Enhanced control of integrating cascade processes with time delays using modified Smith predictor

This paper presents a simple cascade controller in the enhanced modified Smith predictor structure for control of integrating processes. The proposed structure consists of two control loops, a secondary inner loop and a primary outer loop. The method has totally three controllers of which the secondary loop has one controller and the primary loop has two controllers. The secondary loop controller is designed using IMC technique. The primary loop set-point tracking and disturbance rejection controllers are designed using direct synthesis method. The primary set-point tracking controller is designed as a PID with lag filter and the primary disturbance rejection controller is designed as a PD with lead-lag filter. Simulation studies have been carried out on various cascade integrating processes with/without zero. The present method gives significant disturbance rejection both in the inner and outer loops and also shows significant improvement when compared to the recently reported methods.     

Nitrogen balances in farmers fields under alternative uses of a cover crop legume: a case study from Nicaragua

Canavalia brasiliensis (canavalia), a drought tolerant legume, was introduced into the smallholder traditional crop-livestock production system of the Nicaraguan hillsides as green manure to improve soil fertility or as forage during the dry season for improving milk production. Since nitrogen (N) is considered the most limiting nutrient for agricultural production in the target area, the objective of this study was to quantify the soil surface N budgets at plot level in farmers fields over two cropping years for the traditional maize/bean rotation and the alternative maize/canavalia rotation. Mineral fertilizer N, seed N and symbiotically fixed N were summed up as N input to the system. Symbiotic N₂ fixation was assessed using the ¹⁵N natural abundance method. Nitrogen output was quantified as N export via harvested products. Canavalia derived in average 69% of its N from the atmosphere. The amount of N fixed per hectare varied highly according to the biomass production, which ranged from 0 to 5,700 kg ha^?1. When used as green manure, canavalia increased the N balance of the maize/canavalia rotation but had no effect on the N uptake of the following maize crop. When used as forage, it bears the risk of a soil N depletion up to 41 kg N ha^?1 unless N would be recycled to the plot by animal manure. Without N mineral fertilizer application, the N budget remains negative even if canavalia was used as green manure. Therefore, the replenishment of soil N stocks by using canavalia may need a few years, during which the application of mineral N fertilizer needs to be maintained to sustain agricultural production.     

A new open-framework zinc arsenate [C4N3H16]2[Zn5(AsO4)4(HAsO4)2]

A three-dimensional zinc arsenate with an interrupted zeolitic framework (?IIO), [C₄N₃H₁₆]₂[Zn₅(AsO₄)₄(HAsO₄)₂], I has been synthesized solvothermally. The structure is built up from ZnO₄, AsO₄ and HAsO₄ tetrahedral units connected alternatively through their vertices forming the 3-D structure possessing one-dimensional channels bound by 10 T-atoms (T = Zn, As). The framework density of the structure is 10.4 T-atoms which indicates considerable openness in its structure.     

Multiuser MIMO OFDM Based TDD/TDMA for Next Generation Wireless Communication Systems

Multiple-input multiple-output (MIMO) wireless technology in combination with orthogonal frequency division multiplexing (MIMO OFDM) is an attractive air-interface solution for next-generation wireless local area networks (WLANs), wireless metropolitan area networks (WMANs), and fourth-generation mobile cellular wireless systems. In this paper, one multiuser MIMO OFDM systems with TDD/TDMA was proposed for next-generation wireless mobile communications, i.e., TDD/TDMA 4G, which can avoid or alleviate the specific limitations of existing techniques designed for multiuser MIMO OFDM systems in broadband wireless mobile channel scenarios, i.e., bad performance and extreme complexity of multiuser detectors for rank-deficient multiuser MIMO OFDM systems with CDMA as access modes, extreme challenges of spatial MIMO channel estimators in rank-deficient MIMO OFDM systems, and exponential growth complexity of optimal sub-carrier allocations for OFDMA-based MIMO OFDM systems. Furthermore, inspired from the Steiner channel estimation method in multi-user CDMA uplink wireless channels, we proposed a new design scheme of training sequence in time domain to conduct channel estimation. Training sequences of different transmit antennas can be simply obtained by truncating the circular extension of one basic training sequence, and the pilot matrix assembled by these training sequences is one circular matrix with good reversibility. A novel eigenmode transmission was also given in this paper, and data symbols encoded by space–time codes can be steered to these eigenmodes similar to MIMO wireless communication systems with single-carrier transmission. At the same time,, an improved water-filling scheme was also described for determining the optimal transmit powers for orthogonal eigenmodes. The classical water-filling strategy is firstly adopted to determine the optimal power allocation and correspondent bit numbers for every eigenmode, followed by a residual power reallocation to further determine the additional bit numbers carried by every eigenmode. Compared with classical water-filling schemes, it can also obtain larger throughputs via residual power allocation. At last, three typical implementation schemes of multiuser MIMO OFDM with TDMA, CDMA and OFDMA, i.e., TDD/TDMA 4G, VSF-OFCDM and FuTURE B3G TDD, were tested by numerical simulations. Results indicated that the proposed multiuser MIMO OFDM system schemes with TDD/TDMA, i.e., TDD/TDMA 4G, can achieve comparable system performance and throughputs with low complexity and radio resource overhead to that of DoCoMo MIMO VSF-OFCDM and FuTURE B3G TDD.     

建立投资风险管理体系，立对3G时代多网络建设

3G时代,电信运营商经营的网络建设范围向移动＋固定网络,2G＋3G网络发展,网络结构愈加复杂。电信运营商投资控制难度不断加大,投资风险也逐渐升高。电信运营商需要加强投资风险管理意识．建立一套从规划层面到项目管理、贯穿投资前中后各个环节的投资风险管理体系,从而降低整体投资风险,提升投资效率。     

基于HCI层的蓝牙开发

本文对蓝牙的体系结构、主机控制器接口(HCI)层及HCI指令和HCI事件进行了简要介绍,探讨了基于HCI层的蓝牙开发模式,阐述了蓝牙点对点的ALC数据传输的主要过程,提出了蓝牙HCI指令函数封装的一般方法,为蓝牙的嵌入式应用开发提供一般思路。     

帕卡特水电站设计径流量计算

通过建立月降雨径流模型,采用月降雨量推求月径流量,并考虑了与产生径流量有关的气象要素和流域相关参数,对帕卡特水电站的设计径流量进行了计算。     

西枝江水利枢纽工程建设水资源论证有关内容分析

对西枝江水利枢纽工程工程区域水资源时空分布特点及开发利用现状进行了分析,并对工程的取水地点、取水量、取水方式及用水、退水方式进行了研究,分析了该工程的用水和退水对周边环境和其他用水户的影响,论证了工程开发取水的合理性,并提出水资源保护措施和建议。     

利用解析法计算倒垂孔有效孔径及中心的改进方法

解析法在计算倒垂孔有效孔径及中心时逐步受到重视。通过对倒垂孔有效孔径的求解过程进行几何分析和理论归纳,提出一种改进的计算倒垂孔有效孔径和中心的解析方法,并给出基于Visual Basic计算机语言的算法框图。根据该方法开发了一套实用性强的计算程序,可以快速、精确地计算有效孔径和中心,并已在工程实际应用中得到验证,取得了良好效果。     

脂肪替代品的现状及展望

概述了脂肪替代品的发展现状、基本类型以及它们各自的特点和应用范围。并提出脂肪替代品的发展趋势和前景