Archive for September, 2011

September 28, 2011

One, two, bits of spin

There seems to be a good deal of activity in quantum computing implementations using qubits based on spin states of one or two electrons. Alternative implementations involve photons, ions, or several other possibilities. So far, spin qubit implementations have been lagging somewhat. This is even though there are advantages of using spin qubits, since the implementation can involve solid-state semiconductor technology, which of course is now very sophisticated.

New research now seems to be advancing spin qubit technology. Among the earlier challenges were reading out single qubit states and addressing individual qubits among others in a group. Solutions to these issues has made possible single and double qubit operations. So the next stage is being able to deal with more than two spin qubits at a time in a solid-state system.

One, two, bits of spin

Over the last decade, the experimental emphasis for spin qubits has been on demonstrating the required criteria for a viable scheme for quantum computing. This has been driven primarily by groups at Harvard and Delft universities. The next stage is to go to higher numbers of coupled qubits and demonstrate more complex quantum gate operations and algorithms. The paper by Brunner et al. is a necessary step forward. It is clear that the spin qubit system currently lags behind other quantum computer implementation schemes. Solid-state based schemes, especially semiconductor ones, have always held the promise, however, that the enormous progress from decades of device integration technology development could one day lead to scalability not feasible with other schemes. To achieve this, however, we need parallel work on spin qubits in different materials to optimize coherence times, device designs, and architectures and to explore hybrid technology based on exploiting the most useful properties of different schemes.

Further reading:

Two-Qubit Gate of Combined Single-Spin Rotation and Interdot Spin Exchange in a Double Quantum Dot

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September 28, 2011

One-Third of Sun-Like Stars Have Earth-Like Planets in the Habitable Zone

News of new extrasolar planet discoveries keeps coming, fast and furious. It’s hard to keep track of the latest. There are some very strange planets out there. But what really interests most people, it seems, is how many planets out there are like Earth. Apparently there’s this deep-seated desire to to find places in the universe that seem familiar.

Unfortunately, that’s not easy. In the first place, Earth is a relatively small planet, as are most rocky planets, in contrast to larger “gas giant” planets. It is these small, rocky planets that should be most like Earth, especially in terms of allowing for “life as we know it”. Although there are several different methods of detecting extrasolar planets, they’re all more likely to notice larger planets than smaller ones.

Secondly, only planets that orbit in a narrow range of distances from their host star are neither too hot nor too cold to permit the existence of liquid water and a decent atmosphere on the planet’s surface. The size of the range depends on the size and (relatedly) the brightness of the star. For stars that are reasonably close in size to our own, it’s easier to detect any kind of planet closer to the star than farther out. Usually too close to be in the habitable zone.

For these two reasons alone, present extrasolar planet searches are likely to seriously undercount Earthlike planets in a star’s habitable zone. However, by analyzing the data already accumulated on extrasolar planets around stars similar in size to the Sun, and making a reasonable assumption, the data can be extrapolated to suggest roughly how many planets similar to Earth are out there, even though we can’t yet detect most of them.

The assumption is that the pattern of existence and location for smaller planets is similar to the pattern for larger planets we can detect. With that assumption, the conclusion stated in the title here is at least plausible.

One-Third of Sun-Like Stars Have Earth-Like Planets In Habitable Zone  – Technology Review

What interests most astronomers is how many exoplanets orbit at a greater distance, inside the habitable zone. Most of these planets are too far away from their stars to have been picked up by Kepler yet. But Traub says his data analysis provides a way to work out how many their ought to be.

That’s because he’s found a power law that describes how the number of stars with a given orbital period. So all he has to do is assume a longer orbital period equivalent to being in the habitable zone to work out how many planets there ought to be at this distance.

Here’s the answer: “About one-third of FGK stars are predicted to have at least one terrestrial, habitable-zone planet,” he says.

Further reading:

Terrestrial, Habitable-Zone Exoplanet Frequency from Kepler

September 28, 2011

Blood Pressure Drugs May Lengthen Lives of Some Cancer Patients

It appears that a certain class of drugs (beta-blockers) used to control high blood pressure may also be helpful for people with some cancers, at least by slowing the progression of the disease.

How does this happen? It seems that earlier studies had shown that a couple of stress hormones – epinephrine and norepinephrine – bind to certain tumor cell receptors. When that happens, the cell is stimulated to produce vascular endothelial growth factor and two immune system interleukins. The result is an enhancement of blood supply to the tumor, thus promoting growth and metastasis.

But beta-blockers block the receptors, and hence inhibit effects of the hormones. Theoretically this should inhibit tumor development. In order to test this hypothesis, a large database of Danish cancer patient records was examined. It was found that melanoma patients who were also taking beta-blockers had their chances of surviving a specified number of years improved by 13%. Not a lot, but a benefit nevertheless. And the value of reducing effects from stress hormones was demonstrated. Perhaps other drugs may have larger effects. Lowering stress levels may help too.

Blood Pressure Drugs May Lengthen Lives of Melanoma Patients – Ohio State University

Beta-blocker drugs, commonly used to treat high blood pressure, may also play a major role in slowing the progression of certain serious cancers, based on a new study.

A review of thousands of medical records in the Danish Cancer Registry showed that patients with the skin cancer melanoma, and who also were taking a specific beta-blocker, had much lower mortality rates than did patients not taking the drug.

Further reading:

β-Blockers and Survival among Danish Patients with Malignant Melanoma: A Population-Based Cohort Study

September 28, 2011

Astronomers Discover New Standard Candle

Just a few days ago there was a story about a new type of “standard candle” for use in measuring very large astronomical distances. Such standard candles have been lacking when the distances to be measured are a bit more than halfway back to the big bang – around 7 or 8 billion light-years. Consequently, it’s very difficult to obtain reasonably precise data about many things that happened in the early universe, such as the rate at which the universe was expanding then. This is a major problem since phenomena such as dark energy are difficult to theorize about without good data.

Now another type of standard candle has been identified, and it also makes it possible to gauge large distances – even to objects whose light was emitted about 1.5 billion years after the big bang, at a distance of 12 billion light-years (redshift z~4).

Astronomers Discover New Standard Candle – Technology Review

In theory, distance should be simple to work out. If you know the intrinsic brightness of an object, a simple measure of its apparent brightness will tell you how far away it is (since brightness falls as an inverse square of its distance).

So in astronomy, the problem of distance is intimately linked to the problem of knowing an object’s intrinsic brightness.

But that’s hard. There’s simply no way to tell the intrinsic brightness of most stars and galaxies and so no way to work out their distance.

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September 27, 2011

Five easy mutations to make bird flu a lethal pandemic

This is pretty scary. It’s been a concern all along, of course, that such mutations could occur, but now it has been actually verified… in ferrets. One has to feel sorry for the ferrets…. And we think we have enough problems already. Just wait.

Five easy mutations to make bird flu a lethal pandemic – New Scientist

H5N1 bird flu can kill humans, but has not gone pandemic because it cannot spread easily among us. That might change: five mutations in just two genes have allowed the virus to spread between mammals in the lab. What’s more, the virus is just as lethal despite the mutations.

“The virus is transmitted as efficiently as seasonal flu,” says Ron Fouchier of the Erasmus Medical Centre in Rotterdam, the Netherlands, who reported the work at a scientific meeting on flu last week in Malta.

September 27, 2011

Brain wiring continues

Well, that’s a relief! To suppose that brain development more or less stops at the end of adolescence implies all that happens afterwards is just adding data. Surely there’s more to things like prudence, levelheadedness, and understanding of others than just added data.

Brain wiring continues – University of Alberta

It has been a long-held belief in medical communities that the human brain stopped developing in adolescence. But now there is evidence when examining the development of wiring in some parts of the brain this is not in fact the case, thanks to medical research conducted in the Department of Biomedical Engineering by researcher Christian Beaulieu, an Alberta Innovates – Health Solutions scientist, and by his PhD student at the time, Catherine Lebel. Lebel recently moved to the United States to work at UCLA, where she is a post-doctoral fellow working with an expert in brain-imaging research.

“This is the first long-range study, using a type of imaging that looks at brain wiring, to show that in the white matter there are still structural changes happening during young adulthood,” says Lebel. “The white matter is the wiring of the brain; it connects different regions to facilitate cognitive abilities. So the connections are strengthening as we age in young adulthood.”

Further reading:

Longitudinal Development of Human Brain Wiring Continues from Childhood into Adulthood

September 25, 2011

How microbes train our immune system

The mammalian immune system is a complex but impressive product of evolution. It’s able to defend the body against a wide variety of pathogens, and even to some extent against cancer cells. But to do its job most effectively, the cellular agents of the system need to be trained to distinguish their proper targets from other cells in the body that need to be left alone.

Among the cells that need to be left alone are not only all the body’s own cells, which are descendants of a single fertilized egg. There are also about ten times as many bacterial cells in the intestines, which help digest food and cause no problems (as long as they stay in the intestines). But they need to avoid attack from the immune system. How this protection from attack comes about has not been understood. Research just published doesn’t give nearly a complete answer, but does make some significant progress.

The immune system’s primary agents for implementing the system’s policies are T cells. Although there are a number of different types of T cells, they can be sorted roughly into two categories: regulatory T cells and effector T cells. The effector cells are the ones that take action against pathogens that they recognize. The regulatory cells can send signals to the effector cells to temper their activity around cells that need to be protected from the immune system.

Immature T cells originate in bone marrow. Receptors on their surfaces are able to recognize a vast number of protein antigens. These cells are matured in the thymus. T cells which recognize antigens that identify the body’s own cells mature into regulatory T cells. The rest mature into effector T cells.

What the new research has found, in studies on mice, is that regulatory T cells in the intestines also recognize antigens that signify benign intestinal bacteria. Since that could not plausibly have happened in the thymus, it must have occurred in the intestines, where the bacteria are found. But the mechanism behind this is still unknown.

How microbes train our immune system – Nature News

Not all foreign particles in the body warrant destruction, however. Microbes living harmlessly, and often helpfully, in the body evade the immune system’s wrath, but researchers don’t know how. Chyi-Song Hsieh of Washington University School of Medicine in St Louis, Missouri, and his colleagues now report that these microbes seem to provide localized instruction in the gut, telling immature T cells that recognize them to develop into regulatory T cells.

Previous work had suggested that regulatory T cells could be induced outside the thymus, but this is the first demonstration that such peripherally generated cells actually exist.

Further reading:

Colon identified as a seat of immune cell learning

Peripheral education of the immune system by colonic commensal microbiota

September 25, 2011

Better Lithium-Ion Batteries Are On The Way

Battery technology has a long history, as the first batteries were invented in 1800 by Alessandro Volta. Progress has been continual, but slow. The requirement is to store as much electrical energy as possible in something with the lowest weight, while allowing repeated recharging – all at a reasonable cost. Lithium-ion batteries in general do the best job to date.

However, as users of everything from cell phones to portable computers to electric and hybrid cars know, existing batteries either don’t seem to go long enough between recharging or they add too much weight. The need for improvements is becoming even more urgent, since much more battery capacity will be required to store electrical energy from renewable but intermittent sources like wind and solar.

The main problem with current lithium-ion batteries is the limited capacity of battery anodes made of carbon. Anodes made of silicon (carbon’s closest chemical relative) could permit the storage of much more energy. However, silicon particles in anodes need to be coated with a more conductive material. Carbon is still being used for this, but due to repeated swelling and shrinking of the silicon during the charge/discharge cycle, contact with the carbon degrades. The new development here is a conductive polymer material that can replace the carbon and still maintain tight contact with the silicon particles.

Better Lithium-Ion Batteries Are On The Way From Berkeley Lab

A team of scientists at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has designed a new kind of anode that can absorb eight times the lithium of current designs, and has maintained its greatly increased energy capacity after over a year of testing and many hundreds of charge-discharge cycles.

The secret is a tailored polymer that conducts electricity and binds closely to lithium-storing silicon particles, even as they expand to more than three times their volume during charging and then shrink again during discharge. The new anodes are made from low-cost materials, compatible with standard lithium-battery manufacturing technologies.

Further reading:

Battery tech improving as demand soars

New Li-Ion battery to give eight times the power of regular ones?

Polymers with Tailored Electronic Structure for High Capacity Lithium Battery Electrodes

September 25, 2011

Electrons surf between qubits

Another week, another interesting development in quantum computing. This time the task addressed is moving quantum information around inside a quantum computer. As usual, the qubit information is encoded in electron spin, so the goal is to move the electrons around without experiencing decoherence that would disrupt the information. Two teams published papers this week in Nature explaining how they’ve accomplished at least part of the task.

In both cases, the electrons are moved in a channel on a semiconductor surface, between two quantum dots, spaced 3 or 4 microns apart. The force to move the electrons is supplied by a small piezoelectric actuator. In one case it was possible to move an electron back and forth 60 times, for a total distance of .25 mm. Although the total travel time is less than the normal decoherence time, both teams have yet to prove that decoherence is avoided.

Electrons surf between qubits – physicsworld.com

Two independent groups of physicists have taken an important step towards the creation of a practical quantum computer by showing how to transfer single electrons over relatively long distances between quantum dots. Both schemes involve using sound waves on the surface of a material to propel electrons between the quantum dots – which are sub-micron-sized pieces of semiconductor. The teams are confident that they will soon be able to show that electrons arrive at their destination with their quantum information intact, making the system a viable “quantum data bus” for a quantum computer.

Further reading:

Electron tennis plays well for quantum computing

On-demand single-electron transfer between distant quantum dots

Electrons surfing on a sound wave as a platform for quantum optics with flying electrons

September 24, 2011

Stems cells are potential source of cancer-fighting T cells

The human immune system is, in principle, capable of killing cancer cells all by itself, without need for any extra drugs or doses of radiation. But that supposes the immune system is able to distinguish cancer cells from healthy body cells, since it’s not a good thing when the immune system targets healthy cells.

Stems cells are potential source of cancer-fighting T cells

Adult stem cells from mice converted to antigen-specific T cells — the immune cells that fight cancer tumor cells — show promise in cancer immunotherapy and may lead to a simpler, more efficient way to use the body’s immune system to fight cancer, according to Penn State College of Medicine researchers.

“Cancer immunotherapy is a promising method to treat cancer patients,” said Jianxsun Song, assistant professor of microbiology and immunology. “Tumors grow because patients lack the kind of antigen-specific T cells needed to kill the cancer. An approach called adoptive T cell immunotherapy generates the T cells outside the body, which are then used inside the body to target cancer cells.”

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