Proper motions and velocity asymmetries in the RW Aur jet

We present adaptive optics spectro-imaging observations of the RW Aur jet in optical forbidden lines, at an angular resolution of 0.4 arcsec. Comparison with HST data taken 2 years later shows that proper motions in the blueshifted and redshifted lobes are in the same ratio as their radial velocities, a direct proof that the velocity asymmetry in this jet is real and not an emissivity effect. The inferred jet inclination to the line of sight is i = 46 +/- 3 degrees. The inner knot spacing appears best explained by time variability with at least two modes: one irregular and asymmetric (possibly random) on timescales of <3-10 yr, and another more regular with ~ 20 yr period. We also report indirect evidence for correlated velocity and excitation gradients in the redshifted lobe, possibly related to the blue/red velocity and brightness asymmetry in this system.Comment: 4 pags, 3 figure

Electric Field Effects on Graphene Materials

Understanding the effect of electric fields on the physical and chemical properties of two-dimensional (2D) nanostructures is instrumental in the design of novel electronic and optoelectronic devices. Several of those properties are characterized in terms of the dielectric constant which play an important role on capacitance, conductivity, screening, dielectric losses and refractive index. Here we review our recent theoretical studies using density functional calculations including van der Waals interactions on two types of layered materials of similar two-dimensional molecular geometry but remarkably different electronic structures, that is, graphene and molybdenum disulphide (MoS$_2$). We focus on such two-dimensional crystals because of they complementary physical and chemical properties, and the appealing interest to incorporate them in the next generation of electronic and optoelectronic devices. We predict that the effective dielectric constant ($\varepsilon$) of few-layer graphene and MoS$_2$ is tunable by external electric fields ($E_{\rm ext}$). We show that at low fields ($E_{\rm ext}^{}<0.01$ V/\AA) $\varepsilon$ assumes a nearly constant value $\sim$4 for both materials, but increases at higher fields to values that depend on the layer thickness. The thicker the structure the stronger is the modulation of $\varepsilon$ with the electric field. Increasing of the external field perpendicular to the layer surface above a critical value can drive the systems to an unstable state where the layers are weakly coupled and can be easily separated. The observed dependence of $\varepsilon$ on the external field is due to charge polarization driven by the bias, which show several similar characteristics despite of the layer considered.Comment: Invited book chapter on Exotic Properties of Carbon Nanomatter: Advances in Physics and Chemistry, Springer Series on Carbon Materials. Editors: Mihai V. Putz and Ottorino Ori (11 pages, 4 figures, 30 references

GABAA receptor dependent synaptic inhibition rapidly tunes KCC2 activity via the Cl--sensitive WNK1 kinase

This is the final version of the article. Available from the publisher via the DOI in this record.There is another ORE record for this publication: http://hdl.handle.net/10871/33406The K+-Cl-co-transporter KCC2 (SLC12A5) tunes the efficacy of GABAAreceptor-mediated transmission by regulating the intraneuronal chloride concentration [Cl-]i. KCC2 undergoes activity-dependent regulation in both physiological and pathological conditions. The regulation of KCC2 by synaptic excitation is well documented; however, whether the transporter is regulated by synaptic inhibition is unknown. Here we report a mechanism of KCC2 regulation by GABAAreceptor (GABAAR)-mediated transmission in mature hippocampal neurons. Enhancing GABAAR-mediated inhibition confines KCC2 to the plasma membrane, while antagonizing inhibition reduces KCC2 surface expression by increasing the lateral diffusion and endocytosis of the transporter. This mechanism utilizes Cl-as an intracellular secondary messenger and is dependent on phosphorylation of KCC2 at threonines 906 and 1007 by the Cl--sensing kinase WNK1. We propose this mechanism contributes to the homeostasis of synaptic inhibition by rapidly adjusting neuronal [Cl-]ito GABAAR activity.This work was supported in part by Inserm, Sorbonne Université-UPMC, as well as the Fondation pour la Recherche Médicale (Equipe FRM DEQ20140329539 to J.C.P.), the Human Frontier Science Program (RGP0022/2013 to J.C.P.) and the Fondation pour la Recherche sur le Cerveau (to S.L.). Equipment at the IFM was also supported by DIM NeRF from Région Ile-de-France and by the FRC/Rotary ‘Espoir en tête’. M.H. was the recipient of a doctoral fellowship from the Université Pierre and Marie Curie, as well as from Bio-Psy Laboratory of excellence. K.T.K. is supported by the National Institutes of Health, the Simons Foundation, and the March of Dimes Foundation Basil O’Connor Award. The Poncer/Lévi lab is affiliated with the Paris School of Neuroscience (ENP) and the Bio-Psy Laboratory of excellence

Three-Dimensional Simulations of Jets from Keplerian Disks: Self--Regulatory Stability

We present the extension of previous two-dimensional simulations of the time-dependent evolution of non-relativistic outflows from the surface of Keplerian accretion disks, to three dimensions. The accretion disk itself is taken to provide a set of fixed boundary conditions for the problem. The 3-D results are consistent with the theory of steady, axisymmetric, centrifugally driven disk winds up to the Alfv\'en surface of the outflow. Beyond the Alfv\'en surface however, the jet in 3-D becomes unstable to non-axisymmetric, Kelvin-Helmholtz instabilities. We show that jets maintain their long-term stability through a self-limiting process wherein the average Alfv\'enic Mach number within the jet is maintained to order unity. This is accomplished in at least two ways. First, poloidal magnetic field is concentrated along the central axis of the jet forming a ``backbone'' in which the Alfv\'en speed is sufficiently high to reduce the average jet Alfv\'enic Mach number to unity. Second, the onset of higher order Kelvin-Helmholtz ``flute'' modes (m \ge 2) reduce the efficiency with which the jet material is accelerated, and transfer kinetic energy of the outflow into the stretched, poloidal field lines of the distorted jet. This too has the effect of increasing the Alfv\'en speed, and thus reducing the Alfv\'enic Mach number. The jet is able to survive the onset of the more destructive m=1 mode in this way. Our simulations also show that jets can acquire corkscrew, or wobbling types of geometries in this relatively stable end-state, depending on the nature of the perturbations upon them. Finally, we suggest that jets go into alternating periods of low and high activity as the disappearance of unstable modes in the sub-Alfv\'enic regime enables another cycle of acceleration to super-Alfv\'enic speeds.Comment: 57 pages, 22 figures, submitted to Ap

β-Secretase 1’s Targeting Reduces Hyperphosphorilated Tau, Implying Autophagy Actors in 3xTg-AD Mice

β-site APP cleaving enzyme 1 (BACE1) initiates APP cleavage, which has been reported to be an inducer of tau pathology by altering proteasome functions in Alzheimer's disease (AD). However, the exact relationship between BACE1 and PHF (Paired Helical Filaments) formation is not clear. In this study, we confirm that BACE1 and Hsc70 are upregulated in the brains of AD patients, and we demonstrate that both proteins show enhanced expression in lipid rafts from AD-affected triple transgenic mouse brains. BACE1 targeting increased Hsc70 levels in the membrane and cytoplasm fractions and downregulated Hsp90 and CHIP in the nucleus in the hippocampi of 3xTg-AD mice. However, these observations occurred in a proteasome-independent manner in vitro. The BACE1miR-induced reduction of soluble hyperphosphorylated tau was associated with a decrease in MAPK activity. However, the BACE1 RNAi-mediated reduction of hyperphosphorylated tau was only blocked by 3-MA (3-methyladenine) in vitro, and it resulted in the increase of Hsc70 and LAMP2 in lipid rafts from hippocampi of 3xTg-AD mice, and upregulation of survival and homeostasis signaling. In summary, our findings suggest that BACE1 silencing neuroprotects reducing soluble hyperphosphorylated tau, modulating certain autophagy-related proteins in aged 3xTg-AD mice

The host galaxy of OJ 287 revealed by optical and near-infrared imaging

The BL Lacertae object OJ 287 (z = 0.306) has unique double-peaked optical outbursts every ~12 years, and it presents one of the best cases for a small-separation binary supermassive black hole (SMBH) system, with an extremely massive primary log (M_BH/M_Sun) ~ 10.3. However, the host galaxy is unresolved or only marginally detected in all optical studies so far, indicating a large deviation from the bulge mass - SMBH mass relation. We have obtained deep, high spatial resolution i-band and K-band images of OJ~287 when the target was in a low state, which enable us to detect the host galaxy. We find the broad-band photometry of the host to be consistent with an early type galaxy with M_R = -22.5 and M_K = -25.2, placing it in the middle of the host galaxy luminosity distribution of BL Lacertae objects. The central supermassive black hole is clearly overmassive for a host galaxy of that luminosity, but not unprecedented, given some recent findings of other ``overmassive'' black holes in nearby galaxies.Comment: Accepted for publication in Astrophysical Journa

New constraints on protostellar jet collimation from high-density gas UV tracers

The analysis of high-resolution profiles of the semiforbidden UV lines of C III](1908) and Si III](1892) in the spectra of T Tauri stars (TTSs) shows the following : (1) There is C III](1908) and Si III](1892) emission at velocities that are similar to those observed in the optical forbidden lines formed in the TTSs jets. The luminosity of the UV lines is comparable to that of the optical lines. (2) The comparison between the optical and UV light curves indicates that the C III](1908) and Si III](1892) emission of RY Tau is not associated with accretion shocks, but it is produced farther than 2 R-* from the star. (3) The profiles of the UV semiforbidden lines are significantly broader than those of the optical forbidden lines. These profiles cannot be produced in a narrow collimated beam, and they are most likely produced in a bow-shaped shock wave formed at the base of the optical jet, where the hot gas emits in a broad range of projected radial velocities. (4) The atmosphere of RU Lup contributes significantly to the Si III](1892) emission. (5) A puzzling narrow feature is observed close to the C III](1908) line. The feature is blueshifted by -260 km s(-1), which corresponds to the wind terminal velocity measured in the P Cygni profile of the Mg II (UV1) lines. Moreover, constraints are derived on the characteristics of the C III](1908) and Si III](1892) emitting region in RY Tau. It is shown that 4.7 less than or equal to log T-e less than or equal to 5.0 and 10(9) cm(-3) less than or equal to N-e less than or equal to 10(11) cm(-3) provided that the emission is produced in a collisional plasma and that the 1665 Angstrom feature observed in low-dispersion International Ultraviolet Explorer (IUE) spectra is confirmed to be O III](1665) emission produced in the wind. These very high densities are difficult to generate in the shocks produced by the magnetic pinching of centrifugally driven magnetized disk winds. The data also suggest that the shocked layer has a radius of some few stellar radii and it is closer than similar to 38 R-* to the star

Observations of T-Tauri Stars using HST-GHRS: I. Far Ultraviolet Emission Lines

We have analyzed GHRS data of eight CTTS and one WTTS. The GHRS data consists of spectral ranges 40 A wide centered on 1345, 1400, 1497, 1550, and 1900 A. These UV spectra show strong SiIV, and CIV emission, and large quantities of sharp (~40 km/s) H2 lines. All the H2 lines belong to the Lyman band and all the observed lines are single peaked and optically thin. The averages of all the H2 lines centroids for each star are negative which may indicate that they come from an outflow. We interpret the emission in H2 as being due to fluorescence, mostly by Ly_alpha, and identify seven excitation routes within 4 A of that line. We obtain column densities (10^12 to 10^15 cm^-2) and optical depths (~1 or less) for each exciting transition. We conclude that the populations are far from being in thermal equilibrium. We do not observe any lines excited from the far blue wing of Ly_alpha, which implies that the molecular features are excited by an absorbed profile. SiIV and CIV (corrected for H2 emission) have widths of ~200 km/s, and an array of centroids (blueshifted lines, centered, redshifted). These characteristics are difficult to understand in the context of current models of the accretion shock. For DR Tau we observe transient strong blueshifted emission, perhaps the a result of reconnection events in the magnetosphere. We also see evidence of multiple emission regions for the hot lines. While CIV is optically thin in most stars in our sample, SiIV is not. However, CIV is a good predictor of SiIV and H2 emission. We conclude that most of the flux in the hot lines may be due to accretion processes, but the line profiles can have multiple and variable components.Comment: 67 pages, 19 figures, Accepted in Ap

Vertical Field Effect Transistor based on Graphene-WS2 Heterostructures for flexible and transparent electronics

The celebrated electronic properties of graphene have opened way for materials just one-atom-thick to be used in the post-silicon electronic era. An important milestone was the creation of heterostructures based on graphene and other two-dimensional (2D) crystals, which can be assembled in 3D stacks with atomic layer precision. These layered structures have already led to a range of fascinating physical phenomena, and also have been used in demonstrating a prototype field effect tunnelling transistor - a candidate for post-CMOS technology. The range of possible materials which could be incorporated into such stacks is very large. Indeed, there are many other materials where layers are linked by weak van der Waals forces, which can be exfoliated and combined together to create novel highly-tailored heterostructures. Here we describe a new generation of field effect vertical tunnelling transistors where 2D tungsten disulphide serves as an atomically thin barrier between two layers of either mechanically exfoliated or CVD-grown graphene. Our devices have unprecedented current modulation exceeding one million at room temperature and can also operate on transparent and flexible substrates

Epithelial-mesenchymal transitions: the importance of changing cell state in development and disease

The events that convert adherent epithelial cells into individual migratory cells that can invade the extracellular matrix are known collectively as epithelial-mesenchymal transition (EMT). Throughout evolution, the capacity of cells to switch between these two cellular states has been fundamental in the generation of complex body patterns. Here, we review the EMT events that build the embryo and further discuss two prototypical processes governed by EMT in amniotes: gastrulation and neural crest formation. Cells undergo EMT to migrate and colonize distant territories. Not surprisingly, this is also the mechanism used by cancer cells to disperse throughout the body