¨Uber nilpotente Bahnen, einfache Singularit¨aten und modular invariante Partitionsfunktionen

Helmke, Stefan Univ. Hamburg 1994 국내박사

Ruling against the rulers: Court-executive relations in Argentina under dictatorship and democracy

Helmke, Gretchen The University of Chicago 2000 해외박사(DDOD)

This study is about court-executive relations under dictatorship and democracy. Set in the context of contemporary Latin America, the puzzle I seek to explain is why judges who lack basic institutional security rule against the government in power, and sometimes against the very government by whom they were appointed. Drawing on classic and contemporary institutionalist theories that treat judges as strategic decision-makers, I argue that executives exert control over judges through two related but distinct mechanisms: selection and sanctioning. Where my study differs from the existing scholarship is with the idea that whenever the threat of sanctions is posed by incoming governments, sanctioning can undo the effects of selection. I refer to the phenomenon that emerges as “strategic defection.” In stark contrast to existing accounts, the core prediction is that anti-governmental rulings follow a reverse legal-political cycle in which the court shifts against its own appointers at the end of the government's term. The result is a simple but powerful theory that accounts for why, when, and how judges rule against the government and that sheds new light on the limits to executive power in presidentialist systems. To evaluate this new theoretical approach to inter-branch relations, I draw on a range of original empirical data on court-executive relations in Argentina gathered during fourteen months of field research in Buenos Aires. Along with a series of elite interviews with politicians, judges, and lawyers, and qualitative analyses of several leading cases under dictatorship and democracy in key areas such as human rights, economic privatization, and executive powers, I present original systematic data on judicial decisions drawn from a database that I constructed. The database contains nearly 4,000 votes by justices in decisions handed down by the Argentine Supreme Court over the last two and half decades. I conclude with an evaluation of the normative implications of the study and with an assessment of the future research agenda it provides for the comparative analyses of inter-branch relations more generally.

Studies of solute transport through fractured till in Iowa

Helmke, Martin Frederick Iowa State University 2003 해외박사(DDOD)

Fractures may provide pathways for agricultural chemicals to reach aquifers through till units that have traditionally been considered effective barriers to contaminant transport. Till units were studied at three sites in Iowa that represented three landform regions, till ages from 12.5 to >730 ka, and depths from 1 to 27.5 m. Fractures were present at all study locations and at all depths, including one site where fractures intersected an aquifer at 30 m depth. Laboratory experiments using eight large (0.40 to 0.45 m in length and 0.43 m in diameter), undisturbed columns of till showed bulk hydraulic conductivity (<italic>K_b</italic>) ranging from 7.7 × 10<super>−10</super> to 3.8 × 10<super>−5</super> m/s, which is generally greater than the matrix hydraulic conductivity reported in the literature. Laboratory experiments with KBr, PFBA, PIPES, KNO₃, and atrazine as tracers were used to produce breakthrough curves (BTCs). First arrival velocities of Br ranged from 0.004 to 64.8 m/d—10 to 100 times faster than predicted using the equivalent porous medium (EPM) assumption. Similar velocities of NO₃ and atrazine were observed for columns collected from depths of less than 3 m. In deeper columns, sorption (atrazine) and degradation (NO₃ and atrazine) retarded transport. Tracers were not affected significantly by fracture origin or orientation. Separation of conservative tracers with different aqueous diffusion coefficients was observed during the rising and tailing limbs of BTCs, which indicates that matrix diffusion was a controlling process. Laboratory BTCs were compared against model-simulated BTCs using three approaches: the Mobile-Immobile Model (MIM), the Parallel-plate Discrete Fracture Model (PDFM), and a 3-Dimensional Discrete Fracture Model (3-D DFM). All three model approaches were reasonable predictors of the BTCs (goodness-of-fit statistic <italic>d₁</italic> ranged from 0.751 to 0.959). The results of this study demonstrate that fractures may have a controlling influence on solute transport through till units in Iowa. Contaminants may be transported rapidly through thin aquitards of fractured till, but non-conservative compounds are likely to be retarded or degraded in thicker till units. Fractures should be considered in groundwater studies in glaciated regions and in assessments of aquifer vulnerability to non-point source pollution.

Essays on Index Investing

Helmke, Anna Theresa University of Pennsylvania ProQuest Dissertations 2024 해외박사(DDOD)

The shift from active to passive investing has been one of the most important trends in finance over the past decade. Index investing, through open-end mutual funds and exchange-traded funds (ETFs), has emerged as the preferred strategy for long-term portfolio management across retail investors and a growing number of institutional investors. Mutual funds and ETFs control nearly equal portions of the over $9tn in assets under management (AUM) within U.S-registered public index funds. Despite the perceived advantages of ETFs-including superior tax efficiency, intraday trading, and lower minimum investments-index mutual funds continue to maintain a substantial presence, prompting questions about their role in the world of passive investing.In this dissertation, I study the payoff differences between ETFs and index open-end mutual funds over the short and long term. I build a model and establish that same-index ETFs and mutual funds provide liquidity at different horizons. I challenge the conventional wisdom that ETFs are inherently more liquid than open-end mutual funds solely because they are traded intra-day on exchange. Investors facing higher (lower) liquidity needs prefer mutual funds (ETFs). Since they can be redeemed at net asset value (NAV), mutual funds holding illiquid assets provide higher payoffs when investors must liquidate fund shares at short notice. Yet, the resulting payoff complementarities make them underperform ETFs in the long run. ETFs, however, are subject to mispricing and illiquidity in the short term, particularly in times of market stress, due to arbitrageurs' balance-sheet constraints. In equilibrium, both funds coexist when investors face heterogeneous liquidity needs.My model generates novel, testable predictions concerning the competition and future trajectory of index ETFs and mutual funds. ETFs are particularly suited for less liquid asset classes with a relatively patient investor base. Regulators should encourage retirement plan sponsors to add ETFs to the investment menu, given their potential advantages. Additionally, swing pricing not only reduces externalities among mutual funds investors but can also help mutual funds maintain a larger size vis-a-vis ETFs. Multi-share class fund structures benefit shareholders in the mutual fund share classes at the expense of investors in the ETF share class.