排序方式: 共有29条查询结果,搜索用时 15 毫秒
1.
Cayetano Di Bartolo Rodolfo Gambini Jorge Griego 《Communications in Mathematical Physics》1993,158(2):217-240
A set of coordinates in the non-parametric loop-space is introduced. We show that these coordinates transform under infinite dimensional linear representations of the diffeomorphism group. An extension of the group of loops in terms of these objects is proposed. The enlarged group behaves locally as an infinite dimensional Lie group. Ordinary loops form a subgroup of this group. The algebraic properties of this new mathematical structure are analyzed in detail. Applications of the formalism to field theory, quantum gravity and knot theory are considered. 相似文献
2.
Yanes EG Gratz SR Sutton RM Stalcup AM 《Fresenius' Journal of Analytical Chemistry》2001,369(5):412-417
The enantioseparation capabilities of three different functionalized beta-cyclodextrins, two sulfated beta-cyclodextrins with 4 and 15 nominal degrees of substitution and a phosphated beta-cyclodextrin with 8 degrees of substitution, were compared. While anodic detection was used with both sulfated cyclodextrins, the phosphated cyclodextrin required cathodic detection suggesting either lower ionization of the phosphated cyclodextrin or generally lower affinity of the analytes for the phosphated cyclodextrin. The effects of several experimental parameters were evaluated with respect to enantioseparation. The degrees of substitution of the cyclodextrin, pH of the background electrolyte as well as the concentration of the functionalized beta-cyclodextrin, each had a significant influence on the successful enantiomeric separation of the chiral drugs investigated. 相似文献
3.
A. C. Yanes A. Santana-Alonso J. Méndez-Ramos J. del-Castillo 《Applied physics. B, Lasers and optics》2013,113(4):589-596
Transparent nano-glass-ceramics containing KYF4 nanocrystals were successfully obtained by the sol–gel method, doped with Eu3+ and co-doped with Yb3+ and Tm3+ ions. Precipitation of cubic KYF4 nanocrystals was confirmed by X-ray diffraction and high-resolution transmission electron microscope images. Excitation and emission spectra let us to discern between ions into KYF4 nanocrystals and those remaining in a glassy environment, supplemented with time-resolved photoluminescence decays, that also clearly reveal differences between local environments. Unusual high-energy up-conversion emissions in the UV range were obtained in Yb3+–Tm3+ co-doped samples, and involved mechanisms were discussed. The intensity of these high-energy emissions was analyzed as a function of Yb3+ concentration, heat treatment temperature of precursor sol–gel glasses and pump power, determining the optimum values for potential optical applications as highly efficient UV up-conversion materials in UV solid-state lasers. 相似文献
4.
J. del-Castillo A. C. Yanes J. Méndez-Ramos V. K. Tikhomirov V. V. Moshchalkov V. D. Rodríguez 《Journal of Sol-Gel Science and Technology》2010,53(3):509-514
89.5(SiO2)10(PbF2)0.5(REF3) silicate glasses have been prepared using room temperature sol–gel processing of Si(OCH2CH3)4, Pb(CH3COO)2·3H2O, RE(CH3COO)3·nH2O and trifluoroacetic acid as a fluorinating agent, where RE stands for rare-earth ions, such as Yb3+, Er3+, Ho3+, Tm3+, or combinations of those ions. On heat treatment of these glasses at about 300–400 °C, the rare-earth doped spherical PbF2 nanocrystals precipitate within SiO2 glass matrix providing transparent nano-structured glass–ceramics, while the diameter of the nanocrystals can be set in the range from 5 to 25 nm by varying time and temperature of the heat
treatment. The structural and photoluminescence studies confirm the incorporation of rare-earth ions into the PbF2 nanocrystals and white and tuneable colour up-conversion luminescence has been detected in case of Yb3+-Er3+-Tm3+ and Yb3+-Ho3+-Tm3+ co-doped nanocrystals by varying dopant ratio and pump power. 相似文献
5.
Yanes O Avilés FX Wenzel R Nazabal A Zenobi R Calvete JJ 《Journal of the American Society for Mass Spectrometry》2007,18(4):600-606
Proteomic profiling involves identification and quantification of protein components in complex biological systems. Most of the mass profiling studies performed with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) have been restricted to peptides and small proteins (<20 kDa) because the sensitivity of the standard ion detectors decreases with increasing ion mass. Here we perform a protein profiling study of the snake venom Sistrurus miliarius barbouri, comparing 2D gel electrophoresis and reversed-phase high-performance liquid chromatography (HPLC) with a high mass cryodetector MALDI-TOF instrument (Macromizer), whose detector displays an uniform sensitivity with mass. Our results show that such MS approach can render superior analysis of protein complexity compared with that obtained with the electrophoretic and chromatographic approaches. The summation of ion impacts allows relative quantification of different proteins, and the number of ion counts correlates with the peak areas in the reversed-phase HPLC. Furthermore, the sensitivity reached with the high mass cryodetection MS technology clearly exceeds the detection limit of standard high-sensitivity staining methods. 相似文献
6.
A. C. Yanes J. J. Velázquez J. del-Castillo J. Méndez-Ramos V. D. Rodríguez 《Journal of Sol-Gel Science and Technology》2009,51(1):4-9
Nanostructured transparent glass-ceramics with composition of 95SiO2–5LaF3 co-doped with 0.3Yb3+, 0.1Ho3+ and 0.1Tm3+ (mol%) were synthesized by thermal treatment of precursor sol–gel derived glasses. X-ray diffraction and transmission electron
microscopy analysis point out the precipitation of hexagonal LaF3 nanocrystals with diameter ranging from 11 to 20 nm in these nano-glass-ceramics. White light generation by means of efficient
blue, green and red up-conversion luminescence under infrared excitation at 980 nm was observed and involved mechanisms were
analyzed. Colour tuneability is achieved by varying the up-conversion emission ratios as a function of pump power. 相似文献
7.
J. J. Velázquez V. D. Rodríguez A. C. Yanes J. del Castillo J. Méndez-Ramos 《Applied physics. B, Lasers and optics》2012,108(3):577-583
95SiO2?C5LaF3 sol-gel derived nano-glass-ceramics single doped with Eu3+ or Sm3+ and codoped with both of them were successfully obtained. XRD measurements confirm the precipitation of LaF3 nanocrystals after the ceramming process, with mean size ranging from 10 to 20?nm which increases with the thermal treatment temperature. The incorporation of rare-earth ions into precipitated LaF3 nanocrystals was confirmed from luminescence spectra. Intense yellow-red emissions were detected under UV and blue light excitation in single and codoped samples. The effect of codoping with Eu3+ and Sm3+ ions and the energy transfer mechanism between them have been analyzed in order to increase the yellow-red emissions. 相似文献
8.
T. Lopez J. Stockel J. Peraza M. E. Torres A. C. Yanes 《Crystal Research and Technology》1995,30(5):677-683
The paper reports on the growth of single crystals of zinc tartrate, by reaction of aqueous solutions of tartaric acid (L +) and zinc chloride in silica gels. The grown crystals have been characterized by X-ray, infrared spectroscopy, qualitative elemental analysis, thermoanalytical techniques, and electromagnetic studies. 相似文献
9.
E. G. Yanes S. R. Gratz R. M. C. Sutton A. M. Stalcup 《Analytical and bioanalytical chemistry》2001,369(5):412-417
The enantioseparation capabilities of three different functionalized β-cyclodextrins, two sulfated β-cyclodextrins with 4 and 15 nominal degrees of substitution and a phosphated β-cyclodextrin with 8 degrees of substitution, were compared. While anodic detection was used with both sulfated cyclodextrins, the phosphated cyclodextrin required cathodic detection suggesting either lower ionization of the phosphated cyclodextrin or generally lower affinity of the analytes for the phosphated cyclodextrin. The effects of several experimental parameters were evaluated with respect to enantioseparation. The degrees of substitution of the cyclodextrin, pH of the background electrolyte as well as the concentration of the functionalized β-cyclodextrin, each had a significant influence on the successful enantiomeric separation of the chiral drugs investigated. 相似文献
10.