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Radiation Pressure (radiation + pressure)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Radiation pressure induced splitting of resonant modes in a nanocrystal-coated microcavity

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2006
M. Gerlach
Abstract Melamine formaldehyde microspheres were coated with a soft polyelectrolyte multilayer (PAH/PSS) and one monolayer of CdTe nanocrystals. A micro-PL setup was used to trap the sample within the tightly focused laser beam. The radiation pressure was used to deform the spherical shape of the polyelectrolyte multilayer which changes the optical properties of the resonance modes (whispering gallery modes) in the microcavity. Optically induced shifting and splitting of the resonances were observed with changing characteristics based on varying particular parameters such as laser intensity and focus position. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Opportunities for the stratospheric collection of dust from short-period comets

METEORITICS & PLANETARY SCIENCE, Issue 11 2002
Scott MESSENGER
These comets have had the rare characteristics of low eccentricity, low inclination orbits with nodes very close to 1 AU. Dust from these comets is directly injected into Earth-crossing orbits by radiation pressure, unlike the great majority of interplanetary dust particles collected in the stratosphere which spend millennia in space prior to Earth-encounter. Complete dust streams from these comets form within a few decades, and appreciable amounts of dust are accreted by the Earth each year regardless of the positions of the parent comets. Dust from these comets could be collected in the stratosphere and identified by its short space exposure age, as indicated by low abundances of implanted solar-wind noble gases and/or lack of solar flare tracks. Dust from Grigg-Skjellerup probably has the highest concentration at Earth orbit. We estimate that the proportion of dust from this comet will reach at least several percent of the background interplanetary dust flux in the >40 ,m size range during April 23,24 of 2003. [source]

What controls the C iv line profile in active galactic nuclei?

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2005
Alexei Baskin
ABSTRACT The high-ionization lines in active galactic nuclei (AGN), such as C iv, tend to be blueshifted with respect to the lower-ionization lines, such as H,, and often show a strong blue excess asymmetry not seen in the low-ionization lines. There is accumulating evidence that the H, profile is dominated by gravity, and thus provides a useful estimate of the black hole mass in AGN. The shift and asymmetry commonly seen in C iv suggest that non-gravitational effects, such as obscuration and radiation pressure, may affect the line profile. We explore the relation between the H, and C iv profiles using the ultraviolet (UV) spectra available for 81 of the 87 z, 0.5 PG quasars in the Boroson & Green sample. We find the following. (1) Narrow C iv lines (full width at half-maximum, FWHM < 2000 km s,1) are rare (,2 per cent occurrence rate) compared with narrow H, lines (,20 per cent). (2) In most objects where the H, FWHM < 4000 km s,1 the C iv line is broader than H,, but the reverse is true when the H, FWHM > 4000 km s,1. This argues against the view that C iv generally originates closer to the centre, compared with H,. (3) C iv appears to provide a significantly less accurate, and possibly biased estimate of the black hole mass in AGN, compared with H,. (4) All objects where C iv is strongly blueshifted and asymmetric have a high L/LEdd, but the reverse is not true. This suggests that a high L/LEdd is a necessary but not sufficient condition for generating a blueshifted asymmetric C iv emission. (5) We also find indications for dust reddening and scattering in ,normal' AGN. In particular, PG quasars with a redder optical,UV continuum slope show weaker C iv emission, stronger C iv absorption and a higher optical continuum polarization. [source]

Ab initio simulations of accretion disc instability

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2004
V. Teresi
ABSTRACT We show that accretion discs, both in the subcritical and supercritical accretion rate regime, may exhibit significant amplitude luminosity oscillations. The luminosity time behaviour has been obtained by performing a set of time-dependent two-dimensional smoothed particle hydrodynamics simulations of accretion discs with different values of , and accretion rate. In this study, to avoid any influence of the initial disc configuration, we produced the discs injecting matter from an outer edge far from the central object. The period of oscillations is 2,50 s for the two cases, and the variation amplitude of the disc luminosity is 1038,1039 erg s,1. An explanation of this luminosity behaviour is proposed in terms of limit cycle instability; the disc oscillates between a radiation pressure dominated configuration (with a high luminosity value) and a gas pressure dominated one (with a low luminosity value). The origin of this instability is the difference between the heat produced by viscosity and the energy emitted as radiation from the disc surface (the well-known thermal instability mechanism). We support this hypothesis showing that the limit cycle behaviour produces a sequence of collapsing and refilling states of the innermost disc region. [source]