Characterizing the influence of neutron fields in causing single-event effects using portable detectors

The malfunction of semiconductor devices caused by cosmic rays is known as Single Event Effects(SEEs). In the atmosphere, secondary neutrons are the dominant particles causing this effect. The neutron flux density in atmosphere is very low. For a good statistical certainty, millions of device hours are required to measure the event rate of a device in the natural environment. Event rates obtained in such testings are accurate. To reduce the cost and time of getting the event rate, a device is normally taken to artificial accelerated neutron beams to measure its sensitivity to neutrons. Comparing the flux density of the beam and the flux density of a location in the atmosphere, the real time event rate can be predicted by the event rate obtained. This testing method was standardized as the neutron accelerated soft error rate (ASER) testing in JEDEC JESD89A standard. However, several life testings indicated that the neutron flux density predictions given by the accelerated testings can have large errors. Up to a factor of 2 discrepancy was reported in the literature. One of the major error sources is the equivalence of the absolute neutron flux density in the atmosphere and in accelerated beam. This thesis proposes an alternative accelerated method of predicting the real-time neutron error rate by using proxy devices. This method can avoid the error introduced by the uncertainty in the neutron flux density. The Imaging Single Event Effect Monitor (ISEEM) is one of the proxy devices. It is the instrument originally developed by Z. Török and his co-workers in the University of Central Lancashire. A CCD was used as the sensitive element to detect neutrons. A large amount of data sets acquired by Török were used in this work. A re-engineered ISEEM has been developed in this work to improve ISEEM performance in life testings. Theoretical models have been developed to analyze the response of ISEEM in a wide range of neutron facilities and natural environment. The agreement of the measured and calculated cross-sections are within the error quoted by facilities. Because of the alpha contamination and primary proton direct ionization effects, performance of ISEEM in life testings appeared to be weak

Performance evaluation of warehouses with automated storage and retrieval technologies.

In this dissertation, we study the performance evaluation of two automated warehouse material handling (MH) technologies - automated storage/retrieval system (AS/RS) and autonomous vehicle storage/retrieval system (AVS/RS). AS/RS is a traditional automated warehouse MH technology and has been used for more than five decades. AVS/RS is a relatively new automated warehouse MH technology and an alternative to AS/RS. There are two possible configurations of AVS/RS: AVS/RS with tier-captive vehicles and AVS/RS with tier-to-tier vehicles. We model the AS/RS and both configurations of the AVS/RS as queueing networks. We analyze and develop approximate algorithms for these network models and use them to estimate performance of the two automated warehouse MH technologies. Chapter 2 contains two parts. The first part is a brief review of existing papers about AS/RS and AVS/RS. The second part is a methodological review of queueing network theory, which serves as a building block for our study. In Chapter 3, we model AS/RSs and AVS/RSs with tier-captive vehicles as open queueing networks (OQNs). We show how to analyze OQNs and estimate related performance measures. We then apply an existing OQN analyzer to compare the two MH technologies and answer various design questions. In Chapter 4 and Chapter 5, we present some efficient algorithms to solve SOQN. We show how to model AVS/RSs with tier-to-tier vehicles as SOQNs and evaluate performance of these designs in Chapter 6. AVS/RS is a relatively new automated warehouse design technology. Hence, there are few efficient analytical tools to evaluate performance measures of this technology. We developed some efficient algorithms based on SOQN to quickly and effectively evaluate performance of AVS/RS. Additionally, we present a tool that helps a warehouse designer during the concepting stage to determine the type of MH technology to use, analyze numerous alternate warehouse configurations and select one of these for final implementation

Analytical modeling of an autonomous vehicle storage/retrieval system.

Automated vehicle storage/retrieval system (AVS/RS) technology is relatively new. It has been applied successfully in several European facilities in 1990s. AVS/RS is a flexible system that is a viable alternative to automated storage/retrieval systems (AS/RS), a traditional material handling technology that has been in existence for more than fifty years. There are very few papers in the literature that focus on the use of analytical models for estimating performance measures of AVS/RS. In this thesis, queuing network theory is used to model an AVS/BS system to analyze its performance. The manufacturing system performance analyzer (MPA) is an open queuing network (OQN) analyzer based on the parametric decomposition method. This thesis models the AVS/RS and uses MPA to analyze the performance of an AVS/RS configuration. A simulation model based on discrete events is also generated by Promodel to allow comparison of MPA results with those of simulation. A web interface for conceptualizing AVS/RS and AS/RS designs is presented in this thesis. This on-line tool provides a convenient and friendly interface between warehouse designers and time analytical model tool. Pour case studies of algorithms embedded in the web interface are presented in the thesis. An initial warehouse design is first analyzed by MPA. After this, several improvements of this initial design are evaluated. Experimental results are provided to show that the OQN methodology can he applied effectively to analyze an AVS/RS when vehicle utilization is between 60% and 85%. MPA is a better choice than simulation to quickly evaluate alterilate configuration of the AVS/RS. Additionally, two more experiments are conducted to compare MPA with another AVS/RS system performance analyzer. MPA models AVS/RS under the tier-captive configuration, whereas the other model assumes the tier-to-tier configuration