Some effects of particle size on the sintering of titanium and a master sintering curve model

The press-and-sinter method of producing net shapes was applied to titanium alloys. The quantitative effects of the particle size of titanium and Ti-6Al-4V powders on the green and sintered densities were examined. Most powders were pressed at 100 to 800 MPa and sintered under vacuum at 1100 °C, 1200 °C, or 1300 °C for 2 hours. The green density was higher for coarser powders and for powders with a wider size distribution. The sintered density was higher for finer powders and for powders with a wider size distribution. The densification parameter was little affected by the compaction pressure but increased as the particle size was reduced. An empirical model of densification based on the master sintering curve approach was developed, with the activation energy for densification of titanium found to be approximately 160 kJ/mol

Artificial Immune System-based algorithm for vehicle routing problem with time window constraint for the delivery of agri-fresh produce

This paper addresses the problem of delivering continuously deteriorating agri-fresh produce from a wholesaler to a number of retailers, within specific time windows. The prime objective is to decide the routes in such a way that the overall cost incurred in transportation, deterioration and penalty is minimised. To model these conflicting objectives a mathematical modelling approach is proposed. The Vehicle Routing Problem with Time Windows (VRPTW) is a Non-deterministic Polynomial-time hard (NP-hard) problem, without considering the business constraints, and becomes computationally prohibitive with the increase in number of retailers. To solve the VRPTW within feasible time limits, Artificial Immune System (AIS)-based solution methodology is proposed. The algorithm is tested on real-life instances generated from Azadpur wholesale market, New Delhi (India). An experiment is performed on the same problems with other algorithms, such as Genetic Algorithm (GA) and Simulated Annealing (SA), to compare the effectiveness and efficiency of the proposed approach. It is found from the quality of solution and rate of convergence that AIS performed better compared to the other applied approaches

Immunity to Campylobacter: its role in risk assessment and epidemiology

Acquired immunity is an important factor in the epidemiology of campylobacteriosis in the developing world, apparently limiting symptomatic infection to children of less than two years. However, also in developed countries the highest incidence is observed in children under five years and the majority of Campylobacter infections are asymptomatic, which may be related to the effects of immunity and/or the ingested doses. Not accounting for immunity in epidemiological studies may lead to biased results due to the misclassification of Campylobacter-exposed but apparently healthy persons as unexposed. In risk assessment studies, health risks may be overestimated when immunity is neglected