11,121 research outputs found
AN INTRODUCTION TO SPATIAL MODELING IN FISHERIES ECONOMICS
Resource /Energy Economics and Policy,
HST/STIS Imaging of the Host Galaxy of GRB980425/SN1998bw
We present HST/STIS observations of ESO 184-G82, the host galaxy of the
gamma-ray burst GRB 980425 associated with the peculiar Type Ic supernova
SN1998bw. ESO 184-G82 is found to be an actively star forming SBc sub-luminous
galaxy. We detect an object consistent with being a point source within the
astrometric uncertainty of 0.018 arcseconds of the position of the supernova.
The object is located inside a star-forming region and is at least one
magnitude brighter than expected for the supernova based on a simple
radioactive decay model. This implies either a significant flattening of the
light curve or a contribution from an underlying star cluster.Comment: 12 pages, 2 figures, AASTeX v5.02 accepted for publication in ApJ
Letter
Millimeter wave satellite concepts, volume 1
The identification of technologies necessary for development of millimeter spectrum communication satellites was examined from a system point of view. Development of methodology based on the technical requirements of potential services that might be assigned to millimeter wave bands for identifying the viable and appropriate technologies for future NASA millimeter research and development programs, and testing of this methodology with selected user applications and services were the goals of the program. The entire communications network, both ground and space subsystems was studied. Cost, weight, and performance models for the subsystems, conceptual design for point-to-point and broadcast communications satellites, and analytic relationships between subsystem parameters and an overall link performance are discussed along with baseline conceptual systems, sensitivity studies, model adjustment analyses, identification of critical technologies and their risks, and brief research and development program scenarios for the technologies judged to be moderate or extensive risks. Identification of technologies for millimeter satellite communication systems, and assessment of the relative risks of these technologies, was accomplished through subsystem modeling and link optimization for both point-to-point and broadcast applications
A microscopic quantum dynamics approach to the dilute condensed Bose gas
We derive quantum evolution equations for the dynamics of dilute condensed
Bose gases. The approach contains, at different orders of approximation, for
cases close to equilibrium, the Gross Pitaevskii equation and the first order
Hartree Fock Bogoliubov theory. The proposed approach is also suited for the
description of the dynamics of condensed gases which are far away from
equilibrium. As an example the scattering of two Bose condensates is discussed.Comment: 8 pages, submitted to Phys. Rev.
Resonance superfluidity in a quantum degenerate Fermi gas
We consider the superfluid phase transition that arises when a Feshbach
resonance pairing occurs in a dilute Fermi gas. We apply our theory to consider
a specific resonance in potassium-40, and find that for achievable experimental
conditions, the transition to a superfluid phase is possible at the high
critical temperature of about 0.5 T_F. Observation of superfluidity in this
regime would provide the opportunity to experimentally study the crossover from
the superfluid phase of weakly-coupled fermions to the Bose-Einstein
condensation of strongly-bound composite bosons.Comment: 4 pages, 3 figure
Tangled Nature: A model of emergent structure and temporal mode among co-evolving agents
Understanding systems level behaviour of many interacting agents is
challenging in various ways, here we'll focus on the how the interaction
between components can lead to hierarchical structures with different types of
dynamics, or causations, at different levels. We use the Tangled Nature model
to discuss the co-evolutionary aspects connecting the microscopic level of the
individual to the macroscopic systems level. At the microscopic level the
individual agent may undergo evolutionary changes due to mutations of
strategies. The micro-dynamics always run at a constant rate. Nevertheless, the
system's level dynamics exhibit a completely different type of intermittent
abrupt dynamics where major upheavals keep throwing the system between
meta-stable configurations. These dramatic transitions are described by a
log-Poisson time statistics. The long time effect is a collectively adapted of
the ecological network. We discuss the ecological and macroevolutionary
consequences of the adaptive dynamics and briefly describe work using the
Tangled Nature framework to analyse problems in economics, sociology,
innovation and sustainabilityComment: Invited contribution to Focus on Complexity in European Journal of
Physics. 25 page, 1 figur
Electronic structure theory of the hidden order material URuSi
We report a comprehensive electronic structure investigation of the
paramagnetic (PM), the large moment antiferromagnetic (LMAF), and the hidden
order (HO) phases of URuSi. We have performed relativistic
full-potential calculations on the basis of the density functional theory
(DFT), employing different exchange-correlation functionals to treat electron
correlations within the open -shell of uranium. Specifically, we
investigate---through a comparison between calculated and low-temperature
experimental properties---whether the electrons are localized or
delocalized in URuSi. We also performed dynamical mean field theory
calculations (LDA+DMFT) to investigate the temperature evolution of the
quasi-particle states at 100~K and above, unveiling a progressive opening of a
quasi-particle gap at the chemical potential when temperature is reduced. A
detailed comparison of calculated properties with known experimental data
demonstrates that the LSDA and GGA approaches, in which the uranium
electrons are treated as itinerant, provide an excellent explanation of the
available low-temperature experimental data of the PM and LMAF phases. We show
furthermore that due to a materials-specific Fermi surface instability a large,
but partial, Fermi surface gapping of up to 750 K occurs upon antiferromagnetic
symmetry breaking. The occurrence of the HO phase is explained through
dynamical symmetry breaking induced by a mode of long-lived antiferromagnetic
spin-fluctuations. This dynamical symmetry breaking model explains why the
Fermi surface gapping in the HO phase is similar but smaller than that in the
LMAF phase and it also explains why the HO and LMAF phases have the same Fermi
surfaces yet different order parameters. Suitable derived order parameters for
the HO are proposed to be the Fermi surface gap or the dynamic spin-spin
correlation function.Comment: 23 pages, 20 figure
The necessity of tailored control of irrupting pest populations driven by pulsed resources
Resource pulses are widespread phenomena in diverse ecosystems. Irruptions of generalist consumers and corresponding generalist predators often follow such resource pulses. This can have severe implications on the ecosystem and also on the spread of diseases or on regional famines. Suitable management strategies are necessary to deal with these systems. In this study, we develop a general model to investigate optimal control for such a system and apply this to a case study from New Zealand. In particular, we consider the dynamics of beech masting (episodic synchronous seed production) leading to rodent outbreaks and subsequent stoat (Mustela erminea) irruptions. Here, stoat control happens via secondary poisoning. The results show that the main driver of the optimal control timing (June) is the population density of the control vector. Intermediate control levels are superior to higher levels if the generalist consumer is necessary as a control vector. Finally, we extend the model to a two-patch metapopulation model, which indicates that, as a consequence of the strong vector dependence, a strategy of alternating control patches yields better results than static control. This highlights that besides control level, also the design impacts the control success. The results presented in this study reveal important insights for proper pest management in the New Zealand case study. However, they also generally indicate the necessity of tailored control in such systems
Millimeter wave satellite concepts. Volume 1: Executive summary
The objectives of the program were: (1) development of methodology based on the technical requirements of potential services that might be assigned to millimeter wave bands for identifying the viable and appropriate technologies for future NASA millimeter research and development programs, and (2) testing of this methodology with user applications and services. The scope of the program included the entire communications network, both ground and space subsystems. The reports include: (1) cost, weight, and performance models for the subsystems, (2) conceptual design for point-to-point and broadcast communications satellites, (3) analytic relationships between subsystem parameters and an overall link performance, (4) baseline conceptual systems, (5) sensitivity studies, (6) model adjustment analyses, (7) identification of critical technologies and their risks, (8) brief R&D program scenarios for the technologies judged to be moderate or extensive risks
‘It's a double whammy’ A qualitative study of illness uncertainty in individuals with Parkinson's disease in the context of COVID-19
Objectives: The purpose of this study was to explore the experiences of individuals with Parkinson's through the theoretical lens of illness uncertainty during the first UK full lockdown period (March–June 2020) put in place due outbreak of the COVID-19 pandemic. Methods: Individual semi-structured interviews were carried out via telephone in May 2020 with 10 individuals with Parkinson's (six men and four women) recruited from Parkinson's UK. Interviews were recorded and transcribed verbatim, and thematic analysis was adopted to analyse the resulting data. Results: Four overarching themes emerged from the interview data: (1) COVID-19 amplifying existing fears and difficulties around the uncertainty of Parkinson's; (2) practical and psychological efforts to manage uncertainty; (3) benefit-finding as a way of acknowledging the positives of lockdown; (4) risk and future management in the context of uncertainty. Discussion: Participants reported a range of implicit and explicit strategies to cope with the ‘double whammy’ of uncertainty caused by having Parkinson's during a global pandemic. While these were generally successful in maintaining well-being, it is important that such successful accounts are used to help inform novel strategies and interventions targeting individuals who might need additional support
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