1,931 research outputs found
Casimir Force between a Dielectric Sphere and a Wall: A Model for Amplification of Vacuum Fluctuations
The interaction between a polarizable particle and a reflecting wall is
examined. A macroscopic approach is adopted in which the averaged force is
computed from the Maxwell stress tensor. The particular case of a perfectly
reflecting wall and a sphere with a dielectric function given by the Drude
model is examined in detail. It is found that the force can be expressed as the
sum of a monotonically decaying function of position and of an oscillatory
piece. At large separations, the oscillatory piece is the dominant
contribution, and is much larger than the Casimir-Polder interaction that
arises in the limit that the sphere is a perfect conductor. It is argued that
this enhancement of the force can be interpreted in terms of the frequency
spectrum of vacuum fluctuations. In the limit of a perfectly conducting sphere,
there are cancellations between different parts of the spectrum which no longer
occur as completely in the case of a sphere with frequency dependent
polarizability. Estimates of the magnitude of the oscillatory component of the
force suggest that it may be large enough to be observable.Comment: 18pp, LaTex, 7 figures, uses epsf. Several minor errors corrected,
additional comments added in the final two sections, and references update
Who I Am: The Meaning of Early Adolescentsâ Most Valued Activities and Relationships, and Implications for Self-Concept Research
Self-concept research in early adolescence typically measures young peopleâs self-perceptions of competence in specific, adult-defined domains. However, studies have rarely explored young peopleâs own views of valued self-concept factors and their meanings. For two major self domains, the active and the social self, this mixed-methods study identified factors valued most by 526 young people from socioeconomically diverse backgrounds in Ireland (10-12 years), and explored the meanings associated with these in a stratified subsample (n = 99). Findings indicate that self-concept scales for early adolescence omit active and social self factors and meanings valued by young people, raising questions about content validity of scales in these domains. Findings also suggest scales may under-represent girlsâ active and social selves; focus too much on some school-based competencies; and, in omitting intrinsically salient self domains and meanings, may focus more on contingent (extrinsic) rather than true (intrinsic) self-esteem
A2A: 21,000 bulge stars from the ARGOS survey with stellar parameters on the APOGEE scale
We use the data-driven method, The Cannon, to bring 21,000 stars from the
ARGOS bulge survey, including 10,000 red clump stars, onto the parameter and
abundance scales of the cross-Galactic survey, APOGEE, obtaining rms precisions
of 0.10 dex, 0.07 dex, 74 K, and 0.18 dex for [Fe/H], [Mg/Fe], Teff, and
log(g), respectively. The re-calibrated ARGOS survey - which we refer to as the
A2A survey - is combined with the APOGEE survey to investigate the abundance
structure of the Galactic bulge. We find X-shaped [Fe/H] and [Mg/Fe]
distributions in the bulge that are more pinched than the bulge density, a
signature of its disk origin. The mean abundance along the major axis of the
bar varies such that the stars are more [Fe/H]-poor and [Mg/Fe]-rich near the
Galactic center than in the long bar/outer bulge region. The vertical [Fe/H]
and [Mg/Fe] gradients vary between the inner bulge and long bar with the inner
bulge showing a flattening near the plane that is absent in the long bar. The
[Fe/H]-[Mg/Fe] distribution shows two main maxima, an ``[Fe/H]-poor [Mg/Fe]-
rich'' maximum and an ``[Fe/H]-rich [Mg/Fe]-poor'' maximum, that vary in
strength with position in the bulge. In particular, the outer long bar close to
the Galactic plane is dominated by super-solar [Fe/H], [Mg/Fe]-normal stars.
Stars composing the [Fe/H]-rich maximum show little kinematic dependence on
[Fe/H], but for lower [Fe/H] the rotation and dispersion of the bulge increase
slowly. Stars with [Fe/H]<-1 dex have a very different kinematic structure than
stars with higher [Fe/H]. Comparing with recent models for the Galactic
boxy-peanut bulge, the abundance gradients and distribution, and the relation
between [Fe/H] and kinematics suggest that the stars comprising each maximum
have separate disk origins with the ``[Fe/H]-poor [Mg/Fe]-rich'' stars
originating from a thicker disk than the ``[Fe/H]-rich [Mg/Fe]-poor'' stars.Comment: 26 pages, 29 figures, revised version as submitted to A&A following
referee repor
Using atomic interference to probe atom-surface interaction
We show that atomic interference in the reflection from two suitably
polarized evanescent waves is sensitive to retardation effects in the
atom-surface interaction for specific experimental parameters. We study the
limit of short and long atomic de Broglie wavelength. The former case is
analyzed in the semiclassical approximation (Landau-Zener model). The latter
represents a quantum regime and is analyzed by solving numerically the
associated coupled Schroedinger equations. We consider a specific experimental
scheme and show the results for rubidium (short wavelength) and the much
lighter meta-stable helium atom (long wavelength). The merits of each case are
then discussed.Comment: 11 pages, including 6 figures, submitted to Phys. Rev. A, RevTeX
sourc
A statistical network analysis of the HIV/AIDS epidemics in Cuba
The Cuban contact-tracing detection system set up in 1986 allowed the
reconstruction and analysis of the sexual network underlying the epidemic
(5,389 vertices and 4,073 edges, giant component of 2,386 nodes and 3,168
edges), shedding light onto the spread of HIV and the role of contact-tracing.
Clustering based on modularity optimization provides a better visualization and
understanding of the network, in combination with the study of covariates. The
graph has a globally low but heterogeneous density, with clusters of high
intraconnectivity but low interconnectivity. Though descriptive, our results
pave the way for incorporating structure when studying stochastic SIR epidemics
spreading on social networks
Theory of decoherence in a matter wave Talbot-Lau interferometer
We present a theoretical framework to describe the effects of decoherence on
matter waves in Talbot-Lau interferometry. Using a Wigner description of the
stationary beam the loss of interference contrast can be calculated in closed
form. The formulation includes both the decohering coupling to the environment
and the coherent interaction with the grating walls. It facilitates the
quantitative distinction of genuine quantum interference from the expectations
of classical mechanics. We provide realistic microscopic descriptions of the
experimentally relevant interactions in terms of the bulk properties of the
particles and show that the treatment is equivalent to solving the
corresponding master equation in paraxial approximation.Comment: 20 pages, 4 figures (minor corrections; now in two-column format
Myers' type theorems and some related oscillation results
In this paper we study the behavior of solutions of a second order
differential equation. The existence of a zero and its localization allow us to
get some compactness results. In particular we obtain a Myers' type theorem
even in the presence of an amount of negative curvature. The technique we use
also applies to the study of spectral properties of Schroedinger operators on
complete manifolds.Comment: 16 page
Direct Analysis of Aerosolized Chemical Warfare Simulants Captured on a Modified Glass-Based Substrate by âPaper-Sprayâ Ionization
Paper spray ionization mass spectrometry offers a rapid alternative platform requiring no sample preparation. Aerosolized chemical warfare agent (CWA) simulants trimethyl phosphate, dimethyl methylphosphonate, and diisopropyl methylphosphonate were captured by passing air through a glass fiber filter disk within a disposable paper spray cartridge. CWA simulants were aerosolized at varying concentrations using an in-house built aerosol chamber. A custom 3D-printed holder was designed and built to facilitate the aerosol capture onto the paper spray cartridges. The air flow through each of the collection devices was maintained equally to ensure the same volume of air sampled across methods. Each approach yielded linear calibration curves with R2 values between 0.98â0.99 for each compound and similar limits of detection in terms of disbursed aerosol concentration. While the glass fiber filter disk has a higher capture efficiency (â40%), the paper spray method produces analogous results even with a lower capture efficiency (â1%). Improvements were made to include glass fiber filters as the substrate within the paper spray cartridge consumable. Glass fiber filters were then treated with ammonium sulfate to decrease chemical interaction with the simulants. This allowed for improved direct aerosol capture efficiency (>40%). Ultimately, the limits of detection were reduced to levels comparable to current worker population limits of 1 Ă 10â6 mg/m3
Mothers of Soldiers in Wartime: A National News Narrative
National news media represent mothers of US combat soldiers in the Iraq War as archetypal good mothers, that is, mothers who continue their maternal work even after their children are deployed. However, not all mothers are depicted as the archetypal patriotic mother, i.e., a good mother who is also stoic and silent about the war and her child\u27s role in it. Mothers of soldiers are portrayed as good mothers who sometimes also voice their attitudes about the war effort. The maternal attitudes ranged from complete support for the war to opposition to the war but support for the soldiers. The findings suggest a picture of wartime motherhood that is more nuanced than the historical image of the patriotic mother suggests
Methods of asymptotic analysis in cavity quantum electrodynamics
The energy-level shift of a ground-state atom in front of a nondispersive dielectric half-space is calculated by quantizing the electric field by means of a normal-mode expansion and applying second-order perturbation theory to the electric-dipole Hamiltonian muE. It is shown that the contributions to this shift coming from traveling and from evanescent waves can be combined into a single expression which lends itself readily to asymptotic analysis for large atom-surface separations, while in the opposite asymptotic regime when the atom is close to the surface the combined expression is less convenient. Employing a Greens-function formalism instead of the normal-mode expansion leads directly to the combined formula, and in that case it is advantageous to be able to apply the same transformation backwards and split the energy shift into a sum of distinct contributions corresponding to different physical processes. The analysis serves to shed light on common sources of error in the literature and paves the way for the study of more complicated models in cavity quantum electrodynamics
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