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Now showing items 65 - 80 of 36624

  • Preparation and Thermoelectric Properties of n-Type Bi2Te2.7Se0.3:D (m)

    Lee, Go-Eun   Eum, A-Young   Song, Kwon-Min   Kim, Il-Ho   Lim, Young Soo   Seo, Won-Seon   Choi, Byeong-Jun   Hwang, Chang-Won  

    Bismuth chalcogenides such as p-type (Bi,Sb)(2)Te-3 and n-type Bi-2(Te,Se)(3) are excellent thermoelectric materials near room temperature. They can form homogeneous solid solutions because Bi2Te3, Sb2Te3, and Bi2Se3 have the same class of crystal symmetry. The thermoelectric figure of merit can be improved by increasing the power factor through doping and/or by reducing the thermal conductivity by forming a solid solution. In this study, n-type Bi2Te2.7Se0.3:D (m) (D: dopant such as I, Cu, Ag) solid solutions were prepared by encapsulated melting and hot pressing. The undoped solid solution had a power factor (PF) of 1.71 mW m(-1) K-1 at 323 K and a figure of merit (ZT) of 0.55 at 423 K. The ZT value was improved due to the increased PF by I or Cu doping, and maximum ZT values were obtained as 1.13 for Bi2Te2.7Se0.3:I-0.0075 and 0.74 for Bi2Te2.7Se0.3:Cu-0.01 at 423 K. However, the thermoelectric properties of Ag-doped Bi2Te2.7Se0.3 solid solutions barely improved.
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  • Mathias A. L. (MAL) Fobi, M. D. F.A.C.S., F.I.C.S., F.A.C.N

    Wiener, Rudolf   Shikora, Scott A.  

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  • SMOOTH MODULE l REPRESENTATIONS OF GL(m)(D)

    Minguez, Alberto   Secherre, Vincent  

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  • Theoretical study of substitution effect in superalkali OM3 (M=Li, Na, K)

    Tong, Jing   Li, Ying   Wu, Di   Wu, Zhi-Jian  

    A class of superalkalies OM3 (M = Li, Na, K) and their corresponding cations OM3+ were theoretically investigated. The OM3 molecules possess very low adiabatic ionization potentials (AIPs) of 2.842-3.558 eV at the CCSD(T)/6-311+G(3df) level. It was found that the ionization potentials of OM3 depend on the nature of the peripheral ligand atom and can be efficiently decreased upon replacing the M atom with the more electropositive one. Such superalkalies characterized by lower ionization potentials add candidates to the research on superatoms and can be used in the synthesis of new nontraditional salts where strong reducers are involved. (C) 2013 Elsevier B. V. All rights reserved.
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  • Higher D or Li: probes of physics beyond the standard model

    Keith A. Olive   Patrick Petitjean   Elisabeth Vangioni   Joseph Silk  

    Standard big bang nucleosynthesis (BBN) at the baryon density determined by the microwave anisotropy spectrum predicts an excess of 7Li compared to observations by a factor of 4–5. In contrast, BBN predictions for D/H are somewhat below (but within 2σ of) the weighted mean of observationally determined values from quasar absorption systems. Solutions to the 7Li problem which alter the nuclear processes during or subsequent to BBN often lead to a significant increase in the deuterium abundance consistent with the highest values of D/H seen in absorption systems. Furthermore, the observed D/H abundances show considerable dispersion. Here, we argue that those systems with D/H ≃ 4 × 10−5 may be more representative of the primordial abundance and as a consequence, those systems with lower D/H would necessarily have been subject to local processes of deuterium destruction. This can be accounted for by models of cosmic chemical evolution able to destroy in situ deuterium due to the fragility of this isotope.
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  • On the interaction of Li–D films with nitrogen and oxygen at room temperature

    A. S. Popkov   S. A. Krat   Yu. M. Gasparyan   Ya. A. Vasina   A. A. Pisarev  

    The interaction between Li–D films obtained via deposition in magnetron discharge with nitrogen and oxygen is investigated. It is shown that exposure to these gases at a pressure of 4000 Pa does not lead to a significant decrease in the amount of deuterium in the film unlike the case of water vapor. The release of deuterium from Li–D films during thermal-desorption analysis occurs mainly in a narrow temperature range at 650–700 K in the case of as-deposited films and after gas exposure. The amplitude of the low-temperature region in the TDS spectrum increases after oxygen exposure.
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  • Yenido?an D?neminde Hipoglisemiye Yakla??m

    Sangün, ?zlem   Dündar, Bumin  

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  • Ford, Los Alamos win $6 M R&D grant

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  • Higher D or Li: probes of physics beyond the standard model

    Keith A. Olive   Patrick Petitjean   Elisabeth Vangioni and Joseph Silk  

    Standard big bang nucleosynthesis (BBN) at the baryon density determined by the microwave anisotropy spectrum predicts an excess of 7Li compared to observations by a factor of 4–5. In contrast, BBN predictions for D/H are somewhat below (but within 2σ of) the weighted mean of observationally determined values from quasar absorption systems. Solutions to the 7Li problem which alter the nuclear processes during or subsequent to BBN often lead to a significant increase in the deuterium abundance consistent with the highest values of D/H seen in absorption systems. Furthermore, the observed D/H abundances show considerable dispersion. Here, we argue that those systems with D/H ≃ 4 × 10−5 may be more representative of the primordial abundance and as a consequence, those systems with lower D/H would necessarily have been subject to local processes of deuterium destruction. This can be accounted for by models of cosmic chemical evolution able to destroy in situ deuterium due to the fragility of this isotope.
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  • Fundamental studies of H2 interaction with MAl3 clusters [M=Li, Sc, Ti, Zr]

    Samolia, Madhu   Dhilip Kumar, T.J.  

    Complex metal hydride is a promising hydrogen storage material for automobile applications due to its reversible storage capacity. The presence of transition metal halide is found to improve significantly the kinetics of H 2 adsorption and desorption processes. Experimental studies have indicated the formation of distorted MAl 3 phase where M = Sc, Ti, Zr. In this study, a first-principles density functional study has been performed to investigate the hydrogen interaction and saturation on stable tetrahedral MAl 3 clusters [M = Li, Sc, Ti, and Zr] by employing spin-polarized hybrid and non-local density functionals. On saturation, the first H 2 molecule undergoes chemisorption in the transition metals while further loading results in physisorption with the Kubas-type H 2 interaction. Activation energy barrier for the H 2 dissociation over the cluster is calculated to be ~0.2 eV for the transition metals. Effect of external electric field on the MAl 3H 4 cluster with molecular H 2 is studied which leads to polarization of physisorbed H 2 and the cluster. The results offer an explanation for catalysts role in improving the kinetics of H 2 sorption process in complex metal hydrides. [All rights reserved Elsevier].
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  • On the interaction of Li–D films with nitrogen and oxygen at room temperature

    Popkov, A. S.   Krat, S. A.   Gasparyan, Yu. M.   Vasina, Ya. A.   Pisarev, A. A.  

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  • ML and UMVU estimation in the M/D/1 queuing system

    Srinivas, V.   Kale, B. K.  

    In the imbedded Markov chain (IMC) analysis of M/G/1 queuing system, X-1, X-2, ..., X-n, ... form a sequence of i.i.d random variables. where X-n denotes the number of customer arrivals during the service time of customer. In the M/D/1 queue, the distribution of common random variable X is the Poisson distribution with mean , the traffic intensity. This fact is utilized for maximum likelihood (ML) and uniformly minimum variance unbiased (UMVU) estimation of traffic intensity, performance measures, transition probabilities of IMC, and correlation functions of departure process, based on a sample of fixed size n from P() distribution. Also, consistent asymptotic normality (CAN) property of ML estimators (MLEs) is established. The MLEs and UMVUEs are compared.
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  • Density functional studies of magic clusters Ga13M(M=Li, Na, K, and Rb)

    Tang, Chunmei   Chen, Shengwei   Zhu, Weihua   Zhang, Aimei   Zhang, Kaixiao  

    Density functional studies are performed on the structures, stabilities, electronic properties, and polarizabilities of the Ga13M(M = Li, Na, K, and Rb) clusters, which have closed electronic shell structures, enhanced stabilities, large HOMO-LUMO energy gaps, high vertical ionization potentials, and low vertical electron affinities. All of these properties are characteristic of a magic cluster and can be well understood by the jellium model. Therefore, we strongly suggest Ga13M(M = Li, Na, K, and Rb) are magic clusters and promising as building blocks in developing cluster-assembled materials. The calculated vertical electron affinity of Ga-13 is close to that of bromine, implying it would be like a halogen atom in the Ga13M molecule. The static linear polarizabilities and first-order hyperpolarizabilities of Ga13M clusters are significantly larger than those of Ga-13 because of their lower symmetries and higher delocalization of p electrons. (C) 2013 Elsevier B.V. All rights reserved.
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  • Supergravity as generalised geometry II:Ed(d)× ?+and M theory

    André Coimbra   Charles Strickland-Constable…  

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  • Thermoelectric Properties of (Na(1-y)M(y))(1.4)Co(2)O(4) (M = Sr, Li)

    Li, Ying   Ma, Beiyue   Jiang, Maofa   Wang, Zhenming  

    Oxide thermoelectric materials (Na(1-y) M (y) )(1.4)Co(2)O(4) (M = Sr, Li; y = 0 to 0.4) were prepared by a sol-gel method. The influence of doping on the thermoelectric properties was investigated, and the phase composition was characterized by x-ray diffraction. Experimental results showed that the main crystalline phase of the undoped and Sr/Li-doped samples was gamma-Na(1.4)Co(2)O(4). The thermoelectric properties of Na(1.4)Co(2)O(4) can be improved slightly by doping with Sr. Doping with Li improves the thermoelectric properties of Na(1.4)Co(2)O(4). For a doping fraction of y = 0.1, the electrical conductivity of (Na(1-y) Li (y) )(1.4)Co(2)O(4) at 288 K achieves its maximum value of 301.19 (Omega mm)(-1). The Seebeck coefficient and power factor of (Na(1-y) Li (y) )(1.4)Co(2)O(4) at 288 K achieve their maximum values of 172.28 mu V K(-1) and 7.44 mW m(-1) K(-2) at a doping fraction of y = 0.4.
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  • Bosonic vertex representations of the toroidal superalgebras in type D(m,n)

    Jing, Naihuan   Xu, Chongbin  

    In this paper, vertex representations of the 2-toroidal Lie superalgebras of type D(m, n) are constructed using both bosonic fields and vertex operators based on their loop algebraic presentation.
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