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排序方式: 共有603条查询结果,搜索用时 93 毫秒
91.
Andrea Bírov Emil vajdlenka Jn Cvengros Viera Dostlíkov 《European Journal of Lipid Science and Technology》2002,104(5):271-277
This paper presents the results of two methods employed to determine the methyl ester (ME) fraction in mixed fuels prepared from MEs of higher fatty acids and fossil Diesel fuel. The first method is based on determining the ester number of the mixed fuel. The second one utilises the measurement of the carbonyl band intensity in the mixed fuel by infrared (IR) spectroscopy. The ME fraction in the tested mixed fuels was always set to 30 wt‐%. Applying the first method the ester numbers of mixed fuels were determined and the ME fraction was defined using an averaged molar mass of ME. The differences between the values of the measured and real fraction of ME varied between −0.2 and +0.8 wt‐%. If the value of the average molar mass of ME was not known, the molar mass of methyl oleate was used as a reference. Thereby the differences in determining the ME fraction in mixed fuels ranged between −0.1 and +0.9 wt‐%. Employing the IR spectroscopy method the differences between the measured and the real fraction of ME varied between −1.0 and +0.5 wt‐%. Both methods are suitable to determine the ME fraction in mixed fuels. 相似文献
92.
Roychowdhury H Agrawal GP Wolf E 《Journal of the Optical Society of America. A, Optics, image science, and vision》2006,23(4):940-948
Expressions are derived for the cross-spectral density matrix of an electromagnetic Gaussian Schell-model beam propagating through a paraxial ABCD system. Using the recently developed unified theory of coherence and polarization of electromagnetic beams and the ABCD matrix for gradient-index fibers, we study the changes of the spectral density, of the spectral degree of polarization, and of the spectral degree of coherence of such a beam as it travels through the fiber. Effects of material dispersion are also considered. 相似文献
93.
Deng L Trepat X Butler JP Millet E Morgan KG Weitz DA Fredberg JJ 《Nature materials》2006,5(8):636-640
Material moduli of the cytoskeleton (CSK) influence a wide range of cell functions. There is substantial evidence from reconstituted F-actin gels that a regime exists in which the moduli scale with frequency with a universal exponent of 3/4. Such behaviour is entropic in origin and is attributable to fluctuations in semiflexible polymers driven by thermal forces, but it is not obvious a priori that such entropic effects are responsible for the elasticity of the CSK. Here we demonstrate the existence of such a regime in the living cell, but only at high frequencies. Fast events scaled with frequency in a manner comparable to semiflexible-polymer dynamics, but slow events scaled with a non-universal exponent that was systematically smaller than 3/4 and probably more consistent with a soft-glass regime. These findings strongly suggest that at smaller timescales elasticity arises from entropic fluctuations of a semiflexible-filament network, whereas on longer timescales slow (soft-glass-like) dynamics of a different origin prevail. The transition between these two regimes occurred on timescales of the order of 0.01 s, thus setting within the slow glassy regime cellular events such as spreading, crawling, contracting, and invading. 相似文献
94.
Xu C Miranda-Nieves D Ankrum JA Matthiesen ME Phillips JA Roes I Wojtkiewicz GR Juneja V Kultima JR Zhao W Vemula PK Lin CP Nahrendorf M Karp JM 《Nano letters》2012,12(8):4131-4139
Monitoring the location, distribution and long-term engraftment of administered cells is critical for demonstrating the success of a cell therapy. Among available imaging-based cell tracking tools, magnetic resonance imaging (MRI) is advantageous due to its noninvasiveness, deep penetration, and high spatial resolution. While tracking cells in preclinical models via internalized MRI contrast agents (iron oxide nanoparticles, IO-NPs) is a widely used method, IO-NPs suffer from low iron content per particle, low uptake in nonphagocytotic cell types (e.g., mesenchymal stem cells, MSCs), weak negative contrast, and decreased MRI signal due to cell proliferation and cellular exocytosis. Herein, we demonstrate that internalization of IO-NP (10 nm) loaded biodegradable poly(lactide-co-glycolide) microparticles (IO/PLGA-MPs, 0.4-3 μm) in MSCs enhances MR parameters such as the r(2) relaxivity (5-fold), residence time inside the cells (3-fold) and R(2) signal (2-fold) compared to IO-NPs alone. Intriguingly, in vitro and in vivo experiments demonstrate that internalization of IO/PLGA-MPs in MSCs does not compromise inherent cell properties such as viability, proliferation, migration and their ability to home to sites of inflammation. 相似文献
95.
Hechang Lei Kefeng Wang Rongwei Hu Hyejin Ryu Milinda Abeykoon Emil S Bozin Cedomir Petrovic 《Science and Technology of Advanced Materials》2012,13(5)
Iron chalcogenide superconductors have become one of the most investigated superconducting materials in recent years due to high upper critical fields, competing interactions and complex electronic and magnetic phase diagrams. The structural complexity, defects and atomic site occupancies significantly affect the normal and superconducting states in these compounds. In this work we review the vortex behavior, critical current density and high magnetic field pair-breaking mechanism in iron chalcogenide superconductors. We also point to relevant structural features and normal-state properties. 相似文献
96.
Collecting silver artefacts has traditionally been a very popular hobby.Silver is addictive,therefore the number of potential collectors and investors appears to grow each year.Unfortunately,increases in the interest and buying potentials resulted in a number of forgeries manufactured and introduced to the open antique market.The items such as early silver candlesticks dictate a very high price,for many high quality fakes show very good appearances and matching similarities with originals.Such copies are tr... 相似文献
97.
Wise Erica H.; Sturm Cynthia A.; Nutt Roberta L.; Rodolfa Emil; Schaffer Jack B.; Webb Carol 《Canadian Metallurgical Quarterly》2010,41(4):288
As a profession we are committed to maintaining and enhancing our competence as psychologists in order to most effectively serve the public throughout our careers. While this is a widely shared commitment among psychologists, there is considerably less consensus regarding how best to accomplish this goal. This dilemma is examined from the ethical, educational and legal perspectives. The American Psychological Association (APA) Ethics Code clearly articulates that competence is an ethical duty, although there is little guidance provided in the code as to how to meet this standard. As a profession we have tended to focus on the construct of life-long learning and we have incorporated this principle into our education and training standards. In fact, APA accreditation requires that doctoral programs inculcate this value into our foundational training. The majority of Psychology Licensing Boards have addressed this issue through the endorsement of mandatory continuing education requirements that primarily focus on hours and the content or structure of approved programs. Potential limitations to our ability to effectively self-assess our professional training needs are discussed and several innovative models are presented for integrating effective self-assessment and continuing education. Three invited experts provide commentaries that further explore the challenges and dilemmas posed by the ethical, legal and professional duty to maintain and enhance competence throughout our professional careers. These commentaries broaden the considerations, provide practical suggestions from other professions and provide a vision for the future. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
98.
99.
Abstract The concept of the Rayleigh range, well known in the theory of coherent beams, is generalized to a class of partially coherent beams. Curves are presented which show the dependence of the Rayleigh range on the spot size of the beam and on the spectral degree of coherence of the light in the plane of the waist. 相似文献
100.
Abstract The spectral properties and the coherence properties of Gaussian Schell-model beams, propagating in dispersive and absorbing media, are discussed. Unlike in free space, the ratio of the transverse spectral correlation length to the beam width is found to increase on propagation. Consequently upon propagation the beam becomes spatially more coherent at each frequency. Numerical results for the spectrum and for the degrees of spectral and of temporal coherence of the field are presented for some selected values of the beam parameters and for several values of the propagation distance. Propagation in a gain medium is also briefly discussed. 相似文献