Biochemistry.

Ricin is classified as a type 2 ribosome-inactivating protein (RIP). Whereas type 1 RIPs are composed of a single protein chain that possesses catalytic activity, type 2 RIPs, also known as holotoxins, are composed of two different protein chains that form a heterodimeric complex. Type 2 RIPs consist of an A chain that is functionally equivalent to a type 1 RIP, covalently connected by a single disulfide bond to a B chain that is catalytically inactive, but serves to mediate transport of the A-B protein complex from the cell surface, via vesicle carriers, to the lumen of the endoplasmic reticulum (ER). Both type 1 and type 2 RIPs are functionally active against ribosomes "in vitro"; however, only type 2 RIPs display cytotoxicity due to the lectin-like properties of the B chain. To display its ribosome-inactivating function, the ricin disulfide bond must be reductively cleaved.

Biosynthesis.

Ricin is synthesized in the endosperm of castor oil plant seeds. The ricin precursor protein is 576 amino acid residues in length and contains a signal peptide (residues 1–35), the ricin A chain (36–302), a linker peptide (303–314), and the ricin B chain (315–576). The N-terminal signal sequence delivers the prepropolypeptide to the endoplasmic reticulum (ER) and then the signal peptide is cleaved off. Within the lumen of the ER the propolypeptide is glycosylated and a protein disulfide isomerase catalyzes disulfide bond formation between cysteines 294 and 318. The propolypeptide is further glycosylated within the Golgi apparatus and transported to protein storage bodies. The propolypeptide is cleaved within protein bodies by an endopeptidase to produce the mature ricin protein that is composed of a 267 residue A chain and a 262 residue B chain that are covalently linked by a single disulfide bond.

Structure.

In terms of structure, ricin closely resembles abrin-a, an isotoxin of abrin. The quaternary structure of ricin is a globular, glycosylated heterodimer of approximately 60–65 kDa. Ricin toxin A chain and ricin toxin B chain are of similar molecular weights, approximately 32 kDa and 34 kDa, respectively.  While other plants contain the protein chains found in ricin, both protein chains must be present to produce toxic effects. For example, plants that contain only protein chain A, such as barley, are not toxic because without the link to protein chain B, protein chain A cannot enter the cell and do damage to ribosomes.

Entry into the cytoplasm.

Ricin B chain binds complex carbohydrates on the surface of eukaryotic cells containing either terminal N-acetylgalactosamine or beta-1,4-linked galactose residues. In addition, the mannose-type glycans of ricin are able to bind to cells that express mannose receptors. RTB has been shown to bind to the cell surface on the order of 10-10 ricin molecules per cell surface.  The profuse binding of ricin to surface membranes allows internalization with all types of membrane invaginations. The holotoxin can be taken up by clathrin-coated pits, as well as by clathrin-independent pathways including caveolae and macropinocytosis. Intracellular vesicles shuttle ricin to endosomes that are delivered to the Golgi apparatus. The active acidification of endosomes is thought to have little effect on the functional properties of ricin. Because ricin is stable over a wide pH range, degradation in endosomes or lysosomes offers little or no protection against ricin. Ricin molecules are thought to follow retrograde transport via early endosomes, the trans-Golgi network, and the Golgi to enter the lumen of the endoplasmic reticulum (ER).  For ricin to function cytotoxically, RTA must be reductively cleaved from RTB to release a steric block of the RTA active site. This process is catalysed by the protein PDI (protein disulphide isomerase) that resides in the lumen of the ER. Free RTA in the ER lumen then partially unfolds and partially buries into the ER membrane, where it is thought to mimic a misfolded membrane-associated protein. Roles for the ER chaperones GRP94, EDEM and BiP have been proposed prior to the 'dislocation' of RTA from the ER lumen to the cytosol in a manner that uses components of the endoplasmic reticulum-associated protein degradation (ERAD) pathway. ERAD normally removes misfolded ER proteins to the cytosol for their destruction by cytosolic proteasomes. Dislocation of RTA requires ER membrane-integral E3 ubiquitin ligase complexes, but RTA avoids the ubiquitination that usually occurs with ERAD substrates because of its low content of lysine residues, which are the usual attachment sites for ubiquitin. Thus, RTA avoids the usual fate of dislocated proteins (destruction that is mediated by targeting ubiquitinylated proteins to the cytosolic proteasomes). In the mammalian cell cytosol, RTA then undergoes triage by the cytosolic molecular chaperones Hsc70 and Hsp90 and their co-chaperones, as well as by one subunit (RPT5) of the proteasome itself, that results in its folding to a catalytic conformation, which de-purinates ribosomes, thus halting protein synthesis.

Ribosome inactivation.

RTA has rRNA N-glycosylase activity that is responsible for the cleavage of a glycosidic bond within the large rRNA of the 60S subunit of eukaryotic ribosomes. RTA specifically and irreversibly hydrolyses the N-glycosidic bond of the adenine residue at position 4324 (A4324) within the 28S rRNA, but leaves the phosphodiester backbone of the RNA intact. The ricin targets A4324 that is contained in a highly conserved sequence of 12 nucleotides universally found in eukaryotic ribosomes. The sequence, 5’-AGUACGAGAGGA-3’, termed the sarcin-ricin loop, is important in binding elongation factors during protein synthesis. The depurination event rapidly and completely inactivates the ribosome, resulting in toxicity from inhibited protein synthesis. A single RTA molecule in the cytosol is capable of depurinating approximately 1500 ribosomes per minute.

Depurination reaction.

Within the active site of RTA, there exist several invariant amino acid residues involved in the depurination of ribosomal RNA. Although the exact mechanism of the event is unknown, key amino acid residues identified include tyrosine at positions 80 and 123, glutamic acid at position 177, and arginine at position 180. In particular, Arg180 and Glu177 have been shown to be involved in the catalytic mechanism, and not substrate binding, with enzyme kinetic studies involving RTA mutants. The model proposed by Mozingo and Robertus, based on X-ray structures, is as follows:

Toxicity.

Ricin is very toxic if inhaled, injected, or ingested. It can also be toxic if dust contacts the eyes or if it is absorbed through damaged skin. It acts as a toxin by inhibiting protein synthesis. It prevents cells from assembling various amino acids into proteins according to the messages it receives from messenger RNA in a process conducted by the cell's ribosome (the protein-making machinery) – that is, the most basic level of cell metabolism, essential to all living cells and thus to life itself. Ricin is resistant, but not impervious, to digestion by peptidases. By ingestion, the pathology of ricin is largely restricted to the gastrointestinal tract, where it may cause mucosal injuries. With appropriate treatment, most patients will make a decent recovery.  Because the symptoms are caused by failure to make protein, they may take anywhere from hours to days to appear, depending on the route of exposure and the dose. When ingested, gastrointestinal symptoms can manifest within six hours; these symptoms do not always become apparent. Within two to five days of exposure to ricin, effects of ricin on the central nervous system, adrenal glands, kidneys, and liver appear.  Ingestion of ricin causes pain, inflammation, and hemorrhage in the mucosal membranes of the gastrointestinal system. Gastrointestinal symptoms quickly progress to severe nausea, vomiting, diarrhea, and difficulty swallowing (dysphagia). Haemorrhage causes bloody feces (melena) and vomiting blood (hematemesis). The low blood volume (hypovolemia) caused by gastrointestinal fluid loss can lead to organ failure in the pancreas, kidney, liver, and GI tract and progress to shock. Shock and organ failure are indicated by disorientation, stupor, weakness, drowsiness, excessive thirst (polydipsia), low urine production (oliguria), and bloody urine (hematuria).  Symptoms of ricin inhalation are different from those caused by ingestion. Early symptoms include a cough and fever.  When skin or inhalation exposure occur, ricin can cause an allergy to develop. This is indicated by edema of the eyes and lips; asthma; bronchial irritation; dry, sore throat; congestion; skin redness (erythema); skin blisters (vesication); wheezing; itchy, watery eyes; chest tightness; and skin irritation.  An antidote has been developed by the UK military, although it has not yet been tested on humans. Another antidote developed by the US military has been shown to be safe and effective in lab mice injected with antibody-rich blood mixed with ricin, and has had some human testing.  Symptomatic and supportive treatments are available for ricin poisoning. Existing treatments emphasize minimizing the effects of the poison. Possible treatments include intravenous fluids or electrolytes, airway management, assisted ventilation, or giving medications to remedy seizures and low blood pressure. If the ricin has been ingested recently, the stomach can be flushed by ingesting activated charcoal or by performing gastric lavage. Survivors often develop long-term organ damage. Ricin causes severe diarrhea and vomiting, and victims can die of circulatory shock or organ failure; inhaled ricin can cause fatal pulmonary edema or respiratory failure. Death typically occurs within 3–5 days of exposure.  Vaccination is possible by injecting an inactive form of protein chain A. This vaccination is effective for several months due to the body's production of antibodies to the foreign protein. In 1978 Bulgarian defector Vladimir Kostov survived a ricin attack similar to the one on Georgi Markov, probably due to his body's production of antibodies. When a ricin-laced pellet was removed from the small of his back it was found that some of the original wax coating was still attached. For this reason only small amounts of ricin had leaked out of the pellet, producing some symptoms but allowing his body to develop immunity to further poisoning.  The seeds of "Ricinus communis" are commonly crushed to extract castor oil. As ricin is not oil-soluble, little is found in the extracted castor oil. The extracted oil is also heated to more than to denature any ricin that may be present. The remaining spent crushed seeds, called variously the "cake", "oil cake", and "press cake", can contain up to 5% ricin. While the oil cake from coconut, peanuts, and sometimes cotton seeds can be used as either cattle feed and/or fertilizer, the toxic nature of castor beans precludes their oil cake from being used as feed unless the ricin is first deactivated by autoclaving. Accidental ingestion of "Ricinus communis" cake intended for fertilizer has been reported to be responsible for fatal ricin poisoning in animals.  Deaths from ingesting castor plant seeds are rare, partly because of their indigestible seed coat, and because some of the ricin is deactivated in the stomach. The pulp from eight beans is considered dangerous to an adult. Rauber and Heard have written that close examination of early 20th century case reports indicates that public and professional perceptions of ricin toxicity "do not accurately reflect the capabilities of modern medical management".  Most acute poisoning episodes in humans are the result of oral ingestion of castor beans, 5–20 of which could prove fatal to an adult. Swallowing castor beans rarely proves to be fatal unless the bean is thoroughly chewed. The survival rate of castor bean ingestion is 98%. In 2013 a 37-year-old woman in the United States survived after ingesting 30 beans. Victims often manifest nausea, diarrhea, fast heart rate, low blood pressure, and seizures persisting for up to a week. Blood, plasma, or urine ricin or ricinine concentrations may be measured to confirm diagnosis. The laboratory testing usually involves immunoassay or liquid chromatography-mass spectrometry.

Therapeutic applications.

Although no approved therapeutics are currently based on ricin, it does have the potential to be used in the treatment of tumors, as a "magic bullet" to destroy targeted cells. Because ricin is a protein, it can be linked to a monoclonal antibody to target cancerous cells recognized by the antibody. The major problem with ricin is that its native internalization sequences are distributed throughout the protein. If any of these native internalization sequences are present in a therapeutic agent, the drug will be internalized by, and kill, untargeted non-tumorous cells as well as targeted cancerous cells.  Modifying ricin may sufficiently lessen the likelihood that the ricin component of these immunotoxins will cause the wrong cells to internalize it, while still retaining its cell-killing activity when it is internalized by the targeted cells. However, bacterial toxins, such as diphtheria toxin, which is used in denileukin diftitox, an FDA-approved treatment for leukemia and lymphoma, have proven to be more practical. A promising approach for ricin is to use the non-toxic B subunit (a lectin) as a vehicle for delivering antigens into cells, thus greatly increasing their immunogenicity. Use of ricin as an adjuvant has potential implications for developing mucosal vaccines.

Regulation.

In the US, ricin appears on the select agents list of the Department of Health and Human Services, and scientists must register with HHS to use ricin in their research. However, investigators possessing less than 1000 mg (1g) are exempt from regulation.  Ricin is classified as an extremely hazardous substance in the United States as defined in Section 302 of the US Emergency Planning and Community Right-to-Know Act (42 U.S.C. 11002), and is subject to strict reporting requirements by facilities that produce, store, or use it in significant quantities.

Chemical or biological warfare agent.

The United States investigated ricin for its military potential during World War I. At that time it was being considered for use either as a toxic dust or as a coating for bullets and shrapnel. The dust cloud concept could not be adequately developed, and the coated bullet/shrapnel concept would violate the Hague Convention of 1899 (adopted in U.S. law at 32 Stat. 1903), specifically Annex §2, Ch.1, Article 23, stating "... it is especially prohibited... [t]o employ poison or poisoned arms". World War I ended before the United States weaponized ricin.  During World War II the United States and Canada undertook studying ricin in cluster bombs. Though there were plans for mass production and several field trials with different bomblet concepts, the end conclusion was that it was no more economical than using phosgene. This conclusion was based on comparison of the final weapons, rather than ricin's toxicity (LCt ~10 mg/min/m. Ricin was given the military symbol W or later WA. Interest in it continued for a short period after World War II, but soon subsided when the US Army Chemical Corps began a program to weaponize sarin.  The Soviet Union also possessed weaponized ricin. The KGB developed weapons using ricin which were used outside the Soviet bloc, most famously in the Markov assassination.  In spite of ricin's extreme toxicity and utility as an agent of chemical/biological warfare, production of the toxin is difficult to limit. The castor bean plant from which ricin is derived is a common ornamental and can be grown at home without any special care.  Under both the 1972 Biological Weapons Convention and the 1997 Chemical Weapons Convention, ricin is listed as a schedule 1 controlled substance. Despite this, more than of castor beans are processed each year, and approximately 5% of the total is rendered into a waste containing negligible concentrations of undenatured ricin toxin.<ref name="http://www.ansci.cornell.edu/plants/toxicagents/ricin.html"></ref>  Ricin is several orders of magnitude less toxic than botulinum or tetanus toxin, but the latter are harder to come by. Compared to botulinum or anthrax as biological weapons or chemical weapons, the quantity of ricin required to achieve LD over a large geographic area is significantly more than an agent such as anthrax (tons of ricin vs. only kilogram quantities of anthrax). Ricin is easy to produce, but is not as practical or likely to cause as many casualties as other agents. Ricin is easily denatured by temperatures over meaning many methods of deploying ricin would generate enough heat to denature it. Once deployed, an area contaminated with ricin remains dangerous until the bonds between chain A or B have been broken, a process that takes two or three days. In contrast, anthrax spores may remain lethal for decades. Jan van Aken, a German expert on biological weapons, explained in a report for The Sunshine Project that Al Qaeda’s experiments with ricin suggest their inability to produce botulinum or anthrax.

Developments.

A biopharmaceutical company called Soligenix, Inc. has licensed an anti-ricin vaccine called RiVax from Vitetta et al. at UT Southwestern. The vaccine is safe and immunogenic in mice, rabbits, and humans. It has completed two successful clinical trials. Soligenix has been issued a US patent for Rivax. The ricin vaccine candidate has been granted orphan drug status in the US and the EEC and is currently in clinical trials in the US. Grants from the National Institute of Allergy and Infectious Diseases and the US Food and Drug Administration have supported development of the vaccine candidate.

Incidents.

Ricin has been involved in a number of incidents. In 1978, the Bulgarian dissident Georgi Markov was assassinated by Bulgarian secret police who surreptitiously shot him on a London street with a modified umbrella using compressed gas to fire a tiny pellet contaminated with ricin into his leg. He died in a hospital a few days later and his body was passed to a special poison branch of the British Ministry of Defence that discovered the pellet during an autopsy. The prime suspects were the Bulgarian secret police: Georgi Markov had defected from Bulgaria some years previously and had subsequently written books and made radio broadcasts that were highly critical of the Bulgarian communist regime. However, it was believed at the time that Bulgaria would not have been able to produce the pellet, and it was also believed that the KGB had supplied it. The KGB denied any involvement, although high-profile KGB defectors Oleg Kalugin and Oleg Gordievsky have since confirmed the KGB's involvement. Earlier, Soviet dissident Aleksandr Solzhenitsyn also suffered (but survived) ricin-like symptoms after an encounter in 1971 with KGB agents.  Ten days before the attack on Georgi Markov another Bulgarian defector, Vladimir Kostov, survived a similar attack. Kostov was standing on an escalator of the Paris metro when he felt a sting in his lower back above the belt of his trousers. He developed a fever, but recovered. After Markov's death the wound on Kostov's back was examined and a ricin-laced pellet identical to the one used against Markov was removed.  Several terrorists and terrorist groups have experimented with ricin and caused several incidents of the poisons being mailed to US politicians. For example, on 29 May 2013 two anonymous letters sent to New York City Mayor Michael Bloomberg contained traces of it. Another was sent to the offices of Mayors Against Illegal Guns in Washington, D.C. A letter containing ricin was also alleged to have been sent to American President Barack Obama at the same time. An actress, Shannon Richardson, was later charged with the crime, to which she pleaded guilty that December. On 16 July 2014, Richardson was sentenced to 18 years in prison plus a restitution fine of $367,000. On 2 October 2018, two letters suspected of containing ricin were sent to The Pentagon; one addressed to Secretary of Defense James Mattis, and the other to Chief of Naval Operations, Admiral John Richardson. A letter was received on 23 July 2019 at Pelican Bay State Prison in California which claimed to contain a suspicious substance. Authorities later confirmed it contained ricin; no detrimental exposures were identified.  In 2020, some media in the Czech Republic reported (based on intelligence information) that a person carrying Russian diplomatic passport and ricin had arrived in Prague with an intention to assassinate three politicians, however Vladimir Putin, the president of Russia, called it fake. The targets should have been: First, Zdeněk Hřib, the mayor of Prague (capital of the Czech Republic), who was involved in renaming the Prague's square "Pod Kaštany", where Russian embassy is situated, to the Square of Boris Nemtsov, an opposition politician assassinated in Kremlin in 2015. Second, Ondřej Kolář, the mayor of the Prague 6 municipality, who was involved in removing the controversial statue to the Soviet-era Marshal Konev. Third, Pavel Novotný, the mayor of Prague's southwestern Řeporyje district. All of these three politicians had received police protection. Later, the Czech president Miloš Zeman claimed that the police protection of Zdeněk Hřib is a publicity stunt. Zeman also confused ricin with castor oil and claimed that ricin is a non-poisonous laxative.

In popular culture.

Ricin has been used as a plot device, such as in the television series "Breaking Bad".  The popularity of "Breaking Bad" inspired several real-life criminal cases involving ricin or similar substances. Kuntal Patel from London attempted to poison her mother with abrin after the latter interfered with her marriage plans. Daniel Milzman, a 19-year-old former Georgetown University student, was charged with manufacturing ricin in his dorm room, as well as the intent of "[using] the ricin on another undergraduate student with whom he had a relationship". Mohammed Ali from Liverpool, England was convicted after attempting to purchase 500 mg of ricin over the dark web from an undercover FBI agent. He was sentenced, on 18 September 2015, to eight years imprisonment.

Ricin ( ), a lectin (a carbohydrate-binding protein) produced in the seeds of the castor oil plant, "Ricinus communis", is a highly potent toxin. A dose of purified ricin powder the size of a few grains of table salt can kill an adult human. The median lethal dose (LD) of ricin for mice is around 22 micrograms per kilogram of body weight via intraperitoneal injection. Oral exposure to ricin is far less toxic. An estimated lethal oral dose in humans is approximately 1 milligram per kilogram.

蓖麻毒蛋白(英语:Ricin)是从蓖麻籽中所萃取出来的一种毒性蛋白质,几乎对所有的真核细胞都具有杀伤作用。蓖麻毒蛋白的纯品是一种白色粉末或结晶体,无味,可溶于稀酸或盐类,不溶于苯、甲苯、乙醇、乙醚、三氯甲烷等有机溶剂,干热时具有良好的稳定性。蓖麻毒蛋白存在多种类型,如结晶型、B-型、D型、E型、T3型、G型等,不同类型的蓖麻毒蛋白毒性不尽相同,其中以D型的毒性最大。


History.

In ancient times.

The profession of the ferryman is embodied in Greek mythology in Charon, the boatman who transported souls across the River Styx to the Underworld.  Speculation that a pair of oxen propelled a ship having a water wheel can be found in 4th century Roman literature ""Anonymus De Rebus Bellicis"". Though impractical, there is no reason why it could not work and such a ferry, modified by using horses, was used in Lake Champlain in 19th-century America. See Experiment (horse powered boat).

Notable services.

Europe.

The busiest seaway in the world, the English Channel, connects Great Britain and mainland Europe, with ships sailing from the UK ports of Dover, Newhaven, Portsmouth and Plymouth to French ports, such as Calais, Dunkirk, Dieppe, Roscoff, Cherbourg-Octeville, Caen, St Malo and Le Havre. The busiest ferry route to France is the Dover to Calais crossing with approximately 9,168,000 passengers using the service in 2018. Ferries from Great Britain also sail to Belgium, the Netherlands, Norway, Spain and Ireland. Some ferries carry mainly tourist traffic, but most also carry freight, and some are exclusively for the use of freight lorries. In Britain, car-carrying ferries are sometimes referred to as RORO (roll-on, roll-off) for the ease by which vehicles can board and leave. The busiest single ferry route in terms of the number of departures is across the northern part of Øresund, between Helsingborg, Scania, Sweden and Elsinore, Denmark. Before the Øresund bridge was opened in July 2000, car and "car and train" ferries departed up to seven times every hour. This has since been reduced, but a car ferry still departs from each harbor every 15 minutes during daytime. The route is around and the crossing takes 22 minutes. Today, all ferries on this route are constructed so that they do not need to turn around in the harbors. This also means that the ferries lack stems and sterns, since the vessels sail in both directions. Starboard and port-side are dynamic, depending on the direction the ferry sails. Despite the short crossing, the ferries are equipped with restaurants (on three out of four ferries), cafeterias, and kiosks. Passengers without cars often make a double or triple return journey in the restaurants; for this, a single journey ticket is sufficient. Passenger and bicycle passenger tickets are inexpensive compared with longer routes. Large cruiseferries sail in the Baltic Sea between Finland, Åland, Sweden, Estonia, Latvia and Saint Petersburg, Russia and from Italy to Sardinia, Corsica, Spain and Greece. In many ways, these ferries are like cruise ships, but they can also carry hundreds of cars on car decks. Besides providing passenger and car transport across the sea, Baltic Sea cruise-ferries are a popular tourist destination unto themselves, with multiple restaurants, nightclubs, bars, shops and entertainment on board. Also many smaller ferries operate on domestic routes in Finland, Sweden and Estonia.  The south-west and southern parts of the Baltic Sea has several routes mainly for heavy traffic and cars. The ferry routes of Trelleborg-Rostock, Trelleborg-Travemünde, Trelleborg-Świnoujście, Gedser-Rostock, Gdynia-Karlskrona, and Ystad-Świnoujście are all typical "transports" ferries. On the longer of these routes, simple cabins are available. The Rødby-Puttgarden route also transports day passenger trains between Copenhagen and Hamburg, and on the Trelleborg-Sassnitz route, it also has capacities for the daily night trains between Berlin and Malmö.  In Istanbul, ferries connect the European and Asian shores of Bosphorus, as well as Princes Islands and nearby coastal towns. In 2014, İDO transported 47 million passengers, the largest ferry system in the world.

North America.

Due to the numbers of large freshwater lakes and length of shoreline in Canada, various provinces and territories have ferry services.  BC Ferries operates the third largest ferry service in the world which carries travellers between Vancouver Island and the British Columbia mainland on the country's west coast. This ferry service operates to other islands including the Gulf Islands and Haida Gwaii. In 2015, BC Ferries carried more than 8 million vehicles and 20 million passengers.  Canada's east coast has been home to numerous inter- and intra-provincial ferry and coastal services, including a large network operated by the federal government under CN Marine and later Marine Atlantic. Private and publicly owned ferry operations in eastern Canada include Marine Atlantic, serving the island of Newfoundland, as well as Bay, NFL, CTMA, Coastal Transport, and STQ. Canadian waters in the Great Lakes once hosted numerous ferry services, but these have been reduced to those offered by Owen Sound Transportation and several smaller operations. There are also several commuter passenger ferry services operated in major cities, such as Metro Transit in Halifax, Toronto Island ferries in Toronto and SeaBus in Vancouver. Washington State Ferries operates the most extensive ferry system in the continental United States and the second largest in the world by vehicles carried, with ten routes on Puget Sound and the Strait of Juan de Fuca serving terminals in Washington and Vancouver Island. In 2016, Washington State Ferries carried 10.5 million vehicles and 24.2 million riders in total.  The Alaska Marine Highway System provides service between Bellingham, Washington and various towns and villages throughout Southeast and Southwest Alaska, including crossings of the Gulf of Alaska. AMHS provides affordable access to many small communities with no road connection or airport.  The Staten Island Ferry in New York City, sailing between the boroughs of Manhattan and Staten Island, is the nation's single busiest ferry route by passenger volume. Unlike riders on many other ferry services, Staten Island Ferry passengers do not pay any fare to ride it. New York City also has a network of smaller ferries, or "water taxis", that shuttle commuters along the Hudson River from locations in New Jersey and Northern Manhattan down to the midtown, downtown and Wall Street business centers. Several ferry companies also offer service linking midtown and lower Manhattan with locations in the boroughs of Queens and Brooklyn, crossing the city's East River. New York City Mayor Bill de Blasio announced in February 2015 that city would begin an expanded Citywide Ferry Service some time in 2017 linking heretofore relatively isolated communities such as Manhattan's Lower East Side, Soundview in The Bronx, Astoria and the Rockaways in Queens and such Brooklyn neighborhoods as Bay Ridge, Sunset Park, and Red Hook with existing ferry landings in Lower Manhattan and Midtown Manhattan. This service was finally launched as NYC Ferry in May, 2017.  The New Orleans area also has many ferries in operation that carry both vehicles and pedestrians. Most notable is the Algiers Ferry. This service has been in continuous operation since 1827 and is one of the oldest operating ferries in North America.  In New England, vehicle-carrying ferry services between mainland Cape Cod and the islands of Martha's Vineyard and Nantucket are operated by The Woods Hole, Martha's Vineyard and Nantucket Steamship Authority, which sails year-round between Woods Hole and Vineyard Haven as well as Hyannis and Nantucket. Seasonal service is also operated from Woods Hole to Oak Bluffs from Memorial Day to Labor Day. As there are no bridges or tunnels connecting the islands to the mainland, The Steamship Authority ferries in addition to being the only method for transporting private cars to or from the islands, also serves as the only link by which heavy freight and supplies such as food and gasoline can be trucked to the islands. Additionally, Hy-Line Cruises operates high speed catamaran service from Hyannis to both islands, as well as traditional ferries, and several smaller operations run seasonal passenger only service primarily geared towards tourist day-trippers from other mainland ports, including New Bedford, (New Bedford Fast Ferry) Falmouth, (Island Queen ferry and Falmouth Ferry) and Harwich (Freedom Cruise Line). Ferries also bring riders and vehicles across Long Island Sound to such Connecticut cities as Bridgeport and New London, and to Block Island in Rhode Island from points on Long Island.  Transbay commuting in the San Francisco Bay Area was primarily ferry based until the advent of automobiles in the 1940s and most bridges in the area were built to supplant ferry services. By the 1970s, ferries were primarily used by tourists with Golden Gate Ferry, an organization under the ownership as the same governing body as the Golden Gate Bridge, left as the sole commute operator. The 1989 Loma Prieta earthquake prompted restoration of service to the East Bay. The modern ferry network is primarily under the authority of San Francisco Bay Ferry, connecting with cities as far as Vallejo. Tourist excursions are also offered by Blue & Gold Fleet and Red & White Fleet. A ferry serves Angel Island (which also accepts private craft). Alcatraz is served exclusively by ferry service administered by the National Park Service. Until the completion of the Mackinac Bridge in the 1950s, ferries were used for vehicle transportation between the Lower and the Upper Peninsulas of Michigan, across the Straits of Mackinac in the United States. Ferry service for bicycles and passengers continues across the straits for transport to Mackinac Island, where motorized vehicles are almost completely prohibited. This crossing is made possible by three ferry lines, Arnold Transit Company, Shepler's Ferry, and Star Line Ferry.  A ferry service runs between Milwaukee, Wisconsin and Muskegon, Michigan operated by Lake Express. Another ferry SS Badger operates between Manitowoc, Wisconsin and Ludington, Michigan. Both cross Lake Michigan.  Mexico has ferry services run by Baja Ferries that connect La Paz located on the Baja California Peninsula with Mazatlán and Topolobampo. Passenger ferries also run from Playa del Carmen to the island of Cozumel.  North Carolina is home to the second-largest ferry system in the United States.

Oceania.

In Australia, two Spirit of Tasmania ferries carry passengers and vehicles across Bass Strait, the body of water that separates Tasmania from the Australian mainland, often under turbulent sea conditions. These run overnight but also include day crossings in peak time. Both ferries are based in the northern Tasmanian port city of Devonport and sail to Melbourne  The double-ended Freshwater-class ferry cuts an iconic shape as it makes its way up and down Sydney Harbour New South Wales, Australia between Manly and Circular Quay  In New Zealand, ferries connect Wellington in the North Island with Picton in the South Island, linking New Zealand's two main islands. The route is, and is run by two companies – government-owned Interislander, and independent Bluebridge, who say the trip takes three and half hours.

Asia.

In Hong Kong, Star Ferry carry passengers across Victoria Harbour. Other carriers ferry travellers between Hong Kong Island and outlying islands like Cheung Chau, Lantau Island and Lamma Island.  The Malaysian state of Penang is home to the oldest ferry service in the country. This service, now renamed Rapid Ferry, connects the Raja Tun Uda Ferry Terminal at Weld Quay in George Town on Penang Island with the Sultan Abdul Halim Ferry Terminal in Butterworth on Peninsular Malaysia. It has also become a tourist attraction among foreigners.  Batamfast Fast Ferry transport passengers from Singapore's HarbourFront Centre and Tanah Merah Ferry Terminal to Indonesia's Batam Centre Ferry Terminal.

India.

India's ro-ro ferry service between Ghogha and Dahej was inaugurated by Prime Minister Narendra Modi on 22 October 2017. It aims to connect South Gujarat and Saurashtra currently separated by 360 km of roadway to 31 km of ferry service. It is a part of the larger Sagar Mala project.  Water transport in Mumbai consists of ferries, hovercrafts, and catamarans, operated by various government agencies as well as private entities. The Kerala State Water Transport Department (SWTD), operating under the Ministry of Transport, Government of Kerala, India regulates the inland navigation systems in the Indian state of Kerala and provides inland water transport facilities. It stands for catering to the passenger and cargo traffic needs of the inhabitants of the waterlogged areas of the Districts of Alappuzha, Kottayam, Kollam, Ernakulam, Kannur and Kasargode. SWTD ferry service is also one of the most affordable modes to enjoy the beauty of the scenic Kerala backwaters.

Types.

Ferry designs depend on the length of the route, the passenger or vehicle capacity required, speed requirements and the water conditions the craft must deal with.

Double-ended.

Double-ended ferries have interchangeable bows and sterns, allowing them to shuttle back and forth between two terminals without having to turn around. Well-known double-ended ferry systems include the BC Ferries, the Staten Island Ferry, Washington State Ferries, Star Ferry, several ferries on the North Carolina Ferry System, and the Lake Champlain Transportation Company. Most Norwegian fjord and coastal ferries are double-ended vessels. All ferries from southern Prince Edward Island to the mainland of Canada were double-ended. This service was discontinued upon completion of the Confederation Bridge. Some ferries in Sydney, Australia and British Columbia are also double-ended. In 2008, BC Ferries launched three of the largest double-ended ferries in the world.

Hydrofoil.

Hydrofoils have the advantage of higher cruising speeds, succeeding hovercraft on some English Channel routes where the ferries now compete against the Eurotunnel and Eurostar trains that use the Channel Tunnel. Passenger-only hydrofoils also proved a practical, fast and relatively economical solution in the Canary Islands, but were recently replaced by faster catamaran "high speed" ferries that can carry cars. Their replacement by the larger craft is seen by critics as a retrograde step given that the new vessels use much more fuel and foster the inappropriate use of cars in islands already suffering from the impact of mass tourism.

Hovercraft.

Hovercraft were developed in the 1960s and 1970s to carry cars. The largest was the massive SR.N4 which carried cars in its centre section with ramps at the bow and stern between England and France. The hovercraft was superseded by catamarans which are nearly as fast and are less affected by sea and weather conditions. Only one service now remains, a foot passenger service between Portsmouth and the Isle of Wight run by Hovertravel.

Catamaran.

Since 1990 high speed catamarans have revolutionised ferry services, replacing hovercraft, hydrofoils and conventional monohull ferries. In the 1990s there were a variety of builders, but the industry has consolidated to two builders of large vehicular ferries between 60 and 120 metres. Incat of Hobart, Tasmania favours a Wave-piercing hull to deliver a smooth ride, while Austal of Perth, Western Australia builds ships based on SWATH designs. Both these companies also compete in the smaller river ferry industry with a number of other ship builders.  Stena Line once operated the largest catamarans in the world, the Stena HSS class, between the United Kingdom and Ireland. These waterjet-powered vessels, displaced 19,638 tonnes, accommodating 375 passenger cars and 1,500 passengers. Other examples of these super-size catamarans are found in the Brittany Ferries fleet with the Normandie Express and the Normandie Vitesse.

Roll-on/roll-off.

Roll-on/roll-off ferries (RORO) are large conventional ferries named for the ease by which vehicles can board and leave.

Cruiseferry / RoPax.

A cruiseferry is a ship that combines the features of a cruise ship with a roll-on/roll-off ferry. They are also known as RoPax for their combined Roll on/Roll Off and passenger design.

Fast RoPax ferry.

Fast RoPax ferries are conventional ferries with a large garage intake and a relatively large passenger capacity, with conventional diesel propulsion and propellers that sail over. Pioneering this class of ferries was Attica Group, when it introduced Superfast I between Greece and Italy in 1995 through its subsidiary company Superfast Ferries. Cabins, if existent, are much smaller than those on cruise ships.

Turntable ferry.

This type of ferry allows vehicles to load from the "side". The vehicle platform can be turned. When loading, the platform is turned sideways to allow sideways loading of vehicles. Then the platform is turned back, in line with the vessel, and the journey across water is made.

Pontoon ferry.

Pontoon ferries carry vehicles across rivers and lakes and are widely used in less-developed countries with large rivers where the cost of bridge construction is prohibitive. One or more vehicles are carried on a pontoon with ramps at either end for vehicles to drive on and off. Cable ferries are usually pontoon ferries, but pontoon ferries on larger rivers are motorised and able to be steered independently like a boat.

Train ferry.

A train ferry is a ship designed to carry railway vehicles. Typically, one level of the ship is fitted with railway tracks, and the vessel has a door at either or both of the front and rear to give access to the wharves.

Foot ferry.

Foot ferries are small craft used to ferry foot passengers, and often also cyclists, over rivers. These are either self-propelled craft or cable ferries. Such ferries are for example to be found on the lower River Scheldt in Belgium and in particular the Netherlands. Regular foot ferry service also exists in the capital of the Czech Republic, Prague, and across the Yarra River in Melbourne, Australia at Newport. Restored, expanded ferry service in the Port of New York and New Jersey uses boats for pedestrians only.

Cable ferry.

Very short distances may be crossed by a cable or chain ferry, which is usually a pontoon ferry (see above), where the ferry is propelled along and steered by cables connected to each shore. Sometimes the cable ferry is human powered by someone on the boat. Reaction ferries are cable ferries that use the perpendicular force of the current as a source of power. Examples of a current propelled ferry are the four Rhine ferries in Basel, Switzerland. Cable ferries may be used in fast-flowing rivers across short distances. With an ocean crossing of approximately 1900 metres, the cable ferry between Vancouver Island and Denman Island in British Columbia; is the longest one in the world.  Free ferries operate in some parts of the world, such as at Woolwich in London, England (across the River Thames); in Amsterdam, Netherlands (across the IJ waterway); along the Murray River in South Australia, and across many lakes in British Columbia. Many cable ferries operate on lakes and rivers in Canada, among them a cable ferry that charges a toll operates on the Rivière des Prairies between Laval-sur-le-Lac and Île Bizard in Quebec, Canada. In Finland there were 40 road ferries (cable ferries) in 2009, on lakes, rivers and on sea between islands.

Air ferries.

In the 1950s and 1960s, travel on an "air ferry" was possible—airplanes, often ex-military, specially equipped to take a small number of cars in addition to foot passengers. These operated various routes including between the United Kingdom and Continental Europe. Companies operating such services included Channel Air Bridge, Silver City Airways, and Corsair.  The term is also applied to any "ferrying" by air, and is commonly used when referring to airborne military operations.

Docking.

Ferries often dock at specialized facilities designed to position the boat for loading and unloading, called a ferry slip. If the ferry transports road vehicles or railway carriages there will usually be an adjustable ramp called an apron that is part of the slip. In other cases, the apron ramp will be a part of the ferry itself, acting as a wave guard when elevated and lowered to meet a fixed ramp at the terminus – a road segment that extends partially underwater or meet the ferry slip.

Records.

Gross tonnage.

The world's largest ferries are typically those operated in Europe, with different vessels holding the record depending on whether length, gross tonnage or car vehicle capacity is the metric.

Oldest.

On 11 October 1811, inventor John Stevens' ship the "Juliana", began operation as the first steam-powered ferry (service was between New York City, and Hoboken, New Jersey).  The Elwell Ferry, a cable ferry in North Carolina, travels a distance of, shore to shore, with a travel time of five minutes.  A contender as oldest ferry in continuous operation is the Mersey Ferry from Liverpool to Birkenhead, England. In 1150, the Benedictine Priory at Birkenhead was established. The monks used to charge a small fare to row passengers across the estuary. In 1330, Edward III granted a charter to the Priory and its successors for ever: "the right of ferry there... for men, horses and goods, with leave to charge reasonable tolls". However, there may have been a short break following the Dissolution of the monasteries.  Another claimant as the oldest ferry service in continuous operation is the Rocky Hill - Glastonbury Ferry, running between the towns of Rocky Hill and Glastonbury, Connecticut. Established in 1655, the ferry has run continuously since, only ceasing operation every winter when the river freezes over. A long running salt water ferry service is the Halifax/Dartmouth ferry, running between the cities of Halifax and Dartmouth, Nova Scotia, which has run year-round since 1752, and is currently run by the region's transit authority, Metro Transit. However, the Mersey Ferry predates it as the oldest salt water ferry.

Fastest.

The gas turbine powered "Luciano Federico L" operated by Montevideo-based Buquebus, holds the Guinness World Record for the fastest car ferry in the world, in service between Montevideo, Uruguay and Buenos Aires, Argentina: its maximum speed, achieved in sea trials, was. It can carry 450 passengers and 52 cars along the route.

Sustainability.

The contributions of ferry travel to climate change have received less scrutiny than land and air transport, and vary considerably according to factors like speed and the number of passengers carried. Average carbon dioxide emissions by ferries per passenger-kilometre seem to be. However, ferries between Finland and Sweden produce of CO, with total emissions equalling a CO equivalent of, while ferries between Finland and Estonia produce of CO with total emissions equalling a CO equivalent of.

Alternative fuels.

With the price of oil at high levels, and with increasing pressure from consumers for measures to tackle global warming, a number of innovations for energy and the environment were put forward at the Interferry conference in Stockholm. According to the company Solar Sailor, hybrid marine power and solar wing technology are suitable for use with ferries, private yachts and even tankers.  Alternative fuels are becoming more widespread on ferries. The fastest passenger ferry in the world Buquebus, runs on LNG, while Sweden's Stena plans to operate its 1500-passenger ferries on methanol in 2015. Both fuels reduce emissions considerably and replace costly diesel fuel.  Megawatt-class battery electric ferries operate in Scandinavia, with several more scheduled for operation. As of 2017, the world's biggest purely electric ferry was the MF Tycho Brahe, which operates on the Helsingør–Helsingborg ferry route across the Øresund between Denmark and Sweden. The ferry weights 8414 tonnes, and has an electric storage capacity of more than 4 MWh.  Since 2015, Norwegian ferry company Norled has operated the electrical car ferry "" on the Lavik-Opedal connection on the E39 north of Bergen. The connection Anda-Lote, further north on the Norwegian west coast, will be the world's first connection served only by electrical car ferries. The first of the two ships, "MF Gloppefjord", was put into operation in January 2018. The owner, Fjord1, has commissioned a further seven battery-powered ferries to be in operation from 2020.  A total of 60 battery powered car ferries are expected to be operational in Norway within 2021.  Since 15 August 2019, Ærø Municipality operated with the E-ferry Ellen between the southern Danish ports of Fynshav to Søby, on the island of Ærø. The e-ferry is capable of carrying 30 vehicles and 200 passengers and is powered by a battery "with an unprecedented capacity" of.  The vessel can sail up to between charges – seven times farther than previously possible for an e-ferry. It will now need to prove it can provide up to seven return trips per day. The European Union, which supported the project, aims to roll out 100 or more of these ferries by 2030.

Accidents.

The following notable maritime disasters involved ferries.

See also.

<br

A ferry is a merchant vessel used to carry passengers, and sometimes vehicles and cargo, across a body of water. A passenger ferry with many stops, such as in Venice, Italy, is sometimes called a water bus or water taxi.

渡轮,亦称为摆渡船、交通船,在固定航线上用来运输乘客的商船,一般提供双向运送服务。渡轮有时也运送载具与货物,有时因其功能不同而被称作「水上巴士」或「水上出租车」。渡船对岛屿与位于水边的都市来说是一种大众运输系统,对于两点间的运输来说,渡船的成本比建造桥梁或隧道都来得低。但缺点是易受气候影响而停航。


Terminology.

Toxins are often distinguished from other chemical agents by their method of production—the word toxin does not specify method of delivery (compare with venom and the broader meaning of poison—all substances that can also cause disturbances to organisms). It simply means it is a biologically produced poison.  According to an International Committee of the Red Cross review of the Biological Weapons Convention, "Toxins are poisonous products of organisms; unlike biological agents, they are inanimate and not capable of reproducing themselves", and "Since the signing of the Constitution, there have been no disputes among the parties regarding the definition of biological agents or toxins".  According to Title 18 of the United States Code, "... the term "toxin" means the toxic material or product of plants, animals, microorganisms (including, but not limited to, bacteria, viruses, fungi, rickettsiae or protozoa), or infectious substances, or a recombinant or synthesized molecule, whatever their origin and method of production..."  A rather informal terminology of individual toxins relates them to the anatomical location where their effects are most notable:  On a broader scale, toxins may be classified as either exotoxins, being excreted by an organism, or endotoxins, that are released mainly when bacteria are lysed.

Biotoxins.

The term "biotoxin" is sometimes used to explicitly confirm the biological origin. Biotoxins can be further classified, for example, as fungal biotoxins, microbial toxins, plant biotoxins, or animal biotoxins.  Toxins produced by microorganisms are important virulence determinants responsible for microbial pathogenicity and/or evasion of the host immune response.  Biotoxins vary greatly in purpose and mechanism, and can be highly complex (the venom of the cone snail contains dozens of small proteins, each targeting a specific nerve channel or receptor), or relatively small protein.  Biotoxins in nature have two primary functions:  Some of the more well known types of biotoxins include:

Environmental toxins.

The term "environmental toxin" can sometimes explicitly include synthetic contaminants such as industrial pollutants and other artificially made toxic substances. As this contradicts most formal definitions of the term "toxin", it is important to confirm what the researcher means when encountering the term outside of microbiological contexts.  Environmental toxins from food chains that may be dangerous to human health include:

Finding information about toxins.

In general, when scientists determine the amount of a substance that may be hazardous for humans, animals and/or the environment they determine the amount of the substance likely to trigger effects and if possible establish a safe level. In Europe, the European Food Safety Authority produced risk assessments for more than 4,000 substances in over 1,600 scientific opinions and they provide open access summaries of human health, animal health and ecological hazard assessments in their: OpenFoodTox database. The OpenFoodTox database can be used to screen potential new foods for toxicity.  The Toxicology and Environmental Health Information Program (TEHIP) at the United States National Library of Medicine (NLM) maintains a comprehensive toxicology and environmental health web site that includes access to toxins-related resources produced by TEHIP and by other government agencies and organizations. This web site includes links to databases, bibliographies, tutorials, and other scientific and consumer-oriented resources. TEHIP also is responsible for the Toxicology Data Network (TOXNET), an integrated system of toxicology and environmental health databases that are available free of charge on the web.  TOXMAP is a Geographic Information System (GIS) that is part of TOXNET. TOXMAP uses maps of the United States to help users visually explore data from the United States Environmental Protection Agency's (EPA) Toxics Release Inventory and Superfund Basic Research Programs.

Computational resources for prediction of toxic peptides and proteins.

One of the bottlenecks in peptide/protein-based therapy is their toxicity. Recently, "in silico" models for predicting toxicity of peptides and proteins, developed by Gajendra Pal Singh Raghava's group, predict toxicity with reasonably good accuracy. The prediction models are based on machine learning technique and quantitative matrix using various properties of peptides. The prediction tool is freely accessible to public in the form of web server.

Misuse of the term.

When used non-technically, the term "toxin" is often applied to any toxic substance, even though the term toxicant would be more appropriate. Toxic substances not directly of biological origin are also termed poisons and many non-technical and lifestyle journalists follow this usage to refer to toxic substances in general.  In the context of quackery and alternative medicine, the term "toxin" is used to refer to any substance alleged to cause ill health. This could range from trace amounts of potentially dangerous pesticides, to supposedly harmful substances produced in the body by intestinal fermentation (auto-intoxication), to food ingredients such as table sugar, monosodium glutamate (MSG), and aspartame.

A toxin is a poisonous substance produced within living cells or organisms; synthetic toxicants created by artificial processes are thus excluded. The term was first used by organic chemist Ludwig Brieger (1849–1919), derived from the word toxic.

本文所指的毒素(英语:Toxin),是指生物体所生产出来的毒物(poison),这个术语最早是由有机化学家路德维希(Ludwig Brieger)所提出。这些物质通常是一些会干扰生物体中其他大分子作用的蛋白质,例如蓖麻毒蛋白。由生物体产生的、极少量即可引起动物中毒的物<unk>。毒素在其严重程度差异很大,从一般轻微的急性(如蜂蜇)或是几乎立即致命的(如肉毒毒素)。


Introduction.

In the hydraulic analogy, current flowing through a wire (or resistor) is like water flowing through a pipe, and the voltage drop across the wire is like the pressure drop that pushes water through the pipe. Conductance is proportional to how much flow occurs for a given pressure, and resistance is proportional to how much pressure is required to achieve a given flow. (Conductance and resistance are reciprocals.)  The voltage drop (i.e., difference between voltages on one side of the resistor and the other), not the voltage itself, provides the driving force pushing current through a resistor. In hydraulics, it is similar: The pressure difference between two sides of a pipe, not the pressure itself, determines the flow through it. For example, there may be a large water pressure above the pipe, which tries to push water down through the pipe. But there may be an equally large water pressure below the pipe, which tries to push water back up through the pipe. If these pressures are equal, no water flows. (In the image at right, the water pressure below the pipe is zero.)  The resistance and conductance of a wire, resistor, or other element is mostly determined by two properties:  Geometry is important because it is more difficult to push water through a long, narrow pipe than a wide, short pipe. In the same way, a long, thin copper wire has higher resistance (lower conductance) than a short, thick copper wire.  Materials are important as well. A pipe filled with hair restricts the flow of water more than a clean pipe of the same shape and size. Similarly, electrons can flow freely and easily through a copper wire, but cannot flow as easily through a steel wire of the same shape and size, and they essentially cannot flow at all through an insulator like rubber, regardless of its shape. The difference between copper, steel, and rubber is related to their microscopic structure and electron configuration, and is quantified by a property called resistivity.  In addition to geometry and material, there are various other factors that influence resistance and conductance, such as temperature; see below.

Conductors and resistors.

Substances in which electricity can flow are called conductors. A piece of conducting material of a particular resistance meant for use in a circuit is called a resistor. Conductors are made of high-conductivity materials such as metals, in particular copper and aluminium. Resistors, on the other hand, are made of a wide variety of materials depending on factors such as the desired resistance, amount of energy that it needs to dissipate, precision, and costs.

Ohm's law.

For many materials, the current "I" through the material is proportional to the voltage "V" applied across it: over a wide range of voltages and currents. Therefore, the resistance and conductance of objects or electronic components made of these materials is constant. This relationship is called Ohm's law, and materials which obey it are called "ohmic" materials. Examples of ohmic components are wires and resistors. The current–voltage graph of an ohmic device consists of a straight line through the origin with positive slope.  Other components and materials used in electronics do not obey Ohm's law; the current is not proportional to the voltage, so the resistance varies with the voltage and current through them. These are called "nonlinear" or "nonohmic". Examples include diodes and fluorescent lamps. The current-voltage curve of a nonohmic device is a curved line.

Relation to resistivity and conductivity.

The resistance of a given object depends primarily on two factors: What material it is made of, and its shape. For a given material, the resistance is inversely proportional to the cross-sectional area; for example, a thick copper wire has lower resistance than an otherwise-identical thin copper wire. Also, for a given material, the resistance is proportional to the length; for example, a long copper wire has higher resistance than an otherwise-identical short copper wire. The resistance and conductance of a conductor of uniform cross section, therefore, can be computed as  where formula_5 is the length of the conductor, measured in metres (m), "A" is the cross-sectional area of the conductor measured in square metres (m2), σ (sigma) is the electrical conductivity measured in siemens per meter (S·m), and ρ (rho) is the electrical resistivity (also called "specific electrical resistance") of the material, measured in ohm-metres (Ω·m). The resistivity and conductivity are proportionality constants, and therefore depend only on the material the wire is made of, not the geometry of the wire. Resistivity and conductivity are reciprocals: formula_6. Resistivity is a measure of the material's ability to oppose electric current.  This formula is not exact, as it assumes the current density is totally uniform in the conductor, which is not always true in practical situations. However, this formula still provides a good approximation for long thin conductors such as wires.  Another situation for which this formula is not exact is with alternating current (AC), because the skin effect inhibits current flow near the center of the conductor. For this reason, the "geometrical" cross-section is different from the "effective" cross-section in which current actually flows, so resistance is higher than expected. Similarly, if two conductors near each other carry AC current, their resistances increase due to the proximity effect. At commercial power frequency, these effects are significant for large conductors carrying large currents, such as busbars in an electrical substation, or large power cables carrying more than a few hundred amperes.  The resistivity of different materials varies by an enormous amount: For example, the conductivity of teflon is about 10 times lower than the conductivity of copper. Loosely speaking, this is because metals have large numbers of "delocalized" electrons that are not stuck in any one place, so they are free to move across large distances. In an insulator, such as Teflon, each electron is tightly bound to a single molecule so a great force is required to pull it away. Semiconductors lie between these two extremes. More details can be found in the article: Electrical resistivity and conductivity. For the case of electrolyte solutions, see the article: Conductivity (electrolytic).  Resistivity varies with temperature. In semiconductors, resistivity also changes when exposed to light. See below.

Measuring resistance.

An instrument for measuring resistance is called an ohmmeter. Simple ohmmeters cannot measure low resistances accurately because the resistance of their measuring leads causes a voltage drop that interferes with the measurement, so more accurate devices use four-terminal sensing.

Static and differential resistance.

Many electrical elements, such as diodes and batteries do "not" satisfy Ohm's law. These are called "non-ohmic" or "non-linear", and their current–voltage curves are "not" straight lines through the origin.  Resistance and conductance can still be defined for non-ohmic elements. However, unlike ohmic resistance, non-linear resistance is not constant but varies with the voltage or current through the device; i.e., its operating point. There are two types of resistance:

AC circuits.

Impedance and admittance.

When an alternating current flows through a circuit, the relation between current and voltage across a circuit element is characterized not only by the ratio of their magnitudes, but also the difference in their phases. For example, in an ideal resistor, the moment when the voltage reaches its maximum, the current also reaches its maximum (current and voltage are oscillating in phase). But for a capacitor or inductor, the maximum current flow occurs as the voltage passes through zero and vice versa (current and voltage are oscillating 90° out of phase, see image below). Complex numbers are used to keep track of both the phase and magnitude of current and voltage:  where:  The impedance and admittance may be expressed as complex numbers that can be broken into real and imaginary parts:  where "R" and "G" are resistance and conductance respectively, "X" is reactance, and "B" is susceptance. For ideal resistors, "Z" and "Y" reduce to "R" and "G" respectively, but for AC networks containing capacitors and inductors, "X" and "B" are nonzero.  formula_12 for AC circuits, just as formula_13 for DC circuits.

Frequency dependence of resistance.

A key feature of AC circuits is that the resistance and conductance can be frequency-dependent, a phenomenon known as the universal dielectric response. One reason, mentioned above is the skin effect (and the related proximity effect). Another reason is that the resistivity itself may depend on frequency (see Drude model, deep-level traps, resonant frequency, Kramers–Kronig relations, etc.)

Energy dissipation and Joule heating.

Resistors (and other elements with resistance) oppose the flow of electric current; therefore, electrical energy is required to push current through the resistance. This electrical energy is dissipated, heating the resistor in the process. This is called "Joule heating" (after James Prescott Joule), also called "ohmic heating" or "resistive heating".  The dissipation of electrical energy is often undesired, particularly in the case of transmission losses in power lines. High voltage transmission helps reduce the losses by reducing the current for a given power.  On the other hand, Joule heating is sometimes useful, for example in electric stoves and other electric heaters (also called "resistive heaters"). As another example, incandescent lamps rely on Joule heating: the filament is heated to such a high temperature that it glows "white hot" with thermal radiation (also called incandescence).  The formula for Joule heating is: where "P" is the power (energy per unit time) converted from electrical energy to thermal energy, "R" is the resistance, and "I" is the current through the resistor.

Dependence of resistance on other conditions.

Temperature dependence.

Near room temperature, the resistivity of metals typically increases as temperature is increased, while the resistivity of semiconductors typically decreases as temperature is increased. The resistivity of insulators and electrolytes may increase or decrease depending on the system. For the detailed behavior and explanation, see Electrical resistivity and conductivity.  As a consequence, the resistance of wires, resistors, and other components often change with temperature. This effect may be undesired, causing an electronic circuit to malfunction at extreme temperatures. In some cases, however, the effect is put to good use. When temperature-dependent resistance of a component is used purposefully, the component is called a resistance thermometer or thermistor. (A resistance thermometer is made of metal, usually platinum, while a thermistor is made of ceramic or polymer.)  Resistance thermometers and thermistors are generally used in two ways. First, they can be used as thermometers: By measuring the resistance, the temperature of the environment can be inferred. Second, they can be used in conjunction with Joule heating (also called self-heating): If a large current is running through the resistor, the resistor's temperature rises and therefore its resistance changes. Therefore, these components can be used in a circuit-protection role similar to fuses, or for feedback in circuits, or for many other purposes. In general, self-heating can turn a resistor into a nonlinear and hysteretic circuit element. For more details see Thermistor#Self-heating effects.  If the temperature "T" does not vary too much, a linear approximation is typically used: where formula_16 is called the "temperature coefficient of resistance", formula_17 is a fixed reference temperature (usually room temperature), and formula_18 is the resistance at temperature formula_17. The parameter formula_16 is an empirical parameter fitted from measurement data. Because the linear approximation is only an approximation, formula_16 is different for different reference temperatures. For this reason it is usual to specify the temperature that formula_16 was measured at with a suffix, such as formula_23, and the relationship only holds in a range of temperatures around the reference.  The temperature coefficient formula_16 is typically +3×10 K to +6×10 K for metals near room temperature. It is usually negative for semiconductors and insulators, with highly variable magnitude.

Strain dependence.

Just as the resistance of a conductor depends upon temperature, the resistance of a conductor depends upon strain. By placing a conductor under tension (a form of stress that leads to strain in the form of stretching of the conductor), the length of the section of conductor under tension increases and its cross-sectional area decreases. Both these effects contribute to increasing the resistance of the strained section of conductor. Under compression (strain in the opposite direction), the resistance of the strained section of conductor decreases. See the discussion on strain gauges for details about devices constructed to take advantage of this effect.

Light illumination dependence.

Some resistors, particularly those made from semiconductors, exhibit "photoconductivity", meaning that their resistance changes when light is shining on them. Therefore, they are called "photoresistors" (or "light dependent resistors"). These are a common type of light detector.

Superconductivity.

Superconductors are materials that have exactly zero resistance and infinite conductance, because they can have V = 0 and I ≠ 0. This also means there is no joule heating, or in other words no dissipation of electrical energy. Therefore, if superconductive wire is made into a closed loop, current flows around the loop forever. Superconductors require cooling to temperatures near 4K with liquid helium for most metallic superconductors like niobium–tin alloys, or cooling to temperatures near 77K with liquid nitrogen for the expensive, brittle and delicate ceramic high temperature superconductors. Nevertheless, there are many technological applications of superconductivity, including superconducting magnets.

In electronics and electromagnetism, the electrical resistance of an object is a measure of its opposition to the flow of electric current. The inverse quantity is, and is the ease with which an electric current passes. Electrical resistance shares some conceptual parallels with the notion of mechanical friction. The SI unit of electrical resistance is the ohm (Ω), while electrical conductance is measured in siemens (S).

在电磁学里,电阻是一个物体对于电流通过的阻碍能力,以方程序定义为


History and development.

Wiktionary was brought online on December 12, 2002, following a proposal by Daniel Alston and an idea by Larry Sanger, co-founder of Wikipedia. On March 28, 2004, the first non-English Wiktionaries were initiated in French and Polish. Wiktionaries in numerous other languages have since been started. Wiktionary was hosted on a temporary domain name (wiktionary.wikipedia.org) until May 1, 2004, when it switched to the current domain name., Wiktionary features over 25.9 million entries across its editions. The largest of the language editions is the English Wiktionary, with over 6.3 million entries, followed by the Malagasy Wiktionary with over 6 million bot-generated entries and the French Wiktionary with over 3.7 million. Forty-one Wiktionary language editions now contain over 100,000 entries each.  Most of the entries and many of the definitions at the project's largest language editions were created by bots that found creative ways to generate entries or (rarely) automatically imported thousands of entries from previously published dictionaries. Seven of the 18 bots registered at the English Wiktionary created 163,000 of the entries there.  Another of these bots, "ThirdPersBot," was responsible for the addition of a number of third-person conjugations that would not have received their own entries in standard dictionaries; for instance, it defined "smoulders" as the "third-person singular simple present form of smoulder." Of the 648,970 definitions the English Wiktionary provides for 501,171 English words, 217,850 are "form of" definitions of this kind. This means its coverage of English is slightly smaller than that of major monolingual print dictionaries. The "Oxford English Dictionary", for instance, has 615,000 headwords, while "Merriam-Webster's Third New International Dictionary of the English Language, Unabridged" has 475,000 entries (with many additional embedded headwords). Detailed statistics exist to show how many entries of various kinds exist.  The English Wiktionary does not rely on bots to the extent that some other editions do. The French and Vietnamese Wiktionaries, for example, imported large sections of the Free Vietnamese Dictionary Project (FVDP), which provides free content bilingual dictionaries to and from Vietnamese. These imported entries make up virtually all of the Vietnamese edition's contents. Almost all non-Malagasy-language entries of the Malagasy Wiktionary were copied by bot from other Wiktionaries. Like the English edition, the French Wiktionary has imported the approximately 20,000 entries from the Unihan database of Chinese, Japanese, and Korean characters. The French Wiktionary grew rapidly in 2006 thanks in large part to bots copying many entries from old, freely licensed dictionaries, such as the eighth edition of the "Dictionnaire de l'Académie française" (1935, around 35,000 words), and using bots to add words from other Wiktionary editions with French translations. The Russian edition grew by nearly 80,000 entries as "LXbot" added boilerplate entries (with headings, but without definitions) for words in English and German.  As of December 2019, en.wiktionary has over 700,000 gloss definitions and over 1,100,000 total definitions (including different forms) for English entries alone, with a total of over 6,100,000 entries across all languages.

Logos.

Wiktionary has historically lacked a uniform logo across its numerous language editions. Some editions use logos that depict a dictionary entry about the term "Wiktionary", based on the previous English Wiktionary logo, which was designed by Brion Vibber, a MediaWiki developer. Because a purely textual logo must vary considerably from language to language, a four-phase contest to adopt a uniform logo was held at the Wikimedia Meta-Wiki from September to October 2006. Some communities adopted the winning entry by "Smurrayinchester", a 3×3 grid of wooden tiles, each bearing a character from a different writing system. However, the poll did not see as much participation from the Wiktionary community as some community members had hoped, and a number of the larger wikis ultimately kept their textual logos.  In April 2009, the issue was resurrected with a new contest. This time, a depiction by "AAEngelman" of an open hardbound dictionary won a head-to-head vote against the 2006 logo, but the process to refine and adopt the new logo then stalled. In the following years, some wikis replaced their textual logos with one of the two newer logos. In 2012, 55 wikis that had been using the English Wiktionary logo received localized versions of the 2006 design by "Smurrayinchester". In July 2016, the English Wiktionary adopted a variant of this logo., 135 wikis, representing 61% of Wiktionary's entries, use a logo based on the 2006 design by "Smurrayinchester", 33 wikis (36%) use a textual logo, and three wikis (3%) use the 2009 design by "AAEngelman".

Accuracy.

To ensure accuracy, the English Wiktionary has a policy requiring that terms be "attested". Terms in major languages such as English and Chinese must be verified by:  For less-documented languages such as Creek and extinct languages such as Latin, one use in a permanently recorded medium or one mention in a reference work is sufficient verification.

Critical reception.

Critical reception of Wiktionary has been mixed. In 2006 Jill Lepore wrote in the article "Noah's Ark" for "The New Yorker,"  There's no show of hands at "Wiktionary". There's not even an editorial staff. "Be your own lexicographer!", might be "Wiktionary's" motto. Who needs experts? Why pay good money for a dictionary written by lexicographers when we could cobble one together ourselves?  "Wiktionary" isn't so much republican or democratic as Maoist. And it's only as good as the copyright-expired books from which it pilfers.  Keir Graff's review for "Booklist" was less critical:  Is there a place for Wiktionary? Undoubtedly. The industry and enthusiasm of its many creators are proof that there's a market. And it's wonderful to have another strong source to use when searching the odd terms that pop up in today's fast-changing world and the online environment. But as with so many Web sources (including this column), it's best used by sophisticated users in conjunction with more reputable sources.  References in other publications are fleeting and part of larger discussions of Wikipedia, not progressing beyond a definition, although David Brooks in "The Nashua Telegraph" described it as "wild and woolly". One of the impediments to independent coverage of Wiktionary is the continuing confusion that it is merely an extension of Wikipedia. In 2005, "PC Magazine" rated Wiktionary as one of the Internet's "Top 101 Web Sites", although little information was given about the site.  The measure of correctness of the inflections for a subset of the Polish words in the English Wiktionary showed that this grammatical data is very stable. Only 131 out of 4748 Polish words have had their inflection data corrected.

Wiktionary data in natural language processing.

Wiktionary has semi-structured data. Wiktionary lexicographic data can be converted to machine-readable format in order to be used in natural language processing tasks.  Wiktionary data mining is a complex task. There are the following difficulties: (1) the constant and frequent changes to data and schemata, (2) the heterogeneity in Wiktionary language edition schemata and (3) the human-centric nature of a wiki.  There are several parsers for different Wiktionary language editions:  Examples of natural language processing tasks which have been solved with the help of Wiktionary data include:

Wiktionary is a multilingual, web-based project to create a free content dictionary of terms (including words, phrases, proverbs, etc.) in all natural languages and a number of artificial languages. These entries may contain definitions, pronunciation guides, inflections, usage examples, related terms, images for illustration, among other features. It is collaboratively edited via a wiki. Its name is a portmanteau of the words "wiki" and "dictionary". It is available in 171 languages and in Simple English. Like its sister project Wikipedia, Wiktionary is run by the Wikimedia Foundation, and is written collaboratively by volunteers, dubbed "Wiktionarians". Its wiki software, MediaWiki, allows almost anyone with access to the website to create and edit entries.

维基词典(英语:Wiktionary),是维基百科的姊妹工程,它的目标是创建一个基于所有语言的自由的词典。该项目于2002年12月12日启动,发起人是维基人Daniel Alston。


History of religious categories.

In world cultures, there have traditionally been many different groupings of religious belief. In Indian culture, different religious philosophies were traditionally respected as academic differences in pursuit of the same truth. In Islam, the Quran mentions three different categories: Muslims, the People of the Book, and idol worshipers.

Christian categorizations.

Initially, Christians had a simple dichotomy of world beliefs: Christian civility versus foreign heresy or barbarity. In the 18th century, "heresy" was clarified to mean Judaism and Islam; along with paganism, this created a fourfold classification which spawned such works as John Toland's "Nazarenus, or Jewish, Gentile, and Mahometan Christianity", which represented the three Abrahamic religions as different "nations" or sects within "religion" itself, the "true monotheism."  Daniel Defoe described the original definition as follows: "Religion is properly the Worship given to God, but 'tis also applied to the Worship of Idols and false Deities." At the turn of the 19th century, in between 1780 and 1810, the language dramatically changed: instead of "religion" being synonymous with spirituality, authors began using the plural, "religions," to refer to both Christianity and other forms of worship. Therefore, Hannah Adams's early encyclopedia, for example, had its name changed from "An Alphabetical Compendium of the Various Sects..." to "A Dictionary of All Religions and Religious Denominations".  In 1838, the four-way division of Christianity, Judaism, Mahommedanism (archaic terminology for Islam) and Paganism was multiplied considerably by Josiah Conder's "Analytical and Comparative View of All Religions Now Extant among Mankind". Conder's work still adhered to the four-way classification, but in his eye for detail he puts together much historical work to create something resembling the modern Western image: he includes Druze, Yezidis, Mandeans, and Elamites under a list of possibly monotheistic groups, and under the final category, of "polytheism and pantheism," he listed Zoroastrianism, "Vedas, Puranas, Tantras, Reformed sects" of India as well as "Brahminical idolatry," Buddhism, Jainism, Sikhism, Lamaism, "religion of China and Japan," and "illiterate superstitions" as others.  The modern meaning of the phrase "world religion," putting non-Christians at the same level as Christians, began with the 1893 Parliament of the World's Religions in Chicago. The Parliament spurred the creation of a dozen privately funded lectures with the intent of informing people of the diversity of religious experience: these lectures funded researchers such as William James, D. T. Suzuki, and Alan Watts, who greatly influenced the public conception of world religions.  In the latter half of the 20th century, the category of "world religion" fell into serious question, especially for drawing parallels between vastly different cultures, and thereby creating an arbitrary separation between the religious and the secular. Even history professors have now taken note of these complications and advise against teaching "world religions" in schools. Others see the shaping of religions in the context of the nation-state as the "invention of traditions."

Classification.

Religious traditions fall into super-groups in comparative religion, arranged by historical origin and mutual influence. Abrahamic religions originate in West Asia, Indian religions in the Indian subcontinent (South Asia) and East Asian religions in East Asia. Another group with supra-regional influence are Afro-American religion, which have their origins in Central and West Africa.

Religious demographics.

One way to define a major religion is by the number of current adherents. The population numbers by religion are computed by a combination of census reports and population surveys (in countries where religion data is not collected in census, for example the United States or France), but results can vary widely depending on the way questions are phrased, the definitions of religion used and the bias of the agencies or organizations conducting the survey. Informal or unorganized religions are especially difficult to count.  There is no consensus among researchers as to the best methodology for determining the religiosity profile of the world's population. A number of fundamental aspects are unresolved:

Medium-sized religions.

The following are medium-sized world religions: Also Daesoon Jinrihoe, a Korean religion, claims six million followers.  Although “The Korean census in 1995 found 62,000 Koreans who indicated Daesoon Jinrihoe as their religious affiliation, and they were even less in the census of 2005... the census’ result was clearly grossly underestimated, and not consistent with the crowds attending both special ceremonies and the daily activities in thousands of Daesoon Jinrihoe’s branches throughout the country.”

Trends in adherence.

"World Christian Encyclopedia".

Following is some available data based on the work of the "World Christian Encyclopedia":

The world's principal religions and spiritual traditions may be classified into a small number of major groups, although this is by no means a uniform practice. This theory began in the 18th century with the goal of recognizing the relative levels of civility in societies (which in many modern cultures would be considered offensive).

世界主要宗教在20世纪根据比较宗教学的研究,依照其基本哲学观念和神学范畴来分类,但对于如何划分宗教信仰人群,尚有许多问题没有完全解决,包括:


History.

Franz Josef Strauß (1915–1988) had left behind the strongest legacy as a leader of the party, having led the party from 1961 until his death in 1988. His political career in the federal cabinet was unique in that he had served four ministerial posts in the years between 1953 and 1969. From 1978 until his death in 1988, Strauß served as the Minister-President of Bavaria. Strauß was the first leader of the CSU to be a candidate for the German chancellery in 1980. In the 1980 federal election, Strauß ran against the incumbent Helmut Schmidt of the Social Democratic Party of Germany (SPD), but lost thereafter as the SPD and the Free Democratic Party (FDP) managed to secure an absolute majority together, forming a social-liberal coalition.  The CSU has led the Bavarian state government since it came into existence in 1946, save from 1954 to 1957 when the SPD formed a state government in coalition with the Bavaria Party and the state branches of the GB/BHE and FDP. Before the 2008 elections in Bavaria, the CSU perennially achieved absolute majorities at the state level by itself. This level of dominance is unique among Germany's 16 states. Edmund Stoiber took over the CSU leadership in 1999. He ran for Chancellor of Germany in 2002, but his preferred CDU/CSU–FDP coalition lost against the SPD candidate Gerhard Schröder's SPD–Green alliance.  In the 2003 Bavarian state election, the CSU won 60.7% of the vote and 124 of 180 seats in the state parliament. This was the first time any party had won a two thirds majority in a German state parliament. "The Economist" later suggested that this exceptional result was due to a backlash against Schröder's government in Berlin. The CSU's popularity declined in subsequent years. Stoiber stepped down from the posts of Minister-President and CSU chairman in September 2007. A year later, the CSU lost its majority in the 2008 Bavarian state election, with its vote share dropping from 60.7% to 43.4%. The CSU remained in power by forming a coalition with the FDP. In the 2009 general election, the CSU received only 42.5% of the vote in Bavaria in the 2009 election, which constitutes its weakest showing in the party's history.  The CSU made gains in the 2013 Bavarian state election and the 2013 federal election, which were held a week apart in September 2013. The CSU regained their majority in the Bavarian Landtag and remained in government in Berlin. They have three ministers in Angela Merkel's current cabinet, namely Horst Seehofer (Minister of the Interior, Building and Community), Andreas Scheuer (Minister of Transport and Digital Infrastructure) and Gerd Müller (Minister for Economic Cooperation and Development).  The CSU forms after 2018 Bavarian state election on October 14, 2018 a new government with partner Free Voters of Bavaria.

Relationship with the CDU.

The CSU is the sister party of the Christian Democratic Union (CDU). Together, they are called The Union. The CSU operates only within Bavaria and the CDU operates in all other states, but not Bavaria. While virtually independent, at the federal level the parties form a common CDU/CSU faction. No Chancellor has ever come from the CSU, although Strauß and Edmund Stoiber were CDU/CSU candidates for Chancellor in the 1980 federal election and the 2002 federal election, respectively, which were both won by the Social Democratic Party of Germany (SPD). Below the federal level, the parties are entirely independent.  Since its formation, the CSU has been more conservative than the CDU. The CSU and the state of Bavaria decided not to sign the "Grundgesetz" of the Federal Republic of Germany as they could not agree with the division of Germany into two states after World War II. Although Bavaria like all German states has a separate police and justice system (distinctive and non-federal), the CSU has actively participated in all political affairs of the German Parliament, the German government, the German Bundesrat, the parliamentary elections of the German President, the European Parliament and meetings with Mikhail Gorbachev in Russia.  Like the CDU, the CSU is pro-European, although some Eurosceptic tendencies were shown in the past.

Leaders.

Ministers-President.

The CSU has contributed eleven of the twelve Ministers-President of Bavaria since 1945, with only Wilhelm Hoegner (1945–1946, 1954–1957) of the SPD also holding the office.

The Christian Social Union in Bavaria (, CSU) is a Christian-democratic and conservative political party in Germany. The CSU operates only in Bavaria while its larger counterpart, the Christian Democratic Union (CDU), operates in the other fifteen states of Germany. It differs from the CDU by being somewhat more conservative in social matters, following the Catholic social teaching. The CSU is considered the "de facto" successor of the Weimar-era Catholic Bavarian People's Party.

巴伐利亚基督教社会联盟(),简称基社盟(CSU),是德国巴伐利亚州的一个政党。在联邦层面该党和其姐妹党德国基督教民主联盟(基民盟)在联邦议会共同组成一个党团。作为联盟党,基民盟并不会在巴伐利亚和基社盟竞争公职,基社盟只在巴伐利亚参选,而基民盟在其他的联邦州参选。