优控主轴转速系统极限切削深度

对优控主轴转速系统的极限切削深度进行了试验考证。考证结果表明 :与未控主轴转速系统相比 ,优控主轴转速系统的极限切削深度明显提高 ,利用主轴转速寻优控制方法可以大幅度提高机床的切削效率。     

Resilience and survivability in communication networks: Strategies,principles, and survey of disciplines

The Internet has become essential to all aspects of modern life, and thus the consequences of network disruption have become increasingly severe. It is widely recognised that the Internet is not sufficiently resilient, survivable, and dependable, and that significant research, development, and engineering is necessary to improve the situation. This paper provides an architectural framework for resilience and survivability in communication networks and provides a survey of the disciplines that resilience encompasses, along with significant past failures of the network infrastructure. A resilience strategy is presented to defend against, detect, and remediate challenges, a set of principles for designing resilient networks is presented, and techniques are described to analyse network resilience.     

真空灭弧室 配电开关 断路器和接触器的高可靠性元件

自从20世纪50年代中期将真空灭弧室(VI)用作配电操作开关、断路器和接触器的电流分断元件以来,其作用逐步增强.在电路的开断和配电保护领域,该电气产品已经占统治地位.真空灭弧室甚至被引入到电力输送中的通断产品的领域上.真空灭弧室受到追捧的原因有:结构紧凑、适用范围广、成本低、极好的电寿命和机械寿命,以及使用方便.其中,最重要的优点是公认的高可靠性.     

Vacuum packed particles as flexible endoscope guides with controllable rigidity

In order to fully benefit from the functionalities of flexible endoscopes in surgery a simple shaft-guide that can be used to support the flexible endoscope shaft is required. Such a shaft-guide must be flexible during insertion into the human body and rigidified when properly positioned to support the flexible endoscope shaft. A shaft-guide called ‘Vacu-SL’ was designed, consisting of a foil tube, filled with particles, that is rigidified by creating a vacuum in its tube. It is expected that the bending stiffness of a loaded, rigidified Vacu-SL shaft-guide is significantly influenced by the shape, hardness and size of the filler particles used. The goal of this study was to find the relations between the filler particles’ size, shape and hardness and a rigidified Vacu-SL shaft-guide’s bending stiffness. Vacu-SL test models were made using polystyrene, acrylic glass, glass, steel, and corundum particles as spheres, pebbles and granulate, with average diameters between 0.16–1.7 mm. These test models were rigidified and then loaded in a tensile tester. The forces needed for 5 and 10 mm deflections of the rigidified test models were measured. The results show that particle size, shape and hardness all influence a rigidified Vacu-SL shaft-guide’s bending stiffness. Size and hardness showed an optimum and granules performed better than spheres. Although the maximally measured bending stiffness might be insufficient to enable proper guidance of flexible endoscope shafts, the results suggest several ways to successfully improve the Vacu-SL shaft-guide.     

Sabbatical leave: Who gains and how much?

A rigorous quasi-experiment tested the ameliorative effects of a sabbatical leave, a special case of respite from routine work. We hypothesized that (a) respite increases resource level and well-being and (b) individual differences and respite features moderate respite effects. A sample of 129 faculty members on sabbatical and 129 matched controls completed measures of resource gain, resource loss, and well-being before, during, and after the sabbatical. Among the sabbatees, resource loss declined and resource gain and well-being rose during the sabbatical. The comparison group showed no change. Moderation analysis revealed that those who reported higher respite self-efficacy and greater control, were more detached, had a more positive sabbatical experience, and spent their sabbatical outside their home country enjoyed more enhanced well-being than others. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Forecasting Construction Manpower Demand by Gray Model

Construction is a labor-intensive industry that is heavily reliant on the availability of local manpower. The construction workload also fluctuates in either a cyclical or random manner. As a result, there is always either a shortage or surplus of manpower. Although a number of good forecasting models have been developed, they require input of sufficient and good-quality data to produce accurate results. The aim of this paper is to explore the use of the gray model in forecasting construction manpower based on a limited amount of data. A wide range of forecasting models in the literature is first reviewed. A single-variable first-order gray model is then proposed to forecast construction manpower one quarter ahead. The model is tested using manpower data based on the Quarterly Report on General Household Survey published by the Census and Statistics Department of the HKSAR Government. Data from 64 quarters, covering the first quarter of 1992 to the fourth quarter of 2007, are included. A computer program is formulated to manipulate all of the calculations involved. Based on the minimum mean absolute percentage error (MAPE) criterion, it is found that the optimal sample size is 5. Based on the input of data from five quarters, the MAPE of the overall forecast is only 3.21%, and the maximum absolute percentage error is 8.92%. It is thus concluded that the gray model produces very accurate results. The results of this study also suggest that this model is applicable to forecasts of other time series particularly when limited data are available.     

Distance-based tree models for ranking data

Ranking data has applications in different fields of studies, like marketing, psychology and politics. Over the years, many models for ranking data have been developed. Among them, distance-based ranking models, which originate from the classical rank correlations, postulate that the probability of observing a ranking of items depends on the distance between the observed ranking and a modal ranking. The closer to the modal ranking, the higher the ranking probability is. However, such a model basically assumes a homogeneous population and does not incorporate the presence of covariates.To overcome these limitations, we combine the strength of a tree model and the existing distance-based models to build a model that can handle more complexity and improve prediction accuracy. We will introduce a recursive partitioning algorithm for building a tree model with a distance-based ranking model fitted at each leaf. We will also consider new weighted distance measures which allow different weights for different ranks in formulating more flexible distance-based tree models. Finally, we will apply the proposed methodology to analyze a ranking dataset of Inglehart’s items collected in the 1999 European Values Studies.     

Utility of the RT3 triaxial accelerometer in free living: An investigation of adherence and data loss

There is strong evidence for the protective effects of physical activity on chronic health problems. Activity monitors can objectively measure free living occupational and leisure time physical activity. Utility is an important consideration when determining the most appropriate monitor for specific populations and environments. Hours of activity data collected, the reasons for activity hours not being recorded, and how these two factors might change over time when using an activity monitor in free living are rarely reported. This study investigated user perceptions, adherence to minimal wear time and loss of data when using the RT3 activity monitor in 21 healthy adults, in a variety of occupations, over three (7 day) repeated weeks of measurement in free living. An activity diary verified each day of monitoring and a utility questionnaire explored participant perceptions on the usability of the RT3. The RT3 was worn for an average of 14 h daily with 90% of participants having complete data sets. In total 6535.8 and 6092.5 h of activity data were collected from the activity diary and the RT3 respectively. An estimated 443.3 h (6.7%) of activity data were not recorded by the RT3. Data loss was primarily due to battery malfunction (45.2%). Non-adherence to wear time accounted for 169.5 h (38.2%) of data loss, of which 14 h were due to occupational factors. The RT3 demonstrates good utility for free living activity measurement, however, technical issues and strategies to manage participant adherence require consideration with longitudinal and repeated measures studies.     

Case Studies on an Approach to Multiple Autonomous Vehicle Motion Coordination

1 Introduction With the increasing applications of autonomous vehicles and AGVsin dynamic andstrictly constrained envi-ronments in manufacturing, material handling and automated container terminals , coordination of a team ofAGVs’motion has became one of the keyissues significantly affectingthe productivity.The problemof motioncoordinationin a bidirectional path networkis hard to solve because of the (1) dynamic traffic conditionsinthenetwork environment with many bottleneckareas ;(2) verys…     

Electricity rates for the zero marginal cost grid

The electricity industry is rapidly changing: costs are increasingly dominated by capital and technology is turning loads into resources. This is similar to the early days of the Internet. Building on rate-structures used in the communications industry, utilities of the future should offer customers a portfolio of service contract options that provide a signal to the utility regarding the type and amount of infrastructure that should be deployed.