共查询到20条相似文献，搜索用时 15 毫秒
1.
林区公路工程建设是林业生产中一项十分重要的工作。根据本人多年实践经验,总结出了用可编程序计数器对林区公路工程勘测设计中平曲线(圆曲线、复曲线、回头曲线等)测设参数进行编程计算的方法。在野外勘测设计中,只需输入平曲线半径、转向角或弧长、弦长等数据,就能快速、准确地计算出圆曲线及细部测设参数,不仅提高了工作效率,而且提高了设计质量和设计水平。 相似文献
2.
The application of time–temperature superposition principle (TTSP) to orthotropic creep in dry Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) was investigated through a sequence of short-term tensile creep for longitudinal (L), radial (R), and tangential (T) specimens in the temperature range of 30–150 °C. A visual assessment for the validity of TTSP was carried out by applying the approximated complex plane (ACP). The results showed that TTSP was well matched for R and T specimens using horizontal shift factor to construct master curves. As for L specimen, an additional vertical shift factor was applied to construct a smooth master curve, owing to the temperature-dependent compliance. Based on the application of ACP, the creep model governed by a power law was proposed to successfully depict the master curve for each main anatomy direction. The present study partially provided the firsthand data in verifying the applicability of TTSP of the orthotropic viscoelasticity of Chinese fir wood, and successfully constructed the rheological model to predict the orthotropic creep response. More importantly, the result can function as the base to the structural safety designs for the engineering structures of Chinese fir in practice. 相似文献
3.
Planted Forest and Diverse Cultures in Ecological Village Planning: A Case Study in Tarama Island,Okinawa Prefecture,Japan 总被引：1，自引：1，他引：0
Traditional village landscapes that were planned with a combination of local traditional beliefs and the Feng Shui concepts of ‘ho:go’, featured in remaining patches of flourishing planted forest on Ryukyu Islands, were estimated to have been built about 300 years ago. This study sought to clarify the actual landscape composition and map the layout and distribution of landscape elements, with a focus on understanding the dimension of the widespread Feng Shui woods. The cultural landscape combines shapes of patches of greening, corridors of planted forest belts and intersecting roads, scattered areas of water and clustered human settlements. On the relatively flat islands, a forest belt about 15 m wide was planted to curve in front of the village and be connected with the preserved natural forest on the low hills behind the settlements to shape a green protective circle with a radius of about 400 m. The grounds of each house were surrounded by one row of trees. Thousands of big Fukugi trees were found surrounding the settlements and sacred sites. These forest belts are almost completely connected and shape green corridors providing habitat for flora and fauna. Inside the village, roads have been designed to meander, and thus function to mitigate damage from strong winds. In Okinawa, utaki (sacred places dedicated to a guardian deity of hamlets) and the remains of old springs also consist of important landscape units. Such a traditional aesthetic village landscape embodies the harmony of man and nature, or ‘people living in the forests’. A cultural landscape with ecological context needs to be reevaluated as a rural planning style in island topography, and promoted as a tourist attraction in order to better conserve it. 相似文献
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A new method has been developed for detecting localized defects such as edge knots using a bending deflection curve. The coordinates
of a bottom edge (edgeline) of an unloaded piece of lumber are extracted from a digital image, and a bending deflection curve
is obtained from the displacement of the edgeline of the lumber using a digital image correlation (DIC) technique. Depending
on the knots within the beam, the bending deflection curve is shifted from the curve of a defect-free beam. The measured bending
deflection curve is regressed to a theoretical curve by elementary beam theory. A finite element method (FEM) model of the
beams including defects as simplified knot structure has been performed. Comparison between the bending experiment and FEM
analysis shows that cross-sectional reductions cause characteristic variations in the bending deflection curves depending
on the position of encased knots, and local grain distortions cause variations in the curves depending on the direction of
spike knots. Using the residual variance between the measured deflection curve and a polynomial regression curve, it is possible
to detect knots at which failures initiate.
Part of this article was presented at the 57th Annual Meeting of the Japan Wood Research Society, Hiroshima, Japan, August
2007 相似文献
6.
Mehran Roohnia Amirhooman Hemmasi Ali Yavari Habibolla Khademieslam Behzad Bazyar 《Journal of Wood Science》2014,60(5):321-326
In the present study, elastic properties of scarf-jointed oak (Quercus castaneifolia) timbers with the application of two different types of adhesives (polyvinyl acetate and isocyanate) were evaluated using free flexural vibration of free–free beam method in different flexural directions of vibration, i.e., tangential and redial directions. Samples were taken from trees of Hyrcanian forests in Iran with nominal dimensions of 20 × 20 × 360 mm3. Comparing the results of elastic properties of clear oak wood beams with scarf-jointed samples wood showed that scarf joints with the bonding angles of 70° and 75°, covered by polyvinyl acetate adhesive, did not demonstrate any significant effect on modules of elasticity. Scarf-jointed beams with smaller joint angles (60° and 65°) were considerably weaker or totally unreliable in their moduli of elasticity. It is also shown that the magnitude of effect gets worst by using isocyanate rather than polyvinyl acetate adhesive. 相似文献
7.
We selectively assessed the thermal and hygrothermal treatment times of duplex heat-treated samples from the softwood hinoki cypress (Chamaecyparis obtusa) and the hardwood Japanese zelkova (Zelkova serrata) using near-infrared (NIR) spectroscopy with principal component analysis (PCA) and spectral-kinetic analysis. Wood samples from each species were thermally or hygrothermally treated at 120, 130, 150, and 180 °C, and the second-derivative spectra of these samples in the 6300–5450 cm?1 range, where moisture content has the smallest effect, were then subjected to PCA. The master curve that was calculated by kinetic analysis successfully explained changes in the first principal component (PC1) scores with thermal treatment time for all temperatures. The angles between the PC1 loadings that explained the spectral variation due to thermal and hygrothermal treatment were 79° for hinoki and 80° for zelkova. Thus, calculation of the inner product between the second-derivative spectra of duplex heat-treated wood and a loading vector that explained the spectral variation due to thermal or hygrothermal treatment allowed us to selectively assess the thermal and hygrothermal treatment times. 相似文献
8.
To prevent, detect, and protect against forest fires, forest personnel need to define rules for determining forest fire risk. In Portugal, all municipalities must annually produce forest fire risk(FFR) maps. To produce more reliable FFR maps more easily, we developed an open source model using the Modeler plugin of SEXTANTE in the program QGIS version 2.0 Dufour. The model provides all the maps involved in the FFR model(susceptibility map, hazard map, vulnerability map, economic value map,and potential loss map) and was produced according to Portuguese Forest Authority's(AFN, Autoridade Florestal Nacional) rules for determining the FFR. This model was tested for the Portuguese municipality Santa Maria da Feira, where 40 % of the total municipality area falls in the category ‘‘very high' or ‘‘high' fire risk. The ‘‘very high'fire risk area is mainly classified as broad-leaved forest and has the steepest slopes(15 %). The distance of burned areas to roads was also analyzed; the proportion of burned areas increased with increasing distance to the main roads.In addition, 92.6 % of the ‘‘high' and ‘‘very high' risk zones were located in areas with lower elevation. These results confirmed that forest fire is strongly influenced not only by environmental factors but also by anthropogenic factors. The procedure implemented here was compared with our open source application already available in QGIS and also to the same procedure implemented in GIS proprietary software. Although the results were obviously the same, the model developed here presents several advantages over the other two approaches. Besides being faster,it is easy to change the model parameters according to user needs(i.e., to the rules of different countries), and can be modified and adapted to other variables and other areas to create risk maps for different natural phenomena(e.g.,floods, earthquakes, landslides). The model is easy to use and to create risk and hazard maps rapidly in a free, open source environment that does not require any programming knowledge. 相似文献
9.
Surface quality and gluing performance of black spruce samples prepared by peripheral straight-edge knife planing and sanding were studied. Four wavelengths (1.5, 1.9, 3.1, and 6.5 mm) and four rake angles (15°, 20°, 25°, and 30°) were tested for peripheral planing. Three feed speeds (4, 10.5, and 17 m/min) and three grit size sandpapers (80, 100, and 120) were studied for sanding. The resulting surfaces were glued with an isocyanate adhesive and tested to evaluate their gluing performance (shear strength and percent wood failure). Results revealed that planing with a rake angle of 20° and wavelengths of up to 3.1 mm produced wood surfaces with adequate glueline shear strength. Sanding with 80-grit sandpaper produced the best glueline shear strength, regardless of feed speed. After accelerated aging, the loss of gluing performance was lower for the sanded samples compared with that of planed samples. In general, sanding process produced better wood surfaces for bonding with the adhesive studied. 相似文献
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The effects of temperature and moisture content on selected mechanical properties associated with the chipping process were evaluated. In chipping, mechanical properties such as shear parallel to the grain, cleavage, and bending are involved. Matched samples of heartwood and sapwood were obtained from freshly harvested logs of black spruce and balsam fir to determine the variation of the studied mechanical properties between ?30 and 20 °C, at intervals of 10 °C. Moisture content (MC), basic density (BD), and annual ring width (RW) were measured for each sample. For both wood species, temperature had a significant effect on all mechanical properties under freezing conditions (below 0 °C). This effect was more important for sapwood than for heartwood, which was explained by the difference in MC between these two types of wood. Between 0 and 20 °C, temperature and type of wood did not show any significant effect on the mechanical properties. Multiple regression models were obtained to predict the mechanical properties. These regressions showed that MC was the most important factor to explain the mechanical properties below 0 °C. However, for temperatures of 0 °C and higher, BD was the principal factor to predict the mechanical properties. RW was not a significant factor to predict any mechanical property. Cleavage was the most sensitive one to changes in temperature followed by shear, modulus of rupture, and modulus of elasticity. These results could be of great importance in the chipping process. 相似文献
12.
Arezoo Soltani Prem L. Sankhayan Ole Hofstad Farshid Eshraghi Abbas Arabmazar 《Small-Scale Forestry》2017,16(3):347-365
Construction of new roads in rural areas is closely linked to market accessibility and economic growth. It also leads to exploitation of natural resources that may accelerate deforestation. These conflicting effects of an improved road network on rural development and depletion of forest resources present a serious challenge to policy makers interested in sustainable development. This paper investigates the effects of road networks on biological and socio-economic behaviour. The analysis was conducted by using a non-linear bio-economic model for a community in southern Zagros, Iran where they manage the adjoining forest according to traditional rules. Data for the model were obtained through village surveys and published resources. The model followed a holistic approach by incorporating a number of livelihood activities, such as, crop cultivation, goat husbandry, charcoal production and hiring out of community labour, along with several logical resource constraints. It was run over a period of 45 years. The results showed that new roads can either fuel forest degradation or contribute to forest protection depending on the choice of policy options. The study concludes that construction of new roads should be accompanied by policies aimed at higher state controls over newly accessible forest areas through regulatory measures, creation of new non-farm employment opportunities and strengthening of traditional institutions through providing extension services for local communities and facilitating NGO involvement so as to minimize the adverse effects on forest resources. 相似文献
13.
Data on thermal-death kinetics of bark beetles are essential to develop phytosanitary heat treatments for pine wood and pine wood packaging materials. Using a heating block system, effects of different heating rates between 44 and 50°C at 2°C intervals on destruction of Dendroctonus armandi adult insect were examined. Heat resistance of the insects was found to increase at low heating rates (0.1 or 0.5°C/min). Therefore, the thermal-death kinetics of the beetles were determined at a high heating rate of 5.0°C/min which simulated the rapid dielectric heating of wood products. Results showed that the thermal death curve of D. armandi followed a zero-order reaction kinetic model, indicating the heat destruction rate of the beetle at different treatment temperatures to be independent of their population size. The required thermal holding times to result in destruction of the entire population were 40, 8, 4, and 2?min at 44°C, 46°C, 48°C, and 50°C, respectively. The evaluated thermal-death kinetic data are useful in developing effective beetle elimination quarantine protocols for the wood. A 50°C ?2?min heat treatment with a heating rate of ～5°C/min can be effectively used for disinfesting bark wood materials. 相似文献
14.
Pai, an arid forest in Sindh Province of Pakistan,is important for the environmental, social, economic development and conservation of ecosystems of the province. Considering the significance of the forest for Sindh and the calls from the local population for its deforestation,we quantified the spatial and temporal variation in the vegetation of the forest and land surface temperature(LST)using optical and thermal Landsat satellite data. Our analysis of temporal(1987–2014) images with Arc GIS10.1 revealed that the dense forest area was greatest at725 ha(37 % of the total forest area) during 2013 while it was smallest at 217 ha(11 %) in 1992. The sparse forest area peaked during 1987 at 1115 ha(58 %) under shrubs whereas it was smallest at 840 ha(43 %) in 1992, and the maximum deforestation of Pai forest occurred during 1992.Spatial change in vegetation over a period of about27 years(1987–2014) revealed that vegetation increased on an area of 735 ha(37 %), decreased on 427 ha(22 %),and there was no change on 808 ha(41 %) of the forest.Variation in temperature between shaded(dense forest) and unshaded areas(bare land) of the forest was from 6 to10 °C. While the temperature difference between areas with sparse forest and bare land ranged from 4 to 6 °C. An inverse relationship between LST and NDVI of Pai forest with coefficients of determination of 0.944 and 0.917 was observed when NDVI was plotted against minimum and maximum LST, respectively. The vegetation in the forest increased with time and the areas of more dense Pai forest supported lower surface temperature and thus air temperature. 相似文献
15.
Franz Holzleitner Christian Kanzian Karl Stampfer 《European Journal of Forest Research》2011,130(2):293-301
Round wood supply in Austria is often affected by different factors such as bottlenecks or oversupply due to changing market, weather and road conditions. An additional factor impacting the complex wood supply chain is the rising transport costs from the landing to the sawmill. Logging trucks are the primary transportation technology used from the forest to the customer??s site. The objectives of this study were to analyze the actual situation and characteristics of typical trucking activities for round wood supply from the region to an Austrian sawmill. The study used time and fuel consumption, proportion of travel on forest roads and average speed on different functional road classes to estimate productivity and costs. Data collection including GPS-tracking was done using fleet management equipment built into the driver??s cabin. The GPS-routes were analyzed in ArcGIS 9.3 based on the national road network and its attributes. The sawmill studied with a yearly demand of 600,000 m3 round wood was located in southern Austria. In total, more than 2,000 round trips operated by seven logging trucks recorded close to 100,000 km. The transport distance from the forest to the sawmill averaged 51 km. The average share on forest roads within a route to the sawmill was 14.2% with an average speed of 13.5 km/h, whereby the forest road is defined as road with minor importance. Transport costs from the forest site to the sawmill with a truck and trailer were ? 11/m3 solid timber based on an average load size of 25 m3. An average 0.77 l of diesel fuel per kilometer was consumed during a round trip including all work phases. A trip to an interim storage location consumed 2.05 l/km due to the number of work phases without driving distance. 相似文献
16.
The spined soldier bug, Podisus maculiventris (Say), is a generalist predator that can control >75 insect pests in various agroecosystems. Despite valuable results from the previous studies, thermal development and survival of P. maculiventris over a wide range of temperatures had not been elucidated completely. This study was conducted to investigate the stage-specific development and survival of P. maculiventris at eight constant temperatures (13.2, 18.4, 21.7, 23.7, 27.2, 32.7, 35.2, and 40.6 °C) covering the entire thermal range for P. maculiventris development. Completion of egg development was observed at 13.2–32.7 °C, whereas nymphs successfully developed into adults at 18.4–32.7 °C. Survival model using log-normal equations showed bell-shape patterns for all stages, and temperatures resulting in highest survival of P. maculiventris were 19.9, 24.3, and 24.5 °C for egg, nymph, and egg to adult, respectively. Developmental rates at the eight temperatures were fitted with a nonlinear Briere model, which estimated optimal temperatures for development as 31.2, 30.6, and 30.6 °C for egg, nymph, and egg to adult, respectively. Operative thermal ranges (i.e., in-between the lower and upper developmental thresholds) were estimated to be 8.9–35.2, 12.8–35.2, and 12.7–35.2 °C for egg, nymph, and egg to adult, respectively. In a linear model, the lower thresholds were 10.9, 13.1, and 13.0 °C for egg, nymph, and egg to adult, respectively. Findings herein provide comprehensive data and explanations on optimal temperature and thermal requirement for P. maculiventris, which can be used to optimize environmental condition in mass rearing and predicting phenology of P. maculiventris in the field. 相似文献
17.
Growth of commercial forestry is highly dependent on the availability of fast-growing planting materials. Consequently, the efficient utilization of fast-growing plantations can greatly impact productivity. The objectives of this study were to evaluate variations in the growth potential of two clones and to estimate the average stem radial growth advantage of a fast-growing clone using data obtained from Sappi landholdings in eastern South Africa and a mixed modelling approach that permits the incorporation of covariance structure into the statistical model. During the first 2 years of growth, the stem radius of nine trees each of two clones was measured using dendrometer attached to the tree. A second-degree fractional polynomial model was chosen to show the functional relationship between stem radius and tree age. Growth of the two hybrid clones differed significantly. The Eucalyptus grandis × Eucalyptus urophylla clone grew faster than the E. grandis × camaldulensis clone, indicating better genetic potential for rapid growth and yield. This study can be considered as starting point to further compare the potential for rapid growth of several hybrid clones using the longitudinal data modelling approach. 相似文献
18.
Amphiphobic wood has successfully been fabricated using a combination of O2 plasma surface activation and coating of pre-hydrolyzed methyltrimethoxysilane (MTMS). The effect of O2 plasma activation on surface chemistry and surface roughness was investigated using X-ray photoelectron spectroscopy and laser scanning confocal microscope profilometry, respectively. Pre-hydrolyzed MTMS was used to impart oleophobicity to both softwood and hardwood samples with tunable hydrophilicity by adjusting the sonication time during pre-hydrolysis. Depending on hydrolysis time, the coated wood samples display wetting behavior ranging from superhydrophilic/oleophobic (immediate water absorption; motor oil contact angles 63.5° for hardwood and 62.4° for softwood) to amphiphobic (water contact angles 104.3° for hardwood and 91.1° for softwood; motor oil contact angles 68.7° for hardwood and 63.9° for softwood), without affecting visual appearance of the wood. For all plasma-activated MTMS-coated wood samples, no absorption of motor oil is observed for several months, indicating stable oil resistance. The intrinsic porosity of wood is also partially retained after coating. 相似文献
19.
In order to understand the reason why glycerin pre-treatment can accelerate the deformation fixation of compressed wood, the
interaction between glycerin and wood at various temperatures was investigated in this study from stress relaxation approach.
The compression stress relaxation curves of poplar (Populus cathayana Rehd.) samples impregnated with glycerin were measured at temperatures ranging from 25 to 180°C, together with the curves
of oven-dry wood at temperatures between 100 and 180°C for comparison. The activation energy was calculated according to the
Eyring’s absolute rate reaction theory. The results showed that temperature had very obvious effect on stress relaxation for
both glycerin-treated wood (GTW) and oven-dry wood. The stress released very fast at higher temperatures. Glycerin showed
an accelerating effect on stress relaxation. At temperatures exceeding 120°C, a complete relaxation of the stress could be
expected. While for untreated wood, it cannot be reached until 160°C. By calculating the apparent activation energy (ΔE) of
GTW at different temperatures, it is clear that two mechanisms are responsible for different temperature ranges. From 40 to
100°C, ΔE is only 8.24 kJ/mol, which corresponds to the hydrogen bonds formed between wood and glycerin molecules; from 120
to 180°C, ΔE reached 81.38 kJ/mol, which corresponds to the degradation of hemicelluloses or lignin, and during this process,
new cross-linking would happen. 相似文献
20.
本文介绍具有缓和曲线圆曲线的2种测设方法:a.分布测设缓和曲线和圆曲线;b.在直缓点或缓直点1次设站连续测设近端缓和曲线和圆曲线。同时给出2种测设方法的切线支距法和偏角法的公式。 相似文献