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Structural Parameters (structural + parameter)
Selected AbstractsLong-Term Monitoring and Identification of Bridge Structural ParametersCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 2 2009Serdar Soyoz This three-span 111-m long bridge is instrumented with 13 acceleration sensors at both the superstructure and the columns. The sensor data are transmitted to a server computer wirelessly. Modal parameters of the bridge, that is, the frequencies and the modal shapes were identified by processing 1,707 vibration data sets collected under traffic excitations, based on which the bridge structural parameters, stiffness and mass, and the soil spring values were identified by employing the neural network technique. The identified superstructure stiffness at the beginning of the monitoring was 97% of the stiffness value based on the design drawings. In the identified modal frequencies, a variation from ,10% to +10% was observed over the monitoring period. In the identified stiffness values of the bridge superstructure, a variation from ,3% to +3% was observed over the monitoring period. Based on the statistical analysis of the collected data for each year, 5% decrease in the first modal frequency and 2% decrease in the superstructure stiffness were observed over the 5-year monitoring period. Probability density functions were obtained for stiffness values each year. Stiffness threshold values for the collapse of the bridge under the operational loading can be determined. Then the number of years can be assessed for which the area under the proposed probability density functions is greater than the threshold value. So the information obtained in this study is valuable for studying aging and long-term performance assessment of similar bridges. [source] Low Skeletal Muscle Mass Is Associated With Poor Structural Parameters of Bone and Impaired Balance in Elderly Men,The MINOS Study,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 5 2005Pawel Szulc MD Abstract In 796 men, 50-85 years of age, decreased relative skeletal muscle mass index was associated with narrower bones, thinner cortices, and a consequent decreased bending strength (lower section modulus), as well as with impaired balance and an increased risk of falls. Introduction: In men, appendicular skeletal muscle mass (ASM) is correlated positively with BMC and areal BMD (aBMD). In elderly men, low muscle mass and strength (sarcopenia) is associated with difficulties in daily living activities. The aim of this study was to evaluate if ASM is correlated with bone size, mechanical properties of bones, balance, and risk of falls in elderly men. Materials and Methods: This study used 796 men, 50-85 years of age, belonging to the MINOS cohort. Lifestyle factors were evaluated by standardized questionnaires. Estimates of mechanical bone properties were derived from aBMD measured by DXA. ASM was estimated by DXA. The relative skeletal muscle mass index (RASM) was calculated as ASM/(body height)2.3. Results: After adjustment for age, body size, tobacco smoking, professional physical activity, and 17,-estradiol concentration, RASM was correlated positively with BMC, aBMD, external diameter, and cortical thickness (r = 0.17-0.34, p < 0.0001) but not with volumetric BMD. Consequently, RASM was correlated with section modulus (r = 0.29-0.39, p < 0.0001). Men in the lowest quartile of RASM had section modulus of femoral neck and distal radius lower by 12-18% in comparison with men in the highest quartile of RASM. In contrast, bone width was not correlated with fat mass, reflecting the load of body weight (except for L3), which suggests that the muscular strain may exert a direct stimulatory effect on periosteal apposition. After adjustment for confounding variables, a decrease in RASM was associated with increased risk of falls and of inability to accomplish clinical tests of muscle strength, static balance, and dynamic balance (odds ratio per 1 SD decrease in RASM, 1.31-2.23; p < 0.05-0.001). Conclusions: In elderly men, decreased RASM is associated with narrower bones and thinner cortices, which results in a lower bending strength. Low RASM is associated with impaired balance and with an increased risk of falls in elderly men. It remains to be studied whether low RASM is associated with decreased periosteal apposition and with increased fracture risk in elderly men, and whether the difference in skeletal muscle mass between men and women contributes to the between-sex difference in fracture incidence. [source] Crystal growth, optical and luminescence properties of (Ce,Sr)-doped PrAlO3 single crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2007A. Novoselov Abstract Using the micro-pulling-down method, (Ce,Sr)-doped PrAlO3 square-shaped single crystals (4×4×12 mm) were grown. Structural parameters studied by X-ray powder diffraction were consistent with R3m space group. Compositional homogeneity was checked with electron probe micro-analysis and found quite uniform. Absorption spectra and luminescence characteristics under UV and X-ray excitations were measured at room temperature with no Ce-related emission appeared. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Probing the influence of stereoelectronic effects on lithium affinity in 1,3- and 1,4-dioxa systemsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7 2001Bishwajit Ganguly Abstract A combined computational and structural study of the lithium affinity (LA) of O,C,O systems exhibiting the anomeric effect and of O, C,C,O systems exhibiting the gauche effect is presented. QM ab initio calculations using the MP2/6,31G* basis set were carried out on the gas-phase lithium affinities of dimethoxymethane (DMOM), dimethoxyethane (DMOE), 1,3-dioxane (DOX) and cis - and trans -tetraoxadecalin (TOD), along with that of dimethyl ether and of its dimer as reference compounds. Structural parameters were retrieved from the Cambridge Structural Database (CSD) for diethyl ether dimer and O,C,C,O lithium complexes and these agreed well with the calculated data. The computed lithium affinities of dimethoxymethane and dimethoxyethane were found to be conformationally dependent. The LAs are conformationally dependent (wherever applicable) and decrease in the order: (Me2O)2 >,DMOE >,DMOM >,DOD >,DOX >,trans -TOD, but cis -TOD restores the high LA (better than DMOE) by virtue of multiple coordination. Copyright © 2001 John Wiley & Sons, Ltd. [source] Sorption of HOC in soils with carbonaceous contamination: Influence of organic-matter compositionJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2005Kerstin Abelmann Abstract Detailed information about structure and composition of organic sorbents is required to understand their impact on sorption capacity and sorption kinetic of organic pollutants. Therefore, the chemical composition of organic material from 18 geosorbents was investigated by solid-state 13C nuclear-magnetic-resonance (NMR) spectroscopy. Structural parameters such as aromaticity, polarity, and alkyl-C content were related to the Freundlich sorption exponent (1/n) and the sorption coefficient . The geosorbents included three natural and four combusted coals (carbonaceous material), three Histosols, five mineral soils from Germany containing inputs of technogenic carbonaceous material, derived from industrial activities, and four non-contaminated mineral soils from Germany. Equilibrium sorption was measured for five hydrophobic organic compounds and analyzed with the solubility-normalized Freundlich sorption isotherm. With increasing maturation degree, the proportion of polar constituents decreases from the natural soils to the coals. In contrast to the non-polluted mineral soils, the soils with technogenic input are characterized by high aromaticity and low polarity. A positive correlation between sorption coefficient and aromaticity was found. The Freundlich exponent (1/n) is negatively correlated with the aromaticity, denoting an increase of adsorption processes with increasing aromaticity. Likewise, the contribution of partitioning decreases. This sorption mechanism predominates only if the organic matter in the samples contains a high proportion of polar compounds. Sorption von HOC in Böden mit kohleartiger Kontamination: Einfluss der Zusammensetzung des organischen Materials Um den Einfluss von organischen Sorbenten auf die Sorptionskapazität und die Kinetik organischer Schadstoffe zu verstehen, müssen detaillierte Informationen über deren Struktur und Zusammensetzung vorliegen. Aus diesem Grund wurde das organische Material von 18 Geosorbenten mittels der Festkörper- 13C-NMR-Spektroskopie untersucht. Strukturelle Parameter wie zum Beispiel die Aromatizität, die Polarität und der Alkyl-C-Gehalt wurden mit dem Freundlich-Exponenten 1/n und dem Sorptionskoeffizienten korreliert. Die Geosorbenten bestehen aus drei natürlichen und vier thermisch behandelten Kohlen, drei Histosolen und fünf deutschen Mineralböden, die technogenes kohlehaltiges Material aus industriellen Aktivitäten enthalten, sowie vier nicht kontaminierten deutschen Böden. Die Gleichgewichtssorption wurde für fünf hydrophobe, organische Verbindungen gemessen und mit Hilfe der löslichkeitsnormalisierten Freundlich-Isotherme analysiert. Der Anteil der polaren Komponenten nimmt von den natürlichen Böden zu den Kohlen mit zunehmendem Inkohlungsstadium ab. Im Gegensatz zu den nicht kontaminierten Mineralböden weisen die Böden mit technogenen Bestandteilen eine hohe Aromatizität und eine geringe Polarität auf. Zwischen dem und der Aromatizität ergab sich ein positiver Zusammenhang. Der Freundlich Exponent (1/n) korreliert negativ mit der Aromatizität. Dies weist auf eine Zunahme der Adsorptionsprozesse mit Erhöhung der Aromatizität hin. Der Beitrag der Partitionierung sinkt ebenfalls. Dieser Sorptionsmechanismus dominiert nur in den Proben, in denen das organische Material einen hohen Anteil polarer Bestandteile besitzt. [source] Zirconocene-catalyzed copolymerization of methyl methacrylate with other methacrylate monomersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2004Giorgos Karanikolopoulos Abstract Statistical copolymers of methyl methacrylate (MMA) with n -butyl-, s -butyl, t -butyl-, n -hexyl-, decyl-, stearyl-, allyl-, trimethylsilyl- and trimethylsilyloxyethyl methacrylate were prepared by zirconocene-catalyzed copolymerization. The reactivity ratios of MMA copolymers with butyl-, hexyl-, and stearyl methacrylate were estimated using the Finemann,Ross, the inverted Finemann,Ross, and the Kelen,Tüdos graphical methods. Structural parameters of the copolymers were obtained from the calculated dyad sequences, derived by using the reactivity ratios. The effect of the nature of the methacrylate ester group and the catalytic system used on the copolymer structure is discussed. The glass-transition temperature (Tg) values of MMA copolymers with butyl- and hexyl methacrylate were measured and examined in the frame of several theoretical equations, allowing the prediction of these Tg values. The best fit was obtained using Barton and Johnston equations, taking the monomer sequence distribution of the copolymers into account. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3761,3774, 2004 [source] The Role of Filler Networking in Fatigue Crack Propagation of Elastomers under High-Severity ConditionsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 2 2009Manfred Klüppel Abstract Structural parameters of the filler network have been evaluated by fitting quasi-static stress/strain cycles to the dynamic flocculation model. It is found that the size of filler clusters as well as the strength of filler,filler bonds increase with filler loading and carbon black activity (specific surface). This correlates with the behavior of the tear resistance obtained for pulsed loading under high-severity conditions, implying that the characteristics of the filler network govern the fracture properties of filled elastomers. The behavior of the power law exponent of fatigue crack propagation versus tearing energy can be explained by flash temperature effects in the crack tip area. [source] Structural parameters of Mayall II = G1 in M31MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007J. Ma ABSTRACT Mayall II = G1 is one of the most luminous globular clusters (GCs) known in M31. New deep, high-resolution observations with the Advanced Camera for Surveys on the Hubble Space Telescope are used to provide accurate photometric data to the smallest radii yet. In particular, we present the precise variation of ellipticity and position angle, and of surface brightness for the core of the object. Based on these accurate photometric data, we redetermine the structural parameters of G1 by fitting a single-mass isotropic King model. We derive a core radius, rc= 0.21 ± 0.01 arcsec (= 0.78 ± 0.04 pc), a tidal radius, rt= 21.8 ± 1.1 arcsec (= 80.7 ± 3.9 pc), and a concentration index c= log (rt/rc) = 2.01 ± 0.02. The central surface brightness is 13.510 mag arcsec,2. We also calculate the half-light radius, at rh= 1.73 ± 0.07 arcsec (= 6.5 ± 0.3 pc). The results show that, within 10 core radii, a King model fits the surface brightness distribution well. We find that this object falls in the same region of the MV versus log Rh diagram as , Centauri, M54 and NGC 2419 in the Milky Way. All three of these objects have been claimed to be the stripped cores of now defunct dwarf galaxies. We discuss in detail whether GCs, stripped cores of dwarf spheroidals and normal dwarf galaxies form a continuous distribution in the MV versus log Rh plane, or if GCs and dwarf spheroidals constitute distinct classes of objects; we present arguments in favour of this latter view. [source] Technical note: Occlusal fingerprint analysis: Quantification of tooth wear patternAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 4 2009Ottmar Kullmer Abstract Information about food ingestion and mastication behavior during the lifespan of an individual is encoded in the dental occlusal wear pattern. To decode this information, we describe a new method called occlusal fingerprint analysis (OFA). Structural parameters of wear facets on the occlusal surface of teeth are quantified from digitized casts for the interpretation of occlusal aspects. The OFA provides an individual three-dimensional dental occlusal compass that indicates the major pathways of interaction between antagonists, revealing information about development, spatial position, and enlargement of wear facets. Humans develop a very similar overall pattern of crown contacts, although specific characteristics of wear facets reflect an individual's occlusal relationships and masticatory behavior. We hypothesize that the wear pattern is a unique character and therefore valuable for individual identification. Furthermore we suggest that OFA, when further developed, may be useful for identification of behavioral, biological, and chemical factors affecting crown morphology. Am J Phys Anthropol, 2009. © 2009 Wiley-Liss, Inc. [source] A Novel Heavy-Atom Label for Side-Specific Peptide Iodination: Synthesis, Membrane Incorporation and X-ray ReflectivityCHEMPHYSCHEM, Issue 9-10 2009Philipp E. Schneggenburger Abstract A novel iodine peptide label for X-ray analysis of membrane-active peptide structures is applied to solid-phase peptide synthesis. The resulting pore-structured labeled peptide as well as a non-labeled reference were reconstituted in lipid bilayer stacks (see scheme). The results indicate the exhibition of a membrane-spanning ,5.6 -double helical peptide structure and illustrate the quality of the new label. Structural parameters, such as conformation, orientation and penetration depth of membrane-bound peptides and proteins that may function as channels, pores or biocatalysts, are of persistent interest and have to be probed in the native fluid state of a membrane. X-ray scattering in combination with heavy-atom labeling is a powerful and highly appropriate method to reveal the position of a certain amino acid residue within a lipid bilayer with respect to the membrane normal axis up to a resolution of several Ångstrøm. Herein, we report the synthesis of a new iodine-labeled amino acid building block. This building block is intended for peptide incorporation to provide high intensities for electron density difference analysis of X-ray reflectivity data and improve the labeling potential for the lipid bilayer head-group and water region. The novel building block as well as the commercially available non-iodinated analogue, required for X-ray scattering, was implemented in a transmembrane peptide motif via manual solid-phase peptide synthesis (SPPS) following the fluorenylmethyloxycarbonyl (Fmoc)-strategy. The derived peptides were reconstituted in lipid vesicles as well as in highly aligned multilamellar lipid stacks and investigated via circular dichroism (CD) and X-ray reflectivity. Thereby, it has been revealed that the bulky iodine probe neither causes conformational change of the peptide structure nor lamellar disordering of the membrane complexes. [source] Structural parameters of the vastus medialis muscle and its relationship to patellofemoral joint deteriorationCLINICAL ANATOMY, Issue 3 2007J. Peeler Abstract Vastus medialis (VM) muscle dysfunction and abnormal limb alignment are commonly observed in patients who experience changes in patellofemoral joint (PFJ) function, leading many clinicians to assume that there is a direct relationship between VM structural parameters, leg alignment, and PFJ dysfunction. This study tested the hypothesis that there is a relationship between structural parameters of the VM muscle, limb alignment, and the location and severity of patellofemoral joint deterioration (PFJD). The dissection study used 32 limbs from 24 intact cadavers. Data were collected on limb alignment, angle of VM muscle fibers below the superior aspect of the patella, length of VM inserting on the medial aspect of the patella, and severity and location of PFJD. Parametric and nonparametric statistical analyses illustrated that PFJD was most commonly located on the middle third of the medial half of the patellar articular surface. The severity of PFJD did not vary with location. There was no significant correlation between any of VM insertion length, VM fiber angle, limb alignment, and PFJD location and severity lpar;r2 < 0.34). The results of this study did not support the hypothesis of a relationship between structural parameters of the VM muscle, limb alignment, and the location and severity of PFJD in this subject group. Future research should examine the relationship between functional parameters of the entire quadriceps muscle group and PFJ dysfunction. Clin. Anat. 20:307,314, 2007. © 2006 Wiley-Liss, Inc. [source] Decentralized Parametric Damage Detection Based on Neural NetworksCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 3 2002Zhishen Wu In this paper, based on the concept of decentralized information structures and artificial neural networks, a decentralized parametric identification method for damage detection of structures with multi-degrees-of-freedom (MDOF) is conducted. First, a decentralized approach is presented for damage detection of substructures of an MDOF structure system by using neural networks. The displacement and velocity measurements from a substructure of a healthy structure system and the restoring force corresponding to this substructure are used to train the decentralized detection neural networks for the purpose of identifying the corresponding substructure. By using the trained decentralized detection neural networks, the difference of the interstory restoring force between the damaged substructures and the undamaged substructures can be calculated. An evaluation index, that is, relative root mean square (RRMS) error, is presented to evaluate the condition of each substructure for the purpose of health monitoring. Although neural networks have been widely used for nonparametric identification, in this paper, the decentralized parametric evaluation neural networks for substructures are trained for parametric identification. Based on the trained decentralized parametric evaluation neural networks and the RRMS error of substructures, the structural parameter of stiffness of each subsystem can be forecast with high accuracy. The effectiveness of the decentralized parametric identification is evaluated through numerical simulations. It is shown that the decentralized parametric evaluation method has the potential of being a practical tool for a damage detection methodology applied to structure-unknown smart civil structures. [source] Estimating Labor Demand with Fixed Costs*INTERNATIONAL ECONOMIC REVIEW, Issue 1 2004Paola Rota We consider a dynamic model in which firms decide whether or not to vary labor in the presence of fixed costs. By exploiting the first-order condition for optimality, we derive a semireduced form in which firms' intertemporal employment is defined by a standard marginal productivity condition augmented by a forward-looking term. We obtain a marginal productivity equilibrium relation that takes into account the future alternatives of adjustment or nonadjustment that firms face. We use the structural parameter from this condition to estimate the fixed cost within a discrete decision process. Fixed costs are about 15 months' labor cost. [source] Structural Effects on the Electronic Absorption Properties of 5,6-Dihydroxyindole Oligomers: The Potential of an Integrated Experimental and DFT Approach to Model Eumelanin Optical Properties,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2008Marco D'Ischia Elucidation of the relationships between structural features and UV,visible absorption properties of 5,6-dihydroxyindole oligomers is an essential step towards an understanding of the unique optical properties of eumelanins. Herein, we report the first combined experimental and density functional theory (DFT) investigation of the 5,6-dihydroxyindole oligomers so far isolated. 2,2,-Biindolyl 2 and the 2,4,-biindolyl 3 absorb at longer wavelengths relative to 2,7,-biindolyl 4 and their spectra were well predicted by DFT analysis. The absorption bands of 2,4,:2,,4,,- and 2,4,:2,,7,,-triindolyls 5 and 6 also fall at different wavelengths and can be interpreted by DFT simulations as being due to a combination of two main separate transitions. Tetramer 7, in which two 2,4,-biindolyl units are linked through a 2,3,-connection, exhibits a broad chromophore extending over the entire UV range without well defined absorption maxima. Within the dimer,tetramer range examined, three key points emerge: (1) an increase in oligomer chain length does not result in any regular and predictable bathochromic shift; (2) a marked broadening of the absorption bands occurs when going from the monomer to the tetramer structure; and (3) the mode of coupling of the indole units is a crucial, hitherto unrecognized, structural parameter affecting the electronic absorption properties of 5,6-dihydroxyindole oligomers. It is concluded that use of experimentally characterized oligomeric scaffolds as a basis for DFT calculations is a most promising approach to building reliable structural models for studies of eumelanins optical properties. [source] Relation between Mössbauer spectroscopy and geometrical frustration factors in MCr1.9857Fe0.02O4 (M = Co, Zn)PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2007Kang Ryong Choi Abstract In order to elucidate the role of Cr ions in MCr2O4(M = Co, Zn) exhibiting geometrically frustration and multiferroic property, we have substituted a small amount of Fe ions for Cr sites and investigated the magnetic behavior of Fe ions with Mössbauer spectroscopy. The crystal structure was found to be single-phase cubic spinel with space group of Fd3m. The lattice constants a0 and the internal structural parameter (x) of the oxygen were determined to be 8.340, 8.331 Å and 0.261 and 0.260, respectively. The Mössbauer absorption spectra at 4.2 K show that the well-developed two sextets are superposed with small difference of hyperfine fields(Hhf). The hyperfine fields of CoCr1.9857Fe0.02O4 and ZnCr1.9857Fe0.02O4 were determined to be 490 , 480 kOe and 460 , 450 kOe, respectively. Isomer shift values (,) of the two sextets are found to be 0.33 , 0.35 mm/s relative to those of Fe metal, which are consistent with the high spin Fe3+ charge state. From the results of Mössbauer measurement, it is suggested that Cr3+ ions have two different magnetic sites, and there is a correlation between hyperfine fields and degree of magnetic geometrical frustration. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Correlation between electro-physical characteristics and elastic properties of cadmium selenide filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2004Victor S. Grinevich Abstract A number of anomalous electrophysical and photoelectrical properties of polycrystalline CdSe was investigated. This data analysis gave the possibility to state that the anomalous dependencies are conditioned by structural transformations in double phased cadmium selenide. It was established, that these electrophysical phenomena are determined by the structural parameter , ,rm , ,-CdSe phase inclusion radius change in the ,-CdSe phase matrix. The anomalous properties nature is chemical bonds destruction at the nanoscale boundary between two phases of CdSe. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The dual role of a loop with low loop contact distance in folding and domain swappingPROTEIN SCIENCE, Issue 7 2002Apichart Linhananta Abstract , helices, , strands, and loops are the basic building blocks of protein structure. The folding kinetics of , helices and , strands have been investigated extensively. However, little is known about the formation of loops. Experimental studies show that for some proteins, the formation of a single loop is the rate-determining step for folding, whereas for others, a loop (or turn) can misfold to serve as the hinge loop region for domain-swapped species. Computer simulations of an all-atom model of fragment B of Staphylococcal protein A found that the formation of a single loop initiates the dominant folding pathway. On the other hand, the stability analysis of intermediates suggests that the same loop is a likely candidate to serve as a hinge loop for domain swapping. To interpret the simulation result, we developed a simple structural parameter: the loop contact distance (LCD), or the sequence distance of contacting residues between a loop and the rest of the protein. The parameter is applied to a number of other proteins, including SH3 domains and prion protein. The results suggest that a locally interacting loop (low LCD) can either promote folding or serve as the hinge region for domain swapping. Thus, there is an intimate connection between folding and domain swapping, a possible cause of misfolding and aggregation. [source] Long-Term Monitoring and Identification of Bridge Structural ParametersCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 2 2009Serdar Soyoz This three-span 111-m long bridge is instrumented with 13 acceleration sensors at both the superstructure and the columns. The sensor data are transmitted to a server computer wirelessly. Modal parameters of the bridge, that is, the frequencies and the modal shapes were identified by processing 1,707 vibration data sets collected under traffic excitations, based on which the bridge structural parameters, stiffness and mass, and the soil spring values were identified by employing the neural network technique. The identified superstructure stiffness at the beginning of the monitoring was 97% of the stiffness value based on the design drawings. In the identified modal frequencies, a variation from ,10% to +10% was observed over the monitoring period. In the identified stiffness values of the bridge superstructure, a variation from ,3% to +3% was observed over the monitoring period. Based on the statistical analysis of the collected data for each year, 5% decrease in the first modal frequency and 2% decrease in the superstructure stiffness were observed over the 5-year monitoring period. Probability density functions were obtained for stiffness values each year. Stiffness threshold values for the collapse of the bridge under the operational loading can be determined. Then the number of years can be assessed for which the area under the proposed probability density functions is greater than the threshold value. So the information obtained in this study is valuable for studying aging and long-term performance assessment of similar bridges. [source] Structural Model Updating and Health Monitoring with Incomplete Modal Data Using Gibbs SamplerCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 4 2006Jianye Ching It is based on the Gibbs sampler, a stochastic simulation method that decomposes the uncertain model parameters into three groups, so that the direct sampling from any one group is possible when conditional on the other groups and the incomplete modal data. This means that even if the number of uncertain parameters is large, the effective dimension for the Gibbs sampler is always three and so high-dimensional parameter spaces that are fatal to most sampling techniques are handled by the method, making it more practical for health monitoring of real structures. The approach also inherits the advantages of Bayesian techniques: it not only updates the optimal estimate of the structural parameters but also updates the associated uncertainties. The approach is illustrated by applying it to two examples of structural health monitoring problems, in which the goal is to detect and quantify any damage using incomplete modal data obtained from small-amplitude vibrations measured before and after a severe loading event, such as an earthquake or explosion. [source] Significance of Modeling Error in Structural Parameter EstimationCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 1 2001Masoud Sanayei Structural health monitoring systems rely on algorithms to detect potential changes in structural parameters that may be indicative of damage. Parameter-estimation algorithms seek to identify changes in structural parameters by adjusting parameters of an a priori finite-element model of a structure to reconcile its response with a set of measured test data. Modeling error, represented as uncertainty in the parameters of a finite-element model of the structure, curtail capability of parameter estimation to capture the physical behavior of the structure. The performance of four error functions, two stiffness-based and two flexibility-based, is compared in the presence of modeling error in terms of the propagation rate of the modeling error and the quality of the final parameter estimates. Three different types of parameters are used in the parameter estimation procedure: (1) unknown parameters that are to be estimated, (2) known parameters assumed to be accurate, and (3) uncertain parameters that manifest the modeling error and are assumed known and not to be estimated. The significance of modeling error is investigated with respect to excitation and measurement type and locations, the type of error function, location of the uncertain parameter, and the selection of unknown parameters to be estimated. It is illustrated in two examples that the stiffness-based error functions perform significantly better than the corresponding flexibility-based error functions in the presence of modeling error. Additionally, the topology of the structure, excitation and measurement type and locations, and location of the uncertain parameters with respect to the unknown parameters can have a significant impact on the quality of the parameter estimates. Insight into the significance of modeling error and its potential impact on the resulting parameter estimates is presented through analytical and numerical examples using static and modal data. [source] Design of passive systems for control of inelastic structuresEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 6 2009Gian Paolo Cimellaro Abstract A design strategy for control of buildings experiencing inelastic deformations during seismic response is formulated. The strategy is using weakened, and/or softened, elements in a structural system while adding passive energy dissipation devices (e.g. viscous fluid devices, etc.) in order to control simultaneously accelerations and deformations response during seismic events. A design methodology is developed to determine the locations and the magnitude of weakening and/or softening of structural elements and the added damping while insuring structural stability. A two-stage design procedure is suggested: (i) first using a nonlinear active control algorithm, to determine the new structural parameters while insuring stability, then (ii) determine the properties of equivalent structural parameters of passive system, which can be implemented by removing or weakening some structural elements, or connections, and by addition of energy dissipation systems. Passive dampers and weakened elements are designed using an optimization algorithm to obtain a response as close as possible to an actively controlled system. A case study of a five-story building subjected to El Centro ground motion, as well as to an ensemble of simulated ground motions, is presented to illustrate the procedure. The results show that following the design strategy, a control of both peak inter-story drifts and total accelerations can be obtained. Copyright © 2008 John Wiley & Sons, Ltd. [source] Output-only structural identification in time domain: Numerical and experimental studiesEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 4 2008M. J. Perry Abstract By identifying changes in stiffness parameters, structural damage can be detected and monitored. Although considerable progress has been made in this research area, many challenges remain in achieving robust structural identification based on incomplete and noisy measurement signals. The identification task is made even more difficult if measurement of input force is to be eliminated. To this end, an output-only structural identification strategy is proposed to identify unknown stiffness and damping parameters. A non-classical approach based on genetic algorithms (GAs) is adopted. The proposed strategy makes use of the recently developed GA-based method of search space reduction, which has shown to be able to accurately and reliably identify structural parameters from measured input and output signals. By modifying the numerical integration scheme, input can be computed as the parameter identification task is in progress, thereby eliminating the need to measure forces. Numerical and experimental results demonstrate the power of the strategy in accurate and efficient identification of structural parameters and damage using only incomplete acceleration measurements. Copyright © 2007 John Wiley & Sons, Ltd. [source] Large displacement behaviour of a structural model with foundation uplift under impulsive and earthquake excitationsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 3 2003Giuseppe Oliveto Abstract This paper considers the dynamical behaviour of a structural model with foundation uplift. The equations of motion of the system considered are derived for large displacements thus allowing for the eventual overturning of the system. The transition conditions between successive phases of motion, derived in terms of the specific Lagrangian co-ordinates used in the formulation of the equations of motion, present innovative aspects which resolve some previously inexplicable behaviour in the structural response reported in the literature. The dynamical behaviour of the model is considered under impulsive and long-duration ground motions. The minimum horizontal acceleration impulses for the uplift and the overturning of the system are evaluated in analytical form. The sensitivity of the model to uplifting and to overturning under impulsive excitations is established as a function of few significant structural parameters. Numerical applications have been performed changing either the structural parameters or the loading parameter, in order to analyse several dynamical behaviours and also to validate the analytical results. For earthquake ground motions the results, reported in the form of response spectra, show that linearized models generally underestimate, sometimes significantly, the structural response. Copyright © 2003 John Wiley & Sons, Ltd. [source] On-line identification of non-linear hysteretic structural systems using a variable trace approachEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 9 2001Jeng-Wen Lin Abstract In this paper, an adaptive on-line parametric identification algorithm based on the variable trace approach is presented for the identification of non-linear hysteretic structures. At each time step, this recursive least-square-based algorithm upgrades the diagonal elements of the adaptation gain matrix by comparing the values of estimated parameters between two consecutive time steps. Such an approach will enforce a smooth convergence of the parameter values, a fast tracking of the parameter changes and will remain adaptive as time progresses. The effectiveness and efficiency of the proposed algorithm is shown by considering the effects of excitation amplitude, of the measurement units, of larger sampling time interval and of measurement noise. The cases of exact-, under-, over-parameterization of the structural model have been analysed. The proposed algorithm is also quite effective in identifying time-varying structural parameters to simulate cumulative damage in structural systems. Copyright © 2001 John Wiley & Sons, Ltd. [source] Solving, Estimating, and Selecting Nonlinear Dynamic Models Without the Curse of DimensionalityECONOMETRICA, Issue 2 2010Viktor Winschel We present a comprehensive framework for Bayesian estimation of structural nonlinear dynamic economic models on sparse grids to overcome the curse of dimensionality for approximations. We apply sparse grids to a global polynomial approximation of the model solution, to the quadrature of integrals arising as rational expectations, and to three new nonlinear state space filters which speed up the sequential importance resampling particle filter. The posterior of the structural parameters is estimated by a new Metropolis,Hastings algorithm with mixing parallel sequences. The parallel extension improves the global maximization property of the algorithm, simplifies the parameterization for an appropriate acceptance ratio, and allows a simple implementation of the estimation on parallel computers. Finally, we provide all algorithms in the open source software JBendge for the solution and estimation of a general class of models. [source] Financial Innovation and the Transactions Demand for CashECONOMETRICA, Issue 2 2009Fernando Alvarez We document cash management patterns for households that are at odds with the predictions of deterministic inventory models that abstract from precautionary motives. We extend the Baumol,Tobin cash inventory model to a dynamic environment that allows for the possibility of withdrawing cash at random times at a low cost. This modification introduces a precautionary motive for holding cash and naturally captures developments in withdrawal technology, such as the increasing diffusion of bank branches and ATM terminals. We characterize the solution of the model, which qualitatively reproduces several empirical patterns. We estimate the structural parameters using micro data and show that quantitatively the model captures important economic patterns. The estimates are used to quantify the expenditure and interest rate elasticity of money demand, the impact of financial innovation on money demand, the welfare cost of inflation, and the benefit of ATM ownership. [source] What does Monetary Policy Reveal about a Central Bank's Preferences?ECONOMIC NOTES, Issue 3 2003Efrem Castelnuovo The design of monetary policy depends on the targeting strategy adopted by the central bank. This strategy describes a set of policy preferences, which are actually the structural parameters to analyse monetary policy making. Accordingly, we develop a calibration method to estimate a central bank's preferences from the estimates of an optimal Taylor,type rule. The empirical analysis on US data shows that output stabilization has not been an independent argument in the Fed's objective function during the Greenspan's era. This suggests that the output gap has entered the policy rule only as leading indicator for future inflation, therefore being only instrumental (to stabilize inflation) rather than important per se. (J.E.L.: C61, E52, E58). [source] Aquatic macroinvertebrates in the altes land, an intensely used orchard region in Germany: Correlation between community structure and potential for pesticide exposureENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2006Christoph Schäfers Abstract To assess the impact of pesticides on aquatic organisms under realistic worst-case conditions, a macroinvertebrate community of small ditches was sampled at 40 sites of the orchard region Altes Land near Hamburg, Germany. To differentiate between pesticide impact and other variables, the ditches selected for sampling were located at different distances along grassland, unused apple orchards, and orchards managed with integrated and/or organic crop protection methods. Samples of macroinvertebrates were taken on five dates over two years. In addition to biological data, water chemistry and structural parameters were measured. For each sampling site, a potential for exposure was calculated on the basis of the distance of the ditch to the nearest row of trees and the depth and width of the ditch. The neighborhood to either grassland or orchards turned out to have a larger impact on the macroinvertebrate community than the potential for exposure. Therefore, grassland sites were omitted from further evaluation. Remaining sites were grouped into low exposure (sites at unused orchards), medium exposure (distance of 3,5 m [track] between trees and ditch), and high exposure (trees close to the ditch, mean distance , 1.5 m). Principal response curves showed differences in community structure between the three exposure groups over time. Whereas for sites from the high exposure group significant differences from low exposure was observed in all seasons, significant differences between low and medium were observed only occasionally. Effects were less pronounced in samples taken at springtime before the starting pesticide applications, suggesting some community recovery. Species richness was negatively correlated to exposure potential. Isopoda, Eulamellibranchiata, and insects, especially Ephemeroptera, showed a high negative correlation with the potential for pesticide exposure, suggesting that these taxa are sensitive to the pesticide use in the orchards. [source] Prediction of biodegradation from the atom-type electrotopological state indicesENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2001Jarmo Huuskonen Abstract A group contribution method based on atom-type electrotopological state indices for predicting the biodegradation of a diverse set of 241 organic chemicals is presented. Multiple linear regression and artificial neural networks were used to build the models using a training set of 172 compounds, for which the approximate time for ultimate biodegradation was estimated from the results of a survey of an expert panel. Derived models were validated by using a leave-25%-out method and against two test sets of 12 and 57 chemicals not included in the training set. The squared correlation coefficient (r2) for a linear model with 15 structural parameters was 0.76 for the training set and 0.68 for the test set of 12 molecules. The model predicted correctly the biodegradation of 48 chemicals in the test set of 57 molecules, for which biodegradability was presented as rapid or slow. The use of artificial neural networks gave better prediction for both test sets when the same set of parameters was tested as inputs in neural network simulations. The predictions of rapidly biodegradable chemicals were more accurate than the predictions of slowly bio-degradable chemicals for both the regression and neural network models. [source] Structural Trends in Divalent Benzil Bis(thiosemicarbazone) ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2005David G. Calatayud Abstract Redox-related changes in the biological properties of copper bis(thiosemicarbazones) are induced by the backbone of the ligand. To get information about how these changes depend on the structural parameters, three X-ray structures of complexes with different behaviour of the benzil bis(thiosemicarbazone) ligand have been determined. These include two almost planar copper(II) complexes with different grades of deprotonation in the ligand and a ZnII complex in which the ligand acts as a monoanion and a nitrate group is bonded to the metal ion in a square-based pyramid. The changes in the backbone bond lengths agree with the variation in the ionic radius and with the grade of electronic charge delocalisation in the chelate rings; these have consequences for the coordination sphere, allowing the metal to fit slightly better into the ligand cavity, which in turn may affect the complex stability and the redox potential. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] | ||||||||||||||||||||||||||||||||||||||||||||||||||||