Sunday, September 12, 2010

‘GREENER’ THAN EXPECTED

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It is not an easy task to compare the environmental effects of battery powered cars to those caused by conventionally fuelled automobiles. The degree to which manufacture, usage and disposal of the batteries used to store the necessary electrical energy are detrimental to the environment is not exactly known. Now, for the first time, a team of Empa scientists have made a detailed life cycle assessment (LCA) or ecobalance of lithium-ion (Li-ion) batteries, in particular the chemically improved (i.e. more environmentally friendly) version of the ones most frequently used in electric vehicles.

The investigation shows that if the power used to charge the battery is not derived from purely hydroelectric sources, then it is primarily the operation of the electric car, which has an environmental impact, exactly as is the case with conventionally fuelled automobiles. The size of the environmental footprint depends on which sources of power are used to "fuel" the e-mobile. The Li-ion battery itself has, in contrast, a limited effect on the LCA of the electric vehicle. This is contrary to initial expectations that the manufacture of the batteries could negate the advantages of the electric drive.

Battery powered electric cars are often promoted as the ideal solution to the challenges of future mobility, since they produce no exhaust gases in operation. Li-ion batteries have established themselves over competing lead-acid and nickel metal-hydride (NiMH) types because they are lighter and can store more energy. Li-ion batteries are also basically maintenance-free, display no memory effect (loss of capacity when repeatedly charged after partial discharge), have a low self-discharge rate and are regarded as safe and long-lived. For these reasons they find use in many products such as laptop computers. But are they also environmentally friendly?

Researchers at Empa's "Technology and Society Laboratory" decided to find out for sure. They calculated the ecological footprints of electric cars fitted with Li-ion batteries, taking into account all possible relevant factors, from those associated with the production of individual parts all the way through to the scrapping of the vehicle and the disposal of the remains, including the operation of the vehicle during its lifetime. Data with which to evaluate the rechargeable batteries was not available and had to be obtained specifically for this purpose. In doing so the researchers made intentionally unfavorable assumptions. One such was to ignore the fact that after use in a car, a battery might well be used in a stationary setting for other purposes. Other relevant LCA information was obtained from the "ecoinvent" database (www.ecoinvent.org), managed by Empa. The electric vehicles evaluated were equivalent in size and performance to a VW Golf, and the power used to charge the batteries was assumed to be derived from sources representing an average European electricity mix.

A new petrol-engined car, meeting the Euro 5 emission regulations, was used for comparison. It consumes on average 5.2 liter per 100 kilometers when put through the New European Driving Cycle (NEDC), a value significantly lower than the European average. In this respect, therefore, the conventional vehicle belongs to the best of its class on the market.

The study shows that the electric car's Li-ion battery drive is in fact only a moderate environmental burden. At most only 15 per cent of the total burden can be ascribed to the battery (including its manufacture, maintenance and disposal). Half of this figure, that is about 7.5 per cent of the total environmental burden, occurs during the refining and manufacture of the battery's raw materials, copper and aluminium. The production of the lithium, in the other hand, is responsible for only 2.3 per cent of the total. "Lithium-ion rechargeable batteries are not as bad as previously assumed," according to Dominic Notter, coauthor of the study which has just been published in the scientific journal "Environmental Science & Technology".

The outlook is not as rosy when one looks at the operation of an electric vehicle over an expected lifetime of 150'000 kilometers. The greatest ecological impact is caused by the regular recharging of the battery, that is, the "fuel" of the e-car. "Refueling" with electricity sourced from a mixture of atomic, coal-fired and hydroelectric power stations, as is usual in Europe, results in three times as much pollution as from the Li-ion battery alone. It is therefore worth considering alternative power sources: If the electricity is generated exclusively by coal-fired power stations, the ecobalance worsens by another 13 per cent. If, on the other hand, the power is purely hydroelectric, then this figure improves by no less than 40 per cent.

The conclusion drawn by the Empa team: a petrol-engined car must consume between three and four liters per 100 kilometers (or about 70 mpg) in order to be as environmentally friendly as the e-car studied, powered with Li-ion batteries and charged with a typical European electricity mix.

(Photo: Wikipedia)

Empa - a Research Institute of the ETH Domain

EYE MOVEMENTS REVEAL READERS WANDERING MINDS

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It’s not just you…everybody zones out when they’re reading. For a new study published in Psychological Science, a journal of the Association for Psychological Science, scientists recorded eye movements during reading and found that the eyes keep moving when the mind wanders—but they don’t move in the same way as they do when you’re paying attention.

Erik Reichle, a psychological scientist at the University of Pittsburgh, is interested in how the brain controls eye movements. “The goal is to understand how things like word comprehension and visual attention control eye movements,” he says. Most people who study reading think that the eyes sample the information on the page and the reading mind essentially takes what it’s given, without giving much direction back to the eyes. Reichle suspected that was wrong, and thought looking at mindless reading would be an interesting way to illuminate what happens when the mind is engaged. He cowrote the study with Andrew E. Reineberg of the University of Pittsburgh and Jonathan W. Schooler of the University of California, Santa Barbara.

Four undergraduate students at the University of Pittsburgh volunteered for the project. Each one came to the lab for a dozen or more one-hour reading sessions of Jane Austen’s Sense and Sensibility, chosen because it’s “fairly easy but a little bit dry,” says Reichle. “We started with Kafka’s The Trial, but people found it too engaging.” While the student read the book on a screen, a computer tracked their eye movements. They were asked to push a button marked “Z” when they noticed themselves “zoning out.” The computer also asked every few minutes if they’d just been paying attention or zoning out.

The eyes did different things while a person was paying attention than when their mind was wandering. In normal reading, the eye fixates on a word, then zips to another word. The eye spends longer on words that are less common. But when someone’s mind was wandering, the eyes did not follow these patterns. They also fixated for longer on individual words. “It was almost like they were just mechanically plodding along,” Reichle says. This suggests that the prevailing belief in his field is wrong—in fact, when people are reading, eye movements are strongly linked to the language processing going on in the brain.

Association for Psychological Science

DRAMATIC CLIMATE CHANGE IS UNPREDICTABLE

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The fear that global temperature can change very quickly and cause dramatic climate changes that may have a disastrous impact on many countries and populations is great around the world. But what causes climate change and is it possible to predict future climate change? New research from the Niels Bohr Institute at the University of Copenhagen shows that it may be due to an accumulation of different chaotic influences and as a result would be difficult to predict. The results have just been published in Geophysical Research Letters.

For millions of years the Earth's climate has alternated between about 100,000 years of ice age and approximately 10-15,000 years of a warm climate like we have today. The climate change is controlled by the Earth's orbit in space, that is to say the Earth's tilt and distance from the sun. But there are also other climatic shifts in the Earth's history and what caused those?

By analysing the ice cores that are drilled through the more than three kilometer thick ice sheet in Greenland, scientists can obtain information about the temperature and climate going back around 140,000 years.

The most pronounced climate shifts besides the end of the ice age is a series of climate changes during the ice age where the temperature suddenly rose 10-15 degrees in less than 10 years. The climate change lasted perhaps 1000 years, then - bang – the temperature fell drastically and the climate changed again. This happened several times during the ice age and these climate shifts are called the Dansgaard-Oeschger events after the researchers who discovered and described them. Such a sudden, dramatic shift in climate from one state to another is called a tipping point. However, the cause of the rapid climate change is not known and researchers have been unable to reproduce them in modern climate models.

"We have made a theoretical modelling of two different scenarios that might trigger climate change. We wanted to investigate if it could be determined whether there was an external factor which caused the climate change or whether the shift was due to an accumulation of small, chaotic fluctuations", explains Peter Ditlevsen, a climate researcher at the Niels Bohr Institute.

He explains that in one scenario the climate is like a seesaw that has tipped to one side. If sufficient weight is placed on the other side the seesaw will tip – the climate will change from one state to another. This could be, for example, an increase in the atmospheric content of CO2 triggering a shift in the climate.

In the second scenario the climate is like a ball in a trench, which represents one climate state. The ball will be continuously pushed by chaos-dynamical fluctuations such as storms, heat waves, heavy rainfall and the melting of ice sheets, which affect ocean currents and so on. The turmoil in the climate system may finally push the ball over into the other trench, which represents a different climate state.

Peter Ditlevsen's research shows that you can actually distinguish between the two scenarios and it was the chaos-dynamical fluctuations that were the triggering cause of the dramatic climate changes during the ice age. This means that they are very difficult to predict.

But what about today – what can happen to the climate of the future? "Today we have a different situation than during the ice age. The Earth has not had such a high CO2 content in the atmosphere since more than 15 million years ago, when the climate was very warm and alligators lived in England. So we have already started tilting the seesaw and at the same time the ball is perhaps getting kicked more and could jump over into the other trench. This could mean that the climate might not just slowly gets warmer over the next 1000 years, but that major climate changes theoretically could happen within a few decades", estimates Peter Ditlevsen, but stresses that his research only deals with investigating the climate of the past and not predictions of the future climate.

(Photo: Peter Ditlevsen)

University of Copenhagen

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