van der Waals interaction between internal aqueous droplets and the external aqueous phase in double emulsions

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.     

Visual microscopic studies on hetero-aggregation and selective aggregation

 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     

Reactions of o-aminonitriles with isocyanates. 2. A facile synthesis of imidazo[1,2-c]quinazoline-2,5-(3H,6H)dione

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 ).     

YBa2Cu3Ox超导体的光谱研究

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YBa₂Cu₂O_x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¹A_1g(3d¹⁰)-¹E_g和~3E_g(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。     

Static and frequency dependent polarizabilities and hyperpolarizabilities of H2Sn

The structure–polarization relationship was investigated in a series of polysulfanes, H₂S_n. The reported results demonstrate that the forms of change of the polarizability components, α_ii, and the second hyperpolarizability components, γ_iiii, as well as the average values α and γ, respectively, of H₂S_n 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 H₂S_n 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 H₂S_n 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 H₂S_n. At the ab initio level, the electronic and the vibrational contributions to polarizabilities and hyperpolarizabilities were both computed for several members of H₂S_n. 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 H₂S_n on their polarizabilities and second hyperpolarizabilities. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1698–1715, 1998     

相对论性核与乳胶(Ag)碰撞中灰粒子的系统研究 *

用描写相对论性核 核碰撞的LUCIAE模型和相应的事件产生器系统地研究了 1 4.6 ,6 0和 2 0 0AGeV的O核、2 0 0AGeV的Si和S核以及 1 1 .6AGeV的Au核与乳胶 (Ag)碰撞中灰粒子产生的平均多重数、多重数分布以及角分布 3个物理量同入射能量、射弹质量及碰撞中心度间的关系 ,还研究了再散射在灰粒子产生机制中的作用 .LUCIAE的这些研究结果与相应的EMU0 1乳胶实验结果都相一致 .     

算术级数中的陈景润定理 *

设N为一充分大的偶数且q≥ 1 ,(l_i,q) =1 (i=1 ,2 ) ,l₁+l₂ ≡N(modq) .证明了方程N =p+P₂ ,p≡l1(modq) ,P₂ ≡l₂ (modq)对区间 1 ,N^1/37中除了ON^1/37log^-5 N个例外的整数q ,都有无穷多解 ,其中p是素数 ,P₂ 为一至多有2个素因子的殆素数 .     

Spatio-temporal development of the filaments due to the thermal self-focusing instability near the critical surface in ionospheric plasmas

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.     

Shift coordinates, stretch lines and polyhedral structures for Teichmüller space

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.     

Wγγ production as a test of three- and four-gauge-boson couplings at LHC and SSC

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.