3,100 research outputs found
Body-based senses enhance knowledge of directions in large-scale environments
Previous research has shown that inertial cues resulting from passive transport through a large environment do not necessarily facilitate acquiring knowledge about its layout. Here we examine whether the additional body-based cues that result from active movement facilitate the acquisition of spatial knowledge. Three groups of participants learned locations along an 840-m route. One group walked the route during learning, allowing access to body-based cues (i.e., vestibular, proprioceptive, and efferent information). Another group learned by sitting in the laboratory, watching videos made from the first group. A third group watched a specially made video that minimized potentially confusing head-on-trunk rotations of the viewpoint. All groups were tested on their knowledge of directions in the environment as well as on its configural properties. Having access to body-based information reduced pointing error by a small but significant amount. Regardless of the sensory information available during learning, participants exhibited strikingly common biases
A Reanalysis of the Hydrodynamic Theory of Fluid, Polar-Ordered Flocks
I reanalyze the hydrodynamic theory of fluid, polar ordered flocks. I find
new linear terms in the hydrodynamic equations which slightly modify the
anisotropy, but not the scaling, of the damping of sound modes. I also find
that the nonlinearities allowed {\it in equilibrium} do not stabilize long
ranged order in spatial dimensions ; in accord with the Mermin-Wagner
theorem. Nonequilibrium nonlinearities {\it do} stabilize long ranged order in
, as argued by earlier work. Some of these were missed by earlier work; it
is unclear whether or not they change the scaling exponents in .Comment: 6 pages, no figures. arXiv admin note: text overlap with
arXiv:0909.195
The benefits of using a walking interface to navigate virtual environments
Navigation is the most common interactive task performed in three-dimensional virtual environments (VEs), but it is also a task that users often find difficult. We investigated how body-based information about the translational and rotational components of movement helped participants to perform a navigational search task (finding targets hidden inside boxes in a room-sized space). When participants physically walked around the VE while viewing it on a head-mounted display (HMD), they then performed 90% of trials perfectly, comparable to participants who had performed an equivalent task in the real world during a previous study. By contrast, participants performed less than 50% of trials perfectly if they used a tethered HMD (move by physically turning but pressing a button to translate) or a desktop display (no body-based information). This is the most complex navigational task in which a real-world level of performance has been achieved in a VE. Behavioral data indicates that both translational and rotational body-based information are required to accurately update one's position during navigation, and participants who walked tended to avoid obstacles, even though collision detection was not implemented and feedback not provided. A walking interface would bring immediate benefits to a number of VE applications
Increased HCO production in the outer disk around HD 163296
Three formaldehyde lines were observed (HCO 3--2, HCO
3--2, and HCO 3--2) in the protoplanetary disk
around the Herbig Ae star HD 163296 with ALMA at 0.5 arcsecond (60 AU) spatial
resolution. HCO 3--2 was readily detected via imaging, while
the weaker HCO 3--2 and HCO 3--2 lines
required matched filter analysis to detect. HCO is present throughout most
of the gaseous disk, extending out to 550 AU. An apparent 50 AU inner radius of
the HCO emission is likely caused by an optically thick dust continuum. The
HCO radial intensity profile shows a peak at 100 AU and a secondary bump at
around 300 AU, suggesting increased production in the outer disk. Different
parameterizations of the HCO abundance were compared to the observed
visibilities with minimization, using either a characteristic
temperature, a characteristic radius or a radial power law index to describe
the HCO chemistry. Similar models were applied to ALMA Science Verification
data of CO. In all modeling scenarios, fits to the HCO data show an
increased abundance in the outer disk. The overall best-fit HCO model shows
a factor of two enhancement beyond a radius of 27020 AU, with an inner
abundance of . The HCO emitting region has a lower
limit on the kinetic temperature of K. The CO modeling suggests
an order of magnitude depletion in the outer disk and an abundance of in the inner disk. The increase in HCO outer disk emission
could be a result of hydrogenation of CO ices on dust grains that are then
sublimated via thermal desorption or UV photodesorption, or more efficient
gas-phase production beyond about 300 AU if CO is photodisocciated in this
region
COMPTEL gamma ray and neutron measurements of solar flares
COMPTEL on the Compton Gamma Ray Observatory has measured the flux of x‐rays and neutrons from several solar flares. These data have also been used to image the Sun in both forms of radiation. Unusually intense flares occurred during June 1991 yielding data sets that offer some new insight into of how energetic protons and electrons are accelerated and behave in the solar environment. We summarize here some of the essential features in the solar flare data as obtained by COMPTEL during June 1991
Neutron and gamma‐ray measurements of the solar flare of 1991 June 9
The COMPTEL Imaging Compton Telescope on‐board the Compton Gamma Ray Observatory measured significant neutron and γ‐ray fluxes from the solar flare of 9 June 1991. The γ‐ray flux had an integrated intensity (≳1 MeV) of ∼30 cm−2, extending in time from 0136 UT to 0143 UT, while the time of energetic neutron emission extended approximately 10 minutes longer, indicating either extended proton acceleration to high energies or trapping and precipitation of energetic protons. The production of neutrons without accompanying γ‐rays in the proper proportion indicates a significant hardening of the precipitating proton spectrum through either the trapping or extended acceleration process
Uniformity of V minus Near Infrared Color Evolution of Type Ia Supernovae, and Implications for Host Galaxy Extinction Determination
From an analysis of SNe 1972E, 1980N, 1981B, 1981D, 1983R, 1998bu, 1999cl,
and 1999cp we find that the intrinsic V-K colors of Type Ia SNe with
multi-color light curve shape (MLCS) parameter -0.4 < Delta < +0.2 suggest a
uniform color curve. V-K colors become bluer linearly with time from roughly
one week before B-band maximum until one week after maximum, after which they
redden linearly until four weeks after maximum. V-H colors exhibit very similar
color evolution. V-J colors exhibit slightly more complex evolution, with
greater scatter. The existence of V minus near infrared color relations allows
the construction of near infrared light curve templates that are an improvement
on those of Elias et al. (1985).
We provide optical BVRI and infrared JHK photometry of the Type Ia supernovae
1999aa, 1999cl, and 1999cp. SN 1999aa is an overluminous "slow decliner" (with
Delta = -0.47 mag). SN 1999cp is a moderately bright SN unreddened in its host.
SN 1999cl is extremely reddened in its host. The V minus near infrared colors
of SN 1999cl yield A_V = 2.01 +/- 0.11 mag. This leads to a distance for its
host galaxy (M 88) in agreement with other distance measurements for members of
the Virgo cluster.Comment: 57 pages, 13 postscript figures, to appear in the August 20, 2000,
issue of the Astrophysical Journal. Contains updated references and a number
of minor corrections dealt with when page proofs were correcte
Proportion Regulation in Globally Coupled Nonlinear Systems
As a model of proportion regulation in differentiation process of biological
system, globally coupled activator-inhibitor systems are studied. Formation and
destabilization of one and two cluster state are predicted analytically.
Numerical simulations show that the proportion of units of clusters is chosen
within a finite range and it is selected depend on the initial condition.Comment: 11 pages (revtex format) and 5 figures (PostScript)
An Iterated Global Mascon Solution with Focus on Land Ice Mass Evolution
Land ice mass evolution is determined from a new GRACE global mascon solution. The solution is estimated directly from the reduction of the inter-satellite K-band range rate observations taking into account the full noise covariance, and formally iterating the solution. The new solution increases signal recovery while reducing the GRACE KBRR observation residuals. The mascons are estimated with 10-day and 1-arc-degree equal area sampling, applying anisotropic constraints for enhanced temporal and spatial resolution of the recovered land ice signal. The details of the solution are presented including error and resolution analysis. An Ensemble Empirical Mode Decomposition (EEMD) adaptive filter is applied to the mascon solution time series to compute timing of balance seasons and annual mass balances. The details and causes of the spatial and temporal variability of the land ice regions studied are discussed
Antarctica, Greenland and Gulf of Alaska Land-Ice Evolution from an Iterated GRACE Global Mascon Solution
We have determined the ice mass evolution of the Antarctica and Greenland ice sheets (AIS and GIS) and Gulf of Alaska (GOA) glaciers from a new GRACE global solution of equal-area surface mass concentration parcels (mascons) in equivalent height of water. The mascons were estimated directly from the reduction of the inter-satellite K-band range-rate (KBRR) observations, taking into account the full noise covariance, and formally iterating the solution. The new solution increases signal recovery while reducing the GRACE KBRR observation residuals. The mascons were estimated with 10 day and 1 arc degree equal-area sampling, applying anisotropic constraints. An ensemble empirical mode decomposition adaptive filter was applied to the mascon time series to compute annual mass balances. The details and causes of the spatial and temporal variability of the land-ice regions studied are discussed. The estimated mass trend over the total GIS, AIS and GOA glaciers for the time period 1 December 2003 to 1 December 2010 is -380 plus or minus 31 Gt a(exp -1), equivalent to -1.05 plus or minus 0.09 mma(exp -1) sea-level rise. Over the same time period we estimate the mass acceleration to be -41 plus or minus 27 Gt a(exp -2), equivalent to a 0.11 plus or minus 0.08 mm a(exp -2) rate of change in sea level. The trends and accelerations are dependent on significant seasonal and annual balance anomalies
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