Soft Condensed Matter
Tunable mass separation via negative mobility (1901.10439v1)
Aleksandra Słapik, Jerzy Łuczka, Peter Hänggi, Jakub Spiechowicz
2019-01-29
A prerequisite for isolating diseased cells requires a mechanism for effective mass-based separation. This objective, however, is generally rather challenging because typically no valid correlation exists between the size of the particles and their mass value. We consider an inertial Brownian particle moving in a symmetric periodic potential and subjected to an externally applied unbiased harmonic driving in combination with a constant applied bias. In doing so we identify a most efficient separation scheme which is based on the anomalous transport feature of negative mobility, meaning that the immersed particles move in the direction opposite to the acting bias. This work is first of its kind in demonstrating a tunable separation mechanism in which the particle mass targeted for isolation is effectively controlled over a regime of nearly two orders of mass-magnitude upon changing solely the frequency of the external harmonic driving. This approach may provide mass selectivity required in present and future separation of a diversity of nano and micro-sized particles of either biological or synthetic origin.
Preferential Root Tropism Induced by Structural Inhomogeneities in 2D Wet Granular Media (1901.10402v1)
Cesare M. Cejas, Lawrence A. Hough, Raphaël Beaufret, Jean-Christophe Castaing, Christian Frétigny, Rémi Dreyfus
2019-01-29
We investigate certain aspects of the physical mechanisms of root growth in a granular medium and how these roots adapt to changes in water distribution induced by the presence of structural inhomogeneities in the form of solid intrusions. Physical intrusions such as a square rod added into the 2D granular medium modify water distribution by maintaining robust capillary action, pumping water from the more saturated areas at the bottom of the cell towards the less saturated areas near the top of the cell while the rest of the medium is slowly devoid of water via evaporation. This water redistribution induces `preferential tropism' of roots, guiding the roots and permitting them to grow deeper into more saturated regions in the soil. This further allows more efficient access to available water in the deeper sections of the medium thereby resulting to increased plant lifetime
Tracking the connection between disorder and energy landscape in glasses using geologically hyperaged amber (1901.10229v1)
E. A. A. Pogna, A. I. Chumakov, C. Ferrante, M. A. Ramos, T. Scopigno
2019-01-29
Fossil amber offers the unique opportunity of investigating an amorphous material which has been exploring its energy landscape for more than 110 Myears of natural aging. By applying different x-ray scattering methods to amber before and after annealing the sample to erase its thermal history, we identify a link between the potential energy landscape and the structural and vibrational properties of glasses. We find that hyperaging induces a depletion of the vibrational density of states in the THz region, also ruling the sound dispersion and attenuation properties of the corresponding acoustic waves. Critically, this is accompanied by a densification with structural implications different in nature from that caused by hydrostatic compression. Our results, rationalized within the framework of fluctuating elasticity theory, reveal how upon approaching the bottom of the potential energy landscape (9% decrease in the fictive temperature
) the elastic matrix becomes increasingly less disordered (6%) and longer-range correlated (22%).
Homogeneous nucleation of ice (1901.10213v1)
Haiyang Niu, Yi Isaac Yang, Michele Parrinello
2019-01-29
Ice nucleation is a process of great relevance in physics, chemistry, technology and environmental sciences, much theoretical and experimental efforts have been devoted to its understanding, but still it remains a topic of intense research. We shed light on this phenomenon by performing atomistic based simulations. Using metadynamics and a carefully designed set of collective variables, reversible transitions between water and ice are able to be simulated. We find that water freezes into a stacking disordered structure with the all-atom TIP4P/Ice model, and the features of the critical nucleus of nucleation at the microscopic level are revealed. Our results are in agreement with recent experimental and other theoretical works and confirm that nucleation is preceded by a large increase in tetrahedrally coordinated water molecules.
Colloidal Brazil nut effect in microswimmer mixtures induced by motility contrast (1901.10201v1)
Soudeh Jahanshahi, Celia Lozano, Borge ten Hagen, Clemens Bechinger, Hartmut Löwen
2019-01-29
We numerically and experimentally study the segregation dynamics in a binary mixture of microswimmers which move on a two-dimensional substrate in a static periodic triangular-like light intensity field. The motility of the active particles is proportional to the imposed light intensity and they possess a motility contrast, i.e., the prefactor depends on the species. In addition, the active particles also experience a torque aligning their motion towards the direction of the negative intensity gradient. We find a segregation of active particles near the intensity minima where typically one species is localized close to the minimum and the other one is centered around in an outer shell. For a very strong aligning torque, there is an exact mapping onto an equilibrium system in an effective external potential that is minimal at the intensity minima. This external potential is similar to (height-dependent) gravity, such that one can define effective
heaviness' of the self-propelled particles. In analogy to shaken granular matter in gravity, we define acolloidal Brazil nut effect' if the heavier particles are floating on top of the lighter ones. Using extensive Brownian dynamics simulations, we identify system parameters for the active colloidal Brazil nut effect to occur and explain it based on a generalized Archimedes' principle within the effective equilibrium model: heavy particles are levitated in a dense fluid of lighter particles if their effective mass density is lower than that of the surrounding fluid. We also perform real-space experiments on light-activated self-propelled colloidal mixtures which confirm the theoretical predictions.
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