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Studied Systems (studied + system)
Selected AbstractsA new method for transient stability analysisELECTRICAL ENGINEERING IN JAPAN, Issue 3 2007Naoto Yorino Abstract This paper proposes a brand-new method for transient stability analysis in power systems. The proposed method directly computes the critical trajectory for a given contingency to obtain the critical condition of the studied system. Although the method may be useful for general nonlinear dynamic systems, it is applied to the problem of obtaining a controlling UEP, unstable equilibrium point, which provides inevitable information for the energy function methods to assess transient stability. Namely, the proposed method effectively yields a critical trajectory on PEBS together with the controlling UEP, thus improving the conventional BCU method. The effectiveness of the proposed method is demonstrated in 3-machine 9-bus and 6-machine 30-bus systems. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(3): 26,33, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20245 [source] Integrating the scene length characteristics of MPEG video bitstreams into a direct broadcast satellite network with return channel systemINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2004Fatih Alagöz Abstract In order to optimize the network resources, we should incorporate all the available information into the network design. However, incorporating irrelevant information may increase the design complexity and/or decrease the performance of the network. In this paper, we investigate the relevance of integrating the scene length characteristics of moving pictures expert group (MPEG) coded video bitstreams into a direct broadcast satellite (DBS) network with return channel system (DVB-RCS). Due to the complexity of the studied system, unless disputable simplifications are made, it is hard to achieve a mathematical foundation for this integration. Our analysis relies on extensive set of simulations. Firstly, we achieve the scene length distributions for MPEG bitstreams based on the proposed scene change models and their subjective observations of the actual video. We show that these models may be used to estimate the scene length of MPEG bitstreams. We then integrate this estimation into a DBS network simulator. Finally, we show that the scene length characteristics may be used to improve the DBS network performance under certain conditions. Copyright © 2004 John Wiley & Sons, Ltd. [source] Habitat heterogeneity overrides the species,area relationshipJOURNAL OF BIOGEOGRAPHY, Issue 4 2008András Báldi Abstract Aim, The most obvious, although not exclusive, explanation for the increase of species richness with increasing sample area (the species,area relationship) is that species richness is ultimately linked to area-based increases in habitat heterogeneity. The aim of this paper is to examine the relative importance of area and habitat heterogeneity in determining species richness in nature reserves. Specifically, the work tests the hypothesis that species,area relationships are not positive if habitat heterogeneity does not increase with area. Location, Sixteen nature reserves (area range 89,11,030 ha) in central Hungary. Methods, Four-year faunistic inventories were conducted in the reserves involving c. 70 fieldworkers and 65 taxonomists. CORINE 50,000 land-cover maps were used for calculating the heterogeneity of the reserve landscape (number of habitat types, number of habitat patches and total length of edges). Results, Large reserves were less heterogeneous than small reserves, probably because large reserves were established in large blocks of unproductive land whereas small reserves tended to be in more fertile land. In total, 3975 arthropod species were included in the analysis. The slope of the species,area relationship was positive only for Neuroptera and Trichoptera. There was no significant relationship in the other nine taxa examined (Collembola, Acari, Orthoptera, Thysanoptera, Coleoptera, Araneae, Diplopoda, Chilopoda, Diptera). The density (number of species ha,1) of all species, however, showed a positive correlation with heterogeneity. Main conclusions, The general lack of fit of species,area relationships in this study is inconsistent with most previous published studies. Importantly, and unlike many other studies, habitat heterogeneity was not correlated with reserve area in the studied system. In the absence of this source of covariation, stronger relationships were identified that suggested a fundamental link between species richness and habitat heterogeneity. The results indicate that habitat heterogeneity rather than area per se is the most important predictor of species richness in the studied system. [source] XRD studies, vibrational spectra, and molecular structure of 1H-imidazo [4,5-b]pyridine based on DFT quantum chemical calculationsJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2010L. Dymi Abstract The molecular structures and vibrational properties of 1H -imidazo[4,5-b]pyridine in its monomeric and dimeric forms are analyzed and compared to the experimental results derived from the X-ray diffraction (XRD), infrared (IR), and Raman studies. The theoretical data are discussed on the basis of density functional theory (DFT) quantum chemical calculations using Lee,Yang,Parr correlation functional (B3LYP) and 6-31G(d,p) basis. This compound crystallizes in orthorhombic structure, space group Pna21(C2v9) and Z = 4. The planar conformation of the skeleton and presence of the NH···N hydrogen bond was found to be characteristic for the studied system. The temperature dependence of IR and Raman modes was studied in the range 4,294 K and 8,295 K, respectively. The normal modes, which are unique for the imidazopyridine derivatives are identified. Copyright © 2009 John Wiley & Sons, Ltd. [source] Host plant quality and defence against parasitoids: no relationship between levels of parasitism and a geometrid defoliator immunoassayOIKOS, Issue 6 2008Netta Klemola Host plant quality has a major influence on the performance, and ultimately on the fitness of an herbivorous insect, but may also have indirect effects on the third trophic level by affecting an herbivore's defensive ability against natural enemies. In a three-year field study, we examined the effects of natural food quality on the ability of autumnal moths, Epirrita autumnata (Lepidoptera, Geometridae), to defend themselves against parasitoids. In each year, we confirmed the variation in quality of host trees (mountain birch, Betulapubescens ssp. czerepanovii) by determining the mass of pupae reared in mesh bags attached to the trees and the water content of leaves. Individuals grown on high quality trees possessed significantly higher encapsulation rate of a foreign antigen as pupae compared to those on low quality trees during the first and third study years; a parallel trend was also found in the second study year, although this difference was not statistically significant. However, in spite of observed differences in encapsulation rates, individuals reared on high and low quality trees did not differ in their levels of parasitisation when exposed to hymenopteran parasioids in the wild and thus were equally vulnerable. Accordingly, the encapsulation response seems not to play a major role on the population ecology scale in the studied system. Our findings also stress the importance of direct resistance tests, which should be conducted along with tests of insect immune function. [source] Influence of the relative humidity on film formation by vapor induced phase separationPOLYMER ENGINEERING & SCIENCE, Issue 4 2003H. Caquineau The formation of polymer films produced by the phase separation process occurring when a cast poly(etherimide)/N-Methyl-2-Pyrrolidone solution was exposed to humid air was studied. It was found that above a relative humidity value of 27%, the films presented a cell-like structure. The size of the cells was shown to decrease when the relative humidity increased. This effect was more pronounced at the film/substrate interface than near the surface. A cell-size gradient from one face of the film to the other was also clearly observed. A phenomenological model has been proposed to explain the morphology obtained by a phase separation induced by the water vapor in the studied system, takin into account thermodynamics and kinetics considerations. In this model, the cell-like structure setting up is shown to result from a nucleation and growth process accompanied by a coalescence coarsening. It was illustrated by a composition path on the ternary phase diagram. It was shown how the relative humidity influenced the film composition leading to the preferential nucleation compared to the growth and coalescence of the cells. Finally, it was found that the cell-size anisotropy resulted in the solvent and non-solvent mass transfers in the film, bringing to the fore the determining role of kinetics. [source] Oxidative Inorganic Multilayers for Polypyrrole Film GenerationADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Mikko Salomäki Abstract A controlled nanoscale fabrication of conducting polymer films sets severe requirements for the preparation method and substrate. A new and versatile approach for producing thin polypyrrole films on a variety of surfaces is presented. Purely inorganic thin films are first prepared from poly(metaphosphate) and tetravalent metal ions using a sequential layer-by-layer technique. Redox-active cerium(IV) polyphosphate multilayer and redox-inactive zirconium(IV) and hafnium(IV) polyphosphate multilayers are prepared. Cerium-based polyphosphate films grow exponentially with the number of layers but multilayers containing zirconium or hafnium exhibit a linear buildup process. All the studied systems produce relatively smooth films with initial bilayer thickness less than 2,nm. The cerium(IV) containing film is redox-active, which is shown by its capability to form a polypyrrole layer on its surface by oxidation of pyrrole monomers in the adjacent aqueous solution. This is a general method to produce thin oxidative films of arbitrary size and form on a wide variety of surfaces. [source] Factorial design analysis of the catalytic activity of di-imine copper(II) complexes in the decomposition of hydrogen peroxideINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2001W. A. Alves Factorial design analysis was applied to the study of the catalytic activity of di-imine copper(II) complexes, in the decomposition of hydrogen peroxide. The studied complexes show a tridentate imine ligand (apip), derived from 2-acetylpyridine and 2-(2-aminoethyl)pyridine, and a hydroxo or an imidazole group at the fourth coordination site of the copper ion. The factorial design models for both [Cu(apip)imH]2+ and [Cu(apip)OH]+ were similar. Increasing the peroxide concentration from 3.2 × 10,3 to 8.1 × 10,3 mol L,1 resulted in increased oxygen formation. Increasing the pH from 7 to 11 also increased oxygen formation and had an effect about twice as large as the peroxide one. Both complexes also had an important interaction effect between peroxide concentration and pH. However, increasing the catalyst concentration led to a decrease in total oxygen formation. The obtained results were corroborated by further data, achieved by using the usual univariate method, and helped to elucidate equilibrium steps occurring in the studied systems. In very alkaline solutions, the studied [Cu(apip)imH]2+ complex can form the corresponding dinuclear species, [Cu2(apip)2im]3+. While the mononuclear complex proved to be an efficient catalyst in hydrogen peroxide decomposition, the corresponding dinuclear compound seemed to be able to coordinate with the dioxygen molecule, inhibiting its observed release. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 472,479, 2001 [source] The Liapunov's second method for continuous time difference equationsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 15 2003P. PepeArticle first published online: 10 OCT 200 Abstract Among many other cases such as economic and lossless propagation models, continuous time difference equations are encountered as the internal dynamics in a class of non-linear time delay systems, when controlled by a suitable state feedback which drives the output exponentially to zero. The Liapunov's second method for these infinite dimensional systems has not been extensively investigated in the literature. This paper has the aim of filling this gap. Liapunov's second method theorems for checking the stability and the asymptotic stability of this class of infinite dimensional systems are built up, in both a finite and an infinite dimensional setting. In the finite dimensional setting, the Liapunov function is defined on finite dimensional sets. The conditions for stability are given as inequalities on continuous time. No derivatives are involved, as in the dynamics of the studied systems. In the infinite dimensional setting, the continuous time difference equation is transformed into a discrete time system evolving on an infinite dimensional space, and then the classical Liapunov theorem for the system in the new form is written. In this paper the very general case is considered, that is non-linear continuous time difference equations with multiple non commensurate delays are considered, and moreover the functions involved in the dynamics are allowed to be discontinuous, as well as the initial state. In order to study the stability of the internal dynamics in non-linear time delay feedback systems, an exogenous disturbance is added, which goes to zero exponentially as the time goes to infinity. An example is considered, from non-linear time delay feedback theory. While the results available in the literature are inconclusive as far as the stability of that example is concerned, such stability is proved to hold by the theorems developed in this paper, and is validated by simulation results. Copyright © 2003 John Wiley & Sons, Ltd. [source] Micromechanical behavior related to the nanostructure of biodegradable polyestersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010M. E. Cagiao Abstract The microhardness of a series of biodegradable polyesters was determined. The nanostructural features of these materials were studied by wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), and differential scanning calorimetry. Analysis of the SAXS and WAXS patterns allowed direct derivation of the degree of crystallinity and crystal thickness values, and correlations of the micromechanical properties are presented. The differences in the thermal and mechanical properties exhibited by the studied systems and the ones found in other aromatic polyesters are explained as due to the different chemical natures of the monomeric units. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] IDEA: Interface dynamics and energetics algorithmJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 15 2007D. Duca Abstract IDEA, interface dynamics and energetics algorithm, was implemented, in FORTRAN, under different operating systems to mimic dynamics and energetics of elementary events involved in interfacial processes. The code included a parallel elaboration scheme in which both the stochastic and the deterministic components, involved in the developed physical model, worked simultaneously. IDEA also embodied an optionally running VISUAL subroutine, showing the dynamic energy changes caused by the surface events, e.g., occurring at the gas-solid interface. Monte Carlo and ordinary differential equation system subroutines were employed in a synergistic way to drive the occurrence of the elementary events and to manage the implied energy flows, respectively. Biphase processes, namely isothermal and isobaric adsorption of carbon monoxide on nickel, palladium, and platinum surfaces, were first studied to test the capability of the code in modeling real frames. On the whole, the simulated results showed that IDEA could reproduce the inner characteristics of the studied systems and predict properties not yet experimentally investigated. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source] Relationship between substituent effect and aromaticity , Part III: naphthalene as a transmitting moiety for substituent effectJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2007Tadeusz M. Krygowski Abstract Molecular geometry of 10 isomeric nitronaphtholate ions (excluding peri - and ortho -type substituted systems), 1- and 2-naphtholate ions, 1- and 2-nitronaphthalene, meta - and para -nitrophenolate, phenolate, and nitrobenzene were optimized at B3LYP/6-311G** level of approximation. Substituent effect stabilization energy (SESE), geometry-based aromaticity index HOMA, magnetism-based indices NICS, NICS(1), NICS(1)zz, and parameters characterizing Bond Critical Points (BCP) (,, ,2,, ellipticity, ion/cov) of the Bader AIM theory were used to characterize transmitting properties for substituent effect through the naphthalene moiety. It results from our study that the studied systems could be clearly divided into two groups, (i) a para -type group, where the intramolecular charge transfer between the , -electron donating and , -electron accepting substituents can be described by canonical forms with charge separation (as in the case of para -nitrophenolate) and (ii) a meta -type group, where this transfer requires using canonical forms with double charge separation (as in the case of meta -nitrophenolate). Copyright © 2007 John Wiley & Sons, Ltd. [source] Microemulsion Polymerization Modeling Based on the Experimental Conversion Trend and its DerivativeMACROMOLECULAR SYMPOSIA, Issue 1 2008F. López-Serrano Abstract In this work, the microemulsion polymerization modeling problem is addressed with an integrodifferential approach. The procedure was applied to experimental data, previously presented, on the microemulsion polymerization of hexyl methacrylate (C6MA) and styrene (STY). It was found that: (i) the nucleation rate is not linear with time, as assumed before, (ii) a vitreous effect is observed even in reactions where the polymer's glass transition temperature is lower than the reaction temperature, (iii) radical entry to polymer particles and coagulation among particles are negligible, (iv) the rate decrease interval is also caused by a reduction of active sites, (v) a mechanism in which micelles provide monomer to living particles was detected, and (vi) a simple three-parameter mechanistic model was obtained, capable of describing the studied systems. [source] Variability in the structure of epiphytic assemblages of the Mediterranean seagrass Posidonia oceanica in relation to depthMARINE ECOLOGY, Issue 3 2009Ugo Nesti Abstract The aim of the present study was to evaluate whether the variability in the structure of the epiphytic assemblages of leaves and rhizomes of the Mediterranean seagrass Posidonia oceanica differed between depths at a large spatial scale. A hierarchical sampling design was used to compare epiphytic assemblages at two different depths (10 and 20 m) in terms of both species composition and abundance and patterns of spatial variability in the Tuscan Archipelago (North Western Mediterranean Sea, Italy). Results showed significant differences in the structure of assemblages on rhizomes and leaves at different depths. These differences were related to species composition and abundance; differences were not significant for total biomass, total percentage cover and percentage cover of animals and algae. Whereas the higher variability was observed among shoots in all the studied systems, patterns of spatial variability at the other spatial scales investigated differed between the two studied depths. Moreover, in the present study, analogous patterns between depths resulted for both the assemblages of leaves and rhizomes, suggesting that factors that change with depth can be responsible for the spatial variability of both the assemblages (leaves and rhizomes), and operate regardless of the microclimatic conditions and the structure of assemblages. [source] The representation of root processes in models addressing the responses of vegetation to global changeNEW PHYTOLOGIST, Issue 1 2000F. I. WOODWARD The representation of root activity in models is here confined to considerations of applications assessing the impacts of changes in climate or atmospheric [CO2]. Approaches to modelling roots can be classified into four major types: models in which roots are not considered, models in which there is an interplay between only selected above-ground and below-ground processes, models in which growth allocation to all parts of the plants depends on the availability and matching of the capture of external resources, and models with explicit treatments of root growth, architecture and resource capture. All models seem effective in describing the major root activities of water and nutrient uptake, because these processes are highly correlated, particularly at large scales and with slow or equilibrium dynamics. Allocation models can be effective in providing a deeper, perhaps contrary, understanding of the dynamic underpinning to observations made only above ground. The complex and explicit treatment of roots can be achieved only in small-scale highly studied systems because of the requirements for many initialized variables to run the models. [source] Poisson's ratio of simple planar ,isotropic' solids in two dimensionsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2007Konstantin V. Tretiakov Abstract The influence of molecular geometry on the Poisson's ratio has been investigated for a few two-dimensional (2D) hard body systems (hard discs, hard dimers, hard cyclic trimers, and hard cyclic hexamers) forming elastically isotropic solid phases. The Poisson's ratio of the studied periodic and aperiodic solids was determined by Monte Carlo simulations using the analysis of the box fluctuations in the constant pressure ensemble (NpT) with variable box shape. The results obtained for all the studied systems showed that the Poisson's ratio grows when the density is decreased. It has been also found that the Poisson's ratio decreases with increasing number of discs in the molecule and its value for hard trimers is negative near close packing. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Hyperbranched macromolecules through donor-acceptor type copolymerization of allyl,vinylene bifunctional monomers,POLYMER INTERNATIONAL, Issue 10 2002O Rzaev, Zakir M Abstract Present review is an attempt to generalize and systematize the results accumulated in synthesis of cyclolinear and hyperbranched reactive macromolecules via radical alternating copolymerization of various bifunctional monomers containing donor and acceptor type double bonds. Synthesis of hyperbranched reactive macromolecules was carried out using complex-radical cyclocopolymerization of donor-acceptor type bifunctional monomers such as monoallyl ester of maleic acid (MAM), allyl acrylate (AA), allyl methacrylate (AM), allyl trans -cinnamate (AC), methylallylmaleate (MeAM), methylallylfumarate (MAF) and allyl-,-(N-maleimido)acetate (AMI), and maleic anhydride (MA) and styrene (St) as typical acceptor and donor comonomers, respectively. The kinetic parameters of these reactions, constants of cyclization, complex-formation and copolymerization, as well as the ratios of chain growth rates for the participation of monomeric charge transfer complexes and free monomers, were all determined. It was demonstrated that in the studied systems, copolymerizations predominantly proceed according to alternating mechanism with formation of macromolecules having cyclolinear structure in the steady-state and hyperbranched structure in the high conversion conditions. It was shown that formation of linear and hyperbranched macromolecules containing allyl or vinylene groups in the side chain occurs selectively carry out and depends on the nature of used comonomer. General schemes and proposed mechanism of hyperbranching and crosslinking reactions were also described. Some useful properties of synthesized reactive copolymers were discussed. © 2002 Society of Chemical Industry. [source] | |||||||||||||||||||