6,123 research outputs found
Hubble Ultraviolet Spectroscopy of Jupiter Trojans
We present the first ultraviolet spectra of Jupiter Trojans. These
observations were carried out using the Space Telescope Imaging Spectrograph on
the Hubble Space Telescope and cover the wavelength range 200-550 nm at low
resolution. The targets include objects from both of the Trojan color
subpopulations (less-red and red). We do not observe any discernible absorption
features in these spectra. Comparisons of the averaged UV spectra of less-red
and red targets show that the subpopulations are spectrally distinct in the UV.
Less-red objects display a steep UV slope and a rollover at around 450 nm to a
shallower visible slope, whereas red objects show the opposite trend.
Laboratory spectra of irradiated ices with and without HS exhibit
distinct UV absorption features; consequently, the featureless spectra observed
here suggest HS alone is not responsible for the observed color
bimodality of Trojans, as has been previously hypothesized. We propose some
possible explanations for the observed UV-visible spectra, including complex
organics, space weathering of iron-bearing silicates, and masked features due
to previous cometary activity.Comment: 7 pages, 4 figures, accepted by A
Defining Lyfe in the Universe: From Three Privileged Functions to Four Pillars
Motivated by the need to paint a more general picture of what life is—and could be—with respect to the rest of the phenomena of the universe, we propose a new vocabulary for astrobiological research. Lyfe is defined as any system that fulfills all four processes of the living state, namely: dissipation, autocatalysis, homeostasis, and learning. Life is defined as the instance of lyfe that we are familiar with on Earth, one that uses a specific organometallic molecular toolbox to record information about its environment and achieve dynamical order by dissipating certain planetary disequilibria. This new classification system allows the astrobiological community to more clearly define the questions that propel their research—e.g., whether they are developing a historical narrative to explain the origin of life (on Earth), or a universal narrative for the emergence of lyfe, or whether they are seeking signs of life specifically, or lyfe at large across the universe. While the concept of “life as we don’t know it” is not new, the four pillars of lyfe offer a novel perspective on the living state that is indifferent to the particular components that might produce it
Emergence, Construction, or Unlikely? Navigating the Space of Questions regarding Life's Origins
We survey some of the philosophical challenges and pitfalls within origins
research. Several of these challenges exhibit circularities, paradoxes, or
anthropic biases. We present origins approaches in terms of three broad
categories: unlikely (life's origin was a chance event), construction (life's
origin was a stepwise series of synthesis and assembly processes), and
emergence (life was always an amalgam of many parallel processes from which the
living state emerged as a natural outcome of physical driving forces). We
critically examine some of the founding and possibly misleading assumptions in
these categories. Such assumptions need not be detrimental to scientific
progress as long as their limits are respected. We conclude by attempting to
concisely state the most significant enigmas still remaining in the origins
field and suggest routes to solve them
Inference and Optimization of Real Edges on Sparse Graphs - A Statistical Physics Perspective
Inference and optimization of real-value edge variables in sparse graphs are
studied using the Bethe approximation and replica method of statistical
physics. Equilibrium states of general energy functions involving a large set
of real edge-variables that interact at the network nodes are obtained in
various cases. When applied to the representative problem of network resource
allocation, efficient distributed algorithms are also devised. Scaling
properties with respect to the network connectivity and the resource
availability are found, and links to probabilistic Bayesian approximation
methods are established. Different cost measures are considered and algorithmic
solutions in the various cases are devised and examined numerically. Simulation
results are in full agreement with the theory.Comment: 21 pages, 10 figures, major changes: Sections IV to VII updated,
Figs. 1 to 3 replace
Silk-fibronectin protein alloy fibres support cell adhesion and viability as a high strength, matrix fibre analogue
Silk is a natural polymer with broad utility in biomedical applications because it exhibits general biocompatibility and high tensile material properties. While mechanical integrity is important for most biomaterial applications, proper function and integration also requires biomaterial incorporation into complex surrounding tissues for many physiologically relevant processes such as wound healing. In this study, we spin silk fibroin into a protein alloy fibre with whole fibronectin using wet spinning approaches in order to synergize their respective strength and cell interaction capabilities. Results demonstrate that silk fibroin alone is a poor adhesive surface for fibroblasts, endothelial cells, and vascular smooth muscle cells in the absence of serum. However, significantly improved cell attachment is observed to silk-fibronectin alloy fibres without serum present while not compromising the fibres' mechanical integrity. Additionally, cell viability is improved up to six fold on alloy fibres when serum is present while migration and spreading generally increase as well. These findings demonstrate the utility of composite protein alloys as inexpensive and effective means to create durable, biologically active biomaterials.T32 EB006359 - NIBIB NIH HH
The atmosphere of Pluto as observed by New Horizons
In July 2015, the New Horizons spacecraft flew through the Pluto system at high speed, humanity's first close look at this enigmatic system on the outskirts of our solar system. In a series of papers, the New Horizons team present their analysis of the encounter data downloaded so far: Moore et al. present the complex surface features and geology of Pluto and its large moon Charon, including evidence of tectonics, glacial flow, and possible cryovolcanoes. Grundy et al. analyzed the colors and chemical compositions of their surfaces, with ices of H_2O, CH_4, CO, N_2, and NH_3 and a reddish material which may be tholins. Gladstone et al. investigated the atmosphere of Pluto, which is colder and more compact than expected and hosts numerous extensive layers of haze. Weaver et al. examined the small moons Styx, Nix, Kerberos, and Hydra, which are irregularly shaped, fast-rotating, and have bright surfaces. Bagenal et al. report how Pluto modifies its space environment, including interactions with the solar wind and a lack of dust in the system. Together, these findings massively increase our understanding of the bodies in the outer solar system. They will underpin the analysis of New Horizons data, which will continue for years to come
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