405 research outputs found

    Magnetic Properties of the low dimensional spin system (VO)2_2P2_2O7_{7}: ESR and susceptibility

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    Experimental results on magnetic resonance (ESR) and magnetic susceptibility are given for single crystalline (VO)2_2P2_2O7_{7}. The crystal growth procedure is briefly discussed. The susceptibility is interpreted numerically using a model with alternating spin chains. We determine JJ=51 K and ή\delta=0.2. Furthermore we find a spin gap of ≈6\approx 6meV from our ESR measurements. Using elastic constants no indication of a phase transition forcing the dimerization is seen below 300 K.Comment: 7 pages, REVTEX, 7 figure

    Unterschiede in Futteraufnahmeverhalten und Energieumsatz zwischen “genetisch schlanken” und “genetisch adipösen” Katern

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    Involvement of mossy cells in sharp wave-ripple activity in vitro

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    The role of mossy cells (MCs) of the hippocampal dentate area has long remained mysterious. Recent research has begun to unveil their significance in spatial computation of the hippocampus. Here, we used an in vitro model of sharp wave-ripple complexes (SWRs), which contribute to hippocampal memory formation, to investigate MC involvement in this fundamental population activity. We find that a significant fraction of MCs (~47%) is recruited into the active neuronal network during SWRs in the CA3 area. Moreover, MCs receive pronounced, ripple-coherent, excitatory and inhibitory synaptic input. Finally, we find evidence for SWR-related synaptic activity in granule cells that is mediated by MCs. Given the widespread connectivity of MCs within and between hippocampi, our data suggest a role for MCs as a hub functionally coupling the CA3 and the DG during ripple-associated computations

    The 1991 Field Evaluation of Herbicides on Small Fruit, Vegetables and Ornamental Crops

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    The establishment of this field-testing procedure provides the chemical industry, through its partial support, and the Arkansas Experiment Station the opportunity to evaluate herbicide performance on small fruit, vegetable and ornamental crops grown under Arkansas conditions. This report also provides a means for disseminating information to interested people and public-service weed scientists

    Analytical Bethe Ansatz for closed and open gl(n)-spin chains in any representation

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    We present an "algebraic treatment" of the analytical Bethe Ansatz. For this purpose, we introduce abstract monodromy and transfer matrices which provide an algebraic framework for the analytical Bethe Ansatz. It allows us to deal with a generic gl(n)-spin chain possessing on each site an arbitrary gl(n)-representation. For open spin chains, we use the classification of the reflection matrices to treat all the diagonal boundary cases. As a result, we obtain the Bethe equations in their full generality for closed and open spin chains. The classifications of finite dimensional irreducible representations for the Yangian (closed spin chains) and for the reflection algebras (open spin chains) are directly linked to the calculation of the transfer matrix eigenvalues. As examples, we recover the usual closed and open spin chains, we treat the alternating spin chains and the closed spin chain with impurity

    Rhythmic dynamics and synchronization via dimensionality reduction : application to human gait

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    Reliable characterization of locomotor dynamics of human walking is vital to understanding the neuromuscular control of human locomotion and disease diagnosis. However, the inherent oscillation and ubiquity of noise in such non-strictly periodic signals pose great challenges to current methodologies. To this end, we exploit the state-of-the-art technology in pattern recognition and, specifically, dimensionality reduction techniques, and propose to reconstruct and characterize the dynamics accurately on the cycle scale of the signal. This is achieved by deriving a low-dimensional representation of the cycles through global optimization, which effectively preserves the topology of the cycles that are embedded in a high-dimensional Euclidian space. Our approach demonstrates a clear advantage in capturing the intrinsic dynamics and probing the subtle synchronization patterns from uni/bivariate oscillatory signals over traditional methods. Application to human gait data for healthy subjects and diabetics reveals a significant difference in the dynamics of ankle movements and ankle-knee coordination, but not in knee movements. These results indicate that the impaired sensory feedback from the feet due to diabetes does not influence the knee movement in general, and that normal human walking is not critically dependent on the feedback from the peripheral nervous system

    Fermentation in vitro-vorverdauter GrĂŒnfutter im Caesitec

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    Productive restructuring and the reallocation of work and employment: a survey of the “new” forms of social inequality

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    O propĂłsito do presente artigo consiste em questionar a inevitabilidade dos processos de segmentação e precarização das relaçÔes de trabalho e emprego, responsĂĄveis pela inscrição de “novas” formas de desigualdade social que alicerçam o actual modelo de desenvolvimento das economias e sociedades. Visa-se criticar os limites da lĂłgica econĂŽmica e financeira, de contornos globais, que configuram um “novo espĂ­rito do capitalismo”, ou seja, uma espĂ©cie de divinização da ordem natural das coisas. ImpĂ”e-se fazer, por isso, um pĂ©riplo analĂ­tico pelas transformaçÔes em curso no mercado de trabalho, acompanhado pela vigilĂąncia epistemolĂłgica que permita enquadrar e relativizar as (di)visĂ”es neoliberais e teses tecnodeterministas dominantes. A perspectivação de cenĂĄrios sobre o futuro do trabalho encerrarĂĄ este pĂ©riplo, permitindo-nos alertar para os condicionalismos histĂłrico-temporais, para a urgĂȘncia de se desocultar o que de ideolĂłgico e polĂ­tico existe nas actuais lĂłgicas de racionalização e para os processos de ressimbolização do trabalho e emprego enquanto “experiĂȘncia social central” na contemporaneidade.The scope of this paper is to question the inevitability of the processes of segmentation and increased precariousness of the relations of labor and employment, which are responsible for the introduction of “new” forms of social inequality that underpin the current model of development of economies and societies. It seeks to criticize the limits of global financial and economic logic, which constitute a “new spirit of capitalism,” namely a kind of reverence for the natural order of things. It is therefore necessary to conduct an analytical survey of the ongoing changes in the labor market, accompanied by epistemological vigilance which makes it possible to see neoliberal (di)visions and dominant technodeterministic theses in context. The enunciation of scenarios on the future of work will conclude this survey and will make it possible to draw attention to both the historical and temporal constraints and to the urgent need to unveil what is ideological and political in the prevailing logic of rationalization and processes to reinstate work and employment as a “central social experience” in contemporary times

    Reinforcement versus Fluidization in Cytoskeletal Mechanoresponsiveness

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    Every adherent eukaryotic cell exerts appreciable traction forces upon its substrate. Moreover, every resident cell within the heart, great vessels, bladder, gut or lung routinely experiences large periodic stretches. As an acute response to such stretches the cytoskeleton can stiffen, increase traction forces and reinforce, as reported by some, or can soften and fluidize, as reported more recently by our laboratory, but in any given circumstance it remains unknown which response might prevail or why. Using a novel nanotechnology, we show here that in loading conditions expected in most physiological circumstances the localized reinforcement response fails to scale up to the level of homogeneous cell stretch; fluidization trumps reinforcement. Whereas the reinforcement response is known to be mediated by upstream mechanosensing and downstream signaling, results presented here show the fluidization response to be altogether novel: it is a direct physical effect of mechanical force acting upon a structural lattice that is soft and fragile. Cytoskeletal softness and fragility, we argue, is consistent with early evolutionary adaptations of the eukaryotic cell to material properties of a soft inert microenvironment
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