15,473 research outputs found
Water production function of sorghum for Northeast Brazil.
The results of an experiment to determine the water production function of sorghum for Northeast Brazilian conditions are reported. The experiment was designed in two random blocks consisting of four growth states for irrigation deficit and four levels of nitrogen. The crop response to water was found to be of quadratic nature. Regression coeficients were developed for each nitrogen and growth stage treatment between water use and grain yields. The most critical stage was found to be the vegetative stage followed by flowering and grainn formation stages. The yield response factors as according to Doorenbos and Kassam were found to with differente irrigation levels. A modified linear equation has been suggested. The coefficients of this modifieed equation have been determined for all four stages and for the four nitrogen levels for sorghum. The higest average water use efficiency of 109:3 kg haa-1 cm -1 of water and highest obtainable grain yield of 4.92 t/ha was found to be at 425 mm of water use and 45 kt/ha of nitrogen. The crop coefficients (Kc) to compute crop water use from pan evaporation vary between 0.4 and 0.81 with an average for the whole growing period of 0.75
E11 and Spheric Vacuum Solutions of Eleven- and Ten dimensional Supergravity Theories
In view of the newly conjectured Kac-Moody symmetries of supergravity
theories placed in eleven and ten dimensions, the relation between these
symmetry groups and possible compactifications are examined. In particular, we
identify the relevant group cosets that parametrise the vacuum solutions of AdS
x S type.Comment: discussion improve
The Nambu sum rule and the relation between the masses of composite Higgs bosons
We review the known results on the bosonic spectrum in various NJL models
both in the condensed matter physics and in relativistic quantum field theory
including He-B, He-A, the thin films of superfluid He-3, and QCD
(Hadronic phase and the Color Flavor Locking phase). Next, we calculate bosonic
spectrum in the relativistic model of top quark condensation suggested in
\cite{Miransky}. In all considered cases the sum rule appears that relates the
masses (energy gaps) of the bosonic excitations in each channel
with the mass (energy gap) of the condensed fermion as . Previously this relation was established by Nambu in \cite{Nambu}
for He-B and for the s - wave superconductor. We generalize this relation
to the wider class of models and call it the Nambu sum rule. We discuss the
possibility to apply this sum rule to various models of top quark condensation.
In some cases this rule allows to calculate the masses of extra Higgs bosons
that are the Nambu partners of the 125 GeV Higgs.Comment: Latex, 15 page
Online Harmonic/Percussive Separation Using Smoothness/Sparseness Constraints
(Abstract to follow
Ab Initio Molecular Dynamics on the Electronic Boltzmann Equilibrium Distribution
We prove that for a combined system of classical and quantum particles, it is
possible to write a dynamics for the classical particles that incorporates in a
natural way the Boltzmann equilibrium population for the quantum subsystem. In
addition, these molecular dynamics do not need to assume that the electrons
immediately follow the nuclear motion (in contrast to any adiabatic approach),
and do not present problems in the presence of crossing points between
different potential energy surfaces (conical intersections or spin-crossings).
A practical application of this molecular dynamics to study the effect of
temperature in molecular systems presenting (nearly) degenerate states - such
as the avoided crossing in the ring-closure process of ozone - is presented.Comment: published in New J. Phy
The interplay between double exchange, super-exchange, and Lifshitz localization in doped manganites
Considering the disorder caused in manganites by the substitution of Mn by Fe
or Ga, we accomplish a systematic study of doped manganites begun in previous
papers. To this end, a disordered model is formulated and solved using the
Variational Mean Field technique. The subtle interplay between double exchange,
super-exchange, and disorder causes similar effects on the dependence of T_C on
the percentage of Mn substitution in the cases considered. Yet, in
LaCaMnGaO our results suggest a quantum
critical point (QCP) for , associated to the localization of
the electronic states of the conduction band. In the case of
LaCaMnFeO (with ) no such QCP is expected.Comment: 6 pages + 3 postscript figures. Largely extended discussio
Higher-Derivative Boson Field Theories and Constrained Second-Order Theories
As an alternative to the covariant Ostrogradski method, we show that
higher-derivative relativistic Lagrangian field theories can be reduced to
second differential-order by writing them directly as covariant two-derivative
theories involving Lagrange multipliers and new fields. Despite the intrinsic
non-covariance of the Dirac's procedure used to deal with the constraints, the
explicit Lorentz invariance is recovered at the end. We develop this new
setting on the grounds of a simple scalar model and then its applications to
generalized electrodynamics and higher-derivative gravity are worked out. For a
wide class of field theories this method is better suited than Ostrogradski's
for a generalization to 2n-derivative theoriesComment: 31 pages, Plain Te
Atomic Diffusion and Mixing in Old Stars I. VLT/FLAMES-UVES Observations of Stars in NGC 6397
We present a homogeneous photometric and spectroscopic analysis of 18 stars
along the evolutionary sequence of the metal-poor globular cluster NGC 6397
([Fe/H] = -2), from the main-sequence turnoff point to red giants below the
bump. The spectroscopic stellar parameters, in particular stellar-parameter
differences between groups of stars, are in good agreement with broad-band and
Stroemgren photometry calibrated on the infrared-flux method. The spectroscopic
abundance analysis reveals, for the first time, systematic trends of iron
abundance with evolutionary stage. Iron is found to be 31% less abundant in the
turnoff-point stars than in the red giants. An abundance difference in lithium
is seen between the turnoff-point and warm subgiant stars. The impact of
potential systematic errors on these abundance trends (stellar parameters, the
hydrostatic and LTE approximations) is quantitatively evaluated and found not
to alter our conclusions significantly. Trends for various elements (Li, Mg,
Ca, Ti and Fe) are compared with stellar-structure models including the effects
of atomic diffusion and radiative acceleration. Such models are found to
describe the observed element-specific trends well, if extra (turbulent) mixing
just below the convection zone is introduced. It is concluded that atomic
diffusion and turbulent mixing are largely responsible for the sub-primordial
stellar lithium abundances of warm halo stars. Other consequences of atomic
diffusion in old metal-poor stars are also discussed.Comment: 20 pages (emulateapj), 11 figures, accepted for publication in Ap
Bohr-Sommerfeld Quantization of Periodic Orbits
We show, that the canonical invariant part of corrections to the
Gutzwiller trace formula and the Gutzwiller-Voros spectral determinant can be
computed by the Bohr-Sommerfeld quantization rules, which usually apply for
integrable systems. We argue that the information content of the classical
action and stability can be used more effectively than in the usual treatment.
We demonstrate the improvement of precision on the example of the three disk
scattering system.Comment: revte
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