Testing the modified dependence of the radiative strength function on different excitation energies in the light nucleus 28Al

The spectrum of random functions of level density as well as radiative strength functions of dipole E1- and M1-transitions of 28Al were determined. Obtained functions can reproduce very precisely the intensity of the two-step cascade following the radiative capture of thermal neutrons for a given energy of the primary transitions. The density of the observed intermediate levels can be reproduced correctly using the mean value of these functions. In this work we proposed a new hypothesis about the dependence of radiative strength functions for gamma-transitions in heated nucleus on the energy of excited levels. The results provide a solid basis that this new hypothesis allows to get realistic estimation on the parameters of nuclear structure in any nucleus, including the light ones.

Theory and experiments of liquid phase epitaxial growth Part 1

Characterization of the liquid phase epitaxial growth is in the scope of the present paper. The determination of the main parameters of the process such as the stationary growth rate, the time constant, the stationary supercooling, the kinetic coefficient, the initial growth rate, the crystallization mechanism are under consideration. Pursuing this aim a differential equation has been obtained which allows obtaining the dependences of the supersaturation, the growth rate and the growth layer thickness on the duration of growth. These dependences allow the determination of the above mentioned process parameters. Two mechanisms of crystallization are considered - the normal growth and the growth assisted by the screw dislocations. The two dimensional nuclei growth has not been considered because an analytical solution of the equation was not possible. Some of the theoretical contentions are confirmed by the experiments. Using the obtained values of the parameters dependences are defined. Good agreement between theory and experimental results is observed.

Shielding of metals from the corrosion induced by water and humidity by using scratch resistant and hydrophobic silica coatings

The objective of the present paper is to demonstrate the effect of sol-gel derived scratch resistant coatings on different metal surfaces for anticorrosive applications. However, practical applications are limited by problems intrinsic to sol-gel processing or specific of coating/metal systems. Coatings aimed to improve oxidation and wet corrosion resistance have been studied the most. The results published in the literature show that sol-gel coatings may offer good protection against oxidation. More difficult is to achieve a protection against wet corrosion. An important aspect of the application of the sol-gel method for coating metallic objects is also the deposition technique.

Exchange interaction in itinerant-electron metamagnetism

The exchange interaction in itinerant-electron metamagnetism is investigated theoretically. In fact, by considering spin-up and spin-down electrons in an itinerant-electron metamagnetic gas in the presence of an external magnetic field, we show that the difference between the Fermi energies of the spin-up and spin-down electrons equals, up to a multiplicative constant, the absolute value of the matrix element of the Hamiltonian operator relative to the interaction in question. Furthermore, the Stoner formula for the electronic energy of the gas is used to study the size of the exchange interaction.

Calculation of the optical transmittance in cadmium oxide by considering oxygen plasma

By considering the partial pressure of oxygen in the deposition process of cadmium oxide, we calculate the maximum transmittance of cadmium oxide in the visible range, which is achieved at the so-called optimum partial pressure of oxygen, this value of pressure being a key figure of merit. Our formulation agrees with experimental measurements and is consistent with the so-called plasma-optical effect. At this point, an exhaustive evaluation of previous experimental data is performed by doing a detailed comparison among the results from different authors and by performing numerical estimations (including estimations from experimental data) of relevant physical quantities. In fact, a comprehensive discussion relative to comparison between experimental measurements and our theoretical results is presented.

Recycled ceramic composite for automobile brake pad application

Ceramic tile/steel slag-graphite-Arabic gum composite has been developed using conventional casting techniques for brake pad applications. Chemical properties of the phases present in the matrix of the developed composite were examined using X-ray diffractometer. Spatial configuration of the phases was viewed using Scanning Electron Microscope. Wear and thermal properties of the developed composite were also investigated. Correlation between the properties of the developed composite and the commercial grade brake pads were made. Results showed partial homogenity of the second phase particle within the ceramic matrix. The developed composite brake pad showed a better friction property than the commercial grade brake pads up to 200 s while above this duration, the reverse was the case. The developed composite brake displayed lower wear rates and better thermal stability than the commercial grades implying optimum combination of good wear resistance, friction property and thermal stability up to 200 s. Since brake application while driving is an intermittent short span process (< 3 minutes), the developed composite could serve as a replacement for asbestos brake pad for automobile applications.

Rotational and gas temperatures of molecular deuterium in a hollow cathode glow discharge

We report the results of optical emission spectroscopy measurements of rotational Trot and translational (gas) temperature of deuterium molecules. The light source was a low-voltage high-pressure hollow cathode (HC) glow discharge with titanium cathode operated in deuterium. The rotational temperature of excited electronic states of D2 was determined from the intensity distribution in the rotational structure of Q-branches of the two Fulcher-α diagonal bands: [ν′ = ν″ = 2] and [ν′ =ν″ = 3]. The population of the excited energy levels, determined from relative line intensities, was used to derive the radial distributions of the temperature of the excited and the ground state of the deuterium molecule.

Analysis of luminescence of Eu3+ doped Lu2Ti2O7 powders with Judd-Ofelt theory

Eu3+ doped Lu2Ti2O7 particles of 6 to 10 nm in diameter are prepared by Pechini-type polymerized complex route based on polyesterification between citric acid (CA) and ethylene glycol. X-ray diffraction measurements confirmed that Eu3+ doped Lu2Ti2O7 powders crystallized in the face-centered cubic lattice (Fd3m). Emission spectra displayed characteristic 5D0 →7 FJ (J = 0, 1, 2, 3 and 4) spin forbidden f-f electronic transitions of the Eu3+ ions with the most pronounced emission coming from 5D0 →7 F2 and with the emission decays varying between 0.75 and 0.60 ms for samples doped with different concentration of Eu3+. The Judd-Ofelt theory was applied to the experimental data for the quantitative determination of optical parameters such as Ω2, Ω4 Judd-Ofelt parameters, radiative and nonradiative transition rates and emission quantum efficiency. It was observed that, for all the samples, Ω2 >> Ω4. The luminescence quantum yields were calculated by means of the Judd-Ofelt theory and the highest value 60.83 % is obtained for particles doped with concentration of 3 % Eu3+.

Shapiro steps in the commensurate structures with integer value of the winding number

Dynamical mode locking phenomena and the appearance of Shapiro steps are studied in commensurate structures with integer values of winding number in the dc- and ac-driven overdamped Frenkel-Kontorova model. While in the standard case with sinusoidal substrate potential, the system reduces to the single particles model in which only harmonic steps exist and analytical form for the step size can be revealed, in the case of deformable potential, the presence of many degrees of freedom strongly influences the Shapiro steps. Whole series of subharmonic steps appear, and the two types of response functions, the one for the commensurate structures with odd and the one for the commensurate structures with even winding number have been observed.

Structural and optical properties of europium doped Y2O3 nanoparticles prepared by self-propagation room temperature reaction method

Europium-doped yttrium oxide nanoparticles with different doping concentrations were prepared by self-propagation room temperature reaction method. This simple synthesis method provides particles in the range of 12nm to 50 nm, depending on the temperature of calcination. In all cases, the nanopowders showed intense red emission upon excitation with ultraviolet radiation. Structural and optical characterization showed that the nanoparticles obtained after calcination at 1100°C have smaller unit cell volume and microstrain and longer emission lifetimes compared to the nanoparticles obtained after calcination at 600°C and 800°C. The maximal emission intensity was found for the sample doped with 5at% of Eu3+.