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Superposition

Distribution by Scientific Domains
Chemistry29%
Engineering15%
Earth and Environmental Science14%
Physics and Astronomy13%
Polymers and Materials Science10%
Medical Sciences6%
Mathematics and Statistics5%
Life Sciences3%
2 Other Domains5%
Distribution within Chemistry
Crystallography34%
Protein Science6%
13 Other Subdomains60%

Kinds of Superposition

  • coherent superposition
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  • temperature superposition
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    Terms modified by Superposition

  • superposition error
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  • superposition method
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  • superposition principle
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    Selected Abstracts

    Darwin would be proud: Bioturbation, dynamic denudation, and the power of theory in science

    GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 1 2002
    D. L. Johnson
    Charles Darwin's worm book influenced many early researchers who, following his lead, demonstrated how soil biota mechanically generate new strata and soil horizons, as well as blur or destroy them. Such early observations on biomechanical processes failed to find visibility in our models of landscape evolution for several reasons, chief of which are (1) except for ichnology, an Earth sciences tradition of adopting frameworks where biomechanical processes are absent and (2) a lapse of over 100 years after Darwin before a genetic language backed by supporting theory appeared that could showcase the importance of such processes. Examples of influential Earth science frameworks in which biomechanical processes are absent are the V.V. Dokuchaev,USDA,H. Jenny soil formational (five factors) paradigm, W.M. Davis' geographical cycle, the W. Penck,L.C. King,R.V. Ruhe backwasting-pedimentation concept, the stratigraphic Law of Superposition, and other traditional approaches to archaeology, geomorphology, and pedology. Examples of recent genetic language that serve to ameliorate the problem are soil thickness concepts, biomantle, bioturbation, faunalturbation, floralturbation, and pedoturbation. Examples of recent supporting theory that incorporate biomechanical processes are soil evolution, biomantle evolution, dynamic pedogenesis, and the dynamic denudation framework advocated here. Dynamic denudation is a unified synthesis that elevates bioturbation to parity levels with other major archaeogenic, geomorphogenic, and pedogenic processes. The general framework and its principal elements are summarized and simulated by diagrams and augmented by photographs taken in disparate parts of the world. The model has useful explanatory and predictive value in archaeology, geomorphology, pedology, and other surficial process research. © 2002 John Wiley & Sons, Inc. [source]

    Application of Superposition with Nonlinear Head-Dependent Fluxes

    GROUND WATER, Issue 2 2008
    Timothy Durbin
    While superposition is commonly used to address linear ground water problems, it can also be used to address certain nonlinear problems. In particular, it can be used to address problems with nonlinear head-dependent fluxes, where the problem can be separated conveniently into steady-state and transient-state components. Superposition can be used to simulate the transient-state head changes independently from the steady-state heads. The problems addressable by superposition include phreatophyte discharges, stream-aquifer interactions, spring discharges, and drain discharges. Each of these represents a nonlinear head-dependent flux, where the flux depends on the elevation of the land surface or some other feature. Superposition is applied by referencing elevations to the local steady-state water table and by imposing the negative of the steady-state flux on the transient-state problem. [source]

    Superposition of the output pulses under synchronous discharge in a multiple-electrode-pair laser

    MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2002
    Lihua Ye
    Abstract If the pressure, voltage, and other discharge parameters of a multiple-electrode-pair laser are held constant, there is a nonlinear pulse energy enhancement effect when several sets of electrode pairs are triggered synchronously. The mechanism of the effect is analyzed and a reasonable theoretical model, which is in agreement with the experimental results, is built. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 207,211, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10418 [source]

    Single- or multistage regulation in complex life cycles: does it make a difference?

    OIKOS, Issue 2 2000
    Barbara Hellriegel
    Data on the different stages of complex life cycles are often rather unbalanced, especially those concerning the effects of density. How does this affect our understanding of a species' population dynamics? Two discrete three-stage models with overlapping generations and delayed maturation are constructed to address this question. They assume that survival or emigration in any life stage and/or reproduction can be density dependent. A typical pond-breeding amphibian species with a well-studied larval stage serves as an example. Numerical results show that the population dynamics resulting from density dependence at a single (e.g. the larval) stage can be decisively and unpredictably modified by density dependence in additional stages. Superposition of density-dependent processes could thus be one reason for the difficulties in identifying density dependence in the field. Moreover, in a simulated source-refuge system with habitat-specific density-dependent dispersal of juveniles density dependence in multiple stages can stabilize or destabilize the dynamics and produce misleading age structures. From an applied perspective this model shows that excluding multistage regulation prematurely clearly affects our ability to predict consequences of human impacts. [source]

    Influence of electron-phonon coupling on transport through a quantum dot in the Kondo regime

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2009
    wirkowicz
    Abstract Transport through a quantum dot attached to nonmagnetic electrodes subject to spin bias and charge bias is studied theoretically within the non-equilibrium Green function formalism and effects of local vibrational modes are analysed. A presence of phonons strongly influences the spin and charge conductance characteristics leading to an appearance of phonon satellites apart from Kondo peaks. Superposition of the main Kondo resonances and their phonon satellites in the conductance curves corresponding to two individual spin channels can lead to a variety of peak patterns in dependence on the charge voltage applied to the system (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Solution structure and proposed domain,domain recognition interface of an acyl carrier protein domain from a modular polyketide synthase

    PROTEIN SCIENCE, Issue 10 2007
    Viktor Y. Alekseyev
    Abstract Polyketides are a medicinally important class of natural products. The architecture of modular polyketide synthases (PKSs), composed of multiple covalently linked domains grouped into modules, provides an attractive framework for engineering novel polyketide-producing assemblies. However, impaired domain,domain interactions can compromise the efficiency of engineered polyketide biosynthesis. To facilitate the study of these domain,domain interactions, we have used nuclear magnetic resonance (NMR) spectroscopy to determine the first solution structure of an acyl carrier protein (ACP) domain from a modular PKS, 6-deoxyerythronolide B synthase (DEBS). The tertiary fold of this 10-kD domain is a three-helical bundle; an additional short helix in the second loop also contributes to the core helical packing. Superposition of residues 14,94 of the ensemble on the mean structure yields an average atomic RMSD of 0.64 ± 0.09 Å for the backbone atoms (1.21 ± 0.13 Å for all non-hydrogen atoms). The three major helices superimpose with a backbone RMSD of 0.48 ± 0.10 Å (0.99 ± 0.11 Å for non-hydrogen atoms). Based on this solution structure, homology models were constructed for five other DEBS ACP domains. Comparison of their steric and electrostatic surfaces at the putative interaction interface (centered on helix II) suggests a model for protein,protein recognition of ACP domains, consistent with the previously observed specificity. Site-directed mutagenesis experiments indicate that two of the identified residues influence the specificity of ACP recognition. [source]

    Precursor complex structure of pseudouridine synthase TruB suggests coupling of active site perturbations to an RNA-sequestering peripheral protein domain

    PROTEIN SCIENCE, Issue 8 2005
    Charmaine Hoang
    Abstract The pseudouridine synthase TruB is responsible for the universally conserved post-transcriptional modification of residue 55 of elongator tRNAs. In addition to the active site, the "thumb," a peripheral domain unique to the TruB family of enzymes, makes extensive interactions with the substrate. To coordinate RNA binding and release with catalysis, the thumb may be able to sense progress of the reaction in the active site. To establish whether there is a structural correlate of communication between the active site and the RNA-sequestering thumb, we have solved the structure of a catalytically inactive point mutant of TruB in complex with a substrate RNA, and compared it to the previously determined structure of an active TruB bound to a reaction product. Superposition of the two structures shows that they are extremely similar, except in the active site and, intriguingly, in the relative position of the thumb. Because the two structures were solved using isomorphous crystals, and because the thumb is very well ordered in both structures, the displacement of the thumb we observe likely reflects preferential propagation of active site perturbations to this RNA-binding domain. One of the interactions between the active site and the thumb involves an active site residue whose hydrogen-bonding status changes during the reaction. This may allow the peripheral RNA-binding domain to monitor progress of the pseudouridylation reaction. [source]

    Konstruktionsprinzipien an der Vorder- und Hinterpfote der Hauskatze (Felis catus).

    ANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 1 2005

    Zusammenfassung Die Innervationsverhältnisse an der Vorder- und Hintergliedmaße der Katze wurden erneut untersucht, um die Darstellung der Muskelinnervation zu komplettieren (Abb.1,4). Mit Hilfe von speziellen Bewegungsanalysen wird der Beitrag der Pfotenmuskeln beim Gleichgewicht, in der Fortbewegung sowie bei spezifischen Manipulationen an den jeweiligen Einzelphasen eines Bewegungszyklus ermittelt. Die funktionellen Überlegungen sind in Abb. 5,11 graphisch aufbereitet. Figure Abb. 1.,. Übersichtsschema vom Plexus brachialis der Hauskatze, Medialansicht (nach Roos, 1989). C6, C7, C8, T1 = Ventraläste der 6. bis 8. Hals- und des 1. Brustnerven; (T2) = gelegentlicher Zuschuß vom Ventralast des 2. Brustnerven. ax N. axillaris: ax + fakultativer Muskelast zum M. teres major, ax 1 Gelenkast an das Schultergelenk und Muskelast zum M. teres minor, ax 2 Muskeläste zur Pars scapularis und Pars acromialis des M. deltoideus, ax 3 weiterer Gelenkast zum Schultergelenk, ax 4 Muskeläste zum M. cleidobrachialis, ax 5 N. cutaneus brachii lateralis cranialis, ax 6 N. cutaneus antebrachii cranialis; mc N. musculocutaneus: mc1 Muskelast zum M. coracobrachialis und Gelenkast zum Schultergelenk, mc 2 Muskeläste zum M. biceps brachii und zum M. brachialis, mc 3 Gelenkast zum Ellbogengelenk, mc 4 N. cutaneus antebrachii medialis; me N. medianus: me 1 Gelenkast zum Ellbogengelenk, me 2 , me 8 Rami musculares: me 2 zum M. pronator teres, me 3 zum M. flexor carpi radialis, me 4, 4, zum Caput humerale des M. flexor digitalis profundus, me 5, 5, zum M. flexor digitalis superficialis, me 6 zum Caput radiale des M. flexor digitalis profundus, me 7 zum M. pronator quadratus, me 8 zum M. interflexorius dist lis, me 9 Hautast zum Karpalbereich, me 10 Ramus medialis, me 11 Ramus lateralis, me 12 N. digitalis palmaris I abaxialis, me 13 , me 15 Nn. digitales palmares I, II, III communes; ra N. radialis: ra 1 , ra 4 Rami musculares proximales: ra 1, 1, zum Caput longum des M. triceps brachii, ra 2 zum M. tensor fasciae antebrachii, ra 3 zum Caput laterale, Caput mediale und Caput accessorium des M. triceps brachii, ra 4 zum M. anconaeus, ra 5 Ramus profundus, ra 6 Gelenkast zum Ellbogengelenk, ra 7 , ra 8 Rami musculares distales: ra 7 zum M. brachioradialis und zu den Mm. extensores carpi radialis longus et carpi radialis brevis, ra 8 zum M. extensor digitalis communis, ra 8, zum M. supinator, M. abductor digiti primi longus, M. extensor digiti primi et secundi, M. extensor carpi ulnaris und M. extensor digitalis lateralis, ra 9 Ramus superficialis, ra 10 N. cutaneus brachii lateralis caudalis, ra 11 Ramus medialis, ra 12 Ramus lateralis, ra 13 N. cutaneus antebrachii lateralis, ra 14 N. dig talis I abaxialis, ra 15 , ra 17 Nn. digitales dorsales I, II, III communes, ra 18 Ramus communicans; s N. suprascapularis: s 1 Muskeläste zum M. supraspinatus, s 2 Gelenkäste zum Schultergelenk, s 3 Muskelast zum M. infraspinatus; ul N. ulnaris: ul 1 Muskelast zum M. anconaeus, ul 2 Gelenkast zum Ellbogengelenk, ul 3 , ul 6 Rami musculares: ul 3 zum Caput ulnare und ul 4 zum Caput humerale des M. flexor carpi ulnaris, ul 5,5, zum Caput humerale und ul 6 zum Caput ulnare des M. flexor digitalis profundus, ul 7 Ramus dorsalis, ul 8 sein Hautast, ul 9 N. digitalis dorsalis V abaxialis, ul 10 N. digitalis dorsalis IV communis, ul 11 Ramus palmaris, ul 12 Hautast zum Karpalbüschel und Karpalballen sowie Muskeläste zu den besonderen Muskeln der 5. Zehe, ul 13 Ramus profundus zu den tiefen Zehenmuskeln (siehe Abb. 2), ul 14 Ramus superficialis, ul 15 N. digitalis palmaris V abaxialis, ul 16 N. digitalis palmaris IV communis. Meßbalken 10 mm. Figure Abb. 2.,. Ramifikation der Nerven für die kurzen Zehenmuskeln der (linken) Vorderpfote der Hauskatze, Palmaransicht, schematisiert. Orientierungspunkte: 1 Os carpi accessorium, 2 Ligamentum accessoriometacarpeum, medialer Anteil; I , V Mittelfuß- und Zehenstrahlen; Umrisse des Sohlen- und der Zehenballen strichliert. me N. medianus: me 10 Ramus medialis und me 11 Ramus lateralis des N. medianus, me 12 N. digitalis palmaris I abaxialis. ul N. ulnaris: ul 7 Ramus dorsalis, ul 11 Ramus palmaris, ul 12 Muskelast zu M. abductor digiti V und M. flexor digiti V, ul 13 Ramus profundus, ul 14 Ramus superficialis, ul 15 N. digitalis palmaris V abaxialis, ul 16 N. digitalis palmaris IV communis, ul 17 N. metacarpeus palmaris V, ul 18 N. metacarpeus palmaris IV lateralis, ul 18, N. metacarpeus palmaris IV medialis, ul 19 Muskelast zu M. adductor digiti V und Mm. lumbricales IV und V, ul 20 N. metacarpeus palmaris III, ul 21 N. metacarpeus II, ul 22 Muskeläste zu M. adductor pollicis und M. flexor pollicis brevis. Weitere Muskeläste sind gekennzeichnet mit Quadraten zu den Mm. adductores II und V, mit Kreisen zu den Mm. lumbricales, mit Pfeilen zu den Mm. interossei manus. Figure Abb. 3.,. Übersichtsschema vom Plexus lumbosacralis der Hauskatze, Medialansicht. L4, L5, L6, L7, S1, S2, S3 = Ventraläste der 4. , 7. Lenden- und 1. , 3. Kreuznerven. f N. femoralis: f 1 N. saphenus, f 2,7 Muskeläste für f 2, 2, M. sartorius, f 3,5 Bäuche des M. quadratus femoris, f 6 M. pectineus, f 7 M. gracilis, f 8 Gelenkast zum (medialen) Femorotibial- und Femoropatellargelenk, f 9 Rami cutanei; fc N. fibularis (peronaeus) communis: fc 1 Muskelast für den M. fibularis longus (alternativer Ursprung strichliert); fp N. fibularis (peronaeus) profundus: fp 1,3 Muskeläste für fp 1 M. tibialis cranialis, fp 2 M. extensor digitalis longus, fp 3 M. extensor hallucis longus, fp 4 N. metatarsalis dorsalis, fp 5 Muskelast zum M. extensor digitalis brevis; fs N. fibularis (peronaeus) superficialis: fs 1, 1, Muskeläste zum M. extensor digitalis lateralis, fs 2 zum M. fibularis brevis, fs 3 Ramus lateralis, fs 4 Ramus medialis, fs 5 Nn. digitales dorsales communes II , IV, fs 6 Nn. digitales dorsales proprii für die 2. bis 5. Zehe; g N. glutaeus cranialis bzw. caudalis: g 1 zum M. glutaeus medius, g 2 zum M. tensor fasciae latae, g 3 zum M. glutaeus profundus, g 4 zum M. piriformis, g 5 M. glutaeus superficialis, g 6 M. glutaeofemoralis; is N. ischiadicus: is 1 Muskeläste zu den Mm. gemelli und M. obturatorius internus, is 2, 2, zum M. biceps femoris, is 3 zum M. semitendinosus, is 4 zum M. semimembranosus, is 5 zum M. abductor cruris caudalis (tenuissimus); ti N. tibialis: ti 1 N. cutaneus surae caudalis, ti 2 Gelenkast zum (lateralen) Femorotibialgelenk, ti 3,5 Muskeläste für ti 3 Caput mediale des M. gastrocnemius, ti 4 Caput laterale des M. gastrocnemius sowie M. flexor digitalis superficialis und M. flexor hallucis longus, ti 5,5, M. popliteus, M. flexor digitalis profundus, M. tibialis caudalis und M. soleus, ti 6 N. plantaris medialis, ti 7 N. plantaris lateralis, ti 8 Ramus profundus (s. auch Abb. 4), ti 9 Muskelast zum M. flexor digitalis brevis, ti 10 Nn. digitales plantares communes II , IV, ti 11 Nn. digitales plantares proprii für die 2. , 5. Zehe; ob N. obturatorius: ob 1,5 Muskeläste für ob 1 M. pectineus, ob 2 M. adductor longus, ob 3 M. adductor magnus, ob 4 M. gracilis, ob 5 M. obturatorius externus. Meßbalken 10 mm. Figure Abb. 4.,. Ramifikation der Nerven für die kurzen Zehenmuskeln der (linken) Hinterpfote der Hauskatze, Plantaransicht, schematisiert. Orientierungspunkte: 1 Tuber calcanei; II , V Mittelfuß- und Zehenstrahlen; Umrisse des Sohlen- und der Zehenballen strichliert. ti N. tibialis: ti 6 N. plantaris medialis, ti 7 N. plantaris lateralis, ti 8 Ramus profundus, ti 9 Muskelast zum M. flexor digitalis brevis, ti 10 Nn. digitales plantares communes II und III, ti 11 N. digitalis plantaris II abaxialis, ti 12 N. metatarseus plantaris V, ti 13 N. metatarseus plantaris IV lateralis, ti 13, N. metatarseus plantaris IV medialis, ti 14 Muskelast zu den Mm. adductores digiti II und V, ti 15 N. metatarseus plantaris III, ti 16 N. metatarseus plantaris II, ti 17 Muskelast zum M. abductor digiti V, ti 18 Muskelast zum M. quadratus plantae, ti 19 Stamm des N. digitalis plantaris communis IV und N. digitalis plantaris V abaxialis. Weitere Muskeläst sind gekennzeichnet mit hochstehenden Rechtecken zu den Mm. digitales flexores breves, mit Quadraten zu den Mm. adductores II und V, mit Kreisen zu den Mm. lumbricales, mit Pfeilen zu den Mm. interossei pedis. Figure Abb. 5.,. Statik der Hauskatze in Normalstellung (nach Roos, 1989) (Sk) Lage des Schwerpunkts des Körpers; das gefällte Lot, die Schwerelinie, trifft die Unterstützungsfläche, d.h. das Rechteck zwischen den Gliedmaßenspitzen. Figure Abb. 6.,. Prinzip der Zuggurtung an der Vorder- (rechts) und Hintergliedmaße (links) der Hauskatze. Das Schwerelot der Hintergliedmaße (Sh) aus dem Hüftgelenk und das Schwerelot der Vordergliedmaße (Sv) aus dem Rumpfschultergelenk treffen die Fußungsflächen der Hinter- bzw. Vorderpfote. Die zur Aufrechterhaltung des Gleichgewichts notwendige minimale Zuggurtung der Gelenke erfolgt durch folgende Muskeln: 1 kranialer Bauch des M. semimembranosus, 2 Mm. vastus lateralis, vastus medialis und vastus intermedius des M. quadriceps femoris, 3 M. soleus, 4 plantare Endsehnen der Mm. interossei pedis, 5 M. supraspinatus, 6 Caput laterale, Caput mediale und Caput accessorium des M. triceps brachii, 7 Caput ulnare des M. flexor carpi ulnaris, 8 Mm. extensorii carpi radialis longus und carpi radialis brevis, 9 palmare Endsehnen der Mm. interossei manus. Einzelheiten im Text. Figure Abb. 7.,. Dynamik der Vorderpfote der Hauskatze in der Fortbewegung. Obere Reihe: Diagramme der Schrittbewegung der Vorderpfote, nach Röntgenbildern auf dem Laufband (in Anlehnung an Caliebe et al., 1991, kombiniert und ergänzt, Ergänzungen strichliert). Untere Reihen: Änderung der Gelenkwinkel und daraus abgeleitete Kontraktionen, evtl. Superpositionen sowie Entspannung verschiedener Muskeln oder Muskelgruppen: Große dunkle Pfeile = Beginn der Kontraktion, kleine Pfeile = anhaltende Kontraktion, gestreifte Pfeile = Superposition, helle Pfeile = Beginn der Entspannung 1 Beuger des Karpalgelenks, 2 Strecker des Karpalgelenks, 3 Wirkung des M. flexor carpi radialis als Adduktor, 4 Wirkung des M. extensor carpi radialis als Abduktor der Vorderpfote, 5 M. flexor digitalis superficialis, 6 lange Zehenstrecker, 7 Mm. interossei manus, 8 entspannter M. flexor digitalis profundus (manus) läßt das Krallenbein in Schonstellung. Seqq: Sequenzen 1,35. Figure Abb. 8.,. Dynamik der Hinterpfote der Hauskatze in der Fortbewegung. Obere Reihe: Diagramme der Schrittbewegung der Hinterpfote, nach Röntgenbildern auf dem Laufband (in Anlehnung an Kuhtz-Buschbeck et al., 1994, maßstab- und synchrongerecht eingerichtet und ergänzt, Ergänzungen strichliert). Untere Reihen: Änderung der Gelenkwinkel und daraus abgeleitete Kontraktionen, evtl. Superpositionen sowie Entspannung verschiedener Muskeln oder Muskelgruppen: Große dunkle Pfeile = Beginn der Kontraktion, kleine Pfeile = anhaltende Kontraktion, gestreifte Pfeile = Superposition, helle Pfeile = Beginn der Entspannung 1 Beuger des Tarsalgelenks, 2 Strecker des Tarsalgelenks, 3 M. flexor digitalis superficialis (pedis), 4 lange Zehenstrecker, 5 Mm. interossei pedis, 6 entspannt bleibender M. flexor digitalis profundus (pedis). Seqq: Sequenzen 1,35. Figure Abb. 9.,. Vorderpfote der Hauskatze in ihrer Funktion als Fangorgan, schematisiert. Obere Reihe: Perspektivische Darstellung nach Beobachtung an Freilaufkatzen, teilweise ergänzt nach Röntgenbildern von Boczek-Funcke et al. (1998). Untere Reihen: Bewegungsablauf aufgelöst nach den drei Bewegungsebenen S = Sagittalebene, A Abduktion , Adduktion, R = Rotationsebene. Einzelheiten im Text. Seqq: Sequenzen 1,5. Wirkungslinien der aktiven Muskeln: 1 M. flexor digitalis superficialis, 2 M. extensor digitalis communis und M. extensor digitalis lateralis, 3 M. flexor digitalis profundus, 4 Mm. interossei manus, 4, seine axialen Bäuche, 4, seine abaxialen Bäuche, 5 M. adductor digiti V, 6 M. adductor digiti II, 7 M. adductor pollicis, 8 M. extensor pollicis et indicis, 9 M. abductor digiti V und M. flexor digiti V, 10 M. abductor pollicis longus, 11 M. abductor digiti II, 12 M. flexor pollicis brevis, 13 M. pronator teres und M. pronator quadratus, 14 M. brachioradialis und M. supinator. Figure Abb. 10.,. Spezielle Bewegungen der Hinterpfote vor (oben) und während des Spurtstarts (unten), schematisiert. Situation in der S , Ebene. 1,4 Muskeln in Unterstützungskontraktion: 1 zweiköpfiger M. gastrocnemius, 2 M. soleus, 3 M. extensor hallucis longus, 4 M. tibialis cranialis, 5 M. flexor digitalis superficialis, 6 Mm. interossei pedis, 7 M. extensor digitalis longus, 8 M. extensor digitalis brevis, 9 M. flexor digitalis profundus. Figure Abb. 11.,. Dynamik bei der Kletterhaltung der Hinterpfote der Hauskatze, schematisch. Links Grundhaltung, rechts Spreizung und Streckung der Zehen II , V; der Mittelfuß nimmt an der Spreizung nicht teil. Beteiligte Muskeln: 1 M. adductor digiti V, 2 M. adductor digiti II, 3 M. abductor digiti V, 4 axiale Bäuche der Mm. interossei II , V pedis, 5 abaxiale Bäuche der Mm. interossei II , V pedis. Einzelheiten im Text. Summary Principles of construction in the forepaw and hindpaw of the domestic cat (Felis catus). 4. Innervation of muscles and analysis of locomotion. The innervation relations of the fore- and hindlimb of the cat were newly investigated to complete the interpretation of the muscle innervation (Figs 1,4). By means of special motion studies the contribution of paw muscles was determined during balance, locomotion as well as under specific manipulation of the prevailing sincle phases of the motion cycle. The functional considerations are graphically prepared in Figs 5,11. [source]

    N -Phenyl- N,-pyridylureas: stereochemical basis for anti­convulsant activity

    ACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2006
    Arthur Camerman
    4-[N -(2-Chloro-6-methyl­phen­yl)ureido]pyridinium chloride, C13H13ClN3O+·Cl, (CI-953 hydro­chloride), crystallizes with Z, = 2 in P. In both mol­ecules, the methyl groups and Cl atoms on the benzene rings are disordered. The benzene rings of mol­ecules A and B adopt two conformations, differing by a rotation of 180° about the C,N bond to the ureido group, in an approximate 1:1 ratio. This disorder is further enhanced by the rotation of the methyl groups in both adopted positions. The pyridine and benzene rings inter­sect at angles of 102.1,(1) and 111.3,(1)° for A and B, respectively. Hydrogen bonding is mediated by Cl, anions, resulting in indirect connectivity between the mol­ecules. Superposition of the mol­ecular structure, after 180° rotation about an amide bond, with that of phenytoin shows that the chemically different mol­ecules possess stereochemical features in common, which may explain their common activities. [source]

    Structure of the newly found green turtle egg-white ribonuclease

    ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 7 2010
    Somporn Katekaew
    Marine green turtle (Chelonia mydas) egg-white ribonuclease (GTRNase) was crystallized from 1.1,M ammonium sulfate pH 5.5 and 30% glycerol using the sitting-drop vapour-diffusion method. The structure of GTRNase has been solved at 1.60,Å resolution by the molecular-replacement technique using a model based on the structure of RNase 5 (murine angiogenin) from Mus musculus (46% identity). The crystal belonged to the monoclinic space group C2, with unit-cell parameters a = 86.271, b = 34.174, c = 39.738,Å, , = 90, , = 102, , = 90°. GTRNase consists of three helices and seven ,-strands and displays the ,+, folding topology typical of a member of the RNase A superfamily. Superposition of the C, coordinates of GTRNase and RNase A superfamily members indicates that the overall structure is highly similar to that of angiogenin or RNase 5 from M. musculus (PDB code 2bwl) and RNase A from Bos taurus (PDB code 2blz), with root-mean-square deviations of 3.9 and 2.0,Å, respectively. The catalytic residues are conserved with respect to the RNase A superfamily. The three disulfide bridges observed in the reptilian enzymes are conserved in GTRNase, while one further disulfide bond is required for the structural stability of mammalian RNases. GTRNase is expressed in egg white and the fact that its sequence has the highest similarity to that of snapping turtle pancreatic RNase suggests that the GTRNase secreted from oviduct cells to form egg white is probably the product of the same gene as activated in pancreatic cells. [source]

    CFD Study of Effects of Module Geometry on Forced Convection in a Channel with Non-Conducting Fins and Flow Pulsation

    CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 10 2010
    B. O. Olayiwola
    Abstract CFD simulations were carried out to investigate the effects of the module geometry on forced convection in a rectangular channel containing series of regularly spaced non-conducting baffles with flow oscillation. The simulations were performed at constant wall temperature. Steady-flow Reynolds numbers Re in the range of 200 and 600 were studied. The results of the CFD simulations show that, for the effect fin spacing to be significant on heat transfer enhancement in finned system with oscillating flow, the oscillating flow velocity must be higher than the mean flow velocity. Superposition of oscillation yields increasing heat transfer performance with increasing fin height. Fin geometry with pyramidal shape yields highest performance in terms of the heat transfer effectiveness. [source]

    Non-stationary plane problem of the successive origination of stress concentrators in a loaded body.

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 12 2008
    Finite deformations, their superposition
    Abstract The first (for the given class of problems) results of solving non-stationary plane problems of non-simultaneous origination of holes and inclusions in a preliminary loaded solid with initial finite strains are presented and discussed. It is taken into account that the origination of a hole or an inclusion produces additional finite deformations (at least, at the vicinity of the hole) superimposed ,physically' on the finite initial ones. The problem is solved using the theory of repeated superposition of large deformations. It is supposed that the shape of stress concentrators is given at the moment of their origination. Calculations were made with the use of the specialized computer package ,Superposition' based on finite-element method. Stress fields are presented at different times. The change of maximal stresses in time is also presented. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    On the inversion of multicomponent NMR relaxation and diffusion decays in heterogeneous systems

    CONCEPTS IN MAGNETIC RESONANCE, Issue 2 2005
    Raffaele Lamanna
    Abstract The analysis of the decay of NMR signals in heterogeneous samples requires the solution of an ill-posed inverse problem to evaluate the distributions of relaxation and diffusion parameters. Laplace transform is the most widely accepted algorithm used to describe the NMR decay in heterogeneous systems. In this article we suggest that a superposition of Fredholm integrals, with different kernels, is a more suitable model for samples in which liquid and solid-like phases are both present. In addition, some algorithms for the inversion of Laplace and Fredholm inverse problems are illustrated. The quadrature methods and regularization function in connection with the use of nonlinear discretization grids are also discussed. The described inversion algorithms are tested on simulated and experimental data, and the role of noise is discussed. © 2005 Wiley Periodicals, Inc. Concepts Magn Reson Part A 26A: 78,90, 2005 [source]

    Stability of surface waves at magnetized plasma , metal interface

    CONTRIBUTIONS TO PLASMA PHYSICS, Issue 7 2003
    Yu. A. Akimov
    Abstract The stability of high-frequency potential surface waves at a dense magnetized plasma , metal interface with respect to a low-frequency plasma density modulation is studied in the point of view of the surface waves control. The discussion is addressed to the situation, when an external steady magnetic field is directed perpendicularly to the interface. The nonlinear interaction process of the high-frequency surface wave, its satellites and the low-frequency plasma density perturbation is investigated. It is shown that the low-frequency plasma density perturbation can be represented as a superposition of forced waves of surface and volume types and can lead to an additional attenuation of the surface waves. This attenuation arises when the surface wave amplitude exceeds the threshold value. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Superimposed Elastic Stockings: Pressure Measurements

    DERMATOLOGIC SURGERY, Issue 3 2007
    ANDRÉ CORNU-THENARD MD
    BACKGROUND High-compression stockings over 40 mmHg are often difficult or even impossible to apply. A specific technique is frequently used to overcome this problem: a high-compression stocking is replaced by two or even three lower compression stockings that are applied on top of each other, thereby reducing the effort of application. To our knowledge, however, no study concerning therapeutic stockings has demonstrated that the forces exerted by two or three superimposed stockings are additive. OBJECTIVE The objective was to evaluate if the pressures exerted by two or three superimposed elastic stockings are additive. MATERIAL AND METHODS A series of measurements was performed in vitro using an apparatus fitted with a pressure sensor on four different premade elastic stockings applied separately and then superimposed. The actual pressure measurement obtained with superimposed stockings was compared to arithmetic sum of the pressures produced by each of the stockings used. RESULTS The pressures produced by superimposed stockings are adequately predicted from the pressure given by each of the stockings used in the superposition, with correlation coefficients higher than 0.9. CONCLUSION Under our experimental conditions, the superimposed elastic stocking pressures additivity hypothesis is confirmed. In vivo studies should be conducted to confirm those results. [source]

    Instability investigation of cantilevered seacliffs

    EARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2008
    Adam P. Young
    Abstract Wave action is a fundamental mechanism in seacliff erosion, whereby wave undercutting creates an unstable cantilevered seacliff profile and can lead to large catastrophic cliff failures, thus threatening coastal infrastructure. This study investigated the instability of two such failures that occurred in Solana Beach, California, by combining terrestrial LIDAR scanning, cantilever beam theory and finite element analysis. Each landslide was detected by evaluating the surface change between subsequent high resolution digital terrain models derived from terrestrial LIDAR data. The dimensions of failed cantilever masses were determined using the surface change measurements and then incorporated into failure stress analysis. Superimposing stress distributions computed from elastic cantilever beam theory and finite element modeling provided a method to back-calculate the maximum developed tensile and shear stresses along each failure plane. The results of the stress superposition revealed that the bending stresses caused by the cantilevered load contributed the majority of stress leading to collapse. Both shear and tensile failure modes were investigated as potential cliff failure mechanisms by using a comparison of the back-calculated failure stresses to material strengths found in laboratory testing. Based on the results of this research, the tensile strength of the cliff material was exceeded at both locations, thus causing the cliffs to collapse in tension. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Semi-empirical model for site effects on acceleration time histories at soft-soil sites.

    EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 11 2004
    Part 1: formulation, development
    Abstract A criterion is developed for the simulation of realistic artificial ground motion histories at soft-soil sites, corresponding to a detailed ground motion record at a reference firm-ground site. A complex transfer function is defined as the Fourier transform of the ground acceleration time history at the soft-soil site divided by the Fourier transform of the acceleration record at the firm-ground site. Working with both the real and the imaginary components of the transfer function, and not only with its modulus, serves to keep the statistical information about the wave phases (and, therefore, about the time variation of amplitudes and frequencies) in the algorithm used to generate the artificial records. Samples of these transfer functions, associated with a given pair of soft-soil and firm-ground sites, are empirically determined from the corresponding pairs of simultaneous records. Each function included in a sample is represented as the superposition of the transfer functions of the responses of a number of oscillators. This formulation is intended to account for the contributions of trains of waves following different patterns in the vicinity of both sites. The properties of the oscillators play the role of parameters of the transfer functions. They vary from one seismic event to another. Part of the variation is systematic, and can be explained in terms of the influence of ground motion intensity on the effective values of stiffness and damping of the artificial oscillators. Another part has random nature; it reflects the random characteristics of the wave propagation patterns associated with the different events. The semi-empirical model proposed recognizes both types of variation. The influence of intensity is estimated by means of a conventional one-dimensional shear wave propagation model. This model is used to derive an intensity-dependent modification of the values of the empirically determined model parameters in those cases when the firm-ground earthquake intensity used to determine these parameters differs from that corresponding to the seismic event for which the simulated records are to be obtained. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    Assembly of Dinuclear CuII Rigid Blocks by Bridging Azido or Poly(thiocyanato)chromates: Synthesis, Structures and Magnetic Properties of Coordination Polymers and Polynuclear Complexes

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2010
    Sergey V. Kolotilov
    Abstract Reaction of a dinuclear cationic copper(II) complex of 4,4,-[2-(3-hydroxyiminobutyl)imino]biphenyl [CuII2(LH)2]2+ with N3, resulted in the formation of a dinuclear azido [CuII2(LH)2(N3)2(H2O)2] complex or a 2D coordination polymer [CuII2(LH)2(N3)2]n. Reaction of the dinuclear complex with [CrIII(NCS)6]3, or [CrIII(NCS)4(NH3)2], produced a 2D polymer {[CuII2(LH)2(CH3CN)2]3[CrIII(NCS)6]2}n or a 1D chain, constructed from tetranuclear units {[CuII2(LH)2][CrIII(NCS)4(NH3)2]2}n. Structures of the compounds were determined by X-ray crystallography and complexes were characterised by the temperature dependency of the magnetic susceptibility and by ESR spectroscopy. Magnetic properties of homometallic compounds were fit with the model of a dimer with the Hamiltonian , = ,J,1·,2. For heterometallic complexes ,MT curves were fit as the superposition of magnetism resulting from both [CuII2(LH)2]2+ and the adjacent CrIII -containing anion. J values for the complexes lie in the range from ,12.74(4) to ,17.77(8) cm,1. It was shown that the 4,4,-biphenyl bridge efficiently mediates exchange interactions. [source]

    Effects of toroidal HVDC ground electrode on earth-return circuits

    EUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 5 2002
    W. Machczy
    This paper presents a method of evaluation of currents and potentials, excited by conductive effects of high-voltage direct-current (HVDC) transmission system, along two parallel earth-return circuits such as pipelines and cables buried in the vicinity of a toroidal ground electrode. It is assumed that the system considered is linear and that the earth is an isotropic, homogeneous medium of finite conductivity. Conductive coupling between earth-return circuits is taken into account, whereas the reaction of the conductors' currents on the electrode current is disregarded. The transmission line model of the conductor with earth-return, a segmental linear approximation of the curve of the primary earth potential distribution along the conductor and the concept of superposition have been used in the method. It should be pointed out, that the method does not require the time consuming numerical integration. The technical applications of the method are illustrated by examples. [source]

    Fatigue of shot peened 7075-T7351 SENB specimen , A 3-D analysis

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 6 2006
    T. HONDA
    ABSTRACT As-received or shot peened 7075-T7351 single-edged notch bend (SENB) specimens, 8.1-mm thick, were fatigued at a constant maximum load and at stress ratios of R= 0.1 and 0.8 to predetermined numbers of fatigue cycles or to failure. The SENB specimens were then fractured by overload and the tunnelling crack profiles were recorded. The crack-growth rate, da/dN, after crack initiation at the notch was determined by crack-profile measurement and fractography at various fatigue cycles. The shot peened surface topography and roughness was also evaluated by three-dimensional (3-D) laser scanning microscopy. Residual stresses in the as-received specimens and those generated by shot peening at Almen scales of 0.004A, 0.008A, 0.012A and 0.016A, were measured by an X-ray diffraction stress analyser with an X-ray target, CrK, every 0.1 mm to a depth of 1 mm. The 3-D stress intensity factor of the curved crack front was determined by the superposition of the 3-D finite element solutions of the stress intensity factor of the loaded SENB specimen without the residual stress and the stress intensity factor of the unloaded SENB specimen with a prescribed residual stress distribution. da/dN versus the resultant stress intensity factor amplitude, ,KI, plots showed that while the residual stress locally retarded the crack-growth rate it had no effect on the overall crack-propagation rate. [source]

    Theoretical crack path prediction

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1-2 2005
    H. A. RICHARD
    ABSTRACT In many practical cases, the crack growth leads to abrupt failure of components and structures. For reasons of a reliable quantification of the endangerment due to sudden fracture of a component, therefore, it is of enormous importance to know the threshold values, the crack paths and the growth rates for the fatigue crack growth as well as the limiting values for the beginning of unstable crack growth (fracture toughness). This contribution deals with the complex problem of a,however initiated,crack, that is subjected to a mixed-mode loading. It will present the hypotheses and concepts, which describe the superposition of Mode I and Mode II (plane mixed mode) as well as the superposition of all three modes (Mode I, II and III) for spatial loading conditions. Those concepts admit a quantitative appraisal of such crack situations and a characterization of possible crack paths. [source]

    Low-Temperature Superionic Conductivity in Strained Yttria-Stabilized Zirconia

    ADVANCED FUNCTIONAL MATERIALS, Issue 13 2010
    Michael Sillassen
    Abstract Very high lateral ionic conductivities in epitaxial cubic yttria-stabilized zirconia (YSZ) synthesized on single-crystal SrTiO3 and MgO substrates by reactive direct current magnetron sputtering are reported. Superionic conductivities (i.e., ionic conductivities of the order ,1 ,,1cm,1) are observed at 500,°C for 58-nm-thick films on MgO. The results indicate a superposition of two parallel contributions , one due to bulk conductivity and one attributable to conduction along the film,substrate interface. Interfacial effects dominate the conductivity at low temperatures (<350,°C), showing more than three orders of magnitude enhancement compared to bulk YSZ. At higher temperatures, a more bulk-like conductivity is observed. The films have a negligible grain-boundary network, thus ruling out grain boundaries as a pathway for ionic conduction. The observed enhancement in lateral ionic conductivity is caused by a combination of misfit dislocation density and elastic strain in the interface. These very high ionic conductivities in the temperature range 150,500,°C are of great fundamental importance but may also be technologically relevant for low-temperature applications. [source]

    Duplex architecture and late-orogenic backthrusting in Foredeep Units of the Northern Apennines (Italy)

    GEOLOGICAL JOURNAL, Issue 4 2008
    Andrea Cerrina Feroni
    Abstract The Northern Apennines of Italy is a fold and thrust belt that resulted from the NE-ward progressive overthrusting of a Mesoalpine stacking (the ocean-derived Ligurian Units) onto the detached sedimentary cover of the Adria plate continental margin (Foredeep Units). The Futa Pass area represents a key sector for the reconstruction of the deformation history of two Foredeep Units (Acquerino and Carigiola Units). The tectonic evolution of this sector is characterized by the superposition of three main deformation stages, with a constant NNE,SSW compression direction. The oldest structure is represented by the NNE-verging Acquerino Unit duplex structure, the roof thrust of which is represented by the Ligurian stacking basal thrust. The interpretation of this structure as a large-scale duplex is supported by the presence in the outer sectors of the Northern Apennines belt of Ligurian Units directly overthrust on younger Foredeep Units. In the second deformation stage the NNE-verging Tavaiano Thrust developed. This regionally significant tectonic surface juxtaposes the Acquerino Unit (already developed as a duplex) and the overlying Ligurian Units, onto the Carigiola Unit. During this stage the fault pattern of the Carigiola Unit was also developed, characterized by two conjugate fault systems, coherent with a NNE,SSW maximum compression direction. During the last deformation stage, a backthrusting with a top-to-the SSW sense of movement (the Marcoiano Backthrust) brings the Carigiola Unit and its tectonic cover over the Acquerino and Ligurian Units, with the development of a large footwall syncline. The deformation history presented here differs from previous studies, and so provides a contribution to the debate on Northern Apennines tectonic evolution. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Desert environments: landscapes and stratigraphy

    GEOLOGY TODAY, Issue 5 2009
    Peter G. Fookes
    It is common to think of hot deserts, i.e. hot arid or dry lands, as areas of little rain situated in the middle parts of the world, that are simply ,just there'. However, most of the world's deserts have a long geological history, sometimes of 50 million years or more and ways have been developing for some time now, particularly from geomorphological studies, of not only erecting the law of superposition of strata for the desert but also ,absolute' dating. The authors have often worked commercially in deserts world-wide but their recent experiences in the Oman have brought home to them the excellent work that has been going on in the last two or three decades in evaluating the geological history of deserts. The Oman experience is described in a feature in the next issue. [source]

    Magma flow in the East Greenland dyke swarm inferred from study of anisotropy of magnetic susceptibility: magmatic growth of a volcanic margin

    GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2004
    Jean-Paul Callot
    SUMMARY Volcanic passive margins (VPMs) are characterized by large volumes of melt emplaced within the lithosphere during break-up processes. Several data and a recently proposed conceptual model of volcanic margin development suggest that VPMs are fed from localized crustal zones of magma storage, underlying large polygenetic volcanoes localized above diapir-like instabilities of the asthenosphere. We investigated the magma flow pattern within the coast-parallel dyke swarm of the East Greenland VPM, which is the only outcropping VPM, over a distance of 125 km. The 44 sampled dykes are representative of the successive families of intrusions. Igneous petrofabrics are constrained by the measurements of the anisotropy of magnetic susceptibility. The magnetic fabrics are of medium to low anisotropy (P, < 1.08) and show moderately oblate ellipsoids (T > 0). Flow-related fabrics are recorded in 75 per cent of the sampled dykes. We infer the flow directions from the imbrication geometry of the magnetic foliation planes at the dyke margins, and check the results by measuring the preferred orientation of plagioclase in thin sections cut in the magnetic principal planes. Due to probable fabric superposition, the magnetic lineation represents the zone axis for the distribution of magnetic foliation plane. We obtained 23 reliable flow directions that are predominantly horizontal and directed away from identified crustal reservoirs. This flow pattern supports the proposed model of VPM growth, and emphasizes the localized nature of the magma sources in the mantle. The entire flood basalt sequence appears to have been fed by a restricted number of crustal reservoirs and associated dyke swarms. [source]

    Crustal underplating and its implications for subsidence and state of isostasy along the Ninetyeast Ridge hotspot trail

    GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2000
    Ingo Grevemeyer
    Recent seismic field work has revealed high lower-crustal velocities under Ninetyeast Ridge, Indian Ocean, indicating the presence of crustal underplating (Grevemeyer et al. 2000). We used results from Ocean Drilling Program (ODP) drill cores and cross-spectral analysis of gravity and bathymetric data to study the impact of the underplating body on the subsidence history and the mode of isostatic compensation along Ninetyeast Ridge. Compared with the adjacent Indian basin, the subsidence of Ninetyeast Ridge is profoundly anomalous. Within the first few millions of years after crustal emplacement the ridge subsided rapidly. Thereafter, however, subsidence slowed down significantly. The most reliable model of isostasy suggests loading of a thin elastic plate on and beneath the seafloor. Isostatic compensation of subsurface loading occurs at a depth of about 25 km, which is in reasonably good agreement with seismic constraints. Subsurface loading is inherently associated with buoyant forces acting on the lithosphere. The low subsidence may therefore be the superposition of cooling of the lithosphere and uplift due to buoyant material added at the base of the crust. A model including prolonged crustal growth in the form of subcrustal plutonism may account for all observations. [source]

    A damage mechanics model for power-law creep and earthquake aftershock and foreshock sequences

    GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2000
    Ian G. Main
    It is common practice to refer to three independent stages of creep under static loading conditions in the laboratory: namely transient, steady-state, and accelerating. Here we suggest a simple damage mechanics model for the apparently trimodal behaviour of the strain and event rate dependence, by invoking two local mechanisms of positive and negative feedback applied to constitutive rules for time-dependent subcritical crack growth. In both phases, the individual constitutive rule for measured strain , takes the form ,(t),=,,0,[1,+,t/m,]m, where , is the ratio of initial crack length to rupture velocity. For a local hardening mechanism (negative feedback), we find that transient creep dominates, with 0,<,m,<,1. Crack growth in this stage is stable and decelerating. For a local softening mechanism (positive feedback), m,<,0, and crack growth is unstable and accelerating. In this case a quasi-static instability criterion , , , can be defined at a finite failure time, resulting in the localization of damage and the formation of a throughgoing fracture. In the hybrid model, transient creep dominates in the early stages of damage and accelerating creep in the latter stages. At intermediate times the linear superposition of the two mechanisms spontaneously produces an apparent steady-state phase of relatively constant strain rate, with a power-law rheology, as observed in laboratory creep test data. The predicted acoustic emission event rates in the transient and accelerating phases are identical to the modified Omori laws for aftershocks and foreshocks, respectively, and provide a physical meaning for the empirical constants measured. At intermediate times, the event rate tends to a relatively constant background rate. The requirement for a finite event rate at the time of the main shock can be satisfied by modifying the instability criterion to having a finite crack velocity at the dynamic failure time, dx/dt , VR,, where VR is the dynamic rupture velocity. The same hybrid model can be modified to account for dynamic loading (constant stress rate) boundary conditions, and predicts the observed loading rate dependence of the breaking strength. The resulting scaling exponents imply systematically more non-linear behaviour for dynamic loading. [source]

    Application of Superposition with Nonlinear Head-Dependent Fluxes

    GROUND WATER, Issue 2 2008
    Timothy Durbin
    While superposition is commonly used to address linear ground water problems, it can also be used to address certain nonlinear problems. In particular, it can be used to address problems with nonlinear head-dependent fluxes, where the problem can be separated conveniently into steady-state and transient-state components. Superposition can be used to simulate the transient-state head changes independently from the steady-state heads. The problems addressable by superposition include phreatophyte discharges, stream-aquifer interactions, spring discharges, and drain discharges. Each of these represents a nonlinear head-dependent flux, where the flux depends on the elevation of the land surface or some other feature. Superposition is applied by referencing elevations to the local steady-state water table and by imposing the negative of the steady-state flux on the transient-state problem. [source]

    A Method for Evaluating Horizontal Well Pumping Tests

    GROUND WATER, Issue 5 2004
    David E. Langseth
    Predicting the future performance of horizontal wells under varying pumping conditions requires estimates of basic aquifer parameters, notably transmissivity and storativity. For vertical wells, there are well-established methods for estimating these parameters, typically based on either the recovery from induced head changes in a well or from the head response in observation wells to pumping in a test well. Comparable aquifer parameter estimation methods for horizontal wells have not been presented in the ground water literature. Formation parameter estimation methods based on measurements of pressure in horizontal wells have been presented in the petroleum industry literature, but these methods have limited applicability for ground water evaluation and are based on pressure measurements in only the horizontal well borehole, rather than in observation wells. This paper presents a simple and versatile method by which pumping test procedures developed for vertical wells can be applied to horizontal well pumping tests. The method presented here uses the principle of superposition to represent the horizontal well as a series of partially penetrating vertical wells. This concept is used to estimate a distance from an observation well at which a vertical well that has the same total pumping rate as the horizontal well will produce the same drawdown as the horizontal well. This equivalent distance may then be associated with an observation well for use in pumping test algorithms and type curves developed for vertical wells. The method is shown to produce good results for confined aquifers and unconfined aquifers in the absence of delayed yield response. For unconfined aquifers, the presence of delayed yield response increases the method error. [source]

    Numerical simulation of bolt-supported tunnels by means of a multiphase model conceived as an improved homogenization procedure

    INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 13 2008
    Patrick de Buhan
    Abstract This paper examines the possibility of applying a homogenization procedure to analyze the convergence of a tunnel reinforced by bolts, regarded as periodically distributed linear inclusions. Owing to the fact that a classical homogenization method fails to account for the interactions prevailing between the bolts and the surrounding ground and thus tends to significantly overestimate the reinforcement effect in terms of convergence reduction, a so-called multiphase model is presented and developed, aimed at improving the classical homogenization method. Indeed, according to this model, the bolt-reinforced ground is represented at the macroscopic scale as the superposition of two mutually interacting continuous phases, describing the ground and the reinforcement network, respectively. It is shown that such a multiphase approach can be interpreted as an extension of the homogenization procedure, thus making it possible to capture the ground,reinforcement interaction in a proper way, provided the constitutive parameters of the model and notably those relating to the interaction law can be identified from the reinforced ground characteristics. The numerical implementation of this model in a finite element method-based computer code is then carried out, and a first illustrative application is finally presented. Copyright © 2008 John Wiley & Sons, Ltd. [source]