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Saturday, September 15, 2012

SCIENCE NEWS

1.Uncertainty not so certain after all
Physicists may need to tweak what they think they know about Werner Heisenberg’s famous uncertainty principle.

Measuring light particles doesn’t push them as far into the realm of quantum fuzziness as once thought, new research suggests. The work doesn’t invalidate the principle underlying all of modern quantum theory, but may have implications for supersecure cryptography and other quantum applications.

“The real Heisenberg uncertainty principle is alive and well,” says Lee Rozema, a graduate student at the University of Toronto whose team reports the finding in the Sept. 7 Physical Review Letters. “It’s really just this [one aspect] that needs to be updated.”

In its most famous articulation, Heisenberg’s uncertainty principle states that it’s possible at a given moment to know either the position or momentum of a particle, but not both. This relationship can be written out mathematically. But Heisenberg first came up with the idea in a slightly different fashion using slightly different mathematics. That version says the more you disturb a particle, the less precisely you can measure a particular property of it, and vice versa.

As an example, Heisenberg imagined shining particles of light on an electron and, by watching how the light bounced off it, deducing the position of the electron. But each time the light particles impart a little of their momentum to the electron, thus blurring how well scientists can measure the system. “This is how Heisenberg thought, but it wasn’t what was rigorously proven later,” says Rozema. “Physicists quite often confuse the two.”

Heisenberg’s original version still works for the light/electron example, Rozema says, but not in more general cases — as most scientists have assumed.

In 2003, Japanese physicist Masanao Ozawa showed mathematically that Heisenberg’s first version couldn’t be right. Earlier this year, he and a research team at the University of Vienna reported lab experiments confirming this.

Now, the Toronto physicists have weighed in with what they call a more direct measurement. They took single light particles, or photons, and measured two directions in which the light waves oscillated. The first measurement was a “weak” probe, gently inquiring about oscillations in one direction and then the other. Then the scientists made a “strong” measurement, directly probing whether that first, weak measurement had disturbed the system.

By combining the weak and strong measurements, Rozema’s team showed that the measured oscillations did not fit the mathematics of Heisenberg’s first formulation of the uncertainty idea. In other words, shrinking the inaccuracy of a particle measurement (making it more precise) doesn’t disturb the particle quite as much as scientists had thought.

“It is possible for both the inaccuracy and the disturbance to be small, although not both strictly zero,” says Howard Wiseman, a physicist at Griffith University in Brisbane, Australia, who proposed the measurement the Toronto team used.

The discovery is important for anyone trying to build an unbreakable quantum code. Quantum cryptography relies on the fact that eavesdroppers would be spotted by the disturbance they make. If the disturbance is smaller than expected, then eavesdroppers might be harder to detect.

“The new relation will open up new science and technology in the field of quantum information,” says Ozawa, now of Nagoya University. “It also presents a profound philosophical problem.”


2.Brain’s white matter diminished in isolated mice
Changes in the brains of mice that were isolated as young pups may help explain the profound behavioral problems of severely neglected children. The mouse experiments suggest that neglect during a specific developmental window irreversibly stunts brain development, researchers report in the Sept. 14 Science.

Over the last decade, researchers have catalogued brain deficits and behavioral problems in Romanian orphans who were raised in bare-bones environments with little social stimulation. Many of these children display hyperactivity, impulsivity and compulsive behavior such as arm flapping. Although superficially friendly, these kids have trouble forming meaningful relationships.

By studying mice that had been isolated early in life, researchers led by Gabriel Corfas of Children’s Hospital Boston and Harvard Medical School hoped to uncover how social deprivation can affect the developing brain. After the mice had weaned, the researchers put them into one of three environments: One was a deluxe suite, enriched with fresh toys every other day and populated by friends of similar ages, one was a standard laboratory cage holding four mice, and one was a holding cell for total isolation.

After two weeks, mice in the deluxe suite and the regular cage showed no abnormalities in their behavior or brains. But mice that were isolated showed big changes. These animals were socially stunted, showing less signs of exploratory behavior and a diminished working memory. What’s more, the researchers uncovered stunted development in the brain’s white matter, which helps nerve cells communicate.

In a brain region called the prefrontal cortex, isolated mice had less of a fatty insulating substance called myelin that wraps around nerve cells and helps carry their messages. This part of the brain is thought to be crucial for high-level tasks like social interactions. Myelin-making cells called oligodendrocytes were also stunted. Normally these cells have elaborate, winding tendrils full of complex branches. But isolated mice’s oligodendrocytes were smaller and less elaborate, with fewer branches. The result “shows how sensitive the development of myelin is to experience,” Corfas says.

The two-week period after weaning was critical. If isolation happened three weeks after weaning, the mice didn’t show these deficits. Nor could the isolation effects be reversed later by moving the isolated mice into a better situation.

“What I find fascinating is that this is the neurobiological counterpart of the behavioral changes,” says pediatric neurologist Harry Chugani of Wayne State University in Detroit and Children’s Hospital of Michigan.

This result echoes what Chugani and his colleagues have seen in their studies of neglected Romanian orphans. Children moved from an orphanage to a foster home before age 2 do much better than children removed later. During this window, social interaction has a profound effect on the brain, Chugani says. “The brain demands that you present it with a certain environment.”

Corfas and his team also turned up some clues about how social isolation can lead to these brain changes. When the team reduced production of a molecule called ErbB3 receptor protein, mice raised in an enriched environment acted more like mice raised in isolation. They also found that production of another protein, called neuregulin-1, is muted by isolation.

These molecules have been implicated in schizophrenia and bipolar disorder, Corfas says, as have alterations in white matter in the brain — raising the possibility that the effects of social isolation could be similar to what happens in those disorders.

For now, Corfas says, the team is looking for a way to undo the harm.


3.Water boils sans bubbles
Dip your finger in a bucket of water and then quickly dip it in molten lead — you won’t get burned, thanks to an insulating layer of steam that forms around the finger. Chemists have now exploited this phenomenon, known as the Leidenfrost effect, to boil water without making bubbles.

The researchers covered a steel ball with Glaco Mirror Coat, a water-hating material, along with some other water-repelling chemicals. This turned the sphere’s exterior into a nanoscale mountain range peppered with deep valleys. Heating the sphere to 400º Celsius and dropping it in room-temperature water spurred boiling, but no furious bubbles, the team reports in Sept. 13 Nature. The water near the sphere became vapor that got trapped in the valleys on the sphere’s surface. Eventually this sheet of vapor slipped off and a new one formed.

Treating the surface of another sphere to make it water-loving had the opposite effect, locking the water in the violent bubbling phase. Manipulating this phase-chemistry could lead to tricks for reducing drag on ships or preventing forceful bubbling explosions in labs or kitchens.


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