Hybrid Systems (hybrid + system)

Distribution by Scientific Domains
Distribution within Engineering


Selected Abstracts


Electropolymerized Self-Assembled Monolayers of a 3,4-Ethylenedioxythiophene-Thiophene Hybrid System,

ADVANCED FUNCTIONAL MATERIALS, Issue 15 2008
Maiténa Oçafrain
Abstract Self-assembled monolayers (SAMs) of a conjugated bithiophenic system connected to an alkanethiol chain have been deposited on gold surface. The electroactive bithiophenic system involves a 3,4-ethylenedioxythiophene (EDOT) unit and a thiophene ring on which an alkanethiol is attached at the internal , -position via a sulfide linkage. The analysis of the structure of the SAMs by IR spectroscopy, ellipsometry, contact angle measurement and X-ray photoelectron spectroscopy (XPS) provides consistent results indicating compact monolayers in which the alkyl linkers are arranged in an almost vertical fashion while the bithiophenic-conjugated systems are essentially parallel to the surface. Cyclic voltammetry shows that application of a few potential scans to SAMs immersed in a medium containing only a supporting electrolyte leads to the typical electropolymerization curves while the CV of the electrooxized monolayer exhibits a reversible cyclic voltammogram characteristic of a stable electroactive extended conjugated system. The characterization of the electropolymerized monolayers by IR spectroscopy, ellipsometry, contact angle measurement, and XPS indicates compact monolayers. The analysis of the current voltage characteristics of the monolayers by conducting AFM before and after electrooxidation shows that the enhancement of the effective conjugation resulting from electropolymerization leads to a significant increase of the transport properties. [source]


Stability analysis and guaranteed domain of attraction for a class of hybrid systems: an LMI approach

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 5 2003
S. Palomino Bean
Abstract This paper presents sufficient conditions for the regional stability problem for switched piecewise affine systems, a special class of Hybrid Systems. This class of systems are described by an affine differential equation of the type x,=A(,)x+b(,), where x denotes the continuous state vector and , is a vector of logical variables that modifies the local model of the system in accordance with the continuous dynamics. Using a Lyapunov function of the type v(x)=x,P(x)x, we present LMI conditions that, when feasible, guarantee local stability of the origin of the switched system. Examples of switched affine systems are used to illustrate the results. Copyright © 2003 John Wiley & Sons, Ltd. [source]


Seismic behaviour of hybrid systems made of PR composite frames coupled with dissipative bracings

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 6 2008
C. Amadio
Abstract The paper investigates the dynamic behaviour of hybrid systems made of partially restrained (PR) steel,concrete composite frames coupled with viscoelastic dissipative bracings. A numerical model that accounts for both the resisting mechanisms of the joint and the viscoelastic contribution of the dissipative bracing is introduced and briefly discussed. The model is first validated against experimental outcomes obtained on a one-storey two-bay composite frame with partial strength semi-rigid joints subjected to free vibrations. A number of time-history analyses under different earthquake ground motions and peak ground accelerations are then carried out on the same type of frame. The purpose is to investigate the influence of the type of beam-to-column connection and property of the viscoelastic bracing on the performance of the hybrid system. The inherent stiffness of the bare PR frame and the plastic hysteresis of the beam-to-column joints, which always lead to only limited damage in the joint, are found to provide a significant contribution to the overall structural performance even under destructive earthquakes. This remark leads to the conclusion that the viscoelastic bracing can be effectively used within the hybrid system. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Efficient Removal of Anionic Surfactants Using Mesoporous Functionalised Hybrid Materials

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 25 2009
Carmen Coll
Abstract A new hybrid system for surfactant removal from water has been developed using mesoporous material (MCM-41) functionalised with suitable binding groups. Solid S1, S2 and S3 were prepared by reaction of the mesoporous material with N -methyl- N, -(propyltrimethoxysilyl)imidazolium chloride, (3-aminopropyl)trimethoxysilane or 4-[(triethoxysilylpropylthio)methyl]pyridine, respectively. The functionalised materials were characterised following standard solid-state techniques. The final prepared solids consist of a siliceous MCM-41-type mesoporous support with the surface decorated by imidazolium, amine and pyridine binding groups suitable for anion coordination. Equilibrium adsorption studies of linear alkylbenzenesulfonate (LAS) using S1, S2 and S3 in water have been carried out. The obtained adsorption data were correlated with a Langmuir isotherm model that gives an acceptable description of the experimental data. The maximum surfactant uptake/binding site (mol,mol,1) and the surfactant adsorption capacity (mmol,g,1) for materials S1, S2 and S3 were calculated. S1 shows a positive-charged functionalised surface that is independent of the pH of the solution, whereas S2 and S3 are functionalised with neutral groups that need to be protonated in order to display electrostatic binding interactions with the anionic surfactants. Therefore, whereas the adsorption capacity of S1 is pH-independent, S2 and S3 display larger LAS adsorption at acidic pH. The adsorption ability at a certain pH follows the order S1 >> S3 > S2. A remarkable maximum surfactant adsorption of 1.5 mmol per gram of material was observed for S1 at neutral pH. S2 and S3 behave as poorer adsorbents and show maximum surfactant adsorption of 0.197 and 0.335 mmol per gram of material, respectively, at pH 2.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]


Insights into the design of a hybrid system between Anabaena ferredoxin-NADP+ reductase and bovine adrenodoxin

FEBS JOURNAL, Issue 4 2003
Merche Faro
The opportunity to design enzymatic systems is becoming more feasible due to detailed knowledge of the structure of many proteins. As a first step, investigations have aimed to redesign already existing systems, so that they can perform a function different from the one for which they were synthesized. We have investigated the interaction of electron transfer proteins from different systems in order to check the possibility of heterologous reconstitution among members of different chains. Here, it is shown that ferredoxin-NADP+ reductase from Anabaena and adrenodoxin from bovine adrenal glands are able to form optimal complexes for thermodynamically favoured electron transfer reactions. Thus, electron transfer from ferredoxin-NADP+ reductase to adrenodoxin seems to proceed through the formation of at least two different complexes, whereas electron transfer from adrenodoxin to ferredoxin-NADP+ reductase does not take place due because it is a thermodynamically nonfavoured process. Moreover, by using a truncated adrenodoxin form (with decreased reduction potential as compared with the wild-type) ferredoxin-NADP+ reductase is reduced. Finally, these reactions have also been studied using several ferredoxin-NADP+ reductase mutants at positions crucial for interaction with its physiological partner, ferredoxin. The effects observed in their reactions with adrenodoxin do not correlate with those reported for their reactions with ferredoxin. In summary, our data indicate that although electron transfer can be achieved in this hybrid system, the electron transfer processes observed are much slower than within the physiological partners, pointing to a low specificity in the interaction surfaces of the proteins in the hybrid complexes. [source]


Photo-induced Charge Transfer and Relaxation of Persistent Charge Carriers in Polymer/Nanocrystal Composites for Applications in Hybrid Solar Cells

ADVANCED FUNCTIONAL MATERIALS, Issue 23 2009
Marc Daniel Heinemann
Abstract The photo-induced charge transfer and the dynamics of persistent charge carriers in blends of semiconducting polymers and nanocrystals are investigated. Regioregular poly(3-hexylthiophene) (P3HT) is used as the electron donor material, while the acceptor moiety is established by CdSe nanocrystals (nc-CdSe) prepared via colloidal synthesis. As a reference system, organic blends of P3HT and [6,6]-phenyl C61 -butyric acid methyl ester (PCBM) are studied as well. The light-induced charge transfer between P3HT and the acceptor materials is studied by photoluminescence (PL), photo-induced absorption (PIA) and light-induced electron spin resonance spectroscopy (LESR). Compared to neat P3HT samples, both systems show an intensified formation of polarons in the polymer upon photo-excitation, pointing out successful separation of photogenerated charge carriers. Additionally, relaxation of the persistent charge carriers is investigated, and significant differences are found between the hybrid composite and the purely organic system. While relaxation, reflected in the transient signal decay of the polaron signal, is fast in the organic system, the hybrid blends exhibit long-term persistence. The appearance of a second, slow recombination channel indicates the existence of deep trap states in the hybrid system, which leads to the capture of a large fraction of charge carriers. A change of polymer conformation due to the presence of nc-CdSe is revealed by low temperature LESR measurements and microwave saturation techniques. The impact of the different recombination behavior on the photovoltaic efficiency of both systems is discussed. [source]


Estimation of orthotropic thermal conductivity of honeycomb material

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 8 2002
Nagahisa Ogasawara
Abstract An experimental,computational hybrid system for measurement of thermal conductivity of orthotropic materials is developed. The system consists of two experimental parts and a finite element analysis part. First, the temperature distribution generated by uniform heating is measured with a thermal video system, and the thermal conductivity of Z direction is calculated. Second, the temperature distribution generated by small area heating is measured with the system. In the final step, thermal transfer analyses simulating the experiment support efficient data, and thermal conductivity of in-plane directions is estimated by comparison between experimental and analytical temperature distributions. The orthotropic equivalent thermal conductivity of honeycomb materials obtained by this system agreed with the theoretical values. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(8): 617,625, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10063 [source]


Tunnel stability analysis during construction using a neuro-fuzzy system

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 15 2005
José Luis Rangel
Abstract This paper presents an alternative strategy to evaluate the stability of tunnels during the design and construction stages based on a hybrid system, composed by neural, neuro-fuzzy and analytical solutions. A prototype of this system is designed using a database formed by 261 cases, 45 real and the rest synthetic. This system is capable of reproducing the displacements induced at the periphery of the tunnel before and after support installation. The stability of the excavation process is evaluated using a criterion that considers dimensionless parameters based on the shear strength of the media, the induced deformation level in the ground, the plastic radii and the advance of excavation without support. The efficiency and validity of the prototype is verified with two examples of actual tunnels, one included in the database used to train the system and the other not included. The results of both examples show a better approximation than other commonly used techniques. Copyright © 2005 John Wiley & Sons, Ltd. [source]


2D nearly orthogonal mesh generation

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2004
Yaoxin Zhang
Abstract The Ryskin and Leal (RL) system is the most widely used mesh generation system for the orthogonal mapping. However, when this system is used in domains with complex geometry, particularly in those with sharp corners and strong curvatures, serious distortion or overlapping of mesh lines may occur and an acceptable solution may not be possible. In the present study, two methods are proposed to generate nearly orthogonal meshes with the smoothness control. In the first method, the original RL system is modified by introducing smoothness control functions, which are formulated through the blending of the conformal mapping and the orthogonal mapping; while in the second method, the RL system is modified by introducing the contribution factors. A hybrid system of both methods is also developed. The proposed methods are illustrated by several test examples. Applications of these methods in a natural river channel are demonstrated. It is shown that the modified RL systems are capable of producing meshes with an adequate balance between the orthogonality and the smoothness for complex computational domains without mesh distortions and overlapping. Copyright © 2004 John Wiley & Sons, Ltd. [source]


Hybrid adaptive control for non-linear uncertain impulsive dynamical systems

INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 6 2005
Wassim M. Haddad
Abstract A direct hybrid adaptive control framework for non-linear uncertain hybrid dynamical systems is developed. The proposed hybrid adaptive control framework is Lyapunov-based and guarantees partial asymptotic stability of the closed-loop hybrid system; that is, asymptotic stability with respect to part of the closed-loop system states associated with the hybrid plant states. Furthermore, hybrid adaptive controllers guaranteeing attraction of the closed-loop system plant states are also developed. Finally, two numerical examples are provided to demonstrate the efficacy of the proposed hybrid adaptive stabilization approach. Copyright © 2004 John Wiley & Sons, Ltd. [source]


Analysis of the current methods used to size a wind/hydrogen/fuel cell-integrated system: A new perspective

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 12 2010
H. G. Geovanni
Abstract As an alternative to the production and storage of intermittent renewable energy sources, it has been suggested that one can combine several renewable energy technologies in one system, known as integrated or hybrid system, that integrate wind technology with hydrogen production unit and fuel cells. This work assesses the various methods used in sizing such systems. Most of the published papers relate the use of simulation tools such as HOMER, HYBRID2 and TRNSYS, to simulate the operation of different configurations for a given application in order to select the best economic option. But, with these methods one may not accurately determine certain characteristics of the energy resources available on a particular site, the profiles of estimated consumption and the demand for hydrogen, among other factors, which will be the optimal parameters of each subsystem. For example, velocity design, power required for the wind turbine, power required for the fuel cell and electrolyzer and the storage capacity needed for the system. Moreover, usually one makes excessive use of bi-parametric Weibull distribution function to approximate the histogram of the observed wind to the theoretical, which is not appropriate when there are bimodal frequency distributions of wind, as is the case in several places in the world. A new perspective is addressed in this paper, based on general system theory, modeling and simulation with a systematic approach and the use of exergoeconomic analysis. There are some general ideas on the advantages offered in this method, which is meant for the implementation of wind/hydrogen/fuel cell-integrated systems and in-situ clean hydrogen production. Copyright © 2009 John Wiley & Sons, Ltd. [source]


Integrated model framework for the evaluation of an SOFC/GT system as a centralized power source

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 1 2004
Michihisa Koyama
Abstract New power generation technologies are expected to reduce various environmental impacts of providing electricity to urban regions for some investment cost. Determining which power generation technologies are most suitable for meeting the demand of a particular region requires analysis of tradeoffs between costs and environmental impacts. Models simulating different power generation technologies can help quantify these tradeoffs. An Internet-based modelling infrastructure called DOME (distributed object-based modelling environment) provides a flexible mechanism to create integrated models from independent simulation models for different power generation technologies. As new technologies appear, corresponding simulation models can readily be added to the integrated model. DOME was used to combine a simulation model for hybrid SOFC (solid oxide fuel cell) and gas turbine system with a power generation capacity and dispatch optimization model. The integrated models were used to evaluate the effectiveness of the system as a centralized power source for meeting the power demand in Japan. Evaluation results indicate that a hybrid system using micro-tube SOFC may reduce CO2 emissions from power generation in Japan by about 50%. Copyright © 2004 John Wiley & Sons, Ltd. [source]


Stochastic models for chemically reacting systems using polynomial stochastic hybrid systems

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 15 2005
João Pedro Hespanha
Abstract A stochastic model for chemical reactions is presented, which represents the population of various species involved in a chemical reaction as the continuous state of a polynomial stochastic hybrid system (pSHS). pSHSs correspond to stochastic hybrid systems with polynomial continuous vector fields, reset maps, and transition intensities. We show that for pSHSs, the dynamics of the statistical moments of its continuous states, evolves according to infinite-dimensional linear ordinary differential equations (ODEs), which can be approximated by finite-dimensional nonlinear ODEs with arbitrary precision. Based on this result, a procedure to build this types of approximation is provided. This procedure is used to construct approximate stochastic models for a variety of chemical reactions that have appeared in literature. These reactions include a simple bimolecular reaction, for which one can solve the Master equation; a decaying,dimerizing reaction set which exhibits two distinct time scales; a reaction for which the chemical rate equations have a continuum of equilibrium points; and the bistable Schögl reaction. The accuracy of the approximate models is investigated by comparing with Monte Carlo simulations or the solution to the Master equation, when available. Copyright © 2005 John Wiley & Sons, Ltd. [source]


Design aspects of satellite,cellular hybrid wireless systems

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2002
Tamer ElBatt
Abstract In this paper we investigate various issues related to the design of satellite,cellular hybrid systems. First, we review the fundamental problems of channel partitioning and call admission/assignment. Second, we study the impact of different frequency reuse constraints, in both layers, on the optimum channel partitioning. Third, we investigate, analytically and via simulation, the effect of reducing the cell size. We emphasize the blocking-forced termination probabilities trade-off for pure cellular and satellite,cellular hybrid systems. Accordingly, an optimization problem with respect to the cell size is formulated. Finally, we search for the optimum dynamic call re-assignment policy that improves the system capacity at the expense of the complexity associated with tearing down a connection in one system and setting-up an alternative one in the other system. For a small hybrid system, we characterized the optimum re-assignment policies that minimize the blocking probability, dropping probability, and a weighted cost function of these probabilities. Copyright © 2002 John Wiley & Sons, Ltd. [source]


The DEAD-box RNA helicase DDX1 interacts with RelA and enhances nuclear factor kappaB-mediated transcription

JOURNAL OF CELLULAR BIOCHEMISTRY, Issue 2 2009
Musarat Ishaq
Abstract DEAD-box RNA helicases constitute the largest family of RNA helicases and are involved in many aspects of RNA metabolism. In this study, we identified RelA (p65), a subunit of nuclear factor-kappaB (NF-,B), as a cellular co-factor of DEAD-box RNA helicase DDX1, through mammalian two hybrid system and co-immunoprecipitation assay. Additionally, confocal microscopy and chromatin immunoprecipitation assays confirmed this interaction. In NF-,B dependent reporter gene assay, DDX1 acted as a co-activator to enhance NF-,B-mediated transcription activation. The functional domains involved were mapped to the carboxy terminal transactivation domain of RelA and the amino terminal ATPase/helicase domain of DDX1. The DDX1 trans-dominant negative mutant lacking ATP-dependent RNA helicase activity lost it transcriptional inducer activity. Moreover, depletion of endogenous DDX1 by specific small interfering RNAs significantly reduced NF-,B-dependent transcription. Taken together, the results suggest that DDX1 may play an important role in NF-,B-mediated transactivation, and revelation of this regulatory pathway may help to explore the novel mechanisms for regulating NF-,B transcriptional activity. J. Cell. Biochem. 106: 296,305, 2009. © 2008 Wiley-Liss, Inc. [source]


Allochronic differentiation among Daphnia species, hybrids and backcrosses: the importance of sexual reproduction for population dynamics and genetic architecture

JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 2 2004
T. Jankowski
Abstract Seasonal dynamics of the abundance, sexual reproduction and genetic architecture in a Daphnia hyalina-galeata hybrid complex were studied in the large and deep Lake Constance. We found evidence for the occurrence of first and second order hybridization. Our study revealed strong differences between the parental species not only regarding their seasonal dynamics, genetic architecture and diversity, but also their sexual reproductive behaviour. The overwintering D. hyalina showed low genetic diversity, no genetic differentiation during the season, and reproduced sexually in autumn, whereas D. galeata reached higher levels of genetic diversity, reproduced sexually in early summer, and exhibited changes in genetic structure during the season, but was only present from spring to autumn. However, in both species sexual reproduction was a rare event, and daphnids, including hybrids, reproduced predominantly asexually. This allows long-term persistence of hybrids as well without continuing hybridization events. Within all variables studied, F1 and F2 hybrids showed an intermediate pattern, whereas proposed backcross hybrids were more similar to their respective parentals. These differences in phenotype as well as significant differences in pairwise Fst values between parentals suggest that gene flow seems to be relatively low in the Lake Constance hybrid system. We found evidence for unidirectional introgression by backcrossing from D. galeata to D. hyalina and found a decrease in at least one of the proposed introgressed alleles in the hyalina -backcross while the season progressed. Our findings suggest allochronic differentiation within this hybrid population and different microevolutionary trajectories of the parental species, which will be discussed in the light of the ongoing reoligotrophication process of Lake Constance. [source]


Preparation of LiMn2O4 powders via spray pyrolysis and fluidized bed hybrid system

AICHE JOURNAL, Issue 7 2006
Izumi Taniguchi
Abstract A novel technique has been developed to directly produce fine ceramic powders from liquid solution using a spray pyrolysis and fluidized bed hybrid system. Using this technique, the preparation of lithium manganese oxides LiMn2O4, which are the most promising cathode materials for lithium-ion batteries, has been carried out for various superficial gas velocities U0 = 0.30-0.91 m/s, static bed heights Ls = 50-150 mm, and medium particle sizes dpm,g = 294-498 ,m. The resulting powders had spherical nanostructured particles that comprised primary particles with a few tens of nanometer in size, and they exhibited a pure cubic spinel structure without any impurities in the XRD patterns. Moreover, the as-prepared powders showed better crystallinity and smaller specific surface area than those by conventional spray pyrolysis. The effects of process parameters on powder properties, such as specific surface area and crystallinity, were investigated for a wide range of superficial gas velocities and static bed heights. An as-prepared sample was used as cathode active materials for lithium-ion batteries and the cell performance has been investigated. Test experiments in the electrochemical cell Li/1M LiClO4 in PC/LiMn2O4 demonstrated that the sample prepared by the present technique was superior to that by the conventional spray pyrolysis and solid-state reaction method. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source]


Natural hybridization between Senecio jacobaea and Senecio aquaticus: molecular and chemical evidence

MOLECULAR ECOLOGY, Issue 8 2004
HEATHER KIRK
Abstract Hybridization is known to be involved in a number of evolutionary processes, including species formation, and the generation of novel defence characteristics in plants. The genus Senecio of the Asteraceae family is highly speciose and has historically demonstrated significant levels of interspecific hybridization. The evolution of novel chemical defence characteristics may have contributed to the success of Senecio hybrids. Chemical defence against pathogens and herbivores has been studied extensively in the model species Senecio jacobaea, which is thought to hybridize in nature with Senecio aquaticus. Here, we use amplified fragment length polymorphisms (AFLPs) and pyrrolizidine alkaloid (PA) composition to confirm that natural hybridization occurs between S. jacobaea and the closely related species S. aquaticus. AFLPs are also used to estimate the ancestry of hybrids. We also demonstrate that even highly back-crossed hybrids can possess a unique mixture of defence chemicals specific to each of the parental species. This hybrid system may therefore prove to be useful in further studies of the role of hybridization in the evolution of plant defence and resistance. [source]


Porous silicon/metal nanocomposite with tailored magnetic properties

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2009
Petra Granitzer
Abstract Porous silicon (PS) templates in the meso/macro porous regime with oriented pores clearly separated from each other and filled in a galvanic deposition process with various metals, especially ferromagnetic ones are magnetically investigated. The employment of different metals (e.g. Ni, Co, NiCo) together with the variation of the electrochemical deposition parameters modifies the structural characteristics of the PS/metal nanocomposite and thus leads to distinct magnetic properties of the hybrid system. Furthermore the use of different PS-templates which means a change of the pore-diameter and interpore spacing results also in various magnetic characteristics, especially influences on the magnetic interactions among the deposited metal nanostructures. Therefore the specimens show tailored magnetic properties like coercivity, squareness and magnetic anisotropy. The achieved nanocomposite merges electronic properties of a semiconductor with nanomagnetism and therefore opens the possibility of integrated spin-based electronic devices. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Temperature dependence of a twofold magnetic behaviour of a nanoscopic metal/silicon hybrid system , a comparison between Ni/Si and Co/Si

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2009
K. Rumpf
Abstract The investigated hybrid nanocomposite consists of a porous silicon template with electrochemically embedded Ni or Co nanostructures and offers magnetic characteristics which can be tailored by the electrochemical process parameters during fabrication. A twofold magnetic behaviour can be observed, a first one due to the spinmagnetism at magnetic fields below the saturation magnetization of the deposited metals and a second non-saturating term at higher fields (> 1 T up to 7 T) above the saturation magnetization. In case of Ni deposited within the pores this non-saturating term shows a paramagnetic characteristic and follows exactly the Curie-Weiss law, whereas for Co/porous silicon samples the temperature dependent magnetization shows some deviations from the Curie Weiss law. In this high field region a difference in the temperature dependence between Ni and Co is observed whereas the non-saturating term does not depend on the geometry of the embedded nanostructures in contrast to the ferromagnetic behaviour at lower magnetic fields. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Mass spectrometric characterization of 4-oxopentanoic acid and gas-phase ion fragmentation mechanisms studied using a triple quadrupole and time-of-flight analyzer hybrid system and density functional theory

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2008
Basem Kanawati
4-Oxopentanoic acid was characterized experimentally by electrospray ionization using a triple quadrupole and time-of-flight analyzer hybrid system. This compound was chosen as a model substance for small organic compounds bearing an acetyl and a carboxyl group. Collision-induced dissociation experiments at different activation energies were performed to elucidate possible fragmentation pathways. These pathways were also studied on the theoretical level using density functional theory (DFT) B3LYP/6-311++G(3df,3pd)//B3LYP/6-31+G(d)+ZPVE calculations. CO2 ejection from the [M,H], anion of 4-oxopentanoic acid was observed and the fragmentation pathway studied by DFT reveals a new concerted mechanism for CO2 elimination accompanied by an intramolecular proton transfer within a pentagonal transition state structure. Successive elimination of water and CO from the [M,H], anion of 4-oxopentanoic acid was also observed. A rearrangement in the primary deprotonated ketene anion produced after water elimination was found on the theoretical level and leads to CO elimination from the primary product anion [M,H,H2O],. Energy diagrams along the reaction coordinates of the fragmentation pathways are presented and discussed in detail. Mulliken charge distributions of some important structures are presented. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Reformer and membrane modules plant to optimize natural gas conversion to hydrogen

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2009
M. De Falco
Abstract Membrane technology may play a crucial role in the efficient production of hydrogen from natural gas and heavy hydrocarbons. The present work assesses the performance of a hydrogen production plant utilizing by reformer and membrane modules (RMM), by which the hydrogen produced in reaction units is separated by Pd-based membranes. A major advantage of RMM architecture is the shift of chemical equilibria favoring hydrogen production due to the removal of hydrogen through membranes at each reaction step, thus improving hydrogen yield while simultaneously allowing methane conversion at temperatures below 650 °C. Lower operating temperatures allow location of the modules downstream of a gas turbine, achieving an efficient hybrid system producing electric power and hydrogen with a significant reduction in energy consumption of approximately 10% relative to conventional systems. Fundamental concepts are analyzed and integrated into a process scheme. Effects of variables including reactor temperature outlet, steam-to-carbon ratio and recycle ratio throughout pinch and sensitivity analysis are described. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]


Integrated control method for a fuel cell hybrid system

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2009
Hongwen He
Abstract To apply a fuel cell engine (FCE) on a hybrid electric vehicle, an integrated control method is put forward according to the driving characteristics of the vehicle. The FCE's output power is self-regulated to minimize hydrogen consumption and at the same time to meet the driving power requirement of the vehicle. For the difference of the power output dynamics, the actual power difference between the FCE and the vehicle load is compensated passively by a secondary power battery pack. Vehicle experiments show that the fuel cell hybrid system works well without any adverse influence on the vehicle power performance. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source]


Quantification of chemical,polymer surface interactions in microfluidic cell culture devices

BIOTECHNOLOGY PROGRESS, Issue 2 2009
Hui Xu
Abstract Microfluidic cell culture devices have been used for drug development, chemical analysis, and environmental pollutant detection. Because of the decreased fluid volume and increased surface area to volume ratio, interactions between device surfaces and the fluid is a key element that affects the performance and detection accuracy of microfluidic devices, particularly if fluid is recirculated by a peristaltic pump. However, this issue has not been studied in detail in a microfluidic cell culture environment. In this study, chemical loss and contaminant leakage from various polymer surfaces in a microfluidic setup were characterized. The effects of hydrophilic coating with Poly (vinyl alcohol), Pluronic® F-68, and multi-layer ionic coating were measured. We observed significant surface adsorption of estradiol, doxorubicin, and verapamil with PharMed® BPT tubing, whereas PTFE/BPT and stainless steel/BPT hybrid tubing caused less chemical loss in proportion to the fraction of BPT tubing in the hybrid system. Contaminants leaching out of the BPT tubing were found to be estrogen receptor agonists as determined by estrogen-induced green fluorescence expression in an estrogen responsive Ishikawa cell line and also caused interference with an estradiol enzyme-linked immunosorbent assay (ELISA) assay. Stainless steel/BPT hybrid tubing caused the least interference with ELISA. In summary, polymer surface and chemical interactions inside microfluidic systems should not be neglected and require careful investigations when results from a microfluidic system are compared with results from a macroscale cell culture setup. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source]


Lanthanide (Eu3+, Tb3+) Centered Mesoporous Hybrids with 1,3-Diphenyl-1,3-Propanepione Covalently Linking SBA-15 (SBA-16) and Poly(methylacrylic acid)

CHEMISTRY - AN ASIAN JOURNAL, Issue 7 2010
Ya-Juan Li Dr.
Abstract 1,3-Diphenyl-1,3-propanepione (DBM)-functionalized SBA-15 and SBA-16 mesoporous hybrid materials (DBM-SBA-15 and DBM-SBA-16) are synthesized by co-condensation of modified 1,3-diphenyl-1,3-propanepione (DBM-Si) and tetraethoxysilane (TEOS) in the presence of Pluronic P123 and Pluronic F127 as a template, respectively. The as-synthesized mesoporous hybrid material DBM-SBA-15 and DBM-SBA-16 are used as the first precursor, and the second precursor poly(methylacrylic acid) (PMAA) is synthesized through the addition polymerization reaction of the monomer methacrylic acid. These precursors then coordinate to lanthanide ions simultaneously, and the final mesoporous polymeric hybrid materials Ln(DBM-SBA-15)3PMAA and Ln(DBM-SBA-16)3PMAA (Ln=Eu, Tb) are obtained by a sol-gel process. For comparison, binary lanthanide SBA-15 and SBA-16 mesoporous hybrid materials (denoted as Ln(DBM-SBA-15)3 and Ln(DBM-SBA-16)3) are also synthesized. The luminescence properties of these resulting materials are characterized in detail, and the results reveal that ternary lanthanide mesoporous polymeric hybrid materials present stronger luminescence intensities, longer lifetimes, and higher luminescence quantum efficiencies than the binary lanthanide mesoporous hybrid materials. This indicates that the introduction of the organic polymer chain is a benefit for the luminescence properties of the overall hybrid system. In addition, the SBA-15 mesoporous hybrids show an overall increase in luminescence lifetime and quantum efficiency compared with SBA-16 mesoporous hybrids, indicating that SBA-15 is a better host material for the lanthanide complex than mesoporous silica SBA-16. [source]


Clinical Diagnosis at the Crossroads

CLINICAL PSYCHOLOGY: SCIENCE AND PRACTICE, Issue 3 2006
David Watson
There is widespread dissatisfaction with the existing diagnostic system articulated in the Diagnostic and Statistical Manual of Mental Disorders (DSM). The current DSM system is atheoretical, cumbersome to use, and plagued by the problems of comorbidity and heterogeneity. We explore two possible alternative approaches: (a) reorganizing the diagnostic classes and (b) the implementation of fully dimensional schemes. We then discuss the possibility that DSM-V will be a hybrid system, with Axis I remaining categorical and Axis II becoming dimensional. We conclude with a discussion of the merits,as well as the disadvantages,of creating two different taxonomic systems, one designed for psychopathology researchers and the other for practicing clinicians. [source]


Seismic behaviour of hybrid systems made of PR composite frames coupled with dissipative bracings

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 6 2008
C. Amadio
Abstract The paper investigates the dynamic behaviour of hybrid systems made of partially restrained (PR) steel,concrete composite frames coupled with viscoelastic dissipative bracings. A numerical model that accounts for both the resisting mechanisms of the joint and the viscoelastic contribution of the dissipative bracing is introduced and briefly discussed. The model is first validated against experimental outcomes obtained on a one-storey two-bay composite frame with partial strength semi-rigid joints subjected to free vibrations. A number of time-history analyses under different earthquake ground motions and peak ground accelerations are then carried out on the same type of frame. The purpose is to investigate the influence of the type of beam-to-column connection and property of the viscoelastic bracing on the performance of the hybrid system. The inherent stiffness of the bare PR frame and the plastic hysteresis of the beam-to-column joints, which always lead to only limited damage in the joint, are found to provide a significant contribution to the overall structural performance even under destructive earthquakes. This remark leads to the conclusion that the viscoelastic bracing can be effectively used within the hybrid system. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Winter diatom blooms in a regulated river in South Korea: explanations based on evolutionary computation

FRESHWATER BIOLOGY, Issue 10 2007
DONG-KYUN KIM
Summary 1. An ecological model was developed using genetic programming (GP) to predict the time-series dynamics of the diatom, Stephanodiscus hantzschii for the lower Nakdong River, South Korea. Eight years of weekly data showed the river to be hypertrophic (chl. a, 45.1 ± 4.19 ,g L,1, mean ± SE, n = 427), and S. hantzschii annually formed blooms during the winter to spring flow period (late November to March). 2. A simple non-linear equation was created to produce a 3-day sequential forecast of the species biovolume, by means of time series optimization genetic programming (TSOGP). Training data were used in conjunction with a GP algorithm utilizing 7 years of limnological variables (1995,2001). The model was validated by comparing its output with measurements for a specific year with severe blooms (1994). The model accurately predicted timing of the blooms although it slightly underestimated biovolume (training r2 = 0.70, test r2 = 0.78). The model consisted of the following variables: dam discharge and storage, water temperature, Secchi transparency, dissolved oxygen (DO), pH, evaporation and silica concentration. 3. The application of a five-way cross-validation test suggested that GP was capable of developing models whose input variables were similar, although the data are randomly used for training. The similarity of input variable selection was approximately 51% between the best model and the top 20 candidate models out of 150 in total (based on both Root Mean Squared Error and the determination coefficients for the test data). 4. Genetic programming was able to determine the ecological importance of different environmental variables affecting the diatoms. A series of sensitivity analyses showed that water temperature was the most sensitive parameter. In addition, the optimal equation was sensitive to DO, Secchi transparency, dam discharge and silica concentration. The analyses thus identified likely causes of the proliferation of diatoms in ,river-reservoir hybrids' (i.e. rivers which have the characteristics of a reservoir during the dry season). This result provides specific information about the bloom of S. hantzschii in river systems, as well as the applicability of inductive methods, such as evolutionary computation to river-reservoir hybrid systems. [source]


Thermo-Economic Modelling and Optimisation of Fuel Cell Systems,

FUEL CELLS, Issue 1 2005
F. Marechal
Abstract This paper describes and illustrates the application of a methodology for thermo-economic design and optimisation of fuel cell systems. This methodology combines the use of process simulation and process integration techniques to compute thermo-economic performances of fuel cell systems that will be used in a multi-objective optimisation framework. The method allows the generation of integrated fuel cell system configurations and their corresponding optimal operating conditions. It should be used as a preliminary design methodology, allowing the identification of promising system configurations, which would be further analysed. The methodology and the thermo-economic models are described and demonstrated for the design of PEMFC hybrid systems, combining fuel cell and gas turbine technologies. [source]


Fuel Cell Vehicle Simulation , Part 1: Benchmarking Available Fuel Cell Vehicle Simulation Tools

FUEL CELLS, Issue 3 2003
K.H. Hauer
Abstract Fuel cell vehicle simulation is one method for systematic and fast investigation of the different vehicle options (fuel choice, hybridization, reformer technologies). However, a sufficient modeling program, capable of modeling the different design options, is not available today. Modern simulation programs should be capable of serving as tools for analysis as well as development. Shortfalls of the existing programs, initially developed for internal combustion engine hybrid vehicles, are: (i)Insufficient modeling of transient characteristics; (ii) Insufficient modeling of the fuel cells system; (iii) Insufficient modeling of advanced hybrid systems; (iv) Employment of a non-causal (backwards looking) structure; (v) Significant shortcomings in the area of controls. In the area of analysis, a modeling tool for fuel cell vehicles needs to address the transient dynamic interaction between the electric drive train and the fuel cell system. Especially for vehicles with slow responding on-board fuel processor, this interaction is very different from the interaction between a battery (as power source) and an electric drive train in an electric vehicle design. Non-transient modeling leads to inaccurate predictions of vehicle performance and fuel consumption. When applied in the area of development, the existing programs do not support the employment of newer techniques, such as rapid prototyping. This is because the program structure merges control algorithms and component models, or different control algorithms (from different components) are lumped together in one single control block and not assigned to individual components as they are in real vehicles. In both cases, the transfer of control algorithms from the model into existing hardware is not possible. This paper is the first part of a three part series and benchmarks the "state of the art" of existing programs. The second paper introduces a new simulation program, which tries to overcome existing barriers. Specifically it explicitly recognizes the dynamic interaction between fuel cell system, drive train and optional additional energy storage. [source]