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41.
研究基于扩展Leslie投影矩阵的离散尺度结构种群模型的最优收获问题,约束条件包括生态平衡和开发成本等.运用凸优化理论证明了最优收获策略的存在性,导出了最优收获模式,应用模型参数给出了收获比率.结论显示:最优策略具有两阶段结构. 相似文献
42.
Lung-Hui Chen 《复变函数与椭圆型方程》2015,60(5):707-731
We study the inverse spectral problem in an interior transmission eigenvalue problem. The Cartwright’s theory in value distribution theory gives a connection between the distributional structure of the eigenvalues and the asymptotic behaviours of its defining functional determinants. Given a sufficient quantity of transmission eigenvalues, we prove a uniqueness of the refraction index in inhomogeneous medium as an uniqueness problem in entire function theory. The asymptotically periodical structure of the zero set of the solutions helps to locate infinitely many eigenvalues of infinite degree of freedom. 相似文献
43.
Co‐polymeric hydrogels consisting of N‐vinyl‐2‐pyrrolidone (NVP) and acrylic acid (AAc) were synthesized and evaluated for release of a model drug, i.e., vitamin B12. Release studies in simulated gastric fluid (pH 1.2) and intestinal fluid (pH 7.4), at 37°C, showed the hydrogels to be pH sensitive. An in vitro release study by ‘traditional dissolution test’ (TDT) showed that percent drug released from the hydrogel was nearly 8.6±2.1 and 83.2±4.8 in the media of pH 1.2 and 6.8, respectively. However, in order to incorporate in vivo GI conditions such as acidic pH and high water content in the stomach, low water content and the presence of a semi–solid mass in the large intestine, a new test model, called flow through diffusion cell (FTDC) was also used. The two approaches yielded almost different release profiles. The gels were characterized by thermogravimetric analysis and FTIR spectroscopy. 相似文献
44.
Sutanjay Saxena 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(5):387-393
The dynamic release of drug propranolol HCl from the propranolol HCl–resin complex (PRC) loaded calcium alginate beads has been studied in the buffer media of pH 1.2 at the physiological temperature 37°C. The PRC encapsulated beads demonstrated nearly 58.04% release while naked PRC particles released 98.00% drug in 24 h in the gastric fluid. The amount of drug released was found to increase with and decrease in the amount of sodium alginate in the beads. Similarly, with the increase in the amount of entrapped PRC particles within the beads, the quantity of drug released was also observed to increase. The degree of crosslinking of beads also affected the release kinetics. Interestingly, the release from naked PRC particles followed ‘first‐order’ kinetics while PRC particles, entrapped in calcium–alginate beads, exhibited ‘diffusion controlled’ release behavior as indicated by liner nature of fractional release vs. √t plot. 相似文献
45.
46.
Characteristic properties of elastomers can be tailored by embedding them with filler particles. Along with enhancing the overall properties of the composite, filler particles also induce some inelastic effects. In this paper, a finite element computational model is used to study the effect of microstructure morphology in filled elastomers, on its macroscopic large deformation behavior. A multiphase material model that accounts for the hypothesis of shift in glass transition temperature in the vicinity of the filler particle is developed to simulate the interphase between the fillers and the matrix. It also accounts for the breakdown and re-aggregation of filler networks under cyclic loading. Examples at the microstructural level, demonstrating the dynamics of the interphase using the developed multiphase model have been successfully simulated. The obtained results are in good qualitative agreement with the Mullins effect. Therefore, computational experiments using this methodology enable the prediction of the experimentally observed softening behavior in filled elastomers based on its microstructure evolution. 相似文献
47.
《Comptes Rendus Chimie》2014,17(4):310-315
Submicron non-aqueous emulsions, of interest for biomedical and cosmetic formulations, were developed for the system comprising poly(ethylene glycol) (PEG) 400 and Miglyol 812, an enzymatic degradable liquid glycerine ester. These emulsions, with PEG 400 as continuous phase and Miglyol 812 droplets, in the size range of 200 nm, were stabilized by a poly(butadiene)-b-poly(2-vinylpyridine) (PBut-b-P2VP) block copolymer with a composition close to 50/50 wt%. The droplet size, stability and the rheological characteristics were examined as a function of the copolymer concentration. An original aspect of these anhydrous emulsions, with a water miscible continuous phase, is their water dispersibility without additional surfactant. In fact, the initial anhydrous emulsion is sterically stabilized and after water addition at low pH, the protonated P2VP sequence of the copolymer provides the electro-steric stabilization. This oil-in-water emulsion is characterized by sub micron sized Miglyol 812 droplets in an aqueous phase of PEG 400 and water at pH 1. 相似文献
48.
《Comptes Rendus Chimie》2014,17(7-8):687-700
The influence of the presence of H2O on the contact between carbon, used as model soot, and a model four-way catalyst (1% Pt–10% BaO/Al2O3) was investigated. NOx adsorption/TPD cycles at 300 °C together with XRD, XPS and DRIFTS characterizations showed that only surface nitrate species are destabilized by the carbon present in the catalytic bed, leading to a decrease of the NOx storage capacity and carbonate species formation. In another way, injection of water in the reactive gas flow decreases also the NOx storage capacity of the catalyst, but promotes the formation of stable nitrate species. A non-cumulative effect of carbon and water was observed. It was proposed that a competition between the destabilization, by carbon, of weakly bonded surface nitrate species and the enhancement of bulk nitrate species formation in the presence of water occurs. 相似文献
49.
Jiankang Deng Jing Hu Juanjuan Zhao Nan An Kuijing Liang Qinghua Wang Zhiqiang Zhang Rongrong Wu Fuyuan Zhang 《Arabian Journal of Chemistry》2021,14(7):103195
This study established a ferric ion (Fe3+) detection method as a result of the fluorescence quenching effect of Fe3+ on carbon dots (CDs). Specifically, we proposed, a green microwave synthesis route towards fluorescent CDs that requires only the brewer’s spent grain as starting materials. Transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectra and X-ray photoelectron spectroscopy were performed to investigate the CDs characteristic: morphology, size distribution, functional groups, and composition, respectively. The experimental results, which were run under optimal experimental conditions, indicated that the fluorescence intensity and concentration of Fe3+ were within the desired linear range (0.3–7 μM). The detection limit of this assay towards Fe3+ was 95 nM. The proposed method showed significant selectivity with respect to interfering ions. We evaluated the potential application of this method with tap water, lake water and fetal bovine serum as real samples. Additionally, the CDs could be served as superior bioimaging probes in Hela cells as a result of their excellent optical stability and good biocompatibility. In a word, the present study provides a new idea for CDs derived from the waste of agricultural products for detecting food or environmental contaminants and cell imaging. 相似文献