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61.
K. M. McHugh H. W. Sarkas J. G. Eaton C. R. Westgate K. H. Bowen 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1989,12(1-4):3-6
We report the development of an ion source for generating intense, continuous beams of both positive and negative cluster ions. This device is the result of the marriage of the inert gas condensation method with techniques for injecting electrons directly into expanding jets. In the preliminary studies described here, we have observed cluster ion size distributions ranging fromn=1?400 for Pb n + and Pb n ? , and fromn=12?5700 for Li n ? . 相似文献
62.
Landis CA Payne MM Eaton DL Anthony JE 《Journal of the American Chemical Society》2004,126(5):1338-1339
The cycloaromatization of acyclic enediynes typically requires very high temperatures (>160 degrees C) and dilute conditions to proceed in a synthetically useful yield. These conditions hinder reaction throughput, inhibiting the use of this reaction for the large-scale production of materials. The reaction of sodium telluride with acyclic arenediynes yields the corresponding tellurepine, which under gentle heating extrudes Te degrees to yield the cycloaromatization product. We have developed conditions that form sodium telluride from inexpensive tellurium metal in situ, and that also perform the desilylation of silylated arenediynes in the same process. Under our conditions, we are able to perform desilylation and cycloaromatization at temperatures as low as 40 degrees C and on a scale as large as 5 g in standard laboratory glassware. 相似文献
63.
Michael J. Benson Christopher J. Elkins Paul D. Mobley Marcus T. Alley John K. Eaton 《Experiments in fluids》2010,49(1):43-55
Magnetic resonance imaging (MRI) was used to measure the three-dimensional, time-averaged concentration distribution in a
turbulent two-stream mixing layer. Test fluids and MRI scanning parameters were chosen to give good signal linearity, and
a calibration/normalization procedure was developed to reduce the concentration measurement uncertainty. Plain deionized water
mixing with a solution of 0.8% gadopentetate dimeglumine in deionized water were selected as test fluids. The concentration
of the marked water was measured on an array of 220,000 0.69 mm3 voxels covering the entire flow apparatus. Planar laser-induced fluorescence experiments were performed on the flow centerplane
to provide validation data. The uncertainty of a single voxel measurement was estimated to be less than 12% with the largest
source of uncertainty being turbulent dephasing. Averaging two runs in which the marked water was switched between the two
streams reduced the uncertainty to only 4%. The complete magnetic resonance concentration (MRC) procedure including the adjustment
of scanning parameters, a background run, two reference/calibration runs, and multiple concentration measurement runs can
be completed in 2–3 h. This work establishes MRC as a viable technique for studying the mixing in complex turbulent liquid
flows. 相似文献
64.
Electron spin relaxation times and rapid scan EPR imaging of pH‐sensitive amino‐substituted trityl radicals 下载免费PDF全文
Hanan B. Elajaili Joshua R. Biller Mark Tseitlin Ilirian Dhimitruka Valery V. Khramtsov Sandra S. Eaton Gareth R. Eaton 《Magnetic resonance in chemistry : MRC》2015,53(4):280-284
Carboxy‐substituted trityl (triarylmethyl) radicals are valuable in vivo probes because of their stability, narrow lines, and sensitivity of their spectroscopic properties to oxygen. Amino‐substituted trityl radicals have the potential to monitor pH in vivo, and the suitability for this application depends on spectral properties. Electron spin relaxation times T1 and T2 were measured at X‐band for the protonated and deprotonated forms of two amino‐substituted triarylmethyl radicals. Comparison with relaxation times for carboxy‐substituted triarylmethyl radicals shows that T1 exhibits little dependence on protonation or the nature of the substituent, which makes it useful for measuring O2 concentration, independent of pH. Insensitivity of T1 to changes in substituents is consistent with the assignment of the dominant contribution to spin lattice relaxation as a local mode that involves primarily atoms in the carbon and sulfur core. Values of T2 vary substantially with pH and the nature of the aryl group substituent, reflecting a range of dynamic processes. The narrow spectral widths for the amino‐substituted triarylmethyl radicals facilitate spectral‐spatial rapid scan electron paramagnetic resonance imaging, which was demonstrated with a phantom. The dependence of hyperfine splittings patterns on pH is revealed in spectral slices through the image. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
65.
de la Fuente JM Alcántara D Eaton P Crespo P Rojas TC Fernandez A Hernando A Penadés S 《The journal of physical chemistry. B》2006,110(26):13021-13028
The preparation, characterization and the magnetic properties of gold and gold-iron oxide glyconanoparticles (GNPs) are described. Glyconanoparticles were prepared in a single step procedure in the presence of aqueous solution of thiol functionalized neoglycoconjugates and either gold salts or both gold and iron salts. Neoglycoconjugates of lactose and maltose disaccharides with different linkers were used. Iron-free gold or gold-iron oxide GNPs with controlled gold-iron ratios were obtained. The average core-size diameters are in the range of 1.5-2.5 nm. The GNPs are fully characterized by (1)H NMR spectrometry, transmission electron microscopy (TEM), and UV-vis and X-ray absorption (XAS) spectroscopies. Inductive plasma-atomic emission spectrometry (ICP) and elemental analysis gave the average number of neoglycoconjugates per cluster. The magnetic properties were measured in a SQUID magnetometer. The most remarkable results was the observation of a permanent magnetism up to room temperature in the iron-free gold GNPs, that was not present in the corresponding gold-iron oxide GNPs. 相似文献
66.
Gupton JT Telang N Banner EJ Kluball EJ Hall KE Finzel KL Jia X Bates SR Welden RS Giglio BC Eaton JE Barelli PJ Firich LT Stafford JA Coppock MB Worrall EF Kanters RP Keertikar K Osterman R 《Tetrahedron》2010,66(47):9113-9122
Studies directed at the synthesis of (Z)-5-benzylidene-4-arylpyrrol-2(5H)-ones from (Z)-3-aryl-3-haloenoic acids are described. The successful strategy relies on the preparation of (Z)-3-aryl-3-haloenoic acids from acetophenones through the corresponding (Z)-3-aryl-3-haloenals and the conversion of the (Z)-3-aryl-3-haloenoic acids to (Z)-5-benzylidene-4-aryl-5H-furan-2-ones. The furanones were subsequently treated with primary amines and dehydrated to the corresponding (Z)-5-benzylidene-4-arylpyrrol-2(5H)-ones. 相似文献
67.
Frequency-resolved optical gating is used to characterize the propagation of intense femtosecond pulses in a nonlinear, dispersive medium. The combined effects of diffraction, normal dispersion, and cubic nonlinearity lead to pulse splitting. The role of the phase of the input pulse is studied. The results are compared with the predictions of a three-dimensional nonlinear Schr?dinger equation. 相似文献
68.
Robert H. Higgins Monique R. Watson William J. Faircloth Quentin L. Eaton Harvey Jenkins 《Journal of heterocyclic chemistry》1988,25(2):383-387
Preparation of the trimethylsilyl ethers of 1-alkyl-3-azetidinols from non-hindered primary amines and epichlorohydrin by conversion of the intermediate 1-(alkylamino)-3-chloro-2-propanols to their trimethylsilyl ethers by either N-(trimethylsilyl)acetamide or by 1-(trimethylsilyl)imidazole followed by ring closure in acetonitrile is described. This sequence of reactions fails for aromatic amines, but appears to be general for all primary aliphatic amines, although the condensation of hindered amines with epichlorohydrin occurs slowly. Several novel azetidinols, in which the N-alkyl substituent itself contains a second heterocyclic system, are reported. In addition, the pKA's of several m. and p-substituted 1-benzylazetidinols correlates well with the Hammett equation. 相似文献
69.
B.K. Nayak B. Eaton J.A.A. Selvan J. McLeskey M.C. Gupta R. Romero G. Ganguly 《Applied Physics A: Materials Science & Processing》2005,80(5):1077-1080
Semiconductor laser (=805 nm) crystallization of hydrogenated amorphous silicon (a-Si:H) deposited on a low-cost fluoride-doped tin-oxide-coated glass substrate is demonstrated. X-ray diffraction confirms that the structure of the polycrystalline silicon thus formed shows (111), (220), and (311) peaks. A sharp Raman peak at 520 cm-1 further confirms the crystallization. Atomic force microscope images of a Secco-etched laser-treated sample reveal the granular structure of the poly-Si. Grains as big as 10 times the film thickness are readily obtained and sample as thick as 5000 Å is easily crystallized. The method can be extended to films with a thickness of several microns. PACS 42.55.Px; 42.62.Cf; 81.05.Gc 相似文献
70.
Owenius R Eaton GR Eaton SS 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,172(1):168-175
Electron spin relaxation times for four triarylmethyl (trityl) radicals at room temperature were measured by long-pulse saturation recovery, inversion recovery, and electron spin echo at 250 MHz, 1.5, 3.1, and 9.2 GHz in mixtures of water and glycerol. At 250 MHz T(1) is shorter than at X-band and more strongly dependent on viscosity. The enhanced relaxation at 250 MHz is attributed to modulation of electron-proton dipolar coupling by tumbling of the trityl radicals at rates that are comparable to the reciprocal of the resonance frequency. Deuteration of the solvent was used to distinguish relaxation due to solvent protons from the relaxation due to intra-molecular electron-proton interactions at 250 MHz. For trityl-CD(3), which contains no protons, modulation of dipolar interaction with solvent protons dominates T(1). For proton-containing radicals the relative importance of modulation of intra- and inter-molecular proton interactions varies with solution viscosity. The viscosity and frequency dependence of T(1) was modeled based on dipolar interaction with a defined number of protons at specified distances from the unpaired electron. At each of the frequencies examined T(2) decreases with increasing viscosity consistent with contributions from T(1) and from incomplete motional averaging of anisotropic hyperfine interaction. 相似文献