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1.
A. A. F. Wasfy M. S. Amine M. M. H. Arief S. G. Donia A. A. Aly 《Phosphorus, sulfur, and silicon and the related elements》2013,188(5):1359-1368
4-(5,5-Dioxodibenzothiophen-2-yl)-4-oxo-2-butenoic acid ( 1 ) was condensed with compounds containing active methylene groups under Michael reaction conditions to form the Michael adducts 2a-c , 3a-c , and 4a-b . The behavior of Michael adduct towards the action of hydrazine hydrate was investigated. The compounds were tested for biological properties. 相似文献
2.
Soher S. Maigali Mohamed H. Arief Marwa EL-Hussieny Fouad M. Soliman 《Phosphorus, sulfur, and silicon and the related elements》2013,188(2):190-204
Abstract The reaction of nucleophilic phosphacumulene ylides with visnaginone and khellinone afforded the corresponding phosphanylidene and furochromene derivatives. Moreover, pyranochromenes were obtained from the reaction of chromene carbaldehydes with phosphacumulenes. On the other hand, the phosphanylidene-cyclobutylidenes and their dimers were produced from the reaction of furochromene carbaldehydes with the same phosphonium reagents. 相似文献
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Road signs must provide a conspicuous signal to a wide variety of drivers over a broad range of environmental and geometric
conditions. Recently, there are an increasing number of applications in which light emitting diodes (LEDs) are used as the
light source, including critical transportation signaling. In the presence of fog, the resulting visual signal is disturbed
due to light scattering by airborne water droplets. By measuring LED brightness with human spectral sensitivity in various
densities and various droplet sizes (10, 30, 50, and 100 μm), it is understood that the particle size distribution (fog droplet
size) and density of fog does affect visibility in fog. The colored LEDs that contain a yellow component had high brightness
evaluation, blue component had low brightness evaluation in all densities and different droplet sizes. The result in this
paper can contribute to air and land traffic safety and the prevention of accidents. 相似文献
5.
New two-dimensional (2D) bismuth and three-dimensional (3D) lead based coordination polymers containing pyridine-2,5-dicarboxylate ligands (H(2)pydc) have been synthesized hydrothermally and characterized by single crystal X-ray diffraction. Bi(3)(μ(3)-O)(2)(pydc)(2)(Hpydc)(H(2)O)(2) (1), which crystallizes in the space group P1? (a = 8.7256(5) ?, b = 11.1217(7) ?, c = 14.0933(9) ?, α = 85.239(1)°, β = 98.582(1)°, γ = 71.106(1)°), has a 3D structure that contains Bi(6)O(4) clusters that connect into 2D sheets via linking ligands. The sheets form a 3D supramolecular structure via hydrogen bonding along the z-axis. Pb(pydc)(H(2)O) (2), which crystallizes in the space group P2(1)/c (a = 10.8343(14) ?, b = 11.2099(15) ?, c = 6.6573(9) ?, β = 90.697(2)°), contains 1D chains of corner-sharing distorted face capped trigonal prisms that are connected into a 3D framework via the pydc ligand. In addition, the ligands are hydrogen bonded to each other. Both 1 and 2 are single component "white" light emitting phosphors and are shown to exhibit "white" luminescence that covers a much wider spectral range than is observed for the as received H(2)pydc ligand. 相似文献
6.
M. Budiman E. M. Hsu H. K. Haugen G. A. Botton 《Applied Physics A: Materials Science & Processing》2010,98(4):849-853
Bulk irradiation of crystalline α-quartz was performed with ∼170-fs laser pulses with a wavelength of 800 nm focused below the sample surface. Investigations
were carried out using transmission electron microscopy on a cross-sectional specimen prepared using focused ion beam techniques.
We observed alternating amorphous–crystalline structures with sharp transitions and associated density changes, surrounded
by a highly strained crystalline structure. The alternating sub-surface structures are parallel to the laser’s electric field
polarization and exhibit a spacing which is close to the laser wavelength in air. Cracking was also observed in the near proximity
of these structures. 相似文献
7.
The ordered double-perovskites Sr(2)MOsO(6) (M = Cu, Ni) consisting of 3d and 5d transition-metal magnetic ions (M(2+) and Os(6+), respectively) are magnetic insulators; the magnetic susceptibilities of Sr(2)CuOsO(6) and Sr(2)NiOsO(6) obey the Curie-Weiss law with dominant antiferromagnetic and ferromagnetic interactions, respectively, and the zero-field-cooled and field-cooled susceptibility curves of both compounds diverge below ~20 K. In contrast, the available density functional studies predicted both Sr(2)CuOsO(6) and Sr(2)NiOsO(6) to be metals. We resolved this discrepancy on the basis of systematic density functional calculations. The magnetic insulating states of Sr(2)MOsO(6) are found only when a substantially large on-site repulsion is employed for the Os atom, although it is a 5d element. The cause for the divergence between the zero-field-cooled and field-cooled susceptibility curves in both compounds and the reason for the difference in their dominant magnetic interactions were investigated by examining their spin exchange interactions. 相似文献
8.
苏本堂 《数学物理学报(A辑)》1999,(Z1)
设a<b是整数,G=(V(G),E(G))是一个图.G的一个支撑子图F称为G的一个[a,b]-因子,若对任意的υ∈EV(G),有a≤d_F(υ)≤b.本文得到了下列结果:设1≤a≤b是整数,G是一个阶为n的图,最小度δ(G)≥a且>(a+b)(2a+2b-3)如果对于G的任意两个不相邻的顶点u,υ有N_G(u)UN_G(υ)≥an,则G有一个[a,b]-因子. 相似文献
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ABSTRACT Design of structures using a variety of two-dimensional finite elements is considered in this paper. An efficient technique of computing first-order derivatives of pointwise stress constraints for simple and higher-order two-dimensional (membrane) finite elements is presented. Computational aspects of design sensitivity vector calculation, using a semi-analytical method versus traditional methods are presented. Implementation of a fully-stressed design approach to find a suitable initial estimate leads to increased computational efficiency. These aspects of the design procedure are illustrated through analysis of numerical examples. Experience indicates that a suitable mix of low and higher-order elements yields the most efficient and accurate design model. 相似文献
10.
Water imbibition during the waterflooding process of oil production only sweeps part of the oil present. After water disrupts
the oil continuity, most oil blobs are trapped in porous rock by capillary forces. Developing an efficient waterflooding scheme
is a difficult task; therefore, an understanding of the oil trapping mechanism in porous rock is necessary from a microscopic
viewpoint. The development of microfocused X-ray CT scanner technology enables the three-dimensional visualization of multiphase
phenomena in a pore-scale. We scanned packed glass beads filled with a nonwetting phase (NWP) and injected wetting phase (WP)
in upward and downward injections to determine the microscopic mechanism of immiscible displacement in porous media and the
effects of buoyancy forces. We observed the imbibition phenomena for small capillary numbers to understand the spontaneous
imbibition mechanism in oil recovery. This study is one of the first attempts to use a microfocused X-ray CT scanner for observing
the imbibition and trapping mechanisms. The trapping mechanism in spontaneous imbibition is determined by the pore configuration
causing imbibition speed differences in each channel; these differences can disrupt the oil continuity. Gravity plays an important
role in spontaneous imbibition. In upward injection, the WP flows evenly and oil is trapped in single or small clusters of
pores. In downward injection, the fingering phenomena determine the amount of trapped oil, which is usually in a network scale.
Water breakthrough causes dramatic decrease in the oil extraction rate, resulting in lower oil production efficiency. 相似文献