36 research outputs found
Particle acceleration in cooling flow clusters of galaxies: the case of Abell 2626
It has recently been proposed a theoretical model which accounts for the
origin of radio mini-halos observed in some cooling flow clusters as related to
electron re-acceleration by MHD turbulence (Gitti, Brunetti & Setti 2002). The
MHD turbulence is assumed to be frozen into the flow of the thermal ICM and
thus amplified in the cooling flow region. Here we present the application of
this model to a new mini-halo candidate, the cluster A2626, and compare the
results with those obtained for the mini-halo in the Perseus cluster. We
present VLA data at 330 MHz and 1.5 GHz of the diffuse radio emission observed
in A2626, and we show that its main properties can be explained by the model.
We find that the power necessary for the re-acceleration of the relic electron
population is only a factor ~ 0.7% of the maximum power that can be extracted
by the cooling flow (as estimated on the basis of the standard model). We also
discuss the observational properties of known mini-halos in connection with
those of host clusters, showing that the radio power of mini--halos increases
with the maximum power of cooling flows. This trend is expected in the
framework of the model. Possible effects of new Chandra and XMM-Newton
estimates of on this trend are considered: we conclude that even if
earlier derived cooling rates were overestimated, cooling flow powers are still
well above the radio powers emitted by mini-halos.Comment: 12 pages, 11 figures, accepted for publication in Astronomy &
Astrophysic
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Short-term stream water temperature observations permit rapid assessment of potential climate change impacts
Assessment of potential climate change impacts on stream water temperature (Tâ) across large scales remains challenging for resource managers because energy exchange processes between the atmosphere and the stream environment are complex and uncertain, and few long-term datasets are available to evaluate changes over time. In this study, we demonstrate how simple monthly linear regression models based on short-term historical Tâ observations and readily available interpolated air temperature (Tâ) estimates can be used for rapid assessment of historical and future changes in Tâ. Models were developed for 61 sites in the southeastern USA using â„18 months of observations and were validated at sites with longer periods of record. The Tâ models were then used to estimate temporal changes in Tâ at each site using both historical estimates and future Tâ projections. Results suggested that the linear regression models adequately explained the variability in Tâ across sites, and the relationships between Tâ and Tâ remained consistent over 37 years. We estimated that most sites had increases in historical annual mean Tâ between 1961 and 2010 (mean of +0.11 °C decadeâ»Âč). All 61 sites were projected to experience increases in Tâ from 2011 to 2060 under the three climate projections evaluated (mean of +0.41 °Cdecadeâ»Âč). Several of the sites with the largest historical and future Tâ changes were located in ecoregions home to temperature-sensitive fish species. This methodology can be used by resource managers for rapid assessment of potential climate change impacts on stream water temperature
Eating Disorder Behaviors Are Increasing: Findings from Two Sequential Community Surveys in South Australia
Background: evidence for an increase in the prevalence of eating disorders is inconsistent. Our aim was to determine change in the population point prevalence of eating disorder behaviors over a 10-year period. \ud
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Methodology/Principal Findings: eating disorder behaviors were assessed in consecutive general population surveys of men and women conducted in 1995 (n = 3001, 72% respondents) and 2005 (n = 3047, 63.1% respondents). Participants were randomly sampled from households in rural and metropolitan South Australia. There was a significant (all p,0.01) and over two-fold increase in the prevalence of binge eating, purging (self-induced vomiting and/or laxative or diuretic misuse) and strict dieting or fasting for weight or shape control among both genders. The most common diagnosis in 2005 was either binge eating disorder or other ââeating\ud
disorders not otherwise specifiedââ (EDNOS; n = 119, 4.2%). \ud
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Conclusions/Significance: in this population sample the point prevalence of eating disorder behaviors increased over the past decade. Cases of anorexia nervosa and bulimia nervosa, as currently defined, remain uncommon
Single Molecule Conformational Memory Extraction: P5ab RNA Hairpin
Extracting kinetic models from single
molecule data is an important
route to mechanistic insight in biophysics, chemistry, and biology.
Data collected from force spectroscopy can probe discrete hops of
a single molecule between different conformational states. Model extraction
from such data is a challenging inverse problem because single molecule
data are noisy and rich in structure. Standard modeling methods normally
assume (i) a prespecified number of discrete states and (ii) that
transitions between states are Markovian. The data set is then fit
to this predetermined model to find a handful of rates describing
the transitions between states. We show that it is unnecessary to
assume either (i) or (ii) and focus our analysis on the zipping/unzipping
transitions of an RNA hairpin. The key is in starting with a very
broad class of non-Markov models in order to let the data guide us
toward the best model from this very broad class. Our method suggests
that there exists a folding intermediate for the P5ab RNA hairpin
whose zipping/unzipping is monitored by force spectroscopy experiments.
This intermediate would not have been resolved if a Markov model had
been assumed from the onset. We compare the merits of our method with
those of others
Interaction of two imidazolium gemini surfactants with two model proteins BSA and HEWL
Gemini surfactants and their interactions with proteins have gained considerable scientific interest, especially when amyloidogenic proteins are taken into account. In this work, the influence of two selected dicationic (gemini) surfactants (3,3âČ-[1,8-(2,7-dioxaoctane)]bis(1-dodecylimidazolium) chloride and 3,3âČ-[1,12-(2,11-dioxadodecane)]bis(1-dodecylimidazolium) chloride) on two model proteins, bovine serum albumin (BSA) and hen egg white lysozyme (HEWL), have been investigated. A pronounced and sophisticated influence on BSA structure has been revealed, including a considerable change of protein radius of gyration as well as substantial alteration of its secondary structure. Radius of gyration has been found to rise significantly with addition of surfactants and to fall down for high surfactants concentration. Similarly, a remarkable fall of secondary structure (α-helix content) has been observed, followed by its partial retrieval for high surfactants concentration. A strong aggregation of BSA has been observed for a confined range of surfactants concentrations as well. In case of HEWL-gemini system, on the other hand, the protein-surfactant interaction was found to be weak. Molecular mechanisms explaining such behaviour of protein-surfactant systems have been proposed. The differences of properties of both studied surfactants have also been discussed
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Towards the solution of the many-electron problem in real materials: Equation of state of the hydrogen chain with state-of-the-art many-body methods
We present numerical results for the equation of state of an infinite chain of hydrogen atoms. A variety of modern many-body methods are employed, with exhaustive cross-checks and validation. Approaches for reaching the continuous space limit and the thermodynamic limit are investigated, proposed, and tested. The detailed comparisons provide a benchmark for assessing the current state of the art in many-body computation, and for the development of new methods. The ground-state energy per atom in the linear chain is accurately determined versus bond length, with a confidence bound given on all uncertainties