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Many Patterns (many + pattern)

Distribution by Scientific Domains

Life Sciences	50%

Selected Abstracts

Complex-valued multidirectional associative memory

ELECTRICAL ENGINEERING IN JAPAN, Issue 1 2007
Masaki Kobayashi
Abstract Hopfield model is a representative associative memory. It was improved to Bidirectional Associative Memory (BAM) by Kosko and to Multidirectional Associative Memory (MAM) by Hagiwara. They have two layers or multilayers. Since they have symmetric connections between layers, they ensure convergence. MAM can deal with multiples of many patterns, such as (x1,x2,,), where xm is the pattern on layer m. Copyright © 2004 Wiley Periodicals, Inc. Noest, Hirose, and Nemoto proposed complex-value Hopfield model. Lee proposed complex-valued Bidirectional Associative Memory. Zemel proved the rotation invariance of complex-valued Hopfield model. It means that the rotated pattern in also stored. In this paper, the complex-valued Multidirectional Associative Memory is proposed. The rotation invariance is also proved. Moreover it is shown by computer simulation that the differences of angles of given patterns are automatically reduced. At first we define complex-valued Multidirectional Associative Memory. Then we define the energy function of network. With the energy function, we prove that the network ensures convergence. Next, we define the learning law and show the characteristic of recall process. The characteristic means that the differences of angles of given patterns are automatically reduced. Especially we prove the following theorem. In the case that only a multiple of patterns is stored, if patterns with different angles are given to each layer, the differences are automatically reduced. Finally, we investigate whether the differences of angles influence the noise robustness. It is found to reduce the noise robustness, because the input to each layer becomes small. We show this by computer simulations. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(1): 39,45, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20387 [source]

Spatial variation in the duration of the rainy season in monsoonal Australia

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 14 2001
Garry D. Cook
Abstract Climatological research in the tropics of northern Australia has focused particularly on the Australian summer monsoon. However, the timing of many ecologically important processes is determined not by the monsoon but by extra-monsoonal rainfall events. These events produce a temporal pattern of wet and dry spells that is at least as important ecologically as the amount of rain. We defined the rainy season as that period when the probability of 10-day dry spells was less than 0.5, and the wet season as that period within the rainy season when the probability of dry spells was less than 0.1. We applied these criteria to seven stations along a strong north,south rainfall gradient spanning more than 12° of latitude in tropical north Australia. The duration of the rainy and wet seasons in northern Australia decreases with increasing latitude. The timing and duration of these seasons were also affected by the El Niño,Southern Oscillation (ENSO). The relative contribution of temporally isolated rainfall events to both the duration of the rainy season and the amount of rainfall increases with latitude. The geographic variation in these seasons corresponds to many patterns occurring in natural ecosystems. We argue that understanding the extra-monsoon rainfall events is critical to understanding how climate variation affects natural ecosystems. Copyright © 2001 Royal Meteorological Society [source]

Food-web assembly during a classic biogeographic study: species'"trophic breadth" corresponds to colonization order

OIKOS, Issue 5 2008
Denise A. Piechnik
Ecologists have found many patterns in food-web structure. Some, like the constant connectance hypothesis, lack definitive explanatory mechanisms. In response, we investigated whether community assembly mechanisms could explain why trophic complexity consistently scales with species richness among ecosystems. We analyzed how food-web structure developed during the community assembly recorded in Simberloff and Wilson's classic biogeography experiment. Using their arthropod surveys, we constructed six time series of food-webs from pre- and post-defaunation censuses of six experimental islands, and synthesized trophic information for 250 species from the literature and expert sources. We found that the fraction of specialist species increased and the fraction of generalists decreased during food-web assembly. Directed connectance initially declined over time, despite an increase in species richness, but eventually leveled off as predicted by the constant connectance hypothesis of diversity-complexity scaling. The initial decline was explained by later colonization by trophic specialists, probably due to limited resource availability during early colonization. Late-colonizing super-generalists maintained constant connectance at later dates. This relationship between colonization success and trophic breadth helps explain food-web patterns and corroborates assertions that community assembly is systematically influenced by species' trophic breadths. [source]

Does avian species richness in natural patch mosaics follow the forest fragmentation paradigm?

ANIMAL CONSERVATION, Issue 1 2007
D. C. Pavlacky Jr.
Abstract As one approaches the north-eastern limit of pinyon (Pinus spp.) juniper (Juniperus spp.) vegetation on the Colorado Plateau, USA, woodland patches become increasingly disjunct, grading into sagebrush (Artemisia spp.)-dominated landscapes. Patterns of avian species richness in naturally heterogeneous forests may or may not respond to patch discontinuity in the same manner as bird assemblages in fragmented agricultural systems. We used observational data from naturally patchy woodlands and predictions derived from studies of human-modified agricultural forests to estimate the effects of patch area, shape, isolation and distance to contiguous woodland on avian species richness. We predicted that patterns of species richness in naturally patchy juniper woodlands would differ from those observed in fragmented agricultural systems. Our objectives were to (1) estimate the effect of naturally occurring patch structure on avian species richness with respect to habitat affinity and migratory strategy and (2) assess the concordance of the effects to predictions from agricultural forest systems. We used the analogy between populations and communities to estimate species richness, where species are treated as individuals in the application of traditional capture,recapture theory. Information-theoretic model selection showed that overall species richness was explained primarily by the species area relationship. There was some support for a model with greater complexity than the equilibrium theory of island biogeography where the isolation of large patches resulted in greater species richness. Species richness of woodland-dwelling birds was best explained by the equilibrium hypothesis with partial landscape complementation by open-country species in isolated patches. Species richness within specific migratory strategies showed concomitant increases and no shifts in species composition along the patch area gradient. Our results indicate that many patterns of species richness considered to be fragmentation effects may be general consequences of patch discontinuity and are ubiquitous in naturally heterogeneous systems. There was no evidence for the effects of patch shape and distance to contiguous woodland in juniper woodland, suggesting edge effects and dependence upon regional species pools are characteristics of fragmented agricultural systems. Natural patch mosaics may provide benchmarks for evaluating fragmentation effects and managing forests by mimicking natural landscape patterns. [source]