The Economic Impact of AIDS in Sub-Saharan Africa

In this paper, a simple general equilibrium model à la Solow is developed to capture the impact of AIDS on economic growth. To this end, a benchmark model due to Cuddington and Hancock (1994) is extended in various directions. In particular, the sharply declining life expectancy patterns are clearly rejected in the enlarged model through a generic Ben-Porath mechanism. AIDS-related health expenditures are incorporated as well. Using up-do-date optimal forecasting methods, the model applied to South Africa shows that while a relatively short term assessment might not reveal any dramatic AIDS growth effect, the medium/long run impact can be truly devastating. In particular, the heavy trends in mortality and life expectancy currently induced by AIDS are shown to be potentially at least twice more detrimen-tal for per capita economic growth in the period 2020-2030 compared to 2000-2010.Epidemics, Life Expectancy, Economic Growth, AIDS

Characterization of Information Channels for Asymptotic Mean Stationarity and Stochastic Stability of Non-stationary/Unstable Linear Systems

Stabilization of non-stationary linear systems over noisy communication channels is considered. Stochastically stable sources, and unstable but noise-free or bounded-noise systems have been extensively studied in information theory and control theory literature since 1970s, with a renewed interest in the past decade. There have also been studies on non-causal and causal coding of unstable/non-stationary linear Gaussian sources. In this paper, tight necessary and sufficient conditions for stochastic stabilizability of unstable (non-stationary) possibly multi-dimensional linear systems driven by Gaussian noise over discrete channels (possibly with memory and feedback) are presented. Stochastic stability notions include recurrence, asymptotic mean stationarity and sample path ergodicity, and the existence of finite second moments. Our constructive proof uses random-time state-dependent stochastic drift criteria for stabilization of Markov chains. For asymptotic mean stationarity (and thus sample path ergodicity), it is sufficient that the capacity of a channel is (strictly) greater than the sum of the logarithms of the unstable pole magnitudes for memoryless channels and a class of channels with memory. This condition is also necessary under a mild technical condition. Sufficient conditions for the existence of finite average second moments for such systems driven by unbounded noise are provided.Comment: To appear in IEEE Transactions on Information Theor

A simple method for detecting chaos in nature

Chaos, or exponential sensitivity to small perturbations, appears everywhere in nature. Moreover, chaos is predicted to play diverse functional roles in living systems. A method for detecting chaos from empirical measurements should therefore be a key component of the biologist's toolkit. But, classic chaos-detection tools are highly sensitive to measurement noise and break down for common edge cases, making it difficult to detect chaos in domains, like biology, where measurements are noisy. However, newer tools promise to overcome these limitations. Here, we combine several such tools into an automated processing pipeline, and show that our pipeline can detect the presence (or absence) of chaos in noisy recordings, even for difficult edge cases. As a first-pass application of our pipeline, we show that heart rate variability is not chaotic as some have proposed, and instead reflects a stochastic process in both health and disease. Our tool is easy-to-use and freely available

Vulnerability of Water Supply Systems to Droughts

This summary completion report describes the project work completed in three areas: 1) the development and preliminary testing of drought severity and vulnerability indices, 2) the impacts of Utah\u27s 1977 drought, and 3) an operation comparison of stochastic streamflow models. The drought indices were evaluated for three municipal and three irrigation water supply systems in Utah. It was concluded that a continuous loss function to define the effects of water shortage would be more appropriate than the existing assumption that drought-related lossed occur suddenly at a certain degree of water shortage. Information on the impacts of Utah\u27s 1977 drought was collected by surveys of municipal and rural domestic systems, water users in Salt Lake County, and farmers, stockmen, ranchers, and irrigation company officials. Survey results were used to examine drought effects in different regions of the state and with respect to size of municipal supply systems. Despite severe restrictiosn placed on Salt Lake County water users most did not consider the experience an undue burden. The comparison of five stochastic streamflow models on four Utah streams lead to a preliminary model choice strategy which is based on the historical estimates of the lag-one autocorrelation and Hurst coefficients

The bullwhip effect: Progress, trends and directions

This is the final version. Available on open access from Elsevier via the DOI in this recordThe bullwhip effect refers to the phenomenon where order variability increases as the orders move upstream in the supply chain. This paper provides a review of the bullwhip literature which adopts empirical, experimental and analytical methodologies. Early econometric evidence of bullwhip is highlighted. Findings from empirical and experimental research are compared with analytical and simulation results. Assumptions and approximations for modelling the bullwhip effect in terms of demand, forecast, delay, replenishment policy, and coordination strategy are considered. We identify recent research trends and future research directions concerned with supply chain structure, product type, price, competition and sustainability