We describe the activation of out-of-equilibrium collective oscillations of a macromolecule as a classical phonon condensation phenomenon. If a macromolecule is modeled as an open system-that is, it is subjected to an external energy supply and is in contact with a thermal bath to dissipate the excess energy-the internal nonlinear couplings among the normal modes make the system undergo a nonequilibrium phase transition when the energy input rate exceeds a threshold value. This transition takes place between a state where the energy is incoherently distributed among the normal modes and a state where the input energy is channeled into the lowest-frequency mode entailing a coherent oscillation of the entire molecule. The model put forward in the present work is derived as the classical counterpart of a quantum model proposed a long time ago by Fröhlich in an attempt to explain the huge speed of enzymatic reactions. We show that such a phenomenon is actually possible. Two different and complementary THz near-field spectroscopic techniques-a plasmonic rectenna and a microwire near-field probe-have been used in two different labs to eliminate artifacts. By considering an aqueous solution of a model protein, the bovine serum albumin, we find that this protein displays a remarkable absorption feature around 0.314 THz, when driven in a stationary out-of-thermal equilibrium state by means of optical pumping. The experimental outcomes are in very good qualitative agreement with the theory developed in the first part of the paper and in excellent quantitative agreement with the theoretical result, allowing us to identify the observed spectral feature with a collective oscillation of the entire molecule.

Spinal cord injuries (SCI) are disastrous neuropathologies causing permanent disabilities. The availability of different strains of mice is valuable for studying the pathophysiological mechanisms involved in SCI. However, strain differences have a profound effect on spontaneous functional recovery after SCI. CX3CR1+/eGFP and Aldh1l1-EGFP mice that express green fluorescent protein in microglia/monocytes and astrocytes, respectively, are particularly useful to study glial reactivity. Whereas CX3CR1+/eGFP mice have C57BL/6 background, Aldh1l1-EGFP are in Swiss Webster background. We first assessed spontaneous functional recovery in CX3CR1+/eGFP and Aldh1l1-EGFP mice over 6 weeks after lateral spinal cord hemisection. Second, we carried out a longitudinal follow-up of lesion evolution using in vivo T2-weighted magnetic resonance imaging (MRI). Finally, we performed in-depth analysis of the spinal cord tissue using ex vivo T2-weighted MRI as well as detailed histology. We demonstrate that CX3CR1+/eGFP mice have improved functional recovery and reduced anxiety after SCI compared with Aldh1l1-EGFP mice. We also found a strong correlation between in vivo MRI, ex vivo MRI, and histological analyses of the injured spinal cord in both strain of mice. All three modalities revealed no difference in lesion extension and volume between the two strains of mice. Importantly, histopathological analysis identified decreased gliosis and increased serotonergic axons in CX3CR1+/eGFP compared with Aldh1l1-EGFP mice following SCI. These results thus suggest that the strain-dependent improved functional recovery after SCI may be linked with reduced gliosis and increased serotonergic innervation.

Challenges of public health and sustainable development require replacing in food producs animal proteins by plant proteins. In this optics, it is crucial to understand the structure and kinetic of formation of a film of plant proteins film in order to improve the control of emulsions and foams stabilized by these proteins. In this talk I will present experimental results on the interfacial properties of wheat gluten and sunflower proteins. Thanks to a combination of tensiometry, viscoelasticity and ellipsometry, a consistent and rational physical picture of the dynamics of the interfacial properties is achieved. For gluten proteins, a time-concentration superposition of the data is evidenced whatever the subphase concentration, which reveals that protein adsorption at the interface is dominated by bulk diffusion. We propose a consistent physical picture of the multistep diffusion-controlled irreversible adsorption of the gliadin proteins at an air/water interface [1]. Our data shows clearly three different regimes for the film formation (Figure 1). In the first regime, the film elasticity and surface protein concentration increase concomitantly due to the progressive coverage of the interface by proteins. In the second regime, an increase of the dissipative viscoelastic properties is associated to an anomalous evolution of the optical profile that we attribute to conformational changes of the proteins at the interface induced by surface pressure. In the last stage, at even higher surface pressure, the optical profile is not modified while the elasticity of the interfacial layer dramatically increases presumably due to the film gelation as the result of the formation of intermolecular bonds. Overall all our experimental results indicate that wheat gluten displays behaviour typical of soft proteins due to their structural flexibility. Sunflower proteins, by contrast, can be considered as hard proteins, and as such, do not reorganize once adsorbed at an interface and display a simpler film formation dynamics. In addition the failure at high concentration of the time-concentration superposition of the tensiometry and viscoelastic data strongly suggest an aggregation process.

We study the fatigue of a soft glass submitted to repeated oscillatory shear deformation using a unique instrument that simultaneously probes the mechanical response of the sample and its microscopic dynamics. The soft glass, a dense packing of microgel particles, exhibits at rest a spontaneous ballistic dynamics, characterized by compressed exponential relaxations, in line with rearrangements being due to the relaxation of internal stresses in a soft solid. Oscillatory shear measurements show a characteristic single step yielding process. To better understand the microscopic origin of yielding, we couple dynamic light scattering to shear rheology and track both the reversible non affine dynamics and the decay of higher order correlation echoes, up to 500 cycles. Several regimes are found by increasing the shear amplitude. Unperturbed spontaneous solid-like relaxation is measured in the linear regime. In this regime, the non-affinities are fullyreversible and originate presumably from spatial fluctuations of the sample elastic modulus. By contrast, the non-affinities become partially irreversible in the non-linear regime and stem from plastic rearrangements. At the onset of non-linearity (γ~6%), we find that dynamics accelerates sharply but still exhibit a solid-like compressed exponential relaxation. In the fully fluidized regime (γ>30%), the microscopic dynamics is however qualitatively different and exhibits a stretched exponential decay, characteristic of a supercooled liquid. Interestingly, we find over a relatively broad range of strain amplitude, which macroscopically corresponds to the regime of a prominent loss peak in the rheology data, the coexistence of a fast liquid-like mode and a slower solid-like mode. Overall, our experimental results that combine macroscopic and microscopic data provide a rational scenario for the fatigue yielding of a heterogeneous soft solid.

We obtain the asymptotic variance, as the degree goes to infinity, of the normalized number of real roots of a square Kostlan-Shub-Smale random polynomial system of any size. Our main tools are the Kac-Rice formula for the second factorial moment of the number of roots and a Hermite expansion of this random variable.

Aerogels are ultraporous materials with a very low permeability. They exhibithigh specific surface area but, due to their huge porous volume, their mechanical properties are quite poor. Aerogels belong to two main families: inorganic materials as silica, silicates, and a few aluminates and organic aerogels which are easily transformed into carbon aerogels by a simple pyrolysis thermal treatment. In this chapter, we mainly report experiments performed on alcohol-dried aerogels. Due to their broad range of porosity, aerogels canfitin very different applications: from analysis of cosmic dust to nuclear waste containment glasses. Advantages of large porosity are sometimes used directly like in thermal and acoustic insulation, or in catalyzers, but a too high pore volume can also be a drawback like in glass precursor and host matrix. Fortunately, aerogel porosity can be tailored using sintering or room isostatic compression or eventually a combination of both methods. Knowledge in this area allows now to synthesize aerogels with a broad range of porosity and also a very broad range of texture.