63,548 research outputs found
Detecting multineuronal temporal patterns in parallel spike trains
We present a non-parametric and computationally efficient method that detects spatiotemporal firing patterns and pattern sequences in parallel spike trains and tests whether the observed numbers of repeating patterns and sequences on a given timescale are significantly different from those expected by chance. The method is generally applicable and uncovers coordinated activity with arbitrary precision by comparing it to appropriate surrogate data. The analysis of coherent patterns of spatially and temporally distributed spiking activity on various timescales enables the immediate tracking of diverse qualities of coordinated firing related to neuronal state changes and information processing. We apply the method to simulated data and multineuronal recordings from rat visual cortex and show that it reliably discriminates between data sets with random pattern occurrences and with additional exactly repeating spatiotemporal patterns and pattern sequences. Multineuronal cortical spiking activity appears to be precisely coordinated and exhibits a sequential organization beyond the cell assembly concept
On the Observability of Giant Protoplanets in Circumstellar Disks
We investigate the possibility to detect giant planets that are still
embedded in young circumstellar disks. Based on models with different stellar,
planetary, and disk masses, and different radial positions of the planet we
analyze the resulting submillimeter appearance of these systems. We find that
the influence of the planet on the spectral energy distribution could not be
distinguished from that of other disk parameters. However, dust reemission
images of the disks show that the hot region in the proximity of a young
planet, along with the gap, could indeed be detected and mapped with the
Atacama Large Millimeter Array in the case of nearby circumstellar disks
(d<100pc) in approximate face-on orientation.Comment: ApJ, in pres
Detecting planets in protoplanetary disks: A prospective study
We investigate the possibility to find evidence for planets in circumstellar
disks by infrared and submillimeter interferometry. We present simulations of a
circumstellar disk around a solar-type star with an embedded planet of 1
Jupiter mass. The three-dimensional (3D) density structure of the disk results
from hydrodynamical simulations. On the basis of 3D radiative transfer
simulations, images of this system were calculated. The intensity maps provide
the basis for the simulation of the interferometers VLTI (equipped with the
mid-infrared instrument MIDI) and ALMA. While MIDI/VLTI will not provide the
possibility to distinguish between disks with or without a gap on the basis of
visibility measurements, ALMA will provide the necessary basis for a direct gap
detection.Comment: 5 page
Large-scale Vortices in Protoplanetary Disks: On the observability of possible early stages of planet formation
We investigate the possibility of mapping large-scale anti-cyclonic vortices,
resulting from a global baroclinic instability, as pre-cursors of planet
formation in proto-planetary disks with the planned Atacama Large Millimeter
Array (ALMA). On the basis of three-dimensional radiative transfer simulations,
images of a hydrodynamically calculated disk are derived which provide the
basis for the simulation of ALMA. We find that ALMA will be able to trace the
theoretically predicted large-scale anti-cyclonic vortex and will therefore
allow testing of existing models of this very early stage of planet formation
in circumstellar disks.Comment: Accepted by ApJ (Letters section). A preprint version with
high-quality figures can be downloaded from
http://spider.ipac.caltech.edu/staff/swolf/homepage/public/preprints/
vortex.ps.g
Effect of dust grain porosity on the appearance of protoplanetary disks
We theoretically analyze protoplanetary disks consisting of porous dust
grains. In the analysis of observations of protoplanetary disks the dust phase
is often assumed to consist of spherical grains, allowing one to apply the Mie
scattering formalism. However, in reality, the shape of dust grains is expected
to deviate strongly from that of a sphere. We investigate the influence of
porous dust grains on the temperature distribution and observable appearance of
protoplanetary disks for dust grain porosities of up to 60 %. We performed
radiative transfer modeling to simulate the temperature distribution, spectral
energy distribution, and spatially resolved intensity and polarization maps.
The optical properties of porous grains were calculated using the method of
discrete dipole approximation. We find that the flux in the optical wavelength
range is for porous grains higher than for compact, spherical grains. The
profile of the silicate peak at 9.7 um strongly depends on the degree of grain
porosity. The temperature distribution shows significant changes in the
direction perpendicular to the midplane. Moreover, simulated polarization maps
reveal an increase of the polarization degree by a factor of about four when
porous grains are considered, regardless of the disk inclination. The
polarization direction is reversed in selected disk regions, depending on the
wavelength, grain porosity, and disk inclination. We discuss several possible
explanations of this effect and find that multiple scattering explains the
effect best. Porosity influences the observable appearance of protoplanetary
disks. In particular, the polarization reversal shows a dependence on grain
porosity. The physical conditions within the disk are altered by porosity,
which might have an effect on the processes of grain growth and disk evolution.Comment: 12 pages, 18 figure
Tracing the ISM magnetic field morphology: The potential of multi-wavelength polarization measurements
We present a case study to demonstrate the potential of
multi-wavelength polarization measurements. The aim is to investigate the
effects that dichroic polarization and thermal re-emission have on tracing the
magnetic field in the interstellar medium (ISM). Furthermore, we analyze the
crucial influence of imperfectly aligned compact dust grains on the resulting
synthetic continuum polarization maps. We developed an
extended version of the well-known 3D Monte-Carlo radiation transport code MC3D
for multi-wavelength polarization simulations running on an adaptive grid.We
investigated the interplay between radiation, magnetic fields and dust grains.
Our results were produced by post-processing both ideal density distributions
and sophisticated magnetohydrodynamic (MHD) collapse simulations with radiative
transfer simulations. We derived spatially resolved maps of intensity, optical
depth, and linear and circular polarization at various inclination angles and
scales in a wavelength range from 7 to 1 . We
predict unique patterns in linear and circular polarization maps for different
types of density distributions and magnetic field morphologies for test setups
and sophisticated MHD collapse simulations. We show that alignment processes of
interstellar dust grains can significantly influence the resulting synthetic
polarization maps. Multi-wavelength polarization measurements allow one to
predict the morphology of the magnetic field inside the ISM. The interpretation
of polarization measurements of complex structures still remains ambiguous
because of the large variety of the predominant parameters in the ISM.Comment: 14 pages, 12 figures, 1 table, Paper accepted 2014 by A&
Southern California marine sport fishing from privately owned boats: catch and effort for October-December 1982
The catch landed and effort expended by private-boat sport
fishermen were studied in southern California marine waters
between October and December 1982, to determine the impact of one segment of the sport fishery on local marine resources. Fishermen returning from fishing trips were interviewed at launch ramps, hoists, and boat-rental facilities. This report contains quantitative data and statistical estimates of total effort, total catch, catch of preferred species, and length frequencies for those species whose catches are regulated by minimum size limits.
An estimated 157,000 organisms were landed by 57,700 anglers and 4800 divers. The major components of the angler catch were Pacific mackerel, Scomber japonicus (28,700 estimated catch): white croaker, Genyonemus lineatus (24,000 estimated catch); and Pacific bonito, Sarda chiliensis (16,700 estimated catch). These three species represented almost half the total estimated angler catch. Rockfishes, Sebastes spp: were a major catch component; the 35 rockfish species landed made up 24% of the estimated catch. Divers landed an estimated 14,700 fishes and invertebrates. Chief among these were abalone, Haliotis spp. (4200 estimated catch);
rock scallop, Hinnites rugosus (3600 estimated catch); and
California spiny lobster, Panulirus interruptus (2500 estimated catch).
Angler and diver compliance with size-limit regulations was
generally favorable, with diver compliance being particularly scrupulous, especially with invertebrate species. The compliance rate for California halibut, Paralichthys californicus, showed a drop from the previous quarter (July - September 1982) from 70 to 59% legal. During the same time period, size-limit compliance rose from 4 to 20% for Pacific bonito, a species with a tolerance allowing the take of some under-sized fish. (28p.
Debris Disk Radiative Transfer Simulation Tool (DDS)
A WWW interface for the simulation of spectral energy distributions of
optically thin dust configurations with an embedded radiative source is
presented. The density distribution, radiative source, and dust parameters can
be selected either from an internal database or defined by the user. This tool
is optimized for studying circumstellar debris disks where large grains are
expected to determine the far-infrared through millimeter dust reemission
spectral energy distribution. The tool is available at
http://aida28.mpia-hd.mpg.de/~swolf/ddsComment: Comp. Phys. Comm, 2005, in pres
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