Analysis of Stability of a Plasma in Porous Medium

The thermal convection of a plasma in porous medium is investigated in the presence of finite Larmor radius (FLR) and Hall effects. Following linear stability theory and normal mode analysis method, the dispersion relation is obtained. It is found that the presence of a magnetic field (and hence the presence of FLR and Hall effects) introduces oscillatory modes in the system which were, otherwise, non-existent in their absence. When the instability sets in as stationary convection, the FLR may have a stabilizing or destabilizing effect, but a completely stabilizing one for a certain wave-number range. Similarly, the Hall currents may have a stabilizing or destabilizing effect but a completely stabilizing one for the same wave-number range under certain condition, whereas the medium permeability always has a destabilizing effect for stationary convection. Also it is found that the system is stable for 𝑔𝛼𝜅 𝜈𝛽 ≤ 27𝜋 4 4 and under the condition 𝑔𝛼𝜅 𝜈𝛽 > 27𝜋 4 4 , the system becomes unstable.

Effective Interfacial Tension Effect on Kelvin-Helmholtz Instability

The instability of the plane interface between two uniform, superposed and streaming Walters′ B′ viscoelastic fluids through porous medium in the presence of effective interfacial tension is considered. The case of two uniform streaming fluids separated by a horizontal boundary is studied. It is observed, for the special case where the effective interfacial tension is ignored, that the system is stable or unstable for the potentially stable configuration which is in contrast to the case of Rivlin-Ericksen viscoelastic fluid or Newtonian fluid where the system is always stable for the potentially stable configuration. Moreover, if the perturbations in the direction of streaming are ignored, then the perturbations transverse to the direction of streaming are found to be unaffected by the presence of streaming, whereas for perturbations in all other directions there exists instability for a certain wave number range. ‘Effective interfacial tension’ is able to suppress this Kelvin-Helmholtz instability for small wavelength perturbations, the medium porosity reduces the stability range given in terms of a difference in streaming velocities.

Study of the low intensity spectral bands within the infrared spectra of kernels of high-yielding maize hybrids

The nature, role, and significance of low intensity spectral bands con?tained within the infrared spectra of kernels of high-yielding maize hybrids: ZP 341, ZP 434, and ZP 505 were observed in this study. The observations were performed to identify or?ganic molecules and their structural properties. The occurrence of unstable state of organic compounds and their functional groups are conditioned by such a process. The set hypoth?esis holds that there is a necessity to study the existence of many and low intensity spectral bands, not observed so far, occurring in different patterns (low intensity bands, single or grouped). They should be observed and the dynamics of their formation, caused by their different movements, including the possibility of their cancellation or amplification, should be explained. Such spectral bands most often appear in the wave number range of 400-950 cm-1. They occur in several wave numbers up to 3,000 cm-1 and are caused by different types of vibration movements (valence and deformation vibrations) of organic compounds and their functional groups: primary, secondary, and tertiary amides, proteins, free amino acids, alkanes, alkenes, aldehydes, ketones, aromatic compounds, cellulose, carbohydrates, car?boxylic acids, ethers, and alcohols. An unbiased analysis of low intensity spectral bands of maize hybrid kernels reveals that their occurrence is similar. Small differences, for some cases of the occurrence of low intensity spectral bands, can barely be ascertained. In this way, it is possible to establish not only the chemical composition of organic compounds of kernels of observed maize hybrids, but also it is possible to indicate their unstable, confor?mational, and functional properties.

Effective interfacial tension effect on the instability of streaming Rivlin-Ericksen elastico-viscous fluid flow through a porous medium

The instability of the plane interface between two uniform, superposed and streaming Rivlin-Ericksen elastico-viscous fluids through porous media, including the ‘effective interfacial tension’ effect, is considered. In the absence of the ‘effective interfacial tension’ stability/instability of the system as well as perturbations transverse to the direction of streaming are found to be unaffected by the presence of streaming if perturbations in the direction of streaming are ignored, whereas for perturbation in all other directions, there exists instability for a certain wave number range. The ‘effective interfacial tension’ is able to suppress this Kelvin-Helmholtz instability for small wavelength perturbations, the medium porosity reduces the stability range given in terms of a difference in streaming velocities.

Far-infrared properties of helium-doped silicon

Single crystal silicon is an important material used for semiconductor devices and also a potential material in device research. Far-infrared optical properties are studied for the helium ion implanted samples with different fluences of 5.0 × 1016, 1.0 × 1017, 2.0 × 1017, and 4.0 × 1017 cm−2. The absorption coefficient and refractive index of silicon with different helium concentrations are measured in the wave number range from 4 to 85 cm−1 and temperature range from 145 to 520 K. The results show that the absorption coefficient increases with increasing fluence of helium ions, but the refractive index decreases. The correlations between absorption coefficient and refractive index and temperature of all samples are similar. The refractive index increases with temperature in the whole measurement temperature range, but the absorption coefficient has different trends in the different wavebands. The absorption coefficient decreases with the increase of temperature in the region below 12 cm−1; however, the absorption coefficient increases when the wave number is larger than 30 cm−1. The absorption coefficient curves at different wavebands are well fitted by the Drude model. A large number of helium bubbles and defects, such as voids and dislocations have been observed in the implanted area by transmission electron microscopy (TEM), which contributes to the increase of optical absorption.

Dynamics of turbulence under the effect of stratification and internal waves

The objective of this paper is to study the dynamics of small-scale turbulence near a pycnocline, both in the free regime and under the action of an internal gravity wave (IW) propagating along a pycnocline, using direct numerical simulation (DNS). Turbulence is initially induced in a horizontal layer at some distance above the pycnocline. The velocity and density fields of IWs propagating in the pycnocline are also prescribed as an initial condition. The IW wavelength is considered to be larger by the order of magnitude as compared to the initial turbulence integral length scale. Stratification in the pycnocline is considered to be sufficiently strong so that the effects of turbulent mixing remain negligible. The dynamics of turbulence is studied both with and without an initially induced IW. The DNS results show that, in the absence of an IW, turbulence decays, but its decay rate is reduced in the vicinity of the pycnocline, where stratification effects are significant. In this case, at sufficiently late times, most of the turbulent energy is located in a layer close to the pycnocline center. Here, turbulent eddies are collapsed in the vertical direction and acquire the "pancake" shape. IW modifies turbulence dynamics, in that the turbulence kinetic energy (TKE) is significantly enhanced as compared to the TKE in the absence of IW. As in the case without IW, most of the turbulent energy is localized in the vicinity of the pycnocline center. Here, the TKE spectrum is considerably enhanced in the entire wave-number range as compared to the TKE spectrum in the absence of IW.

Preparation and Optical Investigations of [(Sr1-xBix)TiO3]-[2SiO2B2O3]-[CeO2] Glasses

We are reporting synthesis and structural and optical investigation of strontium bismuth titanate borosilicate glasses with addition of one mole percent cerium oxide (CeO2). Glasses were synthesized by conventional rapid melt quench method. XRD studies of the glass samples confirm the amorphous nature. Infrared absorption spectra various strontium bismuth titanate borosilicate glass samples having glass system 60[(Sr1-xBix)TiO3]-39[2SiO2B2O3]-1[CeO2] (x=0.0,0.1,0.2,0.4) were recorded over a continuous spectral range from 400 to 4000 cm−1. IR spectra were analyzed to determine and differentiate of various vibrational modes in the structural change. Raman spectroscopy of all glass samples was also carried out in the wave number range from 200 to 2000 cm−1.

Rietveld Structure Refinement and Cation Distribution of Substituted Nanocrystalline Ni-Zn Ferrites

Ferrite nanoparticles of were prepared by a sol-gel autocombustion method. The prepared samples were shown to have a cubic spinel structure by applying the full pattern fitting of the Rietveld method. The unit cell dimension, discrepancy factor, and interatomic distance have been determined. As the Cr3+ content x increases, the unit cell dimensions and crystallite size are decreased. The IR spectra show two absorption bands in the wave number range of 400 to 600 cm−1.