Effects of climate change and nutrient concentrations on carbon sources for zooplankton in a Tibetan Plateau lake over the past millennium

Journal of Paleolimnology - Autochthonous and allochthonous organic carbon (OC) are important carbon sources for zooplankton in lakes, and changes in the abundance and proportions of those sources...     

Real-time hybrid simulation of structures equipped with viscoelastic-plastic dampers using a user-programmable computational platform

A user-programmable computational/control platform was developed at the University of Toronto that offers real-time hybrid simulation (RTHS) capabilities. The platform was verified previously using several linear physical substructures. The study presented in this paper is focused on further validating the RTHS platform using a nonlinear viscoelastic-plastic damper that has displacement, frequency and temperature-dependent properties. The validation study includes damper component characterization tests, as well as RTHS of a series of single-degree-of-freedom (SDOF) systems equipped with viscoelastic-plastic dampers that represent different structural designs. From the component characterization tests, it was found that for a wide range of excitation frequencies and friction slip loads, the tracking errors are comparable to the errors in RTHS of linear spring systems. The hybrid SDOF results are compared to an independently validated thermalmechanical viscoelastic model to further validate the ability for the platform to test nonlinear systems. After the validation, as an application study, nonlinear SDOF hybrid tests were used to develop performance spectra to predict the response of structures equipped with damping systems that are more challenging to model analytically. The use of the experimental performance spectra is illustrated by comparing the predicted response to the hybrid test response of 2DOF systems equipped with viscoelastic-plastic dampers.     

Improved Method for Estimating Reaction Rates During Push-Pull Tests

The breakthrough curve obtained from a single-well push-pull test can be adjusted to account for dilution of the injection fluid in the aquifer fluid. The dilution-adjusted breakthrough curve can be analyzed to estimate the reaction rate of a solute. The conventional dilution-adjusted method assumes that the ratios of the concentrations of the nonreactive and reactive solutes in the injection fluid vs. the aquifer fluid are equal. If this assumption is invalid, the conventional method will generate inaccurate breakthrough curves and may lead to erroneous conclusions regarding the reactivity of a solute. In this study, a new method that generates a dilution-adjusted breakthrough curve was theoretically developed to account for any possible combination of nonreactive and reactive solute concentrations in the injection and aquifer fluids. The newly developed method was applied to a field-based data set and was shown to generate more accurate dilution-adjusted breakthrough curves. The improved dilution-adjusted method presented here is simple, makes no assumptions regarding the concentrations of the nonreactive and reactive solutes in the injection and aquifer fluids, and easily allows for estimating reaction rates during push-pull tests.     

Building geospatial infrastructure

ABSTRACT

Many visions for geospatial technology have been advanced over the past half century. Initially researchers saw the handling of geospatial data as the major problem to be overcome. The vision of geographic information systems arose as an early international consensus. Later visions included spatial data infrastructure, Digital Earth, and a nervous system for the planet. With accelerating advances in information technology, a new vision is needed that reflects today’s focus on open and multimodal access, sharing, engagement, the Web, Big Data, artificial intelligence, and data science. We elaborate on the concept of geospatial infrastructure, and argue that it is essential if geospatial technology is to contribute to the solution of problems facing humanity.     

Compositional variability on the surface of 1 Ceres revealed through GRaND measurements of high‐energy gamma rays

High‐energy gamma rays (HEGRs) from Ceres’s surface were measured using Dawn's Gamma Ray and Neutron Detector (GRaND). Models of cosmic‐ray‐initiated gamma ray production predict that the HEGR flux will inversely vary with single‐layer hydrogen concentrations for Ceres‐like compositions. The measured data confirm this prediction. The hydrogen‐induced variations in HEGR rates were decoupled from the measurements by detrending the HEGR data with Ceres single‐layer hydrogen concentrations determined by GRaND neutron measurements. Models indicate that hydrogen‐detrended HEGR counting rates correlate with water‐free average atomic mass, which is denoted as <A>*. HEGR variations across Ceres’s surface are consistent with <A>* variations of ±0.5 atomic mass units. Chemical variations in the CM and CI chondrites, our closest analogs to Ceres’s surface, suggest that <A>* variations on Ceres are primarily driven by variations in the concentration of Fe, although other elements such as Mg and S could contribute. Dawn observations have shown that Ceres’s interior structure and surface composition have been modified by some combination of physical (i.e., ice‐rock fractionation) and/or chemical (i.e., alteration) processes that has led to variations in bulk surface chemistry. Locations of the highest inferred <A>* values, and thus possibly the highest Fe and least altered materials, tend to be younger, less cratered surfaces that are broadly associated with the impact ejecta of Ceres’s largest craters.     

Coronal heating events in high-cadence TRACE data

On March 23rd 1999 a set of TRACE (Transition Region and Coronal Explorer) observations were taken in support of Solar and Heliospheric Observatory (SOHO) / TRACE Joint Observing Program 83. The program is designed to look for coronal heating mechanisms operating at high cadence and to observe their dynamical effects on coronal loop density, temperature and magnetic structure. We present here a study of 27 small, dynamic brightening events seen in this data. These events are seen in the quiet-Sun areas surrounding the active region. The data itself consists of 157 171 Å 512×512 arc sec images at 1 arc sec resolution and 9 second cadence, a previously unavailable combination of cadence, resolution and image size. Three classes of events are introduced: complex, intermediate and simple. All three classes share the property of being dynamic on small time and length scales but differ in the complexity of their behavior. We find that the brightenings across all classes exhibit variations as part of a distribution of time scales (90–400 s) peaked around 228 s. The brightenings are no more than 5 arc sec in diameter. Motions between brightenings occur on time scales from 9 to 90 s and on length scales no greater than 10 arc sec. These motions have velocities estimated to be in the range 89–174 km s^?1. The position of these events in the spectrum of previously observed coronal heating events is discussed.