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排序方式: 共有470条查询结果,搜索用时 15 毫秒
121.
Wen L Cheng J Zou H Zhang L Chen J Papadopoulos KD 《Langmuir : the ACS journal of surfaces and colloids》2004,20(19):8391-8397
A mathematical model for analyzing the van der Waals interaction between the internal aqueous droplets (W(1)) and the external aqueous phase (W(2)) of double emulsions has been established. The effects of Hamaker constants of the materials forming the system, especially those of the two different adsorbed surfactant layers with uniform density (A(1) and A(2)), on the van der Waals interaction were investigated. The overall van der Waals interaction across the oil film is a combined result of four individual parts, that is, W(1)-W(2), A(1)-A(2), W(1)-A(1), and A(2)-W(2) van der Waals interaction, and it may be either attractive or repulsive depending on many factors. It was found that the overall van der Waals interaction is dominated by the W(1)-W(2) interaction at large separation distances between the W(1)/O and O/W(2) interfaces, while it is mostly determined by the A(1)-A(2) interaction when the two interfaces are extremely close. Specifically, in the cases when the value of the Hamaker constant of the oil phase is intermediate between those of W(1) and W(2) and there is a thick oil film separating the two interfaces, a weak repulsive overall van der Waals interaction will prevail. If the Hamaker constant of the oil phase is intermediate between those of A(1) and A(2) and the two interfaces are very close, the overall van der Waals interaction will be dominated by the strong repulsive A(1)-A(2) interaction. The repulsive van der Waals interaction at such cases helps stabilize the double emulsions. 相似文献
122.
An optical video microscopic technique was used to study hetero-aggregation and selective aggregation phenomena among n-hexadecane oil drops (40–110 μm in diameter) and two types of polystyrene latex particles (6.76 and 30.2 μm, in diameter),
suspended inside an aqueous medium with pH varying between 1.1 and 12.9. A single drop was produced in situ using a micropipette
inside the aqueous phase-filled glass microcapillary (100–160 μm i.d.) containing the particles. Interactions between the
drop and the solid particles and among the solid particles was achieved by movement of the aqueous medium in and out of a
second micropipette. Drop–particle interactions were distinctly different from particle–particle interactions. It was observed
that the latex particles aggregated irreversibly with the oil drop in all cases except two, viz. for 6.76 μm particles at
around neutral pH whereas the irreversibility of aggregation in particle–particle interactions was only seen at the ends of
the pH spectrum. At around neutral pH, the flocs or clusters of small particles were very weak. Visual observations at each
pH are explained on the basis of the classical DLVO (Derjaguin–Landau–Verwey–Overbeek) theory. Partial wetting of particles
surfaces by oil appears to be a key factor in the irreversibility of drop– particle hetero-aggregation. Results indicate that
the display of reversible, irreversible or weak aggregation depends on the location and depth of the secondary minimum and
that the long-range, attractive, London–van der Waals force is responsible for the initial formation of an aggregate.
Received: 4 July 1996 Accepted: 5 December 1996 相似文献
123.
Eleftherios Paul Papadopoulos 《Journal of heterocyclic chemistry》1981,18(3):515-518
Anthranilonitrile reacts with ethyl isocyanatoacetate to form 2-(3-ethoxycarbonylmethylureido)benzonitrile (3b) which, upon heating, or treatment with a base, undergoes a double cyclization to yield imidazo[1,2-c]-quinazoline-2,5-(3H,6H)dione ( 5 ) in excellent yield. In the presence of acid, 3b is converted into 1,4-dihydro-2,4-dioxo-3-(2H)quinazolineacetic acid ( 11 ), or its ethyl ester ( 10 ). The action of concentrated sulfuric acid converts the adduct 13 of anthranilic acid and ethyl isocyanatoacetate into 2-ethoxycarbonyl-methylamino-4H-3,1 -benzoxazin-4-one ( 14 ). 相似文献
124.
能带是决定固体特性的头等重要的因素。我们用光谱方法对单相YBa2Cu2Ox高T。超导体进行了研究,测量了样品的反射-吸收谱、Raman光谱和荧光光谱.其350和500nm吸收带以及390nm,560nm荧光峰来自晶格中Cu+发光中心,是跃迁过程1A1g(3d10)-1Eg和~3Eg(3d94s1)。其720nm和860nm荧光峰来自Cu2+发光中心,是由于自由离子光谱项2D在八面体晶场、正交晶系晶场中分裂为5个能级之间的跃迁。此外,还有一些光谱可能来自晶格中Cu3+发光中心,其481cm-1和551cm-1声子对说明了312cm-1处声子对与电子系统是强耦合。 相似文献
125.
S. G. Raptis S. M. Nasiou I. N. Demetropoulos M. G. Papadopoulos 《Journal of computational chemistry》1998,19(15):1698-1715
The structure–polarization relationship was investigated in a series of polysulfanes, H2Sn. The reported results demonstrate that the forms of change of the polarizability components, αii, and the second hyperpolarizability components, γiiii, as well as the average values α and γ, respectively, of H2Sn with n are similar. This shows that polarizability components can be easily used to determine corresponding hyperpolarizability data. A remarkable change of the hyperpolarizabilities with the molecular geometry of H2Sn was found. This result can be used for the design of nonlinear optical materials with optimum properties. The present study uses the flexible σ bonded H2Sn and is complementary to the works that considered the effect of conformational changes of π-conjugated systems on their hyperpolarizabities. The present computations were performed using the semiempirical approaches MNDO and MNDO/d, as well as ab initio methods with STO-3G, extended with polarization and diffuse functions, and [3s2p/7s5p2d] sets for H2Sn. At the ab initio level, the electronic and the vibrational contributions to polarizabilities and hyperpolarizabilities were both computed for several members of H2Sn. The frequency dependence of the above contributions and the static limit were discussed. Electron correlation was taken into account for several test cases using MP2 theory. The selected methods and the variety of the approximations on which they rely allow the systematic consideration of the effect of changes of the geometry of H2Sn on their polarizabilities and second hyperpolarizabilities. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1698–1715, 1998 相似文献
126.
127.
128.
Spatio-temporal development of the filaments due to the thermal self-focusing instability near the critical surface in ionospheric plasmas 总被引:1,自引:0,他引:1
N. A. Gondarenko P. N. Guzdar G. M. Milikh A. S. Sharma K. Papadopoulos S. L. Ossakow 《Radiophysics and Quantum Electronics》1999,42(7):589-600
We study fully nonlinear spatio-temporal development of the thermal self-focusing instability of high-power radio waves near
the critical surface of the ionosphere. These simulations improve on our earlier work by including an evolution equation for
the density instead of using the assumption of constant pressure to determine the perturbed density connected with the known
temperature perturbation. Using our two-dimensional nonlinear code we analyze the time scale and associated velocity for the
development of the field-aligned irregularities as they spread from the critical surface both in the underdense as well as
the overdense regions. The scaling of this velocity as a function of the radiated power of the heater electromagnetic wave
(ERP) is determined. We also study the characteristic size of the self-focused filament as a function of ERP. Finally, the
spectrum of the density and temperature fluctuations as well as modifications in the equilibrium values of these parameters
for different values of ERP are presented.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 7, pp. 670–681, July 1999. 相似文献
129.
This paper has two parts. In the first part, we study shift coordinates on a sphere S equipped with three distinguished points and a triangulation whose vertices are the distinguished points. These coordinates
parametrize a space
(S)\widetilde{{\cal T}}(S)
that we call an unfolded Teichmüller space. This space contains Teichmüller spaces of the sphere with
\frak b{\frak b}
boundary components and
\frak p{\frak p}
cusps (which we call generalized pairs of pants), for all possible values of
\frak b{\frak b}
and
\frak p{\frak p}
satisfying
\frak b+\frak p=3{\frak b}+{\frak p}=3
. The parametrization of
[(T)\tilde](S)\widetilde{{\cal T}}(S)
by shift coordinates equips this space with a natural polyhedral structure, which we describe more precisely as a cone over
an octahedron in
\Bbb R3{\Bbb {R}}^3
. Each cone over a simplex of this octahedron is interpreted as a Teichmüller space of the sphere with
\frak b{\frak b}
boundary components and
\frak p{\frak p}
cusps, for fixed
\frak b{\frak b}
and
\frak p{\frak p}
, the sphere being furthermore equipped with an orientation on each boundary component. There is a natural linear action of
a finite group on
[(T)\tilde](S)\widetilde{{\cal T}}(S)
whose quotient is an augmented Teichmüller space in the usual sense. We describe several aspects of the geometry of the space
[(T)\tilde](S)\widetilde{{\cal T}}(S)
. Stretch lines and earthquakes can be defined on this space. In the second part of the paper, we use the shift coordinates
to obtain estimates on the behaviour of stretch lines in the Teichmüller space of a surface obtained by gluing hyperbolic
pairs of pants. We also use the shift coordinates to give formulae that express stretch lines in terms of Fenchel-Nielsen
coordinates. We deduce the disjointness of some stretch lines in Teichmüller space. We study in more detail the case of a
closed surface of genus 2. 相似文献
130.
E. N. Argyres G. Katsilieris O. Korakianitis C. G. Papadopoulos C. Philippides W. J. Stirling 《Physics letters. [Part B]》1992,280(3-4):324-328
The reaction pp→W±γγX is considered at centre-of-mass energies √s = 16 and 40 TeV, including anomalous three- and four- gauge-boson couplings κ and λ. Limits are obtained on these quantities by comparison with the standard model. 相似文献