bluuebunny/crossref_metadata_2025_split huggingface dataset:
Apparent propagation velocity of body waves
Authors: O'Rourke Michael J. , Bloom Mary C. , Dobry Ricardo 
Published: March 2007

AbstractThe apparent horizontal propagation velocity, that is the propagation velocity of seismic waves with respect to the ground surface, is discussed in this paper. This parameter is needed to determine the effects of earthquakes on long structures such as bridges and buried pipelines as well as the torsional rotation of foundations of multi‐storey buildings. A time window intensity tensor introduced by Penzien and Kubo is used herein to determine the predominant directions of ground motion during an earthquake. Considering the reflection of waves at a free surface, an approximate relationship between the predominant direction and the angle of incidence of body waves with respect to the ground surface is presented. Knowing the material properties of the top layer and the angle of incidence, the desired propagation velocity with respect to the ground surface is readily calculated.The median value of the apparent propagation velocity of shear waves for near field sites which recorded the 1971 San Fernando earthquake was determined to be about 2‐1 km/s using the above method. A similar value for the 1979 Imperial Valley earthquake is 3·7 km/s. These values are consistent with the range of values for the apparent propagation velocity determined by other researchers.
Hydrodynamic effects in the dynamic response of concrete gravity dams
Authors: Hall John F. , Chopra Anil K. 
Published: March 2007

AbstractHydrodynamic effects in the acceleration response of concrete gravity dams to harmonic ground motion are investigated. The effects include the presence of water, compressibility of water, interaction between the fluid and underlying foundation medium, shape of the fluid domain, and the extent of excitation applied to an infinite fluid domain under vertical ground motion.
Stochastic response of multistorey yielding frames
Authors: Baber Thomas T. , Wen Yi‐Kwei 
Published: March 2007

AbstractA model for the random vibration of hysteretic and degrading plane frames to Gaussian shot noise or filtered shot noise is presented. The model, which combines the discrete hinge concept previously used in deterministic frame analysis with Bouc's smooth system hysteresis, results in a non‐linear set of differential equations which can be linearized in closed form without recourse to the Krylov‐Bogoliubov assumptions. Solution is iterative in the stationary case and by numerical integration with stepwise updates in the non‐stationary case. Numerical studies are presented of strong girder and strong column two storey, one bay frames. These studies indicate that the model can locate the sites of yielding and provide reasonable values of structural response as compared with simulation data. Moreover, the model can provide a joint by joint breakdown of the structure energy dissipation rate.
Hydrodynamic effects in dynamic response of simple arch dams
Authors: Porter Craig S. , Chopra Anil K. 
Published: March 2007

AbstractThe dynamic responses of simple arch dams, with different radius to height ratios are analysed for three conditions: the dam alone without water, and the dam with full reservoir, considering water to be compressible in one case and neglecting water compressibility in the other case. The complex frequency response functions for accelerations at the dam crest due to the three components of ground motion—upstream‐downstream component, cross‐stream component and vertical component–are presented. Based on these results, the effects of dam‐water interaction, of water compressibility, and of bank motions on dam response are investigated.
Investigation of the elastic characteristics of a three‐storey steel structure using system identification
Authors: Kaya Izak , McNiven Hugh D. 
Published: March 2007

AbstractIn this report, three different models in increasing order of complexity have been used to identify the seismic behaviour of a three‐storey steel structure subjected to arbitrary forcing functions, all of which excite responses within the elastic range. All of the models are constructed using system identification.In the first model, five parameters have been used to identify the frame. Treating the system as a shear building, we assign one stiffness coefficient to each floor and introduce Rayleigh‐type damping with two additional parameters. The mass, assumed to be concentrated at a floor level, is kept constant throughout the study. The parameters are established using a modified Gauss‐Newton algorithm. The match between measured and predicted quantities is satisfactory when these quantities are restricted to floor accelerations or displacements.To remove the constraint imposed by assuming that the frame deforms as a shear building, a second model with eight parameters is introduced, allowing rotations of the joints as independent degrees of freedom. Six of the eight parameters are related to the stiffness characteristics of the structural members while the remaining two are related to damping as before.In constructing the eight‐parameter model, we learned that it is the effective lengths of the members that change during optimization. We also found that the independent response quantities, floor accelerations and joint rotations, must be used in the cost function for the optimization algorithm to converge.The match between measured and predicted quantities for the eight‐parameter model is excellent. The set of parameters derived from the minimum squared error gives a model that shows very good correlation using information on the full duration of the pulse or only a portion of it. Also the same correlation exists between the coefficients obtained from different excitations.In an effort to explain the values of the parameters associated with the girders, an additional degree of freedom, namely, the pitching motion of the shaking table, is introduced as an additional degree of freedom. The paper presents, therefore, a five‐, an eight‐ and, finally, a nine‐parameter model.
Three‐dimensional dynamic analysis for multi‐component earthquake spectra
Authors: Wilson Edward L. , Button Martin R. 
Published: March 2007

AbstractAt the present time, there is a need for a rational approach for the analysis and design of three‐dimensional structures subjected to multi‐component earthquake motions. In this paper, a general design criterion for multi‐component earthquake input is proposed. A new method for three‐dimensional dynamic analysis is presented which estimates maximum displacements, forces or stresses for specified points within a structure. For each maximum value calculated, the corresponding critical angle of earthquake input is evaluated. The method is readily incorporated into existing computer programs for earthquake analysis, allowing one computer run to produce mean maximum response values for all possible angles of earthquake input. Combined axial and bending stresses are calculated at the modal level. It is shown that combining modal stresses yields lower estimates than if stresses are evaluated from maximum axial forces and moments. In addition, the method can be used without modifications to perform design checks for arbitrary blast or seawave spectra.
Frequency‐domain redigitization method for seismic time histories
Authors: Liou D. D. 
Published: March 2007

AbstractThis note presents a numerical method for redigitizing a given time history at a smaller time increment than that used to define the time history without changing its original frequency content. Both the theoretical basis and the numerical procedure of this method are presented. A numerical example is also given in order to demonstrate the advantage of this method over the linear interpolation method commonly used in the industry.
A new approach to the integration of accelerometer data
Authors: Trujillo D. M. , Carter A. L. 
Published: March 2007

AbstractA direct approach to the integration of accelerometer data is presented which depends only on the fact that the final velocity and possibly, the final displacement are known. Using a dynamic programming formulation, the accelerometer record is corrected to account for these cases. The formulation is presented for the general case where velocity, displacement, as well as accelerometer data, are available. A numerical example is included.
The ρ‐family of algorithms for time‐step integration with improved numerical dissipation
Authors: Bazzi G. , Anderheggen E. 
Published: March 2007

AbstractThe dynamic analysis of complex non‐linear structural systems by the finite element approach requires the use of time‐step algorithms for solving the equations of motion in the time domain. Both an implicit and an explicit version of such a time‐step algorithm, called the ρ‐method, the parameter ρ being used for controlling numerical damping in the higher modes, are presented in this paper. For the implicit family of algorithms unconditional stability, consistency, convergence, accuracy and overshoot properties are first discussed and proved. On the basis of the algorithmic damping ratio (dissipation) and period elongation (dispersion) the ρ‐method is then compared with the well‐known implicit algorithms of Hilber, Newmark, Wilson, Park and Houbolt. An explicit version of the algorithm is also derived and briefly discussed. This shows numerical properties similar to the central difference method. Both versions of the algorithm have been implemented in a general purpose computer program which has been often used for both numerical tests and practical applications.
Seismic risk analysis for Northern Iraq
Authors: Puttonen Jari , Varpasuo Pentti 
Published: March 2007

AbstractIn this study the seismic risks of northern Iraq have been evaluated by a probabilistic method. The data contain about 500 earthquakes which occurred between 1840 and 1978. The epicentral locations and magnitudes of the included earthquakes have been presented.A linear relationship between magnitude and frequency has been assumed. The attenuation of intensities has been presented as a function of magnitude and epicentral distance.The seismic risk has been calculated for 225 points of the analysed area. The equiseismal maps related to a certain risk level have been plotted by using these point values of intensities, and assuming a linear variation between the points. The significance of the standard deviation of the attenuation law and the strict lower bound intensity has been investigated by sensitivity analyses.The intensity contours related to the annual return period of 50, 100 and 200 years have been presented, and also the intensity contours with an occurrence probability of 10 per cent during 50, 100 and 200 years have been drawn.
Dynamic behaviour of rigid foundations of arbitrary shape on a halfspace
Authors: Rüucker Werner 
Published: March 2007

AbstractAn approximate method for computation of the compliance functions of rigid plates resting on an elastic or visco‐elastic halfspace excited by forces and moments in all degrees of freedon is presented. The method is based on a Green's function approach. These functions are given for all degrees of freedom in form of well‐behaved integrals. The numerical procedure is described and is used to evaluate the vertical, horizontal, rocking and torsion compliance functions of rectangular plates with side ratios 1 ≤ b/a ≤ 10 and non‐dimensional frequency 0≤a0≤10. It is shown how this method can be extended to problems concerning a linear visco‐elastic halfspace and a halfspace with variable stiffness.
Infinite elements for elastodynamics
Authors: Medina Franciso , Penzien Joseph 
Published: March 2007

AbstractAn axisymmetric infinite element and a three‐dimensional infinite element are developed to solve three‐dimensional elastic wave propagation problems in unbounded media. The elements are capable of transmitting Rayleigh, shear and compressional waves in the frequency domain. A scheme to integrate numerically the characteristic matrices of the elements is formulated based upon Gauss—Laguerre quadrature. Finally, the axisymmetric infinite element is used to find the compliance functions of a rigid circular plate subjected to harmonic loading on a semi‐infinite medium. By using infinite elements, the size of the near field may be kept small. Consequently, the system is characterized by relatively few degrees of freedom, thus providing the analyst with an inexpensive solution.
A re‐evaluation of equivalent linear models for simple yielding systems
Authors: Hadjian A. H. 
Published: March 2007

AbstractCommonly used equivalent linear models for simple yielding systems subjected to harmonic and earthquake excitations are re‐evaluated. It is shown that with respect to damping, these models contain the same basic information. Reported differences in the literature are simply due to scaling: since the product of the equivalent stiffness and equivalent damping is a constant, smaller damping values would be obtained by the use of the small amplitude equivalent stiffnesses. It is argued that for harmonic excitation, the secant stiffness is an appropriate representation of equivalent stiffness, leading to large equivalent damping values that increase with ductility. For earthquake excitation the Iwan proposal is shown to be the preferred model leading to larger damping values than previously reported. A comparison of the models for harmonic and earthquake excitations shows that, in general, and at comparable ductilities, damping values due to harmonic excitation are about five times those due to earthquake excitation, and the period changes due to harmonic excitation are about twice those due to earthquake excitation.
Effects of microbiotic crusts under cropland in temperate environments on soil erodibility during concentrated flow
Authors: Knapen A. , Poesen J. , Galindo‐Morales P. , Baets S. De , Pals A. 
Published: March 2007

AbstractSeveral studies illustrate the wind and water erosion‐reducing potential of semi‐permanent microbiotic soil crusts in arid and semi‐arid desert environments. In contrast, little is hitherto known on these biological crusts on cropland soils in temperate environments where they are annually destroyed by tillage and quickly regenerate thereafter. This study attempts to fill the research gap through (a) a field survey assessing the occurrence of biological soil crusts on loess‐derived soils in central Belgium in space and time and (b) laboratory flume (2 m long) experiments simulating concentrated runoff on undisturbed topsoil samples (0.4 × 0.1 m2) quantifying the microbiotic crust effect on soil erosion rates. Three stages of microbiotic crust development on cropland soils are distinguished: (1) development of a non‐biological surface seal by raindrop impact, (2) colonization of the soil by algae and gradual development of a continuous algal mat and (3) establishment of a well‐developed microbiotic crust with moss plants as the dominant life‐form. As the silt loam soils in the study area seal quickly after tillage, microbiotic soil crusts are more or less present during a large part of the year under maize, sugar beet and wheat, representing the main cropland area. On average, the early‐successional algae‐dominated crusts of stage 2 reduce soil detachment rates by 37%, whereas the well‐developed moss mat of stage 3 causes an average reduction of 79%. Relative soil detachment rates of soil surfaces with microbiotic crusts compared with bare sealed soil surfaces are shown to decrease exponentially with increasing microbiotic cover (b = 0·024 for moss‐dominated and b = 0·006 for algae‐dominated crusts). In addition to ground surface cover by vegetation and crop residues, microbiotic crust occurrence can therefore not be neglected when modelling small‐scale spatial and temporal variations in soil loss by concentrated flow erosion on cropland soils in temperate environments. Copyright © 2007 John Wiley & Sons, Ltd.
High‐resolution interpretative geomorphological mapping of river valley environments using airborne LiDAR data
Authors: Jones Anna F. , Brewer Paul A. , Johnstone Eric , Macklin Mark G. 
Published: March 2007

AbstractThe availability of airborne LiDAR data provides a new opportunity to overcome some of the problems associated with traditional, field‐based, geomorphological mapping such as restrictions on access and constraints of time or cost. The combination of airborne LiDAR data and GIS technology facilitates the rapid production of geomorphological maps of floodplain environments; however, unfiltered LiDAR data, which include vegetation and buildings, are currently more suitable for geomorphological mapping than data that have been filtered to remove these features. Classification of LiDAR data according to elevation in a GIS enables the user to identify and delineate geomorphological features in a manner similar to field mapping, but it is necessary to use a range of classification intervals in order to map the various types of feature that occur within a single reach. Comparison of a LiDAR‐derived geomorphological map with an independently produced field geomorphological map showed a high degree of similarity between the results of the two methods, although ground‐truthing is essential in cases where a high degree of accuracy is required. Ground‐truthing of a LiDAR‐derived geomorphological map showed that around 80% of features mapped using both methods were identified from the LiDAR data, suggesting that the method is suitable for applications such as production of base maps for use in field mapping and selection of sites for detailed investigation. Copyright © 2007 John Wiley & Sons, Ltd.
G protein‐coupled receptor 84, a microglia‐associated protein expressed in neuroinflammatory conditions
Authors: Bouchard Caroline , Pagé Julie , Bédard Andréanne , Tremblay Pierrot , Vallières Luc 
Published: March 2007

AbstractG protein‐coupled receptor 84 (GPR84) is a recently discovered member of the seven transmembrane receptor superfamily whose function and regulation are unknown. Here, we report that in mice suffering from endotoxemia, microglia express GPR84 in a strong and sustained manner. This property is shared by subpopulations of peripheral macrophages and, to a much lesser extent, monocytes. The induction of GPR84 expression by endotoxin is mediated, at least in part, by proinflammatory cytokines, notably tumor necrosis factor (TNF) and interleukin‐1 (IL‐1), because mice lacking either one or both of these molecules have fewer GPR84‐expressing cells in their cerebral cortex than wild‐type mice during the early phase of endotoxemia. Moreover, when injected intracerebrally or added to microglial cultures, recombinant TNF stimulates GPR84 expression through a dexamethasone‐insensitive mechanism. Finally, we show that microglia produce GPR84 not only during endotoxemia, but also during experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis. In conclusion, this study reports the identification of a new sensitive marker of microglial activation, which may play an important regulatory role in neuroimmunological processes, acting downstream to the effects of proinflammatory mediators. © 2007 Wiley‐Liss, Inc.
High‐resolution electroencephalography and source localization in neonates
Authors: Roche‐Labarbe Nadège , Aarabi Ardalan , Kongolo Guy , Gondry‐Jouet Catherine , Dümpelmann Matthias , Grebe Reinhard , Wallois Fabrice 
Published: March 2007

AbstractAlthough Electroencephalography (EEG) source localization is being widely used in adults, this promising technique has not yet been applied to newborns because of technical difficulties, such as lack of data concerning the newborn skull conductivity, thickness, and homogeneity. Using a new type of EEG headcap molded on each baby's head, we aimed to determine whether this technique could be adapted to neonates, and to evaluate the importance of these technical difficulties. We carried out EEG source reconstruction of the recordings of five neonates using dipole fit algorithm. We used four different head models for each neonate, obtained from individual MRI scans: normal skull thickness and conductivity of 0.0042 S/m; normal thickness and conductivity of 0.33 S/m; increased thickness and conductivity of 0.0042 S/m; and normal thickness and conductivity with a modeled bregma fontanel. Dipole locations were consistent with MRI and clinical data. The mean difference between the dipole locations in the 0.0042 and the 0.33 S/m skull layer models was 11.6 ± 2.5 mm, with an average 29.7% decrease in magnitude for the 0.33 S/m model but no significant changes for the dipoles orientation. Skull layer thickness had a large influence on magnitude, but no significant effect on position and orientation. The mean difference between the dipole locations induced by the modeled fontanel was 2.0 ± 2.1 mm, with an average 2.1% increase in magnitude. Our results show that EEG source localization is feasible in neonates. With further development, the technique may prove useful for neurological evaluation of neonates. Hum Brain Mapp, 2008. © 2007 Wiley‐Liss, Inc.
Model‐based clustering of meta‐analytic functional imaging data
Authors: Neumann Jane , Cramon D. Yves von , Lohmann Gabriele 
Published: March 2007

AbstractWe present a method for the analysis of meta‐analytic functional imaging data. It is based on Activation Likelihood Estimation (ALE) and subsequent model‐based clustering using Gaussian mixture models, expectation‐maximization (EM) for model fitting, and the Bayesian Information Criterion (BIC) for model selection. Our method facilitates the clustering of activation maxima from previously performed imaging experiments in a hierarchical fashion. Regions with a high concentration of activation coordinates are first identified using ALE. Activation coordinates within these regions are then subjected to model‐based clustering for a more detailed cluster analysis. We demonstrate the usefulness of the method in a meta‐analysis of 26 fMRI studies investigating the well‐known Stroop paradigm. Hum Brain Mapp, 2008. © 2007 Wiley‐Liss, Inc.
Directed information flow—A model free measure to analyze causal interactions in event related EEG‐MEG‐experiments
Authors: Hinrichs Hermann , Noesselt Toemme , Heinze Hans‐Jochen 
Published: March 2007

AbstractIn a study that combined event related potential (ERP) and magnetic field (ERMF) data, we analyzed the timing and direction of information flow between striate (S) and extrastriate (ES) cortex by applying a generalized mutual information measure (DIT for “directed information transfer”) during a visual spatial attention task. ERP and ERMF recordings showed that selective attention to stimulus arrays in one visual field enhanced late responses (around 200 ms after the stimulus presentation) that were localized in S (ERMF) and ES (ERP) cortex. The results of the DIT analysis indicate there is a significant attention related increase in the flow of information back from ES to S cortex at around 220 ms, with an associated decrease in the flow of information forward from S cortex to ES cortex. These results support the hypothesis that a feedback mechanism guides attention‐related processing in primary visual cortex and provide evidence that DIT can by used to evaluate the direction of information flow between cortical areas. Hum Brain Mapp, 2008. © 2007 Wiley‐Liss, Inc.