51,812 research outputs found
Cold dilute neutron matter on the lattice I: Lattice virial coefficients and large scattering lengths
We study cold dilute neutron matter on the lattice using an effective field
theory. We work in the unitary limit in which the scattering length is much
larger than the interparticle spacing. In this paper we focus on the equation
of state at temperatures above the Fermi temperature and compare lattice
simulations to the virial expansion on the lattice and in the continuum. We
find that in the unitary limit lattice discretization errors in the second
virial coefficient are significantly enhanced. As a consequence the equation of
state does not show the universal scaling behavior expected in the unitary
limit. We suggest that scaling can be improved by tuning the second virial
coefficient rather than the scattering length.Comment: 17 pages, 12 figure
Equation of state and critical behavior of polymer models: A quantitative comparison between Wertheim's thermodynamic perturbation theory and computer simulations
We present an application of Wertheim's Thermodynamic Perturbation Theory
(TPT1) to a simple coarse grained model made of flexibly bonded Lennard-Jones
monomers. We use both the Reference Hyper-Netted-Chain (RHNC) and Mean
Spherical approximation (MSA) integral equation theories to describe the
properties of the reference fluid. The equation of state, the density
dependence of the excess chemical potential, and the critical points of the
liquid--vapor transition are compared with simulation results and good
agreement is found. The RHNC version is somewhat more accurate, while the MSA
version has the advantage of being almost analytic. We analyze the scaling
behavior of the critical point of chain fluids according to TPT1 and find it to
reproduce the mean field exponents: The critical monomer density is predicted
to vanish as upon increasing the chain length while the critical
temperature is predicted to reach an asymptotic finite temperature that is
attained as . The predicted asymptotic finite critical temperature
obtained from the RHNC and MSA versions of TPT1 is found to be in good
agreement with the point of our polymer model as obtained from the
temperature dependence of the single chain conformations.Comment: to appear in J.Chem.Phy
Casimir energy density in closed hyperbolic universes
The original Casimir effect results from the difference in the vacuum
energies of the electromagnetic field, between that in a region of space with
boundary conditions and that in the same region without boundary conditions. In
this paper we develop the theory of a similar situation, involving a scalar
field in spacetimes with compact spatial sections of negative spatial
curvature.Comment: 10 pages. Contribution to the "Fifth Alexander Friedmann
International Seminar on Gravitation and Cosmology," Joao Pessoa, Brazil,
2002. Revised version, with altered Abstract and one new referenc
Trip-Based Public Transit Routing
We study the problem of computing all Pareto-optimal journeys in a public
transit network regarding the two criteria of arrival time and number of
transfers taken. We take a novel approach, focusing on trips and transfers
between them, allowing fine-grained modeling. Our experiments on the
metropolitan network of London show that the algorithm computes full 24-hour
profiles in 70 ms after a preprocessing phase of 30 s, allowing fast queries in
dynamic scenarios.Comment: Minor corrections, no substantial changes. To be presented at ESA
201
Towards a Topological Mechanism of Quark Confinement
We report on new analyses of the topological and chiral vacuum structure of
four-dimensional QCD on the lattice. Correlation functions as well as
visualization of monopole currents in the maximally Abelian gauge emphasize
their topological origin and gauge invariant characterization. The
(anti)selfdual character of strong vacuum fluctuations is reveiled by
smoothing. In full QCD, (anti)instanton positions are also centers of the local
chiral condensate and quark charge density. Most results turn out generically
independent of the action and the cooling/smoothing method.Comment: 14 pages, Contribution to YKIS9
Expression of PIK3CA mutant E545K in the mammary gland induces heterogeneous tumors but is less potent than mutant H1047R.
The phosphoinositide 3-kinase (PI3K) signaling cascade is a key mediator of cellular growth, survival and metabolism and is frequently subverted in human cancer. The gene encoding for the alpha catalytic subunit of PI3K (PIK3CA) is mutated and/or amplified in ∼30% of breast cancers. Mutations in either the kinase domain (H1047R) or the helical domain (E545K) are most common and result in a constitutively active enzyme with oncogenic capacity. PIK3CA(H1047R) was previously demonstrated to induce tumors in transgenic mouse models; however, it was not known whether overexpression of PIK3CA(E545K) is sufficient to induce mammary tumors and whether tumor initiation by these two types of mutants differs. Here, we demonstrate that expression of PIK3CA(E545K) in the mouse mammary gland induces heterogenous mammary carcinomas but with a longer latency than PIK3CA(H1047R)-expressing mice. Our results suggest that the helical domain mutant PIK3CA(E545K) is a less potent inducer of mammary tumors due to less efficient activation of downstream Akt signaling
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