Maximum likelihood estimates for the Hildreth–Houck random coefficients model

We explore maximum likelihood (ML) estimation of the Hildreth–Houck random coefficients model. We show that the global ML estimator can be inconsistent. We develop an alternative LML (local ML) estimator and prove that it is consistent and asymptotically efficient for points in the interior of the parameters. Properties of the LML and comparisons with common method of moments (MM) estimates are done via Monte Carlo. Boundary parameters lead to nonstandard asymptotic distributions for the LML which are described. The LML is used to develop a modification of the LR test for random coefficients. Simulations suggest that the LR test is more powerful for distant alternatives than the Breusch–Pagan (BP) Lagrange multiplier test. A simple modification of the BP test also appears to be more powerful than the BP.     

The non-linear beam via optimal control with bounded state variables

The non-linear beam with bounded deflection is considered as an optimal control problem with bounded state variables. The theory of necessary optimality conditions leads to boundary value problems with jump conditions which are solved by multiple-shooting techniques. A branching analysis is performed which exhibits the different solution structures. In particular, the second bifurcation point is determined numerically. The bifurcation diagram reveals a hysteresis-like behaviour and explains the jumping to a different state at this bifurcation point.     

人下颌骨及颞下颌关节不同受力模型的有限元分析

目的 分析人下颌骨及颞下颌关节两种不同力学模型有限元模拟的结果.方法 通过CT扫描建立包含密质骨、松质骨的完整人下颌骨三维模型,将所获得的三维模型在ICEM CFD软件中划分网格.在建立的网格模型基础上,对前牙咬合的下颌骨分别建立被动肌力加载和主动肌力加载两种生物力学模型,计算并比较其应力分布.结果 两个模型中的应力分布有明显区别.被动肌力加载模型中,应力主要分布于下颌角、磨牙后三角、下颌切迹以及咬合点附近牙冠.主动肌力加载模型中,应力主要分布于髁状突顶点和颈部、下颌角、磨牙后三角以及咬合点附近牙冠.两者的应力分布有一定相似之处,但在髁状突处则有很大不同,这是由于两种模型下髁状突顶点反力的大小悬殊.结论 主动肌力加载模型更接近下颌骨及颞下颌关节的实际受力状态,主动肌力加载模型为前牙咬合下颌骨的合理生物力学模型.     

Producing boundary-breaking texts on disability issues: the personal politics of collaboration

Purpose: This article explores the reflection on a process of inter-collaborative team work to produce a photographic book on caregivers’ experiences of parenting their disabled children. The team of authors consisted of members with diverse backgrounds, including media studies, social science and photography. The purpose of this article was to explore and gain a deeper understanding of the process of boundary breaking, one which is important if we are to develop new knowledges and new ways of thinking about disability. Method: In-depth interviews were conducted with all contributors to the book. Results: Themes emerging from the interviews include the existence of different worlds, crossing boundaries, questions about expertise, conflicting hopes and expectations, and the ethics of anonymity. Conclusion: An account of the anxieties, the frustrations and rewarding aspects of the collaboration is provided. We conclude that “us” and “them” categorization permeates our thinking. It characterizes some of the most simplistic thinking in the world of disability – able-bodied vs. disabled. In reality, there are no such categories, we all reside along a highly differentiated continuum of changing states of impairment and health. If we open ourselves up to this reality, we can meet one another and draw on one another’s knowledge and experience.

Implications for Rehabilitation

• Collaboration between able-bodied researchers and disabled people and their families holds the potential for producing new perspectives on disability and rehabilitation.

• These collaborations may be emotionally challenging and they hold possibilities for a range of conflicts.

• Dealing with these challenges conflicts openly and honestly may lead to a deeper understanding of the issues at stake in disability and rehabilitation.

• We need more examples of reflection on innovative collaborative processes.

     

What do intracerebral electrodes measure?

ObjectiveGain insight and improve our interpretation of measurements from intracerebral electrodes. Determine if interpretation of intracerebral EEG is dependent on electrode characteristics.MethodsWe use intracerebral EEG measurements differing only in the recording electrodes (Dixi or homemade electrodes), and numerical simulations to determine the spatial sensitivity of intracerebral electrodes and its dependence on several parameters.ResultsThere is a difference in the high frequency (>20 Hz) power depending on the electrode type, which cannot be explained by the different contact sizes or distance between contacts. Simulations show that the width of the gap between electrode and brain and the extent of the generators have an effect on sensitivity, while other parameters are less important.ConclusionsThe sensitivity of intracerebral electrodes is not affected in an important way by the dimensions of the contacts, but depends on the extent of generators. The unusual insertion technique of homemade electrodes resulting in a large gap between functional brain and electrodes, explains the observed signal difference.SignificanceNumerical simulation is a useful tool in the choice or design of intracerebral electrodes, and increases our understanding of their measurements. The interpretation of intracerebral EEG is not affected by differences between typical commercially available electrodes.     

Distinguishing research from clinical care in cancer genetics: Theoretical justifications and practical strategies

The relationship between clinical research and clinical care is often perceived as unclear, particularly in highly technological subspecialties. This ambiguity is illustrated in cancer genetics where research protocols are frequently used to provide access to procedures that may be offered as a clinical service in other specialties. The project on which this paper is based investigated lay and expert perceptions of the activities which take place within the cancer genetics clinic. Semi-structured interviews were conducted with 40 individuals who are involved in cancer genetics research in the UK, the majority (18 clinical geneticists, 10 genetic counsellors/nurse specialists) of whom also provide a clinical service. Interviewees emphasised the need to differentiate research from clinical care for service users, and provided regulatory, ethical, economic and translational justifications for distinguishing these activities. A number of strategies for differentiating research from clinical care were described by those who work as healthcare professionals, which involved deliberately displacing these activities in time and space. It is argued that by distinguishing research from clinical care clinical researchers are engaging in a form of boundary work which enables them to manage what they experience as a conflict of interest generated by the different roles they occupy within the cancer genetics clinic. Finally, we discuss the implications of these findings for the process of informed consent.     

Application of the Method of Fundamental Solutions to Potential-based Inverse Electrocardiography

Potential-based inverse electrocardiography is a method for the noninvasive computation of epicardial potentials from measured body surface electrocardiographic data. From the computed epicardial potentials, epicardial electrograms and isochrones (activation sequences), as well as repolarization patterns can be constructed. We term this noninvasive procedure Electrocardiographic Imaging (ECGI). The method of choice for computing epicardial potentials has been the Boundary Element Method (BEM) which requires meshing the heart and torso surfaces and optimizing the mesh, a very time-consuming operation that requires manual editing. Moreover, it can introduce mesh-related artifacts in the reconstructed epicardial images. Here we introduce the application of a meshless method, the Method of Fundamental Solutions (MFS) to ECGI. This new approach that does not require meshing is evaluated on data from animal experiments and human studies, and compared to BEM. Results demonstrate similar accuracy, with the following advantages: 1. Elimination of meshing and manual mesh optimization processes, thereby enhancing automation and speeding the ECGI procedure. 2. Elimination of mesh-induced artifacts. 3. Elimination of complex singular integrals that must be carefully computed in BEM. 4. Simpler implementation. These properties of MFS enhance the practical application of ECGI as a clinical diagnostic tool.     

Shape optimization analysis: First- and second-order necessary conditions

In this paper, first- and second-order necessary conditions for optimality are studied for a domain optimization problem. The optimization problem considered is the minimization of an objective function defined on the domain boundary through the solution of a boundary value problem. In order to derive the first and second variations of the objective function due to boundary variation, the first and second variations of the solution of the boundary value problem are calculated using a perturbation technique. An iterative shape optimization algorithm for potential flow problems in R² with Dirichlet boundary conditions is presented. In the algorithm a boundary element method (BEM) is employed to solve the Laplace equation numerically. The validity and accuracy of the algorithm have been verified on a problem where the final solution is known. Finally, the problem of designing a 90° bend for two-dimensional potential flow is solved.     

Synaptic characteristics of identified pyramidal and multipolar non-pyramidal neurons in the visual cortex of young and adult rabbits. A quantitative Golgi-electron microscope study

The visual cortex of 20 day old rats and rabbits has been considered as mature on the basis of the observations that the dendritic arborization and the overall synaptic population have almost reached their adult stage in these animals. In the present study we have investigated the visual cortex of 20 day and 7 month old (adult) rabbits in order to determine whether this apparent adult appearance also holds for the synaptic organization of individual neurons. Neurons mainly located in layers III and IV of the primary visual cortex (area 17) were Golgi-impregnated, gold toned and deimpregnated and were then, after embedding in plastic, sectioned serially. The number and length of synaptic profiles, and the length of the neuronal boundaries were analysed in every tenth section. From these counts and measurements the size distribution of the synaptic discs, the number of synapses per 100 micron2 neuronal surface and the receptive surface expressed as the percentage of the total neuronal surface covered with synaptic contacts were estimated using stereological methods. At both ages studied, the density of synapses was significantly higher for the non-pyramidal neurons than for the pyramidal neurons. Differences in the amount of receptive surface were parallel to the differences observed for the number of synapses per 100 micron2. At day 20 the receptive surface of the non-pyramidal neurons was significantly larger than that of the pyramidal neurons. The receptive surface of the non-pyramidal neurons in the adult stage was not only larger than that of the pyramidal neurons in the adults, but also larger than that of the day 20 non-pyramidal neurons. From our results the following conclusions can be drawn: (1) The synaptic input received by the pyramidal neurons is mainly established at day 20 of postnatal life, i.e. prior to the establishment of adult visual behaviour. (2) The non-pyramidal neurons complete their maturation in a later stage than the pyramidal neurons. (3) Medium to large sized synaptic contacts are newly formed after day 20 and are mainly added to the synaptic population on dendrites of non-pyramidal neurons. (4) The specific increase in the number of synapses on non-pyramidal neurons is discussed in relation to intracortical inhibition which is thought to be important for the fine regulation of visual function during development.