Simulation Experiments

In a scenario where a vendor books its manufacturing capacity options to multiple retailers it is not unlikely that the vendor runs out of capacity and then it cannot serve more orders until future periods of time. This paper suggests that, once the vendor becomes a bottleneck for the network, it is possible to apply negotiation policies between the different retailers to allow re-allocation of options and then overcome this loose/loose situation. Two simple policies to carry out bookings through negotiation practices, allowing partial bookings and not allowing them, are presented in this study. The effectiveness of this approach is tested with a series of simulation experiments whose main results demonstrate that application of negotiation practices within the network when the vendor has not more available capacity to be booked leads to improve the service level, the overall profit and to diminish the sales opportunity cost.

Dans cet article, nous utilisons la décomposition tensorielle PARAFAC (PARAllel FACtors) en vue de développer une nouvelle approche pour l'égalisation aveugle multi-utilisateur dans le cadre des systèmes de communications sans fil. Le système considéré est basé sur l'utilisation conjointe d'un réseau d'antennes et d'un sur-échantillonnage à la réception. Nous proposons tout d'abord un modèle tridimensionnel du type PARAFAC pour le signal reçu, dont les 3 dimensions sont l'espace, le temps et le sur-échantillonnage. Ensuite, nous présentons un nouveau récepteur aveugle multi-utilisateur pour la séparation des signaux et pour l'égalisation. Le récepteur proposé combine une modélisation PARAFAC, une méthode de sous-espace et l'exploitation de la propriété d'alphabet fini des symboles transmis. Des résultats de simulations sont montrés pour illustrer la performance du récepteur aveugle proposé.

This report presents a general analysis for the performance of WLAN location determination systems. In particular, we present an analytical method for calculating the average distance error and probability of error of WLAN location determination systems. These expressions are obtained with no assumptions regarding the distribution of signal strength or the probability of the user being at a specific location, which is usually taken to be a uniform distribution over all the possible locations in current WLAN location determination systems. We use these expressions to find the optimal strategy to estimate the user location and to prove formally that probabilistic techniques give more accuracy than deterministic techniques, which has been taken for granted without proof for a long time. The analytical results are validated through simulation experiments. We also study the effect of the assumption that the user position follows a uniform distribution over the set of possible locations on the accuracy of WLAN location determination systems. The results show that knowing the probability distribution of the user position can reduce the number of access points required to obtain a given accuracy. However, with a high density of access points, the performance of a WLAN location determination system is consistent under different probability distributions for the user position.

A review of model selection procedures in hidden Markov models reveals contrasting evidence about the reliability and the accuracy of the most commonly used methods. In order to evaluate and compare existing proposals, we develop a Monte Carlo experiment which allows a powerful insight on the behaviour of the most widespread model selection methods. We find that the number of observations, the conditional state-dependent probabilities, and the latent transition matrix are the main factors influencing information criteria and likelihood ratio test results. We also find evidence that, for shorter univariate time series, AIC strongly outperforms BIC.

The application of chiral interlocked host molecules for discrimination of guest enantiomers has been largely overlooked, which is surprising given their unique three-dimensional binding cavities capable of guest encapsulation. Herein, we combined the stringent linear geometric interaction constraints of halogen bonding (XB), the non-covalent interaction between an electrophilic halogen atom and a Lewis base, with highly preorganized and conformationally restricted chiral cavities of [2]rotaxanes to achieve enantioselective anion recognition. Representing the first detailed investigation of the use of chiral XB rotaxanes for this purpose, extensive 1H NMR binding studies and molecular dynamics (MD) simulation experiments revealed that the chiral rotaxane cavity significantly enhances enantio-discrimination compared to the non-interlocked free axle and macrocycle components. Furthermore, by examining the enantioselectivities of a family of structurally similar XB [2]rotaxanes contain...

Radio-Frequency Identification (RFID) technology brings many innovative applications. Of great importance to RFID applications in production economics is misplaced-tag pinpointing (MTP), because misplacement errors fail optimal inventory placement and thus significantly decrease profit. The existing MTP solution [1], originally proposed from a data-processing perspective, collects and processes a large amount of data. It suffers from time inefficiency (and energy-inefficiency as well if active tags are in use). The problem of finding efficient solutions for the MTP problem from the communication protocol design perspective has never been investigated before. In this paper, we propose a series of protocols toward efficient MTP solutions in large RFID systems. The proposed protocols detect misplaced tags using reader positions instead of tag positions to guarantee the efficiency and scalability as system scale grows, because RFID readers are much fewer than tags. Considering applications that employ active tags, we further propose a solution requiring responses from only a subset of tags in favor of energy saving. We also design a distributed protocol that enables each reader to independently detect misplaced tags. We then investigate how to apply the proposed protocols in scenarios with tag mobility. To evaluate the proposed protocols, we analyze their optimal performances to demonstrate their efficiency potential and also conduct extensive simulation experiments. The results show that the proposed protocols can significantly increase the time efficiency and the energy efficiency by over 70 percent on average when compared with the best existing work.

SUMMARYAs radio frequency identification (RFID) tags become more ubiquitously available, they will stay in dynamic environments where tags can freely enter or leave RFID readers' interrogation range. With such a dynamic tag population, there arises a problem of population monitoring, whose purpose is to identify the missing tags that have departed from the reading range and the new tags that have newly entered. This problem is a new problem which cannot be well solved by the conventional tag identification protocols. In this paper, we first show that this traditional approach is inefficient, because it collects all the tag IDs in each scan and ignores the ready‐for‐use knowledge of the tag population in a previous scan. To be more efficient, we present three protocols: (i) a baseline protocol that improves the traditional tag identification protocol by optimizing its length of random number used for collision detection; (ii) a novel one‐phase protocol with easy labor to identify...

Two simulation experiments were conducted to verify whether the idea of virtual force scatter plot algorithm, used for searching solutions of the facility layout problems, may be used as an input to the classical CRAFT and simulated annealing (SA) algorithms. The proposed approach employs a regular grid for specifying possible locations of objects. Three independent variables were investigated in the first experiment, namely, (1) the size of the problem: 16, 36 and 64 objects, (2) the type of links between objects: grid, line, and loop, and (3) the shape of the possible places in which the objects can be situated: circle, row and square. The patterns of possible location places were also adapted to the analysis of examples taken from literature, included in the second experiment. The gathered data were statistically analyzed. The results shows substantial decrease in goal function means for all of the examined experimental conditions, if the proposed starting solutions are applied to the CRAFT algorithm. The application of the approach to SA is profitable in specific tasks. The presented comparative numerical results show, in which circumstances the proposed method is superior over various genetic algorithms and other hybrid approaches. Overall, the experimental data investigation demonstrates the usefulness of the proposed method and encourages further research in this direction.

The paper presents comparative investigation of the effectiveness of three algorithms used for optimizing control panel objects' arrangements. We examined two modified classical approaches involving changing of objects' pairs, that is CRAFT, and its simplified version as well as our implementation of the Simulated annealing concept. Their behavior was investigated in experimental simulation studies of two real-life problems: the truck control panel (small number of objects) and the control panel from a nuclear energy plant (big number of items). The statistical analysis of the obtained results showed the supremacy of the proposed version of the simulated annealing algorithm in both case studies.

A simulation experiment was conducted to verify whether the Link scatter plot algorithm (Grobelny, 1999) used for searching solutions of the facility layout problems may be used as an input to the classical CRAFT algorithm (Buffa et al., 1964) which employs a regular grid for specifying possible locations of objects. Three independent variables were investigated in this study, namely (1) the size of the problem: 16 and 64 objects, (2) the type of links between objects: grid and line types, and (3) the shape of the possible places in which the objects can be situated: square and rectangle having two rows. The gathered data were statistically analysed and the obtained results shows substantial decrease in the goal function means for all of the examined experimental conditions. The experimental data investigation demonstrates the usefulness of the proposed approach and encourages further research in this direction.

Two simulation experiments were conducted to verify whether the idea of virtual force scatter plot algorithm, used for searching solutions of the facility layout problems, may be used as an input to the classical CRAFT and simulated annealing (SA) algorithms. The proposed approach employs a regular grid for specifying possible locations of objects. Three independent variables were investigated in the first experiment, namely, (1) the size of the problem: 16, 36 and 64 objects, (2) the type of links between objects: grid, line, and loop, and (3) the shape of the possible places in which the objects can be situated: circle, row and square. The patterns of possible location places were also adapted to the analysis of examples taken from literature, included in the second experiment. The gathered data were statistically analyzed. The results shows substantial decrease in goal function means for all of the examined experimental conditions, if the proposed starting solutions are applied to the CRAFT algorithm. The application of the approach to SA is profitable in specific tasks. The presented comparative numerical results show, in which circumstances the proposed method is superior over various genetic algorithms and other hybrid approaches. Overall, the experimental data investigation demonstrates the usefulness of the proposed method and encourages further research in this direction.

The paper presents comparative investigation of the effectiveness of three algorithms used for optimizing control panel objects' arrangements. We examined two modified classical approaches involving changing of objects' pairs, that is CRAFT, and its simplified version as well as our implementation of the Simulated annealing concept. Their behavior was investigated in experimental simulation studies of two real-life problems: the truck control panel (small number of objects) and the control panel from a nuclear energy plant (big number of items). The statistical analysis of the obtained results showed the supremacy of the proposed version of the simulated annealing algorithm in both case studies.

The component layout problem requires efficient search of large, discontinuous spaces. The efficient layout planning of a production site is a fundamental task to any project undertaking. This paper describes a genetic algorithm (GA) to solve the problem of optimal facilities layout in manufacturing system design so that material-handling costs are minimized. The performance of the proposed heuristic is tested over problems selected from the literature. Computational results indicate that the proposed approach gives better results compared to many existing algorithms in this area.

Purpose: The aim of this paper is to provide the framework for management of reverse flow of materials in automotive industry. The emphasis is placed on the remanufacturing activities. Materials management in such conditions is a real challenge. The cause for this is parallel use of raw materials and reused materials. Such hybrid flows of materials are characterized by increased level of uncertainty connected with amount, quality and timing. Design/methodology/approach: This paper presents a comprehensive review of remanufacturing and traditional manufacturing. The stabilization of reverse flows is crucial for continuity of remanufacturing operations. The simulation model and results are discussed regarding stabilization of the reverse flows. Findings: Authors identify main problems that appear in the area of combining at the production system forward and reverse flows of materials. The agent-based technology is applied for configuration and stabilization of reverse network.

In a scenario where a vendor books its manufacturing capacity options to multiple retailers it is not unlikely that the vendor runs out of capacity and then it cannot serve more orders until future periods of time. This paper suggests that, once the vendor becomes a bottleneck for the network, it is possible to apply negotiation policies between the different retailers to allow reallocation of options and then overcome this loose/loose situation. Two simple policies to carry out bookings through negotiation practices, allowing partial bookings and not allowing them, are presented in this study. The effectiveness of this approach is tested with a series of simulation experiments whose main results demonstrate that application of negotiation practices within the network when the vendor has not more available capacity to be booked leads to improve the service level, the overall profit and to diminish the sales opportunity cost.

Recently radio frequency identification (RFID) is promoting the rapid development of Internet of things (IoTs) and has been widely applied in numerous industrial applications such as inventory management, object tracking and smart logistics, etc. Tags in some RFID applications can be classified into multiple categories according to the types of objects they are attached to. One of the important functionalities for the multi-category RFID systems is the missing tag cardinality estimation of each category. This paper focuses on solving the missing tag iceberg query problem for multi-category RFID systems, i.e., to determine a set of categories, whose missing tags are more than a threshold, with a required reliability. We firstly propose two basic missing tag iceberg query schemes called MAC-SZE and MAC-HZE, which adopt the singleton-zero estimator (SZE) and homogeneous-zero estimator (HZE) respectively. To further improve the query efficiency, we then propose two segmented enhanced schemes called MAC-SSZE and MAC-SHZE, which eliminate the unnecessary slots in each frame. We conduct theoretical analysis to guarantee the required reliability is satisfied. The simulations are finally conducted and the results illustrate that the proposed missing tag iceberg query schemes greatly outperform other existing one. Index Terms-Iceberg queries; missing tags; multi-category; RFID systems. HONGLONG CHEN et al.: MAC: MISSING TAG ICEBERG QUERIES FOR MULTI-CATEGORY RFID SYSTEMS. * Our proposed missing tag iceberg query schemes can also work in multireader scenario to cover a larger area.

This Paper gives the introduction to Reverse Logistics and Remanufacturing also gives its impact on the industry and most impact on automotive industry and discuss some environmental issues related to the Reverse Logistics. The term Green Logistics and Green Remanufacturing is to develop the safe of user friendly network to the industries. It describes the supply chain management and the third party involvement in the Reverse Logistics process. It shows the comment of literatures on the Reverse Logistics and Remanufacturing on the aspects of supply chain management. Implement of the successful network of reverse logistics for the automotive industry and the effect of environment on Reverse Logistics. It explains the Remanufacturing process in 4R’s concept. At the end concluded some key points related to the paper.

Purpose: The aim of this paper is to provide the framework for management of reverse flow of materials in automotive industry. The emphasis is placed on the remanufacturing activities. Materials management in such conditions is a real challenge. The cause for this is parallel use of raw materials and reused materials. Such hybrid flows of materials are characterized by increased level of uncertainty connected with amount, quality and timing. Design/methodology/approach: This paper presents a comprehensive review of remanufacturing and traditional manufacturing. The stabilization of reverse flows is crucial for continuity of remanufacturing operations. The simulation model and results are discussed regarding stabilization of the reverse flows. Findings: Authors identify main problems that appear in the area of combining at the production system forward and reverse flows of materials. The agent-based technology is applied for configuration and stabilization of reverse network.

This paper addresses the problem of using unrealistic mobility scenarios for simulation of ad-hoc routing protocols. We present CAD-HOC, a cousin tool to Network Simulator (ns), which allows ad-hoc networking experimentation to be performed under visually realistic scenarios such as an airport or a bus terminal, buildings, highways and other facilities. CAD-HOC focuses on capturing the visual scenario and transforming it into mobility and connection benchmarks, which are subsequently fed to ns to drive simulation experiments. Generation of mobility and connection benchmarks is facilitated by allowing the users to choose from Brownian, Column, Pursue, and Nomadic models, or to specify user-defined movements. The tool also provides on-line analyses on ad-hoc mobility, ad-hoc connectivity and message complexity, which give an estimate of the overall ns simulation complexity, as the mobility scenario is built. Comparative simulation based on CAD-HOC generated scenarios raise several questions about the reliability of ns simulation results of ad-hoc routing protocols based on random, non-realistic scenarios.

The present work is intended to address two of the major difficulties that can be found when tackling the estimation of the local orientation of the data in a scene, a task which is usually accomplished by means of the computation of the structure tensor-based directional field. On one hand, the orientation information only exists in the non-homogeneous regions of the dataset, while it is zero in the areas where the gradient (i.e. the first-order intensity variation) remains constant. Due to this lack of information, there are many cases in which the overall shape of the represented objects cannot be precisely inferred from the directional field. On the other hand, the orientation estimation is highly dependent on the particular choice of the averaging window used for its computation (since a collection of neighboring gradient vectors is needed to obtain a dominant orientation), typically resulting in vector fields which vary from very irregular (thus yielding a noisy estimation) to very uniform (but at the expense of a loss of angular resolution). The proposed solution to both drawbacks is the regularization of the directional field; this process extends smoothly the previously computed vectors to the whole dataset while preserving the angular information of relevant structures. With this purpose, the paper introduces a suitable mathematical framework and deals with the d-dimensional variational formulation which is derived from it. The proposed formulation is finally translated into the frequency domain in order to obtain an increase of insight on the regularization problem, which can be understood as a low-pass filtering of the directional field. The frequency domain point of view also allows for an efficient implementation of the resulting iterative algorithm. Simulation experiments involving datasets of different dimensionality prove the validity of the theoretical approach.

Purpose: Many studies demonstrate that DOE, CAE and optimization tools can be very effective in product and process development, however their integration is still under investigation, hampering the applicability of such engineering methods in Industry. This paper presents a Design Of Simulation Experiments (DOSE) method, developed to determine the optimal set of process parameters (factors) for given product requirements (responses).

In a scenario where a vendor books its manufacturing capacity options to multiple retailers it is not unlikely that the vendor runs out of capacity and then it cannot serve more orders until future periods of time. This paper suggests that, once the vendor becomes a bottleneck for the network, it is possible to apply negotiation policies between the different retailers to allow reallocation of options and then overcome this loose/loose situation. Two simple policies to carry out bookings through negotiation practices, allowing partial bookings and not allowing them, are presented in this study. The effectiveness of this approach is tested with a series of simulation experiments whose main results demonstrate that application of negotiation practices within the network when the vendor has not more available capacity to be booked leads to improve the service level, the overall profit and to diminish the sales opportunity cost.

Two simulation experiments were conducted to verify whether the idea of virtual force scatter plot algorithm, used for searching solutions of the facility layout problems, may be used as an input to the classical CRAFT and simulated annealing (SA) algorithms. The proposed approach employs a regular grid for specifying possible locations of objects. Three independent variables were investigated in the first experiment, namely, (1) the size of the problem: 16, 36 and 64 objects, (2) the type of links between objects: grid, line, and loop, and (3) the shape of the possible places in which the objects can be situated: circle, row and square. The patterns of possible location places were also adapted to the analysis of examples taken from literature, included in the second experiment. The gathered data were statistically analyzed. The results shows substantial decrease in goal function means for all of the examined experimental conditions, if the proposed starting solutions are applied to the CRAFT algorithm. The application of the approach to SA is profitable in specific tasks. The presented comparative numerical results show, in which circumstances the proposed method is superior over various genetic algorithms and other hybrid approaches. Overall, the experimental data investigation demonstrates the usefulness of the proposed method and encourages further research in this direction.

Analyzing behavioral patterns of workloads is critical to understanding Cloud computing environments. However, until now only a limited number of real-world Cloud datacenter tracelogs have been available for analysis. This has led to a lack of methodologies to capture the diversity of patterns that exist in such datasets. This paper presents the first large-scale analysis of real-world Cloud data, using a recently released dataset that features traces from over 12,000 servers over the period of a month. Based on this analysis, we develop a novel approach for characterizing workloads that for the first time considers Cloud workload in the context of both user and task in order to derive a model to capture resource estimation and utilization patterns. The derived model assists in understanding the relationship between users and tasks within workload, and enables further work such as resource optimization, energy-efficiency improvements, and failure correlation. Additionally, it provides a mechanism to create patterns that randomly fluctuate based on realistic parameters. This is critical to emulating dynamic environments instead of statically replaying records in the tracelog. Our approach is evaluated by contrasting the logged data against simulation experiments, and our results show that the derived model parameters correctly describe the operational environment within a 5% of error margin, confirming the great variability of patterns that exist in Cloud computing.

Two approximate techniques for analyzing the window size distribution of TCP flows sharing a random early detection (RED) like bottleneck queue are presented. Both methods presented first use a fixed point algorithm to obtain the mean window sizes of the flows, and the mean queue length in the bottleneck buffer. The simpler of the two methods then uses the `square

Abstract-Statistical or asynchronous time division multiplexing of variable bit rate moving image sources is a first step toward packetized video networks. Its goal is to efficiently utilize a common communica-tions channel while maintaining uniform picture quality at the receiver. In this ...

As communication networks provide newer services, signaling is becoming more and more compute intensive compared to present day networks. It is known that under overload conditions, the call throughput (goodput) and the network revenue drops to zero even when transport resources are available. A distributed overload control algorithm for delay-bounded call setup is proposed in this paper. The end-to-end delay bound is budgeted among the switching nodes involved in call setup, and these nodes apply a local overload control with a deterministic delay threshold and drop call requests experiencing higher delays. This algorithm does not depend on feedback on network conditions and makes use of only parameters that can be instrumented locally by the switching node. Using an 1 queueing model with first-in-first-out (FIFO) service discipline at a switching node, two optimized control schemes are considered for local overload control and compared their performance through analysis: one with arrival rate limit and the other with buffer size limit. Though both the schemes minimize the unproductive call processing at heavy load, the latter is found to yield higher call throughput and lower average call setup delays compared to the former. Also, the buffer size required for the scheme with buffer size limit is typically small and call throughput close to the server capacity can be achieved during overload. The performance of the distributed overload control algorithm in a network is evaluated through simulation experiments, using the scheme with buffer size limit for the local overload control. It shows that the average end-to-end delay could be much less than the end-to-end delay bound, providing room for overprovisioning of the delay bounds. The tradeoff between the number of nodes, call throughput, and average end-to-end delay needs to be considered while deciding the route budgeting the end-to-end delay bound among different nodes along the route. These performance results are expected to serve as lower bounds to more sophisticated local call rejection mechanisms such as push-out or time-out along with a last-in-first-out (LIFO) service discipline. Index Terms-Call overload control, communication networks, distributed algorithm, signaling performance. NOMENCLATURE Average call arrival rate. Average call processing time. Number of buffers in the queue. Total delay in a queue (queueing delay), including the call processing time. Call/signaling throughput of the queue (carried load).

Five series of crude oil samples exposed to atmospheric conditions have been analysed at the molecular level, each series comprising several samples originating from the same crude oil but altered to dierent extents. The aim of our investigation was to compare the speci®c impact of abiotic oxidation to other alteration processes such as biodegradation, evaporation and water washing. Bulk analyses revealed that increasing alteration is accompanied by an increase in oxygen content which parallels a relative increase of the proportions, as well as of the molecular weights of the macromolecular constituents of the bitumens. Gas chromatographic±mass spectrometric analyses of polar fractions showed the presence of oxygencontaining compounds (steroid ketones, benzothiophenic acids and sulfones) which result from oxidation of petroleum lipids. The hypothesis that part of these oxygenated compounds results from abiotic oxidation processes rather than from biodegradation is supported, notably, by the fact that oxygen incorporation generally occurred without any diastereomeric discrimination. This is also supported by simulation experiments performed on petroleum lipids, which showed that abiotic oxidation induces cleavage reactions aecting C±C and C±S bonds which may intervene in the transformation of geomacromolecules in the environment by degradation (``depolymerization''). Thus abiotic oxidation may play a major role in the fate of petroleum pollutants in the environment by transforming lipidic organic matter from petroleum into more water soluble and, therefore, more biodegradable constituents. However, these can be more toxic to the environment as the water-soluble fraction may be easily taken up by biota.

A magnetic resonance image may contain truncation artifacts if there are not enough high-frequency data when the conventional Fourier transform method is used for reconstruction. In this paper we propose a method for reducing the artifacts using a multilayer neural network. The network consists of one linear output layer and at least one nonlinear hidden layer. In this method the missing high-frequency components are predicted based on known low-frequency components and are used to reduce the truncation artifacts of the image. The method is tested with simulated data with good results.

The Radio-Frequency Identification (RFID) technology has stimulated many innovative applications. Misplacedtag pinpointing (MTP) is important to RFID applications in production economics because optimal inventory placement can significantly increase profit. Previous research from the database perspective needs to process a large amount of data which is time-consuming to collect (and energy-consuming if active tags are used). How to efficiently address the MTP problem from the protocol design perspective however has not been investigated. In this paper, we propose a series of protocols toward efficient MTP solution in large RFID systems. The proposed protocols detect misplaced tags based on reader positions instead of tag positions to guarantee the efficiency and scalability as system scale grows, because the number of readers is much smaller than that of tags. Considering applications to employ more and more popular active tags, we further propose a solution requiring responses from only partial tags in favor of energy saving. We analyze the optimal performances of proposed protocols to demonstrate their efficiency potential and conduct extensive simulation experiments to evaluate their performance under various scenarios. The results show that the proposed protocols can significantly increase the time efficiency and the energy efficiency by over 70% on average when compared with the state of the art.

This paper addresses the problem of using unrealistic mobility scenarios for simulation of ad-hoc routing protocols. We present CAD-HOC, a cousin tool to Network Simulator (ns), which allows ad-hoc networking experimentation to be performed under visually realistic ...

The demand for weldable 13%Cr pipes with outside diameter such as 18", 20" and 24" has increased greatly. Considering such a requirement, Dalmine and NKK have developed a new production route for OD 20" pipes. Girth welded joints (GTAW) were produced. The mechanical properties of both base material and welded joints meet the target requirements. Corrosion qualification was aimed to determine the Sulfide Stress Cracking (SSC) resistance in slightly sour oil wells. Influence of chloride content (NaCl 5÷25%), H2S partial pressure (1÷10 kPa) and pH (3.5÷5), was assessed. CO 2 corrosion resistance was verified with static exposure tests at medium/high pressure of CO 2 , high chloride (25% NaCl) and temperature up to 150°C.

This paper proposes a new MAC protocol, called request-TDMA/CDMA protocol, for supporting multimedia traffic in wireless networks. The protocol has CDMA laid over TDMA like frame structure which has two kinds of slots, viz., data slots and control slots. The control slot holds the information of the next frame's data slot allocation. Whenever a mobile terminal needs to transmit a message, it sends a request to the base station and enters the contention process. The scheduler at the base station takes into consideration the time of generation of a call, the bit rate requirement and the message length while reserving slots for the entire length of the message generated. Three scheduling algorithms are proposed and their performances are studied for four classes of traffic. We also model our protocol using a two-dimensional Markov chain, and for a given system load we compute the state transition probabilities and derive the average waiting time. By simulation experiments we show that our (hybrid) request-TDMA/CDMA protocol is able to effectively combine the orthogonality of both time and code division multiplexing.

Purpose: The aim of this paper is to provide the framework for management of reverse flow of materials in automotive industry. The emphasis is placed on the remanufacturing activities. Materials management in such conditions is a real challenge. The cause for this is parallel use of raw materials and reused materials. Such hybrid flows of materials are characterized by increased level of uncertainty connected with amount, quality and timing. Design/methodology/approach: This paper presents a comprehensive review of ...

Published data on the effects of different levels of hydrogen sulphide (H2S) and pH in aqueous environments on steels have been reviewed. Both sulphide stress corrosion cracking (SSCC) and hydrogen pressure induced cracking (HPIC) have been considered. The data have been collated and presented on one diagram, and die appropriateness of setting relaxed hardness controls for 'mildly sour* environmental conditions has been discussed. ' otherwise variously known as hydrogen-induced cracking (HIC), stepwise cracking (SWC), blister cracking, and by other terms.

In order to provide adequate quality of service to large-bandwidth calls, such as video conference calls, service providers of integrated-services networks may want to allow some customers to book ahead their calls, i.e., make advanced reservations. We propose a scheme for sharing resources among bookahead calls (that announce their call holding times as well as their call initiation times upon arrival) and non-book-ahead calls (that do not announce their holding times). It is possible to share resources without allowing any calls in progress to be interrupted, but in order to achieve a more e cient use of resources, we think that it may be desirable to occasionally allow a call in progress to be interrupted. (In practice, it may be possible to substitute service degradation, such as bit dropping or coarser encoding of video, for interruption.) Thus, we propose an admission control algorithm in which a call is admitted if an approximate interrupt probability (computed in real time) is below a threshold. Simulation experiments show that the proposed admission control algorithm can be better (i.e., yield higher total utilization or higher revenue) than alternative schemes that do not allow interruption, such as a strict partitioning of resources.

We propose an efficient strategy for resource management for scalable QoS guaranteed real-time communication services. This strategy is based on sink trees, and is particularly well suited for differentiated-services based architectures. We first show that finding a set of sink-trees in a given network is NP-complete. Then we propose a heuristic algorithm that always efficiently produces a set of sink-trees for a given network. Sink-tree based resource management integrates routing and resource reservation along the routes, and therefore has a number of advantages over other resource management scheme, in terms of: admission probability, link resource utilization, flow set up latency, signaling overhead, and routing overhead. In this paper we show by simulation experiments that even for simple cases the sinktree based approach shows excellent results in terms of admission probability.

In this paper, the simulation experiments with different control laws are given, based on a new approach to solving the control tasks for robots in contact with the environment [1]-[5]. The comparison of these control laws with the improved versions of the traditional hybrid control are analyzed, too. The simulation experiments performed on a real-scale six-degreesof-freedom industrial robot demonstrate the advantage of the new control concept and improved performances of the robot interacting with a dynamic environment. The tests conducted on industrial robot Manutec r3 are presented, too.

Statistical or asynchronous time division multiplexing of variable bit rate moving image sources is a first step toward packetized video networks. Its goal is to efficiently utilize a common communications channel while maintaining uniform picture quality at the receiver. In this paper, we present queueing models of such schemes, and use them to assess their probabilistic behavior. First, we analyze the coding bit rate of a single video source as a function of time based on experimental data of a video telephone scene. Various statistical quantities are derived from bit rate data collected with a conditional replenishment interframe coding scheme. Two correlated Markov process models (one in discrete time and one in continuous time) are shown to fit the experimental data and are used to model the input rates of several independent sources into a statistical multiplexer. The continuous-time model is used with a flowequivalent approximate queueing analysis to obtain the common buffer length distribution. The analysis is validated with computer simulations that use the discrete-time source model and take into account the discrete nature of the packet queue. Numerical results are presented for variable channel utilization and number of multiplexed video sources. Our analyses demonstrate the statistical smoothing effect of packetized video in a single link. The multiplexer performance, in terms of the probability of buffering or delaying beyond a certain limit, is shown to improve dramatically as the number of multiplexed sources increases beyond one.

This paper presents a shaper architecture that scales to a large number of connections with diverse burstiness and bandwidth parameters. The architecture arbitrates fairly between connections with conforming cells by carefully integrating leaky-bucket tra c shaping with rate-based scheduling algorithms. Through a careful combination of per-connection queueing and approximate sorting, the shaper performs a small, bounded number of operations in response to each arrival and departure, independent of the number of connections and cells. To handle a wider range of rate parameters, a hierarchical arbitration scheme can reduce the implementation overheads and the interference between competing connections. Simulation experiments demonstrate that the architecture limits shaping delay and tra c distortions, even under heavy congestion.

The Markov-Modulated Poisson Process (MMPP) has been extensively used for modelling bursty traflc generated by multimedia applications because it is able to model the time-varying arrival rate and capture the important correlation between inter-arrival times. However, interconnection networks used in current multicomputers have been mainly anahsed under the assumption of the "non-bursty " Poisson arrival process. This study extends further the application of the MMPP to queueing networks in order to develop a new analytical model for computing message latency in pipelined circuit-switched interconnection networks. Simulation experiments reveal that the model exhibits a good degree of accuracy under various operating conditions.

Many recent studies have convincingly demonstrated that network traffic exhibits a noticeable self-similar nature which has a considerable impact on queuing performance. However, the networks used in current multicomputers have been primarily designed and analyzed under the assumption of the traditional Poisson arrival process, which is inherently unable to capture traffic self-similarity. Consequently, it is crucial to reexamine the performance properties of multicomputer networks in the context of more realistic traffic models before practical implementations show their potential faults. In an effort toward this end, this paper proposes the first analytical model for wormhole-switched k-ary n-cubes in the presence of self-similar traffic. Simulation experiments demonstrate that the proposed model exhibits a good degree of accuracy for various system sizes and under different operating conditions. The analytical model is then used to investigate the implications of traffic self-similarity on network performance. This study reveals that the network suffers considerable performance degradation when subjected to self-similar traffic, stressing the great need for improving network performance to ensure efficient support for this type of traffic.

In this paper, a novel method of adaptive singleended sweep measurement can be used for measurement the mutual inductance transmission line parameters is presented. The principle of this method is based on non-linear frequency response analysis of transmission line parameters. The measurement accuracy is significantly improved by using adaptive signal processing technology to eliminate the power frequency induced voltage and current. In addition, the traditional methods based on series R-L transmission line model, the shunt capacitive effect is ignored. Obviously, these algorithms are not accurate enough, particularly for medium and long transmission line. The proposed optimal algorithm is based on differential equation using the distributed parameter π-model and thus fully considers the effects of shunt capacitance and distributed parameter effects of long lines. This paper presents the theory of the technique, the design of hardware platform and software. The results of the simulation experiments are demonstrate its reliable performance.

This study addresses the adequacy of some theoretical information criteria when using finite mixture modelling on discovering patterns in continuous data. In fact, the selection of an adequate number of clusters is a key issue in deriving complex mixture structures and it is desirable that information criteria used for this end are effective. In order to select among several information criteria, which may support the selection of the correct number of clusters, we conduct a simulation study that is intended to determine which information criteria are more appropriate for mixture model selection when considering data sets with only continuous clustering base variables. As a result, the criterion BIC shows a better performance, that is, it indicates the correct number of the simulated cluster structures more often, when referring to mixtures of continuous clustering base variables.