9,531 research outputs found
Recommended from our members
Mental Imagery and Chunks: Empirical and Computational Findings
To investigate experts’ imagery in chess, players were required to recall briefly-presented positions in which the pieces were placed on the intersections between squares (intersection positions). Position types ranged from game positions to positions where both the piece distribution and location were randomized. Simulations were run with the CHREST model (Gobet & Simon, 2000). The simulations assumed that pieces had to be centered back one by one to the middle of the squares in the mind’s eye before chunks could be recognized. Consistent with CHREST’s predictions, chess players (N = 36), ranging from weak amateurs to grandmasters, exhibited much poorer recall on intersection positions than on standard positions (pieces placed on centers of squares). On the intersection positions, the skill difference in recall was larger on game positions than on the randomized positions. Participants recalled bishops better than knights, suggesting that Stroop-like interference impairs recall of the latter. The data supported both the time parameter in CHREST for shifting pieces in the mind’s eye (125 ms per piece) and the seriality assumption. In general, the study reinforces the plausibility of CHREST as a model of cognition
Recommended from our members
Computational Modelling of Mental Imagery in Chess: A Sensitivity Analysis
An important aim of cognitive science is to build computational models that account for a large number of phenomena but have few free parameters, and to obtain more veridical values for the models’ parameters by successive approximations. A good example of this approach is the CHREST model (Gobet & Simon, 2000), which has simulated numerous phenomena on chess expertise and in other domains. In this paper, we are interested in the parameter the model uses for shifting chess pieces in its mind’s eye (125 ms per piece), a parameter that had been estimated based on relatively sparse experimental evidence. Recently, Waters and Gobet (2008) tested the validity of this parameter in a memory experiment that required players to recall briefly presented positions in which the pieces were placed on the intersections between squares. Position types ranged from game positions to positions where both the piece distribution and location were randomised. CHREST, which assumed that pieces must be centred back to the middle of the squares in the mind’s eye before chunks can be recognized, simulated the data fairly well using the default parameter for shifting pieces. The sensitivity analysis presented in the current paper shows that the fit was nearly optimal for all groups of players except the grandmaster group for which, counterintuitively, a slower shifting time gave a better fit. The implications for theory development are discussed
Transonic flutter study of a wind-tunnel model of a supercritical wing with/without winglet
The model was a 1/6.5-size, semipan version of a wing proposed for an executive-jet-transport airplane. The model was tested with a normal wingtip, a wingtip with winglet, and a normal wingtip ballasted to simulate the winglet mass properties. Flutter and aerodynamic data were acquired at Mach numbers (M) from 0.6 to 0.95. The measured transonic flutter speed boundary for each wingtip configuration had roughly the same shape with a minimum flutter speed near M=0.82. The winglet addition and wingtip mass ballast decreased the wing flutter speed by about 7 and 5 percent, respectively; thus, the winglet effect on flutter was more a mass effect than an aerodynamic effect
The effects of dust evolution on disks in the mid-IR
In this paper, we couple together the dust evolution code two-pop-py with the
thermochemical disk modelling code ProDiMo. We create a series of
thermochemical disk models that simulate the evolution of dust over time from
0.018 Myr to 10 Myr, including the radial drift, growth, and settling of dust
grains. We examine the effects of this dust evolution on the mid-infrared gas
emission, focussing on the mid-infrared spectral lines of C2H2, CO2, HCN, NH3,
OH, and H2O that are readily observable with Spitzer and the upcoming E-ELT and
JWST.
The addition of dust evolution acts to increase line fluxes by reducing the
population of small dust grains. We find that the spectral lines of all species
except C2H2 respond strongly to dust evolution, with line fluxes increasing by
more than an order of magnitude across the model series as the density of small
dust grains decreases over time. The C2H2 line fluxes are extremely low due to
a lack of abundance in the infrared line-emitting regions, despite C2H2 being
commonly detected with Spitzer, suggesting that warm chemistry in the inner
disk may need further investigation. Finally, we find that the CO2 flux
densities increase more rapidly than the other species as the dust disk
evolves. This suggests that the flux ratios of CO2 to other species may be
lower in disks with less-evolved dust populations.Comment: 13 pages, 9 figures, accepted in A&
The circumstellar envelope of AFGL 4106
We present new imaging and spectroscopy of the post-red supergiant binary
AFGL 4106. Coronographic imaging in H-alpha reveals the shape and extent of the
ionized region in the circumstellar envelope (CSE). Echelle spectroscopy with
the slit covering almost the entire extent of the CSE is used to derive the
physical conditions in the ionized region and the optical depth of the dust
contained within the CSE.
The dust shell around AFGL 4106 is clumpy and mixed with ionized gas. H-alpha
and [N II] emission is brightest from a thin bow-shaped layer just outside of
the detached dust shell. On-going mass loss is traced by [Ca II] emission and
blue-shifted absorption in lines of low-ionization species. A simple model is
used to interpret the spatial distribution of the circumstellar extinction and
the dust emission in a consistent way.Comment: 10 pages, 11 figures. Accepted for publication in Astronomy &
Astrophysics Main Journa
Optical absorption in fused silica during TRIGA reactor pulse irradiation
Spectral transmission characteristics of fused silica before, during, and after exposure to reactor irradiation pulse
Variability and nature of the binary in the Red Rectangle Nebula
We present new observations of the central binary inside the Red Rectangle
nebula. The detection of zinc in the optical spectrum confirms that the
peculiar photospheric abundances are due to accretion of circumstellar gas.
Grey brightness variations with the orbital period are observed. They are
interpreted as being due to the variation of the scattering angle with orbital
phase. The small orbital separation of the system is not compatible with
previous normal evolution of the primary on the AGB. We point out the
similarity of the orbital history of this and other similar systems with those
of some close Barium stars and suggest that the nonzero eccentricity of the
orbit is the result of tidal interaction with the circumbinary disk.Comment: 4 pages, 3 figures, A&A Letters accepte
The absence of the 10 um silicate feature in the isolated Herbig Ae star HD 100453
We analyse the optical and IR spectra, as well as the spectral energy
distribution (UV to mm) of the candidate Herbig Ae star HD100453. This star is
particular, as it shows an energy distribution similar to that of other
isolated Herbig Ae/Be stars (HAEBEs), but unlike most of them, it does not have
a silicate emission feature at 10 um, as is shown in Meeus (2001). We confirm
the HAEBE nature of HD100453 through an analysis of its optical spectrum and
derived location in the H-R diagram. The IR spectrum of HD100453 is modelled by
an optically thin radiative transfer code, from which we derive constraints on
the composition, grain-size and temperature distribution of the circumstellar
dust. We show that it is both possible to explain the lack of the silicate
feature as (1) a grain-size effect - lack of small silicate grains, and (2) a
temperature effect - lack of small, hot silicates, as proposed by Dullemond
(2001), and discuss both possibilities.Comment: 9 pages, 7 figures; accepted by A&
The Thermal Structure of the Circumstellar Disk Surrounding the Classical Be Star gamma Cassiopeia
We have computed radiative equilibrium models for the gas in the
circumstellar envelope surrounding the hot, classical Be star Cassiopeia. This calculation is performed using a code that incorporates a
number of improvements over previous treatments of the disk's thermal structure
by \citet{mil98} and \citet{jon04}; most importantly, heating and cooling rates
are computed with atomic models for H, He, CNO, Mg, Si, Ca, & Fe and their
relevant ions. Thus, for the first time, the thermal structure of a Be disk is
computed for a gas with a solar chemical composition as opposed to assuming a
pure hydrogen envelope. We compare the predicted average disk temperature, the
total energy loss in H, and the near-IR excess with observations and
find that all can be accounted for by a disk that is in vertical hydrostatic
equilibrium with a density in the equatorial plane of to
. We also discuss the changes in
the disk's thermal structure that result from the additional heating and
cooling processes available to a gas with a solar chemical composition over
those available to a pure hydrogen plasma.Comment: 11 pages, 8 figures high resolution figures available at
http://inverse.astro.uwo.ca/sig_jon07.htm
Autoclavable addition polyimides for 371 C composite applications
Studies were conducted to improve the thermo-oxidative stability (TOS) of PMR type polyimides by the substitution of para-aminostyrene (PAS) for the nadic ester endcap in second generation PMR polyimides (PMR-2). The nadic endcap which provides the PMR polyimides with their relative ease of fabrication, both by limiting the molecular weight of the prepolymer and by undergoing the final addition cure without volatiles, is also the weak link with regard to TOS. A polyimide formulated with PAS endcaps, called V-CAP, utilizes a two step reaction sequence similar to that of the PMR polyimides and can be easily autoclave molded into low void composite materials. Resin studies included two formulations of both PMR-2 and V-CAP, corresponding to n=9 and n=14 prepolymer stoichiometry. Unidirectional reinforced T40R graphite fiber laminates were fabricated from each of the resins was post-cured in either air at 385 C or nitrogen at 400 C. Composite specimens were aged in air at 371 C and mechanical properties were measured at 371 C before and after exposure
- …