13,397 research outputs found
Parametric Strong Gravitational Lensing Analysis of Abell 1689
(Abridged) We measure the mass distribution of galaxy cluster Abell 1689
within 0.3 Mpc/h_70 of the cluster centre using its strong lensing effect on 32
background galaxies. The multiple images are based on those of Broadhurst et
al. 2005 with some modifications. The cluster profile is explored further out
to ~2.5 Mpc/h_70 with weak lensing shear measurements from Broadhurst et al.
2005b. The masses of ~200 cluster galaxies are measured with Fundamental Plane
in order to accurately model the small scale mass structure in the cluster. The
galaxies are modelled as elliptical truncated isothermal spheres. The dark
matter component of the cluster is described by either non-singular isothermal
ellipsoids (NSIE) or elliptical versions of the universal dark matter profile
(ENFW). We use two dark matter haloes to model the smooth DM in the cluster.
The total mass profile is well described by either an NSIS profile with
sigma=1514+-18 km/s and core radius of r_c=71+-5kpc/h_70, or an NFW profile
with C=6.0+-0.5 and r_200=2.82+-0.11 Mpc/h_70. The errors are assumed to be due
to the error in assigning masses to the individual galaxies in the galaxy
component. The derived total mass is in good agreement with the mass profile of
Broadhurst et al. 05. Using also weak lensing we can constrain the profile
further out to r~2.5 Mpc/h_70. The best fit parameters are then sigma=1499+-15
km/s and r_c=66+-5 kpc/h_70 for the NSIS profile and C=7.6+-0.5 and
r_200=2.55+-0.07 Mpc/h_70 for the NFW profile. Using the same image
configuration as Broadhurst et al. 2005 we obtain a strong lensing model that
is superior to that of Broadhurst et al. 2005 (rms of 2.7'' compared to 3.2'').Comment: 43 pages, 22 figures, submitted to the Monthly Notices of the Royal
Astronomical Society after the first referee report. Full resolution paper
available from http://www.usm.uni-muenchen.de/~halkola/A1689
Weak Lensing Mass Reconstruction: Flexion vs Shear
Weak gravitational lensing has proven to be a powerful tool to map directly
the distribution of dark matter in the Universe. The technique, currently used,
relies on the accurate measurement of the gravitational shear that corresponds
to the first-order distortion of the background galaxy images. More recently, a
new technique has been introduced that relies on the accurate measurement of
the gravitational flexion that corresponds to the second-order distortion of
the background galaxy images. This technique should probe structures on smaller
scales than that of a shear analysis. The goal of this paper is to compare the
ability of shear and flexion to reconstruct the dark matter distribution by
taking into account the dispersion in shear and flexion measurements. Our
results show that the flexion is less sensitive than shear for constructing the
convergence maps on scales that are physically feasible for mapping, meaning
that flexion alone not be used to do convergence map reconstruction, even on
small scales.Comment: Submitted to Ap
Fiscal federalism and risk sharing in Germany: the role of size differences
We study the effect of size differences for an optimal risk sharing system of intergovernmental transfers in Germany. The German fiscal transfer system should account for the fact that an optimal insurance mechanism has the property that smaller states contribute a smaller share of their tax revenue to the redistribution mechanism. -- Wir betrachten die Rolle von Größenunterschieden von Gebietskörperschaften für einen optimalen Risikoausgleich im Rahmen eines föderalen Finanzausgleichs in Deutschland. Zunächst wird der Spielraum für einen möglichen Risikoausgleich durch interregionale Ausgleichszahlungen zwischen Gebietskörperschaften in Deutschland analysiert. Es zeigt sich, dass unsystematische Risiken insbesondere aus längerfristigen Entwicklungsunterschieden bestehen. Für das optimale Transfersystem sollte angesichts möglicher Anreizwirkungen solcher Systeme gelten, dass homogene Gebietskörperschaften einen um so größeren Anteil ihres Steueraufkommens in das interregionale Transfersystem einbringen sollten, je größer sie sind.Fiscal federalism,risk sharing,size asymmetry
On the Reverse Engineering of the Citadel Botnet
Citadel is an advanced information-stealing malware which targets financial
information. This malware poses a real threat against the confidentiality and
integrity of personal and business data. A joint operation was recently
conducted by the FBI and the Microsoft Digital Crimes Unit in order to take
down Citadel command-and-control servers. The operation caused some disruption
in the botnet but has not stopped it completely. Due to the complex structure
and advanced anti-reverse engineering techniques, the Citadel malware analysis
process is both challenging and time-consuming. This allows cyber criminals to
carry on with their attacks while the analysis is still in progress. In this
paper, we present the results of the Citadel reverse engineering and provide
additional insight into the functionality, inner workings, and open source
components of the malware. In order to accelerate the reverse engineering
process, we propose a clone-based analysis methodology. Citadel is an offspring
of a previously analyzed malware called Zeus; thus, using the former as a
reference, we can measure and quantify the similarities and differences of the
new variant. Two types of code analysis techniques are provided in the
methodology, namely assembly to source code matching and binary clone
detection. The methodology can help reduce the number of functions requiring
manual analysis. The analysis results prove that the approach is promising in
Citadel malware analysis. Furthermore, the same approach is applicable to
similar malware analysis scenarios.Comment: 10 pages, 17 figures. This is an updated / edited version of a paper
appeared in FPS 201
Immittance Spectroscopy of Smart Components and Novel Devices
AC small-signal immittance spectroscopy is employed as a viable tool to demonstrate electrical characterization, performance improvement, and quality assurance issues of smart materials-based components and novel devices. The variation in the ac response, complemented via dc measurements within a range of tolerating temperature, delineates competing phenomena occurring in the microstructures of these engineering material systems. The results are presented in a generic manner with possible explanations on the mechanisms for two selected Debye-like (nearly ideal) and non-Debye (non-ideal) low-capacitance resistors. This spectroscopic approach allows systematic development of a representative equivalent circuit, considered to be the characteristic of the devices and components, for specific applications
Ionic conductivity and relaxation dynamics in plastic-crystals with nearly globular molecules
We have performed a dielectric investigation of the ionic charge transport
and the relaxation dynamics in plastic-crystalline 1-cyano-adamantane (CNA) and
in two mixtures of CNA with the related plastic crystals adamantane or
2-adamantanon. Ionic charge carriers were provided by adding 1% of Li salt. The
molecules of these compounds have nearly globular shape and, thus, the
so-called revolving-door mechanism assumed to promote ionic charge transport
via molecular reorientations in other PC electrolytes, should not be active
here. Indeed, a comparison of the dc resistivity and the reorientational
alpha-relaxation times in the investigated PCs, reveals complete decoupling of
both dynamics. Similar to other PCs, we find a significant mixing-induced
enhancement of the ionic conductivity. Finally, these solid-state electrolytes
reveal a second relaxation process, slower than the alpha-relaxation, which is
related to ionic hopping. Due to the mentioned decoupling, it can be
unequivocally detected and is not superimposed by the reorientational
contributions as found for most other ionic conductors.Comment: 9 pages, 7 figure
Microlensing events from the 11-year observations of the Wendelstein Calar Alto Pixellensing Project
We present the results of the decade-long M31 observation from the
Wendelstein Calar Alto Pixellensing Project (WeCAPP). WeCAPP has monitored M31
from 1997 till 2008 in both R- and I-filters, thus provides the longest
baseline of all M31 microlensing surveys. The data are analyzed with the
difference imaging analysis, which is most suitable to study variability in
crowded stellar fields. We extracted light curves based on each pixel, and
devised selection criteria that are optimized to identify microlensing events.
This leads to 10 new events, and sums up to a total of 12 microlensing events
from WeCAPP, for which we derive their timescales, flux excesses, and colors
from their light curves. The color of the lensed stars fall between (R-I) =
0.56 to 1.36, with a median of 1.0 mag, in agreement with our expectation that
the sources are most likely bright, red stars at post main-sequence stage. The
event FWHM timescales range from 0.5 to 14 days, with a median of 3 days, in
good agreement with predictions based on the model of Riffeser et al. (2006).Comment: 44 pages, 16 figures, 5 tables. ApJ accepte
Cosmic variance of the galaxy cluster weak lensing signal
Intrinsic variations of the projected density profiles of clusters of
galaxies at fixed mass are a source of uncertainty for cluster weak lensing. We
present a semi-analytical model to account for this effect, based on a
combination of variations in halo concentration, ellipticity and orientation,
and the presence of correlated haloes. We calibrate the parameters of our model
at the 10 per cent level to match the empirical cosmic variance of cluster
profiles at M_200m=10^14...10^15 h^-1 M_sol, z=0.25...0.5 in a cosmological
simulation. We show that weak lensing measurements of clusters significantly
underestimate mass uncertainties if intrinsic profile variations are ignored,
and that our model can be used to provide correct mass likelihoods. Effects on
the achievable accuracy of weak lensing cluster mass measurements are
particularly strong for the most massive clusters and deep observations (with
~20 per cent uncertainty from cosmic variance alone at M_200m=10^15 h^-1 M_sol
and z=0.25), but significant also under typical ground-based conditions. We
show that neglecting intrinsic profile variations leads to biases in the
mass-observable relation constrained with weak lensing, both for intrinsic
scatter and overall scale (the latter at the 15 per cent level). These biases
are in excess of the statistical errors of upcoming surveys and can be avoided
if the cosmic variance of cluster profiles is accounted for.Comment: 14 pages, 6 figures; submitted to MNRA
A GPU Implementation for Two-Dimensional Shallow Water Modeling
In this paper, we present a GPU implementation of a two-dimensional shallow
water model. Water simulations are useful for modeling floods, river/reservoir
behavior, and dam break scenarios. Our GPU implementation shows vast
performance improvements over the original Fortran implementation. By taking
advantage of the GPU, researchers and engineers will be able to study water
systems more efficiently and in greater detail.Comment: 9 pages, 1 figur
- …