184,551 research outputs found
Approximate Theoretical Calculation of Continuum Opacities
An approxhnate procedure is described for the theoretical calculation of the spectral absorption
coefficient produced by bound-free and free-free transitions in plasmas containing polyelectronic
atoms and ions. Our method of calculation is based on the assumption that only two ionized species make important contributions to the opacity and that these two ionic
constituents are present in equal concentrations. The approximate formulas are shown to yield results that are in good accord with estimates based on detailed numerical computations for nitrogen
A Classification and Analysis of Higgs-flavor Models
A classification is given of Higgs-flavor models. In these models, there are
several Higgs doublets in an irreducible multiplet R_{Phi} of a non-abelian
symmetry G_{Phi}, under which the quarks and leptons do not transform (thus
giving minimal flavor-changing for the fermions). It is found that different
G_{Phi} and R_{Phi} lead to very distinctive spectra of the extra Higgs
doublets, including different numbers of "sequential Higgs" and of "inert
Higgs" that could play the role of dark matter, different mass relations, and
different patterns of SU(2)_L-breaking splittings within the Higgs doublets.Comment: 35 page
Similarity parameters for radiative energy transfer in isothermal and non-isothermal gas mixtures
The similarity groups for multicomponent, reacting gas mixtures with radiative
energy transport are derived (Section I). The resulting relations are used to consider
the feasibility if scaling for flow processes with radiative energy transport under
highly simplified conditions (Sections 2 and 3). Next the scaling parameters are
derived for radiant energy emission from isobaric and isothermal gases for
arbitrary opacities and various spectral line and molecular band models (Section 4).
Scaling parameters for radiant energy emission from isobaric but non-isothermal
systems are discussed for arbitrary opacities and various spectral line and molecular
band models under the restrictions imposed on the allowed temperature profiles for
dispersion and Doppler lines by the Eddington-Barbier approximation (Section 5).
Finally, we consider the radiative scaling properties for representative
temperature profiles for both collision-broadened and Doppler-broadened line
profiles on the basis if exact numerical calculations that we have performed for a
rotational spectral line belonging to a molecular vibration-rotation band. (Section
6). It appears that simple scaling rules generally constitute a fair approximation
for dispersion lines in non-isothermal systems but that corresponding relations
apply to lines with Doppler contour only in the transparent gas regime
Increasing the Capacity of Primary Care Through Enabling Technology.
Primary care is the foundation of effective and high-quality health care. The role of primary care clinicians has expanded to encompass coordination of care across multiple providers and management of more patients with complex conditions. Enabling technology has the potential to expand the capacity for primary care clinicians to provide integrated, accessible care that channels expertise to the patient and brings specialty consultations into the primary care clinic. Furthermore, technology offers opportunities to engage patients in advancing their health through improved communication and enhanced self-management of chronic conditions. This paper describes enabling technologies in four domains (the body, the home, the community, and the primary care clinic) that can support the critical role primary care clinicians play in the health care system. It also identifies challenges to incorporating these technologies into primary care clinics, care processes, and workflow
Nonlinear Evolution of the Magnetohydrodynamic Rayleigh-Taylor Instability
We study the nonlinear evolution of the magnetic Rayleigh-Taylor instability
using three-dimensional MHD simulations. We consider the idealized case of two
inviscid, perfectly conducting fluids of constant density separated by a
contact discontinuity perpendicular to the effective gravity g, with a uniform
magnetic field B parallel to the interface. Modes parallel to the field with
wavelengths smaller than l_c = [B B/(d_h - d_l) g] are suppressed (where d_h
and d_l are the densities of the heavy and light fluids respectively), whereas
modes perpendicular to B are unaffected. We study strong fields with l_c
varying between 0.01 and 0.36 of the horizontal extent of the computational
domain. Even a weak field produces tension forces on small scales that are
significant enough to reduce shear (as measured by the distribution of the
amplitude of vorticity), which in turn reduces the mixing between fluids, and
increases the rate at which bubbles and finger are displaced from the interface
compared to the purely hydrodynamic case. For strong fields, the highly
anisotropic nature of unstable modes produces ropes and filaments. However, at
late time flow along field lines produces large scale bubbles. The kinetic and
magnetic energies transverse to gravity remain in rough equipartition and
increase as t^4 at early times. The growth deviates from this form once the
magnetic energy in the vertical field becomes larger than the energy in the
initial field. We comment on the implications of our results to Z-pinch
experiments, and a variety of astrophysical systems.Comment: 25 pages, accepted by Physics of Fluids, online version of journal
has high resolution figure
Constraints on split-UED from Electroweak Precision Tests
We present strongly improved electroweak precision constraints on the
split-UED model. We find that the dominating effect arises from contributions
to the muon decay rate by the exchange of even-numbered W-boson Kaluza-Klein
modes at tree-level, which so far have not been discussed in the context of UED
models. The constraints on the split-UED parameter space are translated into
bounds on the mass difference of the first Kaluza-Klein mode of fermions and
the lightest Kaluza-Klein mode, which will be tested is the LHC.Comment: 4 pages, 2 figure
Manifestly N=3 supersymmetric Euler-Heisenberg action in light-cone superspace
We find a manifestly N=3 supersymmetric generalization of the
four-dimensional Euler-Heisenberg (four-derivative, or F^4) part of the
Born-Infeld action in light-cone gauge, by using N=3 light-cone superspace.Comment: 9 pages, LaTeX, no figures, macros include
On Modeling and Estimation for the Relative Risk and Risk Difference
A common problem in formulating models for the relative risk and risk
difference is the variation dependence between these parameters and the
baseline risk, which is a nuisance model. We address this problem by proposing
the conditional log odds-product as a preferred nuisance model. This novel
nuisance model facilitates maximum-likelihood estimation, but also permits
doubly-robust estimation for the parameters of interest. Our approach is
illustrated via simulations and a data analysis.Comment: To appear in Journal of the American Statistical Association: Theory
and Method
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