3,235 research outputs found
ResÃduos da cultura de amendoim como fonte de nitrogênio para uma cultura de cobertura de centeio
Leguminous winter cover crops have been utilized in conservation systems to partially meet nitrogen (N) requirements of succeeding summer cash crops, but the potential of summer legumes to reduce N requirements of a winter annual grass, used as a cover crop, has not been extensively examined. This study assessed the N contribution of peanut (Arachis hypogaea L.) residues to a subsequent rye (Secale cereale L.) cover crop grown in a conservation system on a Dothan sandy loam (fine-loamy, kaolinitic, thermic Plinthic Kandiudults) at Headland, AL USA during the 2003-2005 growing seasons. Treatments were arranged in a split plot design, with main plots of peanut residue retained or removed from the soil surface, and subplots as N application rates (0, 34, 67 and 101 kg ha-1) applied in the fall. Peanut residue had minimal to no effect on rye biomass yields, N content, carbon (C) /N ratio, or N, P, K, Ca and Zn uptake. Additional N increased rye biomass yield, and N, P, K, Ca, and Zn uptakes. Peanut residue does not contribute significant amounts of N to a rye cover crop grown as part of a conservation system, but retaining peanut residue on the soil surface could protect the soil from erosion early in the fall and winter before a rye cover crop grows sufficiently to protect the typically degraded southeastern USA soils.Culturas leguminosas de inverno tem sido utilizadas em sistemas conservacionistas para suprimento parcial das necessidades de nitrogênio (N) de culturas subseqüentes de verão, mas o potencial destas culturas leguminosas de verão no sentido de reduzir as necessidades de N de gramÃneas anuais de inverno, utilizadas como culturas de cobertura, ainda não foi extensivamente estudado. Este trabalho avaliou a contribuição dos resÃduos de uma cultura de amendoim (Arachis hypogaea L.) sobre as necessidades de N de uma cultura subsequente de centeio (Secale cereale L.) como cobertura desenvolvida dentro de um sistema conservacionista, em um solo limo-arenoso Dotham (limoso fino, caulinÃtico, Plinthic Kandiudults térmico) de Headland, AL EEUU, durante 2003-2005. Os tratamentos foram arranjados de acordo com um esquema split-plot, com parcelas principais de resÃduos de amendoim retido ou retirado da superfÃcie do solo e, parcelas secundárias de taxas de aplicação de N (0, 34, 67 e 101 kg ha-1) aplicadas no outono. O resÃduo de amendoim teve efeito mÃnimo ou nenhum sobre a produtividade de matéria seca do resÃduo, conteúdo de N, relação carbono (C)/N, ou absorção de N, P, K, Ca e Zn. O N adicional aumentou a produção de biomassa do centeio e as absorções de N, P, K, Ca e Zn. Os resÃduos de amendoim não contribuem com quantidades significativas de N para a cultura de cobertura de centeio desenvolvida como parte do sistema conservacionista, mas a retenção dos resÃduos na superfÃcie podem proteger o solo da erosão no inÃcio do outono e inverno, antes que a cultura de cobertura de centeio pudesse proteger os solos tipicamente degradados do sudoeste dos EEUU
Permutation-adapted complete and independent basis for atomic cluster expansion descriptors
In many recent applications, particularly in the field of atom-centered
descriptors for interatomic potentials, tensor products of spherical harmonics
have been used to characterize complex atomic environments. When coupled with a
radial basis, the atomic cluster expansion (ACE) basis is obtained. However,
symmetrization with respect to both rotation and permutation results in an
overcomplete set of ACE descriptors with linear dependencies occurring within
blocks of functions corresponding to particular generalized Wigner symbols. All
practical applications of ACE employ semi-numerical constructions to generate a
complete, fully independent basis. While computationally tractable, the
resultant basis cannot be expressed analytically, is susceptible to numerical
instability, and thus has limited reproducibility. Here we present a procedure
for generating explicit analytic expressions for a complete and independent set
of ACE descriptors. The procedure uses a coupling scheme that is maximally
symmetric w.r.t. permutation of the atoms, exposing the permutational
symmetries of the generalized Wigner symbols, and yields a permutation-adapted
rotationally and permutationally invariant basis (PA-RPI ACE). Theoretical
support for the approach is presented, as well as numerical evidence of
completeness and independence. A summary of explicit enumeration of PA-RPI
functions up to rank 6 and polynomial degree 32 is provided. The PA-RPI blocks
corresponding to particular generalized Wigner symbols may be either larger or
smaller than the corresponding blocks in the simpler rotationally invariant
basis. Finally, we demonstrate that basis functions of high polynomial degree
persist under strong regularization, indicating the importance of not
restricting the maximum degree of basis functions in ACE models a priori
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