Multi-agent Population Research Articles

Magmatic episodes in the Holy Cross Mountains, Poland – a new contribution from multi-age zircon populations

This contribution reports on new U–Pb zircon age data from magmatic rocks from the Holy Cross Mountains (HCM) of Poland. The analyzed samples were taken from lamprophyre and diabase veins of Podkranów and Janowice-2 as well as from tuff horizon of Kielce Beds (Ludlow). Internal morphologies have been investigated by SEM-BSE and cathodoluminescence images and they have been used as a guide for the selection of genetically various type of grains, e.g. potential auto-, ante- and xenocrysts, that were analyzed by ion microprobe. The U–Pb age of the magmatic events at 414.2 ±6.6 Ma (Kielce tuff), 322 ±12 Ma (Podkranów, lamprophyre), and 300±10 Ma (Janowice-2, diabase) confirmed the time frame of known magmatic activity reported within the HCM, as determined by 40Ar/39Ar geochronology in previous studies. The zircon investigation revealed also multiple populations with record of an earlier pulse of magma system (antecrysts), as well as abundant xenocrysts.

Emergence of Grounded Compositional Language in Multi-Agent Populations

By capturing statistical patterns in large corpora, machine learning has enabled significant advances in natural language processing, including in machine translation, question answering, and sentiment analysis. However, for agents to intelligently interact with humans, simply capturing the statistical patterns is insufficient. In this paper we investigate if, and how, grounded compositional language can emerge as a means to achieve goals in multi-agent populations. Towards this end, we propose a multi-agent learning environment and learning methods that bring about emergence of a basic compositional language. This language is represented as streams of abstract discrete symbols uttered by agents over time, but nonetheless has a coherent structure that possesses a defined vocabulary and syntax. We also observe emergence of non-verbal communication such as pointing and guiding when language communication is unavailable.

Evidence for feedback and stellar-dynamically regulated bursty star cluster formation: the case of the Orion Nebula Cluster

A scenario for the formation of multiple co-eval populations separated in age by about 1 Myr in very young clusters (VYCs, ages less than 10 Myr) and with masses in the range 600–20 000 M⊙ is outlined. It rests upon a converging inflow of molecular gas building up a first population of pre-main sequence stars. The associated just-formed O stars ionise the inflow and suppress star formation in the embedded cluster. However, they typically eject each other out of the embedded cluster within 106 yr, that is before the molecular cloud filament can be ionised entirely. The inflow of molecular gas can then resume forming a second population. This sequence of events can be repeated maximally over the life-time of the molecular cloud (about 10 Myr), but is not likely to be possible in VYCs with mass <300 M⊙, because such populations are not likely to contain an O star. Stellar populations heavier than about 2000 M⊙ are likely to have too many O stars for all of these to eject each other from the embedded cluster before they disperse their natal cloud. VYCs with masses in the range 600–2000 M⊙ are likely to have such multi-age populations, while VYCs with masses in the range 2000–20 000 M⊙ can also be composed solely of co-eval, mono-age populations. More massive VYCs are not likely to host sub-populations with age differences of about 1 Myr. This model is applied to the Orion Nebula Cluster (ONC), in which three well-separated pre-main sequences in the colour–magnitude diagram of the cluster have recently been discovered. The mass-inflow history is constrained using this model and the number of OB stars ejected from each population are estimated for verification using Gaia data. As a further consequence of the proposed model, the three runaway O star systems, AE Aur, μ Col and ι Ori, are considered as significant observational evidence for stellar-dynamical ejections of massive stars from the oldest population in the ONC. Evidence for stellar-dynamical ejections of massive stars in the currently forming population is also discussed.

Beyond ‘functionality’ of handpump-supplied rural water services in developing countries

Many rural point-water sources in developing countries consist of wells or boreholes equipped with handpumps. Various estimates have been made of the functionality of such water points, and functionality is now routinely monitored in national and local surveys of service performance. We argue, however, that a single binary (functional/non-functional) indicator is crude and insufficient to provide much information about service sustainability. We set out a categorization of functionality which includes three sub-categories of functional water points and five non-functional sub-categories, with well/handpump water points in mind. We use a simple model to demonstrate that reduction of high rates of early post-construction abandonment and reduction of total downtimes would greatly improve service performance. We show that functionality levels for multi-age populations of wells or boreholes equipped with handpumps would not normally be expected to exceed about 85 per cent. We recommend going beyond functionality monitoring via the collection of quantitative data on rates of abandonment, frequency and duration of breakdown, combined with descriptive narratives of actions to manage and repair water points, in order to generate more nuanced understanding of service performance.

THE STRUCTURE OF NUCLEAR STAR CLUSTERS IN NEARBY LATE-TYPE SPIRAL GALAXIES FROMHUBBLE SPACE TELESCOPEWIDE FIELD CAMERA 3 IMAGING

We obtained Hubble Space Telescope/Wide Field Camera 3 imaging of a sample of ten of the nearest and brightest nuclear clusters residing in late-type spiral galaxies, in seven bands that span the near-ultraviolet to the near-infrared. Structural properties of the clusters were measured by fitting two-dimensional surface brightness profiles to the images using GALFIT. The clusters exhibit a wide range of structural properties. For six of the ten clusters in our sample, we find changes in the effective radius with wavelength, suggesting radially varying stellar populations. In four of the objects, the effective radius increases with wavelength, indicating the presence of a younger population which is more concentrated than the bulk of the stars in the cluster. However, we find a general decrease in effective radius with wavelength in two of the objects in our sample, which may indicate extended, circumnuclear star formation. We also find a general trend of increasing roundness of the clusters at longer wavelengths, as well as a correlation between the axis ratios of the NCs and their host galaxies. These observations indicate that blue disks aligned with the host galaxy plane are a common feature of nuclear clusters in late-type galaxies, but are difficult to detect in galaxies that are close to face-on. In color-color diagrams spanning the near-UV through the near-IR, most of the clusters lie far from single-burst evolutionary tracks, showing evidence for multi-age populations. Most of the clusters have integrated colors consistent with a mix of an old population (> 1 Gyr) and a young population (~100-300 Myr). The wide wavelength coverage of our data provides a sensitivity to populations with a mix of ages that would not be possible to achieve with imaging in optical bands only.

MULTILEVEL ALIGNMENT MAINTAINS LANGUAGE SYSTEMATICITY

The question how a shared vocabulary can arise in a multi-agent population despite the fact that each agent autonomously invents and acquires words has been solved. The solution is based on alignment: Agents score all associations between words and meanings in their lexicons and update these preference scores based on communicative success. A positive feedback loop between success and use thus arises which causes the spontaneous self-organization of a shared lexicon. The same approach has been proposed for explaining how a population can arrive at a shared grammar, in which we get the same problem of variation because each agent invents and acquires their own grammatical constructions. However, a problem arises if constructions reuse parts that can also exist on their own. This happens particularly when frequent usage patterns, which are based on compositional rules, are stored as such. The problem is how to maintain systematicity. This paper identifies this problem and proposes a solution in the form of multilevel alignment. Multilevel alignment means that the updating of preference scores is not restricted to the constructions that were used in the utterance but also downward and upward in the subsumption hierarchy.

Peculiarities of the habitat of Nucella freycineti (Mollusca: Gastropoda) at volcanogenic vent sites

In the summer of 2008, the abundance, local aggregation structure, growth rate, and life span of the gastropod Nucella freycineti inhabiting the littoral zone of Yankicha Island (Kuriles), which is affected by the postvolcanic activity of the Ushishir Volcano were studied. The parameters varied within a wide range and appreciably depended on the distance mollusk populations were from underwater and land gas-hydrothermal vents, which caused strong heating (up to 48°C) of cold sea waters and the formation of an unusually acidic environment (pH approximately 3.5) in the Kraternaya Bay. The mollusks occurred at a water temperature below 24°C and a pH above 4, but formed multiage populations at a temperature of 2–14°C and a pH of approximately 6.4–8.2.

Interpersonal Pattern Dynamics and Adaptive Behavior in Multiagent Neurobiological Systems: Conceptual Model and Data

ABSTRACT Ecological dynamics characterizes adaptive behavior as an emergent, self-organizing property of interpersonal interactions in complex social systems. The authors conceptualize and investigate constraints on dynamics of decisions and actions in the multiagent system of team sports. They studied coadaptive interpersonal dynamics in rugby union to model potential control parameter and collective variable relations in attacker–defender dyads. A videogrammetry analysis revealed how some agents generated fluctuations by adapting displacement velocity to create phase transitions and destabilize dyadic subsystems near the try line. Agent interpersonal dynamics exhibited characteristics of chaotic attractors and informational constraints of rugby union boxed dyadic systems into a low dimensional attractor. Data suggests that decisions and actions of agents in sports teams may be characterized as emergent, self-organizing properties, governed by laws of dynamical systems at the ecological scale. Further research needs to generalize this conceptual model of adaptive behavior in performance to other multiagent populations.

DOES STELLAR FEEDBACK CREATE H I HOLES? AHUBBLE SPACE TELESCOPE/VERY LARGE ARRAY STUDY OF HOLMBERG II

We use deep Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) F555W and F814W photometry of resolved stars in the M81 Group dwarf irregular galaxy Ho II to study the hypothesis that the holes identified in the neutral interstellar medium (H i) are created by stellar feedback. From the deep photometry, we construct color–magnitude diagrams (CMDs) and measure the star formation histories (SFHs) for stars contained in H i holes from two independent holes catalogs, as well as select control fields, i.e., similar sized regions that span a range of H i column densities. The CMDs reveal young (< 200 Myr) stellar populations inside all H i holes, which contain very few bright OB stars with ages less than 10 Myr, indicating they are not reliable tracers of H i hole locations while the recent SFHs confirm multiple episodes of star formation within most holes. Converting the recent SFHs into stellar feedback energies, we find that enough energy has been generated to have created all holes. However, the required energy is not always produced over a timescale that is less than the estimated kinematic age of the hole. A similar analysis of stars in the control fields finds that the stellar populations of the control fields and H i holes are statistically indistinguishable. However, because we are only sensitive to holes ∼100 pc in diameter, we cannot tell if there are smaller holes inside the control fields. The combination of the CMDs, recent SFHs, and locations of young stars shows that the stellar populations inside H i holes are not coherent, single-aged, stellar clusters, as previously suggested, but rather multi-age populations distributed across each hole. From a comparison of the modeled and observed integrated magnitudes, and the locations and energetics of stars inside of H i holes, we propose a potential new model: a viable mechanism for creating the observed H i holes in Ho ii is stellar feedback from multiple generations of SF spread out over tens or hundreds of Myr, and thus, the concept of an age for an H i hole is intrinsically ambiguous. For H i holes in the outer parts of Ho ii, located beyond the HST/ACS coverage, we use Monte Carlo simulations of expected stellar populations to show that low level SF could provide the energy necessary to form these holes. Applying the same method to the SMC, we find that the holes that appear to be void of stars could have formed via stellar feedback from low level SF. We further find that Hα and 24 μm emission, tracers of the most recent star formation, do not correlate well with the positions of the H i holes. However, UV emission, which traces star formation over roughly the last 100 Myr, shows a much better correlation with the locations of the H i holes.

Modeling and Optimal Centralized Control of a Large-Size Robotic Population

This paper describes an approach to the modeling and control of multiagent populations composed of a large number of agents. The complexity of population modeling is avoided by assuming a stochastic approach, under which the agent distribution over the state space is modeled. The dynamics of the state probability density functions is determined, and a control problem of maximizing the probability of robotic presence in a given region is introduced. The Minimum Principle for the optimal control of partial differential equations is exploited to solve this problem, and it is applied to the mission control of a simulated large robotic population

Pair formation within multi-agent populations

We present a simple model for the formation of pairs in multi-agent populations of type A and B which move freely on a spatial network. Each agent of population A (and B) is labeled as A i (and B j ) with i = 1 ,..., N A (and j = 1 ,..., N B ) and carries its own individual list of characteristics or ‘phenotype’. When agents from opposite populations encounter one another on the network, they can form a relationship if not already engaged in one. The length of time for which any given pair stays together depends on the compatibility of the two constituent agents. Possible applications include the human dating scenario, and the commercial domain where two types of businesses A and B have members of each type looking for a business partner, i.e., A i + B j → R ij . The pair R ij then survives for some finite time before dissociating R ij → A i + B j . There are many possible generalizations of this basic setup. Here, we content ourselves with some initial numerical results for the simplest of network topologies, together with some accompanying analytic analysis.

Predictability of large future changes in a competitive evolving population.

The dynamical evolution of many economic, sociological, biological, and physical systems tends to be dominated by a relatively small number of unexpected, large changes ("extreme events"). We study the large, internal changes produced in a generic multiagent population competing for a limited resource, and find that the level of predictability increases prior to a large change. These large changes hence arise as a predictable consequence of information encoded in the system's global state.

Toward a Sociogenetic Solution

Creole languages are often a point of contention for theoretical linguistics. Broadly defined, creoles result from an amalgamation of two or more languages, when speakers of differing mother tongues need rudimentary communication during economic or social transactions. Creolization occurs if the “invented” system becomes the native language of the speech community. There are several hypotheses for how biological linguistic properties and social contact each bear on the formation of creoles; however, until recently, no reliable method for testing these complex interactions existed. Implementing SWARM 2.1.1, the current model consists of a multiagent population drawn from historical records of Surinamese sugar cane plantations. Each agent in this artificial society is endowed with a demographic profile and linguistic parameters. Three experiments using the SWARM model are described. The results provide viable motivation for advancing a “sociogenetic” solution for the emergence of prototypical creole languages.

CATS: A Complex Adaptive Traffic Simulator

In this paper the authors investigate how the autonomous agents methodology can be used for modeling and simulation of urban traffic systems. The proposed approach allows to directly include subjective measures for characterizing drivers’ behavior throgh a specific information set, different goals and different strategies. A description of the basic agent models as: driver, traffic-light and toll is reported. An object oriented modeling and simulation environment has been implemented in JAVA in order to allow the system to run on different platforms. Moreover JAVA, through is multithread structure is particular well suited to the representation of a multiagent population.