Results 1 - 10 of 32137
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[en] In this study, a cross-linked cellulose aerogel was first prepared using a cellulose wet-gel treated with a mixture of cationic poly (aminoamide)-epichlorohydrin and vinyl acetate ethylene copolymer. Following this, a cross-linked superhydrophobic cellulose aerogel was successfully fabricated using a simplified silanization process. The silane-coated cellulose aerogel exhibited an excellent oil absorption capacity (18 to 65 times the dry weight of the cellulose aerogel) without water absorption, and the recovered dimensions of the cellulose aerogel after compression were improved via the cationic polymer treatment. This material, thus, exhibits great potential as an oil absorbent.
[en] The reaction mechanisms of vinyl acetate with OH radicals in the atmosphere have been studied using the density functional theory method. The geometry parameters and frequencies of all of the stationary points are calculated at the MPWB1K level with the 6-31G(d,p) basis sets. The single-point energy calculations are carried out at the MPWB1K/6- 311+G(3df,2pd) level. The detailed profiles of the potential energy surfaces for the reactions are constructed. Two OH addition and three H abstraction reaction pathways are considered for the reaction of vinyl acetate with OH radicals. The theoretical study shows that the most energetically favorable isomer is that of OH addition to the terminal carbon positions (C1 atom). The α-ester rearrangement, which is characteristic of ester oxidation processes, is confirmed to be thermodynamically and kinetically favorable. The main products of the OH-initiated atmospheric oxidation of vinyl acetate are formaldehyde, formic acetic anhydride, and acetic acid. (author)
[en] The solubility parameter is calculated to express the magnitude and nature of the interactive forces between the polymers and solvents. It measures the affinity between the components of a mixture. To improve the prediction of the solubility parameter, the group contribution method is used to calculate the overall solubility parameter as suggested by Handlebar. Hildebrand’s method is used to predict the interaction between the polymers and solvent. In this study, calculate the solubility parameters of polysulfone (PSU), polyvinyl acetate (PVAc) polymers and dimethylacetamide (DMAc) solvent by Hildebrand method. The PSU and PVAc solubility were found to be 1.52H and 1.7H, respectively. These solubility values show that both polymers were dissolved readily in the DMAc solvent, resulting in a true solution. (author)
[en] In the scanning tunnelling microscope, the many-body Kondo effect leads to a zero-bias feature of the differential conductance spectra of magnetic adsorbates on surfaces. The intrinsic line shape of this Kondo resonance and its temperature dependence in principle contain valuable information. We use measurements on a molecular Kondo system, all- trans retinoic acid on Au(1 1 1), and model calculations to discuss the role of instrumental broadening. The modulation voltage used for the lock-in detection, noise on the sample voltage, and the temperature of the microscope tip are considered. These sources of broadening affect the apparent line shapes and render difficult a determination of the intrinsic line width, in particular when variable temperatures are involved. (paper)
[en] In this work, calibration and correction of cross-talk in atomic force microscopy (AFM) is demonstrated. Several reasons and effects of this inherent problem on experimental results are discussed. We propose a general procedure that can be used on most AFM systems to compensate for cross-talk on the cantilever bending and twisting signals. The method utilizes two initial experiments on a flat surface to achieve an affine transformation between the measured signals and the actual signals. Using this transformation directly on the voltage signals allows us to remove the detrimental effects of cross-talk on AFM-based force measurement experiments. The achieved transformation matrix can be turned into a simple circuit and applied online, by users who have access to the raw signals in the AFM head. As a case study, a lateral deflection based mechanical characterization test for a poly(methyl methacrylate) microfiber that is suspended on a trench is investigated in terms of the effectiveness of the cross-talk compensation.
[en] The work addresses spectroscopy of fourth-order Sum Frequency Generation Echo and Grating responses as an experimental tool to study structure and dynamics at interfaces. First, it addresses experimental geometry to extract background-free fourth-order Echo and Grating responses. Further, the article provides the analytical expressions of the response functions for these nonlinearities. The derived expressions are used to model the χ"("4") two-dimensional spectral responses of a hydrated methyl acetate, which resembles a hydrated carbonyl moiety at the polar outer side of a phospholipid membrane. Orientation, transition dipole moments, and Raman tensors are obtained from the results of classical and quantum calculations, respectively. The numerical studies for the nonlinear responses under different polarization schemes and timings suggest the possibility of securely factoring of spectral contributions of χ_Y_Y_Y_Z_X and χ_Y_Y_Y_Z_Y macroscopic susceptibilities. As such, the nonlinearities provide an experimental perspective on orientation of a generic (low-symmetry) molecular system at interfaces. Besides, the spectral properties of the tensors may reflect correlations of the in-plane and out-of-plane field components specific to the interface. For the case of a phospholipid membrane, the experiment would address in-plane and out-of-plane anisotropy of hydrogen bonding and related dynamics
[en] The decrease in the curing time of ethylene vinyl acetate (EVA) as a result of thermal treatment at high temperature effectively enables solar module production and reduces the module cost below 1.0 USD/Wp. As consequence, the possible minimum electricity cost in the case of the grid-tie solar system with medium illumination could be below 0.15 USD/kWh, which is comparable to that of normal grid. With respect to off-grid solar system, the overall efficiency is mainly relied to the storage stage. A programmed bypass connection set up in a small off-grid solar system based on specific load has improved the efficiency, brought the electricity cost of the small off-grid system closer to that of the grid-tie system. (author)