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No description available.

No description available.

No description available.

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Niobium cavities are important components in modern particle accelerators based on superconducting radio frequency (SRF) technology. The interior of SRF cavities are cleaned and polished in order to produce high accelerating field and low power dissipation on the cavity wall. Current polishing methods, buffered chemical polishing (BCP) and electropolishing (EP), have their advantages and limitations. We seek to improve current methods and explore laser polishing (LP) as a greener alternative of chemical methods. The topography and removal rate of BCP at different conditions (duration, temperature, sample orientation, flow rate) was studied with optical microscopy, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). Differential etching on different crystal orientations is the main contributor to fine grain niobium BCP topography, with gas evolution playing a secondary role. The surface of single crystal and bi-crystal niobium is smooth even after heavy BCP. The topography of fine grain niobium depends on total removal. The removal rate increases with temperature and surface acid flow rate within the rage of 0~20 °C, with chemical reaction being the possible dominate rate control mechanism. Surface flow helps to regulate temperature and avoid gas accumulation on the surface. The effect of surface flow rate on niobium EP was studied with optical microscopy, atomic force microscopy (AFM), and power spectral density (PSD) analysis. Within the range of 0~3.7 cm/s, no significant difference was found on the removal rate and the macro roughness. Possible improvement on the micro roughness with increased surface flow rate was observed. The effect of fluence and pulse accumulation on niobium topography during LP was studied with optical microscopy, SEM, AFM, and PSD analysis. Polishing on micro scale was achieved within fluence range of 0.57~0.90 J/cm 2, with pulse accumulation adjusted accordingly. Larger area treatment was proved possible by overlapping laser tracks at proper ratio. Comparison of topography and PSD indicates that LP smooths the surface in a way similar to EP. The optimized LP parameters were applied to different types of niobium surfaces representing different stages in cavity fabrication. LP reduces the sharpness on rough surfaces effectively, while doing no harm to smooth surfaces. Secondary ion mass spectrometer (SIMS) analysis showed that LP reduces the oxide layer slightly and no contamination occurred from LP. EBSD showed no significant change on crystal structure after LP.

The complex social relationships in society can be understood as a network. In recent years, complex networks have given researchers a more accurate picture of social interactions than aggregation models such as compartmental models had hitherto provided. Compartmental models which collect individuals into population classes based on infection state, for instance, had left out local interactions that could be important for understanding social relationships and attendant phenomena such as epidemics, rumors, etc., in the society. Topics of modeling for complex networks have included the dynamics of social relationships and how they affect disease and opinion spread. Different types of relationships, such as friendly or unfriendly, have been considered. In this dissertation we study social network models in which interactions can be beneficial or detrimental to the parties involved. Motivated by HIV, in which a person's infection status is not readily known to others, we implement a model where individual decisions may affect the disease transmission. Individuals in such a situation may use information about each other's behavior such as the number of connections (degree) to form a risk-benefit assessment for whether to engage in a relationship. We study this model for a single benefit case, and then a multiple benefit case. We also investigate the case where offspring may inherit the benefit of their parents to determine how this affects disease transmission. We find that human behavior and individual differences can affect infection transmission and that adaptation in behavior can mitigate the disease prevalence. Further, we study mutual ratings in a growing social network. We use two types of links, positive for favorable ratings between two nodes, and negative otherwise. We model a social network where positive and negative ratings are assigned preferentially based on existing positive and negative links. Extending previous ideas and analytical methods in the growing networks literature, we study the resulting network structure. For one of the preferential attachment mechanisms we consider, we derive an analytical expression for the joint distribution of positive and negative degrees in the limit of large networks. The insights gleaned in these studies will inform potential investigations of the impact of personal decisions on transmission of STIs such as HIV, and empirical studies of the evolution of friend-foe relationships on online social networks that have mechanisms for users to note or express opinions about other users or the contributions they made.

A gene x environment interaction exists in the expression of anxiety for both human and nonhuman primates, such that individuals who are carriers of the (s) allele of the serotonin transporter genotype (5-HTTLPR) and exposed to early life stress are more at risk for exhibiting anxiety. The hypothalamic-pituitary-adrenal (HPA) axis has also been implicated in anxiety disorders but the relationship between early life/genotype, HPA activity, and anxiety is not well understood. Further, studies linking the HPA axis to anxiety have relied on "point" samples (blood and salivary cortisol) which reflect moments in time rather than long-term activity. The purpose of this dissertation was three fold: (1) to examine anxious behavior in monkeys with different 5-HTTLPR genotypes and rearing environments across the first two years of life, (2) to compare long-term HPA activity (as measured with hair cortisol) with acute HPA activity (as measured with salivary cortisol) in the same period, and (3) to determine which measure of HPA activity predicts anxiety and/or mediates the rearing/genotype influences on anxious behavior. Infant rhesus monkeys (Macaca mulatta, N=61) were mother-peer-reared (MPR, n=21), peer-reared (PR, n=20), or surrogate-peer-reared (SPR, n=20) for 8 months, then all relocated into a large social housing situation for the next 18 months. Monkeys were genotyped for 5-HTTLPR and hair and saliva samples were collected for cortisol analysis at months 6, 12, 18, and 24. Behavior was recorded twice per week per subject from 2-24 months and analyzed for the duration of anxiety, social play, and grooming. Regression analysis established predictors of these behaviors. Rearing condition and sex were significant predictors of anxiety across the two years, and HPA activity added significant predictive power in the first six months only. Mediation of the rearing/anxiety relationship by the HPA axis was not evident. Interestingly, hair (but not salivary) cortisol early in life was positively correlated with later anxious behavior. These findings demonstrate the detrimental effects of adverse early life experience on behavioral development and shed light on the interplay between environment, adrenocortical activity, and anxiety. They further demonstrate the usefulness of a long-term measure of HPA activity in predicting later behavior.