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51.
52.
Soil structure is very important in agriculture since it affects soil and plant root attributes, such as root system distribution, soil water and nutrient transport, and heat transfer. Degraded soil structures may be repaired by wetting and drying cycles due to changes in the soil pore system. Gamma-ray computed tomography (CT) was used as a tool to evaluate the effect of wetting/drying cycles on soil structure repair, using samples collected in aluminum cylinders. A first-generation tomograph with an 241Am source and a 7.62 cm × 7.62 cm NaI(Tl) scintillation crystal detector coupled to a photomultiplier tube were employed. Image analysis and tomographic unit profiles showed that CT can provide an insight into sample structure in order to evaluate repairs and so improves the use of this tool in relation to the judgement of the quality of measured soil physical properties. 相似文献
53.
本文测定了9种农作物种子和几种无性繁殖植物材料的元素重量百分组成、组织密度,根据Hubbell给出的不同元素质量减弱系数、质能吸收系数,计算了农作物种子和无性繁殖植物材料的质量减弱系数和质能吸收系数,并根据特定情况下导出的“相应点剂量转换法”数学模型,计算了农作物种子或无性繁殖植物材料的吸收剂量转换系数。 相似文献
54.
An integrative method to quantify contaminant fluxes in the groundwater of urban areas 总被引:2,自引:2,他引:2
Background, Aims, and Scope Groundwater in urban areas is often contaminated and emission sources can be located close to groundwater wells. The delineation
of contaminant plumes is difficult because of the various potential emission sources. Thus, detection, quantification and
remediation of contaminated sites in a city need more integrative approaches.
Methods A method has been developed which allows quantification of mass fluxes of contaminants in groundwater between control planes.
Budget zones along the flow path are defined to calculate a contaminant balance and to quantitatively reveal input areas.
Concentrations and water budgets are used to calculate mass balances for each contaminant. The city of Darmstadt (Germany)
was chosen to evaluate the method.
Results The groundwater monitoring wells (GMWs) upstream of the city showed anthropogenically superposed background values for all
naturally occurring inorganic species. The contaminant concentrations increased in the city (probably influenced by road traffic,
gas stations, leaking sewers, etc.). Downstream from the city, concentrations usually decreased. Organic compounds typical
for urban environments, such as polycyclic aromatic hydrocarbons (PAH), locally exceeded drinking water regulations. In GMWs
with high concentrations of organic contaminants in the city or downstream from industrial areas, a significant increase in
Fe2+ and Mn2+ could be observed, in some cases coinciding with a decrease in NO3, SO4 and an increase in NH4.
Discussion For typical urban contaminants, a positive budget was calculated in several zones, which shows that emissions from urban sources
are reaching the groundwater. Negative budgets can be mainly explained with diving plumes and degradation. The input calculated
from the individual budget zones is usually higher than the input estimated from urban emissions. Differences between the
calculated and the estimated input can be explained with additional sources or (bio)degradation processes.
Conclusions It was confirmed that high concentrations of contaminants do not necessarily correlate with high fluxes. Integrative approaches
can reveal areas of high contaminant mass input. The results obtained with the new method are plausible compared to the land
use and the estimated urban input. The concentration pattern of Fe2+, Mn2+, SO4 and NO3 is partly due to natural processes, triggered by the degradation of organic matter and organic contaminants.
Recommendations Since this method includes mass balances and flux calculations, avoiding an overestimation of single point contaminant concentration,
it is recommended to use this approach to quantify groundwater contamination in cities. Further research is focusing on the
role of urban soils as natural reservoirs for the input of contaminants. 相似文献
55.
用冷适应的方法致弱鸡肾型传染性支气管炎病毒 总被引:1,自引:0,他引:1
用冷适应的方法 (病毒经囊液接种鸡胚后于 32℃孵化 48h) ,将已鉴定的北京地区鸡肾型传染性支气管炎病毒 (IBV)分离株 Tu,Da,Xi和 Hu分别通过鸡胚传代减毒致弱 ,在一定代次时接种敏感鸡作毒力测定试验 ,结果表明 ,Tu株在传至 46代时 ,Xi株在传至 5 1代时对雏鸡的毒性已大为降低 ,并且分别回归 SPF雏鸡 5代和 3代后不出现返强现象。毒价测定 Tu46和 Xi51 的 EID50 值分别为 10 - 6.3 6/ 0 .2 m l和 10 - 6.70 / 0 .2 m l,而且 Tu株出现稳定增高的趋势。它抵抗同源强毒攻击的最小免疫剂量为 10 - 2 × 0 .5 m l。此外 ,对弱毒株免疫后的雏鸡用标准强毒株Gray攻击以衡量其免疫原性 ,结果 Tu46具有 90 %的保护率。间接 EL ISA对免疫后的抗体水平检测结果反映 ,Tu46免疫鸡体内血清抗体的消长呈规律性变化 ,并在免疫后 2 0天出现最高峰。综合结果表明 ,作者培育的 IBV- Tu46株具有对雏鸡安全、毒价高及较好的免疫原性的特点 ,有希望成为供生产使用的疫苗。 相似文献
56.
汪梦甫 《湖南农业大学学报(自然科学版)》1990,17(2)
本文分析总结了岳阳市及其邻区的地震地质及地震活动特征,并据此划分了潜在震源区和估计了地震活动性参数;利用岳阳地区历史地震等震线资料,得到了其椭园、带形烈度衰减关系;此外,利用该地区与美国西部的烈度衰减关系,由震级烈度法得到了其地震动衰减关系. 相似文献
57.
Yao ZOU Xiaoming ZHU Hassan Mushtaq MUHAMMAD Ping JIANG Yufeng LI 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2015,77(6):653-660
Recently, a series of acute swine erysipelas outbreaks occurred in Eastern China. Eight
strains isolated from cases of septicemia were determined as serotype 1a, and 4 of the
isolates were resistant to acriflavine. One isolate strain named was attenuated
on agar media containing acriflavine dye. The 432-bp hypervariable region in
spaA gene of the field and attenuated strains were amplified and
sequenced. It was further compared with the vaccine strain G4T10,
and thus, the eight field strains can be divided into four spaA-types.
The partial spaA gene analysis also showed that no point mutations
occurred among different archived passages of HX130709 during the attenuation. Results of
pulsed-field gel electrophoresis showed that eight distinct patterns with 22 to 30 DNA
fragment bands were produced from field strains, and twelve distinct patterns with 23 to
27 DNA fragment bands were produced from different passages of the attenuated strains.
Mouse pathogenicity test showed that the mortality of the mice infected with
104 CFU field strains was 100% and the attenuation of strain HX130709
occurred between 46 and 50 passages. All the field and attenuated strains were highly
sensitive to β-lactam antibiotics, tetracyclines and macrolides. So, we can make
conclusions that the acute swine erysipelas outbreaks in Eastern China were caused by
serotype 1a E. rhusiopathiae strains with different biochemical
characteristics, and the virulence of serotype 1a E. rhusiopathiae
strains is unrelated with some point mutations in 432-bp hypervariable region of the
spaA gene. HX130709相似文献
58.
为研究不同声发射(acoustic emission,AE)模态的传播特性与能量衰减模式,依据波动理论提出一种木材AE信号表面横波与内部纵波析取方法,进而建立AE信号能量衰减模型。首先,依据ASTM-E976-2015通过铅芯折断的方式在樟子松锯材表面产生AE源,并在不同位置采集表面横波与内部纵波的AE原始信号,采样频率设置为500 kHz;然后,采用小波分析方法从原始信号中重构AE波形,分析木材AE信号表面横波与内部纵波的传播特性;最后,通过指数函数拟合的方法,构建表面横波与内部纵波能量衰减模型。结果表明:表面横波与内部纵波在樟子松锯材中传播时AE能量均呈明显的指数衰减规律,但在频率分布和传播速率上均有较大差异。表面横波在传播初始阶段主要分布在以80.0 kHz和113.3 kHz为中心的两个中高频段内,随着其在木材表面的传播,高频信号迅速衰减为低频信号。而内部纵波始终处于相对低频段内,其平均传播速率约为表面横波的4.6倍。 相似文献
59.
Ulrich Förstner Joachim Gerth Martina Lindemann Uwe Wittmann 《Journal of Soils and Sediments》2001,1(3):181-187
While remediation and storage of contaminated dredged materials is a key issue at harbour sites, there is another type of
sediment pollution problem, which mainly originates from large-scale dispersion of contaminants in flood-plains, dike foreshores
and polder areas. In recent years, catastrophic cases of sediment contaminations have occurred in connection with the failure
of tailing dams from mines. Unlike problems related to conventional polluted sites, the risks here are primarily connected
with the transporting and depositing of contaminated solids in a catchment area, especially in downstream regions.
A special example demonstrating the dispersion of highly contaminated sediments in a large catchment area will be shown from
the so-called Chemistry Triangle of the upper Elbe River system, Germany. The Spittelwasser area, situated there, was chosen
by the organisers of the international conference ConSoil 2000 for a case comparison and four expert teams from Denmark, Germany,
the Netherlands and the UK were invited to participate in this Case Study. Evaluation of the plan was done by members of the
networks of NICOLE (Network for Industrially Contaminated Land) and CLARINET (Contaminated Land Rehabilition Network).
In the study of the German team, five major groups of technical measures have been identified by the environmental authorities
to be discussed in relation to the Spittelwasser case or for similar problem solutions in contaminated flood-plain areas.
The team came to the conclusion that none of these techniques would be applicable as an individual measure. Instead, a stepwise
approach combining different monitoring techniques and remediation measures was proposed. These would include point excavations
of critical material, promotion of plant growth as an element for stabilising the soil and flood sediments, as well as the
installation of sediment traps.
At the Spittelwasser site, investigations are planned on the effects of natural attenuation processes of organic and inorganic
contaminants in flood-plain sediments and soils. In the practice of this concept, non-destructive, ‘intrinsic’ bonding mechanisms
and their temporal development have thus far found much less recognition compared to destructive processes such as biological
degradation. Yet these so-called ‘diagenetic’ effects, which apart from chemical processes involve an enhanced mechanical
consolidation of soil and sediment components by compaction, loss of water, and mineral precipitations in the pore space,
may induce a quite essential reduction of the reactivity of solid matrices [see Part I ‘Improving Chemical and Biological
Criteria’ (JSS - Journal of Soils and Sediments, Vol 1, No 1, pp 30-36)].
Part IV ‘Subaqueous Storage/Capping of Dredged Material’ will be published in JSS No. 4 (December issue). 相似文献
60.
This paper presents research that was undertaken to determine whether planting deciduous trees, using intensive tree planting schemes, on vacant and underutilized urban land provides significant hydrologic benefits. This work contributes to an ongoing discussion on how to use vacant and underutilized land productively, and may be important to land use decision-makers, whose policies support the use of green infrastructure for stormwater management. Tree growth parameters for four monoculture planting schemes were modeled (all trees had a 50.8 mm caliper at planting) and included (i) 450 Ginkgo biloba, (ii) 92 Platanus × acerifolia, (iii) 120 Acer saccharinum, and (iv) 434 Liquidambar styraciflua, on a 1.6-acre parcel. i-Tree Hydro (formerly UFORE-Hydro) was used to derive a simplified Microsoft Excel-based water balance model to quantify the canopy interception potential and evaporation, based on 7 years (2002–2008) of historical hourly rainfall and mean temperature data in Hamilton, Ontario, Canada. This study revealed that three of the species responded similarly, while one species (L. styraciflua) performed significantly better with respect to total canopy storage potential and evaporation, capturing and evaporating 2.9 m3/tree over the 7 years analyzed, or 1280 m3 for the total tree stand of 434 trees. The analyses presented herein demonstrate that the tree canopy layer was able to intercept and evaporate approximately 6.5%–11% of the total rainfall that falls onto the crown across the 7 years studied, for the G. biloba, P. × acerifolia and A. saccharinum tree stands and 17%–27% for the L. styraciflua tree stand. This study revealed that the rate at which a species grows, the leaf area index of the species as it matures, and the total number of trees to be planted need to be determined to truly understand the behavior and potential benefits of different planting schemes; had the mature leaf area been used as the sole indicator of the stormwater attenuating potential for each species, the A. saccharinum would have been the selected species. Also, had attenuation and evaporation per unit of tree been the only measurement reported, the P. × acerifolia stand would have been deemed the best performing tree, attenuating and evaporating 8.1 m3/tree. While the actual values presented herein may be uncertain because of a lack of locally-derived tree growth models, the approach described warrants further investigation. 相似文献