Search results for "complex"
showing 10 items of 5889 documents
Resolution of β-aminophosphines with chiral cyclopalladated complexes
2005
Abstract Resolution of the racemic chiral β-aminophosphines Ph 2 PCH 2 CH(Ph)NH(Ar) ( L 1 for Ar = C 6 H 5 and L 2 for Ar = 2,6-C 6 H 3 i Pr 2 ) has been investigated by use of different cyclopalladated complexes as chiral agents. The resulting complexes afford diastereomeric adducts in a 1:1 ratio. After successive crystallizations from ethanol, a d.e. of 98% was achieved for one aminophosphine palladium complex, while no significant d.e. was obtained after crystallizations from chlorinated solvents. The X-ray structure analysis has pointed out intermolecular hydrogen interactions N–H⋯Cl between the P,N ligand and the chloride ion, which are responsible for the formation and stabilization …
Role of rock fragment cover on runoff generation and sediment yield in tilled vineyards
2017
Summary The soil in conventional Mediterranean vineyards is an active and non-sustainable source of sediment and water. Lack of vegetation cover, small soil organic matter content and intense ploughing result in large rates of erosion in a millennia-old tillage system. There is a need for soil conservation strategies that enable sustainability of wine and grape production; therefore, it is essential to measure the rates and to investigate the processes and factors of soil erosion. This study evaluated factors that can reduce soil losses in traditional Mediterranean vineyards. The investigation was carried out with 96 rainfall simulation experiments at the pedon scale (0.24 m2) to measure so…
Overland Flow Times of Concentration for Hillslopes of Complex Topography
2016
The time of concentration is an important parameter for predicting peak discharge at the basin outlet and for designing urban infrastructure facilities. In studying the hillslope response, employing hydraulic equations of flow, the shape of the hillslope geometry has often been assumed as rectangular and planar. However, natural hillslopes have complex topographies whose shapes are characterized by irregularly spaced contour lines. Recently, kinematic wave time of concentration has been derived for rectangular and curved parallel hillslopes. This paper extends this work to hillslopes of complex planform geometry, considering the degree of divergence or convergence of the hillslope. The exte…
Application of Magnetic Susceptibility Measurements for Identification of Technogenic Horizons in Soil Profiles on the Example of the Vistula River C…
2017
Studies on magnetic properties of soils have been recently applied in the soil environment quality monitoring in relation to basic physical and chemical properties. However, the issue of distribution of ferrimagnetic materials in particular genetic soil horizons, especially in altered soils, has not yet been considered in environmental studies. The main subject of the research was to evaluate a potential of magnetic susceptibility measurements as implements for supporting the soil classification through indication of particular distinctive genetic horizons in the soil profile. The study objects were soils whose formation was strictly conditioned by hydrotechnical regulations in the area of …
The effect of ash and needle cover on surface runoff and erosion in the immediate post-fire period
2008
Abstract Hillslopes are thought to be most susceptible to enhanced surface runoff and erosion immediately following wildfire due to removal of protective vegetation and litter cover, and in many cases a fire-induced reduction in soil wettability. This enhanced susceptibility declines as vegetation and litter layer recover. For logistical reasons, however, few studies have been able to examine the responses of burnt terrain immediately following burning and little is therefore known about the effect of the wettable ash layer that often covers the ground until it is redistributed or removed by wind or water erosion. Here we quantify the effects of ash and needle cast ground cover on surface r…
Discussion of “Unsteady Stage-Discharge Relationships for Sharp-Crested Weirs” by Firouz Ghasemzadeh, Salah Kouchakzadeh, and Gilles Belaud
2021
I would like to thank the authors for writing this interesting article dealing with unsteady stage-discharge relationships for sharp-crested weirs. The operation of triangular and rectangular sharp-crested weirs in unsteady flow conditions was experimentally investigated. Results indicated the presence of looped rating curves, with transposition of the rising and falling limbs compared to that commonly observed in stream gauge ratings. The authors found that the deviation between steady and unsteady flow rates in the looped rating curves depends on the weir type and the hydrograph gradient (i.e., the temporal depth variation), especially when the latter changes rapidly. Finally, they propos…
Comparison of aggregate stability indices for soil classification and assessment of soil management practices
1989
Summary In view of soil structure analysis and land-use and management history evaluation, several mechanical indices of soil structure were tested on 13 Italian soils. From the wet and dry sieving aggregate distributions, a pseudo-textural aggregation index (Ipta) and a mechanical aggregation index (Ima)) were determined and compared with other soil structure stability indices based on single-sieve analysis. The single-sieve indices S and WSI were good correlated with Ipta and Ima, showing the possibility of substituting the time-consuming aggregate-size distribution determinations. All the soil structure indices were correlated with selected semi-permanent soil characteristics. Soil struc…
Predicting unit plot soil loss in Sicily, south Italy
2008
Predicting soil loss is necessary to establish soil conservation measures. Variability of soil and hydrological parameters complicates mathematical simulation of soil erosion processes. Methods for predicting unit plot soil loss in Sicily were developed by using 5 years of data from replicated plots. At first, the variability of the soil water content, runoff, and unit plot soil loss values collected at fixed dates or after an erosive event was investigated. The applicability of the Universal Soil Loss Equation (USLE) was then tested. Finally, a method to predict event soil loss was developed. Measurement variability decreased as the mean increased above a threshold value but it was low als…
The influence of aspect and vegetation on seasonal changes in erosion under rainfall simulation on a clay soil in Spain
1998
The seasonal and spatial variability of soil erosion under contrasting slope aspects in southeastern Spain was studied by performing and interpreting 84 rainfall simulation experiments conducted at an intensity of 55 mm h−1 during 1 h. The vegetated soils on the north-facing slope and the upper afforested parts had negligible sediment yield, runoff and erosion, while the bare soils on the south-facing slope had very high runoff rates. Runoff sediment concentration decreased over time during simulated rainfall events on the vegetated areas while it increased on the bare ones. Solute release decreased over time on both surface types. Seasonally, runoff sediment concentration was highest in a…
Mono- and polynuclear hydroxo complexes of monophenylthallium(III)
1974
Summary The hydrolysis of PhTl(OH)ClO4 has been studied in a medium 0.3 M in NaClO4 by a potentiometric technique. The complexes formed by the hydrolysis reactions together with their formation constants have been determined by the general minimizing computer programme LETAGROP. The hydrolysis species observed in the pH range 3–5 are the mononuclear [(PhTlOH)(OH)], the dinuclear [(PhTlOH)2(OH)]+ and the dimer [(PhTlOH)2(OH)2]. The formation constants are log *β11=−4.92±0.2, log *β21=−1.52±0.03 and log *β22=−6.11±0.05. Stepwise reactions are then postulated whose formation constants are respectively log (*β21/*β11)=3.40±0.25, log (*β22/*β21)=−4.59±0.08 and log (*β22/*β112)=3.73±0.09.