577 research outputs found
Better astronomical images by selecting moments of good seeing in captured video
This research project attempted to create software by which images of astronomical objects, captured through land based telescopes could, be enhanced to reduce the effects of the earth\u27s turbulent atmosphere. Typically astronomical images are enhanced by registering, shifting and co-adding captured images of an object of interest. Our approach is similar in that co-adding is also utilized, however we take the typical procedure a step further. Our hypothesis is that by selecting certain images from the captured group, via the application of a simple quality metric, the output of the co-adding process will yield a higher quality image than by traditional methods. Further this research aims to use a simple quality metric on incoming video images and process them in much shorter time, ideally near real-time, as opposed to a lengthy post-processing procedure
Measurement of Aerodynamic Heat Transfer to a Deflected Trailing-edge Flap on a Delta Fin in Free Flight at Mach Numbers from 1.5 to 2.6
Flight Measurements of Boundary-layer Temperature Profiles on a Body of Revolution (NACA RM-10) at Mach Numbers from 1.2 to 3.5
Simulation of radio emission from cosmic ray air shower with SELFAS2
We present a microscopic computation of the radio emission from air showers
initiated by ultra-high energy cosmic rays in the atmosphere. The strategy
adopted is to compute each secondary particle contribution of the
electromagnetic component and to construct the total signal at any location.
SELFAS2 is a code which doesn't rely on air shower generators like AIRES or
CORSIKA and it is based on the concept of air shower universality which makes
it completely autonomous. Each positron and electron of the air shower is
generated randomly following relevant distributions and tracking them along
their travel in the atmosphere. We confirm in this paper earlier results that
the radio emission is mainly due to the time derivative of the transverse
current and the time derivative of the charge excess. The time derivative of
the transverse current created by systematic deviations of charges in the
geomagnetic field is usually dominant compared to the charge excess
contribution except for the case of an air shower parallel to the geomagnetic
field.Comment: 17 pages, 21 figure
Search for cool extrasolar giant planets combining coronagraphy, spectral and angular differential imaging
Spectral differential imaging (SDI) is part of the observing strategy of
current and on-going high-contrast imaging instruments on ground-based
telescopes. Although it improves the star light rejection, SDI attenuates the
signature of off-axis companions to the star, just like angular differential
imaging (ADI). However, the attenuation due to SDI has the peculiarity of being
dependent on the spectral properties of the companions. To date, no study has
investigated these effects. Our team is addressing this problem based on data
from a direct imaging survey of 16 stars combining the phase-mask coronagraph,
the SDI and the ADI modes of VLT/NaCo. The objective of the survey is to search
for cool (Teff<1000-1300 K) giant planets at separations of 5-10 AU orbiting
young, nearby stars (<200 Myr, <25 pc). The data analysis did not yield any
detections. As for the estimation of the sensitivity limits of SDI-processed
images, we show that it requires a different analysis than that used in
ADI-based surveys. Based on a method using the flux predictions of evolutionary
models and avoiding the estimation of contrast, we determine directly the mass
sensitivity limits of the survey for the ADI processing alone and with the
combination of SDI and ADI. We show that SDI does not systematically improve
the sensitivity due to the spectral properties and self-subtraction of point
sources.Comment: 5 pages, 2 figure
Digital technologies for population health and health equity gains: the perspective of public health associations
RACE-OC Project: Rotation and variability in the epsilon Chamaeleontis, Octans, and Argus stellar associations
We aim at determining the rotational and magnetic-related activity properties
of stars at different stages of evolution. We focus our attention primarily on
members of young stellar associations of known ages. Specifically, we extend
our previous analysis in Paper I (Messina et al. 2010, A&A 520, A15) to 3
additional young stellar associations beyond 100 pc and with ages in the range
6-40 Myr: epsilon Chamaeleontis (~6 Myr), Octans (~20 Myr), and Argus (~40
Myr). Additional rotational data of eta Chamaeleontis and IC2391 clusters are
also considered. Rotational periods were determined from photometric
time-series data obtained by the All Sky Automated Survey (ASAS) and the Wide
Angle Search for Planets (SuperWASP) archives. With the present study we have
completed the analysis of the rotational properties of the late-type members of
all known young loose associations in the solar neighborhood. Considering also
the results of Paper I, we have derived the rotation periods of 241 targets:
171 confirmed, 44 likely, 26 uncertain. The period of the remaining 50 stars
known to be part of loose associations still remains unknown. This rotation
period catalogue, and specifically the new information presented in this paper
at ~6, 20, and 40 Myr, contributes significantly to a better observational
description of the angular momentum evolution of young stars.Comment: Accepted by Astronomy & Astrophysics. Onlines figures will be
available at CD
Does face inversion change spatial frequency tuning?
International audienceThe authors examined spatial frequency (SF) tuning of upright and inverted face identification using an SF variant of the Bubbles technique (F. Gosselin & P. G. Schyns, 2001). In Experiment 1, they validated the SF Bubbles technique in a plaid detection task. In Experiments 2a-c, the SFs used for identifying upright and inverted inner facial features were investigated. Although a clear inversion effect was present (mean accuracy was 24% higher and response times 455 ms shorter for upright faces), SF tunings were remarkably similar in both orientation conditions (mean r = .98; an SF band of 1.9 octaves centered at 9.8 cycles per face width for faces of about 6 degrees ). In Experiments 3a and b, the authors demonstrated that their technique is sensitive to both subtle bottom-up and top-down induced changes in SF tuning, suggesting that the null results of Experiments 2a-c are real. The most parsimonious explanation of the findings is provided by the quantitative account of the face inversion effect: The same information is used for identifying upright and inverted inner facial features, but processing has greater sensitivity with the former
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Hurricanes and Climate: The U.S. CLIVAR Working Group on Hurricanes
While a quantitative climate theory of tropical cyclone formation remains elusive, considerable progress has been made recently in our ability to simulate tropical cyclone climatologies and to understand the relationship between climate and tropical cyclone formation. Climate models are now able to simulate a realistic rate of global tropical cyclone formation, although simulation of the Atlantic tropical cyclone climatology remains challenging unless horizontal resolutions finer than 50 km are employed. This article summarizes published research from the idealized experiments of the Hurricane Working Group of U.S. Climate and Ocean: Variability, Predictability and Change (CLIVAR). This work, combined with results from other model simulations, has strengthened relationships between tropical cyclone formation rates and climate variables such as midtropospheric vertical velocity, with decreased climatological vertical velocities leading to decreased tropical cyclone formation. Systematic differences are shown between experiments in which only sea surface temperature is increased compared with experiments where only atmospheric carbon dioxide is increased. Experiments where only carbon dioxide is increased are more likely to demonstrate a decrease in tropical cyclone numbers, similar to the decreases simulated by many climate models for a future, warmer climate. Experiments where the two effects are combined also show decreases in numbers, but these tend to be less for models that demonstrate a strong tropical cyclone response to increased sea surface temperatures. Further experiments are proposed that may improve our understanding of the relationship between climate and tropical cyclone formation, including experiments with two-way interaction between the ocean and the atmosphere and variations in atmospheric aerosols
Hurricanes and Climate: the U.S. CLIVAR Working Group on Hurricanes
While a quantitative climate theory of tropical cyclone formation remains elusive, considerable progress has been made recently in our ability to simulate tropical cyclone climatologies and understand the relationship between climate and tropical cyclone formation. Climate models are now able to simulate a realistic rate of global tropical cyclone formation, although simulation of the Atlantic tropical cyclone climatology remains challenging unless horizontal resolutions finer than 50 km are employed. The idealized experiments of the Hurricane Working Group of U.S. CLIVAR, combined with results from other model simulations, have suggested relationships between tropical cyclone formation rates and climate variables such as mid-tropospheric vertical velocity. Systematic differences are shown between experiments in which only sea surface temperature is increases versus experiments where only atmospheric carbon dioxide is increased, with the carbon dioxide experiments more likely to demonstrate a decrease in numbers. Further experiments are proposed that may improve our understanding of the relationship between climate and tropical cyclone formation, including experiments with two-way interaction between the ocean and the atmosphere and variations in atmospheric aerosols
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