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Université de Fribourg

Inclined layer convection in a colloidal suspension with negative Soret coefficient at large solutal Rayleigh numbers

Italia, Matteo ; Croccolo, Fabrizio ; Scheffold, Frank ; Vailati, Alberto

In: The European Physical Journal E, 2014, vol. 37, no. 10, p. 1–6

Convection in an inclined layer of fluid is affected by the presence of a component of the acceleration of gravity perpendicular to the density gradient that drives the convective motion. In this work we investigate the solutal convection of a colloidal suspension characterized by a negative Soret coefficient. Convection is induced by heating the suspension from above, and at large solutal...

Université de Fribourg

Principles and Fundamentals of Optical Imaging

Scheffold, Frank

In: Optical Imaging of Neocortical Dynamics, 2014, vol. 85, p. 19–32

In this chapter I will give a brief general introduction to optical imaging and then discuss in more detail some of the methods specifically used for imaging cortical dynamics today. Absorption and fluorescence microscopy can be used to form direct, diffraction-limited images but standard methods are often only applicable to superficial layers of cortical tissue. Two-photon microscopy takes an...

Université de Fribourg

Laser Speckle Imaging of Cerebral Blood Flow

Zakharov, Pavel ; Scheffold, Frank ; Weber, Bruno

In: Optical Imaging of Neocortical Dynamics, 2014, vol. 85, p. 255–271

Optical imaging of cerebral hemodynamics has been used extensively to investigate the complex interplay between neurons and the blood-borne supply of oxygen and energy substrates. Among several techniques, the so-called laser speckle imaging (LSI) has found widespread applications for studying (patho-)physiological aspects of neurovascular coupling. LSI is a rather simple and cost-effective...

Université de Fribourg

The jamming elasticity of emulsions stabilized by ionic surfactants

Scheffold, Frank ; Wilking, James N. ; Haberko, Jakub ; Cardinaux, Frédéric ; Mason, Thomas G.

In: Soft Matter, 2014, vol. 10, no. 28, p. 5040–5044

Oil-in-water emulsions composed of colloidal-scale droplets are often stabilized using ionic surfactants that provide a repulsive interaction between neighboring droplet interfaces, thereby inhibiting coalescence. If the droplet volume fraction is raised rapidly by applying an osmotic pressure, the droplets remain disordered, undergo an ergodic–nonergodic transition, and jam. If the applied...

Université de Fribourg

Charactrisation of particle assemblies by 3D cross correlation light scattering and diffusing wave spectroscopy

Scheffold, Frank

In: SPIE Proceedings, 2014, vol. 9232: International Conference on Optical Particle Characterization (OPC 2014), p. 923203–923203–4

To characterize the structural and dynamic properties of soft materials and small particles, information on the relevant mesoscopic length scales is required. Such information is often obtained from traditional static and dynamic light scattering (SLS/DLS) experiments in the single scattering regime. In many dense systems, however, these powerful techniques frequently fail due to strong multiple...

Université de Fribourg

Crossover between entropic and interfacial elasticity and osmotic pressure in uniform disordered emulsions

Mason, Thomas G. ; Scheffold, Frank

In: Soft Matter, 2014, vol. 10, no. 36, p. 7109–7116

We develop a simple predictive model of the osmotic pressure Π and linear shear elastic modulus G′p of uniform disordered emulsions that includes energetic contributions from entropy and interfacial deformation. This model yields a smooth crossover between an entropically dominated G′p ∼...

Université de Fribourg

Numerical study of Anderson localization of terahertz waves in disordered waveguides

Lapointe, Clayton P. ; Zakharov, Pavel ; Enderli, F. ; Feurer, T. ; Skipetrov, S. E. ; Scheffold, Frank

In: EPL (Europhysics Letters), 2014, vol. 105, no. 3, p. 34002

We present a numerical study of electromagnetic wave transport in disordered quasi–one-dimensional waveguides at terahertz frequencies. Finite element method calculations of terahertz wave propagation within LiNbO3 waveguides with randomly arranged air-filled circular scatterers exhibit an onset of Anderson localization at experimentally accessible length scales. Results for the average...

Université de Fribourg

Linear and nonlinear rheology of dense emulsions across the glass and the jamming regimes

Scheffold, Frank ; Cardinaux, Frédéric ; Mason, Thomas G.

In: Journal of Physics: Condensed Matter, 2013, vol. 25, no. 50, p. 502101

We discuss the linear and nonlinear rheology of concentrated microscale emulsions, amorphous disordered solids composed of repulsive and deformable soft colloidal spheres. Based on recent results from simulation and theory, we derive quantitative predictions for the dependences of the elastic shear modulus and the yield stress on the droplet volume fraction. The remarkable agreement with...

Université de Fribourg

Elasticity and glassy dynamics of dense emulsions

Cardinaux, Frédéric ; Mason, Thomas G. ; Scheffold, Frank

In: AIP Conference Proceedings, 2013, vol. 1518, p. 222–226

We present a rheology and light scattering study of the dynamical properties of dense emulsions at volume fractions ranging from viscous liquid to deeply jammed states. From temporally and spatially revolved dynamic light scattering we obtain detailed information about the internal dynamics. Our measurements thus allow a direct study of heterogeneous nature of the relaxation processes involved in...

Université de Fribourg

Direct laser writing of three-dimensional network structures as templates for disordered photonic materials

Haberko, Jakub ; Muller, Nicolas ; Scheffold, Frank

In: Physical Review A, 2014, vol. 88, no. 4, p. 043822

In the present article we substantially expand on our recent study about the fabrication of mesoscale polymeric templates of disordered photonic network materials [Haberko and Scheffold, Opt. Expr. 21, 1057 (2013)]. We present a detailed analysis and discussion of important technical aspects related to the fabrication and characterization of these fascinating materials. Compared to our initial...