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  • 1
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    Quantum impurities in the two-dimensional spin one-half Heisenberg antiferromagnet (2002)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2002-03-02
    Description: The study of randomness in low-dimensional quantum antiferromagnets is at the forefront of research in the field of strongly correlated electron systems, yet there have been relatively few experimental model systems. Complementary neutron scattering and numerical experiments demonstrate that the spin-diluted Heisenberg antiferromagnet La2Cu1-z(Zn,Mg)(z)O4 is an excellent model material for square-lattice site percolation in the extreme quantum limit of spin one-half. Measurements of the ordered moment and spin correlations provide important quantitative information for tests of theories for this complex quantum-impurity problem.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Vajk, O P -- Mang, P K -- Greven, M -- Gehring, P M -- Lynn, J W -- New York, N.Y. -- Science. 2002 Mar 1;295(5560):1691-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics, Stanford University, Stanford, CA 94309, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11872834" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    Complex species interactions and the dynamics of ecological systems: long-term experiments (2001)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2001-07-28
    Description: Studies that combine experimental manipulations with long-term data collection reveal elaborate interactions among species that affect the structure and dynamics of ecosystems. Research programs in U.S. desert shrubland and pinyon-juniper woodland have shown that (i) complex dynamics of species populations reflect interactions with other organisms and fluctuating climate; (ii) genotype x environment interactions affect responses of species to environmental change; (iii) herbivore-resistance traits of dominant plant species and impacts of "keystone" animal species cascade through the system to affect many organisms and ecosystem processes; and (iv) some environmental perturbations can cause wholesale reorganization of ecosystems because they exceed the ecological tolerances of dominant or keystone species, whereas other changes may be buffered because of the compensatory dynamics of complementary species.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Brown, J H -- Whitham, T G -- Morgan Ernest, S K -- Gehring, C A -- New York, N.Y. -- Science. 2001 Jul 27;293(5530):643-50.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA. jhbrown@unm.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11474100" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Arizona ; Desert Climate ; *Ecosystem ; Environment ; Genotype ; *Gymnosperms ; Moths/physiology ; Plants ; Population Dynamics ; *Rodentia/physiology ; Time Factors ; *Trees ; Weather
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
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    The medial frontal cortex and the rapid processing of monetary gains and losses (2002)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2002-03-23
    Description: We report the observation of neural processing that occurs within 265 milliseconds after outcome stimuli that inform human participants about gains and losses in a gambling task. A negative-polarity event-related brain potential, probably generated by a medial-frontal region in or near the anterior cingulate cortex, was greater in amplitude when a participant's choice between two alternatives resulted in a loss than when it resulted in a gain. The sensitivity to losses was not simply a reflection of detecting an error; gains did not elicit the medial-frontal activity when the alternative choice would have yielded a greater gain, and losses elicited the activity even when the alternative choice would have yielded a greater loss. Choices made after losses were riskier and were associated with greater loss-related activity than choices made after gains. It follows that medial-frontal computations may contribute to mental states that participate in higher level decisions, including economic choices.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gehring, William J -- Willoughby, Adrian R -- New York, N.Y. -- Science. 2002 Mar 22;295(5563):2279-82.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Psychology, University of Michigan, 525 East University, Ann Arbor, MI 48109-1109, USA. wgehring@umich.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11910116" target="_blank"〉PubMed〈/a〉
    Keywords: Adult ; Choice Behavior/*physiology ; *Economics ; Electroencephalography ; Evoked Potentials/physiology ; Female ; Gambling/*psychology ; Gyrus Cinguli/*physiology ; Humans ; Male ; Time Factors
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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