Aging Scaled Brownian Motion

Scaled Brownian motion (SBM) is widely used to model anomalous diffusion of passive tracers in complex and biological systems. It is a highly non-stationary process governed by the Langevin equation for Brownian motion, however, with a power-law time dependence of the noise strength. Here we study the aging properties of SBM for both unconfined and confined motion. Specifically, we derive the ensemble and time averaged mean squared displacements and analyze their behavior in the regimes of weak, intermediate, and strong aging. A very rich behavior is revealed for confined aging SBM depending on different aging times and whether the process is sub- or superdiffusive. We demonstrate that the information on the aging factorizes with respect to the lag time and exhibits a functional form, that is identical to the aging behavior of scale free continuous time random walk processes. While SBM exhibits a disparity between ensemble and time averaged observables and is thus weakly non-ergodic, strong aging is shown to effect a convergence of the ensemble and time averaged mean squared displacement. Finally, we derive the density of first passage times in the semi-infinite domain that features a crossover defined by the aging time.Comment: 10 pages, 8 figures, REVTe

Migration of cloud services and deliveries to higher education

This paper discusses the adoption of cloud computing in education. It emphasizes the view that cloud computing is vital in the education sector because of its ability to reduce the overall costs of IT infrastructure installation and maintenance, improvement of efficiency, and the sharing of IT resources among students. The flexibility of cloud computing and its reliability makes it more appropriate for use in the educational environment. The Leeds Beckett University cloud project utilizes the SAS Educational Value-Added Assessment System, which gives lecturers the opportunity to deliver accurate content to students while monitoring their progress. Contemporary educational institutions must look forward to improve their research and education through cloud computing

Developing a fuzzy expert system to predict the risk of neonatal death

Introduction: This study aims at developing a fuzzy expert system to predict the possibility of neonatal death. Materials and Methods: A questionnaire was given to Iranian neonatologists and the more important factors were identified based on their answers. Then, a computing model was designed considering the fuzziness of variables having the highest neonatal mortality risk. The inference engine used was Mamdani's method and the output was the risk of neonatal death given as a percentage. To validate the designed system, neonates' medical records real data at a Tehran hospital were used. MATLAB software was applied to build the model, and user interface was developed by C# programming in Visual Studio platform as bilingual (English and Farsi user interface). Results: According to the results, the accuracy, sensitivity, and specificity of the model were 90, 83 and 97, respectively. Conclusion: The designed fuzzy expert system for neonatal death prediction showed good accuracy as well as proper specificity, and could be utilized in general hospitals as a clinical decision support tool. ©2016 Reza Safdari, Maliheh Kadivar, Mostafa Langarizadeh, Ahmadreaza Farzaneh Nejad, Farzaneh Kermani

Simulation of the microlevel damage evolution in polymer matrix composites

A 3D Isogeometric Interface-Enriched Generalized Finite Element Method (IIGFEM) is developed to analyze problems with complex, discontinuous gradient fields commonly observed in the structural analysis of heterogeneous materials including polymer matrix composites [1]. In the proposed approach, the mesh generation process is significantly simplified by utilizing simple structured meshes that do not conform to the complex microstructure of the heterogeneous media. Non-Uniform Rational B-Splines, commonly used in computer-aided design, are adopted in the IIGFEM to augment the finite element approximation space and capture the weak discontinuity present along material interfaces. The IIGFEM offers many advantages, such as the simplicity and accuracy of numerical integration, the straightforward implementation of essential boundary conditions, and the flexibility in the choice of the local solution refinement The ability to model complex material interfaces and the mesh independence are two of key features of the IIGFEM that enable it to tackle problems with evolving material response, such as computational study of damage in solids. Here, we utilize the IIGFEM scheme to study the impact of microstructural details on the initiation and evolution of the damage in polymer matrix composites. For this purpose, in this study, we incorporate a three-parameter isotropic damage model [2] into our IIGFEM solver to capture the fracture response of the matrix in a unidirectional composite layer. To bypass numerical issues associated with mesh bias, we use a viscous regularization scheme proposed by Simo and Ju [3]. The numerical stability of the proposed approach is studied and its advantages and limitations are discussed in detail. Finally, a number of numerical examples are presented to demonstrate the effect of RVE size and filler volume fraction on the damage behavior of fiber-reinforced polymer matrix composites. REFERENCES [1] Safdari, M., Najafi, A.R., Sottos, N.R., Geubelle, P.H. An Isogeometric Interface-Enriched Generalized Finite Element Method (IGFEM) for problems with complex discontinuous gradient field. Submitted (2014). [2] Matous, K., Kulkarni, M.G., Geubelle, P.H. Multiscale cohesive failure modeling of heterogeneous adhesives. Journal of the Mechanics and Physics of Solids. 2008, 56, 1511–1533. [3] Simo, J.C., Ju, J.W. Strain- and stress-based continuum damage models—ii. computational aspects. International Journal of Solids and Structures. 1987, 23(7), 841–869

A NURBS-based interface-enriched generalized finite element scheme for the computational analysis and design of high temperature microvascular composites

Computational studies on multifunctional microvascular composite materials for high temperature application have focused on simple microchannel geometries [1–2]. Motivated by recent advances in the manufacturing of microvascular composites based on a sacrificial fiber technique that allows a complex network of curved microchannels to be embedded in the material [3], we develop an Interface Enriched Generalized Finite Element Method (IGFEM) [4] with Non-Uniform Rational B-Splines (NURBS) to analyze the impact of the microchannel network on the thermal field in the composite component [5]. By capturing the gradient discontinuity present at the microchannels, the method is able to simulate efficiently and accurately the thermal response of the microvascular composite without the need for a mesh that conforms to the geometry of the microchannels. We show that near-optimal convergence rate can be achieved and that IGFEM is more accurate than standard finite element method for coarse meshes when the enrichment functions are constructed using the NURBS description of the curved microchannels. Verification studies conducted against a detailed multiphysics model based on the Navier–Stokes equation for the fluid shows that the much simpler line source/sink model is very accurate for problems involving microvascular plates and fins. Various application problems are presented to demonstrate the efficiency, flexibility and accuracy of the proposed method. REFERENCES [1] Soghrati, S., Thakre, P.R., White, S.R., Sottos, N.R., Geubelle, P.H. Computational modeling and design of actively-cooled microvascular materials. Int. J. Heat Mass Transfer. 2012, 55, 5309–5321 [2] Soghrati, S., Najafi, A.R., Hughes, K.M., Lin, J.H., White, S.R., Sottos, N.R., Geubelle, P.H. Computational analysis of actively-cooled 3D woven microvascular composites using a stabilized interface-enriched generalized finite element method. Int. J. Heat Mass Transfer. 2013, 65, 153–164. [3] Esser-Kahn, A.P., Thakre, P.R., Dong, H., Patrick, J.F., Vlasko-Vlasov, V.K., Sottos, N.R., Moore, J.S., White, S.R. Three-dimensional microvascular fiber-reinforced composites. Advanced Materials. 2011, 23, 3654–3658. [4] Soghrati, S., Aragón, A.M., Duarte, C.A., Geubelle, P.H. An interface-enriched generalized FEM for problems with discontinuous gradient fields. Int. J. Numer. Methods Eng. 2012, 89, 991–1008. [5] Tan, M.H.Y., Safdari, M., Najafi, A.R., Geubelle, P.H. A NURBS-based interface-enriched generalized finite element scheme for the thermal analysis and design of microvascular composites. 2014 (submitted)

Crossover from anomalous to normal diffusion: truncated power-law noise correlations and applications to dynamics in lipid bilayers

The emerging diffusive dynamics in many complex systems shows a characteristic crossover behaviour from anomalous to normal diffusion which is otherwise fitted by two independent power-laws. A prominent example for a subdiffusive-diffusive crossover are viscoelastic systems such as lipid bilayer membranes, while superdiffusive-diffusive crossovers occur in systems of actively moving biological cells. We here consider the general dynamics of a stochastic particle driven by so-called tempered fractional Gaussian noise, that is noise with Gaussian amplitude and power-law correlations, which are cut off at some mesoscopic time scale. Concretely we consider such noise with built-in exponential or power-law tempering, driving an overdamped Langevin equation (fractional Brownian motion) and fractional Langevin equation motion. We derive explicit expressions for the mean squared displacement and correlation functions, including different shapes of the crossover behaviour depending on the concrete tempering, and discuss the physical meaning of the tempering. In the case of power-law tempering we also find a crossover behaviour from faster to slower superdiffusion and slower to faster subdiffusion. As a direct application of our model we demonstrate that the obtained dynamics quantitatively described the subdiffusion-diffusion and subdiffusion-subdiffusion crossover in lipid bilayer systems. We also show that a model of tempered fractional Brownian motion recently proposed by Sabzikar and Meerschaert leads to physically very different behaviour with a seemingly paradoxical ballistic long time scaling

Development of a store-and-forward telescreening system of diabetic retinopathy: lessons learned from Iran

Background: The present study describes the development and identity phases of a teleophthalmology system used for screening of diabetic retinopathy. Methods: A questionnaire was used to identify the main factors necessary for diagnosis of diabetic retinopathy and the features required for a teleophthalmology system. In the second phase, a web-based prototype of the system was designed using the data collected in the previous phase. In the final phase, the system was optimized based on the users� ideas and comments; then, it was evaluated through a standard usability testing questionnaire. Results: The results showed that the lowest average percentages were related to ethnicity (61), optometrist�s office address (61), and consultant physician�s office address (65). A web-based prototype was designed using the Visual Studio and Dreamweaver programming tools. This system comprised patient identity data, medical history, clinical data, and retinal images of the patient. The mean score of usability testing and user satisfaction including specialists, residents, and optometrist was 7.3, 7.1 and 7.3 (out of a total 9), respectively. The evaluation results revealed that the system was classified as good. Conclusion: The telescreening system suggested in the current study could be helpful in timely diagnosis. Moreover, it would reduce the treatment costs and complexities. Regardless of the positive points of telemedicine systems, one of the most challenges in this study was the Internet infrastructure to design and apply the system. The future studies, therefore, could focus on the application of cell phone technology for rendering teleophthalmology. © 2018, Springer International Publishing AG

Development of a store-and-forward telescreening system of diabetic retinopathy: lessons learned from Iran

Background: The present study describes the development and identity phases of a teleophthalmology system used for screening of diabetic retinopathy. Methods: A questionnaire was used to identify the main factors necessary for diagnosis of diabetic retinopathy and the features required for a teleophthalmology system. In the second phase, a web-based prototype of the system was designed using the data collected in the previous phase. In the final phase, the system was optimized based on the users� ideas and comments; then, it was evaluated through a standard usability testing questionnaire. Results: The results showed that the lowest average percentages were related to ethnicity (61), optometrist�s office address (61), and consultant physician�s office address (65). A web-based prototype was designed using the Visual Studio and Dreamweaver programming tools. This system comprised patient identity data, medical history, clinical data, and retinal images of the patient. The mean score of usability testing and user satisfaction including specialists, residents, and optometrist was 7.3, 7.1 and 7.3 (out of a total 9), respectively. The evaluation results revealed that the system was classified as good. Conclusion: The telescreening system suggested in the current study could be helpful in timely diagnosis. Moreover, it would reduce the treatment costs and complexities. Regardless of the positive points of telemedicine systems, one of the most challenges in this study was the Internet infrastructure to design and apply the system. The future studies, therefore, could focus on the application of cell phone technology for rendering teleophthalmology. © 2018 Springer International Publishing A