Search results for "LEM"
showing 10 items of 23327 documents
Cobalt Clusters with Cubane-Type Topologies Based on Trivacant Polyoxometalate Ligands.
2016
Four novel cobalt-substituted polyoxometalates having cobalt cores exhibiting cubane or dicubane topologies have been synthesized and characterized by IR, elemental analysis, electrochemistry, UV-vis spectroscopy, X-ray single-crystal analysis, and magnetic studies. The tetracobalt(II)-substituted polyoxometalate [Co4(OH)3(H2O)6(PW9O34)](4-) (1) consists of a trilacunary [B-α-PW9O34](9-) unit which accommodates a cubane-like {Co(II)4O4} core. In the heptacobalt(II,III)-containing polyoxometalates [Co7(OH)6(H2O)6(PW9O34)2](9-) (2), [Co7(OH)6(H2O)4(PW9O34)2]n(9n-) (3), and [Co7(OH)6(H2O)6(P2W15O56)2](15-) (4), dicubane-like {Co(II)6Co(III)O8} cores are encapsulated between two heptadentate [B…
Reactivity of di-n-butyl-dicyclopentadienylzirconium towards amido stabilized stannylenes
2009
Abstract Reaction of Sn[(N(C 6 H 3 i Pr 2 -2,6)(SiMe 3 )] 2 and [{Sn(N(C 6 H 3 i Pr 2 -2,6)(SiMe 3 )(μ-Cl) 2 ] with di- n -butyl-dicyclopentadienylzirconium yielded the trimetallic a carbene-like complex {[(N(C 6 H 3 i Pr 2 -2,6)(SiMe 3 )]( n -Bu)Sn} 2 Cp 2 Zr. The oxidation of {[(N(C 6 H 3 i Pr 2 -2,6)(SiMe 3 )]( n -Bu)Sn} 2 Cp 2 Zr by oxygen gives the five-membered dioxadistannazirconacyclic complex {[(N(C 6 H 3 i Pr 2 -2,6)(SiMe 3 )]( n -Bu)Sn} 2 O 2 Cp 2 Zr.
Optimal Dynamic Portfolio Risk Management
2016
Numerous econometric studies report that financial asset volatilities and correlations are time-varying and predictable. Over the past decade, this knowledge has stimulated increasing interest in various dynamic portfolio risk control techniques. The two basic types of risk control techniques are: risk control across assets and risk control over time. At present, the two types of risk control techniques are not implemented simultaneously. There has been surprisingly little theoretical study of optimal dynamic portfolio risk management. In this paper, the author fills this gap in the literature by formulating and solving the multi-period portfolio choice problem. In terms of dynamic portfoli…
Effect of AlR3 (R = Me, Et, iBu) addition on the composition and microstructure of ethylene/1-olefin copolymers made with post-metallocene complexes …
2018
The effect of trialkylaluminum compound (AlR3, where R = Me, Et, iBu) addition on the performance of the [LigZrCl]2(μ-O)/AliBu3/Ph3CB(C6F5)4 and LigTiCl2/AliBu3/Ph3CB(C6F5)4 (Lig = Me2N(CH2)2N(CH2-2-O-3,5-tBu2-C6H2)2) catalysts in ethylene/1-olefin copolymerization was investigated. The presence of AlMe3 in the feed during the copolymerization process catalyzed by the diamine-bis(phenolate) zirconium catalyst greatly increases the amount of incorporated comonomer and leads to microstructural changes, e.g., the formation of blocky and alternating sequences of 1-olefin units. Moreover, the use of AlMe3 limits the reaction yield and decreases the molecular weight of the produced copolymers. Th…
Diagenetic stability of non-traditional stable isotope systems (Ca, Sr, Mg, Zn) in teeth – An in-vitro alteration experiment of biogenic apatite in i…
2021
Stable isotope ratios and trace element concentrations of fossil bones and teeth are important geochemical proxies for the reconstruction of diet and past environment in archaeology and palaeontology. However, since diagenesis can significantly alter primary diet-related isotope signatures and elemental compositions, it is important to understand and quantify alteration processes. Here, we present the results of in-vitro alteration experiments of dental tissues from a modern African elephant molar reacted in aqueous solutions at 30 °C and 90 °C for 4 to 63 days. Dental cubes with ≈ 3 mm edge length, comprising both enamel and dentin, were placed into 2 mL of acidic aqueous sol…
Partitioning of nitrogen during melting and recycling in subduction zones and the evolution of atmospheric nitrogen
2019
Abstract The subduction of sediment connects the surface nitrogen cycle to that of the deep Earth. To understand the evolution of nitrogen in the atmosphere, the behavior of nitrogen during the subduction and melting of subducted sediments has to be estimated. This study presents high-pressure experimental measurements of the partitioning of nitrogen during the melting of sediments at sub-arc depths. For quantitative analysis of nitrogen in minerals and glasses, we calibrated the electron probe micro-analyzer on synthetic ammonium feldspar to measure nitrogen concentrations as low as 500 μg g−1. Nitrogen abundances in melt and mica are used together with mass balance calculations to determi…
Constraining electric resistivity tomography by direct push electric conductivity logs and vibracores: An exemplary study of the Fiume Morto silted r…
2018
The inversion of geoelectric data is nonunique. Therefore, electric resistivity tomography (ERT) usually results in different subsurface models that fit observed apparent resistivity values equally well. To reduce the uncertainty, constraints on the geometry and resistivity of subsurface structures can be incorporated into the ERT inversion. We test different ways of constraining ERT by applying (1) improved starting models, (2) structural constraints, and (3) structural and resistivity constraints. A priori information is needed for these approaches, which is acquired from direct push electrical conductivity (DP-EC) logs and vibracores in our study. We found that adapting high vertical re…
Modeling the Effects of Climate Change on the Supply of Phosphate-Phosphorus
2009
The transfer of phosphorus from terrestrial to aquatic ecosystems is a key route through which climate can influence aquatic ecosystems. A number of climatic factors interact in complex ways to regulate the transfer of phosphorus and modulate its ecological effects on downstream lakes and reservoirs. Processes influencing both the amount and timing of phosphorus export from terrestrial watersheds must be quantified before we can assess the direct and indirect effects of the weather on the supply and recycling of phosphorus. Simulation of the export of phosphorus from the terrestrial environment is complicated by the fact that it is difficult to describe seasonal and inter-annual variations …
High Resolution X-ray Spectroscopy of T Tauri Stars in the Taurus-Auriga Complex
2006
Differences have been reported between the X-ray emission of accreting and non-accreting stars. Some observations have suggested that accretion shocks could be responsible for part of the X-ray emission in Classical T Tauri stars (CTTS). We present high-resolution X-ray spectroscopy of nine pre-main sequence stars in order to test the proposed spectroscopic differences between accreting and non-accreting pre-main sequence stars. We use X-ray spectroscopy from the XMM-Newton Reflection Grating Spectrometers and the EPIC instruments. We interpret the spectra using optically thin thermal models with variable abundances, together with an absorption column density. For BP Tau and AB Aur we deriv…
Environmental and biological factors are joint drivers of mercury biomagnification in subarctic lake food webs along a climate and productivity gradi…
2021
Subarctic lakes are getting warmer and more productive due to the joint effects of climate change and intensive land-use practices (e.g. forest clear-cutting and peatland ditching), processes that potentially increase leaching of peat- and soil-stored mercury into lake ecosystems. We sampled biotic communities from primary producers (algae) to top consumers (piscivorous fish), in 19 subarctic lakes situated on a latitudinal (69.0-66.5 degrees N), climatic (+3.2 degrees C temperature and +30% precipitation from north to south) and catchment land-use (pristine to intensive forestry areas) gradient. We first tested how the joint effects of climate and productivity influence mercury biomagnific…