Endogenous skill cycles

This paper explores the ability of a class of one-sector models to generate endogenous skills cycles. Skills cycles are here defined as endogenous fluctuations of the composition of equilibrium allocation of labor services. We consider a one sector economy in which there exist one type of capital stock and a finite number of different labor services, which are assumed to be heterogeneous along the skill/productivity dimension. We apply the Hopf bifurcation theorem and provide necessary conditions on the model’s parameters for having a closed orbit as the economy’s stable set. We also develop a numerical example (based on the United States economy) showing how this closed orbit can appear under reasonable parameter values.     

The automobile in a system context: The past 80 years and the next 20 years

The diffusion of automobiles in nine countries is seen in terms of the Volterra equations developed for ecological systems. Three parameter logistic equations fit the evolution of the car population perfectly. The behavior suggests a quasi-biological, internally generated determinism that belies the significance of engineering, economics, marketing, and media as diffusion stimuli. Their role is seen to be more a response to, than an initiator of, change. Once diffusion is complete, their significance increases, however. Car safety appears to be controlled by societal “set points.”     

Infrastructures for movement

Human history demonstrates that the movement of men and information has always been of paramount importance. The size of communities is determined by the territory that is readily accessible by movement capability. Using a version of Darwinian ideas in the form of Lotka's equations of competition between species as an analogy, air transport and other elements of the transportation infrastructure are examined. It is found that they exhibit extreme dynamic stability over time at all hierarchical levels.     

Longevity and life expectancy

The increase in life expectancy at all ages during the last two centuries is in need of a quantitative model capable of resuming the whole process under a single concept and simple mathematics. The basic hypothesis was that through improved hygiene, medicine, and life-style, the stumbling blocks to the full expression of longevity were progressively removed. The mathematics of learning processes was then applied to the secular evolution of life expectancy at various ages. The hypothesis proved very fertile. Logistic equations fit long strings of statistical data, covering the evolution of life expectancy at various ages, for both sexes, and in many European nations for almost two centuries. These life expectancy increases seem to move progressively to a common asymptote of about 79 years for men and about 84 years for women. It is suggested that these values are taken as a definition of longevity, presumably explicitating a coding in DNA. The evolution of life expectancy during the last couple of centuries appears to follow consistent paths precisely mapped with simple mathematics. This opens the way to more integrated and holistic theories.     

Human population dynamics revisited with the logistic model: how much can be modeled and predicted?

"We revive the logistic model, which was tested and found wanting in early-20th-century studies of aggregate human populations, and apply it instead to life expectancy (death) and fertility (birth)....For death...the logistic portrays the situation crisply. Human life expectancy is reaching the culmination of a two-hundred year-process that forestalls death until about 80 for men and the mid 80s for women. No breakthroughs in longevity are in sight unless genetic engineering comes to help. For birth, the logistic covers quantitatively its actual morphology. However, because we have not been able to model this essential parameter in a predictive way over long periods, we cannot say whether the future of human population is runaway growth or slow implosion...From a niche point of view, resources are the limits to numbers, and access to resources depends on technologies. The logistic makes clear that for homo faber, the limits to numbers keep shifting. These moving edges may most confound forecasting the long-run size of humanity."     

Primary energy substitution models: On the interaction between energy and society

This paper describes an attempt to develop a “synthetic” model of primary energy substitution, using certain rules which proved fruitful in describing the substitution of other commodities. This model will be used for forecasting, and for checking the validity of certain objectives set for R&D in the field of energy.