Visual Analysis of Robot and Animal Colonies

Graphical & digital media application

Methods for Reliable Robot Vision with a Dioptric System

Image processin

Charge and Current in the Quantum Hall Matrix Model

We extend the quantum Hall matrix model to include couplings to external electric and magnetic fields. The associated current suffers from matrix ordering ambiguities even at the classical level. We calculate the linear response at low momenta -- this is unambigously defined. In particular, we obtain the correct fractional quantum Hall conductivity, and the expected density modulations in response to a weak and slowly varying magnetic field. These results show that the classical quantum Hall matrix models describe important aspects of the dynamics of electrons in the lowest Landau level. In the quantum theory the ordering ambiguities are more severe; we discuss possible strategies, but we have not been able to construct a good density operator, satisfying the pertinent lowest Landau level commutator algebra.Comment: 12 pages, no figures; a logical error below the proposed density operator (46) in version 1 is corrected, and the claim that this density operator satisfy the magnetic algebra (2) is withdrawn. Some formulations have been changed and a few misprints correcte

Quantum and thermal spin relaxation in diluted spin ice: Dy(2-x)MxTi2O7 (M = Lu, Y)

We have studied the low temperature a.c. magnetic susceptibility of the diluted spin ice compound Dy(2-x)MxTi2O7, where the magnetic Dy ions on the frustrated pyrochlore lattice have been replaced with non-magnetic ions, M = Y or Lu. We examine a broad range of dilutions, 0 <= x <= 1.98, and we find that the T ~ 16 K freezing is suppressed for low levels of dilution but re-emerges for x > 0.4 and persists to x = 1.98. This behavior can be understood as a non-monotonic dependence of the quantum spin relaxation time with dilution. The results suggest that the observed spin freezing is fundamentally a single spin process which is affected by the local environment, rather than the development of spin-spin correlations as earlier data suggested.Comment: 26 pages, 9 figure

Application of Model-driven engineering to multi-agent systems: a language to model behaviors of reactive agents

Many users of multi-agent systems (MAS) are very commonly disinclined to model and simulate using current MAS platforms. More specifically, modeling the dynamics of a system (in particular the agents' behaviors) is very often a challenge to MAS users. This issue is more often observed in the domain of socio-ecological systems (SES), because SES domain experts are rarely programmers. Indeed, the majority of MAS platforms were not conceived taking into consideration domain-experts who are non-programmers. Most current MAS tools are not dedicated to SES, or nor do they possess an easily understandable formalism to represent the behaviors of agents. Moreover, because it is platform-dependent, a model realized in a given MAS platform cannot be properly used on another platform due to incompatibility between MAS platforms. To overcome these limitations, we propose a domain-specific language (DSL) to describe the behaviors of reactive agents, regardless of the MAS platform used for simulation. To achieve this result, we used model-driven engineering (MDE), an approach that provides tools to develop DSLs from a meta-model (abstract syntax), textual editors with syntax highlighting (for the concrete syntax) and code generation capabilities (for source-code generation of a model). As a result, we implemented a language and a textual editor that allow SES domain experts to describe behaviors in three different ways that are close to their natural expression: as equations when they are familiar with these, as a sequence of activities close to natural language or as an activity diagram to represent decisions and a sequence of behaviors using a graphic formalism. To demonstrate interoperability, we also developed code generators targeting two different MAS platforms (Cormas and Netlogo). We tested the code generators by implementing two SES models with the developed DSL. The generated code was targeted to both MAS platforms (Cormas and Netlogo), and successfully simulated in one of them. We conclude that the MDE approach provides adequate tools to develop DSL and code generators to facilitate MAS modeling and simulation by non-programmers. Concerning the DSL developed, although the behavioral aspect of MAS simulation is part of the complexity of modeling in MAS, there are still other essential aspects of model and simulation of MAS that are yet to be explored, such as model initialization and points of view on the model simulated worl

New combinations in the tribe Urgineeae (Asparagaceae subfam. Scilloideae) with comments on contrasting taxonomic treatments

As part of a taxonomic revision of tribe Urgineeae, and informed by morphological and phylogenetic evidence obtained in the last decade, we present 17 new combinations in Austronea, Indurgia, Schizobasis, Tenicroa, Thuranthos, Urgineopsis, and Vera-duthiea. These are for taxa recently described in Drimia sensu latissimo or otherwise named during the past century. We include type information for all considered taxa and designate lectotypes for Drimia pauciflora, Urginea salmonea and U. sebirii. We discuss recent analytic and synthetic approaches to taxonomic arrangements for the Urgineeae and reinforce the support of an analytic treatment that recognises several genera characterised by distinct syndromes of morphological characters, biogeography and molecular evidence

Susceptibility and dilution effects of the kagome bi-layer geometrically frustrated network. A Ga-NMR study of SrCr_(9p)Ga_(12-9p)O_(19)

We present an extensive gallium NMR study of the geometrically frustrated kagome bi-layer compound SrCr_(9p)Ga_(12-9p)O_(19) (Cr^3+, S=3/2) over a broad Cr-concentration range (.72<p<.95). This allows us to probe locally the kagome bi-layer susceptibility and separate the intrinsic properties due to the geometric frustration from those related to the site dilution. Our major findings are: 1) The intrinsic kagome bi-layer susceptibility exhibits a maximum in temperature at 40-50 K and is robust to a dilution as high as ~20%. The maximum reveals the development of short range antiferromagnetic correlations; 2) At low-T, a highly dynamical state induces a strong wipe-out of the NMR intensity, regardless of dilution; 3) The low-T upturn observed in the macroscopic susceptibility is associated to paramagnetic defects which stem from the dilution of the kagome bi-layer. The low-T analysis of the NMR lineshape suggests that the defect can be associated with a staggered spin-response to the vacancies on the kagome bi-layer. This, altogether with the maximum in the kagome bi-layer susceptibility, is very similar to what is observed in most low-dimensional antiferromagnetic correlated systems; 4) The spin glass-like freezing observed at T_g=2-4 K is not driven by the dilution-induced defects.Comment: 19 pages, 19 figures, revised version resubmitted to PRB Minor modifications: Fig.11 and discussion in Sec.V on the NMR shif

Robust association between autistic traits and psychotic-like experiences in the adult general population: epidemiological study from the 2007 Adult Psychiatric Morbidity Survey and replication with the 2014 APMS

Background Studies have shown that there are overlapping traits and symptoms between autism and psychosis but no study to date has addressed this association from an epidemiological approach in the adult general population. Furthermore, it is not clear whether autistic traits are associated with specific symptoms of psychosis or with psychosis in general. We assess these associations for the first time by using the Adult Psychiatric Morbidity Survey (APMS) 2007 and the APMS 2014, predicting an association between autistic traits and probable psychosis, and specific associations between autistic traits and paranoia and strange experiences. Methods Participants (N = 7353 in 2007 and 7500 in 2014) completed the Psychosis Screening Questionnaire (PSQ) and a 20-item version of the Autism Quotient (AQ-20). Binomial logistic regressions were performed using AQ-20 as the independent variable and probable psychosis and specific symptoms as dependent variables. Results In the APMS 2007 dataset, significant associations were found between autism traits and probable psychosis, paranoia, thought insertion, and strange experiences. These results were replicated in APMS 2014 but with the additional significant association between autistic traits and hallucinations. Participants in the highest quartile of the AQ-20, compared with the lowest quartile, had an increased risk of probable psychosis of odds ratio (OR) = 15.5 [95% confidence interval (CI) 4.57–52.6] in APMS 2007 and OR = 22.5 (95% CI 7.64–66.3) in APMS 2014. Conclusions Autistic traits are strongly associated with probable psychosis and psychotic experiences with the exception of mania. Limitations such as the cross-sectional nature of the study are discussed

Capability, opportunity, and motivation to enact hygienic practices in the early stages of the COVID‐19 outbreak in the United Kingdom

Objectives The COVID‐19 pandemic is one of the greatest global health threats facing humanity in recent memory. This study aimed to explore influences on hygienic practices, a set of key transmission behaviours, in relation to the Capability, Opportunity, Motivation‐Behaviour (COM‐B) model of behaviour change (Michie et al., 2011). Design Data from the first wave of a longitudinal survey study were used, launched in the early stages of the UK COVID‐19 pandemic. Methods Participants were 2025 adults aged 18 and older, representative of the UK population, recruited by a survey company from a panel of research participants. Participants self‐reported motivation, capability, and opportunity to enact hygienic practices during the COVID‐19 outbreak. Results Using regression models, we found that all three COM‐B components significantly predicted good hygienic practices, with motivation having the greatest influence on behaviour. Breaking this down further, the subscales psychological capability, social opportunity, and reflective motivation positively influenced behaviour. Reflective motivation was largely driving behaviour, with those highest in reflective motivation scoring 51% more on the measure of hygienic practices compared with those with the lowest scores. Conclusions Our findings have clear implications for the design of behaviour change interventions to promote hygienic practices. Interventions should focus on increasing and maintaining motivation to act and include elements that promote and maintain social support and knowledge of COVID‐19 transmission. Groups in particular need of targeting for interventions to increase hygienic practices are males and those living in cities and suburbs

Stability and dynamics of free magnetic polarons

The stability and dynamics of a free magnetic polaron are studied by Monte Carlo simulation of a classical two-dimensional Heisenberg model coupled to a single electron. We compare our results to the earlier mean-field analysis of the stability of the polaron, finding qualitative similarity but quantitative differences. The dynamical simulations give estimates of the temperature dependence of the polaron diffusion, as well as a crossover to a tunnelling regime.Comment: 4 pages including 4 .eps figure