Kink-Antikink Unbinding Transition in the Two Dimensional Fully Frustrated XY Model

We carry out the first numerical simulations to directly confirm the existence of a kink-antikink unbinding transition, T_w, along Ising-like domain walls in the two dimensional fully frustrated XY model. We comment on the possible implications of kink-antikink unbinding for the bulk phase transitions of the model.Comment: 8 pages, 10 figures - expanded version of original submission as accepted by Phys. Rev. B. Some correction to the analysis lead to an increase in the value of the kink unbinding transition temperatur

Anamorphic raytracing for synthetic alcove holographic stereograms

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Architecture, 1986.Bibliography: leaves 48-49.by Michael A. Teitel.M.S

Clinical Utility of Echocardiography in Former Preterm Infants with Bronchopulmonary Dysplasia.

BackgroundThe clinical utility of echocardiography for the diagnosis of pulmonary vascular disease (PVD) in former preterm infants with bronchopulmonary dysplasia (BPD) is not established. Elevated pulmonary vascular resistance (PVR) rather than pulmonary artery pressure (PAP) is the hallmark of PVD. We evaluated the utility of echocardiography in infants with BPD in diagnosing pulmonary hypertension and PVD (PVR >3 Wood units × m2) assessed by cardiac catheterization.MethodsA retrospective single center study of 29 infants born ≤29 weeks of gestational age with BPD who underwent cardiac catheterization and echocardiography was performed. PVD was considered present by echocardiography if the tricuspid valve regurgitation jet peak velocity was >2.9 m/sec, post-tricuspid valve shunt systolic flow velocity estimated a right ventricular systolic pressure >35 mm Hg, or systolic septal flattening was present. The utility (accuracy, sensitivity, and positive predictive value [PPV]) of echocardiography in the diagnosis of PVD was tested. Subgroup analysis in patients without post-tricuspid valve shunts was performed. Echocardiographic estimations of right ventricular pressure, dimensions, function, and pulmonary flow measurements were evaluated for correlation with PVR.ResultsThe duration between echocardiography and cardiac catheterization was a median of 1 day (interquartile range, 1-4 days). Accuracy, sensitivity, and PPV of echocardiography in diagnosing PVD were 72%, 90.5%, and 76%, respectively. Accuracy, sensitivity, and PPV increased to 93%, 91.7%, and 100%, respectively, when infants with post-tricuspid valve shunts were excluded. Echocardiography had poor accuracy in estimating the degree of PAP elevation by cardiac catheterization. In infants without post-tricuspid valve shunts, there was moderate to good correlation between indexed PVR and right ventricular myocardial performance index (rho = 0.89, P = .005), systolic to diastolic time index (0.84, P < .001), right to left ventricular diameter ratio at end systole (0.66, P = .003), and pulmonary artery acceleration time (0.48, P = .05).ConclusionsEchocardiography performs well in screening for PVD in infants with BPD and may be diagnostic in the absence of a post-tricuspid valve shunt. However, cardiac catheterization is needed to assess the degree of PAP elevation and PVR. The diagnostic utility of echocardiographic measurements that correlate with PVR should be evaluated prospectively in this patient population

Lattice Gas Dynamics; Application to Driven Vortices in Two Dimensional Superconductors

A continuous time Monte Carlo lattice gas dynamics is developed to model driven steady states of vortices in two dimensional superconducting networks. Dramatic differences are found when compared to a simpler Metropolis dynamics. Subtle finite size effects are found at low temperature, with a moving smectic that becomes unstable to an anisotropic liquid on sufficiently large length scales.Comment: 5 pages, 4 figure

Finite-Size-Scaling at the Jamming Transition: Corrections to Scaling and the Correlation Length Critical Exponent

We carry out a finite size scaling analysis of the jamming transition in frictionless bi-disperse soft core disks in two dimensions. We consider two different jamming protocols: (i) quench from random initial positions, and (ii) quasistatic shearing. By considering the fraction of jammed states as a function of packing fraction for systems with different numbers of particles, we determine the spatial correlation length critical exponent $\nu\approx 1$, and show that corrections to scaling are crucial for analyzing the data. We show that earlier numerical results yielding $\nu<1$ are due to the improper neglect of these corrections.Comment: 5 pages, 4 figures -- slightly revised version as accepted for Phys. Rev. E Rapid Communication

Vortex lattce melting in 2D superconductors and Josephson arrays

Monte Carlo simulations of 2D vortex lattice melting in a thin superconducting film (or alternatively an array of Josephson junctions) are performed in the London limit. Finite size scaling analyses are used to make a detailed test of the dislocation mediated melting theory of KTNHY. We find that the melting transition is weakly first order, with a jump in the shear modulus very close to that predicted by the KTNHY theory. No hexatic liquid phase is found.Comment: 12 pages, 4 figures (available on request from [email protected]), REVTEX [we revise our conclusion on the order of the melting transition from second to first order - new figure 4 added

Interpretation of Ultrasonic Scattering Measurements by Various Flaws from Theoretical Studies

Let me begin by saying that this is part of a program which is very much complementary to and is helped by the experimental program; so I\u27ll repeat, in part, some of the overview comments that Bruce Thompson made this morning. We\u27ve regarded our role as one of trying to plug into the overall program those aspects of the theory of elastic wave scattering which can be developed in a utilitarian way in terms of modern analytical and computational techniques, in a form which I hope can be useful in signal processing, interpretation, design of experiment, etc. To outline our point of view, I\u27m going to first give a survey of what we have been doing and then give some of the results. It\u27s rather shocking to think of the amount of money that goes into an experimental program and its interpretation, if the interpretation is done in terms of acoustic or scalar wave scattering theories, when the differences from proper elastic theory can be as great as those which Bruce Thompson pointed to this morning