1,865 research outputs found
Can giant radio halos probe the merging rate of galaxy clusters?
Radio and X-ray observations of galaxy clusters probe a direct link between
cluster mergers and giant radio halos (RH), suggesting that these sources can
be used as probes of the cluster merging rate with cosmic time. In this paper
we carry out an explorative study that combines the observed fractions of
merging clusters (fm) and RH (fRH) with the merging rate predicted by
cosmological simulations and attempt to infer constraints on merger properties
of clusters that appear disturbed in X-rays and of clusters with RH. We use
morphological parameters to identify merging systems and analyze the currently
largest sample of clusters with radio and X-ray data (M500>6d14 Msun, and
0.2<z<0.33, from the Planck SZ cluster catalogue). We found that in this sample
fm~62-67% while fRH~44-51%. The comparison of the theoretical f_m with the
observed one allows to constrain the combination (xi_m,tau_m), where xi_m and
tau_m are the minimum merger mass ratio and the timescale of merger-induced
disturbance. Assuming tau_m~ 2-3 Gyr, as constrained by simulations, we find
that the observed f_m matches the theoretical one for xi_m~0.1-0.18. This is
consistent with optical and near-IR observations of clusters in the sample
(xi_m~0.14-0.16). The fact that RH are found only in a fraction of merging
clusters may suggest that merger events generating RH are characterized by
larger mass ratio; this seems supported by optical/near-IR observations of RH
clusters in the sample (xi_min~0.2-0.25). Alternatively, RH may be generated in
all mergers but their lifetime is shorter than \tau_m (by ~ fRH/fm). This is an
explorative study, however it suggests that follow up studies using the
forthcoming radio surveys and adequate numerical simulations have the potential
to derive quantitative constraints on the link between cluster merging rate and
RH at different cosmic epochs and for different cluster masses.Comment: 10 pages, 3 figures, accepted for publication in A&
153 MHz GMRT follow-up of steep-spectrum diffuse emission in galaxy clusters
In this paper we present new high sensitivity 153 MHz Giant Meterwave Radio
Telescope follow-up observations of the diffuse steep spectrum cluster radio
sources in the galaxy clusters Abell 521, Abell 697, Abell 1682. Abell 521
hosts a relic, and together with Abell 697 it also hosts a giant very steep
spectrum radio halo. Abell 1682 is a more complex system with candidate steep
spectrum diffuse emission. We imaged the diffuse radio emission in these
clusters at 153 MHz, and provided flux density measurements of all the sources
at this frequency. Our new flux density measurements, coupled with the existing
data at higher frequencies, allow us to study the total spectrum of the halos
and relic over at least one order of magnitude in frequency. Our images confirm
the presence of a very steep "diffuse component" in Abell 1682. We found that
the spectrum of the relic in Abell 521 can be fitted by a single power-law with
from 153 MHz to 5 GHz. Moreover, we confirm that the halos
in Abell 521 and Abell 697 have a very steep spectrum, with
and respectively. Even with the inclusion of the 153 MHz
flux density information it is impossible to discriminate between power-law and
curved spectra, as derived from homogeneous turbulent re-acceleration. The
latter are favored on the basis of simple energetic arguments, and we expect
that LOFAR will finally unveil the shape of the spectra of radio halos below
100 MHz, thus providing clues on their origin.Comment: 11 pages, 6 figures, 3 tables, accepted for publication in A&
The connection between radio halos and cluster mergers and the statistical properties of the radio halo population
We discuss the statistical properties of the radio halo population in galaxy
clusters. Radio bi-modality is observed in galaxy clusters: a fraction of
clusters host giant radio halos while the majority of clusters do not show
evidence of diffuse cluster-scale radio emission. The radio bi-modality has a
correspondence in terms of dynamical state of the hosting clusters showing that
merging clusters host radio halos and follow the well known radio--X-ray
correlation, while more relaxed clusters do not host radio halos and populate a
region well separated from that correlation. These evidences can be understood
in the framework of a scenario where merger-driven turbulence re-accelerate the
radio emitting electrons. We discuss the main statistical expectations of this
scenario underlining the important role of upcoming LOFAR surveys to test
present models.Comment: 11 pages, 2 figures, Invited talk at the conference "Diffuse
Relativistic Plasmas", Bangalore, 1-4 March 2011; accepted for publication in
the Journal of Astrophysics and Astronom
Astrocyte function is affected by aging and not Alzheimer's disease: A preliminary investigation in hippocampi of 3xTg-AD mice
Old age is a risk factor for Alzheimer's disease (AD), which is characterized by hippocampal impairment together with substantial changes in glial cell functions. Are these alterations due to the disease progression or are they a consequence of aging? To start addressing this issue, we studied the expression of specific astrocytic and microglial structural and functional proteins in a validated transgenic model of AD (3×Tg-AD). These mice develop both amyloid plaques and neurofibrillary tangles, and initial signs of the AD-like pathology have been documented as early as three months of age. We compared male 3×Tg-AD mice at 6 and 12 months of age with their wild-type age-matched counterparts. We also investigated neurons by examining the expression of both the microtubule-associated protein 2 (MAP2), a neuronal structural protein, and the brain-derived neurotrophic factor (BDNF). The latter is indeed a crucial indicator for synaptic plasticity and neurogenesis/ neurodegeneration. Our results show that astrocytes are more susceptible to aging than microglia, regardless of mouse genotype. Moreover, we discovered significant agedependent alterations in the expression of proteins responsible for astrocyte-astrocyte and astrocyte-neuron communication, as well as a significant age-dependent decline in BDNF expression. Our data promote further research on the unexplored role of astroglia in both physiological and pathological aging
On the absence of radio halos in clusters with double relics
Pairs of radio relics are believed to form during cluster mergers, and are
best observed when the merger occurs in the plane of the sky. Mergers can also
produce radio halos, through complex processes likely linked to turbulent
re-acceleration of cosmic-ray electrons. However, only some clusters with
double relics also show a radio halo. Here, we present a novel method to derive
upper limits on the radio halo emission, and analyse archival X-ray Chandra
data, as well as galaxy velocity dispersions and lensing data, in order to
understand the key parameter that switches on radio halo emission. We place
upper limits on the halo power below the
correlation for some clusters, confirming that clusters with double relics have
different radio properties. Computing X-ray morphological indicators, we find
that clusters with double relics are associated with the most disturbed
clusters. We also investigate the role of different mass-ratios and
time-since-merger. Data do not indicate that the merger mass ratio has an
impact on the presence or absence of radio halos (the null hypothesis that the
clusters belong to the same group cannot be rejected). However, the data
suggests that the absence of radio halos could be associated with early and
late mergers, but the sample is too small to perform a statistical test. Our
study is limited by the small number of clusters with double relics. Future
surveys with LOFAR, ASKAP, MeerKat and SKA will provide larger samples to
better address this issue.Comment: 12 pages, 7 figures, MNRAS accepte
Optimizing the Use of Behavioral Locking for High-Level Synthesis
The globalization of the electronics supply chain requires effective methods to thwart reverse engineering and IP theft. Logic locking is a promising solution, but there are many open concerns. First, even when applied at a higher level of abstraction, locking may result in significant overhead without improving the security metric. Second, optimizing a security metric is application-dependent and designers must evaluate and compare alternative solutions. We propose a meta-framework to optimize the use of behavioral locking during the high-level synthesis (HLS) of IP cores. Our method operates on chip’s specification (before HLS) and it is compatible with all HLS tools, complementing industrial EDA flows. Our meta-framework supports different strategies to explore the design space and to select points to be locked automatically. We evaluated our method on the optimization of differential entropy, achieving better results than random or topological locking: 1) we always identify a valid solution that optimizes the security metric, while topological and random locking can generate unfeasible solutions; 2) we minimize the number of bits used for locking up to more than 90% (requiring smaller tamper-proof memories); 3) we make better use of hardware resources since we obtain similar overheads but with higher security metric
Parametrical analysis of the degradation of gas phase trichloroetylene in a photocatalytic reactor with titanium dioxide coated glass fiber meshes
El estudio de la degradación de Tricloroetileno (TCE) en aire en un reactor fotocatalÃtico con dióxido de titanio depositado sobre un lecho fijo ha permitido obtener en un trabajo previo, una expresión cinética que contempla la influencia de la concentración del contaminante, la Radiación Incidente y el efecto competitivo del agua y el TCE por los sitios activos del catalizador(1). En este trabajo se resuelve numéricamente la ecuación diferencial en derivadas parciales de transferencia de materia en un reactor fotocatalÃtico constituido por mallas de vidrio con dióxido de titanio depositado e irradiadas mediante radiación UV. Esta solución numérica evita la introducción de un coeficiente de transferencia de materia sobre la superficie catalÃtica, obtenido a partir de correlaciones tÃpicas para interfaces gas-sólido bajo el régimen de flujo correspondiente(2,3). Modificando los parámetros relevantes del sistema resulta posible simular el comportamiento del reactor bajo distintas condiciones de operación.The analysis of Trichloroethylene (TCE) degradation in air in a photocatalytic reactor with titanium dioxide coated on a fixed bed has provided in a previous work, a Kinetic expression which takes into account the pollutant concentration, the Incident Radiation and the competition between water and TCE for the photocatalytic active sites(1). In this work, the numerical solution of the mass transfer partial differential equation in a photocatalytic reactor with glass fiber meshes coated with titanium dioxide and UV irradiated is accomplished. This numerical solution avoids the use of a mass transfer coefficient over the catalytic surface, obtained by means of typical correlations for gas-solid interfaces under the correspondent flow regime(2,3). Changing the relevant system parameters, it is possible to simulate the reactor behaviour under different operation conditions.Fil: Esterkin, C. R.. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria QuÃmica. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria QuÃmica; ArgentinaFil: Negro, Antonio Carlos. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria QuÃmica. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria QuÃmica; ArgentinaFil: Cassano, Alberto Enrique. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria QuÃmica. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria QuÃmica; ArgentinaFil: Alfano, Orlando Mario. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria QuÃmica. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria QuÃmica; Argentin
Quantitative analysis of basic fibroblast growth factor and vascular endothelial growth factor in human colorectal cancer.
Tumour growth is angiogenesis dependent. Some authors suggest a prognostic role of microvessel count in colorectal cancer. We tested the role of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) in the switch to the angiogenic phenotype in 35 patients with colorectal cancer at different stages of disease. We evaluated the two angiogenic factors, by enzyme-linked immunosorbent assay (ELISA), in tumour, peritumoral mucosa, pathological mesenteric and peripheral blood. We used ten endoscopic intestinal biopsies and ten peripheral blood samples from healthy subjects as control. bFGF was significantly lower in tumour tissues and in peritumoral mucosas than in healthy mucosas, whereas VEGF was up-regulated in tumours but not in peritumoral mucosa. Both angiogenic factors were greatly increased in mesenteric blood. VEGF tumour and serum levels were significantly correlated with the stage of disease. bFGF tumour and serum concentration were not correlated with the stage of disease. The high levels of bFGF in mesenteric blood suggest that this growth factor might be abnormally released from tumour tissue and peritumoral mucosa and could function as an early effector in the switch to the angiogenic phenotype. In contrast, VEGF, whose levels show a significant correlation with the stage of disease, could act in a following step, supporting tumour progression
GMRT 150 MHz follow up of diffuse steep spectrum radio emission in galaxy clusters
It has been recently found that a few galaxy clusters host diffuse radio halo
emission with very steep synchrotron spectra ( > 1.6), which may be
classified as Ultra Steep Spectrum Radio Halos (USSRHs). USSRHs are expected in
the turbulence re-acceleration model for the origin of cluster radio halos, and
are best discovered and studied at low frequencies. We performed GMRT follow up
observations of three galaxy clusters at 150MHz, selected from the GMRT radio
halo survey, which are known to host an USSRH or candidate very steep spectrum
diffuse emission. This project is aimed to characterize the low frequency
spectrum of USSRHs for a detailed study of their origin and connection with
cluster mergers. We present preliminary results at 150 MHz of the cluster A697.Comment: 4 pages, 2 figures, Proceedings of the conference "Non-thermal
phenomena in colliding galaxy clusters" (Nice, 15-18 November 2010
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