Comparative study of the electronic structure and optical properties of the Heusler alloys Co2MGa and Co2MAl (M = Fe and Ni)

The electronic structure and optical properties of the Heusler alloys Co2NiGa, Co2NiAl, Co2FeGa, and Co2FeAl are reported and compared in this work. In the Fe-based alloys, Co2FeGa and Co2FeAl, the electronic structure is found to have 100% spin polarization with the indirect energy gap in the [Formula: see text]-[Formula: see text] direction, whereas in Co2NiGa and Co2NiAl, the density of states is metallic in both spin projections with spin polarization of 55% (Co2NiGa) and 37% (Co2NiAl). Total and Co partial magnetic moments of all Heusler alloys for the optimized lattice parameters were found in a good agreement with previous calculations and experimental data. The frequency dependence of the real and imaginary parts of the complex dielectric constant for the Heusler alloys is studied in the spectrum region of 0.08–5 eV. The research results are discussed based on the performed calculations of the electronic structure. It was found that the character of variations of the spectral parameters of the alloys is typical for media with the metallic conductivity. In the IR region, the mechanism of the intraband acceleration of electrons by the light wave field dominates. The significant changes in the optical spectrum, magnetic moment, spin polarization and electronic structure were revealed in Co2MGa and Co2MAl for different M atoms which motivate further investigations of the Co-based Heusler alloys as promising materials for spintronics.

L-Band SAR Co-Polarized Phase Difference Modeling for Corn Fields

This research aims at modeling the microwave backscatter of corn fields by coupling an incoherent, interaction-based scattering model with a semi-empirical bulk vegetation dielectric model. The scattering model is fitted to co-polarized phase difference measurements over several corn fields imaged with fully polarimetric synthetic aperture radar (SAR) images with incidence angles ranging from 20° to 60°. The dataset comprised two field campaigns, one over Canada with the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR, 1.258 GHz) and the other one over Argentina with Advanced Land Observing Satellite 2 (ALOS-2) Phased Array type L-band Synthetic Aperture Radar (PALSAR-2) (ALOS-2/PALSAR-2, 1.236 GHz), totaling 60 data measurements over 28 grown corn fields at peak biomass with stalk gravimetric moisture larger than 0.8 g/g. Co-polarized phase differences were computed using a maximum likelihood estimation technique from each field’s measured speckled sample histograms. After minimizing the difference between the model and data measurements for varying incidence angles by a nonlinear least-squares fitting, well agreement was found with a root mean squared error of 24.3° for co-polarized phase difference measurements in the range of −170.3° to −19.13°. Model parameterization by stalk gravimetric moisture instead of its complex dielectric constant is also addressed. Further validation was undertaken for the UAVSAR dataset on earlier corn stages, where overall sensitivity to stalk height, stalk gravimetric moisture, and stalk area density agreed with ground data, with the sensitivity to stalk diameter being the weakest. This study provides a new perspective on the use of co-polarized phase differences in retrieving corn stalk features through inverse modeling techniques from space.

Determination of the complex dielectric permeability of liquid at the radiation frequency 32 GHz

Method and device for measuring the complex dielectric constant of liquids are described. The real part of the complex dielectric constant calculated from the conditions for the maximum and minimum of the measured interference dependence of the reflection coefficient on the layer depth. The imaginary part determined by selection to the maximum coincidence of the calculated and measured dependences of the reflection coefficient.

An Estimation of the Optical Constants of Copper Based on the FEFF 9 Package

The FEFF software package is based on a first-principles real space Green function (RSMS) scattering theory to calculate X-ray absorption fine-structure (XAFS), and forward scattering amplitudes (FSA). From these, an energy-dependent complex dielectric constant can be calculated, and from it other “optical constants”, like the complex index of refraction, absorption coefficient, the reflectance, and energy-loss function, can be derived. A procedure to estimate these using FEFF version 9 is outlined applied to crystalline metallic copper as an example, and the results compared to values taken from the literature.

About theory of extended interaction klystron and drift space in the form of medium with complex permittivity

Purpose of this work is to construct a theory of extended interaction klystron with ordinary distributed resonators, but with a drift space in the form of medium with complex permittivity. Methods. For this, a hybrid of extended interaction klystron and an amplifier with a complex permittivity is considered in the framework of the weak signal approximation. Two types of configurations of a extended interaction klystron were considered: with two and three distributed resonators. For a two-resonator klystron with distributed interaction, two cases are considered: without reflections from the ends of distributed resonators and the case when the input binder is fully matched to the external transmission line, and for the second distributed resonator, the so-called condition of critical coupling of the “hot” resonator with the transmission line is satisfied. For a three-resonator klystron with distributed interaction, the case is considered without reflections from the ends of distributed resonators. Results and conclusion. According to the results of the developed theory of a weak signal in a extended interaction klystron with ordinary distributed resonators and a drift space with a complex dielectric constant, by choosing the parameters, it is possible to achieve a greater gain at a length that is shorter than in a conventional extended interaction klystron, all other things being equal. In addition, the presence of an intermediate distributed resonator makes it possible to increase the gain while maintaining the full length of the device.

THE INFLUENCE OF THE SALTITY OF THE MOISTURIZING SOLUTION ON THE DIELECTRIC PERMEABILITY OF CLAYS IN THE FREQUENCY RANGE FROM 1 MHZ TO 8 GHZ

The article presents the results of measurements of the complex dielectric constant of clays saturated with NaCl solution of various concentrations in a wide frequency range. The measurements were carried out at positive temperatures. It was revealed that several relaxation processes are observed in the spectra. A model is proposed that makes it possible to take into account the relaxation processes and their dependence on the concentration of the salt solution. The concentration practically does not affect the parameters of the processes, in contrast to the temperature.

Study the Effect of Heat Treatment and Pressure on some the Optical Properties of the Pure PVA Nano Polymer

In this study, some optical properties were studied of the pure vinyl polyvinyl alcohol (PVA) nanopolymer (German origin). Under the influence of different temperatures and pressures of PVA. Where 25 samples were prepared for the purpose of conducting the research. Which studied the study of these samples was done by recording the absorbance and transmittance spectra of the wavelengths (200-900) nm. From them, absorbance, transmittance, reflectivity, absorption coefficient, refractive index, extinction coefficient, complex dielectric constant were calculated. At different temperatures (25,40, 80, 120, 160)°C. And with different pressures within the range (7.5,8,8.5,9,9.5) MPa. The results are that the permeability of the polymer (PVA) at different temperatures for each pressure decreases with increasing temperature, and that all other calculated optical properties increase with increasing temperature.

DIELECTRIC RELAXATION IN CLAYS SATURATED WITH WATER-OIL EMULSION IN A WIDEBAND OF FREQUENCIES AT POSITIVE AND NEGATIVE TEMPERATURES

The results of measuring the complex dielectric constant of clays saturated with an oil-water emulsion in various ratios in a wide frequency range are presented. The measurements were used out at positive and negative temperatures. It was revealed that several relaxation processes are observed in the spectra. The processes parameters significantly depend on the temperature and the ratio of water and hydrocarbon to the saturating mixture. A model is proposed that makes it possible to take into account relaxation processes and their dependence on temperature.

Relaxation Dynamics of Ethanol and N-Butanol in Diesel Fuel Blends from Terahertz Spectroscopy

Binary blends of ethanol-diesel, n-butanol-diesel, ethanol-biodiesel, and n-butanol-biodiesel have been analyzed with terahertz time-domain spectroscopy in a full range of concentrations and at room temperature. The real and imaginary parts of the complex dielectric constant of the blends were obtained from the spectra and fitted to the Debye model at low volume concentrations (up to 7.5% for ethanol in diesel and up to 20% for butanol in diesel, ethanol in biodiesel, and butanol in biodiesel blends), considering the number of relaxation processes recommended in the literature for each pure component (single for diesel, double for biodiesel, and triple for alcohols). The results indicate that the faster relaxation time in low alcohol mixtures is longer than in pure alcohols. This relaxation time increases as the alcohol content increases. The excess of the real and of imaginary parts of the dielectric constant were individually determined. The analysis of such excess and of its different contributions (volume, contrast, and interactions) suggests that the intermolecular interactions between the different components of the blends dominate the relaxation dynamics in each pseudo-binary system. Ethanol was found to move blends further away from ideal behavior than n-butanol. In fact, these latter blends showed the most ideal behavior, suggesting that the length of the alcohol carbon chain plays an important role. This information allows a possible link between the nonlinear behavior of the physicochemical properties of the blends (e.g., viscosity and surface tension) and the molecular interactions between their constituent molecules. This relation could have direct application for monitoring the fuel composition and quality in the vehicle control systems.

Reduced Graphene Oxide/Polyvinyl Alcohol Nanofibers Fabricated by Electrospinning Technique as An Ideal Candidate for Organic Solar Cell Devices

Functionalization of rGO that previously obtained by chemical reduction using hydrazine hydrate, has been done by changing its morphology into nanofiber with electrospinning technique and using PVA as a polymer matrix. The rGO nanofibers that had been formed were then characterized using Fourier Transformation-Infra Red (FTIR) spectroscopy, Scanning Electron Microscopy (SEM), and UV-Vis Spectrophotometer. FTIR spectroscopy confirmed the presence of C – C group and C = O group in nanofibers. SEM showed the change of nanofibers morphology which is marked by the increasing of fibres diameter and the hollow fibres become brighter. Furthermore, the effect of rGO concentration to nanofiber optical properties was confirmed by UV-Vis spectrophotometer. According to this characterization, the absorbance of rGO/PVA nanofiber is decreased due to increased rGO concentration. The detail of optical properties of rGO is studied through complex refractive index and dielectric constant in which Kramers-Kronig transformation is then employed to calculate complex refractive index and complex dielectric constant. From the data, the optical properties of rGO/PVA nanofibers indicating that rGO/PVA nanofibers can be applied as transparent electrode an organic solar cell devices.