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Bound
Kinds of Bound Terms modified by Bound Selected AbstractsUPPER BOUNDS ON THE MINIMUM COVERAGE PROBABILITY OF CONFIDENCE INTERVALS IN REGRESSION AFTER MODEL SELECTIONAUSTRALIAN & NEW ZEALAND JOURNAL OF STATISTICS, Issue 3 2009Paul Kabaila Summary We consider a linear regression model, with the parameter of interest a specified linear combination of the components of the regression parameter vector. We suppose that, as a first step, a data-based model selection (e.g. by preliminary hypothesis tests or minimizing the Akaike information criterion , AIC) is used to select a model. It is common statistical practice to then construct a confidence interval for the parameter of interest, based on the assumption that the selected model had been given to us,a priori. This assumption is false, and it can lead to a confidence interval with poor coverage properties. We provide an easily computed finite-sample upper bound (calculated by repeated numerical evaluation of a double integral) to the minimum coverage probability of this confidence interval. This bound applies for model selection by any of the following methods: minimum AIC, minimum Bayesian information criterion (BIC), maximum adjusted,R2, minimum Mallows' CP and,t -tests. The importance of this upper bound is that it delineates general categories of design matrices and model selection procedures for which this confidence interval has poor coverage properties. This upper bound is shown to be a finite-sample analogue of an earlier large-sample upper bound due to Kabaila and Leeb. [source] LOWER BOUNDS TO THE POPULATION SIZE WHEN CAPTURE PROBABILITIES VARY OVER INDIVIDUALSAUSTRALIAN & NEW ZEALAND JOURNAL OF STATISTICS, Issue 2 2008Chang Xuan Mao Summary The problem of estimating population sizes has a wide range of applications. Although the size is non-identifiable when a population is heterogeneous, it is often useful to estimate the lower bounds and to construct lower confidence limits. A sequence of lower bounds, including the well-known Chao lower bound, is proposed. The bounds have closed-form expressions and are estimated by the method of moments or by maximum likelihood. Real examples from epidemiology, wildlife management and ecology are investigated. Simulation studies are used to assess the proposed estimators. [source] All Bound up Together: The Woman Question in African American Public Culture, 1830,1900 by Martha S. JonesGENDER & HISTORY, Issue 1 2009JOHN A. KIRK No abstract is available for this article. [source] ,Bound from Either Side': The Limits of Power in Carolingian Marriage Disputes, 840,870GENDER & HISTORY, Issue 3 2007Rachel Stone The article discusses four marriage disputes in ninth-century Francia which involved noblemen: Count Stephen of the Auvergne, Count Boso of Italy, Baldwin of Flanders and the royal vassal Falcric. All these men were affected by Carolingian reforming measures on consanguineous marriage, divorce and raptus (abduction). The article examines how gender and social status affected the forms of power and the strategies used by different parties in the cases: archbishops and popes, kings, the women involved and the noblemen themselves. A paradoxical situation is revealed: despite the patriarchal basis of Carolingian society, the power even of elite men over women and marriage was often highly contingent. Yet such restrictions on power did not imperil the gender order: the masculinity of the men involved in these marriage disputes was not questioned. [source] Modulation of the Lifetime of Water Bound to Lanthanide Metal Ions in Complexes with Ligands Derived from 1,4,7,10-Tetraazacyclododecane Tetraacetate (DOTA)HELVETICA CHIMICA ACTA, Issue 5 2005Shanrong Zhang A series of di- and tetraamide derivatives of DOTA were synthesized, and their lanthanide(III) complexes were examined by multinuclear 1H-, 13C-, and 17O-NMR spectroscopy, and compared with literature data of similar, known complexes (Table). All ligands formed structures similar to the parent [LnIII(DOTA)], complexes, with four N-atoms and four O-atoms from DOTA and one O-atom from the inner-sphere water molecules. Interestingly, the lifetimes ,M of the inner-sphere, metal-bound water molecules vary widely, ranging from nano- to milliseconds, depending on the identity of the pendent amide side chains. In general, positively charged [LnIII(DOTA-tetraamide)]3+ complexes display the longest residence times (high ,M values), while complexes with additional charged functional groups on the extended amides display much smaller ,M values, even when the side groups are not directly coordinated to the central Ln3+ ions. The design of novel [LnIII(DOTA-tetraamide)]3+ complexes with a wide, tunable range of ,M values is of prime importance for the application of fast-responding, paramagnetic chemical-exchange-saturation-transfer (PARACEST) imaging agents used for the study of physiological and metabolic processes. [source] A Photosynthetic Reaction Center Covalently Bound to Carbon Nanotubes,ADVANCED MATERIALS, Issue 22 2007I. Carmeli The photosystem reaction center I is covalently bound to carbon nanotubes using carbodiimide chemistry. The hybrid systems are characterized by atomic force microscopy, and UV-VIS spectroscopy, indicating a high degree of conjugation between the photosystem reaction center and the carbon nanotubes. Three different architectures for optoelectronic circuits are presented, which have the potential to serve as basis for molecular optoelectronic devices. [source] Unfairness of measurement-based admission controls in a heterogeneous environmentINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 9 2001Yuan-Cheng Lai Abstract Admission controls are required to determine whether new connections should be admitted to networks. These controls ensure the quality of service (QoS) for data transmission. This paper introduces three measurement-based admission control algorithms called Measured Sum, Hoeffding Bound, and Adaptive Weight Factor. The unfairness of these algorithms in a heterogeneous environment is investigated. Simulation results indicate that the fairness of the Measured Sum exceeds that of the other methods. Admission of connections with large peak rates or travelling many hops can be difficult. Copyright © 2001 John Wiley & Sons, Ltd. [source] Wheelchair Users Are Not Necessarily Wheelchair BoundJOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 4 2002Rory A. Cooper PhD No abstract is available for this article. [source] Characterization of fibronectin assembly by platelets adherent to adsorbed laminin-111JOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 5 2006J. CHO Summary.,Background: Various types of laminin (LN) are ubiquitous components of basement membrane and exposed to blood upon localized damage of vascular endothelial cells. Fibronectin is a plasma protein that is insolubilized into fibrils in a regulated fashion by, for example, lysophosphatidic acid (LPA)-stimulated fibroblasts or platelets spread on supportive adhesive ligands. Objective: To study assembly of plasma fibronectin by LPA-activated platelets adherent to LN-111 via ,6,1 integrin. Results: Platelets adherent to LN-111-bound plasma fibronectin or its N-terminal 70 kD fragment in fibrillar arrays at the periphery of spread platelets under static but not shear conditions. Formation of fibronectin arrays under static conditions was inhibited by co-incubation with the N-terminal 70 kD fragment or with a 49-amino acid peptide that binds to the N-terminal region of fibronectin. Approximately 7000 fibronectin dimers bound per adherent platelet with a Kd of 50 nm. Bound 70 kD fragment was readily solubilized with deoxycholate (DOC), whereas bound fibronectin became progressively insoluble. Bound 70 kD fragment became resistant to DOC extraction after treatment with a cell-impermeable, reducible crosslinker. Crosslinked 70 kD fragment was found in a high molecular weight complex. As with fibroblasts, signaling molecules modulating actin cytoskeletal organization controlled expression of binding sites for the N-terminal 70 kD region of fibronectin on adherent platelets. Conclusions: These results indicate that platelets adherent to LN-111 via ,6,1 support subsequent assembly of fibronectin, but possibly only under conditions of intermittent or stagnant blood flow. [source] A Bound on Synchronically Interpretable StructureMIND & LANGUAGE, Issue 3 2004Jon M. Slack This paper embeds the classical account within a neural network framework, exploring the encoding of syntactically-structured objects over the synchronic-diachronic characteristics of networks. Synchronic structure is defined in terms of temporal binding and the superposition of states. To accommodate asymmetric relations, synchronic structure is subject to the type uniqueness constraint (TUC). The nature of synchronic structure is shown to underlie X-bar theory that characterizes the phrasal structure of human languages. The derivation differentiates core X-bar properties from language-specific properties. [source] Books and Bodies, Bound and UnboundORBIS LITERARUM, Issue 2 2009Thomas Pettitt A recent trend in literary history, cultural studies and folkloristics has been a ,corporeal turn', which focuses on how bodies are constructed and understood in texts and other cultural productions. A significant contribution from Guillemette Bolens identifies two distinct corporal constructions in medieval narrative: the contained body (an envelope vulnerable to penetration) and the articulated body (limbs and joints designed for motion). This perception is here extended to include narrative constructions of the environment (enclosures versus avenues and junctions). Furthermore Bolens's suggestion that articulated and contained bodies are mainly to be found, respectively, in oral tradition and textual culture, is elaborated to the thesis that the contained constructions will be particularly at home in the printed book, whose dominance is associated with cultural containment from a variety of perspectives. And a shift from predominantly articulated constructions to predominantly contained is indeed discernible in the wonder tale ,Red Riding Hood', as it modulates from oral tradition to printed fairy tale. Concluding speculations suggest that if the cultural dominance of the printed book has been a (,Gutenberg') parenthesis, the tale should now be reverting to articulated constructions as it escapes from books into the digital media and Internet technology. [source] Bound and unextractable pesticidal plant residues: chemical characterization and consumer exposurePEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 7 2004Heinrich Sandermann Jr Abstract Plants are well known to incorporate pesticides into bound and unextractable residues that resist solubilization in common laboratory solvents and are therefore not accessible to standard residue analysis. A characterization of such residues has been proposed for incorporation rates above trigger values of 0.05 mg kg,1 parent pesticide equivalents, or percentage values of 10% (United States Environmental Protection Agency, 1995) or 25% (Commission of the European Communities, 1997) of the total radioactive residue. These trigger values are often exceeded. The present review describes the current status of the chemical characterization and animal bioavailability of bound and unextractable residues that may be xenobiotic in nature or result from natural recycling of simple degradation products. The latter case represents a mechanism of detoxification. Bound residues have been shown to be covalent or non-covalent in nature. With regard to the plant matrix molecules involved, incorporation into proteins, lignins, pectins, hemicelluloses and cutins has been demonstrated, and four covalent linkage types are known. Animal feeding experiments have revealed cases of low as well as high bioavailability. Many of the studies are limited by experimental uncertainties and by results only being reported as relative percentage values rather than absolute exposure. A preliminary value of absolute exposure from bound and unextractable residues is derived here for the first time from eight case studies. The mean exposure (ca 1.5 mg kg,1 pesticidal equivalents) exceeds some of the existing maximum residue levels (MRLs) of residual free pesticides that are typically in the range of 0.05,1 mg kg,1. A mathematical framework for the correction of current maximum residue levels is presented for cases of highly bioavailable bound residues. As bound pesticidal residues in food plants could represent a source of significant consumer exposure, an experimental test scheme is proposed here. It consists of basic chemical characterization, model digestibility tests and, in exceptional cases, animal bioavailability and additional toxicological studies. Copyright © 2004 Society of Chemical Industry [source] Rightward Bound: Making America Conservative in the 1970s , Edited by Bruce J. Schulman and Julian E. ZelizerTHE HISTORIAN, Issue 2 2010David T. Courtwright No abstract is available for this article. [source] Low-Symmetry Iron Oxide Nanocrystals Bound by High-Index Facets,ANGEWANDTE CHEMIE, Issue 36 2010Jingzhou Yin Gut in Form: ,-Fe2O3 -Tetrakaidekaeder (siehe Bild, links) und abgeschrägte ,-Fe2O3 -Parallelepipede (rechts) mit exponierten hochindizierten Flächen wurden in hohen Ausbeuten erhalten. Die magnetischen Eigenschaften beider Proben unterscheiden sich, offenbar aufgrund ihrer unterschiedlichen Formen und hochindizierten Flächen. [source] Tuning the Electronic Communication between Redox Centers Bound to Insulating Surfaces,ANGEWANDTE CHEMIE, Issue 18 2010Dodzi Zigah Kommunikationskontrolle: Die elektronische Kommunikation zwischen Ferrocenylzentren an Siliciumoberflächen kann effizient gesteuert werden, und zwar laut elektrochemischer Rastermikroskopie (SECM) sowohl über die Oberflächenbedeckung der elektroaktiven Einheiten als auch über die Art des Redoxvermittlers. Die laterale Ladungspropagation kann so von einem extrem langsamen bis zu einem sehr schnellen Prozess genau abgestimmt werden. [source] Crystal Structure of HIV-1 Reverse Transcriptase Bound to a Non-Nucleoside Inhibitor with a Novel Mechanism of Action,ANGEWANDTE CHEMIE, Issue 10 2010Séverine Freisz Anders als andere nichtnucleosidische Inhibitoren der Reversen Transkriptase (NNRTI, Bindungsstelle blau hervorgehoben) von HIV-1 konkurriert DAVP-1 mit dem Nucleotidsubstrat. Eine Röntgenstrukturanalyse von nichtligierter Reverser Transkriptase mit gebundenem DAVP-1 zeigt die neue Bindungsstelle nahe dem aktiven Polymerasezentrum. (Die Bindungsstelle für nucleosidanaloge Inhibitoren der Reversen Transkriptase (NRTI) ist rot hervorgehoben.) [source] Cyclization of TEMPO Radicals Bound to Metalladithiolene Induced by SOMO,HOMO Energy-Level Conversion,ANGEWANDTE CHEMIE, Issue 3 2010Tetsuro Kusamoto TEMPO-funktionalisierte Metalladithiolene [M(tempodt)2]n, (M=Au3+, n=1; M=Ni2+, n=2) zeichnen sich durch eine einzigartige elektronische Struktur bezüglich SOMO und HOMO aus. Die Einelektronenoxidation von [M(tempodt)2]n, führt zur Bildung eines ,-Radikals im ,-konjugierten Gerüst, das eine intramolekulare Cyclisierung auslöst (siehe Bild). [source] Altered Interatrial Conduction Detected in MADIT II Patients Bound to Develop Atrial FibrillationANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 3 2009Fredrik Holmqvist M.D., Ph.D. Background: Changes in P-wave morphology have recently been shown to be associated with interatrial conduction route used, without noticeable changes of P-wave duration. This study aimed at exploring the association between P-wave morphology and future atrial fibrillation (AF) development in the Multicenter Automatic Defibrillator Trial II (MADIT II) population. Methods: Patients included in MADIT-II without a history of AF with sinus rhythm at baseline who developed AF during the study ("Pre-AF") were compared to matched controls without AF development ("No-AF"). Patients were followed for a mean of 20 months. A 10-minute high-resolution bipolar ECG recording was obtained at baseline. Signal-averaged P waves were analyzed to determine orthogonal P-wave morphology, P-wave duration, and RMS20. The P-wave morphology was subsequently classified into one of three predefined types using an automated algorithm. Results: Thirty patients (age 68 ± 7 years) who developed AF during MADIT-II were compared with 60 patients (age 68 ± 8 years) who did not. P-wave duration and RMS20 in the Pre-AF group was not significantly different from the No-AF group (143 ± 21 vs 139 ± 30 ms, P = 0.26, and 2.0 ± 1.3 vs 2.1 ± 1.0 ,V, P = 0.90). The distribution of P-wave morphologies was shifted away from Type 1 in the Pre-AF group when compared to the No-AF group (Type 1/2/3/atypical; 25/60/0/15% vs 10/63/10/17%, P = 0.04). Conclusions: This study is the first to describe changes in P-wave morphology in patients prior to AF development. The results indicate that abnormal interatrial conduction may play a role in AF development in patients with prior myocardial infarction and congestive heart failure. [source] In vivo saturation binding of GABA-A receptor ligands to estimate receptor occupancy using liquid chromatography/tandem mass spectrometryBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 1 2009Seth C. Hopkins Abstract Typically, the dose-occupancy curves for GABA-A receptor ligands are determined using in vivo binding of [3H]flumazenil. This study describes in vivo binding experiments without the use of tracer ligands. Bound and free fractions were measured directly using a highly sensitive LC/MS/MS detection method after in vivo administration of the GABA-A ligands zolpidem, (RS)-zopiclone, L-838417 and flumazenil, to demonstrate affinity and saturation of the filter-retained, membrane-bound fraction. The in vivo binding of flumazenil and L-838417 both saturated around 200,nm, at a similar level to the specific binding of (S)-zopiclone after doses of the racemic zopiclone, using (R)-zopiclone to estimate non-specific binding. This saturable component represented an estimate of benzodiazepine binding sites available on GABA-A receptors in vivo (200,nm). Dose-occupancy curves were constructed to estimate the dose required to achieve 50% occupancy and matched estimates obtained with tracer methods. In contrast to tracer methods, this method is uniquely suitable to the demonstration of stereoselective binding of the (S)-isomer in vivo after doses of racemic zopiclone. These results demonstrate that the LC/MS/MS measurements of total drug concentrations typically used in early drug development can be adapted to provide information about receptor occupancy in vivo. Copyright © 2009 John Wiley & Sons, Ltd. [source] Prediction of the 3D Structure of FMRF-amide Neuropeptides Bound to the Mouse MrgC11 GPCR and Experimental ValidationCHEMBIOCHEM, Issue 13 2007Jiyoung Heo Dr. Abstract We report the 3D structure predicted for the mouse MrgC11 (mMrgC11) receptor by using the MembStruk computational protocol, and the predicted binding site for the F-M-R-F-NH2 neuropeptide together with four singly chirally modified ligands. We predicted that the R-F-NH2 part of the tetrapeptide sticks down into the protein between the transmembrane (TM) domains 3, 4, 5, and 6. The Phe (F-NH2) interacted favorably with Tyr110 (TM3), while the Arg makes salt bridges to Asp161 (TM4) and Asp179 (TM5). We predicted that the Met extends from the binding site, but the terminal Phe residue sticks back into an aromatic/hydrophobic site flanked by Tyr237, Leu238, Leu240, and Tyr256 (TM6), and Trp162 (TM4). We carried out subsequent mutagenesis experiments followed by intracellular calcium-release assays that demonstrated the dramatic decrease in activity for the Tyr110Ala, Asp161Ala, and Asp179Ala substitutions, which was predicted by our model. These experiments provide strong evidence that our predicted G protein-coupled receptor (GPCR) structure is sufficiently accurate to identify binding sites for selective ligands. Similar studies were made with the mMrgA1 receptor, which did not bind the R-F-NH2 dipeptide; we explain this to be due to the increased hydrophobic character of the binding pocket in mMrgA1. [source] How Many Hydrogen Atoms Can Be Bound to a Metal?CHEMINFORM, Issue 4 2005Predicted MH12 Species Abstract For Abstract see ChemInform Abstract in Full Text. [source] The Predicted 3D Structures of the Human M1 Muscarinic Acetylcholine Receptor with Agonist or Antagonist BoundCHEMMEDCHEM, Issue 8 2006Joyce Yao-chun Peng Abstract The muscarinic acetylcholine G-protein-coupled receptors are implicated in diseases ranging from cognitive dysfunctions to smooth-muscle disorders. To provide a structural basis for drug design, we used the MembStruk computational method to predict the 3D structure of the human M1 muscarinic receptor. We validated this structure by using the HierDock method to predict the binding sites for three agonists and four antagonists. The intermolecular ligand,receptor contacts at the predicted binding sites agree well with deductions from available mutagenesis experiments, and the calculated relative binding energies correlate with measured binding affinities. The predicted binding site of all four antagonists is located between transmembrane (TM) helices,3, 4, 5, 6, and 7, whereas the three agonists prefer a site involving residues from TM3, TM6, and TM7. We find that Trp,157(4) contributes directly to antagonist binding, whereas Pro,159(4) provides an indirect conformational switch to position Trp,157(4) in the binding site (the number in parentheses indicates the TM helix). This explains the large decrease in ligand binding affinity and signaling efficacy by mutations of Trp,157(4) and Pro,159(4) not previously explained by homology models. We also found that Asp,105(3) and aromatic residues Tyr,381(6), Tyr,404(7), and Tyr,408(7) are critical for binding the quaternary ammonium head group of the ligand through cation,, interactions. For ligands with a charged tertiary amine head group, we suggest that proton transfer from the ligand to Asp,105(3) occurs upon binding. Furthermore, we found that an extensive aromatic network involving Tyr,106(3), Trp,157(4), Phe,197(5), Trp,378(6), and Tyr,381(6) is important in stabilizing antagonist binding. For antagonists with two terminal phenyl rings, this aromatic network extends to Trp,164(4), Tyr,179(extracellular loop,2), and Phe,390(6) located at the extracellular end of the TMs. We find that Asn,382(6) forms hydrogen bonds with selected antagonists. Tyr381(6) and Ser,109(3) form hydrogen bonds with the ester moiety of acetylcholine, which binds in the gauche conformation. [source] Interpersonal Interactions and the Bounds of AgencyDIALECTICA, Issue 2 2007Jesús H. Aguilar According to the Causal Theory of Action, actions are causally produced events and causal transitivity seems to apply to all such events. However, strong intuitions support the idea that actions cannot be transitively caused. This is a tension that has plagued this theory's effort to account for action. In particular, it has fueled a serious objection suggesting that this theory of action seriously distorts the attribution of agency when two agents interact with each other. Based on Donald Davidson's analysis of the accordion effect and the nature of actions, I provide an answer to the problem of agential attribution. It is an answer that shows that the Causal Theory of Action can unambiguously attribute agency without resorting to a stipulation or denying that actions can be transitively caused. I then identify the sources of the problematic intuitions in the need to recognize spheres of agential influence and preserve their integrity. [source] Best Nonparametric Bounds on Demand ResponsesECONOMETRICA, Issue 6 2008Richard Blundell This paper uses revealed preference inequalities to provide the tightest possible (best) nonparametric bounds on predicted consumer responses to price changes using consumer-level data over a finite set of relative price changes. These responses are allowed to vary nonparametrically across the income distribution. This is achieved by combining the theory of revealed preference with the semiparametric estimation of consumer expansion paths (Engel curves). We label these expansion path based bounds on demand responses as E-bounds. Deviations from revealed preference restrictions are measured by preference perturbations which are shown to usefully characterize taste change and to provide a stochastic environment within which violations of revealed preference inequalities can be assessed. [source] Changes in the Distribution of Male and Female Wages Accounting for Employment Composition Using BoundsECONOMETRICA, Issue 2 2007Richard Blundell This paper examines changes in the distribution of wages using bounds to allow for the impact of nonrandom selection into work. We show that worst case bounds can be informative. However, because employment rates in the United Kingdom are often low, they are not informative about changes in educational or gender wage differentials. Thus we explore ways to tighten these bounds using restrictions motivated from economic theory. With these assumptions, we find convincing evidence of an increase in inequality within education groups, changes in educational differentials, and increases in the relative wages of women. [source] Bounds on Parameters in Panel Dynamic Discrete Choice ModelsECONOMETRICA, Issue 3 2006Bo E. Honoré Identification of dynamic nonlinear panel data models is an important and delicate problem in econometrics. In this paper we provide insights that shed light on the identification of parameters of some commonly used models. Using these insights, we are able to show through simple calculations that point identification often fails in these models. On the other hand, these calculations also suggest that the model restricts the parameter to lie in a region that is very small in many cases, and the failure of point identification may, therefore, be of little practical importance in those cases. Although the emphasis is on identification, our techniques are constructive in that they can easily form the basis for consistent estimates of the identified sets. [source] Despotism without Bounds: The French Secret Police and the Silencing of Dissent in London, 1760,1790HISTORY, Issue 296 2004SIMON BURROWS Through an examination of the policing of dissident French refugees in London between 1760 and 1790, this article contends that recent historians have tended to over-emphasize the reforming nature of the Bourbon government in the decades prior to the French Revolution, especially under Louis XVI, and overlooked the more repressive and ,despotic' aspects of the regime. It reveals that the Paris police or French secret agents adopted a variety of clandestine methods in their attempts to silence dissident exiles, including attempts at kidnap, and allegedly murder. As much of this police activity was reported in the British press and French printed texts, both before and during the French Revolution, and several of the exiles were celebrated writers or future revolutionary leaders, it was widely known among informed contemporaries. The article therefore contends that the French revolutionaries' allegations of despotism and suspicions of monarchic conspiracies were more deeply rooted in experience than recent historiography has tended to suggest. At the same time, reports of the attempts of the ,despotic' French government to suppress the activities of Frenchmen on British soil helped to reinforce a British national identity based on the celebration of the liberties France lacked. [source] From Feminist Thinking to Ecological Thinking: Determining the Bounds of CommunityHYPATIA, Issue 1 2008HEIDI E. GRASSWICK First page of article [source] Hybrid domain decomposition algorithms for compressible and almost incompressible elasticityINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2010Clark R. Dohrmann Abstract Overlapping Schwarz methods are considered for mixed finite element approximations of linear elasticity, with discontinuous pressure spaces, as well as for compressible elasticity approximated by standard conforming finite elements. The coarse components of the preconditioners are based on spaces, with a number of degrees of freedom per subdomain which are uniformly bounded, which are similar to those previously developed for scalar elliptic problems and domain decomposition methods of iterative substructuring type, i.e. methods based on nonoverlapping decompositions of the domain. The local components of the new preconditioners are based on solvers on a set of overlapping subdomains. In the current study, the dimension of the coarse spaces is smaller than in recently developed algorithms; in the compressible case all independent face degrees of freedom have been eliminated while in the almost incompressible case five out of six are not needed. In many cases, this will result in a reduction of the dimension of the coarse space by about one half compared with that of the algorithm previously considered. In addition, in spite of using overlapping subdomains to define the local components of the preconditioner, values of the residual and the approximate solution need only to be retained on the interface between the subdomains in the iteration of the new hybrid Schwarz algorithm. The use of discontinuous pressures makes it possible to work exclusively with symmetric, positive-definite problems and the standard preconditioned conjugate gradient method. Bounds are established for the condition number of the preconditioned operators. The bound for the almost incompressible case grows in proportion to the square of the logarithm of the number of degrees of freedom of individual subdomains and the third power of the relative overlap between the overlapping subdomains, and it is independent of the Poisson ratio as well as jumps in the Lamé parameters across the interface between the subdomains. Numerical results illustrate the findings. Copyright © 2009 John Wiley & Sons, Ltd. [source] Bounds on outputs of the exact weak solution of the three-dimensional Stokes problemINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10 2009Zhong Cheng Abstract A method for obtaining rigorous upper and lower bounds on an output of the exact weak solution of the three-dimensional Stokes problem is described. Recently bounds for the exact outputs of interest have been obtained for both the Poisson equation and the advection-diffusion-reaction equation. In this work, we extend this approach to the Stokes problem where a novel formulation of the method also leads to a simpler flux calculation based on the directly equilibrated flux method. To illustrate this technique, bounds on the flowrate are calculated for an incompressible creeping flow driven by a pressure gradient in an endless square channel with an array of rectangular obstacles in the center. Copyright © 2009 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||