A study was carried out to evaluate the effect of shelterwood cutting methods on stand structure and regeneration density. Data were collected from a northern hardwood forest stands in Iran with Fagus orientalis Lipsk...A study was carried out to evaluate the effect of shelterwood cutting methods on stand structure and regeneration density. Data were collected from a northern hardwood forest stands in Iran with Fagus orientalis Lipsky as dominant species, with/without shelterwood cutting operation. Results clearly demonstrate that the management of Fagus orientalis Lipsky with shelterwood cutting system affected the frequency and diversity of the understory herbaceous species. The frequency of Viola silvestris Lam., Asperula odorata L., Carex spp. and Rubus hyr-canus Juz increased significantly after shelterwood cutting. The DBH （diameter at breast height） of commercial species in control stands （57.50±2.15 cm） was greater than that in treated stands （50.67±1.88 cm）, whereas the total height of trees was similar between treated and control plots （21±0.5 m）. The number of Parrotia persica seedlings increased by 13.2% from 1995 to 2005 whereas the number of Fagus orientalis and Carpinus betulus seedlings significantly decreased from 1995 to 2005. In conclusion, it confirms that instead of shelterwood cutting method other silvicultural practices such as selection cutting method should be applied for the mountainous beech stands of Hyrcanian forests.展开更多
A high order boundary element method was developed for the complex velocity potential problem. The method ensures not only the continuity of the potential at the nodes of each element but also the velocity. It can be ...A high order boundary element method was developed for the complex velocity potential problem. The method ensures not only the continuity of the potential at the nodes of each element but also the velocity. It can be applied to a variety of velocity potential problems. The present paper, however, focused on its application to the problem of water entry of a wedge with varying speed. The continuity of the velocity achieved herein is particularly important for this kind of nonlinear free surface flow problem, because when the time stepping method is used, the free surface is updated through the velocity obtained at each node and the accuracy of the velocity is therefore crucial. Calculation was made for a case when the distance S that the wedge has travelled and time t follow the relationship s=Dtα, where D and α are constants, which is found to lead to a self similar flow field when the effect due to gravity is ignored.展开更多
It is a challenge to select an optimal set of devices to accomplish a graph-based ubiquitous service and execute it continuously under the circumstances of dynamic environments and limited device capability. We elabor...It is a challenge to select an optimal set of devices to accomplish a graph-based ubiquitous service and execute it continuously under the circumstances of dynamic environments and limited device capability. We elaborate a Synergy- aware Selection Mechanism （SSM） considering synergetic among devices. In the SSM, we design a distributed algorithm to integrate the devices and a dynamic updating weight method. The simulation results show that SSM can make devices composed together to ensure the continuity and smoothness of service展开更多
文摘A study was carried out to evaluate the effect of shelterwood cutting methods on stand structure and regeneration density. Data were collected from a northern hardwood forest stands in Iran with Fagus orientalis Lipsky as dominant species, with/without shelterwood cutting operation. Results clearly demonstrate that the management of Fagus orientalis Lipsky with shelterwood cutting system affected the frequency and diversity of the understory herbaceous species. The frequency of Viola silvestris Lam., Asperula odorata L., Carex spp. and Rubus hyr-canus Juz increased significantly after shelterwood cutting. The DBH （diameter at breast height） of commercial species in control stands （57.50±2.15 cm） was greater than that in treated stands （50.67±1.88 cm）, whereas the total height of trees was similar between treated and control plots （21±0.5 m）. The number of Parrotia persica seedlings increased by 13.2% from 1995 to 2005 whereas the number of Fagus orientalis and Carpinus betulus seedlings significantly decreased from 1995 to 2005. In conclusion, it confirms that instead of shelterwood cutting method other silvicultural practices such as selection cutting method should be applied for the mountainous beech stands of Hyrcanian forests.
文摘A high order boundary element method was developed for the complex velocity potential problem. The method ensures not only the continuity of the potential at the nodes of each element but also the velocity. It can be applied to a variety of velocity potential problems. The present paper, however, focused on its application to the problem of water entry of a wedge with varying speed. The continuity of the velocity achieved herein is particularly important for this kind of nonlinear free surface flow problem, because when the time stepping method is used, the free surface is updated through the velocity obtained at each node and the accuracy of the velocity is therefore crucial. Calculation was made for a case when the distance S that the wedge has travelled and time t follow the relationship s=Dtα, where D and α are constants, which is found to lead to a self similar flow field when the effect due to gravity is ignored.
文摘It is a challenge to select an optimal set of devices to accomplish a graph-based ubiquitous service and execute it continuously under the circumstances of dynamic environments and limited device capability. We elaborate a Synergy- aware Selection Mechanism （SSM） considering synergetic among devices. In the SSM, we design a distributed algorithm to integrate the devices and a dynamic updating weight method. The simulation results show that SSM can make devices composed together to ensure the continuity and smoothness of service
