This study simulated the transport and storage conditions of ethanol in water certified reference material (CRM) produced
by the Chemical Metrology Division of Inmetro—DQUIM with the purpose of estimating the measurement uncertainty related to
stability. The short-term stability study was performed on five different mass fractions (w) in terms of mg ethanol/g solution of the ethanol in water CRM. The nominal values are w = 0.5, 0.9, 1.1, 3.8 and 4.6 mg/g, at temperatures of 4 and 60 °C. On the other hand, the long-term stability study was developed
on four different mass fractions (nominal values): w = 0.5, 0.9, 1.1 and 4.6 mg/g, at a temperature of 20 °C. This paper will show the data from the long-term stability study
that took place over 52 weeks. The method used complies with ISO Guide 35, the BCR Guideline for Feasibility Studies and ISO
Guide 34. According to the statistical parameters used in both studies, the stability of ethanol in water CRM was confirmed
for all of the mass fractions studied. 相似文献
In silico research in medicine is thought to reduce the need for expensive clinical trials under the condition of reliable mathematical models and accurate and efficient numerical methods. In the present work, we tackle the numerical simulation of reaction–diffusion equations modeling human ischemic stroke. This problem induces peculiar difficulties like potentially large stiffness which stems from the broad spectrum of temporal scales in the nonlinear chemical source term as well as from the presence of steep spatial gradients in the reaction fronts, spatially very localized. Furthermore, simulations on realistic 3D geometries are mandatory in order to describe correctly this type of phenomenon. The main goal of this article is to obtain, for the first time, 3D simulations on realistic geometries and to show that the simulation results are consistent with those obtain in experimental studies or observed on MRI images in stroke patients.For this purpose, we introduce a new resolution strategy based mainly on time operator splitting that takes into account complex geometry coupled with a well-conceived parallelization strategy for shared memory architectures. We consider then a high order implicit time integration for the reaction and an explicit one for the diffusion term in order to build a time operator splitting scheme that exploits efficiently the special features of each problem. Thus, we aim at solving complete and realistic models including all time and space scales with conventional computing resources, that is on a reasonably powerful workstation. Consequently and as expected, 2D and also fully 3D numerical simulations of ischemic strokes for a realistic brain geometry, are conducted for the first time and shown to reproduce the dynamics observed on MRI images in stroke patients. Beyond this major step, in order to improve accuracy and computational efficiency of the simulations, we indicate how the present numerical strategy can be coupled with spatial adaptive multiresolution schemes. Preliminary results in the framework of simple geometries allow to assess the proposed strategy for further developments. 相似文献
Rainwater is a very low concentrated matrix and, for dissolved organic matter (DOM) characterization, an efficient extraction procedure is essential. Isolation procedures based on the adsorption onto XAD-8 and C-18 sorbents have been used in the literature for rainwater DOM isolation, but a comparison between these procedures is lacking. In this work, UV-visible and molecular fluorescence spectroscopies highlighted differences between rainwater DOM isolated by DAX-8 (replacement for XAD-8) and by C-18. It was possible to recover higher rainwater DOM percentage by the C-18 based procedure than by the DAX-8 one. Rainwater protein-like compounds were better concentrated by the C-18 procedure than by the DAX-8 one, while humic-like compounds were similarly concentrated by both procedures. Furthermore, rainwater DOM extracted by the C-18 procedure was more representative of the global matrix, while DAX-8 preferentially extracted humic-like compounds. 相似文献
Here is described the preparation of four new rhodium(II) complexes bearing axial NHC ligands. The presence of electron-withdrawing bridging ligands resulted in an enhanced reactivity in the arylation of aldehydes with boronic acids when compared with the tetraacetate counterparts. Complex 15 (Rh2tfa4(IPr)2) proved to be the most active catalyst for this transformation allowing the selective conversion of aromatic, aliphatic and vinyl aldehydes into the respective alcohols in excellent yields. It was demonstrated that the good group tolerance could be further extended to aromatic and conjugated ketones. DFT calculations carried out on this system showed the complementarily of the bridging ligands and axial ligand in these dinuclear complexes. It was also disclosed that Rh(II)/NHC catalytic system can promote the racemization of 1-phenyl ethanol. 相似文献
When can an (n-k)×(n-k) normal matrix B be imbedded in an n×n normal matrix A? This question was studied for the first time 50 years ago by Ky Fan and Gordon Pall, who gave the complete answer in the case k=1. Since then, a few authors obtained additional results. In this note, we show how an approach inspired by the Hermitian case can throw some light on the problem. 相似文献
A rationalization of stereoselectivity : The mechanisms of proline‐catalyzed and imidazole‐co‐catalyzed intramolecular Baylis–Hillman reactions have been studied by using density functional theory methods. The computational data has allowed us to rationalize the experimental outcome, validating some of the mechanistic steps proposed in the literature, as well as to propose new ones that considerably change and improve our understanding of the full reaction path (see scheme).
New silver complexes of general formula [Ag(O3SCF3)(PPh2{bzt})n] (n = 1–3, bzt = benzo[1,2-b;4,3-b′]dithiophene) have been synthesized and characterized. Spectroscopic studies shown neutral ligand fluxionallity, typical of silver(I) complexes. The solid state structure of the complexes was determined by X-ray crystallographic studies, showing a decrease in structure complexity with increasing number of neutral ligands in silver coordination sphere: [Ag(O3SCF3)(PPh2{bzt})] is a dimer with two bridging triflate anions, further linked into polymeric bidimensional chains along bc plane, through Ag?Ph close contacts; Ag(O3SCF3)(PPh2{bzt})2] is also a dimmer with two bridging triflate anions, displaying an interesting packing feature, with zig-zag alignment of bzt groups along direction b; [Ag(O3SCF3)(PPh2{bzt})3] is a monomer. 相似文献
Two conformational polymorphs of trans‐chlorido(phenyl)bis(triphenylphosphine)nickel(II), [Ni(C6H5)Cl(C18H15P)2], (1), viz. orange needle‐shaped crystals (form I) and brown prism‐shaped crystals (form II), were obtained under different crystallization conditions from a mixture of toluene and n‐hexane, and characterized by single‐crystal X‐ray diffraction at low temperature. These two forms were compared with that published previously [Zeller, Herdtweck & Strassner (2003). Eur. J. Inorg. Chem. pp. 1802–1806], characterized at room temperature. Additionally, blue–green prisms of a 1:1 cocrystal of complex (1) with chloridobis(triphenylphosphine)nickel(I), (2), viz.trans‐chlorido(phenyl)bis(triphenylphosphine)nickel(II)–chloridobis(triphenylphosphine)nickel(I) (1/1), [Ni(C6H5)Cl(C18H15P)2]·[NiCl(C18H15P)2], (3), were obtained concomitantly with form I. In forms I and II, as well as in the cocrystal, the overall crystal packings are determined by an energetic interplay between intramolecular torsions and weak intermolecular C—H...π and C—H...Cl interactions. 相似文献
A new disubstituted terpyridine ligand and the corresponding tri‐copper(II) complex have been prepared and characterised. The binding affinity and binding mode of this tri‐copper complex (as well as the previously reported mono‐ and di‐copper analogues) towards duplex DNA were determined by using UV/Vis spectroscopic titrations and fluorescent indicator displacement (FID) assays. These studies showed the three complexes to bind moderately (in the order of 104 M ?1) to duplex DNA (ct‐DNA and a 26‐mer sequence). Furthermore, the number of copper centres and the nature of the substituents were found to play a significant role in defining the binding mode (intercalative or groove binding). The nuclease potential of the three complexes was investigated by using circular plasmid DNA as a substrate and analysing the products by agarose‐gel electrophoresis. The cleaving activity was found to be dependent on the number of copper centres present (cleaving potency was in the order: tri‐copper>di‐copper>mono‐copper). Interestingly, the tri‐copper complex was able to cleave DNA without the need of external co‐reductants. As this complex displayed the most promising nuclease properties, cell‐based studies were carried out to establish if there was a direct link between DNA cleavage and cellular toxicity. The tri‐copper complex displayed high cytotoxicity against four cancer cell lines. Of particular interest was that it displayed high cytotoxicity against the cisplatin‐resistant MOLT‐4 leukaemia cell line. Cellular uptake studies showed that the tri‐copper complex was able to enter the cell and more importantly localise in the nucleus. Immunoblotting analysis (used to monitor changes in protein levels related to the DNA damage response pathway) and DNA‐flow cytometric studies suggested that this tri‐copper(II) complex is able to induce cellular DNA damage. 相似文献