Molecular velocity auto-correlation of simple liquids observed by NMR MGSE method

The velocity auto-correlation spectra of simple liquids obtained by the NMR method of modulated gradient spin echo show features in the low frequency range up to a few kHz, which can be explained reasonably well by a $t^{-3/2}$ long time tail decay only for non-polar liquid toluene, while the spectra of polar liquids, such as ethanol, water and glycerol, are more congruent with the model of diffusion of particles temporarily trapped in potential wells created by their neighbors. As the method provides the spectrum averaged over ensemble of particle trajectories, the initial non-exponential decay of spin echoes is attributed to a spatial heterogeneity of molecular motion in a bulk of liquid, reflected in distribution of the echo decays for short trajectories. While at longer time intervals, and thus with longer trajectories, heterogeneity is averaged out, giving rise to a spectrum which is explained as a combination of molecular self-diffusion and eddy diffusion within the vortexes of hydrodynamic fluctuations.Comment: 8 pages, 6 figur

Fitting the integrated Spectral Energy Distributions of Galaxies

Fitting the spectral energy distributions (SEDs) of galaxies is an almost universally used technique that has matured significantly in the last decade. Model predictions and fitting procedures have improved significantly over this time, attempting to keep up with the vastly increased volume and quality of available data. We review here the field of SED fitting, describing the modelling of ultraviolet to infrared galaxy SEDs, the creation of multiwavelength data sets, and the methods used to fit model SEDs to observed galaxy data sets. We touch upon the achievements and challenges in the major ingredients of SED fitting, with a special emphasis on describing the interplay between the quality of the available data, the quality of the available models, and the best fitting technique to use in order to obtain a realistic measurement as well as realistic uncertainties. We conclude that SED fitting can be used effectively to derive a range of physical properties of galaxies, such as redshift, stellar masses, star formation rates, dust masses, and metallicities, with care taken not to over-interpret the available data. Yet there still exist many issues such as estimating the age of the oldest stars in a galaxy, finer details ofdust properties and dust-star geometry, and the influences of poorly understood, luminous stellar types and phases. The challenge for the coming years will be to improve both the models and the observational data sets to resolve these uncertainties. The present review will be made available on an interactive, moderated web page (sedfitting.org), where the community can access and change the text. The intention is to expand the text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics & Space Scienc

Josephson junctions as resonant detectors

The single resonance is treated of a cavity, which is driven by an appropriately biased Josephson junction and an external field at resonance frequency. We describe a tunable Fabry-Pérot cavity, based on a flat point-contact device, as a possible narrow-band detector of far-infrared radiation. Preliminary experimental data for this system indicate that the principle works, but that the coupling of tunnel currents with the resonance still falls short by an order of magnitude. Modifications are discussed that will improve its performance.Nous étudions la résonance d'une cavité couplée à une jonction Josephson correctement polarisée et soumise à un champ à la fréquence de résonance. Nous décrivons une cavité Fabry-Pérot accordable, mettant en jeu un dispositif à contact à pointe, qui peut être utilisée comme détecteur sélectif d'un rayonnement infrarouge lointain. Des données expérimentales préliminaires montrent que le principe est correct, mais que le couplage entre la jonction et la cavité est encore trop faible d'un ordre de grandeur. Des modifications qui amélioreront les performances sont décrites

Neutron scattering study of the dynamics in dense argon gas

Applied Science