Syntheses of bismaleimides with ester units and their polymerization with diamines

Five structurally different bismaleimides were synthesized by reaction between 3(4)‐maleimidobenzylchloride with various diphenols. They were characterized by infrared (IR) and proton nuclear magnetic resonance (¹H‐NMR) spectroscopy. Thermal characterization of monomers and their polymers was accomplished by differential scanning calorimetry (DSC) and dynamic thermogravimetric analysis (TGA). Polyaminobismaleimides having inherent viscosities of 0.1–0.4 dL/g were prepared by Michael addition of diamines to bismaleimides. The polymers are soluble in solvents as DMF, NMP, and DMSO, and afforded film from their solutions. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 750–757, 2002; DOI 10.1002/app.10294     

Spectra of long primitive binary BCH codes cannot approach thebinomial distribution

Usually spectra (weight distributions) of primitive binary BCH codes are supposed to approximate binomial weight distributions well for a wide range of code rates and code lengths. It is shown that for any fixed code rate R<1 spectra of long (N→∞) primitive binary BCH codes cannot approximate the binomial distribution at all     

Optical and structural investigations on iron-containing phosphate glasses

The article reports the preparation and complex characterization of iron-containing phosphate glasses considered to be ecological materials, as they contain non-toxic compounds related to environment. The oxide system Li₂O?CMgO?C(CaO)?CAl₂O₃?CP₂O₅?C(FeO/Fe₂O₃) was investigated in respect to its structural changes caused by MgO replacement with CaO and by the iron addition. UV?Cvis?CNIR (ultraviolet?Cvisible?Cnear infrared) spectroscopy as well as thermo-gravimetric (TG) measurements, differential thermo-analysis (DTA), X-ray diffraction (XRD) analysis, electronic paramagnetic resonance (EPR), and Mossbauer (nuclear gamma resonance) spectroscopy have been used to investigate redox states and coordination symmetry of iron, together with vitreous network changes during the heat treatment up to 1000 °C. UV?Cvis?CNIR transmission spectroscopy revealed no structural modifications when MgO was substituted by CaO, but noteworthy absorption bands attributed to Fe²⁺/Fe³⁺ species. TG analysis made in the 20?C1000 °C range shows low weight loss accompanied by several thermal effects, as evidenced by DTA. XRD patterns for the glass samples heat treated at about 700 °C revealed the presence of different phosphate crystalline phases containing Mg, Al, and Fe ions. EPR spectroscopy revealed the presence of paramagnetic Fe³⁺ ions and the change of the first coordination symmetry, when the samples are heated below the vitreous transition temperature. Mossbauer spectroscopy has evidenced two paramagnetic species, Fe²⁺ and Fe³⁺, both in octahedral coordination symmetry and a clustering process supported by only Fe³⁺ ions.     

An atomic force microscopy statistical analysis of laser‐induced azo‐polyimide periodic tridimensional nanogrooves

The surface morphology of azo‐polyimide films was investigated after 355nm Nd: YAG laser irradiation with two different incident fluencies. Atomic force microscopy (AFM) was employed to correlate the laser‐induced tridimensional nanogrooved surface relief with the incident fluence and the number of irradiation pulses. The height images revealed that the grooves depth increased even tens of times by increasing the incident fluence, using the same numbers of irradiation pulses. For low incident fluence, the films were uniformly patterned till 100 pulses of irradiation. Instead, when using higher fluence, after 15 pulses of irradiation the accuracy of the surface relief definition was reduced. This behavior could be explained by means of two different mechanisms, one that suppose the film photo‐fluidization due to the cis‐trans isomerization processes of the azo‐groups and the second one responsible for the directional mass displacement. The dominant surface direction and parameters like isotropy, periodicity, and period were evaluated from the polar representation for texture analysis, revealing the appearance of ordered and directionated nanostructures for most of the experimental conditions. Also, the graphical studies of the functional volume parameters have evidenced the improvement of the relief structuration during surface nanostructuration. The correlation of these statistical texture parameters with the irradiation characteristics is important in controlling the alignment of either the liquid crystals or the cells/tissues on patterned azo‐polyimide surfaces for optoelectronic devices and implantable biomaterials, respectively. Microsc. Res. Tech. 76:914–923, 2013. © 2013 Wiley Periodicals, Inc.     

Synthesis,characterization, and antifungal activity of nystatin—gum arabic conjugates

Nystatin, a polyene tetraene antibiotic widely used in the treatment of mycoses, was coupled with oxidized polysaccharide gum Arabic, by forming Schiff base structures between amine groups of antibiotics and aldehyde groups of modified carbohydrate. Imine conjugates synthesized in this way were reduced with sodium borohydride to secondary amines. Two imine and two amine conjugates were obtained with different nystatin content. The conjugates were characterized by UV–Vis, FTIR, ¹H NMR spectroscopy, and thermogravimetric analysis. Solubility in water, unlike nystatin, and significant activity against Candida albicans and Aspergillus niger with minimum inhibitory concentrations in range of 3.125–6.25 μg mL^?1 and 6.25–25 μg mL^?1, respectively, indicate that the chemical integrity and the biological function of these compounds were retained. A comparison of stability of the conjugates in the dry form, solution and under different pH values showed that the conjugates exhibited better stability than pure drug. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Modeling the combined effects of pH, temperature and ascorbic acid concentration on the heat resistance of Alicyclobacillus acidoterrestis

In this study, thermal inactivation parameters (D- and z-values) of Alicyclobacillus acidoterrestris spores in McIlvaine buffers at different pH, apple juice and apple nectar produced with and without ascorbic acid addition were determined. The effects of pH, temperature and ascorbic acid concentration on D-values of A. acidoterrestris spores were also investigated using response surface methodology. A second order polynomial equation was used to describe the relationship between pH, temperature, ascorbic acid concentration and the D-values of A. acidoterrestris spores. Temperature was the most important factor on D-values, and its effect was three times higher than those of pH. Although the statistically significant, heat resistance of A. acidoterrestris spores was not so influenced from the ascorbic acid within the concentration studied. D-values in apple juice and apple nectars were higher than those in buffers as heating medium at similar pH. The D-values ranged from 11.1 (90 °C) to 0.7 min (100 °C) in apple juice, 14.1 (90 °C) to 1.0 min (100 °C) in apple nectar produced with ascorbic acid addition, and 14.4 (90 °C) to 1.2 min (100 °C) in apple nectar produced without ascorbic acid addition. However, no significant difference in z-values was observed among spores in the juices and buffers at different pH, and it was between 8.2 and 9.2 °C. The results indicated that the spores of A. acidoterrestris may survive in fruit juices and nectars after pasteurization treatment commonly applied in the food industry.     

Finite element analysis of GTAW arc under different shielding gases

The aim of this work is to use COMSOL software as a tool for solving the 2-D Magnetohydrodynamics (MHD) problem in the Gas Tungsten Arc Welding (GTAW) arc under the shielding gases argon, helium, nitrogen and argon + 10% hydrogen. COMSOL 3.5a worked perfectly for solving multiphysics phenomena, including the Navier-Stokes flow equation, the heat transfer equation and the Maxwell Equation. COMSOL software can be utilized to simulate the temperature and velocity profile in the GTAW arc after some validation procedures. Cumbersome experimental work can be avoided by using this numerical instrument.For our study, we compared the numerically calculated temperature profile and maximum plasma velocity under argon shielding gas and maximum temperature of a nitrogen arc with experimental results found in the literature. We also compared the numerically calculated velocity profile with another numerical solution found in the literature. Our comparisons showed good agreement. The highest temperature was in the nitrogen arc, while the highest voltage was in the helium arc. The highest total energy was in the helium arc similar to the voltage value. The highest plasma velocity values were obtained in the nitrogen and helium arcs. The most constricted arc was calculated in the nitrogen arc.     

Influence of the micro- and nanoscale local mechanical properties of the interfacial transition zone on impact behavior of concrete made with different aggregates

The influence of the microscale local mechanical properties of the interfacial transition zone (ITZ) on macro-level mechanical response and impact behavior is studied for concretes made with copper slag and gravel aggregates. 3D nanotech vertical scanning interferometry, scanning electron microscopy coupled with energy dispersive X-ray micro-analysis, digital image analysis, and 3D X-ray computed tomography were used to characterize the microstructures and the ITZs. It was deduced that a stronger and denser ITZ in the copper slag specimen would reduce its vulnerability to stiffness loss and contribute to its elastic and more ductile response under impact loading. The analysis also indicated that a significant degeneration in the pore structure of the gravel specimen associated with a relatively weaker and non-homogeneous ITZ occurred under impact. Finally, it was also concluded that increased roughness of ITZ may contribute to the load-carrying capacity of concrete under impact by improving contact point interactions and energy dissipation.     

Relationship between pinning mechanism and excess conductivity analysis of x wt% C4H6O5 (x = 0.0, 4.0, and 6.0)-added bulk MgB2

Journal of Materials Science: Materials in Electronics - The influence of x wt% C4H6O5 (malic acid) (x?=?0.0, 4.0, and 6.0) addition on excess conductivity in bulk MgB2 superconductors...     

Using causal models to distinguish between neurogenesis-dependent and -independent effects on behaviour

There has been a substantial amount of research on the relationship between hippocampal neurogenesis and behaviour over the past 15 years, but the causal role that new neurons have on cognitive and affective behavioural tasks is still far from clear. This is partly due to the difficulty of manipulating levels of neurogenesis without inducing off-target effects, which might also influence behaviour. In addition, the analytical methods typically used do not directly test whether neurogenesis mediates the effect of an intervention on behaviour. Previous studies may have incorrectly attributed changes in behavioural performance to neurogenesis because the role of known (or unknown) neurogenesis-independent mechanisms was not formally taken into consideration during the analysis. Causal models can tease apart complex causal relationships and were used to demonstrate that the effect of exercise on pattern separation is via neurogenesis-independent mechanisms. Many studies in the neurogenesis literature would benefit from the use of statistical methods that can separate neurogenesis-dependent from neurogenesis-independent effects on behaviour.