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Sliding
Kinds of Sliding Terms modified by Sliding Selected AbstractsSliding,window neural state estimation in a power plant heater lineINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 8 2001A. Alessandri Abstract The state estimation problem for a section of a real power plant is addressed by means of a recently proposed sliding-window neural state estimator. The complexity and the nonlinearity of the considered application prevent us from successfully using standard techniques as Kalman filtering. The statistics of the distribution of the initial state and of noises are assumed to be unknown and the estimator is designed by minimizing a given generalized least-squares cost function. The following approximations are enforced: (i) the state estimator is a finite-memory one, (ii) the estimation functions are given fixed structures in which a certain number of parameters have to be optimized (multilayer feedforward neural networks are chosen from among various possible nonlinear approximators), (iii) the algorithms for optimizing the parameters (i.e., the network weights) rely on a stochastic approximation. Extensive simulation results on a complex model of a part of a real power plant are reported to compare the behaviour of the proposed estimator with the extended Kalman filter. Copyright © 2001 John Wiley & Sons, Ltd. [source] Experimental Evidence for Grain-Boundary Sliding in Ultrafine-Grained Aluminum Processed by Severe Plastic Deformation,ADVANCED MATERIALS, Issue 1 2006Q. Chinh Evidence for grain boundary sliding in ultrafine-grained aluminum after processing with equal channel angular pressing (ECAP) is presented (see Figure). Pure aluminum is used as a model material; depth sensing indentation testing and atomic force microscopy are used to measure the nature of the displacements around indentations for samples in an annealed and work-hardened condition, and after processing using ECAP. [source] Phylogenetic inference regarding Parergodrilidae and Hrabeiella periglandulata (,Polychaeta', Annelida) based on 18S rDNA, 28S rDNA and COI sequencesJOURNAL OF ZOOLOGICAL SYSTEMATICS AND EVOLUTIONARY RESEARCH, Issue 4 2004J. Jördens Abstract Parergodrilidae and Hrabeiella periglandulata are Annelida showing different combinations of clitellate-like and aclitellate characters. Similarities between both of these taxa and Clitellata have widely been regarded as the result of convergent evolution due to similar selection pressures. The position of the three taxa in the phylogenetic system of Annelida is still in debate. However, in analyses based on 18S rDNA sequences a close relationship of Parergodrilidae with Orbiniidae and Questidae was suggested. To infer their phylogeny the sequences of the 28S rDNA and of the cytochrome oxidase I (COI) gene of Stygocapitella subterranea, Parergodrilus heideri and H. periglandulata were determined. The data were extended by sequences of various species including species from Clitellata and Orbiniidae. Prior to tree reconstruction the dataset was analysed in detail for phylogenetic content by applying a sliding window analysis, a likelihood mapping and Modeltest V.3.04. Subsequently, generalized parsimony and maximum likelihood methods were employed. Clade robustness was estimated by bootstrapping. In addition, combined analyses of the sequences of 18S rDNA and 28S rDNA as well as of 18S rDNA, 28S rDNA and COI were performed. The combination of the data of the two structure genes and a mitochondrial gene improved the resolution obtained with the single datasets slightly. These analyses support a close relationship of Parergodrilidae and Orbiniidae but cannot resolve the position of H. periglandulata. In every analysis Clitellata cluster within ,Polychaeta', confirming previous investigations. Zusammenfassung Die Parergodrilidae und Hrabeiella periglandulata sind Annelida, die unterschiedliche Kombinationen von Clitellaten- und Nicht-Clitellaten-Merkmalen aufweisen. Die Übereinstimmungen zwischen Parergodrilidae, H. periglandulata und Clitellata sind jedoch meistens als Ergebnis konvergenter Evolution auf Grund ähnlicher Selektionsdrücke gedeutet worden. Die Stellung der drei Taxa im phylogenetischen System der Annelida ist noch immer in Diskussion. Analysen, die auf 18S rDNA Sequenzen basieren, weisen jedoch auf eine wahrscheinliche engere Verwandtschaft der Parergodrilidae mit den Orbiniidae und Questidae hin. Um die Phylogenie dieser Taxa aufzuklären, wurden die Sequenzen der 28S rDNA und des COI Gens von Stygocapitella subterranea, P. heideri and H. periglandulata bestimmt. Die Daten wurden durch Sequenzen verschiedener weiterer Arten erweitert, die auch Arten der Clitellata und Orbiniidae umfassen. Vor der phylogenetischen Rekonstruktion wurde der Datensatz im Detail auf das enthaltene phylogenetische Signal durch eine Sliding Window Analyse, ein Likelihood Mapping und Modeltest V.3.04 getestet. Anschließend wurden generalisierte Parsimonie und Maximum Likelihood Methoden angewendet. Die Robustheit der Bäume wurde durch Parsimonie-Bootstrapping abgeschätzt. Zusätzlich wurden kombinierte Analysen der Sequenzen von 18S rDNA und 28S rDNA als auch von 18S rDNA, 28S rDNA und COI durchgeführt. Die Kombination der Daten der beiden Strukturgene und eines mitochondrialen Gens verbesserten geringfügig die Auflösung verglichen mit den Einzelanalysen. Diese Analysen unterstützen eine nahe Verwandtschaft der Parergodrilidae mit den Orbiniidae aber die Stellung von H. periglandulata kann nicht angegeben werden. In jeder Analyse bilden die Clitellata ein Cluster innerhalb der ,Polychaeta', eine Bestätigung früherer Untersuchungen. [source] Introital ultrasonography: a comparison of women with stress incontinence due to urethral hypermobility and continent womenBJU INTERNATIONAL, Issue 4 2006Jordi Cassadó OBJECTIVE To determine if there is a variable on introital ultrasonography (IUS) that can be used to distinguish between women with stress urinary incontinence (SUI) due to urethral hypermobility (UH) and continent women. PATIENTS AND METHODS This single-centre, prospective, blind, cohort, observational study comprised 383 women (245 continent and 138 incontinent) who were all appropriately informed volunteers selected according to the inclusion criteria. IUS with a convex probe was performed on all women; the measurement plane was standardized and coordinates were obtained at rest and on straining. Several distances were measured to determine if any provided an objective distinction between continent and incontinent women. RESULTS Among all the IUS variables assessed, sliding (calculated as the difference between the distance urethra-bladder neck, U-BN, at rest and under stress) was the best for distinguishing continent and incontinent women. The receiver operating characteristic curves showed that with a threshold of 8 mm, sliding had a sensitivity of 92% and a specificity of 79.6% for detecting SUI due to UH. The distances symphysis-urethra (S-U) and U-BN at rest could also discriminate, but with lower significance. CONCLUSIONS IUS is an important tool for diagnosing SUI; there are three independent variables, one dynamic (sliding) and two static (distances S-U and U-BN), that can be used to distinguish between continent women and those with SUI due to UH. Sliding is the most reliable, as it has the highest sensitivity and specificity. We think that the simplicity, low financial cost and reliability of IUS could allow it to be a routine procedure for physicians working in incontinence units. [source] Effect of Oxygen on Methane Steam Reforming in a Sliding Discharge ReactorCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 5 2006F. Ouni Abstract Hydrogen-rich gas can be efficiently produced in compact plasma reformers by the conversion of a variety of hydrocarbon fuels, including natural gas and gasoline. This article describes experimental and modeling progress in plasma reforming of methane using a sliding discharge reactor (SDR). Experiments have been carried out in a compact device operating at low consumed power (1,2,kW). Previous studies of methane steam reforming using a SDR at atmospheric pressure show promising results (H2 concentration higher than 55,%). In order to study the effect of oxygen on the methane conversion and thus hydrogen production, a small amount of oxygen in the range of 7,20,% was added to the CH4 -H2O mixture. An unexpected result was that under our experimental conditions in the SDR oxygen did not have any influence on the methane conversion. Almost the totality of added oxygen is recovered intact. Moreover, part of the H2 produced was transformed into water by reaction with O2. A model describing the chemical processes based on classical thermodynamics is also proposed. The results indicate that the reactor design has to be improved in order to increase conversion and hydrogen production. [source] Molecular-Recognition and Binding Properties of Cyclodextrin-Conjugated PolyrotaxanesCHEMPHYSCHEM, Issue 8 2006Hak Soo Choi Dr. Sliding and rotation of cyclodextrins (CDs) along the polymer main chain of polyrotaxanes significantly increases the binding ability for and molecular recognition of guest molecules by multifaceted inclusion complexation (see schematic diagram). The cyclodextrin-conjugated polyrotaxanes were obtained by attaching ,-CDs to an ,-CD/poly(ethylene glycol) polyrotaxane backbone via peptide bonds. [source] Fast simulation of skin slidingCOMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 2-3 2009Xiaosong Yang Abstract Skin sliding is the phenomenon of the skin moving over underlying layers of fat, muscle and bone. Due to the complex interconnections between these separate layers and their differing elasticity properties, it is difficult to model and expensive to compute. We present a novel method to simulate this phenomenon at real-time by remeshing the surface based on a parameter space resampling. In order to evaluate the surface parametrization, we borrow a technique from structural engineering known as the force density method (FDM)which solves for an energy minimizing form with a sparse linear system. Our method creates a realistic approximation of skin sliding in real-time, reducing texture distortions in the region of the deformation. In addition it is flexible, simple to use, and can be incorporated into any animation pipeline. Copyright © 2009 John Wiley & Sons, Ltd. [source] Improving realism of a surgery simulator: linear anisotropic elasticity, complex interactions and force extrapolationCOMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 3 2002Guillaume Picinbono Abstract In this article, we describe the latest developments of the minimally invasive hepatic surgery simulator prototype developed at INRIA. The goal of this simulator is to provide a realistic training test bed to perform laparoscopic procedures. Therefore, its main functionality is to simulate the action of virtual laparoscopic surgical instruments for deforming and cutting tridimensional anatomical models. Throughout this paper, we present the general features of this simulator including the implementation of several biomechanical models and the integration of two force-feedback devices in the simulation platform. More precisely, we describe three new important developments that improve the overall realism of our simulator. First, we have developed biomechanical models, based on linear elasticity and finite element theory, that include the notion of anisotropic deformation. Indeed, we have generalized the linear elastic behaviour of anatomical models to ,transversally isotropic' materials, i.e. materials having a different behaviour in a given direction. We have also added to the volumetric model an external elastic membrane representing the ,liver capsule', a rather stiff skin surrounding the liver, which creates a kind of ,surface anisotropy'. Second, we have developed new contact models between surgical instruments and soft tissue models. For instance, after detecting a contact with an instrument, we define specific boundary constraints on deformable models to represent various forms of interactions with a surgical tool, such as sliding, gripping, cutting or burning. In addition, we compute the reaction forces that should be felt by the user manipulating the force-feedback devices. The last improvement is related to the problem of haptic rendering. Currently, we are able to achieve a simulation frequency of 25,Hz (visual real time) with anatomical models of complex geometry and behaviour. But to achieve a good haptic feedback requires a frequency update of applied forces typically above 300,Hz (haptic real time). Thus, we propose a force extrapolation algorithm in order to reach haptic real time. Copyright © 2002 John Wiley & Sons, Ltd. [source] Strikingly fast microtubule sliding in bundles formed by Chlamydomonas axonemal dynein,CYTOSKELETON, Issue 6 2010Susumu Aoyama Abstract Chlamydomonas axonemal extracts containing outer-arm dynein bundle microtubules when added in the absence of ATP. The bundles dissociate after addition of ATP (Haimo et al., Proc Natl Acad Sci USA 76:5759,5768, 1979). In the present study, we investigated the ATP-induced bundle dissociation process using caged ATP. Application of ,0.5 mM ATP induced microtubule sliding at ,30 ,m·s,1, which was 1.5 times faster than the microtubule sliding observed in protease-treated axonemes and five times faster than microtubule gliding on glass surfaces coated with outer-arm dynein. Bundles formed by mutant dynein molecules that lack one of the three heavy chains (HCs) displayed similar high-speed intermicrotubule sliding. These results suggest that Chlamydomonas outer-arm dynein molecules, when aligned, can translocate microtubules at high speed and that the high-speed sliding under load-free conditions does not require the complete set of the three HCs. It is likely that each of the three HCs has the ability to produce high-speed sliding, which should be an important property for their cooperation. © 2010 Wiley-Liss, Inc. [source] Thinking about flagellar oscillationCYTOSKELETON, Issue 8 2009Charles J. Brokaw Abstract Bending of cilia and flagella results from sliding between the microtubular outer doublets, driven by dynein motor enzymes. This review reminds us that many questions remain to be answered before we can understand how dynein-driven sliding causes the oscillatory bending of cilia and flagella. Does oscillation require switching between two distinct, persistent modes of dynein activity? Only one mode, an active forward mode, has been characterized, but an alternative mode, either inactive or reverse, appears to be required. Does switching between modes use information from curvature, sliding direction, or both? Is there a mechanism for reciprocal inhibition? Can a localized capability for oscillatory sliding become self-organized to produce the metachronal phase differences required for bend propagation? Are interactions between adjacent dyneins important for regulation of oscillation and bend propagation? Cell Motil. Cytoskeleton 2008. © 2008 Wiley-Liss, Inc. [source] Membrane associated nonmuscle myosin II functions as a motor for actin-based vesicle transport in clam oocyte extractsCYTOSKELETON, Issue 10 2007Ana S. DePina Abstract Nonmuscle myosin II (Myo2) has been shown to associate with membranes of the trans -Golgi network and to be involved in Golgi to ER retrograde protein transport. Here, we provide evidence that Myo2 not only associates with membranes but functions to transport vesicles on actin filaments (AFs). We used extracts from unactivated clam oocytes for these studies. AFs assembled spontaneously in these extracts and myosin-dependent vesicle transport was observed upon activation. In addition, actin bundles formed and moved relative to each other at an average speed of ,0.30 ,m/s. Motion analysis revealed that vesicles moved on the spontaneously assembled AFs at speeds greater than 1 ,m/s. The motor on these vesicles was identified as a member of the nonmuscle Myo2 family based on sequence determination by Edman chemistry. Vesicles in these extracts were purified by sucrose gradient centrifugation and movement was reconstituted in vitro using skeletal muscle actin coated coverslips. When peripheral membrane proteins of vesicles including Myo2 were removed by salt stripping or when extracts were treated with an antibody specific to clam oocyte nonmuscle Myo2, vesicle movement was inhibited. Blebbistatin, a Myo2 specific inhibitor, also blocked vesicle movement. Myo2 light chain kinase activity was found to be essential for vesicle movement and sliding of actin bundles. Together, our data provide direct evidence that nonmuscle Myo2 is involved in actin-dependent vesicle transport in clam oocytes. Cell Motil. Cytoskeleton 2007. © 2007 Wiley-Liss, Inc. [source] Evidence for a sliding-resistance at the tip of the trypanosome flagellumCYTOSKELETON, Issue 12 2006David Woolley Abstract Motility in trypanosomes is achieved through the undulating behaviour of a single "9 + 2" flagellum; normally the flagellar waves begin at the flagellar tip and propagate towards the base. For flagella in general, however, propagation is from base-to-tip and it is believed that bend formation, and sustained regular oscillation, depend upon a localised resistance to inter-doublet sliding - which is normally conferred by structures at the flagellar base, typically the basal body. We therefore predicted that in trypanosomes there must be a resistive structure at the flagellar tip. Electron micrographs of Crithidia deanei, Herpetomonas megaseliae, Trypanosoma brucei and Leishmania major have confirmed that such attachments are present. Thus, it can be assumed that in trypanosomes microtubule sliding at the flagellar tip is resisted sufficiently to permit bend formation. Cell Motil. Cytoskeleton 2006. © 2006 Wiley-Liss, Inc. [source] High speed sliding of axonemal microtubules produced by outer arm dyneinCYTOSKELETON, Issue 2 2005Raviraja N. Seetharam Abstract To study dynein arm activity at high temporal resolution, axonemal sliding was measured field by field for wild type and dynein arm mutants of Tetrahymena thermophila. For wt SB255 cells, when the rate of data acquisition was 60 fps, about 5× greater than previously published observations, sliding was observed to be discontinuous with very high velocity sliding (average 196 ,m/sec) for a few msec (1 or 2 fields) followed by a pause of several fields. The sliding velocities measured were an order of magnitude greater than rates previously measured by video analysis. However, when the data were analyzed at 12 fps for the same axonemes, consistent with previous observations, sliding was linear as the axonemes extended several times their original length with an average velocity of ,10 ,m/sec. The pauses or stops occurred at approximately 200 and 300% of the initial length, suggesting that dynein arms on one axonemal doublet were initially active to the limit of extension, and then the arms on the next doublet became activated. In contrast, in a mutant where OADs are missing, sliding observed at 60 fps was continuous and slow (5 ,m/sec), as opposed to the discontinuous high-velocity sliding of SB255 and of the mutant at the permissive temperature where OADs are present. High-velocity step-wise sliding was also present in axonemes from an inner arm dynein mutant (KO6). These results indicate that the high-speed discontinuous pattern of sliding is produced by the mechanochemical activity of outer arm dynein. The rate of sliding is consistent with a low duty ratio of the outer arm dynein and with the operation of each arm along a doublet once per beat. Cell Motil. Cytoskeleton 60:96,103, 2005. © 2004 Wiley-Liss, Inc. [source] Microtubule displacements at the tips of living flagellaCYTOSKELETON, Issue 3 2002Geraint G. Vernon Abstract We have observed that the flagellar axoneme of the Chinese hamster spermatozoon undergoes periodic changes in length at the same frequency as the flagellar beat. The amplitude of the length oscillation recorded at the tip is maximally about 0.5 ,m or 0.2% of the total length. In some favourable cells, it was possible to see the opposing "halves" of the axoneme moving at the tip in a reciprocating manner and 180° out-of-phase. This behaviour, when analysed quantitatively, is broadly consistent with predictions made from the sliding-doublet theory of ciliary and flagellar motility and thus it constitutes an additional verification of the theory, for the first time in a living cell. However, on close examination, there is a partial mismatch between the timing of the length oscillation and the phase of the beat cycle. We deduce from this that there is some sliding at the base of the flagellum, sliding that is accommodated by elastic compression of the connecting piece. Micrographic evidence for such compression is presented. Cell Motil. Cytoskeleton 52:151,160, 2002. © 2002 Wiley-Liss, Inc. [source] Sensitivity to communicative relevance tells young children what to imitateDEVELOPMENTAL SCIENCE, Issue 6 2009Victoria Southgate How do children decide which elements of an action demonstration are important to reproduce in the context of an imitation game? We tested whether selective imitation of a demonstrator's actions may be based on the same search for relevance that drives adult interpretation of ostensive communication. Three groups of 18-month-old infants were shown a toy animal either hopping or sliding (action style) into a toy house (action outcome), but the communicative relevance of the action style differed depending on the group. For the no prior information group, all the information in the demonstration was new and so equally relevant. However, for infants in the ostensive prior information group, the potential action outcome was already communicated to the infant prior to the main demonstration, rendering the action style more relevant. Infants in the ostensive prior information group imitated the action style significantly more than infants in the no prior information group, suggesting that the relevance manipulation modulated their interpretation of the action demonstration. A further condition (non-ostensive prior information) confirmed that this sensitivity to new information is only present when the ,old' information had been communicated, and not when infants discovered this information for themselves. These results indicate that, like adults, human infants expect communication to contain relevant content, and imitate action elements that, relative to their current knowledge state or to the common ground with the demonstrator, is identified as most relevant. [source] Overbank deposition along the concave side of the Red River meanders, Manitoba, and its geomorphic significanceEARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2005Gregory R. Brooks Abstract Slow earth sliding is pervasive along the concave side of Red River meanders that impinge on Lake Agassiz glaciolacustrine deposits. These failures form elongated, low-angled (c. 6 to 10°) landslide zones along the valleysides. Silty overbank deposits that accumulated during the 1999 spring freshet extend continuously along the landslide zones over hundreds of metres and aggraded the lower slopes over a distance 50 to 80 m from the channel margin. The aggradation is not obviously related to meander curvature or location within a meander. Along seven slope profiles surveyed in 1999 near Letellier, Manitoba, the deposits locally are up to 21 cm thick and generally thin with increasing distance from, and height above, the river. Local deposit thickness relates to distance from the channel, duration of inundation of the landslide surface, mesotopography, and variations in vegetation cover. Immediately adjacent to the river, accumulated overbank deposits are up to 4 m thick. The 1999 overbank deposits also were present along the moderately sloped (c. 23 to 27°) concave banks eroding into the floodplain, but the deposits are thinner (locally up to c. 7 cm thick) and cover a narrower area (10 to 30 m wide) than the deposits within the landslide zones. Concave overbank deposition is part of a sediment reworking process that consists of overbank aggradation on the landslide zones, subsequent gradual downslope displacement from earth sliding, and eventually reworking by the river at the toe of the landslide. The presence of the deposits dampens the outward migration of the meanders and contributes to a low rate of contemporary lateral channel migration. Concave overbank sedimentation occurs along most Red River meanders between at least Emerson and St. Adolphe, Manitoba. © Her Majesty the Queen in right of Canada. [source] Seismic response analysis of multidrum classical columnsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 10 2005Dimitrios Konstantinidis Abstract This paper presents a numerical investigation on the seismic response of multidrum classical columns. The motivation for this study originates from the need to understand: (a) the level of ground shaking that classical multidrum columns can survive, and (b) the possible advantages or disadvantages of retrofitting multidrum columns with metallic shear links that replace the wooden poles that were installed in ancient times. The numerical study presented in this paper is conducted with the commercially available software Working Model 2DÔ, which can capture with fidelity the sliding, rocking, and slide-rocking response of rigid-body assemblies. This paper validates the software Working Model by comparing selected computed responses with scarce analytical solutions and the results from in-house numerical codes initially developed at the University of California, Berkeley, to study the seismic response of electrical transformers and heavy laboratory equipment. The study reveals that relative sliding between drums happens even when the g -value of the ground acceleration is less than the coefficient of friction, µ, of the sliding interfaces and concludes that: (a) typical multidrum classical columns can survive the ground shaking from strong ground motions recorded near the causative faults of earthquakes with magnitudes Mw=6.0,7.4; (b) in most cases multidrum classical columns free to dislocate at the drum interfaces exhibit more controlled seismic response than the monolithic columns with same size and slenderness; (c) the shear strength of the wooden poles has a marginal effect on the sliding response of the drums; and (d) stiff metallic shear links in-between column drums may have an undesirable role on the seismic stability of classical columns and should be avoided. Copyright © 2005 John Wiley & Sons, Ltd. [source] A Dynamically Entangled Coordination Polymer: Synthesis, Structure, Luminescence, Single-Crystal-to-Single-Crystal Reversible Guest Inclusion and Structural TransformationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2010Arshad Aijaz Abstract A ZnII coordination polymer {[Zn2(cpa)2(bpy)]·3H2O}n (1) (cpa2, = 4-(methoxycarbonyl)benzoate and bpy = 4,4,-bipyridine) has been synthesized under solvothermal condition and structurally characterized. This coordination polymer has nanotubular threefold entangled (2D,3D) structure with embedded water molecules; the water molecules can be partially exchanged in reversible single-crystal-to-single-crystal (SC-SC) fashion by different solvent molecules like methanol, ethanol and acetone giving rise to {[Zn2(cpa)2(bpy)]·(0.5MeOH)·(2.5H2O)}n (2), {[Zn2(cpa)2(bpy)]·(0.5EtOH)·(0.5H2O)}n (3) and {[Zn2(cpa)2(bpy)]·(0.5Me2CO)·(H2O)}n (4). Inclusion of EtOH or MeOH leaves the size of the voids in the framework unaltered. Inclusion of acetone, however, is accompanied by shrinking of the voids in the framework. Heating of 1 at 100 °C under vacuum for 4 h affords the de-solvated compound, {Zn2(cpa)2(bpy)}n (1,). Single-crystal X-ray structure of 1, shows sliding of the individual nanotubular components expanding the overall framework. Thus, the coordination polymer exhibits dynamic motion of the molecular components in SC-SC fashion. All compounds were further characterized via IR spectroscopy, PXRD, elemental and TGA analysis. When 1 is placed in benzene at 100 °C for 2 days, compound {[Zn2(cpa)2(bpy)]·(2.5H2O)}n (5) is formed in a SC-SC fashion where coordination number of ZnII ion increases from four to five. Compound 1 also exhibits reversible guest-dependent photoluminescence properties. [source] Microstructure and Mechanical Performance of Brand-New Al0.3CrFe1.5MnNi0.5 High-Entropy Alloys,ADVANCED ENGINEERING MATERIALS, Issue 10 2009Wei-Yeh Tang The microstructure, hardening behavior, and adhesive wear behavior of Al0.3CrFe1.5MnNi0.5 high-entropy alloys were investigated. All alloys exhibit superior adhesive wear resistance to cast iron FC-300, bearing steel SUJ-2, and hot-mold steel SKD-61. The superior wear resistance of the alloys is attributable to the formation of , phase during the furnace cooling from the homogenization at 1100 °C or the in situ formation of the ,phase induced by the high interface temperature and severe plastic deformation during wear sliding. [source] High-strain-rate Superplasticity in a Nanostructured Al-Mg AlloyADVANCED ENGINEERING MATERIALS, Issue 4 2005B. Q. Han In this work, the authors report high-strain-rate superplasticity in a nanostructured Al-7.5%Mg alloy with a mean grain size of 90 nm processed via consolidation of cryomilled Al-Mg powders. Tensile ductility with an elongation of 291% was observed at a strain rate of 10-1 s-1 and at a temperature of 573 K. Noteworthy is the fact that the microstructure is essentially stable during testing at 573 K. Grain boundary sliding is suggested to be the dominant deformation mechanism in the superplastic deformation of the nanostructured Al-Mg alloy. [source] Creep failure mechanisms of a Ti-6Al-4V thick plateFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2001F. J. Seco The creep failure operating mechanisms of a 17-mm thick plate of a Ti,6Al,4V alloy in various heat treating conditions have been investigated. Specimens in the as-received, mill-annealed, condition (50 min maintenance at 720 °C and air cooled as the final step of the thermomechanical process) showed the lowest creep resistance and their metallographic analysis revealed that the temperature-activated dislocation climb was the mechanism responsible for the failure and that observed holes were generated by plastic deformation, rather than by creep cavitation. Conversely, maximum times to failure were recorded in beta-annealed specimens (1030 °C for 30 min, air cooled and aged for 2 h at 730 °C). The fracture surfaces of these broken specimens exhibited an intergranular morphology that was attributed to grain boundary sliding along the former beta grains. Finally, alpha,beta field-annealed samples (940 °C 4 h, and furnace cooled to 700 °C) possessed intermediate lives between those of mill-annealed and beta-annealed specimens and the failure operating mechanism was diffusional creep by the nucleation and coalescence of the creep cavities generated at the alpha,beta interfaces and the triple points. [source] Molecular mechanism of DNA replication-coupled inactivation of the initiator protein in Escherichia coli: interaction of DnaA with the sliding clamp-loaded DNA and the sliding clamp-Hda complexGENES TO CELLS, Issue 6 2004Masayuki Su'etsugu In Escherichia coli, the ATP-DnaA protein initiates chromosomal replication. After the DNA polymerase III holoenzyme is loaded on to DNA, DnaA-bound ATP is hydrolysed in a manner depending on Hda protein and the DNA-loaded form of the DNA polymerase III sliding clamp subunit, which yields ADP-DnaA, an inactivated form for initiation. This regulatory DnaA-inactivation represses extra initiation events. In this study, in vitro replication intermediates and structured DNA mimicking replicational intermediates were first used to identify structural prerequisites in the process of DnaA-ATP hydrolysis. Unlike duplex DNA loaded with sliding clamps, primer RNA-DNA heteroduplexes loaded with clamps were not associated with DnaA-ATP hydrolysis, and duplex DNA provided in trans did not rescue this defect. At least 40-bp duplex DNA is competent for the DnaA-ATP hydrolysis when a single clamp was loaded. The DnaA-ATP hydrolysis was inhibited when ATP-DnaA was tightly bound to a DnaA box-bearing oligonucleotide. These results imply that the DnaA-ATP hydrolysis involves the direct interaction of ATP-DnaA with duplex DNA flanking the sliding clamp. Furthermore, Hda protein formed a stable complex with the sliding clamp. Based on these, we suggest a mechanical basis in the DnaA-inactivation that ATP-DnaA interacts with the Hda-clamp complex with the aid of DNA binding. [source] The loose coupling mechanism in molecular machines of living cellsGENES TO CELLS, Issue 1 2000Fumio Oosawa Living cells have molecular machines for free energy conversion, for example, sliding machines in muscle and other cells, flagellar motors in bacteria, and various ion pumps in cell membranes. They are constructed from protein molecules and work in the nm (nanometer), pN (piconewton) and ms (millisecond) ranges, without inertia. In 1980s, a question was raised of whether the input,output or influx,efflux coupling in these molecular machines is tight or loose, and an idea of loose coupling was proposed. Recently, the long-distance multistep sliding of a single myosin head on an actin filament, coupled with the hydrolysis of one ATP molecule, was observed by Yanagida's group using highly developed techniques of optical microscopy and micromanipulation. This gave direct evidence for the loose coupling between the chemical reaction and the mechanical event in the sliding machine. In this review, I will briefly describe a historical overview of the input,output problem in the molecular machines of living cells. [source] Sediment Distribution Around Glacially Abraded Bedrock Landforms (Whalebacks) at Lago Tranquilo, ChileGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 3 2005Neil F. Glasser Whalebacks are convex landforms created by the smoothing of bedrock by glacial processes. Their formation is attributed to glacial abrasion either by bodies of subglacial sediment sliding over bedrock or by individual clasts contained within ice. This paper reports field measurements of sediment depth around two whaleback landforms in order to investigate the relationship between glacigenic deposits and whaleback formation. The study site, at Lago Tranquilo in Chilean Patagonia, is situated within the Last Glacial Maximum (LGM) ice limits. The two whalebacks are separated by intervening depressions in which sediment depths are generally 0.2 to 0.3 m. Two facies occur on and around the whalebacks. These facies are: (1) angular gravel found only on the surface of the whalebacks, interpreted as bedrock fracturing in response to unloading of the rock following pressure release after ice recession, and (2) sandy boulder-gravel in the sediment-filled depressions between the two whalebacks, interpreted as an ice-marginal deposit, with a mixture of sediment types including basal glacial and glaciofluvial sediment. Since the whalebacks have heavily abraded and striated surfaces but are surrounded by only a patchy and discontinuous layer of sediment, the implication is that surface abrasion of the whalebacks was achieved primarily by clasts entrained in basal ice, not by subglacial till sliding. [source] The role of friction and secondary flaws on deflection and re-initiation of hydraulic fractures at orthogonal pre-existing fracturesGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2006Xi Zhang SUMMARY In this study, we explore the nature of plane-strain hydraulic fracture growth in the presence of pre-existing fractures such as joints without or with secondary flaws. The 2-D plane-strain fracture studied can be taken as a cross-section through the short dimensions of an elongated 3-D fracture or as an approximate representation of the leading edge of a 3-D fracture where the edge curvature is negligible. The fluid-driven fracture intersects a pre-existing fracture to which it is initially perpendicular and is assumed not to immediately cross, but is rather deflected into the pre-existing fracture. The intersection results in branching of the fracture and associated fluid flow into the pre-existing fracture. Further growth results in opening and frictional sliding along the pre-existing fracture. Fracture propagation in an impermeable homogeneous elastic medium and fluid invasion into a pre-existing fracture are both driven by an incompressible, Newtonian fluid injected at a constant rate. The frictional stress on the surfaces of pre-existing fractures is assumed to obey the Coulomb law. The governing equations for quasi-static fluid-driven fracture growth are given and a scaling is introduced to help identify important parameters. The displacement discontinuity method and the finite difference method are employed to deal with this coupling mechanism of rock fracture and fluid flow. In order to account for fluid lag, a method for separately tracking the crack tip and the fluid front is included in the numerical model. Numerical results are obtained for internal pressure, frictional contact stresses, opening and shear displacements, and fluid lag size, as well as for fracture re-initiation from secondary flaws. After fracture intersection, the hydraulic fracture growth mode changes from tensile to shearing. This contributes to increased injection pressure and to a reduction in fracture width. In the presence of pre-existing fractures, the fluid-driven cracks can be arrested or retarded in growth rate as a result of diversion of fluid flow into and frictional sliding along the pre-existing fractures. Frictional behaviour significantly affects the ability of the fluid to enter or penetrate the pre-existing fracture only for those situations where the fluid front is within a certain distance from the intersecting point. Importantly, fluid penetration requires higher injection pressure for frictionally weak pre-existing fractures. Fracture re-initiation from secondary flaws can reduce the injection pressure, but re-initiation is suppressed by large sliding on pre-existing fractures that are frictionally weak. [source] Studies on ,precarious rocks' in the epicentral area of the AD 1356 Basle earthquake, SwitzerlandGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2005Peter Schürch SUMMARY For the first time precarious rocks have been analysed in the epicentral area of the AD 1356 Basle earthquake in northern Switzerland. Several cliff sites in flat-lying, thickly bedded Upper Jurassic coral limestones in the Jura Mountains were investigated. Seven blocks are regarded as precarious with respect to earthquake strong ground motions. The age of these precarious rocks could not be determined directly as for instance by radiometric dating methods; however, based on slope degradation processes it can be concluded that the formation of these blocks predates the AD 1356 Basle earthquake. The acceleration required to topple a precarious rock from its pedestal is estimated using geometrical data for individual block sections and earthquake strong-motion records from stations on rock sites in the European Strong-Motion Database as input data for the computer program ROCKING V1.0 from the Seismological Laboratory, University of Nevada, Reno. The calculations indicate that toppling of a precarious rock largely depends on earthquake strength but also on the frequency spectrum of the signal. Although most investigated precarious rocks are surprisingly stable for ground motions similar to those expected to have occurred during the AD 1356 Basle earthquake, at least two blocks are clearly precariously balanced, with peak toppling accelerations lower than 0.3 g. Possible reasons why these blocks did not topple during the AD 1356 Basle earthquake include incomplete separation from their base, sliding of precarious rocks, their size, lower than assumed ground accelerations and/or duration of shaking. [source] Analytical and 3-D numerical modelling of Mt. Etna (Italy) volcano inflationGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2005A. Bonaccorso SUMMARY Since 1993, geodetic data obtained by different techniques (GPS, EDM, SAR, levelling) have detected a consistent inflation of the Mt. Etna volcano. The inflation, culminating with the 1998,2001 strong explosive activity from summit craters and recent 2001 and 2002 flank eruptions, is interpreted in terms of magma ascent and refilling of the volcanic plumbing system and reservoirs. We have modelled the 1993,1997 EDM and GPS data by 3-D pressurized sources to infer the position and dimension of the magma reservoir. We have performed analytical inversions of the observed deformation using both spheroidal and ellipsoidal sources embedded in a homogeneous elastic half-space and by applying different inversion methods. Solutions for these types of sources show evidence of a vertically elongated magma reservoir located 6 km beneath the summit craters. The maximum elevation of topography is comparable to such depth and strong heterogeneities are inferred from seismic tomography; in order to assess their importance, further 3-D numerical models, employing source parameters extracted from analytical models, have been developed using the finite-element technique. The deformation predicted by all the models considered shows a general agreement with the 1993,1997 data, suggesting the primary role of a pressure source, while the complexities of the medium play a minor role under elastic conditions. However, major discrepancies between data and models are located in the SE sector, suggesting that sliding along potential detachment surfaces may contribute to amplify deformation during the inflation. For the first time realistic features of Mt. Etna are studied by a 3-D numerical model characterized by the topography and lateral variations of elastic structure, providing a framework for a deeper insight into the relationships between internal sources and tectonic structures. [source] On strike-slip faulting in layered mediaGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2002Maurizio Bonafede Summary We study the effects of structural inhomogeneities on the stress and displacement fields induced by strike-slip faults in layered media. An elastic medium is considered, made up of an upper layer bounded by a free surface and welded to a lower half-space characterized by different elastic parameters. Shear cracks with assigned stress drop are employed as mathematical models of strike-slip faults, which are assumed to be vertical and planar. If the crack is entirely embedded within the lower medium (case A), a Cauchy-kernel integral equation is obtained, which is solved by employing an expansion of the dislocation density in Chebyshev polynomials. If the crack is within the lower medium but it terminates at the interface (case B), a generalized Cauchy singularity appears in the integral kernel. This singularity affects the singular behaviour of the dislocation density at the crack tip touching the interface. Finally, the case of a crack crossing the interface is considered (case C). The crack is split into two interacting sections, each placed in a homogeneous medium and both open at the interface. Two coupled generalized Cauchy equations are obtained and solved for the dislocation density distribution of each crack section. An asymptotic study near the intersection between the crack and the interface shows that the dislocation densities for each crack section are bounded at the interface, where a jump discontinuity is present. As a corollary, the stress drop must be discontinuous at the interface, with a jump proportional to the rigidity contrast between the adjoining media. This finding is shown to have important implications for the development of geometrical complexities within transform fault zones: planar strike-slip faults cutting across layer discontinuities with arbitrary stress drop values are shown to be admissible only if the interface between different layers becomes unwelded during the earthquake at the crack/interface junction. Planar strike-slip faulting may take place only in mature transform zones, where a repetitive earthquake cycle has already developed, if the rheology is perfectly elastic. Otherwise, the fault cannot be planar: we infer that strike-slip faulting at depth is plausibly accompanied by en-echelon surface breaks in a shallow sedimentary layer (where the stress drop is lower than prescribed by the discontinuity condition), while ductile deformation (or steady sliding) at depth may be accommodated by multiple fault branching or by antithetic faulting in the upper brittle layer (endowed with lower rigidity but higher stress). [source] Radio-tracking gravel particles in a large braided river in New Zealand: a field test of the stochastic theory of bed load transport proposed by EinsteinHYDROLOGICAL PROCESSES, Issue 3 2001H. M. Habersack Abstract Hans A. Einstein initiated a probabilistic approach to modelling sediment transport in rivers. His formulae were based on theory and were stimulated by laboratory investigations. The theory assumes that bed load movement occurs in individual steps of rolling, sliding or saltation and rest periods. So far very few attempts have been made to measure stochastic elements in nature. For the first time this paper presents results of radio-tracing the travel path of individual particles in a large braided gravel bed river: the Waimakariri River of New Zealand. As proposed by Einstein, it was found that rest periods can be modelled by an exponential distribution, but particle step lengths are better represented by a gamma distribution. Einstein assumed an average travel distance of 100 grain-diameters for any bed load particle between consecutive points of deposition, but larger values of 6·7 m or 150 grain-diameters and 6·1 m or 120 grain-diameters were measured for two test particle sizes. Together with other available large scale field data, a dependence of the mean step length on particle diameter relative to the D50 of the bed surface was found. During small floods the time used for movement represents only 2·7% of the total time from erosion to deposition. The increase in percentage of time being used for transport means that it then has to be regarded in stochastic transport models. Tracing the flow path of bed load particles between erosion and deposition sites is a step towards explaining the interactions between sediment transport and river morphology. Copyright © 2001 John Wiley & Sons, Ltd. [source] A discrete thermodynamic approach for anisotropic plastic,damage modeling of cohesive-frictional geomaterialsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 12 2010Q. Z. Zhu Abstract A discrete plastic,damage model is developed for cohesive-frictional geomaterials subjected to compression-dominated stresses. Macroscopic plastic strains of material are physically generated by frictional sliding along weakness planes. The evolution of damage is related to the evolution of weakness planes physically in connection with the propagation of microcracks. A discrete approach is used to account for anisotropic plastic flow and damage evolution, by introducing two stress invariants and one plastic hardening variable for each family of sliding weakness planes. Plastic flow in each family is coupled with damage evolution. The proposed model is applied to typical geomaterials and comparisons between numerical predictions and experimental data are presented. Copyright © 2009 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||