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- 검색키워드
- 저자 : Knapen, Johan H. (검색결과 11 건)
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The role of frontal and parietal brain areas in bistable perception.
Knapen, Tomas,Brascamp, Jan,Pearson, Joel,van Ee, Raymond,Blake, Randolph The Society 2011 The Journal of neuroscience Vol.31 No.28
<P>When sensory input allows for multiple, competing perceptual interpretations, observers' perception can fluctuate over time, which is called bistable perception. Imaging studies in humans have revealed transient responses in a right-lateralized network in the frontal-parietal cortex (rFPC) around the time of perceptual transitions between interpretations, potentially reflecting the neural initiation of transitions. We investigated the role of this activity in male human observers, with specific interest in its relation to the temporal structure of transitions, which can be either instantaneous or prolonged by periods during which observers experience a mix of both perceptual interpretations. Using both bistable apparent motion and binocular rivalry, we show that transition-related rFPC activity is larger for transitions that last longer, suggesting that rFPC remains active as long as a transition lasts. We also replicate earlier findings that rFPC activity during binocular rivalry transitions exceeds activity during yoked transitions that are simulated using video replay. However, we show that this established finding holds only when perceptual transitions are replayed as instantaneous events. When replay, instead, depicts transitions with the actual durations reported during rivalry, yoked transitions and genuine rivalry transitions elicit equal activity. Together, our results are consistent with the view that at least a component of rFPC activation during bistable perception reflects a response to perceptual transitions, both real and yoked, rather than their cause. This component of activity could reflect the change in sensory experience and task demand that occurs during transitions, which fits well with the known role of these areas in attention and decision making.</P>
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Meidt, Sharon E.,Schinnerer, Eva,Knapen, Johan H.,Bosma, Albert,Athanassoula, E.,Sheth, Kartik,Buta, Ronald J.,Zaritsky, Dennis,Laurikainen, Eija,Elmegreen, Debra,Elmegreen, Bruce G.,Gadotti, Dimitri IOP Publishing 2012 The Astrophysical journal Vol.744 No.1
<P>With the aim of constructing accurate two-dimensional maps of the stellar mass distribution in nearby galaxies from Spitzer Survey of Stellar Structure in Galaxies 3.6 and 4.5 mu m images, we report on the separation of the light from old stars from the emission contributed by contaminants. Results for a small sample of six disk galaxies (NGC 1566, NGC 2976, NGC 3031, NGC 3184, NGC 4321, and NGC 5194) with a range of morphological properties, dust content, and star formation histories are presented to demonstrate our approach. To isolate the old stellar light from contaminant emission (e.g., hot dust and the 3.3 mu m polycyclic aromatic hydrocarbon (PAH) feature) in the IRAC 3.6 and 4.5 mu m bands we use an independent component analysis (ICA) technique designed to separate statistically independent source distributions, maximizing the distinction in the [3.6]-[4.5] colors of the sources. The technique also removes emission from evolved red objects with a low mass-to-light ratio, such as asymptotic giant branch (AGB) and red supergiant (RSG) stars, revealing maps of the underlying old distribution of light with [3.6]-[4.5] colors consistent with the colors of K and M giants. The contaminants are studied by comparison with the non-stellar emission imaged at 8 mu m, which is dominated by the broad PAH feature. Using the measured 3.6 mu m/8 mu m ratio to select individual contaminants, we find that hot dust and PAHs together contribute between similar to 5% and 15% to the integrated light at 3.6 mu m, while light from regions dominated by intermediate-age (AGB and RSG) stars accounts for only 1%-5%. Locally, however, the contribution from either contaminant can reach much higher levels; dust contributes on average 22% to the emission in star-forming regions throughout the sample, while intermediate-age stars contribute upward of 50% in localized knots. The removal of these contaminants with ICA leaves maps of the old stellar disk that retain a high degree of structural information and are ideally suited for tracing stellar mass, as will be the focus in a companion paper.</P>
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THE THICK DISK IN THE GALAXY NGC 4244 FROM S<sup>4</sup>G IMAGING
Comeró,n, Sé,bastien,Knapen, Johan H.,Sheth, Kartik,Regan, Michael W.,Hinz, Joannah L.,Gil de Paz, Armando,Mené,ndez-Delmestre, Karí,n,Muñ,oz-Mateos, Juan-Carlos,Seibert, IOP Publishing 2011 The Astrophysical journal Vol.729 No.1
<P>If thick disks are ubiquitous and a natural product of disk galaxy formation and/or evolution processes, all undisturbed galaxies that have evolved during a significant fraction of a Hubble time should have a thick disk. The late-type spiral galaxy NGC 4244 has been reported as the only nearby edge-on galaxy without a confirmed thick disk. Using data from the Spitzer Survey of Stellar Structure in Galaxies (S(4)G) we have identified signs of two disk components in this galaxy. The asymmetries between the light profiles on both sides of the mid-plane of NGC 4244 can be explained by a combination of the galaxy not being perfectly edge-on and a certain degree of opacity of the thin disk. We argue that the subtlety of the thick disk is a consequence of either a limited secular evolution in NGC 4244, a small fraction of stellar material in the fragments which built the galaxy, or a high amount of gaseous accretion after the formation of the galaxy.</P>
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Comeró,n, Sé,bastien,Elmegreen, Bruce G.,Knapen, Johan H.,Salo, Heikki,Laurikainen, Eija,Laine, Jarkko,Athanassoula, E.,Bosma, Albert,Sheth, Kartik,Regan, Michael W.,Hinz, Joannah L.,de Pa IOP Publishing 2011 The Astrophysical journal Vol.741 No.1
<P>Most, if not all, disk galaxies have a thin (classical) disk and a thick disk. In most models thick disks are thought to be a necessary consequence of the disk formation and/or evolution of the galaxy. We present the results of a study of the thick disk properties in a sample of carefully selected edge-on galaxies with types ranging from T = 3 to T = 8. We fitted one-dimensional luminosity profiles with physically motivated functions-the solutions of two stellar and one gaseous isothermal coupled disks in equilibrium-which are likely to yield more accurate results than other functions used in previous studies. The images used for the fits come from the Spitzer Survey of Stellar Structure in Galaxies (S(4)G). We found that thick disks are on average more massive than previously reported, mostly due to the selected fitting function. Typically, the thin and thick disks have similar masses. We also found that thick disks do not flare significantly within the observed range in galactocentric radii and that the ratio of thick-to-thin disk scale heights is higher for galaxies of earlier types. Our results tend to favor an in situ origin for most of the stars in the thick disk. In addition, the thick disk may contain a significant amount of stars coming from satellites accreted after the initial buildup of the galaxy and an extra fraction of stars coming from the secular heating of the thin disk by its own overdensities. Assigning thick disk light to the thin disk component may lead to an underestimate of the overall stellar mass in galaxies because of different mass-to-light ratios in the two disk components. On the basis of our new results, we estimate that disk stellar masses are between 10% and 50% higher than previously thought and we suggest that thick disks are a reservoir of 'local missing baryons.'</P>
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Comeró,n, Sé,bastien,Elmegreen, Bruce G.,Knapen, Johan H.,Sheth, Kartik,Hinz, Joannah L.,Regan, Michael W.,Gil de Paz, Armando,Muñ,oz-Mateos, Juan-Carlos,Mené,ndez-Delmestre, K IOP Publishing 2011 ASTROPHYSICAL JOURNAL LETTERS - Vol.738 No.2
<P>NGC 4013 is a nearby Sb edge-on galaxy known for its 'prodigious' Hi warp and its 'giant' tidal stream. Previous work on this unusual object shows that it cannot be fitted satisfactorily by a canonical thin+thick disk structure. We have produced a new decomposition of NGC 4013, considering three stellar flattened components (thin+thick disk plus an extra and more extended component) and one gaseous disk. All four components are considered to be gravitationally coupled and isothermal. To do so, we have used the 3.6 mu m images from the Spitzer Survey of Stellar Structure in Galaxies. We find evidence for NGC 4013 indeed having a thin and a thick disk and an extra flattened component. This smooth and extended component (scale height z(EC) similar to 3 kpc) could be interpreted as a thick disk or as a squashed ellipsoidal halo and contains similar to 20% of the total mass of all three stellar components. We argue it is unlikely to be related to the ongoing merger or due to the off-plane stars from a warp in the other two disk components. Instead, we favor a scenario in which the thick disk and the extended component were formed in a two-stage process, in which an initially thick disk has been dynamically heated by a merger soon enough in the galaxy history to have a new thick disk formed within it.</P>
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Brascamp, Jan W,van Boxtel, Jeroen J A,Knapen, Tomas H J,Blake, Randolph Published by the MIT Press with the Cognitive Neur 2010 Journal of cognitive neuroscience Vol.22 No.10
<P>The elements most vivid in our conscious awareness are the ones to which we direct our attention. Scientific study confirms the impression of a close bond between selective attention and visual awareness, yet the nature of this association remains elusive. Using visual afterimages as an index, we investigate neural processing of stimuli as they enter awareness and as they become the object of attention. We find evidence of response enhancement accompanying both attention and awareness, both in the phase-sensitive neural channels characteristic of early processing stages and in the phase-insensitive channels typical of higher cortical areas. The effects of attention and awareness on phase-insensitive responses are positively correlated, but in the same experiments, we observe no correlation between the effects on phase-sensitive responses. This indicates independent signatures of attention and awareness in early visual areas yet a convergence of their effects at more advanced processing stages.</P>
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ARRAKIS: atlas of resonance rings as known in the S<sup>4</sup>G
Comeró,n, S.,Salo, H.,Laurikainen, E.,Knapen, J. H.,Buta, R. J.,Herrera-Endoqui, M.,Laine, J.,Holwerda, B. W.,Sheth, K.,Regan, M. W.,Hinz, J. L.,Muñ,oz-Mateos, J. C.,Gil de Paz, A.,Men&eac Springer-Verlag 2014 Astronomy and astrophysics Vol.562 No.-
<P>Context. Resonance rings and pseudorings (here collectively called rings) are thought to be related to the gathering of material near dynamical resonances caused by non-axisymmetries in galaxy discs. This means that they are the result of secular evolution processes that redistribute material and angular momentum in discs. Studying them may give clues on the formation and growth of bars and other disc non-axisymmetries. Aims. Our aims are to produce a catalogue and an atlas of the rings detected in the Spitzer Survey of Stellar Structure in Galaxies (S<SUP>4</SUP>G) and to conduct a statistical study of the data in the catalogue. Methods. We traced the contours of rings previously identified and fitted them with ellipses. We found the orientation of bars by studying the galaxy ellipse fits from the S<SUP>4</SUP>G pipeline 4. We used the galaxy orientation data obtained by the S<SUP>4</SUP>G pipeline 4 to obtain intrinsic ellipticities and orientations of rings and the bars. Results. ARRAKIS contains data on 724 ringed galaxies in the S<SUP>4</SUP>G. The frequency of resonance rings in the S<SUP>4</SUP>G is of 16 ±1% and 35 ±1% for outer and inner features, respectively. Outer rings are mostly found in Hubble stages −1 ≤T≤ 4. Inner rings are found in a broad distribution that covers the range −1 ≤T≤7. We confirm that outer rings have two preferred orientations, namely parallel and perpendicular to the bar. We confirm a tendency for inner rings to be oriented parallel to the bar, but we report the existence of a significant fraction (maybe as large as 50%) of inner features that have random orientations with respect to the bar. These misaligned inner rings are mostly found in late-type galaxies (T ≥4). We find that the fraction of barred galaxies hosting outer (inner) rings is ~1.7 times (~1.3 times) that in unbarred galaxies. Conclusions. We confirm several results from previous surveys as well as predictions from simulations of resonant rings and/or from manifold flux tube theory. We report that a significant fraction of inner rings in late-type galaxies have a random orientation with respect to the bar. This may be caused by spiral modes that are decoupled from the bar and dominate the Fourier amplitude spectrum at the radius of the inner ring. The fact that rings are only mildly favoured by bars suggests that those in unbarred galaxies either formed because of weak departures from the axisymmetry of the galactic potential or that they are born because of bars that were destroyed after the ring formation.</P>
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Kim, Taehyun,Sheth, Kartik,Hinz, Joannah L.,Lee, Myung Gyoon,Zaritsky, Dennis,Gadotti, Dimitri A.,Knapen, Johan H.,Schinnerer, Eva,Ho, Luis C.,Laurikainen, Eija,Salo, Heikki,Athanassoula, E.,Bosma, Al IOP Publishing 2012 The Astrophysical journal Vol.753 No.1
<P>Tidal debris around galaxies can yield important clues on their evolution. We have identified tidal debris in 11 early-type galaxies (T <= 0) from a sample of 65 early types drawn from the Spitzer Survey of Stellar Structure in Galaxies (S(4)G). The tidal debris includes features such as shells, ripples, and tidal tails. A variety of techniques, including two-dimensional decomposition of galactic structures, were used to quantify the residual tidal features. The tidal debris contributes similar to 3%-10% to the total 3.6 mu m luminosity of the host galaxy. Structural parameters of the galaxies were estimated using two-dimensional profile fitting. We investigate the locations of galaxies with tidal debris in the fundamental plane and Kormendy relation. We find that galaxies with tidal debris lie within the scatter of early-type galaxies without tidal features. Assuming that the tidal debris is indicative of recent gravitational interaction or merger, this suggests that these galaxies have either undergone minor merging events so that the overall structural properties of the galaxies are not significantly altered, or they have undergone a major merging events but already have experienced sufficient relaxation and phase mixing so that their structural properties become similar to those of the non-interacting early-type galaxies.</P>
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Comeró,n, Sé,bastien,Elmegreen, Bruce G.,Salo, Heikki,Laurikainen, Eija,Athanassoula, E.,Bosma, Albert,Knapen, Johan H.,Gadotti, Dimitri A.,Sheth, Kartik,Hinz, Joannah L.,Regan, Michael W. IOP Publishing 2012 The Astrophysical journal Vol.759 No.2
<P>Breaks in the radial luminosity profiles of galaxies have until now been mostly studied averaged over disks. Here, we study separately breaks in thin and thick disks in 70 edge-on galaxies using imaging from the Spitzer Survey of Stellar Structure in Galaxies. We built luminosity profiles of the thin and thick disks parallel to midplanes and we found that thin disks often truncate (77%). Thick disks truncate less often (31%), but when they do, their break radius is comparable with that in the thin disk. This suggests either two different truncation mechanisms-one of dynamical origin affecting both disks simultaneously and another one only affecting the thin disk-or a single mechanism that creates a truncation in one disk or in both depending on some galaxy property. Thin disks apparently antitruncate in around 40% of galaxies. However, in many cases, these antitruncations are an artifact caused by the superposition of a thin disk and a thick disk, with the latter having a longer scale length. We estimate the real thin disk antitruncation fraction to be less than 15%. We found that the ratio of the thick and thin stellar disk mass is roughly constant (0.2 < M-T/M-t < 0.7) for circular velocities v(c) > 120 km s(-1), but becomes much larger at smaller velocities. We hypothesize that this is due to a combination of a high efficiency of supernova feedback and a slower dynamical evolution in lower-mass galaxies causing stellar thin disks to be younger and less massive than in higher-mass galaxies.</P>
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