Antibiotic

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Testing the susceptibility of Staphylococcus aureus to antibiotics by the Kirby-Bauer disk diffusion method. Antibiotics diffuse out from antibiotic-containing disks and inhibit growth of S. aureus resulting in a zone of inhibition.

 

معرفی سایتی مرجع در زمینه نت اتودهای معروف

Wigwam قطعه ای برای گیتار کلاسیک

قطعات سطح بندی شده گیتار کلاسیک

افسون بروس اسپرینگستین

نگاهی به آلبوم‌ها و فعالیت‌های مارک نوفلر، گرداننده گروه پرآوازه دایر استریتز

نگاهی به آلبومها و ویژگی‌های گروه پرآوازه «پلیس

صد آلبوم برتر راك تاريخ موسيقي معرفي شدند

نرم افزار آموزشی Music Theory Basics

Filomena Moretti

Mediterranean Sundance

 

دسته بندي ها : همه بخشها اخبار پزشكیبیماریها و درمانمقالات پزشكیداروهای گیاهیمطالب كوتاه جالبگوناگون

پروتز

پرتوشناسی

پاندمی

پروتئین P-gp

پاراتیون

پاتوژن

افزایش اشتها در مبتلایان به ایدز

از آنجایى كه در مبتلایان به ایدز، اختلال در حس چشایى وجود دارد ، منجر به كاهش اشتها و در نتیجه لاغرى مفرط در آنها مى شود. بنابراین برای بهبود وضعیت اشتها ،در زیر به برخى مواد غذایى اشتها آور اشاره مى كنیم:

دانشی که یک نوازنده بعنوان موزیسین باید بدان آگاه باشد شناخت از موسیقی و اجزای آن میباشد نه تنها اشراف به نت ها و قواعد تئوریک بلکه توجه کافی به فلسفه هنر و موسیقی - تاریخ موسیقی و شناخت دوره های موسیقی و تاثیر سایر هنرها بر موسیقی و غیره میباشد. که سعی میشود طی مباحث پیوسته به هر یک از آنها پرداخته شود. اما مبانی موسیقی ومباحث مربوط به آن

مسلما با وجود کتابهای بسیار مفید در این زمینه لزومی نیست تا این مطالب در سایت قرار گیرد اما باتوجه به اینکه در آموزش گیتار یکی از مراحل آموزش شناخت تئوری موسیقیست سعی شده است تا با گردآوری و جمع بندی از کتابهای مختلف به هدف نهایی مطلوبی برسیم.

تئوری پایه ای موسیقی

خواص صداها

تئوری موسقی ـ کشش ها ۱

اموزش گیتار قسمت ۲

ارمیک

• کلیپ هایی از جسی کوک

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                                    Jalap

• Common name:  Jalap
• Source: www.glamor.tk
• CONDUCTION: www.prowl.blogfa.com
• Writer: nima saketi
• Email: prowl.nima@gmail.com
• Botanical Source:  Jalap has a fleshy, tuberous, pyriform root, with numerous roundish tubercles. The stems are numerous, smooth, brownish, very slightly rough, with a tendency to twist, twinning about surrounding bodies. The leaves are long petioled, the first hastate, the succeeding ones cordate, acuminate, mucronate, smooth, deeply incised at base, and conspicuously veined beneath. Peduncles axillary, 2-flowered, rarely 3, twisted, as long as the petioles. Calyx has no bracts; composed of 5 smooth, obtuse, mucronate sepals. The corolla is funnel-shaped, purple, with a long, somewhat clavate tube, and an undulated limb, with 5 plaits. Stamens 5; filaments smooth, unequal, and longer than the corolla tube; anthers white, oblong-linear, and projecting. Ovary slender, and 2-celled; stigma simple, capitate, and deeply furrowed. Capsule 2-celled; cells 2-seeded; seeds unknown.
• History:  It is only within comparatively recent years that any certainty has existed in relation to the plant from which jalap root is obtained. It was first spoken of in 1609, as Bryonia mechoacana nigricans, then it was regarded by Ray as Convolvulus Americanus jalapium dictus, after which Tournefort, being deceived by persons who asserted that they had seen the plant growing, referred it to a species of Mirabilis. Balfour placed it as the Exogonium purga, and Linnaeus named it Convolvulus jalapa, and thus much difference of opinion existed until, in 1827, when Dr. J. R. Coxe, of Philadelphia, succeeded in obtaining perfect flowers from roots of the true plant furnished to him from their native soils, and thus first made its true character known to the scientific world.

The name of Ipomoea purga was bestowed upon the plant by Wenderoth and Hayne, but as the authorities of this country have, undoubtedly, the first claim, it may be viewed as fixed that I. jalapa, the name originally given to it by Nuttall, is the official plant.

The jalap plant is found in a deep, rich, vegetable soil, at an elevation of nearly 6000 feet above the level of the sea, growing in Mexico, near Chicanquiaco and Xalapa, from which last named place it is usually exported, and from which it has also obtained its name. It is generally imported in bags, containing 100 or 200 pounds. The root is the official part, and is gathered in all seasons, but principally in March and April, when the young shoots are appearing. The plant may be cultivated in the southern parts of the United States.

In 1866, Dr. D. Hanbury planted a root or tuber of Jalap in a garden, near London, and obtained promising results. It is now successfully grown in Jamaica and in India, especially in the Nilgherry hills of that country.

According to Warden (1887), the jalap tubers of India are not of first quality. Jalap is a very variable drug, much of it being of an inferior quality. The best kind is that known as the Vera Cruz variety. Several related, and often inferior drugs, e. g., Tampico jalap, have appeared on the market.

• Description: 

When fresh, the root is black externally, white and milky within, and varies in size according to its age, from that of a walnut to that of a moderate-sized turnip. It is dried in net bags over the fire, sometimes whole, and sometimes in sections. It is often preyed upon by insects which, however, leave its active part untouched, rendering it consequently more energetic. Jalap thus preyed upon is used for procuring the resin, but should not be given internally, except in much smaller doses than for the ordinary root.

Jalap is rather difficult to polvorize, but if triturated with cream of tartar, sugar of milk, or other hard salt, the process of polvorization is facilitated, and the powder rendered much finer. When in powder, the color is a pale grayish-brown, and when in contact with the mucus membrane of the air-tube, causes coughing and sternutation, with an increased discharge of saliva. Its solvents are water, alcohol, or spirits. Water takes up a small portion of its cathartic principle, but considerable of an amylaceous and mucilaginous extractive matter. Alcohol dissolves the resin, on which its cathartic virtues depend. Ether only partially dissolves it. Diluted alcohol completely extracts its active properties.

• Action, Medical Uses, and Dosage:  Jalap is an irritant and cathartic, operating energetically, occasioning profuse liquid stools with griping, and sometimes sickness at stomach, or even vomiting. Large doses produce violent hypercatharsis, sometimes terminating fatally.

When applied to a wound, it is said to induce purgation. Notwithstanding its activity, it is a safe and convenient purgative, much in use among the profession, and is useful in all cases where it is desirable to produce an energetic influence on the bowels, or to obtain large evacuations.

If intestinal inflammations are present it should not be used.

United with the bitartrate of potassium, its hydragogue properties are much increased, and thus it proves beneficial in dropsies, as well as in some forms of scrofula. Jalap, however, is suitable for excitable, active conditions, and may be used where a cooling effect is desired, as when it is necessary to evacuate the bowels in febrile disorders.

Inflammatory conditions of the biliary apparatus are exceptions to the rule that it should not be used in gastro-intestinal inflammations. When the rectum is impacted with a hard, fecal mass, the expulsion of the latter is facilitated by the purgative action of jalap, which greatly augments the intestinal secretions; all cases of constipation, due to dryness of the mucus membranes, through inactivity of the intestinal glands, are relieved by jalap. The dose for this latter purpose may be 5 grains in the morning, repeated for several days. When a stimulating laxative can not be used because of hemorrhoids, jalap may be employed, and it is likewise efficient as a derivative in cerebral disorders.

It is stated that the aqueous extract of jalap, the root having been previously exhausted of its resin by alcohol, will exert no cathartic influence, but will operate as a powerful diuretic, but I have not been able to procure this effect, though having made a trial in several cases (King). Three grains of jalap, taken an hour before each meal, act as a slight nauseant, destroying a desire for food among persons who are apt to eat too freely. If jalap is digested in ether, its nauseous taste and smell will be wholly removed without lessening its cathartic power. A biscuit is sometimes made for those to whom it is extremely nauseous and disagreeable; 5 drachms of jalap, 30 of sugar, and 4 ounces of flour, are made into 15 biscuits after the usual mode; 1 biscuit is a dose. The tendency of jalap to gripe and nauseate, may be obviated by adding to the dose 1 or 2 grains of camphor, or 3 grains of cloves. The dose of powdered jalap is from 10 to 30 grains (the aqueous extract ought not to be used, except as a diuretic)of the tincture, from 1 to 4 fluid drachms; the resin, or alcoholic extract, is given in from 2 to 8-grain doses, being usually rubbed up with sugar, or in emulsion, for the purpose of lessening its disposition to produce painful irritation of the intestinal mucus membrane.

As a hydragogue, 2 drachms of the bitartrate of potassium are added to 10 or 30 grains of polvorize jalap. Convolvulin (rhodeoretin) purges violently in 3 or 4-grain doses, and appears to be the active principle of jalap. Specific jalap, 10 to 20 drops every 4 hours for its specific uses. Though not an anthelmintic, jalap is often given to hasten the expulsion of worm, after agents have been given for their stupefaction or destruction.

• Specific Indications and Uses:  Constipation from deficient secretion of intestinal glands; pain and griping in lower bowel; colic, with stercoraceous vomiting; general gastro-intestinal torpor.
• TAMPICO JALAP:  This is the Mexican Purga de Sierra Gorda, and is derived from the Ipomoea simulans, (Hanbury). It much resembles the jalap tuber in appearance, odor, and taste. While it is difficult to distinguish some of the tubers from those of true jalap, most of the Tampico tubers are smaller and more elongated, more corky and shriveled, and show an absence of little scars crosswise the roots so noticeable in true jalap. It yields a resin (10 to 15 per cent). Fl?ckiger obtained 10 per cent of it. It is completely soluble in ether. Spirgatis (1870) named the resin tampicin. It is converted into tampicic acid by means of concentrated alkalies. Acids resolve it into sugar and tampicolic acid , thus showing its glucosidal character, analogously to that of convolvulin. It has purgative properties.
• Mirabilis jalapa (Linn?): The tubers of this species, which somewhat resemble jalap, may be distinguished by the presence of needle-like raphides of calcium oxalate.
• Ipomoea turpethum, (R. Brown): Turpeth root. This is the Turbith v?g?tal of the French Codex. It is not very similar in appearance to jalap. It contains a resin (4 per cent), of which turpethin, the ether-soluble portion, a glucosid, behaves like resin of jalap in relation to acids and alkalies. Bases convert it into turpethic acid, methyl-crotonic acid, traces of formic, and methyl-ethyl-acetic acids, etc.
• Ipomoea nil, Roth (Convolvulus nil, Linn?; Pharbitis nil, Choisy):  Seeds called kaladana in India, and are slightly purgative. They are black, triangular, with a rounded back, and have a sweetish taste, followed by an acrid sensation. They yield pharbitisin (identical with convolvulin) and a volatile oil. The seeds are roasted and given in powder.
• Ipomoea triloba (Pharbitis triloba, Ipomoea hederacea):  The seeds of the Japanese plant known as kengashi, yield convolvulin, and are employed like kaladana.
• MECHOACAN: This product, probably of a convolvulaceous plant, comes in gray or whitish circular sections or fragments, somewhat farinaceous, and destitute of the circles of resinous cells. It sometimes occurs as an adulterant of jalap, but its detection is not difficult. It is feebly cathartic.
• ORIZABA ROOT. This is variously known as Woody, Light, or Fusiform jalap, Male jalap, Jalap tops or stalks, and is the Mexican Purgo macho. It is derived from the Ipomoea orizabensis, Ledanois. This root is fusiform, and sometimes occurs in commerce in transverse slices, but more frequently in rectangular blocks. Its longitudinal wrinkles are deeper than those of jalap. Its color is also lighter. From the latter it may be known by the radiations on transverse section, and by leaving, when fractured, projecting bundles of fibrous vessels. Chemically, it closely resembles jalap. Its chief constituent is jalapin , so named by Mayer (para-rhodeoretin of Kayser), and should not be confounded with the jalapin of Buchner and Herberger, which is convolvulin. Mayer's jalapin differs from convolvulin in that ether and acetone freely dissolve it. Poleck (1892) proposes for it the name orizabin, as Prof. Maisch has done in 1887. Alkalies change it into water-soluble jalapic acid . Diluted acids convert it into sugar and jalapinol , insoluble in water; probably identical with jalapinolic acid , obtainable from scammony resin. Jalapin (orizabin) is oxidized by nitric acid to carbonic, isobutyric, and ipomic acid, the latter an isomer of sebacic acid (compare convolvulin). Jalapin (Mayer's) has been shown by Spirgatis to be identical with scammonin, both in chemical and purgative qualities, a fact more recently confirmed by Th. Poleck.
• Ipomoea pandurata, Meyer (Convolvulus panduratus, Linn?):  Wild potato.
  This plant, likewise known as Wild jalap, Man in the Ground, Mechameck, Man of the Earth, etc., has a perennial, very large, tapering root, with several stems from the same root, from 4 to 8 feet long, round, slender, purplish, smooth or nearly so, trailing or twinning. Leaves 2 or 3 inches long, about the same width, broadly cordate at base, acuminate, entire, or wavy, alternate, sometimes panduriform, smooth, deep-green above, paler beneath, on long petioles. Flowers white, dull-purple toward the base, large, opening in the forenoon; peduncles axillary, longer than the petioles, cymose, branching at the top, several-flowered. Corolla large, campanulate, 2 or 3 inches long. Calyx smooth, 5-parted, naked; sepals ovate-oblong stamens white, the length of the tube; anthers oblong. Style white, thread-like; stigma capitate, bilobed. Capsule oblong, 2-celled, 4-seeded, without intermediate partitions (L.?W.?G.).
• Wild potato is indigenous to the United States, growing in light and sandy soils, from Connecticut and west New York, southward and westward, and flowering from June to August; it rarely grows North, but is found in some parts of South America. The root is the medicinal part, it is very large, being from 2 to 8 feet in length, and from 2 to 4 or 5 inches in diameter, branched at the bottom, brownish-yellow externally, whitish and lactescent internally, furrowed lengthwise, and of a disagreeable odor and bitter, rather acrid taste; about 75 per cent in weight is lost in drying. It is generally met with in transverse, circular sections, which are somewhat tawny externally, whitish with diverging lines internally, and not readily powdered; the powder is somewhat grayish. Water or alcohol extracts its active properties, but diluted alcohol or spirits are its best solvents. It contains resin, bitter-extractive, sugar, starch, gum, a body resembling tannic acid, etc. The resin is purgative. It consists of an acid, and a non acid portion. It is a glucosid, and exists to the extent of 1.5 per cent.

The active principles of this plant are unknown. It possesses mild cathartic properties, acting gently in doses of from 40 to 60 grains of the powdered root. The infusion taken in wineglassful doses every hour, has been effective in dropsy, strangury, and calculous affections. It seems also to exert an influence over the lungs, liver, and kidneys, without excessive diuresis or catharsis. The saturated tincture is more energetic than the powdered root, decoccion, or extract. It is asserted that the Indians can handle rattlesnakes with impunity after wetting their hands with the milky juice of this root.

Copyright: www.prowl.blogfa.com

2007-12-25

HMS Onslow & HMS Pakenham
the 1/700 Tamiya 'O' Class Destroyer

By: Keith Butterley

History
The 'O' and 'P' class destroyers were the first of their kind built under the Emergency War Programme. They were born of the need for the Royal Navy to quickly replace many of its aging destroyers due to the clouds of war gathering in Europe. It was decided in an effort to cut costs and building time, that they would use the same machinery as the 'J' class, but with a simpler armament. These ships were designed for general fleet, patrol and escort duties. The 'O' class was ordered on September 3, 1939, with the HMS Oribi being the first completed in July 1941. Other ships were the Obdurate, Obedient, Offa, Onslaught, Onslow (leader), Opportune and Orwell. The similiar 'P' class was ordered on October 20, 1939, with the HMS Porcupine being finished in June 1941. The rest of the class was Pakenham (leader), Paladin, Panther, Partridge, Pathfinder, Penn and Petard.

All these ships served with distinction throughout the war. Their most famous action occurred in December 1942, while escorting convoy JW51B the Onslow, Obedient, Orwell, Obdurate, Oribi and the 'A' class destroyer Achates held off the Lutzow, Hipper and six KM destroyers for six hours. Finally HM cruisers Jamaica and Sheffield arrived and finally drove the Germans off, without loss. The Paladin, Oribi and Onslow were also responsible for individual U-boat kills, while the Pakenham and Petard shared one. The Pakenham, Panther and Porcupine were all lost while in the Mediterranean.

The Tamiya kit builds up to a fairly good representation of this class. However out of the box they can only be built as the two leaders, Onslow and Pakenham, modification of the aft gun house is required to do other members of the class. I relied heavily on Nat Richards' article from the IPMS Quarterly Review to make the changes in the kit that was necessary to make an accurate leader. The White Ensign Models O Class PE set was used to give them that much needed extra detail. To bring the kit up to a proper 1/700 scale, you need to lengthen the hull 1mm., however I chose not to do this, too scary! I scratch-built the RDF shacks, behind the bridge using plastic card, as they did not come with the kit. The splinter shields around the 4" HA gun were filed away and replaced them with PE fret. I am sure that if scaled out the originals would have been akin to Maginot Line fortifications.

HMS Pakenham

I chose to model the HMS Onslow with her lattice mast. This was added during her re-fit after the Barents Sea battle. I painted her in the Special home Fleet Destroyer Design white/G45/G20/B30. This scheme required a lot of masking due to its many sharp angle lines, but it certainly turns the kit into quite a stunning model. The Pakenham was done in a Western Approaches scheme WA blue/white. To the best of my knowledge she never carried this scheme, but I have always liked it, so there !!!

This kit does require a lot of work to make a decent model, but with the addition of the morePE set and the modifications per Nat Richards, it can be turned into a very good model.

Copyright © prowl2003

سايتهاي مرجع:

http://partituras.8m.com/

http://archive.digitalguitararchive.com

http://www.klassiskgitar.net/freescores.html

http://www.free-scores.com

http://www.eythorsson.com

http://www.delcamp.net/classicalguitar/sheetmusic.html

http://dirk.meineke.free.fr

http://www.e-tabs.org ( تبلچر)

Geyser

 

 

Struttura a sifone

Geysir in Cile

Geyser Strokkur in Islanda

Il geyser è una tipologia di sorgente di acqua calda che ha delle eruzioni periodiche che creano delle colonne di acqua calda e vapore. Il nome geyser deriva da Geysir che è il nome del più noto geyser islandese.

Essi sono una manifestazione del vulcanismo secondario, che si ha quando è presente una caratteristica struttura a sifone. In essa ci sono rocce permeabili, nelle quali circola l'acqua, dirette prima verso il basso e poi verso l'alto, circondate da rocce impermeabili, e nelle vicinanze è poi posta una camera magmatica. L'acqua entra nella struttura a sifone ed è riscaldata a causa della vicina camera magmatica, ma la profondità e la conseguente pressione litostatica impediscono che essa diventi vapore. In seguito risale in superficie e, con una pressione minore, l'acqua e il vapore sono liberi di esplodere in getti periodici. Il periodo è dovuto proprio al tempo necessario affinché il sifone si riempia.

I geyser sono abbastanza rari in quanto richiedono una combinazione di caratteri geologici e climatici che esistono solo in poche aree. Ci sono sei zone nelle quali si trovano molti geyser:

• Il parco nazionale di Yellowstone (Wyoming, Stati Uniti)
• L'Islanda
• La zona di Taupo, (North Island, Nuova Zelanda)
• La penisola di Kamchatka, (Russia)
• La zona di El Tatio (Cile)
• L'isola di Umnak sulle isole Aleutine (Alaska, Stati Uniti)

Si trovano in prossimità di vulcani o nei luoghi ove la crosta terrestre è meno spessa.

Tra i geyser più famosi vi sono quelli situati in Islanda ove vi è il Gran Geyser, che ha dato universalmente il nome al fenomeno, con getti alti da 30 a 40 metri. Cominciò la sua attività nel XIV secolo per cessare all'inizio del XX secolo. Fortunatamente sopravvive il vicino Strokkur, i cui getti raggiungono i venti metri: hanno una frequenza di circa cinque/otto minuti e i salti dell'acqua possono essere spettacolarmente due o tre. Intorno al sito si trovano altre sorgenti di acqua calda, il Piccolo Geysir, torrenti caldi e depositi minerali che rendono la zona simile a quella di "un altro pianeta": vedere per credere.

www.prowl.blogfa.com

www.glamor.tk

Geyser

 

 

Strokkur geyser, Iceland

A geyser is a type of hot spring that erupts periodically, ejecting a column of hot water and steam into the air. The name geyser comes from Geysir, the name of an erupting spring at Haukadalur, Iceland; that name, in turn, comes from the Icelandic verb gjósa, “to gush”.

The formation of geysers requires a favourable hydrogeology which exists in only a few places on Earth, and so they are fairly rare phenomena. About 1,000 exist worldwide, with about half of these in Yellowstone National Park, U.S..^[1] Geyser eruptive activity may change or cease due to ongoing mineral deposition within the geyser plumbing, exchange of functions with nearby hot springs, earthquake influences, and human intervention.^[2]

Erupting fountains of liquefied nitrogen have been observed on Neptune's moon Triton, as have possible signs of carbon dioxide eruptions from Mars' south polar ice cap. These phenomena are also often referred to as geysers. Instead of being driven by geothermal energy, they seem to rely on solar heating aided by a kind of solid-state greenhouse effect. On Triton, the nitrogen may erupt to heights of 8 km.

Contents [hide] 1 Eruptions 2 Types of geysers 3 Biology of geysers 4 Numbers and distribution 5 Misnamed geysers 6 Geysers on Triton 7 References 8 See also 9 External links

[ Eruptions

1. Steam rises from heated water	2. Pulses of water swell upward
3. Surface is broken	4. Ejected water spouts upward and falls back

Geyser activity, like all hot spring activity, is caused by surface water gradually seeping down through the ground until it meets rock heated by magma. The geothermally heated water then rises back toward the surface by convection through porous and fractured rock. Geysers differ from noneruptive hot springs in their subterranean structure; many consist of a small vent at the surface connected to one or more narrow tubes that lead to underground reservoirs of water.

As the geyser fills, the water at the top of the column cools off, but because of the narrowness of the channel, convective cooling of the water in the reservoir is impossible. The cooler water above presses down on the hotter water beneath, not unlike the lid of a pressure cooker, allowing the water in the reservoir to become superheated, i.e. to remain liquid at temperatures well above the boiling point.

Ultimately, the temperatures near the bottom of the geyser rise to a point where boiling begins; steam bubbles rise to the top of the column. As they burst through the geyser's vent, some water overflows or splashes out, reducing the weight of the column and thus the pressure on the water underneath. With this release of pressure, the superheated water flashes into steam, boiling violently throughout the column. The resulting froth of expanding steam and hot water then sprays out of the geyser hole.

Eventually the water remaining in the geyser cools back to below the boiling point and the eruption ends; heated groundwater begins seeping back into the reservoir, and the whole cycle begins again. The duration of eruptions and time between successive eruptions vary greatly from geyser to geyser; Strokkur in Iceland erupts for a few seconds every few minutes, while Grand Geyser in the U.S. erupts for up to 10 minutes every 8–12 hours.

[ Types of geysers

Vixen Geyser in Yellowstone

There are two types of geysers: fountain geysers erupt from pools of water, typically in a series of intense, even violent, bursts; and cone geysers which erupt from cones or mounds of siliceous sinter (also known as geyserite), usually in steady jets that last anywhere from a few seconds to several minutes. Old Faithful, perhaps the best-known geyser at Yellowstone National Park, is an example of a cone geyser. Grand Geyser, the tallest predictable geyser on earth, also at Yellowstone National Park, is an example of a fountain geyser.

The intense transient forces inside erupting geysers are the main reason for their rarity. There are many volcanic areas in the world that have hot springs, mud pots and fumaroles, but very few with geysers. This is because in most places, even where other necessary conditions for geyser activity exist, the rock structure is loose, and eruptions will erode the channels and rapidly destroy any nascent geysers.

Most geysers form in places where there is volcanic rhyolite rock which dissolves in hot water and forms mineral deposits called siliceous sinter, or geyserite, along the inside of the plumbing systems. Over time these deposits cement the rock together tightly, strengthening the channel walls and enabling the geyser to persist.

Geysers are fragile phenomena and if conditions change, they can ‘die’. Many geysers have been destroyed by people throwing litter and debris into them; others have ceased to erupt due to dewatering by geothermal power plants. The Great Geysir of Iceland has had periods of activity and dormancy. During its long dormant periods, eruptions were sometimes humanly-induced — often on special occasions — by the addition of surfactants to the water. Inducing eruptions at Geysir is no longer done, as the forced eruptions were damaging the geyser's special plumbing system. Following an earthquake in Iceland in 2000 the geyser became somewhat more active again. Initially the geyser erupted about eight times a day. As of July 2003, Geysir erupts several times a week.

Hyperthermophiles produce some of the bright colors of Grand Prismatic Spring, Yellowstone National Park

[ Biology of geysers

Main article: Thermophile, Hyperthermophile.

The specific colours of geysers derive from the fact that despite the apparently harsh conditions, life is often found in them (and also in other hot habitats) in the form of thermophilic prokaryotes. No known eukaryote can survive over 60 °C (140 °F).

In the 1960s, when the research of biology of geysers first appeared, scientists were generally convinced that no life can survive above around 73 °C (163 °F)—the upper limit for the survival of cyanobacteria, as the structure of key cellular proteins and deoxyribonucleic acid (DNA) would be destroyed. The optimal temperature for thermophilic bacteria was placed even lower, around 55 °C (131 °F).^{[citation needed]}

However, the observations proved that it actually is possible for life to exist at high temperatures and that some bacteria prefer even temperatures higher than boiling point of water. Dozens of such bacteria are known nowadays.^{[citation needed]} Thermophiles prefer temperatures from 50 to 70 °C whilst hyperthermophiles grow better at temperatures as high as 80 to 110 °C. As they have heat-stable enzymes that retain their activity even at high temperatures, they have been used as a source of thermostable tools, that are important in medicine and biotechnology, for example in manufacturing antibiotics, plastics, detergents (by the use of heat-stable enzymes lipases, pullulanases and proteases), and fermentation products (for example ethanol is produced).^{[citation needed]} The fact that such bacteria exist also stretches our imagination about life on other celestial bodies, both inside and outside of solar system. Among these, the first discovered and the most important for biotechnology is Thermus aquaticus.^{[citation needed]}

 Numbers and distribution

Eruption of White Dome Geyser in Yellowstone

Geysers are quite rare, requiring a combination of water, heat, and fortuitous plumbing. The combination exists in few places on Earth. The five largest geyser fields in the world are:^[3]

1. Yellowstone National Park, Wyoming, United States, North America
2. Dolina Geiserov, Kamchatka Peninsula, Russia, Asia - partially destroyed by a mudslide on June 3, 2007.
3. El Tatio, Atacama Desert, Chile, South America
4. Taupo Volcanic Zone, North Island, New Zealand, Oceania
5. Iceland, Europe

There used to be two large geysers fields in Nevada — Beowawe and Steamboat Springs — but they were destroyed by the installation of nearby geothermal power plants. At the plants, geothermal drilling reduced the available heat and lowered the local water table to the point that geyser activity could no longer be sustained. There are more individual geysers around the world, in California, Peru, Bolivia, Mexico, Dominica, Azores, Kenya, Slovakia and Japan, but no other large clusters.

Yellowstone is the largest geyser locale, containing thousands of hot springs, and between three and five hundred geysers. Yellowstone includes the tallest active geyser (Steamboat Geyser in Norris Geyser Basin), as well as the renowned Old Faithful Geyser, Beehive Geyser, Giantess Geyser, Lion Geyser, Plume Geyser, Aurum Geyser, Castle Geyser, Sawmill Geyser, Grand Geyser, Oblong Geyser, Giant Geyser, Daisy Geyser, Grotto Geyser, Fan & Mortar Geysers, & Riverside Geyser, all in the Upper Geyser Basin.

Many of New Zealand’s geysers have been destroyed by humans in the last century. Several New Zealand geysers have also become dormant or extinct by natural means. The main remaining field is Whakarewarewa at Rotorua. Two thirds of the geysers at Orakei Korako were flooded by the Ohakuri hydroelectric dam in 1961. The Wairakei field was lost to a geothermal power plant in 1958. The Taupo Spa field was lost when the Waikato River level was deliberately altered in the 1950s. The Rotomahana field was destroyed by the Mount Tarawera eruption in 1886. Waimangu Geyser, which existed from 1900 to 1904, was the largest geyser ever known. It ceased to erupt after a landslide covered its crater. Small numbers of geysers still exist at other places within the Taupo Volcanic Zone including Ketetahi, Tokaanu and Wai-O-Tapu.

 Misnamed geysers

In a number of places where there is geothermal activity wells have been drilled and fitted with impermeable casements that allow them to erupt like geysers. Though these so-called artificial geysers, technically known as erupting geothermal wells, are not true geysers, they can be quite spectacular. Little Old Faithful Geyser, in Calistoga, California, is probably an erupting geothermal well.^{[citation needed]}

Sometimes drilled cold-water wells erupt in a geyser-like manner due to the build-up of pressure from dissolved carbon dioxide in the water. These are not true geysers either, but are often called cold-water geysers. The best known of these is probably Crystal Geyser, near Green River, Utah.^[4]

A perpetual spouter is a natural hot spring that spouts water constantly. Some of these are incorrectly called geysers, but because they are not periodic in nature they are not considered true geysers.

[edit] Geysers on Triton

Dark streaks deposited by geysers on Triton

One of the great surprises of the Voyager 2 flyby of Neptune in 1989 was the discovery of geysers on its moon, Triton. Astronomers noticed dark plumes rising to some 8 km above the surface, and depositing material up to 150 km downstream.

All the geysers observed were located between 40° and 60°S, the part of Triton's surface close to the subsolar point. This indicates that solar heating, although very weak at Triton's great distance from the Sun, probably plays a crucial role. It is thought that the surface of Triton probably consists of a semi-transparent layer of frozen nitrogen, which creates a kind of greenhouse effect, heating the frozen material beneath it until it breaks the surface in an eruption. A temperature increase of just 4 K above the ambient surface temperature of 38 K could drive eruptions to the heights observed.

Geothermal energy may also be important. Unusually for a major satellite, Triton orbits Neptune in a retrograde orbit—that is, in the opposite direction to Neptune's rotation. This generates tidal forces which are causing Triton's orbit to decay, so that in several billion years time it will reach its Roche limit [1] with Neptune. The tidal forces may also generate heat inside Triton, in the same way as Jupiter's gravity generates tidal forces on Io which drive its extreme volcanic activity.

Each eruption of a Triton geyser may last up to a year, and during this time about 0.1 km³ of material may be deposited downwind. Voyager's images of Triton's southern hemisphere show many streaks of dark material laid down by geyser activity.

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A large field of investigation that includes the study of all changes associated with an organism as it progresses through the life cycle. The life cycles of all multicellular organisms exhibit many similarities. That is, as an organism progresses from one generation to the next there is a series of common processes: for example, gametogenesis, fertilization, embryogenesis, cell differentiation, tissue differentiation, organogenesis, maturation, growth, reproduction, senescence, and death.

Analysis of all of the events associated with an organism as it progresses through its life cycle employs a multiplicity of approaches. Tremendous strides have been made in describing at the molecular level the developmental process of cell differentiation. However, the molecular control mechanisms which regulate cell differentiation are not known. Tissue and organ differentiation, as well as morphogenesis, are processes which have been described in detail for many situations, but little is known about the physical and chemical nature of the mechanisms involved. A complete understanding of the development of an organism will require an appreciation and comprehension of the changes which occur at all levels of organization as an organism traverses its life cycle.

The major unifying theme in biology is evolution. Not only has evolution led to the wide variety of organisms now present on Earth, but also evolution has modified the initial processes and patterns of development to the diversity of types currently encountered. This evolution of developmental parameters in multicellular organisms began as single-celled organisms became multicellular. The development of a multicellular organism entails a host of problems not faced by a single-celled organism. For example, cells in one part of the aggregate must coordinate their activities with cells in other parts, nutrients and oxygen must be provided to all cells, and water balance must be maintained.

Developmental biologists have focused on two central areas: the processes and associated mechanisms by which cells become different, that is, cell differentiation; and the processes and associated mechanisms by which patterns are created, that is, morphogenesis.

Current theories state that cells become different by expressing different genes. Thus, a liver cell is different from a muscle cell, not because it contains different genes or genetic information, but because it expresses different sets of genes. This explanation of cell differences is based upon the results of three types of experimental analysis. (1) Some plant cells are totipotent; that is, for tobacco, carrot, and a few other plant species, it has been demonstrated that a single cell (not a gamete) can divide and undergo morphogenesis to form a fertile plant. (2) Nuclei from some differentiated animal cells are totipotent. That is, a nucleus from a differentiated cell can be injected into a mature egg which has had its nucleus removed or destroyed, and the injected nucleus can direct normal development of the organism. (3) The sequences of nucleotides in the DNA of all cells in an organism appear to be the same; that is, DNA-DNA hybridization of DNA from different cell types indicates that the different cell types do not have unique DNA base sequences. Since these results indicate that all cells contain the complete genome for an organism, different cell types appear to arise as a result of the expression of unique sets of genes in each cell type. See also Cell differentiation; Developmental genetics; Gene action; Somatic cell genetics.

Initially the cells of a developing embryo are not restricted in their developmental potential or fate, but as embryogenesis proceeds, a cell's developmental potential becomes restricted or fixed. Restriction of developmental fate is called determination. Two mechanisms have been identified that bring about determination. The first involves the presence of unique factors, called cytoplasmic determinants, which are products of the maternal genome and are located in specific areas of some animal eggs. The cells which come to contain these determinants differentiate along specific pathways. The second mechanism is induction, a process by which two tissues interact so that one or both differentiate along specific pathways. A classic example of induction is the action of mesoderm on the overlaying ectoderm in the frog embryo at the time of gastrulation. The mesoderm acts on the ectoderm, causing it to form the neural plate. Only ectoderm of a certain developmental age is capable of responding to the mesoderm, and this ectoderm is said to be competent. See also Embryonic induction.

Developmental biologists have gained substantial insights into the molecular bases for determination in model organisms such as Drosophila. At least three sets of cytoplasmic determinants (maternal gene products) are present in the fly egg: determinants for germ-cell formation, determinants controlling dorsal-ventral polarity, and determinants for the anterior-posterior polarity. Some of these determinants are messenger ribonucleic acids (mRNAs) coding for proteins which are transcriptional regulators (that is, proteins that regulate gene activity).

Morphogenesis involves the production of form and structure by integrating the differentiation of many different cells and cell types into specific spatial patterns. This higher level of organization has been difficult to investigate in terms of establishing mechanisms. The processes of determination, competence, and induction are involved. One of the greatest challenges faced by developmental biologists is to bridge the gap between genes and patterns. It is clear that patterns are a result of gene activity, but the relationship between genes and patterns in most organisms is not well understood. See also Animal morphogenesis; Plant morphogenesis.