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991.
992.
The cost distributions of both the parallel hybrid-hash join and the parallel join-index join algorithms proposed in the above-named work (ibid., vol.1, p.329-43, Sept. 1989) are presented in more detail. The result shows that almost the entire relation may need to be retrieved from disk, though the join selectivity is low. A table of semi-join selectives and cube sizes is given to show the condition that the join-index method performs better than the hybrid-hash method, i.e., the really low selectivity for the join-index method. An error in one of the cost formulas is corrected, and a more efficient method on the final join in the join-index method is proposed 相似文献
993.
994.
995.
F. D. McDaniel B. L. Doyle C. H. Seager D. S. Walsh G. Vizkelethy D. K. Brice C. Yang P. Rossi M. Nigam M. El Bouanani G. V. Ravi Prasad J. C. Schwartz L. T. Mitchell J. L. Duggan 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2002,190(1-4):1-10
A new ion beam analysis-based, single ion technique called the time to first photon has been developed to measure the decay of the luminescence signal of phosphors. Such measurements are currently needed to study luminescence decay mechanisms following high-density excitations and to identify strongly luminescent phosphor coatings with short lifetimes for ion photon emission microscopy (IPEM). The samples for this technique consist of thin phosphor layers placed or coated on the surface of PIN diodes. Single ions from an accelerator strike this sample and simultaneously create ion beam induced luminescence (IBIL) from the phosphor that is measured by a single-photon-detector, and an ion beam induced charge collection (IBICC) signal in the PIN diode. In this case, the IBICC signal provides the start pulse and the IBIL signal the stop pulse to a time to amplitude converter. It is straightforward to show that this approach also measures a signal proportional to activity versus time with an accuracy of 5% as long as the number of detected photons per ion is less than 0.1, which usually requires the use of absorbers for the IBIL detector or electronic discrimination for the IBIL signals. Details of the new analysis are given together with examples of luminescence decay measurements of several ceramic phosphors being considered to coat IPEM samples. IPEM is currently being developed at Sandia National Laboratory (SNL), the University of North Texas in Denton, and the Universities and INFN of Padova and Torino. 相似文献
996.
997.
998.
Development of nano indium tin oxide (ITO) grains by alkaline hydrolysis of In(III) and Sn(IV) salts
Indium tin oxide (ITO) nano powders of different compositions (In: Sn = 90: 10, 70: 30 and 50: 50) were prepared by heat treatment
(300-450°C) of mixed hydroxides of In(III) and Sn(IV). The hydroxides were obtained by the reaction of aq. NH3 with mixed aq. solutions of In(NO3)3 and SnCl4. FTIR and TG/DTA studies revealed that powders existed as In(OH)3H2O—SnO3H2H2O in the solid state and then they transformed to In2O3—SnO2 via some metastable intermediates after 300°C. Cubic phase of In2O3 was identified by XRD for the oxides up to 30% of Sn. Particle size measurements of the solid dispersed in acetone and SEM
study for microstructure showed that the oxides were in the nano range (55-75 nm) whereas the size range determined from Debye-Scherrer
equation were 11–24 nm. 相似文献
999.
凝析气藏物质平衡方程的改进与应用 总被引:5,自引:0,他引:5
为了提高凝析气藏油气采收率,通常采用目前最有效的循环注气保持地层压力的开采方式。在此开采方式下,直接采用气藏物质平衡方程进行地质储量计算将出现很大偏差。针对这种情况,将气藏物质平衡方程进行了改进,得到凝析气藏在注气开发方式下的物质平衡方程。 相似文献
1000.
In this paper we develop and compare several heuristic methods for solving the general two-dimensional cutting stock problem.
We follow the Gilmore-Gomory column generation scheme in which at each iteration a new cutting pattern is obtained as the
solution of a subproblem on one stock sheet. For solving this subproblem, in addition to classical dynamic programming, we
have developed three heuristic procedures of increasing complexity, based on GRASP and Tabu Search techniques, producing solutions
differing in quality and in time requirements. In order to obtain integer solutions from the fractional solutions of the Gilmore-Gomory
process, we compare three rounding procedures, rounding up, truncated branch and bound and the solution of a residual problem.
We have coded and tested all the combinations of algorithms and rounding procedures. The computational results obtained on
a set of randomly generated test problems show their relative efficiency and allow the potential user to choose from among
them, according to the available computing time.
Rceived: January 9, 2001 / Accepted: December 10, 2001 相似文献