1,4-Diazepines Bearing Thieno(2,3-b)Thiophene and Cyclohexene Carboxylate Moieties

Bis[thieno(3,2-b)-1,4-diazepine] (4) and bis[imidazo(1′,2′)thieno(3,2-b)-1,4-diazepine (7) derivatives were prepared starting with thieno(2,3-b)thiophenes (1) and (2), respectively. Also, benzodiazepine derivatives (11a–f) were prepared via a reaction of cyclohexenone carboxylates (8a–f) with cyclohexylamine and chloroacetyl chloride followed by cyclization. Also, dibenzoazepines (13) and (14a,b) were prepared via a reaction of (8a) with o-phenylenediamine and o-aminophenol or o-aminothiophenol.     

Algorithms for interface treatment and load computation in embedded boundary methods for fluid and fluid–structure interaction problems

Embedded boundary methods for CFD (computational fluid dynamics) simplify a number of issues. These range from meshing the fluid domain, to designing and implementing Eulerian‐based algorithms for fluid–structure applications featuring large structural motions and/or deformations. Unfortunately, embedded boundary methods also complicate other issues such as the treatment of the wall boundary conditions in general, and fluid–structure transmission conditions in particular. This paper focuses on this aspect of the problem in the context of compressible flows, the finite volume method for the fluid, and the finite element method for the structure. First, it presents a numerical method for treating simultaneously the fluid pressure and velocity conditions on static and dynamic embedded interfaces. This method is based on the exact solution of local, one‐dimensional, fluid–structure Riemann problems. Next, it describes two consistent and conservative approaches for computing the flow‐induced loads on rigid and flexible embedded structures. The first approach reconstructs the interfaces within the CFD solver. The second one represents them as zero level sets, and works instead with surrogate fluid/structure interfaces. For example, the surrogate interfaces obtained simply by joining contiguous segments of the boundary surfaces of the fluid control volumes that are the closest to the zero level sets are explored in this work. All numerical algorithms presented in this paper are applicable with any embedding CFD mesh, whether it is structured or unstructured. Their performance is illustrated by their application to the solution of three‐dimensional fluid–structure interaction problems associated with the fields of aeronautics and underwater implosion. Copyright © 2011 John Wiley & Sons, Ltd.     

An Investigation of the Plasma Composition in Plasma-enhanced Hot Filament Catalytic Chemical Vapor Deposition of Carbon Nanotubes

A mixture of acetylene, hydrogen and ammonia (C₂H₂/H₂/NH₃) is used to produce carbon nanotubes (CNTs) by a plasma-enhanced catalytic chemical vapor deposition process either without (PE CCVD) or with hot filaments-assistance (PE HF CCVD). A mathematical model based on Chemkin^™ computer package is used for analyzing specific conditions of nanotube synthesis. Simulations are compared with optical emission spectroscopy (OES) measurements. Morphological and structural investigations on the grown carbon nanostructures are also performed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was shown that the significant change in the density and the morphology of the CNTs grown in the presence of NH₃ could be mainly explained by the gas phase formation of CN and HCN. Both species display a high etching activity, whereas the species C, CH, CH₂, CH₂(S), C₂ and C₂H are expected to be the most probable carbon nanotube precursors.     

Design of passive polarization rotator based on silica photonic crystal fiber

We propose and analyze a novel (to the best of our knowledge) design of a polarization rotator (PR) based on silica photonic crystal fiber. The proposed design has a rectangular core region with a slanted sidewall. The simulation results are obtained using the full vectorial finite difference method as well as the full vectorial finite difference beam propagation method. The numerical results reveal that the suggested PR can provide a nearly 100% polarization conversion ratio with a device length of 3102 μm.     

Mind the gap: a new insight into the tip leakage vortex using stereo-PIV

The tip leakage vortex (TLV), which develops in the clearance between the rotor and the stator of axial hydro turbines, has been studied for decades. Yet, many associated phenomena are still not understood. For instance, it remains unclear how the clearance size is related to the occurrence of cavitation in the vortex, which can lead to severe erosion. Experiments are here carried out on the influence of the clearance size on the tip vortex structure in a simplified case study. A NACA0009 hydrofoil is used as a generic blade in a water tunnel while the clearance between the blade tip and the wall is varied. The 3D velocity fields are measured using Stereo Particle Image Velocimetry (SPIV) in three planes located downstream of the hydrofoil for different values of the upstream velocity, the incidence angle and a large number of tip clearances. The influence of the flow conditions on the structure of the TLV is described through changes in the vortex intensity, core axial flow, vortex center position and wandering motion amplitude. Moreover, high-speed visualizations are used to highlight the vortex core trajectory and clearance flow alteration, turning into a wall jet as the tip clearance is reduced. The measurements clearly reveal the existence of a specific tip clearance for which the vortex strength is maximum and most prone to generating cavitation.     

Fast computation of the wall distance in unsteady Eulerian fluid-structure computations

Highly nonlinear, turbulent, dynamic, fluid-structure interaction problems characterized by large structural displacements and deformations, as well as self-contact and topological changes, are encountered in many applications. For such problems, the Eulerian computational framework, which is often equipped with an embedded (or immersed) boundary method for computational fluid dynamics, is often the most appropriate framework. In many circumstances, it requires the computation of the time-dependent distance from each active mesh vertex of the embedding mesh to the nearest embedded discrete surface. Such circumstances include, for example, modeling turbulence using the Spalart-Allmaras or detached eddy simulation turbulence models and performing adaptive mesh refinement in order to track the boundary layer. Evaluating at each time step the distance to the wall is computationally prohibitive, particularly in the context of explicit-explicit fluid-structure time-integration schemes. Hence, this paper presents two complementary approaches for reducing this computational cost. The first one recognizes that many quantities depending on the wall distance are relatively insensitive to its inaccurate evaluation in the far field. Therefore, it simplifies a state-of-the-art algorithm for computing the wall distance accordingly. The second approach relies on an effective wall distance error estimator to update the evaluation of the wall distance function only when otherwise, a quantity of interest that depends on it would become tainted by an unacceptable level of error. The potential of combining both approaches for dramatically accelerating the computation of the wall distance is demonstrated with the Eulerian simulation of the inflation of a disk-gap-band parachute system in a supersonic airstream.     

Local Near-Beltrami Structure and Depletion of the Nonlinearity in the 3D Navier–Stokes Flows

Journal of Nonlinear Science - Computational simulations of turbulent flows indicate that the regions of low dissipation/enstrophy production feature high degree of local alignment between the...     

Optical biopsy of breast cancer tissue

In this paper, we report results of Fluorescence Emission Spectra (FES) and Stokes Shift Spectra (SSS) of 19 cancer tissue of invasive ductal carcinoma of different grades in comparison with normal breast tissues (obtained away from tumor regions). We were able to get distinct differences in the spectral features of normal and malignant tissues in terms of the ratios of concentrations of biomolecules like tryptophan, collagen and NADH. The sensitivity and specificity were in the range of 75%. What was all the more important was the parallelism in the spectral features of normal and malignant breast tissue pieces of above set of subjects. The objective of our research is to evolve one such protocol and the first step is the spectral characterization of in vitro optical analyses of excised tumor tissues.     

Utilization of 2-ylidene-4-thiazolidinones in the synthesis of heterocyclic compounds. Part I: Synthesis of pyrazoles

2-Ylidene and 2,5-diylidene-4-thiazolidinones 2a–d were synthesized and converted into pyrazole derivatives 4a–d by reaction with hydrazine hydrate. A mechanism of this novel conversion is suggested.     

Pseudo bond graph tunnel greenhouse model with accurate longwave/shortwave radiations model

This research work is focused on the construction of an accurate longwave/shortwave radiation model on a tunnel greenhouse pseudo-bond graph model, widely used in Tunisia. This model includes sun position, useful incoming solar radiation model, sky longwave radiation model, inside longwave and shortwave radiation model. The key idea is to use bond graphs allowing a lumped modelling approach which is suitable for control applications. Furthermore, an evaluation of some longwave radiative model components was made, noting that these components are particularly sensitive regarding to the thermal behaviour of the model.

Experimental tunnel greenhouse data are used as validation elements for the present model with globally good results. A comparative study was also performed between the present model and a previous bond graph model containing a simplistic radiative model. Practical simulation results show a clear improvement compared with the previous model.