Equal-mobility bed load transport in a small, step-pool channel in the Ouachita Mountains     

Daniel A. Marion  Frank Weirich 《Geomorphology》2003,55(1-4):139

Equal-mobility transport (EMT) of bed load is more evident than size-selective transport during near-bankfull flow events in a small, step-pool channel in the Ouachita Mountains of central Arkansas. Bed load transport modes were studied by simulating five separate runoff events with peak discharges between 0.25 and 1.34 m³/s (1.0- to 1.6-year recurrence intervals) in a natural channel using controlled releases from a storage tank. EMT occurrence was investigated using four different bed load relationships suggested by previous research. With each of these approaches, the relationship of a given bed load characteristic (D_max, distribution percentile, displacement distance and skewness) to some independent factor (τ_c*, τ and grain size) was assessed to determine which transport mode was evident. Regression models derived using combinations of these four relationships with different datasets provide seven separate tests. Five of the seven tests indicate that EMT occurred or was predominant. Several reasons may explain the apparent contradictory results, but the confounding effects of changes in the structural arrangements of bed material prior to or during the events seem particularly important.  相似文献   

Simultaneous and Sensitive HPLC Determination of Mono‐ and Disaccharides,Uronic Acids,and Amino Sugars after Derivatization by Reductive Amination     

Klaus Fischer  Marion Wacht  Axel Meyer 《洁净——土壤、空气、水》2003,31(2):134-144

The reductive amination of low‐molecular‐weight saccharides, uronic acids, and amino sugars, followed by a separation of the derivates by means of ion‐pair chromatography or RP‐HPLC, offers an interesting alternative to HPAEC‐PAD for the environmental analysis of these compounds. Under this aspect various potential amination reagents, i.e., p‐amino‐benzoic acid (p‐AMBA), p‐AMBA propyl ester, 1‐aminopyrene, 2‐(2‐aminophenyl)indole, and 4‐aminoazobenzene, were tested with regard to the formation of derivates and to the chromatographic properties of the formed derivates. p‐AMBA, p‐AMBA propyl ester and 4‐aminoazobenzene proved to be especially suited, because they facilitate the amination of all carbohydrate reference components together with a complete separation and sensible detection (detection limits < 0.5 mg/L) of the derivates. Mainly the following elution sequence was ascertained: amino sugars (hexosamines) / disaccharide(s) / monosaccharides (hexoses) / hexuronic acid(s) / N‐acetyl‐D‐glucosamine. Detection limits down to 0.1 μmol/L were realized using p‐AMBA as reagent, facilitating the determination of the target compounds in landfill leachates and lysimeter percolates. Applying the p‐AMBA propyl ester for derivatization, chromatographic interferences with weakly retained derivates and the coelution of the reagent with its galactosamine derivate can be avoided, since the ester elutes after its derivates unlike p‐AMBA itself.  相似文献   

Interference processes on scouring at bed sills     

Mario A. Lenzi  Andrea Marion  Francesco Comiti 《地球表面变化过程与地形》2003,28(1):99-110

The local scouring downstream of bed sills forming a sequence for bed stabilization in steep channels has been investigated in a laboratory flume. The initial bed slopes ranged from 0·078 to 0·148. The bed alluvium was characterised by a non‐uniform grain size distribution. The results show that when the ratio between the critical water depth h_c and the sill spacing L rises above a characteristic value the scouring dynamics become heavily affected by the presence of the downstream sill, associated with the onset of a form of “interference” which renders the scouring process less effective. The difference with an “undisturbed” case is demonstrated. Self‐affinity of scour holes is confirmed and the scour length appears to be the reference parameter from which the scour depth might be evaluated. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Tropospheric water vapour soundings by lidar at high Arctic latitudes     

Michael Gerding  Christoph Ritter  Marion Müller  Roland Neuber 《Atmospheric Research》2004,71(4):289-302

Ground-based lidars can provide continuous observations of tropospheric humidity profiles using the Raman scattering of light by water vapour and nitrogen molecules. We will present specific humidity profiles obtained at the high Arctic location Ny-Ålesund (Spitsbergen, 79°N). Under nighttime conditions the observations cover a range from about 500 m altitude up to the upper troposphere. Daylight limits the observations to the lower troposphere, depending on atmospheric transmission and the water vapour content. In a case study on 29 January, simultaneous observations of humidity and aerosol extinction show distinct differences in the various altitudes during the advection of aerosol-rich air masses. In the boundary layer, the aerosol is less affected by the humidity. In the free troposphere, the lidar ratio was observed to be up to 60 sr with some evidence for the uptake of water vapour by the aerosol particles. In another case study from 28 February 2002, the influence of the mean wind direction and the orography on the water vapour concentration near the ground and in the free troposphere will be discussed. During wintertime, a humidity inversion up to about 1.5 km altitude with dry air near the ground has frequently been found with wind from the southeast. Such local effects and small-scale structures observed by stationary lidar mostly cannot be resolved by other sounding methods like passive satellite soundings.  相似文献   

Magmatische und metasomatische Prozesse in Graniten,insbesondere Zweiglimmergraniten     

O. H. Erdmannsdörffer  Marion Peters-Radzyk 《Contributions to Mineralogy and Petrology》1948,1(2-3):213-250

Ohne Zusammenfassung  相似文献   

Change in carbon flux (1960–2015) of the Red River (Vietnam)     

Thi Phuong Quynh Le  Nhu Da Le  Viet Nga Dao  Emma Rochelle-Newall  Thi Mai Huong Nguyen  Cyril Marchand  Thi Thuy Duong  Thi Xuan Binh Phung 《Environmental Earth Sciences》2018,77(18):658

Global riverine carbon concentrations and fluxes have been impacted by climate and human-induced changes for many decades. This paper aims to reconstruct the longterm carbon concentrations and carbon fluxes of the Red River, a system under the coupled pressures of environmental change and human activity. Based on (1) the relationships between particulate and dissolved organic carbon (POC, DOC) or dissolved inorganic carbon (DIC), and suspended sediments (TSS) or river water discharge and on (2) the available detailed historical records of river discharge and TSS concentration, the variations of the Red River carbon concentration and flux were estimated for the period 1960–2015. The results show that total carbon flux of the Red River averaged 2555?±?639 kton C year^?1. DIC fluxes dominated total carbon fluxes, representing 64% of total, reflecting a strong weathering process from carbonate rocks in the upstream basin. Total carbon fluxes significantly decreased from 2816 kton C year^?1 during the 1960s to 1372 kton C year^?1 during the 2010s and showed clear seasonal and spatial variations. Organic carbon flux decreased in both quantity and proportion of the total carbon flux from 40.9% in 1960s to 14.9% in 2010s, reflecting the important impact of dam impoundment. DIC flux was also reduced over this period potentially as a consequence of carbonate precipitation in the irrigated, agricultural land and the reduction of the Red River water discharge toward the sea. These decreases in TSS and carbon fluxes are probably partially responsible for different negatives impacts observed in the coastal zone.  相似文献   

Nocturnal temperature changes over tropics during CAWSES-III campaign: Comparison with numerical models and satellite data     

U. Jaya Prakash Raju  P. Keckhut  Y. Courcoux  M. Marchand  S. Bekki  B. Morel  H. Bencherif  A. Hauchecorne 《Journal of Atmospheric and Solar》2010,72(16):1171-1179

In the frame of the third CAWSES tidal campaign in June–August 2007, lidar and satellite data were collected and compared with numerical models. Continuous nocturnal middle atmospheric temperature measurements performed with a Rayleigh lidar located at La Reunion Island (20.8°S–55.5°E) were obtained for three subsequent nights. The results clearly show the presence of tidal components with a downward phase propagation. Comparisons with SABER satellite data show good agreement on tidal amplitude; however, some differences on the structures are reported probably due to the zonal nature of the retrieval provided by the SABER data. The observed tidal components are compared with two different numerical models such as the 2D global scale wave model and the 3D-GCM LMDz-REPROBUS. Both models reveal good agreement with temperature lidar patterns, while simulated tidal amplitudes are smaller by a factor of around 2–2.5 K.  相似文献   

SIESTA, a time domain, general purpose simulation program for the VIRGO experiment     

B. Caron  L. Derome  R. Flaminio  X. Grave  F. Marion  B. Mours  D. Verkindt  F. Cavalier  A. Vicer 《Astroparticle Physics》1999,10(4):2650-386

In this paper we present the simulation program that has been developed for the VIRGO gravitational wave detection experiment. Although this program — SIESTA — is still evolving, it has reached a stage where the design requirements have been largely fulfilled. We first remind the needs and the choices which have steered the program design and led to the present structure. The contents of the program is then reviewed, the performances are discussed, and some typical applications are briefly described.  相似文献   

Seasonal changes in blood cells of Arctic char (Salvelinus alpinus L.) from a high mountain lake     

Rudolf Hofer  Marion Stoll  Nikolaus Romani  Franz Koch  Holmer Sordyl 《Aquatic Sciences - Research Across Boundaries》2000,62(4):308-319

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A first application of a marine inductive source electromagnetic configuration with remote electric dipole receivers: Palinuro Seamount,Tyrrhenian Sea          下载免费PDF全文

Roxana Safipour  Sebastian Hölz  Marion Jegen  Andrei Swidinsky 《Geophysical Prospecting》2018,66(7):1415-1432

We study a new marine electromagnetic configuration that consists of a ship‐towed inductive source transmitter and a series of remote electric dipole receivers placed on the seafloor. The approach was tested at the Palinuro Seamount in the southern Tyrrhenian Sea, at a site where massive sulphide mineralization has been previously identified by shallow drilling. A 3D model of the Palinuro study area was created using bathymetry data, and forward modelling of the electric field diffusion was carried out using a finite volume method. These numerical results suggest that the remote receivers can theoretically detect a block of shallowly buried conductive material at up to ～100 m away when the transmitter is located directly above the target. We also compared the sensitivity of the method using either a horizontal loop transmitter or a vertical loop transmitter and found that when either transmitter is located directly above the mineralized zone, the vertical loop transmitter has sensitivity to the target at a farther distance than the horizontal loop transmitter in the broadside direction by a few tens of metres. Furthermore, the vertical loop transmitter is more effective at distinguishing the seafloor conductivity structure when the vertical separation between transmitter and receiver is large due to the bathymetry. As a horizontal transmitter is logistically easier to deploy, we conducted a first test of the method with a horizontal transmitter. Apparent conductivities are calculated from the electric field transients recorded at the remote receivers. The analysis indicates higher apparent seafloor conductivities when the transmitter is located near the mineralized zone. Forward modelling suggests that the best match to the apparent conductivity data is obtained when the mineralized zone is extended southward by 40 m beyond the zone of previous drilling. Our results demonstrate that the method adds value to the exploration and characterization of seafloor massive sulphide deposits.  相似文献