Suchergebnisse

Gravitational instability arising from thermal fluctuations in a static universe in considered in an extrapolation of a weakly non linear approximation, to calculate the mean square angular momentum of proto-galaxies at the critical time at which these protogalaxies detach themselves from the primeval homogeneous medium. The mean angular momentum of a given volume, containing in the mean a mass M, and the mean angular momentum of a given mass M, are shown to be quite different. It is suggested that it is the latter which should be compared with the observed angular momentum of galaxies. A numerical application shows that such a picture cannot account for the observed angular momentum of the Galaxy and at the same time for the existence of dwarf galaxies. A simple calculation suggests however that tidal interactions arising between neighbouring protogalaxies after the critical time of detachment would easily account for the observed angular momentum of spiral galaxies, if these interactions take place before the universe is set in a state of fully developed expansion

The problem of the stability of a cylindrical plasma towards purely radial oscillations considered in a previous article is rediscussed in terms of amended boundary conditions for the solutions of Maxwell equations in the infinite empty space surrounding the plasma. The case of a plane plasma layer which admits of a complete analytical treatment suggests, for the case of cylindrical symmetry, the existence of asymptotic solutions which are succintly discussed.

The vibrational stability of a gaseous star is discussed, in the case of non-radial oscillations.
We show that the degeneracy which, in this case, affects the adiabatic proper-value problem remains complete, even if the generation of nuclear energy and the radiative conductibility are taken into account.
Numerical computations have been made for a non-radial oscillation of the standard model. Owing to the fact that the variations of density and temperature vanish at the center of the star, we find a very high stability, increasing with the temperature exponent in the law of generation of nuclear energy.

The stationary oscillations of an isothermal infinite atmosphere are discussed ; we obtain again the critical frequency found by S. Rosseland, but our interpretation, based on the concept of kinetic energy, leads to a somewhat different physical meaning. The case of a Roche atmosphere of infinite radius (p ~ r-α) is also discussed ; in this case, we do not obtain any critical frequency, owing to the slower decrease of density.

In the Western world around 360 in every 100,000 individuals have inflammatory bowel disease (IBD), a relapsing-remitting autoimmune disease that affects the gastrointestinal tract. Its impact on individual functioning across physical and psychosocial domains is significant and psychological distress is a common feature, with research suggesting that active IBD is associated with one of the highest rates of depression and anxiety of all chronic illnesses. Despite the high prevalence of mental health co-morbidities in IBD, psychological illness remains largely undertreated, with studies showing.

A new type of interlace, the three-dimensional (3D) audio display, is being developed to enhance cockpit displays in military aircraft. In order to synthesize a sound's location in space, head-related transfer functions are measured for many sound source positions (in space) and incorporated in digital filters, which are then used to synthesize location. However, most military aircraft have communication systems that are band-limited in frequency response, as are most recently designed auditory displays currently used in military applications. The present study investigated the effects of limiting signal bandwidth on sound localization. Results show that broadband signals encompassing frequencies from 0 to (at least) 13 kHz are required in order for listeners to accurately localize signals actually presented from a range of spatial locations. These results have clear implications for the design and implementation of 3D spatial synthesis systems in military aircraft. Communications systems should be capable of carrying broadband signals and acoustic signals used in 3D audio displays should also be broadband in nature.