Friction effect on stresses in ensiled granular media     

Jamila Rahmoun  Olivier Millet  Jrme Fortin 《Computers and Geotechnics》2009,36(7):1113-1124

We develop, in this paper, an analytical approach of continuous medium type which improves the theory of Janssen and other existing approaches of the same type. This approach allows to calculate the stresses in any point of the ensiled granular medium and to represent as well qualitatively as quantitatively the stress saturation effect. The influence of the friction angles is studied.  相似文献   

Temporal variability of throughfall as a function of the canopy development stage: from seasonal to intra-event scale     

José Bandeira Brasil  Eunice Maia de Andrade  Helba Araújo de Queiroz Palácio  Julio Cesar Neves dos Santos  Pedro Henrique Augusto Medeiros 《水文科学杂志》2020,65(10):1640-1651

ABSTRACT

The interception process impacts rainfall magnitude and intensity under the canopy. In this study, the effect of plant interception on throughfall characteristics was assessed in the deciduous Caatinga vegetation, at different canopy development stages and for temporal scales ranging from seasonal to the intra-event scale. Throughfall and stemflow percentages were slightly higher at the onset of the rainy season, when leaf area density is low, with resulting lower interception losses. However, there was no statistical difference among the variables at the seasonal scale. At the intra-event scale, average and maximum throughfall intensity at different time intervals showed statistical difference between the stages of canopy development. Regardless of leaf area density and rainfall depth, vegetation is able to retain all the water up to 2 min in the beginning of each rainfall event with accumulated rainfall smaller than 0.6 mm. Furthermore, the Caatinga vegetation attenuates the rainfall intensity by 30–40%.  相似文献   

Some data on the comendite type area of S. Pietro and S. Antioco islands,Sardinia     

V. Araña  F. Barberi  R. Santacroce 《Bulletin of Volcanology》1974,38(2):725-736

A summary of the available data on the peralkaline rocks of S. Pietro and S. Antioco islands, together with, new chemical analyses and some preliminary K-Ar ages are reported. Peralkaline rocks occur as ignimbrites, lava flows and domes usually deeply affected by hydrothermal alteration. Pantelleritic varieties are found within the dominantly comenditic association, which display K₂O contents higher than Na₂O ones. K-Ar data indicate that these peralkaline rocks have a middle Miocene age (? 15 m.y.). They occur in close field association with coheval andesitic and subalkaline acid volcanics belonging to the final products of the Tertiary calc-alkaline volcanic cicle of Sardinia.  相似文献   

Comparative efficacy of brown, green and red seaweeds in the control of root infecting fungi and okra     

V. Sultana  S. Ehteshamul-Haque  J. Ara  M. Athar 《International Journal of Environmental Science and Technology》2005,2(2):129-132

The effect of soil amendment by brown, green and red seaweeds was studied in controlling the root rot infecting fungi of okra seedlings in the greenhouse. The soil amendment with seaweeds Stokeyia indica, Padina pavonia (brown), Solieria robusta (red), at 1% w/w redaced Macrophomina phaseolina, Rhizoctonia solani and Fusarium solani infection on okra roots. Codium iyengarii (green) at 0.5 % w/w was effective against F solani, while at 1% w/w was found phytotoxic. S. robusta showed better control of F. solani infection when used with Pseudomonas aeruginosa than either used alone. S. robusta produced better plant height and fresh weight of shoot than P. aeruginosa. Results of the present study suggest that the use of brown seaweeds S. indica and P. pavonia alone and S. robusta alone or in combination with P. aeruginosa have great potential to control root-infecting fungi of okra with enhancement of plant growth. These seaweeds alone or in combination with P. aeruginosa may be utilized as biological control of root infecting fungi of okra.  相似文献   

eta Carinae: Binarity Confirmed     

Damineli A  Kaufer A  Wolf B  Stahl O  Lopes DF  de Araújo FX 《The Astrophysical journal》2000,536(2):L101-L104

Gas giant planets have been detected in orbit around an increasing number of nearby stars. Two theories have been advanced for the formation of such planets: core accretion and disk instability. Core accretion, the generally accepted mechanism, requires several million years or more to form a gas giant planet in a protoplanetary disk like the solar nebula. Disk instability, on the other hand, can form a gas giant protoplanet in a few hundred years. However, disk instability has previously been thought to be important only in relatively massive disks. New three-dimensional, "locally isothermal," hydrodynamical models without velocity damping show that a disk instability can form Jupiter-mass clumps, even in a disk with a mass (0.091 M middle dot in circle within 20 AU) low enough to be in the range inferred for the solar nebula. The clumps form with initially eccentric orbits, and their survival will depend on their ability to contract to higher densities before they can be tidally disrupted at successive periastrons. Because the disk mass in these models is comparable to that apparently required for the core accretion mechanism to operate, the models imply that disk instability could obviate the core accretion mechanism in the solar nebula and elsewhere.  相似文献   

Coastal risk forecast system     

André Sabino  Pedro Poseiro  Armanda Rodrigues  Maria Teresa Reis  Conceição J. Fortes  Rui Reis  João Araújo 《Journal of Geographical Systems》2018,20(2):159-184

The run-up and overtopping by sea waves are two of the main processes that threaten coastal structures, leading to flooding, destruction of both property and the environment, and harm to people. To build early warning systems, the consequences and associated risks in the affected areas must be evaluated. It is also important to understand how these two types of spatial information integrate with sensor data sources and the risk assessment methodology. This paper describes the relationship between consequences and risk maps, their role in risk management and how the HIDRALERTA system integrates both aspects in its risk methodology. It describes a case study for Praia da Vitória Port, Terceira Island, Azores, Portugal, showing that the main innovations in this system are twofold: it represents the overtopping flow and consequent flooding, which are critical for coastal and port areas protected by maritime structures, and it works also as a risk assessment tool, extremely important for long-term planning and decision-making. Moreover, the implementation of the system considers possible known variability issues, enabling changes in its behaviour as needs arise. This system has the potential to become a useful tool for the management of coastal and port areas, due to its capacity to effectively issue warnings and assess risks.  相似文献   

The massive winds of luminous peculiar B-type stars     

F. X. de Araújo  J. A. de Freitas Pacheco 《Astrophysics and Space Science》1994,219(2):267-273

The wind characteristics of a small group of luminous B-type stars are investigated. They present a momentum problem, similar to but not as obvious as that seen in Wolf-Rayet stars. However, there is no violation of a fundamental limit since the energy to be extracted from the radiation field is small. Moreover, their mass loss rates can be roughly reproduced in the context of a radiation-driven wind provided we make use of larger values for the radiative parameterk.  相似文献   

Fish assemblages as indicators of water quality in the middle Thames estuary, England (1980–1989)     

Francisco Gerson Araújo  W. Peter Williams  Roland G. Bailey 《Estuaries and Coasts》2000,23(3):305-317

Fish abundance and environmental data collected over ten years (1980–1989) from the middle Thames estuary, England, were analyzed to detect temporal trends in fish populations and relationship with environmental parameters, and to assess water quality. Fish were collected from the cooling water intake screens of West Thurrock power station, situated 35.5 km below London Bridge, in the mid-estuary. Marine species abundance were highly seasonal, with peaks in December–March for herring (Clupea harengus), sprat (Sprattus sprattus), 3-spined-stickleback (Gasterosteus aculeatus), and poor cod (Trisopterus minutus); July–August for flounder (Platichthys flesus); and September–December for sand goby (Pomatoschistus minutus), whiting (Merlangius merlangus), bass (Dicentrarchus labrax), plaice (Pleuronectes platessa), and dab (Limanda limanda). Bimodal seasonal patterns of peaks or unclear seasonality in abundance characterized marine estuarine-dependent sole (Solea solea), Nilsson's pipefish (Syngnathus rostelattus) (April/May and September/October), and pouting (Trisopterus luscus) (May and November/December); the estuarine smelt (Osmerus eperlanus) (October and January) and the catadromous eel (Anguilla anguilla) (June and October). There was substantial variation in the abundance of common species over the period of ten years, with herring, sand goby, flounder, and plaice showing a stable abundance in 1980–1984, increasing sharply in 1985–1986, and then decreasing successively through the remainder of the decade (1987–1989). The first half of the decade was a period of higher abundance for less tolerant species such as smelt, sprat, and poor cod, while the second half showed higher abundances of species tolerant to harsh environmental conditions such as sand goby, flounder, eel, and plaice. A general pattern of stable fish populations with a slight trend of deterioration was found to emerge over the years, related to the number of species and quantities of common species. Multivariate techniques of principal component and canonical correspondence ordinations were used for assessing relationships between fish populations abundance and environmental variables. The most significant environmental variables correlated with fish species were temperature and dissolved oxygen. High abundances of flounder were associated with high temperature, while high abundance of poor cod, sprat, herring, and 3-spined-stickleback were associated with high dissolved oxygen, flow, ammonical nitrogen, and low temperature. Plaice, whiting, sand goby, bass, and dab were preferentially found in high salinity and suspended solids, while smelt and sole were likely to prefer average values or showed no clear preferences.  相似文献   

Assessment of the geometry and volumes of small surface water reservoirs by remote sensing in a semi-arid region with high reservoir density     

Bruno Pereira  Till Francke  Geraldo Ramalho  Saskia Foerster  José Carlos De Araújo 《水文科学杂志》2019,64(1):66-79

Water fluxes in highly impounded regions are heavily dependent on reservoir properties. However, for large and remote areas, this information is often unavailable. In this study, the geometry and volume of small surface reservoirs in the semi-arid region of Brazil were estimated using terrain and shape attributes extracted by remote sensing. Regression models and data classification were used to predict the volumes, at different water stages, of 312 reservoirs for which topographic information is available. The power function used to describe the reservoir shapes tends to overestimate the volumes; therefore, a modified shape equation was proposed. Among the methods tested, four were recommended based on performance and simplicity, for which the mean absolute percentage errors varied from 24 to 39%, in contrast to the 94% error achieved with the traditional method. Despite the challenge of precisely deriving the flooded areas of reservoirs, water management in highly reservoir-dense environments should benefit from volume prediction based on remote sensing.  相似文献   

Regional Structural Analysis by Remote Sensing for Mineral Exploration,Paraiba State,Northeast Brazil     

Chan Chiang Liu  Manoel de Araújo Sousa Jr.  Tumkur Rajarao Gopinath 《国际地球制图》2013,28(1):70-77

Abstract

Photogeological techniques were used to analyze Landsat‐TM images of the Paraiba State, which resulted in the identification of the following structures: lineaments of regional extent, short en echelon lineaments, intricate ramification of the wrench system, and infrastructures among major lineaments and circular or ring structures. This lineament map was correlated to existing geological maps, to areas of known hydrothermal mineralization (Cu, Au, Mo, Ni, W and Ti), and the lineament map was verified in the field reconnaissance. Due to lack of systematic studies of the geology and natural resources of the region the mineral exploration is still in rudimentary stages. The objective of this research is to emphasize the detection and analysis of lineaments, their patterns, and geometry and their relations with the occurrence of mineral resources and its exploration in areas as yet explored. A large number of mineral‐bearing pegmatites of the region are controlled by major lineaments and associated minor lineaments. It is believed that the structures of interest in search for mineral deposits are warping part of the minor shear zones, the intersections of short and regional lineaments, and the circular features.  相似文献