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Search Results: 1 - 10 of 401487 matches for " Ardeshir M. Ebtehaj "
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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.
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.
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.
MUC2 mRNA detection in peripheral blood and bone marrow of breast cancer patients reveals micrometastasis  [PDF]
Negar Khazan, Ardeshir Ghavamzadeh, Anna S. Boyajyan, Gohar M. Mkrtchyan, Kamran Alimoghaddam, Seyed H. Ghaffari
Natural Science (NS) , 2013, DOI: 10.4236/ns.2013.51006
Abstract:

Tumor dissemination to distant organ is the main cause of death. Therefore there is urgent need to set up sensitive methods for early detection of circulating tumor cells (CTCs) and disseminated tumor cells (DTCs) in peripheral blood (PB) and bone marrow (BM) specimens of breast cancer patients. We aim to detect MUC2 mRNA positive cells in PB and BM of breast cancer patients; to relate this to patient relapse. In this study to detect MUC2 mRNA positive cells (tumor marker), PB and BM samples were collected from 50 breast cancer patients after operation and before adjuvant therapy with 20 PB from healthy individuals as negative controls. Chi-square test was used to analyze data. MUC2 mRNA by using Real-time PCR was detected in 9 (18%) of PB and in 10 (20%) of BM samples and none of the healthy individuals. The relapse rate among MUC2-positive patients was significance in BM (P < 0.004) and MUC2-positive patients had a shorter disease free survival than the negative patients in BM samples (p < 0.05). This study shows MUC2 can be a suitable marker for detection of micrometastasis in breast cancer patients at early stages of cancer.

Application of Self-Organizing Map for Exploration of REEs’ Deposition  [PDF]
Mohammadali Sarparandeh, Ardeshir Hezarkhani
Open Journal of Geology (OJG) , 2016, DOI: 10.4236/ojg.2016.67045
Abstract: Varieties of approaches and algorithms have been presented to identify the distribution of elements. Previous researches based on the type of problem, categorized their data in proper clusters or classes. This means that the process of solution could be supervised or unsupervised. In cases, where there is no idea about dependency of samples to specific groups, clustering methods (unsupervised) are applied. About geochemistry data, since various elements are involved, in addition to the complex nature of geochemical data, clustering algorithms would be useful for recognition of elements distribution. In this paper, Self-Organizing Map (SOM) algorithm, as an unsupervised method, is applied for clustering samples based on REEs contents. For this reason the Choghart Fe-REE deposit (Bafq district, central Iran), was selected as study area and dataset was a collection of 112 lithology samples that were assayed with laboratory tests such as ICP-MS and XRF analysis. In this study, input vectors include 19 features which are coordinates x, y, z and concentrations of REEs as well as the concentration of Phosphate (P2O5) since the apatite is the main source of REEs in this particular research. Four clusters were determined as an optimal number of clusters using silhouette criterion as well as k-means clustering method and SOM. Therefore, using self-organizing map, study area was subdivided in four zones. These four zones can be described as phosphate type, albitofyre type, metasomatic and phosphorus iron ore, and Iron Ore type. Phosphate type is the most prone to rare earth elements. Eventually, results were validated with laboratory analysis.
Delineation of Geochemical Anomalies Based on Cu by the Boxplot as an Exploratory Data Analysis (EDA) Method and Concentration-Volume (C-V) Fractal Modeling in Mesgaran Mining Area, Eastern Iran  [PDF]
Mohammadreza Agharezaei, Ardeshir Hezarkhani
Open Journal of Geology (OJG) , 2016, DOI: 10.4236/ojg.2016.610093
Abstract: The target in this investigation is separation and delineation of geochemical anomalies for the single element Cu in Mesgaran mining area, eastern Iran. Mesgaran mining area is located in south part of Sarbishe county with about 29 Km distance to the county center. This region is part of an Ophiolite sequence and the copper anomalies seem to be related to a volcanic massive sulfide (VMS) deposit whose main part (massive sulfide Lens) has been eroded. In order to delineate Cu anomalies, the boxplot as an Exploratory Data Analysis (EDA) method and concentration-volume (C-V) Fractal modeling are employed. Both of the methods reveal low-deep anomalies which are highly correlated with geological and geophysical studies. As the main result of this study we show that Fractal modeling in spite of the Boxplot, is not recommended for complex geological settings. The proved shallow anomalies recorded by geophysical studies and defined by the used methods are in accordance to the stringer zone of a volcanic massive sulfide (VMS) deposit in Mesgaran mining area which means this region is the bottom of a VMS deposit and geochemical anomalies are related to the remained parts of the deposit.
A Preliminary Report on the Feasibility of Outpatient Autologous Stem Cell Transplantation in Iran
Ardeshir Ghavamzadeh,Abolghasem Allahyari,Kamran Alimoghaddam,M Esfandbod
International Journal of Hematology-Oncology and Stem Cell Research , 2009,
Abstract: "nIntroduction: Autologous stem cells have greatly influenced the treatment of a variety of malignancies including Hodgkin/non-Hodgkins lymphoma and acute leukemias. This is a preliminary study comparing the time of engraftment, mortality rate and cost of treatment in outpatient versus inpatient autologous stem cell transplantation (SCT) in Iran. "nPatients and Methods: 11 outpatients (6 Hodgkin Lymphoma (HL), 3 Non-Hodgkin Lymphoma (NHL) and 2 Acute Myeloid Leukemia (AML)) were compared with 32 inpatients (15 HL, 8 NHL and 9 AML) from May, 2008 to December, 2008. All patients were in complete remission and without significant organ failure. They received conditioning regimen (CEAM for NHL and HL, Busulfan and Etoposide for AML) and stem cell infusion in hospital. The day after SCT, the outpatient group was discharged and followed up by an outpatient SCT team to be re-hospitalized, if indicated. "nResults: For outpatients and inpatients, the median period to WBC engraftment was 11 and 12 days (p-value=0.03), the timeframe to PLT engraftment was 15 and 25 days (p-value=0.20) and the number of transfused single-donor PLT was 3 and 4.5 units (p-value=0.21). The duration of neutropenic fever was 6 and 9 days (p-value=0.001), the duration of hospitalization after SCT was 0 and 16 (p-value<0.001), respectively. All outpatients are alive but three inpatients died between days +35 and +100 following SCT due to transplantation complications. The cost of the drugs used for treatment of neutropenic fever was 6 times higher in the inpatient group. "nConclusion: The outpatient autologous SCT in malignant hematological disorders is feasible and comparable to inpatient protocols in Iran.
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