Search results for "general [Pulsars]"
showing 10 items of 19888 documents
Nitrogen broadening of SF6 transitions in the nu3 band
2001
Abstract Nitrogen induced pressure-broadened halfwidths of a number of ν3 transitions of SF6 are calculated using the complex Robert–Bonamy (CRB) formalism. The calculations are made at 200, 250, 296 and 350 K and the temperature dependence of the halfwidths are determined. The intermolecular potential is taken as a sum of the leading electrostatic and Lennard-Jones [6] , [7] , [8] , [9] , [10] , [11] , [12] atom–atom components. The dynamics of the collision process are correct to second order in time. The calculated halfwidths are used to simulate the ν3 spectrum, which is compared to a simulation made using the HITRAN96 halfwidths and measurements made at the Universite Pierre et Marie C…
First M87 Event Horizon Telescope Results. III. Data Processing and Calibration
2019
We present the calibration and reduction of Event Horizon Telescope (EHT) 1.3 mm radio wavelength observations of the supermassive black hole candidate at the center of the radio galaxy M87 and the quasar 3C 279, taken during the 2017 April 5–11 observing campaign. These global very long baseline interferometric observations include for the first time the highly sensitive Atacama Large Millimeter/submillimeter Array (ALMA); reaching an angular resolution of 25 μas, with characteristic sensitivity limits of ~1 mJy on baselines to ALMA and ~10 mJy on other baselines. The observations present challenges for existing data processing tools, arising from the rapid atmospheric phase fluctuations, …
First M87 Event Horizon Telescope Results. II. Array and Instrumentation
2019
The Event Horizon Telescope (EHT) is a very long baseline interferometry (VLBI) array that comprises millimeter- and submillimeter-wavelength telescopes separated by distances comparable to the diameter of the Earth. At a nominal operating wavelength of ~1.3 mm, EHT angular resolution (λ/D) is ~25 μas, which is sufficient to resolve nearby supermassive black hole candidates on spatial and temporal scales that correspond to their event horizons. With this capability, the EHT scientific goals are to probe general relativistic effects in the strong-field regime and to study accretion and relativistic jet formation near the black hole boundary. In this Letter we describe the system design of th…
First M87 Event Horizon Telescope Results. I. the Shadow of the Supermassive Black Hole
2019
When surrounded by a transparent emission region, black holes are expected to reveal a dark shadow caused by gravitational light bending and photon capture at the event horizon. To image and study this phenomenon, we have assembled the Event Horizon Telescope, a global very long baseline interferometry array observing at a wavelength of 1.3 mm. This allows us to reconstruct event-horizon-scale images of the supermassive black hole candidate in the center of the giant elliptical galaxy M87. We have resolved the central compact radio source as an asymmetric bright emission ring with a diameter of 42 ± 3 μas, which is circular and encompasses a central depression in brightness with a flux rati…
First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole
2019
We present measurements of the properties of the central radio source in M87 using Event Horizon Telescope data obtained during the 2017 campaign. We develop and fit geometric crescent models (asymmetric rings with interior brightness depressions) using two independent sampling algorithms that consider distinct representations of the visibility data. We show that the crescent family of models is statistically preferred over other comparably complex geometric models that we explore. We calibrate the geometric model parameters using general relativistic magnetohydrodynamic (GRMHD) models of the emission region and estimate physical properties of the source. We further fit images generated fro…
Ancient DNA from European early neolithic farmers reveals their near eastern affinities.
2010
The first farmers from Central Europe reveal a genetic affinity to modern-day populations from the Near East and Anatolia, which suggests a significant demographic input from this area during the early Neolithic.
Early Holocene ritual complexity in South America: the archaeological record of Lapa do Santo (east-central Brazil)
2016
Early Archaic human skeletal remains found in a burial context in Lapa do Santo in east-central Brazil provide a rare glimpse into the lives of hunter-gatherer communities in South America, including their rituals for dealing with the dead. These included the reduction of the body by means of mutilation, defleshing, tooth removal, exposure to fire and possibly cannibalism, followed by the secondary burial of the remains according to strict rules. In a later period, pits were filled with disarticulated bones of a single individual without signs of body manipulation, demonstrating that the region was inhabited by dynamic groups in constant transformation over a period of centuries.
The Maya wall paintings from Chajul, Guatemala
2020
The recent renovation of a house in Chajul in western Guatemala has revealed an unparalleled set of wall paintings, most probably from the Colonial period (AD 1524–1821). The iconography of the murals combines pre-Columbian elements with imported European components in a domestic rather than a religious setting, making them a unique example of Colonial-period art. Here, the authors present the results of iconographic, chemical and radiocarbon analyses of the Chajul house paintings. Dating to the seventeenth to eighteenth centuries AD, the paintings may be connected to a revival of the local religious organisation (cofradías) in the context of waning Spanish colonial control.
Obsidian in the Upper Palaeolithic of Iberia
2021
Submitted by André Pereira (andrepereira@letras.ulisboa.pt) on 2021-07-28T13:04:08Z No. of bitstreams: 1 obsidian-in-the-upper-palaeolithic-of-iberia.pdf: 35662679 bytes, checksum: 4c261781e3211c52c02d47cc36e26d98 (MD5) Approved for entry into archive by Manuel Botelheiro Moreno (manuelmoreno@campus.ul.pt) on 2021-07-28T16:31:42Z (GMT) No. of bitstreams: 1 obsidian-in-the-upper-palaeolithic-of-iberia.pdf: 35662679 bytes, checksum: 4c261781e3211c52c02d47cc36e26d98 (MD5) Made available in DSpace on 2021-07-28T16:32:40Z (GMT). No. of bitstreams: 1 obsidian-in-the-upper-palaeolithic-of-iberia.pdf: 35662679 bytes, checksum: 4c261781e3211c52c02d47cc36e26d98 (MD5) Previous issue date: 2021 info:eu…
Sierra del Colmenar 1A, a new late Messinian (Late Miocene) locality in the Bajo Segura Basin (SE Spain): biostratigraphic and palaeoenvironmental im…
2017
In this paper, we have studied a new micromammal site from the Sierra del Colmenar section (Elche, SE Spain), named Sierra del Colmenar 1A (SCO-1A), representing the uppermost levels of Messinian age of the Bajo Segura Basin. The sedimentary context of this locality corresponds to a costal lagoon with marine influence. The fossil site has yielded remains of Apodemus aff. gorafensis, Paraethomys meini, Apocricetus alberti, Occitanomys alcalai, Ruscinomys sp., Eliomys cf. truci, Muscardinus sp., Parasorex ibericus, Prolagus michauxi and Soricidae indet. Based on this assemblage, we propose a Late Miocene age (MN13) for the locality SCO-1A, matching the previously inferred age for the stratigr…