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81.
We describe a method for predicting detection limits of minority elements in electron energy loss spectroscopy (EELS), and its implementation as a software package that gives quantitative predictions for user-specified materials and experimental conditions. The method is based on modeling entire energy loss spectra, including shot noise as well as instrumental noise, and taking into account all the relevant experimental parameters. We describe the steps involved in modeling the entire spectrum, from the zero loss up to inner shell edges, and pay particular attention to the contributions to the pre-edge background. The predicted spectra are used to evaluate the signal-to-noise ratios (SNRs) for inner shell edges from user-specified minority elements. The software also predicts the minimum detectable mass (MDM) and minimum mass fraction (MMF). It can be used to ascertain whether an element present at a particular concentration should be detectable for given experimental conditions, and also to quickly and quantitatively explore ways of optimizing the experimental conditions for a particular EELS analytical task. We demonstrate the usefulness of the software by confirming the recent empirical observation of single atom detection using EELS of phosphorus in thin carbon films, and show the effect on the SNR of varying the acquisition parameters. The case of delta-doped semiconductors is also considered as an important example from materials science where low detection limits and high spatial resolution are essential, and the feasibility of such characterization using EELS is assessed. 相似文献
82.
A novel and efficient reduction of various prochiral ketones such as acetopehones, alpha-azido aryl ketones, beta-ketoesters, and aliphatic acyclic and cyclic ketones to the corresponding optically acive secondary alcohols with moderate to excellent chemical yield was achieved by using Daucus carota, root plant cells under extremely mild and environmentally benign conditions in aqueous medium, has been described. Many of these optically active alcohols are the potential chiral building blocks for the synthesis of pharmaceutically important molecules and asymmetric chiral ligands. Hence, this biocatalytic approach is found to be the most suitable for the preparation of a wide range of chiral alcohols and gave inspiration for the development of a new biotechnological process. 相似文献
83.
The influence of metal ions on the conformation of dimethyl phosphate anion around its O-P bonds, has been studied theoretically. The perturbation caused due to metal ions like Na+ and Mg2+ seems to affect the free dimethyl phosphate anion conformation to a considerable extent. In particular, the fully extended conformation becomes much more favourable in the metal ion dimethyl phosphate complex. 相似文献
84.
The spin density distribution in a few hydrocarbon radicals has been calculated using orthogonalized atomic orbitals in the Unrestricted Hartree-Fock formalism of Amos and Snyder and including certain more important two-electron hybrid and exchange integrals and all the core-resonance integrals. Our calculated spin densities for the cation and anion radicals of alternant hydrocarbons, which are now different due to the breakdown of the pairing theorem, are, in general, of the right relative order so that even the simple McConnell type of relation can account partly for the observed differences in the proton splittings between cations and anions. The proton splittings for position 2 of naphthalene and anthracene radical ions are correctly predicted, thus clearing up the well-known cation-anion anomaly for this position. Comparative calculations have been made to show that the spin density results are worsened with the neglect of the integrals of the type mentioned before. An empirical analysis correlating the observed 13C splittings and the spin density results over a non-orthogonal basis set shows that the available 13C splittings in alternant hydrocarbon radical ions can be explained with a set of sigma-pi parameters which are consistent with the theory. It is shown that even though the spin densities in cations and anions may be different, these can lead to similar 13C splittings. 相似文献
85.
Eight 4-arylidene-2-phenyl-5(4H)-oxazolones (azlactones) have been prepared via Erlenmeyer synthesis from aromatic aldehydes and hippuric acid using calcium acetate under solvent-free conditions with microwave irradiation. 相似文献
86.
Summary The aquation ofcis-[(en)2Co(CO2H)2]+ tocis-[(en)2Co(OH2)(CO2H)]2+ is catalysed by Cu2+ and the rate equation, –d[complex]t/dt=(kCu[Cu2+]+kH [H+]) [complex)T is valid at [Cu2+]T=0.01–0.1, I=0.5 and [HClO4]=0.005 mol dm–3. The rate measurements are reported at 30, 35, 40 and 45°C and the rate and activation parameters for the Cu2+ and H+-catalysed paths are: kH(35°C)=(2.44±0.09)×10–2 dm3 mol–1 s–1, H=83±13 kJ mol–1, S=–8±42 JK–1 mol–1, k
Cu
(35°C)=(3.30±0.09)×10–3 dm3 mol–1 s–1, H=73.2±6.1 kJ mol–1, S=–55±20 JK–1 mol–1. The formate-bridged innersphere binuclear complex,cis-[(en)2Co{(O2CH)2Cu}]3+ may be involved as the catalytically active intermediate in the copper(II)-catalysed path, just as the corresponding H+-bridged species presumed to be present in the acidcatalysed path. 相似文献
87.
The kinetics of oxidation of Norfloxacin [1‐ethyl‐6‐fluoro‐1,4‐dihydro‐4‐oxo‐7‐(l‐piperazinyl)‐3‐quinoline carboxylic acid] by chloramine‐B and N‐chlorobenzotriazole has been studied in aqueous acetic acid medium (25% v/v) in the presence of perchloric acid at 323 K. For both the oxidants, the reaction follows a first‐order dependence on [oxidant], a fractional‐order on [Norfloxacin], and an inverse‐fractional order on [H+]. Dependence of reaction rate on ionic strength, reaction product, dielectric constant, solvent isotope, and temperature is studied. Kinetic parameters are evaluated. The reaction products are identified. The proposed reaction mechanism and the derived rate equation are consistent with the observed kinetic data. Formation and decomposition constants for substrate–oxidant complexes are evaluated. ©1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 153–158, 1999 相似文献
88.
The kinetics of the oxidation of diazepam (DZ) by Chloramine-B (CAB) has been studied in aqueous hydrochloric acid medium. The oxidation reaction follows the rate law: The dependence of the reaction rate on temperature is studied and activation parameters for the rate-determining step are evaluated. The dielectric constant of the medium has a small effect on the rate. Ionic strength and the reaction product benzenesulfonamide have no effect on the reaction rate. The solvent isotope effect is studied. A probable mechanism for the observed kinetic data is proposed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 605–611, 1998 相似文献
89.
The kinetics of oxidation of diazepam (DZ) by 1-chlorobenzotriazole (CBT) has been studied in HClO4 medium in the temperature range of 293–323 K. The reactions followed a first order dependence on [CBT], fractional order
each in [H+] and [DZ]. Activation parameters were evaluated. A negative entropy of activation indicated the involvement of a rigid complex
in the activated state. Variation of reaction rate with dielectric constant and the ionic strength are consistent with a mechanism
involving the decomposition of a dipole in the rate-determining step. Rate equation is derived to account for the observed
kinetic data and the proposed reaction mechanism. 相似文献
90.
The steady flow in a parallel plate channel rotating with an angular velocity Ω and subjected to a constant transverse magnetic
field is analysed. An exact solution of the governing equations is obtained. The solution in the dimensionless form contains
two parameters: the Hartmann number, M
2, and K
2 which is the reciprocal of the Ekman number. The effects of these parameters on the velocity and magnetic field distributions
are studied. For large values of the parameters, there arise thin boundary layers on the walls of the channel. 相似文献