A Keplerian gaseous disk around the B0 star R Mon

We present high-angular resolution observations of the circumstellar disk around the massive Herbig Be star R Mon (M~8 Msun) in the continuum at 2.7mm and 1.3mm and the CO 1->0 and 2->1 rotational lines. Based on the new 1.3mm continuum image we estimate a disk mass (gas+dust) of 0.007 Msun and an outer radius of <150 AU. Our CO images are consistent with the existence of a Keplerian rotating gaseous disk around this star. Up to our knowledge, this is the most clear evidence for the existence of Keplerian disks around massive stars reported thus far. The mass and physical characteristics of this disk are similar to thoseof the more evolved T Tauri stars and indicate a shorter timescale for the evolution and dispersal of circumstellar disks around massive stars which lose most of their mass before the star becomes visible.Comment: 5 page

Discovery of Water Vapor in the High-redshift Quasar APM 08279+5255 at z = 3.91

We report a detection of the excited 2_(20)-2_(11) rotational transition of para-H_2O in APM 08279+5255 using the IRAM Plateau de Bure Interferometer. At z = 3.91, this is the highest-redshift detection of interstellar water to date. From large velocity gradient modeling, we conclude that this transition is predominantly radiatively pumped and on its own does not provide a good estimate of the water abundance. However, additional water transitions are predicted to be detectable in this source, which would lead to an improved excitation model. We also present a sensitive upper limit for the hydrogen fluoride (HF) J = 1-0 absorption toward APM 08279+5255. While the face-on geometry of this source is not favorable for absorption studies, the lack of HF absorption is still puzzling and may be indicative of a lower fluorine abundance at z = 3.91 compared with the Galactic interstellar medium

Modelling the Molecular Gas in NGC 6240

We present the first observations of H$^{13}$CN$(1-0)$, H$^{13}$CO$^+(1-0)$ and SiO$(2-1)$ in NGC\,6240, obtained with the IRAM PdBI. Combining a Markov Chain Monte Carlo (MCMC) code with Large Velocity Gradient (LVG) modelling, and with additional data from the literature, we simultaneously fit three gas phases and six molecular species to constrain the physical condition of the molecular gas, including mass$-$luminosity conversion factors. We find $\sim10^{10}M_\odot$ of dense molecular gas in cold, dense clouds ($T_{\rm k}\sim10$\,K, $n_{{\rm H}_2}\sim10^6$\,cm$^{-3}$) with a volume filling factor $<0.002$, embedded in a shock heated molecular medium ($T_{\rm k}\sim2000$\,K, $n_{{\rm H}_2}\sim10^{3.6}$\,cm$^{-3}$), both surrounded by an extended diffuse phase ($T_{\rm k}\sim200$\,K, $n_{{\rm H}_2}\sim10^{2.5}$\,cm$^{-3}$). We derive a global $\alpha_{\rm CO}=1.5^{7.1}_{1.1}$ with gas masses $\log_{10}\left(M / [M_\odot]\right)=10.1_{10.0}^{10.8}$, dominated by the dense gas. We also find $\alpha_{\rm HCN} = 32^{89}_{13}$, which traces the cold, dense gas. The [$^{12}$C]/[$^{13}$C] ratio is only slightly elevated ($98^{230}_{65}$), contrary to the very high [CO]/[$^{13}$CO] ratio (300-500) reported in the literature. However, we find very high [HCN]/[H$^{13}$CN] and [HCO$^+$]/[H$^{13}$CO$^+$] abundance ratios $(300^{500}_{200})$ which we attribute to isotope fractionation in the cold, dense clouds.Comment: 27 pages, 17 figures, 9 tables. Accepted in Ap

Interferometric Observations of Powerful CO Emission from the three Submillimeter Galaxies at z=2.30, 2.51 and 3.35

We report IRAM Plateau de Bure, millimeter interferometry of three z=~2.4 to 3.4, SCUBA deep field galaxies. Our CO line observations confirm the rest-frame UV/optical redshifts, thus more than doubling the number of confirmed, published redshifts of the faint submillimeter population and proving their high-z nature. In all three sources our measurements of the intrinsic gas and dynamical mass are large (1e10 to 1e11 Msun). In at least two cases the data show that the submillimeter sources are part of an interacting system. Together with recent information gathered in the X-ray, optical and radio bands our observations support the interpretation that the submm-population consists of gas rich (gas to dynamical mass ratio ~0.5) and massive, composite starburst/AGN systems, which are undergoing a major burst of star formation and are evolving into m*-galaxies.Comment: only minor modifications to comply with the ApJL edition rule

A semi-implicit, second-order-accurate numerical model for multiphase underexpanded volcanic jets

Abstract. An improved version of the PDAC (Pyroclastic Dispersal Analysis Code, Esposti Ongaro et al., 2007) numerical model for the simulation of multiphase volcanic flows is presented and validated for the simulation of multiphase volcanic jets in supersonic regimes. The present version of PDAC includes second-order time- and space discretizations and fully multidimensional advection discretizations in order to reduce numerical diffusion and enhance the accuracy of the original model. The model is tested on the problem of jet decompression in both two and three dimensions. For homogeneous jets, numerical results are consistent with experimental results at the laboratory scale (Lewis and Carlson, 1964). For nonequilibrium gas–particle jets, we consider monodisperse and bidisperse mixtures, and we quantify nonequilibrium effects in terms of the ratio between the particle relaxation time and a characteristic jet timescale. For coarse particles and low particle load, numerical simulations well reproduce laboratory experiments and numerical simulations carried out with an Eulerian–Lagrangian model (Sommerfeld, 1993). At the volcanic scale, we consider steady-state conditions associated with the development of Vulcanian and sub-Plinian eruptions. For the finest particles produced in these regimes, we demonstrate that the solid phase is in mechanical and thermal equilibrium with the gas phase and that the jet decompression structure is well described by a pseudogas model (Ogden et al., 2008). Coarse particles, on the other hand, display significant nonequilibrium effects, which associated with their larger relaxation time. Deviations from the equilibrium regime, with maximum velocity and temperature differences on the order of 150 m s−1 and 80 K across shock waves, occur especially during the rapid acceleration phases, and are able to modify substantially the jet dynamics with respect to the homogeneous case

A Cross-Layer Location-Based Approach for Mobile-Controlled Connectivity

We investigate into the potentiality of an enhanced Power and Location-based Vertical Handover (PLB-VHO) approach, based on a combination of physical parameters (i.e., location and power attenuation information), for mobile-controlled connectivity across UMTS and WLAN networks. We show that the location information in a multiparameter vertical handover can significantly enhance communication performance. In the presented approach a power attenuation map for the visited area is built and kept updated by exploiting the information sharing of power measurements with other cooperating mobile devices inside the visited networks. Such information is then used for connectivity switching in handover decisions. The analytical model for the proposed technique is first presented and then compared with a traditional Power-Based approach and a simplified Location-Based technique. Simulation results show the effectiveness of PLB-VHO approach, in terms of (i) network performance optimization and (ii) limitation of unnecessary handovers (i.e., mitigation ofping-pong effect)

The dusty disk around VV Ser

We have carried out observations at millimeter and centimeter wavelengths towards VV Ser using the Plateau de Bure Interferometer and the Very Large Array. This allows us to compute the SED from near infrared to centimeter wavelengths. The modeling of the full SED has provided insight into the dust properties and a more accurate value of the disk mass. The mass of dust in the disk around VV Ser is found to be about 4 10^(-5) Msun, i.e. 400 times larger than previous estimates. Moreoever, the SED can only be accounted for assuming dust stratification in the vertical direction across the disk. The existence of small grains (0.25--1 micron) in the disk surface is required to explain the emission at near- and mid-infrared wavelengths. The fluxes measured at millimeter wavelengths imply that the dust grains in the midplane have grown up to very large sizes, at least to some centimeters.Comment: To appear in Ap

Simplified and yet Turing universal spiking neural P systems with communication on request

The file attached to this record is the author's final peer reviewed version.Spiking neural P systems are a class of third generation neural networks belonging to the framework of membrane computing. Spiking neural P systems with communication on request (SNQ P systems) are a type of spiking neural P system where the spikes are requested from neighbouring neurons. SNQ P systems have previously been proved to be universal (computationally equivalent to Turing machines) when two types of spikes are considered. This paper studies a simpli ed version of SNQ P systems, i.e. SNQ P systems with one type of spike. It is proved that one type of spike is enough to guarantee the Turing universality of SNQ P systems. Theoretical results are shown in the cases of the SNQ P system used in both generating and accepting modes. Furthermore, the influence of the number of unbounded neurons (the number of spikes in a neuron is not bounded) on the computation power of SNQ P systems with one type of spike is investigated. It is found that SNQ P systems functioning as number generating devices with one type of spike and four unbounded neurons are Turing universal

Insights into the formation and dynamics of coignimbrite plumes from one-dimensional models

Coignimbrite plumes provide a common and effective mechanism by which large volumes of fine-grained ash are injected into the atmosphere. Nevertheless, controls on formation of these plumes as a function of eruptive conditions are still poorly constrained. Herein, two 1-D axysymmetric steady state models were coupled, the first describing the parent pyroclastic density current and the second describing plume rise. Global sensitivity analysis is applied to investigate controls on coignimbrite plume formation and describe coignimbrite source and the maximum plume height attained. For a range of initial mass flow rates between 108 and 1010 kg/s, modeled liftoff distance (the distance at which neutral buoyancy is attained), assuming radial supercritical flow, is controlled by the initial flow radius, gas mass fraction, flow thickness, and temperature. The predicted decrease in median grain size between flow initiation and plume liftoff is negligible. Calculated initial plume vertical velocities, assuming uniform liftoff velocity over the pyroclastic density current invasion area, are much greater (several tens of m/s) than those previously used in modeling coignimbrite plumes (1 m/s). Such velocities are inconsistent with the fine grain size of particles lofted into coignimbrite plumes, highlighting an unavailability of large clasts, possibly due to particle segregation within the flow, prior to plume formation. Source radius and initial vertical velocity have the largest effect on maximum plume height, closely followed by initial temperature. Modeled plume heights are between 25 and 47 km, comparable with Plinian eruption columns, highlighting the potential of such events for distributing fine-grained ash over significant areas