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21.
The formation of regular colloid patterns in free-standing smectic films at the transition from the smectic-C to the isotropic
or nematic phase is well known experimentally. The self-organization of isotropic or nematic droplets is caused by their mutual
interaction, mediated by elastic distortions of the local director in the surrounding liquid crystal. These distortions are
related to the anchoring conditions of the director at the droplet border. We describe analytically the energetics of the
liquid crystal environment of a single droplet in one-constant approximation. A method of complex analysis, Conformal Mapping,
is employed. Following a suggestion of Dolganov et al. (Phys. Rev. E. 73, 041706 (2006)), energetics of chain and grid patterns built from the colloids are investigated numerically in order to explain
experimentally observed formations and their director fields. 相似文献
22.
Petit M Daoudi A Ismaili M Buisine JM 《The European physical journal. E, Soft matter》2006,20(3):327-333
We report the effect of an anisotropic polymer network formed from an achiral photoreactive monomer in a short-pitch chiral
SmC* phase on the distortion and the unwinding of the helical structure of the ferroelectric phase. The electro-optical behaviour
and ferroelectric properties were experimentally determined for films containing various polymer concentrations. The critical
field, Eu, for the transition from the distorted structure to the homogeneous state was measured as a function of polymer concentration.
A linear increase of Eu
versus polymer concentration was observed, showing that the helical structure of the short-pitch SmC* phase was stabilized by the
polymer network. This behaviour was expected to be a consequence of the increase of the apparent elastic constants of the
ferroelectric liquid crystal stabilized by the anisotropic polymer network films. The polymer network morphology was investigated
using atomic-force microscopy, revealing a twisted structure of the polymer fibers. This twisted structure was transferred
onto a polymer network during the polymerization process within a short-pitch SmC* phase. The increase of the apparent elasticity
can then be interpreted by a strong interaction between polymer network and the liquid-crystal molecules. From our experimental
data, the coupling coefficient, Wp, characterizing this interaction was evaluated for all studied polymer concentrations. 相似文献
23.
D. Caprion 《The European physical journal. E, Soft matter》2009,28(3):305-313
We report Monte Carlo simulations of a model discotic molecule embedded in cylindrical pores. We consider a planar anchoring
of the molecules on the surface for two different cylinder radii: R
* = 5 and R
* = 10 , in units of the molecular diameter. For both radii, we note that the system is progressively structured in concentric
shells when decreasing the temperature. With the small radius, we observe continuous transitions from an isotropic to a nematic
phase and then to a crystal one. The radius of the pores is sufficiently small to force the crystal to grow along their main
axis. However some orientational discrepancies are observed: some samples present a zigzag configuration. With the big radius,
the situation is more complex and it is likely that different scenarios are available. The crystals can be built along the
main axis of the cylinders, as for the small radius, but also in any other direction. Thus we observe samples with different
orientational domains. In the case of crystals oriented along the nanopore axis, we note that only the first 5 shells close
to the wall are sensitive to it. 相似文献
24.
Molecular dynamics(MD) simulations are performed to explore the layering structure and liquid–liquid transition of liquid water confined between two graphene sheets with a varied distance at different pressures. Both the size of nanoslit and pressure could cause the layering and liquid–liquid transition of the confined water. With increase of pressure and the nanoslit's size, the confined water could have a more obvious layering. In addition, the neighboring water molecules firstly form chain structure, then will transform into square structure, and finally become triangle with increase of pressure. These results throw light on layering and liquid–liquid transition of water confined between two graphene sheets. 相似文献
25.
Maximilian J. Uttinger Sebastian Boldt Simon E. Wawra Tobias D. Freiwald Cornelia Damm Johannes Walter Dietmar Lerche Wolfgang Peukert 《Particle & Particle Systems Characterization》2020,37(7):2000108
Analytical centrifugation (AC) has recently shown great potential for the accurate determination of particle size distributions. The well-established LUMiSizer(R) is customized by a new design allowing for higher rotor speeds, improved thermal insulation, and measurement cell assembly. The latter enables sedimentation analysis of nanoparticles (NPs) in sector-shaped centerpieces. The measurement window of AC experiments is assessed by the Peclet (Pe) number. It is shown that at low Pe numbers (0.7 < Pe < 30), sedimentation, and diffusion can be accurately and simultaneously analyzed from the sedimentation boundaries within one experiment. Moreover, sedimentation properties can be reliably determined up to Pe numbers of 4000. The thermal characteristic throughout the sedimentation analysis is validated by measuring polystyrene particles at elevated temperatures. Moreover, the performance of the setup is demonstrated by determining the sedimentation properties of SiO2 NPs at intermediate Pe numbers in excellent agreement with results from analytical ultracentrifugation experiments. Finally, for the first time, an accurate analysis of the core–shell properties of Au NPs via AC is presented. By combining the analysis of sedimentation and diffusional properties at low Pe numbers, the shell thickness of the stabilizer cetyltrimethylammonium bromide alongside the core diameter distribution of the Au NPs is determined. 相似文献
26.
Olga V. Kalashnikova Michael J. Garay Anthony B. Davis John V. Martonchik 《Journal of Quantitative Spectroscopy & Radiative Transfer》2011,112(13):2149-2163
The impact of tropospheric aerosols on climate can vary greatly based upon relatively small variations in aerosol properties, such as composition, shape and size distributions, as well as vertical layering. Polarimetric measurements have been advocated in recent years as an additional tool to better understand and retrieve the aerosol properties needed for improved predictions of aerosol radiative forcing on climate. The goal of this study is to introduce a formal approach to assessing the sensitivity of both intensity and polarization signals to absorbing aerosol layering, explicitly accounting for instrument measurement uncertainties. If ignored, sensitivity to aerosol height can introduce biases in aerosol property retrievals at short (ultraviolet or blue) wavelengths; if properly exploited, it may enable the extraction of some basic information on aerosol profiles. Employing a vector successive-orders-of-scattering (SOS) radiative transfer code, we conducted modeling experiments to determine how the measured Stokes vector elements are affected at 446 nm (blue band) by the vertical distribution, mixing and layering of smoke and dust aerosols under the assumption of a simple Lambertian surface and predefined aerosol microphysical properties. We find that smoke and dust vertical layering, if ignored, can introduce biases in radiometric and polarimetric aerosol property retrievals for aerosol optical depth (AOD) above 0.3 (polarimetric) and AOD above 0.5 (radiometric), and should, therefore, be accounted for in retrievals at high aerosol loadings. 相似文献
27.
MPPC low-level-light imaging enhancement algorithm based on sub-window box filtering北大核心CSCD 下载免费PDF全文
针对多像素光子计数器(MPPC)进行微光成像时,图像受光照不足和噪声影响出现的图像亮度低、对比度差、边缘模糊等问题,提出一种基于子窗口盒式滤波的自适应微光图像处理算法。为了减少算法运行时间的同时突出图像的边缘细节信息,利用子窗口盒式滤波器对图像进行分层得到基础层和细节层;对基础层图像采用自适应阈值直方图均衡化拉伸对比度,细节层图像采用自适应增益控制方式进行增强;根据基础层图像中有效灰度值个数占总灰度的比值自适应确定融合系数,将基础层图像与细节层图像融合得到增强后图像。通过微光实验平台设置3组不同照度的微光环境进行实验仿真,验证了本文算法在保持边缘信息和增强细节方面获得了更好的效果。实验结果表明本文算法在标准差、信息熵、平均梯度等客观评价方面优于改进前算法,提升了微光图像的成像效果。 相似文献
28.
29.
We discuss the structure and physical origin of corona patterns observed around solid or liquid spherical inclusions in freely
suspended smectic films. Such patterns are observed when droplets or solid beads of micrometer size are sprayed onto the films.
They are found in the smectic C phase and in the smectic A phase above such a smectic C phase, but disappear, for example,
at the transition into a lower-temperature smectic B phase. We show that these structures are equivalent to splay domains
found in the meniscus of freely suspended films, originating from surface-induced spontaneous splay. 相似文献
30.
Conradi M Ziherl P Sarlah A Musevic I 《The European physical journal. E, Soft matter》2006,20(2):231-236
We study the structure of a free-standing smectic-A film around a micron-size polystyrene colloid adsorbed onto the film.
We find that a colloid or a cluster of colloids is surrounded by an optically distinct and radially decorated meniscus ending
with a sharp edge. The observed strong and finite-range attraction between the adsorbed colloids is driven by the fusion of
menisci. We interpret the structure of the smectic meniscus in terms of a model dominated by the surface free energy and we
argue that the characteristic appearance of the meniscus is due to layer undulations. 相似文献