This paper presents a novel approach to computing tight upper bounds on the processor utilization for general real-time systems where tasks are composed of subtasks and precedence constraints may exist among subtasks of the same task. By careful analysis of preemption effects among tasks, the problem is formulated as a set of linear programming (LP) problems. Observations are made to reduce the number of LP problem instances required to be solved, which greatly improves the computation time of the utilization bounds. Furthermore, additional constraints are allowed to be included under certain circumstances to improve the quality of the bounds. 相似文献
To investigate the mechanism of high elongation of natural rubber attained by the ‘racking method’, a strip of smoked-sheet was elongated up to 150 times in length, by stretching rapidly at room temperature and forcing to shrink at 75-80 °C repeatedly. On X-ray diffraction, a typical fibre pattern with an amorphous ring appeared already at ×10 (stretch ratio=10). The degree of crystallinity increased to the level of 17-18% at ×20 and turned to decrease after ×60, but the degree of crystallite orientation reached at a high level already at ×10 and did not change significantly and the half-height width of reflection profiles stayed almost at a constant level, while the Young's modulus increased up to ca. 300 MPa at ×100 and then fell rather discontinuously. It was assumed that some fractions of chain segments between entanglements were gradually broken in each step of stretching operation, rather than disentangled and slipped. 相似文献
A series of short fibre reinforced styrene butadiene rubber (SBR) composites were prepared by incorporating sisal fibres of
different lengths and different concentrations. The vulcanization behaviour and the properties of the vulcanizates were measured
by the relevant ASTM procedures. The processing characteristics such as green strength and mill shrinkage were improved by
the addition of fibres. The properties like tensile strength, tear strength, moduli at 10% and 20% elongations were found
to be maximum for composites containing longitudinally oriented fibres of length 6 mm. Mixes containing 35 phr loading of
fibres and bonding agent showed better mechanical performance than others. The failure behaviour of tensile and tear specimens
have been analysed by scanning electron microscopy techniques.
Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995 相似文献
This paper concerns the following problem: given a set of multi-attribute records, a fixed number of buckets and a two-disk system, arrange the records into the buckets and then store the buckets between the disks in such a way that, over all possible orthogonal range queries (ORQs), the disk access concurrency is maximized. We shall adopt the multiple key hashing (MKH) method for arranging records into buckets and use the disk modulo (DM) allocation method for storing buckets onto disks. Since the DM allocation method has been shown to be superior to any other allocation methods for allocating an MKH file onto a two-disk system for answering ORQs, the real issue is knowing how to determine an optimal way for organizing the records into buckets based upon the MKH concept.
A performance formula that can be used to evaluate the average response time, over all possible ORQs, of an MKH file in a two-disk system using the DM allocation method is first presented. Based upon this formula, it is shown that our design problem is related to a notoriously difficult problem, namely the Prime Number Problem. Then a performance lower bound and an efficient algorithm for designing optimal MKH files in certain cases are presented. It is pointed out that in some cases the optimal MKH file for ORQs in a two-disk system using the DM allocation method is identical to the optimal MKH file for ORQs in a single-disk system and the optimal average response time in a two-disk system is slightly greater than one half of that in a single-disk system. 相似文献
This paper is the first part of a work devoted to the setting-up of a methodology for the mechanical behaviour characterization of rubber-like materials, using a digital speckle extensometer. We present here the experimental approach, specific to large strain measurements. The proposed method is based on in-plane kinematics measurements using an optical extensometer. The whole two-dimensional field of in-plane displacements is obtained by a digital image processing. We discuss then the correlation calculations and how to achieve the optimal subset matching. Next, we specify how to derive the principal stretch ratios, and the accuracy on these components, issued from a subsequent numerical calibration.Finally, we present experimental data dealing with a carbon black, filled natural rubber, issued from uniaxial traction tests, pure shear tests, and tensile tests performed on double-edge notched tensile specimens. 相似文献