https://en.citizendium.org/api.php?action=feedcontributions&user=Anderson+Osagie&feedformat=atomCitizendium - User contributions [en]2022-01-19T05:16:30ZUser contributionsMediaWiki 1.24.1https://en.citizendium.org/wiki?title=Fluid_dynamics&diff=100692969Fluid dynamics2010-07-26T04:01:57Z<p>Anderson Osagie: Fixed a typo</p>
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<div>{{subpages}}<br />
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{{Image|Flow in multi-tube heat exchanger.jpg|right|275px|Liquid flow across the tubes in a nuclear power plant heat exchanger.}} <br />
'''Fluid dynamics''', also often called '''fluid mechanics''', is the branch of [[physics]] that deals with the flow of [[fluid]]s, i.e., [[liquid]]s and [[gas]]es. It is an adaptation of [[Newton's laws of motion]] to a medium that is treated as if it were continuous. That is, the molecular structure of matter is, for the most part, not considered within the science of fluid dynamics. One therefore classifies fluid dynamics as being a ''continuum theory''. Also, in most of fluid dynamics the underlying mechanical laws are taken as those of [[classical physics]], i.e., the effects of [[relativity]] or [[quantum physics]] are usually ignored.<ref>{{cite book|author=D.J. Acheson|title=Elementary Fluid Dynamics|edition=1st Edition|publisher=Oxford University Press|year=1990|id=ISBN 0-19-859679-0}}</ref><ref>{{cite book|author=G.K. Batchelor|title=An Introduction to Fluid Dynamics|edition=1st Edition|publisher=Cambridge University Press|year=1967|id=ISBN 0-521-04118-X}}</ref><br />
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Since the most common liquid on [[Earth]] is [[water]], and the most common gas is [[air]], fluid dynamics encompasses the descriptions of water and air, sometimes called, respectively, ''[[hydrodynamics]]'' and ''[[aerodynamics]]''. In fact, one of the major results of fluid dynamics is the understanding that over a wide range of conditions the flow of air and the flow of water can be addressed using the same set of equations from physics. There are unique areas of either subject that require special considerations. For example, the sub-field of hydrodynamics addresses problems having to do with the motion of waves on the surface of a body of water, although a special case of "hydrodynamic testing" evaluates waves in the high-explosive compression system of [[nuclear weapon]]s. Similarly, the sub-field of aerodynamics (often referred to as ''gas dynamics'') addresses problems involving the [[Gas compressor|compression]] of gases. <br />
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Issues of fluid dynamics are addressed by experiment, theory and analysis, and increasingly by computation. The field of ''[[computational fluid dynamics]]'' or CFD, as it is often called, has grown immensely in step with the increasing power of computers and the development of ever more efficient and ingenious algorithms for flow simulation. Similarly, the field of experimental fluid dynamics employs ever more sophisticated techniques involving [[laser]]s and high-speed imaging. Many of the images produced by experiment or computation of fluid flows have great aesthetic appeal.<br />
<br />
While fluid dynamics may be considered a mature subject, since it has been pursued for several centuries and most of the great [[physicist]]s, [[engineer]]s and [[applied mathematician]]s have made contributions to it, it still holds many unresolved problems. The problem of ''[[turbulence]]'' is usually cited as one of the great unsolved mysteries of fluid dynamics and by extension of [[classical mechanics]]. While many properties of turbulent flows are understood, a deductive theory of turbulence from the basic equations of fluid dynamics has not been given. Indeed, the phenomenology of fluid flows is considerably better understood, through theory and experiments, than the basic mathematical properties of the governing equations. Oftentimes, the differential equations used to solve systems (e.g., the Navier-Stokes equation) are simplified versions. Physicists and engineers typically proceed with their analyses under the assumption that the basic mathematical equations have the properties necessary to describe a physical system, i.e., that they are [[well-posed problem|well-posed]]. <br />
<ref> A system of equations is well-posed if it has a unique solution that changes continuously if the initial data change continuously.</ref><br />
and have [[smooth curve|smooth]] solutions<br />
<ref>A curve or function is called smooth if its derivative is continuous.</ref>,<br />
even though some of these properties have not been proven and present major challenges.<br />
<br />
==Sub-fields of fluid dynamics==<br />
<br />
There are various sub-fields of fluid dynamics, each with their own flavor and distinct set of problems and issues. The more important sub-fields are: <br />
<br />
{{col-begin}}<br />
{{col-break|width=25%}}<br />
*[[Aerodynamics]]<br />
*[[Computational fluid dynamics]]<br />
*[[Hydrodynamics]]<br />
{{col-break}}<br />
*[[Hydrostatics]]<br />
*[[Magnetohydrodynamics]]<br />
*[[Rheology]]<br />
{{col-end}}<br />
<br />
The overall study of fluid dynamics also includes: types of fluid flow (laminar and turbulent, viscous and inviscid, Newtonian and non-Newtonian); fluid properties and phenomena; mathematical equations, models and concepts; and applications or usages in fields of study such [[climate]], [[engineering]], [[geophysics]], [[hydraulics]], [[meteorology]], [[oceanography]], [[superfluids]] and others.<br />
<br />
==References==<br />
{{reflist}}</div>Anderson Osagiehttps://en.citizendium.org/wiki?title=Fluid_dynamics&diff=100692968Fluid dynamics2010-07-26T04:00:33Z<p>Anderson Osagie: Mentioning the Navier-Stokes equations</p>
<hr />
<div>{{subpages}}<br />
<br />
{{Image|Flow in multi-tube heat exchanger.jpg|right|275px|Liquid flow across the tubes in a nuclear power plant heat exchanger.}} <br />
'''Fluid dynamics''', also often called '''fluid mechanics''', is the branch of [[physics]] that deals with the flow of [[fluid]]s, i.e., [[liquid]]s and [[gas]]es. It is an adaptation of [[Newton's laws of motion]] to a medium that is treated as if it were continuous. That is, the molecular structure of matter is, for the most part, not considered within the science of fluid dynamics. One therefore classifies fluid dynamics as being a ''continuum theory''. Also, in most of fluid dynamics the underlying mechanical laws are taken as those of [[classical physics]], i.e., the effects of [[relativity]] or [[quantum physics]] are usually ignored.<ref>{{cite book|author=D.J. Acheson|title=Elementary Fluid Dynamics|edition=1st Edition|publisher=Oxford University Press|year=1990|id=ISBN 0-19-859679-0}}</ref><ref>{{cite book|author=G.K. Batchelor|title=An Introduction to Fluid Dynamics|edition=1st Edition|publisher=Cambridge University Press|year=1967|id=ISBN 0-521-04118-X}}</ref><br />
<br />
Since the most common liquid on [[Earth]] is [[water]], and the most common gas is [[air]], fluid dynamics encompasses the descriptions of water and air, sometimes called, respectively, ''[[hydrodynamics]]'' and ''[[aerodynamics]]''. In fact, one of the major results of fluid dynamics is the understanding that over a wide range of conditions the flow of air and the flow of water can be addressed using the same set of equations from physics. There are unique areas of either subject that require special considerations. For example, the sub-field of hydrodynamics addresses problems having to do with the motion of waves on the surface of a body of water, although a special case of "hydrodynamic testing" evaluates waves in the high-explosive compression system of [[nuclear weapon]]s. Similarly, the sub-field of aerodynamics (often referred to as ''gas dynamics'') addresses problems involving the [[Gas compressor|compression]] of gases. <br />
<br />
Issues of fluid dynamics are addressed by experiment, theory and analysis, and increasingly by computation. The field of ''[[computational fluid dynamics]]'' or CFD, as it is often called, has grown immensely in step with the increasing power of computers and the development of ever more efficient and ingenious algorithms for flow simulation. Similarly, the field of experimental fluid dynamics employs ever more sophisticated techniques involving [[laser]]s and high-speed imaging. Many of the images produced by experiment or computation of fluid flows have great aesthetic appeal.<br />
<br />
While fluid dynamics may be considered a mature subject, since it has been pursued for several centuries and most of the great [[physicist]]s, [[engineer]]s and [[applied mathematician]]s have made contributions to it, it still holds many unresolved problems. The problem of ''[[turbulence]]'' is usually cited as one of the great unsolved mysteries of fluid dynamics and by extension of [[classical mechanics]]. While many properties of turbulent flows are understood, a deductive theory of turbulence from the basic equations of fluid dynamics has not been given. Indeed, the phenomenology of fluid flows is considerably better understood, through theory and experiments, than the basic mathematical properties of the governing equations. Physicists and engineers typically proceed with their analyses under the assumption that the basic mathematical equations have the properties necessary to describe a physical system, i.e., that they are [[well-posed problem|well-posed]]. Oftentimes, the differential equations used to solve systems (e.g., the Navier-Stokes equation) are simplified versions.<br />
<ref> A system of equations is well-posed if it has a unique solution that changes continuously if the initial data change continuously.</ref><br />
and have [[smooth curve|smooth]] solutions<br />
<ref>A curve or function is called smooth if its derivative is continuous.</ref>,<br />
even though some of these properties have not been proven and present major challenges.<br />
<br />
==Sub-fields of fluid dynamics==<br />
<br />
There are various sub-fields of fluid dynamics, each with their own flavor and distinct set of problems and issues. The more important sub-fields are: <br />
<br />
{{col-begin}}<br />
{{col-break|width=25%}}<br />
*[[Aerodynamics]]<br />
*[[Computational fluid dynamics]]<br />
*[[Hydrodynamics]]<br />
{{col-break}}<br />
*[[Hydrostatics]]<br />
*[[Magnetohydrodynamics]]<br />
*[[Rheology]]<br />
{{col-end}}<br />
<br />
The overall study of fluid dynamics also includes: types of fluid flow (laminar and turbulent, viscous and inviscid, Newtonian and non-Newtonian); fluid properties and phenomena; mathematical equations, models and concepts; and applications or usages in fields of study such [[climate]], [[engineering]], [[geophysics]], [[hydraulics]], [[meteorology]], [[oceanography]], [[superfluids]] and others.<br />
<br />
==References==<br />
{{reflist}}</div>Anderson Osagiehttps://en.citizendium.org/wiki?title=Facebook&diff=100692963Facebook2010-07-26T03:37:37Z<p>Anderson Osagie: Added a comment about the upcoming film based on the "controvery" surrounding the founding of Facebook</p>
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<div>{{subpages}}<br />
'''Facebook''' is a [[social networking]] [[website]] owned by [[Facebook, Inc]] and based in [[California]]. In 2004 it was founded by [[Mark Zuckerberg]], then a student at [[Harvard University]], and was initially only for Harvard students, before expanding to other [[Ivy League]] colleges, then institutions worldwide, until finally opening to anyone aged 13 or over.<br />
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Facebook's system allows users to join networks of people organized by region, workplace or educational institution. It also allows membership of 'groups' on virtually any topic. The site is a popular resource for political campaigning and activism as well as for keeping in touch with friends and colleagues.<br />
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There has been some controversy surrounding Facebook's founding. In 2008, it was sued by the founders of [[ConnectU]], for whom Zuckerberg had done work in college. In 2010, it was sued by Paul Ceglia, who claimed to own 84% of Zuckerberg's shares.<ref>Bob Van Voris, [http://www.bloomberg.com/news/2010-07-20/facebook-lawyer-unsure-whether-founder-mark-zuckerberg-signed-contract.html|Facebook Lawyer `Unsure' Whether Founder Mark Zuckerberg Signed Contract], Bloomberg</ref> This controversy is detailed in the upcoming motion picture entitled "The Social Network."<br />
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In 2007, the social networking research [[Danah Boyd]] published research claiming that the difference between users of Facebook and [[MySpace]] is a one of class. Boyd describes Facebook users as being primarily:<br />
<blockquote>goodie two shoes, jocks, athletes, or other "good" kids... from families who emphasize education and going to college... primarily white, but not exclusively... in honors classes, looking forward to the prom, and live in a world dictated by after school activities<ref name=boyd-class>danah boyd, [http://www.danah.org/papers/essays/ClassDivisions.html Viewing American class divisions through Facebook and MySpace]</ref></blockquote><br />
Boyd compares this to MySpace:<br />
<blockquote>MySpace is still home for Latino/Hispanic teens, immigrant teens, "burnouts," "alternative kids," "art fags," punks, emos, goths, gangstas, queer kids, and other kids who didn't play into the dominant high school popularity paradigm. These are kids whose parents didn't go to college, who are expected to get a job when they finish high school. These are the teens who plan to go into the military immediately after schools. Teens who are really into music or in a band are also on MySpace. MySpace has most of the kids who are socially ostracized at school because they are geeks, freaks, or queers.<ref name=boyd-class/></blockquote><br />
In the context of the U.S. military, Boyd reports that "Soldiers are on MySpace; officers are on Facebook"<ref name=boyd-class />. Elsewhere, Boyd has described MySpace as being "the ghetto of the digital landscape", the move by middle-class white teenagers from MySpace to Facebook as "a modern incarnation of White Flight", and the structural division along class lines of the two sites as dangerous and a potential breeding ground for intolerance and lack of understanding<ref>Gillian Reagan, [http://www.observer.com/2009/media/battle-between-facebook-and-myspace-digital-white-flight In the Battle Between Facebook and MySpace, A Digital 'White Flight'], The New York Observer</ref>.<br />
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== References ==<br />
<references /></div>Anderson Osagiehttps://en.citizendium.org/wiki?title=Application_programming_interface&diff=100690159Application programming interface2010-07-19T01:13:21Z<p>Anderson Osagie: Added Microsoft's CLR as an additional example of an application service abstraction</p>
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An '''application programming interface''' (API) is the set of conventions by which a user application program written for a specific purpose communicates with software infrastructure such as the [[operating system]], [[data base management services]], [[web services]], etc. APIs are specific to programming languages, although there may be multiple APIs to access the same service. <br />
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The application service presented may be by a physical computer, or an abstraction such as a [[Java virtual machine]] or a [[.NET]] [[common language runtime]].<br />
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User applications, in this context, could serve either human or computer users. A web browser, word processor, or computer game is an application with a human interface. Alternatively, an electrical power grid manager, a missile guidance system or the control of a cardiac pacemaker is an application that serves a computer.<br />
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The term "application layer", in [[Computer networking reference models]], refers to the services that support applications, not the applications themselves. APIs provide access to the top of the application layer.</div>Anderson Osagiehttps://en.citizendium.org/wiki?title=Avionics&diff=100690144Avionics2010-07-19T00:56:54Z<p>Anderson Osagie: Stressing the importance of the weight constraint on avionics and redundancy in the wiring.</p>
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<div>{{subpages}}<br />
'''Avionics''' are electronic components and subsystems intended to be integrated into the core functions of an aircraft. Some of the constraints that apply to avionics, as opposed to electronics in general, are the need not to interfere with other systems, to meet the space, weight and environmental constraints of aircraft, and to be maintainable. <br />
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All modern aircraft have avionics for flight control, [[navigation]], communications, and safety. While flight controls operated by the crew, or an [[autopilot]], once were linked mechanically or hydraulically to engines and aerodynamic steering structures, most controls are "fly by wire", with the actuation of the engine or aerodynamic component by local electric motor(s). These systems are often interconnected with multiple levels of redundancy in case of electrical failure.<br />
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Military aircraft have a wide range of avionics for detecting threats and targets, [[fire control (military)|fire control]] and defensive systems, the latter primarily being forms of [[electronic warfare]]. While early aircraft ran wires to individual components, the trend went to common [[bus (network topology)|bus]] standards such as [[MIL-STD-1553]], and increasingly to ruggedized versions of [[COTS]] communications media such as [[Ethernet|Gigabit Ethernet]].</div>Anderson Osagie