bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of support conditions on the fire behaviour of steel and composite beams
Authors: Moss Peter J. , Buchanan Andrew H. , Seputro Jenny , Wastney Clayton , Welsh Richard 
Published: April 2004

AbstractThe fire behaviour of a structural steel beam or a steel and concrete composite beam in a fire compartment depends on many factors including the nature of the supports at the ends of the beam.This paper describes a detailed analytical investigation into the effects of support conditions on the fire performance of steel and composite steel‐concrete beams exposed to linearly increasing temperature with time, as well as to standard and parametric fires.The support conditions include simply supported, fully fixed, and a range of intermediate cases, providing varying levels of axial and flexural restraint. In each case, a comparison of the deflected shape with the evolving internal forces shows unusual but predictable behaviour, strongly dependent on the stress–strain relationship of the steel. In addition to the standard support conditions, a spring was used to simulate the effect of axial restraint provided by adjacent spans of a multi‐span beam. This case showed that the spring stiffness had a very considerable influence on the behaviour of the beam and the time to failure under an increasing fire temperature.This paper gives new insight into the structural performance of steel and composite beams, observed in recent fires such as the eight storey steel frame at Cardington. There are major implications for structural designers. Copyright © 2004 John Wiley & Sons, Ltd.
Key events in the structural response of a composite steel frame structure in fire
Authors: Usmani A. S. , Lamont S. 
Published: April 2004

AbstractThe structural design of composite steel frame buildings in fire has traditionally been based on single element behaviour, under standard fire conditions. This approach is widely recognized as unsatisfactory and there is a general consensus that it leads to excessive fire protection being applied to the steel members based on grossly inaccurate assumptions about whole structure behaviour in fire. A great deal of research has been carried out to understand the mechanics of whole structure behaviour in fire. This paper presents a summary of this research by computational analysis of a small but realistic steel‐frame composite structure with mainly unprotected beams and fully fire‐protected columns.The main purpose of this paper is to highlight a number of key events that define the response of the steel frame structure in fire. Some of these events can be observed in real fire tests (such as Cardington), however, others have only been discovered by careful analysis of the output data from computational analyses supported by fundamental theoretical analysis. For instance, an event has been discovered entirely from computational modelling of the above‐mentioned small structure with no similar events observed in experiments or reported in the literature. This particular event involves a sudden and sharp increase in deflection of the whole floor at particular steel temperatures during the fire. If this event occurred in a real structure, it might cause an overload of the floor because of the dynamic effect of this instability (unaccounted for in the static analysis performed here) leading to compartment breach or collapse.All these events will be presented in order of appearance as the compartment fire progresses and the member temperatures increase. The reason for the occurrence of each event will be discussed supported by simple analysis of the relevant structural mechanics and brief discussion of design implications. Copyright © 2004 John Wiley & Sons, Ltd.
Examples of fire engineering design for steel members, using a standard curve versus a new parametric curve
Authors: Barnett C. R. , Clifton G. C. 
Published: April 2004

AbstractThis paper presents examples of the differences that can occur when a standard time‐temperature curve and a parametric time‐temperature curve are used to determine temperatures likely to be reached by uninsulated and insulated steel members during a fire. For low and moderate structural fire severity situations, determination of the adequacy of a steel member by comparing the temperature reached in a ‘design fire’ with the limiting temperature based on the member heat sink characteristics, extent of insulation and utilization factor is becoming increasingly common fire engineering design practice. For this it is important to have an accurate and widely applicable parametric fire model as is practicable.The standard time‐temperature curve used in the examples is the ISO 834 curve. The two parametric time‐temperature curves used in the paper are the Eurocode parametric curve and a recently developed one termed the ‘BFD curve’. The latter has been found to fit the results of a wide range of actual fire tests more closely than do existing parametric curves and is mathematically simpler in form.The shape of the BFD curve and the parameters used to define it bear a strong relationship to both the pyrolysis coefficient (R/Avhv0.5) and the opening factor, F02. The curve also models the development of fire without the need for time shifts. It uses a single and relatively simple equation to generate the temperature of both the growth and decay phases of a fire in a building and only three factors are required to derive the curve. These factors are (i) the maximum gas temperature, (ii) the time at which this maximum temperature occurs, and (iii) a shape constant for the curve. If desired, the shape constant can be different on the growth and the decay sides to model a very wide range of natural fire conditions and test results.This paper presents an overview of the background to the BFD curve. It then illustrates its use in a simple fire engineering design application, where the adequacy of a steel beam is checked using the Eurocode parametric curve and the BFD curve to represent the fire. Copyright © 2004 John Wiley & Sons, Ltd.
Improvement of MEAs for Direct‐Methanol Fuel Cells by Tuned Layer Preparation and Coating Technology
Authors: Lindermeir A. , Rosenthal G. , Kunz U. , Hoffmann U. 
Published: April 2004

AbstractLarge scale production of membrane electrode assemblies (MEAs) for fuel cells requires a fabrication technology, which is not only based on electrochemical phenomena but also takes into account aspects of materials processing and conversion. For the fabrication of MEAs for DMFC a production sequence consisting of wet ball‐milling, wet spray coating and calendering was developed at the ICVT Clausthal. This has a proven ability for the preparation of diffusion backings and catalyst layers with high reproducibility. To improve MEA performance, investigations concerning the influence of layer fabrication and composition are made with respect to the resulting morphology of the structures. Intermediates and MEAs are evaluated by conductivity measurements, determination of permeability values and current density‐voltage characteristics supported by SEM and optical microscopy.
Recent Advances to the Development of Low‐Temperature Solid Oxide Fuel Cells
Authors: Xia C. , Lang Y. , Meng G. 
Published: April 2004

AbstractWhile existing solid oxide fuel cell (SOFC) technology has demonstrated much higher energy efficiency with minimal pollutant emission than the conventional technologies, the costs of the current SOFC systems are still prohibitive for broad commercialization. To be economically competitive, both the cost of materials and the cost of fabrication must be dramatically reduced. One effective approach to cost reduction is to reduce the operating temperature; many cell components, including interconnect, heat exchangers, and other structural or balance‐of‐plant components, can be fabricated from much less expensive materials when the operating temperature is sufficiently low. However, the interfacial polarization resistances increase rapidly as the operating temperature is reduced. This paper will address the critical issues in creating electrodes and interfaces of minimal polarization resistance in order to minimize internal electrochemical losses at low temperatures. In particular, design, fabrication, and characterization of composite electrodes consisting of silver and bismuth oxide will be discussed. Another approach to cost reduction is to reduce the cost of fabrication. Dense electrolyte films supported on porous anodes fabricated by screen‐printing and dry press will be presented.
The Influence of Mass Transfer on a Porous Fuel Cell Electrode
Authors: Sun Y.‐P. , Scott K. 
Published: April 2004

AbstractA one‐dimensional model for a porous fuel cell electrode using a liquid electrolyte with dissolved reactant is presented. The model consists of a Poisson, second‐order ordinary differential equation, describing the effect of the electric field and a one‐dimensional; Fickian diffusion, second‐order ordinary differential equation describing the concentration variation associated with diffusion. The model accounts for mass transport and heterogeneous electrochemical reaction. The solution of this model is by the approximate Adomian polynomial method and is used to determine lateral distributions of concentration, overpotential and current density and overall cell polarisation. The model is used to simulate the effects of important system and operating parameters, i.e. local diffusion rates, and mass transport coefficients and electrode polarisation behaviour.
The Status and Prospects of Key Materials for the Proton Exchange Membrane Fuel Cell at the Dalian Institute of Chemical Physics
Authors: Yu H. , Yi B. 
Published: April 2004

AbstractThe development of key materials for proton exchange membrane fuel cells including electrocatalysts, electrodes, proton exchange membranes and bipolar plates in DICP are introduced in this paper. The basic fundamentals and the most recent progress in the key materials have been discussed. The preparation methods of electrocatalysts have been reviewed. Characteristics of various electrode preparation methods are also introduced. A new electrode design and prospective manufacturing methods are indicated. The disadvantages of the present exchange membrane are presented. The results of proton exchange membrane degradation mechanisms are given. Studies of the Nafion/PTFE membrane, blending membrane and PBI membrane are reviewed. Developmental trends of the membrane in both the medium and long term are previewed. Different bipolar plates are compared.
Ethanol and Acetaldehyde Adsorption on a Carbon‐Supported Pt Catalyst: A Comparative DEMS Study
Authors: Wang H. , Jusys Z. , Behm R.J. 
Published: April 2004

AbstractThe adsorption of ethanol and acetaldehyde on carbon Vulcan supported Pt fuel cell catalyst and the electrochemical desorption of the adsorption products were studied, using electrochemical measurements and differential electrochemical mass spectrosmetry (DEMS), under continuous flow conditions. Faradaic current adsorption transients at different constant adsorption potentials, which also include CO adsorption for comparison, show pronounced effects of the adsorption potential and the nature of the reactant molecule. Acetaldehyde adsorption is much faster than ethanol adsorption at all potentials. Pronounced Had induced blocking effects for ethanol adsorption are observed at very cathodic adsorption potentials, < 0.16 V, while for acetaldehyde adsorption this effect is much less significant. Comparison of the adsorption charge for CO adsorption with the H‐upd charge allows differentiation between H‐displacement and double‐layer charging effects. Continuous bulk oxidation is observed for both reactants at potentials > 0.31 V; for acetaldehyde adsorption, increasing bulk reduction is found at low potentials. Based on the electron yield per CO2 molecule formed and on the similarity with the CO stripping characteristics the dominant stable adsorbate is CO, coadsorbed with smaller amounts of (partly oxidized) hydrocarbon decomposition fragments, which are also oxidized at higher potentials (> 0.85 V) and which can be reductively desorbed as methane or, to a very small extent, as ethane. The presence of small amounts of adsorbed C2 species and the oxidative dissociation of these species in the main CO oxidation potential range is clearly demonstrated by increased methane desorption after a potential shift to 0.85 V. The data demonstrate that the Pt/Vulcan catalyst is very reactive for C‐C bond breaking upon adsorption of these reactants.
Early stages of oligodendrocyte development in the embryonic murine spinal cord proceed normally in the absence of Hoxa2
Authors: Nicolay Danette J. , Doucette J. Ronald , Nazarali Adil J. 
Published: April 2004

AbstractRecent discoveries have enhanced our knowledge of the transcriptional control of oligodendrocyte (OG) development. In particular, the transcription factors (TFs) Olig2, Pax6, and Nkx2.2 have been shown to be important in the specification and/or maturation of the OG lineage. Although numerous other TFs are expressed by OGs, little is known regarding their role(s) in oligodendrogenesis. One such TF is the homeobox gene Hoxa2, which was recently shown to be expressed by O4+ pro‐oligodendrocytes. The objectives of this study were to examine the expression of Hoxa2 during the early stages of OG development, as well as to determine whether Hoxa2 is required for specification and/or early maturation of OGs. Immunocytochemical analysis of primary mixed glial cultures demonstrated that Hoxa2 was expressed throughout oligodendrogenesis, diminishing only with the acquisition of a myelinating phenotype. Serial transverse spinal cord sections from embryonic days 12.5, 14.25, 16, and 18 Hoxa2+/+, Hoxa2+/−, and Hoxa2−/− mice were subjected to single and double immunohistochemical analysis in order to examine Hoxa2, Olig2, Nkx2.2, and Pax6 expression profiles. Results obtained from Hoxa2+/+ and Hoxa2+/− mice suggested that Hoxa2 was expressed by migratory oligodendroglial cells. In addition, comparison of spinal cord sections obtained from Hoxa2+/+, Hoxa2+/−, and Hoxa2−/− mice suggested that specification and early maturation of OGs proceeded normally in the absence of Hoxa2, since there were no obvious alterations in the expression patterns of Olig2, Nkx2.2, and/or Pax6. Hence, although Hoxa2 is expressed throughout OG development, it does not appear to be critical for early stages of oligodendrogenesis in the murine spinal cord. © 2004 Wiley‐Liss, Inc.
Olfactory ensheathing cell grafts have minimal influence on regeneration at the dorsal root entry zone following rhizotomy
Authors: Riddell John S. , Enriquez‐Denton Manuel , Toft Andrew , Fairless Richard , Barnett Susan C. 
Published: April 2004

AbstractThe effectiveness of grafts of olfactory ensheathing cells (OECs) as a means of promoting functional reconnection of regenerating primary afferent fibers was investigated following dorsal root injury. Adult rats were subjected to dorsal root section and reanastomosis and at the same operation a suspension of purified OECs was injected at the dorsal root entry zone and/or into the sectioned dorsal root. Regeneration of dorsal root fibers was then assessed after a survival period ranging from 1 to 6 months. In 11 animals, electrophysiology was used to look for evidence of functional reconnection of regenerating dorsal root fibers. However, electrical stimulation of lesioned dorsal roots failed to evoke detectable cord dorsum or field potentials within the spinal cord of any of the animals examined, indicating that reconnection of regenerating fibers with spinal cord neurones had not occurred. In a further 11 rats, immunocytochemical labeling and biotin dextran tracing of afferent fibers in the lesioned roots was used to determine whether regenerating fibers were able to grow into the spinal cord in the presence of an OEC graft. Although a few afferent fibers could be seen to extend for a limited distance into the spinal cord, similar minimal in‐growth was seen in control animals that had not been injected with OECs. We therefore conclude that OEC grafts are of little or no advantage in promoting the in‐growth of regenerating afferent fibers at the dorsal root entry zone following rhizotomy. © 2004 Wiley‐Liss, Inc.
Specific characteristic of radial glia in the human fetal telencephalon
Authors: Zecevic Nada 
Published: April 2004

AbstractPhenotypic characteristics of cells in the developing human telencephalic wall were analyzed using electron microscopy and immunocytochemistry with various glial and neuronal cell markers. The results suggest that multiple defined cell types emerge in the neocortical proliferative zones and are differentially regulated during embryonic development. At 5–6 weeks gestation, three major cell types are observed. Most proliferating ventricular zone (VZ) cells are labeled with radial glial (RG) markers such as vimentin, glial fibrillary acidic protein (GFAP), and glutamate astrocyte‐specific transporter (GLAST) antibodies. A subpopulation of these RG cells also express the neuronal markers β III‐tubulin, MAP‐2, and phosphorylated neurofilament SMI‐31, in addition to the stem cell marker nestin, indicating their multipotential capacity. In addition, the presence of VZ cells that immunoreact only with neuronal markers indicates the emergence of restricted neuronal progenitors. The number of multipotential progenitors in the VZ gradually decreases, whereas the number of more restricted progenitors increases systematically during the 3‐month course of human corticogenesis. These results suggest that multipotential progenitors coexist with restricted neuronal progenitors and RG cells during initial corticogenesis in the human telencephalon. Since the multipotential VZ cells disappear during the major wave of neocortical neurogenesis, the RG and restricted neuronal progenitors appear to serve as the main sources of cortical neurons. Thus, the diversification of cells in human VZ and overlying subventricular zone (SVZ) begins earlier and is more pronounced than in rodents. © 2004 Wiley‐Liss, Inc.
Interleukin‐10 attenuates production of HSV‐induced inflammatory mediators by human microglia
Authors: Marques Cristina P. , Hu Shuxian , Sheng Wen , Cheeran Maxim C‐J. , Cox Diana , Lokensgard James R. 
Published: April 2004

AbstractInfection of the central nervous system (CNS) with herpes simplex virus (HSV)‐1 initiates a rapidly progressive, necrotizing, and fatal encephalitis in humans. Even with the advent of antiviral therapy, effective treatments for HSV‐1 brain infection are limited because the cause of the resulting neuropathogenesis is not completely understood. We previously reported that human microglial cells, while nonproductively infected, respond to HSV‐1 by producing robust amounts of pro‐inflammatory mediators, such as tumor necrosis factor(TNF), interleukin (IL)‐1β, CCL5 (RANTES), and CXCL10 (IP‐10). Although initiation of immune responses by glial cells is an important protective mechanism in the CNS, unrestrained inflammatory responses may result in irreparable brain damage. To elucidate the potential immunomodulatory role of anti‐inflammatory cytokines, we investigated the effects of IL‐4, IL‐10, and transforming growth factor (TGF)‐β on microglial cell cytokine and chemokine production in response to HSV‐1. Results from these studies demonstrated a consistent IL‐10‐mediated suppression of TNF‐α (60% ± 2%), IL‐1β (68% ± 3%), CCL5 (62 ± 4%), but not CXCL10 production by HSV‐1‐infected microglial cells. This inhibition was associated with decreased HSV‐1‐induced activation of NF‐κB. These results suggest that IL‐10 has the ability to regulate microglial cell production of immune mediators and thereby, dampen the pro‐inflammatory response to HSV‐1. © 2004 Wiley‐Liss, Inc.
Heterosynaptic metaplastic regulation of synaptic efficacy in CA1 pyramidal neurons of rat hippocampus
Authors: Le Ray Didier , Fernández De Sevilla David , Belén Porto Ana , Fuenzalida Marco , Buño Washington 
Published: April 2004

AbstractThe induction threshold, and the magnitude and direction of changes in synaptic plasticity may depend on the previous history of neuronal activity. This phenomenon, termed “metaplasticity,” could play an important role in integration processes by coordinating the modulation of synapses. Although metaplasticity has been analyzed extensively, its underlying cellular mechanisms remain largely unknown. Using in vitro electrophysiological and computer simulation approaches, we investigated the contribution of the slow Ca2+‐dependent afterhyperpolarization (sAHP) in the metaplastic control of the induction of long‐term potentiation (LTP) at convergent CA3‐CA1 pyramidal neuron synapses. We report that classical conditioning protocols may lead to the simultaneous induction of a sustained homosynaptic LTP and a potentiation of the sAHP that endured ≈1 h. The sAHP potentiation dramatically altered the spike responses of the CA1 pyramidal neuron. Of particular interest was the reduction of the CA1 neuron excitability and, consequently, of the capacity of a nonpotentiated synaptic input to elicit spikes while the sAHP was potentiated. This reduction in excitability temporarily prevented nonpotentiated synaptic inputs to exhibit an LTP induced by presynaptic tetanization. This metaplasticity was strongly resistant to increases in the magnitude of synaptic tetanization protocols. We propose that this heterosynaptic metaplasticity, mediated by intrinsic cellular mechanisms, triggered by brief periods of activity, and relying on changes of a slow Ca2+‐activated K+ current, may contribute to adjusting the efficacy of synaptic connections and shaping network behavior to regulate integration processes. © 2004 Wiley‐Liss, Inc.
Biocompatibility and biodegradation of a bone composite containing tricalcium phosphate and genipin crosslinked gelatin
Authors: Yao Chun‐Hsu , Liu Bai‐Shuan , Hsu Shan‐Hui , Chen Yueh‐Sheng , Tsai Chin‐Chuan 
Published: April 2004

AbstractA biodegradable composite (GGT) containing tricalcium phosphate ceramic particles and genipin crosslinked gelatin was developed for use as a bone substitute. The objective of this study was to assess the biocompatibility and the osteoconductivity of the GGT composite on new bone formation in vitro. Additionally, biodegradation and biocompatibility of the GGT composite in animals were investigated. Results of the GGT composites cocultured with osteoblasts showed that the concentration of genipin used as a crosslinking agent should be <0.5 wt % to avoid cytotoxicity. For in vivo degradation studies, we found that when the concentration of genipin in the composite <0.5 wt % was not enough to fully crosslink the gelatin, it results in a rapid degradation of the gelatin–genipin mixture. However, we also found that the foreign body capsule surrounding the GGT composite containing 1.0 wt % of the genipin was much thicker than that in the other three groups, that is, the composites containing 0.05, 0.1, and 0.5 wt % of the genipin. We therefore concluded that the ideal concentration of genipin used in the GGT was 0.5 wt %. Finally, we examined the organ culture units, which were maintained in cultured medium for 5 weeks. Morphology of tissue was observed and the quantitative evaluation of the regenerated bone was determined. We found that the GGT composites containing 0.5 wt % of the genipin had an excellent biocompatibility and could produce osteoconduction for the regenerating bone tissues. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 69A: 709–717, 2004
New regular embeddings of n‐cubes Qn
Authors: Kwon Young Soo 
Published: April 2004

AbstractWe investigate highly symmetrical embeddings of the n‐dimensional cube Qn into orientable compact surfaces which we call regular embeddings of Qn. We derive some general results and construct some new families of regular embeddings of Qn. In particular, for n = 1, 2,3(mod 4), we classify the regular embeddings of Qn which can be expressed as balanced Cayley maps. © 2004 Wiley Periodicals, Inc. J Graph Theory 46: 297–312, 2004