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Search Results: 1 - 10 of 12976 matches for " Ardeshir Mohammad Ebtehaj "
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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.
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.
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.
Epistemic Learning Programs A Calculus for Describing Epistemic Action Models
Mohammad Ardeshir Rasoul Ramezanian
Computer Science , 2013,
Abstract: Dynamic Epistemic Logic makes it possible to model and reason about information change in multi-agent systems. Information change is mathematically modeled through epistemic action Kripke models introduced by Baltag et al. Also, van Ditmarsch interprets the information change as a relation between epistemic states and sets of epistemic states and to describe it formally, he considers a special constructor LB called learning operator. Inspired by this, it seems natural to us that the basic source of information change in a multi-agent system should be learning an announcement by some agents together, privately, concurrently or even wrongly. Hence moving along this path, we introduce the notion of a learning program and prove that all fi?nite K45 action models can be described by our learning programs
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.
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.
Epidemiology of drowning in Isfahan province, center of Iran
Ardeshir Sheikhazadi,Mohammad Hasan Ghadyani
Journal of Research in Medical Sciences , 2009,
Abstract: BACKGROUND: Drowning is a preventable cause of morbidity and ortality. We studied drowning deaths in Isfahan province, focusing on the activity victims were involved in and the setting of the incident. METHODS: Retrospective analysis was done on all drowning deaths eferred to Legal Medicine Organization of Isfahan province over a period of 5 years from 1 January 2002 to 31 December 2006. RESULTS: During these 5 years, 355 persons suffered fatal drowning in Isfahan province. The annual incidence rate was 1.6 per 100000 population (2.6 & 0.4 for males and females, respectively). Mean age was 21.99 ± 14.86 and M/F ratio was 6.5:1. Most victims were 15-24 and 5-14 years of age (172 and 62 decedents, 3.0 and 1.8 per 100000 population/ year, respectively). Most incidents occurred in natural settings, of which rivers, canals, lakes and ponds were the most common sites, respectively. The most frequently connected activity was swimming and wading, followed by accidental fall into water. The manner of death was found as following: 85.1% accidental, 1.7% suicidal, 0.3% homicidal and 12.9% undetermined. CONCLUSIONS: Although the drowning related mortality in Isfahan province is comparable to developed countries, effective prevention of drowning with better programming and policies might reduce its rate. KEYWORDS: Drowning, epidemiology, public health, Isfahan province, Iran.
The $Σ$_1 Provability Logic of HA
Mohammad Ardeshir,S. Mojtaba Mojtahedi
Mathematics , 2014,
Abstract: In this paper we introduce a modal theory $H_{\sigma}$, which is sound and complete for arithmetical $\Sigma$_1 substitutions in ${\bf HA}$, in other words, we will show that $H_{\sigma}$ is the $\Sigma$_1-provability logic of ${\bf HA}$. Moreover we will show that $H_{\sigma}$ is decidable. As a by-product of these results, we show that ${\bf HA} + \Box\bot$ has de Jongh property.
A Mathematical Optimization Model for Locating Telecenters  [PDF]
Morteza Tabatabaie Shourijeh, Mohammad Kermanshah, Amir Reza Mamdoohi, Ardeshir Faghri, Khaled Hamad
Applied Mathematics (AM) , 2012, DOI: 10.4236/am.2012.33040
Abstract: Telecommuting is a Transportation Demand Management strategy to partially or completely replace the daily commute with telecommunication technologies. Research has revealed that telecommuting can be effectively done from special places provided for this purpose called telecenters. In telecenter-based telecommuting, trip lengths are shortened due to change in the location of work places. Thus suitable locations of telecenters play an important role in increasing the beneficial impacts of telecommuting in the transportation systems. In this research, a mathematical optimization model for finding optimal location and capacity of telecenters is proposed. This model is a bi-objective linear program, and a Fuzzy Goal Programming method with a preemptive structure is used to solve it. Telecommuting demand is classified into three groups of telecommuters and a priority structure that assigns the higher priority class to the closer telecenters is also incorporated into the model. The proposed model is implemented in a case study of finding optimal location of telecenters for government employees in Tehran (capital of Iran) metropolitan area. The base model is solved and its sensitivity to different parameters has been analyzed based on which, an optimal model is selected. The solution of this model is an optimal pattern for distribution of telecommuting capacities and yields the most system-wide benefits from implementation of telecommuting.
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