34,827 research outputs found
Coding of the Reach Vector in Parietal Area 5d
Competing models of sensorimotor computation predict different topological constraints in the brain. Some models propose population coding of particular reference frames in anatomically distinct nodes, whereas others require no such dedicated subpopulations and instead predict that regions will simultaneously code in multiple, intermediate, reference frames. Current empirical evidence is conflicting, partly due to difficulties involved in identifying underlying reference frames. Here, we independently varied the locations of hand, gaze, and target over many positions while recording from the dorsal aspect of parietal area 5. We find that the target is represented in a predominantly hand-centered reference frame here, contrasting with the relative code seen in dorsal premotor cortex and the mostly gaze-centered reference frame in the parietal reach region. This supports the hypothesis that different nodes of the sensorimotor circuit contain distinct and systematic representations, and this constrains the types of computational model that are neurobiologically relevant
The Intrinsic Ellipticity of Spiral Disks
We have measured the distribution of intrinsic ellipticities for a sample of
28 relatively face-on spiral disks. We combine H-alpha velocity fields and R
and I-band images to determine differences between kinematic and photometric
inclination and position angles, from which we estimate intrinsic ellipticities
of galaxy disks. Our findings suggest disks have a log-normal distribution of
ellipticities (mean epsilon =0.06) and span a range from epsilon= 0 (circular)
to epsilon=0.2. We are also able to construct a tight Tully-Fisher relation for
our face-on sample. We use this to assess the contribution of disk ellipticity
on the observed Tully-Fisher scatter.Comment: 4 pages, 2 figures, to appear in "Disks of Galaxies: Kinematics,
Dynamics and Perturbations" (ASP Conference Series), eds E.Athanassoula and
A. Bosm
The influence of dust properties on the mass loss in pulsating AGB stars
We are currently studying carbon based dust types of relevance for
carbon-rich AGB stars, to obtain a better understanding of the influence of the
optical and chemical properties of the grains on the mass loss of the star. An
investigation of the complex interplay between hydrodynamics,radiative transfer
and chemistry has to be based on a better knowledge of the micro-physics of the
relevant dust species.Comment: 4 pages, 2 figures. Proceedings for IAU Colloquium 185 "Radial and
Nonradial Pulsations as Probes of Stellar Physics
Dust grain properties in atmospheres of AGB stars
We present self-consistent dynamical models for dust driven winds of
carbon-rich AGB stars. The models are based on the coupled system of
frequency-dependent radiation hydrodynamics and time-dependent dust formation.
We investigate in detail how the wind properties of the models are influenced
by the micro-physical properties of the dust grains that enter as parameters.
The models are now at a level where it is necessary to be quantitatively
consistent when choosing the dust properties that enters as input into the
models. At our current level of sophistication the choice of dust parameters is
significant for the derived outflow velocity, the degree of condensation and
the estimated mass loss rates of the models. In the transition between models
with and without mass-loss the choice ofmicro-physical parameters turns out to
be very significant for whether a particular set of stellar parameters will
give rise to a dust-driven mass loss or not.Comment: 10 pages, 3 figures. To appear in: Modelling of Stellar Atmospheres,
N.E. Piskunov, W.W. Weiss, D.F. Gray (eds.), IAU Symposium Vol. xxx.
Proceedings for the IAU Symposium 210, Uppsala, June 200
A Face-On Tully-Fisher Relation
We construct the first "face-on" Tully-Fisher (TF) relation for 24 galaxies
with inclinations between 16 degrees and 41 degrees. The enabling measurements
are integral-field, echelle spectroscopy from the WIYN 3.5m telescope, which
yield accurate kinematic estimates of disk inclination to 15 degrees. Kinematic
inclinations are of sufficient accuracy that our measured TF scatter of 0.42
mag is comparable to other surveys even without internal-absorption
corrections. Three of four galaxies with significant kinematic and photometric
asymmetries also have the largest deviations from our TF relation, suggesting
that asymmetries make an important contribution to TF scatter. By measuring
inclinations below 40 degrees, we establish a direct path to linking this
scatter to the unprojected structure of disks and making non-degenerate
dynamical mass-decompositions of spiral galaxies.Comment: 13 pages, 3 figures (2 color). Accepted for publication in ApJ
Letter
Correlation effects on the electronic structure of TiOCl: a NMTO+DMFT study
Using the recently developed N-th order muffin-tin orbital-based downfolding
technique in combination with the Dynamical Mean Field theory, we investigate
the electronic properties of the much discussed Mott insulator TiOCl in the
undimerized phase. Inclusion of correlation effects through this approach
provides a description of the spectral function into an upper and a lower
Hubbard band with broad valence states formed out of the orbitally polarized,
lower Hubbard band. We find that these results are in good agreement with
recent photo-emission spectra.Comment: 4 pages, 3 figure
Robustness of baryon-strangeness correlation and related ratios of susceptibilities
Using quenched lattice QCD simulations we investigate the continuum limit of
baryon-strangeness correlation and other related conserved charge-flavour
correlations for temperatures T_c<T\le2T_c. By working with lattices having
large temporal extents (N_\tau=12, 10, 8, 4) we find that these quantities are
almost independent of the lattice spacing, i.e, robust. We also find that these
quantities have very mild dependence on the sea quark mass and acquire values
which are very close to their respective ideal gas limits. Our results also
confirm robustness of the Wroblewski parameter.Comment: Published versio
A framework for detection and classification of events in neural activity
We present a method for the real time prediction of punctate events in neural
activity, based on the time-frequency spectrum of the signal, applicable both
to continuous processes like local field potentials (LFP) as well as to spike
trains. We test it on recordings of LFP and spiking activity acquired
previously from the lateral intraparietal area (LIP) of macaque monkeys
performing a memory-saccade task. In contrast to earlier work, where trials
with known start times were classified, our method detects and classifies
trials directly from the data. It provides a means to quantitatively compare
and contrast the content of LFP signals and spike trains: we find that the
detector performance based on the LFP matches the performance based on spike
rates. The method should find application in the development of neural
prosthetics based on the LFP signal. Our approach uses a new feature vector,
which we call the 2D cepstrum.Comment: 30 pages, 6 figures; This version submitted to the IEEE Transactions
in Biomedical Engineerin
Augmented space recursion for partially disordered systems
Off-stoichiometric alloys exhibit partial disorder, in the sense that only
some of the sublattices of the stoichiometric ordered alloy become disordered.
This paper puts forward a generalization of the augmented space recursion (ASR)
(introduced earlier by one of us (Mookerjee et al 1997(*))) for systems with
many atoms per unit cell. In order to justify the convergence properties of ASR
we have studied the convergence of various moments of local density of states
and other physical quantities like Fermi energy and band energy. We have also
looked at the convergence of the magnetic moment of Ni, which is very sensitive
to numerical approximations towards the k-space value 0.6 with the
number of recursion steps prior to termination.Comment: Latex 2e, 21 Pages, 13 Figures, iopb style file attache
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