1,552 research outputs found
Outgassing measurement of the aluminum alloy UHV chamber
A large vacuum chamber (580 mm diameter) was fabricated from an aluminum alloy surface treated by a special process normally used on small chambers. The chamber was tested unbaked and baked at various temperatures, pressures, and holding periods. The chamber was filled with N2 gas, and the outgassing rate was measured after one hour. Then the ultimate pressure was measured. Outgassing rates for baked and unbaked groups were compared. It is concluded that the same surface treatment technique can be used on both large and small chambers produced by the same special extrusion process
Ultrastructural changes of intercellular junctions in rat ascites hepatoma cells with calcium depletion.
To analyse the effect of ethylenediamine tetraacetate (EDTA) on tumour cell adhesiveness, fine structure of intercellular junctions of rat ascites hepatoma cells AH136B and AH7974 (both forming cell islands in vivo) was first compared. The close contact of the apical portion of both cell islands was composed of tight junctions with a narrow gap. The close contact of the inner portion of AH136B cell islands was largely by simple apposition, while that of AH7974 cell islands had many intermediate junctions and desmosomes. Treatment with EDTA (2 mM) induced morphological alteration of simple apposition, intermediate junctions and desmosomes, but tight junctions remained intact. The effect of EDTA on such junctional complexes seemed to be partially reversible on readministration of Ca ions. Changes in desmosomes, as confirmed on AH7974 cells, were initiated by disappearance of the central disc of electron-dense materials, followed by marked opening of intercellular space and disappearance of endoplasmic laminar plaque. These results suggest that Ca ions may be concerned with maintaining the integrity of junctional complexes other than tight junctions
Reflective Ghost Imaging through Turbulence
Recent work has indicated that ghost imaging may have applications in
standoff sensing. However, most theoretical work has addressed
transmission-based ghost imaging. To be a viable remote-sensing system, the
ghost imager needs to image rough-surfaced targets in reflection through long,
turbulent optical paths. We develop, within a Gaussian-state framework,
expressions for the spatial resolution, image contrast, and signal-to-noise
ratio of such a system. We consider rough-surfaced targets that create fully
developed speckle in their returns, and Kolmogorov-spectrum turbulence that is
uniformly distributed along all propagation paths. We address both classical
and nonclassical optical sources, as well as a computational ghost imager.Comment: 13 pages, 3 figure
Classical Rotons in Cold Atomic Traps
We predict the emergence of a roton minimum in the dispersion relation of
elementary excitations in cold atomic gases in the presence of diffusive light.
In large magneto-topical traps, multiple-scattering of light is responsible for
the collective behavior of the system, which is associated to an effective
Coulomb-like interaction between the atoms. In optically thick clouds, the
re-scattered light undergoes diffusive propagation, which is responsible for a
stochastic short-range force acting on the atoms. We show that the dynamical
competition between these two forces results on a new polariton mode, which
exhibits a roton minimum. Making use of Feynman's formula for the static
structure factor, we show that the roton minimum is related to the appearance
of long-range order in the system.Comment: 5 pages, 3 figure
Light-cone fluctuations and the renormalized stress tensor of a massless scalar field
We investigate the effects of light-cone fluctuations over the renormalized
vacuum expectation value of the stress-energy tensor of a real massless
minimally coupled scalar field defined in a ()-dimensional flat space-time
with topology . For modeling the influence of
light-cone fluctuations over the quantum field, we consider a random
Klein-Gordon equation. We study the case of centered Gaussian processes. After
taking into account all the realizations of the random processes, we present
the correction caused by random fluctuations. The averaged renormalized vacuum
expectation value of the stress-energy associated with the scalar field is
presented
Intermediate Element Abundances in Galaxy Clusters
We present the average abundances of the intermediate elements obtained by
performing a stacked analysis of all the galaxy clusters in the archive of the
X-ray telescope ASCA. We determine the abundances of Fe, Si, S, and Ni as a
function of cluster temperature (mass) from 1--10 keV, and place strong upper
limits on the abundances of Ca and Ar. In general, Si and Ni are overabundant
with respect to Fe, while Ar and Ca are very underabundant. The discrepancy
between the abundances of Si, S, Ar, and Ca indicate that the alpha-elements do
not behave homogeneously as a single group. We show that the abundances of the
most well-determined elements Fe, Si, and S in conjunction with recent
theoretical supernovae yields do not give a consistent solution for the
fraction of material produced by Type Ia and Type II supernovae at any
temperature or mass. The general trend is for higher temperature clusters to
have more of their metals produced in Type II supernovae than in Type Ias. The
inconsistency of our results with abundances in the Milky Way indicate that
spiral galaxies are not the dominant metal contributors to the intracluster
medium (ICM). The pattern of elemental abundances requires an additional source
of metals beyond standard SNIa and SNII enrichment. The properties of this new
source are well matched to those of Type II supernovae with very massive,
metal-poor progenitor stars. These results are consistent with a significant
fraction of the ICM metals produced by an early generation of population III
stars.Comment: 18 pages, 11 figures, 7 tables. Submitted to Ap
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