实时数据流系统降载方法研究

随着信息技术的发展，出现了大量的数据流应用，如传感器数据处理、网络监控、金融数据分析等。在这些应用中，数据是一种连续、时变、有序、无限的序列，查询大多数都是采用连续查询方式。这种数据和查询的连续性对管理系统的资源需求很大。当系统资源不能满足查询处理要求，即查询处理任务超过系统的最大处理能力，用户的查询将得不到及时、正确地处理。同时，如果查询处理时间超过了查询截止期需求，查询结果就没有意义，甚至会造成灾难性后果。目前，很多研究都集中于数据流系统的降载，对支持实时查询处理的实时数据流系统降载的研究比较少。 本论文主要研究支持实时查询处理的实时数据流管理系统中的降载方法，主要包括如下三个方面：随机降载方法、语义降载方法与共享滑动窗口连接操作的降载方法。最后，通过实时数据流管理系统测试平台验证了所提出算法在提高系统吞吐量与降低截止期错失率方面表现出良好的性能。 针对实时数据流应用需求，提出了一种适合实时查询的数据流处理框架结构RT-DSPA和相应的多层过载处理策略MLOHS，为降载方法的研究提供一个框架基础。RT-DSPA分为用户层、DSMS层以及数据源层多个功能模块，具有多层性、可扩展性、健壮性以及可配置性的特点。 在随机降载方面，提出了一种基于数据流流速的负载估计算法；在实时数据流处理框架与负载估计算法的基础上，提出了一种截止期敏感的随机降载算法RLS-EDA。由于系统负载经常波动较大，该算法利用截止期的特点，使用暂存所丢弃元组技术充分地利用CPU空闲资源，使降载执行后系统的吞吐量得到提高，进而尽可能地降低查询截止期错失率；最后，讨论了降载过程中的队列维护策略、含共享操作符查询网络中的降载位置以及降载操作符插入查询网络的算法。实验结果表明，在系统负载波动较大的情况下，RLS-EDA算法表现出良好的性能。 在充分了解数据流及查询特征的情况下，语义降载表现出更好的降载效果。为明确语义降载时使用到的语义，提出了元组价值、价值等级的概念，给出价值等级划分时发生冲突的解决方法。设计了适合实时数据流管理系统的价值等级–执行开销优先级表和截止期–价值密度优先级表，其在确定优先级时可考虑多维因素。基于这两种优先级表设计，提出了相对应的语义降载算法SLS-PT-VD&EC和SLS-PT-D&TVD。基于优先级表的语义降载算法能够灵活地满足用户的不同需求，同时提高系统降载时的性能。 最后，针对共享滑动窗口连接操作符的过载情况，利用查询截止期的特点，提出了一种基于暂存丢弃元组技术的共享滑动窗口连接的降载算法LS-SJRT；为减小LS-SJRT算法的降载开销，提出了一种改进的基于调节滑动窗口宽度的共享滑动窗口连接降载算法LS-SJRT-CW。实验结果显示这两种算法在共享连接操作符过载时都能够表现出较好的性能。

Control of vortex shedding at moderate Reynolds numbers

The suppression method of vortex shedding from a circular cylinder has been studied experimentally in the Reynolds number range from 300 to 1600. The test is performed in a water channel. The model cylinder is 1 cm in diameter and 38 cm in length. A row of small rods of 0.18 cm in diameter and 1.5 cm in length are perpendicularly connected to the surface of the model cylinder and distributed along the meridian, The distance between the neighboring rods and the angle of attack of the rods can be changed so that the suppression effect on vortex shedding can be adjusted. The results show that vortex shedding can be suppressed effectively if the distance between the neighboring rods is smaller than 3 times and the cylinder diameter and the angle of attack is in the range of 30degreesless than or equal tobeta<90&DEG;.

Effects of 'sinking in' and 'piling up' on estimating the contact area under load in indentation

The phenomena of the 'piling up' and 'sinking-in' of surface profiles in conical indentation in elastic-plastic solids with work hardening are studied using dimensional and finite-element analysis. The degree of sinking in and piling up is shown to depend on the ratio of the initial yield strength Y to Young's modulus E and on the work-hardening exponent n. The widely used procedure proposed by Oliver and Pharr for estimating contact depth is then evaluated systematically. By comparing the contact depth obtained directly from finite-element calculations with that obtained from the initial unloading slope using the Oliver-Pharr procedure, the applicability of the procedure is discussed.

Increasing Critical Sensitivity of the Load/Unload Response Ratio before Large Earthquakes with Identified Stress Acclumulation Pattern

The Load/Unload Response Ratio (LURR) method is proposed for short-to-intermediate-term earthquake prediction [Yin, X.C., Chen, X.Z., Song, Z.P., Yin, C., 1995. A New Approach to Earthquake Prediction — The Load/Unload Response Ratio (LURR) Theory, Pure Appl. Geophys., 145, 701–715]. This method is based on measuring the ratio between Benioff strains released during the time periods of loading and unloading, corresponding to the Coulomb Failure Stress change induced by Earth tides on optimally oriented faults. According to the method, the LURR time series usually climb to an anomalously high peak prior to occurrence of a large earthquake. Previous studies have indicated that the size of critical seismogenic region selected for LURR measurements has great influence on the evaluation of LURR. In this study, we replace the circular region usually adopted in LURR practice with an area within which the tectonic stress change would mostly affect the Coulomb stress on a potential seismogenic fault of a future event. The Coulomb stress change before a hypothetical earthquake is calculated based on a simple back-slip dislocation model of the event. This new algorithm, by combining the LURR method with our choice of identified area with increased Coulomb stress, is devised to improve the sensitivity of LURR to measure criticality of stress accumulation before a large earthquake. Retrospective tests of this algorithm on four large earthquakes occurred in California over the last two decades show remarkable enhancement of the LURR precursory anomalies. For some strong events of lesser magnitudes occurred in the same neighborhoods and during the same time periods, significant anomalies are found if circular areas are used, and are not found if increased Coulomb stress areas are used for LURR data selection. The unique feature of this algorithm may provide stronger constraints on forecasts of the size and location of future large events.

Acoustic Emission Experiments of Rock Failure under Load Simulating the Hypocenter Condition

A series of acoustic emission (AE) experiments of rock failure have been conducted under cyclic load in tri-axial stress tests. To simulate the hypocenter condition the specimens are loaded by the combined action of a constant stress, intended to simulate

Load-Unload Response Ratio and Accelerating Moment/Energy Release Critical Region Scaling and Earthquake Prediction

The main idea of the Load-Unload Response Ratio (LURR) is that when a system is stable, its response to loading corresponds to its response to unloading, whereas when the system is approaching an unstable state, the response to loading and unloading becomes quite different. High LURR values and observations of Accelerating Moment/Energy Release (AMR/AER) prior to large earthquakes have led different research groups to suggest intermediate-term earthquake prediction is possible and imply that the LURR and AMR/AER observations may have a similar physical origin. To study this possibility, we conducted a retrospective examination of several Australian and Chinese earthquakes with magnitudes ranging from 5.0 to 7.9, including Australia's deadly Newcastle earthquake and the devastating Tangshan earthquake. Both LURR values and best-fit power-law time-to-failure functions were computed using data within a range of distances from the epicenter. Like the best-fit power-law fits in AMR/AER, the LURR value was optimal using data within a certain epicentral distance implying a critical region for LURR. Furthermore, LURR critical region size scales with mainshock magnitude and is similar to the AMR/AER critical region size. These results suggest a common physical origin for both the AMR/AER and LURR observations. Further research may provide clues that yield an understanding of this mechanism and help lead to a solid foundation for intermediate-term earthquake prediction.

Comparison of Various Adhesion Contact Theories and the Influence of Dimensionless Load Parameter

Three models, JKR (Johnson, Kendall and Roberts), DMT (Derjaguin, Muller, and Toporov) andMD (Maugis-Dugdale),are compared with the Hertz model in dealing with nano-contact problems. It has been shown that both the dimensionless load parameter, P D P=.1/4

Simulation of the Load-Unload Response Ratio and Critical Sensitivity in the Lattice Solid Model

The Load-Unload Response Ratio (LURR) method is an intermediate-term earthquake prediction approach that has shown considerable promise. It involves calculating the ratio of a specified energy release measure during loading and unloading where loading and unloading periods are determined from the earth tide induced perturbations in the Coulomb Failure Stress on optimally oriented faults. In the lead-up to large earthquakes, high LURR values are frequently observed a few months or years prior to the event. These signals may have a similar origin to the observed accelerating seismic moment release (AMR) prior to many large earthquakes or may be due to critical sensitivity of the crust when a large earthquake is imminent. As a first step towards studying the underlying physical mechanism for the LURR observations, numerical studies are conducted using the particle based lattice solid model (LSM) to determine whether LURR observations can be reproduced. The model is initialized as a heterogeneous 2-D block made up of random-sized particles bonded by elastic-brittle links. The system is subjected to uniaxial compression from rigid driving plates on the upper and lower edges of the model. Experiments are conducted using both strain and stress control to load the plates. A sinusoidal stress perturbation is added to the gradual compressional loading to simulate loading and unloading cycles and LURR is calculated. The results reproduce signals similar to those observed in earthquake prediction practice with a high LURR value followed by a sudden drop prior to macroscopic failure of the sample. The results suggest that LURR provides a good predictor for catastrophic failure in elastic-brittle systems and motivate further research to study the underlying physical mechanisms and statistical properties of high LURR values. The results provide encouragement for earthquake prediction research and the use of advanced simulation models to probe the physics of earthquakes.

The instability analysis of saturated soil under shear load

A theoretical description of shear instability is presented in a system of equations. It is shown that two types of instability may exist. One of them is dominated by pore pressure softening while the other by strain softening. A criterion combining pore pressure softening, strain hardening, and volume strain coefficient is obtained and practical implications are discussed.

Control of Vortex Shedding at Moderate Reynolds Numbers

介绍通过实验对圆柱尾流旋涡脱落进行抑制的方法及其结果.实验模型的展径比为38,实验的雷诺数范围为3×102～1.6×103.抑制方法是在圆柱（直径为D）表面沿展向每隔一定间距伸出一直径0.18D、长度为1.5D的小棒.实验结果表明,当棒间距小于3D,棒与来流夹角在30°～90°范围内,可有效抑制旋涡脱落.

Asymptotic analysis based on K-S constitutive law for a rubber wedge compressed by a line load at its tip

In the present paper, a rubber wedge compressed by a line load at its tip is asymptotically analyzed using a special constitutive law proposed by Knowles and Sternberg (K-S elastic law) [J. Elasticity 3 (1973) 67]. The method of dividing sectors proposed by Gao [Theoret. Appl. Fract, Mech. 14 (1990) 219] is used. Domain near the wedge tip can be divided into one expanding sector and two narrowing sectors. Asymptotic equations of the strain-stress field near the wedge tip are derived and solved numerically. The deformation pattern near a wedge tip is completely revealed. A special case. i.e. a half space compressed by a line load is solved while the wedge angle is pi.

The Newest Developments Of Load-Unload Response Ratio (Lurr)

The Load Unload Response Ratio (LURR) method is an intermediate-term earthquake prediction approach that has shown considerable promise. It is inspiring that its predictions using LURR have been improving. Since 2004 we have made a major breakthrough in intermediate-term earthquake forecasting of the strong earthquakes on the Chinese mainland using LURR and successfully predicted the Pakistan earthquake with magnitude M 7.6 on October 8, 2005. The causes for improving the prediction in terms of LURR have been discussed in the present paper.