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《Physics letters. A》2020,384(35):126893
Here, the thermoelectric (TE) properties of Na0.74Co1xNbxO2 (x=0.05,0.10) compounds are investigated experimentally and computationally. The experimental measurements are conducted in 300620 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.  相似文献   

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《Physics letters. A》2019,383(22):2652-2657
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, Γ=(4.20±0.35)×108Km, the solid-liquid interfacial energy, σSL=180.68±23.48mJ/m2 and the grain boundary energy, σGB=309.30±29.47mJ/m2, in the Al/Al-Sn-Mg system have been calculated from the measured grain boundary shapes.  相似文献   

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《Physics letters. A》2020,384(36):126930
We consider quantum bosons with contact interactions at the Lowest Landau Level (LLL) of a two-dimensional isotropic harmonic trap. At linear order in the coupling parameter g, we construct a large, explicit family of quantum states with energies of the form E0+gE1/4+O(g2), where E0 and E1 are integers. Any superposition of these states evolves periodically with a period of 8π/g until, at much longer time scales of order 1/g2, corrections to the energies of order g2 may become relevant. These quantum states provide a counterpart to the known time-periodic behaviors of the corresponding classical (mean field) theory.  相似文献   

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《Physics letters. A》2020,384(13):126265
The exact solvability and impressive pedagogical implementation of the harmonic oscillator's creation and annihilation operators make it a problem of great physical relevance and the most fundamental one in quantum mechanics. So would be the position-dependent mass (PDM) oscillator for the PDM quantum mechanics. We, hereby, construct the PDM creation and annihilation operators for the PDM oscillator via two different approaches. First, via von Roos PDM Hamiltonian and show that the commutation relation between the PDM creation Aˆ+ and annihilation Aˆ operators, [Aˆ,Aˆ+]=1AˆAˆ+1/2=Aˆ+Aˆ+1/2, not only offers a unique PDM-Hamiltonian Hˆ1 but also suggests a PDM-deformation in the coordinate system. Next, we use a PDM point canonical transformation of the textbook constant mass harmonic oscillator analog and obtain yet another set of PDM creation Bˆ+ and annihilation Bˆ operators, hence an “apparently new” PDM-Hamiltonian Hˆ2 is obtained. The “new” PDM-Hamiltonian Hˆ2 turned out to be not only correlated with Hˆ1 but also represents an alternative and most simplistic user-friendly PDM-Hamiltonian, Hˆ=(pˆ/2m(x))2+V(x); pˆ=iħx, that has never been reported before.  相似文献   

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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 (λ1=11.1μm,λ2=14.1μm and λTHz=60μm). 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.  相似文献   

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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 Pd=0.9 (@SNR=20dB) under very low false alarm probability Pf=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.  相似文献   

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《Physics letters. A》2020,384(27):126687
We investigate the phase transitions in the Ising model on a layered square lattice with first-(J1) and second-(J2) neighbor intralayer interactions and interlayer couplings (J). The thermodynamics of the system is evaluated within a cluster mean-field approximation, which allows us to identify the nature of the thermally driven phase transitions hosted by the model. As a result, we find that interlayer couplings reduce the region of first-order phase transitions between paramagnetic and superantiferromagnetic states. We also find that the interlayer couplings reduce the frustration effects by reducing the entropy content of the low-temperature phases. Our results suggest that tricriticality is present in the special case J=J1, which is in qualitative agreement with recent Monte Carlo simulations for the model.  相似文献   

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