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11.
J. A. Kamalakar K. V. S. Bhaskar A. S. Laxmi Prasad R. Ranjith K. A. Lohar R Venketeswaran T. K. Alex 《Journal of Earth System Science》2005,114(6):725-731
Lunar Laser Ranging Instrument (LLRI) proposed for the first Indian lunar mission Chandrayaan-1 is aimed to study the topography
of the Moon’s surface and its gravitational field by precisely measuring the altitude from a polar orbit around the Moon.
Altimetry data close to the poles of the Moon would also be available from the instrument, which was not covered by earlier
missions. This instrument supplements the terrain mapping camera and hyperspectral imager payloads on Chandrayaan-1. The instrument
consists of a diode pumped Nd:YAG pulsed laser transmitter having 10 nsec pulse width and a receiver system. The receiver
system features 17 cm diameter Ritchey—Chrétien collecting optics, Si Avalanche Photo Detector (APD), preamplifiers, constant
fraction discriminators, time-of-flight measurement unit and spacecraft interface. Altimeter resolution of better than 5 m
is targeted. The received signal strength of LLRI depends on laser pulse backscatter from the Moon’s surface. Moon’s surface
being a poor reflector, the choice of receiver size and its type and the selection of detector play an important role in getting
a good signal-to-noise ratio and in turn achieving the target resolution. At the same time, the spacecraft puts a limitation
on payload size and weight. This paper discusses the proposed LLRI system for Chandrayaan-1 and signal-to-noise ratio estimation. 相似文献
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Chandrashekhar M. Biradar Prasad S. Thenkabail Praveen Noojipady Yuanjie Li Venkateswarlu Dheeravath Hugh Turral Manohar Velpuri Murali K. Gumma Obi Reddy P. Gangalakunta Xueliang L. Cai Xiangming Xiao Mitchell A. Schull Ranjith D. Alankara Sarath Gunasinghe Sadir Mohideen 《International Journal of Applied Earth Observation and Geoinformation》2009
The overarching goal of this study was to produce a global map of rainfed cropland areas (GMRCA) and calculate country-by-country rainfed area statistics using remote sensing data. A suite of spatial datasets, methods and protocols for mapping GMRCA were described. These consist of: (a) data fusion and composition of multi-resolution time-series mega-file data-cube (MFDC), (b) image segmentation based on precipitation, temperature, and elevation zones, (c) spectral correlation similarity (SCS), (d) protocols for class identification and labeling through uses of SCS R2-values, bi-spectral plots, space-time spiral curves (ST-SCs), rich source of field-plot data, and zoom-in-views of Google Earth (GE), and (e) techniques for resolving mixed classes by decision tree algorithms, and spatial modeling. The outcome was a 9-class GMRCA from which country-by-country rainfed area statistics were computed for the end of the last millennium. The global rainfed cropland area estimate from the GMRCA 9-class map was 1.13 billion hectares (Bha). The total global cropland areas (rainfed plus irrigated) was 1.53 Bha which was close to national statistics compiled by FAOSTAT (1.51 Bha). The accuracies and errors of GMRCA were assessed using field-plot and Google Earth data points. The accuracy varied between 92 and 98% with kappa value of about 0.76, errors of omission of 2–8%, and the errors of commission of 19–36%. 相似文献
14.
Ulva sp. and Gracilaria sp. were found colonizing shell surfaces of an acorn barnacle, Megabalanus tintinnabulum. However, this association was not noticed in the case of Balanus amphitrite, which was a co‐inhabitant. Such a difference in intergeneric interactions with the algae was examined in laboratory experiments. For this, the influence that extracts of algae, extracts of algae‐associated bacteria and natural leachants from M. tintinnabulum exerted on cyprid metamorphosis of B. amphitrite was examined. Extracts of algae and associated bacteria showed no effect on the metamorphosis of B. amphitrite. This may be attributed to absence of cue‐specific sugars in the exopolysaccharides and culture supernatants of bacteria. On the other hand, natural leachants of M. tintinnabulum, which showed the presence of N‐acetyl‐d ‐glucosamine, a known algal spore attractant, also inhibited metamorphosis of B. amphitrite. Thus, hosting specific epibionts could have important roles in the segregation of barnacle population. 相似文献
15.
Laboratory Simulation of Flow through Single Fractured Granite 总被引:2,自引:1,他引:1
16.
Modeling the Effects of Heterogeneity and Anisotropy on the Excavation Damaged/Disturbed Zone (EDZ) 总被引:2,自引:0,他引:2
S. H. Wang C. I. Lee P. G. Ranjith C. A. Tang 《Rock Mechanics and Rock Engineering》2009,42(2):229-258
Summary When modeling the mechanical behavior of underground excavations, it is necessary to include the influence of the rock mass
characteristics on the Excavation Damaged/Disturbed Zone (EDZ). In this paper, the Realistic Failure Process Analysis code,
RFPA, is used to model the extent of the EDZ. The inhomogeneous characteristics of rock at the mesoscopic level are included
by assuming that the material properties of the constituent elements conform to a Weibull distribution; the anisotropy is
incorporated as a transversely isotropic medium; the non-elastic characteristic is simulated via an elastic damage-based constitutive
law. A finite element program is adopted as the basic stress analysis tool. In this study, a notable feature is that no a
priori assumptions need to be made about where and how fracture and failure will occur – cracking can take place spontaneously
and can exhibit a variety of mechanisms when certain local stress conditions are met. The deformation and failure process
of anisotropic rock around excavations of different geometries is analyzed, and compared to experimental tests, showing similar
fracture patterns. Additionally, the effect of confining stress and of different material layers is modeled and discussed.
It is found that the model clearly illustrates that fracturing, both initiation and propagation, occurs as a combination of
the stress concentrations and weakness planes introduced via the transverse anisotropy – which could represent either foliations
or ubiquitous joint sets.
Correspondence: Dr. Shuhong Wang, Box 265, School of Resource and Civil Engineering, Northeastern University, Shenyang 110004,
P.R. China 相似文献
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Yingnan Wang Hieu T. Tran Giang D. Nguyen Pathegama G. Ranjith Ha H. Bui 《国际地质力学数值与分析法杂志》2020,44(10):1417-1445
This paper focuses on the modelling of mixed-mode fracture using the conventional smoothed particle hydrodynamics (SPH) method and a mixed-mode cohesive fracture law embedded in the particles. The combination of conventional SPH and a mixed-mode cohesive model allows capturing fracture and separation under various loading conditions efficiently. The key advantage of this framework is its capability to represent complex fracture geometries by a set of cracked SPH particles, each of which can possess its own mixed-mode cohesive fracture with arbitrary orientations. Therefore, this can naturally capture complex fracture patterns without any predefined fracture topologies. Because a characteristic length scale related to the size of the fracture process zone is incorporated in the constitutive formulation, the proposed approach is independent from the spatial discretisation of the computational domain (or mesh independent). Furthermore, the anisotropic fracture responses of materials can be naturally captured thanks to the orientation of the fracture process zone embedded at the particle level. The performance of the proposed approach demonstrates its potentials in modelling mixed-mode fracture of rocks and similar quasi-brittle materials. 相似文献
19.
The Effect of Specimen Size on Strength and Other Properties in Laboratory Testing of Rock and Rock-Like Cementitious Brittle Materials 总被引:1,自引:0,他引:1
William?J.?DarlingtonEmail author Pathegama?G.?Ranjith S.?K.?Choi 《Rock Mechanics and Rock Engineering》2011,44(5):513-529
The effect of specimen size on the measured unconfined compressive strength and other mechanical properties has been studied
by numerous researchers in the past, although much of this work has been based on specimens of non-standard dimensions and
shapes, and over a limited size range. A review of the published literature was completed concentrating on the presentation
of research pertaining to right cylindrical specimens with height:diameter ratios of 2:1. Additionally, new data has been
presented considering high strength (70 MPa) cement mortar specimens of various diameters ranging from 63 to 300 mm which
were tested to failure. Currently, several models exist in the published literature that seek to predict the strength–size
relationship in rock or cementitious materials. Modelling the reviewed datasets, statistical analysis was used to help establish
which of these models best represents the empirical evidence. The findings presented here suggest that over the range of specimen
sizes explored, the MFSL (Carpinteri et al. in Mater Struct 28:311–317, 1995) model most closely predicts the strength–size relationship in rock and cementitious materials, and that a majority of the
empirical evidence supports an asymptotic value in strength at large specimen diameters. Furthermore, the MFSL relationship
is not only able to model monotonically decreasing strength–size relationships but is also equally applicable to monotonically
increasing relationships, which although shown to be rare do for example exist in rocks with fractal distributions of hard
particles. 相似文献
20.
K.M.A.S.Bandara P.G.Ranjith T.D.Rathnaweera W.A.M.Wanniarachchi S.Q.Yang 《地学前缘(英文版)》2021,12(6):376-393
Crushing and embedment are two critical downhole proppant degradation mechanisms that lead to a significant drop in production outputs in unconventional oil/gas stimulation projects.These persistent production drops due to the non-linear responses of proppants under reservoir conditions put the future utilization of such advanced stimulation techniques in unconventional energy extraction in doubt.The aim of this study is to address these issues by conducting a comprehensive experimental approach.According to the results,whatever the type of proppant,all proppant packs tend to undergo significant plastic deformation under the first loading cycle.Moreover,the utilization of ceramic proppants(which retain proppant pack porosity up to 75%),larger proppant sizes(which retain proppant pack porosity up to 15.2%)and higher proppant concentrations(which retain proppant pack porosity up to 29.5%)in the fracturing stimulations with higher in-situ stresses are recommended to de-escalate the critical consequences of crushing associated issues.Similarly,the selection of resin-coated proppants over ceramic and sand proppants may benefit in terms of obtaining reduced proppant embedment.In addition,selection of smaller proppant sizes and higher proppant concentrations are suggested for stimulation projects at depth with sedimentary formations and lower in-situ stresses where proppant embedment pre-dominates.Furthermore,correlation between proppant embedment with repetitive loading cycles was studied.Importantly,microstructural analysis of the proppant-embedded siltstone rock samples revealed that the initiation of secondary induced fractures.Finally,the findings of this study can greatly contribute to accurately select optimum proppant properties(proppant type,size and concentration)depending on the oil/gas reservoir char-acteristics to minimize proppant crushing and embedment effects. 相似文献