Archive for September 25th, 2011

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 –

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