Navigation Capacity Research Articles

Has the Three‐Gorges Dam made the Poyang Lake wetlands wetter and drier?

The Three‐Georges Dam holds many records in the history of engineering. While the dam has produced benefits in terms of flood control, hydropower generation and increased navigation capacity of the Yangtze River, serious questions have been raised concerning its impact on both upstream and downstream ecosystems. It has been suggested that the dam operation intensifies the extremes of wet and dry conditions in the downstream Poyang Lake, and affects adversely important local wetlands. A floodgate has been proposed to maintain the lake water level by controlling the flow between the Poyang Lake and Yangtze River. Using extensive hydrological data and generalized linear statistical models, we demonstrated that the dam operation induces major changes in the downstream river discharge near the dam, including an average “water loss”. The analysis also revealed considerable effects on the Poyang Lake water level, particularly a reduced level over the dry period from late summer to autumn. However, the dam impact needs to be further assessed based on long‐term monitoring of the lake ecosystem, covering a wide range of parameters related to hydrological and hydraulic characteristics of the lake, water quality, geomorphological characteristics, aquatic biota and their habitat, wetland vegetation and associated fauna.

A JTIDS/INS/DGPS navigation system with pseudorange differential information transmitted over Link-16: design and implementation

As the battle environment becomes more complicated, the demand for higher accuracy and better anti-jam capacity of navigation has been increasing. The conventional JTIDS/INS/GPS integrated navigation cannot meet the demands of certain situations such as precision strike and formation flight. A new system that introduces the differential GPS into JTIDS/INS/GPS integration system is proposed to improve the navigation performance in the modern combined operations. In this system, the differential information of DGPS is transmitted through the communication data link of Link-16. As a result, the system resources are efficiently utilized and the controllability and anti-jam performance of the system are significantly enhanced. A hybrid slot allocation protocol (HSAP) that combines a static slot allocation algorithm and a dynamic slot allocation algorithm and the corresponding source-chosen mechanisms are proposed. The performance of the JTIDS/INS/GPS integration navigation using the differential GPS information from one or multiple base stations is studied and compared with that of the system without using the differential GPS information. Furthermore, the performance of the integration navigation using HSAP is compared with that of the system using static slot allocation algorithm. We show that navigation accuracy based on the differential GPS is improved, and using HSAP also leads to higher localization accuracy.

Factor Associated with Neutral Sphingomyelinase Activity Mediates Navigational Capacity of Leukocytes Responding to Wounds and Infection: Live Imaging Studies in Zebrafish Larvae

Factor associated with neutral sphingomyelinase activity (FAN) is an adaptor protein that specifically binds to the p55 receptor for TNF (TNF-RI). Our previous investigations demonstrated that FAN plays a role in TNF-induced actin reorganization by connecting the plasma membrane with actin cytoskeleton, suggesting that FAN may impact on cellular motility in response to TNF and in the context of immune inflammatory conditions. In this study, we used the translucent zebrafish larvae for in vivo analysis of leukocyte migration after morpholino knockdown of FAN. FAN-deficient zebrafish leukocytes were impaired in their migration toward tail fin wounds, leading to a reduced number of cells reaching the wound. Furthermore, FAN-deficient leukocytes show an impaired response to bacterial infections, suggesting that FAN is generally required for the directed chemotactic response of immune cells independent of the nature of the stimulus. Cell-tracking analysis up to 3 h after injury revealed that the reduced number of leukocytes is not due to a reduction in random motility or speed of movement. Leukocytes from FAN-deficient embryos protrude pseudopodia in all directions instead of having one clear leading edge. Our results suggest that FAN-deficient leukocytes exhibit an impaired navigational capacity, leading to a disrupted chemotactic response.

'I Work with the Community, Not the Parties!' The Political and Practical Dilemmas of South Africa's State-Employed Community Development Workers

During the past few years within South Africa, there has been a proliferation of state-led community work and community development initiatives. Examples include the National Community Development Worker Programme (CDWP), the Community Works Programme and also the Community Practitioner Programme. The backdrop for such initiatives is increasing violent protests within disaffected communities, usually emergent from people's anger at ineffective social and public service delivery and also endemic unemployment. Often, communities view state institutions, including state-led community development programmes with a mixture of hope for service delivery and mistrust, at the failure to deliver. This article draws on data from twenty interviews with two cohorts of social and community development workers within South Africa, conducted during 2010 and 2011. The first cohort represent new community development workers employed within the CDWP; the second cohort represent senior community practitioners, having worked a minimum of ten years within the field in South Africa. Analysis of the findings consider how these social and community workers are learning to negotiate the political, practical and leadership dilemmas of their ambiguous position both in and against the state. Furthermore, the discussion considers the need for social and community workers to improve their political literacy and acquire navigational capacities, and also explores ways forward for the CDWP as a whole.

Towards a unification of movement ecology and biogeography: conceptual framework and a case study on Afrotropical ducks

AbstractAim We present elements of a new conceptual framework for the unification of biogeography and movement ecology, and demonstrate the value of the new framework using a case study of two species of Afrotropical duck (Anatidae) across a latitudinal gradient.Location Southern Africa.Methods The first part of the paper rests on logic and philosophy. For the second (case study) section, we used data from up to 3 years of satellite telemetry for 26 individuals of two species of Afrotropical duck, the Egyptian goose (Alopochen aegyptiaca) and red‐billed teal (Anas erythrorhyncha), from three different populations with moulting sites spread across 17 degrees of latitude. We compared quantitative measures of movement patterns using principal components analysis and boxplots.Results We argue that unpacking the concept of dispersal into the fundamental elements of movement (internal drivers, external drivers, navigation capacity, and motion capacity) provides a more solid basis for contrasting competing hypotheses in biogeographical studies. We found, surprisingly, that red‐billed teal, a ‘highly nomadic’ species, moved with a relatively high degree of consistency at each of our three study latitudes, while Egyptian geese, a ‘resident’ species, showed latitude‐dependent variation in their movements. However, much of the latitude‐related variation for Egyptian geese was driven by their annual moult migrations, rather than directly by fluctuations in resource availability. Internal factors appear to dominate movements and probably determine the species ranges of both of our study species.Main conclusions The integration of biogeography and movement ecology, through a more sophisticated view of mechanisms formerly lumped together under ‘dispersal’, offers a fertile area for further research. The biogeography of Afrotropical ducks appears to be strongly influenced by internal factors. Biogeographical patterns in this taxon may thus be best understood (and modelled) as a long‐term response to environmental stochasticity, rather than as a deliberate selection of optimal habitat. Latitudinal comparisons emerge as a valuable way of gaining insights into the drivers of movement for widespread species.

‘At the next junction, turn left’: attitudes towards Sat Nav use

While there is established academic literature on cartography and Geographical Information Systems (GIS), to date there has been scant investigation of attitudes towards the use of Satellite Navigation (Sat Nav) as a technology of navigation and the issues that may arise from its use. However, the impacts of Sat Nav tools on cartographic literacy, spatial awareness and graphicacy should be matters of interest and concern to geographers. This paper is an initial investigation of people's attitudes towards, and experiences of, Sat Nav. Based on a survey of undergraduate geography students (n = 46), navigational capacities and technological aspects of Sat Nav are regarded positively, whereas negative attitudes are associated with technological, safety and financial attributes of Sat Nav use. Distinctions were made between traditional navigational technologies such as paper‐based maps and Sat Nav. Crucially, the digital spatial representations of Sat Nav were not perceived as maps but as a distinctive navigational tool. Students also expressed concerns about the potential implications of reduced use of other navigational tools on their cartographic literacy and spatial awareness. We demonstrate that Sat Nav use is intrinsically changing people's wayfinding behaviour, processes and practices of navigation, and their understanding of what ‘maps’ are and do. Fundamentally, Sat Nav is not viewed or used in the same way as more traditional technologies of navigation. We assert that geographers should engage more actively with current interdisciplinary dialogues on wayfinding navigational technologies and spatial and cartographic literacy.

Individual effects of varying stimulation intensity and response criteria on area of activation for different muscles in humans. A study using navigated transcranial magnetic stimulation

BackgroundWhen using transcranial magnetic stimulation, a stimulation intensity defined as a certain level above the threshold for activation of a hand muscle is commonly used, disregarding the fact that the areas of activation for different muscles may have varying response characteristics intra- and interindividually. ObjectiveTo study the response characteristics of different muscles and compare them within and between individuals. Also to investigate the effect of varying stimulation intensity (defined in two different ways) and amplitude criterion for response, on the sizes of the activation areas for different muscles. MethodsA system of transcranial magnetic stimulation with navigation capacity where the stimulation intensity can be defined in terms of the electric field strength in the tissue was used. Four different muscles were investigated in healthy adults. The threshold for activation at rest (RMT) of the different muscles and their respective areas of activation were quantified using three different stimulus intensities (100, 110 and 120% RMT) and two criteria for response amplitude (20 and 50 μV). ResultsResponses could readily be determined using 20 μV as response limit. The RMTs for different muscles varied within and between individuals. The degree to which the area depended on stimulation intensity differed between muscles intra- and interindividually. All results were statistically significant (P < 0.05 or less). ConclusionsThe response characteristics vary between muscles within an individual and between individuals for a certain muscle. Thus, for optimal accuracy when delineating the activation area, the investigation should be adapted to each particular muscle.

Research and Design of Range Positioning System Based on Ultrasonic Sensor for Intelligent Mobile Robot

The technology of mobile robot is an important branch in robot research. In order to endow robot with capacity of intelligent control and autonomous navigation, and solve the problems such as high cost and large power consumption, a range positioning system based on ultrasonic sensor for intelligent mobile robot is designed in this paper. The system makes robot achieve some functions such as alarming, obstacle avoidance and the positioning.

Image-guided Navigation System for Robot-based Vessel intervention Surgery Based on Conventional Single Plane C- Arm

Remote-controlled interventional robots are widely studied in recent years to reduce the radiation exposure of operators in catheter-based vessel intervention surgery (VIS). Compared with manual operation, robot-based surgery relies more on image-guided navigation information. As the conventional C-Arm is used widely and has poor navigation capacity, the application of interventional robot is limited. In this paper, a new image-guided navigation system for interventional robots is proposed. This system provides useful navigation information based on single plane fluoroscopy x-ray images, which could improve the accuracy and efficiency of robot-based VIS under conventional C-Arm system. To validate the system, phantom-based and animal experiments are performed. The accuracy of 3D reconstruction is tested by comparing the distance between reconstructed positions with real values, and the efficacy of the system is testified by performing simulating robot-based VIS. Experimental results show that this navigation system has adequate accuracy and can indeed improve the efficiency of VIS.© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of ICESB 2011

The rolling horizon procedure on deterministic lockage co‐scheduling to the two dams of the Three Gorges Project

PurposeThe purpose of this paper is to propose a rolling horizon procedure (RHP) to deal with the large‐scale and strongly NP‐hard problem on cooperative lockage‐timetables and service‐policies of the five locks in the Three Gorges Project.Design/methodology/approachRHP based approach is composed of a series of periodical short‐time sub‐optimizations instead of global optimization. Each of the sub‐optimizations is modeled by a mixed‐integer‐programming and solved by a branch and bound algorithm with terminal penalty.FindingsThe RHP method is found to be effective and efficient. The size of the rolling horizon is positively correlated to the total weighted area of ships.Research limitations/implicationsPrecision of short‐time predictions is the main limitation.Originality/valueThis procedure promotes the navigation capacity of the Three Gorges Project and proposes a solution to the lockage‐scheduling problem of the Three Gorges Project.

Agent‐based Modeling of Animal Movement: A Review

AbstractAnimal movement is a complex spatiotemporal phenomenon that has intrigued researchers from many disciplines. Interactions among animals, and between animals and the environments that they traverse, play an important role in the development of the complex ecological and social systems in which they are embedded. Agent‐based models have been increasingly applied as a computational approach to the study of animal movement across landscapes. In this article, we present a review of agent‐based models in which the simulation of animal movement processes and patterns is the central theme. Our discussion of these processes is focused on four key components: internal states, external factors, motion capacities, and navigation capacities. These four components have been identified in the emerging movement ecology research paradigm and are important for modeling animal movement behavior. Because agent‐based models allow for an individual‐based approach that encapsulates these four components, the underlying processes that drive animal behavior can be deeply explored using this technique. A set of challenges and issues remain, however, for agent‐based models of animal movement. In this article, we review the existing literature and identify potential research directions that could help address these challenges.

Experiential Wisdom and Optimal Experience: Interviews with Three Distinguished Lifelong Learners

The present article suggests that lifelong learning is enhanced by the capacity to make experiential course corrections that lead back to states of interest and flow experience. The notion of experiential wisdom is introduced to describe such a capacity for navigation. A person with experiential wisdom recognizes that optimal experiences are more likely to occur when an affectively charged intuitive mode works in synchrony with a deliberative rational mode and is better able to cultivate situations where the interrelation of these two modes is optimized. The first part of the article provides a framework for understanding experiential wisdom and the regulation of optimal experience. The second part illustrates the practice of experiential wisdom by drawing on interviews with three distinguished lifelong learners—poet Mark Strand, social scientist Donald Campbell, and medical researcher Jonas Salk.

Visual Motion Processing in Aging and Alzheimer's Disease

Aging and Alzheimer's disease (AD) are accompanied by impairments of autonomous navigation and spatial orientation that commonly demand the abandonment of driving and independent living. We have studied the neuronal mechanisms of navigation using single neurons in monkey cerebral cortex, finding a specific population of cells that processes the visual motion patterns of optic flow that provide important cues about self-movement. We have found that AD patients show pronounced deficits in the perceptual processing of optic flow, with different patterns of less severe impairment in mild cognitive impairment and cognitive aging. These perceptual deficits occur in subjects who show difficulties in real-world navigation that can be linked to visual associative processing impairments. Human neurophysiological recordings reveal a robust link between navigational capacity and cortical information processing in aging and AD. We conclude that visual information processing is progressively impaired in aging and AD. We speculate that these behavioral impairments reflect the progress of mechanistically linked cortical pathophysiologies that are manifestations of the fateful transition from cognitive aging to AD.

Isolation and characterization of a magnetotactic bacterial culture from the Mediterranean Sea

The widespread magnetotactic bacteria have the peculiar capacity of navigation along the geomagnetic field. Despite their ubiquitous distribution, only few axenic cultures have been obtained worldwide. In this study, we reported the first axenic culture of magnetotactic bacteria isolated from the Mediterranean Sea. This magneto-ovoid strain MO-1 grew in chemically defined O(2) gradient minimal media at the oxic-anoxic transition zone. It is phylogenetically related to Magnetococcus sp. MC-1 but might represent a novel genus of Proteobacteria. Pulsed-field gel electrophoresis analysis indicated that the genome size of the MO-1 strain is 5 ± 0.5 Mb, with four rRNA operons. Each cell synthesizes about 17 magnetosomes within a single chain, two phosphorous-oxygen-rich globules and one to seven lipid storage granules. The magnetosomes chain seems to divide in the centre during cell division giving rise to two daughter cells with an approximately equal number of magnetosomes. The MO-1 cell possesses two bundles of seven individual flagella that were enveloped in a unique sheath. They swam towards the north pole with a velocity up to 300 μm per second with frequent change from right-hand to left-hand helical trajectory. Using a magneto-spectrophotometry assay we showed that MO-1 flagella were powered by both proton-motive force and sodium ion gradient, which is a rare feature among bacteria.

Multiple movement modes by large herbivores at multiple spatiotemporal scales

Recent theory suggests that animals should switch facultatively among canonical movement modes as a complex function of internal state, landscape characteristics, motion capacity, and navigational capacity. We tested the generality of this paradigm for free-ranging elk (Cervus elaphus) over 5 orders of magnitude in time (minutes to years) and space (meters to 100 km). At the coarsest spatiotemporal scale, elk shifted from a dispersive to a home-ranging phase over the course of 1-3 years after introduction into a novel environment. At intermediate spatiotemporal scales, elk continued to alternate between movement modes. During the dispersive phase, elk alternated between encamped and exploratory modes, possibly linked to changes in motivational goals from foraging to social bonding. During the home-ranging phase, elk movements were characterized by a complex interplay between attraction to preferred habitat types and memory of previous movements across the home-range. At the finest temporal and spatial scale, elk used area-restricted search while browsing, interspersed with less sinuous paths when not browsing. Encountering a patch of high-quality food plants triggered the switch from one mode to the next, creating biphasic movement dynamics that were reinforced by local resource heterogeneity. These patterns suggest that multiphasic structure is fundamental to the movement patterns of elk at all temporal and spatial scales tested.

The movement ecology and dynamics of plant communities in fragmented landscapes

A conceptual model of movement ecology has recently been advanced to explain all movement by considering the interaction of four elements: internal state, motion capacity, navigation capacities, and external factors. We modified this framework to generate predictions for species richness dynamics of fragmented plant communities and tested them in experimental landscapes across a 7-year time series. We found that two external factors, dispersal vectors and habitat features, affected species colonization and recolonization in habitat fragments and their effects varied and depended on motion capacity. Bird-dispersed species richness showed connectivity effects that reached an asymptote over time, but no edge effects, whereas wind-dispersed species richness showed steadily accumulating edge and connectivity effects, with no indication of an asymptote. Unassisted species also showed increasing differences caused by connectivity over time, whereas edges had no effect. Our limited use of proxies for movement ecology (e.g., dispersal mode as a proxy for motion capacity) resulted in moderate predictive power for communities and, in some cases, highlighted the importance of a more complete understanding of movement ecology for predicting how landscape conservation actions affect plant community dynamics.

Trends and missing parts in the study of movement ecology

Movement is important to all organisms, and accordingly it is addressed in a huge number of papers in the literature. Of nearly 26,000 papers referring to movement, an estimated 34% focused on movement by measuring it or testing hypotheses about it. This enormous amount of information is difficult to review and highlights the need to assess the collective completeness of movement studies and identify gaps. We surveyed 1,000 randomly selected papers from 496 journals and compared the facets of movement studied with a suggested framework for movement ecology, consisting of internal state (motivation, physiology), motion and navigation capacities, and external factors (both the physical environment and living organisms), and links among these components. Most studies simply measured and described the movement of organisms without reference to ecological or internal factors, and the most frequently studied part of the framework was the link between external factors and motion capacity. Few studies looked at the effects on movement of navigation capacity, or internal state, and those were mainly from vertebrates. For invertebrates and plants most studies were at the population level, whereas more vertebrate studies were conducted at the individual level. Consideration of only population-level averages promulgates neglect of between-individual variation in movement, potentially hindering the study of factors controlling movement. Terminology was found to be inconsistent among taxa and subdisciplines. The gaps identified in coverage of movement studies highlight research areas that should be addressed to fully understand the ecology of movement.

Movement Strategies of Seed Predators as Determinants of Plant Recruitment Patterns

Plant recruitment in nature exhibits several distinctive patterns ranging from hump shaped to monotonically decreasing with distance from the seed source. We investigate the role of postdispersal seed predation in shaping these patterns, introducing a new mechanistic model that explicitly accounts for the movement strategy used by seed eaters. The model consists of two partial differential equations describing the spatiotemporal dynamics of both seed and predator densities. The movement strategy is defined by how predators move in response to the different cues they can use to search for seeds. These cues may be seed density, seed intake, distance from the plant, density of conspecific foragers, or a mixture of these four. The model is able to reproduce all the basic plant recruitment patterns found in the field. We compare the results to those of the ideal free distribution (IFD) theory and show that hump-shaped plant recruitment patterns cannot be generated by IFD predators and, in general, by foragers that respond exclusively to seed density. These foragers can produce only nonincreasing patterns, the shapes of which are determined by the foragers' navigation capacities. In contrast, hump-shaped patterns can be produced by distance-responsive predators or by foragers that use conspecifics as a cue for seed abundance.

Detecting navigational deficits in cognitive aging and Alzheimer disease using virtual reality

Older adults get lost, in many cases because of recognized or incipient Alzheimer disease (AD). In either case, getting lost can be a threat to individual and public safety, as well as to personal autonomy and quality of life. Here we compare our previously described real-world navigation test with a virtual reality (VR) version simulating the same navigational environment. Quantifying real-world navigational performance is difficult and time-consuming. VR testing is a promising alternative, but it has not been compared with closely corresponding real-world testing in aging and AD. We have studied navigation using both real-world and virtual environments in the same subjects: young normal controls (YNCs, n = 35), older normal controls (ONCs, n = 26), patients with mild cognitive impairment (MCI, n = 12), and patients with early AD (EAD, n = 14). We found close correlations between real-world and virtual navigational deficits that increased across groups from YNC to ONC, to MCI, and to EAD. Analyses of subtest performance showed similar profiles of impairment in real-world and virtual testing in all four subject groups. The ONC, MCI, and EAD subjects all showed greatest difficulty in self-orientation and scene localization tests. MCI and EAD patients also showed impaired verbal recall about both test environments. Virtual environment testing provides a valid assessment of navigational skills. Aging and Alzheimer disease (AD) share the same patterns of difficulty in associating visual scenes and locations, which is complicated in AD by the accompanying loss of verbally mediated navigational capacities. We conclude that virtual navigation testing reveals deficits in aging and AD that are associated with potentially grave risks to our patients and the community.

Analysis of WASp function during the wound inflammatory response – live-imaging studies in zebrafish larvae

Wiskott-Aldrich syndrome protein (WASp) is haematopoietically restricted, and is the causative protein underlying a severe human disorder that can lead to death due to immunodeficiency and haemorrhaging. Much is known about the biochemistry of WASp and the migratory capacity of WASp-defective cells in vitro, but in vivo studies of immune-cell behaviour are more challenging. Using the translucency of zebrafish larvae, we live-imaged the effects of morpholino knockdown of WASp1 (also known as Was) on leukocyte migration in response to a wound. In embryos at 22 hours post-fertilisation, primitive macrophages were impaired in their migration towards laser wounds. Once a circulatory system had developed, at 3 days post-fertilisation, we observed significantly reduced recruitment of neutrophils and macrophages to ventral fin wounds. Cell-tracking studies indicated that fewer leukocytes leave the vessels adjacent to a wound and those that do exhibit impaired navigational capacity. Their cell morphology appears unaltered but their choice of leading-edge pseudopodia is more frequently incorrect, leading to impaired chemotaxis. We also identified two zebrafish mutants in WASp1 by TILLING, one of which was in the WIP-binding domain that is the hotspot for human lesions, and mutants exhibited the same deficiencies in wound inflammation and thrombus formation as WASp1 morphants.