74 research outputs found

    Specific Heat of a Three Dimensional Metal Near a T=0 Magnetic Transition with Dynamic Exponent z=2,3,4

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    We derive expressions for the universal contribution to the specific heat of a three-dimensional metal near a zero-temperature phase transition with dynamic exponent z=2,3z=2,3, or 4. The results allow a quantitative comparison of theory to data. We illustrate the application of our results by analyzing data for Ce1−x_{1-x}Lux_xCu2_2Si2_2, which has been claimed to be near a quantum critical point.Comment: 23 pages, revtex. For figures, send mail to [email protected]

    Records and sequences of records from random variables with a linear trend

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    We consider records and sequences of records drawn from discrete time series of the form Xn=Yn+cnX_{n}=Y_{n}+cn, where the YnY_{n} are independent and identically distributed random variables and cc is a constant drift. For very small and very large drift velocities, we investigate the asymptotic behavior of the probability pn(c)p_n(c) of a record occurring in the nnth step and the probability PN(c)P_N(c) that all NN entries are records, i.e. that X1<X2<...<XNX_1 < X_2 < ... < X_N. Our work is motivated by the analysis of temperature time series in climatology, and by the study of mutational pathways in evolutionary biology.Comment: 21 pages, 7 figure

    Dealing with Food and Eggs in Mouthbrooding Cichlids: Structural and Functional Trade-Offs in Fitness Related Traits

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    As in any vertebrate, heads of fishes are densely packed with functions. These functions often impose conflicting mechanical demands resulting in trade-offs in the species-specific phenotype. When phenotypical traits are linked to gender-specific parental behavior, we expect sexual differences in these trade-offs. This study aims to use mouthbrooding cichlids as an example to test hypotheses on evolutionary trade-offs between intricately linked traits that affect different aspects of fitness. We focused on the oral apparatus, which is not only equipped with features used to feed and breathe, but is also used for the incubation of eggs. We used this approach to study mouthbrooding as part of an integrated functional system with diverging performance requirements and to explore gender-specific selective environments within a species.Because cichlids are morphologically very diverse, we hypothesize that the implications of the added constraint of mouthbrooding will primarily depend on the dominant mode of feeding of the studied species. To test this, we compared the trade-off for two maternal mouthbrooding cichlid species: a "suction feeder" (Haplochromis piceatus) and a "biter" (H. fischeri). The comparison of morphology and performance of both species revealed clear interspecific and intersex differences. Our observation that females have larger heads was interpreted as a possible consequence of the fact that in both the studied species mouthbrooding is done by females only. As hypothesized, the observed sexual dimorphism in head shape is inferred as being suboptimal for some aspects of the feeding performance in each of the studied species. Our comparison also demonstrated that the suction feeding species had smaller egg clutches and more elongated eggs.Our findings support the hypothesis that there is a trade-off between mouthbrooding and feeding performance in the two studied haplochromine cichlids, stressing the importance of including species-specific information at the gender level when addressing interspecific functional/morphological differences

    Eculizumab improves fatigue in refractory generalized myasthenia gravis

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