Assessment of high-resolution methods for numerical simulations of compressible turbulence with shock waves

Flows in which shock waves and turbulence are present and interact dynamically occur in a wide range of applications, including inertial confinement fusion, supernovae explosion, and scramjet propulsion. Accurate simulations of such problems are challenging because of the contradictory requirements of numerical methods used to simulate turbulence, which must minimize any numerical dissipation that would otherwise overwhelm the small scales, and shock-capturing schemes, which introduce numerical dissipation to stabilize the solution. The objective of the present work is to evaluate the performance of several numerical methods capable of simultaneously handling turbulence and shock waves. A comprehensive range of high-resolution methods (WENO, hybrid WENO/central difference, artificial diffusivity, adaptive characteristic-based filter, and shock fitting) and suite of test cases (Taylor–Green vortex, Shu–Osher problem, shock-vorticity/entropy wave interaction, Noh problem, compressible isotropic turbulence) relevant to problems with shocks and turbulence are considered. The results indicate that the WENO methods provide sharp shock profiles, but overwhelm the physical dissipation. The hybrid method is minimally dissipative and leads to sharp shocks and well-resolved broadband turbulence, but relies on an appropriate shock sensor. Artificial diffusivity methods in which the artificial bulk viscosity is based on the magnitude of the strain-rate tensor resolve vortical structures well but damp dilatational modes in compressible turbulence; dilatation-based artificial bulk viscosity methods significantly improve this behavior. For well-defined shocks, the shock fitting approach yields good results.     

Molybdatophosphoric Acid/NaNO2/Wet SiO2 as an Efficient System for the Aromatization of 1,2‐Dihydroquinolines under Mild and Heterogeneous Conditions

A combination of molybdatophosphoric acid and NaNO₂ in the presence of wet SiO₂ was used as an effective oxidizing agent for the oxidation of 1,2‐dihydroquinolines to their corresponding quinoline derivatives in dichlomethane at room temperature with excellent yields.     

Modification of the Scaled Particle Theory for Solubility of Non-Polar Gases in Water

In this work based on the modified scaled particle theory (SPT), the solubility of non-polar gases (He, Ar, N₂, H₂, O₂, CO₂ and CH₄) in water has been studied over a wide range of temperatures. Calculations of Henry’s law constant by the SPT are related to the inherent physical properties and parameters of solvent and solute, all of which are considered temperature dependent. The temperature dependence of molar volume and hard sphere diameter of solvent and polarizability of solute have the most significant effects on the solubilities of gases in water. The average relative deviation is less than 3 %. Also, the effect of different mixing rules in the application of SPT to prediction of gas solubility has been studied.     

Polyvinylimidazole/sol–gel composite as a novel solid‐phase microextraction coating for the determination of halogenated benzenes from aqueous solutions

A polyvinylimidazole/sol–gel composite is proposed as a novel solid‐phase microextraction fiber to extract five halobenzenes from the headspace of aqueous solutions in combination with gas chromatography with mass spectrometry. The prepared fiber was characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The obtained results showed that porous polyvinylimidazole/sol–gel composite was chemically deposited on fused silica fiber. The effect of important extraction parameters including extraction temperature, extraction time, and salt content were investigated. The optimum conditions were as follows: extraction temperature 25°C, extraction time 20 min, and salt concentration 30 w/v%. Detection limits and relative standard deviations of the developed method for halogenated benzenes were below 0.1 pg/mL and 15%, respectively. Repeatability of the proposed method, explained by relative standard deviation, varied between 5.48 and 9.15% (n = 5). The limits of detection (S/N = 3) ranged between 0.01 and 0.10 ng/L using gas chromatography with mass spectrometry with selected ion monitoring mode. For real sample analysis, three types of water samples with different matrices (ground, surface, and tap water) were studied. The optimized procedure was applied to extraction and method validation of halogenated benzenes in spiked water samples.     

Analysis of tamoxifen and its main metabolites in plasma samples of breast cancer survivor female athletes: Multivariate and chemometric optimization

A sensitive method based on liquid chromatography combined with a diode array detector was developed and validated to simultaneously determine tamoxifen, and its active metabolites N-desmethyltamoxifen, 4-hydroxytamoxifen, and endoxifen in human plasma samples. The green and sustainable vortex-assisted dispersive liquid-phase microextraction technique based on the natural hydrophobic deep eutectic solvent was used for the extraction and preconcentration of the analytes. Chemometrics and multivariate analysis were used to optimize the independent variables including the type and volume of deep eutectic solvent, extraction time, and ionic strength. Under optimal conditions, calibration curves were linear in a suitable range with the lower limits of quantification (0.8–10.0 μg/L), which covered the relevant concentrations of the analytes in plasma samples for a clinical study. Intra- and interday precision evaluated at three concentrations for the analytes were lower than 8.2 and 12.1%, respectively. Accuracy was in the range of 94.9–104.7%. The applicability of the developed method on human plasma samples illustrated the range 45.1–72.8, 98.4–128.3, 0.9–1.2, and 2.7–6.1 μg/L for tamoxifen, N-desmethyltamoxifen, 4-hydroxytamoxifen, and endoxifen, respectively. The validated method can be effective for the pharmacokinetics, pharmacodynamics, and therapeutic drug monitoring studies of tamoxifen and its main metabolites in biological fluids.     

Adsorptive Stripping Voltammetric Determination of Imipramine and Amitriptiline at a Nanoclay Composite Carbon Ionic Liquid Electrode

A new carbon nanocomposite electrode has been designed by incorporation of montmorillonite nanoclay into a carbon ionic liquid electrode for the electrochemical determination of imipramine (IMP) and amitriptyline (AMT). They are expected to accumulate on the electrode surface through the cooperative interaction of ionic liquid and clay with the drugs. The proposed electrode also possesses attractive electrocatalytic effects towards the drugs especially AMT. Low detection limits of 19 nM for IMP and 24 nM for AMT were achieved. The proposed nanocomposite electrode exhibits good applicability for monitoring IMP and AMT in pharmaceutical formulations and blood serum samples.     

Computational studies on the conformational preference of N-(Thiazol-2-yl) benzamide

N-(Thiazol-2-yl) benzamide 1 substructures are found in some of bioactive compounds. In some of protein/ligand co-crystals, the 1 moiety adopts a conformer in which the amide O and the thiazole S atoms are close. In fact, in the crystalline structure of 1 , the O—S distance is even shorter than Van der Waals radius. Although the natural bond orbital analysis finds a weak stabilizing interaction between O and S atoms, the attractive dipole–dipole interaction between the amide N─H and thiazole N atom seems to play a more significant role. Moreover, an intramolecular O—H hydrogen bonding in dimeric forms found to have an important role in the conformation preference of 1 . Computational details for the stability of conformers have been discussed using quantum theory of atoms in molecules, natural bond orbital (NBO) and noncovalent interaction index analysis.     

Structures,g-tensors,and hyperfine coupling constants of L-α-alanine radicals in radiation dosimetry: An ab initio molecular dynamics simulation study

Alanine is used as a transfer standard dosimeter for gamma ray and electron beam calibration. An important factor affecting its dosimetric response is humidity which can lead to errors in absorbed dose calculations. Ab initio molecular dynamics calculations were performed to determine the environmental effects on the electron paramagnetic resonance (EPR) parameters of L-α-alanine radicals in acidic and alkaline solutions. A new result, not dissimilar to the closed-shell amino acid molecule alanine, is that the non-zwitterionic form of the alanine radical is the stable form in the gas phase while the zwitterionic neutral alanine radical is not a stable structure in the gas phase. Geometric and EPR parameters of radicals in both gas and solution phases are found to be dependent on hydrogen bonding of water molecules with the polar groups and on dynamic solvation. Calculations on the optimized free radicals in the gas phase revealed that for the neutral radical, hydrogen bonding to water molecules drives a decrease in the magnitudes of g-tensor components g _xx and g _yy without affecting neither g _zz component nor the hyperfine coupling constants (HFCCs). The transfer from the gas to solution phase of the alanine radical anion is accompanied with an increase in the spin density on the carboxylic group's oxygen atoms. However, for the neutral radical, this transfer from gas to solution phase is accompanied with the decrease in the spin density on oxygen atoms. Calculated isotropic HFCCs and g-tensor of all radicals are in good agreement with experiment in both acidic and alkaline solutions.     

Adsorption properties of H2O2 trapped inside a boron phosphide nanotube

Abstract  

The behavior of H₂O₂ adsorbed inside a [4,4] armchair boron phosphide nanotube (BPNT) was studied by using density functional calculations. Geometry optimizations were carried out at the B3LYP/6-31G* level of theory using the Gaussian 03 suite of programs. We present the nature of the H₂O₂ interactions inside the nanotube. The interaction between the guest species (H₂O₂) and the nanotube and the dipole moments of the different geometries are discussed. The results show that the binding energies and the dipole moments of the nanotube depend on the orientation and location of the H₂O₂ inside the tube. Among the parallel orientation (AT) and perpendicular orientations (PTA and PTP), the PTA and PTP geometries of the H₂O₂ are unstable whereas the AT-state geometries show stabilization of the guest species inside the BPNT. For AT orientations, the value of the dihedral angle of the H₂O₂ trapped inside the BPNT in the most stable conformation displays a notable change with respect to free H₂O₂. Also, with change of tube type, more efficient binding could not be achieved, and only the orientation and location of the H₂O₂ inside the tube play an important role in determining the binding energy. The polarization of the BPNT in the presence of the guest species in the PT state is higher than that of the AT state. Adsorption of H₂O₂ in the AT state slightly reduces the energy gap of the pristine BPNTs and slightly increases their electrical conductance.