Showing papers by "University of Bath published in 1997"

Endlessly single-mode photonic crystal fiber.

Abstract: We made an all-silica optical fiber by embedding a central core in a two-dimensional photonic crystal with a micrometer-spaced hexagonal array of air holes. An effective-index model confirms that such a fiber can be single mode for any wavelength. Its useful single-mode range within the transparency window of silica, although wide, is ultimately bounded by a bend-loss edge at short wavelengths as well as at long wavelengths.

A Participatory Inquiry Paradigm

Abstract: This article starts with a critique of Guba and Lincoln's outline of competing paradigms for research, in particular arguing that the constructivist position fails to account for experiential knowi...

Phase-matched excitation of whispering-gallery-mode resonances by a fiber taper

Abstract: We show that high-Q whispering-gallery modes in fused-silica microspheres can be efficiently excited by an optical fiber taper. By adjusting the taper diameter to match the ropagation constant of the mode in the taper with that of the resonant mode of interest, one can couple more than 90% of the light into the sphere. This represents a significant improvement in excitation efficiency compared with other methods and is, we believe, the most efficient excitation of a high- Q microcavity resonance by a monomode optical fiber yet demonstrated.

Arbitrage with Fractional Brownian Motion

Abstract: Fractional Brownian motion has been suggested as a model for the movement of log share prices which would allow long–range dependence between returns on different days. While this is true, it also allows arbitrage opportunities, which we demonstrate both indirectly and by constructing such an arbitrage. Nonetheless, it is possible by looking at a process similar to the fractional Brownian motion to model long–range dependence of returns while avoiding arbitrage.

Bacterial templating of ordered macrostructures in silica and silica-surfactant mesophases

Abstract: The synthesis of inorganic frameworks with specified and organized pore networks is of potential importance in catalysis1,2, separation technology3 and biomaterials engineering4,5. Ordered arrangements of porous channels have been produced in silica-based materials by post-synthetic removal of surfactant templates from inorganic–organic mesostructures6,7. The resulting pore sizes are commensurate with the packing dimensions of the organic molecules, and are currently limited to length scales of up to 10nm. Here we show how a bacterial superstructure, consisting of a thread of coaligned multicellular filaments of Bacillus subtilis8,9, can be used to extend the length scale of inorganic materials patterning. We produce ordered macroporous fibres of either amorphous silica or ordered mesoporous silica6,7 (MCM-41) by template-directed mineralization of the interfilament spaces followed by removal of organic material by heating to 600°C. The inorganic macrostructures consist of a macroporous framework of 0.5-μm-wide channels with curved walls of either silica or mesoporous silica, 50 to 200 nm in thickness. The formation of ordered pores in the MCM-41 replica on both the mesoscopic and macroscopic length scales illustrates how supramolecular and supercellular templates might be combined for the fabrication of inorganic materials with structural hierarchy.

Synthesis of cadmium sulphide superlattices using self-assembled bacterial S-layers

Abstract: Methods for organizing materials at the nanometre scale have advanced tremendously in recent years1,2. One important objective is the synthesis of patterned arrays of inorganic nanocrystals3,4,5,6, whose optical, electronic and magnetic properties might find technological uses, for example as memory elements. Techniques such as colloidal crystallization7,8,9, monolayer deposition10,11,12, multilayer casting13, molecular crosslinking14,15, the use of complementary interactions16,17 and the synthesis of nanoparticles in patterned etch pits18 have been used to organize nanocrystals into superlattices. Here we describe the use of bacterial S-layers — self-assembled, two-dimensionally ordered films of proteins that feature in many bacterial cell walls — as templates for the in situ nucleation of ordered two-dimensional arrays of cadmium sulphide nanocrystals about 5 nm in size. Nucleation of the inorganic phase is confined to the pores between subunits in the S-layers. Two-tier stacks of nanoparticles can be formed in the presence of double-layered protein crystals. The structural diversity of S-layers19,20, their ease of self-assembly on a wide range of substrates and the potential for surface chemical modification suggest that this approach could be exploited to offer a wide range of ordered nanoparticle arrays.

The Consultancy Process — An Insecure Business?†

Abstract: This paper examines the practices and perceptions of management consultants and their clients. The existing literature, which emphasizes managerial anxiety in accounting for the persistent use of consultants and, relatedly, the transience of management ideas is critically developed. It is argued that such accounts tend to be abstracted from the power relations of organizations and capitalism and to portray management as passive victims of confident consultants. An alternative interactive model is proposed, which is based on reciprocal and self-defeating concerns of clients and consultants to secure a sense of identity and control. This is explored empirically, highlighting the hitherto neglected active role of managers in resisting consultancy and the pressures and anxieties experienced by consultants. The account selectively draws on secondary sources as well as interview, documentary and survey research of IT strategy consultants and clients in the UK financial services sector.

Finding Small Roots of Univariate Modular Equations Revisited

Abstract: An alternative technique for finding small roots of univariate modular equations is described. This approach is then compared with that taken in (Coppersmith, 1996), which links the concept of the dual lattice (see (Cassels, 1971)) to the LLL algorithm (see (Lenstra et al., 1982)). Timing results comparing both algorithms are given, and practical considerations are discussed. This work has direct applications to several low exponent attacks on the RSA cryptographic scheme (see (Coppersmith, 1996)).

Whatever Happened to Organizational Anthropology? A Review of the Field of Organizational Ethnography and Anthropological Studies

Abstract: L'A. rappelle que le champ d'etude du comportement organisationnel a ete, a l'origine, cree par des anthropologues, notamment par les etudes pionnieres de Hawthorne, et celles de W. F. Whyte, premier anthropologue social a avoir ecrit un ouvrage de reference sur le comportement organisationnel ; mais les deux domaines se sont separes et les etudes organisationnelles ont graduellement perdu contact avec les qualites essentielles de l'anthropologie. Cet article propose une speculation sur la nature de la quete ethnographique et sur ce que l'on gagnerait a reconcilier etudes organisationnelles et anthropologie. Il passe en revue l'etat des recherches dans ce champ et souligne les differents aspects (methode, paradigme, rhetorique et ecriture) de l'ethnographie que le champ organisationnel devra considerer s'il est amene a prendre le tournant anthropologique. Apres avoir fait le constat du manque d'historicite, de contextualite et de processualite de la theorie des organisations, il note que, de son cote, l'anthropologie repond a de telles demandes et, dans ce sens, est porteuse de reelles alternatives pour le developpement futur de ce domaine de recherche. Enfin il insiste sur ce qu'il considere comme les qualites dictinctives de la recherche ethnographique et sur ce qu'elles pourraient apporter a la recherche sur les organisations si elles etaient plus largement adoptees

Social Assistance in Oecd Countries

Abstract: This article presents selected results from the first comparative study of social assistance across all 24 countries of the OECD. The scope of social assistance, discussed in the first section, is drawn to include all means-tested benefits in cash and kind, including those which provide benefits to higher income groups. The second section then presents in formation on the main programmes in each country, expenditures and groups of beneficia ries, trends over time, administrative struc tures, and operation of means tests. It concludes by developing a new measure of assistance benefit levels with which to evaluate different countries' systems. The third section distils from the country differences eight pat terns, or 'assistance regimes', varying from the limited, discretionary, decentralized models of Switzerland and Norway to the extensive, national, rights-based programmes of the English-speaking world; and from the relative generosity of Scandinavia and Australia to the low, marginalizing benefits of th...

Continuation of blowup solutions of nonlinear heat equations in several space dimensions

Abstract: The possible continuation of solutions of the nonlinear heat equation in R N R+ ut = u m + u p with m> 0 ;p > 1 ; after the blowup time is studied and the different continuation modes are discussed in terms of the exponents m and p Thus, for m +p 2 we find a phenomenon of nontrivial continuation where the regionfx : u(x;t )= 1g is bounded and propagates with finite speed This we call incomplete blowup For N 3 and p>m ( N +2 )= (N 2) we find solutions that blow up at finite t = T and then become bounded again for t>T Otherwise, we find that blowup is complete for a wide class of initial data In the analysis of the behavior for large p, a list of critical exponents appears whose role is described We also discuss a number of related problems and equations We apply the same technique of analysis to the problem of continuation after the onset of extinction, for example, for the equation ut = u m u p ;m > 0 :

The Crystal Structure of Citrate Synthase from the Hyperthermophilic Archaeon Pyrococcus furiosus at 1.9 Å Resolution

Abstract: The crystal structure of the closed form of citrate synthase, with citrate and CoA bound, from the hyperthermophilic Archaeon Pyrococcus furiosus has been determined to 1.9 A. This has allowed direct structural comparisons between the same enzyme from organisms growing optimally at 37 degrees C (pig), 55 degrees C (Thermoplasma acidophilum) and now 100 degrees C (Pyrococcus furiosus). The three enzymes are homodimers and share a similar overall fold, with the dimer interface comprising primarily an eight alpha-helical sandwich of four antiparallel pairs of helices. The active sites show similar modes of substrate binding; moreover, the structural equivalence of the amino acid residues implicated in catalysis implies that the mechanism proceeds via the same acid-base catalytic process. Given the overall structural and mechanistic similarities, it has been possible to make detailed structural comparisons between the three citrate synthases, and a number of differences can be identified in passing from the mesophilic to thermophilic to hyperthermophilic citrate synthases. The most significant of these are an increased compactness of the enzyme, a more intimate association of the subunits, an increase in intersubunit ion pairs, and a reduction in thermolabile residues. Compactness is achieved by the shortening of a number of loops, an increase in the number of atoms buried from solvent, an optimized packing of side chains in the interior, and an absence of cavities. The intimate subunit association in the dimeric P. furiosus enzyme is achieved by greater complementarity of the monomers and by the C-terminal region of each monomer folding over the surface of the other monomer, in contrast to the pig enzyme where the C-terminus has a very different fold. The increased number of intersubunit ion pairs is accompanied by an increase in the number involved in networks. Interestingly, all loop regions in the P. furiosus enzyme either are shorter or contain additional ion pairs compared with the pig enzyme. The possible relevance of these structural features to enzyme hyperthermostability is discussed.

Variations in self-determination across the stages of change for exercise in adults.

Abstract: This study explored the relationship between self-determination in the regulation of exercise behavior and stage of change for exercise. Deci and Ryan (1985, 1990) outlined a continuum of behavioral regulation that ranges from non-self-determined regulation (external regulation) to completely self-determined regulation (intrinsic regulation). Prochaska and DiClemente (1984) outlined five stages of behavior change that range from no thoughts of changing (precontemplation) to maintenance of change (maintenance). In our study, 314 individuals completed measures of regulation in exercise behavior and stage of change for exercise. Discriminant function analysis revealed that those in the latter stages of change were more self-determined in their behavioral regulation than those in the early stages of change. An analysis of variance indicated that self-determination increased from the lower to the upper stages of change. Results endorse the importance of motivational considerations in understanding the change process.

Nonlinear propagation applied to the improvement of resolution in diagnostic medical ultrasound

Abstract: Medical B-mode scanners operating under conditions typically encountered during clinical work produce ultrasonic wave fields that undergo nonlinear distortion. In general, the resulting harmonic beams are narrower and have lower sidelobe levels than the fundamental beam, making them ideal for imaging purposes. This work demonstrates the feasibility of nonlinear harmonic imaging in medical scanners using a simple broadband imaging arrangement in water. The ultrasonic system comprises a 2.25-MHz circular transducer with a diameter of 38 mm, a membrane hydrophone, also with a diameter of 38 mm, and a polymer lens with a focal length of 262 mm. These components are arranged coaxially giving an imaging geometry similar to that used in many commercial B-scanners, but with a receiver bandwidth sufficient to record the first four harmonics. A series of continuous wave and pulse-echo measurements are performed on a wire phantom to give 1-D transverse pressure profiles and 2-D B-mode images, respectively. The refle...

Roles, responsibilities, and relationships in mentoring: a literature review and agenda for research

Abstract: Mentoring in the preparation and education of teachers is of interest and concern in many countries. In the USA, mentoring plays an important role in the inservice education of teachers (Little, 1992). In other countries, including England and Australia, the time that preservice or student teachers spend in schools on initial teacher education (ITE) courses has increased in recent years (Department for Education, 1992; Tisher, 1995) accompanied by necessary redistribution of responsibility and resources from higher education institutions (HEIs) to school. Schools and mentors are increasingly equal partners with the university in the preparation of new teachers. Some have greeted the shift with unreserved enthusiasm: It offer(s) the opportunity for a quantum increase in the power and effectiveness of ITT (initial teacher training) (Tomlinson, 1995, p. 2). Others have responded with alarm, warning that mentoring may become simply a label for a new bureaucracy of teacher training (Smith & Alfrod, 1993, p. 104). The mentoring literature illuminates the roots of both the enthusiasm and the alarm. The inadequacy of theory-practice models of teacher education (Goodlad, 1990) and the increased adoption of reflective practice approaches to teacher education (Schon, 1987) concentrate attention on the work of schools in ITE. For some, the moves toward school-based training are the overdue empowerment of teachers as equal partners in the education of student teachers (Wilkin, 1992b). Recent research into how student teachers learn to teach has increasingly emphasized the need for student teachers to recognize previously constructed images and beliefs about teaching and examine the impact of these history-based personal beliefs on their professional development (Calderhead & Robson, 1991; Cole & Knowles, 1993; Holt-Reynolds, 1992; Johnson, 1993; Watzlawick, 1978). This emphasis casts doubt on the applicability of traditional academic HEI environments as conducive settings for learning to teach (Elliott & Calderhead, 1993). Much literature on mentoring is either descriptive or declarative with little analysis or theoretical underpinning to the study and practice of mentoring. This paucity is cause for concern. The reasons for the largely pragmatic approaches characterizing much of the current literature are easily understood. For example, the speed with which legislation in England (Department for Education, 1992) had to be implemented led to an almost inevitable emphasis on the management of the transition. This emphasis was exacerbated by implementation happening within schools, institutions where the prevailing culture tends to be one where doing is given greater value than thinking (Fenstermacher, 1992; Richert, 1994). In consequence, several studies provide overviews of mentoring and its management (McIntyre, Hagger & Burn, 1994; Wilkin, 1992b), but few examine or analyze the intricacies of mentoring interactions (Glickman & Bey, 1990), how mentoring relationships operate between the individuals involved, or how and what student teachers learn from their mentoring experiences. In this article, I review literature relevant to an examination of the nature of these interactions between mentor and student teacher. This review has limited scope and does not represent a full or comprehensive review of all mentoring literature. I do not consider many important issues, such as mentors' pedagogical and subject knowledge, the impact of institutional cultures, and the management and implementation of mentoring programs. Approaches to Examining the Literature on Mentoring Four distinct but related approaches characterize research into mentoring. First, some writers have examined the particular expertise of the different personnel involved in the training of student teachers and developed distinct roles and responsibilities for those involved. Second, other writers have taken a functional approach, identifying the stages of development that student teachers go through and developing corresponding models of mentoring designed to meet the mentee's current needs. …

Photocarcinogenesis: an overview

Abstract: Photocarcinogenesis represents the sum of a complex of simultaneous and sequential biochemical events that ultimately lead to the occurrence of skin cancer These events, initiated by UV radiation of appropriate wavelength, include the formation of DNA photoproducts: DNA repair; mutation of proto-oncogenes and tumor suppressor genes; UV-production of radical species with subsequent effects on mutation and extra-nuclear function; and other epigenetic events that influence the course of carcinogenesis The epigenetic influences may include immunological responses, antioxidant defenses, and dietary factors This review represents an effort to provide current research results in the aforementioned areas and an attempt to meld these events into a comprehensive overview of photocarcinogenesis If effective prevention and intervention strategies for skin cancer are to developed, a more thorough understanding of the disease process is imperative

Environmental/economic dispatch using fuzzy logic controlled genetic algorithms

Abstract: The paper presents the application of a fuzzy logic controlled genetic algorithm (FCGA) to power system environmental/economic dispatch. The authors first propose an improved genetic algorithm with two fuzzy controllers based on some heuristics to adaptively adjust the crossover probability and mutation rate during the optimisation process. The implementation of the fuzzy crossover and mutation controllers is described. The proposed FCGA can be applied to wide range of optimisation problems. The validity of the proposed algorithm is illustrated on environmental/economic dispatch of a six-generator power system. Its performance is compared with conventional GAs and the Newton-Raphson method. The results are very encouraging.

A Review of the Concept of Visual Literacy

Abstract: Many people from very diverse disciplines have attempted to define the concept of Visual Literacy (VL), but with little general consensus so far. This is probably due to the fact that those representing the different disciplines and paradigms are each wanting to interpret Visual Literacy in a way that reflects and flatters their contribution or way of thinking. As a consequence, a theoretical concept with seemingly little practical value has been created, but cannot be used productively until an agreed definition is established. It is self evident that if a concept does not have a broadly accepted definition, if the theory behind it is confusing, and if its viability on practical terms is a matter of continuing controversy, then the only reasonable way to cope with it is to abandon it. Nevertheless, with the exception of very few and of minor importance cases, no serious attempt has ever been made towards discarding VL altogether.

Synthesis of Barium Sulfate Nanoparticles and Nanofilaments in Reverse Micelles and Microemulsions

Abstract: Supersaturated reverse micelles and microemulsions containing either AOT (sodium bis(2-ethylhexylsulfosuccinate)), C12EO4 (poly(oxyethylene-4-dodecyl ether)), or DDAB (didodecyldimethylammonium bromide) surfactants have been used as organized reaction microenvironments for barium sulfate precipitation. Nanoclusters of amorphous barium sulfate, 2−4 nm in size, were formed in association with BaNaAOT reverse micelles. In contrast, highly elongated filaments of crystalline barium sulfate, with lengths up to 100 μm and aspect ratios of 1000, were formed in BaNaAOT microemulsions. The individual filaments were single crystals of barite elongated predominantly along the [010] axis and in some instances consisted of coaligned nanofilaments, 20−50 nm in width. Similar reactions in C12EO4 reverse micelles and microemulsions afforded barite nanocrystals, 5−7 nm in dimension and tabular-shaped barite crystals, up to 400 nm in size, respectively. Rhombic crystals of barite, approximatety 200 nm in size, were deposite...

The Potential Approach to the Term Structure of Interest Rates and Foreign Exchange Rates

Abstract: It is possible to specify a model for interest rates in various ways, by giving the dynamics of the spot rate or of the forward rates, for example. A less well–developed approach is to specify the law of the state–price density process directly. In abstract, the state–price density process is a positive supermartingale, and the theory of Markov processes provides a rich framework for the generation of examples of such things. We show how this can be done, and provide simple examples (some familiar, some new) where prices of derivatives can be computed very easily. One benefit of the potential approach is that it becomes very easy to model the yield curve in many countries at once, together with the exchange rates between them.

Molecular recognition of human angiogenin by placental ribonuclease inhibitor—an X-ray crystallographic study at 2.0 Å resolution

Abstract: Human placental RNase inhibitor (hRI), a leucine-rich repeat protein, binds the blood vessel-inducing protein human angiogenin (Ang) with extraordinary affinity (Ki <1 fM). Here we report a 2.0 A resolution crystal structure for the hRI-Ang complex that, together with extensive mutagenesis data from earlier studies, reveals the molecular features of this tight interaction. The hRI-Ang binding interface is large and encompasses 26 residues from hRI and 24 from Ang, recruited from multiple domains of both proteins. However, a substantial fraction of the energetically important contacts involve only a single region of each: the C-terminal segment 434-460 of hRI and the ribonucleolytic active centre of Ang, most notably the catalytic residue Lys40. Although the overall docking of Ang resembles that observed for RNase A in the crystal structure of its complex with the porcine RNase inhibitor, the vast majority of the interactions in the two complexes are distinctive, indicating that the broad specificity of the inhibitor for pancreatic RNase superfamily proteins is based largely on its capacity to recognize features unique to each of them. The implications of these findings for the development of small, hRI-based inhibitors of Ang for therapeutic use are discussed.

A transformation of respondently conditioned stimulus function in accordance with arbitrarily applicable relations

Abstract: Adult male subjects saw a sexual film clip paired with a nonsense syllable (C1). Similarly, an emotionally neutral film clip was paired with a second nonsense syllable (C3). Responses to the nonsense syllables were recorded as skin resistance responses. Subjects were also trained in a series of related conditional discriminations, using the C1 and C3 stimuli, from which the following equivalence relations were predicted; A1-B1-C1, A2-B2-C2, and A3-B3-C3. Some subjects were given matching-to-sample (equivalence) tests after the conditional discrimination training (Experiment 1), whereas others were not (Experiment 2). Subjects were tested for a transformation of eliciting functions by presenting the A1 and A3 stimuli, which were related through equivalence to C1 and C3, respectively. Five of the 6 subjects who showed significantly greater conditioned responses to C1 than to C3, also showed significantly greater skin resistance responses to A1 than to A3. Two additional subjects demonstrated a transformation of an eliciting stimulus function in accordance with five-member equivalence relations (Experiment 3), and another 5 subjects demonstrated similar effects in accordance with the relations of sameness and opposition (Experiment 4).