The Quantitative Discrimination between Shrinkage and Gas Microporosity in Cast Aluminum Alloys Using Spatial Data Analysis

Microporosity in cast aluminum alloys may originate from hydrogen gas evolution, microshrinkage, or a combination of both. A spatial analysis method for the quantitative discrimination between shrinkage and gas porosity is presented and explained. It is shown that shrinkage pores can be selected and analyzed separately from gas pores by nearest-neighbor analysis. The principles of spatial statistics are discussed, and the types of spatial point patterns, complete spatial randomness, and nearest-neighbor cluster analysis are reviewed with respect to microporosity analysis. The pore distribution of a cast Al–7% Si (A356) foundry alloy is used as an example.     

The surface tension of molten aluminum and Al-Si-Mg alloy under vacuum and hydrogen atmospheres

The surface tensions of pure molten aluminum, A356 alloy (Al-7 pct Si-0.3 pct Mg), and strontium-modified A356 alloy have been measured under vacuum and hydrogen atmospheres using the sessile drop technique. The values obtained for pure aluminum at 680 °C and for A356 alloy and modified A356 alloy at 630 °C are 1.007, 0.889, and 0.844 N/m, respectively, when measured under vacuum. The addition of hydrogen gas to the atmosphere of the liquid droplet has no significant effect on the surface tension of the unmodified A356 alloy, while it lowers the surface tension of the modified alloy to 0.801 N/m. This effect is possibly due to the formation of SrH₂.     

A MECHANISM OF BLACK SPECK FORMATION IN ENAMEL RESULTING FROM REBOILING OF THE GROUND COAT*

Experimental and microscopic evidence is given to show that rebolling of a ground coat results from a fracture when refiring the ground-coat enamel. Air fills the cracks and connected bubbles. The cracks are sealed over and there is an expansion of the bubbles downward toward the base metal into the oxide layer. No evidence has been found which indicates that reboiling is caused by evolution of gas from the metal.     

Resource Management for Broadband Access over Time-Division Multiplexed Passive Optical Networks

Passive optical networks are a prominent broadband access solution to tackle the "last mile" bottleneck in telecommunications infrastructure. Data transmission over standardized PONs is divided into time slots. Toward the end of PON performance improvement, a critical issue relies on resource management in the upstream transmission from multiple optical network units (ONUs) to the optical line terminal (OLT). This includes resource negotiation between the OLT and the associated ONUs, transmission scheduling, and bandwidth allocation. This article provides an overview of the resource management issues along with the state-of-the-art schemes over time-division multiplexed PONs (TDM-PONs). We categorize the schemes in the literature based on their features, and compare their pros and cons. Moreover, we introduce a unified state space model under which all TDM-PON resource management schemes can be evaluated and analyzed for their system level characteristics. Research directions are also highlighted for future studies.     

A batch foaming visualization system with extensional stress-inducing ability

In typical plastic foaming processes, plastics are subjected to various amount of stress/strain, which can induce cell nucleation and affect the final cell morphology of plastic foams. Despite many valuable insights in previous work on stress-induced foaming, further studies are needed to clarify the subject. While in-line observations of foaming processes provide useful cell growth and interaction data, a controllable stress/strain field cannot be easily induced in a plastic sample to evaluate its effect. This study presents a novel batch foaming in-situ visualization system that was developed to capture the foaming process of a plastic specimen under controllable extensional strain. Using the in-situ visualization system, this study explored the effects of extensional stress/strain on the foaming behaviors of polystyrene blown by carbon dioxide under various processing conditions. It was observed that cell density increased with the application of extensional strain and that this effect was more apparent at low processing temperatures and with the addition of talc.     

Myosin motors with artificial lever arms

The myosin head consists of a globular catalytic domain and a light chain binding domain (LCBD). The coupling efficiency between ATP hydrolysis and myosin-induced actin movement is known to decline as the LCBD is truncated or destabilized. However, it was not clear whether the observed alteration in the production of force and movement reflects only the mechanical changes to the length of the LCBD or whether these changes also affect the kinetic properties of the catalytic domain. Here we show that replacement of the LCBD with genetically engineered domains of similar rigidity and dimensions produces functional molecular motors with unchanged kinetic properties. The resulting single-chain, single-headed motors were produced in Dictyostelium discoideum and obtained after purification from a standard peptone-based growth medium at levels of up to 12 mg/l. Their actin motility properties are similar or greater than those of native myosin. Rates of 2.5 and 3.3 microm/s were observed for motor domains fused to one or two of these domains, respectively. Their kinetic and functional similarity to the extensively studied myosin subfragment 1 (S1) and their accessibility to molecular genetic approaches makes these simple constructs ideal models for the investigation of chemo-mechanical coupling in the myosin motor.     

Parent-offspring relationships in apomictic guayule

The genetic base of guayule (Parthenium argentatum Gray) germ plasm that is available is narrow; yet, significant variability has been described within this germ plasm. This variability is surprising because guayule reproduces by facultative apomixis (asexual reproduction by seed), but evidence suggests that progress through selection is feasible. It has been hypothesized that this variation has arisen through periodic sexual reproduction; however, this has not been quantified. This study was designed to describe and compare eight components of yield and the expression of two isozyme systems in twenty parent plants and half-sib, open-pollinated families from each parent. Extensive variation for all characters was found among both the parents and the progeny, with fresh and dry weights being highly correlated to rubber yield. Parent-offspring regressions were not significantly different from zero. This implies low heritabilities for the major components of yield in guayule, and we believe that family selection, rather than single-plant selection, may generate higher-yielding and more genetically uniform lines at an escalated rate than single-plant selection. Periodic sexuality resulting in genetic variation was estimated by differences in isozyme expression within the half-sib families. Fifteen of the twenty progeny families were polymorphic for either esterase or peroxidase or both isozymes. This amount of sexuality is significant, and guayule must be considered an open-pollinated crop. We conclude from this study that we should rethink our breeding procedures to include controlled pollination and family selection.     

Wheat aleurone: separation, composition, health aspects, and potential food use

Over the last three decades substantial attention has been given to the role of dietary fiber in health and disease, in particular diabetes, cardiovascular disease, intestinal health, and some types of cancer. As a result the food industry started to add back fiber to refined foods and develop fiber rich foods. Scientists suggested that whole grain foods are superior to foods enriched with fibers obtained/synthesized using enzyme treatment, and thermal or chemical processing because the content of bioactive components and micronutrients in whole grain is more abundant. This triggered interest in how to isolate the micronutrient rich aleurone fiber fraction from wheat. Aleurone is a single cell layer at the inner site of the bran. It contains most of the minerals, vitamins, phenolic antioxidants, and lignans of the wheat grain. Novel milling and dry-fractionation techniques have recently allowed for full-scale separation of aleurone cells from the other layers of wheat bran, yielding a fiber rich concentrate which potentially contains many of the "whole grain kernel bioactives," which recently have been used in a variety of studies. The present review highlights available data on aleurone isolation, composition, intestinal physiology, and its metabolism and potential health benefits as well as its use in food.     

Kinetics and uptake mechanisms for monomethylmercury between freshwater algae and water

Uptake kinetics of monomethylmercury chloride (MeHgCl) were measured for two species of green algae (Selenastrum capricomutum and Cosmarium botrytis), one blue-green algae (Schizothrix calcicola), and one diatom (Thalassiosira weissflogii), algal species that are commonly found in natural surface waters. Species differences were found with the two green algae giving the highest uptake rates, and one of them (Cosmarium) showing differences between cultures having widely different cell age (exponential versus stationary), where increases in uptake rate for cells 30 days old were about 25 times greater than cells only 3 days old when weights of cells were considered. Both Schizothrix and Thalassiosira exhibited nearly the same lower uptake rates, approximately 20 times lower than the two green algal species. Experiments with photosystem inhibitors, uncouplers, gamma-radiation, light deprivation, and extended range uptake all point to an active transport mechanism for MeHgCl.