bluuebunny/crossref_metadata_2025_split huggingface dataset:
A role for plasmacytoid dendritic cells in the rapid IL‐18‐dependent activation of NK cells following HSV‐1 infection
Authors: Barr Daniel P. , Belz Gabrielle T. , Reading Patrick C. , Wojtasiak Magdalena , Whitney Paul G. , Heath William R. , Carbone Francis R. , Brooks Andrew G. 
Published: April 2007

AbstractNatural killer (NK) cells play a crucial role in the initial response to viral infections but the mechanisms controlling their activation are unclear. We show a rapid and transient activation of NK cells that results in the production of IFN‐γ immediately following infection with herpes simplex virus type 1 (HSV‐1). Activation of NK cells leading to synthesis of IFN‐γ was not mediated by a direct interaction with virus but required the presence of additional cell types and was largely dependent on the cytokine IL‐18, but not IL‐12. HSV‐1‐induced IFN‐γ expression by NK cells in vitro was impaired in spleen cultures depleted of CD11c+ cells. Conversely, coculture of NK cells with virus‐exposed conventional DC or plasmacytoid (p)DC restored the production of IFN‐γ, indicating that multiple DC subsets could mediate NK cell activation. While conventional DC populations stimulated NK cells independently of IL‐18, they were less effective than pDC in promoting NK cell IFN‐γ expression. In contrast, the potent stimulation of NK cells by pDC was dependent on IL‐18 as pDC from IL‐18‐deficient mice only activated a similar proportion of NK cells as conventional DC. These data identify IL‐18 as a crucial factor for pDC‐mediated NK cell regulation.
Development of real‐time pseudo dynamic testing
Authors: Nakashima Masayoshi , Kato Hiroto , Takaoka Eiji 
Published: April 2007

AbstractThis paper presents a study for the development of a system capable of performing real‐time pseudo dynamic testing. The system combines the basics of the pseudo dynamic test with a dynamic actuator, a digital displacement transducer and a digital servo‐mechanism. The digital servo‐mechanism has been introduced to ensure accurate displacement and velocity control, in which digital feedback control with a time interval of 2 msec has been performed continuously during actuator motion. Using the system, pseudo dynamic tests under sinusoidal and earthquake ground motion are carried out for a structure having a viscous damper, demonstrating that a perfectly real‐time pseudo dynamic test can be achieved by incorporating the modified central difference method into an extra buffer operation of the digital servo‐mechanism. The responses solved by the pseudo dynamic tests are compared with the responses of the test structure as well as those obtained from post‐numerical analysis, and it is found that the real‐time pseudo dynamic test conducted in this study is accurate.
Soil amplification based on seismometer array and microtremor observations in Chiba, Japan
Authors: Lu Lin , Yamazaki Fumio , Katayama Tsuneo 
Published: April 2007

AbstractSoil amplification characteristics of earthquake ground motion were investigated in terms of peak ground acceleration and transfer function based on the Chiba array observation records. The amplification of peak ground acceleration occurred mostly at the top soft layer and was similar for the three components. The effects of non‐linear response of soil deposits on the transfer function were examined. Transfer functions calculated by ensemble average were close for the two horizontal components while those obtained from a smoothing operation were generally different. Both the transfer functions from the ensemble average and the smoothing operation underestimated the gain factor around the natural frequencies. A two‐step smoothing procedure was proposed and a rotary spectrum was used to improve the estimation of the transfer function. Microtremors were observed at the locations of the boreholes where seismometers are buried. The power spectrum and spatial coherency of the microtremors were compared with those of the earthquake ground motion. Emphasis was placed on the wavetypes which dominated the peaks in the power spectra.
Non‐linear seismic response analysis using vector superposition methods
Authors: Léger P. , Dussault S. 
Published: April 2007

AbstractComputational algorithms based on the pseudo‐force method (PFM) and the tangent spectrum method (TSM) for the seismic analysis of elasto‐plastic MDOF structures by mode superposition are presented. The emphasis is put on the effect of the truncation of higher modes on the convergence of the ductility demand and energy dissipated during the earthquake. Eigenvectors and load‐dependent vectors have been used in comparative analyses. Applications on a flexible 25‐storey building and a stiff, 5‐storey shear building indicate that, for a flexible structure, the ductility demand computed from the PFM is more sensitive to basis truncation than that computed from the TSM. However, for the stiff structure, the opposite behaviour is observed. The results indicate that the use of load‐dependent vectors in inelastic analyses maintains the computational advantages found for elastic analyses in previous investigations. Although the PFM is more stable and computationally more effective than the TSM, it does not provide any information on the evolution of tangent modal properties in time that reflects dynamic response modification as the structure becomes inelastic.
Generation of critical stochastic earthquakes
Authors: Srinivasan Mukund , Corotis Ross , Ellingwood Bruce 
Published: April 2007

AbstractA stochastic critical excitation is defined as that excitation with a given variance that maximizes the variance in the dynamic response of a system. A non‐stationary filtered shot noise is used to develop a stochastic critical excitation model of an earthquake ground motion process, and the response statistics for a linear system are determined in both time and frequency domains. The sensitivity of response to several assumed earthquake pulse arrival rate functions is examined. Responses to recorded strong ground motion and to stochastic critical excitations with the same total energy are compared to assess the degree of conservatism in the procedure. An application of the procedure to seismic qualification of equipment is presented.
Response of pile foundations to rayleigh waves and obliquely incident body waves
Authors: Kaynia Amir M. , Novak Milos 
Published: April 2007

AbstractThe paper presents results of a study on the harmonic response of piles and pile groups embedded in a halfspace to various forms of seismic waves. These include the Rayleigh wave as well as obliquely incident P, SV and SH waves. The pertinent mixed boundary value problems of pile‐soil‐pile interaction are solved by a numerical model of the boundary integral nature. All modes of foundation vibrations, i.e. translational, rocking and torsional, are included in the model. The results presented are used to highlight the salient features of the seismic response of piles. In addition, the influence of certain pile‐soil parameters, such as pile rigidity and pile spacing, on the seismic behaviour of pile foundations is investigated.
Torsion in two buildings—1987 whittier narrows earthquake
Authors: Lu Shi , Hall William J. 
Published: April 2007

AbstractStudy of the data from the extensively instrumented buildings in the 1987 Whittier Narrows earthquake suggests that torsional modes probably were excited in buildings that outwardly appear quite symmetric. Accordingly this study involves: (i) investigation of the observed response of two low‐rise buildings in both the elastic and moderately inelastic domains, (ii) comparison of such behaviour with the results obtained from modelling studies, and (iii) examination of the possible effects arising from stronger shaking. The study was directed towards attempting to provide a partial answer to the critical question of whether or not the torsional response was important in the gross total response of these low‐rise buildings, and to what extent torsional concepts should be considered in design. Also the numerical results were extrapolated to examine the survivability of the same buildings if subjected to a somewhat stronger earthquake. The ultimate goal was to contribute insight to the practical guidelines for design and analysis of low‐rise buildings subjected to strong ground motion.
Dynamic interaction analysis of a circular cylindrical shell of finite length in a half‐space
Authors: Cheung Y. K. , Zhu J. X. 
Published: April 2007

AbstractA study on the transient response of a circular cylindrical shell of finite length embedded in a homogeneous, isotropic and linear elastic half‐space is presented. The soil‐structure system is subjected to suddenly applied explosion waves. The numerical method employed is a combination of the time domain semi‐analytical boundary element method used for the semi‐infinite soil medium and the finite strip method used for the circular cylindrical shell. The two methods are combined through equilibrium and compatibility conditions at the soil‐structure interface. The dynamic responses at the interface between the soil medium and the structure for every time step are obtained. Numerical examples are presented in detail to demonstrate the use and versatility of the proposed method. The following parameters are found to affect the response: (1) the slenderness ratio of the length over the diameter of the shell, L/D; (2) the relative wall thickness, h/a; (3) the relative stiffness ratio between the shell and the medium, Es/Em; and (4) the incidence angle of the explosion wave, α.
Lumped‐parameter model and recursive evaluation of interaction forces of semi‐infinite uniform fluid channel for time‐domain dam‐reservoir analysis
Authors: Wolf John P. , Paronesso Antonio 
Published: April 2007

AbstractTo calculate the hydrodynamic interaction forces of the reservoir directly in the time‐domain, the dynamic stiffness of each mode of the semi‐infinite uniform fluid channel is either represented by a lumped‐parameter model with frequency‐independent real coefficients of the springs, dashpots and masses and with only a few additional internal degrees of freedom, or the interaction forces are calculated recursively. For each mode characterized by its eigenvalue, the coefficients of the lumped‐parameter model and the recursive coefficients are specified, which can be used directly in a practical application. The procedures exhibit many advantages: the only approximation (replacing the rigorous dynamic stiffness by a ratio of two polynomials) can be evaluated visibly. No unfamiliar discrete‐time manipulations such as the z‐transformation are used. The stiffness, damping and mass matrices corresponding to the lumped‐parameter model are automatically symmetrical. Stability of the procedures is also guaranteed. Combining the lumped‐parameter model of the semi‐infinite uniform channel with the finite‐element discretization of the irregular fluid region or calculating the interaction forces recursively allows a reservoir of arbitrary shape to be analysed directly in the time domain. Non‐linearities in the dam can, thus, be taken into consideration in a seismic analysis.
Efficient mode superposition algorithm for seismic analysis of non‐linear structures
Authors: Villaverde Roberto , Hanna Melad M. 
Published: April 2007

AbstractA step‐by‐step integration method is proposed to compute within the framework of the conventional mode superposition technique the response of bilinear hysteretic structures subjected to earthquake ground motions. The method is computationally efficient because only a few modes are needed to obtain an accurate estimate of such a response, and because it does not require the use of excessively small time steps to avoid problems of accuracy or stability. It is developed on the basis that the non‐linear terms in the equations of motion for non‐linear systems may be considered as additional external forces, and the fact that by doing so such equations of motion can be interpreted as the equations of motion of an equivalent linear system, excited by a modified ground motion. These linear equations are then subjected to a conventional modal decomposition and transformed, as with linear systems, into a set of independent differential equations, each representing the system's response in one of its modes of vibration. To increase the efficiency of the method and account properly for the participation of higher modes, these independent equations are solved using the Nigam‐Jennings technique in conjunction with the so‐called mode acceleration method. The accuracy and efficiency of the method is verified by means of a comparative study with solutions obtained with a conventional direct integration method. In this comparative study, including only a few modes, the proposed method accurately predicts the seismic response of three two‐dimensional frame structures, but requiring only, on an average, about 47 per cent less computer time than when the direct integration method is used.
Hybrid isolation systems for equipment protection
Authors: Inaudi José A. , Kelly James M. 
Published: April 2007

AbstractThis paper presents a formulation for earthquake resistant design of optimum hybrid isolation systems for sensitive equipment protection. The hybrid system under consideration consists of laminated rubber bearings, viscodampers and a set of actuators which, grounded on the main structural system, deliver forces on the basement of the isolated substructure mounted on the main structural system. An integrated design procedure for the passive and active components of the isolation system is developed aiming at acceleration reduction under random excitation. Linear models are used for the isolated structure, the main structural system and the isolation system. Fractional derivative Maxwell elements are used to model the mechanical behaviour of the viscodampers. The active component of the isolation system applies forces proportional to the absolute velocity of the isolated piece of equipment. Constraints in the deformation capacity of the isolators as well as constraints in the capacity of the actuators are considered for the design of an optimal hybrid isolation system. Simple numerical examples are developed herein to illustrate the design procedure. The superiority of hybrid systems over passive systems in reducing acceleration response is demonstrated.
Inelastic seismic response of code‐designed multistorey frame buildings with regular asymmetry
Authors: Duan X. N. , Chandler A. M. 
Published: April 2007

AbstractBased on an asymmetric multistorey frame building model, this paper investigates the influence of a building's higher vibration modes on its inelastic torsional response and evaluates the adequacy of the provisions of current seismic building codes and the modal analysis procedure in accounting for increased ductility demand in frames situated at or near the stiff edge of such buildings. It is concluded that the influence of higher vibration modes on the response of the upper‐storey columns of stiff‐edge frames increases significantly with the building's fundamental uncoupled lateral period and the magnitude of the stiffness eccentricity. The application of the equivalent static torsional provisions of certain building codes may lead to non‐conservative estimates of the peak ductility demand, particularly for structures with large stiffness eccentricity. In these cases, the critical elements are vulnerable to excessive additional ductility demand and, hence, may be subject to significantly more severe structural damage than in corresponding symmetric buildings. It is found that regularly asymmetric buildings excited well into the inelastic range may not be conservatively designed using linear elastic modal analysis theory. Particular caution is required when applying this method to the design of stiff‐edge frame elements in highly asymmetric structures.
Seismic energy demands on reinforced concrete moment‐resisting frames
Authors: Tso W. K. , Zhu T. J. , Heidebrecht A. C. 
Published: April 2007

AbstractThis paper examines the seismic energy demands on reinforced concrete ductile moment‐resisting frames. Three frames having 4, 10 and 18 storeys, representing low, medium and tall frames, were designed to the current Canadian seismic provisions and structural design requirements. Three groups of earthquake records having different frequency contents were selected as input ground motions. The input, hysteretic and damping energies were evaluated for these three frames and correlation was established with other response parameters. The use of equivalent single‐degree‐of‐freedom systems to estimate the energy demands on these frames was examined in order to simplify the computational effort. It is shown that the energy demand concept together with the equivalent single‐degree‐of‐freedom system is a viable design approach for low‐rise frames. Additional research to allow for the higher modal effect is required before the same concept can be extended to medium and tall frames.
Optimum damping in linear isolation systems
Authors: Inaudi Jose A. , Kelly James M. 
Published: April 2007

AbstractOptimum isolation damping for minimum acceleration response of base‐isolated structures subjected to stationary random excitation is investigated. Three linear models are considered to account for the energy dissipation mechanism of the isolation system: a Kelvin element, a linear hysteretic element and a standard solid linear element, commonly used viscoelastic models for isolation systems comprising natural rubber bearings and viscous dampers. The criterion selected for optimality is the minimization of the mean‐square floor acceleration response. The effects of the frequency content of the excitation and superstructure properties on the optimum damping and on the mean‐square acceleration response are addressed. The study basically shows that the attainable reduction in the floor acceleration largely depends on the energy dissipation mechanism assumed for the isolation system as well as on the frequency content of the ground acceleration process. Special care should be taken in accurately modelling the mechanical behaviour of the energy dissipation devices.
A design study of an energy‐dissipating cladding system
Authors: Cohen Julie Mark , Powell Graham H. 
Published: April 2007

AbstractA design study has been conducted to explore the use of structural cladding panels with energy‐dissipating cladding‐to‐frame connections for seismic‐resistant design. The study identifies several issues involved in the modelling and analysis of frames with energy‐dissipating cladding‐to‐frame connections, establishes concepts for design, and provides a preliminary assessment of the force and deformation demands that are likely to be placed on panels and connections. Non‐linear dynamic analyses indicate that the clad frames perform well, based on observations about maximum interstorey drifts, maximum plastic hinge rotations in the frames, and maximum ductility demands on the cladding‐to‐frame connections.
Spectral analysis of systems with non‐classical damping using classical mode superposition technique
Authors: Jangid R. S. , Datta T. K. 
Published: April 2007

AbstractA spectral method for random vibration analysis of a structural system with non‐proportional damping is presented using classical (undamped) mode superposition technique. The method obtains the frequency response function of the system by solving the dynamic equilibrium equations in generalized co‐ordinates through an iterative process. The iterative solution is written in closed form and the proof for convergence of the iterative process is given. Numerical examples show the convergence characteristics of the process and an excellent accuracy of the obtained results. The method turns out to be computationally more efficient than the conventional methods of spectral analysis using damped mode shapes and frequencies.
Optimum tuned‐mass dampers for minimizing steady‐state response of support‐excited and damped systems
Authors: Tsai Hsiang‐Chuan , Lin Guan‐Cheng 
Published: April 2007

AbstractA numerical searching procedure to find the optimum tuning frequency and damping ratio of the tuned‐mass damper which can reduce the steady‐state response of damped main systems to a minimum level is developed and applied to the two different harmonic excitation sources, support motion of fixed‐displacement amplitude and support motion of fixed‐acceleration amplitude. The explicit formulae for these optimum parameters are then derived through a sequence of curve‐fitting schemes. It has been found that, as the error of the explicit formulae is negligible, they provide a convenient tool to compute the optimum parameters in engineering applications.The numerical results show that the tuned‐mass damper is less effective in reducing the system's response when there is a high level of damping incorporated into the system. It is also found that the optimum tuning frequency is strongly influenced by the damping level of a system, especially in regard to the fixed‐acceleration support motion, but the optimum damping ratio of the tuned‐mass damper is not sensitive to the damping level of a system. The response of the damped system using the undamped optimum value as the damping of the tuned‐mass damper is not much different from the response using the damped optimum value.
Instrumental seismological data since 1900 for northeastern Italy
Authors: Margottini Claudio , Martini Guido , Slejko Dario 
Published: April 2007

AbstractStatistical analyses on a catalogue of instrumental data for earthquakes in northeastern Italy since 1900 are presented. The different types of magnitude, which are the main parameters under study, have been evaluated so as to be as homogeneous as possible. Comparisons of the different magnitude values show linear dependence, at least in the medium magnitude range represented by the available data set. Correlations between the magnitude most significant for this region and chosen macroseismic data indicate a methodology for assessing the macroseismic magnitude of historical earthquakes which seems to be stable.
Modal analysis of a DAM–Foundation system based on an FE–BE method in the time domain
Authors: Touhei Terumi , Ohmachi Tatsuo 
Published: April 2007

AbstractA modal analysis procedure based on an FE–BE method in the time domain is first formulated and then applied to a dam–foundation system. In the application, horizontal and vertical impulsive responses are calculated for the system having six different impedance ratios. Modal characteristics such as natural frequencies, damping ratios and mode shapes are evaluated from the Fourier spectra of the responses. The proposed procedure allows analysis of not only the underdamped but also the overdamped modes. According to the analysis, the radiation damping pertinent to the vertical vibration is half of that pertinent to the horizontal vibration and the interaction effect on the modes is not negligibly small when the impedance ratio exceeds 0·3.
Dynamic behaviour of pile foundations in homogeneous and non‐homogeneous media
Authors: Miura Kenji , Kaynia Amir M. , Masuda Kiyoshi , Kitamura Eiji , Seto Yutaka 
Published: April 2007

AbstractA three‐dimensional formulation based on Green's functions of cylindrical loads in layered semi‐infinite media is employed to investigate the dynamic behaviour of piles in homogeneous and non‐homogeneous half spaces. The pile‐soil‐pile interaction taking place in pile groups is incorporated in the model. The results presented in this paper include the dynamic stiffnesses and dampings of single piles as well as those of representative 2 × 2 and 4 × 4 square pile groups in the soil media considered in this study. In addition, the distribution of forces applied on the pile cap among the individual piles in a group is investigated.