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Manifold
Kinds of Manifold Selected AbstractsA Modular Injection System, Multilevel Sampler, and Manifold for Tracer TestsGROUND WATER, Issue 6 2003Brian J. Mailloux Ground water injection and sampling systems were developed for bacterial transport experiments in both homogenous and heterogeneous unconsolidated, surficial aquifers. Two types of injection systems, a large single tank and a dynamic mixing tank, were designed to deliver more than 800 L of amended ground water to the aquifer over 12 hours, without altering the ground water temperature, pH, Eh, or dissolved gas composition. Two types of multilevel samplers (MLSs) were designed and installed. Permanent MLSs performed well for the homogenous surficial aquifer, but their installation procedure promoted vertical mixing, which could obfuscate experimental data obtained from vertically stratified, heterogeneous aquifers. A novel, removable MLS was designed to fit in 2- and 4-inch wells. Expandable O-rings between each sampling port hydraulically isolated each port for sample collection when a nut was tightened at the land surface. A low-cost vacuum manifold system designed to work with both MLS designs used 50 mL centrifuge tubes to efficiently sample 12 MLS ports with one peristaltic pump head. The integrated system was developed and used during four field campaigns over a period of three years. During each campaign, more than 3000 ground water samples were collected in less than one week. This system should prove particularly useful for ground water tracer, injection, and push-pull experiments that require high-frequency and/or high-density sampling. [source] ChemInform Abstract: A New Manifold for the Morita Reaction: Diene Synthesis from Simple Aldehydes and Acrylates/Acrylonitrile Mediated by Phosphines.CHEMINFORM, Issue 10 2008Anders Palmelund Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Dominant Texture and Diffusion Distance ManifoldsCOMPUTER GRAPHICS FORUM, Issue 2 2009Jianye Lu Abstract Texture synthesis techniques require nearly uniform texture samples, however identifying suitable texture samples in an image requires significant data preprocessing. To eliminate this work, we introduce a fully automatic pipeline to detect dominant texture samples based on a manifold generated using the diffusion distance. We define the characteristics of dominant texture and three different types of outliers that allow us to efficiently identify dominant texture in feature space. We demonstrate how this method enables the analysis/synthesis of a wide range of natural textures. We compare textures synthesized from a sample image, with and without dominant texture detection. We also compare our approach to that of using a texture segmentation technique alone, and to using Euclidean, rather than diffusion, distances between texture features. [source] The heterogeneity of causes and courses of attention-deficit/hyperactivity disorderACTA PSYCHIATRICA SCANDINAVICA, Issue 5 2009H-C. Steinhausen Objective:, Attention-deficit / Hyperactivity Disorder (ADHD) is a frequent mental disorder with onset in childhood and persistence into adulthood in a sizeable number of people. Despite a rather simple clinical definition, ADHD has many facets because of frequent co-morbid disorders and varying impact on psychosocial functioning. Thus, there is considerable heterogeneity in various domains. Method:, A review of recent research findings in: i) selected domains of aetiology reflecting the role of genes, brain structures and functioning and the interplay of causal factors and ii) clinical heterogeneity in terms of co-morbidities, gender effects, courses and outcomes. Results:, Molecular genetic studies have identified a number of candidate genes which have a small effect on behavioural variation in ADHD. In the most recent Genome Scan Meta Analysis of seven ADHD linkage studies, genome-wide significant linkage was identified on chromosome 16. The volume of both the total brain and various regions including the prefrontal cortex, the caudate nucleus and the vermis of the cerebellum is smaller in ADHD. Functional MRI has documented a specific deficit of frontostriatal networks in ADHD. Integrative aetiological models have to take the interaction of gene and environment on various dysfunctions into account. Clinical heterogeneity results from frequent associations with various co-morbidities, the impact of the disorder on psychosocial functioning, and gender effects. Partly, these effects are evident also in the course and outcome of ADHD. Conclusion:, ADHD is a chronic mental disorder with a complex aetiology. So far, various neurobiological factors have been identified that need to be studied further to better understand their interaction with environmental factors. The clinical presentation and the long-term course of ADHD are manifold. [source] Tangential-projection algorithm for manifold representation in unidentifiable model updating problemsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 4 2002Lambros S. Katafygiotis Abstract The problem of updating a structural model and its associated uncertainties by utilizing structural response data is addressed. In an identifiable case, the posterior probability density function (PDF) of the uncertain model parameters for given measured data can be approximated by a weighted sum of Gaussian distributions centered at a number of discrete optimal values of the parameters at which some positive measure-of-fit function is minimized. The present paper focuses on the problem of model updating in the general unidentifiable case for which certain simplifying assumptions available for identifiable cases are not valid. In this case, the PDF is distributed in the neighbourhood of an extended and usually highly complex manifold of the parameter space that cannot be calculated explicitly. The computational difficulties associated with calculating the highly complex posterior PDF are discussed and a new adaptive algorithm, referred to as the tangential-projection (TP) algorithm, allowing for an efficient approximate representation of the above manifold and the posterior PDF is presented. Using this approximation, expressions for calculating the uncertain predictive response are established. A numerical example involving noisy data is presented to demonstrate the proposed method. Copyright © 2002 John Wiley & Sons, Ltd. [source] Construction and Evaluation of a Gold Tubular Electrode for Flow Analysis: Application to Speciation of Antimony in Water SamplesELECTROANALYSIS, Issue 6 2007Rodrigo Santos Abstract A tubular gold electrode (TGE) is described for the first time by summarizing the important aspects of its construction and evaluation. Applicability of the TGE is evaluated in the speciation of Sb(III) and Sb(V) using anodic stripping voltammetry in a single flow manifold. Studies with surface active interferences and metallic cations were performed. The proposed conditions for antimony determination showed good tolerance towards cationic, anionic and nonionic surface active substances. A linear response for antimony was obtained for solutions containing significant amounts of several metallic cations. Linear calibration curves for Sb(III) were obtained in the range 1,10,ppb with a detection limit of 0.19,ppb (CV=2.91%, n=5, [Sb(III)]=5,ppb). For Sb(V), linear calibration curves were in the range 1,15,ppb with a detection limit of 0.32,ppb (CV=1.41%, n=5, [Sb(V)]=5,ppb). The figures of merit achieved sustain for the good applicability of the proposed method as it allows the determination of antimony at levels below maximum values permitted in consuming waters. Results of antimony concentration determined in water samples were validated against the ICP-MS reference procedure or compared with reference water samples. [source] Ruthenium-to-Platinum Interactions in ,6,,1 NCN-Pincer Arene Heterobimetallic Complexes: An Experimental and Theoretical StudyEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 29 2010Sylvestre Bonnet Abstract A series of ,6,,1 -heterobimetallic complexes have been prepared in which a [Ru(,6 -arene)(C5R5)]+ fragment (R = H or Me) and an ,1 -NCN-pincer platinum fragment are combined within the same molecule. In complexes [2]+ and [3]+, the ruthenium and platinum centers are ,6 and ,1 coordinated, respectively, to the same arene ring, whereas in [4A]+ and [5A]+ they are coordinated to two different arene rings that are linked with a covalent bond ([4A]+) or an ethyl bridge ([5A]+). Upon changing the organic manifold between both metal centers, very strong ([2]+) to very weak ([5A]+) ruthenium-to-platinum interactions are obtained. Experimentally, X-ray crystal structures show an increaing steric hindrance when the Ru,Pt distance diminishes, and electrochemical and 195Pt NMR spectroscopic studies show a decreasing electron density on platinum from [5A]+ to [2]+. Theoretical DFT calculations were undertaken, which show an increasing charge on platinum from [5A]+ to [2]+. Our theoretical analysis shows that the particularly strong ruthenium-to-platinum electronic interactions in [2]+ and [3]+ do not come from binding of ruthenium to platinum, but from the pincer Cipso sharing its electron density between both metal centers, which decreases the , donation to platinum, and from increased backdonation of the platinum d electrons into the , system of the arene ring. [source] Coherent state path integral and super-symmetry for condensates composed of bosonic and fermionic atomsFORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 9-10 2007B. Mieck Abstract A super-symmetric coherent state path integral on the Keldysh time contour is considered for bosonic and fermionic atoms which interact among each other with a common short-ranged two-body potential. We investigate the symmetries of Bose-Einstein condensation for the equivalent bosonic and fermionic constituents with the same interaction potential so that a super-symmetry results between the bosonic and fermionic components of super-fields. Apart from the super-unitary invariance U(L | S) of the density terms, we specialize on the examination of super-symmetries for pair condensate terms. Effective equations are derived for anomalous terms which are related to the molecular- and BCS- condensate pairs. A Hubbard-Stratonovich transformation from ,Nambu'-doubled super-fields leads to a generating function with super-matrices for the self-energy whose manifold is given by the orthosympletic super-group Osp(S,S | 2L). A nonlinear sigma model follows from the spontaneous breaking of the ortho-symplectic super-group Osp(S,S | 2L) to the coset decomposition Osp(S,S | 2L) \ U(L | S), U(L | S). The invariant subgroup U(L | S) for the vacuum or background fields is represented by the density terms in the self-energy whereas the super-matrices on the coset space Osp(S,S | 2L) \ U(L | S) describe the anomalous molecular and BCS- pair condensate terms. A change of integration measure is performed for the coset decomposition Osp(S,S | 2L) \ U(L | S) , U(L | S), including a separation of density and anomalous parts of the self-energy with a gradient expansion for the Goldstone modes. The independent anomalous fields in the actions can be transformed by the inverse square root of the metric tensor of Osp(S,S | 2L) \ U(L | S) so that the non-Euclidean integration measure with super-Jacobi-determinant can be removed from the coherent state path integral and Gaussian-like integrations remain. The variations of the independent coset fields in the effective actions result in classical field equations for a nonlinear sigma model with the anomalous terms. The dynamics of the eigenvalues of the coset matrices is determined by Sine-Gordon equations which have a similar meaning for the dynamics of the molecular- and BCS-pair condensates as the Gross-Pitaevskii equation for the coherent wave function in BEC phenomena. [source] String theory: exact solutions, marginal deformations and hyperbolic spacesFORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 2 2007D. Orlando Abstract This thesis is almost entirely devoted to studying string theory backgrounds characterized by simple geometrical and integrability properties. The archetype of this type of system is given by Wess-Zumino-Witten models, describing string propagation in a group manifold or, equivalently, a class of conformal field theories with current algebras. We study the moduli space of such models by using truly marginal deformations. Particular emphasis is placed on asymmetric deformations that, together with the CFT description, enjoy a very nice spacetime interpretation in terms of the underlying Lie algebra. Then we take a slight detour so to deal with off-shell systems. Using a renormalization-group approach we describe the relaxation towards the symmetrical equilibrium situation. In he final chapter we consider backgrounds with Ramond-Ramond field and in particular we analyze direct products of constant-curvature spaces and find solutions with hyperbolic spaces. [source] Flux compactification of M-theory on compact manifolds with Spin(7) holonomy,FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 11-12 2005D. Constantin At the leading order, M-theory admits minimal supersymmetric compactifications if the internal manifold has exceptional holonomy. The inclusion of non-vanishing fluxes in M-theory and string theory compactifications induce a superpotential in the lower dimensional theory, which depends on the fluxes. In this work, we check the conjectured form of this superpotential in the case of warped M-theory compactifications on Spin(7) holonomy manifolds. We perform a Kaluza-Klein reduction of the eleven-dimensional supersymmetry transformation for the gravitino and we find by direct comparison the superpotential expression. We check the conjecture for the heterotic string compactified on a Calabi-Yau three-fold as well. The conjecture can be checked indirectly by inspecting the scalar potential obtained after the compactification of M-theory on Spin(7) holonomy manifolds with non-vanishing fluxes. The scalar potential can be written in terms of the superpotential and we show that this potential stabilizes all the moduli fields describing deformations of the metric except for the radial modulus. All the above analyses require the knowledge of the minimal supergravity action in three dimensions. Therefore we calculate the most general causal ,, =1 three-dimensional, gauge invariant action coupled to matter in superspace and derive its component form using Ectoplasmic integration theory. We also show that the three-dimensional theory which results from the compactification is in agreement with the more general supergravity construction. The compactification procedure takes into account higher order quantum correction terms in the low energy effective action. We analyze the properties of these terms on a Spin(7) background. We derive a perturbative set of solutions which emerges from a warped compactification on a Spin(7) holonomy manifold with non-vanishing flux for the M-theory field strength and we show that in general the Ricci flatness of the internal manifold is lost, which means that the supergravity vacua are deformed away from the exceptional holonomy. Using the superpotential form we identify the supersymmetric vacua out of this general set of solutions. [source] M-theory and gauged supergravities,FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 2 2005D. Roest Abstract We present a pedagogical discussion of the emergence of gauged supergravities from M-theory. First, a review of maximal supergravity and its global symmetries and supersymmetric solutions is given. Next, different procedures of dimensional reduction are explained: reductions over a torus, a group manifold and a coset manifold and reductions with a twist. Emphasis is placed on the consistency of the truncations, the resulting gaugings and the possibility to generate field equations without an action. Using these techniques, we construct a number of gauged maximal supergravities in diverse dimensions with a string or M-theory origin. One class consists of the CSO gaugings, which comprise the analytic continuations and group contractions of SO(n) gaugings. We construct the corresponding half-supersymmetric domain walls and discuss their uplift to D- and M-brane distributions. Furthermore, a number of gauged maximal supergravities are constructed that do not have an action. [source] The Place of Islam in the Geography of Religion: Trends and IntersectionsGEOGRAPHY COMPASS (ELECTRONIC), Issue 5 2007Richard Gale This article reviews recent geographical research on Islam and Muslim identities. In the wake of the events of 11 September 2001, the forms taken by public debate surrounding Muslim communities and societies have been manifold and not always edifying. In the present political climate, where public attitudes to a particular suite of issues are often as misinformed as they are deeply held, the need for academics to furnish insights born out of robust research is acute. While the responses of academics to debates coalescing around Muslim communities and identities have emanated predominantly from religious studies, sociology and anthropology, geographers, with their attention to the spatial components inherent to the articulation of social identities, are making an increasingly significant contribution to our knowledge in this field. This article reviews this contribution, focusing on four areas in which geographical research on Islam has been most pronounced: Muslim residential segregation and ,community cohesion'; the relationship between Islamic dress codes and spatial context in the articulation of Muslim gender identities; the contestation of space that has attended the architectural expression of Muslim identity in urban landscapes and the spatial politics embedded in the construction of Muslim identities at simultaneously national and transnational scales. While the predominant focus is therefore geographical, the article also establishes linkages to other writings on the spatiality of Islam where relevant to the specific themes under discussion. [source] Estimation of the Euler method error on a Riemannian manifoldINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 11 2002Andrzej Bielecki Abstract This article presents an estimation of the Euler method on a Riemannian manifold. A distance between the nth iteration of the cascade generated by the time- h map of a gradient flow and the nth iteration of the cascade generated by the Euler method of this flow is estimated. The application possibilities of the presented estimation are also discussed. Copyright © 2002 John Wiley & Sons, Ltd. [source] Geodesic finite elements for Cosserat rodsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 13 2010Oliver Sander Abstract We introduce geodesic finite elements as a new way to discretize the non-linear configuration space of a geometrically exact Cosserat rod. These geodesic finite elements naturally generalize standard one-dimensional finite elements to spaces of functions with values in a Riemannian manifold. For the special orthogonal group, our approach reproduces the interpolation formulas of Crisfield and Jeleni,. Geodesic finite elements are conforming and lead to objective and path-independent problem formulations. We introduce geodesic finite elements for general Riemannian manifolds, discuss the relationship between geodesic finite elements and coefficient vectors, and estimate the interpolation error. Then we use them to find static equilibria of hyperelastic Cosserat rods. Using the Riemannian trust-region algorithm of Absil et al. we show numerically that the discretization error depends optimally on the mesh size. Copyright © 2009 John Wiley & Sons, Ltd. [source] Automatic CAD model topology generationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2006Paresh S. Patel Abstract Computer aided design (CAD) models often need to be processed due to the data translation issues and requirements of the downstream applications like computational field simulation, rapid prototyping, computer graphics, computational manufacturing, and real-time rendering before they can be used. Automatic CAD model processing tools can significantly reduce the amount of time and cost associated with the manual processing. The topology generation algorithm, commonly known as CAD repairing/healing, is presented to detect commonly found geometrical and topological issues like cracks, gaps, overlaps, intersections, T-connections, and no/invalid topology in the model, process them and build correct topological information. The present algorithm is based on the iterative vertex pair contraction and expansion operations called stitching and filling, respectively, to process the model accurately. Moreover, the topology generation algorithm can process manifold as well as non-manifold models, which makes the procedure more general and flexible. In addition, a spatial data structure is used for searching and neighbour finding to process large models efficiently. In this way, the combination of generality, accuracy, and efficiency of this algorithm seems to be a significant improvement over existing techniques. Results are presented showing the effectiveness of the algorithm to process two- and three-dimensional configurations. Copyright © 2006 John Wiley & Sons, Ltd. [source] Dimensionality estimate of the manifold in chemical composition space for a turbulent premixed H2 + air flame,INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2004Shaheen R. Tonse The dimensionality () of manifolds of active chemical composition space has been measured using three different approaches: the Hausdorff geometrical binning method, Principal Component Analysis, and the Grassberger-Procaccia cumulative distribution method. A series of artificial manifolds is also generated using a Monte Carlo approach to discern the advantages and limitations of the three methods. Dimensionality is quantified for different levels of turbulent intensity in a simulation of the interactions of a 2D premixed hydrogen flame with a localized region of turbulence superimposed over the cold region upstream of the flame front. The simulations are conducted using an adaptive mesh refinement code for low Mach number reacting flows. By treating the Ns species and temperature of the local thermo-chemical state as a point in multidimensional chemical composition space, a snapshot of a flame region is mapped into chemical composition space to generate the manifold associated with the 2-D flame system. An increase in was observed with increasing turbulent intensity for all three methods. Although each method provides useful information, the Grassberger-Procaccia method is subject to fewer artifacts than the other two thereby providing the most reliable quantification of . © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 326,336, 2004 [source] Hyperchaotic behaviour of two bi-directionally coupled Chua's circuitsINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 6 2002Barbara Cannas Abstract In this paper, a non-linear bi-directional coupling of two Chua's circuits is presented. The coupling is obtained by using polynomial functions that are symmetric with respect to the state variables of the two Chua's circuits. Both a transverse and a tangent system are studied to ensure a global validity of the results in the state space. First, it is shown that the transverse system is an autonomous Chua's circuit, which directly allows the evaluation of the conditions on its chaotic behaviour, i.e. the absence of synchronization between the coupled circuits. Moreover, it is demonstrated that the tangent system is also a Chua's circuit, forced by the transverse system; therefore, its dynamics is ruled by a time-dependent equation. Thus, the calculus of conditional Lyapunov exponents is necessary in order to exclude antisynchronization along the tangent manifold. The properties of the transverse and tangent systems simplify the study of the coupled Chua's circuits and the determination of the conditions on their hyperchaotic behaviour. In particular, it is shown that hyperchaotic behaviour occurs for proper values of the coupling strength between the two Chua's circuits. Finally, numerical examples are given and discussed. Copyright © 2002 John Wiley & Sons, Ltd. [source] Arbutin determination in medicinal plants and creamsINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 2 2009W. Thongchai Synopsis A simple flow injection (FI) manifold with spectrophotometric detection was fabricated and tested for arbutin determination. It is based on the measurement of a red-coloured product at 514 nm formed by the complexation reaction between arbutin and 4-aminoantipyrine (4-AP) in the presence of hexacyanoferrate (III) in an alkaline medium. On injecting 300 ,L standard solutions at various concentrations of arbutin into the FI system under optimum conditions, a linear calibration graph over the range of 1.0,30.0 ,g mL,1 arbutin was established. It is expressed by the regression equation y = 0.2188 ± 0.0036x + 0.1019 ± 0.0366 (r2 = 0.9990, n = 5). The detection limit (3,) and the limit of quantitation (10,) were 0.04 ,g mL,1 and 0.13 ,g mL,1, respectively. The RSD of intraday and interday precisions were found to be 1.2,1.4% and 1.7,2.7%, respectively. The method was successfully applied in the determination of arbutin in four selected fruits and three commercial whitening cream extracts with the mean recoveries of the added arbutin over the range of 96.2,99.0%. No interference effects from some common excipients used in commercial whitening creams were observed. The method is simple, rapid, selective, accurate, reproducible and relatively inexpensive. Résumé Un collecteur simple pour injection en flux (FI) avec détection spectrométrique a été fabriqué et testé pour le dosage de l'arbutine. Son principe repose sur la mesure à 514 nm du produit rouge formé par la réaction de complexation entre l'arbutine et le 4-aminoantipyrine (4-AP) en présence d'hexacyanoferrate (III) en milieu alcalin. On procède à une injection de 300 ,L des solutions standards à diverses concentrations d'arbutine dans le système FI aux conditions optimales, puis on réalise un graphe de calibration linéaire dans l'intervalle de 1,0 à 30,0 ,g mL,1 d'arbutine. Le graphe correspond à l'équation de régression y = 0.2188 ± 0.0036x + 0.1019 ± 0.0366 (r2 = 0.9990, n = 5). La limite de détection (3,) et la limite de quantification (10,) sont respectivement de 0.04 ,g mL,1 et 0.13 ,g mL,1. La RSD des précisions intra et inter jours sont respectivement de 1.2,1.4% et 1.7,2.7%. La méthode a été appliquée avec succès à la mesure de l'arbutine dans 4 fruits sélectionnés et 3 extraits de crèmes de blanchiment commercialisées avec une recouvrance moyenne de l'arbutine ajoutée de 96.2 à 99%. Aucune interférence avec les excipients communément utilisés dans les crèmes de blanchiment commerciales n'a été observée. La méthode est simple, rapide, sélective, précise, reproductible et relativement bon marché. [source] An experimental investigation on manifold-injected hydrogen as a dual fuel for diesel engine system with different injection durationINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 15 2009N. Saravanan Abstract Stringent emission norms and rapid depletion of petroleum resources have resulted in a continuous effort to search for alternative fuels. Hydrogen is one of the best alternatives for conventional fuels. Hydrogen has both the benefits and limitation to be used as a fuel in an automotive engine system. In the present investigation, hydrogen was injected into the intake manifold by using a hydrogen gas injector and diesel was introduced in the conventional, mode which also acts as an ignition source for hydrogen combustion. The flow rate of hydrogen was set at 5.5,l,min,1 at all the load conditions. The injection timing was kept constant at top dead center (TDC) and injection duration was adjusted to find the optimized injection condition. Experiments were conducted on a single cylinder, four stroke, water-cooled, direct injection diesel engine coupled to an electrical generator. At 75% load the maximum brake thermal efficiency for hydrogen operation at injection timing of TDC and with injection duration of 30°CA is 25.66% compared with 21.59% for diesel. The oxides of nitrogen (NOX) emission are 21.7,g,kWh,1 for hydrogen compared with diesel of 17.9,g,k,Wh,1. Smoke emissions reduced to 1 Bosch smoke number (BSN) in hydrogen compared with diesel of 2.2 BSN. Hydrogen operation in the dual fuel mode with diesel exhibits a better performance and reduction in emissions compared with diesel in the entire load spectra. Copyright © 2009 John Wiley & Sons, Ltd. [source] Transcritical CO2 refrigerator and sub-critical R134a refrigerator: A comparison of the experimental resultsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 12 2009Ciro Aprea Abstract This paper describes experiments comparing a commercial available R134a refrigeration plant subjected to a cold store and a prototype R744 (carbon dioxide) system working as a classical ,split-systems' to cool air in residential applications in a transcritical cycle. Both plants are able to develope a refrigeration power equal to 3000,W. The R744 system utilizes aluminium heat exchangers, a semi-hermetic compressor, a back-pressure valve and a thermostatic expansion valve. The R134a refrigeration plant operates using a semi-hermetic reciprocating compressor, an air condenser followed by a liquid receiver, a manifold with two expansion valves, a thermostatic one and a manual one mounted in parallel, and an air cooling evaporator inside the cold store. System performances are compared for two evaporation temperatures varying the temperature of the external air running over the gas-cooler and over the condenser. The refrigeration load in the cold store is simulated by means of some electrical resistances, whereas the air evaporator of the R744 plant is placed in a very large ambient. The results of the comparison are discussed in terms of temperature of the refrigerants at the compressor discharge line, of refrigerants mass flow rate and of coefficient of performance (COP). The performances measured in terms of COPs show a decrease with respect to the R134a plant working at the same external and internal conditions. Further improvements regarding the components of the cycle are necessary to use in a large-scale ,split-systems' working with the carbon dioxide. Copyright © 2009 John Wiley & Sons, Ltd. [source] Using matching distance in size theory: A surveyINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 5 2006Michele d'Amico Abstract In this survey we illustrate how the matching distance between reduced size functions can be applied for shape comparison. We assume that each shape can be thought of as a compact connected manifold with a real continuous function defined on it, that is a pair (,,, : , , ,), called size pair. In some sense, the function , focuses on the properties and the invariance of the problem at hand. In this context, matching two size pairs (,, ,) and (,,, ,) means looking for a homeomorphism between , and ,, that minimizes the difference of values taken by , and , on the two manifolds. Measuring the dissimilarity between two shapes amounts to the difficult task of computing the value , = inff maxP,, |,(P) , ,(f(P))|, where f varies among all the homeomorphisms from , to ,,. From another point of view, shapes can be described by reduced size functions associated with size pairs. The matching distance between reduced size functions allows for a robust to perturbations comparison of shapes. The link between reduced size functions and the dissimilarity measure , is established by a theorem, stating that the matching distance provides an easily computable lower bound for ,. Throughout this paper we illustrate this approach to shape comparison by means of examples and experiments. © 2007 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 16, 154,161, 2006 [source] Segmenting youth voting behaviour through trusting,distrusting relationships: a conceptual approachINTERNATIONAL JOURNAL OF NONPROFIT & VOLUNTARY SECTOR MARKETING, Issue 3 2004Janine Dermody This paper reviews current evidence on the declining political engagement of British youth. What emerges is that causes of their political disaffection are manifold and complex, but trust, distrust and cynicism feature strongly. Traditional approaches to trust and distrust fail to recognise this complexity; consequently this paper offers a more sophisticated conceptual framework that examines trust and distrust as separate but linked dimensions, as advocated by Lewicki, McAllister and Bies.[Lewicki, R. J., McAllister D. J. and Bies R. J. (1998) ,Trust and distrust: New relationships and realities', Academy of Management Review, Vol. 23, No. 3, pp. 438,458.] From the analysis four segments of ,voter' types are identified. By segmenting voters in this way, marketers can design strategies to help increase young people's trust and reduce their distrust, thereby increasing their propensity to vote in future elections. A synopsis of marketing aims to stimulate the ,youth vote' is presented along with areas for further research. Copyright © 2004 Henry Stewart Publications [source] Effective collision strengths for electron-impact excitation of transitions within the ground 1s2 2s2 2p4 manifold of O-like Fe18+INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 9 2009Juan A. Santana Abstract Collision strengths have been computed for the electron impact excitations of parity and spin forbidden transitions within the ground 1s22s22p4 manifold of Fe XIX (Fe18+). The calculations were carried out using a relativistic R-matrix close-coupling method based on the effective many-body Hamiltonian. Twenty-six target states were included in the close-coupling expansion. Effective collision strengths, assuming a Maxwellian electron velocity distribution, were evaluated for all transitions within the ground configuration. Good agreement is found with previous Breit-Pauli R-matrix calculations at low electron temperatures, 5.0 , log Te , 6.0 K, for all the transitions, whereas significant differences are found for electron temperatures in the range 6.0 , log Te , 7.0 K. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Interaction of a two-level cyclic XY n -spin model with a two-mode cavity field in off-resonant statesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2008Horacio Grinberg Abstract The interaction of the XY n -spin cyclic model with a two-mode cavity field in the rotating-wave approximation is investigated in the framework of a generalized Jaynes,Cummings two-level system consisting of the vacuum state and a thermally averaged manifold of excited sates. Computation of the energy of this manifold allows this interaction to be examined in off-resonant states. Time evolution of the population inversion, photon distribution, and temperature distribution for an excited initial state are computed via second- and third-order perturbation expansion of the time evolution operator matrix elements for the excited and ground states, respectively and for an ideal squeezed initial coherent state of the cavity field. It was assumed that the two modes have initially the same photon distribution. The pattern of the spin population inversion appears as a manifestation of multiple and complicated inerferences, which is mathematically reflected in a double discrete summation that appears in the calculation of the dynamics. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Resonances and pseudoresonances in a potential with attractive coulomb tail: A study using analytic-continuation techniquesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2003Imke B. Müller Abstract The performance of the complex absorbing potential (CAP) and the complex scaling (CS) methods in the detection and calculation of complex Siegert energies is studied using a 1-D long-range attractive model potential. This potential is constructed to mimic molecular properties, in particular an attractive Coulombic term, to allow one to draw conclusions on molecular ab initio studies. Analyzing the spectrum of the model potential, one compact bound state embedded in the manifold of Rydberg states is found that shows artificial resonance characteristics when applying the CAP and the CS methods. This pseudoresonance problem is less pronounced in the calculation using the CS method than in that using the CAP method. Despite this deficiency, the CAP method is shown to possess advantages over CS when dealing with physical resonances under conditions that simulate the application of standard basis sets in ab initio calculations. The accuracy of the Siegert energy is shown to be maintained when applying a subspace projection technique to the CAP method. This technique reduces the computational demand significantly and leads to an important improvement of the CAP method, which should be of particular significance in molecular applications. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 [source] Disc structure function and its potential for repairINTERNATIONAL JOURNAL OF RHEUMATIC DISEASES, Issue 1 2002J. Melrose The intervertebral disc (IVD) is the largest predominantly avascular, aneural, alymphatic structure of the human body. It provides articulation between adjoining vertebral bodies and also acts as a weight-bearing cushion dissipating axially applied spinal loads. The IVD is composed of an outer collagen-rich annulus fibrosus (AF) and a central proteoglycan (PG)-rich nucleus pulposus (NP). Superior and inferior cartilaginous endplates (CEPs), thin layers of hyaline-like cartilage, cover the ends of the vertebral bodies. The AF is composed of concentric layers (lamellae) which contain variable proportions of type I and II collagen, this tissue has high tensile strength. The NP in contrast is a gelatinous PG-rich tissue which provides weight-bearing properties to the composite disc structure. With the onset of age, cells in the NP progressively die as this tissue becomes depleted of PGs, less hydrated and more fibrous as the disc undergoes an age-dependent fibrocartilaginous transformation. Such age-dependent cellular and matrix changes can decrease the discs' biomechanical competence and trauma can further lead to failure of structural components of the disc. Annular defects are fairly common and include vertebral rim-lesions, concentric (circumferential) annular tears (separation of adjacent annular lamellae) and radial annular tears (clefts which initiate within the NP). While vascular in-growth around annular tears has been noted, evidence from human post-mortem studies indicate they have a limited ability to undergo repair. Several experimental approaches are currently under evaluation for their ability to promote the repair of such annular lesions. These include growth of AF fibrochondrocytes on a resorbable polycaprolactone (PCL) bio-membrane.1 Sheets of fibrochondrocytes lay down type-I collagen and actin stress fibres on PCL. These matrix components are important for the spatial assembly of the collagenous lamella during annular development and correct phenotypic expression of cells in biomatrices.1 An alternative approach employs preparation of tissue engineered IVDs where AF and NP cells are separately cultured in polyglycolic acid and sodium alginate biomatrices, either separately or within a manifold designed to reproduce the required IVD dimensions for its use as a prospective implant device.2 AF and NP cells have also been grown on tissue culture inserts after their recovery from alginate bead culture to form plugs of tissue engineered cartilage.3 A key component in this latter strategy was the stimulation of the high density disc cell cultures with osteogenic protein-1 (OP-1) 200 ng/mL.3 This resulted in the production of tissue engineered AF and NP plugs with compositions, histochemical characteristics and biomechanical properties approaching those of the native disc tissues.2,3 Such materials hold reat promise in future applications as disc or annular implants. The introduction of appropriate genes into disc cells by gene transduction methodology using adenoviral vectors or ,gene-gun' delivery systems also holds considerable promise for the promotion of disc repair processes.4 Such an approach with the OP-1 gene is particularly appealing.5 The anchoring of discal implants to vertebral bodies has also been evaluated by several approaches. A 3D fabric based polyethylene biocomposite holds much promise as one such anchorage device6 while biological glues used to seal fibrocartilaginous structures such as the AF and meniscus8 following surgical intervention, also hold promise in this area. Several very promising new experimental approaches and strategies are therefore currently under evaluation for the improvement of discal repair. The aforementioned IVD defects are a common cause of disc failure and sites of increased nerve in-growth in symptomatic IVDs in man and are thus often sources of sciatic-type pain. Annular defects such as those described above have formerly been considered incapable of undergoing spontaneous repair thus a clear need exists for interventions which might improve on their repair. Based on the rapid rate of progress and the examples outlined above one may optimistically suggest that a successful remedy to this troublesome clinical entity will be developed in the not so distant future. References 1JohnsonWEBet al. (2001) Directed cytoskeletal orientation and intervertebral disc cell growth: towards the development of annular repair techniques. Trans Orthop Res Soc26, 894. 2MizunoHet al. (2001) Tissue engineering of a composite intervertebral disc. Trans Orthop Res Soc26, 78. 3MatsumotoTet al. (2001) Formation of transplantable disc shaped tissues by nucleus pulposus and annulus fibrosus cells: biochemical and biomechanical properties. Trans Orthop Res Soc26, 897. 4NishidaKet al. (2000) Potential applications of gene therapy to the treatment of intervertebral disc disorders. Clin Orthop Rel Res379 (Suppl), S234,S241. 5MatsumotoTet al. (2001) Transfer of osteogenic protein-1 gene by gene gun system promotes matrix synthesis in bovine intervertebral disc and articular cartilage cells. Trans Orthop Res Soc26, 30. 6ShikinamiY , Kawarada (1998) Potential application of a triaxial three-dimensional fabric (3-DF) as an implant. Biomaterials19, 617,35. [source] Robust tracking control for a class of MIMO nonlinear systems with measurable output feedbackINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 1 2008Ya-Jun Pan Abstract This paper proposes a robust output feedback controller for a class of nonlinear systems to track a desired trajectory. Our main goal is to ensure the global input-to-state stability (ISS) property of the tracking error nonlinear dynamics with respect to the unknown structural system uncertainties and external disturbances. Our approach consists of constructing a nonlinear observer to reconstruct the unavailable states, and then designing a discontinuous controller using a back-stepping like design procedure to ensure the ISS property. The observer design is realized through state transformation and there is only one parameter to be determined. Through solving a Hamilton,Jacoby inequality, the nonlinear control law for the first subsystem specifies a nonlinear switching surface. By virtue of nonlinear control for the first subsystem, the resulting sliding manifold in the sliding phase possesses the desired ISS property and to certain extent the optimality. Associated with the new switching surface, the sliding mode control is applied to the second subsystem to accomplish the tracking task. As a result, the tracking error is bounded and the ISS property of the whole system can be ensured while the internal stability is also achieved. Finally, an example is presented to show the effectiveness of the proposed scheme. Copyright © 2007 John Wiley & Sons, Ltd. [source] Feedback stabilization of bifurcations in multivariable nonlinear systems,Part II: Hopf bifurcationsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 4 2007Yong Wang Abstract In this paper we derive necessary and sufficient conditions of stabilizability for multi-input nonlinear systems possessing a Hopf bifurcation with the critical mode being linearly uncontrollable, under the non-degeneracy assumption that stability can be determined by the third order term in the normal form of the dynamics on the centre manifold. Stabilizability is defined as the existence of a sufficiently smooth state feedback such that the Hopf bifurcation of the closed-loop system is supercritical, which is equivalent to local asymptotic stability of the system at the bifurcation point. We prove that under the non-degeneracy conditions, stabilizability is equivalent to the existence of solutions to a third order algebraic inequality of the feedback gains. Explicit conditions for the existence of solutions to the algebraic inequality are derived, and the stabilizing feedback laws are constructed. Part of the sufficient conditions are equivalent to the rank conditions of an augmented matrix which is a generalization of the Popov,Belevitch,Hautus (PBH) rank test of controllability for linear time invariant (LTI) systems. We also apply our theory to feedback control of rotating stall in axial compression systems using bleed valve as actuators. Copyright © 2006 John Wiley & Sons, Ltd. [source] Sliding mode control of boost and buck-boost power converters using the dynamic sliding manifoldINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 14 2003Yuri B. Shtessel Abstract Non-minimum phase tracking control is studied for boost and buck-boost power converters. A sliding mode control algorithm is developed to track directly a causal voltage tracking profile given by an exogenous system. The approximate causal output non-minimum phase asymptotic tracking in non-linear boost and buck-boost power converters is addressed via sliding mode control using a dynamic sliding manifold (DSM). Use of DSM allows the stabilization of the internal dynamics when the output tracking error tends asymptotically to zero in the sliding mode. The sliding mode controller with DSM links features of conventional sliding mode control (insensitivity to matched non-linearities and disturbances) and a conventional dynamic compensator (accommodation to unmatched disturbances). Numerical examples demonstrate the effectiveness of the sliding mode controller even for a known time-varying load. Copyright © 2003 John Wiley & Sons, Ltd. [source] Perspectives on Models of Job PerformanceINTERNATIONAL JOURNAL OF SELECTION AND ASSESSMENT, Issue 4 2000Chockalingam Viswesvaran Contemporary models of job performance are reviewed. Links between task performance, contextual performance, organizational citizenship behaviors, counterproductivity and organizational deviance are pointed out. Measurement issues in constructing generic models applicable across jobs are discussed. Implications for human resource management in general, and performance appraisal for selection and assessment in particular, are explored. It is pointed out that the different dimensions or facets of individual job performance hypothesized in the literature are positively correlated. This positive manifold suggests the presence of a general factor which represents a common variance shared across all the dimensions or facets. Although no consensus exists in the extant literature on the meaning and source of this shared variance (i.e., the general factor), rater idiosyncratic halo alone does not explain this general factor. Future research should explain the common individual differences determinants of performance dimensions. [source] | |||||||||||||||||||||||||||||||