External Cue Effects on Memory for Spatial Location within a Rotated Task Field

Abstract

We propose a mathematical model of the Path Integration (PI) process. Its core assumption is that orientations of a path are summarized by circular probability distributions. We compare our model with classical, deterministic models of PI and find that, although they are indistinguishable in terms of information encoded, the probabilistic model is more parsimonious when considering navigation strategies. We show how sensory events can enrich the probability distributions memorized, resulting in a continuum of navigation strategies, from PI to stimulus-triggered response. We analyze the combination of circular probability distributions (e.g., multicue fusion), and demonstrate that, contrary to the linear case, adding orientation cues does not always increase reliability of estimates. We discuss experimental predictions entailed by our model.     

MHD modeling of the outer heliosphere: Achievements and challenges

An overview is presented of magnetic-field-related effects in the solar wind (SW) interaction with the local interstellar medium (LISM) and the different theoretical approaches used in their investigation. We discuss the possibility that the interstellar magnetic field (ISMF) introduces north–south and east–west asymmetries of the heliosphere, which might explain observational data obtained by the Voyager 1 and Voyager 2 spacecraft. The SW–LISM interaction parameters that are responsible for the deflection of the interstellar neutral hydrogen flow from the direction of propagation of neutral helium in the inner heliosheath are outlined. The possibility of a strong ISMF, which increases the heliospheric asymmetry and the H–He flow deflection, is discussed. The effect of the combination of a slow-fast solar wind during solar minimum over the Sun’s 11-year activity cycle is illustrated. The consequences of a tilt between the Sun’s magnetic and rotational axes are analyzed. Band-like areas of an increased magnetic field distribution in the outer heliosheath are sought in order to discover regions of possible 2–3 kHz radio emission.     

The X-ray/Gamma-ray Spectrometer on the Near Earth Asteroid Rendezvous Mission

An X-ray/gamma-ray spectrometer has been developed as part of a rendezvous mission with the near-Earth asteroid, 433 Eros, in an effort to answer fundamental questions about the nature and origin of asteroids and comets. During about 10 months of orbital operations commencing in early 1999, the X-ray/Gamma-ray Spectrometer will develop global maps of the elemental composition of the surface of Eros. The instrument remotely senses characteristic X-ray and gamma-ray emissions to determine composition. Solar excited X-ray fluorescence in the 1 to 10 keV range will be used to measure the surface abundances of Mg, Al, Si, Ca, Ti, and Fe with spatial resolutions down to 2 km. Gamma-ray emissions in the 0.1 to 10 MeV range will be used to measure cosmic-ray excited elements O, Si, Fe, H and naturally radioactive elements K, Th, U to surface depths on the order of 10 cm. The X-ray spectrometer consists of three gas-filled proportional counters with a collimated field of view of 5° and an energy resolution of 850 eV @ 5.9 keV. Two sunward looking X-ray detectors monitor the incident solar flux, one of which is the first flight of a new, miniature solid-state detector which achieves 600 eV resolution @ 5.9 keV. The gamma-ray spectrometer consists of a NaI(Tl) scintillator situated within a Bismuth Germanate (BGO) cup, which provides both active and passive shielding to confine the field of view and eliminate the need for a massive and costly boom. New coincidence techniques enable recovery of single and double escape events in the central detector. The NaI(Tl) and BGO detectors achieve energy resolutions of 8.7% and 14%, respectively @ 0.662 MeV. A data processing unit based on an RTX2010 microprocessor provides the spacecraft interface and produces 256-channel spectra for X-ray detectors and 1024-channel spectra for the raw, coincident, and anti-coincident gamma-ray modes. This paper presents a detailed overview of the X-ray/Gamma-ray Spectrometer and describes the science objectives, measurement objectives, instrument design, and shows some results from early in-flight data.     

Evidence for a shock wave in visible light and radio observations of the 1980 June 29 event

Shock waves, as evidenced by type II radio bursts, often accompany flares and coronal mass ejection transients. At present, the density enhancements observed by coronagraphs are believed by some to be ejected matter from the low corona, and by others to be the compressed material behind a shock front. If the former is correct, one would expect in some cases to see a density enhancement, associated with the compression region of the shock, some distance ahead of the transient ejecta. Such a density enhancement has not been previously reported.The coronal transient of 1980 June 29 (0233 UT) was observed with the High Altitude Observatory's Coronagraph/Polarimeter aboard SMM. This flare-associated coronal transient event was well observed with the Culgoora Radioheliograph, including a well-developed type II burst. Visible on the coronagraph images is a faint circular arc moving out well ahead of the transient loops. This arc is moving at more than 900 km s^?1 while the transient itself is moving at a speed of about 600 km s^?1. Both the arc and transient appear to have originated either prior to the X-ray flare or at some height above the flare at the time of the flare. The type II burst observed at Culgoora is associated with the transient loops, and no type II emission is identified with the faint arc.Due to its great speed, we interpret the faint arc as a manifestation of a shock wave, but also envision a separate shock wave associated with the transient loops as evidenced by the type II emission. Preliminary density measurements are consistent with this interpretation, and show the outer shock wave associated with the faint arc to have a Mach number M_A ≤ 1.7. At present we have no convincing explanation for the lack of a type II burst in association with the arc.This work was supported in part by NASA through grants NSG-7287 and NAGW-91 to the University of Colorado, Boulder, and S-55989 to the High Altitude Observatory, National Center for Atmospheric Research. The National Center for Atmospheric Research, NCAR, is sponsored by the National Science Foundation.     

IR circuit board and IC failure detection

This paper describes research and development efforts in the use of infrared (IR) laser beams for detecting failures in integrated circuits resident on printed circuit boards. This work involves taking advantage of the transparency of the silicon substrate of ICs to radiation in the near infrared (NIR) spectrum to devise a non-invasive method for imaging the component circuitry of the IC. The implication is that a means to see into the physical structure of an integrated circuit can be created by using lasers tuned to these wavelengths. While the silicon substrate is transparent to the laser, the circuit paths and devices embedded within the substrate are readily visible since their metallic composition is opaque to laser energy at this wavelength. A laser test fixture consisting of a 1064 nm continuous wave laser, CCD camera, and image acquisition board is used to generate images from flip-chip integrated circuits. Multiresolution image processing techniques are then applied to the resulting images to identify potential defects.     

Light elements and their isotopes in SNC meteorites and the Martian atmosphere

Nitrogen isotopes have played an important part in the acceptance of the hypothesis that SNC meteorites derive from Mars. As a result, these meteorites can be investigated for their carbon, sulphur, and hydrogen systematics with a view to learning something about the environmental conditions on the planet. Important aspects of the role of carbon, present in the form of carbon dioxide as an atmospheric gas and leading to the formation of carbonates by weathering or hydrothermal activity, can be established. The presence of indigenous organics is an intriguing possibility. A variety of new or emerging techniques which could improve our understanding of SNC meteorites and might be applied to a returned Martian sample are discussed.     

Plant molecular biology in the space station era: utilization of KSC fixation tubes with RNAlater

Spaceflight experiments involving biological specimens face unique challenges with regard to the on orbit harvest and preservation of material for later ground-based analyses. Preserving plant material for gene expression analyses requires that the tissue be prepared and stored in a manner that maintains the integrity of RNA. The liquid preservative RNAlater (Ambion) provides an effective alternative to conventional freezing strategies, which are limited or unavailable in current spaceflight experiment scenarios. The spaceflight use of RNAlater is enabled by the Kennedy space center fixation tube (KFT), hardware designed to provide the necessary containment of fixatives during the harvest and stowage of biological samples in space. Pairing RNAlater with the KFT system provides a safe and effective strategy for preserving plant material for subsequent molecular analyses, a strategy that has proven effective in several spaceflight experiments. Possible spaceflight scenarios for the use of RNAlater and KFTs are explored and discussed.     

The search for companions to Epsilon Eridani

The authors review efforts to examine the star Epsilon Eridani and determine the possibility for the existence of an Earth-like planet. Early data indicated that there must be a habitable ecosphere about 82.5 million Km from the primary. Research into the existence of another planetary system determined that Epsilon Eridani was a binary star with an Oort cloud system, indicating the possibility of planet formation. A review of the evidence suggests that the presence of the small red Dwarf companion star precludes the existence of a planetary system surrounding Epsilon Eridani. It is suggested that observations continue to provide further data about the formation of binary systems.     

Studies of radio frequency interference at Parkes Observatory

During 16 weeks of continuous SETI observing at the Parkes Observatory in New South Wales, Australia, a set of time-averaged data with 643 Hz resolution were recorded and returned to the SETI Institute for post-processing. These data are the 14 second (10 frame) average powers in each of 15,552 “subband” channels covering 10 MHz of the spectrum in both right and left circular polarizations that were used by the signal detection hardware to baseline and threshold the 1 Hz high resolution SETI spectra. The observations covered frequencies from 1.2 to 3 GHz, tracking 209 stellar targets across the sky. The data at each frequency were averaged over all directions and then interrogated to attempt to determine the prevalence of radio frequency interference (RFI). Estimates were made for the probability of encountering RFI at a particular frequency. Particular attention has been paid to those portions of the spectrum that are allocated as primary use status, or footnote protection for radioastronomy. This sixteen-week snapshot of the RFI situation at Parkes is by now out of date. Unfortunately, a year later, the situation has undoubtedly worsened.