Thermodynamic Contributions of Various Metal-Nucleotide Complexes Binding to Yeast Phosphoglycerate Kinase

The purpose of this study was to determine the thermodynamic parameters of various enzyme-substrate complexes of Yeast Phosphoglycerate Kinase by using Isothermal Titration Calorimetry (ITC). The addition of metal-nucleotide substrate to a PGK solution elicited an exothermic response ranging from 0.5 kilocalories to 2.8 kilocalories. Titrations of MgATP and MgADP into PGK yielding binary complexes generated a greater amount of heat than titrations of MgADP into PGA-PGK and MgAMP-PCP into PGA-PGK yielding ternary complexes. The entropic contribution of the ternary complex formations was significantly greater than binary complex formations. Although entropic and enthalpic contributions varied, the Gibbs free energy remained relatively constant for the binary and ternary enzyme-substrate complexes. This data suggests that the entropic contribution becomes more dominant when PGA was added to form ternary complex of enzyme and ligand. The titration of sugar substrate, 3-phosphoglyceric acid (PGA), into a PGK solution yielded an endothermic signal. The magnitude of the thermodynamic parameters remained elusive however. Numerous different regulatory molecules, which share many of the ionic characteristics of PGA, have been demonstrated to bind PGK in as many as six different regions within the catalytic core and along the periphery of the protein. As a result, titrations of PGA into PGK did not yield interpretable thermodynamic data. Enthalpy is a global entity encompassing the heat change of the entire system, and consequently each titration likely included PGA binding at the desired active site in addition to a combination of other binding events at different areas of the enzyme. Finally, the addition of sulfate to the various PGK complexes increased the dissociation constant of most of the substrates from the binary and ternary enzyme-substrate complexes and altered all thermodynamic properties of these complexes

Forcing welfare recipients into a lose-lose situation : political economy and Families First

The media have portrayed this new round of welfare reform as innovative and revolutionary. Welfare recipients are finally forced back into the workforce and can no longer rely on the federal government for a lifetime of financial security. The recent wave of media coverage portrays welfare recipients and employment as an independent phenomenon. This thesis delves into these complex issues by studying economic trends in the last half of the twentieth century and their effect on the economy. It also analyzes welfare recipients\u27 ability to find financially sustainable employment in this new economy, appropriately labeled the age of global capitalism. Historical analysis and political economy are used as theoretical foundations for this paper to show how these phenomena are linked. Manufacturing industries have been the basis of the American economy since its foundation. In the last half of the twentieth century, services industries grew, overtaking manufacturing as the largest employer in the United States. This trend and the introduction of global capitalism produced dramatic changes in the economic structure of the United States. The manufacturing sector of the economy is disappearing. An enlarging dead-end employment branch is rising to absorb the leftover employees of the former middle class employment bracket. A bifurcated economy has risen as in the wake of the collision of all these phenomena. The result is two employment tracks; that of the knowledge-intensive work force, and the uneducated, low paying, minimal stability employees. The latest phase of welfare reform requires welfare recipients to enter the work force. There are immediate time limits and life time limits to enforce this policy. This thesis was aimed at discovering what economic prospect welfare recipients have now that they are being thrust into employment. Fifteen in-depth interviews were conducted to discover the types of job welfare recipients have held in the past, what training is available to them, and for what kinds of employment they will be eligible in the future. This study found that welfare recipients are being pushed into the lower employment echelon. The training system for Families First is decentralized and prepares individuals for employment with low pay and stability, usually in the services industries. With the added costs of health care, transportation, childcare, and food, welfare recipients are forced off of welfare and into the working poor population

Parity effect in ground state localization of antiferromagnetic chains coupled to a ferromagnet

We investigate the ground states of antiferromagnetic Mn nanochains on Ni(110) by spin-polarized scanning tunneling microscopy in combination with theory. While the ferrimagnetic linear trimer experimentally shows the predicted collinear classical ground state, no magnetic contrast was observed for dimers and tetramers where non-collinear structures were expected based on ab-initio theory. This striking observation can be explained by zero-point energy motion for even numbered chains derived within a classical equation of motion leading to non classical ground states. Thus, depending on the parity of the chain length, the system shows a classical or a quantum behavior.Comment: 5 pages, 4 figures and supplementary informatio

What kind of individual support activities in interventions foster pre-service and beginning teachers’ self-efficacy? A meta-analysis

During the early stages of the teaching profession, pre-service and beginning teachers often participate in individual support activities intended to develop their teacher self-efficacy. These individual support activities (modeling, feedback on lesson plans or lessons, and reflection) are provided as part of an intervention by a mentor, cooperating teacher, instructor, or supervisor. We conducted a meta-analysis to investigate the effectiveness of these interventions and the individual support activities for pre-service and beginning teachers’ self-efficacy. We found a medium-sized overall effect of interventions on teacher self-efficacy based on 28 studies (49 effect sizes) in our meta-analysis. Providing feedback on lesson plans amplified the intervention effect (large effect). However, this moderator effect slightly missed the significance level of 0.05. The moderator effect of providing feedback on lesson plans was stable after controlling for mastery experiences and methodological moderator variables. Implications for future interventions regarding teacher self-efficacy for early career teachers are discussed

Design, production and characterization of mirrors for ultra-broadband, high-finesse enhancement cavities

To enable the enhancement of few-cycle pulses in high-finesse passive optical resonators, a novel complementary-phase approach is considered for the resonator mirrors. The design challenges and first experimental results are presented.Comment: 3 page

A Comprehensive Numerical Approach to Coil Placement in Cerebral Aneurysms: Mathematical Modeling and In Silico Occlusion Classification

Endovascular coil embolization is one of the primary treatment techniques for cerebral aneurysms. Although it is a well established and minimally invasive method, it bears the risk of sub-optimal coil placement which can lead to incomplete occlusion of the aneurysm possibly causing recurrence. One of the key features of coils is that they have an imprinted natural shape supporting the fixation within the aneurysm. For the spatial discretization our mathematical coil model is based on the Discrete Elastic Rod model which results in a dimension-reduced 1D system of differential equations. We include bending and twisting responses to account for the coils natural curvature. Collisions between coil segments and the aneurysm-wall are handled by an efficient contact algorithm that relies on an octree based collision detection. The numerical solution of the model is obtained by a symplectic semi-implicit Euler time stepping method. Our model can be easily incorporated into blood flow simulations of embolized aneurysms. In order to differentiate optimal from sub-optimal placements, we employ a suitable in silico Raymond-Roy type occlusion classification and measure the local packing density in the aneurysm at its neck, wall-region and core. We investigate the impact of uncertainties in the coil parameters and embolization procedure. To this end, we vary the position and the angle of insertion of the microcatheter, and approximate the local packing density distributions by evaluating sample statistics

Enhancement cavities for attosecond physics

The work presented in this thesis was aimed at developing a high-repetition rate source of coherent radiation in the extreme ultra-violet (XUV) spectral region, envisaging applications in attosecond physics or precision metrology in the XUV. Due to the lack of laser oscillators operating in the XUV, the method of choice was the frequency upconversion of a near-infrared laser via the nonlinear process of high-order harmonic generation. Obtaining sufficient XUV photon flux per pulse at repetition rates of several tens of MHz, despite the inherently low conversion efficiency, requires a powerful driving source. To date, passive enhancement of ultrashort pulses in an external resonator has been the most successful strategy in meeting this demand. In this thesis four main achievements towards extending this technique and understanding its limitations are presented. A first experiment was dedicated to obtaining shorter intracavity pulses without compromising the high average power available from Yb-based laser technology. To this end, we spectrally broadened and temporally compressed the pulses prior to the enhancement in a broadband resonator. Aside from being a prerequisite for time-domain applications, shorter intracavity pulses led to improved conditions for the harmonic generation process. Furthermore, we addressed the task of extracting the intracavity generated XUV light. We established two methods for geometrical XUV output coupling, one employing the fundamental mode of the cavity, and the other a tailored transverse mode, which offers additional degrees of freedom to shape the harmonic emission. Both techniques are particularly suited for the intracavity generation of attosecond pulses, because they afford an unparalleled flexibility for the resonator design, and exhibit a broadband output coupling efficiency approaching unity for short-wavelength radiation. This enabled a significant improvement of the crucial parameters, photon flux and photon energy. In a combined experimental and theoretical study, we investigated the ionization-related intensity limitations observed in state-of-the-art enhancement cavities. The quantitative modeling of the nonlinear interaction allows for an estimation of the achievable intracavity parameters and for a global optimization of the XUV photon flux. Based on this model, we proposed a strategy to mitigate this limitation by using the nonlinearity in combination with customized cavity optics for a further spectral broadening and temporal compression of the pulse in the resonator. More importantly, this work establishes enhancement cavities as a tool to investigate nonlinear light-matter interactions with the increased sensitivity provided by the resonator. The last study was dedicated to the technological challenge of building a resonator in which the electric field of the circulating pulse is reproduced at each round-trip. This is an essential prerequisite to generate identical XUV emission with each driving pulse. By tailoring the spectral phase of the cavity mirrors we succeeded in enhancing pulses of less than 30 fs (less than nine cycles of the driving field) to a few kilowatts of average power with zero pulse-to-pulse carrier-to-envelope phase slip. At similar pulse durations, the generation of isolated attosecond pulses has already been demonstrated in single-pass geometries. In conclusion, the results presented in this thesis are milestones on the way to a powerful, compact and coherent source of ultrashort XUV radiation. The unique property of the source, that is, its high repetition rate lays the foundation for advancing attosecond physics and precision spectroscopy in the XUV regionZiel dieser Arbeit war die Entwicklung einer Quelle die kohärentes Licht im extrem-ultravioletten (XUV) Spektralbereich mit sehr hohen Repetitionsraten liefert und neue Forschungsfelder in der Attosekundenphysik oder der Präzisionsmetrologie im XUV ermöglicht. Aufgrund des Nichtvorhandenseins an Laseroszillatoren in diesem Spektralbereich beruht die Quelle auf der Erzeugung hoher Harmonischer von Laserlicht im nahen Infrarot. Um trotz inhärent niedriger Konversionseffizienz ausreichend XUV Photonen pro Puls bei Wiederholraten von mehreren 10MHz zu erhalten, sind hohe treibende Leistungen nötig. Vom heutigen Standpunkt ist dafür die passive Überhöhung von Laserpulsen in einem externen Resonator der vielversprechendste Ansatz. Mit der vorliegenden Arbeit werden vier Beiträge zur Erweiterung dieser Technik geleistet und neue Limitierungen aufgezeigt. Das erste Experiment befasste sich damit, kürzere Pulsdauern im Resonator zu erzielen, ohne auf die hohen Durchschnittsleistungen der Yb-Lasersysteme zu verzichten. Dies gelang durch spektrale Verbreiterung und anschließender zeitlicher Kompression der Pulse vor der Überhöhung in einem breitbandigen Resonator. Neben der Notwendigkeit kürzerer treibender Laserpulse für die angestrebten Anwendungen im Zeitbereich konnte gezeigt werden, dass sich mit kürzerer Pulsdauer auch die Bedingungen für die XUV Erzeugung verbessern. Außerdem wurden zwei neue geometrische Verfahren zur Auskopplung der XUV Strahlung aus dem Resonator demonstriert. Beim ersten Verfahren wird der Resonator mit der fundamentalen transversalen Mode betrieben. Das Zweite basiert auf einer speziell angepassten Feldverteilung im Resonator, wodurch neue Freiheitsgrade für die Erzeugung der Harmonischen ermöglicht werden. Beide Methoden eignen sich ideal für die Auskopplung von Attosekundenpulsen, da sie mit einer großen Flexibilität des Resonatordesigns einhergehen und eine Auskopplungseffizienz bieten, die für kurzwellige Strahlung gegen 100% tendiert. So konnten die beiden wichtigsten Parameter, die Photonenenergie und der Photonenfluss, deutlich erweitert bzw. gesteigert werden. In einer weiteren Studie wurden ionisationsbedingte Intensitätslimitierungen im Resonator in Theorie und Experiment untersucht. Die Modellierung der nichtlinearen Wechselwirkung im Resonator erlaubt erstmals eine Abschätzung der erreichbaren Pulsparameter und damit eine vollständige Optimierung des XUV Photonenflusses. Darauf aufbauend wurde eine Strategie vorgeschlagen, um die Beschränkung der Intensität zu entschärfen: Diese nutzt die Nichtlinearität in Verbindung mit speziellen Resonatorspiegeln, um eine weitere spektrale Verbreiterung und Pulskompression im Resonator zu erreichen. Darüber hinaus etabliert dieser Forschungsbeitrag Überhöhungsresonatoren als Messinstrumente zur präzisen Charakterisierung von nichtlinearen Wechselwirkungen. Der letzte Teil der Arbeit widmet sich der technologischen Herausforderung den Resonator so auszulegen, dass sich das elektrische Feld des Pulses von Umlauf zu Umlauf am Interaktionspunkt reproduziert. Dies ist eine notwendige Voraussetzung für identische XUV Erzeugung bei jedem treibenden Puls. Durch Optimierung der spektralen Phase der Resonatorspiegel konnte ein umlaufender Puls von weniger als 30 fs (weniger als neun Zyklen des elektrischen Feldes) bei einigen Kilowatt mittlerer Leistung erreicht werden, dessen elektrisches Feld konstant bleibt. Für vergleichbare treibende Pulsdauern wurde bereits in Experimenten ohne Resonator die Erzeugung isolierter XUV Pulse mit Pulsdauern im Attosekundenbereich gezeigt. Zusammenfassend stellen diese Ergebnisse Meilensteine auf dem Weg zu einer kompakten, leistungsstarken Quelle von kohärenter, gepulster XUV Strahlung dar, deren Alleinstellungsmerkmal die hohe Repetitionsrate, weitere Fortschritte in der Attosekundenphysik und der Frequenzkammspektroskopie ermöglicht