The relaxation of twist in nematic liquid crystals

A critical twist angle, above which twist can relax homogeneously, has been observed in the liquid crystals MBBA and 5CB. The results suggest that (2K₂₂ ? K₃₃) increases through zero on heating and at T_c becomes equal to K₁₁.     

The cluster analysis technique of pattern recognition: application to the trace metal composition of cardiovascular tissues.

Application of the statistical method of cluster analysis as a pattern recognition technique was investigated by classification of cardiovascular tissues on the basis of their trace metal composition. The distribution patterns of 13 trace metals among 17 tissues of the heart and its appended blood vessels were determined. Cluster analysis of the data resulted in ready differentiation of tissues derived from ordinary and specialized myocardium from those of blood vessels and heart valves. Further similarities and differences among the 17 tissues were identified by comparing the patterns generated when different numbers of groups (i.e., 3, 4, 5, 6, and 7 groups) were designated. It is suggested that cluster analysis may provide a generally useful tool in the interpretation of data from multi-phasic laboratory testing procedures.     

The temperature dependence of the monomer reactivity ratios in the copolymerization of styrene with phenyl and tert-butyl cinnamates

Styrene (M₁) has been copolymerized with the phenyl and tert-butyl esters (M₂) of [carboxyl-¹⁴C]cinnamic acid at temperatures between 40 and 130°, using azoisobutyronitrile as initiator. The compositions of the copolymers have been determined by liquid scintillation counting; since [M₁] ? [M₂], a simplified form of the copolymer composition equation could be used for determining the reactivity ratio r₁ graphically. Arrhenius parameters have been derived; the energies of activation favour cross propagation whereas the frequency factors favour self propagation. Although the latter effect slightly predominates, there is no evidence of significant steric factors; similar behaviour was observed when cinnamic acid and its methyl and ethyl esters were copolymerized with styrene. However, a comparison of the Arrhenius parameters and the Taft substitution constants shows that polar effects, and not steric effects, are responsible for controlling the individual reactivity differences within the ester series.     

Assignment of proton NMR spectra and conformational analysis by two-dimensional heteronuclear relayed correlation NMR spectroscopy

The method of two-dimensional heteronuclear relayed correlation spectroscopy was used to establish the assignment of the severely overcrowded part of the proton spectrum of menthol by relating it to the previously assigned carbon spectrum. Extrapolation of the signal-to-noise ratio obtained with overnight data accumulation on a 10 mM solution suggests that this experiment should be feasible on as little as 10 mg of a moderate-sized organic compound.     

Baryon production by primordial black holes

The evaporation of primordial black holes (PBH's) by the Hawking process can produce an excess of baryons over anti-baryons. Assuming a power-law form of the initial mass spectrum of PBH's and taking into account the observational constraints on that spectrum we calculate the baryon excess produced. We find that if the spectrum is steep ($\text{α?3.5}$) or cut off for masses above ～ 10⁹ g, the observed baryon/photon ratio of ～ 10^?9 can be produced by PBH evaporations.     

Dissipative structures in a soluble non-linear reaction-diffusion system

The steady state solutions of a non-linear reaction diffusion system are evaluated exactly. This bifurcation diagram as well as their stability is discussed.     

Stochastic analysis of a nonequilibrium phase transition: Some exact results

A system involving all-or-none transitions away from equilibrium is considered. Under the assumption of spatially homogeneous fluctuations an integral representation of the solution of the master equation is derived, which permits an exact evaluation of the variance in the thermodynamic limit. A systematic perturbative solution of the master equation is also developed. Both approaches yield “classical” exponents describing the divergence of the second-order variance as the instability point is approached on either side. Finally, at the instability point the second-order variance is shown to diverge as the $\text{3}\text{2}$ power of the volume.     

Potentiometric stripping analysis for manganese(II) in natural waters

Potentiometric stripping analysis (p.s.a.) methods for the measurement of manganese(II) in natural waters are described; batch and flow approaches are discussed. The more versatile flow p.s.a. technique is suitable for concentrations in the range 2 nM–30 μM. Application of these techniques is illustrated by measurements in a variety of natural waters. Interferences arising from manganese—copper interactions in the mercury electrode can be suppressed by the addition of zinc or gallium depending on the concentration of the interfering copper. The relative merits of the batch and flow p.s.a. techniques are discussed.     

A probability model for computer system overhead

Two models for computer system overhead are developed by considering the number of jobs in the system as an immigration-death process. The models developed relate the death rates to the state of the process. The first model uses the total numver of jobs in the system as the state of the processe. The second model classifies the jobs in the system according to the priority classes unsed in the computer system.In the model based on the total number of jobs in the system, the death rate when the system is in the state i, μ_i, is μ_i = μ min(i, x₀) where μ and x₀ are parameters to be estimated by maximum likelihood. In the second model, the death rate for jobs in the k^th priority class when the state of the system is i = (i₁…,i_p), μ_i^(k) is given by $\text{μ}{}_{\mathrm{i}}{}^{\mathrm{(k)}}\text{=μ}{}^{\mathrm{(k)}}\text{i}{}_{\mathrm{k}}\text{min}\text{(1,}\text{x}{}_0\text{i·1}\text{)}$. Computational difficulties in finding the maximum likelihood estimates of the parameters for this model are noted.     

Elastic electron scattering from 40Ar

Cross sections for elastic electron scattering from ⁴⁰Ar have been measured for the momentum transfer range from 0.59 to 1.31 fm^?1. We have analyzed with the Fourier-Bessel ansatz our data as well as the data of former experiments. The rms charge radius we have found is 3.423(14) fm. The results are in excellent agreement with latest muonic data. Furthermore, we have reanalyzed former ⁴⁰Ca data and have discussed the ⁴⁰Ca- ⁴⁰Ar charge distribution.