151 research outputs found
Replication Code for: "Too Much Skin-in-the-Game? The Effect of Mortgage Market Concentration on Credit and House Prices"
No full textThese files contain the code to replicate the calibration and generate the tables in Appendix B of the paper
Dynamique de l'aimantation ultrarapide induite par des électrons chauds polarisés dans des structures à valve de spin basées sur un ferrimagnet
No full textFemtosecond laser pulses can be used to induce ultrafast changes of the magnetization in magnetic materials. Several microscopic mechanisms have been proposed to explain the observations, including the transport of ultrashort spin-polarized hot-electrons (SPHE). Such ultrafast spin currents find growing interest because of the recent challenges in ultrafast spintronics however they are only poorly characterized. One of the key challenges is to characterize the spin-polarized ultrafast currents and the microscopic mechanisms behind SPHE induced manipulation of the magnetization, especially in the case of technologically relevant ferrimagnetic alloys. In my thesis work, I investigate the sub-picosecond spin current-induced demagnetization dynamics in rare-earth (RE) and transition metal (TM) alloy systems. To distinguish the element-specific dynamics, I utilized the element selective technique of Time-resolved X-Ray Magnetic Circular Dichroism at the large-scale infrastructure HZB-BESSY II – Berlin.Les impulsions laser femtosecondes peuvent être utilisées pour induire des changements ultrarapides de l'aimantation dans les matériaux magnétiques. Plusieurs mécanismes microscopiques ont été proposés pour expliquer les observations, notamment le transport d'impulsions ultra courtes d'électrons chauds polarisés en spin (SPHE). Ces courants de spin ultrarapides suscitent un intérêt croissant en raison des défis récents de la spintronique ultrarapide, mais ils restent très mal caractérisés. L'un des principaux défis consiste à caractériser les courants ultrarapides polarisés en spin et les mécanismes microscopiques à l'origine de la manipulation de l'aimantation induite par ces SPHE, en particulier dans le cas des alliages ferrimagnétiques à fort intérêt technologique.Dans mon travail de thèse, j'étudie la dynamique de désaimantation induite par le courant de spin sub-picoseconde dans les systèmes d'alliages de terres rares (RE) et de métaux de transition (TM). Pour distinguer la dynamique spécifique à chaque élément, j'ai utilisé la technique de dichroïsme circulaire magnétique à rayons X, résolu en temps dans une Très Grande Infrastructures de Recherche : HZB-BESSY II – Berlin
Polarized hot electron induced ultrafast magnetization dynamics in ferrimagnet based spin valve structures
No full textThe generation of spin currents is a key ingredient in the spintronics based memory devices such as spin transfer torques magnetic random access memory. Advances in ultrafast magnetism [1] in the last decade have demonstrated that the switching time can be reduced to the sub picosecond time scales with low power consumption [1]. Ever since this pioneer works, several experiments on ferromagnetic 3d transition metals have studied the ultrafast spin dynamics induced by such fs spin currents in spin valve structures [2 7], while recent studies suggest that antiferromagnetic materials are more promising for ultrafast spintronics [8]. Among these AFM materials, the rare earth transition metal RE TM alloys represent model systems [8,9]. Here, I investigate the sub picosecond and picosecond spin current induced demagnetization dynamics in RE TM alloys. To distinguish the element specific dynamics, I used the element selective technique of Time resolved X Ray Magnetic Circular Dichroism available at the large scale infrastructures HZB BESSY II Berlin. In this thesis work, the focus is on studying the ultrafast demagnetization dynamics of thin buried ferrimagnetic layer FeGd and CoGd alloys , using the ultrashort spin polarized hot electron SPHE pulses as a pump and ultrashort X rays as a probe. I have explored the impact of SPHE induced effect on two different spin valve structures consisting of out of plane Fe74Gd26 Cu Co Pt 3 , and of an in plane Co61Gd39 Cu CoPt. The key findings are summarized as follows In Fe74Gd26 based spin valves In the case of out of plane Fe74Gd26 based spin valves, we investigated the spin polarized hot electron induced dynamics of Fe 3d and Gd 4f moments, and through fitting, crucial parameters such as demagnetization time, hot electron pulse width, and recovery were obtained. The estimation of hot electron pulses highlighted their elongation as they traversed different capping layers. I observed that ultrafast spin current accelerated the Fe3d dynamics in the case of P configuration, which shows that antiparallel spins between Fe3d and SPHE spins help in the demagnetization of the Fe3d sublattice. Theoretical calculations based on atomistic spin dynamics with STT successfully reproduced the spin dependent demagnetization dynamics at Fe and Gd edges. The calculations approximated that the thin polarizer film Co Pt could generate 100 polarization of the spin current and show that the spin polarization of the SPHE current out of Co Pt multilayers is opposite to the Co magnetization. 2 In Co61Gd39 based spin valves A slow demagnetization of the hot electron induced dynamics at Gd4f sublattice could be related to the concentration of such alloys irrespective of the excitation source laser light or hot electron pulses . I observed that ultrafast spin current accelerated the Gd4f dynamics in the case of AP configuration, which shows that parallel spins between Gd4f and SPHE spins help the demagnetization of Gd4f sublattice. The surface sensitive soft X ray photoelectron spectroscopy XPS technique has evidenced a concentration profile of Gd at the surface of the GdCo alloy. The profile shows an enhanced Gd content in the first 2 nm in Co65Gd35, whereas, for a Co80Gd20 alloy, a single segregated Gd monolayer on the top of an almost homogenous alloy was define
Nuclear Safety related Cybersecurity Impact Analysis and Security Posture Monitoring
No full textThe Electrical Power Systems (EPS) are indispensable for a Nuclear Power Plant (NPP). The EPS are essential for plant start-up, normal operation, and emergency conditions. Electrical power systems are necessary not only for power generation, transmission, and distribution but also to supply reliable power for plant operation and control system during safe operation, Design Basis Conditions (DBC) and Design Extension Conditions (DEC). According to IAEA Specific Safety Guide SSG-34, EPS are essentially the support systems of many plant equipment. Electrical system, which supply power to plant systems important to nuclear safety, are essential to the safety of an NPP.
In recent years, due to the digitization of Instrumentation and Control (I&C) systems, along with their enhanced accuracy, ease of implementing complex functions and flexibility, have been also exposed to sophisticated cyber threats. Despite physical separation and redundant electrical power supply sources, malicious cyber-attacks performed by insiders or outsiders might disrupt the power flow and result in an interruption in the normal operation of an NPP. Therefore, for the uninterrupted operation of a plant, it is crucial to contemplate cybersecurity in the EPS design and implementation. Considering multiple cyber threats, the main objectives of this research work are finding out security vulnerabilities in electrical power systems, simulating potential cyber-attacks and analyzing the impacts of these attacks on the electrical components to protect the electrical systems against these cyber-attacks.
An EPS testbed at a small scale was set up, which included commercial I&C and electrical equipment significant for the cybersecurity analysis. The testbed equipment comprises of electrical protection relay (IEC 60255), controller, operating panel, engineering workstation computer, simulation model, etc. to monitor and control the power supply of one or more electrical equipment responsible for a regular operation in an NPP. Simulated cybersecurity attacks were performed using this testbed and the outcomes were examined in multiple iterations, after adding or changing security controls (cybersecurity countermeasures). Analyzing the cybersecurity and performing cyber-attacks on these systems are very advantageous for a real power plant to prepare and protect the plant equipment before any malicious attack happens. This research work conclusively presents cybersecurity analysis, including basic and sophisticated cyber-attack scenarios to understand and improve the cybersecurity posture of EPS in an NPP. The approach was completed by considering the process engineering systems (e.g. reactor core cooling systems) as attack targets and investigating the EPS specific security Defense-in-Depth (DiD) design together with the Nuclear Safety DiD concepts.:CHAPTER 1 INTRODUCTION
1.1 Motivation
1.2 Technical Background
1.3 Objectives of the Ph.D. Project
1.4 State of the Art in Science and Technology
CHAPTER 2 FUNDAMENTALS OF CYBERSECURITY AND ELECTRICAL CONTROL AND PROTECTION CONCEPTS
2.1 Electrical Power System
2.2 Electrical Protection System
2.3 Cyber-Physical System
2.4 Industrial Control System
2.5 Safety I&C and Operational I&C Systems
2.6 Safety Objective Oriented Top-Down Approach
2.7 Cybersecurity Concept
2.8 Threat Identification and Characterization in NPP
2.8.1 Design Basis Threat
2.8.2 Attacker Profile
2.8.1 Reported Real-Life NPP Cyber-Attack Examples
2.9 Security Levels
2.10 Summary
CHAPTER 3 CYBER-PHYSICAL PROCESS MODELING
3.1 Introduction
3.2 Single Line Diagrams of Different Operational Modes
3.3 Design
3.4 Block Diagram of Simulink Model
3.5 Implementation of Simulink Blocks
3.5.1 Power Generation
3.5.2 Grid Feed
3.5.3 House Load (Feed Water Pump)
3.6 OPC UA Communication
3.7 Summary
CHAPTER 4 CYBER THREAT SCENARIOS FOR EPS
4.1 Introduction
4.2 Cyber-Physical System for EPS
4.3 Cyber Threats and Threat Sources
4.3.1 Cyber Threats
4.3.2 Threat Sources
4.4 Cybersecurity Vulnerabilities
4.4.1 Vulnerabilities in EPS
4.4.2 Vulnerabilities in ICS
4.5 Attacker Modeling
4.6 Basic Cyber Threat Scenarios for EPS
4.6.1 Scenario-1: Physical Access to Electrical Cabinets
4.6.2 Scenario-2: Modification of Digital Protection Devices
4.7 Potential Advanced Cyber Threat Scenarios for EPS
4.7.1 Scenario-1: Alteration of a Set-point of the Protection Relay
4.7.2 Scenario-2: Injection of Malicious Packets
4.7.3 Scenario-3: False Trip Command
4.7.4 Scenario-4: Availability Attack on Protection Relay or SCADA System
4.7.5 Scenario-5: Permanent Damage to Physical Component
4.7.6 Scenario-6: Protocol-wise Attack on Operator Panel
4.8 Threat Scenario for Simulink model
4.9 Summary
CHAPTER 5 EPS TESTBED DESCRIPTION
5.1 Introduction
5.2 Basic Industrial Automation Architecture
5.3 Need for Testbeds
5.4 Proposed EPS Testbed
5.4.1 Testbed Architecture
5.4.2 Testbed Implementation
5.5 EPS Physical Testbed Applications
5.5.1 Modeling and Simulation of Power System Faults
5.5.2 Modeling of Cyber-Attacks
5.6 Summary
CHAPTER 6 EXPERIMENTAL AND IMPACT ANALYSIS OF CYBER THREAT SCENARIOS
6.1 Outline
6.2 Normal Operation and Control
6.3 Possibilities to Cause Failure in the Primary or Secondary Cooling Systems
6.4 Implementation of Cybersecurity Threat Scenarios
6.4.1 Alteration of a Relay Set-Point during Plant Start-Up Phase
6.4.2 Alteration of a Controller Set-Point during Normal Operation Phase
6.4.3 Availability Attack on Control and Protection System
6.4.4 Severe Damage to a Physical Component due to Overcurrent
6.5 Experimentally Assessed Cyber-attacks
6.6 Summary
CHAPTER 7 SUMMARY AND OUTLOOK
REFERENCES
SCIENTIFIC PUBLICATIONS
GLOSSAR
Dynamique de l'aimantation ultrarapide induite par des électrons chauds polarisés dans des structures à valve de spin basées sur un ferrimagnet
No full textLes impulsions laser femtosecondes peuvent être utilisées pour induire des changements ultrarapides de l'aimantation dans les matériaux magnétiques. Plusieurs mécanismes microscopiques ont été proposés pour expliquer les observations, notamment le transport d'impulsions ultra courtes d'électrons chauds polarisés en spin (SPHE). Ces courants de spin ultrarapides suscitent un intérêt croissant en raison des défis récents de la spintronique ultrarapide, mais ils restent très mal caractérisés. L'un des principaux défis consiste à caractériser les courants ultrarapides polarisés en spin et les mécanismes microscopiques à l'origine de la manipulation de l'aimantation induite par ces SPHE, en particulier dans le cas des alliages ferrimagnétiques à fort intérêt technologique.Dans mon travail de thèse, j'étudie la dynamique de désaimantation induite par le courant de spin sub-picoseconde dans les systèmes d'alliages de terres rares (RE) et de métaux de transition (TM). Pour distinguer la dynamique spécifique à chaque élément, j'ai utilisé la technique de dichroïsme circulaire magnétique à rayons X, résolu en temps dans une Très Grande Infrastructures de Recherche : HZB-BESSY II – Berlin.Femtosecond laser pulses can be used to induce ultrafast changes of the magnetization in magnetic materials. Several microscopic mechanisms have been proposed to explain the observations, including the transport of ultrashort spin-polarized hot-electrons (SPHE). Such ultrafast spin currents find growing interest because of the recent challenges in ultrafast spintronics however they are only poorly characterized. One of the key challenges is to characterize the spin-polarized ultrafast currents and the microscopic mechanisms behind SPHE induced manipulation of the magnetization, especially in the case of technologically relevant ferrimagnetic alloys. In my thesis work, I investigate the sub-picosecond spin current-induced demagnetization dynamics in rare-earth (RE) and transition metal (TM) alloy systems. To distinguish the element-specific dynamics, I utilized the element selective technique of Time-resolved X-Ray Magnetic Circular Dichroism at the large-scale infrastructure HZB-BESSY II – Berlin
Impact of Social Determinants of Health Interventions on Diabetes-Related Health Outcomes and Health Service Use
No full textSocial determinants of health (SDOH) such as food insecurity, lack of insurance, transportation deficits, and financial instability are associated with poor health outcomes, increased healthcare use and costs and diminished quality of life for individuals with chronic diseases such as diabetes. Addressing SDOH in clinical settings is essential for comprehensive care, yet research on the effectiveness of SDOH interventions in healthcare use, costs, and quality of life is limited. This dissertation evaluates two SDOH interventions for patients with diabetes in South Carolina’s largest health system.
The first study assessed the costs and cost-effectiveness of a multidisciplinary teams-based program for underinsured and uninsured pregnant women with diabetes (pre-existing Type 1 or Type 2 or gestational diabetes) and SDOH needs. A microcosting approach was used to assess program costs, including costs for fixed resources (e.g., diabetes technology), team member time, SDOH supplies, diabetes treatment, and outpatient costs. A Markov cohort model was used to estimate the incremental program costs in reducing diabetes-related hospitalizations in pregnancy compared to standard care. Compared to standard care (mean [SD] = 19,951 per pregnancy (range = 76,526.90). The standard care group dominated in cost-effectiveness for all diabetes type except gestational diabetes (187.40 greater increase in primary care costs over six months and improved quality of life. Total healthcare, inpatient, and emergency department costs, and clinical outcomes did not differ between groups.
These findings suggest that SDOH programs may enhance patient engagement and quality of life in diabetes care but incur significant costs, raising important budgetary implications for health systems and policy discussions. Future research should prioritize evaluating underexplored costs and outcomes associated with SDOH programs and examine program features to understand their impact on patient health
Essays In Housing Markets And Financial Fragility
No full textThis dissertation is motivated by the housing crisis of 2008. It consists of three chapters. In the first chapter, Too Much Skin-in-the-Game? The Effect of Mortgage Market Concentration on Credit and House Prices, I propose a new theory to help explain the housing crisis. During the housing boom, a small number of institutions - the government-sponsored enterprises (GSEs) and a few banks - held most of U.S. mortgage risk. I develop a theory in which such concentration of mortgage exposure can explain features of the housing crisis. I show that large lenders with many outstanding mortgages have incentives to extend risky credit to prop up house prices. An increase in concentration can lead to a boom with worsening credit quality and a subsequent bust with widespread defaults.
In the second chapter, Concentration and Lending in Mortgage Markets, joint with Ronel Elul and David Musto, we attempt to test the theory described in the first chapter. We provide evidence that concentration in mortgage markets can create perverse lending incentives. We exploit variation in the size of the GSEs\u27 outstanding mortgage exposure across MSAs. Using a loan-level dataset, we provide evidence that the GSEs were more likely to engage in high-risk activities in areas where they had a large exposure to outstanding mortgages. We also provide evidence that this relationship is driven by an incentive to keep house prices high.
In the final chapter, Housing Booms and the Crowding-Out Effect, joint with Itay Goldstein, we study the effect that investment in real estate assets has on the economy. We develop a theory in which housing price booms can sometimes lead to a crowding-out of corporate investment. We show that an increase in real estate prices does not necessarily increase aggregate investment even when firms actively use real estate assets as collateral to borrow against and invest the proceeds in positive NPV projects. We argue that at times, it can be optimal to decrease the price of housing rather than to support high housing prices to stimulate the economy and characterize when this is the case
Link Weight Tolerance: A study of betweenness centrality and data transmission in complex networks
No full textLinks play a significant role in the functioning of a complex network. The aim of this thesis is to study the links in a weighted network by introducing two new concepts. The link betweenness centrality of a link is defined as the fraction of shortest paths between all pairs of nodes in a graph that traverses that link. Although link betweenness is a widely known measure that characterizes the link, we introduce the concept, link weight tolerance, to understand the extent to which the weight of the link can be increased or decreased such that the shortest paths in the graph are unaffected, therefore the link betweenness of the links remain the same. We develop a method to generate the positive and negative tolerance of a link. We use examples to illustrate the algorithm and discuss the results. Prior to introducing this concept, in addition to surveying existing network theory measures, we also analyse the metric, betweenness centrality and describe the methods used to generate weighted and unweighted random graphs. To extend the concept of link betweenness, we introduce the second concept, link tension. Link tension provides the information related to the ability of the link to handle transmission of data and shows us the links that are important in a network.Electrical Engineering | Embedded System
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