bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantification of dexamethasone and corticosterone in rat biofluids and fetal tissue using highly sensitive analytical methods: assay validation and application to a pharmacokinetic study
Authors: Samtani Mahesh N. , Jusko William J.
Published: March 2007

A sensitive, specific, accurate and precise LC/MS/MS method was developed for the simultaneous measurement of dexamethasone and corticosterone in rat plasma. The method was extended to dexamethasone analysis in rat plasma ultrafiltrate and fetal tissues. Samples were processed using SPE involving Oasis HLB cartridges, which offered complete extraction recovery for the analytes. Samples were subsequently analyzed using LC/MS/MS. A structurally related corticosteroid, prednisolone, was used as the internal standard. Using a 500 µL plasma sample, limits of quantification of 0.2 and 2.0 ng/mL were achievable for dexamethasone and corticosterone. This level of sensitivity allowed characterization of maternal/fetal dexamethasone profiles after administration of multiple doses of dexamethasone sodium phosphate to rats. However, this sensitivity was not satisfactory for corticosterone during pharmacokinetic studies involving dexamethasone due to its strong adrenosuppressive effect. This led us to investigate the suitability of a commercially available radioimmunoassay kit, which through extensive testing and minor modifications was found to offer extremely sensitive, specific, accurate and precise analysis of corticosterone. Knowledge of the steroid profiles captured using these highly sensitive analytical tools may potentially help in the optimization of corticosteroid therapy during pregnancy. Copyright © 2007 John Wiley & Sons, Ltd.
A multiresidue method for the analysis of pesticide residues in polished rice (Oryza sativa L.) using accelerated solvent extraction and gas chromatography and confirmation by mass spectrometry
Authors: Cho Soon‐Kil , Abd El‐Aty A. M. , Park Young‐Seok , Choi Jeong‐Heui , Khay Sathya , Kang Cheol‐Ah , Park Byung‐Jun , Kim Sun‐Ju , Shim Jae‐Han
Published: March 2007

An analytical procedure using accelerated solvent extraction and gas chromatography with an electron capture detector has been optimized to simultaneously determine the residue of two insecticides (diazinon and EPN) and one fungicide (isoprothiolane) in polished rice and was confirmed by GC–mass spectrometry. Several parameters, including temperature, pressure, solvent ratio, cell size and cell cycle, were thoroughly investigated to find the optimal extraction conditions. The average recoveries of the three pesticides were between 82.7 and 126.4% at spiking levels of 0.1 and 0.5 ppm. The relative standard deviations were less than 7% for all of the recovery tests. The optimum accelerated solvent extraction operating conditions were 100°C, 1500 atm, acetone–n‐hexane (20:80 v/v) as the extraction solvent, two cycles, and a cell size of 33 ml. The total extraction time was approximately 20 min. The optimized procedure has also been applied to the determination of diazinon, isoprothiolane and EPN in real rice samples. In conclusion, accelerated solvent extraction was used for the first time for the analysis of diazinon, isoprothiolane and EPN in polished rice and offers the possibility of a fast and simple process for obtaining a quantitative extraction of the studied pesticides. Copyright © 2007 John Wiley & Sons, Ltd.
Development of an ion‐pair HPLC method for investigation of energy charge changes in cerebral ischemia of mice and hypoxia of Neuro‐2a cell line
Authors: Chen Yunyun , Xing Dongming , Wang Wei , Ding Yi , Du Lijun
Published: March 2007

The determination of adenine nucleotides and energy charge (EC) has great importance in the characterization of cerebral ischemic injury and post‐ischemic recovery. An IP‐HPLC method was developed for the quantification of AMP, ADP, ATP and EC in cerebral ischemia and hypoxia of the Neuro‐2a cell line. The chromatographic conditions were: a Zorbax SB‐C18 reversed‐phase column; mobile phase 100 mm KH2PO4, 1 mm tetrabutylammonium hydroxide, and 2.5% acetonitrile, brought to pH 7.0 with potassium hydroxide (4 m), filtered through a 0.45 µm Millipore filter and degassed prior to use. The flow‐rate was 1.0 mL/min. The injection volume was 20 µL. Detection was performed at a wavelength of 254 nm under a constant temperature (27 ± 1°C). The method was validated by means of linearity, using calibration curves constructed with five concentration levels of each compound. The limit of detection was also determined. The system precision was calculated as the coefficient of variation for five injections for each compound tested. Cerebral tissue was homogenized (4°C) in 1 mL of an ice‐cold 6% trichloroacetic acid that contained ATPase inhibitor and obtained good recovery (>90%). The results show that the described method for the determination of adenine nucleotides by HPLC has good linearity, limit of detection, precision and specificity, and is simple and rapid to perform. Copyright © 2007 John Wiley & Sons, Ltd.
Nanotechnology in cardiovascular medicine
Authors: Patel Devang N. , Bailey Steven R.
Published: March 2007

Nanotechnology is a new field of science and technology that has already had significant impact in the development of novel products in industry. In medicine, application of nanotechnology has the potential to develop new imaging agents, pharmaceutical drugs and medical devices with unique physical and chemical properties. This article reviews the potential for various nanoparticles in cardiovascular imaging and therapeutics, nanoporous structures for sensing and implant based drug delivery, and self‐assembled monolayers for surface modification and implant based drug delivery. © 2007 Wiley‐Liss, Inc.
Modelling of multi‐block data
Authors: Höskuldsson Agnar , Svinning Ketil
Published: March 2007

Here is presented a unified approach to modelling multi‐block regression data. The starting point is a partition of the data X into L data blocks, X = (X1, X2,…,XL), and the data Y into M data‐blocks, Y = (Y1, Y2,…,YM). The methods of linear regression, X→Y, are extended to the case of a linear relationship between each Xi and Yj, Xi→Yj. A modelling strategy is used to decide if the residual Xi should take part in the modelling of one or more Yjs. At each step the procedure of finding score vectors is based on well‐defined optimisation procedures. The principle of optimisation is based on that the score vectors should give the sizes of the resulting Yjs loading vectors as large as possible. The partition of X and Y are independent of each other. The choice of Yj can be Xj, Yi = Xi, thus including the possibility of modelling X→Xi, i = 1,…,L. It is shown how these methods can be extended to a network of data blocks. Examples of the optimisation procedures in a network are shown. The examples chosen are the ones that are useful to work within industrial production environments. The methods are illustrated by simulated data and data from cement production. Copyright © 2007 John Wiley & Sons, Ltd.
Pre‐processing in biochemometrics: correction for path‐length and temperature effects of water in FTIR bio‐spectroscopy by EMSC
Authors: Martens Harald , Bruun Susanne W. , Adt Isabelle , Sockalingum Ganesh D. , Kohler Achim
Published: March 2007

The term ‘biochemometrics’ is proposed. Methodology is presented for simplifying high‐resolution phenotyping measurements, in terms of multivariate modelling methods in order to stabilise FTIR bio‐spectroscopy data. Irrelevant gas contributions from water vapour and CO2 in the instrument light path are modelled and removed, in order to avoid having to wait for N2 purging. Variations in the infrared spectroscopy (IR) spectrum of water with temperature are described in terms of two model component spectra. These additive water variations are quantified and eliminated by Extended Multiplicative Signal Correction (EMSC), along with various physical signal variations of additive and multiplicative nature due to, for example, sample or instrument temperature. Sample temperature is predicted from the EMSC model parameters. The models developed for Attenuated Total Reflection (ATR) measurements of pure water at different temperatures are tested successfully in independent water samples as well as in the in vivo monitoring of Candida albicans growing and decaying on the ATR crystal of the same instrument. Copyright © 2007 John Wiley & Sons, Ltd.
Unusual Bond Formation in Aspartic Protease Inhibitors: A Theoretical Study
Authors: Pilmé Julien , Berthoumieux Hélène , Robert Vincent , Fleurat‐Lessard Paul
Published: March 2007

The origin of the formation of the weak bond N|⋅⋅⋅CO involved in an original class of aspartic protease inhibitors was investigated by means of the electron localization function (ELF) and explicitly correlated wave‐function (MRCI) analysis. The distance between the electrophilic C and the nucleophilic N centers appears to be controlled directly by the polarity and proticity of the medium. In light of these investigations, an unusual dative NC bonding picture was characterized. Formation of this bond is driven by the enhancement of the ionic contribution C+O−induced mainly by the polarization effect of the near N lone pair, and to a lesser extent by a weak charge delocalization N→CO. Although the main role of the solvating environment is to stabilize the ionic configuration, the protic solvent can enhance the C+O−configuration through a slight but cumulative charge transfer towards water molecules in the short NC distance regime. Our revisited bond scheme suggests the possible tuning of the NCO interaction in the design of specific inhibitors.
G‐Quadruplex Recognition by Quinacridines: a SAR, NMR, and Biological Study
Authors: Hounsou Candide , Guittat Lionel , Monchaud David , Jourdan Muriel , Saettel Nicolas , Mergny Jean‐Louis , Teulade‐Fichou Marie‐Paule
Published: March 2007

The synthesis of a novel group of quinacridine‐based ligands (MMQs) is described along with an evaluation of their G‐quadruplex binding properties. A set of biophysical assays was applied to characterize their interaction with DNA quadruplexes: FRET–melting experiments and equilibrium microdialysis were used to evaluate their quadruplex affinity and their ability to discriminate quadruplexes across a broad panel of DNA structures. All data collected support the proposed model of interaction of these compounds with G‐quadruplexes, which is furthermore confirmed by a solution structure determined by 2D NMR experiments. Finally, the activity of the MMQ series against tumor cell growth is reported, and the data support the potential of quadruplex‐interactive compounds for use in anticancer approaches.
Overcoming Tumor Drug Resistance with High‐Affinity Taxanes: A SAR Study of C2‐Modified 7‐Acyl‐10‐Deacetyl Cephalomannines
Authors: Yang Chun‐Gang , Barasoain Isabel , Li Xuan , Matesanz Ruth , Liu Ronghua , Sharom Frances J. , Yin Da‐Li , Díaz J. Fernando , Fang Wei‐Shuo
Published: March 2007

A series of C2‐modified 10‐deacetyl‐7‐propionyl cephalomannine derivatives was designed, prepared, and biologically evaluated. Some C2 meta‐substituted benzoate analogues showed potent activity against both drug‐sensitive and drug‐resistant tumor cells in which resistance is mediated through either P‐gp overexpression or β‐tubulin mutation mechanisms. The taxoid 15 b and related compounds are of particular interest, as they are much more cytotoxic than paclitaxel, especially against drug‐resistant tumor cells; they are able to kill both drug‐resistant and drug‐sensitive cells (low R/S ratio), and they have high affinity for β‐tubulin. Our research results led to an important hypothesis, that is, a taxane with very high binding affinity for β‐tubulin is able to counteract drug resistance, which may assist in future taxane‐based drug‐discovery efforts.
MR imaging of antigen‐induced arthritis with a new, folate receptor‐targeted contrast agent
Authors: Saborowski Olaf , Simon Gerhard H. , Raatschen Hans‐Juergen , Wendland Michael F. , Fu Yanjun , Henning Tobias , Baehner Rick , Corot Claire , Chen Mei‐Hsiu , Daldrup‐Link Heike E.
Published: March 2007

The purpose of this study was to investigate if the new folate receptor‐targeted Gd‐chelate P866 may enhance immune‐mediated arthritis. A monoarthritis was induced in the right knee of 15 Sprague–Dawley rats. MR imaging of both knees was performed at 2 T before and up to 2 h and 24 h after injection (p.i.) of P866 (n = 3 dose finding study and n = 6, 0.02 mmol Gd/kg), the non‐FR targeted P866 analog P1001 (n = 3 at 24 h after P866‐administration, 0.02 mmol Gd/kg) or Gd‐DOTA (n = 6, 0.1 mmol Gd/kg). Pulse sequences comprised T1‐SPGR 80°/50 ms/1.7 ms (flip angle/TR/TE) and inversion recovery 10°/3000 ms/1500 ms/50–3050, 10 000 ms (flip angle/TR/TE/TI) sequences. ΔSI‐data and T1‐relaxation times of arthritic knees and contralateral normal knees were determined. Folate receptor expression was confirmed with histopathology. All three contrast agents showed an initial perfusion effect with significantly higher ΔSI‐data of arthritic knees compared with normal knees (p < 0.05). In addition, P866, but not P1001 or Gd‐DOTA, showed a prolonged enhancement of the synovitis. Compared with precontrast values, the T1‐relaxation times of inflamed synovia were significantly decreased at 2 h p.i. of P866 (p < 0.05), but not P1001 or Gd‐DOTA (p > 0.05). Histopathology confirmed the presence of folate receptors in the inflamed joints, but not normal joints. Thus, results suggest a specific accumulation of the folate receptor‐targeted Gd‐chelate P866 in this arthritis model. Copyright © 2007 John Wiley & Sons, Ltd.
Upper bound limit analysis using discontinuous quadratic displacement fields
Authors: Makrodimopoulos A. , Martin C. M.
Published: March 2007

The classical lower and upper bound theorems allow the exact limit load for a perfectly plastic structure to be bracketed in a rigorous manner. When the bound theorems are implemented numerically in combination with the finite element method, the ability to obtain tight bracketing depends not only on the efficient solution of the arising optimization problem, but also on the effectiveness of the elements employed. Elements for (strict) upper bound analysis pose a particular difficulty since the flow rule is required to hold throughout each element, yet it can only be enforced at a finite number of points. For over 30 years, the standard choice for this type of analysis has been the constant strain element combined with discontinuities in the displacement field. Here we show that, provided certain conditions are observed, conventional linear strain triangles and tetrahedra can also be used to obtain strict upper bounds for a general convex yield function, even when the displacement field is discontinuous. A specific formulation for the Mohr–Coulomb criterion
in plane strain is given in terms of second‐order cone programming, and example problems are solved using both continuous and discontinuous quadratic displacement fields. Copyright © 2007 John Wiley & Sons, Ltd.
Ultrafast Voltammetry for Probing Interfacial Electron Transfer in Molecular Wires
Authors: Amatore Christian , Maisonhaute Emmanuel , Schöllhorn Bernd , Wadhawan Jay
Published: March 2007

Electron transfer inside self‐assembled monolayers made from complex redox‐active oligophenylenevinylene molecular wires is examined by ultrafast cyclic voltammetry. Rate constants above 106 s−1 are measured when the electroactive moieties are easily accessible to counterions from the electrolyte. These counterion movements are necessary to compensate the local charge created upon electron transfer. Conversely, if the redox center is buried within long hydrophobic diluents, the counterion movement towards the redox entity becomes rate limiting, thus drastically altering the rate magnitude and its physical meaning. This change in the mechanism is examined both for superexchange or when one electron‐hopping step is involved.
Numerical chromosome variation and mitotic segregation defects in the adult brain of teleost fish
Authors: Rajendran R. Samuel , Zupanc Marianne M. , Lösche Andreas , Westra Jurjen , Chun Jerold , Zupanc Günther K.H.
Published: March 2007

Teleost fish are distinguished by their enormous potential for the generation of new cells in both the intact and the injured adult brain. Here, we present evidence that these cells are a genetic mosaic caused by somatic genomic alteration. Metaphase chromosome spreads from whole brains of the teleost Apteronotus leptorhynchus revealed an euploid complement of 22 chromosomes in only 22% of the cells examined. The rate of aneuploidy is substantially higher in brain cells than in liver cells, as shown by both metaphase chromosome spreads and flow cytometric analysis. Among the aneuploid cells in the brain, approximately 84% had fewer, and the remaining 16% more, than 22 chromosomes. Typically, multiple chromosomes were lost or gained. The aneuploidy is putatively caused by segregation defects during mitotic division. Labeling of condensed chromosomes of M‐phase cells by phosphorylated histone‐H3 revealed laggards, anaphase bridges, and micronuclei, all three of which indicate displaced mitotic chromosomes. Quantitative analysis has shown that in the entire brain on average 14% of all phosphorylated histone‐H3‐labeled cells exhibit such signs of segregation defects. Together with the recent discovery of aneuploidy in the adult mammalian brain, the results of the present investigation suggest that the loss or gain of chromosomes might provide a mechanism to regulate gene expression during development of new cells in the adult vertebrate brain. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2007.
The accuracy of regulatory cost estimates: a study of the London congestion charging scheme
Authors: Sherrington Chris , Moran Dominic
Published: March 2007

This paper considers the accuracy of regulatory cost estimates using the London congestion charging scheme as a case study. In common with other regulations, ex ante estimates of the direct costs of the scheme were produced by the regulator, Transport for London. Reviews of a number of environmental and industrial regulations have shown that ex ante costs tend to exceed the ex post (or outturn) costs. This study finds that while Transport for London moderately overestimated the total costs of the scheme (by 16%) there was a significant overestimate of chargepayer compliance costs (by 64%). The main reasons for this were greater than expected reductions in traffic and unanticipated technological innovation. As the compliance cost is essentially the cost of transacting payment of the charge, these results have wider implications for other similar regulations. One example is the proposed national road user charging in the UK, where it could reasonably be expected that the ex post cost of compliance will again be lower than the ex ante estimate, and that compliance costs will continue to reduce over time. Copyright © 2007 John Wiley & Sons, Ltd and ERP Environment.
Cyanometalate Cages with Exchangeable Terminal Ligands
Authors: Boyer Julie L. , Yao Haijun , Kuhlman Matthew L. , Rauchfuss Thomas B. , Wilson Scott
Published: March 2007

The coordination chemistry of the unusual metallo‐ligand Cs⊂[CpCo(CN)3]4[Cp*Ru]3 (Cs⊂Co4Ru3) is described with attention to the behavior of the ligand itself, its binding to Lewis‐acidic metal cations, and its ability to stabilize catalytically relevant Ru–PPh3 fragments. A series of tests demonstrate that the “rim” [CpCo(CN)3]– groups in Cs⊂Co4Ru3 are exchangeable. Upon treatment with [(MeC5H4)Co(CN)3]– (Co′) Cs⊂Co4Ru3 undergoes vertex exchange to give Cs⊂Co4–xCo′xRu3. Similarly the cage is degraded by CO. Most convincing, Cs⊂Co4Ru3 reacts with PhNH3OTf to precipitate the polymer PhNH3CpCo(CN)3 and form the molecular box [Cs⊂Co4Ru4]+. Treatment of Cs⊂Co4Ru3 with [M(NCMe)x]PF6 (M = Cu, Ag) gave the Lewis acidic cages {Cs⊂[CpCo(CN)3]4[Cp*Ru]3M(NCMe)}PF6, which reacted with tertiary phosphane ligands to give adducts [Cs⊂Co4Ru3M(PPh3)]PF6. Lewis acidic octahedral vertices were installed using Fe, Ni, and Ru reagents. The boxes [Cs⊂Co4Ru3M(NCMe)3]2+ (M = Ni, Fe) formed readily from the reaction Cs⊂Co4Ru3 with [Ni(NCMe)6](BF4)2 and [Fe(NCMe)6](PF6)2. Displacement of the MeCN ligands gives [Cs⊂Co4Ru3Ni(9‐ane‐S3)](BF4)2. A series of boxes were prepared by the reaction of Cs⊂Co4Ru3 and RuCl2(PPh3)3, RuHCl(PPh3)3, and [(C6H6)Ru(NCMe)3](PF6)2. The derivative of the hydride, [Cs⊂Co4Ru3Ru(NCMe)(PPh3)2](PF6)2, was characterized crystallographically.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Nanovehicles Based Bioassay Labels
Authors: Liu Guodong , Wang Jun , Wu Hong , Lin Yingying , Lin Yuehe
Published: March 2007

In this article, we review recent advances of our group in nanoparticle labels based bioassay. Apoferritin and silica nanoparticles have been used as nanovehicles to load large amount of markers for highly sensitive bioassay. Markers loaded apoferritin, apoferritin‐templated metallic phosphate nanoparticles, and poly[guanine] coated silica nanoparticles have been prepared, characterized and used as labels for highly sensitive bioassay of protein and DNA. Dissociation and reconstitution characteristics at different pH as well as the special cavity structure of apoferritin nanovehicle provides a simple and convenient route to prepare versatile nanoparticle labels and avoid the complicated and tedious synthesis process of conventional nanoparticle labels. The optical and electrochemical characteristics of the prepared nanoparticle labels are easily controlled by loading different optical or electrochemical markers. Additionally, the use of apoferritin nanovehicle as template for synthesis of metallic phosphate nanoparticle labels offers fast route to prepare uniform‐size metallic nanoparticle labels for electrochemical bioassay and avoids the traditional harsh dissolution conditions to dissolve metallic nanoparticle tags (that is, the strong‐acid dissolution of quantum dots and gold nanoparticles) during the stripping analysis step. Silica nanoparticle has also been used as nanovehicle to carry thousands of poly[guanine] tracers, which was used to enhance the oxidation current of Ru(bpy)$\rm{ {_{3}^{2+}}}$, resulting in enhanced sensitivity of electrochemical immunoassay. The new nanovehicle‐based labels have been used for highly sensitive electrochemical detection of DNA and protein biomarkers, such as tumor necrosis factor‐alpha (TNF‐α). The high sensitivity and selectivity make these labels a useful addition to the armory of nanoparticle‐based bioassay. The new nanovehicles based labels hold great promise for multiplex protein and DNA detection and for enhancing the sensitivity of other bioassays.
Nanoparticle‐Based Electrochemical Bioassays of Proteins
Authors: Wang Joseph
Published: March 2007

This article reviews a variety of new nanoparticle/biomolecule assemblies for advanced electrical detection of proteins. Effective methods for the reliable and trace measurements of proteins are highly desired for facilitating the diagnosis of disease states and improving drug discovery. Ultrasensitive monitoring of biomolecular interactions of proteins is particularly challenging owing to the absence of PCR‐like amplification protocols and their greater nonspecific binding to solid supports compared to oligonucleotides. Recent activity has led to innovative and powerful nanoparticle‐based immunoassays and aptamer bioassays of proteins based on a variety of electrochemical detection schemes. The enormous signal enhancement associated with the use of nanoparticle amplifying labels and with the formation of nanoparticle‐protein assemblies provides the basis for ultrasensitive electrochemical detection of proteins. Such protocols rely on the use of colloidal gold tags, semiconductor (quantum dot) tracers, ‘carrier’ (amplification) nanomaterials, or magnetic (separation) beads, in connection to electrochemical stripping measurement of the metal tag. Remarkable ‘PCR‐like’ sensitivity has been achieved by coupling particle‐based amplification units and various amplification processes. The use of nanocrystal tracers for designing electrochemical coding protocols for detecting multiple proteins will also be documented.
Doubly Modified Electrodes for the Selective Determination of Dopamine in the Presence of Interfering Species
Authors: Xu Guang‐Ri , Zhang Y. P. , Tao Jian Zhong , Kim Sunghyun , Bae Zun‐Ung
Published: March 2007

In this paper, we describe the double modification of the glassy carbon electrode surface with two polymer layers for the selective determination of dopamine. The first layer was the electropolymerized macrocyclic nickel complex acting as an electrocatalyst for the dopamine oxidation and the second layer the polyurethane benzyl L‐glutamate (PUBLG) for screening interfering species. Hydrolyzed PUBLG (PU‐C) showed a better screening effect. Thus prepared GC/Ni(II) complex film/PU‐C electrodes exhibited improved selectivity and better performance than unmodified counterparts, with minimum passivation even in the presence of large excess of interferents. Under optimal conditions, these electrodes showed a linear response over a dopamine concentration range of 2.5×10−7 and 3.0×10−5 M with a correlation coefficient of 0.999 and detection limit (at S/N=3) of 8.0×10−8 M. The recoveries of dopamine in the 5‐fold diluted human urine sample were 96.9% for 4 measurements. The rate constant for the dopamine oxidation measured by the rotating disk electrode was found to be 1.1×10−3 cm s−1.
Natural frequencies and modes of rhombic mindlin plates
Authors: Raju K. Kanaka , Hinton E.
Published: March 2007

The natural frequencies and mode shapes of thin and moderately thick rhombic plates are obtained using a 9‐noded Lagrangian quadrilateral isoparametric plate element based on Mindlin's theory. The effects of rotatory inertia are included. Plates with a wide range of skew angles and boundary conditions are considered and wherever possible the present results are compared with earlier published work.
Free and steady state vibration of non‐linear structures using a finite element–non‐linear eigenvalue technique
Authors: Wellford L. Carter , Dib G. M. , Mindle W.
Published: March 2007

The problem of free vibration of non‐linear structures is considered initially. It is shown that this problem can be represented as a non‐linear eigenvalue problem. Variational principles for non‐linear eigenvalue problems are defined. These variational principles are implemented with finite element models to define numerical approximations for the free vibration problem. The solution of these approximate equations provides a set of non‐linear modal vectors and natural frequencies which vary with the amplitude of the solution. The non‐linear eigenvalue parameters can be used in modal expansion approximations for the non‐linear transient or steady state response of structural systems. To demonstrate the proposed techniques the free vibration and steady state vibration characteristics of a geometrically non‐linear circular plate are determined.
Collapse of a model for ductile reinforced concrete frames under extreme earthquake motions
Authors: Takizawa Haruo , Jennings Paul C.
Published: March 2007

A mathematical formulation is presented for modelling the dynamic process of failure of a class of ductile, moment‐resisting, reinforced concrete (R/C) frame buildings when subjected to intense earthquake motion. The formulation includes the geometrically non‐linear term that accounts for the destabilizing action of gravity. In many cases of practical interest, in which the structures have strong columns and weak girders, the employed method of synthesizing the restoring force properties can provide a satisfactory description of the structural deformation at large deflections. By modelling approximately the effects of gravity, cracking, yielding and degradation of stiffness, the study is intended to aid the understanding of the process of failure in this type of ductile R/C structure, and to relate the mechanics of collapse to characteristics of the excitation. The collapse of R/C frames having strong girders and weak columns, which can develop sway mechanisms at a single storey, is not considered in this study.

Special examination is made of the capacity to resist short‐duration motions consisting of a few pulses versus the capacity to resist motions of longer duration. For the class of structures modelled, the results indicate an extremely low destructive capability associated with short‐duration motions, even when they have very high accelerations. The application in research of a two‐parameter characterization of the severity of ground motion in terms of intensity and duration is also examined.
Structural identification in the frequency domain from earthquake records
Authors: McVerry Graeme H.
Published: March 2007

A method has been developed to identify the parameters of the lower modes of a linear, time‐invariant model of a structure from its recorded earthquake response. The identification is performed by selecting the parameters to obtain a least squares fit over a specified frequency band between the unsmoothed, complex‐valued finite Fourier transform of the recorded acceleration response and the corresponding transform calculated from the response of the model. By including the effects of the initial and final conditions in the analysis, only a portion of the recorded excitation and response acceleration histories need be considered. The method is demonstrated first by an application to generated test data, and then to measured earthquake response.
Optimum absorber parameters for simple systems
Authors: Warburton G. B. , Ayorinde E. O.
Published: March 2007

In the classical problem a damped one degree‐of‐freedom absorber system is attached to a main system, which has one degree of freedom and is undamped. The optimum values of absorber stiffness and damping, which will minimize the resonant response of the main mass, are well known. In this paper the effect on these optimum conditions of light damping in the main system is studied. The authors show that optimum parameters for absorbers, which are attached to beams and plates, can be obtained simply and accurately from those for an equivalent one degree‐of‐freedom main system. This depends upon the concept of an effective mass for the elastic body and the representation of its response by the single relevant mode. It will be shown in a later paper that for more complex elastic bodies such as cylindrical shells, for which the natural frequencies are more closely spaced, these simple concepts do not predict accurately optimum absorber parameters.
Seismic torsional provisions for dynamic eccentricity
Authors: Tso W. K. , Dempsey K. M.
Published: March 2007

A study is made of the dynamic torsional response of a single mass partially symmetric system to ground excitation. Using the response spectrum technique, the torsional response and dynamic eccentricity are determined as functions of the eccentricity of the system and its uncoupled frequency ratio. It is shown that the dynamic eccentricity can best be expressed as a bilinear function of eccentricity. For the critical condition which occurs when the uncoupled frequency ratio is unity, a comparison is made with the torsional provisions of five seismic codes (Canada, Mexico, New Zealand, ATC3 and Germany). It is shown that the first four codes underestimate the torsional moment, and also the edge displacement of the system, significantly when the eccentricity is small and the uncouped torsional and lateral frequencies are close.
Seismic qualification of electrical equipment using a uniaxial test
Authors: De Silva Clarence W.
Published: March 2007

The analytical development of a uniaxial test for the seismic qualification of electrical equipment is presented. This method comprises a single test using a uniaxial excitation having certain minimum intensity applied at the base of the test package in a predetermined optimal direction. It is anticipated that the proposed procedure would be more economical and less time consuming than, but functionally equivalent to, presently employed series of multiaxial tests. The test is shown to be superior to the symmetric tests. The determination of the minimum intensity of the optimal orientation of the base excitation requires a preliminary frequency response test which is a slightly more elaborate version of the sine sweep test presently employed to determine the resonance frequencies of the test package. A simulated test is presented to compare the proposed method with the uncorrelated triaxial test and the symmetric uniaxial test.
The effect of column mass on shear building vibrations
Authors: Lubliner J.
Published: March 2007

In the usual assignment of mass for shear building models, the mass of the columns is lumped with the mass of the floor at each floor level. In order to account for frequencies of modes higher than N in an N‐storey building, however, additional column masses must be identified. In this note, such additional masses are located at the mid‐height of each column, and the characteristics of the shapes and frequencies of the resulting higher mode set are investigated.
Parkfield, California, Earthquake of June 1966: Interpretation of the strong motion records
Authors: Shoja‐Taheri Jafar
Published: March 2007

A detailed seismological interpretation of the strong motion records was attempted for the 1966 Parkfield earthquake, California. Velocity and displacement traces integrated from the corresponding recorded accelerograms were found most valuable in studying the earthquake mechanism and wave forms. A double‐couple right‐lateral strike — slip mechanism (along the San Andreas fault) is consistent with the recorded direct S‐waves originating from the hypocentre. High energy arrivals observed on the velocity traces are interpreted as S‐waves (‘stopping phases’) that originated at the termination of the rupture towards the south‐east of the San Andreas fault. A double‐couple left‐lateral strike–slip mechanism is suggested as the cause of this rupture termination.

From particle velocity diagrams of the stopping phases in the horizontal plane, the rupture length was found to be between 20 and 28 km. Corresponding rupture velocities are estimated to be 2·5 ± 0·1 and 3·1 ± 0·5 km/s. The inference from the strong motion records is that Love waves were more excited at the south‐western than the north‐eastern side of the fault, whereas the Rayleigh waves were more energetic at the north‐eastern than the south‐western side of the fault.
Seismic response of precast concrete walls
Authors: Becker James M. , Llorente Carlos , Mueller Peter
Published: March 2007

Large panel precast concrete structures are built in major seismic regions throughout the world. The seismic behaviour of such structures is strongly dependent upon the characteristics of both the horizontal and vertical connections. The limiting behaviour of precast systems, however, is basically dependent upon the horizontal connection. The influence of horizontal connections can be studied in terms of the behaviour of a simple wall—a vertical stack of panels having only horizontal connections.

This paper reports on research into the seismic behaviour of simple precast concrete walls. The research was carried out through the development of computer‐based modelling techniques capable of including the typical behavioural characteristics associated with horizontal joints. The model assumes that all non‐linear, inelastic behaviour is concentrated in the connection regions and that the precast panels remain linear elastic. This assumption allows the precast panels to be modelled as statically condensed ‘super‐elements’ and the connection regions as interface elements. The above modelling technique allows for non‐linear‐inelastic seismic analysis that is capable of handling both rocking type motions throughout the height of the structure and slippage due to shear in the plane of the connection.

A series of parametric studies are presented to illustrate the potential influence of rocking and slip on precast walls with both regular reinforcement and post‐tensioning. These studies demonstrate the period elongation associated with the nonlinear‐elastic rocking phenomenon. Shear slip is found to occur only when friction coefficients are extremely low or when the normal forces across the connections are low. This latter case occurs only in low buildings or in the upper floors of tall buildings.

The paper concludes with a brief discussion of the design implications of these results. Particular attention is paid to the problems stemming from the force concentrations associated with rocking and shear slip.
Effects of horizontally propagating waves on the response of structures with a soft first storey
Authors: Wolf J. P. , Obernhuber P.
Published: March 2007

The influence of insulating a structure with a soft first storey (horizontally elastic or elastoplastic or horizontally and vertically elastic) is investigated for horizontally propagating waves. A comprehensive parametric study for a simple structure excited by SH‐ and R‐waves is performed. A reactor building is examined for a horizontally propagating historic earthquake. Compared to a conventional structure, travelling‐wave effects become more important for R‐waves in a structure with a horizontal soft first storey. For SH‐waves, the opposite applies.
Hydrodynamic pressure on arch dams—by a mapping finite element method
Authors: Nath B.
Published: March 2007

A novel Finite Element Method (FEM) is proposed for the analysis of the uncoupled hydrodynamic pressures generated on arch dams due to a steady‐state ground acceleration. In this method the equation governing hydrodynamic pressures and also the prescribed boundary conditions are all transformed from the Cartesian space to a logarithmically condensed cylindrical polar space; in this process the physical configuration of the reservoir‐dam is also mapped into an ‘image’ domain. The transformed governing equation is then solved in the image domain, subject to the transformed boundary conditions, using standard finite elements. Because physical dimensions are logarithmically condensed in the image space, the proposed method is particularly suitable for dealing with large or very large aspect‐ratio reservoir‐dam systems, economically and efficiently.

The high degree of accuracy which the proposed method is capable of, and also the simple way in which it can be applied to complex reservoir‐dam shapes, have been demonstrated by means of examples. The method has also been applied to study the uncoupled hydrodynamic pressures on the upstream face of a cylindrical arch dam, generated by a steady‐state vertical ground acceleration.
A replacement for the srss method in seismic analysis
Authors: Wilson E. L. , Der Kiureghian A. , Bayo E. P.
Published: March 2007

It is well‐known that the application of the Square‐Root‐of‐Sum‐of‐Squares (SRSS) method in seismic analysis for combining modal maxima can cause significant errors. Nevertheless, this method continues to be used by the profession for significant buildings. The purpose of this note is to present an improved technique to be used in place of the SRSS method in seismic analysis.

A Complete Quadratic Combination (CQC) method is proposed which reduces errors in modal combination in all examples studied. The CQC method degenerates into the SRSS method for systems with well‐spaced natural frequencies. Since the CQC method only involves a small increase in numerical effort, it is recommended that the new approach be used as a replacement for the SRSS method in all response spectrum calculations.
Dynamic response of flexible rectangular foundations on an elastic half‐space
Authors: Iguchi M. , Luco J. E.
Published: March 2007

An approximate method for the analysis of the dynamic interaction between a flexible rectangular foundation and the soil with consideration of the out‐of‐plane deformation of the foundation is presented. The procedure is based on an extension of the subdivision method developed by Wong and Luco for rigid foundations.

Numerical results describing the influence of the flexibility of the foundation on the vertical and rocking impedance functions and on the contact stresses between the foundation and the soil are presented. The possibility of representing a flexible foundation by an equivalent rigid foundation having the same force‐displacement relationships is also discussed. The results obtained indicate that at low frequencies, the dynamic stiffness coefficients for flexible foundations are lower than those for a rigid foundation of the same area. At higher frequencies the opposite behaviour is observed. The radiation damping coefficients for flexible foundations are significantly lower than those for a rigid foundation of the same area.
Longitudinal vibration of non‐homogeneous earth dams
Authors: Abdel‐Ghaffar Ahmed M. , Koh Aik‐Siong
Published: March 2007

Two‐dimensional analytical elastic models are developed for evaluating dynamic characteristics, namely natural frequencies and modes of vibration of a wide class of earth dams in a direction parallel to the dam axis. In these models the non‐homogeneity of the dam materials is taken into account by assuming a specific variation of the stiffness properties along the depth (due to the continuous increase in confining pressure). In addition, both shear and normal (axial) deformations are considered. Cases having constant elastic moduli, linear and trapezoidal variations of elastic moduli, and elastic moduli increasing as the one‐half, one‐third, two fifths, and a general (l/m)th powers of the depth are studied. Dynamic properties of three real earth dams in a seismically active area (Southern California) estimated from their earthquake records (input ground motion and crest response in the longitudinal direction) as well as results from full‐scale dynamic tests on one of these dams (including ambient and forced vibration tests) are compared with those from the suggested models. It was found that the models in which the shear modulus and the modulus of elasticity of the dam material vary along the depth are the most appropriate representations for predicting the dynamic characteristics. The agreement between the experimental and earthquake data and the theoretical results from some of the models is reasonably good.
Simulation of earthquake ground motions using autoregressive moving average (ARMA) models
Authors: Polhemus N. W. , Cakmak A. S.
Published: March 2007

Parsimonious representations of recorded earthquake acceleration time series are obtained by fitting stationary autoregressive moving average models after a variance‐stabilizing transformation. Simulated acceleration series are then constructed by generating realizations from the fitted stationary models and applying the reverse transformation. As demonstrated on three components of a typical series, the response spectra for the observed and simulated series show good agreement for periods of less than eight seconds. Further, the model parameters for the three components are very similar, suggesting a consistency which could be useful for identifying site‐specific characteristics.
Analysis and prevention of suspension bridge flutter in construction
Authors: Brancaleoni F. , Brotton D. M.
Published: March 2007

It is known that the maximum danger of flutter‐type aerodynamic instability for suspension bridges occurs during the early erection phases of the deck.

The effectiveness of two different provisional measures for increasing the instability critical windspeed in such conditions is evaluated for a long span suspension bridge with flat box stiffening girder.
The dynamics of a rigid foundation on the surface of an elastic half‐space
Authors: Hamidzadeh‐Eraghi H. R. , Grootenhuis P.
Published: March 2007

The response of a rigid rectangular foundation block resting on an elastic half‐space has been determined by considering first the displacement functions for any position on the surface of an unloaded half‐space due to a harmonic point force. The influence of the foundation has been taken into account by assuming a relaxed condition at the interface, i.e. a uniform displacement under the foundation and that the sum of the point forces must equal the total applied force. The three motions of vertical, horizontal and rocking have been considered and numerical values for the in‐phase and the quadrature components of the displacement functions are presented for a Poisson's ratio of 0.25. The effect of the mass and inertia of the foundation can be allowed for by an impedance matching technique. Response curves and non‐dimensional resonant frequency curves are given for a square and a rectangular foundation for different mass and inertia ratios and for several values of Poisson's ratio. These curves are for design purposes and are an addition to similar published curves for circular and infinitely long rectangular foundations. Some of the calculated results have been verified by a laboratory experiment.
Non‐parametric identification of a class of nonlinear multidegree dynamic systems
Authors: Masri S. F. , Bekey G. A. , Sassi H. , Caughey T. K.
Published: March 2007

A non‐parametric identification technique is presented for chain‐like multidegree‐of‐freedom non‐linear dynamic systems. The method uses information about the state variables of non‐linear systems to express the system characteristics in terms of two‐dimensional orthogonal functions. The technique is applied to a model of a steel frame that has been extensively investigated both analytically and experimentally. The method can be used with deterministic or random excitation to identify dynamic systems with arbitrary non‐linearities, including those with hysteretic characteristics. It is also shown that the method is easy to implement and needs much less computer time and storage requirements compared to the Wiener‐kernel approach. The method is shown to have low sensitivity to the effects of additive noise in the experimental data.
Three‐dimensional hybrid modelling of soil‐structure interaction
Authors: Gupta Sunil , Penzien Joseph , Lin T. W. , Yeh C. S.
Published: March 2007

A three‐dimensional hybrid model for the analysis of soil‐structure interaction under dynamic conditions is developed which takes advantage of the desirable features of the finite element and substructure methods and which minimizes their undesirable features. The modelling is achieved by partitioning the total soil‐structure system into a near‐field and a far‐field with a hemispherical interface. The near‐field, which consists of the structure to be analysed and a finite region of soil around it, is modelled by finite elements. The semi‐infinite far‐field is modelled by distributed impedance functions at the interface which are determined by system identification methods. Numerical results indicate that the proposed model makes possible realistic and economical assessment of three‐dimensional soil‐structure interaction for both surface and embedded structures.
An improved hammer‐impact technique for strong shear wave generation
Authors: Maiguma Teruki
Published: March 2007

As part of fundamental research on seismic energy sources, a series of experiments was made to improve the field procedures for producing SH waves by using the so‐called plank‐striking method and also to develop more adequate techniques to generate high‐energy shear waves. Based on the results obtained, a flexible impact device which is similar to a slingshot was made to apply a relatively strong impulse at the surface of the ground. This shear wave generator was demonstrated to have desired features in its low cost operation, easy repeatability, high reproducibility and relatively large output strength. Such a shear source, therefore, provides a useful means of evaluating dynamic characteristics of the foundation soils accurately and economically which can play an important role in current earthquake engineering.