2,134 research outputs found
Lower bounds for nodal sets of eigenfunctions
We prove lower bounds for the Hausdorff measure of nodal sets of
eigenfunctions.Comment: To appear in Communications in Mathematical Physics; revised to
include two additional references and update bibliographic informatio
Some Curvature Problems in Semi-Riemannian Geometry
In this survey article we review several results on the curvature of
semi-Riemannian metrics which are motivated by the positive mass theorem. The
main themes are estimates of the Riemann tensor of an asymptotically flat
manifold and the construction of Lorentzian metrics which satisfy the dominant
energy condition.Comment: 25 pages, LaTeX, 4 figure
The Cauchy problems for Einstein metrics and parallel spinors
We show that in the analytic category, given a Riemannian metric on a
hypersurface and a symmetric tensor on , the metric
can be locally extended to a Riemannian Einstein metric on with second
fundamental form , provided that and satisfy the constraints on
imposed by the contracted Codazzi equations. We use this fact to study the
Cauchy problem for metrics with parallel spinors in the real analytic category
and give an affirmative answer to a question raised in B\"ar, Gauduchon,
Moroianu (2005). We also answer negatively the corresponding questions in the
smooth category.Comment: 28 pages; final versio
Initial Data for General Relativity with Toroidal Conformal Symmetry
A new class of time-symmetric solutions to the initial value constraints of
vacuum General Relativity is introduced. These data are globally regular,
asymptotically flat (with possibly several asymptotic ends) and in general have
no isometries, but a group of conformal isometries. After
decomposing the Lichnerowicz conformal factor in a double Fourier series on the
group orbits, the solutions are given in terms of a countable family of
uncoupled ODEs on the orbit space.Comment: REVTEX, 9 pages, ESI Preprint 12
Vacuum Spacetimes with Future Trapped Surfaces
In this article we show that one can construct initial data for the Einstein
equations which satisfy the vacuum constraints. This initial data is defined on
a manifold with topology with a regular center and is asymptotically
flat. Further, this initial data will contain an annular region which is
foliated by two-surfaces of topology . These two-surfaces are future
trapped in the language of Penrose. The Penrose singularity theorem guarantees
that the vacuum spacetime which evolves from this initial data is future null
incomplete.Comment: 19 page
Association of smoking and nicotine dependence with pre-diabetes in young and healthy adults.
INTRODUCTION: Several studies have shown an increased risk of type 2 diabetes among smokers. Therefore, the aim of this analysis was to assess the relationship between smoking, cumulative smoking exposure and nicotine dependence with pre-diabetes.
METHODS: We performed a cross-sectional analysis of healthy adults aged 25-41 in the Principality of Liechtenstein. Individuals with known diabetes, Body Mass Index (BMI) >35 kg/m² and prevalent cardiovascular disease were excluded. Smoking behaviour was assessed by self-report. Pre-diabetes was defined as glycosylated haemoglobin between 5.7% and 6.4%. Multivariable logistic regression models were done.
RESULTS: Of the 2142 participants (median age 37 years), 499 (23.3%) had pre-diabetes. There were 1,168 (55%) never smokers, 503 (23%) past smokers and 471 (22%) current smokers, with a prevalence of pre-diabetes of 21.2%, 20.9% and 31.2%, respectively (p <0.0001). In multivariable regression models, current smokers had an odds ratio (OR) of pre-diabetes of 1.82 (95% confidential interval (CI) 1.39; 2.38, p <0.0001). Individuals with a smoking exposure of <5, 5-10 and >10 pack-years had an OR (95% CI) for pre-diabetes of 1.34 (0.90; 2.00), 1.80 (1.07; 3.01) and 2.51 (1.80; 3.59) (p linear trend <0.0001) compared with never smokers. A Fagerström score of 2, 3-5 and >5 among current smokers was associated with an OR (95% CI) for pre-diabetes of 1.27 (0.89; 1.82), 2.15 (1.48; 3.13) and 3.35 (1.73; 6.48) (p linear trend <0.0001).
DISCUSSION: Smoking is strongly associated with pre-diabetes in young adults with a low burden of smoking exposure. Nicotine dependence could be a potential mechanism of this relationship
Does Young's equation hold on the nanoscale? A Monte Carlo test for the binary Lennard-Jones fluid
When a phase-separated binary () mixture is exposed to a wall, that
preferentially attracts one of the components, interfaces between A-rich and
B-rich domains in general meet the wall making a contact angle .
Young's equation describes this angle in terms of a balance between the
interfacial tension and the surface tensions ,
between, respectively, the - and -rich phases and the wall,
. By Monte Carlo simulations
of bridges, formed by one of the components in a binary Lennard-Jones liquid,
connecting the two walls of a nanoscopic slit pore, is estimated from
the inclination of the interfaces, as a function of the wall-fluid interaction
strength. The information on the surface tensions ,
are obtained independently from a new thermodynamic integration method, while
is found from the finite-size scaling analysis of the
concentration distribution function. We show that Young's equation describes
the contact angles of the actual nanoscale interfaces for this model rather
accurately and location of the (first order) wetting transition is estimated.Comment: 6 pages, 6 figure
Simulation of fluid-solid coexistence in finite volumes: A method to study the properties of wall-attached crystalline nuclei
The Asakura-Oosawa model for colloid-polymer mixtures is studied by Monte
Carlo simulations at densities inside the two-phase coexistence region of fluid
and solid. Choosing a geometry where the system is confined between two flat
walls, and a wall-colloid potential that leads to incomplete wetting of the
crystal at the wall, conditions can be created where a single nanoscopic
wall-attached crystalline cluster coexists with fluid in the remainder of the
simulation box. Following related ideas that have been useful to study
heterogeneous nucleation of liquid droplets at the vapor-liquid coexistence, we
estimate the contact angles from observations of the crystalline clusters in
thermal equilibrium. We find fair agreement with a prediction based on Young's
equation, using estimates of interface and wall tension from the study of flat
surfaces. It is shown that the pressure versus density curve of the finite
system exhibits a loop, but the pressure maximum signifies the "droplet
evaporation-condensation" transition and thus has nothing in common with a van
der Waals-like loop. Preparing systems where the packing fraction is deep
inside the two-phase coexistence region, the system spontaneously forms a "slab
state", with two wall-attached crystalline domains separated by (flat)
interfaces from liquid in full equilibrium with the crystal in between;
analysis of such states allows a precise estimation of the bulk equilibrium
properties at phase coexistence
On the topology and area of higher dimensional black holes
Over the past decade there has been an increasing interest in the study of
black holes, and related objects, in higher (and lower) dimensions, motivated
to a large extent by developments in string theory. The aim of the present
paper is to obtain higher dimensional analogues of some well known results for
black holes in 3+1 dimensions. More precisely, we obtain extensions to higher
dimensions of Hawking's black hole topology theorem for asymptotically flat
() black hole spacetimes, and Gibbons' and Woolgar's genus
dependent, lower entropy bound for topological black holes in asymptotically
locally anti-de Sitter () spacetimes. In higher dimensions the genus
is replaced by the so-called -constant, or Yamabe invariant, which is a
fundamental topological invariant of smooth compact manifolds.Comment: 15 pages, Latex2e; typos corrected, a convention clarified, resulting
in the simplification of certain formulas, other improvement
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