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Optical Media Preservation
The preservation of optical media is essential because it is a resource in libraries, and stores audio, video, and computer data to be accessed by patrons. While optical discs are generally more reliable and durable than older media types, (magnetic tape, LPs and other records) environmental conditions and/or poor handling can result in lost information. Types of media The two broad types of optical discs are Compact Discs (CDs) and DVDs. Data is retrieved by both CDs and DVDs by devices that focus a laser light beam against the reflective layer allowing data to be read. The data layer, supported by the polycarbonate substrate can be metallic or dye-based, depending on the disc type. The reflective and data layers of CDs are just below the label and a thin sheet of polycarbonate substrate. A much thicker layer of the substrate supports and protects the bottom of the disc. The reflective and data layers of double-sided DVDs are in the center of the disc structure, housed between tw ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Preservation (library And Archival Science)
In Library science, library and archival science, preservation is a set of preventive conservation activities aimed at prolonging the life of a record, book, or object while making as few changes as possible. Preservation activities vary widely and may include monitoring the condition of items, maintaining the temperature and humidity in collection storage areas, writing a plan in case of emergencies, digitizing items, writing relevant metadata, and increasing accessibility. Preservation, in this definition, is practiced in a library or an archive by a librarian, archivist, or other professional when they perceive a record is in need of maintenance. Preservation should be distinguished from interventive Conservation and restoration of books, manuscripts, documents and ephemera, conservation and restoration, which refers to the treatment and repair of individual items to slow the process of decay, or restore them to a usable state. Preventive conservation is occasionally used int ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phase Changing Film
Phase or phases may refer to: Science *State of matter, or phase, one of the distinct forms in which matter can exist *Phase (matter), a region of space throughout which all physical properties are essentially uniform *Phase space, a mathematical space in which each possible state of a physical system is represented by a point — this equilibrium point is also referred to as a "microscopic state" **Phase space formulation, a formulation of quantum mechanics in phase space *Phase (waves), the position of a point in time (an instant) on a waveform cycle **Instantaneous phase, generalization for both cyclic and non-cyclic phenomena * AC phase, the phase offset between alternating current electric power in multiple conducting wires **Single-phase electric power, distribution of AC electric power in a system where the voltages of the supply vary in unison **Three-phase electric power, a common method of AC electric power generation, transmission, and distribution *Phase problem, the l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Audio CD
Compact Disc Digital Audio (CDDA or CD-DA), also known as Digital Audio Compact Disc or simply as Audio CD, is the standard format for audio compact discs. The standard is defined in the ''Red Book'', one of a series of Rainbow Books (named for their binding colors) that contain the technical specifications for all CD formats. The first commercially available audio CD player, the Sony CDP-101, was released October 1982 in Japan. The format gained worldwide acceptance in 1983–84, selling more than a million CD players in those two years, to play 22.5 million discs. Beginning in the 2000s, CDs were increasingly being replaced by other forms of digital storage and distribution, with the result that by 2010 the number of audio CDs being sold in the U.S. had dropped about 50% from their peak; however, they remained one of the primary distribution methods for the music industry. In the 2010s, revenues from digital music services, such as iTunes, Spotify, and YouTube, match ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Compact Disc
The compact disc (CD) is a Digital media, digital optical disc data storage format that was co-developed by Philips and Sony to store and play digital audio recordings. In August 1982, the first compact disc was manufactured. It was then released in October 1982 in Japan and branded as ''Compact Disc Digital Audio, Digital Audio Compact Disc''. The format was later adapted (as CD-ROM) for general-purpose data storage. Several other formats were further derived, including write-once audio and data storage (CD-R), rewritable media (CD-RW), Video CD (VCD), Super Video CD (SVCD), Photo CD, Picture CD, Compact Disc-Interactive (CD-i) and Enhanced Music CD. Standard CDs have a diameter of and are designed to hold up to 74 minutes of uncompressed stereo digital audio or about 650 mebibyte, MiB of data. Capacity is routinely extended to 80 minutes and 700 mebibyte, MiB by arranging data more closely on the same sized disc. The Mini CD has various diameters ranging from ; t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
C2 Error
A C2 error, also known as E32 error, is a read error of a Compact Disc. C2 errors can to a degree be recovered by the hardware error detection and correction scheme. A CD drive can have extraction errors when the data on the disc is not readable due to scratches or smudges. The drive can compensate by supplying a "best guess" of what the missing data was, then supplying the missing data. C2 error correction is an analysis over many interleaved frames, an improvement over C1 error correction, which analyzed just one frame, resulting in more accurate data correction. C2 error correction codes are also used by the Digital Audio Tape (DAT) format. Some copy protection schemes add false C2 errors to discs to discourage copying. While causing data loss on Video CDs (''Mode 2 Form 2'') and Audio CDs, individual C2 errors are correctable on data CDs (using ''Mode 1'' and ''Mode 2 Form 1''). Measurement C2 errors can be measured using surface error scanning, and are usually caused b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Disc Rot
Disc rot is the tendency of compact disc, CD, DVD, or other optical discs to become unreadable because of physical or chemical deterioration. The causes include oxidation of the reflective layer, physical scuffing and abrasion of disc, reactions with contaminants, ultra-violet light damage, and de-bonding of the adhesive used to adhere the layers of the disc together. Causes In CDs, the reflective layer is immediately beneath a thin protective layer of lacquer, and is also exposed at the edge of the disc. The lacquer protecting the edge of an optical disc can usually be seen without magnification. It is rarely uniformly thick; thickness variations are usually visible. The reflective layer is typically aluminium, which reacts easily with several commonly encountered chemicals such as oxygen, sulfur, and certain Ion, ions carried by liquid water. In ordinary use, a surface layer of aluminium oxide is formed quickly when an aluminium surface is exposed to the atmosphere; it serves as P ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photochemical Reaction
Organic photochemistry encompasses organic reactions that are induced by the action of light. The absorption of ultraviolet light by organic molecules often leads to reactions. In the earliest days, sunlight was employed, while in more modern times ultraviolet lamps are employed. Organic photochemistry has proven to be a very useful synthetic tool. Complex organic products can be obtained simply. History Early examples were often uncovered by the observation of precipitates or color changes from samples that were exposed to sunlights. The first reported case was by Ciamician that sunlight converted santonin to a yellow photoproduct: An early example of a precipitate was the photodimerization of anthracene, characterized by Yulii Fedorovich Fritzsche and confirmed by Elbs. Similar observations focused on the dimerization of cinnamic acid to truxillic acid. Many photodimers are now recognized, e.g. pyrimidine dimer, thiophosgene, diamantane. Another example was uncovered by Egbe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
UV Ray
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight, and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights. Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack the energy to ionize atoms, it can cause chemical reactions and causes many substances to glow or fluoresce. Consequently, the chemical and biological effects of UV are greater than simple heating effects, and many practical applications of UV radiation derive from its interactions with organic molecules. Short-wave ultraviolet light damages DNA and sterilizes surfaces with which it comes into contact. For huma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Error Detection And Correction
In information theory and coding theory with applications in computer science and telecommunication, error detection and correction (EDAC) or error control are techniques that enable reliable delivery of digital data over unreliable communication channels. Many communication channels are subject to channel noise, and thus errors may be introduced during transmission from the source to a receiver. Error detection techniques allow detecting such errors, while error correction enables reconstruction of the original data in many cases. Definitions ''Error detection'' is the detection of errors caused by noise or other impairments during transmission from the transmitter to the receiver. ''Error correction'' is the detection of errors and reconstruction of the original, error-free data. History In classical antiquity, copyists of the Hebrew Bible were paid for their work according to the number of stichs (lines of verse). As the prose books of the Bible were hardly ever ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Redundancy (information Theory)
In information theory, redundancy measures the fractional difference between the entropy of an ensemble , and its maximum possible value \log(, \mathcal_X, ). Informally, it is the amount of wasted "space" used to transmit certain data. Data compression is a way to reduce or eliminate unwanted redundancy, while forward error correction is a way of adding desired redundancy for purposes of error detection and correction when communicating over a noisy channel of limited capacity. Quantitative definition In describing the redundancy of raw data, the rate of a source of information is the average entropy per symbol. For memoryless sources, this is merely the entropy of each symbol, while, in the most general case of a stochastic process, it is :r = \lim_ \frac H(M_1, M_2, \dots M_n), in the limit, as ''n'' goes to infinity, of the joint entropy of the first ''n'' symbols divided by ''n''. It is common in information theory to speak of the "rate" or "entropy" of a language. Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Format War
A format war is a competition between similar but mutually incompatible technical standards that compete for the same market, such as for data storage devices and recording formats for electronic media. It is often characterized by political and financial influence on content publishers by the developers of the technologies. Developing companies may be characterized as engaging in a format war if they actively oppose or avoid interoperable open-industry technical standards in favor of their own. A format war emergence can be explained because each vendor is trying to exploit cross-side network effects in a two-sided market. There is also a social force to stop a format war: when one of them wins as ''de facto'' standard, it solves a coordination problemEdna Ullmann-Margalit: ''The Emergence of Norms'', Oxford Un. Press, 1977. (or Clarendon Press 1978) for the format users. 1800s * Rail gauge. The Gauge War in Britain pitted the Great Western Railway, which used broad gauge, ag ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
