Molecular Weight Distributions in Coupled Polymers Using Z‐Transform

A study of end‐to‐end coupling reactions of bifunctional linear prepolymers of the Schulz–Flory type is presented by use of Z‐transform. The application of Z‐transform allows one to derive exact expressions for the change of molecular weight distributions in dependence of the progress of the coupling reaction. After coupling the distribution is also of Schulz–Flory type, however, it depends in a relatively complicated manner on the extent of reaction of the prepolymer and on the extent of the coupling reaction. Further expressions are derived for various dependencies including the influence of the extent of coupling on the average molecular weights, chain lengths, and polymolecularity. By implementation of the Mark–Houwink–Sakurada equation, a correlation between intrinsic viscosity and the progress of coupling reaction is shown.     

Measurement of π−p → π0π0n at 6, 8 and 12 GeV/c

All γ's and the neutron from the reaction π^?p → π⁰π⁰n are detected. The magnitude of the π⁰π⁰ S-wave and the cosine of its phase angle (relative to the known D-wave) are determined. The I = 0 amplitude, S₀, is near the unitarity limit in the range 600 to 900 MeV and again around 1200 MeV.     

Electroproduction of η-meson at the S11 (1535) resonance

The reaction e^? + p → e^? + p + η has been studied in the region of the S₁₁ (1535)-resonance by detecting the recoil proton in coincidence with the scattered electron. The reaction has been observed at three four-momentum transfers of the virtual photon: q² = 0.2, 0.28 and 0.4 (GeV/c). First results of the differential cross section measurements are given and compared with quark model calculations.     

Absorption of scattered light in colloidal systems of aggregated particles

Scattering and extinction of colloidal systems containing either nonabsorbing or strongly absorbing spherical particles of some nanometers in diameter were examined in the wavelength range from the near UV to the near IR. If aggregation occurs, scattering and extinction are modified with respect to the single sphere systems. The influence of aggregation can best be recognized for absorbing particles when already the single sphere shows resonant extinction. In this case, the resonance of the single sphere splits into many new resonances for the aggregate, most of which are positioned at larger wavelengths than the single sphere resonance. They strongly depend on the size and shape of the aggregate.Looking at the scattering, additional problems arise in systems of absorbing particles caused by reabsorption by neighboring spheres or aggregates. A simple model was developed to interpret the obtained scattering data.     

A new method for the detection of Raman scattering from atmospheric pollutants

The Fabry-Perot interferometer can be used as a periodic filter for the sorting of spectra using the rotational Raman effect. Thus it is possible to detect low concentrations of impurities in the presence of the major atmospheric constituents. The parameters of importance in making these measurements and the expected results from this technique are discussed from theoretical computations.     

Prenatal stress and subsequent exposure to chronic mild stress influence dendritic spine density and morphology in the rat medial prefrontal cortex

Background  

Both prenatal stress (PS) and postnatal chronic mild stress (CMS) are associated with behavioral and mood disturbances in humans and rodents. The aim of this study was to reveal putative PS- and/or CMS-related changes in basal spine morphology and density of pyramidal neurons in the rat medial prefrontal cortex (mPFC).     

Verification of an optical metrology system (ARAMIS) by comparing experimental data with FE calculations and continuum approaches

Optical 3D field measuring systems, based on DIC (Digital Image Correlation) deliver kinematic quantities. They are appropriate devices helping to understand the material behavior especially at high strains. One problem of these systems is the missing information about material points located behind the observed surface of the specimen, which is needed to assign the full deformation gradient. Different ways of dealing with raw point coordinate data that is confidently given by the metrology system lead to different kinematic results. To ensure the correctness of strain-like results determined by the system, they are compared to analytical and finite element calculations. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Terahertz response and colossal Kerr rotation from the surface states of the topological insulator Bi2Se3

We report the THz response of thin films of the topological insulator Bi2Se3. At low frequencies, transport is essentially thickness independent showing the dominant contribution of the surface electrons. Despite their extended exposure to ambient conditions, these surfaces exhibit robust properties including narrow, almost thickness-independent Drude peaks, and an unprecedentedly large polarization rotation of linearly polarized light reflected in an applied magnetic field. This Kerr rotation can be as large as 65° and can be explained by a cyclotron resonance effect of the surface states.