Difference in dwarf galaxy surface brightness profiles as a function of environment

We investigate surface brightness profiles (SBPs) of dwarf galaxies in field, group, and cluster environments. With deep $BVI$ images from the Korea Microlensing Telescope Network Supernova Program, SBPs of 38 dwarfs in the NGC 2784 group are fitted by a single exponential or double exponential model. We find that 53% of the dwarfs are fitted with single exponential profiles ("Type I"), while 47% of the dwarfs show double exponential profiles. 37% of all dwarfs have smaller sizes of the outer part than inner part ("Type II"), while 10% have a larger sized outer than inner part ("Type III"). We compare these results with those in the field and in the Virgo cluster, where SBP types of 102 field dwarfs are compiled from a previous study and SBP types of 375 cluster dwarfs are measured using SDSS $r$-band images. As a result, the distributions of SBP types are different in three environments. Common SBP types of the field, the NGC 2784 group, and the Virgo cluster are Type II, Type I and II, and Type I and III profiles, respectively. After comparing sizes of dwarfs in different environments, we suggest that since sizes of some dwarfs are changed due to the environmental effects, SBP types are able to be transformed and the distributions of SBP types in three environments are different. We discuss possible environmental mechanisms on the transformation of SBP types.Comment: 28 pages, 7 figures, 5 tables, accepted to Ap

Virtual learning environments – help or hindrance for the ‘disengaged’ student?

The introduction of virtual learning environments (VLEs) has been regarded by some as a panacea for many of the problems in today’s mass numbers modular higher education system. This paper demonstrates that VLEs can help or hinder student engagement and performance, and that they should be adapted to the different types of learner. A project is described that aimed to investigate whether the introduction of a VLE can assist ‘disengaged’ students, drawing on click count tracking data and student performance. The project took place in the context of two very large undergraduate modules (850 and 567 students) in a Business School of a new university in the UK. In an adaptation of a model of learner engagement in Web-enhanced environments, four distinct learner types have emerged: model, traditionalist, geek and disengaged. There was evidence that use of the VLE exacerbated, rather than moderated, the differences between these learner types

The zCOSMOS survey: the role of the environment in the evolution of the luminosity function of different galaxy types

Aims. An unbiased and detailed characterization of the galaxy luminosity function (LF) is a basic requirement in many astrophysical issues: it is of particular interest in assessing the role of the environment in the evolution of the LF of different galaxy types. Methods. We studied the evolution in the B band LF to redshift z ~ 1 in the zCOSMOS 10k sample, for which both accurate galaxy classifications (spectrophotometric and morphological) and a detailed description of the local density field are available. Results. The global B band LF exhibits a brightening of ~0.7 mag in M^* from z ~ 0.2 to z ~ 0.9. At low redshifts (z -20), while the bright end is populated mainly by spectrophotometric early types. At higher redshift, spectrophotometric late-type galaxies evolve significantly and, at redshift z ~ 1, the contribution from the various types to the bright end of the LF is comparable. The evolution for spectrophotometric early-type galaxies is in both luminosity and normalization: M* brightens by ~0.6 mag but φ^∗ decreases by a factor ~1.7 between the first and the last redshift bin. A similar behaviour is exhibited by spectrophotometric late-type galaxies, but with an opposite trend for the normalization: a brightening of ~0.5 mag is present in M^*, while φ^∗ increases by a factor ~1.8.
Studying the role of the environment, we find that the global LF of galaxies in overdense regions has always a brighter M^* and a flatter slope. In low density environments, the main contribution to the LF is from blue galaxies, while for high density environments there is an important contribution from red galaxies to the bright end.
The differences between the global LF in the two environments are not due to only a difference in the relative numbers of red and blue galaxies, but also to their relative luminosity distributions: the value of M^* for both types in underdense regions is always fainter than in overdense environments. These results indicate that galaxies of the same type in different environments have different properties.
We also detect a differential evolution in blue galaxies in different environments: the evolution in their LF is similar in underdense and overdense regions between z ~ 0.25 and z ~ 0.55, and is mainly in luminosity. In contrast, between z ~ 0.55 and z ~ 0.85 there is little luminosity evolution but there is significant evolution in φ^∗, that is, however, different between the two environments: in overdense regions φ^∗ increases by a factor ~1.6, while in underdense regions this increase reaches a factor ~2.8. Analyzing the blue galaxy population in more detail, we find that this evolution is driven mainly by the bluest types. Conclusions. The “specular” evolution of late- and early-type galaxies is consistent with a scenario where a part of blue galaxies is transformed in red galaxies with increasing cosmic time, without significant changes in the fraction of intermediate-type galaxies. The bulk of this tranformation in overdense regions probably happened before z ~ 1, while it is still ongoing at lower redshifts in underdense environments

On the performance of a hybrid genetic algorithm in dynamic environments

The ability to track the optimum of dynamic environments is important in many practical applications. In this paper, the capability of a hybrid genetic algorithm (HGA) to track the optimum in some dynamic environments is investigated for different functional dimensions, update frequencies, and displacement strengths in different types of dynamic environments. Experimental results are reported by using the HGA and some other existing evolutionary algorithms in the literature. The results show that the HGA has better capability to track the dynamic optimum than some other existing algorithms.Comment: This paper has been submitted to Applied Mathematics and Computation on May 22, 2012 Revised version has been submitted to Applied Mathematics and Computation on March 1, 201

Redundant neural vision systems: competing for collision recognition roles

Ability to detect collisions is vital for future robots that interact with humans in complex visual environments. Lobula giant movement detectors (LGMD) and directional selective neurons (DSNs) are two types of identified neurons found in the visual pathways of insects such as locusts. Recent modelling studies showed that the LGMD or grouped DSNs could each be tuned for collision recognition. In both biological and artificial vision systems, however, which one should play the collision recognition role and the way the two types of specialized visual neurons could be functioning together are not clear. In this modeling study, we compared the competence of the LGMD and the DSNs, and also investigate the cooperation of the two neural vision systems for collision recognition via artificial evolution. We implemented three types of collision recognition neural subsystems – the LGMD, the DSNs and a hybrid system which combines the LGMD and the DSNs subsystems together, in each individual agent. A switch gene determines which of the three redundant neural subsystems plays the collision recognition role. We found that, in both robotics and driving environments, the LGMD was able to build up its ability for collision recognition quickly and robustly therefore reducing the chance of other types of neural networks to play the same role. The results suggest that the LGMD neural network could be the ideal model to be realized in hardware for collision recognition

Bringing nature back into cities: urban land environments, indigenous cover and urban restoration

1. The restoration of urban ecosystems is an increasingly important strategy to maintain and enhance indigenous biodiversity as well as reconnecting people to the environment. High levels of endemism, the sensitivity of species that have evolved without humans, and the invasion of exotic species have all contributed to severe depletion of indigenous biodiversity in New Zealand. In this work, we analysed national patterns of urban biodiversity in New Zealand and the contribution that urban restoration can make to maximising and enhancing indigenous biodiversity. 2. We analysed data from two national databases in relation to the 20 largest New Zealand cities. We quantified existing indigenous biodiversity within cities, both within the core built up matrix and in centroid buffer zones of 5, 10 and 20 km around this urban centre. We analysed the type and frequency of land environments underlying cities as indicators of the range of native ecosystems that are (or can potentially be) represented within the broader environmental profile of New Zealand. We identified acutely threatened land environments that are represented within urban and periurban areas and the potential role of cities in enhancing biodiversity from these land environments. 3. New Zealand cities are highly variable in both landform and level of indigenous resource. Thirteen of 20 major land environments in New Zealand are represented in cities, and nearly three-quarters of all acutely threatened land environments are represented within 20 km of city cores nationally. Indigenous land cover is low within urban cores, with less than 2% on average remaining, and fragmentation is high. However, indigenous cover increases to more than 10% on average in the periurban zone, and the size of indigenous remnants also increases. The number of remaining indigenous landcover types also increases from only 5 types within the urban centre, to 14 types within 20 km of the inner urban cores. 4. In New Zealand, ecosystem restoration alone is not enough to prevent biodiversity loss from urban environments, with remnant indigenous cover in the urban core too small (and currently too degraded) to support biodiversity long-term. For some cities, indigenous cover in the periurban zone is also extremely low. This has significant ramifications for the threatened lowland and coastal environments that are most commonly represented in cities. Reconstruction of ecosystems is required to achieve a target of 10% indigenous cover in cities: the addition of land to land banks for this purpose is crucial. Future planning that protects indigenous remnants within the periurban zone is critical to the survival of many species within urban areas, mitigating the homogenisation and depletion of indigenous flora and fauna typical of urbanisation. A national urban biodiversity plan would help city councils address biodiversity issues beyond a local and regional focus, while encouraging predominantly local solutions to restoration challenges, based on the highly variable land environments, ecosystems and patch connectivity present within different urban areas

Passenger Flows in Underground Railway Stations and Platforms, MTI Report 12-43

Urban rail systems are designed to carry large volumes of people into and out of major activity centers. As a result, the stations at these major activity centers are often crowded with boarding and alighting passengers, resulting in passenger inconvenience, delays, and at times danger. This study examines the planning and analysis of station passenger queuing and flows to offer rail transit station designers and transit system operators guidance on how to best accommodate and manage their rail passengers. The objectives of the study are to: 1) Understand the particular infrastructural, operational, behavioral, and spatial factors that affect and may constrain passenger queuing and flows in different types of rail transit stations; 2) Identify, compare, and evaluate practices for efficient, expedient, and safe passenger flows in different types of station environments and during typical (rush hour) and atypical (evacuations, station maintenance/ refurbishment) situations; and 3) Compile short-, medium-, and long-term recommendations for optimizing passenger flows in different station environments

A cognitive hierarchy model of learning in networks

This paper proposes a method for estimating a hierarchical model of bounded rationality in games of learning in networks. A cognitive hierarchy comprises a set of cognitive types whose behavior ranges from random to substantively rational. SpeciÖcally, each cognitive type in the model corresponds to the number of periods in which economic agents process new information. Using experimental data, we estimate type distributions in a variety of task environments and show how estimated distributions depend on the structural properties of the environments. The estimation results identify signiÖcant levels of behavioral hetero-geneity in the experimental data and overall conÖrm comparative static conjectures on type distributions across task environments. Surprisingly, the model replicates the aggregate pat-terns of the behavior in the data quite well. Finally, we found that the dominant type in the data is closely related to Bayes-rational behavior

Dynamical Objectivity in Quantum Brownian Motion

Classical objectivity as a property of quantum states---a view proposed to explain the observer-independent character of our world from quantum theory, is an important step in bridging the quantum-classical gap. It was recently derived in terms of spectrum broadcast structures for small objects embedded in noisy photon-like environments. However, two fundamental problems have arisen: a description of objective motion and applicability to other types of environments. Here we derive an example of objective states of motion in quantum mechanics by showing a formation of dynamical spectrum broadcast structures in the celebrated, realistic model of decoherence---Quantum Brownian Motion. We do it for realistic, thermal environments and show their noise-robustness. This opens a potentially new method of studying quantum-to-classical transition.Comment: 6 pages, 3 figures, accepted for publication in EP