The influence of clearance on friction, lubrication and squeaking in large diameter metal-on-metal hip replacements

Large diameter metal-on-metal bearings (MOM) are becoming increasingly popular, addressing the needs of young and more active patients. Clinical data has shown excellent short-to-mid-term results, though incidences of transient squeaking have been noted between implantation and up to 2 years post-operative. Geometric design features, such as clearance, have been significant in influencing the performance of the bearings. Sets of MOM bearings with different clearances were investigated in this study using a hip friction simulator to examine the influence of clearance on friction, lubrication and squeaking. The friction factor was found to be highest in the largest clearance bearings under all test conditions. The incidence of squeaking was also highest in the large clearance bearings, with all bearings in this group squeaking throughout the study. A very low incidence of squeaking was observed in the other two clearance groups. The measured lubricating film was found to be lowest in the large clearance bearings. This study suggests that increasing the bearing clearance results in reduced lubricant film thickness, increased friction and an increased incidence of squeaking

Boundedness, compactness and Schatten-class membership of weighted composition operators

The boundedness and compactness of weighted composition operators on the Hardy space ${\mathcal H}^2$ of the unit disc is analysed. Particular reference is made to the case when the self-map of the disc is an inner function. Schatten-class membership is also considered; as a result, stronger forms of the two main results of a recent paper of Gunatillake are derived. Finally, weighted composition operators on weighted Bergman spaces $\mathcal{A}^2 \alpha(\mathbb{D})$ are considered, and the results of Harper and Smith, linking their properties to those of Carleson embeddings, are extended to this situation.Comment: 12 page

Rationalisation of patterns of competing reactivity by X-ray structure determination : reaction of isomeric (benzyloxythienyl)oxazolines with a base

Funding: We thank EPSRC (UK) for a DTA studentship to ADH (Grant EP/L505079/1) and the EPSRC UK National Mass Spectrometry Facility at Swansea University.Three isomeric (benzyloxythienyl)oxazolines 9 , 11 and 13 have been prepared and are found, upon treatment with strong base, to undergo either Wittig rearrangement or intramolecular attack of the benzylic anion on the oxazoline function to give products derived from cleavage of the initially formed 3-aminothienofuran products. This pattern of reactivity is directly linked to the distance between the two reactive groups as determined by X-ray diffraction, with the greatest distance in 11 leading to exclusive Wittig rearrangement, the shortest distance in 13 giving exclusively cyclisation-derived products, and the intermediate distance in 9 leading to both processes being observed. The corresponding N-butyl amides were also obtained in two cases and one of these undergoes efficient Wittig rearrangement leading to a thieno[2,3-c]pyrrolone product.Publisher PDFPeer reviewe

An Integer Programming Approach to the Student-Project Allocation Problem with Preferences over Projects

The Student-Project Allocation problem with preferences over Projects (SPA-P) involves sets of students, projects and lecturers, where the students and lecturers each have preferences over the projects. In this context, we typically seek a stable matching of students to projects (and lecturers). However, these stable matchings can have different sizes, and the problem of finding a maximum stable matching (MAX-SPA-P) is NP-hard. There are two known approximation algorithms for MAX-SPA-P, with performance guarantees of 2 and 32 . In this paper, we describe an Integer Programming (IP) model to enable MAX-SPA-P to be solved optimally. Following this, we present results arising from an empirical analysis that investigates how the solution produced by the approximation algorithms compares to the optimal solution obtained from the IP model, with respect to the size of the stable matchings constructed, on instances that are both randomly-generated and derived from real datasets. Our main finding is that the 32 -approximation algorithm finds stable matchings that are very close to having maximum cardinality

Reaction Times Altered by Anterior Cruciate Ligament Tear

The anterior cruciate ligament (ACL) tear is associated with declined performance upon return to sport, with high rates of reinjury. Despite ACL reconstruction, ACL tears induce neuroplasticity, increasing reliance on vision and preparation time in movement. This increased reliance on vision and time could lead to motor control strategy deficits under sport-specific tasks. PURPOSE: To determine if ACL injury results in slower muscle onsets in a reactive stepping task and if this is affected by preparation. METHODS: Reactive balance was assessed in ACL (N=6) and healthy control (CON; N=12) participants using a lean and release device to initiate a temporally unpredictable perturbation to prompt reactions by taking a right or left step dictated via leg blocks. 75% of the time, a predetermined right or left step was taken more often (i.e., frequent step; FS) to create unpredictability. The FS leg was counterbalanced midway through testing. Prior to a perturbation, participants viewed the leg blocks move (proactive; P), or were given 400ms of vision prior to release (reactive; R). Muscle onsets were measured by electromyography sensors. Two separate two-way ANOVAs with Bonferroni post-hoc analyses (p ≤ 0.05) assessed differences in muscle onset between each leg (dominant, nondominant), across groups (CON, ACL), and by preparation time (P, R). RESULTS: The FS reaction was consistently faster (p \u3c 0.05). The ANOVA results had main effects for legs (p \u3c 0.05), and groups (p \u3c 0.05). When the infrequent step was taken, significance was evident, but Bonferroni post-hoc analyses showed significance only in the CON group, where dominant legs (104 ± 55 ms) were faster than nondominant legs (171 ± 50 ms; p \u3c .0001), but not in the ACLR group between uninjured legs (78 ± 36 ms), and injured legs (113 ± 39 ms) (p = 0.2277). There was no significance when comparing preparation time between groups. CONCLUSION: Regardless of condition, the FS was consistently faster, but the ACLR group showed a decreased ability to slow muscle onset when asked to stop action in the FS to initiate the infrequent step. Yet, there is no significant difference between groups regardless of the preparation time given. Such results suggest an impaired motor control strategy after ACL injury, but muscle onset may not be a sensitive enough measure to definitively conclude

Functional topology inference from network events

In this paper we present a novel approach for inferring functional connectivity within a large-scale network from time series of emitted node events. We do so under the following constraints: (a) non-stationarity of the underlying connectivity, (b) sparsity of the time-series of events, and (c) absence of an explicit model describing how events propagate through the network. We develop an inference method whose output is an undirected weighted network, where the weight of an edge between two nodes denotes the probability of these nodes being functionally connected. Two nodes are assumed to be functionally connected if they show significantly more coincident or short-lagged events than randomly picked pairs of nodes with similar levels of activity. We develop a model of time-varying connectivity whose parameters are determined by maximising the model’s predictive power from one time window to the next. We assess the accuracy, efficiency and scalability of our method on a real dataset of network events spanning multiple months

Network Events in a Large Commercial Network: What can we learn?

ISP and commercial networks are complex and thus difficult to characterise and manage. Network operators rely on a continuous flow of event log messages to identify and handle service outages. However, there is little published information about such events and how they are typically exploited. In this paper, we describe in as much detail as possible the event logs and network topology of a major commercial network. Through analysing the network topology, textual information of events and time of events, we highlight opportunities and challenges brought by such data. In particular, we suggest that the development of methods for inferring functional connectivity could unlock more of the informational value of event log messages and assist network management operators

Inferring functional connectivity from time-series of events in large scale network deployments

To respond rapidly and accurately to network and service outages, network operators must deal with a large number of events resulting from the interaction of various services operating on complex, heterogeneous and evolving networks. In this paper, we introduce the concept of functional connectivity as an alternative approach to monitoring those events. Commonly used in the study of brain dynamics, functional connectivity is defined in terms of the presence of statistical dependencies between nodes. Although a number of techniques exist to infer functional connectivity in brain networks, their straightforward application to commercial network deployments is severely challenged by: (a) non-stationarity of the functional connectivity, (b) sparsity of the time-series of events, and (c) absence of an explicit model describing how events propagate through the network or indeed whether they propagate. Thus, in this paper, we present a novel inference approach whereby two nodes are defined as forming a functional edge if they emit substantially more coincident or short-lagged events than would be expected if they were statistically independent. The output of the method is an undirected weighted graph, where the weight of an edge between two nodes denotes the strength of the statistical dependence between them. We develop a model of time-varying functional connectivity whose parameters are determined by maximising the model's predictive power from one time window to the next. We assess the accuracy, efficiency and scalability of our method on two real datasets of network events spanning multiple months and on synthetic data for which ground truth is available. We compare our method against both a general-purpose time-varying network inference method and network management specific causal inference technique and discuss its merits in terms of sensitivity, accuracy and, importantly, scalability

Feeling good about being hungry: food-related thoughts in eating disorder

Objectives: This study explores the relationships to food and hunger in women living with anorexic type eating difficulties and asks how imagery-based elaborations of food and eating thoughts are involved in their eating restraint, and recovery. Design: The qualitative idiographic approach of Interpretative Phenomenological Analysis (IPA) was used. Four in-depth semi-structured interviews were conducted with women self-selected as having experienced anorexia or anorexic like behaviour. Methods: The data was analysed using IPA and an audit of the analysis was conducted to ensure that the process followed had been systematic and rigorous and appropriately considered reflexivity. Results: Hunger was perceived positively by participants as confirmation that they were achieving their goal of losing weight, or avoiding weight gain. Hunger conferred a sense of being in control for the participants. Intrusive thoughts about food were reported as being quickly followed by elaborative mental imagery of the positive aspects of weight loss, and the negative consequences of eating. Imagery appeared to serve to maintain anorexic behaviours rather than to motivate food seeking. However, negative imagery of the consequences of anorexia were also described as supporting recovery. Conclusions: The finding that physiological sensations of hunger were experienced as positive confirmation of maintaining control has potentially important clinical and theoretical implications. It suggests further attention needs to be focused upon how changes in cognitive elaboration, involving mental imagery, are components of the psychological changes in the development of, maintenance of, and recovery from, anorexia

Access to diarylmethanols by Wittig rearrangement of ortho-, meta- and para-benzyloxy-N-butylbenzamides

Authors thank EPSRC (UK) for a DTA studentship to ADH (Grant EP/L505079/1), EPSRC (UK) and CRITICAT Centre for Doctoral Training for a studentship to RAI (Grant code: EP/L016419/1) and the EPSRC UK National Mass Spectrometry Facility at Swansea University.The N-butyl amide group, CONHBu, has been found to be an effective promoter of the [1,2]-Wittig rearrangement of aryl benzyl ethers and thus allow the two-step synthesis of isomerically-pure substituted diarylmethanols starting from simple hydroxybenzoic acid derivatives. The method is compatible with a wide range of functional groups including methyl, methoxy and fluoro, although not with nitro and, unexpectedly, is applicable to meta as well as ortho and para isomeric series.Publisher PDFPeer reviewe