Reticulospinal and corticospinal axon regeneration after complete spinal cord injury

Neuroprosthetic rehabilitation demonstrated that significant functional benefit could be achieved with lumbosacral neuromodulation in both human and animal models of spinal cord injury. It promoted the recovery of voluntary leg movements through the reorganization of residual reticulospinal and propriospinal projections pathways. However, in case of complete spinal cord injuries (SCI), which isolate the circuits under the lesion from any supraspinal control, the outcome of neuroprosthetic rehabilitation is still not sufficient. Indeed, it will require the restoration of robust regrowth and sprouting of several types of axons across the injury. Axons fail to regrow across spinal lesions because of different inhibitory mechanisms. It has been demonstrated that this spontaneous axon regeneration failure can be reversed by i) stimulating the neuronal intrinsic growth capacity using viral technology, ii) remodeling the lesion core with growth factors, in order to create a more permissive environment, and iii) guiding axons with chemo-attractive molecules across and beyond the SCI site. It was thus demonstrated that propriospinal axons are able to regrow and build a robust descending bridge across complete SCIs when the needed facilitators are provided. However, this robust propriospinal bridging failed to promote functional recovery by itself. It might be explained by an insufficient descending motor control partly supported by other systems such as the reticulospinal tract (RtST) and the corticospinal tract (CST). Therefore we wanted to study the regenerative potential of the RtST and CST pathways. The RtST arises from the brainstem and reaches for the spinal cord acting as relay for descending motor cortical commands. The CST is the main descending motor cortical command arising from the primary motor cortex. In the present study, we applied the same strategy to enhance sprouting and regrowth of reticulospinal and corticospinal neurons across anatomically complete SCI. We first activated the neuronal intrinsic growth capacity of both tracts using viral technology. The lesion environment was then remodeled with growth factors, delivered using a biocompatible hydrogel. Finally, we established chemical axon guidance using chemoattractant molecules. These interventions were delivered with a spatiotemporal profile corresponding to the axon growth sequence during development. We did not obtain any CST regeneration, due to the severe crush injury model inducing extensive CST axons degeneration probably caused by ischemic phenomenon. Regarding the RtST, we obtained significant reticulospinal regeneration into the lesion core with some fibers growing across the lesion reaching the healthy caudal tissue. This regeneration remained limited though as compared with the propriospinal results indicating the importance of identifying complementary strategies to increase the density of the regenerated tract and to attract the axons in the healthy tissue below the SCI. Our ultimate goal is to restore anatomical communications across complete SCI and promote their functional integration using neuroprosthetic rehabilitation program

Effect of Measurement on the Periodicity of the Coulomb Staircase of a Superconducting Box

We report on the effect of the back-action of a Single Cooper Pair Transistor electrometer (E) on the measurement of charge on the island of a superconducting box (B). The charge is e-periodic in the gate bias of B when E is operated near voltages 2Delta/e or 4Delta/e. We show that this is due to quasiparticle poisoning of B at a rate proportional to the number of quasiparticle tunneling events in E per second. We are able to eliminate this back action and recover 2e charge periodicity using a new measurement method based on switching current modulation of E.Comment: 4 pages, 4 figures, revised versio

The Inductive Single-Electron Transistor (L-SET)

We demonstrate a sensitive method of charge detection based on radio-frequency readout of the Josephson inductance of a superconducting single-electron transistor. Charge sensitivity $1.4 \times 10^{-4}e/\sqrt{Hz}$, limited by preamplifier, is achieved in an operation mode which takes advantage of the nonlinearity of the Josephson potential. Owing to reactive readout, our setup has more than two orders of magnitude lower dissipation than the existing method of radio-frequency electrometry. With an optimized sample, we expect uncoupled energy sensitivity below $\hbar$ in the same experimental scheme.Comment: 10 page

Photon mediated interaction between distant quantum dot circuits

Engineering the interaction between light and matter is an important goal in the emerging field of quantum opto-electronics. Thanks to the use of cavity quantum electrodynamics architectures, one can envision a fully hybrid multiplexing of quantum conductors. Here, we use such an architecture to couple two quantum dot circuits . Our quantum dots are separated by 200 times their own size, with no direct tunnel and electrostatic couplings between them. We demonstrate their interaction, mediated by the cavity photons. This could be used to scale up quantum bit architectures based on quantum dot circuits or simulate on-chip phonon-mediated interactions between strongly correlated electrons

Chemical analysis and aqueous solution properties of Charged Amphiphilic Block Copolymers PBA-b-PAA synthesized by MADIX

We have linked the structural and dynamic properties in aqueous solution of amphiphilic charged diblock copolymers poly(butyl acrylate)-b-poly(acrylic acid), PBA-b-PAA, synthesized by controlled radical polymerization, with the physico-chemical characteristics of the samples. Despite product imperfections, the samples self-assemble in melt and aqueous solutions as predicted by monodisperse microphase separation theory. However, the PBA core are abnormally large; the swelling of PBA cores is not due to AA (the Flory parameter chiPBA/PAA, determined at 0.25, means strong segregation), but to h-PBA homopolymers (content determined by Liquid Chromatography at the Point of Exclusion and Adsorption Transition LC-PEAT). Beside the dominant population of micelles detected by scattering experiments, capillary electrophoresis CE analysis permitted detection of two other populations, one of h-PAA, and the other of free PBA-b-PAA chains, that have very short PBA blocks and never self-assemble. Despite the presence of these free unimers, the self-assembly in solution was found out of equilibrium: the aggregation state is history dependant and no unimer exchange between micelles occurs over months (time-evolution SANS). The high PBA/water interfacial tension, measured at 20 mN/m, prohibits unimer exchange between micelles. PBA-b-PAA solution systems are neither at thermal equilibrium nor completely frozen systems: internal fractionation of individual aggregates can occur.Comment: 32 pages, 16 figures and 4 tables submitted to Journal of Interface and Colloidal Scienc

Variable Selection and Model Averaging in Semiparametric Overdispersed Generalized Linear Models

We express the mean and variance terms in a double exponential regression model as additive functions of the predictors and use Bayesian variable selection to determine which predictors enter the model, and whether they enter linearly or flexibly. When the variance term is null we obtain a generalized additive model, which becomes a generalized linear model if the predictors enter the mean linearly. The model is estimated using Markov chain Monte Carlo simulation and the methodology is illustrated using real and simulated data sets.Comment: 8 graphs 35 page

Coherent coupling of a single spin to microwave cavity photons

Electron spins and photons are complementary quantum-mechanical objects that can be used to carry, manipulate and transform quantum information. To combine these resources, it is desirable to achieve the coherent coupling of a single spin to photons stored in a superconducting resonator. Using a circuit design based on a nanoscale spin-valve, we coherently hybridize the individual spin and charge states of a double quantum dot while preserving spin coherence. This scheme allows us to achieve spin-photon coupling up to the MHz range at the single spin level. The cooperativity is found to reach 2.3, and the spin coherence time is about 60ns. We thereby demonstrate a mesoscopic device suitable for non-destructive spin read-out and distant spin coupling.Comment: minor differences with published versio

Simulation laser d'impacts de particules de très grande vitesse

Le laser au néodyme du GRECO I.L.M. délivrant des impulsions de l'ordre de 100 J en quelques ns, nous a permis de simuler des impacts de micrométéorites silicatées de quelques dixièmes de μg, de vitesse comprise entre 5 et 45 km/s, sur une cible d'aluminium. Les cratères produits dans la cible sont hémisphériques, et le rapport Km, de la masse éjectée sur la masse de la particule incidente simulée, varie avec la vitesse d'impact Vp selon la loi Km = 1,17 V 1,52p

Conserved spin and orbital phase along carbon nanotubes connected with multiple ferromagnetic contacts

We report on spin dependent transport measurements in carbon nanotubes based multi-terminal circuits. We observe a gate-controlled spin signal in non-local voltages and an anomalous conductance spin signal, which reveal that both the spin and the orbital phase can be conserved along carbon nanotubes with multiple ferromagnetic contacts. This paves the way for spintronics devices exploiting both these quantum mechanical degrees of freedom on the same footing.Comment: 8 pages - minor differences with published versio