## About

32

Publications

2,386

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839

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Citations since 2016

Introduction

**Skills and Expertise**

## Publications

Publications (32)

We experimentally and numerically study the dynamics of a mono-disperse packing of self-propelled hard disks inside a hexagonal arena. The packings are dense, with area fractions close to the maximal geometrically allowed value $\phi_{hcp}$ in two dimension. Frustration of the hexagonal order, obtained by removing a few particles, leads to the form...

We propose a conservative two-dimensional particle model in which particles
carry a continuous and classical spin. The model includes standard
ferromagnetic interactions between spins of two different particles, and a
nonstandard coupling between spin and velocity of the same particle inspired by
the coupling observed in self-propelled hard discs....

We study the spatially homogeneous phases of polar active particles in the low density limit, and specifically the transition from the isotropic phase to collective polar motion. We show that the fundamental quantity of interest for the stability of the isotropic phase is the forward component of the momentum change induced by binary scattering eve...

Colloidal systems observed in video microscopy are often analysed using the displacements correlation matrix of particle positions. In non-thermal systems, the inverse of this matrix can be interpreted as a pair-interaction potential between particles. If the system is thermally agitated, however, only an effective interaction is accessible from th...

We develop a cavity-based method which allows to extract thermodynamic properties from position information in hard-sphere/disk systems. So far, there are available-volume and free-volume methods. We add a third one, which we call available volume after take-out, and which is shown to be mathematically equivalent to the others. In applications, whe...

We show that low density homogeneous phases of self propelled hard disks
exhibit a transition from isotropic to polar collective motion, albeit of a
qualitatively distinct class from the Vicsek one. In the absence of noise, an
abrupt discontinuous transition takes place between the isotropic phase and a
fully polar absorbing state. Increasing the n...

We study the properties of correlation matrices widely used in the
characterisation of vibrational modes in colloidal materials. We show that the
eigenvectors in the middle of the spectrum are strongly mixed, but that at both
the top and the bottom of the spectrum it is possible to extract a good
approximation to the true eigenmodes of an elastic s...

We study the spatially homogeneous phases of polar active particles in the
low density limit, and specifically the transition from the isotropic to the
polar phase. We identify the forward component of the change of momentum
induced by collisions as a fundamental quantity of interest. We propose an
ansatz for the angular distribution of velocities...

The vibrational modes of pristine and polycrystalline monolayer colloidal crystals composed of thermosensitive microgel particles are measured using video microscopy and covariance matrix analysis. At low frequencies, the Debye relation for two-dimensional harmonic crystals is observed in both crystal types; at higher frequencies, evidence for van...

Studies by video microscopy on fluctuating colloids measure the real-space
cross-correlations in particle motion. This set of correlations is then treated
as a matrix, in order to study the spectrum and mode structure. We show that in
general the modes are modified by the truncation of the full real-space
correlations. We perform a theoretical anal...

We consider the theory of fluctuations of a colloidal solid observed in a confocal slice. For a cubic crystal we study the evolution of the projected elastic properties as a function of the anisotropy of the crystal using numerical methods based on the fast Fourier transform. In certain situations of high symmetry we find exact analytic results for...

Recent confocal experiments on colloidal solids motivate a fuller study of
the projection of three-dimensional fluctuations onto a two-dimensional
confocal slice. We show that the effective theory of a projected crystal
displays several exceptional features, such as non-standard exponents in the
dispersion relations. We provide analytic expressions...

Organized structures produced by dynamic self-assembly are often observed in animal groups. Static self-assembly, however, has to date only been observed at the cellular and sub-cellular levels. The aim of this study was to analyse organized structures in immobile whirligig beetle groups on the water surface. We used theoretical and computational a...

Recent confocal experiments on colloidal solids, as well as jammed and disordered materials, motivate a fuller study of the projection of three-dimensional fluctuations onto a two-dimensional confocal slice. We show that the effective theory of a projected crystal displays several exceptional features, and we give analytic expressions relating thre...

Numerous microfluidic experiments have revealed non-trivial traffic dynamics when droplets flow through a channel including a single loop. A complex encoding of the time intervals between the droplets is achieved by the binary choices they make as they enter the loop. Very surprisingly, another set of experiments has demonstrated that the addition...

The correlations of the fluctuating stress tensor are calculated in an
equilibrium molecular-dynamics simulation of a Lennard--Jones liquid. We define
a coarse-grained local stress tensor which can be calculated numerically and
which allows for the first time to determine the stress correlation function
both in time and in space. Our findings corro...

We investigate theoretically the onset of capillary-gravity waves created by a small object moving at the water-air interface. It is well established that, for straight uniform motion, no steady waves appear at velocities below the minimum phase velocity c(min)=23 cm/s. At higher velocities, the emission of capillary-gravity waves creates an additi...

We present a theoretical model for the evolution of mixture concentrations in a micro-pervaporation device, similar to those recently presented experimentally. The described device makes use of the pervaporation of water through a thin PDMS membrane to build up a solute concentration profile inside a long microfluidic channel. We simplify the evolu...

The overall traffic of droplets in a network of microfluidic channels is strongly influenced by the liquid properties of the moving droplets. In particular, the effective hydrodynamic resistance of individual droplets plays a key role in their global behavior. Here we propose two simple and low-cost experimental methods for measuring this parameter...

We propose a simple model to analyze the traffic of droplets in microfluidic "dual networks." Such functional networks which consist of two types of channels, namely, those accessible or forbidden to droplets, often display a complex behavior characteristic of dynamical systems. By focusing on three recently proposed configurations, we offer an exp...

The accumulation of small particles is analyzed in stationary flows through channels of variable width at small Reynolds number. The combined influence of pressure, viscous drag and thermal fluctuations is described by means of a Fokker–Planck equation for the particle density. It is shown that for extended spherical particles the shape of the flui...

Statistical properties of neuron firing are studied in the framework of a nonlinear leaky integrate-and-fire model that is driven by a slow periodic subthreshold signal. The firing events are characterized by first passage time densities. The experimentally better accessible interspike interval density generally depends on the sojourn times in a re...

Molecules that only differ by their chirality, so-called enantiomers, often possess different properties with respect to their biological function. Therefore, the separation of enantiomers presents a prominent challenge in molecular biology and has long been a main pursuit of organic chemistry. We suggest a new separation technique for chiral molec...

A finite-element algorithm for computing free-surface flows driven by arbitrary body forces is presented. The algorithm is primarily designed for the microfluidic parameter range where (i) the Reynolds number is small and (ii) force-driven pressure and flow fields compete with the surface tension for the shape of a stationary free surface. The free...

We present an approximate analytical expression for escape rates of time-dependent driven stochastic processes with an absorbing boundary such as the driven leaky integrate-and-fire model for neural spiking. The novel approximation is based on a discrete state Markovian modeling of the full long-time dynamics with time-dependent rates. It is valid...

The flow profile in a capillary gap and the pumping efficiency of an acoustic micropump employing surface acoustic waves is investigated both experimentally and theoretically. Ultrasonic surface waves on a piezoelectric substrate strongly couple to a thin liquid layer and generate a quadrupolar streaming pattern within the fluid. We use fluorescenc...

The statistics of transitions between the metastable states of a periodically
driven bistable Brownian oscillator are investigated on the basis of a
two-state description by means of a master equation with time-dependent rates.
The results are compared with extensive numerical simulations of the Langevin
equation for a sinusoidal driving force. Ver...

Analytical expressions are put forward to investigate the forced spiking activity of abstract neuron models such as the driven leaky integrate-and-fire model. The method is valid in a wide parameter regime beyond the restraining limits of weak driving (linear response) and/or weak noise. The novel approximation is based on a discrete state Markovia...

The stochastic integrate-and-fire model presents a simple description of the spiking behavior of neurons.In this model a neuron ``fires'' if an Ornstein-Uhlenbeck process crosses a prescribed threshold. After the firing the process is assumed to be in a refractory state, and from there it is put back into its initial, active state.This process can...

Analytical expressions are put forward to investigate the forced spiking activity of abstract neuron models such as the driven leaky integrate-and-fire (LIF) model. The method is valid in a wide parameter regime beyond the restraining limits of weak driving (linear response) and/or weak noise. The novel approximation is based on a discrete state Ma...

## Projects

Project (1)