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Search Results: 1 - 10 of 714561 matches for " A. M. Ebtehaj "
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Variational Data Assimilation via Sparse Regularization
A. M. Ebtehaj,M. Zupanski,G. Lerman,E. Foufoula-Georgiou
Physics , 2013, DOI: 10.3402/tellusa.v66.21789
Abstract: This paper studies the role of sparse regularization in a properly chosen basis for variational data assimilation (VDA) problems. Specifically, it focuses on data assimilation of noisy and down-sampled observations while the state variable of interest exhibits sparsity in the real or transformed domain. We show that in the presence of sparsity, the $\ell_{1}$-norm regularization produces more accurate and stable solutions than the classic data assimilation methods. To motivate further developments of the proposed methodology, assimilation experiments are conducted in the wavelet and spectral domain using the linear advection-diffusion equation.
On evaluation of ShARP passive rainfall retrievals over snow-covered land surfaces and coastal zones
Ardeshir M. Ebtehaj,Rafael L. Bras,Efi Foufoula-Georgiou
Physics , 2015,
Abstract: For precipitation retrievals over land, using satellite measurements in microwave bands, it is important to properly discriminate the weak rainfall signals from strong and highly variable background surface emission. Traditionally, land rainfall retrieval methods often rely on a weak signal of rainfall scattering on high-frequency channels (85 GHz) and make use of empirical thresholding and regression-based techniques. Due to the increased ground surface signal interference, precipitation retrieval over radiometrically complex land surfaces, especially over snow-covered lands, deserts and coastal areas, is of particular challenge for this class of retrieval techniques. This paper evaluates the results by the recently proposed Shrunken locally linear embedding Algorithm for Retrieval of Precipitation (ShARP), over a radiometrically complex terrain and coastal areas using the data provided by the Tropical Rainfall Measuring Mission (TRMM) satellite. To this end, the ShARP retrieval experiments are performed over a region in Southeast Asia, partly covering the Tibetan Highlands, Himalayas, Ganges-Brahmaputra-Meghna river basins and its delta. We elucidate promising results by ShARP over snow covered land surfaces and at the vicinity of coastlines, in comparison with the land rainfall retrievals of the standard TRMM-2A12 product. Specifically, using the TRMM-2A25 radar product as a reference, we provide evidence that the ShARP algorithm can significantly reduce the rainfall over estimation due to the background snow contamination and markedly improve detection and retrieval of rainfall at the vicinity of coastlines. During the calendar year 2013, we demonstrate that over the study domain the root mean squared difference can be reduced up to 38% annually, while the reduction can reach up to 70% during the cold months.
Non-Smooth Variational Data Assimilation with Sparse Priors
Ardeshir M. Ebtehaj,Efi Foufoula-Georgiou,Sara Q. Zhang,Arthur Y. Hou
Physics , 2012,
Abstract: This paper proposes an extension to the classical 3D variational data assimilation approach by explicitly incorporating as a prior information, the transform-domain sparsity observed in a large class of geophysical signals. In particular, the proposed framework extends the maximum likelihood estimation of the analysis state to the maximum a posteriori estimator, from a Bayesian perspective. The promise of the methodology is demonstrated via application to a 1D synthetic example.
Variational Downscaling, Fusion and Assimilation of Hydrometeorological States via Regularized Estimation
Ardeshir Mohammad Ebtehaj,Efi Foufoula-Georgiou
Physics , 2012, DOI: 10.1002/wrcr.20424
Abstract: Improved estimation of hydrometeorological states from down-sampled observations and background model forecasts in a noisy environment, has been a subject of growing research in the past decades. Here, we introduce a unified framework that ties together the problems of downscaling, data fusion and data assimilation as ill-posed inverse problems. This framework seeks solutions beyond the classic least squares estimation paradigms by imposing proper regularization, which are constraints consistent with the degree of smoothness and probabilistic structure of the underlying state. We review relevant regularization methods in derivative space and extend classic formulations of the aforementioned problems with particular emphasis on hydrologic and atmospheric applications. Informed by the statistical characteristics of the state variable of interest, the central results of the paper suggest that proper regularization can lead to a more accurate and stable recovery of the true state and hence more skillful forecasts. In particular, using the Tikhonov and Huber regularization in the derivative space, the promise of the proposed framework is demonstrated in static downscaling and fusion of synthetic multi-sensor precipitation data, while a data assimilation numerical experiment is presented using the heat equation in a variational setting.
Antibacterial Effect of Authochlorous Lactobacillus Strains Isolated from Traditional Yogurts
Ebtehaj Pishva,Nazila Hassannia,Mohammad Reza Fazeli,Asghar Havaee
Pakistan Journal of Nutrition , 2009,
Abstract: It is obvious that some of resident gastrointestinal bacterial flora represented by Lactobacilli have protective role in pathogenic infections. There are many examples of probiotic effect of Lactic Acid bacteria on enteropathgens. Lactic acid bacteria are derived from the intestinal microbiota of healthy humans or dairy products. These bacteria interact with the diet and the host, contributing to protection against intestinal pathogens through colonization resistance and providing nutritional and colonic health benefits via their metabolic activities. In this study we isolated strains of Lactobacilli from Iranian traditional yogurts and identified by biochemical tests. We tested antibacterial activity of strains against Escherchia coli and salmonella typhi by spot test method. Then we assayed zone of pathogenic bacteria. Also, we determined death kinetic of pathogenic bacteria. Most of Lactobacilli strains had potential activity against the enteropathogenic bacteria of E. coli and Salmonella. This antagonistic effect against E. coli was more than Salmonella. Lactobacillus Casei showed the most preventive effect. Activity of probiotics in prevention and treatment of infections by E. coli and salmonella are effective.
Shrunken Locally Linear Embedding for Passive Microwave Retrieval of Precipitation
Ardeshir Mohammad Ebtehaj,Rafael Luis Bras,Efi Foufoula-Georgiou
Physics , 2014, DOI: 10.1109/TGRS.2014.2382436
Abstract: This paper introduces a new Bayesian approach to the inverse problem of passive microwave rainfall retrieval. The proposed methodology relies on a regularization technique and makes use of two joint dictionaries of coincidental rainfall profiles and their corresponding upwelling spectral radiative fluxes. A sequential detection-estimation strategy is adopted, which basically assumes that similar rainfall intensity values and their spectral radiances live close to some sufficiently smooth manifolds with analogous local geometry. The detection step employs a nearest neighborhood classification rule, while the estimation scheme is equipped with a constrained shrinkage estimator to ensure stability of retrieval and some physical consistency. The algorithm is examined using coincidental observations of the active precipitation radar (PR) and passive microwave imager (TMI) on board the Tropical Rainfall Measuring Mission (TRMM) satellite. We present promising results of instantaneous rainfall retrieval for some tropical storms and mesoscale convective systems over ocean, land, and coastal zones. We provide evidence that the algorithm is capable of properly capturing different storm morphologies including high intensity rain-cells and trailing light rainfall, especially over land and coastal areas. The algorithm is also validated at an annual scale for calendar year 2013 versus the standard (version 7) radar (2A25) and radiometer (2A12) rainfall products of the TRMM satellite.
Compressive Earth Observatory: An Insight from AIRS/AMSU Retrievals
Ardeshir Mohammad Ebtehaj,Efi Foufoula-Georgiou,Gilad Lerman,Rafael Luis Bras
Physics , 2014, DOI: 10.1002/2014GL062711
Abstract: We demonstrate that the global fields of temperature, humidity and geopotential heights admit a nearly sparse representation in the wavelet domain, offering a viable path forward to explore new paradigms of sparsity-promoting data assimilation and compressive recovery of land surface-atmospheric states from space. We illustrate this idea using retrieval products of the Atmospheric Infrared Sounder (AIRS) and Advanced Microwave Sounding Unit (AMSU) on board the Aqua satellite. The results reveal that the sparsity of the fields of temperature is relatively pressure-independent while atmospheric humidity and geopotential heights are typically sparser at lower and higher pressure levels, respectively. We provide evidence that these land-atmospheric states can be accurately estimated using a small set of measurements by taking advantage of their sparsity prior.
Study on Parasexual Recombination between Pyricularia oryzae and Pyricularia grisea  [PDF]
M. A. Monsur, M. Kusaba
Agricultural Sciences (AS) , 2018, DOI: 10.4236/as.2018.93023
Abstract: Rice blast fungus is notorious for changeability in pathogenicity, but it lacks sexual life cycle. It can be postulated that such an imperfect fungus has another mechanism for generating genetic variations. Recent studies concerning comparative genomics reveal that parasexual recombination may play important role in the evolution of rice blast fungus. To observe the parasexualism of rice blast (Pyricularia oryzae) and crabgrass blast (Pyricularia grisea) fungus double inoculation and punch method were applied in this experiment. A total of 520 isolates collected from the double inoculated lesions was subjected to PCR-RFLP analysis of the ITS region to identify subcultures of the inoculated rice blast isolates. As a result, four isolates from the three double inoculated lesions with SA13-1ME and TP106 were identified as subcultures of TP106. To access the recombination genotypes, a total of 17 isolates from the three lesions was subjected to MAGGY-DNA fingerprint analysis. However, recombinant DNA fingerprint patterns between TP106 and SA13-1ME were not detected among the 17 isolates. Although TP022 was not recovered from the double inoculated lesions, the fact that TP106 was recovered from the double inoculated lesion indicates that rice blast fungus can invade and colonized in blast lesion on crabgrass. The opportunistic infection on the double inoculated lesions observed in this study potentially provides new insight into the life cycle of rice blast pathogen.
Economic Valuation of Sea Level Rise Impacts on Agricultural Sector: Damietta Governorate, Egypt  [PDF]
M. A. Abdrabo, M. A. Hassaan
Journal of Environmental Protection (JEP) , 2014, DOI: 10.4236/jep.2014.52012
Abstract:

The Nile Delta is considered to be one of the most vulnerable river deltas to Sea Level Rise (SLR) in the world. SLR is expected to affect large agricultural areas of the Nile Delta, either through inundation or higher levels and salinity of groundwater. It could be argued that such impacts would augment the problems experienced already in the area in terms of high groundwater table and salinity levels. In order to guide policy and decision making, especially in terms of assessing the economics of various adaptation options, there is a need to provide estimates of potential economic damage that could result from such changes. The paper in hand aims to estimate the economic value of potential primary impacts of higher levels of groundwater table due to expected SLR on agriculture productivity in Damietta Governorate as one of the Nile Delta coastal governorates. To conduct such an assessment, relationship between groundwater table level and agricultural productivity was first investigated in relevant literature. This was followed by reviewing prevailing conditions in the agricultural sector in the study area. Thereafter, a regression analysis for the main crops in the study area, between crop yield and groundwater table levels, was conducted. Based on the developed regression, a GIS (Geographic Information System)-based hydrological model, and a production economic model, were employed to assess economic value of higher levels of groundwater table impacts on agriculture productivity. It was found that future accumulative crop yield loss was estimated, using segmented linear regression, up to the year 2100 to be as much as L.E. 6.43 billion. It is worth mentioning that these

Contribution of Animal Agriculture to Greenhouse Gases Production in Swaziland  [PDF]
A. M. Dlamini, M. A. Dube
American Journal of Climate Change (AJCC) , 2014, DOI: 10.4236/ajcc.2014.33024
Abstract: The economy of Swaziland is depended on agriculture. In 2009, it was reported that agriculture, forestry, and manufacturing contributed 42% of Swaziland’s Gross Domestic Product (GDP). Besides economic importance, animal agriculture is important for food production and life sustenance. It is also viewed as a symbol of wealth and high social status particularly for the rural folks. Despite the merits of agricultural activities, agricultural production, particularly animal production, has been incriminated for an accelerated emission of greenhouse gases. These gases are responsible for global warming and climate change. The aim of this study was to determine the contribution of animal agriculture to greenhouse gases production and to elicit adaptation strategies to climate change and the role of modern technologies as mitigating measures. The minor and major greenhouse gases produced by farm animals were computed using the IPCC spread sheet for calculation of greenhouse gases emissions. The minor greenhouse gases produced by farm animals were NOx and CO2 and the major gasses included CH4 and N2O. The greenhouse gas that was emitted the most by farm animals was CH4, 24 Gg or 600 CO2e per annum. Ruminants were the major producers of methane. The producers of the least greenhouse gases emissions were non ruminants. Livestock produced 0.87 Gg of N2O per annum, a global warming potential of 259 CO2e. Feeding ammoniated straw and silage inoculating with transgenic rumen bacteria, animal breeding and manure storage techniques, use of biogas digester with methane gas recovery and emphasis on non ruminant production were possible strategies that could be employed to reduce greenhouse gases production from the livestock sector. It was recommended that feed preservation technologies, selection strategies, water harvesting, storage and recycling strategies and intensive livestock production systems could be used as adaptation strategies to climate change in livestock production.
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