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201.
Secondary ion mass spectrometry measurements show that Earth's representative lower mantle minerals synthesized in a natural peridotitic composition can dissolve considerable amounts of hydrogen. Both MgSiO3-rich perovskite and magnesiowüstite contain about 0.2 weight percent (wt%) H2O, and CaSiO3-rich perovskite contains about 0.4 wt% H2O. The OH absorption bands in Mg-perovskite and magnesiowüstite were also confirmed with the use of infrared microspectroscopic measurements. Earth's lower mantle may store about five times more H2O than the oceans.  相似文献   
202.
203.
Shear tests were conducted on nailed joints in wood that were loaded perpendicular to the grain; these joints had 21 specifications depending on different combinations of wood species, nail dimensions, number of nails, and edge distances of the main members, and their effects on the shear resistance of the nailed joints were also investigated. The nailed joints with CN75 nails had higher initial stiffness than the joints with CN50 nails, provided the initial stiffness of nailed joints connected with 3 or 5 nails was not always a simple product of the number of nails and the initial stiffness of nailed joints connected with a nail, and instead depended on the combination of wood species of the main member and nail dimensions. When the edge distance decreased, the maximum load and energy capacity decreased, thereby affecting the energy capacity. The maximum load of the nailed joints with CN75 nails may be smaller than those with CN50 nails depending on the combination of wood species and nail dimensions. When the edge distance of the nailed joints was less than 26 mm, the energy capacity of the nailed joints with CN75 nails was less than or similar to those with CN50 nails.  相似文献   
204.
Transgenic mangium trees (Acacia mangium) overexpressing xyloglucanase (AaXEG2) were generated by spraying flower buds with Agrobacterium solution and allowing seeds to develop. The overexpression of xyloglucanase decreased xyloglucan content in the cell walls and increased stem length and diameter. The leaves of the transgenic seedlings exhibited accelerated heteroblastic development, proceeding from the stage of three bipinnate leaves to that of enlarging petiole 2 weeks earlier than wild type seedlings did.  相似文献   
205.
Wood formation of trees that grow along the seasons has an annual rhythm. Due to this rhythm, physiological research on the mechanism of wood formation has been difficult to conduct in a typical experimental room. In the present study, we observed the wood tissue formation in a shortened annual cycle system, which was developed for poplar trees grown in a growth chamber with dormant and non-dormant cycles. Poplar trees were grown in this system by repeating the cycle three times. The resulting wood tissue consisted of three growth rings and very similar structures were observed around the ring boundary of the wood in a field-grown stem. This result suggests that the shortened annual cycle system can be adopted as a model for physiological, cell biological and molecular research of wood and annual ring formation.  相似文献   
206.
There is more to sustainable forest management than reduced impact logging. Partnerships between multiple actors are needed in order to create the institutional context for good forest governance and sustainable forest management and stimulate the necessary local community involvement. The idea behind this is that the parties would be able to achieve more jointly than on their own by combining assets, knowledge, skills and political power of actors at different levels of scale. This article aims to demonstrate by example the nature and variety of forest-related partnerships in Brazilian Amazonia. Based on the lessons learned from these cases and the authors’ experience, the principal characteristics of successful partnerships are described, with a focus on political and socioeconomic aspects. These characteristics include fairly negotiated partnership objectives, the active involvement of the public sector as well as impartial brokers, equitable and cost-effective institutional arrangements, sufficient and equitably shared benefits for all the parties involved, addressing socioeconomic drawbacks, and taking measures to maintain sustainable exploitation levels. The authors argue that, in addition to product-oriented partnerships which focus on sustainable forest management, there is also a need for politically oriented partnerships based on civil society coalitions. The watchdog function of these politically oriented partnerships, their awareness-raising campaigns regarding detrimental policies and practices, and advocacy for good forest governance are essential for the creation of the appropriate legal and political framework for sustainable forest management.  相似文献   
207.
Recent discovery of a phase transition from perovskite to post-perovskite suggests that the physical properties of Earth's lowermost mantle, called the D' layer, may be different from those of the overlying mantle. We report that the electrical conductivity of (Mg0.9Fe0.1)SiO3 post-perovskite is >10(2) siemens per meter and does not vary greatly with temperature at the conditions of the D' layer. A post-perovskite layer above the core-mantle boundary would, by electromagnetic coupling, enhance the exchange of angular momentum between the fluid core and the solid mantle, which can explain the observed changes in the length of a day on decadal time scales. Heterogeneity in the conductivity of the lowermost mantle is likely to depend on changes in chemistry of the boundary region, not fluctuations in temperature.  相似文献   
208.
Transmission of ovine herpesvirus-2 (OvHV-2) in sheep via natural contact and nasal secretions was examined. OvHV-2-free lambs were produced by separating newborn lambs from their mothers within 5 days of birth and raising them in an isolation facility. Transmission experiments via natural contact were conducted by keeping OvHV-2-free lambs with OvHV-2-infected sheep of different ages. Six of the infected ewes in this experiment were pregnant and gave birth during the experimental period. OvHV-2 was not transmitted from the adult sheep, though viral DNA was consistently detected in their peripheral blood leukocytes (PBL). On the other hand, OvHV-2 was transmitted from recently infected lambs to sheep at 10 or 12 weeks after the onset of contact. In addition, we attempted the experimental transmission of OvHV-2 via nasal secretions, by transferring nasal washings from infected sheep to the nostrils of uninfected sheep. Sheep receiving the nasal washings from infected adult sheep maintained their negative status for 15 months, whereas sheep receiving nasal washings from recently infected lambs acquired OvHV-2 by 8 months. The results of these experiments support that OvHV-2 is more easily transmitted to negative sheep by recently infected lambs than by adult sheep. Further, it is supposed that the nasal cavity is a portal for entry and shedding of infectious OvHV-2 in sheep.  相似文献   
209.
Post-perovskite phase transition in MgSiO3   总被引:2,自引:0,他引:2  
In situ x-ray diffraction measurements of MgSiO3 were performed at high pressure and temperature similar to the conditions at Earth's core-mantle boundary. Results demonstrate that MgSiO3 perovskite transforms to a new high-pressure form with stacked SiO6-octahedral sheet structure above 125 gigapascals and 2500 kelvin (2700-kilometer depth near the base of the mantle) with an increase in density of 1.0 to 1.2%. The origin of the D" seismic discontinuity may be attributed to this post-perovskite phase transition. The new phase may have large elastic anisotropy and develop preferred orientation with platy crystal shape in the shear flow that can cause strong seismic anisotropy below the D" discontinuity.  相似文献   
210.
农业土壤一旦被粪便性病菌污染,将给人类带来潜在的感染病菌的风险。通过选择大肠杆菌作为粪便性病菌的模式菌接种于土壤中,在温室条件下采用日晒热消毒法对大肠杆菌进行灭菌试验,探讨日晒消毒法的生物安全控制效果。结果表明,13晒处理使土壤温度在1周内升至40℃,并在大部分处理时期维持在40—46%;处理区土壤中的大肠杆菌数在1周内从10^5cfu/g干土降至检测限以下(〈0.08cfu/g干土),而对照区土壤中的大肠杆菌数在4周后仍可被检测出。由此可知,温室土壤在因施用未腐熟堆肥或动物粪便而被病菌污染时,13晒消毒是快速有效的生物安全控制手段。  相似文献   
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