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The lack of closed representations for the density functions of the α-stable distributions, when considering Bayesian inference using Markov Chain Monte Carlo methods, has historically lead to the ...

SYNOPSIS During 1988/89 studies were done on the use of single mules and two-mule teams to slip tree lengths in pine thinning and clearfell operations in the Knysna and George area of the Southern Cape, with estimates given of the productivity and cost which can be expected. Actual production rates achieved by two-mule teams in the same area during 1999 are compared to the 1988/89 estimates and the production rates suggested by Zaremba (1976). The conclusion is that mules can still be a proposition for slipping timber by contractors, but contractors should be assisted with regard to the planning of the operation to obtain the optimum productivity.

The genetics of resistance in wheat (Triticum aestivum L.) to loose smut caused by Ustilago tritici (Pers.) Rostr. is not well understood. In this study the inheritance of loose smut resistance was studied in two androgenetically derived doubled haploid populations and two inbred random head-to-row populations. The loose smut resistant experimental wheat line HY377 was crossed with the loose smut susceptible line L8474-D1 and the resistant line SC8021V2. Androgenetically derived doubled haploid populations and F4-derived random inbred line populations were produced from each of the crosses HY377/L8474-D1 and HY377/SC8021V2. Lines derived from each cross were grown in the growth room and inoculated with individual and a mixture of races of loose smut. The segregation of resistance between HY377 and L8474-D1 to races T2, T10, T19, and T39 in both doubled haploid and random inbred line populations fit the expected ratio for a single major gene. The same populations inoculated to race T15 showed a different d...

Extract As previously reported (Taylor and Foy 1985; Keltjens and Ulden 1987; Grauer and Horst 1990; Galvez and Clark 1991), plant species and varieties widely differ in Al tolerance. Although many hypotheses about the physiological mechanism(s) involved in Al tolerance have been formulated, the mechanism(s) has not been elucidated. However, it is obvious that when exposed to Al at high concentrations, Al-tolerant plants seem to be able to avoid the toxicity by refraining from excess uptake of Al or by chelating of Al in the rhizosphere or in the roots. In such ways, Al can not affect the growth of tolerant plants (Foy et al. 1978).

Nitrogen (N) supply increased yield, leaf % N at 10 days after silking (DAS) and at harvesting, the contents of ribulose‐1,5‐bisphosphate carboxylase (RUBISCO) and soluble protein, and the activities of phosphoenolpyruvate carboxylase (PEPC), and ferredoxin‐glutamate synthase (Fd‐GOGAT), but not of glutamine synthetase (GS) for six tropical maize (Zea mays L) cultivars. Compared to plants fertilized with 10 kg N/ha, plants inoculated with a mixture of Azospirillum sp. (strains Sp 82, Sp 242, and Sp Eng‐501) had increased grain % protein, and leaf % N at 10 DAS and at harvest, but not grain yield. Compared to plants fertilized with either 60 or 180 kg N/ha, Azospirillum‐inoculated plants yielded significantly less, and except for GS activity, which was not influenced by N supply, had lower values for leaf % N at 10 DAS and at harvest, for contents of soluble protein and RUBISCO, and for the activities of PEPC and Fd‐GOGAT. Yield was positively correlated to leaf % N both at 10 DAS and at harvest, ...

Positron lifetime and microhardness measurements have been performed on untreated, thermal-aged, neutron-irradiated, and postirradiation-annealed samples of reactor pressure vessel steels with the purpose of investigating the mechanisms of irradiation-induced hardening and recovery of the mechanical properties in these materials. The positron lifetime experiments have not revealed any evidence of the formation of a significant concentration of voids or vacancy clusters in samples irradiated at [approximately]290 C with fluences [le]2.71 [times] 10[sup 23] n/m[sup 2] (E[gt]1 MeV), but they suggest a dislocation annealing induced by the irradiation. Isochronal annealing experiments with neutron-irradiated samples show a simultaneous recovery in their positron lifetime and microhardness at [approximately]340 C. From the microhardness measurements, the yield strength of the irradiated material has been estimated. The results appear to be consistent with a model of hardening due to irradiation-induced dissolution of precipitates with formation of small metastable precipitates after postirradiation aging and recovery induced by the disappearance of these metastable precipitates.

Production rates of cable yarding by fixed skyline in Southern Africa were found to be low, usually between 50 m3 to 60 m3 of timber per day on average. Investigations identified four major sources of lost productivity. Implementation of simple techniques selected to reduce losses resulted in a quadrupling of productivity though only a tripling is expected in the long term.

Positron annihilation measurements in neutron-irradiated MgO crystals show that the positron lifetime is shorter than in as-grown crystals, suggesting that most of the defects produced by neutron irradiations are positively charged. The concentration of the neutral anion vacancy (possibly also the neutral anion divacancy) is estimated to be no more than ∼ 1016 cm−3 for samples irradiated to a dose of 1017 to 1019 n cm−2. Annealing experiments on the neutron-irradiated crystals show a significant increase in the positron lifetime after anneals at 900 K. The increase is attributed to positron trapping by anion—vacancy aggregates. A lifetime of (284±15)ps is tentatively assigned to positrons trapped in these aggregates.

The demand for timber in southern Africa is increasing and this is resulting in the afforestation of areas which require cable yarding when harvested. The demand for cable yarders, essentially fixed skylines, is therefore increasing rapidly. Stress is being placed on the productivity of skylines since about half the timber has a piece size of under 0,2 m3. Work study analyses showed that much productivity was lost from slow carriage turn-about times caused mainly by inefficient choking techniques, slow carriage speeds, small load masses caused again by inefficient choking and by unwarranted delays. The productivity of the skyline was nearly tripled by fitting an automatic transmission gearbox to the drive to increase carriage speed, by using a single locking carriage that could also accommodate tag lines, and by the development and use of suitable tag lines. Timber piece size had little effect on timber productivity.

Hydrogenolysis of 2,3,5-tri-O-benzoyl-6-O-trityl-D-galactono-1,4-lactone (2) gave the corresponding 3-deoxy-D-xylo-hexono-1,4-lactone derivative (3), which on treatment with HBr in acetic acid afforded 2,5-di-O-benzoyl-6-bromo-3,6-dideoxy-D-xylo-hexono 1,4-lactone (4). Hydrogenation of 4 led to 3,6-dideoxy-D-xylo-hexono-1,4-lactone dibenzoate (6). The overall yield of 6 from D-galactono-1, 4-lactone (1) was about 59%. Alternatively, compound 6 was prepared (67% overall yield from 1) by hydrogenolysis of 6-bromo-6-deoxy-D-galactono-1,4-lactone tribenzoate (5), obtained by treatment of 2 with HBr in dry dichloromethane. Diisoamylborane reduction of 6 gave an anomeric mixture of 2,5-di-O-benzoyl-3,6-dideoxy-α, β-D-xylo-hexofuranose (7), which on O-debenzoylation afforded 3,6-dideoxy-D-xylo-hexose (abequose, 8) whose tautomeric equilibrium was studied by 13C NMR spectroscopy. Acetylation of 7 gave the 1-O-acetyl derivative (9) mainly in the β anomeric configuration. Tin (IV) chloride promoted glycosy...

(1990). Long Length Timber and its Transport. South African Forestry Journal: Vol. 154, No. 1, pp. 72-73.

Elemental tellurium is reduced by thioureadioxide in alkaline medium, leading to disodium telluride or ditelluride, depending on the amount of thioureadioxide used. The intermediate disodium telluride or ditelluride reacts “in situ” with alkyl halides to give dialkyltellurides or dialkylditellurides in high yield.

The model hepatotoxine carbon tetrachloride (CC14) was used to study haloalkane free radical-induced lipid peroxidation in isolated rat hepatocytes at steady state oxygen partial pressures (pO,) between 0.2 and IOOmmHg. Equilibrium oxygen conditions were achieved by using an oxystat system.Monitoring of hepatocellular oxygen uptake, malondialdehyde-formation and low-level chemilumine-scence during incubations of CC14-supplemented hepatocytes indicated a drastic stimulation of lipid peroxidation at p02-levels between 1 and lOmmHg. Above and below this pO2-region the potency of CC14 to induce lipid peroxidation sharply decreased. The evaluation of cellular damages by determining trypan blue exclusion and lactate dehydrogenase leakage revealed that in the presence of CC14 hepatocellular injury was significantly increased at those pO2-levels which were optimal for CC14-mediated lipid peroxidation.The present results demonstrate that CC14 is a potent inducer of lipid peroxidation also in the intact hepatocyte,...

SYNOPSIS Large scale extraction of shortwood E. grandis timber by means of a semi-mechanised system in hilly terrain gives high productivity from clearfellings. The system employs wheeled tractors and manually loaded low-bed trailers for infield shortwood harvesting. Loads of five to six tons are transshipped in bundled form by crane to road-haulage vehicles. Handling times are given for each operation for different categories of pole mass and load size.