911 research outputs found

    Galaxy cluster mergers

    Full text link
    We present the results of an Eulerian adaptive mesh refinement (AMR) hydrodynamical and N-body simulation in a Λ\LambdaCDM cosmology. The simulation incorporates common cooling and heating processes for primordial gas. A specific halo finder has been designed and applied in order to extract a sample of galaxy clusters directly obtained from the simulation without considering any resimulating scheme. We have studied the evolutionary history of the cluster halos, and classified them into three categories depending on the merger events they have undergone: major mergers, minor mergers, and relaxed clusters. The main properties of each one of these classes and the differences among them are discussed. The collisions among galaxy clusters are produced naturally by the non-linear evolution in the simulated cosmological volume, no controlled collisions have been considered. We pay special attention to discuss the role of merger events as a source of feedback and reheating, and their effects on the existence of cool cores in galaxy clusters, as well as in the scaling relations.Comment: 17 pages, 11 figures, accepted for publication in MNRA

    A Novel and Cost-Effective Monitoring Approach for Outcomes in an Australian Biodiversity Conservation Incentive Program

    Get PDF
    We report on the design and implementation of ecological monitoring for an Australian biodiversity conservation incentive scheme - the Environmental Stewardship Program. The Program uses competitive auctions to contract individual land managers for up to 15 years to conserve matters of National Environmental Significance (with an initial priority on nationally threatened ecological communities). The ecological monitoring was explicitly aligned with the Program's policy objective and desired outcomes and was applied to the Program's initial Project which targeted the critically endangered White Box-Yellow Box-Blakely's Red Gum Grassy Woodland and Derived Native Grassland ecological community in south eastern Australia. These woodlands have been reduced to <3% of their original extent and persist mostly as small remnants of variable condition on private farmland. We established monitoring sites on 153 farms located over 172,232 sq km. On each farm we established a monitoring site within the woodland patch funded for management and, wherever possible, a matched control site. The monitoring has entailed gathering data on vegetation condition, reptiles and birds. We also gathered data on the costs of experimental design, site establishment, field survey, and data analysis. The costs of monitoring are approximately 8.5% of the Program's investment in the first four years and hence are in broad accord with the general rule of thumb that 5-10% of a program's funding should be invested in monitoring. Once initial monitoring and site benchmarking are completed we propose to implement a novel rotating sampling approach that will maintain scientific integrity while achieving an annual cost-efficiency of up to 23%. We discuss useful lessons relevant to other monitoring programs where there is a need to provide managers with reliable early evidence of program effectiveness and to demonstrate opportunities for cost-efficiencies.Specialist staff within SEWPaC assisted in the design of the monitoring program to ensure its policy relevance. The funders contributed to development of the monitoring program but this did not prejudice the content of the paper in any way. The funders had no role in data collection, analysis and interpretation of results. The funders read and suggested improvements to the manuscript and agreed to publication

    Performance of a novel fast transients detection system

    Get PDF
    We investigate the signal-to-noise ratio (S/N) of a new incoherent dedispersion algorithm optimized for FPGA-based architectures intended for deployment on the Australian SKA Pathfinder and other Square Kilometre Array precursors for fast transients surveys. Unlike conventional CPU- and GPU-optimized incoherent dedispersion algorithms, this algorithm has the freedom to maximize the S/N by way of programmable dispersion profiles that enable the inclusion of different numbers of time samples per spectral channel. This allows, for example, more samples to be summed at lower frequencies where intra-channel dispersion smearing is larger, or it could even be used to optimize the dedispersion sum for steep spectrum sources. Our analysis takes into account the intrinsic pulse width, scatter broadening, spectral index and dispersion measure of the signal, and the system's frequency range, spectral and temporal resolution, and number of trial dedispersions. We show that the system achieves better than 80% of the optimal S/N where the temporal resolution and the intra-channel smearing time are smaller than a quarter of the average width of the pulse across the system's frequency band (after including scatter smearing). Coarse temporal resolutions suffer a Δt –1/2 decay in S/N, and coarse spectral resolutions cause a Δv–1/2 decay in S/N, where Δt and Δv are the temporal and spectral resolutions of the system, respectively. We show how the system's S/N compares with that of matched filter and boxcar filter detectors. We further present a new algorithm for selecting trial dispersion measures for a survey that maintains a given minimum S/N performance across a range of dispersion measures

    A Perspective of Preconception Health Activities in the United States

    Get PDF
    Objectives: Information regarding the type and scope of preconception care programs in the United States is scant. We evaluated State Title V measurement and indicator data and abstracts presented at the National Summit on Preconception Care (June 2005) in order to identify existing programs and innovative strategies for preconception health promotion. Methods: We used the web-based Title V Information System to identify state Performance Measures and Priority Needs pertaining to preconception health as reported for the 2005–2010 Needs Assessment Cycle. We also present a detailed summary of the abstracts presented at the National Summit on Preconception Care. Results: A total of 23 states reported a Priority Need that focused on preconception health and health care. Forty-two states and jurisdictions identified a Performance Measure associated with preconception health or a related indicator (e.g., folic acid, birth spacing, family planning, unintended pregnancy, and healthy weight). Nearly 60 abstracts pertaining to preconception care were presented at the National Summit and included topics such as research, programs, patient or provider toolkits, clinical practice strategies, and public policy. Conclusions: Strategies for improving preconception health have been incorporated into numerous programs throughout the United States. Widespread recognition of the benefits of preconception health promotion is evidenced by the number of states identifying related indicators

    Empirical evidence for unique hues?

    Get PDF
    Red, green, blue, yellow, and white have been distinguished from other hues as unique. We present results from two experiments that undermine existing behavioral evidence to separate the unique hues from other colors. In Experiment 1 we used hue scaling, which has often been used to support the existence of unique hues, but has never been attempted with a set of non-unique primaries. Subjects were assigned to one of two experimental conditions. In the "unique" condition, they rated the proportions of red, yellow, blue, and green that they perceived in each of a series of test stimuli. In the "intermediate" condition, they rated the proportions of teal, purple, orange, and lime. We found, surprisingly, that results from the two conditions were largely equivalent. In Experiment 2, we investigated the effect of instruction on subjects' settings of unique hues. We found that altering the color terms given in the instructions to include intermediate hues led to significant shifts in the hue that subjects identified as unique. The results of both experiments question subjects' abilities to identify certain hues as unique

    Baryon fractions in clusters of galaxies: evidence against a preheating model for entropy generation

    Get PDF
    The Millennium Gas project aims to undertake smoothed-particle hydrodynamic resimulations of the Millennium Simulation, providing many hundred massive galaxy clusters for comparison with X-ray surveys (170 clusters with kTsl > 3 keV). This paper looks at the hot gas and stellar fractions of clusters in simulations with different physical heating mechanisms. These fail to reproduce cool-core systems but are successful in matching the hot gas profiles of non-cool-core clusters. Although there is immense scatter in the observational data, the simulated clusters broadly match the integrated gas fractions within r500 . In line with previous work, however, they fare much less well when compared to the stellar fractions, having a dependence on cluster mass that is much weaker than is observed. The evolution with redshift of the hot gas fraction is much larger in the simulation with early preheating than in one with continual feedback; observations favour the latter model. The strong dependence of hot gas fraction on cluster physics limits its use as a probe of cosmological parameters.Comment: 16 pages, 18 figures, 4 tables. Accepted for publication in MNRA

    Explore, Scale Up, Move Out: Three Phases to Managing Change under Conditions of Uncertainty

    Get PDF
    Private sector development is dominated by the use of ‘good practice’ solutions, driven by a desire of the development donors to control the outcome of development initiatives – with limited success. Bottom?up participatory approaches are more appropriate to find solutions for the complex challenge of market and private sector development. Theory?based approaches are used to design and deliver solutions to economic development challenges. We argue that these approaches have limited potential to manage interventions that target systemic change in complex contexts. On the other hand, alternative approaches based on emergence have some essential shortcomings from the perspective of the international development system. Based on our own working experience, we propose a pragmatic way forward that aims to build on the strengths of emergence?based approaches in complex contexts but is designed to work in the current development environment

    Validation of mDurance, A Wearable Surface Electromyography System for Muscle Activity Assessment

    Get PDF
    The authors wish to thank all participants for their assistance and to Irene Cantarero-Villanueva Ph.D. and Paula Postigo-Martín, of the Department of Physiotherapy (University of Granada, Spain), for providing us with their laboratories and materials so that this study could be carried out.The mDurance® system is an innovative digital tool that combines wearable surface electromyography (sEMG), mobile computing and cloud analysis to streamline and automatize the assessment of muscle activity. The tool is particularly devised to support clinicians and sport professionals in their daily routines, as an assessment tool in the prevention, monitoring rehabilitation and training field. This study aimed at determining the validity of the mDurance system for measuring muscle activity by comparing sEMG output with a reference sEMG system, the Delsys® system. Fifteen participants were tested during isokinetic knee extensions at three different speeds (60, 180, and 300 deg/s), for two muscles (rectus femoris [RF] and vastus lateralis [VL]) and two different electrodes locations (proximal and distal placement). The maximum voluntary isometric contraction was carried out for the normalization of the signal, followed by dynamic isokinetic knee extensions for each speed. The sEMG output for both systems was obtained from the raw sEMG signal following mDurance's processing and filtering. Mean, median, first quartile, third quartile and 90th percentile was calculated from the sEMG amplitude signals for each system. The results show an almost perfect ICC relationship for the VL (ICC > 0.81) and substantial to almost perfect for the RF (ICC > 0.762) for all variables and speeds. The Bland-Altman plots revealed heteroscedasticity of error for mean, quartile 3 and 90th percentile (60 and 300 deg/s) for RF and at mean and 90th percentile for VL (300 deg/s). In conclusion, the results indicate that the mDurance® sEMG system is a valid tool to measure muscle activity during dynamic contractions over a range of speeds. This innovative system provides more time for clinicians (e.g., interpretation patients' pathologies) and sport trainers (e.g., advising athletes), thanks to automatic processing and filtering of the raw sEMG signal and generation of muscle activity reports in real-time

    The impact of mergers on relaxed X-ray clusters - III. Effects on compact cool cores

    Full text link
    (Abridged) We use the simulations presented in Poole et al. 2006 to examine the effects of mergers on compact cool cores in X-ray clusters. We propose a scheme for classifying the morphology of clusters based on their surface brightness and entropy profiles. Three dominant morphologies emerge: two hosting compact cores and central temperatures which are cool (CCC systems) or warm (CWC systems) and one hosting extended cores which are warm (EWC systems). We find that CCC states are disrupted only after direct collisions between cluster cores in head-on collisions or during second pericentric passage in off-axis mergers. By the time they relax, our remnant cores have generally been heated to warm core (CWC or EWC) states but subsequently recover CCC states. The only case resulting in a long-lived EWC state is a slightly off-axis 3:1 merger for which the majority of shock heating occurs during the accretion of a low-entropy stream formed from the disruption of the secondary's core. Compression prevents core temperatures from falling until after relaxation thus explaining the observed population of relaxed CWC systems with no need to invoke AGN feedback. The morphological segregation observed in the L_x-T_x and beta-r_c scaling relations is reflected in our simulations as well. However, none of the cases we have studied produce sufficiently high remnant central entropies to account for the most under-luminous EWC systems observed. Lastly, systems which initially host central metallicity gradients do not yield merger remnants with flat metallicity profiles. Taken together, these results suggest that once formed, compact core systems are remarkably stable against disruption from mergers. It remains to be demonstrated exactly how the sizable observed population of extended core systems was formed.Comment: 19 pages, 8 figures, submitted for publication in MNRA
    • …
    corecore