4,208 research outputs found
Strong lensing optical depths in a \LambdaCDM universe
We investigate strong gravitational lensing in the concordance CDM
cosmology by carrying out ray-tracing along past light cones through the
Millennium Simulation, the largest simulation of cosmic structure formation
ever carried out. We extend previous ray-tracing methods in order to take full
advantage of the large volume and the excellent spatial and mass resolution of
the simulation. As a function of source redshift we evaluate the probability
that an image will be highly magnified, will be highly elongated or will be one
of a set of multiple images. We show that such strong lensing events can almost
always be traced to a single dominant lensing object and we study the mass and
redshift distribution of these primary lenses. We fit analytic models to the
simulated dark halos in order to study how our optical depth measurements are
affected by the limited resolution of the simulation and of the lensing planes
that we construct from it. We conclude that such effects lead us to
underestimate total strong-lensing cross sections by about 15 percent. This is
smaller than the effects expected from our neglect of the baryonic components
of galaxies. Finally we investigate whether strong lensing is enhanced by
material in front of or behind the primary lens. Although strong lensing
lines-of-sight are indeed biased towards higher than average mean densities,
this additional matter typically contributes only a few percent of the total
surface density.Comment: version accepted for publicatio
Studying Attractor Symmetries by Means of Cross Correlation Sums
We use the cross correlation sum introduced recently by H. Kantz to study
symmetry properties of chaotic attractors. In particular, we apply it to a
system of six coupled nonlinear oscillators which was shown by Kroon et al. to
have attractors with several different symmetries, and compare our results with
those obtained by ``detectives" in the sense of Golubitsky et al.Comment: LaTeX file, 16 pages and 16 postscript figures; tarred, gzipped and
uuencoded; submitted to 'Nonlinearity
Beta-Adrenergic Receptor Blockade By Propranolol Enhances Retention In A Multitrial Passive-Avoidance Procedure
The effect of beta -adrenergic receptor blockade on retention in a mildly aversive passive-avoidance procedure was investigated. Rats were given passive-avoidance training-1 trial per day for 4 days-and were administered saline, the centrally and peripherally acting beta -adrenergic blocker propranolol (4 or 10 mg/kg ip), or the peripherally acting P-adrenergic blocker sotalol (4 or 10 mg/kg ip) immediately or 2 hr after the Ist trial. Enhanced retention occurred only with the higher dose (10 mg/kg) of propranolol and only when it was administered immediately after training. The enhanced retention produced by propranolol is discussed in terms of opposing, regionally specific actions of beta -adrenergic receptor-mediated neural circuits on modulation of memory
New sequence variants detected at DXS10148, DXS10074 and DXS10134 loci
A great amount of population and forensic genetic data are available for X-STRs supporting the need for
having a common and accurate nomenclature among laboratories allowing for better communication,
data exchange, and data comparison. DXS10148, DXS10074 and DXS10134 are commonly used X-STRs
particularly due to their inclusion in the commercial kit Investigator Argus X-12 (Qiagen). Samples from
West Africa and Iraq were sequenced for all three X-STRs allowing the detection of new DNA sequence
variants. At DXS10148, variation was detected at four bases downstream from the flanking region from
the repeat motif. The sequence AAGG-AAAG has been detected for the first time as a varying (AAGGAAAG)1–3 motif, in the present work. One additional string when compared to the common one (AAGGAAAG)2 adds eight bases to the fragment size of the tetranucleotide STR. This means that 2 repeats are
added in these cases to the fragment size of the allele, while the presence of only one copy will reduce the
expected allele size by 2 repeats. At DXS10074 two varying stretches consisting of AC and AG dinucleotide
repeats were observed in the upstream flanking region, six bases from the main repeat core that also
influence the expected allele size. DXS10134 revealed a simpler nomenclature in the Guinea-Bissau
sample set when compared to the previously described allele nomenclature. This detected new hidden
variation also has impact on the actual allele nomenclature at this locus as it contributes to a new class of
short alleles so far undetected in other studies.info:eu-repo/semantics/publishedVersio
Enhanced Retention In The Passive-Avoidance Task By 5-HT1A Receptor Blockade Is Not Associated With Increased Activity Of The Central Nucleus Of The Amygdala
The effect of blockade of S-HT1A receptors was investigated on (1) retention in a mildly aversive passive-avoidance task, and (2) spontaneous single-unit activity of central nucleus of the amygdala (CeA) neurons, a brain site implicated in modulation of retention. Systemic administration of the selective S-HT1A antagonist NAN-190 immediately after training markedly-and dose-dependently-facilitated retention in the passive-avoidance task; enhanced retention was time-dependent and was not attributable to variations in wattages of shock received by animals. Systemic administration of NAN-190 had mixed effects on spontaneous single-unit activity of CeA neurons recorded extracellularly in vivo; microiontophoretic application of S-HT, in contrast, consistently and potently suppressed CeA activity. The present findings-that S-HT1A receptor blockade by NAN-190 (1) enhances retention in the passive-avoidance task, and (2) does not consistently increase spontaneous neuronal activity of the CeA-provide evidence that a serotonergic system tonically inhibits modulation of retention in the passive-avoidance task through activation of the S-HT1A receptor subtype at brain sites located outside the CeA
Weak gravitational lensing in the standard Cold Dark Matter model, using an algorithm for three-dimensional shear
We investigate the effects of weak gravitational lensing in the standard Cold
Dark Matter cosmology, using an algorithm which evaluates the shear in three
dimensions. The algorithm has the advantage of variable softening for the
particles, and our method allows the appropriate angular diameter distances to
be applied to every evaluation location within each three-dimensional
simulation box. We investigate the importance of shear in the distance-redshift
relation, and find it to be very small. We also establish clearly defined
values for the smoothness parameter in the relation, finding its value to be at
least 0.88 at all redshifts in our simulations. From our results, obtained by
linking the simulation boxes back to source redshifts of 4, we are able to
observe the formation of structure in terms of the computed shear, and also
note that the major contributions to the shear come from a very broad range of
redshifts. We show the probability distributions for the magnification, source
ellipticity and convergence, and also describe the relationships amongst these
quantities for a range of source redshifts. We find a broad range of
magnifications and ellipticities; for sources at a redshift of 4, 97{1/2}% of
all lines of sight show magnifications up to 1.3 and ellipticities up to 0.195.
There is clear evidence that the magnification is not linear in the
convergence, as might be expected for weak lensing, but contains contributions
from higher order terms in both the convergence and the shear.Comment: 14 pages, LaTeX, 15 figures include
The non-Gaussian tail of cosmic-shear statistics
Due to gravitational instability, an initially Gaussian density field
develops non-Gaussian features as the Universe evolves. The most prominent
non-Gaussian features are massive haloes, visible as clusters of galaxies. The
distortion of high-redshift galaxy images due to the tidal gravitational field
of the large-scale matter distribution, called cosmic shear, can be used to
investigate the statistical properties of the LSS. In particular, non-Gaussian
properties of the LSS will lead to a non-Gaussian distribution of cosmic-shear
statistics. The aperture mass () statistics, recently introduced as
a measure for cosmic shear, is particularly well suited for measuring these
non-Gaussian properties. In this paper we calculate the highly non-Gaussian
tail of the aperture mass probability distribution, assuming Press-Schechter
theory for the halo abundance and the `universal' density profile of haloes as
obtained from numerical simulations. We find that for values of
much larger than its dispersion, this probability distribution is closely
approximated by an exponential, rather than a Gaussian. We determine the
amplitude and shape of this exponential for various cosmological models and
aperture sizes, and show that wide-field imaging surveys can be used to
distinguish between some of the currently most popular cosmogonies. Our study
here is complementary to earlier cosmic-shear investigations which focussed
more on two-point statistical properties.Comment: 9 pages, 5 figures, submitted to MNRA
Parallel Evaluation of Multi-join Queries
A number of execution strategies for parallel evaluation of multi-join queries have been proposed in the literature. In this paper we give a comparative performance evaluation of four execution strategies by implementing all of them on the same parallel database system, PRISMA/DB. Experiments have been done up to 80 processors. These strategies, coming from the literature, are named: Sequential Parallel, Synchronous Execution, Segmented Right-Deep, and Full Parallel. Based on the experiments clear guidelines are given when to use which strategy.
This is an extended abstract; the full paper appeared in Proc. ACM SIGMOD'94, Minneapolis, Minnesota, May 24–27, 199
Morphology control of zinc oxide films via polysaccharide-mediated, low temperature, chemical bath deposition
In this study we present a three-step process for the low-temperature chemical bath deposition of crystalline ZnO films on glass substrates. The process consists of a seeding step followed by two chemical bath deposition steps. In the second step (the first of the two bath deposition steps), a natural polysaccharide, namely hyaluronic acid, is used to manipulate the morphology of the films. Previous experiments revealed a strong influence of this polysaccharide on the formation of zinc oxide crystallites. The present work aims to transfer this gained knowledge to the formation of zinc oxide films. The influence of hyaluronic acid and the time of its addition on the morphology of the resulting ZnO film were investigated. By meticulous adjustment of the parameters in this step, the film morphology can be tailored to provide an optimal growth platform for the third step (a subsequent chemical bath deposition step). In this step, the film is covered by a dense layer of ZnO. This optimized procedure leads to ZnO films with a very high electrical conductivity, opening up interesting possibilities for applications of such films. The films were characterized by means of electron microscopy, X-ray diffraction and measurements of the electrical conductivity.BMB
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