Diagnostic and therapeutic complexity of Susac syndrome.

A 40-year-old man who attended the emergency department with a scotoma in right eye. He mentioned hearing difficulties and headache for months and he had sensory and motor deficits in the previous days. In the ophthalmic examination, the right eye had areas of arterial occlusion. MRI revealed hyperintense lesions. The patient was diagnosed with Susac syndrome. He was treated with systemic steroids, however, it was not enough to control the condition. Rituximab and intravenous immunoglobulins were added, which allowed the improvement of neurological symptoms, but the alteration of the visual field and the hearing defect did not recover. Early diagnosis of this pathology is essential, since delaying treatment can cause irreversible consequences. Sometimes it is difficult given the wide variety of symptoms and the course of the disease. Ocular manifestations may raise suspicion when the general symptoms are nonspecific.

Designing soft materials with interfacial instabilities in liquid films.

Natural soft materials harness hierarchy and structures at all scales to build function. Adapting this paradigm to our technological needs, from mechanical, phononic and photonic metamaterials to functional surfaces prompts the development of new fabrication pathways with improved scalability, design flexibility and robustness. Here we show that the inherent periodicity of the Rayleigh-Taylor instability in thin polymeric liquid films can be harnessed to spontaneously fabricate structured materials. The fluidic instability yields pendant drops lattices, which become solid upon curing of the polymer, thereby permanently sculpting the interface of the material. We solve the inverse design problem, taming the instability, so that the structures we form can be tailored, over a range of sizes spanning over two decades. This all-in-one methodology could potentially be extended down to the scales where continuum mechanics breaks down, while remaining scalable.

Designing the ammonium cation to achieve a higher hydrophilicity of bistriflimide-based ionic liquids.

In this work, we have found complete water miscibility for a priori, water immiscible (highly hydrophobic) ionic liquids by chemical manipulation of the quaternary ammonium cation grafted with hydroxyethyl moieties. Specifically, we were able to obtain bistriflimide-based ionic liquids completely miscible with water, even below room temperature. The underlying reason is the full integration of the OH groups of the cation in the continuous H-bonded network of water.

Patterns of Carbon Nanotubes by Flow-Directed Deposition on Substrates with Architectured Topographies.

We develop and perform continuum mechanics simulations of carbon nanotube (CNT) deployment directed by a combination of surface topography and rarefied gas flow. We employ the discrete elastic rods method to model the deposition of CNT as a slender elastic rod that evolves in time under two external forces, namely, van der Waals (vdW) and aerodynamic drag. Our results confirm that this self-assembly process is analogous to a previously studied macroscopic system, the "elastic sewing machine", where an elastic rod deployed onto a moving substrate forms nonlinear patterns. In the case of CNTs, the complex patterns observed on the substrate, such as coils and serpentines, result from an intricate interplay between van der Waals attraction, rarefied aerodynamics, and elastic bending. We systematically sweep through the multidimensional parameter space to quantify the pattern morphology as a function of the relevant material, flow, and geometric parameters. Our findings are in good agreement with available experimental data. Scaling analysis involving the relevant forces helps rationalize our observations.

Fluorination effects on the thermodynamic, thermophysical and surface properties of ionic liquids.

This paper reports the thermal, thermodynamic, thermophysical and surface properties of eight ionic liquids with fluorinated alkyl side chain lengths equal or greater than four carbon atoms. Melting and decomposition temperatures were determined together with experimental densities, surface tensions, refractive indices, dynamic viscosities and ionic conductivities in a temperature interval ranging from 293.15 to 353.15 K. The surface properties of these fluorinated ionic liquids were discussed and several thermodynamic functions, as well as critical temperatures, were estimated. Coefficients of isobaric thermal expansion, molecular volumes and free volume effects were calculated from experimental values of density and refractive index and compared with previous data. Finally, Walden plots were used to evaluate the ionicity of the investigated ionic liquids.

Fabrication of slender elastic shells by the coating of curved surfaces.

Various manufacturing techniques exist to produce double-curvature shells, including injection, rotational and blow molding, as well as dip coating. However, these industrial processes are typically geared for mass production and are not directly applicable to laboratory research settings, where adaptable, inexpensive and predictable prototyping tools are desirable. Here, we study the rapid fabrication of hemispherical elastic shells by coating a curved surface with a polymer solution that yields a nearly uniform shell, upon polymerization of the resulting thin film. We experimentally characterize how the curing of the polymer affects its drainage dynamics and eventually selects the shell thickness. The coating process is then rationalized through a theoretical analysis that predicts the final thickness, in quantitative agreement with experiments and numerical simulations of the lubrication flow field. This robust fabrication framework should be invaluable for future studies on the mechanics of thin elastic shells and their intrinsic geometric nonlinearities.

Propulsion and Instability of a Flexible Helical Rod Rotating in a Viscous Fluid.

We combine experiments with simulations to investigate the fluid-structure interaction of a flexible helical rod rotating in a viscous fluid, under low Reynolds number conditions. Our analysis takes into account the coupling between the geometrically nonlinear behavior of the elastic rod with a nonlocal hydrodynamic model for the fluid loading. We quantify the resulting propulsive force, as well as the buckling instability of the originally helical filament that occurs above a critical rotation velocity. A scaling analysis is performed to rationalize the onset of this instability. A universal phase diagram is constructed to map out the region of successful propulsion and the corresponding boundary of stability is established. Comparing our results with data for flagellated bacteria suggests that this instability may be exploited in nature for physiological purposes.

Untangling the mechanics and topology in the frictional response of long overhand elastic knots.

We combine experiments and theory to study the mechanics of overhand knots in slender elastic rods under tension. The equilibrium shape of the knot is governed by an interplay between topology, friction, and bending. We use precision model experiments to quantify the dependence of the mechanical response of the knot as a function of the geometry of the self-contacting region, and for different topologies as measured by their crossing number. An analytical model based on the nonlinear theory of thin elastic rods is then developed to describe how the physical and topological parameters of the knot set the tensile force required for equilibrium. Excellent agreement is found between theory and experiments for overhand knots over a wide range of crossing numbers.

Shapes of a suspended curly hair.

We investigate how natural curvature affects the configuration of a thin elastic rod suspended under its own weight, as when a single strand of hair hangs under gravity. We combine precision desktop experiments, numerics, and theoretical analysis to explore the equilibrium shapes set by the coupled effects of elasticity, natural curvature, nonlinear geometry, and gravity. A phase diagram is constructed in terms of the control parameters of the system, namely the dimensionless curvature and weight, where we identify three distinct regions: planar curls, localized helices, and global helices. We analyze the stability of planar configurations, and describe the localization of helical patterns for long rods, near their free end. The observed shapes and their associated phase boundaries are then rationalized based on the underlying physical ingredients.

Geometry-induced rigidity in nonspherical pressurized elastic shells.

We present results from an experimental investigation of the indentation of nonspherical pressurized elastic shells with a positive Gauss curvature. A predictive framework is proposed that rationalizes the dependence of the local rigidity of an indented shell on the curvature in the neighborhood of the locus of indentation, the in-out pressure differential, and the material properties. In our approach, we combine classic theory for spherical shells with recent analytical developments for the pressurized case, and proceed, for the most part, by analogy, guided by our own experiments. By way of example, our results elucidate why an eggshell is significantly stiffer when compressed along its major axis, as compared to doing so along its minor axis. The prominence of geometry in this class of problems points to the relevance and applicability of our findings over a wide range of length scales.

New insights into the chemistry of fac-[Ru(CO)3]²âº fragments in biologically relevant conditions: the CO releasing activity of [Ru(CO)3Cl2(1,3-thiazole)], and the X-ray crystal structure of its adduct with lysozyme.

Complexes of the general formula fac-[Ru(CO)(3)L(3)](2+), namely CORM-2 and CORM-3, have been successfully used as experimental CO releasing molecules (CO-RMs) but their mechanism of action and delivery of CO remain unclear. The well characterized complex [Ru(CO)(3)Cl(2)(1,3-thiazole)] (1) is now studied as a potential model CO-RM of the same family of complexes using LC-MS, FTIR, and UV-vis spectroscopy, together with X-ray crystallography. The chemistry of [Ru(CO)(3)Cl(2)(1,3-thiazole)] is very similar to that of CORM-3: it only releases residual amounts of CO to the headspace of a solution in PBS7.4 and produces marginal increase of COHb after long incubation in whole blood. 1 also reacts with lysozyme to form Ru adducts. The crystallographic model of the lysozyme-Ru adducts shows only mono-carbonyl Ru species. [Ru(H(2)O)(4)(CO)] is found covalently bound to a histidine (His15) and to two aspartates (Asp18 and Asp119) at the protein surface. The CO release silence of both 1 and CORM-3 and their rapid formation of protein-Ru(CO)(x)(H(2)O)(y) (x=1,2) adducts, support our hypothesis that fac-[Ru(CO)(3)L(3)] CO-RMs deliver CO in vivo through the decay of their adducts with plasma proteins.

Scratching as a fracture process: from butter to steel.

We present results of a hybrid experimental and theoretical investigation of the fracture scaling in scratch tests and show that scratching is a fracture dominated process. Validated for paraffin wax, cement paste, Jurassic limestone and steel, we derive a model that provides a quantitative means to relate quantities measured in scratch tests to fracture properties of materials at multiple scales. The scalability of scratching for different probes and depths opens new venues towards miniaturization of our technique, to extract fracture properties of materials at even smaller length scales.

Rolling ribbons.

We present the results of a combined experimental and theoretical investigation of rolling elastic ribbons. Particular attention is given to characterizing the steady shapes that arise in static and dynamic rolling configurations. In both cases, above a critical value of the forcing (either gravitational or centrifugal), the ribbon assumes a two-lobed, peanut shape similar to that assumed by rolling droplets. Our theoretical model allows us to rationalize the observed shapes through consideration of the ribbon's bending and stretching in response to the applied forcing.

The clapping book: wind-driven oscillations in a stack of elastic sheets.

We present a hybrid experimental and theoretical study on the oscillatory behavior exhibited by multiple thin sheets under aerodynamic loading. Our clapping book consists of a stack of paper, clamped at the downstream end and placed in a wind tunnel with steady flow. As pages lift off, they accumulate onto a bent stack held up by the wind. The book collapses shut once the elasticity and weight of the pages overcome the aerodynamic force; this process repeats periodically. We develop a theoretical model that predictively describes this periodic clapping process.

Localization through surface folding in solid foams under compression.

We report a combined experimental and theoretical study of the compression of a solid foam coated with a thin elastic film. Past a critical compression threshold, a pattern of localized folds emerges with a characteristic size that is imposed by an instability of the thin surface film. We perform optical surface measurements of the statistical properties of these localization zones and find that they are characterized by robust exponential tails in the strain distributions. Following a hybrid continuum and statistical approach, we develop a theory that accurately describes the nucleation and length scale of these structures and predicts the characteristic strains associated with the localized regions.

Forcing independent velocity distributions in an experimental granular fluid.

We present experimental results on the velocity statistics of a granular fluid with an effective stochastic thermostat, in a quasi-two-dimensional configuration. We find the base state, as measured by the single particle velocity distribution P(c) in the central high-probability regions, to be well described by P(c)=f{MB}[1+a2S2(c2)] : It deviates from a Maxwell-Boltzmann f{MB} by a second order Sonine polynomial S2(c2) with a single adjustable parameter a2. We find a2 to be a function of the filling fraction and independent of the driving over a wide range of frequencies and accelerations. Moreover, there is a consistent overpopulation in the distribution's tails, which scale as P proportional, variant exp(-A x c{3/2}) . To our knowledge, this is the first time that Sonine deviations have been measured in an experimental system.

Caging dynamics in a granular fluid.

We report an experimental investigation of the caging motion in a uniformly heated granular fluid for a wide range of filling fractions, varphi. At low varphi the classic diffusive behavior of a fluid is observed. However, as varphi is increased, temporary cages develop and particles become increasingly trapped by their neighbors. We statistically analyze particle trajectories and observe a number of robust features typically associated with dense molecular liquids and colloids. Even though our monodisperse and quasi-2D system is known to not exhibit a glass transition, we still observe many of the precursors usually associated with glassy dynamics. We speculate that this is due to a process of structural arrest provided, in our case, by the presence of crystallization.

Crystallization of a quasi-two-dimensional granular fluid.

We experimentally investigate the crystallization of a uniformly heated quasi-2D granular fluid as a function of the filling fraction. Our experimental results for the Lindemann melting criterion, the radial distribution function, the bond order parameter, and the statistics of topological changes at the particle level are the same as those found in simulations of equilibrium hard disks. This direct mapping suggests that the study of equilibrium systems can be effectively applied to study nonequilibrium steady states such as those found in our driven and dissipative granular system.

Phases of granular segregation in a binary mixture.

We present results from an extensive experimental investigation into granular segregation of a shallow binary mixture in which particles are driven by frictional interactions with the surface of a vibrating horizontal tray. Three distinct phases of the mixture are established viz. binary gas (unsegregated), segregation liquid, and segregation crystal. Their ranges of existence are mapped out as a function of the system's primary control parameters using a number of measures based on Voronoi tessellation. We study the associated transitions and show that segregation can be suppressed as the total filling fraction of the granular layer, C, is decreased below a critical value, Cc, or if the dimensionless acceleration of the driving, gamma, is increased above a value gammac.

Cracks in thin sheets: when geometry rules the fracture path.

We study the propagation of brittle fractures coupled to large out-of-plane bending, as when a brittle elastic thin sheet is cut by a moving object. Taking into account the separation of the film's bending and stretching energies and using fracture theory we show that such cracks propagate according to a simple set of geometrical rules in the limit of small thickness. In particular, this provides some insight into the geometrical origin of the oscillatory fracture patterns reported in two recent experiments. Numerical integration of our geometrical rules accurately reproduces both the shape of the fracture pattern and the detailed time evolution of the propagation of the crack tip, for various geometries of the cutting object.