1.
Nobel Prize in Physiology or Medicine
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The Nobel Prize in Physiology or Medicine, administered by the Nobel Foundation, is awarded once a year for outstanding discoveries in the fields of life sciences and medicine. It is one of five Nobel Prizes established in 1895 by Swedish chemist Alfred Nobel, Nobel was personally interested in experimental physiology and wanted to establish a prize for progress through scientific discoveries in laboratories. The Nobel Prize is presented to the recipient at a ceremony on 10 December, the anniversary of Nobels death, along with a diploma. The front side of the medal provides the profile of Alfred Nobel as depicted on the medals for Physics, Chemistry. As of 2015,106 Nobel Prizes in Physiology or Medicine have been awarded to 198 men and 12 women. The first Nobel Prize in Physiology or Medicine was awarded in 1901 to the German physiologist Emil von Behring, for his work on serum therapy and this includes one to António Egas Moniz in 1949 for the prefrontal leucotomy, bestowed despite protests from the medical establishment. Other controversies resulted from disagreements over who was included in the award, the 1952 prize to Selman Waksman was litigated in court, and half the patent rights awarded to his co-discoverer Albert Schatz who was not recognized by the prize. The 1962 prize awarded to James D, since the Nobel Prize rules forbid nominations of the deceased, longevity is an asset, one prize being awarded as long as 50 years after the discovery. Alfred Nobel was born on 21 October 1833 in Stockholm, Sweden into a family of engineers and he was a chemist, engineer and inventor who amassed a fortune during his lifetime, most of it from his 355 inventions of which dynamite is the most famous. He was interested in experimental physiology and set up his own labs in France, in 1888, Nobel was surprised to read his own obituary, titled The merchant of death is dead, in a French newspaper. Though Nobel wrote several wills during his lifetime, the last was written a little over a year before he died at the age of 63, because his will was contested, it was not approved by the Storting until 26 April 1897. After Nobels death, the Nobel Foundation was set up to manage the assets of the bequest, in 1900, the Nobel Foundations newly created statutes were promulgated by Swedish King Oscar II. According to Nobels will, the Karolinska Institutet in Sweden, a medical school, today, the prize is commonly referred to as the Nobel Prize in Medicine. It was important to Nobel that the prize be awarded for a discovery, per the provisions of the will, only select persons are eligible to nominate individuals for the award. Past Nobel laureates may also nominate, until 1977, all professors of Karolinska Institutet together decided on the Nobel Prize in Physiology or Medicine. Therefore, the Nobel Assembly was constituted, consisting of 50 professors at Karolinska Institutet. It elects the Nobel Committee with 5 members who evaluate the nominees, the Secretary who is in charge of the organization, in 1968, a provision was added that no more than three persons may share a Nobel prize. True to its mandate, the Committee has selected researchers working in the sciences over those who have made applied contributions
2.
Leiden University
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Leiden University, located in the city of Leiden, is the oldest university in the Netherlands. The university was founded in 1575 by William, Prince of Orange, the Dutch Royal Family and Leiden University still have a close relationship, Queens Juliana and Beatrix and King Willem-Alexander are all former students. Leiden University has seven faculties, over 50 departments and enjoys an international reputation. Shanghai Jiao Tong Universitys 2011 Academic Ranking of World Universities ranked Leiden University as the 29th best university worldwide, the Times Higher Education World University Rankings consistently rank Leiden University as the best university in Continental Europe for Arts and Humanities. During this time Leiden was home to figures as René Descartes, Rembrandt, Christiaan Huygens, Hugo Grotius, Baruch Spinoza. The university is a member of the Coimbra Group, the Europaeum, Leiden University houses more than 40 national and international research institutes. In 1575, the emerging Dutch Republic did not have any universities in its northern heartland, the only other university in the Habsburg Netherlands was the University of Leuven in southern Leuven, firmly under Spanish control. It is said the choice fell on Leiden as a reward for the defence of Leiden against Spanish attacks in the previous year. Ironically, the name of Philip II of Spain, Williams adversary, appears on the foundation certificate. Philip II replied by forbidding any subject to study in Leiden, renowned philosopher Baruch Spinoza was based close to Leiden during this period and interacted with numerous scholars at the university. At the end of the century, Leiden University again became one of Europes leading universities. At the world’s first university low-temperature laboratory, professor Heike Kamerlingh Onnes achieved temperatures of one degree above absolute zero of −273 degrees Celsius. In 1908 he was also the first to succeed in liquifying helium, Kamerlingh Onnes was awarded the Nobel Prize for Physics in 1913. In 2005 the manuscript of Einstein on the theory of the monatomic ideal gas was discovered in one of Leidens libraries. Of the seventy-seven Spinozapremie, nineteen were granted to professors of the Universiteit Leiden, literary historian Frits van Oostrom was the first professor of Leiden to be granted the Spinoza award for his work on developing the NLCM centre into a top research centre. Among other leading professors are Wim Blockmans, professor of Medieval History, the portraits of many famous professors since the earliest days hang in the university aula, one of the most memorable places, as Niebuhr called it, in the history of science. The University Library, which has more than 5 and it houses the largest collections worldwide on Indonesia and the Caribbean. Scholars from all over the world visit Leiden University Library, the oldest in the Netherlands, the anatomical and pathological laboratories of the university are modern, and the museums of geology and mineralogy have been restored
3.
Quartz
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Quartz is the second most abundant mineral in Earths continental crust, behind feldspar. There are many different varieties of quartz, several of which are semi-precious gemstones, since antiquity, varieties of quartz have been the most commonly used minerals in the making of jewelry and hardstone carvings, especially in Eurasia. The word quartz is derived from the German word Quarz and its Middle High German ancestor twarc, the Ancient Greeks referred to quartz as κρύσταλλος derived from the Ancient Greek κρύος meaning icy cold, because some philosophers apparently believed the mineral to be a form of supercooled ice. Today, the rock crystal is sometimes used as an alternative name for the purest form of quartz. Quartz belongs to the crystal system. The ideal crystal shape is a six-sided prism terminating with six-sided pyramids at each end, well-formed crystals typically form in a bed that has unconstrained growth into a void, usually the crystals are attached at the other end to a matrix and only one termination pyramid is present. However, doubly terminated crystals do occur where they develop freely without attachment, a quartz geode is such a situation where the void is approximately spherical in shape, lined with a bed of crystals pointing inward. α-quartz crystallizes in the crystal system, space group P3121 and P3221 respectively. β-quartz belongs to the system, space group P6222 and P6422. These space groups are truly chiral, both α-quartz and β-quartz are examples of chiral crystal structures composed of achiral building blocks. The transformation between α- and β-quartz only involves a comparatively minor rotation of the tetrahedra with respect to one another, although many of the varietal names historically arose from the color of the mineral, current scientific naming schemes refer primarily to the microstructure of the mineral. Color is an identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. Pure quartz, traditionally called rock crystal or clear quartz, is colorless and transparent or translucent, common colored varieties include citrine, rose quartz, amethyst, smoky quartz, milky quartz, and others. The most important distinction between types of quartz is that of macrocrystalline and the microcrystalline or cryptocrystalline varieties, the cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline. Chalcedony is a form of silica consisting of fine intergrowths of both quartz, and its monoclinic polymorph moganite. Other opaque gemstone varieties of quartz, or mixed rocks including quartz, often including contrasting bands or patterns of color, are agate, carnelian or sard, onyx, heliotrope, amethyst is a form of quartz that ranges from a bright to dark or dull purple color. The worlds largest deposits of amethysts can be found in Brazil, Mexico, Uruguay, Russia, France, Namibia, sometimes amethyst and citrine are found growing in the same crystal. It is then referred to as ametrine, an amethyst is formed when there is iron in the area where it was formed
4.
Electromagnet
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An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. The magnetic field disappears when the current is turned off, electromagnets usually consist of insulated wire wound into a coil. A current through the wire creates a field which is concentrated in the hole in the center of the coil. The main advantage of an electromagnet over a permanent magnet is that the field can be quickly changed by controlling the amount of electric current in the winding. However, unlike a permanent magnet that needs no power, an electromagnet requires a supply of current to maintain the magnetic field. Electromagnets are also employed in industry for picking up and moving heavy objects such as scrap iron. Danish scientist Hans Christian Ørsted discovered in 1820 that electric currents create magnetic fields, british scientist William Sturgeon invented the electromagnet in 1824. His first electromagnet was a piece of iron that was wrapped with about 18 turns of bare copper wire. The iron was varnished to insulate it from the windings, when a current was passed through the coil, the iron became magnetized and attracted other pieces of iron, when the current was stopped, it lost magnetization. Sturgeon displayed its power by showing that although it only weighed seven ounces, however, Sturgeons magnets were weak because the uninsulated wire he used could only be wrapped in a single spaced out layer around the core, limiting the number of turns. Beginning in 1830, US scientist Joseph Henry systematically improved and popularized the electromagnet, the first major use for electromagnets was in telegraph sounders. A portative electromagnet is one designed to just hold material in place, a tractive electromagnet applies a force and moves something. The solenoid is a coil of wire, and the plunger is made of a such as soft iron. Applying a current to the solenoid applies a force to the plunger, the plunger stops moving when the forces upon it are balanced. For example, the forces are balanced when the plunger is centered in the solenoid, the maximum uniform pull happens when one end of the plunger is at the middle of the solenoid. For units using inches, pounds force, and amperes with long, slender, solenoids, for example, a 12-inch long coil with a long plunger of 1-square inch cross section and 11,200 ampere-turns had a maximum pull of 8.75 pounds. The maximum pull is increased when a stop is inserted into the solenoid. The stop becomes a magnet that will attract the plunger, it adds little to the pull when the plunger is far away
5.
Arrow
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An arrow is a shafted projectile that is shot with a bow. It predates recorded history and is common to most cultures, an arrow usually consists of a shaft with an arrowhead attached to the front end, with fletchings and a nock at the other. The oldest evidence of stone-tipped projectiles, which may or may not have been propelled by a bow, dating to c.64,000 years ago, were found in Sibudu Cave, South Africa. The oldest evidence of the use of bows to shoot arrows dates to about 10,000 years ago and they had shallow grooves on the base, indicating that they were shot from a bow. The oldest bow so far recovered is about 8,000 years old, archery seems to have arrived in the Americas with the Arctic small tool tradition, about 4,500 years ago. Arrow sizes vary greatly across cultures, ranging from eighteen inches to five feet, however, most modern arrows are 75 centimetres to 96 centimetres, most war arrows from an English ship sunk in 1545 were 76 centimetres. Very short arrows have been used, shot through a guide attached either to the bow or to the archers wrist and these may fly farther than heavier arrows, and an enemy without suitable equipment may find himself unable to return them. The shaft is the structural element of the arrow, to which the other components are attached. Traditional arrow shafts are made from wood, bamboo or reeds, while modern shafts may be made from aluminium, carbon fibre reinforced plastic. Such shafts are made from an aluminium core wrapped with a carbon fibre outer. The stiffness of the shaft is known as its spine, referring to how little the shaft bends when compressed, hence, an arrow which bends less is said to have more spine. In order to strike consistently, a group of arrows must be similarly spined, center-shot bows, in which the arrow passes through the central vertical axis of the bow riser, may obtain consistent results from arrows with a wide range of spines. Higher draw-weight bows will generally require stiffer arrows, with more spine to give the amount of flex when shot. The weight of a shaft can be expressed in GPI. The length of a shaft in inches multiplied by its GPI rating gives the weight of the shaft in grains, for example, a shaft that is 30 inches long and has a GPI of 9.5 weighs 285 grains, or about 18 grams. This does not include the elements of a finished arrow. Sometimes a shaft will be made of two different types of wood fastened together, resulting in what is known as a footed arrow, known by some as the finest of wood arrows, footed arrows were used both by early Europeans and Native Americans. Footed arrows will typically consist of a length of hardwood near the head of the arrow
6.
Silver
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Silver is a metallic element with symbol Ag and atomic number 47. The symbol Ag stems from Latin argentum, derived from the Greek ὰργὀς, a soft, white, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. The metal is found in the Earths crust in the pure, free form, as an alloy with gold and other metals. Most silver is produced as a byproduct of copper, gold, lead, Silver is more abundant than gold, but it is much less abundant as a native metal. Its purity is measured on a per mille basis, a 94%-pure alloy is described as 0.940 fine. As one of the seven metals of antiquity, silver has had a role in most human cultures. Silver has long valued as a precious metal. Silver metal is used in many premodern monetary systems in bullion coins, Silver is used in numerous applications other than currency, such as solar panels, water filtration, jewelry, ornaments, high-value tableware and utensils, and as an investment medium. Silver is used industrially in electrical contacts and conductors, in specialized mirrors, window coatings, Silver compounds are used in photographic film and X-rays. Dilute silver nitrate solutions and other compounds are used as disinfectants and microbiocides, added to bandages and wound-dressings, catheters. Silver is similar in its physical and chemical properties to its two neighbours in group 11 of the periodic table, copper and gold. This distinctive electron configuration, with an electron in the highest occupied s subshell over a filled d subshell. Silver is a soft, ductile and malleable transition metal. Silver crystallizes in a cubic lattice with bulk coordination number 12. Unlike metals with incomplete d-shells, metallic bonds in silver are lacking a covalent character and are relatively weak and this observation explains the low hardness and high ductility of single crystals of silver. Silver has a brilliant white metallic luster that can take a polish. Protected silver has greater optical reflectivity than aluminium at all wavelengths longer than ~450 nm, at wavelengths shorter than 450 nm, silvers reflectivity is inferior to that of aluminium and drops to zero near 310 nm. The electrical conductivity of silver is the greatest of all metals, greater even than copper, during World War II in the US,13540 tons of silver were used in electromagnets for enriching uranium, mainly because of the wartime shortage of copper
7.
Electrometer
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An electrometer is an electrical instrument for measuring electric charge or electrical potential difference. There are many different types, ranging from historical handmade mechanical instruments to high-precision electronic devices, modern electrometers based on vacuum tube or solid-state technology can be used to make voltage and charge measurements with very low leakage currents, down to 1 femtoampere. A simpler but related instrument, the electroscope, works on similar principles, the gold-leaf electroscope was one of the first sensitive instruments used to indicate electric charge. It is still used for science demonstrations but has been superseded in most applications by electronic measuring instruments, the instrument consists of two thin leaves of gold foil suspended from an electrode. When the electrode is charged by induction or by contact, the leaves acquire similar electric charges and their separation is a direct indication of the net charge stored on them. On the glass opposite the leaves, pieces of tin foil may be pasted, the leaves may be enclosed in a glass envelope to protect them from drafts, and the envelope may be evacuated to minimize charge leakage. A further cause of charge leakage is ionizing radiation, so to prevent this and this principle has been used to detect ionizing radiation, as seen in the quartz fibre electrometer and Kearny fallout meter. This type of electroscope usually acts as an indicator and not a measuring device, the Braun electroscope replaced the gold-leaf electroscope for more accurate measurements. The instrument was developed in the 18th century by researchers, among them Abraham Bennet. While the term quadrant electrometer eventually referred to Kelvins version, this term was first used to describe a simpler device and it consists of an upright stem of wood, to which is affixed to a semicircle of ivory. From the center there hangs a light cork ball upon a pivot, when the instrument is placed upon a charged body, the stem participates and repels the cork ball. The amount of repulsion may be read off the graduated semicircle and this design uses torsion to give a measurement more sensitive than repulsion of gold leaves or cork-balls. It consists of a cylinder with a glass tube on top. In the axes of the tube is a thread, the lower end of this holds a bar of gum lac. Through another aperture on the cylinder, another gum lac rod with gilt balls may be introduced and this is called the carrier rod. If the lower ball of the rod is charged when it is entered into the aperture. An index and scale is attached to the top of the glass rod. The number of degrees twisted to bring the balls back together is in proportion of the amount of charge of the ball of the carrier rod
8.
Thomas Lewis (cardiologist)
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Sir Thomas Lewis, CBE, FRS, FRCP was a British cardiologist. He coined the term clinical science, Lewis was born in Taffs Well, Cardiff, Wales, the son of Henry Lewis, a mining engineer, and his wife Catherine Hannah. He was educated at home by his mother, apart from a year at Clifton College, which he left due to ill-health, and the final two years by a tutor. Already planning to become a doctor, at the age of sixteen he began a Bachelor of Science course at University College, Cardiff, in 1902 he entered University College Hospital in London to train as a doctor, graduating MBBS with the gold medal in 1905. The same year he was awarded a Doctor of Science degree from the University of Wales for his research work and he remained at UCH for the rest of his life, beginning as a house physician. From 1907 he also worked at the Royal Naval Hospital, Greenwich and the City of London Hospital, in 1911 he was appointed lecturer in cardiac pathology at UCH and in 1913 was promoted to assistant physician in clinical work. He was elected Fellow of the Royal College of Physicians in 1913, while still a house physician, Lewis began physiological research, carrying out fundamental research on the heart, the pulse and blood pressure. Accordingly, Lewis is considered the father of clinical cardiac electrophysiology, the first use of electrocardiography in clinical medicine was in 1908. In that year, Thomas Lewis and Arthur MacNalty employed electrocardiography to diagnose heart block, in 1909, with James MacKenzie, Lewis founded the journal Heart, A Journal for the Study of the Circulation, which he renamed Clinical Science in 1933. In 1913, he published the book Clinical Electrocardiography, the first treaty on electrocardiography, Lewis was elected a Fellow of the Royal Society in 1918. He was promoted to physician at UCH in 1919. During the First World War, Lewis worked at the Military Heart Hospital in Hampstead and was appointed to the first full-time clinical research post in Britain, at the Medical Research Committee. He directed a study of the known as soldiers heart and, having established it was not a cardiological problem. In 1918 he wrote the monograph The Soldiers Heart and the Effort Syndrome, after the war, he established the clinical research department at UCH and continued his work on cardiac arrhythmia. In 1925 he switched his focus from cardiography to vascular reactions of the skin and he was awarded the Royal Societys Royal Medal in 1927 for his researches on the vascular system, following upon his earlier work on the mammalian heart-beat. Next, he switched his focus to peripheral vascular disease, especially Raynauds disease and his 1932 book Diseases of the Heart became a standard medical text. In 1930, he founded the Medical Research Society and he was awarded the Royal Societys Copley Medal in 1941 for his clinical and experimental investigations upon the mammalian heart. He was only the second clinician to receive it, after Lord Lister in 1902 and he served as vice-president of the Royal Society from 1943 to 1945
9.
Willem Einthoven
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Willem Einthoven was a Dutch doctor and physiologist. He invented the first practical electrocardiogram in 1903 and received the Nobel Prize in Medicine in 1924 for it, Einthoven was born in Semarang on Java in the Dutch East Indies, the son of Louise Marie Mathilde Caroline and Jacob Einthoven. His father, a doctor, died when Einthoven was a child and his mother returned to the Netherlands with her children in 1870 and settled in Utrecht. His father was of Jewish and Dutch descent, and his mothers ancestry was Dutch, in 1885, Einthoven received a medical degree from the University of Utrecht. He became a professor at the University of Leiden in 1886, in 1902, he became member of the Royal Netherlands Academy of Arts and Sciences. He died in Leiden in the Netherlands and is buried in the graveyard of the Reformed Church at 6 Haarlemmerstraatweg in Oegstgeest, beginning in 1901, Einthoven completed a series of prototypes of a string galvanometer. This device used a thin filament of conductive wire passing between very strong magnets. When a current passed through the filament, the field created by the current would cause the string to move. A light shining on the string would cast a shadow on a roll of photographic paper. The original machine required water cooling for the powerful electromagnets, required 5 people to operate it and this device increased the sensitivity of the standard galvanometer so that the electrical activity of the heart could be measured despite the insulation of flesh and bones. Although later technological advances brought about better and more portable EKG devices and his assignment of the letters P, Q, R, S and T to the various deflections is still used. The term Einthovens triangle is named for him and it refers to the imaginary inverted equilateral triangle centered on the chest and the points being the standard leads on the arms and leg. After his development of the galvanometer, Einthoven went on to describe the electrocardiographic features of a number of cardiovascular disorders. Later in life, Einthoven turned his attention to the study of acoustics, in 1924, Einthoven was awarded the Nobel Prize in Medicine for inventing the first practical system of electrocardiography used in medical diagnosis. M. Luyendijk-Elshout, Einthoven, Willem, in Biografisch Woordenboek van Nederland, biography Willem Einthoven at the National Library of the Netherlands Moukabary, T. Willem Einthoven, Father of electrocardiography. Works by or about Willem Einthoven at Internet Archive
10.
Wayback Machine
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The Internet Archive launched the Wayback Machine in October 2001. It was set up by Brewster Kahle and Bruce Gilliat, and is maintained with content from Alexa Internet, the service enables users to see archived versions of web pages across time, which the archive calls a three dimensional index. Since 1996, the Wayback Machine has been archiving cached pages of websites onto its large cluster of Linux nodes and it revisits sites every few weeks or months and archives a new version. Sites can also be captured on the fly by visitors who enter the sites URL into a search box, the intent is to capture and archive content that otherwise would be lost whenever a site is changed or closed down. The overall vision of the machines creators is to archive the entire Internet, the name Wayback Machine was chosen as a reference to the WABAC machine, a time-traveling device used by the characters Mr. Peabody and Sherman in The Rocky and Bullwinkle Show, an animated cartoon. These crawlers also respect the robots exclusion standard for websites whose owners opt for them not to appear in search results or be cached, to overcome inconsistencies in partially cached websites, Archive-It. Information had been kept on digital tape for five years, with Kahle occasionally allowing researchers, when the archive reached its fifth anniversary, it was unveiled and opened to the public in a ceremony at the University of California, Berkeley. Snapshots usually become more than six months after they are archived or, in some cases, even later. The frequency of snapshots is variable, so not all tracked website updates are recorded, Sometimes there are intervals of several weeks or years between snapshots. After August 2008 sites had to be listed on the Open Directory in order to be included. As of 2009, the Wayback Machine contained approximately three petabytes of data and was growing at a rate of 100 terabytes each month, the growth rate reported in 2003 was 12 terabytes/month, the data is stored on PetaBox rack systems manufactured by Capricorn Technologies. In 2009, the Internet Archive migrated its customized storage architecture to Sun Open Storage, in 2011 a new, improved version of the Wayback Machine, with an updated interface and fresher index of archived content, was made available for public testing. The index driving the classic Wayback Machine only has a bit of material past 2008. In January 2013, the company announced a ground-breaking milestone of 240 billion URLs, in October 2013, the company announced the Save a Page feature which allows any Internet user to archive the contents of a URL. This became a threat of abuse by the service for hosting malicious binaries, as of December 2014, the Wayback Machine contained almost nine petabytes of data and was growing at a rate of about 20 terabytes each week. Between October 2013 and March 2015 the websites global Alexa rank changed from 162 to 208, in a 2009 case, Netbula, LLC v. Chordiant Software Inc. defendant Chordiant filed a motion to compel Netbula to disable the robots. Netbula objected to the motion on the ground that defendants were asking to alter Netbulas website, in an October 2004 case, Telewizja Polska USA, Inc. v. Echostar Satellite, No.02 C3293,65 Fed. 673, a litigant attempted to use the Wayback Machine archives as a source of admissible evidence, Telewizja Polska is the provider of TVP Polonia and EchoStar operates the Dish Network
11.
Einthoven's triangle
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Einthovens triangle is an imaginary formation of three limb leads in a triangle used in electrocardiography, formed by the two shoulders and the pubis. The shape forms an equilateral triangle with the heart at the center that produces zero potential when the voltages are summed. It is named after Willem Einthoven, who theorized its existence, Einthoven used these measuring points, by immersing the hands and foot in pails of salt water, as the contacts for his string galvanometer, the first practical ECG machine. Lead I – This axis goes from shoulder to shoulder, with the negative electrode placed on the right shoulder and this results in a 0 degree angle of orientation. I = L A − R A Lead II – This axis goes from the arm to the left leg, with the negative electrode on the shoulder. This results in a +60 degree angle of orientation, I I = L L − R A Lead III- This axis goes from the left shoulder to the right or left leg. This results in a degree angle of orientation. I I I = L L − L A Electrodes may be placed distally or proximally on the limb without affecting the recording. The leg electrode acts as a lead, and either the right or left leg can be used as a grounding lead without an effect on the ECG results. Each lead measures the field created by the heart during the depolarization and repolarization of myocytes. The electric field can be represented as a vector that changes continuously, though Einthovens triangle is no longer used in contemporary ECGs, Einthovens triangle can be helpful in the identification in incorrect placement of leads. Incorrect placement of leads can lead to error in the recording, if the arm electrodes are reversed, lead I changes polarity, causing lead II and lead III to switch. If the right arm electrode is reversed with the electrode, lead II also changes polarity, causing lead I to become lead III. Reversal of the arm and leg causes a change in polarity of lead III and switching of leads I
12.
Electric current
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An electric current is a flow of electric charge. In electric circuits this charge is carried by moving electrons in a wire. It can also be carried by ions in an electrolyte, or by both ions and electrons such as in an ionised gas. The SI unit for measuring a current is the ampere. Electric current is measured using a device called an ammeter, electric currents cause Joule heating, which creates light in incandescent light bulbs. They also create magnetic fields, which are used in motors, inductors and generators, the particles that carry the charge in an electric current are called charge carriers. In metals, one or more electrons from each atom are loosely bound to the atom and these conduction electrons are the charge carriers in metal conductors. The conventional symbol for current is I, which originates from the French phrase intensité de courant, current intensity is often referred to simply as current. The I symbol was used by André-Marie Ampère, after whom the unit of current is named, in formulating the eponymous Ampères force law. The notation travelled from France to Great Britain, where it became standard, in a conductive material, the moving charged particles which constitute the electric current are called charge carriers. In other materials, notably the semiconductors, the carriers can be positive or negative. Positive and negative charge carriers may even be present at the same time, a flow of positive charges gives the same electric current, and has the same effect in a circuit, as an equal flow of negative charges in the opposite direction. Since current can be the flow of positive or negative charges. The direction of current is arbitrarily defined as the same direction as positive charges flow. This is called the direction of current I. If the current flows in the direction, the variable I has a negative value. When analyzing electrical circuits, the direction of current through a specific circuit element is usually unknown. Consequently, the directions of currents are often assigned arbitrarily
