bluuebunny/crossref_metadata_2025 huggingface dataset:
Hypertext information security model for organizations
Authors: Kwok Lam‐for
Published: July 2002

States that traditional information security models address only the micro view of how to maintain a secure environment by controlling the flows of information within protection systems and the access to controlled data items. Argues that these models do not aim to, and cannot, reflect the information security level of an organization. Describes an information security model using a hypertext approach. The model aims to prepare a macro view of the current information security situation in order to provide an overview of the information security risk to a wider audience in an organization. An administrative information system has been analysed to demonstrate the hypertext information security model.
The role of service level agreements in IT service delivery
Authors: Larson Kent D.
Published: July 2002

Introduces the concept of service level agreements (SLAs) in IT service provision, especially in the case of outsourced service provision. Reports the experience of several consulting engagements and surveys to substantiate suggested frameworks and checklists. Discusses the reasons for exercising rigour around SLAs. Differentiates between SLAs negotiated for internal versus external service providers. Describes the structure of good service level agreements. Outlines the most important elements of measurement for monitoring service level performance. Concludes with the importance of SLAs to the management of commercial relationships in which services are provided.
Informetrics: an emerging subdiscipline in information science
Authors: Wormell Irene
Published: July 2002

The Centre for Informetric Studies (CIS) was launched in 1996 by the Royal School of Library and Information Science in Copenhagen. The head of centre presents the CIS, giving a sample of activities and research programmes. The emerging field of informetrics is described in a historical perspective as a subfield of bibliometrics. The new approach combines advanced information retrieval theories and methodologies with the scientific study of information flows. CIS aims to apply improved bibliometric methods not only to scientometrics studies and research evaluations of science and technology, but also to the analysis of their mutual societal, industrial and other special relations. This means an extension of traditional bibliometric analyses to cover non‐scholarly communities in which information is produced, communicated and used. It is also an appeal to modern LIS professionals to face the challenge of this new area of quantitative studies, and to explore the databases not only as a registry but also as a tool for analytical work. The possibilities for LIS professionals to raise their positions in information work hierarchies are emphasised, as well as the exploration of informetric techniques to support “informed” management decisions and policy making.
The role of human Web assistants in e‐commerce: an analysis and a usability study
Authors: Åberg Johan , Shahmehri Nahid
Published: July 2002

Electronic commerce has recently shown enormous potential to take over a significant share of the sales market. There is a need to provide services that can reach individual computer users with different information profiles and levels of expertise. In this article the concept of Web assistants, human assistants working in an electronic Web shop, is presented. This human‐computer collaboration provides intelligent and adaptive services via an integrated communication media. A prototype of a Web assistant system has been implemented. While browsing through the system the user can call for human assistance should the need arise. Presents the results of a usability study performed on the prototype system. Recent commercial moves in the direction discussed in this article increase the importance of the usability study. The results are encouraging, especially when it comes to the attitude aspects of usability. The subjects were extremely enthusiastic about the concept of Web assistants and its implications. The human Web assistant who participated in the field trial highlighted the importance of user modelling. Although the system is mainly in the context of electronic commerce, it can be used in many other contexts. These include home automation, digital libraries, and technical support, to name a few.
Product searching with shopping bots
Authors: Rowley Jennifer
Published: July 2002

Shopping bots are an important new innovation which support consumers with the product search and identification stage in e‐shopping. This paper reviews the search facilities offered by shopping bots. A number of shopping bots that include books in their product range, have been visited with a view to analysing their search facilities. Using trial searches for three different best‐selling books, title, author, and keyword search facilities available in a number of bots were further investigated. Finally the output from the search in terms of the number of items, and suppliers identified, and the price, was analysed. The effectiveness of bots does not only depend upon search facilities but also depends upon product coverage, and other added value features such as publisher and consumer reviews. Consumer search behaviour, in general, and the way in which consumers will use shopping bots are fruitful areas for further research.
The impact of global information on Africa
Authors: Thapisa A.P.N.
Published: July 2002

Refers to the growing popularity of “Fidonet” in Africa and compares it with the Internet. Acknowledges that developing countries may miss the information revolution because they lack national information infrastructures and the knowledge and skills required to provide the relevant content for them. Argues that global information should promote human development in areas such as education, health, social services and commercial activity. The Conference of African Ministers recently declared support for the building of Africa’s information highway, recognizing the need for African countries to develop information networks for full Internet connectivity, enabling access to the same information systems for Africa’s economic recovery and sustainable development.
Searching the Web: a survey of EXCITE users
Authors: Spink Amanda , Bateman Judy , Jansen Bernard J.
Published: July 2002

Web search services are now a major source of information for a growing number of people. We need to know more about how users search Web search engines to improve the effectiveness of their information retrieval. This paper reports results from a major study exploring users’ information searching behavior on the EXCITE Web search engine. The study is the first to investigate Web users’ successive searching behavior as they conduct related searches
An analysis of fraud on the Internet
Authors: Baker C. Richard
Published: July 2002

This paper examines the issue of fraud on the Internet and discusses three areas with significant potential for misleading and fraudulent practices, namely: securities sales and trading; electronic commerce; and the rapid growth of Internet companies. The first section of the paper discusses securities fraud on the Internet. Activities that violate US securities laws are being conducted through the Internet, and the US Securities and Exchange Commission has been taking steps to suppress these activities. The second section of the paper discusses fraud in electronic commerce. The rapid growth of electronic commerce, and the corresponding desire on the part of consumers to feel secure when engaging in electronic commerce, has prompted various organizations to develop mechanisms to reduce concerns about fraudulent misuse of information. It is questionable, however, whether these mechanisms can actually reduce fraud in electronic commerce. The third section of the paper discusses the potential for fraud arising from the rapid growth of Internet companies, often with little economic substance and lacking traditional management and internal controls. The paper examines the three areas of potential Internet fraud mentioned above and suggest ways in which these abuses may be combated.
Characterization of the laminated object manufacturing (LOM) process
Authors: Park Joon , Tari Michael J. , Hahn H. Thomas
Published: July 2002

Laminated object manufacturing (LOM) is a rapid prototyping process where a part is built sequentially from layers of paper. Studied in the present paper are the precision and accuracy of the LOM process and the dimensional stability of LOM parts. The process was found to exhibit both constant and random sources of error in the part dimensions. The dimensional error was the largest normal to the plane of the paper, exacerbated by the moisture absorption and subsequent swelling. The key process parameters were identified and optimized for sufficient bonding and cutting accuracy.
A novel system for fused deposition of advanced multiple ceramics
Authors: Jafari M.A. , Han W. , Mohammadi F. , Safari A. , Danforth S.C. , Langrana N.
Published: July 2002

In this article we present the system that we have developed at Rutgers University for the solid freeform fabrication of multiple ceramic actuators and sensors. With solid free form fabrication, a part is built layer by layer, with each layer composed of roads of material forming the boundary and the interior of the layer. With our system, up to four different types of materials can be deposited in a given layer with any geometry. This system is intended for fabrication of functional parts; therefore the accuracy and precision of the fabrication process are of extreme importance.
A thermal model of polymer degradation during selective laser sintering of polymer coated ceramic powders
Authors: Vail Neal K. , Balasubramanian Badrinarayan , Barlow Joel W. , Marcus Harris L.
Published: July 2002

Reports that measurable amounts of polymer degradation occur during the fabrication of objects from polymer coated ceramic powders by selective laser sintering (SLS). Argues that because the binder is important in achieving strong green parts that can be handled with minimal breakage during post‐processing operations, it is essential to minimize the extent of binder losses. As the first step towards understanding the mechanisms of binder degradation, this paper presents a thermal model of the physical system, noting that the agreement between theory and experiment are good. The model is used to help determine the most influential parameters affecting binder losses during fabrication from polymer coated powders. Predicts that adjustments to laser beam diameter, laser scanning distance and gaseous environment will strongly affect polymer binder degradation during processing. Further predicts correctly that polymer degradation during SLS processing is not sensitive to the inherent degradation kinetics of the polymer.
A characterisation of corporate memory as a knowledge system
Authors: Beckett Ronald C.
Published: July 2002

Any organisation, even a newly formed one, will have its own repertoire of practices and routines that reflect the purpose of the organisation and the prior experience of the people in it. This leads to the notion of a “corporate memory”. This paper presents a systems‐engineering style of characterisation comprised eight sub‐processes linked by knowledge and/or data flows that result in day‐to‐day actions within the organisation. The nature of flows between the sub‐processes is examined, considering the types of knowledge involved, and factors that may facilitate or inhibit the flow of knowledge. The model has proven useful in understanding what drives the organisation, and in developing a form of diagnostic tool to study how to better share knowledge within the organisation.
Valuation accuracy, variation and bias in the context of standards and expectations
Authors: Crosby Neil
Published: July 2002

Valuation accuracy usually conjures up images of empirical studies of comparisons between sales and valuations and different valuations of the same properties, and a number of references to these studies are included in the paper. However, this paper concentrates on the institutional influences which impact on valuations and their accuracy. The overall aim of this paper is to examine the legal interpretation of valuation inaccuracy in the UK. This might seem a bit parochial in the context of a World Valuation Congress. However, cases in many countries in the Commonwealth form precedents for each other and therefore decisions in, for example, the UK and Australasia, are drawn on by others in reaching decisions. The paper also reaches conclusions which have wider implications for all jurisdictions which have valuation disputes settled in courts, tribunals and any other quasi‐judicial body.
Single amino acid substitutions on the surface ofEscherichia colimaltose‐binding protein can have a profound impact on the solubility of fusion proteins
Authors: Fox Jeffrey D. , Kapust Rachel B. , Waugh David S.
Published: July 2002

Proteins are commonly fused toEscherichia colimaltose‐binding protein (MBP) to enhance their yield and facilitate their purification. In addition, the stability and solubility of a passenger protein can often be improved by fusing it to MBP. In a previous comparison with two other highly soluble fusion partners, MBP was decidedly superior at promoting the solubility of a range of aggregation‐prone proteins. To explain this observation, we proposed that MBP could function as a general molecular chaperone in the context of a fusion protein by binding to aggregation‐prone folding intermediates of passenger proteins and preventing their self‐association. The ligand‐binding cleft in MBP was considered a likely site for peptide binding because of its hydrophobic nature. We tested this hypothesis by systematically replacing hydrophobic amino acid side chains in and around the cleft with glutamic acid. None of these mutations affected the yield or solubility of MBP in its unfused state. Each MBP was then tested for its ability to promote solubility when fused to three passenger proteins: green fluorescent protein, p16, and E6. Mutations within the maltose‐binding cleft (W62E, A63E, Y155E, W230E, and W340E) had little or no effect on the solubility of the fusion proteins. In contrast, three mutations near one end of the cleft (W232E, Y242E, and I317E) dramatically reduced the solubility of the same fusion proteins. The mutations with the most profound effect on solubility were shown to reduce the global stability of MBP.
Coherent Measures of Risk
Authors: Artzner Philippe , Delbaen Freddy , Eber Jean‐Marc , Heath David
Published: July 2002

In this paper we study both market risks and nonmarket risks, without complete markets assumption, and discuss methods of measurement of these risks. We present and justify a set of four desirable properties for measures of risk, and call the measures satisfying these properties “coherent.” We examine the measures of risk provided and the related actions required by SPAN, by the SEC/NASD rules, and by quantile‐based methods. We demonstrate the universality of scenario‐based methods for providing coherent measures. We offer suggestions concerning the SEC method. We also suggest a method to repair the failure of subadditivity of quantile‐based methods.
Specific contribution of human T‐type calcium channel isotypes (α1G, α1H and α1I) to neuronal excitability
Authors: Chemin Jean , Monteil Arnaud , Perez‐Reyes Edward , Bourinet Emmanuel , Nargeot Joël , Lory Philippe
Published: July 2002

In several types of neurons, firing is an intrinsic property produced by specific classes of ion channels. Low‐voltage‐activated T‐type calcium channels (T‐channels), which activate with small membrane depolarizations, can generate burst firing and pacemaker activity. Here we have investigated the specific contribution to neuronal excitability of cloned human T‐channel subunits. Using HEK‐293 cells transiently transfected with the human α1G (CaV3.1), α1H (CaV3.2) and α1I (CaV3.3) subunits, we describe significant differences among these isotypes in their biophysical properties, which are highlighted in action potential clamp studies. Firing activities occurring in cerebellar Purkinje neurons and in thalamocortical relay neurons used as voltage clamp waveforms revealed that α1G channels and, to a lesser extent, α1H channels produced large and transient currents, while currents related to α1I channels exhibited facilitation and produced a sustained calcium entry associated with the depolarizing after‐potential interval. Using simulations of reticular and relay thalamic neuron activities, we show that α1I currents contributed to sustained electrical activities, while α1G and α1H currents generated short burst firing. Modelling experiments with the NEURON model further revealed that the α1G channel and α1I channel parameters best accounted for T‐channel activities described in thalamocortical relay neurons and in reticular neurons, respectively. Altogether, the data provide evidence for a role of α1I channel in pacemaker activity and further demonstrate that each T‐channel pore‐forming subunit displays specific gating properties that account for its unique contribution to neuronal firing.
Gas Jet–Workpiece Interactions in Laser Machining
Authors: Chen Kai , Yao Y. Lawrence , Modi Vijay
Published: July 2002

Laser machining efficiency and quality are closely related to gas pressure, nozzle geometry, and standoff distance. Modeling studies of laser machining rarely incorporate gas effects in part because of the complex structure and turbulent nature of jet flow. In this paper, the interaction of a supersonic, turbulent axisymmetric jet with the workpiece is studied. Numerical simulations are carried out using an explicit, coupled solution algorithm with solution-based mesh adaptation. The model is able to make quantitative predictions of the pressure, mass flow rate as well as shear force at the machining front. Effect of gas pressure and nozzle standoff distance on structure of the supersonic shock pattern is studied. Experiments are carried out to study the effect of processing parameters such as gas pressure and standoff distance. The measured results are found to match and hence validate the simulations. The interaction of the oblique incident shock with the normal standoff shock is found to contribute to a large reduction in the total pressure at the machining front and when the nozzle pressure is increased beyond a certain point. The associated reduction in flow rate, fluctuations of pressure gradient and shear force at the machining front could lower the material removal capability of the gas jet and possibly result in a poorer surface finish. The laser cutting experiments show that the variation of cut quality are affected by shock structures and can be represented by the mass flow rate. [S1087-1357(00)01702-0]
Non-Destructive Machinability Characterization of Materials Through a Correlation With Rate of Strain Sensitivity
Authors: Sprague Jeffrey A. , Eleftheriou Evangelos C. , Bates Charles E.
Published: July 2002

The results of this work establish a foundation on which the development of experimental practices and instrumentation can be based for quick measurement of machinability in a non-destructive manner. The objective of the investigation presented was to establish an experimental correlation between rate of strain, or rate of loading, and the machinability of cast irons. Such an investigation would require the availability of a very large pool of machinability data, and high speed straining of materials. Through an experimental method utilizing drop tests, the correlation was established and verified through large numbers of drillability tests on cast iron specimens supplied by industrial affiliates. [S1087-1357(00)01802-5]
A New Approach to Shock Isolation and Vibration Suppression Using a Resetable Actuator1
Authors: Bobrow, James E. , Jabbari, and Faryar , Thai Khiem
Published: July 2002

A novel low power control technique along with a new class of actuators is developed for shock isolation and control of structural vibrations. In contrast to other techniques, including conventional viscous or rate damping, the force produced by the actuator has no velocity dependence. Several experimental, analytical, and simulation results are presented in support of this new, semi-active technique for structural control. The basic approach is to manipulate the system stiffness through the use of resetable actuators. With the proposed control approach, the actuator behaves like a linear spring. However, at appropriate times, the effective unstretched length of the actuator is changed—or reset—to extract energy from the vibrating structure. Experimental validation of the actuator model, analytical results on stability and actuator-placement, and simulation results for earthquake applications are presented. [S0022-0434(00)01603-8]
Transient Response of a Cross-Flow Charge Air Intercooler and Its Influence on Engine Operation
Authors: Hribernik Ales , Moskwa John J.
Published: July 2002

To examine the influence of intercooler thermal inertia on transient engine operation, a 2D model of an air-to-air, cross-flow heat exchanger has been developed. Finned passages of heat exchanger core have been subdivided into separate channels of charge and cooling air, respectively. A two-step Lax-Wendroff differential method has been used to solve one-dimensional, nonhomentropic, unsteady, compressible fluid flow in each channel. Simultaneously, the Saul’yev explicit method has been applied to compute the 2D temperature distribution along the dividing plate. The Wieting correlation has been used to compute the local convection heat transfer coefficient and friction factor. The model has been verified against steady-state experimental data and then incorporated into an engine cycle simulation program based on “Filling-Emptying” method. Two engine transients have been simulated; the acceleration of the engine from idle to rated engine speed at constant load, and deceleration from rated power to rated torque by increasing the load torque. The first example shows the warming up of the intercooler, while in the second example intercooler temperatures are decreasing. The results have been compared with the predictions of an additional set of simulations, where the NTU-effectiveness method has been used to simulate the intercooler, and the thermal inertia of intercooler has been neglected. The results of both sets of simulations are discussed in the paper. [S0022-0434(00)02003-7]
Dynamic Optimization of Startup and Load-Increasing Processes in Power Plants—Part II: Application
Authors: Bausa J. , Tsatsaronis G.
Published: July 2002

In the first part of this study, a general method for solving dynamic optimization problems has been presented: the dynamic process model, consisting of first-order ordinary differential equations (ODEs) and algebraic equations, is discretized over the time horizon using well established methods for the solution of ODEs. The discretized system is then treated as large-scale non-linear parameter optimization problem. This transformation is implemented in a user-friendly software package. An application of this software is demonstrated in the present paper by optimizing the process of rapid load-increase in a single-pressure combined-cycle power plant. The power plant is described with a simplified model that consists of 18 first order ordinary differential equations and 67 algebraic equations. For this model a time-optimal operation associated with a load increase from 50 percent to 75 percent of base load is calculated by considering given restrictions on some temperature gradients.
Evaluation and Application of Data Sources for Assessing Operating Costs for Mechanical Drive Gas Turbines in Pipeline Service
Authors: Smalley Anthony J. , Mauney David A. , Ash Daniel I. , Clowney Sam L. , Pappas George P.
Published: July 2002

This paper evaluates and demonstrates how the public domain data provided by individual interstate pipeline companies to FERC, when combined with individual company equipment lists, can be used to regress industry information on cost of operations and maintenance, fuel gas used, and cost of fuel and power. The paper describes the methods of analysis and identifies their limitations. The paper presents results of such regression analysis as average and variance of cost and fuel usage for industrial gas turbines and aeroderivative gas turbines. It provides further comparisons between gas turbine prime movers, reciprocating engine prime movers, and electric motor drives, and presents annual costs per installed horsepower as a function of turbine size. The paper is based on work performed for PRC International and the Gas Research Institute. [S0742-4795(00)01003-6]
Streamwise Curvature Effect on the Incompressible Turbulent Mean Velocity Over Curved Surfaces
Authors: Kim N. , Rhode D. L.
Published: July 2002

A curvature law of the wall, which determines the mean velocity profile, is analytically derived for near-wall turbulent flows to include strong curved-channel wall curvature effects through a perturbation analysis. The new law allows improved analysis of such flows, and it provides the basis for improved wall function boundary conditions for their computation (CFD), even for strong curvature cases. The improved law is based on the algebraic eddy viscosity and curvature-corrected mixing length concepts, the latter of which is a linear function of the gradient Richardson number. To include the complete Richardson number effects, the local streamline curvature effects in the gradient Richardson number are kept. To overcome the mathematical difficulty of keeping all of these local streamline curvature terms, an innovative nonconstant-parameter perturbation solution technique is successfully applied. [S0098-2202(00)00903-2]
Approximate Method for the Determination of the Bending Strength Geometry Factor for External Spur and Helical Gear Teeth
Authors: Pedrero J. I. , Fuentes A. , Estrems M.
Published: July 2002

The methods currently available for the determination of the AGMA J-factor require iterative procedures in order to compute the value of the critical section parameter, which is necessary to compute the tooth thickness at the critical section and the height of the Lewis parabola. This paper presents an approximate, non-iterative method for the determination of the AGMA J-factor for involute, external gear teeth, which is based on the approximate determination of the critical section. The method is valid for any tool geometry, including rack-type or pinion-type generation, and considers tool offsets, center distance modifications and backlash. [S1050-0472(00)00903-X]
Forced Convection in High Porosity Metal Foams
Authors: Calmidi V. V. , Mahajan R. L.
Published: July 2002

This paper reports an experimental and numerical study of forced convection in high porosity (ε∼0.89–0.97) metal foams. Experiments have been conducted with aluminum metal foams in a variety of porosities and pore densities using air as the fluid medium. Nusselt number data has been obtained as a function of the pore Reynolds number. In the numerical study, a semi-empirical volume-averaged form of the governing equations is used. The velocity profile is obtained by adapting an exact solution to the momentum equation. The energy transport is modeled without invoking the assumption of local thermal equilibrium. Models for the thermal dispersion conductivity, kd, and the interstitial heat transfer coefficient, hsf, are postulated based on physical arguments. The empirical constants in these models are determined by matching the numerical results with the experimental data obtained in this study as well as those in the open literature. Excellent agreement is achieved in the entire range of the parameters studied, indicating that the proposed treatment is sufficient to model forced convection in metal foams for most practical applications. [S0022-1481(00)01903-4]
A Reexamination of Residual Stresses in Thin Films and of the Validity of Stoney’s Estimate
Authors: Hui C. Y. , Conway H. D. , Lin Y. Y.
Published: July 2002

The residual stresses in thin films are explained using elementary mechanics. In particular, the range of validity of the well-known Stoney’s formula is examined using a strength of materials approach. An improved formula is obtained. The results of these analyses can also be used to compute energy release rates for cracks in thin film systems. Some simple examples of such applications are given. [S1043-7398(00)01603-0]
Thermoelastic Instability With Consideration of Surface Roughness and Hydrodynamic Lubrication
Authors: Jang J. Y. , Khonsari M. M.
Published: July 2002

An idealized model consisting of a surface with high thermal conductivity separated by a film of liquid lubricant from a rough surface with low thermal conductivity is developed to study thermoelastic instability. The governing equations are derived and solved for the critical speed beyond which thermoelastic instability leading to the formation of hot spots is likely to occur. A series of dimensionless parameters is introduced which characterizes the thermoelastic behavior of the system. It is shown the surface roughness and the lubricant film thickness both play an important role on the threshold of instability. [S0742-4787(00)00104-1]
Low Velocity Impact and Compression-After-Impact Response of Z-Pin Reinforced Core Sandwich Composites
Authors: Vaidya U. K. , Palazotto A. N. , Gummadi L. N. B.
Published: July 2002

In the current work, sandwich composite structures with innovative constructions referred to as Z-pins, or truss core pins, are investigated. The Z-pin core sandwich construction offers enhanced transverse stiffness, high damage resistance, and multi-functional benefits. The present study deals with analysis of low-velocity impact (LVI) of Z-pin sandwich plate, and experimental studies of compression-after-impact characterization. Experimental studies on LVI of Z-pin sandwich plate considered in the analysis have been reported in Vaidya, et al., 1999, “Low Velocity Impact Response of Laminated Sandwich Composites with Hollow and Foam-Filled Z-Pin Reinforced Core,” Journal of Composites Technology and Research, JCTRER, 21, No. 2, Apr., pp. 84–97, where the samples were subjected to 11, 20, 28, 33, and 40 J of impact energy. The LVI analysis is developed with regards to Z-pin buckling as a primary failure mode (and based on experimental observations). A finite element model accounting for buckling of the pins has been developed and analyzed using ABAQUS. This paper also presents experimental results on compression-after-impact (CAI) studies which were performed on the sandwich composites with Z-pin reinforced core “with” and “without” foam. The experimental LVI tests were performed in Vaidya, et al., 1999, “Low Velocity Impact Response of Laminated Sandwich Composites with Hollow and Foam-Filled Z-Pin Reinforced Core,” Journal of Composites Technology and Research, JCTRER, 21, No. 2, Apr., pp. 84–97. The results indicate that selective use of Z-pin core is a viable idea in utilizing space within the core for sandwich composites in structural applications. [S0094-4289(00)02904-2]
An Optimization Approach to the Determination of the Boundaries of Manipulator Workspaces
Authors: Snyman J. A. , du Plessis L. J. , Duffy Joseph
Published: July 2002

An optimization approach to computing the boundaries of the workspaces of planar manipulators is presented. This numerical method consists of finding a suitable radiating point in the output coordinate space and then determining the points of intersection of a representative pencil of rays, emanating from the radiating point, with the boundary of the accessible set. This is done by application of a novel constrained optimization approach that has the considerable advantage that it may easily be automated. The method is illustrated by its application to two planar mechanisms, namely a planar Stewart platform and a planar redundantly controlled serial manipulator. In addition to the exterior boundaries of the workspace, interior curves that represent configurations at which controllability and mobility may be limited, are also mapped. The optimization methodology, implemented here for the planar case, may readily be extended to spatial Stewart platforms. [S1050-0472(00)00304-4]
Towards a Better Understanding of Modeling Feasibility Robustness in Engineering Design
Authors: Du Xiaoping , Chen Wei
Published: July 2002

In robust design, it is important not only to achieve robust design objectives but also to maintain the robustness of design feasibility under the effect of variations (or uncertainties). However, the evaluation of feasibility robustness is often a computationally intensive process. Simplified approaches in existing robust design applications may lead to either over-conservative or infeasible design solutions. In this paper, several feasibility-modeling techniques for robust optimization are examined. These methods are classified into two categories: methods that require probability and statistical analyses and methods that do not. Using illustrative examples, the effectiveness of each method is compared in terms of its efficiency and accuracy. Constructive recommendations are made to employ different techniques under different circumstances. Under the framework of probabilistic optimization, we propose to use a most probable point (MPP) based importance sampling method, a method rooted in the field of reliability analysis, for evaluating the feasibility robustness. The advantages of this approach are discussed. Though our discussions are centered on robust design, the principles presented are also applicable for general probabilistic optimization problems. The practical significance of this work also lies in the development of efficient feasibility evaluation methods that can support quality engineering practice, such as the Six Sigma approach that is being widely used in American industry. [S1050-0472(00)00904-1]
Reduced Weight Design of a Flexible Rotor with Ball Bearing Stiffness Characteristics Varying with Rotational Speed and Load
Authors: Lee Dong-Soo , Choi Dong-Hoon
Published: July 2002

This paper presents an effective design approach for reducing the weight of a flexible rotor in ball bearings with rotational speed and load dependent stiffness characteristics under constraints on the system eigenvalues and bearing fatigue life. Design variables are chosen to be the inner radii of shaft elements, the positions of ball bearings, and the preloads on the bearings. The stiffness characteristics of high speed ball bearings are completely described as functions of applied loads and spin speed, and applied to the dynamic behavior analysis of a rotor-bearing system. A transfer matrix method is used to obtain eigenvalues of the system and an augmented Lagrange multiplier (ALM) method is employed as an optimization technique. A multi-stepped rotor supported by two angular contact ball bearings is analyzed and designed to show the speed and load dependent stiffness effect on the system dynamic behavior and to demonstrate the effectiveness of the proposed optimum design approach. The results show that the effect of the stiffness on the system dynamic behavior is noticeable and that the suggested design approach is effective. [S0739-3717(00)00803-5]
Active-Passive Hybrid Constrained Layer for Structural Damping Augmentation
Authors: Liu Yanning , Wang K. W.
Published: July 2002

A new surface-damping concept with an active-passive hybrid constraining layer (HCL) is proposed to improve the damping performance of traditional active constrained layer (ACL) systems. Instead of using a pure piezoelectric constraining layer, passive and active materials are used together to constrain the viscoelastic material layer. A generic model of the HCL treatment is presented. Nondimensional equations of motion and boundary and connecting conditions are derived. The closed-form solutions to the equations are developed and analyzed. Tabletop tests are also performed to verify the feasibility of the new damping concept. It is shown that by properly selecting a passive constraining material and assigning appropriate lengths for the active and passive constraining parts, HCL can outperform a system with a pure active PZT coversheet, both in terms of its fail-safe ability and closed-loop damping performance. [S0739-3717(00)01503-8]
Active Control of Low Frequency Modes in an Aircraft Fuselage Using Spatially Weighted Arrays
Authors: Lane Steven A. , Clark Robert L. , Southward Steve C.
Published: July 2002

Acoustic enclosures such as aircraft cabins often display lightly damped modal behavior at low frequencies where passive treatments are impractical due to mass and volume constraints. This work presents a feedback control approach using dynamic H2 controllers implemented with spatially weighted arrays of collocated pressure sensors and constant volume-velocity actuators. The open-loop system is shaped using spatially weighted transducer arrays to yield increased pole-zero separation, which results in better closed-loop performance. The transducer arrays are weighted to emphasize coupling to a particular acoustic mode or modes, which facilitates global control of the targeted dynamics. This work presents a method to determine the spatial weighting vectors for the transducer arrays from frequency response measurements. The development and implementation of low-order, dynamic H2 control laws is also discussed. Experimental results are presented for a single-mode and a multiple-mode controller implemented on an aircraft fuselage section, and demonstrate significant reduction of the targeted acoustic modes. To the best of the authors’ knowledge, this is the first experimental implementation of a feedback controller of this type capable of achieving such levels of global reduction in a three-dimensional acoustic system. [S0739-3717(00)02303-5]
Creep Relaxation of Residual Stresses Around Cold Expanded Holes
Authors: Garcia-Granada A. A. , Lacarac V. D. , Holdway P. , Smith D. J. , Pavier M. J.
Published: July 2002

The cold expansion of fastener holes in aircraft components is a standard technique to improve fatigue life. There is concern that the beneficial residual stresses arising from cold expansion may relax due to creep. This paper describes experimental measurement and finite element prediction of cold expansion residual stresses and their redistribution after creep, with and without additional mechanical load. Experimental measurements of near-surface stresses used an X-ray diffraction technique while average through-the-thickness stresses were measured using a new method based on Sachs’ boring. This new method allowed non-axisymmetric residual stresses to be measured, as was the case when creep relaxation occurred with mechanical load. Axisymmetric and three dimensional finite element analyses were used to predict the stress distribution through the thickness of the component showing good agreement with measurement. Creep relaxation of residual stress does indeed occur, but some benefit of the cold expansion remains, particularly when creep relaxation is combined with the application of mechanical load.
Evaluation of Idea Generation Methods for Conceptual Design: Effectiveness Metrics and Design of Experiments
Authors: Shah Jami J. , Kulkarni Santosh V. , Vargas-Hernandez Noe
Published: July 2002

A wide range of formal methods have been devised and used for idea generation in conceptual design. Experimental evidence is needed to support claims regarding the effectiveness of these methods in promoting idea generation in engineering design. Towards that goal this paper presents a set of effectiveness metrics experimental methods, data collection and analysis techniques. Statistically based Design of Experiments (DOE) principles were used in developing the guidelines. Four classes of operating variables were considered to characterize the design problem and the environment. The effectiveness metrics proposed are based on outcome and consists of the quantity, quality, novelty, and variety of ideas generated. Two experimental approaches have been developed. In the Direct Method, the influence of the type of design problem and various parameters related to the procedure of an idea generation method is measured by using the method in its entirety. In the Indirect Method, each idea generation method is decomposed into key components and its overall effectiveness is predicted by experimentally studying the effectiveness of its components and their mutual interactions. [S1050-0472(00)02004-3]
Tracking and Regulation Control of a Mobile Robot System With Kinematic Disturbances: A Variable Structure-Like Approach
Authors: Dixon W. E. , Dawson D. M. , Zergeroglu E.
Published: July 2002

This paper presents the design of a variable structure-like tracking controller for a mobile robot system. The controller provides robustness with regard to bounded disturbances in the kinematic model. Through the use of a dynamic oscillator and a Lyapunov-based stability analysis, we demonstrate that the position and orientation tracking errors exponentially converge to a neighborhood about zero that can be made arbitrarily small (i.e., the controller ensures that the tracking error is globally uniformly ultimately bounded (GUUB)). In addition, we illustrate how the proposed tracking controller can also be utilized to achieve GUUB regulation to an arbitrary desired setpoint. An extension is also provided that illustrates how a smooth, time-varying control law can be utilized to achieve setpoint regulation despite parametric uncertainty in the kinematic model. Simulation results are presented to demonstrate the performance of the proposed controllers. [S0022-0434(00)00504-9]
Variable Structure Control of Engine Idle Speed With Estimation of Unmeasurable Disturbances
Authors: Stotsky A. , Egardt B. , Eriksson S.
Published: July 2002

A new controller for throttle and spark advance to control the engine speed at idle under unknown time varying disturbances is proposed in this paper. By using measurements of the engine speed the disturbance estimator is designed to reconstruct a disturbance torque. The controller is formulated so that the throttle is used as much as possible as a main tool to produce a torque and spark advance is used to compensate intake to torque production delay. The stability of the system is proved via Lyapunov function method. [S0022-0434(00)01304-6]
Maximal Wall Shear Stress in Arterial Stenoses: Application to the Internal Carotid Arteries
Authors: Lorthois Sylvie , Lagre´e Pierre-Yves , Marc-Vergnes Jean-Pierre , Cassot Francis
Published: July 2002

Maximal wall shear stress (MWSS) in the convergent part of a stenosis is calculated by the interactive boundary-layer theory. A dimensional analysis of the problem shows that MWSS depends only on a few measurable parameters. A simple relationship between MWSS and these parameters is obtained, validated, and used to calculate the magnitude of MWSS in a carotid stenosis, as a function of the patency of the circle of Willis and the stenotic pattern. This demonstrates the huge effect of collateral pathways. Elevated MWSS are observed even in moderate stenoses, provided they are associated with a contralateral occlusion, a large anterior, and narrow posterior communicating arteries, suggesting a potential risk of embolus release in this configuration. [S0148-0731(00)01506-5]
Performance Improvement of Gas Liquid Cylindrical Cyclone Separators Using Integrated Level and Pressure Control Systems
Authors: Wang Shoubo , Mohan Ram S. , Shoham Ovadia , Marrelli Jack D. , Kouba Gene E.
Published: July 2002

The performance of gas-liquid cylindrical cyclone (GLCC©) separators for two-phase flow metering loop can be improved by eliminating liquid overflow into the gas leg or gas blow-out through the liquid leg, utilizing suitable integrated control systems. In this study, a new integrated control system has been developed for the GLCC, in which the control is achieved by a liquid control valve in the liquid discharge line and a gas control valve in the gas discharge line. Simulation studies demonstrate that the integrated level and pressure control system is highly desirable for slugging conditions. This strategy will enable the GLCC to operate at constant pressure so as not to restrict well flow and simultaneously prevent liquid carry-over and gas carry-under. Detailed experimental studies have been conducted to evaluate the improvement in the GLCC operational envelope for liquid carry-over with the integrated level and pressure control system. The results demonstrate that the GLCC equipped with integrated control system is capable of controlling the liquid level and GLCC pressure for a wide range of flow conditions. The experimental results also show that the operational envelope for liquid carry-over is improved twofold at higher liquid flow rate region and higher gas flow rate region. GLCC performance is also evaluated by measuring the operational envelope for onset of gas carry-under. [S0195-0738(00)00804-9]
Sliding Mode Observer-Based Synthesis of State Derivative-Free Model Reference Adaptive Control of Distributed Parameter Systems
Authors: Orlov Y. V.
Published: July 2002

This paper presents control laws for distributed parameter systems of parabolic and hyperbolic types which, on the one hand ensure robustness with respect to small dynamic uncertainties and disturbances, and on the other hand, permit on-line plant parameter estimation. The novelty of the algorithms proposed is (a) in the construction of a sliding mode-based state derivative observer and (b) in the inclusion of this observer into a model reference adaptive controller which thereby regularizes the ill-posed identification problem itself. Apart from this, the controllers constructed do not suffer from on-line computation of spatial derivatives of the measurement data, and hence they are of reduced sensitivity with respect to the measurement noise. [S0022-0434(00)02104-3]
Evaluation of the Moisture Sensitivity of Molding Compounds of IC’s Packages
Authors: Fre´mont H. , Dele´tage J. Y. , Pintus A. , Danto Y.
Published: July 2002

Plastic encapsulated devices are of great interest against their ceramic or metallic counterparts, as they permit significant cost reductions. However, they are more sensitive to moisture ingress, which can lead to reliability problems. Moisture can penetrate either through the polymer or along the interface between the leads and the encapsulant. Samples of 3 different polymers usually used for IC’s encapsulation, either pure or containing a lead frame with the lead terminations, were aged under different RH conditions. Results show that the penetration through the polymer is preponderant face to the progression along the leads. In a first approach, this penetration can be considered as a diffusion process, following the Fick’s law; the diffusion coefficient D and the saturation coefficient S can be deduced from the measurements as a function of the relative humidity. These values can be used in finite element simulations, in order to evaluate the moisture ingress as a function of time within an IC of a given geometry. Moisture diffusion within these new resins is a very long process. In fact, a first “saturation” occurs after a few hours of aging, but if samples are left longer in the oven, a new diffusion process occurs, not leading to a real saturation. Hence processes different than pure fickian diffusion occur in the polymers.