Biomedical subjects

J M Luck

Publications and source records attributed to J M Luck.

16 recordsLinked to original sources

PubMed2003

Random symmetric matrices with a constraint: the spectral density of random impedance networks.

We derive the mean eigenvalue density for symmetric Gaussian random N x N matrices in the limit of large N, with a constraint implying that the row sum of matrix elements should vanish. The result is shown to be equivalent to a result found recently for the average density of resonances in random impedance networks [Y.V. Fyodorov, J. Phys. A 32, 7429 (1999)]. In the case of banded matrices, the analytical results are compared with those extracted from the numerical solution of Kirchhoff equations for quasi-one-dimensional random impedance networks.

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PubMed2001

Aging, phase ordering, and conformal invariance.

In a variety of systems which exhibit aging, the two-time response function scales as R(t,s) approximately s(-1-a)f(t/s). We argue that dynamical scaling can be extended towards conformal invariance, thus obtaining the explicit form of the scaling function f. This quantitative prediction is confirmed in several spin systems, both for T<T(c) (phase ordering) and T = T(c) (nonequilibrium critical dynamics). The 2D and 3D Ising models with Glauber dynamics are studied numerically, while exact results are available for the spherical model with a nonconserved order parameter, both for short-ranged and long-ranged interactions, as well as for the mean-field spherical spin glass.

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PubMed1999

Models of competitive learning: complex dynamics, intermittent conversions, and oscillatory coarsening.

We present two models of competitive learning, which are respectively interfacial (i.e., where the interiors of domains are unaffected by the rules of the model) and cooperative (i.e., where the bulk as well as the interface of an individual domain is governed by the rules of the model) learning. This learning is outcome related, so that spatially and temporally local environments influence the conversion of a given site between one of two different types. We focus here on the behavior of the models at coexistence, which yields critical behavior and the existence of a phase involving a type of coarsening which is oscillatory in nature. In the discussion we speculate on, among other issues, the likely behavior of the models away from coexistence.

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PubMed1984

Estimation of continental Os/Os values by using Os/Os and Nd/Nd ratios in marine manganese nodules.

The relationship between (187)Os/(186)Os and (143)Nd/(144)Nd in different manganese nodule fields is used to determine the (187)Os/(186)Os ratio of the continental terrains bounding the major ocean basins. The Atlantic Ocean drainages yield (187)Os/(186)Os of about 11; the Pacific Ocean, between 25 and 36; and the western Indian Ocean, 20. By assuming a two-component continental crust composed of "ultramafic rocks" (high Os concentration, low (187)Os/(186)Os) and "granite" with only radiogenic (187)Os produced in accessory Re-bearing molybdenite, the ultramafic contribution to weathering is about 0.2%. Some or most of this may come from the alteration of oceanic ultramafics.

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PubMed1981