Studies of elastic gamma ray scattering were pursued independently by the groups of Prof. Ghose and the author for several decades in spite of somewhat meagre support. Several techniques for such studies developed by the two groups and some of the results obtained in the energy range from tens of keV to about 1.5 MeV are described briefly. The theoretical background necessary for understanding these results is also outlined. The results showed the importance of Modified Relativistic Form Factor (MRFF) approximation in the explanation of atomic Rayleigh scattering cross sections in the small angle regime and the necessity for an inclusion of real Delbrück scattering amplitudes at large scattering angles. Dispersion corrections to form factor amplitudes or the so-called anomalous scattering factors are shown to be needed at photon energies close to electron binding energy thresholds. A few promising future extensions of such studies are indicated at the end. 相似文献
The Partial Charge Model was developed to predict the hydroxylation, polymerization, and precipitation of ions. The purpose
of this study is to evaluate the Partial Charge Model for describing the polymerization of silica in aqueous solutions. The
Partial Charge Model predicts the stability of ions and complexes based on the assumption that the stable species will have
the same electronegativity as the mean electronegativity of the solution. The silica system was chosen for model validation
because of the rare availability of self-consistent thermodynamic data on many dissolved but polymerized silicate anions,
including both linear and cyclical species. The electronegativity of each species was calculated using the Partial Charge
Model and the results were plotted against the stability constants for the ions. The silicate anions segregated into groups
on the plot based on the number of charges per silicon atom in the polymer. Plots of the log of the stability constant versus
the change in electronegativity produced a linear relationship for the silica polymers containing one negative charge per
silicon atom, which resulted in an r2 of 0.9978. Thus, the Partial Charge Model successfully describes the thermodynamics of silica polymerization in aqueous solution
for species that are sufficiently alike, but was not accurate for all silica species. 相似文献
The Bohlmann-Rahtz reaction has been used to prepare 2,3,6-trisubstituted pyridines suitable for use in library synthesis. The synthesis of piperidine substituted nicotinic acid derivative 9 has been optimised and carried out on a large scale to give ca. 500 g of scaffold which was used in the generation of the pyridine library 11. 相似文献
LetD be a bounded plane domain (with some smoothness requirements on its boundary). LetBp(D), 1≤p<∞, be the Bergmanp-space ofD. In a previous paper we showed that the “natural projection”P, involving the Bergman kernel forD, is a bounded projection fromLp(D) ontoBp(D), 1<p<∞. With this we have the decompositionLp(D)=Bp(D)⊕Bq⊥(D,p–1+q–=1, 1<p< ∞. Here, we show that the annihilatorBq⊥(D) is the space of allLp-complex derivatives of functions belonging to Sobolev space and which vanish on the boundary ofD. This extends a result of Schiffer for the casep=2. We also study certain operators onLp(D). Especially, we show that, whereI is the identity operator and ? is an operator involving the adjoint of the Bergman kernel. Other relationships relevant toBq⊥(D) are studied. 相似文献
An expression for the product of a single-cycle class [(1)N - P(p)]N and an arbitrary class [(1)l1(2)l …? (N)lN]N of the symmetric group has recently been conjectured. This expression involves a sum over a relatively small number of reduced class sums, depending on p indices. A further conjecture is formulated and demonstrated, according to which reduced class coefficients (RCCS ) involving cycles whose length is expressed by means of a single index can be related to corresponding coefficients in the product of [(1)N - P+1(p - 1)]N with an arbitrary class sum. Consequently, the problem of evaluating the general class sum product reduces to that of obtaining a relatively small set of fundamental RCCS containing no single-index cycles. The conjectures mentioned can be used to evaluate the product [(1)N - p(p)]N · [(1)N - q(q)]N in terms of fundamental RCCS that can all be obtained from the product [(r)]r · [(r)]r, where r = min(p, q). For the latter product, we use a result due to Boccara. 相似文献
Solutions of selenium(IV) standards with different acid matrices were stored in containers constructed of boosilicate glass, conventional polyethylene, and fluorinated ethylenepropylene (teflon FEP). After 50 days of storage in FEP, there were highly significant losses of Se(IV) from standards in either 5% HCl/5% H2SO4, or 5% H2SO4. Increasing the hydrochloric acid concentration, e.g., 15% HCl/5% H2SO4, greatly reduced this loss. Addition of selenium-75 (selenate-free) indicated that the losses did not result from physical adsorption onto container surfaces. It is shown that the losses were caused by oxidation of Se(IV) to Se(VI). 相似文献
The experimental electron density distribution in taurine, 2-aminoethane sulfonic acid, 1, has been determined from high-resolution X-ray diffraction data collected at a temperature of 100 K. Taurine crystallizes as a zwitterion in the monoclinic space group P2(1)/c. Topological analysis of the experimental electron density and a comparison with high-level theoretical gas-phase calculations show that the crystal environment has a significant influence on the electronic configuration of the sulfonate moiety in 1, which in the crystal is more delocalized than in the gas phase. This crystal effect is mainly due to hydrogen bonding. 相似文献
Colloidal forces between bitumen surfaces in aqueous solutions were measured with an atomic force microscope (AFM). The results showed a significant impact of solution pH, salinity, calcium and montmorillonite clay addition on both long-range (non-contact) and adhesion (pull-off) forces. Weaker long-range repulsive forces were observed under conditions of lower solution pH, higher salinity and higher calcium concentration. Lower solution pH, salinity and calcium concentration resulted in a stronger adhesion forces. The addition of montmorillonite clays increased long-range repulsive forces and decreased adhesion forces, particularly when co-added with calcium ions. The measured force profiles were fitted with extended DLVO theory to show the repulsive electrostatic double layer and attractive hydrophobic forces being the dominant components in the long-range forces between the bitumen surfaces. At a very short separation distance (less than 4–6 nm), a strong repulsion of steric origin was observed. The findings provide a fundamental understanding of bitumen emulsion stability and a mechanism of bitumen “aeration” in bitumen recovery processes from oil sands. 相似文献
The vapor pressure of pure liquid indium, and the sum of pressures of (In) and (In2O) species over the condensed phase mixture {In} + <In2O3>, contained in a silica vessel, have been measured by Knudsen effusion and Langmuir free vaporization methods in the temperatue range 600 to 950°C. Mass spectrometric studies reported in the literature show that (In) and (In2O) are the important species in the vapor phase over the {In} + <In2O3 >; mixture. The vapor pressure of (In2O) corresponding to the reaction, deduced from the present measurements is given by the equation, The “apparent evaporation coefficient” for the condensed phase mixture is approximately 0.8. The energy for the dissociation (In2O) molecule into atoms calculated from the above equation is D°0 = 180.0 (± 1.0) kcal mol?1. 相似文献
The electrospray ionisation-ion trap mass spectrometry (ESI-MSn) of selected hypnotic drugs, i.e. zopiclone, zolpidem, flunitrazepam and their metabolites have been investigated. Sequential product ion fragmentation experiments (MSn) have been performed in order to elucidate the degradation pathways for the [M+H]+ ions and their predominant fragment ions. These MSn experiments show certain characteristic fragmentations in that functional groups are generally cleaved from the ring systems as neutral molecules such as H2O, CO, CO2, NO2, amines and HF. When an aromatic entity is present in a drug molecule together with a nitrogen-containing saturated ring structure as with zopiclone and its N-desmethyl metabolite fragmentation initially occurs at the latter ring with the former being resistant to fragmentation. The structures of fragment ions proposed for ESI-MSn can be supported by electrospray ionisation-quadrupole time-of-flight mass spectrometry (ESI-QTOF-MS).These molecules can be identified and determined in mixtures at low ng/ml concentrations by the application of liquid chromatography (LC)-ESI-MSn which can be used for their analysis in saliva samples.This paper includes a tabulation of mass losses/signals at low m/z values for these hypnotic drugs and many others in recent publications which will be of value in the characterisation of drug metabolites of unknown structure and also natural product pharmaceuticals isolated from plants, etc. 相似文献