Interstitial gas and density segregation of vertically vibrated granular media

Mechanical vibration patterns elicit behavioral transitions and habituation in crawling Drosophila larvae

How animals respond to repeatedly applied stimuli, and how animals respond to mechanical stimuli in particular, are important questions in behavioral neuroscience. We study adaptation to repeated mechanical agitation using the Drosophila larva. Vertical vibration stimuli elicit a discrete set of responses in crawling larvae: continuation, pause, turn, and reversal. Through high-throughput larva tracking, we characterize how the likelihood of each response depends on vibration intensity and on the timing of repeated vibration pulses. By examining transitions between behavioral states at the population and individual levels, we investigate how the animals habituate to the stimulus patterns. We identify time constants associated with desensitization to prolonged vibration, with re-sensitization during removal of a stimulus, and additional layers of habituation that operate in the overall response. Known memory-deficient mutants exhibit distinct behavior profiles and habituation time constants. An analogous simple electrical circuit suggests possible neural and molecular processes behind adaptive behavior.

Diversity and controllability of particle distribution under coupling vibration and airflow

The vertical, horizontal, and three-dimensional (3D) distribution of binary particles with different diameters are investigated simultaneously in a cylindrical container under coupling vibration and airflow. Airflow is blown into the vertically vibrating granular bed from its bottom with vibration frequency of f = 15, 30, and 45 Hz; vibration acceleration Γ = 2-7; and air velocity u = 0-1.82 m s^-1 (fluidization number u/u_mf = 0-1.49). In our experiments, several distribution states have been observed, such as the mixing state, where particles are uniformly mixed; Brazil nut separation (BN), where large particles rise to the top; reverse Brazil nut separation (RBN), where large particles sink to the bottom; horizontal separation (HS), where binary particles separate horizontally; and combined distribution of BN/RBN and HS, in which one type of particles is above the other and close to one side of the container wall. Briefly, the vertical distribution forms five pattern types, and the horizontal distribution has four pattern types. The resultant pattern of 3D distribution exhibits 15 pattern types. These patterns can be always obtained under the conditions of certain control parameters, but the condition differs with the diameter ratio of binary particles. Phase diagrams of vertical, horizontal, and 3D distributions are drawn to provide the excitation condition of various patterns. These experimental results contribute to the further understanding of the entire distribution of particles and the control of particle distribution for different industry requirements.

Symmetrically periodic segregation in a vertically vibrated binary granular bed

Periodic segregation behaviors in fine mixtures of copper and alumina particles, including both percolation and eruption stages, are experimentally investigated by varying the ambient air pressure and vibrational acceleration. For the cases with moderate air pressure, the heaping profile of the granular bed keeps symmetrical in the whole periodic segregation. The symmetrical shape of the upper surface of the granular bed in the eruption stage, which resembles a miniature volcanic eruption, could be described by the Mogi model that illuminates the genuine volcanic eruption in the geography. When the air pressure increases, an asymmetrical heaping profile is observed in the eruption stage of periodic segregation. With using the image processing technique, we estimate a relative height difference between the copper and the alumina particles as the order parameter to quantitatively characterize the evolution of periodic segregation. Both eruption and percolation time, extracted from the order parameter, are plotted as a function of the vibration strength. Finally, we briefly discuss the air effect on the granular segregation behaviors.

Segregation in mixtures of granular chains and spherical grains under vertical vibration

We experimentally investigate segregation behaviors of binary granular mixtures consisting of granular chains and spherical grains with different interstitial media under vertical vibrations. A quantitative criterion is proposed to locate the boundaries between different vibrating phases. The water-immersed granular mixture exhibits two interesting types of segregation behaviors: chain-on-top and sandwich patterns. However, the phenomenon of sandwich segregation is absent for the air-immersed mixture. The topological differences of phase diagrams between two different environments indicate that the interstitial fluid plays an important role on the granular demixing. Additionally, the phase behaviors of mixtures for the different chain lengths show a not significant discrepancy. Finally, the vibrating thickness ratio determining the phase boundary characterizes the mixing extent of the granular bed. The estimated ratios for various chain lengths exhibit a monotonically decreasing dependence, when the vibration frequency increases.

Effects of gas flow on granular size separation

A gas flow is introduced into a vibrating bed from its perforated bottom to clarify the effects of gas flow on granular size separation. The rising or sinking time of a single intruder does not follow a monotonic relationship, and the granular mixtures show four different types of distribution with increasing gas velocity. The different drag forces exerted on large particles and small ones are the main factors that influence the granular size separation. Under the "wall effect" the gas flow may speed up the rising of the large particle, and cause a change in size distribution.