10,648 research outputs found
Learning by a nerual net in a noisy environment - The pseudo-inverse solution revisited
A recurrent neural net is described that learns a set of patterns in the
presence of noise. The learning rule is of Hebbian type, and, if noise would be
absent during the learning process, the resulting final values of the weights
would correspond to the pseudo-inverse solution of the fixed point equation in
question. For a non-vanishing noise parameter, an explicit expression for the
expectation value of the weights is obtained. This result turns out to be
unequal to the pseudo-inverse solution. Furthermore, the stability properties
of the system are discussed.Comment: 16 pages, 3 figure
Reptation in the Rubinstein-Duke model: the influence of end-reptons dynamics
We investigate the Rubinstein-Duke model for polymer reptation by means of
density-matrix renormalization group techniques both in absence and presence of
a driving field. In the former case the renewal time \tau and the diffusion
coefficient D are calculated for chains up to N=150 reptons and their scaling
behavior in N is analyzed. Both quantities scale as powers of N: and with the asymptotic exponents z=3 and x=2, in agreement
with the reptation theory. For an intermediate range of lengths, however, the
data are well-fitted by some effective exponents whose values are quite
sensitive to the dynamics of the end reptons. We find 2.7 <z< 3.3 and 1.8 <x<
2.1 for the range of parameters considered and we suggest how to influence the
end reptons dynamics in order to bring out such a behavior. At finite and not
too small driving field, we observe the onset of the so-called band inversion
phenomenon according to which long polymers migrate faster than shorter ones as
opposed to the small field dynamics. For chains in the range of 20 reptons we
present detailed shapes of the reptating chain as function of the driving field
and the end repton dynamics.Comment: RevTeX 12 Pages and 14 figure
Does individual variation in metabolic phenotype predict fish behaviour and performance?
There is increasing interest in documenting and explaining the existence of marked intraspecific variation in metabolic rate in animals, with fishes providing some of the best-studied examples. After accounting for variation due to other factors, there can typically be a two to three-fold variation among individual fishes for both standard and maximum metabolic rate (SMR and MMR). This variation is reasonably consistent over time (provided that conditions remain stable), and its underlying causes may be influenced by both genes and developmental conditions. In this paper, current knowledge of the extent and causes of individual variation in SMR, MMR and aerobic scope (AS), collectively its metabolic phenotype, is reviewed and potential links among metabolism, behaviour and performance are described. Intraspecific variation in metabolism has been found to be related to other traits: fishes with a relatively high SMR tend to be more dominant and grow faster in high food environments, but may lose their advantage and are more prone to risk-taking when conditions deteriorate. In contrast to the wide body of research examining links between SMR and behavioural traits, very little work has been directed towards understanding the ecological consequences of individual variation in MMR and AS. Although AS can differ among populations of the same species in response to performance demands, virtually nothing is known about the effects of AS on individual behaviours such as those associated with foraging or predator avoidance. Further, while factors such as food availability, temperature, hypoxia and the fish's social environment are known to alter resting and MMRs in fishes, there is a paucity of studies examining how these effects vary among individuals, and how this variation relates to behaviour. Given the observed links between metabolism and measures of performance, understanding the metabolic responses of individuals to changing environments will be a key area for future research because the environment will have a strong influence on which animals survive predation, become dominant and ultimately have the highest reproductive success. Although current evidence suggests that variation in SMR may be maintained within populations via context-dependent fitness benefits, it is suggested that a more integrative approach is now required to fully understand how the environment can modulate individual performance via effects on metabolic phenotypes encompassing SMR, MMR and AS
Combining Hebbian and reinforcement learning in a minibrain model
A toy model of a neural network in which both Hebbian learning and
reinforcement learning occur is studied. The problem of `path interference',
which makes that the neural net quickly forgets previously learned input-output
relations is tackled by adding a Hebbian term (proportional to the learning
rate ) to the reinforcement term (proportional to ) in the learning
rule. It is shown that the number of learning steps is reduced considerably if
, i.e., if the Hebbian term is neither too small nor too
large compared to the reinforcement term
Het Nederlandse agrocomplex 2002
Dit rapport geeft inzicht in de economische ontwikkeling van het Nederlandse agrocomplex. Dit omvat de land- en tuinbouw en de daarmee samenhangende handel en industrie. Op basis van de gereviseerde Nationale Rekeningen is voor de periode 1995-2000 de veranderende betekenis van het agrocomplex gekwantificeerd in termen van toegevoegde waarde, werkgelegenheid en handelssaldo. In de analyse zijn deelcomplexen onderscheiden voor glastuinbouw, opengrondstuinbouw, akkerbouw, grondgebonden veehouderij en intensieve veehouderij
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