Lattice-Boltzmann simulations of the dynamics of polymer solutions in periodic and confined geometries

A numerical method to simulate the dynamics of polymer solutions in confined geometries has been implemented and tested. The method combines a fluctuating lattice-Boltzmann model of the solvent [Ladd, Phys. Rev. Lett. 70, 1339 (1993)] with a point-particle model of the polymer chains. A friction term couples the monomers to the fluid [Ahlrichs and Dunweg, J. Chem. Phys. 111, 8225 (1999)], providing both the hydrodynamic interactions between the monomers and the correlated random forces. The coupled equations for particles and fluid are solved on an inertial time scale, which proves to be surprisingly simple and efficient, avoiding the costly linear algebra associated with Brownian dynamics. Complex confined geometries can be represented by a straightforward mapping of the boundary surfaces onto a regular three-dimensional grid. The hydrodynamic interactions between monomers are shown to compare well with solutions of the Stokes equations down to distances of the order of the grid spacing. Numerical results are presented for the radius of gyration, end-to-end distance, and diffusion coefficient of an isolated polymer chain, ranging from 16 to 1024 monomers in length. The simulations are in excellent agreement with renormalization group calculations for an excluded volume chain. We show that hydrodynamic interactions in large polymers can be systematically coarse-grained to substantially reduce the computational cost of the simulation. Finally, we examine the effects of confinement and flow on the polymer distribution and diffusion constant in a narrow channel. Our results support the qualitative conclusions of recent Brownian dynamics simulations of confined polymers [Jendrejack et al., J. Chem. Phys. 119, 1165 (2003) and Jendrejack et al., J. Chem. Phys. 120, 2513 (2004)].     

Identification of radical structures on 1‐pentamethylbenzyl‐3‐ethylimidazoliumsilver(I)bromide and 1,3‐bis(pentamethylbenzyl)‐4,5‐dimethylbenzimidazoliumsilver(I)bromide exposed to gamma rays: an EPR study

1‐Pentamethylbenzyl‐3‐ethylimidazoliumsilver(I)bromide and 1,3‐bis(pentamethylbenzyl)‐4,5dimethylbenzimidazoliumsilver(I)bromide and their Ag⁺ complexes were synthesized and their polycrystal forms were produced by recrystallization in dichloromethane/Et₂O solvent system. Structural determinations were carried out by ¹H NMR and ¹³C NMR with a Varian 400 NMR system using tetramethylsilane as internal standard and CDCl₃ as solvent. The disappearance of acidic N‐heterocyclic carbene proton showed the formation of Ag(I) complexes. Also, elemental analyses were carried out. Electron paramagnetic resonance (EPR) measurements were performed to determine the formed radical structure on the samples irradiated at the room temperature for 72 h by using ⁶⁰Co‐source with dose rate of 0.680 kGy. The EPR measurements were carried out in the temperature range of 200 K–450 K. Identical radicals were determined on the irradiated compounds. It was observed that the shapes of the spectra of the samples were independent of the temperature but, the resonance line intensities changed linearly with the temperature. Also, it was detected that the free radical on the 1‐pentamethylbenzyl‐3‐ethylimidazoliumsilver(I)bromide is not stable compared to that on the 1,3‐bis(pentamethylbenzyl)‐4,5dimethylbenzimidazoliumsilver(I)bromide. Copyright © 2016 John Wiley & Sons, Ltd.     

Identification of radiation‐induced radical structure in azocalix[4]arene: an EPR study

A macrocyclic azocalix[4]arene (1) based ester derivative was synthesized. The single crystals of azocalix[4]arene were produced by slow evaporation of concentrated ethyl acetate solutions. These single crystals were exposed to ⁶⁰Co gamma rays with a dose rate of 0.980 kGy h^‐1 for 48 and 72 h to produce a stable free radical. Electron paramagnetic resonance (EPR) measurements were performed in three mutually perpendicular planes of the single crystal in the magnetic field, in addition, temperature dependence of the EPR signal was studied between 120 K and 450 K. The spectra were found to be temperature and angular dependent. Analysis based on the spectra recorded showed that a free radical was formed by fission of a C–H bond. This radical is described as ^?C_aHC_bH₃ The averages of the principal values of the hyperfine parameters and g‐factor are: g = 2.0034, A_Ha = 1.28 mT, A_H1=H2 = 1.00 mT, and A_H3 = 0.49 mT. Copyright © 2013 John Wiley & Sons, Ltd.     

Multilevel quasi-interpolation on a sparse grid with the Gaussian

Motivated by the recent multilevel sparse kernel-based interpolation (MuSIK) algorithm proposed in Georgoulis et al. (SIAM J. Sci. Comput. 35, 815–832, 2013), we introduce the new quasi-multilevel sparse interpolation with kernels (Q-MuSIK) via the combination technique. The Q-MuSIK scheme achieves better convergence and run time when compared with classical quasi-interpolation. Also, the Q-MuSIK algorithm is generally superior to the MuSIK methods in terms of run time in particular in high-dimensional interpolation problems, since there is no need to solve large algebraic systems. We subsequently propose a fast, low complexity, high-dimensional positive-weight quadrature formula based on Q-MuSIKSapproximation of the integrand. We present the results of numerical experimentation for both quasi-interpolation and quadrature in high dimensions.     

Using Raman Spectroscopy to Investigate the Molecular Level Characteristics of Endometriosis

Optics and Spectroscopy - Endometriosis is a benign gynecologic disorder. It is particularly common among young women and may make pregnancy difficult. In this study molecular level...     

Biological screening of some Turkish medicinal plant extracts for antimicrobial and toxicity activities

Screening of antibacterial activity and toxicity of 22 aqueous plant extracts from 17 Turkish plants was conducted. Antibacterial activity was performed with six bacteria including Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Streptococcus pyogenes, Staphylococcus aureus and Staphylococcus epidermidis. Extracts of Tussilago farfara leaves, Helichyrsum plicatum flowers, Solanum dulcamara aerial parts and Urtica dioica leaves gave the best inhibitory activity against S. pyogenes, S. aureus and S. epidermidis. Of the 22 plant extracts, 20 extracts displayed toxicity (LC50 was <1000 mg L(-1)) in the brine shrimp bioassay. For radish seed bioassay, two different determinations (root length and seed germination) were performed with a comparison between two concentrations (50,000 mg L(-1) and 10,000 mg L(-1)). At low concentration (10,000 mg L(-1)), S. dulcamara aerial parts and Primula vulgaris leaf extracts were observed to inhibit the root length more than the other plant extracts. Also, the most inhibitive plant extract for seed germination was obtained with S. dulcamara aerial parts.     

Effect of fiber modification with carboxymethyl cellulose on the efficiency of a microparticle flocculation system

Carboxymethyl cellulose (CMC) has been used widely to enhance dry strength of paper and uniformity of sheet in the papermaking industry. Besides these positive effects, it may affect the fines retention and dewatering processes negatively. These negative effects are mainly seen when fiber modifications with high CMC dosages are studied in laboratory scale. In this paper, the effect of fiber modification with CMC on the deposition of precipitated calcium carbonate (PCC) and on the dewatering process in the presence of cationic polyacrylamide (CPAM)/bentonite microparticle flocculation system is examined. It was determined that fiber modification with 10 mg g⁻¹ of CMC decreased PCC deposition at the initial addition of CPAM and gave better PCC deposition at 2 mg g⁻¹ of CPAM. It was also observed that PCC deposition on unmodified fibers is higher at lower CPAM concentration. PCC deposition was found as almost stable after a maximum value obtained at 0.5 mg g⁻¹ of bentonite concentration for fiber modified with 40 mg g⁻¹ of CMC. This indicates that interaction between CPAM and bentonite particles changed due to higher surface charge and CMC conformation on fibers. Results of the dewatering experiments showed that CMC modification increased the drainage time due to a denser and more plugged sheet. This negative effect was compensated with higher concentrations of CPAM and bentonite. On the other hand, dewatering is also affected by the mass ratio of CMC and CPAM, which was not the optimum one in this study at lower of CPAM. Thus, the increase in the drainage time in the presence of CMC on the fiber surface could be also caused by incorrect ratios of chemicals because the effect of CMC on the drainage time was not observed at higher concentrations of CPAM.     

Bending behavior of a bi-morph piezoelectric curved beam

A simple and concise mathematical model describing the deformation and the electrical behavior of a bi-morph piezoelectric curved sensor subjected to pure bending is developed. In particular, the influence of the couple moment on the electrical potential generated in the sensor is investigated and the results are presented in graphical form. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dibutyltin-3-hydroxyflavone bromide: A fluorescent inhibitor of F1F0-ATPase

Dibutyltin-3-hydroxyflavone bromide [Bu₂SnBr-(of)] is a fluorescent inhibitor (excitation max, 395 nm; emission max., 450 nm) of mitochondrial F₁F₀–ATPase which does not inhibit F₁–ATPase. Bu₂SnBr(of) binding to mitochondria and submitochondrial particles results in a 10-fold fluorescence enhancement which correlates with the amount of F₁F₀–ATPase in the inner membrane. Enhancement is not affected by respiratory-chain substrates, ATP, uncoupling agents, ionophores or respiratory-chain inhibitors. It is reversed by tributyltin chloride (Bu₃SnCl), indicating competition for a common triorganotin-binding site on the F₀ segment of F₁F₀–ATPase. Enhancement is not reversed by dialkyltins, monoalkyltins, tributyl-lead acetate, efrapeptin or oligomycin. Bu₂SnBr(of) is thus a new class of fluorescent probe of the F₀ segment of F₁F₀–ATPase which titrates F₀.