Effects of profile errors on lubrication performance of helical gears

Analysis of the elastohydrodynamic lubrication (EHL) of gears generally assumes that the tooth flanks are smooth surfaces. There is considerable interest in establishing the extent to which smooth surface analyses are distorted by the presence of surface roughness. The current paper concerns a different scale of deviation from the specified surface profile, namely involute profile error. The paper quantifies the deviation from the smooth surface behaviour using standard profile error measurements, and also considers how the means by which profile error is measured influences the outcome/conclusions. Transient EHL analyses of the meshing cycle of helical gears taking profile error data from a gear measuring machine are compared with analyses using equivalent measurements determined by the waviness from surface profilometer measurements

Effects of profile errors on lubrication performance of helical gears

This paper presents the results of a series of transient elastohydrodynamic lubrication (EHL) analyses of the meshing cycle of helical gears. Previous workers have analysed helical gears using a range of techniques, including thin slice models and models which take into account the effects of three-dimensional surface roughness. Previous work by the Cardiff group has investigated the effects of tooth micro-geometry (tip relief) on contact pressures and lubrication performance. The current work investigates the effect of tooth profile errors (deviations from the involute form) on elastohydrodynamic performance. The profile errors were measured on helical test gears using a Klingelnberg P65 gear measuring machine. The gears are of 6mm normal module, 20º reference pressure angle, 26.3º base helix angle, and 44mm face width, with the wheel having 24 teeth and the pinion 23 teeth. The gears were analysed over the meshing cycle, and the transmitted load was chosen such that the maximum Hertzian contact pressure would be 1.6 GPa in the example shown here. The tooth load corresponding to the contact pressure of 1.6 GPa is 60 kN with Hertzian semi dimensions a = 0.5 mm and b = 36 mm. Profile error and tip relief geometry was included in the surface geometry based on the digital profile information obtained from the Klingelnberg measurements. It should be emphasised that the profile deviations are at much lower spatial frequencies than surface roughness effects – indeed profile errors would usually be removed by the standard filtering process applied to measurements of gear surface finish. Figure 1 shows a comparison of film thickness contours for the smooth (upper) case (with tip relief) and the case including profile errors in addition to tip relief (lower). The presence of the profile error features can be seen to have a significant effect on the lubricant film thickness, with the loadbearing area developing a series of grooves. Between the grooves, the loadbearing surface develops ridges which give rise to elevated contact pressures significantly above those found in the smooth result. These are plotted in Figure 2 which is a section. through the contact at x = 0, which is the meshing contact line. The effects of profile errors on lubrication performance of helical gears can be clearly seen in these results, and the paper goes on to discuss the implications of these rarely considered effects for surface longevity

The Subaru-XMM-Newton Deep Survey (SXDS) VIII.: Multi-wavelength Identification, Optical/NIR Spectroscopic Properties, and Photometric Redshifts of X-ray Sources

We report the multi-wavelength identification of the X-ray sources found in the Subaru-XMM-Newton Deep Survey (SXDS) using deep imaging data covering the wavelength range between the far-UV to the mid-IR. We select a primary counterpart of each X-ray source by applying the likelihood ratio method to R-band, 3.6micron, near-UV, and 24micron source catalogs as well as matching catalogs of AGN candidates selected in 1.4GHz radio and i'-band variability surveys. Once candidates of Galactic stars, ultra-luminous X-ray sources in a nearby galaxy, and clusters of galaxies are removed there are 896 AGN candidates in the sample. We conduct spectroscopic observations of the primary counterparts with multi-object spectrographs in the optical and NIR; 65\% of the X-ray AGN candidates are spectroscopically-identified. For the remaining X-ray AGN candidates, we evaluate their photometric redshift with photometric data in 15 bands. Utilising the multi-wavelength photometric data of the large sample of X-ray selected AGNs, we evaluate the stellar masses, M*, of the host galaxies of the narrow-line AGNs. The distribution of the stellar mass is remarkably constant from z=0.1 to 4.0. The relation between M* and 2--10 keV luminosity can be explained with strong cosmological evolution of the relationship between the black hole mass and M*. We also evaluate the scatter of the UV-MIR spectral energy distribution (SED) of the X-ray AGNs as a function of X-ray luminosity and absorption to the nucleus. The scatter is compared with galaxies which have redshift and stellar mass distribution matched with the X-ray AGN. The UV-NIR SEDs of obscured X-ray AGNs are similar to those of the galaxies in the matched sample. In the NIR-MIR range, the median SEDs of X-ray AGNs are redder, but the scatter of the SEDs of the X-ray AGN broadly overlaps that of the galaxies in the matched sample.Comment: Accepted for publication in PASJ Subaru special issue. 42 pages, 22 figures. Entire contents of Tables 3, 8, 9, 10, and 11, and ASCII format tables are available from http://www.astr.tohoku.ac.jp/~akiyama/SXDS/index.htm

The Astronomy of Aboriginal Australia

The traditional cultures of Aboriginal Australians include a significant astronomical component, which is usually reported in terms of songs or stories associated with stars and constellations. Here we argue that the astronomical components extend further, and include a search for meaning in the sky, beyond simply mirroring the earth-bound understanding. In particular, we have found that traditional Aboriginal cultures include a deep understanding of the motion of objects in the sky, and that this knowledge was used for practical purposes such as constructing calendars. We also present evidence that traditional Aboriginal Australians made careful records and measurements of cyclical phenomena, and paid careful attention to unexpected phenomena such as eclipses and meteorite impacts.Comment: 8 pages, 5 figures, IAU 260 conference proceeding

How Ordinary Elimination Became Gaussian Elimination

Newton, in notes that he would rather not have seen published, described a process for solving simultaneous equations that later authors applied specifically to linear equations. This method that Euler did not recommend, that Legendre called "ordinary," and that Gauss called "common" - is now named after Gauss: "Gaussian" elimination. Gauss's name became associated with elimination through the adoption, by professional computers, of a specialized notation that Gauss devised for his own least squares calculations. The notation allowed elimination to be viewed as a sequence of arithmetic operations that were repeatedly optimized for hand computing and eventually were described by matrices.Comment: 56 pages, 21 figures, 1 tabl

A generalized equilibrium model for predicting daily to interannual shoreline response

Coastal zone management requires the ability to predict coastline response to storms and longer-term seasonal to interannual variability in regional wave climate. Shoreline models typically rely on extensive historical observations to derive site-specific calibration. To circumvent the challenge that suitable data sets are rarely available, this contribution utilizes twelve 5+ year shoreline data sets from around the world to develop a generalized model for shoreline response. The shared dependency of model coefficients on local wave and sediment characteristics is investigated, enabling the model to be recast in terms of these more readily measurable quantities. Study sites range from microtidal to macrotidal coastlines, spanning moderate- to high-energy beaches. The equilibrium model adopted here includes time varying terms describing both the magnitude and direction of shoreline response as a result of onshore/offshore sediment transport between the surf zone and the beach face. The model contains two coefficients linked to wave-driven processes: (1) the response factor (φ) that describes the "memory" of a beach to antecedent conditions and (2) the rate parameter (c) that describes the efficiency with which sand is transported between the beach face and surf zone. Across all study sites these coefficients are shown to depend in a predictable manner on the dimensionless fall velocity (Ω), that in turn is a simple function of local wave conditions and sediment grain size. When tested on an unseen data set, the new equilibrium model with generalized forms of φ and c exhibited high skill (Brier Skills Score, BSS = 0.85)

Iron, Meat and Health

This article is a summary of the publication “Iron and Health” by the Scientific Advisory Committee on Nutrition (SACN) to the U.K. Government (2010), which reviews the dietary intake of iron and the impact of different dietary patterns on the nutritional and health status of the U.K. population. It concludes that several uncertainties make it difficult to determine dose-response relationships or to confidently characterize the risks associated with iron deficiency or excess. The publication makes several recommendations concerning iron intakes from food, including meat, and from supplements, as well as recommendations for further research

Community and School Choice: Geographies of Care and Responsibility

This paper draws on elements of critical discursive psychology in order to explore some of the issues and concerns raised by parents’ responses to the policy and practice of school choice. Drawing on data from a group of mothers of diverse social class and racial backgrounds, this paper examines the dilemmas some mothers engage with in their role as chooser—reconciling competing rationalities for choosing or trying to manage contradictions. A central argument of this paper is that the policy and political context shaping the emergence of school choice in Britain has provisionally secured the development of certain trends in education—consumerism, individualism and competition. Alongside and coupled with this has been the veneration of a narrow utilitarian conception of parents as consumers of education services, defined as people who share the capacity and willingness to maximize the utility of their decisions in a rationally self-interested way. This paper questions the value of this approach as a framing for understanding the aspirations, motivations and fantasies informing parents’ school choice and highlights instead the ways in which some mothers articulate the importance of community in their decision-making practices

Disease-associated alleles in genome-wide association studies are enriched for derived low frequency alleles relative to HapMap and neutral expectations

<p>Abstract</p> <p>Background</p> <p>Genome-wide association studies give insight into the genetic basis of common diseases. An open question is whether the allele frequency distributions and ancestral vs. derived states of disease-associated alleles differ from the rest of the genome. Characteristics of disease-associated alleles can be used to increase the yield of future studies.</p> <p>Methods</p> <p>The set of all common disease-associated alleles found in genome-wide association studies prior to January 2010 was analyzed and compared with HapMap and theoretical null expectations. In addition, allele frequency distributions of different disease classes were assessed. Ages of HapMap and disease-associated alleles were also estimated.</p> <p>Results</p> <p>The allele frequency distribution of HapMap alleles was qualitatively similar to neutral expectations. However, disease-associated alleles were more likely to be low frequency derived alleles relative to null expectations. 43.7% of disease-associated alleles were ancestral alleles. The mean frequency of disease-associated alleles was less than randomly chosen CEU HapMap alleles (0.394 vs. 0.610, after accounting for probability of detection). Similar patterns were observed for the subset of disease-associated alleles that have been verified in multiple studies. SNPs implicated in genome-wide association studies were enriched for young SNPs compared to randomly selected HapMap loci. Odds ratios of disease-associated alleles tended to be less than 1.5 and varied by frequency, confirming previous studies.</p> <p>Conclusions</p> <p>Alleles associated with genetic disease differ from randomly selected HapMap alleles and neutral expectations. The evolutionary history of alleles (frequency and ancestral vs. derived state) influences whether they are implicated in genome-wide assocation studies.</p