Pulping characteristics of Pinus patula grown in Zimbabwe (ODNRI Bulletin No. 8)

Twenty trees of Pinus patula, growing on five sites in Zimbabwe as part of a progeny test, were examined and their pulping characteristics determined. The trees were from the same full-sib family and were 12 years old. No relationship between site, and wood density and fibre dimensions could be inferred because the differences between trees within a site were found to be greater than the differences between sites. All of the trees were pulped by the sulphate process: when constant digestion conditions with 18% active alkali were used, the yield of pulp from individual trees was from 41.3 to 44.9%. All of the pulps had a good tensile strength, but few had tearing strength sufficient for wrapping paper. Trees suitable for the production of pulps with high tearing strength were most likely to grow on the Grasslands site. For the twenty trees, there was a poor correlation between the rate of growth of a tree and the tearing strength of pulp produced from it; but within any one site the slowest growing tree was most likely to yield the pulp with the highest tearing strength

Study of Ni and Zn doped CeOFeAs: Effect on the structural transition and specific heat capacity

We have systematically studied the substitution of nonmagnetic Zn and magnetic Ni at iron sites in Ce based oxypnictide. The parent compound (CeOFeAs) shows an anomaly in resistivity around 150 K due to structural transition from tetragonal (space group: P4/nmm) to orthorhombic structure (space group: Cmma). Substitution of Zn suppresses this anomaly to lower temperature (~130 K) but Ni substitution does not show any anomaly around this temperature and the compound behaves like a metal. Further, we find that non magnetic (Zn) doping leads to higher impurity scattering as compared to magnetic Ni doping. Similar to the resistivity measurement, the specific heat shows another jump near 4 K for CeOFeAs. This is attributed to the ordering of Ce3+ moments. This peak shifts to 3.8 K for Zn substituted compound and there is no change in the ordering temperature in the Ni substituted CeOFeAs. These peaks are broadened in applied magnetic field (5 T) and the calculated magnetic entropy tends to saturate at the same value for 0 T and 5 T external magnetic field.Comment: 16 pages Text+Fig

Nearly extensive sequential memory lifetime achieved by coupled nonlinear neurons

Many cognitive processes rely on the ability of the brain to hold sequences of events in short-term memory. Recent studies have revealed that such memory can be read out from the transient dynamics of a network of neurons. However, the memory performance of such a network in buffering past information has only been rigorously estimated in networks of linear neurons. When signal gain is kept low, so that neurons operate primarily in the linear part of their response nonlinearity, the memory lifetime is bounded by the square root of the network size. In this work, I demonstrate that it is possible to achieve a memory lifetime almost proportional to the network size, "an extensive memory lifetime", when the nonlinearity of neurons is appropriately utilized. The analysis of neural activity revealed that nonlinear dynamics prevented the accumulation of noise by partially removing noise in each time step. With this error-correcting mechanism, I demonstrate that a memory lifetime of order $N/\log N$ can be achieved.Comment: 21 pages, 5 figures, the manuscript has been accepted for publication in Neural Computatio

Pulping characteristics of Pinus oocarpa from Uganda

The results of the examination of a sample of Pinus oocarpa, approximately 10 years old, grown in plantations in Uganda are reported and compared with those obtained from a sample grown in its natural habitat, Belize. The sample from Uganda had a wood density of 382 kg m-3 which was much lower than that of the sample from Belize, 530 kg m-3. The Ugandan sample also had a lower resin content and the fibres were shorter, narrower, and thinner-walled. Using the sulphate pulping process, under different conditions the Ugandan sample yielded between 41.8% and 48.4% of pulp with a kappa number from 23.7 to 53.1. Samples of Pinus oocarpa from their natural habitats are reported to yield pulps with properties similar to those of Southern pines from the USA, with high tearing strength, and moderate bursting and tensile strengths. The Ugandan samples yielded pulps with similar bursting and tensile strengths, but low tearing strength. The effects are reported of bleaching the pulp by a four-stage sequence of successive applications of chlorine, sodium hydroxide, sodium hypochlorite and chlorine dioxide. Differences between the Ugandan and Belize samples are principally attributed to the lower age of the former