Super star clusters and their emission lines

Super star clusters (SSCs) are young massive objects typically observed in starburst galaxies. They consist of millions of stars occupying volumes only several parsecs across. Recent infrared observations of SSCs reveal strong emission lines with moderately supersonic widths (FWHM ~ 50 – 100 km s−1). An additional, much broader and weaker line component is present in some cases. Using 2D and 3D hydrodynamic simulations, we study models of SSCs in the so-called bimodal regime, which occurs if the stellar density inside the cluster exceeds a certain limit. We confirm the existence of the bimodal solution predicted analytically and suggest an explanation for double-component line profiles: the narrow component is formed close to the cluster center by repressurizing shocks compressing the rarefied gas cooled down due to the thermal instability into dense cold clumps, while the broad component is created by the wind, which cools down at a certain distance from the cluster.

Structural Properties of Strontium Vanadate Glasses

Structural studies of the strontium vanadate glasses of compositions xV2O5–(100 − x)SrO are reported. X-ray diffractograms, density, and oxygen molar volume, etc., of the glasses show that single-phase and homogeneous glasses were obtained in the composition domain x = 50 to 90 mol%. The network structure for the glass compositions with 90 and 80 mol% V2O5 is built up of the VO5 polyhedra, while the other glass compositions consist of the VO4 polyhedra. Density and glass transition temperature are observed to decrease with an increase in the V2O5 content. The magnetic susceptibility of the glasses shows an increase of concentration of the reduced V4+ ion with the increase of vanadium oxide content in the compositions. The well-resolved electron spin resonance structure observed for the glass composition with 50 mol% V2O5 gradually becomes poor and reduces to a single component line, which has been attributed to the increase of the hopping rate of charge carriers with the increase of the V2O5 content in the compositions.

Robot Technology in the Shipyard Production Environment

This paper presents the current status of robot technology in the shipyard production environment. The focus is on a case study in which a computer-integrated and robotized web and component line is presented. This production line will be fully operational by mid-1995. An overview has also been included of the most relevant technologies with regard to robot production in the shipbuilding industry, and how these technologies contributed to the introduction of robots in shipyards. The need for integrating the robots with the rest of the shipyard's material flow, computer systems and organization is discussed, followed by a brief survey of emerging technologies which may be useful for the shipbuilding community.

Does Attention Have Different Effects on Line Orientation and Line Arrangement Discrimination?

Visual search and texture segregation studies have led to the inference that stimuli differing in the orientation of their component line segments can be distinguished without focal attention, whereas stimuli that differ only in the arrangement of line segments cannot. In most of this research, the locus of attention has not been explicitly manipulated. In the first experiment presented here, attention was directed to a relevant peripheral target by a cue presented near the target location or at the fovea. Effects of attention on orientation discrimination were assessed in a two-alternative forced-choice task with targets that were either: (1) lines that slanted obliquely to the right or left, or were horizontal or vertical, or (2) Y-like targets that had a short arm leading obliquely right or left of a vertical line. In some groups, a four-alternative forced-choice test with lines at 0°, 45°, 90°, and 135° orientations was used. Discrimination of these targets (i.e. targets that differ in the orientation of component line segments) was only minimally facilitated as the time between the onset of the valid cue and the onset of the target (cue-target stimulus onset asynchrony, SOA) was increased from 0 or 17 msec to 267 msec. In contrast, discrimination of targets that did not differ in the orientation of component line segments but differed in line arrangement (T-like characters), was greatly facilitated by longer cue-target SOAs. In Experiment 2, a cue misdirected attention on 20% of the trials. A decrement occurred on incorrectly cued trials in comparison to correctly cued trials for both types of stimuli used (lines and Ts). The results from these experiments suggest that discrimination of line orientation benefits less from focal attention than does discrimination of line arrangement, but that both discriminations suffer when attention must be disengaged from an irrelevant spatial location.