Thermal degradation behaviour of a nearly alternating copolymer of vinylidene cyanide with 2,2,2-trifluoroethyl methacrylate

The thermal decomposition under non-oxidative conditions of a copolymer of vinylidene cyanide (VCN) and 2,2,2-trifluoroethyl methacrylate (MATRIF) was investigated by thermogravimetry (TG) and Pyrolysis-GC-MS. The type and composition of the pyrolytic products and the shape of the TG curve indicate that both the main thermal degradation process, with onset at 368 °C, and a minor weight loss at around 222 °C are mainly associated with random main-chain scission. The kinetic parameters were determined by means of dynamic and, in the case of the main degradation stage, also isothermal methods. The results obtained from the dynamic methods (Friedman, Flynn-Wall-Ozawa, and Kissinger, respectively) are in good agreement with those obtained from isothermal TG data. The activation energy was in the 177-213 kJ/mol range for the first stage, and 224-295 kJ/mol for the second stage, the highest respective values being determined from the kinetic analysis according to the Kissinger method.     

Salt crystallization during evaporation: impact of interfacial properties

Salt damage in stone results in part from crystallization of salts during drying. We study the evaporation of aqueous salt solutions and the crystallization growth for sodium sulfate and sodium chloride in model situations: evaporating droplets and evaporation from square capillaries. The results show that the interfacial properties are of key importance for where and how the crystals form. The consequences for the different forms of salt crystallization observed in practice are discussed.     

The elastic echo problem

We consider a homogeneous isotropic unbounded linear elastic medium Ω??³, having a free boundary Γ. A forcing f (t, x ) creates an incident displacement field u ₀(t, x ). This primary field is scattered by Γ giving rise to a secondary field or echo, for which we determine the asymptotic behaviour in time. These results are obtained via the use of an tension of the time‐dependent scattering theory of C. Wilcox. Copyright © 2003 John Wiley & Sons, Ltd.     

Repulsive and attractive critical Casimir forces

When confining vacuum fluctuations between two identical walls, the Casimir force manifests itself as a mutual attraction of the walls. When confining concentration fluctuations of a binary liquid mixture, an analogous force should exist near the critical temperature T_C; it is called the critical Casimir force. Here we show experimentally that this purely entropic force can be either attractive or repulsive, depending on the boundary conditions for the fluctuations. For symmetrical boundary conditions an attractive force is found while asymmetrical ones lead to a repulsive force. This is observed directly by confining the fluctuations in a thin wetting film. Depending on the boundary conditions either a thinning or a thickening of the film is observed when T→T_C.     

Electrical probing of endothelial cell behaviour on a fibronectin/polystyrene/thiol/gold electrode by Faradaic electrochemical impedance spectroscopy (EIS)

The electrochemical impedance spectroscopy (EIS) technique has been shown to be an effective tool for monitoring endothelial cell behaviour on a multilayer functionalised gold electrode. Polystyrene, a reproducible model substrate, is deposited as a thin layer on a thiol functionalised gold electrode. Fibronectin, a protein promoting endothelial cell adhesion, is then adsorbed on the polystyrene surface. The different steps of this multilayer assembly are characterized by Faradaic impedance. The charge transfer resistance and the capacitance for the total layer are modified at each step according to the electrical properties of each layer. This gives the endothelial cells' electrical state in terms of its resistive and capacitive properties. In this study, the endothelial cell layer presents a specific charge transfer resistance equal to 1.55 kOmega cm(2) with no large defects in the cell layer, and a specific capacitance equal to few microF cm(-2) explained by the existence of pseudopods. These electrical properties are correlated to the endothelial cell viability, adhesion and cytoskeleton organization.     

Acute and Subacute Toxicity and Cytotoxicity of Opuntia Dillenii (Ker-Gawl) Haw. Seed Oil and Its Impact on the Isolated Rat Diaphragm Glucose Absorption

This study aims to assess the safety of the Opuntia dillenii (Ker-Gawl) haw. seed oil (ODSO) and its effect on the glucose absorption activity of the isolated rat hemidiaphragm. This oil’s safety was studied by exploring its acute (doses 1, 3, 5, and 7 mL/kg) and subacute (doses 1 and 2 mL/kg) toxicities in albino mice and Wistar rats, respectively. The safety of the ODSO was also assessed by studying its effect on the HepG2 cell viability in vitro. The effect of ODSO, or combined with the insulin, on the glucose absorption activity of isolated rat hemidiaphragm was evaluated at the dose 1 g/L in vitro. The results demonstrated the safety of ODSO. Indeed, this study showed that this oil does not produce any mortality or signs of toxicity after the single-dose administration in mice. Additionally, the daily intake of the ODSO during four weeks does not induce a significant variation in the biochemical parameters and body weight of rats compared with the control group. Besides, the cell viability of HepG2 did not change in the presence of ODSO. On the other hand, the ODSO increased the glucose absorption activity of the isolated rat hemidiaphragm, and this activity was significantly enhanced when combined with insulin. This study confirms, on one side, the safety of this oil and its efficacy and, on the other side, encourages its potential use as a complement to treat diabetes.     

Simultaneous Determination of Cimetidine and Related Compounds in Pharmaceuticals by HPLC on a Porous Graphitic Carbon Column

A high-performance liquid chromatographic method has been developed for determination of cimetidine and its main related compounds, 4-hydroxymethyl-5-methylimidazol (MH), N-cyano-N',N''-dimethylguanidine (Carbonate), 1-methyl-3-[2-[[(5-methyl-1H-imidazol-4-yl)methyl]sulfonyl]ethyl]guanidine (Guanidine), 2-cyano-1-methyl-3-[2-[[(5-methyl-1H-imidazol-4-yl)methyl]sulfonyl] (Sulfoxide), and 1-[(methylamino)[[2-[[(5-methyl-1H-imidazol-4-yl)methyl]sulfonyl]ethyl]amino]methylene]urea (Amide). Chromatographic separation was achieved on a porous graphitic carbon (PGC) column with a gradient 17:83 to 19:81 (v/v) acetonitrile-0.05 M potassium phosphate buffer containing 0.40% pentane sulfonic acid at pH 2.5. Analysis was performed at a flow-rate of 1 mL min^?1 and the detection wavelength was 228 nm. Calibration plots were linear in the concentration ranges 0.25 to 83 µg mL^?1 for cimetidine and Carbonate, 0.25 to 75 µg mL^?1 for Guanidine, Amide, and Sulfoxide, and 0.25 to 100 µg mL^?1 for MH, with correlation coefficients (R ²) between 0.9990 and 0.9998. The lowest detectable concentration of cimetidine and Amide was 0.07 µg mL^?1; for MH, Carbonate, Guanidine, and Sulfoxide it was 0.06 µg mL^?1. Method repeatability (intraday) and reproducibility (interday) was always less than 2% (n=5). The proposed liquid chromatographic method was successfully used for analysis of commercially available cimetidine dosage forms; recoveries were from 99.2 to 100.8%.     

Ferromagnetism and ferroelectricity in Eu<Emphasis Type="Italic">X</Emphasis> (<Emphasis Type="Italic">X</Emphasis> = <Emphasis Type="Italic">O</Emphasis>, <Emphasis Type="Italic">S</Emphasis>): pressure effects

Ferromagnetism and ferroelectricity in Eu monochalcogenides have been investigated by ab initio density functional theory in the DFT+U approach. Exchange interaction parameters and Curie temperatures under pressure are studied and discussed using Heisenberg Hamiltonian with first and second-nearest-neighbor interactions. The calculations showed that the hydrostatic pressure perfectly improves the Curie temperature (EuO: T _C = 175 K; EuS: T _C = 33.8 K) and in the other hand it cannot induce the spontaneous polarization (P _s ). The effect of uniaxial and biaxial pressure is also studied. Although the uniaxial strains slightly increases the Curie temperature, it ensures the ferrolectricity in these systems by producing a spontaneous polarization of the order of P _s (EuO) = 57.50 μC/cm² and P _s (EuS) = 42.86 μC/cm² with pressures of 5% and 4%, respectively. The search for new model systems is a necessity to better understand the physics related to multiferroïc materials and to consider possible applications.