117 research outputs found
Spin noise of itinerant fermions
We develop a theory of spin noise spectroscopy of itinerant, noninteracting,
spin-carrying fermions in different regimes of temperature and disorder. We use
kinetic equations for the density matrix in spin variables. We find a general
result with a clear physical interpretation, and discuss its dependence on
temperature, the size of the system, and applied magnetic field. We consider
two classes of experimental probes: 1. electron-spin-resonance (ESR)-type
measurements, in which the probe response to a uniform magnetization increases
linearly with the volume sampled, and 2. optical Kerr/Faraday rotation-type
measurements, in which the probe response to a uniform magnetization increases
linearly with the length of the light propagation in the sample, but is
independent of the cross section of the light beam. Our theory provides a
framework for interpreting recent experiments on atomic gases and conduction
electrons in semiconductors and provides a baseline for identifying the effects
of interactions on spin noise spectroscopy
Coregulated Genes Link Sulfide:Quinone Oxidoreductase and Arsenic Metabolism in Synechocystis sp. Strain PCC6803
Although the biogeochemistry of the two environmentally hazardous compounds arsenic and sulfide has been extensively investigated, the biological interference of these two toxic but potentially energy-rich compounds has only been hypothesized and indirectly proven. Here we provide direct evidence for the first time that in the photosynthetic model organism Synechocystis sp. strain PCC6803 the two metabolic pathways are linked by coregulated genes that are involved in arsenic transport, sulfide oxidation, and probably in sulfide-based alternative photosynthesis. Although Synechocystis sp. strain PCC6803 is an obligate photoautotrophic cyanobacterium that grows via oxygenic photosynthesis, we discovered that specific genes are activated in the presence of sulfide or arsenite to exploit the energy potentials of these chemicals. These genes form an operon that we termed suoRSCT, located on a transposable element of type IS4 on the plasmid pSYSM of the cyanobacterium. suoS (sll5036) encodes a light-dependent, type I sulfide:quinone oxidoreductase. The suoR (sll5035) gene downstream of suoS encodes a regulatory protein that belongs to the ArsR-type repressors that are normally involved in arsenic resistance. We found that this repressor has dual specificity, resulting in 200-fold induction of the operon upon either arsenite or sulfide exposure. The suoT gene encodes a transmembrane protein similar to chromate transporters but in fact functioning as an arsenite importer at permissive concentrations. We propose that the proteins encoded by the suoRSCT operon might have played an important role under anaerobic, reducing conditions on primordial Earth and that the operon was acquired by the cyanobacterium via horizontal gene transfer
Multivariate analysis of 1.5 million people identifies genetic associations with traits related to self-regulation and addiction
Behaviors and disorders related to self-regulation, such as substance use, antisocial behavior and attention-deficit/hyperactivity disorder, are collectively referred to as externalizing and have shared genetic liability. We applied a multivariate approach that leverages genetic correlations among externalizing traits for genome-wide association analyses. By pooling data from ~1.5 million people, our approach is statistically more powerful than single-trait analyses and identifies more than 500 genetic loci. The loci were enriched for genes expressed in the brain and related to nervous system development. A polygenic score constructed from our results predicts a range of behavioral and medical outcomes that were not part of genome-wide analyses, including traits that until now lacked well-performing polygenic scores, such as opioid use disorder, suicide, HIV infections, criminal convictions and unemployment. Our findings are consistent with the idea that persistent difficulties in self-regulation can be conceptualized as a neurodevelopmental trait with complex and far-reaching social and health correlates
The participatory turn in radioactive waste management:Deliberation and the social-technical divide
National policies for long-term management of radioactive waste have for decades been driven by technical experts. The pursuit of these technocratic policies led in many countries to conflict with affected communities. Since the late 1990s, however, there has been a turn to more participatory approaches. This participatory turn reflects widespread acknowledgement in the discourse of policy actors and implementing organisations of the importance of social aspects of radioactive waste management and the need to involve citizens and their representatives in the process. This appears to be an important move towards democratisation of this particular field of technological decision making but, despite these developments, technical aspects are still most often brought into the public arena only after technical experts have defined the ‘problem’ and decided upon a ‘solution’. This maintains a notional divide between the treatment of technical and social aspects of radioactive waste management and raises pressing questions about the kind of choice affected communities are given if they are not able to debate fully the technical options. The article aims to contribute to better understanding and addressing this situation by exploring the complex entanglement of the social and the technical in radioactive waste management policy and practice, analysing the contingent configurations that emerge as sociotechnical combinations. Drawing upon empirical examples from four countries that have taken the participatory turn - Belgium, Slovenia, Sweden and the United Kingdom – the article describes the different ways in which sociotechnical combinations have been constructed, and discusses their implications for future practice
The GALAH survey: tracing the Galactic disk with Open Clusters
Open clusters are unique tracers of the history of our own Galaxy's disk.
According to our membership analysis based on \textit{Gaia} astrometry, out of
the 226 potential clusters falling in the footprint of GALAH or APOGEE, we find
that 205 have secure members that were observed by at least one of the survey.
Furthermore, members of 134 clusters have high-quality spectroscopic data that
we use to determine their chemical composition. We leverage this information to
study the chemical distribution throughout the Galactic disk of 21 elements,
from C to Eu. The radial metallicity gradient obtained from our analysis is
0.0760.009 dex kpc, which is in agreement with previous works
based on smaller samples. Furthermore, the gradient in the [Fe/H] - guiding
radius (r) plane is 0.0730.008 dex kpc. We show
consistently that open clusters trace the distribution of chemical elements
throughout the Galactic disk differently than field stars. In particular, at
given radius, open clusters show an age-metallicity relation that has less
scatter than field stars. As such scatter is often interpreted as an effect of
radial migration, we suggest that these differences are due to the physical
selection effect imposed by our Galaxy: clusters that would have migrated
significantly also had higher chances to get destroyed. Finally, our results
reveal trends in the [X/Fe]rage space, which are important
to understand production rates of different elements as a function of space and
time.Comment: 18 pages, 10 figures, accepted for publication MNRA
The GALAH survey: Co-orbiting stars and chemical tagging
We present a study using the second data release of the GALAH survey of
stellar parameters and elemental abundances of 15 pairs of stars identified by
Oh et al 2017. They identified these pairs as potentially co-moving pairs using
proper motions and parallaxes from Gaia DR1. We find that 11 very wide (>1.7
pc) pairs of stars do in fact have similar Galactic orbits, while a further
four claimed co-moving pairs are not truly co-orbiting. Eight of the 11
co-orbiting pairs have reliable stellar parameters and abundances, and we find
that three of those are quite similar in their abundance patterns, while five
have significant [Fe/H] differences. For the latter, this indicates that they
could be co-orbiting because of the general dynamical coldness of the thin
disc, or perhaps resonances induced by the Galaxy, rather than a shared
formation site. Stars such as these, wide binaries, debris of past star
formation episodes, and coincidental co-orbiters, are crucial for exploring the
limits of chemical tagging in the Milky Way.Comment: 14 pages, 9 figures, submitted to MNRAS. Updated for Gaia DR2 value
The GALAH survey: Co-orbiting stars and chemical tagging
We present a study using the second data release of the GALAH survey of
stellar parameters and elemental abundances of 15 pairs of stars identified by
Oh et al 2017. They identified these pairs as potentially co-moving pairs using
proper motions and parallaxes from Gaia DR1. We find that 11 very wide (>1.7
pc) pairs of stars do in fact have similar Galactic orbits, while a further
four claimed co-moving pairs are not truly co-orbiting. Eight of the 11
co-orbiting pairs have reliable stellar parameters and abundances, and we find
that three of those are quite similar in their abundance patterns, while five
have significant [Fe/H] differences. For the latter, this indicates that they
could be co-orbiting because of the general dynamical coldness of the thin
disc, or perhaps resonances induced by the Galaxy, rather than a shared
formation site. Stars such as these, wide binaries, debris of past star
formation episodes, and coincidental co-orbiters, are crucial for exploring the
limits of chemical tagging in the Milky Way.Comment: 14 pages, 9 figures, submitted to MNRAS. Updated for Gaia DR2 value
The GALAH Survey: Stellar streams and how stellar velocity distributions vary with Galactic longitude, hemisphere and metallicity
Using GALAH survey data of nearby stars, we look at how structure in the
planar (u,v) velocity distribution depends on metallicity and on viewing
direction within the Galaxy. In nearby stars, with distance d < 1 kpc, the
Hercules stream is most strongly seen in higher metallicity stars [Fe/H] > 0.2.
The Hercules stream peak v value depends on viewed galactic longitude, which we
interpret as due to the gap between the stellar stream and more circular orbits
being associated with a specific angular momentum value of about 1640 km/s kpc.
The association of the gap with a particular angular momentum value supports a
bar resonant model for the Hercules stream.
Moving groups previously identified in Hipparcos observations are easiest to
see in stars nearer than 250 pc, and their visibility and peak velocities in
the velocity distributions depends on both viewing direction (galactic
longitude and hemisphere) and metallicity. We infer that there is fine
structure in local velocity distributions that varies over distances of a few
hundred pc in the Galaxy.Comment: accepted for publication in MNRA
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