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排序方式: 共有577条查询结果,搜索用时 390 毫秒
81.
82.
白河为黄河源区典型弯曲河流,2016年和2017年对白河9处典型河湾进行了考察采样。分析表明,白河河湾凸岸植被呈环形条带状分布,一般有2~3个植被群落;湾顶从前至后的树木尺寸显示出明显的由低矮到高大的梯度变化。对凸岸树芯和圆盘样本进行年轮分析,获取了树木的分布和树龄数据,提出了通过树木年轮和距离计算河湾迁移速率的方法。通过绘制树龄分布云图找出关键样本,测算白河河湾迁移速率为0.38~6.1 m/a,与遥感影像估算得出的迁移速率基本一致。对白河河湾迁移速率与水流流速、河宽、滩高等数据进行回归分析,建立多元线性回归模型,结果表明水流流速和比降是白河河湾迁移速率的主要影响因素,迁移速率与流速和比降均成正比。 相似文献
83.
84.
Euan Smith Rodney L. Heckaman Karl Lang John Penczek Johan Bergquist 《Journal of the Society for Information Display》2020,28(6):548-556
Historically displays used three colorants in an additive system. During that time, the CIE chromaticity diagram adequately illustrated color capability. Modern displays are not constrained by this additive architecture, and the diagram can fail in its purpose. This is demonstrated by analysis and a large number of display measurements. A device‐independent methodology using CIE 1976 L*a*b* color gamut volume is described that provides a robust means to determine the size of the color gamut. This methodology is then extended to the ‘gamut rings’ diagram as a solution for visualizing color capability that directly correlates to color gamut volume. It is further shown how the methodology can be applied to determine the intersection between two gamut volume boundaries. 相似文献
85.
86.
P. Pawlus 《Tribology International》1993,26(1)
This paper presents results of the measurement of the surface roughness and other physical properties of the outer layer of honed cylinders. The cylinders tested had various surface topographies as a result of honing by abrasive tools of differing design. The results of wear measurements of the cylinders and piston rings mating with them during automotive gasoline Polonez 1500 engine operation under artificially increased dustiness conditions are presented and analysed. 相似文献
87.
精密内圆磨削过程的灰色系统模型研究与质量控制系统设计 总被引:1,自引:0,他引:1
预报补偿与控制技术是提高精密内圆磨削质量的有效途径。在分析轴承内圈内圆磨削质量的基础上,指出精密内圆磨削过程可视为一典型的灰色系统,灰色系统GM(1,1)模型将有助于进一步认识内圆磨削过程的本质。建模仿真结果表明,GM(1,1)模型可以较好地描述工件磨削尺寸误差序列的趋势项,基于此,就可以对内圆磨削过程实施预报补偿控制。设计了旨在提高轴承内圈内圆磨削质量和效率的控制系统。 相似文献
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89.
《Food Control》2016
Foods with high added value, such as Iberian dry-cured products, are susceptible to fraud. Many attempts have been made to differentiate the commercial/quality categories of Iberian dry-cured hams by analytical determinations. However, as discrimination by such means is not fully reliable, legislation to prevent fraudulent practice is based on administrative controls and certification. Here, new analytical approaches based on ultrahigh resolution mass spectrometry (UHRMS) and crystallographic techniques applied to the lipid fraction, in combination with chemometrics, are studied. The results of the triacylglycerol profile determined by UHRMS and the fingerprint provided by the thermograms obtained by differential scanning calorimetry offer the promise of analytic discrimination of Iberian dry-cured ham categories. In addition, these determinations, in combination with chemometrics, may prove extremely useful to authenticate many foods containing high to moderate amounts of lipids. 相似文献
90.
The crystalline microstructure and polymorphism of C-type starch from Chinese yam were evaluated by scanning electron microscope (SEM), 13C cross-polarization magic-angle spinning NMR (13C CP/MAS NMR) and powder X-ray diffraction (XRD) technique and acid hydrolysis method. Morphological changes during acid hydrolysis showed that the amorphous or the less crystalline areas were essentially located at the center part of C-type starch granules whereas the semi-crystalline and amorphous growth rings were found mainly in the outer part of the granules. 13C CP/MAS NMR and XRD results revealed that B-type allomorph was hydrolyzed more rapidly than A-type one. The amorphous or less crystalline areas were predominantly composed of B-allomorph whereas the outer semi-crystalline and amorphous growth rings were mostly composed of A-type allomorph. The A- and B-type allomorph coexisted in the individual C-type starch granule. B-type allomorph basically existed at the center part of the granules which was surrounded by the A-type allomorph in the peripheral part of granules. 相似文献