Monday, January 14, 2008

Mitsubishi introduce Laser TV

Bringing their considerable laser expertise to bear in a flat panel TV, the electronics giant Mitsubishi this week at the Consumer Electronics Show (CES) in Las Vegas, introduced a 65in laser TV.

Alongside a regular Plasma TV in 2006, Mitsubishi's laser TV looked stunning, although there was no such comparison with this latest demo. Nevertheless, at first glance, contrast and colours from this innovative piece of kit looked absolutely stunning.

At half the weight, and using quarter of the electricity of conventional plasma and LCD TVs, laser offers more than stunning picture quality.

Very few details have been released by Mitsubishi relating to potential availability of their laser prototype, but if the reaction of attendees at the CES is anything to go by, they will be pulling out all the stops to create a commercially viable product.

The Absolute Latest in HDTVs

Straight from CES, we have laser TVs, concept TVs, and gaming LCD TVs, as well as an onslaught of new plasma and LCD TVs ready to invade your living room. Take a look.

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Sony's newly announced XEL-1 OLED (Organic Light Emitting Diode) television is available for sale in Sony Style stores, effective immediately. (See our video for more information.) The TV is the first OLED television to ship in North America. The impressively thin, 11-inch set has an angled, articulating arm that's attached to a base, and the unit's depth is just 3mm. Its OLED technology delivers deep blacks, a 1,000,000:1 contrast ratio, accurate colors and details, and a bright picture--all with no backlight and lower-than-typical power consumption. --Greg Adler and the PCW CES Team,141210-c,hdtv/article.html#

Cheap Ethanol from Tires and Trash

GM teams with a startup aiming to produce low-cost biofuels.

Fuel fibers: A bundle of hollow fibers is the heart of a new process for making ethanol from sources other than corn. Organic materials are heated up to form a mixture of hydrogen, carbon dioxide, and carbon monoxide. When the pictured bioreactor is in operation, the gases flow through the center of the fibers and feed bacteria growing on the outside. The bacteria convert the gases into ethanol.
Credit: Kevin Bullis

Yesterday at the North American International Auto Show in Detroit, General Motors announced a partnership with Coskata of Warrenville, IL, a new company that claims it can make ethanol from wood chips, grass, and trash--including old tires--for a dollar a gallon. That's significantly less than it costs to make the biofuel from corn grain, which is the source of almost all the ethanol made in the United States.

Coskata executives, who until the announcement had kept the company's existence and technology under wraps, say they have developed a hybrid approach involving both thermochemical and biological processes for making ethanol. Until now, most researchers have focused on developing either thermochemical or biological methods. Coskata says that besides being cheaper than other ethanol production processes under development, its technology uses less energy and water.

GM will give financial, technical, and marketing support to Coskata to help it scale up its process, which so far has been demonstrated only at the lab scale. Coskata is completing a pilot-scale ethanol production facility and will announce locations for a 40,000-gallon-per-year facility and a 100-million-gallon-per-year commercial-scale plant later this year.

Coskata joins a number of other companies looking for ways to make biofuels from alternative sources. A new federal mandate, signed into law late last month, calls for 36 billion gallons of biofuels to be produced by 2022; of that, 21 billion gallons is to come from sources other than corn grain. But so far technology for making ethanol from such feedstocks has not been proved commercially.

The Coskata process begins with gasification, a well-known technology that involves heating up a wide range of organic materials until their components disassociate and form synthesis gas, a mixture of hydrogen, carbon monoxide, and carbon dioxide. Then, instead of using chemical catalysts to convert the syngas into various alcohols as is done in conventional processes (see "Breaking Ground on Cellulosic Ethanol"), Coskata uses new strains of bacteria to convert it into ethanol. Since ethanol is the only product, the technique produces a better overall yield than catalytic processes. Bacteria are also easier to work with than catalysts in some ways. For example, they're not as particular about the ratio of gases in the syngas. "It is theoretically possible to feed our organism exclusively carbon monoxide and it will make ethanol from that," says Richard Tobey, vice president of R&D and engineering at Coskata. "You can't do that with the catalytic approaches."

The hybrid system makes it practical to use an alternative to the conventional distillation step used in ethanol production; the Coskata version uses only half as much energy. In this alternative process, called vapor permeation, water and ethanol vapor pass through a tubelike membrane. By the end, almost all the water has been removed, leaving behind ethanol that's 99.7 percent pure. Ordinary fermentation processes produce a broth of water and ethanol full of processed biomass that would clog up such a membrane.

At least one other company has tried a hybrid approach to making ethanol: the biofuels company BRI Energy found similar bacteria that can process syngas. But Andy Aden, a senior researcher investigating cellulosic ethanol at the National Renewable Energy Laboratory in Golden, CO, says one problem with such approaches is that it's been difficult to make the syngas accessible to the bacteria, since syngas doesn't dissolve easily in water. Coskata has tackled this problem with a new bioreactor design in which bacteria grow in dense biofilms on the outside of hollow fibers. Syngas is pumped through the inside of these fibers and diffuses through them directly to the biofilm. Aden says the biofilm approach sounds promising, although he cautions that such systems have been difficult to scale up to the commercial scale.

While Coskata says its process can work with a very wide range of feedstocks, in practice it might be best suited for specific materials. "I think that it will work very well for woody materials and maybe almost uniquely well for municipal solid waste and some of these other high-carbon wastes, like tires," says Bruce Dale, a professor of chemical engineering and materials science at Michigan State University. But he says biological approaches could work better with feedstocks such as switchgrass.

So far the company makes ethanol only a few drips at a time. The economics of the process at the commercial scale will depend on a number of factors, including how much the feedstock costs and whether the system works well in larger bioreactors.

Growing New Hearts from Old

Donor hearts could make good scaffolding for new organs.

An empty heart: Researchers have created new hearts using decellularized rat and pig hearts as scaffolds. In this series, a heart containing cells (top) becomes a scaffold stripped of cells (bottom).
Credit: University of Minnesota
Watch Doris Taylor and her team make new hearts.

Scientists at the University of Minnesota have taken a big step toward making replacement organs with the recipients' cells. In experiments performed on rats and pigs, the researchers stripped donor hearts of their cells to create scaffolds on which the recipients' cells were grown. The hope is that a similar approach might someday prove useful to human patients with end-stage heart disease. In theory, these novel hearts could prove to be better than traditional donor hearts because they are less likely to cause an immune response.

"It's an audacious, gutsy, exciting piece of work," says Buddy Ratner, a professor of bioengineering and chemical engineering at the University of Washington, who was not involved in the research. Still, substantial hurdles remain before the approach might be applicable to human patients.

"This is just a first proof of concept, showing that it's not completely crazy" to try to decellularize a whole heart and repopulate it with new cells, says Doris Taylor, director of the Center for Cardiovascular Repair at the University of Minnesota. Her team's work was published yesterday in Nature Medicine online.

In order to create decellularized scaffolds, Taylor and her team perfused rat hearts with detergents. When the cells were removed, a complex architecture of white extracellular matrix remained. The anatomy of the heart chambers seemed to be intact, as did the valves and blood vessels, says Taylor.

The researchers reseeded the scaffolds with cardiac and endothelial cells taken from rats. Then they placed these constructs in bioreactors that simulated blood pressure, electrical stimulation, and other aspects of cardiac physiology. "We wanted to treat the cells as if they were in a heart and see if they behaved accordingly," Taylor says. After four days, the cells in the hearts began to contract. After eight days, the hearts were able to pump with about 2 percent of the force of an adult rat heart, according to the paper.

"This is the ultimate biomimetic approach to cardiac tissue engineering," says Gordana Vunjak-Novakovic, a professor of biomedical engineering at Columbia University. A decellularized whole heart matrix provides "practically an ideal scaffold," she says, since it preserves much of the composition, structure, and mechanical properties of the heart.

In theory, if hearts could be made this way for human patients, they might offer an alternative to traditional donor hearts. Theoretically, patients would not need to take immunosuppressant drugs since the new constructs would be built with their own cells.

Still, the method would require a cadaver heart (or possibly a pig heart) from which to make the scaffold. It still "takes a heart to make a heart, and we can't spare any hearts at the moment," says Ratner.

Another challenge would be securing appropriate human cells--in sufficient quantity--to repopulate the scaffold. Adult heart-muscle cells, or cardiomyoctyes, do not proliferate, says Vunjak-Novakovic. Nor can these cells be made from readily available sources such as adult cells derived from bone marrow. Resident stem cells are a potential source, but they are not plentiful. Embryonic stem cells are also a possibility, but they need to be directed to differentiate into a desired tissue and customized in order to be accepted by patients.

Additional challenges, which might prove more difficult for larger human hearts, include loading the scaffold with the appropriate numbers of cells, keeping the cells alive with sufficient nutrients and oxygen, and having them mature properly.

Creating a heart that is electrically stable over long periods of time may also be difficult, says Richard Lee, a cardiologist at Brigham and Women's Hospital, in Boston, and a professor at Harvard Medical School.

In addition, the heart would have to be able to exist in vivo for long periods of time without causing blood clots or strokes. "There's a long way to go before you could actually feel like this is on the horizon" for treating patients, says Lee.

In recent years, research on cardiac tissue engineering has proliferated greatly. Many groups now use cells in conjunction with various kinds of scaffolding material to try to reconstruct either vascular or cardiac tissue structure.

While the heart envisioned by Taylor might be an alternative to transplant for some patients with end-stage heart disease or congestive heart failure, other work is aimed at repairing localized areas of damage, such as that caused by myocardial infarction, or heart attack.

For instance, several groups are currently working on cardiac patches, which are bands of engineered tissue that can be surgically applied over a damaged area of the heart in order to help restore its function.

Researchers working on cardiac patches face some of the same challenges that Taylor's group does: securing appropriate cells, growing them on a scaffold, and successfully integrating them into the body, says Vunjak-Novakovic. Her group is engineering patches using human adult stem cells and human embryonic stem cells, with the goal of revascularizing and rebuilding cardiac structure in an area that has been damaged by a heart attack. Cardiac patches have shown some promise in animal studies but have yet to be tested in human trials.

Taylor says that her team's decellularized heart technology might also be used to create a portion of a heart like a wall or a ventricle, or a section of tissue that could be used as a patch.

Another approach is to inject cells into damaged heart regions with the hope of rebuilding or repairing heart tissue and vasculature. Lee says that injecting bone-marrow cells into the heart's arteries has shown some success in improving ejection fraction (the percentage of blood ejected with each beat) and other measures of heart function in human clinical trials.

Given the enormous number of patients in need of new options, Lee adds, "everything should be on the table. We can't give up on any approach, no matter how wild or improbable, until we get better treatments to these people."

Turning Waste Heat into Power

Research shows that silicon is as efficient as pricier materials.

Cool customer: This image, produced by a scanning electron microscope, shows a rough silicon nanowire bridging two heating pads--one serving as a heat source and the other as a sensor. Researchers have found that 50-nanometer-wide silicon nanowires have drastically lower heat conductivity than bulk silicon but retain their electrical conductivity. Thus the nanowires show potential as thermoelectric materials--ones that convert heat into electricity and vice versa.
Credit: A. Hochbaum

Silicon, in the form of photovoltaic cells, is good at generating electricity from sunlight. New research shows that it could also make a good thermoelectric: a material that converts heat into electricity and vice versa. Since silicon is more abundant than the leading thermoelectric materials and has a vast manufacturing infrastructure behind it, it could eventually yield cheap devices for generating power from engines' waste heat or from solar heat.

In this week's Nature, University of California, Berkeley, chemistry professor Peidong Yang and his colleagues report having fabricated silicon nanowires that generate electricity when a temperature differential is applied across them. Until now, silicon has been considered a bad thermoelectric material. But according to Yang, "the performance of the nanowires is already comparable to the best existing thermoelectric material."

Thermoelectric devices have been around since the early 1960s, usually made from either bismuth telluride or lead telluride. They are used mainly for cooling: when a voltage is applied across a thermoelectric material, it gets hotter on one side and cooler on the other. Thermoelectric coolers are popularly used in portable picnic coolers and cooling car seats.

But more exciting applications lie in energy efficiency and energy generation. Thermoelectrics could be used to convert waste heat generated by car engines into electricity. Even more attractive is the idea of thermoelectrics' harnessing the sun's heat to create electricity. But bismuth telluride and lead telluride are not efficient enough, so devices made from them are costly as well as bulky, because they require more material.

Thermoelectrics would have to be at least twice as efficient as they now are to be used for cheap power generation, says Mildred Dresselhaus, a thermoelectrics pioneer and physics and electrical-engineering professor at MIT. Using nanoscale structures instead of bulk crystals of the materials can increase their efficiency, she says. Nanostructures block the flow of heat but allow electrons to flow easily. But processing and nanostructuring bismuth telluride is not easy.

Silicon, on the other hand, "is much easier to process, has a big processing infrastructure behind it," Yang says. "Silicon also has a much lower cost than bismuth telluride." The problem with silicon is that it is a bad thermoelectric. A good thermoelectric needs to be two things: a good electrical conductor and a bad heat conductor. Silicon conducts both heat and electricity very well.

Yang and his colleagues reduced silicon's thermal conductivity by using silicon nanowires. They fabricated an array of silicon nanowires that are between 20 and 300 nanometers in diameter. Nanowire synthesis often involves liquefying a nanoparticle and inducing it to grow, much like a hair. But that produces nanowires with smooth surfaces. The chemical etching method that Yang's team uses results instead in nanowires that have rough surfaces. The researchers found that wires that are about 50 nanometers wide retain electrical conductivity but have only one-hundredth the thermal conductivity. This results in a thermoelectric efficiency close to that of some commercial bismuth telluride materials.

No current theory explains why the nanowires' thermal conductivity goes down so drastically. One of the reasons, Yang believes, is that the nearly one-dimensional nanowires and the wires' rough edges block the flow of phonons, which are particles that carry heat. But the complete picture remains unclear.

Ali Shakouri, an electrical-engineering professor at the University of California, Santa Cruz, says that researchers will have to understand how the physics works before they can improve the technology enough to produce commercial devices. Furthermore, using nanowires for energy conversion and power generation has its own limitations, Shakouri says. Such applications require large arrays of nanowires, but in the Nature paper, Yang and his colleagues measured the electrical properties of individual nanowires. The researchers will have to make sure that those properties translate to entire nanowire arrays, says Shakouri: "Variations and interactions between nanowires could take away some advantages."

Still, he says, "this is important work that could have a big impact." Shakouri points not only to the demonstration of silicon's potential as a thermoelectric, but also to the unique engineering that the researchers used to make rough nanowires. "The new way of playing with material properties is very interesting," he says. "It could open up a way to improve thermoelectrics that could be applied to other materials."

Yang and his colleagues, meanwhile, are already thinking about how to improve their nanowires' performance. They plan to reduce the size of the nanowires and make their surfaces rougher than they already are. That should enhance their thermoelectric properties, Yang says. The researchers also plan to make and test an actual thermoelectric device using silicon nanowires.