scholarly journals A Model of Stochastic Collisions as the Cause of Clumps in Debris Disks

2004 ◽  
Vol 202 ◽  
pp. 399-401
Author(s):  
M. C. Wyatt ◽  
W. R. F. Dent ◽  
J. S. Greaves ◽  
W. S. Holland
Keyword(s):  
Simple Model ◽  
Debris Disks ◽  
Heuristic Model ◽  
Detailed Model ◽  
Debris Disk ◽  
Collisional Evolution

We present a heuristic model for the collisional evolution of material in a debris disk. This is used to consider the probability that the 2-3% brightness clump observed in the sub-mm Fomalhaut disk is caused by stochastic collisions between large planetesimals. While this simple model finds that the probability that the clump is caused by collisions is low (about 1 in 80,000), a more detailed model is required to ascertain its true likelihood.

scholarly journals Adaptive Exponential Integrate-and-Fire Model as an Effective Description of Neuronal Activity

2005 ◽  
Vol 94 (5) ◽  
pp. 3637-3642 ◽  
Author(s):  
Romain Brette ◽  
Wulfram Gerstner
Keyword(s):  
Simple Model ◽  
Expressive Power ◽  
Detailed Model ◽  
Fire Model ◽  
Integrate And Fire ◽  
Conductance States ◽  
Effective Description ◽  
High Conductance

We introduce a two-dimensional integrate-and-fire model that combines an exponential spike mechanism with an adaptation equation, based on recent theoretical findings. We describe a systematic method to estimate its parameters with simple electrophysiological protocols (current-clamp injection of pulses and ramps) and apply it to a detailed conductance-based model of a regular spiking neuron. Our simple model predicts correctly the timing of 96% of the spikes (±2 ms) of the detailed model in response to injection of noisy synaptic conductances. The model is especially reliable in high-conductance states, typical of cortical activity in vivo, in which intrinsic conductances were found to have a reduced role in shaping spike trains. These results are promising because this simple model has enough expressive power to reproduce qualitatively several electrophysiological classes described in vitro.

scholarly journals The Debris Disk Explorer: a balloon-borne coronagraph for observing debris disks

2013 ◽  
Author(s):  
Lewis C. Roberts ◽  
Geoffrey Bryden ◽  
Wesley Traub ◽  
Stephen Unwin ◽  
John Trauger ◽  
...  
Keyword(s):  
Debris Disks ◽  
Debris Disk

scholarly journals Long‐Term Collisional Evolution of Debris Disks

2008 ◽  
Vol 673 (2) ◽  
pp. 1123-1137 ◽  
Author(s):  
Torsten Lohne ◽  
Alexander V. Krivov ◽  
Jens Rodmann
Keyword(s):  
Debris Disks ◽  
Collisional Evolution

scholarly journals On the solar system—debris disk connection

2007 ◽  
Vol 3 (S249) ◽  
pp. 347-354 ◽  
Author(s):  
Amaya Moro-Martín
Keyword(s):  
Solar System ◽  
Debris Disks ◽  
Debris Disk

AbstractThis paper emphasizes the connection between solar and extra-solar debris disks: how models and observations of the Solar System are helping us understand the debris disk phenomenon, and vice versa, how debris disks are helping us place our Solar System into context.

scholarly journals OH and HO<sub>2</sub> chemistry in clean marine air during SOAPEX-2

2004 ◽  
Vol 4 (1) ◽  
pp. 419-470
Author(s):  
R. Sommariva ◽  
A.-L. Haggerstone ◽  
L. J. Carpenter ◽  
N. Carslaw ◽  
D. J. Creasey ◽  
...  
Keyword(s):  
Free Radical ◽  
Simple Model ◽  
Southern Ocean ◽  
Marine Boundary Layer ◽  
Austral Summer ◽  
Chemical Mechanism ◽  
Detailed Model ◽  
Model Calculations ◽  
Chemical Complexity ◽  
The Poor

Abstract. Model-measurement comparisons of HOx in extremely clean air ([NO]<3  ppt) are reported. Measurements were made during the second Southern Ocean Photochemistry Experiment (SOAPEX-2), held in austral summer 1999 at the Cape Grim Baseline Air Pollution Station in north-western Tasmania, Australia. The free-radical chemistry was studied using a zero-dimensional box-model based upon the Master Chemical Mechanism (MCM). Two versions of the model were used, with different levels of chemical complexity, to explore the role of hydrocarbons upon free-radical budgets under very clean conditions. The "detailed" model was constrained to measurements of CO, CH4 and 15 NMHCs, while the "simple" model contained only the CO and  CH4 oxidation mechanisms, together with inorganic chemistry. The OH and HO2 (HOx) concentrations predicted by the two models agreed to within 5–10%. The model results were compared with the HOx concentrations measured by the FAGE (Fluorescence Assay by Gas Expansion) technique during four days of clean Southern Ocean marine boundary layer (MBL) air. The models overestimated OH concentrations by about 10% on two days and about 20% on the other two days. HO2 concentrations were measured during two of these days and the models overestimated the measured concentrations by about 40%. Better agreement with measured HO2 was observed by using data from several MBL aerosol measurements to estimate the aerosol surface area and by increasing the HO2 uptake coefficient to unity. This reduced the modelled HO2 overestimate by ~40%, with little effect on OH, because of the poor HO2 to OH conversion at the low ambient NOx concentrations. Local sensitivity analysis and Morris One-At-A-Time analysis were performed on the "simple" model, and showed the importance of reliable measurements of j(O1D) and [HCHO] and of the kinetic parameters that determine the efficiency of  O(1D) to OH and HCHO to HO2 conversion. A 2σ standard deviation of 30–40% for OH and 25–30% for HO2 was estimated for the model calculations using a Monte Carlo technique coupled with Latin Hypercube Sampling (LHS). A rate of production analysis, which demonstrates the relevance of  HCHO as a radical source, coupled with the poor performance of the models with respect to the concentrations of formaldehyde and peroxides, suggest that there are significant uncertainties in the chemical mechanism.

scholarly journals ACS Coronagraphic Observations of Optically Thin Debris Disks

2004 ◽  
Vol 221 ◽  
pp. 449-457
Author(s):  
Mark Clampin ◽  
John Krist ◽  
David R. Ardila ◽  
David A. Golimowski ◽  
Holland C. Ford ◽  
...  
Keyword(s):  
Angular Resolution ◽  
Debris Disks ◽  
Reference Star ◽  
Point Spread Functions ◽  
Point Spread ◽  
Imaging Mode ◽  
Debris Disk ◽  
Advanced Camera For Surveys

The Advanced Camera for Surveys (ACS) offers a coronagraphic imaging mode with angular resolution of 0.026″pixel−1. In combination with with the appropriate subtraction of reference star point spread functions (PSF) the coronagraph is capable of achieving contrast ratios of ∼1000. We present some of the first ACS observations of the optically thin debris disk HD141569A and discuss new results from these observations.

scholarly journals Comprehensive Census and Complete Characterization of Nearby Debris Disk Stars

2015 ◽  
Vol 10 (S314) ◽  
pp. 179-182
Author(s):  
Tara H. Cotten ◽  
Inseok Song
Keyword(s):  
Large Scale ◽  
Complete Characterization ◽  
High Resolution Spectroscopy ◽  
Debris Disks ◽  
Infrared Excess ◽  
History Of ◽  
Debris Disk ◽  
Host Stars ◽  
Comprehensive Study

AbstractDebris disks are intimately linked to planetary system evolution since the rocky material surrounding the host stars is believed to be due to secondary generation from the collisions of planetesimals. With the conclusion and lack of future large scale infrared excess survey missions, it is time to summarize the history of using excess emission in the infrared as a tracer of debris and exploit all available data as well as provide a comprehensive study of the parameters of these important objects. We have compiled a catalog of infrared excess stars from peer-reviewed articles and performed an extensive search for new debris disks by cross-correlating the Tycho-2 and AllWISE catalogs. This study will conclude following the thorough examination of each debris disk star's parameters obtained through high-resolution spectroscopy at various facilities which is currently ongoing. We will maintain a webpage (www.debrisdisks.org) devoted to these infrared excess sources and provide various resources related to our catalog creation, SED fitting, and data reduction.

scholarly journals Constraining the detectability of water ice in debris disks

2019 ◽  
Vol 629 ◽  
pp. A141
Author(s):  
M. Kim ◽  
S. Wolf ◽  
A. Potapov ◽  
H. Mutschke ◽  
C. Jäger
Keyword(s):  
Scattered Light ◽  
Spectral Energy ◽  
Debris Disks ◽  
Water Ice ◽  
Spatially Resolved ◽  
Infrared Telescope ◽  
Effective Medium Theories ◽  
Debris Disk ◽  
Highly Porous ◽  
Entire Planet

Context. Water ice is important for the evolution and preservation of life. Identifying the distribution of water ice in debris disks is therefore of great interest in the field of astrobiology. Furthermore, icy dust grains are expected to play important roles throughout the entire planet formation process. However, currently available observations only allow deriving weak conclusions about the existence of water ice in debris disks. Aims. We investigate whether it is feasible to detect water ice in typical debris disk systems. We take the following ice destruction mechanisms into account: sublimation of ice, dust production through planetesimal collisions, and photosputtering by UV-bright central stars. We consider icy dust mixture particles with various shapes consisting of amorphous ice, crystalline ice, astrosilicate, and vacuum inclusions (i.e., porous ice grains). Methods. We calculated optical properties of inhomogeneous icy dust mixtures using effective medium theories, that is, Maxwell-Garnett rules. Subsequently, we generated synthetic debris disk observables, such as spectral energy distributions and spatially resolved thermal reemission and scattered light intensity and polarization maps with our code DMS. Results. We find that the prominent ~3 and 44 μm water ice features can be potentially detected in future observations of debris disks with the James Webb Space Telescope (JWST) and the Space Infrared telescope for Cosmology and Astrophysics (SPICA). We show that the sublimation of ice, collisions between planetesimals, and photosputtering caused by UV sources clearly affect the observational appearance of debris disk systems. In addition, highly porous ice (or ice-rich aggregates) tends to produce highly polarized radiation at around 3 μm. Finally, the location of the ice survival line is determined by various dust properties such as a fractional ratio of ice versus dust, physical states of ice (amorphous or crystalline), and the porosity of icy grains.

scholarly journals Debris Disks and Multiplicity within the 75pc Volume-limited A-Star (VAST) Survey

2013 ◽  
Vol 8 (S299) ◽  
pp. 334-335
Author(s):  
R. J. De Rosa ◽  
B. Smith ◽  
J. Bulger ◽  
J. Patience ◽  
C. Marois ◽  
...  
Keyword(s):  
Future Study ◽  
Large Scale ◽  
Binary Systems ◽  
Debris Disks ◽  
Companion Star ◽  
Large Sample ◽  
Planetary Mass ◽  
Debris Disk

AbstractWe present the preliminary findings of an investigation of the multiplicity of debris disk stars identified within our Volume-limited A-star (VAST) multiplicity survey. Previous studies have produced conflicting results regarding the multiplicity fraction of debris disk-hosting stars compared with non-excess stars. By combining our large-scale volume-limited AO survey of A-type stars with the all-sky WISE catalogue, we have investigated the frequency of binary companions to a large sample of A-type stars with and without measured 22μm excess. The results of this study will allow for a greater understanding of the interaction between a companion star and a circumstellar debris disk, informing future study into the formation and stability of planetary-mass companions within binary systems.

Incorporating Culture and Competition for Status into Quantitative Financial Epidemiology Models

2014 ◽  
pp. 1-17
Author(s):  
Donald D. Hackney ◽  
Daniel L. Friesner ◽  
Matthew Q. McPherson
Keyword(s):  
Consumer Behavior ◽  
Simple Model ◽  
Psychological Factors ◽  
Conspicuous Consumption ◽  
Consumer Debt ◽  
Policy Makers ◽  
Detailed Model ◽  
Ecological Characteristics

This chapter extends the financial epidemiology literature as it applies to the acquisition of consumer debt. A recent manuscript provided a very simple model to illustrate how conspicuous consumption within a community (in the vernacular, “keeping up with the Joneses”) can lead to situations where a contagion of financial insolvency may occur (Friesner, McPherson, & Hackney, 2014). However, that model simply illustrates the feasibility of modeling both conspicuous consumption and financial contagions in a single framework. It does not explicitly incorporate most of the epidemiological, socio-cultural, and psychological factors that drive decisions to use debt to finance conspicuous consumption. In this chapter, the authors build a much more detailed model of financial epidemiology that includes (or can be extended to include) most of the salient ecological characteristics advanced by financial economists (neoclassical or heterodox) and epidemiologists. The model can be used to illustrate specific characteristics that promote (or inhibit) consumer behavior that pushes the household into financial exigency. The results can therefore provide a more informative basis for policy makers to reduce the prevalence of bankruptcy or other financial insolvency within a community as a whole.

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