1,931 research outputs found
On the occurrence of Radio Halos in galaxy clusters - Insight from a mass-selected sample
Giant radio halos (RH) are diffuse Mpc-scale synchrotron sources detected in
a fraction of massive and merging galaxy clusters. An unbiased study of the
statistical properties of RHs is crucial to constrain their origin and
evolution. We aim at investigating the occurrence of RHs and its dependence on
the cluster mass in a SZ-selected sample of galaxy clusters, which is as close
as possible to be a mass-selected sample. Moreover, we analyse the connection
between RHs and merging clusters. We select from the Planck SZ catalogue
(Planck Collaboration XXIX 2014) clusters with
at z=0.08-0.33 and we search for the presence of RHs using the NVSS for z<0.2
and the GMRT RH survey (GRHS, Venturi et al. 2007, 2008) and its extension
(EGRHS, Kale et al. 2013, 2015) for 0.2<z<0.33. We use archival Chandra X-ray
data to derive information on the clusters dynamical status. We confirm that RH
clusters are merging systems while the majority of clusters without RH are
relaxed, thus supporting the idea that mergers play a fundamental role in the
generation of RHs. We find evidence for an increase of the fraction of clusters
with RHs with the cluster mass and this is in line with expectations derived on
the basis of the turbulence re-acceleration scenario. Finally, we discuss the
effect of the incompleteness of our sample on this result.Comment: 11 pages, 7 figures, accepted for publication in A&
The Extended GMRT Radio Halo Survey I: New upper limits on radio halos and mini-halos
A fraction of galaxy clusters host diffuse radio sources called radio halos,
radio relics and mini-halos. We present the sample and first results from the
Extended GMRT Radio Halo Survey (EGRHS)- an extension of the GMRT Radio Halo
Survey (GRHS, Venturi et al. 2007, 2008). It is a systematic radio survey of
galaxy clusters selected from the REFLEX and eBCS X-ray catalogs . Analysis of
GMRT data at 610/ 235/ 325 MHz on 12 galaxy clusters are presented. We report
the detection of a newly discovered mini-halo in the cluster RXJ1532.9+3021 at
610 MHz. A small scale relic (~200 kpc) is suspected in the cluster Z348. We do
not detect cluster-scale diffuse emission in 11 clusters. Robust upper limits
on the detection of radio halo of size of 1 Mpc are determined. We also present
upper limits on the detections of mini-halos in a sub-sample of cool-core
clusters. The upper limits for radio halos and mini-halos are plotted in the
radio power- X-ray luminosity plane and the correlations are discussed. Diffuse
extended emission, not related to the target clusters, but detected as
by-products in the sensitive images of two of the cluster fields (A689 and
RXJ0439.0+0715) are reported. Based on the information about the presence of
radio halos (or upper limits), available on 48 clusters out of the total sample
of 67 clusters (EGRHS+GRHS), we find that ~23% of the clusters host radio
halos. The radio halo fraction rises to ~31%, when only the clusters with X-ray
luminosities >8x10^44 erg/s are considered. Mini-halos are found in ~50 % of
cool-core clusters. A qualitative examination of the X-ray images of the
clusters with no diffuse radio emission indicates that a majority of these
clusters do not show extreme dynamical disturbances and supports the idea that
mergers play an important role in the generation of radio halos/relics.Comment: 21 pages, 18 figures, 3 tables, accepted for publication in A&
Revisiting scaling relations for giant radio halos in galaxy clusters
Many galaxy clusters host Megaparsec-scale radio halos, generated by
ultrarelativistic electrons in the magnetized intracluster medium. Correlations
between the power of radio halos and the thermal properties of the hosting
clusters were established in the last decade, including the connection between
the presence of a halo and cluster mergers. The X-ray luminosity and redshift
limited Extended GMRT Radio Halo Survey provides a rich and unique dataset for
statistical studies of the halos. We uniformly analyze the radio and X-ray data
for the GMRT cluster sample, and use the new Planck SZ catalog, to revisit the
correlations between the power of halos and the thermal properties of galaxy
clusters. We find that the radio power of halos at 1.4 GHz scales with the
cluster X-ray (0.1--2.4 keV) luminosity computed within R_500 as P_1.4
L_500^2.0. Our bigger and more homogenous sample confirms that the X-ray
luminous (L_500 > 5x10^44 erg/s) clusters branch into two populations --- radio
halos lie on the correlation, while clusters with upper limits to radio-halo
emission are well below that correlation. This bimodality remains if we excise
cool cores from the X-ray luminosities. Correlating with Planck data, we find
that P_1.4 scales with the cluster integrated SZ signal within R_500 as P_1.4
Y_500^2.1, in line with previous findings. However, contrary to previous
studies that were limited by incompleteness and small sample size, we find that
the "SZ-luminous" Y_500 > 6x10^-5 Mpc^2 clusters show a bimodal behavior
similar to that in the radio-X-ray diagram. Bimodality of both correlations can
be traced to clusters dynamics, with radio halos found exclusively in merging
clusters. These results confirm the key role of mergers for the origin of giant
radio halos, suggesting that they trigger the relativistic particle
acceleration.Comment: 16 pages, 7 figures, accepted for publication in ApJ on September 12,
201
The Extended GMRT Radio Halo Survey II: Further results and analysis of the full sample
The intra-cluster medium contains cosmic rays and magnetic fields that are
manifested through the large scale synchrotron sources, termed as radio halos,
relics and mini-halos. The Extended Giant Metrewave Radio Telescope (GMRT)
Radio Halo Survey (EGRHS) is an extension of the GMRT Radio Halo Survey (GRHS)
designed to search for radio halos using GMRT 610/235 MHz observations. The
GRHS+EGRHS consists of 64 clusters in the redshift range 0.2 -- 0.4 that have
an X-ray luminosity larger than 5x10^44 erg/s in the 0.1 -- 2.4 keV band and
with declinations > -31 deg in the REFLEX and eBCS X-ray cluster catalogues. In
this second paper in the series, GMRT 610/235 MHz data on the last batch of 11
galaxy clusters and the statistical analysis of the full sample are presented.
A new mini-halo in RXJ2129.6+0005 and candidate diffuse sources in Z5247, A2552
and Z1953 are discovered. A unique feature of this survey are the upper limits
on the detections of 1 Mpc sized radio halos; 4 new are presented here making a
total of 31 in the survey. Of the sample, 58 clusters that have adequately
sensitive radio information were used to obtain the most accurate occurrence
fractions so far. The occurrence of radio halos in our X-ray selected sample is
~22%, that of mini-halos is 13% and that of relics is ~5%. The radio power -
X-ray luminosity diagrams for the radio halos and mini-halos with the
detections and upper limits are presented. The morphological estimators namely,
centroid shift (w), concentration parameter (c) and power ratios (P_3/P_0)
derived from the Chandra X-ray images are used as proxies for the dynamical
states of the GRHS+EGRHS clusters. The clusters with radio halos and mini-halos
occupy distinct quadrants in the c-w, c-P_3/P_0 and w - P_3/P_0 planes,
corresponding to the more and less morphological disturbance, respectively. The
non-detections span both the quadrants.Comment: 24 pages, 5 tables, 25 figures, accepted for publication in A&
ELVIS - ELectromagnetic Vector Information Sensor
The ELVIS instrument was recently proposed by the authors for the Indian
Chandrayaan-1 mission to the Moon and is presently under consideration by the
Indian Space Research Organisation (ISRO). The scientific objective of ELVIS is
to explore the electromagnetic environment of the moon. ELVIS samples the full
three-dimensional (3D) electric field vector, E(x,t), up to 18 MHz, with
selective Nyqvist frequency bandwidths down to 5 kHz, and one component of the
magnetic field vector, B(x,t), from a few Hz up to 100 kHz.As a transient
detector, ELVIS is capable of detecting pulses with a minimum pulse width of 5
ns. The instrument comprises three orthogonal electric dipole antennas, one
magnetic search coil antenna and a four-channel digital sampling system,
utilising flexible digital down conversion and filtering together with
state-of-the-art onboard digital signal processing.Comment: 8 pages, 3 figures. Submitted to the DGLR Int. Symposium "To Moon and
Beyond", Bremen, Germany, 2005. Companion paper to arXiv:astro-ph/050921
IMECE2010-38092 AN INVESTIGATION OF ENTERPRISE RESOURCE PLANNING IMPLEMENTATION: EMPIRICAL EVIDENCE FROM INDIAN COMPANIES
ABSTRACT Due to globalization, there is tremendous demand on Indian companies to lower costs, enlarge product assortment, improve product quality, and provide reliable delivery dates through effective and efficient coordination of production and distribution activities. To achieve these conflicting goals, companies must constantly re-engineer or change their business practices and employ information systems like Enterprise Resource Planning (ERP). However, implementing ERP system is a difficult and high cost proposition. There are mixed results of success and failure in different companies. With a survey of manufacturing companies in India and subsequent detailed case study in one ERP implemented company, this study analyzes various parameters of ERP implementations with factor analysis and logit regression analysis. It is revealed that with clear goals of ERP implementation and proper ERP software selection, the companies are benefited in reducing inventory, improving customer service and other intangible benefits. The top management support, strong and meaningful training program are found the enabling factors of its success. It is argued that this study and ERP implementation model proposed in this paper is valuable to researchers and practitioners interested in implementing ERP system. The findings will also be helpful in extracting the better results from ERP implementation
Development and Airworthiness Certification of the Ti6Al4V Inlet Casing Inner Forging
The inlet casing inner has manufactured using Ti-6Al-4V alloy through a closed die-forging route. It undergoes cyclic loads in addition to operating in extreme conditions in high-temperature environments. The demanding mission requirement of these engines necessitates the inlet casing inner to be flawless throughout its life cycle while retaining its structural integrity. It makes the qualification for airworthiness of the casing, a daunting task. In addition, the qualification tests also help to evaluate the design and manufacturing processes (closed die forging) of the inlet casing inner. The tests also provide data for further improvement of the inlet casing inner in terms of strength and fatigue life. It helps to ensure that the inlet casing inner will be able to perform as expected throughout its operational life. All the batch and consolidated test results comply with the relevant ASTM, MIL standards, and test schedule requirements
High Temperature Ferromagnetism with Giant Magnetic Moment in Transparent Co-doped SnO2-d
Occurrence of room temperature ferromagnetism is demonstrated in pulsed laser
deposited thin films of Sn1-xCoxO2-d (x<0.3). Interestingly, films of
Sn0.95Co0.05O2-d grown on R-plane sapphire not only exhibit ferromagnetism with
a Curie temperature close to 650 K, but also a giant magnetic moment of about 7
Bohr-Magneton/Co, not yet reported in any diluted magnetic semiconductor
system. The films are semiconducting and optically highly transparent.Comment: 12 pages, 4 figure
Perceived risk factors for severe Covid-19 symptoms and their association with health behaviours: Findings from the HEBECO study
Background: There remains uncertainty about Covid-19 risk factors. We examined UK adults’ risk perceptions for severe Covid-19 symptoms and whether engaging in concurrent health behaviours is associated with risk perceptions. /
Methods: Cross-sectional analysis of data from the HEBECO study where 2206 UK adults classified potential factors (age 70+, ethnic minority, medical comorbidities, vaping, smoking cigarettes, alcohol drinking, regular physical activity, being overweight, eating unhealthy foods, using nicotine replacement therapy – NRT, lower income, poor housing, being a keyworker) as either increasing, decreasing, or having no impact on severe Covid-19 symptoms. Logistic regressions examined whether engaging in health behaviours was associated with risk perceptions after adjusting for socio-demographic characteristics, health conditions and other behaviours. /
Results: The great majority (89-99%) of adults classified age 70+, having comorbidities, being a key worker, overweight, and from an ethnic minority as increasing the risk. People were less sure about alcohol drinking, vaping, and nicotine replacement therapy use (17.4-29.5% responding ‘don’t know’). Relative to those who did not, those who smoked tobacco, vaped and consumed alcohol had significantly (all p<0.015) higher odds (aORs=1.58 to 5.80) for classifying these behaviours as ‘no impact’ or ‘decreasing risk’, and lower odds (aORs=.25 to .72) for classifying as ‘increasing risk’. Similarly, eating more fruit and vegetables was associated with classifying unhealthy diet as ‘increasing risk’ (aOR=1.37,1.12-1.69), and exercising more with classifying regular physical activity as ‘decreasing risk’ (aOR=2.42,1.75-3.34). /
Conclusions: Risk perceptions for severe Covid-19 symptoms were lower for adults’ own health behaviours, evidencing optimism bias. /
Implications: These risk perceptions may form barriers to changing one’s own unhealthy behaviours or make one less responsive to interventions that refer to the risk of Covid-19 as a motivating factor. Thus, in some cases risk perceptions could help sustain unhealthy behaviours and exacerbate inequalities in health behaviours and outcomes
Discovering Valuable Items from Massive Data
Suppose there is a large collection of items, each with an associated cost
and an inherent utility that is revealed only once we commit to selecting it.
Given a budget on the cumulative cost of the selected items, how can we pick a
subset of maximal value? This task generalizes several important problems such
as multi-arm bandits, active search and the knapsack problem. We present an
algorithm, GP-Select, which utilizes prior knowledge about similarity be- tween
items, expressed as a kernel function. GP-Select uses Gaussian process
prediction to balance exploration (estimating the unknown value of items) and
exploitation (selecting items of high value). We extend GP-Select to be able to
discover sets that simultaneously have high utility and are diverse. Our
preference for diversity can be specified as an arbitrary monotone submodular
function that quantifies the diminishing returns obtained when selecting
similar items. Furthermore, we exploit the structure of the model updates to
achieve an order of magnitude (up to 40X) speedup in our experiments without
resorting to approximations. We provide strong guarantees on the performance of
GP-Select and apply it to three real-world case studies of industrial
relevance: (1) Refreshing a repository of prices in a Global Distribution
System for the travel industry, (2) Identifying diverse, binding-affine
peptides in a vaccine de- sign task and (3) Maximizing clicks in a web-scale
recommender system by recommending items to users
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