壳聚糖膜固定生物活性短肽RGDS的研究

为改善壳聚糖对细胞的特异性吸附,采用水溶性碳二亚胺将生物活性短肽精氨酸-甘氨酸-天冬氨酸-丝氨酸(RGDS)固定到壳聚糖膜的表面,采用X射线光电子能谱检测固定多肽前后的壳聚糖膜表面,发现反应后壳聚糖膜表面氮元素含量增大,Nls和Cls曲线拟合谱中酰胺键增多,表明RGDS短肽已固定到壳聚糖膜的表面;人角膜缘上皮细胞体外培养实验表明,固定RGDS后壳聚糖膜的细胞黏附率有了明显提高,固定RGDS后的壳聚糖膜在角膜组织工程支架等方面有更好的应用潜力。     

Dynamic simulations of multicomponent lipid membranes over long length and time scales

We present a stochastic phase-field model for multicomponent lipid bilayers that explicitly accounts for the quasi-two-dimensional hydrodynamic environment unique to a thin fluid membrane immersed in aqueous solution. Dynamics over a wide range of length scales (from nanometers to microns) for durations up to seconds and longer are readily accessed and provide a direct comparison to fluorescence microscopy measurements in ternary lipid-cholesterol mixtures. Simulations of phase separation kinetics agree with experiment and elucidate the importance of hydrodynamics in the coarsening process.     

Dynamic scaling in phase separation kinetics for quasi-two-dimensional membranes

We consider the dynamics of phase separation in lipid bilayer membranes, modeled as flat two-dimensional liquid sheets within a bulk fluid, both in the creeping flow approximation. We present scaling arguments that suggest asymptotic coarsening in these systems is characterized by a length scale R(t) ~ t(1/2) for critical (bicontinuous) phase separation and R(t) ~t(1/3) for off-critical concentrations (droplet morphology). In this limit, the bulk fluid is the primary source of dissipation. We also address these questions with continuum stochastic hydrodynamic simulations. We see evidence of scaling violation in critical phase separation, where isolated circular domains coarsen slower than elongated ones. However, we also find a region of apparent scaling where R(t) ~ t(1/2) is observed. This appears to be due to the competition of thermal and hydrodynamic effects. We argue that the diversity of scaling exponents measured in experiment and prior simulations can in part be attributed to certain measurements lying outside the asymptotic long-length-scale regime, and provide a framework to help understand these results. We also discuss a few simple generalizations to confined membranes and membranes in which inertia is relevant.     

共振辐射的理论研究——Holstein方程的解

解决介质中共振辐射的关键问题是求解Holstein方程。本文直接利用算符运算将方程积分,给出了激发态粒子集居数的含无限项的级数表达式。基于对这个级数高阶系数的极限行为的研究,成功地克服了无穷项求和的困难,整理出一个在任意给定精度下都只含有限项的解式,由它可以计算出任何时刻的结果。 关键词：     

Exchange bias and anisotropy in the Fe/KCoF3 structure

A new type of ferromagnet/antiferromagnet structure (Fe/KCoF₃) was deposited by molecular beam epitaxy. Unidirectional and uniaxial anisotropies of 5.1 and 3.4 kA/m were measured at 23 K using ferromagnetic resonance. Magnetization measurements at 5 K showed a hysteresis loop shift of 6 kA/m due to exchange bias. Significant enhancement of four-fold anisotropy was found at low temperatures in the samples with polycrystalline KCoF₃ structure.     

Astrophysical S-factors from asymptotic normalization coefficients

S-factors for direct capture reactions can be found at astrophysical energies from asymptotic normalization coefficients which provide the normalization of the tail of the overlap function. For example the overlap for ⁸B → ⁷Be+p defines the S-factor for ⁷Be (p, γ)⁸B. Peripheral transfer reactions offer a technique to determine these asymptotic normalization coefficients. As a test of the technique, the ¹⁶O(³He, d)¹⁷F reaction has been used to determine asymptotic normalization coefficients for transitions to the ground and first excited states of ¹⁷F. The S-factors for ¹⁶O(p, γ)¹⁷F calculated from these ¹⁷F → ¹⁶O+p asymptotic normalization coefficients are found to be in very good agreement with recent measurements. Following the same technique, the ¹⁰B(⁷Be, ⁸B)⁹Be and ¹⁴N(⁷Be, ⁸B)¹³C reactions have been used to measure the asymptotic normalization coefficient for ⁷Be(p, γ)⁸B. This result provides an indirect determination of S ₁₇(0).     

Nonlinear behavior in magnetic transients

We examine the motion of a spin subject to a static external field, dynamic demagnetizing fields, and a relatively weak oscillatory driving field. More specifically, we study the initial transient behavior just after all these fields are turned on and present analytic calculations based on an approximation scheme for the motion of the spin. We find that two modes - a mode at the driving frequency and a mode at the natural resonant frequency - play an important role in the initial transient. Because of the nonlinear nature of the spin equations of motion, one also finds, only in the initial transient, modes with doubled frequencies of the initial two modes and modes involving the sum and difference frequencies of the initial two modes. We also examine large amplitude transients in specific cases through numerical calculations.     

Magnetostatic interface waves in ferromagnets

We derive the dispersion relation for magnetostatic surface waves guided by the interface between two ferromagnets. The applied field and saturation magnetization are parallel to the interface. The propagation of surface waves parallel to the interface is nonreciprocal and is limited to a restricted set of directions. An analytical expression is found for the critical angle, beyond which propagation is not allowed.