[en] We present a method for extracting tunnelling amplitudes from perturbation expansions which are always divergent and not Borel-summable. We show that they can be evaluated by an analytic continuation of variational perturbation theory. The power of the method is illustrated by calculating the imaginary parts of the partition function of the anharmonic oscillator in zero spacetime dimensions and of the ground state energy of the anharmonic oscillator for all negative values of the coupling constant g and show that they are in excellent agreement with the exactly known values. As a highlight of the theory we recover from the divergent perturbation expansion of the tunnelling amplitude the action of the instanton and the effects of higher loop fluctuations around it

[en] Neuroblastoma x glioma hybrid cells were generated by cell fusion of the 6-thioguanine-resistant clonal mouse neuroblastoma cells and the bromodeoxyuridine-resistant rat glioma cells, selection, and cloning. Every characteristics generally ascribed to neurons has been observed with the hybrid cells. The paper explores the morphological differentiation of hybrid cells, procedures for testing the hormonal regulation of intracellular levels of cyclic, [³H]AMP in hybrid cells, hormonal regulation of adenylate cyclase in homogenates of hyrbid cells, intracellular levels of cyclic GMP, and uptake of guanidinium ions in hybrid cells

[en] It is shown that slowly and smoothly decreasing hadron form factors (e.g. of the dipole type) are inconsistent with a confining quark potential in nonrelativistic quark models. Relativistic effects are able to remedy the situation. This is shown by presenting a quasi-relativistic quark model based on a specific assumption about the approximate behaviour of the gluon cloud amounting to a model of dressed quarks with momentum-independent energies, but with no additional gluons. The large anomalous magnetic moment of the proton can only be understood when all three quarks are treated on equal footing as in the bag model, ruling out the quark-diquark hypothesis

[en] We present a method for evaluating divergent series with factorially growing coefficients of equal sign. The method is based on an analytic continuation of variational perturbation theory from the regime of alternating signs. We demonstrate its power first by applying it to the exactly known partition function of the anharmonic oscillator in zero space-time dimensions (the simple integral). Then we consider the quantum-mechanical case of one space-time dimension and derive the imaginary part of the ground-state energy of the anharmonic oscillator for all negative values of the coupling constant g, including the non-analytic tunnelling regime at small -g. As a highlight of the theory we extract, from the divergent perturbation expansion, the action of the critical bubble and the contribution of the higher loop fluctuations around the bubble. (Some figures in this article are in colour only in the electronic version.)

[en] We show that in applications of variational theory to quantum field theory it is essential to account for the correct Wegner exponent ω governing the approach to the strong coupling, or scaling, limit. Otherwise the procedure does not converge at all or to the wrong limit. This casts doubt on all papers applying the so-called δ expansion to quantum field theory

[en] We set up and solve a recursion relation for all even moments of a two-dimensional stiff polymer (Porod-Kratky wormlike chain) and determine from these moments a simple analytic expression for the end-to-end distribution applicable for all persistence lengths