79 research outputs found
Gold seal of Viṣṇuvarman
No full textFigure 52 in
To engrave his virtues on the disc of the moon… Inscriptions of the Aulikaras and Their Associates
Dániel Balogh, 2019
Gold seal of Viṣṇuvarman. Left: four faces of the object. Right: mirror image of inscribed face and hand tracing of inscription. Photograph courtesy of Devendra Handa, tracing by the author
Role of Risk Stratification and Genetics in Sudden Cardiac Death
No full textSudden cardiac death (SCD) is a major public health issue due to its increasing incidence in the general population and the difficulty in identifying high-risk individuals. Nearly 300,000-350,000 patients in the United States and 4- to 5 million patients in the world die from SCD. Coronary artery disease and advanced heart failure are the main etiology for SCD. Ischemia of any cause precipitates lethal arrhythmias, and ventricular tachycardia and ventricular fibrillation are the most common lethal arrhythmias precipitating SCD. Pulse-less electrical activity, brady-arrhythmia and electromechanical dissociation also result in SCD. Most sudden cardiac deaths occur out-of-the-hospital setting, so it is difficult to estimate the public burden, which results in overestimating the incidence of SCD. The insufficiency and limited predictive value of various indicators and criteria for SCD result in the increasing incidences. As a result, there is a need to develop better risk stratification criteria and find modifiable variables to decrease the incidence. Primary and secondary prevention and treatment of SCD need further research. This critical review is focused on the etiology, risk factors, prognostic factors and importance of risk stratification of SCD.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
Approximability of modularity clustering and related results
No full textFor the problem of Modularity Clustering, first introduced by Newman and Girvan in 2004, we are given a graph and the goal is to partition the vertex set into an unknown number of clusters such that we maximize a certain objective function which evaluates the fitness of the clusters. This fitness function measures the statistically surprising distribution of edges between different clusters and in the clusters themselves. Despite having found widespread popularity in the fields of biology and social sciences, this problem is known to be NP-hard and up till the work in this thesis, only heuristics were known. In this thesis, we initiate a study of the approximability of modularity clustering. We give the first approximation algorithms and the first hardness of approximation results for the problem. In doing so, we employ various techniques like semidefinite programming and the regularity lemma. Our main results in- clude a factor 1.0009 inapproximability for dense graphs and a logarithmic (in the degree) approximation for sparse graphs. We also extend some of these results to directed and weighted graphs and the more general problem of Max-cut where negative edge weights are allowed.Ph. D.Includes bibliographical referencesIncludes vitaby Devendra J. Desa
Refractory vasospasm of the left anterior descending artery causing hemodynamic instability after percutaneous coronary intervention
No full textRefractory coronary vasospastic angina is prone to fatal outcomes. Therefore, it is crucial that the most suitable treatment strategy be promptly elected so as to avert further cardiac complications. Here, authors present the clinical course of profound refractory coronary vasospastic angina in a 50-year-old man. Authors elected to manage the patient through stent implantation. Despite, a complication of perforation followed by refractory coronary vasospasm, authors elected to implant a second stent to relieve the patient from all symptoms
Developing Protection schemes for Offshore Wind Parks
No full textThe increasing demand for electricity and the need to decelerate the use of fossil fuels to prevent a dramatic climate change have urged the need for new sources of energy. Thus, electrical sustainable energy is an ever growing field. Investigations into performance improvements and extraction of maximum benefits from Renewable Energy Sources (RES) is the need of the hour. In particular, wind power contributes to a significant share of renewable electricity generation and has seen great leaps in terms of implemented technologies. The advancements in wind turbine technology have introduced converter based generation, thereby affecting the electrical grid's inertia and short circuit current contributions. These short circuit contributions have been of particular interest for protection engineers in the development of protection systems worldwide. TenneT, which is the TSO of the Netherlands, faces the challenge regarding the protection scheme implementation for their upcoming offshore wind farm connections involving Type 4 Wind Turbines (WT). The lower magnitudes of current flow, post fault and the presence of balanced currents irrespective of the type of fault are some of the major challenges. The system starting from the busbar (where WTs are connected) is owned by the system operator and the WT along with the cable connecting to the busbar, or the Point of Common Coupling (PCC) is an asset of the Wind Park Operator (WPO). Non-technical issues such as the ownership of components at the point of common coupling between the wind park operators and the system operators together along with the technical challenges described earlier necessitates the development of a standard protection scheme that provides satisfactory performance. Implementation of end-to-end connection protection system for the individual component protection is also challenging considering the challenges associated with the ownership of the assets. Therefore , it is necessary to analyse the performance of conventional protection systems (single unit operation). The performance of definite time overcurrent, directional overcurrent, under voltage and distance protection have been studied for faults on PCC and the infeed WPO strings. The study aims at finding the right choice of primary and back up protections that are independent of the type of short circuit currents available by the generation technologies. In addition, the research aims to develop a new busbar protection scheme that can detect and identify the fault location with the challenges explained before. Following the undesirable behaviour observed with overcurrent and directional overcurrent protection system the author then proposes two new schemes using conventional protection systems. The considerations regarding successful operation of under voltage protection and distance protection are further addressed. Finally, a new scheme involving fault generated travelling waves to detect fault on the network is extensively tested. All the protection systems are then compared to describe their merits and demerits to make a decision about the primary and backup protection implemented.Electrical Engineering | Electrical Power Engineerin
Electrokinetically-driven deterministic lateral displacement for particle separation in microfluidic device
No full textAn electrokinetically driven deterministic lateral displacement device is proposed for the continuous, two-dimensional fractionation of suspensions in microfluidic platforms. The suspended species are driven through an array of regularly spaced cylindrical posts by applying an electric field across the device. We explore the entire range of orientations of the driving field with respect to the array of obstacles and show that, at specific forcing angles, particles of different size migrate in different directions, thus enabling continuous, two-dimensional separation. We discuss a number of features observed in the motion of the particles, including directional locking and sharp transitions between migration angles upon variations in the direction of the force, that are advantageous for high-resolution two-dimensional separation. A simple model based on individual particle–obstacle interactions accurately describes the migration angle of the particles depending on the orientation of the driving field and can be used to reconfigure the electric field depending on the composition of the samples.Peer reviewe
Fractional Calculus and its Applications in Physics
No full textThis eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac
American Society of Biomechanics Journal of Biomechanics Award 2013: Cortical bone tissue mechanical quality and biological mechanisms possibly underlying atypical fractures
No full textThe biomechanics literature contains many well-understood mechanisms behind typical fracture types that have important roles in treatment planning. The recent association of "atypical" fractures with long-term use of drugs designed to prevent osteoporosis has renewed interest in the effects of agents on bone tissue-level quality. While this class of fracture was recognized prior to the introduction of the anti-resorptive bisphosphonate drugs and recently likened to stress fractures, the mechanism(s) that lead to atypical fractures have not been definitively identified. Thus, a causal relationship between these drugs and atypical fracture has not been established. Physicians, bioengineers and others interested in the biomechanics of bone are working to improve fracture-prevention diagnostics, and the design of treatments to avoid this serious side-effect in the future. This review examines the mechanisms behind the bone tissue damage that may produce the atypical fracture pattern observed increasingly with long-term bisphosphonate use. Our recent findings and those of others reviewed support that the mechanisms behind normal, healthy excavation and tunnel filling by bone remodeling units within cortical tissue strengthen mechanical integrity. The ability of cortical bone to resist the damage induced during cyclic loading may be altered by the reduced remodeling and increased tissue age resulting from long-term bisphosphonate treatment. Development of assessments for such potential fractures would restore confidence in pharmaceutical treatments that have the potential to spare millions in our aging population from the morbidity and death that often follow bone fracture.Peer reviewe
Resilient operations of smart electricity networks under security and reliability failures
No full textThis electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: Ph. D. in Computational Science and Engineering, Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2019Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 265-276).Blackouts (or cascading failures) in Electricity Networks (ENs) can result in severe consequences for economic activity, human safety and national security. Recent incidents suggest that risk of blackouts due to cyber-security attacks and extreme weather events is steadily increasing in many regions of the world.This thesis develops a systematic approach to evaluate and improve the resilience of ENs by addressing following questions: (a) How to model security and reliability failures and assess their impact on ENs? (b) What strategies EN operators can implement to plan for and quickly respond to such failures and minimize their overall impact? (c) How to leverage the operational flexibility of "smart" ENs to implement these strategies in a structured manner and provide guarantees against worst-case failure scenarios? We focus on three classes of cyber-physical failures: (i) Inefficient or unsafe economic dispatch decisions induced by an external hacker who exploits the vulnerabilities of control center software; (ii) Simultaneous disruption of a large number of customer-side components (loads and/or distributed generators) by a strategic remote adversary; (iii) Correlated failures of power system components caused by storm events (or hurricanes) with high-intensity wind fields.We develop new network models to capture the impact of these failures, while accounting for a broad range of operator response actions. These actions include: partial load control, pre-emptive disconnection of non-critical loads, active and reactive power supply by Distributed Energy Resources (DERs) capable of providing grid-forming services, and formation of microgrid islands. We develop practically relevant operational strategies to improve the ENs' resilience to failure classes (i) and (ii) (resp. (iii)) based on solutions of bilevel mixed integer programming (resp. two-stage stochastic optimization) formulations. Our bilevel mixed integer programming formulations capture the worst-case impacts of attacks on radial distribution networks operating under grid-connected or microgrid configurations.For the case when the operator response can be modeled as continuous decision variables, we provide a greedy heuristic that exploits the radial network structure and provides near-optimal solutions. For the more general case of mixed-binary decision variables, we develop a computationally tractable solution approach based on Benders Decomposition method. This approach can be used to evaluate the value of timely response actions in reducing various losses to the network operator during contingencies induced by attacker-induced failures. We provide some guidelines on improving the network resilience by proactive allocation of contingency resources, and securing network components in a strategic manner. Furthermore, under reasonable assumptions, we show that myopically reconnecting the disrupted components can be eective in restoring the network operation back to nominal condition.Our two-stage stochastic optimization formulation is motivated by the need of a decision-theoretic framework for allocating DERs and other contingency resources in ENs facing the risk of multiple failures due to high-intensity storm events. The stochastic model in this formulation captures the dependence of probabilistic failure rates on the spatio-temporal wind intensities. Importantly, the formulation allows for the formation of microgrid islands (powered by the allocated DERs), and considers joint DER dispatch and component repair decisions over a multi-period restoration time horizon. We present computational results based on the classical sample average approximation method, with Benders Decomposition applied to solve the mixed-binary programs associated with the restoration stage. Finally, we compare the optimal repair decisions with a simpler greedy scheduling strategy that satisfies soft-precedence constraints."Financial support provided by EPRI grant for "Modeling the Impact of ICT Failures on the Resilience of Electric Distribution Systems" (contract ID: 10000621), and NSF project "CPS Frontiers: Collaborative Research: Foundations Of Resilient CybErphysical Systems (FORCES)" (award number: CNS-1239054)"--Page 5by Devendra Shelar.Ph. D. in Computational Science and EngineeringPh.D.inComputationalScienceandEngineering Massachusetts Institute of Technology, Department of Civil and Environmental Engineerin
Fractional Calculus and its Applications in Physics
No full textThis eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac
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