Phonons and thermodynamics of unmixed and disordered Li0.6FePO4.

The lithium-storage material Li(0.6)FePO(4) was studied by inelastic neutron scattering and differential scanning calorimetry. Li(0.6)FePO(4) undergoes a transformation from a two-phase mixture (heterosite and triphylite) to a disordered solid-solution at 200 degrees C. Phonon densities of states (DOS) obtained from the inelastic neutron scattering were similar for the two-phase sample measured at 180 degrees C and the disordered sample measured at 220 degrees C. The vibrational entropy of transformation is 1.8 +/-0.9 J/(K mol), which is smaller than the configurational entropy difference of approximately 3.1 J/(K mol). The measured enthalpy of the disordering transition was estimated as 2.5 kJ/mol. The phonon data show a small change in lattice dynamics upon disordering.

On the relation between base-rate and cost-benefit learning in simulated medical diagnosis.

Observers completed a series of simulated medical diagnosis tasks that differed in category discriminability and base-rate/cost-benefit ratio. Point, accuracy, and decision criterion estimates were closer to optimal (a) for category d' = 2.2 than for category d' = 1.0 or 3.2, (b) when base-rates as opposed to cost-benefits were manipulated, and (c) when the cost of an incorrect response resulted in no point loss (nonnegative cost) as opposed to a point loss (negative cost). These results support the "flat-maxima" and competition between reward and accuracy (COBRA) hypotheses. A hybrid model that instantiated simultaneously both hypotheses was applied to the data. The model parameters indicated that (a) the reward-maximizing decision criterion quickly approached the optimal criterion, (b) the importance placed on accuracy maximization early in learning was larger when the cost of an incorrect response was negative as opposed to nonnegative, and (c) by the end of training the importance placed on accuracy was equal for negative and nonnegative costs.

Partitioning of carbon an SO2-sulfur in a native grassland.

The seasonal assimilation and within-plant partitioning of 14CO2-carbon and 35SO2-sulfur in field plots of mixed-grass prairie was investigated, as was the dry deposition of 35SO2 onto surfaces of dead leaves, litter, and soil, and possible effects of continuous low-level SO2 fumigation on these processes. The proportion of total net-assimilated carbon found below-ground was 45% in May, 51% in July, and 17% in September. As the season progressed, greater proportions of assimilate were partitioned to 5-20 cm depths and less to the 0-5 cm depth. Rhizomes and crowns received greater proportions in late season. Significant fractions of total 34SO2-deposited sulfur were recovered on dead leaf surfaces as well as litter and soil, suggesting estimates of SO2 removal based on stomatal resistance alone are inadequate. Only 4% to 7% of total deposited sulfur was translocated belowground, with most going to 0-5 cm roots. In July much greater proportions of the total translocated SO2-sulfur were found in deeper depths than in September. On SO2-fumigated plots roots had lower total sulfur concentrations than controls. Furthermore, while on control plots total sulfur in roots at 5-20 cm increased from May to July and decreased from July to September, on fumigated plots there was a decrease followed by an increase suggesting that SO2 uptake by shoots interferes with the normal pattern of root sulfur uptake and redistribution within the plant. Continuous SO2 fumigation also seemed to stimulate root growth in July, possibly through a stimulation of photosynthesis.

The effects of water- and nitrogen-induced stresses on plant community structure in a semiarid grassland.

A replicated factorial experiment was designed to test the hypothesis that manipulating inputs of water and mineral nitrogen to a semiarid grassland would disrupt existing interactions resulting in alteration of the structure of the primary producer community. Alteration of community structure was measured as either changes in growing season average biomass of 6 functional groups of plants or their relative contribution to total biomass.Additions of water greatly increased total biomass and resulted in the replacement of one of the dominant functional groups by a subordinate group. The water plus nitrogen treatment resulted in large biomass increases in two of the dominant functional groups, elimination of succulents as an important component of community structure, and establishment of several introduced weedy species. Continuation of the experiment will likely result in complete dominance of the water plus nitrogen treatment by these introduced species.Despite the large changes in community structure observed as a result of water- and nitrogen-induced stresses we conclude that the shortgrass prairie in northcentral Colorado is asymptotically stable with respect to these influences.

Nitrogen budget of a shortgrass prairie ecosystem.

A N budget is presented for a shortgrass prairie ecosystem. The grassland was ungrazed by domestic herbivores. The quantities of N in various plant, animal, microorganism, and soil components of the ecosystem are estimated for the date when aboveground living biomass was at its maximum for the growing season of 1973. Annual transfers of N between the various compartments were also estimated.Of the total N, 99.5% was in organic forms. The relatively inert heteropolycondensate fraction of the organic matter in the soils contained 88.8% of the N. Living organisms contained 4.2% and dead but recognizable organisms or part thereof contained 6.5% of the total N. Belowground animals contained more than 10 times as much N as abovegroud animals, but combined, animals contained less than 0.1% of the total in the system. Living plant material contained 2.5% of the total N. Seventy-two percent of the living plant N was below ground. Microorganisms contained 1.4% of the total N.Total N uptake by plants from soil solution was 2.9 g·m-2·yr-1. Aerial portions of plants were allocated 1.9 N·m-2·yr-1 although apparently 26% of this amount came from internally recycled sources. The heteropolycondensate fraction of the soil contributed 0.7 g N·m-2·yr-1 to mineral forms, but these components of the system were assumed to be in steady state; thus an equal amount of mineral N was allocated back to the source. Mineralization of N from plant residues was sufficient to account for all of the N taken up by plants from soil solution. Soil animals immobilized about 0.4 g N·m-2·yr-1 while the amount shunted to aboveground animals was trivial.

Molecular structure of starch-type polysaccharides from Hericium ramosum and Hericium coralloides.

Starch isolated from the fungi Hericium ramosum and Hericium coralloides differs from that of higher plants in that it consists only of short-chain amylose molecules (32 to 45 glucose units long).