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Artificial neural network modelling has recently attracted much attention as a new technique for estimation and forecasting in economics and finance. The chief advantages of this new approach are that such models can usually find a solution for very complex problems, and that they are free from the assumption of linearity that is often adopted to make the traditional methods tractable. In this paper we compare the performance of Back‐Propagation Artificial Neural Network (BPN) models with the traditional econometric approaches to forecasting the inflation rate. Of the traditional econometric models we use a structural reduced‐form model, an ARIMA model, a vector autoregressive model, and a Bayesian vector autoregression model. We compare each econometric model with a hybrid BPN model which uses the same set of variables. Dynamic forecasts are compared for three different horizons: one, three and twelve months ahead. Root mean squared errors and mean absolute errors are used to compare quality of forecasts. The results show the hybrid BPN models are able to forecast as well as all the traditional econometric methods, and to outperform them in some cases. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
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Stimulation of adrenal chromaffin cells results in a rise in the concentration of intracellular free calcium which initiates catecholamine secretion by exocytosis. An understanding of the molecular basis of exocytosis will require knowledge of the sites of action of calcium. A role for calmodulin has been implicated in secretion from chromaffin cells, and isolated granule membranes bind both calmodulin and a series of cytosolic proteins in a calcium-dependent fashion. Here, we demonstrate that one of the cytosolic granule-binding proteins with a relative molecular mass (Mr) of 70,000 (70K) is a form of the calmodulin-regulated actin-binding protein caldesmon, first isolated from smooth muscle. Cytoplasmic gels assembled from an adrenal medullary extract in the absence of Ca2+ contained actin and the 70K protein. The association of both of these proteins with the cytoplasmic gel was inhibited by a micromolar concentration of Ca2+. In addition, we have demonstrated that the 70K protein is localized at the periphery of chromaffin cells. These results are consistent with the notion that 70K protein (caldesmon) has a role in regulating the organization of actin filaments of the cell periphery during the secretory process. 相似文献
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Norman H. Weitzel 《西北部美国博物学家》2011,65(2)
Field research on the dispersal of fecal sacs by parent White-breasted Nuthatches ( Sitta carolinensis ) was conducted on the eastern slopes of the Sierra Nevada in northwestern Nevada. Fecal sacs were dropped 6-60 m from the nest, with 56% of the total droppings ( n = 66) being dropped 48-60 m away. Ninety-five percent of sac dispersal was in the southwest quadrant, the food-foraging site. Also, 75% of non-sac flights during the nestling phase were in the direction of the foraging area, a dead, mature Jeffrey pine ( Pinus jeffreyi ). Fecal sac dispersal by parent Whitebreasted Nuthatches may reduce or eliminate detection of nestlings by avian predators. 相似文献
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