643 research outputs found
Crystallization of the C-terminal domain of the mouse brain cytosolic long-chain acyl-CoA thioesterase
The mammalian long-chain acyl-CoA thioesterase, the enzyme that catalyses the hydrolysis of acyl-CoAs to free fatty acids, contains two fused 4HBT (4-hydroxybenzoyl-CoA thioesterase) motifs. The C-terminal domain of the mouse long-chain acyl-CoA thioesterase (Acot7) has been expressed in bacteria and crystallized. The crystals were obtained by vapour diffusion using PEG 2000 MME as precipitant at pH 7.0 and 290 K. The crystals have the symmetry of space group R32 ( unit-cell parameters a = b = 136.83, c = 99.82 angstrom, gamma = 120 degrees). Two molecules are expected in the asymmetric unit. The crystals diffract to 2.4 angstrom resolution using the laboratory X-ray source and are suitable for crystal structure determination
Frustration - how it can be measured
A misfit parameter is used to characterize the degree of frustration of
ordered and disordered systems. It measures the increase of the ground-state
energy due to frustration in comparison with that of a relevant reference
state. The misfit parameter is calculated for various spin-glass models. It
allows one to compare these models with each other. The extension of this
concept to other combinatorial optimization problems with frustration, e.g.
p-state Potts glasses, graph-partitioning problems and coloring problems is
given.Comment: 10 pages, 1 table, no figures, uses revtex.st
On the Quasiparticle Description of Lattice QCD Thermodynamics
We propose a novel quasiparticle interpretation of the equation of state of
deconfined QCD at finite temperature. Using appropriate thermal masses, we
introduce a phenomenological parametrization of the onset of confinement in the
vicinity of the predicted phase transition. Lattice results of the energy
density, the pressure and the interaction measure of pure SU(3) gauge theory
are excellently reproduced. We find a relationship between the thermal energy
density of the Yang-Mills vacuum and the chromomagnetic condensate _T.
Finally, an extension to QCD with dynamical quarks is discussed. Good agreement
with lattice data for 2, 2+1 and 3 flavour QCD is obtained. We also present the
QCD equation of state for realistic quark masses.Comment: 20 pages, 10 eps figure
Shopping centre siting and modal choice in Belgium: a destination based analysis
Although modal split is only one of the elements considered in decision-making on new shopping malls, it remarkably often arises in arguments of both proponents and opponents. Today, this is also the case in the debate on the planned development of three major shopping malls in Belgium. Inspired by such debates, the present study focuses on the impact of the location of shopping centres on the travel mode choice of the customers. Our hypothesis is that destination-based variables such as embeddedness in the urban fabric, accessibility and mall size influence the travel mode choice of the visitors. Based on modal split data and location characteristics of seventeen existing shopping centres in Belgium, we develop a model for a more sustainable siting policy. The results show a major influence of the location of the shopping centre in relation to the urban form, and of the size of the mall. Shopping centres that are part of a dense urban fabric, measured through population density, are less car dependent. Smaller sites will attract more cyclists and pedestrians. Interestingly, our results deviate significantly from the figures that have been put forward in public debates on the shopping mall issue in Belgium
Time decay of the remanent magnetization in the spin glass model at T=0
Using the zero-temperature Metropolis dynamics, the time decay of the
remanent magnetization in the Edward-Anderson spin glass model with a
uniform random distribution of ferromagnetic and antiferromagnetic interactions
has been investigated. Starting from the saturation, the magnetization per spin
reveals a slow decrease with time, which can be approximated by a power
law:, . Moreover, its
relaxation does not lead it into one of the ground states, and therefore the
system is trapped in metastable isoenergetic microstates remaining magnetized.
Such behaviour is discussed in terms of a random walk the system performs on
its available configuration space.Comment: 9 pages, 3 figure
Relationship between spatial proximity and travel-to-work distance : the effect of the compact city
In this paper, an assessment is made of the relationship between selected aspects of spatial proximity (density, diversity, minimum commuting distance, jobs-housing balance and job accessibility) and reported commuting distances in Flanders (Belgium). Results show that correlations may depend on the considered trip end. For example, a high residential density, a high degree of spatial diversity and a high level of job accessibility are all associated with a short commute by residents, while a high job density is associated with a long commute by employees. A jobs-housing balance close to one is associated with a short commute, both by residents and by employees. In general, it appears that the alleged sustainability benefits of the compact city model are still valid in a context of continuously expanding commuting trip lengths
Action Principle and Algebraic Approach to Gauge Transformations in Gauge Theories
The action principle is used to derive, by an entirely algebraic approach,
gauge transformations of the full vacuum-to-vacuum transition amplitude
(generating functional) from the Coulomb gauge to arbitrary covariant gauges
and in turn to the celebrated Fock-Schwinger (FS) gauge for the abelian (QED)
gauge theory without recourse to path integrals or to commutation rules and
without making use of delta functionals. The interest in the FS gauge, in
particular, is that it leads to Faddeev-Popov ghosts-free non-abelian gauge
theories. This method is expected to be applicable to non-abelian gauge
theories including supersymmetric ones.Comment: LaTeX, 12 pages, Corrected typo
Microscopic Treatment of Binary Interactions in the Non-Equilibrium Dynamics of Partially Bose-condensed Trapped Gases
In this paper we use microscopic arguments to derive a nonlinear
Schr\"{o}dinger equation for trapped Bose-condensed gases. This is made
possible by considering the equations of motion of various anomalous averages.
The resulting equation explicitly includes the effect of repeated binary
interactions (in particular ladders) between the atoms. Moreover, under the
conditions that dressing of the intermediate states of a collision can be
ignored, this equation is shown to reduce to the conventional Gross-Pitaevskii
equation in the pseudopotential limit. Extending the treatment, we show first
how the occupation of excited (bare particle) states affects the collisions,
and thus obtain the many-body T-matrix approximation in a trap. In addition, we
discuss how the bare particle many-body T-matrix gets dressed by mean fields
due to condensed and excited atoms. We conclude that the most commonly used
version of the Gross-Pitaevskii equation can only be put on a microscopic basis
for a restrictive range of conditions. For partial condensation, we need to
take account of interactions between condensed and excited atoms, which, in a
consistent formulation, should also be expressed in terms of the many-body
T-matrix. This can be achieved by considering fluctuations around the
condensate mean field beyond those included in the conventional finite
temperature mean field, i.e. Hartree-Fock-Bogoliubov (HFB), theory.Comment: Resolved some problems with printing of figure
Effects of growth rate, size, and light availability on tree survival across life stages: a demographic analysis accounting for missing values and small sample sizes.
The data set supporting the results of this article is available in the Dryad repository, http://dx.doi.org/10.5061/dryad.6f4qs. Moustakas, A. and Evans, M. R. (2015) Effects of
growth rate, size, and light availability on tree survival across life stages: a demographic analysis accounting for missing values.Plant survival is a key factor in forest dynamics and survival probabilities often vary across life stages. Studies specifically aimed at assessing tree survival are unusual and so data initially designed for other purposes often need to be used; such data are more likely to contain errors than data collected for this specific purpose
Trajectories for the Wave Function of the Universe from a Simple Detector Model
Inspired by Mott's (1929) analysis of particle tracks in a cloud chamber, we
consider a simple model for quantum cosmology which includes, in the total
Hamiltonian, model detectors registering whether or not the system, at any
stage in its entire history, passes through a series of regions in
configuration space. We thus derive a variety of well-defined formulas for the
probabilities for trajectories associated with the solutions to the
Wheeler-DeWitt equation. The probability distribution is peaked about classical
trajectories in configuration space. The ``measured'' wave functions still
satisfy the Wheeler-DeWitt equation, except for small corrections due to the
disturbance of the measuring device. With modified boundary conditions, the
measurement amplitudes essentially agree with an earlier result of Hartle
derived on rather different grounds. In the special case where the system is a
collection of harmonic oscillators, the interpretation of the results is aided
by the introduction of ``timeless'' coherent states -- eigenstates of the
Hamiltonian which are concentrated about entire classical trajectories.Comment: 37 pages, plain Tex. Second draft. Substantial revision
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