Effectiveness of large booms as nutation dampers for spin stabilized spacecraft

The issue of using long slender booms as pendulous nutation damping devices on spinning aircraft is discussed. Motivation comes from experience with the Galileo Spacecraft, whose magnetometer boom also serves as a passive nutation damper for the spacecraft. Performance analysis of a spacecraft system equipped with such systems are relatively insensitive to changes in the damping constant of the device. However, the size and arrangement of such a damper raises important questions concerning spacecraft stability in general

Neonatal Mortality and Maternal/Child Health Care in Nigeria: An Impact Analysis

Reducing the rate of mortality in neonates to as low as 12 per 1,000 live births is one of the clearly spelt out aims of the third tenet of the Sustainable Development Goals (SDG) because of its importance to the dynamics of population. While there have been various studies focused majorly on the causes, rates and determinants of neonatal mortality in Nigeria, studies on the impact of maternal/child care characteristics on neonatal mortalityand the potential implication of failing to attain the SDG target for neonatal mortality have seemingly been neglected. In this study, we undertake an analysis of the impact of maternal / child care characteristics on neonatal mortality using the logistic regression model. Results from the study showed that antenatal care (P-value = 0.000, odds ratio = 0.546 for women who visited the hospital during pregnancy on more than 5 occasions), post natal care (P-value = 0.004, odds ratio = 0.402 for women who received early neonatal care from skilled medical personnel), place ofdelivery (P-value = 0.000, odds ratio = 0.592 for babies that were delivered in a government hospital) and skill of birth attendant (P-value = 0.000, odds ratio = 0.706 for babies who were delivered by trained doctors/nurses/midwives) had significant impact on neonatal mortality at the 95% confidence level implying that improved maternal health care: before, during and immediately after delivery as well as the quality of care to motherand child are both important and necessary to the reduction of neonatal mortality in Nigeria. To achieve the sustainable development target for neonatal mortality, it is therefore recommended that stake holders in the public health sector improve the quality of existing health care facilities and access to quality services. Keywords: Neonatal mortality, logistic regression, maternal care, child health care, Nigeri

Dwarf Dark Matter Halos

We study properties of dark matter halos at high redshifts z=2-10 for a vast range of masses with the emphasis on dwarf halos with masses 10^7-10^9 Msun/h. We find that the density profiles of relaxed dwarf halos are well fitted by the NFW profile and do not have cores. We compute the halo mass function and the halo spin parameter distribution and find that the former is very well reproduced by the Sheth & Tormen model while the latter is well fitted by a lognormal distribution with lambda_0 = 0.042 and sigma_lambda = 0.63. We estimate the distribution of concentrations for halos in mass range that covers six orders of magnitude from 10^7 Msun/h to 10^13} Msun/h, and find that the data are well reproduced by the model of Bullock et al. The extrapolation of our results to z = 0 predicts that present-day isolated dwarf halos should have a very large median concentration of ~ 35. We measure the subhalo circular velocity functions for halos with masses that range from 4.6 x 10^9 Msun/h to 10^13 Msun/h and find that they are similar when normalized to the circular velocity of the parent halo. Dwarf halos studied in this paper are many orders of magnitude smaller than well-studied cluster- and Milky Way-sized halos. Yet, in all respects the dwarfs are just down-scaled versions of the large halos. They are cuspy and, as expected, more concentrated. They have the same spin parameter distribution and follow the same mass function that was measured for large halos.Comment: Accepted to be pusblished by ApJ, 12 pages, 8 figures, LaTeX (documentclass preprint2). Differences with respect to the previous submission are: (i) abstract was modified slightly to make it more transparent to the reader, (ii) an extra figure has been added, and (3) some minor modifications to the main text were also don

Heating of the IGM

Using the cosmic virial theorem, Press-Schechter analysis and numerical simulations, we compute the expected X-ray background (XRB) from the diffuse IGM with the clumping factor expected from gravitational shock heating. The predicted fluxes and temperatures are excluded from the observed XRB. The predicted clumping can be reduced by entropy injection. The required energy is computed from the two-point correlation function, as well as from Press-Schechter formalisms. The minimal energy injection of 1 keV/nucleon excludes radiative or gravitational heating as a primary energy source. We argue that the intergalactic medium (IGM) must have been heated through violent processes such as massive supernova bursts. If the heating proceeded through supernova explosions, it likely proceeded in bursts which may be observable in high redshift supernova searches. Within our model we reproduce the observed cluster luminosity-temperature relation with energy injection of 1 keV/nucleon if this injection is assumed to be uncorrelated with the local density. These parameters predict that the diffuse IGM soft XRB has a temperature of ~1 keV with a flux near 10 keV/cm^2 s str keV, which may be detectable in the near future.Comment: to appear in ApJ Lett., 11 pages incl 1 figur

Investigating the Influence ofWeb 2.0 Tools on the Group Cohesion of Pre-service Teachers

The study investigated the Influence of Web 2.0 Tools on the Group Cohesion of Pre-service teachers in cooperative learning classroom. It adopted the two-group post-test only quasi experimental design. Task and social cohesion were the two dimensions of Group Cohesion that were studied. The sample was seventy (70) fourth year students from the Department of Educational Management, University of Port Harcourt, Rivers State, Nigeria. The sample size was seventy (70) fourth year students from one teaching option (Economics) in the Department of Educational Management who offered the course Computer in Education during the 2013/2014 session. It was an intact class. The technique used for selecting this sample was purposive sampling. The instrument for data collection was Group Cohesion Questionnaire designed by Carless and De Paola (2000). The internal consistency of the Group Cohesion Questionnaire was determined by the authors. Using a sample of students outside the study sample, the researcher used the split-half method to determine the reliability of the instrument. Cronbachs coefficient alpha was reported at .680. Research questions were answered using mean and standard deviation while hypotheses were analysed using Z-test. The results showed that there was no significant difference in the task and social cohesion of students who used web 2.0 technologies and those who did not. Though, the major findings showed that web 2.0 technologies did not significantly affect students task and social cohesion, incidental findings showed that students communication and information literacy skills were improved as they worked online. Thus, the researchers recommended that Web 2.0 technologies should be adopted in higher institutions.</jats:p

Triggering the Formation of Halo Globular Clusters with Galaxy Outflows

We investigate the interactions of high-redshift galaxy outflows with low-mass virialized (Tvir < 10,000K) clouds of primordial composition. While atomic cooling allows star formation in larger primordial objects, such "minihalos" are generally unable to form stars by themselves. However, the large population of high-redshift starburst galaxies may have induced widespread star formation in these objects, via shocks that caused intense cooling both through nonequilibrium H2 formation and metal-line emission. Using a simple analytic model, we show that the resulting star clusters naturally reproduce three key features of the observed population of halo globular clusters (GCs). First, the 10,000 K maximum virial temperature corresponds to the ~ 10^6 solar mass upper limit on the stellar mass of GCs. Secondly, the momentum imparted in such interactions is sufficient to strip the gas from its associated dark matter halo, explaining why GCs do not reside in dark matter potential wells. Finally, the mixing of ejected metals into the primordial gas is able to explain the ~ 0.1 dex homogeneity of stellar metallicities within a given GC, while at the same time allowing for a large spread in metallicity between different clusters. To study this possibility in detail, we use a simple 1D numerical model of turbulence transport to simulate mixing in cloud-outflow interactions. We find that as the shock shears across the side of the cloud, Kelvin-Helmholtz instabilities arise, which cause mixing of enriched material into > 20% of the cloud. Such estimates ignore the likely presence of large-scale vortices, however, which would further enhance turbulence generation. Thus quantitative mixing predictions must await more detailed numerical studies.Comment: 21 pages, 11 figures, Apj in pres

Theoretical And Artificial Neural Network Computation and Analysis Of Global Solar Radiation At Enugu with Atmospheric Parameter

Records of measured sunshine hour’s data for a period of seventeen years (1991-2007) at Enugu 7.550N, 6.470E and 141.50m within the south-east zone of Nigeria were used to compute the global solar radiation of the same location with theoretical and artificial neural network models. The first part of the results (ie January to May )  has similar values with the third part (October to December). This indicate that weather conditions of the location  of study is of two periods, rainy and dry seasons. The values of the results also shows that global solar radiation is directly proportional to sunshine hours both for measured, theoretical and artificial neural network computations. Again Correlation of the two models show high performance of neural network over theoretical computation, as the neural network coefficent of determination R2 = 0.96 while coefficent of determination of theoretical computation  is R2 = 0.91 respectively. The above result shows that the two models has the ability of computing global solar radiation with sunshine hours, but the artificial neural network computation is  more accurate.   Keywords: Atmospheric parameters, theoretical, neural network, Global solar radiation and sunshine hours