Fragmentary Structure Research Articles

Study of Structure and Small-Scale Fragmentation in TMC-1

Large-scale C(sup 18)O maps show that the Taurus molecular cloud 1 (TMC-1) has numerous cores located along a ridge which extends about 12 minutes by at least 35 minutes. The cores traced by C(sup 18)O are about a few arcminutes (0.1-0.2 pc) in extent, typically contain about 0.5-3 solar mass, and are probably gravitationally bound. We present a detailed study of the small-scale fragmentary structure of one of these cores, called core D, within TMC-1 using very high spectral and spatial resolution maps of CCS and CS. The CCS lines are excellent tracers for investigating the density, temperature, and velocity structure in dense cores. The high spectral resolution, 0.008 km /s, data consist mainly of single-dish, Nyquist-sampled maps of CCS at 22 GHz with 45 sec spatial resolution taken with NASA's 70 m DSN antenna at Goldstone. The high spatial resolution spectral line maps were made with the Very Large Array (9 sec resolution) at 22 GHz and with the OVRO millimeter array in CCS and CS at 93 GHz and 98 GHz, respectively, with 6 sec resolution. These maps are supplemented with single-dish observations of CCS and CC(sup 34)S spectra at 33 GHz using a NASA 34 m DSN antenna, CCS 93 GHz, C(sup 34)S (2-1), and C(sup 18)O (1-0) single-dish observations made with the AT&T Bell Laboratories 7 m antenna. Our high spectral and spatial CCS and CS maps show that core D is highly fragmented. The single-dish CCS observations map out several clumps which range in size from approx. 45 sec to 90 sec (0.03-0.06 pc). These clumps have very narrow intrinsic line widths, 0.11-0.25 km/s, slightly larger than the thermal line width for CCS at 10 K, and masses about 0.03-0.2 solar mass. Interferometer observations of some of these clumps show that they have considerable additional internal structure, consisting of several condensations ranging in size from approx. 10 sec- 30 sec (0.007-0.021 pc), also with narrow line widths. The mass of these smallest fragments is of order 0.01 solar mass. These small-scale structures traced by CCS appear to be gravitationally unbound by a large factor. Most of these objects have masses that fall below those of the putative proto-brown dwarfs (approx. less than 0.1 solar mass). The presence of many small gravitationally unbound clumps suggests that fragmentation mechanisms other than a purely Jeans gravitational instability may be important for the dynamics of these cold dense cores.

Variational method for calculating the anharmonic vibrations of polyatomic molecules using a combined morse-anharmonic basis taking into account the fragmentary structure of molecules

A method of variational solution of anharmonic vibration problems using a mixed Morse—anharmonic basis is proposed. The basis functions are the products of the Morse oscillator eigenfunctions for vibrations of peripheral bonds, the harmonic oscillator eigenfunctions for almost harmonic skeletal and deformation vibrations, and the anharmonic basis functions for essentially anharmonic skeletal and deformation vibrations. The anharmonic basis wave functions are taken as a linear combination of the Morse and harmonic oscillator eigenfunctions. The introduction of the combined Morse—anharmonic functions allows one to factorize the solution of a problem into a series of individual blocks according to the fragmentary structure of molecules.

The mechanisms of phase transformation in diffusion couples of the Cu-Si system

The mechanisms of diffusional transformation in a series of couples belonging to the Cu-Si system were studied. The couples consist of elemental materials or intermediate phases. For the Cu-Si couple it was found that the diffusion layer comprises the Cu 3Si (η″) phase solely. For the Cu 5Si(γ)-Si couple the diffusion zone contains the η″-phase subdivided into two morphologically different parts. In the cu-η″ and Cu-γ couples, formation of a narrow reaction zone with fragmentary structure took place. Models for processes occurring in each of the couples during diffusional annealing were put forward. It was shown that the dual microstructure of the η″-phase in the γ-Si couple can be attributed to different formation mechanisms on either side of the growing phases.

On the evolution of a system of intergalactic clouds

The presence of L a -forests in the spectra of quasars is considered as proof of the fragmentary structure of the intergalactic medium. The masses of the “clumps” (of clouds) will increase as they merge together. Once the radial concentration of neutral hydrogen in a cloud attains its critical value, star formation begins, and the cloud turns into a galaxy. Certain physical properties of clouds are considered and a new approach to the investigation of the evolution of systems of clouds is proposed.

Shock propagation in a turbulent cloud

view Abstract Citations (12) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Shock Propagation in a Turbulent Cloud Kimura, Toshiya ; Tosa, Makoto Abstract A 2D hydrodynamical simulation is used to investigate the effect of internal turbulence of molecular clouds on the shock waves propagating in the clouds. A model of a turbulent molecular cloud dynamically interacting with the surrounding H II region, which strongly compresses the cloud from the surface, is considered. A shock wave is generated from the cloud surface and propagates into the cloud, where a supersonic random velocity field and large density fluctuation are present. The turbulence strongly affects the propagation of the shock wave to cause a very complex and fragmentary structure in the shocked gas. Behind the distorted shock, many high-density gas clumps are formed. It is argued that the interaction of the internal turbulence of a molecular cloud and a shock wave will play an important role in the formation of high-density gas clumps and stars when a molecular cloud interacts with an expanding H II region. Publication: The Astrophysical Journal Pub Date: April 1993 DOI: 10.1086/172463 Bibcode: 1993ApJ...406..512K Keywords: Hydrodynamic Equations; Molecular Clouds; Shock Wave Interaction; Shock Wave Propagation; Turbulence Effects; Computational Astrophysics; H Ii Regions; Velocity Distribution; Astrophysics; HYDRODYNAMICS; ISM: CLOUDS; ISM: KINEMATICS AND DYNAMICS; ISM: MOLECULES; SHOCK WAVES; TURBULENCE full text sources ADS |

The properties of dense molecular cloud cores

Abstract Results of recent studies of dense interstellar molecular clouds are discussed. Observations in molecular lines excited at high densities revealed dense cores in many clouds with gas densities n ∼ (0.3 ÷ 3) × 105 cm−9, kinetic temperatures Tk ∼ 10 ÷ 100 K, masses (0.3 ÷ 104) M⊙. The cores are close to the virial equilibrium. There are correlations between velocity dispersion and size, between mass and size and some others similar to those found for less dense clouds but with different coefficients. Implicit indications of fragmentary structure on 40’ scales are obtained.

Pulsed dye laser diagnostics of vacuum arc cathode spots

The ignition and arc phases of vacuum arcs were investigated using differential dye laser absorption photography with simultaneous high spatial (micrometer) and temporal (nanosecond) resolution. The discharge duration was 800 ns, the current 50-150 A, the electrode material copper, and the cathode-anode distance less than 50 mu m. A 0.4 ns laser pulse (tunable, gamma =480-530 nm) was used to obtain momentary absorption photographs of the cathode region. During ignition, an optically thick anode plasma expanded toward the cathode, decaying within 25 ns after bridging the electrode gap. In the arc phase, a fragmentary structure of the cathode spots was observed in situ for the first time. The microspots have a characteristic size of 5-10 mu m. They appear and disappear on a nanosecond time scale. The plasma density of the microspots was estimated to be greater than (3-6)*10/sup 26/ m/sup -3/. >

Fragmentary crystal structures of high-T c superconductors

A description of high-Tc structures in the form of different fragment packets allows us to identify theoretically the structures of the same type. It is shown that superconductivity in such substances is connected with the peculiarities of their fragmentary structure.

Fragmentary structure in the L1551 molecular outflow

We have obtained a high resolution map of the 12CO J=3—2 emission in the vicinity of HH102 in the L1551 molecular outflow. The data reveal the presence of several bright clumps within the thin shell of low-velocity blue-shifted outflowing gas. There is evidence for further fragmentation in the clumps, as signified by the high derived excitation temperatures and low beam-filling factors. The region of peculiarly energetic activity associated with HH102 coincides with the projected location of impact of a radio jet from IRS5 with the dense ambient gas surrounding the outflow cavity.

Fragmentary structure in the L1551 molecular outflow

We have obtained a high resolution map of the 12CO J=3—2 emission in the vicinity of HH102 in the L1551 molecular outflow. The data reveal the presence of several bright clumps within the thin shell of low-velocity blue-shifted outflowing gas. There is evidence for further fragmentation in the clumps, as signified by the high derived excitation temperatures and low beam-filling factors. The region of peculiarly energetic activity associated with HH102 coincides with the projected location of impact of a radio jet from IRS5 with the dense ambient gas surrounding the outflow cavity.

Application of the solid phase capillary activity factor to predict phase distribution

It is known that due to the free-energy minimization principle, chemically nonreacting substances are segregated on sintering and form a fragmentary structure of the sintered material. To judge the segragation ability of substances, this communication offers a comparative factor to assess the capillary activity of solid phases.

The hyperfine structure of the predissociated stateB?0+ of IBr

TheB′0+ state of IBr is strongly predissociated which leads to fragmentary rovibrational structure and level broadening. Using Doppler free laser polarization spectroscopy, the hyperfine structure of the sharpest rotational lines of several band fragments in theB′−X system was investigated for the first time. The hyperfine analysis yields a strong vibrational dependence of the nuclear quadrupole interaction for Br and the nuclear spin-rotation interaction for I and Br.

Structure and properties of dense periclase refractories prepared from laminated granules

On the basis of laminated granules we prepared dense periclase refractories with a higher thermal-shock resistance than that of ordinary articles prepared by sintering solid granules. The technical properties are determined by the degree of development of a fragmentary structure which depends on the size of the granules, the composition of their outside layer, and the composition of the bonding mass in the batch.

Sintering and some problems of composite materials in the Al2O3-Al2TiO5 system

The sintering, mechanical, and thermophysical characteristics of composites of Al2O3 and Al2TiO5 and the connection between these parameters and the microstructure and thermal-shock resistance have been studied. Extremal properties have been found in the compositions containing 30–50% of Al2TiO5. The excellent thermal-shock resistance of the composites is the result of the fragmentary structure which increases the destructive energy of the specimen under thermal-shock. The anomalous increase in the high-temperature ultimate strength of the composites containing 30–50% of Al2TiO5 in the 20–1200°C is demonstrated; this is the result of the separation of the decomposition products of Al2TiO5 along the crystal boundaries of the refractory base and of the elastic-stressed state which arises.

Periclase refractories after testing in high-temperature equipment

The periclase materials made from pure MgO obtained from a coarse-grained batch and characterized by a fragmented structure have been tested in plasma equipment at temperatures above 2000°C. The articles have satisfactory resistance in the test conditions, have a stable structure, and do not react with alkali-metal additives. The penetration of articles by alkalis and the loss by them of their electroinsulation properties were quite insignificant after the tests. This makes it possible to recommend the articles of a fragmentary structure made from pure MgO for more prolonged testing.

The Fragmentary Class Structure

The Fragmentary Class Structure

Book Review: Economy and Class Structure, The Fragmentary Class Structure

Book Review: Economy and Class Structure, The Fragmentary Class Structure

Book Reviews: Wittgenstein and Scientific Knowledge, Racial Disadvantage in Britain, Language and Materialism: Developments in Semiology and the Theory of the Subject, Sabotage: A Study in Industrial Conflict, Rationality, Education and the Social Organization of Knowledge, Aspects of Illness, Common Factors/Vulgar Factions, Ruling Class, Ruling Culture: Studies of Conflict, Power and Hegemony in Australian Life, The Fragmentary Class Structure, Rural

Book Reviews: Wittgenstein and Scientific Knowledge, Racial Disadvantage in Britain, Language and Materialism: Developments in Semiology and the Theory of the Subject, Sabotage: A Study in Industrial Conflict, Rationality, Education and the Social Organization of Knowledge, Aspects of Illness, Common Factors/Vulgar Factions, Ruling Class, Ruling Culture: Studies of Conflict, Power and Hegemony in Australian Life, The Fragmentary Class Structure, Rural

The Children's Hearing System: Part 1. The Limits to Legislative action

Abstract In April 1971 the fragmentary and topsy-like juvenile court structure in Scotland gave way to a more homogeneous system located at the interstices of law-enforcement and social work. The reforms consequent upon the Social Work (Scotland) Act 1968 have been described in detail elsewhere.1 Briefly they involve taking the management of juvenile offenders, with certain exceptions and subject to specific safeguards, out of the criminal courts and vesting it in a system, formally characterised by voluntarism, informality, and a commitment to treatment. At the apex of the system is a tribunal (the children's hearing) presided over by laymen (and women), and concerned not with questions of guilt or innocence, but with issues of treatment and disposal. Reference to this tribunal is controlled by an independent local authority official, known as the reporter,2 and is to rest solely on “the needs of the individual child.” In line with this requirement the hearing's unit of activity is the child,3 or more ac...

The effect of growth conditions on the structural and electrical properties of the SiGe heteroepitaxial system

Abstract The present study is a logical continuation of previous investigations of the SiGe heteroepitaxial system (HES). The primary object of this work was to define the conditions for the formation of fragmentary structure (FS) in the SiSi e Ge system, where Si e designates a homoepitaxial silicon film. It is shown that, after the Ge film deposition, decrease of the HES cooling rate to 2 °C min −1 makes it possible to obtain the HES without FS for a Ge film thickness d of approximately 3 μm and to improve the heterodiode I–V characteristics. The distribution of defects through the film thickness has also been studied.