Disk models for cataclysmic variables

This paper presents disk models for cataclysmic variables in which convection in the central layers has been included. The calculation of the vertical structure at different points is presented. The models have a central mass of 1M _⊙ and matter fluxes of 10^?9, 10^?8, and 10^?7 M _⊙ yr^?1. The corresponding luminosities are 1.86, 1.86×10 and 1.86×10² L _⊙.     

A unified state model of orbital trajectory and attitude dynamics

The trajectory and attitude dynamics of an orbital spacecraft are defined by a unified state model, which enables efficient and rapid machine computation for mission analysis, orbit determination and prediction, satellite geodesy and reentry analysis. The state variables are momenta — a general form for attitude, and a parametric form for orbital motion. The orbital parameters are the velocity state characteristics of the orbital hodograph. The coordinate variables are sets of four Euler parameters, which define the rotation transformation by the quaternion algebra. The unified state model possesses many analytical properties which are invaluable for dynamical system synthesis, numerical analysis and machine solution: regularization, unified matrix algebra, state graphs and transforms. The analytic partials of position and velocity with the state and coordinate variables are presented, as well as representative perturbation functions such as air drag, gravitational potential harmonics, and propulsion thrust.     

Quantifying contributions of snowmelt water to streamflow using graphical and chemical hydrograph separation

In this study, we characterize the snowmelt hydrological response of nine headwater watersheds in southeast Wyoming by separating streamflow into three components using a combination of tracer and graphical approaches. First, continuous 15-min records of specific conductance (SC) from 2016 to 2018 were used to separate streamflow into annual contributions, representing water that contributes to streamflow in a given year that entered the watershed in the same year being considered, and perennial contributions, representing water that contributes to streamflow in a given year that entered the watershed in previous years. Then, diurnal streamflow cycles occurring during the snowmelt season were used to graphically separate annual contributions into rapid diurnal snowmelt contributions, representing water with the relatively fastest hydrological response and shortest residence time, and delayed annual contributions, representing water with relatively longer residence time in the watershed before becoming streamflow. On average, mean annual total streamflow was comprised of between 22% and 46% perennial contributions, 7% and 14% rapid diurnal snowmelt contributions, and 46% and 55% delayed annual contributions across the watersheds. A hysteresis index describing SC-discharge patterns indicated that, annually, most watersheds showed negative, concave, anti-clockwise hysteretic direction suggesting faster flow pathways dominate streamflow on the rising limb of the annual hydrograph relative to the falling limb. At the daily timescale during snowmelt-induced diurnal streamflow cycles, hysteresis was negative, but with a clockwise direction, implying that rapid diurnal snowmelt contributions generated from the concurrent daily snowmelt, with lower SC, arrived after delayed annual contribution peaks and preferentially contributed on the falling limb of diurnal cycles. South-facing watersheds were more susceptible to early season snowmelt at slower rates, resulting in less annual and more perennial contributions. Conversely, north-facing watersheds had longer snow persistence and larger proportions of annual contributions and rapid diurnal snowmelt contributions. Watersheds with surficial geology dominated by glacial deposits had a lower proportion of rapid diurnal snowmelt contributions compared to watersheds with large percentages of bedrock surficial geology.     

Isotope mixing models require individual isotopic tracer content for correct quantification of sediment source contributions

The use of isotopic tracers for sediment source apportionment is gaining interest with recent introduction of compound‐specific stable isotope tracers. The method relies on linear mixing of source isotopic tracers, and deconvolution of a sediment mixture initially quantifies the contribution of sources to the mixture's tracer signature. Therefore, a correction to obtain real sediment source proportions is subsequently required. As far as we are aware, all published studies to date have used total isotopic tracer content or a proxy (e.g., soil carbon content) for this post‐unmixing correction. However, as the relationship between the isotopic tracer mixture and the source mixture is different for each isotopic tracer, post‐unmixing corrections cannot be carried out with one single factor. This contribution presents an isotopic tracer model structure—the concentration‐dependent isotope mixing model (CD‐IMM)—to overcome this limitation. Herein, we aim to clarify why the “conventional” approach to converting isotopic tracer proportions to source proportions using a single factor is wrong. In an initial mathematical assessment, error incurred by not using CD‐IMM (NCD‐IMM) in unmixing two sources with two isotopic tracers showed a complex relation as a function of relative tracer contents. Next, three artificial mixtures with different proportions of three soil sources were prepared and deconvoluted using ¹³C of fatty acids using CD‐IMM and NCD‐IMM. Using NCD‐IMM affected both accuracy (mean average error increased up to a threefold compared with the CD‐IMM output) and precision (interquartile range was up to 2.5 times larger). Finally, as an illustrative example, the proportional source contribution reported in a published study was recalculated using CD‐IMM. This resulted in changes in estimated source proportions and associated uncertainties. Content of isotopic tracers is seldom reported in published work concerning use of isotopic tracers for sediment source partitioning. The magnitude of errors made by miscalculation in former studies is therefore difficult to assess. With this contribution, we hope the community will acknowledge the limitations of prior approaches and use a CD‐IMM in future studies.     

Homogenization of spatial patterns of hydrologic response in artificially drained agricultural catchments

Anthropogenic modifications to the landscape, with agricultural activities being a primary driver, have resulted in significant alterations to the hydrologic cycle. Artificial drainage, including surface and subsurface drainage (tile drains), is one of the most extensive manipulations in agricultural landscapes and thus is expected to provide a distinct signature of anthropogenic modification. This study adopts a data synthesis approach in an effort to characterize the signature of artificial subsurface drainage. Daily discharge data from 24 basins across the state of Iowa, which encapsulate a range of anthropogenic modifications, are assessed using a variety of flow metrics. Results indicate that the presence of artificial subsurface drainage leads to a homogenization of landscape hydrologic response. Non‐tiled watersheds exhibit a decrease in the area‐normalized peak discharge and an increase in the baseflow ratio (baseflow/streamflow) with increases in the spatial scale, while scale invariance is apparent in tiled basins. Within‐basin variability in hydrograph recession coefficients also appears to decrease with increases in the proportion of the catchment that is artificially drained. Finally, the differences between tiled and non‐tiled landscapes disappear at scales greater than approximately 2200 km², indicating that this may be a threshold scale for studying the effects of tile drainage. This decrease in within‐basin variability and the scale invariance of hydrologic metrics in artificially drained watersheds are attributed to the creation of a bypass flow hydrologic pathway that bypasses the complexity of the catchment travel paths. Spatial homogeneity in responses implies that it may be possible to develop more parsimonious hydrologic models for these regions. Copyright © 2013 John Wiley & Sons, Ltd.     

Origin and age of The Hillocks and implications for post‐glacial landscape development in the upper Lake Wakatipu catchment,New Zealand

Ambiguous landscape histories can arise from equivocal or incomplete geomorphological, sedimentological or geochronological evidence. In this study, we apply quantitative analyses to robustly assess the origin and age of a field of rounded mounds, known as ‘The Hillocks’. Using clast analysis, the sediment is shown to be consistent with a landslide origin but inconsistent with other glacial sediments in the region. Cosmogenic ¹⁰Be exposure age dating suggests The Hillocks formed ~8 ka. Ground‐penetrating radar reveals that the deposit rests upon deltaic foreset beds; combined with topographical data, we calculate a deposit volume of ~15–27 M m³, consistent with the estimated volume of the proposed source area. Overall, our data support a rock avalanche origin, indicating that by 8 ka the valley was ice‐free at The Hillocks’ location, and the level of Lake Wakatipu was lower than 340 m asl by this time. The Dart River delta shoreline was situated somewhere between The Hillocks and the present day shoreline at that time, and has prograded at a maximum average rate of 1 m a^?1 since ~8 ka. These findings are significant given the lack of landforms by which to constrain glacial or post‐glacial landscape histories in this region of New Zealand. Copyright © 2019 John Wiley & Sons, Ltd.     

Numerical modeling of strongly coupled microscale multiphase flow and solid deformation

When fluid flows in porous media under subsurface conditions, significant deformation can occur. Such deformation is dependent on structural and phase characteristics. In this paper, we investigate the effect of multiphase flow on the deformation of porous media at the pore scale by implementing a strongly coupled partitioned solver discretized with finite volume (FV) technique. Specifically, the role of capillary forces on grain deformation in porous media is investigated. The fluid and solid subdomains are meshed using unstructured independent grids. The model is applied for solving multiphase coupled equations and is capable of capturing pore scale physics during primary drainage by solving the Navier-Stokes equation and advecting fluid indicator function using volume of fluid (VOF) while the fluid is interacting with a nonlinear elastic solid matrix. The convergence of the coupled solver is accelerated by Aitken underrelaxation. We also reproduce geomechanical stress conditions, at the pore scale, by applying uniaxial stress on the solid while simultaneously solving the multiphase fluid-solid interaction problem to investigate the effect of external stress on fluid occupancy, velocity-field distribution, and relative permeability. We observe that the solid matrix exhibits elasto-capillary behavior during the drainage sequence. Relative permeability endpoints are shifted on the basis of the external stress exerted.