Fabrication of high-aspect-ratio metallic micro-structures by reverse exposure method

Master'sMASTER OF ENGINEERIN

Essays in macroeconomics and finance

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Economics, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 142-150).The first chapter proposes a model of booms and busts in housing and non-housing consumption driven by the interplay between relatively low interest rates and an expansion of credit, triggered by further decline in interest rates and relaxing collateral requirements. When credit becomes available, households would like to borrow in order to frontload consumption, and this increases demand for housing and non-housing consumption. If the increase in the demand for housing translates into an increase in prices, then credit is fueled further, this time endogenously, because of the role of housing as collateral. Because a lifetime budget constraint still applies, even in the absence of a financial crisis, the initial expansion in housing and non-housing consumption will be followed by a period of contraction, with declining consumption and house prices. My mechanism clarifies that boom-bust dynamics will be accentuated in regions with inelastic supply of housing and muted in elastic regions. In line with qualitative predictions of my model, I provide evidence that differences in regions' elasticity of housing and initial relaxation of collateral constraints can explain most of the 2000-2006 boom and the subsequent bust in house prices and consumption across US counties. The second chapter (co-authored with Daron Acemoglu, Simon Johnson, James Kwak and Todd Mitton) studies the value of political connections during turbulent times and shows the announcement of Tim Geithner as President-elect Obamas nominee for Treasury Secretary in November 2008 produced a cumulative abnormal return for financial firms with which he had a personal connection. This return was around 15 percent from day 0 through day 10, relative to other comparable financial firms. This result holds across a range of robustness checks and regardless of whether we measure connections in terms of meetings he had in 2007-08, non-profit board memberships he shared with financial services executives, or firms with headquarters in New York City. There were subsequently abnormal negative returns for connected firms when news broke that Geithners conrmation might be derailed by tax issues. We argue that this value of connections reflects the perceived impact of relying on the advice of a small network of financial sector executives during a time of acute crisis and heightened policy discretion. The third chapter (co-authored with Adam Ashcraft and Kunal Gooriah) studies the impact of skin-in-the game on the performance of securitized assets using evidence from conduit commercial mortgage backed securities (CMBS) market. A unique feature of this market is that an informed investor purchases the bottom 5 percent of the capital structure, known as the B-piece, conducting independent screening of loans from which all other investors benefit. However, during the recent credit boom, a secondary market for B-pieces developed, permitting these investors to significantly reduce their skin in the game. In this paper, we document, that after controlling for all information available at issue, the percentage of the B-piece that is sold by these investors has a significant adverse impact on the probability that more senior tranches ultimately default. The result is robust to the use of an instrumental variables strategy which relies on the greater ability of larger B-piece buyers to to sell these positions given the need for large pools of collateral. Moreover we show the risk associated with this agency problem was not priced.by Amir Reza Mohsenzadeh Kermani.Ph.D

The Value of Connections in Turbulent Times: Evidence from the United States

We thank Isil Erel, Taylor Nadauld, and René Stulz for sharing data. For helpful comments we thank Josh Angrist, Caroline Hoxby, Suresh Naidu, Francesco Trebbi, and people who provided comments during or after our talks at MIT, Northwestern, Harvard Business School, the International Monetary Fund, the University of Alberta, BYU, Yale, the University of California at Berkeley, and the 2012 Econometric Society meetings. We are also grateful for constructive suggestions from some former officials.The announcement of Timothy Geithner as nominee for Treasury Secretary in November 2008 produced a cumulative abnormal return for financial firms with which he had a connection. This return was about 6% after the first full day of trading and about 12% after ten trading days. There were subsequently abnormal negative returns for connected firms when news broke that Geithner’s confirmation might be derailed by tax issues. Excess returns for connected firms may reflect the perceived impact of relying on the advice of a small network of financial sector executives during a time of acute crisis and heightened policy discretion

Modeling of carbon dioxide solubility in ionic liquids based on group method of data handling

Due to industrial development, the volume of carbon dioxide (CO2) is rapidly increasing.. Several techniques have been used to eliminate CO2 from the output gas mixtures. One of these methods is CO2 capturing by ionic liquids (ILs). Computational models for estimating the CO2 solubility in ILS is of utmost importance. In this research, a white box model in the form of a mathematical correlation using the largest data bank in literature is presented by the group method of data handling (GMDH). This research investigates the application of GMDH intelligent method as a powerful computational approach for predicting CO2 solubility in different ionic liquids with temperature lower and upper than 324 K. In this regard, 4726 data points including the solubility of CO2 in 60 ILs were used for model development Moreover, seven different ionic liquids were selected to perform the external test. To evaluate the validity and efficiency of the suggested model, regression analysis was implemented on the actual and estimated target values. As a result, a proper fit between the experimental and predicted data was obtained and presented by various figures and statistical parameters. It is also worth noting that the predicted negative values in the proposed models are considered zero. Also, the results of the established correlation were compared to other proposed models exist in the literature of ionic liquids. The terminal form of the models suggested by GMDH approach and obtained based on temperature are two simple mathematical correlations by exerting input parameters of temperature (T), pressure (P), critical temperature (Tc ), critical pressure (Pc ) and, acentric factor (ω) which does not suffer from the black box property of other neural network algorithms. The model suggested in this work, would be a promising one which can act as an efficient predictor for CO2 solubility estimation in ILs and is capable of being used in different industries

Computational vs. qualitative: analyzing different approaches in identifying networked frames during the Covid-19 crisis

Despite the increasing adaption of automated text analysis in communication studies, its strengths and weaknesses in framing analysis are so far unknown. Fewer efforts have been made to automatic detection of networked frames. Drawing on the recent developments in this field, we harness a comparative exploration, using Latent Dirichlet Allocation (LDA) and a human-driven qualitative coding process on three different samples. Samples were comprised of a dataset of 4,165,177 million tweets collected from Iranian Twittersphere during the Coronavirus crisis, from 21 January, 2020 to 29 April, 2020. Findings showed that while LDA is reliable in identifying the most prominent networked frames, it misses to detects less dominant frames. Our investigation also confirmed that LDA works better on larger datasets and lexical semantics. Finally, we argued that LDA could give us some primary intuitions, but qualitative interpretations are indispensable for understanding the deeper layers of meaning

Towards Optimized and Constant-Time CSIDH on Embedded Devices

We present an optimized, constant-time software library for commutative supersingular isogeny Diffie-Hellman key exchange (CSIDH) proposed by Castryck et al. which targets 64-bit ARM processors. The proposed library is implemented based on highly-optimized field arithmetic operations and computes the entire key exchange in constant-time. The proposed implementation is resistant to timing attacks. We adopt optimization techniques to evaluate the highest performance CSIDH on ARM-powered embedded devices such as cellphones, analyzing the possibility of using such a scheme in the quantum era. To the best of our knowledge, the proposed implementation is the first constant-time implementation of CSIDH and the first evaluation of this scheme on embedded devices. The benchmark result on a Google Pixel 2 smartphone equipped with 64-bit high-performance ARM Cortex-A72 core shows that it takes almost 12 seconds for each party to compute a commutative action operation in constant-time over the 511-bit finite field proposed by Castryck et al. However, using uniform but variable-time Montgomery ladder with security considerations improves these results significantly

Rectangular Symmetry Morphologies in a Topographically Templated Block Copolymer

Using an array of majority-block-functionalized posts makes it possible to locally control the self-assembly of a block copolymer and achieve several morphologies on a single substrate. A template consisting of a square symmetry array of posts produces a square-symmetry lattice of microdomains, which doubles the areal density of features.Semiconductor Research CorporationFENA CenterSemiconductor Research Corporation. Nanoscale Research InitiativeSingapore-MIT AllianceNational Science Foundation (U.S.)Taiwan Semiconductor Manufacturing CompanyTokyo Electron LimitedNational University of Singapor

Optimized Supersingular Isogeny Key Encapsulation on ARMv8 Processors

In this work, we present highly-optimized constant-time software libraries for Supersingular Isogeny Key Encapsulation (SIKE) protocol on ARMv8 processors. Our optimized hand-crafted assembly libraries provide the most efficient timing results on 64-bit ARM-powered devices. Moreover, the presented libraries can be integrated into any other cryptography primitives targeting the same finite field size. We design a new mixed implementation of field arithmetic on 64-bit ARM processors by exploiting the A64 and Advanced SIMD processing units working in parallel. Using these techniques, we are able to improve the performance of the entire protocol by the factor of 5 times compared to optimized C implementations on 64-bit ARM high-performance cores, providing 83-, 124-, and 159-bit quantum-security levels. Furthermore, we compare the performance of our proposed library with the previous highly-optimized ARMv8 assembly library available in the literature. The implementation results illustrate the overall 10% performance improvement in comparison with previous work, highlighting the benefit of using mixed implementation over relatively-large finite field size