Deformation and fracture of a particle-reinforced aluminum alloy composite: Part I. Experiments

Mechanical tests were performed on a powder-metallurgically processed 7093/SiC/15p discontinuously reinforced aluminum (DRA) composite in different heat-treatment conditions, to determine the influence of matrix characteristics on the composite response. The work-hardening exponent and the strain to failure varied inversely to the strength, similar to monolithic Al alloys, and this dependence was independent of the dominant damage mode. The damage consisted of SiC particle cracks, interface and near-interface debonds, and matrix rupture inside intense slip bands. Fracture surfaces revealed particle fracture-dominated damage for most of the heat-treatment conditions, including an overaged (OA) condition that exhibited a combination of precipitates at the interface and a precipitate-free zone (PFZ) in the immediate vicinity. In the highly OA conditions and in a 450 °C as-rolled condition, when the composite strength became less than 400 MPa, near-interface matrix rupture became dominant. A combination of a relatively weak matrix and a weak zone around the particle likely contributed to this damage mode over that of particle fracture. Fracture-toughness tests show that it is important to maintain a proper geometry and testing procedure to obtain valid fracture-toughness data. Overaged microstructures did reveal a recovery of fracture toughness as compared to the peak-aged (PA) condition, unlike the lack of toughness recovery reported earlier for a similar 7XXX (Al-Zn-Cu-Mg)-based DRA. The PA material exhibited extensive localization of damage and plasticity. The low toughness of the DRA in this PA condition is explored in detail, using fractography and metallography. The damage and fracture micromechanisms formed the basis for modeling the strength, elongation, toughness, and damage, which are described in Part II of this work. This article is based on a presentation made in the Symposium “Mechanisms and Mechanics of Composites Fracture” held October 11–15, 1998, at the TMS Fall Meeting in Rosemont, Illinois, under the auspices of the TMS-SMD/ASM-MSCTS Composite Materials Committee.     

Storage and affinity properties of Murraya koenigii trypsin inhibitor

The Murraya Koenigii trypsin inhibitor was found to be the major protein component of the seed extract. The quantity of protein was determined to be approximately 20% of total protein extracted by simple buffer extraction. During different stages of seed development after flowering, the protein concentrations were found to be 5.27, 5.5, 8.5, 18.8 and 20% in 7, 19, 25, 37 and 55 days, respectively. During seed germination, protein degradations were observed from 20% to 12, 7 and 2% in 13, 16 and 22 days, respectively. This inhibitor, earlier purified using ion-exchange and gel filtration chromatography, was purified in single step by affinity column, using Cibacron blue 3GA, with substantial increase in yield. In partial internal sequencing by MALDI-TOF-TOF, six peptides of varying length, totalling 98 amino acid residues, exhibited similarities to the sequences from protease inhibitors, storage proteins and homeodomain-like proteins.     

Performance study of solar cooker with modified utensil

A performance study of the box-type solar cooker was made with special emphasis on the shape of lid of the utensils used in a solar cooker. The study revealed that the performance of a solar cooker can be improved if a utensil with a concave shape lid is used instead of a plain lid, generally provided with the solar cooker. The stagnation temperature for a utensil having a concave lid was about 2–7% more than the utensil with a normal lid. The time required for heating the water up to the same temperature in both the utensils was reduced by about 1–13% when a concave shape lid was used.     

Multi-band frequency compression for reducing the effects of spectral masking

Sensorineural hearing loss is associated with widening of auditory filter bandwidths, leading to increased spectral masking and degraded speech perception. Multi-band frequency compression can be used for reducing the effects of spectral masking. In this technique, the speech spectrum is divided into a number of analysis bands and spectral samples in each of these bands are compressed towards the band center by a constant compression factor. Implementation of the scheme with different types of frequency mappings, bandwidths, and segmentation for processing is investigated. Listening tests conducted for assessing the quality and intelligibility of the processed speech gave best results for critical bandwidth based compression using spectral segment mapping and pitch-synchronous processing.     

Genetic resistance of three genotypes of goats to experimental infection with Haemonchus contortus

A total of 46 weaned kids of three genotypes aged about 4-5 months were used to evaluate the effects of trickle infection with a sheep strain of Haemonchus contortus. A completely randomized 3 x 2 factorial design was used. Factors were genotype (Thai native (TN), 75% TN x 25% Anglo-Nubian (AN) and 50% TN x 50% AN) and parasite (control and infected). The animals were infected with 750 infective larvae (L3) of H. contortus three times a week for 3 weeks, with a total of 6750 larvae. The experiment lasted 9 weeks. Each week animals were weighed, faecal egg counts done and blood examined for haematological and biochemical variables. Twenty-seven kids were slaughtered at the end of experiment for worm recovery. Weight gain of infected animals was lower than those of uninfected controls (P < 0.05). The genotype 50% TN x 50% AN had higher growth rate than TN and 75% TN x 25% AN genotypes (P < 0.05). Eggs per gram of faeces (EPG) were significantly higher in 50% TN x 50% AN kids than in TN (P < 0.0005) and 75% TN x 25% AN (P < 0.0001) kids. There was a large variation in the EPG of individual animals within a genotype. The percent establishment of L3 was 8.2% in TN, 16.97% in 50% TN x 50% AN and 17.91% in 75% TN x 25% AN kids. TN kids had worm counts lower than 50% TN x 50% AN (P < 0.05) and 75% TN x 25% AN (P = 0.07) kids. Infection had a significant effect on packed cell volume (PCV), haemoglobin, total protein and albumin. The decrease in the level of these blood parameters was less in TN kids than in 50% TN x 50% AN and 75% TN x 25% AN kids. There was no significant difference between genotypes in the values of total and differential leucocyte counts and mean corpuscular volume (MCV). It can be concluded that TN goats are more resistant to H. contortus than 50% TN x 50% AN goats. However, under the present experimental conditions, the liveweight gain of 50% TN x 50% AN was higher than the TN goats.     

Implicit Spatial Contextual Learning in Healthy Aging.

Three experiments investigated the aging of implicit spatial and spatiotemporal context learning in 2 tasks. In contextual cuing, people learn to use repeated spatial configurations to facilitate search for a target, whereas in higher order serial learning, they learn to use subtle sequence regularities to respond more quickly and accurately to a series of events. Results reveal a dissociation; overall contextual cuing is spared in healthy aging, whereas higher order sequence learning is impaired in the same individuals. This finding suggests that these 2 forms of implicit learning rely on different neural substrates that age differently; the results are also consistent with recent evidence that fronto-striatal circuits are particularly susceptible to decline in health aging. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Veterinary ethics in the liberalized market: the Zambian environment

BACKGROUND: This study was performed to assess the functional capacity of the survivors of septal myectomy for the treatment of hypertrophic obstructive cardiomyopathy in long-term follow-up as assessed by dobutamine stress echocardiography. METHODS: Sixty-nine patients with hypertrophic obstructive cardiomyopathy underwent septal myectomy between 1975 and 1996. The mean age was 25.4 +/- 13.6 years (range, 6-58 years), and 10 of the patients were women. The early mortality was 4.3%. Hospital survivors (95.7%) were followed up for a mean of 43.8 +/- 28.7 months (range, 6-114 months). RESULTS: The postoperative mean functional capacity of the group was 1.47 +/- 0.56. No late deaths were reported. Forty-nine patients (74.2%) were evaluated with standard echocardiographic techniques, and 29 (43.9%) patients underwent dobutamine stress echocardiography. There was a significant decrease in the thickness of the interventricular septum after surgery. The mean preoperative and postoperative septal thickness was 1.99 +/- 0.59 cm (range, 1.3-3.8 cm) and 1.55 +/- 0.41 cm (range, 0.96-2.8 cm), respectively (p < 0.004). The mean posterior wall thickness was significantly less than the preoperative value (p = 0.008) and the left ventricular end-diastolic diameter was slightly greater in the postoperative measurements, but the difference was not significant (p = 0.162). Postoperative left ventricular outflow systolic gradients were reduced significantly when compared with preoperative values (preoperative mean, 78.4 +/- 33.6 mm Hg, range, 50-212 mm Hg versus postoperative mean, 17.9 +/- 15.9 mm Hg: range, 0-40 mm Hg; p < 0.0001). CONCLUSION: Septal myectomy for patients with hypertrophic obstructive cardiomyopathy is a safe procedure with excellent clinical and functional results in the long-term follow-up.     

Failure of Tungsten Carbide Rolls from a Wire and Rod Mill

The paper presents the failure analysis of tungsten carbide rolls for the Wire and Rod Mill (WRM) and establishes the failure reasons and the corrective and preventive actions taken to improve roll performance. A sharp continuous increase in failure rate and decrease in average time between failure (ATBF) was observed during 2001 to 2004. The increase in premature failure of these rolls (16 rolls in 2003 and 38 rolls in 2004) raised the cost of operations. Due to unscheduled stoppage of the mill after roll failures, the unplanned mill delays also increased, causing production losses. The analysis revealed significant increase in premature failure of rolls in the finishing stands 19, 22, 23, and 24 and prefinishing stand 14. The primary causes of such failures were faulty roll cooling and roll mounting and accumulation of cobbles. Implementation of modified cooling headers, a calibrated gage to monitor hydraulic pressure during roll mounting, and eddy current inspection resulted in decreasing the trend in roll failure and increasing the trend in ATBF.     

Direct estimation of quantile functions using the maximum entropy principle

The paper presents a distribution free method for estimating the quantile function of a non-negative random variable using the principle of maximum entropy (MaxEnt) subject to constraints specified in terms of the probability-weighted moments estimated from observed data. Traditionally, MaxEnt is used for estimating the probability density function under specified moment constraints. The density function is then integrated to obtain the cumulative distribution function, which needs to be inverted to obtain a quantile corresponding to some specified probability. For correct modelling of the distribution tail, higher order moments must be considered in the analysis. However, the higher order (>2) moment estimates from a small sample of data tend to be highly biased and uncertain. The difficulty in obtaining accurate moment estimates from small samples has been the main impediment to the application of the MaxEnt Principle in extreme quantile estimation. The present paper is an attempt to overcome this problem by the use of probability-weighted moments (PWMs), which are essentially the expectations of order statistics. In contrast with ordinary statistical moments, higher order PWMs can be accurately estimated from small samples. By interpreting the PWM as the moment of quantile function, the paper derives an analytical form of quantile function using MaxEnt principle. Monte Carlo simulations are performed to assess the accuracy of MaxEnt quantile estimates computed from small samples.