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121.
A new approach to the determination of afiatoxins B1, B2, G1 and G2 is given; the method involves high-performance liquid chromatography with amperometric detection in the differential-pulse mode at the dropping mercury electrode with 1-s drop time. These aflatoxins can be determined simultaneously with good resolution but with some compromise in sensitivity. The detection limit of underivatized aflatoxin standards is around 5 ng. Average recoveries of aflatoxins from peanut butter by the Beebe method were G2 81%, G1 87%, B2 77% and B1 76%. 相似文献
122.
Irache JM Huici M Konecny M Espuelas S Campanero MA Arbos P 《Molecules (Basel, Switzerland)》2005,10(1):126-145
Bioadhesive nanoparticles have been proposed as carriers for the oral delivery of poorly available drugs and facilitate the use of this route. This work summarises some experiments describing the bioadhesive potential of Gantrez nanoparticles fluorescently labeled with rhodamine B isothiocyanate. The adhesive potential of Gantrez was found to be stronger when folded as nanoparticles than in the solubilised form. Conventional nanoparticles displayed a tropism for the upper areas of the gastrointestinal tract, with a maximum of adhesion 30 min post-administration and a decrease in the adhered fraction along the time depending on the given dose. The cross-linkage of nanoparticles with increasing amounts of 1,3-diaminopropane stabilised the resulting carriers and prolonged their half-life in an aqueous environment; although, the adhesive capacity of nanoparticles, the intensity and the relative duration of the adhesive interactions within the gut as a function of the cross-linking degree. Finally, nanoparticles were coated with either gelatin or albumin. In the first case, the presence of gelatin dramatically decreased the initial capacity of these carriers to interact with the gut mucosa and the intensity of these phenomenons. In the latter, bovine serum albumin coated nanoparticles (BSA-NP) showed an important tropism for the stomach mucosa without further significant distribution to other parts of the gut mucosa. 相似文献
123.
Monica?HanslienEmail author Kenneth H.?Karlsen Aslak?Tveito 《BIT Numerical Mathematics》2005,45(4):725-741
We analyze an explicit finite difference scheme for the general form of the Hodgkin-Huxley model, which is a nonlinear partial
differential equation coupled to a set of ODEs. The system of equations describes propagation of an electrical signal in excitable
cells. We prove that the numerical solution is bounded in the L∞-norm and L2 converges to a unique solution. The L∞-bound, which is the key point of our analysis, is proved by showing that the discrete solutions are invariant in a physically
relevant bounded region. For the convergence proof we use the compactness method.
AMS subject classification (2000) 65F20 相似文献
124.
We developed a rapid and non-toxic method for the preparation of colloidal gold nanoparticles (GNPs) by using tryptophan (Trp) as reducing/stabilizing agent. We show that the temperature has a major influence on the kinetics of gold ion reduction and the crystal growth, higher temperatures favoring the synthesis of anisotropic nanoparticles (triangles and hexagons). The as-synthesized nanostructures were characterized by UV–Vis absorption spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), fluorescence, and surface-enhanced Raman scattering (SERS) spectroscopy. The UV–Vis measurements confirmed that temperature is a critical factor in the synthesis process, having a major effect on the shape of the synthesized GNPs. Moreover, fluorescence spectroscopy was able to monitor the quenching of the Trp fluorescence during the in situ synthesis of GNPs. Using Trp as molecular analyte to evaluate the SERS efficiency of as-prepared GNPs at different temperatures, we demonstrated that the Raman enhancement of the synthesized gold nanoplates is higher than that of the gold spherical nanoparticles. 相似文献
125.
Tutuianu M Inderwildi OR Bessler WG Warnatz J 《The journal of physical chemistry. B》2006,110(35):17484-17492
Density functional theory (DFT) quantum chemical calculations are used to determine adsorption energies and geometries of NO, NO(2), CO(2), and H(2)O on a barium oxide (100) surface. The study includes two adsorption geometries for NO(2). All species form thermodynamically stable adsorbates, and adsorption strength increases in the order NO(2) < H(2)O < NO = CO(2). The influence of surface coverage on adsorption energy is investigated for all species, and a strong coverage dependence is observed. For CO(2), a chemisorbed, carbonate-type structure is identified; the adsorption from the gas phase is nonactivated. Numerical calculations of the competitive adsorption/desorption equilibria of the four species show that, under typical engine exhaust gas composition, the BaO surface is carbonated to a large extent. The results indicate that carbon dioxide plays an essential role in the surface processes during NO(x)() storage on BaO, where it can block a large part of available surface sites. 相似文献
126.
Zhou B Lin Y Veca LM Fernando KA Harruff BA Sun YP 《The journal of physical chemistry. B》2006,110(7):3001-3006
Single-walled carbon nanotubes (SWNTs) were well-functionalized for a study of their defect-derived luminescence properties. The soluble nanotube sample was homogeneously dispersed in poly(vinyl alcohol) (PVA) films via solution-phase mixing and then wet-casting. The PVA films embedded with the functionalized SWNTs were strongly luminescent according to spectroscopic and confocal microscopic results. The luminescence from the films was highly polarized, with the observed anisotropy value approaching the limit for collinear absorption and emission dipole moments. The films were mechanically stretched to align the embedded nanotubes, and results from luminescence measurements of the stretched films suggested that the excitation was strongly in favor of the direction along the nanotube axis. Mechanistic implications of the polarization spectroscopy results for the luminescent functionalized nanotubes in the polymeric matrix with and without the mechanic alignment are discussed. 相似文献
127.
Gulmini M Appolonia L Framarin P Mirti P 《Analytical and bioanalytical chemistry》2006,386(6):1815-1822
Twelve finds from archaeological excavations carried out in the Aosta region (Italy) were studied by scanning electron microscopy
coupled with energy-dispersive X-ray detection (SEM–EDS). The archaeological samples were shards of glazed pottery dating
from the fourth to the seventh century AD. Analysis of ceramic bodies revealed a general homogeneity in composition among
the studied samples and the use of a noncalcareous clay for their manufacture; however, two shards stand out due to their
high iron contents. Glazes proved to be high-lead products with more than 70% PbO in all of the samples investigated but one.
For the latter, a composition poorer in lead and richer in silicon, aluminium and iron was found. SEM observation of the contact
region between body and glaze suggests that the vitreous coatings were mostly obtained by applying the glazing components
onto the unfired clay body; moreover, a comparison between clay and glaze compositions suggests the use of a lead compound
mixed with a silica-rich material, not a lead compound by itself. 相似文献
128.
Juan Dávila Manuel del Pino Monica Musso Juncheng Wei 《Archive for Rational Mechanics and Analysis》2006,182(2):181-221
We consider the boundary value problem
where Ω is a smooth and bounded domain in ℝ2 and λ > 0. We prove that for any integer k ≧ 1 there exist at least two solutions u
λ
with the property that the boundary flux satisfies up to subsequences λ → 0,
where the ξ
j
are points of ∂Ω ordered clockwise in j. 相似文献
129.
130.
The adsorption of benzene, toluene, and chlorobenzene on single-walled carbon nanotubes (SWCNTs) with and without acid oxidation was conducted to investigate the influences of derivative groups on benzene rings and functional groups from SWCNTs on adsorption by SWCNTs. The SWCNTs of high purity were chosen and moderate acid oxidation was performed so that the surface physical properties remained unchanged after acid oxidation and the influences of acid oxidation on adsorption were only contributed from the modification of the surface chemistry of SWCNTs. The oxygen-containing surface groups introduced by acid oxidation obstructed the interactions between functional groups of nonpolar benzene derivatives and C-rings of SWCNTs significantly. The dispersive interaction between the partially positive H+ of the methyl group and the oxygen-containing surface groups slightly increased the adsorption of toluene on oxidized SWCNTs at high solution pH. The thermodynamic of adsorption was also studied at different temperatures. 相似文献