Public Release: 

Physics tip sheet #19 - June 26, 2002

American Physical Society

1) Major climate models don't represent reality
R. B. Govindan, D. Vyushin, A. Bunde, S. Brenner, S. Havlin,. H.-J. Schellnhuber
Physical Review Letters (Print issue: July 8, 2002)

Seven leading global climate models were tested for certain statistical properties that reflect real climate behavior. None of the models correctly reproduce these properties but the models perform better when they incorporate the effect of aerosols rather than just greenhouse gases. Scenarios that only consider greenhouse gases tend to overestimate climate trends. The study provides an independent evaluation that aerosols must be considered to realistically model climate change as claimed in the recent IPCC Climate Change report.

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2) Nanospintronics: a single-spin transistor
M. Ciorga, A. Wensauer, M. Pioro-Ladriere, M. Korkusinski, J. Kyriakidis, A. S. Sachrajda, P. Hawrylak
Physical Review Letters (Print issue: June 24, 2002)

Spintronics is a relatively new field in which the electron's spin, not just its charge, can be exploited in devices and circuits. The ultimate spintronics degree of control would come from controlling a circuit at the level of a single spin. These physicists are the first to create a prototype of a single-spin transistor, which consists of a quantum dot connected to spin-polarized leads. The impressive control of spin achieved at the quantum dot may play a role in the future solid state form of quantum computing where the unit of quantum manipulation, the qubit might consist of specially prepared spin states.

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3) Dehydration of fingernails
B. Schulz, D. Chan, J. Bäckström, M. Rübhausen
Physical Review E (Print issue: June 2002)

Properties of biological systems can be difficult to study as many tests destroy samples. The technique demonstrated in this experiment looks at the example of how fingernails hydrate and dehydrate over timescales of a few minutes. The authors shone polarized light onto fingernails and looked at the polarization of the reflected light, which changes depending on the properties of the nails such as how much water has been absorbed into the keratin structure. The experiment demonstrates the effective of this technique for studying processes in biological systems in a non-invasive way over relatively short timescales.

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4) Word association is a small world
A. E. Motter, A. P. S. de Moura, Y.-C. Lai, P. Dasgupta
Physical Review E (Print issue: June 2002)

If you try to connect two words, such as "actor" and "universe" by linking words via a thesaurus, how many steps would it take? An analysis of a thesaurus containing over 30,000 words, each of which is linked to about 60 others shows that the shortest path from one word to another is surprisingly small at just over three steps. Less than one per cent of word pairs are separated by more than four steps. The authors suggest that this connectivity is related to memory and other cognitive processes that are associative, in which information is retrieved by connecting similar concepts. (Solution: actor - character - nature - universe.)

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5) Overloading senses
M. Copelli, A. C. Roque, R. F. Oliveira, O. Kinouchi
Physical Review E (Print issue: June 2002)

Our senses need to cope with a wide range of input, from extremely weak signals, which still need to register, through to intense signals, which shouldn't overload our senses. This study shows how our senses can have such a wide-ranging response to input. It is based on a bottom-up approach beginning with microscopic laws. The approach is used to effectively model neurons and the authors suggest that this understanding could lead to better ways of designing artificial sensors.

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6) Building perfection from broken parts
D. Challet, N. F. Johnson
Physical Review Letters (Print issue: July 8, 2002)

In modern technology, quality control of microscopic parts is difficult and many devices are known to contain broken elements. However, it seems likely that you could connect a range of parts with different flaws to create a working device. It might seem that the best thing to do is to use all of your broken parts and hope to get the best result but this study shows that is not the case. You may end up incorporating a part with such a serious defect that it prevents the entire device from working. The authors show that from any set of defective nanoscale parts, you should use exactly half of them to get the best-working device.

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