22,389 research outputs found
Emergent BCS regime of the two-dimensional fermionic Hubbard model: ground-state phase diagram
A significant part of the phase diagram of the two-dimensional fermionic
Hubbard model for moderate interactions and filling factors ()
is governed by effective Fermi liquid physics with weak BCS-type instabilities.
We access this regime in a controlled way by a combination of the bold-line
diagrammatic Monte Carlo method with an additional ladder-diagram summation
trick and semi-analytic treatment of the weak instability in the Cooper
channel. We obtain the corresponding ground-state phase diagram in the
plane describing the competition between the and wave superfluid
states. We also claim the values of the dimensionless BCS coupling constants
controlling the superfluid at the phase boundaries, which prove to be
very small up to .Comment: 5 pages, 5 figure
Dynamical critical scaling and effective thermalization in quantum quenches: the role of the initial state
We explore the robustness of universal dynamical scaling behavior in a
quantum system near criticality with respect to initialization in a large class
of states with finite energy. By focusing on a homogeneous XY quantum spin
chain in a transverse field, we characterize the non-equilibrium response under
adiabatic and sudden quench processes originating from a pure as well as a
mixed excited initial state, and involving either a regular quantum critical or
a multicritical point. We find that the critical exponents of the ground-state
quantum phase transition can be encoded in the dynamical scaling exponents
despite the finite energy of the initial state. In particular, we identify
conditions on the initial distribution of quasi-particle excitation which
ensure Kibble-Zurek scaling to persist. The emergence of effective thermal
equilibrium behavior following a sudden quench towards criticality is also
investigated, with focus on the long-time dynamics of the quasi-particle
excitation. For a quench to a regular quantum critical point, this observable
is found to behave thermally provided that the system is prepared at
sufficiently high temperature, whereas thermalization fails to occur in
quenches taking the system towards a multi-critical point. We argue that the
observed lack of thermalization originates in this case in the asymmetry of the
impulse region that is also responsible for anomalous multicritical dynamical
scaling.Comment: 18 pages, 13 eps color figures, published versio
Quantum Levy flights and multifractality of dipolar excitations in a random system
We consider dipolar excitations propagating via dipole-induced exchange among
immobile molecules randomly spaced in a lattice. The character of the
propagation is determined by long-range hops (Levy flights). We analyze the
eigen-energy spectra and the multifractal structure of the wavefunctions. In 1D
and 2D all states are localized, although in 2D the localization length can be
extremely large leading to an effective localization-delocalization crossover
in realistic systems. In 3D all eigenstates are extended but not always
ergodic, and we identify the energy intervals of ergodic and non-ergodic
states. The reduction of the lattice filling induces an ergodic to non-ergodic
transition, and the excitations are mostly non-ergodic at low filling.Comment: 5 pages, 6 figure
TESTING THE VIABILITY OF AREA YIELD INSURANCE FOR COTTON AND SOYBEANS IN THE SOUTHEAST
GRP is essentially a put option on the NASS estimate of the county average yield. Purchasers of GRP are exposed to geographic basis risk. This study uses farm- and county-level yield data to examine the viability of area yield insurance for cotton and soybean farms in the southeastern U.S.Risk and Uncertainty,
p38α (MAPK14) critically regulates the immunological response and the production of specific cytokines and chemokines in astrocytes.
In CNS lesions, "reactive astrocytes" form a prominent cellular response. However, the nature of this astrocyte immune activity is not well understood. In order to study astrocytic immune responses to inflammation and injury, we generated mice with conditional deletion of p38α (MAPK14) in GFAP+ astrocytes. We studied the role of p38α signaling in astrocyte immune activation both in vitro and in vivo, and simultaneously examined the effects of astrocyte activation in CNS inflammation. Our results showed that specific subsets of cytokines (TNFα, IL-6) and chemokines (CCL2, CCL4, CXCL1, CXCL2, CXCL10) are critically regulated by p38α signaling in astrocytes. In an in vivo CNS inflammation model of intracerebral injection of LPS, we observed markedly attenuated astrogliosis in conditional GFAPcre p38α(-/-) mice. However, GFAPcre p38α(-/-) mice showed marked upregulation of CCL2, CCL3, CCL4, CXCL2, CXCL10, TNFα, and IL-1ÎČ compared to p38αfl/fl cohorts, suggesting that in vivo responses to LPS after GFAPcre p38α deletion are complex and involve interactions between multiple cell types. This finding was supported by a prominent increase in macrophage/microglia and neutrophil recruitment in GFAPcre p38α(-/-) mice compared to p38αfl/fl controls. Together, these studies provide important insights into the critical role of p38α signaling in astrocyte immune activation
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