Geometry and Topology of Structure in Amorphous Solids

The geometrical concept of an ideal solid and a method for its construction are presented as novel contributions to the understanding of atomic arrangements in amorphous solids. This ideal amorphous structure serves as a base-line model for atomic arrangements and as a universal reference from which any changes in atomic arrangement can be measured. The model is intended to represent the ideal structure of amorphous solids and not the way a real glass is formed. This provides for amorphous materials the same kind of base-line reference as an ideal crystal does for real crystalline materials, or tiling patterns for quasi-crystalline materials. Characteristic properties are described, including Debye X-ray scattering to show how relevant information can be derived about the presence of vacancies and compositional changes.     

Impact of natural infestation of Amblyomma variegatum on the liveweight gain of male Gudali cattle in Adamawa (Cameroon)

The effect of natural tick infestation on the liveweight gain (LWG) of male Gudali zebu cattle was studied throughout a year by comparing the performances of two herds, one of which was submitted to weekly acaricidal treatment and the other was left untreated against ticks. Six species of ticks were identified on the untreated animals: Amblyomma variegatum, Boophilus decoloratus, Rhipicephalus lunulatus, Rhipicephalus turanicus, Hyalomma nitidum and Hyalomma marginatum rufipes. Most of the losses observed in the untreated herd during the rainy season were due to A. variegatum, and the loss in LWG was estimated to be 55-76 g per engorged female A. variegatum. The infestation also leads to wounds and to lesions of dermatophilosis. There was an interval between the peak infestation by A. variegatum and the appearance of weight loss owing to them. The control of ticks on the Gudali zebu in Adamawa, during the months of high infestation by A. variegatum adults, is economically profitable. On the other hand, the performances of the two herds during the dry season were similar, showing that infestation by larvae and nymphs of A. variegatum has no impact on the zebu LWG, and that tick control during that period is not profitable.     

Optimized dairy grazing systems in the northeast United States and New Zealand. I. Model description and evaluation.

Parallels exist in the recent developments of dairy systems in the Northeast United States and New Zealand because of greater use of pasture grazing and feed supplements, respectively. Lessons can be learned from each system. However, major differences exist between the regions in the patterns of pasture production, the costs of supplementary feed, and milk prices. These differences affect the optimum use of feed. In this paper, a linear programming model developed to determine optimum feeding strategies for dairy systems in each country is presented. The model optimizes grazing management (rotation lengths) and the conservation of pasture subject to constraints on their use. Other feed resources include N fertilizer, grain, corn silage, and alfalfa silage. All feeds are represented in energy terms. The substitution of pasture intake by grain and forage supplements is included, and cow performance can be optimized by choosing from 73 seasonal calving herds that vary in calving date, lactation length, and daily milk production. The model predicts that marginal responses to grain feeding are between 1.35 and 1.8 kg of milk/kg of grain dry matter supplement, well within the range of responses reported in the literature. Evaluation of the model against data from nine grazing system treatments in New Zealand and two in Pennsylvania showed that model predictions averaged +3% (New Zealand) and +0.04% (Northeast) of measured milk production. The model could be used with confidence to study systems in both the Northeast United States and New Zealand.     

Processing Aids: The Effect of Polymethyl Methacrylate on the Fusion of Rigid Poly(vinyl chloride)

The fusion process of a PVC dryblend, both with and without a PMMA processing aid, was studied in a Brabender Plasticorder over a range of mixer temperatures. charge masses and rotor speeds. The progress of fusion was monitored by the examination of the morphology of the PVC samples taken during different stages of the fusion process. The technique of examining the acetone-swollen samples by optical microscopy before and after shearing,¹ provided an insight to the mechanism of action of the PMMA processing aid. The study established that the PMMA processing aid modified both the inter-grain coefficient of friction and the packed density which had a significant effect on the initiation of the fusion process. The fusion process of both PVC compounds, i.e. with and without PMMA processing aid, was shown to proceed via a comminution mechanism, where the PVC grains were randomly broken into sub-grains and primary particle agglomerates. Concurrent with this breakdown, the cohesion of PVC agglomerates was observed.     

Crystallization behaviour of isotactic polypropylene/linear low density polyethylene blends

Crystallization behaviour of isotactic polypropylene/linear low density polyethylene (iPP/LLDPE) blends has been investigated by optical microscopy and DSC. Crystallization of iPP depends upon blend composition and thermal history. When blended with LLDPE, the crystallization temperature of iPP, T_c, decreased slightly. Crystallinity did not change in the range 0-80wt% LLDPE; there were only slight changes in the crystalline structure, but LLDPE seemed to resist forming the β type of spherulites. Below 80 wt% of LLDPE, iPP was a continuous phase. The iPP spherulite growth rate was almost constant; however, overall crystallization decreased due to decreasing primary nuclei density.     

Effect of low frequency vibrations on void content in composite materials

Eliminating common defects such as voids, bubbles, and poor adhesion at interfaces will increase the quality of laminated sandwich composite structure. This work reports experimental research and analysis of the effect of mechanical vibrations applied to the curing system of composite materials production, particularly for minimizing void content. Range of frequency of vibrations covered was from 10 to 50 Hz, for different period of vibrations. The composite laminates were made by hand lay-up using glass fibers and vinyl-ester resin, and examined under microscope to determine types and quantity of defects. The results showed reduction in void content when vibrations were applied for 30 min.     

Controlled fabrication of multilayered 4-(pyrrole-1-yl) benzoate supported poly(3,4-ethylenedioxythiophene) linked hybrid films of Prussian blue type nickel hexacyanoferrate

The ability of 4-(pyrrole-1-yl) benzoic acid (PyBA) to form monolayer-type carboxylate-derivatized ultra-thin organic films on solid electrode surfaces was explored here to attract coordinatively and immobilize Ni²⁺ ions at the electrode/electrolyte interface. In the next step, the system was exposed to Fe(CN)₆³⁻ or Fe(CN)₆⁴⁻ solution to form a robust nickel hexacyanoferrate (NiHCF) layer. By repeated and alternate treatments in solutions of PyBA, Ni²⁺ cations, and Fe(CN)₆³⁻ or Fe(CN)₆⁴⁻ anions, the amount of the material could be increased systematically in a controlled fashion to form three-dimensional multilayered NiHCF-based assemblies. The layer-by-layer method was also extended to the growth of hybrid conducting polymer stabilized NiHCF films in which the initial PyBA-anchored NiHCF layer (formed on glassy carbon) was subsequently exposed (a desired number of times) through alternate immersions to the monomer (3,4-ethylenedioxythiophene), Fe(CN)₆³⁻ and Ni²⁺ solutions. During voltammetric potential cycling (electropolymerization) in the external supporting electrolyte solution, poly(3,4-ethylenedioxythiophene) or PEDOT linked NiHCF-based multilayered films were produced. They were characterized by good stability and high dynamics of charge transport.     

Prediction of the Bursting Pressure of Oriented Plastic Bottles

The introduction of biaxially oriented PET bottles to replace conventional glass bottles for packaging carbonated soft drinks has been a very successful commercial endeavor. The scientific approach to optimum design of thermoplastic bottles seems to lag behind technological developments. Very few scientific papers have been published on this subject.     

The elastic change of volume in pressurized bottles made from polymeric materials

The relations describing the elastic change of volume of thermoplastic cylindrical pressurized containers are presented. Discussions have been made on various cases including isotropic (i.e., un-oriented), uniaxially, and biaxially oriented materials. These relations are expected to be helpful for selecting the optimum processing conditions (i.e., draw ratio) in order to achieve the desired properties of polymeric pressurized containers.