2,497 research outputs found
The INTEGRAL/SPI response and the Crab observations
The Crab region was observed several times by INTEGRAL for calibration
purposes. This paper aims at underlining the systematic interactions between
(i) observations of this reference source, (ii) in-flight calibration of the
instrumental response and (iii) the development and validation of the analysis
tools of the SPI spectrometer. It first describes the way the response is
produced and how studies of the Crab spectrum lead to improvements and
corrections in the initial response. Then, we present the tools which were
developed to extract spectra from the SPI observation data and finally a Crab
spectrum obtained with one of these methods, to show the agreement with
previous experiments. We conclude with the work still ahead to understand
residual uncertainties in the response.Comment: 4 pages, 4 figures, Proc. of the 5th INTEGRAL Workshop (Feb. 16-20
2004), to be published by ES
Beyond Zel'dovich-Type Approximations in Gravitational Instability Theory --- Pad\'e Prescription in Spheroidal Collapse ---
Among several analytic approximations for the growth of density fluctuations
in the expanding Universe, Zel'dovich approximation in Lagrangian coordinate
scheme is known to be unusually accurate even in mildly non-linear regime. This
approximation is very similar to the Pad\'e approximation in appearance. We
first establish, however, that these two are actually different and independent
approximations with each other by using a model of spheroidal mass collapse.
Then we propose Pad\'e-prescribed Zel'dovich-type approximations and
demonstrate, within this model, that they are much accurate than any other
known nonlinear approximations.Comment: 4 pages, latex, 3 figures include
Quasi-local evolution of cosmic gravitational clustering in the weakly non-linear regime
We investigate the weakly non-linear evolution of cosmic gravitational
clustering in phase space by looking at the Zel'dovich solution in the discrete
wavelet transform (DWT) representation. We show that if the initial
perturbations are Gaussian, the relation between the evolved DWT mode and the
initial perturbations in the weakly non-linear regime is quasi-local. That is,
the evolved density perturbations are mainly determined by the initial
perturbations localized in the same spatial range. Furthermore, we show that
the evolved mode is monotonically related to the initial perturbed mode. Thus
large (small) perturbed modes statistically correspond to the large (small)
initial perturbed modes. We test this prediction by using QSO Ly
absorption samples. The results show that the weakly non-linear features for
both the transmitted flux and identified forest lines are quasi-localized. The
locality and monotonic properties provide a solid basis for a DWT
scale-by-scale Gaussianization reconstruction algorithm proposed by Feng & Fang
(Feng & Fang, 2000) for data in the weakly non-linear regime. With the
Zel'dovich solution, we find also that the major non-Gaussianity caused by the
weakly non-linear evolution is local scale-scale correlations. Therefore, to
have a precise recovery of the initial Gaussian mass field, it is essential to
remove the scale-scale correlations.Comment: 22 pages, 13 figures. Accepted for publication in the Astrophysical
Journa
The effect of point sources on satellite observations of the cosmic microwave background
We study the effect of extragalactic point sources on satellite observations
of the cosmic microwave background (CMB). In order to separate the
contributions due to different foreground components, a maximum-entropy method
is applied to simulated observations by the Planck Surveyor satellite. In
addition to point sources, the simulations include emission from the CMB and
the kinetic and thermal Sunyaev-Zel'dovich (SZ) effects from galaxy clusters,
as well as Galactic dust, free-free and synchrotron emission. We find that the
main input components are faithfully recovered and, in particular, that the
quality of the CMB reconstruction is only slightly reduced by the presence of
point sources. In addition, we find that it is possible to recover accurate
point source catalogues at each of the Planck Surveyor observing frequencies.Comment: 12 pages, 9 figures, submitted to MNRA
The Optical - Infrared Colors of CORALS QSOs: Searching for Dust Reddening Associated With High Redshift Damped Lyman Alpha Systems
The presence of dust in quasar absorbers, such as damped Lyman alpha (DLA)
systems, may cause the background QSO to appear reddened. We investigate the
extent of this potential reddening by comparing the optical-to-infrared (IR)
colors of QSOs with and without intervening absorbers. Our QSO sample is based
on the Complete Optical and Radio Absorption Line System (CORALS) survey of
Ellison et al (2001). We have obtained near-simultaneous B and K band
magnitudes for subset of the CORALS sample and supplemented our observations
with further measurements published in the literature. To account for
redshift-related color changes, the B-K colors are normalized using the Sloan
Digital Sky Survey (SDSS) QSO composite. The mean normalized B-K color of the
DLA sub-sample is +0.12, whereas the mean for the no-DLA sample is -0.10; both
distributions have RMS scatters ~0.5. Neither a student's T-test nor a KS test
indicate that there is any significant difference between the two color
distributions. Based on simulations which redden the colors of QSOs with
intervening DLAs, we determine a reddening limit which corresponds to E(B-V) <
0.04 (SMC-like extinction) at 99% confidence (3 sigma), assuming that E(B-V) is
the same for all DLAs. Finally, we do not find any general correlation between
absorber properties (such as [Fe/Zn] or neutral hydrogen column density) and
B-K color. One of these two QSOs shows evidence for strong associated
absorption from X-ray observations, an alternative explanation for its very red
color. We conclude that the presence of intervening galaxies causes a minimal
reddening of the background QSO.Comment: Accepted for publication in A
SPI Measurements of the Diffuse Galactic Hard X-ray Continuum
INTEGRAL Spectrometer SPI data from the first year of the Galactic Centre
Deep Exposure has been analysed for the diffuse continuum from the Galactic
ridge. A new catalogue of sources from the INTEGRAL Imager IBIS has been used
to account for their contribution to the celestial signal. Apparently diffuse
emission is detected at a level ~10% of the total source flux. A comparison of
the spectrum of diffuse emission with that from an analysis of IBIS data alone
shows that they are consistent. The question of the contribution of unresolved
sources to this ridge emission is still open.Comment: Proceedings of the 5th INTEGRAL Workshop, Munich 16-20 February 2004.
ESA SP-552. Reference to Terrier et al. (2004) updated to include astro-ph
versio
Fast Evaluation of Interlace Polynomials on Graphs of Bounded Treewidth
We consider the multivariate interlace polynomial introduced by Courcelle
(2008), which generalizes several interlace polynomials defined by Arratia,
Bollobas, and Sorkin (2004) and by Aigner and van der Holst (2004). We present
an algorithm to evaluate the multivariate interlace polynomial of a graph with
n vertices given a tree decomposition of the graph of width k. The best
previously known result (Courcelle 2008) employs a general logical framework
and leads to an algorithm with running time f(k)*n, where f(k) is doubly
exponential in k. Analyzing the GF(2)-rank of adjacency matrices in the context
of tree decompositions, we give a faster and more direct algorithm. Our
algorithm uses 2^{3k^2+O(k)}*n arithmetic operations and can be efficiently
implemented in parallel.Comment: v4: Minor error in Lemma 5.5 fixed, Section 6.6 added, minor
improvements. 44 pages, 14 figure
Ultrastructure of Cooked Spaghetti
Several electron microscopy (EM) complementary techniques (scanning electron microscopy, freeze-fracturing and thin-sectioning) have been applied in the ultrastructural study of spaghetti.
Experimental spaghetti have been produced starting from two semolinas from the same wheat cultivar and using a low temperature (LT) and very high temperature (VHT) drying schemes.
Cooking quality of these products was not related to the quantity of the main components present in semolina. however, the drying conditions (temperature and humidity) and the nature of the cooking water greatly influenced cooking characteristics.
The three EM techniques were used to detected differences in protein and starch organization in relationship to spaghetti quality. Structural differences present in the uncooked product were more evident after cooking. in particular, in each high quality spaghetti, interesting macromolecular arrangements were always found inside starch granules. These new structures, which were dramatically promoted by VHT drying, exhibited an exceptional resistance to alpha-amylase digestion
Kinetic theory for non-equilibrium stationary states in long-range interacting systems
We study long-range interacting systems perturbed by external stochastic
forces. Unlike the case of short-range systems, where stochastic forces usually
act locally on each particle, here we consider perturbations by external
stochastic fields. The system reaches stationary states where external forces
balance dissipation on average. These states do not respect detailed balance
and support non-vanishing fluxes of conserved quantities. We generalize the
kinetic theory of isolated long-range systems to describe the dynamics of this
non-equilibrium problem. The kinetic equation that we obtain applies to
plasmas, self-gravitating systems, and to a broad class of other systems. Our
theoretical results hold for homogeneous states, but may also be generalized to
apply to inhomogeneous states. We obtain an excellent agreement between our
theoretical predictions and numerical simulations. We discuss possible
applications to describe non-equilibrium phase transitions.Comment: 11 pages, 2 figures; v2: small changes, close to the published
versio
One, four or 100 genera? A new classification of the cone snails
International audienc
- …