Species selection and assessment of eco-engineering effects of seedlings for biogeomorphological landscape experiments     

Ivar R. Lokhorst  Sjoukje I. de Lange  Gerard van Buiten  Sanja Selaković  Maarten G. Kleinhans 《地球表面变化过程与地形》2019,44(14):2922-2935

Landscape experiments of fluvial environments such as rivers and deltas are often conducted with live seedlings to investigate effects of biogeomorphological interactions on morphology and stratigraphy. However, such experiments have been limited to a single species, usually alfalfa (Medicago sativa), whereas important environments in nature have many different vegetation types and eco-engineering effects. Landscape experimentation would therefore benefit from a larger choice of tested plant species. For the purpose of experimental design our objective was to identify fast-germinating and fast-growing species and determine their sensitivity to flow conditions during and after settling, their maximum growth, hydraulic resistance and added bank strength. We tested germination time and seedling growth rate of 18 candidate species with readily available seeds that are fast growing and occur at waterlines, plus Medicago sativa as a control. We selected five species that germinate and develop within days and measured properties and eco-engineering effects depending on plant age and density, targeting typical experimental conditions of 0–0.3 m/s flow velocity and 0–30 mm water depth. Tested eco-engineering effects include bank strength and flow resistance. We found that Rumex hydrolapathum can represent riparian trees. The much smaller Veronica beccabunga and Lotus pedunculatus can represent grass and saltmarsh species as they grow in dense patches with high flow resistance but are readily erodible. Sorghum bicolor grows into tall, straight shoots, which add significantly to bank strength, but adds little flow resistance and may represent sparse hardwood trees. Medicago sativa also grows densely under water, suggesting a use for mangroves and perhaps peat. In stronger and deeper flows the application of all species changes accordingly. These species can now be used in a range of landscape experiments to investigate combined effects on living landscape patterns and possible facilitation between species. The testing and treatment methodology can be applied to new species and other laboratory conditions. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd. © 2019 The Authors Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd © 2019 The Authors Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.  相似文献   

The planet formation imager     

John D. Monnier  Stefan Kraus  Michael J. Ireland  Fabien Baron  Amelia Bayo  Jean-Philippe Berger  Michelle Creech-Eakman  Ruobing Dong  Gaspard Duchêne  Catherine Espaillat  Chris Haniff  Sebastian Hönig  Andrea Isella  Attila Juhasz  Lucas Labadie  Sylvestre Lacour  Stephanie Leifer  Antoine Merand  Ernest Michael  Stefano Minardi  Christoph Mordasini  David Mozurkewich  Johan Olofsson  Claudia Paladini  Romain Petrov  Jörg-Uwe Pott  Stephen Ridgway  Stephen Rinehart  Keivan Stassun  Jean Surdej  Theo ten Brummelaar  Neal Turner  Peter Tuthill  Kerry Vahala  Gerard van Belle  Gautam Vasisht  Ed Wishnow  John Young  Zhaohuan Zhu 《Experimental Astronomy》2018,46(3):517-529

The Planet Formation Imager (PFI, www.planetformationimager.org) is a next-generation infrared interferometer array with the primary goal of imaging the active phases of planet formation in nearby star forming regions. PFI will be sensitive to warm dust emission using mid-infrared capabilities made possible by precise fringe tracking in the near-infrared. An L/M band combiner will be especially sensitive to thermal emission from young exoplanets (and their disks) with a high spectral resolution mode to probe the kinematics of CO and H₂O gas. In this paper, we give an overview of the main science goals of PFI, define a baseline PFI architecture that can achieve those goals, point at remaining technical challenges, and suggest activities today that will help make the Planet Formation Imager facility a reality.  相似文献   

Automated Analyte Separation by Ion Chromatography Using a Cobot Applied to Geological Reference Materials for Li Isotope Composition     

Marie L. Kuessner  Alkiviadis Gourgiotis  Gerard Manhs  Julien Bouchez  Xu Zhang  Jrme Gaillardet 《Geostandards and Geoanalytical Research》2020,44(1):57-67

The demand for large and reliable data sets on isotopic composition has increased in geochemistry and environmental sciences over recent years. We present an automated ion chromatographic separation method using a robotic pipetting arm, termed ‘ChemCobOne’, to reduce sample separation time. Its performance was tested for lithium isotope separation in geological reference materials using a single‐step separation with HCl (0.2 mol l^?1) and a 2 ml resin volume. This refined lithium purification method does not forfeit precision, accuracy or purity compared with manual sample processing. In addition, a δ⁷Li value for NASS‐6 of 30.99 ± 0.50‰ (2s) (95% CI = 0.14‰, n = 44) was determined and the first δ⁷Li values for the granite rock reference material GS‐N (?0.57 ± 0.25‰ (2s), 95% CI = 0.15‰, n = 15), and for the soil reference material NIST SRM 2709a (?0.37 ± 0.67‰ (2s), 95% CI = 0.15‰, n = 63) are proposed.  相似文献   

Observations of the initial 3D flow from a ship's propeller     

Wei-Haur Lam  Gerard Hamill  Desmond Robinson  Srinivasan Raghunathan 《Ocean Engineering》2010,37(14-15):1380-1388

The present paper was aimed at presenting the time-averaged velocity and turbulence intensity at the initial plane from a ship's propeller. The flow characteristics of a ship's propeller jet are of particular interest for the researchers investigating the jet induced seabed damage as documented in the previous studies. Laser Doppler Anemometry (LDA) measurements show that the axial component of velocity is the main contributor to the velocity magnitude at the initial plane of a ship's propeller jet. The tangential component contributes to the rotation while the radial component which contributes to the diffusion, are the second and third largest contributors to the velocity magnitude. The maximum tangential and radial velocity components at the initial plane are approximately 82% and 14% of the maximum axial velocity component, respectively. The axial velocity distribution at the initial plane shows two peaked ridges with a low velocity core at the rotation axis. The turbulence intensity distribution shows a three-peaked profile at the initial plane.  相似文献   

In Situ measurement of transverse isotropy in shallow-water marine sediments     

Patricia A. Berge  Subhashis Mallick  Gerard J. Fryer  Noël Barstow  Jerry A. Carter  George H. Sutton  John I. Ewing 《Geophysical Journal International》1991,104(2):241-254

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Seismic waves in stratified anisotropic media   总被引：4，自引：0，他引：4  

Gerard J. Fryer  L. Neil Frzzer 《Geophysical Journal International》1984,78(3):691-710

Summary. The response of a structure composed of anisotropic strata can be built up from the reflection and transmission properties of individual interfaces using a slightly modified version of the recursion scheme of Kennett. This scheme is conveniently described in terms of scatterer operators and scatterer products. The effects of a free surface and the introduction of a simple point source at any depth can be accommodated in a manner directly analogous to the treatment for isotropic structures. As in the isotropic case the results so obtained are stable to arbitrary wavenumbers. For isotropic media, synthetic seismograms can be constructed by computing the structure response as a function of frequency and radial wavenumber, then performing the appropriate Fourier and Hankel transforms to obtain the wavefield in time-distance space. Such a scheme is convenient for any system with cylindrical symmétry (including transverse isotropy). Azimuthally anisotropic structures, however, do not display cylindrical symmétry; for these the transverse component of the wavenumber vector will, in general, be non-zero, with the result that phase, group, and energy velocities may all diverge. The problem is then much more conveniently addressed in Cartesian coordinates, with the frequency-wavenumber to time-distance transformation accomplished by 3-D Fourier transform.  相似文献   

The orientation of pre-transient coronal magnetic fields     

Gerard Trottet  R. M. MacQueen 《Solar physics》1980,68(1):177-186

Loop-like white light coronal transients are generally believed to be nearly planar sheets which are thin compared to the loop extent; however, this picture may be questioned since virtually no observations (of the more than 100 transient events observed during 1973–74 Skylab period) show such loops edge-on. From the group of transient events studied by Munro etal. (1979) for which definite surface associations exist, we find loop transients are strongly correlated with filament regions where the filament axis was oriented north-south. From direct soft X-ray observations of an expanding arch, the possible identification of the soft X-ray signature of footpoints of transient loops, and monochramatic observations of low coronal loops, we infer that loop-like coronal transients have their origin in low-lying coronal loops nearly co-planar with the north-south aligned filament axis. The situation with respect to non-loop events is less clear; such events apparently often arise from more complex filament geometries. Possible reasons for the preference of transients to arise from north-south filament-oriented regions are discussed.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

The structure of coronal magnetic loops     

Riccardo Giachetti  Gerard Van Hoven  Claudio Chiuderi 《Solar physics》1977,55(2):371-386

We present the second part of a complete theory for the plasma and field structure of a cool coronal arch, corresponding to those observed in the EUV from Skylab. The global magneto-hydrodynamic (MHD) stability of a previously described equilibrium-loop model is evaluated, and compared with that of an unmodified ambient force-free field. The influence of the photospheric boundary condition is also evaluated, producing a specification of stability limits which depend on the relative field and plasma pressures and scale widths. The resulting restrictions on the allowable field configuration of a coronal loop are then compared with observed values. The implications of this general method for deducing small-scale coronal magnetic-field structure from the measured plasma profile of an emissive feature are also described.  相似文献   

Apollo 15 and 16 results of the integrated geochemical experiment     

I. Adler  J. I. Trombka  P. Lowman  R. Schmadebeck  H. Blodget  E. Eller  L. Yin  R. Lamothe  G. Osswald  J. Gerard  P. Gorenstein  P. Bjorkholm  H. Gursky  B. Harris  J. Arnold  A. Metzger  R. Reedy 《Earth, Moon, and Planets》1973,7(3-4):487-504

A number of experiments carried in orbit on the Apollo 15 and 16 spacecraft were used in the compositional mapping of the lunar surface. The observations involved measurements of secondary (fluorescent) X-rays, gamma rays and alpha particle emissions. A large scale compositional map of over 20% of the lunar surface was obtained for the first time. It was possible to demonstrate significant chemical differences between the mare and the highlands, to find specific areas of high radioactivity and to learn something about the composition of the Moon's hidden side.Paper dedicated to Professor Harold C. Urey on the occasion of his 80th birthday on 29 April 1973.  相似文献   

Evaluating approximations for halo merging histories     

Rachel S. Somerville  Gerard Lemson  Tsafrir S. Kolatt  Avishai Dekel 《Monthly notices of the Royal Astronomical Society》2000,316(3):479-490

We study the merging history of dark matter haloes in N -body simulations and semi-analytical 'merger trees' based on the extended Press–Schechter (EPS) formalism. The main focus of our study is the joint distribution of progenitor number and mass as a function of redshift and parent halo mass. We begin by investigating the mean quantities predicted directly by the Press–Schechter (PS) and EPS formalism, such as the halo mass and conditional mass functions, and compare these predictions with the results of the simulations. The higher moments of this distribution are not predicted by the EPS formalism alone and must be obtained from the merger trees. We find that the Press–Schechter model deviates from the simulations at the level of 30–50 per cent on certain mass scales, and that the sense of the discrepancy changes as a function of redshift. We show that this discrepancy is reflected in the higher moments of the distribution of progenitor mass and number. We investigate some related statistics such as the accretion rate and the mass ratio of the largest two progenitors. For galaxy sized haloes ( M ∼10¹² M_⊙), we find that the merging history of haloes, as represented by these statistics, is well reproduced in the merger trees compared with the simulations. The agreement deteriorates for larger mass haloes. We conclude that merger trees based on the extended Press–Schechter formalism provide a reasonably reliable framework for semi-analytical models of galaxy formation.  相似文献