共查询到10条相似文献，搜索用时 171 毫秒
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Potential errors in measurement of nonuniform sap flow using heat dissipation probes 总被引：1，自引：0，他引：1
The empirical calibration of Granier-type heat dissipation sap flow probes that relate temperature difference (DeltaT) to sap velocity (v) was reevaluated in stems of three tropical tree species. The original calibration was confirmed when the entire heated probe was in contact with conducting xylem, but mean v was underestimated when part of the probe was in contact with nonconducting xylem or bark. Analysis of the effects of nonuniform sap velocity profiles on heat dissipation estimates showed that errors increased as v and the proportion of the probe in nonconducting wood increased. If half of a 20-mm probe is in sapwood with a v of 0.15 mm s(-1) and the other half is in nonconducting wood, then mean v for the whole probe can be underestimated by as much as 50%. A correction was developed that can be used if the proportion of the probe in nonconducting wood is known. Even with the entire heated probe in contact with conducting xylem, v would be underestimated when radial velocity gradients are present. In this case, the error would be smaller except when velocity gradients are very steep, as can occur in species with ring-porous wood anatomy. Errors occur because the relationship between DeltaT and v is nonlinear. Mean DeltaT along the probe is therefore not a measure of mean v, and users of heat dissipation probes should not assume that v is integrated along the length of the probe. The same type of error can occur when DeltaT is averaged through time while v is changing, but the error is small unless there are sudden, step changes between zero and high sap velocity. It is recommended that relatively short probes (20 mm or less) be used and that probes longer than the depth of conducting sapwood be avoided. Multiple probes inserted to a range of depths should be used in situations where steep gradients in v are expected. If these conditions are met, heat dissipation probes remain useful and widely applicable for measuring sap flow in woody stems. 相似文献
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研究了碱法制浆副产物麦草碱木质素的磺化产品磺化碱木质素(SWSL)作为混凝土减水剂使用的性能,掺量(相时于水泥的质量分数,下同)为0.25%时,掺SWSL的混凝土减水率达13.5%,较掺木质素磺酸钙(CLS)的(10.2%)高,混凝土3天和7天龄期抗压强度比仅为113%和105%,较掺CLS的(134%和125%)低.SWSL在水泥浆碱性溶液中具有较好起泡性和泡沫稳定性,有较高的减水率,但泡径较粗且分布不均匀,最大泡径为2 mm,导致硬化砂浆密度减小,孔径小于0.01 mm的气孔比例相对较少,孔径在0.01～0.05 mm范围的较多,抗压强度下降.SWSL的磺化度为1.1 mmol/g,重均相对分子质量(MW)为4 424,较木钙(11 370)低.较低的磺化度使SWSL的分散性能比木钙差. 相似文献
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Prof. Dr. F. N. Zaki K. T. Awadallah M. A. Gesraha M. M. A. Ibrahim 《Journal of pest science》1995,68(6):140-141
The braconid parasitoidMeteorus rubens (Nees) is a gregarious larval parasitoid ofAgrotis ipsilon (Hufn.). An olfactometer was used to check the attractiveness of the parasitoid to Hexane extract (kairomone) of its host that could be used in conjunction with releases of natural enemies. Female wasps are attracted in high numbers to the kairomone, compared with males. Respective rates of 94.3 and 22.3% are reported. In the control (no kairomone was used), the corresponding figures are 5.7 and 3.3%. 相似文献
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植被遥感研究的新思路--走出传统光谱理论应用的误区 总被引：5，自引：0，他引：5
对遥感中沿用几十年的植被光谱理论提出质疑,阐述了传统植被遥感中存在的误区,提出新的观点及研究思路。第一次提出干旱植被指数(LDVI)和综合植被指数(IVI)的概念,探讨了干旱地区草原植被的信息提取及定量分析方法。 相似文献
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Mikko Mönkkönen Pasi Reunanen Janne S. Kotiaho Artti Juutinen Olli-Pekka Tikkanen Jari Kouki 《European Journal of Forest Research》2011,130(5):717-727
Setting aside parcels of land is the main conservation strategy to reduce the rate of biodiversity loss worldwide. Because
funding for biological conservation is limited, it is important to distinguish the most efficient ways to use it. Here, we
assess implications of alternative measures to conserve biodiversity in managed boreal forest landscapes. We calculated four
alternative spatio-temporal scenarios and compared these to the current management regime over 100-year time period. In the
alternative scenarios, a fixed amount of funding was invested in (1) permanent large reserves (each tens of ha in size), (2)
permanent small reserves (each a few ha in size), (3) temporary small reserves (based on 10-year contracts with private land
owners), and (4) green-tree retention (small groups of trees retained on clear-cuts). To assess biodiversity implications,
we used habitat suitability indices to calculate overall habitat availability for five groups of red-listed and habitat-specific
species associated with decaying spruce logs. The possibilities for timber harvests did not differ among the scenarios, but
biodiversity performance was different. The scenarios with permanent reserves tended to outperform other scenarios, suggesting
that conservation policies based on permanent reserves are the most cost-efficient in the long term. Results, however, varied
among time scales and species groups. In the short term, a strategy of investment in temporary small reserves was the most
efficient. Habitat for species associated with old spruce dead-wood and preferring shade was rare throughout all simulations,
and therefore, it is likely that these species cannot be sustained in managed forests. Species that live on fresh dead-wood
and are associated with forest edges coped well in all scenarios suggesting that such species will persist in managed landscapes
without additional conservation efforts. Explicit definition of conservation objectives and time frames for conservation action
are thus prerequisites for successful conservation planning. 相似文献
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微波辅助提取柚皮精油的研究 总被引：7，自引：0，他引：7
进行了微波辅助提取柚皮精油的实验。结果表明,石油醚是微波辅助提取柚皮精油的最佳溶剂,液料质量比、物料含水率、粒度、微波功率等因素对微波辅助提取柚皮精油有较大影响。通过实验得到了柚皮精油提取的最佳工艺条件：物料粒度60目,物料含水率7．4％,总液料质量比14：1,微波功率300w,提取两次,每次微波辐射时间3min。提取液进行真空浓缩至不再有溶剂蒸出,得精油粗产品。往精油粗产品中加入乙醇溶解,放入～15℃冰箱中冷冻48h,离心分离去除树脂状物质,过滤,滤液进行真空浓缩后,即得精油,产率约2．09％,精油纯度99．0％。与传统的直接加热提取法相比,微波辅助提取法所用时间仅为直接加热提取法的1／20。 相似文献
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东莞市生态景观林林分改造效果研究 总被引：2，自引：0，他引：2
对广东省东莞市大岭山森林公园低效相思类林分进行改造,4．5a生时采用样方法进行林分生态效益和景观效益的调查。结果表明：（1）选用的红锥、樟树、山苍子等几个树种生长表现最好,高、径生长都较快,其中红锥、樟树的表现尤其优秀;（2）改造后的林分草本层物种达到了3．8—9．4种,平均为6．33种;多样性指数为0．80～1．92,平均为1．39;均匀度指数为0．61～0．87,平均为0．77;生态优势度0．30～0．58,平均为0．35,林分整体生物多样性较好;（3）林地表层土壤（0～25em）疏松,持水能力较强。林分最大持水深15mm,其中林地土壤占98．24％。（4）在相思林下用2年生苗木进行套种改造,采用较高的造林措施,可以在2—3年内形成景观效果,林分复层林冠基本成型,林相有初步的季节变化。 相似文献
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Wild service tree [Sorbus torminalis (L.) Crantz] is a forest tree widespread in Europe, characterized by a scattered distribution. Its hermaphroditic flowers
are pollinated by insects, and outcrossing is the prominent mating system, also due to the presence of gametophytic self-incompatibility.
Genetic diversity and differentiation of 22 populations from northwestern Italy were investigated by means of variation scored
at 53 polymorphic RAPD (Random Amplified Polymorphic DNA) loci. Populations differed in genetic variation, with Shannon diversity
index ranging from 0.166 to 0.469. According to Analysis of Molecular Variance (AMOVA), most of the genetic variation was
found within populations (61.78%) with a significant proportion of variance attributable to genetic differences between regions
(23.60%) and between populations (14.62%). Evidence for isolation by distance was found in the set of populations sampled.
The effect of habitat fragmentation on genetic variation was also evaluated. The efficacy of RAPD markers in analysing genetic
variation, and the contribution of the results in terms of the preservation of biodiversity are discussed. 相似文献