bluuebunny/crossref_metadata_2025_split huggingface dataset:
Integrin signaling in early sea urchin development
Authors: Burke Robert Douglas , Brothers Elizabeth , Matviw Andrea 
Published: April 2007

AbstractThe eggs and cleavage stage embryos of many animals express integrins and signal transduction components, yet comparatively little is known of the signaling complexes formed or the role of integrin signaling in early development. Genomic approaches have revealed the complement of integrin signaling components expressed in early sea urchin development. We review what is known about the distribution and function of integrins, integrin ligands, and integrin signal transduction proteins expressed during this critical phase of development. Immediately after fertilization integrins are expressed on the apical surface of the egg where the receptors interact with several potential ligands in the hyaline layer. The apical integrin complex is essential for reorganization of the egg cortex. During cleavage the blastocoel forms and a second integrin complex forms on the basal surface of blastomeres interacting with basal lamina components of the extracellular matrix. The integrin subunits of the apical and basal complexes differ and localization data indicate the apical and basal complexes may contain different scaffolding proteins and different kinases. We propose that there are two independent integrin‐based signaling complexes formed during cleavage and blastula formation that may have distinct and essential functions in early development. The sea urchin is an excellent model for studies of these pathways and a number of approaches are available to determine their roles in early development.
“Birth of the cool”: Using sea urchin zygotes to study centrosome duplication, cell division, and cytokinesis
Authors: Halpin Elizabeth S. , Hinchcliffe Edward H. 
Published: April 2007

AbstractThe successful division of the cell depends on several morphological events that must be coordinated in a cell cycle dependent fashion. Crucial to this process is the remodeling of the cytoskeleton to both establish the bipolar spindle during mitosis, and cleave the cell into two daughters during cytokinesis. From the standpoint of the cytoskeleton, this process begins during interphase with the duplication of the centrosome; it is the two daughter centrosomes that will assemble the poles of the mitotic spindle and establish its necessary bipolarity. Following the cell cycle transition into mitosis, the spindle must assemble in order to properly align the sister chromatids at the center of the cell, and release the “wait anaphase checkpoint”. As the spindle transports the disjoined sister chromatids to the spindle poles, the cell must rapidly undergo cytokinesis, cleaving the cell into two – the plane of cleavage being established by the spindle itself. Understanding the temporal regulation and molecular basis for these events has come from extensive experiments using a variety of model systems, and has benefited from cell biological, molecular genetic, and biophysical approaches. One of the earliest and most important model systems for studying mitosis is the sea urchin zygote. With their large size, rapid/synchronous cell cycles, and advantages for conduct of biochemical and cytological investigations on the same system, fertilized sea urchin eggs have revealed many of the fundamental properties of centrosome duplication, cell division and cytokinesis. Here we review several key studies that have utilized the sea urchin zygote to explore mechanisms that coordinate and drive two of the major cytoskeletal events of mitotic division – centrosome duplication and cytokinesis.
Protein and lipid signaling in membrane fusion: nuclear envelope assembly
Authors: Larijani Banafshé , Poccia Dominic 
Published: April 2007

AbstractMembrane fusion is important in many cell processes including membrane trafficking, mitotic reconstitution of organelles, viral infection and fertilization. Several fusion events occur just prior and subsequent to fertilization in the sea urchin, including the sperm acrosomal reaction, fusion of sperm and egg plasma membranes, exocytosis of cortical granules, reassembly of the sperm nuclear envelope and fusion of the male and female pronuclear envelopes leading to the zygote nucleus of the one‐cell embryo. The study of male pronuclear membrane dynamics with cell‐free extracts of fertilized sea urchin eggs has revealed several novel features, in particular a structural role arising from altering phospholipids prior to nuclear membrane formation. Fusion of chromatin‐bound membrane vesicles in vitro can be triggered by either GTP hydrolysis or exogenous phosphatidyl inositol phospholipase C (PI‐PLC). Recent data strongly implicate a role for diacylglycerol in nuclear envelope formation as a structural destabilizing lipid in membrane fusion. Moreover, the endogenous enzyme, PI‐PLCγ, is >100‐fold enriched in a nuclear envelope precursor vesicle population (MV1) that is required for nuclear envelope assembly. NMR and mass spectrometry analyses show that MV1 contains high levels of phosphoinositides, including the substrate of PLCγ, compared to the other nuclear envelope precursor membranes. MV1 exists in eggs as vesicles in the cortex distinct from the endoplasmic reticulum which contributes most of the nuclear envelope membrane. PLCγ is activated by a tyrosine kinase in response to GTP hydrolysis at an early stage of nuclear envelope formation suggesting a role in initiation of fusion and revealing aspects of a signaling mechanism leading to fusion. The binding of MV1 to two poles of the sperm nucleus offers spatial as well as temporal control of the initiation phase.
Control of intelligent nonlinear adaptive systems under earthquake excitation
Authors: Masri S. F. , Chavakula S. , Caughey T. K. 
Published: April 2007

AbstractA semi‐active control procedure which utilizes a class of nonlinear auxiliary mass dampers with adaptive parameters is presented. Among the major features of this approach is its simplicity, robustness, and lack of need of a mathematical model of the structure whose motion is to be controlled. Numerical simulation results as well as experimental studies with a simple laboratory test structure (reported in a cited reference) demonstrate the feasibility of the proposed approach.
Robustly stable active structural control
Authors: Kozodoy D. A. , Spanos P. D. 
Published: April 2007

AbstractDue to various model uncertainties, most existing control strategies may lead to arbitrarily small stability margins. This paper presents anH2/H2nested control synthesis which combines advantages of the classicalH2andH2‐approaches, and guarantees robust stability. SpecialH2‐maximum andH2‐ultimate system norms are introduced by generalizing the concept of the standardL1,H2andH2norms. These norms reduce the conservatism of the control design specifications while retaining all the benefits of the standardH2‐norm. Both stochastic and deterministic interpretations are addressed. The effectiveness of the new method is illustrated by a numerical example.
Nonlinear response of structures with sliding base isolation
Authors: Bozzo L. , Barbat A. H. 
Published: April 2007

AbstractIt is accepted that sliding or friction base isolation systems effectively protect structures subjected to severe earthquakes. Precise modeling of the sliding connection is, however, still difficult since various parameters influence the friction coefficient. Simplified models, such as those based on a constant friction coefficient, are convenient to understand the behavior of sliding structures and to identify general trends. However, this article shows that for final structural designs (and in particular if the building enters in the nonlinear range) these trends should be used carefully. The purpose of the article is to discuss the general behavior of structures supported on sliding connections and to describe a simple numeric model to take into account variations in the friction coefficient. The numeric model enables to represent complex force‐displacement relationships for the sliding bearings. The model is used to perform a preliminary evaluation of the influence in the response caused by changes in the friction coefficient for elastic and elasto‐plastic structures. The variations in the friction coefficient are obtained from experimental testing for a class of teflon‐based connections.
Chaotic behaviour of hysteretic oscillators
Authors: Battaini M. , Casciati F. 
Published: April 2007

AbstractAttention is focused on low‐damping‐rubber base‐isolators. Instead of thinking in terms of intelligent materials, this paper pursues the definition of conditions of behaviour which result intelligent in view of a coupling with an active control device (hybrid control). In particular, situations which show a chaotic behaviour of the dynamic response to external excitations are promising in terms of control efficiency. The regions of chaotic behaviour are identified by evaluation of the corresponding Lyapunov exponents.
The main sources of helicopter vibration and noise emissions and adaptive concepts to reduce them
Authors: Breitbach E. , Büter A. 
Published: April 2007

AbstractThis paper deals with the sources of helicopter vibration and noise emissions. It shows and evaluates adaptive concepts to reduce them. The main reasons for these emissions are aerodynamic effects such as blade‐vortex‐inter action (BVI), aerodynamic hysteresis, and local transonic effects at the forward moving blade.After a review of conventional control concepts to reduce the vibrations and/or sound emissions, the possibilities to realise an adaptive rotorblade are explained.The understanding of the interaction between the aerodynamic sources and the resulting vibrations and noise is the basis of the design of optimal control concepts.
Hybrid feedback‐feedforward control for vibration suppression
Authors: de Man Pierre , Preumont André 
Published: April 2007

AbstractThis paper evaluates a hybrid feedback‐feedforward controller for vibration suppression. The synergy between the two types of controllers is pointed out. The feedforward control extends the bandwidth of the controller for steady state disturbances with a correlated reference, while the feedback control reduces drastically the impulse response of lightly damped structures, avoiding the problems associated with truncation. The hybrid controller does not require additional actuator and sensor. Two applications are presented in the area of vibration attenuation and precision pointing. In each case the theoretical advantage of the hybrid controller is confirmed by experiments.
On krylov matrices and controllability of n‐dimensional linear time‐invariant state equations
Authors: Maćkiewicz Andrzej , Almansa Francisco López , Inaudi José A. 
Published: April 2007

AbstractThe classical Rosenbrock's algorithm (based on the Gauss elimination method) for n‐dimensional linear time invariant state equation matrices is analysed and modernized. The method of orthogonal similarity reduction to block Hessenberg form is used to assure numerical stability. The updated version of the Rosenbrock's algorithm is then justified in a very easy way using properties of Krylov matrices. Additionally, this algorithm can be used to determine an equivalence transformation which converts an n‐dimensional linear state equation into a controllable form (or a time invariant one into an equivalent observable form). It is advantageous for big and medium size problems and can be easily parallelized. Numerical examples are presented.
Feedback controllers for active vibration suppression
Authors: Petitjean B. , Legrain I. 
Published: April 2007

AbstractThe aim of the present paper is to investigate two strategies for the active control of plate vibrations, using distributed sensors and actuators (PVDF patches) working on a wide frequency band. The two strategies correspond to the two ends of a spectrum ranging from very robust/less efficient schemes (analog static output feedback) to less robust/very efficient schemes (here ‘frequency shaped LQG’).Both have been experimentally tested and have given successful attenuations; the efficiency of both approaches is demonstrated on sensor signals involved in the control loop as well as on radiated pressure measurements, which constitute an independent index of performance.It is shown that ‘frequency shaped LQG’ is a viable approach to feedback control of lightly damped structures, and that its robustness can be enhanced through a careful design.LQG is a model‐based method, and hence requires the modeling of the active structure. Two approaches are investigated in this paper: a finite element model and a identified model built from the experimentally measured transfer functions.
Response of base isolated systems equipped with tuned mass dampers to random excitations
Authors: Palazzo B. , Petti L. , de Ligio M. 
Published: April 2007

AbstractA new structural system conceived to control Base Isolated System vibrations under random excitations is analyzed. The new system combines the Tuned Mass Damping strategy with the Isolation concept in order to obtain a new system which principally attenuates the effects of the seismic excitation components with frequencies close to the fundamental natural vibration one. The Random response of equivalent linear Base Isolated Systems controlled by Tuned Mass Dampers subject to horizontal random excitations is analyzed. Considering the superstructure motion described by its first modal contribution, a three‐degree‐of‐freedom linear model subject to stationary Gaussian excitations, modelled by the modified Kanai‐Tajimi power density spectrum, was used in this analysis. The standard deviation response ratio of the new system respect to the one of the base isolated system was evaluated based on a wide range of parameters. Optimal parameters which minimize structural response were also obtained.
Active control of drillstring vibrations by mode localization
Authors: Yigit A. S. , Al‐Ansary M. D. , Khalid M. 
Published: April 2007

AbstractA method of controlling vibrations in a drillstring is proposed. The method is based on altering the system eigenstructure by feedback such that the closed loop system mode shapes are spatially confined to small geometric regions. Both active and passive means can be used to realize the resulting designs. Simulations are used to show the effect of limited actuator placement and robustness to parameter uncertainties.
Effects of structural uncertainties on TMD design: A reliability‐based approach
Authors: Papadimitriou C. , Katafygiotis L. S. , Au Siu‐Kui 
Published: April 2007

AbstractThis study investigates the effects of structural uncertainties on the design and performance evaluation of passive tuned mass dampers (TMD) used for vibration control. A probabilistic optimal design methodology is presented in which time‐invariant uncertain structural parameters are modelled by random variables with prescribed probability distribution. Unlike conventional TMD designs based on minimizing the mean‐square response, a reliability‐based performance index is considered in the proposed design which properly accounts for uncertainties in load and structural models. An approximate asymptotic expansion is used to compute the multidimensional reliability integrals arising in the proposed optimal design methodology. Accuracy and effectiveness issues are addressed by comparing results obtained using this approximation with corresponding results obtained by numerical integration. The importance of structural uncertainties is demonstrated by applying the methodology to a single degree of freedom structure subjected to broadband excitations that are modelled by stationary white noise. It is found that the consideration of structural uncertainties improves substantially the robustness of the TMD design. Also, the reliability‐based TMD‐design methodology results into significantly larger structural reliability compared to that obtained by the conventional design approach based on minimizing the mean‐square response.
Concept of super‐high‐rise building (DIB‐200)
Authors: Kobori Takuji , Ban Shigeru , Kubota Toshihiko , Yamada Kazuhiko 
Published: April 2007

AbstractThis report presents an overall study on how the concept of a 200‐story super‐high‐rise building can be realized. In the beginning, various planning requirements appertaining to the architecture, appurtenant utilities, disaster prevention, and construction are briefly discussed. Next, structural studies, i.e. design criteria, external loads requiring study, and the results of response analyses, are described in more detail. Examination of these items confirms that it is possible to construct a 200‐story super‐high‐rise building by applying the currently available technology. However, it is found that a seismic response control system is essential for improving the living comfort of such a building.
Free spanning ductile vierendeel frame: A system for high‐rise buildings in seismic areas
Authors: Banavalkar P. V. 
Published: April 2007

AbstractThe paper has described the composition and structural behavior of a free spanning ductile frame system to be used in seismic areas. The inelastic performance, ductility, and redundancy of the system is compared with a conventional ductile moment resisting frame. It is shown that the structural performance of the system is equal or better than the conventional system. The paper also describes successful application of the system to commercial high‐rise buildings.
Tuned‐pendulum mass damper installed in crystal tower
Authors: Nagase Tadashi , Hisatoku Toshiharu 
Published: April 2007

AbstractA new damper to reduce the lateral vibration of buildings has been developed and installed in a 37‐story office building: Crystal Tower, Osaka. The tower has a slender proportion of height—width ratio 6. The damper can decrease wind‐induced motion by 50%. Crystal Tower is the first high‐rise building with this damper in Japan, and the damper weight, 540 tons (1190 kips), is large compared with others in use elsewhere in the world. The damper is a pendulum‐type tuned‐mass damper and the ice thermal storage tanks for air conditioning are used as the moving mass of the damper. The TMD of Crystal Tower, therefore, needs no additional mass weight nor space for installing. This paper presents some intrinsic features of the damper and demonstrates how simple and practical the damper is. Special considerations are given both to the connecting joints between the tank and the building and also to the sloshing behavior of the liquid contents. Typhoon and earthquake records observed in Crystal Tower have proved that the damper works as well as expected.
Experimental testing of ductile cladding connections for building facades
Authors: Pinelli Jean‐Paul , Moor Christian , Craig James I. , Goodno Barry J. 
Published: April 2007

AbstractA ductile cladding connection is a special connecting device between a facade cladding panel and a building structure that is designed to dissipate energy when subjected to an earthquake. The effect of such a device is to reduce the overall seismic response of the structure. A special testing machine was designed to test the behavior of these advanced cladding connections. The machine, which is specially suited for the recording and evaluation of ductility and damping properties, is described. Its main characteristics are both the ability to load a specimen in shear simultaneously in two orthogonal directions without inducing any axial stress, and the flexibility to test a wide variety of different damping mechanisms with different geometric configurations. The machine was used to test a family of advanced cladding connections that employs ductile flexural action to achieve high and stable levels of ductility for repeated cyclic load applications. A lumped‐parameter mechanical model for these connections was identified from selected test data, and the predicted cyclic behavior was shown to agree well with test data. The model is simple and suitable for incorporation into nonlinear structural analysis programs.
Masonry wall frame design and performance
Authors: Hart Gary C. , Priestley M. J. Nigel , Seible Frieder 
Published: April 2007

AbstractTall masonry building in active seismic or severe wind regions have typically been designed as shear wall buildings. This paper presents an alternative lateral force resisting system cailed a wall frame. This new masonry system is particularly advantageous for seismic and windy regions because it utilizes the nonlinear inelastic load deformation characteristics of the masonry beams and is thus a ductile system. Basic design assumptions and experimental test data are presented.
Dynamic characteristics of five tall buildings during strong and low‐amplitude motions
Authors: Çlelebi M. , Phan L. T. , Marshall R. D. 
Published: April 2007

AbstractThe objectives of this paper are to present (1) a comparison of dynamic characteristics of five buildings determined from recorded strong‐motion response data and from low‐amplitude (ambient vibration) tests, and (2) a description of the low‐amplitude ambient testing and PC‐based data‐acquisition approach that is integrated with the permanent strong‐motion instrumentation in the five buildings. All five buildings are within the San Francisco Bay area and the strong‐motion dynamic characteristics are extracted from the October 17, 1989 Loma Prieta earthquake response records. Ambient vibration tests on the same five buildings were conducted in September 1990. Analyses of strong‐motion response and low‐amplitude test data have been performed by many investigators. The present study differs from numerous previous investigations because (1) in this study, accelerometers in the five permanently‐instrumented buildings were used during the low‐amplitude testing, and (2) rapid screening of the strong‐motion response data was achieved with a concerted use of system identification software. The results show for all cases that the fundamental periods and corresponding percentages of critical damping determined from low‐amplitude tests are appreciably lower than those determined from strong‐motion response records. The data set collected during this study is a useful contribution to the data base of dynamic characteristics of engineered structures and reconfirms the differences between the dynamic characteristics identified from strong‐motion records and from low‐amplitude tests.
An efficient resizing technique for the design of tall steel buildings subject to multiple drift constraints
Authors: Chan Chun‐Man , Grierson Donald E. 
Published: April 2007

AbstractThis paper presents an efficient resizing technique for the optimum design of tall steel building frameworks. Specifically, an ‘optimality criteria’ method is applied to minimize the weight of a lateral load‐resisting structural system of fixed topology subject to constraints on interstorey drift. By exploiting the fact for building frameworks that member forces are relatively insensitive to changes in member sizes, rigorously‐derived optimality criteria are shown to be readily satisfied through an iterative pseudo‐discrete optimization procedure that converges in but a few cycles to a least‐weight design using commercial‐standard steel sections. While not considered herein, it is a simple matter to extend the stiffness‐based design procedure to account also for strength requirements. Two building framework examples are presented to illustrate the features of the design optimization method.