542 research outputs found
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Overview of the national spallation neutron source with emphasis on the target station
The technologies that are being utilized to design and build a state-of-the-art neutron spallation source, the National Spallation Neutron Source (NSNS), are discussed. Emphasis is given to the technology issues that present the greatest scientific challenges. The present facility configuration, ongoing analysis and the planned hardware research and development program are also described
Recommended from our members
The national spallation neutron source target station: A general overview
The technologies that are being utilized to design and build a state-of-the-art neutron spallation source, the National Spallation Neutron Source (NSNS), are discussed. Emphasis is given to the technology issues that present the greatest scientific challenges. The present facility configuration, ongoing analysis and the planned hardware research and development program are also described
YREC: The Yale Rotating Stellar Evolution Code
The stellar evolution code YREC is outlined with emphasis on its applications
to helio- and asteroseismology. The procedure for calculating calibrated solar
and stellar models is described. Other features of the code such as a non-local
treatment of convective core overshoot, and the implementation of a
parametrized description of turbulence in stellar models, are considered in
some detail. The code has been extensively used for other astrophysical
applications, some of which are briefly mentioned at the end of the paper.Comment: 10 pages, 2 figures, ApSS accepte
Coulomb gauge approach to (qqg)over-bar hybrid mesons
An effective Coulomb gauge Hamiltonian, H-eff, is used to calculate the light ( u (u) over barg), strange ( s (s) over barg) and charmed (c (c) over barg) hybrid meson spectra. For the same two parameter H-eff providing glueball masses consistent with lattice results and a good description of the observed u, d, s and c quark mesons, a large-scale variational treatment predicts that the lightest hybrid has J(PC) = 0(++) and mass 2.1 GeV. The lightest exotic 1(-+) state is just above 2.2 GeV, near the upper limit of lattice and flux tube predictions. These theoretical formulations all indicate that the observed 1(-+) pi(1)(1600) and, more clearly, pi(1)(1400) are not hybrid states. The Coulomb gauge approach further predicts that in the strange and charmed sectors, respectively, the ground state hybrids have 1(+-) with masses 2.1 and 3.8 GeV, while the. rst exotic 1( +) states are at 2.4 and 4.0 GeV. Finally, using our hybrid wavefunctions and the Franck-Condon principle, a novel experimental signature is presented to assist heavy hybrid meson searches
Trust in the public sector: Is there any evidence for a long-term decline?
Concerns with declining public trust in government have become a permanent element of the contemporary political discourse. This concern also extends to levels of citizens’ trust in the public administration and public services. Trust is said to be declining, and this decline is generally seen as detrimental to public service delivery. In this article, we examine the main elements in this discussion, review the existing international survey data and summarise the main findings for OECD countries. Citizens’ trust in the public sector is found to fluctuate, and the data generally do not show consistently declining levels of trust. Furthermore, in some countries there simply is insufficient data to come to any conclusions at all about time trends in citizen trust in the public sector.
Points for practitioners
This article summarises some of the survey material on citizens’ trust in the public administration. It allows practitioners to compare trends in public trust in their country across time and space. The findings lead us to reject the hypothesis of a universal decline of trust in the public sector. The article warns against using opinion poll results without considering context. The long-term and comparative perspective on citizens’ trust in the public sector is all too often absent from the policy discourse that is frequently based on assumptions and ad-hoc approaches
The Fueling and Evolution of AGN: Internal and External Triggers
In this chapter, I review the fueling and evolution of active galactic nuclei
(AGN) under the influence of internal and external triggers, namely intrinsic
properties of host galaxies (morphological or Hubble type, color, presence of
bars and other non-axisymmetric features, etc) and external factors such as
environment and interactions. The most daunting challenge in fueling AGN is
arguably the angular momentum problem as even matter located at a radius of a
few hundred pc must lose more than 99.99 % of its specific angular momentum
before it is fit for consumption by a BH. I review mass accretion rates,
angular momentum requirements, the effectiveness of different fueling
mechanisms, and the growth and mass density of black BHs at different epochs. I
discuss connections between the nuclear and larger-scale properties of AGN,
both locally and at intermediate redshifts, outlining some recent results from
the GEMS and GOODS HST surveys.Comment: Invited Review Chapter to appear in LNP Volume on "AGN Physics on All
Scales", Chapter 6, in press. 40 pages, 12 figures. Typo in Eq 5 correcte
Evidence for a narrow dip structure at 1.9 GeV/c in diffractive photoproduction
A narrow dip structure has been observed at 1.9 GeV/c in a study of
diffractive photoproduction of the final state performed by the
Fermilab experiment E687.Comment: The data of Figure 6 can be obtained by downloading the raw data file
e687_6pi.txt. v5 (2nov2018): added Fig. 7, the 6 pion energy distribution as
requested by a reade
Metal enrichment processes
There are many processes that can transport gas from the galaxies to their
environment and enrich the environment in this way with metals. These metal
enrichment processes have a large influence on the evolution of both the
galaxies and their environment. Various processes can contribute to the gas
transfer: ram-pressure stripping, galactic winds, AGN outflows, galaxy-galaxy
interactions and others. We review their observational evidence, corresponding
simulations, their efficiencies, and their time scales as far as they are known
to date. It seems that all processes can contribute to the enrichment. There is
not a single process that always dominates the enrichment, because the
efficiencies of the processes vary strongly with galaxy and environmental
properties.Comment: 18 pages, 8 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 17; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
Quantum magnetism in two dimensions: From semi-classical N\'eel order to magnetic disorder
This is a review of ground-state features of the s=1/2 Heisenberg
antiferromagnet on two-dimensional lattices. A central issue is the interplay
of lattice topology (e.g. coordination number, non-equivalent nearest-neighbor
bonds, geometric frustration) and quantum fluctuations and their impact on
possible long-range order. This article presents a unified summary of all 11
two-dimensional uniform Archimedean lattices which include e.g. the square,
triangular and kagome lattice. We find that the ground state of the spin-1/2
Heisenberg antiferromagnet is likely to be semi-classically ordered in most
cases. However, the interplay of geometric frustration and quantum fluctuations
gives rise to a quantum paramagnetic ground state without semi-classical
long-range order on two lattices which are precisely those among the 11 uniform
Archimedean lattices with a highly degenerate ground state in the classical
limit. The first one is the famous kagome lattice where many low-lying singlet
excitations are known to arise in the spin gap. The second lattice is called
star lattice and has a clear gap to all excitations.
Modification of certain bonds leads to quantum phase transitions which are
also discussed briefly. Furthermore, we discuss the magnetization process of
the Heisenberg antiferromagnet on the 11 Archimedean lattices, focusing on
anomalies like plateaus and a magnetization jump just below the saturation
field. As an illustration we discuss the two-dimensional Shastry-Sutherland
model which is used to describe SrCu2(BO3)2.Comment: This is now the complete 72-page preprint version of the 2004 review
article. This version corrects two further typographic errors (three total
with respect to the published version), see page 2 for detail
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