Limiting conditional distributions for birth-death processes

In a recent paper one of us identified all of the quasi-stationary distributions for a non-explosive, evanescent birth-death process for which absorption is certain, and established conditions for the existence of the corresponding limiting conditional distributions. Our purpose is to extend these results in a number of directions. We shall consider separately two cases depending on whether or not the process is evanescent. In the former case we shall relax the condition that absorption is certain. Furthermore, we shall allow for the possibility that the minimal process might be explosive, so that the transition rates alone will not necessarily determine the birth-death process uniquely. Although we shall be concerned mainly with the minimal process, our most general results hold for any birth-death process whose transition probabilities satisfy both the backward and the forward Kolmogorov differential equations

Melhoria da qualidade ambiental de terras agricultáveis por meio da silvopastagem no sudeste dos Estados Unidos

Nossa hipótese é de que devido à habilidade das árvores seqüestrarem carbono (C) no perfil profundo do solo e remover o excesso de nutrientes dos solos, o sistema de silvopastagem agroflorestal poderia melhorar a qualidade ambiental de terras agricultáveis. Para testar esta hipótese, dois grupos de experimentos foram conduzidos em duas ordens de solos na Florida, Espodossolos e Ultissolos, com dois objetivos principais: i) determinar a acumulação de C do solo e investigar as fontes de C para as plantas nas frações dos solos, e ii) quantificar o fósforo solúvel em água (FSA) e estimar a capacidade de armazenamento de fósforo no solo (CAFS). O C total em ambos os solos foi maior sob o sistema de silvopastagem do que sob pastagens com menos árvores, particularmente nas profundidades mais baixas. A análise por assinatura de isótopo estável sugeriu que as plantas C3 (neste caso, slash pine, Pinis elliotti) contribuíram mais para a fração estável do carbono do que plantas C4 (neste caso, bahiagrass, Paspalum notatum) nas profundidades dos solos acima de 1 m. O FSA foi consistentemente maior em pastagens com poucas árvores, enquanto que a CAFS foi mais baixa neste sistema, sugerindo a grande probabilidade do fósforo ser mais facilmente movido do solo sob pastagens com poucas árvores do que nos sob silvopastagem. Deste modo, a presença de árvores em pastagens contribuiu para C mais estável nos perfis dos solos e o mais baixo FSA e a maior CAFS indicaram os grandes benefícios ambientais fornecidos pelos sistemas de silvopastagem comparados com as pastagens com poucas árvores em condições ecológicas similares.We hypothesized that, because of the ability of trees to sequester carbon (C) in the deep soil profile and remove excess nutrients from soils, the silvopastoral agroforestry system could enhance the environmental quality of the agricultural lands. To test this hypothesis, two sets of experiments were conducted in two soil orders in Florida, Spodosols and Ultisols, with two major objectives: i) determining the soil C accumulation and tracing the plant sources of C in soil fractions, and ii) quantifying water soluble phosphorus (WSP) and estimating the Soil P Storage Capacity (SPSC). Total C in both soil orders was greater under silvopasture than in treeless pastures, particularly at lower depths. Stable-isotope signature analysis suggested that C3 plants (in this case, slash pine, Pinus elliotii) contributed to a more stable C fraction than C4 plants (in this case, bahiagrass, Paspalum notatum) at soil depths up to 1 m. WSP was consistently higher in treeless pastures, while the remaining SPSC was lower in this land-use system, suggesting the greater likelihood of P moving out of the soil under treeless pasture than in silvopasture. Thus, the presence of trees in pastures contributed to more stable C within the soil profiles, lower WSP, and greater SPSC, indicating more environmental benefits provided by silvopastoral systems as compared to treeless pastures under similar ecological settings

2-Commodity Integer Network Synthesis Problem

We consider the following 2-commodity, integer network synthesis problem: Given two n×n, non-negative, symmetric, integer-valued matrices R = (rij) and S = (sij) of minimum flow requirements of 2 different commodities, construct an undirected network G = [N, E, c] on node set N = {1, 2, . . . , n} with integer edge capacities {c(e) : e ∈ E}, such that: (i) for any two pairs (i, j) and (k, l), i ≠ j, k ≠ l, of nodes in N, we can simultaneously send rij units of flow of commodity 1 from i to j and skl units of flow of commodity 2 from k to l in G; and (ii) z = Σ {c(e) : e ∈ E} is minimum. We present strongly polynomial, combinatorial algorithms for certain special cases of the problem; and for the general problem, we present a strongly polynomial, combinatorial algorithm that produces a feasible solution with objective function value no more than (the optimal objective function value +3)

Biological productivity and fishery potential in the coastal waters off Bombay

Fishery potential of the nearshore waters of Bombay is estimated from the observed values of biological productivity at different trophic levels. The rate of primary and secondary production is relatively higher in the polluted coastal waters of Versova, Mahim and Thana. Observed mean benthic standing stock in the polluted creek waters is far less than the relatively unpolluted coastal regions off Bombay. Results suggest that the higher productivity at the lower trophic levels due to pollution, may not end up with high tertiary production. Therefore, such polluted regions are to be classified as special ecosystems where the transfer coefficient may be far less than the assumed 10% conversion factor

Ecology of Indian estuaries-XI. A preliminary survey of the fishery resources of the Ashtamudi estuarine system

The fish fauna of the Ashtamudi, the second largest estuarine system in Kerala (8°53'-9°02' N Lat. and 76°31'-76°41' E Long.) is listed. 97 species belonging to 39 families have been recorded, ofwhich69 are commercially important contributing to the fisheries of the Ashtamudi Estuary. Mullets, cichlids and the glassy perchlets are the most abundant groups and contribute appreciably to the landings. Results revealed that the estuarine system supports a good capture fishery which is seasonal. Majority of the fish fauna in the estuary are marine elements recruited from the adjoining Arabian Sea. An inventory of the craft and gear employed is presented and the sources of pollution in the estuarine system are described, aquacultural prospects of this area are discussed

Formation of polycrystalline SnS layers by a two-step process

Thin films of SnS have been produced by a novel two-stage process. This involved the deposition of thin films of Sn onto glass substrates using d.c. magnetron sputtering followed by conversion of the metallic layers into the compound by annealing in the presence of elemental sulfur. All the layers synthesised were found to be polycrystalline, the grain size and crystallinity of the layers increasing with increasing annealing temperature. The precursor layers sulfurised at temperatures 350°C, were found to be non-stoichiometric and X-ray diffraction data indicated the presence of a range of binary phases other than SnS. The best SnS layers were synthesised for annealing temperatures between 300 and 350°C. These layers were found to be stoichiomentric with a strong {111} preferred orientation. The stoichiometric SnS layers had resistivities of 1.5×102 ?cm and Arrhenius plots of the resistivity gave an activation energy of 0.65 eV. The optical energy band gap of the layers was 1.35 eV. These p-type layers could find application as absorber layers in thin film solar cells

Faraday rotation in graphene

We study magneto--optical properties of monolayer graphene by means of quantum field theory methods in the framework of the Dirac model. We reveal a good agreement between the Dirac model and a recent experiment on giant Faraday rotation in cyclotron resonance. We also predict other regimes when the effects are well pronounced. The general dependence of the Faraday rotation and absorption on various parameters of samples is revealed both for suspended and epitaxial graphene.Comment: 10 pp; v2: typos corrected and references added, v3, v4: small changes and more reference