Production inventory with service time and interruptions

This paper considers an (s,S) production inventory system with positive service time, with time for producing each item following Erlang distribution. Customers arrive according to a Poisson process. A customer who arrives when there is no inventory in the system is considered lost. On the other hand, a customer who finds a busy server with at least one inventory in the system joins a queue of infinite capacity. When the inventory level falls to s, production process is switched on, and it is switched off when the inventory level reaches back to S. Service time to each customer also follows an Erlang distribution. The service of a customer may be interrupted, where the time for such a phenomenon follows an exponential distribution, whenever it occurs. An interrupted service, after repair, resumes from where it was stopped. The correction/repair time follows an exponential distribution. We assume that the service of a single customer may encounter any number of interruptions and that the customer being served waits there until his service is completed. Moreover, at a time the server is subject to at most one interruption. We also assume that no inventory is lost due to a service interruption. Like the service process, the production process also is subject to interruptions, where the duration to an interruption follows an exponential distribution. However, in contrast to the service interruption, in the case of interruption to production process, we assume that the item being processed is lost because of interruption. That is, the production process, on being interrupted, restarts from the beginning, after repair. The repair time of an interrupted production process follows exponential distribution. Few of the last service phases are assumed to be protected in the sense that the service will not be interrupted while being in these phases. The same is assumed for the production process also.

The model is analysed as a level-independent quasi-birth–death process. We apply a novel method to obtain an explicit expression for the necessary and sufficient condition for the stability of the system under study. This method works even if we assume general phase-type distributions for the production as well as the service processes, and hence can be used to characterise the stability of inventory systems where the assumption of disallowing the customers to join the system, when there is a shortage of inventory has been made. Under stability, we apply matrix analytic methods to compute the system state distribution. In consequence to that, several system performance measures have been derived, and their dependence on the system parameters has been studied numerically.     

Use of Objective-Based Undergraduate Research Project Experience as a Graduate Student Recruitment Tool

This paper describes experience in using hands-on undergraduate research exposure as a tool to identify and recruit potentially successful graduate students. Undergraduate students with an interest in graduate education work toward a well-defined goal under the guidance of the faculty member, typically supporting a senior graduate student on his/her thesis research. The quality of the undergraduate research is maintained by requiring that the results of the research be presented at a major technical conference. It is found that a large percentage of such undergraduate students ultimately enroll and succeed in graduate school.     

A novel trench clustered insulated gate bipolar transistor (TCIGBT)

A new trench clustered insulated gate bipolar transistor (TCIGBT) is reported. In this device, a multitude of UMOS cathode cells is enclosed within a common n-well and p-well. The TCIGBT provides a unique "self-clamping" feature to protect the trenches from high electric fields. The simulation results based on 1.2 kV nonpunchthrough technology indicate an improvement of 25% in on state and 28% in the turn-off losses in comparison to the state-of-the-art trench IGBT. The saturation current levels of the TCIGBT, which can be designed independent of the forward drop, are also lower.     

Surface modification of CP-Ti to improve the fretting-corrosion resistance: Thermal oxidation vs. anodizing

Fretting corrosion is one of the important reasons for the failure of prosthesis made of titanium and titanium alloys under in vivo condition. The fretting-corrosion behaviour of untreated, anodized and thermally oxidized commercially pure titanium (CP-Ti) in Ringer's solution was evaluated based on the change in free corrosion potential (FCP) measured as a function of time. A comparison of the performance of untreated, anodized and thermally oxidized CP-Ti under fretting-corrosion conditions is reported for the first time in this paper. The study reveals that surface modification of CP-Ti by both anodizing and thermal oxidation improved the fretting-corrosion resistance of CP-Ti and among them the performance of thermally oxidized CP-Ti is superior to that of the anodized one. Adhesive galling is the predominant wear mechanism for untreated CP-Ti, adhesive wear and delamination are found to be operative for anodized CP-Ti whereas an abrasive wear mechanism is operative for thermally oxidized CP-Ti when they are fretted against an alumina ball.     

New Technology Introduction and Implementation: The Case of Paging Technology in the Ratlam Division of Indian Railways

Concomitant to the liberalisation policy and market reforms in India has been the issue of declining budgetary support for public sector organisations. Hitherto, Indian Railways, the biggest publicly-owned enterprise, has largely been supported by the exchequer. Since the early 1990s, however, the Railways has had to operate increasingly as a commercial rather than a social organisation. One of the ways of improving efficiency is to introduce efficiency-enhancing technologies. This paper is a case study of the introduction of paging technology to the Ratlam Division of Indian Railways. It describes the process of planning and implementation, the HRM implications of the adoption and how the process was successfully managed. It aims at shedding further light on the nature and the processes whereby technologies eventually gain company recognition and acceptance.     

Corrigendum Static Frequency Assignment in Cellular Networks

Abstract. No abstract.     

Case study of safe lowering of an in service gas pipeline

This paper describes an experimental investigation carried out involving instrumentation, measurement and monitoring of stresses in a large diameter gas pipeline during its lowering operations. It also highlights the ingenious techniques developed and adopted to overcome the difficulties pertaining to long leadwires, measurement of existing strains on the curved surface of a pipeline and protection of strain gauge installations. These novel methods were used to ensure smooth and proper functioning of strain gauge instrumentation even under the severe field conditions at site for more than two weeks, till the lowering operations and pipeline monitoring was successfully completed.     

Further remarks on sequential estimation of a scale parameter in exponential distributions with an unknown location

The sequential procedure developed by Govindarajulu and Sarkar [Sequential estimation of scale parameter in exponential distributions with unknown location. Utilitas Math.40, 161–178 (1991)] for estimating the scale parameter of an exponential distribution, when the location parameter is unknown, is further analyzed. Generalizing the results of Govindarajulu and Sarkar, the ‘asymptotic risk-efficiency’ of the sequential procedure is established for the general loss function. A simple method of obtaining the asymptotic distribution of the stopping time is given. For the case of quadratic loss function and linear cost of sampling, a much simpler proof for obtaining the second-order approximations for the risk is provided.