Pure liquids described as concentrated cluster dispersions

The Fulcher-Tammann-Hesse-Vogel equation, ln = A + B/(T – T ₀ ), is shown to be equivalent to the general viscosity-composition relationship, ln _r =k f /(1 – f ), for binary mixtures. The Cailletet-Mathias law of the Rectilinear Diameter is rearranged to represent a density mixture formula for two components. Temperature-independent viscosities and densities can then be calculated for dense, solid cluster fractions, dispersed in a low-density, low-viscosity non-clustered continuous phase. The cluster fraction decreases with temperature. The value ofT ₀ is shown to be related to the liquid- or solid-like behavior of the clusters. For liquids with a vapor pressure < 1 mm Hg at the melting point, the calculated cluster volume fraction suggests close packing of clusters, ranging in shape from monodisperse spheres to polydisperse non-spherical particles. Examples are given for molecular liquids, molten metals, and molten salts. The size of the clusters is estimated from the heat of evaporation.     

A stereoselective synthesis of 9-(3-O-benzyl-5-O-tetrahydropyranyl-β-d-arabinofuranosyl)adenine, a potentially useful intermediate for ribonucleoside synthesis

A novel synthesis for preparing 9-(3-O-benzyl-5-O-tetrahydropyranyl-β-d-arabinofuranosyl)adenine (6) has been developed which does not require sub zero temperatures or exotic reagents. A key step in this synthesis is the selective protection of the 3′-OH of ara-A with a benzyl group. The 5′-OH is then selectively protected with DHP to yield 6, a potentially useful intermediate. A synthesis of 9-(2,3-dideoxy-2-fluoro-β-d-threo-pentofuranosyl)adenine (1, FddA), an anti-viral compound, is given to illustrate the utility of this new approach.     

Magnetoelectric effect in cobalt ferrite-barium titanate composites and their electrical properties

CoFe₂O₄-BaTiO₃ composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ɛ′) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac conductivity was derived from dielectric constant (ɛ′) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric conversion factor has been studied as a function of magnetic field.     

Vortices in time-periodic shear flow

Vortices emerging in geophysical turbulence may experience deformations due to the non-uniform ambient flow induced by neighbouring vortices. At first approximation this ambient flow is modeled by a linear shear flow. It is well known from previous studies that the vortex may be (partially) destructed through removal of weak vorticity at the vortex edge—a process referred to as ‘stripping’. While most previous studies considered a stationary external shear flow, we have examined the behaviour of the vortex embedded in a linear shear flow whose strength changes harmonically in time. Aspects of the vortex dynamics and the (chaotic) transport of tracers have been studied by both laboratory experiments and numerical simulations based on a simple kinematical model.     

General viscosity-composition relationship for dispersions,solutions and binary liquid systems

An equation for the viscosity of a mixture of two imaginary Newtonian liquids is derived. In the derivation the mathematical assumption is used that the effective activation energy for viscous flow of a binary liquid mixture is a linear combination of the reciprocals of the activation energy of the components. It contains two dependent fitting constants and has the same structure as the Mooney equation for dispersions of spherical solid particles, the Huggins equation for polymer solutions and is identical to an equation by Hoffmann and Rother, when written in the variables that the last authors used.As a consequence it can be shown that the viscosity of binary liquid mixtures, liquid resion solutions, dispersions of solid spherical particles and polymer solutions can be described very well by one and the same equation, up to the highest concentrations.It has further been found that the viscosity of dispersions of non-spherical particles, solutions of solids in organic solvents and solutions of electrolytes and non-electrolytes in water can also be described by this formula. The equation permits the construction of a straight line on which all liquids can be plotted.An algebraic analysis of the equation shows that each series of viscosity composition data can be placed in one of three rheological groups independent of the type of fraction that is used to characterize the composition.Seventy-four binary systems, covering a wide range of liquids have been used to show the applicability of the developed equation.It has been found that in most cases the data are best described by splitting them into two regions, each with its own set of dependent constants. General symbol for the fraction or concentration of the component with the higher viscosity determining the composition of a binary mixture [—] - _v Volume fraction of the component with the higher viscosity [—] - _w Weight fraction of the component with the higher viscosity [—] - _mw Molecular weight fraction of the component with the higher viscosity [—] - c Concentration of the component with the higher viscosity [g/cm³] - E ₂,E ₁,E Activation energy for viscous flow referring to the component with the higher viscosity, the lower viscosity and the viscosity of the binary mixtures, respectively [J] - ₂, ₁, Experimental parameter (with the dimension of energy) referring to the component with the higher viscosity, the component with the lower viscosity and to the binary mixtures, respectively [J] - ₁, ₂ Viscosity of the component with the lower and the higher viscosity, respectively [Pa · s] - Viscosity of a binary mixture [Pa · s] - [] The usual intrinsic viscosity of the component with the highest viscosity [cm³/g] - _r / ₁ [—] - _{sp r} – 1 [—] - [] -intrinsic viscosity [—] - [] _v Volume intrinsic viscosity [—] - [] _w Weight intrinsic viscosity [—] - [] _c Concentration intrinsic viscosity, identical to [] [cm³/g] - T _e Temperature at which the two liquids have the same viscosity [K] - _e Viscosity at temperatureT _e [Pa · s] - P ₁,P ₂ Density of the component with the lower and the higher viscosity, respectively - R Gas constant [J · Mol^–1 · K^–1]     

The onset of coulomb explosions in polyatomic molecules

With the development of high intensity femtosecond lasers, the ionisation and dissociation dynamics of molecules has become an area of considerable interest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and benzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 nm). Results are presented and contrasted for laser beam intensities around 10(15) and 10(16) W cm(-2). For the lower intensities, the mass spectra yield dominant singly charged parent ions. Additionally, the appearance of doubly charged parent ions is evident for carbon disulphide, toluene and benzaldehyde with envelopes of doubly charged satellite species existing in these local regions. Carbon disulphide also reveals a small triply charged component. Such atomic-like features are thought to be a strong fingerprint of FLMS at these intensities. However, upon increasing the laser intensity to approximately 10(16) W cm(-2), parent ion dominance decreases and the appearance of multiply charged atomic species occurs, particularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly ionised parent species which can subsequently blow apart. Copyright 1999 John Wiley & Sons, Ltd.