The Milky Way's Dark Matter Halo Appears To Be Lopsided

The atomic hydrogen gas (H I) disk in the outer region (beyond similar to 10 kpc from the center) of Milky Way can provide valuable information about the structure of the dark matter halo. The recent three-dimensional thickness map of the outer H I disk from the all sky 21 cm line Leiden/Argentine/Bonn survey, gives us a unique opportunity to investigate the structure of the dark matter halo of Milky Way in great detail. A striking feature of this new survey is the north-south (N-S) asymmetry in the thickness map of the atomic hydrogen gas. Assuming vertical hydrostatic equilibrium under the total potential of the Galaxy, we derive the model thickness map of the H I gas. We show that simple axisymmetric halo models, such as softened isothermal halo (producing a flat rotation curve with V-c similar to 220 km s(-1)) or any halo with density falling faster than the isothermal one, are not able to explain the observed radial variation of the gas thickness. We also show that such axisymmetric halos along with different H I velocity dispersion in the two halves, cannot explain the observed asymmetry in the thickness map. Amongst the nonaxisymmetric models, it is shown that a purely lopsided (m = 1, first harmonic) dark matter halo with reasonable H I velocity dispersion fails to explain the N-S asymmetry satisfactorily. However, we show that by superposing a second harmonic (m = 2) out of phase onto a purely lopsided halo, e. g., our best fit and more acceptable model A (with parameters epsilon(1)(h) = 0.2, epsilon(2)(h) = 0.18, and sigma(H I) = 8.5 km s(-1)) can provide an excellent fit to the observation and reproduce the N-S asymmetry naturally. The emerging picture of the asymmetric dark matter halo is supported by the. cold dark matter halos formed in the cosmological N-body simulation.

Liver transplantation in children: Experience with the development of an Australian pilot programme. The Queensland Liver Transplantation Programme

Children with end-stage liver disease now form a major sub-group of patients considered suitable for liver transplantation (ltp), and enjoy better survival statistics after transplantation than do adults. Since June 1984, a paediatric ltp programme has been developed in Brisbane with an initial working relationship and ongoing close links with two USA centres (Pittsburgh, and the UCLA Medical Center). Fourteen children with end-stage liver disease have been referred to the Queensland Liver Transplantation Programme for formal assessment. Following frank, informed discussion with their parents, 10 of these children were offered the option of ltp. During the transition stage, two infants with biliary atresia were referred to UCLA at their parents' request and, subsequently, eight children aged from 9 months to 6 years have been placed on a transplant candidacy list in Brisbane. A donor procurement team with access to a Queensland Government jet has been available to cover all mainland States except Western Australia. Six of the children have now had orthotopic ltp (two children at the UCLA Medical Center; four children at the Royal Children's Hospital, Brisbane). One UCLA patient died with a non-functioning graft, and one Brisbane patient died 5 weeks post-transplant with rejection, hepatic artery thrombosis and sepsis. The other four children are alive and well, three with normal liver function and one with unexplained intrahepatic cholestasis, during the 1-20 month follow-up to date. Three further children have died of their liver disease without a donor of an appropriate blood group and size being found, and one patient still awaits a suitable donor. The experience of these authors suggests that ltp is a major advance in the treatment of paediatric liver disease, and that the procedure can be carried out successfully in Australia with initial results comparable with leading overseas centres. The procedure requires the full array of services of a major paediatric tertiary care facility, an intensive team effort with awareness of the special needs of children, and a widespread procurement capability. A major problem for Australia is the procurement of sufficient numbers of optimal paediatric donor livers.

Unsteady compressible 3-dimensional boundary-layer flow near an asymmetric stagnation point with mass transfer

The heat and mass transfer for unsteady laminar compressible boundary-layer flow, which is asymmetric with respect to a 3-dimensional stagnation point (i.e. for a jet incident at an angle on the body), have been studied. It is assumed that the free-stream velocity, wall temperature, and surface mass transfer vary arbitrarily with time and also that the gas has variable properties. The solution in the neighbourhood of the stagnation point has been obtained by series expansion in the longitudinal distance. The resulting partial differential equations have been solved numerically using an implicit finite-difference scheme. The results show that, in contrast with the symmetric flow, the maximum heat transfer does not occur at the stagnation point. The skin-friction and heat-transfer components due to asymmetric flow are only weakly affected by the mass transfer as compared to those components associated with symmetric flow. The variation of the wall temperature with time has a strong effect on the heat transfer component associated with the symmetric part of the flow. The skin friction and heat transfer are strongly affected by the variation of the density-viscosity product across the boundary layer. The skin friction responds more to the fluctuations of the free stream oscillating velocities than the heat transfer. The results have been compared with the available results and they are found to be in excellent agreement.

The possible influence of curvature and rotation on ocean currents

Recent laboratory investigations have shown that rotation and (streamwise) curvature can have spectacular effects on momentum transport in turbulent shear flows. A simple model that takes account of these effects (based on an analogy with buoyant flows) utilises counterparts of the Richardson number Rg and the Monin-Oboukhov length. Estimates of Rg for meanders in ocean currents like the Gulf Stream show it to be of order 1 or more, while laboratory investigations reveal strong effects even at |Rg|∼0·1. These considerations lead to the conclusion that at a cyclonic bend in the Gulf Stream, a highly unstable flow in the outer half of the jet rides over a highly stable flow in the inner half. It is conjectured that the discrepancies noticed between observation and the various theories of Gulf Stream meanders, and such phenomena as the observed detachment of eddies from the Gulf Stream, may be due to the effects of curvature and rotation on turbulent transport.

Film cooling at hypersonic Mach numbers using forward facing array of micro-jets

Experimental investigations are carried out in the IISc hypersonic shock tunnel on film cooling effectiveness of a single jet (diameter 2 mm and 0.9 mm), and an array forward facing of micro-jets (diameter 300 mu m each) of same effective area (corresponding to the respective single jet). The single jet and the corresponding micro-jets are injected from the stagnation zone of a blunt cone model (58, apex angle and nose radius of 35 mm). Nitrogen and Helium are injected as coolant gases. Experiments are performed at freestream Mach number 5.9, at 0 degrees angle of attack, with a stagnation enthalpy of 1.84 MJ/kg, with and without injections. The ratios of the jet stagnation pressure to the freestream pitot pressure used in the present study are 1.2 and 1.45. Up to 50% reduction in surface heat transfer rate was observed with the array of micro-jets, compared to that of the respective single jet with nitrogen as the coolant, while the corresponding eduction was up to 37% for helium injection, with the schlieren flow visualizations showing no major change in the shock standoff distance, and thus no major changes in other aerodynamic aspects such as drag.

A note on mass transfer in turbulent wall jets

THE PROCESS of mass transfer from saturated porous surfaces virtual origin ; exposed to turbulent air streams finds many practical applitransverse coordinate; cations. In many cases, the air stream will be in the form of a height of nozzle above flat plate--radial wall jet; wall jet over the porous surface. The aerodynamics of both plane and radial wall jets have been investigated in detail and a vast amount of literature is available on the subject [l-3].

Magnetic Field Due to the Self-Gravity-Induced Electric Polarization of a Rotating Massive Body

he notion of the gravity-induced electric field has been applied to an entire self-gravitating massive body. The resulting electric polarization of the otherwise neutral body, when taken in conjunction with the latter's rotation, is shown to generate an axial-magnetic field of the right type and order of magnitude for certain astrophysical objects. In the present treatment the electric polarization is calculated in the ion-continuum Thomas-Fermi approximation while the electrodynamics of the continuous medium is treated in the nonrelativistic approximation.

Ignition delay studies on hydrocarbon fuel with and without additives

Single pulse shock tube facility has been developed in the High Temperature Chemical Kinetics Lab, Aerospace Engineering Department, to carry out ignition delay studies and spectroscopic investigations of hydrocarbon fuels. Our main emphasis is on measuring ignition delay through pressure rise and by monitoring CH emission for various jet fuels and finding suitable additives for reducing the delay. Initially the shock tube was tested and calibrated by measuring the ignition delay of C2H6-O2 mixture. The results are in good agreement with earlier published works. Ignition times of exo-tetrahdyrodicyclopentadiene (C10H16), which is a leading candidate fuel for scramjet propulsion has been studied in the reflected shock region in the temperature range 1250 - 1750 K with and without adding Triethylamine (TEA). Addition of TEA results in substantial reduction of ignition delay of C10H16.

The new binary pulsar and the observation of gravitational spin precession

The possibility of observing gravitational spin precession due to spin-orbit coupling in a binary pulsar system is considered. An analysis is presented which can aid in delineating the relevant physical effects from pulse-structure data. In this analysis, it is assumed that the pulsar radiation emanates from a cone whose axis is tilted with respect to the axis of rotation. It is found that the time-averaged pulse width and polarization sweep vary periodically with time and that this variation has a periodicity of the order of the spin-precession frequency averaged over a complete revolution. It is concluded that for an orbital period of about 180 years, it suffices to measure polarization data with an accuracy of a few parts in 100 over a period of six months to a year in order to uncover the effects of spin precession. The consistency of the analysis is checked, and the calculations are applied to a recently discovered binary pulsar.

Evaluation of k-epsilon and RNG turbulence models for confined swirling and non-swirling flow

In a very recent study [1] the Renormalisation Group (RNG) turbulence model was used to obtain flow predictions in a strongly swirling quarl burner, and was found to perform well in predicting certain features that are not well captured using less sophisticated models of turbulence. The implication is that the RNG approach should provide an economical and reliable tool for the prediction of swirling flows in combustor and furnace geometries commonly encountered in technological applications. To test this hypothesis the present work considers flow in a model furnace for which experimental data is available [2]. The essential features of the flow which differentiate it from the previous study [1] are that the annular air jet entry is relatively narrow and the base wall of the cylindrical furnace is at 90 degrees to the inlet pipe. For swirl numbers of order 1 the resulting flow is highly complex with significant inner and outer recirculation regions. The RNG and standard k-epsilon models are used to model the flow for both swirling and non-swirling entry jets and the results compared with experimental data [2]. Near wall viscous effects are accounted for in both models via the standard wall function formulation [3]. For the RNG model, additional computations with grid placement extending well inside the near wall viscous-affected sublayer are performed in order to assess the low Reynolds number capabilities of the model.

Circadian Rhythm Disruptions and Health

The doctoral thesis defined connections between circadian rhythm disruptions and health problems. Sleep debt, jet-lag, shift work, as well as transitions into and out of the daylight saving time may lead to circadian rhythm disruptions. Disturbed circadian rhythm causes sleep deprivation and decrease of mood and these effects may lead to higher accident rates and trigger mental illnesses. Circadian clock genes are involved in the regulation of the cell cycle and metabolism and thus unstable circadian rhythmicity may also lead to cancer development. In publications I-III it was explored how transitions into and out of the daylight saving time impact the sleep efficiency and the rest-activity cycles of healthy individuals. Also it was explored whether the effect of transition is different in fall as compared to spring, and whether there are subgroup specific differences in the adjustment to transitions into and out of daylight saving time. The healthy participants of studies I-III used actigraphs before and after the transitions and filled in the morningness-eveningness and seasonal pattern assessment questionnaires. In publication IV the incidence of hospital-treated accidents and manic episodes was explored two weeks before and two weeks after the transitions into and out of the daylight saving time in years 1987-2003. In publication V the relationship between circadian rhythm disruption and the prevalence of Non-Hodgkin lymphoma was studied. The study V consisted of all working aged Finns who participated in the national population census in 1970. For our study, all the cancers diagnosed during the years 1971-1995 were extracted from the Finnish Cancer Register and linked with the 1970 census files. In studies I-III it was noticed that transitions into and out of the daylight saving time disturbs the sleep-wake cycle and the sleep efficiency of the healthy participants. We also noticed that short sleepers were more sensitive than long sleepers for sudden changes in the circadian rhythm. Our results also indicated that adaptation to changes in the circadian rhythm is potentially sex, age and chronotype-specific. In study IV no significant increase in the occurrence of hospital treated accidents or manic episodes was noticed. However, interesting observations about the seasonal fluctuation of the occurrence rates of accidents and manic episodes were made. Study V revealed that there might be close relationship between circadian rhythm disruption and cancer. The prevalence of Non-Hodgkin lymphoma was the highest among night workers. The five publications included in this thesis together point out that disturbed circadian rhythms may have adverse effect on health. Disturbed circadian rhythms decrease the quality of sleep and weaken the sleep-wake cycle. A continuous circadian rhythm disruption may also predispose individuals to cancer development. Since circadian rhythm disruptions are common in modern society they might have a remarkable impact on the public health. Thus it is important to continue circadian rhythm research so that better prevention and treatment methods can be developed. Keywords: Circadian rhythm, daylight saving time, manic episodes, accidents, Non-Hodgkin lymphoma 11

Some Studies on Hydrogen-Oxygen Diffusion Flame

The opposed-jet diffusion flame has been considered with four step reaction kinetics for hydrogenoxygen system. The studies have revealed that the flame broadening reduces and maximum temperature increases as pressure increases. The relative importance of different reaction steps have been brought out in different regions (unstable, near extinction and equilibrium). The present studies have also led to the deduction of the oveall reaction rate constants of an equivalent single step reaction using matching of a certain overall set of parameters for four step reaction scheme and equivalent single step reaction.

Description of accretion induced outflows from ultra-luminous sources to under-luminous AGNs

We study the energetics of the accretion-induced outflow and then plausible jet around black holes/compact objects using a newly developed disc-outflow coupled model. Inter-connecting dynamics of outflow and accretion essentially upholds the conservation laws. The energetics depend strongly on the viscosity parameter α and the cooling factor f which exhibit several interesting features. The bolometric luminosities of ultra-luminous X-ray binaries (e.g. SS433) and family of highly luminous AGNs and quasars can be reproduced by the model under the super-Eddington accretion flows. Under appropriate conditions, low-luminous AGNs (e.g. Sagittarius A*) also fit reasonably well with the luminosity corresponding to a sub-Eddington accretion flow with f→1.

Topological close packed mu phase formation and the determination of diffusion parameters in the Co-Mo system

The study on the formation and growth of topological close packed (TCP) compounds is important to understand the performance of turbine blades in jet engine applications. These deleterious phases grow mainly by diffusion process in the superalloy substrate. Significant volume change was found because of growth of the p phase in Co-Mo system. Growth kinetics of this phase and different diffusion parameters, like interdiffusion, intrinsic and tracer diffusion coefficients are calculated. Further the activation energy, which provides an idea about the mechanism, is determined. Moreover, the interdiffusion coefficient in Co(Mo) solid solution and impurity diffusion coefficient of Mo in Co are determined.

Numerical Study of Heat Transfer From Pin-Fin Heat Sink Using Steady and Pulsated Impinging Jets

This paper investigates numerically the heat transfer characteristics of confined slot jet impingement on a pin-fin heat sink. A variety of pin-fin heat sinks is investigated, and the resulting enhancement of heat transfer studied. The distribution of heat transfer coefficient on the top surface of the base plate and that along the fin height are examined. Both steady and pulsated jets are studied. It is observed that for a steady jet impingement on a pin-fin heat sink, the effective heat transfer coefficient increases with fin height, leading to a corresponding decrease in base plate temperature for the same heat flux. In the case of pulsated jets, the influence of pulse frequency and the Reynolds number is examined, and their effect on the effective heat transfer coefficient is studied.