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

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

VALUE OF INCREASING KERNEL UNIFORMITY

Kernel size uniformity is an important physical quality attribute in terms of processing efficiency, quality control, and milling yield. This study developed optimal grain sorting strategies for elevators to use to increase kernel size uniformity and determined the size of potential benefits from sorting. Cluster analysis and global optimization were used to sort grain loads to increase kernel size uniformity. Cluster analysis and global optimization increased the percent flour yield relative to no sorting by 0.13% and 0.32% respectively. Cluster analysis and global optimization increased the daily milling income relative to no sorting by 105 dollars (5%) and 266 dollars (13%) respectively.Crop Production/Industries,

VALUE OF INCREASING KERNEL UNIFORMITY

Kernel uniformity is an important quality attribute that can now be measured at low cost. This study analyzes the profitability of sorting to increase wheat kernel uniformity. Nonlinear programming is used to sort grain loads to maximize flour yield by increasing uniformity of kernel size and kernel hardness. Results of this analysis suggest increases in flour yield due to higher kernel uniformity are not enough to outweigh the costs of sorting.Crop Production/Industries,

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,