Sensitivity to initial conditions in stochastic systems.
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Biomedical subjects
Publications and source records attributed to G Nicolis.
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In this work, the incidence of nuchal nevus flammeus was studied in 205 patients suffering from various forms of alopecia areata, as well as in a group of 555 volunteers without alopecia areata examined in our outpatient clinic. The incidence of nuchal nevus flammeus in the totalis-universalis form of alopecia areata was 58.2% (examined patients, n = 79), in ophiasis-extensive forms 22.8% (examined patients, n = 70) and in simple forms of alopecia areata 3.6% (examined patients, n = 56). In the group of 555 volunteers without alopecia areata the incidence of nuchal nevus flammeus was 4.5%. Our results show that nuchal nevus flammeus could be a valuable skin marker indicating a more severe course of alopecia areata.
Pituitary adenomas that secrete gonadotropins are generally believed to arise spontaneously rather than as a response to chronic primary gonadal failure. However, two women who were found to have gonadotroph adenomas several years after ovarian ablation have been reported. We describe a middle-aged man who developed bitemporal hemianopia and was found to have a large pituitary tumor 35 yr after castration. He had never received any replacement therapy. The tumor was considered to be a primary gonadotroph adenoma, rather than secondary gonadotroph hyperplasia, on the basis of its secretory capabilities, its reticulin patterns, and its specific immunostaining for human FSH beta, human LH beta, and alpha-subunit. Furthermore, the tumor did not decrease appreciably in size after 12 months of testosterone treatment, although plasma gonadotropin levels decreased. Unless the association of primary gonadal failure with a gonadotroph adenoma was coincidental, it suggests that some human gonadotroph adenomas may be secondary to failure of the gonads.
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The oxygen isotope record of the last million years, as provided by a deep sea core sediment, is analyzed by a method recently developed in the theory of dynamical systems. The analysis suggests that climatic variability is the manifestation of a chaotic dynamics described by an attractor of fractal dimensionality. A quantitative measure of the limited predictability of the climatic system is provided by the evaluation of the time-correlation function and the largest positive Lyapounov exponent of the system.
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