Showing papers by "Cardiff University published in 1998"

A comparison of rapid prototyping technologies

Abstract: Until recently, prototypes had to be constructed by skilled model makers from 2D engineering drawings. This is a time-consuming and expensive process. With the advent of new layer manufacturing and CAD/CAM technologies, prototypes may now be rapidly produced from 3D computer models. There are many different rapid prototyping (RP) technologies available. This paper presents an overview of the current technologies and comments on their strengths and weaknesses. Data are given for common process parameters such as layer thickness, system accuracy and speed of operation. A taxonomy is also suggested, along with a preliminary guide to process selection based on the end use of the prototype.

Fibrocartilage in tendons and ligaments — an adaptation to compressive load

Abstract: Where tendons and ligaments are subject to compression, they are frequently fibrocartilaginous. This occurs at 2 principal sites: where tendons (and sometimes ligaments) wrap around bony or fibrous pulleys, and in the region where they attach to bone, i.e. at their entheses. Wrap-around tendons are most characteristic of the limbs and are commonly wider at their point of bony contact so that the pressure is reduced. The most fibrocartilaginous tendons are heavily loaded and permanently bent around their pulleys. There is often pronounced interweaving of collagen fibres that prevents the tendons from splaying apart under compression. The fibrocartilage can be located within fascicles, or in endo- or epitenon (where it may protect blood vessels from compression or allow fascicles to slide). Fibrocartilage cells are commonly packed with intermediate filaments which could be involved in transducing mechanical load. The ECM often contains aggrecan which allows the tendon to imbibe water and withstand compression. Type II collagen may also be present, particularly in tendons that are heavily loaded. Fibrocartilage is a dynamic tissue that disappears when the tendons are rerouted surgically and can be maintained in vitro when discs of tendon are compressed. Finite element analyses provide a good correlation between its distribution and levels of compressive stress, but at some locations fibrocartilage is a sign of pathology. Enthesis fibrocartilage is most typical of tendons or ligaments that attach to the epiphyses of long bones where it may also be accompanied by sesamoid and periosteal fibrocartilages. It is characteristic of sites where the angle of attachment changes throughout the range of joint movement and it reduces wear and tear by dissipating stress concentration at the bony interface. There is a good correlation between the distribution of fibrocartilage within an enthesis and the levels of compressive stress. The complex interlocking between calcified fibrocartilage and bone contributes to the mechanical strength of the enthesis and cartilage-like molecules (e.g. aggrecan and type II collagen) in the ECM contribute to its ability to withstand compression. Pathological changes are common and are known as enthesopathies.

Social Identity Theory's Self-Esteem Hypothesis: A Review and Some Suggestions for Clarification

Abstract: Distinctions are made between global and specific, personal and social, and trait and state self-esteem, and these are used to structure a review of over 40 studies concerning social identity theory's hypothesis that (a) intergroup discrimination elevates self-esteem and (b) low self-esteem motivates discrimination. It is observed that researchers have tended to employ measures of global personal trait self-esteem in their investigations of this self-esteem hypothesis, and it is argued that measures of specific social state self-esteem are more consistent with social identity theory's assumptions. Although no convincing evidence is found for the self-esteem hypothesis in its full and unqualified form, it is argued that this is due to a lack of specificity in its formulation and it is suggested that a more qualified and specific version of the hypothesis may be more appropriate.

Regional Systems of Innovation: An Evolutionary Perspective

Abstract: The authors develop the concept of regional systems of innovation and relate it to preexisting research on national systems of innovation They argue that work conducted in the ‘new regional science’ field is complementary to systems of innovation approaches They seek to link new regional work to evolutionary economics, and argue for the development of evolutionary regional science Common elements of interest to evolutionary innovation research and new regional science are important in understanding processes of agglomeration, trust building, innovation, institutions, and learning in regional systems The authors develop analytical frameworks for designating regional systems of innovation in terms of distinction between institutions and organisations, hard and soft infrastructures, and the cultural superstructure They conclude that an evolutionary approach assists understanding of regional potential for developing systemic innovation

Simulation of Land Development through the Integration of Cellular Automata and Multicriteria Evaluation

Abstract: Cellular automata (CA) simulation has become a popular method of exploring the behaviour of all kinds of self-organising systems. The city may clearly be viewed as such a system but one with a particularly complex set of transition rules. Many natural processes such as the spread of fire or vegetation can be modelled by a simple set of local rules. Insofar as the development of a piece of land depends on the neighbourhood situation as well as on the characteristics of a site, urban evolution can be treated in much the same way, with transition rules translating the evaluation of the location into a land conversion outcome. If this modelling paradigm is to be used to gain insight into real-world urban development processes, there is a need to discover ways of capturing the richness of land conversion behaviour in the simplifying mechanisms of CA. Our paper contributes to this research agenda by integrating multicriteria evaluation (MCE) into a CA simulation in order to define nondeterministic, multidimensional, and multilevel transition rules. An analytical hierarchy process is used to implement MCE-derived transition rules. The integrated MCE - CA model may be used in a gaming mode to explore how urban form evolves under different development regimes caricatured by the set of multicriteria weights. We use it to test loosely hypotheses about the nature of the regimes that have governed the expansion of a fast-growing southern Chinese city.

The antidepressant era

Abstract: Acknowledgments Introduction Of Illness, Disease, and Remedies The Discovery of Antidepressants Other Things Being Equal The Trials of Therapeutic Empiricism A Pleasing Look of Truth The Luke Effect From Oedipus to Osheroff Postscript Appendix: Current Major Physical Treatments for Depression Notes Index

Deconstructing Communicative Rationality: A Critique of Habermasian Collaborative Planning

Abstract: What has becomes known in recent years as communicative or collaborative planning has forged a new hegemony in planning theory. Described by some as the paradigm of the 1990s, it proposes a fundamental challenge to the practice of planning that seeks both to explain where planning has gone wrong and (more controversially) to identify ways forward. The broad approach itself and advocates of it have lacked the advantage of any critique. This paper provides such an opportunity. Following a brief outline of communicative action, we identify three broad areas of concern that militate against the option of a collaborative planning approach. More specifically, we identify problematic assumptions in Habermas's original theoretical distinction of communicative action as a fourth separate concept of sociological action. Although we accept its useful dissection of planning and the role of values and consensus-building in decision-settings, we consider that collaborative planning theory fails to incorporate adequately the peculiar political and professional nuances that exist in planning practice. We conclude our critique by raising programmatic points for planning theory and practice in general.

BacSim, a simulator for individual-based modelling of bacterial colony growth

Abstract: Summary: The generic, quantitative, spatially explicit, individual-based model BacSim was developed to simulate growth and behaviour of bacteria. The potential of this approach is in relating the properties of microscopic entities – cells – to the properties of macroscopic, complex systems such as biofilms. Here, the growth of a single Escherichia coli cell into a colony was studied. The object-oriented program BacSim is an extension of Gecko, an ecosystem dynamics model which uses the Swarm toolkit for multi-agent simulations. The model describes bacterial properties including substrate uptake, metabolism, maintenance, cell division and death at the individual cell level. With the aim of making the model easily applicable to various bacteria under different conditions, the model uses as few as eight readily obtainable parameters which can be randomly varied. For substrate diffusion, a two-dimensional diffusion lattice is used. For growth-rate-dependent cell size variation, a conceptual model of cell division proposed by Donachie was examined. A mechanistic version of the Donachie model led to unbalanced growth at higher growth rates, whereas including a minimum period between subsequent replication initiations ensured balanced growth only if this period was unphysiologically long. Only a descriptive version of the Donachie model predicted cell sizes correctly. For maintenance, the Herbert model (constant specific rate of biomass consumption) and for substrate uptake, the Michaelis-Menten or the Best equations were implemented. The simulator output faithfully reproduced all input parameters. Growth characteristics when maintenance and uptake rates were proportional to either cell mass or surface area are compared. The authors propose a new generic measure of growth synchrony to quantify the loss of synchrony due to random variation of cell parameters or spatial heterogeneity. Variation of the maximal uptake rate completely desynchronizes the simulated culture but variation of the volume-at-division does not. A new measure for spatial heterogeneity is introduced: the standard deviation of substrate concentrations as experienced by the cells. Spatial heterogeneity desynchronizes population growth by subdividing the population into parts synchronously growing at different rates. At a high enough spatial heterogeneity, the population appears to grow completely asynchronously.

Identifying Managerial Influences on Exporting: Past Research and Future Directions:

Abstract: Research on exporting frequently stresses the role of managerial characteristics as influences on the export behavior of the firm. This article reviews the conceptual, methodological, and empirical...

Value Stream Management

Abstract: Value Stream Management is a new strategic and operational approach to the data capture, analysis, planning and implementation of effective change within the core cross‐functional or cross‐company processes required to achieve a truly lean enterprise. This paper describes the method in detail including a summary of the previous Value Stream Mapping approach and its weaknesses. The new approach involves a strategic review of a business or supply chain's activities, the delimitation of key processes and the mapping of these processes. A description of how to analyze and synthesize these data is followed by a section on an approach to planning strategic and operational change together with a framework in which to do this. The benefits and limitations of the new approach are summarized.

Mosquito carboxylesterases: a review of the molecular biology and biochemistry of a major insecticide resistance mechanism.

Abstract: The major mechanism of organophosphorus insecticide resistance in Culex mosquitoes involves the elevation of one or more esterases. The general mechanism underlying this resistance is the amplification of the structural genes. This review covers the classification of the mosquito esterases in the context of classical esterase nomenclature. The function of the amplified esterases and the structure of the amplified DNA on which they occur are also described. Implications of information on the esterase amplicons are discussed in relation to the evolution and migration of insecticide resistance in Culex.

Adaptive Markov Chain Monte Carlo through Regeneration

Abstract: Markov chain Monte Carlo (MCMC) is used for evaluating expectations of functions of interest under a target distribution π. This is done by calculating averages over the sample path of a Markov chain having π as its stationary distribution. For computational efficiency, the Markov chain should be rapidly mixing. This sometimes can be achieved only by careful design of the transition kernel of the chain, on the basis of a detailed preliminary exploratory analysis of π. An alternative approach might be to allow the transition kernel to adapt whenever new features of π are encountered during the MCMC run. However, if such adaptation occurs infinitely often, then the stationary distribution of the chain may be disturbed. We describe a framework, based on the concept of Markov chain regeneration, which allows adaptation to occur infinitely often but does not disturb the stationary distribution of the chain or the consistency of sample path averages.

Central role of heterocellular gap junctional communication in endothelium-dependent relaxations of rabbit arteries

Abstract: 1. The contribution of gap junctions to endothelium-dependent relaxation was investigated in isolated rabbit conduit artery preparations pre-constricted by 10 μM phenylephrine (PhE).2Acetylcholine (ACh) relaxed the thoracic aorta by ≈60 % and the superior mesenteric artery (SMA) by ≈90 %. A peptide possessing sequence homology with extracellular loop 2. of connexin 43 (Gap 27, 300 μM) inhibited relaxation by ≈40 % in both artery types. Gap 27 also attenuated the endothelium-dependent component of the relaxation induced by ATP in thoracic aorta but did not modify force development in response to PhE. 3. NG-nitro-L-arginine methyl ester (L-NAME, 300 μM), an inhibitor of NO synthase, attenuated ACh-induced relaxation by ≈90 % in the aorta but only by ≈40 % in SMA (P < 0.05). Residual L-NAME-insensitive relaxations were almost abolished by 300 μM Gap 27 in aorta and inhibited in a concentration-dependent fashion in SMA (≈50 % at 100 μM and ≈80 % at 10 mM). Gap 27 similarly attenuated the endothelium-dependent component of L-NAME-insensitive relaxations to ATP in aorta. 4. Responses to cyclopiazonic acid, which stimulates endothelium-dependent relaxation through a receptor-independent mechanism, were also attenuated by Gap 27, whereas this peptide exerted no effect on the NO-mediated relaxation induced by sodium nitroprusside in preparations denuded of endothelium. 5. ACh-induced relaxation of ‘sandwich’ mounts of aorta or SMA were unaffected by Gap 27 but completely abolished by L-NAME. 6. We conclude that direct heterocellular communication between the endothelium and smooth muscle contributes to endothelium-dependent relaxations evoked by both receptor-dependent and -independent mechanisms. The inhibitory effects of Gap 27 peptide do not involve homocellular communication within the vessel wall or modulation of NO release or action.

The Genetic Testing of Children

Abstract: The importance of genetic diseases in childhood has grown over the course of this century as that of infectious diseases and malnutrition has diminished, at least in developed countries. Accordingly, many of the children now requiring medical attention are recognised as suffering from genetic conditions. Making the diagnosis of a genetic disorder in an affected child is therefore a standard clinical activity. Establishing such a diagnosis has traditionally depended upon finding evidence of the disease process but is increasingly turning to genetic investigations that identify the underlying, genetic cause of the disorder. Such genetic tests can be carried out on any tissue and at any age, from conception onwards, because they do not depend upon the condition having manifested itself in any way. It is therefore possible to identify healthy children who will, in the future, develop a genetic disease; it is also possible to identify those who are healthy carriers of a disease which will never affect them but which may be of relevance to their own future children.

Incremental Eigenanalysis for Classification

Abstract: Eigenspace models are a convenient way to represent sets of observations with widespread applications, including classification. In this paper we describe a new constructive method for incrementally adding observations to an eigenspace model. Our contribution is to explicitly account for a change in origin as well as a change in the number of eigenvectors needed in the basis set. No other method we have seen considers change of origin, yet both are needed if an eigenspace model is to be used for classification purposes. We empirically compare our incremental method with two alternatives from the literature and show our method is the more useful for classification because it computes the smaller eigenspace model representing the observations.

Market orientation and dimensions of strategic orientation

Abstract: The specific domain of market orientation has been the subject of much scrutiny this decade. Both conceptual and empirical advances have been made to establish the marketing orientation construct as central to marketing decisions, business activities and organizational culture. However, a lacuna remains in understanding how market orientation may be related to competitive strategy. It is argued that market oriented activities and behaviours are articulated through strategic means which guides the firm in its product‐market. Conceptualized as “strategic orientation of the business enterprise”, competitive strategy is discussed as an important vehicle through which market orientation may be manifest. Six dimensions of strategic orientation are presented and statistical analyses, of data generated from a survey of medium and large industrial manufacturing businesses, specified “proactiveness”, “analysis” and “futurity” as positive and significant in their association with firms’ levels of market orientation. Discussion of these findings is made, along with various conclusions and implications of the study for executive and academic audiences.

Hippocampal lesions disrupt navigation based on cognitive maps but not heading vectors

Abstract: Animals can find a hidden goal in several ways. They might use a cognitive map that encodes information about the geometric relationship between the goal and two or more landmarks. Alternatively, they might use a heading vector that specifies the direction and distance of the goal from a single landmark. Rats with damage to the hippocampus have difficulty in finding a hidden goal. Here we determine which of the above strategies is affected by such damage. Rats were required to swim in a water maze to a submerged platform, which was always at the same distance and direction from a landmark. The platform and landmark remained in the same place for the four trials of each session, but they were moved to a new position at the start of a session. Rats with damage to the hippocampus found the platform more efficiently than did normal rats in the first trial of a session but, in contrast to normal rats, their performance did not improve during a session. Our results indicate that hippocampally damaged rats are able to navigate by means of heading vectors but not cognitive maps.

Values as truisms:evidence and implications

Abstract: Three experiments tested the general hypothesis that values are cultural truisms-that is, beliefs that are widely shared and rarely questioned. Experiment 1 examined specifically whether people lack cognitive support for their values. It was predicted and found that analyzing one's reasons for particular values caused the values to change, a finding that would be expected only if individuals lack cognitive support for their values. Experiment 2 verified that analyzing reasons caused value change only when participants were not provided with cognitive support for their values. Experiment 3 found that the effect of analyzing reasons generalized across a range of ind vidual-differences variables. Experiment 3 also showed that analyzing reasons resulted in value ratings that were less predictive of relevant attitudes than pre-reasons-analysis value ratings, but only for high self-monitors.

Can loyalty schemes really build loyalty

Abstract: Customer loyalty schemes have blossomed in the era of customer retention, and have been willingly embraced by both retailers and consumers alike. Today’s loyalty schemes are modelled on the AAdvantage Programme; a frequent flier programme initiated by American Airlines in 1981, and lessons from the air‐line industry are briefly introduced. The primary purpose of this paper is to evaluate the extent to which loyalty schemes really can build loyalty. In order to do this, four categories of loyalty as identified in the literature are considered. Given existing criticisms of loyalty schemes it is concluded that such schemes have an important role to play in situations where no loyalty or spurious loyalty is evident. However, where sustainable loyalty is the ultimate goal, customer loyalty schemes are of importance only as part of a coherent value proposition.

Biofilms on Indwelling Urethral Catheters Produce Quorum-Sensing Signal Molecules In Situ and In Vitro

Abstract: Acylated homoserine lactones (AHLs) are chemical signals that mediate population density-dependent (quorum-sensing) gene expression in numerous gram-negative bacteria. In this study, gram-negative bacilli isolated from catheters were screened for AHL production by a cross-feeding assay utilizing an AHL-responsive Agrobacterium tumefaciens reporter strain. Positive reactions were obtained from 14 isolates of Pseudomonas aeruginosa; negative or weakly positive reactions were recorded for isolates of five other species. P. aeruginosa biofilms were then produced on catheters in a physical model of the bladder. Sections of colonized all-silicone catheters gave positive reactions for the quorum-sensing signal molecules as did sections that had been cleaned of biofilm and autoclaved. Control sections of unused catheters were negative in the tests. Sections from four of nine catheters that had been freshly removed from patients gave positive reactions for AHLs. Cleaned autoclaved sections of three of these catheters also gave strongly positive reactions for AHLs. These results demonstrate that AHLs are produced by biofilms as they develop on the catheters both in vitro in the model and in vivo in the patient’s bladder. They represent the first demonstration of AHL production by biofilms in a clinical setting.