4,662 research outputs found
Heating Hot Atmospheres with Active Galactic Nuclei
High resolution X-ray spectroscopy of the hot gas in galaxy clusters has
shown that the gas is not cooling to low temperatures at the predicted rates of
hundreds to thousands of solar masses per year. X-ray images have revealed
giant cavities and shock fronts in the hot gas that provide a direct and
relatively reliable means of measuring the energy injected into hot atmospheres
by active galactic nuclei (AGN). Average radio jet powers are near those
required to offset radiative losses and to suppress cooling in isolated giant
elliptical galaxies, and in larger systems up to the richest galaxy clusters.
This coincidence suggests that heating and cooling are coupled by feedback,
which suppresses star formation and the growth of luminous galaxies. How jet
energy is converted to heat and the degree to which other heating mechanisms
are contributing, eg. thermal conduction, are not well understood. Outburst
energies require substantial late growth of supermassive black holes. Unless
all of the approximately 10E62 erg required to suppress star formation is
deposited in the cooling regions of clusters, AGN outbursts must alter
large-scale properties of the intracluster medium.Comment: 60 pages, 12 figures, to appear in 1997 Annual Reviews of Astronomy
and Astrophysics. This version supersedes the April 2007 version in Reviews
in Advance (references and minor corrections were added), and is similar to
the one scheduled to appear in Volume 45 of ARA
GOLLUM: a next-generation simulation tool for electron, thermal and spin transport
We have developed an efficient simulation tool 'GOLLUM' for the computation
of electrical, spin and thermal transport characteristics of complex
nanostructures. The new multi-scale, multi-terminal tool addresses a number of
new challenges and functionalities that have emerged in nanoscale-scale
transport over the past few years. To illustrate the flexibility and
functionality of GOLLUM, we present a range of demonstrator calculations
encompassing charge, spin and thermal transport, corrections to density
functional theory such as LDA+U and spectral adjustments, transport in the
presence of non-collinear magnetism, the quantum-Hall effect, Kondo and Coulomb
blockade effects, finite-voltage transport, multi-terminal transport, quantum
pumps, superconducting nanostructures, environmental effects and pulling curves
and conductance histograms for mechanically-controlled-break-junction
experiments.Comment: 66 journal pages, 57 figure
Analysis domain model for shared virtual environments
The field of shared virtual environments, which also
encompasses online games and social 3D environments, has a
system landscape consisting of multiple solutions that share great functional overlap. However, there is little system interoperability between the different solutions. A shared virtual environment has an associated problem domain that is highly complex raising difficult challenges to the development process, starting with the architectural design of the underlying system. This paper has two main contributions. The first contribution is a broad domain analysis of shared virtual environments, which enables developers to have a better understanding of the whole rather than the part(s). The second contribution is a reference domain model for discussing and describing solutions - the Analysis Domain Model
Research opportunities in bone demineralization, phase 3
Bone demineralization, calcium responses to weightlessness, endocrine responses to weightlessness, mechanisms of bone loss, biomedical research, pathogenesis, and endocrine effects are discussed
Aeronautical Engineering: A continuing bibliography, supplement 120
This bibliography contains abstracts for 297 reports, articles, and other documents introduced into the NASA scientific and technical information system in February 1980
Hybrid Satellite-Terrestrial Communication Networks for the Maritime Internet of Things: Key Technologies, Opportunities, and Challenges
With the rapid development of marine activities, there has been an increasing
number of maritime mobile terminals, as well as a growing demand for high-speed
and ultra-reliable maritime communications to keep them connected.
Traditionally, the maritime Internet of Things (IoT) is enabled by maritime
satellites. However, satellites are seriously restricted by their high latency
and relatively low data rate. As an alternative, shore & island-based base
stations (BSs) can be built to extend the coverage of terrestrial networks
using fourth-generation (4G), fifth-generation (5G), and beyond 5G services.
Unmanned aerial vehicles can also be exploited to serve as aerial maritime BSs.
Despite of all these approaches, there are still open issues for an efficient
maritime communication network (MCN). For example, due to the complicated
electromagnetic propagation environment, the limited geometrically available BS
sites, and rigorous service demands from mission-critical applications,
conventional communication and networking theories and methods should be
tailored for maritime scenarios. Towards this end, we provide a survey on the
demand for maritime communications, the state-of-the-art MCNs, and key
technologies for enhancing transmission efficiency, extending network coverage,
and provisioning maritime-specific services. Future challenges in developing an
environment-aware, service-driven, and integrated satellite-air-ground MCN to
be smart enough to utilize external auxiliary information, e.g., sea state and
atmosphere conditions, are also discussed
Ion mobility-mass spectrometry for structural characterization and applied \u27omics: A study in neurodegenerative diseases
Huntington\u27s disease is neurodegenerative disease caused by an expanded polyglutamine-coding CAG repeat in exon 1 of the huntingtin gene. Huntingtin exon 1 forms the primary toxic amyloid structure in Huntington\u27s disease; disease severity is directly correlated with polyglutamine length. Recent works have shown that fully formed amyloid plaques may not represent the most toxic species in Huntington\u27s disease; the most neurotoxic species may be small, diffuse oligomer (4 - 20 monomer units) that are precursors to amyloid plaques. While the polyglutamine region is undisputed as the primary constituent of amyloid structure, aggregation kinetics and morphology are regulated by the presence of flanking sequences that are N- and C-terminal to theamyloid forming tract. The first seventeen residues of huntingtin exon 1 (Nt17) can form an amphipathic &agr;-helix depending upon solution conditions and the presence of a binding partner, and in most cases, mediates oligomer formation. C-terminal to the polyglutamine tract is a proline-rich region, or in the case of a model peptide a polyproline region (polyP), that can form a polyproline-type II (PPII) helix, which may regulate Nt17 in huntingtin protein with short polyglutamine regions. Much is unknown regarding residue-specific Nt17-Nt17 and Nt17-polyP interactions. The work described here utilized state-of-the-art deuterium exchange mass spectrometry techniques to identify critical hydrophilic residues in early stages of oligomer formation. Monomeric and multimeric conformations of Nt17, idependent og the polyglutamine domain, were then studied using ion mobility-mass spectrometry and molecular dynamics to gain insight into the earliest stages of Nt17-Nt17 association, and thus, aggregation. Monomeric and multimeric Nt17 could form extended helices in the gas phase. Key hydrophilic residues were chemically modified, which resulted in a sharp decline in multimer formation. Finally, Nt17-polyP interactions were probed using gas-phase deuterium exchange mass spectrometry, supplemented with molecular dynamics and an exchange kinetics model. The obtained gas-phase structures showed a reduction in Nt17 extended &agr;-helix, when compared to a monomeric and extended homodimeric conformation. Thus, it is hypothesized that polyP regulates Nt17 by not allowing transition to the amphipathic &agr;-helix. The results of this study examine the structural heterogeneity of a sequence thought to drive a potentially toxic aggregate morphology, pinpoint key residues in early oligomer formation, and provide strategies for regulation of oligomer formation
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