bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tungsten(VI) and Molybdenum(VI) Complexes with Soft Thioether Ligand Coordination – Synthesis, Spectroscopic and Structural Studies
Authors: Davis Martin F. , Levason William , Light Mark E. , Ratnani Raju , Reid Gillian , Saraswat Keerti , Webster Michael 
Published: March 2007

AbstractReaction of WX6 (X = Cl or Br) with O(SiMe3)2 in CH2Cl2, followed by addition of MeCN and a further equivalent of O(SiMe3)2 in CH2Cl2 gives [WO2X2(MeCN)2] in situ, which subsequently react with the dithioethers MeS(CH2)2SMe, iPrS(CH2)2SiPr or 1,4‐dithiane to afford the first series of WVI thioether complexes, [WO2X2(dithioether)]. The very moisture‐sensitive yellow complexes have been characterised by microanalysis, IR, 1H and 13C{1H} NMR spectroscopy, which indicate cis‐dioxido and trans‐dihalide arrangements in the monomers with two thioether donor atoms completing the very distorted octahedral geometry (confirmed by a crystal structure of [WO2Cl2{iPrS(CH2)2SiPr}]). The strongly polymerised WO2X2 compounds themselves are not useful synthons for the preparation of the WVI thioether complexes and substitution of the dimethoxyethane ligand in [WO2Cl2{MeO(CH2)2OMe}] by dithioethers is also incomplete. Molybdenum(VI) dioxidodichloride thioether complexes of the form [MoO2Cl2(L)] (L = iPrS(CH2)2SiPr, 1,4‐dithiane, κ2‐[15]aneS2O3, κ2‐[14]aneS4 and κ2‐[12]aneS4) ([15]aneS2O3 = 1,4‐dithia‐7,10,13‐trioxacyclopentadecane, [14]aneS4 = 1,4,8,11‐tetrathiacyclotetradecane, [12]aneS4 = 1,4,7,10‐tetrathiacyclododecane) and the unusual dinuclear [Mo2O4Cl4{o‐C6H4(CH2SMe)2}2] are obtained by direct treatment of MoO2Cl2 with the appropriate ligand. The [Mo2O4Cl4{o‐C6H4(CH2SMe)2}2] adopts an unexpected metallocyclic structure with cis‐MoCl2 units and bridging bidentate dithioether (confirmed crystallographically). The structure of a new polymorph of [WO2Cl2{MeO(CH2)2OMe}] is also described.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Small and Versatile – Formyl Anion and Dianion Equivalents
Authors: Kirschning Andreas , Kujat Christof , Luiken Silke , Schaumann Ernst 
Published: March 2007

AbstractThis account provides a short overview of the synthetically important class of formyl anions and the less studied formyl dianion equivalents. A brief literature survey, which particularly focusses on asymmetric homologation strategies, is complemented by a detailed description of lithiated (dimethoxymethyl)diphenylphosphane oxide, which is an ideal formyl anion equivalent in reactions with aldehydes. Under acidic conditions the intermediate ketene O,O‐acetals afford homologated carboxylic esters whereas asymmetric dihydroxylation of ketene acetals leads to collapse of the intermediate diols furnishing the corresponding α‐hydroxy carboxylic esters with high stereocontrol. Additionally, it is demonstrated that the silyl‐substituted carbanion may be looked upon as a latent dianion that can react either with two electrophiles or with bis‐electrophiles, the latter transformation yielding ring‐closure coproducts. It is advantageous if the electrophiles are epoxides or epoxides carrying a remote leaving group. The carbanion will ring‐open the epoxide and allow a C→O silyl shift, thus generating the new carbanion. This then reacts with the second electrophile, either inter‐ or intramolecularly. The versatility of these two formyl anion equivalents is demonstrated by selected examples from natural product synthesis.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Palladium‐Catalyzed Formation of Cyclic Ethers – Regio‐, Stereo‐ and Enantioselectivity of the Reaction
Authors: Zawisza Anna , Fenêt Bernard , Sinou Denis 
Published: March 2007

AbstractAn efficient and stereoselective synthesis of 3‐alkyl‐3‐hydroxymethyl‐5‐vinyltetrahydrofurans is described by the Pd0‐catalyzed cyclization of the methyl carbonates of ω,ω‐bis(hydroxymethyl)‐α,β‐unsaturated alcohols. The use of chiral ligands gave the corresponding THF derivatives in low to moderate enantiomeric ratios. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Recent Advances in the Catalytic Asymmetric Nitroaldol (Henry) Reaction
Authors: Palomo Claudio , Oiarbide Mikel , Laso Antonio 
Published: March 2007

AbstractCatalyst‐controlled enantioselective nitroaldol (or Henry) reactions are presented. These reactions represent powerful C–C bond‐forming tools and the resulting nitro alcohol (nitroaldol) products can be transformed into a number of nitrogen‐ and oxygen‐containing derivatives (nitroalkenes, amino alcohols, amino acids etc.). In addition to substrate‐controlled nitroaldol reactions (not covered), catalytic systems that provide good stereoselectivity have been developed in recent years. Through the use of preformed silyl nitronates as activated substrates, catalytic systems involving metallic Lewis acids or tetraalkylammonium salts have been deployed in fluoride‐mediated nitroaldol reactions. In a further advance, catalytic systems capable of promoting direct nitroaldol reactions between unmodified nitroalkanes and aldehydes (ketones) with high yields and stereoselectivities have been developed. To this end, ambifunctional systems based on La, Zn, Cu, Co and Mg metal species are described, together with some organocatalysts. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Intramolecular Dipolar Cycloaddition Reactions to Give Substituted Indoles – A Formal Synthesis of Deethylibophyllidine
Authors: Coldham Iain , Dobson Benjamin C. , Fletcher Stephen R. , Franklin Andrew I. 
Published: March 2007

AbstractA four‐step route to the tetracyclic ring system found in a number of indole alkaloids is described using stereoselective dipolar cycloaddition reactions of azomethine ylides. The ylides were derived from N‐protected 2‐butenylindole‐3‐carbaldehydes, which were prepared in three steps from 2‐methylindole. Condensation of these aldehydes with a variety of alkylamino esters or amino acids or with N‐methylhydroxylamine gave the required azomethine ylides or nitrone that undergo intramolecular cycloaddition onto the pendant, unactivated alkene. The cycloaddition sets up two new rings and up to three new stereocentres stereoselectively. After cycloaddition with N‐allylglycine, N‐deallylation provided the N‐unsubstituted product and this constitutes a formal synthesis of the alkaloid deethylibophyllidine. The cycloaddition chemistry was also shown to be amenable as a route to the alkaloid ibophyllidine or epiibophyllidine, although the use of 2‐(allylamino)butyric acid to prepare the azomethine ylide can favour competing iminium ion isomerisation and hydrolysis.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Rapid bonding of Pyrex glass microchips
Authors: Akiyama Yoshitake , Morishima Keisuke , Kogi Atsuna , Kikutani Yoshikuni , Tokeshi Manabu , Kitamori Takehiko 
Published: March 2007

AbstractA newly developed vacuum hot press system has been specially designed for the thermal bonding of glass substrates in the fabrication process of Pyrex glass microchemical chips. This system includes a vacuum chamber equipped with a high‐pressure piston cylinder and carbon plate heaters. A temperature of up to 900°C and a force of as much as 9800 N could be applied to the substrates in a vacuum atmosphere. The Pyrex substrates bonded with this system under different temperatures, pressures, and heating times were evaluated by tensile strength tests, by measurements of thickness, and by observations of the cross‐sectional shapes of the microchannels. The optimal bonding conditions of the Pyrex glass substrates were 570°C for 10 min under 4.7 N/mm2 of applied pressure. Whereas more than 16 h is required for thermal bonding with a conventional furnace, the new system could complete the whole bonding processes within just 79 min, including heating and cooling periods. Such improvements should considerably enhance the production rate of Pyrex glass microchemical chips. Whereas flat and dust‐free surfaces are required for conventional thermal bonding, especially without long and repeated heating periods, our hot press system could press a fine dust into glass substrates so that even the areas around the dust were bonded. Using this capability, we were able to successfully integrate Pt/Ti thin film electrodes into a Pyrex glass microchip.
Air quality monitoring using heterogeneous networks
Authors: Fassò Alessandro , Cameletti Michela , Nicolis Orietta 
Published: March 2007

AbstractIn this paper, we consider some approaches to spatio‐temporal modeling of environmental data obtained from an heterogeneous network.Besides discussing modeling details for spatio‐temporal dynamics and calibration of different instruments, we consider crossvalidation issues and extensions to the monitoring network assessment based on sensitivity analysis.We then consider a case study based on the heterogeneous network related to fine particulate matter (PM10) coming from the Po Valley, North Italy. Copyright © 2007 John Wiley & Sons, Ltd.
The generation of stochastic load functions to simulate wind loading on structures
Authors: Wyatt T. A. , May H. I. 
Published: March 2007

AbstractThe simplest form of input required for step‐by‐step simulation of response of a structure to a gusty wind is a stochastic process having Gaussian distribution and a specified power spectrum. Methods for generating such a process are described in detail, and the extension outlined for generating a number of partially correlated input processes having specified power spectra and cross‐spectra.
Behaviour of subaqueous tunnels during earthquakes
Authors: Okamoto Shunzo , Tamura Choshiro 
Published: March 2007

AbstractThree‐dimensional models of a subaqueous tunnel were built on a shaking table and vibrated for the purpose of investigating the dynamic behaviour of the tunnel. The material of the soft surface layer was gelatin gel and that of the tunnel was silicon rubber.In addition, earthquake observations at the site of the real subaqueous tunnel have been carried out using accelerometers and strain gauges set on the walls of the tunnel. At the site, micro‐tremors were also measured.In these studies, it was noted that non‐uniform displacements of the ground along the tunnel axis were caused by variations of the dynamic behaviour of the ground, and that the tunnel deforms correspondingly to the varying deformations of the ground.From these experimental results, a mathematical model of the subaqueous tunnel was formulated for anti‐seismic design studies.
Scattering of plane sh waves by a semi‐cylindrical canyon
Authors: Trifunac M. D. 
Published: March 2007

AbstractThe two‐dimensional scattering and diffraction of plane SH waves by a semi‐cylindrical canyon is analysed for a general angle of wave incidence. The closed‐form solution of the problem shows that the surface topography can have prominent effects on incident waves only when the wavelengths of incident motion are short compared to the radius of a canyon. The surface amplification of displacement amplitudes around and in the canyon changes rapidly from one point to another, but the amplification is always less than 2. The over‐all trends of amplification pattern are determined by two principal parameters: (1) γ, the angle of incidence of plane SH waves, and (2) η, the ratio of radius of the canyon to one‐half wave length of incident waves. The higher η leads to greater complexity of the pattern of surface displacement amplitudes characterized by more abrupt changes of amplification from one point to another, while γ mainly determines the over‐all trends of displacement amplitudes. For grazing and nearly grazing incidences, for example, a strong shadow zone is developed behind the canyon.The qualitative analysis of the topographic effects on the Pacoima Dam accelerogram,1 based on the semi‐cylindrical canyon, suggests that this strong‐motion record was not seriously affected by surface topography of the recording site.
Stability and accuracy analysis of direct integration methods
Authors: Bathe K. J. , Wilson E. L. 
Published: March 2007

AbstractA systematic procedure is presented for the stability and accuracy analysis of direct integration methods in structural dynamics. Amplitude decay and period elongation are used as the basic parameters in order to compare various integration methods. The specific methods studied are the Newmark generalized acceleration scheme, the Houbolt method and the Wilson θ‐method. The advantages of each of these methods are discussed. In addition, it is shown how the direct integration of the equations of motion is related to the mode superposition analysis.
Hydrodynamic pressures and response of gravity dams to vertical earthquake component
Authors: Chakrabarti P. , Chopra Anil K. 
Published: March 2007

AbstractHydrodynamic pressures and structural response of concrete gravity dams, including dam‐reservoir interaction, due to the vertical component of earthquake ground motions are investigated. The response of the dam is approximated by the deformations in the fundamental mode of vibration, and the effects of deformability of bed rock on hydrodynamic pressures are recognized in the analysis. Expressions for the complex frequency response functions for the dam displacement, dam acceleration and lateral hydrodynamic force are derived. These results along with the Fast Fourier Transform algorithm are utilized to compute the time‐history of responses of dams of 100, 300 and 600 ft height, with full reservoir, for different values of elastic modulus of mass concrete: 3.0, 3.5, 4.0, 4.5 and 5.0 million psi, to the vertical component of El Centro, 1940, and Taft, 1952, ground motions. It is concluded that the hydrodynamic forces caused by vertical ground motion are affected substantially by damreservoir interaction and depend strongly on the modulus of elasticity of the dam. The dam response to the vertical component of ground motion is compared with that due to the horizontal component. It is concluded that because the vertical component of ground motion causes significant hydrodynamic forces in the horizontal direction on a vertical upstream face, responses to the vertical component of ground motion are of special importance in analysis of concrete gravity dams subjected to earthquakes.
Earthquake resistance of buildings with a ‘soft’ first storey
Authors: Chopra A. K. , Clough D. P. , Clough R. W. 
Published: March 2007

AbstractThe dynamic, bi‐linear response behaviour of a series of eight storey shear buildings subjected to simulated earthquake excitation is studied. The specific objective of the investigation is to determine under what conditions a yielding first storey can adequately protect the upper storeys from significant yielding. Two classes of buildings are considered: stiff (0.5 sec period) and flexible (2.0 sec period), and the basic parameters considered in the yielding first storey are the yield force level and the bi‐linear stiffness. The results demonstrate that a very low yield force level and an essentially perfectly plastic yielding mechanism are required in the first storey to provide effective protection to the superstructure. Moreover, the required displacement capacity of such an effective first storey mechanism is found to be very large.
The vibration frequencies of an elastically supported cantilever column with variable cross‐section and distributed axial load
Authors: Glück J. 
Published: March 2007

AbstractThe solution for transverse vibration frequencies of an elastically supported cantilevered column with continuously varying cross‐section under distributed axial load is developed. Boundary conditions are formulated for fixed and elastic support. Values of the fundamental frequency are tabulated for various cross‐sections and axial load distributions due to self‐weight as functions of the ratios between the rigidities and also the axial loads at the fixed and free ends, the ratio between the actual and critical buckling axial load, the degree of polynomial approximation and the rotational stiffness of the elastic support.
Free vibrations of coupled shear walls
Authors: Mukherjee P. R. , Coull A. 
Published: March 2007

AbstractThe continuous connection method of analysis is extended to deal with the free vibrations of a coupled shear wall structure. The natural modes and frequencies are determined from the Galerkin technique, and the dynamic response following an imposed lateral displacement is evaluated. A comparison is made between theoretical predictions of natural frequencies and the results from tests on model structures.
On the choice of the acceptable seismic risk
Authors: Grandori G. , Benedetti D. 
Published: March 2007

AbstractThe proper choice of the acceptable seismic risk requires an accurate cost‐benefit analysis. As is well known these analyses present considerable difficulties if one wishes to face the problem in a general way from the technical point of view. Besides, there are no generally accepted criteria for formulating a quantitative evaluation of the intangibles, among which the most important is the risk to human life. However, it appears indispensable that research should be started in the field which leads to some numerical resultsIn this paper a simplified analytical model is proposed and the problem of intangibles is discussed. The basic idea is that the comparison with other risks is the most realistic instrument for the choice of an acceptable level of the specific considered risk. The conclusion reached is that a fundamental index for comparison and decision is the incremental cost of investment necessary to save, on average, one human life a year. An evaluation of such an index, valid as a first approximation, is given for this simplified model.
Torsional and coupled vibrations of embedded footings
Authors: Novak M. , Sachs K. 
Published: March 2007

AbstractAn approximate analytical solution is presented for torsional vibrations of footings partially embedded into a semi‐infinite medium or a stratum. Simple formulas derived for pure torsional motion make it possible to apply a correction for the effect of embedment to the known solutions of surface footings. The solution completes an approach to the analysis of all modes of footing vibrations, including the coupled modes. The approach to coupled modes is illustrated by the solution of coupled response involving horizontal translation, rocking and torsion. Formulas are presented for stiffness and damping coefficients that can be used in the analysis of embedded footings or structures supported by such footingsField experiments were conducted with concrete footings featuring circular, square and rectangular bases and variable embedment depths. The experimental results were compared with theoretical predictions of pure torsional vibrations.
Analysis of strong earthquake ground motion for prediction of response spectra
Authors: Trifunac Mihailo D. 
Published: March 2007

AbstractPrediction of response spectra for earthquake engineering purposes is considered from a new point of view based on the dislocation theory of earthquakes. It is shown that the traditional scaling of response spectra by the predicted peak acceleration should be limited to the high‐frequency end of the spectrum, and that the peak acceleration in the near field is not strongly correlated with earthquake magnitude. The amplitude of the long‐period end of response spectrum at source to station distances greater than about 10 source dimensions should be scaled with seismic moment, while for distances less than about one source dimension this amplitude should be proportional to the permanent ground displacement. To reconcile the existing extensive data on seismicity of active regions based on magnitude scale, it is shown that magnitude can be used to determine approximately the seismic moment.
Accelerograph calibration and accelerogram correction
Authors: Skinner R. I. , Stephenson W. R. 
Published: March 2007

AbstractWhen measured earthquake accelerations are used as a basis for structural design, then acceleration errors of a few per cent are usually acceptable. However a number of tasks in structural design, and in earthquake engineering research, require measured accelerations with errors limited to a few parts per thousand. Such tasks include those which call for the calculation of angular accelerations, the comparison of acceleration spectra or the calculation of relative displacementAccurate accelerations may be obtained from existing accelerographs by applying the results of an accurate static calibration to an accelerogram, and then applying corrections for the effects of accelerometer resonance. This paper concentrates attention on the correction of static errors, including sensing direction errors and cross‐axis interaction errors. For completeness there is a brief discussion of dynamic errors, which depend on accelerometer periods and dampings. It is concluded that earthquake accelerations may be obtained with errors of not much more than 0·001 g, the resolution of a typical accelerograph, at least for periods greater than 0·2 sec. When the accelerations have shorter periods, larger errors may arise due to the limited accuracy of the corrections for dynamic errorsThe static calibration of accelerographs, and the corresponding record correction procedures, are illustrated by application to the M.O.2 accelerograph.
Structural response to random acoustic excitation
Authors: Bhat B. Rama , Rao B. V. A. , Wagner Hans 
Published: March 2007

AbstractThe design of aerospace structures necessitates the study of their behaviour in intense acoustic environments. This is more so in recent times due to an increase in power of the vehicles. The present paper deals with an investigation of the response of structures such as flat, stiffened plates to such environments. A peaked type of power spectral density of excitation is assumed, which is more realistic and representative of actual random acoustic excitations than the conventionally assumed white noise type excitations, either ideal or band‐limited. The space correlation of the excitation field is assumed to be unity over the plate surface. Generalized harmonic analysis is used to obtain responses such as auto‐correlation functions and mean square values of both accelerations and stresses. To obtain the response quantities of stiffened plates the approximate method of analysis suggested by Lin12 is used.
Minimal structural response under random excitation using the vibration absorber
Authors: Wirsching Paul H. , Campbell Gary W. 
Published: March 2007

AbstractThe equations of motion are derived for the first mode response of a linear multistorey structure having a linear vibration absorber attached to the roof. Furthermore, the variance of the first mode response to a gaussian white noise lateral base acceleration (as a model of earthquake excitation) is determined. Smallest possible values of the variance of the response along with corresponding absorber parameters are established using an optimization program. It is demonstrated that the absorber is quite effective in reducing first mode response for 5‐ and 10‐storey structures even with relatively small values of the absorber mass. Moreover, minimal responses for the randomly excited single‐degree‐of‐freedom system have been determined, and a design example is presented. The absorber system has potential application not only in earthquake engineering but also in aerospace and terrestrial vehicle design.