161 research outputs found
Rapid Formation of Ice Giant Planets
The existence of Uranus and Neptune presents severe difficulties for the core
accretion model for the formation of ice giant planets. We suggest an
alternative mechanism, namely disk instability leading to the formation of gas
giant protoplanets, coagulation and settling of dust grains to form ice/rock
cores at their centers, and photoevaporation of their gaseous envelopes by a
nearby OB star, as a possible means of forming ice giant planets.Comment: TeX file, 20 pages, no figures, 1 table, accepted by Icarus,
Preprints available at http://www.ciw.edu/boss/ftp/planets/icaice.p
Politics, Voice, and Just Transition: Who has a Say in Climate Change Decision Making, and Who Does Not
The city of Bristol, UK, set out to pursue a just transition to climate change in 2020. This paper explores what happened next. We set out to study how just transition is unfolding politically on the ground, focusing on procedural justice. Over the course of a year, we conducted interviews and observations to study decision making at three levels â public sector, private sector and civil society. We found that not only is it difficult to define what just transition means, even for experts, but that the process of deciding how to pursue such a transition is highly exclusionary, especially to women and ethnic minorities. We therefore argue there is an urgency to revise decision-making procedures and ensure that there is ample opportunity to feed into decision-making processes by those who are typically excluded. Inclusive decision making must be embedded into the process of just transition from the beginning and throughout its implementation â it is not a step that can be âticked offâ and then abandoned, but rather an ongoing process that must be consistently returned to. Finally, we conclude that cities have the unique opportunity to pilot bottom-up participatory approaches and to feed into the process of how a just transition might be pursued at the global level â for example, through their participation in the United Nations Framework for the Convention on Climate Change (UNFCCC) Conference of the Parties (COP) processes
The Carnegie Astrometric Planet Search Program
We are undertaking an astrometric search for gas giant planets and brown
dwarfs orbiting nearby low mass dwarf stars with the 2.5-m du Pont telescope at
the Las Campanas Observatory in Chile. We have built two specialized
astrometric cameras, the Carnegie Astrometric Planet Search Cameras (CAPSCam-S
and CAPSCam-N), using two Teledyne Hawaii-2RG HyViSI arrays, with the cameras'
design having been optimized for high accuracy astrometry of M dwarf stars. We
describe two independent CAPSCam data reduction approaches and present a
detailed analysis of the observations to date of one of our target stars, NLTT
48256. Observations of NLTT 48256 taken since July 2007 with CAPSCam-S imply
that astrometric accuracies of around 0.3 milliarcsec per hour are achievable,
sufficient to detect a Jupiter-mass companion orbiting 1 AU from a late M dwarf
10 pc away with a signal-to-noise ratio of about 4. We plan to follow about 100
nearby (primarily within about 10 pc) low mass stars, principally late M, L,
and T dwarfs, for 10 years or more, in order to detect very low mass companions
with orbital periods long enough to permit the existence of habitable,
Earth-like planets on shorter-period orbits. These stars are generally too
faint and red to be included in ground-based Doppler planet surveys, which are
often optimized for FGK dwarfs. The smaller masses of late M dwarfs also yield
correspondingly larger astrometric signals for a given mass planet. Our search
will help to determine whether gas giant planets form primarily by core
accretion or by disk instability around late M dwarf stars.Comment: 48 pages, 9 figures. in press, Publ. Astron. Soc. Pacifi
Relation of Variations in the Human Factor to Financial Returns in Farming
This archival publication may not reflect current scientific knowledge or recommendations. Current information available from University of Minnesota Agricultural Experiment Station: http://www.maes.umn.edu
Recommended from our members
Use of a fluorinated probe to quantitatively monitor amino acid binding preferences of ruthenium(ii) arene complexes.
In order to address outstanding questions about ruthenium complexes in complex biological solutions, 19F NMR spectroscopy was used to follow the binding preferences between fluorinated RuII(η6-arene)(bipyridine) complexes and protected amino acids and glutathione. Reporting what ruthenium compounds bind to in complex environments has so far been restricted to relatively qualitative methods, such as mass spectrometry and X-ray spectroscopic methods; however, quantitative information on the species present in the solution phase cannot be inferred from these techniques. Furthermore, using 1H NMR, in water, to distinguish and monitor a number of different complex RuII(η6-arene) adducts forming is challenging. Incorporating an NMR active heteroatom into ruthenium organometallic complexes provides a quantitative, diagnostic 'fingerprint' to track solution-phase behaviour and allow for unambiguous assignment of any given adduct. The resulting 19F NMR spectra show for the first time the varied, dynamic behaviour of organoruthenium compounds when exposed to simple biomolecules in complex mixtures. The rates of formation of the different observed species are dramatically influenced by the electronic properties at the metal, even in a closely related series of complexes in which only the electron-donating properties of the arene ligand are altered. Preference for cysteine binding is absolute: the first quantitative solution-phase evidence of such behaviour
Controlled Ligand Exchange Between Ruthenium Organometallic Cofactor Precursors and a NaĂŻve Protein Scaffold Generates Artificial Metalloenzymes Catalysing Transfer Hydrogenation
Funder: PeterhouseAbstract: Many natural metalloenzymes assemble from proteins and biosynthesised complexes, generating potent catalysts by changing metal coordination. Here we adopt the same strategy to generate artificial metalloenzymes (ArMs) using ligand exchange to unmask catalytic activity. By systematically testing RuII(η6âarene)(bipyridine) complexes designed to facilitate the displacement of functionalised bipyridines, we develop a fast and robust procedure for generating new enzymes via ligand exchange in a protein that has not evolved to bind such a complex. The resulting metal cofactors form peptidic coordination bonds but also retain a nonâbiological ligand. Tandem mass spectrometry and 19F NMR spectroscopy were used to characterise the organometallic cofactors and identify the proteinâderived ligands. By introduction of ruthenium cofactors into a 4âhelical bundle, transfer hydrogenation catalysts were generated that displayed a 35âfold rate increase when compared to the respective small molecule reaction in solution
Catching Element Formation In The Act
Gamma-ray astronomy explores the most energetic photons in nature to address
some of the most pressing puzzles in contemporary astrophysics. It encompasses
a wide range of objects and phenomena: stars, supernovae, novae, neutron stars,
stellar-mass black holes, nucleosynthesis, the interstellar medium, cosmic rays
and relativistic-particle acceleration, and the evolution of galaxies. MeV
gamma-rays provide a unique probe of nuclear processes in astronomy, directly
measuring radioactive decay, nuclear de-excitation, and positron annihilation.
The substantial information carried by gamma-ray photons allows us to see
deeper into these objects, the bulk of the power is often emitted at gamma-ray
energies, and radioactivity provides a natural physical clock that adds unique
information. New science will be driven by time-domain population studies at
gamma-ray energies. This science is enabled by next-generation gamma-ray
instruments with one to two orders of magnitude better sensitivity, larger sky
coverage, and faster cadence than all previous gamma-ray instruments. This
transformative capability permits: (a) the accurate identification of the
gamma-ray emitting objects and correlations with observations taken at other
wavelengths and with other messengers; (b) construction of new gamma-ray maps
of the Milky Way and other nearby galaxies where extended regions are
distinguished from point sources; and (c) considerable serendipitous science of
scarce events -- nearby neutron star mergers, for example. Advances in
technology push the performance of new gamma-ray instruments to address a wide
set of astrophysical questions.Comment: 14 pages including 3 figure
- âŠ