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791.
Chung‐Yang Chuang Trong‐Ming Don Wen‐Yen Chiu 《Journal of polymer science. Part A, Polymer chemistry》2009,47(19):5126-5136
In this research, thermo‐ and pH‐responsive chitosan‐based porous nanoparticles were prepared by the temperature‐dependent self assembly method. The chitosan‐graft‐poly(N‐isopropylacrylamide) (CS‐g‐PNIPAAm) copolymer solution was prepared through polymerization of N‐isopropylacrylamide (NIPAAm) monomer in the presence of chitosan (CS) solution using cerium ammounium nitrate as the initiator. Then, CS‐g‐PNIPAAm solution was diluted by deionized water and heated to 40 °C for CS‐g‐PNIPAAm self‐assembly. After that, CS‐g‐PNIPAAm assembled to form micelles in which shell layer was CS. Crosslinking agent was used to reinforce the micelle structure to form nanoparticle. The molar ratio of CS/NIPAAm in the feed mixture was changed to investigate its effect on structure, morphology, thermal‐ and pH‐responsive properties of the nanoparticles. TEM images showed that a porous structure of nanoparticles was developed. The synthesized nanoparticles carried positive charges on the surface and exhibited stimuli‐responsive properties, and their mean diameter thus could be manipulated by changing pH value and temperature of the environment. The nanoparticles showed a continuous release of the encapsulated doxycycline hyclate up to 10 days during an in‐vitro release experiment. These porous particles with environmentally sensitive properties are expected to be utilized in hydrophilic drug delivery system. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5126–5136, 2009 相似文献
792.
A high-order particle-source-in-cell (PSIC) algorithm is presented for the computation of the interaction between shocks, small scale structures, and liquid and/or solid particles in high-speed engineering applications. The improved high-order finite difference weighted essentially non-oscillatory (WENO-Z) method for solution of the hyperbolic conservation laws that govern the shocked carrier gas flow, lies at the heart of the algorithm. Finite sized particles are modeled as points and are traced in the Lagrangian frame. The physical coupling of particles in the Lagrangian frame and the gas in the Eulerian frame through momentum and energy exchange, is numerically treated through high-order interpolation and weighing. The centered high-order interpolation of the fluid properties to the particle location is shown to lead to numerical instability in shocked flow. An essentially non-oscillatory interpolation (ENO) scheme is devised for the coupling that improves stability. The ENO based algorithm is shown to be numerically stable and to accurately capture shocks, small flow features and particle dispersion. Both the carrier gas and the particles are updated in time without splitting with a third-order Runge–Kutta TVD method. One and two-dimensional computations of a shock moving into a particle cloud demonstrates the characteristics of the WENO-Z based PSIC method (PSIC/WENO-Z). The PSIC/WENO-Z computations are not only in excellent agreement with the numerical simulations with a third-order Rusanov based PSIC and physical experiments in [V. Boiko, V.P. Kiselev, S.P. Kiselev, A. Papyrin, S. Poplavsky, V. Fomin, Shock wave interaction with a cloud of particles, Shock Waves, 7 (1997) 275–285], but also show a significant improvement in the resolution of small scale structures. In two-dimensional simulations of the Mach 3 shock moving into forty thousand bronze particles arranged in the shape of a rectangle, the long time accuracy of the high-order method is demonstrated. The fifth-order PSIC/WENO-Z method with the fifth-order ENO interpolation scheme improves the small scale structure resolution over the third-order PSIC/WENO-Z method with a second-order central interpolation scheme. Preliminary analysis of the particle interaction with the flow structures shows that sharp particle material arms form on the side of the rectangular shape. The arms initially shield the particles from the accelerated flow behind the shock. A reflected compression wave, however, reshocks the particle arm from the shielded area and mixes the particles. 相似文献
793.
Hoon‐Je Cho Do‐Hoon Hwang Jong‐Don Lee Nam‐Sung Cho Sang‐Kyu Lee Jonghee Lee Young Kwan Jung Hong‐Ku Shim 《Journal of polymer science. Part A, Polymer chemistry》2008,46(3):979-988
Novel blue‐emitting germanium‐containing poly(p‐phenylenevinylene) (PPV) derivatives with well‐defined conjugation lengths were synthesized via Wittig‐condensation polymerizations. The polymers can be color‐tuned by the introduction of various chromophores into the PPV‐based polymer backbones. The photoluminescence (PL) spectra of the polymers, GePVK (containing carbazole moieties), GeMEH (containing dialkoxybenzene moieties), and GePTH (containing phenothiazine moieties), were found to exhibit blue, greenish blue, and green emissions, respectively. GePTH produces more red‐shifted emission than GeMEH and GEPVK, resulting in green emission, and the solution and solid state PL spectra of GePVK consist of almost blue emission. The electroluminescence spectra of GeMEH and GePTH contain yellowy green and yellow colors, respectively. Interestingly, GePVK exhibits white emission with CIE coordinates of (0.33, 0.37) due to electroplex emission in the light‐emitting diodes. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 979–988, 2008 相似文献
794.
D. L. Roth Michael P. Cohen R. Michaelson Don Chakerian Michael Reeken 《Mathematical Intelligencer》2000,22(1):5-6
The Mathematical Intelligencer encourages comments about the material in this issue. Letters to the editor should be sent
to the editor-in-chief, Chandler Davis. 相似文献
795.
796.
797.
It is widely accepted from noise models that the extracted performance parameters such as spatial and temporal NEDT do not depend on the number of samples, which are used to estimate the noise values. Experimental studies have determined that noise values depend on the number of sampled data because of other noise contribution or its frequency dependence. This, however, creates ambiguities since unique values NEDT cannot be established without fixing the number of frames to be utilized. However in the frequency domain, values of parameters can be easily established at certain frequency. In the frequency domain it is also easier to study the noise contribution originating from various noise sources such as from the ROIC. This presentation will present preliminary analysis of spatial and temporal noise in the frequency domain by utilizing the power of FFT analysis. 相似文献
798.
Mehdi Asghari‐Khiavi Adam Mechler Keith R. Bambery Don McNaughton Bayden R. Wood 《Journal of Raman spectroscopy : JRS》2009,40(11):1668-1674
The effects of fixation and dehydration procedures on heme environment inside human erythrocytes were examined using resonance Raman spectroscopy. The resonance Raman spectroscopic data along with far‐infrared spectra show that hemoglobin in air‐dried red blood cells and those fixed in the precipitating fixatives, methanol and acetone, changes to hemichrome, a low‐spin component in which the sixth coordination site of the iron is occupied by the imidazole group of the distal histidine. The cross‐linking fixatives, formaldehyde and glutaraldehyde, maintain hemoglobin in its native conformational state (oxyhemoglobin) as evidenced by the appearance of the oxygen ligand marker bands along with the skeletal sensitive modes. However, polymerization with cross‐linking fixatives increases the auto‐oxidation kinetics of hemoglobin and gradually oxidizes it to the met state. Moreover, the dehydration of a red blood cell under N2 results in a change of oxyhemoglobin to a six coordinate low‐spin FeII derivative of hemoglobin, hemochrome. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
799.
在相同的反应体系中当ph值从约9.5调变至11时分别合成出双中孔SiO2和六方中孔SiO2材料,并用XRD、N2吸附、TEM、TG/DTA和FTIR等测试手段对合成产物进行了表征。实验结果表明,双中孔SiO和六 方中孔SiO2是合成中必然出现的两种不同的中孔物相。与六方中孔SiO2相比,双中孔SiO2也具有典型中孔 材料的特征XRD谱图,虽然仅呈现一个易让人产生不完全晶化误解的相对较宽的单XRD衍射峰(d=5.2nm),但它却给出一种独特的N2吸附等温线和窄的双峰中孔孔径分布曲线。由于孔壁的无定形及表面活性剂分子与SiO2骨架间相似的相互作用,两类材料给出类似的FTIR谱图和TG/DTA曲线。然而,在双中孔SiO2的FTIR谱图中960cm处峰强度的微小变化可能意味着在锻烧脱除模板剂后双中孔SiO2较六方中孔SiO2具有更高的骨架聚合度。 相似文献
800.
Don Hadwin 《Mathematische Annalen》2000,316(2):201-213
We show that if S is a pure subnormal operator, then the minimal normal extension can be written as with . We also extend the Kaplansky density theorem by proving that if is a unital -algebra of operators, then every subnormal contraction in is a (SOT) limit of normal contractions in . We prove similar results for subnormal tuples.
Received: 26 July 1998 / in final form: 30 March 1999 相似文献