848 research outputs found
A tree-based approach for modelling interception loss from evergreen oak mediterranean savannas
Evaporation of rainfall intercepted by tree canopies is usually an important part of the overall water balance of forested catchments and there have been many studies dedicated to measuring and modelling rainfall interception loss. These studies have mainly been conducted in dense forests; there have been few studies on the very sparse forests which are common in dry and semi-arid areas. Water resources are scarce in these areas making sparse forests particularly important. Methods for modelling interception loss are thus required to support sustainable water management in those areas. In very sparse forests, trees occur as widely spaced individuals rather than as a continuous forest canopy. We therefore suggest that interception loss for this vegetation type can be more adequately modelled if the overall forest evaporation is derived by scaling up the evaporation from individual trees. The evaporation rate for a single tree can be estimated using a simple Dalton-type diffusion equation for water vapour as long as its surface temperature is known. From theory, this temperature is shown to be dependent upon the available energy and windspeed. However, the surface temperature of a fully saturated tree crown, under rainy conditions, should approach the wet bulb temperature as the radiative energy input to the tree reduces to zero. This was experimentally confirmed from measurements of the radiation balance and surface temperature of an isolated tree crown. Thus, evaporation of intercepted rainfall can be estimated using an equation which only requires knowledge of the air dry and wet bulb temperatures and of the bulk tree-crown aerodynamic conductance. This was taken as the basis of a new approach for modelling interception loss from savanna-type woodland, i.e. by combining the Dalton-type equation with the Gash’s analytical model to estimate interception loss from isolated trees. This modelling approach was tested using data from two Mediterranean savanna-type oak woodlands in southern Portugal. For both sites, simulated interception loss agreed well with the observations indicating the adequacy of this new methodology for modelling interception loss by isolated trees in savanna-type ecosystems. Furthermore, the proposed approach is physically based and requires only a limited amount of data. Interception loss for the entire forest can be estimated by scaling up the evaporation from individual trees accounting for the number of trees per unit area
High glucose and diabetes increase the release of [3H]-D-aspartate in retinal cell cultures and in rat retinas
Several evidences suggest that glutamate may be involved in retinal neurodegeneration in diabetic retinopathy (DR). For that reason, we
investigated whether high glucose or diabetes affect the accumulation and the release of [3H]-D-aspartate, which was used as a marker of the
glutamate transmitter pool. The accumulation of [3H]-D-aspartate did not change in cultured retinal neural cells treated with high glucose (30 mM)
for 7 days. However, the release of [3H]-D-aspartate, evoked by 50 mM KCl, significantly increased in retinal cells exposed to high glucose.
Mannitol, which was used as an osmotic control, did not cause any significant changes in both accumulation and release of [3H]-D-aspartate. In the
retinas, 1 week after the onset of diabetes, both the accumulation and release of [3H]-D-aspartate were unchanged comparing to the retinas of agematched
controls. However, after 4 weeks of diabetes, the accumulation of [3H]-D-aspartate in diabetic retinas decreased and the release of [3H]-Daspartate
increased, compared to age-matched control retinas.
These results suggest that high glucose and diabetes increase the evoked release of D-aspartate in the retina, which may be correlated with the
hypothesis of glutamate-induced retinal neurodegeneration in DR
Drought-induced photosynthetic inhibition and autumn recovery in two Mediterranean oak species (Quercus ilex and Quercus suber)
Responses of leaf water relations and photosynthesis
to summer drought and autumn rewetting were studied
in two evergreen Mediterranean oak species, Quercus ilex
spp. rotundifolia and Quercus suber. The predawn leaf water
potential (ΨlPD), stomatal conductance (gs) and photosynthetic
rate (A) at ambient conditions were measured seasonally
over a 3-year period. We also measured the photosynthetic
response to light and to intercellular CO2 (A/PPFD and A/
Ci response curves) under water stress (summer) and after recovery
due to autumn rainfall. Photosynthetic parameters,
Vcmax, Jmax and triose phosphate utilization (TPU) rate, were
estimated using the Farquhar model. RuBisCo activity, leaf
chlorophyll, leaf nitrogen concentration and leaf carbohydrate
concentration were also measured. All measurements
were performed in the spring leaves of the current year. In
both species, the predawn leaf water potential, stomatal conductance
and photosynthetic rate peaked in spring, progressively
declined throughout the summer and recovered upon
autumn rainfall. During the drought period, Q. ilex maintained
a higher predawn leaf water potential and stomatal
conductance than Q. suber. During this period, we found that
photosynthesis was not only limited by stomatal closure, but
was also downregulated as a consequence of a decrease in the
maximum carboxylation rate (Vcmax) and the light-saturated
rate of photosynthetic electron transport (Jmax) in both species.
The Vcmax and Jmax increased after the first autumnal
rains and this increase was related to RuBisCo activity, leaf
nitrogen concentration and chlorophyll concentration. In addition,
an increase in the TPU rate and in soluble leaf sugar
concentration was observed in this period. The results obtained
indicate a high resilience of the photosynthetic apparatus
to summer drought as well as good recovery in the
following autumn rains of these evergreen oak species
Nonextensive statistical effects in protoneutron stars
We investigate the bulk properties of protoneutron stars in the framework of
a relativistic mean field theory based on nonextensive statistical mechanics,
characterized by power-law quantum distributions. We study the relevance of
nonextensive statistical effects on the beta-stable equation of state at fixed
entropy per baryon, in presence and in absence of trapped neutrinos, for
nucleonic and hyperonic matter. We show that nonextensive statistical effects
could play a crucial role in the structure and in the evolution of the
protoneutron stars also for small deviations from the standard Boltzmann-Gibbs
statistics.Comment: 9 pages, 7 figure
Heat stress and ACTH administration on cortisol and insulin-like growth factor I (IGF-I) levels in lactating Holstein cows
Physiological and productive responses were studied in five Holstein cows in thermal comfort (T1), stress
by exogenous adrenocorticotropic hormone (ACTH) administration (T2) and heat stress (T3) to compare
acute and punctual stress (ACTH) and prolonged stress (heat stress). During T1 and T2, cows were
housed in a climatic-free stall barn. In T3, the animals were kept in a climatic room (air temperature of
37°C from 08:00 to 13:00 h, and of 26°C from 14:00 to 07:00 h) for 7 days. Milk yield, rectal temperature
(RT), respiratory rate (RR) and blood samples were obtained before, during and after all treatments. In
T1 at 08:00 h, RT and RR were below the upper critical limit. Simultaneously, cortisol and insulin
growth-factor I (IGF-I) were within the normal limits. After ACTH administration (T2), cortisol
significantly increased, reaching maximum levels at 60 min and returning to basal levels at 300 min.
However, IGF-I was not affected. During T3, Holstein cows did not effectively dissipate their body
temperature and RT, RR and cortisol significantly increased. There was a 26.6% reduction in milk
production after heat stress (P < .05). Prolonged heat stress was more stressful and cows had higher
levels of CORT in T3 than in T2 even before the increase in body temperature. Although the total
amount of cortisol and IGF-I presented a negative and significant Pearson correlation (r = −0.79), IGF-I was not significantly influenced by heat stress or ACTH administration, and the relationship between
IGF-I and heat stress remains controversial
Nonextensive statistical effects in the quark-gluon plasma formation at relativistic heavy-ion collisions energies
We investigate the relativistic equation of state of hadronic matter and
quark-gluon plasma at finite temperature and baryon density in the framework of
the non-extensive statistical mechanics, characterized by power-law quantum
distributions. We impose the Gibbs conditions on the global conservation of
baryon number, electric charge and strangeness number. For the hadronic phase,
we study an extended relativistic mean-field theoretical model with the
inclusion of strange particles (hyperons and mesons). For the quark sector, we
employ an extended MIT-Bag model. In this context we focus on the relevance of
non-extensive effects in the presence of strange matter.Comment: 12 pages, 5 figure
Effect of artificial shading on performance and reproductive parameters of semi-confined young Brangus bulls
Thirty Brangus bulls were used in a 90-d study to assess the effect of artificial shading on the performance and
reproductive characteristics of semi-confined cattle. Animals were kept in four one-ha paddocks in two groups of
eight for shade treatment (5 m²/animal of 80% solar block shade cloth) and two groups of seven animals in no-shade
treatment. Each treatment had two homogeneous groups, each divided into heavy-bulls (351-450 kg) and light-bulls
(300-350 kg). Time spent under shade, time standing, average daily gain, testicular development and sperm quality
were investigated. Animals spent 24% of the daylight under the shade and no-shaded bulls spent more time standing
(P 0.05) and testicular development between shaded and
no-shaded animals. However, scrotal perimeter was higher for shaded light animals compared to no-shaded light
bulls (P < 0.10). Sperm motility increase during the experimental period for shaded animals (P < 0.05) and sperm
abnormalities were higher for the shaded ones (P < 0.05). Although the results did not indicate pronounced benefits on
cattle performance, this resource was an important alternative because it appears to provide an improvement in some
reproductive parameters and ensure a better thermal comfort to the animals
Searching for planar signatures in WMAP
We search for planar deviations of statistical isotropy in the Wilkinson
Microwave Anisotropy Probe (WMAP) data by applying a recently introduced
angular-planar statistics both to full-sky and to masked temperature maps,
including in our analysis the effect of the residual foreground contamination
and systematics in the foreground removing process as sources of error. We
confirm earlier findings that full-sky maps exhibit anomalies at the planar
() and angular () scales and , which
seem to be due to unremoved foregrounds since this features are present in the
full-sky map but not in the masked maps. On the other hand, our test detects
slightly anomalous results at the scales and in the
masked maps but not in the full-sky one, indicating that the foreground
cleaning procedure (used to generate the full-sky map) could not only be
creating false anomalies but also hiding existing ones. We also find a
significant trace of an anomaly in the full-sky map at the scale
, which is still present when we consider galactic cuts of
18.3% and 28.4%. As regards the quadrupole (), we find a coherent
over-modulation over the whole celestial sphere, for all full-sky and cut-sky
maps. Overall, our results seem to indicate that current CMB maps derived from
WMAP data do not show significant signs of anisotropies, as measured by our
angular-planar estimator. However, we have detected a curious coherence of
planar modulations at angular scales of the order of the galaxy's plane, which
may be an indication of residual contaminations in the full- and cut-sky maps.Comment: 15 pages with pdf figure
Perturbations of generic Kasner spacetimes and their stability
This article investigates the stability of a generic Kasner spacetime to
linear perturbations, both at late and early times. It demonstrates that the
perturbation of the Weyl tensor diverges at late time in all cases but in the
particular one in which the Kasner spacetime is the product of a
two-dimensional Milne spacetime and a two-dimensional Euclidean space. At early
times, the perturbation of the Weyl tensor also diverges unless one imposes a
condition on the perturbations so as to avoid the most divergent modes to be
excited.Comment: 17 pages, 6 figure
Effects of anisotropic dynamics on cosmic strings
The dynamics of cosmic strings is considered in anisotropic backgrounds. In
particular, the behaviour of infinitely long straight cosmic strings and of
cosmic string loops is determined. Small perturbations of a straight cosmic
string are calculated. The relevance of these results is discussed with respect
to the possible observational imprints of an anisotropic phase on the behaviour
of a cosmic string network.Comment: 16 pages, 9 figures; matches version published in JCA
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