Central Nervous System Vascular Malformations

32 page(s

k-d Darts: Sampling by k-Dimensional Flat Searches

We formalize the notion of sampling a function using k-d darts. A k-d dart is a set of independent, mutually orthogonal, k-dimensional subspaces called k-d flats. Each dart has d choose k flats, aligned with the coordinate axes for efficiency. We show that k-d darts are useful for exploring a function's properties, such as estimating its integral, or finding an exemplar above a threshold. We describe a recipe for converting an algorithm from point sampling to k-d dart sampling, assuming the function can be evaluated along a k-d flat. We demonstrate that k-d darts are more efficient than point-wise samples in high dimensions, depending on the characteristics of the sampling domain: e.g. the subregion of interest has small volume and evaluating the function along a flat is not too expensive. We present three concrete applications using line darts (1-d darts): relaxed maximal Poisson-disk sampling, high-quality rasterization of depth-of-field blur, and estimation of the probability of failure from a response surface for uncertainty quantification. In these applications, line darts achieve the same fidelity output as point darts in less time. We also demonstrate the accuracy of higher dimensional darts for a volume estimation problem. For Poisson-disk sampling, we use significantly less memory, enabling the generation of larger point clouds in higher dimensions.Comment: 19 pages 16 figure

Incorporating habitat distribution in wildlife disease models: conservation implications for the threat of squirrelpox on the Isle of Arran

Emerging infectious diseases are a substantial threat to native populations. The spread of disease through naive native populations will depend on both demographic and disease parameters, as well as on habitat suitability and connectivity. Using the potential spread of squirrelpox virus (SQPV) on the Isle of Arran as a case study, we develop mathematical models to examine the impact of an emerging disease on a population in a complex landscape of different habitat types. Furthermore, by considering a range of disease parameters, we infer more generally how complex landscapes interact with disease characteristics to determine the spread and persistence of disease. Specific findings indicate that a SQPV outbreak on Arran is likely to be short lived and localized to the point of introduction allowing recovery of red squirrels to pre-infection densities; this has important consequences for the conservation of red squirrels. More generally, we find that the extent of disease spread is dependent on the rare passage of infection through poor quality corridors connecting good quality habitats. Acute, highly transmissible infectious diseases are predicted to spread rapidly causing high mortality. Nonetheless, the disease typically fades out following local epidemics and is not supported in the long term. A chronic infectious disease is predicted to spread more slowly but can remain endemic in the population. This allows the disease to spread more extensively in the long term as it increases the chance of spread between poorly connected populations. Our results highlight how a detailed understanding of landscape connectivity is crucial when considering conservation strategies to protect native species from disease threats

Efficient Algorithms for Generating Provably Near-Optimal Cluster Descriptors for Explainability

Improving the explainability of the results from machine learning methods has become an important research goal. Here, we study the problem of making clusters more interpretable by extending a recent approach of [Davidson et al., NeurIPS 2018] for constructing succinct representations for clusters. Given a set of objects $S$, a partition $\pi$ of $S$ (into clusters), and a universe $T$ of tags such that each element in $S$ is associated with a subset of tags, the goal is to find a representative set of tags for each cluster such that those sets are pairwise-disjoint and the total size of all the representatives is minimized. Since this problem is NP-hard in general, we develop approximation algorithms with provable performance guarantees for the problem. We also show applications to explain clusters from datasets, including clusters of genomic sequences that represent different threat levels

Jobseekers Regime and Flexible New Deal, the Six Month Offer and Support for the Newly Unemployed evaluations: An early process study

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Individual Differences in Amygdala and Ventromedial Prefrontal Cortex Activity are Associated with Evaluation Speed and Psychological Well-being

Using functional magnetic resonance imaging, we examined whether individual differences in amygdala activation in response to negative relative to neutral information are related to differences in the speed with which such information is evaluated, the extent to which such differences are associated with medial prefrontal cortex function, and their relationship with measures of trait anxiety and psychological well-being (PWB). Results indicated that faster judgments of negative relative to neutral information were associated with increased left and right amygdala activation. In the prefrontal cortex, faster judgment time was associated with relative decreased activation in a cluster in the ventral anterior cingulate cortex (ACC, BA 24). Furthermore, people who were slower to evaluate negative versus neutral information reported higher PWB. Importantly, higher PWB was strongly associated with increased activation in the ventral ACC for negative relative to neutral information. Individual differences in trait anxiety did not predict variation in judgment time or in amygdala or ventral ACC activity. These findings suggest that people high in PWB effectively recruit the ventral ACC when confronted with potentially aversive stimuli, manifest reduced activity in subcortical regions such as the amygdala, and appraise such information as less salient as reflected in slower evaluative speed

Posterior interosseous nerve localization within the proximal forearm - a patient normalized parameter

AIM To provide a “patient-normalized” parameter in the proximal forearm. METHODS Sixty-three cadaveric upper extremities from thirty-five cadavers were studied. A muscle splitting approach was utilized to locate the posterior interosseous nerve (PIN) at the point where it emerges from beneath the supinator. The supinator was carefully incised to expose the midpoint length of the nerve as it passes into the forearm while preserving the associated fascial connections, thereby preserving the relationship of the nerve with the muscle. We measured the transepicondylar distance (TED), PIN distance in the forearm’s neutral rotation position, pronation position, supination position, and the nerve width. Two individuals performed measurements using a digital caliper with inter-observer and intra-observer blinding. The results were analyzed with the Wilcoxon-Mann-Whitney test for paired samples. RESULTS In pronation, the PIN was within two confidence intervals of 1.0 TED in 95% of cases (range 0.7-1.3 TED); in neutral, within two confidence intervals of 0.84 TED in 95% of cases (range 0.5-1.1 TED); in supination, within two confidence intervals of 0.72 TED in 95% of cases (range 0.5-0.9 TED). The mean PIN distance from the lateral epicondyle was 100% of TED in a pronated forearm, 84% in neutral, and 72% in supination. Predictive accuracy was highest in supination; in all cases the majority of specimens (90.47%-95.23%) are within 2 cm of the forearm position-specific percentage of TED. When comparing right to left sides for TEDs with the signed Wilcoxon-Mann-Whitney test for paired samples as well as a significance test (with normal distribution), the P-value was 0.0357 (significance - 0.05) indicating a significant difference between the two sides. CONCLUSION This “patient normalized” parameter localizes the PIN crossing a line drawn between the lateral epicondyle and the radial styloid. Accurate PIN localization will aid in diagnosis, injections, and surgical approaches

Fractionation of potentially toxic elements in urban soils from five European cities by means of a harmonised sequential extraction procedure

The revised (four-step) BCR sequential extraction procedure has been applied to fractionate the chromium, copper, iron, manganese, nickel, lead and zinc contents in urban soil samples from public-access areas in five European cities. A preliminary inter-laboratory comparison was conducted and showed that data obtained by different laboratories participating in the study were sufficiently harmonious for comparisons to be made between cities and land types (e.g. parks, roadside, riverbanks, etc.). Analyte recoveries by sequential extraction, with respect to direct aqua regia digestion, were generally acceptable (100 ± 15%). Iron, nickel and, at most sites, chromium were found mainly in association with the residual phase of the soil matrix. Copper was present in the reducible, oxidisable and residual fractions, whilst zinc was found in all four sequential extracts. Manganese was strongly associated with reducible material as, in some cities, was lead. This is of concern because high lead concentrations were present in some soils (>500 mg kg−1) and the potential exists for remobilisation under reducing conditions. As would be expected, extractable metal contents were generally highest in older, more heavily industrialised cities. Copper, lead and zinc showed marked (and often correlated) variations in concentrations between sites within the same city whereas manganese and, especially, iron, did not. No overall relationships were, however, found between analyte concentrations and land use, nor between analyte partitioning and land use

The repeatability and reproducibility of four techniques for measuring horizontal heterophoria: Implications for clinical practice

PURPOSE: Convergence insufficiency, the most common binocular vision anomaly, is characterised by a receded near point of convergence and an exophoria which is at least 4 prism dioptres (Δ) larger at near than at distance. However, the repeatability of standard heterophoria measures are poorly understood. This study assessed the ability of four common heterophoria tests to detect differences of 4Δ by evaluating the inter- and intra-examiner variability of the selected techniques. METHODS: Distance and near horizontal heterophorias of 20 visually-normal adults were measured with the alternating prism cover test, von Graefe prism dissociation, Howell Card and Maddox Rod by two examiners at two separate visits using standardised instructions and techniques. We investigated inter- and intra-examiner variability using repeatability and reproducibility indices, as well as Bland-Altman analysis with acceptable limits of agreement defined as ±2Δ. RESULTS: The Howell card test had the lowest intra-examiner variability at both distance and near, as well as the best 95% limits of agreement (±1.6Δ for distance and ±3.7Δ for near). Inter-examiner reproducibility results were similar, although at near the alternating prism cover test had better repeatability (1.1Δ, 95% confidence intervals −1.1Δ to 4.0Δ) than the Howell card (1.4Δ, 95% confidence intervals −1.9Δ to 5.9Δ). CONCLUSION: The low repeatability of many standard clinical heterophoria tests limits the ability to reliably detect a 4Δ difference. The Howell Card provided the most repeatable and reproducible results indicating that this technique should be used to detect small changes in heterophoria magnitude and direction