In this study, hydrophobic silica aerogels were synthesized from rice husk ash-derived sodium silicate through sol-gel processing, solvent exchange, surface modification and ambient pressure drying. By volume, 10% of trimethylchlorosilane (TMCS) in 90% of n-hexane was used as a hydrophobic solution in the surface modification process. The physical and chemical properties of silica aerogels were characterized by density and porosity measurements, scanning electron microscopy (SEM), Fourier transforms infrared (FTIR) spectroscopy, Brunauer–Emmett–Teller theory (BET) and dynamic scanning calorimetry (DSC). The hydrogels prepared were in the form of 2.5 ± 0.5 mm beads and then converted into alcogels through solvent exchange with ethanol for repetition of 3, 6 and 9 days. It is found that the optimal quality of silica aerogels with the BET surface area as high as 668.82 m2/g was obtained from the alcogels of the solvent exchange period of 9 days. Depending on the size of the gel’s block, a longer solvent exchange period will ensure adequate removal of pore water. Post heat treatment on silica aerogels obtained from the 9 days of solvent exchange at 200, 300 and 400 °C for 2 h results in slight decreased of aerogel’s density from 0.048 g/cm3 to 0.039 g/cm3 and the hydrophobicity of the aerogels is decreased above 380 °C as confirmed by DSC analysis.
Microemulsions with a palm oil-based emollient, i.e., medium-chain triglyceride (MCT), and water or glycerol, stabilized by
two oppositely charged ionic surfactants and a medium-chain alcohol, were investigated. The results showed that only the water-in-MCT
or the glycerol-in-MCT microemulsions were prominent. The maximum solubilization of the MCT emollient was higher in cetyltrimethyl
ammonium bromide, i.e., the positively charged surfactant that contained a nitrogen atom, than the negatively charged surfactant
sodium dodecyl sulfate. However, the results did not lend themselves for selecting any decisive factor that would explain
the different solubilization behavior encountered in the investigated aqueous and nonaqueous systems. 相似文献
In part 11 a series of implicit finite element algorithms for the geometrically nonlinear structural problem were proposed. These algorithms were shown to be computationally efficient because they require the solution of a linear system rather than a nonlinear system at each time point. In addition, because of the conservative nature of the algorithms, their stability properties are easily assessed. One algorithm was shown to be unconditionally stable.In part 2 the convergence of the proposed algorithms is demonstrated. It is shown that for the consistent algorithm, additional conditions must be satisfied to insure convergence. In fact, one of the proposed algorithms is shown to be unconditionally stable but conditionally convergent. 相似文献
Existing vegetation indices and red-edge techniques have been widely used for the assessment of vegetation status and vegetation health from remote-sensing instruments. This study proposed and applied optimized Airborne Imaging Spectrometer for Applications (AISA) airborne hyperspectral indices in assessing and mapping stressed oil palm trees. Six vegetation indices, four red-edge techniques, a standard supervised classifier and three optimized AISA spectral indices were compared in mapping diseased oil palms using AISA airborne hyperspectral imagery. The optimized AISA spectral indices algorithms used newly defined reflectance values at wavelength locations of 734 nm (near-infrared (NIR)) and 616 nm (red). The selection of these two bands was based on laboratory statistical analysis using field spectroradiometer reflectance data. These two bands were then applied to the AISA airborne hyperspectral imagery using the three optimized algorithms for AISA data. The newly formulated AISA hyperspectral indices were D2 = R616/R734, normalized difference vegetation index a (NDVIa)?=?(R734 – R616)/(R734?+?R616) and transformed vegetation index a (TVIa)?=?((NDVIa?+?0.5)/(abs (NDVIa?+?0.5))?×?[abs (NDVIa?+?0.5)]1/2. The classification results from the optimized AISA hyperspectral indices were compared with the other techniques and the optimized AISA spectral indices obtained the highest overall accuracy. D2 and NDVIa obtained 86% of overall accuracy followed by TVIa with 84% of overall accuracy. 相似文献
In addition to more than 200 endogenously produced post-translational modifications, a detailed analysis of 2-D gel-separated proteins must also consider other modifications that a protein can experience during various steps of its separation. This review describes the use of matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry to investigate some of these modifications, which can originate during sample preparation and/or during the separation phase. The analyses described were mostly conducted at pH 9-9.5, and yielded reliable information on stable adduct formation that involved protein-bound amino acids and a number of gel components, including acrylamide derivatives, gel cross-linkers, and Immobiline chemicals. The -SH group of Cys was found to be the prime target of such adducts; however, longer reaction times revealed the involvement of the epsilon-NH2 of Lys. The same analysis revealed that the failure to achieve full reduction/alkylation prior to any electrophoretic step could result in protein-protein interaction, which could lead to a number of spurious spots in the final 2-D map. The implications of these modifications on the MS analysis in particular and on proteome research in general are discussed. 相似文献
Octahedral manganese oxide molecular sieves (OMS-2) modified by impregnation of TiO2 exhibit a higher catalytic activity for oxidation of styrene with tert-butylhydroperoxide in comparison to titanium-incorporated OMS-2, where the styrene conversions were ca. 70% and 45–50%, respectively. The framework of titanium species has no effect on the enhancement of catalytic activity, while the non-framework of titanium species induces a synergetic effect that enhances the oxidation of styrene with tert-butylhydroperoxide. 相似文献
The use of magnesium-doped ceramics has been described to modify brushite cements and improve their biological behavior. However, few studies have analyzed the efficiency of this approach to induce magnesium substitution in brushite crystals. Mg-doped ceramics composed of Mg-substituted β-TCP, stanfieldite and/or farringtonite were reacted with primary monocalcium phosphate (MCP) in the presence of water. The cement setting reaction has resulted in the formation of brushite and newberyite within the cement matrix. Interestingly, the combination of SAED and EDX analyses of single crystal has indicated the occurrence of magnesium substitution within brushite crystals. Moreover, the effect of magnesium ions on the structure, and mechanical and setting properties of the new cements was characterized as well as the release of Ca2 + and Mg2 + ions. Further research would enhance the efficiency of the system to incorporate larger amounts of magnesium ions within brushite crystals. 相似文献
This paper is concerned with second-order approximations to the steady-state principal parametric resonance response of a vertically mounted flexible cantilever beam subjected to a vertical harmonic base motion. The unimodal form of the nonlinear equation describing the in-plane large amplitude parametric response of the beam, derived in Krishnamurthy (Ph.D. Thesis, Department of Mechanical Engineering, Washington State University, 1986) based on the previous analysis in Crespo da Silva and Glynn (Journal of Structural Mechanics 1978; 6:437–48), is analysed using the harmonic balance (HB) and the perturbation method of multiple time scales (MMS). Single term HB, two terms HB, and second-order MMS with reconstitution version I (Nayfeh and Sanchez, Journal of Sound and Vibration 1989; 24:483–97) and version II (Rahman and Burton, Journal of Sound and Vibration 1989; 133:369–79) approximations to the steady-sate frequency–amplitude curves of the principal parametric resonance for each of the first four natural modes of the cantilever beam are compared with each other and with those obtained by numerically integrating the unimodal equation of motion. The time transformation
is used in obtaining these approximations; also detuning is used in obtaining the square of the forcing MMS approximations. The obtained results show that, for the problem under consideration, the MMS version II is, in comparison with MMS version I, simpler to apply and leads to qualitatively more accurate second-order results. These results, however, show that the MMS version II tends to produce appreciable over corrections to the first-order results and may breakdown at relatively low response amplitudes, whereas the two terms HB solutions tend to improve the first-order results and lead to fairly accurate results even for relatively large response amplitudes. 相似文献
beta(1-39) amyloid peptide is one of the components of the cerebral amyloid deposits that are characteristic of Alzheimer's disease. Solid-phase synthesis of this peptide resulted in a fairly complex crude product containing both the target peptide and a number of side products. High-performance liquid chromatography coupled to electrospray ionization mass spectrometry allowed rapid and reliable identification of both the desired peptide and most of the side products which were found to have relative molecular masses above and below that of the target peptide. 相似文献