Limits on the dark matter particle mass from black hole growth in galaxies

I review the properties of degenerate fermion balls and investigate the dark matter distribution at galactic centers using NFW, Moore and isothermal density profiles. I show that dark matter becomes degenerate for particles masses of a few keV at distances less than a few parsec from the center of our galaxy. To explain the galactic center black hole of mass of $\sim 3.5 \times 10^{6}M_{\odot}$ and a supermassive black hole of $\sim 3 \times 10^{9}M_{\odot}$ at a redshift of 6.41 in SDSS quasars, the mass of the fermion ball is assumed to be between $3 \times 10^{3} M_{\odot}$ and $3.5 \times 10^{6}M_{\odot}$. This constrains the mass of the dark matter particle between $0.6 {\rm keV}$ and $82 {\rm keV}$. The lower limit on the dark matter mass is improved to about {\rm 6 keV} if exact solutions of Poisson's equation are used in the isothermal power law case. The constrained dark matter particle could be interpreted as a sterile neutrino.Comment: 3 pages, To be published in Proceedings of the 11th Marcel Grossmann meeting on general relativity, 23-29 July 2006, Berlin, German

Heavy neutrino balls and the supermassive dark object at the Galactic center

Includes bibliographical references.Massive neutrinos were the first proposed, and still remain the most natural, particle candidate for the dark matter. We investigate here the properties and astrophysical implications of self-gravitating degenerate heavy neutrino matter. Neutrinos of 10 to 25 keV/c² might cluster around the sun forming a halo of a few solar masses and a few light years radius. We calculate the perihelion shifts of planetary and asteroidal orbits that are expected due to the presence of a conjectured degenerate heavy neutrino halo around the sun. While the General Relativistic perihelion shifts are positive, those due to a possible dark matter halo are in general negative. A neutrino mass around ~16 keV is consistent with the observed mass excesses within the orbits of various outer planets, as obtailled from astrometrical data and Voyager 1 and 2 and Pioneer 10 and 11 ranging data. We then study the general relativistic effects on degenerate neutrino balls using the Tolman-Oppenheimer-Yolkoff (TOV ) equations of hydrostatic equilibrium. An extension of the TOV equations is made to describe the detailed properties of supermassive neutrino balls around compact objects such as white dwarfs and neutron stars. We further show that the supermassive compact dark object near Sgr A* at the Galactic center could be an extended object rather than a black hole. In fact these two scenarios can be distinguished by tracking the orbit of one of the fast moving stars near the Galactic center. VVe finally calculate the emission spectrum of the supermassive compact dark object using the standard accretion theory and show that the calculated radio wave to infrared emission spectrum between λ = 0.3 cm and λ = 10-³ cm is consistent with the observations

Dark Matter and Sterile Neutrinos

Dark matter has been recognized as an essential part of matter for over 70 years now, and many suggestions have been made, what it could be. Most of these ideas have centered on Cold Dark Matter, particles that are predicted in extensions of standard particle physics, such as supersymmetry. Here we explore the concept that dark matter is sterile neutrinos, particles that are commonly referred to as Warm Dark Matter. Such particles have keV masses, and decay over a very long time, much longer than the Hubble time. In their decay they produce X-ray photons which modify the ionization balance in the very early universe, increasing the fraction of molecular Hydrogen, and thus help early star formation. Sterile neutrinos may also help to understand the baryon-asymmetry, the pulsar kicks, the early growth of black holes, the minimum mass of dwarf spheroidal galaxies, as well as the shape and smoothness of dark matter halos. As soon as all these tests have been made quantitative in their various parameters, we may focus on the creation mechanism of these particles, and could predict the strength of the sharp X-ray emission line, expected from any large dark matter assembly. A measurement of this X-ray emission line would be definitive proof for the existence of may be called weakly interacting neutrinos, or WINs.Comment: 18 pages, To appear in Proceedings of the 11th Marcel Grossmann Meeting on General Relativity, 23-29 July 2006, Berlin, German

Origin and physics of the highest energy cosmic rays: What can we learn from Radio Astronomy?

Here in this lecture we will touch on two aspects, one the new radio methods to observe the effects of high energy particles, and second the role that radio galaxies play in helping us understand high energy cosmic rays. We will focus here on the second topic, and just review the latest developments in the first. Radio measurements of the geosynchrotron radiation produced by high energy cosmic ray particles entering the atmosphere of the Earth as well as radio \v{C}erenkov radiation coming from interactions in the Moon are another path; radio observations of interactions in ice at the horizon in Antarctica is a related attempt. Radio galaxy hot spots are prime candidates to produce the highest energy cosmic rays, and the corresponding shock waves in relativistic jets emanating from nearly all black holes observed. We will review the arguments and the way to verify the ensuing predictions. This involves the definition of reliable samples of active sources, such as black holes, and galaxies active in star formation. The AUGER array will probably decide within the next few years, where the highest energy cosmic rays come from, and so frame the next quests, on very high energy neutrinos and perhaps other particles.Comment: 11 pages, To appear in Proceedings of International School of Astrophysics at Ultra-high Energies, 20-27 June, 2006, Erice, Sicily, Ital

The impact of performance contracts on the effectiveness of the local government Administration, Gasabo district as the case study

This study was about the impact of Performance contracts on the effectiveness of local government administration. It was intended to find out whether Performance contracts contribute to effectiveness of governmental activities taking a case study of Gasabo District. The general objective of this study was to analyze the role of Performance contracts in ensuring efficiency and effectiveness of local government administration; especially in Gasabo District and Rwanda as a country in general. Specific objectives of the study were: to find out the Performance contracts that are signed by the mayors, to find out whether current job performance is better than that of before the introduction of performance contracts policy i.e., before 2006, to enhance the local leaders in implementation of their roles and came up with recommendations on how Performance contracts can best be done. Different literatures were reviewed in relation to the topic that is to say Performance contracts related issues such as Performance contract enforcement reports and the like. In methodology, the researcher used population of the study, sample size, sample selection technique, data collection instruments such as questionnaires, interviews, observation, and documentary study. It included the practice of evaluating the goodness and badness of decisions made during the course of research work. The sample population was 61 employees of Gasabo District. It was an aid to decision making and facilitated the process of completing whole the book in terms of thinking, analysis, evaluation and interpretation of the data collected from the field. This comprises an orderly intellectual process and an orderly system of arrangement that enabled the one to reach the aspect of knowledge. It was a conceptual process that coordinated a set of investigation operations and techniques. According to Gaige Wilson (1989:142) documentary study is a system that formerly acknowledges the sources you consult for your research and to the full bibliographical entries at the end of research. The key findings revealed significant improvements in the wellbeing of the society in different sectors of life but there still remain some constraints such as, scarcity of resources both financial and human and the over targeting of expectations (goals). Even though Performance contracts are signed between leaders, there still remains poverty and illiteracy within the local population as revealed by the local leaders in the interview with the researcher. It was noticed that in Gasabo District, Performance contracts contribute highly to the workers’ Performance which also led to improved institutional Performance. Then, different suggestions were made with regard to how Performance contracts should be over emphasized in order to maintain good Performance that led to eventual socio- economic growth. Lastly, the researcher has contributed much for the impact of Performance contracts on the effectiveness of the local government administration, but there are other underground ideas, and a combination of related factors which were not talked about (shown/tackled) for instance: ‘what are the challenges of Performance contracts in Rwanda?’ referring to Performance contracts policy, hope that it will be tackled by other researchers in further research

Effect of Human Resource Management Practices on Employees’ Commitment in Telecommunication Industry, a Case of Rwanda Telecommunication

This study sought to investigate the effect of Human Resource Management Practices on employees’ commitment in the Tele-communication industry. The specific objective of the study includes to assess the effect of employee resourcing on employees’ commitment in the Tele-Communication Industry, to evaluate the effect training on employees’ commitment in the Tele-Communication Industry, to assess the effect of rewarding on employees’ commitment in the Tele-Communication Industry and to determine how career management affects employees’ commitment in the Tele-Communication Industry. The study used the intellectual capital theory, human relations theory, resource-based theory and the learning organizational theory to support the study. This study adopted a mixed research design. The study targeted 4 tele-communication institutions in Rwanda namely MTN Rwanda, Airtel Rwanda, VOH Radio, Trans-Africa telecommunications. The total target population was 274 respondents and focused on a sample size of 103 respondents. The study used stratified random sampling technique as the sampling technique. The researcher collected primary data using structured and unstructured questionnaires. Data was analyzed using inferential statistics and processed using Statistical Package for Social Sciences (SPSS) Version 22, multiple regression analysis was used to establish the relations between the independent and dependent variables. ANOVA was used to test the hypothesis and was based on the alpha level or the significance level. Research findings were presented in form of frequency distribution graphs, pie charts and tables. The study found that HRM practices of employee resourcing, training and development, rewarding and career management had a positive and significant effect on employees’ commitment. The study findings revealed that employee resourcing strategy helps organizations to get the most suitable workforce with appropriate qualities, knowledge and capabilities. Training was also found to increase the motivation levels of employees through instilling knowledge, skills and abilities. Findings led to the conclusion that human resource management practices had a positive effect on employees’ commitment in the telecommunication industry in Rwanda. The study recommends that employee resourcing, training and development, rewarding and career management should be considered and implemented by telecommunication companies in order to enhance employees’ commitment. This will enhance employees’ commitment and in turn improves the performance of the organization

Teaching surgical skills in a resource-limited setting: Comparing massed versus distributed practice in an ultrasound-guided breast biopsy simulator

Background: Teaching surgical skills in the simulation lab has increased markedly compared to teaching only in the operating room. Although many studies have been performed investigating the optimal teaching methodology for skills acquisition, there is no consensus on the best method. Massed and distributed practices are important methods in teaching procedural skills. Considering the limited human and logistical resources in low and middle-income settings, it is valuable to understand the optimal methodology for learning and acquiring surgical skills. Methods: Thirty-two core needle biopsy-naïve first-year residents and final year medical students rotating in general surgery were enrolled in and completed the study at University Teaching Hospital of Kigali, a tertiary, teaching and referral hospital in Kigali, Rwanda. They were assigned to a “massed” group (i.e., one time, 3-hour practice) or “distributed” group (i.e., 1-hour practice per week for 3 weeks). Trainees were taught ultrasound-guided core needle biopsy on a high-fidelity breast simulator. All participants completed pre- and post-tests and an evaluation of skill retention was performed one month after completion of the training. Analysis of performance was completed, and p-value ≤ 0.05 was considered statistically significant. Results: There was no difference between performance on the pretest (p=0.985) and the posttest (p=0.680). Both groups demonstrated improvement after implementation of the simulation training when comparing pretest and posttest results (p<0.001); there were no differences in the evaluation of skills retention after one month after the training between the two groups (p=0.273). Conclusions: The results of this study demonstrate that both groups have improved significantly their knowledge and skills. Trainees have similar retention of skills in ultrasound guided core needle biopsy on a breast simulator whether trained under a massed or distributed practice schedule. Both methods may be considered in our setting for teaching surgical skills. Keywords: surgical simulation; resource-limited setting; global surgery

The motion of stars near the Galactic center: A comparison of the black hole and fermion ball scenarios

After a discussion of the properties of degenerate fermion balls, we analyze the orbits of the stars S0-1 and S0-2, which have the smallest projected distances to Sgr A*, in the supermassive black hole as well as in the fermion ball scenarios of the Galactic center. It is shown that both scenarios are consistent with the data, as measured during the last six years by Genzel et al. and Ghez et al. The free parameters of the projected orbit of a star are the unknown components of its velocity v_z and distance z to Sgr A* in 1995.4, with the z-axis being in the line of sight. We show, in the case of S0-1 and S0-2, that the z-v_z phase-space which fits the data, is much larger for the fermion ball than for the black hole scenario. Future measurements of the positions or radial velocities of S0-1 and S0-2 could reduce this allowed phase-space and eventually rule out one of the currently acceptable scenarios. This may shed some light into the nature of the supermassive compact dark object, or dark matter in general at the center of our Galaxy.Comment: 30 pages, 12 figures, Latex, aasms4 styl