General responses to salt stress have been investigated in the halophyte Plantago crassifolia. Seed germination was strongly inhibited by NaCl, although seed viability and germination capacity were not affected by salt pre-treatments. A concentration-dependent inhibition of plant growth was observed in the presence of NaCl, which was accompanied by the accumulation of Na+ ions in the leaves, as determined by cation exchange HPLC. A 20-fold increase of proline content in leaves was observed when plants were treated with 500 m
NaCl, suggesting a protective role against high salinity stress for this amino acid, whose possible mechanism of action is discussed. 相似文献
Summary. The methods for designing pillars in underground mines are fundamentally based on empirical formulae that do not take into
account the quality of the rock mass as an input parameter. This makes them difficult to apply in other types of ground that
are different to those used to establish each empirical formula.
To avoid this inconvenience, the present paper examines existing empirical formulae to then propose a modification of these
formulae adjusting the resistance of the pillars on the basis of the RMR (Bieniawski’s Rock Mass Rating). The compression
safety factor of the pillars is analyzed for each modified formula and a study is carried out of shear failure if planes of
weakness exist in the pillars. Finally, the safety factors of the pillars in a marble mine situated in Alicante (Southern
Spain) were calculated in order to validate the new formulae.
From the results obtained, it is concluded that this new formulation determines the safety factor of pillars of the mine with
greater reliability, provided that the pillars are isolated. At the same time, the introduction of the RMR in the formulae
results in a better fit of the strength of each pillar to the characteristics of the rock mass. 相似文献
Direct census of shoots tagged in permanent plots was used to assess the present (2000–2002)Posidonia oceanica population dynamics in 25 meadows along the Spanish Mediterranean Coast. Shoot density ranged from 154±8 to 1,551±454 shoots
m−2, absolute shoot mortality from 5±0 to 249±53 shoots m−2 yr−1, and absolute shoot recruitment from <5 ±1 to 62±42 shoots m−2yr−1. Specific shoot mortality and recruitment rates, which are mathematically and statistically (p>0.05) independent of shoot
density, varied from 0.015±0.006 to 0.282±0.138 yr−1 and 0.018±0.005 to 0.302±0.093 yr−1, respectively. Absolute shoot mortality rate was scaled to shoot density (Pearson correlation, r=0.78, p<0.0001), and variability
in specific shoot recruitment rate was partially due to differences in the percentage of growing apexes, which produce most
of the recruits within the population (Pearson correlation, r=0.50, p<0.001), demonstrating the existence of structural constraints
on shoot demography. Shoot half-life was estimated to range from 2.5 to 60.4 yr and meadow turnover times between 6.7 yr and
more than a century, provided current estimates of shoot mortality, recruitment rates, and density remain uniform. There were
differences in shoot mortality and recruitment at the regional scale, with the meadows developing along the coast of the Spanish
mainland experiencing the highest shoot mortality (Tukey test, p<0.05) and tending to exhibit the highest shoot recruitment.
The low shoot recruitment did not balance shoot mortality in most (60%) of the meadows, showing a prevalence of declining
populations among the 25 meadows studied (Wilcoxon ranked sign test, p<0.0005). This study demonstrates the power of direct
census of seagrass shoots in permanent plots to evaluate the present status of seagrass meadows, to detect on-going population
decline, and to provide some insight onto the possible factors involved. The incorporation of direct census of seagrass meadows
to monitoring programs will help provide the early-warning signals necessary to support management decisions to conserve seagrass
meadows. 相似文献
This article aims at providing a simple way for water quality monitoring in a set of reservoirs using an earth observation‐based approach and the assessment of the use of this technique for a monitoring network in order to meet the requirements and objectives of the Water Framework Directive (WFD) by the Member States of the European Union. The study carried out was preformed in 42 reservoirs of the Ebro River Basin, in the northeast of Spain. The proposed methodology is based on the development of an algorithm for the estimation of water quality by means of LANDSAT TM band reflectance. Some band ratios were used in the model as well. Trophic State Index (TSI), calculated by means of Secchi Disc Transparency data, was estimated using a forward stepwise multiple regression analysis and the TM2 band and TM1/TM2 ratio. The final results showed a large variability in water quality across reservoirs. Moreover, substantial spatial heterogeneity was also observed in the water bodies. These results demonstrate the likelihood of developing a monitoring network based on remote sensing techniques for the implementation of the WFD. 相似文献
The European Water Framework Directive requires the development of new and accurate methodologies, addressing the assessment of the physico-chemical status of transitional and coastal waters; these are considered by the Directive as the supporting elements for the final evaluation of the Ecological Quality Status.
This contribution develops new approaches in the determination of the physico-chemical status, solving some problems detected in previous contributions, i.e.: (a) fitting the classification of water bodies and typologies, by means of the stretching of the typologies, according to the natural salinity gradient of types; (b) defining reference conditions, based upon the new approach to typologies, (c) proposing accurate multivariate methodologies, in determining the physico-chemical status of the transitional and coastal waters, based upon the defined typologies and references; and (d) discussion of the results obtained by reference to methodological aspects and water quality evolution in the Basque Country, Spain (as a case-study), during the last decade. 相似文献
Consider the Earth-Moon-particle system as a Restricted Three Body Problem. There are two equilateral libration points. In the actual world system, those points are no longer relative equilibrium points mainly due to the effect of the Sun and to the noncircular motion of the Moon around the Earth. In this paper we present the problem as a perturbation of the RTBP and we look for the dynamical equivalent of L4,5. It turns out to be a quasiperiodic orbit. It is obtained for a simplified model but the procedure to obtain it is general and can be carried out with an additional computational effort. 相似文献
A discussion of the effects of Soil-Structure Interaction (SSI) on the formulation of active structural control algorithms is presented. Two approaches for incorporating SSI effects in linear optimal control theory are developed: one which performs the control analysis on a structure with a fixed base and then considers the effects of SSI on the controlled structural response; and another which performs the control analysis using a structural equation of motion reformulated to include SSI effects. The two control formulations are studied and compared using a single-degree-of-freedom structure supported through a rigid foundation resting on a linear, elastic half-space. Results show that control effectiveness is affected by the approach used in formulating the equations of motion of the interacting system. 相似文献
On the basis of numerical modelling and statistical investigations of the horizontal electrical inhomogeneities (narrow fractures, change of conductance of the surface sediments) ρmin magnetotelluric (MT)-sounding curves were found to be less distorted and, therefore, they can be used for the determination of deep conducting formations in the crust and upper mantle.Carefully selected MT curves indicate the crustal conductive layer at depths of 7–13 km and the conductive asthenosphere between 50 and 80 km.The relatively shallow position of the asthenosphere corresponds to the high heat flow (q > 80 mWm?1) in the Pannonian basin according to the empirical relation derived by Ádám (1978). 相似文献