VLA Limits for Intermediate Mass Black Holes in Three Globular Clusters

The observational evidence for central black holes in globular clusters has been argued extensively, and their existence has important consequences for both the formation and evolution of the cluster. Most of the evidence comes from dynamical arguments, but the interpretation is difficult, given the short relaxation times and old ages of the clusters. One of the most robust signatures for the existence of a black hole is radio and/or X-ray emission. We observed three globular clusters, NGC6093 (M80), NGC6266 (M62), and NGC7078 (M15), with the VLA in the A and C configuration with a 3-sigma noise of 36, 36 and 25 microJy, respectively. We find no statistically-significant evidence for radio emission from the central region for any of the three clusters. NGC6266 shows a 2-sigma detection. It is difficult to infer a mass from these upper limits due to uncertainty about the central gas density, accretion rate, and accretion model.Comment: 5 pages, accepted for publication in the Astronomical Journa

A Comparison of Permanent Magnet and Wound Rotor Synchronous Machines for Portable Power Generation

Permanent magnet and wound rotor synchronous machines (PMSMs and WRSMs) are often used in diesel engine-based portable power generation systems. In these applications, there is a growing desire to improve machine efficiency in order to reduce fossil fuel requirements. In addition, there is a desire to reduce mass to improve mobility. To attempt to address these competing performance objectives, a system analyst is confronted with numerous choices, including machine type (PM or WR), converter architecture (active/passive), and control. Herein, to assist the analyst, design tools capable of performing automated multi-objective optimization of PMSMs and WRSMs connected to both active and passive rectifiers are described. The tools are then used to derive tradeoffs between mass and efficiency for a 3 kW application

Design and Evaluation of Zirconia Based Thermal Barrier Powders for Advanced Engines

Advanced utility, diesel and turbines engines used widely in aerospace, chemical and oil industries are based on plasma sprayed thermal barrier coatings. The successful performance of these coatings during servicing are relied mostly on the careful design, selection and analysis of zirconia-based ceramic powders stabilized with yttria and ceria. Different design of sampling techniques relevant for each evaluates property is a key factor to obtain reliable data. Significant property differences were observed for single and mixed powders. In the present work the particle size, its distribution, apparent density, flow rate, biased standard deviation, unbiased standard deviation and phases were characterized using sieving, flowmeter, scanning electron microscopy (SEM), X-ray diffraction (XRD), step scanning X-ray diffraction, energy dispersive spectroscopy (EDS), electron microprobe analysis (EPMA) and FT-IR. Two single alloyed zirconia powders of zirconia- 25 wt% CeO2-2.5 wt% Y2O3 (Sulzer Metco 205NS) and zirconia- 8 wt% Y2O3 (Sulzer Metco 204NS-G) and mixture of these powders 80 wt% (Sulzer Metco 205NS) and 20 wt% (Sulzer Metco 204NS-G) were investigated. The particle shape has a remarkable effect on the flow rate and apparent density rather than the other properties. The particle distribution gives important noticeable information for the plasma spraying coatings

The Role of Social Capital, Collective Efficacy, and Webs of Support in Supporting First Year Students: Experiences From the Exploratory Studies Program at the University of Nebraska Omaha

Historically, graduation rates for students entering the University of Nebraska Omaha as “undecided” were abysmal. The Exploratory Studies Program was created to support students who enter the university without a major (Explorers), half of them being first-generation, who often equate their indecision with not belonging at the university and face an array of barriers in higher education. Explorers embedded in a “web of support” of faculty, peer mentors, and advisors help to normalize the process of finding a best-fit major and navigating the complexities of academia, well-being, and future career development. The current article employs sociological and human development paradigms to demonstrate how social capital, collective efficacy, and webs of support can improve student belonging in their first year in university and help buffer barriers to success in higher education. In addition, this framework offers educators a powerful tool to work collaboratively with “undecided” students to augment persistence toward graduation

Covert Quantum Communication Over Optical Channels

We explore the problem of covertly communicating qubits over the lossy thermal-noise bosonic channel, which is a quantum-mechanical model of many practical channels, including optical. Covert communication ensures that an adversary is unable to detect the presence of transmissions, which are concealed in channel noise. We investigate an achievable lower bound on quantum covert communication using photonic dual-rail qubits. This encoding has practical significance, as it has been proposed for long-range repeater-based quantum communication over optical channels

Prevalence of Tobacco Use and Physical Activity among Adult Sierra Leonean Population

The current burden of non-communicable diseases (NCDs) and their risk factors such as tobacco use and physical inactivity remain largely unknown in Sierra Leone. Thus, this study was conducted to document the prevalence of tobacco use and physical activity among the adult Sierra Leonean population with a specific objective of determining the sex and age prevalence. A cross sectional population based survey utilising the multi-stage cluster sampling strategy was used. A total of 5,483 individuals aged 25-64 years of both sexes were recruited into the survey. The World Health Organisation (WHO) STEPwise approach to surveillance instrument was adapted and questionnaire was administered to one individual in selected household. The data was analysed and graphed using Epi-Info software version 3.4.3 and graph pad prism version 5.1 respectively. The analyses showed that 34% of the respondents use tobacco products with 26% engaged in smoking tobacco products and 8% were smokeless tobacco users at the time of this study. The average age of commencing tobacco smoking was 21 years; with 92% and 96% of the male and female daily smokers smoking at least six manufactured tobacco respectively. Seventy four percent (74%) and 69% of the non-smoking respondents were exposed to environmental tobacco smoke (ETS) at home and workplace respectively. The study further revealed that 15%, 23% and 87% of the total respondents reported no work-, transport- or recreational- related physical activity respectively; and were therefore classified as physically inactive. The lowest level of physical activity was reported in the recreation domain. Even those who reported moderate physical activity at work or from travel, their median metabolic equivalent (MET) was not sufficient to achieve a level of physical activity that is beneficial to their health. In conclusion, a significant proportion of the population is exposed either directly or indirectly to tobacco smoke, and a large proportion of the adult population is physically inactivity. Thus, NCD prevention policy addressing lifestyle changes such as no smoking should not be limited to work places but should be population based. Keywords: Non-communicable diseases, Physical activity, Risk factors, Sierra Leone, Tobacc