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961.
962.
963.
This paper presents an on-line method for detecting washboarding generated in bandsaws. It uses a parameter based on the shape of sawing force amplitude distributions. The curve of the probability density function of the parallel sawing force amplitude obeyed a normal distribution for the normal sawn surface, but it changed to an M-shaped distribution when washboarding appeared on the sawn surface of the workpiece. The curve of probability density function of the normal sawing force amplitude obeyed the normal distribution for any sawn surface investigated. The workpiece including a knot did not influence use of the parameter for detecting the appearance of washboarding. 相似文献
964.
Four populations representing the entire natural distribution range of Pinus brutia (Ten.) in Crete (Greece) were sampled to determine: (1) Altitudinal variation within populations of Lassithi, Vorizia, Koustagerako, and Samaria, and; (2) Longitudinal variation among the four populations, based on morphological and anatomical differences in cone, needle and seed characteristics. Samples were collected from 10 trees per altitude, at three altitudes in each population. A total of 12 morphological and anatomical traits from needles, cones and seeds were analyzed to assess the altitudinal and longitudinal variations of the species in the island. The number of teeth per cm showed significant (P<0.01) differences between altitudes in Samaria, Vorizia and Lassithi, while needle length, width and the number of resin canals showed significant differences (P<0.01) between altitudes in Koustagerako. Cone width showed patterns of variation along the altitudinal gradient in Koustagerako, Samaria and Vorizia. Most traits had their highest means at the middle altitudes (650masl) in all the four populations. Overall, no clear altitudinal differentiation was detected, probably due to high rate of gene flow. Longitudinal variability showed a clear pattern of differentiation along the east–west climatic gradient. Needle length, width, sheath length, number of teeth per cm and the number of resin canals were the most useful traits for determining the climatic gradient clines. 相似文献
965.
V. Sivakumar R. Anandalakshmi R. R. Warrier B. G. Singh Mulualem Tigabu P. C. Odén 《New Forests》2007,34(3):281-291
The germination of Casuarina equisetifolia Forst seed lots is low (40–50%) even when freshly collected. This study aimed at upgrading the germination performance by
removing non-germinable seeds using petroleum flotation technique. Seeds collected from 19 individual trees in seedling seed
orchards in India were assessed using X-ray to determine the proportion of different seed lot fractions. The feasibility of
petroleum ether as a separation medium was tested. Morphological characters of floating and sunken seeds were further studied
using image analysis technique to examine their effects on the separation efficiency. The X-ray analysis revealed a large
quantity of shrivelled, empty and insect-damaged seeds, altogether accounting 50%, which were the causes of low percentage
germination of un-graded seed lots (48%). Petroleum flotation resulted in 90% germination in the sunken fraction and 4% in
the floating fraction. The separation was distinct for most seed lots, except few seed lots that had relatively low germination
in the sunken fractions and more than 10% germination in the floating fractions. As a whole, petroleum flotation appears to
be a feasible technique to upgrade the germination of C. equisetifolia seed lots, and its efficacy is influenced by wing surface area, seed density and wing quotient of filled and empty seeds. 相似文献
966.
Takaaki Fujimoto Kazuhito Kita Kazuko Uchiyama Makoto Kuromaru Hisashi Akutsu Kazuyuki Oda 《Journal of Forest Research》2006,11(3):157-163
Age trends in variance components and heritability of overall wood density, earlywood and latewood density, and latewood proportion
were investigated in 29-year-old trees of 19 full-sib families of hybrid larch (Larix gmelinii var. japonica × Larix kaempferi) F1. The age–age correlation and optimum selection age for these traits were also estimated and genetic and phenotypic correlations
between wood density and radial growth rate were calculated for each growth ring. Intraring wood density data were obtained
using X-ray densitometry. The coefficient of additive genetic variance was stable over all ages, whereas the coefficient of
environmental variances gradually decreased with increasing age, resulting in increases in heritability estimates with age
for overall density. The latewood proportion had the highest heritability estimates at all ages, ranging from 0.44 to 0.66.
Overall density and its various components at 28 years of age showed strong genetic correlations with their respective traits
at all younger ages. Optimum selection ages for the wood density traits ranged from 8 to 14 years, at which point maximum
gain efficiencies per year were obtained. There were negative correlations between wood density and radial growth rate at
early ages, although these relationships tended to be weaker with increasing age. These results suggest that selection at
a young age is effective for wood density, but particular care must be taken in selecting trees with an improved radial growth
rate because rapid growth will result in a low-density wood product, especially in the early growth period. 相似文献
967.
Greenhouse trials with containerized Eucalyptus globulus and E. urophylla seedlings were made to determine effective inoculum spore densities (Scleroderma cepa from temperate Australia, and S. citrinum from sub-tropical China) and spore storage conditions (fresh spores or spores stored for 5 years at room temperature or at
4 °C; S. albidum, S. areolatum and S. cepa from Western Australia). Inoculation with 106 or 108 spores/seedling increased eucalypt growth by up to 46% in height and 42% in dry weight compared to non-inoculated seedlings
at 12 weeks after inoculation. Mycorrhizal formation was poor at 102 spores/seeding. Spores stored at 4 °C for 5 years were as effective in forming mycorrhizas as freshly collected spores when
a standard density of 106 spores/seedling was applied. It is recommended that spore densities ≥104 be used for inoculation of containerised eucalypts and that spores be stored at 4 °C until use. 相似文献
968.
观光木播种苗生长规律及育苗技术研究 总被引:3,自引:1,他引:3
用有序样本聚类分析法将观光木1年生播种苗生长过程划分为4个时期:出苗期(2月26日-5月20日)、幼苗期(5月21日-7月20日)、速生期(7月21日-10月20日)和生长后期(10月21日-11月20日)。不同播种期的试验表明:冬播观光木比春播提早16 d萌发,苗高、地径生长量和总生物量分别比春播提高13.3%、15.1%和18.8%。采用沙藏可促进种子提早萌发和提高场圃发芽率。不同密度试验表明,观光木育苗采用60株.m-2的密度较好。 相似文献
969.
George I. Mantanis Jozef Martinka Charalampos Lykidis Libor Ševčík 《Wood material science & engineering》2020,15(5):303-311
ABSTRACT The objective of the work was to evaluate the efficacy of two new polyphosphate-based fire retardants (FRs) and one commercial product named Siriono® on the fire performance and physical–mechanical properties of medium density fibreboard (MDF) fabricated in the laboratory from Scots pine (Pinus sylvestris L.) wood. The fibres were treated with aqueous solutions of fire retardants, at 12% loading (dry salt on dry wood), and bonded with a melamine urea formaldehyde (MUF) adhesive. The physical and mechanical properties of panels were assessed using the European standards, whereas their fire performance was evaluated using an in-house method and the Cone calorimeter. In overall, the chemicals added enhanced the fire and smoke properties of the panels to varying degrees. Critical FR parameters such as peak heat release rate (peak HRR), total heat release (THR) and total smoke production (TSP) were significantly improved in the FR-treated panels, as exhibited in cone calorimeter tests. However, the internal bond strength of treated panels largely decreased by the addition of fire retardants, while thickness swell and water absorption negatively affected to a significant extent. In contrast, the formaldehyde release of the panels was considerably decreased at the E1 class level, with the incorporation of the polyphosphate-based additives. 相似文献
970.
我国鲜切花物流发展问题的探讨 总被引:7,自引:1,他引:7
鲜切花物流是指鲜切花从供应地向接受地的实体流动过程。经对我国鲜切花物流面临的问题作出分析,在借鉴其他国家和地区先进经验的基础上,结合我国的具体情况为鲜切花物流的发展提出了一些建议。 相似文献