Formulating the Net Gain of MISO-SFN in the Presence of Self-Interferences

In this study, an analytical formula for multiple-input single-output single frequency network gain (MISO-SFNG) is investigated. To formulate the net MISO-SFNG, we derived the average signal to interference plus noise ratio (SINR) where the gain achieved by the distributed MISO diversity as a function of power imbalance is curve-fitted. Further, we analyzed the losses owing to self-interferences resulting from the delay spread and imperfect channel estimation. We verified the accuracy and effectiveness of the derived formula by comparing the measurement results with the analytical results. The derived formula helps to understand how various system factors affect the gain under a given condition. The formula can be used to evaluate the MISO-SFNG and to predict the MISO-SFN coverage in various system configurations

Pulsar Magnetosphere : A General Relativistic Treatment

A fully general relativistic description of the pulsar magnetosphere is provided. To be more concrete, a study of the pulsar magnetosphere is performed in the context of general relativistic magnetohydrodynamics (MHD) employing the so-called Grad-Shafranov approach. Not surprisingly, the resulting Grad-Shafranov equations and all the other related general relativistic MHD equations turn out to take essentially the same structures as those for the (rotating) black hole magnetosphere. Other different natures between the two cases including the structure of singular surfaces of MHD flows in each magnetosphere are essentially encoded in the different spacetime (metric) contents. In this way, the pulsar and the black hole magnetospheres can be described in an unified fashion. Particularly, the direction of poloidal currents circulating in the neutron star magnetosphere turns out to be the same as that of currents circulating in the black hole magnetosphere which, in turn, leads to the pulsar and the black hole spin-downs via the ``magnetic braking''.Comment: 42 pages, 3 figures, Mon. Not. R. Astron. Soc.(MNRAS), in pres

An investigation of energy-based planned maintenance of offshore drilling mud pumps.

Mud pumps used on offshore installations for drilling operations have been known to experience unpredictable breakdowns, including during critical stages of drilling. The fluid end has been identified as requiring more maintenance work due to component failure, compared to the power end. The most common maintenance strategies in use include breakdown maintenance, time-based maintenance and condition monitoring. Time-based maintenance, based on running hours, is the most commonly preferred method by most, if not all, mud pump operators. However, the nature of drilling operations require pump performance with variable loads (pressures), variable speed characteristics and time-based maintenance would not be able to account for the different operating conditions within any identical time frames. To address this shortcoming, this research looked at the postulation that material wear loss is related to the energy expended and developed a dedicated reciprocating wear test system to identify and investigate the effect of operating variables on the wear loss of piston rubbers, which was considered to be the most problematic of the fluid end components

The relation of cytokines of IL-17/IL-23 axis to Th1/Th2 cytokines and disease activity in systemic lupus erythematosus

INTRODUCTION: Interleukin (IL)-17 is recently linked to the pathogenesis of systemic lupus erythematosus (SLE) but its relation to disease activity has not been well characterised. The objectives of this study were to examine the relation of serum cytokine levels from the IL-17/IL-23 axis (IL-17, IL-23) to Th1 (IL-12, IFN-γ), Th2 (IL-10, IL-6, IL-4) cytokines and disease activity in SLE patients. METHODS: Serum cytokines were measured by enzyme-linked immunosorbent assays. Disease activity was determined by SLE disease activity index (SLEDAI), anti-dsDNA antibody, C3 and C4 levels. RESULTS: Serum levels of IL-17, IL-10 and IFN-γ were higher in SLE patients (n=70) compared to age- and sexmatched controls (n=14) [P<0.001]. Higher serum IL-23 level was found in active lupus patients who had cutaneous manifestation (P=0.003) and serositis (P=0.03) compared to those who had not. Serum IL-17 was not different between patients who had active lupus nephritis (n=23), non-renal active lupus (n=13) and inactive disease (n=34) [P=0.23]. However, an inverse correlation between serum IL-17 with proteinuria was found among all SLE patients (r= –0.27, P=0.03). Serum IL-17 level was, otherwise, not related to SLEDAI, glomerular filtration rate, activity or chronicity score and ISN/RPS class among patients with active lupus nephritis and was not found to correlate with serum IFN-γ or IL-10. CONCLUSIONS: Elevated serum IL-23 was found in patients with inflammatory manifestations including cutaneous involvement and serositis. Serum IL-17 level was not shown to correlate with disease activity but demonstrated an inverse correlation with proteinuria suggesting urinary loss of IL-17 and its involvement in lupus renal pathology.published_or_final_versionThe 15th Medical Research Conference (15th MRC), Department of Medicine, University of Hong Kong, Hong Kong, 16 January 2010. In Hong Kong Medical Journal, 2010, v. 16 n. 1, suppl. 1, p. 45, abstract no. 7

The Stream-Stream Collision after the Tidal Disruption of a Star Around a Massive Black Hole

A star can be tidally disrupted around a massive black hole. It has been known that the debris forms a precessing stream, which may collide with itself. The stream collision is a key process determining the subsequent evolution of the stellar debris: if the orbital energy is efficiently dissipated, the debris will eventually form a circular disk (or torus). In this paper, we have numerically studied such stream collision resulting from the encounter between a 10^6 Msun black hole and a 1 Msun normal star with a pericenter radius of 100 Rsun. A simple treatment for radiative cooling has been adopted for both optically thick and thin regions. We have found that approximately 10 to 15% of the initial kinetic energy of the streams is converted into thermal energy during the collision. The angular momentum of the incoming stream is increased by a factor of 2 to 3, and such increase, together with the decrease in kinetic energy, significantly helps the circularization process. Initial luminosity burst due to the collision may reach as high as 10^41 erg/sec in 10^4 sec, after which the luminosity increases again (but slowly this time) to a steady value of a few 10^40 erg/sec in a few times of 10^5 sec. The radiation from the system is expected to be close to Planckian with effective temperature of \~10^5K.Comment: 19 pages including 12 figures; Accepted for publication in Ap

Role of scattering-factor anisotropy in electron, positron, and photon holography

We have studied the angular anisotropy in the scattering factor of electrons, positrons, and photons in solids. We show that as a function of angle, the maximum number of dips in the scattering factor's magnitude and jumps of near π in its phase are related to the angular momenta of the bound and resonance states of the potential. The effect of the scattering factor's anisotropy on low-energy electron and positron holographic wave-front reconstruction is discussed. Applying the variable-axis small-cone method, a good-quality reconstructed image is only possible within angular regions where the scattering factor is near isotropic. Thus the usable window for low-energy electron wave-front reconstruction is element dependent; the window size decreases as the atomic number increases. Positrons, on the other hand, are like photons and are not bound by the potential. For positrons or photons, there is no elemental dependence of the usable window and the entire backscattering regime is suitable for holographic reconstruction. We have established two rules that predict the maximum number of magnitude dips and phase jumps in the scattering factor for any element.published_or_final_versio