Turbulence Statistics Above And Within Two Amazon Rain Forest Canopies   总被引：1，自引：1，他引：0  

B. Kruijt  Y. Malhi  J. Lloyd  A. D. Norbre  A. C. Miranda  M. G. P. Pereira  A. Culf  J. Grace 《Boundary-Layer Meteorology》2000,94(2):297-331

The turbulence structure in two Amazon rain forestswas characterised for a range of above-canopystability conditions, and the results compared withprevious studies in other forest canopies and recenttheory for the generation of turbulent eddies justabove forest canopies. Three-dimensional wind speedand temperature fluctuation data were collectedsimultaneously at up to five levels inside and abovetwo canopies of 30–40 m tall forests, during threeseparate periods. We analysed hourly statistics, jointprobability distributions, length scales, spatialcorrelations and coherence, as well as power spectraof vertical and horizontal wind speed.The daytime results show a sharp attenuation ofturbulence in the top third of the canopies, resultingin very little movement, and almost Gaussianprobability distributions of wind speeds, in the lowercanopy. This contrasts with strongly skewed andkurtotic distributions in the upper canopy. At night,attenuation was even stronger and skewness vanishedeven in the upper canopy. Power spectral peaks in thelower canopy are shifted to lower frequencies relativeto the upper canopy, and spatial correlations andcoherences were low throughout the canopy. Integrallength scales of vertical wind speed at the top of thecanopy were small, about 0.15 h compared to avalue of 0.28 h expected from the shear lengthscale at the canopy top, based on the hypothesis that theupper canopy air behaves as a plane mixing layer. Allthis suggests that, although exchange is not totallyinhibited, tropical rain forest canopies differ from other forests in that rapid, coherentdownward sweeps do not penetrate into the lowercanopy, and that length scales are suppressed. This isassociated with a persistent inversion of stability inthat region compared to above-canopy conditions. Theinversion is likely to be maintained by strong heatabsorption in the leaves concentrated near thecanopy top, with the generally weak turbulence beingunable to destroy the temperature gradients over thelarge canopy depth.  相似文献   

The story of galaxy evolution in full colour     

Richard S Ellis  Roberto G Abraham  Jarle Brinchmann  Felipe Menanteau 《Astronomy& Geophysics》2000,41(2):2.10-2.16

A Holy Grail of modern astronomy is understanding the origin of Edwin Hubble's morphological sequence of galaxy types. What made some collapsing gas clouds turn into elegant spiral systems like our own Milky Way, whereas others became smooth, featureless ellipticals? More fundamentally, does the taxonomic scheme introduced by Hubble in the 1920s have any physical relevance? The Space Telescope that bears Hubble's name is providing answers to these and other questions in the context of modern theories of structure formation.
Richard S Ellis, Roberto G Abraham, Jarle Brinchmann and Felipe Menanteau show how modern telescopes producing colourful images are pointing the way to understanding galaxy evolution.  相似文献   

Quantum Instability of Magnetized Stellar Objects     

R. González Felipe  H. J. Mosquera Cuesta  A. Pérez Martínez  H. Pérez Rojas 《中国天文和天体物理学报》2005,5(4):399-411

The equations of state for degenerate electron and neutron gases are studied in the presence of magnetic fields. After including quantum effects in the investigation of the structural properties of these systems, it is found that some hypermagnetized stars can be unstable according to the criterion of stability of pressures. Highly magnetized white dwarfs should collapse producing a supernova type Ia, while superstrong magnetized neutron stars cannot stand their own magnetic field and must implode, too. A comparison of our results with a set of the available observational data of some compact stars is also presented, and the agreement between this theory and observations is verified.  相似文献   

Improving reservoir description by using geostatistical and multivariate data analysis techniques     

Henrique Garcia Pereira  António Costa e Silva  Amilcar Soares  Luis Ribeiro  Justino de Carvalho 《Mathematical Geosciences》1990,22(8):879-913

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High-Frequency Response of the Atmospheric Electric Potential Gradient Under Strong and Dry Boundary-Layer Convection     

Ricardo Conceição  Hugo Gonçalves Silva  Alec Bennett  Rui Salgado  Daniele Bortoli  Maria João Costa  Manuel Collares Pereira 《Boundary-Layer Meteorology》2018,166(1):69-81

The spectral response of atmospheric electric potential gradient gives important information about phenomena affecting this gradient at characteristic time scales ranging from years (e.g., solar modulation) to fractions of a second (e.g., turbulence). While long-term time scales have been exhaustively explored, short-term scales have received less attention. At such frequencies, space-charge transport inside the planetary boundary layer becomes a sizeable contribution to the potential gradient variability. For the first time, co-located (Évora, Portugal) measurements of boundary-layer backscatter profiles and the 100-Hz potential gradient are reported. Five campaign days are analyzed, providing evidence for a relation between high-frequency response of the potential gradient and strong dry convection.  相似文献   

Biogeochemical behavior of Ampelozizyphus amazonicus Ducke in the Pitinga mining district, Amazon, Brazil     

M. C. Lima e Cunha  V. P. Pereira  E. Menegotto  A. C. Bastos Neto  L. D. Oliveira  M. L. L. Formoso 《Environmental Geology》2008,55(6):1355-1362

The vegetal species Ampelozizyphus amazonicus Ducke (Rhamnaceae Family) was chosen as a sampling medium for the lateritic surfaces of the Pitinga Mine in the Amazon region, in order to study the biogeochemical behavior of this species and compare it with the chemical composition of a reference plant. The Pitinga mining district is one of the largest producers of tin in the world. This district contains unique deposits of cryolite and rare metals such as Zr, Nb, Ta, Y and REEs related to granitic bodies that intrude into the volcanic and acid pyroclastic rocks. The results showed that the species A. amazonicus predominantly concentrates significant levels of Zr, Nb, Ta, Th, Be, Sc over U, Hf, Ga and In. These elements are characteristic of the mineral paragenesis for the region, suggesting that this plant can provide a representative sampling medium future geochemical exploration programs in the region.  相似文献   

Facies analyses and volcanic setting of the giant Neves Corvo massive sulfide deposit,Iberian Pyrite Belt,Portugal     

Carlos J. P. Rosa  Jocelyn McPhie  Jorge M. R. S. Relvas  Zélia Pereira  Tomás Oliveira  Nelson Pacheco 《Mineralium Deposita》2008,43(4):449-466

In the Iberian Pyrite Belt, volcanic rocks are relatively scarce, accounting for approximately only 25% of the geologic record, with the remaining 75% consisting of sedimentary units. This association is very clear in the host succession to the Neves Corvo massive sulfide deposit in Portugal. The Neves Corvo host succession comprises the products of explosive and effusive rhyolitic eruptions intercalated with mudstone that records a submarine below-wave-base environment and provides precise biostratigraphic age constraints. The first and second volcanic events involved eruptions at local intrabasinal vents. The first event generated thick beds of fiamme breccia that are late Famennian in age. The fiamme were originally pumice clasts produced by explosive eruptions and were subsequently compacted. The second event was the late Strunian (latest Famennian) effusion of rhyolitic lava that was pervasively quench-fragmented. The third and final event is younger than the massive sulfide deposits poorly represented in the mine area and minor compared with the two other events. The integration of biostratigraphic data with the volcanic facies architecture indicates that the Neves Corvo ore deposits are similar in age to the late Strunian rhyolitic lava. Although regionally the Iberian Pyrite Belt is essentially a sedimentary succession, ore formation at Neves Corvo can be closely linked to discrete volcanic events that produced a relatively narrow range of volcanic facies.  相似文献   

Vitellogenin in winter flounder (Pleuronectes americanus) from Long Island Sound and Boston Harbor     

J. J. Pereira  J. Ziskowski  R. Mercaldo-Allen  C. Kuropat  D. Luedke  E. Gould 《Estuaries and Coasts》1992,15(3):289-297

Vitellogenin is an egg-yolk precursor protein in teleosts which is crucial to the survival of larvae. Manufactured in the liver, where pollutants are known to accumulate, and transported to the ovary by the blood, its synthesis by the liver or uptake by the gonad can be compromised by accumulation of xenobiotics. In three studies, winter flounder (Pleuronectes americanus) blood samples were taken to determine normal levels of vitellogenin during the reproductive cycle, and to learn how its production might be affected in degraded environments. Specifically, these studies followed the seasonal cycle of vitellogenin production in winter flounder through monthly sampling at relatively clean (Shoreham, New York) and degraded areas (Black Rock and New Haven harbors, Connecticut) in Long Island Sound; examined the relationship between parental vitellogenin levels and survival of offspring by sampling fish that had been spawned at the Milford Laboratory for a reproductive success study; and determined the effect of gross liver lesions on vitellogenin production by sampling flounder from Boston Harbor, Massachusetts, which have been reported to have a high prevalence of liver tumors. Blood vitellogenin levels were determined by measuring alkali-labile phosphate (ALP). Large fish (>30 cm) from the two degraded sites had elevated serum ALP levels relative to those from the clean area. Lowered total ovarian lipid levels in large fish from Black Rock Harbor suggested impaired vitellogenin uptake. There were no significant differences in serum ALP among the small (≤30 cm) fish from the three sampling sites. Boston Harbor flounder with gross liver lesions had lower ALP values than fish without such lesions. There were no significant differences in ALP values among the spawned fish.  相似文献   

UV observations of the symbiotic star EG And     

Claudio Bastos Pereira 《Astrophysics and Space Science》1996,240(1):1-11

EG And is a S-type symbiotic star. Presented are UV observations made by IUE from 1978 to 1991. From these observations the electron density and the electron temperature were obtained. The size of the Heii emitting region was estimated as 7.3R. Line and continuum variations confirm the binary nature of EG And.  相似文献   

A two-surface plasticity model for stiff clay   总被引：1，自引：1，他引：0  

P. Y. Hong  J. M. Pereira  A. M. Tang  Y. J. Cui 《Acta Geotechnica》2016,11(4):871-885

This paper presents a constitutive model for describing some important features of the behavior of natural stiff clay evidenced experimentally such as the limited elastic zone, the presence of strain hardening and softening, and the smooth transition from elastic behavior to a plastic one. The model, namely ACC-2, is an adapted Modified Cam Clay model with two yield surfaces: similarly to bounding surface plasticity theory, an additional yield surface—namely Inner yield surface—was adopted to account for the plastic behavior inside the conventional yield surface. A progressive plastic hardening mechanism was introduced with a combined volumetric-deviatoric hardening law associated with the Inner yield surface, enabling the plastic modulus to vary smoothly during loading paths. The main feature of the proposed model is that its constitutive equations can be simply formulated based on the consistency condition for the Inner yield surface, so that it can be efficiently implemented in a finite element code using a stress integration scheme similar to that of the Modified Cam Clay model. Furthermore, it is proved to be an appropriate model for natural stiff clay: the simulations of a set of tests along different mechanical loading paths on natural Boom Clay show good agreement with the experimental results.  相似文献