bluuebunny/crossref_metadata_2025 huggingface dataset:
Confinement of Thermoresponsive Hydrogels in Nanostructured Porous Silicon Dioxide Templates
Authors: Segal E. , Perelman L. A. , Cunin F. , Di Renzo F. , Devoisselle J.‐M. , Li Y. Y. , Sailor M. J.
Published: April 2007

A thermoresponsive hydrogel, poly(N‐isopropylacrylamide) (poly(NIPAM)), is synthesized in situ within an oxidized porous Si template, and the nanocomposite material is characterized. Infiltration of the hydrogel into the interconnecting nanoscale pores of the porous SiO2 host is confirmed by scanning electron microscopy. The optical reflectivity spectrum of the nanocomposite hybrid displays Fabry–Pérot fringes characteristic of thin film interference, enabling direct, real‐time observation of the volume phase transition of the confined poly(NIPAM) hydrogel. Reversible optical reflectivity changes are observed to correlate with the temperature‐dependent volume phase transition of the hydrogel, providing a new means of studying nanoscale confinement of responsive hydrogels. The confined hydrogel displays a swelling and shrinking response to changes in temperature that is significantly faster than that of the bulk hydrogel. The porosity and pore size of the SiO2 template, which are precisely controlled by the electrochemical synthesis parameters, strongly influence the extent and rate of changes in the reflectivity spectrum of the nanocomposite. The observed optical response is ascribed to changes in both the mechanical and the dielectric properties of the nanocomposite.
An attainable region approach for production planning of multiproduct processes
Authors: Sung Charles , Maravelias Christos T.
Published: April 2007

A novel approach is presented for the solution of production planning problems for multiproduct processes. A mixed‐integer programming (MIP) scheduling model is analyzed off‐line to obtain a convex approximation of feasible production levels and a convex underestimation of total production cost as a function of production levels. The two approximating functions are expressed via linear inequalities that involve only planning variables yet provide all the relevant scheduling information necessary to solve the planning problem with high quality. A rolling horizon algorithm is also presented for generation (if necessary) of detailed schedules. © 2007 American Institute of Chemical Engineers AIChE J, 2007
Binding of bioactive phytochemical piperine with human serum albumin: A spectrofluorometric study
Authors: Suresh Dodda Venkatanna , Mahesha Honsigere G. , Rao A. G. Appu , Srinivasan Krishnapura
Published: April 2007

Piperine, the bioactive alkaloid compound of the spice black pepper (Piper nigrum) exhibits a wide range of beneficial physiological and pharmacological activities. Being essentially water‐insoluble, piperine is presumed to be assisted by serum albumin for its transport in blood. In this study, the binding of piperine to serum albumin was examined by employing steady state and time resolved fluorescence techniques. Binding constant for the interaction of piperine with human serum albumin, which was invariant with temperature in the range of 17–47°C, was found to be 0.5 × 105M−1, having stoichiometry of 1:1. At 27°C, the van't Hoff enthalpy ΔH° was zero; ΔS° and ΔG° were found to be 21.4 cal mol−1 K−1 and −6.42 kcal mol−1. The binding constant increased with the increase of ionic strength from 0.1 to 1.0M of sodium chloride. The decrease of Stern–Volmer constant with increase of temperature suggested that the fluorescence quenching is static. Piperine fluorescence showed a blue shift upon binding to serum albumin, which reverted with the addition of ligands —triiodobenzoic acid and hemin. The distance between piperine and tryptophan after binding was found to be 2.79 nm by Förster type resonance energy transfer calculations. The steady state and time resolved fluorescence measurements suggest the binding of piperine to the subdomain IB of serum albumin. These observations are significant in understanding the transport of piperine in blood under physiological conditions. © 2007 Wiley Periodicals, Inc. Biopolymers 86: 265–275, 2007.

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Young people's perceptions and experiences of leaving high school early: an exploration
Authors: Lee Trish , Breen Lauren
Published: April 2007

Research suggests it is important for students to feel a sense of belonging to their school. Students who do not belong at school often attempt to satisfy this need through membership in antisocial groups, or they drop out from school altogether. The current study explored the perceptions and experiences of the school context held by young people who have left school early. Twelve young people aged 16–19 years were interviewed on their experiences of school and their wellbeing as a result of leaving school early. Constructionist grounded theory methodology formed the basis of the data analysis. The early leaving process was identified as having three phases; exclusion from school, the transition into workforce and the ‘now’ phase. The results identified factors in the school context that contributed to early student withdrawal. Furthermore, the research has implications for creating a ‘normative narrative’ (Rappaport, 2000) in relation to early school leavers. Copyright © 2007 John Wiley & Sons, Ltd.
A Genomic Screening Approach to the Structure‐Guided Identification of Drug Candidates from Natural Sources
Authors: Hornung Andreas , Bertazzo Marcelo , Dziarnowski Agnieszka , Schneider Kathrin , Welzel Katrin , Wohlert Sven‐Eric , Holzenkämpfer Meike , Nicholson Graeme J. , Bechthold Andreas , Süssmuth Roderich D. , Vente Andreas , Pelzer Stefan
Published: April 2007

The potential of actinomycetes to produce natural products has been exploited for decades. Recent genomic sequence analyses have revealed a previously unrecognized biosynthetic potential and diversity. In order to rationally exploit this potential, we have developed a sequence‐guided genetic screening strategy. In this “genome mining” approach, genes that encode tailoring enzymes from natural product biosyntheses pathways serve as indicator genes for the identification of strains that have the genetic potential to produce natural products of interest. We chose halogenases, which are known to be involved in the synthesis of halometabolites as representative examples. From PCR screening of 550 randomly selected actinomycetes strains, we identified 103 novel putative halogenase genes. A phylogenetic analysis of the corresponding putative halogenases, and the determination of their sequential context with mass spectrometric analysis of cultures filtrates revealed a distinct correlation between the sequence and secondary metabolite class of the halometabolite. The described screening strategy allows rapid access to novel natural products with predetermined structural properties.
SorF: A Glycosyltransferase With Promiscuous Donor Substrate Specificity in vitro
Authors: Kopp Maren , Rupprath Carsten , Irschik Herbert , Bechthold Andreas , Elling Lothar , Müller Rolf
Published: April 2007

Glycosylations are well‐established steps in numerous biosynthetic pathways, and the attached sugar moieties often influence the specificity or pharmacology of the modified compounds. The sorangicins belong to the polyketide family of natural products, and exhibit antibiotic activity through inhibition of bacterial RNA polymerase. We have identified the sorangicin biosynthetic gene cluster in the producing myxobacterium Sorangium cellulosum So ce12. Within the cluster, sorF encodes a putative glycosyltransferase. To determine its function in sorangicin biosynthesis, SorF was heterologously expressed as a fusion protein in Escherichia coli. After purification by affinity chromatography, SorF was found to glucosylate sorangicin A in vitro, utilizing UDP‐α‐D‐glucose as the natural donor substrate. Additionally, SorF showed high flexibility towards further UDP‐ and dTDP‐sugars and was able to transfer several other sugar moieties—α‐D‐galactose, α‐D‐xylose, β‐L‐rhamnose, and 6‐deoxy‐4‐keto‐α‐D‐glucose—onto the aglycon. SorF is therefore one of the rare glycosyltransferases able to transfer both D‐ and L‐sugars, and could thus be used to generate novel sorangiosides.
A Comparison of Phosphaferrocene and Phospharuthenocene Ligands in Rh+‐Catalysed Enamide Hydrogenation Reactions: Superior Performance of the Phospharuthenocene
Authors: Carmichael Duncan , Goldet Gabrielle , Klankermayer Jürgen , Ricard Louis , Seeboth Nicolas , Stankevič Marek
Published: April 2007

Enantiopure Cp*‐substituted 3,4‐dimethyl‐5‐phenylphosphametallocene‐2‐methanols (M=Fe, Ru) have been prepared from the corresponding 2‐carboxy‐(−)‐menthylphospholide anion and elaborated into 2‐CH2PPh2 phosphametallocenes (13: M=Fe; 14: M=Ru) and 2‐CH2PtBuR substituted phospharuthenocenes (R=tBu, Me). The crystal structures of complexes [Rh(1,5‐cod)(η2‐L)]+BF4− (L=13, 14) reveal significantly different aryl group configurations. Comparative studies of the hydrogenation of para‐substituted N‐acetylcinnamate esters with these pre‐catalysts show a superior performance for the phospharuthenocene derivative in terms of both rate and enantioselectivity.
Preparation and Characterization of a Novel Organic–Inorganic Nanohybrid “Cerasome” Formed with a Liposomal Membrane and Silicate Surface
Authors: Katagiri Kiyofumi , Hashizume Mineo , Ariga Katsuhiko , Terashima Takashi , Kikuchi Jun‐ichi
Published: April 2007

A novel class of organic–inorganic hybrids, the so‐called cerasomes, which have a bilayer vesicular structure and a silicate surface, has been synthesized by combination of sol–gel reaction and self‐assembly of organoalkoxysilanes with a molecular structure analogous to lipids. We have synthesized two cerasome‐forming organoalkoxysilanes, N‐[N‐(3‐triethoxysilyl)propylsuccinamoyl]dihexadecylamine (1) and N,N‐dihexadecyl‐N α‐[6‐[(3‐triethoxysilyl)propyldimethylammonio]hexanoyl]glycinamide bromide (2), and investigated the synthetic conditions of the cerasomes and their structural characteristics. For the proamphiphilic 1, the cerasome was obtained under restricted pH conditions where acid‐catalyzed hydrolysis of the triethoxysilyl moiety proceeded without disturbing the vesicle formation. In contrast, the amphiphilic 2, additionally having a hydrophilic quaternary ammonium group, formed stable dispersions of the cerasome in a wide pH range. The hydrolysis behavior of the triethoxysilyl groups was monitored by 1H NMR spectroscopy. Morphology of the cerasomes having the liposomal vesicular structure was confirmed by TEM observations. Extent of the development of siloxane networks through condensation among the silanol groups on the cerasome surface was evaluated by using MALDI‐TOF‐MS spectrometry. Formation of oligomers of the cerasome‐forming lipids in the vesicle was clearly confirmed. Due to the siloxane network formation, the cerasome showed remarkably high morphological stability compared with a reference liposome, as evaluated by surfactant dissolution measurements.
Validation and comparison of contemporary prognostic models in primary myelofibrosis
Authors: Tefferi Ayalew , Huang Jocelin , Schwager Susan , Li Chin‐Yang , Wu Wenting , Pardanani Animesh , Mesa Ruben A.
Published: April 2007

BACKGROUND.

Survival in primary myelofibrosis (PMF) is predicted by several prognostic scoring systems (PSSs); the most widely recognized is that of Dupriez. Two other PSSs, Cervantes and Mayo, were recently reported as being more useful in younger patients. The current study compares these 3 PSSs among all age groups.

METHODS.

The Mayo Clinic PMF database was queried to identify a consecutive series of patients in whom pretreatment bone marrow and complete blood count (CBC), obtained within 6 months of diagnosis, were available for review.

RESULTS.

Among 334 study patients (median age, 57 years), median survival was 70 months. Multivariable analysis of all 6 adverse prognostic factors utilized in the aforementioned PSSs (ie, hemoglobin <10 g/dL, leukocyte count <4 or >30 × 109/L, constitutional symptoms, circulating blasts ≥1%, platelet count <100 × 109/L, absolute monocyte count ≥1 × 109/L) identified all but platelet count as being significant. The Mayo PSS, which is based on the 4 CBC‐derived parameters (ie, hemoglobin, platelet, leukocyte, and monocyte counts), displayed a better hazard ratio profile compared with the other 2 PSSs in identifying long‐lived patients as well as delineating intermediate‐risk disease category. The latter effect was even more pronounced in patients younger than age 60 years.

CONCLUSIONS.

The Mayo PSS for survival in PMF is an objective CBC‐derived prognostic model that might be superior in its performance over that of either the Dupriez and Cervantes PSSs. Cancer 2007. © 2007 American Cancer Society.
Proportion of long‐term event‐free survivors and lifetime of adult patients not cured after a standard acute lymphoblastic leukemia therapeutic program
Authors: Le Quoc‐Hung , Thomas Xavier , Ecochard Reneé , Iwaz Jean , Lheéritier Veéronique , Michallet Mauricette , Fiere Denis
Published: April 2007

BACKGROUND.

In adult acute lymphoblastic leukemia, treatment results generally are expressed in terms of overall survival or disease‐free survival at 3 years. In this investigation, the authors attempted to express the results in terms of the proportion of long‐term disease‐free survivors and in terms of lifetime in patients who developed recurrent disease or died.

METHODS.

Univariate and multivariate analyses were used to assess the influence of different covariates on the 2 result criteria in 922 participants in the Adult Acute Lymphoblastic Leukemia‐94 multicenter trial.

RESULTS.

The proportion of long‐term survivors was 21.5% (95% confidence interval [95% CI], 18.1–25.4%) and was higher in women than in men. The proportion decreased with increasing age, white blood cell count, and lactate dehydrogenase level. The lowest proportion was observed in patients ages 44 years to 55 years (11.4%; 95% CI, 7–17.9%) and in patients with the t(9;22) BCR‐ABL karyotype (13.4%; 95% CI, 8.8–19.8%), and the highest proportion was observed in patients with the t(4;11) MLL‐AF4 karyotype (31.3%; 95% CI, 18.2–48.3%). The mean expected lifetime of patients who were not cured was 11.4 months (95% CI, 9.1–14.1 months). It was longer in men than in women and was shorter with increasing age, performance status, hemoglobin level, and white blood cell count.

CONCLUSIONS.

The results of this study highlighted and specified the importance of some classic prognostic factors in patients with acute lymphoblastic leukemia. Cancer 2007. © 2007 American Cancer Society.
Epigenetic combination therapy as a tumor‐selective treatment approach for hepatocellular carcinoma
Authors: Venturelli Sascha , Armeanu Sorin , Pathil Anita , Hsieh Chih‐Jen , Weiss Thomas S. , Vonthein Reinhard , Wehrmann Manfred , Gregor Michael , Lauer Ulrich M. , Bitzer Michael
Published: April 2007

BACKGROUND.

Innovative epigenetic therapeutics comprise histone deacetylase inhibitors (HDAC‐I) and demethylating agents (DA). It was recently found that HDAC‐I compounds exhibit profound therapeutic activities against hepatocellular carcinoma (HCC). A comprehensive preclinical investigation was performed on the potential of a combined HDAC‐I/DA epigenetic regimen for the highly chemotherapy‐resistant HCC entity.

METHODS.

Human HCC‐derived cell lines or primary human hepatocytes (PHH) were treated with HDAC‐I compound suberoylanilide hydroxamic acid (SAHA) or DA compound 5‐aza‐2′‐deoxycytidine (5‐aza‐dC) or both and examined for cellular damage, proliferation, histone acetylation pattern, and DNA methylation. In vivo activities were investigated in a xenograft hepatoma model.

RESULTS.

Monotherapeutic application of SAHA or 5‐aza‐dC was found to induce substantial antiproliferative effects in HCC‐derived cells, strongly enhanced by combined SAHA and 5‐aza‐dC treatment. PHH from different human donors did not exhibit any relevant cellular damage even when applying high doses of the combination regimen, whereas HCC‐derived cell lines showed a dose‐dependent damage. In vivo testing demonstrated a statistical significant inhibition of hepatoma cell growth for the combined treatment regime.

CONCLUSIONS.

Because the combined HDAC‐I/DA epigenetic approach was found to produce significant antitumor effects in HCC model systems and did not impair cellular integrity of untransformed hepatocytes, this combination therapy is now considered for further investigation in clinical trials. Cancer 2007;109:2132–41. © 2007 American Cancer Society.
Towards building a conflict‐free mobile distributed file system
Authors: Boukerche Azzedine , Al‐Shaikh Raed A.
Published: April 2007

The rising demand for mobile computing has created a need for an improved file system that supports mobile clients. Current file systems with support for mobility provide availability through file replicas that are cached at the client side. However, mobile clients may experience different obstacles with regards to the local cache, such as the limited network bandwidth, the intermittent connection, and serious conflicts when synchronizing back to the server. In this paper, we propose a novel mobile distributed file system design, which provides high availability and reliable storage for files and guarantees that file operations are executed regardless of concurrency and failure issues. The design is intended to fit mobile clients (e.g. PDAs and cell phones) that have limited storage space and cannot store all of the data they need, and yet require access to these data at all times. We adopt a server‐side caching in order to guarantee sufficient caching space to all mobile clients, and to ensure the availability of files in the case of clients' failures. We present our algorithm, describe its implementation, simulate its high availability functions, and report on its performance evaluation using a cluster of workstations. Our simulation results indicate clearly that our algorithm exhibits a significant degree of automation and conflict‐free mobile file system. Copyright © 2007 John Wiley & Sons, Ltd.
Mobility management in hybridad‐hocnetworks and the Internet environment
Authors: Denko M. K.
Published: April 2007

The integration of mobilead‐hocnetworks (MANETs) with the Internet provides flexible and multi‐hop communication capability in hybrid wired and wireless networks. Existing architectures for integrating these networks use Mobile IP andad‐hocrouting protocols with fixed gateways. In this paper, we propose a mobility management scheme based on a mobile gateways (MGs) architecture. We designed a buffering mechanism for micro‐ and macro‐mobility management in hybrid networks. The performance of mobility management with optimized handover (MM‐OH), optimized handover with prediction (MM‐OHP) and forced handover (MM‐FH) are evaluated using simulation. Our simulation results show that a buffering mechanism coupled with the hybrid gateway discovery results in a higher packet delivery ratio for MM‐OH and MM‐OHP compared with the MM‐FH scheme. The MM‐OHP scheme has a lower number of handovers compared with the MM‐OH scheme. Moreover, the simulation experiments reveal that the speed of the MG has a relatively higher impact on performance than the speed of mobile nodes. Copyright © 2007 John Wiley & Sons, Ltd.
EZRP: an enhanced zone‐based routing protocol forad‐hocnetworks
Authors: Koyama A. , Arai J. , Barolli L. , Durresi A.
Published: April 2007

In mobilead‐hocnetworks (MANETs), the nodes intercommunicate through single‐hop and multi‐hop paths in a peer‐to‐peer fashion. Intermediate nodes between two pairs of communication nodes act as routers. Thus, the nodes operate both as hosts and routers. The nodes are mobile, so the topology of the network may change rapidly and unexpectedly. One well‐known routing protocol forad‐hocnetworks is the Zone Routing Protocol (ZRP). However, when the protocol searches for a new route, it sends many useless control packets, which increase the network load and decrease the network performance. In this paper, we propose an Enhanced Zone Routing Protocol (EZRP). In EZRP, each node calculates the reliability of the route. In the case of a reliable route, the source node sends the data packet directly to the destination node using that route without route searching. In the case of an unreliable route, the source node searches for a new route again. We show that the network performance can be improved by using EZRP. Copyright © 2007 John Wiley & Sons, Ltd.
Classification and generation of schedules for VLIW processors
Authors: Kessler Christoph , Bednarski Andrzej , Eriksson Mattias
Published: April 2007

Exact methods for optimal instruction scheduling are gaining importance. They differ, however, considerably in the assumed processor model and in the space of schedules searched for an optimal solution. We identify and analyze different classes of schedules for VLIW processors. The classes are induced by various common techniques for generating or enumerating them, such as integer linear programming or list scheduling with backtracking. In particular, we study the relationship between VLIW schedules and their equivalent linearized forms (which may be used, e.g., with superscalar processors), and we identify classes of VLIW schedules that can be created from a linearized form using VLIW compaction methods that are just the static equivalents of dynamic instruction dispatch algorithms of in‐order and out‐of‐order issue superscalar processors. For example, we study the class of greedy schedules and show that, if all instructions have multiblock reservation tables, it is safe for time optimization to consider greedy schedules only. We also show that, in certain situations, certain schedules generally cannot be constructed by incremental scheduling algorithms that are based on topological sorting of the data dependence graph. We summarize our findings as a hierarchy of classes of VLIW schedules. These results can sharpen the interpretation of the term ‘optimality’ used with various methods for optimal VLIW scheduling, and may help to identify classes that can be safely ignored when searching for an optimal schedule. Copyright © 2007 John Wiley & Sons, Ltd.
Efficient search‐space pruning for integrated fusion and tiling transformations
Authors: Gao Xiaoyang , Krishnamoorthy Sriram , Sahoo Swarup Kumar , Lam Chi‐Chung , Baumgartner Gerald , Ramanujam J. , Sadayappan P.
Published: April 2007

Compile‐time optimizations involve a number of transformations such as loop permutation, fusion, tiling, array contraction etc. The selection of the appropriate transformation to minimize the execution time is a challenging task. We address this problem in the context of tensor contraction expressions involving arrays too large to fit in main memory. Domain‐specific features of the computation are exploited to develop an integrated framework that facilitates the exploration of the entire search space of optimizations. In this paper, we discuss the exploration of the space of loop fusion and tiling transformations in order to minimize the disk I/O cost. These two transformations are integrated and pruning strategies are presented that significantly reduce the number of loop structures to be evaluated for subsequent transformations. The evaluation of the framework using representative contraction expressions from quantum chemistry shows a dramatic reduction in the size of the search space using the strategies presented. Copyright © 2007 John Wiley & Sons, Ltd.
NADPH oxidase of human dendritic cells: Role in Candida albicans killing and regulation by interferons, dectin‐1 and CD206
Authors: Donini Marta , Zenaro Elena , Tamassia Nicola , Dusi Stefano
Published: April 2007

Human monocyte‐derived DC express the enzyme NADPH oxidase, responsible for ROS production. We show that Candida albicans did not activate NADPH oxidase in DC, and was poorly killed by these cells. However, Candida‐killing activity increased upon DC stimulation with the NADPH oxidase activator PMA and was further enhanced by DC treatment with IFN‐α or IFN‐γ. This fungicidal activity took place at high DC‐to‐Candida ratio, but decreased at low DC‐to‐yeast ratio, when Candida inhibited the NADPH oxidase by contrasting the assembly of the enzyme on DC plasma membrane. The NADPH oxidase inhibitor diphenyliodonium chloride abrogated the PMA‐dependent DC candidacidal capacity. Engagement of β‐glucan receptor dectin‐1 induced NADPH oxidase activation in DC that was depressed by mannose‐binding receptor CD206 co‐stimulation. Candida was internalized by DC through mannose‐binding receptors, but not through dectin‐1, thus explaining why Candida did not elicit NADPH oxidase activity. Our results indicate that NADPH oxidase is involved in DC Candida‐killing activity, which is increased by IFN. However, Candida escapes the oxidative damage by inhibiting NADPH oxidase and by entering DC through receptors not involved in NADPH oxidase activation.
Blockade of TREM‐2 exacerbates experimental autoimmune encephalomyelitis
Authors: Piccio Laura , Buonsanti Cecilia , Mariani Margherita , Cella Marina , Gilfillan Susan , Cross Anne H. , Colonna Marco , Panina‐Bordignon Paola
Published: April 2007

Triggering receptor expressed on myeloid cells (TREM‐2) is a membrane receptor associated with DAP12 that is expressed primarily in myeloid cells, including dendritic cells and microglia, and promotes fusion of osteoclast precursors into multinucleated cells. A rare autosomal recessive condition, Nasu‐Hakola disease (NHD) is associated with loss‐of‐function mutations in DAP12 and TREM‐2. The brain pathology observed in NHD patients suggests that disruption of the TREM‐2/DAP12 pathway leads to neurodegeneration with demyelination and axonal loss. In this study, we have characterized TREM‐2 protein expression on microglia using a newly produced monoclonal antibody directed against the mouse TREM‐2 receptor. We report that TREM‐2 expression is up‐regulated in the spinal cord during both the early inflammatory and chronic phases of myelin oligodendrocyte glycoprotein (MOG)35–55 peptide‐induced experimental autoimmune encaphalomyelitis (EAE). We also demonstrate that TREM‐2 is highly expressed on microglial cells in the central nervous system (CNS) during EAE and that blockade of TREM‐2 during the effector phase of EAE results in disease exacerbation with more diffuse CNS inflammatory infiltrates and demyelination in the brain parenchyma. These results demonstrate a critical role for TREM‐2 during inflammatory responses in the CNS.
An improved response spectrum method for calculating seismic design response. Part 2: Non‐classically damped structures
Authors: Maldonado G. O. , Singh M. P.
Published: April 2007

A response spectrum method which combines the analytical advantage of the mode acceleration formulation and the practical advantage of the mode displacement formulation is developed for seismic response calculation of non‐classically damped structures. It reduces the error associated with the truncation of the high frequency modes without explicitly using them in the analysis. The method is especially effective for calculating the response of stiff structural systems and also for calculating the response quantities which are strongly affected by high frequency modes. Even with flexible structures, it is shown to provide more accurate response results than the results obtained with the mode displacement approach.
Effects of ground motion spatial variability on the response of cable‐stayed bridges
Authors: Nazmy Aly S. , Abdel‐Ghaffar Ahmed M.
Published: April 2007

In order to extend our knowledge of the performance of long‐span bridges under earthquake loading the effects of spatial variability of ground motion on the structural response of cable‐stayed bridges are studied; the result can be useful to practising bridge engineers. The multiple‐support excitation analysis is described, and two three‐dimensional models representing the modern and future trends in cable‐stayed bridge design are utilized to shed some light on salient features of the seismic response characteristics of these modern bridges. In addition, models of steel‐ and concrete‐design alternates of an existing bridge are considered. Differential ground motion records (obtained from dense instrument arrays) are used as synchronous and non‐synchronous support motions; in addition, non‐dispersive seismic waves travelling along the bridge are considered. The bridge response to non‐uniform ground motion is compared to its response to uniform input. An overview of the unique dynamic characteristics of these cable‐supported bridges is also presented. Finally, the study, which was used in the seismic design of several existing cable‐stayed bridges in U.S. and Canada, indicates that the response quantities may increase substantially from the non‐uniform input ground motion, especially for more rigid bridges and for bridges having different dynamic properties of the local soils at the supporting points, but the degree of increase depends upon the specific problem, in particular upon the aspects of span length, rigidity and structural redundancy. Thus, the response to non‐uniform input ground motion should be examined for these bridges.
A unified mode combination theory for stationary response of structural systems
Authors: Igusa Takeru
Published: April 2007

A general theory of mode combination is developed for structural systems subjected to stationary stochastic excitation. The analysis begins with a brief review of a mode combination expression for first‐order systems. Then, new fundamental properties of this result are developed. These properties are used to establish common analytical foundations and make new extensions of previously developed mode combination results for under‐critically damped, classically damped, cascaded and non‐linear structures. In the second part of the paper, an efficient and general mode combination method is developed for cascaded structures. It is shown how the unified mathematical framework established herein can be applied to cascaded structures composed of different types of substructures without the need to derive separate mode combination expressions.
The system damping, the system frequency and the system response peak amplitudes during in‐plane building‐soil interaction
Authors: Todorovska M. I. , Trifunac M. D.
Published: April 2007

The system damping, the system frequency, the relative building response and the base rocking response peak amplitudes are studied, as those depend on the building mass and height, the flexibility of the soil, the structural damping, the type of incident waves and their angle of incidence. A linear two‐dimensional model is used, which assumes the soil to be a homogeneous isotropic half‐space, the foundation supporting the building to be a rigid embedded cylinder, and in which the building model is an equivalent single‐degree‐of‐freedom oscillator. The system frequency and the system damping ratio are determined by measuring the width and the frequency of the peak in the transfer function of the oscillator relative response, using the analogy with the half‐power method for a single‐degree‐of‐freedom fixed‐base oscillator. Previous similar studies are for dynamic soil‐structure interaction only, and for simplified models in which the stiffness of the soil and the damping due to radiation are represented by springs and dashpots. The study in this paper differs from the previous studies in that the wave passage effects (or the kinematic interaction) are also included, and that no additional simplifications of the model are made. Results are shown for excitation by plane P‐ and SV‐waves.
Response spectrum analysis of structures subjected to spatially varying motions
Authors: Berrah Mounir , Kausel Eduardo
Published: April 2007

An important aspect of earthquake loads exerted on extended structures, or structures founded on several foundations, is the spatial variability of the seismic motion. Hence, a rigorous earthquake resistant design of lifeline structures should account for the spatial character of the seismic input, at least in an approximate way.

A procedure is proposed which enables addressing the problem of multiply supported structures, subjected to imperfectly correlated seismic excitations, by means of an extension to the response spectrum method. A modified response spectrum model is developed for the design of extended facilities subjected to single and multicomponent ground motion. The modification procedure is based on adjusting each spectral value of the given design response spectrum by means of a correction factor, which depends on the structural properties and on the characteristics of the wave propagation phenomenon. Finally, the theoretical model is validated through digital simulation of seismic ground motion, whereby model predictions are found to be in good agreement with exact results.
Predictive control of base‐isolated structures
Authors: Inaudi J. , López‐Almansa F. , Kelly J. M. , Rodellar J.
Published: April 2007

A control design for absolute motion reduction of base‐isolated structures subjected to earthquake excitation is presented herein. The control objective is to provide a vibration‐free environment for sensitive equipment protection. Predictive control theory is used for the control design. This theory allows the designer to handle time delays generated by the dynamics of actuators. The study reported herein demonstrates, by numerical simulation, the efficacy of this controller in reducing acceleration response in the superstructure in the presence of delays. Stability analysis, frequency response and response to ground motion excitation are developed to assess the characteristics of the controller.
Design of torsionally unbalanced structural systems based on code provisions I: Ductility demand
Authors: Tso W. K. , Zhu T. J.
Published: April 2007

Using a three element single mass model, this paper presents the ductility demands on the elements of torsionally unbalanced systems when subjected to strong earthquake shaking. Torsionally unbalanced systems based on nine structural configurations are considered, ranging from torsionally stiff systems with the centre of rigidity (CR) centrally located to torsionally flexible systems with CR eccentrically located. The strength of the elements is designed based on the Canadian and New Zealand codes, and the Uniform Building Code (UBC) of the United States. It is shown that all three codes can limit the ductility demands on the elements to that of a similar but torsionally balanced system when the system is torsionally stiff. However, substantial additional ductility demands on the element at the stiff edge of the system exist for torsionally flexible systems when the New Zealand code or UBC is used. The large ductility demand is caused by the low strength of the stiff‐edge element permitted by these codes.
Orientation error estimation of buried seismographs in array observation
Authors: Yamazaki Fumio , Lu Lin , Katayama Tsuneo
Published: April 2007

Array observation is an efficient tool to investigate various characteristics of earthquake ground motion. However, seismographs used in arrays may involve unexpected errors in their orientations. Methods of orientation error estimation were developed in three‐dimensional space by comparing recorded ground motions at a reference point with those at a checking point. A maximum cross‐correlation method and a maximum coherence method were proposed and their accuracy was demonstrated. The earthquake ground motions recorded in the Chiba array and in two other arrays were used in numerical examples. Non‐trivial orientation errors were detected for all these arrays. The cross‐correlation coefficients and the coherence values between two points increased significantly by correcting the estimated orientation errors.
Dynamic characteristics of multiple substructures with closely spaced frequencies
Authors: Xu Kangming , Igusa Takeru
Published: April 2007

This paper considers a main structure supporting a large number of substructures. The substructures have closely spaced natural frequencies, and the combined main structure/multiple substructures system is subjected to harmonic or wide‐band forces. The goal is to characterize the effects of the substructures on the response of the main structure.

A special, fundamental case is studied in detail, where the substructures are oscillators with equal stiffnesses and equally spaced natural frequencies. The exact response expressions for the combined system are in terms of a complicated rational polynomial. However, by taking the limit where the number of substructures becomes large, the response expressions reduce to simple, physically meaningful results. It is found that the multiple substrutures are equivalent to a single viscous damping which is added to the damping of the main structure. An example illustrates how the results can be applied to passive vibration control of large structures.
Transient elastodynamic analysis by time domain bem in cylindrical coordinates
Authors: Lei Z. X. , Tham L. G. , Cheung Y. K.
Published: April 2007

A time domain boundary element in a cylindrical coordinate system is developed for the analysis of wave propagation in a half space. The integral formulation is based on Graffi's dynamic reciprocal theorem and Stokes' fundamental solutions. The field quantities (displacements and tractions) are expressed as products of Fourier series in the tangential direction and linear polynomials in the other spatial directions. Gaussian integration is used to integrate the non‐singular parts of the integral equations, whereas the integration of the singular components, which are either of order 1/r or 1/r2, is handled by special numerical schemes. In the time marching aspect, the field quantities are assumed to vary linearly in the temporal direction as well.

Examples for wave propagation due to various forms of surface excitations are reported to demonstrate the accuracy of the method.
One‐dimensional modelling of the non‐linear far field in soil–structure‐interaction analysis
Authors: Wolf John P. , Paronesso Antonio
Published: April 2007

In a bounded domain elasto‐plastic wave propagation can be modelled accurately using the finite‐element method. As is even the case for an elastic analysis, an unbounded domain, e.g. a semi‐infinite soil or fluid, can, however, not be represented in this manner, as any spatial discretization has to be avoided. For one‐dimensional wave propagation with a bi‐linear elasto‐plastic material law involving one stress component an analytical solution exists. The latter is used in modelling the non‐linear far field of an unbounded medium using a rigorous bookkeeping procedure of the generated elastic and plastic waves propagating in both directions. The need for a non‐linear model of the far field arises, as in a two‐dimensional representation of soil‐structure interaction the surface waves do not decay.
A FE–BE method for dynamic analysis of dam–foundation–reservoir systems in the time domain
Authors: Touhei Terumi , Ohmachi Tatsuo
Published: April 2007

By coupling FEM and BEM, a numerical method was developed for dynamic response analyses of dam–foundation–reservoir systems in the time domain. During formulation, the weighted residual procedure was applied to the coupling of several equations of motion for solid and fluid in the FE and BE regions, and an algorithm similar to the Newmark beta procedure was finally obtained. The algorithm is advantageous in that it takes into account all the effects of dam–foundation, dam–reservoir and reservoir–foundation interactions, as well as of the absorption of both elastodynamic and hydrodynamic waves at the boundaries of the foundation and the reservoir. To demonstrate the validity of the present method, the impulsive response of a dam–foundation–reservoir system was calculated using the algorithm, and showed a good agreement with the existing results obtained by other researchers.
Inelastic response and design criteria of plan‐wise asymmetric systems
Authors: De Stefano Mario , Faella Giuseppe , Ramasco Roberto
Published: April 2007

The study of the torsional response of buildings in the inelastic range of behaviour is of great interest since the ability of structures to resist strong earthquakes mainly relies on their ductility and capacity for energy dissipation. Furthermore, an examination of the performance of structures during past earthquakes demonstrates that plan‐asymmetric buildings suffered greater damage due to torsional response. The paper deals with this subject by analysing a model which idealizes a one‐storey building with resisting elements oriented along two perpendicular directions. In addition to the parameters of the elastic behaviour, the inelastic system response depends on full yield capacity and plan‐wise strength distribution. The influence of the criterion adopted for the design of resisting elements on local ductility demand and damage has been evaluated by parametric analysis. In particular, a comparison has been carried out between systems with equal design levels for all elements and systems with design levels dependent on the element location. For a given elastic behaviour and total capacity, the strength distributions in plan have been defined which minimize ductility demand and structural damage. Finally, based on these findings, responses from models designed according to several seismic codes have been compared.
Base isolation by free rolling rods under basement
Authors: Lin Tsung‐Wu , Hone Chao‐Chi
Published: April 2007

A new base isolation method is proposed for the protection of structures. Because of the efficiency of the isolation devices, the isolated structure may be made to remain elastic throughout major earthquakes. This device consists of two sets of mutually orthogonal free rolling rods under the basement of the structure. Since the coefficient of rolling friction of the rods is very small in practice, the structure can be isolated excellently from the support excitation. In this paper, the analytical method and the response of the isolated system for different parameters, such as the periods of the structure, the coefficient of rolling friction and the masses of rolling rods, are presented. The results indicate that the proposed method is excellent in isolating the structure from support excitations, as expected.
An indirect boundary element method applied to simulate the seismic response of alluvial valleys for incident P, S and Rayleigh waves
Authors: Sánchez‐Sesma F. J. , Ramos‐Martínez J. , Campillo M.
Published: April 2007

A boundary integral formulation is presented and applied to model the ground motion on alluvial valleys under incident P, S and Rayleigh waves. It is based on integral representations for the diffracted and the refracted elastic waves using single‐layer boundary sources. This approach is called indirect BEM in the literature as the sources' strengths should be obtained as an intermediate step. Boundary conditions lead to a system of integral equations for boundary sources. A discretization scheme based on the numerical and analytical integration of exact Green's functions for displacements and tractions is used. Various examples are given for two‐dimensional problems of diffraction of elastic waves by soft elastic inclusion models of alluvial deposits in an elastic half‐space. Results are displayed in both frequency and time domains. These results show the significant influence of locally generated surface waves in seismic response and suggest approximations of practical interest. For shallow alluvial valleys the response and its resonant frequencies are controlled by a coupling mechanism that involves both the simple one‐dimensional shear beam model and the propagation of surface waves.
Damped resonant appendages to increase inherent damping in buildings
Authors: Villaverde Roberto , Koyama Leslie A.
Published: April 2007

It is demonstrated that the addition of a tuned mass‐spring‐dashpot system with a relatively small mass and a high damping ratio can be an effective way to increase the inherent damping characteristics of buildings and reduce, thus, their response to earthquake excitations. The demonstration is based on a theoretical formulation and on numerical and experimental studies that confirm this formulation. In the theoretical formulation, it is shown first that, if certain conditions are satisfied, the damping ratios in two of the modes of the system that is formed by a building and an appendage in resonance are approximately equal to the average of the corresponding damping ratios of the building and the appendage. Based on this finding, it is then shown that an attached appendage with a high damping ratio and tuned to the fundamental frequency of a building may increase the damping ratio in the fundamental mode of the building to a value close to half the damping ratio of the appendage. In the numerical study, the response of a ten‐storey shear building is analysed under two different earthquake ground motions with and without the proposed resonant appendages. Appendages with damping ratios of 20 and 30 per cent are considered. In this study, it is found that under one of the ground motions the maximum displacement of the building's roof is reduced 30 per cent with the appendage with 20 per cent damping and 39 per cent with the one with 30 per cent damping. Similarly, with these two appendages the building's base shear is reduced 31 and 41 per cent, respectively. In the experimental study, a wooden three‐storey structural model is tested in a shaking table with and without an appendage designed and constructed to have a damping ratio of 53‐5 per cent. The test is conducted under random and sinusoidal base excitations. In the shaking table test under random excitation, the attached appendage reduces the response of the model 38‐6 per cent, while in that under sinusoidal vibration 45‐2 per cent.
Modelling of material non‐linearities in steel structures subjected to transient dynamic loading
Authors: Elnashai A. S. , Izzuddin B. A.
Published: April 2007

This paper is concerned with the modelling of the behaviour of steel under cyclic and dynamic loading conditions. After a general discussion regarding the requirements for accurate and efficient modelling in dynamics, two models are described and implemented. The bilinear stress‐strain constitutive relationship with kinematic hardening is widely used in many computer codes, hence is used for ‘control’ purposes. The multisurface plasticity model is said to exhibit the important qualities of strain hardening, softening and relaxation to a mean stress. This model is described in detail and notes on model parameter evaluation are given. A number of validation examples are presented, due to the complexity of implementation of the multisurface formulation. This is followed by comparisons between the bilinear response predictions and those of the multisurface model for cyclic and dynamic tests on beam‐columns. It is concluded that in the absence of material test data under cyclic loading, the bilinear model provides acceptably accurate response predictions. However, the multisurface model provides a significantly closer fit to experimental results, due to its ability to model a yield plateau and a non‐linear strain‐hardening regime as well as cyclic degradation. It can also be used for new types of steel where no distinct yield point is observed.