This paper includes a survey on sorne modern methods that are used for describing and analyzing behavior of complex systems. It is believed that most safety problems arise in the interface between the controlling parts and other controlled subsystems. Therefore, a prerequisite for a good interface is an accurate definition of the system. Two objectives are evaluated: the description power and the analysis power for safety and timing properties. This is done by describing and analyzing a simple system that is composed of two doors, which are restricted by time and "safety" requirements. It is found that although good description methods do exist, their usefulness for analyzing safety timed properties is very limited.

This paper presents statistical analysis supporting stylized facts about sovereign wealth funds (SWFs). It discusses the forces leading to the growth of SWFs, including the role of fuel exports and ongoing current account surpluses, and large hoarding of international reserves. It analyzes the degree to which measures of SWF governance and transparency compare with national norms of behavior. We provide evidence that many countries with SWFs are characterized by good governance, but weak democratic institutions, as compared to other nonindustrial countries. We also present a model with which we compare the optimal degree of diversification abroad by a central bank versus that of a sovereign wealth fund. We show that if the central bank manages its foreign assets with the objective of reducing the probability of sudden stops, it will place a high weight on the downside risk of holding risky assets abroad and will tend to hold primarily safe foreign assets. In contrast, if the sovereign wealth fund, acting on behalf of the Treasury, maximizes the expected utility of a representative domestic agent, it will opt for relatively greater holding of more risky foreign assets. We discuss how the degree of a country’s transparency may affect the size of the foreign asset base entrusted to a wealth fund’s management, and show that, for relatively low levels of public foreign assets, assigning portfolio management independence to the central bank may be desirable. However, for a large enough foreign asset base, the opportunity cost associated with the limited portfolio diversification of the central bank induces authorities to establish a wealth fund in pursuit of higher returns.

This paper studies the empirical and theoretical association between the duration of a pegged exchange rate and the cost experienced upon exiting the regime. We confirm empirically that exits from pegged exchange rate regimes during the past two decades have often been accompanied by crises, the cost of which increases with the duration of the peg before the crisis. We explain these observations in a framework in which the exchange rate peg is used as a commitment mechanism to achieve inflation stability, but multiple equilibria are possible. We show that there are ex ante large gains from choosing a more conservative not only in order to mitigate the inflation bias from the well-known time inconsistency problem, but also to steer the economy away from the high inflation equilibria. These gains, however, come at a cost in the form of the monetary authority’s lesser responsiveness to output shocks. In these circumstances, using a pegged exchange rate as an anti-inflation commitment device can create a “trap” whereby the regime initially confers gains in anti-inflation credibility, but ultimately results in an exit occasioned by a big enough adverse real shock that creates large welfare losses to the economy. We also show that the more conservative is the regime in place and the larger is the cost of regime change, the longer will be the average spell of the fixed exchange rate regime, and the greater the output contraction at the time of a regime change.

This paper clarifies one of the puzzling results of the economic growth literature: the impact of military expenditure is frequently found to be non-significant or negative, yet most countries spend a large fraction of their GDP on defense and the military. We start by empirical evaluation of the non-linear interactions between military expenditure, external threats, corruption, and other relevant controls. While growth falls with higher levels of military spending, given the values of the other independent variables, we show that military expenditure in the presence of threats increases growth. We explain the presence of these non-linearities in an extended version of Barro and Sala-i-Martin (1995), allowing the dependence of growth on the severity of external threats, and on the effective military expenditure associated with these threats.

Understanding biology at the molecular level has been driving technological advances in biological and medical science for many years. Methods for probing molecular systems are often dependent on sampling the concerted actions of large assemblies of molecules rather than for studying individual molecules operating in isolation. Most methods used in experimental biology are largely insensitive to the activity of a single molecule. Over the past twenty five years, advances in a variety of disciplines have been employed which allow researchers to use single molecule approaches to for examining biomolecules, a development which has had remarkable implications for advancing the understanding of cellular processes. Single molecule techniques have been used to resolve questions about everything from replication, recombination, transcription and translation and protein folding, among other subjects.

The structure-function relationship in biology is central to the understanding of cellular processes, and has provided one of the most significant intellectual frameworks for understanding molecular pathways. Its success is validated by numerous studies using X-ray crystallography that now routinely allow researchers to make rational predictions explaining why and how biomolecules interact. The famous "lock and key" model for enzymatic function perhaps best exemplifies this framework. Despite their predictive power, structure-functional relationships often gloss over a basic fact of biological systems--both structure and function may in fact possess a remarkable degree of dynamism.

This dissertation summarizes my efforts to develop and refine methods for interrogating the dynamical properties of single molecules, with a particular emphasis on studying structural properties of DNA and examining protein-DNA interactions. I provide an overview of fluorescence, FRET and fluorescence lifetime spectroscopy in Chapter 1, and discuss the methods I developed using fluorescence lifetime to examine conformational fluctuations of sub-persistence length segments of DNA. In Chapter 2, I describe a microfluidic-based platform developed in the Shimon Weiss Lab for conducting single molecule FRET assays, which was used to exploit persistence length changes in DNA upon hybridization to screen context-dependent RNA polymerase transcription. Finally, in Chapter 3, I describe a new detector with improved red spectrum sensitivity, which provides a foundation for further work applying fluorescence lifetime analysis to studying structural perturbations in DNA on nanosecond timescales.

Are countries with unregulated capital flows more vulnerable to currency crises? Efforts to answer this question properly must control for “self selection” bias since countries with liberalized capital accounts may also have more sound economic policies and institutions that make them less likely to experience crises. We employ a matching and propensity score methodology to address this issue in a panel analysis of developing countries. Our results suggest that, after controlling for sample selection bias, countries with liberalized capital accounts experience a lower likelihood of currency crises. That is, when two countries have the same likelihood of allowing free movement of capital (based on historical evidence and a very similar set of economic and political characteristics)—and one country imposes controls and the other does not-- the country without controls has a lower likelihood of experiencing a currency crisis. This result is at odds with the conventional wisdom and suggests that the benefits of capital market liberalization for external stability are substantial.

Are countries with unregulated capital flows more vulnerable to currency crises? Efforts to answer this question properly must control for “self selection” bias since countries with liberalized capital accounts may also have more sound economic policies and institutions that make them less likely to experience crises. We employ a matching and propensity score methodology to address this issue in a panel analysis of developing countries. Our results suggest that, after controlling for sample selection bias, countries with liberalized capital accounts experience a lower likelihood of currency crises. That is, when two countries have the same likelihood of allowing free movement of capital (based on historical evidence and a very similar set of economic and political characteristics)—and one country imposes controls and the other does not-- the country without controls has a lower likelihood of experiencing a currency crisis. This result is at odds with the conventional wisdom and suggests that the benefits of capital market liberalization for external stability are substantial.