ORCID Profile
0000-0002-4766-2664
Current Organisation
Spaceage Geoconsulting
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Publisher: Springer Science and Business Media LLC
Date: 09-05-2019
Publisher: Wiley
Date: 08-04-2005
DOI: 10.1002/CPE.897
Publisher: Society of Exploration Geophysicists
Date: 2002
DOI: 10.1190/1.1817030
Publisher: Wiley
Date: 29-10-2021
DOI: 10.1002/NSG.12179
Abstract: I propose a simple and sufficiently robust data‐based semi‐automated interpretation of a total magnetic intensity profile to delineate an isolated fracture or a fractured zone embedded within a homogeneous host medium. The interpretation technique, which is based on the premise of induced magnetization, uses a model of a thin, two‐dimensional dipping sheet embedded in a homogeneous half‐space. The proposed quantitative interpretation uses a set of closed form formulae in delineating model parameters in those the Hilbert transform, the first‐ and second‐order derivatives of the local litude of the zero‐order analytical signal are the essential components. The locations of zero crossings of the first‐ and second‐order derivatives of analytical signal and the Hilbert transform remain the essential keys in estimating structural parameters of the model. The magnetic susceptibility contrast is delineated from the peak litude of the analytical signal. An appropriately designed Savitzky–Golay derivative filter and Hilbert–Noda transformation matrix are used as robust and efficient data‐processing tools. An additional tool, Newton's root finding algorithm, is proposed for locating the zero crossings. The reconstructed data fit is validated using a statistical appraisal, and the estimated model parameters are defined with an uncertainty measure using the confidence limit. The proposed technique has been applied to synthetic data generated from a model depicting a realistic ex le, and also on field data from two ex les, one of which closely resembles the ex le of synthetic data and the other as a benchmark ex le. Numerical experiments validate the applicability of the method.
Publisher: Elsevier BV
Date: 11-2013
Publisher: Wiley
Date: 18-10-2019
DOI: 10.1111/ANS.15466
Publisher: Informa UK Limited
Date: 12-2011
Publisher: Elsevier BV
Date: 08-2015
Publisher: International Union of Geological Sciences
Date: 15-06-2023
Publisher: Elsevier BV
Date: 06-2014
Publisher: Springer Science and Business Media LLC
Date: 02-2021
Publisher: Elsevier BV
Date: 05-2002
Publisher: Society of Exploration Geophysicists
Date: 11-2004
DOI: 10.1190/1.1836820
Publisher: Wiley
Date: 02-2020
Abstract: Acute perforated erticulitis is frequently observed and spans a spectrum in the severity of its presentation. Emergency surgery is required in patients with generalized peritonitis however, a large proportion of patients are clinically stable with localized peritonitis. This article aimed to examine this specific group of patients by reviewing the outcomes of their conservative management. A systematic literature search was performed on the MEDLINE and PubMed databases. The management outcomes of patients undergoing non-operative treatment for acute perforated erticulitis were synthesized and tabulated. Of 479 patients, 407 (85%) were successfully managed non-operatively. In total 70 (14.6%) patients failed non-operative treatment and underwent operative surgical management, and two (0.4%) died. Emergency surgery includes a Hartmann's operation (40%) and resection with anastomosis with or without stoma (24%), laparoscopic lavage (16%) and surgical drainage (20%). The success rate of conservative management was 94.0% and 71.4% for patients with pericolic and distant free air, respectively. Treatment failure was associated with a high volume of free air, distant free air and the presence of abscess. Conservative management is safe and successful in patients with acute perforated erticulitis without generalized peritonitis. The early recognition of patients who show clinical signs of persistent perforation is important to ensure the success of this strategy.
Publisher: Elsevier BV
Date: 11-2010
Publisher: Wiley
Date: 07-1999
Publisher: Springer Science and Business Media LLC
Date: 02-03-2023
Publisher: Society of Exploration Geophysicists
Date: 09-2017
Abstract: I have developed an improved practical method for interpreting a symmetrical-shaped potential field anomaly due to an isolated source body of regular geometric configuration. The method uses the first-order horizontal derivative of the logarithmically transformed absolute value of the anomaly in estimating the source-body parameters, such as the location, depth of burial, and shape factor. To tackle noise in data, a regularization technique is designed, which ensures a robust estimate of the first-order derivative of logarithmically transformed data. The regularization technique uses an optimal value of regularization parameter that, although noise dependent, requires no a priori knowledge of the noise level in the data. A graphical method is designed to determine an optimal value of the regularization parameter from the position of the local minimum of a specially defined functional with respect to the regularization parameters. Numerical tests have been conducted on the noise-contaminated synthetic data to validate the proposed method. The successful application of the method on published field data for the gravity and magnetic anomaly suggests the applicability of the method.
Publisher: Oxford University Press (OUP)
Date: 06-2013
Publisher: Informa UK Limited
Date: 2005
Publisher: Informa UK Limited
Date: 06-2000
DOI: 10.1071/EG00495
Publisher: Society of Exploration Geophysicists
Date: 11-2003
DOI: 10.1190/1.1635056
Abstract: Seismic waveform inversion is a highly challenging task. Nonlinearity, nonuniqueness, and robustness issues tend to make the problem computationally intractable. We have developed a simple regularized Gauss‐Newton–type algorithm for the inversion of seismic data that addresses several of these issues. The salient features of our algorithm include an efficient approach to sensitivity computation, a strategy for band‐limiting the Jacobian matrix, and a novel approach to computing regularization weight that is iteration adaptive. In this paper, we first review various forward modeling and differential seismogram computation algorithms and then evaluate different strategies for choosing the regularization weight. Under the assumption of locally 1D earth models, we design an efficient algorithm by rearranging recursion formula in the reflection matrix approach to compute plane wave seismograms and the Fréchet derivative matrix as a by‐product of forward modeling. We then demonstrate that in a gradient‐descent–type optimization scheme, regularization is critical for obtaining stable and geologically realistic solutions. Although, in most applications, the regularization weight (relative importance between data and model misfit) is chosen in an ad‐hoc manner the robustness in model estimation and computational stability improve significantly by allowing adaptivity in the choice of the regularization weight in each iterative step. We evaluate performances of several methods, namely, an L‐curve approach, generalized cross‐validation technique, and methods based on a discrepancy principle with application to field ocean‐bottom‐cable data, and we propose a new hybrid approach in computing iteration adaptive regularization weight for prestack inversion.
Publisher: Springer Science and Business Media LLC
Date: 17-01-2023
Publisher: Technical University of Kosice, Faculty of Electrical Engineering and Informatics
Date: 12-2017
Publisher: Oxford University Press (OUP)
Date: 02-10-2018
DOI: 10.1093/GJI/GGY402
Publisher: Wiley
Date: 29-03-2017
Publisher: Society of Exploration Geophysicists
Date: 2002
DOI: 10.1190/1.1817412
Publisher: Wiley
Date: 14-11-2020
Publisher: Oxford University Press (OUP)
Date: 02-05-2006
Publisher: Elsevier BV
Date: 08-2014
Publisher: Society of Exploration Geophysicists
Date: 2002
DOI: 10.1190/1.1817414
Publisher: Springer Science and Business Media LLC
Date: 18-05-2017
Publisher: Elsevier BV
Date: 11-2010
No related grants have been discovered for Indrajit Roy.