41 research outputs found
Euclidean Wilson loops and Minimal Area Surfaces in Minkowski AdS3
The AdS/CFT correspondence relates Wilson loops in N=4 SYM theory to minimal
area surfaces in AdS5xS5 space. If the Wilson loop is Euclidean and confined to
a plane (t,x) then the dual surface is Euclidean and lives in Minkowski AdS3.
In this paper we study such minimal area surfaces generalizing previous results
obtained in the Euclidean case. Since the surfaces we consider have the
topology of a disk, the holonomy of the flat current vanishes which is
equivalent to the condition that a certain boundary Schroedinger equation has
all its solutions anti-periodic. If the potential for that Schroedinger
equation is found then reconstructing the surface and finding the area become
simpler. In particular we write a formula for the Area in terms of the
Schwarzian derivative of the contour. Finally an infinite parameter family of
analytical solutions using Riemann Theta functions is described. In this case,
both the area and the shape of the surface are given analytically and used to
check the previous results.Comment: 45 pages, 4 figures, LaTe
A note on the S-matrix bootstrap for the 2d O(N) bosonic model
In this work we apply the S-matrix bootstrap maximization program to the 2d
bosonic O(N) integrable model which has N species of scalar particles of mass m
and no bound states. Since in previous studies theories were defined by
maximizing the coupling between particles and their bound states, the main
problem appears to be to find what other functional can be used to define this
model. Instead, we argue that the defining property of this integrable model is
that it resides at a vertex of the convex space determined by the unitarity and
crossing constraints. Thus, the integrable model can be found by maximizing any
linear functional whose gradient points in the general direction of the vertex,
namely within a cone determined by the normals to the faces intersecting at the
vertex. This is a standard problem in applied mathematics, related to
semi-definite programming and solvable by fast available numerical algorithms.
The information provided by the numerical solution is enough to reproduce the
known analytical solution without using integrability, namely the Yang-Baxter
equation. This situation seems quite generic so we expect that other theories
without continuous parameters can also be found by maximizing linear
functionals in the convex space of allowed S-matrices.Comment: 32 pages, 9 figures, LaTeX. v2: references adde
Double-helix Wilson loops: case of two angular momenta
Recently, Wilson loops with the shape of a double helix have played an
important role in studying large spin operators in gauge theories. They
correspond to a quark and an anti-quark moving in circles on an S3 (and
therefore each of them describes a helix in RxS3). In this paper we consider
the case where the particles have two angular momenta on the S3. The string
solution corresponding to such Wilson loop can be found using the relation to
the Neumann-Rosochatius system allowing the computation of the energy and
angular momenta of the configuration. The particular case of only one angular
momentum is also considered. It can be thought as an analytic continuation of
the rotating strings which are dual to operators in the SL(2) sector of N=4
SYM.Comment: 30 pages, 2 figures, LaTeX. v2: Small corrections, reference adde
Rotational knee laxity: Reliability of a simple measurement device in vivo
<p>Abstract</p> <p>Background</p> <p>Double bundle ACL reconstruction has been demonstrated to decrease rotational knee laxity. However, there is no simple, commercially-available device to measure knee rotation. The investigators developed a simple, non-invasive device to measure knee rotation. In conjunction with a rigid boot to rotate the tibia and a force/moment sensor to allow precise determination of torque about the knee, a magnetic tracking system measures the axial rotation of the tibia with respect to the femur. This device has been shown to have acceptable levels of test re-test reliability to measure knee rotation in cadaveric knees.</p> <p>Methods</p> <p>The objective of this study was to determine reliability of the device in measuring knee rotation of human subjects. Specifically, the intra-tester reliability within a single testing session, test-retest reliability between two testing sessions, and inter-tester reliability were assessed for 11 male subjects with normal knees.</p> <p>Results</p> <p>The 95% confidence interval for rotation was less than 5° for intra-tester, test-retest, and inter-tester reliability, and the standard error of measurement for the differences between left and right knees was found to be less than 3°.</p> <p>Conclusion</p> <p>It was found that the knee rotation measurements obtained with this device have acceptable limits of reliability for clinical use and interpretation.</p
Transtibial ACL reconstruction technique fails to position drill tunnels anatomically in vivo 3D CT study
Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures
Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo
Classical string solutions in the AdS/CFT correspondence
This dissertation studies the properties of fields generated by moving charged particles in a strongly interacting gauge theory. In classical electro-magnetism, calculating the fields produced by moving charges is straight forward, but in a strongly interacting non-abelian theory, such as QCD, this not the case due to large quantum effects and the theory being non-linear. Recently, the AdS/CFT correspondence made these calculations feasible, though still non-trivial. Interestingly from a physics point of view, the fields produced by the moving charges are represented by a string. Solving for the string\u27s changing shape is possible due to a nice mathematical application of integrability techniques involving Riemann Theta functions. The first case of consideration is a quark and anti-quark rotating about their center of mass. Such a configuration is described by a rigidly rotating open string with endpoints in the boundary of AdS5. Various cases of angular motion of the quark/anti-quark pair in the boundary is analyzed using an associated 1-d integrable Neumann-Rosochatius system. A solution is found from which the energy and angular momenta of the configuration, ie, the field between the charged particles, is calculated after being properly regularized. The work continues by investigating open strings with endpoints in the boundary of AdS that follow more generic trajectories. Utilizing integrability techniques, the equations of motion are solved when the string moves in AdS3. The Pohlmeyer reduction reduces the equations of motion to a generalized Sinh-Gordon equation from which three cases are studied: the Liouville, Sinh-Gordon, and Cosh-Gordon equations. Solutions to the Sinh and Cosh-Gordon equations are written in terms of Riemann Theta functions and numerical examples of these solutions are presented
The evolved slowly pulsating B star 18 Peg
The predicted width of the upper main sequence in stellar evolution models depends on the empirical calibration of the convective overshooting parameter. Despite decades of discussions, its precise value is still unknown and further observational constraints are required to gauge it. Irrgang et al. ([1]) showed that the B3 III giant 18 Peg is one of the most evolved members of the class of slowly pulsating B (SPB) stars and, thus, bears tremendous potential to derive a tight lower limit for the width of the upper main sequence. In addition, 18 Peg turns out to be part of a single-lined spectroscopic binary system with an eccentric, more than 6-year orbit. The orbital solution, in combination with the absence of additional signatures of the secondary component in the spectroscopic data and the spectral energy distribution, lead to the conclusion that all the observations of 18 Peg are fully compatible with the assumption that the secondary component is either a main-sequence star with a mass of 1-4 M⊙ or a neutron star
The evolved slowly pulsating B star 18 Peg
The predicted width of the upper main sequence in stellar evolution models depends on the empirical calibration of the convective overshooting parameter. Despite decades of discussions, its precise value is still unknown and further observational constraints are required to gauge it. Irrgang et al. ([1]) showed that the B3 II