The Experts below are selected from a list of 47301 Experts worldwide ranked by ideXlab platform
Nicole Verheulpen Heymans - One of the best experts on this subject based on the ideXlab platform.
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constitutive equations for Polymer viscoelasticity derived from hierarchical models in cases of failure of time temperature superposition
Signal Processing, 2003Co-Authors: Nicole Verheulpen HeymansAbstract:Hierarchical viscoelastic elements whose Behaviour is intermediate between linear elasticity and Newtonian viscosity (springpots) have been introduced previously into classical analog models describing linear viscoelastic Behaviour. This approach allows a concise description of typical Polymer Behaviour, including non-exponential relaxation, memory effects and hierarchy of viscoelastic transitions. This approach is extended in the present work to describe complex Behaviour, including failure of time-temperature superposition in a semi-crystalline Polymer, and the terminal transition from self-similar viscoelasticity to pure flow in a thermoplastic elastomer. Tschoegl's formulation of a finite Gross Marvin ladder model is generalized and applied to other models, and this approach is compared with Friedrich's method based on application of an exponential cutoff to the relaxation function. The method is illustrated using dynamic mechanical measurements on a triblock adhesive in isothermal frequency sweeps. This material displays thermorheological complexity precluding application of time-temperature superposition. Tschoegl's formulation affords a better description of this material than Friedrich's approach. The method described here is a useful alternative to time-temperature superposition requiring a limited number of adjustable parameters.
Vipul Periwal - One of the best experts on this subject based on the ideXlab platform.
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from Polymers to quantum gravity triple scaling in rectangular random matrix models
Nuclear Physics, 1993Co-Authors: Robert C Myers, Vipul PeriwalAbstract:Abstract Rectangular N × M matrix models can be solved in several qualitatively distinct large-N limits, since two independent parameters govern the size of the matrix. Regarded as models of random surfaces, these matrix models interpolate between branched Polymer Behaviour and two-dimensional quantum gravity. We solve such models in a “triple-scaling” regime in this paper, with N and M becoming large independently. A correspondence between phase transitions and singularities of mappings from R 2 to R 2 is indicated. At different critical points, the scaling Behaviour is determined by (i) two decoupled ordinary differential equations; (ii) an ordinary differential equation and a finite-difference equation; or (iii) two coupled partial differential equations. The Painleve II equation arises (in conjuction with a difference equation) at a point associated with branched Polymers. For critical points described by partial differential equations, there are dual weak-coupling/strong-coupling expansions. It is conjectured that the new physics is related to microscopic topology fluctuations.
Abdur Rahman Salman - One of the best experts on this subject based on the ideXlab platform.
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An investigation into the drug release mechanisms of Polymeric solid dispersions
2020Co-Authors: Abdur Rahman SalmanAbstract:Personalised polypills, which includes multiple drugs in a single pill tailored for individual patients, has gained a lot of research interests with the emergence of pharmaceutical 3D printing. A distinct feature of polypill is to be able to release each drug in a controlled manner. However, currently, there are limited tools to aid the design of such solid dosage forms with desired drug release kinetics. In this work, the drug release mechanisms of a wide range of solid dispersions formed using Polymers and model drugs covering a wide range of physicochemical properties were investigated to generate a large dataset with an attempt to develop a simulation strategy for achieving a desired drug release profile. Building a dataset and using the dataset toward simulation building the data to be reproducible and reliable. The sources of errors throughout the manufacturing and the performance measurements of 3D printed example solid dosage forms were first investigated to assess the reproducibility and reliability of the experimental data generated to build the dataset. This was the focus of chapter 3. Thereafter, chapter 4 systematically investigated the Behaviour of a wide range of pure Polymers to enable the prediction of the Behaviour of Polymer blends. The Polymer Behaviour studied include hydration, swelling, and erosion. Addition of the drug and investigating the effect on formulation Behaviour was the focus of chapter 5. Chapter 6 used statistical approaches such as principal component analysis as a factor reduction technique and K-means clustering to classify the Behaviour of the Polymer-drug dispersions. These statistical approaches successfully demonstrated that correlating Polymer Behaviours and drug release profiles can be used to predict the selection of Polymer(s) for a given drug to achieve a desired drug release profile. Further upscaling of the dataset is crucial to enhance analysis
Han Zhao - One of the best experts on this subject based on the ideXlab platform.
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a study of specimen thickness effects in the impact tests on Polymers by numeric simulations
Polymer, 1998Co-Authors: Han ZhaoAbstract:Experimental data of Polymer Behaviour at high strain rates in the literature, mostly obtained with a split Hopkinson pressure bar (SHPB), shows a dependence on the thickness of the specimen. This paper investigates this so-called thickness effect and tries to clarify the doubts on the equilibrium assumption in SHPB tests on Polymers by numerical simulations. Fictitious specimens of different thickness with rate sensitive Polymer-like constitutive model (Eyring's model) are used to simulate basic data of SHPB test. The comparison between the given Behaviours and those derived from the simulated tests provides an objective appreciation of the quality of tests on Polymers (with thin or thick specimen). Results of the simulation prove that the equilibrium assumptions can still be safely used in the case of test on Polymers, and indicate that the thickness effect is mainly due to the radial inertia and friction considerations.
Robert C Myers - One of the best experts on this subject based on the ideXlab platform.
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from Polymers to quantum gravity triple scaling in rectangular random matrix models
Nuclear Physics, 1993Co-Authors: Robert C Myers, Vipul PeriwalAbstract:Abstract Rectangular N × M matrix models can be solved in several qualitatively distinct large-N limits, since two independent parameters govern the size of the matrix. Regarded as models of random surfaces, these matrix models interpolate between branched Polymer Behaviour and two-dimensional quantum gravity. We solve such models in a “triple-scaling” regime in this paper, with N and M becoming large independently. A correspondence between phase transitions and singularities of mappings from R 2 to R 2 is indicated. At different critical points, the scaling Behaviour is determined by (i) two decoupled ordinary differential equations; (ii) an ordinary differential equation and a finite-difference equation; or (iii) two coupled partial differential equations. The Painleve II equation arises (in conjuction with a difference equation) at a point associated with branched Polymers. For critical points described by partial differential equations, there are dual weak-coupling/strong-coupling expansions. It is conjectured that the new physics is related to microscopic topology fluctuations.