bluuebunny/crossref_metadata_2025_split huggingface dataset:
Trajectory Planning of Quadrotor Systems for Various Objective Functions
Authors: Heidari Hamidreza , Saska Martin 
Published: May 2020

SUMMARYQuadrotors are unmanned aerial vehicles with many potential applications ranging from mapping to supporting rescue operations. A key feature required for the use of these vehicles under complex conditions is a technique to analytically solve the problem of trajectory planning. Hence, this paper presents a heuristic approach for optimal path planning that the optimization strategy is based on the indirect solution of the open-loop optimal control problem. Firstly, an adequate dynamic system modeling is considered with respect to a configuration of a commercial quadrotor helicopter. The model predicts the effect of the thrust and torques induced by the four propellers on the quadrotor motion. Quadcopter dynamics is described by differential equations that have been derived by using the Newton–Euler method. Then, a path planning algorithm is developed to find the optimal trajectories that meet various objective functions, such as fuel efficiency, and guarantee the flight stability and high-speed operation. Typically, the necessary condition of optimality for a constrained optimal control problem is formulated as a standard form of a two-point boundary-value problem using Pontryagin’s minimum principle. One advantage of the proposed method can solve a wide range of optimal maneuvers for arbitrary initial and final states relevant to every considered cost function. In order to verify the effectiveness of the presented algorithm, several simulation and experiment studies are carried out for finding the optimal path between two points with different objective functions by using MATLAB software. The results clearly show the effect of the proposed approach on the quadrotor systems.
Pushing partnerships: corporate influence on research and policy via the International Life Sciences Institute
Authors: Steele Sarah , Ruskin Gary , Stuckler David 
Published: May 2020

AbstractObjective:There are concerns that some non-profit organisations, financed by the food industry, promote industry positions in research and policy materials. Using Freedom of Information (FOI) requests, we test the proposition that the International Life Sciences Institute (ILSI), one prominent non-for profit in international health and nutrition research, promotes industry positions.Design:U.S. Right to Know filed five FOI from 2015 to 2018 covering communications with researchers at four US institutions: Texas A&M, University of Illinois, University of Colorado and North Carolina State University. It received 15 078 pages, which were uploaded to the University of California San Francisco’s Industry Documents Library. We searched the Library exploring it thematically for instances of: (1) funding research activity that supports industry interests; (2) publishing and promoting industry-sponsored positions or literature; (3) disseminating favourable material to decision makers and the public and (4) suppressing views that do not support industry.Results:Available emails confirmed that ILSI’s funding by corporate entities leads to industry influence over some of ILSI activities. Emails reveal a pattern of activity in which ILSI sought to exploit the credibility of scientists and academics to bolster industry positions and promote industry-devised content in its meetings, journal and other activities. ILSI also actively seeks to marginalise unfavourable positions.Conclusions:We conclude that undue influence of industry through third-party entities like ILSI requires enhanced management of conflicts of interest by researchers. We call for ILSI to be recognised as a private sector entity rather than an independent scientific non-profit, to allow for more appropriate appraisal of its outputs and those it funds.
A Post‐2013 Dropoff in Total Ozone at a Third of Global Ozonesonde Stations: Electrochemical Concentration Cell Instrument Artifacts?
Authors: Stauffer Ryan M. , Thompson Anne M. , Kollonige Debra E. , Witte Jacquelyn C. , Tarasick David W. , Davies Jonathan , Vömel Holger , Morris Gary A. , Van Malderen Roeland , Johnson Bryan J. , Querel Richard R. , Selkirk Henry B. , Stübi Rene , Smit Herman G. J. 
Published: May 2020

AbstractAn international effort to improve ozonesonde data quality and to reevaluate historical records has made significant improvements in the accuracy of global network data. However, between 2014 and 2016, ozonesonde total column ozone (TCO; O3) at 14 of 37 regularly reporting stations exhibited a sudden dropoff relative to satellite measurements. The ozonesonde TCO drop is 3–7% compared to satellite and ground‐based TCO, and 5–10% or more compared to satellite stratospheric O3 profiles, compromising the use of recent data for trends, although they remain reliable for other uses. Hardware changes in the ozonesonde instrument are likely a major factor in the O3 dropoff, but no single property of the ozonesonde explains the findings. The bias remains in recent data. Research to understand the dropoff is in progress; this letter is intended as a caution to users of the data. Our findings underscore the importance of regular ozonesonde data evaluation.
Solar Energetic Proton Access to the Near‐Equatorial Inner Magnetosphere
Authors: Filwett Rachael J. , Jaynes Allison N. , Baker Daniel N. , Kanekal Shrikanth G. , Kress Brian , Blake J. Bern 
Published: May 2020

AbstractIn this study we examine the ability of protons of solar origin to access the near‐equatorial inner magnetosphere. Here we examine four distinct solar proton events from 20–200 MeV, concurrent with both quiet time and storm time conditions using proton data from the ACE satellite in the solar wind upstream of Earth and data from the Relativistic Electron Proton Telescope (REPT) instrument aboard Van Allen Probes. We examine the direct flux correspondence between interplanetary space and the inner magnetosphere. Small substructures in interplanetary space are observable in the REPT flux profiles, which can penetrate down to L values of ≤4. Furthermore, there are orbit‐to‐orbit variations in the west‐to‐east anisotropic flux ratios. The anisotropic flux ratios are used as a proxy for cutoff energies and display cutoff variations with L shell and energy. The dependence of the anisotropic flux ratio on Dst values is shown. The results paint a picture of highly dynamic spatial and temporal proton cutoff rigidities in the near‐equatorial inner magnetosphere.
Impact of Higher Spatial Atmospheric Resolution on Precipitation Extremes Over Land in Global Climate Models
Authors: Bador Margot , Boé Julien , Terray Laurent , Alexander Lisa V. , Baker Alexander , Bellucci Alessio , Haarsma Rein , Koenigk Torben , Moine Marie‐Pierre , Lohmann Katja , Putrasahan Dian A. , Roberts Chris , Roberts Malcolm , Scoccimarro Enrico , Schiemann Reinhard , Seddon Jon , Senan Retish , Valcke Sophie , Vanniere Benoit 
Published: May 2020

AbstractFiner grids in global climate models could lead to an improvement in the simulation of precipitation extremes. We assess the influence on model performance of increasing spatial resolution by evaluating pairs of high‐ and low‐resolution forced atmospheric simulations from six global climate models (generally the latest CMIP6 version) on a common 1° × 1° grid. The differences in tuning between the lower and higher resolution versions are as limited as possible, which allows the influence of higher resolution to be assessed exclusively. We focus on the 1985–2014 climatology of annual extremes of daily precipitation over global land, and models are compared to observations from different sources (i.e., in situ‐based and satellite‐based) to enable consideration of observational uncertainty. Finally, we address regional features of model performance based on four indices characterizing different aspects of precipitation extremes. Our analysis highlights good agreement between models that precipitation extremes are more intense at higher resolution. We find that the spread among observations is substantial and can be as large as intermodel differences, which makes the quantitative evaluation of model performance difficult. However, consistently across the four precipitation extremes indices that we investigate, models often show lower skill at higher resolution compared to their corresponding lower resolution version. Our findings suggest that increasing spatial resolution alone is not sufficient to obtain a systematic improvement in the simulation of precipitation extremes, and other improvements (e.g., physics and tuning) may be required.
Reply to Comments by N. Sultan on “Sedimentation Controls on Methane‐Hydrate Dynamics Across Glacial/Interglacial Stages: An Example From International Ocean Discovery Program Site U1517, Hikurangi Margin”
Authors: Screaton E. J. , Torres M. E. , Dugan B. , Heeschen K. U. , Mountjoy J. J. , Ayres C. , Rose P. S. , Pecher I. A. , Barnes P. M. , LeVay L. J. 
Published: May 2020

AbstractScreaton et al. (2019, https://doi.org/10.1029/2019GC008603) examined the role of sedimentation, sea level, and bottom water temperature (BWT) changes due to glaciation as drivers for the downward migration of the base of gas hydrate stability and gas hydrate formation. International Ocean Discovery Program (IODP) Site U1517 in the Hikurangi margin was used as a case study because data at this site document a marked increase in chloride over a broad depth range, which was attributed to recent gas hydrate formation. In a comment on Screaton et al. (2019, https://doi.org/10.1029/2019GC008603), Sultan (2020, https://doi.org/10.1029/2019gc008846) used a linear thermal profile to argue that inferences and characterization of methane hydrate at IODP Site U1517 were incorrect because some occur below his estimated base of gas hydrate stability (BGHS). Based on this apparent discrepancy, Sultan (2020, https://doi.org/10.1029/2019gc008846) further stated that low‐chloride spikes may be unreliable indicators of methane hydrate occurrence. In this reply, we emphasize that unsteady‐state, and thus nonlinear, thermal profiles are likely in areas experiencing active sedimentation and bottom‐water temperature (BWT) changes. The resulting deviation from steady‐state temperature profile shifts the BGHS downward. In addition, sedimentation has the potential to bury methane hydrate more rapidly than it dissociates, helping to explain how methane hydrate could be observed below the BGHS. We also review the supporting evidence for gas‐hydrate occurrence at Site U1517 and the criteria used for Site U1517 site selection.
Simulation of Natural Iron Oxide Alteration in Soil: Conversion of Synthetic Ferrihydrite to Hematite Without Artificial Dopants, Observed With Magnetic Methods
Authors: Bilardello Dario , Banerjee Subir K. , Volk Michael W. R. , Soltis Jennifer A. , Penn R. Lee 
Published: May 2020

AbstractWe present new results on the conversion of pure, undoped synthetic ferrihydrite, wet‐annealed at pH 6.56 and 90°C without stabilizing ligands, to nanophase goethite, hematite, and an intermediate magnetic phase, nanophase maghemite. Our analyses included magnetic field and temperature‐dependent properties and characterization by powder X‐ray diffraction, Mössbauer spectra, and high‐resolution transmission electron microscopy. We sampled alteration products after 0.5 hr, and then in a geometric progression to 32 hr, yielding a detailed examination of the earliest alteration phases. There are many similarities to the latest studies of pure ferrihydrite alteration but with a significant difference: We observe early appearance of oriented nanophase goethite along with a soft magnetic contribution, while rhombohedral hematite crystals form later, as reported in previous studies. Our observations attest to the non‐uniqueness of the magnetic enhancement process and to its strong dependence on environmental conditions, with important implications for use of the hematite/goethite ratio as a paleoprecipitation proxy.
Where Do Cold Air Outbreaks Occur, and How Have They Changed Over Time?
Authors: Smith Erik T. , Sheridan Scott C. 
Published: May 2020

AbstractCold air outbreaks (CAOs) occur in many regions of the globe and can be detrimental to the agricultural industry and human health, especially in less prepared regions. A systematic CAO classification was developed using two different climate reanalysis data sets from 1979–2018. Trends in CAOs were calculated for different regions across the globe and the results from each reanalysis data set compared with one another to identify discrepancies. CAOs occur more frequently in the Northern Hemisphere than the Southern Hemisphere with the highest number of CAOs in Europe, Central Eurasia, and North America. CAOs were found to have decreased in spatial extent, frequency, duration, and magnitude across much of the globe, particularly across Alaska, Canada, and the North Atlantic, while an increase in CAOs was observed in Eastern Europe, Central Eurasia, and the Southern Ocean. Early and late winter CAOs have also become much less frequent in most regions.
Anthropogenic Intensification of Surface Ocean Interannual pCO2 Variability
Authors: Gallego M. Angeles , Timmermann Axel , Friedrich Tobias , Zeebe Richard E. 
Published: May 2020

AbstractWe use several global coupled atmosphere‐ocean‐biogeochemistry models from the Coupled Model Intercomparison Project (CMIP5) to show that the global interannual variability of the sea surface pCO2 (calculated as 1σ) will increase by ∼64 ± 20% by 2040–2090 relative to the beginning of the industrial revolution under the RCP8.5 scenario. All models agree that the increase in variability is a consequence of a larger background pCO2 and a lower buffering capacity that enhance the response of pCO2 to the fluctuations of surface temperature (T) and dissolved inorganic carbon (DIC). The most skillful group of models under present‐day conditions shows a future global decrease in DIC fluctuations that will weaken the pCO2 interannual variability (IAV). The remaining uncertainties in the projected evolution of pCO2 variability regionally highlight the need for continuous carbon monitoring programs which will contribute to a better understanding of the oceanic carbon sink's response to increased green house emissions.
Circulation and Tides in a Cooler Upper Atmosphere: Dynamical Effects of CO2 Doubling
Authors: Liu Huixin , Tao Chihiro , Jin Hidekatsu , Nakamoto Yusuke 
Published: May 2020

AbstractThermosphere cooling is a known effect of increasing CO2 in the atmosphere. In this study, we explore the changes of thermosphere circulation and tides in the cooled thermosphere via a doubled CO2 numerical experiment using the Ground‐to‐topside Atmosphere Ionosphere model for Aeronomy (GAIA). The results reveal three major features. (1) The thermosphere cools about 10 K more around solstices than equinoxes, more at the summer pole than the winter pole. (2) The meridional circulation shifts downward and strongly accelerates by 5–15 m s−1. (3) The tidal activity experiences dramatic changes, with a 40–60% reduction in the semidiurnal tides (SW2) throughout the thermosphere but an 30–50% enhancement in diurnal tides (DW1) below 200 km altitude. The nonmigrating tide DE3 has only minor changes. These changes in temperature, meridional circulation, and tides are persistent features in all seasons and can profoundly affect the spatial distribution and diurnal cycles of the ionospheric responses to CO2 doubling via atmosphere composition and electrodynamics.
Potential for Early Forecast of Moroccan Wheat Yields Based on Climatic Drivers
Authors: Lehmann J. , Kretschmer M. , Schauberger B. , Wechsung F. 
Published: May 2020

AbstractWheat production plays an important role in Morocco. Current wheat forecast systems use weather and vegetation data during the crop growing phase, thus limiting the earliest possible release date to early spring. However, Morocco's wheat production is mostly rainfed and thus strongly tied to fluctuations in rainfall, which in turn depend on slowly evolving climate dynamics. This offers a source of predictability at longer time scales. Using physically guided causal discovery algorithms, we extract climate precursors for wheat yield variability from gridded fields of geopotential height and sea surface temperatures which show potential for accurate yield forecasts already in December, with around 50% explained variance in an out‐of‐sample cross validation. The detected interactions are physically meaningful and consistent with documented ocean‐atmosphere feedbacks. Reliable yield forecasts at such long lead times could provide farmers and policy makers with necessary information for early action and strategic adaptation measurements to support food security.
Poloidal‐ and Toroidal‐Mode Mantle Flows Underneath the Cascadia Subduction Zone
Authors: Zhu Hejun , Li Xueyan , Yang Jidong , Stern Robert J. , Lumley David E. 
Published: May 2020

AbstractSeveral hypotheses have been proposed to explain intriguing circular shear wave splitting patterns in the Pacific Northwest, invoking either 2‐D entrained flows or 3‐D return flows. Here, we present some hitherto unidentified, depth‐dependent anisotropic signatures to reconcile different conceptual models. At depths shallower than 200 km, the fast propagation directions of seismic waves to the west of the Rocky Mountain are aligned sub‐parallel to the subduction direction of the Juan de Fuca and Gorda Plates. This pattern is consistent with previous onshore/offshore shear wave splitting measurements and indicates that 2‐D entrained flows dominate at shallower depths. From 300 to 500 km, two large‐scale return flows are revealed, one circulating around Nevada and Colorado and the other running around the edge of the descending Juan de Fuca slab. These observations suggest the development of toroidal‐mode mantle flows, driven by the fast rollback of the narrow, fragmented Juan de Fuca and Gorda slabs.
Empirical Models for Predicting Water and Heat Flow Properties of Permafrost Soils
Authors: O'Connor Michael T. , Cardenas M. Bayani , Ferencz Stephen B. , Wu Yue , Neilson Bethany T. , Chen Jingyi , Kling George W. 
Published: May 2020

AbstractWarming and thawing in the Arctic are promoting biogeochemical processing and hydrologic transport in carbon‐rich permafrost and soils that transfer carbon to surface waters or the atmosphere. Hydrologic and biogeochemical impacts of thawing are challenging to predict with sparse information on arctic soil hydraulic and thermal properties. We developed empirical and statistical models of soil properties for three main strata in the shallow, seasonally thawed soils above permafrost in a study area of ~7,500 km2 in Alaska. The models show that soil vertical stratification and hydraulic properties are predictable based on vegetation cover and slope. We also show that the distinct hydraulic and thermal properties of each soil stratum can be predicted solely from bulk density. These findings fill the gap for a sparsely mapped region of the Arctic and enable regional interpolation of soil properties critical for determining future hydrologic responses and the fate of carbon in thawing permafrost.
The Groundbreaking Experiment in Earthquake Control at Rangely, Colorado, Revisited
Authors: Byrne H. , Silva J. A. , Plesch A. , Juanes R. , Shaw J. H. 
Published: May 2020

AbstractEarthquakes caused by human activities are a growing societal concern. A pioneering study of induced seismicity in the 1970s involved cooperation between the U.S. Geological Survey and Chevron, Inc., to adjust operations in the Rangely oil field, Colorado, to initiate and control earthquakes. Here we revisit this experiment using coupled flow and geomechanical modeling to determine the physical mechanisms that caused these earthquakes and investigate the strength and state of stress acting on the fault that sourced them. The controlled nature of the Rangely experiment, combined with data from decades of field operations, presents a unique opportunity to understand the phenomenon of induced seismicity in ways that can be applied to manage these risks.
The Influence of Internal Climate Variability on Projections of Synoptically Driven Beijing Haze
Authors: Callahan Christopher W. , Mankin Justin S. 
Published: May 2020

AbstractBeijing has suffered a series of poor air quality (“haze”) episodes which have damaged human health and economic growth. Beijing's haze is generally driven by pollutant‐trapping meteorological conditions, but climate model projections differ on how these conditions will evolve under forcing. Such differences are driven in part by (1) disagreements over which meteorological conditions matter most and (2) an undersampling of internal variability in projections. To resolve these differences, we show that Beijing haze is associated with anticyclonic circulation, thereby linking multiple meteorological ingredients to a single process well simulated by models. We use this to inform our assessment of future haze risks in both a multimodel ensemble and a single‐model large ensemble, partitioning model uncertainty and internal variability. We estimate that forcing increases haze‐favorable conditions, but internal variability significantly affects these projections, emphasizing the importance of fully sampling sources of uncertainty to ensure accurate projections of haze risks.
A microfluidically controlled concave–convex membrane lens using an addressing operation system
Authors: Yao Shouju , Zhou Zhou , He Gonghan , Zhang Kunpeng , Huang Xiang , Qiu Bing , Sun Daoheng 
Published: May 2020

AbstractElectrical control toolkits for microlens arrays are available to some extent, but for applications in environments with strong electromagnetic fields, radiation, or deep water, non-electrical actuation and control strategies are more appropriate. An integrated digital microfluidic zoom actuating unit with a logic addressing unit for a built-in membrane lens array, e.g., a flexible bionic compound eye, is developed and studied in this article. A concave–convex membrane fluidic microvalve, which is the component element of the logic gate, actuator, and microlens, is proposed to replace the traditional solenoid valve. The functions of pressure regulation and decoding can be obtained by incorporating microvalves into fluidic networks according to equivalent circuit designs. The zoom actuating unit contains a pressure regulator to adjust the focal length of lenses with three levels, and the logic addressing unit contains a decoder to choose a typical lens from a hexagonal lens array. The microfluidic chip control system is connected flexibly to the actuating part, a membrane lens array. It is shown from a simulation and experimental demonstration that the designed and fabricated system, which is composed of a whole microfluidic zoom unit, addressing technology, and a microlens array, works well. Because these components are constructed in the same fabrication process and operate with the same work media and driving source, the system can be made highly compatible and lightweight for applications such as human-machine interfaces and soft robots.