Comparative performance of squeeze film air journal bearings made of aluminium and copper

This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited. Copyright @ 2012 The Authors - The article can be accessed from the links below.This article has been made available through the Brunel Open Access Publishing Fund.Two tubular squeeze film journal bearings, made from Al 2024 T3 and Cu C101, were excited by driving the single-layer piezoelectric actuators at a 75-V AC with a 75-V DC offset. The input excitation frequencies were coincident with the 13th modal frequency, at 16.32 and 12.18 kHz for the respective Al and Cu bearings, in order to produce a ‘triangular’ modal shape. The paper also provided a CFX model, used to solve the Reynolds equation and the equation of motion, to explain the squeeze film effect of an oscillating plate with pressure end leakage. The dynamic characteristics of both bearings were studied in ANSYS and then validated by experiments with respect to their squeeze film thickness and load-carrying capacity. It was observed that whilst both bearings did levitate a load when excited at mode 13, the Al bearing showed a better floating performance than Cu bearing. This is due to the fact that the Al bearing had a higher modal frequency and a greater amplitude response than the Cu bearing.This article is made available through the Brunel Open Access Publishing Fund

Factors influencing branchless banking for microfinance in Sudan: Theoretical perspectives and future directions

In Sudan more than 40% live below the poverty line and getting basic financial service poses a challenge to financial institutions. Most of these unserved populations live in far-flung areas that make it difficult for microfinance institutions to reach them. But the enormous growth of mobile technology industry has created new opportunity to expand financial services to this unserved population. Branchless banking is one of the latest technologies that have been employed in different developing countries to expand financial services to the unbanked poor. Despite the potential benefits and relevance of Branchless banking to Sudan, there are still very few studies on Branchless banking in Sudan. To address this gap in the literature, this study aims to investigate the factors that are essential to the development of branchless banking in Sudan using mobile technology. This is a research-in-progress paper, the critical review of the literature so far revealed that there are essential factors for the success of branchless banking in Sudan e.g. the identification of the industry key players and their roles, the enabling regulatory environment, the infrastructure readiness and Sudanese cultural values. The paper will provide regulators and policy makers in Sudan a way forward to expedite the development of suitable Branchless banking for microfinance in Sudan

Epigenomes in Cardiovascular Disease.

If unifying principles could be revealed for how the same genome encodes different eukaryotic cells and for how genetic variability and environmental input are integrated to impact cardiovascular health, grand challenges in basic cell biology and translational medicine may succumb to experimental dissection. A rich body of work in model systems has implicated chromatin-modifying enzymes, DNA methylation, noncoding RNAs, and other transcriptome-shaping factors in adult health and in the development, progression, and mitigation of cardiovascular disease. Meanwhile, deployment of epigenomic tools, powered by next-generation sequencing technologies in cardiovascular models and human populations, has enabled description of epigenomic landscapes underpinning cellular function in the cardiovascular system. This essay aims to unpack the conceptual framework in which epigenomes are studied and to stimulate discussion on how principles of chromatin function may inform investigations of cardiovascular disease and the development of new therapies

Bovine trypanosomosis in three districts of Southwest Oromia, Ethiopia

A study was carried out from September 2007 to March 2008 to determine the prevalence of trypanosomosis and the apparent tsetse densities and other biting flies as well as to evaluate community awareness about the disease and its control method in three districts of west Shoa zone in Oromia. From a total of 1200 animals examined, (600 in the late rainy and 600 in the dry seasons) the prevalence of trypanosomosis was found to be 33.5% and 17.83% in the late rainy and dry seasons, respectively. There was a statistically significant difference in prevalence was observed (p<0.05) between the two seasons. The mean PCV values of the parasitaemic and aparasitaemic animals during the late rainy season were 20.19% and 26.75% while during the dry season 18.75% and 23.97%, respectively. A fly-survey was conducted by using 90 monoconical pyramidal traps and revealed that three tsetse species, namely G. pallidipes, G. m. submorsitans and G. f. fuscipes were found along with other biting flies (tabanids and muscids) in the study area. The apparent densities of tsetse flies were significantly different (p<0.05) during the two study. The overall apparent densities of tsetse flies were found to be 2.87 fly/trap/day (95% CI= 1.04-5.77%) and 1.26 flay/tap/day (95% CI= 1.17-2.07%) in late rainy and dry seasons, respectively. G. f. fuscipes and G. pallidipes appear to be the dominant tsetse species in the study area. The proportion of female tsetse flies caught was higher in both seasons. The apparent density of biting flies (tabanids and muscids) was significantly higher (p<0.05) in the late rainy season (1.49 fly/trap/day, 18.66 fly/trap/day) than the dry season (0.77 fly/trap/day, 15.04 fly/trap/day) respectively. Poor infrastructure, absence of trypanosomosis and vector control activities in the area have worsen the situation and hence require professional intervention

Women’s willingness to use emergency contraception: Experience at Chris Hani Baragwanath Academic Hospital, Johannesburg, South Africa

Access to emergency contraception (EC) has little restriction in South Africa. EC is a contraceptive method that can be used by women up to 7 days after unprotected intercourse. It can be used in the following situations: when no contraceptive has been used; for condom accidents; after intrauterine contraceptive device expulsion; when a contraceptive method has been incorrectly used, or contraceptive pills missed; if there has been a >3-hour delay in taking the progestogen-only pill, a >2-week delay for intramuscular depot medroxyprogesterone acetate or a >1-week delay for intramuscular norethisterone enanthate; or after delayed placement or early removal or dislodgement of a contraceptive transdermal patch or vaginal ring

Wing-tip vortex dynamics at moderate Reynolds numbers

The flow over a flat-tipped wing at three Reynolds numbers: Re=1×104, Re=4×104, and Re=1×105 is investigated using direct numerical simulation. A set of grid independent results are obtained which allow for the dynamics of the tip flow, trailing vortices, and their interplay with the boundary layer dynamics to be examined in detail. The results show significant changes across the Reynolds number range. At the lowest Reynolds number, a single trailing vortex forms downstream of the trailing edge, whereas multiple vortices form over the tip at higher Reynolds numbers. The tip geometry is shown to be important with regard to the development of different structures and in the transition of the flow from laminar to turbulent. This is due to unstable shear layers, with turbulent flow becoming entrained in the vortex cores at higher Reynolds numbers. These changing vortex dynamics mean that the value of the minimum vortex core pressure and its location change with Reynolds number. This has important consequences for cavitation inception and scaling for hydrodynamic applications. The influence of the tip flow on the boundary layer is further considered by comparing the flow with that of an infinite-span wing. Analysis of the two cases shows that the tip flow reduces the effective angle of attack, which prevents the flow separation at the leading edge that is responsible for the boundary layer transition for the infinite-span case. This, in turn, changes the character of the trailing edge flow which would have significant consequences on the trailing edge noise

Combining tower mixing ratio and community model data to estimate regional-scale net ecosystem carbon exchange by boundary layer inversion over 4 flux towers in the U.S.A.

We evaluated an idealized boundary layer (BL) model with simple parameterizations using vertical transport information from community model outputs (NCAR/NCEP Reanalysis and ECMWF Interim Analysis) to estimate regional-scale net CO2 fluxes from 2002 to 2007 at three forest and one grassland flux sites in the United States. The BL modeling approach builds on a mixed-layer model to infer monthly average net CO2 fluxes using high-precision mixing ratio measurements taken on flux towers. We compared BL model net ecosystem exchange (NEE) with estimates from two independent approaches. First, we compared modeled NEE with tower eddy covariance measurements. The second approach (EC-MOD) was a data-driven method that upscaled EC fluxes from towers to regions using MODIS data streams. Comparisons between modeled CO2 and tower NEE fluxes showed that modeled regional CO2 fluxes displayed interannual and intra-annual variations similar to the tower NEE fluxes at the Rannells Prairie and Wind River Forest sites, but model predictions were frequently different from NEE observations at the Harvard Forest and Howland Forest sites. At the Howland Forest site, modeled CO2 fluxes showed a lag in the onset of growing season uptake by 2 months behind that of tower measurements. At the Harvard Forest site, modeled CO2 fluxes agreed with the timing of growing season uptake but underestimated the magnitude of observed NEE seasonal fluctuation. This modeling inconsistency among sites can be partially attributed to the likely misrepresentation of atmospheric transport and/or CO2gradients between ABL and the free troposphere in the idealized BL model. EC-MOD fluxes showed that spatial heterogeneity in land use and cover very likely explained the majority of the data-model inconsistency. We show a site-dependent atmospheric rectifier effect that appears to have had the largest impact on ABL CO2 inversion in the North American Great Plains. We conclude that a systematic BL modeling approach provided new insights when employed in multiyear, cross-site synthesis studies. These results can be used to develop diagnostic upscaling tools, improving our understanding of the seasonal and interannual variability of surface CO2 fluxes

Refinement Type Inference via Horn Constraint Optimization

We propose a novel method for inferring refinement types of higher-order functional programs. The main advantage of the proposed method is that it can infer maximally preferred (i.e., Pareto optimal) refinement types with respect to a user-specified preference order. The flexible optimization of refinement types enabled by the proposed method paves the way for interesting applications, such as inferring most-general characterization of inputs for which a given program satisfies (or violates) a given safety (or termination) property. Our method reduces such a type optimization problem to a Horn constraint optimization problem by using a new refinement type system that can flexibly reason about non-determinism in programs. Our method then solves the constraint optimization problem by repeatedly improving a current solution until convergence via template-based invariant generation. We have implemented a prototype inference system based on our method, and obtained promising results in preliminary experiments.Comment: 19 page