Asymptotic scaling in a model class of anomalous reaction-diffusion equations

We analyze asymptotic scaling properties of a model class of anomalous reaction-diffusion (ARD) equations. Numerical experiments show that solutions to these have, for large $t$, well defined scaling properties. We suggest a general framework to analyze asymptotic symmetry properties; this provides an analytical explanation of the observed asymptotic scaling properties for the considered ARD equations.Comment: To appear in J. Nonlin. Math. Phy

Asymptotic scaling symmetries for nonlinear PDEs

In some cases, solutions to nonlinear PDEs happen to be asymptotically (for large $x$ and/or $t$) invariant under a group $G$ which is not a symmetry of the equation. After recalling the geometrical meaning of symmetries of differential equations -- and solution-preserving maps -- we provide a precise definition of asymptotic symmetries of PDEs; we deal in particular, for ease of discussion and physical relevance, with scaling and translation symmetries of scalar equations. We apply the general discussion to a class of ``Richardson-like'' anomalous diffusion and reaction-diffusion equations, whose solution are known by numerical experiments to be asymptotically scale invariant; we obtain an analytical explanation of the numerically observed asymptotic scaling properties. We also apply our method to a different class of anomalous diffusion equations, relevant in optical lattices. The methods developed here can be applied to more general equations, as clear by their geometrical construction

Asymptotic symmetries of difference equations on a lattice

It is known that many equations of interest in Mathematical Physics display solutions which are only asymptotically invariant under transformations (e.g. scaling and/or translations) which are not symmetries of the considered equation. In this note we extend the approach to asymptotic symmetries for the analysis of PDEs, to the case of difference equations

A DTA/GC for the in Situ Identification of the Martian Surface Material

The composition and mineralogy of the Martian surface material remain largely unknown. To determine its composition and mineralogy, several techniques are being considered for in situ analyses of the Martian surface material during missions to Mars. We have successfully developed, constructed, and tested a laboratory DTA/GC. The DTA is a Dupont model 1600 high temperature DTA coupled with a GC equipped with a MID detector. The system is operated by a Sun Sparc 11 workstation. When gas evolves during a thermal chemical event, it is shunted into the GC and the temperature is recorded in association with the specific thermal event. We have used this laboratory instrument to define experimental criteria necessary for determining the composition and mineralogy of the Martian surface in situ (e.g., heating of sample to 1100 C to distinguish clays). Our studies indicate that DTA/GC will provide a broad spectrum of mineralogical and evolved gas data pertinent to exobiology, geochemistry, and geology

Paleobiomarkers and defining exobiology experiments for future Mars experiments

Mars is a cold, dry planet with an oxidizing surface bombarded by ultraviolet and ionizing radiation, making prospects for an extant Mars biota bleak. Yet, it is suggested that early Earth and early Mars were similar enought that life may have evoled on Mars. If life did evolve on Mars, what evidence for its existence might we find? What constitutes a Martian paleobiomarker, and how can we distinguish such a marker from abiotically produced substances? The topics studied to answer this question include carbon and nitrogen cycling, as well as the stability and relative abundance of their intermediates in microbially dominated ecosystems. The microbially dominated ecosystems studied are the crytoendolithic microbial community living within sand rocks, the endoevaporite microbial community living inside salt crystals, and the microbial communities living beneath perennially ice-covered lakes and hypersaline ponds. The nitrogen cycle of these communities ranges from simple, where only assimilation occurs, to the more complex, where a complete cycle occurs. The carbon cycle of these communities appears to be complete

Ecological considerations for possible Martian biota

Current climatic and geological evidence suggests that, like early Earth, conditions on ancient Mars may also have been favorable for the origin and evolution of life. The primordial atmospheres of the two planets were quite similar, composed primarily of CO2, N2, and water vapor at a total atmospheric pressure of approximately 1 bar. Each of these gases are important for the evolution of biological systems. With the exception of nitrogen, there seems to have been a sufficient supply of the biogenic elements C, H, O, P, and S (CHOPS) on early Mars for life to have evolved. It was postulated that primordial Mars contained only 18 mb of nitrogen in the form of N2 given that only fixed nitrogen is utilized by living systems. Laboratory tests performed at a total pressure of 1 bar and various partial pressures of dinitrogen (pN2 1-780 mb) show that nitrogen fixing organisms grow at pN2's of 18 mb or less, although the biomass and growth rates are decreased. The calcualted in vivo Km's ranged from 46 mb to 130 mb. If organisms adapted on Earth to a pH2 of 780 mb are capable of growing at these low partial pressures, it is conceivable that nitrogen was not the limiting factor in the evolution of life on early Mars

Legumes for Organic Cropping Systems

A field experiment which focuses on the yield performance of both durum wheat and sunflower included in a twoyear rotation between wheat/subterranean clover and sunflower was carried out in an organic farm in Central Italy. Three factors were included in the experiment according to a factorial design: a) two different previous crop sequences (four years of alfalfa, four years of annual crops); b) three fertilization levels (without and with animal manure incorporated at 15 or 40 cm depth); c) three durum wheat genotypes (Appulo, Arcangelo and Daunia cvs). The results obtained show that a previous alfalfa meadow allows the succeeding crops (wheat and sunflower) to achieve an appropriate and stable grain yield (about 4 and 3 t ha-1, respectively) even without organic manure for two consecutive cycles. When the durum wheat follows an annual crop sequence, grain yield appears unstable and the different levels of organic fertilizer determine a negative effect in the first cycle and a positive effect in the second cycle. The reseeding capability of sunflower was reduced by animal manure treatments and, consequently, the subclover biomass and its nitrogen content were generally lower in fertilized plots. Anyway, subclover biomass, which was ploughed in after reseeding as a green manure for sunflower, proved to be effective in stabilizing sunflower grain yield, especially in plots without any organic fertilization

Alternative Cropping Systems with Self Reseeding Annual Legumes in a Mediterranean Environment

Self-reseeding winter annual legumes (subclover and snail medic) have the potential to induce a significant shift towards a less energy-intensive and more environmentally friendly management in the modern and specialized cereal cropping systems. Nevertheless their use is practically unknown in mixed stands with winter cereals, where they can contribute to supply nitrogen and to reduce herbicides input. We conceived an alternative cropping system where an annual legume performs, respectively, as living mulch in a winter cereal (winter wheat), as a cover crop after reseeding and as dry mulch for the succeeding summer cereal (corn). Trials carried out at the Tuscia University (Central Italy) in the period 1995-1997 showed that almost all the tested legumes cultivars were able both to grow sufficiently as a living mulch in the wheat and to provide a good re-establishment and an abundant mulch after the wheat harvest for the next corn. Trifolium yanninicum cv Trikkala and Trifolium subterraneum cvs Karridale and Mount Barker ranked first in reseeding capacity (up to 400 seedlings m-2) and mulch production (up to 5 t ha-1). No difference in grain yield between wheat with a living mulch and wheat in pure stand was found when legumes, such as Trifolium yanninicum cvs Trikkala and Larisa, Trifolium brachycalycinum cv Clare, Trifolium subterraneum cv Nungarin and Medicago scutellata cv Kelson, were grown in binary mixture with wheat. The aboveground biomass production of the succeeding irrigated corn crop was largely dependent on the amount of legume dry mulch left upon the ground

A global occurrence database of the Atlantic blue crab Callinectes sapidus

The Atlantic blue crab Callinectes sapidus is a portunid native to the western Atlantic, from New England to Uruguay. The species was introduced in Europe in 1901 where it has become invasive; additionally, a significant northward expansion has been emphasized in its native range. Here we present a harmonized global compilation of C. sapidus occurrences from native and non-native distribution ranges derived from online databases (GBIF, BISON, OBIS, and iNaturalist) as well as from unpublished and published sources. The dataset consists of 40,388 geo-referenced occurrences, 39,824 from native and 564 from non-native ranges, recorded in 53 countries. The implementation of quality controls imposed a severe reduction, in particular from online databases, of the records selected for inclusion in the dataset. In addition, a technical validation procedure was used to flag entries showing identical coordinates but different year of record, in-land occurrences and those located close to the coast. Similarly, a flagging system identified entries outside the known distribution of the species, or associated with unsuccessful introductions

Halorubrum chaoviator sp. nov., a haloarchaeon isolated from sea salt in Baja California, Mexico, Western Australia and Naxos, Greece

hree halophilic isolates, strains Halo-G*T, AUS-1 and Naxos II, were compared. Halo-G* was isolated from an evaporitic salt crystal from Baja California, Mexico, whereas AUS-1 and Naxos II were isolated from salt pools in Western Australia and the Greek island of Naxos, respectively. Halo-G*T had been exposed previously to conditions of outer space and survived 2 weeks on the Biopan facility. Chemotaxonomic and molecular comparisons suggested high similarity between the three strains. Phylogenetic analysis based on the 16S rRNA gene sequences revealed that the strains clustered with Halorubrum species, showing sequence similarities of 99.2–97.1 %. The DNA–DNA hybridization values of strain Halo-G*T and strains AUS-1 and Naxos II are 73 and 75 %, respectively, indicating that they constitute a single species. The DNA relatedness between strain Halo-G*T and the type strains of 13 closely related species of the genus Halorubrum ranged from 39 to 2 %, suggesting that the three isolates constitute a different genospecies. The G+C content of the DNA of the three strains was 65.5–66.5 mol%. All three strains contained C20C20 derivatives of diethers of phosphatidylglycerol, phosphatidylglyceromethylphosphate and phosphatidylglycerolsulfate, together with a sulfated glycolipid. On the basis of these results, a novel species that includes the three strains is proposed, with the name Halorubrum chaoviator sp. nov. The type strain is strain Halo-G*T (=DSM 19316T =NCIMB 14426T =ATCC BAA-1602T)