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排序方式: 共有64条查询结果,搜索用时 31 毫秒
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MJ Lazaro AA Herod M Domin Y Zhuo CA Islas R Kandiyoti 《Rapid communications in mass spectrometry : RCM》1999,13(14):1401-1412
Three methods for determining a 'safe' estimate for high-mass limits of MALDI spectra of coal derived liquids were explored, using a sample of coal-tar pitch and its pyridine-insoluble fraction. Co-addition of increasing numbers of single-shot spectra (10, 30, 50 and 100 pulses) showed visually observable reductions in noise levels, consistent with robust and statistically meaningful signals. Three separate types of post-acquisition calculation were used to identify high-mass limits of the spectra. (i) A literature method indicated high-mass limits similar to those observed visually-as a shift from baseline at the highest masses, nearly 350 000 u for the coal tar pitch and about 390 000 u for its pyridine insoluble fraction. (ii) Comparing instrument signal with pre-selected multiples of the standard deviation, upper mass estimates of between 40-60 000 u for the coal-tar pitch and about 95 000 u for its pyridine-insoluble fraction were found. (iii) Calculation of the slope was used to identify 'lift-off' of the spectrum from baseline. The angle between the smoothed spectrum and the baseline was matched to a pre-selected value (e.g. 0.5 degrees and 1 degrees ). However, the arbitrary specification of the key parameter did not establish this last method on a firm basis. The choice of a criterion for estimating high-mass limits of MALDI spectra remains a semi-quantitative procedure; a reasonably conservative high-mass limit may be estimated by comparison of signal with five times the standard deviation. However, evaluation of size exclusion chromatograms of the present samples using polystyrene standards suggests that molecular mass distributions of pitch samples arrived at by MALDI mass spectrometry are, at least partly, determined by the limitations of available instruments. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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A. Pashkin K. Thirunavukkuarasu Y.-L. Mathis W. Kang C. A. Kuntscher 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(4):285-290
We present measurements of the infrared response of the
quasi-one-dimensional organic conductor (TMTSF)2FSO3 along
(E
) and perpendicular (E
) to the
stacking axis as a function of temperature. Above the
metal-insulator transition related to the anion ordering the
optical conductivity spectra show a Drude-like response. Below the
transition an energy gap of about 1500 cm-1 (185 meV) opens,
leading to the corresponding charge transfer band in the optical
conductivity spectra. The analysis of the infrared-active
vibrations gives evidence for the long-range crystal structure
modulation below the transition temperature and for the
short-range order fluctuations of the lattice modulation above the
transition temperature. We also report about a new infrared mode
at around 710 cm-1 with a peculiar temperature behavior, which
has so far not been observed in any other (TMTSF)2X salt
showing a metal-insulator transition. A qualitative model based on
the coupling between the TMTSF molecule vibration and the
reorientation of electrical dipole moment of the FSO3 anion is
proposed, in order to explain the anomalous behavior of this new
mode. 相似文献
44.
V. I. Torgashev Yu. I. Yuzyuk V. V. Lemanov C. A. Kuntscher 《Physics of the Solid State》2006,48(4):765-773
Polarized Raman and IR reflectance spectra of single-crystal samples of Pb1 ? x CaxTiO3 perovskite solid solutions (x = 0, 0.03, 0.04, 0.15, 0.23, 0.28, 0.34, 0.38, 0.40, 0.45, 0.50) are recorded for the first time over the frequency range 6 < v < 1200 cm?1 at temperatures of 290–620 K. Primary attention is focused on the low-frequency lattice dynamics, where the phonon spectral response exhibits an anomalous behavior in the concentration range 0.38 < x < 0.40. At room temperature, a new phase state, tentatively identified as polar, is found to exist in the Pb1 ? x CaxTiO3 solid solutions for x > 0.40. 相似文献
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为了实现采摘机器人在复杂的自然场景下正确识别树上果实,来完成果实采摘,研究了不同环境下柑橘的识别方法.针对复杂的自然环境的影响及传统方法的局限性,在可见光和近红外区域择选5个特征波长滤波片,采集得到5幅滤波后的图像,并利用光谱角分类算法完成柑橘识别.试验结果表明,在光照角度、光照强度等不同条件下,柑橘的识别准确度达到96%.研究表明,滤波片光谱图像技术结合光谱角分类算法可以有效地识别自然场景下的成熟柑橘. 相似文献
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