Geometrical and energetical feasibility of a highly extended chain conformation for isotactic polystyrene

Highly extended, four-atom helices with $\text{h = 5.1}\text{A}\text{?}$ and t = 60° are geometrically feasible for a vinyl polymer. The energetical feasibility for the case of isotactic polystyrene (in crystalline gels) is discussed on the basis of appropriate conformational maps.     

Fast local intensity fluctuations in a pulsed untuned dye laser

Intensity fluctuations in a pulsed dye laser are studied. Fluctuations are local and very fast. The onset of the fluctuating regime coincides with the laser threshold. The average Fourier spectrum of fluctuations shows three broad peaks at frequencies v ₁=55 MHz, v ₂=110 MHz, v ₃=165 MHz. The three frequencies remain unchanged when resonator geometrical and optical parameters are changed. Nevertheless the amplitude of fluctuations is easily affected by such changes and by the solution temperature. The application of the Grassberger-Procaccia algorithm to the experimental fluctuations gives slope convergence (between 3 and 5) in some cases. This seems to indicate that the origin of fluctuations is chaotic-deterministic.     

EPR characterization of new phosphavinyl σ radicals

A number of radicals have been added to 1,3-bis(2,4,6-tri-tert-butylphenyl)diphospha-allene at low temperature in cyclopropane solution. Addition of thiyl and alkoxyl radicals occurs regiospecifically to one of the phosphorus atoms leading to new phosphavinyl radicals, isoelectronic with vinyl radicals, which have been characterised by means of EPR spectroscopy. The results of ab initio calculations are in agreement with the experimentally determined spectral parameters and suggest that these radicals are bent, with a PCP bond angle of ca. 150°. In contrast, silyl and germyl radicals appear to add to the carbon atom of the phosphaallene.     

Statistical mechanics results in the P(φ)2 quantum field theory

We apply ideas and methods from classical statistical mechanics to study the P(φ)₂ self-coupled two-dimensional Boson field theory in the Euclidean region. In particular, we consider correlation inequalities of Griffiths type; the thermodynamic limit for the pressure, the average interaction and the entropy; and the equilibrium equations for states associated with a given interaction.     

The sign of the electron exchange interaction in binuclear vanadyl tartrate

An analysis of the asymmetric line broadening in the solution electron resonance spectrum of vanadyl tartrate demonstrates that the exchange interaction is positive. The separation between the two vanadyl units is shown to increase slightly when the complex passes from a solid to a fluid solution.     

Importance of longitudinal contributions to backward inelastic electron scattering

Coulomb contributions of multipolarity 2 are calculated for backward (θ = 180°) inelastic electron scattering by our improved DWBA code. General features are studied such as nuclear charge (Z) dependence, energy transfer dependence, momentum transfer dependence as well as the angle dependence near θ = 180°, with the help of a simple model for the transition charge density. We compare these features with PWBA and other simple approximations. We show, as a specific example, that the C2 contribution is comparable to the M1 and E2 multipole form factors for inelastic scattering to the rotational excited states of ¹⁸¹Ta.     

Test of three-body contact Skyrme forces with spin excitations in deformed nuclei

Experimental data on spin M1 strength distributions in even-even rare-earth nuclei are compared to theoretical results of selfconsistent HF+RPA calculations with separable spin-spin residual interactions derived from the two alternative versions (two-body density-dependent and three-body contact terms) of the Skyrme force Sk3. It is shown that the two versions produce quite different spin M1 strength distributions, though they generate the same HF mean field. The experimental data favour the two-body over the three-body version of the Skyrme interactions Sk1–Sk6.     

The pion form factor at a timelike momentum transfer of approximately 1 fm from π electroproduction at threshold

From an extrapolation of threshold π⁺ electroproduction data combined with a kinematical constraint at an unphysical point, we derive the value of the pion form factor at a time-like value of the momentum transfer k²_π 1 fm⁻². The result is F_π(k²_π) = 1.19 ± 0.1. From this value, using a twice subtracted dispersion relation, we obtain r_π 0.98 ± 0.24 fm.