bluuebunny/crossref_metadata_2025 huggingface dataset:
An efficient algorithm for computing object poses in a modular fixture or gripper
Authors: Qian Wen‐Han , Qiao Hong
Published: August 2002

Modular or reconfigurable fixtures (or grippers) can reduce manufacturing costs and time remarkably. Computing the poses of a given object in a modular fixture is a basic but tedious technique for designing and using such fixtures. This article presents an efficient algorithm for computing the poses. Starting from a unified expression of the outline of an object, this algorithm searches all matching poses automatically. If the outline consists of straight lines and circular arcs only, all the unknown variables can be calculated sequentially by substituting known (or tentative) data in respective expressions, without solving complicated simultaneous equations. When applied to arbitrary outlines, it involves nothing more than common interpolation. The search process is visualized through diagrams that clearly display the occurrence of matching poses. The computer programs are universally applicable. Only the data of the object outline and the fixture configuration need be input. Case studies show that the programs run fast and yield accurate results. © 2002 Wiley Periodicals, Inc.
Three‐dimensional localization of thin‐walled sheet metal parts for robotic assembly
Authors: Park Edward J. , Mills James K.
Published: August 2002

This article presents a technical demonstration of a system for determining the three‐dimensional spatial location of complexly shaped, thin‐walled sheet metal parts grasped by robots during assembly. For successful part assembly, the precise location of grasped parts (essential for successful mating of parts) must be achieved. A localization system is implemented to determine the accurate position and orientation of a sheet metal part that has been picked up by a robot from an arbitrary location. The proposed localization system employs a novel sensing method, utilizing laser‐based proximity and edge detectors, to extract the part feature data in real time. These geometrical feature data are incorporated into an existing localization algorithm, which is based on the singular value decomposition formulation of the part localization problem. The sensing method is particularly effective in measuring 3‐D feature geometry (i.e., thin edges) of sheet metal parts. An experimental single‐robot test bed has been developed to demonstrate the feasibility of the part localization concept for a single sheet metal part. The experimental results obtained from the test bed demonstrate that the system can be effectively used for the localization of thin‐walled sheet metal parts. © 2002 Wiley Periodicals, Inc.
On singular behaviors of impedance‐based repeatable control for redundant robots
Authors: Wang Chau‐Chang , Kumar Vijay
Published: August 2002

This article addresses the association between the unstiffening phenomena in structural mechanics and the algorithmic singularities encountered in the impedance‐based repeatable control algorithms used to command redundant manipulators. It is well known that velocity control schemes such as the pseudoinverse control schemes do not guarantee repeatability for redundant manipulators. In other words, for a closed end‐effector trajectory, the joints do not, in general, exhibit a closed trajectory. One way to overcome this problem is to model each joint with compliance and incorporate a second‐order correction term for the pseudoinverse. With this model, the joint configuration adopted by the manipulator at a given point in task space is one which minimizes the artificial potential energy of the system and is locally unique. In terms of statics, this is equivalent to saying that the elastic structure reaches its static equilibrium under external load. Keep this analogy in mind. We know that the impedance control commands the manipulator to mimic the behavior of an elastic articulated chain. For any phenomena observable on a real elastic structure, we should be able to find its counterpart embedded in the impedance control. In this article, we analyze the performance of such repeatable control algorithms from the point of view of structure mechanics. Singularities in the algorithm are examined and their significance in mechanics are also discussed. © 2001 John Wiley & Sons, Inc.
A discrete event approach to the command sequence replanning and control in a teleprogramming system
Authors: Cho Young‐Jo , Akella Prasad , Kotoku Tetsuo , Tanie Kazuo
Published: August 2002

A command sequence replanning and control method, which enables the slave system to autonomously recover from error conditions, is proposed in a telerobot system. A task model described as a form of the controlled Petri net (CPN) is used as a prior knowledge for the slave system to carry out the given task successfully without the operator's aid even in unexpected error conditions. The CPN model incorporates the contact states and transitional motions between them that possibly exist in the task execution process. The motion command is automatically generated from the master system and transmitted to the slave whenever the contact state changes in the master model. Referring to the CPN model and the given motion commands, the slave system detects if the actual contact state is unexpected and then plans the recovery path from the unexpected state. The feasibility of the command sequence replanning and control algorithm is verified through an example to perform a simple part‐mating task. © 2001 John Wiley & Sons, Inc.
Building and navigating a network of local minima
Authors: Kim Seung‐Woo , Boley Daniel
Published: August 2002

We present a novel method that constructs and navigates a network of local minima of potential fields defined over multidimensional spaces. Though motivated by problems of motion planning for robotic manipulators, similar techniques have been proposed for use in other domains such as molecular chemistry and drug design. The method is based on building a roadmap of paths connecting local minima of a potential function. The novel approach consists of an up‐hill search strategy used to climb out of local minima and find new nearby local minima, without doubling back on previous local minima. With this up‐hill search strategy, one can find local minima otherwise difficult to encounter, and one can focus the search to specific local minima and specific directions from those local minima. The construction of the roadmap can be done in parallel with very little communication. We present extensive simulation results. © 2001 John Wiley & Sons, Inc.
Robustness of time‐scale learning of robot motions to uncertainty in acquired knowledge
Authors: Cheah C.C.
Published: August 2002

A disadvantage of present iterative learning control algorithms is that they are generally applicable only in cases where a certain task is performed over and over again. Consequently, if knowledge or control inputs acquired from learning a task can be used on similar tasks, learning will be more efficient. Recently, several methods for constructing the control input of a new motion based on the control inputs acquired from previous learning of similar tasks have been proposed. However, these methods assumed that the perfect control inputs could be obtained from the previous learning. In practice, the control inputs could never be obtained exactly from learning in the presence of certain uncertainties such as disturbance and measurement noises. In addition, it is also not known for sure how the basic motion patterns should be chosen for learning. In this article, the robustness problem of the time‐scale learning control to uncertainty in the acquired learning control inputs is formulated and solved. From the analysis, certain new insights such as its implication to choices of basic motion patterns for time‐scale learning will be discussed. Simulation results of a 3‐link robot are presented to illustrate the analysis. © 2001 John Wiley & Sons, Inc.
Achieving a cooperative behavior in a dual‐arm robot system via a modular control structure
Authors: Caccavale Fabrizio , Natale Ciro , Siciliano Bruno , Villani Luigi
Published: August 2002

In this paper the problem of achieving a cooperative behavior in a dual‐arm robot system is addressed. A control strategy is conceived in which one robot is position controlled and devoted to task execution, whereas a suitable compliance is conferred to the end effector of the other robot to cope with unavoidable misalignment between the two arms and task planning inaccuracies. A modular control structure is adopted that allows the selection of the proper operating mode for each robot, depending on the task requirements. The proposed approach is experimentally tested in two different tasks involving the two robots in the laboratory setup. First, a parts‐mating task of peg‐in‐hole type is executed; the robot carrying the peg is position controlled, whereas the robot holding the hollow part is controlled to behave as a mechanical impedance. Then, a pressure‐forming task is executed, in which a disk‐shaped tool is required to align with a flat surface while exerting a desired pressure; in this case, the robot carrying the disk is position controlled, whereas the robot holding the surface is force controlled. © 2001 John Wiley & Sons, Inc.
Spatial variability of biotic and abiotic factors of the aquatic habitat in French Guiana
Authors: Tejerina‐Garro Francisco Leonardo , De Mérona Bernard
Published: August 2002

Research on tropical fish ecology in South America is focused mainly on the effect of environmental variables on aquatic organisms. Physical, chemical and biological characteristics of water measured at a local scale (local variables) are used, although geomorphological and hydrological factors measured at a regional scale (regional variables), as well as temporal and spatial heterogeneity, can also be considered. However, the use of this multi‐scale approach increases the perceived complexity, heterogeneity and variability of rivers. Thus, it is important to determine the magnitude of habitat variability and those parameters having the greatest influence on it. In this study, 28 stations distributed on 16 different rivers in French Guiana were sampled during high water at a meso spatial scale. Physical features of the rivers were sampled along an 800‐m stretch, where nine transversal transects were established on the main channel. At each river, 17 local and six regional variables were measured. Local variables relating to the physical characteristics of the channel bank and main channel and regional variables characterizing the whole basin and the position of the station in the basin were qualitatively and quantitatively described. All variables were submitted to multivariate analysis in order to determine their relative contribution to total variance. Two quantitative regional variables (drainage area upstream from stationandriver drainage basin), five quantitative local variables (channel width,water temperature,channel depth,Secchi transparencyandconductivity) and one qualitative local variable (channel substrate) were shown to differentiate the 16 rivers sampled. This result shows the poor contribution of qualitative variables compared with quantitative ones. Gradual change in qualitative variables is probably responsible for this poor contribution to the total variance; thus, the use of such variables is not possible for spatial habitat differentiation in this study. Copyright © 2001 John Wiley & Sons, Ltd.
Approximation algorithms for the covering Steiner problem
Authors: Konjevod Goran , Ravi R. , Srinivasan Aravind
Published: August 2002

The covering Steiner problem is a generalization of both thek‐MST and the group Steiner problems: given an edge‐weighted graph, with subsets of vertices called the groups, and a nonnegative integer value (called the requirement) for each group, the problem is to find a minimum‐weight tree spanning at least the required number of vertices of every group. When all requirements are equal to 1, this becomes the group Steiner problem, while if there is only one group which contains all vertices of the graph the problem reduces tok‐MST withkequal to the requirement of this unique group. We discuss two different (but equivalent) linear relaxations of the problem for the case when the given graph is a tree and construct polylogarithmic approximation algorithms based on randomized LP rounding of these relaxations. By using a probabilistic approximation of general metrics by tree metrics due to Bartal, our algorithms also solve the covering Steiner problem on general graphs with a further polylogarithmic worsening in the approximation ratio. © 2002 Wiley Periodicals, Inc. Random Struct. Alg., 20:465–483, 2002
The scaling window of the 2‐SAT transition
Authors: Bollobás Béla , Borgs Christian , Chayes Jennifer T. , Kim Jeong Han , Wilson David B.
Published: August 2002

We consider the random 2‐satisfiability (2‐SAT) problem, in which each instance is a formula that is the conjunction ofmclauses of the formx∨y, chosen uniformly at random from among all 2‐clauses onnBoolean variables and their negations. Asmandntend to infinity in the ratiom/n→α, the problem is known to have a phase transition at αc=1, below which the probability that the formula is satisfiable tends to one and above which it tends to zero. We determine the finite‐size scaling about this transition, namely the scaling of the maximal windowW(n, δ)=(α−(n,δ), α+(n,δ)) such that the probability of satisfiability is greater than 1−δ for α<α−and is less than δ for α>α+. We show thatW(n,δ)=(1−Θ(n−1/3), 1+Θ(n−1/3)), where the constants implicit in Θ depend on δ. We also determine the rates at which the probability of satisfiability approaches one and zero at the boundaries of the window. Namely, form=(1+ε)n, where ε may depend onnas long as |ε| is sufficiently small and |ε|n1/3is sufficiently large, we show that the probability of satisfiability decays like exp(−Θ(nε3)) above the window, and goes to one like 1−Θ(n−1|ε|−3below the window. We prove these results by defining an order parameter for the transition and establishing its scaling behavior innboth inside and outside the window. Using this order parameter, we prove that the 2‐SAT phase transition is continuous with an order parameter critical exponent of 1. We also determine the values of two other critical exponents, showing that the exponents of 2‐SAT are identical to those of the random graph. © 2001 John Wiley & Sons, Inc. Random Struct. Alg., 18: 201–256 2001
Avoiding a giant component
Authors: Bohman Tom , Frieze Alan
Published: August 2002

Lete1, e′1;e2, e′2;…;ei, e′i;⋅⋅⋅ be a sequence of ordered pairs of edges chosen uniformly at random from the edge set of the complete graphKn(i.e. we sample with replacement). This sequence is used to form a graph by choosing at stagei,i=1,…, one edge fromei,e′ito be an edge in the graph, where the choice at stageiis based only on the observation of the edges that have appeared by stagei. We show that these choices can be made so thatwhpthe size of the largest component of the graph formed at stage 0.535nis polylogarithmic inn. This resolves a question of Achlioptas. © 2001 John Wiley & Sons, Inc. Random Struct. Alg., 19, 75–85, 2001
Rain attenuation statistics from rain cell diameters and heights
Authors: Bryant G. H. , Adimula I. , Riva C. , Brussaard G.
Published: August 2002

The prediction of satellite link attenuation is generally based on the point rainfall rate for 0.01 per cent of the year. The physical quantity used to determine attenuation is rain rate, whereas the 0.01 per cent point is a more complex parameter, not obviously related to the dynamics of rain structure. The dynamics of the horizontal and vertical structure of rain are directly related to rain rate, rainfall volume, local geology and climate. If attenuation is to be predicted from rain rate it would be better to use a single parameter that remains substantially the same in most environments. This is not the case with the 0.01 per cent point. It is argued in this paper that a breakpoint in the rain‐rate exceedances occurs close to 105 mm/h. Rain can be divided at the breakpoint into two broad classes: below this point it is more uniformly distributed over the area of rainfall; above, it has an increasingly more complex horizontal varaiability, with intense rain columns embedded in a background of less intense rain. By replacing the climatic zone dependent 0.01 per cent point rain rate with the fixed rain rate of 105 mm/h, a model for attenuation calculation can be derived that relates the mechanics of the physical processes to rain rate and elevation angle. The model has been developed and tested against the ITU‐R model using the full measured rain‐rate exceedances for each site in the ITU‐R data bank. Attenuation exceedances have been shown to depend on the shape of the rain‐rate exceedance curve, whereas the ITU‐R model generates the same curve shape for all sites, because it uses only one rain rate,R0.01. The new model performs at least as well as the ITU‐R model for temperate climates and considerably better for tropical climates. For sites with no measured rain rate it is recommended that a generalized rain‐rate exceedance curve be used, especially for tropical regions. Copyright © 2001 John Wiley & Sons, Ltd.
Doppler spread characteristics of satellite personal communication channels
Authors: Frigyes I. , Molnár B. G. , Vallet R. , Herczku Z. , Bodnár Z.
Published: August 2002

The paper presents a general description of Doppler characteristics of the complex LEO satellite (low earth orbit) to ground terminal channel of S‐PCS (satellite personal communication system). The difference between the terrestrial and satellite PCS radio channels is pointed out. It is shown that in the latter there is a nonzero (average) Doppler shift and a spread being independent of the radial speed of the satellite; this is in contrast to terrestrial situations in which the average Doppler shift is zero. It is also shown that in contrast to terrestrial situations there is no unique relation between the incoming ray angle of arrival and Doppler shift. Doppler spectrum is computed for a realistic distribution of scatterers close to the ground terminal; the spectral density is proportional to 1/ν3if the ground terminal is stationary, whereνdenotes the Doppler frequency. Copyright © 2001 John Wiley & Sons, Ltd.
Topological design, routing and capacity dimensioning for ISL networks in broadband LEO satellite systems
Authors: Werner Markus , Frings Jochen , Wauquiez Frédéric , Maral Gérard
Published: August 2002

This paper considers the network design of intersatellite link (ISL) networks in broadband LEO satellite systems, where the major challenge is the topology dynamics. First, a general method to design convenient ISL topologies for connection‐oriented operation is presented, and a reference topology for numerical studies is derived. A permanent virtual topology is then defined on top of the orbiting physical one, thus forming a framework for discrete‐time dynamic traffic routing. On this basis, heuristic and optimization approaches for the combined routing and dimensioning task, operating on discrete time steps, are presented and their performance is numerically compared. It is shown that minimizing the worst‐case link capacity is an appropriate target function, which can be formulated as linear optimization problem with linear constraints. Using linear programming (LP) techniques, the dimensioning results are clearly better than with simple heuristic approaches. Copyright © 2001 John Wiley & Sons, Ltd.
Propagation considerations and fading countermeasures for mobile multimedia services
Authors: Jahn Axel
Published: August 2002

This paper presents a summary of land mobile satellite (LMS) channel characteristics derived from several measurement campaigns. Narrowband and wideband measurements allow a broad interpretation of the LMS channels. Channel models and its parameters have been derived from the measured data as well. Furthermore, the impact of the LMS channel on the communication service is investigated and possible countermeasures are discussed. Link margins, power control schemes and satellite diversity can compensate the fading on the transmission links. The benefit of adaptive receivers and the dependence on the signal bandwidth are investigated, too. Copyright © 2001 John Wiley & Sons, Ltd.
Posture estimation based on motion and structure models
Authors: Ogaki Kenichi , Iwai Yoshio , Yachida Masahiko
Published: August 2002

Sensing of human motion is very important for human–computer interactive applications such as virtual reality, gesture recognition, and communication. A vision system is suitable for human–computer interaction since this involves passive sensing and the system can estimate the motion of the user without any discomfort for the user. In this paper, we propose an algorithm for fast posture estimation of the user from an image sequence by using the position information of the hands and head. Our algorithm is founded on a model‐based method. The parameters of a geometric model are calculated from human kinematics. It is inadequate to obtain a unique solution from the image information such as position of the head and hands. The unknown parameters are predicted by the motion models and the previous posture parameters, then the unknown parameters are adjusted by a minimization method. We present experimental results to evaluate our proposed method in simulation and with real images. © 2001 Scripta Technica, Syst Comp Jpn, 32(4): 48–58, 2001
A color image compression scheme based on the adaptive orthogonalized transform, accelerated by improvement of the dictionary
Authors: Miura Takashi
Published: August 2002

The paper proposes an improvement of coding performance for a color image compression scheme based on the adaptive orthogonalized transform (AOT). The paper proposes that the performance of the coder will be accelerated by reducing the dictionary size to 25% and by maintaining the approximation gain of the LBG algorithm by virtue of the fact that the AOT increases the approximation gain of the dictionary. The effectiveness of the proposal is confirmed by numerical experiments. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(8): 1–8, 2002; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/scj.10218
Analysis and recognition of a human head's movement from an image sequence
Authors: Abe Yuichi , Hagiwara Masafumi
Published: August 2002

In this paper, we propose a method to analyze and recognize human head movements from monocular image sequences based on few constraints. First, the background image photographed beforehand is used to extract the human region from the image sequence. Next, the skin‐colored regions are extracted, and the low brightness and low saturation pixels are set as the candidate eye regions. Then the face region is determined from the multiple skin‐colored regions and the hair region is extracted based on the face region. Finally, the left and right eye regions are determined from the candidate eye regions. Thus, effective information for posture estimation such as the eye positions, face region, and hair region is extracted from the input image. A genetic algorithm (GA) is applied to fit the extracted information to a 3D head model and estimate the head posture. By creating an approximate 3D head model, the system adapts to an indeterminate large number of humans. Since an image sequence is input, the information in the previous image can be used. Thus, the possible human movements and the angles of the joints area prioriknowledge and are reflected in the parameters. The lack of information for the 3D posture estimation problem from a monocular image sequence is alleviated. © 2001 Scripta Technica, Syst Comp Jpn, 32(5): 36–45, 2001
3D space coding using virtual object surface
Authors: Takano Takahide , Naemura Takeshi , Harashima Hiroshi
Published: August 2002

Visual information in 3D space has become the subject of much research in fields like 3D image communications and virtual reality. The huge amount of visual information in 3D space, however, makes the establishment of an efficient compression technique indispensable. In this regard, the authors have already proposed the concept of “space coding” that makes use of the redundancy in space itself, and have been investigating a specific coding technique that uses a multidimensional discrete cosine transform (DCT). In this paper, we extend this technique and propose a new coding technique that takes the structural characteristics of the object into account. To be more specific, we propose the concept of a “virtual object surface” as a technique for describing an object in structural terms taking compression rate into account, and attempt to improve coding efficiency with this technique. We also describe experiments performed to compare this technique with other techniques, and demonstrate the feasibility of the proposed technique on the basis of the results obtained. In addition, we examine a coding technique for performing high‐speed image synthesis from compressed data. © 2001 Scripta Technica, Syst Comp Jpn, 32(12): 47–59, 2001
Development of a diagnostic supporting tool for a circulatory system model of living body
Authors: Asami Ken'ichi , Kitamura Tadashi
Published: August 2002

The purpose of this research is to develop a computer‐aided tool for diagnostic and educational support of the living‐body circulatory system using the Human model devised by Coleman. The Human model is a dynamic model described by simultaneous differential equations, and consists of 25 physiological modules, such as the cardiovascular system, respiratory control, and kidney function, whose variables are exchanged with each other in order to emulate human‐body circulatory phenomena. For application of the human model to diagnosis and education, the supporting tool should have the capability of qualitative analysis to explain the causal relationships of numerical values of relevant variables in the model. We develop a supporting function to analyze the hierarchical structure of variables and parameters. The tool can be used to diagnose the causes of an unusual variable by path tracking in the human model. Furthermore, this supporting tool provides for editing of mathematical expressions for the purpose of validating the model. © 2001 Scripta Technica, Syst Comp Jpn, 32(14): 1–11, 2001
A temporal link mechanism for hypermedia broadcasting
Authors: Sumiya Kazutoshi , Noda Reiko , Tanaka Katsumi
Published: August 2002

We propose in this paper a time‐dependent link scheme for hypermedia. The management of the links accompanying updates in hypermedia is a major subject; in particular, it is an important problem in hypermedia dealing with content which depends on time. This scheme will realize the dynamic creation and expiration functions of links as well as the automatic link control function. We have packaged a prototype system called Mille‐feuille using the proposed time‐dependent link scheme and have confirmed the scheme's validity. This scheme can also be realized by using the extensible markup language (XML). © 2001 Scripta Technica, Syst Comp Jpn, 32(14): 54–66, 2001
A group learning support system enhancing the externalization of thinking
Authors: Kusunoki Fusako , Sugimoto Masanori , Hashizume Hiromichi
Published: August 2002

This paper discusses a group learning support system that promotes the externalization of thinking and sharing of understanding. The proposed system has the following two features. (1) Game characteristics are introduced in order to motivate the participation of the learners. (2) By combining a board game with computer simulation, externalization of thinking and sharing of understanding are supported. The effectiveness of the proposed system was evaluated experimentally in a primary school. The results confirmed the effectiveness of the proposed system. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(6): 93–100, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1136
Part of speech tagging with min‐max modular neural networks
Authors: Ma Qing , Lu Bao‐Liang , Isahara Hitoshi , Ichikawa Michinori
Published: August 2002

A parts of speech (POS) tagging system using neural networks has been developed by Ma and colleagues. This system can tag unlearned data with a much higher accuracy than that of the Hidden Markov Model (HMM), which is the most popular method of POS tagging. It does so by learning a small Thai corpus on the order of 10,000 words that are ambiguous as to their POSs. However, the three‐layer perceptron used in the system has slow convergence and low learning accuracy even on such a small amount of data. It is therefore difficult to improve accuracy by incrementing the epoch of learning or by increasing the amount of learning data. To solve this problem, the tagging system of this paper makes use of the min‐max modular (M3) neural network of Lu and colleagues. This new system learns faster and has a higher learning accuracy compared with the old one, by decomposing large, complicated POS tagging problems into many smaller, easier problems. Learning accuracy can be improved by using the same learning data and larger data sets can be learned, which results in a much higher tagging accuracy. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(7): 30–39, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1139
Speech recognition under noisy environments using segmental unit input HMM
Authors: Yamamoto Kazumasa , Nakagawa Seiichi
Published: August 2002

In this paper, we apply a segmental unit input HMM to noisy speech recognition. In this modeling, several successive frames are combined and treated as an input vector. We expect that the segmental unit input HMM will be effective for noisy speech recognition because segmental statistics considering correlation between frames reduce noise effects when the correlation of noise between frames is assumed to be small. In recognition experiments, we compared the segmental unit input HMM with a conventional frame‐based HMM and found the segmental unit input HMM to be superior. We also compared the segmental unit input HMM with dynamic cepstral coefficients, which have both static and dynamic features, and found that the segmental unit input HMM is more effective than the dynamic cepstrum. We also combined the segmental unit input HMM with a spectral subtraction method and confirmed the effectiveness of the method. Additionally, in experiments using acoustic models trained with noisy speech, the segmental unit input HMM outperformed the conventional HMM. From these results, we propose PMC for the segmental unit input HMM. Experimental results showed the PMC for segmental unit input HMM offered better recognition performance than the original PMC. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(8): 111–120, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1151
The Winnipeg Principles, WTO and sustainable development: proposed policies for reconciling trade and the environment
Authors: Tisdell Clem
Published: August 2002

There is a widespread belief that the WTO has made virtually no concessions to environmentalists about their concerns arising from free trade and the process of globalization. There are concerns that these processes may undermine prospects for sustainable development. Following the United Nations Conference on Environment and Development held in Rio de Janeiro in 1992, the International Institute for Sustainable Development was established to advocate policies to support sustainable development within Canada and globally. In 1994, it proposed the Winnipeg Principles as a means for reconciling international trade and development so as to achieve sustainable development (IISD, 1994a,b). These seven principles are outlined in this article and assessed. Although the International Institute for Sustainable Development had hoped through these principles to influence the work programme of the Environment and Trade Committee of WTO, it seems to have little effect. Probably if these principles had been seriously considered by WTO, the serious social conflicts which emerged globally at the beginning of this century would have been avoided, and we would be in a better position to understand the complex links between trade, environment and sustainable development and adopt relevant policies. Copyright © 2001 John Wiley & Sons, Ltd and ERP Environment
Determining the role of surfaces and interfaces in the powder metallurgy processing of aluminum alloy powders
Authors: Anderson Iver E. , Foley James C.
Published: August 2002

The current options for solid‐state consolidation processing of powder‐based advanced aluminum alloys have been very limited and complicated, resulting in a segregation of the applications primarily to the aerospace segment. Throughout any consolidation sequence for aluminum powders, the oxide and/or hydroxide films on the typical powder surfaces can interfere with densification and interparticle bonding. In fact, the consolidation sequence for many low‐strength aluminum alloy powder metallurgy parts involves transient liquid‐phase sintering to massively disrupt the powder surfaces, producing improved bonding but introducing a coarsened resolidification microstructure. Although preventing aluminum oxide formation is nearly impossible during aluminum powder production, the gas atomization reaction synthesis (GARS) method—an advanced powder production technique—can modify the oxide coating and enable improved consolidation processing. This report compares the effects of the GARS process and other representative atomization processes on the surface structure and properties of aluminum powders and on their ability to sinter. The powders were characterized with transmission electron microscopy, scanning electron microscopy, Auger electron spectroscopy, quadrapole mass spectroscopy and with a new ultrasonic method for in situ sensing of the evolution of sintering. In general, a marked reduction in the surface film thickness and in the level of chemisorbed moisture and moisture‐borne impurities was observed in the GARS powders. This change in powder surface characteristics also was effective in promoting sintering processes in the GARS powders, as monitored by our new technique. An initial direct comparison of explosivity for the different types of aluminum powder revealed that the GARS powder also had a reduced hazard level. All of these findings indicate that the GARS approach to aluminum powder production may enable mass‐produced lightweight powder metallurgy parts from advanced aluminum alloys with simple consolidation processing techniques. Copyright © 2001 John Wiley & Sons, Ltd.
Error performance analysis of artificial neural networks applied to Rutherford backscattering
Authors: Vieira A. , Barradas N. P. , Jeynes C.
Published: August 2002

We have developed a code based on artificial neural networks (ANN) to analyse Rutherford backscattering data. In particular, we have applied the code to the analysis of germanium implants in silicon substrates. Here, we study the reliability and accuracy of the quantitative results obtained. We first constructed three different training data sets. The first data set was fully general. On the second one, we restricted the experimental conditions to well‐defined values, and on the third we also restricted the implantation parameters (depth and dose of implant) to a narrower range. We then studied the trade‐off between generality and accuracy of the ANNs obtained. Furthermore, for a given architecture we applied two different training processes. The first was backpropagation on the whole data set. In the second we excluded, after an initial training phase, all the training cases with errors double the average and then continued training. Each of the processes was applied to the three different data sets. We report the performance of the ANNs so obtained when applied to real experimental data. Copyright © 2001 John Wiley & Sons, Ltd.
Electron transport in solids for quantitative surface analysis
Authors: Werner Wolfgang S. M.
Published: August 2002

The influence of electron transport on the signal generation process in electron beam techniques is reviewed. A survey of the fundamental physical quantities for the electron–solid interaction is presented and sources for these quantities in the literature as well as semi‐empirical formulae are given. The theoretical approaches used to describe multiple scattering in solids are outlined. These include the partial intensity approach and the continuous slowing down approximation to describe multiple energy losses and the transport approximation to tackle multiple deflections. A detailed description of the Monte Carlo technique is presented because this constitutes an effective means to study transport processes. The different theoretical approaches are illustrated in a survey of applications. These include: quantitative description of the surface sensitivity in Auger and photoelectron spectroscopy; line shape analysis of electron spectra; extracting information on the compositional depth profile from the combined energy/angular distribution in an electron spectrum; quasi‐elastic electron reflection; inelastic electron backscattering; depth distribution of production of x‐rays caused by electron bombardment; and the surface sensitivity in total electron yield electron spectroscopy. These applications demonstrate that the outlined approaches have a broad field of application, not only for electrons with energies ranging from thermal to the relativistic energy range, but also for other microbeam analysis techniques. Copyright © 2001 John Wiley & Sons, Ltd.
Longitudinal profiles of health care providers
Authors: Bronskill Susan E. , Normand Sharon‐Lise T. , Beth Landrum Mary , Rosenheck Robert A.
Published: August 2002

Provider profiling is the activity of collecting, comparing and reporting quality of care measures for individuals, groups, agencies and institutions that provide health care services. Univariate provider profiles, such as hospital‐specific mortality rates, have been constructed using cross‐sectional data based on posterior summaries or maximum likelihood estimates. As data continue to be collected over time, the construction and interpretation of longitudinal profiles of health care providers will become increasingly important. Longitudinal series can be used to improve the precision of estimates – a feature that is particularly important for providers who treat a small number of patients per year. We extend and apply hierarchical models to examine and classify provider performance over time using two examples, one in the area of cardiology and the other in mental health. Performance is evaluated using the squared Mahalanobis distance and posterior probabilities based on this distance. By comparing providers based on level and temporal trend simultaneously, conservative but comprehensive assessments of performance are possible. Furthermore, the longitudinal profiles developed are easily interpreted and flexible, making them of practical use to policy‐makers. Copyright © 2002 John Wiley & Sons, Ltd.
A competing risk approach to the analysis of trials of alternative intra‐uterine devices (IUDs) for fertility regulation
Authors: Tai Bee‐Choo , Peregoudov Alexander , Machin David
Published: August 2002

The methods of survival analysis have had a profound influence on the way that studies concerned with the safety and efficacy of intra‐uterine devices (IUDs) for fertility control have been designed, conducted, analysed and reported. For example, the Kaplan–Meier technique has been used to summarize the results of controlled clinical trials of alternative devices and the logrank test used to make any comparisons. A particular feature of IUD studies is the large number of possible causes of failure (reasons for discontinuation of the device). These lead to considerations of competing risks, where in this framework, the discontinuations are considered as competing causes of contraceptive failure. In this context, we compare the net and crude probability estimates of discontinuation rates using continuous time and argue for the routine use of the latter. We use data from a randomized multi‐centre trialon the long‐term safety and efficacy of two IUDs, TCu220C and TCu380A, for illustration. Copyright © 2001 John Wiley & Sons, Ltd.
Jointly modelling the relationship between survival and pulmonary function in cystic fibrosis patients
Authors: Schluchter Mark D. , Konstan Michael W. , Davis Pamela B.
Published: August 2002

Modelling the relationship between pulmonary function and survival in cystic fibrosis (CF) is complicated by the fact that measures of pulmonary function commonly used such as the forced expiratory volume in one second (FEV1) are measured with error, and patients with the poorest lung function are increasingly censored by death, that is, data are available only for the patients who have survived to the current age. We assume a linear random effects model for FEV1 per cent predicted, where the random intercept and slope of FEV1per cent predicted, along with a specified transformation of the age at death follow a trivariate normal distribution. We illustrate how this model can be used to describe the relationship between age at death and parameters of the individual patient's regression of FEV1per cent predicted versus age, such as the slope and the intercept or true value of FEV1per cent predicted at a given age. We also illustrate how the model provides empirical Bayes estimates of these individual parameters. In particular, we explore how the predicted value of the age at death might be used as a prognostic or severity index. The model and methods are illustrated on a cohort of 188 cystic fibrosis patients with a common genotype (homozygous for the ΔF508 mutation), born on or after 1965 and followed at the CF Center at the Rainbow Babies and Children's Hospital, Cleveland, OH, U.S.A. Copyright © 2002 John Wiley & Sons, Ltd.
Analysis of ambulatory blood pressure monitor data using a hierarchical model incorporating restricted cubic splines and heterogeneous within‐subject variances
Authors: Lambert Paul C. , Abrams Keith R. , Jones David R. , Halligan Aidan W. F. , Shennan Andrew
Published: August 2002

Hypertensive disorders of pregnancy are associated with significant maternal and foetal morbidity. Measurement of blood pressure remains the standard way of identifying individuals at risk. There is growing interest in the use of ambulatory blood pressure monitors (ABPM), which can record an individual's blood pressure many times over a 24‐hour period. From a clinical perspective interest lies in the shape of the blood pressure profile over a 24‐hour period and any differences in the profile between groups. We propose a two‐level hierarchical linear model incorporating all ABPM data into a single model. We contrast a classical approach with a Bayesian approach using the results of a study of 206 pregnant women who were asked to wear an ABPM for 24 hours after referral to an obstetric day unit with high blood pressure. As the main interest lies in the shape of the profile, we use restricted cubic splines to model the mean profiles. The use of restricted cubic splines provides a flexible way to model the mean profiles and to make comparisons between groups. From examining the data and the fit of the model it is apparent that there were heterogeneous within‐subject variances in that some women tend to have more variable blood pressure than others. Within the Bayesian framework it is relatively easy to incorporate a random effect to model the between‐subject variation in the within‐subject variances. Although there is substantial heterogeneity in the within‐subject variances, allowing for this in the model has surprisingly little impact on the estimates of the mean profiles or their confidence/credible intervals. We thus demonstrate a powerful method for analysis of ABPM data and also demonstrate how heterogeneous within‐subject variances can be modelled from a Bayesian perspective. Copyright © 2001 John Wiley & Sons, Ltd.
The effect of outliers on confidence interval procedures for cost‐effectiveness ratios
Authors: Indurkhya Alka , Gardiner Joseph C. , Luo Zhehui
Published: August 2002

Cost‐effectiveness ratio (CER) is defined as the ratio of the difference in cost between a test and standard health care programme to the difference in benefit, respectively. Methods to obtain confidence intervals for CERs are either variants of Fieller's method (1954), or bootstrap methods. We study the effect of outliers in cost measures on the precision of confidence interval procedures for CERs. In particular the performance of the procedures under single and multiple case influential deletion diagnostics, respectively, are evaluated. Simulation studies suggest that the bias‐corrected percentile bootstrap procedure gives better precision and coverage under either diagnostic. Copyright © 2001 John Wiley & Sons, Ltd.
Latent class marginal regression models for modelling youthful drug involvement and its suspected influences
Authors: Reboussin Beth A. , Anthony James C.
Published: August 2002

In longitudinal behavioural studies, it is common to have multiple categorical indicators for measuring a theoretical construct of interest. A latent class model is presented that accounts for the structure in a set of correlated, categorical variables measured at discrete time periods, drawing information from these variables to form a smaller number of latent classes. The dependence of the resulting latent class model parameters on suspected factors over time is simultaneously modelled using a baseline‐category logistic regression model. Estimation of the model parameters is achieved using an estimating equations procedure. A motivating example is provided from a longitudinal study of suspected linkages between monitoring or supervision by parents and the occurrence of drug use behaviours in an epidemiologic sample of school‐attending youths. Copyright © 2001 John Wiley & Sons, Ltd.
A flexible design for multiple armed screening trials
Authors: Sargent Daniel J. , Goldberg Richard M.
Published: August 2002

The goal of a screening trial is to examine several treatments with the intention of selecting one or more treatment(s) for further testing. Such a trial frequently occurs in the phase II setting, with the intention that the selected treatment be formally compared to a standard treatment in a phase III clinical trial. In this framework it is not essential that the very best treatment is definitely selected (such a decision would require a formal phase III trial), rather it is important that a substantially inferior treatment is not selected when a superior treatment exists. The level of evidence required to select a treatment based on this standard is lower than the evidence required to definitively order treatments. This paper introduces a flexible design for such trials, the flexibility coming from the use of a particular decision rule. The proposed rule states that if the observed difference in the success rates of the treatments is larger than some prespecified quantity d, then the treatment with the highest observed success rate is selected. However, if the observed difference is less than or equal to d, other factors may be considered in the selection. The goal of this design is to mirror clinical practice, where a treatment's success probability is often only one of many considerations in determining a treatment recommendation for a particular patient. Copyright © 2001 John Wiley & Sons, Ltd.