4,093 research outputs found
Acoustic, thermal and flow processes in a water filled nanoporous glasses by time-resolved optical spectroscopy
We present heterodyne detected transient grating measurements on water filled
Vycor 7930 in the range of temperature 20 - 90 degrees C. This experimental
investigation enables to measure the acoustic propagation, the average density
variation due the liquid flow and the thermal diffusion in this water filled
nano-porous material. The data have been analyzed with the model of Pecker and
Deresiewicz which is an extension of Biot model to account for the thermal
effects. In the whole temperature range the data are qualitatively described by
this hydrodynamic model that enables a meaningful insight of the different
dynamic phenomena. The data analysis proves that the signal in the intermediate
and long time-scale can be mainly addressed to the water dynamics inside the
pores. We proved the existence of a peculiar interplay between the mass and the
heat transport that produces a flow and back-flow process inside the
nano-pores. During this process the solid and liquid dynamics have opposite
phase as predicted by the Biot theory for the slow diffusive wave.
Nevertheless, our experimental results confirm that transport of elastic energy
(i.e. acoustic propagation), heat (i.e. thermal diffusion) and mass (i.e.
liquid flow) in a liquid filled porous glass can be described according to
hydrodynamic laws in spite of nanometric dimension of the pores. The data
fitting, based on the hydrodynamic model, enables the extraction of several
parameters of the water-Vycor system, even if some discrepancies appear when
they are compared with values reported in the literature.Comment: 32 pages, 11 figure
The optical light curve of GRB 970228 refined
We present the R and V light curves of the optical counterpart of GRB 970228.
A critical analysis of all the available data is made in light of the results
achieved in the recent GRB Symposium held in Huntsville and by considering the
latest information from the HST images on the underlying nebulosity.Comment: 3 pages, 2 .ps figures, Nuclear Physics style file espcrc2.sty
included. To appear in the proceedings of the conference "The Active X-Ray
Sky: Results from BeppoSAX and Rossi-XTE", Rome, Italy, 21-24 October, 1997.
L. Scarsi, H. Bradt, P. Giommi and F. Fiore editors, Nuc. Phys. B Proc. Supp
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