452 research outputs found
Native breeds of the oaxaqueña Mixteca of México
The Mixteca region is one of the most important areas of the Pacific Mexico with respect to the extensive farming, where the special richness of the Creole population of hens, sheep, goats, cattle, pigs and in a lower wake horses, turkeys and honey bees. Instead of this richness and its socio-economic importance in this region, few scientific studies have been developed about these animals. In this communication, we are developing a description of the most important population existing in this region, pointing out some aspects about their origin, geographical localization, management system, etc. Presently, the lines proposed by FAO for the conservation of the genetic resources is sensitising Mexico and all Latin-America for the conservation of their own resources. In this way, we can stand out the decay of this region in the enclosing of their breed in the international scientific community, what it is shown in the absence of most of them in publications such us the world watch list or the DAD-IS program.La Mixteca es una de las regiones ganaderas extensivas más importantes del México PacÃfico, destacada por su gran riqueza en poblaciones criollas de gallinas, ovinos, caprinos, bovinos, porcinos y en menor medida equinos, pavos y abejas. A pesar de esta riqueza y de su importante repercusión socio-económica en esta región, son escasos los estudios cientÃficos realizados sobre estos animales. En este trabajo se realiza una descripción de las principales poblaciones existentes, precisando algunos aspectos sobre su origen, ubicación geográfica, sistema de manejo, producción y opciones de futuro. En la actualidad las lÃneas impuestas por el programa global de la FAO para la conservación de los recursos genéticos está sensibilizando a México y a toda América Latina en pro de la conservación de sus propios recursos. En este sentido cabe destacar el retraso de esta región en incorporar sus razas a la comunidad cientÃfica internacional, lo que queda demostrado por la ausencia de la mayorÃa de ellos en publicaciones como el World Watch List o el programa DAD-IS
Can surface flux transport account for the weak polar field in cycle 23?
To reproduce the weak magnetic field on the polar caps of the Sun observed
during the declining phase of cycle 23 poses a challenge to surface flux
transport models since this cycle has not been particularly weak. We use a
well-calibrated model to evaluate the parameter changes required to obtain
simulated polar fields and open flux that are consistent with the observations.
We find that the low polar field of cycle 23 could be reproduced by an increase
of the meridional flow by 55% in the last cycle. Alternatively, a decrease of
the mean tilt angle of sunspot groups by 28% would also lead to a similarly low
polar field, but cause a delay of the polar field reversals by 1.5 years in
comparison to the observations.Comment: 9 pages, 8 figures, Space Science Reviews, accepte
Positive pion absorption on 3He using modern trinucleon wave functions
We study pion absorption on 3He employing trinucleon wave functions
calculated from modern realistic NN interactions (Paris, CD Bonn). Even though
the use of the new wave functions leads to a significant improvement over older
calculations with regard to both cross section and polarization data, there are
hints that polarization data with quasifree kinematics cannot be described by
just two-nucleon absorption mechanisms.Comment: 14 pages, 6 figure
Barrier effects on the collective excitations of split Bose-Einstein condensates
We investigate the collective excitations of a single-species Bose gas at T=0
in a harmonic trap where the confinement undergoes some splitting along one
spatial direction. We mostly consider onedimensional potentials consisting of
two harmonic wells separated a distance 2 z_0, since they essentially contain
all the barrier effects that one may visualize in the 3D situation. We find,
within a hydrodynamic approximation, that regardless the dimensionality of the
system, pairs of levels in the excitation spectrum, corresponding to
neighbouring even and odd excitations, merge together as one increases the
barrier height up to the current value of the chemical potential. The
excitation spectra computed in the hydrodynamical or Thomas-Fermi limit are
compared with the results of exactly solving the time-dependent
Gross-Pitaevskii equation. We analyze as well the characteristics of the
spatial pattern of excitations of threedimensional boson systems according to
the amount of splitting of the condensate.Comment: RevTeX, 12 pages, 13 ps figure
Incoherent Photoproduction of -mesons from the Deuteron near Threshold
Incoherent photoproduction of the -meson on the deuteron is studied for
photon energies from threshold to 800 MeV. The dominant contribution, the
N-N amplitude, is described within an isobar model. The final
state interaction derived from the CD-Bonn potential is included and found to
be important for the description of the production cross section close to
threshold. Possible effects from the final state interaction are
discussed.Comment: 11 pages, revtex, including 6 figure
Effective Hamiltonian and unitarity of the S matrix
The properties of open quantum systems are described well by an effective
Hamiltonian that consists of two parts: the Hamiltonian of the
closed system with discrete eigenstates and the coupling matrix between
discrete states and continuum. The eigenvalues of determine the
poles of the matrix. The coupling matrix elements
between the eigenstates of and the continuum may be very
different from the coupling matrix elements between the eigenstates
of and the continuum. Due to the unitarity of the matrix, the
\TW_k^{cc'} depend on energy in a non-trivial manner, that conflicts with the
assumptions of some approaches to reactions in the overlapping regime. Explicit
expressions for the wave functions of the resonance states and for their phases
in the neighbourhood of, respectively, avoided level crossings in the complex
plane and double poles of the matrix are given.Comment: 17 pages, 7 figure
Active flux seasonality of the small dominant migratory crustaceans and mesopelagic fishes in the Gulf of California during June and October
The biological carbon pump is the process that transports carbon vertically out of the mixed layer in the ocean. Besides the sinking flux of organic particles, active flux due to the daily vertical migration of zooplankton and micronekton promotes a significant carbon transport not fully accounted for or understood in the world’s oceans. The diversity and abundance of epipelagic and mesopelagic species in the Gulf of California has been extensively studied, but the role of micronekton in carbon export has not yet been investigated. We studied the carbon flux promoted by juvenile and adult mesopelagic fishes and crustaceans (Decapoda and Euphausiidae) during the transition from the cold to warm period (June) and the onset of the warm season (October) in 2018. We provide the first estimation of migrant biomass and respiratory flux of the most abundant migratory species of mesopelagic fishes, decapods and euphausiids in the Gulf of California. The micronekton species collected accounted for a large biomass of mesopelagic fishes and pelagic crustaceans. The average migrant biomass estimates were 151.5 ± 101.2 mg C·m−2 during June and 90.9 ± 75.3 mg C·m−2 during October. The enzymatic activity of the electron transfer system (ETS) was measured as an estimate of their respiratory rates. Average specific ETS activity was significantly different between fishes and decapods, and between fishes and euphausiids (p < 0.05). The respiratory flux of fishes was predominant in the Gulf of California, followed by pelagic decapods and euphausiids. Seasonal changes in respiratory flux were observed for fishes (June: 6.1 ± 1.5 mg C·m−2·d−1; October: 3.2 ± 1.8 mg C·m−2·d−1) and decapods (June: 0.4 mg C·m−2·d−1; October: 0.7 ± 0.05 mg C·m−2·d−1). Respiratory flux estimation by crustaceans (decapods and euphausiids) and fishes together was 6.86 mg C·m−2·d−1 during June, and 4.21 mg C·m−2·d−1 during October 2018, suggesting a functional role of this large micronektonic fauna in the biological carbon export in this region.3,26
Patchiness and Demographic Noise in Three Ecological Examples
Understanding the causes and effects of spatial aggregation is one of the
most fundamental problems in ecology. Aggregation is an emergent phenomenon
arising from the interactions between the individuals of the population, able
to sense only -at most- local densities of their cohorts. Thus, taking into
account the individual-level interactions and fluctuations is essential to
reach a correct description of the population. Classic deterministic equations
are suitable to describe some aspects of the population, but leave out features
related to the stochasticity inherent to the discreteness of the individuals.
Stochastic equations for the population do account for these
fluctuation-generated effects by means of demographic noise terms but, owing to
their complexity, they can be difficult (or, at times, impossible) to deal
with. Even when they can be written in a simple form, they are still difficult
to numerically integrate due to the presence of the "square-root" intrinsic
noise. In this paper, we discuss a simple way to add the effect of demographic
stochasticity to three classic, deterministic ecological examples where
aggregation plays an important role. We study the resulting equations using a
recently-introduced integration scheme especially devised to integrate
numerically stochastic equations with demographic noise. Aimed at scrutinizing
the ability of these stochastic examples to show aggregation, we find that the
three systems not only show patchy configurations, but also undergo a phase
transition belonging to the directed percolation universality class.Comment: 20 pages, 5 figures. To appear in J. Stat. Phy
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