A Herschel [C II] Galactic plane survey II: CO-dark H2 in clouds

ABRIDGED: Context: HI and CO large scale surveys of the Milky Way trace the diffuse atomic clouds and the dense shielded regions of molecular hydrogen clouds. However, until recently, we have not had spectrally resolved C+ surveys to characterize the photon dominated interstellar medium, including, the H2 gas without C, the CO-dark H2, in a large sample of clouds. Aims: To use a sparse Galactic plane survey of the 1.9 THz [C II] spectral line from the Herschel Open Time Key Programme, Galactic Observations of Terahertz C+ (GOT C+), to characterize the H2 gas without CO in a statistically significant sample of clouds. Methods: We identify individual clouds in the inner Galaxy by fitting [CII] and CO isotopologue spectra along each line of sight. We combine these with HI spectra, along with excitation models and cloud models of C+, to determine the column densities and fractional mass of CO-dark H2 clouds. Results: We identify 1804 narrow velocity [CII] interstellar cloud components in different categories. About 840 are diffuse molecular clouds with no CO, 510 are transition clouds containing [CII] and 12CO, but no 13CO, and the remainder are dense molecular clouds containing 13CO emission. The CO-dark H2 clouds are concentrated between Galactic radii 3.5 to 7.5 kpc and the column density of the CO-dark H2 layer varies significantly from cloud-to-cloud with an average 9X10^(20) cm-2. These clouds contain a significant fraction of CO-dark H2 mass, varying from ~75% for diffuse molecular clouds to ~20% for dense molecular clouds. Conclusions: We find a significant fraction of the warm molecular ISM gas is invisible in HI and CO, but is detected in [CII]. The fraction of CO-dark H2 is greatest in the diffuse clouds and decreases with increasing total column density, and is lowest in the massive clouds.Comment: 21 pages, 19 figures, accepted for publication in A&A (2014

Evolving Material Porosity on an Additive Manufacturing Simulation with the Generalized Method of Cells

The effect of material porosity on final part distortion and residual stresses in a selective laser sintering manufacturing simulation is presented here. A time-dependent thermomechanical model is used with the open-source FEA software CalculiX. Effective homogenized material properties for Inconel 625 are precomputed using NASAs Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC). The evolving porosity of the material is estimated with each pass of the laser beam during simulation runtime. A comparison with a homogenous model and the evolving model shows that the evolving porous model predicts larger distortions with greater residual stresses

Remarks on "Calculation of the quarkonium spectrum and mbm_{b}, mcm_{c} to order αs4\alpha_{s}^{4}"

In a recent paper, we included two-loop, relativistic one-loop, and second-order relativistic tree level corrections, plus leading nonperturbative contributions, to obtain a calculation of the lower states in the heavy quarkonium spectrum correct up to, and including, O( alpha /sub s//sup 4/) and leading Lambda /sup 4//m/sup 4/ terms. The results were obtained with, in particular, the value of the two- loop static coefficient due to Peter; this has been recently challenged by Schroder. In our previous paper we used Peter's result; in the present one we now give results with Schroder's, as this is likely to be the correct one. The variation is slight as the value of b/sub 1/ is only one among the various O( alpha /sub s//sup 4/) contributions. With Schroder's expression we now have m/sub b/=5001 /sub -66//sup +104/ MeV, m/sub b/(m/sub b//sup 2/)=4454/sub -29//sup +45/ MeV, m/sub c/=1866/sub -133//sup +215/ MeV, m/sub c/(m/sub c //sup 2/)=1542/sub -104//sup +163/ MeV. Moreover, Gamma ( Upsilon to e/sup +/e/sup -/)=1.07+or-0.28 keV(expt=1.320+or-0.04 keV) and the hyperfine splitting is predicted to be M( Upsilon )-M( eta )=47/sub -13//sup +15/ MeV. (10 refs)

Search for grain growth towards the center of L1544

In dense and cold molecular clouds dust grains are surrounded by thick icy mantles. It is however not clear if dust growth and coagulation take place before the switch-on of a protostar. This is an important issue, as the presence of large grains may affect the chemical structure of dense cloud cores, including the dynamically important ionization fraction, and the future evolution of solids in protoplanetary disks. To study this further, we focus on L1544, one of the most centrally concentrated pre-stellar cores on the verge of star formation, and with a well-known physical structure. We observed L1544 at 1.2 and 2 mm using NIKA, a new receiver at the IRAM 30 m telescope, and we used data from the Herschel Space Observatory archive. We find no evidence of grain growth towards the center of L1544 at the available angular resolution. Therefore, we conclude that single dish observations do not allow us to investigate grain growth toward the pre-stellar core L1544 and high sensitivity interferometer observations are needed. We predict that dust grains can grow to 200 $\mu$m in size toward the central ~300 au of L1544. This will imply a dust opacity change by a factor of ~2.5 at 1.2 mm, which can be detected using the Atacama Large Millimeter and submillimeter Array (ALMA) at different wavelengths and with an angular resolution of 2".Comment: 12 pages, 14 figures. Accepted for publication in A&

Striations in the Taurus molecular cloud: Kelvin-Helmholtz instability or MHD waves?

The origin of striations aligned along the local magnetic field direction in the translucent envelope of the Taurus molecular cloud is examined with new observations of 12CO and 13CO J=2-1 emission obtained with the 10~m submillimeter telescope of the Arizona Radio Observatory. These data identify a periodic pattern of excess blue and redshifted emission that is responsible for the striations. For both 12CO and 13CO, spatial variations of the J=2-1 to J=1-0 line ratio are small and are not spatially correlated with the striation locations. A medium comprised of unresolved CO emitting substructures (cells) with a beam area filling factor less than unity at any velocity is required to explain the average line ratios and brightness temperatures. We propose that the striations result from the modulation of velocities and the beam filling factor of the cells as a result of either the Kelvin-Helmholtz instability or magnetosonic waves propagating through the envelope of the Taurus molecular cloud. Both processes are likely common features in molecular clouds that are sub-Alfvenic and may explain low column density, cirrus-like features similarly aligned with the magnetic field observed throughout the interstellar medium in far-infrared surveys of dust emission.Comment: 11 pages, 4 figures. Accepted for publication in MNRA

An Overview of the Coverage with ENC in the Mesoamerican Regional Hydrographic Commission and the Caribbean Sea - MACHC

Hydrographic offices worldwide started the production of Electronic Nautical Charts (ENCs) based on paper nautical charts, generating various designs in their schemes. The design of electronic nautical cartography schemes in the Regional Hydrographic Commissions (RHC) is analyzed, in order to understand the existence of schemes adopted by an entire region, or electronic nautical cartography schemes defined by countries with the capacity to produce them worldwide. The review allows us to know the state of the art in the regional schemes, methodologies and / or parameters used in their definition, and level of compliance with international regulations. In addition, questionnaires were carried out, which were used to acquire complementary information on hydrographic services, and this combined with the analyzes will determine the strengths and weaknesses in the current ENC coverage. Taking maritime safety into account, the investigations were conducive to presenting a methodological proposal for regional standardized ENC schemes. This article has been organized into five points, the first one presents the analysis of the coverage of current electronic charts, taking into account the metadata of the coverage used by the different Regional Hydrographic Commissions. In the second, a survey carried out to several Hydrographic Services is presented, including: the review and registration of relevant aspects of the ENC schemes at the RHCs level, as well as the socialization and issuance of the survey to the RENC Member States. IC-ENC; in the third, the results of the analysis of the information collected on the designs of the current ENC schemes in the RHCs that responded to the survey; the fourth presents the strengths and weaknesses found in specific cases of the current ENC schemes; and finally, in the fifth, the work in progress by the subgroup for the ENC Regional Scheme in the MACHC is evidenced.Los servicios hidrográficos de todo el mundo iniciaron la producción de Cartas Náuticas Electrónicas (ENCs) basadas en las cartas náuticas de papel, generando varios diseños de esquemas. Se analiza los diseños de esquemas de cartografía náutica electrónica en las Comisiones Hidrográficas Regionales (CHR) para conocer la existencia de esquemas adoptados por una región entera, o esquemas de cartografía náutica electrónica definidos por países con la capacidad para producirlos de manera global. Este estudio permite conocer los últimos avances en los esquemas regionales, las metodologías y/o parámetros utilizados en su definición y su nivel de cumplimiento de la normativa internacional. Además, se realizaron cuestionarios que se usaron para adquirir información complementaria sobre servicios hidrográficos, y esto combinado con los análisis determinará los puntos fuertes y débiles de la cobertura ENC actual. Teniendo en cuenta la seguridad marítima, las investigaciones fueron favorables a presentar una propuesta metodológica para esquemas ENC regionales normalizados. El artículo está organizado en cinco puntos, el primero presenta el análisis de la cobertura de las cartas electrónicas actuales, teniendo en cuenta los metadatos de la cobertura usada por las diferentes Comisiones Hidrográficas Regionales. En el segundo se presenta una encuesta realizada a varios Servicios Hidrográficos, incluyendo: revisión y registro de aspectos relevantes de los esquemas ENC al nivel de las CHRs, además de la socialización y remisión de la encuesta a los Estados Miembros del RENC IC-ENC; en el tercero, los resultados del análisis de la información recogida sobre los diseños de los esquemas ENC actuales en las CHRs que respondieron a la encuesta; el cuarto presenta los puntos fuertes y débiles encontrados en casos específicos de esquemas ENC actuales; y finalmente en el quinto se evidencia el trabajo en curso por el subgrupo para el Esquema Regional de ENC en la MACHC.Les Services hydrographiques du monde entier ont commencé à produire des cartes électroniques de navigation (ENC) à partir des cartes marines papier, générant ainsi divers modèles de schémas. La conception des schémas de cartes électroniques de navigation dans les Commissions hydrographiques régionales (CHR) est analysée, afin de connaître l'existence de schémas adoptés par une région entière, ou de schémas de cartes de navigation électroniques définis par des pays ayant la capacité de les produire dans le monde entier. Cette étude nous permet de connaître les dernières avancées des schémas régionaux, les méthodologies et/ou les paramètres utilisés dans leur définition, et leur niveau de conformité avec les réglementations internationales. En outre, des questionnaires ont été réalisés et ont permis d'obtenir des informations complémentaires sur les services hydrographiques, ce qui, combiné aux analyses, permettra de déterminer les forces et les faiblesses de la couverture actuelle en ENC. En tenant compte de la sécurité maritime, les investigations ont permis de présenter une proposition méthodologique pour des schémas ENC régionaux normalisés. Cet article s'articule autour de cinq points : le premier point présente l'analyse de la couverture des cartes électroniques actuelles, en tenant compte des métadonnées de couverture utilisées par les différentes Commissions hydrographiques régionales. Au second point, une enquête réalisée auprès de plusieurs Services hydrographiques est présentée, comprenant : l'examen et l'enregistrement des aspects pertinents des schémas ENC au niveau des CHR, ainsi que la socialisation et la diffusion de l’enquête auprès des Etats membres du RENC IC-ENC ; au troisième point, les résultats de l'analyse des informations recueillies sur la conception des schémas ENC actuels dans les CHR qui ont répondu à l’enquête ; le quatrième point présente les forces et les faiblesses constatées dans des cas spécifiques de schémas ENC actuels ; et enfin le cinquième point met en évidence le travail en cours du sous-groupe pour le schéma régional d'ENC au sein de la CHMAC

Ionized gas at the edge of the Central Molecular Zone

To determine the properties of the ionized gas at the edge of the CMZ near Sgr E we observed a small portion of the edge of the CMZ near Sgr E with spectrally resolved [C II] 158 micron and [N II] 205 micron fine structure lines at six positions with the GREAT instrument on SOFIA and in [C II] using Herschel HIFI on-the-fly strip maps. We use the [N II] spectra along with a radiative transfer model to calculate the electron density of the gas and the [C II] maps to illuminate the morphology of the ionized gas and model the column density of CO-dark H2. We detect two [C II] and [N II] velocity components, one along the line of sight to a CO molecular cloud at -207 km/s associated with Sgr E and the other at -174 km/s outside the edge of another CO cloud. From the [N II] emission we find that the average electron density is in the range of about 5 to 25 cm{-3} for these features. This electron density is much higher than that of the warm ionized medium in the disk. The column density of the CO-dark H$_2$ layer in the -207 km/s cloud is about 1-2X10{21} cm{-2} in agreement with theoretical models. The CMZ extends further out in Galactic radius by 7 to 14 pc in ionized gas than it does in molecular gas traced by CO. The edge of the CMZ likely contains dense hot ionized gas surrounding the neutral molecular material. The high fractional abundance of N+ and high electron density require an intense EUV field with a photon flux of order 1e6 to 1e7 photons cm{-2} s{-1}, and/or efficient proton charge exchange with nitrogen, at temperatures of order 1e4 K, and/or a large flux of X-rays. Sgr E is a region of massive star formation which are a potential sources of the EUV radiation that can ionize the gas. In addition X-ray sources and the diffuse X-ray emission in the CMZ are candidates for ionizing nitrogen.Comment: 12 pages, 9 figure

Glitch-free discretely programmable clock generation on chip

In this paper we describe a solution for a glitch-free discretely programmable clock generation unit (DPGC). The scheme is compatible with a GALS communication scheme in the sense that clock gating and clock pausing are possible. Besides, the proposed scheme does not require waiting for a new clock as the frequency change is seen as almost instantaneously. A prototype has been designed for a 0.13µm triple-well CMOS process technology to also study the properties of the scheme with respect to voltage scaling

Technology exploration for adaptive power and frequency scaling in 90nm CMOS

In this paper we examine the expectations and limitations of design technologies such as adaptive voltage scaling (AVS) and adaptive body biasing (ABB) in a modern deep sub-micron process. To serve this purpose, a set of ring oscillators was fabricated in a 90nm triple-well CMOS technology. The analysis hereby presented is based on two ring oscillators running at 822MHz and 93MHz, respectively. Measurement results indicate that it is possible to reach 13.8x power savings by 3.4x frequency downscaling using AVS, ±11% power and ±8% frequency tuning at nominal conditions using ABB only, 22x power savings with 5x frequency downscaling by combining AVS and ABB, as well as 22x leakage reduction