Dynamic model for failures in biological systems

A dynamic model for failures in biological organisms is proposed and studied both analytically and numerically. Each cell in the organism becomes dead under sufficiently strong stress, and is then allowed to be healed with some probability. It is found that unlike the case of no healing, the organism in general does not completely break down even in the presence of noise. Revealed is the characteristic time evolution that the system tends to resist the stress longer than the system without healing, followed by sudden breakdown with some fraction of cells surviving. When the noise is weak, the critical stress beyond which the system breaks down increases rapidly as the healing parameter is raised from zero, indicative of the importance of healing in biological systems.Comment: To appear in Europhys. Let

EACOF: A Framework for Providing Energy Transparency to enable Energy-Aware Software Development

Making energy consumption data accessible to software developers is an essential step towards energy efficient software engineering. The presence of various different, bespoke and incompatible, methods of instrumentation to obtain energy readings is currently limiting the widespread use of energy data in software development. This paper presents EACOF, a modular Energy-Aware Computing Framework that provides a layer of abstraction between sources of energy data and the applications that exploit them. EACOF replaces platform specific instrumentation through two APIs - one accepts input to the framework while the other provides access to application software. This allows developers to profile their code for energy consumption in an easy and portable manner using simple API calls. We outline the design of our framework and provide details of the API functionality. In a use case, where we investigate the impact of data bit width on the energy consumption of various sorting algorithms, we demonstrate that the data obtained using EACOF provides interesting, sometimes counter-intuitive, insights. All the code is available online under an open source license. http://github.com/eaco

ROLLOVER HEDGING

Both market advisors and researchers have often suggested rollover hedging as a way of increasing producer returns. This study tests whether rollover hedging can increase expected returns for producers. For rollover hedging to increase expected returns, futures prices must follow a mean-reverting process. Using both the return predictability test based on long-horizon regression and the variance ratio test, we find that mean reversion does not exist in futures prices for corn, wheat, soybeans, soybean oil and soybean meal. The findings are consistent with the weak form of market efficiency. The results of the study imply that rollover hedging should not be seriously considered as a marketing alternative. As long as the commodity markets are efficient, the efforts of producers to improve returns through market timing strategies will meet limited success over time.Rollover hedging, mean reversion, market efficiency, Marketing,

MARKET INVERSION IN COMMODITY FUTURES PRICES

As opposed to a normal market, an inverted market has a negative price of storage or spread. Market inversions in nearby spreads rarely occur during early months of the crop year since stocks are usually abundant after harvest. However, market inversions frequently occur when the spreads are observed across crop years near the end of the crop year. The regressions of spreads on the logarithm of U.S. quarterly stocks show that there exists a positive relationship between the spread and the level of stocks, and further implies that when stocks are scarce, markets will be inverted. Simulations are conducted to determine whether a market inversion is a signal to sell the stocks. The results of the paired-difference tests reveal that as the crop cycle advances towards the end of the crop year, market inversions clearly reflect the market's signal to release stocks in anticipation of new crop supplies. The regressions of actual returns to storage on predicted returns to storage clearly show that a market inversion is a signal to sell. The results support the behavioral finance hypothesis that producers are choosing to hold excess stocks because of some type of biased expectations.Demand and Price Analysis,

Macromolecular separation through a porous surface

A new technique for the separation of macromolecules is proposed and investigated. A thin mesh with pores comparable to the radius of gyration of a free chain is used to filter chains according to their length. Without a field it has previously been shown that the permeability decays as a power law with chain length. However by applying particular configurations of pulsed fields, it is possible to have a permeability that decays as an exponential. This faster decay gives much higher resolution of separation. We also propose a modified screen containing an array of holes with barb-like protrusions running parallel to the surface. When static friction is present between the macromolecule and the protrusion, some of the chains get trapped for long durations of time. By using this and a periodic modulation of an applied electric field, high resolution can be attained.Comment: 18 pages latex, 6 postscript figures, using psfi