3,693 research outputs found
Relativistic dynamical polarizability of hydrogen-like atoms
Using the operator representation of the Dirac Coulomb Green function the analytical method in perturbation theory is employed in obtaining solutions of the Dirac equation for a hydrogen-like atom in a time-dependent electric field. The relativistic dynamical polarizability of hydrogen-like atoms is calculated and analysed
Relativistic dynamical polarizability of hydrogen-like atoms
Using the operator representation of the Dirac Coulomb Green function the
analytical method in perturbation theory is employed in obtaining solutions of
the Dirac equation for a hydrogen-like atom in a time-dependent electric field.
The relativistic dynamical polarizability of hydrogen-like atoms is calculated
and analysed.Comment: 15 pages, 3 figures (not included, but hard copies are available upon
request
Retrieval of material properties of monolayer transition-metal dichalcogenides from magnetoexciton energy spectra
Reduced exciton mass, polarizability, and dielectric constant of the
surrounding medium are essential properties for semiconduction materials, and
they can be extracted recently from the magnetoexciton energies. However, the
acceptable accuracy of the previously suggested method requires very high
magnetic intensity. Therefore, in the present paper, we propose an alternative
method of extracting these material properties from recently available
experimental magnetoexciton s-state energies in monolayer transition-metal
dichalcogenides (TMDCs). The method is based on the high sensitivity of exciton
energies to the material parameters in the Rytova-Keldysh model. It allows us
to vary the considered material parameters to get the best fit of the
theoretical calculation to the experimental exciton energies for the ,
, and states. This procedure gives values of the exciton reduced mass
and 2D polarizability. Then, the experimental magnetoexciton spectra compared
to the theoretical calculation gives also the average dielectric constant.
Concrete applications are presented only for monolayers WSe and WS from
the recently available experimental data. However, the presented approach is
universal and can be applied to other monolayer TMDCs. The mentioned fitting
procedure requires a fast and effective method of solving the Schr\"{o}dinger
of an exciton in monolayer TMDCs with a magnetic field. Therefore, we also
develop such a method in this study for highly accurate magnetoexciton
energies.Comment: 8 pages, 4 figures, 4 table
Precision constraints on radiative neutrino decay with CMB spectral distortion
We investigate the radiative decay of the cosmic neutrino background, and its
impact on the spectrum of the cosmic microwave background (CMB) that is known
to be a nearly perfect black body. We derive exact formulae for the decay of a
heavier neutrino into a lighter neutrino and a photon, , and of absorption as its inverse, , by
accounting for the precise form of the neutrino momentum distribution. Our
calculations show that if the neutrinos are heavier than eV,
the exact formulae give results that differ by 50%, compared with
approximate ones where neutrinos are assumed to be at rest. We also find that
spectral distortion due to absorption is more important for heavy neutrino
masses (by a factor of 10 going from a neutrino mass of 0.01 eV to 0.1
eV). By analyzing the CMB spectral data measured with COBE-FIRAS, we obtain
lower limits on the neutrino lifetime of s
(95% C.L.) for the smaller mass splitting and s for the larger mass splitting. These represent up to one order of
magnitude improvement over previous CMB constraints. With future CMB
experiments such as PIXIE, these limits will improve by roughly 4 orders of
magnitude. This translates to a projected upper limit on the neutrino magnetic
moment (for certain neutrino masses and decay modes) of , where is the Bohr magneton. Such constraints would
make future precision CMB measurements competitive with lab-based constraints
on neutrino magnetic moments.Comment: 14 pages, 9 figures. v2: Added a number of references and
clarifications. Matches version published in PR
Virtual and Soft Pair Corrections to Polarized Muon Decay Spectrum
Radiative corrections to the muon decay spectrum due to soft and virtual
electron--positron pairs are calculated.Comment: 10pp, 2 PS figs, details of calculations are adde
Opinion Dynamics With Cross-Coupling Topics: Modeling and Analysis
To model the cross couplings of multiple topics, we develop a set of rules for opinion updates of a group of agents. The rules are used to design or assign values to the elements of weighting matrices. The cooperative and anticooperative couplings are modeled in both the inverse-proportional and proportional structures. The behaviors of opinion dynamics are analyzed using a nullspace property of the state-dependent matrix-weighted Laplacian matrices and a Lyapunov candidate. Various consensus properties of the state-dependent matrix-weighted Laplacian matrices are predicted according to the interagent network topology and interdependent topical coupling topologies
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The impact of environmental and climatic variation on the spatiotemporal trends of hospitalized pediatric diarrhea in Ho Chi Minh City, Vietnam.
It is predicted that the integration of climate-based early warning systems into existing action plans will facilitate the timely provision of interventions to diarrheal disease epidemics in resource-poor settings. Diarrhea remains a considerable public health problem in Ho Chi Minh City (HCMC), Vietnam and we aimed to quantify variation in the impact of environmental conditions on diarrheal disease risk across the city. Using all inpatient diarrheal admissions data from three large hospitals within HCMC, we developed a mixed effects regression model to differentiate district-level variation in risk due to environmental conditions from the overarching seasonality of diarrheal disease hospitalization in HCMC. We identified considerable spatial heterogeneity in the risk of all-cause diarrhea across districts of HCMC with low elevation and differential responses to flooding, air temperature, and humidity driving further spatial heterogeneity in diarrheal disease risk. The incorporation of these results into predictive forecasting algorithms will provide a powerful resource to aid diarrheal disease prevention and control practices in HCMC and other similar settings
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