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121.
提出了一种基于混沌序列的跳频信号源的设计及硬件实现方法;该方法基于FPGA技术,以Logistic混沌映射电路作为跳频序列发生器,以直接数字频率合成器作为跳频信号源的基础;在FPGA上完成数字频率合成,并利用高性能的AD9777实现数模转换;实验测试结果表明,该信号源在2MHz~32MHz频率范围内,实现了16个频点的跳变频率且性能良好,能够满足实际工程的需要。 相似文献
122.
The optimal tracking problem for multiple‐input multiple‐output linear‐time‐invariant discrete‐time systems with communication constraints in the feedback path is studied in this paper. The tracking performance is measured by the energy of the error signal between the output of the plant and the reference signal. The objective is to obtain an optimal tracking performance, attainable by all possible stabilizing compensators. It is shown that the optimal tracking performance consists of two parts, one depends on the nonminimum phase zeros and zero direction of the given plant, as well as the reference input signal direction, and the other depends on the nonminimum phase zeros, unstable poles, and pole direction of the given plant, as well as the bandwidth and additive white Gaussian noise of the communication channel. It is also shown that, if the constraint of the communication channel does not exist, the optimal tracking performance reduces to the existing tracking performance of the control system without communication constraints. A typical example is given to illustrate the theoretical results. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
123.
Gary Gibson Xia Sheng Dick Henze Si‐Ty Lam Patricia Beck Yoocharn Jeon Zhang‐Lin Zhou Brad Benson Qin Liu Gregg Combs Tim Koch Kent Biggs 《Journal of the Society for Information Display》2012,20(10):552-558
Reflective displays are advantageous in applications requiring low power or daylight readability. However, there are no low‐cost reflective technologies capable of displaying bright colors. By employing photoluminescence to more efficiently use ambient light, we created a prototype display that provides bright, full color in a simple, low‐cost architecture. This prototype includes a novel electrokinetic shutter, a layer that incorporates patterned luminescent red, green, and blue sub‐pixel elements, and a novel optical out‐coupling scheme. The luminescent elements convert otherwise‐wasted portions of the incident spectrum to light in the desired color band, resulting in improved color saturation and lightness. This prototype provides a color gamut that is superior to competing reflective display technologies that utilize color filters in single‐layer side‐by‐side sub‐pixel architectures. The current prototype is capable of switching in <0.5 s; future displays based on an alternative electro‐optic shutter technology should achieve video rate operation. A transflective version of this technology has also been prototyped. The transflective version utilizes its backlight with a power efficiency that is at least three times that of a conventional liquid crystal display. These photoluminescence‐based technologies enable a host of applications ranging from low‐power mobile products and retail pricing signage to daylight readable signage for outdoor advertising segments. 相似文献
124.
We propose an approach for dependence tree structure learning via copula. A nonparametric algorithm for copula estimation is presented. Then a Chow-Liu like method based on dependence measure via copula is proposed to estimate maximum spanning bivariate copula associated with bivariate dependence relations. The main advantage of the approach is that learning with empirical copula focuses on dependence relations among random variables, without the need to know the properties of individual variables as well as without the requirement to specify parametric family of entire underlying distribution for individual variables. Experiments on two real-application data sets show the effectiveness of the proposed method. 相似文献
125.
Xi‐Sheng Zhan Zhi‐Hong Guan Rui‐Quan Liao Fu‐Shun Yuan 《Asian journal of control》2012,14(6):1608-1616
The analysis method of optimal tracking performance is proposed for multiple‐input multiple‐output (MIMO) linear time‐invariant (LTI) systems under disturbance rejection. An H2 criterion of the error signal between the output of the plant and the reference signal is used as a measure for the tracking performance. Spectral factorization is applied to obtain the optimal solution of the system tracking error. The explicit expressions are derived for this minimal tracking error with respect to random reference signals under disturbance rejection. It is shown that the nonminimum phase zeros, the zero direction, the unstable poles, the pole direction of a given plant, statistical characteristics of the reference input signal, and disturbance signal have a negative effect on a feedback system's ability to reduce the system error with disturbance rejection. The results show that the optimal tracking performance will further be damaged because of disturbance rejection. Some typical examples are given to illustrate the theoretical results. 相似文献
126.
Web服务器生成Cookies并作为文本存贮于用户计算机硬盘或内存中,是实现Web应用认证的主要手段。本文分析了Cookie认证机制的实现过程与特点,并且论述了该认证机制易遭受的安全威胁以及安全需求,并给出实现安全Cookie认证的方法与措施。 相似文献
127.
SIMD单元集成已经成为提高处理器性能的重要途径之一。虽然定点SIMD单元的硬件复用低成本设计技术已经较为成熟,但是,大部分浮点SIMD单元的硬件设计还停留在简单的硬件复制方法上。本文针对日益增长的128位高精度浮点操作的计算需求,提出了其相应的SIMD低成本硬件结构方案。综合实验结果表明,所提出的SIMD浮点乘加单元比传统128位高精度浮点乘加单元具有更加优化的性能与面积参数。 相似文献
128.
采用塑性加工方法,本文初步探索了预变形对PREP高温合金粉末及热等静压后合金显微组织的影响.结果表明,粉末预变形可以促进热处理后粉末组织的均匀化,并可降低合金的再结晶温度,改善合金组织,消除部分枝晶,对提高粉末的利用率及降低粉末高温合金盘件的成本具有较大的实际意义. 相似文献
129.
130.