Effects of Fluids on the Simulated Clinical-Dental Machining of a Glass Ceramic

Effects of fluids on material removal rate, chipping damage, and surface roughness in the simulated clinical-dental machining of a dental-type glass ceramic were investigated. Significant differences in removal rate were obtained among the fluids investigated, but only a 4 wt% boric acid solution gave a higher removal rate than conventionally used water. Chipping damage was substantially lower for the boric acid and an oil-emulsion coolant compared with other fluids tested. Surface roughness was independent of the fluids used. The results indicate that improvement can be achieved in both material removal rate and machining damage by the appropriate selection of coolant chemistry.     

Defect chemistry of langasite III: Predictions of electrical and gravimetric properties and application to operation of high temperature crystal microbalance

The electrical and gravimetric properties of langasite, La₃Ga₅SiO₁₄, are related to its underlying defect and transport processes via previously developed predictive defect and transport models. These models are used here to calculate the dependence of the partial ionic and electronic conductivities and the mass change for langasite as functions of temperature, dopant type and level and pO₂. Doping strategies devised for minimizing conductivity in langasite based on use conditions are described. For example, the required dopant level to achieve minimum conductivity and thus minimum electrical losses in acceptor-doped langasite is shown to depend on the operating pO₂. Likewise intrinsic mass changes in langasite, dependent on dopant level, pO₂ and temperatures, if high enough, can mask mass changes induced in active layers applied to langasite when used as a microbalance. For example, the model predicts that the dopant level in donor-doped langasite has less of an impact on intrinsic mass change due to external environmental changes when compared to acceptor-doped langasite. The models are also applied in defining acceptable operating limits needed to achieve and/or the design of properties for desired levels of microbalance resolution and sensitivity.     

Roller compacted concrete with contaminated recycled aggregates

Recycling waste building materials from construction and demolition (C&D) sites is increasingly investigated for economical and environmental reasons. Roller compacted concrete (RCC) is a special dry concrete mix; laid down and compacted like a soil, it is especially used for the construction of massive structures like dams or large horizontal surfaces like road foundation. In this paper, natural concrete slabs were cured in water, sea water, chloride solutions or sulphate solutions and then crushed to obtain virgin and contaminated (polluted) recycled aggregates. The aim of this research is the total replacement (100% coarse and fine) of natural aggregates (NA) by recycled concrete aggregates (RA) in the composition of a roller compacted concrete. The natural and recycled aggregates are characterised and compared. The mechanical properties and durability performances of concrete with contaminated RA are analysed. The experimental results showed that the polluted RA are much richer in chlorides than in sulphates and are leached if they are soaked in water. Significant differences were observed between the properties of original and new concrete and the results demonstrated the need of taking these contaminations into account.     

An efficiency-optimization controller for induction motor drives

When working close to their nominal operating point, induction motors are high-efficiency machines. However, at low load, efficiency is greatly reduced when magnetization flux is maintained at nominal value. Therefore, it is necessary to adjust the flux level according to the load, so as to decrease iron and copper losses. This paper deals with a field-oriented scheme for induction motor drives leading to efficiency optimization. It is based on optimal power factor tracking by adjusting magnetization current component with to respect the torque current component. Simulation results are presented to highlight the feasibility and validity of the proposed method     

Testing Address Decoder Faults in Two-Port Memories: Fault Models, Tests, Consequences of Port Restrictions, and Test Strategy

A two-port memory contains two duplicated sets of address decoders, which operate independently. Testing such memories requires the use of single-port tests as well as special two-port tests; the test strategy determines which tests have to be used. Many two-port memories have ports which are read-only or write-only; this impacts the possible tests for single-port and two-port memories, as well as the test strategy. In this paper the effects of interference and shorts between the address decoders of the two ports on the fault modeling are investigated. Fault models and their tests are introduced. In addition, the consequences of the port restrictions (read-only or write-only ports) on the fault models and tests are discussed, together with the test strategy.     

Contact stress distributions in a turbine disc dovetail type joint - a comparison of photoelastic and finite element results

Two dimensional photoelastic frozen stress techniques were used to investigate the stress distributions of an axially loaded dovetail joint as is found in the design of some turbine blade-disc fixings. The internal stress distributions were obtained by the shear difference method and were compared to results obtained by using the finite element method. It was found that steep principal stress gradients were present immediately below the contact surfaces in the zone adjacent to the fillet radius of the dovetail fixing, which could be an important consideration in the fatigue strength of the joint. The finite element model used gave the same trends of stress as the photoelastic model, predicted higher peak principal stresses and did not exhibit the same detailed variations of stress distribution.     

2099 Aluminum-Lithium with Key-Locked Inserts for Aerospace Applications

The purpose of this study was to determine the acceptability of nonpenetrating, key-locked inserts in 2099 aluminum-lithium. The tests conducted to make this assessment were: (1) microscopic examination for thread damage and delaminations after key installation, (2) pull-out load at 21 °C (70 °F) and −179 °C (−290 °F), and (3) mechanical cycling tests at room temperature and −179 °C (−290 °F). The test results indicated that for the three sizes evaluated, key-locked inserts in 2099-T6 and 2099-T8 were acceptable and although delaminations did occur on some T6 temper specimens, it was only as a failure mode at ultimate load and such behavior was judged to be acceptable.     

Heat capacities of both PMMA stereomers: Comparison between atomistic simulation and experimental data

The domains of time and space generally covered by full atomistic simulation (AS) to represent the glass transition temperature, T_g, are very small. Physical interpretations of the phenomena occurring at this transition are inevitably limited. To specifically address such limitation, behavior of the heat capacity that accounts for the freezing of the degrees of freedom as temperature is decreased, is investigated. The selected polymer is poly(methyl methacrylate) since it offers the opportunity to exhibit a different T_g according to the tacticity of its chain. AS and experimental data are thus compared to a theoretical model that takes into account three contributions to the leap in the heat capacity occurring at T_g. The comparison discloses that an excellent agreement is obtained between simulated and experimental contributions from vibrations and free volume. However, from an AS viewpoint changes in the conformation weakly contribute to this leap. Despite this discrepancy local contributions to the glass transition as predicted by atomistic simulation, are sufficient to determine T_g.     

Design of a commercial solar-powered greenhouse

A completely solar-powered greenhouse complex has been designed for climate controlled food production in hot, humid environments. The concept uses passive design features to provide irrigation water from saline water sources. This paper discusses the overall system concept and the solar still subsystem which has been designed to provide a continuous fresh water supply. While incorporating many innovative features, the use of proven technologies and passive design results in a system that should compete economically with current, more traditional designs.     

An Efficient Digital Confidentiality Scheme Based on Commutative Chaotic Polynomial

Multimedia Tools and Applications - One of the most critical aspects of this technologically progressive era is the propagation of information through an unsecured communication channel. The...