No abstract

Clusters of biological organisms often show diverse collective motions. Considering the physical properties of active elements with mutual interactions, we propose a mathematical model of collective motion. Several kinds of cluster motion seen in nature, including collective rotation, chaos, and wandering, occur in computer simulations of our deterministic model. By introducing a set of dimensionless parameters, we categorize the collective motions and obtain their phase diagram. We analyze the collective motions with a disorder parameter and Lyapunov spectra to characterize their transitions. [S0031-9007(96)00218-9]

We have investigated a simple coevolutionary network model incorporating three processes-changes of opinions, homophily, and heterophily. In this model, each node holds one of G opinions and changes its opinion, as in the voter model. Homophily is the tendency for connections to form between individuals of the same opinions and heterophily is the opposite effect. If there is no heterophily, this model corresponds to the Holme and Newman model [Phys. Rev. E 74, 056108 (2006)]. We show that the behavior of this model without heterophily can be understood in terms of a mean field approximation. We also find that this model with heterophily exhibits topologically complicated behaviors such as the small-world property.

SUMMARY Acoustic pulses were detected fiom a patient treated by a pulsed proton radiation beam. The dose rate of the proton beam was 0.3 cGy/pulse. The signals from 100 to 700 pulses were accumulated to improve the signal to noise ratio. After accumulation, the random noise level was negligibly small compared to the signal. These results suggest the feasibility of non-invasive monitoring of proton dose distributions in patients by sensing acoustic pulses generated during irradiation by a pulsed proton radiation beam. Radiat Oncol Invest 1995;3:42-45. 0 1995 Wdey-Liss, lnc.

Time-resolved acoustic pulses generated in water and in soft tissue by pulsed proton beam irradiation were observed. The spatial resolution of depth dose distribution in the clinically applied beam intensity is estimated about 3 mm by means of TOF measurement. The dependence of the acoustic signal intensity on the temperature of medium was examined. Proportionality of acoustic pulse intensity to absorbed dose per pulse was confirmed as well. These results suggest the possibility of clinical application to monitor dose distribution in the patient's body during irradiation of pulsed proton beam.

No abstract

No abstract

The dispersal of cells from an initially constrained location is a crucial aspect of many physiological phenomena ranging from morphogenesis to tumour spreading. In such processes, the way cell-cell interactions impact the motion of single cells, and in turn the collective dynamics, remains unclear. Here, the spreading of micro-patterned colonies of non-cohesive cells is fully characterized from the complete set of individual trajectories. It shows that contact interactions, chemically mediated interactions and cell proliferation each dominates the dispersal process on different time scales. From data analysis and simulation of an active particle model, we demonstrate that contact interactions act to speed up the early population spreading by promoting individual cells to a state of higher persistence, which constitutes an as-yet unreported contact enhancement of locomotion. Our findings suggest that the current modeling paradigm of memoryless interacting active particles may need to be extended to account for the possibility of internal states and history-dependent behaviour of motile cells