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?     

基于AD5545的可编程宽带直流信号放大器

设计了一种增益可手动数字设置或程控设置且无调节电位器的宽带直流放大器。该放大器主要以单片机MSP430和继电器组作为电路的主要控制部分,由使用D/A转换器AD5545控制的放大电路、前级信号调理电路、后级功率放大电路和滤波器组成,实现了增益连续可调的功能。该放大器在0～60dB范围内连续可调,输出信号无明显失真,在0～5MHz范围内信号可放大60dB,最大输出电压为8V。     

数控自动编程技术现状和发展方向

数控程序作为将设计转化成现实的信息载体,直接控制机床的切削动作,是数控加工的关键。随着计算机技术的迅速发展,计算机数控与CAD/CAM软件不断推陈出新,性能越来越完善,功能越来越强大,并且代表了以后机械制造业的发展方向。但我国制造业中数控技术与CAD/CAM技术应用水平仍然非常低。     

出砂强敏感稠油油藏低效水驱转热采政策界限研究——以林东馆三段稠油油藏为例

林樊家油田林东馆三段地质条件复杂,地层敏感性强,供液差,产能低,油稠,出砂严重,多年来采用了各种工艺措施,均未取得好的水驱开采效果。文章运用数值模拟手段,分析了低水驱的主要原因和论证了低效水驱转蒸汽热采可行性。在此基础上,研究了该块低效水驱转蒸汽热采的开发经济技术政策界限。开发实践表明,低效水驱稠油油藏通过转热采可大幅提高采收率,同时研究成果对同类油藏的开发具有重要指导意义。     

土地利用总体规划实施保证体系

作为土地利用总体规划重要一环的实施保证体系常常不被重视,笔者在参与众多地区的土地利用总体规划基础上,认为土地利用总体规划实施保障体系包括土地利用分区和分区管制措施、土地整理复垦、荒地开发与中低产田改造等内容。其中的核心部分是土地利用分区和分区管制措施。对每一部分的详细内容作了详细阐述。     

龙丽高速公路(K92+945-K93+105)石方路基控爆施工

文章详细介绍了浙江龙丽高速公路K92+945-K93+105段高陡石方路堑在保证其下方的省道通行安全及交通畅通的情况下所采取的安全防护、控制爆破及施工组织措施。     

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.     

When and why do countries break their national fiscal rules?

This paper identifies determinants of compliance with various types of national numerical fiscal rules. Based on 51 fiscal rules in force in EU member states from 1995 to 2015, the analysis identifies determinants among specific rule characteristics and their fiscal frameworks, as well as their political, (socio-)economic and supranational environments. While the average compliance across all rules and countries is around 50%, compliance with rules constraining stock (rather than flow) variables, set out in coalitional agreements, as well as rules covering larger parts of general government finances is significantly higher. Furthermore, independent monitoring and enforcement bodies (issuing real-time alerts) turn out to be significantly associated with a higher probability of compliance. Several theories of the deficit bias of governments due to government fragmentation, decentralization and political budget cycles are also significant with regards to compliance with fiscal rules. However, neither the economic environment or business cycle, nor forecast errors (except for an unexpectedly higher primary balance) on average seem to play a significant role.     

国际贸易对碳减排协议的促进作用——理论框架及减排意愿的数值一般均衡情景模拟

全球碳减排谈判是具有外部性特征的多方合作博弈。文章首先构建一个单一商品无贸易多国模型,对各国的碳减排意愿进行刻画,利用相关数据对不同情景下的各国碳减排意愿进行数值一般均衡模拟;在此基础上,将国际贸易因素引入模型,重新对各国的减排意愿进行情景模拟。数值模拟结果表明:(1)经济规模越大,全球变暖持续的时间跨度越长,温度上升带来的效用损失越大,各国单方面减排意愿越强;(2)国际贸易的存在更有利于各国碳减排意愿的提高,因为各国通过减产实现减排的同时,其贸易条件得到改善,从而将减产带来的效用损失部分转嫁到其他各国;(3)当前,假借碳减排之名而抬头的新贸易保护主义不仅无法促进各国碳减排,反而将阻碍全球碳减排协议的达成。     

基于fluent的综采工作面采空区内瓦斯浓度场研究

本文通过数值模拟采空区内瓦斯浓度场,从理论上确定了瓦斯浓度的分布情况。进而在对综采工作面瓦斯治理提供了科学的理论依据。