Optimal replacement policies for systems with multiple standbycomponents

The authors consider two new preventive replacement policies for a multiple-component cold-standby system. The failure rate of the component in operation is constant. The system is inspected at random points over time to determine whether it is to be replaced. The replacement decision is based on the number of failed components at the time of inspection. There are two replacement options if the complete system fails during operation: (i) replace the system if an inspection reveals that it has failed (system failure is not self-announcing), and (ii) replace the system the instant it fails (system failure is self-announcing). There is a threshold value on the number of failed components (at the time of inspection) which minimizes the mean total cost. The authors develop a simple efficient procedure to find the optimal threshold value. They compare the cost of operating a system that is inspected at random points in time, with the cost of operating a system that is monitored continuously through an attached monitoring device, and discuss cost tradeoffs     

Web cache replacement policies: a pragmatic approach

Research involving Web cache replacement policy has been active for at least a decade. In this-article we would like to claim that there is a sufficient number of good policies, and further proposals would only produce minute improvements. We argue that the focus should be fitness for purpose rather than proposing any new policies. Up to now, almost all policies were purported to perform better than others, creating confusion as to which policy should be used. Actually, a policy only performs well in certain environments. Therefore, the goal of this article is to identify the appropriate policies for proxies with different characteristics, such as proxies with a small cache, limited bandwidth, and limited processing power, as well as suggest policies for different types of proxies, such as ISP-level and root-level proxies.     

Optimal ordering policies and optimal number of minimal repairs before replacement

Many maintenance policies in the literature have assumed that whenever a unit is to be replaced, a new unit is immediately available. However, if the procurement lead time is not negligible an odering policy should determine when to order a spare and when to replace the operating unit. This paper presents a model for determining the optimal ordering point and the optimal number of minimal repairs before replacement which include the optimal number of minimal repairs before replacement of Park as a special case. We derive the expected cost per unit time in the steady-state as a criterion of optimality and seek the optimum policy by minimizing that cost. Finally, we present the numerical examples for illustration.     

香港互联互通新政策要点

2001年9月11日，香港电讯管理局在电讯盈科的请求下发布了咨询文件，对原有的互联互通及相关竞争政策进行了探讨，以适应竞争环境变化的要求。2002年3月18日，电讯管理局发布修订后的“电讯局长声明”，就固定网络运营商之间的关系、网络互连的配置架构及基本原则、互连网络之间的通信交换、网络运营商之间的收费原则，以及互联点等相关原则进行了阐述。本文就声明中的部分内容作简要介绍。固网运营商之间的关系香港电讯管理局向固定电信网络的经营者发放固定电讯网络服务（FTNS）牌照，FTNS牌照要求持牌商：（在香港的固定点之间或在香…     

Two new direct-coupled astable multivibrators

New direct-coupled astable multivibrators are introduced in which the collectors and the bases of both emitter-bias transistors are directly coupled to each other. They may be considered to be a modification of the direct-coupled bistable circuit. The switching action takes place by means of a capacitor in each emitter circuit. Triangular waves are generated at the transistor emitters.     

Two new ternary line codes

Two new ternary line codes are presented. Although the two codes are similar, they differ with respect to error propagation properties and power spectral densities. The codes are relatively simple, yet they satisfy tight channel input restrictions, making them suitable for use in practical baseband communications systems.<>     

Optimal replacement policies for k-out-of-nsystems

The authors study a discrete-time, infinite-horizon, dynamic programming model for the replacement of components in a binary k -out-of-n:F system. The goal is to trade off the component replacement and system failure costs. Under the criterion of minimizing the long-run average cost per period, it is optimal to follow a critical component policy (CCP), viz., a policy specified by a critical component set and the rule: replace a component if and only if it is failed and is in the critical component set. Computing an optimal CCP is a binary nonlinear programming problem, which can be solved by searching through a set with O(n^k-1) points. This approach to finding an optimal CCP is practical when k is small. In particular, assuming s-independent components, it requires O(n^2k-1) calculations. The authors analyze in detail the two most important cases with small k: the series (1-out-of-n:F) system and the 2-out-of-n:F system     

Distance-based recent use (DRU): an enhancement to instruction cache replacement policies for transition energy reduction

According to the International Technology Roadmap for Semiconductors (ITRS), the minimum feature size for microprocessors will shrink to 40 nm by 2010. Leakage currents in devices fabricated at these dimensions have been shown to be so dominant that design methodologies driven by power budgets will face challenges in reducing static power in addition to active power. An effective solution to tackle static power is to transition devices to a low-static-power sleep mode using special circuit-level techniques. However, these transitions come with energy costs, and as these techniques are perfected, and devices transition more often to sleep state, the relative contribution of transition energy to total energy will increase. To deal with the transition overhead, often used techniques are history-based and concentrate only on recognizing when to transition, but do not provide for reducing total transitions without adversely effecting the total sleep time of the devices. In this paper, we study transition-overhead reduction in associative instruction caches. We take advantage of the fact that many programs, particularly those for multimedia applications, spend most of their time in loops and most execution is near-sequential (high spatial locality). We present a technique called DRU (Distance-based Recent Use), which constrains near-sequential fetches to a single bank from the set of associative banks. Evaluation of DRU for different replacement policies in a system-level environment using Mediabench's applications and with various processor architectures (including SPARC and MIPS) have shown energy savings between 20%-28% with negligible hardware and timing overheads.     

AC-PDP保护层用的两种新材料

介绍了两种AC-PDP保护层用新材料。这两种新型保护层是：在MgO基层上交替沉积的LaF2／MgO多层保护层和在MgO基层上沉积的LaF3单层保护层。现已证实：它们在降低PDP的着火和维持电压方面是有效的,且能提高PDP的亮度。     

用于非线性机动目标跟踪的新型IMM算法

针对在非线性机动目标跟踪中存在的滤波器易发散、机动检测有延迟等问题,把Unscented Kalman Filter(UKF)引进到交互多模型算法(IMM)中,设计了交互多模型UKF滤波器。并利用目标运动模型集概率的相对变化率设计了自适应交互多模型UKF滤波器,最后进行了计算机仿真。蒙特卡罗仿真结果表明,两种滤波算法都具备UKF滤波器精度高、稳定性好、不易发散的优点,同时不需了解目标机动的先验信息,适合于实际应用;并且自适应交互多模型UKF滤波器具有更好的跟踪效果。     

Two new canonic single-CFOA oscillators with single resistor controls

Although a number of single current feedback op-amps (CFOA)-based single-resistance-controlled oscillators (SRCO) have appeared in earlier literature, only six of them are canonic (i.e., requiring only two capacitors and only three resistors). The object of this brief is to add to this list two new canonic single-CFOA-based SRCO configurations. An evaluation of these two new circuits has been carried out and their workability of has been confirmed by experimental results based upon AD844 CFOAs.     

Two new low-power Full Adders based on majority-not gates

Two novel low-power 1-bit Full Adder cells are proposed in this paper. Both of them are based on majority-not gates, which are designed with new methods in each cell. The first cell is only composed of input capacitors and CMOS inverters, and the second one also takes advantage of a high-performance CMOS bridge circuit. These kinds of designs enjoy low power consumption, a high degree of regularity, and simplicity. Low power consumption is targeted in implementation of our designs. Eight state-of-the-art 1-bit Full Adders and two proposed Full Adders are simulated using 0.18 μm CMOS technology at many supply voltages. Simulation results demonstrate improvement in terms of power consumption and power-delay product (PDP).     

Two new cascade resonator-in-a-loop filter configurations fortracking multiple sinusoids

Two adaptive configuration arrangements for tracking multiple sinusoids are introduced: a simple cascade of resonators-in-loops and a more elaborately interconnected structure. Simulation results demonstrate that these structures can successfully track and enhance multiple sinusoids, especially effectively when using the latter adaptive configuration     

Two new algorithms for tracking arterial parameters innonstationary noise conditions

Two new algorithms with reduced sensitivity to the changing environment are applied to tracking arterial circulation parameters. They are variants of the Least-Squares (LS) algorithm with Variable Forgetting factor (LSVF), and of the Constant Forgetting factor-Covariance Modification (CFCM) LS algorithm, devised to overcome their main practical deficiencies related to noise level sensitivity and the high number of design variables, respectively. To this end, adaptive mechanisms are incorporated to estimate observation noise variance in LSVF and the rate of change for the different parameters in CFCM. Specific computer simulation experiments are presented to compare their effectiveness with the original counterparts and to provide guidelines for their optimal tuning at different noise levels. Moreover, algorithm performance degradation, consequent on changes in the noise level compared to that assumed during the tuning phase, is analyzed. In particular, it is shown that, when the noise level changes with respect to the tuning value, the new LSVF algorithm is much more robust than the original one, whose performance degrades rapidly. The new CFCM algorithm is characterized by a reduced number of design variables with respect to its original counterpart. Nevertheless, it can be preferred only when low noise signals are used for estimation     

On protective buffer policies

Studies buffering policies which provide different loss priorities to packets/cells, while preserving packet ordering (space priority disciplines). These policies are motivated by the possible presence, within the same connection, of packets with different loss probability requirements or guarantees, e.g., voice and video coders or rate control mechanisms. The main contribution of the paper is the identification and evaluation of buffering policies which preserve packet ordering and guarantee high priority packets performance (loss probability), irrespective of the traffic intensity and arrival patterns of low priority packets. Such policies are termed protective policies. The need for such policies arises from the difficulty to accurately characterize and size low priority traffic, which can generate large and unpredictable traffic variations over short periods of time. The authors review previously proposed buffer admission policies and determine if they satisfy such “protection” requirements. Furthermore, they also identify and design new policies, which for a given level of protection maximize low priority throughput