Derivation of a rod theory for multiphase materials

A rigorous derivation is given of a rod theory for a multiphase material, starting from three-dimensional nonlinear elasticity. The stored energy density is supposed to be nonnegative and to vanish exactly on a set consisting of two copies of the group of rotations SO(3). The two potential wells correspond to the two crystalline configurations preferred by the material. We find the optimal scaling of the energy in terms of the diameter of the rod and we identify the limit, as the diameter goes to zero, in the sense of Γ-convergence.     

Glass Transition Behavior in Se-Rich Ge-Se Alloys

Differential scanning calorimetry (DSC) was utilized to study the behavior of six Ge-Se glasses containing 0, 5, 10, 15, 17.5 and 20 at.% Ge during the glass transition. These alloys readily form glasses and can be prepared by quenching in air. Moreover, their behavior depends greatly on the composition. This work reveals that two additional properties must be considered: the variation in the glass transition temperature and different structural relaxation. The quantity used to quantify the relaxation was the enthalpy relaxation as this measures the heat lost by the glass during annealing. Given the complexity of the relaxation process, the experimental results were analysed by means of the empirical Kohlrausch-Williams-Watts relaxation model. This revised version was published online in July 2006 with corrections to the Cover Date.     

(S)‐5‐Benzylimidazolidine‐2,4‐dione monohydrate

The crystal structure of the title compound, C₁₀H₁₀N₂O₂·H₂O, also known as l ‐5‐benzylhydantoin monohydrate, is described in terms of two‐dimensional supramolecular arrays built up from infinite chains assembled via N—H...O and O—H...O hydrogen bonds among the organic molecules and solvent water molecules, with graph‐set R³₃(10)C(5)C²₂(6). The hydrogen‐bond network is reinforced by stacking of the layers through C—H...π interactions.     

Thermal Stability Study of Fe-Ni-Based Alloys Determination of T-HR-T and T-T-T diagrams

The low-temperature parts of the temperature-heating rate-transformation (T-HR-T) and temperature-time transformation (T-T-T) diagrams were obtained for crystallization processes. A knowledge of the kinetic model governing crystallization is not needed because both transformation curves can be obtained from non-isothermal calorimetric experiments. The calorimetric study was performed by means of differential scanning calorimetry. The method was applied to analyse crystallization processes of Fe-Ni-based amorphous alloys prepared by melt spinning. The compositions studied were Fe₄₀Ni₄₀P₁₄Si₆, Fe₄₀Ni₄₀P₁₀Si₁₀ and Fe₄₀Ni₄₀P₆Si₁₄. A good concordance was observed between the experimental T-HR-T curves obtained by calculation and the experimental data, which verifies the reliability of the method. In the T-T-T diagrams, the agreement was good in process B1, while in processes A1 and C1 there are small differences that could be related to different crystallization products obtained in isothermal/non-isothermal experiments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Theoretical Study of Intradimer Mechanism for Diamond Growth over Diamond (100)

The study of the energetics of the accepted intradimer diamond growth mechanism over (100) diamond surface is presented. The calculations were made in a density functional approach with the DGauss code using a DZVP2 basis set and a BLYP interchange and correlation potential. A simple 9-carbon cluster modeling the (100) diamond surface was used; its validity is discussed in relation with other calculations that used larger model clusters. The mechanism, presented in six steps, is based in the Harris and Garrison's work that considers the methyl radical as the main growth precursor agent and the breaking of the dimer surface bond with the corresponding methylene radical formation as a prior step to the formation of a CH₂-bridge structure, which is a feasible step; in contrast to these molecular dynamics results, Huang and Frenklach, using semiempirical methods, consider the breaking of the dimer surface bond and the formation of a CH₂-bridge structure as one step and this step as the energetically determinant of the mechanism. They also found an activation energy barrier for the interaction between a radical surface center with a H and CH₃. The present work tries to discern between these two ideas by calculating the activation barriers and the reaction energies for each step of the Harris and Garrison's mechanism in a density functional approach and comparing them to the results of Huang and Frenklach. The energy calculations point toward the scission of the dimer bond (step 4) as the determinant step; this step is endothermic, with an energy barrier of 50.43 kcal-mol^–1. On the other hand, the formation of the CH₂-bridge structure (step 5) is a feasible step with an energy barrier of 13.57 kcal-mol^–1. The adsorption of CH₃ (step 2) and H (step 6) species over radical surface sites did not involve any energy barriers, as it would be hoped. These steps were strongly exothermic and are close to the thermodynamic values for C—C and C—H bond energies. The removal of methylic hydrogen (step 3) did not show any problem because the activation barrier is only 3.68 kcal-mol^–1 less than the removal of a surface hydrogen (step 1), which has an energy barrier of 19.59 kcal-mol^–1. All steps, except number 4, were exothermic.     

Strategies for solving matrix effects in the analysis of sulfathiazole in honey samples using three-way photochemically induced fluorescence data

A widely employed compound for honey treatment, sulfathiazole (ST), was determined in commercial honey samples, employing a combination of photochemically induced fluorescence excitation-emission matrices (EEMs) and chemometric processing of the recorded second-order data. Parallel Factor Analysis (PARAFAC) and Self-Weighted Alternating Trilinear Decomposition (SWATLD) methods were used for calibration. An appropriately designed calibration with a set of standards composed of 18 samples, coupled to the use of the second-order advantage offered by the applied chemometric techniques, allowed quantitation of sulfathiazole in spiked commercial honey samples. No previous separation or sample pretreatment steps were required. The results were compared with other calibration methods such as N-PLS and PLS-1 that produced good results on synthetic samples but not on the investigated commercial honey samples.     

Solution of the Fokker-Planck equation for the shock wave problem

An eigenexpansion solution of the time-independent Brownian motion Fokker-Planck equation is given for a situation in which the external acceleration is a step function. The solution describes the heavy-species velocity distribution function in a binary mixture undergoing a shock wave, in the limit of high dilution of the heavy species and negligible width of the light-gas internal shock. The diffusion solution is part of the eigenexpansion. The coefficients of the series of eigenfunctions are obtained analytically with transcendentally small errors of order exp(–1/M), whereM 1 is the mass ratio. Comparison is made with results from a hypersonic approximation.     

Analysis of Li distribution in ultrathin all-solid-state Li-ion battery (ASSLiB) by neutron depth profiling (NDP)

Lithium-ion batteries are promising energy storage technology devices. They possess many advantages, including high energy density, flexible and lightweight construction and considerable durability. The rapid development of nanotechnologies can further improve their capacity, cycle life and safety. In this experiment, Li-ion diffusion in an all-solid lithium-ion battery (ASSLiB) was studied using the Neutron Depth Profiling (NDP) nuclear analytical technique. The thin ASSLiB system was synthesised by RF magnetron sputtering. The experiment showed that NDP is a very efficient experimental tool for direct analysis of Li distribution in Li batteries. It has been found that the depth profile of Li strongly depends on the state of charge of the battery. About one-third of the total number of Li in ASSLiB can move between the electrodes during charging / discharging. It has been also shown, using the multipixel detectors, that the lateral distribution of Li in ASSLiB is not homogeneous. This can mean, for example, that the position of Li is affected by structural defects that may arise due to variation of the volume or stress of the battery during charging or discharging. In the work are presented first results of measurements performed on ASSLiB of a 1?µm thickness.