Search results for "RECONSTRUCTION"
showing 10 items of 784 documents
Simulated one-pass list-mode: an approach to on-the-fly system matrix calculation.
2013
In the development of prototype systems for positron emission tomography a valid and robust image reconstruction algorithm is required. However, prototypes often employ novel detector and system geometries which may change rapidly under optimization. In addition, developing systems generally produce highly granular, or possibly continuous detection domains which require some level of on-the-fly calculation for retention of measurement precision. In this investigation a new method of on-the-fly system matrix calculation is proposed that provides advantages in application to such list-mode systems in terms of flexibility in system modeling. The new method is easily adaptable to complicated sy…
An experimental study of the stability problem in discrete tomography
2003
This paper introduces the topic of discrete tomography, briefly showing its main applications, algorithms and new prospects of research. It focuses on the still open problem of stability, facing it from an experimental point of view. In particular an extensive simulation lets verify the robustness of a well known reconstruction technique for binary convex objects, calculating the probability of finding solutions compatible with a given set of noisy projections. © 2005 Elsevier Ltd. All rights reserved.
A Memetic Algorithm for Binary Image Reconstruction
2008
This paper deals with a memetic algorithm for the reconstruction of binary images, by using their projections along four directions. The algorithm generates by network flows a set of initial images according to two of the input projections and lets them evolve toward a solution that can be optimal or close to the optimum. Switch and compactness operators improve the quality of the reconstructed images which belong to a given generation, while the selection of the best image addresses the evolution to an optimal output.
Optimal Paths on Urban Networks Using Travelling Times Prevision
2012
We deal with an algorithm that, once origin and destination are fixed, individuates the route that permits to reach the destination in the shortest time, respecting an assigned maximal travel time, and with risks measure below a given threshold. A fluid dynamic model for road networks, according to initial car densities on roads and traffic coefficients at junctions, forecasts the future traffic evolution, giving dynamical weights to a constrained 𝐾 shortest path algorithm. Simulations are performed on a case study to test the efficiency of the proposed procedure.
Subsignal-based denoising from piecewise linear or constant signal
2011
15 pages; International audience; n the present work, a novel signal denoising technique for piecewise constant or linear signals is presented termed as "signal split." The proposed method separates the sharp edges or transitions from the noise elements by splitting the signal into different parts. Unlike many noise removal techniques, the method works only in the nonorthogonal domain. The new method utilizes Stein unbiased risk estimate (SURE) to split the signal, Lipschitz exponents to identify noise elements, and a polynomial fitting approach for the sub signal reconstruction. At the final stage, merging of all parts yield in the fully denoised signal at a very low computational cost. St…
Signal Restoration via a Splitting Approach
2012
International audience; In the present study, a novel signal restoration method from noisy data samples is presented and is termed as "signal split (SSplit)" approach. The new method utilizes Stein unbiased risk estimate estimator to split the signal, the Lipschitz exponents to identify noise elements and a heuristic approach for the signal reconstruction. However, unlike many noise removal techniques, the present method works only in the non-orthogonal domain. Signal restoration was performed on each individual part by finding the best compromise between the data samples and the smoothing criteria. Statistical results are quite promising and suggest better performance than the conventional…
High resolution in currents reconstruction applying the extrapolation matrix and spectrum replies
2007
A faster method for the reconstruction of currents has been proposed. For this a new algorithm has been used which extrapolates a 2D signal in less time than the iterative method of Papoulis. Results exposed in this paper show the likeness of the reconstructed currents with the new algorithm with those of the iterative method and the improvement that might be obtained in these new currents with regard to the iterative one. Furthermore, results show the higher speed of the new matrix method.
Upper Palaeolithic hunter-gatherer subsistence in Mediterranean coastal environments: an isotopic study of the diets of earliest directlyt-dated huma…
2011
Abstract The subsistence of hunter-gatherers in the Mediterranean Basin has been the object of few studies, which have not fully clarified the role of aquatic resources in their diets. Here we present the results of AMS radiocarbon dating and of isotope analyses on the earliest directly-dated human remains from Sicily, the largest island in the Mediterranean Sea. The radiocarbon determinations show that the Upper Palaeolithic (Epigravettian) humans from Grotta di San Teodoro (15 232–14 126 cal. BP) and Grotta Addaura Caprara (16 060–15 007 cal. BP) date to the Late-glacial and were possibly contemporary. The diets of these individuals were dominated by the protein of large terrestrial mamma…
8000 years of coastal changes on a western Mediterranean island: A multiproxy approach from the Posada plain of Sardinia
2018
Abstract A multi-proxy palaeoenvironmental investigation was conducted to reconstruct the Holocene history of coastal landscape change in the lower Posada coastal plain of eastern Sardinia. In the Mediterranean region, coastal modifications during the Holocene have been driven by a complex interplay between climate, geomorphological processes and human activity. In this paper, millennial-scale human-sea level-environment interactions are investigated near Posada, one of the largest coastal plains in eastern Sardinia. Biostratigraphic and palynological approaches were used to interpret the chrono-stratigraphy exhibited by a series of new cores taken from the coastal plain. This new study elu…
Pre‐instrumental summer precipitation variability in northwestern Greece from a high‐elevation Pinus heldreichii network
2021
The spatiotemporal variability of precipitation is of vital importance to Mediterranean ecology and economy, but pre‐instrumental changes are not well understood. Here, we present a millennial‐length June–July precipitation reconstruction derived from a network of 22 Pinus heldreichii high‐elevation sites in the Pindus Mountains of northwestern Greece. Tree‐ring width chronologies from these sites cohere exceptionally well over the past several hundred years (r1467–2015 = 0.64) revealing coherence at inter‐annual to centennial timescales across the network. The network mean calibrates significantly against instrumental June–July precipitation over the past 40 years (r1976–2015 = 0.71), even…