Are the Formation and Abundances of Metal-Poor Stars the Result of Dust Dynamics?

Large dust grains can fluctuate dramatically in their local density, relative to gas, in neutral, turbulent disks. Small, high-redshift galaxies (before reionization) represent ideal environments for this process. We show via simple arguments and simulations that order-of-magnitude fluctuations are expected in local abundances of large grains under these conditions. This can have important consequences for star formation and stellar abundances in extremely metal-poor stars. Low-mass stars could form in dust-enhanced regions almost immediately after some dust forms, even if the galaxy-average metallicity is too low for fragmentation to occur. The abundances of these 'promoted' stars may contain interesting signatures, as the CNO abundances (concentrated in large carbonaceous grains and ices) and Mg and Si (in large silicate grains) can be enhanced or fluctuate independently. Remarkably, otherwise puzzling abundance patterns of some metal-poor stars can be well-fit by standard core-collapse SNe yields, if we allow for fluctuating dust-to-gas ratios. We also show that the observed log-normal-like distribution of enhancements in these species agrees with our simulations. Moreover, we confirm Mg and Si are correlated in these stars, with abundance ratios similar to those in local silicate grains. Meanwhile [Mg/Ca], predicted to be nearly invariant from pure SNe yields, shows large enhancements as expected in the dust-promoted model, preferentially in the [C/Fe]-enhanced metal-poor stars. This suggests that (1) dust exists in second-generation star formation, (2) dust-to-gas ratio fluctuations occur and can be important for star formation, and (3) light element abundances of these stars may be affected by the chemistry of dust where they formed, rather than directly tracing nucleosynthesis.Comment: 13 pages, 6 figures, accepted to ApJ (replaced with published version

Hollow spherical rotors fabricated by electroplating

Equatorial bands are fabricated to provide a locating fit for the hemispheres of hollow spherical rotors which are then jointed by electroplating. Several nonmagnetic materials may be used to form the joint, such as aluminum, copper, iron, gold, plantinum, and zinc

Querying XML data streams from wireless sensor networks: an evaluation of query engines

As the deployment of wireless sensor networks increase and their application domain widens, the opportunity for effective use of XML filtering and streaming query engines is ever more present. XML filtering engines aim to provide efficient real-time querying of streaming XML encoded data. This paper provides a detailed analysis of several such engines, focusing on the technology involved, their capabilities, their support for XPath and their performance. Our experimental evaluation identifies which filtering engine is best suited to process a given query based on its properties. Such metrics are important in establishing the best approach to filtering XML streams on-the-fly

Nonproliferation Regime Compliance: Prediction and Measure Using UNSCR 1540

This dissertation investigates factors that predict compliance with international regimes, specifically the Non-Proliferation Regime. Generally accepted in international relations literature, is Krasner’s (1983) definition that regimes are “sets of implicit or explicit principles, norms, rules, and decision-making procedures around which actor expectations converge in a given [issue] area of international relations.” Using institutionalization as a framework, I hypothesize that compliance is a function of the respect for which a nation has for the rule of law. I investigate the NP regime through the lens of United Nations Security Council Resolution 1540, a mandate for member nations to enact domestic legislation criminalizing the proliferation of Weapons of Mass Destruction. Using NP regime compliance and implementation of UNSCR 1540’s mandates as dependent variables, I test the hypotheses with the following independent variables: rule of law, political competition, and regional compliance. I also present qualitative case studies on Argentina, South Africa, and Malaysia. The quantitative results of these analyses indicated a strong relationship between rule of law and regional compliance and a nation’s compliance with the overall NP regime and implementation of UNSCR 1540. These results indicate a nation will institutionalize the NP norms, and comply with the specifics of implementation. The results of in-depth analysis of Argentina, South Africa, and Malaysia showed that predicting an individual nation’s compliance is more complex than descriptions of government capacity or geography. Argentina and South Africa, expected by the hypotheses to exhibit low to medium compliance and implementation, scored high and well above their region for both measures. Malaysia, expected to score high in compliance, scored low. Findings thus reveal that rule of law is probably less influential on individual cases and regional compliance and cooperation better predictors of a nation’s compliance with a security regime

A Study of Officer\u27s Use of Leadership Skills Learned in the Navy\u27s Intermediate Officer Leadership Course

The U.S. Navy\u27s present-day leadership training program, referred to as the Leadership Continuum, provides for leadership training for all enlisted personnel and officers at initial entry into the naval service and at designated career milestones until retirement. The Leadership Continuum evolved from a series of formal Navy leadership training programs dating back to the late 1970s. The Navy has expended a considerable amount of fiscal resources over the past 20 years in an attempt to provide quality leadership training to its personnel. However, past studies have revealed that leadership training course graduates are provided with little to no incentives by their supervisors to utilize the leadership skills learned after they returned to their jobs. This study analyzed survey responses from Intermediate Officer Leadership Course (IOLC) graduates to determine whether the problem observed in the past continued to be a problem in the contemporary Navy context. Specifically, the study attempted to determine what barriers and incentives graduates encountered that either hindered or encouraged their use of acquired IOLC leadership skills back on the job. Descriptive statistics were used to analyze and compare the distributed frequency of responses among the various sub-groups. An analysis of variance (ANOVA) was used to test for statistical significance between the sub-groups\u27 responses. To reduce the possibility of revealing false-positive findings, all statistically significant ANOVA results were evaluated by both the Liberal Statistical Difference (LSD) and the Scheffe Post Hoc tests. The findings of the study revealed that the majority of respondents were able to utilize leadership skills acquired during IOLC on the job. Attempts to utilize Command Climate skills, however, were somewhat problematic when compared against the other three IOLC sub-units studied (Leadership Models, Situational Communications and Delegation). Female IOLC graduates took longer, on average, to apply acquired leadership skills on the job compared to the male graduates. The barriers most frequently identified by IOLC graduates that hindered their use of acquired leadership skills on the job was resistance to change from subordinates and peers. The incentives identified most frequently by IOLC graduates when attempting to apply acquired leadership skills on the job were (a) open lines of communications with subordinates and immediate superiors and (b) receptiveness from subordinates. A number of findings about relationships between skill use on the one hand and contextual or demographic variables on the other were judged to be statistically significant by both the LSD and the Scheffe Post Hoc tests

In-situ sputtering from the micromanipulator to enable cryogenic preparation of specimens for atom probe tomography by focused-ion beam

Workflows have been developed in the past decade to enable atom probe tomography analysis at cryogenic temperatures. The inability to control the local deposition of the metallic precursor from the gas-injection system (GIS) at cryogenic temperatures makes the preparation of site-specific specimens by using lift-out extremely challenging in the focused-ion beam. Schreiber et al. exploited redeposition to weld the lifted-out sample to a support. Here, we build on their approach to attach the region-of-interest and additionally strengthen the interface with locally sputtered metal from the micromanipulator. Following standard focused-ion beam annular milling, we demonstrate atom probe analysis of Si in both laser pulsing and voltage mode, with comparable analytical performance as a presharpened microtip coupon. Our welding approach is versatile, as various metals could be used for sputtering, and allows similar flexibility as the GIS in principle

TennisSense: a multi-sensory approach to performance analysis in tennis

The TennisSense Project, that is run in collaboration with Tennis Ireland, aims to create the infrastructure required to digitally capture physical, tactical and physiological data from tennis players in order to assist in their coaching and improved performance. This study examined the potential for using Wireless Inertial Monitoring Units (WIMU) to model the biomechanical aspects of the tennis stroke and for developing coaching tools that utilise this information. There is significant evidence in the current literature that the ability to accurately capture and model the accelerations, angular velocities and orientations involved in the tennis stroke could facilitate a major step forward in the application of biomechanics to tennis coachin