Studies on the dynamics of limited filaments

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 56).A study on the dynamics of filaments in the presence of a diagnostic, conductive limiter is presented. Plasma filaments are coherent structures present in many fusion devices and transport a significant amount of particles and energy to vacuum chamber walls. The theories of filament propagation are based on a circuit model of current closure loops within the filament and are described herein. Two experimental configurations based on different modes of filament generation are utilized in the Versatile Toroidal Facility (VTF) to test the model. Along with the experimental observations of filament propagation, measurements of limiter sheath resistance are made and shown to depend upon environmental conditions and filament parameters. One experimental configuration creates long filaments (-6 meters) using electron cyclotron resonance heating (ECRH) and a toroidally symmetric solenoid. The other utilizes a newly constructed Argon plasma gun breaking down injected gas for creating short (~1 meter) plasma filaments. Arrays of Langmuir probes track the path of the plasma particles while the limiters are constructed to generate a uniform vertical electric field along its conductive side and measure the parallel current collected. Agreement is found with the model in a region of strongly negative vertical electric fields. Current collection data extends agreement to larger regions with eventual breakdown at strongly positive electric fields due to complex current collection and escape paths.by Jeffrey David Bonde.S.B

Transcription factor Ap-2alpha is necessary for development of embryonic melanophores, autonomic neurons and pharyngeal skeleton in zebrafish

The genes that control development of embryonic melanocytes are poorly defined. Although transcription factor Ap-2a is expressed in neural crest (NC) cells, its role in development of embryonic melanocytes and other neural crest derivatives is unclear because mouse Ap-2a mutants die before melanogenesis. We show that zebrafish embryos injected with morpholino antisense oligonucleotides complementary to ap-2a (ap-2a MO) complete early morphogenesis normally and have neural crest cells. Expression of c-kit, which encodes the receptor for the Steel ligand, is reduced in these embryos, and, similar to zebrafish c-kit mutant embryos, embryonic melanophores are reduced in number and migration. The effects of ap-2a MO injected into heterozygous and homozygous c-kit mutants support the notion that Ap-2a works through C-kit and additional target genes to mediate melanophore cell number and migration. In contrast to c-kit mutant embryos, in ap-2a MO-injected embryos, melanophores are small and under-pigmented, and unexpectedly, analysis of mosaic embryos suggests Ap-2a regulates melanophore differentiation through cell non-autonomous targets. In addition to melanophore phenotypes, we document reduction of other neural crest derivatives in ap-2a MO-injected embryos, including jaw cartilage, enteric neurons, and sympathetic neurons. These results reveal that Ap-2a regulates multiple steps of melanophore development, and is required for development of other neuronal and nonneuronal neural crest derivatives.This work was supported by NIH grant HD22486 to J.S.E. and a Carver Foundation seed grant to R.A.C. C. d’., and M.A. were supported by grants ICM P99-137-f and Fondecyt 1031003. E.K.O. was supported by Grant T32 DC00040 (Bruce Gantz, PI)

Collisionless Energy and Momentum Coupling of a High-Beta Expansion to an Ambient Plasma

Magnetized plasma expansions from explosive phenomena often have characteristically large ratios of kinetic ram pressure to the ambient magnetic field pressure, β≫1. In the presence of a tenuous, ambient plasma, collisions are incapable of transferring much energy due to the high relative velocities. These expansions, however, generate large magnetic field variations, ΔB/B∼1, in the form of a diamagnetic cavity as well as potentially large electric fields. A high-β expansion was created using a laser-produced plasma that expanded, v_exp=1.28?〖10〗^7 cm/s, β∼〖10〗^6, into a uniform, magnetized background plasma. The processes that are capable of transferring energy and momentum from the high-β expansion to the ambient plasma without collisions were explored. The combination of a magnetic probe and a novel emissive probe yielded measurements of the total electromagnetic field in three-dimensions. These constituted the first measurements of the total electric field in such an environment. The electrostatic field structure comprised the predicted inward field of a diamagnetic cavity as well as previously unobserved features including an outward field associated with a magnetic field compression and an intense electrostatic pulse preceding the LPP. All these components were stronger than the largest observed induced electric field from Faraday’s law. Direct measurements of argon ion velocities moving through these fields were made with a planar, laser-induced fluorescence diagnostic which showed ions being pulled inward against the expansion direction. Orbit solvers show that the characteristic velocity observed, v_r=-3?〖10〗^5 cm/s, is consistent with the measured fields. The inward electrostatic field exhibited a linear variation with the magnetic field while the outward field and pulse exhibited at most a weak dependence. No significant differences in the fields were observed between helium and argon background plasmas. A qualitative model to describe the evolution of the high-β expansion in the context of weak coupling was developed. The model and the experimental field structure yielded important scaling relations for similar expansions and a qualitative extrapolation to the strong-coupling case

A multiple-criteria algorithm for smart parking: Making fair and preferred parking reservations in smart cities

Smart cities are struggling with using public space efficiently and decreasing pollution at the same time. For this governments have embraced smart parking initiatives, which should result in a high utilization of public space and minimization of the driving, in this way reducing the emissions of cars. Yet, simply opening data about the availability of public spaces results in more congestions as multiple cars might be heading for the same parking space. In this work, we propose a Multiple Criteria based Parking space Reservation (MCPR) algorithm, for reserving a space for a user to deal with parking space in a fair way. Users' requirements are the main driving factor for the algorithm and used as criteria in MCPR. To evaluate the algorithm, simulations for three set of user preferences were made. The simulation results show that the algorithm satisfied the users' request fairly for all the three preferences. The algorithm helps users automatically to find a parking space according to the users' requirements. The algorithm can be used in a smart parking system to search for a parking space on behalf of user and send parking space information to the user.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Information and Communication Technolog

Laboratory Observation of Localized Onset of Magnetic Reconnection

Magnetic reconnection is a fundamental process in plasmas that results in the often explosive release of stored magnetic energy, but the trigger for its onset is not well understood. We explore this trigger for fast reconnection in toroidal experiments using a magnetic x-type geometry in the strong guide-field regime. We find that the onset occurs asymmetrically: the reconnection begins on one side of the torus and propagates around approximately at the Alfvén speed. The fast reconnection occurs only in the presence of a global plasma mode, which breaks the axisymmetry and enables the current at the x line to decrease sharply. A simple semiempirical model is used to describe the onset’s growth rate.United States. Dept. of Energy (Grant No. DEFG02- 06ER54878)National Science Foundation (U.S.) and United States. Dept. of Energy (Grant No. DE-FG02- 03ER54712)United States. Dept. of Energy. Center for Multiscale Plasma Dynamics (CMPD) (Grant No. DE-FC02-04ER54786

Prognosis of right ventricular failure in patients with left ventricular assist device based on decision tree with SMOTE.

<p>Right ventricular failure is a significant complication following implantation of a left ventricular assist device (LVAD), which increases morbidity and mortality. Consequently, researchers have sought predictors that may identify patients at risk. However, they have lacked sensitivity and/or specificity. This study investigated the use of a decision tree technology to explore the preoperative data space for combinatorial relationships that may be more accurate and precise. We retrospectively analyzed the records of 183 patients with initial LVAD implantation at the Artificial Heart Program, University of Pittsburgh Medical Center, between May 1996 and October 2009. Among those patients, 27 later required a right ventricular assist device (RVAD+) and 156 remained on LVAD (RVAD-) until the time of transplantation or death. A synthetic minority oversampling technique (SMOTE) was applied to the RVAD+ group to compensate for the disparity of sample size. Twenty-one resampling levels were evaluated, with decision tree model built for each. Among these models, the top six predictors of the need for an RVAD were transpulmonary gradient (TPG), age, international normalized ratio (INR), heart rate (HR), aspartate aminotransferase (AST), prothrombin time, and right ventricular systolic pressure. TPG was identified to be the most predictive variable in 15 out of 21 models, and constituted the first splitting node with 7 mmHg as the breakpoint. Oversampling was shown to improve the senstivity of the models monotonically, although asymptotically, while the specificity was diminished to a lesser degree. The model built upon 5X synthetic RVAD+ oversampling was found to provide the best compromise between sensitivity and specificity, included TPG (layer 1), age (layer 2), right atrial pressure (layer 3), HR (layer 4,7), INR (layer 4, 9), alanine aminotransferase (layer 5), white blood cell count (layer 5,6, &7), the number of inotrope agents (layer 6), creatinine (layer 8), AST (layer 9, 10), and cardiac output (layer 9). It exhibited 85% sensitivity, 83% specificity, and 0.87 area under the receiver operating characteristic curve (RoC), which was found to be greatly improved compared to previously published studies.</p

Decision tree for adjuvant right ventricular support in patients receiving a left ventricular assist device.

<p>BACKGROUND: Right ventricular (RV) failure is a significant complication after implantation of a left ventricular assist device (LVAD). It is therefore important to identify patients at risk a priori. However, prognostic models derived from multivariate analyses have had limited predictive power.</p> <p>METHODS: This study retrospectively analyzed the records of 183 LVAD recipients between May 1996 and October 2009; of these, 27 later required a RVAD (RVAD(+)) and 156 remained on LVAD only (RVAD(-)) until transplant or death. A decision tree model was constructed to represent combinatorial non-linear relationships of the pre-operative data that are predictive of the need for RVAD support.</p> <p>RESULTS: An optimal set of 8 pre-operative variables were identified: transpulmonary gradient, age, right atrial pressure, international normalized ratio, heart rate, white blood cell count, alanine aminotransferase, and the number of inotropic agents. The resultant decision tree, which consisted of 28 branches and 15 leaves, identified RVAD(+) patients with 85% sensitivity, RVAD(-) patients with 83% specificity, and exhibited an area under the receiver operating characteristic curve of 0.87.</p> <p>CONCLUSIONS: The decision tree model developed in this study exhibited several advantages compared with existing risk scores. Quantitatively, it provided improved prognosis of RV support by encoding the non-linear, synergic interactions among pre-operative variables. Because of its intuitive structure, it more closely mimics clinical reasoning and therefore can be more readily interpreted. Further development with additional multicenter, longitudinal data may provide a valuable prognostic tool for triage of LVAD therapy and, potentially, improve outcomes.</p