arXiv subjects

Pascal Martin

Publications and source records attributed to Pascal Martin.

5 recordsLinked to original sources

arXiv2025

Marrying critical oscillators with traveling waves shapes nonlinear sound processing in the cochlea

The cochlea's capacity to process a broad range of sound intensities has been linked to nonlinear amplification by critical oscillators. However, while the increasing sensitivity of a critical oscillator upon decreasing the stimulus magnitude comes with proportionally sharper frequency tuning and slower responsiveness -- critical slowing down, the observed bandwidth of cochlear frequency tuning and the cochlear response time vary little with sound level. Because the cochlea operates as a distributed system rather than a single critical oscillator, it remains unclear whether criticality can serve as a fundamental principle for cochlear amplification. Here we tackle this challenge by integrating tonopically distributed critical oscillators in a traveling-wave model of the cochlea. Importantly, critical oscillators generically provide spatial buildup of energy gain from energy pumping into the waves and a key nonlinearity. In addition, our nonlinear model accounts for viscoelastic coupling between the oscillators. The model produces, with a single set of parameters, a family of cochlear tuning curves that quantitatively describe experimental data over a broad range of input levels. Overall, the interplay between generic nonlinear properties of local critical oscillators and distributed effects from traveling waves gives rise to a collective nonlinear response that preserves the power-law responsiveness afforded by criticality, but without paying the price of critical slowing down.

physics.bio-ph↗

arXiv2024

UltraCortex: Submillimeter Ultra-High Field 9.4 T Brain MR Image Collection and Manual Cortical Segmentations

The UltraCortex repository (https://www.ultracortex.org) houses magnetic resonance imaging data of the human brain obtained at an ultra-high field strength of 9.4 T. It contains 86 structural MR images with spatial resolutions ranging from 0.6 to 0.8 mm. Additionally, the repository includes segmentations of 12 brains into gray and white matter compartments. These segmentations have been independently validated by two expert neuroradiologists, thus establishing them as a reliable gold standard. This resource provides researchers with access to high-quality brain imaging data and validated segmentations, facilitating neuroimaging studies and advancing our understanding of brain structure and function. Existing repositories do not accommodate field strengths beyond 7 T, nor do they offer validated segmentations, underscoring the significance of this new resource.

cs.CV↗

arXiv2021

Fast Fisher-Lee approach for conductance calculations on BTB-based molecular junctions: effects of isomerization and electrode coupling

In this work, we have implemented the Fisher-Lee formalism to couple non-equilibrium Green functions with tight-binding Density Functional to tackle large molecular systems. This method is used to determine the decay constant of a set of oligomers based on seven different monomers taken from the literature in the non-resonant tunneling regime. Results show good agreement with experimental measurements. The approach is then applied to explore the conformational pattern effect as well as the asymmetry and the strength of coupling with the electrode of bisthienylbenzene oligomers sandwiched between gold (Au),titanium (Ti)and graphene (G)) electrodes The results indicate that conformational patterns have low impact on the conductance, since the delocalization of {\pi}-electrons exhibits similar behavior for all the conformations explored. The calculated attenuation factor is found to be comparable with the strength of contact coupling (Ti > Au = G). Electronic analysis of metal-molecule interactions reveals the ionic nature of Ti-C bonds, through the emergence of a local dipole contributing to the work function variation of 0.35 eV. In addition, the Ti d-orbitals are found to be strongly coupled with the lowest unoccupied orbital (LUMO) of BTB, thus facilitating charge transfer from Ti to the molecule, at the origin of this strong interfacial dipole. However, the Au-C bond is found to be similar to the C-C bond, with pure covalent character. The results confirm the hole transport mechanism observed experimentally in the cases of Au-(BTB)n-Au and Au-(BTB)n-Ti, and predict possible combined mechanism of both hole and electron transport in the case of Ti(BTB)n-Ti.

cond-mat.mes-hall↗

arXiv2018

Rectification effect in organic junctions based on aryl thin films covalently attached to a multilayer graphene electrode

The quantum interaction between molecules and electrode s material at molecules-electrode interfaces is a major ingredient in the electronic transport properties of organic junctions. Driven by the coupling strength between the two materials, it results mainly in a broadening and an energy shift of the interacting molecular orbitals. Using new electrodes materials, such as the recent semi-conducting two-dimensional nanomaterials, has become a recent challenge in the field of molecular-organic electronics that opens new possibilities for controlling the interfacial electronic properties and thus the charge injection properties. In this article, we report the use of atomically thin two-dimensional multilayer graphene films as base electrode in organic junctions with a vertical architecture. The interfacial electronic structure dominated by the covalent bonding between bis-thienyl benzene diazonium-based molecules and the multilayer graphene electrode has been probed by ultraviolet photoelectron spectroscopy and the results compared with those obtained on junctions with standard Au electrodes. Room temperature injection properties of such interfaces have been also explored by electronic transport measurements. We find that, despite strong variations of the density of states, the Fermi energy and the injection barriers, both organic junctions with Au base electrodes and multilayer graphene base electrodes show similar electronic responses. We explain this observation by the strong orbital coupling occurring at the bottom electrode-bis(thienyl) benzene molecules interface and by the pinning of the hybridized molecular orbitals.

physics.app-ph↗

arXiv2018

Quantifying entropy production in active fluctuations of the hair-cell bundle from time irreversibility and uncertainty relations

We introduce lower bounds for the rate of entropy production of an active stochastic process by quantifying the irreversibility of stochastic traces obtained from mesoscopic degrees of freedom. Our measures of irreversibility reveal signatures of time's arrow and provide bounds for entropy production even in the case of active fluctuations that have no drift. We apply these irreversibility measures to experimental recordings of spontaneous hair-bundle oscillations in mechanosensory hair cells from the ear of the bullfrog. By analysing the fluctuations of only the tip position of hair bundles, we reveal irreversibility in active oscillations and estimate an associated rate of entropy production of at least $\sim 3 k_{\rm B}$/s, on average. Applying thermodynamic uncertainty relations, we predict that measuring both the tip position of the hair bundle and the mechano-electrical transduction current that enters the hair cell leads to tighter lower bounds for the rate of entropy production, up to $\sim 10^3 k_{\rm B}$/s in the oscillatory regime.

cond-mat.stat-mech↗