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Linear Structures (linear + structure)
Selected AbstractsI,Time, Topology and Physical GeometryARISTOTELIAN SOCIETY SUPPLEMENTARY VOLUME, Issue 1 2010Tim Maudlin The standard mathematical account of the sub-metrical geometry of a space employs topology, whose foundational concept is the open set. This proves to be an unhappy choice for discrete spaces, and offers no insight into the physical origin of geometrical structure. I outline an alternative, the Theory of Linear Structures, whose foundational concept is the line. Application to Relativistic space-time reveals that the whole geometry of space-time derives from temporal structure. In this sense, instead of spatializing time, Relativity temporalizes space. [source] System identification of linear structures based on Hilbert,Huang spectral analysis.EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 10 2003Part 2: Complex modes Abstract A method, based on the Hilbert,Huang spectral analysis, has been proposed by the authors to identify linear structures in which normal modes exist (i.e., real eigenvalues and eigenvectors). Frequently, all the eigenvalues and eigenvectors of linear structures are complex. In this paper, the method is extended further to identify general linear structures with complex modes using the free vibration response data polluted by noise. Measured response signals are first decomposed into modal responses using the method of Empirical Mode Decomposition with intermittency criteria. Each modal response contains the contribution of a complex conjugate pair of modes with a unique frequency and a damping ratio. Then, each modal response is decomposed in the frequency,time domain to yield instantaneous phase angle and amplitude using the Hilbert transform. Based on a single measurement of the impulse response time history at one appropriate location, the complex eigenvalues of the linear structure can be identified using a simple analysis procedure. When the response time histories are measured at all locations, the proposed methodology is capable of identifying the complex mode shapes as well as the mass, damping and stiffness matrices of the structure. The effectiveness and accuracy of the method presented are illustrated through numerical simulations. It is demonstrated that dynamic characteristics of linear structures with complex modes can be identified effectively using the proposed method. Copyright © 2003 John Wiley & Sons, Ltd. [source] Geometries, vibrational frequencies, and electron affinities of X2Cl (X=C,Si,Ge) clustersINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2007Feng-You Hao Abstract Ab initio quantum chemical calculations have been performed on X2Cl, and X2Cl (X = C, Si, Ge) clusters. The geometrical structures, vibrational frequencies, electronic properties and dissociation energies are investigated at the Hartree,Fock (HF), Møller,Plesset second- and fourth-order (MP2, MP4), CCSD(T) level with the 6-311+G(d) basis set. The X2Cl (X = C, Si, Ge) and X2Cl, (X = Si, Ge) take a bent shape obtained at the ground state, while C2Cl, has a linear structure. The impact on internal electron transfer between the X2Cl and the corresponding anional clusters is studied. The three different types of electron affinities (EAs) at the CCSD(T) are reported. The most reliable adiabatic electronic affinities, obtained at the CCSD(T)/cc-pvqz level of theory, are predicted to be 3.30, 2.62, and 1.98 eV for C2Cl, Si2Cl, and Ge2Cl, respectively. The calculated EAs of C2Cl and Ge2Cl are in good agreement with theoretical results reported. The correlation effects and basis sets effects on the geometrical structures and dissociation energies are discussed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Binding and release studies of a cationic drug from a star-shaped four-arm poly(ethylene oxide)- b -poly(methacrylic acid)JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2010E. He Abstract Star-shape polymers possess higher densities of terminal functional groups and three-dimensional tetrahedron structure that induce significantly different association and interactions with drug compared to linear structure of identical molecular weights. Four-arm poly(ethylene oxide)- b -poly(methacrylic acid) block copolymer was synthesized by atom transfer radical polymerization technique, and it self-assembled into core-shell micelles and extended unimers at low and high pH respectively. The negatively charged carboxylate groups on the polymer chains interacted with a cationic drug through electrostatic interaction forming polymer/drug complexes stabilized by biocompatible hydrophilic PEO segments. The hydrodynamic radius (Rh) of the polymeric aggregates and polymer/drug complexes ranged from 46 to 84,nm and 32 to 55,nm at pH of 4.6 and 8.0 respectively, making them suitable for drug delivery applications. The thermodynamic parameters and interactions between polymer and drug were determined by isothermal titration calorimetric technique. The electrostatic force, hydrogen bonding and hydrophobic interactions controlled the characteristics of polymer/drug formation and complexes when the molar ratios of drug and polymer were varied. Drug selective electrode system was used to measure the dynamic release of imipramine hydrochloride (IPH) from multi-arm PEO- b -PMAA star polymer. The release exponent n was greater than 0.5 indicating a non-Fickian type diffusion behavior, where the release behavior was dominated by chain relaxation induced by ion exchange that was dependent on pH. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:782,793, 2010 [source] Imaging appearance of the symptomatic perforating artery in patients with lacunar infarction: Occlusion or other vascular pathology?ANNALS OF NEUROLOGY, Issue 2 2001Joanna M. Wardlaw FRCR Lacunar infarction is associated with distinct clinical features. It is thought to result from occlusion of a deep perforating artery in the basal ganglia, centrum semiovale, or brainstem. However, occluded perforating arteries have only rarely been observed at postmortem in patients with lacunar stroke and have not been noted previously on imaging despite the increasing sophistication of the techniques. We observed nine patients with lacunar stroke imaged with computed tomography and magnetic resonance imaging in whom we observed a linear structure with density or signal features consistent with an occluded (or at least abnormal) perforating artery associated with the relevant lacunar infarct. The appearance might also have been caused by a leak of blood and fluid into the perivascular space around the artery, as in several patients the width of the tubular vessel-like structure (>1mm in diameter) was greater than the expected width of a perforating artery (<0.8mm in diameter). This interpretation is supported by the fact that the area of infarction was usually around the abnormal vessel, not at the end of it. We describe the patients' clinical and imaging features, and discuss alternative explanations for the imaging appearance and the implications for gaining insights into the cause of lacunar infarction. [source] Self-Assembled Monolayers of Alkoxy-Substituted Octadehydrodibenzo[12]annulenes on a Graphite Surface: Attempts at peri -Benzopolyacene Formation by On-Surface PolymerizationCHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2010Kazukuni Tahara Dr. Abstract Self-assembled monolayers of a series of tetraalkoxy-substituted octadehydrodibenzo[12]annulene (DBA) derivatives 1,c,g possessing butadiyne linkages were studied at the 1,2,4-trichlorobenzene (TCB) or 1-phenyloctane/graphite interface by scanning tunneling microscopy (STM). The purpose of this research is not only to investigate the structural variation of two-dimensional (2D) monolayers, but also to assess a possibility for peri -benzopolyacene formation by two-dimensionally controlled polymerization on a surface. As a result, the formation of three structures, porous, linear, and lamella structures, were observed by changing the alkyl chain length and the solute concentration. The formation of multilayers of the lamella structure was often observed for all compounds. The selection of molecular networks is basically ascribed to intermolecular and molecule,substrate interactions per unit area and network density. The selective appearance of the linear structure of 1,d is attributed to favorable epitaxial registry matching between the substrate lattice and the overlayer lattice. Even though the closest interatomic distance between the diacetylenic units of the DBAs in the lamella structure (,0.6,nm) is slightly larger compared to the typical distances necessary for topochemical polymerization, the reactivity toward external stimuli (electronic-pulse irradiation from an STM tip and UV irradiation) was investigated. Unfortunately, no evidence for polymerization of the DBAs on the surface was observed. The present results indicate the necessity for further designing a suitable system for the on-surface construction of structurally novel conjugated polymers, which are otherwise difficult to prepare. [source] System identification of linear structures based on Hilbert,Huang spectral analysis.EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 10 2003Part 2: Complex modes Abstract A method, based on the Hilbert,Huang spectral analysis, has been proposed by the authors to identify linear structures in which normal modes exist (i.e., real eigenvalues and eigenvectors). Frequently, all the eigenvalues and eigenvectors of linear structures are complex. In this paper, the method is extended further to identify general linear structures with complex modes using the free vibration response data polluted by noise. Measured response signals are first decomposed into modal responses using the method of Empirical Mode Decomposition with intermittency criteria. Each modal response contains the contribution of a complex conjugate pair of modes with a unique frequency and a damping ratio. Then, each modal response is decomposed in the frequency,time domain to yield instantaneous phase angle and amplitude using the Hilbert transform. Based on a single measurement of the impulse response time history at one appropriate location, the complex eigenvalues of the linear structure can be identified using a simple analysis procedure. When the response time histories are measured at all locations, the proposed methodology is capable of identifying the complex mode shapes as well as the mass, damping and stiffness matrices of the structure. The effectiveness and accuracy of the method presented are illustrated through numerical simulations. It is demonstrated that dynamic characteristics of linear structures with complex modes can be identified effectively using the proposed method. Copyright © 2003 John Wiley & Sons, Ltd. [source] Structural damage detection using the optimal weights of the approximating artificial neural networksEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2002Shih-Lin Hung Abstract This work presents a novel neural network-based approach to detect structural damage. The proposed approach comprises two steps. The first step, system identification, involves using neural system identification networks (NSINs) to identify the undamaged and damaged states of a structural system. The partial derivatives of the outputs with respect to the inputs of the NSIN, which identifies the system in a certain undamaged or damaged state, have a negligible variation with different system errors. This loosely defined unique property enables these partial derivatives to quantitatively indicate system damage from the model parameters. The second step, structural damage detection, involves using the neural damage detection network (NDDN) to detect the location and extent of the structural damage. The input to the NDDN is taken as the aforementioned partial derivatives of NSIN, and the output of the NDDN identifies the damage level for each member in the structure. Moreover, SDOF and MDOF examples are presented to demonstrate the feasibility of using the proposed method for damage detection of linear structures. Copyright © 2001 John Wiley & Sons, Ltd. [source] Synthesis of Carboxyl-Tethered Symmetric Conjugated Polyenes as Fluorescent Transmembrane Probes of Lipid BilayersEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2003Ernesto Quesada Abstract The synthesis of a new series of fluorescent transmembrane probes in which two hydrophilic methyl ester or carboxyl groups are connected by a polymethylene chain, with four, five or six conjugated double bonds in a central position, is reported. The length of the linear structures was designed to match the width of typical lipid bilayers. These bolaamphiphilic compounds result, with overall yields higher than 80%, from an easy PdII -catalyzed double cross-coupling between terminal acetylene esters and conjugated 1,,-dihalopolyenes, followed by selective triple bond partial reduction with activated zinc, and iodine isomerization to the all-(E) isomer. An alternative approach, based on a Stille double cross-coupling between the appropriate all-(E)-,-halopolyenes and (E)-bis(tributylstannyl)ethene, yielded mixtures that could not be resolved by standard chromatographic methods due to the presence of other simultaneous coupling reactions, which are also discussed in detail. Nevertheless, the Stille method can be of utility for the obtention of carbonyl-polyene conjugated analogs. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Organization of Coordination Polymers on Surfaces by Direct SublimationADVANCED MATERIALS, Issue 20 2009Lorena Welte Sublimation and surface reassembly of coordination polymers is achieved due to the reversibility of the coordination bonds. Atomic force microscopy images show linear structures on surfaces, as expected for a 1D coordination polymer [source] Optimal vibration control of continuous structures by FEM: Part I,the optimality equationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 12 2002W. Szyszkowski Abstract The governing equations of the problem of optimal vibration control of continuous linear structures are derived in the form of a set of fourth-order ordinary differential equations in the time domain. The equations decouple in the modal space and become suitable for handling by the FEM technique with the time domain subdivided into ,finite time' elements of class C1. It is demonstrated that the standard beam element with cubic Hermitian interpolation functions, routinely used in a static analysis of beams, can conveniently be substituted for the required ,finite time' element. Copyright © 2002 John Wiley & Sons, Ltd. [source] A dual algorithm for the topology optimization of non-linear elastic structuresINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2009C. S. Jog Abstract Dual algorithms are ideally suited for the purpose of topology optimization since they work in the space of Lagrange multipliers associated with the constraints. To date, dual algorithms have been applied only for linear structures. Here we extend this methodology to the case of non-linear structures. The perimeter constraint is used to make the topology problem well-posed. We show that the proposed algorithm yields a value of perimeter that is close to that specified by the user. We also address the issue of manufacturability of these designs, by proposing a variant of the standard dual algorithm, which generates designs that are two-dimensional although the loading and the geometry are three-dimensional. Copyright © 2008 John Wiley & Sons, Ltd. [source] A new numerical algorithm for sub-optimal control of earthquake excited linear structuresINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2001Mehmet Bakioglu Abstract Exact optimal classical closed,open-loop control is not achievable for the buildings under seismic excitations since it requires the whole knowledge of earthquake in the control interval. In this study, a new numerical algorithm for the sub-optimal solution of the optimal closed,open-loop control is proposed based on the prediction of near-future earthquake excitation using the Taylor series method and the Kalman filtering technique. It is shown numerically that how the solution is related to the predicted earthquake acceleration values. Simulation results show that the proposed numerical algorithm are better than the closed-loop control and the instantaneous optimal control and proposed numerical solution will approach the exact optimal solution if the more distant future values of the earthquake excitation can be predicted more precisely. Effectiveness of the Kalman filtering technique is also confirmed by comparing the predicted and the observed time history of NS component of the 1940 El Centro earthquake. Copyright © 2001 John Wiley & Sons, Ltd. [source] Theoretical studies on structures and electronic spectra of linear carbon chains C2nH+ (n = 1,5)INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2009Jinglai Zhang Abstract The density functional theory (DFT) and the complete active space self-consistent-field (CASSCF) method have been used for full geometry optimization of carbon chains C2nH+ (n = 1,5) in their ground states and selected excited states, respectively. Calculations show that C2nH+ (n = 1,5) have stable linear structures with the ground state of X3, for C2H+ or X3,, for other species. The excited-state properties of C2nH+ have been investigated by the multiconfigurational second-order perturbation theory (CASPT2), and predicted vertical excitation energies show good agreement with the available experimental values. On the basis of our calculations, the unsolved observed bands in previous experiments have been interpreted. CASSCF/CASPT2 calculations also have been used to explore the vertical emission energy of selected low-lying states in C2nH+ (n = 1,5). Present results indicate that the predicted vertical excitation and emission energies of C2nH+ have similar size dependences, and they gradually decrease as the chain size increases. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Homo- and copolymerization of ethylene and norbornene with bis(,-diketiminato) titanium complexes activated with methylaluminoxaneJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2008Yongfei Li Abstract Homo- and copolymerization of ethylene and norbornene were investigated with bis(,-diketiminato) titanium complexes [ArNC(CR3)CHC(CR3)NAr]2TiCl2 (R = F, Ar = 2,6-diisopropylphenyl 2a; R = F, Ar = 2,6-dimethylphenyl 2b; R = H, Ar = 2,6-diisopropylphenyl 2c; R = H, Ar = 2,6-dimethylphenyl 2d) in the presence of methylaluminoxane (MAO). The influence of steric and electric effects of complexes on catalytic activity was evaluated. With MAO as cocatalyst, complexes 2a,d are moderately active catalysts for ethylene polymerization producing high-molecular weight polyethylenes bearing linear structures, but low active catalysts for norbornene polymerization. Moreover, 2a,d are also active ethylene,norbornene (E,N) copolymerization catalysts. The incorporation of norbornene in the E,N copolymer could be controlled by varying the charged norbornene. 13C NMR analyses showed the microstructures of the E,N copolymers were predominantly alternated and isolated norbornene units in copolymer, dyad, and triad sequences of norbornene were detected in the E,N copolymers with high incorporated content of norbornene. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 93,101, 2008 [source] | ||||||||||||||||