Complex Spatial Environments Research Articles

Collective motion of binary chiral particle mixtures with environmental complex noise.

The strategies for demixing and sorting mixed-chirality particles are crucial in the biochemical and pharmaceutical industries. However, whether chiral mixed particles can effectively separate in more complex spatial environments remains unresolved. In this paper, we explore the collective motion of binary chiral particle mixtures with environmental complex noise in the binary chiral Vicsek model (BCVM). We discover that the noisy region ratio, λ, significantly influences the separation behavior and spatial distribution of binary mixtures, unveiling system states not observed in uniform environments. Additionally, varying the chirality of particles reveals four distinct phases in our model. In the Vicsek bands phase (small chirality), an increase in λ can, under certain conditions, promote segregation rather than consistently hindering the demixing process. Conversely, for large chirality, localized dynamics and a homogeneous phase emerge, reducing the impact of λ on separation behavior. Notably, when chirality and activity are comparable, macrodrops and microflock phases appear, with a mixed-segregated state transition occurring at a critical λ_{c}. For λ<λ_{c}, chiral separation occurs with particles confined to the noise-free region. However, when λ>λ_{c}, particles gradually migrate to the noisy region, disrupting the separation. Further, we discuss the effects of multiple factors, including chirality, velocity, noise magnitude, particle number, and system size on λ_{c}. We also identify an optimal interaction radius at which λ_{c} reaches its peak value. Our findings may inspire strategies for achieving spontaneous demixing and spatial migration of mixed-chirality particles in complex environments.

Analysis of collision avoidance in honeybee flight.

Insects are excellent at flying in dense vegetation and navigating through other complex spatial environments. This study investigates the strategies used by honeybees (Apis mellifera) to avoid collisions with an obstacle encountered frontally during flight. Bees were trained to fly through a tunnel that contained a solitary vertically oriented cylindrical obstacle placed along the midline. Flight trajectories of bees were recorded for six conditions in which the diameter of the obstructing cylinder was systematically varied from 25 mm to 160 mm. Analysis of salient events during the bees' flight, such as the deceleration before the obstacle, and the initiation of the deviation in flight path to avoid collisions, revealed a strategy for obstacle avoidance that is based on the relative retinal expansion velocity generated by the obstacle when the bee is on a collision course. We find that a quantitative model, featuring a controller that extracts specific visual cues from the frontal visual field, provides an accurate characterization of the geometry and the dynamics of the manoeuvres adopted by honeybees to avoid collisions. This study paves the way for the design of unmanned aerial systems, by identifying the visual cues that are used by honeybees for performing robust obstacle avoidance flight.

An Efficient Fault-Tolerant Protection Method for L0 BTB

Branch prediction structures are increasingly used in space processors due to their crucial role in improving processor performance. Due to radiation effects such as Single Event Upset (SEU) causing system failures, it is necessary to provide protection techniques for branch prediction modules against complex spatial environments. In this paper, we proposed a simple, efficient, low-power, and fault-tolerant design scheme for L0 BTB consisting of a master-slave and a check-decision module. The strategy sets up the L0 BTB structure as a master-slave structure and adds an error check to detect single-bit errors. Experimental results show that we achieve 100% fault tolerance without a loss hit rate. The increase in resource usage is 1.1x, and the path delay increases by 8.1%, superior to other methods. The L0 BTB is a fully-associative structure and multiple entries are accessed simultaneously, which introduces significant power consumption. We added a low-power design for the master-slave module to reduce the query power consumption by 65.9%. In addition, we also applied the scheme to the RAS module. The experimental results demonstrate that our approach is an efficient, generic, fault-tolerant design scheme that can be deployed to different register files.

Adult neurogenesis alters response to an aversive distractor in a labyrinth maze without affecting spatial learning or memory.

Adult neurogenesis has been implicated in learning and memory of complex spatial environments. However, new neurons also play a role in nonmnemonic behavior, including the stress response and attention shifting. Many commonly used spatial tasks are very simple, and unsuitable for detecting neurogenesis effects, or are aversively motivated, making it difficult to dissociate effects on spatial learning and memory from effects on stress. We have therefore created a novel complex spatial environment, the flex maze, to enable reward-mediated testing of spatial learning in a flexibly configurable labyrinth. Using a pharmacogenetic method to completely inhibit neurogenesis in adulthood, we found that rats lacking new neurons (TK rats) and wild type controls completed and remembered most mazes equally well. However, control rats were slower to complete peppermint-scented mazes than other mazes, while neurogenesis-deficient rats showed no effect of mint on maze behavior, completing these mazes significantly faster than control rats. Additional testing found that wild type and TK rats showed similar detection of, avoidance of, and glucocorticoid response to the mint odor. These results suggest that spatial learning and memory in a labyrinth task is unaffected by the loss of new neurons, but that these cells affect the ability of an aversive stimulus to distract rats from completing the maze.

Homogenization approximations for unidirectional transport past randomly distributed sinks

Abstract Transport in biological systems often occurs in complex spatial environments involving random structures. Motivated by such applications, we investigate an idealized model for solute transport past an array of point sinks, randomly distributed along a line, which remove solute via first-order kinetics. Random sink locations give rise to long-range spatial correlations in the solute field and influence the mean concentration. We present a non-standard approach in evaluating these features based on rationally approximating integrals of a suitable Green’s function, which accommodates contributions varying on short and long lengthscales and has deterministic and stochastic components. We refine the results of classical two-scale methods for a periodic sink array (giving more accurate higher-order corrections with non-local contributions) and find explicit predictions for the fluctuations in concentration and disorder-induced corrections to the mean for both weakly and strongly disordered sink locations. Our predictions are validated across a large region of parameter space.

On the roles of landscape heterogeneity and environmental variation in determining population genomic structure in a dendritic system

Dispersal and natural selection are key evolutionary processes shaping the distribution of phenotypic and genetic diversity. For species inhabiting complex spatial environments however, it is unclear how the balance between gene flow and selection may be influenced by landscape heterogeneity and environmental variation. Here, we evaluated the effects of dendritic landscape structure and the selective forces of hydroclimatic variation on population genomic parameters for the Murray River rainbowfish, Melanotaenia fluviatilis across the Murray-Darling Basin, Australia. We genotyped 249 rainbowfish at 17,503 high-quality SNP loci and integrated these with models of network connectivity and high-resolution environmental data within a riverscape genomics framework. We tested competing models of gene flow before using multivariate genotype-environment association (GEA) analysis to test for signals of adaptive divergence associated with hydroclimatic variation. Patterns of neutral genetic variation were consistent with expectations based on the stream hierarchy model and M.fluviatilis' moderate dispersal ability. Models incorporating dendritic network structure suggested that landscape heterogeneity is a more important factor determining connectivity and gene flow than waterway distance. Extending these results, we also introduce a novel approach to controlling for the unique effects of dendritic network structure in GEA analyses of populations of aquatic species. We identified 146 candidate loci potentially underlying a polygenic adaptive response to seasonal fluctuations in stream flow and variation in the relative timing of temperature and precipitation extremes. Our findings underscore an emerging predominant role for seasonal variation in hydroclimatic conditions driving local adaptation and are relevant for informing proactive conservation management.

A common periodic representation of interaural time differences in mammalian cortex

Binaural hearing, the ability to detect small differences in the timing and level of sounds at the two ears, underpins the ability to localize sound sources along the horizontal plane, and is important for decoding complex spatial listening environments into separate objects – a critical factor in ‘cocktail-party listening’. For human listeners, the most important spatial cue is the interaural time difference (ITD). Despite many decades of neurophysiological investigations of ITD sensitivity in small mammals, and computational models aimed at accounting for human perception, a lack of concordance between these studies has hampered our understanding of how the human brain represents and processes ITDs. Further, neural coding of spatial cues might depend on factors such as head-size or hearing range, which differ considerably between humans and commonly used experimental animals. Here, using magnetoencephalography (MEG) in human listeners, and electro-corticography (ECoG) recordings in guinea pig—a small mammal representative of a range of animals in which ITD coding has been assessed at the level of single-neuron recordings—we tested whether processing of ITDs in human auditory cortex accords with a frequency-dependent periodic code of ITD reported in small mammals, or whether alternative or additional processing stages implemented in psychoacoustic models of human binaural hearing must be assumed. Our data were well accounted for by a model consisting of periodically tuned ITD-detectors, and were highly consistent across the two species. The results suggest that the representation of ITD in human auditory cortex is similar to that found in other mammalian species, a representation in which neural responses to ITD are determined by phase differences relative to sound frequency rather than, for instance, the range of ITDs permitted by head size or the absolute magnitude or direction of ITD.

Head Shadow and Binaural Squelch for Unilaterally Deaf Cochlear Implantees.

Cochlear implants (CIs) can improve speech-in-noise performance for listeners with unilateral sensorineural deafness. But these benefits are modest and in most cases are limited to head-shadow advantages, with little evidence of binaural squelch. The goal of the investigation was to determine whether CI listeners with normal hearing or moderate hearing loss in the contralateral ear would receive a larger head-shadow benefit for target speech and noise originating from opposite sides of the head, and whether listeners would experience binaural squelch in the free field in a test involving interfering talkers. Eleven CI listeners performed a speech-identification task in the presence of interfering noise or speech. Six listeners had single-sided deafness (normal or near-normal audiometric thresholds in the acoustic ear) and five had asymmetric hearing loss (hearing loss in the acoustic ear treated with a hearing aid). Listeners were tested with the acoustic ear only and bilaterally with the CI turned on. One set of conditions examined head-shadow effects with target speech and masking noise presented from azimuths of 0 or ±108 degrees. A second set of conditions examined binaural squelch, with target speech presented from the front and interfering talkers symmetrically placed on both sides. On average, the largest head-shadow benefit (5 dB) occurred when the target and masking noise were presented on opposite sides of the head. Listeners also showed an average of 2 dB of squelch, but only when the target speech was masked by interfering talkers of the same sex as the target. CIs provide listeners with unilateral deafness important benefits for speech perception in complex spatial environments, including a larger head-shadow benefit when speech and noise originate on opposite sides of the head, and an improved ability to perceptually organize an auditory scene with multiple competing voices.The views expressed in this abstract are those of the authors and do not reflect the official policy of the Department of Army/Navy/Air Force, Department of Defense, or US Government.

Riverscape genomics of a threatened fish across a hydroclimatically heterogeneous river basin.

Understanding how natural selection generates and maintains adaptive genetic diversity in heterogeneous environments is key to predicting the evolutionary response of populations to rapid environmental change. Detecting selection in complex spatial environments remains challenging, especially for threatened species where the effects of strong genetic drift may overwhelm signatures of selection. We carried out a basinwide riverscape genomic analysis in the threatened southern pygmy perch (Nannoperca australis), an ecological specialist with low dispersal potential. High-resolution environmental data and 5162 high-quality filtered SNPs were used to clarify spatial population structure and to assess footprints of selection associated with a steep hydroclimatic gradient and with human disturbance across the naturally and anthropogenically fragmented Murray-Darling Basin (Australia). Our approach included FST outlier tests to define neutral loci, and a combination of spatially explicit genotype-environment association analyses to identify candidate adaptive loci while controlling for the effects of landscape structure and shared population history. We found low levels of genetic diversity and strong neutral population structure consistent with expectations based on spatial stream hierarchy and life history. In contrast, variables related to precipitation and temperature appeared as the most important environmental surrogates for putatively adaptive genetic variation at both regional and local scales. Human disturbance also influenced the variation in candidate loci for adaptation, but only at a local scale. Our study contributes to understanding of adaptive evolution along naturally and anthropogenically fragmented ecosystems. It also offers a tangible example of the potential contributions of landscape genomics for informing insitu and ex situ conservation management of biodiversity.

Automated Search-Based Robustness Testing for Autonomous Vehicle Software

Autonomous systems must successfully operate in complex time-varying spatial environments even when dealing with system faults that may occur during a mission. Consequently, evaluating the robustness, or ability to operate correctly under unexpected conditions, of autonomous vehicle control software is an increasingly important issue in software testing. New methods to automatically generate test cases for robustness testing of autonomous vehicle control software in closed-loop simulation are needed. Search-based testing techniques were used to automatically generate test cases, consisting of initial conditions and fault sequences, intended to challenge the control software more than test cases generated using current methods. Two different search-based testing methods, genetic algorithms and surrogate-based optimization, were used to generate test cases for a simulated unmanned aerial vehicle attempting to fly through an entryway. The effectiveness of the search-based methods in generating challenging test cases was compared to both a truth reference (full combinatorial testing) and the method most commonly used today (Monte Carlo testing). The search-based testing techniques demonstrated better performance than Monte Carlo testing for both of the test case generation performance metrics: (1) finding the single most challenging test case and (2) finding the set of fifty test cases with the highest mean degree of challenge.

Cell Biology 2.0

Cell Biology 2.0

Binaural temporal fine structure sensitivity, cognitive function, and spatial speech recognition of hearing-impaired listeners (L)

The relationships between spatial speech recognition (SSR; the ability to understand speech in complex spatial environments), binaural temporal fine structure (TFS) sensitivity, and three cognitive tasks were assessed for 17 hearing-impaired listeners. Correlations were observed between SSR, TFS sensitivity, and two of the three cognitive tasks, which became non-significant when age effects were controlled for, suggesting that reduced TFS sensitivity and certain cognitive deficits may share a common age-related cause. The third cognitive measure was also significantly correlated with SSR, but not with TFS sensitivity or age, suggesting an independent non-age-related cause.

Autonomous Navigation for Unmanned Aerial Vehicles Based on Chaotic Bionics Theory

In this paper a new reactive mechanism based on perception-action bionics for multi-sensory integration applied to Unmanned Aerial Vehicles (UAVs) navigation is proposed. The strategy is inspired by the olfactory bulb neural activity observed in rabbits subject to external stimuli. The new UAV navigation technique exploits the use of a multiscroll chaotic system which is able to be controlled in real-time towards less complex orbits, like periodic orbits or equilibrium points, considered as perceptive orbits. These are subject to real-time modifications on the basis of environment changes acquired through a Synthetic Aperture Radar (SAR) sensory system. The mathematical details of the approach are given including simulation results in a virtual environment. The results demonstrate the capability of autonomous navigation for UAV based on chaotic bionics theory in complex spatial environments.

Planning for the sun: urban forms as a Mesopotamian response to the sun

Urban forms create complex spatial environments which form, and are formed by, the lives of their inhabitants. Part of the construction of any urban environment is the formation of a light environment created by the interaction of the architecture with the changing natural light conditions through the day and over the year. This paper considers the construction of an appropriate and meaningful light environment to have been an essential factor in the development of urban form in ancient Mesopotamian cities, where strong summer sunlight constituted a serious limit to human activity and the sources of natural light held a high symbolic and religious value. The form and layout of ancient Mesopotamian cities is here examined in terms of the sort of light environments the architecture would have produced. Using the example of residential housing at ancient Ur, an analysis of the urban light environment demonstrates both functional and symbolic manipulation of sunlight through architectural form.

Autonomous guidance for intelligent missiles based on chaotic perception—action dynamics

In this article a new reactive mechanism based on perception—action dynamics for multi-sensory integration applied to an intelligent missile guidance system is proposed. The strategy is inspired by the olfactory bulb neural activity observed in rabbits subject to external stimuli. The new missile guidance technique exploits the use of a multiscroll chaotic system which is able to be controlled in real-time towards less complex orbits, such as periodic orbits or equilibrium points, considered as perceptive orbits. These are subject to real-time modifications on the basis of environmental changes acquired through a synthetic aperture radar sensory system. The mathematical details of the approach are given including simulation results in a virtual environment. The results demonstrate the capability of autonomous guidance for missile in complex spatial environments.

Maze exploration and learning in C. elegans

The soil dwelling nematode, Caenorhabditis (C.) elegans, is a popular model system for studying behavioral plasticity. Noticeably absent from the C. elegans literature, however, are studies evaluating worm behavior in mazes. Here, we report the use of microfluidic mazes to investigate exploration and learning behaviors in wild-type C. elegans, as well as in the dopamine-poor mutant, cat-2. The key research findings include: (1)C. elegans worms are motivated to explore complex spatial environments with or without the presence of food/reward, (2) wild-type worms exhibit a greater tendency to explore relative to mutant worms, (3) both wild-type and mutant worms can learn to make unconditioned responses to food/reward, and (4) wild-type worms are significantly more likely to learn to make conditioned responses linking reward to location than mutant worms. These results introduce microfluidic mazes as a valuable new tool for biological behavioral analysis.

Espaces configurants : le déploiement de l'organisation

Configuring Spaces : Deploying Organisation. Despite the wide-spread deployment of Closed Circuit Television (CCTV) throughout most major cities Western Europe, and the importance of surveillance to contemporary debates within the social sciences, there remains relatively little detailed research concerned with the ways in which these technologies are used to oversee and manage complex spatial environments. In this paper, we examine how personnel in the operation centres of an unban transport system, or metro, use a range of tools and technologies to identify problems and events and implement a coordinated response. We consider how personnel configure views of the space to make sense of and interpret the conduct of the travelling public in organisationally relevant ways. We examine how they shape the ways in which both passengers and staff see and respond to each others' actions and the spatial environment. In addressing how personnel constitute the sense and significance of the scenes, we reflect on the development of information systems that are designed to scrutinise video images and automatically detect problems and events.

Neural foundations of emerging route knowledge in complex spatial environments

Behavioral evidence suggests that spatial knowledge derived from ground-level navigation can consist of both route and survey knowledge. Neuroimaging and lesion studies aiming to identify the neural structures responsible for topographical learning in humans have yielded partially inconsistent results, probably due to the lack of an effective behavioral parameter allowing for a reliable distinction between different representations. Therefore, we employed a novel virtual reality environment that provides accuracy and reaction time measures precisely indicating the emergence of route vs. survey knowledge. Functional magnetic resonance imaging (fMRI) was used to localize brain regions involved in the acquisition of pure route knowledge in the form of associations between consecutive landmark views and the direction of intermediate movements. Participants were scanned during repeated encoding of the complex environment from a first-person, ground-level perspective. Behavioral data revealed emerging route knowledge in 11 out of 14 subjects. Overall comparisons between encoding and control conditions identified activation in medial frontal gyrus, retrosplenial cortex and posterior inferior parietal cortex. Most importantly, only posterior inferior parietal regions showed increasing activation across sessions, thus paralleling behavioral measures of route expertise. Given the established role of the posterior parietal cortex in spatial processing, this area is thought to provide the pivotal spatial link between two landmarks encountered in immediate temporal succession.

A City Metaphor to Support Navigation in Complex Information Spaces

A major problem in modern information systems is to locate information and to re-find information one has seen before. Systems like the World Wide Web are heavily interlinked, but do not show structures that help users to navigate the information it contains. The use of appropriate navigation metaphors can help to make the structure of modern information systems easier to understand and therefore easier to use.We propose a conceptual user interface metaphor based on the structure of a city. Cities are very complex spatial environments and people know how to get information, how to reach certain locations in a city, and how to make use of the available infrastructure, etc. Cities provide a rich set of navigational infrastructure that lends itself to creating sub-metaphors for navigational tools. A city metaphor makes this existing knowledge about a structured environment available to the user of a computerized information system.We first focus on several properties necessary for future user interfaces (or user interface metaphors) that will distinguish them from current systems, like the richness of information or the use of visualizations to show the structure of information spaces. We also describe the strengths and problems of spatial user-interface metaphors. Then we present the structure of the information city metaphor, its structuring and navigation metaphors and what we see as its main advantages and problems. We further outline a few scenarios of how an Information City might work. Finally, we compare implementing this metaphor using either a textual or a graphical virtual environment or a combination.