6,753 research outputs found
High Energy Quark-Antiquark Elastic scattering with Mesonic Exchange
We studies the high energy elastic scattering of quark anti-quark with an
exchange of a mesonic state in the channel with .
Both the normalization factor and the Regge trajectory can be calculated in
PQCD in cases of fixed (non-running) and running coupling constant. The
dependence of the Regge trajectory on the coupling constant is highly
non-linear and the trajectory is of order of in the interesting physical
range.Comment: 29 page
The Small-x Behaviour of the Singlet Polarized Structure Function g_2 in the Double Logarithmic Approximation
The small-x behavior of the singlet contributions to the polarized structure
function g_2(x,Q^2) is calculated in the double-logarithmic approximation of
perturbative QCD. The dominant contribution is due to the gluons which, in
contrast to the unpolarized case, mix with the fermions also in the small-x
domain. We find a power-like growth in 1/x in the odd-signature parts of the
amplitude with the same power as in the singlet function g_1(x,Q^2) at x<< 1.Comment: 20 pages, latex, 3 ps figure
Saturation and geometric scaling in DIS at small x
We present various aspects of the saturation model which provides good
description of inclusive and diffractive DIS at small x. The model uses parton
saturation ideas to take into account unitarity requirements. A new scaling
predicted by the model in the small x domain is successfully confronted with
the data.Comment: Presented at New Trends in HERA Physics 2001, Ringberg Castle,
Tegernsee, Germany, 17-22 June 2001, minor corrections, some references adde
The perioperative use of oral anticoagulants during surgical procedures for carpal tunnel syndrome. A preliminary study
Contains fulltext :
87781.pdf (publisher's version ) (Closed access)BACKGROUND: To evaluate the feasibility of designing a randomized controlled study whether open carpal tunnel release (OCTR) surgery can be performed safely under systemic anticoagulant therapy using acetylsalicylacid (ASA) or acenocoumarol (ACM), this preliminary, observational study was performed. METHODS: Prospectively, during 1 year, data were collected from all patients who underwent conventional OCTR at the neurosurgical department of the Canisius Wilhelmina Hospital, Nijmegen, The Netherlands. Patients continued anticoagulant treatment perioperatively. RESULTS: A total of 364 patients were operated on, of whom 45 continued ASA and seven ACM treatment. Only one patient using ASA complained of a postoperative subcutaneous hemorrhage. In the control group without anticoagulants, none of the patients had a bleeding postoperatively. CONCLUSION: Continuation of anticoagulant treatment is safe for OCTR. The adverse effects of stopping treatment for surgery can be severe. As a result of this study, we have changed our surgery protocol for OCTR and continue anticoagulant treatment perioperatively.1 juli 201
Saturation Effects in Deep Inelastic Scattering at low and its Implications on Diffraction
We present a model based on the concept of saturation for small and
small . With only three parameters we achieve a good description of all Deep
Inelastic Scattering data below . This includes a consistent treatment
of charm and a successful extrapolation into the photoproduction regime. The
same model leads to a roughly constant ratio of diffractive and inclusive cross
section.Comment: 24 pages, 12 figures, Latex-fil
Conformal invariant saturation
We show that, in onium-onium scattering at (very) high energy, a transition
to saturation happens due to quantum fluctuations of QCD dipoles. This
transition starts when the order correction of the dipole loop is
compensated by its faster energy evolution, leading to a negative interference
with the tree level amplitude. After a derivation of the the one-loop dipole
contribution using conformal invariance of the elastic 4-gluon amplitude in
high energy QCD, we obtain an exact expression of the saturation line in the
plane (Y,L) where Y is the total rapidity and L, the logarithm of the onium
scale ratio. It shows universal features implying the Balitskyi - Fadin -
Kuraev - Lipatov (BFKL) evolution kernel and the square of the QCD triple
Pomeron vertex. For large L, only the higher BFKL Eigenvalue contributes,
leading to a saturation depending on leading log perturbative QCD
characteristics. For initial onium scales of same order, however, it involves
an unlimited summation over all conformal BFKL Eigenstates. In all cases,
conformal invariance is preserved for the saturation mechanism based on dipole
loops.Comment: 15 pages,3 eps figures; Version to be published in Nucl.Phys.B., one
more figure, writing improvements, results and conclusion unchange
The correlation potential in density functional theory at the GW-level: spherical atoms
As part of a project to obtain better optical response functions for nano
materials and other systems with strong excitonic effects we here calculate the
exchange-correlation (XC) potential of density-functional theory (DFT) at a
level of approximation which corresponds to the dynamically- screened-exchange
or GW approximation. In this process we have designed a new numerical method
based on cubic splines which appears to be superior to other techniques
previously applied to the "inverse engineering problem" of DFT, i.e., the
problem of finding an XC potential from a known particle density. The
potentials we obtain do not suffer from unphysical ripple and have, to within a
reasonable accuracy, the correct asymptotic tails outside localized systems.
The XC potential is an important ingredient in finding the particle-conserving
excitation energies in atoms and molecules and our potentials perform better in
this regard as compared to the LDA potential, potentials from GGA:s, and a DFT
potential based on MP2 theory.Comment: 13 pages, 9 figure
Loading a Bose-Einstein Condensate onto an Optical Lattice: an Application of Optimal Control Theory to The Non Linear Schr\"odinger Equation
Using a set of general methods developed by Krotov [A. I. Konnov and V. A.
Krotov, Automation and Remote Control, {\bf 60}, 1427 (1999)], we extend the
capabilities of Optimal Control Theory to the Nonlinear Schr\"odinger Equation
(NLSE). The paper begins with a general review of the Krotov approach to
optimization. Although the linearized version of the method is sufficient for
the linear Schr\"odinger equation, the full flexibility of the general method
is required for treatment of the nonlinear Schr\"odinger equation. Formal
equations for the optimization of the NLSE, as well as a concrete algorithm are
presented. As an illustration, we consider a Bose-Einstein condensate initially
at rest in a harmonic trap. A phase develops across the BEC when an optical
lattice potential is turned on. The goal is to counter this effect and keep the
phase flat by adjusting the trap strength. The problem is formulated in the
language of Optimal Control Theory (OCT) and solved using the above
methodology. To our knowledge, this is the first rigorous application of OCT to
the Nonlinear Schr\"odinger equation, a capability that is bound to have
numerous other applications.Comment: 11 pages, 4 figures, A reference added, Some typos correcte
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