旋转磁场中磁孔的聚集
Aggregation of magnetic holes in a rotating magnetic field
摘要：
实验研究了旋转磁场作用下磁流体层中磁性粒子的场致聚集。在施加在流体层的平面中旋转的磁场之后，单个颗粒开始形成二维（2D）簇，如双峰、三角形和更复杂的结构。这些集群一次又一次地聚集，形成更大的集群。在这个非平衡过程中，形成了一个广泛的集群大小，并计算的标度指数，$z$和$z'$，集群的数量$N(t)\sim t^{z'}$和平均集群大小$S(t)\sim t^{z}$。该过程可以被描述为扩散限制的团簇-团簇聚集。我们发现，在实验过程中发生的所有大小的集群，落在一个单一的曲线，作为动态标度理论预测。但特征标度指数$z',\: z$和交叉指数$Δ$并不具有普适性。用粒子追踪法研究了扩散系数$D_{s}$与团簇尺寸$s$的关系。星系团的运动具有\textit{\emph{Brownian}}运动的特征。平均扩散系数$<D_{s}>$取决于簇大小$s$，其为幂律$<D_{s}>\propto s^γ$，其中$γ$的值与$γ=-0.62\pm0.19$一样不同，并且$γ=-2.08 \pm 0。在其中两个实验中发现。
英文摘要：
We have experimentally investigated field induced aggregation of nonmagnetic particles confined in a magnetic fluid layer when rotating magnetic fields were applied. After application of a magnetic field rotating in the plane of the fluid layer, the single particles start to form two-dimensional (2D) clusters, like doublets, triangels, and more complex structures. These clusters aggregated again and again to form bigger clusters. During this nonequilibrium process, a broad range of cluster sizes was formed, and the scaling exponents, $z$ and $z'$, of the number of clusters $N(t)\sim t^{z'}$and average cluster size $S(t)\sim t^{z}$ were calculated. The process could be characterized as diffusion limited cluster-cluster aggregation. We have found that all sizes of clusters that occured during an experiment, fall on a single curve as the dynamic scaling theory predicts. Hovewer, the characteristic scaling exponents $z',\: z$ and crossover exponents $Δ$ were not universal. A particle tracking method was used to find the dependence of the diffusion coefficients $D_{s}$ on cluster size $s$. The cluster motions show features of \textit{\emph{Brownian}} motion. The average diffusion coefficients $<D_{s}>$ depend on the cluster sizes $s$ as a power law $<D_{s}>\propto s^γ$ where values of $γ$ as different as $γ=-0.62\pm0.19$ and $γ=-2.08\pm0. were found in two of the experiments.
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