Editor's Page

Abstract

The various steps of mine planning and control in open pits are described in connection with the appropriate mathematical models. Modern hardware for control and communication 18 summarily described. The gains which are to be realized by the various degrees of truck dispatching are discussed as well as the potential for future developments.     

Response Time in Data Broadcast Systems: Mean,Variance and Tradeoff

Data broadcast has been suggested as a promising method of information dissemination [2,33]. In such an environment, the information server cannot afford to serve the requests from a large population of users individually. Instead, the server uses a broadcast channel to deliver information to all users. A single transmission of a data item satisfies all pending requests for that item. The response time of a request depends on the broadcast time of the desired data item, which is scheduled by the server according to the overall demands for various data items. Therefore, the response time may vary in a large range. We argue that, in addition to mean response time, the variance of response time should also be taken into account by the broadcast scheduler. In this paper, we address the issue of variance optimization in regard to response time. Building on our previous research on mean response time optimization, we propose an algorithm which can minimize the variance of response time. Furthermore, we evaluate an algorithm that facilitates a tradeoff between the mean and variance of response time. Numerical examples that illustrate the performance of our algorithms are also presented.     

Fair queueing with service envelopes (FQSE): a cousin-fair hierarchical scheduler for subscriber access networks

In this paper, we propose and investigate the characteristics of a fair queueing with service envelopes (FQSE) algorithm-a hierarchical fair-share scheduling algorithm for access networks based on a remote scheduling system such as Ethernet passive optical networks (EPON) or cable TV network. FQSE is designed to overcome the limiting factors of a typical remote scheduling system such as large control-plane delay, limited control-plane bandwidth, and significant queue switch-over overhead. The algorithm is based on a concept of service envelope-a function representing the fair allocation of resources based on a global network condition called satisfiability parameter (SP). We define properties of cousin-fairness and sibling-fairness and show the FQSE to be cousin-fair. FQSE is unique in that it is the only hierarchical algorithm that is simultaneously cousin-fair. Furthermore, we show the necessary techniques to adapt FQSE to variable-sized packet-based networks. We analyze FQSE performance in EPON serving 1024 independent queues and demonstrate FQSE's ability to provide guaranteed bandwidth to each queue and to share the excess bandwidth fairly.     

Protecting multicast sessions in WDM optical mesh networks

Recent advances in wavelength-division-multiplexing (WDM) technology are expected to facilitate bandwidth-intensive multicast applications. However, a single fiber (bundle) cut on such a network can disrupt the transmission of information to several destination nodes on a "light tree"-based multicast session. Thus, it is imperative to protect multicast sessions e.g., by reserving resources along backup trees. We show that, if a backup tree is directed-link-disjoint to its primary counterpart, then data loss can be prevented in the event of any single link failure. We provide mathematical formulations for efficient routing and wavelength assignment (RWA) of several multicast sessions (including their backup trees for dedicated protection) at a globally optimum cost. We present these formulations for networks equipped with two kinds of multicast-capable switch architectures: one using the opaque (O-E-O) approach and the other using transparent (all-optical) approach. We expand our formulations to accommodate sparse splitting constraints in a network, in which an optical splitter has limited splitting fanout and each node has a limited number of such splitters. We develop a profit-maximizing model that would enable a network operator to be judicious in selecting sessions and simultaneously routing the chosen ones optimally. We illustrate the solutions obtained from solving these optimization problem formulations for a representative-size network.     

Reliability of large periphery GaN-on-Si HFETs

GaN devices exhibit excellent potential for use in many RF applications. However, commercial acceptance of the technology has been hindered by the scarcity and non-statistical nature of reliability results. In this work we present a full device level reliability study of GaN-on-Si HFETs. Reliability results on this technology include three-temperature DC data that show an activation energy of 1.7 eV and an average failure time >10⁷ h at 150 °C. Additionally, long duration DC lifetest (30 000 device hours) and RF lifetest (4000 device hours) results demonstrate a repeatable low drift process. Environmental tests such as autoclave and ESD demonstrate the ruggedness of the material system and technology. Finally, initial failure analysis is discussed.     

Characterization and Studies on Hydro Dynamically Stable Operation of an Angular Jet SOG for COIL

Chemical oxygen-iodine Laser (COIL) is one of the fast emerging high power laser source for near Infrared (λ=1.315μm) laser generation. The heart of the system is the singlet oxygen generator (SOG) which is a pumping source for this laser. A Jet type SOG with a novel approach was designed and fabricated. Singlet oxygen was taken out of the SOG at an angle of 40° thus avoiding the carry over of droplets, which is one of the major drawbacks of horizontal system. The preliminary results have been reported in our earlier publication. The present paper discusses the performance of this generator for various operational conditions viz. diluent's gas nitrogen / helium, basic hydrogen peroxide composition, generator pressure and gas velocity. Further, conditions for the stable operation from generator as well as chlorine injection point of view have been identified.     

Real‐time causal message ordering in multimedia systems

Messages that are sent to and received by multiple sites need to have a consistent order imposed by all sites. Causal ordering allows the cause and effect relations of messages to be maintained. This paper presents an algorithm that ensures that multimedia data with real‐time deadlines are delivered to the application layer in causal order. The algorithm is designed to ensure that any message that arrives at a destination site before its deadline will be delivered to the application before the message expires. In addition, by focusing on a form of causal ordering violations caused by “the triangle inequality”, this algorithm has a low overhead with respect to the amount of information that must be appended to each message. This revised version was published online in June 2006 with corrections to the Cover Date.     

Hierarchical Delay Test Generation

Delay testing is used to detect timing errors in a digital circuit.In this paper, we report a tool called MODET forautomatic test generation for path delay faults in modular combinational circuits. Our technique usesprecomputed robust delay tests for individual modules to computerobust delay tests for the module-level circuit. We present alongest path theorem at the module level ofabstraction which specifies the requirements for path selectionduring delay testing. Based on this theorem, we propose a pathselection procedure in module-level circuits and report efficientalgorithms for delay test generation. MODET hasbeen tested against a number of hierarchical circuits with impressivespeedups in relation to gate-level test generation.     

Analysis of the probability of transaction abort and throughput oftwo timestamp ordering algorithms for database systems

The author analyzes and compares the performance of two timestamp ordering concurrency control algorithms, namely, the basic and multiversion, for database systems. The multiversion algorithm improves the performance of the basic timestamp ordering algorithm by keeping multiple versions of data objects. The author discusses the performance enhancement in the multiversion algorithm over the basic algorithm. The author also discusses the storage overhead due to multiple versions of data objects in the multiversion algorithm. The exact performance model of these algorithms is so complex that it is impossible to find a closed-form solution. The author reduces the complexity of the analysis by analyzing a single transaction in isolation and reflects the presence of other transactions on the isolated transaction by the probability of conflict/abort. The analysis provides useful insight into the performance of these algorithms     

Optimal placement of piezoelectric patches over a smart structure

Control of structural vibrations has significant applications in manufacturing, infrastructure engineering, aerospace engineering and various consumer products. In last two decades, considerable attention has been focused to suppress structural vibrations using active vibration control technique. Various researchers have proposed various optimization criteria for optimal placement of piezoelectric patches over a smart structure to suppress vibrations using various optimization techniques. This paper presents a review of various optimization criteria and techniques that have been used by various researchers in the field of smart structures. Mathematical expressions of objective functions of twelve optimization criteria have been presented and their justifications have been reasoned. Step by step procedures of commonly used optimization techniques have also been presented.