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1.
Jo?o?Pedro?Ferreira Jo?o?Alexandre?Rodrigues Inês?Teodora?Elias?da?FonsecaEmail author 《Journal of Solid State Electrochemistry》2004,8(4):260-271
The electrochemical behaviour of copper in neutral buffered and non-buffered synthetic seawater and in pure chloride solutions has been studied by cyclic voltammetry, weight loss measurements, open circuit potential and scanning electron microscopy (SEM). Values of the repassivation potentials of Cu in non-buffered and buffered synthetic seawater, at 50 mV s–1, were 0.12 and 0.46 V vs. SCE, respectively. The sharpness, heights and location of the different peaks as well as their charges were shown to be influenced by the composition of the solution, buffering conditions, deoxygenation, polarization potential and time. High chloride concentrations lead to higher oxidation charges. The anodic and the cathodic charges were shown to increase as the chloride concentration increases. The open circuit potential transients of copper in non-deoxygenated, non-buffered synthetic seawater indicate pitting from the beginning of the exposure, while in buffered solutions the pitting appeared only after a quite long exposure period, i.e. after 40 days. Corrosion rates of Cu samples after 3 months of immersion were higher in solutions of pure chloride (0.5 M) than in synthetic seawater. After six months the differences were even more noticeable. SEM images have showed a somewhat higher density of pits on copper samples immersed in the chloride solution (0.5 M), in comparison with those in synthetic seawater. 相似文献
2.
Sewwandi Abeywardana Annabelle L. Cantu Teodora Nedic Michael P. Schramm 《Tetrahedron letters》2018,59(37):3393-3396
The synthesis and properties of a variety of substituted BODIPY diesters is presented. We find that certain substitution patterns afford appreciable yields of the target compounds and that electronic effects result in predicable differential fluorescent behavior. Challenges to further water solubilize these dyes and/or provide new points of attachment for biological tagging remain, these strategies are discussed. 相似文献
3.
A series of flexibly linked bis(pyridinium) salts with various counterions (Br?, PF6?, BF4? and OTf-) was designed and prepared starting from corresponding N-alkylated 4-pyridones precursors with mesogenic 3,4,5-tris(alkyloxy)benzyl moieties (alkyl = dodecyl or tetradecyl). These salts were investigated for their liquid crystalline properties by a combination of differential scanning calorimetry, polarising optical microscopy and temperature-dependent powder X-ray diffraction (XRD). Their thermal stability was checked by thermogravimetric analysis. All bis(pyridinium) salts, except the triflate salt with shorter terminal carbon chain, display an enantiotropic liquid crystalline behaviour with a hexagonal columnar (Colh) phase assigned on the basis of its characteristic texture and XRD studies. It was found that these luminescent bis(pyridinium) salts show weak emission in dichloromethane solutions at room temperature and a pronounced red-shifted emission in solid state. The emission properties of these bis(pyridinium) salts do not depend significantly on the nature of counterion employed. 相似文献
4.
We construct certain Lagrange, Hermite and Birkhoff-type operators, which interpolate a given function and some of its derivatives
on the border of a triangle with one curved side, as well as some of their product and Boolean sum operators. We study the
interpolation properties and the order of accuracy (degree of exactness and precision set) of the constructed operators, respectively
the remainders of the corresponding interpolation formulas. Finally, we give some numerical examples. 相似文献
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6.
Gustavo Merola Stefano Gentili Franco Tagliaro Teodora Macchia 《Analytical and bioanalytical chemistry》2010,397(7):2987-2995
A simple procedure combining headspace solid-phase microextraction (HS-SPME) and gas chromatography–mass spectrometry (GC/MS)
to detect and quantify amphetamines, ketamine, methadone, cocaine, cocaethylene and ∆9-tetrahydrocannabinol (THC) in hair is described. This procedure allows, in a single sample, even scant, analysis of drugs
requiring different analytical conditions. A hair sample (10 mg) is washed and subjected to acidic hydrolysis. Then the HS-SPME
is carried out (10 min at 90 °C) for amphetamines, ketamine, methadone, cocaine and cocaethylene. For derivatization of analytes,
the fibre is introduced into the headspace of another closed vial containing acetic anhydride. After a chromatographic run,
an alkaline hydrolysis for THC analysis is carried out in the same vial containing the hair sample previously used. For adsorption,
the solid-phase microextraction needle is inserted into the headspace of the vial and the fibre is exposed for 30 min at 150 °C.
For derivatization of analytes, the fibre is introduced into the headspace of another closed vial containing N-methyl-N-(trimethylsilyl)trifluoroacetamide. The GC/MS parameters were the same for both chromatographic runs. The linearity was proved
to be between 0.01 and 10.00 ng/mg. The repeatability (intra- and interday precision) was below 10% as the coefficient of
variation for all compounds. The accuracy, as the relative recovery, was 96.2–103.5% (spiked samples) and 88.6–101.7% (quality
control sample). The limit of detection ranged from 0.01 to 0.12 ng/mg, and the limit of quantification ranged from 0.02 to
0.37 ng/mg. Application of the procedure to real hair samples is described. To the best of our knowledge, the proposed procedure
combining HS-SPME and GC/MS is the first one be to successfully applied to the simultaneous determination of most of the common
recreational drugs, including THC, in a single hair sample. 相似文献
7.
We use some interpolation operators and some Bernstein type operators for construction of surfaces which satisfy some given conditions. 相似文献
8.
Marcus J. Grote Teodora Mitkova 《Journal of Computational and Applied Mathematics》2010,234(12):3283-3302
Explicit local time-stepping methods are derived for time dependent Maxwell equations in conducting and non-conducting media. By using smaller time steps precisely where smaller elements in the mesh are located, these methods overcome the bottleneck caused by local mesh refinement in explicit time integrators. When combined with a finite element discretisation in space with an essentially diagonal mass matrix, the resulting discrete time-marching schemes are fully explicit and thus inherently parallel. In a non-conducting source-free medium they also conserve a discrete energy, which provides a rigorous criterion for stability. Starting from the standard leap-frog scheme, local time-stepping methods of arbitrarily high accuracy are derived for non-conducting media. Numerical experiments with a discontinuous Galerkin discretisation in space validate the theory and illustrate the usefulness of the proposed time integration schemes. 相似文献
9.
Klein DJ Ivanciuc T Ryzhov A Ivanciuc O 《Combinatorial chemistry & high throughput screening》2008,11(9):723-733
Reaction networks are viewed as derived from ordinary molecular structures related in reactant-product pairs so as to manifest a chemical super-structure. Such super-structures then are candidates for applications in a general combinatoric chemistry. Notable additional characterization of a reaction super-structure occurs when such reaction graphs are directed, as for example when there is progressive substitution (or addition) on a fixed molecular skeleton. Such a set of partially ordered entities is in mathematics termed a poset, which further manifests a number of special properties, as then might be utilized in different applications. Focus on the overall "super-structural" poset goes beyond ordinary molecular structure in attending to how a structure fits into a (reaction) network, and thereby brings an extra "dimension" to conventional stereochemical theory. The possibility that different molecular properties vary smoothly along chains of interconnections in such a super-structure is a natural assumption for a novel approach to molecular property and bioactivity correlations. Different manners to interpolate/extrapolate on a poset network yield quantitative super-structure/activity relationships (QSSARs), with some numerical fits, e.g., for properties of polychlorinated biphenyls (PCBs) seemingly being quite reasonable. There seems to be promise for combinatoric posetic ideas. 相似文献
10.
The structural parameters, electronic properties, and infrared frequencies of three binuclear ruthenium complexes, [(NH(3))(5)Ru(pyrazine)Ru(NH(3))(5)](n+), n = 4-6, have been investigated with density functional theory. Structural analysis demonstrates that the structure of the mixed-valence 5+, or [II,III], is not an intermediate of the reduced 4+, or [II,II], and the oxidized 6+, or [III,III], compounds. Electronic structure comparison shows that the Ru d(yz) antibonding orbital is empty when n = 5 and 6 and occupied, when n = 4. The infrared frequencies have been calculated for a sequence of models with increasingly detailed accounts of counterions, ranging from the free Creutz-Taube 5+ ion, over jellium embedded, COnductor-like Screening MOdel (COSMO), to the experimental structure of the triclinic [II,III](tos)(5).4H(2)O (tos = p-toluenesulfonate) crystal. Analysis of the Ru vibrations shows that the spectra for the two symmetry-inequivalent Ru atoms are essentially the same. We find that Ru-Ru modes exist near three well-defined frequencies in the solid: at 145, 285, and 345 cm(-1). Similar results are also obtained for the simplified jellium and COSMO models. The spectral properties of these vibrational correlations testify to the existence of two coupled Ru atoms in the same charge state. 相似文献