System Concepts for the Scout Explorer

NASA\u27s Explorer program is being expanded to include a series of Scout-class science missions. These small spacecraft will be supported by a Standard System, including a spacecraft bus and a transportable ground station. The system concept is being developed in anticipation of an experiment solicitation in 1988. The spacecraft will be a Sun, vertical and star pointer, momentum stabilized, with S-band communications direct to ground stations. The transportable ground stations allow Principal Investigators to assume complete control of the spacecraft. The Standard System is optional to each mission and may be used in part, in total, or not at all

Interactive access and management for four-dimensional environmental data sets using McIDAS

Significant accomplishments in the past year are presented and include the following: (1) enhancements to VIS-5D; (2) Implementation of the VIS AD System; and (3) numerical modeling applications. Focus of current research and plans for next year in the following areas are briefly discussed: (1) continued development and application of the VIS-AD system; (2) further enhancements to VIS-5D; and (3) plans for modeling applications

Management and display of four-dimensional environmental data sets using McIDAS

Over the past four years, great strides have been made in the areas of data management and display of 4-D meteorological data sets. A survey was conducted of available and planned 4-D meteorological data sources. The data types were evaluated for their impact on the data management and display system. The requirements were analyzed for data base management generated by the 4-D data display system. The suitability of the existing data base management procedures and file structure were evaluated in light of the new requirements. Where needed, new data base management tools and file procedures were designed and implemented. The quality of the basic 4-D data sets was assured. The interpolation and extrapolation techniques of the 4-D data were investigated. The 4-D data from various sources were combined to make a uniform and consistent data set for display purposes. Data display software was designed to create abstract line graphic 3-D displays. Realistic shaded 3-D displays were created. Animation routines for these displays were developed in order to produce a dynamic 4-D presentation. A prototype dynamic color stereo workstation was implemented. A computer functional design specification was produced based on interactive studies and user feedback

The VIS-AD data model: Integrating metadata and polymorphic display with a scientific programming language

The VIS-AD data model integrates metadata about the precision of values, including missing data indicators and the way that arrays sample continuous functions, with the data objects of a scientific programming language. The data objects of this data model form a lattice, ordered by the precision with which they approximate mathematical objects. We define a similar lattice of displays and study visualization processes as functions from data lattices to display lattices. Such functions can be applied to visualize data objects of all data types and are thus polymorphic

Hubble Space Telescope Imaging of the Ultracompact Blue Dwarf Galaxy HS 0822+3542: An Assembling Galaxy in a Local Void?

We present deep U, narrow-V, and I-band images of the ultracompact blue dwarf galaxy HS 0822+3542, obtained with the Advanced Camera for Surveys / High Resolution Channel of the Hubble Space Telescope. This object is extremely metal-poor (12 + log(O/H) = 7.45) and resides in a nearby void. The images resolve it into two physically separate components that were previously described as star clusters in a single galaxy. The primary component is only \~100 pc in maximum extent, and consists of starburst region surrounded by a ring-like structure of relatively redder stars. The secondary component is ~50 pc in size and lies at a projected distance of ~80 pc away from the primary, and is also actively star-forming. We estimate masses ~10^7 M(sol) and ~10^6 M(sol) for the two components, based on their luminosities, with an associated dynamical timescale for the system of a few Myr. This timescale and the structure of the components suggests that a collision between them triggered their starbursts. The spectral energy distributions of both components can be fitted by the combination of recent (few Myr old) starburst and an evolved (several Gyr old) underlying stellar population, similar to larger blue compact dwarf galaxies. This indicates that despite its metal deficiency the object is not forming its first generation of stars. However, the small sizes and masses of the two components suggests that HS 0822+3542 represents a dwarf galaxy in the process of assembling from clumps of stars intermediate in size between globular clusters and objects previously classified as galaxies. Its relatively high ratio of neutral gas mass to stellar mass (~1) and high specific star formation rate, log(SFR/M(sol) = -9.2, suggests that it is still converting much of its gas to stars.Comment: 11 pages, 2 figures, accepted for publication in Astrophysical Journal Letter

Adapting to time: Duration channels do not mediate human time perception

Accurately encoding the duration and temporal order of events is essential for survival and important to everyday activities, from holding conversations to driving in fastflowing traffic. Although there is a growing body of evidence that the timing of brief events (< 1 s) is encoded by modality-specific mechanisms, it is not clear how such mechanisms register event duration. One approach gaining traction is a channel-based model; this envisages narrowly-tuned, overlapping timing mechanisms that respond preferentially to different durations. The channelbased model predicts that adapting to a given event duration will result in overestimating and underestimating the duration of longer and shorter events, respectively. We tested the model by having observers judge the duration of a brief (600 ms) visual test stimulus following adaptation to longer (860 ms) and shorter (340 ms) stimulus durations. The channel-based model predicts perceived duration compression of the test stimulus in the former condition and perceived duration expansion in the latter condition. Duration compression occurred in both conditions, suggesting that the channel-based model does not adequately account for perceived duration of visual events

Distribution of independent components of binocular natural images

An influential theory of the function of early processing in the visual cortex is that it forms an efficient coding of ecologically valid stimuli. In particular, correlations and differences between visual signals from the two eyes are believed to be of great importance in solving both depth from disparity and binocular fusion. Techniques such as independent-component analysis have been developed to learn efficient codings from natural images; these codings have been found to resemble receptive fields of simple cells in V1. However, the extent to which this approach provides an explanation of the functionality of the visual cortex is still an open question. We compared binocular independent components with physiological measurements and found a broad range of similarities along with a number of key differences. In common with physiological measurements, we found components with a broad range of both phase- and position-disparity tuning. However, we also found a larger population of binocularly anticorrelated components than have been found physiologically. We found components focused narrowly on detecting disparities proportional to half-integer multiples of wavelength rather than the range of disparities found physiologically. We present the results as a detailed analysis of phase and position disparities in Gabor-like components generated by independent-component analysis trained on binocular natural images and compare these results to physiology. We find strong similarities between components learned from natural images, indicating that ecologically valid stimuli are important in understanding cortical function, but with significant differences that suggest that our current models are incomplete

An Isosurface Continuity Algorithm for Super Adaptive Resolution Data

We present the chain-gang algorithm for isosurface rendering of super adaptive resolution (SAR) volume data in order to minimize (1) the space needed for storage of both the data and the isosurface and (2) the time taken for computation. The chain-gan

IXPE Mission System Concept and Development Status

The Goal of the Imaging X-Ray Polarimetry Explorer (IXPE) Mi SMEX), is to expand understanding of high-energy astrophysical processes and sources, in support of NASAs first science objective in Astrophysics: Discover how the universe works. IXPE, an international collaboration, will conduct X-ray imaging polarimetry for multiple categories of cosmic X-ray sources such as neutron stars, stellar-mass black holes, supernova remnants and active galactic nuclei. The Observatory uses a single science operational mode capturing the X-ray data from the targets. The IXPE Observatory consists of spacecraft and payload modules built up in parallel to form the Observatory during system integration and test. The payload includes three X-ray telescopes each consisting of a polarization-sensitive, gas pixel X-ray detector, paired with its corresponding grazing incidence mirror module assembly (MMA). A deployable boom provides the correct separation (focal length) between the detector units (DU) and MMAs. These payload elements are supported by the IXPE spacecraft which is derived from the BCP-small spacecraft architecture. This paper summarizes the IXPE mission science objectives, updates the Observatory implementation concept including the payload and spacecraft ts and summarizes the mission status since last years conference