805 research outputs found
Proposal for Parasitic Dual Target Irradiation with Muon Spill Beam Behind FNAL Experiment 319.
Growing spatial correlations of particle displacements in a simulated liquid on cooling toward the glass transition
We define a correlation function that quantifies the spatial correlation of
single-particle displacements in liquids and amorphous materials. We show for
an equilibrium liquid that this function is related to fluctuations in a bulk
dynamical variable. We evaluate this function using computer simulations of an
equilibrium glass-forming liquid, and show that long range spatial correlations
of displacements emerge and grow on cooling toward the mode coupling critical
temperature
Is the plateau state in GRS 1915+105 equivalent to canonical hard states?
GRS1915+105 is a very peculiar black hole binary that exhibits
accretion-related states that are not observed in any other stellar-mass black
hole system. One of these states, however -- referred to as the plateau state
-- may be related to the canonical hard state of black hole X-ray binaries.
Both the plateau and hard state are associated with steady, relatively lower
X-ray emission and flat/inverted radio emission, that is sometimes resolved
into compact, self-absorbed jets. However, while generally black hole binaries
quench their jets when the luminosity becomes too high, GRS1915+105 seems to
sustain them despite the fact that it accretes at near- or super-Eddington
rates. In order to investigate the relationship between the plateau and the
hard state, we fit two multi-wavelength observations using a steady-state
outflow-dominated model, developed for hard state black hole binaries. The data
sets consist of quasi-simultaneous observations in radio, near-infrared and
X-ray bands. Interestingly, we find both significant differences between the
two plateau states, as well as between the best-fit model parameters and those
representative of the hard state. We discuss our interpretation of these
results, and the possible implications for GRS 1915+105's relationship to
canonical black hole candidates.Comment: accepted for publication in MNRA
Overfishing and nutrient pollution interact with temperature to disrupt coral reefs down to microbial scales
Losses of corals worldwide emphasize the need to understand what drives reef decline. Stressors such as overfishing and nutrient pollution may reduce resilience of coral reefs by increasing coral?algal competition and reducing coral recruitment, growth and survivorship. Such effects may themselves develop via several mechanisms, including disruption of coral microbiomes. Here we report the results of a 3-year field experiment simulating overfishing and nutrient pollution. These stressors increase turf and macroalgal cover, destabilizing microbiomes, elevating putative pathogen loads, increasing disease more than twofold and increasing mortality up to eightfold. Above-average temperatures exacerbate these effects, further disrupting microbiomes of unhealthy corals and concentrating 80% of mortality in the warmest seasons. Surprisingly, nutrients also increase bacterial opportunism and mortality in corals bitten by parrotfish, turning normal trophic interactions deadly for corals. Thus, overfishing and nutrient pollution impact reefs down to microbial scales, killing corals by sensitizing them to predation, above-average temperatures and bacterial opportunism
Scientific Opportunities with an X-ray Free-Electron Laser Oscillator
An X-ray free-electron laser oscillator (XFELO) is a new type of hard X-ray
source that would produce fully coherent pulses with meV bandwidth and stable
intensity. The XFELO complements existing sources based on self-amplified
spontaneous emission (SASE) from high-gain X-ray free-electron lasers (XFEL)
that produce ultra-short pulses with broad-band chaotic spectra. This report is
based on discussions of scientific opportunities enabled by an XFELO during a
workshop held at SLAC on June 29 - July 1, 2016Comment: 21 pages, 12 figure
Anomalous nonlinear X-ray Compton scattering
X-ray scattering is typically used as a weak linear atomic-scale probe of matter. At high intensities, such as produced at free-electron lasers, nonlinearities can become important, and the probe may no longer be considered weak. Here we report the observation of one of the most fundamental nonlinear X-rayâmatter interactions: the concerted nonlinear Compton scattering of two identical hard X-ray photons producing a single higher-energy photon. The X-ray intensity reached 4 Ă 1020 W cmâ2, corresponding to an electric field well above the atomic unit of strength and within almost four orders of magnitude of the quantum-electrodynamic critical field. We measure a signal from solid beryllium that scales quadratically in intensity, consistent with simultaneous non-resonant two-photon scattering from nearly-free electrons. The high-energy photons show an anomalously large redshift that is incompatible with a free-electron approximation for the ground-state electron distribution, suggesting an enhanced nonlinearity for scattering at large momentum transfer
Anomalous nonlinear X-ray Compton scattering
X-ray scattering is typically used as a weak linear atomic-scale probe of matter. At high intensities, such as produced at free-electron lasers, nonlinearities can become important, and the probe may no longer be considered weak. Here we report the observation of one of the most fundamental nonlinear X-rayâmatter interactions: the concerted nonlinear Compton scattering of two identical hard X-ray photons producing a single higher-energy photon. The X-ray intensity reached 4 Ă 1020 W cmâ2, corresponding to an electric field well above the atomic unit of strength and within almost four orders of magnitude of the quantum-electrodynamic critical field. We measure a signal from solid beryllium that scales quadratically in intensity, consistent with simultaneous non-resonant two-photon scattering from nearly-free electrons. The high-energy photons show an anomalously large redshift that is incompatible with a free-electron approximation for the ground-state electron distribution, suggesting an enhanced nonlinearity for scattering at large momentum transfer
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An interlaboratory comparison of techniques for extracting and analyzing trapped gases in ice cores
We undertook an interlaboratory comparison of techniques used to extract and analyze trapped gases in ice cores. The intercomparison included analyses of standard reference gases and samples of ice from the Greenland Ice Sheet Project 2 (GISP2) site. Concentrations of COâ, CHâ, the ÎŽÂčâžO of Oâ, the ÎŽÂčâ”N of Nâ, and the Oâ/Nâ, and Ar/Nâ ratios were measured in air standards and ice core sampries. The standard reference scales for COâ and CHâ were consistent at the ±2% level. The ΎᎌÂČ/Nâ and ÎŽÂčâžO of Oâ measurements showed substantial deviations between the two laboratories able to measure these ratios. The deviations are probably related to errors associated with calibration of the working standards. The ÎŽáŽŹÊł/Nâ and ÎŽÂčâ”N of Nâ measurements were consistent. Five laboratories analyzed the
CHâ concentration in a 4.2-m section of the GISP2 ice core. The average of 20 discrete CHâ
measurements was 748±10 parts per billion by volume (ppbv). The standard deviation of these measurements was close to the total analytical uncertainty associated with the measurements. In all cases, those laboratories employing a dry extraction technique determined higher CHâ values than laboratories using a wet extraction technique. The origin of this difference is unclear but may involve uncertainties associated with blank corrections. Analyses of the COâ concentration of trapped gases showed extreme variations which cannot be explained by analytical uncertainties alone. Three laboratories measured the [COâ] on 21 discrete depths yielding an average value of 283±13 parts per million by volume (ppmv). In this case, the standard deviation was roughly a factor of 2 greater than the analytical uncertainties. We believe the variability in the measured [COâ] results from impurities in the ice which may have compromised the [COâ] of trapped gases in Greenland ice
Investment in online self-evaluation tests: A theoretical approach
BACKGROUND: Large-scale traumatic events may burden any affected public health system with consequential charges. One major post-disaster, expense factor emerges form early psychological interventions and subsequent, posttraumatic mental health care. Due to the constant increase in mental health care costs, also post-disaster public mental health requires best possible, cost-effective care systems. Screening and monitoring the affected population might be one such area to optimize the charges. METHODS: This paper analyzes the potential cost-effectiveness of monitoring a psychologically traumatized population and to motivate individuals at risk to seek early treatment. As basis for our model served Grossman's health production function, which was modified according to fundamental concepts of cost-benefit analyzes, to match the basic conditions of online monitoring strategies. We then introduce some fundamental concepts of cost-benefit analysis. RESULTS: When performing cost-benefit analyses, policy makers have to consider both direct costs (caused by treatment) and indirect costs (due to non-productivity). Considering both costs sources we find that the use of Internet-based psychometric screening instruments may reduce the duration of future treatment, psychological burden and treatment costs. CONCLUSION: The identification of individuals at risk for PTSD following a disaster may help organizations prevent both the human and the economic costs of this disease. Consequently future research on mental health issues should put more emphasis on the importance of monitoring to detect early PTSD and focus the most effective resources within early treatment and morbidity prevention
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