731 research outputs found
Etude Comparative Des Couts DâEntretien Du Sol En Culture Immature Dâhevea
L'entretien au sol en culture immature d'hévéa (Hevea brasilensis) est une des composantes de l'itinéraire technique qu'il convient de maîtriser, en vue de réduire les coûts de production (main d'oeuvre, des travaux, etc.) en année d'exploitation. Aussi, la diversification des méthodes d'entretien est-elle nécessaire pour l'optimisation des coûts liés à la culture. Encore faut-il que ce choix soit économiquement raisonné. Le présent travail vise à réaliser une étude comparative des coûts d'entretien au sol des cultures immatures d'hévéa conformément aux pratiques en cours: entretiens manuel ou mécanique, chimique et mixte (chimique et mécanique). Un test d'égalité des moyennes d'échantillons appariés a montré qu'il n'y a pas eu de différence significative entre les écarts de coûts au niveau des années de culture et des opérations, si l'on développe l'entretien chimique ou l'entretien mixte. Par contre, l'analyse de l'influence des entretiens envisagés a montré une réduction de 12,31 % du temps de travail par l'entretien chimique, et de 21,04 %, en entretien mixte. La pratique de l'entretien mixte est donc à préconiser quand bien même la main d'oeuvre constitue un facteur prépondérant à maitriser.Mots clés: Hévéa, coûts d’entretien, culture immature, entretien mixte, Côte d’IvoireImmature rubber crop maintenance (Hevea brasilensis) is a technique that must be controlled in order to reduce production costs (labour, costs of work) in a year of cultivation. Thus, diversification of maintenance techniques are necessary in order to optimize production costs. Besides, this choice should be economically rational. The work aims to conduct a comparative study of the cost of immature rubber culture in accordance with current practices: mechanical, chemical and mixed techniques (chemical and mechanical). A paired sample test showed that there was no significant difference between yearly costs of culture and exploitation when chemical or mixed maintenance techniques were considered. However, analysis showed a reduction of 12.31 % of work time with chemical maintenance and 21.04 % for mixed maintenance. Therefore, mixed maintenance practice appeared to be the major workforce that has to be mastered
Diffuse Hard X-ray Sources Discovered with the ASCA Galactic Plane Survey
We found diffuse hard X-ray sources, G11.0+0.0, G25.5+0.0, and G26.6-0.1 in
the ASCA Galactic plane survey data. The X-ray spectra are featureless with no
emission line, and are fitted with both models of a thin thermal plasma in
non-equilibrium ionization and a power-law function. The source distances are
estimated to be 1-8 kpc, using the best-fit NH values on the assumption that
the mean density in the line of sight is 1 H cm^-3. The source sizes and
luminosities are then 4.5-27 pc and (0.8-23)x10^33 ergs/s. Although the source
sizes are typical to supernova remnants (SNR) with young to intermediate ages,
the X-ray luminosity, plasma temperature, and weak emission lines in the
spectra are all unusual. This suggests that these objects are either shell-like
SNRs dominated by X-ray synchrotron emission, like SN 1006, or, alternatively,
plerionic SNRs. The total number of these classes of SNRs in our Galaxy is also
estimated.Comment: 17 pages, 9 figures; to appear in Ap
Magnetic fields from inflation?
We consider the possibility of generation of the seeds of primordial magnetic
field on inflation and show that the effect of the back reaction of this field
can be very important. Assuming that back reaction does not spoil inflation we
find a rather strong restriction on the amplitude of the primordial seeds which
could be generated on inflation. Namely, this amplitude recalculated to the
present epoch cannot exceed in scales. This field seems to be
too small to be amplified to the observable values by galactic dynamo
mechanism.Comment: 10 page
Thermal and Non-thermal X-Rays from the LMC Super Bubble 30 Dor C
We report on the discovery of thermal and non-thermal X-rays from the shells
of the super bubble (SB) 30 Dor C in the Large Magellanic Cloud (LMC). The
X-ray morphology is a nearly circular shell with a radius of about 40 pc, which
is bright on the northern and western sides. The spectra of the shells are
different from region to region. The southern shell shows clear emission lines,
and is well fitted with a model of a thin-thermal plasma (kT = 0.21keV) in
non-equilibrium ionization (NEI) plus a power-law component. This thermal
plasma is located inside of the H alpha emission, which is the outer edge of
the shell of the SB. The northern and western sides of the SB are dim in H
alpha emission, but are bright in non-thermal (power-law) X-rays with a photon
index of 2.1-2.9. The non-thermal X-ray shell traces the outer boundary of the
radio shell. These features of thin-thermal and non-thermal X-rays are similar
to those of SN 1006, a prototype of synchrotron X-ray shell, but the
non-thermal component of 30 Dor C is about ten-times brighter than that of SN
1006. 30 Dor C is the first candidate of an extragalactic SB, in which
energetic electrons are accelerating in the shell. The age is much older than
that of SN 1006, and hence the particle acceleration time in this SB may be
longer than those in normal shell-like SNRs. We found point-like sources
associated with some of tight star clusters. The X-ray luminosity and spectrum
are consistent with those of young clusters of massive stars. Point-like
sources with non-thermal spectra are also found in the SB. These may be
background objects (AGNs) or stellar remnants (neutron stars or black holes).Comment: 11 pages, 6 figures, Accepted for publication in ApJ, the paper with
full resolution images in
http://www-cr.scphys.kyoto-u.ac.jp/member/bamba/Paper/30DorC.pd
Fine Structures of Shock of SN 1006 with the Chandra Observation
The north east shell of SN 1006 is the most probable acceleration site of
high energy electrons (up to ~ 100 TeV) with the Fermi acceleration mechanism
at the shock front. We resolved non-thermal filaments from thermal emission in
the shell with the excellent spatial resolution of Chandra. The thermal
component is extended widely over about ~ 100 arcsec (about 1 pc at 1.8 kpc
distance) in width, consistent with the shock width derived from the Sedov
solution. The spectrum is fitted with a thin thermal plasma of kT = 0.24 keV in
non-equilibrium ionization (NEI), typical for a young SNR. The non-thermal
filaments are likely thin sheets with the scale widths of ~ 4 arcsec (0.04 pc)
and ~ 20 arcsec (0.2 pc) at upstream and downstream, respectively. The spectra
of the filaments are fitted with a power-law function of index 2.1--2.3, with
no significant variation from position to position. In a standard diffusive
shock acceleration (DSA) model, the extremely small scale length in upstream
requires the magnetic field nearly perpendicular to the shock normal. The
injection efficiency (eta) from thermal to non-thermal electrons around the
shock front is estimated to be ~ 1e-3 under the assumption that the magnetic
field in upstream is 10 micro G. In the filaments, the energy densities of the
magnetic field and non-thermal electrons are similar to each other, and both
are slightly smaller than that of thermal electrons. in the same order for each
other. These results suggest that the acceleration occur in more compact region
with larger efficiency than previous studies.Comment: 24 pages, 11 figures, Accepted for publication in ApJ, the paper with
full resolution images in
http://www-cr.scphys.kyoto-u.ac.jp/member/bamba/Paper/SN1006.pd
Electric-magnetic duality and the conditions of inflationary magnetogenesis
The magnetogenesis scenarios triggered by the early variation of the gauge
coupling are critically analyzed. In the absence of sources, it is shown that
the electric and magnetic power spectra can be explicitly computed by means of
electric-magnetic duality transformations. The remnants of a pre-inflationary
expansion and the reheating process break explicitly electric-magnetic duality
by inducing Ohmic currents. The generation of large-scale magnetic field and
the physical distinction between electric and magnetic observables stems, in
this class of models, from the final value reached by the conductivity of the
plasma right after inflation. Specific numerical examples are given. The
physical requirements of viable magnetogenesis scenarios are spelled out.Comment: 25 pages, 9 figure
Theoretical framework of entangled-photon generation from biexcitons in nano-to-bulk crossover regime with planar geometry
We have constructed a theoretical framework of the biexciton-resonant
hyperparametric scattering for the pursuit of high-power and high-quality
generation of entangled photon pairs. Our framework is applicable to
nano-to-bulk crossover regime where the center-of-mass motion of excitons and
biexcitons is confined. Material surroundings and the polarization correlation
of generated photons can be considered. We have analyzed the entangled-photon
generation from CuCl film, by which ultraviolet entangled-photon pairs are
generated, and from dielectric microcavity embedding a CuCl layer. We have
revealed that in the nano-to-bulk crossover regime we generally get a high
performance from the viewpoint of statistical accuracy, and the generation
efficiency can be enhanced by the optical cavity with maintaining the high
performance. The nano-to-bulk crossover regime has a variety of degrees of
freedom to tune the entangled-photon generation, and the scattering spectra
explicitly reflect quantized exciton-photon coupled modes in the finite
structure.Comment: 18 pages, 10 figure
Governing accelerating Universe via newly reconstructed Hubble parameter by employing empirical data simulations
A new parametrization of the phenomenological Hubble parameter is proposed to
explore the issue of the cosmological landscape. The constraints on model
parameters are derived through the Markov Chain Monte Carlo (MCMC) method by
employing a comprehensive union of datasets such as 34 data points from cosmic
chronometers (CC), 42 points from baryonic acoustic oscillations (BAO), a
recently updated set of 1701 Pantheon (P22) data points derived from Type
Ia supernovae (SNeIa), and 162 data points from gamma-ray bursts (GRB). The
kinematic behavior of the models is also investigated by encompassing the
transition from deceleration to acceleration and the evolution of the jerk
parameter. From the analysis of the parametric models, it is strongly indicated
that the Universe is currently undergoing an accelerated phase. Furthermore,
the models are compared by using the Akaike Information Criterion (AIC) and
Bayesian Information Criterion (BIC), so that a comparative assessment of model
performance can be available.Comment: 17 pages, 6 figure
Growth factor in f(T) gravity
We derive the evolution equation of growth factor for the matter over-dense
perturbation in gravity. For instance, we investigate its behavior in
power law model at small redshift and compare it to the prediction of
CDM and dark energy with the same equation of state in the framework
of Einstein general relativity. We find that the perturbation in gravity
grows slower than that in Einstein general relativity if \p f/\p T>0 due to
the effectively weakened gravity.Comment: 15 pages,1 figure; v2,typos corrected; v3, discussions added,
accepted by JCA
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