An atomic-scale depiction of the SketchSET shows three wires (green bars) converging on the central island (center green area), which can house up to two electrons. Electrons tunnel from one wire to another through the island. Conditions on the third wire can result in distinct conductive properties. Credit: U. Pittsburgh
A University of Pittsburgh-led team has created a single-electron transistor that provides a building block for new, more powerful computer memories, advanced electronic materials, and the basic components of quantum computers.
The researchers report in Nature Nanotechnology that the transistor’s central component—an island only 1.5 nanometers in diameter—operates with the addition of only one or two electrons. That capability would make the transistor important to a range of computational applications, from ultradense memories to quantum processors, powerful devices that promise to solve problems so complex that all of the world’s computers working together for billions of years could not crack them.
In addition, the tiny central island could be used as an artificial atom for developing new classes of artificial electronic materials, such as exotic superconductors with properties not found in natural materials, explained lead researcher Jeremy Levy, a professor of physics and astronomy in Pitt’s School of Arts and Sciences. Levy worked with lead author and Pitt physics and astronomy graduate student Guanglei Cheng, as well as with Pitt physics and astronomy researchers Feng Bi, Daniela Bogorin, and Cheng Cen. The Pitt researchers worked with a team from the University of Wisconsin at Madison led by materials science and engineering professor Chang-Beom Eom, including research associates Chung Wun Bark, Jae-Wan Park, and Chad Folkman. Also part of the team were Gilberto Medeiros-Ribeiro, of HP Labs, and Pablo F. Siles, a doctoral student at the State University of Campinas in Brazil.
Levy and his colleagues named their device SketchSET, or sketch-based single-electron transistor, after a technique developed in Levy’s lab in 2008 that works like a microscopic Etch A SketchTM, the drawing toy that inspired the idea. Using the sharp conducting probe of an atomic force microscope, Levy can create such electronic devices as wires and transistors of nanometer dimensions at the interface of a crystal of strontium titanate and a 1.2 nanometer thick layer of lanthanum aluminate. The electronic devices can then be erased and the interface used anew.
The SketchSET—which is the first single-electron transistor made entirely of oxide-based materials—consists of an island formation that can house up to two electrons. The number of electrons on the island—which can be only zero, one, or two—results in distinct conductive properties. Wires extending from the transistor carry additional electrons across the island.
One virtue of a single-electron transistor is its extreme sensitivity to an electric charge, Levy explained. Another property of these oxide materials is ferroelectricity, which allows the transistor to act as a solid-state memory. The ferroelectric state can, in the absence of external power, control the number of electrons on the island, which in turn can be used to represent the 1 or 0 state of a memory element. A computer memory based on this property would be able to retain information even when the processor itself is powered down, Levy said. The ferroelectric state also is expected to be sensitive to small pressure changes at nanometer scales, making this device potentially useful as a nanoscale charge and force sensor.
Since August 2010, Levy has led a $7.5 million, multi-institutional project to construct a semiconductor with properties similar to SketchSET, he said. Funded by the U.S. Air Force Office of Scientific Research’s Multi-University Research Initiative (MURI) program, the five-year effort is intended to overcome some of the most significant challenges related to the development of quantum information technology. Levy works on that project with researchers from Cornell, Stanford, the University of California at Santa Barbara, the University of Michigan, and UW-Madison.
Provided by University of Pittsburgh
“Researchers create super-small transistor, artificial atom powered by single electrons.” April 18th, 2011. http://www.physorg.com/news/2011-04-super-small-transistor-artificial-atom-powered.html
Smallpox Vaccine Wikimedia Commons
By Rebecca BoylePosted 04.13.2011 at 12:00 pm
Humanity’s worst scourge, the smallpox virus, may finally wind up on death row in May if health officials decide to destroy the last known samples. The virus was eliminated in human populations more than 30 years ago, but several international groups want to kill any remaining virus samples stored in test tubes on two continents.
Destruction of the smallpox virus, which was eradicated in the 1970s, has been mulled since 1980, but World Health Organization officials renewed debate about the matter earlier this year and will decide the viruses’ fate at an upcoming meeting.
Two labs possess the last known live samples of the variola virus — the Centers for Disease Control and Prevention in Atlanta, and a Russian facility in Siberia. Officials in developing nations, where smallpox is more likely to spread should it resurface, have been pushing for their destruction since 1980. The World Health Assembly decided to kill the samples in 1996, but they have been granted stays of execution in the decade and a half since, with the United States, Russia and others arguing the virus samples could seed new vaccines and potential treatments for infected patients.
In January, WHO officials again started discussions about whether to destroy the samples. The World Health Assembly will decide in May. LiveScience reviews the controversy here.
Epidemiologists believe smallpox has killed about one-third of those it has infected throughout history, accounting for hundreds of millions of victims dating back to ancient Egypt. A decade-long global vaccination effort eliminated the virus from human populations; the last natural case was found in October 1977 in Somalia. The elimination of Rinderpest, a cattle plague, will be only the second such disease eradication story in human history.
Officials in the U.S. and Russia have said they will fight efforts to set a destruction date, arguing the viruses are needed for research and to guard against bioterrorism. Some fear nations like North Korea or Iran may possess secret samples, although those countries deny it.
Biography: Jonas Salk Developer of Polio Vaccine Jonas Salk Date of birth: October 28, 1914 Jonas Salk Date of death: June 23, 1995 Back to Jonas Salk Biography In America in the 1950s, summertime was a time of fear and anxiety for many parents; this … by The American Academy of Achievement
In America in the 1950s, summertime was a time of fear and anxiety for many parents; this was the season when children by the thousands became infected with the crippling disease poliomyelitis, or polio. This burden of fear was lifted forever when it was announced that Dr. Jonas Salk had developed a vaccine against the disease. Salk became world-famous overnight, but his discovery was the result of many years of painstaking research.
Jonas Salk was born in New York City. His parents were Russian-Jewish immigrants who, although they themselves lacked formal education, were determined to see their children succeed, and encouraged them to study hard. Jonas Salk was the first member of his family to go to college. He entered the City College of New York intending to study law, but soon became intrigued by medical science.
While attending medical school at New York University, Salk was invited to spend a year researching influenza. The virus that causes flu had only recently been discovered and the young Salk was eager to learn if the virus could be deprived of its ability to infect, while still giving immunity to the illness. Salk succeeded in this attempt, which became the basis of his later work on polio.
After completing medical school and his internship, Salk returned to the study of influenza, the flu virus. World War II had begun, and public health experts feared a replay of the flu epidemic that had killed millions in the wake of the First World War. The development of vaccines controlled the spread of flu after the war and the epidemic of 1919 did not recur.
In 1947, Salk accepted an appointment to the University of Pittsburgh Medical School. While working there, with the National Foundation for Infantile Paralysis, Salk saw an opportunity to develop a vaccine against polio, and devoted himself to this work for the next eight years.
In 1955 Salk’s years of research paid off. Human trials of the polio vaccine effectively protected the subject from the polio virus. When news of the discovery was made public on April 12, 1955, Salk was hailed as a miracle worker. He further endeared himself to the public by refusing to patent the vaccine. He had no desire to profit personally from the discovery, but merely wished to see the vaccine disseminated as widely as possible.
Salk’s vaccine was composed of “killed” polio virus, which retained the ability to immunize without running the risk of infecting the patient. A few years later, a vaccine made from live polio virus was developed, which could be administered orally, while Salk’s vaccine required injection. Further, there was some evidence that the “killed” vaccine failed to completely immunize the patient. In the U.S., public health authorities elected to distribute the “live” oral vaccine instead of Salk’s. Tragically, the preparation of live virus infected some patients with the disease, rather than immunizing them. Since the introduction of the original vaccine, the few new cases of polio reported in the United States were probably caused by the “live” vaccine which was intended to prevent them.
In countries where Salk’s vaccine has remained in use, the disease has been virtually eradicated.
In 1963, Salk founded the Jonas Salk Institute for Biological Studies, an innovative center for medical and scientific research. Jonas Salk continued to conduct research and publish books, some written in collaboration with one or more of his sons, who are also medical scientists.
Salk’s published books include Man Unfolding (1972), The Survival of the Wisest(1973), World Population and Human Values: A New Reality (1981), and Anatomy of Reality (1983).
Dr. Salk’s last years were spent searching for a vaccine against AIDS. Jonas Salk died on June 23, 1995. He was 80 years old.
In the summer of 1950 fear gripped the residents of Wytheville, Virginia. Movie theaters shut down, baseball games were cancelled and panicky parents kept their children indoors — anything to keep them safe from an invisible invader. Outsiders sped t…
American Experience: The Polio Crusade
Airs Monday, April 12, 2010 at 9 p.m. on KPBS TV
Credit: March of Dimes
Above: Nurse and child with polio. This program is the story of the largest public health experiment in American history — the effort to eradicate polio, one of the 20th-century’s most dreaded diseases.
April 9, 2010
It was the largest public health experiment in American history – a crusade that eradicated polio, one of the 20th century’s most dreaded diseases. The polio epidemic terrified Americans for decades, affecting thousands of children, leaving many crippled, paralyzed or condemned to life in an iron lung.
In the mid-twentieth century, the National Foundation for Infantile Paralysis (predecessor to today’s March of Dimes) pioneered a new approach to philanthropy, raising money a dime at a time from millions of small donors. The nonprofit enlisted poster children, celebrities, presidents, and other partners in their high-profile campaigns. View the photos.
But on April 26, 1954, hope emerged. At the Franklin Sherman Elementary School in McLean, Virginia, six-year-old Randy Kerr stood at the head of a long line of children and waited patiently while a nurse gently rolled up his sleeve, then filled a syringe with a cherry-colored liquid containing the world’s first polio vaccine.
Developed just a few years earlier by virologist Jonas Salk, the polio vaccine had not yet been widely tested on humans. No one was certain it was safe or whether it could provide effective protection against the disease. In the coming weeks, nearly two million school children in 44 states received the shots. The Salk vaccine trials were the dramatic culmination of years of research and a multi-million dollar investment, made up in large part by public donations.
Based in part on David Oshinsky’s Pulitzer Prize-winning book, “Polio: An American Story,” “The Polio Crusade” chronicles a decades-long crusade, fueled by the bold leadership of a single philanthropy and its innovative public relations campaign, and features a bitter battle between two scientists and the breakthrough of a now-forgotten woman researcher.
The 20th-century effort to eradicate polio is chronicled. Included: lawyer Basil O’Connor (1892-1972), who developed the “March of Dimes” concept to help fund research; the competition between polio researchers Jonas Salk and Albert Sabin.
|Poliomyelitis is a viral disease. There are three types of poliovirus and many strains of each type. The virus enters through the mouth and multiplies in the throat and gastrointestinal tract, then moves into the bloodstream and is carried to the central nervous system where it replicates and destroys the motor neuron cells. Motor neurons control the muscles for swallowing, circulation, respiration, and the trunk, arms, and legs.
Human nerve cells have a protruding protein structure on their surface whose precise function is unknown. When poliovirus encounters the nerve cells, the protruding receptors attach to the virus particle, and infection begins. Once inside the cell, the virus hijacks the cell’s assembly process, and makes thousands of copies of itself in hours. The virus kills the cell and then spreads to infect other cells.
|Many types of human cells have receptors that fit the poliovirus; no one knows why the virus favors motor neurons over other cells for replication.|
|For every 200 or so virus particles that encounter a susceptible cell, only one will successfully enter and replicate.|
|In tissue culture, poliovirus enters cells and replicates in six to eight hours, yielding 10,000 to 100,000 virus particles per cell.|
|One way the human immune system protects itself is by producingantibodies that engage the protein covering of the poliovirus, preventing the virus from interacting with another cell.|
|There are three types of poliovirus: 1, 2, and 3. Type 1 is the most virulent and common. Both the Salk and Sabin vaccines are “trivalent” that is, active against all three virus types. Type 2 poliovirus has not been detected anywhere in the world since 1999.|
|A person who gets polio is immune to future infection from the virus type that caused the polio.|
|These models are an adaptation of James Hogle’s image of the poliovirus and were specially cast in bronze for the exhibit. They are the first three dimensioanl representations of the poliovirus
Poliovirus Capsid Model and Scientific Art
A Vaccine to Prevent Polio
Life cycle of the poliovirus
Illustration courtesy NMAH
James Hogle in his Harvard Medical School lab, 2000