The cultivation of natural stocks     

C.C. Lucas 《Marine pollution bulletin》1979,10(3):69-73

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Lava lakes on Io: observations of Io's volcanic activity from Galileo NIMS during the 2001 fly-bys     

Rosaly M.C Lopes  Lucas W Kamp  Peter Mouginis-Mark  Jani Radebaugh  Jason Perry  R.W Carlson  the Galileo NIMS  SSI Teams 《Icarus》2004,169(1):140-174

Galileo's Near-Infrared Mapping Spectrometer (NIMS) obtained its final observations of Io during the spacecraft's fly-bys in August (I31) and October 2001 (I32). We present a summary of the observations and results from these last two fly-bys, focusing on the distribution of thermal emission from Io's many volcanic regions that give insights into the eruption styles of individual hot spots. We include a compilation of hot spot data obtained from Galileo, Voyager, and ground-based observations. At least 152 active volcanic centers are now known on Io, 104 of which were discovered or confirmed by Galileo observations, including 23 from the I31 and I32 Io fly-by observations presented here. We modify the classification scheme of Keszthelyi et al. (2001, J. Geophys. Res. 106 (E12) 33 025-33 052) of Io eruption styles to include three primary types: promethean (lava flow fields emplaced as compound pahoehoe flows with small plumes <200 km high originating from flow fronts), pillanian (violent eruptions generally accompanied by large outbursts, >200 km high plumes and rapidly-emplaced flow fields), and a new style we call “lokian” that includes all eruptions confined within paterae with or without associated plume eruptions). Thermal maps of active paterae from NIMS data reveal hot edges that are characteristic of lava lakes. Comparisons with terrestrial analogs show that Io's lava lakes have thermal properties consistent with relatively inactive lava lakes. The majority of activity on Io, based on locations and longevity of hot spots, appears to be of this third type. This finding has implications for how Io is being resurfaced as our results imply that eruptions of lava are predominantly confined within paterae, thus making it unlikely that resurfacing is done primarily by extensive lava flows. Our conclusion is consistent with the findings of Geissler et al. (2004, Icarus, this issue) that plume eruptions and deposits, rather than the eruption of copious amounts of effusive lavas, are responsible for Io's high resurfacing rates. The origin and longevity of islands within ionian lava lakes remains enigmatic.  相似文献   

Factors that contribute to the elongation of drumlins beneath the Green Bay Lobe,Laurentide Ice Sheet     

Lucas K. Zoet  J. Elmo Rawling III  Jacob B. Woodard  Nolan Barrette  David M. Mickelson 《地球表面变化过程与地形》2021,46(13):2540-2550

Drumlin shape has been hypothesized to correlate with ice-flow duration and slip speed, but modern-day analogues and the Coulomb nature of till render the basis of these correlations in question. The evolution of flow-parallel subglacial landforms is of importance for ice flow because the form drag they provide may be a dominant factor in regulating glacier slip speeds. Here we examine the relationship between drumlin shape and cumulative slip displacement (i.e. time-integrated slip speed) as a dominant glaciological control on drumlin shape. First, a new method is developed that allows slip speed to be estimated for deformable bedded glaciers along a flow line from an ice surface profile. Then, reconstructed surface profiles for ice margin chronologies of the Green Bay Lobe (GBL) are used to construct and estimate the spatially varying cumulative slip displacement for use in comparison with drumlin elongation ratios. We focus on a sector of the GBL near the central flow line where the geology is simple and glaciological controls are likely to dominate bedform development. Using Bayesian statistical analysis, a positive and statistically robust relationship between cumulative slip displacement and drumlin elongation ratio is found. Our analysis indicates that drumlin shape could be used to infer palaeo glacier slip speeds if time under the ice can be well constrained and geologic influences are minimal. These findings also suggest that drumlin-supplied drag could decrease with increased cumulative slip displacement in the absence of rigid geologic features that fix drumlin positions.  相似文献   

Distinct styles of fluvial deposition in a Cambrian rift basin   总被引：1，自引：0，他引：1  

Maurício G. M. Santos  Renato P. Almeida  Lucas P. S. Godinho  André Marconato  Nigel P. Mountney 《Sedimentology》2014,61(4):881-914

Process‐based and facies models to account for the origin of pre‐vegetation (i.e. pre‐Silurian) preserved fluvial sedimentary architectures remain poorly defined in terms of their ability to account for the nature of the fluvial conditions required to accumulate and preserve architectural elements in the absence of the stabilizing influence of vegetation. In pre‐vegetation fluvial successions, the repeated reworking of bars and minor channels that resulted in the generation and preservation of broad, tabular, stacked sandstone‐sheets has been previously regarded as the dominant sedimentary mechanism. This situation is closely analogous to modern‐day poorly vegetated systems developed in arid climatic settings. However, this study demonstrates the widespread presence of substantially more complex stratigraphic architectures. The Guarda Velha Formation of Southern Brazil is a >500 m‐thick synrift fluvial succession of Cambrian age that records the deposits and sedimentary architecture of three distinct fluvial successions: (i) an early rift‐stage system characterized by coarse‐grained channel elements indicative of a distributive pattern with flow transverse to the basin axis; and two coeval systems from the early‐ to climax‐rift stages that represent (ii) an axially directed, trunk fluvial system characterized by large‐scale amalgamated sandy braid‐bar elements, and (iii) a distributive fluvial system characterized by multi‐storey, sandy braided‐channel elements that flowed transverse to the basin axis. Integration of facies and architectural‐element analysis with regional stratigraphic basin analysis, palaeocurrent and pebble‐provenance analysis demonstrates the mechanisms responsible for preserving the varied range of fluvial architectures present in this pre‐vegetation, rift‐basin setting. Identified major controls that influenced pre‐vegetation fluvial sedimentary style include: (i) spatial and temporal variation in discharge regime; (ii) the varying sedimentological characteristics of distinct catchment areas; (iii) the role of tectonic basin configuration and its direct role in influencing palaeoflow direction and fluvial style, whereby both the axial and transverse fluvial systems undertook a distinctive response to syn‐depositional movement on basin‐bounding faults. Detailed architectural analyses of these deposits reveal significant variations in geometry, with characteristics considerably more complex than that of simple, laterally extensive, stacked sandstone‐sheets predicted by most existing depositional models for pre‐vegetation fluvial systems. These results suggest that the sheet‐braided style actually encompasses a varied number of different pre‐vegetation fluvial styles. Moreover, this study demonstrates that contemporaneous axial and transverse fluvial systems with distinctive architectural expressions can be preserved in the same overall tectonic and climatic setting.  相似文献   

Observational Investigation of the Statistical Properties of Surface-Layer Turbulence in a Suburban Area of São Paulo,Brazil: Objective Analysis of Scaling-Parameter Accuracy and Uncertainties     

da Silveira  Lucas Cardoso  de Oliveira  Amauri Pereira  Sánchez  Maciel Piñero  Codato  Georgia  Ferreira  Maurício Jonas  Marques Filho  Edson Pereira  Božnar  Marija Zlata  Mlakar  Primož 《Boundary-Layer Meteorology》2022,185(2):161-195

Boundary-Layer Meteorology - Statistical properties of turbulence, specifically variances of velocity components, temperature, water vapor, and carbon dioxide densities, are observationally...  相似文献   

Adsorption and affinity of Escherichia coli to different aggregate sizes of a silty clay soil     

Filipe BEHRENDS KRAEMER  Celio Ignaicio CHAGAS  Diego Julian COSENTINO  Lucas Alejandro GARIBALDI 《国际泥沙研究》2013,28(4):535-543

The sediments produced by water erosion are the main source of pollution of agricultural origin of surface water bodies. These sediments may be associated to bacteria, compromising the quality of nearby water bodies. Therefore, to understand this biological contamination, it is necessary to find out the adsorption capacity and bacterial affmity to aggregate sizes that may result in a differential sedimentation. To this end, in the present work, the distribution, adsorption capacity and affinity to different aggregate sizes of two strains of Escherichia coli in two liquid media of contrasting ionic strength were evaluated in a silty clay soil. The 〈2 μm fraction showed a higher proportion of bacteria than the other aggregate sizes （48%）, whereas among the fractions 〉2 μm, the 20-50μm fraction was the one that showed the highest bacterial adsorption in both liquid media （37.9%）. On the other hand, the highest values of bacterial affinity were found in the 20 to 50 lain fraction （coarse silt） in the low ionic strength media and 20--50 and 〉50 μm in the high ionic strength media. However, the bacterial strains used revealed only some trends in the modification of these variables. This work contributes to the development and implementation of strategies to mitigate pollution, such as control of sediment generation and its subsequent capture in filter strips.  相似文献   

A shallow though extensive H₂ 2.122-μm imaging survey of Taurus–Auriga–Perseus – I. NGC 1333, L1455, L1448 and B1     

C. J. Davis  P. Scholz  P. Lucas  M. D. Smith  A. Adamson 《Monthly notices of the Royal Astronomical Society》2008,387(3):954-968

We discuss wide-field near-infrared (near-IR) imaging of the NGC 1333, L1448, L1455 and B1 star-forming regions in Perseus. The observations have been extracted from a much larger narrow-band imaging survey of the Taurus–Auriga–Perseus complex. These H₂ 2.122-μm observations are complemented by broad-band K imaging, mid-IR imaging and photometry from the Spitzer Space Telescope , and published submillimetre CO   J = 3–2  maps of high-velocity molecular outflows. We detect and label 85 H₂ features and associate these with 26 molecular outflows. Three are parsec-scale flows, with a mean flow lobe length exceeding 11.5 arcmin. 37 (44 per cent) of the detected H₂ features are associated with a known Herbig–Haro object, while 72 (46 per cent) of catalogued HH objects are detected in H₂ emission. Embedded Spitzer sources are identified for all but two of the 26 molecular outflows. These candidate outflow sources all have high near-to-mid-IR spectral indices (mean value of  α∼ 1.4  ) as well as red IRAC 3.6–4.5 μm and IRAC/MIPS 4.5–24.0 μm colours: 80 per cent have [3.6]–[4.5] > 1.0 and [4.5]–[24] > 1.5. These criteria – high α and red [4.5]–[24] and [3.6]–[4.5] colours – are powerful discriminants when searching for molecular outflow sources. However, we find no correlation between α and flow length or opening angle, and the outflows appear randomly orientated in each region. The more massive clouds are associated with a greater number of outflows, which suggests that the star formation efficiency is roughly the same in each region.  相似文献   

Pressure and shear stress caused by raindrop impact at the soil surface: Scaling laws depending on the water depth          下载免费PDF全文

Amina Nouhou Bako  Frédéric Darboux  François James  Christophe Josserand  Carine Lucas 《地球表面变化过程与地形》2016,41(9):1199-1210

Raindrop impact is an important process in soil erosion. Through its pressure and shear stress, raindrop impact causes a significant detachment of the soil material, making this material available for transport by sheet flow. Thanks to the accurate Navier–Stokes equations solver Gerris, we simulate the impact of a single raindrop of diameter D, at terminal velocity, on water layers of different thickness h: , , D, 2D, in order to study pressures and shear stresses involved in raindrop erosion. These complex numerical simulations help in understanding precisely the dynamics of the raindrop impact, quantifying in particular the pressure and the shear stress fields. A detailed analysis of these fields is performed and self‐similar structures are identified for the pressure and the shear stress on the soil surface. The evolution of these self‐similar structures are investigated as the aspect ratio h/D varies. We find that the pressure and the shear stress have a specific dependence on the ratio between the drop diameter and the water layer thickness, and that the scaling laws recently proposed in fluid mechanics are also applicable to raindrops, paving the road to obtain effective models of soil erosion by raindrops. In particular, we obtain a scaling law formula for the dependence of the maximum shear stress on the soil on the water depth, a quantity that is crucial for quantifying erosion materials. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Links Between Weather Phenomena and Characteristics of Refractivity Measured by Precipitation Radar   总被引：1，自引：1，他引：0  

Lucas Besson  Chiraz Boudjabi  Olivier Caumont  Jacques Parent du Chatelet 《Boundary-Layer Meteorology》2012,143(1):77-95

Refractivity depends on meteorological parameters such as temperature and water vapour pressure and can be measured using a weather radar. A realistic atmospheric simulation from the Meso-NH numerical model is used in order to describe and establish the relation between refractivity and the dynamic and thermodynamic phenomena responsible for the development and propagation of convection. These investigations lead to discussion of the complementarity between the refractivity and the convective available potential energy. The relation observed between the refractivity signal and the meteorological parameters calls the refractivity measurement into question, since it is based on phase differentiation with time and space and can be degraded by phase aliasing problems. These aliasing problems increase with the radar frequency (perceptible in the S-band, serious in the C-band, and more serious in the X-band) and also with the integration range and sampling time. Thus, a statistical approach permits us to simulate the possibility of measuring the refractivity with operational radar during convective events. A typical case in the south-east region of France is selected to simulate measurements by radar (S-band, C-band, X-band) in convective systems, in order to evaluate the measurement feasibility, particularly in terms of phase ambiguity, related to temporal and spatial sampling, of a future implementation of the refractivity measurement over the French operational radar network. This numerical statistical approach is completed with a similar study using in-situ measurements performed at the Trappes station. The seasonal and diurnal dependencies of aliasing are investigated, leading to clarification of the impact of the turbulent fluxes on the refractivity measurement.  相似文献   

Possible evidence for underlying non‐linear dynamics in steep‐faced glaciodeltaic progradational ­successions     

Andrew Richards  Peter Phipps  Neil Lucas 《地球表面变化过程与地形》2000,25(11):1181-1200

Steep‐faced glaciodeltaic progradational successions are often studied in order to reconstruct the behaviour of the glacial feeder system, or changes in the sediment sink. This paper analyses the magnitude and frequency of depositional events associated with steep‐faced glacier‐fed progradational successions recorded in Scandinavia and Ireland. The successions exhibit depositional patterns that may be interpreted as a function of underlying non‐linear dynamics. A number of the sequences display fractal scaling in the frequency and thickness of foreset units. Other successions demonstrate chaotic patterns and strong relationships between delta‐front angle and bed thicknesses, suggesting that the progradation of such sequences is self‐organized, and to an extent occurs independently of forcing by the feeder system that provides sediment to the delta front. These patterns of sedimentation appear to be a function of the steepness of the delta front and/or the textural characteristics of the sediment. This paper provides further evidence for the simultaneous presence of order and chaos in Earth surface processes and calls into question the extent to which palaeoenvironmental reconstructions may be made from steep‐faced progradational successions. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献