notably greater longevity and being overweight or obese. Diabetes mellitus occurs throughout the world, but is more common (especially type 2) in the more developed countries. The greatest increase in prevalence is, however, occurring in low- and middle-income countries including in Asia and Africa, where most patients will probably be found by 2030. The increase in incidence in developing countries follows the trend of urbanization and lifestyle changes, including increasingly sedentary lifestyles, less physically demanding work and the global nutrition transition, marked by increased intake of foods that are high energy-dense but nutrient-poor (often high in sugar and saturated fats, sometimes referred to as the Western pattern diet). The risk of getting type 2 diabetes has been widely found to be associated with lower socio-economic position across countries. The WHO estimates that diabetes resulted in 1.5 million deaths in 2012, making it the 8th leading cause of death. However another 2.2 million deaths worldwide were attributable to high blood glucose and the increased risks of associated complications (e.g. heart disease, stroke, kidney failure), which often result in premature death and are often listed as the underlying cause on death certificates rather than diabetes.
  • 1.1K
  • 23 Nov 2022
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