67,650 research outputs found
Finite size corrections to the blackbody radiation laws
We investigate the radiation of a blackbody in a cavity of finite size. For a
given geometry, we use semiclassical techniques to obtain explicit expressions
of the modified Planck's and Stefan-Boltzmann's blackbody radiation laws as a
function of the size and shape of the cavity. We determine the range of
parameters (temperature, size and shape of the cavity) for which these effects
are accessible to experimental verification. Finally we discuss potential
applications of our findings in the physics of the cosmic microwave background
and sonoluminescence.Comment: 5 pages, 1 figure, journal versio
No solvable lambda-value term left behind
In the lambda calculus a term is solvable iff it is operationally relevant.
Solvable terms are a superset of the terms that convert to a final result
called normal form. Unsolvable terms are operationally irrelevant and can be
equated without loss of consistency. There is a definition of solvability for
the lambda-value calculus, called v-solvability, but it is not synonymous with
operational relevance, some lambda-value normal forms are unsolvable, and
unsolvables cannot be consistently equated. We provide a definition of
solvability for the lambda-value calculus that does capture operational
relevance and such that a consistent proof-theory can be constructed where
unsolvables are equated attending to the number of arguments they take (their
"order" in the jargon). The intuition is that in lambda-value the different
sequentialisations of a computation can be distinguished operationally. We
prove a version of the Genericity Lemma stating that unsolvable terms are
generic and can be replaced by arbitrary terms of equal or greater order.Comment: 43 page
The June 2012 transit of Venus. Framework for interpretation of observations
Ground based observers have on 5/6th June 2012 the last opportunity of the
century to watch the passage of Venus across the solar disk from Earth. Venus
transits have traditionally provided unique insight into the Venus atmosphere
through the refraction halo that appears at the planet outer terminator near
ingress/egress. Much more recently, Venus transits have attracted renewed
interest because the technique of transits is being successfully applied to the
characterization of extrasolar planet atmospheres. The current work
investigates theoretically the interaction of sunlight and the Venus atmosphere
through the full range of transit phases, as observed from Earth and from a
remote distance. Our model predictions quantify the relevant atmospheric
phenomena, thereby assisting the observers of the event in the interpretation
of measurements and the extrapolation to the exoplanet case. Our approach
relies on the numerical integration of the radiative transfer equation, and
includes refraction, multiple scattering, atmospheric extinction and solar limb
darkening, as well as an up to date description of the Venus atmosphere. We
produce synthetic images of the planet terminator during ingress/egress that
demonstrate the evolving shape, brightness and chromaticity of the halo.
Guidelines are offered for the investigation of the planet upper haze from
vertically-unresolved photometric measurements. In this respect, the comparison
with measurements from the 2004 transit appears encouraging. We also show
integrated lightcurves of the Venus/Sun system at various phases during transit
and calculate the respective Venus-Sun integrated transmission spectra. The
comparison of the model predictions to those for a Venus-like planet free of
haze and clouds (and therefore a closer terrestrial analogue) complements the
discussion and sets the conclusions into a broader perspective.Comment: 14 pages; 14 figures; Submitted on 02/06/2012; A&A, accepted for
publication on 30/08/201
From Perturbation Theory to Confinement: How the String Tension is built up
We study the spatial volume dependence of electric flux energies for SU(2)
Yang-Mills fields on the torus with twisted boundary conditions. The results
approach smoothly the rotational invariant Confinement regime. The would-be
string tension is very close to the infinite volume result already for volumes
of . We speculate on the consequences of our result for
the Confinement mechanism.Comment: 6p, ps-file (uuencoded). Contribution to Lattice'93 Conference
(Dallas, 1993). Preprint INLO-PUB 18/93, FTUAM-93/4
Interplay between optical, viscous and elastic forces on an optically trapped Brownian particle immersed in a viscoelastic fluid
We provide a detailed study of the interplay between the different
interactions which appear in the Brownian motion of a micronsized sphere
immersed in a viscoelastic fluid measured with optical trapping interferometry.
To explore a wide range of viscous, elastic and optical forces, we analyze two
different viscoelastic solutions at various concentrations, which provide a
dynamic polymeric structure surrounding the Brownian sphere. Our experiments
show that, depending of the fluid, optical forces, even if small, slightly
modify the complex modulus at low frequencies. Based on our findings, we
propose an alternative methodology to calibrate this kind of experimental
set-up when non-Newtonian fluids are used. Understanding the influence of the
optical potential is essential for a correct interpretation of the mechanical
properties obtained by optically-trapped probe-based studies of biomaterials
and living matter.Comment: Accepted for publication in Applied Physics Letter
How soft is a single protein?: Stress-strain curve of antibody pentamers with 5 pN and 50 pm resolutions
Understanding the mechanical functionalities of complex biological systems requires the measurement of the mechanical compliance of their smallest components. Here, we develop a force microscopy method to quantify the softness of a single antibody pentamer by measuring the stressâstrain curve with force and deformation resolutions, respectively, of 5 pN and 50 pm. The curve shows three distinctive regions. For ultrasmall compressive forces (5â75 pN), the protein's central region shows that the strain and stress are proportional (elastic regime). This region has an average Young's modulus of 2.5 MPa. For forces between 80 and 220 pN, the stress is roughly proportional to the strain with a Young's modulus of 9 MPa. Higher forces lead to irreversible deformations (plastic regime). Full elastic recovery could reach deformations amounting to 40% of the protein height. The existence of two different elastic regions is explained in terms of the structure of the antibody central region. The stressâstrain curve explains the capability of the antibody to sustain multiple collisions without any loss of biological functionality.This work was supported by grants from MINECO (Spain), CSD2010-00024 and the European Research Council ERC-AdG-340177 (3DNanoMech)Peer reviewe
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