579 research outputs found
Inventory of macroalgal epiphytes on the seagrass Thalassia testudinum (Hydrocharitaceae) in Parque Nacional Cahuita, Caribbean coast of Costa Rica
Seagrass epiphytes play an important role in seagrass habitats; however, available information from Central America is scarce. The present study focuses on macroalgal epiphytes on leaves of the seagrass Thalassia testudinum in the seagrass meadows at Punta Cahuita, Caribbean coast of Costa Rica, and it is the first one of its kind in Costa Rica. A representative amount for each algal epiphyte species found was collected, preserved and identified to the lowest possible taxon. Preserved samples of each species were deposited in the Herbarium of the Universidad de Costa Rica. A total of 26 species of macroalgae were found: 15 species belonging to Rhodophyta, four to Chlorophyta, six to the class Phaeophyceae, and one diatom species which could not be identified. The present inventory reports three species that are new for the phycological flora of Costa Rica, four species are reported for the first time for the Caribbean coast of Costa Rica, and 17 are new reports for the Parque Nacional Cahuita area. Epiphyte species number might further rise if sampling efforts and the study area increased. Rev. Biol. Trop. 56 (Suppl. 4): 163-174. Epub 2009 June 30.Los epífitos de pasto marino juegan un papel impor-
tante en el hábitat de pastos marinos. Sin embargo, la
información disponible sobre este tema en América Central
es muy limitada. Este estudio se enfoca en las macroalgas
epífitas de hojas del pasto marino Thalassia testudinum en
las praderas de pasto marino de Punta Cahuita, costa Caribe
de Costa Rica y es el primero de su tipo para Costa Rica.
Una cantidad representativa para cada especie de epífito
algal encontrada se colectó, preservó e identificó al menor
taxon posible. Muestras preservadas para cada especie fue-
ron depositadas en el Herbario de la Universidad de Costa
Rica (USJ). Se encontró un total de 26 especies de macroal-
gas: 15 especies de Rhodophyta, cuatro de Chlorophyta,
seis pertenecientes a la clase Phaeophyceae y una especie
de diatomea que no fue posible identificar. El inventario
reporta tres especies por primera vez para la flora fico-
lógica de Costa Rica, cuatro especies son reportadas por
primera vez para el Caribe de Costa Rica y 17 especies
son nuevos reportes para el Parque Nacional Cahuita. Se
comparan nuestros resultados con aquellos obtenidos en
estudios similares en la región y se especula que el número
de especies de epífitos podría aumentar de ser ampliado el
esfuerzo de recolecta y el área de estudio.Universidad de Costa Rica/[]/UCR/Costa RicaUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de BiologíaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR
Improving the Accuracy of a Machine Tool with Three Linear Axes using a Laser Tracker as Measurement System
This paper presents a real way to improve machine tool accuracy using interferometry techniques based on laser tracker as measurement system. This is based on an indirect measurement of the geometric error of the MT; characterizing their combined effect though volumetric verification. This technique can be used to verify all types of machine through its kinematic model, relating measured points with the laser tracker and nominal points. Using non-lineal optimization techniques the difference between pair of points are reduced. Finally, it provides the approximation functions of the machine tool geometric errors used to compensate theirs influence on MT accuracy. As it is a mathematical compensation result of an optimization procedure, the improvement on MT accuracy should be validate using the same or external measurement system. This paper shows that volumetric verification provides an real improvement of the MT accuracy
Point-contact spectroscopy of the borocarbide superconductor YNi2B2C
Point-contact (PC) spectroscopy measurements on YNi2B2C single crystals in
the normal and superconducting (SC) state (T_c=15.4K) for the main
crystallographic directions are reported. The PC study reveals the
electron-phonon interaction (EPI) function with a dominant maximum around 12meV
and a further weak structure (kink or shallow broad maximum) at higher energy
at about 50meV. Other phonon maxima at 20, 24 and 32meV specified in the phonon
DOS of YNi2B2C by neutron measurements [PRB, V.55, 9058 (1997)] are not
resolved in the PC spectra pointing out to the main role of the low energy
phonon modes in EPI. Directional study of the SC gap results in
\Delta_[100]=1.5meV for the a- direction and \Delta_[001]=2.4meV along the
c-axis which may point to anisotropic and/or multiband behavior. Noteworthy,
the critical temperature T_c in all cases corresponds to that of bulk samples.
The value 2\Delta_[001]/kT_c=3.6 is close to the BCS one of 3.52, and the
temperature dependence \Delta(T) is BCS-like, while for the a-direction
\Delta(T) deviates from mean-field BCS behavior above T_c/2. The directional
variation in \Delta can be attributed to the multiband nature of the SC state
in YNi2B2C predicted 10 years ago (PRL, V.80, 1730 (1998)).Comment: 3 figs, 2 pages, presented on M2S-HTSC Conference, July 9-14, 2006,
Dresde
STM study of multiband superconductivity in NbSe2 using a superconducting tip
We present a method to produce superconducting tips to be used in Scanning
Tunneling Microscopy/Spectroscopy experiments. We use these tips to investigate
the evolution of the electronic density of states of NbSe2 from 0.3K up to its
critical temperature (7.2K). The use of a superconducting tip (Pb) as
ounterelectrode provides an enhancement of the different features related to
the DOS of NbSe2 in the tunneling conductance curves, along all the studied
thermal range. The analysis of the experimental results gives evidence of the
presence of multiband superconductivity in NbSe2.Comment: 5 pages, 5 figures, PDF fil
Data-driven model for the assessment of mycobacterium tuberculosis transmission in evolving demographic structures
In the case of tuberculosis (TB), the capabilities of epidemic models to produce quantitatively robust forecasts are limited by multiple hindrances. Among these, understanding the complex relationship between disease epidemiology and populations’ age structure has been highlighted as one of the most relevant. TB dynamics depends on age in multiple ways, some of which are traditionally simplified in the literature. That is the case of the heterogeneities in contact intensity among different age strata that are common to all airborne diseases, but still typically neglected in the TB case. Furthermore, while demographic structures of many countries are rapidly aging, demographic dynamics are pervasively ignored when modeling TB spreading. In this work, we present a TB transmission model that incorporates country-specific demographic prospects and empirical contact data around a data-driven description of TB dynamics. Using our model, we find that the inclusion of demographic dynamics is followed by an increase in the burden levels predicted for the next decades in the areas of the world that are most hit by the disease today. Similarly, we show that considering realistic patterns of contacts among individuals in different age strata reshapes the transmission patterns reproduced by the models, a result with potential implications for the design of age-focused epidemiological interventions
Adequacy of technical and commercial alternatives applied to machine tool verification using laser tracker
Besides presenting a volumetric verification technique that allows characterization of the different geometric errors of a machine tool (MT) depending on its kinematic chain and geometry through a kinematic model, this paper investigates the influence of measurement tools and techniques available on the final accuracy of the MT. Volumetric verification based on a laser tracker (LT) relates the coordinates of the tool with the coordinates of the LT, including it into the kinematic model. Using a non-lineal optimization process, approximation functions that characterize the joint influence of MT geometric errors are obtained. However, measurement data will be affected by previous compensation of the MT, the accuracy of the measurement system, LT measurement technology, the type of retroreflector used, and techniques used to improve data accuracy, among other sources of errors. This paper studies the adequacy of different commercial alternatives such as: retroreflectors, LTs from different manufacturers, etc., that can be applied in MT verification using a long-range MT. As the accuracy is strongly affected by the uncertainty of its angular encoders, the multilateration technique tries to improve data accuracy using only LT radial information. Nonetheless, a new bundle adjustment which uses radial and angular information is presented in current metrology software. This paper studies both techniques and analyzes their adequacy for MT verification too
Very Low Temperature Tunnelling Spectroscopy in the heavy fermion superconductor PrOsSb
We present scanning tunnelling spectroscopy measurements on the heavy fermion
superconductor PrOsSb. Our results show that the superconducting gap
opens over a large part of the Fermi surface. The deviations from isotropic BCS
s-wave behavior are discussed in terms of a finite distribution of values of
the superconducting gap.Comment: 4 pages, 4 figure
EL EMPRESARIADO COMO FUENTE DE LA SEGREGACION POR SEXO
Este artículo presenta una parte de una amplia investigación cuyo objetivo era proponer Políticas Activas Institucionales para favorecer la inserción laboral de las mujeres en sectores o profesiones en las que estén subrepresentadas. El trabajo trata de profundizar en el comportamiento del empresariado para determinar cual es su grado de responsabilidad e influencia en la segregación sexual del mercado de trabajo. Para ello se realizó un estudio cualitativo. Los resultados nos muestran un aumento de la sensibilización. Los empresarios creen que no es justo, pero no se sienten responsables. Demandan una mayor participación del Gobierno y de la sociedad en general, a la vez que reconocen desconocer las políticas activas institucionales existentes
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