In computer networking, a network host, Internet host, host, or Internet node is a computer connected to the Internet - or more generically - to any type of data network. A network host can host information resources as well as application software for providing network services.
Every Internet host has one or more IP addresses uniquely assigned to the host. The addresses are assigned either manually by the computer administrator, or automatically at start-up by means of the Dynamic Host Configuration Protocol (DHCP).
Every host is a physical network node (i.e. a network device), but not every physical network node is a host. Network devices such as modems and network switches are usually not assigned host addresses, and are not considered hosts. Devices such as network printers and hardware routers are assigned IP addresses, but since they are not general-purpose computers, they are sometimes not considered as hosts.
Wednesday, April 14, 2010
Radar tracker
A classical rotating air surveillance radar system detects target echoes against a background of noise. It reports these detections (known as "plots") in polar coordinates representing the range and bearing of the target. In addition, noise in the radar receiver will occasionally exceed the detection threshold of the radar's Constant false alarm rate detector and be incorrectly reported as targets (known as false alarms). The role of the radar tracker is to monitor consecutive updates from the radar system (which typically occur once every few seconds, as the antenna rotates) and to determine those sequences of plots belonging to the same target, whilst rejecting any plots believed to be false alarms. In addition, the radar tracker is able to use the sequence of plots to estimate the current speed and heading of the target. When several targets are present, the radar tracker aims to provide one track for each target, with the track history often being used to indicate where the target has come from.
When multiple radar systems are connected to a single reporting post, a multiradar tracker is often used to monitor the updates from all of the radars and form tracks from the combination of detections. In this configuration, the tracks are often more accurate than those formed from single radars, as a greater number of detections can be used to estimate the tracks. In addition to associating plots, rejecting false alarms and estimating heading and speed, the radar tracker also acts as a filter, in which errors in the individual radar measurements are smoothed out. In essence, the radar tracker fits a smooth curve to the reported plots and, if done correctly, can increase the overall accuracy of the radar system. A multisensor tracker extends the concept of the multiradar tracker to allow the combination of reports from different types of sensor - typically radars, secondary surveillance radars, identification friend or foe (IFF) systems and electronic support measures (ESM) data. A radar track will typically contain the following information
* Position (in two or three dimensions)
* Heading
* Speed
* Unique track number
In addition, and depending on the application or tracker sophistication, the track will also include:
* Civilian SSR Modes A, C, S information
* Military IFF Modes 1, 2, 3, 4 and 5 information
* Call sign information
* ADS-B information
* Track reliability or uncertainty information
When multiple radar systems are connected to a single reporting post, a multiradar tracker is often used to monitor the updates from all of the radars and form tracks from the combination of detections. In this configuration, the tracks are often more accurate than those formed from single radars, as a greater number of detections can be used to estimate the tracks. In addition to associating plots, rejecting false alarms and estimating heading and speed, the radar tracker also acts as a filter, in which errors in the individual radar measurements are smoothed out. In essence, the radar tracker fits a smooth curve to the reported plots and, if done correctly, can increase the overall accuracy of the radar system. A multisensor tracker extends the concept of the multiradar tracker to allow the combination of reports from different types of sensor - typically radars, secondary surveillance radars, identification friend or foe (IFF) systems and electronic support measures (ESM) data. A radar track will typically contain the following information
* Position (in two or three dimensions)
* Heading
* Speed
* Unique track number
In addition, and depending on the application or tracker sophistication, the track will also include:
* Civilian SSR Modes A, C, S information
* Military IFF Modes 1, 2, 3, 4 and 5 information
* Call sign information
* ADS-B information
* Track reliability or uncertainty information
Crytography
Cryptography (or cryptology; from Greek κρυπτός, kryptos, "hidden, secret"; and γράφω, gráphō, "I write", or -λογία, -logia, respectively) is the practice and study of hiding information. Modern cryptography intersects the disciplines of mathematics, computer science, and engineering. Applications of cryptography include ATM cards, computer passwords, and electronic commerce.
Until modern times cryptography referred almost exclusively to encryption, which is the process of converting ordinary information (plaintext) into unintelligible gibberish (i.e., ciphertext). Decryption is the reverse, in other words, moving from the unintelligible ciphertext back to plaintext. A cipher (or cypher) is a pair of algorithms that create the encryption and the reversing decryption. The detailed operation of a cipher is controlled both by the algorithm and in each instance by a key. This is a secret parameter (ideally known only to the communicants) for a specific message exchange context. Keys are important, as ciphers without variable keys can be trivially broken with only the knowledge of the cipher used and are therefore less than useful for most purposes. Historically, ciphers were often used directly for encryption or decryption without additional procedures such as authentication or integrity checks.
In colloquial use, the term "code" is often used to mean any method of encryption or concealment of meaning. However, in cryptography, code has a more specific meaning. It means the replacement of a unit of plaintext (i.e., a meaningful word or phrase) with a code word (for example, apple pie replaces attack at dawn). Codes are no longer used in serious cryptography—except incidentally for such things as unit designations (e.g., Bronco Flight or Operation Overlord)—since properly chosen ciphers are both more practical and more secure than even the best codes and also are better adapted to computers.
Some use the terms cryptography and cryptology interchangeably in English, while others (including US military practice generally) use cryptography to refer specifically to the use and practice of cryptographic techniques and cryptology to refer to the combined study of cryptography and cryptanalysis.English is more flexible than several other languages in which cryptology (done by cryptologists) is always used in the second sense above. In the English Wikipedia the general term used for the entire field is cryptography (done by cryptographers).
The study of characteristics of languages which have some application in cryptography (or cryptology), i.e. frequency data, letter combinations, universal patterns, etc., is called cryptolinguistics.
Until modern times cryptography referred almost exclusively to encryption, which is the process of converting ordinary information (plaintext) into unintelligible gibberish (i.e., ciphertext). Decryption is the reverse, in other words, moving from the unintelligible ciphertext back to plaintext. A cipher (or cypher) is a pair of algorithms that create the encryption and the reversing decryption. The detailed operation of a cipher is controlled both by the algorithm and in each instance by a key. This is a secret parameter (ideally known only to the communicants) for a specific message exchange context. Keys are important, as ciphers without variable keys can be trivially broken with only the knowledge of the cipher used and are therefore less than useful for most purposes. Historically, ciphers were often used directly for encryption or decryption without additional procedures such as authentication or integrity checks.
In colloquial use, the term "code" is often used to mean any method of encryption or concealment of meaning. However, in cryptography, code has a more specific meaning. It means the replacement of a unit of plaintext (i.e., a meaningful word or phrase) with a code word (for example, apple pie replaces attack at dawn). Codes are no longer used in serious cryptography—except incidentally for such things as unit designations (e.g., Bronco Flight or Operation Overlord)—since properly chosen ciphers are both more practical and more secure than even the best codes and also are better adapted to computers.
Some use the terms cryptography and cryptology interchangeably in English, while others (including US military practice generally) use cryptography to refer specifically to the use and practice of cryptographic techniques and cryptology to refer to the combined study of cryptography and cryptanalysis.English is more flexible than several other languages in which cryptology (done by cryptologists) is always used in the second sense above. In the English Wikipedia the general term used for the entire field is cryptography (done by cryptographers).
The study of characteristics of languages which have some application in cryptography (or cryptology), i.e. frequency data, letter combinations, universal patterns, etc., is called cryptolinguistics.
Thursday, April 8, 2010
Tv channel
A television channel is a physical or virtual channel over which a television station or television network is distributed. For example, in North America, "channel 2" refers to the broadcast or cable band of 54 to 60 MHz, with carrier frequencies of 55.25 MHz for NTSC analog video (VSB) and 59.75 MHz for analog audio (FM), or 55.31 MHz for digital ATSC (8VSB). Channels may be shared by many different television stations or cable-distributed channels depending on the location and service provider.
Depending on the multinational bandplan for a given region, analog television channels are typically 6, 7, or 8 MHz in bandwidth, and therefore television channel frequencies vary as well. Channel numbering is also different. Digital television channels are the same for legacy reasons, however through multiplexing, each physical radio frequency (RF) channel can carry several digital subchannels. On satellites, each transponder normally carries one channel, however small, independent channels can be used on each transponder, with some loss of bandwidth due to the need for guard bands between unrelated transmissions. ISDB, used in Japan and Brazil, has a similar segmented mode.
Channel separation on over-the-air channels is accomplished by skipping at least one channel between two analog stations' frequency allocations. (It should be noted that there are gaps between certain channels, where numbers are sequential, but frequencies are not contiguous, such as the skip from VHF low to high, and the jump to UHF.) On cable TV, it is possible to use adjacent channels only because they are all at the same power, something which could only be done over the air if the two stations were transmitted at the same power and height from the same location. For digital TV, selectivity is inherently better, therefore channels adjacent (either to analog or digital stations) can be used even in the same area.
Depending on the multinational bandplan for a given region, analog television channels are typically 6, 7, or 8 MHz in bandwidth, and therefore television channel frequencies vary as well. Channel numbering is also different. Digital television channels are the same for legacy reasons, however through multiplexing, each physical radio frequency (RF) channel can carry several digital subchannels. On satellites, each transponder normally carries one channel, however small, independent channels can be used on each transponder, with some loss of bandwidth due to the need for guard bands between unrelated transmissions. ISDB, used in Japan and Brazil, has a similar segmented mode.
Channel separation on over-the-air channels is accomplished by skipping at least one channel between two analog stations' frequency allocations. (It should be noted that there are gaps between certain channels, where numbers are sequential, but frequencies are not contiguous, such as the skip from VHF low to high, and the jump to UHF.) On cable TV, it is possible to use adjacent channels only because they are all at the same power, something which could only be done over the air if the two stations were transmitted at the same power and height from the same location. For digital TV, selectivity is inherently better, therefore channels adjacent (either to analog or digital stations) can be used even in the same area.
Blogs
A blog (a contraction of the term "web log")[1] is a type of website, usually maintained by an individual with regular entries of commentary, descriptions of events, or other material such as graphics or video. Entries are commonly displayed in reverse-chronological order. "Blog" can also be used as a verb, meaning to maintain or add content to a blog.
Many blogs provide commentary or news on a particular subject; others function as more personal online diaries. A typical blog combines text, images, and links to other blogs, Web pages, and other media related to its topic. The ability of readers to leave comments in an interactive format is an important part of many blogs. Most blogs are primarily textual, although some focus on art (Art blog), photographs (photoblog), videos (Video blogging), music (MP3 blog), and audio (podcasting). Microblogging is another type of blogging, featuring very short posts.
As of December 2007, blog search engine Technorati was tracking more than 112,000,000 blogs
Many blogs provide commentary or news on a particular subject; others function as more personal online diaries. A typical blog combines text, images, and links to other blogs, Web pages, and other media related to its topic. The ability of readers to leave comments in an interactive format is an important part of many blogs. Most blogs are primarily textual, although some focus on art (Art blog), photographs (photoblog), videos (Video blogging), music (MP3 blog), and audio (podcasting). Microblogging is another type of blogging, featuring very short posts.
As of December 2007, blog search engine Technorati was tracking more than 112,000,000 blogs
clothing
A feature of all modern human societies is the wearing of clothing, a category encompassing a wide variety of materials that cover the body. The primary purpose of clothing is functional, as a protection from the elements. Clothes also enhance safety during hazardous activities such as hiking and cooking, by providing a barrier between the skin and the environment. Further, clothes provide a hygienic barrier, keeping toxins away from the body and limiting the transmission of germs.
Clothing performs important social and cultural functions. A uniform, for example, may identify civil authority figures, such as police and army personnel, or it may identify team, group or political affiliations. In many societies, norms about clothing reflect standards of modesty, religion, gender, and social status. Clothing may also function as a form of adornment and an expression of personal taste or style.
Throughout history, many materials have been used for clothes. Materials have ranged from leather and furs, to weaved and woven materials, to elaborate and exotic natural and synthetic fabrics. Recent scientific research estimates that humans have been wearing clothing for as long as 650,000 years.[1] Others claim that clothing probably did not originate until the Neolithic Age (the "New Stone Age").[citation needed]
Articles carried rather than worn (such as purses), worn on a single part of the body and easily removed (scarves), worn purely for adornment (jewellery), or those which serve a function other than protection (eyeglasses), are normally considered accessories rather than clothing.
Clothing performs important social and cultural functions. A uniform, for example, may identify civil authority figures, such as police and army personnel, or it may identify team, group or political affiliations. In many societies, norms about clothing reflect standards of modesty, religion, gender, and social status. Clothing may also function as a form of adornment and an expression of personal taste or style.
Throughout history, many materials have been used for clothes. Materials have ranged from leather and furs, to weaved and woven materials, to elaborate and exotic natural and synthetic fabrics. Recent scientific research estimates that humans have been wearing clothing for as long as 650,000 years.[1] Others claim that clothing probably did not originate until the Neolithic Age (the "New Stone Age").[citation needed]
Articles carried rather than worn (such as purses), worn on a single part of the body and easily removed (scarves), worn purely for adornment (jewellery), or those which serve a function other than protection (eyeglasses), are normally considered accessories rather than clothing.
Siemens mobile
Siemens cellular telephones were mobile phones produced by Siemens AG.
In 2005 the Taiwanese company BenQ acquired the financially bleeding mobile phone subsidiary from Siemens and gained the exclusive right to use Siemens trademark for 5 years. Before transferring the mobile phone subsidiary to BenQ, Siemens invested 250 million euros and wrote down assets amounting to 100 million euros [1]. Siemens also acquired a 2.5% stake in BenQ for 50 million euros. BenQ subsequently released mobile phones under the BenQ-Siemens brand, from its German unit.
In 2006, this German unit filed for bankruptc
In 2005 the Taiwanese company BenQ acquired the financially bleeding mobile phone subsidiary from Siemens and gained the exclusive right to use Siemens trademark for 5 years. Before transferring the mobile phone subsidiary to BenQ, Siemens invested 250 million euros and wrote down assets amounting to 100 million euros [1]. Siemens also acquired a 2.5% stake in BenQ for 50 million euros. BenQ subsequently released mobile phones under the BenQ-Siemens brand, from its German unit.
In 2006, this German unit filed for bankruptc
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