柑桔高接换种最适时期与方法

柑桔高接换种最适时期与方法叶伟其（浙江省丽水地区实验林场３２３００）我场及一些试验点，１９９０年开始，对陆续引进的２０余种柑桔新品种，以温州蜜柑和柑为中间砧，在不同的时期，采用多种嫁接方法，进行了高接换种。现将有关最适宜高接时期和方法的结果介绍如下．...

垃圾的危害——写在附则Ⅴ生效之际

73/78公约的附则Ⅴ已于1988年12月31日生效。 同附则Ⅲ、附则Ⅳ(有关包装物质污染和船舶生活污水污染)一样,附则Ⅴ也是任选附则。所谓任选附则是指接受公约正文的各国政府,只有义务执行关于油污染的附则Ⅰ和关于有毒液体物质造成污染的附则Ⅱ。结果,许多国家推迟接受三个任选附则,附则Ⅴ在制定15年后才生效。 现在,附则Ⅴ终于生效,这是迄今为止在防止垃圾污染海洋方面迈出的最大一步。在近几十年中,垃圾污染海洋的问题日益严重。

Adaptive clustering hierarchy routing for delay tolerant network

Adaptive clustering hierarchy routing(ACHR) establishes a clusters-based hierarchical hybrid routing algorithm with two-hop local visibility for delay tolerant network(DTN).The major contribution of ACHR is the combination of single copy scheme and multi-copy scheme and the combination of hop-by-hop and multi-hop mechanism ACHR,which has the advantages in simplicity,availability and well-expansibility.The result shows that it can take advantage of the random communication opportunities and local network connectivity,and achieves 1.6 times delivery ratio and 60% overhead compared with its counterpart.

QoS Guarantees of Multiuser Video Streaming over Wireless Links: Delay Constraint and Packet Priority Drop

To provide a certain level of Quality of Service (QoS) guarantees for multiuser wireless downlink video streaming transmissions, we propose a multiuser scheduling scheme for QoS guarantees. It is based on the classic Queue-Length-Based (QLB)-rate maximum scheduling algorithm and integrated with the delay constraint and the packet priority drop. We use the large deviation principle and the effective capacity theory to construct a new analysis model to find each user's queue length threshold (delay constraint) violation probability. This probability corresponds to the upper bound of the packet drop probability, which indicates a certain level of statistical QoS guarantees. Then, we utilize the priority information of video packets and introduce the packet priority drop to further improve the quality perceived by each user. The simulation results show that the average Peak Signal to Noise Ratio (PSNR) value of the priority drop is 0.8 higher than that of the non-priority drop and the PSNR value of the most badly damaged video frame in the priority drop is on an average 4 higher than that of the non-priority drop.

A unified approach of PID controller design for unstable processes with time delay

This paper addresses a unified approach of the PID controller design for low as well as high order unstable processes with time delay.The design method is based on the direct synthesis(DS)approach to achieve the enhanced load disturbance rejection.To improve the servo response,a two-degree of freedom control scheme has been considered.A suitable guideline has been provided to select the desired reference model in the DS scheme.The direct synthesis controller has been approximated to the PID controller using the frequency response matching method.A consistently better performance has been obtained in comparison with the recently reported methods.

A new approach for teleoperation rendezvous and docking with time delay

Teleoperation rendezvous and docking can be used as a backup for autonomous rendezvous and docking (RVD) for an unmanned spacecraft or for guiding the chaser docking with an uncooperative target.The inherent teleoperation time delay is a rigorous problem,especially when the chaser is teleoperated on the ground.To eliminate the effect of time delay,a new approach for teleoperation RVD is studied.The characteristics of teleoperation RVD are analyzed by comparisons with the teleoperation robot and with manually controlled RVD;the relative motion of the chaser is predicted based on the C-W equation;and the processed measure information with time delay through the Kalman filter is utilized to correct the current prediction.Experimental results verify that the approach produces an 18% enhanced success rate of teleoperation RVD compared with direct visual feedback,and consumes less time and fuel.The developed approach also solves the time delay problem effectively.Teleoperation RVD using this method can be applied as a useful backup for autonomous RVD.

A delayed SEIRS epidemic model with impulsive vaccination and nonlinear incidence rate

In this paper, a delayed SEIRS epidemic model with nonlinear incidence rate and impul- sive vaccination is investigated. In vaccination strategy, we perform impulsive vaccina- tion of newborn infants. Using the discrete dynamic system determined by stroboscopic map, we obtain an infection-free periodic solution and establish conditions, on which the solution is globally attractive. We also conclude that the disease is permanent if the parameters of the model satisfy appropriate conditions. Finally, we illustrate the effec- tiveness of our theorems with numerical simulation. The results obtained in this paper are a good extension of the results obtained in [J. Hou and Z. Teng, Continuous and impulsive vaccination of SEIR epidemic models with saturation incidence rate, Math. Comput, Simulat. 79 （2009） 3038 3054] to the corresponding delayed SEIRS epidemic model with nonlinear incidence rate and impulsive vaccination.

STABILITY ANALYSIS OF A DELAYED SIRS EPIDEMIC MODEL WITH VACCINATION AND NONLINEAR INCIDENCE

In this paper, an SIRS epidemic model with time delay and vaccination is investigated. By analyzing the corresponding characteristic equation, the local stability of diseasefree equilibrium of the model is established. By constructing Lyapunov functional, sufficient conditions are established for the local stability of an endemic equilibrium of the model. Further, a threshold value is obtained. By using comparison arguments, it is proved when the threshold value is less than unity, the diseasefree equilibrium is globally asymptoti cally stable. When the threshold value is greater than unity, by using an iteration scheme and by constructing appropriate Lyapunov functional, respectively, sufficient conditions are derived for the global stability of the endemic equilibrium of the model. Numerical simulations are carried out to illustrate the theoretical results.