Performance Thresholds in Managerial Incentive Contracts

Performance thresholds are commonly used in executive compensation contracts. We examine the contractual nonlinearity associated with performance thresholds and its incentive implications. Incorporating a performance threshold into a standard principal-agent model of a linear contract, we show that pay schemes using a performance threshold are optimal. By truncating a linear scheme at poor performance, the threshold mitigates agency costs associated with the downside risk of production. Examining CEO compensation data, we find evidence of the role of performance thresholds. As a consequence of under-threshold performance, the tobit estimator is shown to increase pay-performance sensitivity, notably improving upon the standard OLS estimator.published_or_final_versio

A case of cerebellar hypoplasia in a Chinese infant with osteogenesis imperfecta

We report a unique case of unilateral cerebellar hypoplasia in a young Chinese girl with osteogenesis imperfecta type IV. Magnetic resonance imaging showed mild basilar invagination and impression. Although unilateral cerebellar hypoplasia and osteogenesis imperfecta may have been coincidental diagnoses, we propose possible mechanisms for unilateral cerebellar hypoplasia secondary to osteogenesis imperfecta. For example, cerebellar hypoplasia may have been because of vascular disruption or direct compression to the posterior circulation in utero. Foetuses with osteogenesis imperfecta are more susceptible to the above risks compared to the normal foetus because of associated craniocervical anomalies and a poorly ossified skull.published_or_final_versio

Preparation and characterization of polycaprolactone microspheres by electrospraying

This is the author accepted manuscript. Published online: 13 Sep 2016. The final version to be made available from the publisher via the DOI in this record.The ability to reproducibly produce and effectively collect electrosprayed polymeric microspheres with controlled morphology and size in bulk form is challenging. In this study, microparticles were produced by electrospraying polycaprolactone (PCL) of various molecular weights and solution concentrations in chloroform, and by collecting materials on different substrates. The resultant PCL microparticles were characterized by optical and electron microscopy to investigate the effect of molecular weight, solution concentration, applied voltage, working distance and flow rate on their morphology and size. The work demonstrates the key role of a moderate molecular weight and/or solution concentration in the formation of spherical PCL particles via an electrospraying process. Increasing the applied voltage was found to produce smaller and more uniform PCL microparticles. There was a relatively low increase in the particle average size with an increase in the working distance and flow rate. Four types of substrates were adopted to collect electrosprayed PCL particles: a glass slide, aluminium foil, liquid bath and copper wire. Unlike 2D bulk structures collected on the other substrates, a 3D tubular structure of microspheres was formed on the copper wire and could find application in the construction of 3D tumour mimics.The financial support received from the Cancer Research UK (CRUK) and Engineering and Physical Sciences Research Council (ESPRC) Cancer Imaging Centre in Cambridge and Manchester (C8742/A18097) is acknowledged

Diffusion tensor imaging for the evaluation of treatment-induced neurotoxicity in childhood medulloblastoma

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Diffusion tensor MR imaging in the evaluation of Wallerian degeneration in pediatric strokes: work-in-progress

Poster Session - Pediatric Brain MR Imaging: no. 2090We use DTI to detect and quantify Wallerian degeneration (WD) in pediatric MCA strokes. Fractional anisotropy (FA) and mean diffusivity (MD)of the infarction, ipsilateral internal capsule (PLIC) and cerebral peduncle (CP) were measured in nine children and compared to the matched contralateral side. WD was characterized by statistically significant differences in FA, but not MD, of the ipsilateral PLIC and CP compared to normal side. FA was reduced in all children, whilst corresponding hyperintense signals on T2W were seen in five children. DTI is more sensitive than conventional MRI and can be used to detect and quantify WD.published_or_final_versio

Resting-state fMRI using passband balanced steady-state free precession

OBJECTIVE: Resting-state functional MRI (rsfMRI) has been increasingly used for understanding brain functional architecture. To date, most rsfMRI studies have exploited blood oxygenation level-dependent (BOLD) contrast using gradient-echo (GE) echo planar imaging (EPI), which can suffer from image distortion and signal dropout due to magnetic susceptibility and inherent long echo time. In this study, the feasibility of passband balanced steady-state free precession (bSSFP) imaging for distortion-free and high-resolution rsfMRI was investigated. METHODS: rsfMRI was performed in humans at 3 T and in rats at 7 T using bSSFP with short repetition time (TR = 4/2.5 ms respectively) in comparison with conventional GE-EPI. Resting-state networks (RSNs) were detected using independent component analysis. RESULTS AND SIGNIFICANCE: RSNs derived from bSSFP images were shown to be spatially and spectrally comparable to those derived from GE-EPI images with considerable intra- and inter-subject reproducibility. High-resolution bSSFP images corresponded well to the anatomical images, with RSNs exquisitely co-localized to the gray matter. Furthermore, RSNs at areas of severe susceptibility such as human anterior prefrontal cortex and rat piriform cortex were proved accessible. These findings demonstrated for the first time that passband bSSFP approach can be a promising alternative to GE-EPI for rsfMRI. It offers distortion-free and high-resolution RSNs and is potentially suited for high field studies.published_or_final_versio

Review: optical fiber sensors for civil engineering applications

Optical fiber sensor (OFS) technologies have developed rapidly over the last few decades, and various types of OFS have found practical applications in the field of civil engineering. In this paper, which is resulting from the work of the RILEM technical committee “Optical fiber sensors for civil engineering applications”, different kinds of sensing techniques, including change of light intensity, interferometry, fiber Bragg grating, adsorption measurement and distributed sensing, are briefly reviewed to introduce the basic sensing principles. Then, the applications of OFS in highway structures, building structures, geotechnical structures, pipelines as well as cables monitoring are described, with focus on sensor design, installation technique and sensor performance. It is believed that the State-of-the-Art review is helpful to engineers considering the use of OFS in their projects, and can facilitate the wider application of OFS technologies in construction industry

Oscillating epidemics in a dynamic network model: stochastic and mean-field analysis

An adaptive network model using SIS epidemic propagation with link-type-dependent link activation and deletion is considered. Bifurcation analysis of the pairwise ODE approximation and the network-based stochastic simulation is carried out, showing that three typical behaviours may occur; namely, oscillations can be observed besides disease-free or endemic steady states. The oscillatory behaviour in the stochastic simulations is studied using Fourier analysis, as well as through analysing the exact master equations of the stochastic model. By going beyond simply comparing simulation results to mean-field models, our approach yields deeper insights into the observed phenomena and help better understand and map out the limitations of mean-field models

Emergence of scale-free close-knit friendship structure in online social networks

Despite the structural properties of online social networks have attracted much attention, the properties of the close-knit friendship structures remain an important question. Here, we mainly focus on how these mesoscale structures are affected by the local and global structural properties. Analyzing the data of four large-scale online social networks reveals several common structural properties. It is found that not only the local structures given by the indegree, outdegree, and reciprocal degree distributions follow a similar scaling behavior, the mesoscale structures represented by the distributions of close-knit friendship structures also exhibit a similar scaling law. The degree correlation is very weak over a wide range of the degrees. We propose a simple directed network model that captures the observed properties. The model incorporates two mechanisms: reciprocation and preferential attachment. Through rate equation analysis of our model, the local-scale and mesoscale structural properties are derived. In the local-scale, the same scaling behavior of indegree and outdegree distributions stems from indegree and outdegree of nodes both growing as the same function of the introduction time, and the reciprocal degree distribution also shows the same power-law due to the linear relationship between the reciprocal degree and in/outdegree of nodes. In the mesoscale, the distributions of four closed triples representing close-knit friendship structures are found to exhibit identical power-laws, a behavior attributed to the negligible degree correlations. Intriguingly, all the power-law exponents of the distributions in the local-scale and mesoscale depend only on one global parameter -- the mean in/outdegree, while both the mean in/outdegree and the reciprocity together determine the ratio of the reciprocal degree of a node to its in/outdegree.Comment: 48 pages, 34 figure