Study of the Tribological Behavior of a Thrust Washer Bearing

This study addresses the mechanisms that distress a flat-faced thrust washer bearing system. This washer bearing system separates a helical gear and its carrier within a gearset. It was found that the bearing can experience distress by the combination of rotational speed, axial load, and the sequence and rate of their application. Distress is defined as a sudden rise in the real-time frictional torque and temperature.

The various tests suggest the presence of hydrodynamic effects at certain rotational speeds and axial load combinations marked by decreases in the calculated effective coefficient of friction with decreases in velocity. In the tested cases, a distinct increase in the coefficient of friction occurs at the instant of distress.     

The Dynamic Properties of Annular Gas Squeeze Film Dampers

The step jump method is used to characterize the stiffness and damping of flat-faced gas lubricated squeeze film dampers. Analytic solution of a linearized form of the isothermal and compressible Reynolds equation yields closed form expressions for the step and frequency responses of the gas film. Results from the step jump method obtained both analytically and numerically are shown to be good approximations of the gas film stiffness and damping. A Prony series is proven to be an effective constitutive model capable of representing the stiffness and damping of the gas film in both the time and frequency domains in analytic form. Using the analytic constitutive model, closed form solutions for the motion of squeeze film dampers are now possible.     

Elevated burnout predicts the onset of musculoskeletal pain among apparently healthy employees.

Musculoskeletal (MS) pain is highly prevalent in the working population, often resulting in chronic disability. Burnout represents accumulated exposure to work-related stresses and therefore could predict the incidence of MS pain. We investigated prospectively the extent to which changes in the levels of burnout over time predict new cases of MS pain. Participants were 1,704 apparently healthy employed men and women who underwent periodic health examination at three points of time (T1, T2, and T3), over a period of about three years. We used the T1 to T2 changes in the levels of burnout, depressive symptoms, and anxiety to predict the onset of new cases of MS pain between T2 and T3, while controlling for possible confounders. Logistic regression results indicated that the T1–T2 change in burnout levels was associated with a 2.09-fold increased risk of MS pain (95% confidence interval = 1.07–4.10). No support was found for the possibility of reverse causation; that is, that MS pain predicts subsequent elevations of burnout levels. It was concluded that burnout might be a risk factor in the development of MS pain in apparently healthy individuals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A method for estimating the spatial distribution of soil moisture of arid microenvironments by close range thermal infrared imaging

The topsoil moisture content, its spatial distribution and dynamics, are important variables in understanding the response of arid eco‐geomorphic hill slope systems to rainfall. This study presents a method of measuring the soil moisture within a shrub's microenvironment by employing thermal infrared (TIR) imaging. A model for converting soil moisture (SMCM) is based on multi‐temporal TIR images. The method incorporates data from in situ measurements of soil temperature, moisture content and local meteorological variables collected simultaneously with TIR imaging. The results obtained, together with the high spatial resolution of the TIR images, demonstrated the efficacy of this method for mapping soil moisture on micro‐scale and also the potential for spatial analysis and change detection over time.     

Flexible manufacturing systems evaluation: An alternative approach

The purpose of this article is to integrate the von Neumann-Morgenstern theory of utility functions and the mean-variance approach of portfolio analysis within the computational framework of selecting a production technology to replace an existing one. A stochastic, static one-period problem is formulated, and a measure that takes into account both the capital costs of implementing the new technology and the random monetary value of its output is identified to solve the problem. The properties of this measure are discussed particularly with reference to the optimal selection decision. An example is described to illustrate the methodology.     

Corrosion behaviour of hot-pressed austenitic stainless steel in H2SO4 solutions at room temperature

The corrosion behavior of hot-pressed stainless steel (HPSS) of Type 316 was investigated. Samples of HPSS with porosity of 10–30% were prepared. The influence of the porosity factor on corrosion behaviour was investigated by potentiodynamic polarization, open circuit potential, identification of corrosion products by EDAX and SEM observation.It was found that porosity of the HPSS is the main factor affecting corrosion resistance. High porosity results in low corrosion resistance. The open circuit potential of the HPSS is about ? 200 mV (VSCE) as compared to 200 mV for the wrought 316 stainless steel. The potentiodynamic measurements indicate that cathodic concentration polarization is achieved at a relatively low current density and secondary active-passive transition is observed at a relatively high current density in HPSS as compared to wrought 316 stainless steel.It is suggested that the main mechanism affecting the low corrosion resistance of HPSS in H₂SO₄ is the evolution of hydrogen concentration cells due to electrolytic stagnation in the interconnected open pores. As a result the surfaces of the interconnected open pores act as an active anode and the engineering sample surface acts as an active cathode.     

Direct bonding of GaAs films on silicon circuits by epitaxial liftoff

Epitaxial liftoff has emerged as a viable technique to integrate GaAs with silicon. The technique relies on the separation of a thin epi-GaAs film from its substrate followed by direct bonding of the thin film to a silicon substrate. The silicon substrate has to meet certain planarity and smoothness conditions in order to obtain high quality bonding. Unfortunately, processed silicon IC chips do not satisfy these conditions. In this paper, we report on the results of two different planarization techniques, plasma etch back and chemical-mechanical polishing, to integrate GaAs LEDs with silicon circuits using epitaxial liftoff. 4 by 8 arrays of GaAs LEDs have been integrated with silicon driver circuits using plasma etch back. We also have lifted off areas as large as 500 mm² and bonded them on 5″ device wafers by chemical-mechanical polishing. This can be essential for mass production of optoelectronic devices based on epitaxial liftoff.     

Digital Low-Pass Differentiation for Biological Signal Processing

Digital low-pass differentiation is often required in processing various biological or biomechanical data. However, both the nature of biological signals and the use of micro-or minicomputers in such applications imply the need for simple, low-order, and fast differentiation methods, rather than sophisticated high-order algorithms. Responding to this need, we investigate here the low-pass first- and second-order digital differentiation from both theoretical and practical points of view, in order to achieve good and simple algorithms. In contrast with most of the research works previously done in this field, whose main aim was to achieve better accuracy even in the cost of using quite high-order algorithms, we restrict ourselves in this study only to low orders, being interested not only in the accuracy achieved, but also in the simplicity of the algorithm. After discussing the theoretical considerations concerning our optimum low-pass differentiation filters, we present our simple low-order filters and show them to be not only very convenient for use, but also almost optimum.     

Surface-sediment dynamics in a dust source from spaceborne multispectral thermal infrared data

This study utilized spaceborne multispectral thermal infrared (TIR) data to document spatial relationships of surface sediments over time in a modern depositional environment associated with dust emissions, Soda Lake playa, Mojave Desert, United States. The approach employed here involved time-series TIR data acquired from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and a linear spectral mixture analysis. An automated algorithm was applied to derive emissivity image endmembers. Evaluation of the chosen endmembers revealed that they can be categorized into five major spectra classes based on diagnostic absorption features. Each spectrum has been identified in relation to mineral abundance and soil arrangement that are common in playa settings: A, “clayey silt-rich crust”; B, “intermediate-salt crust”; C, “quartz-rich deposit”; D, “salt-rich rough crust”; E, “sulfate-rich crust”. Spectral classes A-B-C-D yielded the lowest RMS errors (0-0.025) over time in the iterative deconvolution algorithm between the measured and modeled spectra. The produced fractional abundance images show high areal concentrations for clayey silt-rich crust, salt-rich rough crust, and quartz-rich deposit, as the first surficial mapping of Soda Lake. Significant changes in the spatial relationships of the major surface sediments in Soda Lake were observed after a flooding event (2005) and a relatively dry period (2006). The approach utilized in this study can be advantageous for continuous monitoring of environments characterized by a small area and a complex surface, which may enable a better understanding of their responses to climate changes and potential for dust emissions.     

The stress corrosion cracking of welded austenitic stainless steels in MgCl2 solutions in the presence of NaI additions

The influence of Nal additions on the stress corrosion cracking (SCC) of Type 304L and 316L welded stainless steels in 42 wt% aqueous MgCl₂ solution at 154°C has been investigated. The results indicate clearly that addition of 1 N NaI to the boiling MgCl₂ solution prevents SCC of the welded steels. The I⁻ can act as an effective cathodic inhibitor. The correlation between mechanical properties, fracture morphology and the mechanism of the inhibition behaviour of I⁻ on SCC is discussed.