Computing the survival probability density function in jump-diffusion models: A new approach based on radial basis functions

We propose a numerical method to compute the survival (first-passage) probability density function in jump-diffusion models. This function is obtained by numerical approximation of the associated Fokker–Planck partial integro-differential equation, with suitable boundary conditions and delta initial condition. In order to obtain an accurate numerical solution, the singularity of the Dirac delta function is removed using a change of variables based on the fundamental solution of the pure diffusion model. This approach allows to transform the original problem to a regular problem, which is solved using a radial basis functions (RBFs) meshless collocation method. In particular the RBFs approximation is carried out in conjunction with a suitable change of variables, which allows to use radial basis functions with equally spaced centers and at the same time to obtain a sharp resolution of the gradients of the survival probability density function near the barrier. Numerical experiments are presented in which several different kinds of radial basis functions are employed. The results obtained reveal that the numerical method proposed is extremely accurate and fast, and performs significantly better than a conventional finite difference approach.     

Floating modular drug delivery systems with buoyancy independent of release mechanisms to sustain amoxicillin and clarithromycin intra-gastric concentrations

Release modules of amoxicillin and clarithromycin combined in a single dosage form designed to float in the gastric content and to sustain the intra-gastric concentrations of these two antibiotics used for the eradication of Helicobacter pylori have been studied. The modules having a disc shape with curved bases were formulated as hydrophilic matrices. Two modules of clarithromycin were assembled by sticking the concave base of one module to the concave base of the other, creating an internal void chamber. The final dosage form was a floating assembly of three modules of clarithromycin and two of amoxicillin in which the drug release mechanism did not interfere with the floatation mechanism. The assembled system showed immediate in vitro floatation at pH 1.2, lasting 5?h. The in vitro antibiotics release profiles from individual modules and assembled systems exhibited linear release rate during buoyancy for at least 8?h. The predicted antibiotic concentrations in the stomach maintained for long time levels significantly higher than the respective minimum inhibitory concentrations (MIC). In addition, an in vivo absorption study performed on beagle dogs confirmed the slow release of clarithromycin and amoxicillin from the assembled system during the assembly’s permanence in the stomach for at least 4?h.     

Hybrid meshing using constrained Delaunay triangulation for viscous flow simulations

In this paper, we present a generalized prismatic hybrid meshing method for viscous flow simulations. One major difficulty in implementing a robust prismatic hybrid meshing tool is to handle boundary layer mesh collisions, and normally an extra data structure (e.g. quadtree in two‐dimensional and octree in three‐dimensional) is required. The proposed method overcomes this difficulty via an heuristic approach, and it only relies on constrained delaunay triangulation/tetrahedralization(CDT). No extra data structures are required. Geometrical reasoning is used to approximate the maximum marching distance of each point by walking through the CDT. This is combined with post‐processing of marching vectors and distance and prohibition of multilevel differences to form an automatic and robust mechanism to remove boundary layer mesh collisions. Benefiting from the matureness of CDT techniques, the proposed method is robust, efficient and simple to implement. Its capability is demonstrated by generating quality prismatic hybrid meshes for industrial models with complex geometries. The proposed method is believed to be able considerably reduce the effort to implement a robust hybrid prismatic mesh generator for viscous flow simulations. © 2016 The Authors. International Journal for Numerical Methods in Engineering. Published by John Wiley & Sons Ltd.     

A GIS-Based Score System for Siting and Sizing of Created or Restored Wetlands: Two Case Studies

Water bodies are impacted by watershed loads in terms of nutrients and xenobiotics. This impact impairs the designated uses of the water body. Often preventive actions and end-of-pipe treatments do not reach the acceptable load to ensure the water quality standard in the water body. Wetlands are suitable tools for improving the self-purification capacity of a water system and can be used as a tool to reduce pollutant loads in a river network.This paper presents a methodology for the Siting and Sizing of created or restored wetlands at the watershed level, based on Geographical Information Systems (GIS) technique and estimations of wetland required area. The final outputs of the methodology are a Land Score System for Siting and a first rough estimation for the Sizing. The combination of these two elements is expected to be useful as a planning tool for watershed management and wetland planning.In order to assess the reliability of the procedure two very different case-studies are considered.     

Symmetry and phase-selected NMR spectra of liquid crystalline samples

It is demonstrated that the NMR spectra of liquid crystalline samples can be simplified by using multiple quantum filtering. In a system of N spin-12 nuclei, the N or (N-1)-multiple quantum filtered spectra (NQF or (N-1)QF) contain lines which originate only from transitions among the eigenstates belonging to the highest symmetry class of the spin permutation group. In addition the NQF spectra are divided further into two sets of lines which differ in phase by 180 degrees. A method for simulating and analysing multiple quantum filtered spectra is described, with examples from molecules with up to eight interacting spins.     

Analysis of the transverse heat transfer coefficients in a dual channel ITER-type cable-in-conduit conductor

This paper describes a new method to determine the equivalent heat transfer coefficients, i.e., radial and azimuthal, in CICC’s with parallel cooling channels. The method is based on the measurement of the steady state temperature response to a step heating. The experiment is modelled by a set of transport equations for the temperature distribution that contain explicitly the parametric dependence on the transverse heat transfer coefficients. The equations are solved analytically and the values of the equivalent transverse heat transfer coefficients are obtained as the best fit of the experimental temperature distributions. We show the results obtained with the method by application to a short length sample experiment in the SULTAN test facility using an ITER-type CICC with special instrumentation, and with heaters to generate a variety of heat slugs. The values of heat transfer coefficient are consistent with expected values, based in particular on the theory of dispersion in porous media.     

Dynamic scaling in sputter grown tungsten thin films

The evolution of a tungsten thin film grown by magnetron sputtering was studied using a dynamic scaling approach. Film growth was followed in-situ and in real-time by monitoring both the specular and the diffuse X-ray scattered intensities as a function of the time of deposition. The analysis of the scattering data allowed us to determine the two Power Spectral Density (PSD) functions, which describe the thin film topography. The time-dependent PSD-function, which describes the dynamic of the external film surface, is found to obey a universal scaling form, which characterizes the thin film growth. The data collapse of these PSDs into a single master curve was achieved using scaling exponents α = 0.18 ± 0.02 and β = 0.06 ± 0.01. In addition, by analyzing the temporal variation of the roughness conformity, it has been demonstrated that the replication factor decreases exponentially with increasing film thickness and spatial frequency. Hence, for a 25 nm thick film the vertical correlation disappears for spatial frequencies p greater than 3.6 μm^− 1.