bluuebunny/crossref_metadata_2025_split huggingface dataset:
Proline Organocatalysis as a New Tool for the Asymmetric Synthesis of Ulosonic Acid Precursors.
Authors: Enders Dieter , Gasperi Tecla 
Published: April 2007

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Oligonucleotide Analogues with Integrated Bases and Backbone. Part 13. Synthesis and Association of Ethynylene‐Linked Self‐Complementary Dimers.
Authors: Zhang Xiaomin , Bernet Bruno , Vasella Andrea 
Published: April 2007

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Aromatic Compounds Produced by Periconia atropurpurea, an Endophytic Fungus Associated with Xylopia aromatica.
Authors: Teles Helder Lopes , Sordi Renata , Silva Geraldo Humberto , Castro‐Gamboa Ian , Bolzani Vanderlan da Silva , Pfenning Ludwig Heinrich , Magalhaes de Abreu Lucas , Costa‐Neto Claudio Miguel , Young Maria Claudia Marx , Araujo Angela Regina 
Published: April 2007

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Perfluoroketene Dithioacetals: Versatile Building Blocks Toward Trifluoromethyl Heterocycles
Authors: Portella Charles , Bouillon Jean‐Philippe 
Published: April 2007

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Chemistry and Synthesis of Highly Oxygenated Alkaloids from Amaryllidaceae: Lycoricidine, Narciclasine, Pancratistatin, and Analogues
Authors: Chapleur Y. , Chretien F. , Ahmed S. Ibn , Khaldi M. 
Published: April 2007

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
3‐(4′‐Geranyloxy‐3′‐methoxyphenyl)‐2‐trans‐propenoic Acid: A Novel Promising Cancer Chemopreventive Agent
Authors: Curini Massimo , Epifano Francesco , Genovese Salvatore , Marcotullio Maria Carla , Menghini Luigi 
Published: April 2007

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Natural Products with Taxol‐like Antitumor Activity — Synthetic Approaches to the Sarcodictyins and Eleutherobin
Authors: Gennari Cesare 
Published: April 2007

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Diffraction effects between foundations due to incident rayleigh waves
Authors: Triantafyllidis Th. , Neidhart Th. 
Published: April 2007

AbstractThe dynamic behaviour of a finite number of rigid, adjacent foundations on the surface of a linear‐elastic, isotropic and homogeneous halfspace due to a far‐field excitation of the Rayleigh type is the subject of the present work. The dynamic behaviour of this system differs from that of a single foundation subjected to the same excitation due to the existence of the natural coupling between adjacent foundations caused by the wave propagation through the underlying soil. For the determination of the diffraction forces acting on the foundations an analytical procedure is followed. The stresses at the interfaces between the foundations and subsoil are approximated by series expansions of orthogonal polynomials. It is interesting to notice that, apart from the loads appearing in the direction of incidence, additional loads perpendicular to the given incidence direction act on the foundations due to scattered waves. Their intensity depends on the excitation frequency and the distance between the foundations. The method followed here can be applied for the determination of the dynamic loads acting on fixed foundations in the case of a seismic excitation of relatively long duration.
Non‐linear earthquake response of concrete gravity dams part 1: Modelling
Authors: El‐Aidi Bahaa , Hall John F. 
Published: April 2007

AbstractA finite element procedure to model the non‐linear earthquake response of concrete gravity dam systems is presented. A two‐dimensional idealization is adopted for the dam and water in order to simplify the analysis and reduce the computational effort. The foundation of the dam is modelled as a rigid rectangular massless plate attached to a three‐dimensional viscoelastic half‐space. The non‐linear behaviour is represented by smearing techniques and includes tensile cracking with subsequent opening, closing and sliding, as well as water cavitation in the reservoir. Special treatments are applied to suppress spurious oscillations in the water response associated with cavitation and to prevent cracks in the dam from spreading into wide zones. Experience from non‐linear analyses is cited as it affects the design of the algorithm.
Dependence of fourier spectrum amplitudes of recorded earthquake accelerations on magnitude, local soil conditions and on depth of sediments
Authors: Trifunac M. D. 
Published: April 2007

AbstractNew empirical scaling equations of Fourier amplitude spectra of strong earthquake shaking are presented for the site characterization in terms of local geologic and local soil conditions simultaneously. It is shown that using only the local soil site classification may lead to biased results, and it is suggested that both soil and geologic conditions should be used together in estimation of the site specific spectrum amplitudes.
Free‐field response from inclined body waves in a viscoelastic random medium
Authors: Hryniewicz Z. , Hermans A. J. 
Published: April 2007

AbstractThis paper deals with the free‐field response of the in‐plane motion resulting from a combination of inclined incident body waves. The amplification of waves in a viscoelastic layer with stochastic changes in the elastic properties and density is investigated. The method used is that of Karal and Keller and is based on the idea of the fundamental matrix. The third order correlations are neglected. The resulting integro‐differential equations for the average displacements are solved by the Laplace transform. Generally, analysis indicates that the stochastic changes in the shear modulus and density enhance the damping in a significant manner. However, increases in the waves' amplification can arise in the case of a small dimensionless frequency and uncorrelated stochastic changes of material parameters.
Modal analysis of vibrating viscoplastic composite beams on multiple supports
Authors: Fotiu P. , Irschik H. 
Published: April 2007

AbstractA vibration analysis for viscoplastic, shear deformable composite beams is presented, where non‐linear strains consistently are treated as an additional loading of the linear elastic structure due to fictitious sources of eigenstresses. Therefore, linear solution methods such as mode superposition and Green's functions become applicable, and a fast, computer‐oriented solution strategy is developed. The non‐linear structural response is found as the sum of the corresponding linear elastic response and the solution due to the additional loading by the inelastic strains, where the sources of eigenstresses are calculated from the material's law in a time‐stepping procedure. The method is demonstrated using a composite sandwich beam with thin surface layers on multiple supports, which are excited independently. Elastoplastic material behaviour of endochronic type as well as a viscoplastic material's law are considered simultaneously.
A simple non‐linear model for the investigation of the effects of the gap closure at the abutment joints of short bridges
Authors: Maragakis Emmanuel A. , Thornton Greg , Saiidi Mehdi , Siddharthan Raj 
Published: April 2007

AbstractClosure of the gap at the abutment joints of bridges has been the source of extensive damage during the 1971 San Fernando and more recent earthquakes. In this paper a model for the investigation of the effects of this gap closure is presented and analysed. The focus of the model is the representation of the non‐linear response of the bridge abutments, the foundation and the columns. The model is used for the investigation of the response of a short bridge located in California.
Reduction of vibration by control forces
Authors: Warburton G. B. 
Published: April 2007

AbstractThe concept of reducing vibrations in steady‐state problems by introducing appropriately chosen additional or control forces, which have the same frequency and phase as the original excitation forces, has been the subject of some recent papers. In this paper the normal mode method is used to determine the magnitudes of the control forces. This method is simpler in concept than earlier approaches. It is demonstrated that with a single control force resonant response of multi‐degree‐of‐freedom systems can be reduced substantially, particularly for the fundamental resonance in lightly and moderately damped systems.
Study of the earthquake response of the base‐isolated Law and Justice Center in Rancho Cucamonga
Authors: Papageorgiou Apostolos S. , Lin Bing‐Chang 
Published: April 2007

AbstractThe recorded earthquake response of a base‐isolated building—the Foothill Communities Law and Justice Center in Rancho Cucamonga—shaken by the 1985 Redlands earthquake (ML 4–8) is discussed and analysed by employing system identification techniques. The calculated response of one‐dimensional and three‐dimensional linear structural models is fitted to the recorded motions of the superstructure using the ‘modal minimization method’ for structural identification, in order to determine optimal estimates of the parameters of the dominant modes of the building. Simple one‐dimensional analyses are used to identify also the effective values of key parameters (e.g. damping) of the isolation system. Furthermore, the recorded motions obtained from the densely instrumented foundation (i.e. below the isolation bearings) of the structure and from the free‐field station located 330 ft1 ft =0.3048 m; 1 mile=1.609 km.
from the building show how the presence of the structure affects the incoming seismic waves. It is observed that the transverse component of motion (i.e. the component which is perpendicular to the long dimension of the plan of the building) is affected by the presence of the structure considerably more than the longitudinal component. Factors contributing to this effect are the extreme length of the structure (414 ft) and the rotational motions of the superstructure caused by the spatial variability of ground motion. It is pointed out that, despite the fact that the shift in the effective frequency of the structure induced by the isolation was very small, the elastomeric bearings were very effective in reducing the accelerations transmitted to the structure. This is attributed to the damping capacity of the isolation. Based on the observed response of the building to this small earthquake it can be stated with confidence that the structure performed according to expectations.
A comparative study of performances of various base isolation systems, part II: Sensitivity analysis
Authors: Su Lin , Ahmadi Goodarz , Tadjbakhsh Iradj G. 
Published: April 2007

AbstractA series of numerical experiments on the performance of different base isolation systems for a non‐uniform shear beam structure is carried out. Several base isolation systems are considered and the peak relative displacements and the maximum absolute accelerations of the base‐isolated structure and its base raft under a variety of conditions are evaluated. Several sensitivity analyses for variations in properties of the base isolator and the structure are carried out. A number of different earthquake excitations are also used in the study. The results show that performances of the base isolation systems are not sensitive to small variations in their natural period, damping or friction coefficient. The presence of a frictional element in the isolators reduces their sensitivity to severe variations in frequency content and amplitude of the ground acceleration. In particular, the resilient‐friction base isolators with or without sliding upper plate perform reasonably well under a variety of loading conditions. The rubber bearing type, however, leads to the lowest peak transmitted accelerations for moderate intensity earthquakes.
A fundamental solution due to a periodic point force in the interior of an elastic half‐space
Authors: Banerjee P. K. , Mamoon S. M. 
Published: April 2007

AbstractThe fundamental solution for a periodic point force in the interior of a three‐dimensional, homogeneous, isotropic, elastic half‐space is derived. The method of synthesis and superposition is employed to obtain the solution in the Laplace transform as well as the frequency domain. These correspond to the dynamic equivalent of Mindlin's static half‐space point force solutions. It is reduced, for certain limiting conditions, to the dynamic equivalent of Boussinesq's and Cerruti's problems of a normal and tangential periodic point force respectively, on the boundary of a half‐space. Also, static solutions of Mindlin, Boussinesq and Cerruti are recovered for small frequency parameters. Finally, results are presented and compared with other available solutions.
Sliders and tension controlled reinforced elastomeric bearings combined for earthquake isolation
Authors: Chalhoub Michel S. , Kelly James M. 
Published: April 2007

AbstractEssential requirements from a base isolation system include wind restraint, stability and fail‐safe capacity. A new base isolation system that satisfies all three requirements and possesses other advantages was tested on the earthquake simulator at the University of California under the base of a one‐fourth scale nine storey steel structure. The base behaves as fixed for low magnitude inputs. When sliding starts the rubber bearings provide additional stiffness and recentering. Displacements are better controlled than the ones for a purely elastomeric isolation system. Vertical deflections due to large horizontal drift encountered in solely rubber systems are eliminated. The fail safe capacity is provided by tension restrainers installed inside the rubber bearings, and by the constant contact of the base with the sliders. Base shear hysteresis loops are drastically enlarged by the presence of the sliders.
Three‐dimensional boundary element reservoir model for seismic analysis of arch and gravity dams
Authors: Jablonski A. M. , Humar J. L. 
Published: April 2007

AbstractThe boundary element method has been successfully applied in the past to the analysis of hydrodynamic forces in two‐dimensional infinite as well as two‐ and three‐dimensional finite reservoirs subjected to seismic ground motions. This paper presents the results of more recent research on the application of the constant boundary element method to the 3D analysis of reservoir vibration. Special boundary conditions, previously used in the 2D case, to treat infinite radiation damping and damping from foundation soil and banks have been incorporated in this formulation. Numerical results for vibration of a 3D infinite rectangular reservoir as well as of a 3D infinite reservoir impounded by an arch dam are presented and compared with some existing results obtained by other researchers.
Floor response spectra for base‐isolated multi‐storey structures
Authors: Fan Fa‐Gung , Ahmadi Goodarz 
Published: April 2007

AbstractA study of floor response spectra for a base‐isolated multi‐storey structure under sinusoidal and seismic ground excitations is carried out. Several base isolation systems including the laminated rubber bearing, the pure‐friction, the resilient‐friction, the Électricité de France and the sliding resilient‐friction systems are considered. A sinusoidal ground acceleration and several earthquake accelerograms (including those of El Centro 1940, Pacoima Dam 1971 and Mexico City 1985) are used to evaluate the floor response spectra. The characteristics of the spectra generated by different base isolation systems are studied, and the results are compared with those for the fixed‐base structure. It is shown that the structural contents can be protected against earthquakes by the use of properly designed base isolation systems. In particular, the laminated rubber bearing system appears to be remarkably effective in protecting the secondary systems under a variety of conditions.
System parameters of soil foundations for time domain dynamic analysis
Authors: Jean Wen‐Yu , Lin Tsung‐Wu , Penzien Joseph 
Published: April 2007

AbstractSoil‐structure interaction analysis is usually carried out in the frequency domain, because the compliance functions of the half‐space are known only in the frequency domain. Since non‐linear analysis cannot be carried out in the frequency domain, a system with frequency independent parameters is used to represent the half‐space soil medium so that a nonlinear analysis in the time domain becomes possible. The objective of this paper is to propose a system with lumped parameters, which are independent of frequency, to represent the half‐space soil medium. The proposed frequency independent system consists of a number of real discrete structure elements; thus the existing dynamic analysis programs may be adoptable with little modification.In this paper, the parameters are found by minimizing the sum of the squares of deviations between the steady‐state responses of the theoretical half‐space model and those of the lumped parameter system over a specified frequency range. Once the parameters have been found, the lumped parameter system can be used in practical applications for time domain dynamic analysis of either linear or non‐linear structures. In comparison with the dynamic response of the theoretical half‐space model, the lumped parameter system yields satisfactory results.
Vibration of linear structures due to jump‐discontinuous, non‐interrupted, stochastic processes
Authors: Mironowicz W. , Śniady P. 
Published: April 2007

AbstractThe solution of the problem of vibration of linearly elastic structures, caused by stochastic excitation of non‐interrupted, jump‐discontinuous character, is considered in the paper. Two types of excitation are examined. They form an enhancement of the continuous model which is most often used. The solution in the form of expected values, correlation functions and spectral densities of the deflection of the structure is formulated. Examples illustrating the solution are presented.
Stochastic response of rigid foundations
Authors: Pais Artur Luna , Kausel Eduardo 
Published: April 2007

AbstractWhile the study of kinematic interaction (i.e. the dynamic response of massless foundations to seismic loads) calls, in general, for advanced analytical and numerical techniques, an excellent approximation was proposed recently by Iguchi.1,2 This approximation was used by the authors to analyse embedded foundations subjected to spatially random SH‐wave fields, i.e. motions that exhibit some degree of incoherence. The wave fields considered ranged from perfectly coherent motions (resulting from seismic waves arriving from a single direction) to chaotic motions, resulting from waves arriving simultaneously from all directions. Additional parameters considered were the shape of the foundation (cylindrical or rectangular) and the degree of embedment. It was found that kinematic interaction usually reduces the severity of the motions transmitted to the structure, and that incoherent motions do not exhibit the frequency selectivity (i.e. narrow valleys in the foundation response spectra) that coherent motions do.
On the accuracy of an implicit algorithm for pseudodynamic tests
Authors: Shing Pui‐Shum B. , Manivannan T. 
Published: April 2007

AbstractThe error‐propagation characteristics of an implicit time integration algorithm in pseudodynamic testing are examined. It is shown that the implicit algorithm is superior to explicit integration algorithms in terms of experimental error amplification. The influence of systematic experimental errors is studied and methods for controlling these errors are examined. In spite of the fact that the implicit algorithm is unconditionally stable, it is shown that the integration time interval in a pseudodynamic test is limited by the calibration range of the electronic hardware as well as the degree of participation of the higher modes. Furthermore, the tolerance for experimental errors decreases as the integration time interval increases.
Dynamic response of single‐span beam bridges to a series of moving loads
Authors: Klasztorny Marian , Langer Jan 
Published: April 2007

AbstractThe paper makes a contribution to the problem of a stream of loads crossing a single‐span beam bridge. There are considered the basic load models, in the form of a stream of fixed amplitude forces, unsprung masses and viscoelastic oscillators. The matrix equations of motion of the system are formulated and discussed. The problem of dynamic stability and steady‐state response of a bridge carrying a periodic stream of inertial loads is formulated and solved. The paper also includes a vibration study of a beam bridge subjected to a uniform stream of moving loads, of a limited or unlimited number of load cycles.
Influence of intensity of motion on the seismic response of structures with asymmetric force‐deformation curves
Authors: Ruiz Sonia E. 
Published: April 2007

AbstractAsymmetrically yielding single‐degree‐of‐freedom elastoplastic systems are subjected to simulated accelerograms based on El Centro‐NS, 1940 ground motion (wide frequency band) to calculate the corresponding ductility demands. Results are compared with those corresponding to simulated accelerograms of the SCT‐EW, 1985 Mexico earthquake (narrow frequency band) obtained in a previous work. Results obtained reveal that the characteristics of the excitation influence the response of asymmetrically yielding structures and that the differences found on responses corresponding to both earthquakes are due to frequency content, duration and/or intensity of motion. The effect of the latter concepts is studied using modulating sinusoidal excitations as well as accelerograms recorded on soft and hard soils of Mexico City.Two alternate expressions are proposed to evaluate the increase in ductility demands of structures with asymmetric force‐displacement curves with respect to symmetric ones. Those expressions take into account motion intensity and duration, as well as seismic design coefficient.