Collective Motion and Infromation Dynamics in Systems of Vibrated Active Granular Particles

Biology‟s growing interest in the mechanical and statistical properties of living matter has led physicists to develop flocking models and fabricate artificial analogues of self-propulsion in order to gain better understanding of the complex collective behaviors of living matter. This dissertation research investigates the dynamics of self-propulsion, collective motion, and information propagation in vibrated active systems comprising active granular particles (AGP) with a head-tail structure reminiscent of biological swimmers such as flagellated bacteria and spermatozoa. A novel information-theoretic framework based on connected mutual information (CMI) is introduced to quantify the propagation of speed and polarization fluctuation information in AGP systems comprising 10 to 100 particles. Empirical results show that, when subjected to sinusoidal vibration, AGPs can effectively mimic certain complex collective behaviors of biological systems including spontaneous swarm formation and flocking, intermittent regrouping events, and coherent changes in travel direction. Rigorous nonlinear CMI analyses also reveal that: (i) the speed and polarization fluctuations are independent of each other; (ii) the polarization fluctuation CMI is more effective in discriminating between random and nonlinear dynamical behavior, i.e., compared to the speed fluctuation CMI; and (iii) for every type of active system, there exists a critical number of members that could maximize the sharing of information within the group. The information-theoretic framework introduced in this study can have potential applications to other studies involving various collective phenomena, both in the biological and the artificial realms

Time evolution of neighbor-pair mutual information in collectively moving active granular particles

In recent decades, significant progress has been made in the field of active-matter research. Studies on biological active systems, in particular, have begun to adapt information-theoretic approaches in studying collective behavior in various systems. In this present work, we employ a novel information-theoretic framework based on connected mutual information (CMI) to quantify the similarities in the speed and polarization fluctuations among individuals in a system of 10–100 bio-inspired, vibrated active granular particles. By tracking the evolution of the speed and polarization CMI using 20-s time windows, we find that CMI estimates rise and fall over a 3-min observation period depending on the number of particles and the system\u27s overall mobility. Results of nonlinear analyses also reveal that the speed and polarization fluctuations are independent of each other, and that the sharing of speed and polarization information among active particles is maximized when the system is continuously circulating around the container, and minimized when the system is either jammed or is executing frequent directional switches from clockwise to counter-clockwise circulation and vice versa. The information-theoretic methodologies presented in this work can have potential applications in the study of different biological and artificial active systems

Dynamics of a Rotating Sphere on Free Surface of Vibrated Granular Materials

We investigate the rotational dynamics of a low-density sphere on the free surface of a vertically vibrated granular material (VGM). The dynamical behavior of the sphere is influenced by the external energy input from an electromagnetic shaker which is proportional to ε, where ε is equal to the ratio between the square of the dimensionless acceleration Γ and the square of the vibration frequency f of the container. Empirical results reveal that as the VGM transits from local-to-global convection, an increase in ε generally corresponds to an increase in the magnitudes of the rotational ω RS and translational v CM velocities of the sphere, an increase in the observed tilting angle θ bed of the VGM bed, and a decrease in the time t wall it takes the sphere to roll down the tilted VGM bed and hit the container wall. During unstable convection, an increase in ε results in a sharp decrease in the sphere\u27s peak and mean ω RS, and a slight increase in t wall. For the range of ε values covered in this study, the sphere may execute persistent rotation, wobbling or jamming, depending on the vibration parameters and the resulting convective flow in the system

Acute diverticulitis in heart- and lung transplant patients

Significant gastrointestinal complications have been observed in patients following heart- and lung transplantation. These complications can occur in the immediate post-operative period or remote from the time of transplantation. We retrospectively reviewed the medical records of 268 consecutive, patients who received either heart- or lung transplants at Henry Ford Hospital between 1985 and 1998. Two hundred and thirty-three patients received heart transplants and 35 underwent lung transplantation. Two patients developed acute diverticulitis post transplant, both requiring surgery. Management of acute diverticulitis in the heart- and lung transplant population requires a high index of suspicion. Early and aggressive diagnosis is mandatory. Surgical intervention must be prompt when indicated, with meticulous attention to surgical technique. With appropriate intervention, reasonable outcomes can be expected