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31.
The degree of aluminum toxicity is based on its complexation with organic ligands. One of these complexes is AlEDTA- (Al = aluminum, EDTA = ethylenediaminetetraacetate), the structure of which in aqueous solution has been debated on the basis of X-ray absorption and NMR measurements with different interpretations proposing different coordination. In addition, there is a lack of consensus regarding the relationship of crystalline AlEDTA- and its geometry in solution. This debate must be resolved, not merely for scientific interest, but because the use of an incorrect coordination might lead to the wrong interpretation of bioactivity and kinetics data. In this work, we predict the coordination of Al in aqueous AlEDTA- by employing ab initio calculations and Car-Parrinello molecular dynamics simulations. Our results indicate that AlEDTA- favors Al in octahedral coordination in aqueous solution. Furthermore, the predicted crystalline and solution-phase structures of AlEDTA- are similar and agree well with recent X-ray measurements, supporting the strong chelating nature of this metal-organic complex in aqueous solution. 相似文献
32.
Jarvis RM Johnson HE Olembe E Panneerselvam A Malik MA Afzaal M O'Brien P Goodacre R 《The Analyst》2008,133(10):1449-1452
There is a need for a method to facilitate the development of novel, reproducible colloidal surface-enhanced Raman scattering (SERS) substrates to encourage the use of SERS in applied studies. In this study we show for the first time that by using suitably designed SERS experiments in conjunction with multivariate analysis of variance (MANOVA), an objective assessment of colloidal SERS reproducibility can be made. This is demonstrated with the analyte cresyl violet, but could be extended to any analyte of interest for which reproducible SERS data are needed. 相似文献
33.
Zhao X Flaim E Huynh L Jarvis MJ Cheng P Lavrov VV Blagojevic V Koyanagi GK Bohme DK 《Inorganic chemistry》2006,45(24):9646-9653
Results are reported for experimental measurements of the room-temperature chemical reactions between ground-state Hg*+ ions and 16 important environmental and biological gases: SF6, CO, CO2, N2O, D2O, CH4, CH3F, O2, CH3Cl, OCS, CS2, NH3, C6F6, NO2, NO*, and C6H6. The inductively coupled plasma/selected-ion flow tube tandem mass spectrometer used for these measurements has provided both rate and equilibrium constants. Efficient electron transfer (>19%) is observed with CS2, NH3, C6F6, NO2, NO*, and C6H6, molecular addition occurs with D2O, CH4, CH3F, CH3Cl, and OCS, and SF6, CO, CO2, N2O, and O2 showed no measurable reactivity with Hg*+. Theory is used to explore the stabilities and structures of both the observed and unobserved molecular adducts of Hg*+, and reasonable agreement is obtained with experimental observations, given the uncertainties of the theory and experiments. A correlation is reported between the Hg*+ and proton affinities of the ligands investigated. Solvation of Hg*+ with formic acid was observed to increase the rate of electron transfer from NO* by more than 20%. 相似文献
34.
We study the Maxwell–Dirac equations in a manifestly gauge invariant presentation using only the spinor bilinear scalar and pseudoscalar densities, and the vector and pseudovector currents, together with their quadratic Fierz relations. The internally produced vector potential is expressed via algebraic manipulation of the Dirac equation, as a rational function of the Fierz bilinears and first derivatives (valid on the support of the scalar density), which allows a gauge invariant vector potential to be defined. This leads to a Fierz bilinear formulation of the Maxwell tensor and of the Maxwell–Dirac equations, without any reference to gauge dependent quantities. We show how demanding invariance of tensor fields under the action of a fixed (but arbitrary) Lie subgroup of the Poincaré group leads to symmetry reduced equations. The procedure is illustrated, and the reduced equations worked out explicitly for standard spherical and cylindrical cases, which are coupled third order nonlinear PDEs. Spherical symmetry necessitates the existence of magnetic monopoles, which do not affect the coupled Maxwell–Dirac system due to magnetic terms cancelling. In this paper we do not take up numerical computations. As a demonstration of the power of our approach, we also work out the symmetry reduced equations for two distinct classes of dimension 4 one-parameter families of Poincaré subgroups, one splitting and one non-splitting. The splitting class yields no solutions, whereas for the non-splitting class we find a family of formal exact solutions in closed form. 相似文献
35.
V. Di Sarli A. Di Benedetto G. Russo S. Jarvis E. J. Long G. K. Hargrave 《Flow, Turbulence and Combustion》2009,83(2):227-250
In gas explosions, the unsteady coupling of the propagating flame and the flow field induced by the presence of blockages
along the flame path produces vortices of different scales ahead of the flame front. The resulting flame–vortex interaction
intensifies the rate of flame propagation and the pressure rise. In this paper, a joint numerical and experimental study of
unsteady premixed flame propagation around three sequential obstacles in a small-scale vented explosion chamber is presented.
The modeling work is carried out utilizing large eddy simulation (LES). In the experimental work, previous results (Patel
et al., Proc Combust Inst 29:1849–1854, 2002) are extended to include simultaneous flame and particle image velocimetry (PIV) measurements of the flow field within the
wake of each obstacle. Comparisons between LES predictions and experimental data show a satisfactory agreement in terms of
shape of the propagating flame, flame arrival times, spatial profile of the flame speed, pressure time history, and velocity
vector fields. Computations through the validated model are also performed to evaluate the effects of both large-scale and
sub-grid scale (SGS) vortices on the flame propagation. The results obtained demonstrate that the large vortical structures
dictate the evolution of the flame in qualitative terms (shape and structure of the flame, succession of the combustion regimes
along the path, acceleration-deceleration step around each obstacle, and pressure time trend). Conversely, the SGS vortices
do not affect the qualitative trends. However, it is essential to model their effects on the combustion rate to achieve quantitative
predictions for the flame speed and the pressure peak. 相似文献
36.
Bruce B. Jarvis Yin-Won Lee F.Taha Cömezoḡlu S.Nilgün Cömezoḡlu George A. Bean 《Tetrahedron letters》1985,26(40):4859-4862
An isolate of which is a pathogen on tomatoes in Texas produces a new class of C27 macrocyclic trichothecenes which contains a nonconjugated diene system that includes a vinyl ether group. 相似文献
37.
38.
J. R. Zeevaart W. K. A. Louw Z. I. Kolar J. M. Wagener N. V. Jarvis R. A. M. J. Claessens 《Journal of Radioanalytical and Nuclear Chemistry》2003,257(1):83-91
Blood plasma modeling has proved effective in the evaluation of clinical observations recorded for baboon and rat tests with 153Sm- ethylenediaminetetraphosphonic acid (EDTMP) as well as for 166Ho-EDTMP. In the search for a cure for metastatic bone cancer, 117mSn with its conversion electrons of discrete energies shows low bone marrow toxicity, providing the opportunity to increase the administered dose. Selective accumulation in lesions would capitalize on this advantage. The 10-30 kDa fraction of the water-soluble polymer polyethyleneimine, functionalized with methylene phosphonate groups (PEI-MP) and labeled with 99mTc, has shown selective uptake into bone tumours. This paper relates the speciation of Sn(II)-PEI-MP and other known 117mSn(II) containing bone-seeking radiopharmaceuticals in blood plasma. Apparent formation constants for the complexation of SnII with PEI-MP, DTPA, HEDP and other important blood plasma ligands were measured potentiometrically or estimated by linear free energy relationships (LFER). These data were added to the ECCLES database in order to construct a blood plasma model for SnII. From this model it is predicted that SnII will remain bound to the polymer (PEI-MP) in blood plasma and therefore, have only slight reticuloendothelial uptake. Preliminary primate studies indeed proved that the complex between SnII and PEI-MP remains intact in blood plasma, which is consistent with the observation for PEI-MP labeled with 99mTc. From these data, it was also possible to explain in retrospect the lower bone uptake, the slow blood clearance and the liver uptake of the agents 117mSn(II) DTPA and 117mSn(II) HEDP agents as reported in the literature. 相似文献
39.
40.
Large controlled multiplexing systems are approximated by diffusion type processes yielding a very efficient way of approximation and good numerical methods. The limit equations are an efficient aggregation of the original system, and provide the basis of the actual numerical approximation to the control problem. The numerical approximations have the structure of the original problem, but are generally much simpler. The control can occur in a variety of places; e.g., leaky bucket controllers, control of marked cells at the transmitter buffer, or control of the transmitter speed. From the point of view of the limit equations, those are equivalent. Various forms of the optimal control problem are explored, where the main aim is to control or balance the losses at the control with those due to buffer overflow. It is shown that much can be saved via the use of optimal controls or reasonable approximations to them. We discuss systems with one to three classes of sources, various aggregation methods and control approximation schemes. There are qualitative comparisons of various systems with and without control and a discussion of the variations of control and performance as the systems data and control bounds vary. The approach is a very useful tool for providing both qualitative and quantitative information which would be hard to get otherwise. The results have applications to various forms of the ATM and broadband integrated data networks.The work was partially supported by AFOSR-91-0375 and (AFOSR) F49620-92-J-088-1DEF.The work was partially supported by grants (AFOSR) F49620-92-J-008-1DEF, AFOSR-91-03750.This work was partially supported by DAAH04-93-0070 (ARO) and AFOSR-91-0375. 相似文献