Work during screw rolling

A new technique is proposed to determine the specific volume work of deformation during screw rolling. Methods for determining the work of deformation in various sections of the deformation zone in a piercing mill are considered. The dependence of the work of deformation on the reduction in the deformation zone is obtained. A new approach is proposed to calculate the fracture sensitivity and the working of the structure of continuously cast round billets. The effect of the reduction ratio on the work of deformation in similar piercing mills located at OAO Pervoural’sk Nonvotrubnyi Plant and the Yuzhnotrubnyi Plant is estimated.     

Ongoing control of the transverse thickness fluctuation of cold-rolled high-strength strip

Minimization of the transverse thickness fluctuation is considered, in the production of cold-rolled strip from a blank of multiple-strip width on a five-cell 630 mill. The forces and torques in the multipass rolling of strip produced from intermediate strip with an asymmetric cross section are determined.     

Work of deformation in screw rolling

A method is proposed for determining the unit work of deformation in the broaching of blanks in two-roller screw-rolling mills. A new approach is outlined for assessing the fracture risk and the structure of continuous-cast circular billet. Methods for determining the work of deformation in different sections of the deformation zone are considered. The distribution of the work of deformation due to reduction over the whole deformation zone is determined. The influence of extension on the work of deformation is assessed for similar rolling mills at OAO Pervoural’skii Novotrubnyi Zavod and OAO Yuzhnotrubnyi Zavod.     

Influence of plastic tension-flexure on the wire properties in scale removal and drawing

Technological aspects of scale removal and drawing are considered. The influence of various factors on the geometry and mechanical properties of the wire is compared in drawing with and without a drawplate.     

Power relinquishment versus power sharing: Theoretical clarification and empirical comparison of delegation and participation.

This article presents a theoretical and empirical comparison of delegation and participation. Although the two processes have sometimes been treated as interchangeable, delegation and participation have evolved from two different theoretical perspectives and are used by managers under different sets of conditions. Two studies are reported that examined these differences. The experimental study examined situational factors in Vroom and Yetton's (1973) leadership model that predict differences in managers' reported preferences for delegation or participation. Results indicated that decision importance, subordinate information, and subordinate goal congruence explained 23% of the variance in managers' preferences. The correlational study examined similar situational predictors of supervisors' reported use of delegation and participation with subordinates. These results largely confirmed the findings of the experimental study and also showed supervisor workload as a significant predictor. In addition, objective measures of subordinate performance significantly correlated with the use of delegation but not with participation. The implications of the findings for research on participative decision making are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Design of Scalable Continuous Media Servers

Multimedia applications place high demands for quality-of-service (QoS), performance, and reliability on systems. These stringent requirements make design of cost-effective and scalable systems difficult. Therefore efficient adaptive and dynamic resource management techniques in conjunction with data placement techniques can be of great help in improving performance, scalability, and reliability of such systems. This is the focus of our paper.     

Multiclass Multiserver Threshold-Based Systems: A Study of Noninstantaneous Server Activation

In this paper, we consider performance evaluation of a system which shares K servers (or resources) among N heterogeneous classes of workloads, where server allocation and deallocation for class i is dictated by a class specific threshold-based policy with hysteresis control. In particular, the server activation time for class i is noninstantaneous. There are many systems and applications where a multiclass threshold-based queueing system can be of great use. One important utility of using threshold-based approaches is in situations where applications may incur server usage costs. In these cases, one needs to consider not only the performance aspects but also the resulting cost/performance ratio. The motivation for using hysteresis control is to reduce the unnecessary cost of server setup (or activation) and server removal (or deactivation) whenever there are momentary fluctuations in workload. Moreover, servers in such systems and applications are often needed by multiple classes of workloads and, hence, it is desirable to find good approaches to sharing server resources among the different classes of workloads, preferably without statically partitioning the server pool among these classes. An important and distinguishing characteristic of our work is that we consider the modeling and analysis of a multiclass system with noninstantaneous server activation. The main contributions of this work are: 1) in developing an efficient approximation method for solving such models; 2) in verifying the convergence of our iterative method, and 3) in evaluating the resulting accuracy of the technique for computing performance measures of interest, which can subsequently be used in making system design choices     

Threshold-Based Dynamic Replication in Large-Scale Video-on-Demand Systems

Recent advances in high speed networking technologies and video compression techniques have made Video-on-Demand (VOD) services feasible. A large-scale VOD system imposes a large demand on I/O bandwidth and storage resources, and therefore, parallel disks are typically used for providing VOD service. Although striping of movie data across a large number of disks can balance the utilization among these disks, such a striping technique can exhibit additional complexity, for instance, in data management, such as synchronization among disks during data delivery, as well as in supporting fault tolerant behavior. Therefore, it is more practical to limit the extent of data striping, for example, by arranging the disks in groups (or nodes) and then allowing intra-group (or intra-node) data striping only. With multiple striping groups, however, we may need to assign a movie to multiple nodes so as to satisfy the total demand of requests for that movie. Such an approach gives rise to several design issues, including: (1) what is the right number of copies of each movie we need so as to satisfy the demand and at the same time not waste storage capacity, (2) how to assign these movies to different nodes in the system, and (3) what are efficient approaches to altering the number of copies of each movie (and their placement) when the need for that arises. In this paper, we study an approach to dynamically reconfiguring the VOD system so as to alter the number of copies of each movie maintained on the server as the access demand for these movies fluctuates. We propose various approaches to addressing the above stated issues, which result in a VOD design that is adaptive to the changes in data access patterns. Performance evaluation is carried out to quantify the costs and the performance gains of these techniques.     

Design of fault-tolerant large-scale VOD servers: With emphasis onhigh-performance and low-cost

Recent technological advances in digital signal processing, data compression techniques, and high-speed communication networks have made Video-on-Demand (VOD) servers feasible. A challenging task in such systems is servicing multiple clients simultaneously while satisfying real-time requirements of continuous delivery of objects at specified rates. To accomplish these tasks and realize economies of scale associated with servicing a large user population, a VOD server requires a large disk subsystem. Although a single disk is fairly reliable, a large disk farm can have an unacceptably high probability of disk failure. Furthermore, due to real-time constraints, the reliability requirements of VOD systems are even more stringent than those of traditional information systems. Traditional RAID solutions are inadequate due to poor resource usage. Thus, in this paper, we present alternative schemes which provide a high degree of reliability at low disk storage, bandwidth, and memory costs for on-demand multimedia servers. Moreover, we discuss some of the main issues and trade-offs associated with providing fault tolerance in multidisk VOD systems. We would like to impress upon the reader that one of the main points of this paper is the exposition of trade-offs and issues associated with designing fault-tolerant VOD servers. It is not the case that one fault tolerance scheme is absolutely better than another, but rather that one must understand the trade-offs as well as one's system constraints and then choose a fault tolerance scheme accordingly     

Use of multiple indicators to assess the pollution condition of urban streams: a case study of Bloemspruit,Free State Province,South Africa

The Bloemspruit in the Free State, South Africa, is being polluted by increasing anthropogenic activities alongside the stream. Water quality, macro‐invertebrate diversity and macro‐invertebrate habitats were studied to determine the extent of pollution. Pollution condition was quantified by calculating several indicators. The study revealed that Bloemspruit is highly polluted for the majority of the sampling sites. Two sites had fair water quality, while the water quality at the other sites was either marginal or poor. SASS 5 scores revealed that most macro‐invertebrate families present were pollution tolerant, indicating the poor state of the water. According to the modified IHAS (mIHAS) scores, macro‐invertebrate habitats at two sites were fair, seven adequate/fair and two poor. The relatively low values of the IHI scores confirm that the majority of the sites were affected by human activities. One site was classified as being largely modified because of the degrading effect of a wastewater treatment plant (WWTP) nearby.