古贤碾压混凝土重力坝的坝体极限承载能力研究

古贤碾压混凝土重力坝最大坝高达到200 m级,需要研究坝体的极限承载能力以保障大坝安全。应用容重超载法和水头超载法,坝体结构采用Abaqus软件中Drucker-Prager模型,探讨了不同超载方法下坝体极限承载能力及其差异。通过扩展有限元方法研究了上游面的裂缝扩展对坝体极限承载能力的影响,并用高压水劈裂试验结果校正了该扩展有限元模型的计算参数。分析结果表明:容重超载系数比水头超载系数高64.8%,且两种超载方法的破坏模式存在明显区别;高压水劈裂因素显著降低了坝体极限承载能力,降低幅度在33%~44%之间,高压水劈裂因素使得坝体极限承载能力更加符合实际情况。分析了坝体裂缝扩展情况与容重超载系数之间的关系,并给出了坝体裂缝的处理建议。

Age distribution,polyps and rectal cancer in the Egyptian population-based cancer registry

AIM:To describe the clinical and epidemiologic profiles of the disease and to compare the findings with those generated from the previous hospital-based studies.METHODS:The Gharbiah cancer registry is the only population-based cancer registry in Egypt since 1998.We analyzed the data of all colorectal cancer patients included in the registry for the period of 1999-2007.All medical records of the 1364 patients diagnosed in Gharbiah during the study period were retrieved and the following information abstracted:age,residence,diagnosis date,grade,stage,topology,clinical characteristics,and histology variables.Egyptian census data for 1996 and 2006 were used to provide the general population's statistics on age,sex,residence and other related demographic factors.In addition to age-and sex-specific incidence rate analyses,we analyze the data to explore the incidence distribution by rural-urban differences among the 8 districts of the province.We also compared the incidence rates of Gharbiah to the rates of the Surveillance Epidemiology and End Results(SEER) data of the United States.RESULTS:Over the 9 year-period,1364 colorectal cancer cases were included.The disease incidence under age 40 years was relatively high(1.3/10 5) while the incidence in the age groups 40 and over was very low(12.0/10 5,19.4/10 5 and 21.2/10 5 in the age groups 40-59 years,60-69 years and > 70 years,respectively).The vast majority of tumors(97.2%) had no polyps and 37.2% of the patients presented with primary lesions in the rectum.Colorectal cancer was more common in patients from urban(55%) than rural(45%) areas.Regional differences in colon and rectal cancer incidence in the 8 districts of the study province may reflect different etiologic patterns in this population.The registry data of Egypt shows a slightly higher incidence of colorectal cancer than the United States in subjects under age 40 years.The results also shows significantly lower incidence of colorectal cancer in subjects over age 40 years compared to the same age group in the United States SEER.CONCLUSION:Low rate of polyps,low incidence in older subjects,and high rate of rectal cancer in Egypt.Future studies should explore clinical and molecular disease patterns.

Heat Treatment Effect on Microstructure and Mechanical Properties of Re-Containing Inconel 718 Alloy

The effect of Rhenium additions to the standard Inconel 718 (ST IN718) alloy as well as solution and aging treatments on microstructure and hardness property were studied. The microstructure of Re-containing alloys has higher volume fraction of δ phase than standard alloy. Conventional solution treatment (CST) at 1273 K for 1h precipitates a thin film of δ phase at the grain boundaries as well as needle-like in γ matrix;however, after modified solution at 1440 K for 3 h long, both types of δ phase precipitates entirely vanish from the microstructure. Small colonies of needle-like δ phase start to appear with aging at 1023 K for 4 h, after CST. Prolonging the aging time to 50 h, these colonies enlarge in size and spread in the matrix. XRD and TEM observations were used to identify the precipitation of hard γ” and γ’ phases. The changing in hardness measurements were evidence about the precipitation of these hard phases. CST have higher rate to increase in hardness with aging time comparing to modified solution specimens.

Microstructural Evolution of Cast Hyper-Eutectic Al-18% Si Alloy during Cyclic Semi-Solid Heat Treatment

The cyclic semi-solid heat treatment represents a promising technique for improving microstructure and mechanical properties of a wide range of metallic alloys. In the current research the influence of cyclic semi-solid heat treatment on microstructure of Al-18% Si alloy containing 0.8% Fe has been studied. All specimens were heated in an electrically heated resistance furnace with heating rate of 10°C·min-1 to 585°C. For a complete one cycle heat treatment (5 min heating time), samples after 5 min holding at 585°C were cooled to a temperature of 550°C in still air cooling and the samples were taken out immediately for water quenching. It was found that heat treatment cycles should be limited to 3 cycles or less in order to maintain fine grain size and globular structure without agglomeration and coalescence. Cyclic semi-solid heat treatment changes morphology of iron-rich intermetallics phases to be plate-like and fine plate iron-rich intermetallics phases, in stead of needle-like iron-rich intermetallics phases that are observed in as-cast samples. Cyclic heating shows a relatively higher hardness for all heating cycles compared with as-cast one due to its finer and globular structure. Cyclic semi-solid heat treatment technique results in lower coarsening rate constant compared with isothermal heat treatment one due to coarsening discontinuous effect.

Influence of Semi-Solid Isothermal Heat Treatment on Microstructure and Mechanical Properties of Ductile Cast Iron

In this research, the effect of semi-solid isothermal heat treatment on microstructure, hardness and impact toughness of ductile iron (DI) is studied. Heat-treated air-cooled ductile iron shows spheroid graphite, cementite and fine pearlite matrix structure. At the early stages of heating time (up to 20 min), the DIs show significant decrease in amounts of graphite and significant increase in amounts of cementite. By increasing heating time, above 20 min, the DIs show slightly decrease in amounts of graphite and slightly increase in amounts of cementite. Hardness values increase by increasing heating time. Meanwhile, the impact toughness decrease with increasing heating time. The optimum heating treatment condition for reasonable structure and mechanical properties could be achieved at the temperature of 1165℃ for the heating time range of 10 to 15 min.

Scalable Varied Density Clustering Algorithm for Large Datasets

Finding clusters in data is a challenging problem especially when the clusters are being of widely varied shapes, sizes, and densities. Herein a new scalable clustering technique which addresses all these issues is proposed. In data mining, the purpose of data clustering is to identify useful patterns in the underlying dataset. Within the last several years, many clustering algorithms have been proposed in this area of research. Among all these proposed methods, density clustering methods are the most important due to their high ability to detect arbitrary shaped clusters. Moreover these methods often show good noise-handling capabilities, where clusters are defined as regions of typical densities separated by low or no density regions. In this paper, we aim at enhancing the well-known algorithm DBSCAN, to make it scalable and able to discover clusters from uneven datasets in which clusters are regions of homogenous densities. We achieved the scalability of the proposed algorithm by using the k-means algorithm to get initial partition of the dataset, applying the enhanced DBSCAN on each partition, and then using a merging process to get the actual natural number of clusters in the underlying dataset. This means the proposed algorithm consists of three stages. Experimental results using synthetic datasets show that the proposed clustering algorithm is faster and more scalable than the enhanced DBSCAN counterpart.