On the Synthesis of Isomeric Dithiophene Analogues of Phenathridine- N-oxides

Six of nine o,o\u27-formylnitrobithienyls have been synthesized by the tetrakis(triphenylphosphine)palladium(O)-catalyzed coupling of the three o-bromonitrothiophenes with two of the three o-formylthiopheneboronic acids with sodium carbonate or sodium bicarbonate as base and an ethylene glycol dimethyl ether-water mixture as solvent. In the reaction with 3-formyl-2-thiopheneboronic acid, the coupling was carried out by using triethylamine as base and N,N-dimethylformamide as solvent in an attempt to avoid the facile deboronation of 3-formyl-2-thiopheneboronic acid, but without success. Reduction of the o,o\u27-formylnitrobithienyls gave high yields of the N-oxides of the six isomeric dithienopyridines, which are analogues of phenanthridine-N-oxide. A direct synthesis of one of the dithienopyridines, dithieno[2,3-c:2\u27,3\u27-c]-pyridine, was achieved by the palladium(O)-catalyzed coupling of 2,3-dibromothiophene with 2-formyl-3-thiopheneboranic acid to 3-bromo-2\u27-formyl-2,3\u27- -bithienyl, which was transformed to the 3-azido-2\u27-formyl-2,3\u27- -bithienyl, which upon reduction with hydrogen sulfide underwent ring closure to the phenanthridine analogue

Passing My Husband in the Hallway

Poe

Happiness Came Too Early

Poe

Spatial distribution in Norwegian lemming Lemmus lemmus in relation to the phase of the cycle

Competition between individuals of the same or different species affects spatial distribution of organisms at any given time. Consequently, a species geographical distribution is related to population dynamics through density-dependent processes. Small Arctic rodents are important prey species in many Arctic ecosystems. They commonly show large cyclic fluctuations in abundance offering a potential to investigate how landscape characteristics relates to density-dependent habitat selection. Based on long-term summer trapping data of the Norwegian lemming (Lemmus lemmus) in the Scandinavian Mountain tundra, we applied species distribution modeling to test if the effect of environmental variables on lemming distribution changed in relation to the lemming cycle. Lemmings were less habitat specific during the peak phase, as their distribution was only related to primary productivity. During the increase phase, however, lemming distribution was, in addition, associated with landscape characteristics such as hilly terrain and slopes that are less likely to get flooded. Lemming habitat use varied during the cycle, suggesting density-dependent changes in habitat selection that could be explained by intraspecific competition. We believe that the distribution patterns observed during the increase phase show a stronger ecological signal for habitat preference and that the less specific habitat use during the peak phase is a result of lemmings grazing themselves out of the best habitat as the population grows. Future research on lemming winter distribution would make it possible to investigate the year around strategies of habitat selection in lemmings and a better understanding of a fundamental actor in many Arctic ecosystems.publishedVersio

Review of some classical gravitational superenergy tensors using computational techniques

We use computational algorithms recently developed by us to study completely four index divergence free quadratic in Riemann tensor polynomials in GR. Some results are new and some other reproduce and/or correct known ones. The algorithms are part of a Mathematica package called Tools of Tensor Calculus (TTC)[web address: http://baldufa.upc.es/ttc

Long-term studies of hantavirus reservoir populations in the southwestern United States: a synthesis.

A series of intensive, longitudinal, mark-recapture studies of hantavirus infection dynamics in reservoir populations in the southwestern United States indicates consistent patterns as well as important differences among sites and host-virus associations. All studies found a higher prevalence of infection in older (particularly male) mice; one study associated wounds with seropositivity. These findings are consistent with horizontal transmission and transmission through fighting between adult male rodents. Despite very low rodent densities at some sites, low-level hantavirus infection continued, perhaps because of persistent infection in a few long-lived rodents or periodic reintroduction of virus from neighboring populations. Prevalence of hantavirus antibody showed seasonal and multiyear patterns that suggested a delayed density-dependent relationship between prevalence and population density. Clear differences in population dynamics and patterns of infection among sites, sampling periods, and host species underscore the importance of replication and continuity of long-term reservoir studies. Nevertheless, the measurable associations between environmental variables, reservoir population density, rates of virus transmission, and prevalence of infection in host populations may improve our capacity to model processes influencing infection and predict increased risk for hantavirus transmission to humans

Evolution of predator dispersal in relation to spatio-temporal prey dynamics : how not to get stuck in the wrong place!

Peer reviewedPublisher PD