Uranus evolution models with simple thermal boundary layers

The strikingly low luminosity of Uranus (Teff ~ Teq) constitutes a long-standing challenge to our understanding of Ice Giant planets. Here we present the first Uranus structure and evolution models that are constructed to agree with both the observed low luminosity and the gravity field data. Our models make use of modern ab initio equations of state at high pressures for the icy components water, methane, and ammonia. Proceeding step by step, we confirm that adiabatic models yield cooling times that are too long, even when uncertainties in the ice:rock ratio (I:R) are taken into account. We then argue that the transition between the ice/rock-rich interior and the H/He-rich outer envelope should be stably stratified. Therefore, we introduce a simple thermal boundary and adjust it to reproduce the low luminosity. Due to this thermal boundary, the deep interior of the Uranus models are up to 2--3 warmer than adiabatic models, necessitating the presence of rocks in the deep interior with a possible I:R of $1\times$ solar. Finally, we allow for an equilibrium evolution (Teff ~ Teq) that begun prior to the present day, which would therefore no longer require the current era to be a "special time" in Uranus' evolution. In this scenario, the thermal boundary leads to more rapid cooling of the outer envelope. When Teff ~ Teq is reached, a shallow, subadiabatic zone in the atmosphere begins to develop. Its depth is adjusted to meet the luminosity constraint. This work provides a simple foundation for future Ice Giant structure and evolution models, that can be improved by properly treating the heat and particle fluxes in the diffusive zones.Comment: 13 pages, Accepted to Icaru

Panel Discussion - Management of Eurasian watermilfoil in the United States using native insects: State regulatory and management issues

While researchers have evaluated the potential of native insect herbivores to manage nonindigenous aquatic plant species such as Eurasian watermilfoil ( Myriophyllum spicatum L.), the practical matters of regulatory compliance and implementation have been neglected. A panel of aquatic nuisance species program managers from three state natural resource management agencies (Minnesota, Vermont and Washington) discussed their regulatory and policy concerns. In addition, one ecological consultant attempting to market one of the native insects to manage Eurasian watermilfoil added his perspective on the special challenges of distributing a native biological control agent for management of Eurasian watermilfoil

Phase separation in hydrogen-helium mixtures at Mbar pressures

The properties of hydrogen-helium mixtures at Mbar pressures and intermediate temperatures (4000 to 10000 K) are calculated with first-principles molecular dynamics simulations. We determine the equation of state as a function of density, temperature, and composition and, using thermodynamic integration, we estimate the Gibbs free energy of mixing, thereby determining the temperature, at a given pressure, when helium becomes insoluble in dense metallic hydrogen. These results are directly relevant to models of the interior structure and evolution of Jovian planets. We find that the temperatures for the demixing of helium and hydrogen are sufficiently high to cross the planetary adiabat of Saturn at pressures around 5 Mbar; helium is partially miscible throughout a significant portion of the interior of Saturn, and to a lesser extent in Jupiter.Comment: 6 pages, 7 figures. Published in "Proceedings of the National Academy of Sciences USA

Long-term impact of wheat-based cropping systems on soil biological activity

Non-Peer Reviewe

Field evaluation of the "Bait-lamina test" to determine the soil microfauna feeding activity

Non-Peer ReviewedThe soil microfauna regulate nutrient cycling through predation on soil microorganisms but also through comminution of organic residues in soils. The feeding activity of the soil microfauna has a large impact on nutrient cycling and soil function, but is rarely considered because it is difficult to assess. The Baitlamina test was proposed as a practical mean to assess microfauna feeding activity. The test consists of vertically inserting 16-hole-bearing plastic sticks stuffed with a plant material preparation into the soil. We tested if the plant material used to prepare the bait would be differentially utilized by microfaunal population present under different plant species or mixtures of plants. We evaluated the Bait-lamina test in a 5-year old field experiment with five levels of plant communities (monocultures of Russian wild rye, switchgrass, green needlegrass, or western wheatgrass, and a grass mixture) distributed in four complete blocks, using six levels of bait flavour (Russian wild rye, switchgrass, green needlegrass, western wheatgrass, alfalfa, and wheat bran). Bait-lamina strips were equally spaced at five locations between plant rows. We found that the bait flavour had no significant (P = 0.22) effect on feeding, although the concentration of crude protein in the plant material used in the baits varied (P = 0.006) from 2.9% in switchgrass to 5.9% in Russian wild rye. We found low feeding activity in our field plots over the period of the test ( 13 June to 17 August 2005), with only 2.7% of the lamina (hole stuffing) showing signs of feeding. The data nevertheless revealed that microfauna feeding was more important close to the soil surface (0.5 mm deep), and in Russian wild rye plot mid-rows as compared to green needlegrass or switchgrass plots. Closer to plant rows, however, differences were not significant. We conclude that bait prepared with any plant material used in this study can be used to compare microfauna feeding in different plant stands. We recommend the use of a large number of replicated strips in agricultural field experiments where the microfauna may be scarce

Spatial and temporal dynamics of malaria transmission in rural western Kenya

ABSTRACT: BACKGROUND: Understanding the impact of reducing Plasmodium falciparum malaria transmission requires estimates of the relationship between health outcomes and exposure to infectious mosquitoes. However, measures of exposure such as mosquito density and entomological inoculation rate (EIR) are generally aggregated over large areas and time periods, biasing the outcome-exposure relationship. There are few studies examining the extent and drivers of local variation in malaria exposure in endemic areas. METHODS: We describe the spatio-temporal dynamics of malaria transmission intensity measured by mosquito density and EIR in the KEMRI/CDC health and demographic surveillance system using entomological data collected during 2002-2004. Geostatistical zero inflated binomial and negative binomial models were applied to obtain location specific (house) estimates of sporozoite rates and mosquito densities respectively. Model-based predictions were multiplied to estimate the spatial pattern of annual entomological inoculation rate, a measure of the number of infective bites a person receive per unit of time. The models included environmental and climatic predictors extracted from satellite data, harmonic seasonal trends and parameters describing space-time correlation. RESULTS: Anopheles gambiae s.l was the main vector species accounting for 86% (n=2309) of the total collected mosquitoes with the remainder being Anopheles funestus. Sixty eight percent (757/1110) of the surveyed houses had no mosquitoes. Distance to water bodies, vegetation and day temperature were significantly associated with mosquito density. Overall annual point estimates of EIR were 6.7, 9.3 and 9.6 infectious bites per annum for 2002, 2003 and 2004 respectively. Monthly mosquito density and EIR varied over the study period peaking in May during the wet season. The predicted and observed densities and EIR showed a strong seasonal and spatial pattern over the study area. CONCLUSIONS: Spatio-temporal maps of malaria transmission intensity obtained in this study are not only useful in understanding variability in malaria epidemiology over small areas but also provides a high resolution exposure surface that can be used to analyse the impact of malaria exposure on mortalit

Factors limiting soil microbial growth and activity in wheat-based cropping systems

Non-Peer ReviewedSeveral soil biochemical processes related to soil fertility are microbially mediated. We know very well the factors limiting crop production but know little of the factors limiting the soil microbial community. The goal of this study is to clarify if N, P and C limit soil microbial growth and biochemical processes in the wheat and fallow phases of rotations receiving different N, P and crop residue-C inputs. Soil samples were collected July 28, 2003, and brought to the laboratory. Soils samples were treated with an N, C or P solution, with water only, or left untreated, and incubated for 48 hours. At the end of the incubation period, soil microbial biomass N was determined along with denitrification and nitrogenase activities. The results showed that the microbial activities and growth were limited by soil moisture at the date of sampling. Denitrification and nitrogenase activities were limited by N, P or C. The limiting nutrients varied with N, P and C inputs associated with the cropping system, regardless to soil moisture. The limitation of these elements to soil microbial activity was more frequently encountered under fallow

The development of a position-sensitive CZT detector with orthogonal co-planar anode strips

We report on the simulation, construction, and performance of prototype CdZnTe imaging detectors with orthogonal coplanar anode strips. These detectors employ a novel electrode geometry with non-collecting anode strips in one dimension and collecting anode pixels, interconnected in rows, in the orthogonal direction. These detectors retain the spectroscopic and detection efficiency advantages of single carrier (electron) sensing devices as well as the principal advantage of conventional strip detectors with orthogonal anode and cathode strips, i.e. an N×N array of imaging pixels are with only 2N electronic channels. Charge signals induced on the various electrodes of a prototype detector with 8×8 unit cells (1×1×5 mm3)are compared to the simulations. Results of position and energy resolution measurements are presented and discussed

Proliferation of mycorrhizal fungal species on organic matter improves nitrogen nutrition in Russian wild rye

Non-Peer ReviewedArbuscular mycorrhizal fungi (AMF) facilitate plant growth by aiding nutrient movement to plants especially under low fertility conditions. Arbuscular mycorrhizal fungi generally takes N as NH4+ or NO3-. We hypothesized that AMF enhance soil organic matter decomposition through their stimulating influence on soil microorganisms and help in the transport of nitrogen to plants. Hyphal chambers (HC) containing labelled 15N organic matter (wheat root and shoot) were inserted in pots. Russian wild rye was inoculated or not with three AM fungal species (G. intraradices, G. claroideum, G. clarum) and was grown for six months. The amount of total C retained in the HC was lower in the presence of AMF hyphae as compared to control and substrate C:N ratio was lower indicating that decomposition was faster in AMF colonized systems. The faster rate of decomposition in HC in presence of AMF was concurrent with change in microbial community structure. Higher N uptake and greater plant biomass were measured in AMF treated Russian wild rye as compared to control. Results of the present investigation suggest that presence of AMF hastens organic matter decomposition, thus enhancing soil N fertility and plant growth