bluuebunny/crossref_metadata_2025 huggingface dataset:
NF‐κB‐regulated suppression of T‐bet in T cells represses Th1 immune responses in pregnancy
Authors: McCracken Sharon A. , Hadfield Katrina , Rahimi Zolaikha , Gallery Eileen D. , Morris Jonathan M.
Published: April 2007

The molecular mechanisms that suppress Th1 immune responses in pregnancy are unknown. We assessed the expression of the Th1 cytokine transcription factor T‐bet. We isolated PBMC and T cells from non‐pregnant and pregnant women and demonstrated that T‐bet is specifically down‐regulated in pregnancy under basal and stimulated conditions. Low levels of T‐bet protein were detected in the nuclear fraction of unstimulated PBMC from non‐pregnant, but not pregnant women. Nuclear levels of T‐bet increased in response to PMA/ionomycin in PBMC from non‐pregnant, but not pregnant women. T‐bet expression was greater in whole cell lysates of stimulated CD3+ T cells from non‐pregnant relative to pregnant women. NF‐κB is specifically down‐regulated in T cells in pregnant women, resulting in suppressed expression of Th1 cytokines IL‐2, IFN‐γ and TNF‐α. In this study, down‐regulation of NF‐κB also resulted in diminished expression of T‐bet. PMA induces NF‐κB translocation, T‐bet expression and IL‐2, IFN‐γ and TNF‐α production. Conversely, pre‐incubation with SN50, and NF‐κB oligodeoxyribonucleotide decoys suppressed PMA‐induced NF‐κB translocation and gene transcription, respectively, resulting in diminished T‐bet expression and Th1 cytokine production. Therefore, maintenance of the cytokine environment for pregnancy success is mediated via strict regulation of Th1 immune responses, more specifically through control of NF‐κB and T‐bet transcription.
PPARγ‐dependent regulation of human macrophages in phagocytosis of apoptotic cells
Authors: Majai Gyöngyike , Sarang Zsolt , Csomós Krisztián , Zahuczky Gábor , Fésüs László
Published: April 2007

Macrophages acquire their capacity for efficient phagocytosis of apoptotic cells during their differentiation from monocytes. The peroxisome proliferator‐activated receptor gamma (PPARγ) is highly up‐regulated during this maturation program. We report that addition of PPARγ antagonist during differentiation of human monocytes to macrophages significantly reduced the capacity of macrophages to engulf apoptotic neutrophils, but did not influence phagocytosis of opsonized bacteria. Macrophage‐specific deletion of PPARγ in mice also resulted in decreased uptake of apoptotic cells. The antagonist acted in a dose‐dependent manner during the differentiation of human macrophages and could also reverse the previously observed augmentation of phagocytosis by glucocorticoids. Blocking activation of PPARγ led to down‐regulation of molecular elements (CD36, AXL, TG2 and PTX3) of the engulfment process. Inhibition of PPARγ‐dependent gene expression did not block the anti‐inflammatory effect of apoptotic neutrophils or synthetic glucocorticoid, but significantly decreased production of IL‐10 induced by LPS. Our results suggest that during differentiation of macrophages natural ligands of PPARγ are formed, regulating the expression of genes responsible for effective clearance of apoptotic cells and macrophage‐mediated inflammatory responses.
CD4‐mediated functional activation of human CD4+CD25+ regulatory T cells
Authors: Becker Christian , Kubach Jan , Wijdenes John , Knop Jürgen , Jonuleit Helmut
Published: April 2007

Naturally occurring CD4+CD25+FoxP3+ regulatory T cells (CD25+ Tregs) constitute a specialized population of T cells that is essential for the maintenance of peripheral self‐tolerance. The immune regulatory function of CD25+ Tregs depends upon their activation. We found that anti‐CD4 antibodies activate the suppressive function of human CD25+ Tregs in a dose‐dependent manner. We demonstrate that CD4‐activated CD25+ Tregs suppress the proliferation of CD4+ and CD8+ T cells, their IL‐2 and IFN‐γ production as well as the capacity of CD8+ T cells to re‐express CD25. By contrast, anti‐CD4 stimulation did not induce suppressive activity in conventional CD4+ T cells. These results identify CD4 as a trigger for the suppressive function of CD25+ Tregs and suggest a possible CD4‐mediated exploitation of these cells.
Broadening the Scope of Ancillary Phosphane‐Type Ligands: A Systematic Comparison of PR3, PR2BH3–, and SiR3– and Their Chalcogen Derivatives
Authors: Kückmann Theresa I. , Dornhaus Franz , Bolte Michael , Lerner Hans‐Wolfram , Holthausen Max C. , Wagner Matthias
Published: April 2007

This work describes a systematic experimental and theoretical study of the properties of two series of isoelectronic and largely isosteric ligands, namely PPh2Me, PPh2BH3–, and SiPh2Me– and SPtBu3, SPtBu2BH3–, and SSitBu3–. In addition, we have also investigated the oxo derivatives OPPh2BH3– and OSiPh2Me–. Based on X‐ray crystal structure determinations (Fe–CO and C–O bond lengths) as well as NMR [e.g. δ(13CO)] and IR [ν(CO)] spectroscopic investigations of the corresponding [CpFe(CO)2]+ complexes, we can conclude that, with respect to electron donor strength, phosphanyl borohydrides occupy an intermediate position between phosphanes (weakest donors) and silyl ligands (strongest donors). The same is true for the thio derivatives, although the differences are smaller. In the reaction with [CpFe(CO)2]+, the oxo derivative OPPh2BH3– transfers a hydride ion rather than forming a stable [CpFe(CO)2(OPPh2BH3)] complex. The tendency to undergo hydride‐transfer reactions was studied by density functional calculations for the series PtBu2BH3–, OPtBu2BH3–, and SPtBu2BH3–. The results reveal that OPtBu2BH3– is the strongest and SPtBu2BH3– the weakest hydride donor, in accordance with the experimental observations. Theoretical analysis indicates that the three derivatives PPh2Me, PPh2BH3–, and SiPh2Me– are truly isolobal species despite variations in their charge distributions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Metal Ion Complementarity: Effect of Ring‐Size Variation on the Conformation and Stability of Lead(II) and Cadmium(II) Complexes with Pendant‐Armed Crowns
Authors: Regueiro‐Figueroa Martín , Esteban‐Gómez David , Platas‐Iglesias Carlos , de Blas Andrés , Rodríguez‐Blas Teresa
Published: April 2007

The binding tendencies of the pendant‐armed crown ethers L1–L3 [L1 = N,N′‐bis(benzimidazol‐2‐ylmethyl)‐1,7‐diaza‐12‐crown‐4, L2 = N,N′‐bis(benzimidazol‐2‐ylmethyl)‐1,10‐diaza‐15‐crown‐5) and L3 = N,N′‐bis(benzimidazol‐2‐ylmethyl)‐4,13‐diaza‐18‐crown‐6] towards PbII and CdII have been investigated. The X‐ray crystal structure of [Cd(L3)](ClO4)2·EtOH shows that, in the solid state, the CdII ion is eight‐coordinate and fits quite well into the crown hole, favouring an anti arrangement of the organic receptor. NMR measurements recorded in acetonitrile solution indicate that increasing the crown size induces a conformational change in the series of CdII complexes. The conformation goes from a syn arrangement for L1 to an anti arrangement for L3, passing through a syn [lrarr2] anti equilibrium in the complex derived from L2. On the contrary, no conformational change was observed for the corresponding PbII complexes, which have a syn conformation in all cases. These results have been confirmed by means of density functional theory (DFT) calculations performed by using the B3LYP model. The binding constants obtained from UV/Vis titration experiments in DMSO solution demonstrate that a decrease in the crown size provokes a 102‐fold enhancement of the stability for this series of CdII complexes, whereas for PbII a gradual decrease of the binding constants is observed. Receptor L1 shows a certain degree of selectivity for CdII over PbII, with a selectivity factor > 102. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Hydrolysis of a (2‐Propanol)yttrium Triiodide Complex in the Presence of Glymes: Synthesis and X‐ray Structures of Hydroxo‐Bridged Dinuclear Yttrium Complexes and Their Applications in Materials Science
Authors: Mishra Shashank , Daniele Stéphane , Hubert‐Pfalzgraf Liliane G. , Jeanneau Erwann
Published: April 2007

The reactions of (2‐propanol)yttrium triiodide, Y(iPrOH)4I3, with stoichiometric amounts of water in the presence of di‐, tri‐, and tetraglyme yield a facile synthetic route to hydroxo‐bridged, centrosymmetric dimeric yttrium complexes. These ionic derivatives, [Y2L2(μ‐OH)2(H2O)x(ROH)y]I4 [1: L = triglyme, x = 2, y = 2, R = iPr; 2: L = tetraglyme, x = 2, y = 0; 3·2EtOH: L = diglyme, x = 2, y = 4, R = Et; 4·2EtOH: L = triglyme, x = 4, y = 0; 5: L = tetraglyme, x = 2, y = 2, R = Et] have been characterized by elemental analysis, IR and 1H NMR spectroscopy, as well as by single‐crystal X‐ray diffraction for 3, 4, and 5. Preliminary results on the utility of these ionic derivatives as potential sources of yttrium oxide in high Tc superconductors are also presented.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Bis‐μ‐pyrazolate‐Bridged Dinickel(II) and Dicopper(II) Complexes: An Example of Stereoelectronic Preference of Metal Ions and Stabilization of Mixed‐Valence NiIIINiII Species
Authors: Mishra Vibha , Lloret Francesc , Mukherjee Rabindranath
Published: April 2007

New dimeric nickel(II) and copper(II) complexes [(L)Ni(μ‐L′)]2[ClO4]2 1 and [(L)Cu(μ‐L′)]2[ClO4]2 2, [2‐[3‐(2′‐pyridyl)pyrazol‐1‐ylmethyl]pyridine (L) and 3‐(2‐pyridyl)pyrazole (HL′)] have been synthesized, structurally characterized, and their absorption, magnetic, EPR and redox properties investigated. The crystal structure of 1·MeCN reveals a planar {Ni2(μ‐L′)2}2+ core [Ni···Ni separation: 4.0765(10) Å] in which each distorted octahedral NiII ions is terminally coordinated by a tridentate ligand L and bridged by two HL′ units, in their deprotonated form. The structural analysis of 2·2MeCN reveals two five‐coordinate CuII ions, each terminally coordinated by adopting only a bidentate coordination mode of L, in which the –CH2py arm remains uncoordinated. A similar bridging [Cu···Cu separation: 3.9382(24) Å] as in 1·MeCN is observed. Thus stereoelectronic preferences of NiII and CuII are clearly revealed. Closer inspection of crystal packing diagram of 1·MeCN reveals the formation of 2‐D network structure assembled solely via C–H···π interaction [pyridyl C–H (4‐position) of pyridylpyrazole unit of L and π cloud of pyridine of bridging deprotonated L′ unit]. In 2·2MeCN, however, π···π interactions between uncoordinated pyridyl arms are observed. Variable‐temperature magnetic studies on both complexes indicate the existence of strong antiferromagnetic coupling between the two metal ions (singlet‐triplet energy separation, J = –20 cm–1 for 1 and –200 cm–1 for 2). When investigated by cyclic voltammetry complex 1 displays two quasi‐reversible electron‐transfer reactions at E1/2 = 1.36 V (ΔEp = 110 mV) and 1.79 V (ΔEp = 120 mV) vs. SCE, due to NiIIINiII/NiII2 and NiIII2/NiIIINiII redox processes, respectively. Constant potential electrolysis at 1.50 V vs. SCE leads to the generation of dark green mixed‐valence NiIIINiII species, which is stable enough to be subjected to characterization by UV/Vis and EPR spectroscopy. Compound 2 exhibits only irreversible reductions (cathodic peak potential, Epc = –0.28 V and –0.50 V vs. SCE).(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Stabilizing Factors for Vanadium(IV) in Amavadin
Authors: Hubregtse Ton , Hanefeld Ulf , Arends Isabel W. C. E.
Published: April 2007

Six secondary N‐hydroxy amino acids (amavadin‐based ligands) have been prepared through a strategy with nitrone reduction as its key step. Two of these amino acids are the new amavadin ligand analogues 4a and 4b containing either a phenyl or a benzyl group in combination with a small backbone substituent. In addition, the monoester 5 of the amavadin ligand as well as three N‐alkylated N‐hydroxy aminoacids 6 were prepared. Complexation studies with the new tri‐ and bidentate ligands using HRMS revealed that only amavadin and its two analogues with ligands 4a and 4b are stable in aqueous and aerobic environments and that the complexation of vanadium(IV) with ligands 5 and 6 does not lead to air‐stable vanadium(IV) non‐oxo compounds. An interesting spin‐off of the synthetic work on nitrones is an effective and easily applicable method for the synthesis of racemic N‐hydroxy amino acid esters. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Rapid Preparation of 3‐Deoxyanthocyanidins and Novel Dicationic Derivatives: New Insight into an Old Procedure
Authors: Chassaing Stefan , Kueny‐Stotz Marie , Isorez Géraldine , Brouillard Raymond
Published: April 2007

Common 3‐deoxyanthocyanidins and original dicationic flavylium‐benzopyrylium derivatives are easily and efficiently synthesized through reactions between the corresponding phenols and aryl ethynyl ketones in the presence of aqueous hexafluorophosphoric acid. The mechanism of the reaction is discussed and two competitive pathways are consistent with our results.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Signalling Mechanisms in Anion‐Responsive Push‐Pull Chromophores: The Hydrogen‐Bonding, Deprotonation and Anion‐Exchange Chemistry of Functionalized Azo Dyes
Authors: Ros‐Lis José V. , Martínez‐Máñez Ramón , Sancenón Félix , Soto Juan , Rurack Knut , Weißhoff Hardy
Published: April 2007

A family of azo dyes containing amide (1), urea (2), thiourea (3), carbamate (4) or amino (5) hydrogen‐bond donating groups were synthesized and their response toward anions was studied. Acetonitrile solutions of 1–5 show bright yellow colours, due to charge‐transfer bands in the 375–400 nm region, slightly modulated by the electron donor strength of the group attached to the 4′ end of the 4‐nitroazobenzene scaffold. Anions of different shape and size (i.e., spherical F–,Cl–, Br– and I–, planar and tetrahedral oxoanions such as NO3–, H2PO4– and HSO4–, carboxylates such as acetate and benzoate and the linear anions cyanide and thiocyanate) were employed in the recognition studies. Two different effects were distinguished: (i) bathochromic shifts of <40 nm to pale orange, due to anion coordination, and (ii) strong red shifts of ca. 200 nm with a concomitant colour change to blue, due to deprotonation. This behaviour was explained as a balance between the deprotonation tendency of the binding sites in the different receptors and the proton affinities of the anions. Semiempirical calculations were carried out to evaluate the hydrogen bond‐donating abilities of the anions and the dyes and a good correlation with the experimentally found values was observed. Stability constants for the receptor–anion complexes were determined spectrophotometrically and the different responses toward fluoride and acetate were assessed by NMR titration experiments. Finally, as a special case, we also report the use of this family of compounds as colorimetric carbon dioxide sensors through reaction with the unprotonated forms of the azo dyes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Substituent Effects of the Alkyl Groups: Polarity vs. Polarizability
Authors: Exner Otto , Böhm Stanislav
Published: April 2007

Substituents effects of the alkyl groups, both straight‐chain and branched, were evaluated by means of model reaction series, each comparing the acidities and basicities of the same or very similar compounds. Four such models wereexamined, one based on known gas‐phase experimental data (acidity and basicity of alcohols), the three others on density‐functional calculations at the levels B3LYP/6‐311++G(2df,2pd)//B3LYP/6‐311++G(2df,2pd) or B3LYP/6‐311+G(d,p)//B3LYP/6‐311+G(d,p): acidity and basicity of 4‐substituted bicyclo[2.2.2]octan‐1‐ols, stability of borate anions compared to the stability of ammonium cations, and acidity of imines compared to the basicity of ketones. In all cases the alkyl groups stabilize both the anions and cations; with straight‐chain alkyls the effect is proportional and can be called polarizability effect. However, simple mathematical expression of the polarizability is not correct because the effect on the cations is always stronger than on the anions. Effects of secondary and tertiary alkyls, in some cases also of branched primary alkyls, are different and deviate from the proportionality. They can be interpreted in some cases as steric effects or hyperconjugation. In any case they are different from the effects of straight‐chain alkyls and they are also fundamentally different from the effects of dipolar substituents; both groups should not be correlated together in one reaction series.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
1,3‐Chirality Transfer by Fragmentation of Allylsulfinic Acids: A Diastereoselective Approach to Vinyl Bromides Related to trans‐Hydrindane or trans‐Decalin
Authors: Chochrek Paweł , Wicha Jerzy
Published: April 2007

Diastereoselective approaches to vinyl bromides from bromoallylic alcohols by fragmentation of the respective allylsulfinic acids have been investigated. Bromoallylic alcohols 1a and 6 were transformed into the respective 1,3‐benzothiazol‐2‐yl sulfides 2a and 7 by the Mitsunobu inversion reaction under modified conditions. The sulfides were then oxidized into sulfones 11a and 12a, respectively. Reduction of 11a and 12a with sodium borohydride gave the respective allylsulfinic acid salts 13a and 15 which, without isolation, were treated with aqeous tartaric acid. The salt 13a gave exclusively 5α‐cholestane derivative 14a whereas 15 provided a mixture of the 5α and 5β derivatives 16 and 17 (after deprotection), the former prevailing. In an alternative approach, benzothiazolyl sulfides 2a and 7 were treated sequentially with BH3·THF and LiAlH4 to give thiols 18a and 19a, respectively. Oxidation of thiols 18a and 19a with oxaziridine 21 gave the respective sulfinic acids which, on gentle heating, afforded bromoolefins 14a and 22a, respectively, as the only products. Analogous reaction sequences starting from allylic alcohols devoid of the bromine substituent 1b and 8 have also been studied.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Pd/C: A Recyclable Catalyst for Cyanation of Aryl Bromides
Authors: Zhu Yi‐Zhong , Cai Chun
Published: April 2007

Aryl cyanides have been prepared from the corresponding aryl bromides with potassium hexacyanoferrate(II) usingPd/C as a catalyst. It is shown that the addition of Bu3N is the key factor in obtaining the corresponding aryl cyanides. Furthermore, the catalyst can be recycled by filtration and washing sequences, making the method also attractive for industrial applications.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
General Behavior of the I–E and ΔI–E Curves Obtained when a Multistep Potential is Applied to an Electroactive Monolayer
Authors: Abenza Nuria , Gonzalez Joaquín , Molina Angela
Published: April 2007

Simple, analytical and fully explicit expressions for the I–E curves of a charge transfer process of a diffusionless system corresponding to staircase voltammetry (SCV) are presented. We have analyzed the reversibility influence and our results indicate that SCV curves obtained at different sampled times tend to coincide as the rate constant decreases. Moreover, the current–potential SCV response converts to that corresponding to linear sweep voltammetry (LSV) when the pulse amplitude ΔE→0. We have also obtained the theoretical expression for the response of differential staircase voltammetry (DSCV) which presents two peaks and a cross potential at which ΔI=0.
Amide and Acyl‐Hydrazine Functionalized Calix[4]arenes as Carriers for Hydrogen Phosphate Selective Electrodes
Authors: Yan Zhenning , Li Xia , Xu Yan , Ye Baoxian
Published: April 2007

Anion‐selective solvent polymeric membrane based on hydrogen bond‐forming, neutral ionophores with amide or acyl‐hydrazine groups are described. The use of the two calix[4]arenes results in anion‐selective electrodes with a selectivity for phosphate. The electrodes of the optimum characteristic have the composition of 1 wt% ionophore, 66 wt% o‐NPOE, 33 wt% poly (vinyl chloride) (PVC) and TDMACl (15 or 30 mol% relative to the ionophore 1 and 2, respectively). The optimized membrane electrodes show Nernstian responses towards monohydrogen phosphate (−29.1 and −29.3 mV/decade) based on ionophore 1 and 2, respectively, in a wide concentration range (1.0×10−5 to 1.0×10−2 or 1.0×10−5 to 1.0×10−1 M). The selectivity coefficients are determined with the fixed interference method and the activity ratio method. The electrodes display an anti‐Hofmeister series selectivity pattern and highly selective for HPO42− over Cl−, Br−, CH3COO−, NO3− and SO42−. The lifetime of the electrodes is at least 1 month and their response time is found to be 25 s. The proposed sensors could be put to analytical use both by direct potentiometry as well as potentiometric titration.
Electrocatalytic Reduction of H2O2 and Oxygen on the Surface of Thionin Incorporated onto MWCNTs Modified Glassy Carbon Electrode: Application to Glucose Detection
Authors: Salimi Abdollah , Noorbakhsh Abdollah , Mamkhezri Hussein , Ghavami Raoof
Published: April 2007

A new H2O2 enzymeless sensor has been fabricated by incorporation of thionin onto multiwall carbon nanotubes (MWCNTs) modified glassy carbon electrode. First 50 μL of acetone solution containing dispersed MWCNTs was pipetted onto the surface of GC electrode, then, after solvent evaporations, the MWCNTs modified GC electrode was immersed into an aqueous solution of thionin (electroless deposition) for a short period of time <5–50 s. The adsorbed thin film of thionin was found to facilitate the reduction of hydrogen peroxide in the absence of peroxidase enzyme. Also the modified electrode shows excellent catalytic activity for oxygen reduction at reduced overpotential. The rotating modified electrode shows excellent analytical performance for amperometric determination of hydrogen peroxide, at reduced overpotentials. Typical calibration at −0.3 V vs. reference electrode, Ag/AgCl/3 M KCl, shows a detection limit of 0.38 μM, a sensitivity of 11.5 nA/μM and a liner range from 20 μM to 3.0 mM of hydrogen peroxide. The glucose biosensor was fabricated by covering a thin film of sol–gel composite containing glucose oxides on the surface of thionin/MWCNTs modified GC electrode. The biosensor can be used successfully for selective detection of glucose based on the decreasing of cathodic peak current of oxygen. The detection limit, sensitivity and liner calibration rang were 1 μM, 18.3 μA/mM and 10 μM–6.0 mM, respectively. In addition biosensor can reach 90% of steady currents in about 3.0 s and interference effect of the electroactive existing species (ascorbic acid–uric acid and acetaminophen) is eliminated. The usefulness of biosensor for direct glucose quantification in human blood serum matrix is also discussed. This sensor can be used as an amperometric detector for monitoring oxidase based biosensors.
Determination of Trace Amounts of Copper in Tap Water Samples with a Calix[4]arene Modified Carbon Paste Electrode by Differential Pulse Anodic Stripping Voltammetry
Authors: Canpolat Esra Çelik , Şar Erdem , Coşkun Naciye Yılmaz , Cankurtaran Hüsnü
Published: April 2007

A calix[4]arene modified carbon paste electrode was used for trace determination of copper. The study of the preconcentration of copper as well as the other heavy metal ions at the modified electrode, with subsequent measurement by differential pulse anodic stripping voltammetry (DPASV), indicates the efficient open‐circuit accumulation of the analytes onto the electrode. Many parameters such as the composition of the paste, pH, preconcentration time and stirring rate influence the response of the measurement. The procedure was optimized for copper determination. For a 10‐minute preconcentration time at pH 6.5–7.5, the detection limit (LOD) was 1.1 μg L−1. The optimized method was successfully applied to the determination of copper in tap water sample by means of standard addition procedure. The copper content of the sample was comparable with the result obtained with AAS method.
Dynamic racking tests of curtain wall glass elements with in‐plane and out‐of‐plane motions
Authors: Behr R. A. , Belarbi A. , Culp J. H.
Published: April 2007

This project was conducted to investigate the breakage and fallout behaviour of various types of architectural glass elements in a dry‐glazed curtain wall system under in‐plane and out‐of‐plane dynamic motions. The project was a follow‐up to an earlier project that focused exclusively on in‐plane dynamic racking performance of curtain wall glass elements. The recent data indicated that adding out‐of‐plane motions caused significantly higher amounts of glass breakage and subsequent glass fallout in most glass types that were found during the in‐plane tests to be prone to glass fallout. Specifically, 1/4 in (6 mm) annealed monolithic glass, 1/4 in annealed monolithic glass with a 0·004 in (0·10 mm) PET film (not anchored to the mullions), and 7/16 in (11 mm) fully tempered laminated glass exhibited comparable or higher fallout rates than the already substantial fallout rates that were observed during the in‐plane only racking tests. Unanchored window film was found to be ineffective in resisting post‐breakage glass fallout under dynamic racking motions. In contrast, 1/4 in (6 mm) annealed laminated glass and 7/16 in (11 mm) heat‐strengthened laminated glass exhibited no glass fallout during the out‐of‐plane tests, just as they exhibited no fallout during the in‐plane tests. Out‐of‐plane test results also showed that 3/8 in (10 mm) heat‐strengthened monolithic glass exhibited no fallout, while 3/8 in annealed monolithic glass exhibited very negligible glass fallout. The addition of torsional motions was not found to induce glass fallout in those glass types that resisted glass fallout in previous tests performed without torsional motions.
Seismic fracture of koyna dam: Case study
Authors: Pekau O. A. , Lingmin Feng , Chuhan Zhang
Published: April 2007

The two numerical procedures previously presented by the authors to model crack closure during seismic fracture of concrete gravity dams are employed herein to study the 1967 performance of the Koyna dam. First, a brief description of the general procedure is given, followed by the detailed formulation of the force method for simulation of crack closure. The latter was introduced to prevent the hypothetical overlap phenomenon which was originally assumed in the modelling of crack closure by the impulse method. Also presented are the results obtained for a model of the Koyna dam tested on a shaking table to study the cracking process under simplified loading conditions. Satisfactory agreement between the test and numerical results is shown. Finally, the cracking process of the Koyna dam prototype subjected to the 1967 earthquake is evaluated numerically by employing the aforementioned techniques. From the results, it is concluded that both procedures for simulating the impact effect of crack closing predict complete penetration of the crack through the upper part of the dam, which is consistent with the observed prototype behaviour.
On building finite element models of structures from modal response
Authors: Hjelmstad K. D. , Banan MO. R. , Banan MA. R.
Published: April 2007

We develop two algorithms for estimating member stiffnesses and masses of a structure from measured modal response in conjunction with a finite element model of the structure. The mathematical model has known geometry and topology and parameterized constitutive properties. A few of the natural frequencies are measured and the corresponding modes are sampled at certain locations in space. The proposed algorithms are based on the concept of minimizing the sum of the squares of errors, specified as an index of discrepancy between the model and the structure, over all of the measured modes. The recursive quadratic programming method is used to solve the non‐linear constrained estimation problem. Both proposed estimators can handle incompletely measured models, have robust convergence, and are amenable to modelling of complex structures. We demonstrate the use of our parameter estimation algorithm by applying it to identify the properties of a building from measured data.
A system identification approach to the detection of changes in both linear and non‐linear structural parameters
Authors: Loh Chin‐Hsiung , Tou Iat‐Chun
Published: April 2007

This paper explores the potential of a new time domain identification procedure to detect changes in structural dynamic characteristics on the basis of measurements. This procedure is verified using mathematical models simulated on the computer. The experiments involve two eight‐storey steel structures with and without energy devices, and a 47‐storey building at San Francisco during the Loma Prieta earthquake. The recursive instrumental variable method and extended Kalman filter algorithm are used as identification algorithms. An exploratory investigation is made of the usefulness of various indices, such as mode shape and storey drift, that can be extracted accurately from identification to quantify changes in the characteristics of the physical system. It is concluded that the change of storey drift is the key information to the detection of changes in structural parameters, from which the proposed system identification algorithm can be applied with an appropriate inelastic model to simulate the dynamic behaviour of real structures undergoing strong ground motion excitations.
Three‐dimensional response of a layered cylindrical valley embedded in a layered half‐space
Authors: Luco J. E. , de Barros F. C. P.
Published: April 2007

An indirect boundary integral method to obtain the three‐dimensional response of an infinitely long, layered, viscoelastic valley of arbitrary cross‐section embedded in a layered viscoelastic half‐space is presented. The valley is excited by homogeneous plane waves impinging at an oblique angle with respect to the axis of the valley. The method and associated computer programs are tested by comparison with available results in the limiting two‐dimensional case of incidence normal to the axis of the valley. Additional comparisons with previous three‐dimensional results obtained by a hybrid finite element‐boundary integral method for cylindrical valleys subjected to obliquely incident waves show large differences. However, the results obtained here for an infinitely long valley appear to be in some agreement with earlier results for an elongated prolate semi‐ellipsoidal valley and with results obtained by a discrete wavenumber boundary element approach. An extensive bibliography on the dynamic response of valleys is also presented.
Implications of design philosophies for seismic response of steel moment frames
Authors: Osman Ashraf , Ghobarah A. , Korol R. M.
Published: April 2007

During a severe earthquake, steel moment resisting frames are expected to experience significant inelastic deformation in their members and joints. This behaviour is dependent upon several design parameters such as member sizes, frame's overstrength, member deformation capacities and the detailing of components. In this study, the influence of such aspects on the inelastic response of frames is investigated. Inelastic static and dynamic analyses were performed on four frames of different designs for a typical six‐storey building. The frames were designed and detailed in accordance with current North American code requirements. The computed response of each frame was compared with the behaviour expected by the codes. Recommendations for a design procedure are suggested for improving the structural performance of low‐rise steel frames subjected to strong earthquake excitation.
Doubly asymptotic multi‐directional transmitting boundary for dynamic unbounded medium‐structure‐interaction analysis
Authors: Wolf John P. , Song Chongmin
Published: April 2007

The novel doubly asymptotic multi‐directional transmitting boundary combines the advantages of the doubly asymptotic and multi‐directional formulations. It is rigorous for the low‐frequency limit (static case) and the high‐frequency limit in the wave‐propagation direction perpendicular to the artificial boundary and at all the preselected angles corresponding to various apparent velocities. It is implemented straightforwardly in the finite‐element method. The doubly asymptotic multi‐directional transmitting boundary is temporally local and spatially either global or local depending on the implementation of the static‐stiffness matrix. It leads to much higher accuracy than other transmitting boundaries with the same finite‐element mesh.
Analysis of the failure of interstate 10 freeway ramp during the Northridge earthquake of 17 January 1994
Authors: Broderick B. M. , Elnashai A. S.
Published: April 2007

The response of a reinforced concrete freeway structure damaged during the Northridge earthquake is determined using non‐linear dynamic finite element analysis. The results obtained allow the ability of contemporary analysis techniques to predict the seismic response of such structures to be assessed and the critical aspects of the behaviour of the structure to be identified. Comparison is made with the response predicted using equivalent static analysis and more simplified dynamic analysis, from which the results of the more advanced analysis are shown to be superior. The influence of a number of modelling assumptions, principally with regard to boundary conditions, on the computed response is also assessed. From this, the disparity between the design conditions and those actually pertaining at the time of the earthquake are seen to play a crucial role in the mode of failure of the structure. It is concluded that, upon the development of an accurate structural model, the analytical results correlated well with the behaviour observed in post‐earthquake reconnaissance.
Simplified 3‐D dynamic analysis of structures with flexible diaphragms
Authors: Tena‐Colunga Arturo , Abrams Daniel P.
Published: April 2007

A simplified method of 3‐D dynamic analysis, named 3‐D quasi‐dynamic analysis, is presented. This method has been primarily used to evaluate stress states at identified times of peak dynamic responses of structures with flexible diaphragms. The quasi‐dynamic analysis consists of extracting the accelerations predicted by the time‐step integration analyses of two 2‐D discrete MDOF dynamic models of a given structure (each discrete model corresponding to one of the principal orthogonal directions of the structure) at given times of interest. These accelerations are imposed on a 3‐D representation of the structure (for example, a finite element mesh) as equivalent static forces. Accelerations at the diaphragms are assumed to act over the same tributary areas of the diaphragms considered in the 2‐D discrete dynamic models.

The study of the firehouse of Gilroy (an unreinforced masonry structure with flexible diaphragms) during the Loma Prieta Earthquake is presented to illustrate the 3‐D quasi‐dynamic seismic analysis. This method was compared to the more traditional 3‐D modal time‐step integration and 3‐D response spectra analyses. The quasi‐dynamic analysis had a general good agreement with the more formal, complex and computationally extensive modal time‐step integration analysis. The 3‐D response spectra analysis was very conservative and had a poor correlation with both the quasi‐dynamic and the modal time‐step integration analyses. The case study of the firehouse of Gilroy suggested that if 3‐D effects have to be considered in the evaluation of a given structure, the quasi‐dynamic analysis constitutes a reliable and computationally cheaper alternative to the more traditional methods of 3‐D dynamic analysis.
Tuned mass dampers for structures with closely spaced natural frequencies
Authors: Abé M. , Igusa T.
Published: April 2007

Analytical results are developed for vibration control of structures with one or more Tuned Mass Dampers (TMDs). The input is a harmonic load with a range of possible frequencies. The control objective is to reduce the maximum amplitude of the structural response. Perturbation theory is used with three sets of small parameters: the ratio of TMD and structural modal masses, the damping of the system, and the differences between the structural and loading frequencies. It is shown analytically that for structures with widely spaced natural frequencies, the response can be approximated accurately by the response of the well‐known single‐mode structure/TMD system. For structures with p closely spaced natural frequencies, more general analytical results are developed to describe the coupling between the motions of the p modes of the structure and the multiple TMDs. The results show that at least p TMDs with properly placed attachments to the structure are necessary to control the response. If fewer TMDs are used, the maximum frequency response has a lower bound which is independent of the properties of the TMDs. The TMD placement is shown to be always important, regardless of the spacing of the structure's natural frequencies. The results are illustrated for both lumped‐mass and continuous structures.
Efficient modal analysis for structures with soil‐structure interaction
Authors: Wu Wen‐Hwa , Smith H. Allison
Published: April 2007

An efficient methodology is presented which uses modal analysis implemented in the frequency domain to obtain the structural response of a system with soil‐structure interaction. The interaction effects are represented using a free‐field ground motion modification factor, derived for each mode of vibration and used in the determination of structural response. Applying this algorithm, the advantages of the modal superposition method are fully exploited, and the interaction problem can be solved easily and effectively within the framework of the conventional frequency domain analysis for a fixed‐base structure. In addition, this method produces accurate approximation with less computational effort due to consideration of only the first few vibration modes of the structure.
Effects of weathering on site response
Authors: Davis Rob
Published: April 2007

Nearly all studies of site response under seismic excitation employ idealized site models in which uniform layers of homogeneous soils are separated by perfect interfaces. The impedance mismatch at each interface gives rise to wave reflections which strongly affect the calculated free surface response. In reality, these perfect interfaces may often not exist. Instead, a zone in which materials from both above and below are mingled may form a blurred interface between layers. This article examines the effects of such weathered zones. The zone is modelled by a linearly varying shear modulus so that no abrupt impedance change occurs. Significant differences in response of weathered and unweathered profiles are found.
Investigation of non‐linear site amplification at two downhole strong ground motion arrays in Taiwan
Authors: Wen Kuo‐Liang , Beresnev Igor A. , Yeh Yeong Tein
Published: April 2007

Non‐linear seismic response of soil is studied by comparing the spectral ratios of surface to downhole horizontal accelerations on weak and strong motion. Data from two boreholes are analysed. One is drilled in the alluvial deposits in the south–west quadrant of the SMART 1 array. The second one penetrates Pleistocene terrace deposits in the northern part of the SMART2 array. Observed weak and strong motion spectral ratios are compared with the theoretical ones predicted by the geotechnical soil model which postulates a hysteretic constitutive law. A significant non‐linear response is found at the first site for the events with surface peak acceleration exceeding roughly 0–15g. Deamplification of the strong motion occurred in the frequency range from approximately 1 to 10 Hz. The maximum observed difference between the average weak and strong motion amplification functions of an 11 m‐thick near‐surface stratum is a factor of 2–3. Nonlinear response characteristics are in qualitative agreement with the model. An additional corollary is that the amplification function calculated from the shear wave coda is equivalent to the average amplification calculated over the ensemble of small earthquakes. No statistically significant non‐linear response is detected on the second array, that is tentatively accounted for by the stiffer soil conditions and weaker accelerations achieved at the SMART2 site. The results indicate that the non‐linear amplification can be detectable at certain soil conditions above a threshold acceleration level.
Localized identification of MDOF structures in the frequency domain
Authors: Zhao Q. , Sawada T. , Hirao K. , Nariyuki Y.
Published: April 2007

For the identification of multi‐degree‐of‐freedom structures, it is not practical to identify all of the parameters included in the structures because enormous computation time is required and because identifiability may not be possible. In this paper, a localized identification approach through substructuring is formulated in the frequency domain. A technique of spectral smoothing is incorporated in the approach to deal with noise‐corrupted data. The proposed approach can be used to identify the structural parameters in any part of interest in a structure. The numerical investigations for a lumped mass‐spring‐dashpot system indicate that faster convergence and higher accuracy are achieved and the noise influences on the identified results are reduced greatly by spectral smoothing. The approach also applies to whole‐structure identification if the required records available and the numerical example shows that higher accuracy results are obtained with less cpu time and more poorly guessed initial values as compared with the general complete‐structure identification.
Dynamic behaviour of turbine‐generator‐foundation systems
Authors: Liu Weiming , Novak Milos
Published: April 2007

In this paper a comprehensive investigation on the dynamic characteristics of turbine–generator–foundation systems is performed. All the major components of the system, including turbine–generator casing, shaft, rotors, journal bearings, deck, piers, foundation mat, piles, and soil medium, have been included. Full interaction between the turbine–generator set, the foundation superstructure, and the soil medium, is considered.

A hybrid method is used to establish the mathematical model for the turbine–generator‐foundation system. The analysis is conducted in the frequency domain through complex frequency response analysis. The response in the time domain is obtained by Fourier transform. The seismic excitation is represented as the control motion on the ground surface, which is generated as an artificial earthquake.

A 300 MW turbine‐generator‐foundation system is analysed under excitations from rotor unbalances and earthquakes. The influence of turbine‐generator casing and soil anisotropy on the response of the system is explored. It is found that the presence of casing and soil anisotropy strongly influences the displacements and internal forces of the system under rotor unbalance excitation. Under seismic excitation, however, although the presence of casing and soil anisotropy does affect the displacements of the system, their effect on the internal forces of the system is minimal.
Multi‐directional transmitting boundaries for steady‐state SH waves
Authors: Liao Z. P. , Yang G.
Published: April 2007

The incident steady‐state SH waves in the neighbourhood of a boundary node point are first expanded in terms of a few plane waves at different incident angles, the motion of the boundary point is then related to those of its adjacent node points to form the multi‐directional transmitting boundary conditions, which reduce reflections from the boundary over the entire range of incident angles. This feature of the boundaries is demonstrated by finite element computations of SH motions of a layer fixed at its base, in which the incident wave may travel parallel to the boundary as the frequency of excitation approaches one of the natural frequencies of the system.
An energy approach to sliding of single‐span simply supported slab‐on‐girder steel highway bridges with damaged bearings
Authors: Dicleli Murat , Bruneau Michel
Published: April 2007

This paper investigates the non‐linear inelastic seismic response of existing single‐span simply supported bridges having bearings which can remain stable and slide after their anchor bolts are ruptured. A simplified equivalent model is developed for the inelastic analysis of these single‐span simply supported bridges. Non‐linear inelastic time‐history analyses are conducted for various acceleration inputs. It is found that narrower bridges with longer spans may have considerable sliding displacements and fall off their supports if adequate seat width is not provided. It is also found that for the same ratio of friction coefficient to peak ground acceleration, the sliding displacement of a structural system is linearly proportional to the amplitude of the peak ground acceleration beyond a certain threshold value. This is also demonstrated analytically from an energy approach point of view. The distribution of the energy content of an earthquake, which is related to its velocity time history, can be an indication of the propensity of an earthquake to cause high sliding displacements. Ground motions with high frequency content or high Ap/Vp ratio may produce smaller sliding displacements than ground motions with relatively lower Ap/Vp ratios.
Shifting natural frequencies of plates through preforming
Authors: Mostaghel N. , Fu K. C. , Yu Qiulin
Published: April 2007

Through an energy formulation and the use of a large deflection theory, it is shown that if a thin plate has a slight initial preform, and if its edges are constrained against in–plane displacements, then all of the natural frequencies of the plate will be shifted upward. For a uniform thin plate, the amount of frequency shift depends on the type of boundary conditions and the ratio of the amplitude of preform to the thickness of the plate. Examples of square and rectangular plates preformed in the shape of their first mode shapes are presented. The method holds the promise of shifting or essentially removing a troublesome vibration mode.
Damping in low‐aspect‐ratio, reinforced concrete shear walls
Authors: Farrar Charles R. , Baker William E.
Published: April 2007

Experiments were conducted to measure the damping in low‐aspect‐ratio, reinforced concrete shear walls with the specific intent of obtaining a better understanding of how this parameter changes with increasing stress levels. These experiments and the corresponding results are presented, along with a description of the methods used to estimate damping from measured input and response data and a summary of a numerical study that was undertaken to assess the relative accuracy of these methods. Also presented are the testing methods used in this study, including static cyclic tests, experimental modal analyses, and simulated seismic testing on a shake table. The results are summarized and compared with those obtained by other investigators. In conclusion, an empirical relationship is developed for equivalent viscous damping in low‐aspect‐ratio shear walls as a function of the peak nominal base shear stress the shear wall experiences during a seismic event.