25,800 research outputs found
Antenna subtraction with hadronic initial states
The antenna subtraction method for the computation of higher order
corrections to jet observables and exclusive cross sections at collider
experiments is extended to include hadronic initial states. In addition to the
already known antenna subtraction with both radiators in the final state
(final-final antennae), we introduce antenna subtractions with one or two
radiators in the initial state (initial-final or initial-initial antennae). For
those, we derive the phase space factorization and discuss the allowed phase
space mappings at NLO and NNLO. We present integrated forms for all antenna
functions relevant to NLO calculations, and describe the construction of the
full antenna subtraction terms at NLO on two examples. The extension of the
formalism to NNLO is outlined.Comment: 33 pages, 3 figure
The Clustering of Massive Halos
The clustering properties of dark matter halos are a firm prediction of
modern theories of structure formation. We use two large volume,
high-resolution N-body simulations to study how the correlation function of
massive dark matter halos depends upon their mass and formation history. We
find that halos with the lowest concentrations are presently more clustered
than those of higher concentration, the size of the effect increasing with halo
mass; this agrees with trends found in studies of lower mass halos. The
clustering dependence on other characterizations of the full mass accretion
history appears weaker than the effect with concentration. Using the integrated
correlation function, marked correlation functions, and a power-law fit to the
correlation function, we find evidence that halos which have recently undergone
a major merger or a large mass gain have slightly enhanced clustering relative
to a randomly chosen population with the same mass distribution.Comment: 10 pages, 8 figures; text improved, references and one figure added;
accepted for publication in Ap
Charged multifluids in general relativity
The exact 1+3 covariant dynamical fluid equations for a multi-component
plasma, together with Maxwell's equations are presented in such a way as to
make them suitable for a gauge-invariant analysis of linear density and
velocity perturbations of the Friedmann-Robertson-Walker model. In the case
where the matter is described by a two component plasma where thermal effects
are neglected, a mode representing high-frequency plasma oscillations is found
in addition to the standard growing and decaying gravitational instability
picture. Further applications of these equations are also discussed.Comment: 14 pages (example added), to appear in Class. Quantum Gra
Efficacy, Safety, and Timing of Anticoagulant Thromboprophylaxis for the Prevention of Venous Thromboembolism in Patients With Acute Spinal Cord Injury: A Systematic Review
Study Design: Systematic review. Objectives: The objective of this study was to answer 5 key questions: What is the comparative effectiveness and safety of (1a) anticoagulant thromboprophylaxis compared to no prophylaxis, placebo, or another anticoagulant strategy for preventing deep vein thrombosis (DVT) and pulmonary embolism (PE) after acute spinal cord injury (SCI)? (1b) Mechanical prophylaxis strategies alone or in combination with other strategies for preventing DVT and PE after acute SCI? (1c) Prophylactic inferior vena cava filter insertion alone or in combination with other strategies for preventing DVT and PE after acute SCI? (2) What is the optimal timing to initiate and/or discontinue anticoagulant, mechanical, and/or prophylactic inferior vena cava filter following acute SCI? (3) What is the cost-effectiveness of these treatment options? Methods: A systematic literature search was conducted to identify studies published through February 28, 2015. We sought randomized controlled trials evaluating efficacy and safety of antithrombotic strategies. Strength of evidence was evaluated using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) system. Results: Nine studies satisfied inclusion criteria. We found a trend toward lower risk of DVT in patients treated with enoxaparin. There were no significant differences in rates of DVT, PE, bleeding, and mortality between patients treated with different types of low-molecular-weight heparin or between low-molecular-weight heparin and unfractionated heparin. Combined anticoagulant and mechanical prophylaxis initiated within 72 hours of SCI resulted in lower risk of DVT than treatment commenced after 72 hours of injury. Conclusion: Prophylactic treatments can be used to lower the risk of venous thromboembolic events in patients with acute SCI, without significant increase in risk of bleeding and mortality and should be initiated within 72 hours. © 2017, © The Author(s) 2017
Master equation for collective spontaneous emission with quantized atomic motion
We derive a markovian master equation for the internal dynamics of an
ensemble of two-level atoms including all effects related to the quantization
of their motion. Our equation provides a unifying picture of the consequences
of recoil and indistinguishability of atoms beyond the Lamb-Dicke regime on
both their dissipative and conservative dynamics, and applies equally well to
distinguishable and indistinguishable atoms. We give general expressions for
the decay rates and the dipole-dipole shifts for any motional states, and we
find closed-form formulas for a number of relevant states (Gaussian states,
Fock states and thermal states). In particular, we show that dipole-dipole
interactions and cooperative photon emission can be modulated through the
external state of motion.Comment: 16 pages, 7 figures, minor correction
Scalar arguments of the mathematical functions defining molecular and turbulent transport of heat and mass in compressible fluids
The advection–diffusion equations defining control volume conservation laws in micrometeorological research are analysed to resolve discrepancies in their appropriate scalar variables for heat and mass transport. A scalar variable that is conserved during vertical motions enables the interpretation of turbulent mixing as ‘diffusion’. Gas-phase heat advection is shown to depend on gradients in the potential temperature (θ), not the temperature (T). Since conduction and radiation depend on T, advection–diffusion of heat depends on gradients of both θ and T. Conservation of θ (the first Law of Thermodynamics) requires including a pressure covariance term in the definition of the turbulent heat flux. Mass advection and diffusion are universally agreed to depend directly on gradients in the gas ‘concentration’ (c), a nonetheless ambiguous term. Depending upon author, c may be defined either as a dimensionless proportion or as a dimensional density, with non-trivial differences for the gas phase. Analyses of atmospheric law, scalar conservation and similarity theory demonstrate that mass advection–diffusion in gases depends on gradients, not in density but rather in a conserved proportion. Flux-tower researchers are encouraged to respect the meteorological tradition of writing conservation equations in terms of scalar variables that are conserved through simple air motions.The authors received funding support from Andalusian regional
government project GEOCARBO (P08-RNM-3721),
the National Institute for Agrarian Research and Technology
(INIA; SUM2006–00010-00–00), the Spanish flux-tower network
CARBORED-ES (Science Ministry project CGL2010-
22193-C04–02), and the European Commission collaborative
project GHG Europe (FP7/2007-2013; grant agreement
244122)
Applications of graphics to support a testbed for autonomous space vehicle operations
Researchers describe their experience using graphics tools and utilities while building an application, AUTOPS, that uses a graphical Machintosh (TM)-like interface for the input and display of data, and animation graphics to enhance the presentation of results of autonomous space vehicle operations simulations. AUTOPS is a test bed for evaluating decisions for intelligent control systems for autonomous vehicles. Decisions made by an intelligent control system, e.g., a revised mission plan, might be displayed to the user in textual format or he can witness the effects of those decisions via out of window graphics animations. Although a textual description conveys essentials, a graphics animation conveys the replanning results in a more convincing way. Similarily, iconic and menu-driven screen interfaces provide the user with more meaningful options and displays. Presented here are experiences with the SunView and TAE Plus graphics tools used for interface design, and the Johnson Space Center Interactive Graphics Laboratory animation graphics tools used for generating out out of the window graphics
A classical analogue of entanglement
We show that quantum entanglement has a very close classical analogue, namely
secret classical correlations. The fundamental analogy stems from the behavior
of quantum entanglement under local operations and classical communication and
the behavior of secret correlations under local operations and public
communication. A large number of derived analogies follow. In particular
teleportation is analogous to the one-time-pad, the concept of ``pure state''
exists in the classical domain, entanglement concentration and dilution are
essentially classical secrecy protocols, and single copy entanglement
manipulations have such a close classical analog that the majorization results
are reproduced in the classical setting. This analogy allows one to import
questions from the quantum domain into the classical one, and vice-versa,
helping to get a better understanding of both. Also, by identifying classical
aspects of quantum entanglement it allows one to identify those aspects of
entanglement which are uniquely quantum mechanical.Comment: 13 pages, references update
Hierarchical Bin Buffering: Online Local Moments for Dynamic External Memory Arrays
Local moments are used for local regression, to compute statistical measures
such as sums, averages, and standard deviations, and to approximate probability
distributions. We consider the case where the data source is a very large I/O
array of size n and we want to compute the first N local moments, for some
constant N. Without precomputation, this requires O(n) time. We develop a
sequence of algorithms of increasing sophistication that use precomputation and
additional buffer space to speed up queries. The simpler algorithms partition
the I/O array into consecutive ranges called bins, and they are applicable not
only to local-moment queries, but also to algebraic queries (MAX, AVERAGE, SUM,
etc.). With N buffers of size sqrt{n}, time complexity drops to O(sqrt n). A
more sophisticated approach uses hierarchical buffering and has a logarithmic
time complexity (O(b log_b n)), when using N hierarchical buffers of size n/b.
Using Overlapped Bin Buffering, we show that only a single buffer is needed, as
with wavelet-based algorithms, but using much less storage. Applications exist
in multidimensional and statistical databases over massive data sets,
interactive image processing, and visualization
An Atlas of Warm AGN and Starbursts from the IRAS Deep Fields
We present 180 AGN candidates based on color selection from the IRAS
slow-scan deep observations, with color criteria broadened from the initial
Point-Source Catalog samples to include similar objects with redshifts up to
z=1 and allowing for two-band detections. Spectroscopic identifications have
been obtained for 80 (44%); some additional ones are secure based on radio
detections or optical morphology, although yet unobserved spectroscopically.
These spectroscopic identifications include 13 Sy 1 galaxies, 17 Sy 2 Seyferts,
29 starbursts, 7 LINER systems, and 13 emission-line galaxies so heavily
reddened as to remain of ambiguous classification. The optical magnitudes range
from R=12.0-20.5; counts suggest that incompleteness is important fainter than
R=15.5. Redshifts extend to z=0.51, with a significant part of the sample at
z>0.2. The sample includes slightly more AGN than star-forming systems among
those where the spectra contain enough diagnostic feature to make the
distinction. The active nuclei include several broad-line objects with strong
Fe II emission, and composite objects with the absorption-line signatures of
fading starbursts. These AGN with warm far-IR colors have little overlap with
the "red AGN" identified with 2MASS; only a single Sy 1 was detected by 2MASS
with J-K > 2. Some reliable IRAS detections have either very faint optical
counterparts or only absorption-line galaxies, potentially being deeply
obscured AGN. The IRAS detections include a newly identified symbiotic star,
and several possible examples of the "Vega phenomenon", including dwarfs as
cool as type K. Appendices detail these candidate stars, and the
optical-identification content of a particularly deep set of high-latitude IRAS
scans (probing the limits of optical identification from IRAS data alone).Comment: ApJ Suppl, in press. Figures converted to JPEG/GIF for better
compression; PDF with full-resolution figures available before publication at
http://www.astr.ua.edu/keel/aoagn.pd
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