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51.
Maria S. Vrettou John K. Gallos Demetrios N. Nicolaides 《Journal of heterocyclic chemistry》1988,25(3):813-814
Pyrazino[2,3-b]quinoxaline 1,4-dioxides 3a-e were prepared by reacting Furoxano[3,4-b]quinoxaline with alkynes and alkenes. 相似文献
52.
Bishydroxyiminoquinoxalines 3a-b react with ethyl chloroformate 4 to afford the furazano[3,4-b]quinoxalines 5a-b . Bishydroxyiminobenzoxazines 6a-c on treatment with 4 are converted into the fused oxadiazolones 7a-c and 8a-c along with the bisethoxycarbonyloxyimino-derivatives 9a-c . From the reactions of 4 with the oxanilide dioximes 12a-c compounds 13a-c and 14a-b are obtained. 相似文献
53.
Demetrios Vakratsas 《商业与工业应用随机模型》1998,14(1):85-94
This study suggests that non-monotonic purchase rates, frequently observed in empirical studies of consumer purchase timing, can be an artifact of consumer heterogeneity. We use a theoretical purchase timing model with consumer heterogeneity to develop market scenarios under which non-monotonic rates may obtain. The results suggest that non-monotonic rates are more likely to observe in product markets that are either highly concentrated or where the heavy buyer segment is large. In such markets, therefore, one should not rely on non-monotonic rate curves to predict household purchase incidence. © 1998 John Wiley & Sons, Ltd. 相似文献
54.
55.
Demetrios A. Kappos 《Mathematische Annalen》1947,120(1):43-74
Ohne ZusammenfassungSeinem verehrten Lehrer Prof.C. Carathéodory zum 70. Geburtstag am 13. September 1943 gewidmet. 相似文献
56.
Kostas Kleidis Apostolos Kuiroukidis Demetrios Papadopoulos Loukas Vlahos 《International Journal of Theoretical Physics》2007,46(9):2283-2298
We study the linear magnetohydrodynamic (MHD) equations, both in the Newtonian and the general-relativistic limit, as regards
a viscous magnetized fluid of finite conductivity and discuss instability criteria. In addition, we explore the excitation
of cosmological perturbations in anisotropic spacetimes, in the presence of an ambient magnetic field. Acoustic, electromagnetic
(e/m) and fast-magnetosonic modes, propagating normal to the magnetic field, can be excited, resulting in several implications
of cosmological significance. 相似文献
57.
Photoluminescence of hexagonal boron nitride: Effect of surface oxidation under UV-laser irradiation
We report on the UV laser-induced fluorescence of hexagonal boron nitride (h-BN) following nanosecond laser irradiation under vacuum and in different environments of nitrogen gas and ambient air. The observed fluorescence bands are tentatively ascribed to impurity and mono (VN) or multiple (m-VN with m=2 or 3) nitrogen vacancies. A structured fluorescence band between 300 and 350 nm is assigned to impurity-band transition and its complex lineshape is attributed to phonon replicas. An additional band at 340 nm, assigned to VN vacancies on surface, is observed under vacuum and quenched by adsorbed molecular oxygen. UV-irradiation of h-BN under vacuum results in a broad asymmetric fluorescence at ∼400 nm assigned to m-VN vacancies; further irradiation breaks more B-N bonds enriching the surface with elemental boron. However, no boron deposit appears under irradiation of samples in ambient atmosphere. This effect is explained by oxygen healing of radiation-induced surface defects. Formation of the oxide layer prevents B-N dissociation and preserves the bulk sample stoichiometry. 相似文献
58.
We show that new families of two- and three-dimensional nondiffracting Bessel X waves are possible in linear bidispersive optical systems. These X waves can be observed in both bulk and waveguide configurations as well as in photonic crystal lattices that simultaneously exhibit normal and anomalous dispersive-diffractive properties in different spatial or spatiotemporal coordinates. 相似文献
59.
We investigate the behavior of curves in the space of Riemannian metrics which corresponds to Einstein space-times admitting a Gaussian foliation. Different types of variational principles are formulated and some global dynamical properties of these space-times are obtained.Alexander-von-Humboldt-Fellow. 相似文献
60.
The thin sandwich conjecture in the initial value problem of general relativity is investigated by means of differential geometrical methods, in connection to the definition of arc length in a Wheeler superspace. The conjecture is proved to be false by good physical reasons. Its failure on a flat space is related to the “functional dimension” of the superspace and to the behaviour in the linearized theory of quantum gravitation. 相似文献