Wheat acreage estimation for Haryana using satellite digital data     

V. K. Dadhwal  D. S. Ruhal  T. T. Medhavy  S. D. Jarwal  A. P. Khera  J. Singh  Tara Sharma  J. S. Parihar 《Journal of the Indian Society of Remote Sensing》1991,19(1):1-15

This paper summarizes the procedures adopted and results obtained since 1985–86 for wheat inventory for Haryana using satellite digital data (MSS: 1985–86 to 1987–88, LISS-I: 1988–89 onwards). The approach followed is based on sample segments (10 × 10 km during 1985–86 to 1988–89, 7.5 × 7.5 km during 1989–90) and 10 percent sampling fraction and stratified sample design. There has been consistent improvement in accuracy over the years as judged from lower biases when compared with Bureau of Economics and Statistics (BES) acreage estimates and higher precision. In 1989–90, the state-level estimate achieved an accuracy goal of 90 percent at 90 percent confidence interval. A number of studies which have been carried out to study effect of choice of sensor, acquisition date, stratification approach, classification procedure on wheat inventory are also mentioned.  相似文献   

In dwelling: Implacability,exclusion and acceptance – By Peter King     

Tara Coleman 《New Zealand geographer》2009,65(3):237-238

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The Australia Telescope 20-GHz (AT20G) Survey: the Bright Source Sample     

Marcella Massardi  Ronald D. Ekers  Tara Murphy  Roberto Ricci  Elaine M. Sadler  Sarah Burke  Gianfranco De Zotti  Philip G. Edwards  Paul J. Hancock  Carole A. Jackson  Michael J. Kesteven  Elizabeth Mahony  Christopher J. Phillips  Lister Staveley-Smith  Ravi Subrahmanyan  Mark A. Walker  Warwick E. Wilson 《Monthly notices of the Royal Astronomical Society》2008,384(2):775-802

The Australia Telescope 20-GHz (AT20G) Survey is a blind survey of the whole southern sky at 20 GHz (with follow-up observations at 4.8 and 8.6 GHz) carried out with the Australia Telescope Compact Array from 2004 to 2007.
The Bright Source Sample (BSS) is a complete flux-limited subsample of the AT20G Survey catalogue comprising 320 extragalactic     ) radio sources south of  δ=−15°  with      Jy. Of these, 218 have near simultaneous observations at 8 and 5 GHz.
In this paper we present an analysis of radio spectral properties in total intensity and polarization, size, optical identifications and redshift distribution of the BSS sources. The analysis of the spectral behaviour shows spectral curvature in most sources with spectral steepening that increases at higher frequencies (the median spectral index α, assuming   S ∝ν^α  , decreases from  α^8.6_4.8= 0.11  between 4.8 and 8.6 GHz to  α²⁰_8.6=−0.16  between 8.6 and 20 GHz), even if the sample is dominated by flat spectra sources (85 per cent of the sample has  α²⁰_8.6 > −0.5)  . The almost simultaneous spectra in total intensity and polarization allowed us a comparison of the polarized and total intensity spectra: polarized fraction slightly increases with frequency, but the shapes of the spectra have little correlation. Optical identifications provided an estimation of redshift for 186 sources with a median value of 1.20 and 0.13, respectively, for QSO and galaxies.  相似文献   

Effect of earthquake‐induced axial load fluctuations on asymmetric frame–wall–rocking foundation systems          下载免费PDF全文

Weian Liu  Tara C. Hutchinson  Bruce L. Kutter  Andreas G. Gavras  Manouchehr Hakhamaneshi 《地震工程与结构动力学》2015,44(12):1997-2013

Fluctuations in axial load imposed on a rocking footing will affect its moment capacity, the shape of its moment–rotation hysteresis, and potentially the system's seismic performance. Structural asymmetry increases the likelihood of axial load variation during earthquake excitations. To investigate this issue, a unique centrifuge testing program was carried out on low‐rise frame–wall–rocking foundation systems. In this paper, the seismic behaviors of asymmetric and symmetric models from this test program are systematically compared. Experimental results reveal that placing the lateral force resisting shear wall outboard produces significant axial load fluctuation, which in turn greatly deteriorate the lateral load‐carrying capacity of a foundation rocking dominated frame–wall system, particularly in its weak direction. However, it strengthens the system when loading is towards the shear wall, leading to a highly asymmetric hysteretic response. During earthquake loading, all asymmetric rocking foundation systems observe smaller peak roof accelerations, but larger peak and permanent roof drifts compared with the symmetric systems. Despite these differences in response, the axial load fluctuation and structural asymmetry do not significantly change the relative energy dissipated by the rocking foundations and inelastic structural components within each frame–wall–rocking foundation model. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

A spatially explicit modeling approach to explore scenarios of sustainable agriculture futures     

Tara Sharma  Jeff Carmichael  Brian Klinkenberg 《Journal of the Indian Society of Remote Sensing》2005,33(2):353-363

The transition to agricultural sustainability involves difficult choices and an understanding of the complex trade-offs associated with agricultural activities. Decision support tools and techniques assist in making the informed decisions for a transition to sustainable agriculture. Georgia Basin — Quite Useful Ecosystem Scenario Tool (GB-QUEST) is a computer-based, user-friendly tool that has been developed to look at the future sustainability scenarios of the Georgia Basin in British Columbia. The objective of this paper is to describe the agricultural model that has been developed for implementation in GB-QUEST. We present its framework, spatial methodology for land-use simulation, and the initial results of its application. The agriculture model is a spatial model that examines the social, economic and environmental consequences of user-defined agricultural development strategies. The model simulates changes in the Georgia Basin from the year 2000 to 2040 in decadal steps. User choices of local and global development factors, along with their "worldview" choices, are important inputs in the model that determine the effects on environmental and socio-economic systems. The model has two components — Generation of land-use scenarios, and Development of Indicator models. The first component uses cell-based spatial algorithms to simulate likely changes/conversions in land-use up to the year 2040. The approach used here integrates the functionality of Multi-Criteria Evaluation (MCE) and Cellular Automata (CA) techniques in order to simulate the land-use conversions. It uses Geographic Information Systems (GIS) and remote sensing techniques for creating, storing and deriving the data sets required for the model. The second component develops the indicator models for relating scenario variables to socio-economic and environmental variables such as physical and economic yields, economic operation costs and nutrient surplus per unit area. These indicator models are used to evaluate land-use scenarios generated by the users. The model encourages understanding of sustainability, by allowing one to explore different possible scenarios of the future for their environmental and socio-economic consequences.  相似文献   

Influence of galactic nuclear explosions on the efficiency of the process of star formation     

Anuradha Saha  B. Basu  Tara Bhattacharyya 《Astrophysics and Space Science》1985,116(2):313-324

Periodic explosions in the nucleus of a galaxy generate strong shock waves. The shock waves, in moving outwards, produce highly compressed thin layers of gas at distances much larger than the thickness of the layer. When the gas in this layer undergoes fragmentation, the Jeans mass is found to be much less than that if the fragmentation proceeded under normal gravitational pull. It is, therefore, concluded that the explosive events in the galactic centres make the process of star formation highly efficient in the central region of galaxies.  相似文献   

Mass accretion by the nuclei of disk galaxies     

Anuradha Saha  Tara Bhattacharyya  B. Basu 《Astrophysics and Space Science》1984,107(2):255-270

In this work a model has been proposed to explain how the nucleus of a Galaxy can accumulate mass and becomes supermassive — ultimately giving way to gravitational instability leading to an explosion in the nucleus. The process may be repeated many times during the life-span of a Galaxy. The mass shed by the evolved stars populating the central region of the Galaxy can be attracted toward the nuclear core by gravitational pull. Since the incident gas possesses rotational velocity, the centrifugal repulsion of the gas may balance the gravitational pull of the nucleus; thus infall of mass into the nucleus will ordinarily be inhibited. But dissipative agents — such as the prevailing magnetic field and the viscosity of gas — may be sufficient to destroy the rotational velocity of the incident gas and keep the accretion process efficient. The correlation between rotational velocity of gas and its distance from the centre of the Galaxy has been deduced. The radial equation of motion has been solved and the time-scale during which the nucleus accumulates mass sufficient for explosion, has been estimated.  相似文献   

Recurrent explosions in the nuclei of galaxies     

B. Basu  Tara Bhattacharyya 《Astrophysics and Space Science》1983,96(2):405-416

High-velocity ejection of gas from the central region of galaxies is now an observationally established phenomenon. Such ejections have been attributed to some kind of activities in the nuclei of galaxies. It has been suggested that conditions leading to explosive events periodically prevail in the centre of galaxies causing recurrent explosions and driving the gas thereby outward with sufficiently high velocities. The magnitude of the ejection velocity and the amount of gas driven out will actually depend on the intensity of the activity at the centre. Remnants of recurrent activity have been discovered in the inner region of our Galaxy. The ‘3-kpc’ arm, the 2.4 kpc arm, the molecular ring at 270 pc and some other features are believed to have been caused by periodic activity at the centre of our Galaxy. We have outlined a model that can explain the recurrent explosions in the centre of a galaxy. The boundary of the nucleus of the Galaxy is considered here as a stationary shock front where high velocity gas coming from the outer regions impinges and gets heated and condensed. This condensed, hot gas then flows inwards by intense gravitational pull, but in course of its passage inward it loses its velocity due to radiation pressure and frictional retardation. A layer of dense, hot gas is therefore formed some distance (typically 0.001 pc) away from the centre where short radio and microwaves are trapped. As the density of gas in this layer is enhanced by the inflowing gas, shorter-wave radiation is trapped. The pressure of radiation therefore gradually builds up in the layer which ultimately overcomes the gravitational pull and the layer is blown off violently. The whole process may be completed over and over again at intervals of 10⁶–10⁷ yr.  相似文献   

Detritus fuels ecosystem metabolism but not metazoan food webs in San Francisco estuary's freshwater delta   总被引：1，自引：0，他引：1  

William V. Sobczak  James E. Cloern  Alan D. Jassby  Brian E. Cole  Tara S. Schraga  Andrew Arnsberg 《Estuaries and Coasts》2005,28(1):124-137

Detritus from terrestrial ecosystems is the major source of organic matter in many streams, rivers, and estuaries, yet the role of detritus in supporting pelagic food webs is debated. We examined the importance of detritus to secondary productivity in the Sacramento and San Joaquin River Delta (California, United States), a large complex of tidal freshwater habitats. The Delta ecosystem has low primary productivity but large detrital inputs, so we hypothesized that de tritus is the primary energy source fueling production in pelagic food webs. We assessed the sources, quantity, composition, and bioavailability of organic matter among a diversity of habitats (e.g., marsh sloughs, floodplains, tidal lakes, and deep river channels) over two years to test this hypothesis. Our results support the emerging principle that detritus dominates riverine and estuarine organic matter supply and supports the majority of ecosystem metabolism. Yet in contrast to prevailing ideas, we found that detritus was weakly coupled to the Delta's pelagic food web. Results from independent approaches showed that phytoplankton production was the dominant source of organic matter for the Delta's pelagic food web, even though primary production accounts for a small fraction of the Delta's organic matter supply. If these results are general, they suggest that the value of organic matter to higher trophic levels, including species targeted by programs of ecosystem restoration, is a function of phytoplankton production.  相似文献   

Intradaily variability of water quality in a shallow tidal lagoon: Mechanisms and implications     

Lisa V. Lucas  Deanna M. Sereno  Jon R. Burau  Tara S. Schraga  Cary B. Lopez  Mark T. Stacey  Konstantin V. Parchevsky  Vladimir P. Parchevsky 《Estuaries and Coasts》2006,29(5):711-730

Although surface water quality and its underlying processes vary over time scales ranging from seconds to decades, they have historically been studied at the lower (weekly to interannual) frequencies. The aim of this study was to investigate intradaily variability of three water quality parameters in a small freshwater tidal lagoon (Mildred Island, California). High frequency time series of specific conductivity, water temperature, and chlorophylla at two locations within the habitat were analyzed in conjunction with supporting hydrodynamic, meteorological, biological, and spatial mapping data. All three constituents exhibited large amplitude intradaily (e.g., semidiurnal tidal and diurnal) oscillations, and periodicity varied across constituents, space, and time. Like other tidal embayments, this habitat is influenced by several processes with distinct periodicities including physical controls, such as tides, solar radiation, and wind, and biological controls, such as photosynthesis, growth, and grazing. A scaling approach was developed to estimate individual process contributions to the observed variability. Scaling results were generally consistent with observations and together with detailed examination of time series and time derivatives, revealed specific mechanisms underlying the observed periodicities, including interactions between the tidal variability, heating, wind, and biology. The implications for monitoring were illustrated through subsampling of the data set. This exercise demonstrated how quantities needed by scientists and managers (e.g., mean or extreme concentrations) may be misrepresented by low frequency data and how short-duration high frequency measurements can aid in the design and interpretation of temporally coarser sampling programs. The dispersive export of chlorophylla from the habitat exhibited a fortnightly variability corresponding to the modulation of semidiurnal tidal currents with the diurnal cycle of phytoplankton variability, demonstrating how high frequency interactions can govern long-term trends. Process identification, as through the scaling analysis here, can help us anticipate changes in system behavior and adapt our own interactions with the system.  相似文献