1,727 research outputs found
Bringing the margin to the focus: 10 challenges for riparian vegetation science and management
PerspectiveRiparian zones are the paragon of transitional ecosystems, providing critical
habitat and ecosystem services that are especially threatened by global change.
Following consultation with experts, 10 key challenges were identified to be
addressed for riparian vegetation science and management improvement:
(1) Create a distinct scientific community by establishing stronger bridges
between disciplines; (2) Make riparian vegetation more visible and appreciated
in society and policies; (3) Improve knowledge regarding biodiversity—
ecosystem functioning links; (4) Manage spatial scale and context-based issues;
(5) Improve knowledge on social dimensions of riparian vegetation; (6) Anticipate
responses to emergent issues and future trajectories; (7) Enhance tools to
quantify and prioritize ecosystem services; (8) Improve numerical modeling
and simulation tools; (9) Calibrate methods and increase data availability for
better indicators and monitoring practices and transferability; and (10) Undertake
scientific validation of best management practices. These challenges are
discussed and critiqued here, to guide future research into riparian vegetationinfo:eu-repo/semantics/publishedVersio
p-Type semiconducting properties in lithium-doped MgO single crystals
The phenomenally large enhancement in conductivity observed when Li-doped MgO
crystals are oxidized at elevated temperatures was investigated by dc and ac
electrical measurements in the temperature interval 250-673 K. The
concentration of ([Li]^{0}) centers (Li^{+} ions each with a trapped hole)
resulting from oxidation was monitored by optical absorption measurements.
Both dc and ac experiments provide consistent values for the bulk resistance.
The electricalconductivity of oxidized MgO:Li crystals increases linearly with
the concentration of ([Li]^{0}) centers. The conductivity is thermally
activated with an activation energy of (0.70 +/- 0.01) eV, which is independent
of the ([Li]^{0}) content. The \textit{standard semiconducting} mechanism
satisfactorily explains these results. Free holes are the main contribution to
band conduction as they are trapped at or released from the ([Li]^{0})-acceptor
centers.
In as-grown MgO:Li crystals, electrical current increases dramatically with
time due to the formation of ([Li]^{0}) centers. The activation energy values
between 1.3 and 0.7 eV are likely a combination of the activation energy for
the creation of ([Li]^{0}) centers and the activation energy of ionization of
these centers. Destruction of ([Li]^{0}) centers can be induced in oxidized
crystals by application of an electric field due to Joule heating up to
temperatures at which ([Li]^{0}) centers are not stable.Comment: LaTeX, 20 pages, 9 Encapsulated Postscript Format Figures, use the
version 4.0 of REVTEX 4 macro packag
The psychometric structure of the Spanish language version of the Iowa-Netherlands Comparison Orientation Measure in Spain and Chile
The present study investigated the structure of the Spanish version of the Iowa-Netherlands Comparison Orientation Measure (INCOM-E), an 11-item measure that assesses individual differences in social comparison orientation (SCO), i.e., the extent to which people compare themselves with others. Data came from samples from Spain (n = 1,133) and Chile (n = 2,757). Confirmatory Factor Analyses and Mokken Scale Analyses supported in both samples not the assumed two-factor structure, but a single factor structure, consisting of eight items. The resulting eight-item version of the INCOM-E was reliable in both samples, according the Gutmann's lambda-2 (.82 in Spain and.83 in Chile), and correlated very strongly with the full-length INCOM-E (.93 in Spain and.97 in Chile). In both samples, there were significant sex differences, ps <.001 with small effect sizes, ƞ2 in both samples =.01,but in the Spanish sample women scored higher, and in the Chilean sample men scored higher in SCO. The relationship with age was negative and significant (ps <.001) in both samples, albeit small (r =.22 in Spain and.13 in Chile) Based on the present research, it is advised to use the shortened eight-item version of the INCOM-E in Spanish speaking countries
Movement velocity can be used to estimate the relative load during the bench press and leg press exercises in older women
Background: Movement velocity has been proposed as an effective tool to prescribe
the load during resistance training in young healthy adults. This study aimed to
elucidate whether movement velocity could also be used to estimate the relative load
(i.e., % of the one-repetition maximum (1RM)) in older women.
Methods: A total of 22 older women (age = 68.2 ± 3.6 years, bench press 1RM = 22.3 ±
4.7 kg, leg press 1RM = 114.6 ± 15.9 kg) performed an incremental loading test during
the free-weight bench press and the leg press exercises on two separate sessions.
The mean velocity (MV) was collected with a linear position transducer.
Results: A strong linear relationship between MV and the relative load was
observed for the bench press (%1RM = -130.4 MV + 119.3; r2 = 0.827, standard
error of the estimate (SEE) = 6.10%1RM, p < 0.001) and leg press exercises
(%1RM = -158.3 MV + 131.4; r2 = 0.913, SEE = 5.63%1RM, p < 0.001). No
significant differences were observed between the bench press and leg press exercises
for the MV attained against light-medium relative loads (>70%1RM), while the MV
associated with heavy loads (>80%1RM) was significantly higher for the leg press.
Conclusions: These results suggest that the monitoring of MV could be useful to
prescribe the loads during resistance training in older women. However, it should be
noted that the MV associated with a given %1RM is significantly lower in older
women compared to young healthy individuals
On domain walls in a Ginzburg-Landau non-linear S^2-sigma model
The domain wall solutions of a Ginzburg-Landau non-linear -sigma hybrid
model are unveiled. There are three types of basic topological walls and two
types of degenerate families of composite - one topological, the other
non-topological- walls. The domain wall solutions are identified as the finite
action trajectories (in infinite time) of a related mechanical system that is
Hamilton-Jacobi separable in sphero-conical coordinates. The physical and
mathematical features of these domain walls are thoroughly discussed.Comment: 26 pages, 18 figure
Estudio de factores causales de deserción en alumnos de ciencias veterinarias
La deserción constituye un problema importante del sistema nacional de educación formal. La Facultad de Ciencias Agrarias y Veterinarias de la UCASAL (Salta, Argentina) se propuso determinar la tasa de deserción de alumnos de veterinaria y las posibles causas que inciden en ella. Se efectuó la recolección, organización, presentación y análisis de la información, tomando como población las cohortes de los años 2009 a 2013. El análisis de los datos obtenidos estuvo basado en estadísticas descriptivas (tendencia central, dispersión y coeficiente de variación). El porcentaje de deserción resultó del 33%. Se determinaron las causas del abandono y se formularon estrategias para su corrección. Se estima que tales medidas generarán una disminución de la deserción y por ende una mejor calidad educativa
Answering Twitter Questions: a Model for Recommending Answerers through Social Collaboration
International audienceIn this paper, we specifically consider the challenging task of solving a question posted on Twitter. The latter generally remains unanswered and most of the replies, if any, are only from members of the questioner's neighborhood. As outlined in previous work related to community Q&A, we believe that question-answering is a collaborative process and that the relevant answer to a question post is an aggregation of answer nuggets posted by a group of relevant users. Thus, the problem of identifying the relevant answer turns into the problem of identifying the right group of users who would provide useful answers and would possibly be willing to collaborate together in the long-term. Accordingly, we present a novel method, called CRAQ, that is built on the collaboration paradigm and formulated as a group entropy optimization problem. To optimize the quality of the group, an information gain measure is used to select the most likely " informative " users according to topical and collaboration likelihood predictive features. Crowd-based experiments performed on two crisis-related Twitter datasets demonstrate the effectiveness of our collaborative-based answering approach
Spectro-photometric close pairs in GOODS-S: major and minor companions of intermediate-mass galaxies
(Abriged) Our goal here is to provide merger frequencies that encompass both
major and minor mergers, derived from close pair statistics. We use B-band
luminosity- and mass-limited samples from an Spitzer/IRAC-selected catalogue of
GOODS-S. We present a new methodology for computing the number of close
companions, Nc, when spectroscopic redshift information is partial. We select
as close companions those galaxies separated by 6h^-1 kpc < rp < 21h^-1 kpc in
the sky plane and with a difference Delta_v <= 500 km s^-1 in redshift space.
We provide Nc for four different B-band-selected samples. Nc increases with
luminosity, and its evolution with redshift is faster in more luminous samples.
We provide Nc of M_star >= 10^10 M_Sun galaxies, finding that the number
including minor companions (mass ratio >= 1/10) is roughly two times the number
of major companions alone (mass ratio >= 1/3) in the range 0.2 <= z < 1.1. We
compare the major merger rate derived by close pairs with the one computed by
morphological criteria, finding that both approaches provide similar merger
rates for field galaxies when the progenitor bias is taken into account.
Finally, we estimate that the total (major+minor) merger rate is ~1.7 times the
major merger rate. Only 30% to 50% of the M_star >= 10^10 M_Sun early-type
(E/S0/Sa) galaxies that appear z=1 and z=0 may have undergone a major or a
minor merger. Half of the red sequence growth since z=1 is therefore unrelated
to mergers.Comment: Accepted in A&A. 14 pages, 6 figures, 8 tables. We have tested the
method with a local, volume-limited spectroscopic sample
AGN-Host Galaxy Connection: Morphology and Colours of X-ray Selected AGN at z < 2
The connection between AGN and their host galaxies has been widely studied
over recent years, showing it to be of great importance for providing answers
to some fundamental questions related with AGN fueling mechanisms, their
formation and evolution. Using X-ray and one of the deepest broad-band optical
data sets, we studied morphology and colours in relationship with X-ray
properties for sources at redshifts z < 2.0, using a sample of 262 AGN in the
Subaru/XMM-Newton Deep Survey (SXDS). Morphological classification was obtained
using the galSVM code, one of the new methods useful especially when dealing
with high-redshift sources and low-resolution data. Colour-magnitude diagrams
were studied in relationship with redshift, morphology, X-ray obscuration, and
X-ray-to-optical flux ratio. Finally, the significance of different regions was
analysed on colour-magnitude diagrams, relating the observed properties of AGN
populations with some models of their formation and evolution.Comment: 24 pages, 19 figures, accepted for publication in
Astronomy&Astrophysic
Study of star-forming galaxies in SDSS up to redshift 0.4 II. Evolution from the fundamental parameters: mass, metallicity & SFR
To understand the formation and evolution of galaxies, it is important to
have a full comprehension of the role played by the metallicity, star formation
rate (SFR), morphology, and color. The interplay of these parameters at
different redshifts will substantially affect the evolution of galaxies and, as
a consequence, the evolution of them will provide important clues and
constraints on the galaxy evolution models. In this work we focus on the
evolution of the SFR, metallicity of the gas, and morphology of galaxies at low
redshift in search of signs of evolution. We use the S2N2 diagnostic diagram as
a tool to classify star--forming, composite, and AGN galaxies. We analyzed the
evolution of the three principal BPT diagrams, estimating the SFR and specific
SFR (SSFR) for our samples of galaxies, studying the luminosity and
mass-metallicity relations, and analyzing the morphology of our sample of
galaxies through the g-r color, concentration index, and SSFR. We found that
the S2N2 is a reliable diagram to classify star--forming, composite, and AGNs
galaxies. We demonstrate that the three principal BPT diagrams show an
evolution toward higher values of [OIII]5007/Hb due to a metallicity decrement.
We found an evolution in the mass-metallicity relation of ~ 0.2 dex for the
redshift range 0.3 < z < 0.4 compared to our local one. From the analysis of
the evolution of the SFR and SSFR as a function of the stellar mass and
metallicity, we discovered a group of galaxies with higher SFR and SSFR at all
redshift samples, whose morphology is consistent with those of late-type
galaxies. Finally, the comparison of our local (0.04<z<0.1) with our higher
redshift sample (0.3<z<0.4), show that the metallicity, the SFR and morphology,
evolve toward lower values of metallicity, higher SFRs, and late--type
morphologies for the redshift range 0.3<z<0.4Comment: 16 pages, 15 figures. Accepted for publication in A&
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