A hybrid discontinuous in space and time Galerkin method for wave propagation problems

Medium‐frequency regime and multi‐scale wave propagation problems have been a subject of active research in computational acoustics recently. New techniques have attempted to overcome the limitations of existing discretization methods that tend to suffer from dispersion. One such technique, the discontinuous enrichment method, incorporates features of the governing partial differential equation in the approximation, in particular, the solutions of the homogeneous form of the equation. Here, based on this concept and by extension of a conventional space–time finite element method, a hybrid discontinuous Galerkin method (DGM) for the numerical solution of transient problems governed by the wave equation in two and three spatial dimensions is described. The discontinuous formulation in both space and time enables the use of solutions to the homogeneous wave equation in the approximation. In this contribution, within each finite element, the solutions in the form of polynomial waves are employed. The continuity of these polynomial waves is weakly enforced through suitably chosen Lagrange multipliers. Results for two‐dimensional and three‐dimensional problems, in both low‐frequency and medium‐frequency regimes, show that the proposed DGM outperforms the conventional space–time finite element method. Copyright © 2014 John Wiley & Sons, Ltd.     

Physico‐chemical characterization of alginates isolated from a Tunisian Padina pavonica algae as a sustainable biomaterial

This study focuses on the physico‐chemical characterization of an alginate extracted from seaweed (Padina pavonica) collected on the Tunisian coast. Since alginates display a broad variety of applications, especially in the food and pharmaceutical fields, their quality requires a high certain standard of purity and an accurate knowledge of their composition and structure. With this aim, once extracted the Na‐alginate was purified and then characterized for comparison with a commercially available alginate. Thermal analyses (TGA and DSC) were performed to evaluate the water content, i.e. the moisture loss and the thermal stability of this polysaccharide. Spectroscopic investigations demonstrated similarities but also significant differences between the two samples. NMR spectroscopy enabled determination of the mannuronic/guluronic (M/G) ratio, which happened to be lower for the alginate extracted from P. pavonica algae. SEC, performed in water as eluent, was implemented for determination of the average molecular weight of these water‐soluble polymers and revealed 6‐fold higher molecular weights (M_n and M_w) than the commercial reference. © 2020 Society of Chemical Industry     

Postoperative hypoxaemia: continuous extradural infusion of bupivacaine and morphine vs patient-controlled analgesia with intravenous morphine

We carried out a randomized prospective study in 60 patients who had undergone major abdominal surgery for cancer. For postoperative pain control, 30 patients received continuous extradural infusion of 0.125% bupivacaine 12.5 mg h-1 and morphine 0.25 mg h-1 (EXI group) and 30 received patient-controlled analgesia (PCA) with intravenous morphine (1 mg bolus, 5-min lock-out and maximum dose 20 mg 4h-1). Both groups had general anaesthesia. The two groups were compared for postoperative pain scores, satisfaction, sedation and oxygen saturation. Oxygen saturation was recorded continuously the night before surgery and for two consecutive postoperative nights. Episodes of moderate desaturation (90% > SpO2 85%) were more frequent in the EXI group than in the PCA group (P < 0.05). Pain scores were lower in the EXI group compared with the PCA group at rest and while coughing (P < 0.05). No significant difference was found for patient sedation and satisfaction.     

INVESTIGATION OF NITROGEN COMPOUND TYPES IN HIGH-BOILING PETROLEUM DISTILLATES FROM SAUDI ARABIAN CRUDE OILS

Acids, bases and neutral nitrogen compounds from high-boiling petroleum distillates were separated and further fractionated into fractions containing nitrogen compound types by HPLC on neutral alumina. Acids and bases were separated with anion and cation exchange resins respectively while the neutral nitrogen compounds were removed by complexation with ferric chloride supported on Attapulgus clay. The HPLC fractions were characterized by potentiometric titration for their basic and nonbasic nitrogen contents while infrared spectroscopy was used for the quantitative determination of major compound types present which are pyridines, pyrroles, amides, phenols and carboxylic acids. Characterization of individual nitrogen compounds was accomplished using gas chromatography and gas chromatography -mass spectrometry. The nitrogen compounds identified belong to three compound types which are pyridine, pyrrole and amide.     

Microwave Q-factor of a dielectric resonator sandwiched between two thin films of superconductor

This analysis provides a comparison between the computed and the measured Q-factors of a microwave resonator consisting of a dielectic resonator sandwiched between two thin films of superconductor using the Bose statistics and the Gorter and Casimir model for a two-fluid model. Such comparisons are helpful not only to design ultrahigh-Q resonators but also in considering the theory of thin films of HTS (high-temperature superconductors).     

Polyurethane‐incorporated chitosan/alginate core–shell nano‐particles for controlled oral insulin delivery

Chitosan (CS) and polyurethane‐chitosan (PU‐CS) nano‐particles (NPs) were prepared for the core formation by complex coacervation method whereas alginate (ALG) and PU‐ALG were crosslinked by ionic gelation method to form the protective shell‐layer over the core. Effects of PU incorporation either within the core or shell or both were investigated by different in vitro and in vivo parameters. Fourier transform infrared (FTIR) spectroscopy of different compositions of nano‐particles showed distinct characteristic peaks for CS, PU, and ALG, indicating their presence in variable ratios. Significance of polyurethane‐incorporated systems towards insulin encapsulation efficiency, swelling parameters, insulin release, and in vivo pharmacological effect were also studied. Particle sizes, zeta potential, morphological analysis, mucoadhesion study, and in vivo acute toxicity studies of these core–shell nano‐particles were also performed. Bioavailability of insulin ranged from 9.04% to 11.6% for polyurethane‐incorporated chitosan‐alginate core–shell nano‐particle formulations which was significantly higher than the insulin bioavailability of basic CS/ALG core–shell nano‐particle system. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46365.     

A nonparametric probabilistic approach for quantifying uncertainties in low‐dimensional and high‐dimensional nonlinear models

A nonparametric probabilistic approach for modeling uncertainties in projection‐based, nonlinear, reduced‐order models is presented. When experimental data are available, this approach can also quantify uncertainties in the associated high‐dimensional models. The main underlying idea is twofold. First, to substitute the deterministic reduced‐order basis (ROB) with a stochastic counterpart. Second, to construct the probability measure of the stochastic reduced‐order basis (SROB) on a subset of a compact Stiefel manifold in order to preserve some important properties of a ROB. The stochastic modeling is performed so that the probability distribution of the constructed SROB depends on a small number of hyperparameters. These are determined by solving a reduced‐order statistical inverse problem. The mathematical properties of this novel approach for quantifying model uncertainties are analyzed through theoretical developments and numerical simulations. Its potential is demonstrated through several example problems from computational structural dynamics. Copyright © 2016 John Wiley & Sons, Ltd.     

A multilevel projection‐based model order reduction framework for nonlinear dynamic multiscale problems in structural and solid mechanics

A reduction/hyper reduction framework is presented for dramatically accelerating the solution of nonlinear dynamic multiscale problems in structural and solid mechanics. At each scale, the dimensionality of the governing equations is reduced using the method of snapshots for proper orthogonal decomposition, and computational efficiency is achieved for the evaluation of the nonlinear reduced‐order terms using a carefully designed configuration of the energy conserving sampling and weighting method. Periodic boundary conditions at the microscales are treated as linear multipoint constraints and reduced via projection onto the span of a basis formed from the singular value decomposition of Lagrange multiplier snapshots. Most importantly, information is efficiently transmitted between the scales without incurring high‐dimensional operations. In this proposed proper orthogonal decomposition–energy conserving sampling and weighting nonlinear model reduction framework, training is performed in two steps. First, a microscale hyper reduced‐order model is constructed in situ, or using a mesh coarsening strategy, in order to achieve significant speedups even in non‐parametric settings. Next, a classical offline–online training approach is performed to build a parametric hyper reduced‐order macroscale model, which completes the construction of a fully hyper reduced‐order parametric multiscale model capable of fast and accurate multiscale simulations. A notable feature of this computational framework is the minimization, at the macroscale level, of the cost of the offline training using the in situ or coarsely trained hyper reduced‐order microscale model to accelerate snapshot acquisition. The effectiveness of the proposed hyper reduction framework at accelerating the solution of nonlinear dynamic multiscale problems is demonstrated for two problems in structural and solid mechanics. Speedup factors as high as five orders of magnitude are shown to be achievable. Copyright © 2017 John Wiley & Sons, Ltd.