Heather J Rea - Academia.edu (original) (raw)
Papers by Heather J Rea
Today’s CAD systems are excellent tools for recording the end result of a design process, particu... more Today’s CAD systems are excellent tools for recording the end result of a design process, particularly at the detail design stage. However, they are poor at capturing the rationale and underlying intent within the design itself. As a consequence of this, when changes are required at a later stage in the product’s life cycle, the consequences of these are unclear because the affects of and reasons for previous decisions may not be readily understood since the dependencies within a design are not explicitly represented. Of course an engineer could manually log these dependencies during the design but this would inevitably reduce design productivity, interrupt the engineer’s cognitive creative design process and lengthen design lead times. Also there would be no consistency in the quality or structure of the capturing process or the captured information since this would greatly depend on the individual engineers involved in the process. If CAD systems could automatically capture the re...
Manufacturing Science and Engineering, 1998
Instructions on how to assemble a product, known as assembly plans, are traditionally presented t... more Instructions on how to assemble a product, known as assembly plans, are traditionally presented to operators in the form of a paper document. The quality, clarity and format of this documentation rely largely on planning engineers’ experience and expertise. Inconsistencies can occur from planner to planner or across project departments which effect product quality. This paper presents a novel structured approach to assembly planning for initial application in the small batch, high technology, precision products sector (eg avionics, mechatronics, electronics). The structured approach capturing best practice is designed to assist experienced planners as well as providing a mechanism for training new planners. The common and variable requirements of assembly planning and information delivery systems in the application sector have been researched and defined.
In Life Cycle Engineering, it is vital that the engineering knowledge for the product is captured... more In Life Cycle Engineering, it is vital that the engineering knowledge for the product is captured throughout its life cycle in a formal and structured manner. This will allow the information to be referred to in the future by engineers who did not work on the original design but are wanting to understand the reasons that certain design decisions were made. In the past, attempts were made to try to capture this knowledge by having the engineer record the knowledge manually during a design session. However, this is not only time-consuming but is also disruptive to the creative process. Therefore, the research presented in this paper is concerned with capturing design knowledge automatically using a traditional 2D design environment and also an immersive 3D design environment. The design knowledge is captured by continuously and non-intrusively logging the user during a design session and then storing this output in a structured eXtensible Markup Language (XML) format. Next, the XML da...
Abstract: The collaborative re-use of design and manufacturing data is one way that e-commerce ca... more Abstract: The collaborative re-use of design and manufacturing data is one way that e-commerce can significantly reduce costs and lead times of new products in a demanding global market. This paper describes the development of a 3D Internet-based search engine, which will allow designers to locate parts already in production that have a similar shape to a desired ‘newly designed ’ part. The project anticipates a time when manufacturers will post 3D computer-generated models of their product range on the Internet as a means of advertising their production capabilities (i.e., tooling). The models will either be uploaded to, or harvested from anywhere in the world by, the search engine, which will then analyse the models and store relevant feature indices in a database. To use the system a designer would upload a model of the desired part. The search engine then analyses the shape characteristics of the target model and performs a similarity match through a sieving technique as describ...
The collaborative re-use of design and manufacturing data is one way that e-commerce can signific... more The collaborative re-use of design and manufacturing data is one way that e-commerce can significantly reduce costs and lead times of new products in a demanding global market. This paper describes the development of a 3D Internet-based search engine, which will allow designers to locate parts already in production that have a similar shape to a desired ‘newly designed’ part. The project anticipates a time when manufacturers will post 3D computer-generated models of their product range on the Internet as a means of advertising their production capabilities (i.e., tooling). The models will either be uploaded to, or harvested from anywhere in the world by, the search engine, which will then analyse the models and store relevant feature indices in a database. To use the system a designer would upload a model of the desired part. The search engine then analyses the shape characteristics of the target model and performs a similarity match through a sieving technique as described in this ...
Organisations across sectors such as aerospace, construction, defence and health care are increas... more Organisations across sectors such as aerospace, construction, defence and health care are increasingly being asked not only to provide products in the first instance, but also to support them throughout their service life. Virtually all engineering products are designed using Computer Aided Design (CAD) analysis and simulation systems. Today’s CAD systems are excellent tools for recording the end result of a design process, particularly at the detail design stage. However, they are poor at capturing the rationale and underlying intent within the design itself. If CAD systems could automatically capture the reasoning underlying the development of a design then- even years after the original design had been created- engineers could better understand the consequences of potential upgrades and modifications. In order to study this hypothesis, the authors identified the game software CBBC BAMZOOKi as a useful experimental system for the automated capture of design knowledge. This paper e...
This paper shares our experiences and reflections on a training programme which seeks to build ca... more This paper shares our experiences and reflections on a training programme which seeks to build capacity, across the public research sector in Scotland, for developing and facilitating dialogic approaches to public engagement. We came to an interest in dialogue and deliberation by different routes, but got the opportunity to collaborate on this thanks to institutional funding for culture change around public engagement in the sector. The analytical framework from which we developed the training focuses especially on the micro-politics of communication patterns in deliberative and dialogic engagement processes. The training programme thus sought both to raise awareness of the principles and practices of dialogue, and to build skills in the demanding craft of facilitation. Our training approach has two key features: it integrates theory and practice; and it endeavours to make the general themes of dialogue and deliberation relevant to the specific context of public engagement activitie...
New Review of Information Networking, 2002
Page 1. ShapeSifter: a retrieval system for databases of 3D engineering data Raymond Sung Departm... more Page 1. ShapeSifter: a retrieval system for databases of 3D engineering data Raymond Sung Department of Mechanical Engineering, Heriot-Watt University, Riccarton Campus, Edinburgh, EH14 4AS, UK e-mail: rcwsung@hw.ac.uk ...
Archive Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science 1989 1996, Jun 1, 2005
Effective content-based shape retrieval systems would allow engineers to search databases of thre... more Effective content-based shape retrieval systems would allow engineers to search databases of three-dimensional computer-aided design (CAD) models for objects with specific geometries or features. Much of the academic work in this area has focused on the development of indexing schemes based on different types of three-dimensional to two-dimensional ‘shape functions’. Ideally, the shape function used to generate a distribution should be easy to compute and permit the discrimination of both large and small features. The work reported in this paper describes the properties of three new shape distributions based on computationally simple shape functions. The first shape function calculates the arithmetic difference between distributions derived (using the original D2 distance shape function) from both a three-dimensional model and its convex hull. The second shape function is obtained by sampling the angle between random pairs of facets on the object. The third shape function uses the surface orientation to filter the results of a distance distribution. The results reported in this paper suggest that these novel shape functions improve significantly the ability of shape distributions to discriminate between complex engineering parts.
Picmet 08 2008 Portland International Conference on Management of Engineering Technology, Jul 27, 2008
Within the context of Life Cycle Engineering it is important that structured engineering informat... more Within the context of Life Cycle Engineering it is important that structured engineering information and knowledge are captured at all phases of the product life cycle for future reference. This is especially the case for long life cycle projects which see a large number of engineering decisions made at the early to mid-stages of a product's life cycle that are needed to inform engineering decisions later on in the process. A key aspect of technology management will be the capturing of knowledge throughout the product life cycle. Numerous attempts have been made to apply knowledge capture techniques to formalise engineering decision rationale and processes; however, these tend to be associated with substantial overheads on the engineer and the company through cognitive process interruptions and additional costs/time. Indeed, when life cycle deadlines come closer these capturing techniques are abandoned due the need to produce a final solution. This paper describes work carried out for non-intrusively capturing and formalising product life cycle knowledge by demonstrating the automated capture of engineering processes/rationale using user logging via an immersive virtual reality system for cable harness design and assembly planning. Associated post-experimental analyses are described which demonstrate the formalisation of structured design processes and decision representations in the form of IDEF diagrams and structured engineering change information. Potential future research directions involving more thorough logging of users are also outlined.
In Life Cycle Engineering, it is vital that the engineering knowledge for the product is captured... more In Life Cycle Engineering, it is vital that the engineering knowledge for the product is captured throughout its life cycle in a formal and structured manner. This will allow the information to be referred to in the future by engineers who did not work on the original design but are wanting to understand the reasons that certain design decisions were made. In the past, attempts were made to try to capture this knowledge by having the engineer record the knowledge manually during a design session. However, this is not only time-consuming but is also disruptive to the creative process. Therefore, the research presented in this paper is concerned with capturing design knowledge automatically using a traditional 2D design environment and also an immersive 3D design environment. The design knowledge is captured by continuously and non-intrusively logging the user during a design session and then storing this output in a structured eXtensible Markup Language (XML) format. Next, the XML data is analysed and the design processes that are involved can be visualised by the automatic generation of IDEF0 diagrams. Using this captured knowledge, it forms the basis of an interactive online assistance system to aid future users who are carrying out a similar design task.
Proceedings of 1994 IEEE International Conference on Neural Networks (ICNN'94), 1994
A nominal analytic kinematic model augmented by a neural network (NN) accuracy compensator has be... more A nominal analytic kinematic model augmented by a neural network (NN) accuracy compensator has been used to determine accurately the relationship between robot world space co-ordinates and joint transducer readings. In contrast to model-based calibration approaches which have been used in an attempt to model and identify the specific error source, the NN-based calibration provides a generic model of robot accuracy which accounts for various errors, with the error source information being represented in the distributed network weight connections. A novel network architecture, based on Pi-sigma neural networks, has been designed so that it has sufficient approximations capability, which is equivalent to the higher-order polynomials, to approximate the relationship between the accuracy compensations (both in the world space and in joint space) and robot configurations, while maintaining an efficient network leaning ability. The authors' results for a full-pose calibration of a six DOF (degree of freedom) Puma 560 Robot have shown that the neural network approach can achieve better accuracy compared with the kinematic model-based calibration. The forward neuro-accuracy compensation (compensated in the world space) demonstrates a decrease in the average position and orientation error from 4.35 mm and 2.55 degree to 0.24 mm and 0.44 degree, in the range from 0.90 mm and 0.41 degree to 0.15 mm and 0.37 degree respectively in the calibrated area. In addition, error compensation is much more efficient than conventional numerical iterative compensation algorithms, suggesting that the neuro-accuracy compensator can be implemented on-line
Design Engineering, 2002
ABSTRACT Collaborative re-use of design and manufacturing data is one way that global e-commerce ... more ABSTRACT Collaborative re-use of design and manufacturing data is one way that global e-commerce could significantly reduce development costs and lead times of new products. However the proliferation of web based catalogues for standard components (eg brochure-ware for nuts and washers etc.) only hints at the possible productivity gains if a 3D search engine could be created. Consequently the research reported here is motivated by the belief that shape matching technology is key to enabling a much deeper form of Internet-based ...
The use of virtual reality in interactive design and manufacture has been researched extensively ... more The use of virtual reality in interactive design and manufacture has been researched extensively but the practical application of this technology in industry is still very much in its infancy. This is surprising as one would have expected that, after some 30 years of research commercial applications of interactive design or manufacturing planning and analysis would be widespread throughout the
PICMET '08 - 2008 Portland International Conference on Management of Engineering & Technology, 2008
Within the context of Life Cycle Engineering it is important that structured engineering informat... more Within the context of Life Cycle Engineering it is important that structured engineering information and knowledge are captured at all phases of the product life cycle for future reference. This is especially the case for long life cycle projects which see a large number of engineering decisions made at the early to mid-stages of a product's life cycle that are needed to inform engineering decisions later on in the process. A key aspect of technology management will be the capturing of knowledge throughout the product life cycle. Numerous attempts have been made to apply knowledge capture techniques to formalise engineering decision rationale and processes; however, these tend to be associated with substantial overheads on the engineer and the company through cognitive process interruptions and additional costs/time. Indeed, when life cycle deadlines come closer these capturing techniques are abandoned due the need to produce a final solution. This paper describes work carried out for non-intrusively capturing and formalising product life cycle knowledge by demonstrating the automated capture of engineering processes/rationale using user logging via an immersive virtual reality system for cable harness design and assembly planning. Associated post-experimental analyses are described which demonstrate the formalisation of structured design processes and decision representations in the form of IDEF diagrams and structured engineering change information. Potential future research directions involving more thorough logging of users are also outlined.
Page 1. A Surface Partitioning Spectrum (SPS) for Retrieval and Indexing of 3D CAD Models Heather... more Page 1. A Surface Partitioning Spectrum (SPS) for Retrieval and Indexing of 3D CAD Models Heather J Rea Engineering and Physical Sciences Heriot-Watt University, Edinburgh, UK hjrea@hw.ac.uk Doug ER Clark Mathematical ...
Today’s CAD systems are excellent tools for recording the end result of a design process, particu... more Today’s CAD systems are excellent tools for recording the end result of a design process, particularly at the detail design stage. However, they are poor at capturing the rationale and underlying intent within the design itself. As a consequence of this, when changes are required at a later stage in the product’s life cycle, the consequences of these are unclear because the affects of and reasons for previous decisions may not be readily understood since the dependencies within a design are not explicitly represented. Of course an engineer could manually log these dependencies during the design but this would inevitably reduce design productivity, interrupt the engineer’s cognitive creative design process and lengthen design lead times. Also there would be no consistency in the quality or structure of the capturing process or the captured information since this would greatly depend on the individual engineers involved in the process. If CAD systems could automatically capture the re...
Manufacturing Science and Engineering, 1998
Instructions on how to assemble a product, known as assembly plans, are traditionally presented t... more Instructions on how to assemble a product, known as assembly plans, are traditionally presented to operators in the form of a paper document. The quality, clarity and format of this documentation rely largely on planning engineers’ experience and expertise. Inconsistencies can occur from planner to planner or across project departments which effect product quality. This paper presents a novel structured approach to assembly planning for initial application in the small batch, high technology, precision products sector (eg avionics, mechatronics, electronics). The structured approach capturing best practice is designed to assist experienced planners as well as providing a mechanism for training new planners. The common and variable requirements of assembly planning and information delivery systems in the application sector have been researched and defined.
In Life Cycle Engineering, it is vital that the engineering knowledge for the product is captured... more In Life Cycle Engineering, it is vital that the engineering knowledge for the product is captured throughout its life cycle in a formal and structured manner. This will allow the information to be referred to in the future by engineers who did not work on the original design but are wanting to understand the reasons that certain design decisions were made. In the past, attempts were made to try to capture this knowledge by having the engineer record the knowledge manually during a design session. However, this is not only time-consuming but is also disruptive to the creative process. Therefore, the research presented in this paper is concerned with capturing design knowledge automatically using a traditional 2D design environment and also an immersive 3D design environment. The design knowledge is captured by continuously and non-intrusively logging the user during a design session and then storing this output in a structured eXtensible Markup Language (XML) format. Next, the XML da...
Abstract: The collaborative re-use of design and manufacturing data is one way that e-commerce ca... more Abstract: The collaborative re-use of design and manufacturing data is one way that e-commerce can significantly reduce costs and lead times of new products in a demanding global market. This paper describes the development of a 3D Internet-based search engine, which will allow designers to locate parts already in production that have a similar shape to a desired ‘newly designed ’ part. The project anticipates a time when manufacturers will post 3D computer-generated models of their product range on the Internet as a means of advertising their production capabilities (i.e., tooling). The models will either be uploaded to, or harvested from anywhere in the world by, the search engine, which will then analyse the models and store relevant feature indices in a database. To use the system a designer would upload a model of the desired part. The search engine then analyses the shape characteristics of the target model and performs a similarity match through a sieving technique as describ...
The collaborative re-use of design and manufacturing data is one way that e-commerce can signific... more The collaborative re-use of design and manufacturing data is one way that e-commerce can significantly reduce costs and lead times of new products in a demanding global market. This paper describes the development of a 3D Internet-based search engine, which will allow designers to locate parts already in production that have a similar shape to a desired ‘newly designed’ part. The project anticipates a time when manufacturers will post 3D computer-generated models of their product range on the Internet as a means of advertising their production capabilities (i.e., tooling). The models will either be uploaded to, or harvested from anywhere in the world by, the search engine, which will then analyse the models and store relevant feature indices in a database. To use the system a designer would upload a model of the desired part. The search engine then analyses the shape characteristics of the target model and performs a similarity match through a sieving technique as described in this ...
Organisations across sectors such as aerospace, construction, defence and health care are increas... more Organisations across sectors such as aerospace, construction, defence and health care are increasingly being asked not only to provide products in the first instance, but also to support them throughout their service life. Virtually all engineering products are designed using Computer Aided Design (CAD) analysis and simulation systems. Today’s CAD systems are excellent tools for recording the end result of a design process, particularly at the detail design stage. However, they are poor at capturing the rationale and underlying intent within the design itself. If CAD systems could automatically capture the reasoning underlying the development of a design then- even years after the original design had been created- engineers could better understand the consequences of potential upgrades and modifications. In order to study this hypothesis, the authors identified the game software CBBC BAMZOOKi as a useful experimental system for the automated capture of design knowledge. This paper e...
This paper shares our experiences and reflections on a training programme which seeks to build ca... more This paper shares our experiences and reflections on a training programme which seeks to build capacity, across the public research sector in Scotland, for developing and facilitating dialogic approaches to public engagement. We came to an interest in dialogue and deliberation by different routes, but got the opportunity to collaborate on this thanks to institutional funding for culture change around public engagement in the sector. The analytical framework from which we developed the training focuses especially on the micro-politics of communication patterns in deliberative and dialogic engagement processes. The training programme thus sought both to raise awareness of the principles and practices of dialogue, and to build skills in the demanding craft of facilitation. Our training approach has two key features: it integrates theory and practice; and it endeavours to make the general themes of dialogue and deliberation relevant to the specific context of public engagement activitie...
New Review of Information Networking, 2002
Page 1. ShapeSifter: a retrieval system for databases of 3D engineering data Raymond Sung Departm... more Page 1. ShapeSifter: a retrieval system for databases of 3D engineering data Raymond Sung Department of Mechanical Engineering, Heriot-Watt University, Riccarton Campus, Edinburgh, EH14 4AS, UK e-mail: rcwsung@hw.ac.uk ...
Archive Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science 1989 1996, Jun 1, 2005
Effective content-based shape retrieval systems would allow engineers to search databases of thre... more Effective content-based shape retrieval systems would allow engineers to search databases of three-dimensional computer-aided design (CAD) models for objects with specific geometries or features. Much of the academic work in this area has focused on the development of indexing schemes based on different types of three-dimensional to two-dimensional ‘shape functions’. Ideally, the shape function used to generate a distribution should be easy to compute and permit the discrimination of both large and small features. The work reported in this paper describes the properties of three new shape distributions based on computationally simple shape functions. The first shape function calculates the arithmetic difference between distributions derived (using the original D2 distance shape function) from both a three-dimensional model and its convex hull. The second shape function is obtained by sampling the angle between random pairs of facets on the object. The third shape function uses the surface orientation to filter the results of a distance distribution. The results reported in this paper suggest that these novel shape functions improve significantly the ability of shape distributions to discriminate between complex engineering parts.
Picmet 08 2008 Portland International Conference on Management of Engineering Technology, Jul 27, 2008
Within the context of Life Cycle Engineering it is important that structured engineering informat... more Within the context of Life Cycle Engineering it is important that structured engineering information and knowledge are captured at all phases of the product life cycle for future reference. This is especially the case for long life cycle projects which see a large number of engineering decisions made at the early to mid-stages of a product's life cycle that are needed to inform engineering decisions later on in the process. A key aspect of technology management will be the capturing of knowledge throughout the product life cycle. Numerous attempts have been made to apply knowledge capture techniques to formalise engineering decision rationale and processes; however, these tend to be associated with substantial overheads on the engineer and the company through cognitive process interruptions and additional costs/time. Indeed, when life cycle deadlines come closer these capturing techniques are abandoned due the need to produce a final solution. This paper describes work carried out for non-intrusively capturing and formalising product life cycle knowledge by demonstrating the automated capture of engineering processes/rationale using user logging via an immersive virtual reality system for cable harness design and assembly planning. Associated post-experimental analyses are described which demonstrate the formalisation of structured design processes and decision representations in the form of IDEF diagrams and structured engineering change information. Potential future research directions involving more thorough logging of users are also outlined.
In Life Cycle Engineering, it is vital that the engineering knowledge for the product is captured... more In Life Cycle Engineering, it is vital that the engineering knowledge for the product is captured throughout its life cycle in a formal and structured manner. This will allow the information to be referred to in the future by engineers who did not work on the original design but are wanting to understand the reasons that certain design decisions were made. In the past, attempts were made to try to capture this knowledge by having the engineer record the knowledge manually during a design session. However, this is not only time-consuming but is also disruptive to the creative process. Therefore, the research presented in this paper is concerned with capturing design knowledge automatically using a traditional 2D design environment and also an immersive 3D design environment. The design knowledge is captured by continuously and non-intrusively logging the user during a design session and then storing this output in a structured eXtensible Markup Language (XML) format. Next, the XML data is analysed and the design processes that are involved can be visualised by the automatic generation of IDEF0 diagrams. Using this captured knowledge, it forms the basis of an interactive online assistance system to aid future users who are carrying out a similar design task.
Proceedings of 1994 IEEE International Conference on Neural Networks (ICNN'94), 1994
A nominal analytic kinematic model augmented by a neural network (NN) accuracy compensator has be... more A nominal analytic kinematic model augmented by a neural network (NN) accuracy compensator has been used to determine accurately the relationship between robot world space co-ordinates and joint transducer readings. In contrast to model-based calibration approaches which have been used in an attempt to model and identify the specific error source, the NN-based calibration provides a generic model of robot accuracy which accounts for various errors, with the error source information being represented in the distributed network weight connections. A novel network architecture, based on Pi-sigma neural networks, has been designed so that it has sufficient approximations capability, which is equivalent to the higher-order polynomials, to approximate the relationship between the accuracy compensations (both in the world space and in joint space) and robot configurations, while maintaining an efficient network leaning ability. The authors' results for a full-pose calibration of a six DOF (degree of freedom) Puma 560 Robot have shown that the neural network approach can achieve better accuracy compared with the kinematic model-based calibration. The forward neuro-accuracy compensation (compensated in the world space) demonstrates a decrease in the average position and orientation error from 4.35 mm and 2.55 degree to 0.24 mm and 0.44 degree, in the range from 0.90 mm and 0.41 degree to 0.15 mm and 0.37 degree respectively in the calibrated area. In addition, error compensation is much more efficient than conventional numerical iterative compensation algorithms, suggesting that the neuro-accuracy compensator can be implemented on-line
Design Engineering, 2002
ABSTRACT Collaborative re-use of design and manufacturing data is one way that global e-commerce ... more ABSTRACT Collaborative re-use of design and manufacturing data is one way that global e-commerce could significantly reduce development costs and lead times of new products. However the proliferation of web based catalogues for standard components (eg brochure-ware for nuts and washers etc.) only hints at the possible productivity gains if a 3D search engine could be created. Consequently the research reported here is motivated by the belief that shape matching technology is key to enabling a much deeper form of Internet-based ...
The use of virtual reality in interactive design and manufacture has been researched extensively ... more The use of virtual reality in interactive design and manufacture has been researched extensively but the practical application of this technology in industry is still very much in its infancy. This is surprising as one would have expected that, after some 30 years of research commercial applications of interactive design or manufacturing planning and analysis would be widespread throughout the
PICMET '08 - 2008 Portland International Conference on Management of Engineering & Technology, 2008
Within the context of Life Cycle Engineering it is important that structured engineering informat... more Within the context of Life Cycle Engineering it is important that structured engineering information and knowledge are captured at all phases of the product life cycle for future reference. This is especially the case for long life cycle projects which see a large number of engineering decisions made at the early to mid-stages of a product's life cycle that are needed to inform engineering decisions later on in the process. A key aspect of technology management will be the capturing of knowledge throughout the product life cycle. Numerous attempts have been made to apply knowledge capture techniques to formalise engineering decision rationale and processes; however, these tend to be associated with substantial overheads on the engineer and the company through cognitive process interruptions and additional costs/time. Indeed, when life cycle deadlines come closer these capturing techniques are abandoned due the need to produce a final solution. This paper describes work carried out for non-intrusively capturing and formalising product life cycle knowledge by demonstrating the automated capture of engineering processes/rationale using user logging via an immersive virtual reality system for cable harness design and assembly planning. Associated post-experimental analyses are described which demonstrate the formalisation of structured design processes and decision representations in the form of IDEF diagrams and structured engineering change information. Potential future research directions involving more thorough logging of users are also outlined.
Page 1. A Surface Partitioning Spectrum (SPS) for Retrieval and Indexing of 3D CAD Models Heather... more Page 1. A Surface Partitioning Spectrum (SPS) for Retrieval and Indexing of 3D CAD Models Heather J Rea Engineering and Physical Sciences Heriot-Watt University, Edinburgh, UK hjrea@hw.ac.uk Doug ER Clark Mathematical ...