Di seguito gli interventi pubblicati in questa sezione, in ordine cronologico.
Light is one of the most promising carriers of quantum information. It is robust against decoherence because it does not interact with stray electric and magnetic fields and passes unscathed through transparent matter.
But this prized robustness is also a serious limitation. Photons do not easily interact with each other so processing the information they carry is tricky.
In recent years, however, physicists have worked out how to make photons interact using interferometers and to carry out quantum computations using the output of one interferometer as the input for another.
The trouble is that interferometers are notoriously fickle. Sneeze and they need re-calibrating. So cascades of them tend to be hard to handle.
Today, Jonathan McDonald at the Air Force Research Laboratory in Rome New York, and a few pals reveal a way round this problem.
Their idea is to make holograms of interferometers so that their properties become 'frozen' in glass. This makes them much more stable.
The researchers then plan to stack the interferometers to perform simple quantum computations. "The approach here will "lock" these interferometers within a tempered piece of glass that is resistant to environmental factors," they say.
MacDonald and co suggest using a commercial holographic material called OptiGrate to store these holograms and show how these devices could carry out simple tasks such as quantum teleportation and CNOT logic.
There are two serious limitations to this approach, however. First, these devices are not scalable. The reason is that a hologram requires a certain volume of space to carry out each computation with high fidelity. And since computations scale exponentially in quantum computers, so must the volume.
Second, these devices are not reprogrammable, at least not with today's technology. The reason is that OptiGrate is a write-once material. Re-recordable holographic media are available but not currently with the fidelity that allows this kind of work though clearly that could change in future.
Given these limitations it's easy to dismiss this idea as just another of a growing number of exotic forms of quantum computation that are gathering dust on (metaphorical) library shelves.
But there are a number of emerging applications for the kind of reliable but low-dimensional quantum computations that these devices could perform. These include quantum memory buses, quantum error correction circuits and quantum key distribution relays.
For the moment, no technology does these jobs reliably well, although there are many pretenders for this crown. The difference with McDonald and co's idea is that it ought to be possible to build these devices now with off-the-shelf technology.
In fact, it wouldn't be surprising if this paper was a forerunner for practical work being done to develop prototypes. We'll be watching!
Prototypes will be important for ironing out a number of practical question marks about this approach. For example, these holograms will have to be stacked to carry out even simple quantum computations. But nobody is quite sure whether this output from one hologram can be accurately channelled into the input for another.
There's only one way to find out.
Ref: arxiv.org/abs/1112.3489: Quantum Computing In A Piece Of Glass
Source: Technology Review
Butanol is particularly suited as a transport fuel because it is not water soluble and has higher energy content than ethanol.
Most commonly used raw materials in butanol production have so far been starch and cane sugar. In contrast to this, the starting point in the Aalto University study was to use only lignocellulose, otherwise known as wood biomass, which does not compete with food production. Another new breakthrough in the study is to successfully combine modern pulp - and biotechnology. Finland’s advanced forest industry provides particularly good opportunities to develop this type of bioprocesses.
Wood biomass is made up of three primary substances: cellulose, hemicelluloses and lignin. Of these three, cellulose and hemicellulose can be used as a source of nutrition for microbes in bioprocesses. Along with cellulose, the Kraft process that is currently used in pulping produces black liquor, which can already be used as a source of energy. It is not, however, suitable for microbes. In the study, the pulping process was altered so that, in addition to cellulose, the other sugars remain unharmed and can therefore be used as raw material for microbes.
A method developed at Aalto University in Finland makes it possible to use microbes to produce butanol suitable for biofuel and other industrial chemicals from wood biomass. Credit: Mikko Raskinen
When wood biomass is boiled in a mixture of water, alcohol and sulphur dioxide, all parts of the wood – cellulose, hemicellulose and lignin – are separated into clean fractions. The cellulose can be used to make paper, nanocellulose or other products, while the hemicellulose is efficient microbe raw material for chemical production. Thus, the advantage of this new process is that no parts of the wood sugar are wasted.
In accordance with EU requirements, all fuel must contain 10 per cent biofuel by 2020. A clear benefit of butanol is that a significantly large percentage – more than 20 per cent of butanol, can be added to fuel without having to make any changes to existing combustion engines. The nitrogen and carbon emissions from a fuel mix including more than 20 per cent butanol are significantly lower than with fossil fuels. For example, the incomplete combustion of ethanol in an engine produces volatile compounds that increase odour nuisances in the environment. Estimates indicate that combining a butanol and pulp plant into a modern biorefinery would provide significant synergy benefits in terms of energy use and biofuel production.
The project run by Aalto University is part of the Biorefine technology programme, which is primarily funded by Tekes, the Finnish Funding Agency for Technology and Innovation.
The Biorefine programme is developing new competence based on national strengths and related to the refining of biomass. The overall aim of the project is to increase the refining value of forest residues that cannot be utilised in, for example, the pulp process. The research has been developed by Professor Aadrian van Heiningen and Tom Granström and a group of researchers at Aalto University. Results of findings have been published in scientific journals such as Bioresource Technology. The developed technology has been patented.
Source: Aalto University - via ZeitNews.org
Portugal faces a general strike by workers angered by austerity measures imposed as a condition of a 78-billion euro bailout last year but doubts remain as to whether Thursday's stoppage will receive widespread support. [REUTERS/Hugo Correia]
Portuguese strikers halted trains, shut ports and paralysed most public transport on Thursday in protest at austerity measures that is nevertheless unlikely to temper the government's resolve in implementing the terms of an EU/IMF bailout.
There was little impact outside of the transport sector from the general strike that caused no major output disruptions at companies. The country's second-largest union UGT did not back the strike, unlike in previous work stoppages.
Armenio Carlos, the new Communist leader of CGTP, the country's largest union confederation, wants its 700,000 members to send a signal to the centre-right government that the country will no longer tolerate the erosion of workers' rights, lower salaries and record high unemployment.
"We have to keep staging strikes, struggling. These policies do not resolve anything, we are on the same path as Greece," said Pedro Ramos, 38, and a union coordinator who works for a state waste management company.
Ramos was one of a few hundred CGTP members who gathered on the Rossio Square in downtown Lisbon, preparing to march towards parliament. Many were singing old Communist songs from the days of the 1974 bloodless Carnation revolution that re-established democracy in Portugal.
Asked about the turn-up, he shrugged his shoulders, saying "it's so-so". Other groups were meeting in other points of Lisbon, but their numbers were far below those in last month's peaceful rally that brought together over 100,000 protesters.
The CGTP could not say how many workers had responded to the strike call, but said the railway system was crippled, including the international Lisbon-Madrid route. Lisbon's underground was shut. Many hospitals were only accepting emergencies. It also said rubbish collectors, ports and some schools had shut down across the country.
Many struggled into work, unconvinced by the call to strike and reluctant to lose money in support of it.
"They go on strike and hurt us," said Ana Maria Verissimo, 53, a cleaning lady, as she waited for one of the few buses still running in Lisbon. "This won't resolve anything. They'll have to find another way. If I go on strike, my pay cheque will be lower at the end of the month."
ONE OF SMALLER STRIKES ON MEMORY
There was little evidence of stoppages in the private sector, with Portugal's main exporter, Volkswagen's (VOWG_p.DE) AutoEuropa plant, turning out cars. The government hopes exports will help lead the country out its recession by next year.
Flag carrier airline TAP was flying, and Lisbon airport functioning as normal. Output at Portugal's both oil refineries run by Galp (GALP.LS) was unaffected, according to the company.
"If you compare this strike to the previous general strikes in Portugal's democracy, this one clearly is in the low end," said Antonio Costa Pinto, research professor at the Institute of Social Sciences.
He said the fact that the UGT was not onboard was one factor affecting participation, while the government's recent about-turn regarding pay cuts in public companies due to be privatised "must have dissuaded a certain part of the public sector".
Government spokesman Luis Marques Guedes told a briefing that "the strike does not solve the country's problems and it seems to us that the majority of Portuguese understand that".
The government said it would not provide any figures on participation until the strike is over.
The Portuguese have so far shown little inclination for the kind of frequent and violent protests seen in Greece. The 520,000-strong UGT union has signed up to labour market reforms required by the European Union and IMF in return for the bailout and did not take part in the strike.
The country, facing its worst recession since the 1970s, was forced to take a bailout in May last year after running up large debts. Many economists say it might need a second bailout as the recession deepens, putting its budget targets in doubt and jeopardising its planned return to the bond market in late 2013.
Portugal's core deficit tripled in the first two months of 2012, showing that the economic slump is denting tax revenues and stoking concerns over the fiscal targets.
Still, Standard & Poor's ratings agency said on Thursday a Portuguese debt restructuring is avoidable as its debt level is lower than Greece's and it has shown more capacity to reform.
Portugal is western Europe's poorest country and followed Greece and Ireland in seeking a bailout to handle their crippling debts. Spain and Italy are also now facing austerity measures, and Italy's largest trade union is planning a general strike over labour market reforms.
UGT, which is allied to the opposition Socialist Party, has urged opponents of austerity to show restraint, warning that Portugal could descend into the kind of chaos seen in Greece.
The strikers say the new labour laws, which make it easier to hire and fire staff and which cut compensation for workers, mark the biggest step backwards for workers since Portugal's return to democracy in 1974 after military rule.
By combining a gold alloy with boron carbide, an extremely hard ceramic that’s used in bulletproof vests, a team of EPFL researchers has succeeded in making the world’s toughest 18-karat gold (75% gold). With a Vickers hardness number of 1000, it’s harder than most tempered steels (600 Vickers) and thus almost impossible to scratch, except with a diamond. This discovery is the result of a three-year collaboration between the Mechanical Metallurgy Laboratory in EPFL’s Institute of Materials, under the leadership of Professor Andreas Mortensen, and the Swiss watchmaking company Hublot.
The process for developing this material is relatively complicated. Powdered boron carbide is heated to almost 2000°C, where it forms a rigid, porous structure by a process called sintering. A liquid molten alloy of gold is infiltrated under very high pressure into the pores of this structure, and then solidified, yielding a pore-free composite material. The final material is thus made up of two kinds of crystals that are intimately interconnected in space, like two three-dimensional labyrinths. Because the molten gold used is a previously-made alloy based on 24-karat gold and aluminum (3%) for strength, the final gold is thus 3% aluminum, 75% gold and 22% boron carbide.
By definition, gold is very soft. Managing to harden it to this degree while still maintaining 18-karat purity was a real challenge for the EPFL scientists. They overcame the obstacle by taking the ceramic-metal composite approach. Composite materials are created by artificially combining several materials that conserve their individual characteristics even after they’re assembled. In this they are different from alloys, in which atoms mix together to form a new, homogeneous, material.
The EPFL researchers aren’t the first to play around with different materials in an effort to make more resistant gold. They are, however, the first to have attained this degree of hardness in 18-karat gold. The first watches made using this new gold will be presented in 2012 at BaselWorld, the world watch and jewelry show.
Source: Ecole Polytechnique Federale de Lausanne - via ZeitNews.org
The gross domestic product of the United States -- that oft-cited measure of economic health -- has been ticking upward for the last two years.
But what would you see if you could see a graph of gross domestic happiness?
A team of scientists from the University of Vermont have made such a graph -- and the trend is down.
Reporting in the Dec. 7 issue of the journal PLoS ONE, the team writes, "After a gradual upward trend that ran from January to April, 2009, the overall time series has shown a gradual downward trend, accelerating somewhat over the first half of 2011."
A graph of average happiness measured over a three year period running from Sept. 9, 2008 to Aug. 31, 2011, created by scientists at the University of Vermont using data from Twitter. Published in the journal PLoS ONE, Dec. 7, 2011. A regular weekly cycle is clear with the red and blue of Saturday and Sunday typically the high points -- and an overall downward trend in 2010 and 2011 is clear. Credit: Peter Dodds et al
"It appears that happiness is going down," said Peter Dodds, an applied mathematician at UVM and the lead author on the new study.
How does he know this? From Twitter. For three years, he and his colleagues gathered more than 46 billion words written in Twitter tweets by 63 million Twitter users around the globe.
In these billions of words is not a view of any individual's state of mind. Instead, like billions of moving atoms add up to the overall temperature of a room, billions of words used to express what people are feeling resolve into a view of the relative mood of large groups.
These billions of words contain everything from "the" to "pancakes" to "suicide." To get a sense of the emotional gist of various words, the researchers used a service from Amazon called Mechanical Turk. On this website, they paid a group of volunteers to rate, from one to nine, their sense of the "happiness" -- the emotional temperature -- of the ten thousand most common words in English. Averaging their scores, the volunteers rated, for example, "laughter" at 8.50, "food" 7.44, "truck" 5.48, "greed" 3.06 and "terrorist" 1.30.
The Vermont team then took these scores and applied them to the huge pool of words they collected from Twitter. Because these tweets each have a date and time, and, sometimes, other demographic information -- like location -- they show changing patterns of word use that provide insights into the way groups of people are feeling.
The new approach lets the researchers measure happiness at different scales of time and geography -- whether global patterns over a workweek -- or on Christmas.
And stretched out over the last three years, these patterns of word use show a drop in average happiness.
Or at least at drop in happiness for those who use Twitter. "It does skew toward younger people and people with smartphones and so on -- but Twitter is nearly universal now," Dodds said, "Every demographic is represented."
"Twitter is a signal," Dodds said, "just like looking at the words in the New York Times or Google Books." (Word sources that the team is also exploring in related studies). "They're all a sample," he says. "And indeed everything we say or write is a distortion of what goes on inside our head."
But -- like GDP is a distortion of the hugely complex interactions that make up the economy and yet is still useful -- the new approach by the UVM team provides a powerful sense of the rising and falling pulse of human feelings.
"Individual happiness is a fundamental societal metric," the researchers write in their study. Indeed the ultimate goal of much public policy is to improve and protect happiness. But measuring happiness has been exceedingly difficult by traditional means, like self-reporting in social science surveys. Some of the problems with this approach are that people often don't tell the truth in surveys and the sample sizes are small.
And so efforts to measure happiness have been "overshadowed by more readily quantifiable economic indicators such as gross domestic product," the study notes.
The new approach lets the UVM researchers almost instantaneously look over the "collective shoulder of society," Dodds says. "We get a sense of the aggregate expressions of millions of people," says Dodds's colleague Chris Danforth, a mathematician and a co-author the study, while they are communicating in a "more natural way," he says. And this opens the possibility of taking regular measures of happiness in near real-time -- measurements that could have applications in public policy, marketing and other fields.
The study describes hundreds of insights from the Twitter data, like a clear weekly happiness signal "with the peak generally occurring over the weekend, and the nadir on Monday and Tuesday," they write. And over each day happiness seems to drop from morning to night. "It's part of the general unraveling of the mind that happens over the course of the day," said Dodds.
In the long-term graph that shows an overall drop in happiness, various ups and downs are clearly visible. While the strongest up-trending days are annual holidays like Christmas and Valentine's Day, "all the most negative days are shocks from outside people's routines," Dodds say. Clear drops can be seen with the spread of swine flu, announcement of the U.S. economic bailout, the tsunami in Japan and even the death of actor Patrick Swayze.
"In measuring happiness, we construct a tunable, real-time, remote sensing, and non-invasive, text-based hedonometer," the Vermont scientists write. In other words, a happiness sensor.
Right now the sensor is only available to the researchers, but Dodds, Danforth and their colleagues have in mind a tool that could go "on the dashboard" of policy makers, Dodds says. Or, perhaps, on a real estate website for people exploring communities into which they might move, or, simply, "if someone is flying in a plane they could look at this dashboard and see how the city below them is feeling," he says.
Of course feelings change quickly and the nature of happiness itself is one of the most complex, profound issues of human experience.
"There is an important psychological distinction between an individual's current, experiential happiness and their longer term, reflective evaluation of their life," the scientists write, "and in using Twitter, our approach is tuned to the former kind."
And looking ahead, the Vermont scientists hope that by following the written expressions of individual Twitter users over long time periods, they'll be able to infer details of happiness dynamics "such as individual stability, social correlation and contagion and connections to well-being and health."
Dodds and his colleagues are no strangers to the debates over the role of happiness that can be traced back through Brave New World to Jeremy Bentham, Thomas Aquinas, and Aristotle. "By measuring happiness, we're not saying that maximizing happiness is the goal of society," Dodds says. "It might well be that we need to have some persistent degree of grumpiness for cultures to flourish."
Nevertheless, this study provides a new view on a compelling question: why does happiness seem to be declining?
Source: University of Vermont - via ZeitNews.org
This is especially problematic for victims of severe burns. A new customized sugary gel substance can work wonders to re-grow skin and the associated blood vessels, according to researchers at Johns Hopkins University.
The method involves a specially designed hydrogel, a water-based polymer. This one is made of mostly water with dissolved dextran, a type of sugar, and polyethlyene glycol (a common substance found in everything from antifreeze to laxatives).
We have seen hydrogels used before in creating artificial skin — last winter, Rice University researchers used a PEG hydrogel, doped with human growth factors and platelets, to induce the growth of artificial vessels. But this new one is interesting because the researchers didn’t add anything — no growth factors or anything else. This particular hydrogel’s physical structure apparently rendered that unnecessary. The researchers aren’t even certain how this happened.Sharon Gerecht, an assistant professor of chemical and biomolecular engineering, and her postdoc Guoming Sun set out to use their hydrogel as a wound dressing for severe burns. An artificial skin dressing offers greater protection against infection and promotes healing better than other types of wound coverings, they say in their paper, published in this week’s edition of the Proceedings of the National Academy of Sciences.
In a study involving mice, the researchers removed badly burned skin from the center of a burn wound, and covered this opening with the hydrogel. As a control, they covered some wounds with a material derived from cow collagen, which is currently used to treat human burn victims at the Hopkins Burn Center. The other wounds were left alone with just the hydrogel.
After three weeks, the hydrogel worked even better than the control, the researchers say. This was a surprise, so the team worked out a supplementary study to determine why the hydrogel breaks down so readily and how the animals' bodies were able to use it to generate new dermal tissue. It turns out that the body’s natural inflammatory response — involving neutrophils and macrophages — accumulated easily inside the hydrogel. Its physical structure enabled their easy entry, which promoted the breakdown of the hydrogel and enabling blood vessels to fill it in. Gerecht also believes the hydrogel might recruit bone marrow stem cells, which are naturally induced to differentiate into skin and blood vessel cells.
This is good news, because the faster this process happens, the less chance there is for scarring, Gerecht said in a Hopkins news release.
“Our study clearly demonstrates that dextran hydrogel alone, without the addition of growth factors or cytokines, promotes rapid [vessel growth] and complete skin regeneration, thus holding great potential to serve as a unique device for superior treatment of dermal wounds in clinical applications,” they write.
Source: Popular Science - via ZeitNews.org
Part of a suite of statistical tools called MINE, it can tease out multiple patterns hidden in health information from around the globe, statistics amassed from a season of major league baseball, data on the changing bacterial landscape of the gut, and much more.
The researchers report their findings in a paper appearing in the December 16 2011 issue of the journal Science.
From Facebook to physics to the global economy, the world is filled with data sets that could take a person hundreds of years to analyze by eye. Sophisticated computer programs can search these data sets with great speed, but fall short when researchers attempt to even-handedly detect different kinds of patterns in large data collections.
"There are massive data sets that we want to explore, and within them, there may be many relationships that we want to understand," said Broad Institute associate member Pardis Sabeti, senior author of the paper and an assistant professor at the Center for Systems Biology at Harvard University. "The human eye is the best way to find these relationships, but these data sets are so vast that we can't do that. This toolkit gives us a way of mining the data to look for relationships."
The researchers tested their analytical toolkit on several large data sets, including one provided by Harvard colleague Peter Turnbaugh who is interested in the trillions of microorganisms that live in the gut. Working with Turnbaugh, the research team harnessed MINE to make more than 22 million comparisons and narrowed in on a few hundred patterns of interest that had not been observed before.
"The goal of this statistic is to take data with a lot of different dimensions and many possible correlations and pick out the top ones," said Michael Mitzenmacher, a senior author of the paper and professor of computer science at Harvard University. "We view this as an exploration tool -- it can find patterns and rank them in an equitable way."
One of the tool's greatest strengths is that it can detect a wide range of patterns and characterize them according to a number of different parameters a researcher might be interested in. Other statistical tools work well for searching for a specific pattern in a large data set, but cannot score and compare different kinds of possible relationships. MINE, which stands for Maximal Information-based Nonparametric Exploration, is able to analyze a broad spectrum of patterns.
"Standard methods will see one pattern as signal and others as noise," said David Reshef, a co-first author of the paper who is currently a graduate student in the Harvard-MIT Health Sciences and Technology program and also worked on this project as a graduate student in the department of statistics at the University of Oxford. "There can potentially be a variety of different types of relationships in a given data set. What's exciting about our method is that it looks for any type of clear structure within the data, attempting to find all of them."
Not only does MINE attempt to identify any pattern within the data, but it also attempts to do so with an eye toward capturing different types of patterns equally well. "This ability to search for patterns in an equitable way offers tremendous exploratory potential in terms of searching for patterns without having to know ahead of time what to search for," said David Reshef.
MINE is especially powerful in exploring data sets with relationships that may harbor more than one important pattern. As a proof of concept, the researchers applied MINE to social, economic, health, and political data from the World Health Organization (WHO) and its partners. When they compared the relationship between household income and female obesity, they found two contrasting trends in the data. Many countries follow a parabolic rate, with obesity rates rising with income but peaking and tapering off after income reaches a certain level. But in the Pacific Islands, where female obesity is a sign of status, countries follow a steep trend, with the rate of obesity climbing as income increases.
"Many data sets will contain these types of complicated relationships that are guided by multiple drivers," said Sabeti. MINE is able to identify these. "This greatly extends our capability to find interesting relationships in data."
Researchers can use MINE to generate new ideas and connections that no one has thought to look for before.
"Our tool is a hypothesis generator," said Yakir Reshef, a co-first author of the paper and a Fulbright scholar at the Weizmann Institute of Science. "The standard paradigm is hypothesis-driven science, where you come up with a hypothesis based on your personal observations. But by exploring the data, you get ideas for hypotheses that would never have occurred to you otherwise."
In addition to testing the ability of the suite of tools to detect patterns in biological and health data, the researchers examined data collected from the 2008 baseball season.
"One question that we thought would be particularly interesting would be to see what things were most strongly associated with salary," said David Reshef. The researchers generated a list of relationships, finding that the strongest associations with salary were hits, total bases, and an aggregate statistic that reflects how many runs a player generated for a team. "Given the stakes, baseball is so well documented. We're curious to see what can be done in this realm with tools like MINE."
Researchers from many different fields, including systems biology, computer science, statistics, and mathematics, all contributed to this project. "People are getting better at combining data from different sources, and in some ways, this project is in the spirit of that," said Yakir Reshef. "The project brought together authors from many disciplines. It symbolizes the kind of collaborations that we hope people will use this for in the future."
Other authors who contributed to this work include Hilary Finucane, Sharon Grossman, Gilean McVean, and Eric Lander. Funding for this work was provided by the Packard Foundation, Marshall Aid Commemoration Commission, National Science Foundation, European Research Council, and the National Institutes of Health.
Source: ScienceDaily via ZeitNews.org
As an environmental products fair opened in Tokyo, Sony invited children to put paper into a mixture of water and enzymes, shake it up and wait for a few minutes to see the liquid become a source of electricity, powering a small fan.
"This is the same mechanism with which termites eat wood to get energy," said Chisato Kitsukawa, a public relations manager at Sony.
While academic research has previously taken place on this kind of power generation, proof-of-concept demonstrations are rare, he said.
The performance was part of Sony's drive to develop a sugar-based "bio battery" that turns glucose into power.
Shredded paper or pieces of corrugated board were used at the fair to provide cellulose, a long chain of glucose sugar found in the walls of green plants.
Enzymes are used to break the chain and the resulting sugar is then processed by another group of enzymes in a process that provides hydrogen ions and electrons.
The electrons travel through an outer circuit to generate electricity, while the hydrogen ions combine with oxygen from the air to create water.
"Bio batteries are environmentally friendly and have great potential" as they use no metals or harmful chemicals, Kitsukawa said.
But the technology is a long way from commercial viability because of its low power output. It is currently sufficient to run digital music players but not powerful enough to replace commonly used batteries, he said.
Sony first unveiled test sugar battery technology in 2007 and has since reduced the battery's size into a small sheet.
Another sugar battery was on display at the fair embedded in a Christmas card, which played music when drops of fruit juice were added to it.
Source: PhysOrg via ZeitNews.org
In previous work, Cornell biologist Thomas Seeley clarified how scout bees in a honeybee swarm perform "waggle dances" to prompt other scout bees to inspect a promising site that has been found. If it meets their approval, they, in turn, return to advertise the site with their own dances. Meanwhile, other scouts advertise alternative sites, creating a popularity contest among scouts committed to different sites. When one group exceeds a threshold size, the corresponding site is chosen.
In the new study, Seeley, a professor of neurobiology and behavior, reports with five colleagues in the United States and the United Kingdom that scout bees also use inhibitory "stop signals" -- a short buzz delivered with a head butt to the dancer -- to inhibit the waggle dances produced by scouts advertising competing sites. The strength of the inhibition produced by each group of scouts is proportional to the group's size. This inhibitory signaling helps ensure that only one of the sites is chosen. This is especially important for reaching a decision when two sites are equally good, Seeley said.
A swarm of bees labeled for individual identification. Image: Thomas Seeley
Previous research has shown that bees use stop signals to warn nest-mates about such dangers as attacks at a food source. However, this is the first study to show the use of stop signals in house-hunting decisions.
Such use of stop signals in decision making is "analogous to how the nervous system works in complex brains," said Seeley. "The brain has similar cross inhibitory signaling between neurons in decision-making circuits."
For example, when a goldfish detects the pressure wave of an approaching predator, it receives stimuli from both sides of its body. But if the pressure stimulus is stronger on the right side, brain neurons reporting from the right side will suppress the neurons reporting from the left side, which provides more clarity for the fish and helps it pinpoint the predator's location.
The study was conducted at Shoals Marine Laboratory on Appledore Island, six miles off the New Hampshire/Maine coast, where there are no big trees and no natural nest sites. The researchers brought swarms of bees to the island and offered them two equally good nest boxes. The scout bees that visited both boxes were marked with different colors.
Seeley and colleagues found that scouts that had committed to one box directed their stop signals mainly toward scouts promoting the other box.
"This analysis could not have been done without Shoals Marine Lab," said Seeley. "It's one of the very few places where there are no natural nest sites, so we can put out artificial nest sites and control and watch the whole decision-making process."
Co-authors Patrick Hogan and James Marshall of the University of Sheffield in the United Kingdom explored the implications of the bees' cross-inhibitory signaling by modeling their collective decision-making process. Their analysis showed that stop signaling helps bees to break deadlocks between two equally good sites and so avoid costly dithering.
Co-authors also included researchers from the University of California-Riverside and the University of Bristol, U.K.
The study was funded by the Cornell Agricultural Experiment Station, the University of California-Riverside and the U.K. Biotechnology and Biological Sciences Research Council.
Source: Cornell University via ZeitNews.org
The technique (developed by an international team of scientists in the United States and the United Kingdom), which is the first of its kind to use high-pressure chemistry for making well-developed films and wires of this particular kind of silicon semiconductor, will help scientists to make more-efficient and more-flexible optical fibers. The findings, by an international team led by John Badding, a professor of chemistry at Penn State University, will be published in a future print edition of the Journal of the American Chemical Society.
Badding explained that hydrogenated amorphous silicon -- a noncrystalline form of silicon -- is ideal for applications such as solar cells. Hydrogenated amorphous silicon also would be useful for the light-guiding cores of optical fibers; however, depositing the silicon compound into an optical fiber -- which is thinner than the width of a human hair -- presents a challenge. "Traditionally, hydrogenated amorphous silicon is created using an expensive laboratory device known as a plasma reactor," Badding explained. "Such a reactor begins with a precursor called silane -- a silicon-hydrogen compound. Our goal was not only to find a simpler way to create hydrogenated amorphous silicon using silane, but also to use it in the development of an optical fiber."
A bed of amorphous hydrogenated silicon wires that were prepared in the pores of optical fibers. The wires have been chemically etched out of the optical fiber to reveal them. Scale bar is 100 um. Inset: An array of amorphous hydrogenated silicon tubes deposited in an optical fiber. The optical fiber has been cleaved in half to reveal the array of tubes. The very thin glass walls of the fiber surrounding each tube are largely obscured. Scale bar is 5um. Credit: John Badding lab, Penn State University.
Because traditional, low-pressure chemistry techniques cannot be used for depositing hydrogenated amorphous silicon into a fiber, the team had to find another approach. "While the low-pressure plasma reactor technique works well enough for depositing hydrogenated amorphous silicon onto a surface to make solar cells, it does not allow the silane precursor molecules to be pushed into the long, thin holes in an optical fiber," said Pier J. A. Sazio of the University of Southampton in the United Kingdom and one of the team's leaders. "The trick was to develop a high-pressure technique that could force the molecules of silane all the way down into the fiber and then also convert them to amorphous hydrogenated silicon. The high-pressure chemistry technique is unique in allowing the silane to decompose into the useful hydrogenated form of amorphous silicon, rather than the much less-useful non-hydrogenated form that otherwise would form without a plasma reactor. Using pressure in this way is very practical because the optical fibers are so small."
Optical fibers with a non-crystalline form of silicon have many applications. For example, such fibers could be used in telecommunications devices, or even to change laser light into different infrared wavelengths. Infrared light could be used to improve surgical techniques, military countermeasure devices, or chemical-sensing tools, such as those that detect pollutants or environmental toxins. The team members also hope that their research will be used to improve existing solar-cell technology. "What's most exciting about our research is that, for the first time, optical fibers with hydrogenated amorphous silicon are possible; however, our technique also reduces certain production costs, so there's no reason it could not help in the manufacture of less-expensive solar cells, as well," Badding said.
Source: Pennsylvania State University via ZeitNews.org