沼气混合制冷剂循环液化流程与设备分析

以天然气液化设备为模型,利用Aspen HYSYS软件,设计小型混合制冷剂液化沼气流程,对该流程进行数值模拟,根据PR方程计算出沼气的泡点与露点以及液化率、能耗等。在热力学分析的基础上,计算流程各设备损失,分析产生设备损失的原因,提出降低设备损失的方法。依据模拟结果,建立实验平台对降低损失方法进行验证,结果表明:小型混合制冷剂液化沼气流程具有可行性,液化过程中能耗和损失最大的设备是压缩机,利用储液罐上端的闪蒸气预冷混合制冷剂的方法可使压缩机和冷却器的损失分别减少12.2%和27.2%。     

Response of aspen stands to forest tent caterpillar defoliation and subsequent overstory mortality in northeastern Ontario,Canada

Overstory mortality, understory tree recruitment, and vegetation development were assessed in trembling aspen (Populus tremuloides Michx.) stands following two recent episodes of forest tent caterpillar defoliation (Malacosoma disstria Hbn.) in northeastern Ontario. The results suggest that poplar (aspen and balsam poplar (Populus balsamifera L.)) mortality increased with consecutive years of insect defoliation occurring from the mid-1980s to mid-2000s and the proportion of poplars in the overstory, but decreased with improved pre-defoliation tree vigour (DBH increment). The first outbreak, which lasted from the mid-1980s to early 1990s, was more severe in terms of insect defoliation and contributed more to poplar mortality and decline. The decline began in the late 1990s and peaked in early 2000s. Poplar regeneration and understory shrubs responded rapidly to foliage loss to insect defoliation and mortality of overstory poplars. The regenerated poplars were able to maintain their growth under developing shrubs and residual overstory canopy and numbers were sufficient to compensate for the poplar trees lost to insect infestation. The defoliation-induced overstory decline will accelerate the transition of aspen stands to conifer dominance through enhanced conifer recruitment and growth, and reduced hardwood overstory in aspen-dominated stands, while hardwood dominance will persist in pure aspen stands. From a timber supply perspective, the decline caused by forest tent caterpillar defoliation could delay the availability of aspen stands for harvesting by 40–50 years.     

沼气混合制冷剂循环液化流程与设备火用分析

以天然气液化设备为模型,利用Aspen HYSYS软件,设计小型混合制冷剂液化沼气流程,对该流程进行数值模拟,根据PR方程计算出沼气的泡点与露点以及液化率、能耗等.在热力学分析的基础上,计算流程各设备(火用)损失,分析产生设备(火用)损失的原因,提出降低设备(火用)损失的方法.依据模拟结果,建立实验平台对降低(火用)损失方法进行验证,结果表明:小型混合制冷剂液化沼气流程具有可行性,液化过程中能耗和(火用)损失最大的设备是压缩机,利用储液罐上端的闪蒸气预冷混合制冷剂的方法可使压缩机和冷却器的(火用)损失分别减少12.2％和27.2％.     

Fire history and fire management implications in the Yukon Flats National Wildlife Refuge, interior Alaska

We conducted this investigation in response to criticisms that the current Alaska Interagency Fire Management Plans are allowing too much of the landscape in interior Alaska to burn annually. To address this issue, we analyzed fire history patterns within the Yukon Flats National Wildlife Refuge, interior Alaska. We dated 40 fires on 27 landscape points within the refuge boundaries using standard dendrochorological methods. Fire return intervals based on tree ring data ranged from 37 to 166 years (mean = 90 ± 32 years; N = 38) over the 250 year time frame covered by this study. We found no significant differences in the frequency of fire occurence over time. There was no evidence to suggest that changes in fire management policy have significantly altered the fire regime in the Yukon Flats area. However, the lack of significant differences over time may be due in part to the relatively short time period that fires were actively suppressed in Alaska. The full suppression era (1939–1984) may have been too short to significantly alter the fire regime in all areas of interior Alaska.     

In vitro propagation of European aspen (Populus tremula L.) from axillary buds via organogenesis

Axillary buds from 1-year-old twigs of European aspen (Populus tremula L.) were used for propagation of indigenous aspen clones for further phytoremedial studies. The most intense bud development was seen after the break of dormancy, i.e. from the middle of February until mid-March. Lower infection rates were observed from the axillary buds collected at an urban forest border in comparison to a forest location, accompanied by higher percentages of browning. The optimal medium for shoot induction primarily via callus cultures was Murashige and Skoog mineral salts medium (MS) supplemented by 20 μM zeatin riboside and 1 μM indol acetic acid. The shoots were rooted in half-strength MS medium supplemented by the same hormones, after which they were successfully transferred to a commercial soil mixture. The protocol for aspen propagation is proposed.     

Complex interactions shaping aspen dynamics in the Greater Yellowstone Ecosystem

Loss of aspen (Populus tremuloides) has generated concern for aspen persistence across much of the western United States. However, most studies of aspen change have been at local scales and our understanding of aspen dynamics at broader scales is limited. At local scales, aspen loss has been attributed to fire exclusion, ungulate herbivory, and climate change. Understanding the links between biophysical setting and aspen presence, growth, and dynamics is necessary to develop a large-scale perspective on aspen dynamics. Specific objectives of this research were to (1) map aspen distribution and abundance across the Greater Yellowstone Ecosystem (GYE), (2) measure aspen change in the GYE over the past 50 years (3) determine if aspen loss occurs in particular biophysical settings and (4) investigate the links between biophysical setting and aspen presence, growth, and change in canopy cover. We found that aspen is rare in the GYE, occupying 1.4% of the region. We found an average of 10% aspen loss overall, much lower than that suggested by smaller-scale studies. Aspen loss corresponded with biophysical settings with the lowest aspen growth rates, where aspen was most abundant. The highest aspen growth rates were at the margins of its current distribution, so most aspen occur in biophysical settings less favorable to their growth.     

Aspen patch and migratory bird relationships in the northern Yellowstone ecosystem

We evaluated the effects of aspen patch area and orientation (relative to North and an elevational gradient) on the early breeding season abundance and species richness of migratory and resident birds in the northern ungulate winter range of the Yellowstone ecosystem, USA. Using an information-theoretic model selection approach, we found patch area and basal area of aspen to be the most important covariates for long distance migrants, and patch orientation relative to elevational gradient the most important covariate for residents/short-distance migrants. Basal area of live aspen and aspen snags was marginally important for both migratory strategies, likely because aspen snags are an important habitat for most cavity-nesting species. Landscape ecological theory postulates passive interception of dispersing or migrating organisms by patches of suitable habitat. Our results suggest that residents/short-distance migrants are intercepted by patches that are oriented perpendicular to the elevational gradient of our study region resulting in greater abundances and species richness in those patches. However, long-distance migrants appear to use aspen patches without regard to orientation, but rather to patch area.     

阔叶材（山杨和速生杨）纤维素的形态结构

采用日立Ｓ－１５０型扫描电镜观测了山杨和速生杨纤维素的形态结构。通过观测发现，漂白浆样和未漂浆样显示了各自的某些特点。同时，探讨了原浆和水解后浆样纤维素形态结构的变化状态。     

Clones No 1333 of Populus alba×P.davidiana and No 1132 of P.davidiana×P.alba×P.daviana

IntroductionAspen(Populus~anaDode)isapioneeringspecieswhichiswidelydistributed,welIadapted,andhasgoodqualityoftimber.ItdistributesfromXimalayaMoun-tains,toDaxing'anMountainsandXiaoxing'anMoun-tainsandfromAhaiMountainstoWusulijiangriver,coVerin23provineeso…     

Effects of soil temperature and time of decapitation on sucker initiation of intact Populus tremuloides root systems

Abstract

In a growth chamber experiment, root suckering of aspen (Populus tremuloides Michx.) was assessed in relation to timing of cutting and soil temperature. Aspen seedlings were grown in large pots for 3 years before experimentation. In a 2×2 factorial experiment, 3-year-old seedlings were cut at the end of the dormant period or after leaf flush and grown at two soil temperatures (8 or 20°C) for 39 days. Root systems were evaluated for suckering response and carbohydrate reserve status. There were no differences between the two soil temperatures and times of cut in the number of sucker buds initiated on the roots, but the number of buds that developed into suckers was much greater at 20°C. Cutting the dormant seedlings delayed suckering by nearly a week, resulting in smaller suckers at the time of harvest. However, cutting the seedlings when dormant produced almost twice the number of suckers than when cutting occurred after leaf-out. Total non-structural carbohydrates (TNC) of roots declined from 35.6% of dry weight at the end of the dormant season to 21.6% at the time of leaf-out, but there were no differences between the soil temperature and timing of cut treatments. After the 39 day growth period, root systems had 7% lower root TNC in the 20°C treatment than in the 8°C treatment, likely to support the development of the emerging suckers and higher respiration demands.