Wind tunnel validation of the aerodynamic performance of rain gauges simulated using a CFD approach.

Wind is recognized as the primary cause for the undercatch of solid and liquid precipitation as experienced by catching type gauges. The airflow pattern above the collector, modified by the presence of the gauge body, influences the particle trajectories and reduces the collection of precipitation. Windshields are employed in the field to reduce the impact of wind. As an alternative, measured data are corrected in post-processing using correction functions derived from field data or numerical simulations. Aerodynamic rain gauges have been also developed, with their outer shape designed to reduce the aerodynamic impact of the gauge body on the surrounding airflow. In a previous work, CFD simulations of aerodynamic gauges were performed and the performance of different shapes were compared. The aim of this work is to validate the airflow pattern around the gaugeas predicted by improved CFD simulations by performing wind tunnel tests both in laminar and turbulent base-flow conditions. The airflow in the proximity of the gauge was simulated using the Unsteady Reynolds Average Navier-Stokes (URANS) equations approach. Advantages of the URANS method include the possibility of describing accurate time-varying patterns of the turbulent air velocity field while maintaining acceptable computational requirements. The simulations were performed under two different turbulence conditions in order to assess the role of the base-flow turbulence on the calculated flow pattern. In the first case, the free stream velocity profile is assumed steady and uniform. Under these conditions the time varying pattern of the airflow around the rain gauge collector is due to the instrument aero-dynamics alone. The second case includes a free-stream turbulence intensity approximately equal to 13%, generated by introducing a fixed solid fence upstream the gauge. Validation of the CFD results was provided by realizing the same airflow conditions in the DICCA wind tunnel and measuring the air velocity components in different fixed positions around the collector of the gauge. Results are presented in comparative terms, based on the time-averaged air velocity, the amplitude of the oscillating components and the turbulent kinetic energy

Thermo-fluid dynamic simulation of the Hotplate precipitation gauge.

The present study addresses the aerodynamic response of the recently developed "Hotplate" liquid/solid precipitation gauge when exposed to the wind. The Hotplate gauge employs two heated thin plates to provide a reliable method of precipitation measurement. The measuring principle is based on an algorithm to associate the latent heat needed to evaporate the snow, or the rain, falling on the instrument and the precipitation rate. However, the presence of the instrument body immersed in a wind field is expected to induce significant deformations of the airflow pattern near the gauge, with an impact on the associated catching efficiency. Indeed, the fall trajectories of the hydrometeors when approaching the gauge can be deviated away from the collecting plate resulting, in general, in some underestimation of the precipitation rate. After an initial analysis of real-world "Hotplate" measurements from a field test site located in Marshall, CO (USA) and the comparison with more traditional measurements obtained from a co-located, shielded reference gauge, the role of wind-induced errors is highlighted. The main approach used in this work is based on the numerical simulation of the airflow field around the gauge, using Computational Fluid Dynamics (CFD) to identify areas where the wind-induced updraft, local acceleration and turbulence are significant. The performed CFD airflow simulations use the URANS SST k - \u3c9 modelling scheme, and are the first modelling step to quantify the associated undercatch. These will be possibly coupled in future developments with particle tracking models to derive suitable correction curves for operational purposes. Due to the specific measurement principle exploited by the "Hotplate" gauge, which measures the heat flux needed to evaporate the collected water amount under a constant plate surface temperature, thermo-fluid dynamic simulations are addressed as well. Dedicated tests have been performed in the wind tunnel facility available at DICCA, University of Genoa to validate simulation results. Results indicate that the presence of wind is a relevant source of systematic bias when using the "Hotplate" gauge for the measurement of precipitation, and its effect must be corrected by adopting suitable correction curves as a function of the wind velocity. The magnitude of the correction can be derived from numerical thermo-fluid dynamic simulations and an assessment of the airflow patterns developing around the gauge at various wind velocity regimes is provided in this work. Wind tunnel tests allowed for a substantial validation of the numerical results, and possible improvements of the model are highlighted and proposed for future developments

Automatic Music Playlist Generation via Simulation-based Reinforcement Learning

Personalization of playlists is a common feature in music streaming services, but conventional techniques, such as collaborative filtering, rely on explicit assumptions regarding content quality to learn how to make recommendations. Such assumptions often result in misalignment between offline model objectives and online user satisfaction metrics. In this paper, we present a reinforcement learning framework that solves for such limitations by directly optimizing for user satisfaction metrics via the use of a simulated playlist-generation environment. Using this simulator we develop and train a modified Deep Q-Network, the action head DQN (AH-DQN), in a manner that addresses the challenges imposed by the large state and action space of our RL formulation. The resulting policy is capable of making recommendations from large and dynamic sets of candidate items with the expectation of maximizing consumption metrics. We analyze and evaluate agents offline via simulations that use environment models trained on both public and proprietary streaming datasets. We show how these agents lead to better user-satisfaction metrics compared to baseline methods during online A/B tests. Finally, we demonstrate that performance assessments produced from our simulator are strongly correlated with observed online metric results.Comment: 10 pages. KDD 2

Laboratory assessment of two catching type drop-counting rain gauges.

This study reports the results of laboratory tests performed to assess the performance of three drop counting rain gauges of the catching type , and to propose suitable correction so as to make them compliant with the specifications of the World Meteorological Organisation (WMO) at one minute time resolution for Rainfall Intensity (RI) measurements. The tests were limited to the steady state conditions, with known and constant flow rates provided to the instrument at various reference intensities for a sufficient period of time, in order to compare the measures provided by the gauge with the reference figures (which is known as dynamic calibration). The instruments investigated are manufactured by Ogawa Seiki Co. Ltd (Japan) and the Chilbolton RAL (UK). They are designed as high-sensitivity drop counter type rain gauges. Using a suitable correction algorithm, based on calibration curves as obtained from the tests performed in the laboratory, it is possible to improve the accuracy of the three instruments and to obtain results that are fully compatible with the WMO required measurement uncertainty provided in the CIMO guide (WMO, Pub. No 8), although only within the acceptable measurement ranges. The laboratory tests were performed under known and constant flow rates in closely controlled conditions, according to the recommended procedures developed during the WMO Laboratory Intercomparison of RI gauges and recommended by WMO. The performance in the field may be lower than those observed in the laboratory, due to errors induced by the atmospheric conditions, installation, status of maintenance, etc

Ischemic wound revascularization by the stromal vascular fraction relies on host-donor hybrid vessels

Nonhealing wounds place a significant burden on both quality of life of affected patients and health systems. Skin substitutes are applied to promote the closure of nonhealing wounds, although their efficacy is limited by inadequate vascularization. The stromal vascular fraction (SVF) from the adipose tissue is a promising therapy to overcome this limitation. Despite a few successful clinical trials, its incorporation in the clinical routine has been hampered by their inconsistent results. All these studies concluded by warranting pre-clinical work aimed at both characterizing the cell types composing the SVF and shedding light on their mechanism of action. Here, we established a model of nonhealing wound, in which we applied the SVF in combination with a clinical-grade skin substitute. We purified the SVF cells from transgenic animals to trace their fate after transplantation and observed that it gave rise to a mature vascular network composed of arteries, capillaries, veins, as well as lymphatics, structurally and functionally connected with the host circulation. Then we moved to a human-in-mouse model and confirmed that SVF-derived endothelial cells formed hybrid human-mouse vessels, that were stabilized by perivascular cells. Mechanistically, SVF-derived endothelial cells engrafted and expanded, directly contributing to the formation of new vessels, while a population of fibro-adipogenic progenitors stimulated the expansion of the host vasculature in a paracrine manner. These data have important clinical implications, as they provide a steppingstone toward the reproducible and effective adoption of the SVF as a standard care for nonhealing wounds

On Neglecting Free-Stream Turbulence in Numerical Simulation of the Wind-Induced Bias of Snow Gauges

Numerical studies of the wind-induced bias of precipitation measurements assume that turbulence is generated by the interaction of the airflow with the gauge body, while steady and uniform free-stream conditions are imposed. However, wind is turbulent in nature due to the roughness of the site and the presence of obstacles, therefore precipitation gauges are immersed in a turbulent flow. Further to the turbulence generated by the flow-gauge interaction, we investigated the natural free-stream turbulence and its influence on precipitation measurement biases. Realistic turbulence intensity values at the gauge collector height were derived from 3D sonic anemometer measurements. Large Eddy Simulations of the turbulent flow around a chimney-shaped gauge were performed under uniform and turbulent free-stream conditions, using geometrical obstacles upstream of the gauge to provide the desired turbulence intensity. Catch ratios for dry snow particles were obtained using a Lagrangian particle tracking model, and the collection efficiency was calculated based on a suitable particle size distribution. The collection efficiency in turbulent conditions showed stronger undercatch at the investigated wind velocity and snowfall intensity below 10 mm h−1, demonstrating that adjustment curves based on the simplifying assumption of uniform free-stream conditions do not accurately portray the wind-induced bias of snow measurements

On Neglecting Free-Stream Turbulence in Numerical Simulation of the Wind-Induced Bias of Snow Gauges

Numerical studies of the wind-induced bias of precipitation measurements assume that turbulence is generated by the interaction of the airflow with the gauge body, while steady and uniform free-stream conditions are imposed. However, wind is turbulent in nature due to the roughness of the site and the presence of obstacles, therefore precipitation gauges are immersed in a turbulent flow. Further to the turbulence generated by the flow-gauge interaction, we investigated the natural free-stream turbulence and its influence on precipitation measurement biases. Realistic turbulence intensity values at the gauge collector height were derived from 3D sonic anemometer measurements. Large Eddy Simulations of the turbulent flow around a chimney-shaped gauge were performed under uniform and turbulent free-stream conditions, using geometrical obstacles upstream of the gauge to provide the desired turbulence intensity. Catch ratios for dry snow particles were obtained using a Lagrangian particle tracking model, and the collection efficiency was calculated based on a suitable particle size distribution. The collection efficiency in turbulent conditions showed stronger undercatch at the investigated wind velocity and snowfall intensity below 10 mm h−1, demonstrating that adjustment curves based on the simplifying assumption of uniform free-stream conditions do not accurately portray the wind-induced bias of snow measurements

CFD simulations of a calyx shape rain gauge in a uniform and turbulent wind tunnel environment

The airflow surrounding any precipitation gauge is deformed by the presence of the gauge body, resulting in increased flow velocity above the orifice of the instrument, which deflects the hydrometeors (liquid/solid particles) away from the collector. The main factors of influence are the gauge shape, the wind speed and the type of precipitation, including the particle size distribution (PSD). Currently to reduce the wind effect on precipitation collection wind shields are installed and rain gauges with aerodynamic shape are developed. The method employed in this study is based on the analysis of airflow patterns in the proximity of the gauge collector by means of Computational Fluid Dynamic (CFD) simulations. Validation of the numerical results is obtained by comparison with wind tunnel experiments. These simulations, to be coupled in future developments with a particle tracking model to introduce the dispersed phase (solid/liquid particles), will allow to quantify the Collection Efficiency (CE) of the gauge. The overall objective of the work that includes this study, is to derive suitable correction curves for operational purpose