Rheological Behavior of Slurries and Consolidated Bodies Containing Mixed Silicon Nitride Networks

Two particle networks, each formulated with a different interparticle potential, were mixed to control the rheological properties of ceramic slurries and to develop claylike plasticity in consolidated bodies. A weakly attractive network, containing silicon nitride powder, alkylated with hexadecanol, was mixed with a second slurry containing flocculated (nonalkylated) silicon nitride powder. The elastic modulus and apparent yield stress of concentrated suspensions containing each constituent and their mixtures were found to increase with volume fraction according to a previously reported power law function (exponents of 4.8 and 3.75, respectively). Because of the large difference in the relative strengths of the two networks, the flocculated network overwhelmingly controlled the behavior of the mixed slurries when its volume fraction (relative to total solids) exceeded 0.30. Slurries were consolidated by pressure filtration, and the saturated bodies were tested in uniaxial compression. Bodies containing only alkylated powder packed to a high volume fraction and deformed at a low flow stress. The addition of small amounts of the flocculated network increased the flow stress to produce a body with rheological properties similar to clay.     

Interface modification and characterization in three‐component polymer blends

The effect of interface characteristics on the properties of three‐component polymer blends comprising PP/EVOH/mica and PP/EVOH/glass beads (GB) was investigated (polypropylene‐PP, ethylene‐vinylalcohol‐EVOH). The systems selected are based on the binary PP/EVOH immiscible blend representing a semi‐crystalline apolar polymer (PP) and a semi‐crystalline highly polar copolymer (EVOH), where PP serves as the matrix. A series of the binary and three‐component blends with varying compositions was chosen to study the effect of the molding procedure, i.e. compression versus injection molding. The structures observed by SEM analysis consisted of the filler particles engulfed by the EVOH phase, with some of the minor EVOH component dispersed within the PP matrix. The effects of silane treatment (GB/EVOH interface) and compatibilization, using a maleated‐PP compatibilizer (PP/EVOH interface), were studied in relation to the generated structured and properties. The compatibilizer was added in a unique procedure by which the encapsulated GB/EVOH structures were preserved. The characterization methods used included morphology by Scanning Electron Microscopy, thermal properties and crystallization behavior by Differential Scanning Calorimetry, mechanical properties by tensile testing, and dynamic characteristics by Dynamic Mechanical Thermal Analysis. The work has shown that structure‐performance relationships in the three‐component blends can be varied and controlled.     

Growth of Dense Single Crystals of Potassium Sodium Niobate by a Combination of Solid-State Crystal Growth and Hot Pressing

(K_0.5Na_0.5)NbO₃ (KNN) is a potential lead-free replacement for Pb(Zr, Ti)O₃ (PZT) piezoceramics, but its piezoelectric properties are inferior to those of PZT. By growing single crystals of KNN, it may be possible to improve the piezoelectric properties. Recently, single crystals of KNN were grown by the solid-state crystal growth (SSCG) method, but the crystals were very porous. In this paper, a method of growing dense single crystals by SSCG in a hot press will be described. (110)-oriented single seed crystals of KTaO₃ were buried in KNN powder, with 0.5 mol% of K₄CuNb₈O₂₃ added as a sintering aid. After consolidation by uniaxial and isostatic pressing, the tablets were hot pressed in a two-stage treatment. During hot pressing, dense single crystals of KNN grew using the KTaO₃ seed crystal as a template. The effect of hot pressing on single crystal growth will be discussed.     

Surface analysis of disbonded titanium/sol-gel/polyimide joints

Disbonded lap-shear specimens were analyzed to determine the locus of failure within bonded titanium (Ti) sol-gel polyimide joints. Bonded Ti alloys are being evaluated for use at an operating temperature of 175 °C. Determining the locus of failure for bonded Ti lap-shear specimens is part of a larger effort to develop durable, environmentally safe surface treatments for Ti alloys. Surface-treated Ti alloy (Ti-6Al-4V) plates are bonded in a standard lap-shear specimen configuration and exposed to temperature for specified intervals. The lap-shear bond joint consists of two etched Ti panels coated with a silicon and zirconium containing sol-gel, primed with a polyimide, and then bonded together with adhesive and supporting scrim material. The lap-shear specimens are tested for overall strength and failure modes. Specimens with adhesive failure modes were examined with x-ray photoelectron spectroscopy (XPS) to determine the composition of the bond joint failure layer. Analysis shows that the failure was located closer to the sol-gel/polyimide interface than to the Ti/sol-gel interface. Transmission electron micrographs (TEM) of the cross-sectioned joint confirmed the chemical distribution determined from the XPS data.     

Synthesis and structure of a dimeric scandium bis(μ-methoxy) complex

Reaction of hydrated scandium nitrate with 1,10-phenanthroline (phen) in methanol leads to formation of the unusual dimeric complex [(phen)(NO₃)₂Sc(μ-OMe)₂Sc(NO₃)₂(phen)], in which the scandium centres are eight co-ordinate. The complex features two bridging methoxy ligands, as well as bidentate nitrates and chelating 1,10-phenanthroline ligands.     

Fat deposition, fatty acid composition and meat quality: A review

This paper reviews the factors affecting the fatty acid composition of adipose tissue and muscle in pigs, sheep and cattle and shows that a major factor is the total amount of fat. The effects of fatty acid composition on meat quality are also reviewed. Pigs have high levels of polyunsaturated fatty acids (PUFA), including the long chain (C20-22) PUFA in adipose tissue and muscle. The full range of PUFA are also found in sheep adipose tissue and muscle whereas cattle ‘conserve’ long chain PUFA in muscle phospholipid. Linoleic acid (18:2n − 6) is a major ingredient of feeds for all species. Its incorporation into adipose tissue and muscle in relation to the amount in the diet is greater than for other fatty acids. It is deposited in muscle phospholipid at a high level where it and its long chain products eg aracidonic acid (20:4n − 6) compete well for insertion into phospholipid molecules. Its proportion in pig adipose tissue declines as fat deposition proceeds and is an index of fatness. The same inverse relationships are not seen in ruminant adipose tissue but in all species the proportion of 18:2n − 6 declines in muscle as fat deposition increases. The main reason is that phospholipid, where 18:2n − 6 is located, declines as a proportion of muscle lipid and the proportion of neutral lipid, with its higher content of saturated and monounsaturated fatty acids, increases. Oleic acid (18:1cis − 9), formed from stearic acid (18:0) by the enzyme stearoyl Co-A desaturase, is a major component of neutral lipid and in ruminants the same enzyme forms conjugated linoleic acid (CLA), an important nutrient in human nutrition. Like 18:2n − 6, -linolenic acid (18:3n − 3) is an essential fatty acid and is important to ruminants since it is the major fatty acid in grass. However it does not compete well for insertion into phospholipid compared with 18:2n − 6 and its incorporation into adipose tissue and muscle is less efficient. Greater biohydrogenation of 18:3n − 3 and a long rumen transit time for forage diets also limits the amount available for tissue uptake compared with 18:2n − 6 from concentrate diets. A positive feature of grass feeding is that levels of the nutritionally important long chain n − 3 PUFA are increased ie EPA (20:5n − 3) and DHA (22:6n − 3). Future research should focus on increasing n − 3 PUFA proportions in lean carcasses and the use of biodiverse pastures and conservation processes which retain the benefits of fresh leafy grass offer opportunities to achieve this. The varying fatty acid compositions of adipose tissue and muscle have profound effects on meat quality. Fatty acid composition determines the firmness/oiliness of adipose tissue and the oxidative stability of muscle, which in turn affects flavour and muscle colour. Vitamin E is an essential nutrient, which stabilises PUFA and has a central role in meat quality, particularly in ruminants.     

Tobacco use in six economically disadvantaged communities in the Dominican Republic.

The Dominican Republic is a tobacco-growing country, and tobacco control efforts there have been virtually nonexistent. This study provides a first systematic surveillance of tobacco use in six economically disadvantaged Dominican Republic communities (two small urban, two peri-urban, two rural; half were tobacco growing). Approximately 175 households were randomly selected in each community (total N = 1,048), and an adult household member reported on household demographics and resources (e.g., electricity), tobacco use and health conditions of household members, and household policies on tobacco use. Poverty and unemployment were high in all communities, and significant gaps in access to basic resources such as electricity, running water, telephones/cell phones, and secondary education were present. Exposure to tobacco smoke was high, with 38.4% of households reporting at least one tobacco user, and 75.5% allowing smoking in the home. Overall, 22.5% reported using tobacco, with commercial cigarettes (58.0%) or self-rolled cigarettes (20.1%) the most commonly used types. Considerable variability in prevalence and type of use was found across communities. Overall, tobacco use was higher in males, illiterate groups, those aged 45 or older, rural dwellers, and tobacco-growing communities. Based on reported health conditions, tobacco attributable risks, and World Health Organization mortality data, it is estimated that at least 2,254 lives could potentially be saved each year in the Dominican Republic with tobacco cessation. Although it is expected that the reported prevalence of tobacco use and health conditions represent underestimates, these figures provide a starting point for understanding tobacco use and its prevalence in the Dominican Republic.     

Minimizing decomposition of vaporized hydrogen peroxide for biological decontamination of galvanized steel ducting

The behavior of vaporous hydrogen peroxide (VHP) was examined in clean, room-scale galvanized steel (GS) and polyvinylchloride-coated steel air ducts, to understand how it might be used to decontaminate larger ventilation systems. VHP injected into the GS duct decreased in concentration along the length of the duct, whereas VHP concentrations in the polyvinylchloride coated duct remained essentially constant, suggesting that VHP decomposed at the GS surface. However, decomposition was reduced at lower temperatures (approximately 22 degrees C) and higher flow rates (approximately 80 actual cubic meter per hour). A computational fluid dynamics model incorporating reactive transport was used to estimate surface VHP concentrations where bioaerosol contamination is likelyto reside, and also showed that VHP decomposition was enhanced at bends within the duct, compared to straight sections. Use of G. stearothermophilus indicators, in conjunction with model estimates, indicated that a concentration-contact time of approximately 100 mg/L H2O2(g) x min was required to achieve a 6 log reduction of indicator spores in clean GS duct, at 30 degrees C. When VHP is selected for building decontamination, this work suggests the most efficacious strategy may be to decontaminate GS ducting separately from the rest of the building, as opposed to a single decontamination event in which the ventilation system is used to distribute VHP throughout the entire building.     

A new role for sulfur in arsenic cycling

Sulfur and arsenic often coexist in the environment and share similar microbial redox transformations. We examined the effects of sulfide on aerobic arsenite oxidation in alkaline lake water samples and in laboratory enrichment cultures. Significant arsenite oxidation occurred only in treatments with bacteria present, and production of arsenate was greatly enhanced by the addition of sulfide or thiosulfate. IC-ICP-MS analysis of samples showed that mono- and dithioarsenate formed in arsenite + sulfide amended lake water. Our data indicate that these two thioarsenic compounds are fairly stable in sterile alkaline solutions, but are transformed predominantly to arsenate when bacteria are present. Enrichment culture experiments suggest that sulfur-oxidizing bacteria use free or arsenic-bound sulfur as a growth substrate and directly or indirectly transform arsenite and thioarsenates to arsenate during growth. Increases in cell density resulted in more rapid conversion of arsenite and thioarsenates. The rate and extent of these processes appearto be controlled bythe concentration of bacteria and the ratio of reduced sulfur to arsenite present. Sulfur-driven arsenite oxidation and microbial thioarsenate transformation may be important biogeochemical processes in the arsenic cycle of our study site (Mono Lake, CA, USA) and other alkaline environments as well.     

State laws on youth access to tobacco in the United States: measuring their extensiveness with a new rating system

OBJECTIVE: To develop and implement a rating system evaluating the extensiveness of state laws restricting youth access to tobacco. DESIGN: State laws on youth access to tobacco were analysed and assigned ratings on nine items. Six items addressed specific tobacco-control provisions, and three related to enforcement provisions. For each item, a target was specified reflecting public health objectives. Achieving the target resulted in a rating of +4 points; for three items, a rating of +5 was possible if the target was exceeded. Criteria for lower ratings were established for situations when the target was not met. SETTING: United States. RESULTS: State scores (sum of the ratings across all nine items) ranged from 0-18 in 1993, 2-21 in 1994, and 1-21 in 1995 and 1996, out of a possible total of 39. The average score across states was 7.2 in 1993, 7.9 in 1994, 8.2 in 1995, and 9.0 in 1996. The overall mean rating (per item) was 0.80 in 1993, 0.88 in 1994, 0.91 in 1995, and 1.00 in 1996, on a scale where 4.0 indicates that the target goals (per item) were met. From 1993 to 1996, scores increased for 20 states, decreased for one state, and remained unchanged for the others. The number of states for which state preemption of local tobacco regulation was a factor doubled from 10 states in 1993 to 20 states in 1996. CONCLUSIONS: Although all states have laws addressing youth access to tobacco, this analysis reveals that, as of the end of 1996, the progress towards meeting health policy targets is slow, and state legislation that preempts local tobacco regulation is becoming more common.