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111.
J. Pollanen K.R. Shirer S. Blinstein J.P. Davis H. Choi T.M. Lippman W.P. Halperin L.B. Lurio 《Journal of Non》2008,354(40-41):4668-4674
We discuss two methods by which high porosity silica aerogels can be engineered to exhibit global anisotropy. First, anisotropy can be introduced with axial strain (i.e. axial compression). In addition, intrinsic anisotropy can result during growth and drying stages and, suitably controlled, it can be correlated with preferential radial shrinkage in cylindrical samples. We have performed small angle X-ray scattering (SAXS) to characterize these two types of anisotropy. We show that global anisotropy originating from either strain or shrinkage leads to optical birefringence and that optical cross-polarization studies are a useful characterization of the uniformity of the imposed global anisotropy. 相似文献
112.
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114.
W.-C. Xie 《Journal of sound and vibration》2003,263(3):593-616
The moment Lyapunov exponents of a two-dimensional system under bounded noise parametric excitation are studied in this paper. The method of regular perturbation is applied to obtain weak noise expansions of the moment Lyapunov exponent, Lyapunov exponent, and stability index in terms of the small fluctuation parameter. 相似文献
115.
Nynke A. M. Verhaegh Jeroen S. van Duijneveldt Jan K. G. Dhont Henk N. W. Lekkerkerker 《Physica A》1996,230(3-4):409-436
Mixtures of colloidal silica spheres and polydimethylsiloxane in cyclohexane with a colloid-polymer size ratio of about one were found to phase separate into two fluid phases, one which is colloid-rich and one which is colloid-poor. In this work the phase separation kinetics of this fluid-fluid phase separation is studied for different compositions of the colloid-polymer mixtures, and at several degrees of supersaturation, with small angle light scattering and with light microscopy. The small angle light scattering curve exhibits a peak that grows in intensity and that shifts to smaller wave vector with time. The characteristic length scale that is obtained from the scattering peak is of the order of a few μm, in agreement with observations by light microscopy. The domain size increases with time as
, which might be an indication of coarsening by diffusion and coalescence, like in the case of binary liquid mixtures and polymer blends. For sufficiently low degrees of supersaturation the angular scattering intensity curves satisfy dynamical scaling behavior. 相似文献
116.
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118.
Induced ferroelectric S*C phases are formed by non-chiral SC host phases doped with chiral dipolar guest molecules. In those mixtures the spontaneous polarization Ps and the tilt angle Θ has been investigated as a function of the mole fraction xG of the chiral dopant. In most cases the reduced polarization P0 = PS/ sin Θ has been found to depend linearly on xG. The polarization power which is defined by δP=(∂P0/∂xG)ΔT is discussed in terms of the molecular structure of the chiral dopants. There are systems in which P0(xG) deviates positively from linearity. This behaviour can be understood by considering a local field correction to P0. By assuming a local field of Lorentz type a theoretical relation for P0(xG) has been derived which explains the experimental results. The effect of a local field is considerable if the transverse dipole moment and the polarizability of the chiral dopant are large. 相似文献
119.
本文对四个主要麦芽品质性状—a一淀粉酶活力、麦芽汁粘度、麦芽汁色度和搪化力进行了杂种优势和相关分析.(1)相对优势结果表明,在84个组合次中,呈正向优势的46个,占54.76男,负向优势34个,占40.48男,无显性4个,占4.75男;(2)四个品质性状的中亲优势平均值分别为一6.117、一9.965 40.452和一。.545s a-淀粉酶活力和糖化力的超高亲优势分别为一14.578和一8.201,麦芽汁粘度和色度的超低亲优势分别为5.442和70.455.四个性状杂种优势的变异系数均很大.(3)麦芽汁色度的F,对MP的回归系数(B)和相关系数(r)均达显著水平,分别为。..43和0.50,麦芽汁粘度的相关系数达显著水平,为一。.45,其余均未达显著水平,(4)除麦芽汁色度性状外,另三个性状的中亲优势、超亲优势和特殊配合力的相关均达显著或极显著水平.(5)四个麦芽品质性状间的相关结果表明,仅有a-淀粉酶活力和麦芽汁粘度间呈极显著负相关(r=一0.56').最后,文章根据实验结果,就啤酒大麦麦芽品质改良的遗传育种及其杂种优势应用进行了初步讨论. 相似文献
120.
J P Kiplinger L Contillo W L Hendrick A Grodski 《Rapid communications in mass spectrometry : RCM》1992,6(12):747-752
Derivatization is used to increase both negative-ion sensitivity and positive-ion sequence information in the liquid secondary-ion mass spectra (LSIMS) of a series of peptides. The derivatization method involves acylation with pentafluorobenzoyl fluoride in a single-step reaction, and the reaction mixture is applied directly to the probe tip for analysis. Acylation takes place at the unprotected N-terminus, tyrosine, and lysine. The derivatives exhibit increased signal-to-noise ratio for [M-H]- ions, especially where there is not already an acidic amino acid residue in the peptide. In positive-ion LSIMS, the N-terminal group acts to retain the charge at the N-terminus, simplifying the fragmentation by producing N-terminal fragment ions. It also increases positive-ion fragmentation, sometimes very dramatically, making sequence determination more straightforward. The simplicity of the process, together with the enhancements it provides, make this a generally useful method for obtaining peptide structural information. 相似文献