1,441 research outputs found
A comparison between different treeline types shows contrasting responses to climate fluctuations
Treeline position is mainly determined by growth season temperature, but the response of treelines to climate warming is not uniform worldwide. We compared treeline structure, dynamics and thermal profile in nearby areas with different treeline type, species composition and bioclimatic conditions. We performed a detailed survey of different treeline types in three areas of Italian Alps and northern Apennines. Every tree individual was recorded along altitudinal transects from the closed forest to the species limit. Treeline structure and dynamics were described through altitudinal limits of tree height, density and age. Data were elaborated by principal components analysis. Temperature regime of the three sites was assessed from homogeneous historical climatic data. Treeline was different in the three areas for species composition, shape and dynamics. Both Alpine sites showed diffuse treeline, but only one showed advancing dynamics. Apennine treeline was abrupt and static, with higher temperature at the tree limit. Our study showed the variable dynamics of treelines within a relatively restricted area and the connection between treeline shape and dynamics. An important role is played by species composition, determined by bioclimatic and historical features. These factors should be taken into account when modelling future treeline dynamics at global scale
The REX survey: a search for Radio Emitting X-ray sources
We present the scientific goals, the strategy and the first results of the
REX project, an effort aimed at creating a sizable and statistically complete
sample of Radio Emitting X-ray sources (REX) using the available data from a
VLA survey and the ROSAT PSPC archive. Through a positional cross-correlation
of the two data sets we have derived a sample of about 1600 REX. Among the 393
REX identified so far a high fraction is represented by AGNs, typically radio
loud QSOs and BL Lacs. The remaining sources are galaxies, typically radio
galaxies isolated or in cluster. Thanks to the low flux limits in the radio and
in the X-ray band and the large area of sky covered by the survey, we intend to
derive a new complete and unbiased sample of BL Lacs which will contain both
``RBL'' and ``XBL'' type objects. In this way, the apparent dichotomy resulting
from the current samples of BL Lacs will be directly analyzed in a unique
sample. Moreover, the high number of BL Lacs expected in the REX sample (about
200) will allow an accurate estimate of their statistical properties. To date,
we have discovered 15 new BL Lacs and 11 BL Lac candidates with optical
properties intermediate between those of a typical elliptical galaxy and those
of a typical BL Lac object. These objects could harbour weak sources of
non-thermal continuum in their nuclei and, if confirmed, they could represent
the faint tail of the BL Lac population. The existence of such ``weak'' BL Lacs
is matter of discussion in recent literature and could lead to a re-assessment
of the defining criteria of a BL Lac and, consequently, to a revision of their
cosmological and statistical properties.Comment: 30 pages, 13 figures, accepted for publication to Ap
Emission Line AGNs from the REX survey: Results from optical spectroscopy
We present 71 Emission Line objects selected from the REX survey. Except for
3 of them, for which the presence of an active nucleus is dubious, all these
sources are Active Galactic Nuclei (QSOs, Seyfert galaxies, emission line
radiogalaxies). In addition, we present the spectra of other 19 AGNs included
in a preliminary version of the REX catalog but not in the final one. The
majority (80) of the 90 sources presented in this paper is newly discovered.
Finally, we present the general properties in the radio and in the X-ray band
of all the AGNs discovered so far in the REX survey.Comment: 27 pages. To be published in Astronomy and Astrophysics, Supplement
Series. Better quality figures can be asked to the autho
SDSSJ143244.91+301435.3 at VLBI: a compact radio galaxy in a narrow-line Seyfert 1
We present VLBI observations, carried out with the European Very Long
Baseline Interferometry Network (EVN), of SDSSJ143244.91+301435.3, a radio-loud
narrow-line Seyfert 1 (RLNLS1) characterized by a steep radio spectrum. The
source, compact at Very Large Array (VLA) resolution, is resolved on the
milliarcsec scale, showing a central region plus two extended structures. The
relatively high brightness temperature of all components (5x10^6-1.3x10^8 K)
supports the hypothesis that the radio emission is non-thermal and likely
produced by a relativistic jet and/or small radio lobes. The observed radio
morphology, the lack of a significant core and the presence of a low frequency
(230 MHz) spectral turnover are reminiscent of the Compact Steep Spectrum
sources (CSS). However, the linear size of the source (~0.5kpc) measured from
the EVN map is lower than the value predicted using the turnover/size relation
valid for CSS sources (~6kpc). This discrepancy can be explained by an
additional component not detected in our observations, accounting for about a
quarter of the total source flux density, combined to projection effects. The
low core-dominance of the source (CD<0.29) confirms that
SDSSJ143244.91+301435.3 is not a blazar, i.e. the relativistic jet is not
pointing towards the observer. This supports the idea that
SDSSJ143244.91+301435.3 may belong to the "parent population" of flat-spectrum
RLNLS1 and favours the hypothesis of a direct link between RLNLS1 and compact,
possibly young, radio galaxies.Comment: 8 pages, 3 figures, accepted for publication in MNRA
Soil–plant interactions in a pasture of the Italian Alps
A detailed assessment of a pasture\u2019s functioning based on soil properties characterization, floristic composition, and \u2018functional summary\u2019 by evaluating competitor\u2013stress tolerator\u2013ruderal (CSR) strategies is provided for a doline in Central Italian Alps. A floristic survey was carried out at 35 sampling points, representative of the main topographic features, soil and vegetation types; the functional profile at the community level was evaluated by assessing for each species its Grime\u2019s CSR strategy; each point was characterized through soil profiles and topsoil (0\u201310 cm) sampling; pH, soil organic carbon and total nitrogen, available P, soil humus fraction, root density, bulk density, water content, and available water capacity were determined. Our study showed i) a strong relationship between vegetation, soil properties, topography, and grazing; ii) a prevalence of stress-tolerant strategies; iii) the ability of plant strategy variation to reflect the ecological parameters; and iv) the vegetation potentiality to be an indicator of environmental spatial variability
Comparación entre técnicas bilaminares y regenerativas para recubrir las raíces
El objetivo de este artículo en relación con los estudios publicados en la literatura internacional consiste en comparar las posibilidades terapéuticas que ofrecen las técnicas bilaminares y las de regeneración hística guiada (RHG) para recubrir las superficies radiculares expuestas a causa de las recesiones gingivales. La experimentación se ha realizado con 20 pacientes, 13 hombres y 7 mujeres, con edades de 25/39 años. Se dividió a los pacientes en dos grupos, A y B, según las técnicas quirúrgicas, bilaminar y regenerativa, respectivamente. Los sujetos con recesiones múltiples y adyacentes se asignaron al grupo A. Al considerar los datos de este estudio clínico, coincidentes con los de la literatura internacional, se puede afirmar que el injerto de tejido conectivo es una alternativa válida para la RHG en el tratamiento de las recesiones gingivales. De hecho, las técnicas bilaminares permiten aumentar la cantidad y el espesor de la encía insertada, tratar varias recesiones adyacentes y garantizar una gran predicibilidad en recubrimiento radicular
GPS-based CERN-LNGS time link for Borexino
We describe the design, the equipment, and the calibration of a new GPS based
time link between CERN and the Borexino experiment at the Gran Sasso Laboratory
in Italy. This system has been installed and operated in Borexino since March
2012, and used for a precise measurement of CNGS muon neutrinos speed in May
2012. The result of the measurement will be reported in a different letter.Comment: 13 pages, 11 figure
The CLASS blazar survey: testing the blazar sequence
We discuss the properties of the sources in the CLASS Blazar survey which
aims at the selection of low radio power (P(5GHz)<10^25 W Hz^-1) blazars. We
use VLA data from available catalogues and from our own observations to
constrain the radio core-dominance of the sample which, together with the flat
radio spectral index, is a signature of the blazar activity. X-ray data from
the ROSAT All Sky Survey were also collected in order to constrain the
radio-to-X-ray luminosity ratio (alpha_RX) of the sources. The data analysis
shows that more than 30% of sources at low radio power (P(5 GHz)<10^25 W Hz^-1)
have an alpha_RX steeper than that expected in the framework of the ``blazar
sequence'' recently put forward to unify the high and low power blazars. The
possibility that this result is influenced by contaminating sources in the
current sample is discussed. The conclusion is that, even if a number of
non-blazars (typically CSO/GPS sources) are expected in the survey, it is
unlikely that this constitutes the sole reason for the observed deviation. In
particular, we show 2 examples for which the blazar nature is confirmed from
VLBI data and for which the steep alpha_RX (suggesting a synchrotron peak
frequency below 10^15.5 Hz) and the low radio power (0.6-2x10^24 W Hz^-1) put
these sources outside the ``blazar sequence''. The results presented here show
the importance of a correct and unbiased sampling of the low-power regime of
the blazar population.Comment: 20 pages, accepted for publication in MNRA
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