2,399 research outputs found
Connectivity Differences between Human Operators of Swarms and Bandwidth Limitations
Human interaction with robot swarms (HSI) is a young field with very few user studies that explore operator behavior. All these studies assume perfect communication between the operator and the swarm. A key challenge in the use of swarm robotic systems in human supervised tasks is to understand human swarm interaction in the presence of limited communication bandwidth, which is a constraint arising in many practical scenarios. In this paper, we present results of human-subject experiments designed to study the effect of bandwidth limitations in human swarm interaction. We consider three levels of bandwidth availability in a swarm foraging task. The lowest bandwidth condition performs poorly, but the medium and high bandwidth condition both perform well. In the medium bandwidth condition, we display useful aggregated swarm information (like swarm centroid and spread) to compress the swarm state information. We also observe interesting operator behavior and adaptation of operators' swarm reaction
Neglect Benevolence in Human-Swarm Interaction with Communication Latency
In practical applications of robot swarms with bio-inspired behaviors, a human operator will need to exert control over the swarm to fulfill the mission objectives. In many operational settings, human operators are remotely located and the communication environment is harsh. Hence, there exists some latency in information (or control command) transfer between the human and the swarm. In this paper, we conduct experiments of human-swarm interaction to investigate the effects of communication latency on the performance of a human-swarm system in a swarm foraging task. We develop and investigate the concept of neglect benevolence, where a human operator allows the swarm to evolve on its own and stabilize before giving new commands. Our experimental results indicate that operators exploited neglect benevolence in different ways to develop successful strategies in the foraging task. Furthermore, we show experimentally that the use of a predictive display can help mitigate the adverse effects of communication latency
Insights from the Outskirts: Chemical and Dynamical Properties in the outer Parts of the Fornax Dwarf Spheroidal Galaxy
We present radial velocities and [Fe/H] abundances for 340 stars in the
Fornax dwarf spheroidal from R~16,000 spectra. The targets have been obtained
in the outer parts of the galaxy, a region which has been poorly studied
before. Our sample shows a wide range in [Fe/H], between -0.5 and -3.0 dex, in
which we detect three subgroups. Removal of stars belonging to the most
metal-rich population produces a truncated metallicity distribution function
that is identical to Sculptor, indicating that these systems have shared a
similar early evolution, only that Fornax experienced a late, intense period of
star formation (SF). The derived age-metallicity relation shows a fast increase
in [Fe/H] at early ages, after which the enrichment flattens significantly for
stars younger than ~8 Gyr. Additionally, the data indicate a strong population
of stars around 4 Gyr, followed by a second rapid enrichment in [Fe/H]. A
leaky-box chemical enrichment model generally matches the observed relation but
does not predict a significant population of young stars nor the strong
enrichment at late times. The young population in Fornax may therefore
originate from an externally triggered SF event. Our dynamical analysis reveals
an increasing velocity dispersion with decreasing [Fe/H] from sigma_sys 7.5
km/s to >14 km/s, indicating an outside-in star formation history in a dark
matter dominated halo. The large velocity dispersion at low metallicities is
possibly the result of a non-Gaussian velocity distribution amongst stars older
than ~8 Gyr. Our sample also includes members from the Fornax GCs H2 and H5. In
agreement with past studies we find [Fe/H]=-2.04+-0.04 and a mean radial
velocity RV=59.36+-0.31 km/s for H2 and [Fe/H]=-2.02+-0.11 and RV=59.39+-0.44
km/s for H5. Overall, we find large complexity in the chemical and dynamical
properties, with signatures that additionally vary with galactocentric
distance.Comment: 21 pages, 18 figures, 4 tables, accepted for publication in A&
European market integration and the political economy of corporate adjustment: OTE and Telecom Italia, 1949-2009
Despite the common challenges posed by European market integration and liberalisation, the behaviour of telecommunications operators across Europe suggests a variety of modes of adjustment and paths to privatisation. The article examines the puzzle of divergent responses to liberalisation by OTE and Telecom Italia (TI), casting light on their distinct paths to privatisation and internationalisation. The cases are considered in the context of the Varieties of Capitalism frame, which challenges the perspective that global market integration will lead to convergence in strategies and structures. Thus, the article suggests that the observed differences are largely explained by the domestic actors' preferences, and to a much lesser extent attributed to the globalising forces of technological change and competition
The binary fraction of stars in dwarf galaxies: the case of Leo II
We combine precision radial velocity data from four different published works
of the stars in the Leo II dwarf spheroidal galaxy. This yields a dataset that
spans 19 years, has 14 different epochs of observation, and contains 372 unique
red giant branch stars, 196 of which have repeat observations. Using this
multi-epoch dataset, we constrain the binary fraction for Leo II. We generate a
suite of Monte Carlo simulations that test different binary fractions using
Bayesian analysis and determine that the binary fraction for Leo II ranges from
to , depending on the
distributions of binary orbital parameters assumed. This value is smaller than
what has been found for the solar neighborhood (~0.4-0.6) but falls within the
wide range of values that have been inferred for other dwarf spheroidals
(0.14-0.69). The distribution of orbital periods has the greatest impact on the
binary fraction results. If the fraction we find in Leo II is present in
low-mass ultra-faints, it can artificially inflate the velocity dispersion of
those systems and cause them to appear more dark matter rich than in actuality.
For a galaxy with an intrinsic dispersion of 1 km/s and an observational sample
of 100 stars, the dispersion can be increased by a factor of 1.5-2 for Leo
II-like binary fractions or by a factor of 3 for binary fractions on the higher
end of what has been seen in other dwarf spheroidals.Comment: 14 pages, 11 figures, 3 tables. Published in A
Engineering failure analysis and design optimisation with HiP-HOPS
The scale and complexity of computer-based safety critical systems, like those used in the transport and manufacturing industries, pose significant challenges for failure analysis. Over the last decade, research has focused on automating this task. In one approach, predictive models of system failure are constructed from the topology of the system and local component failure models using a process of composition. An alternative approach employs model-checking of state automata to study the effects of failure and verify system safety properties. In this paper, we discuss these two approaches to failure analysis. We then focus on Hierarchically Performed Hazard Origin & Propagation Studies (HiP-HOPS) - one of the more advanced compositional approaches - and discuss its capabilities for automatic synthesis of fault trees, combinatorial Failure Modes and Effects Analyses, and reliability versus cost optimisation of systems via application of automatic model transformations. We summarise these contributions and demonstrate the application of HiP-HOPS on a simplified fuel oil system for a ship engine. In light of this example, we discuss strengths and limitations of the method in relation to other state-of-the-art techniques. In particular, because HiP-HOPS is deductive in nature, relating system failures back to their causes, it is less prone to combinatorial explosion and can more readily be iterated. For this reason, it enables exhaustive assessment of combinations of failures and design optimisation using computationally expensive meta-heuristics. (C) 2010 Elsevier Ltd. All rights reserved
Evaluating merger effects
This paper proposes a new algorithm with which to identify the potential effect of mergers by comparing the outcomes of interest in areas of overlap for the merging parties vis-a-vis areas of no overlap within a difference-in-differences estimation framework. Utilizing our proposed algorithm enables researchers and policymakers to perform retrospective merger evaluation studies that look at the effects of mergers on both price and non-price aspects. We demonstrate the applicability and value of our proposed methodology by examining the effects on price and product variety of four mergers of the late 1980s and the 1990s on the U.K. car market
Streptococcal hypersensitivity reloaded: severe inflammatory syndrome in Behçet's disease following 23-valent polysaccharide Streptococcus pneumoniae vaccine
The metal-poor Knee in the Fornax Dwarf Spheroidal Galaxy
We present alpha-element abundances of Mg, Si, and Ti for a large sample of
field stars in two outer fields of the Fornax dwarf spheroidal galaxy (dSph),
obtained with VLT/GIRAFFE (R~16,000). Due to the large fraction of metal-poor
stars in our sample, we are able to follow the alpha-element evolution from
[Fe/H]=-2.5 continuously to [Fe/H]=-0.7 dex. For the first time we are able to
resolve the turnover from the Type II supernovae (SNe) dominated,
alpha-enhanced plateau down to subsolar [alpha/Fe] values due to the onset of
SNe Ia, and thus to trace the chemical enrichment efficiency of the galaxy. Our
data support the general concept of an alpha-enhanced plateau at early epochs,
followed by a well-defined "knee", caused by the onset of SNe Ia, and finally a
second plateau with sub-solar [alpha/Fe] values. We find the position of this
knee to be at [Fe/H]=-1.9 and therefore significantly more metal-poor than
expected from comparison with other dSphs and standard evolutionary models.
Surprisingly, this value is rather comparable to the knee in Sculptor, a dSph
about 10 times less luminous than Fornax. Using chemical evolution models, we
find that both the position of the knee as well as the subsequent plateau at
sub-solar level can hardly be explained unless the galaxy experienced several
discrete star formation events with a drastic variation in star formation
efficiency, while a uniform star formation can be ruled out. One possible
evolutionary scenario is that Fornax experienced one or several major accretion
events from gas-rich systems in the past, so that its current stellar mass is
not indicative of the chemical evolution environment at ancient times. If
Fornax is the product of several smaller building blocks, this may also have
implications of the understanding on the formation process of dSphs in general.Comment: 10 pages, 6 Figures, accepted for publication in Ap
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