717 research outputs found
A first-principles study of oxygen vacancy pinning of domain walls in PbTiO3
We have investigated the interaction of oxygen vacancies and 180-degree
domain walls in tetragonal PbTiO3 using density-functional theory. Our
calculations indicate that the vacancies do have a lower formation energy in
the domain wall than in the bulk, thereby confirming the tendency of these
defects to migrate to, and pin, the domain walls. The pinning energies are
reported for each of the three possible orientations of the original Ti-O-Ti
bonds, and attempts to model the results with simple continuum models are
discussed.Comment: 8 pages, with 3 postscript figures embedded. Uses REVTEX and epsf
macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/lh_dw/index.htm
Site characterisation : astronomical seeing from a turbulence-resolving model
A Lunar Laser Ranging (LLR) system is to form part of geodetic instrumentation to be located at a new fundamental space geodetic
observatory for South Africa. For optimal efficiency, LLR requires optical resolution or so-called astronomical seeing conditions of
~1 arc-second in order to deliver usable ranging data. Site characterisation should include a description of astronomical seeing for
various locations on-site and overall atmospheric conditions. Atmospheric turbulence degrades astronomical seeing. In-situ methods
of determining astronomical seeing are difficult, time-consuming and costly. We propose the use of a turbulence-resolving model
to determine and predict astronomical seeing at a site. Large Eddy Simulation NERSC (Nansen Environmental and Remote Sensing
Centre) Improved Code (LESNIC) is a turbulence-resolving simulation code which models atmospheric turbulence. It has been used
to compile a database of turbulence-resolving simulations, referred to as DATABASE64. This database consists of a collection of
LESNIC runs for a stably stratified planetary boundary layer (SBL) over a homogeneous aerodynamically rough surface. Results from
DATABASE64 for the nocturnal boundary layer are employed to render profiles of the vertical distribution of optical turbulence
(CN
2 profiles). Seeing parameter values are also obtained by making use of DATABASE64 results. The CN
2 profiles and seeing
parameter values obtained from DATABASE64 results are compared with general observational results that have been published in
the literature. The values obtained are consistent with results from field campaigns as reported. Turbulence-resolving models, such
as LESNIC, show potential for delivering and predicting profiles and parameters to characterise astronomical seeing, which are
essential prerequisites for establishing an LLR system at the most suitable site and most suitable on-site location. A two-pronged
approach is envisaged – in addition to modelling, quantitative seeing measurements obtained with an on-site seeing monitor will
be used to verify and calibrate results produced by the LESNIC model.http://www.gssa.org.za/index.php?module=htmlpages&func=display&pid=5nf201
Bologna guidelines for diagnosis and management of adhesive small bowel obstruction (ASBO): 2017 update of the evidence-based guidelines from the world society of emergency surgery ASBO working group
Background
Adhesive small bowel obstruction (ASBO) is a common surgical emergency, causing high morbidity and even some mortality. The adhesions causing such bowel obstructions are typically the footprints of previous abdominal surgical procedures. The present paper presents a revised version of the Bologna guidelines to evidence-based diagnosis and treatment of ASBO. The working group has added paragraphs on prevention of ASBO and special patient groups.
Methods
The guideline was written under the auspices of the World Society of Emergency Surgery by the ASBO working group. A systematic literature search was performed prior to the update of the guidelines to identify relevant new papers on epidemiology, diagnosis, and treatment of ASBO. Literature was critically appraised according to an evidence-based guideline development method. Final recommendations were approved by the workgroup, taking into account the level of evidence of the conclusion.
Recommendations
Adhesion formation might be reduced by minimally invasive surgical techniques and the use of adhesion barriers. Non-operative treatment is effective in most patients with ASBO. Contraindications for non-operative treatment include peritonitis, strangulation, and ischemia. When the adhesive etiology of obstruction is unsure, or when contraindications for non-operative management might be present, CT is the diagnostic technique of choice. The principles of non-operative treatment are nil per os, naso-gastric, or long-tube decompression, and intravenous supplementation with fluids and electrolytes. When operative treatment is required, a laparoscopic approach may be beneficial for selected cases of simple ASBO.
Younger patients have a higher lifetime risk for recurrent ASBO and might therefore benefit from application of adhesion barriers as both primary and secondary prevention.
Discussion
This guideline presents recommendations that can be used by surgeons who treat patients with ASBO. Scientific evidence for some aspects of ASBO management is scarce, in particular aspects relating to special patient groups. Results of a randomized trial of laparoscopic versus open surgery for ASBO are awaited
Equidistribution of zeros of holomorphic sections in the non compact setting
We consider N-tensor powers of a positive Hermitian line bundle L over a
non-compact complex manifold X. In the compact case, B. Shiffman and S.
Zelditch proved that the zeros of random sections become asymptotically
uniformly distributed with respect to the natural measure coming from the
curvature of L, as N tends to infinity. Under certain boundedness assumptions
on the curvature of the canonical line bundle of X and on the Chern form of L
we prove a non-compact version of this result. We give various applications,
including the limiting distribution of zeros of cusp forms with respect to the
principal congruence subgroups of SL2(Z) and to the hyperbolic measure, the
higher dimensional case of arithmetic quotients and the case of orthogonal
polynomials with weights at infinity. We also give estimates for the speed of
convergence of the currents of integration on the zero-divisors.Comment: 25 pages; v.2 is a final update to agree with the published pape
Joint Resummation for Higgs Production
We study the application of the joint resummation formalism to Higgs
production via gluon-gluon fusion at the LHC, defining inverse transforms by
analytic continuation. We work at next-to-leading logarithmic accuracy. We find
that at low Q_T the resummed Higgs Q_T distributions are comparable in the
joint and pure-Q_T formalisms, with relatively small influence from threshold
enhancement in this range. We find a modest (about ten percent) decrease in the
inclusive cross section, relative to pure threshold resummation.Comment: 22 pages, LaTeX, 5 figures as eps file
Recoil and Threshold Corrections in Short-distance Cross Sections
We identify and resum corrections associated with the kinematic recoil of the
hard scattering against soft-gluon emission in single-particle inclusive cross
sections. The method avoids double counting and conserves the flow of partonic
energy. It reproduces threshold resummation for high-p_T single-particle cross
sections, when recoil is neglected, and Q_T-resummation at low Q_T, when
higher-order threshold logarithms are suppressed. We exhibit explicit resummed
cross sections, accurate to next-to-leading logarithm, for electroweak
annihilation and prompt photon inclusive cross sections.Comment: minor modifications of the text, some references added. 51 pages,
LaTeX, 6 figures as eps file
Recommended from our members
Untangling a Web of Lies: Exploring Automated Detection of Deception in Computer-Mediated Communication
Safeguarding organizations against opportunism and severe deception in computer-mediated communication (CMC) presents a major challenge to CIOs and IT managers. New insights into linguistic cues of deception derive from the speech acts innate to CMC. Applying automated text analysis to archival email exchanges in a CMC system as part of a reward program, we assess the ability of word use (micro-level), message development (macro-level), and intertextual exchange cues (meta-level) to detect severe deception by business partners. We empirically assess the predictive ability of our framework using an ordinal multilevel regression model. Results indicate that deceivers minimize the use of referencing and self-deprecation but include more superfluous descriptions and flattery. Deceitful channel partners also over structure their arguments and rapidly mimic the linguistic style of the account manager across dyadic e-mail exchanges. Thanks to its diagnostic value, the proposed framework can support firms’ decision-making and guide compliance monitoring system development
The HASHTAG Project: The First Submillimeter Images of the Andromeda Galaxy from the Ground
Observing nearby galaxies with submillimeter telescopes on the ground has two major challenges. First, the brightness is significantly reduced at long submillimeter wavelengths compared to the brightness at the peak of the dust emission. Second, it is necessary to use a high-pass spatial filter to remove atmospheric noise on large angular scales, which has the unwelcome side effect of also removing the galaxy\u27s large-scale structure. We have developed a technique for producing high-resolution submillimeter images of galaxies of large angular size by using the telescope on the ground to determine the small-scale structure (the large Fourier components) and a space telescope (Herschel or Planck) to determine the large-scale structure (the small Fourier components). Using this technique, we are carrying out the HARP and SCUBA-2 High Resolution Terahertz Andromeda Galaxy Survey (HASHTAG), an international Large Program on the James Clerk Maxwell Telescope, with one aim being to produce the first high-fidelity high-resolution submillimeter images of Andromeda. In this paper, we describe the survey, the method we have developed for combining the space-based and ground-based data, and we present the first HASHTAG images of Andromeda at 450 and 850 μm. We also have created a method to predict the CO(J = 3-2) line flux across M31, which contaminates the 850 μm band. We find that while normally the contamination is below our sensitivity limit, it can be significant (up to 28%) in a few of the brightest regions of the 10 kpc ring. We therefore also provide images with the predicted line emission removed
- …