排序方式: 共有36条查询结果,搜索用时 15 毫秒
1.
2.
Mikhail Ivanovich Barnik Ivan Vladimirovich Simdyankin Boris Alexandrovich Umanskii Serguei Petrovich Palto 《Liquid crystals》2020,47(2):273-283
ABSTRACT Electro-optical switching and the liquid crystal (LC) director distribution are studied in spatially periodic electric field for vertically aligned LC with negative dielectric anisotropy. Two electro-optical switching modes characterised by different switching times are observed. These modes are well distinguished optically by choosing proper geometry for the polarisers axes orientation. One of these modes is significantly faster as compared to the other. The fast switching is explained in terms of localised near-to-surface director reorientation. The 3D-numerical simulation shows very good agreement with the experiment: it points out the existence of the disclination lines and field-stabilised walls responsible for the localised director field switching and its relaxation. Possibilities of enhancing the fast mode for high-speed light modulators are discussed. 相似文献
3.
Chong-Kwang Lee Soon-Sik Kwon Seung-Tae Shin E-Joon Choi Soonnam Lee Liang-Chy Chien 《Liquid crystals》2013,40(8):1007-1013
Banana-shaped achiral compounds, the 1,3-phenylene bis[4-(alkenyloxyphenyliminomethyl)benzoate]s, were synthesized with varying length of the alkenyl group; their ferroelectric properties are described. The smectic mesophases, including a switchable chiral smectic C (SmC*) phase, were characterized by differential scanning calorimetry, polarizing optical microscopy and the triangular wave method. The presence of vinyl groups at the ends of the linear side-wings in the banana-shaped achiral molecules, containing a Schiff's base mesogen, induced a decrease in melting temperature and formation of the switchable SmC* phase in the melt. The compound having the octenyloxy group exhibited a spontaneous polarization of 120 nC cm?2 on reversal of an applied electric field. 相似文献
4.
提出了一种计算复色光下人眼视网膜空间像调制度的方法.利用Hartmann-Shack波前传感器测量的波前像差数据,求得眼睛光学系统的调制传递函数;利用CSV-1000测试仪和VAF-1000视锐度测试仪分别测量同一只眼睛的全眼对比敏感度函数以及视锐度,由调制传递函数、对比敏感度函数以及视锐度之间的关联获得复色光下人眼视网膜空间像调制度曲线.结果表明:视网膜空间像调制度曲线与眼光学系统的调制传递函数无关,并且正常人眼(无视网膜疾病)的视网膜空间像调制度值相近.因此多眼的空间像调制度曲线的统计平均值可以作为标准,用来评判人眼视网膜及视神经疾病. 相似文献
5.
Yong-Hyun Kim Ki-Hyun Kim Jan E. Szulejko Min-Suk Bae Richard J.C. Brown 《Analytica chimica acta》2014
For the quantitative analysis of ‘compounds lacking authentic standards or surrogates’ (CLASS) in environmental media, we previously introduced an effective carbon number (ECN) approach to develop an empirical equation for the prediction of their response factor (RF). In this research, a series of laboratory experiments were carried out to benchmark the reliability of an ECN approach for sorbent tube/thermal desorption/gas chromatography (GC)/mass spectrometry (MS) applications. First, the ECN values were determined using external calibration data from 25 reference volatile organic compounds (VOCs) using two MS dectectors (quadrupole (Q) and time-of-flight (TOF)). Then, a certified standard mixture of 54 VOCs was analyzed by each system as a simulated unknown sample. The analytical bias, assessed in terms of percentage difference (PD) between the certified and ECN-predicted mass values, averaged 19.2 ± 16.1% (TOF-MS) and 28.2 ± 27.6% (Q-MS). The bias using a more simplified carbon number (CN)-based prediction increased considerably, yielding 53.4 ± 53.3% (TOF-MS) and 61.7 ± 81.3% (Q-MS). However, the bias obtained using the ECN-based prediction decreased significantly to yield average PD values of 9.84 ± 7.28% (TOF-MS) and 16.8 ± 8.35% (Q-MS), if the comparison was limited to 26 (out of 54) VOCs with CN ≥ 4 (i.e., 25 aromatics and hexachlorobutadiene). 相似文献
6.
Masahiro Watari 《应用光谱学评论》2013,48(6):462-491
AbstractThis review describes the online process monitoring of the melt-state polymer by near-infrared (NIR) spectroscopy and chemometrics. The spectra of linear low-density polyethylene (LLDPE), random polypropylene (RPP), block polypropylene (BPP), and ethylene-vinylacetate (EVA) copolymer in melt states measured by an online monitoring system with a Fourier transform near-infrared spectrometer are discussed. The calibration models for the density of LLDPE, the content of ethylene copolymers in RPP and BPP, and vinylacetate concentration (VA) in EVA copolymers using partial least squares regression are reported. The continuous monitoring of the LLDPE density at the real plant is described as an example of online monitoring using NIR spectroscopy and chemometrics. For the precise prediction of VA in EVA, a combination method using regression and discrimination was inducted. Three compensation methods for the effect of the temperature change in the RPP and BPP samples are shown. Conventional calibration transfer methods are introduced, and a practical calibration transfer method using two samples and its performance are reported using BPP and RPP spectra. Moreover, the possibility of a calibration correction method using one sample for the realization of long-term traceability is indicated by the example of the relocation. 相似文献
7.
K. J. Jalkanen Julian D. Gale P. R. Lassen L. Hemmingsen A. Rodarte I. M. Degtyarenko R. M. Nieminen S. Brøgger Christensen M. Knapp-Mohammady S. Suhai 《Theoretical chemistry accounts》2008,119(1-3):177-190
In this work we present the experimental and theoretical vibrational absorption (VA) and the theoretical vibrational circular
dichroism (VCD) spectra for aframodial. In addition, we present the theoretical VA and VCD spectra for the diasteriomers of
aframodial. Aframodial has four chiral centers and hence has 24 = 16 diasteriomers, which occur in eight pairs of enantiomers. In addition to the four chiral centers, there is an additional
chirality due to the helicity of the entire molecule, which we show by presenting 12 configurations of the 5S,8S,9R,10S enantiomer
of aframodial. The VCD spectra for the diasteriomers and the 12 configurations of one enantiomer are shown to be very sensitive
not only to the local stereochemistry at each chiral center, but in addition, to the helicity of the entire molecule. Here
one must be careful in analyzing the signs of the VCD bands due to the ‘non-chiral’ chromophores in the molecule, since one
has two contributions; one due to the inherent chirality at the four chiral centers, and one due to the chirality of the side
chain groups in specific conformers, that is, its helicity. Theoretical simulations for various levels of theory are compared
to the experimental VA recorded to date. The VCD spectra simulations are presented, but no experimental VCD and Raman spectra
have been reported to date, though some preliminary VCD measurements have been made in Stephens’ lab in Los Angeles. The flexible
side chain is proposed to be responsible for the small size of the VCD spectra of this molecule, even though the chiral part
of the molecule is very rigid and has four chiral centers. In addition to VCD and Raman measurements, Raman optical activity
(ROA) measurements would be very enlightening, as in many cases bands which are weak in both the VA and VCD, may be large
in the Raman and/or ROA spectra. The feasibility of using vibrational spectroscopy to monitor biological structure, function
and activity is a worthy goal, but this work shows that a careful theoretical analysis is also required, if one is to fully
utilize and understand the experimental results. The reliability, reproduceability and uniqueness of the vibrational spectroscopic
experiments and the information which can be gained from them is discussed, as well as the details of the computation of VA,
VCD and Raman (and ROA) spectroscopy for molecules of the complexity of aframodial, which have multiple chiral centers and
flexible side chains.
Festschrift in Honor of Philip J. Stephens’ 65th Birthday. 相似文献
8.
Fei Zhang Wen-Xi Peng Ke Gong Di Wu Yi-Fan Dong Rui Qiao Rui-Rui Fan Jin-Zhou Wang Huan-Yu Wang Xin Wu Daniel La Philipp Azzarello Valentina Gallo Giovanni Ambrosi Andrea Nardinocchi 《中国物理C(英文版)》2016,40(11):116101-116101
The Silicon Tracker (STK) is one of the detectors of the DAMPE satellite used to measure the incidence direction of high energy cosmic rays. It consists of 6 X-Y double layers of silicon micro-strip detectors with 73728 readout channels. It is a great challenge to read out the channels and process the huge volume of data in the harsh environment of space. 1152 Application Specific Integrated Circuits (ASIC) and 384 ADCs are used to read out the detector channels. 192 Tracker Front-end Hybrid (TFH) modules and 8 identical Tracker Readout Board (TRB) modules are designed to control and digitalize the front signals. In this paper, the design of the readout electronics for the STK and its performance are presented in detail. 相似文献
9.
A readout electronics system used for space cosmic-ray charge measurement for multi-channel silicon detectors is introduced in this paper, including performance measurements. A 64-channel charge sensitive ASIC (VA140) from the IDEAS company is used. With its features of low power consumption, low noise, large dynamic range, and high integration, it can be used in future particle detecting experiments based on silicon detectors. 相似文献
10.