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 Creeping flow (flow with Re << 1) past a sphere is described by Stokesí* celebrated solution (1851). The solution is formulated with the help of the streamfunction which ensures mass conservation on a differential level. However, if the streamlines and velocity contours for this flow are plotted, the image suggests that global continuity is violated. This can often lead to some confusion and doubt over the validity of the solution, so a simple demonstration follows to show that Stokesí solution also satisfies global mass conservation, despite the illusion presented by the streamlines and velocity contours.
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Added By - daanish
Subject - Mechanical Engineering
Document Type - Question and Answer


 JPEG Progressive mode vs Sequential mode  
 JPEG standard generally use two type of scan to transmit the image using entropy coding. One is known as progressive mode, while other is known as sequential mode. In sequential mode, every block of image is encoded in a zigzag fashion from low frequencies to high frequencies and transmitted. So, at the receive, we get information in a sequential manner from left to right blocks and top most block to bottom most. While in progressive mode, the encoding for all blocks are done at the same time for same frequency components. So, the DC component of each block is encoded together, followed by first frequency components of all the blocks and so on. Since, progressive mode uses the information from all blocks at the same time, it is useful to implement JPEG using progressive mode for large image sizes. As in that case, information about DC and low frequency components can give average information about image. User can then download the complete image, if he feels the need to store that image. Progressive scan is also efficient in coding because different Huffman table can be used to encode different frequency components. Hence, performance of progressive scan is expected to be better than sequential mode.
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Added By - ravigarg
Subject - Computer Science
Document Type - Term Paper


 Capital Punishment: Two Arguments against the...  
 This paper reviews two arguments against the death penalty, Lethal Injection and Disparity in Justice Argument. Each raises a moral issue against the death penalty. The Lethal Injection argument argues that physician participation is essential to the execution process, but since physicians are morally barred from participating in executions, executions by lethal injections need to be abolished. The Disparity in Justice Argument proceeds from an economic stance and says that a disparity in the awarding of capital punishment exists between wealthy and poor counties. Since this is morally wrong, therefore, it says, capital punishment should be abolished in favor of a punishment that all counties irrespective of their finances can execute equally. This paper argues that while the former argument appears defensible, the latter fails to defend itself against objections raised in this paper.
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Added By - shaswato_dey
Subject - Philosophy
Document Type - Term Paper


 Laminar Separation Bubble  
 This essay focuses on the phenomenon of Laminar Separation Bubble observed at Low Reynolds Numbers. The effect of this bubble on the airfoil characteristics is discussed. Airfoils used at low Reynolds numbers have to be designed taking into consideration the finite space and time occupied by the bubble. Active as well as passive mechanisms to control/delay the formation of the bubble are also mentioned.

For conventional aircraft wings, whose Reynolds number exceeds a million, the flow is typically turbulent with the boundary layer able to strengthen itself by ‘mixing’. Consequently flow doesn’t separate until high angles of attack are encountered. For lower Reynolds numbers, the flow is initially laminar and is prone to separate even under mild adverse pressure gradient. Under certain flow conditions, the separated flow reattaches and forms a Laminar Separation Bubble (Fig. 1) while transitioning from laminar to turbulent state. Laminar separation bubble could modify the effective shape of the airfoil and consequently influence the aerodynamic performance, generally in a negative manner.

The need to understand low Reynolds number (104 to 106) aerodynamics is driven by variety of applicat...
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Added By - anandsaxena
Subject - Aeronautics and Astronautics
Document Type - White Paper


 Physics of flow about lifting bodies  

Physics of lifting bodies is studied in some depth using the NASA Foilsim software freely available on website.With this software we can investigate how an aircraft wing produces lift by changing the values of different factors that affect lift.There are several different versions of FoilSim II which require different levels of experience with the package, knowledge of aerodynamics, and computer technology. An offline version can be downloaded and being interactive a variety of problems can be analyzed using it. In the present work a detailed analysis of ‘Physics of flow about lifting bodies' is studied.

FoilSim is a computer simulator program that calculates the total "lift" of a specified wing. By using this program, the user can prove that the lifting capacity of the wing can remain the same at different airspeeds-as long as the angle of attack is changed to compensate. If the airspeed remains unchanged, an increase in the angle of attack will initially increase the lifting capacity of the wing. 

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Added By - anandsaxena
Subject - Aeronautics and Astronautics
Document Type - White Paper

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