Laser thermal response of a finite slab as a function of the laser pulse parameters

This paper deals with the problem of heating a finite slab using laser radiation in relation to the parameters characterizing the laser pulse, namely: q_max(W/m²), the maximum laser power density, t₀ the time interval required to reach q_max and t_d, the pulse time duration. The pulse shape q(t) is suggested in the form: q(t)=βq_max(t/t_d)(1-(t/t_d))exp-B(t-t₀/t_d), where β and B are parameters. Fitting with published experimental pulse [Ready JF. Effects due to absorption of laser radiation. J Appl Phys 1965;36:462–68] is made. Fourier series expansion technique is considered to solve the problem. The critical time required to initiate melting t_m is estimated for four metallic elements and five semiconductors, namely: Al, Cu, Ag, Au (aluminum, copper, silver, and gold), cadmium sulfide, germanium, silicon, alpha beryllium oxide, and silicon carbide. Five pulses with different characteristic parameters are considered.Computations revealed that the thermal response of the targets is highly affected by q_max and t_o, while the pulse time duration is less effective in determining the value of t_m. Moreover, it is revealed that the relation between t_m and the melting temperature for the same laser pulse is nonlinear for the considered targets under the indicated conditions.     

Preferential Solvation and Solvatochromic Parameters in Mixtures of Poly(ethylene glycol)-400 with Some Molecular Organic Solvents

Polyethylene glycols have become more popular alternate reaction media due to interesting properties like non-toxicity, bio-degradability, and full miscibility with water and organic solvents. Binary mixtures of polyethylene glycols with common solvents can be useful to tune their physical and chemical properties and to facilitate chemical and physical processes. In this study, solvatochromic parameters were spectrophotometrically determined for binary solvent mixtures of poly(ethylene glycol)-400 (PEG-400) with methanol, 2-propanol, 1-butanol, dimethyl sulfoxide, N,N-Dimethylformamide, and dichloromethane under ambient conditions, over the whole range of mole fractions. The solvatochromic parameters showed different trends in protic and aprotic solvents mixed with PEG-400. Methanol/PEG-400 mixtures showed special properties in polarity and polarizability so that the mixtures are more dipolar/polarizable than their pure components. Positive or negative deviations from ideal behavior confirmed that the indicators were involved in a preferential solvation process in the solvent mixtures. These deviations from ideality can be attributed to strong solvent–solvent interactions in the binary mixtures.     

Ethylene/1-Hexene Copolymerization and Synthesis of LLDPE/Nanocarbon Composite through In Situ Polymerization

Copolymerization of ethylene/1-hexene using a modified ZN-type catalyst was carried out in the presence of triethylaluminium as cocatalyst. The optimum copolymerization activity was obtained at Al: Ti = 357: 1, 60°C and the comonomer concentration of 0.6 mol/L in the range studied. Copolymer/nanocarbon (including multiwalled carbon nanotube, graphene nanoplatelet) composites were prepared via in-situ polymerization. The copolymerization activity decreased by addition of the nanocarbon into the reactor. The presence of graphene nanoplatelet in nanocomposites reduced the melting temperature and increased heat of fusion, crystallinity and density of the obtained polymer. In the copolymer/carbon nanotube nanocomposites, decreasing of melting temperature was observed in comparison to pure copolymer, whereas, heat of fusion, crystallinity and density increased. The results of TGA analysis showed that the addition of nanocarbons has improved the thermal stability of obtained copolymers.     

Design and synthesis of new thiobarbituric acid metal complexes as potent protease inhibitors: spectral characterization,thermal analysis and DFT calculations

Five novel metal complexes of thiobarbituric acid (TBAH) have been prepared with the general formulae: [Ti(TBA)₂(H₂O)₂]Cl₂·2H₂O, [Pd(TBA)₂]·4H₂O, Na[Ag(TBA)₂(H₂O)₂]·4H₂O, [Hg(TBA)₂(H₂O)₂] and [Ce(TBA)₂(H₂O)₃]SO₄·H₂O. The complexes have been fully characterized employing physicochemical and diverse spectroscopic techniques (IR, UV–Vis, mass and ¹H NMR) as well as thermal analysis. Elemental analyses and spectroscopic data have showed that the stoichiometries of all complexes were 1:2. Thermal analysis measurements indicated that the complexes have good thermal stability. Density functional theory calculations were carried out at the B3LYP levels of theory with a double basis set, LANL2DZ basis set for titanium, palladium, cerium atoms, or LANL2MB basis set for silver, mercury atoms and 6-31+G(d,p) basis set for the other atoms. The optimized geometry of the ligand and its complexes was obtained based on the optimized structures. The ligand and its metal complexes act as protease inhibitors and repressed their enzymatic activity significantly.     

Effect of dissolution of Θ-phase on characteristic parameters of work-hardening in AL-2·5wt. % Cu alloy

Stress-strain curves of slowly cooled and quenched Al-2·5 wt. % Cu alloy were studied in the temperature range 693 K to 773 K. The linear work-hardening coefficient, the fracture time, the yield stress and the fracture stress of annealed and quenched samples decreased with increasing deformation temperature and exhibited a minimum at 733 K. The X-ray analysis of the slowly cooled and quenched samples showed that the lattice parametera of Al-matrix and the ratioc/a of the tetragonal -phase reached a minimum and a maximum value, respectively, at the dissolution temperature.     

Investigation of thermal properties of some basalt samples in Egypt

This work aims in studying the temperature dependence of the thermal properties (thermal diffusivity, k, specific heat, C _p and thermal conductivity, ) of some basalt group samples, collected from different regions in the eastern desert of Egypt. The thermal properties of these samples were measured in the temperature range from r.t. to 900 K. The average values of the thermal conductivity of these investigated samples lie in the range from 0.4·10^–3 to 2.01·10^–3 cal cm^–1 s^–1 K^–1. This means that these samples are considered as thermal insulating materials. The thermogravimetric analysis (TG) confirmed that these investigated samples are dry rocks. X-ray fluorescence (XRF) and X-ray diffraction (XRD) confirmed that these rock samples have a crystalline phase, the peaks of XRD have a small change in their location as a result of heat treatment. This behaviour was attributed to the oxidation and firing of some minerals after the heat treatment.This revised version was published online in November 2005 with corrections to the Cover Date.     

Voltammetric reduction of 2-(4′-N,N-dimethylaminostyryl)-1-ethyl pyridinium iodide inDMF

The voltammetric reduction mechanism of 2-(4-dimethylaminostyryl)-1-ethyl pyridinium iodide at the hanging dropping mercury electrode has been studied in N,N-dimethylformamide solution containing 0.1 mol dm^–3 tetraethylammonium perchlorate. The depolarizer is reduced via a single diffusion-controlled irreversible two-electron cyclic voltammetric wave. The wave is attributed to the reduction of the azomethine bond of the pyridinium nucleus. Cyclic voltammetric studies indicate that the cv wave follows an ECE mechanism. The chemical reaction is proposed to be a protonation.

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Voltammetrische Reduktion von 2-(4-N,N-Dimethylaminostyryl)-1-ethyl-pyridiniumjodid inDMF

Zusammenfassung Es wurde der voltammetrische Reduktionsmechanismus von 2-(4-N,N-Dimethylaminostyryl)-1-ethyl-pyridiniumjodid in Dimethylformamid-Lösung mit einem Tetraethylammoniumperchlorat-Gehalt von 0.1 mol dm^–3 an der tropfenden Quecksilberelektrode untersucht. Der Depolarisator wird über eine einzige diffusionskontrollierte irreversible Zweielektronenwelle reduziert. Diese Welle wird der Reduktion der Azomethinbindung des Pyridinium-Kerns zugeordnet. Cyclische voltammetrische Untersuchungen zeigen, daß die CV-Welle einem ECE-Mechanismus folgt. Als chemische Reaktion tritt Protonierung ein.