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2.
微纤丝角为细胞次生壁S2层微纤丝排列方向与细胞主轴所形成的夹角,与木材的物理性质、力学性质和化学性质都有着直接的关系。应用x射线衍射法测定了7个杨树无性系(14株样木)胸径处各年轮的微纤丝角,并对应分析和测定了各年轮的木材基本密度、纤维长度、纤维宽度和纤维素含量。研究结果表明,杨树微纤丝角在年轮间存在显著差异,其径向变异规律为从髓心向外以微纤丝角逐渐降低,年轮间的平均微纤丝角在7.8旱?8褐洌荒静幕久芏取⑾宋ざ取⑾宋矶群拖宋睾吭谀曷旨湟泊嬖谙灾钜臁O喙胤治霰砻鳎⑾怂拷怯肽静幕久芏取⑾宋ざ取⑾宋矶群拖宋睾看嬖谙灾母合喙毓叵??0.01),相关系数分别为-0.450、-0.586、-0.516和-0.660。回归分析结果表明,多项式方程可较好地描述杨树微纤丝角与所测定的木材性质的关系,相关系数均在-0.45以上(n=125)。本文的研究结果认为,在今后针对杨树材性改良的育种计划中,微纤丝角是一个重要的选育和改良指标。图3表3参34。 相似文献
4.
Transmittance and reflectance of visible light by sugi wood ( Cryptomeria japonica) were investigated in the longitudinal ( L) and tangential ( T) directions. Transmittance was the highest in the L direction and reflectance was the highest in the T direction, suggesting that structural anisotropy influences transmittance and reflectance. Intra-ring variations observed with a microspectrometer indicated that T transmittance was higher for latewood than for earlywood, but there was no such trend in for L transmittance in which the highest levels occurred near the annual ring boundaries, on either the earlywood or latewood side, and the lowest at the transition from earlywood to latewood. Dependence of L transmittance on wavelength also showed variations according to the intra-ring position. The increasing of transmittance of earlywood at wavelengths?<?500 nm with increasing wavelength was observed, but this was not confirmed for latewood because of absorption by lignin. These observations supported a previously published finding, which was based on measurements in the radial direction, that the number of internal cell wall reflections, rather than density, determines wood lightness. Indeed, in the L direction, most of the incident light passes through lumens in earlywood and through cell walls in latewood, while it is subjected to numerous internal reflections at the interface between lumens and cell walls. This was further confirmed by the transmittance of earlywood being greatly decreased by radial compression. 相似文献
5.
Stem segments of eight five-year-old Norway spruce (Picea abies (L.) Karst.) clones differing in growth characteristics were tested for maximum specific hydraulic conductivity (k(s100)), vulnerability to cavitation and behavior under mechanical stress. The vulnerability of the clones to cavitation was assessed by measuring the applied air pressure required to cause 12 and 50% loss of conductivity (Psi(12), Psi(50)) and the percent loss of conductivity at 4 MPa applied air pressure (PLC(4MPa)). The bending strength and stiffness and the axial compression strength and stiffness of the same stem segments were measured to characterize wood mechanical properties. Growth ring width, wood density, latewood percentage, lumen diameter, cell wall thickness, tracheid length and pit dimensions of earlywood cells, spiral grain and microfibril angles were examined to identify structure-function relationships. High k(s100) was strongly and positively related to spiral grain angle, which corresponded positively to tracheid length and pit dimensions. Spiral grain may reduce flow resistance of the bordered pits of the first earlywood tracheids, which are characterized by rounded tips and an equal distribution of pits along the entire length. Wood density was unrelated to hydraulic vulnerability parameters. Traits associated with higher hydraulic vulnerability were long tracheids, high latewood percentage and thick earlywood cell walls. The positive relationship between earlywood cell wall thickness and vulnerability to cavitation suggest that air seeding through the margo of bordered pits may occur in earlywood. There was a positive phenotypic and genotypic relationship between k(s100) and PLC(4MPa), and both parameters were positively related to tree growth rate. Variability in mechanical properties depended mostly on wood density, but also on the amount of compression wood. Accordingly, hydraulic conductivity and mechanical strength or stiffness showed no tradeoff. 相似文献
6.
Thermal modification at relatively high temperatures (ranging from 150 to 260 °C) is an effective method to improve the dimensional stability and resistance against fungal attack. This study was performed to investigate the impact of heat treatment on the mechanical properties of wood. An industrially-used two-stage heat treatment method under relative mild conditions (< 200 °C) was used to treat the boards. Heat treatment revealed a clear effect on the mechanical properties of softwood species. The tensile strength parallel to the grain showed a rather large decrease, whereas the compressive strength parallel to the fibre increased after heat treatment. The bending strength, which is a combination of the tensile stress, compressive stress and shear stress, was lower after heat treatment. This decrease was less than the decrease of only the tensile strength. The impact strength showed a rather large decrease after heat treatment. An increase of the modulus of elasticity during the bending test has been noticed after heat treatment. Changes and/or modifications of the main wood components appear to be involved in the effects of heat treatment on the mechanical properties. The possible effect of degradation and modification of hemicelluloses, degradation and/or crystallization of amorphous cellulose, and polycondensation reactions of lignin on the mechanical properties of heat treated wood have been discussed. The effect of natural defects, such as knots, resin pockets, abnormal slope of grain and reaction wood, on the strength properties of wood appeared to be affected by heat treatment. Nevertheless, heat treated timber shows potential for use in constructions, but it is important to carefully consider the stresses that occur in a construction and some practical consequences when heat treated timber is used. 相似文献
7.
Growth and wood properties of 20-year-old Scots pine (Pinus sylvestris L.) trees were studied for 6 years in 16 closed chambers providing a factorial combination of two temperature regimes (ambient and elevated) and two carbon dioxide concentrations ([CO2]) (ambient and twice ambient). The elevation of temperature corresponded to the predicted effect at the site of a doubling in atmospheric [CO2]. Annual height and radial growth and wood properties were analyzed during 1997-2002. Physical wood properties analyzed included early- and latewood widths and their proportions, intra-ring wood densities, early- and latewood density and mean fiber length. Chemical wood properties analyzed included concentrations of acetone-soluble extractives, lignin, cellulose and hemicellulose. There were no significant treatment effects on height growth during the 6-year study. Elevated [CO2] increased ring width by 66 and 47% at ambient and elevated temperatures, respectively. At ambient [CO2], elevated temperature increased ring width by 19%. Increased ring width in response to elevated [CO2] resulted from increases in both early- and latewood width; however, there was no effect of the treatments on early- and latewood proportions. Mean wood density, earlywood density and fiber length increased in response to elevated temperature. The chemical composition of wood was affected by elevated [CO2], which reduced the cellulose concentration, and by elevated temperature, which reduced the concentration of acetone-soluble extractives. Thus, over the 6-year period, radial growth was significantly increased by elevated [CO2], and some wood properties were significantly affected by elevated temperature or elevated [CO2], or both, indicating that climate change may affect the material properties of wood. 相似文献
8.
A study of self-binding fibreboards pressed without synthetic adhesives is reported. The board samples of steam-exploded grey alder ( Alnus incana L. Moench) particles hot-pressed under a variety of conditions including moisture content of the mat (8% and 12%), temperature (150°C, 160°C, 170°C and 180°C) and pressure (0.2–8 MPa) are tested for moisture resistance (standard EN 1087-1), decay resistance (standard ENV 12038) and reaction to fire performance (ISO 5660-1). The moisture resistance of the board samples is found to satisfy the standard EN 622-5 for load-bearing medium-density fibreboard for use in humid conditions (MDF.HLS). The tested board samples are not fully resistant to the Trametes versicolor fungus, the mass loss of specimens exceeding 3%. Reaction to fire performance of the self-binding board evaluated by the average rate of heat emission being by about 25% higher is worse compared with MDF.HLS. 相似文献
9.
High levels of growth stress are implicated in causing end splitting of logs, deflection during sawing and deformation of boards as stresses are released during sawing operations. Level of stress is a function of strain and the elastic modulus of the wood (MOE). Levels of peripheral strain can be measured on standing trees and, if the MOE is known, stresses can be estimated. The validity of using peripheral strain measurements relies on underlying theoretical models that relate strain to expected patterns of stress distribution and levels of board deflection. This study evaluates these theoretical relationships by determining relationships of stress and strain with board deflection, end splitting and a range of wood properties. Peripheral strain levels were extremely variable within the bottom log and little evidence was found for consistent patterns of variation, although measurements generally increased with increasing height above ground. Sampling on two sides of the standing tree at breast height appeared to be a suitable strategy, with the mean for these strain readings having a correlation (r) of 0.86 with the average strain in the bottom log. Growth strain was not a reliable predictor of board deflection and cannot be recommended as a non-destructive sampling method. Overall there was a poor relationship between growth strain and board deflection. No consistent relationships were found between a range of wood properties and growth strain or board deflection across both sites. Stress levels were calculated for each tree as the product of growth strain and modulus of elasticity and the relationship between calculated stress and mean board deflection determined. No relationship was found at either site with correlations being very close to zero. The underlying theoretical relationships between stress and strain were examined and several questions raised about the validity of such models. 相似文献
10.
Bamboo is a fiber-reinforced bio-composite since its culm wall is mainly composed of parenchymatous ground tissue in which
vascular bundles are embedded. In order to analyze the mechanical properties of bamboo as a function of its components, tensile
tests were performed on bamboo blocks and the corresponding volume fractions of fiber and parenchymatous ground tissue were
measured. More significant linear relationships were found between tensile properties and volume fractions of the bamboo components.
The tensile strength and modulus of elasticity of bamboo fiber and parenchymatous tissue were estimated according to the linear
equations obtained by regression analysis. The macrographs of fractured bamboo blocks and the micrographs of fracture surfaces
obtained by scanning electron microscope were also analyzed. Further tensile tests on separated bamboo fiber bundles were
analyzed. Results show that the tensile strength of bamboo fiber obtained from the tests on bamboo blocks was higher than
that on separated fiber bundles. This might be due to the interaction between components in bamboo in which parenchymatous
ground tissue can pass loads and distribute the stresses loaded on fibers. 相似文献
11.
Emissions of N 2O from forest soils in Europe are an important source of global greenhouse gas emissions. However, influencing the emission
rates by forest management is difficult because the relations and feedbacks between forest and soils are complex. Process-based
models covering both vegetation and soil biogeochemical processes are frequently used to analyse emission patterns. Particularly,
the simulation of soil C and N turnover processes driving N 2O production, consumption and emission from forest soils requires highly specific input data which renders their regional
application difficult since at this scale, soil conditions are often not well understood. Therefore, a soil C and N model
(DecoNit) has been developed which describes biogeochemical processes with a simplified structure compared to existing carbon/nitrogen
models that nevertheless follows the basic physical and chemical laws involved and which allows to simulate N trace gas emissions.
The DecoNit model was previously calibrated using an extensive dataset on decomposition rates of incubated plant materials,
microbial dynamics and nitrification. The DecoNit model has now been embedded in a modular simulation environment (MoBiLE)
where it is combined with soil water balance and forest process sub-modules. Here, we present the evaluation of MoBiLE-DecoNit
with emission data of N 2O and NO from forest soils of 15 European sites and compare simulation results with a previous study in which a more complex
model (PnET-N-DNDC) was used. Evaluation criteria were as follows: (1) precision of modelled annual average emission rates;
(2) coherence of modelled and measured annual average and daily emissions; (3) a dynamic representation of emission rates
that correspond with the observed variance of fluxes. The results show that MoBiLE-DecoNit captures average annual emission
rates more precisely than the more complex model PnET-N-DNDC. Also the structural underestimation of N trace gas fluxes from
forest soils was resolved. Moreover, we present evidence that the new modelling approach is also somewhat more adequate for
describing inter-daily emission dynamics. The combined MoBiLE-DecoNit is therefore thought to be a promising approach to simulate
forest development and greenhouse gas balances on site and regional scales. 相似文献
12.
Mozambique is a country with vast forestry resources that include native wood species with high commercial value. Thus, the
trade of timber as raw material, as well as wooden finished products are commercial options of considerable valuable for the
country. This work presents information about anatomical characteristics, physical and mechanical properties and use of some
native wood species from Mozambique, namely, Afzelia quanzensis, Androstachys johnsonii, Erytrophleoum suaveolens, Khaya nyasica, Pterocarpus angolensis, Milletia stuhlmannii and the emerging lesser-known species Pericopsis angolensis, Sterculia appendiculata and Sterculia quinqueloba. The study concludes that these Mozambican wood species are similar in several aspects. They are generally described as very
hard, dense, having high mechanical strength and durable. The study also concludes that although the lesser-known wood species,
S. quinqueloba, has similar properties to the traditionally used one, A. quanzensis, it is less used because of its poorly known properties and potential uses. Thus, further research to determine the properties
and suitable end uses of other lesser know species is likely to be beneficial to the country. 相似文献
13.
To analyze the effects of lignin on the destabilization of wood due to quenching, we examined the dielectric properties of
untreated and delignified wood before and after quenching at 20°C from 50 Hz to 100 MHz. For untreated wood, the inflection
points of log ε′ and log σ vs log f and the peak of log(tan δ) vs log f were attributed to interfacial polarization before quenching, and the location of the inflection point shifted to a higher
frequency with increasing moisture content because of changes in the water cluster. After quenching, the inflection points
of log ε′ and log σ and the peak of log(tan δ ) shifted to higher frequency; however, the values of log ε′, log σ recovered to those before quenching with the passage of time. For delignified wood, dielectric relaxation was observed at
a higher frequency than for untreated wood irrespective of quenching. It was inferred that the mobility of water molecules
was influenced by the cluster surroundings because of increased number of adsorption sites in hemicellulose. Moreover, after
quenching, the recovery process did not change greatly over time; it was shown that the matrix structure was affected more
by quenching with the loss of lignin. 相似文献
14.
To investigate the relations between growth and the wood properties of Japanese larch ( Larix kaempferi), six sample trees of varied ages and radial growth were felled and the ring width, ring density, percentage of latewood, and some other factors were determined. There were significant differences in ring density and percentage of latewood between sample trees with vigorous growth and those with poor growth. In corewood the ring density decreased with increasing ring width for all sample trees, whereas in outerwood this trend did not appear. Moreover, the latewood width increased with the increment of ring width only in outerwood, whereas there was almost no change in the corewood. The variation in patterns of ring width, ring density, and percentage of latewood in the radial direction and the relation with height was also studied.Part of this report was presented at the 47th annual meeting of the Japan Wood Research Society, Kochi, April 1997 相似文献
16.
In order to investigate the effects of chemical components and matrix structure on the destabilization of quenched wood, we
examined the physical and mechanical properties of steam-treated wood, hemicellulose-extracted wood, and delignified wood,
which were treated at different levels. For steam-treated and hemicellulose-extracted wood,the relative relaxation modulus
of the quenched sample was lower than that of the respective control sample. For delignified wood, the relative relaxation
modulus fell with weight loss and reached a minimum value at a certain weight loss, and subsequently increased significantly.
The hygroscopicity of all treated samples changed slightly by steaming, whereas increased with removing the component. More-over,
the average volumetric swelling per 1% MC at 100% relative humidity (RH) was less than at 75% RH and 93% RH for component-removed
wood. It was clear that a void structure existed. As a result, the destabilization evaluated by the fluidity (1 - E
t/ E
0) of steam-treated wood was influenced by the amount of adsorbed water. For component-removed wood, destabilization increased
temporarily at lower weight loss because of nonuniform cohesive structure. At high weight loss, destabilization will decreased
because capillary-condensed water gathered in the voids and obstructed the motion of adsorbed water. However, the destabilization
of all treated wood changed less than that of chemically modified wood. 相似文献
17.
Carbon absorbed by forests remains stored in the timber used for wood products, and a change in wood product stock can be
evaluated as substantial removal/emission of atmospheric carbon. Since the carbon storage effect due to harvested wood products
(HWP) might be taken into account in the future framework of carbon mitigation, it is crucial to estimate the carbon fl ow
and stock concerning HWP for the next commitment period. In the present study, we developed a model for estimating the fl
ow and stock of wood products in Japan’s building, furniture, and paper sectors. The HWP carbon storage effect and substitution
effect (carbon reduction by substituting fossil fuels and energy-intensive materials with HWP) up to 2050 were quantitatively
estimated by lifetime analysis. Our model simulation revealed that (i) the carbon stock change in Japan due to HWP would be
evaluated as a large emission if the atmospheric-fl ow approach is adopted, (ii) carbon removal would not significantly increase
if the ratio of newly constructed wooden buildings/furniture remains stable, and (iii) the carbon storage effect together
with the substitution effect would have a significant impact on climate change mitigation if the ratio of newly constructed
wooden buildings/furniture is gradually improved to 70% by 2050. 相似文献
18.
由聚丙烯(PP)、高密度聚乙烯(HDPE)和聚苯乙烯(PS)组成的混合废旧塑料与木粉经高速混合机混合后,采用双螺杆/单螺杆串联挤出机组制备了木粉/混合废旧塑料复合材料。探讨了马来酸酐接枝苯乙烯-乙烯/丁烯-苯乙烯嵌段共聚物(SEBS-g-MAH)和原位接枝马来酸酐(MAH)对木粉/混合废旧塑料复合材料力学性能的影响。结果表明,与使用MAH和DCP的原位反应共混相比,SEBS-g-MAH显著提高了复合材料的抗冲击性能,但对拉伸和弯曲性能的改善不如原位反应共混显著。总的来说,混合废旧塑料制备的复合材料的力学性能要低于纯塑料混合物制备的复合材料,尤其是拉伸断裂伸长率。微观形态研究表明,添加SEBS-g-MAH和原位接枝MAH均可提高木粉与塑料混合物之间的界面相容性,但与添加SEBS-g-MAH相比,原位接枝MAH能更好的改善PP、HDPE、PS与木粉之间的界面结合。原位接枝MAH可被看作是一种改善木粉与塑料混合物间界面相容性的有效途径。此外,采用动态力学分析(DMA)进一步表征了复合材料的储能模量和阻尼因子。 相似文献
19.
Greater organic matter inputs in agroforestry systems contribute to the long-term storage of carbon (C) in the soil, and the
use of simulation models provides an opportunity to evaluate the dynamics of the long-term trends of soil organic carbon (SOC)
stocks in these systems. The objective of this study was to apply the Century model to evaluate the long-term effect of agroforestry
alley crop and sole crop land management practices on SOC stocks and soil C fractions. This study also evaluated the accuracy
between measured field data obtained from a 19-year old tropical (TROP) and 13-year old temperate (TMPRT) alley crop and their
respective sole cropping systems and simulated values of SOC. Results showed that upon initiation of the TROP and TMPRT alley
cropping systems, levels of SOC increased steadily over a ~100 year period. However, the sole cropping systems in both tropical
and temperate biomes showed a decline in SOC. The active and passive C fractions increased in the TROP agroforestry system,
however, in the TMPRT agroforestry system the active and slow fractions increased. The input of organic matter in the TROP
and TMPRT agroforestry systems were 83 and 34% greater, respectively, compared to the sole crops, which likely contributed
to the increased SOC stock and the C fractions in the alley crops over the 100 year period. Century accurately evaluated levels
of SOC in the TROP ( r
2 = 0.94; RMSE = 226 g m −2) and TMPRT ( r
2 = 0.94; RMSE = 261 g m −2) alley crops, and in the TROP ( r
2 = 0.82; RMSE = 101 g m −2) and TMPRT ( r
2 = 0.83; RMSE = 64 g m −2) sole crops. Century underestimated simulated values in the alley cropping systems compared to measured values due to the
inability of the model to account for changes in soil bulk density with increasing organic matter inputs with tree age from
prunings or litterfall. 相似文献
20.
Journal of Pest Science - The fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is a major pest of maize crops and others row crops on the American continent, and this... 相似文献
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