arXiv subjects

Jaume Casademunt

Publications and source records attributed to Jaume Casademunt.

25 records · Page 2Linked to original sources

arXiv2016

Landscape-Inversion Phase Transition in Dipolar Colloids: Tuning the Structure and Dynamics of 2D Crystals

We study the 2D crystalline phases of paramagnetic colloidal particles with dipolar interactions and constrained on a periodic substrate. Combining theory, simulation, and experiments we demonstrate a new scenario of first-order phase transitions that occurs via a complete inversion of the energy landscape, featuring non-conventional properties that allow for: (i) tuning of crystal symmetry; (ii) control of dynamical properties of different crystalline orders via tuning of their relative stability with an external magnetic field; (iii) an equivalent but independent control of the same dynamic properties via temporal modulations of that field; and (iv) non-standard phase-ordering kinetics involving spontaneous formation of transient metastable domains.

cond-mat.soft↗

arXiv2011

Instrinsic oscillations of treadmilling microtubules in a motor bath

We analyse the dynamics of overlapping antiparallel treadmilling microtubules in the presence of crosslinking processive motor proteins that counterbalance an external force. We show that coupling the force-dependent velocity of motors and the kinetics of motor exchange with a bath in the presence of treadmilling leads generically to oscillatory behavior. In addition we show that coupling the polymerization kinetics to the external force through the kinetics of the crosslinking motors can stabilize the oscillatory instability into finite-amplitude nonlinear oscillations and may lead to other scenarios, including bistability.

cond-mat.soft↗

arXiv2006

Dynamic stability of spindles controlled by molecular motor kinetics

We analyze the role of the force-dependent kinetics of motor proteins in the stability of antiparallel arrays of polar filaments, such as those in the mitotic spindle. We determine the possible stable structures and show that there exists an instability associated to the collective behavior of motors that leads to the collapse of the spindle. Our analysis provides a general framework to understand several experimental observations in eukaryotic cell division.

q-bio.SC↗

arXiv2001

The diffusion coefficient of propagating fronts with multiplicative noise

Recent studies have shown that in the presence of noise both fronts propagating into a metastable state and so-called pushed fronts propagating into an unstable state, exhibit diffusive wandering about the average position. In this paper we derive an expression for the effective diffusion coefficient of such fronts, which was motivated before on the basis of a multiple scale ansatz. Our systematic derivation is based on the decomposition of the fluctuating front into a suitably positioned average profile plus fluctuating eigenmodes of the stability operator. While the fluctuations of the front position in this particular decomposition are a Wiener process on all time scales, the fluctuations about the time averaged front profile relax exponentially.

cond-mat.stat-mech↗

arXiv2001

The universality class of fluctuating pulled fronts

It has recently been proposed that fluctuating ``pulled'' fronts propagating into an unstable state should not be in the standard KPZ universality class for rough interface growth. We introduce an effective field equation for this class of problems, and show on the basis of it that noisy pulled fronts in {\em d+1} bulk dimensions should be in the universality class of the {\em (d+1)+1}D KPZ equation rather than of the {\em d+1}D KPZ equation. Our scenario ties together a number of heretofore unexplained observations in the literature, and is supported by previous numerical results.

cond-mat.stat-mech↗

arXiv1996

Motion of buoyant particles and coarsening of solid-liquid mixtures in a random acceleration field

Flow induced by a random acceleration field (g-jitter) is considered in two related situations that are of interest for microgravity fluid experiments: the random motion of an isolated buoyant particle and coarsening of a solid-liquid mixture. We start by analyzing in detail actual accelerometer data gathered during a recent microgravity mission, and obtain the values of the parameters defining a previously introduced stochastic model of this acceleration field. We then study the motion of a solid particle suspended in an incompressible fluid that is subjected to such random accelerations. The displacement of the particle is shown to have a diffusive component if the correlation time of the stochastic acceleration is finite or zero, and mean squared velocities and effective diffusion coefficients are obtained explicitly. Finally, the effect of g-jitter on coarsening of a solid-liquid mixture is considered. Corrections due to the induced fluid motion are calculated, and estimates are given for coarsening of Sn-rich particles in a Sn-Pb eutectic fluid, experiment to be conducted in microgravity in the near future.

patt-sol↗

arXiv1992

Narrow band noise as a model of time-dependent accelerations: study of the stability of a fluid surface in a microgravity environment

We introduce a stochastic model to analyze in quantitative detail the effect of the high frequency components of the residual accelerations onboard spacecraft (often called g-jitter) on fluid motion. The residual acceleration field is modeled as a narrow band noise characterized by three independent parameters: its intensity $G^{2}$, a dominant frequency $Ω$, and a characteristic spectral width $τ^{-1}$. The white noise limit corresponds to $Ωτ\rightarrow 0$, with $G^{2} τ$ finite, and the limit of a periodic g-jitter (or deterministic limit) can be recovered for $Ωτ\rightarrow \infty$, $G^{2}$ finite. The analysis of the response of a fluid surface subjected to a fluctuating gravitational field leads to the stochastic Mathieu equation driven by both additive and multiplicative noise. We discuss the stability of the solutions of this equation in the two limits of white noise and deterministic forcing, and in the general case of narrow band noise. The results are then applied to typical microgravity conditions.

cond-mat↗