A new harvest operation cost model to evaluate forest harvest layout alternatives

In this paper we develop a new model for harvest operation costs that can be used to evaluate stands for potential harvest. The model is based on felling, extraction, and access costs and is unique in its consideration of the interaction between harvest area shapes and access roads. We illustrate the model and evaluate the impact of stand size, volume, and road cost when determining harvest layouts. We also present a generalized case where multiple unit road costs are considered in the same stand.     

Adaptive Bit allocation algorithm based on unsaturated bandwidth of multimode fiber for optical OFDM system

An adaptive bit allocation algorithm for Orthogonal Frequency Division Multiplexing (OFDM) multimode fiber communication system is proposed in this paper, aimed at utilizing the infinite bandwidth of multimode fiber in high frequency region. The algorithm breaks through the limitation that bits are formerly allocated only in fixed bandwidth, and is proved to be effective by simulation. Compared with greedy algorithm, new algorithm is easy to implement, and lowers bit error rate (BER) of each subcarrier effectively.     

Caching popularity-unknown contents for massive communication channels via deep Q-learning

In order to reduce the backhaul link pressure of wireless networks, edge caching technology has been regarded as a promising solution. However, with massive and dynamical communication connections, it is challenging to provide analytical caching solution to achieve the best performance, particularly when the requested contents are changing and their popularities are unknown. In this paper, we propose a deep Q-learning (DQN) method to address the issue of caching placement. Considering a content caching network containing multiple cooperating SBSs with unknown content popularity, we need to determine which content to cache and where to cache. Therefore, the learning network has to be designed for dual aims, one of which is to estimate the content popularities while the other is to assign contents to the proper channels. An elaborate DQN is proposed to make decisions to cache contents with limited storage space of base-station by considering channel conditions. Specifically, the content requests of users are first collected as one of the training samples of the learning network. Second, the channel state information for the massive links are estimated as the other training samples. Then, we train the network based on the proposed method thereby improving spectral efficiency of the entire system and reducing bit-error rate. Our major contribution is to contrive a caching strategy for enhanced performance in massive connection communications without knowing the content popularity. Numerical studies are performed to show that the proposed method acquires apparent performance gain over random caching in terms of average spectral efficiency and bit-error rate of the network.     

Flexibility across and flexibility within: The domain of integer addition and subtraction

To better understand the role that flexibility plays in students’ success on integer addition and subtraction problems, we examined students’ flexibility when solving open number sentences. We define flexibility as the degree to which a learner uses more than one strategy to solve a single task when prompted, as well as the degree to which a learner changes strategies when solving a range of tasks to accommodate task differences. We introduce the categorizations of flexibility within and flexibility across to distinguish these two ways of operationalizing flexibility. We examined flexibility and performance within and among three groups of students — 2nd and 4th graders who had negative numbers in their numerical domains, 7th graders, and college-track 11th graders. Profiles of five students are shared to provide insight in relation to the quantitative findings.     

An efficient explicit framework for determining the lowest structural buckling load using Dynamic Relaxation method

This paper develops an e?cient explicit algorithm for calculating buckling load of structures. Here, the modified Dynamic Relaxation method is utilized so that the first structural buckling load is achieved. The proposed algorithm does not require solving any eigenvalue problem and runs by full vector and iterative operations. Moreover, the suggested procedure is general so that it could be utilized for both symmetric and unsymmetric structures without any additional calculations. For numerical verification, some columns and portal frames are analyzed and the calculated buckling loads are compared with the exact solution and other available approaches. Results show that the proposed algorithm has suitable accuracy and e?ciency that is useful for determining the lowest buckling load of each structure. Moreover, the effect of initial imperfection and time step size on the suggested framework is studies numerically.     

一类最小-最大车辆路线问题的启发式算法研究

针对个性化和多样性的需求,建立以缩短最长子线路为目标的最小-最大车辆路径问题模型, 并提出启发式算法求解。首先,采用自然数编码,使问题变得更简洁;用最佳保留选择法,以保证群体的多样性;引入爬山算法,加强局部搜索能力;其次,对遗传算法求得的精英种群再进行禁忌搜索,保证算法能够收敛到全局最优。最后,通过实例的计算,表明本算法均优于遗传算法和禁忌搜索算法,并为大规模解决实际问题提供思路。     

一种滑动轴承试验台的研制与牙轮钻头镶嵌滑动轴承摩擦磨损性能的台架试验

在石油钻井中，滑动轴承牙轮钻头的应用日益增多，但轴承的工作环境却相当恶劣。为了提高钻头滑动轴承的工作寿命，并为这类轴承的设计提供科学依据，针对其实际应用工况，特殊设计制造了一种ＩＰＧ－２型滑动轴承试验台，并且利用其在３０ｋＮ、４０ｋＮ和５０ｋＮ的３种载荷条件下，对牙轮钻头镶嵌铜合金的滑动轴承进行了台架试验研究，着重考察了铜合金镶嵌区尺寸之大小对轴承摩擦磨损性能的影响。结果表明，在相邻两个镶嵌区之间的基体区表面宽度与铜合金的镶嵌区宽度之比值分别为１、２、３和４的几种镶嵌滑动轴承中，它们的摩擦学性能依次变差，即以第一种镶嵌轴承的摩擦磨损性能最好，这是由于镶嵌材料铜合金的抗剪切强度比钢基体的低，在摩擦力的作用下容易向非镶嵌区基体表面及与之对摩部件表面发生材料转移并形成转移膜的缘故。这种研究结果可以直接应用于钻头滑动轴承的设计。     

石油钻井底部钻具组合大挠度三维分析

精确描述了石油钻井底部钻具组合在三维弯曲井眼中的变形约束条件及边界条件，应用加权余量法，对底部钻具组合静力大挠度问题进行了三维分析研究，并编写了相应的计算机分析程序。该程序可以在普通微机上运行，能迅速模拟计算底部钻具组合任一点的挠度、转角和内力，同时求得钻头对地层的机械作用力和偏转角。通过算例分析，本文初步阐明了井眼曲率及方程中的非线性项对钻头力学特性的影响效果。