728 research outputs found
Observational Evidence for Massive Black Holes in the Centers of Active Galaxies
Naturally occurring water vapor maser emission at 1.35 cm wavelength provides
an accurate probe for the study of accretion disks around highly compact
objects, thought to be black holes, in the centers of active galaxies. Because
of the exceptionally fine angular resolution, 200 microarcseconds, obtainable
with very long baseline interferometry, accompanied by high spectral
resolution, < 0.1 km/s, the dynamics and structures of these disks can be
probed with exceptional clarity. The data on the galaxy NGC4258 are discussed
here in detail. The mass of the black hole binding the accretion disk is 3.9
times 10^7 solar masses. Although the accretion disk has a rotational period of
about 800 years, the physical motions of the masers have been directly measured
with VLBI over a period of a few years. These measurements also allow the
distance from the earth to the black hole to be estimated to an accuracy of 4
percent. The status of the search for other maser/black hole candidates is also
discussed.Comment: 24 pages, 11 figures, latex, uses aaspp4 style file. To be published
in the Journal of Astronomy and Astrophysics (India), proceedings of the
Discussion Meeting on the Physics of Black Holes, Bangalore, India: December
199
Design and Bolometer Characterization of the SPT-3G First-year Focal Plane
During the austral summer of 2016-17, the third-generation camera, SPT-3G,
was installed on the South Pole Telescope, increasing the detector count in the
focal plane by an order of magnitude relative to the previous generation.
Designed to map the polarization of the cosmic microwave background, SPT-3G
contains ten 6-in-hexagonal modules of detectors, each with 269 trichroic and
dual-polarization pixels, read out using 68x frequency-domain multiplexing.
Here we discuss design, assembly, and layout of the modules, as well as early
performance characterization of the first-year array, including yield and
detector properties.Comment: Conference proceeding for Low Temperature Detectors 2017. Accepted
for publication: 27 August 201
ENIGMA and global neuroscience: A decade of large-scale studies of the brain in health and disease across more than 40 countries
This review summarizes the last decade of work by the ENIGMA (Enhancing NeuroImaging Genetics through Meta Analysis) Consortium, a global alliance of over 1400 scientists across 43 countries, studying the human brain in health and disease. Building on large-scale genetic studies that discovered the first robustly replicated genetic loci associated with brain metrics, ENIGMA has diversified into over 50 working groups (WGs), pooling worldwide data and expertise to answer fundamental questions in neuroscience, psychiatry, neurology, and genetics. Most ENIGMA WGs focus on specific psychiatric and neurological conditions, other WGs study normal variation due to sex and gender differences, or development and aging; still other WGs develop methodological pipelines and tools to facilitate harmonized analyses of "big data" (i.e., genetic and epigenetic data, multimodal MRI, and electroencephalography data). These international efforts have yielded the largest neuroimaging studies to date in schizophrenia, bipolar disorder, major depressive disorder, post-traumatic stress disorder, substance use disorders, obsessive-compulsive disorder, attention-deficit/hyperactivity disorder, autism spectrum disorders, epilepsy, and 22q11.2 deletion syndrome. More recent ENIGMA WGs have formed to study anxiety disorders, suicidal thoughts and behavior, sleep and insomnia, eating disorders, irritability, brain injury, antisocial personality and conduct disorder, and dissociative identity disorder. Here, we summarize the first decade of ENIGMA's activities and ongoing projects, and describe the successes and challenges encountered along the way. We highlight the advantages of collaborative large-scale coordinated data analyses for testing reproducibility and robustness of findings, offering the opportunity to identify brain systems involved in clinical syndromes across diverse samples and associated genetic, environmental, demographic, cognitive, and psychosocial factors
Demystifying the coronal line region of active galactic nuclei: spatially resolved spectroscopy with HST
We present an analysis of STIS/HST optical spectra of a sample of ten Seyfert
galaxies aimed at studying the structure and physical properties of the
coronal-line region (CLR). The high-spatial resolution provided by STIS allowed
us to resolve the CLR and obtain key information about the kinematics of the
coronal-line gas, measure directly its spatial scale, and study the mechanisms
that drive the high-ionisation lines. We find CLRs extending from just a few
parsecs (~10 pc) up to 230 pc in radius, consistent with the bulk of the
coronal lines (CLs) originating between the BLR and NLR, and extending into the
NLR in the case of [FeVII] and [NeV] lines. The CL profiles strongly vary with
the distance to the nucleus. We observed line splitting in the core of some of
the galaxies. Line peak shifts, both red- and blue-shifts, typically reached
500 km/s, and even higher velocities (1000 km/s) in some of the galaxies. In
general, CLs follow the same pattern of rotation curves as low-ionisation lines
like [OIII]. From a direct comparison between the radio and the CL emission we
find that neither the strength nor the kinematics of the CLs scale in any
obvious and strong way with the radio jets. Moreover, the similarity of the
flux distributions and kinematics of the CLs and low-ionisation lines, the low
temperatures derived for the gas, and the success of photoionisation models to
reproduce, within a factor of few, the observed line ratios, point towards
photoionisation as the main driving mechanism of CLs.Comment: Accepted for publication in MNRAS. 27 pages, 21 figures, 4 table
Genetic variants for head size share genes and pathways with cancer
The size of the human head is determined by growth in the first years of life, while the rest of the body typically grows until early adulthood1. Such complex developmental processes are regulated by various genes and growth pathways2. Rare genetic syndromes have revealed genes that affect head size3, but the genetic drivers of variation in head size within the general population remain largely unknown. To elucidate biological pathways underlying the growth of the human head, we performed the largest genome-wide association study on human head size to date (N = 79,107). We identified 67 genetic loci, 50 of which are novel, and found that these loci are preferentially associated with head size and mostly independent from height. In subsequent neuroimaging analyses, the majority of genetic variants demonstrated widespread effects on the brain, whereas the effects of 17 variants could be localized to one or two specific brain regions. Through hypothesis-free approaches, we find a strong overlap of head size variants with both cancer pathways and cancer genes. Gene set analyses showed enrichment for different types of cancer and the p53, Wnt and ErbB signalling pathway. Genes overlapping or close to lead variants – such as TP53, PTEN and APC – were enriched for genes involved in macrocephaly syndromes (up to 37-fold) and high-fidelity cancer genes (up to 9-fold), whereas this enrichment was not seen for human height variants. This indicates that genes regulating early brain and cranial growth are associated with a propensity to neoplasia later in life, irrespective of height. Our results warrant further investigations of the link between head size and cancer, as well as its clinical implications in the general population
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