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61.
Ya‐Ching Shen Pei‐Show Shih Yun‐Sheng Lin Yu‐Chi Lin Yao‐Haur Kuo Yuh‐Chi Kuo Ashraf Taha Khalil 《Helvetica chimica acta》2009,92(10):2101-2110
Chemical investigation of the sponge Ircinia formosana resulted in the isolation of seven new linear C22‐sesterterpenoids, irciformonins E–K ( 1 – 7 ) in addition to irciformonin A ( 8 ), a previously isolated furanosesterterpenoid (=a furan‐moiety‐containing sesterterpenoid) from the same species. The structures were determined by interpretation of HR‐ESI‐MS and 2D‐NMR spectra. The structure of irciformonin A ( 8 ) was revised. Compound 5 exhibited significant inhibition of peripheral blood mononuclear cell proliferation induced by phytohemaglutinin. 相似文献
62.
Chien-Ju Shih 《Analytica chimica acta》2009,653(2):200-170
Raman spectroscopy has been used for the quantitative determination of the conversion efficiency at each step in the production of ethanol from biomass. The method requires little sample preparation; therefore, it is suitable for screening large numbers of biomass samples and reaction conditions in a complex sample matrix. Dilute acid or ammonia-pretreated corn stover was used as a model biomass for these studies. Ammonia pretreatment was suitable for subsequent measurements with Raman spectroscopy, but dilute acid-pretreated corn stover generated a large background signal that surpassed the Raman signal. The background signal is attributed to lignin, which remains in the plant tissue after dilute acid pretreatment. A commercial enzyme mixture was used for the enzymatic hydrolysis of corn stover, and glucose levels were measured with a dispersive 785 nm Raman spectrometer. The glucose detection limit in hydrolysis liquor by Raman spectroscopy was 8 g L−1. The mean hydrolysis efficiency for three replicate measurements obtained with Raman spectroscopy (86 ± 4%) was compared to the result obtained using an enzymatic reaction with UV-vis spectrophotometry detection (78 ± 8%). The results indicate good accuracy, as determined using a Student's t-test, and better precision for the Raman spectroscopy measurement relative to the enzymatic detection assay. The detection of glucose in hydrolysis broth by Raman spectroscopy showed no spectral interference, provided the sample was filtered to remove insoluble cellulose prior to analysis. The hydrolysate was further subjected to fermentation to yield ethanol. The detection limit for ethanol in fermentation broth by Raman spectroscopy was found to be 6 g L−1. Comparison of the fermentation efficiencies measured by Raman spectroscopy (80 ± 10%) and gas chromatrography-mass spectrometry (87 ± 9%) were statistically the same. The work demonstrates the utility of Raman spectroscopy for screening the entire conversion process to generate lignocellulosic ethanol. 相似文献
63.
We consider the motion of a two-dimensional interface between air (above) and an irrotational, incompressible, inviscid, infinitely deep water (below), with surface tension present. We propose a new way to reduce the original problem into an equivalent quasilinear system which is related to the interface's tangent angle and a quantity related to the difference of tangential velocities of the interface in the Lagrangian and the arc-length coordinates. The new way is relatively simple because it involves only taking differentiation and the real and the imaginary parts. Then if assuming that waves are periodic, we establish a priori energy inequality. 相似文献
64.
Yow-Jon Lin Chia-Lung Tsai Chia-Jyi Liu Lance Horng Yu-Tai Shih Mu-Shan Wang Chuan-Sheng Jhang Chao-Shien Huang 《Journal of Sol-Gel Science and Technology》2009,52(1):109-112
Co0.2Mg
x
Zn0.8−x
O films prepared with different molar ratio of magnesium acetate to zinc acetate were deposited on substrates by the sol–gel
technique. X-ray diffraction, photoluminescence (PL) and ferromagnetism measurements were used to characterize the Co0.2Mg
x
Zn0.8−x
O diluted magnetic semiconductors. The acceptor-like defects were determined in the PL band and the intensity of the acceptor-related
PL increased with increasing Mg concentration. Therefore, an increase in the number of the acceptor-like defects (zinc vacancies
especially) in the Co0.2Mg
x
Zn0.8−x
O film may lead to the enhancement of the magnetic properties. It is worth noting that changes in Mg concentration and the
number of the acceptor-like defects are important issues for producing strong ferromagnetism Co0.2Mg
x
Zn0.8−x
O films prepared by the sol–gel method. 相似文献
65.
M. Sc. Shih‐Fan Hsu Dipl.‐Chem. Susanne Rommel M. Sc. Philipp Eversfield Dr. Keven Muller Prof. Dr. Elias Klemm Prof. Dr. Werner R. Thiel Prof. Dr. Bernd Plietker 《Angewandte Chemie (International ed. in English)》2014,53(27):7074-7078
Apart from energy generation, the storage and liberation of energy are among the major problems in establishing a sustainable energy supply chain. Herein we report the development of a rechargeable H2 battery which is based on the principle of the Ru‐catalyzed hydrogenation of CO2 to formic acid (charging process) and the Ru‐catalyzed decomposition of formic acid to CO2 and H2 (discharging process). Both processes are driven by the same catalyst at elevated temperature either under pressure (charging process) or pressure‐free conditions (discharging process). Up to five charging–discharging cycles were performed without decrease of storage capacity. The resulting CO2/H2 mixture is free of CO and can be employed directly in fuel‐cell technology. 相似文献
66.
This article gives a quantum‐trajectory demonstration of the observed electric, magnetic, and thermal effects on a quantum dot with circular or elliptic shape. By applying quantum trajectory method to a quantum dot, we reveal the quantum‐mechanical meanings of the classical concepts of backscattering and commensurability, which were used in the literature to explain the peak locations of the magnetoresistance curve. Under the quantum commensurability condition, electronic quantum trajectories in a circular quantum dot are shown to be stationary like a standing wave, whose presence increases the electrical resistance. A hidden quantum effect called magnetic stagnation is discovered and shown to be the main cause of the observed jumps of the magnetoresistance curve. Quantum trajectories in an elliptic quantum dot are found to be chaotic and an index of chaos called Lyapunov exponent is proposed to measure the irregularity of the various quantum trajectories. It is shown that the response of the Lyapunov exponent to the applied magnetic field captures the main features of the experimental magnetoresistance curve. © 2014 Wiley Periodicals, Inc. 相似文献
67.
Microporous poly(vinylidene fluoride) (PVDF) membranes with asymmetric pore structure were prepared by a wet phase inversion process. The polymer was precipitated from a casting solution when immersed in a cold water (gelation) bath. The casting solution was, in most cases, composed of polymer, solvent, and nonsolvent. In this solvent-nonsolvent system, the solvents used were triethylphosphate (TEP) and dimethylsulfoxide (DMSO), and the nonsolvents used were glycerol and ethanol. Mean pore sizes and effective porosity of the microporous membranes were calculated using the gas permeation method. They were studied as a function of evaporation time of wet nascent film, polymer molecular weight, concentration of polymer, and concentration of nonsolvent. The morphology of the membranes was examined by scanning electron microscopy (SEM). 相似文献
68.
Fang‐Chyou Chiu Qiang Fu Ya Peng Hsi‐Hsin Shih 《Journal of Polymer Science.Polymer Physics》2002,40(4):325-337
Metallocene polyethylene (mPE) fractions are recognized as being more homogeneous with respect to short‐chain branch (SCB) distribution as compared with unfractionated mPEs. Differential scanning calorimetry and polarized optical microscopy (POM) were used to study the influences of SCB content on the crystallization kinetics, melting behavior, and crystal morphology of four butyl‐branched mPE fractions. The parent mPE of the studied fractions was also investigated for comparative purposes. mPE fractions showed a much simpler crystallization behavior as compared with their parent mPE during the cooling experiments. The Ozawa equation was successfully used to analyze the nonisothermal crystallization kinetics of the fractions. The Ozawa exponent n decreased from about 3.5 to 2 as the temperature declined for each fraction, indicating the crystal‐growth geometry changed from three‐dimensional to two‐dimensional. For isothermal crystallization, the fraction with a lesser SCB content exhibited a higher crystallization temperature (Tc) window. The results from the Avrami equation analysis showed the exponent n values were around 3 (with minor variation), which implied that the crystal‐growth geometry is pseudo‐three‐dimensional. Both of the activation energies for nonisothermal and isothermal crystallization were determined for each fraction with Kissinger and Arrhenius‐type equations, respectively. Double melting peaks were observed for both nonisothermally or isothermally crystallized specimens. The high‐melting peak was confirmed induced via the annealing effect during heating scans. The Hoffman–Weeks plot was inapplicable in obtaining the equilibrium melting temperature (Tm°) for each fraction. The relationship between Tc and Tm for the fractions is approximately Tm = Tc (°C) + 8.3. The POM results indicated that the crystals of parent or fractions formed under cooling conditions did not exhibit the typical spherulitic morphology as a result of the high SCB content. © 2002 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 325–337, 2002 相似文献
69.
Tzong‐Ming Wu Shih‐Hsiang Lin 《Journal of polymer science. Part A, Polymer chemistry》2006,44(21):6449-6457
Size‐controllable polypyrrole (PPy)/multiwalled carbon nanotube (MWCNT) composites have been synthesized by in situ chemical oxidation polymerization directed by various concentrations of cationic surfactant cetyltrimethylammonium bromide (CTAB). Raman spectra, FTIR, SEM, and TEM were used to characterize their structure and morphology. These results showed that the composites are core (MWCNT)–shell (PPy) tubular structures with the thickness of the PPy layer in the range of 20–40 nm, depending on the concentration of CTAB. Raman and FTIR spectra of the composites are almost identical to those of PPy alone. The electrical conductivities of these composites are 1–2 orders of magnitude higher than those of PPy without MWCNTs. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6449–6457, 2006 相似文献
70.
This study describes the preparation of polyethersulfone (PES)/layered silicate nanocomposites (PLSNs) by mixing PES polymer chain into organically‐modified layered silicate in 1‐methyl‐2‐pyrrolidinone (NMP) solution. Both X‐ray diffraction data and transmission electron microscopy images of PLSNs indicate that the silicate layers were almost exfoliated and randomly distributed into the PES matrix. The mechanical and barrier properties of PLSNs show remarkable enhancement in the storage modulus and water/oxygen permeability when compared with that of neat PES matrix. Surfaces modification of PES and PLSN films with various treated times, system pressures, and radio frequency (RF) powers were performed using a mixture of oxygen (O2) and nitrogen (N2) plasmas. The topographical and physical properties of plasma‐modified PES and PLSN surfaces were investigated using scanning probe microscopy (SPM), contact‐angle measurements, and X‐ray photoelectron spectroscopy (XPS). These results indicate that the surface roughness of PLSNs with the same condition of plasma modification is lower than that of neat PES matrix and is probably due to the increase of stiffness with the presence of inorganic layered silicates in PES matrix. The surface properties of the PES and PLSNs are also changed from hydrophobic to hydrophilic. The XPS spectra suggest that the exposure of the PES and PLSNs to the plasmas led to the combination of etching reactions of polymer surface initiated by plasma and the following addition reactions of new oxygen‐ and nitrogen‐containing functional groups onto polymer surfaces to change their surface properties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3185–3194, 2006 相似文献