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排序方式: 共有456条查询结果,搜索用时 234 毫秒
31.
Alessio Mezzi Eleonora Bolli Saulius Kaciulis Matteo Mastellone Marco Girolami Valerio Serpente Alessandro Bellucci Riccardo Carducci Riccardo Polini Daniele M. Trucchi 《Surface and interface analysis : SIA》2020,52(12):968-974
Thin films of barium fluorides with different thicknesses were deposited on GaAs substrate by electron beam evaporation. The aim of the work was to identify the best growth conditions for the production of coatings with a low work function suitable for the anode of hybrid thermionic-photovoltaic (TIPV) devices. The chemical composition and work function φ of the films with different thicknesses were investigated by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The lowest value of φ = 2.1 eV was obtained for the film with a thickness of ~2 nm. In the valence band spectra of the films at low kinetic energy, near the cutoff, a characteristic peak of negative electron affinity was present. This effect contributed to a further reduction of the film's work function. 相似文献
32.
Gialiana Biagi Irene Giorgi Oreste Livi Valerio Scartoni Silvia Velo Pier Luigi Barili 《Journal of heterocyclic chemistry》1996,33(6):1847-1853
A new 4-(benzotriazol-1-yl)-1,2,3-triazole structure was obtained by the diazotization reaction of either of 1-(2-aminophenyl)-4-carboxamido-5-amino-1H-1,2,3-triazole ( 1c ) or of the corresponding Dimroth isomer 1d . It underwent some common reactions to evaluate its chemical behaviour and structure. An analogous reaction sequence was carried out from the 2-nitro-4-methylphenyl azide, to assign the structure to the nitro derivatives prepared. The structure of the new compounds prepared was confirmed by chemical and spectroscopic methods. 相似文献
33.
In this paper, we discuss techniques by which the aeroacoustic properties of the turbulent flow in a rod-airfoil benchmark
experiment can be inferred from time-resolved PIV measurement. While acoustic measurements can be made directly using microphones,
the proposed techniques provide a means to directly link acoustic waves with specific flow events, which is invaluable in
devising noise mitigation strategies. The approaches are possible thanks to recent improvements in digital and camera technology
that can provide time-resolved measurements in air flows, necessary for the determination of unsteady flow quantities related
to aeroacoustic production. Both techniques are based on Curle’s acoustic analogy, where one is based on Lagrangian determination
of the required quantities, while the other requires all flow quantities to be converted into Fourier modes. Application of
both techniques yields results that are in reasonable agreement with microphone noise measurements for the rod-airfoil experiment. 相似文献
34.
35.
Edward W. Kolb Valerio Marra Sabino Matarrese 《General Relativity and Gravitation》2010,42(6):1399-1412
The cosmological backreaction proposal, which attempts to account for observations without a primary dark energy source in
the stress-energy tensor, has been developed and discussed by means of different approaches. Here, we focus on the concept
of cosmological background solutions in order to develop a framework to study different backreaction proposals. 相似文献
36.
The static dielectric properties of (001)(GaAs)(p)/(AlAs)(p) superlattices have been calculated as a function of their period p for 1< or = p < or =12, starting from density-functional theory. The interplay between quantum confinement and local field effects is shown to be crucial. For light polarized in the growth direction it leads to the otherwise surprising justification of the use of a classical effective medium theory, even for the smallest periods. Only the inclusion of both contributions allows in ab initio and in semiempirical calculations to reproduce the experimentally observed birefringence. 相似文献
37.
It has been shown theoretically that a light amplifier working on the physical principle of stimulated emission should achieve optimal quantum cloning of the polarization state of light. We demonstrate close-to-optimal universal quantum cloning of polarization in a standard fiber amplifier for telecom wavelengths. For cloning 1-->2 we find a fidelity of 0.82, the optimal value being 5 / 6=0.83. 相似文献
38.
Marek L. Główka Zbigniew J. Kamiński Gastone Gilli Valerio Bertolasi 《Journal of chemical crystallography》1986,16(4):569-576
C14H17NO4 crystallizes in the monoclinic space groupP21/n (Z=4) witha=10.208(2),b=10.888(2),c=11.909(2) Å, and=90.89(2)°. The structure was solved by direct methods and refined by full-matrix LSQ to anR factor of 0.036. The 4-oxo-1,3-dioxane ring is in a slightly distorted O(1)-sofa conformation flattened at the C(4) end with the 5-isopropyl substituent in a pseudoaxial position and planar lactone group. The molecules form dimers by means of intermolecular N-HO(4) hydrogen bonds of 3.091(2) Å. The1H NMR spectrum of the title compound shows unusual features. 相似文献
39.
Making use of exact results and quantum Monte Carlo data for the entanglement of formation, we show that the ground state of anisotropic two-dimensional S=1/2 antiferromagnets in a uniform field takes the classical-like form of a product state for a particular value and orientation of the field, at which the purely quantum correlations due to entanglement disappear. Analytical expressions for the energy and the form of such states are given, and a novel type of exactly solvable two-dimensional quantum models is therefore singled out. Moreover, we show that the field-induced quantum phase transition present in the models is unambiguously characterized by a cusp minimum in the pairwise-to-global entanglement ratio R, marking the quantum-critical enhancement of multipartite entanglement. 相似文献
40.
We study the thermodynamics of the spin-S two-dimensional quantum Heisenberg antiferromagnet on the square lattice with nearest (J1) and next-nearest (J2) neighbor couplings in its collinear phase (J(2)/J(1)>0.5), using the pure-quantum self-consistent harmonic approximation. Our results show the persistence of a finite-temperature Ising phase transition for every value of the spin, provided that the ratio J(2)/J(1) is greater than a critical value corresponding to the onset of collinear long-range order at zero temperature. We also calculate the spin and temperature dependence of the collinear susceptibility and correlation length, and we discuss our results in light of the experiments on Li2VOSiO4 and related compounds. 相似文献