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71.
72.
Summary A new gas chromatographic method using an automatic purge-and-trap system coupled to a GC with mass selective detection to analyze styrene at the parts-per-trillions (ng kg–1) level is described. The method shows a good sensitivity and the detection limit is 10 ng kg–1 with a relative standard deviation (RSD) of 4.7% for 164 ng kg–1 styrene in olive oil. This analytical method has been successfully applied to the analysis of styrene in extra-virgin olive oil from the European market. 相似文献
73.
In this Letter, structural properties of liquid Ni20Al80 have been studied through molecular dynamics (MD) simulations, and results agree well with X-ray experiments. The prepeak in the structure factor manifests the existence of medium-range structural order (MRSO) in liquid Ni20Al80. Analyses in MRSO reveal the dominance of ideal icosahedra and defective icosahedra which, furthermore, form clusters and share common atoms. 相似文献
74.
Boris V. L'vov 《Mikrochimica acta》1991,104(1-6):299-308
A basically new mechanism of the thermal decomposition of solids is proposed to explain the mass spectral observations of gaseous molecules of CoO, CuO, Cu2O, NiO, PbO and Mg(OH)2 during the low-temperature decomposition of the anhydrous and hydrated nitrates of these metals. The mechanism consists of two stages: congruent gasification of all reaction products irrespective of their saturated vapor pressure and subsequent condensation of the low-volatility species (oxides and hydroxides). The partial pressures of these species at the appearance temperatures calculated from this theory for the first stage of the process (1–50 mPa) are in agreement with the detection limits of the quadrupole mass spectrometers used in these experiments. The proposed mechanism is supported by other available data obtained by thermal analysis. 相似文献
75.
The ability to quantitatively map the distribution of elements on the micrometer scale and smaller with high sensitivity and isotopic discrimination is unique to ion microscopy. The information contained in ion images can be crucial to the study of the solid state, where chemical heterogeneity is often directly related to observed behavior. The tools of digital image processing allow the extraction of quantitative information from the image data. These techniques coupled with improved instrumentation for the detection of ion images drastically increase the problem solving capabilities of the ion microscope. The use of such methods and instrumentation in the ion microscopic analyses of cell cultures and tissues of biological and biomedical relevance will be discussed. 相似文献
76.
Summary The nematic planar anchoring is usually explained by using simple elastic models: the surface easy axis corresponds to the
surface direction that minimizes the excess of nematic elastic energy. When anisotropic rough substrates are used to align
nematic liquid crystals, due to the complex surface morphology, usual elastic models are not directly applicable. This paper
presents quantitative topographical data of rough substrates, obtained with oblique SiO evaporation under vacuum for nematic
planar anchoring. Experimental data are obtained by means of Atomic Force Microscopy and they are used to demonstrate the
self-affine nature of these substrates and to relate the nematic anchoring with the anisotropy of the local fractal properties
of the substrate itself.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994. 相似文献
77.
This study reports on the effect of input power to hexamethyldisiloxane (HMDSO) plasmas. The power dependence of the plasma-phase species and of the surface chemistry (of the deposits) has been investigated. Neutral and positive molecular species were detected within the plasma using mass spectrometry (MS). Secondary ion mass spectrometry (SIMS) was used to probe the molecular structure of the deposits. The elemental composition of the surface was determined by XPS and the deposition rate was monitored using a vibrating quartz crystal microbalance. Neutral and cationic molecules of mass greater than HMDSO were detected in the plasma. Their formation through ion-molecule reactions is proposed. Changes in the relative concentration of plasma-phase species follow those seen in molecular species detected at the deposit surface. Thus, we believe that the molecular structure of the deposits can be related to the species present in the plasma. While traditionally the dominant mechanism in deposit formation is assumed to be free radical combinations, we propose other possibilities involving cations with the aim of putting forward a new perspective on plasma polymerization mechanisms and thereby stimulating discussion. 相似文献
78.
A quick sample preparation method was used for the determination of sulphur and trace metals in oil and oily products by the ICP with a minitorch. Stable aqueous emulsions of oils and oil products were made by using two kinds of emulsifiers (one with low sulphur content, the other sulfonated). Aqueous standard solutions can be used for the preparation of calibration solutions. The contents of S, Al, Cr, Cu, Fe, Mg, Ni and Pb in aqueous emulsions were determined and the results were in good agreement with the composition of oil standard solutions used for control analysis procedure. 相似文献
79.
Pyrolysis ammonia chemical ionization (PyCI) mass spectrometry was performed on hy-droxyethyl-, hydroxypropyl-,methyl-, hydroxypropylmethyl-, and ethylhydroxyethyl cel-luloses. The mass peaks in the PyCI mass spectra of these cellulose ethers could be assigned to the ions of pyrolytic dissociation products which form via the [2 + 2 + 2] cycloreversion and the Ei elimination pyrolysis pathway. Structural information about the residual amount of nonderivatized cellulose, the relative chain length distributions of the substituents in hydroxyalkyl celluloses, and the end-capping of hydroxyalkyl substituents by alkyl groups in the mixed cellulose ethers is obtained. Interference of secondary pyrolysis products in the PyCI mass spectra is found to be of minor importance, especially in the lower mass regions. © 1995 John Wiley & Sons, Inc. 相似文献
80.
Liquid crystal lens with focus movable in focal plane 总被引:1,自引:0,他引:1
A liquid crystal lens with focus movable in the focal plane is reported. There are three electrodes in the cell. One electrode with a hole in the center is divided into four subelectrodes. The potential of each subelectrode is adjusted to produce a desired asymmetrical phase transformation resulting in off-axis movement of the focus. The potential of another electrode is adjusted to maintain the focus in the focal plane. Movements of the focus in three directions in the focal plane are demonstrated experimentally, and off-axis movement as large as approximately 800 μm is realized. 相似文献