bluuebunny/crossref_metadata_2025 huggingface dataset:
Challenging the boundaries of sameness: leadership through valuing difference
Authors: Walker Allan , Walker John
Published: July 2002

Argues that school leaders face tensions which result from simultaneous and contradictory influences towards sameness and difference. The tensions which influence leaders can be seen in varying forms at the global, macro‐political, policy and school levels. Established ways of working (sameness) continue to dominate school operation and leadership practices. Recommends that government and school leaders deal with these tensions by challenging the sameness underpinning school operation, through valuing and learning from difference within the school community. Suggests challenging sameness in schools can be grounded in valuing and learning from the differences comprising the school community.
Principals and school restructuring: conceptualising challenges as dilemmas
Authors: Dimmock Clive
Published: July 2002

This study aims, first, to chronicle the perceived dilemmas of a group of Australian principals whose worklives were preoccupied with school restructuring. Second, relying on empirical data, it develops a typology of dilemmas. This typology then forms the structure for a more detailed discussion of the nature and source of dilemmas encountered by the participating principals. Data were collected and analysed using qualitative methods, based on semi‐structured interviews with 20 Western Australian primary and secondary principals. The findings suggest two main types of dilemmas – general, values‐based personal‐professional dilemmas, called “states of mind”, and specific, practical, organisational dilemmas. It is argued that improving the knowledge base by using empirical studies and developing typologies and conceptual frameworks, is a necessary step in providing closer insights as to how school leaders perceive and manage the most intractable aspects of their worklives. This, is turn, could lead to improvements in leader preparation and training.
The effects of information system infrastructure and process improvements on supply‐chain time performance
Authors: Jayaram Jayanth , Vickery Shawnee K.
Published: July 2002

An empirical study of 57 top‐tier suppliers to the North American automotive industry examined the direct and complementary effects of information system infrastructure (ISI) and process improvements on time‐based performance. The results show that the three dimensions of ISI – design‐manufacturing integration (DMI), manufacturing technology (MT), and information technology (IT) – directly influenced at least one dimension of time‐based performance. For example, DMI influenced manufacturing lead time, MT influenced new product development time, and IT influenced customer responsiveness. Process improvement also directly influenced supply‐chain time performance. Finally, ISI and process improvement had a positive and complementary effect on time‐based performance. Specifically, the IT factor along with process improvement variables (standardization and concurrent engineering) had a complementary and significant positive influence on time‐based performance. The findings strongly support the idea of joint deployment of information system infrastructure and process improvement to streamline cycle time performance in a supply chain.
A systems perspective on supply chain measurements
Authors: Holmberg Stefan
Published: July 2002

Both practitioners and research scientists have noted a number of problems regarding measurement activities during the past decade. The problems reported suggest that measurement activities are fragmented both within and across organizations. Expands on a systems perspective on supply chain measurements and describes how problems can be communicated, understood and managed by developing methods and tools for describing interrelationships within supply chains. Empirical evidence from a case study of a Swedish home furnishing business supply chain provides data suggesting that firms within a supply chain cannot simply be categorized as either having adopted systems thinking or not. Rather, both structured models indicating a high degree of systems thinking, and problems showing fragmentation, are present. A performance model, which is used to reflect the systemic structure of an underlying supply chain and a potential integrator, is introduced and suggested as the focus of future research initiatives within supply chain measurements.
Natural convection in an inclined porous cavity with variable porosity and thermal dispersion effects
Authors: Hsiao Shih‐Wen
Published: July 2002

The variable porosity and thermal dispersion effects on natural convection in an inclined porous cavity are investigated numerically. The wall effect on porosity is approximated by an exponential function and its effect on thermal dispersion is modeled in terms of a dispersive length. Numerical results show that both variable porosity and thermal dispersion effects increase the temperature gradient adjacent to the wall resulting in the enhancement of surface heat flux. These effects become important when the dimensionless particle diameter is increased. The variable porosity effect increases the fluid velocity near the wall, consequently enhancing convective heat transfer. The Prandtl number effect on the Nusselt number is small for Prandtl number greater than one, but increases as the Prandtl number decreases below one. The effect of thermal conductivity ratio on the Nusselt number is greater at low Rayleigh numbers where conduction heat transfer is predominant. A comparison between theoretical and experimental results shows that the calculated Nusselt numbers which take into account variable porosity and thermal dispersion effects have the best agreement with experimental data.
Exporting Australian higher education: future strategies in a maturing market
Authors: Mazzarol Tim , Hosie Peter
Published: July 2002

Examines the current situation facing Australian higher education institutions engaged in the export of their services. Considers current trends in the world market for international education services, as well as current and future developments in the Australian higher education system. Recent research evidence suggests that the international market for education is reaching maturity. Contends that Australia’s international education sector, especially in the area of higher education, requires greater differentiation and more careful marketing in order to deal with this trend. Outlines some suggestions as to appropriate future strategies for the Australian international education sector.
Accreditation in business education
Authors: Lock Andrew
Published: July 2002

Business school accreditation has been long established in North America. Its development in the UK and Europe is of much more recent origin and has been fuelled primarily by concerns to protect the MBA brand. It is only recently that a European process of whole school accreditation (EQUIS) has emerged, and the process is now continuing with the “second wave” of schools. This paper traces the development of accreditation processes in the USA, the UK, across the European Union and Central and Eastern Europe. It also explores the implications of accreditation and recognition systems for providers and consumers of business qualifications, whether employers or prospective students. The relationship between these systems and national and institutional approaches to academic quality standards is explored. Finally, we analyse the future of the range of accrediting systems in the UK and the wider European Union.
A project planning process for business continuity
Authors: Karakasidis Kon
Published: July 2002

Discusses the formulation of a business recovery plan. As a starting point, presents the business recovery timeline model. Gives a framework of components to be considered in a business continuity project planning process, i.e. a risk reduction programme.
High performance teams and a climate of community
Authors: Beech Nic , Crane Oliver
Published: July 2002

This paper presents an empirically based study of an organisation’s attempt to improve from its existent structure of team working to a higher level of organisational performance through the development of enhanced, or high performance, teams. The research findings are contextualised by brief reviews of the literature in three areas: the contribution of people management to organisational performance, leadership and team working. It is argued that there is a convergence of theoretical development towards what is conceptualised in this paper as a climate of community. The empirical research took a multi‐method approach to examine the development from teams to high performance teams, which focused on “soft” processual inputs, but which had to have both qualitative and quantitative outcomes. The analysis revealed three factors which were crucial to development: transparency, checkability and a climate of community.
The rationality issue in land‐use planning
Authors: Sager Tore
Published: July 2002

There is a strong tradition among land‐use planners to conceive of their task as one of inserting rationality into public decision making. The idea of the rational selection of ends as well as means makes land‐use planners reluctant to take goals as given even if they insist on a difference between planning and politics. A retrospective outline shows how three prominent planning theorists handle the controversial question of rational ends. By applying Habermas’ communicative rationality and the bounded/unbounded distinction, the range of rationality concepts becomes sufficiently wide to serve as a basis for classifying most popular planning modes. With multiple forms of rationality, some new problems arise. How are we, for instance, to rationally choose among forms of rationality in a given situation, and how can the various forms be applied simultaneously?
Mechanical properties of short‐fibre layered composites: prediction and experiment
Authors: Zak G. , Haberer M. , Park C.B. , Benhabib B.
Published: July 2002

As a way of enhancing the mechanical properties of photopolymer‐based parts produced by layered manufacturing (LM) techniques, the use of short glass‐fibre reinforcements has been recently explored in the literature. This paper proposes a novel methodology that utilizes a modified rule‐of‐mixtures model for the prediction of the mechanical properties of such layered composites. The prediction process employs empirical data on (i) the fibre‐matrix interface, (ii) the fibres’ geometrical arrangement within the specimens (i.e. fibre‐orientation distribution), and (iii) the fibre‐length distribution. The effects of the fibre‐orientation and fibre‐length distributions are accounted for in the prediction model by the fibre‐length‐correction and orientation‐efficiency factors. Comparison of extensive experimental results and model‐based predictions of mechanical properties of layered composites demonstrated the effectiveness of the proposed estimation methodology.
Numerical prediction of temperature and density distributions in selective laser sintering processes
Authors: Bugeda Miguel Cervera Gabriel , Lombera Guillermo
Published: July 2002

A finite element model has been developed for the 3D simulation of the sintering of a single track during a selective laser sintering process (SLS). The model takes into account both the thermal and the sintering phenomena involved in the process. Owing to the continuous movement of the laser beam the model takes also into account the transient nature of the problem. This is transformed into a pseudo‐static one through a transformation of the coordinates system of the equations. Nevertheless, this transformation introduces a convective term into the heat equations that produces instabilities in the solution. These instabilities have been solved by using a stream upwind Petrov Galerkin (SUPG) strategy together with a shock capturing scheme. Finally, a fixed point strategy is used for the solution of the analysis. The model has been tested through the solution of some examples.
A noncanonical WD‐repeat protein from the cyanobacterium Synechocystis PCC6803: Structural and functional study
Authors: Hisbergues Michael , Gaitatzes Chrysanthe G. , Joset Françoise , Bedu Sylvie , Smith Temple F.
Published: July 2002

Synechocystis PCC6803 possesses several open reading frames encoding putative WD‐repeat proteins. One, the Hat protein, is involved in the control of a high‐affinity transport system for inorganic carbon that is active when the cells are grown under a limiting concentration of this carbon substrate. The protein is composed of two major domains separated by a hydrophobic linker region of 20 amino acid residues. The N‐terminal domain of Hat has no homolog in standard databases and does not display any particular structural features. Eleven WD repeats have been identified in the C‐terminal moiety. The region encompassing the four terminal WD repeats is essential for growth under a limiting inorganic carbon regime. The region encompassing the two most terminal WD repeats is required for the activity of the high‐affinity transport system. However, because the Hat protein is located in the thylakoids, it should not be itself an element of the transport system. The structural organization of the WD‐containing domain of Hat was modeled from the crystal structure of the G protein β subunit (with seven WD repeats) and of hemopexin (a structural analog with four blades). Functional and structural data argue in favor of an organization of the Hat WD moiety in two subdomains of seven and four WD repeats. The C‐terminal 4‐mer subdomain might interact with another, yet unknown, protein/peptide. This interaction could be essential in modulating the stability of the 4‐mer structure and, thus, the accessibility of this subdomain, or at least of the region encompassing the last two WD repeats.
TM Finder: A prediction program for transmembrane protein segments using a combination of hydrophobicity and nonpolar phase helicity scales
Authors: Deber Charles M. , Wang Chen , Liu Li‐Ping , Prior Andrew S. , Agrawal Shuchi , Muskat Brenda L. , Cuticchia A. Jamie
Published: July 2002

Based on the principle of dual prediction by segment hydrophobicity and nonpolar phase helicity, in concert with imposed threshold values of these two parameters, we developed the automated prediction program TM Finder that can successfully locate most transmembrane (TM) segments in proteins. The program uses the results of experiments on a series of host‐guest TM segment mimic peptides of prototypic sequence KK AAAXAAAAAXAAWAAXAAAKKKK‐amide (where X = each of the 20 commonly occurring amino acids) through which an HPLC‐derived hydropathy scale, a hydrophobicity threshold for spontaneous membrane insertion, and a nonpolar phase helical propensity scale were determined. Using these scales, the optimized prediction algorithm of TM Finder defines TM segments by first searching for competent core segments using the combination of hydrophobicity and helicity scales, and then performs a gap‐joining operation, which minimizes prediction bias caused by local hydrophilic residues and/or the choice of window size. In addition, the hydrophobicity threshold requirement enables TM Finder to distinguish reliably between membrane proteins and globular proteins, thereby adding an important dimension to the program. A full web version of the TM Finder program can be accessed at http://www.bioinformatics‐canada.org/TM/.
Coupling of antibodies via protein Z on modified polyoma virus‐like particles
Authors: Gleiter Stefan , Lilie Hauke
Published: July 2002

Therapeutic application of virus‐based delivery systems often implies a change of the tropism of these vectors. This can be achieved by insertion of polypeptides (e.g., antibody fragments) in viral coat proteins. Such fusion proteins have only been used in viral vectors so far and, as part of a virus, they have not been available for a detailed biophysical characterization. We analyzed a fusion protein called VP1‐Z, which is based on the polyoma virus coat protein VP1 and protein Z. Protein Z is an engineered antibody‐binding domain derived from protein A fromStaphylococcus aureus. The fusion VP1‐Z was constructed by insertion of protein Z in the HI‐loop of VP1. As wild‐type VP1, VP1‐Z formed pentameric capsomers and assembled to VLPs in vitro. The stability of these particles was very similar compared to that of VLPs of wild‐type VP1. Protein Z was fully structured in the fusion protein and was still capable of binding antibodies on the surface of VLPs of VP1‐Z. Using this fusion protein, we could change the tropism of polyoma VLPs toward cells presenting on their surface the antigen of the coupled antibody.
Sialidase‐like Asp‐boxes: Sequence‐similar structures within different protein folds
Authors: Copley Richard R. , Russell Robert B. , Ponting Chris P.
Published: July 2002

Sequence similarity is the most common measure currently used to infer homology between proteins. Typically, homologous protein domains show sequence similarity over their entire lengths. Here we identify Asp box motifs, initially found as repeats in sialidases and neuraminidases, in new structural and sequence contexts. These motifs represent significantly similar sequences, localized to β hairpins within proteins that are otherwise different in sequence and three‐dimensional structure. By performing a combined sequence‐ and structure‐based analysis we detect Asp boxes in more than nine protein families, including bacterial ribonucleases, sulfite oxidases, reelin, netrins, some lipoprotein receptors, and a variety of glycosyl hydrolases. Although the function common to each of these proteins, if any, remains unclear, we discuss possible functions of Asp boxes on the basis of previously determined experimental results and discuss different evolutionary scenarios for the origin of Asp‐box containing proteins.
Prediction of the transmembrane regions of β‐barrel membrane proteins with a neural network‐based predictor
Authors: Jacoboni Irene , Martelli Pier Luigi , Fariselli Piero , De Pinto Vito , Casadio Rita
Published: July 2002

A method based on neural networks is trained and tested on a nonredundant set of β‐barrel membrane proteins known at atomic resolution with a jackknife procedure. The method predicts the topography of transmembrane β strands with residue accuracy as high as 78% when evolutionary information is used as input to the network. Of the transmembrane β‐strands included in the training set, 93% are correctly assigned. The predictor includes an algorithm of model optimization, based on dynamic programming, that correctly models eight out of the 11 proteins present in the training/testing set. In addition, protein topology is assigned on the basis of the location of the longest loops in the models. We propose this as a general method to fill the gap of the prediction of β‐barrel membrane proteins.
Stabilization of hen egg white lysozyme by a cavity‐filling mutation
Authors: Ohmura Tadahiro , Ueda Tadashi , Ootsuka Keiichi , Saito Minoru , Imoto Taiji
Published: July 2002

Stabilization of a protein using cavity‐filling strategy has hardly been successful because of unfavorable van der Waals contacts. We succeeded in stabilizing lysozymes by cavity‐filling mutations. The mutations were checked by a simple energy minimization in advance. It was shown clearly that the sum of free energy change caused by the hydrophobicity and the cavity size was correlated very well with protein stability. We also considered the aromatic–aromatic interaction. It is reconfirmed that the cavity‐filling mutation in a hydrophobic core is a very useful method to stabilize a protein when the mutation candidate is selected carefully.
Sequencing of the ddl gene and modeling of the mutated D‐alanine:D‐alanine ligase in glycopeptide‐dependent strains of Enterococcus faecium
Authors: Gholizadeh Y. , Prevost M. , Van Bambeke F. , Casadewall B. , Tulkens P.M. , Courvalin P.
Published: July 2002

Glycopeptide dependence for growth in enterococci results from mutations in the ddl gene that inactivate the host D‐Ala:D‐Ala ligase. The strains require glycopeptides as inducers for synthesis of resistance proteins, which allows for the production of peptidoglycan precursors ending in D‐Ala‐D‐Lac instead of D‐Ala‐D‐Ala. The sequences of the ddl gene from nine glycopeptide‐dependent Enterococcus faecium clinical isolates were determined. Each one had a mutation consisting either in a 5‐bp insertion at position 41 leading to an early stop codon, an in‐frame 6‐bp deletion causing the loss of two residues (KDVA243‐246 to KA), or single base‐pair changes resulting in an amino acid substitution (E13 → G, G99 → R, V241 → D, D295 → G, P313 → L). The potential consequences of the deletion and point mutations on the 3‐D structure of the enzyme were evaluated by comparative molecular modeling of the E. faecium enzyme, using the X‐ray structure of the homologous Escherichia coli D‐Ala:D‐Ala ligase DdlB as a template. All mutated residues were found either to interact directly with one of the substrates of the enzymatic reaction (E13 and D295) or to stabilize the position of critical residues in the active site. Maintenance of the 3‐D structure in the vicinity of these mutations in the active site appears critical for D‐Ala:D‐Ala ligase activity.
Conformational characterization of oligomeric intermediates and aggregates in β‐lactoglobulin heat aggregation
Authors: Carrotta Rita , Bauer Rogert , Waninge Rianne , Rischel Christian
Published: July 2002

In one of the first studies of isolated intermediates in protein aggregation, we have used circular dichroism and fluorescence spectroscopy to characterize metastable oligomers that are formed in the early steps of β‐lactoglobulin heat aggregation. The intermediates show typical molten globule characteristics (secondary structure content similar to the native and less tight packing of the side chains), in agreement with the belief that partly folded states play a key role in protein aggregation. The far‐UV CD signal bears strong resemblance to that of a known folding intermediate. Cryo‐transmission electron microscopy of the aggregates reveals spherical particles with a diameter of about 50 nm and an internal threadlike structure. Isolated oligomers as well as larger aggregates bind the dye thioflavin T, usually a signature of the amyloid superstructures found in many protein aggregates. This result suggests that the structural motif recognized by thioflavin T can be formed in small oligomers.
Thymidylate kinase of Mycobacterium tuberculosis: A chimera sharing properties common to eukaryotic and bacterial enzymes
Authors: Munier‐Lehmann HÉLÈNE , Chaffotte Alain , Pochet Sylvie , Labesse Gilles
Published: July 2002

We have overexpressed in Escherichia coli the thymidylate kinase of Mycobacterium tuberculosis (TMPKmt). Biochemical and physico‐chemical characterization of TMPKmt revealed distinct structural and catalytic features when compared to its counterpart from yeast (TMPKy) or E. coli (TMPKec). Denaturation of the dimeric TMPKmt by urea under equilibrium conditions was studied by intrinsic fluorescence and circular dichroism (CD) spectroscopy. It suggested a three‐state unfolding mechanism with a monomeric intermediate. On the other hand, 3′‐azido‐3′‐deoxythymidine monophosphate (AZT‐MP), which is substrate for TMPKy and TMPKec acts as a potent competitive inhibitor for TMPKmt. We propose a structural model of TMPKmt in which the overall fold described in TMPKy and TMPKec is conserved and slight differences at the level of primary and 3D‐structure explain strong variations in the phosphorylation rate of substrate analogs. According to the model, we synthesized dTMP analogs acting either as substrates or specific inhibitors of TMPKmt. This approach based on slight structural differences among similar proteins could be applied to other essential enzymes for the design of new species‐specific antimicrobials.
Sleep‐waking discharge patterns of neurons recorded in the rat perifornical lateral hypothalamic area
Authors: Alam Md. Noor , Gong Hui , Alam Tarannum , Jaganath Rajesh , McGinty Dennis , Szymusiak Ronald
Published: July 2002

The perifornical lateral hypothalamic area (PF‐LHA) has been implicated in the control of several waking behaviours, including feeding, motor activity and arousal. Several cell types are located in the PF‐LHA, including projection neurons that contain the hypocretin peptides (also known as orexins). Recent findings suggest that hypocretin neurons are involved in sleep‐wake regulation. Loss of hypocretin neurons in the human disorder narcolepsy is associated with excessive somnolence, cataplexy and increased propensity for rapid eye movement (REM) sleep. However, the relationship of PF‐LHA neuronal activity to different arousal states is unknown. We recorded neuronal activity in the PF‐LHA of rats during natural sleep and waking. Neuronal discharge rates were calculated during active waking (waking accompanied by movement), quiet waking, non‐REM sleep and REM sleep. Fifty‐six of 106 neurons (53 %) were classified as wake/REM‐related. These neurons exhibited peak discharge rates during waking and REM sleep and reduced discharge rates during non‐REM sleep. Wake‐related neurons (38 %) exhibited reduced discharge rates during both non‐REM and REM sleep when compared to that during waking. Wake‐related neurons exhibited significantly higher discharge rates during active waking than during quiet waking. The discharge of wake‐related neurons was positively correlated with muscle activity across all sleep‐waking states. Recording sites were located within the hypocretin‐immunoreactive neuronal field of the PF‐LHA. Although the neurotransmitter phenotype of recorded cells was not determined, the prevalence of neurons with wake‐related discharge patterns is consistent with the hypothesis that the PF‐LHA participates in the regulation of arousal, muscle activity and sleep‐waking states.
Correlations between neuronal morphology and electrophysiological features in the rodent superficial dorsal horn
Authors: Grudt T. J. , Perl E. R.
Published: July 2002

Relationships between the morphology of individual neurones of the spinal superficial dorsal horn (SDH), laminae I and II, and their electrophysiological properties were studied in spinal cord slices prepared from anaesthetized, free‐ranging hamsters. Tight‐seal, whole‐cell recordings were made with pipette microelectrodes filled with biocytin to establish electrophysiological characteristics and to label the studied neurones. Neurones were categorized according to location and size of the somata, the dendritic and axonal pattern of arborization, spontaneous synaptic potentials, evoked postsynaptic currents, pattern of discharge to depolarizing pulses and current‐voltage relationships. Data were obtained for 170 neurones; 13 of these had somata in lamina I and 157 in lamina II. Stimulation of the segmental dorsal root evoked a prompt excitatory response in almost every neurone sampled (161/166) with nearly 3/4 displaying putative monosynaptic EPSCs. The majority of neurones (133/170) fitted one of several distinctive morphological categories. To a considerable extent, neurones with a common morphological configuration and neurite disposition shared electrophysiological characteristics. Five of the 13 lamina I neurones were relatively large with extensive dendritic arborization in the horizontal dimension and a prominent axon directed ventrally and contralaterally. These presumptive ventrolateral projection neurones differed structurally and electrophysiologically from the other lamina I neurones, which had ipsilateral, locally arborizing axons and/or branches entering the dorsal lateral funiculus. One hundred and twenty lamina II neurones fitted one of five morphological categories: islet, central, medial‐lateral, radial or vertical. Central cells were further divided into three groups on functional features. We conclude that the spinal SDH comprises many types of neurones whose morphological characteristics are associated with specific functional features implying diversity in functional organization of the SDH and in its role as a major synaptic termination for thin primary afferent fibres.
Analysis of variance study of the rat cortical layer 4 barrel and layer 5b neurones
Authors: Ito Muneyuki , Kato Miyuki
Published: July 2002

Unique formation of rodent cortical barrels by layer 4 neurones attracts study of the sensory function of cortical input stage neurones (layer 4) compared with that of output stage neurones (layer 5). We have recorded extracellular responses from rat somatosensory cortical neurones to deflections of contralateral vibrissae. Thirty‐two layer 4 barrel neurones and 29 layer 5b neurones were studied. Whisker stimulations were ramp‐and‐hold deflections with one of six different ramp velocities (100–2.5 mm s−1) and one of four different plateau amplitudes (2000–200 μm). Twenty‐four (6 × 4) different stimulus forms were applied to the tip of a whisker trimmed to 10 mm in a predetermined order in stimulus cycles of 20–50 repetitions. Spike counts for a period of 2560 ms in 10 ms bins were summed to construct a matrix of 24 peristimulus histograms for each neurone. Twenty‐four amplitude and 24 velocity values were computed from counts during the plateau and ramp phases, respectively. To determine the amplitude‐ and velocity dependence of a neurone, an amplitude F value (the ratio of variations among‐/within‐amplitude of the amplitude value) and a velocity F value (ratio of variations among‐/within‐velocity of the velocity value) were derived by analysis of variance. The amplitude F value of the layer 4 barrel neurones was greater than that of the layer 5b neurones (P < 0.0001). The velocity F value of the barrel neurones was smaller than that of the layer 5b neurones (P = 0.0226). The results suggests that barrel neurones and layer 5b neurones tend to detect amplitude and velocity components of whisker deflection, respectively.
The effects of common input characteristics and discharge rate on synchronization in rat hypoglossal motoneurones
Authors: Türker K. S. , Powers R. K.
Published: July 2002

Synchronous discharges between a pair of concurrently active motoneurones are thought to arise from the spike‐triggering effects of synaptic inputs shared by the pair. Although there are a number of quantitative indices that have been developed to estimate the strength of this common input, there is still some debate as to whether motoneurone discharge rate affects the values of these indices. The aim of the present study was to test the effects of motoneurone discharge rate on these synchronization indices using known common inputs. To achieve this aim we elicited repetitive discharge in rat hypoglossal motoneurones by combining a suprathreshold injected current step with superimposed noise to mimic the synaptic drive likely to occur during physiological activation. The amplitude of the current step was varied in different trials to achieve discharge rates from 5 to 22 Hz. We first examined the effect of discharge rate on the spike‐triggering efficacy of individual EPSPs. Motoneurones were more responsive to large EPSPs delivered at a low rate when their background discharge rate was relatively low and the probability of the EPSPs evoking an extra spike decreased with increasing discharge rate. However, the opposite dependence was found for small, high‐frequency EPSPs. We then compared the discharge records obtained in several trials in which the same EPSP train was applied repeatedly to the same cell firing at different background discharge rates. The effect of this ‘common input’ on motoneurone discharge probability was determined by compiling cross‐correlation histograms (CCHists) between the discharges of the same cell at different times. The common inputs induced synchronous discharge that gave rise to large central peaks in the CCHists. The relationship between the discharge rate and the level of synchronization changed depending on the synchronization indices used and the amplitude of the common EPSPs. When large EPSPs were used as the common input, the normalized probability of synchronous spikes declined as the discharge rate increased, regardless of the method of normalization used. In contrast, when the common input was composed of a large number of small EPSPs, similar to that likely to occur during physiological activation of motoneurones, different synchronization indices exhibited a positive, a negative or no dependence on the background discharge rate. Indices based on normalizing the number of synchronous spikes by either the number of discharges in the lower frequency train (E), or by the total number of discharges in both trains (S) showed no dependence on background discharge rate and therefore may be the most suitable for quantifying motoneurone synchrony over a range of background discharge rates.
Variable K+ channel subunit dysfunction in inherited mutations of KCNA1
Authors: Rea Ruth , Spauschus Alexander , Eunson Louise H. , Hanna Michael G. , Kullmann Dimitri M.
Published: July 2002

Mutations of KCNA1, which codes for the K+ channel subunit hKv1.1, are associated with the human autosomal dominant disease episodic ataxia type 1 (EA1). Five recently described mutations are associated with a broad range of phenotypes: neuromyotonia alone or with seizures, EA1 with seizures, or very drug‐resistant EA1. Here we investigated the consequences of each mutation for channel assembly, trafficking, gating and permeation. We related data obtained from co‐expression of mutant and wild‐type hKv1.1 to the results of expressing mutant‐wild‐type fusion proteins, and combined electrophysiological recordings in Xenopus oocytes with a pharmacological discrimination of the contribution of mutant and wild‐type subunits to channels expressed at the membrane. We also applied confocal laser scanning microscopy to measure the level of expression of either wild‐type or mutant subunits tagged with green fluorescent protein (GFP). R417stop truncates most of the C‐terminus and is associated with severe drug‐resistant EA1. Electrophysiological and pharmacological measurements indicated that the mutation impairs both tetramerisation of R417stop with wild‐type subunits, and membrane targeting of heterotetramers. This conclusion was supported by confocal laser scanning imaging of enhanced GFP (EGFP)‐tagged hKv1.1 subunits. Co‐expression of R417stop with wild‐type hKv1.2 subunits yielded similar results to co‐expression with wild‐type hKv1.1. Mutations associated with typical EA1 (V404I) or with neuromyotonia alone (P244H) significantly affected neither tetramerisation nor trafficking, and only altered channel kinetics. Two other mutations associated with a severe phenotype (T226R, A242P) yielded an intermediate result. The phenotypic variability of KCNA1 mutations is reflected in a wide range of disorders of channel assembly, trafficking and kinetics.
Postprandial hypotension in response to duodenal glucose delivery in healthy older subjects
Authors: O'Donovan Deirdre , Feinle Christine , Tonkin Anne , Horowitz Michael , Jones Karen Louise
Published: July 2002

Postprandial hypotension occurs frequently in older people and may lead to syncope and falls. Some recent studies suggest that the magnitude of the postprandial fall in blood pressure (BP) is influenced by the rate of gastric emptying. The aim of this study was, therefore, to determine whether the fall in blood pressure induced by intraduodenal glucose is influenced by the rate of nutrient delivery into the small intestine, bypassing the effects of gastric emptying. Eight healthy elderly subjects (four male and four female, age 70.3 ± 3.4 years) were studied on two separate days, in double‐blind, randomised order. Glucose was infused intraduodenally at a rate of either 1 or 3 kcal min−1, for 60 min, (0–60 min) followed by 0.9 % saline for a further 60 min (60–120 min). Blood pressure and heart rate were recorded at baseline and every 3 min during the study. Blood glucose and plasma insulin were also determined. Only the 3 kcal min−1 infusion caused a significant fall in systolic (P < 0.001) and diastolic (P < 0.0001) blood pressure and an increase in the heart rate (P < 0.0001). The rises in blood glucose (P < 0.01) and plasma insulin (P < 0.05) concentrations were greater during the 3 kcal min−1 infusion. We conclude that in healthy older subjects, the magnitude of the fall in blood pressure and increase in heart rate induced by intraduodenal glucose infusion is dependent on the rate of nutrient delivery into the small intestine. These results may have relevance to the treatment of postprandial hypotension.
Observation and Quantification of Gas Bubble Formation on a Mechanical Heart Valve
Authors: Lin Hsin-Yi , Bianccucci Brian A. , Deutsch Steven , Fontaine Arnold A. , Tarbell J. M.
Published: July 2002

Clinical studies using transcranial Doppler ultrasonography in patients with mechanical heart valves (MHV) have detected gaseous emboli. The relationship of gaseous emboli release and cavitation on MHV has been a subject of debate in the literature. To study the influence of cavitation and gas content on the formation and growth of stable gas bubbles, a mock circulatory loop, which employed a Medtronic-Hall pyrolytic carbon disk valve in the mitral position, was used. A high-speed video camera allowed observation of cavitation and gas bubble release on the inflow valve surfaces as a function of cavitation intensity and carbon dioxide CO2 concentration, while an ultrasonic monitoring system scanned the aortic outflow tract to quantify gas bubble production by calculating the gray scale levels of the images. In the absence of cavitation, no stable gas bubbles were formed. When gas bubbles were formed, they were first seen a few milliseconds after and in the vicinity of cavitation collapse. The volume of the gas bubbles detected in the aortic track increased with both increased CO2 and increased cavitation intensity. No correlation was observed between O2 concentration and bubble volume. We conclude that cavitation is an essential precursor to stable gas bubble formation, and CO2, the most soluble blood gas, is the major component of stable gas bubbles. [S0148-0731(00)00204-1]
Three-Dimensional Finite Element Analysis of Several Internal and External Pelvis Fixations
Authors: Garcı´a J. M. , Doblare´ M. , Seral B. , Seral F. , Palanca D. , Gracia L.
Published: July 2002

The Finite Element Method (FEM) can be used to analyze very complex geometries, such as the pelvis, and complicated constitutive behaviors, such as the heterogeneous, nonlinear, and anisotropic behavior of bone tissue or the noncompression, nonbending character of ligaments. Here, FEM was used to simulate the mechanical ability of several external and internal fixations that stabilize pelvic ring disruptions. A customized pelvic fracture analysis was performed by computer simulation to determine the best fixation method for each individual treatment. The stability of open-book fractures with external fixations at either the iliac crests or the pelvic equator was similar, and increased greatly when they were used in combination. However, external fixations did not effectively stabilize rotationally and vertically unstable fractures. Adequate stabilization was only achieved using an internal pubis fixation with two sacroiliac screws. [S0148-0731(00)00905-5]
A Three-Dimensional Thermomechanical Model of Contact Between Non-Conforming Rough Surfaces
Authors: Liu Shuangbiao , Wang Qian
Published: July 2002

A necessary step in understanding failure problems of tribological elements is to investigate the contact performance of rough surfaces subjected to frictional heating. It is essential that the interfacial variables are obtained through solving the interactive thermomechanical contact problem. This paper studies the three dimensional thermomechanical contact of non-conforming rough surfaces, the model of which includes the normal surface displacements caused by the contact pressure, frictional shear, and frictional heating. Influence coefficients and frequency response functions for elastic and thermoelastic displacements, as well as those for temperature rises, are investigated for model construction. In order to develop an accurate and efficient solver, the numerical algorithms with the discrete convolution and fast Fourier transform techniques and the single-loop conjugated gradient method are used. The model modules are numerically verified and the thermomechanical performance of the rough surfaces in a point contact is studied.
Developments in Flaw Evaluation for CANDU Reactor Zr-Nb Pressure Tubes
Authors: Scarth Douglas A. , Smith Ted
Published: July 2002

Delayed hydride cracking (DHC) in Zr-2.5Nb alloy material is of interest to the CANDU (CANada Deuterium Uranium) industry in the context of the potential to initiate DHC at a blunt flaw in a CANDU reactor pressure tube. The material is susceptible to DHC when there is diffusion of hydrogen atoms to the flaw, precipitation of hydride platelets, and development of a hydrided region at the flaw root. The hydrided region can then fracture to the extent that a crack forms, and is able to grow by the DHC crack growth mechanism. The existing CANDU blunt flaw DHC evaluation procedure is based on a threshold peak flaw-tip stress for DHC initiation that is independent of flaw geometry. Work is underway to improve the existing blunt flaw DHC evaluation procedure by developing a methodology that takes into account the effect of flaw geometry parameters. This methodology can, in principle, be applied to any flaw that is found during in-service inspection. The methodology is based on representing the stress relaxation due to hydride formation, and crack initiation, by a process zone. This approach has been used successfully in other engineering applications. A description of how the process-zone methodology can be used to quantify the effect of flaw geometry on the threshold peak stress for DHC initiation is provided. A model that is suitable for actual engineering applications is described, and the engineering model illustrates the dependency of the threshold peak stress for DHC initiation on flaw geometry. Agreement between engineering model predictions and experimental results is reasonable. Various aspects of the DHC initiation problem that are being addressed, in addition to flaw geometry, are described.
An Intersonic Slip Pulse at a Frictional Interface Between Dissimilar Materials
Authors: Adams G. G.
Published: July 2002

Two homogeneous and isotropic elastic half-spaces are acted upon by remote normal and shear tractions. The applied shear stress is less than that which is required to produce overall sliding of the two bodies. The possible existence of a slip pulse is investigated, i.e., a finite-width region, on the interface, of altered normal and shear stress which satisfies the Amontons-Coulomb law of friction. Pulses which travel at a speed which is greater than the minimum shear wave speed and less than the maximum dilatational wave of the two bodies, are of interest in this investigation. Such pulses are shown to exist for sufficient friction and for modest mismatches in material combinations. The pulse is weakly singular at the leading edge and bounded at the trailing edge. Furthermore it travels at speeds just below the lesser dilatational wave speed and in the opposite direction of sliding of the lower wave-speed material. In addition, a pair of equations are given which relate the interfacial normal and shear stress to the interfacial slip velocity. These relations are analogous to the subsonic results of Weertman, but are valid for an arbitrary speed range.
Modeling and Optimization of End Effector Layout for Handling Compliant Sheet Metal Parts
Authors: Ceglarek D. , Li H. F. , Tang Y.
Published: July 2002

Material handling of compliant parts is one of the most critical and underresearched problems in the sheet metal stamping industry. The fundamental shortcoming of currently studied material handling systems for sheet metal stamping is the lack of analysis of its impact on part dimensional quality and production throughput. This paper addresses this problem by development of a generic methodology for modeling and optimization of part holding end-effector layout in order to minimize part dimensional deformation during handling operations. The methodology extends the design of “N-2-1” fixturing layout by adding part movability conditions. It considers part CAD model, handling direction and motion kinematic parameters to determine the best end effector layout. This methodology is realized by integrating FEM part and loading modeling with the optimization algorithm. It can be implemented into the design stage of a stamping line so that the trial and error process, which is current industrial practice, can be greatly shortened and the production throughput increased. Experimental results verify the proposed part holding end-effector layout methodology.
Thermal Interaction at the Interface Between a Porous Medium and an Impermeable Wall
Authors: Kim Sung Jin , Kim Duckjong
Published: July 2002

The present work investigates a heat transfer phenomenon at the interface between a porous medium and an impermeable wall subject to a constant heat flux at the bottom. Currently, two possible thermal boundary conditions (which are called the First Approach and the Second Approach) at the interface are used interchangeably for the thermal analysis of convection in a channel filled with a porous medium. The focus of this paper is to determine which of these thermal boundary conditions is more appropriate in accurately predicting the heat transfer characteristics in a porous channel. To this end, we numerically examine the heat transfer at the interface between a microchannel heat sink (an ideally organized porous medium) and a finite-thickness substrate. From the examination, it is clarified that the heat flux distribution at the interface is not uniform for an impermeable wall with finite thickness. This means that a non-uniform distribution of the heat flux (First Approach) is physically reasonable. When the First Approach is applied to the thermal boundary condition, an additional boundary condition based on the local thermal equilibrium assumption at the interface is used. This additional boundary condition is applicable except in the case of a very thin impermeable wall. Hence, for practical situations, the First Approach with a local thermal equilibrium assumption at the interface is suggested as an appropriate thermal boundary condition. In order to confirm our suggestion, convective flows both in a microchannel heat sink and in a sintered porous channel subject to a constant heat flux condition are analyzed by using the two Approaches separately as a thermal boundary condition at the interface. The analytically obtained thermal resistance of the microchannel heat sink and the numerically obtained overall Nusselt number for the sintered porous channel are shown to be in close agreement with available experimental results when our suggestion for the thermal boundary condition at the interface is applied.
Kinetostatic Modeling of N-DOF Parallel Mechanisms With a Passive Constraining Leg and Prismatic Actuators
Authors: Zhang Dan , Gosselin Cle´ment M.
Published: July 2002

This paper introduces several new types of parallel mechanisms with prismatic actuators whose degree of freedom is dependent on a constraining passive leg connecting the base and the platform. A general kinetostatic model is established for the analysis of the structural rigidity and accuracy of this family of mechanisms. The geometric model of this class of mechanisms is first introduced. Then, a lumped kinetostatic model is proposed in order to account for joint and link compliances. Additionally, the inverse kinematics and velocity equations are given for both rigid-link and flexible-link mechanisms. Finally, a few examples are given to illustrate the results.