131,083 research outputs found
Sphere forming method and apparatus
A system is provided for forming small accurately spherical objects. Preformed largely spherical objects are supported at the opening of a conduit on the update of hot gas emitted from the opening, so the object is in a molten state. The conduit is suddenly jerked away at a downward incline, to allow the molten object to drop in free fall, so that surface tension forms a precise sphere. The conduit portion that has the opening, lies in a moderate vacuum chamber, and the falling sphere passes through the chamber and through a briefly opened valve into a tall drop tower that contains a lower pressure, to allow the sphere to cool without deformation caused by falling through air
An imaging K-band survey - I: The catalogue, star and galaxy counts
We present results from a large area (552\,\sqamin) imaging -band survey
to a 5 limit of . We have optical-infrared colours of
almost all the objects in the sample. Star-galaxy discrimination is performed
and the results used to derive the infrared star and galaxy counts. -band
``no-evolution'' galaxy-count models are constructed and compared with the
observed data. In the infrared, there is no counterpart for the large excess of
faint galaxies over the no-evolution model seen in optical counts. However, we
show that the counts can be remarkably insensitive to evolution under
certain reasonable assumptions. Finally, model predictions for -selected
redshift surveys are derived.Comment: MNRAS in press. 21 pages plain TeX; figs plus table 4 available via
anonymous ftp from /pub/kgb/paper1/sissa.uu at ftp.ast.cam.ac.u
A Comparison of Intermediate Mass Black Hole Candidate ULXs and Stellar-Mass Black Holes
Cool thermal emission components have recently been revealed in the X-ray
spectra of a small number of ultra-luminous X-ray (ULX) sources with L_X > 1
E+40 erg/s in nearby galaxies. These components can be well fitted with
accretion disk models, with temperatures approximately 5-10 times lower than
disk temperatures measured in stellar-mass Galactic black holes when observed
in their brightest states. Because disk temperature is expected to fall with
increasing black hole mass, and because the X-ray luminosity of these sources
exceeds the Eddington limit for 10 Msun black holes (L_Edd = 1.3 E+39 erg/s),
these sources are extremely promising intermediate-mass black hole candidates
(IMBHCs). In this Letter, we directly compare the inferred disk temperatures
and luminosities of these ULXs, with the disk temperatures and luminosities of
a number of Galactic black holes. The sample of stellar-mass black holes was
selected to include different orbital periods, companion types, inclinations,
and column densities. These ULXs and stellar-mass black holes occupy distinct
regions of a L_X -- kT diagram, suggesting these ULXs may harbor IMBHs. We
briefly discuss the important strengths and weaknesses of this interpretation.Comment: 4 pages, 2 color figures, uses emulateapj.sty and apjfonts.sty, subm.
to ApJ
Effective Operators for Double-Beta Decay
We use a solvable model to examine double-beta decay, focusing on the
neutrinoless mode. After examining the ways in which the neutrino propagator
affects the corresponding matrix element, we address the problem of finite
model-space size in shell-model calculations by projecting our exact wave
functions onto a smaller subspace. We then test both traditional and more
recent prescriptions for constructing effective operators in small model
spaces, concluding that the usual treatment of double-beta-decay operators in
realistic calculations is unable to fully account for the neglected parts of
the model space. We also test the quality of the Quasiparticle Random Phase
Approximation and examine a recent proposal within that framework to use
two-neutrino decay to fix parameters in the Hamiltonian. The procedure
eliminates the dependence of neutrinoless decay on some unfixed parameters and
reduces the dependence on model-space size, though it doesn't eliminate the
latter completely.Comment: 10 pages, 8 figure
A new source detection algorithm using FDR
The False Discovery Rate (FDR) method has recently been described by Miller
et al (2001), along with several examples of astrophysical applications. FDR is
a new statistical procedure due to Benjamini and Hochberg (1995) for
controlling the fraction of false positives when performing multiple hypothesis
testing. The importance of this method to source detection algorithms is
immediately clear. To explore the possibilities offered we have developed a new
task for performing source detection in radio-telescope images, Sfind 2.0,
which implements FDR. We compare Sfind 2.0 with two other source detection and
measurement tasks, Imsad and SExtractor, and comment on several issues arising
from the nature of the correlation between nearby pixels and the necessary
assumption of the null hypothesis. The strong suggestion is made that
implementing FDR as a threshold defining method in other existing
source-detection tasks is easy and worthwhile. We show that the constraint on
the fraction of false detections as specified by FDR holds true even for highly
correlated and realistic images. For the detection of true sources, which are
complex combinations of source-pixels, this constraint appears to be somewhat
less strict. It is still reliable enough, however, for a priori estimates of
the fraction of false source detections to be robust and realistic.Comment: 17 pages, 7 figures, accepted for publication by A
Ceramic coatings on smooth surfaces
A metallic coating is plasma sprayed onto a smooth surface of a metal alloy substitute or on a bond coating. An initial thin ceramic layer is low pressure sprayed onto the smooth surface of the substrate or bond coating. Another ceramic layer is atmospheric plasma sprayed onto the initial ceramic layer
A fully (3+1)-D Regge calculus model of the Kasner cosmology
We describe the first discrete-time 4-dimensional numerical application of
Regge calculus. The spacetime is represented as a complex of 4-dimensional
simplices, and the geometry interior to each 4-simplex is flat Minkowski
spacetime. This simplicial spacetime is constructed so as to be foliated with a
one parameter family of spacelike hypersurfaces built of tetrahedra. We
implement a novel two-surface initial-data prescription for Regge calculus, and
provide the first fully 4-dimensional application of an implicit decoupled
evolution scheme (the ``Sorkin evolution scheme''). We benchmark this code on
the Kasner cosmology --- a cosmology which embodies generic features of the
collapse of many cosmological models. We (1) reproduce the continuum solution
with a fractional error in the 3-volume of 10^{-5} after 10000 evolution steps,
(2) demonstrate stable evolution, (3) preserve the standard deviation of
spatial homogeneity to less than 10^{-10} and (4) explicitly display the
existence of diffeomorphism freedom in Regge calculus. We also present the
second-order convergence properties of the solution to the continuum.Comment: 22 pages, 5 eps figures, LaTeX. Updated and expanded versio
Formation of Na2SO4 and K2SO4 in flames doped with sulfur and alkali chlorides and carbonates
High pressure, free-jet expansion, mass spectrometric sampling was used to identify directly and to measure reaction products formed in doped methane-oxygen flames. Flames were doped with SO2 or CH3SH and sodium or potassium chlorides or carbonates. Gaseous NA2SO4 or K2S04 molecules were formed in residence times on the order of msec for each combination of dopants used. Composition profiles of combustion products were measured and compared with equilibrium thermodynamic calculations of product composition
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