The affect of surface finish on the sliding wear of alumina

Two wear regimes were observed for a 95% alumina tested in dry sliding wear conditions using a pin on disc test geometry. Specimens prepared with lapped and polished surfaces exhibited low wear rates at applied loads of 10 and 40 N but ground surfaces wore rapidly at loads of 40 N and above. The surfaces that had experienced high wear rates contained more networks of microcracks and had rougher surface profiles than the mildly worn surfaces. X-ray line broadening analysis indicated that the wear debris had a particle size of 10 to 30 nm and contained plastic deformation, but no evidence of significant plastic deformation was found in the pin surfaces.Theoretical explanations are proposed for the existence of two types of wear behaviour: subsurface crack growth is believed to cause high wear rates, whilst low wear rates are due to a very fine scale abrasion of the surface. Recommendations are made on some of the precautions that should be taken to use alumina successfully in dry sliding wear applications.     

Identification and distribution of tumor necrosis factor alpha receptors in pig corpora lutea

This study examined whether the pig CL contains specific tumor necrosis factor alpha (TNF alpha) receptors and compared the binding affinities and capacities of small and large cell membranes. Aliquots of membranes, isolated from intact or dispersed luteal tissue, were homogenized, and membrane protein content was quantified. Luteal membranes were assayed for specific TNF alpha binding by displacement analysis, with use of [125I]TNF alpha and varying concentrations of unlabeled TNF alpha. Preliminary experiments demonstrated that TNF alpha binding was maximal after incubation at 22 degrees C for 180 min. In addition, [125I]TNF alpha binding was displaced by TNF alpha, but not by other cytokines. Small cell membranes contained a TNF alpha binding site with an affinity (Kd = 11.6-19 nM) different (p < 0.05) from that of the binding site on large cell membranes (Kd = 56.2-99.6 nM). TNF alpha binding capacities were similar in small and large cell membranes. These data demonstrate that pig CL contain specific, saturable TNF alpha binding sites. The higher-affinity binding sites were localized in the small cell population, which contains predominantly endothelial cells and small luteal cells, suggesting that TNF alpha acts primarily on one or both of these cell types within the CL.     

Personal needs, values, and technical preferences in the psychiatric hospital. A replicated study

This study tests the hypothesis that staff and patients try to make their involvement in psychiatric hospitals personally gratifying by fashioning preferences for those specific therapeutic techniques that match or satisfy their personal values and needs. Results of questionnaire data, collected from a total of 397 staff and patients at two psychiatric hospitals at two different times, show two distinctly different combinations of needs, values, and technical preferences. In one, a preference for psychotherapy and somatotherapy correlates highly with a preference or need for structured, cautious, and rule-governed relationships. Underlying these preferences seems to be a common dimension emphasizing a technical attitude towards the psychiatric hospital with true healing provided only by a professional, scientific elite. A second combination shows high correlations between a preference for social therapy and a need for unstructured, open, and trusting relationships. A common dimension underlying these preferences seems to be a moral attitude that stresses the healing power of all human relationships. Treating institutions may be categorized according to whether the technical or moral attitude predominates.     

Maximum entropy two-station cyclic queues with multiple general servers

Summary The efficient implementation and extension of various approximate methods for general queueing networks require the study of two-station cyclic queues. In this paper maximum entropy formalism is used to analyse two-station cyclic queues with multiple general servers and a fixed number of jobs. New robust one step recursions for the queue length distribution are derived and asymptotic connections to infinite capacity queues are established. Links with Birth-Death and global balance solutions are determined and extensions to load dependent servers with Bernoulli feedback are presented. Numerical examples provide useful information on how critically system behaviour is affected by the distributional form of service times and simple bounds for typical performance measures such as throughout and mean queue length are defined. Moreover, the utility of the work as a building block for the approximate analysis of a general central server model is demonstrated.Some of the material included in this paper has been orally presented to the International Workshop on Computer Performance Evaluation, 28–30 April 1986, Sophia-Antipolis (INRIA), France [1]This work is jointly supported by Science and Engineering Research Council (SERC), UK and Metron Technology Ltd., UK, under grants GR/D/12422 and GR/AA/772, respectively     

Detecting Low Velocity Impact Damage in Composite Plate Using Nonlinear Acoustic/Ultrasound Methods

The objective of this work was to image the presence of impact damage by monitoring the nonlinear response of damaged carbon/epoxy composite samples. The presence of microcracks, debonding, delamination, etc… induce the material to behave in a nonlinear elastic fashion highlighted by the presence and amplitude of harmonics in the spectrum of the received signal when the sample is periodically excited at one of its resonance frequencies. The sensitivity of a second harmonic imaging technique (SEHIT) based on material nonlinear elastic effect known as second harmonic generation (SHG) was investigated. The proposed imaging process was used to detect barely visible impact damage (BVID) due to low velocity impact (<12 J). The results showed that the SEHIT methods appear to be highly accurate in assessing the presence and magnitude of damage with a very promising future for both NDT and possibly structural health monitoring (SHM) applications. Moreover the technique was validated with two conventional NDT techniques: pulse thermography and thermosonics. The first NDT method failed in detecting the damage on the impacted face. The second technique was capable of localising and quantifying the damage on the impacted surface agreeing well with the results obtained using the proposed nonlinear imaging method.     

Quantitative evaluation of angular defects by pulsed eddy current thermography

Pulsed eddy current (PEC) thermography employs a combination of PEC and thermographic non-destructive testing (NDT) techniques. This study considers the capabilities of PEC thermography for obtaining quantitative information about cracks set at an angle to the surface. The investigation is implemented by simulating the transient thermal distribution for angular slots, via time-stepping 3D finite element analysis (FEA), with the experimental work undertaken for verification. A slope inclination feature of the transient temperature distribution has been extracted and presented for estimating the angle of slots that is independent of slot depth and length inside the sample. With the identification of the slot angle, quantification of the length/depth of the slot inside the sample can then be made through a maximum temperature amplitude feature. Experimental studies have been undertaken for evaluation of the numerical simulation and transient feature extraction methods.     

Parameter Recovery Studies With a Diagnostic Bayesian Network Model

This paper describes a Bayesian network model for a candidate assessment design that had four proficiency variables and 48 tasks with 3–12 observable outcome variables per task and scale anchors to identify the location of the subscales. The domain experts’ view of the relationship among proficiencies and tasks established a complex prior distribution over 585 parameters. Markov Chain Monte Carlo (MCMC) estimation recovered the parameters of data simulated from the expert model. The sample size and the strength of the prior had only a modest effect on parameter recovery, but did affect the standard error of estimated parameters. Finally, an identifiability issue involving relabeling of proficiency states and permutations of the matrixes is addressed in the context of this study.