6,752 research outputs found
Excitonic effects on coherent phonon dynamics in single wall carbon nanotubes
We discuss how excitons can affect the generation of coherent radial
breathing modes in ultrafast spectroscopy of single wall carbon nanotubes.
Photoexcited excitons can be localized spatially and give rise to a spatially
distributed driving force in real space which involves many phonon wavevectors
of the exciton-phonon interaction. The equation of motion for the coherent
phonons is modeled phenomenologically by the Klein-Gordon equation, which we
solve for the oscillation amplitudes as a function of space and time. By
averaging the calculated amplitudes per nanotube length, we obtain
time-dependent coherent phonon amplitudes that resemble the homogeneous
oscillations that are observed in some pump-probe experiments. We interpret
this result to mean that the experiments are only able to see a spatial average
of coherent phonon oscillations over the wavelength of light in carbon
nanotubes and the microscopic details are averaged out. Our interpretation is
justified by calculating the time-dependent absorption spectra resulting from
the macroscopic atomic displacements induced by the coherent phonon
oscillations. The calculated coherent phonon spectra including excitonic
effects show the experimentally observed symmetric peaks at the nanotube
transition energies in contrast to the asymmetric peaks that would be obtained
if excitonic effects were not included.Comment: submitted to Phys. Rev. B on 7 May 2013, revised on 17 July and 13
August 2013, published 30 August 201
Tooth loss and obstructive sleep apnea signs and symptoms in the US population
The aim of this study is to investigate the relationship between tooth loss and signs and symptoms of obstructive sleep apnea (OSA) in a representative sample of the general US population
Continuous, 8-Paddock, and 16-Paddock Grazing at Two Stocking Rates With Different Breed Types
Last updated: 6/12/200
Role of Allostatic Load in Sociodemographic Patterns of Pain Prevalence in the U.S. Population
Persistent stressors associated with sociodemographic disadvantage exert a physiologic toll, labeled âallostatis loadâ, that contributes to disparities in some health conditions. We investigated the contribution of allostatic load to pain prevalence in US adults. Interviews with 14,184 adults in the 1999â2004 National Health and Nutrition Examination Survey asked about severe headache, pain that lasted >24 hours, and widespread pain. Ten biomarkers of allostatic load were quantified from blood (glycated hemoglobin), serum (C-reactive protein, homocysteine, cholesterol, triglycerides), urine (creatinine, albumin) and physical measurements (body mass index, systolic and diastolic blood pressure). Log-binomial regression models estimated prevalence ratios (PR) and 95% confidence intervals (95%CIs). Prevalence ranged from 3.4% for widespread pain to 26.9% for pain >24 hours. After adjustment for demographic characteristics, low income was associated with greater prevalence of pain >24 hours (PR=1.65, 95%CI=1.49, 1.83), severe headache (PR=2.05, 95%CI=1.68, 2.50) and widespread pain (PR=3.67, 95%CI=2.56, 5.27). Racial/ethnic minorities had lower prevalence of all three pain conditions than non-Hispanic Whites. While greater allostatic load was associated with elevated prevalence of pain, allostatic load did not meaningfully attenuate prevalence ratios associated with income or race/ethnicity. We conclude that greater pain prevalence among low income groups is not explained by greater allostatic load
Secondhand Smoke and Periodontal Disease: Atherosclerosis Risk in Communities Study
Objectives. We investigated the relationship between secondhand smoke and periodontal disease in nonsmokers
Subjective Sleep Quality Deteriorates Before Development of Painful Temporomandibular Disorder
There is good evidence that poor sleep quality increases risk of painful temporomandibular disorder (TMD). However little is known about the course of sleep quality in the months preceding TMD onset, and whether the relationship is mediated by heightened sensitivity to pain. The Pittsburgh Sleep Quality Index was administered at enrollment into the OPPERA prospective cohort study. Thereafter the Sleep Quality Numeric Rating Scale was administered every three months to 2,453 participants. Sensitivity to experimental pressure pain and pinprick pain stimuli was measured at baseline and repeated during follow-up of incident TMD cases (n=220) and matched TMD-free controls (n=193). Subjective sleep quality deteriorated progressively, but only in those who subsequently developed TMD. A Cox proportional hazards model showed that risk of TMD was greater among participants whose sleep quality worsened during follow-up (adjusted hazard ratio=1.73, 95% confidence limits: 1.29, 2.32). This association was independent of baseline measures of sleep quality, psychological stress, somatic awareness, comorbid conditions, non-pain facial symptoms and demographics. Poor baseline sleep quality was not significantly associated with baseline pain sensitivity or with subsequent change in pain sensitivity. Furthermore the relationship between sleep quality and TMD incidence was not mediated via baseline pain sensitivity nor change in pain sensitivity
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A Review of Previous Research in Direct Energy Conversion Fission Reactors
From the earliest days of power reactor development, direct energy conversion was an obvious choice to produce high efficiency electric power generation. Directly capturing the energy of the fission fragments produced during nuclear fission avoids the intermediate conversion to thermal energy and the efficiency limitations of classical thermodynamics. Efficiencies of more than 80% are possible, independent of operational temperature. Direct energy conversion fission reactors would possess a number of unique characteristics that would make them very attractive for commercial power generation. These reactors would be modular in design with integral power conversion and operate at low pressures and temperatures. They would operate at high efficiency and produce power well suited for long distance transmission. They would feature large safety margins and passively safe design. Ideally suited to production by advanced manufacturing techniques, direct energy conversion fission reactors could be produced more economically than conventional reactor designs. The history of direct energy conversion can be considered as dating back to 1913 when Moseleyl demonstrated that charged particle emission could be used to buildup a voltage. Soon after the successful operation of a nuclear reactor, E.P. Wigner suggested the use of fission fragments for direct energy conversion. Over a decade after Wigner's suggestion, the first theoretical treatment of the conversion of fission fragment kinetic energy into electrical potential appeared in the literature. Over the ten years that followed, a number of researchers investigated various aspects of fission fragment direct energy conversion. Experiments were performed that validated the basic physics of the concept, but a variety of technical challenges limited the efficiencies that were achieved. Most research in direct energy conversion ceased in the US by the late 1960s. Sporadic interest in the concept appears in the literature until this day, but there have been no recent significant programs to develop the technology
Efficacious, effective, and embedded interventions: Implementation research in infectious disease control
Background: Research in infectious disease control is heavily skewed towards high end
technology; development of new drugs, vaccines and clinical interventions. Oft ignored, is the
evidence to inform the best strategies that ensure the embedding of interventions into health
systems and amongst populations. In this paper we undertake an analysis of the challenge in the
development of research for the sustainable implementation of disease control interventions.
Results: We highlight the fundamental differences between the research paradigms associated
with the development of technologies and interventions for disease control on the one hand and the research paradigms required for enhancing the sustainable uptake of those very same
interventions within the communities on the other. We provide a definition for implementation
research in an attempt to underscore its critical role and explore the multidisciplinary science
needed to address the challenges in disease control.
Conclusion: The greatest value for money in health research lies in the sustainable and effective implementation of already proven, efficacious solutions. The development of implementation research that can help provide some solutions on how this can be achieved is sorely needed
Highly deformed Ca configurations in Si + C
The possible occurrence of highly deformed configurations in the Ca
di-nuclear system formed in the Si + C reaction is investigated
by analyzing the spectra of emitted light charged particles. Both inclusive and
exclusive measurements of the heavy fragments (A 10) and their
associated light charged particles (protons and particles) have been
made at the IReS Strasbourg {\sc VIVITRON} Tandem facility at bombarding
energies of Si) = 112 MeV and 180 MeV by using the {\sc ICARE}
charged particle multidetector array. The energy spectra, velocity
distributions, and both in-plane and out-of-plane angular correlations of light
charged particles are compared to statistical-model calculations using a
consistent set of parameters with spin-dependent level densities. The analysis
suggests the onset of large nuclear deformation in Ca at high spin.Comment: 33 pages, 11 figure
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