8,731 research outputs found
Age determination by sclerite numbers, and scale variations in six fish species from the Central Amazon (Osteichthyes, Characoidei)
The scales of 6 different species of three families (Brycon cf. melanopterus (Characidae), Semaprochilodus theraponura (Curimatidae), Semaprochilodus taeniulus (Curimatidae), Prochilodus nigricans (Curimatidae), Curimata cf . rutiloides (Curimatidae), Colossoma macropomum (Serrasalmidae)) from the Central Amazon are described with regard to their size, shape, and number of sclerites originated from different parts of the body. For each species the body area is defined from which standard scales should be taken, and age determination is conducted by the sclerite method after WERDER (1983)
Heavy-to-Light Form Factors in the Final Hadron Large Energy Limit of QCD
We argue that the Large Energy Effective Theory (LEET), originally proposed
by Dugan and Grinstein, is applicable to exclusive semileptonic, radiative and
rare heavy-to-light transitions in the region where the energy release E is
large compared to the strong interaction scale and to the mass of the final
hadron, i.e. for q^2 not close to the zero-recoil point. We derive the
Effective Lagrangian from the QCD one, and show that in the limit of heavy mass
M for the initial hadron and large energy E for the final one, the heavy and
light quark fields behave as two-component spinors. Neglecting QCD
short-distance corrections, this implies that there are only three form factors
describing all the pseudoscalar to pseudoscalar or vector weak current matrix
elements. We argue that the dependence of these form factors with respect to M
and E should be factorizable, the M-dependence (sqrt(M)) being derived from the
usual heavy quark expansion while the E-dependence is controlled by the
behaviour of the light-cone distribution amplitude near the end-point u=1. The
usual expectation of the (1-u) behaviour leads to a 1/E^2 scaling law, that is
a dipole form in q^2. We also show explicitly that in the appropriate limit,
the Light-Cone Sum Rule method satisfies our general relations as well as the
scaling laws in M and E of the form factors, and obtain very compact and simple
expressions for the latter. Finally we note that this formalism gives
theoretical support to the quark model-inspired methods existing in the
literature.Comment: Latex2e, 25 pages, no figure. Slight changes in the title and the
phrasing. Misprint in Eq. (25) corrected. To appear in Phys. Rev.
Form factors of heavy-to-light B decays at large recoil
General relations between the form factors of B decays to light mesons are
derived using the heavy quark and large recoil expansion. On their basis the
complete account of contributions of second order in the ratio of the light
meson mass to the large recoil energy is performed. Both ground and excited
final meson states are considered. It is shown that most of the known form
factor relations remain valid after the inclusion of quadratic mass
corrections. The validity of some of such relations requires additional
equalities for the helicity amplitudes. It is found that all these relations
and equalities are fulfilled in the relativistic quark model based on the
quasipotential approach in quantum field theory. The contribution of 1/m_b
corrections to the branching fraction of the rare radiative B decay is
discussed.Comment: 23 pages, revte
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The gathering firestorm in southern Amazonia.
Wildfires, exacerbated by extreme weather events and land use, threaten to change the Amazon from a net carbon sink to a net carbon source. Here, we develop and apply a coupled ecosystem-fire model to quantify how greenhouse gas-driven drying and warming would affect wildfires and associated CO2 emissions in the southern Brazilian Amazon. Regional climate projections suggest that Amazon fire regimes will intensify under both low- and high-emission scenarios. Our results indicate that projected climatic changes will double the area burned by wildfires, affecting up to 16% of the region's forests by 2050. Although these fires could emit as much as 17.0 Pg of CO2 equivalent to the atmosphere, avoiding new deforestation could cut total net fire emissions in half and help prevent fires from escaping into protected areas and indigenous lands. Aggressive efforts to eliminate ignition sources and suppress wildfires will be critical to conserve southern Amazon forests
A library of ab initio Raman spectra for automated identification of 2D materials
Raman spectroscopy is frequently used to identify composition, structure and
layer thickness of 2D materials. Here, we describe an efficient
first-principles workflow for calculating resonant first-order Raman spectra of
solids within third-order perturbation theory employing a localized atomic
orbital basis set. The method is used to obtain the Raman spectra of 733
different monolayers selected from the computational 2D materials database
(C2DB). We benchmark the computational scheme against available experimental
data for 15 known monolayers. Furthermore, we propose an automatic procedure
for identifying a material based on an input experimental Raman spectrum and
illustrate it for the cases of MoS (H-phase) and WTe
(T-phase). The Raman spectra of all materials at different excitation
frequencies and polarization configurations are freely available from the C2DB.
Our comprehensive and easily accessible library of \textit{ab initio} Raman
spectra should be valuable for both theoreticians and experimentalists in the
field of 2D materialsComment: 17 pages, 7 figure
Seleção de hĂbridos de Brachiaria humidicola em diferentes Ă©pocas.
Comissão organizadora: Grácia Maria Soares Rosinha, Alexandra Rocha de Oliveir, Rodrigo Carvalho Alva
Diluted manganese on the bond-centered site in germanium
The functional properties of Mn-doped Ge depend to large extent on the lattice location of the Mn impurities. Here, we present a lattice location study of implanted diluted Mn by means of electron emission channeling. Surprisingly, in addition to the expected substitutional lattice position, a large fraction of the Mn impurities occupies the bond-centered site. Corroborated by ab initio calculations, the bond-centered Mn is related to Mn-vacancy complexes. These unexpected results call for a reassessment of the theoretical studies on the electrical and magnetic behavior of Mn-doped Ge, hereby including the possible role of Mn-vacancy complexes
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