Scattering length and effective range in closed form for the Coulomb plus Yamaguchi potential

From the known expression for the off-shell T-matrix corresponding to the potential consisting of the sum of the Coulomb potential and the Yamaguchi potential, the physical scattering amplitude can be derived in a satisfactory way. We derive simple exact closed formulae for the scattering length a_cs and the effective range r_cs from this amplitude. These are compared with approximate formulae derived by Harrington. Also a few numerical calculations are reported and compared with results obtained by Harrington and by Ali et al.     

On the theory of complex potential scattering

We study the effect of the addition of a complex potential λV_sep to an arbitrary Schrödinger operator H = H₀ + V on the singularities of the S matrix, as a function of λ. Here V_sep is a separable interaction, and λ is a complex coupling parameter. The paths of these singularities are determined to a great extent by certain saddle points in the momentum (or energy) plane. We explain certain critical phenomena recently reported in the literature. Associated with these saddles are branch-type singularities in the complex λ plane, which are dynamical in origin. Some examples are discussed in detail.     

The Development of Solid Spectral Filters for the Regulation of Plant Growth

Phthalocyanine derivatives have been prepared and incorporated into polymer films for use as spectral filters for the modification of plant growth. The unusual absorption characteristics of phthalocyanines, notably the narrow absorption band in the visible region of the electromagnetic spectrum, allows the selective filtering of wavelengths necessary for excitation of either of the two isomeric phytochrome species. The resulting change in the photostationary state for the phytochrome is shown to have a marked effect on the growth characteristics of both chrysanthemums and antirrhinums. Chrysanthemums (short-day plants) grown under a far-red-absorbing film showed a reduction in height (∼14%) and internodal length compared to those grown under a red-absorbing film or a control with no absorption in the visible part of the spectrum; both leaf number and time to flowering were not affected by the presence of the spectral filter. For antirrhinums (long-day plants) both a reduction in height and a substantial increase in leaf area (70%) of the plants grown under the far-red-absorbing film were observed, although flowering was delayed. The potential of these filters as replacements for chemical plant growth regulators is discussed.     

Mode polarization of a single mode gas laser in transverse magnetic fields

The polarizing effect of transverse dc magnetic fields applied to fractions of an isotropic single mode gas laser is theoretically investigated. A method is proposed to obtain prescribed orientations of the polarization plane in relatively weak external fields (He-Ne, 1.153 μ: about 3x10^-3 Wb/m²).     

Features of the hedritic morphology of β‐isotactic polypropylene studied by atomic force microscopy

The lamellar organization of melt‐crystallized β‐isotactic polypropylene was studied by atomic force microscopy (AFM) after permanganic etching. Hedritic objects grown at a high crystallization temperature (140–143 °C) were investigated. Essential features of the hedritic development were revealed by the characteristic projections exposed at the sample surface. A three‐dimensional view of the morphology was obtained by AFM. Hedritic growth proceeded mainly by branching around screw dislocations resulting in new lamellae that further developed. Successive lamellar layers often diverged. Deviation from the planar lamellar habit was observed, varying with the position within the hedrite. Twisting of the lamellae also was observed occasionally in the vicinity of the screw dislocations. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 672–681, 2000     

Model calculation of the electron phonon coupling parameter λ

A simple model is described, in which the influence of two parallel Brillouin zone faces on the electron phonon coupling parameter λ can be studied. In this model it is observed that λ, considered as a function of the Fermi energyE _itF, has a peculiar structure when the Fermi body just passes through the two Bragg planes. Both an enhancement as well as a reduction of the more familiar density of states effect on λ and therefore on the critical temperatureT _itc of superconductors appears to be possible. In this respect approaching a Brillouin zone face turns out to be very favourable. The structure in λ is due to a combination of Umklapp, wave function mixing, and density of states effects. The calculations indicate that it is worthwhile to study these effects in detail in actual systems.