14,327 research outputs found
Calculation of the radiation hazard at supersonic aircraft altitudes produced by an energetic solar flare, 2
Radiation hazard calculations for supersonic aircraft altitudes produced by energetic solar flare of 23 Feb. 196
Fatigue reliability method with in-service inspections
The first reliability method (FORM) has traditionally been applied in a fatigue reliability setting to one inspection interval at a time, so that the random distribution of crack lengths must be recharacterized following each inspection. The FORM presented here allow each analysis to span several inspection periods without explicit characterization of the crack length distribution upon each inspection. The method thereby preserves the attractive feature of FORM in that relatively few realizations in the random variable space need to be considered. Examples are given which show that the present methodology gives estimates which are in good agreement with Monte Carlo simulations and is efficient even for complex components
Hepatic fibrogenesis requires sympathetic neurotransmitters
Background and aims: Hepatic stellate cells (HSC) are activated by liver injury to become proliferative fibrogenic myofibroblasts. This process may be regulated by the sympathetic nervous system (SNS) but the mechanisms involved are unclear. Methods: We studied cultured HSC and intact mice with liver injury to test the hypothesis that HSC respond to and produce SNS neurotransmitters to promote fibrogenesis. Results: HSC expressed adrenoceptors, catecholamine biosynthetic enzymes, released norepinephrine (NE), and were growth inhibited by α- and β-adrenoceptor antagonists. HSC from dopamine β-hydroxylase deficient (Dbh(−/−)) mice, which cannot make NE, grew poorly in culture and were rescued by NE. Inhibitor studies demonstrated that this effect was mediated via G protein coupled adrenoceptors, mitogen activated kinases, and phosphatidylinositol 3-kinase. Injury related fibrogenic responses were inhibited in Dbh(−/−) mice, as evidenced by reduced hepatic accumulation of α-smooth muscle actin(+ve) HSC and decreased induction of transforming growth factor β1 (TGF-β1) and collagen. Treatment with isoprenaline rescued HSC activation. HSC were also reduced in leptin deficient ob/ob mice which have reduced NE levels and are resistant to hepatic fibrosis. Treating ob/ob mice with NE induced HSC proliferation, upregulated hepatic TGF-β1 and collagen, and increased liver fibrosis. Conclusions: HSC are hepatic neuroglia that produce and respond to SNS neurotransmitters to promote hepatic fibrosis
Tight bounds for classical and quantum coin flipping
Coin flipping is a cryptographic primitive for which strictly better
protocols exist if the players are not only allowed to exchange classical, but
also quantum messages. During the past few years, several results have appeared
which give a tight bound on the range of implementable unconditionally secure
coin flips, both in the classical as well as in the quantum setting and for
both weak as well as strong coin flipping. But the picture is still incomplete:
in the quantum setting, all results consider only protocols with perfect
correctness, and in the classical setting tight bounds for strong coin flipping
are still missing. We give a general definition of coin flipping which unifies
the notion of strong and weak coin flipping (it contains both of them as
special cases) and allows the honest players to abort with a certain
probability. We give tight bounds on the achievable range of parameters both in
the classical and in the quantum setting.Comment: 18 pages, 2 figures; v2: published versio
World model learning and inference
Understanding information processing in the brain-and creating general-purpose artificial intelligence-are long-standing aspirations of scientists and engineers worldwide. The distinctive features of human intelligence are high-level cognition and control in various interactions with the world including the self, which are not defined in advance and are vary over time. The challenge of building human-like intelligent machines, as well as progress in brain science and behavioural analyses, robotics, and their associated theoretical formalisations, speaks to the importance of the world-model learning and inference. In this article, after briefly surveying the history and challenges of internal model learning and probabilistic learning, we introduce the free energy principle, which provides a useful framework within which to consider neuronal computation and probabilistic world models. Next, we showcase examples of human behaviour and cognition explained under that principle. We then describe symbol emergence in the context of probabilistic modelling, as a topic at the frontiers of cognitive robotics. Lastly, we review recent progress in creating human-like intelligence by using novel probabilistic programming languages. The striking consensus that emerges from these studies is that probabilistic descriptions of learning and inference are powerful and effective ways to create human-like artificial intelligent machines and to understand intelligence in the context of how humans interact with their world
Scientific basis for safely shutting in the Macondo Well after the April 20, 2010 Deepwater Horizon blowout
As part of the government response to the Deepwater Horizon blowout, a Well Integrity Team evaluated the geologic hazards of shutting in the Macondo Well at the seafloor and determined the conditions under which it could safely be undertaken. Of particular concern was the possibility that, under the anticipated high shut-in pressures, oil could leak out of the well casing below the seafloor. Such a leak could lead to new geologic pathways for hydrocarbon release to the Gulf of Mexico. Evaluating this hazard required analyses of 2D and 3D seismic surveys, seafloor bathymetry, sediment properties, geophysical well logs, and drilling data to assess the geological, hydrological, and geomechanical conditions around the Macondo Well. After the well was successfully capped and shut in on July 15, 2010, a variety of monitoring activities were used to assess subsurface well integrity. These activities included acquisition of wellhead pressure data, marine multichannel seismic pro- files, seafloor and water-column sonar surveys, and wellhead visual/acoustic monitoring. These data showed that the Macondo Well was not leaking after shut in, and therefore, it could remain safely shut until reservoir pressures were suppressed (killed) with heavy drilling mud and the well was sealed with cement
ISO observations of four active galaxies
We present ISO PHOT-S spectra of four galaxies known or suspected to host a
central AGN, selected from the initial Iras/Rosat sample of Boller et al.
(1992). Two of them had no obvious Seyfert features in their previous optical
spectra: IRAS 14201+2956, and IRAS 21582+1018. The latter was bright enough to
also allow SWS observations around selected neon lines, to establish its
excitation. While both PHOT-S spectra are characteristic of starburst-dominated
galaxies, the neon line ratios in IRAS 21582+1018 indicate the presence of a
hard excitation source. New, high-resolution, optical spectra show only a weak,
broad component around Halpha, classifying now these two objects as Sey 1.9
galaxies. The two other galaxies observed are the NLS1 galaxies Mrk 359 and Mrk
1388. Their ISO spectra however do not reveal the typical, strong PAH features
found in the starburst galaxies and are more like those of standard Seyferts.
These results show therefore that, although IR observations were expected to be
able to always reveal the presence of an active nucleus by piercing through the
central obscuration, the result may be ambiguous: the broad band IR energy
distribution can still be dominated by starburts located in a circumnuclear
region, and the AGN appear only in specific observations (high-excitation lines
in the IR, or optical spectra with better quality than classification spectra).
The obscuration needs however to be patchy rather than complete, to explain the
detection of the high-excitation lines or broad Balmer wings. Only high-energy
observations can then establish the strength of the central
AGN and the amount of extinction with certainty.Comment: 8 pages, 8 figures, accepted in Astronomy & Astrophysic
Circular Polarization of Water Masers in the Circumstellar Envelopes of Late Type Stars
We present circular polarization measurements of circumstellar H_2O masers.
The circular polarization detected in the (6_{16}-5_{23}) rotational transition
of the H_{2}O maser can be attributed to Zeeman splitting in the intermediate
temperature and density regime. The magnetic fields are derived using a
general, LTE Zeeman analysis as well as a full radiative transfer method
(non-LTE), which includes a treatment of all hyperfine components
simultaneously as well as the effects of saturation and unequal populations of
the magnetic substates. The differences and relevances of these interpretations
are discussed extensively. The field strengths are compared with previous
detections of the magnetic field on the SiO and OH masers. We show that the
magnetic pressure dominates the thermal pressure by a factor of 20 or more.Comment: 15 pages, 15 figures; accepted for publication in A&A; (Abstract
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