80 research outputs found
Effect of polydispersity on the transport and sound absorbing properties of three-dimensional random fibrous structures
Sophisticated numerical approaches can predict the properties of composite
nonwovens. However, for polydisperse random fibrous media, we need to identify
microstructural descriptors for accurate predictions. We manufactured
polydisperse composite felts with different fibrous structures and
characterized them using scanning electron microscope images. The images showed
a wide distribution of fiber diameters and a decreasing standard deviation of
the azimuthal angle of fibers with increasing compression rate. Current models
could not capture the evolution of their transport properties with compression
rate. Therefore, we developed a fiber network model for the transport processes
of transversely isotropic random fibrous media. The model relates the main
visco-thermal dissipation mechanisms to the largest channels within the fluid
phase, while the smallest channels lead the inertial behaviors. We estimated
the viscous and thermal permeabilities from a representative elementary volume
(REV) with a volume weighted average diameter, and the viscous and thermal
characteristic lengths from a REV with inverse volume weighted average
diameter. A unified empirical model was proposed. The model predictions agree
with the experimental results.Comment: 29 pages, 19 figure
Once is an Instance, Twice is a Hobby: Multiple Optical and Near-Infrared Changing-Look Events in NGC 5273
NGC 5273 is a known optical and X-ray variable AGN. We analyze new and
archival IR, optical, UV, and X-ray data in order to characterize its long-term
variability from 2000 to 2022. At least one changing-look event occurred
between 2011 and 2014, when the AGN changed from a Type 1.8/1.9 Seyfert to a
Type 1. It then faded considerably at all wavelengths, followed by a dramatic
but slow increase in UV/optical brightness between 2021 and 2022. We propose
that NGC 5273 underwent multiple changing-look events between 2000 and 2022 --
starting as a Type 1.8/1.9, NGC 5273 changes-look to a Type 1 only temporarily
in 2002 and again in 2014, reverting back to a Type 1.8/1.9 by 2005 and 2017,
respectively. In 2022, it is again a Type 1 Seyfert with optical and NIR broad
emission lines. We characterize the changing-look events and their connection
to the dynamic accretion and radiative processes in NGC 5273.Comment: 18 pages, 13 figures, 4 tables, submitting to MNRA
Software effort prediction using regression rule extraction from neural networks
10.1109/ICTAI.2010.82Proceedings - International Conference on Tools with Artificial Intelligence, ICTAI245-52PCTI
Experimental determination of the macroscopic fatigue properties of metal hollow sphere structures
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