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Analytical and Simulation Studies of Queueing-Inventory Models with MAP Demands in Batches and Positive Phase Type Services
No full textQueueing-inventory models have many practical applications and have been studied extensively in the literature. Most of the studies focus on models in which the demands occur singly. Only a very few papers analyze models wherein the demands occur in batches. In this paper we consider batch demands in the context of two models, both of which assume that the demands occur according to a versatile Markovian point process. The demands need to be serviced with items from the inventory, and the service times are assumed to be of phase type. The replenishment of the inventory is based on the (s, S)-type policy and the lead times are assumed to be random. These two models are such that in the first model an arriving customer finding the inventory level to be zero will be lost; and in the second model a customer can be lost either at the time of an arrival (wherein the server is idle due to zero inventory) or at the time of a service completion (at which time the inventory level becomes zero). In the second model, all waiting customers are removed from the system due to zero inventory. These two models are studied in steady-state using the classical matrix-analytic methods in single server case, and in the case of multi-server systems we resort to simulation using ARENA. Illustrative examples, including an optimization problem, comparing the two models are presented
A Retrial Queueing Model With Thresholds and Phase Type Retrial Times
Get PDFThere is an extensive literature on retrial queueing models. While a majority of the literature on retrial queueing models focuses on the retrial times to be exponentially distributed (so as to keep the state space to be of a reasonable size), a few papers deal with nonexponential retrial times but with some additional restrictions such as constant retrial rate, only the customer at the head of the retrial queue will attempt to capture a free server, 2-state phase type distribution, and finite retrial orbit. Generally, the retrial queueing models are analyzed as level-dependent queues and hence one has to use some type of a truncation method in performing the analysis of the model. In this paper we study a retrial queueing model with threshold-type policy for orbiting customers in the context of nonexponential retrial times. Using matrix-analytic methods we analyze the model and compare with the classical retrial queueing model through a few illustrative numerical examples. We also compare numerically our threshold retrial queueing model with a previously published retrial queueing model that uses a truncation method
Effect of Nano-clay Filler on the Thermal Breakdown Mechanism and Lifespan of Polypropylene Film under AC Fields
Get PDFThe wide application of nanocomposites in the insulation system has greatly contributed to the performance improvement of power equipment. However, nano fillers are not omnipotent for improving the properties of composite dielectrics. In some situations, nano-modified materials are in fact a compromise of improving some performance features while sacrificing others. In this work, the breakdown characteristics and time-to-failure of polypropylene film with nano-clay fillers have been evaluated under combined thermal stress and AC electric fields. Experiments on plain polypropylene (PP) samples have also been carried out under the same test conditions as control. Test results indicated that the time-to-failure of the samples with nano-clay filler was shorter than those without nano filler, which is different from the previous experience. SEM and EDS analyses were conducted to study how the failure mechanism had taken place in both plain polypropylene and the nano-clay filled polypropylene. The failure phenomenon in these materials can be explained by molecular thermodynamics. The main reason for the premature thermal breakdown of PP nanocomposite is essentially due to the weak coupling between nano-clay filler and polymer matrix. Finally, suggestions are proposed for nano modification methods and lifespan prediction models of composite dielectrics
Renewal Redundant Systems Under the Marshall–Olkin Failure Model. A Probability Analysis
Get PDFIn this paper a two component redundant renewable system operating under the Marshall–Olkin failure model is considered. The purpose of the study is to find analytical expressions for the time dependent and the steady state characteristics of the system. The system cycle process characteristics are analyzed by the use of probability interpretation of the Laplace–Stieltjes transformations (LSTs), and of probability generating functions (PGFs). In this way the long mathematical analytic derivations are avoid. As results of the investigations, the main reliability characteristics of the system—the reliability function and the steady state probabilities—have been found in analytical form. Our approach can be used in the studies of various applications of systems with dependent failures between their elements
A Mathematical Model to Predict the Porosity of Locally Electrodeposited Nickel under Pulsed Voltage Conditions
No full textMetal parts manufactured with engineered porosity offer advantages over traditional parts as they have excellent specific mechanical properties at a lower weight. This is especially of interest in the aerospace and automobile industries. Additive manufacturing allows for creating parts with computer aided design (CAD) modeled lattice structures that offer lightweight parts. However, there is a need for porous structures at the micron scale (\u3c50 µm) which cannot be achieved in a controlled manner using traditional powder-bed based metal additive manufacturing processes. Electrochemical Additive Manufacturing (ECAM) is a novel non-thermal metal additive manufacturing process capable of producing metal 3D parts with engineered porosity at the micron scale. There is a lack of understanding of the cause of porosity and controlling the porosity generated in the parts created using this process. In this paper, the effects of the electrical parameters of deposition, such as the pulse duty cycle and pulse frequency during electrodeposition, on the porosity of the manufactured parts were mathematically modeled. The model predicts that higher frequency electrodeposition leads to more porous structures. The model developed in this study can be used to predict the process parameters needed to deposit nickel microstructures with desired levels of porosity between 20 and 55 %. These model predictions were also validated by experiments. Two mechanisms for the cause of porosity in the deposits were identified. The diffusion-limited deposition phenomenon causing a lack of availability of cations results in larger sized pores and hollow structures to form on the part. The crystal growth and the nucleation process cause micron-scale pores
Grid-connected Converter Without Interfacing Filters: Principle, Analysis and Implementation
No full textIn this paper, the concept of grid-connected inverter without interfacing filters is proposed. Conventional grid-side voltage sensors and traditional phase-locked loop (PLL) are removed. Only the grid current is feedback to implement grid synchronization and decoupled P/Q control. 60-Hz sinusoidal output current is achieved relying on grid-side impedance only. The controller employs virtual impedance to couple with a wide range of grid-side impedance variations. With the proposed controller, the grid-connected inverter is capable of 1) decoupling the output real and reactive power; 2) synchronizing with a grid frequency fluctuation, and 3) tolerating the grid impedance variation. This paper addresses the principle of the proposed method. Multiple simulation results are provided for validation
Safe Return to Campus Playbook: Fall 2020
Get PDFAs we prepare to welcome the Kettering University community to campus for the Fall Term 2020, we are proud to be able to build upon the success of the summer term and the responsible and diligent way that our students, faculty, and staff responded to the challenge presented by the Coronavirus over the term.
Their shared commitment to safety has been truly inspiring as has been their responsible adherence to all guidelines and procedures that we put into place to limit the spread of the virus on our campus and our community. It is because of the way our community has responded that we are confident that we will be able to limit the spread of the virus in our community into our fall term.
The Fall 2020 Playbook details our preparations to help ensure for everyone’s safe return to campus in October. It incorporates lessons learned over the summer, feedback from our community, and the latest information and guidance provided by health officials. Included in the Fall Playbook:
• Requirements for social distancing and face coverings while on campus.
• Monitoring and reporting COVID-19 status or symptoms, and participation in contract tracing. COVID-19 testing availability for all students, staff, and faculty, including free and required testing criteria.
• Delivery and instruction of academic courses. Attendance policies for classes (in- person and virtual). Travel Restrictions and Requirements
• Dining services, events, and gatherings, both on and off campus.
• Other important information covering both on- and off-campus operations, pre-arrival preparations, and move-in.
The Playbook is a living document and is revised frequently. One key to a successful Fall Term 2020 is for everyone to stay informed, so please review it regularly for changes
No Date: MGMT 424/624 Data Visualization
No full textData visualization is a central part of data-science training. This course should appeal to a wide variety of majors besides being a concentration class for BSM-Business Analytics and TECH MBA- Data Analytics & Big Data. Students in this course will learn how to use software for gathering data sets, how to use visualization software, and techniques for finding patterns in data
