Three-Dimensional Solution and Experimental Confirmation for the Electric Resistivity Testing of Surface-Breaking Defects in Green-State Powder Metallurgy Compacts

This paper investigates electrostatic voltage distributions around a surface-breaking flaw due to an injected current of known strength. The direct 3-D solution of the voltage behavior over the flawed surface is obtained numerically by the use of a boundary integral formulation. A novel iteration method is applied to solve the resulting electrostatic integral equation for the unknown surface voltage distribution. In addition to investigating the sensitivity of different flaw sizes to the observed surface voltage distribution, important issues such as suitable probe spacing and current flow orientation are studied. For sufficiently small surface-breaking flaws, a simple image source model is developed to evaluate the voltage response of hairline cracks. The model is tested by comparing it with the developed numerical solution. Experiments aimed at establishing the validity of the modeling approach show remarkable agreement with the theoretical model.     

Optical properties and corrosion behaviour of sputtered Zr-B and Zr-B-N coatings

In this paper, we present results on the structure, optical properties and corrosion behaviour of Zr-B and Zr-B-N coatings employing non-reactive and reactive d.c. magnetron sputter deposition. The addition of nitrogen reduced the grain size—coatings deposited at nitrogen flow rates f(N₂) of less than approximately 14 sccm (standard cm³ min^-1) were extremely fine grained, while nitrogen flow rates of more than 14sccm led to fracture-amorphous coatings with a very smooth surface. The hardness and abrasion resistance decreased with the increase in nitrogen content. Pure Zr-B coatings are silver-greyish with metallic brilliance but nitrogen changes the colour from dark grey or black at low contents to interference colours in the amorphous state. Ellipsometric measurements of the refractive index n and adsorption coefficient k supported the results derived from electron microscopy, colour measurements and mechanical testing. The transition point between the fine-grained and fracture-amorphous structure lies in the range of f(N₂) around 10 sccm. The black coatings deposited with such nitrogen levels showed good corrosion and abrasion resistance combined with a satisfying hardness. In some cases, increasing the nitrogencontent improved the corrosion resistance. In potentio- dynamic experiments, more positive free corrosion and pitting potentials were demonstrated. However, in salt spray testing and immersion testing using an artificial sweat solution, no beneficial effect of high nitrogen additions was noticed. Zr-B-N coatings deposited with nitrogen flow values in the range 10–20 sccm offer an excellent choice for decorative purposes, owing to their dark grey or intense black colour and good corrosion resistance.     

Photolytic crosslinking of poly(p-hydroxystyrene)

Light-induced crosslinking of poly(p-hydroxystyrene) (PPHS) is significantly enhanced by O₂. This was evidenced by molar mass (light scattering measurements) and by gel content determinations which were performed on various polymer samples before and after continuous irradiation at λ_inc = 254 nm. The following mechanism was elucidated with the aid of flash photolysis studies: Crosslinking in the absence or presence of O₂ is mainly due to the combination of phenoxyl type radicals. In the absence of O₂ the latter are exclusively formed by O? H bond cleavage of singlet excited phenolic groups. Triplet excited phenolic groups which are also formed do not deactivate via O? H bond cleavage but react very effectively with O₂. This reaction leads to the formation of HO and additional phenoxyl type radicals. All Commercial and most laboratory-prepared PPHS samples contain chemically bound impurities of quinoid nature. On the basis of results performed with model compounds of low molar mass, it is concluded that triplet excited quinoid groups react effectively with phenolic groups forming phenoxyl type radicals and that they are quite unreactive with respect to the abstraction of alphatic hydrogen atoms. Irradiation of PPHS at λ_inc = 254 nm causes the formation of quinoid groups which absorb strongly at this wavelength. Light absorption by these groups becomes a determining factor with respect to photochemical alteration in the course of further irradiation.     

Carbohydrate type and amount alter intravascular processing and catabolism of plasma lipoproteins in guinea pigs

To test the effects of exchanging dietary complex and simple carbohydrate for fat calories on lipoprotein metabolism, guinea pigs were fed two different fat/carbohydrate ratios: 2.5∶58% (w/w) or 25∶29% (w/w) with either sucrose or starch as the carbohydrate source. Animals fed high-fat had higher plasma low-density lipoprotein (LDL) and hepatic cholesterol concentrations than animals fed low-fat diets (P<0.01). The cholesteryl ester content per particle was higher, and the number of triacylglycerol (TAG) molecules was lower in very low density lipoprotein (VLDL) and LDL from animals fed high-fat diets. Intake of high-fat/sucrose resulted in higher plasma LDL concentrations than intake of high-fat/starch, and animals fed low-fat/starch had the highest plasma TAG concentrations associated with VLDL particles containing more TAG molecules, as well as a TAG-enriched LDL. The activity of plasma lecithin cholesteryl:acyl transferase (LCAT) was highest in animals fed high-fat/sucrose, and heart lipoprotein lipase (LPL) activity was higher in animals fed high-fat diets. Hepatic apoprotein B/E (apo B/E) receptor number (B_max) was increased 21% with low-fat diets (P<0.01). These results suggest that the hypercholesterolemia induced by high-fat and by sucrose intake are associated with a higher plasma LCAT activity which results in a cholesteryl ester-enriched VLDL which, by the action of LPL, might be more readily converted to LDL through the delipidation cascade leading to downregulation of hepatic apo B/E receptors. The hypertriglyceridemia associated with low-fat intake may result from increased production of VLDL TAG, which would explain the increased TAG content and the higher TAG/CE ratio of VLDL from animals fed the low-fat/starch diet.     

Characterisation of cut and chip behaviour for NR,SBR and BR compounds with an instrumented laboratory device

ABSTRACT

Understanding the cut and chip (CC) effect in rubber is important for successful product development for tires used in off-road or poor road conditions and for other demanding applications of rubber. This research describes a laboratory testing method for characterising the CC fracture behaviour of rubber using a device that controls and records multiple applied loads and displacements during cyclic impact to the surface of a solid rubber specimen to mimic and quantify the CC damage experienced by tire tread compounds. To study the capabilities of the instrument, three model compounds were studied that are based on carbon black reinforced compounds of common elastomers used in tire treads: natural rubber (NR), styrene-butadiene rubber (SBR), and butadiene rubber (BR). These polymers have well-established CC tendencies in field performance of tire treads, with NR exhibiting the best CC resistance followed by SBR and finally BR. The same trend was found with the rubber impact testing approach that allowed the CC behaviour to be quantified using a new physical parameter which is the CC propensity (P). The relative ranking for CC resistance for the three compounds followed the fatigue crack growth resistances of the materials but was exactly opposite to the ranking of DIN abrasion resistance. This provides evidence that CC damage from impact by mm-scale asperities and abrasion of rubber against μm-scale asperities exhibit distinct characteristics in rubber.     

A reservoir serves as refuge for adults of the endangered Macquarie perch

Home‐range estimates are an important input to species recovery plans. Our aim was to estimate the home‐range size of the endangered Macquarie Perch in the lower Cotter River catchment, Australia. In total, fourteen home‐range estimates were calculated from intensive radio‐tracking of adult individuals over a minimum of five diel periods in either autumn (n = 5) or spring (n = 9). Home‐range (95% Kernel) and core area (50% Kernel) were calculated by Kernel estimation and corrected for overlap with land. Seasonal estimates of home‐range and core area were not asymptotic in relation to cumulative number of radio‐fixes in four of fourteen cases. The mean within‐season home‐range of adult Macquarie perch was 5.5 ha ranging from 0.2 to 18.4 ha, based on 10 cumulative estimates that were asymptotic in relation to radio‐tracking effort. All five individuals radio‐tracked in autumn occupied a single core area, whereas in spring, six individuals occupied a single core area and three individuals each occupied three core areas. Despite individuals moving on a scale almost comparable to Cotter Reservoir (48.5 ha), only a single radio‐tagged individual was found to leave the reservoir and enter the river. Regional fisheries managers are generally aware of the requirement for Macquarie perch to access flowing water for spawning in south‐eastern Australia; however, in the Cotter River catchment, the protection of habitat for this species within Cotter Reservoir is also paramount. Our study highlights the importance of reservoirs for conserving a threatened aquatic species.     

Carbohydrate molecular weight profiling, sequence, linkage, and branching data: ES-MS and CID

This section summarizes several strategies for a more complete understanding of carbohydrate structure with a focus on glycolipids and glycoprotein glycans. The techniques include periodate oxidation to impart greater molecular specificity to isomeric glycans, methylation to improve sensitivity and the information content within CID spectra, electrospray for "soft" and efficient ionization, and CID to obtain structural detail. The lipophilicity of the products following derivatization contributes to product cleanup by solvent extraction and enhances sensitivity during ES. When combined with CID information, this yields sequence, linkage, and branching information. Oxidation and reduction preceding methylation augments CID analysis with an altered structure that can be profiled at the same sensitivity. Within the context of established motifs, these contrasting profiles corroborate glycan structure and specifically identify isobaric elements transparent in the initial profile. An earlier report indicating ring-opening fragments were essentially absent in low-energy collisions of methylated and natriated oligosaccharides contrasts our observations. However, as this report used a methylated oligomer containing an internal N-acetylhexose as an illustration, the conclusion is plausible (cf., Figure 9). The poor ionization efficiency of FAB and the high matrix background limit the dynamic range in the CID spectrum and, thereby, the ability to unambiguously identify weaker peaks. It would be expected that high-energy CID affords a broader range of fragment types, including ring-opening fragments. In terms of a structural methodology, this is ambivalent since the increase in fragmentation pathways also applies to small molecule eliminations which are usually less informative. In ES-CID-MS, the carbohydrate chemist has a powerful new tool in hand for structural elucidations that can be conducted at the low-picomole level. Parallel developments can be expected to continue for other ionization methods, in particular matrix-assisted desorption/ionization on linear and reflectron time of flight mass spectrometers, and improvement in the performance and sensitivity of high-resolution mass analyzers through the use of focal plane detectors and more sophisticated hardware and software for Fourier transform ion cyclotron resonance mass measurements. These have, as yet, only begun to be applied to carbohydrate structural analysis but should add still more versatility to experimental design in the future.