A Vertex Formalism for Local Ruled Surfaces

We develop a vertex formalism for topological string amplitudes on ruled surfaces with an arbitrary number of reducible fibers embedded in a Calabi-Yau threefold. Our construction is based on large N duality and localization with respect to a degenerate torus action. We also discuss potential generalizations of our formalism to a broader class of Calabi-Yau threefolds using the same underlying principles.Comment: 24 pages, 12 figures; v2: minor changes; v3: explanations added, results unchange

Metastable Quivers in String Compactifications

We propose a scenario for dynamical supersymmetry breaking in string compactifications based on geometric engineering of quiver gauge theories. In particular we show that the runaway behavior of fractional branes at del Pezzo singularities can be stabilized by a flux superpotential in compact models. Our construction relies on homological mirror symmetry for orientifolds.Comment: 22 pages, 1 figure; v2: references adde

Geometric Transitions and Open String Instantons

We investigate the physical and mathematical structure of a new class of geometric transitions proposed by Aganagic and Vafa. The distinctive aspect of these transitions is the presence of open string instanton corrections to Chern-Simons theory. We find a precise match between open and closed string topological amplitudes applying a beautiful idea proposed by Witten some time ago. The closed string amplitudes are reproduced from an open string perspective as a result of a fascinating interplay of enumerative techniques and Chern-Simons computations.Comment: 24 pages, 4 figures, published versio

Self -assembly on strained metallic interfaces, and, Novel collective excitations on metal surfaces

Recent interest in novel physical properties of reduced dimensional systems is spurred by the advance of investigation methods at the nanoscale. Understanding bottom-up techniques for the growth of nanomaterials with novel physical, chemical, and mechanical properties require specialized investigation tools. I am presenting a novel design and performance of an ultra high vacuum scanning tunneling microscope (STM) that allows for large scale (8 mum x 8 mum), fast scanning (3 s for a 100 A x 100 A frame), and atomically resolved studies of reduced dimensional systems on metallic surfaces. The STM proved excellent performance, allowing for variable temperature (100 K to 700 K) and high resolution (\u3c 2 pm at 300 K) structural and dynamical studies on surfaces, as shown by the STM study of the general types of self-assembly processes on strained metallic interfaces. With this new instrument, I performed a complete experimental investigation of the misfit dislocation network of one atom thick Ag films on Ru(0001) and of the restructuring induced by molecular sulfur adsorption when S filled Ag vacancy island are formed. The experiments suggest that the mechanism through which hundreds of Ag atoms are rear-ranging themselves following S deposition is driven by a process of threading dislocation pair annihilation and glide. The experimental observations are explained via an atomistic model, which is based on first-principles interaction parameters. I have found that the self-assembly process is driven by stress relaxation in the Ag film. While the first part of my thesis is focused on the structural properties of low-dimensional metallic systems and instrumentation methods needed to access the nano-scale, in the secand part I investigated a novel low-energy electronic excitation of a metallic surface. I am presenting the first experimental measurement of an acoustic surface plasmon on metal surfaces. The experiment was performed using electron energy loss spectroscopy on Be(0001). This new mode is a collective excitation of the surface electrons. This discovery goes against the traditional wisdom that on metal surfaces only regular (optical) surface plasmons can exist. First-principles calculations show that this mode is caused by the coexistence of a partially occupied surface state band with the underlying bulk electrons

Possibilities to Limit the Values of Clinical and Biochemical Parameters in Experimental Arterial Hypertension

The aim of this study is to estimate the influence of polyphenolic compounds, renin inhibitors (Aliskiren) and their association on clinical and biochemical parameters, on an experimental model of arterial hypertension (AHT). The combination of Aliskiren and polyphenolic extract has the effect of reducing systolic and diastolic blood pressure. Experimental data highlight the hypocholesterolemic, antiatheromatous, hypolipidemic and cardioprotective effects of polyphenolic extracts. The results demonstrate a significant decrease in the measured biochemical parameters of the oxidative stress (unspecific - ceruloplasmin, uric acid and enzyme - GSH-Px and SOD) of the groups treated with polyphenolic extracts. In the polyphenolically protected AHT group there are statistically significant differences compared to the AHT group, regarding the platelet adhesion index. Aliskiren has more evident vascular protective effects when associated with polyphenols in the experimental AHT compared to unprotected hypertensive group. The antioxidant properties of anthocyanins, combined with the vascular properties of these substances, recommend them as promising therapeutic agents in the prevention/therapy of cardiovascular disorders in general and of AHT in particular. The characterization of polyphenolic extracts, as well as the studies on biocompatibility, will constitute the baseline for understanding the mechanisms, by which phytopreparations can be used for preventive or adjuvant therapeutic purposes

The Ruled Vertex and Nontoric del Pezzo Surfaces

We construct the topological partition function of local nontoric del Pezzo surfaces using the ruled vertex formalism.Comment: 16 pages, 4 figure

Dirichlet Branes on Orbifolds

The D-brane spectrum of a class of \Zop_2 orbifolds of toroidally compactified Type IIA and Type IIB string theory is analysed systematically. The corresponding K-theory groups are determined and complete agreement is found. The charge densities of the various branes are also calculated