Characteristics.

Early lobe-finned fishes are bony fish with fleshy, lobed, paired fins, which are joined to the body by a single bone. The fins of lobe-finned fishes differ from those of all other fish in that each is borne on a fleshy, lobelike, scaly stalk extending from the body. The scales of sarcopterygians are true scaloids, consisting of lamellar bone surrounded by layers of vascular bone, dentine-like cosmine, and external keratin. The morphology of tetrapodomorphs, fish that are similar-looking to tetrapods, give indications of the transition from water to terrestrial life (Clack 2009). Pectoral and pelvic fins have articulations resembling those of tetrapod limbs. These fins evolved into the legs of the first tetrapod land vertebrates, amphibians. They also possess two dorsal fins with separate bases, as opposed to the single dorsal fin of actinopterygians (ray-finned fish). The braincase of sarcopterygians primitively has a hinge line, but this is lost in tetrapods and lungfish. Many early sarcopterygians have a symmetrical tail. All sarcopterygians possess teeth covered with true enamel.  Most species of lobe-finned fishes are extinct. The largest known lobe-finned fish was "Rhizodus hibberti" from the Carboniferous period of Scotland which may have exceeded 7 meters in length. Among the two groups of extant (living) species, the coelacanths and the lungfishes, the largest species is the West Indian Ocean coelacanth, reaching in length and weighing up. The largest lungfish is the African lungfish which can reach 2 m (6.6 ft) in length and weigh up to.

Classification.

Taxonomists who subscribe to the cladistic approach include the grouping Tetrapoda within this group, which in turn consists of all species of four-limbed vertebrates. The fin-limbs of lobe-finned fishes such as the coelacanths show a strong similarity to the expected ancestral form of tetrapod limbs. The lobe-finned fishes apparently followed two different lines of development and are accordingly separated into two subclasses, the Rhipidistia (including the Dipnoi, the lungfish, and the Tetrapodomorpha which include the Tetrapoda) and the Actinistia (coelacanths).

Taxonomy.

The classification below follows Benton 2004, and uses a synthesis of rank-based Linnaean taxonomy and also reflects evolutionary relationships. Benton included the Superclass Tetrapoda in the Subclass Sarcopterygii in order to reflect the direct descent of tetrapods from lobe-finned fish, despite the former being assigned a higher taxonomic rank.

Phylogeny.

The cladogram presented below is based on studies compiled by Philippe Janvier and others for the "Tree of Life Web Project", Mikko's Phylogeny Archive and Swartz 2012.

Evolution.

Lobe-finned fishes (sarcopterygians) and their relatives the ray-finned fishes (actinopterygians) comprise the superclass of bony fishes (Osteichthyes) characterized by their bony skeleton rather than cartilage. There are otherwise vast differences in fin, respiratory, and circulatory structures between the Sarcopterygii and the Actinopterygii, such as the presence of cosmoid layers in the scales of sarcopterygians. The earliest fossils of sarcopterygians, found in the uppermost Silurian (ca 418 Ma), closely resembled the acanthodians (the "spiny fish", a taxon that became extinct at the end of the Paleozoic). In the early–middle Devonian (416–385 Ma), while the predatory placoderms dominated the seas, some sarcopterygians came into freshwater habitats.  In the Early Devonian (416–397 Mya), the sarcopterygians split into two main lineages: the coelacanths and the rhipidistians. Coelacanths never left the oceans and their heyday was the late Devonian and Carboniferous, from 385 to 299 Ma, as they were more common during those periods than in any other period in the Phanerozoic; coelacanths (genus "Latimeria") still live today in the open (pelagic) oceans.  The Rhipidistians, whose ancestors probably lived in the oceans near the river mouths (estuaries), left the ocean world and migrated into freshwater habitats. In turn, they split into two major groups: lungfish and the tetrapodomorphs. Lungfish radiated into their greatest diversity during the Triassic period; today fewer than a dozen genera remain. They evolved the first proto-lungs and proto-limbs, adapting to living outside a submerged water environment by the middle Devonian (397–385 Ma).  There are three major hypotheses as to how lungfish evolved their stubby fins (proto-limbs). The traditional explanation is the "shrinking waterhole hypothesis", or "desert hypothesis", posited by the American paleontologist Alfred Romer, who believed that limbs and lungs may have evolved from the necessity of having to find new bodies of water as old waterholes dried up.  A second, the "inter-tidal hypothesis", was published by a team of Polish paleontologists—Grzegorz Niedźwiedzki, Piotr Szrek, Katarzyna Narkiewicz, Marek Narkiewicz, and Per Ahlberg—in 2010. They argued that sarcopterygians may have first emerged unto land from intertidal zones rather than inland bodies of water. Their hypothesis is based on the discovery of the 395 million-year-old Zachełmie tracks in Zachełmie, Świętokrzyskie Voivodeship, Poland, the oldest-ever-discovered fossil evidence of tetrapods.  The third hypothesis is dubbed the "woodland hypothesis" and was proposed by the American paleontologist Greg Retallack in 2011. He argues that limbs may have developed in shallow bodies of water in woodlands as a means of navigating in environments filled with roots and vegetation. He based his conclusions on the evidence that transitional tetrapod fossils are consistently found in habitats that were formerly humid and wooded floodplains.  A fourth, minority hypothesis posits that advancing onto land achieved more safety from predators, less competition for prey, and certain environmental advantages not found in water—such as oxygen concentration (Carroll et al. 2005, as cited by (Hohn-Schulte et al. 2013)), and temperature control (Clack 2007, as cited by (Hohn-Schulte et al. 2013))—implying that organisms developing limbs were also adapting to spending some of their time out of water. However, studies have found that sarcopterygians developed tetrapod-like limbs suitable for walking well before venturing onto land (King 2011, as cited by (Pierce et al. 2012)); this suggests they adapted to walking on the ground-bed under water before they advanced onto dry land.  The first tetrapodomorphs, which included the gigantic rhizodonts, had the same general anatomy as the lungfish, who were their closest kin, but they appear not to have left their water habitat until the late Devonian epoch (385–359 Ma), with the appearance of tetrapods (four-legged vertebrates). Tetrapods are the only tetrapodomorphs which survived after the Devonian.  Non-tetrapod sarcopterygians continued until towards the end of Paleozoic era, suffering heavy losses during the Permian–Triassic extinction event (251 Ma).

References.

Citations.

Carroll RL, Irwin J, Green DM. 2005. Thermal physiology and the origin of terrestriality in vertebrates. Zoological Journey of the Linnean Society. 143:345–358.  Hohn-Schulte, B., H. Preuschoft, U. Witzel, and C. Distler-Hoffmann. 2013. Biomechanics and functional preconditions for terrestrial lifestyle in basal tetrapods, with special consideration of Tiktaalik roseae. Historical Biology 25:167-181.  Clack JA. 2007. Devonian climate change, breathing, and the origin of the tetrapod stem group. Integrative and Comparative Biology. p. 1–14.  King, H.M., Shubin, N.H., Coates, M.I. & Hale, M.E. Behavioural evidence for the evolution of walking and bounding before terrestriality in sarcopterygian fishes. Proceedings of the National Academy of Sciences. USA 108: 21146–21151 (2011).  Pierce, S. E., J. A. Clack, and J. R. Hutchinson. 2012. Three-dimensional limb joint mobility in the early tetrapod Ichthyostega. Nature 486:523-U123.  Clack, J. A. 2009. The fin to limb transition: New data, interpretations, and hypotheses from paleontology and developmental biology. Annual Review of Earth and Planetary Sciences 37:163-179.  Amemiya, C. T., J. Alfoldi, A. P. Lee, S. H. Fan, H. Philippe, I. MacCallum, I. Braasch et al. 2013. The African coelacanth genome provides insights into tetrapod evolution. Nature 496:311-316.

The Sarcopterygii () or lobe-finned fish (from Greek, flesh, and, fin)—sometimes considered synonymous with Crossopterygii ("fringe-finned fish", from Greek, fringe)—constitute a clade (traditionally a class or subclass) of the bony fish. A strict cladistic view shows that some Sarcopterygii evolved into the tetrapods, a superclass including amphibians, reptiles (including dinosaurs and therefore birds), and mammals.

肉鳍鱼总纲(学名:)是硬骨鱼类的一个演化支。此类鱼的特点是鱼鳍中有一个中轴骨,在前鳍的基部上有明显的肌肉组织与分开的两片腹鳍,和之后两栖动物和四足类动物的演化有直接的关联性。此总纲之下包括腔棘鱼纲及肺鱼四足大纲。


Anatomy and Physiology.

The average weight of "Latimeria chalumnae" is 80 kg (176 lb), and they can reach up to 2 m (6.5 ft) in length. Adult females are slightly larger than males. "Latimeria chalumnae" exhibit a deep royal blue color with spots used as a camouflage tactic for hunting prey. Similar anatomical adaptations include the abundance of visual cells such as rods to help see when light is limited. This combined with the West Indian Ocean coelacanth's large eyes aid seeing in dark water.  Similar to cartilaginous fish, "Latimeria chalumnae" have a rectal gland, pituitary gland, pancreas, and spinal cord. To balance osmotic pressure, these fish adopt an efficient mechanism of osmoregulation by retaining urea in their blood.  "Latimeria chalumnae" are ovoviviparous fish that retain their eggs internally until they hatch. They also have low fecundity due to their long gestation period, around 12 months, though not much is known about their age of sexual maturity.

Habitat and Behavior.

"L. chalumnae" are often found between depth, but are sometimes found as deep as. "L. chalumnae" reside in underwater caves at these depths, which may limit their maximum depth range, along with lack of prey. They are known to spend the daytime within theses lava caves, likely for protection from predators, and use the surrounding feeding grounds at night.  Some individuals have been seen performing "headstands" as a feeding behavior, allowing coelacanth to slurp prey from crevices within lava caves. This behavior is made possible due to the coelacanth's ability to move both its upper and lower jaw, which is a unique trait in extant vertebrates.

Population and conservation.

"L. chalumnae" is widely but very sparsely distributed around the rim of the western Indian Ocean, from South Africa northward along the east African coast to Kenya, the Comoros and Madagascar, seemingly occurring in small colonies. In 1991, it was estimated that 2-5 coelacanths were accidentally caught each year from Grand Camoro, making up about 1% of its population. Between 1991 and 1994, there was an estimated 30% total population reduction of the coelacanth. In 1998, the total population of the West Indian Ocean coelacanth was estimated to have been 500 or fewer, a number that would threaten the survival of the species. Near Grand Comoro, an island northwest of Madagascar, a maximum of 370 individuals reside. "L. chalumnae" is listed as critically endangered by IUCN. In accordance with the Convention on International Trade of Endangered Species treaty, the coelacanth was added to Appendix I (threatened with extinction) in 1989. The treaty forbids international trade for commercial purposes and regulates all trade, including sending specimens to museums, through a system of permits.

Discovery.

First discovery in South Africa.

On December 23, 1938, Hendrik Goosen, the captain of the trawler "Nerine", returned to the harbour at East London, South Africa, after a trawl between the Chalumna and Ncera Rivers. The "Latimeria chalumnae" were inhabiting the slopes of Grande Comore and Anjouan islands at depths between. As he frequently did, he telephoned his friend, Marjorie Courtenay-Latimer, curator at East London Museum, to see if she wanted to look over the contents of the catch for anything interesting, and told her of the strange fish he had set aside for her. Correspondence in the archives of the South African Institute for Aquatic Biodiversity (SAIAB, formerly the JLB Smith Institute of Ichthyology) show that Goosen went to great lengths to avoid any damage to this fish and ordered his crew to set it aside for the East London Museum. Goosen later told how the fish was steely blue when first seen but by the time the "Nerine" entered East London harbour many hours later the fish had become dark grey.  Failing to find a description of the creature in any of her books, she attempted to contact her friend, Professor J. L. B. Smith, but he was away for Christmas. Unable to preserve the fish, she reluctantly sent it to a taxidermist. When Smith returned, he immediately recognized it as a coelacanth, known only from fossils. Smith named the fish "Latimeria chalumnae" in honor of Marjorie Courtenay-Latimer and the waters in which it was found. The two discoverers received immediate recognition, and the fish became known as a "living fossil". The 1938 coelacanth is still on display in the East London, South Africa, museum.  However, as the specimen had been stuffed, the gills and skeleton were not available for examination, and some doubt therefore remained as to whether it was truly the same species. Smith began a hunt for a second specimen that would take more than a decade.

The second specimen, "Malania anjouanae".

A second specimen with a missing dorsal fin and deformed tail fin was captured in 1952 off the coast of Anjouan. At the time it was believed to be a new species and placed in a new genus as well, "Malania", named in honour of the Prime Minister of South Africa at the time, Daniel François Malan, without whose help the specimen would not have been preserved with its muscles and internal organs more or less intact.

Taxonomy.

The West Indian Ocean coelacanth ("Latimeria chalumnae") comes from the genus "Latimeria", where it shares one other species within its genus. The other species is the Indonesian coelacanth ("Latimeria menadoensis"). From September 1997-July 1998, two coelacanth fish were discovered off the coast of Manado Tua Island, Sulawesi, Indonesia, different from the "Latimeria chalumnae" discovered near the Comores. The Indonesian coelacanth is identifiable by its grey color.

Genetics.

The genome of "Latimeria chalumnae" was sequenced in 2013 to provide insight into tetrapod evolution. The coelacanth was long believed to be the closest relative to the first tetrapods on land due to its body characteristics. However, genetic sequencing proved that the lungfish is in fact the closest relative to land tetrapods. The full sequence and annotation of the entry is available on the Ensembl genome browser.

The West Indian Ocean coelacanth ("Latimeria chalumnae"), sometimes known as gombessa, African coelacanth, or simply coelacanth, is one of two extant species of coelacanth, a rare order of vertebrates more closely related to lungfish, amphibians, reptiles and mammals than to the common ray-finned fishes. "Latimeria chalumnae" is a crossopterygian.

西印度洋矛尾鱼(学名:),又称东非矛尾鱼,是腔棘鱼目矛尾鱼属的其中一种。原以为总鳍鱼已经全面灭绝,但1938年一名南非渔民捕鱼时竟发现了活体,后又多次在同一海域成功捕获,故被称为“活化石”。目前主要分布于印度洋西南沿海。矛尾鱼一般生活在约400米深的海水中。


History.

Cahors has had a rich history since Celtic times. The original name of the town was Divona or "Divona Cadurcorum", "Divona of the Cadurci," Divona was a fountain, now called "la fontaine des Chartreux", worshiped by the Cadurci, a Celtic people of Gaul before the Roman conquest in the 50s BC. The Cadurci were among the last Celtic tribes to resist the Roman invasion. "Cahors" derives from "Cadurcorum". However, romanization was rapid and profound: Cahors became a large Roman city, with many monuments whose remnants can be seen today. It has declined economically since the Middle Ages, and lost its university in the 18th century. Today it is a popular tourist centre with people coming to enjoy its mediaeval quarter and the 14th-century fortified Valentré bridge. It is the seat of the Diocese of Cahors.  It was also infamous at that time for having bankers that charged interest on their loans. The church in these times said that using money as an end in itself (usury) was a sin. Because of this Cahors became synonymous with this sin, and was mentioned in Dante's Inferno (XI.50) alongside Sodom as wicked.  Pope John XXII, born Jacques Duèze or d'Euse, was born in Cahors in 1249, the son of a shoemaker. In the 2007 Tour de France, Cahors was the start of stage 18.

Geography.

The town is situated north of Toulouse, on the RN20 / A20, connecting the city, via Limoges to Paris and Orléans. The town's height above sea level is between and. The area of the town is, with population density relatively high for France at 309 inhabitants per square kilometre.

Wine.

The area around Cahors produces wine, primarily robust and tannic red wine. Wine from the Cahors appellation must be made from at least 70% Malbec (also called Cot, Auxerrois and Pressac) grape, with a maximum of 30% Merlot or Tannat grape varieties.

Culture.

The Cahors Blues Festival has taken place annually, in July, since 1982.  Snowboarder Famous wine maker

Cahors (; ) is a commune in the western part of Southern France. It is the smallest prefecture among the 13 departments that constitute the Occitanie Region. Main city of the Lot department and historical center of the Quercy, Cahors is home to 19 878 "cadurciennes" and "cadurciens".

卡奥尔(,),法国西南部城市,奥克西塔尼大区洛特省的一个市镇,也是该省的省会和人口最多的城市,下辖卡奥尔区。


Description.

The defining example of a circuit-switched network is the early analog telephone network. When a call is made from one telephone to another, switches within the telephone exchanges create a continuous wire circuit between the two telephones, for as long as the call lasts.  In circuit switching, the bit delay is constant during a connection (as opposed to packet switching, where packet queues may cause varying and potentially indefinitely long packet transfer delays). No circuit can be degraded by competing users because it is protected from use by other callers until the circuit is released and a new connection is set up. Even if no actual communication is taking place, the channel remains reserved and protected from competing users.  While circuit switching is commonly used for connecting voice circuits, the concept of a dedicated path persisting between two communicating parties or nodes can be extended to signal content other than voice. The advantage of using circuit switching is that it provides for continuous transfer without the overhead associated with packets, making maximal use of available bandwidth for that communication. One disadvantage is that it can be relatively inefficient, because unused capacity guaranteed to a connection cannot be used by other connections on the same network. In addition, calls cannot be established or will be dropped if the circuit is broken.

The call.

For call setup and control (and other administrative purposes), it is possible to use a separate dedicated signalling channel from the end node to the network. ISDN is one such service that uses a separate signalling channel while plain old telephone service (POTS) does not.  The method of establishing the connection and monitoring its progress and termination through the network may also utilize a separate control channel as in the case of links between telephone exchanges which use CCS7 packet-switched signalling protocol to communicate the call setup and control information and use TDM to transport the actual circuit data.  Early telephone exchanges were a suitable example of circuit switching. The subscriber would ask the operator to connect to another subscriber, whether on the same exchange or via an inter-exchange link and another operator. The end result was a physical electrical connection between the 2 subscribers' telephones for the duration of the call. The copper wire used for the connection could not be used to carry other calls at the same time, even if the subscribers were in fact not talking and the line was silent.

Alternatives.

In circuit switching, a route and its associated bandwidth is reserved from source to destination, making circuit switching relatively inefficient since capacity is reserved whether or not the connection is in continuous use. Circuit switching contrasts with message switching and packet switching. Both of these methods can make better use of available network bandwidth between multiple communication sessions under typical conditions in data communication networks.  Message switching routes messages in their entirety, one hop at a time, that is, store and forward of the entire message. Packet switching divides the data to be transmitted into packets transmitted through the network independently. Instead of being dedicated to one communication session at a time, network links are shared by packets from multiple competing communication sessions, resulting in the loss of the quality of service guarantees that are provided by circuit switching.  Packet switching can be based on connection-oriented communication or connection-less communication. That is, based on virtual circuits or datagrams.  Virtual circuits use packet switching technology that emulates circuit switching, in the sense that the connection is established before any packets are transferred, and packets are delivered in order.  Connection-less packet switching divides the data to be transmitted into packets, called datagrams, transmitted through the network independently. Each datagram is labeled with its destination and a sequence number for ordering related packets, precluding the need for a dedicated path to help the packet find its way to its destination. Each datagram is dispatched independently and each may be routed via a different path. At the destination, the original message is reordered based on the packet number to reproduce the original message. As a result, datagram packet switching networks do not require a circuit to be established and allow many pairs of nodes to communicate concurrently over the same channel.  Multiplexing multiple telecommunications connections over the same physical conductor has been possible for a long time, but each channel on the multiplexed link was either dedicated to one call at a time, or it was idle between calls.

Circuit switching is a method of implementing a telecommunications network in which two network nodes establish a dedicated communications channel (circuit) through the network before the nodes may communicate. The circuit guarantees the full bandwidth of the channel and remains connected for the duration of the communication session. The circuit functions as if the nodes were physically connected as with an electrical circuit. Circuit switching contrasts with message switching and packet switching.

电路交换(英语:Circuit Switching)是相对于封包交换(或称分组交换)的一个概念。电路交换要求必须首先在通信双方之间建立连接通道。在连接建立成功之后,双方的通信活动才能开始。通信双方需要传递的信息都是通过已经建立好的连接来进行传递的,而且这个连接也将一直被维持到双方的通信结束。在某次通信活动的整个过程中,这个连接将始终占用着连接建立开始时,通信系统分配给它的资源(通道、带宽、时隙、码字等等),这也体现了电路交换区别于封包交换的本质特征。


Direct method.

The most direct method of calculating a modular exponent is to calculate directly, then to take this number modulo. Consider trying to compute, given,, and :  One could use a calculator to compute 4; this comes out to 67,108,864. Taking this value modulo 497, the answer is determined to be 445.  Note that is only one digit in length and that is only two digits in length, but the value is 8 digits in length.  In strong cryptography, is often at least 1024 bits. Consider and, both of which are perfectly reasonable values. In this example, is 77 digits in length and is 2 digits in length, but the value is 1,304 decimal digits in length. Such calculations are possible on modern computers, but the sheer magnitude of such numbers causes the speed of calculations to slow considerably. As and increase even further to provide better security, the value becomes unwieldy.  The time required to perform the exponentiation depends on the operating environment and the processor. The method described above requires multiplications to complete.

Memory-efficient method.

Keeping the numbers smaller requires additional modular reduction operations, bur the reduced size makes each operation faster, saving time (as well as memory) overall.  This algorithm makes use of the identity  The modified algorithm is:  Note that in every pass through step 3, the equation holds true. When step 3 has been executed times, then, contains the answer that was sought. In summary, this algorithm basically counts up by ones until reaches, doing a multiply by and a modulo operation each time it adds one (to ensure the results stay small).  The example,, and is presented again. The algorithm passes through step 3 thirteen times:  The final answer for is therefore 445, as in the first method.  Like the first method, this requires multiplications to complete. However, since the numbers used in these calculations are much smaller than the numbers used in the first algorithm's calculations, the computation time decreases by a factor of at least in this method.  In pseudocode, this method can be performed the following way:

Right-to-left binary method.

A third method drastically reduces the number of operations to perform modular exponentiation, while keeping the same memory footprint as in the previous method. It is a combination of the previous method and a more general principle called exponentiation by squaring (also known as "binary exponentiation").  First, it is required that the exponent be converted to binary notation. That is, can be written as:  In such notation, the "length" of is bits. can take the value 0 or 1 for any such that. By definition,.  The value can then be written as:  The solution is therefore:

Pseudocode.

The following is an example in pseudocode based on Applied Cryptography by Bruce Schneier. The inputs base, exponent, and modulus correspond to,, and in the equations given above.  Note that upon entering the loop for the first time, the code variable base is equivalent to. However, the repeated squaring in the third line of code ensures that at the completion of every loop, the variable base is equivalent to, where is the number of times the loop has been iterated. (This makes the next working bit of the binary exponent exponent, where the least-significant bit is exponent).  The first line of code simply carries out the multiplication in formula_4. If is zero, no code executes since this effectively multiplies the running total by one. If instead is one, the variable base (containing the value of the original base) is simply multiplied in.  In this example, the base is raised to the exponent. The exponent is 1101 in binary. There are four binary digits, so the loop executes four times, with values, and.  First, initialize the result formula_5 to 1 and preserve the value of in the variable : We are done: is now formula_13.  Here is the above calculation, where we compute to the power, performed modulo 497.  Initialize:  We are done: is now formula_22, the same result obtained in the previous algorithms.  The running time of this algorithm is exponent. When working with large values of exponent, this offers a substantial speed benefit over the previous two algorithms, whose time is exponent. For example, if the exponent was 2 = 1048576, this algorithm would have 20 steps instead of 1048576 steps.

Implementation in Lua.

function modPow(b,e,m)

Left-to-right binary method.

We can also use the bits of the exponent in left to right order. In practice, we would usually want the result modulo some modulus. In that case, we would reduce each multiplication result before proceeding. For simplicity, the modulus calculation is omitted here. This example shows how to compute formula_13 using left to right binary exponentiation. The exponent is 1101 in binary; there are 4 bits, so there are 4 iterations.  Initialize the result to 1: formula_24.

Minimum multiplications.

In "The Art of Computer Programming, Vol. 2, Seminumerical Algorithms", page 463, Donald Knuth notes that contrary to some assertions, this method does always give the minimum possible number of multiplications. The smallest counterexample is for a power of 15, when the binary method needs six multiplications. Instead, form "x" in two multiplications, then "x" by squaring "x", then "x" by squaring "x", and finally "x" by multiplying "x" and "x", thereby achieving the desired result with only five multiplications. However, many pages follow describing how such sequences might be contrived in general.

Generalizations.

Matrices.

The -th term of any constant-recursive sequence (such as Fibonacci numbers or Perrin numbers) where each term is a linear function of previous terms can be computed efficiently modulo by computing, where is the corresponding companion matrix. The above methods adapt easily to this application. This can be used for primality testing of large numbers, for example.  A recursive algorithm for codice_1 =, where is a square matrix.

Finite cyclic groups.

Diffie–Hellman key exchange uses exponentiation in finite cyclic groups. The above methods for modular matrix exponentiation clearly extend to this context. The modular matrix multiplication is simply replaced everywhere by the group multiplication.

Reversible and quantum modular exponentiation.

In quantum computing, modular exponentiation appears as the bottleneck of Shor's algorithm, where it must be computed by a circuit consisting of reversible gates, which can be further broken down into quantum gates appropriate for a specific physical device. Furthermore, in Shor's algorithm it is possible to know the base and the modulus of exponentiation at every call, which enables various circuit optimizations.

Software implementations.

Because modular exponentiation is an important operation in computer science, and there are efficient algorithms (see above) that are much faster than simply exponentiating and then taking the remainder, many programming languages and arbitrary-precision integer libraries have a dedicated function to perform modular exponentiation:

Modular exponentiation is a type of exponentiation performed over a modulus. It is useful in computer science, especially in the field of public-key cryptography.

模幂(英语:modular exponentiation)是一种对模进行的幂运算,在计算机科学,尤其是公开密钥加密方面有一定用途。


Medical uses.

Metoprolol is used for a number of conditions, including hypertension, angina, acute myocardial infarction, supraventricular tachycardia, ventricular tachycardia, congestive heart failure, and prevention of migraine headaches.  The different salt versions of metoprolol, metoprolol tartrate and metoprolol succinate, are approved for different conditions and are not interchangeable.  Off-label uses include supraventricular tachycardia and thyroid storm.

Available forms.

Adverse effects.

Adverse effects, especially with higher doses, include dizziness, drowsiness, fatigue, diarrhea, unusual dreams, trouble sleeping, depression, and vision problems. β-blockers, including metoprolol, reduce salivary flow via inhibition of the direct sympathetic innervation of the salivary glands. Metoprolol may also cause the hands and feet to feel cold. Due to the high penetration across the blood-brain barrier, lipophilic beta blockers such as propranolol and metoprolol are more likely than other less lipophilic beta blockers to cause sleep disturbances such as insomnia, vivid dreams and nightmares.  Serious side effects that are advised to be reported immediately include symptoms of bradycardia (resting heart rate slower than 60 beats per minute), persistent symptoms of dizziness, fainting and unusual fatigue, bluish discoloration of the fingers and toes and/or lips, numbness/tingling/swelling of the hands or feet, sexual dysfunction, erectile dysfunction, hair loss, mental/mood changes, depression, breathing difficulty, cough, dyslipidemia and increased thirst. Consuming alcohol while taking metoprolol may cause mild body rashes and is not advised.

Precautions.

Metoprolol may worsen the symptoms of heart failure in some patients, who may experience chest pain or discomfort, dilated neck veins, extreme fatigue, irregular breathing, an irregular heartbeat, shortness of breath, swelling of the face, fingers, feet, or lower legs, weight gain, or wheezing.  This medicine may cause changes in blood sugar levels or cover up signs of low blood sugar, such as a rapid pulse rate. It also may cause some people to become less alert than they are normally, making it dangerous for them to drive or use machines.  Greater care is required with use in those with liver problems or asthma. Stopping this drug should be done slowly to decrease the risk of further health problems.

Pregnancy and breastfeeding.

Risk for the fetus has not been ruled out, per being rated pregnancy category C in the United States. Metoprolol is category C in Australia, meaning that it may be suspected of causing harmful effects on the human fetus (but no malformations). It appears to be safe in breastfeeding.

Overdose.

Excessive doses of metoprolol can cause severe hypotension, bradycardia, metabolic acidosis, seizures, and cardiorespiratory arrest. Blood or plasma concentrations may be measured to confirm a diagnosis of overdose or poisoning in hospitalized patients or to assist in a medicolegal death investigation. Plasma levels are usually less than 200 μg/l during therapeutic administration, but can range from 1–20 mg/l in overdose victims.

Pharmacology.

General pharmacological principles of metoprolol:

Mechanism of action.

Metoprolol blocks β1 adrenergic receptors in heart muscle cells, thereby decreasing the slope of phase 4 in the nodal action potential (reducing Na uptake) and prolonging repolarization of phase 3 (slowing down K release). It also suppresses the norepinephrine-induced increase in the sarcoplasmic reticulum (SR) Ca leak and the spontaneous SR Ca release, which are the major triggers for atrial fibrillation.

Pharmacokinetics.

It undergoes α-hydroxylation and O-demethylation as a substrate of the cytochrome liver enzymes CYP2D6.

Chemistry.

The active substance metoprolol is employed either as metoprolol succinate or as metoprolol tartrate (where 100 mg metoprolol tartrate corresponds to 95 mg metoprolol succinate). The tartrate is an immediate-release formulation and the succinate is an extended-release formulation.

Stereochemistry.

Metoprolol contains a stereocenter and consists of two enantiomers. This is a racemate, i.e. a 1:1 mixture of ("R")- and the ("S")-form:

History.

Metoprolol was first discovered in 1969 by Bengt Ablad and Enar Carlsson.

Legal status.

Within the UK, metoprolol is classified as a prescription-only drug in the beta blocker class and is regulated by the Medicines and Healthcare Products Regulatory Agency (MHRA). The MHRA is a government body set up in 2003 and is responsible for regulating medicines, medical devices, and equipment used in healthcare. The MHRA acknowledges that no product is completely risk free but takes into account research and evidence to ensure that any risks associated are minimal. The use of beta blockers such as metoprolol was approved in the U.S. by the Food and Drug Administration (FDA) in 1967. The FDA has approved beta blockers for the treatment of cardiac arrhythmias, hypertension, migraines, and others. Prescribers may choose to prescribe beta blockers for other treatments if there is just cause even though it is not approved by the FDA. Drug manufacturers, however, are unable to advertise beta blockers for other purposes that have not been approved by the FDA. Since the FDA does not regulate the practice of medicine after the drug has been approved, it is legal to prescribe beta blockers for other treatments such as performance anxiety.

Legislation.

On 23 September 2011, the Medicines and Healthcare products Regulatory Agency (MHRA) granted the Intas Pharmaceuticals Limited marketing authorization (licences) for metoprolol tartrate (50mg and 100mg tablets) for medicinal prescription only; this was after it was established that there were no new or unexpected safety concerns and that the benefits of metoprolol tartrate were greater than the risks. Metoprolol tartrate is a generic version of Lopressor, which was licensed and authorized on 6 June 1997 to Novartis Pharmaceuticals.

In sport.

Metoprolol, due to being a beta blocker, is banned by the world anti-doping agency in some sports. Beta blockers can be used to reduce heart rate and minimize tremors, which can enhance performance in sports such as archery. All beta blockers are banned during and out of competition for archery and shooting. In some sports such as all forms of billiards, darts, and golf, beta blockers are banned during competition only. Furthermore, any form of beta blocker is banned within riflery competitions by the National Collegiate Athletic Association. To detect if beta blockers have been used trace analysis of human urine is analyzed. Uncharged drugs and/or metabolites of beta blockers can be analysed by gas chromatography-mass spectrometry in selected ion monitoring (GC-MS-SIM). However, in modern times it is increasingly difficult to detect the presence of beta blockers used for sports doping purposes. A disadvantage to using GC-MS-SIM is that prior knowledge of the molecular structure of the target drugs/metabolites is required. Modern times have shown a variance in structures and hence novel beta blockers can go undetected.

Lawsuit.

In 2012, an $11million settlement was reached with Toprol XL (time-release formula version of metoprolol) and its generic equivalent metoprolol. The lawsuit involved the pharmaceuticals companies AstraZeneca AB, AstraZeneca LP, AstraZeneca Pharmaceuticals LP, and Aktiebolaget Hassle. The claims of the lawsuit advise that the manufacturers violated antitrust and consumer protection law. Claiming that to increase profits, lower cost generic versions of Toprol XL were intentionally kept off the market. This claim was subsequently denied by the defendants.

Metoprolol, marketed under the tradename Lopressor among others, is a selective β receptor blocker medication. It is used to treat high blood pressure, chest pain due to poor blood flow to the heart, and a number of conditions involving an abnormally fast heart rate. It is also used to prevent further heart problems after myocardial infarction and to prevent headaches in those with migraines. Metoprolol is sold in formulations that can be taken by mouth or given intravenously. The medication is often taken twice a day. The extended-release formulation is taken once per day. Metoprolol may be combined with hydrochlorothiazide (a diuretic) in a single tablet. Common side effects include trouble sleeping, feeling tired, feeling faint, and abdominal discomfort. Large doses may cause serious toxicity. Risk in pregnancy has not been ruled out. It appears to be safe in breastfeeding. Greater care is required with use in those with liver problems or asthma. Stopping this drug should be done slowly to decrease the risk of further health problems. Metoprolol was first made in 1969, patented in 1970, and approved for medical use in 1982. It is on the World Health Organization's List of Essential Medicines, the safest and most effective medicines needed in a health system. It is available as a generic drug. In 2017, it was the sixth most commonly prescribed medication in the United States, with more than 68 million prescriptions.

美托洛尔(英语:Metoprolol),又称美托普洛或美多心安。在美国多以商品名Lopressor(台湾商品名:舒压宁控释锭)贩售,是一种选择性的β-受体阻断剂。用于治疗高血压、心绞痛还有许多和心搏过速有关的症状 。此药物同样也用在预防心肌梗塞后的心血管疾病以及防止和偏头痛相关的头痛症状。 美托洛尔的制剂可以持续在数月间以口服的方式使用或是经静脉注射给予 。一般用量为一天两次 。它另有一种长效配方是可以一天使用一次的 。美托洛尔还可以和氢氯噻嗪属一起混合做成单次复方药锭。 常见的副作用包括失眠、倦怠、昏厥以及肠胃不适。若剂量过大可能造成严重毒性反应 。目前也尚未排除在怀孕期间使用该药物有可能造成危害的可能性,目前研究尚未显示哺乳期间用药的影响。可若病人同时患有肝脏疾病或气喘则需密切观察。在停止服用后,各种副作用将会缓解,且任何因本药物而带来的健康危机也会跟着消失。


Early life and legal career.

Mwanawasa was born in Mufulira, Northern Rhodesia, as the second of 10 children. He held a law degree from the University of Zambia. He worked in private law firms from 1974 until 1978 when he formed his own firm: Mwanawasa & Company. In 1985, Mwanawasa served as Solicitor General in the Zambian government but he went back to private practice in 1986.  In 1989, he led the legal defence team for Lt. Gen Christon Tembo, who was accused by the Kenneth Kaunda government of conspiracy to overthrow the government, which was judged as an act of treason worthy of the death penalty; Tembo won the case against the state, and Mwanawasa's fame among the anti-Kaunda opposition grew. After Frederick Chiluba was elected as President, he appointed Mwanawasa as Vice-President in November 1991. Mwanawasa left his firm in March 1992.

Accident.

Before his party's convention in 1990, Mwanawasa was widely tipped to become the President of the Movement for Multiparty Democracy (MMD), but he declined the overture, citing his young age and inexperience. He opted instead to stand as a member of parliament and won with an overwhelming majority of the popular vote.  On 8 December 1991 Mwanawasa was involved in a serious traffic accident in which his aide died on the spot. He suffered multiple body injuries and was flown to Johannesburg, South Africa for medical treatment. He remained hospitalised for three months. A lasting effect of the accident was his noticeably slurred speech. A commission of inquiry was set up to investigate who was responsible for the alleged assassination attempt.

Politics.

Mwanawasa served as Vice-President until he resigned in July 1994. In 1996 he unsuccessfully contested Chiluba for the presidency of the Movement for Multiparty Democracy. After the loss, Mwanawasa retired from politics until the 2001 election.

2001 election.

In August 2001, the National Executive Committee of MMD elected Mwanawasa as its presidential candidate for the 2001 election. He won the election, held on 27 December 2001, with 29% due to Zambia's first past the post system, beating 10 other candidates including two other former vice-presidents (Godfrey Miyanda and Gen. Christon Tembo); Anderson Mazoka came in a close second with 27%, according to official results. Mwanawasa took office on 2 January 2002. However, the results of the elections were disputed by main opposition parties, including Mazoka's United Party for National Development, which many observers claim had actually won the elections. Both domestic and international election monitors cited serious irregularities with the campaign and election, including vote rigging, flawed voter registration, unequal and biased media coverage, and the MMD's improper use of state resources. In January 2002, three opposition candidates petitioned the Supreme Court to overturn Mwanawasa's victory. While the court agreed that the poll was flawed, it ruled in February 2005 that the irregularities did not affect the results and declined the petition.

First term as president.

In February 2002, Mwanawasa's government filed defamation charges against "Zambia Post" editor Fred M'membe and opposition lawmaker Dipak Patel for an article in which M'membe quoted Patel as calling Mwanawasa a "cabbage", an apparent reference to his injuries.  However, in a move Mwanawasa described as an attempt to promote "national reconciliation", Mwanawasa appointed a number of opposition lawmakers to his cabinet in February 2003, including Patel of the FDD as Minister of Trade, Commerce, and Industry, and Sylvia Masebo of the ZRP as Local Government Minister. However, Godfrey Miyanda, himself also belonging to the opposition, opposed the move and threatened to file a lawsuit over it.  In January 2005, Mwanawasa apologised to the nation for failing to tackle Zambian poverty. About 75% of the country's population lived on less than $1 a day, the United Nations' indicator of absolute poverty.  He was elected as President of the MMD for a five-year term in 2005.

2006 election.

Mwanawasa ran for a second term in the presidential election held on 28 September 2006. Michael Sata of the Patriotic Front was considered his main challenger. His re-election was confirmed on 2 October; according to official results, he received 42.98% of the vote. He was sworn in for another term on 3 October. A few days later, he named a new cabinet and appointed Rupiah Banda as Vice-President.

Policies.

Foreign investors liked Mwanawasa, owing partly to his anti-corruption drive. During his presidency, Zambia received foreign investment. The main driver of economic growth was minerals. Mwanawasa's policies helped to lower inflation and spread some benefits to the poor. Tourists and white farmers diverted from Zimbabwe and helped Zambian economy. Mnwanawasa turned the Zambian town of Livingstone, near Victoria Falls, into a tourist hub. Zambia received a relatively large amount of aid and debt relief because of liberalisation and Mwanawasa's "stolid efforts". Overall, economic growth increased to about 6% per year.  Mwanawasa criticised President Robert Mugabe of neighbouring Zimbabwe. Mwanawasa was one of the first African leaders to publicly do so. When Mwanawasa died, Zimbabwean opposition leader Morgan Tsvangirai was among the first to publicly express grief.  Mwanawasa sold off Konkola Copper Mines to Vedanta for $25m despite an initial asking price of $400m. An amount (i.e. $25m) the company made back in around 3 months and was later making a minimum of $500m in profit per year despite its environmental pollutions of the local community.  Mwanawasa was open to accepting climate immigrants from Kiribati into Zambia, telling Anote Tong that the country had "plenty of room," but a deal was not finalized.

Health.

In April 2006, Mwanawasa experienced a mild stroke.  On 29 June 2008, while in Sharm el-Sheikh, Egypt, for an African Union summit, Mwanawasa was hospitalised due to a second stroke. On 1 July, International SOS evacuated him by air ambulance to France for further treatment. The head of the Egyptian hospital to which Mwanawasa was taken said that the doctors there had stopped the brain haemorrhage and that he was in a semi-comatose state. Vice-President Banda said that his condition was stable, and Minister of Information Mike Mulongoti noted that Mwanawasa had previously suffered from hypertension; Mulongoti also said that Mwanawasa was a "very hard working man" and said that this may have been a factor.  Due to Mwanawasa's incapacitation, Banda became acting President.

Death reports.

On 3 July 2008 news outlets began reporting that Mwanawasa had died in a Paris hospital due to his stroke. The story originated at the Johannesburg-based 702 Talk Radio, which cited Malone Zaza, who claimed to be the head of protocol at Zambia's High Commission in Pretoria, South Africa; however, the commission denied having someone employed at the embassy with that name. Mulongoti, speaking for the government, said the news of Mwanawasa's death was "false," and he urged the South African media to show more restraint in its reporting. As the reports were spreading, South African President Thabo Mbeki called for a moment of silence in Mwanawasa's memory; the South African government quickly expressed regret over this misunderstanding and expressed Mbeki's hopes for Mwanawasa's recovery.

Treatment in France.

Mwanawasa was hospitalised at the Percy Military Hospital, near Paris. In a statement on 7 July 2008, Banda said that Mwanawasa "remain[ed] in a stable condition" but had to undergo surgery, which Banda described as minor, to correct a breathing problem. Banda said on 8 July that this operation was successful. On 11 July, Banda said that Mwanawasa's condition was stable and that his doctors were "satisfied with [his] current status".  Benny Tetamashimba, the MMD's chairman for Information and Publicity, subsequently said that the MMD "should begin looking for a successor" to Mwanawasa as President of the MMD. Mulongoti, speaking on state radio on 14 July, said that Tetamashimba's suggestion did not represent the government's views. United Party for National Development leader Hakainde Hichilema said that Mwanawasa's incapacitation had paralysed the functioning of the government. On 15 July, Patriotic Front leader Michael Sata questioned the official claims about Mwanawasa's health, and he called for a team of doctors to be sent by the Cabinet to examine Mwanawasa; this team would then disclose Mwanawasa's actual condition. On 17 July, the MMD announced that Tetamashimba was facing potential disciplinary action, including the possibility of expulsion from the party. Tetamashimba argued that he had been misunderstood. He also said that Mwanawasa's condition was improving and that he was "responding to treatment", while asserting that the government was functioning smoothly and criticising the opposition call for a team of doctors to report on Mwanawasa's health.  Banda gave another update of Mwanawasa's condition on 24 July, saying that he was making "steady progress... in his recovery". Skepticism regarding Banda's optimistic updates was reportedly widespread. Minister of Health Brian Chituwo, speaking before the National Assembly on 8 August, said that Mwanawasa's "healing process will indeed be long" due to the "serious nature of [his] illness".

Death.

Vice-President Banda said on 18 August that Mwanawasa's condition had suddenly deteriorated and urgent medical intervention was necessary. The intervention was successful, according to Banda, but Mwanawasa remained in serious condition. On 19 August, a family member who wished to remain anonymous stated that Mwanawasa had died early that morning. The news of Mwanawasa's death was confirmed by Banda through a television broadcast on the government-owned Zambia National Broadcasting Corporation (ZNBC). He informed the nation that Mwanawasa had died that morning at 10:30 (8:30 GMT) at the Percy Military Hospital in Paris. Expressing "immense grief and deep sorrow", Banda declared national mourning for seven days and urged Zambians to "remain calm and mourn our President with dignity". The mourning period was extended to 21 days on 21 August.

Reactions to death.

The Patriotic Front's Michael Sata expressed sadness and said that Mwanawasa's death was a "national disaster", urging Zambians to remain calm. The "Zambia Daily Mail", a state-owned newspaper, said that his death marked "a dark day for Zambia" and had left Zambians "shell-shocked and grief-stricken". As the country went into mourning, with flags flying at half-staff, the National Assembly session that had been in progress was indefinitely suspended; a strike by doctors was also suspended, and sporting matches were cancelled, all social events,weddings and birthday parties, were also cancelled. Joyous music in Zambian homes and bars was not heard during the mourning period. This gesture was later noted by the media as proof of the people's love for their president. Former President Kenneth Kaunda paid tribute to Mwanawasa, saying that he was "a true servant of the people who served this country with dignity and honour.... He observed the rule of law and he gallantly fought graft in all its forms.... We have lost a great leader who had a real vision for leadership and problems that face the country."

Funeral.

Acting President Banda announced state funeral arrangements for Mwanawasa on 21 August. According to this programme, after Mwanawasa's body was returned to Zambia, it would first lie in state at Mulungushi International Conference Centre in Lusaka, the capital. The body would then be moved to different provincial capitals from 25 to 29 August, after which it would again lie in state at Mulungushi International Conference Centre until 2 September. His burial, planned for 3 September, was intended to coincide with his birthday; Mwanawasa would have turned 60 years old on that date.  Mwanawasa's body arrived in Lusaka from France aboard a French military aircraft on 23 August. It was received with full military honours; Banda and Kaunda were present for the ceremony, which featured a 21-gun salute and jet fighter planes in the sky. It was then taken to all provincial capitals of Zambia, where members of the public had an opportunity to pay their respects. The body was accompanied by both the opposition and the ruling party leaders beside the first family during the tour.  The burial of Mwanawasa occurred on 3 September at Embassy Park opposite the Zambian Cabinet Office. The funeral was attended by heads of 14 African states, including Mbeki, Zimbabwe's Robert Mugabe, and Tanzania's Jakaya Kikwete. In her eulogy at the funeral, Maureen Mwanawasa said of her husband: "Typical of you, you died on duty. You died a sad man as no one seemed to appreciate your sacrifices. Had you been with us today, I am sure these accolades could have made you happy."

Personal life.

Mwanawasa married Maureen Mwanawasa on 3 September 1988, and they remained married until his death. He had seven children: Miriam, Patrick, Lorna, Chipokota, Matolo, Lubona and Ntembe. Miriam and Patrick were from his first marriage. His wife was a baptised member of the Jehovah's Witnesses but has since been disfellowshiped because of her active role in politics. It is against the faith of Jehovah's Witnesses to take part or sides in politics.  On February 27, 2005, Mwanawasa was baptized by Rev. Rodney Masona, pastor of Twin Palm Baptist Church in Lusaka.  In September 2007, Mwanawasa travelled to Arkansas in the United States to give a speech at Harding University in Searcy and received an honorary doctorate from the college. While in Arkansas, he addressed students and press at the University of Arkansas Clinton School of Public Service about social, economic, and political development in Zambia and the region with specific attention paid to HIV/AIDS in Africa and President Mugabe of Zimbabwe.

Levy Patrick Mwanawasa (3 September 1948 – 19 August 2008) was the third President of Zambia. He ruled the country from January 2002 until his death in August 2008.

利维·帕特里克·姆瓦纳瓦萨(英文Levy Patrick Mwanawasa,1948年-9月3日-2008年-8月19日),赞比亚总统(2002—2008),2002年1月首次当选。


Techniques.

Pattern, Blocking, Detailing, Surfacing, and Smoothening

Tools.

Basic tool set.

A special screw for fixing work to the workbench, and a mallet, complete the carvers kit, though other tools, both specialized and adapted, are often used, such as a router for bringing grounds to a uniform level, bent gouges and bent chisels for cutting hollows too deep for the ordinary tool.

Wood carving process.

Selection.

The nature of the wood being carved limits the scope of the carver in that wood is not equally strong in all directions: it is an anisotropic material. The direction in which wood is strongest is called "grain" (grain may be straight, interlocked, wavy or fiddleback, "etc".). It is smart to arrange the more delicate parts of a design along the grain instead of across it. Often, however, a "line of best fit" is instead employed, since a design may have multiple weak points in different directions, or orientation of these along the grain would necessitate carving detail on end grain, (which is considerably more difficult). Carving blanks are also sometimes assembled, as with carousel horses, out of many smaller boards, and in this way, one can orient different areas of a carving in the most logical way, both for the carving process and for durability. Less commonly, this same principle is used in solid pieces of wood, where the fork of two branches is utilized for its divergent grain, or a branch off of a larger log is carved into a beak (this was the technique employed for traditional Welsh shepherd's crooks, and some Native American adze handles). The failure to appreciate these primary rules may constantly be seen in damaged work, when it will be noticed that, whereas tendrils, tips of birds beaks, etc., arranged across the grain have been broken away, similar details designed more in harmony with the growth of the wood and not too deeply undercut remain intact.  Probably the two most common woods used for carving in North America are basswood (aka tilia or lime) and tupelo; both are hardwoods that are relatively easy to work with. Chestnut, butternut, oak, American walnut, mahogany and teak are also very good woods; while for fine work Italian walnut, sycamore maple, apple, pear, box or plum, are usually chosen. Decoration that is to be painted and of not too delicate a nature is often carved in pine, which is relatively soft and inexpensive.

Sculpture.

A wood carver begins a new carving by selecting a chunk of wood the approximate size and shape of the figure he or she wishes to create or if the carving is to be large, several pieces of wood may be laminated together to create the required size. The type of wood is important. Hardwoods are more difficult to shape but have greater luster and longevity. Softer woods may be easier to carve but are more prone to damage. Any wood can be carved but they all have different qualities and characteristics. The choice will depend on the requirements of carving being done: for example, a detailed figure would need a wood with a fine grain and very little figure as a strong figure can interfere with'reading' fine detail.  Once the sculptor has selected their wood, he or she begins a general shaping process using gouges of various sizes. The gouge is a curved blade that can remove large portions of wood smoothly. For harder woods, the sculptor may use gouges sharpened with stronger bevels, about 35 degrees, and a mallet similar to a stone carver's. The terms "gouge" and "chisel" are open to confusion. Correctly, a gouge is a tool with a curved cross-section and a chisel is a tool with a flat cross-section. However, professional carvers tend to refer to them all as 'chisels'. Smaller sculptures may require the woodcarver to use a knife, and larger pieces might require the use of a saw. No matter what wood is selected or tool used, the wood sculptor must always carve either across or with the grain of the wood, never against the grain.  Once the general shape is made, the carver may use a variety of tools for creating details. For example, a “veiner” or “fluter” can be used to make deep gouges into the surface, or a “v-tool” for making fine lines or decorative cuts. Once the finer details have been added, the woodcarver finishes the surface. The method chosen depends on the required quality of the surface finish. The texture left by shallow gouges gives 'life' to the carving's surface and many carvers prefer this 'tooled' finish. If a completely smooth surface is required general smoothing can be done with tools such as “rasps,” which are flat-bladed tools with a surface of pointed teeth. “Rifflers” are similar to rasps, but smaller, usually double-ended, and of various shapes for working in folds or crevasses. The finer polishing is done with abrasive paper. Large grained paper with a rougher surface is used first, with the sculptor then using finer grained paper that can make the surface of the sculpture slick to the touch.  After the carving and finishing is completed, the artist may seal & colour the wood with a variety of natural oils, such as walnut or linseed oil which protects the wood from dirt and moisture. Oil also imparts a sheen to the wood which, by reflecting light, helps the observer'read' the form. Carvers seldom use gloss varnish as it creates too shiny a surface, which reflects so much light it can confuse the form; carvers refer to this as 'the toffee apple effect'. Objects made of wood are frequently finished with a layer of wax, which protects the wood and gives a soft lustrous sheen. A wax finish (e.g. shoe polish) is comparatively fragile though and only suitable for indoor carvings.

Traditions.

The making of decoys and fish carving are two of the artistic traditions that use wood carvings.

Wood carving is a form of woodworking by means of a cutting tool (knife) in one hand or a chisel by two hands or with one hand on a chisel and one hand on a mallet, resulting in a wooden figure or figurine, or in the sculptural ornamentation of a wooden object. The phrase may also refer to the finished product, from individual sculptures to hand-worked mouldings composing part of a tracery.

杰佛逊县(Jefferson County, Texas)是美国德克萨斯州东南部的一个县,东邻路易斯安那州。面积2,878平方公里。根据美国2000年人口普查,共有人口252,051人。县治博蒙特(Beaumont)。


Discovery.

Schlliemann found the mask in 1876 in a burial shaft designated Grave V at the site "Grave Circle A, Mycenae". The mask is one of five discovered in the royal shaft graves at Mycenae—three in Grave IV and two in Grave V. The faces and hands of two children in Grave III are covered with gold leaf, one covering having holes for the eyes. The mask was designed to be a funeral mask covered in gold.  The faces of the men are not all covered with masks. That they are men and warriors is suggested by the presence of weapons in their graves. The quantities of gold and carefully worked artifacts indicate honor, wealth and status. The custom of clothing leaders in gold leaf is known elsewhere. The Mask of Agamemnon was named by Schliemann after the legendary Greek king of Homer's "Iliad". This mask adorned one of the bodies in the shaft graves at Mycenae. Schliemann took this as evidence the Trojan War was a real historical event.  The mask of Agamemnon was created from a single thick gold sheet, heated and hammered against a wooden background with the details chased on later with a sharp tool. Following his discoveries at the site, Schliemann notified King George of Greece. He is supposed to have told the king in a telegraph, "I have gazed upon the face of Agamemnon". Schliemann later named his son after the legendary king. Close to the end of his life, the archaeologist accepted doubts as to the mask's true owner and is quoted as saying, "So this is not Agamemnon... these are not his ornaments? All right, let's call him Schulze."

Authenticity.

In the latter half of the 20th century and the beginning of the 21st century, the authenticity of the mask has been formally questioned, primarily by William Calder III and David Traill. "Archaeology" magazine has run a series of articles presenting both sides of the debate. By the time of the excavation of the Shaft Graves, the Greek Archaeological Society had taken a hand in supervising Schliemann's work (after the issues at Troy), sending Panagiotis Stamatakis as "ephor", or director, of the excavation, who kept a close eye on Schliemann.  Proponents of the fraud argument center their case on Schliemann's reputation for salting digs with artifacts from elsewhere. The resourceful Schliemann, they assert, could have had the mask manufactured on the general model of the other Mycenaean masks and found an opportunity to place it in the excavation.  The defending advocate(s) point out that the excavation was closed on November 26–27 for Sunday holiday and rain. It was not allowed to reopen until Stamatakis had provided the work with credible witnesses. The three other masks were not discovered until the 28th. The Mask of Agamemnon was found on the 30th.  A second critique is based on style. The Mask of Agamemnon differs from three of the other masks in a number of points: it is three-dimensional rather than flat, one of the facial hairs is cut out, rather than engraved, the ears are cut out, the eyes are depicted as both open and shut, with open eyelids, but a line of closed eyelids across the center, the face alone of all the depictions of faces in Mycenaean art has a full pointed beard with handlebar mustache, the mouth is well-defined (compared to the flat masks), the brows are formed to two arches rather than one.  The defense presented prior arguments that the shape of the lip, the triangular beard and the detail of the beard are nearly the same as the mane and locks of the gold lion-head rhyton from Shaft Grave IV. Schliemann's duplicity, they claim, has been greatly exaggerated, and they also claim that the attackers were conducting a vendetta.  Modern archaeological research suggests that the mask is genuine but predates the period of the Trojan War by 300–400 years. Others date the contents of the find even earlier, to approximately 2500 BC.

The Mask of Agamemnon is a gold funeral mask discovered at the ancient Greek site of Mycenae. The mask, displayed in the National Archaeological Museum of Athens, has been described by Cathy Gere as the ""Mona Lisa" of prehistory".

阿伽门农的面具,是由海因里希·施里曼在1876年对迈锡尼文明的考古中发现,整个面具由黄金制成。高26厘米。制作年份上为公元前1550至公元前1500左右。现藏于雅典国家考古博物馆。海因里希·施里曼根据古希腊传说中的阿伽门农而给这个面具命名为阿伽门农的面具。但现代的观点否认这种说法,认为面具作成年代早过阿伽门农所处的时代大概三百年。


Definition.

A tom drum is a cylindrical drum with no snares. The name came originally from the Anglo-Indian and Sinhala.

Design history.

The first American drum set toms had no rims and were usually what were referred to as "Chinese" tom toms, although these ceremonial drums were made/used in Japan and Korea as well. The pigskin heads were tacked to the wooden shells with metal tacks. Through close collaboration with Gene Krupa's concept of fully tunable toms, the Slingerland drum and banjo company were the first, in 1936, to begin offering fully tuneable tom-toms (top and bottom heads) with metal or wooden rims, tension rods, and lugs. Most Chinese toms were 10 to 14 inches in diameter, but the American drum companies were eventually producing a wider range of diameters and depths. These drums were usually clamped to the bass drum rims or sat in cradles as floor stand drums. The sizes that Krupa chose became the "standard" for many decades and they were 9 X 13" (mounted) and 16 X 16" (floor). Later, mounted on three (or, if larger than 16 X 16, four) legs were attached to the floor tom designs. Together with a snare drum and a bass drum of varying size, the combination of the four drums became a "set". (The term "kit" did not appear until the mid 1960s.)  Later, the mounted toms, known as "hanging toms" or "rack toms", were deepened by one inch each, these sizes being called "power toms". Extra-deep hanging toms, known as "cannon depth", never achieved popularity. All these were double-headed.

Modern versions.

A wide variety of configurations have been available and in use at all levels from advanced student kits upwards. Most toms range in size between in diameter, though floor toms can go as large as.  In the 50s and early 60s, it was common to have only a single hanging tom (a 13") and a single floor tom (16").

Classic rack setups.

A basic rock configuration consists of 12" and 13" hanging toms, and a 16" floor tom with diameter × depth in inches used throughout this article. For a more detailed description of the conventions and their usage, see drum size conventions. A basic fusion configuration refers to a set-up which has 10", 12" and 14" diameter toms, Note that these terms do not imply drum depths, so for example, the 14" in a fusion setup could have depth 10, 11, 12, or could be a 14×14 floor tom.  The terms "fusion" and "rock" are marketing terms invented by drum manufacturing companies, and there is no absolute definition for them; more a case of an accepted norm.  In the 1950-1980s the standard depth rack toms were 12×8 and 13×9. This "classic" configuration is still popular.Concerts came in the early 70s. With Ludwig producing single headed toms in 6x5.5,8x5.5,10x6.5,12x8,13x9,14x10, 15x12 16x14 mounted in pairs on a stand.  "FAST" sizes are 10×8, 12×9, 13×10, etc., a marketing term used by DW, although not unique to DW, but with all drum manufacturers. The "New standard" sizes - 10×9, 12×10, 13×11, etc. are 2" deeper than what was considered "standard" in the 1950s. "Power" toms are one inch deeper than standard, with sizes of 10×9 or 10×10, 12×11, 13×12, which overtook the classic setup in popularity during the 1980s. Square - 10×10, 12×12, 13×13, etc., have been common in the 1980s and 1990s. Hyperdrive are shallow depths made popular initially by Tama: 10×6.5, 12×7, 13×7.5, etc.

Variations.

Single-headed.

Single-headed tom-toms, also known as concert toms, have also been used in drum kits, though their use has fallen off in popularity since the 1970s. "Concert toms" have a single head and a shell slightly shallower than the corresponding double-headed tom. Phil Collins still uses four single-headed rack-mount toms and two floor toms (Gretsch) in his setup. They are generally easier to tune as they have no bottom head to adjust.  The term "concert tom" has also been used to describe double- or single-headed tom-tom drums designed for use in a concert band rather than in a drum kit.

Rototoms.

Rototoms have no shell at all, just a single head and a steel frame. Unlike most other drums, they have a variable definite pitch and some composers write for them as a tuned instrument, demanding specific notes. They can be tuned quickly by rotating the head. Since the head rotates on a thread, this raises or lowers the head relative to the rim of the drum and so increases or decreases the tension in the head.

Gong bass drum.

A gong bass drum (also known as "gong drum"), is a large, single-headed tom often sized at or, with the drumhead being larger than the shell. The sound produced is similar to a bass drum, though it is more open and has longer sustain. They can be mounted with standard floor tom legs, though many drummers mount them at an angle next to the floor tom(s). Notable users include Neil Peart, Stewart Copeland, Bill Bruford, Simon Phillips, Jason Bittner, Mike Portnoy and Dom Howard.

Floor tom.

A floor tom is a double-skin drum, most often but not always as deep as its diameter, traditionally mounted on three legs and to the drummer's right for a right-handed drummer. It is normally the deepest-toned drum played by sticks in the kit, above the bass drum but below all others, and the most resonant, more so than even the bass drum.

Construction and manufacture.

Typically, a tom consists of a shell, chromed or plated metal hardware and head. Shell depth standards vary according to the era of manufacture and the drum style. Tom-toms are typically made in diameters of:,,,,,,, and, with heads to fit.  Tom-toms can be fitted with an adjustable mounting for a floor stand, or attachment to a bass drum or marching rig. They can be single- or double-headed.

Shell.

A crucial factor in achieving superior tone quality and insuring durability, especially with wood, is the creation of perfectly round shells and much research and development has been put into this manufacturing technology.  Shells are often constructed of 6–8 wood plies (often using different woods e. g. mahogany and falkata — birch or maple are commonly used for single-wood plies), solid wood (turned) or man-made materials (e. g. fibreglass, pressed steel, acrylic glass, resin-composite). Wood or composite shells can be finished by laminating in plastic in a large variety of colours and effects (e. g. sparkle or polychromatic); natural wood may be stained or left natural and painted with clear lacquer. Steel is usually chromed, fibreglass self-coloured and acrylic glass tinted or clear.

Hardware.

For drum hardware one or two cast or pressed metal rims attach by threaded tension rods or lugs to nut boxes bolted onto the shell and hold the heads onto the bearing edges of the shell. The tension rod assembly needs to be precision-machined, cast and fitted to enable predictable and secure tuning without inhibiting resonance or introducing extra vibration. All components will be placed under great tension and experience added stresses from playing.  Mounting systems vary greatly, from a simple cast block on the shell which accepts and clamps to a rod attached to a clamp or holder to much more sophisticated arrangements where there is no attachment to the shell, instead a frame clamps to the tuning lugs.  Another sort of rod clamp system allows attachment of the drum to the tom holder without the need of a hole in the drum shell for the rod to pass through. The clamp is attached to the shell at the nodal point with two bolts so as to allow the shell to vibrate freely without degrading the shell's dynamic range and sustain. The nodal point is the location on a shell with the least amount of vibration allowing for the mount to have minimal effect on the resonance of the shell.  Some drummers use a snare stand to hold and to make it easier to position the tom.

A tom drum is a cylindrical drum with no snares, named from the Anglo-Indian and Sinhala language. It was added to the drum kit in the early part of the 20th century. Most toms range in size between in diameter, though floor toms can go as large as. It is not to be confused with a tam-tam, a gong. The Tom is popular and used by players worldwide.

筒鼓,又称高架鼓(英语:tom-tom),是西洋敲击乐器中的一种鼓。属于双皮鼓类。“tom-tom”一词源自印度英语及僧伽罗语。在亚洲或印第安原住民,长久以来把鼓视为沟通工具之一,筒鼓很大程度便是由这类用作传话用的鼓所演变而成的。并于20世纪初先引入爵士鼓中。


Structure and function.

The cambium present between primary xylem and primary phloem is called the "intrafascicular" cambium (within vascular bundles). During secondary growth, cells of medullary rays, in a line (as seen in section; in three dimensions, it is a sheet) between neighbouring vascular bundles, become meristematic and form new "interfascicular" cambium (between vascular bundles). The intrafascicular and interfascicular cambia thus join up to form a ring (in three dimensions, a tube) which separates the primary xylem and primary phloem, the "cambium ring". The vascular cambium produces secondary xylem on the inside of the ring, and secondary phloem on the outside, pushing the primary xylem and phloem apart.  The vascular cambium usually consists of two types of cells:

Maintenance of cambial meristem.

The vascular cambium is maintained by a network of interacting signal feedback loops. Currently, both hormones and short peptides have been identified as information carriers in these systems. While similar regulation occurs in other plant meristems, the cambial meristem receives signals from both the xylem and phloem sides for the meristem. Signals received from outside the meristem act to down regulate internal factors, which promotes cell proliferation and differentiation.

Hormonal regulation.

The phytohormones that are involved in the vascular cambial activity are auxins, ethylene, gibberellins, cytokinins, abscisic acid and probably more to be discovered. Each one of these plant hormones is vital for regulation of cambial activity. Combination of different concentrations of these hormones is very important in plant metabolism.  Auxin hormones are proven to stimulate mitosis, cell production and regulate interfascicular and fascicular cambium. Applying auxin to the surface of a tree stump allowed decapitated shoots to continue secondary growth. The absence of auxin hormones will have a detrimental effect on a plant. It has been shown that mutants without auxin will exhibit increased spacing between the interfascicular cambiums and reduced growth of the vascular bundles. The mutant plant will therefore experience a decrease in water, nutrients, and photosynthates being transported throughout the plant, eventually leading to death. Auxin also regulates the two types of cell in the vascular cambium, ray and fusiform initials. Regulation of these initials ensures the connection and communication between xylem and phloem is maintained for the translocation of nourishment and sugars are safely being stored as an energy resource. Ethylene levels are high in plants with an active cambial zone and are still currently being studied. Gibberellin stimulates the cambial cell division and also regulates differentiation of the xylem tissues, with no effect on the rate of phloem differentiation. Differentiation is an essential process that changes these tissues into a more specialized type, leading to an important role in maintaining the life form of a plant. In poplar trees, high concentrations of gibberellin is positively correlated to an increase of cambial cell division and an increase of auxin in the cambial stem cells. Gibberellin is also responsible for the expansion of xylem through a signal traveling from the shoot to the root. Cytokinin hormone is known to regulate the rate of the cell division instead of the direction of cell differentiation. A study demonstrated that the mutants are found to have a reduction in stem and root growth but the secondary vascular pattern of the vascular bundles were not affected with a treatment of cytokinin.

The vascular cambium is the main growth tissue in the stems and roots of many plants, specifically in dicots such as buttercups and oak trees, gymnosperms such as pine trees, as well as in certain vascular plants. It produces secondary xylem inwards, towards the pith, and secondary phloem outwards, towards the bark. In herbaceous plants, it occurs in the vascular bundles which are often arranged like beads on a necklace forming an interrupted ring inside the stem. In woody plants, it forms a cylinder of unspecialized meristem cells, as a continuous ring from which the new tissues are grown. Unlike the xylem and phloem, it does not transport water, minerals or food through the plant. Other names for the vascular cambium are the main cambium, wood cambium, or bifacial cambium.

维管形成层是植物中纵向贯穿根和茎的一层组织,位于木质部和韧皮部之间,细胞形态扁平,细胞质浓。维管形成层一般由多层细胞所组成,严格说起来,其中只有一层原始细胞,可以不断地向内外分裂而增生细胞,不断增生的子细胞分化为木质部和韧皮部以及射线的细胞,使得植物的根和茎能不断地生长加粗。属于侧生分生组织。