thermal stability of epoxy systems badge (n=0)/1,2-dch and badge (n=0)/ 1,2-dch/vinylcyclohexene dioxide

The thermal degradation of the epoxy system diglycidyl ether of bisphenol A (BADGE n=0)/1,2-diamine cyclohexane (DCH) containing different concentrations of an epoxy reactive diluent was studied by thermogravimetric analysis in order to determine the reaction mechanism of the degradation process and to compare it with the results for the same system without diluent. The value of the activation energy, necessary for this study, was calculated using various integral and differential methods. Values obtained using the different methods were compared to the value obtained by the Flynn-Wall-Ozawa"s method (between 193-240 kJ mol^-1 depending on the diluent concentration) with does not require a knowledge of the nth order reaction mechanism. All the experimental results were compared to master curves in the range of Doyle"s approximation (20-35% of conversion). Analysis of the results suggests that the reaction mechanism could be F₂, F₃, or A₂ type. This revised version was published online in July 2006 with corrections to the Cover Date.     

TTT Cure Diagram

Curing reactions of the epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n=0) and m-xylylenediamine (m-XDA) were studied to calculate time-temperature-transformation (TTT) isothermal cure diagram for this system. Gel times were measured as a function of temperature using solubility test. Differential scanning calorimetry (DSC) was used to calculate the vitrification times. DSC data show a one-to-one relationship between T _g and fractional conversion, a independent of cure temperature. As a consequence, T _g can be used as a measure of conversion. The activation energy for the polymerization overall reaction was calculated from the gel times obtained using the solubility test (41.5 kJ mol^-1). This value is similar to the results obtained for other similar epoxy systems. Isoconversion contours were calculated by numerical integration of the best fitting kinetic model. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pharmacological Activities of Aminophenoxazinones

Aminophenoxazinones are degradation products resulting from the metabolism of different plant species, which comprise a family of natural products well known for their pharmacological activities. This review provides an overview of the pharmacological properties and applications proved by these compounds and their structural derivatives during 2000–2021. The bibliography was selected according to our purpose from the references obtained in a SciFinder database search for the Phx-3 structure (the base molecule of the aminophenoxazinones). Compounds Phx-1 and Phx-3 are among the most studied, especially as anticancer drugs for the treatment of gastric and colon cancer, glioblastoma and melanoma, among others types of relevant cancers. The main information available in the literature about their mechanisms is also described. Similarly, antibacterial, antifungal, antiviral and antiparasitic activities are presented, including species related directly or indirectly to significant diseases. Therefore, we present diverse compounds based on aminophenoxazinones with high potential as drugs, considering their levels of activity and few adverse effects.     

Computation of normal modes of three-dimensional resonators by semiclassical and variational methods: seismological implications

The problem investigated in this paper is that of calculating the eigenfrequencies of the bouncing-ball modes of oscillation of scalar waves in a three-dimensiol, arbitrarily shaped enclosure or resonator. With a view to future applications in seismology, we consider wave resonators limited above by a flat reflector—the earth's surface—and below by a curved one—the sediment/rock interface. The surface of the curved reflector is smooth but otherwise of arbitrary shape. The EBK (Einstein-Brillouin-Keller) method of semiclassical quantization is used to compute the eigenfrequencies. Conventional ray tracing is used to determine the trajectories of the rays in configuration space as well as in the Poincaré surfaces of section needed for the application of the method. For a prescribed set of mode numbers the EBK conditions produce a set of algebraic equations whose solution gives the required eigenfrequency and the corresponding eigentrajectory. Additionally, a system of four nonlinearly coupled ODE's is derived that simulates accurately the trajectories of the bouncing points of rays and can be used as a fast alternative to ray tracing. A variational method based upon the Rayleigh-Ritz formulation is used to obtain bounds on the eigenfrequencies and to determine the resonator's eigenfunctions. For separable and smooth nonseparable domains both approaches give consistent results. If the curvature of the reflector is convex towards the approaching ray, repeated reflections will result in highly unstable ray trajectories which ultimately becomne chaotic. In this case the EBK method fails. A brief discussion of the inherent tendency to chaotic behavior of the multiply reflecting ray system inside arbitrarily shaped enclosures is presented.     

Existence and Multiplicity Results for the Nonlinear Klein-Gordon Equation

In this work, we study the multiplicity of solutions for a stationary nonhomogeneous problem associated to the nonlinear one-dimensional Klein-Gordon Equation. We prove that the existence of positive solutions is equivalent to the solvability of a scalar equation 2F(M) = 1, where F is a real function depending on V. Moreover, we prove some existence and multiplicity results for the Dirichlet problem in the superlinear case.     

Some mathematical properties of gauge transformations with respect to the Coulomb gauge: Variational analysis of an energy functional

As gauge invariance of computed magnetic properties, usually partitioned into diamagnetic and paramagnetic terms, is not achieved within the algebraic approximation, unless ad hoc techniques are adopted, a general variational treatment is analyzed, attempting to minimize the term more difficult to evaluate accurately, i.e., the paramagnetic contribution to magnetic susceptibility, by means of a gauge transformation. It is shown that an absolute minimum in a variational sense cannot be determined a priori. However, a “local” minimum of the paramagnetic contribution to magnetic susceptibility can be arrived at by employing general gauge transformations of polynomial form. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 599–606, 2000     

Elektrolysen

Ohne Zusammenfassung     

Rationalization of the optical rotatory power of chiral molecules into atomic terms: a study of N<Subscript>2</Subscript>H<Subscript>4</Subscript>

We applied a strategy to assign the individual contributions that atoms make to the optical rotation angle and, more generally, to the molecular chirality. The method resolves the optical rotatory power tensor into atomic contributions employing the formalism of the acceleration gauge for the electric dipole and the torque formalism for the magnetic dipolar moment. The gross atomic isotropic contributions have been evaluated for nitrogen and hydrogen in hydrazine, employing Gaussian basis sets of very good quality, in order to achieve the Hartree–Fock limit.From the Proceedings of the 28th Congreso de Químicos Teóricos de Expresión Latina (QUITEL 2002)     

Kinetic study of an epoxy system badge (n=0)/1, 2 dch modified with an epoxy reactive diluent

The curing reaction of an epoxy system consisting of a diglycidyl ether of bisphenol A (n=0) and 1, 2 diaminecyclohexane (DCH) with an epoxy reactive diluent vinylcyclohexane dioxide was studied by temperature modulated differential scanning calorimetry (TMDSC). The models proposed by Kamal and by Horie et al. were employed in the kinetic study. From these studies reaction orders, rate constants, and activation energies were determined. The technique of TMDSC allows to include in the kinetic study the effect of diffusion by means of the mobility factor, calculated from the curves of the complex heat capacity registered during the curing isothermal experiments. The results were compared to those obtained for the same system employing the reaction rate data. This revised version was published online in July 2006 with corrections to the Cover Date.