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461.
462.
Larry J. Baldwin Sudabeh Pakray Raymond N. Castle Milton L. Lee 《Journal of heterocyclic chemistry》1985,22(6):1667-1669
The synthesis of the five isomeric methoxyphenylthiophenes is described. The methoxy compounds were hydrolyzed to yield the hydroxyphenylthiophenes. 相似文献
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Vitreous BeF2 was prepared by two techniques; (1) remelting of a technical grade material, and (2) vacuum distillation/fluoridation. Infrared spectroscopy studies have established that the first material contains about 0.5 wt.% hydroxyl, predicted to be coherently incorporated into the vitreous network as edge-linked [Be(OH)4]2− units. The distilled BeF2 is water-free. The dc electrical conductivity of the remelted BeF2 was measured as σ = (7.9 × 103/T) exp(−24500 cal/mol/RT) ω−1 cm−1 and for the distilled BeF2 as σ = (3.0 × 105/T) exp(−36700 cal/mol/RT ω−1 cm−1 at temperatures to 280°C. Ionic transport studies utilizing a dc electrolysis polarization technique with N2−F2 and H2−HF gas electrodes have demonstrated that the fluorine ion is the transport species. A general model for fluorine transport is proposed based upon a modified anti-Frenkel defect model. The difference in the fluorine transport process for the undistilled grade of BeF2 is seen as a consequence of the anti-Frenkel defect pair interaction with the [Be(OH)4[2− groupings. 相似文献
467.
Liu Y Shabani J Kamburov D Shayegan M Pfeiffer LN West KW Baldwin KW 《Physical review letters》2011,107(26):266802
We report the evolution of the fractional quantum Hall state (FQHS) at a total Landau level (LL) filling factor of ν=7/2 in wide GaAs quantum wells in which electrons occupy two electric subbands. The data reveal subtle and distinct evolutions as a function of density, magnetic field tilt angle, or symmetry of the charge distribution. At intermediate tilt angles, for example, we observe a strengthening of the ν=7/2 FQHS. Moreover, in a well with asymmetric change distribution, there is a developing FQHS when the LL filling factor of the symmetric subband ν(S) equals 5/2 while the antisymmetric subband has a filling factor of 1<ν(A)<2. 相似文献
468.
Liu Y Kamburov D Shayegan M Pfeiffer LN West KW Baldwin KW 《Physical review letters》2011,107(17):176805
We report magnetotransport measurements in wide GaAs quantum wells with a tunable density to probe the stability of the fractional quantum Hall effect at a filling factor of ν=5/2 in the vicinity of the crossing between Landau levels (LLs) belonging to the different (symmetric and antisymmetric) electric subbands. When the Fermi energy (E(F)) lies in the excited-state LL of the symmetric subband, the 5/2 quantum Hall state is surprisingly stable and gets even stronger near this crossing, and then suddenly disappears and turns into a metallic state once E(F) moves to the ground-state LL of the antisymmetric subband. The sharpness of this disappearance suggests a first-order transition. 相似文献
469.
Suppose is a triple of two theories in vocabularies with cardinality λ, and a τ1‐type p over the empty set that is consistent with T1. We consider the Hanf number for the property “there is a model M1 of T1 which omits p, but is saturated”. In [2], we showed that this Hanf number is essentially equal to the Löwenheim number of second order logic. In this paper, we show that if T is superstable, then the Hanf number is less than . 相似文献
470.
Mohamed M. Marei Thomas J. Roussel Robert S. Keynton Richard P. Baldwin 《Analytica chimica acta》2013
Remote unattended sensor networks are increasingly sought after to monitor the drinking water distribution grid, industrial wastewater effluents, and even rivers and lakes. One of the biggest challenges for application of such sensors is the issue of in-field device calibration. With this challenge in mind, we report here the use of anodic stripping coulometry (ASC) as the basis of a calibration-free micro-fabricated electrochemical sensor (CF-MES) for heavy metal determinations. The sensor platform consisted of a photo-lithographically patterned gold working electrode on SiO2 substrate, which was housed within a custom stopped-flow thin-layer cell, with a total volume of 2–4 μL. The behavior of this platform was characterized by fluorescent particle microscopy and electrochemical studies utilizing Fe(CN)63−/4− as a model analyte. The average charge obtained for oxidation of 500 μM ferrocyanide after 60 s over a 10 month period was 176 μC, corresponding to a volume of 3.65 μL (RSD = 2.4%). The response of the platform to copper concentrations ranging from 50 to 7500 ppb was evaluated, and the ASC results showed a linear dependence of charge on copper concentrations with excellent reproducibility (RSD ≤ 2.5%) and accuracy for most concentrations (≤5–10% error). The platform was also used to determine copper and mercury mixtures, where the total metallic content was measurable with excellent reproducibility (RSD ≤ 4%) and accuracy (≤6% error). 相似文献