Stress relaxation of a polymer solution in double-step shear deformations: A separate evaluation of the stress components due to entangled segments of different orientations

When two shear deformations γ₁ and γ₂ are successively applied to an entangled polymeric system, a composite temporary network is formed. In this article a simple method is proposed for evaluating separately the contributions from the component networks of different deformations, γ₁ + γ₂ and γ₂, to the observed shear and normal stresses. The method is applied to literature data for a polystyrene solution. It is revealed that the entangled chain segments formed between the applications of two deformations relax very rapidly, while those formed prior to the first deformation do not relax for quite a long time. The result is in accord with the conjecture based on the tube model of entanglement that the chain ends lose their orientation as the chain creeps out of an oriented tube.     

Stochastic approach to nuclear shell model

We propose a Quantum Monte Carlo diagonalization method for solving the quantum many-body interacting systems. Not only the ground state but also low-lying excited states are obtained with their wave functions. Consequently the level structure of low-lying states can be studied with realistic interactions. After testing this method with⁴⁸Cr, we report that the doubly closed shell probability of⁵⁶Ni is shown to be only 53% in a full pf shell calculation, in contrast to the corresponding probability of⁴⁸Ca which reaches 86%. The most recent results on³²Mg are presented. Presented by T. Otsuka at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September 1–5, 1997. This work was supported in part by Grant-in-Aid for Scientific Research (B) (No. 08454058) from the Ministry of Education, Science and Culture.     

Chemoselective electrolytic chlorination of methyl group of 3-methyl-3-butenoate moiety of thiazoline-azetidinone homologues

Chemoselective electrochlorination of the methyl group on the 3-methyl-3-butenoate moiety of thiazoline-azetidinone derivatives derived from penicillins G and V has been performed in a CH₂Cl₂-H₂O-NaCl-H₂SO₄-(Pt or C electrodes) system by adjusting the amount of electricity passed as well as the concentration of Cl^? in the media.     

Relaxation of shear and normal stresses in step-shear deformation of a polystyrene solution. Comparison with the predictions of the Doi–Edwards theory

The shear stress σ, two components of birefringence, and extinction angle were measured for a concentrated polystyrene solution in step-shear deformation of magnitude of shear 0.3 ≤ γ ≤ 4.0. The stress-optical coefficient did not depend on either γ or time. The first and the second normal-stress differences v₁ and v₂ were evaluated with the use of the stress-optical law. Over a certain range of long times, σ could be factored as σ = γh(γ)G(t) and the quantity h(γ) agreed with the prediction of the Doi–Edwards theory based on the de Gennes tube model of entangled polymer chains. At short times the effect of γ on σ/γ was smaller than at long times. The relaxation spectrum became approximately independent of γ at the short-time end of the rubbery plateau region. The ratios v₁/σ and v₂/v₁ were independent of time and were in quantitative agreement with those predicted by the Doi–Edwards theory: v₁/σ was equal to γ, v₂/v₁ was negative, and |v₂/v₁| decreased with increasing γ.     

Rotational effect in the ionization of a highly excited atom by collision with a polar molecule

If the collisional ionization is chiefly due to energy transfer from the polar-molecule rotation to an electron in a high Rydberg state of the atom, then theory predicts that the cross section averaged over a thermal distribution of rotational states should show step-like structure as a function of the energy of the Rydberg state. This structure has been experimentally detected, and it can be considered as direct evidence of the rotational effect in the collisional ionization.     

Heat capacity of a five-coordinated ferromagnet,chloro bis(N,N-diethyldithiocarbamato)iron(III), in the temperature range from 0.4 to 20 K

The heat capacity of polycrystalline Fe[S₂CN(C₂H₅)₂]₂Cl has been measured in the temperature range from 0.411 to 19.55 K. The transition between ferromagnetic and paramagnetic states is characterized by a sharp λ-type anomaly centered at the Curie temperature, T_c = 2.412 ± 0.008 K. The enthalpy and the entropy of transition are 40.475 J mol^?1 and 11.199 J K^?1mol^?1 (= 1.347 R), respectively. The transition entropy is only 2.81% smaller than R In 4. This fact ascertains that the spin manifold is really a quartet. The ground spin states of the present compound are characterized by a zero-field splitting of the $\text{S =}\text{3}\text{2}$ state into two Kramers' doublets. The overlapping non-cooperative Schottky-type anomaly due to the energy separation between the two Kramers' doublets is separated tentatively from the cooperative heat capacity due to the exchange interaction. Based on a careful analysis of the transition entropy it may be concluded that the magnetic structure of the present complex would be a two-dimensional triangular Ising lattice. The exchange and the Curie-Weiss constants are also determined to be 0.155 and 4.19 K, respectively.     

Excluded volume effect of linear polymer molecules

An approximate closed expression for the excluded volume effect of linear polymer molecules is developed with the aid of a uniform expansion model of perturbed chains. The linear expansion factor α for the end-to-end distance is given by (α³ ? 1) + (3/8) (α⁵ ? α³) = (5/2)z where z is the excluded volume parameter. This equation is numerically close to the Ptitsyn equation in the ordinary range of α; i.e., for 1 ≤ α ≤ 2.