1,683 research outputs found
Broad-Band Soft X-ray Polarimetry
We developed an instrument design capable of measuring linear X-ray
polarization over a broad-band using conventional spectroscopic optics. A set
of multilayer-coated flats reflects the dispersed X-rays to the instrument
detectors. The intensity variation with position angle is measured to determine
three Stokes parameters: I, Q, and U -- all as a function of energy. By
laterally grading the multilayer optics and matching the dispersion of the
gratings, one may take advantage of high multilayer reflectivities and achieve
modulation factors > 50% over the entire 0.2 to 0.8 keV band. This instrument
could be used in a small orbiting mission or scaled up for the International
X-ray Observatory. Laboratory work has begun that would demonstrate the
capabilities of key components.Comment: 6 pages, 3 figures (2 color); to appear in proceedings of "The Coming
of Age of X-ray Polarimetry
Entropy-driven phase transition in a polydisperse hard-rods lattice system
We study a system of rods on the 2d square lattice, with hard-core exclusion.
Each rod has a length between 2 and N. We show that, when N is sufficiently
large, and for suitable fugacity, there are several distinct Gibbs states, with
orientational long-range order. This is in sharp contrast with the case N=2
(the monomer-dimer model), for which Heilmann and Lieb proved absence of phase
transition at any fugacity. This is the first example of a pure hard-core
system with phases displaying orientational order, but not translational order;
this is a fundamental characteristic feature of liquid crystals
A Qualitative And Observational Study Of Post-Modern Parental Roles During The Child's Haematopoietic Stem Cell Transplantation (HSCT) Treatment
Failure of Mean Field Theory at Large N
We study strongly coupled lattice QCD with colors of staggered fermions
in 3+1 dimensions. While mean field theory describes the low temperature
behavior of this theory at large , it fails in the scaling region close to
the finite temperature second order chiral phase transition. The universal
critical region close to the phase transition belongs to the 3d XY universality
class even when becomes large. This is in contrast to Gross-Neveu models
where the critical region shrinks as (the number of flavors) increases and
mean field theory is expected to describe the phase transition exactly in the
limit of infinite . Our work demonstrates that close to second order phase
transitions infrared fluctuations can sometimes be important even when is
strictly infinite.Comment: 4 pages, 3 figure
A Class of Parameter Dependent Commuting Matrices
We present a novel class of real symmetric matrices in arbitrary dimension
, linearly dependent on a parameter . The matrix elements satisfy a set
of nontrivial constraints that arise from asking for commutation of pairs of
such matrices for all , and an intuitive sufficiency condition for the
solvability of certain linear equations that arise therefrom. This class of
matrices generically violate the Wigner von Neumann non crossing rule, and is
argued to be intimately connected with finite dimensional Hamiltonians of
quantum integrable systems.Comment: Latex, Added References, Typos correcte
A projection method for statics and dynamics of lattice spin systems
A method based on Monte Carlo sampling of the probability flows projected
onto the subspace of one or more slow variables is proposed for investigation
of dynamic and static properties of lattice spin systems. We illustrate the
method by applying it, with projection onto the order-parameter subspace, to
the three-dimensional 3-state Potts model in equilibrium and to metastable
decay in a three-dimensional 3-state kinetic Potts model.Comment: 4 pages, 3 figures, RevTex, final version to appear in Phys. Rev.
Let
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
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