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2376) Luis Walter Alvarez

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Opportunities to investigate our world’s smallest components were revolutionized by C.T.R. Wilson’s invention of the cloud chamber and Donald Glaser’s invention of the bubble chamber. In these devices electrically charged particles leave trails behind them. In the latter part of the 1950s, Luis Alvarez further developed the bubble chamber by using liquid hydrogen. He also developed new measurement systems and computer-based methods for analyzing large quantities of data. This has led to the discovery of a number of previously unknown particles.

Summary

Luis Walter Alvarez (June 13, 1911 – September 1, 1988) was an American experimental physicist, inventor, and professor of Spanish descent who was awarded the Nobel Prize in Physics in 1968 for his discovery of resonance states in particle physics using the hydrogen bubble chamber. In 2007 the American Journal of Physics commented, "Luis Alvarez was one of the most brilliant and productive experimental physicists of the twentieth century."

After receiving his PhD from the University of Chicago in 1936, Alvarez went to work for Ernest Lawrence at the Radiation Laboratory at the University of California, Berkeley. Alvarez devised a set of experiments to observe K-electron capture in radioactive nuclei, predicted by the beta decay theory but never before observed. He produced tritium using the cyclotron and measured its lifetime. In collaboration with Felix Bloch, he measured the magnetic moment of the neutron.

In 1940, Alvarez joined the MIT Radiation Laboratory, where he contributed to a number of World War II radar projects, from early improvements to Identification friend or foe (IFF) radar beacons, now called transponders, to a system known as VIXEN for preventing enemy submarines from realizing that they had been found by the new airborne microwave radars. The radar system for which Alvarez is best known and which has played a major role in aviation, most particularly in the post war Berlin airlift, was Ground Controlled Approach (GCA). Alvarez spent a few months at the University of Chicago working on nuclear reactors for Enrico Fermi before coming to Los Alamos to work for Robert Oppenheimer on the Manhattan Project. Alvarez worked on the design of explosive lenses, and the development of exploding-bridgewire detonators. As a member of Project Alberta, he observed the Trinity nuclear test from a B-29 Superfortress, and later the bombing of Hiroshima from the B-29 The Great Artiste.

After the war Alvarez was involved in the design of a liquid hydrogen bubble chamber that allowed his team to take millions of photographs of particle interactions, develop complex computer systems to measure and analyze these interactions, and discover entire families of new particles and resonance states. This work resulted in his being awarded the Nobel Prize in 1968. He was involved in a project to x-ray the Egyptian pyramids to search for unknown chambers. With his son, geologist Walter Alvarez, he developed the Alvarez hypothesis which proposes that the extinction event that wiped out the non-avian dinosaurs was the result of an asteroid impact.

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Luis Alvarez (born June 13, 1911, San Francisco, California, U.S.—died September 1, 1988, Berkeley, California) was an American experimental physicist who was awarded the Nobel Prize for Physics in 1968 for work that included the discovery of many resonance particles (subatomic particles having extremely short lifetimes and occurring only in high-energy nuclear collisions).

Alvarez studied physics at the University of Chicago (B.S., 1932; M.S., 1934; Ph.D., 1936). He joined the faculty of the University of California, Berkeley, in 1936, becoming professor of physics in 1945 and professor emeritus in 1978. In 1938 Alvarez discovered that some radioactive elements decay by orbital-electron capture; i.e., an orbital electron merges with its nucleus, producing an element with an atomic number smaller by one. In 1939 he and Felix Bloch made the first measurement of the magnetic moment of the neutron, a characteristic of the strength and direction of its magnetic field.

Alvarez, Luis
Alvarez, LuisLuis Alvarez (far left) and visiting scientists examining the bubble chamber at the Lawrence Berkeley National Laboratory, California, 1959.
Alvarez worked on microwave radar research at the Massachusetts Institute of Technology, Cambridge (1940–43), and participated in the development of the atomic bomb at the Los Alamos Scientific Laboratory, Los Alamos, New Mexico, in 1944–45. He suggested the technique for detonating the implosion type of atomic bomb. He also participated in the development of microwave beacons, linear radar antennas, the ground-controlled landing approach system, and a method for aerial bombing using radar to locate targets. After World War II Alvarez helped construct the first proton linear accelerator. In this accelerator, electric fields are set up as standing waves within a cylindrical metal “resonant cavity,” with drift tubes suspended along the central axis. The electric field is zero inside the drift tubes, and, if their lengths are properly chosen, the protons cross the gap between adjacent drift tubes when the direction of the field produces acceleration and are shielded by the drift tubes when the field in the tank would decelerate them. The lengths of the drift tubes are proportional to the speeds of the particles that pass through them. In addition to this work, Alvarez also developed the liquid hydrogen bubble chamber in which subatomic particles and their reactions are detected.

In about 1980 Alvarez helped his son, the geologist Walter Alvarez, publicize Walter’s discovery of a worldwide layer of clay that has a high iridium content and which occupies rock strata at the geochronological boundary between the Mesozoic and Cenozoic eras (i.e., about 65.5 million years ago). They postulated that the iridium had been deposited following the impact on Earth of an asteroid or comet and that the catastrophic climatic effects of this massive impact triggered a mass extinction event, killing the dinosaurs. Though initially controversial, this widely publicized theory gradually gained support as the most plausible explanation for the abrupt demise of dinosaurs.

Alvarez’s autobiography, Alvarez: Adventures of a Physicist, was published in 1987.

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2375) Salvador Luria

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Bacteriophages are viruses that attach themselves to bacteria, emptying their genetic material into them, which leads to the rapid spawning of new phage inside the bacteria. By applying genetic concept and developing statistical approaches in their studies of bacteriophages, Max Delbrück, Salvador Luria, and Alfred Hershey were able to shed new light on a range of unanswered questions within genetics. For example, in 1943 Luria and Delbrück proved through statistical investigations that bacteria, like more complex organisms, develop via mutations.

Summary

Salvador Luria (born Aug. 13, 1912, Turin, Italy—died Feb. 6, 1991, Lexington, Mass., U.S.) was an Italian-born American biologist who, along with Max Delbrück and Alfred Day Hershey, won the Nobel Prize for Physiology or Medicine in 1969 for research on bacteriophages, viruses that infect bacteria.

Luria graduated from the University of Turin in 1935 and became a radiology specialist. He fled Italy for France in 1938 and went to the United States in 1940 after learning the techniques of phage research at the Pasteur Institute in Paris. Soon after his arrival, he met Delbrück, through whom he became involved with the American Phage Group, an informal scientific organization devoted to solving the problems of viral self-replication. Working with a member of the group in 1942, Luria obtained one of the electron micrographs of phage particles, which confirmed earlier descriptions of them as consisting of a round head and a thin tail.

In 1943 Luria and Delbrück published a paper showing that, contrary to the current view, viruses undergo permanent changes in their hereditary material. That same year he and Delbrück devised the fluctuation test, which provided experimental evidence that phage-resistant bacteria were the result of spontaneous mutations rather than a direct response to changes in the environment. In 1945 Hershey and Luria demonstrated the existence not only of such bacterial mutants but also of spontaneous phage mutants.

Luria became Sedgwick professor of biology at the Massachusetts Institute of Technology in 1964. In 1974 he became director of the Center for Cancer Research at MIT. He was an author of a college textbook, General Virology (1953), and a popular text for the general reader, Life: The Unfinished Experiment (1973).

Details

Salvador Edward Luria (August 13, 1912 – February 6, 1991) was an Italian microbiologist, later a naturalized U.S. citizen. He won the Nobel Prize in Physiology or Medicine in 1969, with Max Delbrück and Alfred Hershey, for their discoveries on the replication mechanism and the genetic structure of viruses. Salvador Luria also showed that bacterial resistance to viruses (phages) is genetically inherited.

Biography:

Early life

Luria was born Salvatore Luria in Turin, Italy to an influential Italian Sephardi Jewish family. His parents were Davide and Ester (Sacerdote) Luria. He attended the medical school at the University of Turin studying with Giuseppe Levi. There, he met two other future Nobel laureates: Rita Levi-Montalcini and Renato Dulbecco. He graduated from the University of Turin in 1935 and never got a master's degree or a PhD as they were not contemplated by the Italian high educational system (which, on the other hand, was very selective). From 1936 to 1937, Luria served his required time in the Italian army as a medical officer. He then took classes in radiology at the University of Rome. Here, he was introduced to Max Delbrück's theories on the gene as a molecule and began to formulate methods for testing genetic theory with the bacteriophages, viruses that infect bacteria.

In 1938, he received a fellowship to study in the United States, where he intended to work with Delbrück. Soon after Luria received the award, Benito Mussolini's fascist regime banned Jews from academic research fellowships. Without funding sources for work in the U.S. or Italy, Luria left his home country for Paris, France in 1938. As the Nazi German armies invaded France in 1940, Luria fled on bicycle to Marseille where he received an immigration visa to the United States.

Phage research

Luria arrived in New York City on September 12, 1940, and soon changed his first and middle names. With the help of physicist Enrico Fermi, whom he knew from his time at the University of Rome, Luria received a Rockefeller Foundation fellowship at Columbia University. He soon met Delbrück and Hershey, and they collaborated on experiments at Cold Spring Harbor Laboratory and in Delbrück's lab at Vanderbilt University.

His famous experiment with Delbrück in 1943, known as the Luria–Delbrück experiment, demonstrated statistically that inheritance in bacteria must follow Darwinian rather than Lamarckian principles and that mutant bacteria occurring randomly can still bestow viral resistance without the virus being present. The idea that natural selection affects bacteria has profound consequences, for example, it explains how bacteria develop antibiotic resistance.

Luria and Latarjet in 1947 published a quantitative analysis on the effect of ultraviolet irradiation on bacteriophage multiplication during intracellular growth. During the early course of infection they found an increase in bacteriophage resistance to ultraviolet irradiation and then later a decrease. At the time this pattern, known as the Luria-Laterjet effect, was published little was known about the central role of DNA in biology. Later work established that multiple specific DNA repair pathways, encoded by the infecting bacteriophage, contribute to the increase in UV resistance early in infection.

From 1943 to 1950, he worked at Indiana University. His first graduate student was James D. Watson, who went on to discover the structure of DNA with Francis Crick. In January 1947, Luria became a naturalized citizen of the United States.

In 1950, Luria moved to the University of Illinois Urbana–Champaign. In the early 1950s, Luria and Giuseppe Bertani discovered the phenomenon of host-controlled restriction and modification of a bacterial virus: a culture of E. coli can significantly reduce the production of phages grown in other strains; however, once the phage become established in that strain, they also become restricted in their ability to grow in other strains. It was later discovered by other researchers that bacteria produce enzymes that cut viral DNA at particular sequences but not the bacteria's own DNA, which is protected by methylation. These enzymes became known as restriction enzymes and developed into one of the main molecular tools in molecular biology.

Luria won the Nobel Prize in Physiology or Medicine in 1969, with Max Delbrück and Alfred Hershey, for their discoveries on the replication mechanism and the genetic structure of viruses.

Later work

In 1959, he became chair of Microbiology at the Massachusetts Institute of Technology (MIT). At MIT, he switched his research focus from phages to cell membranes and bacteriocins.[citation needed] While on sabbatical in 1963 to study at the Institut Pasteur in Paris, he found that bacteriocins impair the function of cell membranes. Returning to MIT, his lab discovered that bacteriocins achieve this impairment by forming holes in the cell membrane, allowing ions to flow through and destroy the electrochemical gradient of cells. In 1972, he became chair of The Center for Cancer Research at MIT. The department he established included future Nobel Prize winners David Baltimore, Susumu Tonegawa, Phillip Allen Sharp and H. Robert Horvitz.

In addition to the Nobel Prize, Luria received a number of awards and recognitions. He was elected to the American Academy of Arts and Sciences in 1959. He was named a member of the National Academy of Sciences in 1960. In 1964, he was elected to the American Philosophical Society. From 1968 to 1969, he served as president of the American Society for Microbiology. In 1969, he was awarded the Louisa Gross Horwitz Prize from Columbia University together with Max Delbrück, co-winner with Luria of the Nobel Prize in Physiology or Medicine in 1969. In the U.S. he won the 1974 National Book Award in Science for his popular science book Life: the Unfinished Experiment and received the National Medal of Science in 1991.

Political activism

Throughout his career, Luria was an outspoken political advocate. He joined with Linus Pauling in 1957 to protest against nuclear weapon testing. Luria was an opponent of the Vietnam War and a supporter of organized labor. In the 1970s, he was involved in debates over genetic engineering, advocating a compromise position of moderate oversight and regulation rather than the extremes of a complete ban or full scientific freedom. Due to his political involvement, he was blacklisted from receiving funding from the National Institutes of Health for a short time in 1969.

Noam Chomsky describes him as a friend, and claims that Luria attempted to influence Jewish American writer Elie Wiesel's public stance on Israel.

Death

Luria died in Lexington, Massachusetts of a heart attack on 6 February 1991 at the age of 78.

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#6281.

2374) Alfred Hershey

Gist:

Work

Bacteriophages are viruses that attach themselves to bacteria, emptying their genetic material into them, which leads to the rapid spawning of new phage inside the bacteria. By applying genetic concept and developing statistical approaches in their studies of bacteriophages, Max Delbrück, Salvador Luria, and Alfred Hershey were able to shed new light on a range of unanswered questions within genetics. For example, in 1952 Hershey and Martha Chase were able to demonstrate that DNA was transferred from bacteriophages to bacteria, a discovery that confirmed DNA as the bearer of genetic information.

Summary

A.D. Hershey (born Dec. 4, 1908, Owosso, Mich., U.S.—died May 22, 1997, Syosset, N.Y.) was an American biologist who, along with Max Delbrück and Salvador Luria, won the Nobel Prize for Physiology or Medicine in 1969. The prize was given for research done on bacteriophages (viruses that infect bacteria).

Hershey earned a doctorate in chemistry from Michigan State College (now Michigan State University) in 1934 and then took a position at Washington University School of Medicine in St. Louis, Mo. He joined the staff of the Genetics Research Unit of the Carnegie Institution of Washington in 1950 after giving up his position as professor at Washington University. In 1963 he became director of the Genetics Research Unit.

Hershey, Delbrück, and Luria began exchanging information on phage research in the early 1940s. In 1945 Hershey and Luria, working independently, demonstrated the occurrence of spontaneous mutation in both the bacteriophages and the host. The next year, Hershey and Delbrück independently discovered the occurrence of genetic recombination in phages—i.e., that different strains of phages inhabiting the same bacterial cell can exchange or combine genetic material. Delbrück incorrectly interpreted his results as specifically induced mutations, but Hershey and one of his students proved that the results they had obtained were recombinations by showing that the genetic processes in question correspond with the crossing-over of parts of similar chromosomes observed in cells of higher organisms.

Hershey is most noted for the so-called blender experiment that he performed with Martha Chase in 1952. By showing that phage DNA is the principal component entering the host cell during infection, Hershey proved that DNA, rather than protein, is the genetic material of the phage.

Details

Alfred Day Hershey (December 4, 1908 – May 22, 1997) was an American Nobel Prize–winning bacteriologist and geneticist.

Early years

Hershey was born in Owosso, Michigan to Robert Day and Alma Wilbur Hershey. He earned a B.S. in chemistry in 1930, and Ph.D. in bacteriology in 1934 from Michigan State University. Shortly after, Hershey accepted a faculty position at Washington University in St. Louis, serving as an instructor of bacteriology and immunology from 1934 to 1950.

Bacteriophage research

At Washington University, Hershey worked closely with department head Jacques Bronfenbrenner to investigate bacteriophages, or phages—viruses that infect and replicate inside bacteria. Hershey's work on the factors impacting the virus' ability to infect its targets brought him to the attention of fellow phage researchers Max Delbrück and Salvador Luria.

The Phage Group

In 1943, Delbrück invited Hershey to Vanderbilt University to discuss his phage research. Together, with Luria, they would form the core of an informal network of researchers called "the Phage group". Three years later, Hershey and Delbrück would independently discover that different strains of bacteriophage can both exchange genetic material when infecting the same bacterial cell. This process results in hybrid phages containing genetic material from both sources, which Hershey referred to as "genetic recombination".

Hershey left Washington University in 1950 for the Department of Genetics of the Carnegie Institution of Washington, a predecessor of Cold Spring Harbor Laboratory. Two years later, he and Martha Chase would conduct the famous Hershey–Chase, or "Waring Blender" experiment. Their work confirmed that DNA, not protein, was the genetic material of life.

Later years and death

In 1962, Hershey was named director of the Department of Genetics, a position he held until his retirement in 1970. He would live on the grounds of Cold Spring Harbor Laboratory (CSHL) for the rest of his life.

Hershey's work with bacteriophage would earn him a share of the 1969 Nobel Prize in Physiology or Medicine with Delbrück and Luria, "for their discoveries concerning the replication mechanism and the genetic structure of viruses."

Although officially retired from scientific research, Hershey would continue to pursue new projects. In 1971, he edited The Bacteriophage λ, an extensive volume on the subject, published by CSHL Press that same year. In 1981, Hershey became a founding member of the World Cultural Council.

Hershey died from congestive heart failure on May 22, 1997 at his home in Laurel Hollow, New York. He was 88 years old. At the time, he was survived by his wife Harriet Davidson (1918–2000) and their only child, Peter Manning Hershey (1956–1999).

Following his death, Frank Stahl, a member of The Phage Group, wrote: "The Phage Church, as we were sometimes called Phage group, was led by the Trinity of Delbrück, Luria, and Hershey. Delbrück's status as founder and his ex cathedra manner made him the pope, of course, and Luria was the hard-working, socially sensitive priest-confessor. And Al (Hershey) was the saint."