The aim of this work is the description of the chain formation phenomena observed in colloidal suspensions of superparamagnetic nanoparticles under high magnetic fields. We propose a new methodology based on an on-the-fly Coarse-Grain (CG) model. Within this approach, the coarse grain objects of the simulation are not fixed a priori at the beginning of the simulation but rather redefined on the fly. The motion of the CG objects (single particles or aggregates) is described by an anisotropic diffusion model and the magnetic dipole-dipole interaction is replaced by an effective short range interaction between CG objects. The new methodology correctly reproduces previous results from detailed Langevin Dynamics simulations of dispersions of superparamagnetic colloids under strong fields whilst requiring an amount of CPU time orders of magnitude smaller. This substantial improvement in the computational requirements allows the simulation of problems in which the relevant phenomena extends to time scales inaccessible with previous simulation techniques. A relevant example is the waiting time dependence of the relaxation time T_2 of water protons observed in Magnetic Resonance experiments containing dispersions of superparamagnetic colloids, which is correctly predicted by our simulations. Future applications may include other popular real-world applications of superparamagnetic colloids such as the magnetophoretic separation processes.
Orientational bistability and field-controlled switching of a superparamagnetic dimer
Physical and Theoretical Chemistry Laboratory, South Parks Rd, Oxford, OX1 3QZ United Kingdom（物理与理论化学实验室）；Department of Applied Mathematics and Statistics, Colorado School of Mines, Golden, CO, USA（科罗拉多矿业学院应用数学与统计系）
Second-harmonic magnetic response characterizing magnetite-based colloid
非线性二次谐波磁响应（M2）被用来表征葡聚糖涂层的磁铁矿（Fe 3 O 4）纳米粒子的水胶体溶液。基于Gilbert-Landau-Lifshitz方程的超顺磁粒子随机动力学的形式化数据分析确保了通过一组磁性和磁动力学参数（例如平均磁矩、阻尼常数、纵向弛豫时间、磁各向异性场和能量等）对系统进行广泛的量化。结合透射电子显微镜和动态光散射，M2技术允许获得额外的参数，即，葡聚糖涂层厚度和颗粒间磁偶极能量。聚集的胶体纳米粒子被证明是由于磁偶极-偶极（d-d）耦合的相关半径约50 nm内的聚集体内部的磁相关。与d-d耦合帐户，从M2测量回收的聚集体的体积分布是一致的电子显微镜结果。从电子磁共振，SP动力学的突变与外部磁场的增加观察和解释。本研究阐明了一种新的M2为基础的程序，适用于各种SP系统的全面定量表征。
Coarse-graining strategy for modeling effective, highly diffusive fluids with reduced polydispersity: A dynamical study
我们提出了一种粗粒化策略，用于减少混合物中的粒子种类的数量，以实现具有更高扩散的更简单的系统，同时保留总粒子数和特征动态特征。作为应用系统，我们选择了由Kob和Andersen发现的双分散Lennard-Jones样混合物[Phys. Rev. Lett. 73，1376（1994）]，由于流体的多组分特征，其对A型-B型排列的对势的明显非常规选择，具有缓慢的动力学。我们进一步建立在这样形成的粗颗粒和温度无关的单分散系统的平衡结构与径向分布函数类似的混合物对应。该单组分体系还具有类似的动力学特征，如玻璃化转变温度和临界指数，同时服从牛顿力学。这种策略可能最终导致新的纳米粒子/胶体流体的制造，通过实验建模只有输出的有效对电位（S），而没有其他宏观量。
Coarse-graining microscopic strains in a harmonic, two-dimensional solid and its implications for elasticity: non-local susceptibilities and non-affine noise
Coarse-graining to create minimalist models for dynamic, end-linked star-polymer networks
McKetta Department of Chemical Engineering, The University of Texas at Austin（德克萨斯大学奥斯汀分校麦凯塔化学工程系）；Department of Chemical Engineering, Auburn University（奥本大学化学工程系）；Department of Chemical Engineering and Biointerfaces Institute, University of Michigan（密歇根大学生物界面研究所化学工程系）；McKetta Department of Engineering, The University of Texas at Austin（德克萨斯大学奥斯汀分校麦凯塔工程学院）
Lund University（隆德大学）；University of Copenhagen（哥本哈根大学）；CNR Institute of Complex Systems, Uos Sapienza（意大利国家研究委员会复杂系统研究所，萨皮恩扎小组）；Department of Physics, Sapienza University of Rome（罗马萨皮恩扎大学物理系）；Institute of Theoretical Physics, Faculty of Physics, University of Warsaw（华沙大学物理学院理论物理研究所）；Institute of Physical Chemistry, Polish Academy of Sciences（波兰科学院物理化学研究所）；LINXS Institute of Advanced Neutron and X-ray Science, Lund University（隆德大学LINXS高级中子和X射线科学研究所）
