On the incipient formation of bars and channels on alluvial fans     

Nicoletta Tambroni  Giovanni Seminara  Chris Paola 《地球表面变化过程与地形》2019,44(12):2479-2493

The morphodynamics of topographic expansion has been recently investigated both experimentally, by Sittoni et al., (2014) Shaw et al., (2018), and numerically Sittoni et al., 2014. Here, we study the basic mechanism that governs the evolution of topographic and expansions and explore the instability of the bottom topography under conditions of steady but spatially expanding flow. We model the expanding flow via a by configuration where water and sediments are supplied from a central hole and flow on a cone shaped surface confined by lateral walls. The governing equations are the shallow-water equations coupled with the Exner equation, written in cylindrical coordinates. We initially approach the problem analytically by considering the conditions required for the basic state, consisting of a pure radial flow and bottom profile, to lose stability to small amplitude perturbations. This analysis suggests that more than one mode may be unstable, encouraging us to extend the analysis to the nonlinear regime. We do this through numerical modeling of the full governing equations, which allows us to predict the establishment of a bar pattern whose features are similar to those experimentally observed. Two prominent features of the finite-amplitude bar pattern are (1) bar apices are distributed at a radial distance from the inflow consistent with work of Shaw et al. (2018); and (2) that the flow aspect ratio of the interbar areas remain high without provoking further instability. Both features imply that in general expansion acts to reduce bar development relative to an equivalent rectilinear flow. © 2019 John Wiley & Sons,  Ltd.  相似文献   

A response to ‘A comment on geographically weighted regression with parameter-specific distance metrics’     

Binbin Lu  Chris Brunsdon  Martin Charlton  Paul Harris 《International journal of geographical information science》2019,33(7):1300-1312

In this article, we respond to ‘A comment on geographically weighted regression with parameter-specific distance metrics’ by Oshan et al. (2019), published in this journal, where several concerns on the parameter-specific distance metric geographically weighted regression (PSDM GWR) technique are raised. In doing so, we review the developmental timeline of the multiscale geographically weighed regression modelling framework with related and equivalent models, including flexible bandwidth GWR, conditional GWR and PSDM GWR. In our response, we have tried to answer all the concerns raised in terms of applicability, veracity, interpretability and computational efficiency of the PSDM GWR model.  相似文献   

Compositional variability on the surface of 1 Ceres revealed through GRaND measurements of high‐energy gamma rays          下载免费PDF全文

David J. Lawrence  Patrick N. Peplowski  Andrew W. Beck  William C. Feldman  Thomas H. Prettyman  Chris T. Russell  Michael J. Toplis  Jack T. Wilson  Eleonora Ammannito  Julie C. Castillo‐Rogez  M. C. DeSanctis  Scott C. Mest  Adrian Neesemann 《Meteoritics & planetary science》2018,53(9):1805-1819

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.  相似文献   

Methods in Feeld Geology by F. Moseley. W. H. Freeman and Co., Oxford,England, 1981. 211 pp. (including 146 illustrations). Price: £6·50 (Paper); £12·00 (Hardback)     

I. M. Simpson 《Geological Journal》1982,17(2):159-159

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The angular correlation function of K^'∼19.5 galaxies and the detection of a cluster at z=0.775     

Nathan Roche  Stephen A. Eales  Hans Hippelein  Chris J. Willott 《Monthly notices of the Royal Astronomical Society》1999,306(3):538-550

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Eight new δ Scuti stars     

Chris Koen  Ruby Van Rooyen  Francois Van Wyk  Freddy Marang 《Monthly notices of the Royal Astronomical Society》1999,309(4):1051-1062

HD 23194, a member of the Pleiades, was found to pulsate with a period of about 30 min. The literature on the star is reviewed, and it is concluded that it may be a marginal Am star in a binary system. HD 95321 is an evolved Am ( ρ Puppis) star with a 5.1-h periodicity. Mode identification of its pulsation, based on multicolour photometry, suggests that the oscillation is probably non-radial with ℓ=2. We also report on the discovery of six other new δ Scuti stars, some of which may be pulsating in gravity modes.  相似文献   

The 1989 May outburst of the soft X-ray transient GS 2023+338 (V404 Cyg)     

Piotr T. &#;ycki  †  Chris Done †  David A. Smith 《Monthly notices of the Royal Astronomical Society》1999,309(3):561-575

We reanalyse archival Ginga data of the soft X-ray transient source GS 2023+338 covering the beginning of its 1989 May outburst. The source showed a number of rather unusual features: very high and apparently saturated luminosity, dramatic flux and spectral variability (often on ∼1 s time-scale), and generally very hard spectrum, with no obvious soft thermal component characteristic for soft/high state.
We describe the spectrum obtained at the maximum of flux and we demonstrate that it is very different from spectra of other soft X-ray transients at similar luminosity. We confirm previous suggestions that the dramatic variability was the result of heavy and strongly variable photoelectric absorption. We also demonstrate that for a short time the spectrum of the source did look like a typical soft/high state spectrum but that this coincided with very heavy absorption.  相似文献   

A petrographical and geochemical study of quartzose nodules,country rocks,and dike rocks from the Upheaval Dome structure,Utah     

Christian KOEBERL  J. B. PLESCIA  Chris L. HAYWARD  Wolf Uwe REMOLD 《Meteoritics & planetary science》1999,34(6):861-868

Abstract— Upheaval Dome, in Canyonlands National Park, Utah, USA, is a unique structure on the Colorado Plateau. It has earlier been interpreted as an impact structure or as a pinched-off salt diapir. Some subrounded quartzose fragments were found in a ring depression near the eastern margin of the structure and, based on vesicularity and apparent flow structure, the fragments were interpreted by early researchers as “impactites.” Our petrographic studies show no indication of a high-temperature history and are in agreement with a slow, low-temperature formation of the quartz nodules. Composi***ionally, the lag deposit samples are almost pure SiO₂. They show no chemical similarity to any of the possible target rocks (e.g., Navajo Sandstone), from which they should have formed by melting if they were impactites. Instead, the samples have relatively high contents of elements that indicate fluid interaction (e.g., hydrothermal growth), such as As, Sb, Ba, and U, and show positive Ce anomalies. Thus, we interpret the “lag deposit samples” as normal low-temperature (hydrothermally-grown?) quartz that show no indication of being impact-derived. In addition, a petrographic and geochemical analysis of a series of dike samples yielded no evidence for shock metamorphism or a meteoritic component.  相似文献   

Self-Similar Fold Evolution Under Prescribed End-Shortening     

Chris J. Budd  Giles W. Hunt  Mark A. Peletier 《Mathematical Geology》1999,31(8):989-1005

The evolution of single-layer folds under prescribed end-shortening conditions displays folds of varying wavelength. We investigate a simple model of this kind and characterize the long-term behaviour of fold profiles. In particular we determine the evolution of the axial load and the variation of the wavelength, and we show that fold profiles are highly self-similar.  相似文献   

Glacial Geomorphology of Bonney Drift, Taylor Valley, Antarctica   总被引：1，自引：0，他引：1  

S.M. Higgins  George H. Denton  & Chris H. Hendy 《Geografiska Annaler: Series A, Physical Geography》2000,82(2-3):365-389

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