The anabolic effects of parathyroid hormone on cortical bone mass, dimensions and strength--assessed in a sexually mature, ovariectomized rat model

We examined the effect of the pineal neurohormone melatonin (MLT) on protection from viral encephalitis. The antiviral activity of MLT was evaluated in normal mice inoculated with Semliki Forest virus (SFV) and in stressed mice injected with the attenuated non-invasive West Nile virus (WN-25). Administration of MLT (s.c.) daily from 3 days before through 10 days after virus inoculation reduced viremia and significantly postponed the onset of disease and death by 7 to 10 days. Moreover, MLT injection reduced mortality of SFV (10 PFU) inoculated mice from 100% to 44%. In mice inoculated with high dose of SFV (100 PFU), MLT postponed death and reduced mortality by 20%. In all of the surviving mice anti-SFV antibodies were detected 22 days after virus inoculation. Infection of mice stressed by either isolation or dexamethasone injection with WN-25 induced mortality of 75% and 50% respectively, which was reduced by MLT administration to 31% and 25%, respectively. The efficiency of MLT in protecting from lethal viral infections warrants further investigations on its mechanisms of action.     

Comments on the Theory of Unimodal Maps

The paper presents a complementary view on some of the phenomena related to the bifurcation structure of unimodal maps. An approximate renormalization theory for the period-doubling cascade is developed, and a mapping procedure is established that accounts directly for the box-within-a-box structure of the total bifurcation set. This presents a picture in which the homoclinic orbit bifurcations act as a skeleton for the bifurcational set. At the same time, experimental results on continued subharmonic generation for piezoelectrically amplified sound waves, predating the Feigenbaum theory, are called into attention.     

Inflammatory bowel disease and osteoporosis

The relation between inflammatory bowel disease (IBD) and osteoporosis has received increasing attention during the past decade. The prevalence of low bone mass in patients with IBD has been reported to be more than 50%. The development of a quick non-invasive method to diagnose osteoporosis (dual-energy X-ray absorptiometry) provides a practical tool to identify the patient who needs special attention. The aetiology of the bone disease in patients with IBD has still not been elucidated, but corticosteroids may play a major role. Studies on the prevention/treatment of IBD-related osteoporosis are scarce. In a single uncontrolled study hormone replacement therapy proved effective in preventing bone loss in peri- and post-menopausal women with IBD. A placebo-controlled study showed that supplementation with calcium and vitamin D prevents bone loss in patients with Crohn's disease. The present paper reviews our current knowledge on the mechanisms and epidemiology of IBD-related bone disease.     

Entrainment in a disaggregated economic long wave model

This paper investigates how mode-locking and other nonlinear dynamic phenomena arise through the interaction of two capital-producing sectors in a disaggregated economic long wave model. Each sector in isolation produces a self-sustained oscillation with a period and amplitude determined by the characteristics of that sector. However, the sectors interact through their mutual dependence on each other's output for their own production. When this coupling is accounted for, the two sectors tend to synchronize or lock together with a rational proportion between the periods. While keeping the aggregate equilibrium characteristics of the system constant, we study how this locking occurs as a function of the difference in capital lifetimes and as a function of the strength of the coupling between the sectors. Besides mode-locking and quasi-periodic behavior, the observed phenomena include cascades of period-doubling bifurcations, chaos, and intermittency. When the difference in capital lifetimes is very large, the coupled system tends to behave like a one-sector model with a reduced capital content of production.     

Dynamics of a food web model of an aquatic ecosystem

The paper presents a model of an aquatic ecosystem with four species (bacteria, algae, zooplankton and fish) and with three different dead pools (detritus and accessible nutrients in the water column, and nutrients bound to the sediment). The structure of the model is that of a food web with the bacterial population representing the microbial loop. No distinction is made between different nutrients, and all uptake rates are expressed in terms of modified Monod kinetics. Though the model does not explicitly account for shifting abilities of the various species, the modified Monod kinetics enable predators with more than one prey (i.e., zooplankton and fish) to adjust their foraging habits in accordance with the conditions in the system. Simulations of the model show a variety of different solutions, ranging from simple oscillations with the annual periodicity of the external forcing to higher order chaos.     

Mode-locking and chaos in a model of two coupled thermostatically controlled radiators

The paper examines a variety of nonlinear dynamic phenomena arising from the interaction between two thermostatically controlled radiators. Each system operates as a delayed, nonlinear control system and performs self-sustained opening and closing cycles when the slope of the regulator characteristics exceeds a critical value. The coupling is caused by heat exchange between the heated air volumes. As the sensitivity of one of the thermostats is changed, a devil's staircase of frequency-locked oscillations develops. For higher coupling strengths, mode-converting bifurcations, simultaneous periodic solutions and deterministic chaos can be observed.     

Non-invasive study of nerve fibres using laser interference microscopy

This paper presents the results of a laser interference microscopy study of the morphology and dynamical properties of myelinated nerve fibres. We describe the principles of operation of the phase-modulated laser interference microscope and show how this novel technique allows us to obtain information non-invasively about the internal structure of different regions of a nerve fibre. We also analyse the temporal variations in the internal optical properties in order to detect the rhythmic activity in the nerve fibre at different time scales and to shed light on the underlying biological processes. We observe pronounced frequencies in the dynamics of the optical properties and suggest that the oscillatory modes have similar origin in different regions, but different strengths and mutual modulation properties.