M.I. Abd-Elrahman

Kinetics of solid state stability of glycine derivatives as a model for peptides using differential scanning calorimetry

Kinetics of solid state stability of seven derivatives of 3,5-disubstituted tetrahydro-2H-1,3,5-thiadiazine-2-thione (THTT) of glycine as a model for amino acids and peptide drugs were studied using differential scanning calorimetry (DSC). Each DSC curve for each derivative showed an endothermic peak followed by an exothermic one, which could be attributed to the melting and decomposition, respectively. The decomposition activation energy of each derivative was calculated using the Augis and Bennet, Kissinger equations and Mahadevan approximation. Also, the melting activation energies as well as the thermodynamic parameter (enthalpy) for the investigated derivatives were evaluated. The relative stability of the derivatives in the solid state according to the calculated values of the decomposition activation energy, frequency factors and half-life for each derivative could be determined.

Thermal annealing effect on the optical properties of Ag10As30S60 thin film

Chalcogenide Ag10As30S60 thin films are prepared using the thermal evaporation technique from the bulk alloy. Deferential Scanning Calorimetry (DSC) curve reveals two crystallization stages for the bulk. The X-ray examination of the as-prepared and annealed films shows that the sample is crystallized in preferential orientations indicated with peaks corresponding the S8 and ternary AsAg3S3 phases. Transmission spectra show that the as-prepared and annealed films have highly transparent over the visible region. The presence of a sharp absorption edge for all films in the transmission spectra recommends Ag10As30S60 thin films as a good optical filter material. The improvement in transparency upon annealing is due to the enhancement in the crystallinity. The decrease in both optical band gap and refractive index of annealed films after crystallization temperatures is discussed in accordance with the structure changes upon annealing.

Thermal analysis study for the phase determination and instable to metastable transformation of the Co–13Cu alloy

The differential thermal analysis (DTA) is utilized to determine the phase boundary and phase equilibria of Co–Cu alloy having a miscibility gap. Regions for various phase i.e., spinodal and coherent binodal, peritectic, magnetic and the transformation from the two phases to α phase transformations are distinctly determined for the Co–13 at%Cu alloy. The obtained results might indicate the continuity of the decomposition kinetics at the boundary between instable and the metastable regions but an activation barrier is needed. The activation energy for the magnetic transformation is determined to be 182.2 ± 2.1 kJ mol−1.

Heat diffusion over weighted manifolds: A new descriptor for textured 3D non-rigid shapes

This paper proposes an approach for modeling textured 3D non-rigid models based on Weighted Heat Kernel Signature(W-HKS). As a first contribution, we show how to include photometric information as a weight over the shape manifold, we also propose a novel formulation for heat diffusion over weighted manifolds. As a second contribution we present a new discretization method for the proposed equation using finite element approximation. Finally, the weighted heat kernel signature is used as a shape descriptor. The proposed descriptor encodes both the photometric, and geometric information based on the solution of one equation. We also propose a new method to introduce the scale invariance for the weighted heat kernel signature. The performance is tested on two benchmark datasets. The results have indeed confirmed the high performance of the proposed approach on the textured shape retrieval problem, and showed that the proposed method is useful in coping with different challenges of shape analysis where pure geometric and pure photometric methods fail.

Enhancement of thermal stability and degradation kinetics study of poly(vinyl alcohol)/zinc oxide nanoparticles composite

The thermal degradation behaviors of poly(vinyl alcohol) (PVA) and PVA/zinc oxide (ZnO) composite are investigated using differential thermal analysis (DTA). The degradation activation energy (E d), frequency factor (k o) and Avrami exponent (n) as thermal kinetic parameters are calculated from the DTA results. The calculated values of E d are 80.94 and 148.58 kJ mol−1 for PVA and PVA/ZnO composite, respectively, indicating the enhancement of the PVA thermal stability as ZnO nanoparticles are filled in PVA matrix. The n values are evaluated from the shape analyses of degradation peaks. From estimated n values, the degradation mechanisms are determined for both the complexes under investigation.

Thickness and optical constants calculation for chalcogenide-alkali metal Se80Te8(NaCl)12 thin film

Chalcogenide-alkali metal semiconducting thin films of four different thicknesses of Se80Te8(NaCl)12 are deposited from bulk by thermal evaporation technique. The crystallinity of the film improves with increasing of thickness as indicated by the recorded X-ray diffraction patterns. The transmission and reflection spectra are measured in the wavelength range of the incident photons from 250 to 2500nm. The thickness and optical constants of the films are calculated based on Swanepeol method using the interference patterns appeared in the transmission spectra. It is found that the films have absorption mechanism which is an indirect allowed transition. The effect of the film thickness on the refractive index and the high-frequency dielectric constant are studied. With increasing the film thickness, both the absorption coefficient and high-frequency dielectric constant increase while the single-oscillator energy, optical band gap and extinction coefficient decrease.

Optical and Electrical Studies of Se85Te15 Thin Films

The dependence of the optical band gap (E g ) of Se 85 Te 15 thin films on the film thickness and thermal annealing was studied. The value of Eg was found to increase with increasing film thickness. Films annealed at temperatures higher than 353 K showed a decrease in Eg. The effect of the film thickness on the high-frequency dielectric constant (e∞) and carrier concentration (N) was also studied. The effect of thermal annealing on the activation energy for conduction was given and discussed. An amorphous-crystalline transformation in the thin films was observed after annealing at temperatures higher than the glass transition temperature. The crystalline phase resulting from the heat treatment of the as-prepared film was checked by X-ray diffraction observations.