Tradeoff between short-term and long-term adaptation in a changing environment

We investigate the competition dynamics of two microbial or viral strains that live in an environment that switches periodically between two states. One of the strains is adapted to the long-term environment, but pays a short-term cost, while the other is adapted to the short-term environment and pays a cost in the long term. We explore the tradeoff between these alternative strategies in extensive numerical simulations, and present a simple analytic model that can predict the outcome of these competitions as a function of the mutation rate and the time scale of the environmental changes. Our model is relevant for arboviruses, which alternate between different host species on a regular basis.Comment: 9 pages, 3 figures, PRE in pres

High-efficiency, high-power difference-frequency generation of 0.9–1.5 μm light in BBO

An efficient method for generation of high energy pulsed ir light between 0.9 and 1.5 μm is described. The technique uses difference frequency mixing of pulsed, visible dye and Nd:YAG laser light in a 10 mm long BBO crystal. Quantum efficiencies of up to 23% and ir pulse energies up to 4.5 mJ are demonstrated. The low shot-to-shot fluctuations of difference frequency generation in BBO make this technique an attractive alternative to the conventional optical parametric oscillator or Raman shifting methods that are currently used to access this spectral region

Translationally optimal codons associate with aggregation-prone sites in proteins

We analyze the relationship between codon usage bias and residue aggregation propensity in the genomes of four model organisms, Escherichia coli, yeast, fly, and mouse, as well as the archaeon Halobacterium species NRC-1. Using the Mantel-Haenszel procedure, we find that translationally optimal codons associate with aggregation-prone residues. Our results are qualitatively and quantitatively similar to those of an earlier study where we found an association between translationally optimal codons and buried residues. We also combine the aggregation-propensity data with solvent-accessibility data. Although the resulting data set is small, and hence statistical power low, results indicate that the association between optimal codons and aggregation-prone residues exists both at buried and at exposed sites. By comparing codon usage at different combinations of sites (exposed, aggregation-prone sites versus buried, non-aggregation-prone sites; buried, aggregation-prone sites versus exposed, non-aggregation-prone sites), we find that aggregation propensity and solvent accessibility seem to have independent effects of (on average) comparable magnitude on codon usage. Finally, in fly, we assess whether optimal codons associate with sites at which amino acid substitutions lead to an increase in aggregation propensity, and find only a very weak effect. These results suggest that optimal codons may be required to reduce the frequency of translation errors at aggregation-prone sites that coincide with certain functional sites, such as protein-protein interfaces. Alternatively, optimal codons may be required for rapid translation of aggregation-prone regions. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Increasing Water Use Efficiency Through Improved Orifice Design and Operational Procedures for Subirrigation Systems

Two mathematical models describing one-dimensional flow from buried sources and in unsaturated soils were developed. One considered the consumption of water by roots. For the assumed distribution of the root consumption with time and depth, the 10cm (4-in.) deep source provided better water distribution than did 20- and 30-cm (8- and 12-in.) deep sources. Irrigation from zero depth, as in the case of trickle irrigation, appeared to be the best system for the given conditions. Plugging of emitters by particulate materials decreased as the cross-sectional area of the emitter opening was increased. Less than 0.06 atm (1 psig) vacuum had little effect on the flow of emitters tested. Higher vacuum amounts caused the reopening of plugged orifice emitters, but caused plugging of labyrinth emitters. Vacuum-induced plugging of labyrinth emitters resulted from accumulation of silt and fine sand within the flow path. Operation at higher pressures caused limited flow recovery. A theory was proposed for determining pressure distributions in drip laterals where water is uniformly distributed along the lateral's length. The theory provided acceptable design in two tests. Computer-derived design curves were developed. Because 1000 or more emitters may be required for subirrigation of eachacre, emitters need to be both inexpensive and resistant to plugging. Four experimental emitters were designed and constructed. A modification of one microtube emitter is being produced commercially. Two moveable drip systems were proposed. Drip irrigation lines successfully trailed a center-pivot irrigation system. Also a tractor-mounted implement was developed for moving individual drip irrigation laterals

An Investigation of Hydrological Aspects of Water Harvesting

Water harvesting is a potential source of water for arid and semiarid lands. The objectives of this study were to determine combinations of land surface treatments and land forming which result in efficient but inexpensive water harvesting catchments and to determine the optimum shape of catchments. In laboratory studies with inexpensive materials, crude oils exhibited the best sealing properties. However, by six months after application, 750 gal per ac of crude oil had no apparent effect on runoff from field plots. Water harvesting catchments constructed by grading the soil to form V-shaped valleys and then compacting the surface yielded runoff equal to 31 to 43 percent of all precipitation After rains, sand blown from such catchments may damage tender downwind vegetation. Some water erosion occurred, but, after two years, the basic shape and the performance of the catchments had not been damaged by erosion. Chemical weed control is recommended. Hydrographs were successfully modeled by the kinematic wave method. Hydrologic parameters were estimated by a univariate procedure. The initial infiltration of the soil surface had the greatest effect on the amount of runoff. Thus, additional or repeated compaction may be the best practice for increasing runoff from such surfaces. Surface roughness had little effect on the amount of runoff. The results of hydrograph simulation indicate that catchments should be as narrow as can be constructed easily with conventional equipment. A catchment width of 16 ft may be about optimum. Catchment side slopes should be between 0.1 and 0.20 Generally, catchments should be no more than 1/8 mi long. With these side slopes and lengths, channel slopes can be as little as 0.002 without causing excessive loss of runoff. To prevent erosion, channel slopes should not exceed 0.005. Catchment surfaces should be wetted by rain or by sprinkling before rolling. Surfaces should be rolled with a rubber-tired roller for 1.5 to 3 hrs per ac. Drop structures should be installed at elevation changes to prevent erosion. The cost of constructing graded catchments should be $55 per ac or less. The cost of harvested water is expected to be about$8.00 per ac-in. Efficiently-utilized natural runoff should be less expensive water