32,903 research outputs found
Bending Frustration of Lipid-Water Mesophases Based on Cubic Minimal Surfaces
Inverse bicontinuous cubic phases are ubiquitous in lipid-water mixtures and
consist of a lipid bilayer forming a cubic minimal surface, thereby dividing
space into two cubic networks of water channels. For small hydrocarbon chain
lengths, the monolayers can be modeled as parallel surfaces to a minimal
midsurface. The bending energy of the cubic phases is determined by the
distribution of Gaussian curvature over the minimal midsurfaces which we
calculate for seven different structures (G, D, P, I-WP, C(P), S and F-RD). We
show that the free-energy densities of the structures G, D and P are
considerably lower than those of the other investigated structures due to their
narrow distribution of Gaussian curvature. The Bonnet transformation between G,
D, and P implies that these phases coexist along a triple line, which also
includes an excess water phase. Our model includes thermal membrane
undulations. Our qualitative predictions remain unchanged when higher order
terms in the curvature energy are included. Calculated phase diagrams agree
well with the experimental results for 2:1 lauric acid/dilauroyl
phosphatidylcholine and water.Comment: Revtex, 23 pages with 9 postscript figures included, to appear in
Langmui
The Effect of Unions on Productivity in the Public Sector: The Case of Municipal Libraries
[Excerpt] This paper represents our initial efforts at analyzing the effects of unions on productivity in the public sector. We first sketch an analytical framework that can be used to estimate these effects, focusing for expository purposes on municipal public libraries. We initially focus on libraries because considerable effort has been devoted to conceptualizing productivity measures for them and because of the availability of data to implement the framework. After discussing the analytical framework, we present preliminary estimtes of the effects of unions on productivity in public libraries based upon analyses of data from 71 municipal libraries in Massachusetts. We conclude by indicating how these analyses will be extended and the direction that we hope our future research will take
A Realistic Particle Physics Dark Energy Model
We present a realistic dark energy model derived from particle physics. Our
model has essentially no free parameters and has an equivalent fit to the
observational data (CMB, SN1a and LSS) as LCDM and a better fit than the best
effective model. With the lack of a clear determination of the
cosmological parameters theoretical considerations should be taken seriously to
distinguish between dark energy models.Comment: 5 pages, RevTex, 6 figure
Bayesian methods of astronomical source extraction
We present two new source extraction methods, based on Bayesian model
selection and using the Bayesian Information Criterion (BIC). The first is a
source detection filter, able to simultaneously detect point sources and
estimate the image background. The second is an advanced photometry technique,
which measures the flux, position (to sub-pixel accuracy), local background and
point spread function. We apply the source detection filter to simulated
Herschel-SPIRE data and show the filter's ability to both detect point sources
and also simultaneously estimate the image background. We use the photometry
method to analyse a simple simulated image containing a source of unknown flux,
position and point spread function; we not only accurately measure these
parameters, but also determine their uncertainties (using Markov-Chain Monte
Carlo sampling). The method also characterises the nature of the source
(distinguishing between a point source and extended source). We demonstrate the
effect of including additional prior knowledge. Prior knowledge of the point
spread function increase the precision of the flux measurement, while prior
knowledge of the background has onlya small impact. In the presence of higher
noise levels, we show that prior positional knowledge (such as might arise from
a strong detection in another waveband) allows us to accurately measure the
source flux even when the source is too faint to be detected directly. These
methods are incorporated in SUSSEXtractor, the source extraction pipeline for
the forthcoming Akari FIS far-infrared all-sky survey. They are also
implemented in a stand-alone, beta-version public tool that can be obtained at
http://astronomy.sussex.ac.uk/rss23/sourceMiner\_v0.1.2.0.tar.gzComment: Accepted for publication by ApJ (this version compiled used
emulateapj.cls
Action for IIB Supergravity in 10 dimensions
We review the construction of a manifestly covariant, supersymmetric and
SL(2R) invariant action for IIB supergravity in D=10.Comment: 9 pages, LaTeX, Talk given at "Quantum Aspects of Gauge Theories,
Supersymmetry and Unification", Greece, September 199
Domain walls and chaos in the disordered SOS model
Domain walls, optimal droplets and disorder chaos at zero temperature are
studied numerically for the solid-on-solid model on a random substrate. It is
shown that the ensemble of random curves represented by the domain walls obeys
Schramm's left passage formula with kappa=4 whereas their fractal dimension is
d_s=1.25, and therefore is NOT described by "Stochastic-Loewner-Evolution"
(SLE). Optimal droplets with a lateral size between L and 2L have the same
fractal dimension as domain walls but an energy that saturates at a value of
order O(1) for L->infinity such that arbitrarily large excitations exist which
cost only a small amount of energy. Finally it is demonstrated that the
sensitivity of the ground state to small changes of order delta in the disorder
is subtle: beyond a cross-over length scale L_delta ~ 1/delta the correlations
of the perturbed ground state with the unperturbed ground state, rescaled by
the roughness, are suppressed and approach zero logarithmically.Comment: 23 pages, 11 figure
The Effect of Unions on Productivity in the Public Sector: The Case of Libraries
This paper presents an analytical framework that can be used to analyze the effects of unions on productivity in the public sector. Our initial focus is on public libraries because considerable effort has been devoted to conceptualizing library productivity measures and because of the availability of data to implement the framework. Preliminary estimates are presented based upon data from 71 municipal libraries in Massachusetts. We conclude by indicating the direction that our future research on the subject will take.
Topological aspects in non-Abelian gauge theory
We discuss the BRST cohomology and exhibit a connection between the Hodge
decomposition theorem and the topological properties of a two dimensional free
non-Abelian gauge theory having no interaction with matter fields. The
topological nature of this theory is encoded in the vanishing of the Laplacian
operator when equations of motion are exploited. We obtain two sets of
topological invariants with respect to BRST and co-BRST charges on the two
dimensional manifold and show that the Lagrangian density of the theory can be
expressed as the sum of terms that are BRST- and co-BRST invariants.Comment: (1+11) pages, LaTeX, no figure
Scale dependence of cosmological backreaction
Due to the non-commutation of spatial averaging and temporal evolution,
inhomogeneities and anisotropies (cosmic structures) influence the evolution of
the averaged Universe via the cosmological backreaction mechanism. We study the
backreaction effect as a function of averaging scale in a perturbative approach
up to higher orders. We calculate the hierarchy of the critical scales, at
which 10% effects show up from averaging at different orders. The dominant
contribution comes from the averaged spatial curvature, observable up to scales
of 200 Mpc. The cosmic variance of the local Hubble rate is 10% (5%) for
spherical regions of radius 40 (60) Mpc. We compare our result to the one from
Newtonian cosmology and Hubble Space Telescope Key Project data.Comment: 6 pages, 2 figures; v3: substantial modifications, new figure
The intravenous glucose tolerance test and the behaviour of the free fatty acids in the detection of latent diabetes mellitus
- …