1,786 research outputs found
The detailed chemical composition of the terrestrial planet host Kepler-10
Chemical abundance studies of the Sun and solar twins have demonstrated that
the solar composition of refractory elements is depleted when compared to
volatile elements, which could be due to the formation of terrestrial planets.
In order to further examine this scenario, we conducted a line-by-line
differential chemical abundance analysis of the terrestrial planet host
Kepler-10 and fourteen of its stellar twins. Stellar parameters and elemental
abundances of Kepler-10 and its stellar twins were obtained with very high
precision using a strictly differential analysis of high quality CFHT, HET and
Magellan spectra. When compared to the majority of thick disc twins, Kepler-10
shows a depletion in the refractory elements relative to the volatile elements,
which could be due to the formation of terrestrial planets in the Kepler-10
system. The average abundance pattern corresponds to ~ 13 Earth masses, while
the two known planets in Kepler-10 system have a combined ~ 20 Earth masses.
For two of the eight thick disc twins, however, no depletion patterns are
found. Although our results demonstrate that several factors (e.g., planet
signature, stellar age, stellar birth location and Galactic chemical evolution)
could lead to or affect abundance trends with condensation temperature, we find
that the trends give further support for the planetary signature hypothesis.Comment: 12 pages, 11 figures, accepted for publication in MNRA
Predicting Shortâ Term Remembering as Boundedly Optimal Strategy Choice
It is known that, on average, people adapt their choice of memory strategy to the subjective utility of interaction. What is not known is whether an individual’s choices are boundedly optimal. Two experiments are reported that test the hypothesis that an individual’s decisions about the distribution of remembering between internal and external resources are boundedly optimal where optimality is defined relative to experience, cognitive constraints, and reward. The theory makes predictions that are tested against data, not fitted to it. The experiments use a noâ choice/choice utility learning paradigm where the noâ choice phase is used to elicit a profile of each participant’s performance across the strategy space and the choice phase is used to test predicted choices within this space. They show that the majority of individuals select strategies that are boundedly optimal. Further, individual differences in what people choose to do are successfully predicted by the analysis. Two issues are discussed: (a) the performance of the minority of participants who did not find boundedly optimal adaptations, and (b) the possibility that individuals anticipate what, with practice, will become a bounded optimal strategy, rather than what is boundedly optimal during training.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/133633/1/cogs12271-sup-0001-FigS1.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/133633/2/cogs12271-sup-0002-FigS2.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/133633/3/cogs12271.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/133633/4/cogs12271_am.pd
Experimental investigation of taxon-specific response of alkaline phosphatase activity in natural freshwater phytoplankton
It is widely accepted that alkaline phosphatase activity (APA) is an efficient indicator of phosphate limitation in freshwater phytoplankton communities. In this study, we investigated whether the response in APA to phosphate limitation differs among the taxa in a mixed phytoplankton assemblage. We used the new enzyme-labeled fluorescence (ELF) technique, which allows microscopic detection of phosphate limitation in individual cells of multiple species. The most prominent findings of this study were that alkaline phosphatase (AP) was induced in many, but not all taxa and that different taxa, as well as different cells within a single taxon, experienced different degrees of phosphate stress under the same environmental conditions. Our approach was to manipulate the limiting nutrient in a natural freshwater phytoplankton community by incubating lake water in the laboratory. We induced nitrogen (N) or phosphate limitation through additions of inorganic nutrients. Both the ELF assay and bulk APA indicated that the lake phytoplankton were not phosphate limited at the start of the experiment. During the experiment, several chlorophyte taxa (e.g., Eudorina and an unidentified solitary spiny coccoid) were driven to phosphate limitation when inorganic N was added, as evidenced by a higher percentage of ELF-labeled cells relative to controls, whereas other chlorophyte taxa such as Actinastrum and Dicryosphaerium were not phosphate stressed under these conditions. In the phosphate-limited treatments, little or no ELF labeling was observed in any cyanobacterial taxa. Furthermore, all taxa observed after the ELF labeling procedure (>10-mum fraction) were labeled with ELF at least on one occasion, demonstrating the wide applicability of the ELF method. By using ELF labeling in tandem with bulk APA, the resolution and analysis of phosphate limitation was increased, allowing the identification of specific phosphate-stressed taxa
The Met80Ala and Tyr67His/Met80Ala mutants of human cytochrome cshed light on the reciprocal role of Met80 and Tyr67 in regulating ligand access into the heme pocket.
The spectroscopic and functional properties of the single Met80Ala and double Tyr67His/Met80Ala mutants of human cytochrome c have been investigated in their ferric and ferrous forms, and in the presence of different ligands, in order to clarify the reciprocal effect of these two residues in regulating the access of exogenous molecules into the heme pocket. In the ferric state, both mutants display an aquo high spin and a low spin species. The latter corresponds to an OH- ligand in Met80Ala but to a His in the double mutant. The existence of these two species is also reflected in the functional behavior of the mutants. The observation that (i) a significant peroxidase activity is present in the Met80Ala mutants, (ii) the substitution of the Tyr67 by His leads to only a slight increase of the peroxidase activity in the Tyr67His/Met80Ala double mutant with respect to wild type, while the Tyr67His mutant behaves as wild type, as previously reported, suggests that the peroxidase activity of cytochrome c is linked to an overall conformational change of the heme pocket and not only to the disappearance of the Fe-Met80 bond. Therefore, in human cytochrome c there is an interplay between the two residues at positions 67 and 80 that affects the conformation of the distal side of the heme pocket, and thus the sixth coordination of the hem
Energy distributions from three-body decaying many-body resonances
We compute energy distributions of three particles emerging from decaying
many-body resonances. We reproduce the measured energy distributions from
decays of two archetypal states chosen as the lowest and
-resonances in C populated in -decays. These states are
dominated by sequential, through the Be ground state, and direct decays,
respectively. These decay mechanisms are reflected in the ``dynamic'' evolution
from small, cluster or shell-model states, to large distances, where the
coordinate or momentum space continuum wavefunctions are accurately computed.Comment: 4 pages, 4 figures. Accepted for publication in Physical Review
Letter
Population of neutron unbound states via two-proton knockout reactions
The two-proton knockout reaction 9Be(26Ne,O2p) was used to explore excited
unbound states of 23O and 24O. In 23O a state at an excitation energy of
2.79(13) MeV was observed. There was no conclusive evidence for the population
of excited states in 24O.Comment: 6 pages, 3 figures, Proc. 9th Int. Spring Seminar on Nucl. Phys.
Changing Facets of Nuclear Structure, May 20-34, 200
Taxon-specific responses of Southern Ocean diatoms to Fe enrichment revealed by synchrotron radiation FTIR microspectroscopy
© 2014 Author(s). Photosynthesis by marine diatoms contributes substantially to global biogeochemical cycling and ecosystem productivity. It is widely accepted that diatoms are extremely sensitive to changes in Fe availability, with numerous in situ experiments demonstrating rapid growth and increased export of elements (e.g. C, Si and Fe) from surface waters as a result of Fe addition. Less is known about the effects of Fe enrichment on the phenotypes of diatoms, such as associated changes in nutritional value-furthermore, data on taxon-specific responses are almost non-existent. Enhanced supply of nutrient-rich waters along the coast of the subantarctic Kerguelen Island provide a valuable opportunity to examine the responses of phytoplankton to natural Fe enrichment. Here we demonstrate the use of synchrotron radiation Fourier Transform Infrared (SR-FTIR) microspectroscopy to analyse changes in the macromolecular composition of diatoms collected along the coast and plateau of Kerguelen Island, Southern Ocean. SR-FTIR microspectroscopy enabled the analysis of individual diatom cells from mixed communities of field-collected samples, thereby providing insight into in situ taxon-specific responses in relation to changes in Fe availability. Phenotypic responses were taxon-specific in terms of intraspecific variability and changes in proteins, amino acids, phosphorylated molecules, silicate/silicic acid and carbohydrates. In contrast to some previous studies, silicate/silicic acid levels increased under Fe enrichment, in conjunction with increases in carbohydrate stores. The highly abundant taxon Fragilariopsis kerguelensis displayed a higher level of phenotypic plasticity than Pseudo-nitzschia spp., while analysis of the data pooled across all measured taxa showed different patterns in macromolecular composition compared to those for individual taxon. This study demonstrates that taxon-specific responses to Fe enrichment may not always be accurately reflected by bulk community measurements, highlighting the need for further research into taxon-specific phenotypic responses of phytoplankton to environmental change
Exploring Neutron-Rich Oxygen Isotopes with MoNA
The Modular Neutron Array (MoNA) was used in conjunction with a large-gap
dipole magnet (Sweeper) to measure neutron-unbound states in oxygen isotopes
close to the neutron dripline. While no excited states were observed in 24O, a
resonance at 45(2) keV above the neutron separation energy was observed in 23O.Comment: 6 pages, 4 Figures, submitted to Proc. Int. Conf. on Proton Emitting
Nuclei and Related Topics, PROCON0
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