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Selected AbstractsThe effect of gentamicin sulphate on the fracture properties of a manually mixed bone cementFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 6 2007M. BALEANI ABSTRACT This work investigates the effect of adding gentamicin, an antibiotic, on the fracture properties of bone cement. Endurance limit, fatigue crack propagation and fracture toughness were determined for a polymethylmethacrylate-based cement, containing 10% w/w of barium sulphate as radiopacifying agent, and the same formulation modified by the addition of 4.22% w/w of gentamicin sulphate. The antibiotic does not affect the endurance limit nor the fracture toughness of the material. There are significant differences in the parameters of the Paris' law fitting the crack growth data: once the main crack is nucleated, it initially propagates at a lower rate but thereafter accelerates faster in gentamicin loaded bone cement. Despite this difference, the growth rate for the same stress intensity factor remains of the same order of magnitude in both formulations. The addition of 4.22% w/w of gentamicin sulphate to radiopaque bone cement has a negligible total effect on the fracture properties of the material. [source] A framework for fracture modelling based on the material forces concept with XFEM kinematicsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 13 2005Ragnar Larsson Abstract A theoretical and computational framework which covers both linear and non-linear fracture behaviour is presented. As a basis for the formulation, we use the material forces concept due to the close relation between on one hand the Eshelby energy,momentum tensor and on the other hand material defects like cracks and material inhomogeneities. By separating the discontinuous displacement from the continuous counterpart in line with the eXtended finite element method (XFEM), we are able to formulate the weak equilibrium in two coupled problems representing the total deformation. However, in contrast to standard XFEM, where the direct motion discontinuity is used to model the crack, we rather formulate an inverse motion discontinuity to model crack development. The resulting formulation thus couples the continuous direct motion to the inverse discontinuous motion, which may be used to simulate linear as well as non-linear fracture in one and the same formulation. In fact, the linear fracture formulation can be retrieved from the non-linear cohesive zone formulation simply by confining the cohesive zone to the crack tip. These features are clarified in the two numerical examples which conclude the paper. Copyright © 2005 John Wiley & Sons, Ltd. [source] Implicit J2 -bounding surface plasticity using Prager's translation ruleINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 10 2002Francisco J. Montáns Abstract A bounding surface J2 -plasticity model that uses Prager's translation rule is presented. The model preserves Masing's rules and is developed from the same ideas as classical infinitesimal J2 -plasticity, resulting in the same formulation with the exception of the algorithm for the computation of the hardening function. Instead of utilizing a loading surface as in a previous formulation, hardening surfaces are introduced; the formulation is similar to that of multilayer plasticity using Prager's rule, presented in previous work. An implicit algorithm based on the radial return concept is used, and the consistent elastoplastic tangent is also developed in closed form. Examples illustrating anisotropic behaviour are presented and compared to that predicted by a multilayer J2 -plasticity model. The model is also applied to a soil dynamics problem to show the robustness of the algorithm and its applicability to complex loading. Copyright © 2002 John Wiley & Sons, Ltd. [source] Desensitizing Agent Efficacy during Whitening in an At-Risk PopulationJOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 1 2004RALPH H. LEONARD Jr. DDS. ABSTRACT Background: Nightguard vital bleaching (NGVB) has gained acceptance among dentists and patients as a simple and effective procedure to lighten discolored teeth. Although the efficacy and predictability of NGVB have been well established, it has been documented that patients undergoing the procedure may experience side effects such as tooth sensitivity (TS) and gingival irritation (GI). A previous NGVB study suggested that selected participants might benefit from a regimen of a desensitizing agent (DSA)to decrease or prevent TS during whitening. Purpose: The purpose of this study was to determine whether the daily use of an active DSA (UltraEZTM, Ultradent Products Inc., South Jordan, UT, USA) during NGVB would decrease TS in a population at risk for TS when compared with a placebo. Materials and Methods: Forty subjects participated in this single-blind randomized clinical trial. All participants had indicated that they had preexisting TS or other risk factors for TS during NGVB. To evaluate TS caused by the tray alone, participants wore custom-fitted maxillary whitening trays containing no DSA or whitening solution during week 1. Next, participants were randomly assigned to apply either the active DSA or placebo daily for 14 days in the trays for 30 minutes prior to whitening. The placebo was the same formulation as UltraEZ but without the desensitizing agents (3% potassium nitrate and 0.11% by weight fluoride ion). The bleaching solution was a 10% carbamide peroxide whitening solution (OpalescenceTM, Ultradent Inc.). Post treatment, participants were followed up for 1 week, during which time they used neither trays nor solutions. Throughout the study, participants completed a daily diary to record their perceptions of TS and the time spent wearing the tray with the whitening solution. Results: Forty-one percent of the active group had at least 1 day of TS during treatment compared with 78% of the placebo group. The difference was statistically significant (p= .027) using the two-tailed Fisher exact test. [source] Pharmacokinetics and tissue distribution of idarubicin-loaded solid lipid nanoparticles after duodenal administration to ratsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2002Gian Paolo Zara Abstract Idarubicin-loaded solid lipid nanoparticles (IDA-SLN) and idarubicin in solution were prepared and the two formulations were administered to rats, either by the duodenal route or intravenously (iv). The aim of this research was to study whether the bioavailability of idarubicin can be improved by administering IDA-SLN duodenally to rats. Idarubicin and its main metabolite idarubicinol were determined in plasma and tissues by reversed-phase high-performance liquid chromatography. The pharmacokinetic parameters of idarubicin found after duodenal administration of the two formulations were different: area under the curve of concentration versus time (AUC) and elimination half-life were ,21 times and 30 times, respectively, higher after IDA-SLN administration than after the solution administration. Tissue distribution also differed: idarubicin and idarubicinol concentrations were lower in heart, lung, spleen, and kidneys after IDA-SLN administration than after solution administration. The drug and its metabolite were detected in the brain only after IDA-SLN administration, indicating that SLN were able to pass the blood,brain barrier. After iv IDA-SLN administration, the AUC of idarubicin was lower than after duodenal administration of the same formulation. Duodenal administration of IDA-SLN modifies the pharmacokinetics and tissue distribution of idarubicin. The IDA-SLN act as a prolonged release system for the drug. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:1324,1333, 2002 [source] Review article: increasing the dose of oral mesalazine therapy for active ulcerative colitis does not improve remission ratesALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 9 2007A. V. SAFDI Summary Background, Oral mesalazine (mesalamine, 5-aminosalicylic acid) formulations are effective in the treatment of active ulcerative colitis. All formulations contain the same active drug but differ with regard to mechanisms to deliver the drug to the colon. Patients who fail to respond to initial therapy are often administered higher doses of the same formulation. Aim, To review published trials of oral mesalazine formulations in treating active ulcerative colitis and to examine the effect of dose escalation on remission rates. Results, Increasing the doses of oral mesalazine formulations does not result in higher remission rates, although increasing the doses of some formulations has been effective in increasing symptomatic improvement and/or response to treatment. Conclusions, Because oral mesalazine formulations do not demonstrate a significant dose response with regard to induction of remission of active ulcerative colitis, simple dose escalation may not be the most effective course for patients who fail to respond to initial mesalazine treatment. [source] | ||||||||||