1,458 research outputs found
Vibrational nonequilibrium effects in the conductance of single-molecules with multiple electronic states
Vibrational nonequilibrium effects in charge transport through
single-molecule junctions are investigated. Focusing on molecular bridges with
multiple electronic states, it is shown that electronic-vibrational coupling
triggers a variety of vibronic emission and absorption processes, which
influence the conductance properties and mechanical stability of
single-molecule junctions profoundly. Employing a master equation and a
nonequilibrium Green's function approach, these processes are analyzed in
detail for a generic model of a molecular junction and for
benzenedibutanethiolate bound to gold electrodes.Comment: 5 pages, 4 figure
Vibronic effects on resonant electron conduction through single molecule junctions
The influence of vibrational motion on electron conduction through single
molecules bound to metal electrodes is investigated employing first-principles
electronic-structure calculations and projection-operator Green's function
methods. Considering molecular junctions where a central phenyl ring is coupled
via (alkane)thiol-bridges to gold electrodes, it is shown that -- depending on
the distance between the electronic -system and the metal --
electronic-vibrational coupling may result in pronounced vibrational
substructures in the transmittance, a significantly reduced current as well as
a quenching of negative differential resistance effects.Comment: Submitted to Chem. Phys. Lett. (13 pages, 5 figures) this version:
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Correlation of a solar flare with a visual aurora
Correlation of solar flare with visual auror
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Jefferson Lab IR FEL cryomodule modifications and test results
The Infrared Free Electron Laser being constructed at the Thomas Jefferson National Accelerator Facility will require a 42 MeV, 5 mA electron accelerator. The accelerator design requires a 10 MeV injector and a two pass 32 MeV linac, one pass for acceleration and one pass for energy recovery. In order to minimize the cost of the linac, standard CEBAF 1497 MHZ Superconducting Radio Frequency cavities and cryomodules are being used with minimal changes. Two SRF cavities, housed in a quarter cryomodule, operate at a nominal 10 MV/m to provide the injector energy. The linac is composed of one cryomodule, housing eight SRF cavities operating at an average gradient of 8 MV/m. The modifications to the cryomodule are being made to handle the higher beam current, to improve RF control, and to increase machine reliability. The modifications to the higher order mode (HOM) loads, cavity tuners, cavity beam line, warm and cold RF windows, and cryogenic shield are described. Test results from the injector quarter cryomodule are also presented
Hybrid biodegradable membranes of silane-treated chitosan/soy protein for biomedical applications
In recent years, progress in the field of hybrid materials has been accelerated through use of the sol–gel process for creating materials and devices, which benefit from the incorporation of both inorganic and organic components. In this work, organic–inorganic hybrid membranes were prepared from tetraethoxysilane and a blend system composed of chitosan and soy protein. By introducing a small amount of siloxane bond into the chitosan/soy protein system, the chitosan/soy protein hybrid membranes were improved in terms of structure, topography and mechanical properties. It appears that the chitosan/soy protein hybrid membranes were formed by discrete inorganic moieties entrapped in the chitosan/soy protein blend, which improved the stability and mechanical performance assessed by the dynamic mechanical analysis as compared to chitosan/soy protein membrane. Also, in vitro cell culture studies evidenced that the chitosan/soy protein hybrid membranes are non-cytotoxic over a mouse fibroblast-like cell line. The hybrid membranes of silane-treated chitosan/soy protein developed in this work have potential in biomedical applications, including tissue engineering.This work was financially supported by the Portuguese Foundation for Science and Technology - FCT (Grant SFRH/BPD/45307/2008, SFRH/BPD/21786/2009, SFRH/BPD/39331/2007 and SFRH/BD/64601/2009), 'Fundo Social Europeu' - FSE and 'Programa Diferencial de Potencial Humano - POPH' and was partially supported by the FEDER through POCTEP 0330_IBEROMARE_1_P
Evaluation of optical coherence tomography findings in age-related macular degeneration: a reproducibility study of two independent reading centres
International audienceBackground/aims : To determine the reproducibility among readers of two independent certified centers, the Vienna Reading Center (VRC) and the University of Wisconsin-Madison Reading Center (UW-FPRC) for OCT images in age-related macular degeneration (AMD). Methods : Fast macular thickness scans and 6 mm cross hair scans were obtained from 100 eyes with all subtypes of AMD using Stratus OCT. Consensus readings were performed by two certified OCT readers of each Reading Center using their grading protocol. Common variables of both grading protocols, such as presence of cystoid spaces, subretinal fluid, vitreomacular traction and retinal pigment epithelial detachment were compared using kappa statistics. In addition, the intraclass correlation coefficient (ICC) was calculated for center point thickness (CPT) of values remeasured manually in the presence of alignment errors. Results : The reproducibility was dependent on the variable measured with a kappa value of 0.81 for the presence of cystoid spaces, 0.78 for the presence of subretinal fluid and 0.795 for the presence of vitreomacular traction. The lowest reproducibility was found for the presence of retinal pigment epithelial detachment with a kappa value of 0.51. The CPT was remeasured in 29 out of 100 scans at both sites with an ICC of the remeasured thicknesses of 0.92. Conclusion : OCT scan data are crucial in monitoring treatment efficacy in AMD clinical trials. For comparison of results obtained by different Reading Centers, the inter-Reading Center reproducibility is essential. Although the reproducibility is generally high, the reliability depends on the selected morphological parameters
Curation of FOAMS: a Free Open-Access Misophonia Stimuli Database
Misophonia is a disorder of decreased tolerance to certain “trigger” sounds (e.g., chewing, tapping, clicking). While misophonia research is scant in general, studies presenting sounds are especially rare and methodologically variable, likely due to the labor and time required to create stimuli. Thus, we introduce FOAMS: Free Open-Access Misophonia Stimuli, a sound bank publicly available on Zenodo, accompanied by pilot discomfort ratings for 32 of these sounds (4 exemplars of 8 classes). The FOAMS database aims to decrease the burden on researchers, facilitating reproducibility and the pursuit of nuanced research questions to better understand this perplexing disorder
Secondary structure of Ac-Ala-LysH polyalanine peptides (=5,10,15) in vacuo: Helical or not?
The polyalanine-based peptide series Ac-Ala_n-LysH+ (n=5-20) is a prime
example that a secondary structure motif which is well-known from the solution
phase (here: helices) can be formed in vacuo. We here revisit this conclusion
for n=5,10,15, using density-functional theory (van der Waals corrected
generalized gradient approximation), and gas-phase infrared vibrational
spectroscopy. For the longer molecules (n=10,15) \alpha-helical models provide
good qualitative agreement (theory vs. experiment) already in the harmonic
approximation. For n=5, the lowest energy conformer is not a simple helix, but
competes closely with \alpha-helical motifs at 300K. Close agreement between
infrared spectra from experiment and ab initio molecular dynamics (including
anharmonic effects) supports our findings.Comment: 4 pages, 4 figures, Submitted to JPC Letter
PEPPo: Using a Polarized Electron Beam to Produce Polarized Positrons
An experiment demonstrating a new method for producing polarized positrons has been performed at the CEBAF accelerator at Jefferson Laboratory. The PEPPo (Polarized Electrons for Polarized Positrons) concept relies on the production of polarized e+/e− pairs originating from the bremsstrahlung radiation of a longitudinally polarized electron beam interacting within a 1.0 mm tungsten pair-production target. This paper describes preliminary results of measurements using an 8.2 MeV/c electron beam with polarization 84% to generate positrons in the range of 3.1 to 6.2 MeV/c with polarization as high as ∼80%
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