1,532 research outputs found
Experimental and numerical signatures of dynamical crossover in orientationally disordered crystals
By means of NMR experiment and MD computer simulation we investigate the
dynamical properties of a chloroadamantane orientationally disordered crystal.
We find a plastic-plastic dynamical transition at T_x ~ 330 K in the
pico-nanosecond regime. It is interpreted as the rotational analogue of the
Goldstein crossing temperature between quasi-free diffusion and activated
regime predicted in liquids. Below T_x, NMR experimental data are well
described by a Frenkel model corresponding to a strongly anisotropic motion. At
higher temperatures, a drastic deviation is observed toward quasi-isotropic
rotational diffusion. Close to T_x, we observe that two-step relaxations
emerge. An interpretation which is based on the present study of a specific
heat anomaly detected by a recent calorimetric experiment is proposed.Comment: 4 pages, 4 figures; changed abstract and references; corrected figure
A spectral comparison of (379) Huenna and its satellite
We present near-infrared spectral measurements of Themis family asteroid
(379) Huenna (D~98 km) and its 6 km satellite using SpeX on the NASA IRTF. The
companion was farther than 1.5" from the primary at the time of observations
and was approximately 5 magnitudes dimmer. We describe a method for separating
and extracting the signal of a companion asteroid when the signal is not
entirely resolved from the primary. The spectrum of (379) Huenna has a broad,
shallow feature near 1 {\mu}m and a low slope, characteristic of C-type
asteroids. The secondary's spectrum is consistent with the taxonomic
classification of C-complex or X-complex. The quality of the data was not
sufficient to identify any subtle feature in the secondary's spectrum.Comment: 6 pages, 4 figures, 2 tables - Accepted for publication in Icaru
Onset of slow dynamics in difluorotetrachloroethane glassy crystal
Complementary Neutron Spin Echo and X-ray experiments and Molecular Dynamics
simulations have been performed on difluorotetrachloroethane (CFCl2-CFCl2)
glassy crystal. Static, single-molecule reorientational dynamics and collective
dynamics properties are investigated. The orientational disorder is
characterized at different temperatures and a change in nature of rotational
dynamics is observed. We show that dynamics can be described by some scaling
predictions of the Mode Coupling Theory (MCT) and a critical temperature
is determined. Our results also confirm the strong analogy between
molecular liquids and plastic crystals for which -relaxation times and
non-ergodicity parameters are controlled by the non trivial static correlations
as predicted by MCT
Effects of electron-phonon interactions on the electron tunneling spectrum of PbS quantum dots
We present a tunnel spectroscopy study of single PbS Quantum Dots (QDs) as
function of temperature and gate voltage. Three distinct signatures of strong
electron-phonon coupling are observed in the Electron Tunneling Spectrum (ETS)
of these QDs. In the shell-filling regime, the degeneracy of the
electronic levels is lifted by the Coulomb interactions and allows the
observation of phonon sub-bands that result from the emission of optical
phonons. At low bias, a gap is observed in the ETS that cannot be closed with
the gate voltage, which is a distinguishing feature of the Franck-Condon (FC)
blockade. From the data, a Huang-Rhys factor in the range is
obtained. Finally, in the shell tunneling regime, the optical phonons appear in
the inelastic ETS .Comment: 5 pages, 5 figure
Optimizing dual energy cone beam CT protocols for preclinical imaging and radiation research
Objective: The aim of this work was to investigate whether quantitative dual-energy CT (DECT) imaging is feasible for small animal irradiators with an integrated cone-beam CT (CBCT) system.
Methods: The optimal imaging protocols were determined by analyzing different energy combinations and dose levels. The influence of beam hardening effects and the performance of a beam hardening correction (BHC) were investigated. In addition, two systems from different manufacturers were compared in terms of errors in the extracted effective atomic numbers (Z(eff)) and relative electron densities (rho(e)) for phantom inserts with known elemental compositions and relative electron densities.
Results: The optimal energy combination was determined to be 50 and 90kVp. For this combination, Z(eff) and r rho(e) can be extracted with a mean error of 0.11 and 0.010, respectively, at a dose level of 60cGy.
Conclusion: Quantitative DECT imaging is feasible for small animal irradiators with an integrated CBCT system. To obtain the best results, optimizing the imaging protocols is required. Well-separated X-ray spectra and a sufficient dose level should be used to minimize the error and noise for Z(eff) and rho(e). When no BHC is applied in the image reconstruction, the size of the calibration phantom should match the size of the imaged object to limit the influence of beam hardening effects. No significant differences in Z(eff) and rho(e) errors are observed between the two systems from different manufacturers.
Advances in knowledge: This is the first study that investigates quantitative DECT imaging for small animal irradiators with an integrated CBCT system
New European guidelines for the management of dyslipidaemia in cardiovascular prevention
The new guidelines from the European Atherosclerosis Society and the European Society of Cardiology include a number of updated items. In this paper, we summarize 4 of these changes that we consider to be the most pertinent. Firstly, cardiovascular risk is now stratified according to 4 (previously 2) categories: "very high risk" (patients with cardiovascular disease, patients with diabetes > 40 years old who have at least one other risk factor, patients with kidney failure, or patients in primary prevention with a SCORE value > or = 10%); "high risk" (patients in primary prevention with a SCORE value > or = 5% and or = 1% and < 5%); and "low risk" (primary prevention with SCORE < 1%). The SCORE value for patients in primary prevention is estimated using the SCORE table (calibrated for Belgium). Risk in this table may now be corrected according to HDL cholesterol level. Secondly, the therapeutic targets for each category are now more stringent: LDL cholesterol < 70 mg/dl (or reduced by at least 50%) if the risk is "very high"; < 100 mg/dl if the risk is "high"; and < 115 mg/dl if the risk is "moderate". Thirdly, for patients at "high" or "very high" risk, particularly in patients with combined dyslipidaemia, two further therapeutic targets should be considered: non-HDL cholesterol and apolipoprotein B levels. Fourthly, the follow-up of efficacy (lipid profile) and tolerance (hepatic and muscular enzymes) is described in more details so as to harmonize case management in clinical practice.Peer reviewe
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