Flexible polymer composite electromagnetic crystals

The dielectric properties of a ceramic powder (BaTiO₃) filled thermoplastic elastomer (EPDM TPE) were investigated for use in a flexible electromagnetic crystal. Materials were produced that had a high dielectric constant (approximately 9) and low loss tangent (less than 0.01). Materials were extruded and injection molded so as to povide low‐cost processing. Mechanical and electromagnetic test results showed the effect of processing conditions on the final quality of the composite. The shear rate during processing and the number of mixing cycles were found to affect the final material characteristics significantly. An electromagnetic crystal woven from extruded rods showed good reflectivity in the 10–15 GHz region.     

The nucleation of microcellular thermoplastic foam with additives: Part II: Experimental results and discussion

Experiments were performed to validate the model for the nucleation of microcellular foams in amorphous thermoplastic polymers. The polystyrene-zinc stearate system was chosen as the model system. Other additives such as stearic acid and carbon black were also investigated. Molecular weight and orientation effects were studied. Nitrogen and carbon dioxide were used to produce the microcellular bubbles. Results show that amounts of soluble additives at levels just below their solubility limit and high gas saturation pressures yield the most acceptable foams—ones with a large number of uniform small bubbles. In this region, the bubble number is sensitive to both the gas saturation pressure and the concentration of solutes. Increasing the concentration of soluble additives above the solubility limit has little effect on bubble number and almost eliminates the dependence on saturation pressure. Molecular weight and orientation had no effect on the number of bubbles produced. Similarly, carbon black, which is insoluble in and which bonds well to polystyrene, produced no effect on bubble numbers. The agreement between theoretical predictions and experimental results is reasonably good.     

Automatic Construction and Verification of Isotopy Invariants

We extend our previous study of the automatic construction of isomorphic classification theorems for algebraic domains by considering the isotopy equivalence relation. Isotopism is an important generalisation of isomorphism, and is studied by mathematicians in domains such as loop theory. This extension was not straightforward, and we had to solve two major technical problems, namely, generating and verifying isotopy invariants. Concentrating on the domain of loop theory, we have developed three novel techniques for generating isotopic invariants, by using the notion of universal identities and by using constructions based on subblocks. In addition, given the complexity of the theorems that verify that a conjunction of the invariants form an isotopy class, we have developed ways of simplifying the problem of proving these theorems. Our techniques employ an interplay of computer algebra, model generation, theorem proving, and satisfiability-solving methods. To demonstrate the power of the approach, we generate isotopic classification theorems for loops of size 6 and 7, which extend the previously known enumeration results. This work was previously beyond the capabilities of automated reasoning techniques. The author’s work was supported by EPSRC MathFIT grant GR/S31099.     

Open‐celled microcellular thermoplastic foam

A theoritical model of the production of open‐cell microcellular foam is presented. This model allows the prediction of the conditions necessary to produce these materials. Experiments verify the model quite well. The results of the batch processing experiments indicate the processing parameters that promote the development of open‐celled microcellular polystryene foam. A saturation pressure of 17.2 MPa (2500 psig) provides the nucleation density necessary to form an impinged structure with microcellular bubble density. A foaming temperature of 200°C promotes the formation of both internal and surface porosity. A scaled time between 1 and 2.7 seconds develops a foam structure that intrudes a large volume. Samples foamed at 200°C for 1 and 2 seconds possess pores less than 1 μm in diameter. These samples represent scaled times of 1 and 2 seconds. Therefore, to produce open‐celled microcellular polystyrene foam with batch processing, samples should be saturated at approximately 17.2 MPa (2500 psig) and foamed for a scaled time between 1 and 2 seconds.     

Processing parameters for consolidating PEEK/carbon fiber (APC-2) composites

This consolidation of unidirectional APC-2 was studied experimentally to determine the effects of processing parameters (pressure, temperature, and number of layers) on resin flow as measured by the Kozeny constant and the bulk modulus. The Kozeny constant obtained was between 0.0205 and 0.107. It was found to depend on the consolidation pressure, temperature, number of layers, and their interactions at a 99% confidence level. The value of the bulk modulus was found to be between 1.21 MPa (175 psi) and 8.58 MPa (1244 psi). It also was found to depend on the temperature, pressure, number of plies, and their interactions at a 99% confidence level. These results show the critical effects of fiber orientation on resin flow during processing.     

Draft angle and surface roughness effects on stereolithography molds

Stereolithography (SL) is a rapid prototyping process, which allows one to build complex shapes quickly. Current research investigates the possibilities of using this process to make injection molds. This would allow designers to manufacture and test molds easily and rapidly. One of the main issues with this technique is the effects of its surface on the part. Molds built by SL have high roughness. This gives rise to a high friction force between the part and the mold, and increases the ejection force needed to eject the part from the mold. High ejection forces often lead to damage or breakage of the part and the mold. Research was undertaken on the effects of draft angle and roughness on ejection forces. It was found that increasing the draft angle does not necessary assist the ejection of the part. As the draft angle increases, the roughness and hence the friction force between the part and the mold also increase. There is a trade‐off between draft angle and roughness. A model based on Glanvill's equation was developed to predict ejection force and was consistent with experimental results.     

Effects of adsorbed heat labile serum proteins and fibrinogen on adhesion and apoptosis of monocytes/macrophages on biomaterials

A previously established human monocyte culture protocol was used to determine the effects of varying adsorbed proteins on monocyte/macrophage adhesion and survival on dimethyl-silane (DM) or RGD modified glass coverslips. Cells were allowed to adhere for 2 h in the absence of protein or in the presence of serum, fibrinogen (Fg), heat inactivated serum (HIS), serum supplemented with Fg or HIS with Fg. Cell adhesion and apoptosis rates were determined on days 0 (2 h), 3, 7 and 10 of culture. The presence of serum alone in the initial culture was sufficient to optimize monocyte/macrophage adhesion and survival rates. Adding Fg to serum did not increase adhesion nor decrease apoptotic rates. No protein or the addition of HIS during the initial incubation period significantly decreased monocyte/macrophage adhesion and survival on both surfaces, however, the addition of Fg to HIS restored adhesion and survival rates to those seen with in the presence of serum alone on RGD surfaces. These studies demonstrate that monocyte/macrophage adhesion and survival on biomaterial surfaces are optimized by adsorbed heat labile serum proteins while adsorbed Fg plays a surface property-dependent role.     

An integrated,intelligent design environment

An integrated, intelligent design environment was designed and implemented. The heart of the environment is a userfriendly, menu-driven CAD system integrated with an information controller. The system allows the engineer to design in a feature-based, object-oriented manner. Designs are stored in a data base and checked for manufacturability and assembly by an expert system. This paper describes the design of the information integration controller and the man-machine interfaces of the intelligent design system.     

Investigation of the atomic-scale friction and energy dissipation in diamond using molecular dynamics

We have used molecular dynamics simulations to examine friction when two diamond (111) surfaces are placed in sliding contact. The essence of atomic-scale friction was shown to be the mechanical excitation (in the form of vibrational and rotational energy) of the interface lattice layers upon sliding. This excitation was propagated to the rest of the lattice, and eventually dissipated as heat. In general, this excitation increases with increasing applied load; therefore, the atomic-scale friction also increases with load. Flexible hydrocarbon species, chemically bound to the diamond surface, can lead to a significant reduction of mechanical excitation upon sliding at high loads, leading to lower friction. In addition to clarifying the effects of chemically-bound hydrocarbon groups on atomic-scale friction at diamond interfaces, these simulations might also yield insight into more complicated systems, e.g. Langmuir-Blodgett films, and aid in the design of low-friction coatings.