提高平流沉淀池沉淀效果的研究与探讨

试验研究了在模拟平流沉淀池中,设置挡板、溢流堰对浊度去除效果的影响,以及在沉淀区中投放短管填料对浊度去除效果的提高。通过控制不同进水流态、短管填料不同投加方式、不同投放位置、不同投放量的对比,提出提高浊度去除率的最优方法。     

Comparisons of nozzle orifice processing methods using synchrotron X-ray micro-tomography

Based on the high flux synchrotron X-ray of the Shanghai Synchrotron Radiation Facility (SSRF), high precision 3D digital models of diesel nozzle tips have been established by X-ray micro-tomography technology, which reveal the internal surfaces and structures of orifices. To analyze the machining precision and characteristics of orifice processing methods, an approach is presented based on the parameters of the internal structures of nozzle orifices, including the nozzle diameter, the orifice inner surface waviness, the eccentricity distance and the angle between orifices. Using this approach, two kinds of nozzle orifice processing methods, computerized numerical control drilling and electric discharge machining, have been studied and compared. The results show that this approach enables a simple, direct, and comprehensive contrastive analysis of nozzle orifice processing methods. When processing a single orifice, the electric discharge machining method has obvious advantages. However, when there are multiple orifices, the error levels of the two methods are similar in relation to the symmetry of distribution of the orifices.     

图纸扫描误差分析及变形误差纠正

目前,地图的扫描数字化已成为G IS领域中获取数据信息的主要手段之一;从图纸的扫描数字化过程中的误差来源研究入手,分析了地图扫描数字化各项误差对成果质量的影响特征及其大小;就图幅变形误差和应采取的纠正方法进行了试验研究,得出的结论已在土地利用数据库建设等项目的实施过程中得到应用,取得了很好的效果。     

Teachers' technological readiness for online professional development: evidence from the US e-Learning for Educators initiative

Although online professional development (OPD) is recognised as a viable alternative to face-to-face professional development, there are some obstacles to the delivery of effective OPD. This study examines one such obstacle, teachers' technological readiness for OPD participation. In particular, this study examines six research questions regarding the technological readiness of US elementary and secondary educators who participate in OPD. The data source was ‘e-Learning for Educators', a large-scale OPD initiative implemented between 2006 and 2011 in the US. The data show that this population of teachers, in general, report that they believe online professional development is as effective as face-to-face professional development; have easy access to the required technology; possess the required computer/technical skills; and perceive some of these skills to improve with course participation. Though these findings are largely favourable from the perspective of OPD stakeholders, this study also finds some variability among teachers that might warrant possible mitigation strategies.     

Estimating the time-dependent reliability of aging structures in the presence of incomplete deterioration information

The performance of an aging structure is commonly evaluated under the framework of reliability analysis, where the uncertainties associated with the structural resistance and loads should be taken into account. In practical engineering, the probability distribution of resistance deterioration is often inaccessible due to the limits of available data, although the statistical parameters such as mean value and standard deviation can be obtained by fitting or empirical judgments. As a result, an error of structural reliability may be introduced when an arbitrary probabilistic distribution is assumed for the resistance deterioration. With this regard, in this paper, the amount of reliability error posed by different choices of deterioration distribution is investigated, and a novel approach is proposed to evaluate the averaged structural reliability under incomplete deterioration information, which does not rely on the probabilistic weight of the candidate deterioration models. The reliability for an illustrative structure is computed parametrically for varying probabilistic models of deterioration and different resistance conditions, through which the reliability associated with different deterioration models is compared, and the application of the proposed method is illustrated.     

新型的近仙农理论极限码:之型码和级联之型码

This paper introduces a family of error-correcting codes called zigzag codes.A zigzag code is described by a highly structured zigzag graph.Due to the structureal properties of the graph,very low-complexity soft-in,soft-out decoding rules can be implemented.we present a decoding rule,absed on the Max-Log-APP(MLA) formulation,which requires a total of only 20 addition-equivalent-operations per information bit per iteration.Simulation of a rate-1/2 concatenated zigzag code with four constitutent encoders with interlezer length 65536 yields a bit error rate(BER) and of 10^-5 at 0.9 dB and 1.4dB away from the Shannon limit by optimal (APP) and low-cost sub-optimal(MLA) decoders,respectively.     

Indexical Expressions in Word Problems and their Influence on Multiple Referents of the Unknown

When translating word problems into equations, a common error consists of using the same letter to refer to two different quantities. This error, called multiple referents for the unknown, can be connected to the existence of deictic or indexical expressions within the problem statement. This paper aims to analyse the influence of indexical expressions on the incidence of the multiple referents for the unknown error. Results from a quantitative study with 117 Spanish secondary students show a significantly higher number of such type of error when the problem statement contains indexical expressions. The analysis of students’ performances in subsequent interviews indicates that this error may be due to the fragmented reading of statements.     

Reading during sentence composing and error correction: A multilevel analysis of the influences of task complexity

In this study we investigated the role of reading, how writers coordinate editing with other writing processes. In particular, the experiment examines how the cognitive demands of sentence composing and the type of error influence the reading and writing performance. We devised an experimental writing task in which participants corrected an embedded error (orthographic near-neighbors or far-neighbors) and completed a sentence (using 1 or 3 context words)—in either order. Data were collected by logging keystrokes and recording eye-movements. The results revealed that both error and sentence complexity influenced the approach to error-correcting. Participants generally completed the partial sentence first, and then corrected the error (approximately 90% of the items). Task complexity reinforced this tendency. Moreover, in most of these cases, the error was fixated at least once prior to sentence completion. This suggests that the error was detected (at least partially), but the correction response was inhibited. The differences in cognitive load also affect the reading activity during planning. This investigation illustrates how the interplay of two task factors, error and sentence complexity, appears to influence how writers coordinate error-correcting with sentence composing.     

某高拱坝开设大表孔对拱坝应力分布的影响研究

基于三维有限元计算软件ANSYS对某一高145 m的混凝土双曲拱坝进行开设大表孔与不开设表孔方案的计算对比分析,通过分析得出,高拱坝坝顶开设表孔对坝体应力的影响是局部的,主要集中在孔口周边,而对坝体下部几乎没有影响。最后,总结规律,希望为拱坝结构设计及体形优化提供参考。     

机器人装配精度分析的虚拟示教仿真

In this paper, by teaching a 3D robot unit model and playing back to simulate the assembly process in a virtual assembly environment, errors in robot assembly are analyzed. The paper also presents a visualization method for analyzing accuracy of the robot assembly, and studies the influence of the spatial pose of a robot on the success rate of an axis-hole assembly, and accuracy of the robot teaching program in particular. Through integration of various errors and on the basis of assembly accuracy, tolerance of error sources can be reasonably distributed to meet the assembly accuracy requirement, therefore the planning of robot assembly unit can be improved.     

蠕变条件下完整岩石的起裂和扩展准则

The mechanism and criterion of crack initiation and propagation of rocks were investigated by many researchers,And the creep behaviour of rocks was also theoretically and experimentally studied by some scientists and engineers.The characteristics of crack initation and propagation of rocks under creep condition.however,are very improtant for rock engineering and still not paid enough attention by researchers,In this paper,the criterion and mechanism of crack initiation and propagation under creep condition were investigated using specimens collected from sandstone rock formations outcropping in the Emei Mountain,the Sichuan Province of China.Cuboid specimens under three point bending were used in this investigation.All specimens were classified into four sorts and used for Mode-I fracutre of creep frcture tests.The experimental result shows that due to creep deformation.rock crack will inevitably initialt and propagate under a load of KI,which is less than fracture toughness KIC but not less than a constant(marked as KIC2),KIC2 indicates the ability of rock to resist crack initiation and propagation under creep conditions and is less than fracture tough ness KIC.defined as creep fracture toughness in this paper,KIC2 should be considered as an importnat parameter on design and computation of rock engineering.The microstructureal mechanism for crack initiation and propagation of rock materials under creep condition was introduced based on competitive model between softening effect and hardening effect,and the validity of test result was explained.The test result was also verified in rheological theory.When KI is more than KIC2 but less than KIC,rock crack will initiate and propagate after a time interval of sustained loading under creep condition.In order to find the relation between duration of sustained lading.which can lead to crack initiation and propagation,and the initial stress intensity factor KI,an unequal0interval time sequence forecasting and predicting model was introduced,and the relation was obtained for homogeneous and isotropic fine-grained red sandstone.Finally a modified fracture toughness formula was given,in which the influence of fracture process zone(FPZ) was fully considered.     

Combining Principal Component Regression and Artificial Neural Network to Predict Chlorophyll-a Concentration of Yuqiao Reservoir’s Outflow

In order to investigate the eutrophication degree of Yuqiao Reservoir, a hybrid method, combining principal component regression (PCR) and artificial neural network (ANN), was adopted to predict chlorophyll-a concentration of Yuqiao Reservoir’s outflow. The data were obtained from two sampling sites, site 1 in the reservoir, and site 2 near the dam. Seven water variables, namely chlorophyll-a concentration of site 2 at time t and that of both sites 10 days before t, total phosphorus(TP), total nitrogen(TN), dissolved oxygen(DO), and temperature from January 2000 to September 2002, were utilized to develop models. To remove the collinearity between the variables, principal components extracted by principal component analysis were employed as predictors for models. The performance of models was assessed by the square of correlation coefficient, mean absolute error (MAE), root mean square error (RMSE) and average absolute relative error (AARE). Results show that the hybrid method has achieved more accurate prediction than PCR or ANN model. Finally, the three models were applied to predicting the chlorophyll-a concentration in 2003. The predictions of the hybrid method were found to be consistent with the observed values all year round, while the results of PCR and ANN models did not fit quite well from July to October.     

Hardgrind Revisited

The title of the Hardgrind paper (AMA, 1958) is ‘And the first shall be last… ‘. The ‘revisit’ addresses the potential for error when sets of marks for different assessment components (and examination questions) are combined. If allowance is not made for significant differences in mark distribution then errors will be automatically introduced for grading and ranking purposes. This is distinct from setting an overall pass level which is independent of pass rate. The intentions associated with the weightings assigned to assessment components are discussed with regard to interpretation, and to the need for good quality information to produce good quality judgements related to student performance. Issues of professional development as part of quality assurance for professional judgement are discussed with reference to an in‐service programme comprising 19 modules available on disk.     

关于BP神经网络的几点研究

以结构为 3- 5 - 2的网络为例 ,对BP神经网络的稳定性、权值的收敛趋势、样本识别率和网络总误差对权值的影响等做了研究 ,结果表明系统总误差的减小会促使网络权值将向最优方向调整 ,但这种调整有一定极限 .     

对零序有功功率选线方法的探讨

对自动跟踪消弧线圈接地系统进行了仿真研究.结果表明:零序功率震荡和采样误差是造成零序有功功率选线方法不准的两个主要因素.为了减小这两个因素的影响,对零序有功功率选线方法的模型进行了改进,并利用MATLAB软件对改进模型进行了验证.     

Examining the Precision of Cut Scores Within a Generalizability Theory Framework: A Closer Look at the Item Effect

An Angoff standard setting study generally yields judgments on a number of items by a number of judges (who may or may not be nested in panels). Variability associated with judges (and possibly panels) contributes error to the resulting cut score. The variability associated with items plays a more complicated role. To the extent that the mean item judgments directly reflect empirical item difficulties, the variability in Angoff judgments over items would not add error to the cut score, but to the extent that the mean item judgments do not correspond to the empirical item difficulties, variability in mean judgments over items would add error to the cut score. In this article, we present two generalizability-theory–based analyses of the proportion of the item variance that contributes to error in the cut score. For one approach, variance components are estimated on the probability (or proportion-correct) scale of the Angoff judgments, and for the other, the judgments are transferred to the theta scale of an item response theory model before estimating the variance components. The two analyses yield somewhat different results but both indicate that it is not appropriate to simply ignore the item variance component in estimating the error variance.     

非平衡电桥特性的研究

对非平衡电桥的灵敏度和非线性误差进行研究,得到了实验结果和理论值一致的结果:对于灵敏度,当     

非平衡电桥特性的研究

对非平衡电桥的灵敏度和非线性误差进行研究,得到了实验结果和理论值一致的结果：对于灵敏度,当K=1时灵敏度最高,K越大或越小时灵敏度越低;对于非线性误差,则K越大非线性误差越小,K越小非线性误差越大,且非线性误差与输入电阻相对变化量成正比。在应用非平衡电桥进行测量时,若对灵敏度要求较高,而对非线性误差的要求不那么高的情况下,可取K=1;若要求非线性误差尽量小,而对灵敏度的要求不需要太高的情况下,可取K=10。     

Learning programming from erroneous worked-examples. Which type of error is beneficial for learning?

Learning from erroneous worked examples could enhance learning in contrast to problem-solving tasks. The type of error was hypothesized to be a moderator and accuracy of error detection and correction a mediator of this effect. This study examines the influence of simple syntactic (the structure of the code) and complex semantic (the logic or content of the code) errors in a programming scenario. Overall, 128 students were assigned to a two (syntactic errors: yes vs. no) × two (semantic errors: yes vs. no) factorial between-subjects design. Students’ accuracy in error detection and correction, learning performance, mental load, and mental effort were measured. Results showed that learners receiving syntactic errors detected and corrected errors with higher accuracy which leads to higher learning performance. Semantic errors did not influence learning-related variables since semantic errors were too difficult for novice learners to detect and fix. The postulated moderation and mediation could be supported.