58,621 research outputs found
Growth of seven perennial plant species adapted to the Brazilian Semi-Arid.
Growth of seven perennial plant species adapted to the Brazilian Semi-Arid. Abstract - Measuring plant height (y) and canopy diameter (x) in trees may not be an easy task, but stem diameter (z) can be more easily evaluated. This work's objective was two-fold: evaluate the growth of species adapted to the Brazilian Semi-Arid Region in the first two years of age, and obtain linear equations to estimate y and x from z, in those species. A random block design with four replications was employed. The values for x, z, and y were measured biannually from October/2003 to March/2005. Prosopis juliflora and Mimosa caesalpiniaefolia showed the highest stem diameter and plant height values, respectively, and both showed the highest canopy diameter. In the equations to estimate plant height from the stem diameter the value of the coefficient of determination (R2) ranged from 0.76 (Tamarindus indica and Leucaena leucocephala) to 0.92 (Prosopis juliflora and Azadirachta indica). In the equations that allowed to estimate the crown diameter from the stem diameter the R2 value ranged from 0.70 (Leucaena leucocephala) to 0.92 (Azadirachta indica). Crescimento de sete espécies vegetais perenes adaptadas ao Semi-Árido brasileiro. Resumo - A mensuração da altura da planta (y) e do diâmetro da copa (x) em árvores pode não ser tarefa fácil, mas o diâmetro do caule (z) pode ser avaliado mais facilmente. Este trabalho teve por objetivos avaliar o crescimento de espécies adaptadas ao Semi-Árido brasileiro, nos primeiros dois anos de idade, e obter equações lineares para estimar y e x a partir de z, nessas espécies. Utilizou-se o delineamento de blocos ao acaso com quatro repetições. Os valores de x, z e y foram medidos semestralmente de outubro/2003 a março/2005. Prosopis juliflora e Mimosa caesalpiniaefolia apresentaram os maiores diâmetros do caule e altura da planta, respectivamente, e ambas apresentaram o maior diâmetro da copa. Nas equações para estimar a altura da planta a partir do diâmetro do caule, o valor do coeficiente de determinação (R2) variou de 0,76 (Tamarindus indica and Leucaena leucocephala) a 0,92 (Prosopis juliflora and Azadirachta indica). Nas equações que permitiram estimar o diâmetro da copa a partir do diâmetro do caule, o valor de R2 variou de 0,70 (Leucaena leucocephala) a 0,92 (Azadirachta indica)
One-magnon Raman scattering in La(2)CuO(4): the origin of the field-induced mode
We investigate the one-magnon Raman scattering in the layered
antiferromagnetic La(2)CuO(4) compound. We find that the Raman signal is
composed by two one-magnon peaks: one in the B1g channel, corresponding to the
Dzyaloshinskii-Moryia (DM) mode, and another in the B3g channel, corresponding
to the XY mode. Furthermore, we show that a peak corresponding to the XY mode
can be induced in the planar (RR) geometry when a magnetic field is applied
along the easy axis for the sublattice magnetization. The appearance of such
field-induced mode (FIM) signals the existence of a new magnetic state above
the Neel temperature T_N, where the direction of the weak-ferromagnetic moment
(WFM) lies within the CuO(2) planes.Comment: 4 pages, 3 figure
Transverse self-modulation of ultra-relativistic lepton beams in the plasma wakefield accelerator
The transverse self-modulation of ultra-relativistic, long lepton bunches in
high-density plasmas is explored through full-scale particle-in-cell
simulations. We demonstrate that long SLAC-type electron and positron bunches
can become strongly self-modulated over centimeter distances, leading to wake
excitation in the blowout regime with accelerating fields in excess of 20 GV/m.
We show that particles energy variations exceeding 10 GeV can occur in
meter-long plasmas. We find that the self-modulation of positively and
negatively charged bunches differ when the blowout is reached. Seeding the
self-modulation instability suppresses the competing hosing instability. This
work reveals that a proof-of-principle experiment to test the physics of bunch
self-modulation can be performed with available lepton bunches and with
existing experimental apparatus and diagnostics.Comment: 8 pages, 8 figures, accepted for publication in Physics of Plasma
Negative Hopping Magnetoresistance and Dimensional Crossover in Lightly Doped Cuprate Superconductors
We show that, due to the weak ferromagnetism of LaSrCuO, an
external magnetic field leads to a dimensional crossover 2D 3D for the
in-plane transport. The crossover results in an increase of the hole's
localization length and hence in a dramatic negative magnetoresistance in the
variable range hopping regime. This mechanism quantitatively explains puzzling
experimental data on the negative magnetoresistance in the N\'eel phase of
LaSrCuO.Comment: 6 pages, 3 figures; published versio
AGB subpopulations in the nearby globular cluster NGC 6397
It has been well established that Galactic Globular clusters (GCs) harbour
more than one stellar population, distinguishable by the anti-correlations of
light element abundances (C-N, Na-O, and Mg-Al). These studies have been
extended recently to the asymptotic giant branch (AGB). Here we investigate the
AGB of NGC 6397 for the first time. We have performed an abundance analysis of
high-resolution spectra of 47 RGB and 8 AGB stars, deriving Fe, Na, O, Mg and
Al abundances. We find that NGC 6397 shows no evidence of a deficit in Na-rich
AGB stars, as reported for some other GCs - the subpopulation ratios of the AGB
and RGB in NGC 6397 are identical, within uncertainties. This agrees with
expectations from stellar theory. This GC acts as a control for our earlier
work on the AGB of M 4 (with contrasting results), since the same tools and
methods were used.Comment: 10 pages, 7 figures, 8 tables (2 online-only). Accepted for
publication in MNRA
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