具有连续迁徙的近远海渔业系统的优化收获策略

研究一类同时具有比例收获和常量收获的近远海渔业系统的动力学行为和优化控制问题。在种群发展中近海鱼群和远海鱼群进行连续迁徙扩散,为了使得一个收获周期内有最大的经济净收益,应该研究制定合理的收获策略。利用Pontryagin极值原理和一些分析技巧,获得了最优收获策略,得到了收益的具体表达式。     

Global stability of an age-structured population model

We consider a nonlinear discrete-time population model for the dynamics of an age-structured species. This model has the form of a Lure feedback system (well-known in control theory) and is a particular case of the system studied by Townley et al. in Townley et al. (2012). The main objective is to show that, in this case, the range of nonlinearities for which the existence of globally asymptotically stable non-zero equilibrium can be guaranteed is considerably larger than that in the main result in Townley et al. (2012). We illustrate our results with several biologically meaningful examples.     

Helmet design to facilitate thermoneutrality during forest harvesting

The purpose of this investigation was to evaluate the ventilatory characteristics of vented and non-vented helmets for use in forestry harvesting operations. A ventilation index developed by Birnbaum and Crockford (1978) was used to determine the ventilation capacity of twelve helmets varying in design and presence, location, and dimension of vents. Helmets with top vents had higher ventilation indices than non-vented, side and side/top-vented helmets. Ten physically fit men participated in a maximal oxygen consumption test and four trials wearing a non-vented, round-side-vented, round-top-vented or rectangulartop-vented helmet. Trials simulated typical summer environmental conditions (28°C, 80% rh) and physiological work loads (40% V O 2 max) experienced during forest harvesting in New Zealand. The temperature and humidity under the helmet was typically lowest when the helmet with the largest vented area (288 mm 2) in the crown was worn, although physiological responses (temperatures at the tympanum, ear and scalp; humidity at the centre of the helmet) of the participants to wearing the helmets differed significantly during some rest periods only. Top-vented helmets (in this experiment measured 288 mm 2) should be worn to minimize temperature and humidity of the head during forest harvesting operations.     

Helmet design to facilitate thermoneutrality during forest harvesting

The purpose of this investigation was to evaluate the ventilatory characteristics of vented and non-vented helmets for use in forestry harvesting operations. A ventilation index developed by Birnbaum and Crockford (1978) was used to determine the ventilation capacity of twelve helmets varying in design and presence, location, and dimension of vents. Helmets with top vents had higher ventilation indices than non-vented, side and side/top-vented helmets. Ten physically fit men participated in a maximal oxygen consumption test and four trials wearing a non-vented, round-side-vented, round-top-vented or rectangulartop-vented helmet. Trials simulated typical summer environmental conditions (28 degrees C, 80% rh) and physiological work loads (40% VO(2)max) experienced during forest harvesting in New Zealand. The temperature and humidity under the helmet was typically lowest when the helmet with the largest vented area (288 mm(2)) in the crown was worn, although physiological responses (temperatures at the tympanum, ear and scalp; humidity at the centre of the helmet) of the participants to wearing the helmets differed significantly during some rest periods only. Top-vented helmets (in this experiment measured 288 mm(2)) should be worn to minimize temperature and humidity of the head during forest harvesting operations.     

Annual planning of harvesting resources in the forest industry

A cost‐efficient use of harvesting resources is important in the forest industry. The main planning is carried out in an annual resource plan that is continuously revised. The harvesting operations are divided into harvesting and forwarding. The harvesting operation fells trees and puts them in piles in the harvest areas. The forwarding operation collects piles and moves them to storage locations adjacent to forest roads. These operations are conducted by machines (harvesters, forwarders and harwarders), and these are operated by crews living in cities/villages that are within some maximum distance from the harvest areas. Machines, harvest teams and harvest areas have different characteristics and properties and it is difficult to find the best possible match throughout the year. The aim of the planning is to find an annual plan with the lowest possible cost. The total cost is based on three parts: production cost, traveling cost and moving cost. The production cost is the cost for the harvesting and forwarding. The traveling cost is the cost for driving back and forwards (daily) from the home base to the harvest area and the moving cost is associated with moving the machines and equipment between harvest areas. The Forest Research Institute of Sweden (Skogforsk), together with a number of Swedish forest companies, has developed a decision support platform for the planning. One important element of this platform is that it should find high‐quality plans within short computational times. One central element is an optimization model that integrates the assignment of machines to harvest areas and schedules the harvest areas during the year for each machine. The problem is complex and we propose a two‐phase solution method where, first, we solve the assignment problem and, second, the scheduling. In order to be able to control the scheduling in phase 1 as well, we have introduced an extra cost component that controls the geographical distribution of harvest areas for each machine in phase 1. We have tested the solution approach on a case study from one of the larger Swedish forest companies. This case study involves 46 machines and 968 harvest areas representing a log volume of 1.33 million cubic meters. We describe some numerical results and experience from the development and tests.     

Optimum policy in hybrid manufacturing/remanufacturing system

In this study, a hybrid manufacturing/remanufacturing system for a kind of short life cycle product with stochastic demand and stochastic returned products was investigated. The objective is to minimize the total cost of the hybrid system. The impacts of the amount of products manufactured and the proportion of the remanufactured part to the returned products on the total cost of the system were analyzed. Through theoretic analyses and numerical experiments, the relationship between the total cost of the system and the two influential factors were identified. The total cost of the hybrid system could be reduced significantly by setting optimum values of the amount of products manufactured and the proportion of the remanufactured part to the returned products. The sensitivity of the optimum values of the decision variables and the minimum cost with respect to the system parameters were also investigated.     

Decision making policy for RF energy harvesting enabled cognitive radios in decentralized wireless networks

Cognitive radio (CR) paradigm with radio frequency energy harvesting (RFEH) have significant potential to improve the network throughput by utilizing vacant spectrum using battery-operated self-sustainable radio terminals. Research efforts relevant to these paradigms are focused on the mode selection policies which decide when to switch from CR mode (i.e., opportunistic vacant spectrum access mode) to the RFEH mode (i.e., battery charging using ambient RF energy) and vice-versa. So far, very little attention has been paid to the dual but competing task of frequency band selection in CR and RFEH modes under partially observable environment in the decentralized wireless networks. Furthermore, the need of tunable bandwidth frequency band access for CRs and lower subband switching cost (SSC) for energy efficient implementation have made the design of the decision making policy (DMP) more challenging. In this paper, a new CR-RFEH DMP has been proposed for RFEH enabled CR terminals in the decentralized wireless networks. The proposed DMP consists of three sub-units: 1) Bayesian approach based tunable Thompson sampling algorithm for subband statistics estimation, 2) Thompson sampling algorithm based subband access scheme exploiting the past collision events to minimize collisions among CRs, and 3) Mode selection scheme. Simulation results show that the proposed DMP offers 10–35% improvement in the throughput of the decentralized network and 40–90% reduction in the number of subband switchings compared to existing DMPs. The simulation results are then validated using real radio signals on the proposed USRP testbed.     

端到端通信中基于时间转换能量采集的计算迁移方案

在端到端（D2D）通信网络中,为提高移动云计算的有效性,提出了一种基于时间转换能量采集的计算迁移方案。首先,一个流量受限的智能移动终端把其需要迁移的计算任务通过D2D通信以射频信号的形式发送给一个能量受限的智能移动终端,后者利用时间转换方案对接收信号进行能量采集。然后,能量受限终端会为流量受限终端中继任务到云端服务器付出额外的流量消耗。最后,所提的方案被建模为一个最小化终端能量与流量消耗的非凸优化问题,通过优化能量受限终端的时间转换因子、采集能量分配因子以及流量受限终端的传输功率,最终获得了最优方案。仿真结果表明,相比于非协作方案,所提方案通过互惠协作进行计算迁移能有效地减少终端的匮乏资源开销。     

Optimum harvesting area of convex and concave polygon field for path planning of robot combine harvester

Intelligent Service Robotics - This paper presents an optimum harvesting area of a convex and concave polygon for the path planning of a robot combine harvester. A convenient optimum harvesting...     

Optimum block replacement policy over a random time horizon

In this paper we consider the block replacement policy (BRP) for a system operating over a random time horizon. Under such a policy, a system is replaced by a new one either at failure or at a given time interval. The optimality criterion is the expected total replacements cost. Conditions under which an optimal replacement period exits are given. It is shown that BRP over an infinite time horizon is obtained as a particular case of the present work. A numerical example is given to illustrate the proposed replacement model.     

Physiological demands of forest harvesting tasks: A case study of skidding operations

In spite of increased mechanisation, forest harvesting tasks continue to place moderate to heavy physiological demands on employees. A work-heart-rate study of skidder operators in the southern United States during summer months is reported. The study illustrates how data may be obtained without interference with production and the uses of the data for documenting task difficulty and evaluating different work methods. The potential use of work physiology data for harvesting worker selection is indicated although the study data were not entirely successful on this point.     

An optimal forest thinning policy: A simulation approach

This paper provides a model for finding the optimal thinning policy in a pine forest (Pinus halepensis) in Israel. The model simulates the growth of a pine forest stand for timber, under various thinning policies. The annual growth functions are estimated via polynomial regression analysis. The dependent variable is the timber volume of the stand and the explanatory variable is the mean growing space per tree over time. The observations were made over the life span of five experimental parcels in a pine forest in Israel.     

Heart-rate response to forest harvesting work in the south-eastern United States during summer

Abstract

The physiological workload of forest harvesting workers during summer in the south-eastern United States was evaluated by measuring work heart-rate response. The harvesting tasks considered were chainsaw felling, cable skidding, bucking and trimming at the landing, knuckle-boom loader operation, feller-buncher operation and grapple skidding. VO₂ max of the workers ranged from 28 to 53 ml min^?1kg^?1. The WBGT ranged from 20 to 344°C during data collection. The task time-weighed, age-corrected, percent maximum heart-rate response ranged from 42-5 to 69 2°. The data indicate that the manual and semi-mechanized tasks are potentially stressful and that hotter environmental conditions increase the likelihood of higher heart-rate responses. No relationship was found between heart-rate response and three measures of static muscle strength.     

High-order IMEX-WENO finite volume approximation for nonlinear age-structured population model

ABSTRACT

In this article, we design a high-order implicit–explicit weighted non-oscillatory (IMEX-WENO) scheme for the solution of the population age density model with the nonlinear mortality rate as well as fertility rate. The mortality rate is the combination of natural mortality that comes to be unbounded at maximum age and bounded external mortality rate that includes external resources as well as seasonality. The existence of global terms in the mortality function as well as in the boundary condition is the main technical complication which provides high nonlinearity for the model equation. We carefully construct a numerical scheme in such way, that the high-order accuracy is maintained in the global terms and boundary condition. The performance of the designed scheme is shown by comparing with the exact solution of the examples considered.     

一种超宽带能量收集整流天线设计

为了更好地利用空间无线电波RF能量,设计了一款覆盖谐振频率为1～14 GHz宽带天线,并针对2.4 GHz进行整流天线设计.天线主体为一个圆形贴片,在地面通过开圆形槽的方式,改变辐射单元表面电流强度,实现宽带谐振和增强辐射的作用.天线在2.4 GHz处为最佳谐振点,此频段对应的最大增益为6.26 dBi.为了使整流天线...     

网络信息发布优选模型的最优算法

针对网络信息发布中不同终端的承载能力差异,对信息发布的优选问题进行研究,根据建立的简化二叉树模型对其优选方案求解,得出网络信息发布的最优求解算法.     

Design and performance analysis of broadband rectenna for an efficient RF energy harvesting application

This article proposes the design of coplanar waveguide (CPW) fed broadband rectenna for radio frequency (RF) energy harvesting application. The rectenna is designed to operate in the industrial, scientific, and medical (ISM) frequency band of 5.8 GHz. For designing the proposed rectenna, polytetrafluoroethylene (PTFE) dielectric material was used to design, fabricate the CPW fed slot antenna. It was observed that the proposed antenna exhibits the |S₁₁| of ?23.43 dB and achieves the peak antenna gain of 8.56 dBi at 5.8 GHz. Secondly, the CPW fed rectifier circuit which comprises of the matching circuit, rectifying unit, and filter was designed. The measured results showed that the |S₁₁| of ?19 dB and it was perfectly matched with 50 Ω impedance. Finally, the rectenna was designed by integration of antenna with rectifier circuit. The simulated results showed the maximum RF to direct current (DC) conversion efficiency and the output DC voltage of 88% and 445 mV at the load resistance of 1 kΩ. The measured results show the maximum RF to DC conversion efficiency of 73.4% with the output DC voltage of 540 mV at the load resistance of 1 kΩ.