753 research outputs found
A Critique of the Link Approach to Exact Lattice Supersymmetry
We examine the link approach to constructing a lattice theory of N=2 super
Yang Mills theory in two dimensions. The goal of this construction is to
provide a discretization of the continuum theory which preserves all
supersymmetries at non-zero lattice spacing. We show that this approach suffers
from an inconsistency and argue that a maximum of just one of the
supersymmetries can be implemented on the lattice.Comment: 7 page
Adaptive strategies for graph state growth in the presence of monitored errors
Graph states (or cluster states) are the entanglement resource that enables
one-way quantum computing. They can be grown by projective measurements on the
component qubits. Such measurements typically carry a significant failure
probability. Moreover, they may generate imperfect entanglement. Here we
describe strategies to adapt growth operations in order to cancel incurred
errors. Nascent states that initially deviate from the ideal graph states
evolve toward the desired high fidelity resource without impractical overheads.
Our analysis extends the diagrammatic language of graph states to include
characteristics such as tilted vertices, weighted edges, and partial fusion,
which arise from experimental imperfections. The strategies we present are
relevant to parity projection schemes such as optical `path erasure' with
distributed matter qubits.Comment: 4 pages, 4 figures. Typos corrected, nicer figures, neater notation
and better rea
Study of the Wall Thermal Condition Effect in a Lean-Premixed Downscaled Can Combustor Using Large-Eddy Simulation
The primary purpose of this study is to evaluate the ability of LES, with a turbulent combustion model based on steady flamelets, to predict the flame stabilization mechanisms in an industrial can combustor at full load conditions. The test case corresponds to the downscaled Siemens can combustor tested in the high pressure rig at the DLR. The effects of the wall temperature on the prediction capabilities of the codes is investigated by imposing several heat transfer conditions at the pilot and chamber walls. The codes used for this work are Alya and OpenFOAM, which are well established CFD codes in the fluid mechanics community. Prior to the simulation, results for 1-D laminar flames at the operating conditions of the combustor are compared with the detailed solutions. Subsequently, results from both codes at the mid-plane are compared against the experimental data available. Acceptable results are obtained for the axial velocity, while discrepancies are more evident for the mixture fraction and the temperature, particularly with Alya. However, both codes showed that the heat losses influence the size and length of the pilot and main flame.The research leading to these results has received funding through the People Programme (Marie Curie Actions) of the
European Unionâs Seventh Framework Programme (FP7, 2007-2013) under the grant agreement No. FP7-290042 for the project
COPA-GT and the European Unionâs Horizon 2020 Programme (2014-2020) and from Brazilian Ministry of Science, Technology
and Innovation through Rede Nacional de Pesquisa (RNP) under the HPC4E Project, grant agreement No. 689772. The authors
thankfully acknowledge the computer resources, technical expertise and assistance provided by the Red Española de Supercomputación (RES).Peer ReviewedPostprint (author's final draft
The orbital motion, absolute mass, and high-altitude winds of exoplanet HD209458b
For extrasolar planets discovered using the radial velocity method, the
spectral characterization of the host star leads to a mass-estimate of the star
and subsequently of the orbiting planet. In contrast, if also the orbital
velocity of the planet would be known, the masses of both star and planet could
be determined directly using Newton's law of gravity, just as in the case of
stellar double-line eclipsing binaries. Here we report on the detection of the
orbital velocity of extrasolar planet HD209458b. High dispersion ground-based
spectroscopy during a transit of this planet reveals absorption lines from
carbon monoxide produced in the planet atmosphere, which shift significantly in
wavelength due to the change in the radial component of the planet orbital
velocity. These observations result in a mass determination of the star and
planet of 1.00+-0.22 Msun and 0.64+-0.09 Mjup respectively. A ~2 km/sec
blueshift of the carbon monoxide signal with respect to the systemic velocity
of the host star suggests the presence of a strong wind flowing from the
irradiated dayside to the non-irradiated nightside of the planet within the
0.01-0.1 mbar atmospheric pressure range probed by these observations. The
strength of the carbon monoxide signal suggests a CO mixing ratio of 1-3x10-3
in this planet's upper atmosphere.Comment: 11 Pages main article and 6 pages suppl. information: A final, edited
version appears in the 24 May 2010 issue of Natur
Detection of carbon monoxide in the high-resolution day-side spectrum of the exoplanet HD 189733b
[Abridged] After many attempts over more than a decade, high-resolution
spectroscopy has recently delivered its first detections of molecular
absorption in exoplanet atmospheres, both in transmission and thermal emission
spectra. Targeting the combined signal from individual lines in molecular
bands, these measurements use variations in the planet radial velocity to
disentangle the planet signal from telluric and stellar contaminants. In this
paper we apply high resolution spectroscopy to probe molecular absorption in
the day-side spectrum of the bright transiting hot Jupiter HD 189733b. We
observed HD 189733b with the CRIRES high-resolution near-infrared spectograph
on the Very Large Telescope during three nights. We detect a 5-sigma absorption
signal from CO at a contrast level of ~4.5e-4 with respect to the stellar
continuum, revealing the planet orbital radial velocity at 154+4/-3 km s-1.
This allows us to solve for the planet and stellar mass in a similar way as for
stellar eclipsing binaries, resulting in Ms= 0.846+0.068/-0.049 Msun and Mp=
1.162+0.058/-0.039 MJup. No significant absorption is detected from H2O, CO2 or
CH4 and we determined upper limits on their line contrasts here. The detection
of CO in the day-side spectrum of HD 189733b can be made consistent with the
haze layer proposed to explain the optical to near-infrared transmission
spectrum if the layer is optically thin at the normal incidence angles probed
by our observations, or if the CO abundance is high enough for the CO
absorption to originate from above the haze. Our non-detection of CO2 at 2.0
micron is not inconsistent with the deep CO2 absorption from low resolution
NICMOS secondary eclipse data in the same wavelength range. If genuine, the
absorption would be so strong that it blanks out any planet light completely in
this wavelength range, leaving no high-resolution signal to be measured.Comment: A&A, accepted for publication. Fig.1 reduced in qualit
Linear Optical Quantum Computing in a Single Spatial Mode
We present a scheme for linear optical quantum computing using time-bin
encoded qubits in a single spatial mode. We show methods for single-qubit
operations and heralded controlled phase (CPhase) gates, providing a sufficient
set of operations for universal quantum computing with the
Knill-Laflamme-Milburn scheme. Our scheme is suited to available photonic
devices and ideally allows arbitrary numbers of qubits to be encoded in the
same spatial mode, demonstrating the potential for time-frequency modes to
dramatically increase the quantum information capacity of fixed spatial
resources. As a test of our scheme, we demonstrate the first entirely single
spatial mode implementation of a two-qubit quantum gate and show its operation
with an average fidelity of 0.84+-0.07.Comment: 5 pages, 4 figures. Updated to be consistent with the published
versio
Efficient growth of complex graph states via imperfect path erasure
Given a suitably large and well connected (complex) graph state, any quantum
algorithm can be implemented purely through local measurements on the
individual qubits. Measurements can also be used to create the graph state:
Path erasure techniques allow one to entangle multiple qubits by determining
only global properties of the qubits. Here, this powerful approach is extended
by demonstrating that even imperfect path erasure can produce the required
graph states with high efficiency. By characterizing the degree of error in
each path erasure attempt, one can subsume the resulting imperfect entanglement
into an extended graph state formalism. The subsequent growth of the improper
graph state can be guided, through a series of strategic decisions, in such a
way as to bound the growth of the error and eventually yield a high-fidelity
graph state. As an implementation of these techniques, we develop an analytic
model for atom (or atom-like) qubits in mismatched cavities, under the
double-heralding entanglement procedure of Barrett and Kok [Phys. Rev. A 71,
060310 (2005)]. Compared to straightforward postselection techniques our
protocol offers a dramatic improvement in growing complex high-fidelity graph
states.Comment: 15 pages, 10 figures (which print to better quality than when viewed
as an on screen pdf
Efficient scheme for three-photon Greenberger-Horne-Zeilinger state generation
We propose an efficient scheme for the generation of three-photon
Greenberger-Horne-Zeilinger (GHZ) state with linear optics and postselection.
Several devices are designed and a two-mode quantum nondemolition (QND)
detection is introduced to obtain the desired state. It is worth noting that
the states which have entanglement in both polarization and spatial degrees of
freedom are created in one of the designed setups. The method described in the
present scheme can create a large number of three-photon GHZ states in
principle. We also discuss an approach to generate the desired GHZ state in the
presence of channel noise.Comment: 7pages, 3 figure
Predicting the risks of kidney failure and death in adults with moderate to severe chronic kidney disease : multinational, longitudinal, population based, cohort study
Acknowledgments We thank the interdisciplinary chronic disease collaboration, the Grampian data safe haven team, and the Danish health data authority team for their administrative support and facilitating the access to the data sources. We thank the nephrology research group patient and family engagement advisory committee, University of Calgary, for their feedback on relevant prediction time horizons and how to visualise both risk predictions simultaneously (eg, KDpredict app and fig 4). We also thank JosĂš Aponte for his support in developing the KDpredict application.Peer reviewe
Harmonization of epidemiology of acute kidney injury and acute kidney disease produces comparable findings across four geographic populations
Acknowledgements: We acknowledge the support of the Grampian Data Safe Haven (DaSH) facility within the Aberdeen Centre for Health Data Science and the associated financial support of the University of Aberdeen, and NHS Research Scotland (through NHS Grampian investment in DaSH). For more information, visit the DaSH website: http://www.abdn.ac.uk/iahs/facilities/grampian-data-safe-haven.php Dr Sawhney is supported by a Starter Grant for Clinical Lecturers from the Academy of Medical Sciences, Wellcome Trust, Medical Research Council, British Heart Foundation, Arthritis Research UK, the Royal College of Physicians and Diabetes UK [SGL020\1076]. Drs James and Tonelli are supported by Canadian Institutes of Health Research Foundation Grants. Dr Black is supported by Health Data Research UK, which is funded by the UK Medical Research Council, Engineering and Physical Sciences Research Council, Economic and Social Research Council, Department of Health and Social Care (England), Chief Scientist Office of the Scottish Government Health and Social Care Directorates, Health and Social Care Research and Development Division (Welsh Government), Public Health Agency (Northern Ireland), British Heart Foundation and the Wellcome Trust.Peer reviewedPublisher PD
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