A study of the 220 MHz proton resonance spectra for a series of biologically important acridine-type heterocycles

The high resolution proton magnetic resonance spectra of acridine, phenazine, phenoxazine and phenothiazine have been measured at 220 MHz in various solvents and at several temperatures. Spectra for all four molecules were analyzed iteratively and good agreement was obtained between observed and calculated spectra. Significant differences are noted between the coupling constants and chemical shifts of acridine and phenazine on the one hand and phenoxazine and phenothiazine on the other. These differences are attributed to a nonplanar heterocyclic ring conformation for phenoxazine and phenothiazine in solution. Moreover, it is concluded from the temperature measurements that the heterocyclic rings of phenoxazine and phenothiazine are conformationally flexible in the range covered. Possible mechanisms are suggested for the chemical shift and coupling constant changes.     

Space charge regions at silver halide surfaces: Experimental results for undoped AgCl

Vibrating capacitor measurements have been made of the variation with temperature of the surface potential of AgCl single crystals of surface orientation (100), (210), (110) and (111). The magnitude and temperature variation of the surface potential was found to be strongly dependent on the orientation of the free surface. The data are interpreted in terms of a model which attributes the existence of surface space charge potentials to differences in the binding energies of silver ions at surface sites relative to normal interior lattice sites. The results are summarized in terms of the Gibbs free energies ΔG_v^(hkl) for cation vacancy formation and give ΔG_v⁽¹¹⁰⁾ = + 0.01 eV + 5 kT, ΔG_v⁽¹⁰⁰⁾ = ? 0.2eV + 10 kT, ΔG_v⁽²¹⁰⁾ = = ? 0.8eV + 23kT, ΔG_v⁽¹¹¹⁾ = + 0.8 eV ? 20kT. These numbers have large absolute uncertainties but the relative values for the different orientations are reliable. The values of ΔG_v^hkl can be used to calculate the magnitude and sign of the surface space charge fields and allow some predictions on the formation of photographic latent images near free surfaces.     

The Reissner–Sagoci Problem for a Non-homogeneous Half-space with a Surface Constraint

This paper deals with the problem of twisting a non-homogeneous, isotropic, half-space by rotating a circular part of its boundary surface (0 r < a, z = 0) through a given angle. A ring (a < r < b, z = 0) outside the circle is stress-free and the remaining part (r > b, z = 0) is rigidly clamped. The shear modulus is assumed to vary with the cylindrical coordinates, r, z by the relation (z) = ₁(c + z), c 0 where ₁, c and are real constants. Expressions for some quantities of physical importance, such as torque applied at the surface of the disk and stress intensity factors, are obtained. The effects of non-homogeneity on torque and stress intensity factor are illustrated graphically.     

Integrated photoelasticity for axisymmetric problems

A new nondestructive method for analyzing axisymmetric problems is presented. The method uses the integrated optical effects through the whole transverse section of the body, along with the strain-displacement and equilibrium equations to give the separate internal stresses on that section. The method is reasonably general and may be applied to thermoelastic and residual stress problems. Some experimental results are presented and discussed.     

17O NMR spectroscopy of nucleoside derivatives; bonding characteristics of pyrimidine carbonyls

Various uridine derivatives have been selectively enriched (≈ 50%) at the 04 and 02 oxygens, and the ¹⁷O chemical shifts and linewidths measured. The chemical shifts, which are primarily dependent on π-bond-order and hydrogen bonding, show effects that are selective for the 02 and 04 oxygens. In particular, significantly more H-bonding to D₂O and higher π bond order are found for the 04 oxygen.     

Simulation of droplet formation and coalescence using lattice Boltzmann-based single-phase model

A lattice Boltzmann method-based single-phase free surface model is developed to study the interfacial dynamics of coalescence, droplet formation and detachment phenomena related to surface tension and wetting effects. Compared with the conventional multiphase models, the lattice Boltzmann-based single-phase model has a higher computational efficiency since it is not necessary to simulate the motion of the gas phase. A perturbation, which is given in the same fashion as the perturbation step in Gunstensen's color model, is added to the distribution functions of the interface cells for incorporating the surface tension into the single-phase model. The assignment of different mass gradients along the fluid-wall interface is used to model the wetting properties of the solid surface. Implementations of the model are demonstrated for simulating the processes of the droplet coalescence, the droplet formation and detachment from ceiling and from nozzles with different shapes and different wall wetting properties.