3,480 research outputs found
Thunderstorm/environment interactions that affect subsequent convection
Mesoscale kinematics and thermodynamics of severe thunderstorm-baroclinic zone interactions, and the development and evolution of mesoscale pressure systems associated with strong convective storms, are being studied in an ongoing research project
The environments of intermediate-redshift QSOs: 0.3 < z < 0.7
An angular correlation of low significance (2 sigma) is observed between 0.3
< z < 0.5 QSOs and V < 23 galaxies. Overall, the cross-correlation function
between 82 intermediate-redshift (0.3 < z < 0.7), X-ray selected QSOs and V <
24 galaxies is investigated, but no signal is detected for the z > 0.5 QSOs.
After converting to an excess of galaxies physically associated with the QSO,
this lack of strong correlation is shown to be consistent with the clustering
of normal galaxies at the same moderate redshifts. Combined with previous
observations, these results imply that the environments of radio-quiet QSOs do
not undergo significant evolution with respect to the galaxy population over a
wide range of redshifts (0 < z < 1.5). This is in marked contrast to the rapid
increase in the richness of the environments associated with radio-loud QSOs
over the same redshift range.Comment: 12 pages, 8 figures, MNRAS TeX macro, to appear to MNRA
Temporally Asymmetric Fluctuations are Sufficient for the Operation of a Correlation Ratchet
It has been shown that the combination of a broken spatial symmetry in the
potential (or ratchet potential) and time correlations in the driving are
crucial, and enough to allow transformation of the fluctuations into work. The
required broken spatial symmetry implies a specific molecular arrangement of
the proteins involved. Here we show that a broken spatial symmetry is not
required, and that temporally asymmetric fluctuations (with mean zero) can be
used to do work, even when the ratchet potential is completely symmetric.
Temporal asymmetry, defined as a lack of invariance of the statistical
properties under the operation to temporal inversion, is a generic property of
nonequilibrium fluctuation, and should therefore be expected to be quite common
in biological systems.Comment: 17 pages, ps figures on request, LaTeX Article Forma
Interactions Between Convective Storms and Their Environment
The ways in which intense convective storms interact with their environment are considered for a number of specific severe storm situations. A physical model of subcloud wind fields and vertical wind profiles was developed to explain the often observed intensification of convective storms that move along or across thermal boundaries. A number of special, unusually dense, data sets were used to substantiate features of the model. GOES imagery was used in conjunction with objectively analyzed surface wind data to develop a nowcast technique that might be used to identify specific storm cells likely to become tornadic. It was shown that circulations associated with organized meso-alpha and meso-beta scale storm complexes may, on occasion, strongly modify tropospheric thermodynamic patterns and flow fields
Faint blue objects on the Hubble Deep Field North & South as possible nearby old halo white dwarfs
Using data derived from the deepest and finest angular resolution images of
the universe yet acquired by astronomers at optical wavelengths using the
Hubble Space Telescope (HST) in two postage-stamp sections of the sky (Williams
et al. 1996a,b), plus simple geometrical and scaling arguments, we demonstrate
that the faint blue population of point-source objects detected on those two
fields (M\'endez et al. 1996) could actually be ancient halo white dwarfs at
distances closer than about 2 kpc from the Sun. This finding has profound
implications, as the mass density of the detected objects would account for
about half of the missing dark matter in the Milky-Way (Bahcall and Soneira
1980), thus solving one of the most controversial issues of modern astrophysics
(Trimble 1987, Ashman 1992). The existence of these faint blue objects points
to a very large mass locked into ancient halo white dwarfs. Our estimate
indicates that they could account for as much as half of the dark matter in our
Galaxy, confirming the suggestions of the MACHO microlensing experiment (Alcock
et al. 1997). Because of the importance of this discovery, deep follow-up
observations with HST within the next two years would be needed to determine
more accurately the kinematics (tangential motions) for these faint blue old
white dwarfs.Comment: Accepted for publication on The Astrophysical Journal, Part 1. 8
pages (AAS Latex macros V4.0), 1 B&W postscript figure, 2 color postscript
figure
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