Gelation and the production of surface grown polyethylene fibres

Summary In the course of examining the limiting conditions for growth of polyethylene fibres by the surface growth method (1, 2) an unexpected gelation effect was observed. Accordingly a solution, after having been stirred at such elevated temperatures where no visible crystallization can take place, is found to set as a gel after cooling under quiescent conditions. It is established that the ability to form this gel is a necessary condition for fibre production byPennings andZwijnenburg's surface growth method which by the new findings essentially should consist of the stretching of such gels. We verified that material indeed accumulates at the surface of the rotor used in the surface growth method as was originally envisaged, but we now infer that this material consists of gel particles formed during the preceding treatments. This adhesion of the gel to a rotating surface enables it to be readily stretched by an externally introduced fibre as done in the surface growth method. The gel precursor is of interest in its own right. We find that it is a transient structure but with long, up to several hours, persistence time during which the solution `remembers' that it has been stirred. The structure itself is presumably an incipient network forming crystallization induced by localised chain stretching, where the crystal junctions are likely to provide the nuclei for the more permanent fibrous crystals which arise on cooling causing the gel to set. Electron microscopy indeed identified smooth fibres in the gel which could develop into shish-kebabs on appropriate treatment, while the bulk of the gel consists of large single crystal platelets which arise within the network on final cooling to room temperature. Finally we suggest, that many, if not all, shishkebab structures conventionally observed on stirring arise by the stretching of the gel network formed at a preceding stage of the preparation procedure.     

Do light colored scalars exist?

The general question of the properties of light, neutral colored spin-zero particles in QCD is examined. Models with spontaneous breaking of QCD at very large distances, such as that of DeRújula, Giles, and Jaffe and the SO(3) scheme of Slansky, Goldman, and Shaw, require such light colored Higgs scalars. These scalars will form color-singlet hadronic bound states at short distances and estimates are given of bound state masses, decay widths, and production rates in processes such as ψ → γ + X within the MIT bag model. The resulting states are expected in the mass neighborhood ～1.5 GeV and should resemble glueballs.     

Investigation of the fermi edge in sodium tungsten bronzes by photoelectron spectroscopy

High-resolution photoelectron spectra of sodium tungsten bronzes Na _xWO₃ (0.26<x< 0.76) reveal a linear variation in the density of states at the Fermi energy as a function of sodium content. This behaviour does not appear to arise from filling of a rigid conduction band. Magnetic susceptibilities calculated from photoemission data using a simple independent-electron model agree with measured values.     

Polyethylene glycol in copper electrodeposition onto a rotating disk electrode

Many of the proprietary additive formulations that have been proposed to control the properties of metal electrodeposits include water soluble macromolecules. Among these are the hydrodynamically interesting polyethylene glycols ‘Polyox’. In the course of a rotating disk electrode study of the effects of additives in copper electrodeposition the present authors had cause to try the effects of low concentrations of Polyox in an acid copper sulphate plating solution. In the presence of an essential trace of chloride ion Polyox very strongly inhibited deposition below a critical overpotential at which current density rises extremely rapidly with increasing overpotential. These results suggest that below the critical overpotential chloride ions hold a film of Polyox onto the electrode surface and may also give the film some lateral cohesion. The film may be a Polyox-cuprous chloride complex. Striking spiral patterns form at the critical overpotential. Their characteristics are explained as the consequences of electrodeposition on a surface containing submicroscopic protrusions and depressions in conditions where current density increases very rapidly with potential.     

BrdU-positive cells in the neonatal mouse hippocampus following hypoxic-ischemic brain injury

Background  

Mechanisms that affect recovery from fetal and neonatal hypoxic-ischemic (H-I) brain injury have not been fully elucidated. The incidence of intrapartum asphyxia is approximately 2.5%, but the occurrence of adverse clinical outcome is much lower. One of the factors which may account for this relatively good outcome is the process of neurogenesis, which has been described in adult animals. We used a neonatal mouse model to assess new cells in the hippocampus after H-I injury.