Effect of tellurium on electrical and structural properties of sintered silicon nitride ceramics

The effects of tellurium (Te) additives on electrical conductivity, dielectric constant and structural properties of sintered silicon nitride ceramics have been studied. Different amounts of Te (10% and 20%) were added as sintering additives to silicon nitride ceramic powders and sintering was performed. Microstructure and composition were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The electrical conductivity and dielectric constant (ε′) increase exponentially with temperature greater than 800 K. The electrical conductivity and dielectric constant increase but activation energy decreases from 0.72 to 0.33 eV with the increase of Te concentration. However, the conductivity increases five orders of magnitude at the concentration of 10% of Te in Si₃N₄. As the Te concentration increases the sintered silicon nitride ceramics become denser. These types of samples can be used as high temperature semiconducting materials.     

Magnetohydrodynamic Stagnation Point Flow of a Maxwell Nanofluid with Variable Conductivity

This article reports the simultaneous properties of variable conductivity and chemical reaction in stagnation point flow of magneto Maxwell nanofluid.The Buongiorno's theory has been established to picture the inducement of Brownian and thermophrotic diffusions effects.Additionally,the aspect of heat sink/source is reported.The homotopic analysis method(HAM) has been worked out for the solution of nonlinear ODEs.The behavior of inferential variables on the velocity,temperature,concentration and local Nusselt number for Maxwell nanofluid are sketched and discussed.The attained outcomes specify that both the temperature and concentration of Maxwell fluid display analogous behavior,while the depiction of Brownian motion is quite conflicting on both temperature and concentration fields.It is further noted that the influence of variable thermal conductivity on temperature field is similar to that of Brownian motion parameter.Moreover,for the confirmation of our study comparison tables are reported.     

The Determination of 222Rn in Drilling Fluids of the KTB Pilot Borehole Using SSNTD Techniques

²²²Rn dissolved in drilling fluids of the KTB (Kontinentales Tiefbohrprogramm der Bundesrepublik Deutschland) pilot hole has been determined using solid state nuclear track detector (SSNTD) technique:The α-sensitive SSNTD CR-39 was used to measure the a-activity of ²²²Rn. Well-defined conditions for Rn-measurements could be established by employing a mica nuclear track microfilter to separate the detector containing air volume from the volume containing the water. This technique has been applied to determine quantitatively the ²²² Rn-concentration as a function of depth of the borehole down to 4000 m.     

Large-scale collisional energy transfer in laser-pumped metastable Ca atoms: Excitation of resonance states of Ca II

We report the first experimental observation of the excitation of the 4p ² P _{3/2, 1/2} resonance states of Ca II (located at 74 720.4 and 74 497.5 cm^–1 above the ground state of Ca I) following pulsed-laser pumping of the 4s ^{2 1} S _O–4s4p ³P₁ intercombination transition of Ca I (E _ex = 15 210 cm^–1). Large scale collisional transfer of energy between the laser-excited atoms is believed to be responsible for this. This is possibly because sufficient time is available (_rad of the 4s4p ³ P ₁ state is approximately 350 µs) for collisions to build such a high level of excitation. Some interesting additional features of the fluorescence spectra of the laser-pumped Ca vapor, such as temperature dependence of the fluorescence intensities and evolution in time of some selected states, are also presented.     

Intelligent reversible watermarking technique in medical images using GA and PSO

The advances in recording, editing, and broadcasting multimedia contents in digital form motivate to protect these digital contents from illegal use, such as duplication, manipulation, and redistribution. However, watermarking algorithms are designed to satisfy requirements of applications, as different applications have different concerns. We intend to design a watermarking algorithm for applications which require high embedding capacity and imperceptibility, to maintain the integrity of the host signal as well as embedded information. Reversible watermarking is a promising technique which satisfies our requirements. In this paper, we concentrate on improving the watermark capacity and reducing the perceptual degradation of an image. We investigated the Luo's [1] additive interpolation-error expansion algorithm and enhanced it by incorporating with two intelligent techniques: genetic algorithm (GA), and particle swarm optimization (PSO). Genetic algorithm is applied to exploit the correlation of image pixel values to obtain better estimation of neighboring pixel values, which results in optimal balance between information storage capacity and imperceptibility. Particle swarm optimization (intelligent technique) is also applied for the same purpose. Experimental results show that PSO and GA nearly give the same results, but GA outperforms the PSO. Experimental results also reveal that the proposed strategy outperforms the state of art works in terms of perceptual quality and watermarking payload.     

Influence of tungsten doping concentration on the electronic and optical properties of anatase TiO2

The structural, electronic and optical properties of tungsten-doped TiO₂ have been investigated using density functional theory with plane wave basis sets and ultrasoft pseuodopotential. Substitutional W doping at Ti sites create W 5d states just below the conduction band minimum while interstitial W doping gives isolated W 5d states in the middle of forbidden region. Averaged bond lengths show that W doping at Ti sites produce minimum structural distortion as compared to the interstitial W-doped TiO₂. Substitutional W-doped TiO₂ has better visible light absorption compared to interstitial W-doped TiO₂ and has stable configuration which provide reasonable explanation for the experimental findings. Tungsten doping in TiO₂ with different doping concentrations is investigated as an enabling concept for enhancing the visible light absorption. Optical properties show that optimal W doping concentration would improve the visible light absorption. 2.08% W doping concentration gives strong visible and ultraviolet light absorption among all doped models found consistent with experiments.     

Alfvén waves in temperature anisotropic Cairns distributed plasma

The dispersion relations and Landau damping of Alfven waves in kinetic and inertial limits are studied in temperature anisotropic Cairns distributed plasma.In the case of kinetic Alfven waves(KAWs),it is found that the real frequency is enhanced when either the electron perpendicular temperature or the non-thermal parameter A increases.For inertial Alfven waves(IAWs),the real frequency is slightly affected by the electron temperature anisotropy and A.Besides the real frequency,the damping rate of KAWs is reduced when the electron perpendicular temperature or A increases.In the case of IAWs,the temperature anisotropy and A either enhance or reduce the damping rate depending upon the perpendicular wavelength.These results may be helpful to understand the dynamics of KAWs and IAWs in space plasmas where the non-Maxwellian distribution of particles are routinely observed.     

Creation of Laser-Induced Long Ionized Channels in Air Suspension

Russian Physics Journal - The paper deals with the propagation of the powerful laser beam in gas-dispersion systems and atmospheric aerosol background, which is accompanied by a wide spectrum of...