广东交通职业技术学院图书馆服务质量调查分析

通过对广东交通职业技术学院的读者进行图书馆服务质量的问卷调查,从图书馆资源建设、借阅服务、信息服务、环境建设管理以及馆员素质5个层面来了解读者对图书馆服务的真实感受,其目的在于帮助图书馆改善服务质量,以便更好地为读者服务。     

尼龙块型及自润滑铜块型提升架结构导向滑块的对比分析

通过对以尼龙块为导向的提升架结构计算分析发现,尼龙块和螺栓在受到外力时均产生较大的变形,应力超过其许用值;提出了采用自润滑铜块代替尼龙的方案,同时增大所用螺栓的规格,分析表明自润滑铜块和螺栓的强度及变形均满足要求,现场试验结果与理论分析一致,试验表明自润滑铜块能够确保滑板提升结构使用的可靠性。     

侧碰能力提升——前车门中部加强板优化分析

侧碰性能已经作为C-NCAP强制安全论证的一个必要条件,文章介绍了改善汽车侧面碰撞性能的基本方法,并详细介绍了国内某款车为满足侧碰星级而进行车门中部加强板的多个方案的研究。通过CAE强度分析、工艺可行性分析以及经济性分析,探讨了车门中部加强板的最优化改型方案,并对多个备选方案进行详细的分析,最终通过实车碰撞验证了更改方案的切实可行性。在后续车型的车门中部加强板的结构优化中,建议引进高强度材料,避免增加整车质量。     

A simulation evaluation of the maximum approximate composite marginal likelihood (MACML) estimator for mixed multinomial probit models

This paper evaluates the ability of the maximum approximate composite marginal likelihood (MACML) estimation approach to recover parameters from finite samples in mixed cross-sectional and panel multinomial probit models. Comparisons with the maximum simulated likelihood (MSL) estimation approach are also undertaken. The results indicate that the MACML approach recovers parameters much more accurately than the MSL approach in all model structures and covariance specifications. The MACML inference approach also estimates the parameters efficiently, with the asymptotic standard errors being, in general, only a small proportion of the true values. As importantly, the MACML inference approach takes only a very small fraction of the time needed for MSL estimation. In particular, the results suggest that, for the case of five random coefficients, the MACML approach is about 50 times faster than the MSL for the cross-sectional random coefficients case, about 15 times faster than the MSL for the panel inter-individual random coefficients case, and about 350 times or more faster than the MSL for the panel intra- and inter-individual random coefficients case. As the number of alternatives in the unordered-response model increases, one can expect even higher computational efficiency factors for the MACML over the MSL approach. Further, as should be evident in the panel intra- and inter-individual random coefficients case, the MSL is all but practically infeasible when the mixing structure leads to an explosion in the dimensionality of integration in the likelihood function, but these situations are handled with ease in the MACML approach. It is hoped that the MACML procedure will spawn empirical research into rich model specifications within the context of unordered multinomial choice modeling, including autoregressive random coefficients, dynamics in coefficients, space-time effects, and spatial/social interactions.     

Asking the right questions about telecommuting: Avoiding pitfalls in surveying homebased work

In designing travel behavior surveys, the problem is to define “work,” “home,” and similar words that are commonly used in our language but which have acquired a plethora of associated meanings. The difficulty has not been resolved by the many new terms coined to describe non-traditional ways to work. Such words as “telecommuting,” “teleworking,” “at-home work,” “hoteling,” “homebased business,” “road warriors” and “mobile workers,” lack any agreed-upon definitions yet they are used in common parlance as if they did. These new workstyles are of interest to travel planners because they may involve trip reduction. To forecast just how much trip reduction will occur, behavior needs to be measured by objective criteria. To avoid definitional traps, we recommend phrasing questions in terms of measurable variables such as the place of work and the time in days and hours spent at each location. That approach leaves researchers the option of applying their own definitions that fit the context of their analyses. Thus, rather than ask “How many days a week do you telecommute?” the more precise question can be asked: “How many days last week did you work at home instead of going to your usual work location?” This approach has the advantage that information gathered over years can be used unambiguously in various contexts. Definitions can be applied at the point of analysis. This paper illustrates errors and confusion that can arise from casually worded surveys using examples from private and public surveys. The author proposes a set of core questions with four levels of priority for consideration in designing future surveys of travel behavior.     

外接平板型金属夹层结构连接构件极限强度分析

激光焊接钢质夹层结构在国外已用于实船,其连接形式是亟待解决的关键问题之一。基于有限元分析软件ANSYS,研究了面内载荷作用下,I型金属夹层结构外接平板型连接构件的失效模式和极限承载能力,以及5种典型初始缺陷的尺寸和连接构件的设计参数对极限载荷的影响规律。结果显示,连接构件较短时,结构失效的主导因素是焊接接头形成了塑性铰;连接构件较长时,主导因素是连接构件失稳。对于各种类型的初始缺陷,随初始缺陷尺寸的增大,极限载荷均降低;连接构件、以及靠近连接构件的夹层面板和夹层腹板的初始缺陷对极限载荷的影响较大。在控制重量的条件下,欲增大极限承载能力,最有效的途径是增大连接构件厚度,并选取合适的连接构件长度。     

既有线测量新技术

研究目的:解决老既有线测量技术的安全性差、效率低、精度低等问题。研究方法:用坐标法测量既有线。该既有线测量新技术坚持以人为本、安全生产,尽量减少线上工作人数为前提。置镜任意点,每个曲线建立相对独立的直角坐标系,同时完成里程丈量、线路方向、小偏角、轨面高程的测量。研究结果:用坐标法测量既有线,由原来5道顺序流水作业流程缩减成2道顺序作业流程,作业人数由31人减少到13人。完成同样的工作量,减少18个生产人员。线上作业人数由原来的23人减少到4人;最危险的轨道中心作业人数从8人减少到0人,大幅度降低危险系数。研究结论:既有线测量新技术在安全生产、测量精度控制、效率等各方面都有优势。技术更新的目标在于实现电子记录,减少人为错误,实现勘测设计一体化,安全生产,提高效益。     

When is big data big enough? Implications of using GPS-based surveys for travel demand analysis

A number of studies in the last decade have argued that Global Positioning Systems (GPS) based survey offer the potential to replace traditional travel diary surveys. GPS-based surveys impose lower respondent burden, offer greater spatiotemporal precision and incur fewer monetary costs. However, GPS-based surveys do not collect certain key inputs required for the estimation of travel demand models, such as the travel mode(s) taken or the trip purpose, relying instead on data-processing procedures to infer this information. This study assesses the impact that errors in inference can have on travel demand models estimated using data from GPS-based surveys and proposes ways in which these errors can be controlled for during both data collection and model estimation. We use simulated datasets to compare performance across different sample sizes, inference accuracies, model complexities and estimation methods. Findings from the simulated datasets are corroborated with real data collected from individuals living in the San Francisco Bay Area, United States. Results indicate that the benefits of using GPS-based surveys will vary significantly, depending upon the sample size of the data, the accuracy of the inference algorithm and the desired complexity of the travel demand model specification. In many cases, gains in the volume of data that can potentially be retrieved using GPS devices are found to be offset by the loss in quality caused by inaccuracies in inference. This study makes the argument that passively collected GPS-based surveys may never entirely replace surveys that require active interaction with study participants.     

Errors in dynamical fields inferred from oceanographic cruise data: Part II. The impact of the lack of synopticity

Diagnostic studies of ocean dynamics based on the analysis of oceanographic cruise data are usually quite sensitive to observation errors, to the station distribution and to the synopticity of the sampling. The first two sources have been evaluated in the Part I of this work. Here we evaluate synopticity errors for different sampling strategies applied to simulated unstable baroclinic waves. As suggested in previous studies, downstream and upstream cross-front samplings produce larger errors than along-front samplings. In our particular case study, the along-front sampling results in fractional errors (rms error divided by the standard deviation of the field) of about 15% for dynamic height and more than 50% for relative vorticity and vertical velocity. These values are significantly higher than those obtained in Part I for typical observation errors and sampling limitations (about 6% for dynamic height and between 15 and 30% for geostrophic vorticity and vertical velocity).We also propose and test two methods aimed at reducing the impact of the lack of synopticity. The first one corrects the observations using the quasi-geostrophic tendency equation. The second method combines the relocation of stations (based on a system velocity) and the correction of observations (through the estimation of a growth rate). For the fields simulated in this work, the second method gives better results than the first, being able to eliminate practically all synopticity errors in the case of the along-front sampling. In practice, the error reduction is likely to be less effective, since actual fields cannot be expected to have a system velocity as homogeneous as for the single-mode waves simulated in this work.     

反应舵在螺旋桨尾流中的水动力性能

本文对反应舵在螺旋桨尾流中的水动力性能及桨舵干扰进行了研究。舵的水动力及周围流场用面元法计算，螺旋桨性能用无限叶数的简易螺旋桨理论预估。桨舵干扰作用以迭代方法求得。采用面元法计算反应舵的性能，可以更精确地反映较复杂的反应舵表面形状对水动力性能的影响。通过计算得到的舵表面压力分布可看出反应舵节能的原因。本文还对反应舵的操纵性能进行了计算和研讨。