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51.
通过本体聚合方法合成了一系列侧链含苯酰亚胺结构的聚对苯二甲酸乙二酯(PET)共聚酯.研究发现,苯酰亚胺单元的引入不仅提高了共聚酯的玻璃化转变温度(T_g)和高温成炭性,并且大大降低了共聚酯高温下的热分解速率.随着苯酰亚胺含量的增加,共聚酯表现出更高的氧指数(LOI)值和更好的阻燃抗熔滴效果.锥形量热测试结果表明,苯酰亚胺结构的引入可以有效地降低共聚酯的峰值热释放速率(p-HRR)、峰值烟释放速率(p-RSR)和总烟释放量(TSR).通过对纯PET和共聚酯燃烧测试后残炭的结构和形貌分析,发现苯酰亚胺结构有助于共聚酯形成石墨化程度更高的致密炭层,这些炭层起到隔热隔氧和抑制有机可燃烟气挥发的作用,在不引入传统阻燃剂的情况下,赋予共聚酯很好的本征阻燃性及抑烟性. 相似文献
52.
Advanced solvent signal suppression for the acquisition of 1D and 2D NMR spectra of Scotch Whisky 下载免费PDF全文
Will Kew Nicholle G.A. Bell Ian Goodall Dušan Uhrín 《Magnetic resonance in chemistry : MRC》2017,55(9):785-796
A simple and robust solvent suppression technique that enables acquisition of high‐quality 1D 1H nuclear magnetic resonance (NMR) spectra of alcoholic beverages on cryoprobe instruments was developed and applied to acquire NMR spectra of Scotch Whisky. The method uses 3 channels to suppress signals of water and ethanol, including those of 13C satellites of ethanol. It is executed in automation allowing high throughput investigations of alcoholic beverages. On the basis of the well‐established 1D nuclear Overhauser spectroscopy (NOESY) solvent suppression technique, this method suppresses the solvent at the beginning of the pulse sequence, producing pure phase signals minimally affected by the relaxation. The developed solvent suppression procedure was integrated into several homocorrelated and heterocorrelated 2D NMR experiments, including 2D correlation spectroscopy (COSY), 2D total correlation spectroscopy (TOCSY), 2D band‐selective TOCSY, 2D J‐resolved spectroscopy, 2D 1H, 13C heteronuclear single‐quantum correlation spectroscopy (HSQC), 2D 1H, 13C HSQC‐TOCSY, and 2D 1H, 13C heteronuclear multiple‐bond correlation spectroscopy (HMBC). A 1D chemical‐shift‐selective TOCSY experiments was also modified. The wealth of information obtained by these experiments will assist in NMR structure elucidation of Scotch Whisky congeners and generally the composition of alcoholic beverages at the molecular level. 相似文献
53.
Background
High-frequency Doppler imaging is highly potential for detection of blood flow in microcirculation. In a swept-scan system, however, the spectral broadening of tissue clutter limits the detectability of low-velocity flow signal. Conventionally, the scanning speed of transducer has to be reduced to alleviate the clutter interference but at the cost of imaging frame rate. For example, the blood velocity of 0.5 mm/s becomes detectable only with a scanning speed lower than 1 mm/s. In this study, an alternative method is examined by suppressing the clutter magnitude to reduce the interference to flow signal without sacrificing scanning speed.Methods
The method of third harmonic (3f0) transmit phasing can suppress the tissue harmonic clutter by transmitting at the fundamental and the additional 3f0 frequencies to achieve mutual cancellation between the frequency-sum and the frequency-difference components of the second harmonic signal. With 3f0 transmit phasing, the cut-off frequency of wall filtering can be reduced to preserve low-velocity flow without compromising the frame rate.Results
Our results indicate that the 3f0 transmit phasing effectively reduces the harmonic clutter magnitude and thus improves the flow signal-to-clutter ratio. Compared to the conventional counterpart, the clutter-suppressed color flow and power Doppler images show fewer clutter artifacts and is capable of detecting more low-velocity flow of microbubbles. The resultant color-pixel-density also improves with clutter suppression.Conclusion
For the swept-scan high-frequency (>20 MHz) system, 3f0 transmit phasing is capable of providing effective clutter suppression. With the same achievable scanning speed, the resultant Doppler image has higher sensitivity for low-velocity flow and is less susceptible to clutter artifacts. 相似文献54.
Deren Li Tiancheng LiuJianliang Li Zheng ChenKaihuang Liu Zhichao LuShaoxiong Zhou 《Journal of magnetism and magnetic materials》2012,324(9):1655-1658
A system and a method were developed for continuous production of glass-coated microwires with controllable glass thickness and metallic core diameter. Fe-Si-Al flakes were fabricated by planetary ball milling using ethanol as a dispersant. A composite noise suppression sheet was prepared with glass-coated microwires combined with Fe-Si-Al flakes. The characteristics of the conduction noise suppression of the composite sheet were evaluated on a microstrip line in gigahertz frequencies. The conduction electromagnetic noise was effectively suppressed by the composite sheet in broad-band frequency region; the power loss is greater than 70% in the frequency range from 0.7 to 8.5 GHz. 相似文献
55.
S变换是一种集合了窗口傅里叶变换和小波变换优点的时频分析技术,目前一维S变换已成功应用于结构光投影的条纹相位解调中。由于二维S变换可以对图像在两个方向上进行时频分析,具有更优于一维S变换的分析和处理能力。为了完善S变换的条纹相位解调理论,将二维S变换方法引入到基于结构光投影的三维光学测量中,研究了二维S变换在条纹相位解调中的原理及应用,给出了详尽的理论分析,并同一维S变换结果进行了比较。模拟和实验都表明,在条纹图解相中,二维S变换比一维S变换提取的相位精度更高,即使在存在较严重噪声污染的情况下也表现出良好的可靠性,体现出二维S变换提取相位的优势。 相似文献
56.
57.
58.
Sang-Tae LeeByung-Guon Park Moon-Deock Kim Jae-Eung OhSong-Gang Kim Young-Heon KimWoo-Chul Yang 《Current Applied Physics》2012,12(2):385-388
We discuss the role of the Al interlayer in the suppression of pinhole formations and also look at the polarity transition of the AlN layers from N-polarity to Al-polarity when this Al interlayer is present. The AlN layers were grown by molecular beam epitaxy on an AlN nucleation layer. A thin Al interlayer was deposited on the initial nucleated AlN layer after the nitridation of the Al-soaked Si (111) substrates. The AlN layer with an Al interlayer showed a relatively smooth surface with a reduced density of pinholes compared with the AlN layer grown without an Al interlayer. In addition, the AlN layer with an Al interlayer showed some stacking faults in the interface between the Si substrate and the A1N layer. We also identify the polarity change of the AlN layer after the insertion of a thin Al interlayer from N-polarity to Al-polarity by chemical etching. A simple model is constructed to explain the polarity change and the pinhole suppression due to the Al interlayer. 相似文献
59.
Markus M. Hoffmann Hanna S. Sobstyl Vincent A. Badali 《Magnetic resonance in chemistry : MRC》2009,47(7):593-600
A number of suppression pulse sequences including Excitation Sculpting and WATERGATE were incorporated into the standard Carr‐Purcell‐Meiboom‐Gill (CPMG) program for T2 measurement and experimentally evaluated. The chosen suppression schemes were of varying complexity encompassing pulse program elements, such as presaturation, gradients, and selective pulses, which are typically utilized for solvent suppression. The quality of the spectral data and the accuracy of T2 measurements of the investigated suppression schemes were evaluated using three aqueous samples with increasing proton content in the water solvent, i.e. by volume 100% D2O, 80/20% D2O/H2O, and 20/80% D2O/H2O. For signals removed from the water signal, the T2 values were generally very consistent between all pulse sequences tested. T2 measurements can be unreliable for signals too close to the water signal such that they are significantly suppressed as well. Their intensity may actually grow initially through cross relaxation that transfers magnetization back to the solute signal. In turn, this relaxation phenomenon can be exploited to improve the spectral quality of conventional solvent suppression schemes. In favorable cases, even signals that are completely masked by the water signal can be recovered by adding a carefully chosen number of spin echoes with optimized evolution time to conventional water suppression pulse programs, such as Excitation Sculpting or WATERGATE. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
60.
The viscoelastic plate-fluid interaction problem was studied. Forced vibration of the interactive system was investigated,
and the equivalent mechanical models were obtained. The conclusion is that, for some case, the inner damping of the viscoelastic
baffle will play a major role for liquid sloshing suppression.
The project supported by National Natural Science Foundation of China and Astronautics Ministry. 相似文献