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1.
Comparative study on three dynamic modulus of elasticity and static modulus of elasticity for Lodgepole pine lumber 总被引：2，自引：0，他引：2
LIANG Shan-qing FU feng 《林业研究》2007,18(4):309-312
The dynamic and static modulus of elasticity （MOE） between bluestained and non-bluestained lumber of Lodgepole pine were tested and analyzed by using three methods of Non-destructive testing （NDT）, Portable Ultrasonic Non-destructive Digital Indicating Testing （Pundit）, Metriguard and Fast Fourier Transform （FFT） and the normal bending method. Results showed that the dynamic and static MOE of bluestained wood were higher than those of non-bluestained wood. The significant differences in dynamic MOE and static MOE were found between bulestained and non-bluestained wood, of which, the difference in each of three dynamic MOE （Ep. the ultrasonic wave modulus of elasticity, Ems, the stress wave modulus of elasticity and El, the longitudinal wave modulus of elasticity） between bulestained and non-bluestained wood arrived at the 0.01 significance level, whereas that in the static MOE at the 0.05 significance level. The differences in MOE between bulestained and non-bluestained wood were induced by the variation between sapwood and heartwood and the different densities of bulestained and non-bluestained wood. The correlation between dynamic MOE and static MOE was statistically significant at the 0.01 significance level. Although the dynamic MOE values of Ep, Em, Er were significantly different, there exists a close relationship between them （arriving at the 0.01 correlation level）. Comparative analysis among the three techniques indicated that the accurateness of FFT was higher than that of Pundit and Metriguard. Effect of tree knots on MOE was also investigated. Result showed that the dynamic and static MOE gradually decreased with the increase of knot number, indicating that knot number had significant effect on MOE value. 相似文献
2.
《Southern Forests》2013,75(4):277-285
Field establishment of South Africa’s most important commercial pine species, Pinus patula, is severely hampered by the pitch canker fungus, Fusarium circinatum. Importantly, hybrids between P. patula and other pine species tolerant to the pitch canker fungus, such as P. tecunumanii and P. oocarpa, have been identified as an alternative planting stock. In this study, variation in tree volume and dynamic modulus of elasticity (MOEdym) of the P. patula × P. tecunumanii (low- and high-elevation [LE and HE] ecotypes) hybrid was compared with the P. elliottii × P. caribaea hybrid, and the pure species P. tecunumanii (LE) and P. patula. The MOEdym was assessed using the Fakkop TreeSonic microsecond instrument across three sites. The results of the study showed that P. patula × P. tecunumanii LE performed significantly better than P. patula × P. tecunumanii HE for volume and MOEdym, which in turn was significantly better than P. patula. The MOEdym and tree growth decreased with an increase in elevation. There was significant taxon × site interaction for volume and MOEdym. The results of these trials suggested that P. patula × P. tecunumanii LE is a suitable alternative to P. patula in the Sabie region of Mpumalanga in South Africa on frost-free sites, in terms of the traits that were assessed. 相似文献
3.
A method of determining the Young’s modulus of timber using the stress wave propagation velocity without knowing the timber
density was developed in our previous study. This method enables the estimation of Young’s modulus by Monte Carlo simulation
using an existing database of the Young’s modulus versus density relationship as reference. Here, in Part II, we consider
the effect of the reference distribution database on the accuracy of the estimated Young’s modulus by the developed method.
Twelve different reference distribution databases were used in this study, containing Young’s modulus versus density data
for more than 13 000 real-size timber specimens of ten different species. We obtained the following results: (1) the distribution
of Young’s modulus estimated using an arbitrary stress wave propagation velocity depends on the reference distribution database
employed, (2) the most important factor is not that the reference database has data on the same species as the timber in the
test, but rather that the reference distribution database covers the foreseeable range of timber densities within the test,
and (3) the estimation accuracy is higher than about 80% when the database covers many species and has wide ranges of densities
and Young’s moduli. This estimation method was developed in order to measure the Young’s modulus of timber whose density cannot
be measured. Considering that the quality of lumber has a large variation, such estimation accuracy will be useful for practical
applications. 相似文献
4.
In this article, we report on an estimation method for Young’s modulus that entails measuring only the stress wave propagation
velocity of timber built into structures such as wooden buildings. Methods of estimating Young’s modulus that use the stress
wave propagation velocity and characteristic frequency of timber in conjunction with timber density have long been used. In
this article, we propose a method of easily and accurately estimating Young’s modulus from the stress wave propagation velocity
without knowing the timber density. This method is based on a database of wood strength performance and density accumulated
from a variety of research data and the method estimates Young’s modulus by a simulation method. We compared the Young’s moduli
estimated by this method with those obtained by the bending test and by the measurement of the stress wave propagation velocity
and density, and found similar results. This coincidence suggests that the method of estimating Young’s modulus presented
in this article is valid. For example, the method is effective for convenient evaluation on site when determining whether
a wooden building’s structural components should be reused or replaced when repairing or remodeling a building. 相似文献
5.
The effect of moisture content on the stress wave propagation velocity was investigated in order to estimate the Young’s modulus of full-scale timbers in an air-drying state using the measurement of stress wave propagation velocity above the fiber saturation point. Using Japanese cedar lumber, the velocity and the density under high-moisture condition and air-drying states were measured respectively; after measuring the modulus of elasticity in an air-drying state, the moisture content of each condition was measured. By performing numerical analysis on these data, the relationship between the moisture content and the rate of change of velocity of full-scale timbers was derived. This relationship was used to estimate the Young’s modulus of the timber in the air-drying state from the velocity in high-moisture condition. First, the velocity and the Young’s modulus in an air-drying state were estimated accurately from its density, moisture content and velocity under high-moisture condition. In cases where the density could not be measured, using the database of mechanical properties with the Monte Carlo simulation method, the Young’s modulus of the full-scale timber in an air-drying state might be estimated within 20% accuracy from its moisture content and velocity under high-moisture condition. 相似文献
6.
7.
Indigenous management of tropical forest ecosystems: the case of the Kayapó indians of the Brazilian Amazon 总被引：1，自引：0，他引：1
Darrell Addison Posey 《Agroforestry Systems》1985,3(2):139-158
The Kayapó Indians of Brazil's Amazon Basin are described as effective managers of tropical forest, utilizing an extensive inventory of useful native plants that are concentrated by human activity in special forest areas (resource islands, forest fields, forest openings, tuber gardens, agricultural plots, old fields, and trailsides). Long-term transplanting and selection of plants suggest semi-domestication of many species. The overall management strategies of forest also includes many manipulated animal species (birds, fish, bees, mammals) utilized as food and game. Forest patches (apêtê) are created by Indians from campo/cerrado using planting zones made from termite and ant nests mixed with mulch: formation and development of these is briefly discussed, including the implications for new ideas concerning reforestation and campo management. Finally an integrative cognitive model is presented showing the relationships between variants of forest and savanna recognized by the Kayapó. Indigenous knowledge of subtle similarities between conceptually distinct ecological units in the model allows for the interchange of botanical material between microclimates to increase biological diversity in managed areas. It is suggested that indigenous knowledge is extremely important in developing new strategies for forest and campo/cerrado conservation, while improving productiveness of these ecological systems. Such knowledge is not only applicable for Amazônian Indians, but also has far-reaching implications for human populations throughout the humid tropics.This is a preliminary survey of indigenous management strategies that is generated as a part of the Projeto Kayapó , an interdisciplinary ethnobiological research project funded by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (Brazilian National Council for Scientific and Technological Development) and the World Wildlife Fund. I would like to thank Drs. Gerhard Gottsberger and Anthony Anderson for their assistance in collecting plants that are currently being identified to supply more complete data on Kayapó subsistence. I also wish to thank FUNAI (Fundaão Nacional do Índio) for their assistance and support, as well as FAB (Fora Aérea Brasileira) and VOTEC for providing some transportation to/from Gorotire, and the Unevangelized Field Missions for their assistance in providing communication and acquiring supplies. 相似文献
8.
Futoshi Ishiguri Sapit Diloksumpun Jun Tanabe Kazuya Iizuka Shinso Yokota 《Journal of Wood Science》2013,59(6):506-511
Eucalyptus camaldulensis Dehnh. is extensively planted in Thailand to produce wood chips used as raw material for pulp and paper. To promote the utilization of the wood from plantation-grown E. camaldulensis for solid lumber, stress-wave velocity of trees and dynamic Young’s modulus of logs were investigated for 4-year-old trees of eight half-sib families selected for pulpwood production on the basis of the growth characteristics in the previous tree breeding program. For the eight families, the mean stem diameter at 1.3 m above ground level and mean tree height were 7.6 cm and 11.9 m, respectively. The mean stress-wave velocity of eight families was 3.45 km/s. Dynamic Young’s modulus of logs ranged from 7.88 to 17.64 GPa, and the mean value for the eight families was 11.72 GPa. Stress-wave velocity of trees was significantly correlated with dynamic Young’s modulus of logs, suggesting that dynamic Young’s modulus of wood can be evaluated nondestructively by stress-wave velocity of trees. Significant differences in stress-wave velocity and dynamic Young’s modulus of logs were obtained among families. Thus, to promote the utilization of E. camaldulensis wood for solid lumber production, selection of trees with high Young’s modulus should be applied to trees already selected for the growth characteristics in the previous tree breeding program. 相似文献
9.
10.
LiJingwen ZhangHuarong LiJunqing 《中国林学(英文版)》2003,5(3):6-9
Random amplified polymorphic DNA (RAPD) markers were used to analyze genetic variation of Podocarpus imbricatus in Hainan Island and Mainland of China. Two populations of Dacrydium pierrei were used as comparison materials. Both Podocarpus imbricatus and Dacrydium pierrei showed a low level of genetic diversity. However, Podocarpus imbricatus showed higher genetic diversity and higher population differentiation than Dacrydium pierrei. The geographic range may affect the geneticdiversity of Podocarpus imbricatus and Dacrydium pierrei signific antly. The UPGMA cluster tree showed that populations of Podocarpus imbricatus in Hainan Island and Guangxi Zhuang Autonomous Region were closer than those in Yunnan Province,indicating possible gene flow between Hainan Island and Guangxi Zhuang Autonomous Region. The young geological history of Hainan Island and the three times of unification and separation between Hainan Island and the Mainland may give the two species more possibilities of gene flow. 相似文献
11.
12.
本文研究了长江三峡花岗岩地区林地土壤流失特性．结果表明由鳞片状面蚀导致的土壤流失量月分布与月降雨量的分布趋势基本一致，二者呈现出较为明显的线性相关关系．植物盖度≥０．７０的林地土壤流失多集中发生在６～９月份，土壤流失量在５０００ｔ·ｋｍ－２·ａ－１以下．盖度＜０．７的林地土壤流失年内分布时间多在３～１０月份，土壤流失量为５００～６０００ｔ·ｋｍ－２·ａ－１． 相似文献
13.
IntroductionBal11booisl11ainfoodoftl1cgial1tpal1daint`.ildal1dman-fedgiantpandattasfCd111ucl1bal11boobcsldcsconccntratestl1atx`erel11adcofgrainPOwdcrtokccpltsfeedingl1abitsinwiId,buttl1cdigestivcratcofcoarsccclluloseisvery'low,il1botl1ttilda11d111a11-fcdpa11das.Wecanfindthattl1eba111boot'asall11ostl1otdigcstcdfrolllthefCccsthatcol1tai11edl11ucI1bal11boosticks.CI1cl1Yucllulletc.(l993)rcPortedt1lattl1edigcstit'eratcil1bal11boocoarsecelluloscisabout25%ol1lv.Tl1cautl1orsdesiglledthiscxPCrilll… 相似文献
14.
J. Paul McLean Olivier Arnould Jacques Beauchêne Bruno Clair 《Annals of Forest Science》2012,69(3):399-408
Context and aim
This study aimed to examine the effect of the tension wood G‐layer on the viscoelastic properties of wood.Methods
Tension wood and opposite wood samples were obtained from six French Guianese tropical rainforest species (Sextonia rubra, Ocotea guyanensis, Inga alba, Tachigali melinoni, Iyranthera sagotiana and Virola michelii); the tension wood of the former three of these species had a G‐layer, whilst the tension wood from the latter three had no G‐layer. Tensile dynamic mechanical analysis (DMA) was performed on green never dried wood samples in the longitudinal direction with samples submerged in a water bath at a temperature (30°C) and frequency (1 Hz) representative of the conditions experienced by wood within a living tree. Then, DMA was repeated with samples conditioned to an air-dried state. Finally, samples were oven-dried to measure longitudinal shrinkage.Results
Tension wood did not always have a higher longitudinal storage (elastic) modulus than opposite wood from the same tree regardless of the presence or absence of a G‐layer. For the species containing a G‐layer, tension wood had a higher damping coefficient and experienced a greater longitudinal shrinkage upon drying than opposite wood from the same species. No difference was found in damping coefficients between tension wood and opposite wood for the species that had no G‐layer.Conclusion
It is proposed that the different molecular composition of the G-layer matrix has an influence on the viscoelasticity of wood, even if a biomechanical gain is not yet clear. This study shows that rheological properties and longitudinal shrinkage can be used to detect the presence of a G‐layer in tension wood.15.
16.
Kisito Gandji Valère K Salako Achille E Assogbadjo Vincent OA Orekan Romain L Glèlè Kakaï Brice A Sinsin 《Southern Forests》2017,79(2):133-142
This study assessed ecological and socio-economic impacts of a participatory forest management project in the Republic of Benin. The study focused on the Wari-Maro Forest Reserve and the ‘Projet d’Aménagement des Massifs Forestiers’ five years after its completion. A forest inventory was carried out using 37 square plots of 729 m2 each to characterise the population structure of two types of plantations established: plantations with exotic species and plantations with native species. In addition, individual surveys were conducted with local households, organs of joint forest management and forestry officers to evaluate their perceptions about the participatory management of the plantations. Finally, the sustainability of the participatory management was assessed with an established rating system. Results showed that plantations with exotic species were more successful than plantations with native species. Local communities argued that they have not been involved in the plantations design but only in the implementation step and that their standards of living have decreased after the project completion. The rating system used showed that the participatory management of plantations had a short-term sustainability. The findings suggest that future projects should be designed and implemented with better participation of local communities as full partners. 相似文献
17.
Bioevolution is still a main puzzle and attracts many scientists to research on it. Here I present that organisms have two important properties, definite structure and self-reproduction. Based on the number and connection of the structural units, organisms can be divided into three groups, unicellular, particellular and polycellular organisms. It can be called polycellular evolution that organisms evolve from unicellular, particellular to polycellular. Also it can be called diploid evolution that organisms evolve from haplobes to diplobes, two groups based on the reproductive differences. Some concepts like spore, zygote and embryos are redefined in the paper. Moreover, I present that embryos are the most important boundary of bioevolution and organisms can be divided into two evolutionary phases, the lower and the higher. The lower organisms, Kingdom Microbia (kingd. nov.), are inembryonate, which include Acytophyla (phyl. nov.), bacteria, protozoa,fungi and inembryonate algae. The higher organisms are embryonate and have two branches, Kingdom Plantae and Kingdom Animalia.Plantae are sessile and, autotrophic or sporogenic, which include higher plants and Nudembryophyta (phyl. nov.). Animalia are heterotrophic and, motile or gametogenic, which include all multicellular animals. The new system, which reflects the two important phases of bioevolution and two branches of higher organisms, can really correct the problem of different kingdoms in different researches or by different researchers. 相似文献
18.
We investigated the correlation of large fires([300 ha) from 1992 to 2013 within the borders of the Antalya Regional Directorate of Forestry using the Keetch–Byram drought index(KBDI). Daily KBDI values were calculated for each year, and values for the period before the year 2000 differed significantly from those after2000. After 2000(large fires occurred in 2004, 2006, 2007,2008, 2010, and 2013), when KBDI values increased, the KBDI, but not the number of fires, was inversely correlated with the natural log of the burned area(NLBA). While there were both high and low KBDI values when the NLBA was small, only high KBDI values were associated with high NLBA values. Particularly for logarithmic values of 4 and higher, KBDI values increased in parallel with increases in NLBA values. On the basis of a Mann–Whitney U test done in addition to a Pearson correlation test, we found that when the burned areas were grouped according to small and large areas, the KBDI could be used to distinguish the two groups. Using a conditional probability analysis, we found that 4th, 5th and 6th class KBDI values may lead to large fires at the 60 % possibility.Similarly, the possibility of large fires greater than the median burned area in any given 6 years was found to be48 %. In addition, while the mean value of KBDI is 390.51 for the period from May to September for these 6 years, it is 359.93 for the other years. Consequently, the area burned also increased as the KBDI classes(Class 0: 0–99, Class 1:100–199, Class 2: 200–299, Class 3: 300–399, Class 4:400–499, Class 5: 500–599, Class 6: 600–699, and Class 7:700–800) increase. 相似文献
19.
利用生态脆弱度的灰色评判法建立了沙质荒漠化的干扰－应变关系，进而求算了不同荒漠化程度样地的生态脆弱度，结合气候、地貌、植被、土壤等特征指标对东北西部沙质荒漠化地区土地荒漠化作出评价：该区的土地沙质荒漠化可分为强度沙漠化、中度沙漠化、轻度沙漠化、微度沙漠化、潜在沙漠化五个级别，各等级及其相应的生态脆弱性、植被群落多样性、群落稳定性等指标可用于中小尺度的荒漠化土地评价图的绘制，其可作为土地荒漠化防治的重要理论依据． 相似文献