Computing the variance of the forecast error for the holt-winters seasonal models

This paper presents expressions for the variance of the forecast error for arbitrary lead times for both the additive and multiplicative Holt-Winters seasonal forecasting models. It is shown that even when the smoothing constants are chosen to have values between zero and one, when the period is greater than four, the variance may not be finite for some values of the smoothing constants. In addition, the regions where the variance becomes infinite are almost the same for both models. These results are of importance for practitioners, who may choose values for the smoothing constants arbitrarily, or by searching on the unit cube for values which minimize the sum of the squared errors when fitting the model to a data set. It is also shown that the variance of the forecast error for the multiplicative model is nonstationary and periodic.     

Uninterrupted protein synthesis is essential for survival in the early stages of carbontetrachloride-induced hepatocellular necrosis in the mouse

Summary The fatal syndrome produced by cycloheximide given 6 h after a hepatonecrogenic dose of CCl₄ is due neither to direct toxic synergism between CCl₄ and cycloheximide nor to transient sinusoidal thrombosis. It is suggested that survival in the presence of unknown factors released from dying liver cells requires uninterrupted protein synthesis. The life-saving effect of sterilization of the intestine by antibiotics indicates that the gut flora or its products play a vital role in pathogenesis.Acknowledgments. I wish to thank Mr C. R. West for carrying out the statistical analysis, Mrs Brenda Brooks for histological processing, and Berk Pharmaceuticals Ltd for information on Ancrod defibrination in mice.     

Insulin requirement of human leukemic cell lines

Summary The growth characteristics of human leukemic cell lines in serum supplemented medium and in serum free medium with and without the addition of insulin were investigated. No relation was found between the insulin binding capacity of the cells and their hormone-dependence for growth.This work has been supported by grant CT82.00191.04 of CNR Rome and by Regione Piemonte.     

Six scenarios for the future of systems “problem solving”

In this paper six scenarios for the future of systems “problem solving” are investigated in order to ascertain whether an approach can be identified (a) that offers prospects for the long-term survival and success of systems problem solving in practice and (b) that does this without incorporating theoretical contradictions. The six approaches come under the four class headings pragmatism, isolationism, imperialism, and pluralism. The theoretical foundations of each approach are explored in a discursive fashion. This makes explicit to systems practitioners the underlying principles on which their activities are overlaid and puts such approaches into the theoretical context of the six approaches identified herein.     

NADP-isocitric dehydrogenase of gerbil adrenal mitochondria: support of steroid hydroxylation

In gerbil adrenal cortex the activity of intramitochondrial NADP-linked isocitric dehydrogenase (IDH) is up to 10-fold greater than the NAD-linked IDH. The NADP-IDH, apparent Km 0.58 mM, Vmax 280 nmoles/min/mg mitochondrial protein, appears to be the major source of reducing equivalents to support adrenal mitochondrial steroid 11B- and 19-hydroxylation in this species.     

Injection of a soluble sperm fraction into sea-urchin eggs triggers the cortical reaction

Fertilization membranes form around unfertilized sea-urchin eggs after microinjection of a soluble spermatozoa fraction isosmotic with seawater. This demonstrates that the spermatozoon contains a chemical that triggers an increase in cytosolic calcium, leading to exocytosis of cortical granules. It also demonstrates that the triggering mechanism does not require an externally-activated egg-membrane process. Further experiments show that the chemical trigger is not calcium.     

Pigment distribution in cyanobacteria: An in vivo microspectroscopic investigation

Summary In vivo microspectroscopy represents an effective and reliable technique to study pigment composition and distribution. In contrast to traditional extractive techniques, it preserves the integrity of biological specimens, without modifying the nature of the pigments. The spectroscopic apparatus we used is very simple and consists of a common microscope equipped with a monochromator, a photomultiplier, and two pinhole diaphragms. Absorption spectra obtained by means of this apparatus on different species of cyanobacteria are presented.     

Forecasting time series with increasing seasonal variation

Four options for modeling and forecasting time series data containing increasing seasonal variation are discussed, including data transformations, double seasonal difference models and two kinds of transfer function-type ARIMA models employing seasonal dummy variables. An explanation is given for the typical ARIMA model identification analysis failing to identify double seasonal difference models for this kind of data. A logical process of selecting one option for a particular case is outlined, focusing on issues of linear versus non-linear increasing seasonal variation, and the level of stochastic versus deterministic behavior in a time series. Example models for the various options are presented for six time series, with point forecast and interval forecast comparisons. Interval forecasts from data-transformation models are found to generally be too wide and sometimes illogical in the dependence of their width on the point forecast level. Suspicion that maximum likelihood estimation of ARIMA models leads to excessive indications of unit roots in seasonal moving-average operators is reported.