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91.
M.A. Pedrosa C. Hidalgo K.J. McCarthy A. López-Sánchez M.A. Ochando I. Pastor A. Baciero E. Calderón T. Estrada J. Herranz J. López-Razola B. V. Milligen D. Tafalla F. Tabarés The TJ-II Team N. Dreval A. Chmyga S.M. Khrebtov A.D. Komarov S. Kozachok L. Krupnik L. Eliseev A.V. Melnikov 《Czechoslovak Journal of Physics》2003,53(10):877-885
The influence of limiter biasing on plasma confinement, turbulence and plasma flows has been investigated in the TJ-II stellarator. Experimental results show that it is possible to modify global particle confinement and edge plasma parameters with both positive and negative biasing. Significant and minor modifications in the structure of plasma fluctuations have been observed during the transition to improved confinement regimes induced by limiter biasing. These results show evidence of electric field induced improved confinement via multiple mechanisms. The investigation of the relaxation of plasma potential and electric fields shows evidence of two different characteristic decay times. 相似文献
92.
[reaction: see text] Chiral precursors to the intramolecular Diels-Alder reaction using furan as a diene (IMDAF) have been prepared by diastereoselective addition of furyllithium to imines attached to perhydro-1,3-benzoxazines derived from (-)-8-aminomenthol. The acylation of the furylamines with alpha,beta-unsaturated acyl chlorides and subsequent IMDAF reaction under thermal conditions provided the corresponding cycloadducts as single diastereoisomers. The hydrolytic elimination of the chiral template yielded enantiopure perhydroepoxyisoindolones with up to five stereocenters. 相似文献
93.
Ana M. V. Cavaleiro Julio D. Pedrosa de Jesus Robert D. Gillard Peter A. Williams 《Transition Metal Chemistry》1984,9(2):81-82
A number of studies of species formed in the tungsten(VI) oxide-R,R-(+)-tartaric acid-water system have been carried out(1–3). While various species have been proposed, it is generally accepted that three main ones predominate. Two have tungsten: (+)-tartaric acid [(+)-tartH4] ratios of 11 and the third has the same ratio of 12. This latter species cannot be that proposed by Avaloset al.
(3) since both ligands in their structure would have to be present as unidentates.Recently we have shown(4) that high resolution1H and13C n.m.r. studies were particularly useful in delineating the complexes formed in aqueous solution in the analogous molybdenum(VI) system. Thus, we turned our attention to the corresponding tungsten(VI) complexes, especially in view of the controversy surrounding the nature of the species formed in aqueous solution with (+)-tartH4. The results of our studies, presented below, indicate that only a few species are formed, and that these are quite analogous, as might be expected, to the previously described molybdenum(VI) species(4). In addition we have observed the formation of a mixed dimeric species [MoWO4{(+)-tart}2]4–, whose structure is akin to the mono-metallic complexes, as well as the well-characterized antimony(III) and arsenic(III) dimers of (+)-tartH4
(5). 相似文献
94.
Ana Carla S. L. S. Coutinho Solange A. Quintella A. S. Araujo Joana M. F. Barros Anne M. G. Pedrosa V. J. Fernandes Jr. M. J. B. Souza 《Journal of Thermal Analysis and Calorimetry》2007,87(2):457-461
Nanoporous silica with narrow
pore size distribution has attracted increasing attention as a novel material
for separations and reactions involving large molecules. SBA-15 has been synthesized
in an acidic medium using a triblock copolymer as template. In this work,
the SBA-15 was synthesized by the hydrothermal treatment at 373 K for 48 h,
of a gel with the following overall molar composition: 1.0TEOS:0.017P123:5.7HCl:193H2O,
where TEOS is tetraethyl orthosilicate and P123 is poly(ethylene oxide, propylene
oxide and 1,4-dioxane). The obtained material was characterized by thermogravimetry,
X-ray diffraction, infrared spectroscopy and BET surface area. A kinetic study
using the model free model was accomplished in the stage of decomposition
of the template (P123). The obtained value of the apparent activation energy
was ca. 131 kJ mol–1. 相似文献
95.
C. Silva B. Goncalves M. A. Pedrosa C. Hidalgo K. McCarthy E. Calderon J. Herranz I. Pastor O. Orozco 《Czechoslovak Journal of Physics》2005,55(12):1589-1596
Edge polarization experiments were carried out on TJ-II using an electrode. It has been found that the plasma response is
different at densities below and above the threshold value to trigger the spontaneously development of E × B sheared flows. At low densities, the edge plasma potential is fully controlled by external biasing, while at higher densities
it is determined not only by external biasing but also by the electric fields spontaneous developed. Although an improvement
in particle confinement is observed for both polarities, a larger increase is observed for negative electrode bias.
Presented at the Workshop “Electric Fields, Structures and Relaxation in Edge Plasmas”, Tarragona, Spain, July 3–4, 2005. 相似文献
96.
3,5-Dimethylisothiazole reacts sequentially with lithiumdiisopropylamide (molar ratio 1:1) and alkyl halides (in excess) affording 5-alkyl-3-methylisothiazoles in excellent yields. When a two-fold excess of base is used, a mixture of 5-monoalkylated and 3,5-dialkylated products is obtained. Sodium amide was also tried as deprotonating agent, but the yield in final products was lower. 相似文献
97.
Enantiopure morpholine derivatives have been prepared by selenocyclofunctionalization of chiral 3-allyl-2-hydroxymethyl-substituted perhydro-1,3-benzoxazine derivatives. The cyclization occurs in high yields and diastereoselection, although the temperature of the reaction and the structure of the substituent at C-2 and the substitution pattern of the double bond can modify the regio- and stereochemistry of the final products. 相似文献
98.
Ivan Pedrosa Long Ngo Jesse Wei Michael Schuster Houman Mahallati Martin Smith Neil M. Rofsky 《Magnetic resonance imaging》2009
Objective
The objective of this study was to retrospectively analyze the value of dynamic half-Fourier single-shot turbo spin echo (HASTE) imaging in patients with suspected deep venous thrombosis (DVT).Materials and Methods
Fifty-five veins in 24 patients were interrogated using a HASTE sequence with the patients relaxed and in various degrees of Valsalva. Veins were analyzed for changes in caliber (+CAL) and signal intensity (+SI) or in their absence (−CAL and −SI, respectively) and compared with the presence of thrombus on gadolinium-enhanced magnetic resonance imaging.Results
There was no thrombus in veins with the +CAL, +SI pattern (n=40) (P<.01). Five of seven veins (71.4%) with the −CAL, −SI pattern had thrombus (P<.01). A qualitative change in CAL had a sensitivity of 100% and a specificity of 91% for the presence of thrombus. An increase of 1.5 mm in CAL had a sensitivity of 100% and a specificity of 93% for this diagnosis.Conclusion
Dynamic HASTE imaging offers a physiological method to evaluate veins for deep venous thrombosis. 相似文献99.
100.
Ana M. V. S. V. Cavaleiro Victor M. S. Gil Julio D. Pedrosa de Jesus Robert D. Gillard Peter A. Williams 《Transition Metal Chemistry》1984,9(2):62-67
Summary Complex formation between molybdate ions and R,R-(+)-tartaric acid has been studied in aqueous solution, and to a limited extent in DMSO, over a range of concentrations and pH at 298K, using1H and13C n.m.r. techniques. Only four main species are evident; two, which have Mo: L ratios of 11 and 12, are bondedvia a carboxylic oxygen atom and an adjacent hydroxyl oxygen atom. The 12 species forms stereospecifically. The other two main species contain bridging tartaric acid molecules, and a 22 species, also formed stereo-specifically in solution, have been isolated and characterised in the solid state. A limited number of experiments with racemic acid and meso-tartaric acid indicate that only a few species are formed in these systems and with a good deal of stereospecificity also. 相似文献