Streamer discharge inception in a sub-breakdown electric field from a dielectric body with a frequency dependent dielectric permittivity

We study positive streamer inception from the tip of an elongated ice particle. The dielectric permittivity of ice drops from 93 to 3 for electric fields changing on the millisecond timescale [1]. We demonstrate that this effect can be important on the nanosecond time scale of streamer discharge development. The effect makes the streamer propagate with only half the velocity it would have for the dielectric permittivity fixed to 9

Adaptive selection of sampling points for uncertainty quantification

We present a simple and robust strategy for the selection of sampling points in Uncertainty Quantification. The goal is to achieve the fastest possible convergence in the cumulative distribution function of a stochastic output of interest. We assume that the output of interest is the outcome of a computationally expensive nonlinear mapping of an input random variable, whose probability density function is known. We use a radial function basis to construct an accurate interpolant of the mapping. This strategy enables adding new sampling points one at a time, adaptively. This takes into full account the previous evaluations of the target nonlinear function. We present comparisons with a stochastic collocation method based on the Clenshaw-Curtis quadrature rule, and with an adaptive method based on hierarchical surplus, showing that the new method often results in a large computational saving.Comment: 22 pages, 15 figures; to appear in Int. J. Uncertainty Quantificatio

Can falls risk prediction tools correctly identify fall-prone elderly rehabilitation inpatients? A systematic review and meta-analysis

BACKGROUND: Falls of elderly people may cause permanent disability or death. Particularly susceptible are elderly patients in rehabilitation hospitals. We systematically reviewed the literature to identify falls prediction tools available for assessing elderly inpatients in rehabilitation hospitals. METHODS AND FINDINGS: We searched six electronic databases using comprehensive search strategies developed for each database. Estimates of sensitivity and specificity were plotted in ROC space graphs and pooled across studies. Our search identified three studies which assessed the prediction properties of falls prediction tools in a total of 754 elderly inpatients in rehabilitation hospitals. Only the STRATIFY tool was assessed in all three studies; the other identified tools (PJC-FRAT and DOWNTON) were assessed by a single study. For a STRATIFY cut-score of two, pooled sensitivity was 73% (95%CI 63 to 81%) and pooled specificity was 42% (95%CI 34 to 51%). An indirect comparison of the tools across studies indicated that the DOWNTON tool has the highest sensitivity (92%), while the PJC-FRAT offers the best balance between sensitivity and specificity (73% and 75%, respectively). All studies presented major methodological limitations. CONCLUSIONS: We did not identify any tool which had an optimal balance between sensitivity and specificity, or which were clearly better than a simple clinical judgment of risk of falling. The limited number of identified studies with major methodological limitations impairs sound conclusions on the usefulness of falls risk prediction tools in geriatric rehabilitation hospitals

Hyperledger Fabric:Evaluating Endorsement Policy Strategies in Supply Chains

Hyperledger Fabric is a permissioned blockchain solution, in which network participation is controlled by predefined rules. This makes it an attractive platform for enterprise settings. In Fabric, endorsement policies are used to specify the peers that must confirm a transaction before it can be considered as valid and appended to the ledger. This work examines various implications of Fabric's endorsement policy component, for which different endorsement policy strategies (and subsequent trade-offs) are evaluated by modeling two real-world supply chain case studies. This work discusses how vulnerable endorsement policies can lead to admitting inauthentic data on the ledger. To address this issue, several approaches are proposed to balance integrity with limited disclosure of confidential information, with or without hosting a network peer directly. Furthermore, the concept of multi-tenancy in blockchain networks is introduced as a way of reducing the technological barrier in technology adoption

Dietary interventions for maintaining cognitive function in cognitively healthy people in late life

This is the protocol for a review and there is no abstract. The objectives are as follows: In this review we will set out to evaluate the effects of dietary interventions for maintaining cognitive function in cognitively healthy people in late-life

Prediction of lightning inception by large ice particles and extensive air showers

We derive that lightning can start if the electric field is 15% of the breakdown field, and if elongated ice particles of 6 cm length and 100 free electrons per cm3 are present. This is one particular example set from a parameter range that we discuss as well. Our simulations include the permittivity ε(ω) of ice. 100 free electrons per cm3 exist at 5.5 km altitude in air showers created by cosmic particles of at least 5×1015  eV. If the electric field zone is 3 m high and 0.2  km2 in the horizontal direction, at least one discharge per minute can be triggered. The size distribution of the ice particles is crucial for our argument; more detailed measurements would be desirable

Lightning inception from ice particles and extensive air showers

The electric fields in thunderstorms can exceed the breakdown value locally near ice particles present in thunderclouds. But are fields high enough and the regions large enough to initiate a streamer discharge? And where would a sufficient density of free electrons come from to start the discharge in the humid air that rapidly binds electrons in water-clusters