Effect of molecular weight on the morphology and drawing behaviour of melt crystallized linear polyethylene

The effect of molecular weight on the cold drawing behaviour of melt crystallized linear polyethylene has been studied. It is shown that the draw ratio achieved under comparable conditions rises with decreasing $\text{M}\text{?}{}_{\mathrm{w}}$, very high draw ratios (～36) being possible for optimum morphology of the undrawn polymer. The yield behaviour was also examined, and it is shown that the yield stress is affected in a complex fashion by both crystallization conditions and molecular weight. These results are discussed in terms of the crystallization and morphology of the melt crystallized polymer.     

A novel technique for measuring the impact properties of a tough polyethylene

A novel technique is described which enables reliable fracture toughness measurements to be made in impact test on relatively small specimens of a tough polyethylene. Composite specimens have been made in which a tough polyethylene is sandwiched between two layers of a more brittle polyethylene. The overall fracture toughness is interpreted on the basis of simple additivity of the strain energy release rate associated with each of the component layers. Brittle plane strain failures were obtained for specimens in which the relative thickness of the layers was varied over a substantial range and the fracture toughness of each layer determined by suitable extrapolation. The fracture toughness of the brittle layer obtained in this way agreed well with direct measurements on that material.     

A Model for the Diffusion of Moisture in Adhesive Joints. Part I: Equations Governing Diffusion

A methodology is proposed to relate the diffusion coefficient of small penetrant molecules in polymers to temperature, strain, and penetrant concentration. The approach used is based on well-known free volume theories. It is assumed that the transport kinetics is governed by the constant redistribution of the free volume, caused by the segmental motions of the polymeric chains. An expression for the diffusion coefficient is inferred from the temperature, strain, and penetrant concentration dependence of the free volume. The stress dependence of solubility is predicted from the Hildebrand theory. It is shown that the resulting constitutive equations exhibit many features desirable for joint durability studies. Finally, a non-Fickian driving force arising from differential swelling is included in the governing equations.     

Aphid deterrence by glucose esters in glandular trichome exudate of the wild tomato,Lycopersicon pennellii

Settling of the potato aphid,Macrosiphum euphorbiae, on feeding membranes was deterred by methanolic leaf rinses ofLycopersicon pennellii, or of its F₁ with tomato,L. esculentum. The active compounds in theL. pennellii rinsates were identified as 2,3,4-tri-O-acylglucoses bearing short to medium chain length fatty acids. These compounds are localized in the glandular exudate of the type IV trichomes and may accumulate to levels in excess of 400 g/cm². In choice assays, purified glucose esters fromL. pennellii reduced aphid settling at concentrations as low as 25 g/cm²; at concentrations of 150 g/cm² or more, all aphids avoided treated areas. Glucose esters were also active in deterring aphid settling in no-choice assays. At 100 g/ cm², these esters resulted in increased levels of mortality after 48 hr.     

Identification of important image features for pork and turkey ham classification using colour and wavelet texture features and genetic selection

A method to discriminate between various grades of pork and turkey ham was developed using colour and wavelet texture features. Image analysis methods originally developed for predicting the palatability of beef were applied to rapidly identify the ham grade. With high quality digital images of 50–94 slices per ham it was possible to identify the greyscale that best expressed the differences between the various ham grades. The best 10 discriminating image features were then found with a genetic algorithm. Using the best 10 image features, simple linear discriminant analysis models produced 100% correct classifications for both pork and turkey on both calibration and validation sets.     

Optimal design and manufacture of thin‐walled polystyrene structures

In this study, we investigated the implementation of an automatic procedure for optimizing thermoformed thin‐walled structures. Such objects are created in great numbers, especially in the food packaging industry. The methodology for the optimal design of such structures is based on the use of a parameterized geometry model created within an interactive design environment. By varying the parameters associated with the computer‐aided design (CAD) model, one can create a rich variety of possible designs. One can then subject these designs to physical analysis to calculate their physical properties, and thus select an optimal design. The two distinct stages of this process—the prediction of the shape of the thermoformed structure, and the physical behavior of the structure—were validated by experiments. This article reports the experimental investigation of the deformation behavior of polystyrene, the mechanical behavior of specially prepared deformed polystyrene sheets, and the response to loading of a hemispherical structure (used in the validation). POLYM. ENG. SCI., 45:694–703, 2005. © 2005 Society of Plastics Engineers     

Mobility of trace elements from selected Australian fly ashes and its potential impact on aquatic ecosystems

Batch leaching tests have been performed on fly ashes collected from four Australian power stations fuelled by chemically different coals. Two acidic and two alkaline fly ashes were subjected to long-term (144 h) leaching tests, and the behaviour of As, B, Mo and Se was investigated to obtain data on their potential for mobilisation during fly ash-water interactions. All four elements are mobile under different conditions and over different leaching times. The concentrations of these elements released in leaching solutions with initial pH values of 4, 7 and 10 were used to assess the influence of pH conditions on element mobility from the acidic and alkaline fly ashes. The most mobile of the four elements leached were Mo from alkaline fly ashes and B from acidic fly ashes. Arsenic concentration increased with time in leachate solutions from acidic and alkaline fly ashes; however, in solutions in contact with alkaline fly ashes the As concentration, after reaching a maximum, later decreased with time. Selenium mobility shows a similar pattern to that of As, with similar leaching concentrations. Boron has the highest relative mobility of all four elements. A process possibly responsible for the decrease in concentration of B, As and Se in alkaline leaching solutions is the formation of ettringite. Equilibrium between the solid phase (ash) and the leaching solution was not reached in any of the leaching experiments. The pH of the leaching solution is the key factor affecting the mobility of these trace elements in these fly ashes.     

Transfer between pose and illumination training in face recognition.

The relationship between pose and illumination learning in face recognition was examined in a yes–no recognition paradigm. The authors assessed whether pose training can transfer to a new illumination or vice versa. Results show that an extensive level of pose training through a face–name association task was able to generalize to a new illumination (Experiments 1 and 3), but an equal level of illumination training failed to generalize to a new pose (Experiment 2). The transfer of pose training was likely to depend on a relatively extensive level of training because the same faces with reduced level of exposure (Experiment 4) were unable to reproduce the transfer effect. The findings suggest that generalization of pose training may be extended to different types of image variation, whereas generalization of illumination training may be confined within the trained type of variation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modeling the pH dependent hydrolysis of VX for aqueous releases

The fate of chemical warfare agents (CWAs) in aqueous environments is not well characterized. Limited physical and kinetic data are available in the open literature for this class of chemicals, in part due to the dangers associated with exposure to these compounds. As a result, the development of methods for determining the persistence and extent of impact of a waterborne chemical agent release remains largely unanswered. In this study a basic hydrolysis model was developed to track the fate of VX (O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothiolate) from an instantaneous point source aqueous release. Hydrolysis product generation tracking was developed to determine the instantaneous pH within the local dispersive environment. Using instantaneous local pH values, the impact of pH on the persistence of VX hydrolysis rate was investigated for three different aqueous environments with varying dispersive conditions. Modeling results indicate that an accurate characterization of the pH dependence of the hydrolysis rate constant becomes more important in lower pH and lower turbulence environments. With this basic model, estimates of the time and extent of lethality of a VX release can be made.