共查询到20条相似文献,搜索用时 35 毫秒
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《Physics letters. A》2020,384(35):126893
Here, the thermoelectric (TE) properties of Na0.74CoNbxO2 () compounds are investigated experimentally and computationally. The experimental measurements are conducted in 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 and , respectively. The experimental transport properties of these compounds are understood by employing spin-polarized GGA+U (= 4 eV) electronic structure calculations on 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 and , respectively. The optimum value of efficiency for is calculated as ∼ 6.4%, whereas it reaches ∼ 7.5% for . 相似文献
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Yueyue Liu Xiangqian Wang Hongkang Xie Hongmei Feng Xiaolei Li Huiliang Wu Zengtai Zhu Yi Huang Wenshu Liu Genliang Han Jianbo Wang Qingfang Liu 《Physics letters. A》2019,383(34):125986
The effect of bilayer repeats (N) on the static and dynamic magnetic properties of Co/Ni multilayers was investigated. The effective perpendicular magnetic anisotropy constant of multilayers drops from erg/cm3 to erg/cm3 with N increasing from 5 to 11. For Co/Ni multilayers with , sharp magnetization switching was observed. In contrast, Co/Ni multilayers with have a long tail in the hysteresis loop. Ferromagnetic resonance measurements show that intrinsic Gilbert damping changes from 0.021 to 0.016 with increase in N and is inversely proportional to N. This study provides a deep understanding and effective control of magnetic properties of Co/Ni multilayers for spintronics devices. 相似文献
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Dong Wang Han Zhang Hai-Liang Chen Jie Wu Qing-Jun Zang Wen-Cai Lu 《Physics letters. A》2019,383(8):774-780
Stable structures of uranium hydrides at 0–550 GPa were studied using genetic algorithm (GA) combined with density functional theory calculations. We investigated two stoichiometries of U–H system, UH4 and UH10 at high pressure, and properties of UH4, UH8 and UH10. The study found that UH8 is the most stable phase at 100–550 GPa, UH4 is a stable phase at 100–550 GPa, and UH10 could become stable over 450 GPa. For UH10, the most phase is , which was found to be a superconductor with the transition temperature and 15 K at 100, 200, 300, 400 and 550 GPa, respectively. 相似文献
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First principle calculations have been employed to investigate the effects of Y concentration, pressure and temperature on various properties of () alloys using density functional theory (DFT). The full potential linearized augmented plane wave (FP-LAPW) method within a framework of the generalized gradient approximation (GGA) is used to perform the calculated results of this paper. Phase stability of alloys is studied using the total energy versus unit cell volume calculations. The equilibrium lattice parameters of these alloys are in good agreement with the available experimental results. The mechanical stability of alloys is proved using elastic constants calculations. Also, the influence of Y concentration on elastic properties of alloys such as Young's modulus, shear modulus, Poisson's ratio and anisotropy factor are investigated and analyzed. By considering both Pugh's ratio and Poisson's ratio, the ductility and brittleness of these alloys are studied. In addition, the total density of states and orbital's hybridizations of different atoms are investigated and discussed. Moreover, the effect of pressure and temperature on some important thermodynamic properties is investigated. 相似文献
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Dapeng Liu Binod R. Giri Milán Szőri Béla Viskolcz Et-touhami Es-sebbar Aamir Farooq 《Proceedings of the Combustion Institute》2021,38(1):967-976
NOx mitigation is a central focus of combustion technologies with increasingly stringent emission regulations. NOx can also enhance the autoignition of hydrocarbon fuels and can promote soot oxidation. The reaction between allyl radical (C3H5) and NOx plays an important role in the oxidation kinetics of propene. In this work, we measured the absolute rate coefficients for the redox reaction between C3H5 and NOx over the temperature range of 1000–1252 K and pressure range of 1.5–5.0 bar using a shock tube and UV laser absorption technique. We produced C3H5 by shock heating of C3H5I behind reflected shock waves. Using a Ti:Sapphire laser system with frequency quadrupling, we monitored the kinetics of C3H5 at 220 nm. Unlike low-temperature chemistry, the two target reactions, C3H5 + NO → products (R1) and C3H5 + NO2 → products (R2), exhibited a strong positive temperature dependence for this radical-radical type reaction. However, these reactions did not show any pressure dependence over the pressure range of 1.5–5.0 bar, indicating that the measured rate coefficients are close to the high-pressure limit. The measured values of the rate coefficients resulted in the following Arrhenius expressions (in unit of cm3/molecule/s):To our knowledge, these are the first high-temperature measurements of allyl + NOx reactions. The reported data will be highly useful in understanding the interaction of NOx with resonantly stabilized radicals as well as the mutual sensitization effect of NOx on hydrocarbon fuels. 相似文献
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S. Jones J. Melguizo-Gavilanes J.E. Shepherd 《Proceedings of the Combustion Institute》2019,37(2):1597-1604
A combined experimental and numerical study was carried out to investigate thermal ignition by millimeter size ( mm) moving hot spheres in H2-O2-N2 environments over a range of equivalence ratios. The mixtures investigated were diluted with N2 to keep their laminar flame speed constant and comparable to the sphere fall velocity (2.4 m/s) at time of contact with the reactive mixture. The ignition thresholds (and confidence intervals) were found by applying a logistic regression to the data and were observed to increase from lean (; Tsphere = 963 K) to rich (; Tsphere = 1007 K) conditions. Experimental temperature fields of the gas surrounding the hot sphere during an ignition event were, for the first time, extracted using interferometry and compared against simulated fields. Numerical predictions of the ignition thresholds were within 2% of the experimental values and captured the experimentally observed increasing trend between lean and rich conditions. The effect of stoichiometry and dilution on the observed variation in ignition threshold was explained using 0-D constant pressure delay time computations. 相似文献
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We propose two new type sine hyperbolic potentials and . They may become single- or double-well potentials depending on the potential parameters and k. We find that its exact solutions can be written as the confluent Heun functions , in which the energy level E is involved inside the parameter η. The properties of the wave functions, which is strongly relevant for the potential parameters and k, are illustrated. 相似文献
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M.J. Majid 《Physics letters. A》2019,383(9):879-887
We present a new procedure to investigate the I–V characteristics and the conductance for strained SWCNTs. These electronic transport properties have been studied theoretically at zero temperature for zig-zag, armchair and chiral SWCNTs under the effect of the uniaxial tension and torsional strain. The analytical expression of the energy spectrum in the tight binding approximation has been used to calculate the induced current and the conductance through Landauer–Büttiker formalism. It is shown that the conductance for unstrained CNTs at initial values of the voltage can take discrete values which are equal to zero and 4 () for semiconducting and conducting SWCNTs respectively. The emergence of the kinks in the I–V characteristics is due to the discrete electronic spectrum in the SWCNTs. The location and number of kinks are changeable under the effect of strain process. The conductance in a strained armchair CNT decreases to zero under torsional strain, consequently, it will transform the conducting SWCNTs at a threshold value of strain to a semiconducting SWCNT. In contrast, by applying the uniaxial tension on the armchair CNT, the conductance does not change absolutely. There is a different behavior can be observed by applying the strain on zig-zag CNT, where the conductance decreases rapidly and slightly under the influence of uniaxial tension and torsional strain, respectively. We found that the conductance of chiral CNT is not significantly affected by applying the strain under consideration. More interestingly, the band structure of chiral CNT under uniaxial tension and torsional strain have been investigated within the tight binding approximation. 相似文献
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《Physics letters. A》2019,383(17):2114-2119
We provide a detailed analysis of a topological structure of a fermion spectrum in the Hofstadter model with different hopping integrals along the -links (), defined on a honeycomb lattice. We have shown that the chiral gapless edge modes are described in the framework of the generalized Kitaev chain formalism, which makes it possible to calculate the Hall conductance of subbands for different filling and an arbitrary magnetic flux ϕ. At half-filling the gap in the center of the fermion spectrum opens for , a quantum phase transition in the 2D-topological insulator state is realized at . The phase state is characterized by zero energy Majorana states localized at the boundaries. Taking into account the on-site Coulomb repulsion U (where ), the criterion for the stability of a topological insulator state is calculated at , . Thus, in the case of , the topological insulator state, which is determined by chiral gapless edge modes in the gap Δ, is destroyed. 相似文献
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In this paper, we discuss a method based on wavelet analysis for the study of the q-index of the Gaussian distribution. We derive q-index from the scale index, , using the expression; where is a wavelet based tool for measuring the degree of aperiodicity of a dynamical system in the range of . We show that this expression gives consistent results with the numerical approach of q-Gaussian distribution which determines the degree of non-extensivity of a dynamical system in the range of . We also suggest a new entropy calculation method based on the normalized inner scalogram for studying the chaotic characteristics of nonlinear dynamical systems. 相似文献
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Physically natural assumption says that any relaxation process taking place in the time interval , may be represented as a composition of processes taking place during time intervals and where is an arbitrary instant of time such that . For the Debye relaxation such a composition is realized by usual multiplication which claim is not valid any longer for more advanced models of relaxation processes. We investigate the composition law required to be satisfied by the Cole-Cole relaxation and find its explicit form given by an integro-differential relation playing the role of the time evolution equation. The latter leads to differential equations involving fractional derivatives, either of the Caputo or the Riemann-Liouville senses, which are equivalent to the special case of the fractional Fokker-Planck equation satisfied by the Mittag-Leffler function known to describe the Cole-Cole relaxation in the time domain. 相似文献
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Singly-excited states of the two-electron atom cease being bound when (from above), the outer orbital becoming infinitely diffuse. The asymptotic relations where , are demonstrated to hold. Here, is a hydrogenic s orbital with principal quantum number . New, more nuanced light is shed on the already challenged dogma that the Pauli principle keeps the electrons further apart in the triplet than in the corresponding singlet. 相似文献