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  • Articles  (295)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Biological cybernetics 66 (1992), S. 381-387 
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract We present a scheme for systematically reducing the number of differential equations required for biophysically realistic neuron models. The techniques are general, are designed to be applicable to a large set of such models and retain in the reduced system as high a degree of fidelity to the original system as possible. As examples, we provide reductions of the Hodgkin-Huxley system and the A-current model of Connor et al. (1977).
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Biological cybernetics 68 (1993), S. 209-214 
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract We investigate spike initiation and propagation in a model axon that has a slow regenerative conductance as well as the usual Hodgkin-Huxley type sodium and potassium conductances. We study the role of slow conductance in producing repetitive firing, compute the dispersion relation for an axon with an additional slow conductance, and show that under appropriate conditions such an axon can produce a traveling zone of secondary spike initiation. This study illustrates some of the complex dynamics shown by excitable membranes with fast and slow conductances.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Biological cybernetics 70 (1994), S. 397-405 
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract. An important step in visual processing is the segregation of objects in a visual scene from one another and from the embedding background. According to current theories of visual neuroscience, the different features of a particular object are represented by cells which are spatially distributed across multiple visual areas in the brain. The segregation of an object therefore requires the unique identification and integration of the pertaining cells which have to be “bound” into one assembly coding for the object in question. Several authors have suggested that such a binding of cells could be achieved by the selective synchronization of temporally structured responses of the neurons activated by features of the same stimulus. This concept has recently gained support by the observation of stimulus-dependent oscillatory activity in the visual system of the cat, pigeon and monkey. Furthermore, experimental evidence has been found for the formation and segregation of synchronously active cell assemblies representing different stimuli in the visual field. In this study, we investigate temporally structured activity in networks with single and multiple feature domains. As a first step, we examine the formation and segregation of cell assemblies by synchronizing and desynchronizing connections within a single feature module. We then demonstrate that distributed assemblies can be appropriately bound in a network comprising three modules selective for stimulus disparity, orientation and colour, respectively. In this context, we address the principal problem of segregating assemblies representing spatially overlapping stimuli in a distributed architecture. Using synchronizing as well as desynchronizing mechanisms, our simulations demonstrate that the binding problem can be solved by temporally correlated responses of cells which are distributed across multiple feature modules.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Water Resources Association 31 (1995), S. 0 
    ISSN: 1752-1688
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: : Evaluation criteria for reservoir and stream resources were developed to provide decision makers with feedback on environmental consequences of water allocation decisions under conditions of severe sustained drought within the Colorado River Basin by using the AZCOL gaming simulation model. Seven categories of flow dependent resources were identified which highlight resource states associated with reservoirs or river reaches within the AZCOL model. AZCOL directly simulates impact of water management decisions on five resource categories: threatened, endangered or sensitive fish; native nonlisted fish; wetland and riparian elements; national or state wildlife refuges; and hatcheries or other flow dependent facilities. Two additional categories - cold and warm water sport fish - are not modeled explicitly but are incorporated in the evaluation of monetary benefits from recreation on Colorado River waters. Each resource category was characterized at each time step in the simulation according to one of four environmental states: stable, threatened, endangered, or extirpated. Changes in resource states were modeled by time and flow-dependent decision criteria tied to either reservoir level or stream flows within the AZCOL model structure. Gaming results using the AZCOL model indicate environmental impacts would be substantial and that water allocation decisions directly impacted environmental resource states.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Water Resources Association 27 (1991), S. 0 
    ISSN: 1752-1688
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: : The spatial and temporal variability of hydroclimatic elements were investigated in the central and northern Rocky Mountains (Colorado, Idaho, Montana, Utah, and Wyoming) during the 1951–1985 period. The three hydroclimatic elements studied were total water-year (October 1-September 30) streamflow (ST), winter (October 1-March 31) accumulated precipitation (PR), and April 1 snowpack (SN). An analysis of 14 virgin watersheds showed wide spatial djfferences in the temporal variability of SN, PR, and ST, and these were found to be caused largely by basin exposure to moist air flows. The more stable (low variability) basins were those exposed to prevailing northerly to westerly flow, while unstable (high variability) basins were exposed to occasional southwesterly to southeasterly moist flow. Snowpack was the better indicator of ST in 11 of the 14 watersheds, explaining 37 to 87 percent of the ST variance.Analysis of the spatial variability, based on all SN and PR data from across the study area, revealed 11 discrete climatic regions. Both SN and PR exhibited coherent regions of stable and unstable temporal variability. The average variability between stable and unstable regions differed by a factor of two, and the differences were best explained by the exposure of the mountain barrier to moist air flows.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Polar research 5 (1987), S. 0 
    ISSN: 1751-8369
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geography , Geosciences
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Water Resources Association 35 (1999), S. 0 
    ISSN: 1752-1688
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Data from seven Management Systems Evaluation Areas (MSEA) were used to test the sensitivity of a leaching model, Pesticide Root Zone Model-2, to a variety of hydrologic settings in the Midwest. Atrazine leaching was simulated because it was prevalent in the MSEA studies and is frequently detected in the region's groundwater. Short-term simulations used site specific soil and chemical parameters. Generalized simulations used data avail. able from regional soil databases and standardized variables. Accurate short-term simulations were precluded by lack of antecedent atrazine concentrations in the soil profile and water, suggesting that simulations using data for less than five years underestimate atrazine leaching. The seven sites were ranked in order of atrazine detection frequency (concentration 〉 0.2 μg L-1) in soil water at 2 m depth in simulations. The rank order of the sites based on long-term simulations were similar to the ranks of sites based on atrazine detection frequency from groundwater monitoring. Simulations with Map Unit Use File (MUUF) soils data were more highly correlated with ranks of observed atrazine detection frequencies than were short-term simulations using site-specific soil data. Simulations using the MIJUIF data for soil parameters were sufficiently similarity to observed atrazine detection to allow the credible use of regional soils data for simulating leaching with PRZM-2 in a variety of Midwest soil and hydrologic conditions. This is encouraging for regional modeling efforts because soil parameters are among the most critical for operating PRZM-2 and many other leaching models.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Water Resources Association 37 (2001), S. 0 
    ISSN: 1752-1688
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: : The fate of pesticides entering the Riparian Buffer Strips (RBS) has not been well documented. This study compared the transport and fate of atrazine in soil of three-, five-, and nine-year-old switchgrass (Panicum virgatum L.) RBS to that in adjacent soils cropped to a corn-soybean rotation or a grass-alfalfa pasture. Undisturbed soil columns were collected from the RBS and cropped areas within the Bear Creek watershed, near Roland, Iowa. Atrazine and bromide breakthrough curves obtained using intact soil columns under saturated conditions were described by a two-region, mobile-immobile transport model. Preferential flow of bromide and atrazine was evident in five-and nine-year-old RBS soil, but there was little difference in transport characteristics between these two RBS soils and the adjacent cropped soils. There was a trend towards an increase in dispersion coefficients between the five-and nine-year-old RBS sites, which suggests an increased degree of preferential flow with increasing RBS age. Despite similar texture and organic C contents, atrazine sorption was significantly greater in RBS soil than the adjacent cropped soil. Cropped soil degraded atrazine faster than the RBS soil. The rapid degradation of atrazine in the corn-soybean soil adjacent to the five-year-old RBS (atrazine half-life of 19 days) appeared to be due to a larger population of atrazine-degrading microorganisms. Atrazine-degrading microorganisms in the corn-soybean soil were 50,940 cells g-1 soil compared with 2,970 cells g-4 soil in 5-year-old RBS soil which resulted in 60 percent mineralization of [14C-UL-atrazine] in the corn-soybean soil.
    Type of Medium: Electronic Resource
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  • 9
    facet.materialart.
    Unknown
    Chicago : Periodicals Archive Online (PAO)
    Economic development and cultural change. 28:3 (1980:Apr.) 644 
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Virtual reality 3 (1998), S. 187-199 
    ISSN: 1434-9957
    Keywords: Input devices ; Wearable computers ; Empirical study
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract This paper reports on an experiment investigating the functionality and usability of novel input devices on a wearable computer for text entry tasks. Over a 3-week period, 12 subjects used three different input devices to create and save short textual messages. The virtual keyboard, forearm keyboard, and Kordic keypad input devices were assessed for their efficiency and usability in simple text-entry tasks. Results collected included the textual data created by the subjects, the duration of activities, the survey data and observations made by supervisors. The results indicated that the forearm keyboard is the best performer for accurate and efficient text entry while other devices may benefit from more work on designing specialist graphical user interfaces (GUIs) for the wearable computer.
    Type of Medium: Electronic Resource
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