10,365 research outputs found
Stripe phases in high-temperature superconductors
Stripe phases are predicted and observed to occur in a class of
strongly-correlated materials describable as doped antiferromagnets, of which
the copper-oxide superconductors are the most prominent representative. The
existence of stripe correlations necessitates the development of new principles
for describing charge transport, and especially superconductivity, in these
materials.Comment: 5 pp, 1 color eps fig., to appear as a Perspective in Proc. Natl.
Acad. Sci. US
Exact ground states and correlation functions of chain and ladder models of interacting hardcore bosons or spinless fermions
By removing one empty site between two occupied sites, we map the ground
states of chains of hardcore bosons and spinless fermions with infinite
nearest-neighbor repulsion to ground states of chains of hardcore bosons and
spinless fermions without nearest-neighbor repulsion respectively, and
ultimately in terms of the one-dimensional Fermi sea. We then introduce the
intervening-particle expansion, where we write correlation functions in such
ground states as a systematic sum over conditional expectations, each of which
can be ultimately mapped to a one-dimensional Fermi-sea expectation. Various
ground-state correlation functions are calculated for the bosonic and fermionic
chains with infinite nearest-neighbor repulsion, as well as for a ladder model
of spinless fermions with infinite nearest-neighbor repulsion and correlated
hopping in three limiting cases. We find that the decay of these correlation
functions are governed by surprising power-law exponents.Comment: 20 pages, 18 figures, RevTeX4 clas
Localized charged states and phase separation near second order phase transition
Localized charged states and phase segregation are described in the framework
of the phenomenological Ginzburg-Landau theory of phase transitions. The
Coulomb interactions determines the charge distribution and the characteristic
length of the phase separated states. The phase separation with charge
segregation becomes possible because of the large dielectric constant and the
small density of extra charge in the range of charge localization. The phase
diagram is calculated and the energy gain of the phase separated state is
estimated. The role of the Coulomb interaction is elucidated
A note on density correlations in the half-filled Hubbard model
We consider density-density correlations in the one-dimensional Hubbard model
at half filling. On intuitive grounds one might expect them to exhibit an
exponential decay. However, as has been noted recently, this is not obvious
from the Bethe Ansatz/conformal field theory (BA/CFT) approach. We show that by
supplementing the BA/CFT analysis with simple symmetry arguments one can easily
prove that correlations of the lattice density operators decay exponentially.Comment: 3 pages, RevTe
Classical Phase Fluctuations in Incommensurate Peierls Chains
In the pseudogap regime of one-dimensional incommensurate Peierls systems,
fluctuations of the phase of the order parameter prohibit the emergence of
long-range order and generate a finite correlation length. For classical phase
fluctuations, we present exact results for the average electronic density of
states, the mean localization length, the electronic specific heat and the spin
susceptibility at low temperatures. Our results for the susceptibility give a
good fit to experimental data.Comment: 4 Revtex pages, 4 figures, submitted to Phys. Rev. Let
Efficacy of B-cell-targeted therapy with rituximab in patients with rheumatoid arthritis.
BACKGROUND: An open-label study indicated that selective depletion of B cells with the use of rituximab led to sustained clinical improvements for patients with rheumatoid arthritis. To confirm these observations, we conducted a randomized, double-blind, controlled study. METHODS: We randomly assigned 161 patients who had active rheumatoid arthritis despite treatment with methotrexate to receive one of four treatments: oral methotrexate (> or =10 mg per week) (control); rituximab (1000 mg on days 1 and 15); rituximab plus cyclophosphamide (750 mg on days 3 and 17); or rituximab plus methotrexate. Responses defined according to the criteria of the American College of Rheumatology (ACR) and the European League against Rheumatism (EULAR) were assessed at week 24 (primary analyses) and week 48 (exploratory analyses). RESULTS: At week 24, the proportion of patients with 50 percent improvement in disease symptoms according to the ACR criteria, the primary end point, was significantly greater with the rituximab-methotrexate combination (43 percent, P=0.005) and the rituximab-cyclophosphamide combination (41 percent, P=0.005) than with methotrexate alone (13 percent). In all groups treated with rituximab, a significantly higher proportion of patients had a 20 percent improvement in disease symptoms according to the ACR criteria (65 to 76 percent vs. 38 percent, P< or =0.025) or had EULAR responses (83 to 85 percent vs. 50 percent, P< or =0.004). All ACR responses were maintained at week 48 in the rituximab-methotrexate group. The majority of adverse events occurred with the first rituximab infusion: at 24 weeks, serious infections occurred in one patient (2.5 percent) in the control group and in four patients (3.3 percent) in the rituximab groups. Peripheral-blood immunoglobulin concentrations remained within normal ranges. CONCLUSIONS: In patients with active rheumatoid arthritis despite methotrexate treatment, a single course of two infusions of rituximab, alone or in combination with either cyclophosphamide or continued methotrexate, provided significant improvement in disease symptoms at both weeks 24 and 48
State-space solutions to the dynamic magnetoencephalography inverse problem using high performance computing
Determining the magnitude and location of neural sources within the brain
that are responsible for generating magnetoencephalography (MEG) signals
measured on the surface of the head is a challenging problem in functional
neuroimaging. The number of potential sources within the brain exceeds by an
order of magnitude the number of recording sites. As a consequence, the
estimates for the magnitude and location of the neural sources will be
ill-conditioned because of the underdetermined nature of the problem. One
well-known technique designed to address this imbalance is the minimum norm
estimator (MNE). This approach imposes an regularization constraint that
serves to stabilize and condition the source parameter estimates. However,
these classes of regularizer are static in time and do not consider the
temporal constraints inherent to the biophysics of the MEG experiment. In this
paper we propose a dynamic state-space model that accounts for both spatial and
temporal correlations within and across candidate intracortical sources. In our
model, the observation model is derived from the steady-state solution to
Maxwell's equations while the latent model representing neural dynamics is
given by a random walk process.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS483 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
The Albedo, Size, and Density of Binary Kuiper Belt Object (47171) 1999 TC36
We measured the system-integrated thermal emission of the binary Kuiper Belt
Object 1999 TC36 at wavelengths near 24 and 70 microns using the Spitzer space
telescope. We fit these data and the visual magnitude using both the Standard
Thermal Model and thermophysical models. We find that the effective diameter of
the binary is 405 km, with a range of 350 -- 470 km, and the effective visible
geometric albedo for the system is 0.079 with a range of 0.055 -- 0.11. The
binary orbit, magnitude contrast between the components, and system mass have
been determined from HST data (Margot et al., 2004; 2005a; 2005b). Our
effective diameter, combined with that system mass, indicate an average density
for the objects of 0.5 g/cm3, with a range 0.3 -- 0.8 g/cm3. This density is
low compared to that of materials expected to be abundant in solid bodies in
the trans-Neptunian region, requiring 50 -- 75% of the interior of 1999 TC36 be
taken up by void space. This conclusion is not greatly affected if 1999 TC36 is
``differentiated'' (in the sense of having either a rocky or just a non-porous
core). If the primary is itself a binary, the average density of that
(hypothetical) triple system would be in the range 0.4 -- 1.1 g/cm3, with a
porosity in the range 15 -- 70%.Comment: ApJ, in press (May, 2006
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