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1.
A glassy carbon electrode was modified with an electropolymerized film of 1‐naphthylamine in aqueous solution. The electrocatalytic properties of this modified electrode (ME) were investigated using ascorbic acid (AA) as probe molecule. The electrochemical behavior of AA in buffer solution was examined by voltammetry and amperometry. The results showed that the ME exhibited good electrocatalytic activity towards the oxidation of AA, as a consequence, it can be used as amperometric sensor of this analyte in a flow injection system with good sensitivity. Calibration curves were linear over the concentration range 0.05–1.50 mM with a phosphate buffer solution pH 3 as the carrier, the detection limit was 1 ppm (S/N=3). The methods were applied to the determination of AA in beverages and pharmaceutical products. A good correlation with a reference method was attained. 相似文献
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Training American listeners to perceive Mandarin tones 总被引:1,自引:0,他引:1
Wang Y Spence MM Jongman A Sereno JA 《The Journal of the Acoustical Society of America》1999,106(6):3649-3658
Auditory training has been shown to be effective in the identification of non-native segmental distinctions. In this study, it was investigated whether such training is applicable to the acquisition of non-native suprasegmental contrasts, i.c., Mandarin tones. Using the high-variability paradigm, eight American learners of Mandarin were trained in eight sessions during the course of two weeks to identify the four tones in natural words produced by native Mandarin talkers. The trainees' identification accuracy revealed an average 21% increase from the pretest to the post-test, and the improvement gained in training was generalized to new stimuli (18% increase) and to new talkers and stimuli (25% increase). Moreover, the six-month retention test showed that the improvement was retained long after training by an average 21% increase from the pretest. The results are discussed in terms of non-native suprasegmental perceptual modification, and the analogies between L2 acquisition processes at the segmental and suprasegmental levels. 相似文献
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J A Sereno S R Baum G C Marean P Lieberman 《The Journal of the Acoustical Society of America》1987,81(2):512-519
The present study investigated anticipatory labial coarticulation in the speech of adults and children. CV syllables, composed of [s], [t], and [d] before [i] and [u], were produced by four adult speakers and eight child speakers aged 3-7 years. Each stimulus was computer edited to include only the aperiodic portion of fricative-vowel and stop-vowel syllables. LPC spectra were then computed for each excised segment. Analyses of the effect of the following vowel on the spectral peak associated with the second formant frequency and on the characteristic spectral prominence for each consonant were performed. Perceptual data were obtained by presenting the aperiodic consonantal segments to subjects who were instructed to identify the following vowel as [i] or [u]. Both the acoustic and the perceptual data show strong coarticulatory effects for the adults and comparable, although less consistent, coarticulation in the speech stimuli of the children. The results are discussed in terms of the articulatory and perceptual aspects of coarticulation in language learning. 相似文献
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本文利用荧光光谱和园二色光谱了新开花粉蛋白的盐酸胍去折叠过程。结果显示:新开花粉蛋白的盐酸胍去折叠是一个只包含天然蛋白和变性终态的二态过程,与已经报道的天花粉蛋白的盐酸胍去折叠的过程不同。 相似文献
7.
Review of nanofluids for heat transfer applications 总被引:2,自引:0,他引:2
Saeid Vafaei 《中国颗粒学报》2009,7(2)
Research on nanofluids has progressed rapidly since its enhanced thermal conductivity was first repotted about a decade ago,though much controversy and inconsistency have been reported,and insufficient understanding of the formulation and mechanism of nanofluids further limits their applications.This work presents a critical review of research on heat transfer applications of nanofluids with the aim of identifying the limiting factors so as to push forward their further development. 相似文献
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Vijay NS Bhagawati-Prasad Evy De Leenheer Nadine P Keefe Lorna A Ryan Jennifer Carlring Andrew W Heath 《Journal of immune based therapies and vaccines》2010,8(1):1
Active vaccination can be effective as a post-exposure prophylaxis, but the rapidity of the immune response induced, relative
to the incubation time of the pathogen, is critical. We show here that CD40mAb conjugated to antigen induces a more rapid
specific antibody response than currently used immunological adjuvants, alum and monophosphoryl lipid A™. 相似文献
9.
Fernando Moyano Dr. Patricia G. Molina Dr. Juana J. Silber Prof. Leonides Sereno Prof. N. Mariano Correa Prof. 《Chemphyschem》2010,11(1):236-244
Herein, we investigate the behavior of the electroactive molecular probe 6‐propionyl‐2‐dimethyl amino naphthalene (PRODAN) in large unilamellar vesicles (LUV) formed with the phospholipid 1,2‐di‐oleoyl‐sn‐glycero‐3‐phosphatidylcholine (DOPC) by using cyclic voltammetry (CV). The CV studies in pure water confirm our previous spectroscopic results that PRODAN self‐aggregates due to its low water solubility. Moreover, the electrochemical results also reveal that the PRODAN aggregated species are non‐electroactive within the studied electrochemical potential region. In DOPC LUV media, the redox behavior of PRODAN shows how the LUV bilayer interacts with PRODAN aggregated species to form PRODAN monomer species. Moreover, the electrochemical response of PRODAN allows us to propose a model for explaining the electrochemical experimental results and—in conjunction with our measurements—for calculating the value of the partition constant (Kp) of PRODAN between the water and LUV bilayer pseudophases. This value coincides with that obtained through an independent technique. Moreover, our electrochemical model allows us to calculate the diffusion coefficient (D) for the DOPC LUV, which coincides with the D value obtained through dynamic light scattering (DLS). Thus, our data clearly show that electrochemical measurements could be a powerful alternative approach to investigate the behavior of nonionic electroactive molecules embed in a confined environment such as the LUV bilayer. Moreover, we believe that this approach can be used to investigate the behavior of non‐optical molecular drugs embedded in bilayer media. 相似文献
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Mariana N Cortona Nelio R Vettorazzi Juana J Silber Leonides E Sereno 《Journal of Electroanalytical Chemistry》1999,470(2):157
The nitration of naphthalene (NapH) at a Pt electrode in aqueous NaNO2 solutions both in the absence and presence of a non-ionic surfactant, Brij®35 (polyoxyethylene (23) dodecanol), has been studied. The electrochemical behaviour of the reactants NapH and NaNO2 and a mixture of the two was investigated by cyclic voltammetry (CV) to determine the optimal electrolysis conditions. The peak current of NapH decreases with increasing NaNO2 concentration, indicating that the oxidation product of the NO2− ion interacts with the NapH radical cation (NapH+). Controlled potential electrolysis (CPE) was carried out and the products were analysed by HPLC. The main products detected in the micellar medium were 1-nitronaphthalene, 2-nitronaphthalene, 1,2-naphthoquinone, and 1,4-naphthoquinone. In the absence of Brij 35, the naphthoquinones were produced but no nitration products were obtained. In both cases, unknown products are inferred by mass balance, which are believed to be derived from the oxidation of 1,1′-binaphthyl (BinapH) formed by NapH+ coupling in both micellar and aqueous media. A mechanism of nitration by the attack of NO2 to NapH+ is proposed. The higher selectivity for formation of 2-nitronaphthalene in comparison to non-aqueous homogeneous media is attributed to the effect of the micellar microenvironment. 相似文献