With digital equipment becoming increasingly networked, either on wired or wireless networks, for personal and professional use alike, distributed software systems have become a crucial element in information and communications technologies. The study of these systems forms the core of the ARLES' work, which is specifically concerned with defining new system software architectures, based on the use of emerging networking technologies. In this context, we concentrate on the study of distributed systems which bring to life the vision of ubiquitous computing systems, also known as ambient intelligence.

반도체 공정 overview

Positional, structural, and dynamical parameters for all dwarf galaxies in and around the Local Group are presented, and various aspects of our observational understanding of this volume-limited sample are discussed. Over 100 nearby galaxies that have distance estimates reliably placing them within 3 Mpc of the Sun are identified. This distance threshold samples dwarfs in a large range of environments, from the satellite systems of the MW and M31, to the quasi-isolated dwarfs in the outer regions of the Local Group, to the numerous isolated galaxies that are found in its surroundings. It extends to, but does not include, the galaxies associated with the next nearest groups, such as Maffei, Sculptor, and IC 342. Our basic knowledge of this important galactic subset and their resolved stellar populations will continue to improve dramatically over the coming years with existing and future observational capabilities, and they will continue to provide the most detailed information available on numerous aspects of dwarf galaxy formation and evolution. Basic observational parameters, such as distances, velocities, magnitudes, mean metallicities, as well as structural and dynamical characteristics, are collated, homogenized (as far as possible), and presented in tables that will be continually updated to provide a convenient and current online resource. As well as discussing the provenance of the tabulated values and possible uncertainties affecting their usage, the membership and spatial extent of the MW sub-group, M31 sub-group, and the Local Group are explored. The morphological diversity of the entire sample and notable sub-groups is discussed, and timescales are derived for the Local Group members in the context of their orbital/interaction histories. The scaling relations and mean stellar metallicity trends defined by the dwarfs are presented, and the origin of a possible "floor" in central surface brightness (and, more speculatively, stellar mean metallicity) at faint magnitudes is considered.

https://iopscience.iop.org/article/10.1088/0004-6256/144/1/4/pdf

The observed properties of dwarf galaxies in and around the local group

The James Webb Space Telescope (JWST) is a large (6.6 m), cold (<50 K), infrared (IR)-optimized space observatory that will be launched early in the next decade into orbit around the second Earth–Sun Lagrange point. The observatory will have four instruments: a near-IR camera, a near-IR multiobject spectrograph, and a tunable filter imager will cover the wavelength range, 0.6 < ; < 5.0 μ m, while the mid-IR instrument will do both imaging and spectroscopy from 5.0 < ; < 29 μ m. The JWST science goals are divided into four themes. The key objective of The End of the Dark Ages: First Light and Reionization theme is to identify the first luminous sources to form and to determine the ionization history of the early universe. The key objective of The Assembly of Galaxies theme is to determine how galaxies and the dark matter, gas, stars, metals, morphological structures, and active nuclei within them evolved from the epoch of reionization to the present day. The key objective of The Birth of Stars and Protoplanetary Systems theme is to unravel the birth and early evolution of stars, from infall on to dust-enshrouded protostars to the genesis of planetary systems. The key objective of the Planetary Systems and the Origins of Life theme is to determine the physical and chemical properties of planetary systems including our own, and investigate the potential for the origins of life in those systems. Within these themes and objectives, we have derived representative astronomical observations. To enable these observations, JWST consists of a telescope, an instrument package, a spacecraft, and a sunshield. The telescope consists of 18 beryllium segments, some of which are deployed. The segments will be brought into optical alignment on-orbit through a process of periodic wavefront sensing and control. The instrument package contains the four science instruments and a fine guidance sensor. The spacecraft provides pointing, orbit maintenance, and communications. The sunshield provides passive thermal control. The JWST operations plan is based on that used for previous space observatories, and the majority of JWST observing time will be allocated to the international astronomical community through annual peer-reviewed proposal opportunities.

/pdf/the-james-webb-space-telescope-34a78559id.pdf

The James Webb Space Telescope

Cosmology at low frequencies: The 21 cm transition and the high-redshift Universe

Black hole accretion flows can be divided into two broad classes: cold and hot. Whereas cold accretion flows consist of cool optically thick gas and are found at relatively high mass accretion rates, hot accretion flows, the topic of this review, are virially hot and optically thin, and occur at lower mass accretion rates. They are described by accretion solutions such as the advection-dominated accretion flow and luminous hot accretion flow. Because of energy advection, the radiative efficiency of these flows is in general lower than that of a standard thin accretion disk. Moreover, the efficiency decreases with decreasing mass accretion rate. Observations show that hot accretion flows are associated with jets. In addition, theoretical arguments suggest that hot flows should produce strong winds. Hot accretion flows are believed to be present in low-luminosity active galactic nuclei and in black hole X-ray binaries in the hard and quiescent states. The prototype is Sgr A*, the ultralow-luminosity supermassive black hole at our Galactic center. The jet, wind, and radiation from a supermassive black hole with a hot accretion flow can interact with the external interstellar medium and modify the evolution of the host galaxy.

Hot Accretion Flows Around Black Holes

The quasi-steady structure of supercritical accretion flows around a black hole is studied based on two-dimensional radiation-hydrodynamic (2D-RHD) simulations. The supercritical flow is composed of two parts: the disk region and the outflow regions above and below the disk. Within the disk region the circular motion and the patchy density structure are observed, which is caused by Kelvin-Helmholtz instability and probably by convection. The mass accretion rate decreases inward, roughly in proportion to the radius, and the remaining part of the disk material leaves the disk to form the outflow because of the strong radiation pressure force. We confirm that photon trapping plays an important role within the disk. Thus, matter can fall onto the black hole at a rate exceeding the Eddington rate. The emission is highly anisotropic and moderately collimated so that the apparent luminosity can exceed the Eddington luminosity by a factor of a few in the face-on view. The mass accretion rate onto the black hole increases with the absorption opacity (metallicity) of the accreting matter. This implies that the black hole tends to grow faster in metal-rich regions, such as in starburst galaxies or star-forming regions.

https://iopscience.iop.org/article/10.1086/430728/pdf

Supercritical Accretion Flows around Black Holes: Two-dimensional, Radiation Pressure-dominated Disks with Photon Trapping

The quasi-steady structure of super-critical accretion flows around a black hole is studied based on the two-dimensional radiation-hydrodynamical (2D-RHD) simulations. The super-critical flow is composed of two parts: the disk region and the outflow regions above and below the disk. Within the disk region the circular motion as well as the patchy density structure are observed, which is caused by Kelvin-Helmholtz instability and probably by convection. The mass-accretion rate decreases inward, roughly in proportion to the radius, and the remaining part of the disk material leaves the disk to form outflow because of strong radiation pressure force. We confirm that photon trapping plays an important role within the disk. Thus, matter can fall onto the black hole at a rate exceeding the Eddington rate. The emission is highly anisotropic and moderately collimated so that the apparent luminosity can exceed the Eddington luminosity by a factor of a few in the face-on view. The mass-accretion rate onto the black hole increases with increase of the absorption opacity (metalicity) of the accreting matter. This implies that the black hole tends to grow up faster in the metal rich regions as in starburst galaxies or star-forming regions.

https://arxiv.org/pdf/astro-ph/0504168.pdf

Super-critical Accretion Flows around Black Holes: Two-dimensional, Radiation-pressure-dominated Disks with Photon-trapping

Black-hole accretion systems are known to possess several distinct modes (or spectral states), such as low/hard state and high/soft state. Since the dynamics of the corresponding flows is distinct, theoretical models were separately considered for each state. We here propose a unified model based on our new, global, two-dimensional radiation-magnetohydrodynamic simulations. By controlling a density normalization we could for the first time reproduce three distinct modes of accretion flow and outflow with one numerical code. When the density is large (model A), a geometrically thick, very luminous disk forms, in which photon trapping takes place. When the density is moderate (model B), the accreting gas can effectively be cooled by emitting radiation, thus generating a thin disk, i.e., a soft-state disk. When the density is too low for radiative cooling to be important (model C), a disk becomes hot, thick, and faint; i.e., a hard-state disk. The magnetic energy is amplified within the disk up to about twice, 30%, and 20% of the gas energy in models A, B, and C, respectively. Notably, the disk outflows with helical magnetic fields, which are driven either by radiation-pressure force or magnetic-pressure force, are ubiquitous in any accretion modes. Finally, our simulations are consistent with the phenomenological ˛-viscosity prescription; that is, the disk viscosity is proportional to the pressure.

/pdf/global-radiation-magnetohydrodynamic-simulations-of-black-4a61du1p1r.pdf

Global Radiation-Magnetohydrodynamic Simulations of Black-Hole Accretion Flow and Outflow: Unified Model of Three States

Supernova (SN)-driven pregalactic outflows may be an efficient mechanism for distributing the product of stellar nucleosynthesis over large cosmological volumes prior to the reionization epoch. Here, we present results from three-dimensional numerical simulations of the dynamics of SN-driven bubbles as they propagate through and escape the grasp of subgalactic halos with masses M = 108 h-1 M☉ at redshift z = 9. Halos in this mass range are characterized by very short dynamical timescales (and even shorter gas cooling times) and may therefore form stars in a rapid but intense burst before SN "feedback" quenches further star formation. The hydrodynamic simulations use a nested grid method to follow the evolution of explosive multi-SN events operating on the characteristic timescale of a few times 107 yr, the lifetime of massive stars. The results confirm that if the star formation efficiency of subgalactic halos is 10%, a significant fraction of the halo gas will be lifted out of the potential well ("blow-away"), shock the intergalactic medium, and pollute it with metal-enriched material, a scenario recently advocated by Madau, Ferrara, & Rees. The volume filling factor of the ejecta is of order unity. Depending on the stellar distribution, we find that less than 30% of the available SN energy gets converted into kinetic energy of the blown-away material, the remainder being radiated away. It appears that mechanical feedback is less efficient than expected from simple energetic arguments, as off-nuclear SN explosions drive inward-propagating shocks that tend to collect and pile up cold gas in the central regions of the host halo. Low-mass galaxies at early epochs may survive multiple SN events and continue forming stars.

Early Metal Enrichment by Pregalactic Outflows. II. Three-dimensional Simulations of Blow-Away

We present results from three-dimensional numerical simulations of the dynamics of SN-driven bubbles as they propagate through and escape the grasp of subgalactic halos with masses M ~ 10^8 Msun at redshift z=9. The hydrodynamic simulations use a nested grid method to follow the evolution of explosive multi-SN events operating on the characteristic timescale of a few x 10^7 yr, the lifetime of massive stars. The results confirm that, if the star formation efficiency of subgalactic halos is close to 10%, a significant fraction of the halo gas will be lifted out of the potential well (`blow-away'), shock the intergalactic medium, and pollute it with metal-enriched material, a scenario recently advocated by Madau, Ferrara & Rees (2001). The volume filling factor of the ejecta is close to unity. Depending on the stellar distribution, we find that less than 30% of the available SN energy is converted into kinetic energy of the blown away material, the remainder being radiated away. It appears that mechanical feedback is less efficient than expected from simple energetic arguments, as off-nuclear SN explosions drive inward-propagating shocks that tend to collect and pile up cold gas in the central regions of the host halo. Low-mass galaxies at early epochs may survive multiple SN events and continue forming stars.

Masao Mori

Papers

Supercritical Accretion Flows around Black Holes: Two-dimensional, Radiation Pressure-dominated Disks with Photon Trapping

Super-critical Accretion Flows around Black Holes: Two-dimensional, Radiation-pressure-dominated Disks with Photon-trapping

Global Radiation-Magnetohydrodynamic Simulations of Black-Hole Accretion Flow and Outflow: Unified Model of Three States

Early Metal Enrichment by Pregalactic Outflows. II. Three-dimensional Simulations of Blow-Away

Early Metal Enrichment by Pregalactic Outflows: II. Simulations of Blow-away