Kinetics of self-induced aggregation in Brownian particles

We study a model of interacting random walkers that proposes a simple mechanism for the emergence of cooperation in group of individuals. Each individual, represented by a Brownian particle, experiences an interaction produced by the local unbalance in the spatial distribution of the other individuals. This interaction results in a nonlinear velocity driving the particle trajectories in the direction of the nearest more crowded regions; the competition among different aggregating centers generates nontrivial dynamical regimes. Our simulations show that for sufficiently low randomness, the system evolves through a coalescence behavior characterized by clusters of particles growing with a power law in time. In addition, the typical scaling properties of the general theory of stochastic aggregation processes are verified.Comment: RevTeX, 9 pages, 9 eps-figure

Damage Spreading in a Driven Lattice Gas Model

We studied damage spreading in a Driven Lattice Gas (DLG) model as a function of the temperature $T$, the magnitude of the external driving field $E$, and the lattice size. The DLG model undergoes an order-disorder second-order phase transition at the critical temperature $T_c(E)$, such that the ordered phase is characterized by high-density strips running along the direction of the applied field; while in the disordered phase one has a lattice-gas-like behaviour. It is found that the damage always spreads for all the investigated temperatures and reaches a saturation value $D_{sat}$ that depends only on $T$. $D_{sat}$ increases for $TT_c(E=\infty)$ and is free of finite-size effects. This behaviour can be explained as due to the existence of interfaces between the high-density strips and the lattice-gas-like phase whose roughness depends on $T$. Also, we investigated damage spreading for a range of finite fields as a function of $T$, finding a behaviour similar to that of the case with $E=\infty$.Comment: 13 pages, 7 figures. Submitted to "Journal of Statistical Mechanics: Theory and Experiment

Dynamic behavior of anisotropic non-equilibrium driving lattice gases

It is shown that intrinsically anisotropic non-equilibrium systems relaxing by a dynamic process exhibit universal critical behavior during their evolution toward non-equilibrium stationary states. An anisotropic scaling anzats for the dynamics is proposed and tested numerically. Relevant critical exponents can be evaluated self-consistently using both the short- and long-time dynamics frameworks. The obtained results allow us to clarify a long-standing controversy about the theoretical description, the universality and the origin of the anisotropy of driven diffusive systems, showing that the standard field theory does not hold and supporting a recently proposed alternative theory.Comment: 4 pages, 2 figure

Equilibrium and dynamical behavior in the Vicsek model for self-propelled particles under shear

The effects of an externally imposed linear shear profile in the Vicsek model of self-propelled particles is investigated via computer simulations. We find that the applied field changes in a relevant way both the equilibrium and dynamical properties of the original model. Indeed, short time dynamics analysis shows that the order-disordered phase transition disappears under shear, because the flow acts as a symmetry breaking field. Moreover, the coarsening of particle domains is arrested at a characteristic length-scale inversely proportional to shear rate. A generalization of the original Vicsek model where the velocity of particles depends on the local value of the density is also introduced and shows to affect the domain formation

Nanoclusters of crystallographically aligned nanoparticles for magnetic thermotherapy: aqueous ferrofluid, agarose phantoms and ex vivo melanoma tumour assessment

Magnetic hyperthermia is an oncological therapy where magnetic nanostructures, under a radiofrequency field, act as heat transducers increasing tumour temperature and killing cancerous cells. Nanostructure heating efficiency depends both on the field conditions and on the nanostructure properties and mobility inside the tumour. Such nanostructures are often incorrectly bench-marketed in the colloidal state and using field settings far off from the recommended therapeutic values. Here, we prepared nanoclusters composed of iron oxide magnetite nanoparticles crystallographically aligned and their specific absorption rate (SAR) values were calorimetrically determined in physiological fluids, agarose-gel-phantoms and ex vivo tumours extracted from mice challenged with B16-F0 melanoma cells. A portable, multipurpose applicator using medical field settings; 100 kHz and 9.3 kA m−1, was developed and the results were fully analysed in terms of nanoclusters’ structural and magnetic properties. A careful evaluation of the nanoclusters’ heating capacity in the three milieus clearly indicates that the SAR values of fluid suspensions or agarose-gel-phantoms are not adequate to predict the real tissue temperature increase or the dosage needed to heat a tumour. Our results show that besides nanostructure mobility, perfusion and local thermoregulation, the nanostructure distribution inside the tumour plays a key role in effective heating. A suppression of the magnetic material effective heating efficiency appears in tumour tissue. In fact, dosage had to be increased considerably, from the SAR values predicted from fluid or agarose, to achieve the desired temperature increase. These results represent an important contribution towards the design of more efficient nanostructures and towards the clinical translation of hyperthermia.Instituto de Física La PlataInstituto de Investigaciones en Electrónica, Control y Procesamiento de SeñalesInstituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Nanoclusters of crystallographically aligned nanoparticles for magnetic thermotherapy: aqueous ferrofluid, agarose phantom and ex vivo melanoma tumour assessment

Magnetic hyperthermia is an oncologic therapy where magnetic nanostructures, under a radiofrequency field, act as heat transducers increasing tumour temperature and killing cancerous cells. Nanostructure heating efficiency depends both on the field conditions and on the nanostructure properties and mobility inside the tumour. Such nanostructures are often incorrectly bench-marketed in colloidal state and using field settings far off from the recommended therapeutic values. Here, we prepared nanoclusters composed of iron oxide magnetite nanoparticles crystallographically aligned and their specific absorption rate (SAR) values were calorimetrically determined in physiological fluids, agarose-gel-phantoms and ex vivo tumours extracted from mice challenged with B16-F0 melanoma cells. A portable, multipurpose applicator using medical field settings; 100 kHz and 9.3 kA m-1, was developed and the results were fully analysed in terms of nanoclusters structural and magnetic properties. A careful appraisal of the nanoclusters heating capacity in the three milieus clearly indicate that the SAR values of fluid suspensions or agarose-gel-phantoms are not adequate to predict real tissue temperature rise or the dosage needed to heat a tumour. Our results show that besides nanostructure mobility, perfusion and local thermoregulation, nanostructures distribution inside the tumour plays a key role in the effective heating. A suppression of magnetic material effective heating efficiency appears in tumour tissue. In fact, dosage had to be much increased, from the SAR values predicted from fluid or agarose to achieve the desired temperature increase. These results represent an important contribution towards the design of more efficient nanostructures and towards clinical translation of hyperthermia.This research was funded by CONICET (PIPs 897, 154, 524 and 567), UNLP X11/680 and X11/7884, and UBACYT 20020130100024 grants of Argentina and also partially funded by the Spanish Ministry of Economy (MAT2015-64442-R and SEV2015-0496 projects, co-funded with European Social Funds). We acknowledge, O. Moscoso-Londoño for SQUID data acquisition and M. Knobel for the use of Instituto de Física ‘Gleb Wataghin’, Universidade Estadual de Campinas (UNICAMP) magnetometry instrumentation, R. Peralta for her extreme care with cell biological sample preparation for TEM, the Brazilian Nanotechnology National Laboratory (LNNano) for the use of cryo-TEM (project: ME-22346) facilities, Y-TEC S.A. for the use of TEM TALOS F200X under the supervision of A. Floridia and A. Caneiro and F.H. Sánchez, G. Pasquevich and P. Mendoza Zélis for useful discussions during field inductor building. Monte Carlo simulation were performed in UnCaFiyQT-INIFTA-SNCAD. M.B.F.v.Raap, P. C. S. Avruj, L. Rogin, A. Veiga, E. Spinelli, V.Blank, G.P. Saracco and M.A Bab are members of CONICET, and P.A. Soto is a fellow of CONICET, Argentina.Peer reviewe