A Study of Equivalence of SUSY Theories using Adinkras and Super Virasoro Algebras

Supersymmetry (SUSY) theories describe a wide number of quantum field theories with supersymmetric particles interacting. By using two methods, Adinkras and Super Virasoro algebras (SVAs), more information is gained about SUSY theories: (a.) when two representation may be considered equivalent, that is, describing the same physics, and (b.) the derivation of OPE's that do not rely on Wick rotations. Adinkras [1] are objects that encode important information about the theory in graphs. These graphs can be translated into matrices through what is now called a Garden Algebra. In a specfiic example, (d=4, N=4 SUSY theories,) it is found that there are six classes of SUSY theories through studying the Adinkras by one definition. However, using a criterion that is motivated by physical considerations of four dimensional field theories, this number is reduced to only three. Super Virasoro Algebras are close relatives of Super Conformal Algebras that contain a Lie algebra. They can be used to find Operator Product Expansions which are related to two-point correlation functions. By comparison of two different realizations of SVAs (the Geometrically Realization GR and the one developed by Hasiewicz, Thielemans, Troost [2],) we show that one is contained inside the other which allows some new OPEs to be calculated

Calculation of interface tension and stiffness in a two dimensional Ising Model by Monte Carlo simulation

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Physics, 1998.Includes bibliographical references (p. 55).The two dimensional Ising Model is important because it describes various condensed matter systems. At low temperatures, spontaneous symmetry breaking occurs such that two coexisting phases are separated by interfaces. These interfaces can be described as vibrating strings and are characterized by their tension and stiffness. Then the partition function can be calculated as a function of the magnetization with the interface tension and stiffness as parameters. Simulating the two dimensional Ising Model on square lattices of various sizes, the partition function is determined in order to extract the interface tension. The configurations being studied have low probability of actual occurrence and would require a large number of Monte Carlo steps before obtaining a good sampling. By using improved estimators and a trial distribution, fewer steps are needed. Improved estimators decrease the number of steps to achieve a certain level of accuracy. The trial distribution allows increased statistics once the general shape of the probability distribution is calculated from a Monte Carlo simulation. For small lattice sizes, it is easy to run Monte Carlo simulations to generate the trial distribution. At larger lattice sizes, it is necessary to build the trial distribution from a combination of a Monte Carlo simulation and an Ansatz from theory due to lower statistics. The extracted values of the interface tension agree with the analytical solution by Onsager.by Isaac Samuel Chappell, II.S.M

Evaluation of magnetic resonance imaging relaxation time in wrist cartilage with scapholunate ligament injury

Objective: The overall goal of this research is to identify completely non-invasive in vivo markers of cartilage degeneration following wrist injury in order to facilitate assessment and treatment of wrist injuries and prevention of osteoarthritis as a result of injury. In this study, the transverse relaxation time, T2, from magnetic resonance imaging (MRI) of the wrist cartilage of subjects exhibiting unilateral scapholunate dissociation was analyzed to evaluate changes in the biochemical status of the cartilage in the wrist following injury. Methods: Data collection consisted of MRI scans of the wrist using 2 separate 3T scanners. Fourteen subjects were analyzed, each subject completed scans to evaluate T2 relaxation times on both their injured and contralateral (normal) wrist. Scans were conducted with a maximum of 0.390625 mm/pixel in-plane pixel size and 1 mm slice thickness. A series of four time echo scans ranging from 15-80 ms were collected. T2 relaxation time for each subject was calculated by registering these echo time scans and fitting the corresponding intensity values to an exponential decay curve. Results: The T2 results from all subjects indicated no statistically significant changes with presence of injury. The use of two separate MRI scanners of the same strength of magnet coil did not cause a significant change in measurement values. Conclusions: Our data suggests that either T2 relaxation time does not change with the presence of scapholunate injury in the wrist or that the change was insufficient to be detected in this study. The results from this study may function as a baseline for future studies examining the potential positive effect surgical repair has on T2 relaxation times

High Risk of Unexpected Late Fetal Death in Monochorionic Twins Despite Intensive Ultrasound Surveillance: A Cohort Study

BACKGROUND: The rationale for fetal surveillance in monochorionic twin pregnancies is timely intervention to prevent the increased fetal/perinatal morbidity and mortality attributed to twin–twin transfusion syndrome and intrauterine growth restriction. We investigated the residual risk of fetal death after viability in otherwise uncomplicated monochorionic diamniotic twin pregnancies. METHODS AND FINDINGS: We searched an electronic database of 480 completed monochorionic pregnancies that underwent fortnightly ultrasound surveillance in our tertiary referral fetal medicine service between 1992 and 2004. After excluding pregnancies with twin–twin transfusion syndrome, growth restriction, structural abnormalities, or twin reversed arterial perfusion sequence, and monoamniotic and high-order multiple pregnancies, we identified 151 uncomplicated monochorionic diamniotic twin pregnancies with normal growth, normal liquor volume, and normal Doppler studies on fortnightly ultrasound scans. Ten unexpected intrauterine deaths occurred in seven (4.6%) of 151 previously uncomplicated monochorionic diamniotic pregnancies, within 2 wk of a normal scan, at a median gestational age of 34(+1) wk (weeks(+days); range 28(+0) to 36(+3)). Two of the five cases that underwent autopsy had features suggestive of acute late onset twin–twin transfusion syndrome, but no antenatal indicators of transfusional imbalance or growth restriction, either empirically or in a 1:3 gestation-matched case–control comparison. The prospective risk of unexpected antepartum stillbirth after 32 wk was 1/23 monochorionic diamniotic pregnancies (95% confidence interval 1/11 to 1/63). CONCLUSION: Despite intensive fetal surveillance, structurally normal monochorionic diamniotic twin pregnancies without TTTS or IUGR are complicated by a high rate of unexpected intrauterine death. This prospective risk of fetal death in otherwise uncomplicated monochorionic diamniotic pregnancies after 32 wk of gestation might be obviated by a policy of elective preterm delivery, which now warrants evaluation