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Topic Review
Censorship of YouTube
The video-sharing platform YouTube is the second-most popular website as of August 2019, according to Alexa Internet. According to the company's press page, YouTube has more than one billion users, and each day, those users watch more than one billion hours of video. Censorship of it has occurred and continues to occur to varying degrees in most countries throughout the world.
  • 691
  • 25 Oct 2022
Topic Review
AlphaServer
AlphaServer is a series of server computers, produced from 1994 onwards by Digital Equipment Corporation, and later by Compaq and HP. AlphaServers were based on the DEC Alpha 64-bit microprocessor. Supported operating systems for AlphaServers are Tru64 UNIX (formerly Digital UNIX), OpenVMS, MEDITECH MAGIC and Windows NT (on earlier systems, with AlphaBIOS ARC firmware), while enthusiasts have provided alternative operating systems such as Linux, NetBSD, OpenBSD and FreeBSD. The Alpha processor was also used in a line of workstations, AlphaStation. Some AlphaServer models were rebadged in white enclosures as Digital Servers for the Windows NT server market. These so-called "white box" models comprised the following: As part of the roadmap to phase out Alpha-, MIPS- and PA-RISC-based systems in favor of Itanium-based systems at HP, the most recent AlphaServer systems reached their end of general availability on 27 April 2007. The availability of upgrades and options was discontinued on 25 April 2008, approximately one year after the systems were discontinued. Support for the most recent AlphaServer systems, the DS15A, DS25, ES45, ES47, ES80 and GS1280 is being provided by HP Services as of 2008. These systems are scheduled to reach end of support sometime during 2012, although HP has stated that this event may be delayed.
  • 564
  • 25 Oct 2022
Topic Review
Dance Dance Revolution S
Dance Dance Revolution S (ダンスダンスレボリューションS, Dansu Dansu Reboryūshon Esu), commonly abbreviated as DDR S, is a rhythm game by Konami available for the iOS, as part of the company's Dance Dance Revolution series of music video games. Announced by Konami in January 2009, the game was made available via Apple's App Store in Japan on February 27, 2009. It was later made available in the United States and Europe on March 5, 2009 and May 14, 2009 respectively. While gameplay is very similar to other Dance Dance Revolution titles, a new mode dubbed "Shake Mode" is available in which players are able to shake their device in certain directions to the rhythm of the music.
  • 422
  • 25 Oct 2022
Topic Review
Limit Point
In mathematics, a limit point (or cluster point or accumulation point) of a set [math]\displaystyle{ S }[/math] in a topological space [math]\displaystyle{ X }[/math] is a point [math]\displaystyle{ x }[/math] that can be "approximated" by points of [math]\displaystyle{ S }[/math] in the sense that every neighbourhood of [math]\displaystyle{ x }[/math] with respect to the topology on [math]\displaystyle{ X }[/math] also contains a point of [math]\displaystyle{ S }[/math] other than [math]\displaystyle{ x }[/math] itself. A limit point of a set [math]\displaystyle{ S }[/math] does not itself have to be an element of [math]\displaystyle{ S. }[/math] There is also a closely related concept for sequences. A cluster point or accumulation point of a sequence [math]\displaystyle{ (x_n)_{n \in \mathbb{N}} }[/math] in a topological space [math]\displaystyle{ X }[/math] is a point [math]\displaystyle{ x }[/math] such that, for every neighbourhood [math]\displaystyle{ V }[/math] of [math]\displaystyle{ x, }[/math] there are infinitely many natural numbers [math]\displaystyle{ n }[/math] such that [math]\displaystyle{ x_n \in V. }[/math] This definition of a cluster or accumulation point of a sequence generalizes to nets and filters. In contrast to sets, for a sequence, net, or filter, the term "limit point" is not synonymous with a "cluster/accumulation point"; by definition, the similarly named notion of a limit point of a filter (respectively, a limit point of a sequence, a limit point of a net) refers to a point that the filter converges to (respectively, the sequence converges to, the net converges to). The limit points of a set should not be confused with adherent points for which every neighbourhood of [math]\displaystyle{ x }[/math] contains a point of [math]\displaystyle{ S }[/math]. Unlike for limit points, this point of [math]\displaystyle{ S }[/math] may be [math]\displaystyle{ x }[/math] itself. A limit point can be characterized as an adherent point that is not an isolated point. Limit points of a set should also not be confused with boundary points. For example, [math]\displaystyle{ 0 }[/math] is a boundary point (but not a limit point) of set [math]\displaystyle{ \{ 0 \} }[/math] in [math]\displaystyle{ \R }[/math] with standard topology. However, [math]\displaystyle{ 0.5 }[/math] is a limit point (though not a boundary point) of interval [math]\displaystyle{ [0, 1] }[/math] in [math]\displaystyle{ \R }[/math] with standard topology (for a less trivial example of a limit point, see the first caption). This concept profitably generalizes the notion of a limit and is the underpinning of concepts such as closed set and topological closure. Indeed, a set is closed if and only if it contains all of its limit points, and the topological closure operation can be thought of as an operation that enriches a set by uniting it with its limit points.
  • 4.9K
  • 25 Oct 2022
Topic Review
ID-Based Encryption
ID-based encryption, or identity-based encryption (IBE), is an important primitive of ID-based cryptography. As such it is a type of public-key encryption in which the public key of a user is some unique information about the identity of the user (e.g. a user's email address). This means that a sender who has access to the public parameters of the system can encrypt a message using e.g. the text-value of the receiver's name or email address as a key. The receiver obtains its decryption key from a central authority, which needs to be trusted as it generates secret keys for every user. ID-based encryption was proposed by Adi Shamir in 1984. He was however only able to give an instantiation of identity-based signatures. Identity-based encryption remained an open problem for many years. The pairing-based Boneh–Franklin scheme and Cocks's encryption scheme based on quadratic residues both solved the IBE problem in 2001.
  • 695
  • 25 Oct 2022
Topic Review
Setspn
Kerberos (/ˈkɜːrbərɒs/) is a computer-network authentication protocol that works on the basis of tickets to allow nodes communicating over a non-secure network to prove their identity to one another in a secure manner. Its designers aimed it primarily at a client–server model, and it provides mutual authentication—both the user and the server verify each other's identity. Kerberos protocol messages are protected against eavesdropping and replay attacks. Kerberos builds on symmetric-key cryptography and requires a trusted third party, and optionally may use public-key cryptography during certain phases of authentication. Kerberos uses UDP port 88 by default. The protocol was named after the character Kerberos (or Cerberus) from Greek mythology, the ferocious three-headed guard dog of Hades.
  • 921
  • 25 Oct 2022
Topic Review
Test Data Generation
Test data generation, an important part of software testing, is the process of creating a set of data for testing the adequacy of new or revised software applications. It may be the actual data that has been taken from previous operations or artificial data created for this purpose. Test Data Generation is seen to be a complex problem and though a lot of solutions have come forth most of them are limited to toy programs. The use of dynamic memory allocation in most of the code written in industry is the most severe problem that the Test Data Generators face as the usage of the software then becomes highly unpredictable, due to this it becomes harder to anticipate the paths that the program could take making it nearly impossible for the Test Data Generators to generate exhaustive Test Data. However, in the past decade significant progress has been made in tackling this problem better by the use of genetic algorithms and other analysis algorithms. Moreover, Software Testing is an important part of the Software Development Life Cycle and is basically labor-intensive. It also accounts for nearly one third of the cost of the system development. In this view the problem of generating quality test data quickly, efficiently and accurately is seen to be important.
  • 1.4K
  • 25 Oct 2022
Topic Review
Non-Linear Editing System
Non-linear editing is a form of offline editing for audio, video, and image editing. In offline editing, the original content is not modified in the course of editing. In non-linear editing, edits are specified and modified by specialized software. A pointer-based playlist, effectively an edit decision list (EDL), for video or a directed acyclic graph for still images is used to keep track of edits. Each time the edited audio, video, or image is rendered, played back, or accessed, it is reconstructed from the original source and the specified editing steps. Although this process is more computationally intensive than directly modifying the original content, changing the edits themselves can be almost instantaneous, and it prevents further generation loss as the audio, video, or image is edited. A non-linear editing system (NLE) is a video (NLVE) or audio editing (NLAE) digital audio workstation (DAW) system that performs non-destructive editing on source material. The name is in contrast to 20th century methods of linear video editing and film editing.
  • 788
  • 25 Oct 2022
Topic Review
FreeTrack
FreeTrack is a general-purpose optical motion tracking application for Microsoft Windows, released under the GNU General Public License, that can be used with common inexpensive cameras. Its primary focus is head tracking with uses in virtual reality, simulation, video games, 3D modeling, computer aided design and general hands-free computing to improve computer accessibility. Tracking can be made sensitive enough that only small head movements are required so that the user's eyes never leave the screen. A camera is positioned to observe a rigid point model worn by the user, the points of which need to be isolated from background light by means of physical and software filtering. Motion is tracked with up to six degrees of freedom (6DOF): yaw, pitch, roll, left/right, up/down and forward/back. Windows-compatible video devices like webcams are supported, as well as special Nintendo Wii Remote camera, iPhone Truedepth camera with Eyeware Beam, and NaturalPoint cameras (TrackIR, SmartNav and OptiTrack). FreeTrack can output head-tracking data to programs directly using its own open interface, as well as TrackIR, SimConnect and FSUIPC interfaces. Programs that support these interfaces are regarded as being FreeTrack-compatible. FreeTrack can also emulate mouse, keyboard, and joystick (via PPJoy) if a program does not support a direct interface. FreeTrack is coded in Delphi 7 and uses DirectShow and DirectX. Head tracking is achieved using implementations of DeMenthon's four-point iterative pose estimation algorithm (POSIT) and Alter's three point geometric algorithm.
  • 875
  • 24 Oct 2022
Topic Review
Lemniscatic Elliptic Function
In mathematics, a lemniscatic elliptic function is an elliptic function related to the arc length of a lemniscate of Bernoulli studied by Giulio Carlo de' Toschi di Fagnano in 1718. It has a square period lattice and is closely related to the Weierstrass elliptic function when the Weierstrass invariants satisfy g2 = 1 and g3 = 0. In the lemniscatic case, the minimal half period ω1 is real and equal to where Γ is the gamma function. The second smallest half period is pure imaginary and equal to iω1. In more algebraic terms, the period lattice is a real multiple of the Gaussian integers. The constants e1, e2, and e3 are given by The case g2 = a, g3 = 0 may be handled by a scaling transformation. However, this may involve complex numbers. If it is desired to remain within real numbers, there are two cases to consider: a > 0 and a < 0. The period parallelogram is either a square or a rhombus.
  • 1.9K
  • 24 Oct 2022
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