干热河谷典型区元谋县土地利用变化与动态预测

土地利用类型格局变化对于区域经济以及资源可持续发展规划有着显著的影响作用.基于遥感(remote sensing,RS)和地理信息系统(geographic information system,GIS)技术,应用土地利用动态度、土地利用程度指数、土地利用转移矩阵、CA-Markov模型对干热河谷典型区元谋县1990-2020年土地利用变化及2020-2025年的土地利用发展趋势进行了分析.结果 表明:1990-2020年30 a间,元谋县的草地、水域、城镇用地面积增加,林地、耕地、未利用地面积减少,其中城镇用地面积增加速率最大;整体上,元谋县的土地利用变化速度较快,土地利用程度有所提高,但土地利用程度仍处于中等水平;各种土地利用类型在近30 a转换频繁,主要以草地转入,耕地转出为主;CA-Markov模型预测结果表明2020-2025年期间元谋县除草地、林地、水域、其他用地面积呈现下降趋势外,未来耕地、城镇用地面积有所增加,其中城镇用地面积在未来5年内的增长速率为11.05％,预测模型的Kappa系数为0.92,说明模型结果和转换规则可信度较高.研究结果可为元谋县土地资源管理与合理利用提供科学依据.     

一个智能化的CAD图形接口

LOGCAD是我们在微机上开发的一个Turbo Prolog与Auto CAD的连接接口,它解决了设计型专家系统的复杂图形输出问题。本文介绍LOGCAD接口设计思想及关键技术,并以轴零件图的绘制为例,来说明本软件的功能和使用。     

A New Communication Scheme for Threshold Certificate Authority in Ad Hoc Networks

We present a new approach to reduce the communication overhead caused by threshold cryptography using modified multieast protocol and certificate proxy technology. Server nodes maintain a few multieast groups proaetively. A client wanting to update its certificate multieasts its request to a server nodes group through its certificate proxy. At periodie intervals, server nodes refresh their shares of the private key of certificate authority using multicast.     

基于PKI的CA认证中心的搭建

随着网络的普及和人们对网络信息的安全性要求的日益增加，建立一套保证网上传输信息安全性的机制已是刻不容缓。文章着重介绍了PKI系统的组成，实现的各种功能，具体讨论了基于PKI思想的CA认证中心的一种搭建方式，其中包括了CA服务器的搭建，证书的发布和作废等。此外对CA的信任模型也作了讨论。     

Transitional function of DG to CA3 in the hippocampus

Using single cell channel model, the transmission features of CA3-DG network in the hippocampus are investigated. The influence of the stimulation on discharge pattern of pyramidal neurons is analyzed, which shows that it starts with period spiking discharges, followed by period-doubling bifurcation to chaos, and period 3 discharge evolving into chaos, and ultimately a period of bursting discharges. By the synaptic model, the CA3-DG network model is constructed, which analyzes the summation of postsynaptic currents in the network, the influence of postsynaptic current on discharge rhythm as well as the mechanism of bursting discharges. The strong capacity of spatiotemporal encoding in the network indicates the features of CA3 network during the information transmission process in the hippocampus. The modeling result with time delay of the synaptic transmission is in accordance with the experimental phenomena of action potential in the hippocampus.     

RBAC授权数字证书的设计与实现

为了避免传统的数据库存储用户口令验证访问控制权限方式因失窃而引起的不安全,设计了一种RBAC授权数字证书。通过在证书中扩展角色属性,并将角色授权和资源分配与证书的颁发分隔独立,一方面实现了证书对资源的访问控制,另一方面使得角色授权更加灵活。最后对该方式进行了验证实现。     

基于模拟互联网应用环境的密码学数字签名实验方案的设计

在分析密码学传统常见的实验教学方式存在问题的基础上,通过以数字签名实验为实验方式改革的切入口,设计了一个基于模拟互联网环境的实验教学方案进行尝试.通过统计证实,采用新方式实验,能提高学生的学习理论、参加实验的兴趣,提高对知识的掌握能力和学习效率.     

表面活性剂对赤霉菌双羟化去氢表雄酮的影响

考察了表面活性剂对Gibberella intermedia CA3-1双羟化去氢表雄酮生成三羟基雄甾烯酮的影响。在转化体系中添加表面活性剂可以加快Gibberella intermedia CA3-1羟化去氢表雄酮的转化反应并使产物三羟基雄甾烯酮的得率有所提高。Tween-80对转化促进作用明显,在底物投料质量浓度为8g／L,转化72h时产物得率达到53％,较对照实验提高了约5％。研究了表面活性剂添加量对转化的影响以及其对茵体生长的影响,推测表面活性剂促进甾体转化的原因,为表面活性剂在甾体生物转化反应中的应用奠定了基础。     

Modeling and Simulation of P-Aloha,CSMA/CA and MACAW Protocols for Underwater Acoustic Channel

Medium access control( MAC) protocol of underwater acoustic communication network is a key technology for underwater acoustic networks( UANs). Most of the MAC protocols for wireless terrestrial communication networks have been designed with negligible propagation delay. If it is deployed directly in an underwater environment,the UANs will perform inefficiently. In this paper,the characteristics of underwater acoustic channel are modeled and simulated by using the OPNET simulation tool,which are the speed of sound, propagation loss, and four sources for ambient noise: the turbulence,shipping,wind driven waves and thermal noise. The performance of pure Aloha( P-Aloha),carrier sense multiple access with collision avoidance( CSMA / CA) and multiple access collision avoidance for wireless local area network( MACAW) protocols in underwater acoustic channel environment are evaluated. The different performance of protocols in underwater environment is compared in the simulation.