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Hollow Cylinders (hollow + cylinder)

Distribution by Scientific Domains

Polymers and Materials Science	27%

Selected Abstracts

Porothermoelastic analyses of anisotropic hollow cylinders with applications

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 2 2005
Mazen Kanj
Abstract It has been known that material anisotropy and thermal stresses affect borehole stability significantly. Aiming at the experimental studies associated with borehole stability in anisotropic (transversely isotropic) poroelastic materials subject to non-isothermal conditions, this paper details and applies an anisotropic porothermoelastic solution to an unjacketed hollow cylinder in a triaxial set-up. Numerical analyses are presented to demonstrate thermal and material anisotropy effects on the pore pressure and the stress concentrations in and around the geometry of a hollow cylinder subjected to thermal and stress perturbations. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Modelling poroelastic hollow cylinder experiments with realistic boundary conditions

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 12 2004
S. Jourine
Abstract A general poroelastic solution for axisymmetrical plane strain problems with time dependent boundary conditions is developed in Laplace domain. Time-domain results are obtained using numerical inversion of the Laplace transform. Previously published solutions can be considered as special cases of the proposed solution. In particular, we could reproduce numerical results for solid and hollow poroelastic cylinders with suddenly applied load/pressure (Rice and Cleary, Rev. Geophys. Space Phys. 1976; 14:227; Schmitt, Tait and Spann, Int. J. Rock Mech. Min. Sci. 1993; 30:1057; Cui and Abousleiman, ASCE J. Eng. Mech. 2001; 127:391). The new solution is used to model laboratory tests on thick-walled hollow cylinders of Berea sandstone subjected to intensive pressure drawdown. In the experiments, pressure at the inner boundary of the hollow cylinder is observed to decline exponentially with a decay constant of 3,5 1/s. It is found that solutions with idealized step-function type inner boundary conditions overestimate the induced tensile radial stresses considerably. Although basic poroelastic phenomena can be modelled properly at long time following a stepwise change in pressure, realistic time varying boundary conditions predict actual rock behaviour better at early time. Experimentally observed axial stresses can be matched but appear to require different values for , and , than are measured at long time. The proposed solution can be used to calculate the stress and pore pressure distributions around boreholes under infinite/finite boundary conditions. Prospective applications include investigating the effect of gradually changing pore pressure, modelling open-hole cavity completions, and describing the phenomenon of wellbore collapse (bridging) during oil or gas blowouts. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Self-assembled organic nanotubes: Toward attoliter chemistry

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2008
Toshimi Shimizu
Abstract Diverse chemical functionalization of the inner and outer surfaces of the nanotubes enables us to sense and visualize the encapsulation and transport behavior of biomacromolecular guests. The event occurs specifically in attoliter volume nanospace inside the hollow cylinder of the nanotubes. Comparison of the organic nanotube history with that of well-known carbon nanotubes and a variety of molecular building blocks as tube-forming compounds were first introduced. Asymmetric organic nanotubes with different inner and outer surfaces were discussed in terms of molecular design, immobilization of functional moieties, and molecular packing. Finally, the practical examples of the organic nanotubes as a nanocontainer, nanochannel, and nanopipette were also described to feature the concept of "attoliter chemistry." © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2601,2611, 2008 [source]

Effect of implant design on survival and success rates of titanium oral implants: a 10-year prospective cohort study of the ITI® Dental Implant System

CLINICAL ORAL IMPLANTS RESEARCH, Issue 1 2004
Ioannis K. Karoussis
Abstract Aim: The aim of this 10-year study (observation time 8,12 years, mean: 10 years) was to compare the survival rates, success rates and incidences of biological complications using three different implant designs of the ITI® Dental Implant System. Material and methods: In 89 dental patients treated comprehensively, a total of 112 hollow screw (HS), 49 hollow cylinder (HC) and 18 angulated hollow cylinder (AHC) implants were installed depending on the available bone volume and according to prosthetic needs. One and 10 years after surgical placement, clinical and radiographic parameters were assessed. The incidences of peri-implantitis according to various thresholds were registered over 10 years of maintenance. Results: Success criteria at 10 years were set at: pocket probing depth (PPD)5 mm, bleeding on probing (BoP),, bone loss < 0.2 mm annually. The survival rate for HS was 95.4%, for HC 85.7% and for AHC 91.7%. Ninety percent of all the HS, 71% of the HC and 88% of the AHC did not present with an incidence of peri-implantitis over the 10 years, HC having significantly higher incidence of peri-implantitis than HS (P< 0.004). With the success criteria set above, a success rate for HS of 74%, for HC of 63% and for AHC of 61% was identified at 10 years. However, including a definition of PPD6 mm, BoP , and bone loss < 0.2 mm annually for success, the rates for HS were 78%, for HC 65% and for AHC 67%, respectively. Basing success criteria purely on clinical parameters (without radiographic analysis), such as: PPD5 mm and BoP,, the success rates increased to 90%, 76% and 89%, respectively. With PPD6 mm and BoP , as success criteria chosen, the respective rates were 94%, 82% and 94% for HS, HC and AHC implants, respectively. Conclusions: A significantly higher survival rate as well as a significantly lower incidence of peri-implantitis was identified for hollow screw design ITI® Dental Implants after 10 years of service when compared to hollow cylinder design ITI® Dental Implants (95.4% vs. 85.7%; 10% vs. 29%). Depending on the setting of the threshold criteria for success, success rates are highly variable and hence, reporting of success rates with elaboration on the criteria set appears crucial for comparison of different studies. Résumé Le but de ce suivi d'une décennie a été de comparer les taux de survie, les taux de succès et les incidences des complications biologiques de l'utilisation de trois modèles implantaires différents du système ITI® Dental Implant. Chez 89 patients, 112 vis creuses (HS), 49 cylindres creux (HC) et 18 cylindres creux angulés (AHC) ont été placés suivant le volume osseux disponible et les nécessités prothétiques. Une et dix années après leur placement, des paramètres cliniques et radiographiques ont été définis. Les incidences de paroïmplantite relatives aux différents seuils ont été enregistrées durant ces dix années de maintenance. Les succès des critères à dix ans étaient placés à : PPD5 mm, BoP-, perte osseuse <0,2 mm/an. Le taux de survie pour HS était de 95,4%, pour HC de 86% et pour AHC de 92%. Nonante pour cent de tous les HS, 71% des HC et 88% des AHC ne présentaient pas d'incidences de paroïmplantite durant ces dix années, HC ayant une plus importante incidence de paroïmplantite que HS (p<0,004). Grace aux critères de succès indiqués, un taux de succès de 74% pour HS, de 63% pour HC et de 61% pour AHC a été identifié après dix ans. Cependant, en définissant le succès avec PPD6mm, BoP- et perte osseuse <0,2mm/an, les taux étaient de 78% pour HS, de 65% pour HC et de 67% pour AHC. En basant les taux de succès uniquement sur les paramètres cliniques (sans l'analyse radiographique) tels que PPD5 mm et BoP-, les taux de succès augmentaient respectivement à 90, 76 et 89%. Avec PPD6mm et BoP- comme critères de succès, les taux s'élevaient respectivement à 94, 82 et 94%. Un taux de survie significativement plus important ainsi qu'une incidence significativement plus faible de paroïmplantite étaient constatés au niveau des implants vis creuses après dix ans de mise en fonction comparés aux cylindres creux. Suivant l'établissement du seuil pour les critères du succès, les taux de ce succès sont extrêmement variables et rapporter les taux de succès suivant l'élaboration des critères est donc crucial pour comparer différentes études. Zusammenfassung Ziel: Das Ziel dieser 10-Jahresstudie (Beobachtungszeit 8,12 Jahre, Mittelwert: 10 Jahre) war es, bei ITI® -Implantaten mit drei verschiedenen Designs, die Erfolgs- und Überlebensrate zu vergleichen, und das Auftreten von biologischen Zwischenfällen zu untersuchen. Material und Methode: Bei 89 synoptisch behandelten Patienten implantierte man in Abhängigkeit des vorhandenen Knochenvolumens und der prothetischen Anforderungen insgesamt 112 Hohlschraubenimplantate (HS), 49 Hohlzylinderimplantate (HC) und 18 abgewinkelte Hohlzylinderimplantate (AHC). Ein und zehn Jahre nach der Implantation nahm man die klinischen und radiologischen Parameter auf. Eine Periimplantitis registrierte während der 10-jährigen Erhaltungsphase anhand verschiedener Grenzwerte. Resultate: Die Kriterien für einen Erfolg nach 10 Jahren legte man bei den folgenden Werten fest: PPD <5mm, BOP-, jährlicher Knochenverlust <0.2mm. Die Überlebensrate für ein HS lag bei 95.4%, für ein HC bei 85.7% und für ein AHC bei 91.7%. 90% aller HS, 71% aller HC und 88% aller AHC zeigte während den 10 Jahren nie Anzeichen einer Periimplantitis, wobei die HC signifikant häufiger Periimplantitis hatten, als die HS (p<0.004). Mit den oben festgelegten Erfolgskriterien ergab sich nach 10 Jahren für die HS eine Erfolgsrate von 74%, für die HC eine von 63% und für die AHC eine von 61%. Veränderte man die Definition auf "PPD<6mm, BOP -, jährlicher Kochenverlust <0.2mm", so betrugen die Erfolgsraten für die HS 78%, für die HC 65% und für die AHC 67%. Basierten die Erfolgskriterien rein auf klinischen Parametern (PPD <5mm, BOP-, keine röntgenologische Anlyse), so stiegen die Erfolgsraten auf 90%, 76% und 89% an. Wählte man die Erfolgskriterien "PPD <6mm und BOP -", so betrugen die Erfolgsraten für die HS 94%, für die HC 82% und für die AHC 94%. Zusammenfassung: Verglich man nach 10-jähriger Funktion die Hohlschrauben des ITI® -Implantat-Systems mit den Hohlzylindern desselben Systems, so ergab sich für die HS sowohl eine signifikant höher Überlebensrate, wie auch ein selteneres Auftreten von Periimplantitis (95.4% vs. 85.7%; 10% vs. 29%). Die Erfolgsraten variieren in Abhängigkeit der in der Definition eines Erfolges festgelegten Grenzwerten enorm stark. Dies erweist sich im Vergleich von verschiedenen Studien als hinderlich, weil die Definition der Erfolgsraten meist auf verschiedenen Kriterien beruhen. Resumen Intención: La intención de este estudio de 10 años (tiempo de observación 8,12, media: 10 años) fue comparar los índices de supervivencia, índices de éxito e índices de complicaciones biológicas usando tres diferentes diseños de implantes del Sistema de Implantes Dentales ITI®. Material y Métodos: Se instalaron en 89 pacientes dentales tratados completamente un total de 112 tornillos huecos (HS), 49 cilindros huecos (HC) y 18 cilindros huecos angulados (AHC) dependiendo de la disponibilidad de volumen óseo y de acuerdo con las necesidades protésicas. Se valoraron parámetros clínicos y radiográficos uno y diez años tras la colocación quirúrgica. Se registraron las incidencias de periimplantitis de acuerdo con varios umbrales a lo largo de 10 años de mantenimiento. Resultados: Los criterios de éxito a los 10 años se situaron en PPD5mm, BoP-, pérdida ósea < 0.2mm por año. El índice de supervivencia para los HS fue del 95.4%, para los HC del 85.7% y para los AHC del 91.7%. El 90% de los HS, el 71% de los HC y el 88% de los AHC no presentaron ninguna incidencia de periimplantitis a lo largo de los 10 años, HC tuvo una significativamente mayor incidencia de periimplantitis que HS (p< 0.004). Con los criterios de éxito antes mencionados, se identificó un índice de éxito para HS del 74%, para HC del 63% y para AHC del 61% a los 10 años. De todos modos, incluyendo una definición de PPD6mm, BoP, y pérdida ósea <0.2mm al año para tener éxito, los índices para HS fueron del 78%, para HC 65% y para AHC 67%, respectivamente. Basando los criterios de éxito puramente en parámetros clínicos (sin análisis radiográficos), tales como: PPD5mm y BoP-, los índices de éxito subieron hasta el 90%, 76% y 89%, respectivamente. Con el PPD6mm y BoP , como criterios de éxito elegidos, los índices respectivos fueron del 94%,82% y 94% para implantes HS, HC y AHC, respectivamente. Conclusiones: Se identificó un significativamente mayor índice de supervivencia al igual que una menor incidencia de periimplantitis para el diseño de tornillo hueco Implante Dental ITI®. (95.4% vs. 85.7; 10% vs. 29%). Dependiendo de la definición del criterio del umbral de éxito, los índices de éxito son altamente variables y por tanto, los informes de los índices de éxito con elaboración de la definición de criterios parece ser crucial para la comparación de los diferentes estudios. [source]

Application of Inhibitor-Loaded Halloysite Nanotubes in Active Anti-Corrosive Coatings

ADVANCED FUNCTIONAL MATERIALS, Issue 11 2009
Dmitri Fix
Abstract Halloysite particles are aluminum-silicate hollow cylinders with a length of 0.5,1,µm, an outer diameter of ca. 50,nm and a lumen of 15,nm. These nanotubes are used for loading and sustained release of corrosion inhibitors. The inhibitor is kept inside the particles infinitely long under dry conditions. Here, halloysite nanotubes filled with anticorrosive agents are embedded into a SiOx,ZrOx hybrid film. An aluminum plate is dip-coated and immersed into 0.1,M sodium chloride aqueous solution for corrosion tests. A defect in the sol,gel coating induces pitting corrosion on the metal accompanied by a strong anodic activity. The inhibitor is released within one hour from halloysite nanotubes at corrosion spots and suppresses the corrosion process. The anodic activity is successfully restrained and the protection remains for a long time period of immersion in NaCl water solution. The self-healing effect of the sol,gel coating doped with inhibitor-loaded halloysite nanotubes is demonstrated in situ via scanning vibrating electrode technique measurements. [source]

Porothermoelastic analyses of anisotropic hollow cylinders with applications

Modelling poroelastic hollow cylinder experiments with realistic boundary conditions

Explicit solutions for the instantaneous undrained contraction of hollow cylinders and spheres in porous elastoplastic medium

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2002
A. Giraud
Abstract In this article we present closed-form solutions for the undrained variations in stress, pore pressure, deformation and displacement inside hollow cylinders and hollow spheres subjected to uniform mechanical pressure instantaneously applied to their external and internal boundary surfaces. The material is assumed to be a saturated porous medium obeying a Mohr,Coulomb model failure criterion, exhibiting dilatant plastic deformation according to a non-associated flow rule which accounts for isotropically strain hardening or softening. The instantaneous response of a porous medium submitted to an instantaneous loading is undrained, i.e. without any fluid mass exchange. The short-term equilibrium problem to be solved is now formally identical to a problem of elastoplasticity where the constitutive equations involve the undrained elastic moduli and particular equivalent plastic parameters. The response of the model is presented (i) for extension and compression undrained triaxial tests, and (ii) for unloading problems of hollow cylinders and spheres through the use of appropriately developed closed-form solutions. Numerical results are presented for a plastic clay stone with strain hardening and an argilite with strain softening. The effects of plastic dilation, of the strain softening law and also of geometry of the cavity on the behaviour of the porous medium have been underlined. Analytical solutions provide valuable benchmarks enabling various numerical methods in undrained conditions with a finite boundary to be verified. Copyright © 2002 John Wiley & Sons, Ltd. [source]

The World of Carbon Nanotubes: An Overview of CVD Growth Methodologies

CHEMICAL VAPOR DEPOSITION, Issue 6 2006
L. Terranova
Abstract Carbon nanotubes are a new form of completely artificial crystalline carbon, which have never been found as a natural form. These fascinating hollow cylinders can be considered as prototypes of one-dimensional quantum wires, exhibit peculiar chemical-physical properties very different from those of other C-based nanostructures, and are envisaged to have potential in a wide range of applications. This review examines some of the most interesting CVD methodologies employed for the synthesis of carbon nanotubes. The results obtained from different methodologies demonstrate that carbon nanotubes can be grown by CVD under a wide range of experimental conditions, permitting flexible, tunable synthesis. Overall, in the last few years, CVD approaches have emerged as the most promising among those proposed for synthesizing carbon nanotubes. [source]