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71.
72.
Ratcheting motion of liquid drops on gradient surfaces 总被引:2,自引:0,他引:2
Daniel S Sircar S Gliem J Chaudhury MK 《Langmuir : the ACS journal of surfaces and colloids》2004,20(10):4085-4092
The motions of liquid drops of various surface tensions and viscosities were investigated on a solid substrate possessing a gradient of wettability. A drop of any size moves spontaneously on such a surface when the contact angle hysteresis is negligible; but it has to be larger than a critical size in order to move on a hysteretic surface. The hysteresis can, however, be reduced or eliminated with vibration that allows the drop to sample various metastable states, thereby setting it to the path of global energy minima. Significant amplification of velocity is observed with the frequency of forcing vibration matching the natural harmonics of drop oscillation. It is suggested that the main cause for velocity amplification is related to resonant shape fluctuation, which can be illustrated by periodically deforming and relaxing the drop at low frequencies. 相似文献
73.
A reverse phase HPLC method was developed and validated for the simultaneous determination of 2-hydroxy-4-methoxybenzaldehyde
and 2-hydroxy-4-methoxybenzoic acid in the root extracts of Hemidesmus indicus. A comprehensive validation of the method including sensitivity, linearity, reproducibility, accuracy, limit of detection
(LOD) and limit of quantification (LOQ) was conducted using the optimized chromatographic conditions. The method was found
to be linear (r > 0.998) in the range of 5–350 μg mL−1 for 2-hydroxy-4-methoxybenzaldehyde and for 2-hydroxy-4-methoxybenzoic acid (r > 0.999) in the range 10–300 μg mL−1. The method was found to be precise with inter-day precision values (% RSD) in the ranges of 0.61–1.76% for 2-hydroxy-4-methoxybenzaldehyde
and 1.3–2.8% for 2-hydroxy-4-ethoxybenzoic acid while intra-day precisions (% RSD) of two analytes were in the range of 0.41–1.07
and 0.95–2.5%. The limits of detection (LODs) for 2-hydroxy-4-methoxybenzaldehyde and 2-hydroxy-4-methoxybenzoic acid were
0.84 and 2.34 μg mL−1. The described method was fast, sensitive and reproducible, and thus well suited for routine analysis of these two compounds
from root extracts of H. indicus and other plants. 相似文献
74.
The Isotope Exchange Technique (IET) was used to simultaneously measure pure and binary gas adsorption equilibria and kinetics (self-diffusivities) of CH4 and N2 on pelletized 4A zeolite. The experiment was carried out isothermally without disturbing the adsorbed phase. CH4 was selectively adsorbed over N2 by the zeolite because of its higher polarizability. The multi-site Langmuir model described the pure gas and binary adsorption equilibria fairly well at three different temperatures. The selectivity of adsorption of CH4 over N2 increased with increasing pressure at constant gas phase composition and temperature. This curious behavior was caused by the differences in the sizes of the adsorbates. The diffusion of CH4 and N2 into the zeolite was an activated process and the Fickian diffusion model described the uptake of both pure gases and their mixtures. The self-diffusivity of N2 was an order of magnitude larger than that for CH4. The pure gas self-diffusivities for both components were constants over a large range of surface coverages (0 < < 0.5). The self-diffusivities of CH4 and N2 from their binary mixtures were not affected by the presence of each other, compared to their pure gas self-diffusivities at identical surface coverages. 相似文献
75.
76.
Blum AS Moore MH Ratna BR 《Langmuir : the ACS journal of surfaces and colloids》2008,24(17):9194-9197
In this work, we examine the dependence of the fluorescence quantum yield of water-soluble CdSe/ZnS quantum dots on the local environment. The hydrophobicity of the local environment was modified by using different alkyl chain lengths in a set of oligo-ethylene glycols. Our results show that the quantum yield of CdSe/ZnS quantum dots is highest for the longest alkyl chain length, suggesting that a more hydrophobic environment is beneficial for generating bright, water-soluble quantum dots. 相似文献
77.
78.
Pathak Kalyani Das Ratna Jyoti Gogoi Neelutpal Saikia Riya Sarma Himangshu Das Aparoop 《平面色谱法杂志一现代薄层色谱法》2022,35(1):35-41
JPC – Journal of Planar Chromatography – Modern TLC - A sensitive and reliable high-performance thin-layer chromatography (HPTLC) method has been developed to simultaneously estimate... 相似文献
79.
Marina Pilz da Cunha Akhil R. Peeketi Adithya Ramgopal Prof. Ratna K. Annabattula Prof. Albert P. H. J. Schenning 《ChemistryOpen》2020,9(11):1149-1152
Achieving oscillatory motion in polymers without requiring on/off switching of stimuli is a current challenge. Hereby, a free-standing liquid crystal polymer (LCP) is demonstrated to undergo a sustained oscillatory motion when triggered by light, moving back and forth, resembling the motion of a rocking-chair. Two polymer films having different azobenzene photo-switches have been studied, revealing photoswitch requirements as well as illumination conditions necessary to sustain oscillations. The motion presented here shows how feedback loops involving light-triggered actuation, self-shadowing and a shifting center of gravity can be utilized to achieve self-sustained motion in free-standing polymers. 相似文献
80.
Cyril Párkányi Christian Boniface Jean-Jacques Aaron Mame Diabou Gaye Ratna Ghosh László von Szentpály Krishnan S. RaghuVeer 《Structural chemistry》1992,3(4):277-289
Electronic absorption and fluorescence emission spectra of several biologically important pyrimidines were measured at room temperature (298 K) in the following solvents: dioxane, ethyl ether, chloroform, ethyl acetate, 1-butanol, 2-propanol, methanol, dimethylformamide, acetonitrile, and dimethyl sulfoxide. The compounds studied were uracil, thymine, cytosine, 5-fluorouracil, 5-chlorouracil, 5-bromouracil, 5-iodouracil, 2-thiouracil, barbituric acid, and orotic acid. In combination with the ground-state dipole moments of the above compounds, these spectral data were used to determine their lowest excited singlet-state dipole moments using the soivatochromic method. The effects of the solvent upon the spectral properties and of the structure upon the ground and excited singlet-state dipole moments are discussed. For most of the compounds, the excited singlet-state dipole moments are higher than their ground-state counterparts.The theoretical dipole moments for all the pyrimidines listed above, as well as for pyrimidine, alloxan, and uracil-5-carboxylic acid, were calculated by two methods. One approach involved a combination of the PPP (-LCI-SCF-MO) method for the -contribution to the overall dipole moment and the -contribution obtained as a vector sum of the -bond moments and group moments. The second set of theoretical values was obtained by the CNDO/2 method. The results were compared with the experimental dipole moments.Presented, in part, at the XIth IUPAC Symposium on Photochemistry, Lisbon, Portugal, July 27–August 1, 1986, and at the 192nd National Meeting of the American Chemical Society, Anaheim, CA, September 7–12, 1986. Part of this work was carried out at the University of Texas at El Paso, El Paso, TX, during the tenure of one of the authors there (C. P.). This paper is dedicated to Dr. Rudolf Zahradník, the teacher of one of the authors (C. P.) and the authors' friend and colleague. 相似文献