14,945 research outputs found
Gaussian Process Conditional Copulas with Applications to Financial Time Series
The estimation of dependencies between multiple variables is a central
problem in the analysis of financial time series. A common approach is to
express these dependencies in terms of a copula function. Typically the copula
function is assumed to be constant but this may be inaccurate when there are
covariates that could have a large influence on the dependence structure of the
data. To account for this, a Bayesian framework for the estimation of
conditional copulas is proposed. In this framework the parameters of a copula
are non-linearly related to some arbitrary conditioning variables. We evaluate
the ability of our method to predict time-varying dependencies on several
equities and currencies and observe consistent performance gains compared to
static copula models and other time-varying copula methods
MODELLING SEGREGATION THROUGH CELLULAR AUTOMATA: A THEORETICAL ANSWER
This paper is a note in which we prove that Cellular Automata are suitable tools to model multi-agent interactive procedures. In particular, we apply the argument to validate results from simulation tools obtained for the classical model of segregation of Thomas Schelling (1971a).Cellular Automata, segregation, local information
Tissue-nonspecific alkaline phosphatase promotes axonal growth of hippocampal neurons
Axonal growth is essential for establishing neuronal circuits during brain development and for regenerative processes in the adult brain. Unfortunately, the extracellular signals controlling axonal growth are poorly understood. Here we report that a reduction in extracellular ATP levels by tissue-nonspecific alkaline phosphatase (TNAP) is essential for the development of neuritic processes by cultured hippocampal neurons. Selective blockade of TNAP activity with levamisole or specific TNAP knockdown with short hairpin RNA interference inhibited the growth and branching of principal axons, whereas addition of alkaline phosphatase (ALP) promoted axonal growth. Neither activation nor inhibition of adenosine receptors affected the axonal growth, excluding the contribution of extracellular adenosine as a potential hydrolysis product of extracellular ATP to the TNAP-mediated effects. TNAP was colocalized at axonal growth cones with ionotropic ATP receptors (P2X7 receptor), whose activation inhibited axonal growth. Additional analyses suggested a close functional interrelation of TNAP and P2X7 receptors whereby TNAP prevents P2X7 receptor activation by hydrolyzing ATP in the immediate environment of the receptor. Furthermore inhibition of P2X7 receptor reduced TNAP expression, whereas addition of ALP enhanced P2X7 receptor expression. Our results demonstrate that TNAP, regulating both ligand availability and protein expression of P2X7 receptor, is essential for axonal development
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