780 research outputs found
Defining Exercise Performance Metrics for Flight Hardware Development
The space industry has prevailed over numerous design challenges in the spirit of exploration. Manned space flight entails creating products for use by humans and the Johnson Space Center has pioneered this effort as NASA's center for manned space flight. NASA Astronauts use a suite of flight exercise hardware to maintain strength for extravehicular activities and to minimize losses in muscle mass and bone mineral density. With a cycle ergometer, treadmill, and the Resistive Exercise Device available on the International Space Station (ISS), the Space Medicine community aspires to reproduce physical loading schemes that match exercise performance in Earth s gravity. The resistive exercise device presents the greatest challenge with the duty of accommodating 20 different exercises and many variations on the core set of exercises. This paper presents a methodology for capturing engineering parameters that can quantify proper resistive exercise performance techniques. For each specified exercise, the method provides engineering parameters on hand spacing, foot spacing, and positions of the point of load application at the starting point, midpoint, and end point of the exercise. As humans vary in height and fitness levels, the methodology presents values as ranges. In addition, this method shows engineers the proper load application regions on the human body. The methodology applies to resistive exercise in general and is in use for the current development of a Resistive Exercise Device. Exercise hardware systems must remain available for use and conducive to proper exercise performance as a contributor to mission success. The astronauts depend on exercise hardware to support extended stays aboard the ISS. Future plans towards exploration of Mars and beyond acknowledge the necessity of exercise. Continuous improvement in technology and our understanding of human health maintenance in space will allow us to support the exploration of Mars and the future of space exploration
Laboratory Photo-chemistry of PAHs: Ionization versus Fragmentation
Interstellar polycyclic aromatic hydrocarbons (PAHs) are expected to be
strongly processed by vacuum ultraviolet photons. Here, we report experimental
studies on the ionization and fragmentation of coronene (C24H12), ovalene
(C32H14) and hexa-peri-hexabenzocoronene (HBC; C42H18) cations by exposure to
synchrotron radiation in the range of 8--40 eV. The results show that for small
PAH cations such as coronene, fragmentation (H-loss) is more important than
ionization. However, as the size increases, ionization becomes more and more
important and for the HBC cation, ionization dominates. These results are
discussed and it is concluded that, for large PAHs, fragmentation only becomes
important when the photon energy has reached the highest ionization potential
accessible. This implies that PAHs are even more photo-stable than previously
thought. The implications of this experimental study for the photo-chemical
evolution of PAHs in the interstellar medium are briefly discussed
The CO A-X System for Constraining Cosmological Drift of the Proton-Electron Mass Ratio
The band system of carbon monoxide,
which has been detected in six highly redshifted galaxies (), is
identified as a novel probe method to search for possible variations of the
proton-electron mass ratio () on cosmological time scales. Laboratory
wavelengths of the spectral lines of the A-X (,0) bands for have
been determined at an accuracy of
through VUV Fourier-transform absorption spectroscopy, providing a
comprehensive and accurate zero-redshift data set. For the (0,0) and (1,0)
bands, two-photon Doppler-free laser spectroscopy has been applied at the accuracy level, verifying the absorption data. Sensitivity
coefficients for a varying have been calculated for the CO A-X
bands, so that an operational method results to search for -variation.Comment: 7 pages (main article), 3 figures, includes supplementary materia
Size effect in the ionization energy of PAH clusters
We report the first experimental measurement of the near-threshold
photo-ionization spectra of polycyclic aromatic hydrocarbon clusters made of
pyrene C16H10 and coronene C24H12, obtained using imaging photoelectron
photoion coincidence spectrometry with a VUV synchrotron beamline. The
experimental results of the ionization energy are confronted to calculated ones
obtained from simulations using dedicated electronic structure treatment for
large ionized molecular clusters. Experiment and theory consistently find a
decrease of the ionization energy with cluster size. The inclusion of
temperature effects in the simulations leads to a lowering of this energy and
to a quantitative agreement with the experiment. In the case of pyrene, both
theory and experiment show a discontinuity in the IE trend for the hexamer
VUV photo-processing of PAH cations: quantitative study on the ionization versus fragmentation processes
Interstellar polycyclic aromatic hydrocarbons (PAHs) are strongly affected by
the absorption of vacuum ultraviolet (VUV) photons in the interstellar medium
(ISM), yet the branching ratio between ionization and fragmentation is poorly
studied. This is crucial for the stability and charge state of PAHs in the ISM
in different environments, affecting in turn the chemistry, the energy balance,
and the contribution of PAHs to the extinction and emission curves. We studied
the interaction of PAH cations with VUV photons in the 7-20 eV range from the
synchrotron SOLEIL beamline, DESIRS. We recorded by action spectroscopy the
relative intensities of photo-fragmentation and photo-ionization for a set of
eight PAH cations ranging in size from 14 to 24 carbon atoms, with different
structures. At photon energies below ~13.6 eV fragmentation dominates for the
smaller species, while for larger species ionization is immediately competitive
after the second ionization potential (IP). At higher photon energies, all
species behave similarly, the ionization yield gradually increases, leveling
off between 0.8 and 0.9 at ~18 eV. Among isomers, PAH structure appears to
mainly affect the fragmentation cross section, but not the ionization cross
section. We also measured the second IP for all species and the third IP for
two of them, all are in good agreement with theoretical ones confirming that
PAH cations can be further ionized in the diffuse ISM. Determining actual PAH
dication abundances in the ISM will require detailed modeling. Our measured
photo-ionization yields for several PAH cations provide a necessary ingredient
for such models
Real-time motion planning with a fixed-wing UAV using an agile maneuver space
Small fixed-wing unmanned aerial vehicles (UAVs) are becoming increasingly capable of flying at low altitudes and in constrained environments. This paper addresses the problem of automating the flight of a fixed-wing UAV through highly constrained environments. The main contribution of this paper is the development of a maneuver space, integrating steady and transient agile maneuvers for a class of fixed-wing aircraft. The maneuver space is integrated into the rapidly-exploring random trees (RRT) algorithm. The RRT-based motion planner, together with a flight control system, is demonstrated in simulations and flight tests to efficiently generate and execute a motion plan through highly constrained 3D environments in real-time. The flight experimentsâwhich effectively demonstrated the usage of three highly agile maneuversâwere conducted using only on-board sensing and computing
Who Shares and Comments on News?: A Cross-National Comparative Analysis of Online and Social Media Participation
In this article, we present a cross-national comparative analysis of which online news users in practice engage with the participatory potential for sharing and commenting on news afforded by interactive features in news websites and social media technologies across a strategic sample of six different countries. Based on data from the 2016 Reuters Institute Digital News Report, and controlling for a range of factors, we find that (1) people who use social media for news and a high number of different social media platforms are more likely to also engage more actively with news outside social media by commenting on news sites and sharing news via email, (2) political partisans on both sides are more likely to engage in sharing and commenting particularly on news stories in social media, and (3) people with high interest in hard news are more likely to comment on news on both news sites and social media and share stores via social media (and people with high interest in any kind of news [hard or soft] are more likely to share stories via email). Our analysis suggests that the online environment reinforces some long-standing inequalities in participation while countering other long-standing inequalities. The findings indicate a self-reinforcing positive spiral where the already motivated are more likely in practice to engage with the potential for participation offered by digital media, and a negative spiral where those who are less engaged participate less
Otimização das temperaturas de anelamento de marcadores microssatĂ©lites Theobroma grandiflorum para caracterização de resistĂȘncia Ă Moniliophthora perniciosa.
O objetivo desse trabalho foi identificar a temperatura Ăłtima para anelamento de cada primer microssatĂ©lite, desenvolvidos para trabalhos de biologia molecular com a espĂ©cie Theobroma grandiflorum, ligados a resistĂȘncia Ă M. perniciosa
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