7,134 research outputs found
Gamma-rays from dark matter annihilations strongly constrain the substructure in halos
Recently, it has been shown that electrons and positrons from dark matter
(DM) annihilations provide an excellent fit to the Fermi, PAMELA, and HESS
data. Using this DM model, which requires an enhancement of the annihilation
cross section over its standard value to match the observations, we show that
it immediately implies an observable level of gamma-ray emission for the Fermi
telescope from nearby galaxy clusters such as Virgo and Fornax. We show that
this DM model implies a peculiar feature from final state radiation that is a
distinctive signature of DM. Using the EGRET upper limit on the gamma-ray
emission from Virgo, we constrain the minimum mass of substructures within DM
halos to be > 5x10^-3 M_sun -- about four orders of magnitudes larger than the
expectation for cold dark matter. This limits the cutoff scale in the linear
matter power spectrum to k < 35/kpc which can be explained by e.g., warm dark
matter. Very near future Fermi observations will strongly constrain the minimum
mass to be > 10^3 M_sun: if the true substructure cutoff is much smaller than
this, the DM interpretation of the Fermi/PAMELA/HESS data must be wrong. To
address the problem of astrophysical foregrounds, we performed high-resolution,
cosmological simulations of galaxy clusters that include realistic cosmic ray
(CR) physics. We compute the dominating gamma-ray emission signal resulting
from hadronic CR interactions and find that it follows a universal spectrum and
spatial distribution. If we neglect the anomalous enhancement factor and assume
standard values for the cross section and minimum subhalo mass, the same model
of DM predicts comparable levels of the gamma-ray emission from DM
annihilations and CR interactions. This suggests that spectral subtraction
techniques could be applied to detect the annihilation signal.Comment: 5 pages, 2 figures (published version; minor corrections to figures
and result, equation added
Dark Matter and Baryon Fraction at the Virial Radius in Abell 2256
We combine ASCA and ROSAT X-ray data to constrain the radial dark matter
distribution in the primary cluster of A2256, free from the isothermality
assumption. Both instruments indicate that the temperature declines with
radius. The region including the central galaxy has a multicomponent spectrum,
which results in a wide range of allowed central temperatures. We find that the
secondary subcluster has a temperature and luminosity typical of a rich
cluster; however, the ASCA temperature map shows no signs of an advanced
merger. It is therefore assumed that the primary cluster is in hydrostatic
equilibrium. The data then require dark matter density profiles steeper than
rho ~ r^-2.5 in its outer part. Acceptable models have a total mass within
r=1.5 Mpc (the virial radius) of 6.0+-1.5 10^14 Msun at the 90% confidence,
about 1.6 times smaller than the mass derived assuming isothermality. Near the
center, dark matter profiles with and without central cusps are consistent with
the data. Total mass inside the X-ray core (r=0.26 Mpc) is 1.28+-0.08 10^14
Msun, which exceeds the isothermal value by a factor of 1.4. Although the
confidence intervals above may be underestimates since they do not include
possible asymmetry and departures from hydrostatic equilibrium, the behavior of
the mass distribution, if applicable to other clusters, can bring into better
agreement X-ray and lensing mass estimates, but aggravate the ``baryon
catastrophe''. The observed considerable increase in the gas content with
radius, not anticipated by simulations, may imply that a significant fraction
of thermal gas energy comes from sources other than gravity and merger shocks.Comment: Added dynamic argument against advanced merger. Latex, 10 pages, 3
figures; uses emulateapj.sty. ApJ in pres
High-Resolution X-Ray Reflectivity Study of Thin Layered Pt-Electrodes for Integrated Ferroelectric Devices
The structural interface properties of layered Pt/Ti/SiO2/Si electrodes have
been investigated using high-resolution specular and diffuse x-ray reflectivity
under grazing angles. Currently this multilayer system represents a
technological standard as bottom electrodes for ferroelectric thin film
applications. For the electronic and ferroelectric properties of integrated
devices, the film-electrode interface is of crucial importance. We focused on
Pt-100nm/Ti-10nm/SiO2/Si electrodes prepared under annealing conditions as
employed in industrial processing, prior to the deposition of ferroelectric
films. The comparison between annealed and non-annealed electrodes clearly
revealed strong interfacial effects due to interdiffusion and oxidation of Ti,
especially at the Pt-Ti interface. Migration of Ti into the Pt-layer results in
a clear shift of the critical angle due to enclosure of TiO(2-x) within the
Pt-layer. The heterogeneous distribution of TiO(2-x) suggests a diffusion
mechanism mainly along the Pt-grain boundaries. At the SiO2 interface a
relatively weakly oxidized, remaining Ti-layer of 20 Angstroem could be found,
which is most probably correlated with the remaining adhesion to the substrate.Comment: presented at the X-TOP Conference on High-Resolution X-ray
Diffraction and Topography (Sept.13-15 2000), submitted to Journal of Physics
D: Applied Physic
UV Imaging of the Galaxy Cluster CL0939+4713 (Abell 851) at z=0.41
The first UV F300W and F218W WFPC2 observations of the rich galaxy cluster
CL0939+4713 at z=0.41 are presented and discussed. UV/optical two-color and c-m
diagrams of the sources detected in the F300W waveband are constructed. Thanks
to pre-existing HST optical images of the same field a morphological
classification for the majority of these objects is also provided. Moreover,
taking advantage of recent redshift surveys along CL0939+4713 line of sight,
separate diagrams comparing the properties of galaxies belonging to the cluster
and to its close projected field are presented. Possible evolutionary effects
in the UV from z~0.4 to present time are investigated by comparing the
restframe [mid-UV-Optical] colors of galaxies in CL0939+4713 with balloon-borne
data of the Coma cluster, as well as by resorting to suitable galaxy evolution
models. Finally, current attempts to constrain the epoch of the UV-upturn onset
in evolved populations by means of HST UV observations are discussed.Comment: 20 pages, LaTeX, with 6 PostScript figures, Submitted to The
Astrophysical Journal, Figures 1 and 2 have lower resolution than the ApJ
submitted versio
3C 295, a cluster and its cooling flow at z=0.46
We present ROSAT HRI data of the distant and X-ray luminous (L_x(bol)=2.6^
{+0.4}_{-0.2} 10^{45}erg/sec) cluster of galaxies 3C 295. We fit both a
one-dimensional and a two-dimensional isothermal beta-model to the data, the
latter one taking into account the effects of the point spread function (PSF).
For the error analysis of the parameters of the two-dimensional model we
introduce a Monte-Carlo technique. Applying a substructure analysis, by
subtracting a cluster model from the data, we find no evidence for a merger,
but we see a decrement in emission South-East of the center of the cluster,
which might be due to absorption. We confirm previous results by Henry &
Henriksen(1986) that 3C 295 hosts a cooling flow. The equations for the simple
and idealized cooling flow analysis presented here are solely based on the
isothermal beta-model, which fits the data very well, including the center of
the cluster. We determine a cooling flow radius of 60-120kpc and mass accretion
rates of dot{M}=400-900 Msun/y, depending on the applied model and temperature
profile. We also investigate the effects of the ROSAT PSF on our estimate of
dot{M}, which tends to lead to a small overestimate of this quantity if not
taken into account. This increase of dot{M} (10-25%) can be explained by a
shallower gravitational potential inferred by the broader overall profile
caused by the PSF, which diminishes the efficiency of mass accretion. We also
determine the total mass of the cluster using the hydrostatic approach. At a
radius of 2.1 Mpc, we estimate the total mass of the cluster (M{tot}) to be
(9.2 +/- 2.7) 10^{14}Msun. For the gas to total mass ratio we get M{gas}/M{tot}
=0.17-0.31, in very good agreement with the results for other clusters of
galaxies, giving strong evidence for a low density universe.Comment: 26 pages, 7 figures, accepted for publication in Ap
Security of practical private randomness generation
Measurements on entangled quantum systems necessarily yield outcomes that are
intrinsically unpredictable if they violate a Bell inequality. This property
can be used to generate certified randomness in a device-independent way, i.e.,
without making detailed assumptions about the internal working of the quantum
devices used to generate the random numbers. Furthermore these numbers are also
private, i.e., they appear random not only to the user, but also to any
adversary that might possess a perfect description of the devices. Since this
process requires a small initial random seed, one usually speaks of
device-independent randomness expansion.
The purpose of this paper is twofold. First, we point out that in most real,
practical situations, where the concept of device-independence is used as a
protection against unintentional flaws or failures of the quantum apparatuses,
it is sufficient to show that the generated string is random with respect to an
adversary that holds only classical-side information, i.e., proving randomness
against quantum-side information is not necessary. Furthermore, the initial
random seed does not need to be private with respect to the adversary, provided
that it is generated in a way that is independent from the measured systems.
The devices, though, will generate cryptographically-secure randomness that
cannot be predicted by the adversary and thus one can, given access to free
public randomness, talk about private randomness generation.
The theoretical tools to quantify the generated randomness according to these
criteria were already introduced in [S. Pironio et al, Nature 464, 1021
(2010)], but the final results were improperly formulated. The second aim of
this paper is to correct this inaccurate formulation and therefore lay out a
precise theoretical framework for practical device-independent randomness
expansion.Comment: 18 pages. v3: important changes: the present version focuses on
security against classical side-information and a discussion about the
significance of these results has been added. v4: minor changes. v5: small
typos correcte
Is the Butcher-Oemler effect a function of the cluster redshift ?
Using PSPC {\it Rosat} data, we measure x-ray surface brightness profiles,
size and luminosity of the Butcher-Oemler (BO) sample of clusters of galaxies.
The cluster x-ray size, as measured by the Petrosian r_{\eta=2} radius, does
not change with redshift and is independent from x-ray luminosity. On the other
hand, the x-ray luminosity increases with redshift. Considering that fair
samples show no-evolution, or negative luminosity evolution, we conclude that
the BO sample is not formed from the same class of objects observed at
different look-back times. This is in conflict with the usual interpretation of
the Butcher-Oemler as an evolutionary (or redshift-dependent) effect, based on
the assumption that we are comparing the same class of objects at different
redshifts. Other trends present in the BO sample reflect selection criteria
rather than differences in look-back time, as independently confirmed by the
fact that trends loose strength when we enlarge the sample with x-ray selected
sample of clusters. The variety of optical sizes and shapes of the clusters in
the Butcher-Oemler sample, and the Malmquist-like bias, are the reasons for
these selection effects that mimic the trends usually interpreted as changes
due to evolution.Comment: ApJ, in press, scheduled on May, 10 issue. 17 pages & 11 figure
Electronic and phononic properties of the chalcopyrite CuGaS2
The availability of ab initio electronic calculations and the concomitant
techniques for deriving the corresponding lattice dynamics have been profusely
used for calculating thermodynamic and vibrational properties of
semiconductors, as well as their dependence on isotopic masses. The latter have
been compared with experimental data for elemental and binary semiconductors
with different isotopic compositions. Here we present theoretical and
experimental data for several vibronic and thermodynamic properties of CuGa2, a
canonical ternary semiconductor of the chalcopyrite family. Among these
properties are the lattice parameters, the phonon dispersion relations and
densities of states (projected on the Cu, Ga, and S constituents), the specific
heat and the volume thermal expansion coefficient. The calculations were
performed with the ABINIT and VASP codes within the LDA approximation for
exchange and correlation and the results are compared with data obtained on
samples with the natural isotope composition for Cu, Ga and S, as well as for
isotope enriched samples.Comment: 9 pages, 8 Figures, submitted to Phys. Rev
The current state of soil cover in Kazakhstan, problems and solution
The main directions of scientific activity of the U.U.Uspanov Kazakh Research Institute of Soil Science and Agrochemistry is study of regularities in soil formation under anthropogenic pressure; rational use and increase of bio-productivity of soil resources; development of new technologies to improve soil fertility and crop productivity; assessment of the ecological state of soils in the conditions of anthropogenesis and development of measures for their improvement; provision of consulting and practical services for survey and preparation of agrochemical cartograms and map- schemes with various scales
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