The Faintest Dwarf Galaxies Simon, Joshua D
Annual review of astronomy and astrophysics,
08/2019, Letnik:
57, Številka:
1
Journal Article
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The lowest luminosity (
L
) Milky Way satellite galaxies represent the extreme lower limit of the galaxy luminosity function. These ultra-faint dwarfs are the oldest, most dark matter-dominated, most ...metal-poor, and least chemically evolved stellar systems known. They therefore provide unique windows into the formation of the first galaxies and the behavior of dark matter on small scales. In this review, we summarize the discovery of ultra-faint dwarfs in the Sloan Digital Sky Survey in 2005 and the subsequent observational and theoretical progress in understanding their nature and origin. We describe their stellar kinematics, chemical abundance patterns, structural properties, stellar populations, orbits, and luminosity function, as well as what can be learned from each type of measurement. We conclude the following:
In most cases, the stellar velocity dispersions of ultra-faint dwarfs are robust against systematic uncertainties such as binary stars and foreground contamination.
The chemical abundance patterns of stars in ultra-faint dwarfs require two sources of
r
-process elements, one of which can likely be attributed to neutron star mergers.
Even under conservative assumptions, only a small fraction of ultra-faint dwarfs may have suffered significant tidal stripping of their stellar components.
Determining the properties of the faintest dwarfs out to the virial radius of the Milky Way will require very large investments of observing time with future telescopes.
Finally, we offer a look forward at the observations that will be possible with future facilities as the push toward a complete census of the Local Group dwarf galaxy population continues.
The second data release from the Gaia mission (DR2) provides a comprehensive and unprecedented picture of the motions of astronomical sources in the plane of the sky, extending from the solar ...neighborhood to the outer reaches of the Milky Way. I present proper-motion measurements based on Gaia DR2 for 17 ultra-faint dwarf galaxies within 100 kpc of the Milky Way. I compile the spectroscopically confirmed member stars in each dwarf bright enough for Gaia astrometry from the literature, producing member samples ranging from two stars in Triangulum II to 68 stars in Boötes I. From the spectroscopic member catalogs, I estimate the proper motion of each system. I find good agreement with the proper motions derived by the Gaia collaboration for Boötes I and Leo I. The tangential velocities for 14 of the 17 dwarfs are determined to better than 50 km s−1, more than doubling the sample of such measurements for Milky Way satellite galaxies. The orbital pericenters are well constrained, with a mean value of 38 kpc. Only one satellite, Tucana III, is on an orbit passing within 15 kpc of the Galactic center, suggesting that the remaining ultra-faint dwarfs are unlikely to have experienced severe tidal stripping. As a group, the ultra-faint dwarfs are on high-velocity, eccentric, retrograde trajectories, with nearly all of them having space motions exceeding 370 km s−1. A large majority of the objects are currently close to the pericenters of their orbits. In a low-mass (Mvir = 0.9 × 1012 M ) Milky Way potential, eight out of the 17 galaxies lack well-defined apocenters and appear likely to be on their first infall, indicating that the Milky Way mass may be larger than previously estimated or that many of the ultra-faint dwarfs are associated with the Magellanic Clouds. The median eccentricity of the ultra-faint dwarf orbits is 0.79, similar to the values seen in numerical simulations but distinct from the rounder orbits of the more luminous dwarf spheroidals.
•Fatigue and cognitive impairment are amongst the most common and debilitating symptoms of post-COVID-19 syndrome.•Approximately 1 in 3 individuals experienced fatigue 12 or more weeks following ...COVID-19 diagnosis.•Approximately 1 in 5 individuals exhibited cognitive impairment 12 or more weeks following COVID-19 diagnosis.•There was an elevation in proinflammatory markers and functional impairment in a subset of post-COVID individuals.
COVID-19 is associated with clinically significant symptoms despite resolution of the acute infection (i.e., post-COVID-19 syndrome). Fatigue and cognitive impairment are amongst the most common and debilitating symptoms of post-COVID-19 syndrome.
To quantify the proportion of individuals experiencing fatigue and cognitive impairment 12 or more weeks following COVID-19 diagnosis, and to characterize the inflammatory correlates and functional consequences of post-COVID-19 syndrome.
Systematic searches were conducted without language restrictions from database inception to June 8, 2021 on PubMed/MEDLINE, The Cochrane Library, PsycInfo, Embase, Web of Science, Google/Google Scholar, and select reference lists.
Primary research articles which evaluated individuals at least 12 weeks after confirmed COVID-19 diagnosis and specifically reported on fatigue, cognitive impairment, inflammatory parameters, and/or functional outcomes were selected.
Two reviewers independently extracted published summary data and assessed methodological quality and risk of bias. A meta-analysis of proportions was conducted to pool Freeman-Tukey double arcsine transformed proportions using the random-effects restricted maximum-likelihood model.
The co-primary outcomes were the proportions of individuals reporting fatigue and cognitive impairment, respectively, 12 or more weeks following COVID-19 infection. The secondary outcomes were inflammatory correlates and functional consequences associated with post-COVID-19 syndrome.
The literature search yielded 10,979 studies, and 81 studies were selected for inclusion. The fatigue meta-analysis comprised 68 studies, the cognitive impairment meta-analysis comprised 43 studies, and 48 studies were included in the narrative synthesis. Meta-analysis revealed that the proportion of individuals experiencing fatigue 12 or more weeks following COVID-19 diagnosis was 0.32 (95% CI, 0.27, 0.37; p < 0.001; n = 25,268; I2 = 99.1%). The proportion of individuals exhibiting cognitive impairment was 0.22 (95% CI, 0.17, 0.28; p < 0.001; n = 13,232; I2 = 98.0). Moreover, narrative synthesis revealed elevations in proinflammatory markers and considerable functional impairment in a subset of individuals.
A significant proportion of individuals experience persistent fatigue and/or cognitive impairment following resolution of acute COVID-19. The frequency and debilitating nature of the foregoing symptoms provides the impetus to characterize the underlying neurobiological substrates and how to best treat these phenomena.
PROSPERO (CRD42021256965).
Political scientists often criticize psychological approaches to the study of politics on the grounds that many psychological theories were developed on convenience samples of college students or ...members of the mass public, whereas many of the most important decisions in politics are made by elites, who are presumed to differ systematically from ordinary citizens. This paper proposes an overarching framework for thinking about differences between elites and masses, presenting the results of a meta-analysis of 162 paired treatments from paired experiments on political elites and mass publics, as well as an analysis of 12 waves of historical elite and mass public opinion data on foreign policy issues over a 43 year period. It finds political scientists both overstate the magnitude of elite-public gaps in decision-making, and misunderstand the determinants of elite-public gaps in political attitudes, many of which are due to basic compositional differences rather than to elites' domain-specific expertise.
The core methods in today’s econometric toolkit are linear regression for statistical control, instrumental variables methods for the analysis of natural experiments, and differences-in-differences ...methods that exploit policy changes. In the modern experimentalist paradigm, these techniques address clear causal questions such as: Do smaller classes increase learning? Should wife batterers be arrested? How much does education raise wages? Mostly Harmless Econometrics shows how the basic tools of applied econometrics allow the data to speak.
Metabolomics and Isotope Tracing Jang, Cholsoon; Chen, Li; Rabinowitz, Joshua D.
Cell,
05/2018, Letnik:
173, Številka:
4
Journal Article
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Great strides have been made over the past decade toward comprehensive study of metabolism. Mass spectrometry (MS) has played a central role by enabling measurement of many metabolites ...simultaneously. Tracking metabolite labeling from stable isotope tracers can in addition reveal pathway activities. Here, we describe the basics of metabolite measurement by MS, including sample preparation, metabolomic analysis, and data interpretation. In addition, drawing on examples of successful experiments, we highlight the ways in which metabolomics and isotope tracing can illuminate biology.
A roadmap for measuring metabolite concentrations and using isotope tracers to track metabolic activity.
What does dopamine mean? Berke, Joshua D
Nature neuroscience,
06/2018, Letnik:
21, Številka:
6
Journal Article
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Dopamine is a critical modulator of both learning and motivation. This presents a problem: how can target cells know whether increased dopamine is a signal to learn or to move? It is often presumed ...that motivation involves slow ('tonic') dopamine changes, while fast ('phasic') dopamine fluctuations convey reward prediction errors for learning. Yet recent studies have shown that dopamine conveys motivational value and promotes movement even on subsecond timescales. Here I describe an alternative account of how dopamine regulates ongoing behavior. Dopamine release related to motivation is rapidly and locally sculpted by receptors on dopamine terminals, independently from dopamine cell firing. Target neurons abruptly switch between learning and performance modes, with striatal cholinergic interneurons providing one candidate switch mechanism. The behavioral impact of dopamine varies by subregion, but in each case dopamine provides a dynamic estimate of whether it is worth expending a limited internal resource, such as energy, attention, or time.
One-carbon (1C) metabolism, mediated by the folate cofactor, supports multiple physiological processes. These include biosynthesis (purines and thymidine), amino acid homeostasis (glycine, serine, ...and methionine), epigenetic maintenance, and redox defense. Both within eukaryotic cells and across organs, 1C metabolic reactions are compartmentalized. Here we review the fundamentals of mammalian 1C metabolism, including the pathways active in different compartments, cell types, and biological states. Emphasis is given to recent discoveries enabled by modern genetics, analytical chemistry, and isotope tracing. An emerging theme is the biological importance of mitochondrial 1C reactions, both for producing 1C units that are exported to the cytosol and for making additional products, including glycine and NADPH. Increased clarity regarding differential folate pathway usage in cancer, stem cells, development, and adult physiology is reviewed and highlights new opportunities for selective therapeutic intervention.
One-carbon metabolism supports biosynthesis, amino acid homeostasis, epigenetic maintenance, and redox defense. Ducker and Rabinowitz review this metabolism, from the biochemical basics of folate to organismal physiology, with an emphasis on recent advances in understanding one-carbon metabolic cycles, compartmentalization, and pathway activity both in normal physiology and in human disease.
Extremely irradiated hot Jupiters, exoplanets reaching dayside temperatures >2000 K, stretch our understanding of planetary atmospheres and the models we use to interpret observations. While these ...objects are planets in every other sense, their atmospheres reach temperatures at low pressures comparable only to stellar atmospheres. In order to understand our a priori theoretical expectations for the nature of these objects, we self-consistently model a number of extreme hot Jupiter scenarios with the PHOENIX model atmosphere code. PHOENIX is well-tested on objects from cool brown dwarfs to expanding supernovae shells, and its expansive opacity database from the UV to far-IR make PHOENIX well-suited to understanding extremely irradiated hot Jupiters. We find several fundamental differences between hot Jupiters at temperatures >2500 K and their cooler counterparts. First, absorption by atomic metals like Fe and Mg, molecules including SiO and metal hydrides, and continuous opacity sources like H−, all combined with the short-wavelength output of early-type host stars, result in strong thermal inversions, without the need for TiO or VO. Second, many molecular species, including H2O, TiO, and VO are thermally dissociated at pressures probed by transit and eclipse observations, potentially biasing retrieval algorithms that assume uniform vertical abundances. We discuss other interesting properties of these objects, as well as future prospects and predictions for observing and characterizing this unique class of astrophysical object, including the first self-consistent model of the hottest known Jovian planet, KELT-9b.
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