Posts by Jai Ganesh

Jai Ganesh · Dark Discussions at Cafe Infinity

2394) Richard Feynman

Gist:

Work

Following the establishment of the theory of relativity and quantum mechanics, an initial relativistic theory was formulated for the interaction between charged particles and electromagnetic fields. This needed to be reformulated, however. In 1948 in particular, Richard Feynman contributed to creating a new quantum electrodynamics by introducing Feynman diagrams: graphic representations of various interactions between different particles. These diagrams facilitate the calculation of interaction probabilities.

Summary

Richard Phillips Feynman (May 11, 1918 – February 15, 1988) was an American theoretical physicist. He is best known for his work in the path integral formulation of quantum mechanics, the theory of quantum electrodynamics, the physics of the superfluidity of supercooled liquid helium, and in particle physics, for which he proposed the parton model. For his contributions to the development of quantum electrodynamics, Feynman received the Nobel Prize in Physics in 1965 jointly with Julian Schwinger and Shin'ichirō Tomonaga.

Feynman developed a pictorial representation scheme for the mathematical expressions describing the behavior of subatomic particles, which later became known as Feynman diagrams and is widely used. During his lifetime, Feynman became one of the best-known scientists in the world. In a 1999 poll of 130 leading physicists worldwide by the British journal Physics World, he was ranked the seventh-greatest physicist of all time.

He assisted in the development of the atomic bomb during World War II and became known to the wider public in the 1980s as a member of the Rogers Commission, the panel that investigated the Space Shuttle Challenger disaster. Along with his work in theoretical physics, Feynman has been credited with having pioneered the field of quantum computing and introducing the concept of nanotechnology. He held the Richard C. Tolman professorship in theoretical physics at the California Institute of Technology.

Feynman was a keen popularizer of physics through both books and lectures, including a talk on top-down nanotechnology, "There's Plenty of Room at the Bottom" (1959) and the three-volumes of his undergraduate lectures, The Feynman Lectures on Physics (1961–1964). He delivered lectures for lay audiences, recorded in The Character of Physical Law (1965) and QED: The Strange Theory of Light and Matter (1985). Feynman also became known through his autobiographical books Surely You're Joking, Mr. Feynman! (1985) and What Do You Care What Other People Think? (1988), and books written about him such as Tuva or Bust! by Ralph Leighton and the biography Genius: The Life and Science of Richard Feynman by James Gleick.

Details

Richard Feynman (born May 11, 1918, New York, New York, U.S.—died February 15, 1988, Los Angeles, California) was an American theoretical physicist who was widely regarded as the most brilliant, influential, and iconoclastic figure in his field in the post-World War II era.

Feynman remade quantum electrodynamics—the theory of the interaction between light and matter—and thus altered the way science understands the nature of waves and particles. He was co-awarded the Nobel Prize for Physics in 1965 for this work, which tied together in an experimentally perfect package all the varied phenomena at work in light, radio, electricity, and magnetism. The other cowinners of the Nobel Prize, Julian S. Schwinger of the United States and Tomonaga Shin’ichirō of Japan, had independently created equivalent theories, but it was Feynman’s that proved the most original and far-reaching. The problem-solving tools that he invented—including pictorial representations of particle interactions known as Feynman diagrams—permeated many areas of theoretical physics in the second half of the 20th century.

Born in the Far Rockaway section of New York City, Feynman was the descendant of Russian and Polish Jews who had immigrated to the United States late in the 19th century. He studied physics at the Massachusetts Institute of Technology, where his undergraduate thesis (1939) proposed an original and enduring approach to calculating forces in molecules. Feynman received his doctorate at Princeton University in 1942. At Princeton, with his adviser, John Archibald Wheeler, he developed an approach to quantum mechanics governed by the principle of least action. This approach replaced the wave-oriented electromagnetic picture developed by James Clerk Maxwell with one based entirely on particle interactions mapped in space and time. In effect, Feynman’s method calculated the probabilities of all the possible paths a particle could take in going from one point to another.

During World War II Feynman was recruited to serve as a staff member of the U.S. atomic bomb project at Princeton University (1941–42) and then at the new secret laboratory at Los Alamos, New Mexico (1943–45). At Los Alamos he became the youngest group leader in the theoretical division of the Manhattan Project. With the head of that division, Hans Bethe, he devised the formula for predicting the energy yield of a nuclear explosive. Feynman also took charge of the project’s primitive computing effort, using a hybrid of new calculating machines and human workers to try to process the vast amounts of numerical computation required by the project. He observed the first detonation of an atomic bomb on July 16, 1945, near Alamogordo, New Mexico, and, though his initial reaction was euphoric, he later felt anxiety about the force he and his colleagues had helped unleash on the world.

At war’s end Feynman became an associate professor at Cornell University (1945–50) and returned to studying the fundamental issues of quantum electrodynamics. In the years that followed, his vision of particle interaction kept returning to the forefront of physics as scientists explored esoteric new domains at the subatomic level. In 1950 he became professor of theoretical physics at the California Institute of Technology (Caltech), where he remained the rest of his career.

Five particular achievements of Feynman stand out as crucial to the development of modern physics. First, and most important, is his work in correcting the inaccuracies of earlier formulations of quantum electrodynamics, the theory that explains the interactions between electromagnetic radiation (photons) and charged subatomic particles such as electrons and positrons (antielectrons). By 1948 Feynman completed this reconstruction of a large part of quantum mechanics and electrodynamics and resolved the meaningless results that the old quantum electrodynamic theory sometimes produced. Second, he introduced simple diagrams, now called Feynman diagrams, that are easily visualized graphic analogues of the complicated mathematical expressions needed to describe the behaviour of systems of interacting particles. This work greatly simplified some of the calculations used to observe and predict such interactions.

In the early 1950s Feynman provided a quantum-mechanical explanation for the Soviet physicist Lev D. Landau’s theory of superfluidity—i.e., the strange, frictionless behaviour of liquid helium at temperatures near absolute zero. In 1958 he and the American physicist Murray Gell-Mann devised a theory that accounted for most of the phenomena associated with the weak force, which is the force at work in radioactive decay. Their theory, which turns on the asymmetrical “handedness” of particle spin, proved particularly fruitful in modern particle physics. And finally, in 1968, while working with experimenters at the Stanford Linear Accelerator on the scattering of high-energy electrons by protons, Feynman invented a theory of “partons,” or hypothetical hard particles inside the nucleus of the atom, that helped lead to the modern understanding of quarks.

Feynman’s stature among physicists transcended the sum of even his sizable contributions to the field. His bold and colourful personality, unencumbered by false dignity or notions of excessive self-importance, seemed to announce: “Here is an unconventional mind.” He was a master calculator who could create a dramatic impression in a group of scientists by slashing through a difficult numerical problem. His purely intellectual reputation became a part of the scenery of modern science. Feynman diagrams, Feynman integrals, and Feynman rules joined Feynman stories in the everyday conversation of physicists. They would say of a promising young colleague, “He’s no Feynman, but….” His fellow physicists envied his flashes of inspiration and admired him for other qualities as well: a faith in nature’s simple truths, a skepticism about official wisdom, and an impatience with mediocrity.

Feynman’s lectures at Caltech evolved into the books Quantum Electrodynamics (1961) and The Theory of Fundamental Processes (1961). In 1961 he began reorganizing and teaching the introductory physics course at Caltech; the result, published as The Feynman Lectures on Physics, 3 vol. (1963–65), became a classic textbook. Feynman’s views on quantum mechanics, scientific method, the relations between science and religion, and the role of beauty and uncertainty in scientific knowledge are expressed in two models of science writing, again distilled from lectures: The Character of Physical Law (1965) and QED: The Strange Theory of Light and Matter (1985).

When Feynman died in 1988 after a long struggle with cancer, his reputation was still mainly confined to the scientific community; his was not a household name. Many Americans had seen him for the first time when, already ill, he served on the presidential commission that investigated the 1986 explosion of the space shuttle Challenger. He conducted a dramatic demonstration at a televised hearing, confronting an evasive NASA witness by dunking a piece of rubber seal in a glass of ice water to show how predictable the failure of the booster rocket’s rubber seal might have been on the freezing morning of Challenger’s launch. He added his own appendix to the commission’s report on the disaster, emphasizing the space agency’s failures of risk management.

He achieved a growing popular fame after his death, in part because of two autobiographical collections of anecdotes published in the years around his passing, “Surely You’re Joking, Mr. Feynman!”: Adventures of a Curious Character (1985) and “What Do You Care What Other People Think?”: Further Adventures of a Curious Character (1988), which irritated some of his colleagues by emphasizing his bongo playing and his patronage of a topless bar more than his technical accomplishments. Other popular books appeared posthumously, including Six Easy Pieces: Essentials of Physics Explained by Its Most Brilliant Teacher (1994) and Six Not-So-Easy Pieces: Einstein’s Relativity, Symmetry, and Space-Time (1997), and his life was celebrated in an opera (Feynman [2005], by Jack Vees), a graphic novel (Feynman [2011], by Jim Ottaviani and Leland Myrick), and a play (QED [2001], by Peter Parnell), the latter of which was commissioned by and starred Alan Alda.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#10667. What does the term in Geography Cliffed coast mean?

#10668. What does the term in Geography Climate mean?

Jai Ganesh · Jai Ganesh's Puzzles

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#5463. What does the noun bottleful mean?

#5464. What does the adjective bouncy mean?

Jai Ganesh · This is Cool

2446) Constellation

Gist

A constellation is a group of stars that appear to form a pattern or picture in the night sky, named after animals, mythological figures, or objects. These patterns are created by drawing lines between stars from our perspective on Earth, though the stars themselves are often not physically close to each other and are simply in the same direction in the sky. There are 88 officially recognized constellations that astronomers use to map the sky and locate other celestial objects.

A constellation is a group of stars that forms a recognizable pattern in the night sky, often named after a mythological figure, animal, or object. These patterns are created by stars that may be very far apart in reality but appear to be close together from Earth's perspective. There are 88 official constellations recognized by the International Astronomical Union.

Summary

A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object.

The first constellations were likely defined in prehistory. People used them to relate stories of their beliefs, experiences, creation, and mythology. Different cultures and countries invented their own constellations, some of which lasted into the early 20th century before today's constellations were internationally recognized. The recognition of constellations has changed significantly over time. Many changed in size or shape. Some became popular, only to drop into obscurity. Some were limited to a single culture or nation. Naming constellations also helped astronomers and navigators identify stars more easily.

Twelve (or thirteen) ancient constellations belong to the zodiac (straddling the ecliptic, which the Sun, Moon, and planets all traverse). The origins of the zodiac remain historically uncertain; its astrological divisions became prominent c. 400 BC in Babylonian or Chaldean astronomy. Constellations appear in Western culture via Greece and are mentioned in the works of Hesiod, Eudoxus and Aratus. The traditional 48 constellations, consisting of the zodiac and 36 more (now 38, following the division of Argo Navis into three constellations) are listed by Ptolemy, a Greco-Roman astronomer from Alexandria, Egypt, in his Almagest. The formation of constellations was the subject of extensive mythology, most notably in the Metamorphoses of the Latin poet Ovid. Constellations in the far southern sky were added from the 15th century until the mid-18th century when European explorers began traveling to the Southern Hemisphere. Due to Roman and European transmission, each constellation has a Latin name.

In 1922, the International Astronomical Union (IAU) formally accepted the modern list of 88 constellations, and in 1928 adopted official constellation boundaries that together cover the entire celestial sphere. Any given point in a celestial coordinate system lies in one of the modern constellations. Some astronomical naming systems include the constellation where a given celestial object is found to convey its approximate location in the sky. The Flamsteed designation of a star, for example, consists of a number and the genitive form of the constellation's name.

Other star patterns or groups called asterisms are not constellations under the formal definition, but are also used by observers to navigate the night sky. Asterisms may be several stars within a constellation, or they may share stars with more than one constellation. Examples of asterisms include the teapot within the constellation Sagittarius, or the Big Dipper in the constellation of Ursa Major.

Details

A constellation, in astronomy, is any of certain groupings of stars that were imagined—at least by those who named them—to form conspicuous configurations of objects or creatures in the sky. Constellations are useful in assisting astronomers and navigators to locate certain stars.

From the earliest times the star groups known as constellations, the smaller groups (parts of constellations) known as asterisms, and also individual stars have received names connoting some meteorological phenomena or symbolizing religious or mythological beliefs. At one time it was held that the constellation names and myths were of Greek origin; this view has now been disproved, and an examination of the Hellenic myths associated with the stars and star groups in the light of the records revealed by the deciphering of Mesopotamian cuneiforms leads to the conclusion that in many, if not all, cases the Greek myth has a Mesopotamian parallel.

The earliest Greek work that purported to treat the constellations as constellations, of which there is certain knowledge, is the Phainomena of Eudoxus of Cnidus (c. 395–337 bce). The original is lost, but a versification by Aratus (c. 315–245 bce), a poet at the court of Antigonus II Gonatas, king of Macedonia, is extant, as is a commentary by Hipparchus (mid-2nd century bce).

Three hundred years after Hipparchus, the Alexandrian astronomer Ptolemy (100–170 ce) adopted a very similar scheme in his Uranometria, which appears in the seventh and eighth books of his Almagest, the catalog being styled the “accepted version.” The names and orientation of the 48 constellations therein adopted are, with but few exceptions, identical with those used at the present time.

The majority of the remaining 40 constellations that are now accepted were added by European astronomers in the 17th and 18th centuries. In the 20th century the delineation of precise boundaries for all the 88 constellations was undertaken by a committee of the International Astronomical Union. By 1930 it was possible to assign any star to a constellation.

Additional Information

A constellation is a grouping of stars which form a pattern in the sky that is traditionally named after its apparent form or identified with a mythological figure. Modern use of constellations includes identification of general locations for stars and galaxies (i.e. the Andromeda Galaxy). As for which constellation is the most popular, I think that depends upon who you are asking. If you mean which constellation is the one that most people know about, I think that Andromeda might be a good answer, given its famous inhabitant, the Andromeda Galaxy (otherwise known as Messier 31). Regarding how constellations are formed, the fact is that they are not formed by any physical process, nor do the stars that make up a constellation generally have any association with each other. Constellations are usually just chance alignments of stars which appear to be near each other from our vantage point. Finally, yes there is at least one famous red giant star in a constellation. The constellation Taurus contains the red giant star Aldebaran.

Jai Ganesh · This is Cool

Intergalactic space

Gist

Intergalactic space is the vast, extremely low-density region between galaxies. While it is nearly a vacuum, it contains the intergalactic medium (IGM), a tenuous, hot plasma of ionized hydrogen, along with occasional stars and dark matter, all organized in a cosmic filamentary structure. This gas, though sparse, makes up most of the matter in the universe, and is heated enough by events like galactic mergers and active galactic nuclei to be detectable through the X-rays and UV light it emits or absorbs.

Intergalactic space is the vast expanse between galaxies, which is extremely low in density and close to a perfect vacuum. While it may seem empty, it contains a very thin gas called the intergalactic medium (IGM), consisting mostly of hot, ionized hydrogen, along with heavier elements and a small number of stray stars. This matter is hot enough for electrons to be stripped from the hydrogen atoms.

Summary

The space between stars is known as interstellar space, and so the space between galaxies is called intergalactic space. These are the vast empty spaces that sit between galaxies. For example, if you wanted to travel from the Milky Way to the Andromeda galaxy, you would need to cross 2.5 million light-years of intergalactic space.

Intergalactic space is as close as you can get to an absolute vacuum. There's very little dust and debris, and scientists have calculated that there's probably only one hydrogen atom per cubic meter. The density of material is higher near galaxies, and lower in the midpoint between galaxies.

Galaxies are connected by a rarefied plasma that is thought to posses a cosmic filamentary structure, which is slightly denser than the average density of the Universe. This material is known as the intergalactic medium, and it's mostly made up of ionized hydrogen. Astronomers think that the intergalactic medium is about 10 to 100 times denser than the average density of the Universe.

This intergalactic medium can actually be seen by our telescopes here on Earth because it's heated up to tens of thousands, or even millions of degrees. This is hot enough for electrons to escape from hydrogen nuclei during collisions. We can detect the energy released from these collisions in the X-ray spectrum. NASA's Chandra X-Ray Observatory - a space telescope designed to search for X-rays - has detected vast clouds of hot intergalactic medium in regions where galaxies are colliding together in clusters.

Details

Intergalactic space is the physical space between galaxies. Generally free of dust and debris, intergalactic space is very close to a vacuum. The average density of the Universe is less than one atom per cubic meter. The density of the Universe, however, is clearly not uniform; it ranges from relatively high density in galaxies (including very high density in structures within galaxies, such as planets, stars, and black holes) to extremely rarefied conditions in vast voids that have lower density than the Universe's average.

Surrounding and stretching between galaxies, there is a rarefied gas that is thought to possess a cosmic filamentary structure and that is slightly denser than the average density in the Universe. This material is called the intergalactic medium (IGM) and is mostly ionized hydrogen (i.e. a plasma) consisting of equal numbers of electrons and protons. The IGM is thought to exist at a density of 10 to 100 times the average density of the Universe (10 to 100 hydrogen atoms per cubic meter). It reaches densities as high as 1000 times the average density of the Universe in rich clusters of galaxies.

The reason the IGM is thought to be mostly ionized gas is that its temperature is thought to be quite high by terrestrial standards (though some parts of it are only "warm" by astrophysical standards). As gas falls into the Intergalactic Medium from the voids, it heats up to temperatures of {10}^{5} to {10}^{7} K, which is too hot for hydrogen nuclei to retain their electrons. At these temperatures, it is called the Warm-Hot Intergalactic Medium (WHIM). Computer simulations indicate that on the order of half the atomic matter in the universe might exist in this warm-hot, rarefied state. When gas falls from the filamentary structures of the WHIM into the galaxy clusters at the intersections of the cosmic filaments, it can heat up even more, reaching temperatures of {10}^{8} K or more.

Additional Information

The vast voids between galaxies can stretch millions of light-years across and may appear empty. But these spaces actually contain more matter than the galaxies themselves.

"If you took a cubic meter, there would be less than one atom in it," Michael Shull, an astronomer at the University of Colorado Boulder, told Live Science. "But when you add it all up, it's somewhere between 50 and 80% of all the ordinary matter out there."

So, where did all this matter come from? And what's it up to?

The matter between galaxies — often called the intergalactic medium, or IGM for short — is mostly hot, ionized hydrogen (hydrogen that has lost its electron) with bits of heavier elements such as carbon, oxygen and silicon thrown in. While these elements typically don't glow bright enough to be seen directly, scientists know they're there because of the signature they leave on light that passes by.

In the 1960s, astronomers first discovered quasars — incredibly bright and active galaxies in the distant universe — and shortly thereafter, they noticed that the light from the quasars had missing pieces. These pieces had been absorbed by something in between the quasar and the astronomers' telescopes — this was the gas of the IGM. In the decades since, astronomers have discovered vast webs and filaments of gas and heavy elements that collectively contain more matter than all the galaxies combined. Some of this gas was likely left over from the Big Bang, but the heavier elements hint that some of it comes from old stardust, spewed out by galaxies.

While the most-remote regions of the IGM will be eternally isolated from neighboring galaxies as the universe expands, more "suburban" regions play an important role in galaxy life. The IGM under the influence of a galaxy's gravitational pull slowly accumulates onto the galaxy at a rate of about one solar mass (equal to the mass of the sun) per year, which is about the rate of star formation in the disk of the Milky Way.

"IGM is the gas that feeds star formation in galaxies," Shull said. "If we didn't still have gas falling in, being pulled in by gravity, star formation would slowly grind to a halt as the gas [in the galaxy] gets used up."

To probe the IGM, astronomers also have started looking at fast radio bursts that come from distant galaxies. Using both this technique and by examining quasar light, astronomers continue to study the characteristics of the IGM to determine its varying temperatures and densities.

"By measuring the temperature of the gas, you can get a clue as to its origins," Shull said. "It allows us to know how it got heated and how it got there."

Although gas is pervasive between galaxies, it isn't the only thing out there; astronomers have also found stars. Sometimes called intergalactic or rogue stars, these stars are thought to have been flung from their birth galaxies by black holes or collisions with other galaxies.

In fact, stars sailing the void might be fairly common. A 2012 study published in The Astrophysical Journal reported more than 650 of these stars at the edge of the Milky Way, and by some estimates, there could be trillions out there.

Jai Ganesh · Dark Discussions at Cafe Infinity

Cold Quotes - I

1. Every man has his secret sorrows which the world knows not; and often times we call a man cold when he is only sad. - Henry Wadsworth Longfellow

2. Every gun that is made, every warship launched, every rocket fired, signifies in the final sense a theft from those who hunger and are not fed, those who are cold and are not clothed. - Dwight D. Eisenhower

3. If... many influential people have failed to understand, or have just forgotten, what we were up against in the Cold War and how we overcame it, they are not going to be capable of securing, let alone enlarging, the gains that liberty has made. - Margaret Thatcher

4. My words in her mind: cold polished stones sinking through a quagmire. - James Joyce

5. I come from - I came from Wales, and it's a strong, butch society. We were in the war and all that. People didn't waste time feeling sorry for themselves. You had to get on with it. So my credo is get on with it. I don't waste time being soft. I'm not cold, but I don't like being, wasting my time with - life's too short. - Anthony Hopkins

6. A career is wonderful, but you can't curl up with it on a cold night. - Marilyn Monroe

7. I don't know why you use a fancy French word like detente when there's a good English phrase for it - cold war. - Golda Meir

8. Women tend to be more intuitive, or to admit to being intuitive, and maybe the hard science approach isn't so attractive. The way that science is taught is very cold. I would never have become a scientist if I had been taught like that. - Jane Goodall.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#2526. What does the medical term Motor control mean?

Jai Ganesh · Jokes

Q: What did the butter say to the bread?
A: I'm on a roll!
* * *
Q: What do you call it when a mother and child bake bread together?
A: A labor of loaf.
* * *
Q: Why does everyone need bread and water?
A: Loaf makes the world go round.
* * *
Two Biscuits walking across Union Street, One gets hit by a bus.
The other one says, Oh Crumbs!
* * *
You know, when stuck in a jam, you're the bun I want to be with!
* * *

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#9805.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

6300.

.

Jai Ganesh · Exercises

Hi,

2651.

Jai Ganesh · Dark Discussions at Cafe Infinity

2393) Julian Schwinger

Gist:

Work

Following the establishment of the theory of relativity and quantum mechanics, an initial relativistic theory was formulated for the interaction between charged particles and electromagnetic fields. However, partly because the electron’s magnetic moment proved to be somewhat larger than expected, the theory had to be reformulated. Julian Schwinger solved this problem in 1948 through “renormalization” and thereby contributed to a new quantum electrodynamics.

Summary

Julian Seymour Schwinger (born Feb. 12, 1918, New York, N.Y., U.S.—died July 16, 1994, Los Angeles, Calif.) was an American physicist and joint winner, with Richard P. Feynman and Tomonaga Shin’ichirō, of the Nobel Prize for Physics in 1965 for introducing new ideas and methods into quantum electrodynamics.

Schwinger was a child prodigy, publishing his first physics paper at age 16. He earned a bachelor’s degree (1937) and a doctorate (1939) from Columbia University in New York City, before engaging in postdoctoral studies at the University of California at Berkeley with physicist J. Robert Oppenheimer. Schwinger left Berkeley in the summer of 1941 to accept an instructorship at Purdue University, West Lafayette, Ind., and in 1943 he joined the Radiation Laboratory at the Massachusetts Institute of Technology, where many scientists had been assembled to help with wartime research on radar. In the fall of 1945 Schwinger accepted an appointment at Harvard University and in 1947 became one of the youngest full professors in the school’s history. From 1972 until his death, Schwinger was a professor in the physics department at the University of California at Los Angeles.

Schwinger was one of the participants at the meeting held in June 1947 on Shelter Island, Long Island, N.Y., at which reliable experimental data were presented that contradicted the predictions of the English theoretical physicist P.A.M. Dirac’s relativistic quantum theory of the electron. In particular, experimental data contradicted Dirac’s prediction that certain hydrogen electron stationary states were degenerate (i.e., had the same energy as certain other states) as well as Dirac’s prediction for the value of the magnetic moment of the electron. Schwinger made a quantum electrodynamical calculation that made use of the notions of mass and charge renormalization, which brought agreement between theory and experimental data. This was a crucial breakthrough that initiated a new era in quantum field theory. Richard Feynman and Tomonaga Shin’ichirō independently had carried out similar calculations, and in 1965 the three of them shared the Nobel Prize. Their work created a new and very successful quantum mechanical description of the interaction between electrically charged entities and the electromagnetic field that conformed with the principles of Albert Einstein’s special theory of relativity.

Schwinger’s work extended to almost every frontier of modern theoretical physics. He had a profound influence on physics both directly and through being the academic adviser for more than 70 doctoral students and more than 20 postdoctoral fellows, many of whom became the outstanding theorists of their generation.

Details

Julian Seymour Schwinger (February 12, 1918 – July 16, 1994) was a Nobel Prize-winning American theoretical physicist. He is best known for his work on quantum electrodynamics (QED), in particular for developing a relativistically invariant perturbation theory, and for renormalizing QED to one loop order. Schwinger was a physics professor at several universities.

Schwinger is recognized as an important physicist, responsible for much of modern quantum field theory, including a variational approach, and the equations of motion for quantum fields. He developed the first electroweak model, and the first example of confinement in 1+1 dimensions. He is responsible for the theory of multiple neutrinos, Schwinger terms, and the theory of the spin-3/2 field.

Biography:

Early life and career

Julian Seymour Schwinger was born in New York City, to Ashkenazi Jewish parents, Belle (née Rosenfeld) and Benjamin Schwinger, a garment manufacturer, who had emigrated from Poland to the United States. Both his father and his mother's parents were prosperous clothing manufacturers, although the family business declined after the Wall Street Crash of 1929. The family followed the Orthodox Jewish tradition. Julian's older brother Harold Schwinger was born in 1911, seven years before Julian who was born in 1918.

Schwinger was a precocious student. He attended the Townsend Harris High School from 1932 to 1934, a highly regarded high school for gifted students at the time. During high school, Julian had already started reading Physical Review papers by authors such as Paul Dirac in the library of the City College of New York, in whose campus Townsend Harris was then located.

In the fall of 1934, Schwinger entered the City College of New York as an undergraduate. CCNY automatically accepted all Townsend Harris graduates at the time, and both institutions offered free tuition. Due to his intense interest in physics and mathematics, Julian performed very well in those subjects despite often skipping classes and learning directly from books. On the other hand, his lack of interest for other topics such as English led to academic conflicts with teachers of those subjects.

After Julian had joined CCNY, his brother Harold, who had previously graduated from CCNY, asked his ex-classmate Lloyd Motz to "get to know [Julian]". Lloyd was a CCNY physics instructor and Ph.D. candidate at Columbia University at the time. Lloyd made the acquaintance, and soon recognized Julian's talent. Noticing Schwinger's academic problems, Lloyd decided to ask Isidor Isaac Rabi who he knew at Columbia for help. Rabi also immediately recognized Schwinger's capabilities on their first meeting, and then made arrangements to award Schwinger with a scholarship to study at Columbia. At first Julian's bad grades in some subjects at CCNY prevented the scholarship award. But Rabi persisted and showed an unpublished paper on quantum electrodynamics written by Schwinger to Hans Bethe, who happened to be passing by New York. Bethe's approval of the paper and his reputation in that domain were then enough to secure the scholarship for Julian, who then transferred to Columbia. His academic situation at Columbia was much better than at CCNY. He was accepted into the Phi Beta Kappa society and received his B.A. in 1936.

During Schwinger's graduate studies, Rabi felt that it would be good for Julian to visit other institutions around the country, and Julian was awarded a travelling fellowship for the year 37/38 which he spent at working with Gregory Breit and Eugene Wigner. During this time, Schwinger, who previously had already had the habit of working until late at night, went further and made the day/night switch more complete, working at night and sleeping during the day, a habit he would carry throughout his career. Schwinger later commented that this switch was in part a way to retain greater intellectual independence and avoid being "dominated" by Breit and Wigner by simply reducing the duration of contact with them by working different hours.

Schwinger obtained his PhD overseen by Rabi in 1939 at the age of 21.

During the fall of 1939 Schwinger started working at the University of California, Berkeley under J. Robert Oppenheimer, where he stayed for two years as an NRC fellow.

Career

After having worked with Oppenheimer, Schwinger's first regular academic appointment was at Purdue University in 1941. While on leave from Purdue, he worked at the MIT Radiation Laboratory instead of at the Los Alamos National Laboratory during World War II. He provided theoretical support for the development of radar. After the war, Schwinger left Purdue for Harvard University, where he taught from 1945 to 1974. In 1966 he became the Eugene Higgins professor of physics at Harvard.

Schwinger developed an affinity for Green's functions from his radar work, and he used these methods to formulate quantum field theory in terms of local Green's functions in a relativistically invariant way. This allowed him to calculate unambiguously the first corrections to the electron magnetic moment in quantum electrodynamics. Earlier non-covariant work had arrived at infinite answers, but the extra symmetry in his methods allowed Schwinger to isolate the correct finite corrections.

Schwinger developed renormalization, formulating quantum electrodynamics unambiguously to one-loop order.

In the same era, he introduced non-perturbative methods into quantum field theory, by calculating the rate at which electron–positron pairs are created by tunneling in an electric field, a process now known as the "Schwinger effect." This effect could not be seen in any finite order in perturbation theory.

Schwinger's foundational work on quantum field theory constructed the modern framework of field correlation functions and their equations of motion. His approach started with a quantum action and allowed bosons and fermions to be treated equally for the first time, using a differential form of Grassman integration. He gave elegant proofs for the spin-statistics theorem and the CPT theorem, and noted that the field algebra led to anomalous Schwinger terms in various classical identities, because of short distance singularities. These were foundational results in field theory, instrumental for the proper understanding of anomalies.

In other notable early work, Rarita and Schwinger formulated the abstract Pauli and Fierz theory of the spin-3/2 field in a concrete form, as a vector of Dirac spinors, Rarita–Schwinger equation. In order for the spin-3/2 field to interact consistently, some form of supersymmetry is required, and Schwinger later regretted that he had not followed up on this work far enough to discover supersymmetry.

Schwinger discovered that neutrinos come in multiple varieties, one for the electron and one for the muon. Nowadays there are known to be three light neutrinos; the third is the partner of the tau lepton.

In the 1960s, Schwinger formulated and analyzed what is now known as the Schwinger model, quantum electrodynamics in one space and one time dimension, the first example of a confining theory.

Having supervised 73 doctoral dissertations, Schwinger is known as one of the most prolific graduate advisors in physics. Four of his students won Nobel prizes: Roy Glauber, Benjamin Roy Mottelson, Sheldon Glashow and Walter Kohn (in chemistry).

Schwinger had a mixed relationship with his colleagues, because he always pursued independent research, different from mainstream fashion. In particular, Schwinger developed the source theory, a phenomenological theory for the physics of elementary particles, which is a predecessor of the modern effective field theory. It treats quantum fields as long-distance phenomena and uses auxiliary 'sources' that resemble currents in classical field theories. The source theory is a mathematically consistent field theory with clearly derived phenomenological results. The criticisms by his Harvard colleagues led Schwinger to leave the faculty in 1972 for UCLA. It is a story widely told that Steven Weinberg, who inherited Schwinger's paneled office in Lyman Laboratory, there found a pair of old shoes, with the implied message, "think you can fill these?". Based on Schwinger's source theory, Weinberg set the underpinnings of the effective field theory, that is more appreciated among physicists. In spite of the shoes incident, Weinberg gave the credit to Schwinger for the inspiration.

At UCLA, and for the rest of his career, Schwinger continued to develop the source theory and its various applications. After 1989 Schwinger took a keen interest in the non-mainstream research of cold fusion. He wrote eight theory papers about it. He resigned from the American Physical Society after their refusal to publish his papers. He felt that cold fusion research was being suppressed and academic freedom violated. He wrote, "The pressure for conformity is enormous. I have experienced it in editors' rejection of submitted papers, based on venomous criticism of anonymous referees. The replacement of impartial reviewing by censorship will be the death of science."

In his last publications, Schwinger proposed a theory of sonoluminescence as a long-distance quantum radiative phenomenon associated not with atoms, but with fast-moving surfaces in the collapsing bubble, where there are discontinuities in the dielectric constant. The mechanism of sonoluminescence now supported by experiments focuses on superheated gas inside the bubble as the source of the light.

Schwinger was jointly awarded the Nobel Prize in Physics in 1965 for his work on quantum electrodynamics (QED), along with Richard Feynman and Shin'ichirō Tomonaga. Schwinger's awards and honors were numerous even before his Nobel win. They include the first Albert Einstein Award (1951), the U.S. National Medal of Science (1964), honorary D.Sc. degrees from Purdue University (1961) and Harvard University (1962), and the Nature of Light Award of the U.S. National Academy of Sciences (1949). In 1987, Schwinger received the Golden Plate Award of the American Academy of Achievement.

Jai Ganesh · This is Cool

2445) Nitric Oxide

Gist

Nitric oxide (NO) is a colorless gas with the chemical formula NO, which acts as an important signaling molecule in the human body and is also an air pollutant. In the body, it relaxes blood vessels to improve blood flow, aids in neurotransmission, and plays a role in immune responses and other cellular processes. Industrially, it is a source of pollution and can be produced by high temperatures or chemical reactions.

Nitric oxide is used for medical purposes, such as treating respiratory failure in newborns and helping with erectile dysfunction, and is also used in industrial applications. In the body, it's crucial for vasodilation (widening blood vessels), which helps regulate blood flow, blood pressure, and other physiological processes.

Summary

Nitric oxide (nitrogen oxide, nitrogen monooxide, or nitrogen monoxide) is a colorless gas with the formula NO. It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its chemical formula (•N=O or •NO). Nitric oxide is also a heteronuclear diatomic molecule, a class of molecules whose study spawned early modern theories of chemical bonding.

An important intermediate in industrial chemistry, nitric oxide forms in combustion systems and can be generated by lightning in thunderstorms. In mammals, including humans, nitric oxide is a signaling molecule in many physiological and pathological processes. It was proclaimed the "Molecule of the Year" in 1992. The 1998 Nobel Prize in Physiology or Medicine was awarded for discovering nitric oxide's role as a cardiovascular signalling molecule. Its impact extends beyond biology, with applications in medicine, such as the development of sildenafil (Viagra), and in industry, including semiconductor manufacturing.

Nitric oxide should not be confused with nitrogen dioxide (NO2), a brown gas and major air pollutant, or with nitrous oxide (N2O), an anesthetic gas.

Details

Nitric oxide (NO) is a colorless, odorless gas molecule that plays a crucial role in various physiological processes within the human body. It was first discovered in the 18th century, but its significance in biological systems wasn’t fully understood until the late 20th century.

In the body, NO acts as a signaling molecule, participating in the regulation of numerous functions, including vasodilation (the widening of blood vessels), neurotransmission, immune response, and the regulation of inflammation. One of its most notable roles is in the regulation of blood pressure, where it helps to relax and widen blood vessels, thereby improving blood flow.

What is nitric oxide?

Nitric oxide (NO) is a molecule composed of one nitrogen atom and one oxygen atom. It is a colorless and odorless gas at room temperature. It is a crucial signaling molecule in the body involved in various physiological processes.

One of its primary roles is as a vasodilator, meaning it relaxes and widens blood vessels, leading to increased blood flow. This function is vital for regulating blood pressure and delivering oxygen and nutrients to tissues throughout the body.

Nitric oxide also acts as a neurotransmitter. Additionally, it plays a role in the immune system, helping to combat pathogens and regulate inflammation.

Synthesis

NO is synthesized in the body through a process involving the conversion of the amino acid arginine into nitric oxide and citrulline. This synthesis is catalyzed by a family of enzymes called nitric oxide synthases (NOS).

There are three isoforms of nitric oxide synthase:

* Endothelial NOS (eNOS): Found primarily in endothelial cells lining blood vessels, eNOS produces nitric oxide in response to various physiological stimuli, such as shear stress and certain hormones.
* Neuronal NOS (nNOS or NOS1): Present in neurons of the central and peripheral nervous systems, nNOS is involved in neurotransmission and neuromodulation, synthesizing nitric oxide in response to calcium influx during neuronal activation.
* Inducible NOS (iNOS or NOS2): Induced in response to inflammatory stimuli, such as cytokines and bacterial endotoxins, iNOS produces large amounts of NO for immune defense mechanisms and inflammation regulation.

The synthesis of nitric oxide by nitric oxide synthases involves several steps:

* L-arginine binding: The enzyme binds the substrate L-arginine, along with other cofactors such as tetrahydrobiopterin (BH4) and oxygen (O2).
* Conversion to L-citrulline and nitric oxide: Through a series of enzymatic reactions involving the cofactors and molecular oxygen, nitric oxide synthase catalyzes the conversion of L-arginine into nitric oxide and L-citrulline.
* Release of nitric oxide: Once synthesized, NO is released from the enzyme and diffuses freely across cell membranes to exert its physiological effects.

Functions

NO is a versatile molecule with numerous functions in the human body. Some of its key functions include:

* Vasodilation: NO acts as a potent vasodilator, meaning it relaxes and widens blood vessels. This helps to improve blood flow and regulate blood pressure.
* Neurotransmission: Serves as a signaling molecule in the nervous system, facilitating communication between nerve cells (neurons). It plays a role in neurotransmission, synaptic plasticity, and other neurological processes.
* Immune response: It is involved in the immune system’s defense against pathogens. It helps to regulate inflammation and can be produced by immune cells to kill invading bacteria, viruses, and parasites.
* Regulation of platelet function: Helps to regulate platelet aggregation, which is important for preventing excessive blood clotting and maintaining cardiovascular health.
* Smooth muscle relaxation: It relaxes smooth muscles found in various organs and tissues, including the gastrointestinal tract, airways, and urinary bladder. This relaxation helps to regulate processes such as digestion, breathing, and urination.
* Angiogenesis: It plays a role in angiogenesis, the formation of new blood vessels from existing ones. This process is important for tissue repair, wound healing, and the growth of tumors.
* Penile erection: It is a key mediator of penile erection. It stimulates the relaxation of smooth muscle cells in the erectile tissue of the male reproductive organ, leading to increased blood flow and the attainment of an erection.
* Regulation of mitochondrial function: It can modulate mitochondrial respiration and energy production within cells, influencing cellular metabolism and overall energy balance.
* Regulation of gene expression: It can also act as a signaling molecule within cells to regulate gene expression and various cellular processes, including cell proliferation, differentiation, and apoptosis (programmed cell death).

NO rich foods

There are several foods that are naturally rich in nitrates, which can be converted into NO in the body. These foods include:

* Leafy greens: Spinach, kale, arugula, and other leafy greens are high in nitrates.
* Celery: Celery is another vegetable that contains nitrates and can contribute to nitric oxide production.
* Garlic: Garlic contains compounds that can stimulate nitric oxide production and promote cardiovascular health.
* Citrus fruits: Oranges, lemons, and other citrus fruits are rich in vitamin C, which can help support nitric oxide production.
* Pomegranate: Pomegranate juice and seeds contain antioxidants and nitrates that may support NO levels and cardiovascular health.
* Watermelon: Watermelon contains an amino acid called citrulline, which can be converted into arginine, a precursor to nitric oxide.
* Nitrates in Vegetables: Nitrates are compounds found in certain vegetables that can be converted into NO in the body. Examples of nitrate-rich vegetables include spinach, arugula, kale, beetroot, and lettuce.
* Beets and Beetroot Juice: Beets and beetroot juice are well-known for their high nitrate content, which can be converted into nitric oxide.
* Dark Chocolate: Dark chocolate contains flavonoids, which have been shown to support nitric oxide production and cardiovascular health.

Interaction with other drugs

NO can interact with various drugs due to its role as a signaling molecule in many physiological processes. Some interactions include:

* Blood pressure medications: NO donors or drugs that increase NO levels, such as nitroglycerin or other nitrate medications, can enhance the effects of blood pressure-lowering medications like antihypertensives. This interaction can lead to excessive hypotension (low blood pressure).
* Erectile dysfunction drugs: Drugs used to treat erectile dysfunction, such as sildenafil (Viagra), tadalafil (Cialis), and vardenafil (Levitra), work by enhancing the effects of NO, leading to vasodilation and improved blood flow. Combining these drugs with other NO donors or medications that increase NO levels can potentiate their effects and may cause a dangerous drop in blood pressure.
* Anticoagulants and antiplatelet drugs: NO inhibits platelet aggregation and can increase bleeding risk. Combining NO donors or medications that increase NO levels with anticoagulants (e.g., warfarin, heparin) or antiplatelet drugs (e.g., aspirin, clopidogrel) may further enhance the risk of bleeding.
* Drugs affecting nitric oxide synthesis: Medications that affect the synthesis of NO, such as inhibitors of NO synthase (NOS), may interact with drugs that rely on NO signaling for their effects. These interactions can affect cardiovascular function, neurotransmission, and immune response.
* Alpha-blockers: Alpha-blockers, used to treat conditions like benign prostatic hyperplasia (BPH) and hypertension, can interact with NO donors or drugs that increase NO levels, leading to additive effects on blood pressure lowering.
* Drugs affecting cytochrome P450 enzymes: Some drugs can affect the activity of cytochrome P450 enzymes, which are involved in the metabolism of NO donors and other drugs. Interactions with these drugs can alter the metabolism and effectiveness of medications that affect NO levels.

Side effects

While NO is essential for various physiological functions in the body, including vasodilation and neurotransmission, excessive intake or production of nitric oxide can lead to potential complications. Here are some of the possible complications associated with taking excessive amounts of nitric oxide:

* Hypotension: Excessive nitric oxide can cause a significant drop in blood pressure (hypotension). This can lead to symptoms such as dizziness, lightheadedness, fainting, and in severe cases, shock.
* Headaches: Increased levels of nitric oxide can cause headaches, which may range from mild to severe and can be debilitating for some individuals.
* Increased bleeding risk: NO can inhibit platelet aggregation and contribute to increased bleeding risk. Excessive nitric oxide production may lead to prolonged bleeding and difficulty in clot formation.
* Worsening of respiratory conditions: In individuals with certain respiratory conditions such as asthma, excessive nitric oxide production can exacerbate symptoms by causing airway dilation and inflammation.
* Nitric oxide toxicity: In rare cases, excessive exposure to NO gas, particularly in industrial or occupational settings, can lead to toxicity, causing respiratory distress, lung damage, and even death.
* Formation of reactive nitrogen species: Excessive nitric oxide can react with other molecules in the body to form reactive nitrogen species, such as peroxynitrite, which can contribute to oxidative stress, tissue damage, and inflammation.

Additional Information

Nitric oxide (NO) is a colourless toxic gas that is formed by the oxidation of nitrogen. Nitric oxide performs important chemical signaling functions in humans and other animals and has various applications in medicine. It has few industrial applications. It is a serious air pollutant generated by automotive engines and thermal power plants.

Nitric oxide is formed from nitrogen and oxygen by the action of electric sparks or high temperatures or, more conveniently, by the action of dilute nitric acid upon copper or mercury. It was first prepared about 1620 by the Belgian scientist Jan Baptista van Helmont, and it was first studied in 1772 by the English chemist Joseph Priestley, who called it “nitrous air.”

Nitric oxide liquefies at −151.8 °C (−241.2 °F) and solidifies at −163.6 °C (−262.5 °F); both the liquid and the solid are blue in colour. The gas is almost insoluble in water, but it dissolves rapidly in a slightly alkaline solution of sodium sulfite, forming the compound sodium dinitrososulfite, Na2(NO)2SO3. It reacts rapidly with oxygen to form nitrogen dioxide, NO2. Nitric oxide is a relatively unstable, diatomic molecule that possesses a free radical (i.e., an unpaired electron). The molecule can gain or lose one electron to form the ions NO− or NO+.

In the chemical industry, nitric oxide is an intermediate compound formed during the oxidation of ammonia to nitric acid. An industrial procedure for the manufacture of hydroxylamine is based on the reaction of nitric oxide with hydrogen in the presence of a catalyst. The formation of nitric oxide from nitric acid and mercury is applied in a volumetric method of analysis for nitric acid or its salts.

Though it is a toxic gas at high concentrations, nitric oxide functions as an important signaling molecule in animals. It acts as a messenger molecule, transmitting signals to cells in the cardiovascular, nervous, and immune systems. The nitric oxide molecule’s possession of a free radical makes it much more reactive than other signaling molecules, and its small size enables it to diffuse through cell membranes and walls to perform a range of signaling functions in various bodily systems. The body synthesizes nitric oxide from the amino acid L-arginine by means of the enzyme nitric oxide synthase.

The main site of the molecule’s synthesis is the inner layer of blood vessels, the endothelium, though the molecule is also produced by other types of cells. From the endothelium, nitric oxide diffuses to underlying smooth muscle cells and causes them to relax. This relaxation causes the walls of blood vessels to dilate, or widen, which in turn increases blood flow through the vessels and decreases blood pressure. Nitric oxide’s role in dilating blood vessels makes it an important controller of blood pressure. Nitric oxide is also produced by neurons (nerve cells) and is used by the nervous system as a neurotransmitter to regulate functions ranging from digestion to blood flow to memory and vision. In the immune system, nitric oxide is produced by macrophages, which are a type of leukocyte (white blood cell) that engulfs bacteria and other foreign particles that have invaded the body. The nitric oxide released by macrophages kills bacteria, other parasites, and tumour cells by disrupting their metabolism.

Nitric oxide’s role in regulating blood flow and pressure is used by modern medicine in several ways. The drug nitroglycerin has been used since the late 19th century to relieve the condition known as angina pectoris, which is caused by an insufficient supply of blood to the heart muscle. Nitroglycerin was long known to achieve its therapeutic effect by dilating the coronary arteries (thereby increasing the flow of blood to the heart), but why it did so remained unknown until the late 1980s, when researchers realized that the drug serves to replenish the body’s supply of nitric oxide, more of which is then available to relax, and thereby widen, the coronary blood vessels.

Nitric oxide is an important component of the air pollution generated by automotive engines and thermal power-generating plants. When a mixture of air and hydrocarbon fuel is burned in an internal-combustion engine or a power plant, the ordinarily inert nitrogen in the air combines with oxygen at very high temperatures to form nitric oxide. The nitric oxide and hydrocarbon vapours emitted by automotive exhausts and power-plant smokestacks undergo complex photochemical reactions in the lower atmosphere to form various secondary pollutants called photochemical oxidants, which make up photochemical smog. Nitric oxide combines with water vapour in the atmosphere to form nitric acid, which is one of the components of acid rain. Heightened levels of atmospheric nitric oxide resulting from industrial activity were also one of the causes of gradual depletion of the ozone layer in the upper atmosphere. Sunlight causes nitric oxide to react chemically with ozone (O3), thereby converting the ozone to molecular oxygen (O2).

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Jai Ganesh · Dark Discussions at Cafe Infinity

Coin Quotes - I

1. All the perplexities, confusion and distress in America arise, not from defects in their Constitution or Confederation, not from want of honor or virtue, so much as from the downright ignorance of the nature of coin, credit and circulation. - John Adams

2. Peace and justice are two sides of the same coin. - Dwight D. Eisenhower

3. Leadership is the other side of the coin of loneliness, and he who is a leader must always act alone. And acting alone, accept everything alone. - Ferdinand Marcos

4. Silver and gold are not the only coin; virtue too passes current all over the world. - Euripides

5. If you call yourself a leader, then you have to be decisive. If you're decisive, then you have the chance to be a leader. These are two sides to the same coin. - Narendra Modi

6. German and European unification are two sides of the same coin. - Helmut Kohl

7. When the machine had been fastened with a wire to the track, so that it could not start until released by the operator, and the motor had been run to make sure that it was in condition, we tossed a coin to decide who should have the first trial. Wilbur won. - Orville Wright

8. I said, yet again, for Germany, Europe is not only indispensable, it is part and parcel of our identity. We've always said German unity, European unity and integration, that's two parts of one and the same coin. But we want, obviously, to boost our competitiveness. - Angela Merkel.

Jai Ganesh · Jokes

Q: What did the yeast confess to the bag of flour?
A: I loaf you dough much!
* * *
Q: Why did Mama Flour and Papa Yeast tell Baby Bread to get a job?
A: He was just loafing around!
* * *
Q: Why doesn't anyone want to work in a bakery?
A: It's a crumby place to work.
* * *
Q: What Kind of Biscuits Can Fly?
A: Plain Ones.
* * *
Q: When does sourdough bread rise?
A: When you yeast expect it.
* * *

Jai Ganesh · Science HQ

Isotope

Gist

An isotope is a form of a chemical element with the same number of protons but a different number of neutrons than other atoms of the same element. This difference in neutron count gives isotopes the same atomic number but different mass numbers, meaning they have identical chemical properties but different physical properties. For example, carbon-12 and carbon-14 are both isotopes of carbon; they both have six protons, but carbon-12 has six neutrons, while carbon-14 has eight.

An isotope is a version of a chemical element with the same number of protons but a different number of neutrons. This difference in neutrons gives isotopes the same atomic number but different mass numbers, leading to nearly identical chemical properties but different physical properties. For example, carbon-12, carbon-13, and carbon-14 are all isotopes of carbon, each with six protons but a different number of neutrons.

Summary

Isotopes are distinct nuclear species (or nuclides) of the same chemical element. They have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), but different nucleon numbers (mass numbers) due to different numbers of neutrons in their nuclei. While all isotopes of a given element have virtually the same chemical properties, they have different atomic masses and physical properties.

The term isotope comes from the Greek roots isos ("equal") and topos ("place"), meaning "the same place": different isotopes of an element occupy the same place on the periodic table. It was coined by Scottish doctor and writer Margaret Todd in a 1913 suggestion to the British chemist Frederick Soddy, who popularized the term.

The number of protons within the atom's nucleus is called its atomic number and is equal to the number of electrons in the neutral (non-ionized) atom. Each atomic number identifies a specific element, but not the isotope; an atom of a given element may have a wide range in its number of neutrons. The number of nucleons (both protons and neutrons) in the nucleus is the atom's mass number, and each isotope of a given element has a different mass number.

For example, carbon-12, carbon-13, and carbon-14 are three isotopes of the element carbon with mass numbers 12, 13, and 14, respectively. The atomic number of carbon is 6, which means that every carbon atom has 6 protons so that the neutron numbers of these isotopes are 6, 7, and 8 respectively.

Details

An isotope is one of two or more species of atoms of a chemical element with the same atomic number and position in the periodic table and nearly identical chemical behaviour but with different atomic masses and physical properties. Every chemical element has one or more isotopes.

An atom is first identified and labeled according to the number of protons in its nucleus. This atomic number is ordinarily given the symbol Z. The great importance of the atomic number derives from the observation that all atoms with the same atomic number have nearly, if not precisely, identical chemical properties. A large collection of atoms with the same atomic number constitutes a sample of an element. A bar of pure uranium, for instance, would consist entirely of atoms with atomic number 92. The periodic table of the elements assigns one place to every atomic number, and each of these places is labeled with the common name of the element, as, for example, calcium, radon, or uranium.

Not all the atoms of an element need have the same number of neutrons in their nuclei. In fact, it is precisely the variation in the number of neutrons in the nuclei of atoms that gives rise to isotopes. Hydrogen is a case in point. It has the atomic number 1. Three nuclei with one proton are known that contain 0, 1, and 2 neutrons, respectively. The three share the place in the periodic table assigned to atomic number 1 and hence are called isotopes (from the Greek isos, meaning “same,” and topos, signifying “place”) of hydrogen.

Many important properties of an isotope depend on its mass. The total number of neutrons and protons (symbol A), or mass number, of the nucleus gives approximately the mass measured on the so-called atomic-mass-unit (amu) scale. The numerical difference between the actual measured mass of an isotope and A is called either the mass excess or the mass defect.

The term nuclide is used to describe particular isotopes, notably in cases where the nuclear rather than the chemical properties of an atom are to be emphasized. The lexicon of isotopes includes three other frequently used terms: isotones for isotopes of different elements with the same number of neutrons, isobars for isotopes of different elements with the same mass number, and isomers for isotopes identical in all respects except for the total energy content of the nuclei.

The discovery of isotopes

Evidence for the existence of isotopes emerged from two independent lines of research, the first being the study of radioactivity. By 1910 it had become clear that certain processes associated with radioactivity, discovered some years before by French physicist Henri Becquerel, could transform one element into another. In particular, ores of the radioactive elements uranium and thorium had been found to contain small quantities of several radioactive substances never before observed. These substances were thought to be elements and accordingly received special names. Uranium ores, for example, yielded ionium, and thorium ores gave mesothorium. Painstaking work completed soon afterward revealed, however, that ionium, once mixed with ordinary thorium, could no longer be retrieved by chemical means alone. Similarly, mesothorium was shown to be chemically indistinguishable from radium. As chemists used the criterion of chemical indistinguishability as part of the definition of an element, they were forced to conclude that ionium and mesothorium were not new elements after all, but rather new forms of old ones. Generalizing from these and other data, English chemist Frederick Soddy in 1910 observed that “elements of different atomic weights [now called atomic masses] may possess identical (chemical) properties” and so belong in the same place in the periodic table. With considerable prescience, he extended the scope of his conclusion to include not only radioactive species but stable elements as well. A few years later, Soddy published a comparison of the atomic masses of the stable element lead as measured in ores rich in uranium and thorium, respectively. He expected a difference because uranium and thorium decay into different isotopes of lead. The lead from the uranium-rich ore had an average atomic mass of 206.08 compared to 207.69 for the lead from the thorium-rich ore, thus verifying Soddy’s conclusion.

The unambiguous confirmation of isotopes in stable elements not associated directly with either uranium or thorium followed a few years later with the development of the mass spectrograph (see mass spectrometry) by Francis William Aston. His work grew out of the study of positive rays (sometimes called canal rays), discovered in 1886 by Eugen Goldstein and soon thereafter recognized as beams of positive ions. As a student in the laboratory of J.J. Thomson, Aston had learned that the gaseous element neon produced two positive rays. The ions in the heavier ray had masses about two units, or 10 percent, greater than the ions in the lighter ray. To prove that the lighter neon had a mass very close to 20 and that the heavier ray was indeed neon and not a spurious signal of some kind, Aston had to construct an instrument that was considerably more precise than any other of the time. By 1919 he had done so and convincingly argued for the existence of neon-20 and neon-22. Information from his and other laboratories accumulated rapidly in the ensuing years, and by 1935 the principal isotopes and their relative proportions were known for all but a handful of elements.

Additional Information

A family of people often consists of related but not identical individuals. Elements have families as well, known as isotopes. Isotopes are members of a family of an element that all have the same number of protons but different numbers of neutrons.

The number of protons in a nucleus determines the element’s atomic number on the Periodic Table. For example, carbon has six protons and is atomic number 6. Carbon occurs naturally in three isotopes: carbon 12, which has 6 neutrons (plus 6 protons equals 12), carbon 13, which has 7 neutrons, and carbon 14, which has 8 neutrons. Every element has its own number of isotopes.

The addition of even one neutron can dramatically change an isotope’s properties. Carbon-12 is stable, meaning it never undergoes radioactive decay. Carbon-14 is unstable and undergoes radioactive decay with a half-life of about 5,730 years (meaning that after 5,730 years half of the material will have decayed to the stable isotope nitrogen-14). This decay means the amount of carbon-14 in an object serves as a clock, showing the object’s age in a process called “carbon dating.”

Isotopes have unique properties, and these properties make them useful in diagnostics and treatment applications. They are important in nuclear medicine, oil and gas exploration, basic research, and national security.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#10665. What does the term in Geography City-state mean?

#10666. What does the term in Geography Cliff mean?

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#5461. What does the noun blues mean?

#5462. What does the noun blueprint mean?

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#2525. What does the medical term Azotemia mean?

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#9804.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#6299.

Jai Ganesh · Exercises

Hi,

2650.

Jai Ganesh · Exercises

Hi,

Good!

2649.

Jai Ganesh · This is Cool

Ultraviolet

Gist

Ultraviolet (UV) is a type of electromagnetic radiation from the sun and artificial sources, with a shorter wavelength than visible light but longer than X-rays. It is invisible to the human eye and includes three main types: UVA, UVB, and UVC. While beneficial for vitamin D production, excessive UV exposure can cause skin damage, premature aging, and increase the risk of skin cancer.

Ultraviolet (UV) light has shorter wavelengths than visible light. Although UV waves are invisible to the human eye, some insects, such as bumblebees, can see them. This is similar to how a dog can hear the sound of a whistle just outside the hearing range of humans.

Summary

Ultraviolet radiation or UV is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs, Cherenkov radiation, and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights.

The photons of ultraviolet have greater energy than those of visible light, from about 3.1 to 12 electron volts, around the minimum energy required to ionize atoms. Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack sufficient energy, it can induce chemical reactions and cause many substances to glow or fluoresce. Many practical applications, including chemical and biological effects, are derived from the way that UV radiation can interact with organic molecules. These interactions can involve exciting orbital electrons to higher energy states in molecules potentially breaking chemical bonds. In contrast, the main effect of longer wavelength radiation is to excite vibrational or rotational states of these molecules, increasing their temperature. Short-wave ultraviolet light is ionizing radiation. Consequently, short-wave UV damages DNA and sterilizes surfaces with which it comes into contact.

For humans, suntan and sunburn are familiar effects of exposure of the skin to UV, along with an increased risk of skin cancer. The amount of UV radiation produced by the Sun means that the Earth would not be able to sustain life on dry land if most of that light were not filtered out by the atmosphere. More energetic, shorter-wavelength "extreme" UV below 121 nm ionizes air so strongly that it is absorbed before it reaches the ground. However, UV (specifically, UVB) is also responsible for the formation of vitamin D in most land vertebrates, including humans. The UV spectrum, thus, has effects both beneficial and detrimental to life.

The lower wavelength limit of the visible spectrum is conventionally taken as 400 nm. Although ultraviolet rays are not generally visible to humans, 400 nm is not a sharp cutoff, with shorter and shorter wavelengths becoming less and less visible in this range. Insects, birds, and some mammals can see near-UV (NUV), i.e., somewhat shorter wavelengths than what humans can see.

Details

Ultraviolet (UV) light has shorter wavelengths than visible light. Although UV waves are invisible to the human eye, some insects, such as bumblebees, can see them. This is similar to how a dog can hear the sound of a whistle just outside the hearing range of humans.

The Sun is a source of the full spectrum of ultraviolet radiation, which is commonly subdivided into UV-A, UV-B, and UV-C. These are the classifications most often used in Earth sciences. UV-C rays are the most harmful and are almost completely absorbed by our atmosphere. UV-B rays are the harmful rays that cause sunburn. Exposure to UV-B rays increases the risk of DNA and other cellular damage in living organisms. Fortunately, about 95 percent UV-B rays are absorbed by ozone in the Earth's atmosphere.

Scientists studying astronomical objects commonly refer to different subdivisions of ultraviolet radiation: near ultraviolet (NUV), middle ultraviolet (MUV), far ultraviolet (FUV), and extreme ultraviolet (EUV). NASA's SDO spacecraft captured the image below in multiple wavelengths of extreme ultraviolet (EUV) radiation. The false-color composite reveals different gas temperatures. Reds are relatively cool (about 60,000 Celsius) while blues and greens are hotter (greater than one million Celsius).

In 1801, Johann Ritter conducted an experiment to investigate the existence of energy beyond the violet end of the visible spectrum. Knowing that photographic paper would turn black more rapidly in blue light than in red light, he exposed the paper to light beyond violet. Sure enough, the paper turned black, proving the existence of ultraviolet light.

Since the Earth's atmosphere absorbs much of the high-energy ultraviolet radiation, scientists use data from satellites positioned above the atmosphere, in orbit around the Earth, to sense UV radiation coming from our Sun and other astronomical objects. Scientists can study the formation of stars in ultraviolet since young stars shine most of their light at these wavelengths. This image from NASA's Galaxy Evolution Explorer (GALEX) spacecraft reveals new young stars in the spiral arms of galaxy M81.

Chemical processes in the upper atmosphere can affect the amount of atmospheric ozone that shields life at the surface from most of the Sun's harmful UV radiation. Each year, a "hole" of thinning atmospheric ozone expands over Antarctica, sometimes extending over populated areas of South America and exposing them to increased levels of harmful UV rays. The Dutch Ozone Monitoring Instrument (OMI) onboard NASA's Aura satellite measures amounts of trace gases important to ozone chemistry and air quality. The image above shows the amount of atmospheric ozone in Dobson Units—the common unit for measuring ozone concentration. These data enable scientists to estimate the amount of UV radiation reaching the Earth's surface and forecast high-UV-index days for public health awareness.

Aurorae are caused by high-energy waves that travel along a planet's magnetic poles, where they excite atmospheric gases and cause them to glow. Photons in this high-energy radiation bump into atoms of gases in the atmosphere causing electrons in the atoms to excite, or move to the atom's upper shells. When the electrons move back down to a lower shell, the energy is released as light, and the atom returns to a relaxed state. The color of this light can reveal what type of atom was excited. Green light indicates oxygen at lower altitudes. Red light can be from oxygen molecules at a higher altitude or from nitrogen. On Earth, aurorae around the north pole are called the Northern Lights.

The Hubble Space Telescope captured this image of Jupiter's aurora in ultraviolet wrapping around Jupiter's north pole like a lasso.

Additional Information

Ultraviolet (UV) radiation covers the wavelength range of 100–400 nm, which is a higher frequency and lower wavelength than visible light. UV radiation comes naturally from the sun, but it can also be created by artificial sources used in industry, commerce and recreation.

The UV region covers the wavelength range 100-400 nm and is divided into three bands:

* UVA (315-400 nm)
* UVB (280-315 nm)
*UVC (100-280 nm).

As sunlight passes through the atmosphere, all UVC and approximately 90% of UVB radiation is absorbed by ozone, water vapour, oxygen and carbon dioxide. UVA radiation is less affected by the atmosphere. Therefore, the UV radiation reaching the Earth’s surface is largely composed of UVA with a small UVB component.

The amount of UV radiation from the sun that hits the Earth’s surface depends on several factors, including the sun’s height in the sky, latitude, cloud cover, altitude, the thickness of the ozone layer and ground reflection. Reductions in the ozone layer due to human-created pollution increase the amount of UVA and UVB that reaches the surface. This can impact human health, animals, marine organisms and plant life. In humans, increased UV exposure can cause skin cancers, cataracts and immune system damage.

Ultraviolet radiation is that portion of the electromagnetic spectrum extending from the violet, or short-wavelength, end of the visible light range to the X-ray region. Ultraviolet (UV) radiation is undetectable by the human eye, although, when it falls on certain materials, it may cause them to fluoresce—i.e., emit electromagnetic radiation of lower energy, such as visible light. Many insects, however, are able to see ultraviolet radiation.

Ultraviolet radiation lies between wavelengths of about 400 nanometres (1 nanometre [nm] is {10}{-9} metre) on the visible-light side and about 10 nm on the X-ray side, though some authorities extend the short-wavelength limit to 4 nm. In physics, ultraviolet radiation is traditionally divided into four regions: near (400–300 nm), middle (300–200 nm), far (200–100 nm), and extreme (below 100 nm). Based on the interaction of wavelengths of ultraviolet radiation with biological materials, three divisions have been designated: UVA (400–315 nm), also called black light; UVB (315–280 nm), responsible for the radiation’s best-known effects on organisms; and UVC (280–100 nm), which does not reach Earth’s surface.

Ultraviolet radiation is produced by high-temperature surfaces, such as the Sun, in a continuous spectrum and by atomic excitation in a gaseous discharge tube as a discrete spectrum of wavelengths. Most of the ultraviolet radiation in sunlight is absorbed by oxygen in Earth’s atmosphere, which forms the ozone layer of the lower stratosphere. Of the ultraviolet that does reach Earth’s surface, almost 99 percent is UVA radiation.

When the ozone layer becomes thin, however, more UVB radiation reaches Earth’s surface and may have hazardous effects on organisms. For example, studies have shown that UVB radiation penetrates the ocean’s surface and may be lethal to marine plankton to a depth of 30 metres (about 100 feet) in clear water. In addition, marine scientists have suggested that a rise in UVB levels in the Southern Ocean between 1970 and 2003 was strongly linked to a simultaneous decline in fish, krill, and other marine life.

Unlike X-rays, ultraviolet radiation has a low power of penetration; hence, its direct effects on the human body are limited to the surface skin. The direct effects include reddening of the skin (sunburn), pigmentation development (suntan), aging, and carcinogenic changes. Ultraviolet sunburns can be mild, causing only redness and tenderness, or they can be so severe as to produce blisters, swelling, seepage of fluid, and sloughing of the outer skin. The blood capillaries (minute vessels) in the skin dilate with aggregations of red and white blood cells to produce the red coloration. Tanning is a natural body defense relying on melanin to help protect the skin from further injury. Melanin is a chemical pigment in the skin that absorbs ultraviolet radiation and limits its penetration into tissues. A suntan occurs when melanin pigments in cells in the deeper tissue portion of the skin are activated by ultraviolet radiation, and the cells migrate to the surface of the skin. When these cells die, the pigmentation disappears. Persons of light complexion have less melanin pigment and so experience the harmful effects of ultraviolet radiation to a greater degree. The application of sunscreen to the skin can help to block absorption of ultraviolet radiation in such persons.

Constant exposure to the Sun’s ultraviolet radiation induces most of the skin changes commonly associated with aging, such as wrinkling, thickening, and changes in pigmentation. There is also a much higher frequency of skin cancer, particularly in persons with fair skin. The three basic skin cancers, basal- and squamous-cell carcinoma and melanoma, have been linked to long-term exposure to ultraviolet radiation and probably result from changes generated in the DNA of skin cells by ultraviolet rays.

Ultraviolet radiation also has positive effects on the human body, however. It stimulates the production of vitamin D in the skin and can be used as a therapeutic agent for such diseases as psoriasis. Because of its bactericidal capabilities at wavelengths of 260–280 nm, ultraviolet radiation is useful as both a research tool and a sterilizing technique. Fluorescent lamps exploit the ability of ultraviolet radiation to interact with materials known as phosphors that emit visible light; compared with incandescent lamps, fluorescent lamps are a more energy-efficient form of artificial lighting.

UV-ForceAirQuality_UVDifference.webp?width=1350&height=750&name=UV-ForceAirQuality_UVDifference.webp

Jai Ganesh · Dark Discussions at Cafe Infinity

2392) Shin'ichirō Tomonaga

Gist:

Work

Following the establishment of the theory of relativity and quantum mechanics, an initial relativistic theory was formulated for the interaction between charged particles and electromagnetic fields. The theory had to be reformulated, however, partly due to the observation of the Lamb shift in 1947, in which the supposed single energy level within a hydrogen atom was instead proven to be two similar levels. Sin-Itiro Tomonga solved this problem in 1948 through a “renormalization” and thereby contributed to a new quantum electrodynamics.

Summary

Tomonaga Shin’ichirō (born March 31, 1906, Kyōto, Japan—died July 8, 1979, Tokyo) was a Japanese physicist, joint winner, with Richard P. Feynman and Julian S. Schwinger of the United States, of the Nobel Prize for Physics in 1965 for developing basic principles of quantum electrodynamics.

Tomonaga became professor of physics at Bunrika University (later Tokyo University of Education) in 1941, the year he began his investigations of the problems of quantum electrodynamics. World War II isolated him from Western scientists, but in 1943 he completed and published his research. Tomonaga’s theoretical work made quantum electrodynamics (the theory of the interactions of charged subatomic particles with the electromagnetic field) consistent with the theory of special relativity. It was only after the war, in 1947, that his work came to the attention of the West, at about the same time that Feynman and Schwinger published the results of their research. It was found that all three had achieved essentially the same result from different approaches and had resolved the inconsistencies of the old theory without making any drastic changes.

Tomonaga was president of the Tokyo University of Education from 1956 to 1962, and the following year he was named chairman of the Japan Science Council. Throughout his life Tomonaga actively campaigned against the spread of nuclear weapons and urged that resources be spent on the peaceful use of nuclear energy. Most notable of his works available in English translation are Quantum Mechanics (1962) and his Nobel lecture Development of Quantum Electrodynamics: Personal Recollections (1966).

Details

Shinichiro Tomonaga (Tomonaga Shin'ichirō; March 31, 1906 – July 8, 1979), usually cited as Sin-Itiro Tomonaga in English, was a Japanese physicist, influential in the development of quantum electrodynamics, work for which he was jointly awarded the Nobel Prize in Physics in 1965 along with Richard Feynman and Julian Schwinger.

Biography

Tomonaga was born in Tokyo in 1906. He was the second child and eldest son of a Japanese philosopher, Tomonaga Sanjūrō. He entered the Kyoto Imperial University in 1926. Hideki Yukawa, also a Nobel laureate, was one of his classmates during undergraduate school. During graduate school at the same university, he worked as an assistant in the university for three years. In 1931, after graduate school, he joined Nishina's group in RIKEN. In 1937, while working at Leipzig University (Leipzig), he collaborated with the research group of Werner Heisenberg. Two years later, he returned to Japan due to the outbreak of the Second World War, but finished his doctoral degree (Dissertation PhD from University of Tokyo) on the study of nuclear materials with his thesis on work he had done while in Leipzig.

In Japan, he was appointed to a professorship in the Tokyo University of Education (a forerunner of Tsukuba University). During the war he studied the magnetron, meson theory, and his super-many-time theory. In 1948, he and his students re-examined a 1939 paper by Sidney Dancoff that attempted, but failed, to show that the infinite quantities that arise in quantum electrodynamics (QED) can be canceled with each other. Tomonaga applied his super-many-time theory and a relativistic method based on the non-relativistic method of Wolfgang Pauli and Fierz to greatly speed up and clarify the calculations. Then he and his students found that Dancoff had overlooked one term in the perturbation series. With this term, the theory gave finite results; thus Tomonaga discovered the renormalization method independently of Julian Schwinger and calculated physical quantities such as the Lamb shift at the same time.

In 1949, he was invited by Robert Oppenheimer to work at the Institute for Advanced Study in Princeton. He studied a many-body problem on the collective oscillations of a quantum-mechanical system. In the following year, he returned to Japan and proposed the Tomonaga–Luttinger liquid. In 1955, he took the leadership in establishing the Institute for Nuclear Study, University of Tokyo. In 1965, he was awarded the Nobel Prize in Physics, with Julian Schwinger and Richard P. Feynman, for the study of QED, specifically for the discovery of the renormalization method. He died of throat cancer in Tokyo in 1979.

Tomonaga was married in 1940 to Ryōko Sekiguchi. They had two sons and one daughter. He was awarded the Order of Culture in 1952, and the Grand Cordon of the Order of the Rising Sun in 1976.

In recognition of three Nobel laureates' contributions, the bronze statues of Shin'ichirō Tomonaga, Leo Esaki, and Makoto Kobayashi was set up in the Central Park of Azuma 2 in Tsukuba City in 2015.

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