A thermal perspective of flash sintering: The effect of AC current ramp rate on microstructure evolution

In flash sintering experiments, the thermal history of the sample is key to understanding the mechanisms underlying densification rate and final properties. By combining robust temperature measurements with current-ramp-rate control, this study examined the effects of the thermal profile on the flash sintering of yttria-stabilized zirconia, with experiments ranging from a few seconds to several hours. The final density was maximized at slower heating rates, although processes slower than a certain threshold led to grain growth. The amount of grain growth observed was comparable to a similar conventional thermal process. The bulk electrical conductivity correlated with the maximum temperature and cooling rate. The only property that exhibited behavior that could not be attributed to solely the thermal profile was the grain boundary conductivity, which was consistently higher than conventional in flash sintered samples. These results suggest that, during flash sintering, athermal electric field effects are relegated to the grain boundary.     

Viral dynamics of primary viremia and antiretroviral therapy in simian immunodeficiency virus infection

Mathematical modeling of viral replication dynamics, based on sequential measurements of levels of virion-associated RNA in plasma during antiretroviral treatment, has led to fundamental new insights into human immunodeficiency virus type 1 pathogenesis. We took advantage of the simian immunodeficiency virus (SIV)-infected macaque model to perform detailed measurements and mathematical modeling during primary infection and during treatment of established infection with the antiretroviral drug (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA). The calculated clearance half-life for productively infected cells during resolution of the peak viremia of primary infection was on the order of 1 day, with slightly shorter clearance half-lives calculated during PMPA treatment. Viral reproduction rates upon discontinuation of PMPA treatment after 2 weeks were approximately twofold greater than those obtained just prior to initiation of treatment in the same animals, likely reflecting accumulation of susceptible target cells during treatment. The basic reproductive ratio (R0) for the spread of SIV infection in vivo, which represents the number of productively infected cells derived from each productively infected cell at the beginning of infection, was also estimated. This parameter quantifies the extent to which antiviral therapy or vaccination must limit the initial spread of virus to prevent establishment of chronic disseminated infection. The results thus provide an important guide for efforts to develop vaccines against SIV and, by extension, human immunodeficiency virus.     

An expert aid to fault diagnosis and trouble-shooting in satellitecommunications

Presents the Satellite Communications Network Expert (SaNE), a knowledge-based aid designed to provide engineering support for fault diagnosis. The SaNE is composed of two elements: a satcom network model, which simulates the structure and functionality of a system based loosely upon a large military satcom network, and a diagnostic component, which uses knowledge- and model-based reasoning techniques to analyse system anomalies and diagnose possible causes for the alarms such networks generate. The development cycle is described, emphasising lessons learnt during development and testing and the advantages and disadvantages of the techniques applied. The goal of the SaNE project is primarily commercial acceptance rather than innovation. The authors illustrate how novel concepts can be implemented in a practical system without compromising this goal     

Influence of interfacial microcracks on the elastic properties of composites

A model is established to quantify the influence of interfacial microcracks on the elastic properties of a particulate composite using a combination of theoretical and finite element analysis. A unique way to construct physical models which could accommodate both crack size and crack density is proposed. Based on energy principles, the influence of a dilute concentration of interfacial microcracks is first studied. The case of a finite concentration of microcracks is solved subsequently by combining the dilute concentration solutions and the differential scheme. Both cases agreed well with existing composite theories for the limiting condition of complete decohesion. The final model predicts the effective elastic properties as functions of both crack size and microcrack density.     

Getting a handle on MATLAB graphics

Among engineers and scientists, MATLAB is one of the most popular computational packages. Part of MATLAB's popularity stems from its simple, yet sophisticated, graphics capabilities. While basic plots are relatively easy to obtain, specialized plots require a little more effort to produce. This article introduces MATLAB's Handle Graphics, which provides a mechanism to fully control and customize graphics objects in MATLAB. With a basic understanding of Handle Graphics, users can produce plots that meet the unique needs and quality standards commonly required by the profession, several examples are presented to illustrate the concepts.     

Effect of crosslinking agent content, monomer functionality, and repeat unit chemistry on properties of unfilled resins

Seven mechanical/physical properties were used to evaluate 10 unfilled resins: eight aromatic dimethacrylates and two urethane dimethacrylates. Physical property tests included compressive strength, Young's modulus in compression, uniaxial tensile strength, intrinsic yield point, toothbrush abrasion, Knoop hardness, and water sorption. Controlled changes were made in the following four material parameters: amount of crosslinking diluent present in the uncured monomer, functionality of the monomer, repeat unit chemistry of the monomer (urethane vs. aromatic structure) and mode of activation (chemical vs. visible light). Polymers containing a high concentration of crosslinking agent (50 wt%) were found to be tougher and to possess lower hardness than materials containing lesser amounts of crosslinking agent. This was attributed to the flexible nature of the triethylene glycol dimethacrylate crosslinking molecule. Exposure to water plasticized the highly crosslinked materials to the degree that the yield point and elastic modulus were effectively lowered. Most of the tested properties were unaffected by differences in functionality except resistance to toothbrush abrasion, which was enhanced for polymers derived from high functionality monomers. The urethane-based polymers sorbed substantially more water than the aromatic-based materials, which presumably resulted in lower values for surface hardness. However, the urethane resins were very tough, and excellent resistance to toothbrush abrasion was observed. Property differences caused by differences in activation mode were small, although the visible light materials did sorb more water.     

Edible vaccine protects mice against Escherichia coli heat-labile enterotoxin (LT): potatoes expressing a synthetic LT-B gene

The authors have designed and constructed a plant-optimize synthetic gene encoding the Escherichia coli heat-labile enterotoxin B subunit (LT-B), for use in transgenic plants as an edible vaccine against enterotoxigenic E. coli. Expression of the synthetic LT-B gene in potato plants under the control of a constitutive promoter yielded increased accumulation of LT-B in leaves and tubers, as compared to the bacterial LT-B gene. The plant-derived LT-B assembled into native pentameric structures as evidenced by its ability to bind ganglioside. The authors demonstrated immunogenicity by feeding mice the raw tubers and comparing the anti-LT-B serum IgG and faecal IgA to that produced in mice gavaged with bacterial LT-B. Mice were fed three weekly doses of 5 g tuber tissue containing either 20 or 50 micrograms LT-B, or gavaged weekly with 5 micrograms of LT-B from recombinant E. coli. One week after the third dose, mice immunized with potato LT-B had higher levels of serum and mucosal anti-LT-B than those gavaged with bacterial LT-B. Mice were challenged by oral administration of 25 micrograms LT, and protection assessed by comparing the gut/carcass mass ratios. Although none of the mice were completely protected, the higher dose potato vaccine compared favourably with the bacterial vaccine. These findings show that an edible vaccine against E. coli LT-B is feasible.     

Memory in sub-clinical obsessive-compulsive checkers

In a series of experiments we extended the research on possible memory deficits in subclinical obsessive-compulsive Ss who reported excessive checking. Using a variety of memory tests we compared 20 subclinical checkers to 20 Ss without obsessive-compulsive symptomatology. Contrary to hypothesis, checkers remembered self-generated words better than read words just as much as did normals, but they were more likely than normals to report thinking they had studied words that, in fact, had not been on the study list. Further, they more often confused whether they read or generated the words at study. Checkers did not appear to perseverate on already-recalled words on repeated free recall tests any more than did normals. However, checkers remembered fewer actions overall and more often misremembered whether they had performed, observed, or written these actions. Such memory deficits may contribute to the development of excessive checking.