Synthesis and characterization of a new semi-interpenetrating polymer network hydrogel obtained by gamma radiations

A new polyacrylic acid/polyhydroxybutyrate semi-interpenetrating polymer network hydrogel, the s-IPN/PAA-PHB, was prepared by a gamma radiation-induced polymerization. Thermal behavior was studied by thermogravimetric analysis (TG) and Differential scanning calorimetry (DSC), while the s-IPNs composition, FTIR spectra, and swelling kinetics were also determined. It was found that the DSC curve showed a melting point which is attributed to polyhydroxybutyrate. The TG curves showed various stages of degradation which are in correspondence of the presence of crosslinked polyacrylic acid and confirmed the higher thermal stability of the polymer network. The s-IPN/PAA-PHB composition was 10% of PHB and 90% of PAA. Moreover, the network reached approximately 600% of swelling in water, so it behaves like a superabsorbent hydrogel.     

Some polishing experiments on copper in a hyperbolic cell

Some polishing experiments have been carried out on copper anodes in a hyperbolic cell designed by Gilmont and Walton, using orthophosphoric acid as the electrolyte. The results obtained have been compared to those obtained in similar experiments in a Hull cell. It has been found that very similar bands of different reflectivity and polishes are found to form in both the cells. These bands shift with time and a study of such displacements has been made. The results are briefly discussed.     

Thermal properties,nanoscopic structure and swelling behavior of chitosan/(ureasil–polyethylene oxide hybrid) blends

In this work, the effect of chitosan blending on the thermal properties, nanoscopic structure and swelling behavior of ureasil–polyethylene oxide (U-PEO) hybrid materials was examined. Materials were prepared by the sol–gel route using acid catalysts, and the effect of acid (hydrochloric or acetic acid) was also examined. Differential scanning calorimetry results showed that chitosan addition did not provoke appreciable changes in the thermal behavior of the U-PEO. Thermogravimetric curves did not show changes in thermal stability resulting from chitosan blending but were depended on the type of acid catalyst. Small-angle X-ray scattering and nuclear magnetic resonance spectroscopy techniques were used for studying nanoscopic and inner structures, showing the existence of two structural levels and differences in polycondensation degrees. All samples presented fast water uptake with the same initial swelling rate and with a non-Fickian or anomalous transport mechanism. Swelling degree was higher in hybrids prepared with HCl, which possessed less branched siloxane cross-link nodes species, therefore lower polycondensation degree. Also, the magnitude of swelling decreased for hybrids blended with chitosan, which provides a means of tailoring the water uptake by the ureasil–PEO hybrid and to potentiate the control of the release profile of drugs incorporated in these materials.     

Measuring multiple neurochemicals and related metabolites in blood and brain of the rhesus monkey by using dual microdialysis sampling and capillary hydrophilic interaction chromatography-mass spectrometry

In vivo measurement of multiple functionally related neurochemicals and metabolites (NMs) is highly interesting but remains challenging in the field of basic neuroscience and clinical research. We present here an analytical method for determining five functionally and metabolically related polar substances, including acetylcholine (quaternary ammonium), lactate and pyruvate (organic acids), as well as glutamine and glutamate (amino acids). These NMs are acquired from samples of the brain and the blood of non-human primates in parallel by dual microdialysis, and subsequently analyzed by a direct capillary hydrophilic interaction chromatography (HILIC)–mass spectrometry (MS) based method. To obtain high sensitivity in electrospray ionization (ESI)–MS, lactate and pyruvate were detected in negative ionization mode whereas the other NMs were detected in positive ionization mode during each HILIC-MS run. The method was validated for linearity, the limits of detection and quantification, precision, accuracy, stability and matrix effect. The detection limit of acetylcholine, lactate, pyruvate, glutamine, and glutamate was 150 pM, 3 μM, 2 μM, 5 nM, and 50 nM, respectively. This allowed us to quantitatively and simultaneously measure the concentrations of all the substances from the acquired dialysates. The concentration ratios of both lactate/pyruvate and glutamine/glutamate were found to be higher in the brain compared to blood (p < 0.05). The reliable and simultaneous quantification of these five NMs from brain and blood samples allows us to investigate their relative distribution in the brain and blood, and most importantly paves the way for future non-invasive studies of the functional and metabolic relation of these substances to each other.     

Size effect study in magnetoelectric BiFeO3 system

In this paper, we report for the first time finite size effects on Néel temperature (T _N) of magnetoelectric BiFeO₃ system. Novel wet chemical route has been developed to produce fine particles of BiFeO₃ with controlled size and size distribution. Unlike other oxide systems, lattice volume contraction has been observed with decrease in particle size. The decrease in T _N is co-related to unit cell volume contraction occurring with reduction in particle size.     

On Lagrangian–Grassmannian codes

Using the Lagrangian–Grassmannian, a smooth algebraic variety of dimension n(n + 1)/2 that parametrizes isotropic subspaces of dimension n in a symplectic vector space of dimension 2n, we construct a new class of linear codes generated by this variety, the Lagrangian–Grassmannian codes. We explicitly compute their word length, give a formula for their dimension and an upper bound for the minimum distance in terms of the dimension of the Lagrangian–Grassmannian variety.     

Inverse results on row sequences of Hermite–Padé approximation

We consider row sequences of (type II) Hermite–Padé approximations with common denominator associated with a vector f of formal power expansions about the origin. In terms of the asymptotic behavior of the sequence of common denominators, we describe some analytic properties of f and restate some conjectures corresponding to questions once posed by A. A. Gonchar for row sequences of Padé approximants.