The influence of peripheral ligand bulk on nitrogen activation by three‐coordinate molybdenum complexes—A theoretical study using the ONIOM method

Electronic structure methods have been combined with the ONIOM approach to carry out a comprehensive study of the effect of ligand bulk on the activation of dinitrogen with three‐coordinate molybdenum complexes. Calculations were performed with both density functional and CCSD(T) methods. Our results show that not only is there expected destabilization of the intermediate on the pathway due to direct steric interactions of the bulky groups, but also there is significant electronic destabilization as the size of the ligand increases. This latter destabilization is due to the inability of the molecule to accommodate a rotated amide group bound to the molybdenum once the amide reaches a certain size. This destabilization also leads to a clear preference for the triplet intermediate (rather than the singlet intermediate) for bulky substituents which is in agreement with experiment. Overall, the calculated reaction profile for the bulky substituents shows a good correlation with the available experimental data. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009     

Spectroscopic study of BixEu1−xVO4 and BiyGd1−yVO4 mixed oxides

The mixed oxides Bi_xEu_1−xVO₄ and Bi_yGd_1−yVO₄ crystallize in a zircon-type structure, for 0 <x < 0.6 and 0 < y < 0.64, and in a fergusonite-type structure, for 0.94 < x < 1 and 0.93 < y < 1. A process of competition between the dominant and the constrained effects of the lone-pair 6s² of Bi³⁺ is discussed. The diffuse reflectance spectroscopic studies of these mixed oxides are presented. The observed broad bands are attributed to charge transfer processes and the sharp peaks in the Bi_xEu_1−xVO₄ spectra are ascribed to intra-configurational 4f – 4ftransitions of the Eu³⁺ ion. The broad absorption shift in BiLnVO₄ (Ln : Eu and Gd) compounds to the longer wavelengths range, when Bi is introduced in the LnVO₄ lattice, is ascribed to charge transfer processes in a Bi-VO₄ center and are interpreted assuming a Jahn-Teller effect in the excited state of Bi³⁺. The concept of an internal pressure of Bi³⁺ ions is also used to explain the broad A-band shifts.     

两种不锈钢在高压下的状态方程

 测定了两种不锈钢在室温下、4.5 GPa内的p-V关系，并给出了它们的Bridgman方程。根据Bridgman方程的系数a和b，计算了它们的格临爱森参数γ₀、体积模量B₀和B₀的压力导数B₀'。     

Optical and photoemission evidence for a Tomonaga-Luttinger liquid in the Bechgaard salts

Combined optical and photoemission experiments on the quasi-one dimensional Bechgaard salts reveal the non-Fermi liquid character of these prototype quasi-one dimensional interacting electron systems. We show that various aspects of the exotic normal state properties along the chains are consistent with the predictions of the Tomonaga-Luttinger liquid theory. We also discuss the effect of interchain coupling on the insulator-metal transition, associated with the electron confinement-deconfinement crossover. Received 17 May 1999 and Received in final form 13 July 1999     

宇宙常数的Bulk流形的起源

关于宇宙常数问题是个至今没有解决的问题, 它的来源至今还没有一个共识. 从额外维的流形出发, 给出了宇宙常数的,bulk,流形起源的理论, 得到了不同情况下宇宙常数的取值和宇宙常数随时间演化的函数, 并且得到了可拟合现代天文观测的宇宙常数.     

Fe-B-Y-Nb bulk metallic glasses in relation to clusters

Bulk metallic glass formations in the Fe-B-Y-Nb quaternary alloy system were investigated by using the cluster line rule in combination with the minor alloying principle. The Fe-B-Y ternary system was selected as the basic system and the intersections of cluster lines were taken as the basic ternary compositions. The basic compositions were further alloyed with minor amounts of Nb. After 3–5 at.% Nb was added, the basic composition Fe_68.6B_25.7Y_5.7, which was developed from the most densely packed cluster Fe₈B₃, formed 3 mm bulk metallic glasses. These quaternary bulk metallic glasses (Fe_68.6B_25.7Y_5.7)_100−x Nb _x (x = 3–5 at.%) are expressed approximately with a unified simple composition formula: (Fe₈B₃)₁(Y, Nb)₁. The (Fe_68.6B_25.7Y_5.7)₉₇Nb₃ bulk metallic glass has the largest glass forming ability with the following characteristic parameters T _g = 907 K, T _x = 1006 K, T _g/T _l = 0.644, γ = 0.434, and longness t = 22 mm. The combination of the cluster line rule and the minor-alloying principle is a promising new route towards the quantitative composition design of multi-component metallic glasses. Supported by the National Natural Science Foundation of China (Grant Nos. 50671018, 50631010 and 50401020) and the National Basic Research Program of China (Grant No. 2007CB613902)     

Electrical properties of silicon dioxide films fabricated at 700°C. II: Low pressure hydride deposition

We have investigated the effects of different annealing treatments on silicon dioxide films produced from the reaction of dichlorosilane and nitrous oxide at 700° C. The electrical quality of these LPCVD films was evaluated by measuring oxide charge and interface trap densities on metal oxide semiconductor (MOS) capacitors. These densities were measured before and after avalanche injection of electron currents into the oxide films. The results of these studies were as follows. (1) The LPCVD oxide films required a post deposition anneal at 1000° C to produce as-grown charge densities similar to those of a standarddry thermal oxide grown and annealed at 1000° C. (2) Post-injection charge densities of LPCVD films given a post deposition anneal at 1000°C were an order of magnitude greater than those of the standard dry thermal oxide. (3) Different annealing treatments produced a series of dominant electron trapping centers in the oxide bulk₁₇ with capture cross sections ranging from 10⁻¹⁴ cm² to 10⁻¹⁷ cm². (4) The electron traps in the LPCVD oxides films were similar to those previously observed in standardwet thermal oxides grown and annealed above 1000° C.     

Comparative study of bulk and partial digestion methods for airborne PM10-bound elements in a high mineral dust urban site in Constantine,Algeria

When high mineral loads in atmospheric particulate matter (PM) are present, particular attention should be paid to the selection of appropriate acidic digestion protocols for wet chemical analysis. We report on a comparative study of elemental recovery yields from five different pre-analytical acid digestion procedures for mineral-rich urban background PM₁₀ samples collected in the city of Constantine (Northeastern Algeria). Five reference materials (NIST 1633b, UPM 1648, NAT-7, SO-2 and SO-4) were also digested according to the same protocols. The selected acidic digestion/extraction procedures are widely used for PM chemical analysis and comprise P1 (HNO₃/HF/HCl), P2 (HCl/HNO₃), P3 (HCl/H₂O₂/HNO₃), P4 (HNO₃/HF/HClO₄) and P5 (HNO₃/H₂O₂); the latter assisted with microwave digestion. Elemental recovery yields were compared for major and trace elements typically determined in PM for source apportionment analysis and the results evidenced large differences. For most elements, the bulk extraction procedures (requiring the use of HF) allowed a full elemental recovery, particularly for elements that are associated with aluminium silicate species and oxides that are resistant to mild acid attack. In contrast, in the extraction protocols without HF low recovery yields were obtained for elements such as Al, Ti, Zr, Sc and other aluminium silicate-related elements in PM₁₀ samples with high mineral dust load. We highlight that the European standard digestion method EN-14902:2005 should be applied specifically for the metals for which this method was developed, but caution should be taken when the analysis of other elements in PM is required, especially in urban areas where road and vehicle wear dust is likely to be a major component of ambient PM. When using wet chemistry analysis for PM source apportionment studies, we strongly recommend HF bulk dissolution of samples to ensure the reliability of the geochemical information when coupled with an appropriate analytical tool.     

Individual and simultaneous determination of lead, cadmium, and zinc by anodic stripping voltammetry at a bismuth bulk electrode

A bismuth bulk electrode (BiBE) has been investigated as an alternative electrode for the anodic stripping voltammetric (ASV) analysis of Pb(II), Cd(II), and Zn(II). The BiBE, which is fabricated in-house, shows results comparable to those of similar analyses at other Bi-based electrodes. Metal accumulation is achieved by holding the electrode potential at −1.4 V (vs. Ag/AgCl) for 180 s followed by a square wave voltammetric stripping scan from −1.4 to −0.35 V. Calibration plots are obtained for all three metals, individually and simultaneously, in the10-100 μg L⁻¹ range, with a detection limit of 93, 54, and 396 ng L⁻¹ for Pb(II), Cd(II), Zn(II), respectively. A slight reduction in slope is observed for Cd(II) and Pb(II) when the three metals are calibrated simultaneously vs. individually. Comparing the sensitivities of the metals when calibrated individually vs. in a mixture reveals that Zn(II) is not affected by stripping in a mixture. However, Pb(II) and Cd(II) have decreasing sensitivities in a mixture. The optimized method has been successfully used to test contaminated river water by standard addition. The results demonstrate the ability of the BiBE as an alternative electrode material in heavy metal analysis.