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141.
A high-power, low-noise photodetector, in conjunction with a current shunt actuator, is used in an ac-coupled servo to stabilize the intensity of a 10-W cw Nd:YAG laser. A relative intensity noise of 1 x 10(-8) Hz(-1/2) at 10 Hz is achieved. 相似文献
142.
Sun S Lorkovic IM Weiss M Sherman JH Stucky GD Ford PC McFarland EW 《Chemical communications (Cambridge, England)》2004,(18):2100-2101
Metal oxide solid reactants are shown to react with vicinal alkyl dibromides to selectively form olefin oxides and fully regenerable metal bromides. 相似文献
143.
Exclusive proton-antiproton annihilation into two photons at large s ( approximately 10 GeV2) and /t/,/u/ approximately s can be described by a generalized parton picture analogous to the "soft mechanism" in wide-angle real Compton scattering. The two photons are emitted in the annihilation of a single fast quark and antiquark. The matrix element describing the transition of the pp system to a qq pair can be related to the timelike proton elastic form factors as well as to the quark/antiquark distributions measured in inclusive deep-inelastic scattering. The reaction could be studied with the proposed 1.5-15 GeV high-luminosity antiproton storage ring (HESR) at GSI. 相似文献
144.
Arena DA Bartynski RA Nayak RA Weiss AH Hulbert SL Weinert M 《Physical review letters》2003,91(17):176403
The Pd M4VV and M5VV Auger spectra of the 0.1 ML Pd/Ag(100) dilute surface alloy have been measured using Auger-photoelectron coincidence spectroscopy. The M4VV spectrum indicates that Pd 3d(3/2) core holes have a Coster-Kronig decay rate that is approximately 10 times that of Pd metal. Our calculations show that this giant enhancement arises from the local electronic structure of excited Pd atoms at the surface. Anomalous features in the Auger line shape are similar to those seen in dilute bulk PdAg alloys, and these features in the M5VV and M4VV lines are in good agreement with theoretical predictions. 相似文献
145.
The influence of polymerization conditions on the morphology of thin films of poly-(N-methylaniline) (PNMA) was studied. The films were prepared by electropolymerization on gold and platinum electrodes and studied by optical and electron microscopy. It was demonstrated that the film morphology does not depend on the polymerization rate or on the electrode metal. However, it is sensitive to the kind of counter ion of PNMA. The polymers containing acetate or chloride do not form stable films. Polymer films containing phosphate or sulfate display inhomogeneous structures. A formation of sprouts and nanotubes was observed for PNMA sulfate. The films formed by PNMA perchlorate are smooth and transparent (glass-like structure). A sublayer of 4-aminothiophenol increases the adhesion of polymers to the gold surface. 相似文献
146.
The reaction of aryl alkynes with dilute methylene chloride solutions of quaternary ammonium bromide and 20% trifluoroacetic acid produces primarily the syn Markovnikov adducts of hydrogen bromide. At moderate concentrations of the bromide, the principal product is the Markovnikov anti adduct. At high concentrations of bromide, the anti-Markovnikov anti addition product predominates. 相似文献
147.
Paul D Melin F Hirtz C Wytko J Ochsenbein P Bonin M Schenk K Maltese P Weiss J 《Inorganic chemistry》2003,42(12):3779-3787
The respective affinities of various imidazole derivatives, imidazole (ImH), 2-methylimidazole (2-MeImH), 2-phenylimidazole (2-PhImH), N-methylimidazole (N-MeIm), 2-methylbenzimidazole (2-MeBzImH), and 4,5-dimethylbenzimidazole (4,5-Me(2)BzImH), for two phenanthroline (Phen) strapped zinc(II) porphyrin receptors porphen-Zn 1-Zn and 2-Zn have been studied. The formation of a supplementary H-bond considerably enhances the affinity of the zinc(II)-porphen receptor for imidazoles unsubstituted on the pyrrolic nitrogen (ImH) versus N-substituted imidazoles such as N-MeIm. The ImHs subset porphen-Zn complexes are formed with association constants up to 4 orders of magnitude superior to those measured either for N-MeIm as substrate or TPP-Zn as receptor. Distal or proximal binding of the substrates was determined by (1)H NMR measurements and titration. In two cases, the very high stability of the inclusion complex enabled the use of 2D NMR techniques. Excellent correlation between solution and solid-state structures has been obtained. A total of six X-ray structures are detailed in this article showing that the evolution of the shape of the zinc(II) receptor is mostly dependent on the steric constraints induced by the substitution on the imidazole. Hindered guests also progressively induce considerable mobility restrictions and severe distortions on the receptor, especially in the case of 2-MeBzImH and 2-PhImH. 相似文献
148.
pH-mediated field-amplified sample stacking of pharmaceutical cations in high-ionic strength samples 总被引:1,自引:0,他引:1
Capillary electrophoretic separation of samples of physiological origin typically have both poor resolution and efficiency due to destacking. We have previously reported a stacking method for concentration of catecholamines in artificial dialysate, or Ringer's solution. However, pH-mediated sample stacking of other cations has not been investigated. In this report, pH-mediated stacking has been extended to eletripan, dofetilide, doxazosin, sildenafil, UK-103,320, UK-202,581, and CP-122,288. These compounds were chosen without prior structural screening except that they were cationic at the pH of our background electrolyte (BGE). Capillary electrophoretic behavior of samples in BGE is compared with those of samples in Ringer's solution with and without pH-mediated acid stacking. Results indicate that the peak heights and efficiencies for acid-stacked samples are increased compared to the unstacked samples in Ringer's solution or BGE. For example, the peak efficiencies for 5 s injections of eletriptan in BGE and Ringer's solution are 138,000 and 72,000 plates, respectively. In contrast, a 10 s injection of eletriptan followed by acid injection for 16 s produces a peak with 246,000 plates. Evaluation of the stacking effect was performed by comparison of the peak height at similar peak efficiencies for samples in Ringer's solution with and without stacking. Using this method, pH-mediated acid stacking provides a 10- to 27-fold sensitivity enhancement for the seven cations. 相似文献
149.
150.
Jean Weiss 《Journal of inclusion phenomena and macrocyclic chemistry》2001,40(1-2):1-22
The tremendous efforts made in order to control the coordination chemistry of hemoprotein models have considerably enhanced the synthesis of functionalized porphyrins, whose carefully designed architectures allowed for selective bindings of exogenic substrates. The common use of zinc(II) in place of pentacoordinated iron(II) has induced the use of zinc(II) porphyrins as building blocks for selective receptors. These receptors offer a convenient combination of multi-point recognition of substrates, and monitoring of the complexation due to the chromophoric nature of the tetrapyrrolic unit. This review is dedicated to recent progress made in the field of molecular recognition involving multi-point selective binding processes, in whichthe establishment of a strong coordination bond is finely tuned by one or more weak interactions adequately introduced in the architecture of a functionalized zinc(II)-porphyrin. 相似文献