206 research outputs found
VisIVOWeb: A WWW Environment for Large-Scale Astrophysical Visualization
This article presents a newly developed Web portal called VisIVOWeb that aims
to provide the astrophysical community with powerful visualization tools for
large-scale data sets in the context of Web 2.0. VisIVOWeb can effectively
handle modern numerical simulations and real-world observations. Our
open-source software is based on established visualization toolkits offering
high-quality rendering algorithms. The underlying data management is discussed
with the supported visualization interfaces and movie-making functionality. We
introduce VisIVOWeb Network, a robust network of customized Web portals for
visual discovery, and VisIVOWeb Connect, a lightweight and efficient solution
for seamlessly connecting to existing astrophysical archives. A significant
effort has been devoted for ensuring interoperability with existing tools by
adhering to IVOA standards. We conclude with a summary of our work and a
discussion on future developments
Dynamics of Line-Driven Winds from Disks in Cataclysmic Variables. II. Mass Loss Rates and Velocity Laws
We analyze the dynamics of 2D stationary line-driven winds from accretion
disks in cataclysmic variables (CVs), by generalizing the Castor, Abbott and
Klein theory. In paper 1, we have solved the wind Euler equation, derived its
two eigenvalues, and addressed the solution topology and wind geometry. Here,
we focus on mass loss and velocity laws. We find that disk winds, even in
luminous novalike variables, have low optical depth, even in the strongest
driving lines. This suggests that thick-to-thin transitions in these lines
occur. For disks with a realistic radial temperature, the mass loss is
dominated by gas emanating from the inner decade in r. The total mass loss rate
associated with a luminosity 10 Lsun is 10^{-12} Msun/yr, or 10^{-4} of the
mass accretion rate. This is one order of magnitude below the lower limit
obtained from P Cygni lines, when the ionizing flux shortwards of the Lyman
edge is supressed. The difficulties with such small mass loss rates in CVs are
principal, and confirm our previous work. We conjecture that this issue may be
resolved by detailed nonLTE calculations of the line force within the context
of CV disk winds, and/or better accounting for the disk energy distribution and
wind ionization structure. We find that the wind velocity profile is well
approximated by the empirical law used in kinematical modeling. The
acceleration length scale is given by the footpoint radius of the wind
streamline in the disk. This suggests an upper limit of 10 Rwd to the
acceleration scale, which is smaller by factors of a few as compared to values
derived from line fitting.Comment: 14 pages, 3 Postscript figures, also from
http://www.pa.uky.edu/~shlosman/publ.html. Astrophysical Journal, submitte
Recommended from our members
The Energy Diameter Effect
We explore various relations for the detonation energy and velocity as they relate to the inverse radius of the cylinder. The detonation rate-inverse slope relation seen in reactive flow models can be used to derive the familiar Eyring equation. Generalized inverse radii can be shown to fit large quantities of cylinder results. A rough relation between detonation energy and detonation velocity is found from collected JWL values. Cylinder test data for ammonium nitrate mixes down to 6.35 mm radii are presented, and a size energy effect is shown to exist in the Cylinder test data. The relation that detonation energy is roughly proportional to the square of the detonation velocity is shown by data and calculation
Spontaneous Branching of Anode-Directed Streamers between Planar Electrodes
Non-ionized media subject to strong fields can become locally ionized by
penetration of finger-shaped streamers. We study negative streamers between
planar electrodes in a simple deterministic continuum approximation. We observe
that for sufficiently large fields, the streamer tip can split. This happens
close to Firsov's limit of `ideal conductivity'. Qualitatively the tip
splitting is due to a Laplacian instability quite like in viscous fingering.
For future quantitative analytical progress, our stability analysis of planar
fronts identifies the screening length as a regularization mechanism.Comment: 4 pages, 6 figures, submitted to PRL on Nov. 16, 2001, revised
version of March 10, 200
Integrating virtual reality and gis tools for geological mapping, data collection and analysis: An example from the metaxa mine, santorini (Greece)
In the present work we highlight the effectiveness of integrating different techniques and tools for better surveying, mapping and collecting data in volcanic areas. We use an Immersive Virtual Reality (IVR) approach for data collection, integrated with Geographic Information System (GIS) analysis in a well-known volcanological site in Santorini (Metaxa mine), a site where volcanic processes influenced the islandâs industrial development, especially with regard to pumice mining. Specifically, we have focused on: (i) three-dimensional (3D) high-resolution IVR scenario building, based on Structure from Motion photogrammetry (SfM) modeling; (ii) subsequent geological survey, mapping and data collection using IVR; (iii) data analysis, e.g., calculation of extracted volumes, as well as production of new maps in a GIS environment using input data directly from the IVR survey; and finally, (iv) presentation of new outcomes that highlight the importance of the Metaxa Mine as a key geological and volcanological geosite
The Impact of SARS-COVID-19 Outbreak on European Cities Urban Mobility
The global outbreak of the SARS-COVID-19 pandemic has changed our lives, driving an unprecedented transformation of our habits. In response, the authorities have enforced several measures, including social distancing and travel restrictions that lead to the temporary closure of activities centered around schools, companies, local businesses to those pertaining to the recreation category. As such, with a mobility reduction, the life of our cities during the outbreak changed significantly. In this paper, we aim at drawing attention to this problem and perform an analysis for multiple cities through crowdsensed information available from datasets such as Apple Maps, to shed light on the changes undergone during both the outbreak and the recovery. Specifically, we exploit data characterizing many mobility modes like driving, walking, and transit. With the use of Gaussian Processes and clustering techniques, we uncover patterns of similarity between the major European cities. Further, we perform a prediction analysis that permits forecasting the trend of the recovery process and exposes the deviation of each city from the trend of the cluster. Our results unveil that clusters are not typically formed by cities with geographical ties, but rather on the spread of the infection, lockdown measures, and citizensâ reactions
The CORONA business in modern cities
As a response to the global outbreak of the SARS-COVID-19 pandemic, authorities have enforced a number of measures including social distancing, travel restrictions that lead to the "temporary" closure of activities stemming from public services, schools, industry to local businesses. In this poster we draw the attention to the impact of such measures on urban environments and activities. For this, we use crowdsensed information available from datasets like Google Popular Times and Apple Maps to shed light on the changes undergone during the outbreak and the recovery
Blob Ejection from Advection-dominated Accretion Flow II: the Multiwavelength Properties of Light Curves
It has been argued that blobs ejected from advection-dominated accretion flow
through the accretion-ejection instability undergo expansion due to their high
internal energy density. The expanding blobs interact with their surroundings
and form strong shock, which accelerates a group of electrons to be
relativistic. Then flares are formed. This model has advances in two aspects:
shock acceleration and self-consistent injection. We derive an analytical
formula of the injection function of relativistic electrons based on the
Sedov's law. We calculate the time-dependent spectrum of relativistic electrons
in such an expanding blob. The light-travel effect, the evolution of the
electron spectrum due to energy loss, and the escape of relativistic electrons
from the radiating region are considered, as well as the expansion (at
sub-relativistic speed) of the coasting blob. A large number of light curves
spanning wide spaces of parameters have been given in this paper. Regarding the
symmetry, relative amplitude, duration of a flare, and the time lag between
peak fluxes, we find four basic kinds of light curves for the non-expanding
blob, and seven basic kinds of light curves for the expanding blob. We also
calculate the evolution of the photon spectrum from both non-expanding and
expanding blobs. Different shapes in the phase of decreasing luminosity are
then obtained for different parameter values. The photon index, , keeps constant for non-expanding blobs when luminosity decreases, whereas
continues to decrease after the luminosity reaches its
maximum for expanding blobs. It is expected that we can extract the information
of ejected blobs from the observed light curves based on the present model.Comment: 23 pages in emulatapj.sty, accepted by the Astrophysical Journa
- âŠ