Non-Optimal Perceptual Decision in Human Navigation

We highlight that optimal cue combination does not represent a general principle of cue interaction during navigation, extending Rahnev & Denison’s (R&D) summary of nonoptimal perceptual decisions to the navigation domain. However, we argue that the term ‘suboptimality’ does not capture the way visual and nonvisual cues interact in navigational decisions

How You Get There From Here:Interaction of Visual Landmarks and Path Integration in Human Navigation

How do people combine their sense of direction with their use of visual landmarks during navigation? Cue-integration theory predicts that such cues will be optimally integrated to reduce variability, whereas cue-competition theory predicts that one cue will dominate the response direction. We tested these theories by measuring both accuracy and variability in a homing task while manipulating information about path integration and visual landmarks. We found that the two cues were near-optimally integrated to reduce variability, even when landmarks were shifted up to 90°. Yet the homing direction was dominated by a single cue, which switched from landmarks to path integration when landmark shifts were greater than 90°. These findings suggest that cue integration and cue competition govern different aspects of the homing response: Cues are integrated to reduce response variability but compete to determine the response direction. The results are remarkably similar to data on animal navigation, which implies that visual landmarks reset the orientation, but not the precision, of the path-integration system

The Magellanic System: What have we learnt from FUSE?

I review some of the findings on the Magellanic System produced by the Far Ultraviolet Spectroscopic Explorer (FUSE) during and after its eight years of service. The Magellanic System with its high-velocity complexes provides a nearby laboratory that can be used to characterize phenomena that involve interaction between galaxies, infall and outflow of gas and metals in galaxies. These processes are crucial for understanding the evolution of galaxies and the intergalactic medium. Among the FUSE successes I highlight are the coronal gas about the LMC and SMC, and beyond in the Stream, the outflows from these galaxies, the discovery of molecules in the diffuse gas of the Stream and the Bridge, an extremely sub-solar and sub-SMC metallicity of the Bridge, and a high-velocity complex between the Milky Way and the Clouds.Comment: A contributed paper to the FUSE Annapolis Conference "Future Directions in Ultraviolet Spectroscopy.", 5 pages. To appear as an AIP Conference Proceedin

Tracking The Post-BBN Evolution Of Deuterium

The primordial abundance of deuterium produced during Big Bang Nucleosynthesis (BBN) depends sensitively on the universal ratio of baryons to photons, an important cosmological parameter probed independently by the Cosmic Microwave Background (CMB) radiation. Observations of deuterium in high-redshift, low-metallicity QSO Absorption Line Systems (QSOALS) provide a key baryometer, determining the baryon abundance at the time of BBN to a precision of 5%. Alternatively, if the CMB-determined baryon to photon ratio is used in the BBN calculation of the primordial abundances, the BBN-predicted deuterium abundance may be compared with the primordial value inferred from the QSOALS, testing the standard cosmological model. In the post-BBN universe, as gas is cycled through stars, deuterium is only destroyed so that its abundance measured anytime, anywhere in the Universe, bounds the primordial abundance from below. Constraints on models of post-BBN Galactic chemical evolution follow from a comparison of the relic deuterium abundance with the FUSE-inferred deuterium abundances in the chemically enriched, stellar processed material of the local ISM.Comment: 8 pages, 5 figures, to appear in the Proceedings of the Future Directions in Ultraviolet Spectroscopy Conferenc

Intergalactic Baryons in the Local Universe

Simulations predict that shocks from large-scale structure formation and galactic winds have reduced the fraction of baryons in the warm, photoionized phase (the Lya forest) from nearly 100% in the early universe to less than 50% today. Some of the remaining baryons are predicted to lie in the warm-hot ionized medium (WHIM) phase at T=10^5-10^7 K, but the quantity remains a highly tunable parameter of the models. Modern UV spectrographs have provided unprecedented access to both the Lya forest and potential WHIM tracers at z~0, and several independent groups have constructed large catalogs of far-UV IGM absorbers along ~30 AGN sight lines. There is general agreement between the surveys that the warm, photoionized phase makes up ~30% of the baryon budget at z~0. Another ~10% can be accounted for in collapsed structures (stars, galaxies, etc.). However, interpretation of the ~100 high-ion (OVI, etc) absorbers at z<0.5 is more controversial. These species are readily created in the shocks expected to exist in the IGM, but they can also be created by photoionization and thus not represent WHIM material. Given several pieces of observational evidence and theoretical expectations, I argue that most of the observed OVI absorbers represent shocked gas at T~300,000 K rather than photoionized gas at T<30,000 K, and they are consequently valid tracers of the WHIM phase. Under this assumption, enriched gas at T=10^5-10^6 K can account for ~10% of the baryon budget at z<0.5, but this value may increase when bias and incompleteness are taken into account and help close the gap on the 50% of the baryons still "missing".Comment: Invited review to appear in "Future Directions in Ultraviolet Spectroscopy", Oct 20-22, 2008, Annapolis, MD, M. E. Van Steenberg, ed. (April 2009). 8 pages, five figure

Optic Flow Drives Human Visuo-Locomotor Adaptation

SummaryTwo strategies can guide walking to a stationary goal: (1) the optic-flow strategy, in which one aligns the direction of locomotion or “heading” specified by optic flow with the visual goal [1, 2]; and (2) the egocentric-direction strategy, in which one aligns the locomotor axis with the perceived egocentric direction of the goal [3, 4] and in which error results in optical target drift [5]. Optic flow appears to dominate steering control in richly structured visual environments [2, 6–8], whereas the egocentric- direction strategy prevails in visually sparse environments [2, 3, 9]. Here we determine whether optic flow also drives visuo-locomotor adaptation in visually structured environments. Participants adapted to walking with the virtual-heading direction displaced 10° to the right of the actual walking direction and were then tested with a normally aligned heading. Two environments, one visually structured and one visually sparse, were crossed in adaptation and test phases. Adaptation of the walking path was more rapid and complete in the structured environment; the negative aftereffect on path deviation was twice that in the sparse environment, indicating that optic flow contributes over and above target drift alone. Optic flow thus plays a central role in both online control of walking and adaptation of the visuo-locomotor mapping

The Cosmic Origins Spectrograph and the Future of Ultraviolet Astronomy

I describe the capabilities of the Cosmic Origins Spectrograph, scheduled for May 2009 installation on the Hubble Space Telescope. With a factor-of-ten increase in far-UV throughput for moderate resolution spectroscopy, COS will enable a range of scientific programs that study hot stars, AGN, and gas in the interstellar medium, intergalactic medium, and galactic halos. We also plan a large-scale HST Spectroscopic Legacy Project for QSO absorption lines, galactic halos, and AGN outflows. Studies of next-generation telescopes for UV/O astronomy are now underway, including small, medium, and large missions to fill the imminent ten-year gap between the end of Hubble and a plausible launch of the next large mission. Selecting a strategy for achieving these goals will involve hard choices and tradeoffs in aperture, wavelength, and capability.Comment: To appear in Future Directions in Ultraviolet Astronomy (AIP Conf Proc

Summary Report on the High-Speed Characteristics of Six Model Wings Having NACA 65sub1-Series Sections

A summary of the results of wind-tunnel tests to determine the high-speed aerodynamic characteristics of six model wings having NACA 65sub1-series sections is presented in this report. The 8-percent-thick wings were superior to the 10-percent and 12-percent-thick wings from the standpoint of power economy during level flight for Mach numbers above 0.76. However, airplanes that are to fly at Mach numbers below 0.76 will gain aerodynamically if the percentage thickness of the wing and the aspect ratio are both increased. The lift-curve slopes for the 8-percent-thick wings at 0.85 Mach number were roughly twice their low-speed values

Estimating Porosity with Ground-Penetrating Radar Reflection Tomography: A Controlled 3-D Experiment at the Boise Hydrogeophysical Research Site

To evaluate the uncertainty of water-saturated sediment velocity and porosity estimates derived from surface-based, ground-penetrating radar reflection tomography, we conducted a controlled field experiment at the Boise Hydrogeophysical Research Site (BHRS). The BHRS is an experimental well field located near Boise, Idaho. The experimental data set consisted of 3-D multioffset radar acquired on an orthogonal 20 × 30 m surface grid that encompassed a set of 13 boreholes. Experimental control included (1) 1-D vertical velocity functions determined from traveltime inversion of vertical radar profiles (VRP) and (2) neutron porosity logs. We estimated the porosity distribution in the saturated zone using both the Topp and Complex Refractive Index Method (CRIM) equations and found the CRIM estimates in better agreement with the neutron logs. We found that when averaged over the length of the borehole, surface-derived velocity measurements were within 5% of the VRP velocities and that the porosity differed from the neutron log by less than 0.05. The uncertainty, however, is scale dependent. We found that the standard deviation of differences between ground-penetrating-radar-derived and neutron-log-derived porosity values was as high as 0.06 at an averaging length of 0.25 m but decreased to less than 0.02 at length scale of 11 m. Additionally, we used the 3-D porosity distribution to identify a relatively high-porosity anomaly (i.e., local sedimentary body) within a lower-porosity unit and verified the presence of the anomaly using the neutron porosity logs. Since the reflection tomography approach requires only surface data, it can provide rapid assessment of bulk hydrologic properties, identify meterscale anomalies of hydrologic significance, and may provide input for other higherresolution measurement methods

Leadership emergence in walking groups

Understanding the mechanisms underlying the emergence of leadership in multi-agent systems is still under investigation in many areas of research where group coordination is involved. While leadership has been mostly investigated in the case of animal groups, only a few works address the problem of leadership emergence in human ensembles, e.g. pedestrian walking, group dance. In this paper we study the emergence of leadership in the specific scenario of a small walking group. Our aim is to unveil the main mechanisms emerging in a human group when leader or follower roles are not designated a priori. Two groups of participants were asked to walk together and turn or change speed at self-selected times. Data were analysed using time-dependent cross correlation to infer leader-follower interactions between each pair of group members. The results indicate that leadership emergence is due both to contextual factors, such as an individual's position in the group, and to personal factors, such as an individual's characteristic locomotor behaviour. Our approach can easily be extended to larger groups and other scenarios such as team sports and emergency evacuations