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Theoretical Approaches (theoretical + approach)
Selected AbstractsMONTE CARLO SIMULATION OF FAR INFRARED RADIATION HEAT TRANSFER: THEORETICAL APPROACHJOURNAL OF FOOD PROCESS ENGINEERING, Issue 4 2006F. TANAKA ABSTRACT We developed radiation heat transfer models with the combination of the Monte Carlo (MC) method and computational fluid dynamic approach and two-dimensional heat transfer models based on the fundamental quantum physics of radiation and fluid dynamics. We investigated far infrared radiation (FIR) heating in laminar and buoyancy airflow. A simple prediction model in laminar airflow was tested with an analytical solution and commercial software (CFX 4). The adequate number of photon tracks for MC simulation was established. As for the complex designs model, the predicted results agreed well with the experimental data with root mean square error of 3.8 K. Because food safety public concerns are increasing, we applied this model to the prediction of the thermal inactivation level by coupling with the microbial kinetics model. Under buoyancy airflow condition, uniformity of FIR heating was improved by selecting adequate wall temperature and emissivity. [source] SPECIALIZATION AND TRADE: A GAME THEORETICAL APPROACHPACIFIC ECONOMIC REVIEW, Issue 4 2006Shuntian Yao Different from the classical treatment, we adopt a game theoretical approach. Therefore in our models the prices of traded goods are endogenously formulated according to the bidding strategies of the producer-consumers. Furthermore, we assume that in the beginning individuals randomly choose their professions. As a result, with a short-run Nash equilibrium different types of professionals may have different utility levels; while through a dynamic process, a long-run Nash equilibrium with utility equalization is reached. Besides, we also attempt to provide a new algorithm for the computation of general equilibrium models in the Yang-Ng framework. [source] 2,5-Disubstituted Pyrrolidines as Chiral Auxiliaries in Radical Reactions: A Theoretical ApproachEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 25 2010Miglena K. Georgieva Abstract The radical addition to amides derived from chiral 2,5-disubstituted pyrrolidines has been theoretically studied by the use of density functional methods and the results compared with known experimental data. The results agree quite well with those obtained experimentally and allow the full rationalization of the factors influencing the diastereoselectivity. Steric effects are the main factors determining the selectivity, but electronic interactions can also be very important when the attacking alkene is ,,,-conjugated, as in acrylic esters or acrylamides. Additions at the ,- and ,-positions of the amide chain in the auxiliary are subject to different rules, with the former usually yielding high diastereoselectivities both experimentally and theoretically, whereas the latter is theoretically predicted to occur with low selectivity. We fully rationalize these two opposite behaviours and suggest several ways to circumvent this limitation, thus strongly increasing the interest of this type of structure as chiral auxiliaries in radical reactions. [source] Ambiguity in Performance Measurement: A Theoretical Approach to Organisational Uses of Performance MeasurementFINANCIAL ACCOUNTABILITY & MANAGEMENT, Issue 3 2006Jarmo Vakkuri First page of article [source] Product Patent, the Problem of Availability of Patented Drugs and Parallel Trade: A Theoretical ApproachTHE JOURNAL OF WORLD INTELLECTUAL PROPERTY, Issue 4 2010Mainak Mazumdar This article theoretically examines the potential effect of product patent on the availability of an essential drug in developing countries like India. Previous studies have indicated the possibility of a product patent making a drug unavailable in a developing nation. This has been shown under the uniform pricing policy adopted by the multinational company (MNC) that produces the drug. Allowing for price discrimination and comparing it with the above situation, we have argued that the problem of non-availability of a patented drug is, indeed, much less serious. However, successful price discrimination is not possible when markets are not perfectly segmented and "parallel trade" (a form of arbitrage) by the distributors exists. Our model incorporates such a possibility and establishes that even in the presence of parallel trade, the MNC can earn higher profits by supplying the drug to both the developed and the developing nations than by confining itself to the markets of developed countries. [source] 18O Isotope Substitution, Vibrational Coupling and Protein Structure: A Theoretical ApproachCHEMPHYSCHEM, Issue 2 2004Thorsten Koslowski Prof. Dr. Site-specific 18O substitution of two amino acids that are in a close spatial vicinity, but far apart in the primary sequence, exhibits characteristic IR fingerprints; the corresponding spectral shifts of the absorption bands are shown color-coded in the figure. This approach can be used to obtain detailed structural information, for example, about membrane proteins which are difficult to crystallize. [source] Study on the Radius of an Electrical Spherical Micelle: Functional Theoretical ApproachCHINESE JOURNAL OF CHEMISTRY, Issue 4 2004Zheng-Wu Wang Abstract For the purpose of eliminating restriction, the Poisson-Boltzmann (PB) equation, which represents the potential of the electrical double layer of spherical micelles, can be solved analytically only under the lower potential condition, a kind of iterative method in functional analysis theory has been used. The radius of the spherical particle can be obtained from the diagram of the second iterative solution of the potential versus the distance from the center of the particle. The influences of the concentration of the ions, the charge number of ions, the aggregation number of the particle, the dielectric constant of solvent and the temperature of system on the radius also have been studied. [source] Corporate Issues Campaigns: Six Theoretical ApproachesCOMMUNICATION THEORY, Issue 1 2004Janet A. Bridges Through the broader concept of issues management, corporate issues campaigns have been tied to at least six theoretical frameworks. Systems and powerful stakeholder theories focus the organization's choice of issues on which to expend resources; legitimacy gap and issue life-cycle theories explain issue development; and social exchange theory and rhetorical analysis present approaches to practicing issue campaign management. These theories can also be applied to social-issues campaigns. All of the theories emphasize the need for research in campaign management, from understanding the relationships within the multidependencies identified by systems theory to evaluating the costs and benefits of social exchanges presented in campaign messages. This article attempts to explicate these theoretical foundations, present a model of the issues campaign process, and demonstrate the contribution the theories make to issues campaigns. [source] Editor's Introduction: Theoretical Approaches to Communication CampaignsCOMMUNICATION THEORY, Issue 2 2003Joseph N. Cappella First page of article [source] Theoretical approach to the mechanism of reactions between halogen atoms and unsaturated hydrocarbons: The Cl + propene reactionJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 16 2003Pedro Braña Abstract The potential energy surface for the Cl + propene reaction was analyzed at the MP2 level using Pople's 6-31G(d,p) and 6-311+G(d,p), and Dunning's cc-pVDZ and aug-cc-pVDZ basis sets. Two different channels for the addition reaction leading to chloroalkyl radicals and five alternative channels for the abstraction reaction leading to C3H + HCl were explored. The corresponding energy profiles were computed at the QCISD(T)/aug-cc-pVDZ//MP2/aug-cc-pVDZ level of theory. Theoretical results suggest that the previously established mechanism consisting of (1) direct abstraction and (2) addition,elimination steps is instead made up of (1) addition through an intermediate and (2) two-step abstraction processes. No direct abstraction mechanism exists on the potential energy surface. The kinetic equations derived for the new mechanism are consistent with the pressure dependence experimentally observed for this reaction. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 2044,2062, 2003 [source] Block Copolymers Under Shear FlowMACROMOLECULAR THEORY AND SIMULATIONS, Issue 4 2005Igor Rychkov Abstract Summary: Microphase separation transition in block copolymer melts and solutions in equilibrium and under shear flow is reviewed. The non-equilibrium molecular dynamics (NEMD) computer simulation methodology is presented in detail including the derivation of the SLLOD equations of motion, Gaussian thermostat, and operator-splitting symplectic integrators. Results of our recent NEMD computer simulation studies of diblock copolymers in a selective solvent under shear flow are presented. Shear-dependent structural, rheological, and microscopical properties are described. New phase transitions are discovered. The parallel-perpendicular orientational transition in a weak-strong flow is revealed. Theoretical approaches are reviewed including the Edwards Hamiltonian, Landau-Ginzburg model, self-consistent mean field theory, field-theoretic simulation, as well as the time-dependent Landau-Ginzburg framework and its application to the studies of complex fluids. [source] Comparison of Additional Costs for Several Replacement Strategies of Randomly Ageing Reinforced Concrete PipesCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 7 2009Franck Schoefs Some of them carry seawater and can deteriorate with time because of internal corrosion. Because of the low O2 content of aggressive water, slow corrosion is expected for such applications. If the RCPs are not periodically replaced, they will eventually fail. Replacement strategies for these pipes depend on (1) the risks associated with the failure of the water distribution network, and (2) the costs associated with replacing the pipes, including the removal of existing pipes, installation of new pipes, and associated production losses. Because of the lack of statistical data regarding RCP failure, the development of a risk-based replacement strategy is not an easy task. This article demonstrates how predictive models for the evolution of the failure of RCPs and the associated consequences of failure can be used to develop risk-based replacement strategies for RCPs. An application for the replacement strategies of a network modeled as a system consisting of 228 RCPs is presented as a case study. We focus on the assessment of the number of replaced components that governs the costs. The main objective of this article is to provide a theoretical approach for comparing replacement strategies, based on (1) the results of a reliability study, (2) the representation of the distributions of failed components (binomial distribution), and (3) the decision tree representation for replacement of RCPs. A focus on the scatter of the induced costs themselves is suggested to emphasize the financial risk. [source] A new type of migrating zone boundary in electrophoresis: 1.ELECTROPHORESIS, Issue 2 2005General description of boundary behavior based on electromigration dispersion velocity profiles Abstract Till now two principal types of electrophoretic boundaries have been recognized: a steady-state one showing self-sharpening properties and an unsteady-state one showing electromigration dispersion (EMD). In this contribution, the existence of a third (hybrid) type of electrophoretic boundary is revealed, that shows simultaneously: (i) steady-state character with self-sharpening properties in a certain part of the boundary, demarcated by a certain range of its composition; (ii) unsteady-state character with EMD in the resting part. A new theoretical approach to the study of the structure and properties of electrophoretic boundaries is presented, based on EMD velocity profiles representing the dependence of the EMD velocity on the composition in any point of the transition region across the boundary. According to this approach, the linearity or nonlinearity of the EMD velocity profile is recommended as the criterion for distinguishing the actual type of the boundary in question. It is shown that the new type of electrophoretic boundary is not an exotic case but may be observed even in simple systems as, e.g., formed by adjacent zones containing mixtures of current species such as picrate and acetate. Computer simulations are presented which confirm the theoretical conclusions and illustrate the three types of electrophoretic boundaries. [source] Quality Culture: understandings, boundaries and linkagesEUROPEAN JOURNAL OF EDUCATION, Issue 4 2008LEE HARVEY As part of the process of enhancing quality, quality culture has become a taken-for-granted concept intended to support development and improvement processes in higher education. By taking a theoretical approach to examining quality culture, starting with a scholarly examination of the concept of culture, and exploring how it is related to quality, quality improvement and quality assurance, the aim of this paper is to create a better understanding of how one can make sense of quality culture, its boundaries but also its links to the fundamental processes of teaching and learning. [source] Synthesis and Luminescent Properties of Novel Europium(III) Heterocyclic ,-Diketone Complexes with Lewis Bases: Structural Analysis Using the Sparkle/AM1 ModelEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2005Rani Pavithran Abstract Tris(,-diketonato)europium(III) complexes of general formula [Eu(TPI)3·L], with chelating ligands such as 3-phenyl-4-(4-toluoyl)-5-isoxazolone (HTPI) and adduct-forming reagents [L = H2O, tri- n -octylphosphane oxide (TOPO), triphenylphosphane oxide (TPhPO), 1,10-phenanthroline], have been synthesized and characterized by elemental analysis and FT-IR, 1H NMR, and photoluminescence spectroscopy. The coordination geometries of the complexes were calculated using the Sparkle/AM1 (Sparkle model for the calculation of lanthanide complexes within the Austin model 1) model. The ligand,Eu3+ energy-transfer rates were calculated using a model of intramolecular energy transfer in lanthanide coordination complexes reported in the literature. The room-temperature PL spectra of the europium(III) complexes are composed of the typical Eu3+ red emission, assigned to transitions between the first excited state (5D0) and the multiplet (7F0,4). The results clearly show that the substitution of water molecules by TOPO leads to greatly enhanced quantum yields (i.e., 1.3,% vs. 49.5,%) and longer 5D0 lifetimes (220 vs. 980 ,s). This can be ascribed to a more efficient ligand-to-metal energy transfer and a less efficient nonradiative 5D0 relaxation process. The theoretical quantum yields are in good agreement with the experimental quantum yields, which highlights that the present theoretical approach can be a powerful tool for the a priori design of highly luminescent lanthanide complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] An analytic model for the behavior of arbitrary peer-to-peer networksEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 6 2004Rüdiger Schollmeier We present an analytic approach to better understand and design peer-to-peer (P2P) networks, which are becoming increasingly important, as they contribute an amount of traffic often dominating the total traffic in the internet even today. We start from a graph theoretical approach for infinite random networks and enhance that to include the effects of a finite network. Our approach is valid for an arbitrary degree distribution in the network and thus avoids the need for extensive simulation, which would otherwise be required to evaluate the performance of a specific P2P protocol. Our analytic approach can thus be used for improved tailoring of P2P communication as well as to minimize the often excessive signaling traffic. Copyright © 2004 AEI [source] Kähler metrics: String vs field theoretical approachFORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 5-7 2009P. Di Vecchia Abstract We use both a string and a field theoretical approach in order to determine respectively the Kähler metrics of untwisted and twisted open strings attached to magnetized D9 branes in toroidal compactifications. [source] Towards a geography of transnational spaces: Indian transnational communities in AustraliaGLOBAL NETWORKS, Issue 1 2004Carmen Voigt-Graf In this article, the geography of the transnational spaces of Punjabis, Kannadigas and Indo-Fijians is analysed. Punjabis have constructed complex transnational spaces that are virtually global in scale. Kannadigas are engaged in transnational activities linking their places of residence with south India. Indo-Fijians have emerged as a regional transnational community stretching across the Pacific Ocean. On the basis of their experiences, a consistent terminology is suggested and a typology of different models of transnational spaces is developed. This typology provides a tool to compare different transnational communities beyond the Indian experience. It can be seen as a preliminary step in the direction of a more theoretical approach that links the geography of migrant transnational spaces with sociological debates on social space. [source] Jim Bulpitt's Territory and Power in the United Kingdom and Interpreting Political Development: Bringing the State and Temporal Analysis Back InGOVERNMENT AND OPPOSITION, Issue 3 2010Jonathan Bradbury This article addresses the relative neglect of Territory and Power in informing the study of general state political development, both as a theoretical approach and in its application to the UK. It locates Territory and Power as a distinct contribution to two major schools of comparative research. The first section argues that Territory and Power provided an approach that was part of the intellectual turn during the 1980s to bring the state back into the analysis of politics. The second part argues that Territory and Power should be seen also as a contribution to the intellectual turn since the 1980s towards temporal analysis of political development. On these bases future researchers may find Territory and Power more accessible as a work that they can incorporate in their own research. [source] Oligophenylenevinylenes in Spatially Confined Nanochannels: Monitoring Intermolecular Interactions by UV/Vis and Raman Spectroscopy,ADVANCED FUNCTIONAL MATERIALS, Issue 6 2008Mariya Aloshyna Abstract Perhydrotriphenylene-based channel-forming inclusion compounds (ICs) and thin films made of polyphenylenevinylene (PPV)-type oligomers with terminal alkoxy groups are investigated and compared in a combined experimental and theoretical approach. Interchromophore interactions and host-guest interactions are elucidated by UV/Vis and Raman spectroscopy. The impact of the local environment of the chromophore on the optical and photophysical properties is discussed in light of quantum-chemical calculations. In stark contrast to thin films where preferential side-by-side orientation leads to quenching of photoluminescence (PL) via non-emissive traps, the ICs are found to be attractive materials for opto-electronic applications: they offer high chromophore concentrations, but at the same time behave as quasi-isolated entities of tightly packed, well-oriented objects with high PL quantum yields and the possibility of color tuning. [source] Rationalization of the stereochemistry of an addition of dialkyl phosphites to certain chiral aldimines: The experimental and theoretical approachHETEROATOM CHEMISTRY, Issue 2 2002Ryszard B. Nazarski The absolute configuration of an ,-P stereogenic center in two diastereomeric O,O-dialkyl ,-aminophosphonates (3), arising from an induced 1,3-asymmetric phosphite addition to the CN bond of furfural-derived Schiff bases (1), was established from single product 1H NMR data. Such spectra were interpreted with anisotropic shielding in relation to the AM1 and MNDO/d structures of 3; the former ones turned out to be closer to the obtained experimental results (1H NMR spectra of 3, crystallographic database study). Since favored 3-21G geometries of starting imines 1 were modeled as well, it was inferred that a stereochemical outcome of this reaction is governed by Cram selectivity. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:120,125, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10005 [source] Errors in technological systemsHUMAN FACTORS AND ERGONOMICS IN MANUFACTURING & SERVICE INDUSTRIES, Issue 4 2003R.B. Duffey Massive data and experience exist on the rates and causes of errors and accidents in modern industrial and technological society. We have examined the available human record, and have shown the existence of learning curves, and that there is an attainable and discernible minimum or asymptotic lower bound for error rates. The major common contributor is human error, including in the operation, design, manufacturing, procedures, training, maintenance, management, and safety methodologies adopted for technological systems. To analyze error and accident rates in many diverse industries and activities, we used a combined empirical and theoretical approach. We examine the national and international reported error, incident and fatal accident rates for multiple modern technologies, including shipping losses, industrial injuries, automobile fatalities, aircraft events and fatal crashes, chemical industry accidents, train derailments and accidents, medical errors, nuclear events, and mining accidents. We selected national and worldwide data sets for time spans of up to ,200 years, covering many millions of errors in diverse technologies. We developed and adopted a new approach using the accumulated experience; thus, we show that all the data follow universal learning curves. The vast amounts of data collected and analyzed exhibit trends consistent with the existence of a minimum error rate, and follow failure rate theory. There are potential and key practical impacts for the management of technological systems, the regulatory practices for complex technological processes, the assignment of liability and blame, the assessment of risk, and for the reporting and prediction of errors and accident rates. The results are of fundamental importance to society as we adopt, manage, and use modern technology. © 2003 Wiley Periodicals, Inc. Hum Factors Man 13: 279,291, 2003. [source] A micromechanical approach to the strength criterion of Drucker-Prager materials reinforced by rigid inclusionsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 7-8 2004Jean-François Barthélémy Abstract At the microscopic scale, concrete can be considered as a frictional matrix (cement paste) surrounding rigid inclusions (aggregate or sand inclusions). The present paper proposes a theoretical approach to the strength criterion of such a composite material. It is shown that the macroscopic stress states on the yield surface can be obtained from the solution to non-linear viscous problems defined on a representative volume element. The practical determination of the yield surface implements a non-linear homogenization scheme based on the modified secant method. The role of the interface between the matrix and the inclusions is also investigated. Two extreme modellings are considered: perfect bonding and non-frictional interfaces. In both cases, the method yields a macroscopic strength criterion of the Drucker,Prager type. The macroscopic friction angle is a function of that of the matrix and of the volume fraction of the inclusions. In the case of perfect bonding, the inclusions have a reinforcing effect. In contrast, this may not be true for a non-frictional interface. Copyright © 2004 John Wiley & Sons, Ltd. [source] An innovative approach to the theory and practice of organizational analysis: my journey with Elliott JaquesINTERNATIONAL JOURNAL OF APPLIED PSYCHOANALYTIC STUDIES, Issue 4 2005Aldo Schlemenson Abstract This article highlights the author's experience working with Elliott Jaques and his theory for over 35 years in Argentina. It examines the development of Jaques' theoretical approach to organizational theory over two decades, transforming from a psychological to a social theoretical framework. Emphasis is put in the notions of the organizational structure, the hierarchical managerial system, stratification, and the managerial accountability in a manner that allows for a systematic analysis. The "time-span of discretion" instrument is the means for evaluating jobs and for having access to extant organization. This approach allows a process of change combining effectiveness with a humanistic democratization of the workplace and ethics. This article provides examples of projects implemented in the public administration area, verifying the consistency of the theory and its practical applications, in particular concerning individual capabilities, the talent pool, and their evaluation. It contains a Foreword by Dr Carlos Silvani, International Monetary Fund, Washington, D.C. Copyright © 2005 John Wiley & Sons, Ltd. [source] A model for latent heat energy storage systemsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2006Numan Yuksel Abstract In this study, a theoretical approach is proposed for the prediction of time and temperature during the heat charge and discharge in the latent heat storage of phase changed materials (PCM). By the use of the average values of the mean specific heat capacities for the phase-changed materials, analytical solutions are obtained and compared with the available experimental data in the literature. It is shown that decreasing the entry temperature of the working fluid from ,4 to ,15°C has a very dominant and strong effect on the PCM solidification time. The effect of the working fluid flow rate and the material of PCM capsules on the time for complete solidification and total charging is also investigated. The agreement between the present theoretical model results and the experimental data related to the cooling using small spheres and the heat storage using rectangle containers is very good. The largest difference between the present results and the experimental data becomes about 10% when the fluid temperature approaches the phase change temperature at high temperatures. Copyright © 2006 John Wiley & Sons, Ltd. [source] Handling indefinite and maybe information in logical fuzzy relational databasesINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 3 2004Nan-Chen Hsieh In this article, fuzzy set theory uses an extension of the classical logical relational database model. A logical fuzzy relational database model was developed with the aim of manipulating imprecise information and adding deduction capabilities to the database system. The essence of this work is the detailed discussion on fuzzy definite, fuzzy indefinite, and fuzzy maybe information and the development of an information theoretical approach of query evaluation on the logical fuzzy relational database. We define redundancies among fuzzy tuples and the operator of their removal. A complete set of fuzzy relational operations in relational algebra and the calculus of linguistically quantified propositions are included also. © 2004 Wiley Periodicals, Inc. [source] Approximate knowledge modeling and classification in a frame-based language: The system CAININTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 6 2001Colette Faucher In this article, we present an extension of the frame-based language Objlog+, called CAIN, which allows the homogeneous representation of approximate knowledge (fuzzy, uncertain, and default knowledge) by means of new facets. We developed elements to manage approximate knowledge: fuzzy operators, extension of the inheritance mechanisms, and weighting of structural links. Contrary to other works in the domain, our system is strongly based on a theoretical approach inspired from Zadeh's and Dubois' works. We also defined an original instance classification mechanism, which has the ability to take into account the notions of typicality and similarity as they are presented in the psychological literature. Our model proposes consideration of a particular semantics of default values to estimate the typicality between a class and the instance to classify (ITC). In that way, the possibilities of the typicality representation proposed by frame-based languages are exploited. To find the most appropriate solution we do not systematically choose the most specific class that matches the ITC but we retain the most typical solution. Approximate knowledge is used to make the matching used during the classification process more flexible. Taking into account additional knowledge concerning heuristics and elements of cognitive psychology leads to the enrichment of the classification mechanism. © 2001 John Wiley & Sons, Inc. [source] First hyperpolarizabilities of vinylogue organometallic sesquifulvalene chromophores: A DFT studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 12 2006Chaoyong Mang Abstract Static first hyperpolarizabilities of vinylogue mono- and bimetallic sesquifulvalene chromophores, [(,5 -C5H5)M{,,(,5 -C5H4)CHCH(,6 -C7H7)}]+ (M = Fe, Ru, and Os) and [(,5,C5H5)M{,,(,5 -C5H4)CHCH(,6 -C7H7)}Cr(CO)3]+ (M = Fe, Ru, and Os) have been calculated within DFT theoretical approach. The results agree well with the recent Hyper-Rayleigh scattering (HRS) measurements. The coordinated transition metals reduced the magnitude of dipole moment and first hyperpolarizability. The metal-to-ligand charge-transfer contributes to the first hyperpolarizability and, as a result, the rational substitution of coordinated metal could modulate the first hyperpolarizability of the organometallic chromophores. The study would be helpful to understand optical nonlinearities in organometallic complexes. © 2006 Wlley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Theoretical and experimental luminescence quantum yields of coordination compounds of trivalent europiumINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2005Wagner M. Faustino Abstract An appraisal of a semiempirical methodology recently introduced by us for the theoretical calculation of luminescence quantum yields is presented. Six coordination compounds of Eu3+ were considered, possessing either benzoylacetonate or benzoyltrifluoroacetonate, together with either water, 2,2,-bipyridine, or 1,10-phenanthroline as ligands. Their geometries were calculated using the SMLC/AM1 method. The ligand,Eu3+ energy transfer rates were calculated in terms of a model of intramolecular energy transfer processes in lanthanide coordination compounds developed earlier by our group. The luminescence quantum yields of the complexes were calculated by solving numerically a system of rate equations for each compound, and by comparing them with the quantum yields determined spectroscopically. Finally, we show that the theoretical quantum yields correlate linearly with the experimental yields, within their error bars. Such linear correlation indicates that the theoretical approach can be useful for the a priori design of highly luminescent lanthanide coordination compounds. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Performance evaluation of TCP-based applications over DVB-RCS DAMA schemesINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 3 2009M. Luglio Abstract Transmission Control Protocol (TCP) performance over Digital Video Broadcasting,Return Channel via Satellite (DVB-RCS) standard is greatly affected by the total delay, which is mainly due to two components, propagation delay and access delay. Both are significant because they are dependent on the long propagation path of the satellite link. The former is intrinsic and due to radio wave propagation over the satellite channel for both TCP packets and acknowledgements. It is regulated by the control loop that governs TCP. The latter is due to the control loop that governs the demand assignment multiple access (DAMA) signalling exchange between satellite terminals and the network control center, necessary to manage return link resources. DAMA is adopted in DVB-RCS standard to achieve flexible and efficient use of the shared resources. Therefore, performance of TCP over DVB-RCS may degrade due to the exploitation of two nested control loops also depending on both the selected DAMA algorithm and the traffic profile. This paper analyses the impact of basic DAMA implementation on TCP-based applications over a DVB-RCS link for a large set of study cases. To provide a detailed overview of TCP performance in DVB-RCS environment, the analysis includes both theoretical approach and simulation campaign. Copyright © 2009 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||