Lyman Continuum Escape from Inhomogeneous ISM

We have studied the effects of gas density inhomogeneities on the escape of ionising Lyman continuum (Lyc) photons from Milky Way-type galaxies via 3D numerical simulations using the Monte Carlo radiative transfer code CRASH (Ciardi et al. 2001). To this aim a comparison between a smooth Gaussian distribution (GDD) and an inhomogeneous, fractal one (FDD) has been made with realistic assumptions for the ionising stellar sources based on available data in the solar neighborhood. In both cases the escape fraction f_esc increases with ionisation rate N_gamma (although for the FDD with a flatter slope) and they become equal at N_gamma = 2*10^50 s^-1 where f_esc = 0.11. FDD allows escape fractions of the same order also at lower N_gamma, when Lyc photon escape is sharply suppressed by GDD. Values of the escape fraction as high as 0.6 can be reached (GDD) for N_gamma ~ 9*10^50 s^-1, corresponding to a star formation rate (SFR) of roughly 2 M_o yr^-1; at this ionising luminosity the FDD is less transparent (f_esc ~ 0.28). If high redshift galaxies have gas column densities similar to local ones, are characterized by such high SFRs and by a predominantly smooth (i.e.turbulence free) interstellar medium, our results suggest that they should considerably contribute to - and possibly dominate - the cosmic UV background.Comment: 12 pages, 9 figures, MNRAS accepte

Primary and successive events in the Madden–Julian Oscillation

Conventional analyses of the MJO tend to produce a repeating cycle, such that any particular feature cannot be unambiguously attributed to the current or previous event. We take advantage of the sporadic nature of the MJO and classify each observed Madden-Julian (MJ) event as either primary, with no immediately preceding MJ event, or successive, which does immediately follow a preceding event. 40% of MJ events are primary events. Precursor features of the primary events can be unambiguously attributed to that event. A suppressed convective anomaly grows and decays in situ over the Indian Ocean, prior to the start of most primary MJ events. An associated mid-tropospheric temperature anomaly destabilises the atmosphere, leading to the generation of the active MJ event. Hence, primary MJ events appear to be thermodynamically triggered by a previous dry period, although stochastic forcing may also be important. Other theories predict that boundary-layer convergence, humidity, propagation of dynamical structures around the Equator, sea surface temperatures, and lateral forcing by extratropical transients may all be important in triggering an event. Although precursor signals from these mechanisms are diagnosed from reanalysis and satellite observational data in the successive MJ events, they are all absent in the primary MJ events. Hence, it appears that these apparent precursor signals are part of the MJO once it is established, but do not play a role in the spontaneous generation of the MJO. The most frequent starting location of the primary events is the Indian Ocean, but over half of them start elsewhere, from the maritime continent to the western Pacific

Mimicking subsecond neurotransmitter dynamics with femtosecond laser stimulated nanosystems

Existing nanoscale chemical delivery systems target diseased cells over long, sustained periods of time, typically through one-time, destructive triggering. Future directions lie in the development of fast and robust techniques capable of reproducing the pulsatile chemical activity of living organisms, thereby allowing us to mimic biofunctionality. Here, we demonstrate that by applying programmed femtosecond laser pulses to robust, nanoscale liposome structures containing dopamine, we achieve sub-second, controlled release of dopamine – a key neurotransmitter of the central nervous system – thereby replicating its release profile in the brain. The fast delivery system provides a powerful new interface with neural circuits and to the larger range of biological functions that operate on this short timescale

The Atomic to Molecular Transition and its Relation to the Scaling Properties of Galaxy Disks in the Local Universe

We extend existing semi-analytic models of galaxy formation to track atomic and molecular gas in disk galaxies. Simple recipes for processes such as cooling, star formation, supernova feedback, and chemical enrichment of the stars and gas are grafted on to dark matter halo merger trees derived from the Millennium Simulation. Each galactic disk is represented by a series of concentric rings. We assume that surface density profile of infalling gas in a dark matter halo is exponential, with scale radius r_d that is proportional to the virial radius of the halo times its spin parameter $\lambda$. As the dark matter haloes grow through mergers and accretion, disk galaxies assemble from the inside out. We include two simple prescriptions for molecular gas formation processes in our models: one is based on the analytic calculations by Krumholz, McKee & Tumlinson (2008), and the other is a prescription where the H_2 fraction is determined by the kinematic pressure of the ISM. Motivated by the observational results of Leroy et al. (2008), we adopt a star formation law in which $\Sigma_{SFR}\propto\Sigma_{H_2}$ in the regime where the molecular gas dominates the total gas surface density, and $\Sigma_{SFR}\propto \Sigma_{gas}^2$ where atomic hydrogen dominates. We then fit these models to the radial surface density profiles of stars, HI and H_2 drawn from recent high resolution surveys of stars and gas in nearby galaxies. We explore how the ratios of atomic gas, molecular gas and stellar mass vary as a function of global galaxy scale parameters, including stellar mass, stellar surface density, and gas surface density. We elucidate how the trends can be understood in terms of three variables that determine the partition of baryons in disks: the mass of the dark matter halo, the spin parameter of the halo, and the amount of gas recently accreted from the external environment.Comment: Made some minor changes according to the reviewer's suggestion. Accepted by MNRA

Dynamic control of neurochemical release with ultrasonically-sensitive nanoshell-tethered liposomes

The unique surface plasmon resonance of hollow gold nanoshells can be used to achieve drug release from liposomes upon laser stimulation, and adapted to mimic the intricate dynamics of neurotransmission ex vivo in brain preparations. However, to induce a physiological response in vivo requires the degree of temporal precision afforded by laser stimulation, but with a greater depth of penetration through tissue. Here we report that the attachment of hollow gold nanoshells to the surface of robust liposomes results in a construct that is highly sensitive to ultrasonic stimulation. The resulting construct can be remotely triggered by low intensity, therapeutic ultrasound. To our knowledge, this is the first example of nanoparticle-liposome system that can be activated by both laser and acoustic stimulation. The system is capable of encapsulating the neurochemical dopamine, and repeatedly releasing small amounts on-demand in a circulating environment, allowing for precise spatiotemporal control over the release profile

The transcriptional activator Gli2 modulates T-cell receptor signalling through attenuation of AP-1 and NFκB activity

Different tissues contain diverse and dynamic cellular niches, providing distinct signals to tissue-resident or migratory infiltrating immune cells. Hedgehog (Hh) proteins are secreted inter-cellular signalling molecules, which are essential during development and are important in cancer, post-natal tissue homeostasis and repair. Hh signalling mediated by the Hh-responsive transcription factor Gli2 also has multiple roles in T-lymphocyte development and differentiation.Here, we investigate the function of Gli2 in T-cell signalling and activation. Gene transcription driven by the Gli2 transcriptional activator isoform (Gli2A) attenuated T-cell activation and proliferation following T-cell receptor (TCR) stimulation. Expression of Gli2A in T-cells altered gene expression profiles, impaired the TCR-induced Ca2+ flux and nuclear expression of NFAT2, suppressed upregulation of molecules essential for activation, and attenuated signalling pathways upstream of the AP-1 and NFκB complexes, leading to reduced activation of these important transcription factors. Inhibition of physiological Hh-dependent transcription increased NFκB activity upon TCR ligation. These data are important for nderstanding the molecular mechanisms of immunomodulation, particularly in tissues where Hh proteins or other Gli-activating ligands such as TGFβ are upregulated, including during inflammation, tissue damage and repair, and in tumour microenvironments

The long-lived Type IIn SN 2015da: Infrared echoes and strong interaction within an extended massive shell star star star

In this paper we report the results of the first similar to four years of spectroscopic and photometric monitoring of the Type IIn supernova SN 2015da (also known as PSN J13522411+3941286, or iPTF16tu). The supernova exploded in the nearby spiral galaxy NGC 5337 in a relatively highly extinguished environment. The transient showed prominent narrow Balmer lines in emission at all times and a slow rise to maximum in all bands. In addition, early observations performed by amateur astronomers give a very well-constrained explosion epoch. The observables are consistent with continuous interaction between the supernova ejecta and a dense and extended H-rich circumstellar medium. The presence of such an extended and dense medium is difficult to reconcile with standard stellar evolution models, since the metallicity at the position of SN 2015da seems to be slightly subsolar. Interaction is likely the mechanism powering the light curve, as confirmed by the analysis of the pseudo bolometric light curve, which gives a total radiated energy greater than or similar to 10(51) erg. Modeling the light curve in the context of a supernova shock breakout through a dense circumstellar medium allowed us to infer the mass of the prexisting gas to be similar or equal to 8 M-circle dot, with an extreme mass-loss rate for the progenitor star similar or equal to 0.6 M-circle dot yr(-1), suggesting that most of the circumstellar gas was produced during multiple eruptive events. Near- and mid-infrared observations reveal a fluxexcess in these domains, similar to those observed in SN 2010jl and other interacting transients, likely due to preexisting radiatively heated dust surrounding the supernova. By modeling the infrared excess, we infer a mass greater than or similar to 0.4 x 10(-3) M-circle dot for the dustSpanish MICINN gran

Generation of shRNAs from randomized oligonucleotides

Suppression of gene expression by small interfering RNA (siRNA) has proved to be a gene-specific and cost effective alternative to other gene suppression technologies. Short hairpin RNAs (shRNAs) generated from the vector-based expression are believed to be processed into functional siRNAs in vivo, leading to gene silencing. Since an shRNA library carries a large pool of potential siRNAs, such a library makes it possible to knock down gene expression at the genome wide scale. Although much of research has been focused on generating shRNA libraries from either individually made gene specific sequences or cDNA libraries, there is no report on constructing randomized shRNA libraries, which could provide a good alternative to these existing libraries. We have developed a method of constructing shRNAs from randomized oligonucleotides. Through this method, one can generate a partially or fully randomized shRNA library for various functional analyses. We validated this procedure by constructing a p53-specific shRNA. Western blot revealed that the p53-shRNA successfully suppressed expression of the endogenous p53 in MCF-7 cells. We then made a partially randomized shRNA library. Sequencing of 15 randomly picked cloned confirmed the randomness of the library. Therefore, the library can be used for various functional assays, such as target validation when a suitable screening or selection method is available

The evolution of massive black holes and their spins in their galactic hosts

[Abridged] [...] We study the mass and spin evolution of massive black holes within a semianalytical galaxy-formation model that follows the evolution of dark-matter halos along merger trees, as well as that of the baryonic components (hot gas, stellar and gaseous bulges, and stellar and gaseous galactic disks). This allows us to study the mass and spin evolution of massive black holes in a self-consistent way, by taking into account the effect of the gas present in galactic nuclei both during the accretion phases and during mergers. Also, we present predictions, as a function of redshift, for the fraction of gas-rich black-hole mergers -- in which the spins prior to the merger are aligned due to the gravito-magnetic torques exerted by the circumbinary disk -- as opposed to gas-poor mergers, in which the orientation of the spins before the merger is roughly isotropic. These predictions may be tested by LISA or similar spaced-based gravitational-wave detectors such as eLISA/NGO or SGO.Comment: 26 pages, 15 figures. This version includes minor changes to figs 10 and 11 (left-hand panels) described in erratum (MNRAS 440, 1295, 2014, doi: 10.1093/mnras/stu361), see also http://www2.iap.fr/users/barausse/erratum.pd