Operating limits for acoustic measurement of rolling bearing oil film thickness

An ultrasonic pulse striking a thin layer of liquid trapped between solid bodies will be partially reflected. The proportion reflected is a function of the layer stiffness, which in turn depends on the film thickness and its bulk modulus. In this work, measurements of reflection have been used to determine the thickness of oil films in elastohydrodynamic lubricated (EHL) contacts. A very thin liquid layer behaves like a spring when struck by an ultrasonic pulse. A simple quasi-static spring model can be used to determine the proportion of the ultrasonic waves reflected. Experiments have been performed on a model EHL contact between a ball and a flat surface. A transducer is mounted above the contact such that the ultrasonic wave is focused onto the oil film. The reflected signals are captured and passed to a PC for processing. Fourier analysis gives the reflection spectrum that is then used to determine the stiffness of the liquid layer and hence its thickness. In further testing, an ultrasonic transducer has been mounted in the housing of a deep-groove ball bearing to measure the film generated at the outer raceway as each ball passes. Results from both the ball-flat and ball bearing measurements agree well with steady-state theoretical EHL predictions. The limits of the measuring technique, in terms of the measurable rolling bearing size and operating parameters, have been investigated

The Effects of Child-Bearing on Married Women's Labor Supply and Earnings: Using Twin Births as a Natural Experiment

Married women's decisions about child-bearing and market work are importantly interrelated. Although there are many estimates of the effects of fertility on female labor supply few of them have adequately addressed the problems of simultaneity inherent in these choices. In this paper, we use exogenous variations in fertility due to twin births to measure the impact of an unanticipated child on married women's labor supply and earnings. We find that the short-run effects of an unanticipated birth on labor supply are appreciable and have increased in magnitude as more mothers enter the labor market. It also appears that the impact of unanticipated births on earnings and wages has changed from 1980 to 1990. In 1980 reduced labor supply caused a temporary drop in earnings, but in 1990 earnings and wages remained depressed well after the labor supply effects of a twin birth had disappeared.

Acoustic measurement of lubricant-film thickness distribution in ball bearings

An oil-film thickness monitoring system capable of providing an early warning of lubrication failure in rolling element bearings has been developed. The system is used to measure the lubricant-film thickness in a conventional deep groove ball bearing (shaft diameter 80 mm, ball diameter 12.7 mm). The measurement system comprises a 50 MHz broadband ultrasonic focused transducer mounted on the static outer raceway of the bearing. Typically the lubricant-films in rolling element bearings are between 0.1-1.0 μm in thickness and so are significantly smaller than the ultrasonic wavelength. A quasistatic spring model is used to calculate oil-film thickness from the measured reflection coefficient data. An accurate triggering system has been developed to enable multiple reflection coefficient measurements to be made as the contact ellipse sweeps over the measurement location. Experiments are described in which the loading conditions and rotational speed are varied. Lubricant-film thickness distributions measured ultrasonically are described and are shown to agree well with the predictions from classical elastohydrodynamic (EHD) lubrication theory, particularly at high radial loads and low rotary speeds. A range of parameters affecting the performance of the measurement are discussed and the limits of operation of the measurement technique defined. © 2006 Acoustical Society of America

Monitoring of lubricant film failure in a ball bearing using ultrasound

A lubricant-film monitoring system for a conventional deep groove ball bearing (type 6016, shaft diameter 80 mm, ball diameter 12.7 mm) is described. A high-firequency (50 MHz) ultrasonic transducer is mounted on the static outer raceway of the bearing. The transducer is focused on the ball-raceway interface and used to measure the reflection coefficient of the lubricant in the "contact" ellipse between bearing components. The reflection coefficient characterizes the lubricant film and can be used to calculate its thickness. An accurate triggering system enables multiple reflection measurements to be made as each lubricated contact moves past the measurement location. Experiments are described in which bearings were deliberately caused to fail by the addition of acetone, water and sand to the lubricant. The ultrasonic reflection coefficient was monitored as a function of time as the failure occurred. Also monitored were the more standard parameters, temperature and vibration. The results indicate that the ultrasonic measurements are able to detect the failures before seizure. It is also observed that, when us,ed in parallel, these monitoring techniques offer the potential to diagnose the failure mechanism and hence improve predictions of remaining life

Book Reviews

Reviews of the following books: Island in Time: A Natural and Human History of the Islands of Maine by Philip W. Conkling; A Seafaring Legacy: The Photographs, Diaries and Memorabilia of a Maine Sea Captain and His Wife by Julianna FreeHand; Coming of Age on Damariscove Island, Maine by Carl R. Griffin III and Alaric Faulkner; The Identity of the St. Francis Indians by Gordon M. Day; Soldiers, Sailors and Patriots of the Revolutionary War: Maine by Carleton E. Fisher and Sue K. Fisher

On Hexagonal Structures in Higher Dimensional Theories

We analyze the geometrical background under which many Lie groups relevant to particle physics are endowed with a (possibly multiple) hexagonal structure. There are several groups appearing, either as special holonomy groups on the compactification process from higher dimensions, or as dynamical string gauge groups; this includes groups like SU(2),SU(3), G_2, Spin(7), SO(8) as well as E_8 and SO(32). We emphasize also the relation of these hexagonal structures with the octonion division algebra, as we expect as well eventually some role for octonions in the interpretation of symmetries in High Energy Physics.Comment: 9 pages, Latex, 3 figures. Accepted for publication in International Journal of Theoretical Physic

Soot and smoke aerosol may not warm climate

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94810/1/jgrd10551.pd

Conformal holonomy, symmetric spaces, and skew symmetric torsion

We consider the question: can the isotropy representation of an irreducible pseudo-Riemannian symmetric space be realized as a conformal holonomy group? Using recent results of Cap, Gover and Hammerl, we study the representations of SO(2,1), PSU(2,1) and PSp(2,1) as isotropy groups of irreducible symmetric spaces of signature (3,2), (4,4) and (6,8), respectively, describing the geometry induced by a conformal holonomy reduction to the corresponding subgroups. In the case of SO(2,1) we show that conformal manifolds with such a holonomy reduction are always locally conformally flat and hence this group cannot be a conformal holonomy group. This result completes the classification of irreducible conformal holonomy groups in Lorentzian signature. In the case of PSU(2,1), we show that conformal manifolds of signature (3,3) with this holonomy reduction carry, on an open dense subset, a canonical nearly para-Kaehler metric with positive Einstein constant. For PSp(2,1) we also show that there is an open dense subset endowed with a canonical Einstein metric in the conformal class. As a result, after restricting to an open dense subset the conformal holonomy must be a proper subgroup of PSU(2,1) or of PSp(2,1), respectively. Finally, using a recent result of Graham and Willse we prove the following general non-existence result: for a real-analytic, odd-dimensional conformal manifold, the conformal holonomy group can never be given by the isotropy representation of an irreducible pseudo-Riemannian symmetric space unless the isotropy is SO(p+1,q+1).Comment: 39 pages, comments welcome. In version 2 the statement of Theorem 2 is corrected, see also Remark 4 on page 24. In version 3, the technical Lemma 6 in the appendix is changed, typos are corrected and acknowledgements adde

The Grizzly, November 26, 1991

Alcohol Speaker • Hostage Update • Wallace Speaks to Whitians • Barry M. Goldwater Scholarship and Excellence in Education Foundation Program • Keepers of the Flame : King Speaks on Soviet Art • Concert Band & Jazz Ensemble Perform • Reader\u27s Theatre on Soviet Art • John Updike to Speak • CAB Entertainers Enthrall All • An Upheaval of Rumors • Movie Review: Home Alone • Is Pretty Good Good Enough? • The World is Not Red, White, and Blue • Letters: Alcove Access; Halloween Flip-Flop; More Response to Ronnig Letter; Administration Woes; Enough Already!; Ronning Responses Critiqued; A Christian Response • Basketball Opens Season with Losses to Dickinson and Cabrini in Tip-Off Tournament • Kershner goes to Nationals • Ursinus Outswims Washington • Women\u27s Soccer Team in the Works • Women Hoopsters Open Season • Lady Bears Sink Competition • Charity Hoops Game • Lacrosse Ends Seasonhttps://digitalcommons.ursinus.edu/grizzlynews/1285/thumbnail.jp

Global modeling of nitrate and ammonium: Interaction of aerosols and tropospheric chemistry

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95603/1/jgrd12466.pd