1,348 research outputs found
Thermal conductivity of the one-dimensional Fermi-Hubbard model
We study the thermal conductivity of the one-dimensional Fermi-Hubbard model
at finite temperature using a density matrix renormalization group approach.
The integrability of this model gives rise to ballistic thermal transport. We
calculate the temperature dependence of the thermal Drude weight at half
filling for various interactions and moreover, we compute its filling
dependence at infinite temperature. The finite-frequency contributions
originating from the fact that the energy current is not a conserved quantity
are investigated as well. We report evidence that breaking the integrability
through a nearest-neighbor interaction leads to vanishing Drude weights and
diffusive energy transport. Moreover, we demonstrate that energy spreads
ballistically in local quenches with initially inhomogeneous energy density
profiles in the integrable case. We discuss the relevance of our results for
thermalization in ultra-cold quantum gas experiments and for transport
measurements with quasi-one dimensional materials
Comment on "Anomalous Thermal Conductivity of Frustrated Heisenberg Spin Chains and Ladders"
In a recent letter [Phys. Rev. Lett. 89, 156603 (2002); cond-mat/0201300],
Alvarez and Gros have numerically analyzed the Drude weight for thermal
transport in spin ladders and frustrated chains of up to 14 sites and have
proposed that it remains finite in the thermodynamic limit. In this comment, we
argue that this conclusion cannot be sustained if the finite-size analysis is
taken to larger system sizes.Comment: One page REVTeX4, 1 figure. Published version (minor changes
Differential regulation of innate and adaptive immune responses in viral encephalitis.
Viral encephalitis is a global health concern. The ability of a virus to modulate the immune response can have a pivotal effect on the course of disease and the fate of the infected host. In this study, we sought to understand the immunological basis for the fatal encephalitis following infection with the murine coronavirus, mouse hepatitis virus (MHV)-JHM, in contrast with the more attenuated MHV-A59. Distinct glial cell cytokine and chemokine response patterns were observed within 3 days after infection, became progressively more polarized during the course of infection and with the infiltration of leukocytes. In the brain, MHV-JHM infection induced strong accumulation of IFNbeta mRNA relative to IFNgamma mRNA. This trend was reversed in MHV-A59 infection and was accompanied by increased CD8 T cell infiltration into brain compared to MHV-JHM infection. Increased apoptosis appeared to contribute to the diminished presence of CD8 T cells in MHV-JHM-infected brain with the consequence of a lower potential for IFNgamma production and antiviral activity. MHV-JHM infection also induced sustained mRNA accumulation of the innate immune response products interleukin (IL)-6 and IL-1. Furthermore, high levels of macrophage-inflammatory protein (MIP)-1alpha, MIP-1beta, and MIP-2 mRNA were observed at the onset of MHV-JHM infection and correlated with a marked elevation in the number of macrophages in the brain on day 7 compared to MHV-A59 infection. These observations indicate that differences in the severity of viral encephalitis may reflect the differential ability of viruses to stimulate innate immune responses within the CNS and subsequently the character of infiltrating leukocyte populations
Thermal transport of the XXZ chain in a magnetic field
We study the heat conduction of the spin-1/2 XXZ chain in finite magnetic
fields where magnetothermal effects arise. Due to the integrability of this
model, all transport coefficients diverge, signaled by finite Drude weights.
Using exact diagonalization and mean-field theory, we analyze the temperature
and field dependence of the thermal Drude weight for various exchange
anisotropies under the condition of zero magnetization-current flow. First, we
find a strong magnetic field dependence of the Drude weight, including a
suppression of its magnitude with increasing field strength and a non-monotonic
field-dependence of the peak position. Second, for small exchange anisotropies
and magnetic fields in the massless as well as in the fully polarized regime
the mean-field approach is in excellent agreement with the exact
diagonalization data. Third, at the field-induced quantum critical line between
the para- and ferromagnetic region we propose a universal low-temperature
behavior of the thermal Drude weight.Comment: 9 pages REVTeX4 including 5 figures, revised version, refs. added,
typos correcte
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