基于标准编码的频繁子图挖掘算法

频繁子图挖掘是图挖掘的一个重要研究课题.gSpan算法作为一种高效的子图挖掘算法具有较好的执行效率,它通过最右扩展生成频繁子图,但不能保证每次扩展得到的均为标准编码.针对此问题本文提出了一种改进的算法CSGM,它采用ADI++存储结构,能处理更大规模的图集,同时保证每次最右扩展均生成标准编码,既避免了对非标准编码图的支持度计算,也避免了对输入编码是否为标准编码的计算.在实际数据集上运行的实验结果表明它比原算法提高了挖掘效率.     

Concentrations of organophosphorus pesticides in fresh vegetables and related human health risk assessment in Changchun,Northeast China

This study was designed to investigate organophosphorus pesticides (OPs) concentrations in fresh vegetables and estimate potential health risks to inhabitants. A total of 214 samples of seven types of vegetables were collected from Changchun, the capital of Jilin province, one of the most important vegetable production areas. The eleven OPs were analyzed by gas chromatography coupled with flame photometric detector (GC-FPD). Results showed that 23.4% of samples contained OPs above maximum residue limit (MRL), 68.7% of samples below MRL and only 7.9% of samples were found free of OPs. Detection rates of OPs decreased in the following order: diazinon (82.2%) > phorate (45.8%) > dimethoate (29.4%) > parathion-methyl (27.6%) > omethoate (23.8%) > dichlorvos (22.9%) > fenitrothion (21%) > fenthion (18.7%) > parathion (18.2%) > methamidophos (17.3%) > malathion (12.1%). The OPs levels were higher for leafy than for non-leafy vegetables. The percentages of OPs above MRL: welsh onion (82.5%) > radish (37.5%) > pepper (17.2%) > Chinese cabbage (14.3%) > cucumber (3.2%) > eggplant (2.9%) > tomato (0%). 49.5% samples contained two or more OPs. The average target hazard quotients (ave THQ) were all less than one and the average Hazard Index (ave HI) for adults and children were 0.448 and 0.343, respectively. It is concluded that inhabitants who are exposed to average OPs levels may not be endangered by health risk.     

奥-贝球墨铸铁加工表面质量的试验研究

用试验的方法研究了奥－贝球墨铸铁的加工表面形态、已加工表面粗糙度，分析了切削用量和刀具几何角度对加工表面粗糙度的影响．结果表明，已加工表面质量与刀具切削刃不平整及材料组织有关。为提高加工表面质置，必须优选切削参数，重视刀具磨损、后刀面粗糙度及工件材料组织的缺陷。     

High-order compact ADI (HOC-ADI) method for solving unsteady 2D Schrödinger equation

In this paper, a high-order compact (HOC) alternating direction implicit (ADI) method is proposed for the solution of the unsteady two-dimensional Schrödinger equation. The present method uses the fourth-order Padé compact difference approximation for the spatial discretization and the Crank-Nicolson scheme for the temporal discretization. The proposed HOC-ADI method has fourth-order accuracy in space and second-order accuracy in time. The resulting scheme in each ADI computation step corresponds to a tridiagonal system which can be solved by using the one-dimensional tridiagonal algorithm with a considerable saving in computing time. Numerical experiments are conducted to demonstrate its efficiency and accuracy and to compare it with analytic solutions and numerical results established by some other methods in the literature. The results show that the present HOC-ADI scheme gives highly accurate results with much better computational efficiency.     

Experimental and numerical assessment of fracture toughness of dual-phase austempered ductile iron

The effects of the microstructure topology on the fracture toughness of dual-phase austempered ductile iron are studied in this paper by means of finite element modelling and experimental testing. To this end, specimens with matrix microstructures ranging from fully ferrite to fully ausferrite were studied and the preferential zones and phases for crack propagation were identified in every case. The effectiveness of the ausferrite phase as a reinforcement of the ferritic matrix via the encapsulation of the brittle and weak last-to-freeze (LTF) zones was confirmed. The toughening mechanism is consequence of the increment in the crack path longitude as it avoids the encapsulated LTF zones. Besides, the presence of small pools of allotriomorphic ferrite increase the crack propagation resistance of the ausferrite-ferrite matrices.     

A risk-based pesticide residue monitoring tool to prioritize the sampling of fresh produce

Pesticide residues remain a key issue in food safety for consumers. Accordingly, pesticide residue monitoring at all stages of the food chain gains importance. In Europe, fresh produce processing and trading companies are requested to have a company-specific sampling plan that covers all on-site food safety risk issues. In settings where the prevalence of contamination is known and there are a limited number of suppliers, statistical sampling plans are easily designed based on theoretical calculations. Unfortunately, this is not the case in the current setting of fresh produce. In order to provide a workable alternative, empirical guidelines for the design of a risk-based sampling plan, applicable in a broad range of realistic scenarios, are established. These guidelines are based on the opinions of experts regarding the relative importance with respect to risk regarding five criteria related to products and suppliers. These criteria are: supplier guarantee, country of origin, cross-contamination, and processing and product risk. The opinions of the experts are aggregated in order to yield a weighted-sum-based risk indicator. This can facilitate the risk assessment of new scenarios and sample size calculations. While these guidelines for the design of a risk-based sampling plan do not provide guarantees for a statistically demonstrated level of safety, the plan has been proven to be a useable tool during validation. Finally, the use of this tool is demonstrated in a case study.     

Armadillo generation distributed system with geranium Cadcam cluster for solving 2D telegraphic problem

In this paper, the parallel implementation of the iterative alternating direction explicit method by D'Yakonov (IADE-DY) and the Mitchell and Fairweather double sweep method (DS-MF) compared with the alternative direction implicit (ADI) method for solving the 2D telegraphic problem on a distributed system of Armadillo cluster and geranium Cadcam cluster using the parallel virtual machine and message passing interface is presented. We implement the scheduling of n tridiagonal system of equations with the above methods to show improvement on speedup and efficiency with parallel strategies across the two platforms. The single program multiple data model was employed for the implementation. The IADE-DY, DS-MF and ADI are developed by the splitting of the implicit equation using the finite difference discretization on the 2D telegraphic problem. The implementation is discussed in relation to means of the performance parallel strategies and analysis. The model enhances overlap communication and computation to avoid unnecessary synchronization, hence, the method yields significant speedup by the use of the non-blocking communication. We present some analyses that are helpful for speedup and efficiency.     

奥－贝球铁中残余奥氏体含量的研究

用Ｘ射线衍射分析仪测定了Ｓｉ、Ｃｕ、Ｍｏ含量和等温淬火温度、保温时间对奥－贝球铁中残余奥氏体含量的影响规律，在ＳＥＭ下现在分析了残余奥氏体量对试样断裂方式的影响；结果表明，Ｃｕ使残余奥氏体含量提高，Ｍｏ使残余奥氏体含量降低。一定的淬火温度、保温时间和含Ｓｉ量，可使残余奥氏体含量具有最高值，奥氏体含量减少使断裂方式向脆性断裂转变。     

"两步法" 制备等温淬火球铁的研究

由于单一温度下的等温淬火工艺不能同时达到高硬度和高韧性，开发了两步法等温淬火热处理工艺。其原理是：工件经奥氏体化后，先在低温盐浴保温一段时间，使其基体在过冷度较大时大量形核，然后再经高温保温使基体组织转变成具有含碳量较高的残余奥氏体，细化组织，进而提高力学性能。通过在低温不同保温时间下的组织对比，确定较佳的低温盐浴保温时间；然后进行单一温度下等温淬火和两步法热处理工艺试验。将两种工艺的结果进行对比，发现两步法等温淬火工艺得到的组织和性能介于单一温度等温淬火工艺的低温和高温之间。