Investigating the thermoelectric properties of Na0.74Co1−xNbxO2 (x = 0.05,0.10) at high temperature region

Here, the thermoelectric (TE) properties of Na_0.74Co${}_{1-x}$Nb_xO₂ ($x=0.05,0.10$) compounds are investigated experimentally and computationally. The experimental measurements are conducted in $300-620$ K. Positive sign of Seebeck coefficient for both the compounds indicates the dominating p-type character. The maximum experimental values of ZT are observed as ∼ 0.12 and ∼ 0.19 at 620 K for $x=0.05$ and $x=0.10$, respectively. The experimental transport properties of these compounds are understood by employing spin-polarized GGA+U (= 4 eV) electronic structure calculations on $x=0.0625$ compound. On the basis of best experimental and computational matching of transport properties, we have estimated ZT till 1200 K computationally. The highest calculated values of ZT are ∼ 1.36 and ∼ 1.22 at 1200 K for $x=0.05$ and $x=0.10$, respectively. The optimum value of efficiency for $x=0.05$ is calculated as ∼ 6.4%, whereas it reaches ∼ 7.5% for $x=0.10$.     

A study on the phase transformation behaviour of Cu-20wt.Sn alloy produced using powder metallurgy method: Experimental and molecular dynamics modelling

In this study, Cu-20wt.Sn alloy was produced by powder metallurgy (PM) method by using high purity element powders. The phases in the microstructure of the produced alloy were determined by XRD study. The phase transformation behaviour of the alloy was investigated by DSC and modelling method. Moreover, the Cu-20wt.Sn alloy system was modelled with molecular dynamics (MD) simulation based on modified Embedded Atom Method (MEAM). The radial distribution function (RDF) was calculated to determine the structural properties of system during the phase transformations. The experimental results showed that the transformation ($\alpha +\delta$) → ($\alpha +\gamma$) occur at temperature above 500°C. The simulation results showed that the phase transformation $\alpha +\delta \to \alpha +\gamma$ occurs at 550°C temperature. Our simulation results are in reasonable agreement with the experimental data.     

Duality between the SU(2) lattice gauge model and bosonic t − J model

We investigate the duality between the $SU(2)$ lattice gauge model and the bosonic $t-J$ model. We construct the relations between the gauge field operators and particle operators, and map the low-energy regime of the $SU(2)$ lattice gauge model to a $U(1)$ bosonic $t-J$ model coupled with a $U(1)$ gauge field. The mapped model can be interpreted as a bosonic $t-J$ model with particle-hole symmetry, or a mean-field form of the bosonic $t-J$ model with the coexistence of a two-particle pairing and four particle-pairing. The duality between the lattice gauge model and the bosonic $t-J$ model provides a direct connection between gauge theory and strongly correlated systems.     

Thermoelectric coefficient in nanoisland metallic films

We study the thermoelectric properties of island metal films on a dielectric substrate. Dependence of thermoelectric coefficient of metal films on their thickness with the dimensionless conductance $g>1$ and $g<1$ was investigated. Also, the thermopower dependence of island metal structures with $g<1$ on the chemical composition of nanostructures was studied. We found that regardless of tunneling or Drude character of conductivity, the value of the thermoelectric coefficient in island metal films is determined by the properties of film metal element.     

Synthesis and microwave dielectric properties of an electronic ceramic Y2WO6 for wireless communications

Y₂WO₆ ceramics were fabricated via a solid-state reaction method and investigated structure stability, densification, microstructure, and dielectric properties at microwave frequency range. Y₂WO₆ crystallized in a monoclinic structure and stabilized to 1500 ^∘C, beyond which the decomposition of Y₆WO₁₂ occurred. Y₂WO₆ ceramic could be sintered into a compact bulk at 1450 ^∘C, which was characterized by a high relative density ∼ 97.6% and a dense microstructure. The favorable dielectric performances were achieved at 1450 ^∘C with a relative permittivity ${\epsilon }_r\sim 11.4$, a quality factor $Q\times f\sim 42,380$ GHz ($f=8.6$ GHz), and a temperature coefficient of resonant frequency ${\tau }_f\sim -49.0$ ppm/^∘C. The MW properties of Y₂WO₆ suggest that it could be useful candidate material for low-loss dielectric resonators.     

Resonant light absorption and plasmon tunability of lateral triangular Au nanoprisms array

Optical characteristics and electric field distribution of triangular Au nanoprism in a unit and units array under polarized light irradiation were systematically studied by numerical simulation with finite difference time domain method. It is found that the plasmonic properties of the triangular nanoprism are dominated by the electric polarization rather than the wave propagation. The triangular nanoprism presents similar optical response with a strong dipole band under different wave propagations if the electric polarization vectors are parallel to the triangular cross section. The lateral triangular Au nanoprisms array possesses a large tunability of the plasmonic properties contributed from the combined influence of inter-particle distance, particles size, polarization angle and even environmental medium. From the plasmon band shift versus the refractive index, ultra-high local surface plasmon resonance sensitivity (509.96 nm/RIU, figure of $\text{merit}=5.55$) is reached at $\sim 850\text{nm}$, making this array promising for biochemical sensing applications.     

Terahertz generation in quantum cascade structures by two-color deriving fields: An approach to reach inversion population via optical pumping

In this paper, a quantum cascade laser (QCL) design is proposed based on GaAs/AlGaAs material system, which simultaneously operates at three widely separated wavelengths (${\lambda }_1=11.1\mu m,{\lambda }_2=14.1\mu m$ and ${\lambda }_{THz}=60\mu m$). In the design, all the wavelength radiations are achieved by the engineering of the electronic spectrum via the quantum-well widths and the applied electric field in a single active region within a same waveguide. The mid-infrared (mid-IR) wavelengths are obtained by adoption a dual-upper-state active region, and the proposed design aims to use both the mid-IR radiations as the coherent deriving fields to populate the upper THz lasing state to aid the THz-laser population inversion via optical pumping instead of direct electrical injection. A detailed analysis of electronic transport in the structure is carried out using a multi-level rate-equation model. The results show that the proposed structure offers an alternative approach to room temperature THz generation in QCLs.     

Experimental determination of interfacial energy for solid Al in the Al-Sn-Mg eutectic system with Bridgman-type apparatus

The equilibrated grain boundary groove shape of solid Al in equilibrium with Al-Sn-Mg eutectic liquid was observed by using a Bridgman type directional solidification apparatus. The ratio of the thermal conductivity of the equilibrated liquid to the thermal conductivity of solid Al has been obtained as 0.91. In addition, the average Gibbs-Thomson coefficient, $\bar{\mathrm{\Gamma }}=(4.20\pm 0.35)\times {10}^{-8}\mathrm{Km}$, the solid-liquid interfacial energy, ${\sigma }_{SL}=180.68\pm 23.48\text{mJ}/{\text{m}}^2$ and the grain boundary energy, ${\sigma }_{GB}=309.30\pm 29.47\text{mJ}/{\text{m}}^2$, in the Al/Al-Sn-Mg system have been calculated from the measured grain boundary shapes.     

CNN-aided multiple PU spectrum sensing in uncalibrated massive antennas SU system

This paper deploys the Convolutional Neural Network (CNN) to learn and set the statistical test in Spectrum Sensing (SS) task of multiple primary user (PU) sources in massive uncalibrated antennas of secondary users (SU) sharing the same spectrum resources. The proposed deep learning-based SS method (DL-SS) is based on the CNN architecture that has the capability of extracting features of the sample covariance matrices (SCMs) that are given as the network input, improving the overall performance and robustness. The proposed CNN-SS method is compared with nine recent multiple-antennas SS methods, namely the arithmetic–geometric detector (AGM), John’s detector (JD), sphericity detector (SD), generalized likelihood test (GLRT), locally most powerful invariant test (LMPIT), maximum–minimum eigenvalue detector (MME), covariance detector (CAV), Hadamard detector (HD) and volume detector (VD) methods; besides, the proposed method is also compared with five recent state-of-art CNN-based SS methodologies. Performance-complexity trade-off of the proposed and reference SS methods are corroborated via Monte Carlo Simulations (MCS). The proposed CNN-SS method under uncalibrated massive antennas reveals substantial benefits w.r.t. the reference methods and is competitive with others CNN-SS methodologies, both in terms of complexity and performance, achieving detection probability of $P_d=0.9$ $(@SNR=-20\mathrm{dB})$ under very low false alarm probability $P_f=0.1$. Under different figures of merit, the performance of the CNN-based SS detector has revealed to be indubitably superior regarding the state-of-art SS detectors. However, the proposed CNN-based SS detector presents relative computational complexity increases. Hence, to be effective, such a superior operational performance requires a very efficient processing structure in the SU base stations.