19,016 research outputs found
Clustering of DIRBE Light and IR Background
We outline a new method for estimating the cosmic infrared background using
the spatial and spectral correlation properties of infrared maps. The cosmic
infrared background from galaxies should have a minimum fluctuation of the
order of 10\% on angular scales of the order of 1\deg. We show that a linear
combination of maps at different wavelengths can greatly reduce the
fluctuations produced by foreground stars, while not eliminating the
fluctuations of the background from high redshift galaxies. The method is
potentially very powerful, especially at wavelengths where the foreground is
bright but smooth.Comment: 7 pages postcript, talk at "Unveiling the cosmic infrared background"
workshop, College Park, M
Maximal multihomogeneity of algebraic hypersurface singularities
From the degree zero part of logarithmic vector fields along an algebraic
hypersurface singularity we indentify the maximal multihomogeneity of a
defining equation in form of a maximal algebraic torus in the embedded
automorphism group. We show that all such maximal tori are conjugate and in
one-to-one correspondence to maxmimal tori in the degree zero jet of the
embedded automorphism group.
The result is motivated by Kyoji Saito's characterization of quasihomogeneity
for isolated hypersurface singularities and extends its formal version and a
result of Hauser and Mueller.Comment: 5 page
Manufacturing with the Sun
Concentrated solar radiation is now a viable alternative source for many advanced manufacturing processes. Researchers at the National Renewable Energy Laboratory (NREL) have demonstrated the feasibility of processes such as solar induced surface transformation of materials (SISTM), solar based manufacturing, and solar pumped lasers. Researchers are also using sunlight to decontaminate water and soils polluted with organic compounds; these techniques could provide manufacturers with innovative alternatives to traditional methods of waste management. The solar technology that is now being integrated into today's manufacturing processes offer greater potential for tomorrow, especially as applied to the radiation abundant environment available in space and on the lunar surface
A non-perturbative method of calculation of Green functions
A new method for non-perturbative calculation of Green functions in quantum
mechanics and quantum field theory is proposed. The method is based on an
approximation of Schwinger-Dyson equation for the generating functional by
exactly soluble equation in functional derivatives. Equations of the leading
approximation and the first step are solved for -model. At
(anharmonic oscillator) the ground state energy is calculated. The
renormalization program is performed for the field theory at . At
the renormalization of the coupling involves a trivialization of the theory.Comment: 13 pages, Plain LaTex, no figures, some discussion of results for
anharmonic oscillator and a number of references are added, final version
published in Journal of Physics
The large scale gas and dust distribution in the galaxy: Implications for star formation
Infrared Astronomy Observations are presented for the diffuse infrared (IR) emissions from the galactic plane at wavelengths of 60 and 100 microns and the total far infrared intensity and its longitudinal variations in the disk were derived. Using available CO, 5 GHz radio-continuum, and HI data, the IR luminosity per hydrogen mass and the ingrared excess (IRE) ratio in the Galaxy were derived. The longitudinal profiles of the 60 and 100 micron emission were linearly decomposed into three components that are associated with molecular (H2), neutral (HI), and ionized (HII) phases in the interstellar medium (ISM), and the relevant dust properties were derived in each phase. Implications of the findings for various models of the diffuse IR emisison and for star formation in the galactic disk are discussed
Isolation of the Pneumocystis carinii dihydrofolate synthase gene and functional complementation in Saccharomyces cerevisiae
The Pneumocystis carinii gene encoding the enzyme dihydrofolate synthase (DHFS), which is involved in the essential biosynthesis of folates, was isolated from clones of the Pneumocystis genome project, and sequenced. The deduced P. carinii DHFS protein shares 38% and 35% identity with DHFS of Schizosaccharomyces pombe and Saccharomyces cerevisiae, respectively. P. carinii DHFS expressed from a plasmid functionally complemented a S. cerevisiae mutant with no DHFS. Comparison of available DHFSs with highly similar folylpolyglutamate synthases allowed the identification of potential signatures responsible for the specificities of these two classes of enzymes. The results open the way to experimentally analyse the structure and function of P. carinii mono-functional enzyme DHFS, to investigate a possible role of DHFS in the resistance to antifolates of P. jirovecii, the species infecting specifically humans, and to develop a new class of antifolate
1.0 Mm Maps and Radial Density Distributions of Southern Hii/molecular Cloud Complexes
Several 1.0 continuum mapping observations were made of seven southern hemisphere h12/molecular cloud complexes with 65 arcsec resolution. The radial density distribution of the clouds with central luminosity sources was determined observationally. Strong similarities in morphology and general physical conditions were found to exist among all of the southern clouds in the sample
Dirichlet Boundary Value Problems of the Ernst Equation
We demonstrate how the solution to an exterior Dirichlet boundary value
problem of the axisymmetric, stationary Einstein equations can be found in
terms of generalized solutions of the Backlund type. The proof that this
generalization procedure is valid is given, which also proves conjectures about
earlier representations of the gravitational field corresponding to rotating
disks of dust in terms of Backlund type solutions.Comment: 22 pages, to appear in Phys. Rev. D, Correction of a misprint in
equation (4
Determination of the Far-Infrared Cosmic Background Using COBE/DIRBE and WHAM Data
Determination of the cosmic infrared background (CIB) at far infrared
wavelengths using COBE/DIRBE data is limited by the accuracy to which
foreground interplanetary and Galactic dust emission can be modeled and
subtracted. Previous determinations of the far infrared CIB (e.g., Hauser et
al. 1998) were based on the detection of residual isotropic emission in skymaps
from which the emission from interplanetary dust and the neutral interstellar
medium were removed. In this paper we use the Wisconsin H-alpha Mapper (WHAM)
Northern Sky Survey as a tracer of the ionized medium to examine the effect of
this foreground component on determination of the CIB. We decompose the DIRBE
far infrared data for five high Galactic latitude regions into H I and H-alpha
correlated components and a residual component. We find the H-alpha correlated
component to be consistent with zero for each region, and we find that addition
of an H-alpha correlated component in modeling the foreground emission has
negligible effect on derived CIB results. Our CIB detections and 2 sigma upper
limits are essentially the same as those derived by Hauser et al. and are given
by nu I_nu (nW m-2 sr-1) < 75, < 32, 25 +- 8, and 13 +- 3 at 60, 100, 140, and
240 microns, respectively. Our residuals have not been subjected to a detailed
anisotropy test, so our CIB results do not supersede those of Hauser et al. We
derive upper limits on the 100 micron emissivity of the ionized medium that are
typically about 40% of the 100 micron emissivity of the neutral atomic medium.
This low value may be caused in part by a lower dust-to-gas mass ratio in the
ionized medium than in the neutral medium, and in part by a shortcoming of
using H-alpha intensity as a tracer of far infrared emission.Comment: 38 pages, 8 figures. Accepted for publication in Ap
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