Decrease of atmospheric neutron counts observed during thunderstorms.

We report here, in brief, some results of the observation and analysis of sporadic variations of atmospheric thermal neutron flux during thunderstorms. The results obtained with unshielded scintillation neutron detectors show a prominent flux decrease correlated with meteorological precipitations after a long dry period. No observations of neutron production during thunderstorms were reported during the three-year period of data recording

Controlling chemical oscillations in heterogeneous Belousov-Zhabotinsky gels via mechanical strain

We performed theoretical and computational studies to determine the effect of an applied mechanical strain on the dynamic behavior of heterogeneous polymer gels undergoing the oscillatory Belousov-Zhabotinsky (BZ) reaction. In these spatially heterogeneous gels, the catalyst for the reaction is localized in specific patches within the polymer network and the BZ reaction only occurs within these catalyst-containing patches, which we refer to as BZ patches. We focused on a model for a one-dimensional system, and further assumed that the BZ reaction did not affect the degree of swelling within the gel. For gels having one and two BZ patches, we found that a tensile or compressive strain could induce transitions between the oscillatory and nonoscillatory, steady-state regimes of the system. For certain values of the BZ stoichiometric parameter f, these transitions could exhibit a hysteresis. In systems having two oscillating BZ patches, an applied strain could cause a switching between the in-phase and out-of-phase synchronization of the oscillations. The ability to controllably alter the dynamic behavior of BZ gels through mechanical deformations opens up the possibility of using these materials in the design of chemo-mechanical sensors.MIT NSF MRSECUSAR

Designing communicating colonies of biomimetic microcapsules

Using computational modeling, we design colonies of biomimetic microcapsules that exploit chemical mechanisms to communicate and alter their local environment. As a result, these synthetic objects can self-organize into various autonomously moving structures and exhibit ant-like tracking behavior. In the simulations, signaling microcapsules release agonist particles, whereas target microcapsules release antagonist particles and the permeabilities of both capsule types depend on the local particle concentration in the surrounding solution. Additionally, the released nanoscopic particles can bind to the underlying substrate and thereby create adhesion gradients that propel the microcapsules to move. Hydrodynamic interactions and the feedback mechanism provided by the dissolved particles are both necessary to achieve the collective dynamics exhibited by these colonies. Our model provides a platform for integrating both the spatial and temporal behavior of assemblies of “artificial cells,” and allows us to design a rich variety of structures capable of exhibiting complex, cooperative behavior. Due to the cell-like attributes of polymeric microcapsules and polymersomes, material systems are available for realizing our predictions

Convective Self-Sustained Motion in Mixtures of Chemically Active and Passive Particles

We develop a model to describe the behavior of a system of active and passive particles in solution that can undergo spontaneous self-organization and self-sustained motion. The active particles are uniformly coated with a catalyst that decomposes the reagent in the surrounding fluid. The resulting variations in the fluid density give rise to a convective flow around the active particles. The generated fluid flow, in turn, drives the self-organization of both the active and passive particles into clusters that undergo self-sustained propulsion along the bottom wall of a microchamber. This propulsion continues until the reagents in the solution are consumed. Depending on the number of active and passive particles and the structure of the self-organized cluster, these assemblies can translate, spin, or remain stationary. We also illustrate a scenario in which the geometry of the container is harnessed to direct the motion of a self-organized, self-propelled cluster. The findings provide guidelines for creating autonomously moving active particles, or chemical “motors” that can transport passive cargo in microfluidic devices

Designing Mechanomutable Composites: Reconfiguring the Structure of Nanoparticle Networks through Mechanical Deformation

Via a new dynamic, three-dimensional computer model, we simulate the tensile deformation of polymer-grafted nanoparticles that are cross-linked by labile bonds, which can readily rupture and reform. For a range of relatively high strains, the network does not fail, but rather restructures into a stable, ordered structure. Within this network, the reshuffling of the labile bonds enables the formation of this new morphology. The results provide guidelines for designing mechano-responsive hybrid materials that undergo controllable structural transitions through the application of applied forces

Low-Pass Filtering Method for Poisson Data Time Series

Problems of digital processing of Poisson-distributed data time series from various counters of radiation particles, photons, slow neutrons etc. are relevant for experimental physics and measuring technology. A low-pass filtering method for normalized Poisson-distributed data time series is proposed. A digital quasi-Gaussian filter is designed, with a finite impulse response and non-negative weights. The quasi-Gaussian filter synthesis is implemented using the technology of stochastic global minimization and modification of the annealing simulation algorithm. The results of testing the filtering method and the quasi-Gaussian filter on model and experimental normalized Poisson data from the URAGAN muon hodoscope, that have confirmed their effectiveness, are presented