浅析数控曲轴连杆轴颈车床夹具设计的有效改进

数控曲轴连杆颈车床用来加工一般四拐曲轴的连杆颈,该夹具已使用多年,但随着近年来新产品开发数量的增多,已远不能满足使用要求,本文就CF-702数控曲轴连杆轴颈车床的夹具设计,进行有效的改进,具有一定的参考价值。     

Numerical Maximisation of Likelihood: A Neglected Alternative to EM?

There is by now a long tradition of using the EM algorithm to find maximum‐likelihood estimates (MLEs) when the data are incomplete in any of a wide range of ways, even when the observed‐data likelihood can easily be evaluated and numerical maximisation of that likelihood is available as a conceptually simple route to the MLEs. It is rare in the literature to see numerical maximisation employed if EM is possible. But with excellent general‐purpose numerical optimisers now available free, there is no longer any reason, as a matter of course, to avoid direct numerical maximisation of likelihood. In this tutorial, I present seven examples of models in which numerical maximisation of likelihood appears to have some advantages over the use of EM as a route to MLEs. The mathematical and coding effort is minimal, as there is no need to derive and code the E and M steps, only a likelihood evaluator. In all the examples, the unconstrained optimiser nlm available in R is used, and transformations are used to impose constraints on parameters. I suggest therefore that the following question be asked of proposed new applications of EM: Can the MLEs be found more simply and directly by using a general‐purpose numerical optimiser?     

Economic evaluation of BST-CarGel as an adjunct to microfracture vs microfracture alone in knee cartilage surgery

Objectives:

Knee cartilage damage is a common cause of referral for orthopedic surgery. Treatment aims to reduce pain and symptoms by repairing cartilage. Microfracture, the current standard of care, yields good short-term clinical outcomes; however, treatment might fail after 2–3 years. A Chitosan-Beta glycerolphosphate-based medical device (BST-CarGel) is used as an adjunct to microfracture and demonstrates improvements in quantity and quality of repaired tissue, potentially reducing the risk of treatment failure. This study aimed to establish the economic value of BST-CarGel vs microfracture alone in knee cartilage repair from the societal perspective, using Germany as the reference market.

Methods:

A decision tree with a 20-year time-horizon was constructed, in which undesirable clinical events were inferred following initial surgery. These events consisted of pain management, surgery, and total knee replacement. Clinical outcomes were taken from the pivotal clinical trial, supplemented by other literature. Data and assumptions were validated by a Delphi panel. All relevant resource use and costs for procedures and events were considered.

Results:

In a group of patients with all lesion sizes, the model inferred that BST-CarGel yields a positive return on investment at year 4 (with 20-year cumulative cost savings of €6448). Reducing the incremental risk of treatment failure gap between the device and microfracture by 25–50% does not alter this conclusion. Cost savings are greatest for patients with large lesions; results for patients with small lesions are more modest.

Limitations:

Clinical evidence for microfracture and other interventions varies in quality. Comparative long-term data are lacking. The comparison is limited to microfracture and looks only at costs without considering quality-of-life.

Conclusion:

BST-CarGel potentially represents a cost-saving alternative for patients with knee cartilage injury by reducing the risk of clinical events through regeneration of chondral tissue with hyaline characteristics. Since the burden of this condition is high, both to the patient and society, an effective and economically viable alternative is of importance.     

Good News and Bad News: Search from Unknown Wage Offer Distributions

The largest market in national economies is the labor market. Labor market contracting is characterized by job search, often from unknown wage offer distributions. This paper reports experimental tests of finite horizon models of job search in which the wage offer distribution is unknown. Theoretically-optimal search from an unknown wage offer distribution can have the seemingly paradoxical property that some offers will be accepted that are lower than other offers that will be rejected in the same period of the search horizon. Thus the reservation wage property (or lowest acceptable wage path) may not exist. This can occur because an offer that is a priori relatively high (good news) can imply that it is highly probable that search is from a favorable distribution, and such an offer can look unattractive when it is an a posteriori relatively low offer from a favorable distribution (bad news). This paper reports results from experimental treatments for search from unknown distributions in which the reservation wage property does exist and treatments in which it does not exist. We find that the consistency of search behavior with search theory reported in earlier papers is robust to the presence or absence of the reservation wage property and to whether the draws come from known or unknown distributions.     

基于虚拟现实的数控车床结构拆装与仿真系统

基于虚拟现实的数控机床仿真研究一直是虚拟机床领域的热点,本文提出将Virtools三维交互技术运用于数控车床的虚拟拆装与仿真,给出了系统的技术层次结构和开发环境,从机床三维建模和模型数据管理、人机交互、机床部件的运动控制、碰撞检测等方面对系统进行详细研究。最后开发出数控车床内部结构的虚拟拆装仿真系统。     

Controlled information destruction: the final frontier in preserving information security for every organisation

Information security represents the cornerstone of every data processing system that resides in an organisation’s trusted network, implementing all necessary protocols, mechanisms and policies to be one step ahead of possible threats. Starting from the need to strengthen the set of security services, in this article we introduce a new and innovative process named controlled information destruction (CID) that is meant to secure sensitive data that are no longer needed for the organisation’s future purposes but would be very damaging if revealed. The disposal of this type of data has to be controlled carefully in order to delete not only the information itself but also all its splinters spread throughout the network, thus denying any possibility of recovering the information after its alleged destruction. This process leads to a modified model of information assurance and also reconfigures the architecture of any information security management system. The scheme we envisioned relies on a reshaped information lifecycle, which reveals the impact of the CID procedure directly upon the information states.     

不同厚度钢板加固RC梁受力性能的数值模拟研究

钢筋混凝土梁的变形与受力性能与结构的服役环境关系密切,在严酷的自然环境中,混凝土结构常发生劣化而影响其正常使用。本文采用ABAQUS非线性数值模拟方法,开展了不同厚度钢板(Q235钢材)加固钢筋混凝土梁的应力和位移。分析结果表明在梁底粘贴钢板可显著增强混凝土梁的抵抗变形能力,而钢板厚度是影响混凝土梁变形的主要参数。;粘贴钢板所形成的复合截面能够有效降低混凝土的拉伸损伤程度,并有效限制混凝土裂缝的开展,同时也显著降低了纵向受拉钢筋的应力。     

由机械与电子谈数控机床

机械和电子是一对共生体,机械是运动的基础,是运动的实施者;电子是灵魂,是运动的指挥者。二者相互配合,取长补短,相得益彰,共同为人类社会的生产服务。     

芯钢管混凝土节点的芯管壁厚与节点承载力关系的数值分析

对一种已经通过试验研究的钢管混凝土结构的新型节点进行数值分析。这种节点将钢管混凝土柱的钢管在节点区间断,在节点区设置芯钢管,使梁中的纵筋在节点中直通、梁与节点区混凝土成为一体可靠的传递梁中的弯矩、剪力及轴力。本文利用数值分析弥补模型试验数量少的缺陷。选择不同芯钢管壁厚的节点模型进行非线性有限元分析,得出芯钢管壁厚对节点承载力的影响规律。分析结果表明芯钢管壁厚是影响节点承载力的主要因素之一。     

精密车床主轴计算机辅助设计

将普通车床主轴运动机构视为由四个轴组成,每个轴视为分别装有齿轮和轴承等零件的一个子结构的装配体,利用Pro/E分别建立各子结构的三维实体模型,通过对各子结构装配实现对整个车床主轴传动的三维建模,利用Pro/E软件的Mechanism模块对整个机构进行运动学分析和运动仿真。既保证了车床主轴传动的准确性,也大大提高了设计效率。利用该方法可以使得设计人员快速、直观的对普通车床主轴运动机构进行优化设计,降低机床的研发成本,提高机床的可靠性。