10,667 research outputs found
Experimental analysis of the Strato-rotational Instability in a cylindrical Couette flow
This study is devoted to the experimental analysis of the Strato-rotational
Instability (SRI). This instability affects the classical cylindrical Couette
flow when the fluid is stably stratified in the axial direction. In agreement
with recent theoretical and numerical analyses, we describe for the first time
in detail the destabilization of the stratified flow below the Rayleigh line
(i.e. the stability threshold without stratification). We confirm that the
unstable modes of the SRI are non axisymmetric, oscillatory, and take place as
soon as the azimuthal linear velocity decreases along the radial direction.
This new instability is relevant for accretion disks.Comment: 4 pages, 4 figures. PRL in press 200
Spectroscopic Confirmation of the Cl 1604 Supercluster at z~0.9
We present spectroscopic confirmation of the Cl 1604 supercluster at z~0.9.
Originally detected as two individual clusters, Cl 1604+4304 at z = 0.90 and Cl
1604+4321 at z = 0.92, which are closely separated in both redshift and sky
position, subsequent imaging revealed a complex of red galaxies bridging the
two clusters, suggesting that the region contained a large scale structure. We
have carried out extensive multi-object spectroscopy, which, combined with
previous measurements, provides ~600 redshifts in this area, including 230
confirmed supercluster members. We detect two additional clusters that are part
of this structure, Cl 1604+4314 at z = 0.87 and Cl 1604+4316 at z = 0.94. All
four have properties typical of local clusters, with line-of-sight velocity
dispersions between 489 and 962 km/s. The structure is significantly extended
in redshift space, which, if interpreted as a true elongation in real space,
implies a depth of 93 Mpc. We examine the spatial and redshift distribution of
the supercluster members.Comment: Accepted to ApJ Letters. 4 pages with 3 figure
Neutron--Antineutron Oscillations at the Surface of Nuclei
We discuss some aspects of possible neutron--antineutron oscillations in
nuclei. The phenomenon occurs mostly at the surface of nuclei, and hence {\sl
i)} is not very sensitive to medium corrections and {\sl ii)} makes use of the
antinucleon-nucleus interaction in a region probed by experiments at CERN.Comment: Contr. Oak Ridge Workshop on Workshop on Baryon Instability, Latex, 4
pages, comments to [email protected]
Erosive Hit-and-Run Impact Events: Debris Unbound
Erosive collisions among planetary embryos in the inner solar system can lead
to multiple remnant bodies, varied in mass, composition and residual velocity.
Some of the smaller, unbound debris may become available to seed the main
asteroid belt. The makeup of these collisionally produced bodies is different
from the canonical chondritic composition, in terms of rock/iron ratio and may
contain further shock-processed material. Having some of the material in the
asteroid belt owe its origin from collisions of larger planetary bodies may
help in explaining some of the diversity and oddities in composition of
different asteroid groups.Comment: 7 pages, 3 figure
Photometric validation of a model independent procedure to extract galaxy clusters
By means of CCD photometry in three bands (Gunn g, r, i) we investigate the
existence of 12 candidate clusters extracted via a model independent peak
finding algorithm (\cite{memsait}) from DPOSS data. The derived color-magnitude
diagrams allow us to confirm the physical nature of 9 of the cluster
candidates, and to estimate their photometric redshifts. Of the other
candidates, one is a fortuitous detection of a true cluster at z~0.4, one is a
false detection and the last is undecidable on the basis of the available data.
The accuracy of the photometric redshifts is tested on an additional sample of
8 clusters with known spectroscopic redshifts. Photometric redshifts turn out
to be accurate within z~0.01 (interquartile range).Comment: A&A in pres
All-organic dielectric-percolative three-component composite materials with high electromechanical response
By combining the high-dielectric copper phthalocyanine oligomer (PolyCuPc) and conductive polyanline (PANI) within polyurethane (PU) matrix an all-organic three-component dielectric-percolative composite with high dielectric constant is demonstrated. In this three-component composite system, the high-dielectric-constant PolyCuPc particulates enhance the dielectric constant of the PU matrix and this combined two-component dielectric matrix in turn serves as the high-dielectric-constant host for the PANI to realize percolative phenomenon and further enhance the dielectric response. As a result, an electromechanical strain of 9.3% and elastic energy density of 0.4 J/cm(3) under an electric field of 20 V/mum can be induced
Lambda-hypernuclear production in stopped (K-,pion) reactions reexamined
DWIA calculations of Lambda-hypernuclear production rates in stopped K-
reactions on several p-shell targets used recently in experiments by the FINUDA
Collaboration are reported. Chirally motivated K- + N -> pion + Lambda
in-medium transition amplitudes are employed and the sensitivity of the
calculated rates to the initial K- atomic wavefunctions and final pion
distorted waves is studied. The calculated rates are compared with measured
rates, wherever available, confirming earlier observations that (i) the
calculated rates are generally lower than the measured rates, and (ii) the
deeper the K- nuclear potential, the worse is the discrepancy. The A dependence
of the calculated 1s Lambda hypernuclear production rates is discussed for the
first time, providing a useful tool in resolving the issue of depth of the K-
nuclear potential near threshold.Comment: matches published version, including the dubious change of
`revisited' in the title to `reexamined' upon PRC Editor's insistenc
On Normal Subgroups of Coxeter Groups Generated by Standard Parabolic Subgroups
We discuss one construction of nonstandard subgroups in the category of
Coxeter groups.
Two formulae for the growth series of such a subgroups are given.
As an application we construct a flag simple convex polytope, whose
f-polynomial has non-real roots.Comment: 12 pages, figure
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