683 research outputs found
Arbitration and Dispute Settlement in Foreign Indirect Investment. The increasing significance and use of arbitration in international loan agreements, syndicated loans and international bond issues
No full textThis dissertation examines the suitability of arbitration for the resolution of securities regulatory claims and it adoption globally, which has resulted in international arbitration becoming the favoured dispute resolution mechanism in the securities industry. The author explains that disputes arising out of international bilateral and syndicated loan agreements are generally considered to be arbitrable, while international bond disputes are often derived from the controversies over the application of mandatory national laws and the compliance with securities regulation provisions - so the arbitrability of international bond disputes depends on the acceptance of the arbitrability of securities regulatory claims
A monolithically integrated power JFET and Junction Barrier Schottky diode in 4H silicon carbide
No full textEfficiency of power management circuits depends significantly on their constituent switches and rectifiers. The demands of technology are increasingly running up against the intrinsic properties of Si based power devices. 4H-Silicon Carbide (SiC) has superior properties that make it attractive for high power applications. SiC rectifiers are already a competitive choice and SiC switches have also been commercialized recently. Junction Barrier Schottky (JBS) diodes, which combine the advantages of PN and Schottky, have higher Figure of Merit (FOM) as rectifiers. Among switches, a robust and mature process has been developed for Silicon Carbide Vertical Junction Field Effect Transistors (VJFETs), which currently gives it the highest unipolar FOM. Switches are frequently combined with anti-parallel diodes in power circuits. This thesis describes the development of a SiC-based monolithically integrated power switch and diode. Monolithic integration increases reliability and efficiency, and reduces cost. Because of their superior properties and similarities in fabrication, we chose the SiC VJFET and JBS diode as the switch and rectifier. Detailed design, fabrication and characterization of the integrated switch to block above 800 V and conduct current beyond 100 A/cm2 is explained. In this process, the first physics-based 2-D compact model is developed for reverse leakage in a JBS diode as a function of design parameters. Since the gate-channel junctions of SiC VJFETs cannot be assumed to be abrupt, an existing analytical model for Si VJFETs is extended to account for graded gate-channel junctions. Using these analytical models, design rules are developed for the VJFET and JBS diode. Finite element simulations are used to find the best anode layout of the JBS diode and optimize electric field termination in the integrated device to ensure their capability to operate at high voltage. Finally, a spin-on glass based process is developed for filling the gate trenches of the VJFET to improve long-term robustness in extreme environments. The integrated power switch developed in this thesis points to the attractions of monolithic integration in SiC power circuits. Analytical compact design equations derived here will facilitate faster and easier design of switches and rectifiers for desired circuit operation.Ph. D.Includes bibliographical referencesIncludes vitaby Rahul Radhakrishna
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Aspects of localization in topological insulators
No full textThe topological properties of electronic band structures are closely related to the degree of localization possible for the associated wavefunctions. In this dissertation, we investigate certain aspects of this interplay between topology and localization in the context of static as well as driven (Floquet) topological insulators. The first part of this dissertation is motivated by Landau levels, the energy levels of electrons in a two dimensional plane that are subject to a perpendicular magnetic field. Landau levels form a key element of theoretical models of the quantum Hall effect, which inspired the study of topological insulators. Each Landau level is highly degenerate or flat, and is topologically non-trivial. Motivated by Landau levels, we study the topological properties of tight-binding Hamiltonians which only have flat energy levels. We find that the spectral projectors of such Hamiltonians are strictly local. In chapters 2 and 3, we show that in one dimension, compact Wannier functions (and their analogs in the absence of lattice translational invariance) can be constructed if and only if the subspace they span is described by a strictly local projector. Using this insight, in Chapter 4, we present and prove a no-go theorem which says that if a strictly local tight-binding Hamiltonian in two dimensions only has flat bands, then each of the bands must have a Chern number of zero. All results are proven without the requirement of lattice translational invariance. The role of an inequality relating the number of energies of the Hamiltonian and the system size is also clarified.In the second part of this dissertation (Chapter 5), we present some results concerning a delocalization transition that arises in a certain class of Floquet topological insulators.Specifically, we study chiral Floquet topological insulators in one dimension, and show that the localization lengths of eigenstates of the time evolution operator diverge with a universal exponent of two as the time approachs a special point in drive
Topological Triviality of Flat Hamiltonians
No full textLandau levels play a key role in theoretical models of the quantum Hall
effect. Each Landau level is degenerate, flat and topologically non-trivial.
Motivated by Landau levels, we study tight-binding Hamiltonians whose energy
levels are all flat. We demonstrate that in two dimensions, for such
Hamiltonians, the flat bands must be topologically trivial. To that end, we
show that the projector onto each flat band is necessarily strictly local. Our
conclusions do not need the assumption of lattice translational invariance.Comment: 7 pages, 2 figure
Design and Development of a Novel Implantable Prosthetic Vein Valve
No full textOver seven million Americans suffer from Chronic Venous Insufficiency (CVI), a painful and debilitating disease that affects the superficial and deep veins of the legs. Problems associated with CVI include varicose veins, bleeding, ulcerations, severe swelling, deep vein thrombosis, and pulmonary embolism, which may lead to death. The presence of CVI results from damaged (incompetent) one-way vein valves in leg veins. These valves normally allow forward flow of blood to the heart, and prevent blood from pooling at the feet. However, incompetent valves allow reflux of blood, causing clinical problems.
There are few effective clinical therapies for treating CVI. Vein valve transplantation is a surgical option for treatment. However, it is often difficult to find suitable donor valves. Very few prosthetic valves developed in the past have demonstrated sufficient clinical or mechanical functionality. Persistent problems include thrombus formation, leaking valves, and valves that do not open at physiologic pressure gradient. The primary objective of this research was to develop a clinically relevant functional prosthetic vein valve.
The novel prosthetic valve is flexible, biocompatible, has low thrombogenecity, and is easy to manufacture. It was designed to address well-defined consumer needs and functional design requirements. The valve was required to 1) withstand 300 mmHg of backpressure with leakage less than 1.0 mL/min, 2) open with a pressure gradient less than 5 mmHg, and 3) meet criteria 1 and 2 after 500,000 cycles of operation. The valve met these design requirements in bench testing. The valve can open with a pressure gradient of 2.6 0.7 mmHg, and can withstand 300 mmHg with leakage less than 0.5 mL/min. The valve remained functional after opening and closing over 500,000 times. The valve presented in this research is operationally functional, and is a potential solution for treating venous incompetence in CVI patients.M.S
Chiral superconductivity from repulsive interactions in doped graphene
No full textAuthor Manuscript 17 Sep 2011Chiral superconductivity, which breaks time-reversal symmetry, can exhibit a wealth of fascinating properties that are highly sought after for nanoscience applications. We identify doped graphene monolayer as a system where chiral superconductivity can be realized. In this material, a unique situation arises at a doping where the Fermi surface is nested and the density of states is singular. In this regime, d-wave superconductivity can emerge from repulsive electron–electron interactions. Using a renormalization group method, we argue that superconductivity dominates over all competing orders for generic weak repulsive interactions. Superconductivity develops simultaneously in two degenerate d-wave pairing channels. We argue that the resulting superconducting state is of chiral type, with the phase of the superconducting order parameter winding by 4π around the Fermi surface. Realization of this state in doped graphene will prove that superconductivity can emerge from electron–electron repulsion, and will open the door to applications of chiral superconductivity
Adding diversity and realism to LAVA, a vulnerability addition system
No full textThesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 63-64).In this thesis, I designed and implemented several modifications to LAVA, a vulnerability addition system, with the goal of improving realism and diversity of the injected bugs. Specifically, I describe three separate improvements: a method to add fake bugs alongside real ones in order to decrease bug discoverability, two approaches to increase the complexity of the data flow of the inserted bugs, and a standalone program that uses equality saturation to diversify C-source codebases that can be added as a final stage to LAVA. Finally, I present two instances of bug-finding competitions-AutoCTF and Rode0day-that I helped design and run, which leveraged LAVA and the augmentations described in this thesis in order to accomplish their respective goals.by Rahul Sridhar.M. Eng
Pixel Merge Unit
No full textMulti-sample anti-aliasing is a popular technique for reducing geometric aliasing (jagged edges) and is supported in all modern graphics processors. With multi-sampling anti-aliasing, visibility and depth are sampled more than once per pixel, while shading is done only once per pixel per primitive. Although this significantly reduces the appearance of jagged edges around object boundaries, the image quality improvement in non-silhouette regions is hardly noticeable. We propose a hardware unit, called the pixel merge unit, which is located just after the early depth test unit but before the pixel shader. Our unit attempts to reduce the shading rate to once per pixel per group of connected primitives covering a pixel using a novel merging strategy. We demonstrate up to 15% reduction in pixel shader executions. Given the simple implementation that we propose, this is a substantial reduction
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