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  • 1990-1994  (6)
  • 1
    Digitale Medien
    Digitale Medien
    Expression of CD28 on CD8+ and CD4+ Lymphocytes During HIV Infection (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Scandinavian journal of immunology 40 (1994), S. 0 
    Details
    ISSN: 1365-3083
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: CD28 interaction with B7 molecules, expressed on the membranes of antigen-presenting cells, costimulates cytokine production, T-cell proliferation and generation of cytotoxic lymphocytes. The expression of CD28 markers on CD4+ and CD8+ lymphocytes was studied in a group of subjects at various stages of HIV infection. A reduction in the percentage of CD28-bearing CD4+ and CD8+ cell subsets was observed during the asymptomatic stage of the disease. This reduction was more pronounced in AIDS than in non-AIDS patients. At the same time, an increase in the absolute CD8+CD28− cell number (greater in stage A than in stage B and C subjects) was observed in HIV-infected patients. The finding of an altered pattern of CD28 expression on T cells might per se explain certain early defects in the cytokine pattern and in the immune response peculiar to HIV-infected patients.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-3083.1994.tb03494.x
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  • 2
    Digitale Medien
    Digitale Medien
    Approach to equilibrium of Glauber dynamics in the one phase region (1994)
    Springer
    Communications in mathematical physics 161 (1994), S. 447-486 
    Details
    ISSN: 1432-0916
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik , Physik
    Notizen: Abstract Various finite volume mixing conditions in classical statistical mechanics are reviewed and critically analyzed. In particular somefinite size conditions are discussed, together with their implications for the Gibbs measures and for the approach to equilibrium of Glauber dynamics inarbitrarily large volumes. It is shown that Dobrushin-Shlosman's theory ofcomplete analyticity and its dynamical counterpart due to Stroock and Zegarlinski, cannot be applied, in general, to the whole one phase region since it requires mixing properties for regions ofarbitrary shape. An alternative approach, based on previous ideas of Oliveri, and Picco, is developed, which allows to establish results on rapid approach to equilibrium deeply inside the one phase region. In particular, in the ferromagnetic case, we considerably improve some previous results by Holley and Aizenman and Holley. Our results are optimal in the sene that, for example, they show for the first time fast convergence of the dynamicsfor any temperature above the critical one for thed-dimensional Ising model with or without an external field. In part II we extensively consider the general case (not necessarily attractive) and we develop a new method, based on renormalizations group ideas and on an assumption of strong mixing in a finite cube, to prove hypercontractivity of the Markov semigroup of the Glauber dynamics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02101929
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  • 3
    Digitale Medien
    Digitale Medien
    For 2-D lattice spin systems weak mixing implies strong mixing (1994)
    Springer
    Communications in mathematical physics 165 (1994), S. 33-47 
    Details
    ISSN: 1432-0916
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik , Physik
    Notizen: Abstract We prove that for finite range discrete spin systems on the two dimensional latticeZ 2, the (weak) mixing condition which follows, for instance, from the Dobrushin-Shlosman uniqueness condition for the Gibbs state implies a stronger mixing property of the Gibbs state, similar to the Dobrushin-Shlosman complete analyticity condition, but restricted to all squares in the lattice, or, more generally, to all sets multiple of a large enough square. The key observation leading to the proof is that a change in the boundary conditions cannot propagate either in the bulk, because of the weak mixing condition, or along the boundary because it is one dimensional. As a consequence we obtain for ferromagnetic Ising-type systems proofs that several nice properties hold arbitrarily close to the critical temperature; these properties include the existence of a convergent cluster expansion and uniform boundedness of the logarithmic Sobolev constant and rapid convergence to equilibrium of the associated Glauber dynamics on nice subsets ofZ 2, including the full lattice.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02099735
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  • 4
    Digitale Medien
    Digitale Medien
    Approach to equilibrium of Glauber dynamics in the one phase region (1994)
    Springer
    Communications in mathematical physics 161 (1994), S. 487-514 
    Details
    ISSN: 1432-0916
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik , Physik
    Notizen: Abstract We develop a new method, based on renormalization group ideas (block decimation procedure), to prove, under an assumption of strong mixing in a finite cube Λ0, a Logarithmic Sobolev Inequality for the Gibbs state of a discrete spin system. As a consequence we derive the hypercontractivity of the Markov semigroup of the associated Glauber dynamics and the exponential convergence to equilibrium in the uniform norm in all volumes Λ “multiples” of the cube Λ0.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02101930
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  • 5
    Digitale Medien
    Digitale Medien
    On the two-dimensional dynamical Ising model in the phase coexistence region (1994)
    Springer
    Journal of statistical physics 76 (1994), S. 1179-1246 
    Details
    ISSN: 1572-9613
    Schlagwort(e): Ising model ; phase coexistence region
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We consider a Glauber dynamics reversible with respect to the two-dimensional Ising model in a finite square of sideL, in the absence of an external field and at large inverse temperature β. We first consider the gap in the spectrum of the generator of the dynamics in two different cases: with plus and open boundary conditions. We prove that, when the symmetry under global spin flip is broken by the boundary conditions, the gap is much larger than the case in which the symmetry is present. For this latter we compute exactly the asymptotics of −(1/βL) log(gap) asL→∞ and show that it coincides with the surface tension along one of the coordinate axes. As a consequence we are able to study quite precisely the large deviations in time of the magnetization and to obtain an upper bound on the spin-spin time correlation in the infinite-volume plus phase. Our results establish a connection between the dynamical large deviations and those of the equilibrium Gibbs measure studied by Shlosman in the framework of the rigorous description of the Wulff shape for the Ising model. Finally we show that, in the case of open boundary conditions, it is possible to rescale the time withL in such a way that, asL→∞, the finite-dimensional distributions of the time-rescaled magnetization converge to those of a symmetric continuous-time Markov chain on the two-state space {−m *(β),m *(β)},m *(β) being the spontaneous magnetization. Our methods rely upon a novel combination of techniques for bounding from below the gap of symmetric Markov chains on complicated graphs, developed by Jerrum and Sinclair in their Markov chain approach to hard computational problems, and the idea of introducing “block Glauber dynamics” instead of the standard single-site dynamics, in order to put in evidence more effectively the effect of the boundary conditions in the approach to equilibrium.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02187060
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  • 6
    Digitale Medien
    Digitale Medien
    Some remarks on pathologies of renormalization-group transformations for the Ising model (1993)
    Springer
    Journal of statistical physics 72 (1993), S. 1169-1177 
    Details
    ISSN: 1572-9613
    Schlagwort(e): Decimation ; Renormalization-group ; non-Gibbsianness ; Finite-size conditions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The results recently obtained by van Enter, Fernandez, and Sokal on non-Gibbsianness of the measurev =T b μβ,h arising from the application of a single decimation transformationT b , with spacingb, to the Gibbs measure μβ,h , of the Ising model, for suitably chosen large inverse temperatureβ and nonzero external fieldh, are critically analyzed. In particular, we show that if, keeping fixed the same values ofβ, h, andb, one iterates a sufficiently large number of timesn the transformationT b , one obtains a new measurev ′ = (T b )nμβ,h which is Gibbsian and moreover very weakly coupled.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01048184
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