1,272 research outputs found
Thermodynamic Density Matrix renormalization Group Study of the Magnetic Susceptibility of Half-integer Quantum Spin Chains
It is shown that White's density matrix renormalization group technique can
be adapted to obtain thermodynamic quantities. As an illustration, the magnetic
susceptibility of Heisenberg S=1/2 and S=3/2 spin chains are computed. A
careful finite size analysis is made to determine the range of temperatures
where the results are reliable. For the S=1/2 chain, the comparison with the
exact Bethe ansatz curve shows an agreement within 1% down to T=0.05J.Comment: 9 pages, 4 figures. To be published in PR
Critical dynamics in thin films
Critical dynamics in film geometry is analyzed within the field-theoretical
approach. In particular we consider the case of purely relaxational dynamics
(Model A) and Dirichlet boundary conditions, corresponding to the so-called
ordinary surface universality class on both confining boundaries. The general
scaling properties for the linear response and correlation functions and for
dynamic Casimir forces are discussed. Within the Gaussian approximation we
determine the analytic expressions for the associated universal scaling
functions and study quantitatively in detail their qualitative features as well
as their various limiting behaviors close to the bulk critical point. In
addition we consider the effects of time-dependent fields on the
fluctuation-induced dynamic Casimir force and determine analytically the
corresponding universal scaling functions and their asymptotic behaviors for
two specific instances of instantaneous perturbations. The universal aspects of
nonlinear relaxation from an initially ordered state are also discussed
emphasizing the different crossovers that occur during this evolution. The
model considered is relevant to the critical dynamics of actual uniaxial
ferromagnetic films with symmetry-preserving conditions at the confining
surfaces and for Monte Carlo simulations of spin system with Glauber dynamics
and free boundary conditions.Comment: 64 pages, 21 figure
Fishmeal supplementation during ovine pregnancy and lactation protects against maternal stress-induced programming of the offspring immune system
Background: Prenatally stressed offspring exhibit increased susceptibility to inflammatory disorders due to in utero programming. Research into the effects of n-3 PUFAs shows promising results for the treatment and prevention of these disorders. The purpose of this study was to investigate whether maternal fishmeal supplementation during pregnancy and lactation protects against programming of the offspring\u27s immune response following simulated maternal infection. Methods: In order to accomplish this, 53 ewes were fed a diet supplemented with fishmeal (FM; rich in n-3 PUFA) or soybean meal (SM; rich in n-6 PUFAs) from day 100 of gestation (gd 100) through lactation. On gd135, half the ewes from each dietary group were challenged with either 1.2 ÎĽg/kg Escherichia coli lipopolysaccharide (LPS) endotoxin to simulate a bacterial infection, or saline as the control. At 4.5 months of age the offspring\u27s dermal immune response was assessed by cutaneous hypersensitivity testing with ovalbumin (OVA) and candida albicans (CAA) 21 days after sensitization. Skinfold measurements were taken and serum blood samples were also collected to assess the primary and secondary antibody immune response. Results: Offspring born to SM + LPS mothers had a significantly greater change in skinfold thickness in response to both antigens as well as a greater secondary antibody response to OVA compared to all treatments. Conclusions: Supplementation during pregnancy with FM appears to protect against adverse fetal programming that may occur during maternal infection and this may reduce the risk of atopic disease later in life
Ground states of unfrustrated spin Hamiltonians satisfy an area law
We show that ground states of unfrustrated quantum spin-1/2 systems on
general lattices satisfy an entanglement area law, provided that the
Hamiltonian can be decomposed into nearest-neighbor interaction terms which
have entangled excited states. The ground state manifold can be efficiently
described as the image of a low-dimensional subspace of low Schmidt measure,
under an efficiently contractible tree-tensor network. This structure gives
rise to the possibility of efficiently simulating the complete ground space
(which is in general degenerate). We briefly discuss "non-generic" cases,
including highly degenerate interactions with product eigenbases, using a
relationship to percolation theory. We finally assess the possibility of using
such tree tensor networks to simulate almost frustration-free spin models.Comment: 14 pages, 4 figures, small corrections, added a referenc
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