10,077 research outputs found
Reflection positive affine actions and stochastic processes
In this note we continue our investigations of the representation theoretic
aspects of reflection positivity, also called Osterwalder--Schrader positivity.
We explain how this concept relates to affine isometric actions on real Hilbert
spaces and how this is connected with Gaussian processes with stationary
increments
Observations of nitrogen isotope fractionation in deeply embedded protostars
(Abridged) The terrestrial planets, comets, and meteorites are significantly
enriched in 15N compared to the Sun and Jupiter. While the solar and jovian
nitrogen isotope ratio is believed to represent the composition of the
protosolar nebula, a still unidentified process has caused 15N-enrichment in
the solids. Several mechanisms have been proposed to explain the variations,
including chemical fractionation. However, observational results that constrain
the fractionation models are scarce. While there is evidence of 15N-enrichment
in prestellar cores, it is unclear how the signature evolves into the
protostellar phases. Our aim is to measure the 14N/15N ratio around three
nearby, embedded low-to-intermediate-mass protostars. Isotopologues of HCN and
HNC were used to probe the 14N/15N ratio. A selection of H13CN, HC15N, HN13C,
and H15NC transitions was observed with the APEX telescope. The 14N/15N ratios
were derived from the integrated intensities assuming a standard 12C/13C ratio.
The assumption of optically thin emission was verified using radiative transfer
modeling and hyperfine structure fitting. Two sources, IRAS 16293A and R CrA
IRS7B, show 15N-enrichment by a factor of around 1.5-2.5 in both HCN and HNC
with respect to the solar composition. Solar composition cannot be excluded for
the third source, OMC-3 MMS6. Furthermore, there are indications of a trend
toward increasing 14N/15N ratios with increasing outer envelope temperature.
The enhanced 15N abundances in HCN and HNC found in two Class~0 sources
(14N/15N of 160-290) and the tentative trend toward a temperature-dependent
14N/15N ratio are consistent with the chemical fractionation scenario, but
14N/15N ratios from additional tracers are indispensable for testing the
models. Spatially resolved observations are needed to distinguish between
chemical fractionation and isotope-selective photochemistry.Comment: Accepted for publication in Astronomy and Astrophysics. 16 pages, 13
figure
Harmonic analysis of iterated function systems with overlap
In this paper we extend previous work on IFSs without overlap. Our method
involves systems of operators generalizing the more familiar Cuntz relations
from operator algebra theory, and from subband filter operators in signal
processing.Comment: 37 page
Hot water in the inner 100 AU of the Class 0 protostar NGC1333 IRAS2A
Evaporation of water ice above 100 K in the inner few 100 AU of low-mass
embedded protostars (the so-called hot core) should produce quiescent water
vapor abundances of ~10^-4 relative to H2. Observational evidence so far points
at abundances of only a few 10^-6. However, these values are based on spherical
models, which are known from interferometric studies to be inaccurate on the
relevant spatial scales. Are hot cores really that much drier than expected, or
are the low abundances an artifact of the inaccurate physical models? We
present deep velocity-resolved Herschel-HIFI spectra of the 3(12)-3(03) lines
of H2-16O and H2-18O (1097 GHz, Eup/k = 249 K) in the low-mass Class 0
protostar NGC1333 IRAS2A. A spherical radiative transfer model with a power-law
density profile is unable to reproduce both the HIFI data and existing
interferometric data on the H2-18O 3(13)-2(20) line (203 GHz, Eup/k = 204 K).
Instead, the HIFI spectra likely show optically thick emission from a hot core
with a radius of about 100 AU. The mass of the hot core is estimated from the
C18O J=9-8 and 10-9 lines. We derive a lower limit to the hot water abundance
of 2x10^-5, consistent with the theoretical predictions of ~10^-4. The revised
HDO/H2O abundance ratio is 1x10^-3, an order of magnitude lower than previously
estimated.Comment: Accepted by ApJ; 12 pages in emulateapj format; 7 figure
Construction of Parseval wavelets from redundant filter systems
We consider wavelets in L^2(R^d) which have generalized multiresolutions.
This means that the initial resolution subspace V_0 in L^2(R^d) is not singly
generated. As a result, the representation of the integer lattice Z^d
restricted to V_0 has a nontrivial multiplicity function. We show how the
corresponding analysis and synthesis for these wavelets can be understood in
terms of unitary-matrix-valued functions on a torus acting on a certain vector
bundle. Specifically, we show how the wavelet functions on R^d can be
constructed directly from the generalized wavelet filters.Comment: 34 pages, AMS-LaTeX ("amsproc" document class) v2 changes minor typos
in Sections 1 and 4, v3 adds a number of references on GMRA theory and
wavelet multiplicity analysis; v4 adds material on pages 2, 3, 5 and 10, and
two more reference
An extension of Wiener integration with the use of operator theory
With the use of tensor product of Hilbert space, and a diagonalization
procedure from operator theory, we derive an approximation formula for a
general class of stochastic integrals. Further we establish a generalized
Fourier expansion for these stochastic integrals. In our extension, we
circumvent some of the limitations of the more widely used stochastic integral
due to Wiener and Ito, i.e., stochastic integration with respect to Brownian
motion. Finally we discuss the connection between the two approaches, as well
as a priori estimates and applications.Comment: 13 page
ISO far-infrared observations of rich galaxy clusters II. Sersic 159-03
The far-infrared emission from rich galaxy clusters is investigated. Maps
have been obtained by ISO at 60, 100, 135, and 200 microns using the PHT-C
camera. Ground based imaging and spectroscopy were also acquired. Here we
present the results for the cooling flow cluster Sersic 159-03. An infrared
source coincident with the dominant cD galaxy is found. Some off-center sources
are also present, but without any obvious counterparts.Comment: 6 pages, 4 postscript figures, accepted for publication in `Astronomy
and Astrophysics
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