1,492 research outputs found
Entanglement between charge qubits induced by a common dissipative environment
We study entanglement generation between two charge qubits due to the strong
coupling with a common bosonic environment (Ohmic bath). The coupling to the
boson bath is a source of both quantum noise (leading to decoherence) and an
indirect interaction between qubits. As a result, two effects compete as a
function of the coupling strength with the bath: entanglement generation and
charge localization induced by the bath. These two competing effects lead to a
non-monotonic behavior of the concurrence as a function of the coupling
strength with the bath. As an application, we present results for charge qubits
based on double quantum dots.Comment: 9 pages, 7 figure
ASTROD and ASTROD I -- Overview and Progress
In this paper, we present an overview of ASTROD (Astrodynamical Space Test of
Relativity using Optical Devices) and ASTROD I mission concepts and studies.
The missions employ deep-space laser ranging using drag-free spacecraft to map
the gravitational field in the solar-system. The solar-system gravitational
field is determined by three factors: the dynamic distribution of matter in the
solar system; the dynamic distribution of matter outside the solar system
(galactic, cosmological, etc.) and gravitational waves propagating through the
solar system. Different relativistic theories of gravity make different
predictions of the solar-system gravitational field. Hence, precise
measurements of the solar-system gravitational field test all these. The tests
and observations include: (i) a precise determination of the relativistic
parameters beta and gamma with 3-5 orders of magnitude improvement over
previous measurements; (ii) a 1-2 order of magnitude improvement in the
measurement of G-dot; (iii) a precise determination of any anomalous, constant
acceleration Aa directed towards the Sun; (iv) a measurement of solar angular
momentum via the Lense-Thirring effect; (v) the detection of solar g-mode
oscillations via their changing gravity field, thus, providing a new eye to see
inside the Sun; (vi) precise determination of the planetary orbit elements and
masses; (viii) better determination of the orbits and masses of major
asteroids; (ix) detection and observation of gravitational waves from massive
black holes and galactic binary stars in the frequency range 0.05 mHz to 5 mHz;
and (x) exploring background gravitational-waves.Comment: 17 pages, 6 figures, presented to The Third International ASTROD
Symposium on Laser Astrodynamics, Space Test of Relativity and
Gravitational-Wave Astronomy, Beijing, July 14-16, 2006; International
Journal of Modern Physics D, in press (2008
Multicentre observational study of adherence to Sepsis Six guidelines in emergency general surgery
Background
Evidence-based interventions may reduce mortality in surgical patients. This study documented the prevalence of sepsis, adherence to guidelines in its management, and timing of source control in general surgical patients presenting as an emergency.
Methods
Patients aged 16 years or more presenting with emergency general surgery problems were identified over a 7-day period and then screened for sepsis compliance (using the Sepsis Six standards, devised for severe sepsis) and the timing of source control (whether radiological or surgical). Exploratory analyses examined associations between the mode (emergency department or general practitioner) and time of admission, adherence to the sepsis guidelines, and outcomes (complications or death within 30 days).
Results
Of a total of 5067 patients from 97 hospitals across the UK, 911 (18·0 per cent) fulfilled the criteria for sepsis, 165 (3·3 per cent) for severe sepsis and 24 (0·5 per cent) for septic shock. Timely delivery of all Sepsis Six guidelines for patients with severe sepsis was achieved in four patients. For patients with severe sepsis, 17·6–94·5 per cent of individual guidelines within the Sepsis Six were delivered. Oxygen was the criterion most likely to be missed, followed by blood cultures in all sepsis severity categories. Surgery for source control occurred a median of 19·8 (i.q.r. 10·0–35·4) h after diagnosis. Omission of Sepsis Six parameters did not appear to be associated with an increase in morbidity or mortality.
Conclusion
Although sepsis was common in general surgical patients presenting as an emergency, adherence to severe sepsis guidelines was incomplete in the majority. Despite this, no evidence of harm was apparent
The Structure of IR Luminous Galaxies at 100 Microns
We have observed twenty two galaxies at 100 microns with the Kuiper Airborne
Observatory in order to determine the size of their FIR emitting regions. Most
of these galaxies are luminous far-infrared sources, with L_FIR > 10^11 L_sun.
This data constitutes the highest spatial resolution ever achieved on luminous
galaxies in the far infrared. Our data includes direct measurements of the
spatial structure of the sources, in which we look for departures from point
source profiles. Additionally, comparison of our small beam 100 micron fluxes
with the large beam IRAS fluxes shows how much flux falls beyond our detectors
but within the IRAS beam. Several sources with point- like cores show evidence
for such a net flux deficit. We clearly resolved six of these galaxies at 100
microns and have some evidence for extension in seven others. Those galaxies
which we have resolved can have little of their 100 micron flux directly
emitted by a point-like active galactic nucleus (AGN). Dust heated to ~40 K by
recent bursts of non-nuclear star formation provides the best explanation for
their extreme FIR luminosity. In a few cases, heating of an extended region by
a compact central source is also a plausible option. Assuming the FIR emission
we see is from dust, we also use the sizes we derive to find the dust
temperatures and optical depths at 100 microns which we translate into an
effective visual extinction through the galaxy. Our work shows that studies of
the far infrared structure of luminous infrared galaxies is clearly within the
capabilities of new generation far infrared instrumentation, such as SOFIA and
SIRTF.Comment: 8 tables, 23 figure
Numerical optimization of amplitude-modulated pulses in microwave-driven entanglement generation
Microwave control of trapped ions can provide an implementation of high-fidelity two-qubit gates free from errors induced by photon scattering. Furthermore, microwave conductors may be embedded into a scalable trap structure, providing the chip-level integration of control that is desirable for scaling. Recent developments have demonstrated how amplitude modulation of the gate drive can permit a two-qubit entangling operation to become robust against motional mode noise and other experimental imperfections. Here, we discuss a method for the numerical optimization of the microwave pulse envelope to produce gate pulses with improved resilience, faster operation and higher energy efficiency
Resonant neutrino spin-flavor precession and supernova shock revival
A new mechanism of supernova shock revival is proposed, which involves
resonant spin--flavor precession of neutrinos with a transition magnetic moment
in the magnetic field of the supernova. The mechanism can be operative in
supernovae for transition magnetic moments as small as provided
the neutrino mass squared difference is in the range . It is shown that this mechanism can increase the
neutrino--induced shock reheating energy by about 60\%.Comment: 16 pages, latex, 2 figures. added few reference
Three-generation study of neutrino spin-flavor conversion in supernova and implication for neutrino magnetic moment
We investigate resonant spin-flavor (RSF) conversions of supernova neutrinos
which are induced by the interaction of neutrino magnetic moment and supernova
magnetic fields. From the formulation which includes all three-flavor neutrinos
and anti-neutrinos, we give a new crossing diagram that includes not only
ordinary MSW resonance but also magnetically-induced RSF effect. With the
diagram, it is found that four conversions occur in supernova, two are induced
by the RSF effect and two by the pure MSW. We also numerically calculate
neutrino conversions in supernova matter, using neutrino mixing parameters
inferred from recent experimental results and a realistic supernova progenitor
model. The results indicate that until 0.5 seconds after core bounce, the
RSF-induced transition occurs
efficiently (adiabatic resonance), when \mu_\nu \agt 10^{-12} \mu_B
(B_0 / 5 \times 10^{9} \mathrm G)^{-1}, where is the strength of the
magnetic field at the surface of iron core. We also evaluate the energy
spectrum as a function of at the SuperKamiokande detector and the
Sudbury Neutrino Observatory using the calculated conversion probabilities, and
find that the spectral deformation might have possibility to provide useful
information on neutrino magnetic moment as well as magnetic field strength in
supernovae.Comment: 35 pages, 13 figure
Global Analysis of the post-SNO Solar Neutrino Data for Standard and Non-Standard Oscillation Mechanisms
What can we learn from solar neutrino observations? Is there any solution to
the solar neutrino anomaly which is favored by the present experimental
panorama? After SNO results, is it possible to affirm that neutrinos have mass?
In order to answer such questions we analyze the current available data from
the solar neutrino experiments, including the recent SNO result, in view of
many acceptable solutions to the solar neutrino problem based on different
conversion mechanisms, for the first time, using the same statistical
procedure. This allows us to do a direct comparison of the goodness of the fit
among different solutions, from which we can discuss and conclude on the
current status of each proposed dynamical mechanism. These solutions are based
on different assumptions: (a) neutrino mass and mixing, (b) non-vanishing
neutrino magnetic moment, (c) the existence of non-standard flavor-changing and
non-universal neutrino interactions and (d) the tiny violation of the
equivalence principle. We investigate the quality of the fit provided by each
one of these solutions not only to the total rate measured by all the solar
neutrino experiments but also to the recoil electron energy spectrum measured
at different zenith angles by the Super-Kamiokande collaboration. We conclude
that several non-standard neutrino flavor conversion mechanisms provide a very
good fit to the experimental data which is comparable with (or even slightly
better than) the most famous solution to the solar neutrino anomaly based on
the neutrino oscillation induced by mass.Comment: Minor changes in the solar magnetic field profile used, and some
refferences added. Final version to appear in PR
Cell wall organic matrix composition and biomineralization across reef-building coralline algae under global change.
OnlinePublCrustose coralline algae (CCA) are one of the most important benthic substrate consolidators on coral reefs through their ability to deposit calcium carbonate on an organic matrix in their cell walls. Discrete polysaccharides have been recognized for their role in biomineralization, yet little is known about the carbohydrate composition of organic matrices across CCA taxa and whether they have the capacity to modulate their organic matrix constituents amidst environmental change, particularly the threats of ocean acidification (OA) and warming. We simulated elevated pCO₂ and temperature (IPCC RCP 8.5) and subjected four mid-shelf Great Barrier Reef species of CCA to two months of experimentation. To assess the variability in surficial monosaccharide composition and biomineralization across species and treatments, we determined the monosaccharide composition of the polysaccharides present in the cell walls of surficial algal tissue and quantified calcification. Our results revealed dissimilarity among species' monosaccharide constituents, which suggests that organic matrices are composed of different polysaccharides across CCA taxa. We also found that species differentially modulate composition in response to ocean acidification and warming. Our findings suggest that both variability in composition and ability to modulate monosaccharide abundance may play a crucial role in surficial biomineralization dynamics under the stress of OA and global warming.Ellie Bergstrom, Jelle Lahnstein, Helen Collins, Tessa M. Page, Vincent Bulone, and Guillermo Diaz-Pulid
(Micro)evolutionary changes and the evolutionary potential of bird migration
Seasonal migration is the yearly long-distance movement of individuals between their breeding and wintering grounds. Individuals from nearly every animal group exhibit this behavior, but probably the most iconic migration is carried out by birds, from the classic V-shape formation of geese on migration to the amazing nonstop long-distance flights undertaken by Arctic Terns Sterna paradisaea. In this chapter, we discuss how seasonal migration has shaped the field of evolution. First, this behavior is known to turn on and off quite rapidly, but controversy remains concerning where this behavior first evolved geographically and whether the ancestral state was sedentary or migratory (Fig. 7.1d, e). We review recent work using new analytical techniques to provide insight into this topic. Second, it is widely accepted that there is a large genetic basis to this trait, especially in groups like songbirds that migrate alone and at night precluding any opportunity for learning. Key hypotheses on this topic include shared genetic variation used by different populations to migrate and only few genes being involved in its control. We summarize recent work using new techniques for both phenotype and genotype characterization to evaluate and challenge these hypotheses. Finally, one topic that has received less attention is the role these differences in migratory phenotype could play in the process of speciation. Specifically, many populations breed next to one another but take drastically different routes on migration (Fig. 7.2). This difference could play an important role in reducing gene flow between populations, but our inability to track most birds on migration has so far precluded evaluations of this hypothesis. The advent of new tracking techniques means we can track many more birds with increasing accuracy on migration, and this work has provided important insight into migration's role in speciation that we will review here
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