Acidity in Nafion

Hammett acidity functions have been measured for Nafion films equilibrated with a series of nitroaniline dyes in hydrochloric acid solutions. The effect of ionic strength of alkali metal and tetraalky-lammonium bromides on the ability of the Nafion film to donate a proton to Bronsted bases is the reverse of that expected for acid in solution. Absorption of neutral and charged dye is also influenced by the concentration and hydrophobicity of the salt in solution. An interpretation based upon structural spectroscopic studies is discussed.     

Gelatin‐Methacrylamide Hydrogels as Potential Biomaterials for Fabrication of Tissue‐Engineered Cartilage Constructs

Gelatin‐methacrylamide (gelMA) hydrogels are shown to support chondrocyte viability and differentiation and give wide ranging mechanical properties depending on several cross‐linking parameters. Polymer concentration, UV exposure time, and thermal gelation prior to UV exposure allow for control over hydrogel stiffness and swelling properties. GelMA solutions have a low viscosity at 37 °C, which is incompatible with most biofabrication approaches. However, incorporation of hyaluronic acid (HA) and/or co‐deposition with thermoplastics allows gelMA to be used in biofabrication processes. These attributes may allow engineered constructs to match the natural functional variations in cartilage mechanical and geometrical properties.

     

Least‐square collocation and Lagrange multipliers forTaylor meshless method

A recently proposed meshless method is discussed in this article. It relies on Taylor series, the shape functions being high degree polynomials deduced from the Partial Differential Equation (PDE). In this framework, an efficient technique to couple several polynomial approximations has been presented in (Tampango, Potier‐Ferry, Koutsawa, Tiem, Int. J. Numer. Meth. Eng. vol. 95 (2013) pp. 1094–1112): the boundary conditions were applied using the least‐square collocation and the interface was coupled by a bridging technique based on Lagrange multipliers. In this article, least‐square collocation and Lagrange multipliers are applied for boundary conditions, respectively, and least‐square collocation is revisited to account for the interface conditions in piecewise resolutions. Various combinations of these two techniques have been investigated and the numerical results prove their effectiveness to obtain very accurate solutions, even for large scale problems.     

Microwave absorption studies of MgB2 superconductor

Microwave absorption studies have been carried out on MgB₂ superconductor using a standard X-band EPR spectrometer. The modulated low-field microwave absorption signals recorded for polycrystalline (grain size ∼ 10 μm) samples suggested the absence of weak-link character. The field dependent direct microwave absorption has been found to obey a ✓H dependence with two different slopes, which indicated a transition from strongly pinned lattice to flux flow regime.     

Modified high-performance liquid chromatographic method for the determination of ganciclovir in plasma from patients with severe renal impairment.

Using the rapid and sensitive high-performance liquid chromatographic (HPLC) method previously described for the analysis of ganciclovir in plasma, we have observed an interfering peak which co-elutes with the peak of ganciclovir in plasma samples from heart-transplant patients with severe renal insufficiency. A slight modification of this method allows the separation of the two peaks. The modified HPLC method, presented in this paper, is suitable for the accurate determination of ganciclovir in plasma from patients with severe renal impairment.     

Effect of substrate temperature on electrical and magnetic properties of epitaxial La1−x Pb x MnO3 films

Epitaxial La_1−x Pb _x MnO₃ (LPMO) thin films, grown on (100) SrTiO₃ substrates by laser ablation technique at different temperatures between 600 and 850°C, have been characterized for electrical and magnetic properties. The temperature dependence of resistivity showed that the metal-insulator transition temperature (T _MI) decreases with increasing substrate temperature, which has been attributed to decrease in Pb content in the filsm. The YBa₂Cu₃O _x /La_1−x MnO₃ heterostructures, exhibiting both superconductivity and ferromagnetism, have been fabricated.     

Self-scattering in Monte Carlo calculations of transient dynamic response in semiconductors

We have calculated the transient dynamic response in GaAs by a Monte Carlo approach. We find that the results are extremely sensitive to the value of Γ, the self-scattering parameter, which differs from results previously reported in the literature. However, when Г is selected so that $\text{〈Δ t 〉= 1/Г ? 〈τ〉}$, comparable results are obtained to those calculated without utilizing a self-scattering assumption.     

Hot electron transport effects in lead telluride

Velocity-electric field characteristics and evidence for travelling high field domains are reported for hot-electron conduction in single crystal epitaxial films of n-PbTe. Measurements were performed at 77 K, using nanosecond pulse techniques. Contact effects cause differences in the shape of the velocity-field curve and also possibly in the nature of high-field current instabilities. Pulsed Hall measurements reveal substantial time-dependent carrier generation and may indicate the presence of high-field domains.     

Aqueous in situ derivatization of carboxylic acids by an ionic carbodiimide and 2,2,2-trifluoroethylamine for electron-capture detection

We report a technique for the rapid, room temperature derivatization of aqueous carboxylic acids to the corresponding 2,2,2-trifluoroethylamide derivative. 3-Ethyl-1-[3-(dimethylamino)propyl]carbodiimide hydrochloride (EDC) and 2,2,2-trifluoroethylamine hydrochloride (TFEA) were added to aqueous samples of several acids of interest in environmental analytical chemistry, including benzoic acid, ibuprofen, clofibric acid, monochloroacetic acid, dicholoroacetic acid, bromoacetic acid, monochlorophenoxy acetic acid, dichlorophenoxy acetic acid, trichlorophenoxy acetic acid, acetylsalicylic acid, and cholorobenzoic acid. Amidization was essentially complete within ten minutes, and subsequent liquid-liquid extraction of the amides with methyl tert-butyl ether (MTBE) demonstrated recoveries of over 85%. The starting materials, both quaternary ammonium salts, were not co-extracted with the derivative, yielding much cleaner samples than historically obtained from carbodiimide based techniques. The fluorinated amides produced had excellent chromatographic characteristics for gas chromatography and were easily detected by electron-capture detection (ECD) or electron impact mass spectrometry. This method is suggested as a sensitive alternative to more traditional acidification, extraction, and ex situ derivatization techniques.