4,264 research outputs found
Active Carbon and Oxygen Shell Burning Hydrodynamics
We have simulated 2.5 s of the late evolution of a star with full hydrodynamic behavior. We present the first simulations
of a multiple-shell burning epoch, including the concurrent evolution and
interaction of an oxygen and carbon burning shell. In addition, we have evolved
a 3D model of the oxygen burning shell to sufficiently long times (300 s) to
begin to assess the adequacy of the 2D approximation. We summarize striking new
results: (1) strong interactions occur between active carbon and oxygen burning
shells, (2) hydrodynamic wave motions in nonconvective regions, generated at
the convective-radiative boundaries, are energetically important in both 2D and
3D with important consequences for compositional mixing, and (3) a spectrum of
mixed p- and g-modes are unambiguously identified with corresponding adiabatic
waves in these computational domains. We find that 2D convective motions are
exaggerated relative to 3D because of vortex instability in 3D. We discuss the
implications for supernova progenitor evolution and symmetry breaking in core
collapse.Comment: 5 pages, 4 figures in emulateapj format. Accepted for publication in
ApJ Letters. High resolution figure version available at
http://spinach.as.arizona.ed
Analysis and clinical findings of cases positive for the novel synthetic cannabinoid receptor agonist MDMB-CHMICA
Context: MDMB-CHMICA is a synthetic cannabinoid receptor agonist which has caused concern due to its presence in cases of adverse reaction and death. Method: 43 cases of suspected synthetic cannabinoid ingestion were identified from patients presenting at an Emergency Department and from post-mortem casework. These were subjected to liquid-liquid extraction using tertiary-butyl methyl ether and quantitatively analysed by Electospray Ionisation Liquid Chromatography – tandem Mass Spectrometry. For positive samples, case and clinical details were sought and interrogated. Results: 11 samples were found positive for MDMB-CHMICA. Concentrations found ranged from <1 – 22 ng/mL (mean: 6 ng/mL, median: 3 ng/mL). The age range was 15 – 44 years (mean: 26 years, median: 21 years), with the majority (82%) of positive results found in males. Clinical presentations included hypothermia, hypoglycaemia, syncope, recurrent vomiting, altered mental state and serotonin toxicity, with corresponding concentrations of MDMB-CHMICA as low as <1 ng/mL. Duration of hospitalisation ranged from 3 – 24 hours (mean: 12 hours, median: 8 hours). Discussion: The concentration range presented in this case series is indicative of MDMB-CHMICA having a high potency, as is known to be the case for other synthetic cannabinoid receptor agonists. The age range and gender representation were consistent with that reported for users of other drugs of this type. The clinical presentations observed were typical of synthetic cannabinoid receptor agonists and show the difficulties in identifying reactions potentially associated with drugs of this type. Conclusion: The range of MDMB-CHMICA concentrations in Emergency Department presentations (n=9) and post-mortem cases (n=2) was reported. No correlation between the concentration of this drug and clinical presentation or cause of death was reported in this sample. However, the potential for harm associated with low concentrations of MDMB-CHMICA and the
symptoms of toxicity being non-specific was highlighted
Evolution of entanglement within classical light states
We investigate the evolution of quantum correlations over the lifetime of a
multi-photon state. Measurements reveal time-dependent oscillations of the
entanglement fidelity for photon pairs created by a single semiconductor
quantum dot. The oscillations are attributed to the phase acquired in the
intermediate, non-degenerate, exciton-photon state and are consistent with
simulations. We conclude that emission of photon pairs by a typical quantum dot
with finite polarisation splitting is in fact entangled in a time-evolving
state, and not classically correlated as previously regarded
Improved fidelity of triggered entangled photons from single quantum dots
We demonstrate the on-demand emission of polarisation-entangled photon pairs
from the biexciton cascade of a single InAs quantum dot embedded in a GaAs/AlAs
planar microcavity. Improvements in the sample design blue shifts the wetting
layer to reduce the contribution of background light in the measurements.
Results presented show that >70% of the detected photon pairs are entangled.
The high fidelity of the (|HxxHx>+|VxxVx>)/2^0.5 state that we determine is
sufficient to satisfy numerous tests for entanglement. The improved quality of
entanglement represents a significant step towards the realisation of a
practical quantum dot source compatible with applications in quantum
information.Comment: 9 pages. Paper is available free of charge at
http://www.iop.org/EJ/abstract/1367-2630/8/2/029/, see also 'A semiconductor
source of triggered entangled photon pairs', R. M. Stevenson et al., Nature
439, 179 (2006
Precision control of thermal transport in cryogenic single-crystal silicon devices
We report on the diffusive-ballistic thermal conductance of multi-moded
single-crystal silicon beams measured below 1 K. It is shown that the phonon
mean-free-path is a strong function of the surface roughness
characteristics of the beams. This effect is enhanced in diffuse beams with
lengths much larger than , even when the surface is fairly smooth, 5-10
nm rms, and the peak thermal wavelength is 0.6 m. Resonant phonon
scattering has been observed in beams with a pitted surface morphology and
characteristic pit depth of 30 nm. Hence, if the surface roughness is not
adequately controlled, the thermal conductance can vary significantly for
diffuse beams fabricated across a wafer. In contrast, when the beam length is
of order , the conductance is dominated by ballistic transport and is
effectively set by the beam area. We have demonstrated a uniformity of 8%
in fractional deviation for ballistic beams, and this deviation is largely set
by the thermal conductance of diffuse beams that support the
micro-electro-mechanical device and electrical leads. In addition, we have
found no evidence for excess specific heat in single-crystal silicon membranes.
This allows for the precise control of the device heat capacity with normal
metal films. We discuss the results in the context of the design and
fabrication of large-format arrays of far-infrared and millimeter wavelength
cryogenic detectors
Optimal Renormalization Scale and Scheme for Exclusive Processes
We use the BLM method to fix the renormalization scale of the QCD coupling in
exclusive hadronic amplitudes such as the pion form factor and the
photon-to-pion transition form factor at large momentum transfer.
Renormalization-scheme-independent commensurate scale relations are established
which connect the hard scattering subprocess amplitudes that control exclusive
processes to other QCD observables such as the heavy quark potential and the
electron-positron annihilation cross section. The commensurate scale relation
connecting the heavy quark potential, as determined from lattice gauge theory,
to the photon-to-pion transition form factor is in excellent agreement with
data assuming that the pion distribution amplitude is
close to its asymptotic form . We also reproduce the
scaling and normalization of the data at large
momentum transfer. Because the renormalization scale is small, we argue that
the effective coupling is nearly constant, thus accounting for the nominal
scaling behavior of the data. However, the normalization of the space-like pion
form factor obtained from electroproduction experiments is
somewhat higher than that predicted by the corresponding commensurate scale
relation. This discrepancy may be due to systematic errors introduced by the
extrapolation of the electroproduction data to the
pion pole.Comment: 22 pages, Latex, 7 Latex figures. Several references added,
discussion of scale fixing revised for clarity. Final version to appear in
Phys. Rev.
Experimental demonstration of a squeezing enhanced power recycled Michelson interferometer for gravitational wave detection
Interferometric gravitational wave detectors are expected to be limited by
shot noise at some frequencies. We experimentally demonstrate that a power
recycled Michelson with squeezed light injected into the dark port can overcome
this limit. An improvement in the signal-to-noise ratio of 2.3dB is measured
and locked stably for long periods of time. The configuration, control and
signal readout of our experiment are compatible with current gravitational wave
detector designs. We consider the application of our system to long baseline
interferometer designs such as LIGO.Comment: 4 pages 4 figure
Effects of multiple phase transitions in a three-dimensional spherical model of convection in Earth's mantle
Numerical models of mantle convection that incorporate the major mantle phase changes of the transition zone reveal an inherently three-dimensional flow pattern, with cylindrical features and linear features that behave differently in their ability to penetrate the 670-km discontinuity. The dynamics are dominated by accumulation of cold linear downwellings into rounded pools above the endothermic phase change at 670 km depth, resulting in frequent “avalanches” of upper mantle material into the lower mantle. The effect of the exothermic phase transition at 400 km depth is to reduce the overall degree of layering by pushing material through the 670-km phase change, resulting in smaller and more frequent avalanches, and a wider range of morphologies. Large quantities of avalanched cold material accumulate above the coremantle boundary (CMB), resulting in a region of strongly depressed mean temperature at the base of the mantle. The 670-km phase change has a strong effect on the temperature field, with three-distinct regions being visible: (1) the upper mantle, containing linear downwellings and pools of cold material in the transition zone and characterized by a high amplitude long wavelength spectrum; (2) the midmantle, containing quasi-cylindrical avalanche conduits and characterized by a low amplitude, broad spectrum; and (3) the deep mantle, containing large pools of cold, avalanched material and characterized by a high amplitude, ultra-red (i.e., long wavelength) spectrum. The effect on the velocity field is very different. Flow penetration across the 670-km phase change is strongly wavelength-dependent, with easy penetration at long wavelengths but strong inhibition at short wavelengths. Thus, when comparing numerical models with long wavelength seismic tomography, diagnostics based on the density field, such as the radial correlation function, are much more sensitive to the effects of phase transitions than those based on the velocity field. The amplitude of the geoid is not significantly affected by the partial layering, because the contribution from the strong heterogeneity in the transition zone is almost perfectly balanced by the contribution from deflection of the 670-km discontinuity. Avalanches are associated with geoid lows. However, a more complex viscosity structure is required to correctly match the sign of the geoid over slabs in Earth
Shareholder protection, income inequality and social health:a proposed research agenda
This paper develops a proposed research agenda in order to highlight how corporate governance, accounting and company law are relevant to the consideration of income inequality and wider social health. To illustrate this proposed research agenda, this paper draws on corporate governance research in the law and finance tradition, as well as macro-level studies in accounting concerned with the wider corporate governance context, in order to consider the association between shareholder protection, income inequality and child mortality. Under 5 child mortality is an objective indication of a country’s ability to nurture its children. In an influential body of work, La Porta et al. (1997a, 1997b, 1998, 2008) concluded that a common law legal system which protected the interests of shareholders gave rise to better economic and social outcomes. However, drawing on corporate governance and accounting literature we contend that such a conclusion is flawed. The findings of this paper suggest that common law countries (i.e. those with the greater legal protection for investors) have worse social outcomes in terms of under-5 child mortality.PostprintPeer reviewe
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