1,970 research outputs found
Contribución al conocimiento de la vegetación de las montañas marroquíes
Different types of plant communities, till now undetected in Morocco, are here described using the phytosociological method. The following new subassociations and associations are proposed: Anthyllido polycephalae-Stachydetum fontqueri subass. quercetosum rotundifoliae is a machia from the Northern Rif Mountains; Genisto anglicae-Ericetum ciliaris subsass. pinguiculetosum lusitanicae is a heathland from the Bou Hassim range in the Western Rif; Cephalario maroccanae-Inuletum maletii is a megaphorbic community from the Middle Atlas; Bellis caerulescendis-Heracletum sphondyllii is a megaphorbic community from the High Atlas; Arenario armerinae-Sideritetum matris-fillae is a high mountain grassland from the Tichchoukt range in the Middle Atlas. New data are given for the syntaxa already described but with the distribution, variability and ecology not well known. This is the case of the following associations: Polysticho setiferi-Prunetum lusitanicae, a riverine woodland from the W Rif Mountains; Primulo acaulis-Betuletum celtibericae, a birch woodland from the C Rif and Astragaletum numidico-maroccani a high mediterranean mountain plant community from the Western Rif. As a conclusion, the vegetation of the peculiar habitats that occur in reduced areas is only partially known.Se describe con la metodología fitosociológica diferentes tipos de comunidades vegetales, no detectadas hasta el presente en Marruecos. Se proponen las siguientes nuevas asociaciones y subasociaciones: Anthyllido polycephalae-Stachydetum fontqueri subass. quercetosum rotundifoliae corresponde a una maquia de las montañas septentrionales del Rif; Genisto anglicae-Ericetum ciliaris subsass. pinguiculetosum lusitanicae es un brezal del macizo de Bou Hassim en el Rif occidental; Cephalario maroccanae- Inuletum maletii es una formación de megaforbios del Atlas Medio; Bellis caerulescendis-Heracletum sphondyllii es una formación de megaforbios del Gran Atlas; Arenario armerinae-Sideritetum matris-filiae es un pastizal de alta montaña mediterránea del macizo de Tichchoukt en el Atlas Medio. Se aportan nuevos datos para otros sintáxones ya descritos pero con la distribución, variabilidad y ecología poco conocidas. Este es el caso de las asociaciones siguientes: Polysticho setiferi-Prunetum lusitanicae, bosquecillo ripario de las montañas del Rif occidental y central; Primulo acaulis-Betuletum celtibericae, corresponde a un bosque de abedules del Rif central, y Astragaletum numidico-maroccani es una comunidad de caméfitos de alta montaña mediterránea conocida hasta el presente del Rif occidental. Como conclusión se puede aseverar que la vegetación de los hábitats que ocupan áreas reducidas en las montañas marroquíes es conocida de forma parcial
Transient tunneling effects of resonance doublets in triple barrier systems
Transient tunneling effects in triple barrier systems are investigated by
considering a time-dependent solution to the Schr\"{o}dinger equation with a
cutoff wave initial condition. We derive a two-level formula for incidence
energies near the first resonance doublet of the system. Based on that
expression we find that the probability density along the internal region of
the potential, is governed by three oscillation frequencies: one of them refers
to the well known Bohr frequency, given in terms of the first and second
resonance energies of the doublet, and the two others, represent a coupling
with the incidence energy . This allows to manipulate the above frequencies
to control the tunneling transient behavior of the probability density in the
short-time regim
Unitary Chern-Simons matrix model and the Villain lattice action
We use the Villain approximation to show that the Gross-Witten model, in the
weak- and strong-coupling limits, is related to the unitary matrix model that
describes U(N) Chern-Simons theory on S^3. The weak-coupling limit corresponds
to the q->1 limit of the Chern-Simons theory while the strong-coupling regime
is related to the q->0 limit. In the latter case, there is a logarithmic
relationship between the respective coupling constants. We also show how the
Chern-Simons matrix model arises by considering two-dimensional Yang-Mills
theory with the Villain action. This leads to a U(1)^N theory which is the
Abelianization of 2d Yang-Mills theory with the heat-kernel lattice action. In
addition, we show that the character expansion of the Villain lattice action
gives the q deformation of the heat kernel as it appears in q-deformed 2d
Yang-Mills theory. We also study the relationship between the unitary and
Hermitian Chern-Simons matrix models and the rotation of the integration
contour in the corresponding integrals.Comment: 17 pages, Minor corrections to match the published versio
Aspects of quality control of wind profiler measurements in complex topography
It is well known in the scientific community that some remote sensing
instruments assume that sample volumes present homogeneous conditions within
a defined meteorological profile. At complex topographic sites and under
extreme meteorological conditions, this assumption may be fallible depending
on the site, and it is more likely to fail in the lower layers of the
atmosphere. This piece of work tests the homogeneity of the wind field over
a boundary layer wind profiler radar located in complex terrain on the coast
under different meteorological conditions. The results reveal the
qualitative importance of being aware of deviations in this homogeneity
assumption and evaluate its effect on the final product. Patterns of
behavior in data have been identified in order to simplify the analysis of
the complex signal registered.
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The quality information obtained from the homogeneity study under different
meteorological conditions provides useful indicators for the best
alternatives the system can offer to build wind profiles. Finally, the
results are also to be considered in order to integrate them in a quality
algorithm implemented at the product level
Sobre cinco compuestas erróneamente iconografiadas en publicaciones acerca de la biodiversidad de plantas vasculares andorranas
Five Compositae taxa which are illustrated in floristic publications for Andorra are questionable records which appear to have never been collected there in the wild.Se comentan cinco taxones de compuestas que aparecen confusamente ilustrados en publicaciones florísticas de Andorra y que nunca se han recolectado en territorio andorrano
Liquefaction of the Enmedio Island Soil Deposits
The results of field testing and of simplified liquefaction analyses of the Enmedio Island soil deposits are presented and discussed in this paper. It is found that for this case history simple criteria for assessing liquefaction potential yield results in accord with field behavior
Observed and Predicted Liquefaction of a Sand Stratum
Field observations and preliminary studies had led to the conclusion that the sand stratum liquefied only in a limited area during the March 14, 1979 earthquake. Further field studies revealed the presence of the sand layer throughout the Enmedio Island. This fact raised questions as to whether the sand liquefied or not in the whole area. To clarify this question, a research program which included cyclic triaxial testing and numerical analyses was undertaken. The results of this study show that the sand layer did liquefy through the Island; however, due to differences in stratigraphic characteristics, superficial signs of liquefaction were developed only in a restricted zone
Neutrino masses and mixing parameters in a left-right model with mirror fermions
In this work we consider a left-right model containing mirror fermions with
gauge group SU(3). The model has several free parameters which here we have
calculated by using the recent values for the squared-neutrino mass
differences. Lower bound for the mirror vacuum expectation value helped us to
obtain crude estimations for some of these parameters. Also we estimate the
order of magnitude of the masses of the standard and mirror neutrinos.Comment: 13 pages, version submitted to European Physical Journal
Numerical Study of the Seismic Response of an Urban Overpass Support System
A strategic urban overpass is to be built in the so-called transition and hill zones in Mexico City. The subsoil conditions at these zones typically consist on soft to stiff clay and medium to dense sand deposits, randomly interbedded by loose sand lenses, and underlain by rock formations that may outcrop in some areas. Several critical supports of this overpass are going to be instrumented with accelerometers, inclinometers and extensometers to assess their seismic performance during future earthquakes and to generate a database to calibrate soil-structure-interaction numerical models. This paper presents the seismic performance evaluation of one of these supports. The support foundation is a 3.6 by 4.6 m mat, structurally connected to four cast-in-place 0.80 m diameter piles. A finite elements model of the soil-foundation-structure system was developed. Initially, the model was calibrated analyzing the seismic response that an instrumented bridge support exhibited during the June 15th, 1999 Tehuacan (Mw=7) Earthquake. This bridge is located also within the surroundings of Mexico City, but at the lake zone, where highly compressible clays are found. The computed response was compared with the measured response in the free field, box foundation, and structure. Once the model prediction capabilities were established, the seismic response of the critical support of the urban overpass was evaluated for the design earthquake in terms of transfer functions and displacement time histories
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