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排序方式: 共有5697条查询结果,搜索用时 15 毫秒
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65.
Modelling the thermal behaviour of carboxylic acid derivatives with cylcodextrins in the solid-state
Agotonovic-Kustrin S. Glass B. D. Brown M. E. Rotich M. K. 《Journal of Thermal Analysis and Calorimetry》2004,77(2):391-402
The application of classical QSAR and molecular modelling to the inclusion complexation of natural and modified cyclodextrins
(CDs) with carboxylic acid derivatives as guest molecules was examined. Information was available on the thermal behaviour,
in the solid-state of benzoic acid (BA), salicylic acid (SA), and various substituted aminosalicylic acids (3-aminosalicylic
acid, 3-ASA, 4-aminosalicylic acid, 4-ASA and 5-aminosalicylic acid, 5-ASA), as well as on the thermal behaviour of 1:1 molar
ratio physical and kneaded mixtures of these acids with each of three different cyclodextrins, β-, (BCD) 2-hydroxypropyl-β-,
(HPBCD) and γ-cyclodextrin (GCD). The thermal behaviour of the binary (1:1 stoichiometry) mixtures was modelled using stepwise
multiple regression (SMR). Two models for the prediction of the percentage mass loss and enthalpy of dehydration of the physical
mixtures were established with correlation coefficients (r) of 0.79 and 0.92, respectively. Decreased correlation in the thermal behaviour of kneaded mixtures indicated significant
interaction and possible formation of inclusion complexes.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
66.
Our 1D + 1D model of DMFC reveals a new effect. At infinitely small total current in the cell, near the channel inlet forms a “bridge”, a narrow region with finite local current density. The bridge short-circuits the electrodes, thus reducing cell open-circuit voltage. In our previous work the effect is described for the case of equal methanol λa and oxygen λc stoichiometries. In this Letter, we analyze the general case of arbitrary λa and λc. In the case of λa > λc current may occupy finite domain of the cell surface. Asymptotic solution for the case of λa λc shows, that the size of this domain is proportional to oxygen stoichiometry. In the opposite limit of λa λc local current exponentially decreases with the distance along the channel. Asymptotic solutions suggest that the bridge forms regardless of the relationship between λa and λc. In all cases local current density in the bridge increases with the rate of methanol crossover and decreases with the growth of the “rate-determining” stoichiometry. The expression for voltage loss at open-circuit is derived. 相似文献
67.
Guadalupe Fortuño 《Plasma Chemistry and Plasma Processing》1988,8(1):19-34
A parametric study of the etching of Si and SiO2 by reactive ion etching (RIE) was carried out to gain a better understanding of the etching mechanisms. The following fluorocarbons (FCs) were used in order to study the effect of the F-to-Cl atom ratio in the parent molecule to the plasma and the etching properties: CF4, CF3Cl, CF2Cl2, and CFCl3 (FC-14, FC-13, FC-12, and FC-11 respectively). The Si etch rate uniformity across the wafer as a function of the temperature of the wafer and the Si load, the optical emission as a function of the temperature of the load, the etch rate of SiO2 as a function of the sheath voltage, and the mass spectra for each of the FCs were measured. The temperature of the wafer and that of the surrounding Si load strongly influence the etch rate of Si, the uniformity of etching, and the optical emission of F, Cl, and CF2. The activation energy for the etching reaction of Si during CF4 RIE was measured. The etch rate of Si depends more strongly on the gas composition than on the sheath voltage; it seems to be dominated by ion-assisted chemical etching. The etching of photoresist shifted from chemical etching to ion-assisted chemical etching as a function of the F-to-Cl ratio and the sheath voltage. The etch rate of SiO2 depended more strongly on the sheath voltage than on the F-to-Cl ratio. 相似文献
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69.
《Surface and interface analysis : SIA》2003,35(5):445-449
Surface states of polydimethylsiloxane (PDMS) treated by plasma were investigated by x‐ray photoelectron spectroscopy and surface voltage decay. X‐ray photoelectron spectroscopy confirmed the formation of a silica‐like (SiOx, x = 3–4) oxidative surface layer. This layer increased in thickness with increasing exposure duration of plasma. Plasma exposure lowers the surface resistivity from 1.78 × 1014 to 1.09 × 1013 Ω □?1 with increasing plasma treatment time. By measuring the decay time constant of surface voltage, the calculated surface resistivity was compared with the value measured directly by a voltage–current method; good agreement between the two methods was obtained. It was observed that plasma treatment led to a decrease in the thermal activation energy of the surface conduction from 31.0 kJ mol?1 for an untreated specimen to 21.8 kJ mol?1 for a plasma‐treated specimen for 1 h. Our results allow the examination of effects of plasma on the electrical properties of PDMS. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
70.
《Arabian Journal of Chemistry》2022,15(7):103933
In this study, a fingerprint-activity relationship modeling between chemical fingerprints and antirheumatic activity was established, and multivariate statistical analysis was used to evaluate the quality of Taxilli Herba (TH) from different hosts. Characteristic fingerprints of 20 batches of TH samples were generated by high-performance liquid chromatography coupled with triple quadrupole-time of flight tandem mass spectrometry (HPLC-Triple TOF-MS/MS), and the similarity analysis was calculated based on thirteen common characteristic peaks by hierarchical clustering analysis (HCA). Subsequently, nine efficacy markers were discovered by combining fingerprints and antirheumatic activity through grey correlation analysis (GCA) and bivariate correlation analysis (BCA). Meanwhile, the content of 5 constituents in 9 markers was determined by high-performance liquid chromatography coupled with triple quadrupole-linear ion trap tandem mass spectrometry (HPLC-QTRAP-MS/MS). The comprehensive quality of TH was assessed using multivariate statistical analysis, including principal components analysis (PCA) and technique for order preference by similarity to ideal solution (TOPSIS). The results showed that a high dose of TH extract could markedly ameliorate arthritis damage compared to other doses, with flavonoids playing an important role in the antirheumatic activity. The comprehensive quality of samples from Morus alba L. (SS) was superior to those from Liquidambar formosana Hance (FXS). The present study will demonstrate the markers associated with efficacy, and provide an applicable strategy for more comprehensive quality control and evaluation of TH. 相似文献