排序方式： 共有25条查询结果，搜索用时 15 毫秒
1.
Salinity and periodic inundation controls on the soil‐plant‐atmosphere continuum of gray mangroves 
下载免费PDF全文
下载免费PDF全文 Salinity and periodic inundation are both known to have a major role in shaping the ecohydrology of mangroves through their controls on water uptake, photosynthesis, stomatal conductance, gas exchanges, and nutrient availability. Salinity, in particular, can be considered one of the main abiotic regulating factors for halophytes and salt‐tolerant species, due to its influence on water use patterns and growth rate. Ecohydrological literature has rarely focused on the effects of salinity on plant transpiration, based on the fact that the terrestrial plants mostly thrive in low‐saline, unsaturated soils where the role of osmotic potential can be considered negligible. However, the effect of salinity cannot be neglected in the case of tidal species like mangroves, which have to cope with hyperosmotic conditions and waterlogging. We introduce here a first‐order ecohydrological model of the soil/plant‐atmosphere continuum of Avicennia marina—also known as gray mangrove—a highly salt‐tolerant pioneer species able to adapt to hyperarid intertidal zones and characterized by unique morphological and ecophysiological traits. The A. marina's soil‐plant‐atmosphere continuum takes explicitly into account the role of water head, osmotic water potential, and water salinity in governing plant water fluxes. A. marina's transpiration is thus modeled as a function of salinity based on a simple parameterization of salt exclusion mechanisms at the root level and a modified Jarvis' expression accounting for the effects of salinity on stomatal conductance. Consistently with previous studies investigating the physiology of mangroves in response to different environmental drivers, our results highlight the major influence of salinity on mangrove transpiration when contrasted with other potential stressors such as waterlogging and water stress. 相似文献
2.
Weathering characterization for landslides modeling in granitoid rock masses of the Capo Vaticano promontory (Calabria,Italy) 总被引：1，自引：1，他引：0
This work focuses on developing multidisciplinary researches concerning weathering profiles related to landscape evolution of the Capo Vaticano promontory on the Calabria Tyrrhenian side (southern Italy). In this area, the tectonic uplift, occurred at least since Pleistocene, together with the Mediterranean climatic conditions, is the main cause of deep weathering and denudation processes. The latter occurred on the outcropping rocks of the crystalline-metamorphic basement, made up of weathered granitoids, in turn belonging to the Monte Poro granitoid complex (intermediate to felsic plutonic rocks covered by Cenozoic sedimentary successions). Field observations coupled to borehole explorations, geophysical surveys, and minero-petrographical analyses allowed the characterization of the granitoid outcrops typical of the studied area in terms of kind and degree of slope instability. This characterization was based on suitable correlations verified between several factors as weathering degree, elastic properties of rocks, and discontinuity features. Weathering profiles are mainly composed by rock masses varying from completely weathered rock with corestones of highly weathered rock (classes IV–V) to slightly weathered rocks (class II). The weathered rocks are involved in several landslide typologies such as debris flow (frequency 48.5%), translational slide (frequency 33.3%), and minor rock fall and rotational slide (frequency 9%). The achieved data allowed the establishment of a general correlation between weathering degree and type of slope instability. Debris flow-type instabilities are predominant on the steeper slopes, involving very poor rock masses ascribed to the shallowest portions of the weathering class IV. Translational slides are less widespread than the previous ones and often involve a mixture of soil and highly weathered rocks. Rotational slides are more frequently close to the top of the slopes, where the thicknesses of more weathered rocks increase, and involve mainly rock masses belonging to the weathering classes IV and V. Rock falls mostly occur on the vertical escarpments of the road cuts and are controlled by the characteristics of the main discontinuities. The assessment of rock mass rating and slope mass rating, based on the application of the discontinuity data, allowed respectively an evaluation of the quality of rock masses and of the susceptibility of rock slopes to failure. The comparison between the last one and the real stability conditions along the cut slopes shows a good correspondence. Finally, the geological strength index system was also applied for the estimation of rock mass properties. The achieved results give a worthy support for a better understanding of the relationship between the distribution of landslides and the geological features related to different weathering degrees. Therefore, they can provide a reliable tool to evaluate the potential stability conditions of the rock slopes in the studied area and a general reference framework for the study of weathering processes in other regions with similar geological features. 相似文献
3.
4.
The reduced magnetic helicity is a quantity related to the handedness of the magnetic field fluctuations. In the present paper we study the scaling law of the reduced magnetic helicity in fast streams in the solar wind by using high-resolution magnetic field data by the Ulysses spacecraft. We show that at high frequencies both the left-hand and the right-hand helicity survives, implying that there is no predominance of a single sign. In addition, the scaling law of the magnetic helicity exhibits a strong dependence on the data set analyzed and we do not observe any universal behavior. 相似文献
5.
6.
7.
Pure and Applied Geophysics - 相似文献
8.
P. A. Evans A. P. Beardmore K. L. Page J. P. Osborne P. T. O'Brien R. Willingale R. L. C. Starling D. N. Burrows O. Godet L. Vetere J. Racusin M. R. Goad K. Wiersema L. Angelini M. Capalbi G. Chincarini N. Gehrels J. A. Kennea R. Margutti D. C. Morris C. J. Mountford C. Pagani M. Perri P. Romano N. Tanvir 《Monthly notices of the Royal Astronomical Society》2009,397(3):1177-1201
We present a homogeneous X-ray analysis of all 318 gamma-ray bursts detected by the X-ray telescope (XRT) on the Swift satellite up to 2008 July 23; this represents the largest sample of X-ray GRB data published to date. In Sections 2–3 , we detail the methods which the Swift -XRT team has developed to produce the enhanced positions, light curves, hardness ratios and spectra presented in this paper. Software using these methods continues to create such products for all new GRBs observed by the Swift -XRT. We also detail web-based tools allowing users to create these products for any object observed by the XRT, not just GRBs. In Sections 4–6 , we present the results of our analysis of GRBs, including probability distribution functions of the temporal and spectral properties of the sample. We demonstrate evidence for a consistent underlying behaviour which can produce a range of light-curve morphologies, and attempt to interpret this behaviour in the framework of external forward shock emission. We find several difficulties, in particular that reconciliation of our data with the forward shock model requires energy injection to continue for days to weeks. 相似文献
9.
D. Rizzuto C. Guidorzi P. Romano S. Covino S. Campana M. Capalbi G. Chincarini G. Cusumano D. Fugazza V. Mangano A. Moretti M. Perri G. Tagliaferri 《Monthly notices of the Royal Astronomical Society》2007,379(2):619-628
We test the gamma-ray burst (GRB) correlation between temporal variability and peak luminosity of the γ-ray profile on a homogeneous sample of 36 Swift /Burst Alert Telescope (BAT) GRBs with firm redshift determination. This is the first time that this correlation can be tested on a homogeneous data sample. The correlation is confirmed, as long as the six GRBs with low luminosity ( <5 × 1050 erg s−1 in the rest-frame 100–1000 keV energy band) are ignored. We confirm that the considerable scatter of the correlation already known is not due to the combination of data from different instruments with different energy bands, but it is intrinsic to the correlation itself. Thanks to the unprecedented sensitivity of Swift /BAT, the variability/peak luminosity correlation is tested on low-luminosity GRBs. Our results show that these GRBs are definite outliers. 相似文献
10.
When a planetary core composed of condensed matter is accumulated in the primitive solar nebula, the gas of the nebula becomes gravitationally concentrated as an envelope surrounding the planetary core. Models of such gaseous envelopes have been constructed subject to the assumption that the gas everywhere is on the same adiabat as that in the surrounding nebula. The gaseous envelope extends from the surface of the core to the distance at which the gravitational attraction of core plus envelope becomes equal to the gradient of the gravitational potential in the solar nebula; at this point the pressure and temperature of the gas in the envelope are required to attain the background values characteristics of the solar nebula. In general, as the mass of the condensed core increases, increasing amounts of gas became concentrated in the envelope, and these envelopes are stable against hydrodynamic instabilities. However, the core mass then goes through a maximum and starts to decrease. In most of the models tested, the envelopes were hydrodynamically unstable beyond the peak in the core mass. An unstable situation was always created if it was insisted that the core mass contain a larger amount of matter than given by these solutions. For an initial adiabat characterized by a temperature of 450°K and a pressure of 5 × 10?6 atm, the maximum core mass at which instability occurs is approximately 115 earth masses; this value is rather insensitive to the position in the solar nebula or to the background pressure of the solar nebula. However, if the adiabat is lowered, then the core mass corresponding to instability is decreased. Since the core masses found by Podolak and Cameron for the giant planets are significantly less than the critical core mass corresponding to the initial solar nebula adiabat, we conclude that the giant planets obtained their large amounts of hydrogen and helium by a hydrodynamic collapse process in the solar nebula only after the nebula had been subjected to a considerable period of cooling. 相似文献