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排序方式: 共有953条查询结果,搜索用时 15 毫秒
81.
82.
V. Schwämmle A. O. Sousa S. M. de Oliveira 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(4):563-570
Parapatric speciation is studied using an individual-based model with sexual
reproduction. We combine the theory of mutation accumulation for biological ageing
with an environmental selection pressure that varies according to the individuals
geographical positions and phenotypic traits. Fluctuations and genetic diversity of
large populations are crucial ingredients to model the features of evolutionary
branching and are intrinsic properties of the model.
Its implementation on a spatial lattice gives interesting insights into the population
dynamics of speciation on a geographical landscape and the disruptive selection that leads
to the divergence of phenotypes.
Our results suggest that assortative mating is not an obligatory ingredient to obtain
speciation in large populations at low gene flow. 相似文献
83.
Sara Pacelli de Sousa Marcial Guilherme Carneiro Elaine A. Leite 《Journal of nanoparticle research》2017,19(10):340
Paclitaxel (PTX) is a well-known antitumor drug, widely utilized in the treatment of breast, ovarian, head, and neck tumors, among others. The low aqueous solubility (< 1.0 μg/mL; log P = 3.96) limits its use by intravenous route, and alternatives found for the marketed products are associated with high toxicity. Incorporation of PTX into lipid nanocarriers has been considered an interesting nontoxic alternative for this route, but drug loading is usually low. This study aimed to analyze the influence of the lipid composition and three different lipid nanosystems—solid lipid nanoparticles, nanostructured lipid carriers (NLCs), and nanoemulsion—in PTX encapsulation and its biological response. The three proposed systems were prepared by hot melt homogenization followed by ultrasonication. Among the blank formulations first prepared, NLC had the smallest size (74 ± 1 nm), with negative zeta potential (? 11.4 ± 0.1 mV). The incorporation of 0.10 mg/mL PTX into this NLC formulation yielded high and stable encapsulation (0.089 ± 0.003 mg/mL), also supported by polarized light microscopy and differential scanning calorimetry curves. NLC-PTX was very effective against MCF-7 (IC50 25.33 ± 3.17 nM) and MDA-MB-231 breast cancer cell lines (IC50 2.13 ± 0.21 nM), compared to free PTX (IC50 > 500 nM). In addition, no significant cytotoxicity was found against fibroblast cells. Taken together, these results demonstrated that PTX was successfully incorporated into NLC with appropriate physicochemical characteristics for intravenous administration, suggesting that the use of NLC as vehicle to incorporate PTX may be a promising strategy in the treatment of breast cancer. 相似文献
84.
We study the homology theory of ? - modal maps of the interval. We give another proof of the Milnor and Thurston results
about zeta-functions and we give a functorial approach to kneading theory. Our results give explicit methods for computing
the sequences of lap numbers ? (f
k
) and the sequences of numbers of periodic points in an arbitrary interval [x,y].
Received: 25 February 1998 / Accepted: 15 January 1999 相似文献
85.
Paulo C. de Sousa Filho 《Journal of luminescence》2009,129(12):1664-1668
A new solution route for the obtainment of highly pure luminescent rare-earth orthophosphates in hydrothermal conditions was developed. By starting from soluble precursors (lanthanide tripolyphosphato complexes, i.e. with P3O105− as a complexing agent and as an orthophosphate source) and by applying surfactants in a water/toluene medium, the precipitations are confined to reverse micelle structures, thus yielding nanosized and homogeneous orthophosphates. The method was employed to obtain lanthanide-activated lanthanum phosphates, which can be applied as red (LaPO4:Eu3+), green (LaPO4:Ce3+,Tb3+) and blue (LaPO4:Tm3+) phosphors. The produced materials were analyzed by powder X-ray diffractometry, scanning electron microscopy, infrared spectroscopy and luminescence spectroscopy (emission, excitation, lifetimes and chromaticity coordinates). 相似文献
86.
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88.
Ultrasound‐assisted extraction method for the simultaneous determination of emerging contaminants in freshwater sediments 下载免费PDF全文
Diana Nara Ribeiro de Sousa Guilherme Martins Grosseli Antonio Aparecido Mozeto Renato Lajarim Carneiro Pedro Sergio Fadini 《Journal of separation science》2015,38(19):3454-3460
Sediments are the fate of several emerging organic contaminants, such as pharmaceuticals, personal care products and hormones, and therefore an important subject in environmental monitoring studies. In the present work, a simple and sensitive method was developed, validated and applied for the simultaneous extraction of atenolol, caffeine, carbamazepine, diclofenac, ibuprofen, naproxen, propranolol, triclosan, estrone, 17‐β‐estradiol and 17‐α‐ethinylestradiol using ultrasound‐assisted extraction from freshwater sediment samples followed by solid‐phase extraction clean‐up and liquid chromatography with tandem mass spectrometry detection. The solvent type and extraction pH were evaluated to obtain the highest recoveries of the compounds. The best method shows absolute recoveries between 54.0 and 94.4% at 50 ng/g concentration. The method exhibits good precision with relative standard deviation ranging from 1.0–16%. The detection and quantification limits ranged from 0.006–0.067 and 0.016–0.336 ng/g, respectively. The developed method was successfully applied to freshwater sediment samples collected from different sites in Jundiaí River basin of São Paulo State, Brazil. The compounds atenolol, caffeine, propranolol and triclosan were detected in all the sampling sites with concentrations of 13.8, 41.0, 28.5 and 176 ng/g, respectively. 相似文献
89.
Gabriela Furlan Giordano Luis Carlos Silveira Vieira Angelo Luiz Gobbi Renato Sousa Lima Lauro Tatsuo Kubota 《Analytica chimica acta》2015
An integrated platform was developed for point-of-use determination of ethanol in sugar cane fermentation broths. Such analysis is important because ethanol reduces its fuel production efficiency by altering the alcoholic fermentation step when in excess. The custom-designed platform integrates gas diffusion separation with voltammetric detection in a single analysis module. The detector relied on a Ni(OH)2-modified electrode. It was stabilized by uniformly depositing cobalt and cadmium hydroxides as shown by XPS measurements. Such tests were in accordance with the hypothesis related to stabilization of the Ni(OH)2 structure by insertion of Co2+ and Cd2+ ions in this structure. The separation step, in turn, was based on a hydrophobic PTFE membrane, which separates the sample from receptor solution (electrolyte) where the electrodes were placed. Parameters of limit of detection and analytical sensitivity were estimated to be 0.2% v/v and 2.90 μA % (v/v)−1, respectively. Samples of fermentation broth were analyzed by both standard addition method and direct interpolation in saline medium based-analytical curve. In this case, the saline solution exhibited ionic strength similar to those of the samples intended to surpass the tonometry colligative effect of the samples over analyte concentration data by attributing the reduction in quantity of diffused ethanol vapor majorly to the electrolyte. The approach of analytical curve provided rapid, simple and accurate analysis, thus contributing for deployment of point-of-use technologies. All of the results were accurate with respect to those obtained by FTIR method at 95% confidence level. 相似文献
90.