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91.
A nonaqueous electrochromatographic reversed-phase separation method for retinyl esters using continuous bed columns has been developed. The packing material 7 μm Nucleosil 4000 Å C18 was sol–gel bonded in 180 μm I.D. capillaries. The mobile phase used was 2.5 mM lithium acetate in N,N-dimethylformamide–acetonitrile–methanol (2+7+1, v/v). At 350 V/cm and 30°C, this mobile phase composition gave rise to an electroosmotic flow of 1 mm/s. No Joule heating nor bubble formation were observed even at 625 V/cm (17 μA). With a 36 cm Leff column complete separation of the commercially available and synthesized standards (all-trans-retinyl acetate, palmitate, heptadecanoate, stearate, oleoate, and linoleoate) was obtained within 10 min. The within-day and between-day variations of retention times of all-trans-retinyl palmitate were <0.3% relative standard deviation (RSD) (n=3) and <2% RSD (n=6), respectively. The within-day and between-day variations of peak areas were both <2% (both n=3). The columns were used for more than 1 month without degradation. Liver extracts from arctic seal were analyzed. 相似文献
92.
We establish the existence of solvable Lie groups of dimension 4 and left-invariant Riemannian metrics with zero Bach tensor which are neither conformally Einstein nor half conformally flat. 相似文献
93.
Elsa Callini Zuleyha Özlem Kocabas Atakli Bjørn C. Hauback Shin-ichi Orimo Craig Jensen Martin Dornheim David Grant Young Whan Cho Ping Chen Bjørgvin Hjörvarsson Petra de Jongh Claudia Weidenthaler Marcello Baricco Mark Paskevicius Torben R. Jensen Mark E. Bowden Thomas S. Autrey Andreas Züttel 《Applied Physics A: Materials Science & Processing》2016,122(4):353
94.
Nadège Handké Thomas Trimaille Elsa Luciani Marion Rollet Thierry Delair Bernard Verrier Denis Bertin Didier Gigmes 《Journal of polymer science. Part A, Polymer chemistry》2011,49(6):1341-1350
Poly(N‐acryloxysuccinimide) (PNAS) and poly(N‐acryloxysuccinimide‐co‐N‐vinylpyrrolidone) (P(NAS‐co‐NVP)) of adjustable molecular weights and narrow polydispersities were prepared by nitroxide‐mediated polymerization (NMP) in N,N‐dimethylformamide in the presence of free SG1 (N‐tert‐butyl‐N‐1‐diethylphosphono‐(2,2‐dimethylpropyl) nitroxide), with MAMA‐SG1 (N‐(2‐methylpropyl)‐N‐(1‐diethylphosphono‐2,2‐dimethylpropyl)‐O‐(2‐carboxylprop‐2‐yl)hydroxylamine) alkoxyamine as initiator. The reactivity ratios of NAS and NVP were determined to be rNAS = 0.12 and rNVP = 0, indicating a strong alternating tendency for the P(NAS‐co‐NVP) copolymer. NAS/NVP copolymerization was then performed from a SG1‐functionalized poly(D ,L ‐lactide) (PLA‐SG1) macro‐alkoxyamine as initiator, leading to the corresponding PLA‐b‐P(NAS‐co‐NVP) block copolymer, with similar NAS and NVP reactivity ratios as mentioned above. The copolymer was used as a surface modifier for the PLA diafiltration and nanoprecipitation processes to achieve nanoparticles in the range of 450 and 150 nm, respectively. The presence of the functional/hydrophilic P(NAS‐co‐NVP) block, and particularly the N‐succinimidyl (NS) ester moieties at the particle surface, was evidenced by ethanolamine derivatization and zeta potential measurements. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
95.
Zhaokang Hu Elsa Reichmanis 《Journal of polymer science. Part A, Polymer chemistry》2011,49(5):1155-1162
Two electroactive polystyrene derivatives para‐ substituted with π‐conjugated oligothiophene, poly(5‐hexyl‐5″‐(4‐vinylphenyl)‐2,2′:5′,2″‐terthiophene) ( PH3TS ), and poly(5‐hexyl‐5″″‐(4‐vinylphenyl)‐2,2′:5′,2″:5″,2″′:5″′,2″″‐quinquethiophene) ( PH5TS ) have been successfully synthesized via the Stille coupling reaction between tributyltin postfunctionalized poly(4‐(2‐thiophenyl)styrene) ( PTS ) and bromo‐oligothiophene. The effect of the chain length of the pendant oligothiophenes on properties of the resulting polymers including solubility, thermal stability, optical absorption, and electroactivation energy levels has been studied by using a variety of techniques such as thermogravimetric analyzer, differential scanning calorimetry, UV–Vis, Fluorescence, and cyclic voltammetry. With shielding of the hexyl terminal groups attached to the pendant oligothiophene units, no obvious chain aggregation was observed for both PH3TS and PH5TS even in a poor solvent environment. When compared with conventional linear conjugated polymer systems, the concept of grafting electroactive units as pendant side chains via postfunctionalizing aliphatic polymers might offer a strategy to precisely synthesize new electroactive polymer materials for a number of organic electronic applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
96.
97.
Elsa Cantú Ruiz 《School science and mathematics》2011,111(6):300-305
Latinas/os, the largest and fastest growing minority ethnic group in the United States (impels research that focuses on the education of Latinas/os and the need to reduce the achievement gap that persists between Latinas/os and other groups. Such research has gained in popularity; however, it is still very limited. I use my teaching experience with Latina/o students to highlight the need to motivate Latina/o students in Algebra I, a gatekeeper course for many minority students. In addition, also included are several factors affecting Latina/o students' motivation to learn. The call is urgent and researchers and teachers must pay close attention to the mathematics education of Latina/o students and to the positive consequence on the social and economic welfare of America. 相似文献
98.
Cutting and packing problems have been extensively studied in the literature in recent decades, mainly due to their numerous real-world applications while at the same time exhibiting intrinsic computational complexity. However, a major limitation has been the lack of problem generators that can be widely and commonly used by all researchers in their computational experiments. In this paper, a problem generator for every type of two-dimensional rectangular cutting and packing problems is proposed. The problems are defined according to the recent typology for cutting and packing problems proposed by Wäscher, Haußner, and Schumann (2007) and the relevant problem parameters are identified. The proposed problem generator can significantly contribute to the quality of the computational experiments run with cutting and packing problems and therefore will help improve the quality of the papers published in this field. 相似文献
99.
Víctor M. Ovando-Medina Hugo Martínez-Gutiérrez Miguel A. Corona-Rivera Elsa Cervantes-González Jorge Flores-Mejía Lorena Farías-Cepeda 《Colloid and polymer science》2013,291(9):2131-2138
Conductive silver/silver bromide/polypyrrole nanoparticles were obtained by photopolymerization in o/w microemulsions of pyrrole monomer in the presence of silver nitrate as electron acceptor and dopant under UV light irradiation. The microemulsions were prepared using cetyltrimethylammonium bromide (CTAB) as cationic surfactant. The particles were analyzed by scanning electron microscopy (SEM), UV/Vis, Fourier transform infrared spectroscopy, cyclic voltammetry, and X-ray diffraction (XRD). It was observed from SEM analysis that spherical particles can be obtained by this procedure with relatively narrow particles sizes distributions and average particle diameters of the silver cores (Dp) between 39 and 46 nm, which decreases as the surfactant concentration is increased. The conductivities of the resulting materials were between 0.12 and 0.40 S/m. Formation of cores of Ag and AgBr were observed from the XRD analysis, which was ascribed to the reduction of Ag+ to Ag0 and to reaction of Ag+ with the counterion of CTAB surfactant, respectively. 相似文献
100.
The number of binding sites for a given solute in a protein is a most relevant parameter. This number can be derived from
fluorescence quenching data which provides the fraction of sites occupied at a given free solute concentration. Data are generally
treated according to Scatchard′s or Ward′s equations. Lately, a double logarithmic plot of the data has been extensively used
with this purpose. The present communication discus the validity of this procedure. It is concluded that this type of plot
provides an evaluation of the stoichiometry (molecularity) of the binding process but not the number of equivalent binding
sites per protein. 相似文献