1,555 research outputs found
Analysis of multi-sensor data, 12 September - 11 December 1968
Analysis of multi-sensor data obtained by Earth Resources Aircraft Progra
The Onset of Planet Formation in Brown Dwarf Disks
The onset of planet formation in protoplanetary disks is marked by the growth
and crystallization of sub-micron-sized dust grains accompanied by dust
settling toward the disk mid-plane. Here we present infrared spectra of disks
around brown dwarfs and brown dwarf candidates. We show that all three
processes occur in such cool disks in a way similar or identical to that in
disks around low- and intermediate-mass stars. These results indicate that the
onset of planet formation extends to disks around brown dwarfs, suggesting that
planet formation is a robust process occurring in most young circumstellar
disks.Comment: Published in Science 2005, vol 310, 834; 3 pages in final format, 4
figures + 8 pages Supporting Online Material. For final typeset, see
http://www.sciencemag.org/cgi/content/abstract/310/5749/834?eto
Combining in-situ and in-transit processing to enable extreme-scale scientific analysis
pre-printWith the onset of extreme-scale computing, I/O constraints make it increasingly difficult for scientists to save a sufficient amount of raw simulation data to persistent storage. One potential solution is to change the data analysis pipeline from a post-process centric to a concurrent approach based on either in-situ or in-transit processing. In this context computations are considered in-situ if they utilize the primary compute resources, while in-transit processing refers to offloading computations to a set of secondary resources using asynchronous data transfers. In this paper we explore the design and implementation of three common analysis techniques typically performed on large-scale scientific simulations: topological analysis, descriptive statistics, and visualization. We summarize algorithmic developments, describe a resource scheduling system to coordinate the execution of various analysis workflows, and discuss our implementation using the DataSpaces and ADIOS frameworks that support efficient data movement between in-situ and in-transit computations. We demonstrate the efficiency of our lightweight, flexible framework by deploying it on the Jaguar XK6 to analyze data generated by S3D, a massively parallel turbulent combustion code. Our framework allows scientists dealing with the data deluge at extreme scale to perform analyses at increased temporal resolutions, mitigate I/O costs, and significantly improve the time to insight
The First Detailed Look at a Brown Dwarf Disk
The combination of mid-infrared and recent submm/mm measurements allows us to
set up the first comprehensive spectral energy distribution (SED) of the
circumstellar material around a young Brown Dwarf. Simple arguments suggest
that the dust is distributed in the form of a disk. We compare basic models to
explore the disk parameters. The modeling shows that a flat disk geometry fits
well the observations. A flared disk explains the SED only if it has a
puffed-up inner rim and an inner gap much larger than the dust sublimation
radius. Similarities and differences with disks around T Tauri stars are
discussed.Comment: 11 pages, 1 figur
Remnant gas in evolved circumstellar disks: Herschel PACS observations of 10-100 Myr old disk systems
We present Herschel PACS spectroscopy of the [OI] 63 micron gas-line for
three circumstellar disk systems showing signs of significant disk evolution
and/or planet formation: HR 8799, HD 377 and RX J1852.3-3700. [OI] is
undetected toward HR 8799 and HD 377 with 3 sigma upper limits of 6.8 x 10^-18
W m^-2 and 9.9 x 10^-18 W m^-2 respectively. We find an [OI] detection for RX
J1852.3-3700 at 12.3 +- 1.8 x 10^-18 W m^-2. We use thermo-chemical disk models
to model the gas emission, using constraints on the [OI] 63 micron, and
ancillary data to derive gas mass upper limits and constrain gas-to-dust
ratios. For HD 377 and HR 8799, we find 3 sigma upper limits on the gas mass of
0.1-20 Mearth. For RX J1852.3-3700, we find two distinct disk scenarios that
could explain the detection of [OI] 63 micron and CO(2-1) upper limits reported
from the literature: (i) a large disk with gas co-located with the dust (16-500
AU), resulting in a large tenuous disk with ~16 Mearth of gas, or (ii) an
optically thick gas disk, truncated at ~70 AU, with a gas mass of 150 Mearth.
We discuss the implications of these results for the formation and evolution of
planets in these three systems.Comment: Accepted for publication in ApJ, 8 pages ApJ style (incl.
references), 2 figures, 4 table
Dynamic PRA: an Overview of New Algorithms to Generate, Analyze and Visualize Data
State of the art PRA methods, i.e. Dynamic PRA
(DPRA) methodologies, largely employ system
simulator codes to accurately model system dynamics.
Typically, these system simulator codes (e.g., RELAP5 )
are coupled with other codes (e.g., ADAPT,
RAVEN that monitor and control the simulation. The
latter codes, in particular, introduce both deterministic
(e.g., system control logic, operating procedures) and
stochastic (e.g., component failures, variable uncertainties)
elements into the simulation. A typical DPRA analysis is
performed by:
1. Sampling values of a set of parameters from the
uncertainty space of interest
2. Simulating the system behavior for that specific set of
parameter values
3. Analyzing the set of simulation runs
4. Visualizing the correlations between parameter values
and simulation outcome
Step 1 is typically performed by randomly sampling
from a given distribution (i.e., Monte-Carlo) or selecting
such parameter values as inputs from the user (i.e.,
Dynamic Event Tre
Radiative transfer in very optically thick circumstellar disks
In this paper we present two efficient implementations of the diffusion
approximation to be employed in Monte Carlo computations of radiative transfer
in dusty media of massive circumstellar disks. The aim is to improve the
accuracy of the computed temperature structure and to decrease the computation
time. The accuracy, efficiency and applicability of the methods in various
corners of parameter space are investigated. The effects of using these methods
on the vertical structure of the circumstellar disk as obtained from
hydrostatic equilibrium computations are also addressed. Two methods are
presented. First, an energy diffusion approximation is used to improve the
accuracy of the temperature structure in highly obscured regions of the disk,
where photon counts are low. Second, a modified random walk approximation is
employed to decrease the computation time. This modified random walk ensures
that the photons that end up in the high-density regions can quickly escape to
the lower density regions, while the energy deposited by these photons in the
disk is still computed accurately. A new radiative transfer code, MCMax, is
presented in which both these diffusion approximations are implemented. These
can be used simultaneously to increase both computational speed and decrease
statistical noise. We conclude that the diffusion approximations allow for fast
and accurate computations of the temperature structure, vertical disk structure
and observables of very optically thick circumstellar disks.Comment: Accepted for publication in A&
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