An empirical formula for the electron-impact ionization cross-section

An empirical formula with three free parameters is given for the representation of cross-sections for single ionization of atoms and ions from the ground state by electron-impact. Almost all experimental results can be approximated by this formula within 10% over the whole energy range between threshold and 10 keV; all experimental results can be approximated within experimental error. The formula proposed is not suitable to reproduce the exact contour of fine structures in the ionization cross-section curve.     

Electron-impact ionization cross-sections and ionization rate coefficients for atoms and ions from scandium to zinc

Using the empirical formula recently proposed, electron-impact ionization cross-sections for single ionization from the ground state are given for free atoms and for nearly all ionization stages from scandium (Z=21) to zinc (Z=30). For these species ionization rate coefficients are given under the assumption of a Maxwellian distribution of the impacting electrons. Multiple ionization, lowering of ionization potential, or collision limit are not taken into account.     

Counting Complexity Classes for Numeric Computations. III: Complex Projective Sets

In [8] counting complexity classes #P_R and #P_C in the Blum-Shub-Smale (BSS) setting of computations over the real and complex numbers, respectively, were introduced. One of the main results of [8] is that the problem to compute the Euler characteristic of a semialgebraic set is complete in the class FP_R^#PR. In this paper, we prove that the corresponding result is true over C, namely that the computation of the Euler characteristic of an affine or projective complex variety is complete in the class FP_C^#PC. We also obtain a corresponding completeness result for the Turing model.     

Polyethylene–isotactic polypropylene epitaxy: Analysis of the diffraction patterns of oriented biphasic blends

Diffraction patterns of oriented blends of isotactic polypropylene (iPP) and polyethylene (PE) published recently by several authors are analyzed on the basis of a unique epitaxial relationship between the iPP and PE crystal lattices. The contact planes are (100)_PE and (010)_iPP, and the PE chains lie at 50° to the iPP chain axis, parallel to the helical path of the iPP helices, which is formed by rows of side-group methyls.     

Modification of the omega-meson lifetime in nuclear matter

Information on hadron properties in the nuclear medium has been derived from the photoproduction of omega mesons on the nuclei C, Ca, Nb, and Pb using the Crystal Barrel/TAPS detector at the ELSA tagged photon facility in Bonn. The dependence of the omega-meson cross section on the nuclear mass number has been compared with three different types of models: a Glauber analysis, a Boltzmann-Uehling-Uhlenbeck analysis of the Giessen theory group, and a calculation by the Valencia theory group. In all three cases, the inelastic omega width is found to be 130-150 MeV/c(2) at normal nuclear matter density for an average 3-momentum of 1.1 GeV/c. In the rest frame of the omega meson, this inelastic omega width corresponds to a reduction of the omega lifetime by a factor approximately 30. For the first time, the momentum dependent omegaN cross section has been extracted from the experiment and is in the range of 70 mb.     

Polymer and organic molecules ordered via epitaxy: geometrical and molecular interactions

Control of structural order at the molecular level for both conventional linear polymers and conjugated polymers with valuable opto‐electronic properties has major consequence on the macroscopic properties of these polymers. Though the traditional means of orientation of polymer was mechanical deformation, presently extensive works are concerned with a more controlled way of orientation: epitaxial crystallisation. Most of the first documented examples of epitaxial growth of conventional polymers on single crystals followed the well‐established geometrical rules of best matching. However, recent examples show off more subtle rules of selection. Analogous cases, following or breaking the matching rules, have been observed for diacetylenes ordered via epipolymerisation on single crystals. Hereafter, representative examples of the structural matching rules are depicted first, and then recent examples, which depart from the simple geometrical fitting, are described. The analysis of the former leads to define the subtle matching rules applying for polymers linked to their conformational adaptability. The analysis of the latter gives the opportunity to discuss the relative influence of geometrical and molecular interactions between the deposit and the substrate.     

Plastic deformation of polytetramethylene oxide. I. Influence of molecular weight distribution,crystallinity, and structure

Polytetramethylene oxide with a planar zig-zag structure similar to polyethylene can be obtained with narrow molecular weight distributions. The plastic deformation of samples differing in molecular weight, molecular weight distribution, crystallinity, and structure has been studied. The degree of crystallinity of the undeformed annealed samples, as studied by NMR and DSC, leads to a value of the enthalpy of melting ΔH_m = 167 J g⁻¹, supporting the lower of two previously reported values. The low natural draw ratios and low Young's modulus of the drawn samples, together with the effect of blending a small amount of high molecular weight material into a low molecular weight sample, highlight the role of the flexibility and of the high molecular weight tail of the distribution in the plastic deformation process. The stress required for the propagation of the neck and the tensile strength are found to be linear functions of, respectively, the natural and maximum draw ratio.     

Epitaxial crystallization of aliphatic polyesters on trioxane and various aromatic hydrocarbons

Linear polyesters of the diacid-dialcohol type are observed to crystallize epitaxially onto substrate crystals of trioxane, condensed aromatic hydrocarbons, and linear polyphenyls. In line with results previously reported for PE, lattice matching requirements for epitaxy lead to a change in the polymer contact plane on the different substrates. The highly oriented, sometimes single-crystal-like polymer films are formed of stacks of lamellae seen edge on which appear well suited to investigations of the lamellar structure.     

Polymer decoration study in chain folding behavior of solution-grown poly(ethylene oxide) crystals

The polymer decoration method based on the vaporization and condensation-crystallization of polyethylene (PE) upon the fold surface of polymer crystals has been widely used to study the chain folding behavior of the crystals. When this method was utilized to study solution-grown high molecular weight poly (ethylene oxide) (PEO) lamellar crystals, the highly anisotropic, low molecular weight fragment PE decorated become oriented parallel to the fold direction and form rods, which can be observed by transmission electron microscopy (TEM) and electron diffraction (ED). The growth sectors were clearly observed. From the ED patterns the {200} planes of the orthorhombic low molecular weight PE rod crystals can be observed, and the c-axis of these crystals is aligned parallel to the {120} growth planes of the PEO crystals. The decoration results indicate that the major fold orientation of high molecular weight PEO single crystals grown from dilute solution is along the {120} planes. © 1995 John Wiley & Sons, Inc.     

Plasma losses in a toroidal theta-pinch with superposed hexapole

A toroidal theta-pinch discharge with superposed non-helical hexapole field is investigated. The characteristic data of the discharge are: major diameter 52 cm, minor inner diameter of the vacuum vessel 6 cm, maximum magnetic field between 10 and 21 kG, rise time (quarter-cycle) 3.0 μs, maximum temperature between 40 and 100 eV, maximum density between 1 and 3×10¹⁶ cm^?3, beta-values between 0.3 and 1. The plasma confinement times are determined by measuring particle density, temperature and plasma radius. The confinement times are compared with those of models which account for cusp losses, resistive losses, and Bohm diffusion. Measured confinement times are consistent with those expected from cusp losses with a cusp slit-width of one ion gyro-radius. Above electron temperatures of 20 eV, resistive losses are negligible. Bohm diffusion is not consistent with measurements, but is of the same order of magnitude.