Stress singularity analysis in the restorations of premolar class ii cavities

Abstract

This paper presents the singular stress analysis near the apex of a structure formed during dental restoration of a premolar class II cavity. Based on the elasticity theory, the stresses may go to infinity at the junctions of different materials (e.g. dentine, enamel, restoration materials). Tensions will cause material separation and then material fracture. In order to reduce the failure probability, the degree of stress concentration has to be reduced. The stress singularity order and the stress intensity factor are two parameters, which are often used in fracture analysis. The objective of this paper is to find conditions such that non‐singular stress fields are possible. Three critical positions in the restoration structure are discussed.

They are the tips of interface between (1) enamel and restoration; (2) dentine and restoration; and (3) enamel, dentine and restoration. In the last two cases, the restoration may be bonded or debonded to enamel or dentine. After employing Kolosov‐Muskhelishvili complex functions together with the eigenfunction expansion method, the singularity orders are computed theoretically. Weak stress singularity conditions can be sought by properly selecting cutting angles or restoration materials.     

Thermoelectric and mechanical properties of melt spun and spark plasma sintered n-type Yb- and Ba-filled skutterudites

Here we present thermoelectric and mechanical properties of n-type filled-skutterudites produced by a combination of melt spinning of pre-melted charges with subsequent consolidation by spark plasma sintering, a process we refer to as MS-SPS. This combination of processing steps leads to phase-pure n-type filled-skutterudites and obviates more energy and time intensive annealing steps. We show that both the thermoelectric properties and the tensile fracture strength compare favorably to materials made by traditional methods. The process is scalable to at least 80 g billets, such that the transport properties measured on test bars harvested from these larger billets compare favorably to those measured on lab-scale billets (5 g total billet mass). ZT values approaching 1.1 at 750 K were observed in materials made by MS-SPS. In addition, the tensile fracture strength of test bars cut from an 80 g billet is ∼128 MPa at room temperature and decreases with increasing temperature. Fractography of the test bars reveals that the majority failed due to surface and edge flaws with few failures due to volume type flaws. This indicates that the powder metallurgical methods employed to produce these samples is mature.     

SAPPHIRE: A toolkit for building efficient stream programs for medical video analysis

This paper describes the design and implementation of SAPPHIRE – a novel middleware and software development kit for stream programing on a heterogeneous system of multi-core multi-CPUs with optional hardware accelerators such as graphics processing unit (GPU). A stream program consists of a set of tasks where the same tasks are repeated over multiple iterations of data (e.g., video frames). Examples of such programs are video analysis applications for computer-aided diagnosis and computer-assisted surgeries. Our design goal is to reduce the implementation efforts and ease collaborative software development of stream programs while supporting efficient execution of the programs on the target hardware. To validate the toolkit, we implemented EM-Automated-RT software with the toolkit and reported our experience. EM-Automated-RT performs real-time video analysis for quality of a colonoscopy procedure and provides visual feedback to assist the endoscopist to achieve optimal inspection of the colon during the procedure. The software has been deployed in a hospital setting to conduct a clinical trial.     

A genetic algorithm-based approach to machine assignment problem

Over the last few decades, production scheduling problems have received much attention. Due to global competition, it is important to have a vigorous control on production costs while keeping a reasonable level of production capability and customer satisfaction. One of the most important factors that continuously impacts on production performance is machining flexibility, which can reduce the overall production lead-time, work-in-progress inventories, overall job lateness, etc. It is also vital to balance various quantitative aspects of this flexibility which is commonly regarded as a major strategic objective of many firms. However, this aspect has not been studied in a practical way related to the present manufacturing environment.

In this paper, an assignment and scheduling model is developed to study the impact of machining flexibility on production issues such as job lateness and machine utilisation. A genetic algorithm-based approach is developed to solve a generic machine assignment problem using standard benchmark problems and real industrial problems in China. Computational results suggest that machining flexibility can improve the overall production performance if the equilibrium state can be quantified between scheduling performance and capital investment. Then production planners can determine the investment plan in order to achieve a desired level of scheduling performance.     

Ultrasonic Tomographic Imaging of an Encased,Highly Attenuating Solid Medium

Abstract

Ultrasonic tomographic imaging has been performed on a highly attenuating, filled, hydroxyl-terminated polybutadiene, cast into a steel case. The detection of defects and the characterization of solid rocket propellant were thus possible. Extremely low signal levels due to the attenuation and scattering properties of the polymer were present. In addition, a nonideal tomographic reconstruction geometry was present, because of a cylindrical air-filled cavity in the center of the polymer. Complications also arose from high-amplitude guided waves within the steel case, which tended to mask directly transmitted signals through the propellant. These problems were solved using specially designed transducers and pulse-compression signal processing techniques. Modifications to the filtered back-projection reconstruction procedure were made to account for the discontinuity caused by the hole. Images are presented showing the detection of an artificial defect to demonstrate the technique.     

Near optimal process plan selection for multiple jobs in networked based manufacturing using multi-objective evolutionary algorithms

The networked manufacturing offers several advantages in current competitive atmosphere by way of reducing the manufacturing cycle time and maintenance of the production flexibility, thereby achieving several feasible process plans. In this paper, we have addressed a Multi Objective Problem (MOP) which covers-minimize the makespan and to maximize the machine utilization while generating the feasible process plans for multiple jobs in the context of network based manufacturing system. A new multi-objective based Territory Defining Evolutionary Algorithm (TDEA) to resolve the above computationally challenge problem have been developed. In particular, with two powerful Multi-Objective Evolutionary Algorithms (MOEAs), viz. Non-dominated Sorting Genetic Algorithm (NSGA-II) and Controlled Elitist-NSGA-II (CE-NSGA-II) the performance of the proposed TDEA has been compared. An illustrative example along with three complex scenarios is presented to demonstrate the feasibility of the approach. The proposed algorithm is validated and the results are analyzed and compared.     

A Modified Bandwidth K Factor Relationship Due to Parasitic Effects in Semiconductor Lasers

Abstract

A novel relationship between the maximum bandwidth and the bandwidth K factor has been obtained to describe the frequency response of laser diodes under the influence of parasitic effects. The relationship is applicable to the evaluation of the intrinsic bandwidth of quantum well lasers subject to carrier transport effects.     

Ethnically bounded homeownership: qualitative insights on Los Angeles immigrant homeowners’ experiences during the U.S. Great Recession

Immigrant homeowners’ function within ethnic boundaries in the housing market may have helped or hindered them during the recent U.S. Great Recession. This research explores this theme through interviews with immigrant and non-immigrant homeowners from four ethnic communities in Los Angeles County and the non-profit organizations that tried to assist them. Immigrant homeowners turned to co-ethnics for advice and support and formed multigenerational households as a strategy to achieve and sustain homeownership. Language and cultural barriers primed them for risky loans and thwarted their pursuit of refinance and modification when they struggled to make mortgage payments. These findings conform to existing evidence of ethnic segmentation in the housing market and imply that analyses of home buying and homeownership in areas with significant immigrant populations should factor in the role of ethnicity.