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51.
The Suzuki-Miyaura cross-coupling of sterically hindered and electron-rich ortho,ortho′-substituted aryl halides with potassium vinyltrifluoroborate utilizing microwave irradiation has been conducted while adjusting solvent ratio, irradiation time, and catalyst loading to find optimal conditions. Coupling of benzyl 3,5-bis(benzyloxy)-4-bromobenzoate leads to a mixture of the desired styrene derivative and the reduced product. 4-Bromo-1,3,5-trimethoxybenzene, methyl 4-bromo-3,5-dimethoxybenzoate, and mesitylene bromide were also coupled to test the breadth and scope of this methodology. Of these substrates tested only 4-bromo-1,3,5-trimethoxybenzene was not vinylated successfully, which is believed to be due to the electron-rich nature of this system. 相似文献
52.
Laser-fabricated glass microlens arrays 总被引:2,自引:0,他引:2
We report the fabrication of large, laser-formed refractive microlens arrays on doped borosilicate glass. Tuning the laser heat-source properties was found to give precise control over the melt process and the resulting lenslet geometries. Measurements of focal length, index, and surface shapes show excellent uniformity across these arrays. 相似文献
53.
The phase diagram of the system La2(SO4)3Ag2SO4 was studied by DTA, XRD, SEM, and optical methods. One double salt is formed at 67 mole% La2(SO4)3 and this melts incongruently at 876±6°C. A eutectic is formed at 8 mole% La2(SO4)3 and at a temperature of 618±3°C. Suppression of decomposition was effected by the sealed tube method, but some reference is made to experiments conducted with a flowing atmosphere of SO3, SO2 and O2. 相似文献
54.
William R. Barger Robert L. Mowery Jeffrey R. Wyatt 《Journal of chromatography. A》1994,680(2):659-665
Solutions of multiple cations in aqueous solutions at concentrations as low as 200 ppb were analyzed by capillary zone electrophoresis. Aluminum ions were cleanly separated from Li+, K+, Ca2+, Cr3+, Zn2+, CU2+, and other ions less than 6 min after injection of the solution on a 50 cm × 50 μm I.D. uncoated fused-silica capillary column at 15 kV. Indirect detection at 204 nm was carried out using a pH 2.8 background electrolyte containing 5.2 mM ephedrine as a UV-absorbing co-ion and 4.7 mM -hydroxyisobutyric acid as a completing counter ion. Mobilities for Al3+ and 14 other complexed cations were determined for this electrolyte. 相似文献
55.
56.
For pure 4He on Cs a nonwet phase exists below ≈2 K but for dilute 3He–4He mixtures the wetting is reentrant. Measurements of the contact angle with dilute mixtures of liquid helium on Cs can be explained in detail in terms of 3He states together with ripplons at the Cs–He mixture interface, but it is impossible to account for the lower wetting temperatures or contact angles with only 3He states or ripplons. We discuss the influence of surface roughness of the Cs on the contribution of interface excitations to the free energy and suggest that the variety of contact angles found with different samples of Cs is due mainly to their degree of roughness. 相似文献
57.
Preparation of nanoparticles by continuous-flow microfluidics 总被引:1,自引:0,他引:1
Andreas Jahn Joseph E. Reiner Wyatt N. Vreeland Don L. DeVoe Laurie E. Locascio Michael Gaitan 《Journal of nanoparticle research》2008,10(6):925-934
We review a variety of micro- and nanoparticle formulations produced with microfluidic methods. A diverse variety of approaches
to generate microscale and nanoscale particles has been reported. Here we emphasize the use of microfluidics, specifically
microfluidic systems that operate in a continuous flow mode, thereby allowing continuous generation of desired particle formulations.
The generation of semiconductor quantum dots, metal colloids, emulsions, and liposomes is considered. To emphasize the potential
benefits of the continuous-flow microfluidic methodology for nanoparticle generation, preliminary data on the size distribution
of liposomes formed using the microfluidic approach is compared to the traditional bulk alcohol injection method. 相似文献
58.
We describe a measurement of the transmission probability of 4He atoms through a freely suspended slab of superfluid 4He at low temperatures. In our experiment the slab is realized by using an array of parallel cylindrical holes of diameter 51 microm in a glass disc of thickness 190 microm. By controlling the chemical potential, the holes can be made to fill or empty with liquid, and the surface curvature varied. We have measured the transmission of atom beams, generated by a thin-film heater and detected with a sensitive bolometer, through this structure. The results show that the dominant transmission channel is atom-R+ roton-atom with a probability p approximately 0.12 and that R+ rotons can undergo total internal reflection at the free liquid surfaces. 相似文献
59.
Cormier E Walmsley IA Kosik EM Wyatt AS Corner L Dimauro LF 《Physical review letters》2005,94(3):033905
We propose a method for the complete characterization of attosecond duration electromagnetic pulses produced by high harmonic generation in an atomic gas. Our method is based on self-referencing spectral interferometry of two spectrally sheared extreme ultraviolet pulses, which is achieved by pumping the harmonic source with two sheared optical driving pulses. The resulting interferogram contains sufficient information to completely reconstruct the temporal behavior of the electric field. We demonstrate that such a method is feasible, and outline two possible experimental configurations. 相似文献
60.
The group velocity of 93 GHz phonons in liquid 4He has been measured directly at T ? 0.1 K between 0 and 24 bar. Above ~ 12 bar the group velocity falls increasingly below the ultrasonic phase velocity, and at 24 bar the dispersion is consistent with the quadratic deviation below linearity as suggested by neutron scattering. 相似文献