eli turkel | Tel Aviv University (original) (raw)

Papers by eli turkel

23rd Aerospace Sciences Meeting

... Affiliation: AA(National Aeronautics and Space Administration. Langley Research Center, Hampt... more ... Affiliation: AA(National Aeronautics and Space Administration. Langley Research Center, Hampton,VA.), AB(National Aeronautics and Space Administration. Langley Research Center, Hampton, VA.). ... Langley Research Center, Hampton, VA. Publication Date: 02/1985. ...

2012 10th IAPR International Workshop on Document Analysis Systems, 2012

The discipline of First Temple Period epigraphy (the study of writing) relies heavily on manually... more The discipline of First Temple Period epigraphy (the study of writing) relies heavily on manually-drawn facsimiles (black and white images) of ancient inscriptions. This practice may unintentionally mix up documentation and interpretation. The article proposes a new method for evaluating the quality of the facsimile. It is based on a measure, comparing the image of the inscription to the registered facsimile. Some empirical results, supporting the methodology, are presented. The technique is also relevant to quality evaluation of other types of facsimiles and binarization in general.

PloS one, 2017

Most surviving biblical period Hebrew inscriptions are ostraca-ink-on-clay texts. They are poorly... more Most surviving biblical period Hebrew inscriptions are ostraca-ink-on-clay texts. They are poorly preserved and once unearthed, fade rapidly. Therefore, proper and timely documentation of ostraca is essential. Here we show a striking example of a hitherto invisible text on the back side of an ostracon revealed via multispectral imaging. This ostracon, found at the desert fortress of Arad and dated to ca. 600 BCE (the eve of Judah's destruction by Nebuchadnezzar), has been on display for half a century. Its front side has been thoroughly studied, while its back side was considered blank. Our research revealed three lines of text on the supposedly blank side and four "new" lines on the front side. Our results demonstrate the need for multispectral image acquisition for both sides of all ancient ink ostraca. Moreover, in certain cases we recommend employing multispectral techniques for screening newly unearthed ceramic potsherds prior to disposal.

We deal with the general issue of handling statistical data in archaeology for the purpose of ded... more We deal with the general issue of handling statistical data in archaeology for the purpose of deducing sound, justified conclusions. The employment of various quantitative and statistical methods in archaeological practice has existed from its beginning as a systematic discipline in the 19th century (Drower 1995). Since this early period, the focus of archaeological research has developed and shifted several times. The last phase in this process, especially common in recent decades, is the proliferation of collaboration with various branches of the exact and natural sciences. Many new avenues of inquiry have been inaugurated, and a wealth of information has become available to archaeologists. In our view, the plethora of newly obtained data requires a careful reexamination of existing statistical approaches and a restatement of the desired focus of some archaeological investigations. We are delighted to dedicate this article to Israel Finkelstein, our teacher, adviser, colleague, an...

Proceedings of the 4th International Workshop on Historical Document Imaging and Processing, 2017

The problem of finding a prototype for typewritten or handwritten characters belongs to a family ... more The problem of finding a prototype for typewritten or handwritten characters belongs to a family of "shape prior" estimation problems. In epigraphic research, such priors are derived manually, and constitute the building blocks of "paleographic tables". Suggestions for automatic solutions to the estimation problem are rare in both the Computer Vision and the OCR/Handwriting Text Recognition communities. We review some of the existing approaches, and propose a new robust scheme, suitable for the challenges of degraded historical documents. This fast and easy to implement method is employed for ancient Hebrew inscriptions dated to the First Temple period.

Journal of Computational Physics, 2019

2016 15th International Conference on Frontiers in Handwriting Recognition (ICFHR), 2016

Journal of Scientific Computing, 2012

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific ... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et a ̀ la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

ArXiv, 2021

We use the Method of Difference Potentials (MDP) to solve a non-overlapping domain decomposition ... more We use the Method of Difference Potentials (MDP) to solve a non-overlapping domain decomposition formulation of the Helmholtz equation. The MDP reduces the Helmholtz equation on each subdomain to a Calderon’s boundary equation with projection on its boundary. The unknowns for the Calderon’s equation are the Dirichlet and Neumann data. Coupling between neighboring subdomains is rendered by applying their respective Calderon’s equations to the same data at the common interface. Solutions on individual subdomains are computed concurrently using a straightforward direct solver. We provide numerical examples demonstrating that our method is insensitive to interior cross-points and mixed boundary conditions, as well as large jumps in the wavenumber for transmission problems, which are known to be problematic for many other Domain Decomposition Methods.

We consider problems that involve the propagation of waves over large regions of space with smoot... more We consider problems that involve the propagation of waves over large regions of space with smooth, but not necessarily constant, material characteristics, separated by interfaces of arbitrary shape. The external boundaries can also be arbitrarily shaped. We present a numerical methodology for solving such problems that provides high order accuracy. It is based on Calderon’s operators and the method of difference potentials and overcomes the difficulties inherent in more traditional approaches.

We develop a compact fourth order scheme for the three-dimensional elastic wave equation in frequ... more We develop a compact fourth order scheme for the three-dimensional elastic wave equation in frequency space, using the first order velocity-stress formulation. The scheme is implemented numerically for homogeneous media on a staggered grid, and both the acoustic and elastic cases are considered. We use a one-directional point source of impact, for which Pilant developed a closed solution. Numerical results for the acoustic and the elastic cases compare favorably with the analytic solutions and show a very significant improvement over the second order scheme.

We consider acoustic scattering about a general body. This is described by the Helmholtz equation... more We consider acoustic scattering about a general body. This is described by the Helmholtz equation exterior to the body. In order to truncate the infinite domain we use the BGT absorbing boundary condition. The resultant problem in a finite domain is solved by a finite element procedure. This yields a large sparse system of linear equations which is neither symmetric nor positive definite. We solve the system by an iterative Krylov space type method. To increase the rate of convergence a preconditioner is introduced. This preconditioner is based on a different Helmholtz equation with complex coefficients. This preconditioned system is again solved by a Krylov space method with an ILU preconditioner. Computations are presented to show the efficiency of this technique.

The method of difference potentials was originally proposed by Ryaben’kii, and is a generalized d... more The method of difference potentials was originally proposed by Ryaben’kii, and is a generalized discrete version of the method of Calderon’s operators. It handles non-conforming curvilinear boundaries, variable coefficients, and non-standard boundary conditions while keeping the complexity of the solver at the level of a finite-difference scheme on a regular structured grid. Compact finite difference schemes enable high order accuracy on small stencils and so require no additional boundary conditions beyond those needed for the differential equation itself. Previously, we have used difference potentials combined with compact schemes for solving transmission/scattering problems in regions of a simple shape. In this paper, we generalize our previous work to incorporate general shaped boundaries and interfaces.

Journal of Scientific Computing