Last Part (last + part)

Distribution by Scientific Domains

Selected Abstracts

Discrete numerical modelling of rockfill dams

R. Deluzarche
Abstract The aim of this study is to obtain quantitative information on the behaviour of rockfill used in embankment dams, and particularly on the influence of block breakage on the displacement field, from a numerical analysis using the Distinct element method. A methodology is set up to define the resistance of the 2D particles so that the same probability of breaking blocks may be reproduced as in a 3D material. The model uses the discrete element code PFC2D (Itasca Consulting Group Inc., PFC2D (Particle Flow Code in Two Dimensions), Version 3.0, 2002) and considers breakable clusters of 2D balls. The different parameters are determined from experimental data obtained from laboratory tests performed on rock blocks. The model is validated by comparing the results of the simulation of shearing tests with actual triaxial tests on rockfill material published in the literature. The numerical analysis of block crushing in an actual dam is proposed in the last part of this paper. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Numerical algorithms for modelling electrodeposition: Tracking the deposition front under forced convection from megasonic agitation

Michael Hughes
Abstract Electrodeposition is a widely used technique for the fabrication of high aspect ratio microstructures. In recent years, much research has been focused within this area aiming to understand the physics behind the filling of high aspect ratio vias and trenches on substrates and in particular how they can be made without the formation of voids in the deposited material. This paper reports on the fundamental work towards the advancement of numerical algorithms that can predict the electrodeposition process in micron scaled features. Two different numerical approaches have been developed, which capture the motion of the deposition interface and 2-D simulations are presented for both methods under two deposition regimes: those where surface kinetics is governed by Ohm's law and the Butler,Volmer equation, respectively. In the last part of this paper the modelling of acoustic forces and their subsequent impact on the deposition profile through convection is examined. Copyright © 2009 John Wiley & Sons, Ltd. [source]

A finite volume solver for 1D shallow-water equations applied to an actual river

N. Gouta
Abstract This paper describes the numerical solution of the 1D shallow-water equations by a finite volume scheme based on the Roe solver. In the first part, the 1D shallow-water equations are presented. These equations model the free-surface flows in a river. This set of equations is widely used for applications: dam-break waves, reservoir emptying, flooding, etc. The main feature of these equations is the presence of a non-conservative term in the momentum equation in the case of an actual river. In order to apply schemes well adapted to conservative equations, this term is split in two terms: a conservative one which is kept on the left-hand side of the equation of momentum and the non-conservative part is introduced as a source term on the right-hand side. In the second section, we describe the scheme based on a Roe Solver for the homogeneous problem. Next, the numerical treatment of the source term which is the essential point of the numerical modelisation is described. The source term is split in two components: one is upwinded and the other is treated according to a centred discretization. By using this method for the discretization of the source term, one gets the right behaviour for steady flow. Finally, in the last part, the problem of validation is tackled. Most of the numerical tests have been defined for a working group about dam-break wave simulation. A real dam-break wave simulation will be shown. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Glocalizing protest: urban conflicts and the global social movements

Bettina Köhler
The emergence of global social movements is essentially symbolized by the names of cities like Seattle, Genoa or Porto Alegre. This is not accidental, because groups stemming from various parts of the world need places to constitute themselves as movements. But the role of cities in representing great parts of the movements' consciousness also hints at the importance urban struggles have for global protests. The article examines the relationship between urban conflicts and global social movements. By looking for continuities and ruptures between former and current urban conflicts it points out the specificity of the latter: to politicize the contradictions of neoliberal restructuring; to challenge the discursive and institutional terrains of urban politics which were shaped in the 1990s, often with active participation of former movement actors; and, finally, to act simultaneously on various spatial scales. In the last part of the article some examples of ,glocalized' urban protests are presented and analysed, pointing out their ambiguities as well as the specific contribution they can make to the strategic orientation of the global social movements: to fight the destructive influences neoliberal globalization exerts on everyday life and, thereby, to develop alternative forms of societalization. L'apparition des mouvements sociaux mondiaux est essentiellement symbolisée par les noms de ville comme Seattle, Gênes ou Pôrto Alegre. Cela n'a rien de fortuit puisque des groupes issus de plusieurs parties du monde ont besoin de lieux pour se constituer en mouvements. Toutefois, le rôle des villes dans la représentation de vastes pans de la conscience de mouvements suggére l'importance des luttes urbaines pour la contestation planétaire. L'article examine le rapport entre les conflits urbains et les mouvements sociaux mondiaux. En recherchant continuités et ruptures entre l'agitation urbaine antérieure et actuelle, il souligne la spécificité de cette dernière: politiser les contradictions de la restructuration néo-libérale; remettre en cause les terrains discursifs et institutionnels de la politique urbaine dessinés dans les années 1990, souvent avec la participation active d'anciens acteurs des mouvements; et finalement intervenir simultanément sur plusieurs échelles spatiales. La dernière partie de l'article présente et analyse quelques cas de contestations urbaines ,glocalisées', relevant leurs ambiguïtés, ainsi que la contribution qu'elles peuvent apporter à l'orientation stratégique des mouvements sociaux mondiaux: combattre les influences destructrices de la ,globalisation' néo-libérale sur la vie quotidienne et, ce faisant, créer de nouvelles formes sociétales. [source]

John Skelton and the New Fifteenth Century

Kathleen Tonry
John Skelton's writing career took place roughly between 1488 and 1528, years that straddle two centuries and, most awkwardly, two epochs. Perhaps because of that awkwardness he has been a poet marginalized in our literary histories and critical discourse until quite recently. This overview essay suggests that to re-engage Skelton is to test alternative literary histories that think beyond the fifteenth century as a merely transitional moment and that put into play methodologies flexible enough to accommodate inter-related notions of aesthetics and context. This essay traces Skelton's critical tradition as a series of perspectives on the poet's own nimble engagements with form and history. The first section follows the story of formalist and historicist approaches to Skelton working in tension up until the last part of the twentieth century. The second section explores the interventions of the new Skelton scholars. The third and final sections speculate briefly about fresh directions in Skelton scholarship, noticing that many of the themes and questions raised around Skelton over the past century remain open for more extensive development. [source]

An additional phase in PCr use during sustained isometric exercise at 30% MVC in the tibialis anterior muscle

C. J. Houtman
Abstract The occurrence of an abrupt acceleration in phosphocreatine hydrolysis in the tibial anterior muscle during the last part of a sustained isometric exercise at 30% maximal voluntary contraction until fatigue is demonstrated in seven out of eight healthy subjects by applying in vivo31P NMR spectroscopy at 1.5,T field strength. This additional third phase in PCr hydrolysis, is preceded by a common biphasic pattern (first fast then slow) in PCr use. The NMR spectra, as localized by a surface coil and improved by proton irradiation, were collected at a time resolution of 16 s. Mean rates of PCr hydrolysis during exercise were ,0.44,±,0.19% s,1, ,0.07,±,0.04% s,1, and ,0.29,±,0.10% s,1 for the three successive phases. The increased rate of PCr hydrolysis, and also the loss of fine force control evident in the force records are consistent with increased involvement of large, fast-fatiguable units later in the contraction. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Effect of package light transmittance on the vitamin content of milk, part 3: Fortified UHT low-fat milk

Alexander Saffert
Abstract This work is the third and last part of a milk study evaluating the effect of package light transmittance on the vitamin content of milk, in this case on fortified UHT low-fat milk. The milk was stored under light with an intensity of 700,lux in polyethylene terephthalate (PET) bottles with varying light transmittance to monitor the changes in the vitamin A, B2 and D3 contents over a storage period of 12 weeks at 23°C. Milk packed in pigmented PET bottles with the lowest light transmittance, which was stored in the dark under the same experimental conditions, served as the ,control' sample. In clear PET bottles, a reduction of 93% of the initial content was observed for vitamin A and 66% for vitamin D3, while the vitamin B2 content was completely degraded. In all pigmented PET bottles, the vitamin retention was only slightly higher; the losses ranged between 70 and 90% for vitamin A, between 63 and 95% for vitamin B2, and between 35 and 65% for vitamin D3 depending on the pigmentation level. In the dark-stored ,control' sample, a 16% loss could be observed for vitamin A, while the level of vitamins B2 and D3 remained almost stable. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Secretion of Prolactin and Growth Hormone in Relation to Ovarian Activity in the Dog

HS Kooistra
In pregnant bitches an apparent increase in plasma prolactin concentrations is observed during the second half of pregnancy, mean plasma prolactin concentrations peak on the day of parturition, fall for the next 24,48 h and then rise again. During lactation, high plasma prolactin concentrations are observed. Plasma prolactin levels in non-pregnant bitches appear to be lower than in pregnant animals, particularly in the last part of the luteal phase. Pulsatile secretion of prolactin has been observed during the luteal phase and mid-anoestrus. Progression of the luteal phase is found to be associated with an increase in prolactin release. The association of a strong increase of prolactin release and a decrease of plasma progesterone concentrations has also been demonstrated in overtly pseudopregnant bitches. Elevated prolactin secretion during progression of the luteal phase in the bitch may play a role in mammogenesis and is important because of the luteotrophic action of prolactin. Acromegaly is a syndrome of tissue overgrowth and insulin resistance due to excessive growth hormone (GH) production. In the bitch, acromegaly can be induced either by endogenous progesterone or by exogenous progestagens. Progestagen-induced GH production in this species originates from foci of hyperplastic ductular epithelium of the mammary gland. Pulsatile secretion of GH has been observed in normal cyclic bitches. In contrast with the pulsatile GH secretion seen in healthy dogs, the progestagen-induced plasma GH levels in bitches with acromegaly do not have a pulsatile secretion pattern. Just as with prolactin, the plasma progesterone levels influence the secretion pattern of GH in the bitch. The pulsatile secretion pattern of GH changes during the progression of the luteal phase in healthy cyclic bitches, with higher basal GH secretion and less GH being secreted in pulses during the first part of the luteal phase. The progesterone-induced GH production may promote the proliferation and differentiation of mammary gland tissue during the luteal phase of the bitch by local autocrine/paracrine effects and may exert endocrine effects. [source]

Electronic structure and transport properties of quantum dots

M. Tews
Abstract The subject of this paper are electronic properties of isolated quantum dots as well as transport properties of quantum dots coupled to two electronic reservoirs. Thereby special focus is put on the effects of Coulomb interaction and possible correlations in the quantum dot states. First, the regime of sequential tunneling to the reservoirs is investigated. It is shown that in case degenerate states participate in transport, the resonance positions in the differential conductance generally depend on temperature and the degree of degeneracy. This effect can be used to directly probe degeneracies in a quantum dot spectrum. A further effect, characteristic for sequential tunneling events, is the complete blocking of individual channels for transport. A generalisation of the well known spin blockade is found for correlated dot states transitions through which are not directly spin-forbidden. In the second part, the electronic structure of spherical quantum dots is calculated. In order to account for correlation effects, the few-particle Schrödinger equation is solved by an exact diagonalization procedure. The calculated electronic structure compares to experimental findings obtained on colloidal semiconductor nanocrystals by Scanning Tunneling Spectroscopy. It is found that the electric field induced by the tunneling tip is gives rise to a Stark effect which can break the spherical symmetry of the electronic ground state density which is in agreement with wave-function mapping experiments. The symmetry breaking depends on the competition between exchange energy and the Stark energy. Moreover, a systematic dependence on particle number is found for the excitation energies of optical transitions which explains recent experimental findings on self-organized quantum dots. In the last part, co-tunneling in the Coulomb blockade regime is studied. For this end the tunneling current is calculated up to the forth order perturbation theory in the tunnel coupling by a real-time Green's function approach for the non-equilibrium case. The differential conductance calculated for a quantum dot containing up to two interacting electrons shows complex signatures of the excitation spectrum which are explained by a combination of co-tunneling and sequential tunneling processes. Thereby the calculations show a peak structure within the Coulomb blockade regime which has also been observed in experiment. [source]

Ideelle Biegedrillknicklasten von Kreisbogenbindern aus Brettschichtholz mit gebundener Kippachse

BAUTECHNIK, Issue 12 2006
Siegfried Eilering Prof. Dr.-Ing.
Unter Verwendung des statischen Stabilitätskriteriums wird in Verbindung mit der Energiemethode eine spezielle stabbezogene Finite-Elemente-Formulierung entwickelt, mit deren Hilfe ideelle Biegeknick- und Biegedrillknicklasten von BSH-Bogenbindern bequem berechnet werden können. Wegen des geringen numerischen Aufwandes ist diese Formulierung hervorragend für Parameterstudien geeignet, die aufwendige Einzeluntersuchungen auf der Basis von zwei- oder dreidimensionalen FE-Modellen im Normalfall überflüssig machen. Die Ergebnisse einer solchen Studie an BSH-Kreisbogenbindern mit gebundener Obergurt-Kippachse werden im letzten Teil der Arbeit vorgestellt. Bifurcation loads of circular curved beams of glued-laminated timber with continuous lateral support. On the basis of the energy method in connection with the static stability criterion a specific finite element formulation is developed with which bifurcation loads of curved beams of glued-laminated timber can be determined easily. Because of the small numeric effort this procedure is excellently suitable for parameter studies. Extensive single investigations on the basis of two or three-dimensional finite element models become normally superfluous. In the last part of the paper the results of a study are presented at circular curved beams of glued-laminated timber. On condition of a continuous lateral support at the upper chord bifurcation loads are determined and presented graphically. [source]