Journal articles on the topic 'Reconstruction de la densité'
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Rutherford, S., M. E. Mann, T. J. Osborn, K. R. Briffa, P D Jones, R. S. Bradley, and M. K. Hughes. "Proxy-Based Northern Hemisphere Surface Temperature Reconstructions: Sensitivity to Method, Predictor Network, Target Season, and Target Domain." Journal of Climate 18, no. 13 (July 1, 2005): 2308–29. http://dx.doi.org/10.1175/jcli3351.1.
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Abstract Results are presented from a set of experiments designed to investigate factors that may influence proxy-based reconstructions of large-scale temperature patterns in past centuries. The factors investigated include 1) the method used to assimilate proxy data into a climate reconstruction, 2) the proxy data network used, 3) the target season, and 4) the spatial domain of the reconstruction. Estimates of hemispheric-mean temperature are formed through spatial averaging of reconstructed temperature patterns that are based on either the local calibration of proxy and instrumental data or a more elaborate multivariate climate field reconstruction approach. The experiments compare results based on the global multiproxy dataset used by Mann and coworkers, with results obtained using the extratropical Northern Hemisphere (NH) maximum latewood tree-ring density set used by Briffa and coworkers. Mean temperature reconstructions are compared for the full NH (Tropics and extratropics, land and ocean) and extratropical continents only, withvarying target seasons (cold-season half year, warm-season half year, and annual mean). The comparisons demonstrate dependence of reconstructions on seasonal, spatial, and methodological considerations, emphasizing the primary importance of the target region and seasonal window of the reconstruction. The comparisons support the generally robust nature of several previously published estimates of NH mean temperature changes in past centuries and suggest that further improvements in reconstructive skill are most likely to arise from an emphasis on the quality, rather than quantity, of available proxy data.
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Rus, Guillermo, and Juan Melchor. "Logical Inference Framework for Experimental Design of Mechanical Characterization Procedures." Sensors 18, no. 9 (September 7, 2018): 2984. http://dx.doi.org/10.3390/s18092984.
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Optimizing an experimental design is a complex task when a model is required for indirect reconstruction of physical parameters from the sensor readings. In this work, a formulation is proposed to unify the probabilistic reconstruction of mechanical parameters and an optimization problem. An information-theoretic framework combined with a new metric of information density is formulated providing several comparative advantages: (i) a straightforward way to extend the formulation to incorporate additional concurrent models, as well as new unknowns such as experimental design parameters in a probabilistic way; (ii) the model causality required by Bayes’ theorem is overridden, allowing generalization of contingent models; and (iii) a simpler formulation that avoids the characteristic complex denominator of Bayes’ theorem when reconstructing model parameters. The first step allows the solving of multiple-model reconstructions. Further extensions could be easily extracted, such as robust model reconstruction, or adding alternative dimensions to the problem to accommodate future needs.
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Ionita, Sabina, Serban Popescu, and Ioan Lascar. "Polypropylene meshes and other alloplastic implants for soft tissue and cartilage nasal reconstructive surgery – a literature review." Romanian Journal of Rhinology 5, no. 18 (June 1, 2015): 87–94. http://dx.doi.org/10.1515/rjr-2015-0010.
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Abstract BACKGROUND. The reconstructive surgery is a domain in continuous research for new techniques and alloplastic materials for replacement of complex defects. Different biomaterials are used in soft tissue reconstruction including polypropylene meshes covered with collagen, which have the best results in abdominal and pelvic surgery, but are not yet used in nasal surgery. MATERIAL AND METHODS. We analysed the studies from the literature regarding the different alloplastic implants used in nasal reconstruction surgery, their benefits and contraindications for nasal defects. RESULTS. The most used polymers are Silicone, Medpor®, Mersilene® and polypropylene. Silicone is no longer widely used in facial reconstructive surgery because of its many complications. Medpor® (high-density polyethylene) is used for reconstruction of the facial skeleton and for aesthetic contour enhancement, including nasal reconstruction. Mersilene® (polyethylene terephthalate) is used for dorsum nasal defect reconstruction. Gore-Tex® is used for soft-tissue augmentation in the nose and is not recommended as a structural graft. Polypropylene meshes (Marlex®) are widely used in abdominal and chest wall reconstructive surgeries, with few studies on using them in nasal cartilage reconstruction. CONCLUSION. Nasal reconstructive surgery is a difficult part of plastic surgery than can cause many problems to the surgeon, the need for soft tissue and cartilage reconstruction are difficult to solve in a repeatedly operated nose with few autogenous graft options and complex reconstructive surgeries, especially in posttraumatic defects and revision rhinoplasties. There are many alloplastic implants that can be used with excellent results.
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Durbec, M., N. Mayer, D. Vertu-Ciolino, F. Disant, F. Mallein-Gerin, and E. Perrier-Groult. "Reconstruction du cartilage nasal par ingénierie tissulaire à base de polyéthylène de haute densité et d’un hydrogel." Pathologie Biologie 62, no. 3 (June 2014): 137–45. http://dx.doi.org/10.1016/j.patbio.2014.03.001.
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Hasenberger, Birgit, and João Alves. "AVIATOR: Morphological object reconstruction in 3D." Astronomy & Astrophysics 633 (January 2020): A132. http://dx.doi.org/10.1051/0004-6361/201936095.
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Reconstructing 3D distributions from their 2D projections is a ubiquitous problem in various scientific fields, particularly so in observational astronomy. In this work, we present a new approach to solving this problem: a Vienna inverse-Abel-transform based object reconstruction algorithm AVIATOR. The reconstruction that it performs is based on the assumption that the distribution along the line of sight is similar to the distribution in the plane of projection, which requires a morphological analysis of the structures in the projected image. The output of the AVIATOR algorithm is an estimate of the 3D distribution in the form of a reconstruction volume that is calculated without the problematic requirements that commonly occur in other reconstruction methods such as symmetry in the plane of projection or modelling of radial profiles. We demonstrate the robustness of the technique to different geometries, density profiles, and noise by applying the AVIATOR algorithm to several model objects. In addition, the algorithm is applied to real data: We reconstruct the density and temperature distributions of two dense molecular cloud cores and find that they are in excellent agreement with profiles reported in the literature. The AVIATOR algorithm is thus capable of reconstructing 3D distributions of physical quantities consistently using an intuitive set of assumptions.
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He, Yuhang, Zhiheng Ma, Xing Wei, Xiaopeng Hong, Wei Ke, and Yihong Gong. "Error-Aware Density Isomorphism Reconstruction for Unsupervised Cross-Domain Crowd Counting." Proceedings of the AAAI Conference on Artificial Intelligence 35, no. 2 (May 18, 2021): 1540–48. http://dx.doi.org/10.1609/aaai.v35i2.16245.
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This paper focuses on the unsupervised domain adaptation problem for video-based crowd counting, in which we use labeled data as source domain and unlabelled video data as target domain. It is challenging as there is a huge gap between the source and the target domain and no annotations of samples are available in the target domain. The key issue is how to utilize unlabelled videos in the target domain for knowledge learning and transferring from the source domain. To tackle this problem, we propose a novel Error-aware Density Isomorphism REConstruction Network (EDIREC-Net) for cross-domain crowd counting. EDIREC-Net jointly transfers a pre-trained counting model to target domains using a density isomorphism reconstruction objective and models the reconstruction erroneousness by error reasoning. Specifically, as crowd flows in videos are consecutive, the density maps in adjacent frames turn out to be isomorphic. On this basis, we regard the density isomorphism reconstruction error as a self-supervised signal to transfer the pre-trained counting models to different target domains. Moreover, we leverage an estimation-reconstruction consistency to monitor the density reconstruction erroneousness and suppress unreliable density reconstructions during training. Experimental results on four benchmark datasets demonstrate the superiority of the proposed method and ablation studies investigate the efficiency and robustness. The source code is available at https://github.com/GehenHe/EDIREC-Net.
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Jäger, M., P. Hübner, D. Haitz, and B. Jutzi. "A COMPARATIVE NEURAL RADIANCE FIELD (NERF) 3D ANALYSIS OF CAMERA POSES FROM HOLOLENS TRAJECTORIES AND STRUCTURE FROM MOTION." International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLVIII-1/W1-2023 (May 25, 2023): 207–13. http://dx.doi.org/10.5194/isprs-archives-xlviii-1-w1-2023-207-2023.
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Abstract. Neural Radiance Fields (NeRFs) are trained using a set of camera poses and associated images as input to estimate density and color values for each position. The position-dependent density learning is of particular interest for photogrammetry, enabling 3D reconstruction by querying and filtering the NeRF coordinate system based on the object density. While traditional methods like Structure from Motion are commonly used for camera pose calculation in pre-processing for NeRFs, the HoloLens offers an interesting interface for extracting the required input data directly. We present a workflow for high-resolution 3D reconstructions almost directly from HoloLens data using NeRFs. Thereby, different investigations are considered: Internal camera poses from the HoloLens trajectory via a server application, and external camera poses from Structure from Motion, both with an enhanced variant applied through pose refinement. Results show that the internal camera poses lead to NeRF convergence with a PSNR of 25 dB with a simple rotation around the x-axis and enable a 3D reconstruction. Pose refinement enables comparable quality compared to external camera poses, resulting in improved training process with a PSNR of 27 dB and a better 3D reconstruction. Overall, NeRF reconstructions outperform the conventional photogrammetric dense reconstruction using Multi-View Stereo in terms of completeness and level of detail.
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Skamarock, William C., and Maximo Menchaca. "Conservative Transport Schemes for Spherical Geodesic Grids: High-Order Reconstructions for Forward-in-Time Schemes." Monthly Weather Review 138, no. 12 (December 1, 2010): 4497–508. http://dx.doi.org/10.1175/2010mwr3390.1.
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Abstract The finite-volume transport scheme of Miura, for icosahedral–hexagonal meshes on the sphere, is extended by using higher-order reconstructions of the transported scalar within the formulation. The use of second- and fourth-order reconstructions, in contrast to the first-order reconstruction used in the original scheme, results in significantly more accurate solutions at a given mesh density, and better phase and amplitude error characteristics in standard transport tests. The schemes using the higher-order reconstructions also exhibit much less dependence of the solution error on the time step compared to the original formulation. The original scheme of Miura was only tested using a nondeformational time-independent flow. The deformational time-dependent flow test used to examine 2D planar transport in Blossey and Durran is adapted to the sphere, and the schemes are subjected to this test. The results largely confirm those generated using the simpler tests. The results also indicate that the scheme using the second-order reconstruction is most efficient and its use is recommended over the scheme using the first-order reconstruction. The second-order reconstruction uses the same computational stencil as the first-order reconstruction and thus does not create any additional parallelization issues.
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Kunz, Torben, Andrew M. Dolman, and Thomas Laepple. "A spectral approach to estimating the timescale-dependent uncertainty of paleoclimate records – Part 1: Theoretical concept." Climate of the Past 16, no. 4 (August 11, 2020): 1469–92. http://dx.doi.org/10.5194/cp-16-1469-2020.
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Abstract. Proxy records represent an invaluable source of information for reconstructing past climatic variations, but they are associated with considerable uncertainties. For a systematic quantification of these reconstruction errors, however, knowledge is required not only of their individual sources but also of their auto-correlation structure as this determines the timescale dependence of their magnitude, an issue that has been often ignored until now. Here a spectral approach to uncertainty analysis is provided for paleoclimate reconstructions obtained from single sediment proxy records. The formulation in the spectral domain rather than the time domain allows for an explicit demonstration and quantification of the timescale dependence that is inherent in any proxy-based reconstruction uncertainty. This study is published in two parts. In this first part, the theoretical concept is presented, and analytic expressions are derived for the power spectral density of the reconstruction error of sediment proxy records. The underlying model takes into account the spectral structure of the climate signal, seasonal and orbital variations, bioturbation, sampling of a finite number of signal carriers, and uncorrelated measurement noise, and it includes the effects of spectral aliasing and leakage. The uncertainty estimation method, based upon this model, is illustrated by simple examples. In the second part of this study, published separately, the method is implemented in an application-oriented context, and more detailed examples are presented.
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Soufan, Alexandre T., Jan M. Ruijter, Maurice JB Van Den Hoff, and Antoon FM Moorman. "QUANTITATIVE 3D RECONSTRUCTIONS AS IDENTIFICATION TOOL IN HEART DEVELOPMENT." Image Analysis & Stereology 20, no. 3 (May 3, 2011): 193. http://dx.doi.org/10.5566/ias.v20.p193-198.
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A method for displaying quantitative information in 3D reconstructions of the embryonic heart was developed to investigate spatial distributions of cell division and cell density. The method utilizes serial sections to extract morphological as well as quantitative data. The morphological data are used to reconstruct the embryonic heart and the quantitative data are classified and superimposed on the resulting reconstruction. The bias, which would result from size differences between cell populations, was investigated. If present, it would influence the absolute number of particles (nuclei) per volume, although the classification applied on the reconstruction displaying the mitotic fraction remains unchanged. Although the reconstruction displaying the local densities is influenced by the bias, less than 2.5% of the regions is misclassified.
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Bayer, Adrian E., Chirag Modi, and Simone Ferraro. "Joint velocity and density reconstruction of the Universe with nonlinear differentiable forward modeling." Journal of Cosmology and Astroparticle Physics 2023, no. 06 (June 1, 2023): 046. http://dx.doi.org/10.1088/1475-7516/2023/06/046.
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Abstract Reconstructing the initial conditions of the Universe from late-time observations has the potential to optimally extract cosmological information. Due to the high dimensionality of the parameter space, a differentiable forward model is needed for convergence, and recent advances have made it possible to perform reconstruction with nonlinear models based on galaxy (or halo) positions. In addition to positions, future surveys will provide measurements of galaxies' peculiar velocities through the kinematic Sunyaev-Zel'dovich effect (kSZ), type Ia supernovae, the fundamental plane relation, and the Tully-Fisher relation. Here we develop the formalism for including halo velocities, in addition to halo positions, to enhance the reconstruction of the initial conditions. We show that using velocity information can significantly improve the reconstruction accuracy compared to using only the halo density field. We study this improvement as a function of shot noise, velocity measurement noise, and angle to the line of sight. We also show how halo velocity data can be used to improve the reconstruction of the final nonlinear matter overdensity and velocity fields. We have built our pipeline into the differentiable Particle-Mesh FlowPM package, paving the way to perform field-level cosmological inference with joint velocity and density reconstruction. This is especially useful given the increased ability to measure peculiar velocities in the near future.
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Li, Xian, Chao Jiang, Hui Gao, Chunjuan Wang, Chao Wang, and Ping Ji. "Biomechanical Analysis of Various Reconstructive Methods for the Mandibular Body and Ramus Defect Using a Free Vascularized Fibula Flap." BioMed Research International 2020 (March 13, 2020): 1–14. http://dx.doi.org/10.1155/2020/8797493.
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Several different methods exist for reconstructing the mandibular body and ramus defect with the use of a free vascularized fibula flap, but none have adequately addressed the long-term mechanical stability and osseointegration. The aim of this study is to compare the biomechanics of different surgical methods and to investigate the best approach for reconstructing the mandibular body and ramus defect. Five finite element models based on different reconstructive methods were simulated. Stress, strain, and displacement of connective bone sections were calculated for five models and compared. The models were printed using a 3D printer, and stiffness was measured using an electromechanical universal testing machine. The postoperative follow-up cone beam computed tomography (CBCT) was taken at different time points to analyze bone mineral density of connective bone sections. The results showed that the “double up” (DU) model was the most efficient for reconstructing a mandibular body and ramus defect by comparing the mechanical distribution of three sections under vertical and inclined loading conditions of 100 N. The stiffness detection showed that stiffness in the DU and “double down” (DD) models was higher compared with the “single up” (SU), “single down” (SD), and “distraction osteogenesis” (DO) models. We used the DU model for the surgery, and postoperative follow-up CBCT showed that bone mineral density of each fibular connective section increased gradually with time, plateauing at 12 weeks. We conclude that a free vascularized fibula flap of the DU type was the best approach for the reconstruction of the mandibular body and ramus defect. Preoperative finite element analysis and stiffness testing were shown to be very useful for maxillofacial reconstruction.
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Long, Yuanliang, Xingliang Huo, Haojie Liu, Ying Li, and Weihong Sun. "An Extended Simultaneous Algebraic Reconstruction Technique for Imaging the Ionosphere Using GNSS Data and Its Preliminary Results." Remote Sensing 15, no. 11 (June 5, 2023): 2939. http://dx.doi.org/10.3390/rs15112939.
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To generate high-quality reconstructions of ionospheric electron density (IED), we propose an extended simultaneous algebraic reconstruction technique (ESART). The ESART method distributes the discrepancy between the actual GNSS TEC and the calculated TEC among the ray–voxels based on the contribution of voxels to GNSS TEC, rather than the ratio of the length of ray–voxel intersection to the sum of the lengths of all ray–voxel intersections, as is adopted by conventional methods. The feasibility of the ESART method for reconstructing the IED under different levels of geomagnetic activities is addressed. Additionally, a preliminary experiment is performed using the reconstructed IED profiles and comparing them with ionosonde measurements, which provide direct observations of electron density. The root mean square errors (RMSE) and absolute errors of the ESART method, the simultaneous algebraic reconstruction technique (SART) method, and the International Reference Ionosphere (IRI) 2016 model are calculated to evaluate the effectiveness of the proposed method. Compared to the conventional SART method of ionospheric tomography and the IRI-2016 model, the reconstructed IED profiles obtained using the ESART method are in better agreement with the electron density obtained from the ionosondes, especially for the peak electron densities (NmF2). In addition, a case study of an intense geomagnetic storm on 17–19 March 2015 shows that the spatial and temporal features of storm-related ionospheric disturbances can be more clearly depicted using the ESART method than with the SART method.
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Sipkens, T. A., S. J. Grauer, A. M. Steinberg, S. N. Rogak, and P. Kirchen. "New transform to project axisymmetric deflection fields along arbitrary rays." Measurement Science and Technology 33, no. 3 (December 21, 2021): 035201. http://dx.doi.org/10.1088/1361-6501/ac3f83.
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Abstract Axisymmetric tomography is used to extract quantitative information from line-of-sight measurements of gas flow and combustion fields. For instance, background-oriented schlieren (BOS) measurements are typically inverted by tomographic reconstruction to estimate the density field of a high-speed or high-temperature flow. Conventional reconstruction algorithms are based on the inverse Abel transform, which assumes that rays are parallel throughout the target object. However, camera rays are not parallel, and this discrepancy can result in significant errors in many practical imaging scenarios. We present a generalization of the Abel transform for use in tomographic reconstruction of light-ray deflections through an axisymmetric target. The new transform models the exact path of camera rays instead of assuming parallel paths, thereby improving the accuracy of estimates. We demonstrate our approach with a simulated BOS scenario in which we reconstruct noisy synthetic deflection data across a range of camera positions. Results are compared to state-of-the-art Abel-based algorithms. Reconstructions computed using the new transform are consistently more stable and accurate than conventional reconstructions.
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CHUNG, J. W., K. S. SHIN, and S. C. HONG. "ELECTRONIC STRUCTURE AND RECONSTRUCTION OF THE Mo(001) SURFACE." Modern Physics Letters B 07, no. 13n14 (June 20, 1993): 865–80. http://dx.doi.org/10.1142/s0217984993000862.
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Recent developments in understanding the nature of surface electronic structure focused on illuminating the electronic origin of reconstruction of the Mo (001) surface have been reviewed. The long-standing disputes between two competing theoretical models, the charge density wave model and the local bonding model, for the driving mechanism of the reconstructional transition seem to be resolved by recent experimental evidences favoring the Peierls-type 2kF instabilities with significant matrix element effects. Details of recent experimental and theoretical findings for the surface electronic bands are discussed briefly with an emphasis placed on characterizing the surface states and their roles in the reconstruction.
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Krammer, Julia, Sergei Zolotarev, Inge Hillman, Konstantinos Karalis, Dzmitry Stsepankou, Valeriy Vengrinovich, Jürgen Hesser, and Tony M. Svahn. "Evaluation of a new image reconstruction method for digital breast tomosynthesis: effects on the visibility of breast lesions and breast density." British Journal of Radiology 92, no. 1103 (November 2019): 20190345. http://dx.doi.org/10.1259/bjr.20190345.
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Objective: To compare image quality and breast density of two reconstruction methods, the widely-used filtered-back projection (FBP) reconstruction and the iterative heuristic Bayesian inference reconstruction (Bayesian inference reconstruction plus the method of total variation applied, HBI). Methods: Thirty-two clinical DBT data sets with malignant and benign findings, n = 27 and 17, respectively, were reconstructed using FBP and HBI. Three experienced radiologists evaluated the images independently using a 5-point visual grading scale and classified breast density according to the American College of Radiology Breast Imaging-Reporting And Data System Atlas, fifth edition. Image quality metrics included lesion conspicuity, clarity of lesion borders and spicules, noise level, artifacts surrounding the lesion, visibility of parenchyma and breast density. Results: For masses, the image quality of HBI reconstructions was superior to that of FBP in terms of conspicuity,clarity of lesion borders and spicules (p < 0.01). HBI and FBP were not significantly different in calcification conspicuity. Overall, HBI reduced noise and supressed artifacts surrounding the lesions better (p < 0.01). The visibility of fibroglandular parenchyma increased using the HBI method (p < 0.01). On average, five cases per radiologist were downgraded from BI-RADS breast density category C/D to A/B. Conclusion: HBI significantly improves lesion visibility compared to FBP. HBI-visibility of breast parenchyma increased, leading to a lower breast density rating. Applying the HBIR algorithm should improve the diagnostic performance of DBT and decrease the need for additional imaging in patients with dense breasts. Advances in knowledge: Iterative heuristic Bayesian inference (HBI) image reconstruction substantially improves the image quality of breast tomosynthesis leading to a better visibility of breast carcinomas and reduction of the perceived breast density compared to the widely-used filtered-back projection (FPB) reconstruction. Applying HBI should improve the accuracy of breast tomosynthesis and reduce the number of unnecessary breast biopsies. It may also reduce the radiation dose for the patients, which is especially important in the screening context.
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Li, Xuemei, and Yuhua Wang. "Proton imaging of 3D density distribution for dense DT plasmas using regularization method." Laser and Particle Beams 34, no. 2 (February 12, 2016): 210–18. http://dx.doi.org/10.1017/s0263034616000021.
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AbstractThree-dimensional (3D) density distribution of inhomogeneous dense deuterium tritium plasmas in laser fusion is revealed by the energy loss of fast protons going through the plasmas. The fast protons generated in the laser–plasma interaction can be used for the simulation of a plasma density diagnostics. The large linear and ill-posed equation set of the densities of all grids is obtained and then solved by the Tikhonov regularization method after dividing a 3D area into grids and knowing the initial and final energies of the protons. 3D density reconstructions with six proton sources are done without and with random noises added to the final energy. The revealed density is a little smaller than the simulated one in most simulated zones and the error is as much as those of 2D reconstructions with four proton sources. The picture element N is chosen as 2744 with consideration of smoothness and calculation memory of the computers. With fast calculation speed and low error, the Tikhonov regularization method is more suitable for 3D density reconstructions with large calculation amount than simultaneous iterative reconstruction method. Also the analytical expressions between the errors and the noises are established. Furthermore, the density reconstruction method in this paper is particularly suitable for plasmas with small density gradient. The errors without noises and with 2% noises added to the final proton energies are 3 and 20%, respectively, for the homogeneous plasma.
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Seftigen, Kristina, Edward R. Cook, Hans W. Linderholm, Mauricio Fuentes, and Jesper Björklund. "The Potential of Deriving Tree-Ring-Based Field Reconstructions of Droughts and Pluvials over Fennoscandia*,+." Journal of Climate 28, no. 9 (May 1, 2015): 3453–71. http://dx.doi.org/10.1175/jcli-d-13-00734.1.
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Abstract Moisture availability has been identified as one of the most important factors in the context of future climate change. This paper explores the potential of applying a multiproxy approach to dendroclimatology to infer the twentieth-century moisture variability over Fennoscandia. Fields of the warm-season (June–August) standardized precipitation evapotranspiration index (SPEI) were developed from a dense network of precipitation-sensitive annually resolved tree-ring width (TRW), maximum density (MXD), and stable carbon (δ13C) and oxygen (δ18O) isotope chronologies using a point-by-point local regression technique (PPR). Two different approaches were tested for selecting candidate tree-ring predictors of SPEI for each gridpoint reconstruction: a search radius method and a search spatial correlation contour method. As confirmed by a range of metrics of reconstruction fidelity, both methods produced reconstructions showing a remarkably high accuracy in a temporal sense, but with some minor regional differences. As a whole, the spatial skill of the reconstructed fields was generally quite good, showing the greatest performance in the central and southern parts of the target region. Lower reconstruction skills were observed in northern part of the study domain. Regional-scale moisture anomalies were best captured by the reconstructions, while local-scale features were not as well represented. The authors speculate that a spatially and temporally varying tree-ring proxy response to temperature and precipitation in the region may cause some uncertainties in a Fennoscandian hydroclimatic reconstruction; this needs further investigation. Overall, this study shows a great potential for making long-term spatiotemporal reconstructions of moisture variability for the Fennoscandian region using tree-ring data.
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Lu, Zhiqian, Feixiang Long, and Xiaodong He. "Classification and Segmentation Algorithm in Benign and Malignant Pulmonary Nodules under Different CT Reconstruction." Computational and Mathematical Methods in Medicine 2022 (April 21, 2022): 1–6. http://dx.doi.org/10.1155/2022/3490463.
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Background and Objective. Effective segmentation of pulmonary nodules can effectively assist in the diagnosis of benign and malignant pulmonary nodules. We aim to explore the effectiveness of classification and segmentation algorithms in diagnosing benign and malignant pulmonary nodules under different CT reconstructions. Methods. The imaging data of 55 patients with chest CT plain scan in the Xuancheng People’s Hospital were collected retrospectively. The data of each patient included lung window reconstruction, mediastinum reconstruction, and bone window reconstruction. The depth neural network and 3D convolution neural network were used to construct the model and train the classification and segmentation algorithm. The pathological results were the gold standard for benign and malignant pulmonary nodules. The classification and segmentation algorithms under three CT reconstruction algorithms were compared and analyzed by analysis of variance. Results. Under the three CT reconstruction algorithms, the classification accuracy of pulmonary nodule density types was 98.2%, 96.4%, and 94.5%, respectively. The Dice coefficients of all nodule segmentation were 80.32 % ± 5.91 % , 79.83 % ± 6.12 % , and 80.17 % ± 5.89 % , respectively. The diagnostic accuracy between benign and malignant pulmonary nodules under different reconstruction algorithms was 98.2%, 96.4%, and 94.5%, respectively. There was no significant difference in the classification accuracy, Dice coefficients, and diagnostic accuracy of pulmonary nodules under three different reconstruction algorithms (all P > 0.05 ). Conclusion. The depth neural network algorithm combined with 3D convolution neural network has a good efficiency in identifying benign and malignant pulmonary nodules under different CT reconstruction classification and segmentation algorithms.
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Aragon-Calvo, M. A. "Smooth stochastic density field reconstruction." Monthly Notices of the Royal Astronomical Society 503, no. 1 (February 11, 2021): 557–62. http://dx.doi.org/10.1093/mnras/stab403.
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ABSTRACT We introduce a method for generating a continuous, mass-conserving and high-order differentiable density field from a discrete point distribution such as particles or haloes from an N-body simulation or galaxies from a spectroscopic survey. The method consists on generating an ensemble of point realizations by perturbing the original point set following the geometric constraints imposed by the Delaunay tessellation in the vicinity of each point in the set. By computing the mean field of the ensemble we are able to significantly reduce artefacts arising from the Delaunay tessellation in poorly sampled regions while conserving the features in the point distribution. Our implementation is based on the Delaunay Tessellation Field Estimation (DTFE) method; however, other tessellation techniques are possible. The method presented here shares the same advantages of the DTFE method such as self-adaptive scale, mass conservation, and continuity, while being able to reconstruct even the faintest structures of the point distribution usually dominated by artefacts in Delaunay-based methods. Additionally, we also present preliminary results of an application of this method to image denoising and artefact removal, highlighting the broad applicability of the technique introduced here.
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Mohayaee, R., H. Mathis, S. Colombi, and J. Silk. "Reconstruction of primordial density fields." Monthly Notices of the Royal Astronomical Society 365, no. 3 (January 21, 2006): 939–59. http://dx.doi.org/10.1111/j.1365-2966.2005.09774.x.
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Choi, Hayoung, Victor Ginting, Farhad Jafari, and Robert Mnatsakanov. "Modified Radon transform inversion using moments." Journal of Inverse and Ill-posed Problems 28, no. 1 (February 1, 2020): 1–15. http://dx.doi.org/10.1515/jiip-2018-0090.
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AbstractMoment methods to reconstruct images from their Radon transforms are both natural and useful. They can be used to suppress noise or other spurious effects and can lead to highly efficient reconstructions from relatively few projections. We establish a modified Radon transform (MRT) via convolution with a mollifier and obtain its inversion formula. The relationship of the moments of the Radon transform and the moments of its modified Radon transform is derived, and MRT data is used to provide a uniform approximation to the original density function. The reconstruction algorithm is implemented, and a simple density function is reconstructed from moments of its modified Radon transform. Numerical convergence of this reconstruction is shown to agree with the derived theoretical results.
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Buccino, Alessio Paolo, Xinyue Yuan, Vishalini Emmenegger, Xiaohan Xue, Tobias Gänswein, and Andreas Hierlemann. "An automated method for precise axon reconstruction from recordings of high-density micro-electrode arrays." Journal of Neural Engineering 19, no. 2 (March 31, 2022): 026026. http://dx.doi.org/10.1088/1741-2552/ac59a2.
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Abstract Objective: Neurons communicate with each other by sending action potentials (APs) through their axons. The velocity of axonal signal propagation describes how fast electrical APs can travel. This velocity can be affected in a human brain by several pathologies, including multiple sclerosis, traumatic brain injury and channelopathies. High-density microelectrode arrays (HD-MEAs) provide unprecedented spatio-temporal resolution to extracellularly record neural electrical activity. The high density of the recording electrodes enables to image the activity of individual neurons down to subcellular resolution, which includes the propagation of axonal signals. However, axon reconstruction, to date, mainly relies on manual approaches to select the electrodes and channels that seemingly record the signals along a specific axon, while an automated approach to track multiple axonal branches in extracellular action-potential recordings is still missing. Approach: In this article, we propose a fully automated approach to reconstruct axons from extracellular electrical-potential landscapes, so-called ‘electrical footprints’ of neurons. After an initial electrode and channel selection, the proposed method first constructs a graph based on the voltage signal amplitudes and latencies. Then, the graph is interrogated to extract possible axonal branches. Finally, the axonal branches are pruned, and axonal action-potential propagation velocities are computed. Main results: We first validate our method using simulated data from detailed reconstructions of neurons, showing that our approach is capable of accurately reconstructing axonal branches. We then apply the reconstruction algorithm to experimental recordings of HD-MEAs and show that it can be used to determine axonal morphologies and signal-propagation velocities at high throughput. Significance: We introduce a fully automated method to reconstruct axonal branches and estimate axonal action-potential propagation velocities using HD-MEA recordings. Our method yields highly reliable and reproducible velocity estimations, which constitute an important electrophysiological feature of neuronal preparations.
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Pederson, Neil, Kacie Tackett, Ryan W. McEwan, Stacy Clark, Adrienne Cooper, Glade Brosi, Ray Eaton, and R. Drew Stockwell. "Long-term drought sensitivity of trees in second-growth forests in a humid region." Canadian Journal of Forest Research 42, no. 10 (October 2012): 1837–50. http://dx.doi.org/10.1139/x2012-130.
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Classical field methods of reconstructing drought using tree rings in humid, temperate regions typically target old trees from drought-prone sites. This approach limits investigators to a handful of species and excludes large amounts of data that might be useful, especially for coverage gaps in large-scale networks. By sampling in more “typical” forests, network density and species diversity would increase in ways that could potentially improve reconstructions. Ten nonclassical tree-ring chronologies derived from randomly selected trees, trees from logged forests, or both were compared to more classical chronologies and an independent regional drought reconstruction to determine their usefulness for dendrohydroclimatic research. We find that nonclassical chronologies are significantly correlated to classical chronologies and reconstructed drought over the last 2–3 centuries. While nonclassical chronologies have spectral properties similar to those from classical dendroclimatic collections, they do lack spectral power at lower frequencies that are present in the drought reconstruction. Importantly, our results show that tree growth is strongly dependent on moisture availability, even for small, randomly selected trees in cut forests. These results indicate that there could be more data available in areas with few current tree-ring collections for studying climate history and that drought plays an important role in humid forests.
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Himpel, Michael, and André Melzer. "Three-Dimensional Reconstruction of Individual Particles in Dense Dust Clouds: Benchmarking Camera Orientations and Reconstruction Algorithms." Journal of Imaging 5, no. 2 (February 13, 2019): 28. http://dx.doi.org/10.3390/jimaging5020028.
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In dusty plasmas, determining the three-dimensional particle positions and trajectories of individual particles is often required. This paper benchmarks two approaches capable of reconstructing the trajectories of particles in three dimensions. The influences of the particle number, the particle number density, and the orientation of the individual cameras are studied. Additionally, the demands on the desired image quality, required for these algorithms, are discussed. The reader is given practical information for the appropriate reconstruction approach and camera positioning that should/could be used in a specific application.
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Wu, Fupei, Shukai Zhu, and Weilin Ye. "A Single Image 3D Reconstruction Method Based on a Novel Monocular Vision System." Sensors 20, no. 24 (December 9, 2020): 7045. http://dx.doi.org/10.3390/s20247045.
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Three-dimensional (3D) reconstruction and measurement are popular techniques in precision manufacturing processes. In this manuscript, a single image 3D reconstruction method is proposed based on a novel monocular vision system, which includes a three-level charge coupled device (3-CCD) camera and a ring structured multi-color light emitting diode (LED) illumination. Firstly, a procedure for the calibration of the illumination’s parameters, including LEDs’ mounted angles, distribution density and incident angles, is proposed. Secondly, the incident light information, the color distribution information and gray level information are extracted from the acquired image, and the 3D reconstruction model is built based on the camera imaging model. Thirdly, the surface height information of the detected object within the field of view is computed based on the built model. The proposed method aims at solving the uncertainty and the slow convergence issues arising in 3D surface topography reconstruction using current shape-from-shading (SFS) methods. Three-dimensional reconstruction experimental tests are carried out on convex, concave, angular surfaces and on a mobile subscriber identification module (SIM) card slot, showing relative errors less than 3.6%, respectively. Advantages of the proposed method include a reduced time for 3D surface reconstruction compared to other methods, demonstrating good suitability of the proposed method in reconstructing surface 3D morphology.
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Ibrahim, Sharif, Kevin Sonnanburg, Thomas J. Asaki, and Kevin R. Vixie. "Nonasymptotic Densities for Shape Reconstruction." Abstract and Applied Analysis 2014 (2014): 1–14. http://dx.doi.org/10.1155/2014/341910.
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In this work, we study the problem of reconstructing shapes from simple nonasymptotic densities measured only along shape boundaries. The particular density we study is also known as the integral area invariant and corresponds to the area of a disk centered on the boundary that is also inside the shape. It is easy to show uniqueness when these densities are known for all radii in a neighborhood ofr=0, but much less straightforward when we assume that we only know the area invariant and its derivatives for only oner>0. We present variations of uniqueness results for reconstruction (modulo translation and rotation) of polygons and (a dense set of) smooth curves under certain regularity conditions.
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Zhang, Peng, Hans W. Linderholm, Björn E. Gunnarson, Jesper Björklund, and Deliang Chen. "1200 years of warm-season temperature variability in central Scandinavia inferred from tree-ring density." Climate of the Past 12, no. 6 (June 3, 2016): 1297–312. http://dx.doi.org/10.5194/cp-12-1297-2016.
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Abstract. Despite the emergence of new high-resolution temperature reconstructions around the world, only a few cover the Medieval Climate Anomaly (MCA). Here we present C-Scan, a new Scots pine tree-ring density-based reconstruction of warm-season (April–September) temperatures for central Scandinavia back to 850 CE, extending the previous reconstruction by 250 years. C-Scan is based on samples collected in a confined mountain region, adjusted for their differences in altitude and local environment, and standardised using the new RSFi algorithm to preserve low-frequency signals. In C-Scan, the warm peak of MCA occurs ca. 1000–1100 CE, and the Little Ice Age (LIA) between 1550 and 1900 CE. Moreover, during the last millennium the coldest decades are found around 1600 CE, and the warmest 10 and 30 years occur in the most recent century. By comparing C-Scan with other millennium-long temperature reconstructions from Fennoscandia, regional differences in multi-decadal temperature variability, especially during the warm period of the last millennium are revealed. Although these differences could be due to methodological reasons, they may indicate asynchronous warming patterns across Fennoscandia. Further investigation of these regional differences and the reasons and mechanisms behind them are needed.
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Wisselink, Hendrik Joost, Gert Jan Pelgrim, Mieneke Rook, Maarten van den Berge, Kees Slump, Yeshu Nagaraj, Peter van Ooijen, Matthijs Oudkerk, and Rozemarijn Vliegenthart. "Potential for dose reduction in CT emphysema densitometry with post-scan noise reduction: a phantom study." British Journal of Radiology 93, no. 1105 (January 2020): 20181019. http://dx.doi.org/10.1259/bjr.20181019.
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Objective: The aim of this phantom study was to investigate the effect of scan parameters and noise suppression techniques on the minimum radiation dose for acceptable image quality for CT emphysema densitometry. Methods: The COPDGene phantom was scanned on a third generation dual-source CT system with 16 scan setups (CTDIvol 0.035–10.680 mGy). Images were reconstructed at 1.0/0.7 mm slice thickness/increment, with three kernels (one soft, two hard), filtered backprojection and three grades of third-generation iterative reconstruction (IR). Additionally, deep learning-based noise suppression software was applied. Main outcomes: overlap in area of the normalized histograms of CT density for the emphysema insert and lung material, and the radiation dose required for a maximum of 4.3% overlap (defined as acceptable image quality). Results: In total, 384 scan reconstructions were analyzed. Decreasing radiation dose resulted in an exponential increase of the overlap in normalized histograms of CT density. The overlap was 11–91% for the lowest dose setting (CTDIvol 0.035mGy). The soft kernel reconstruction showed less histogram overlap than hard filter kernels. IR and noise suppression also reduced overlap. Using intermediate grade IR plus noise suppression software allowed for 85% radiation dose reduction while maintaining acceptable image quality. Conclusion: CT density histogram overlap can quantify the degree of discernibility of emphysema and healthy lung tissue. Noise suppression software, IR, and soft reconstruction kernels substantially decrease the dose required for acceptable image quality. Advances in knowledge: Noise suppression software, IR, and soft reconstruction kernels allow radiation dose reduction by 85% while still allowing differentiation between emphysema and normal lung tissue.
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Wen, Debao, Sanzhi Liu, and Pingying Tang. "Tomographic reconstruction of ionospheric electron density based on constrained algebraic reconstruction technique." GPS Solutions 14, no. 4 (March 3, 2010): 375–80. http://dx.doi.org/10.1007/s10291-010-0161-0.
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Roy, Rinto, Alexander Tessler, Cecilia Surace, and Marco Gherlone. "Shape Sensing of Plate Structures Using the Inverse Finite Element Method: Investigation of Efficient Strain–Sensor Patterns." Sensors 20, no. 24 (December 9, 2020): 7049. http://dx.doi.org/10.3390/s20247049.
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Methods for real-time reconstruction of structural displacements using measured strain data is an area of active research due to its potential application for Structural Health Monitoring (SHM) and morphing structure control. The inverse Finite Element Method (iFEM) has been shown to be well suited for the full-field reconstruction of displacements, strains, and stresses of structures instrumented with discrete or continuous strain sensors. In practical applications, where the available number of sensors may be limited, the number and sensor positions constitute the key parameters. Understanding changes in the reconstruction quality with respect to sensor position is generally difficult and is the aim of the present work. This paper attempts to supplement the current iFEM modeling knowledge through a rigorous evaluation of several strain–sensor patterns for shape sensing of a rectangular plate. Line plots along various sections of the plate are used to assess the reconstruction quality near and far away from strain sensors, and the nodal displacements are studied as the sensor density increases. The numerical results clearly demonstrate the effectiveness of the strain sensors distributed along the plate boundary for reconstructing relatively simple displacement patterns, and highlight the potential of cross-diagonal strain–sensor patterns to improve the displacement reconstruction of more complex deformation patterns.
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Bashurin, V. P., V. V. Bashurov, Yu D. Bogunenko, G. A. Bondarenko, F. A. Pletenev, and V. A. Starodubtsev. "Quantitative measurement feasibility for 3D distributions of hydrodynamic quantities in the turbulent mixing zone of two gases." Laser and Particle Beams 15, no. 1 (March 1997): 73–82. http://dx.doi.org/10.1017/s0263034600010764.
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In doing research on the turbulent mixing (TM) of two gases different in density, it is of great interest to study experimentally the 3D density distribution pattern of chemically nonreactive gases in the TM zone. For this purpose, noncontact and, particularly, optical techniques to obtain experimental data may be attractive. This article discusses the possibility of using pulsed laser interferometry in this application. Based on this technique, the experiment should result in the mixture density distribution integrated along the light path. Requirements for high-quality interference patterns have been analyzed in application to typical experimental conditions, to show that they may be produced with specific restrictions set on the mixture constitution. Generally, the TM zone has no symmetry. Therefore, the problem of reconstructing 3D density distributions (TDD) of gases can be solved by sufficiently providing many TM zone integral projections (or aspects). It is technically difficult and expensive to achieve this large number of aspects (N> 10). Therefore, it is essential that a reconstruction method be selected to allow the solution of the problem with the least possible number of aspects. Given that the experiment data are incomplete, the reconstruction methods that are based on the concept of maximum data entropy did well. Information a priori about the solution to be sought for an isobaric gas mixture is that its each constituent has invariable density. Thus, a functional data entropy can be defined that is similar to Fermi gas in statistical physics. An algorithm has been suggested for reconstruction as a modified maximum-bounded entropy procedure (Bashurin et al. 1995). This makes reasonable good reconstruction achievable even with as few aspects as N = 4. Experiments on the study of TM of a propane jet in air using a four-aspects laser interferometer were provided and reconstruction of propane concentration distribution was conducted. The results allow determination of the TM zone spectral characteristics.
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Nagatani, Yukihiro, Makoto Yoshigoe, Shinsuke Tsukagoshi, Noritoshi Ushio, Kohei Ohashi, Norihisa Nitta, Tatsuya Kimoto, et al. "Peripheral bronchial luminal conspicuity on dynamic-ventilation computed tomography: association with radiation doses and temporal resolution by using an ex vivo porcine lung phantom." Acta Radiologica 61, no. 12 (March 25, 2020): 1608–17. http://dx.doi.org/10.1177/0284185120911186.
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Background It is still unclear which image reconstruction algorithm is appropriate for peripheral bronchial luminal conspicuity (PBLC) on dynamic-ventilation computed tomography (DVCT). Purpose To assess the influence of radiation doses and temporal resolution (TR) on the association between movement velocity (MV) and PBLC on DVCT. Material and Methods An ex vivo porcine lung phantom with simulated respiratory movement was scanned by 320-row CT at 240 mA and 10 mA. Peak and dip CT density and luminal area adjusted by values at end-inspiration (CTDpeak and CTDdip, luminal area ratio [LAR]) for PBLC and MVs were measured and visual scores (VS) were obtained at 12 measurement points on 13 frame images obtained at half and full reconstructions (TR 340 and 190 ms) during expiration. Size-specific dose estimate (SSDE) was applied to presume radiation dose. VS, CTDpeak, CTDdip, LAR, and their cross-correlation coefficients with MV (CCC) were compared among four methods with combinations of two reconstruction algorithms and two doses. Results The dose at 10 mA was presumed as 26 mA by SSDE for standard proportion adults. VS, CTDdip, CTDpeak, and LAR with half reconstruction at 10 mA (2.52 ± 0.59, 1.016 ± 0.221, 0.948 ± 0.103, and 0.990 ± 0.527) were similar to those at 240 mA except for VS, and different from those with full reconstruction at both doses (2.24 ± 0.85, 0.830 ± 0.209, 0.986 ± 0.065, and 1.012 ± 0.438 at 240 mA) ( P < 0.05). CCC for CTDdip with half reconstruction (–0.024 ± 0.552) at 10 mA was higher compared with full reconstruction (–0.503 ± 0.291) ( P < 0.05). Conclusion PBLC with half reconstruction at 10 mA was comparable to that at 240 mA and better than those with full reconstruction on DVCT.
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Manstein, Carl H. "REPLACEMENT BONE DENSITY IN MANDIBULAR RECONSTRUCTION." Plastic and Reconstructive Surgery 111, no. 1 (January 2003): 525. http://dx.doi.org/10.1097/00006534-200301000-00136.
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Opatrný, T., and D. G. Welsch. "Density-matrix reconstruction by unbalanced homodyning." Physical Review A 55, no. 2 (February 1, 1997): 1462–65. http://dx.doi.org/10.1103/physreva.55.1462.
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Alvarez, R. E. "Biomagnetic Fourier imaging (current density reconstruction)." IEEE Transactions on Medical Imaging 9, no. 3 (1990): 299–304. http://dx.doi.org/10.1109/42.57767.
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Ivanov, M., I. Belikov, P. Hristov, and K. Šafařík. "Track reconstruction in high density environment." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 566, no. 1 (October 2006): 70–74. http://dx.doi.org/10.1016/j.nima.2006.05.029.
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Mazziotti, David A. "Complete reconstruction of reduced density matrices." Chemical Physics Letters 326, no. 3-4 (August 2000): 212–18. http://dx.doi.org/10.1016/s0009-2614(00)00773-9.
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Miao, J., H. Chapman, and D. Sayre. "Image Reconstruction from the Oversampled Diffraction Pattern." Microscopy and Microanalysis 3, S2 (August 1997): 1155–56. http://dx.doi.org/10.1017/s1431927600012666.
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In recording the intensity of the diffraction pattern from an arbitrary object, the phase is lost. This gives rise to the “phase problem”in reconstructing the object in crystallography, where the pattern is sampled at the Bragg peaks. It was shown by Bates and by Hayes that sampling at twice crystallographic density (2x oversampling) in each dimension is sufficient in principle to obtain a full reconstruction of the object. It was pointed out by Sayre in 1991 that the diffraction pattern of a non-crystalline object is continuous, therefore the pattern may be sampled on a finer scale, providing the additional information for the image reconstruction.The loss of phase corresponds to a loss of half the information. It seems therefore that 2x oversampling in each dimension (8x in three dimension) may be unnecessary. We find that oversampling 1.67x in each dimension is sufficient to obtain a reconstruction, even in the presence of noise. However our algorithm fails when we reduce the oversampling factor to 1.58x.
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Büntgen, Ulf, David C. Frank, Daniel Nievergelt, and Jan Esper. "Summer Temperature Variations in the European Alps, a.d. 755–2004." Journal of Climate 19, no. 21 (November 1, 2006): 5606–23. http://dx.doi.org/10.1175/jcli3917.1.
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Abstract Annually resolved summer temperatures for the European Alps are described. The reconstruction covers the a.d. 755–2004 period and is based on 180 recent and historic larch [Larix decidua Mill.] density series. The regional curve standardization method was applied to preserve interannual to multicentennial variations in this high-elevation proxy dataset. Instrumental measurements from high- (low-) elevation grid boxes back to 1818 (1760) reveal strongest growth response to current-year June–September mean temperatures. The reconstruction correlates at 0.7 with high-elevation temperatures back to 1818, with a greater signal in the higher-frequency domain (r = 0.8). Low-elevation instrumental data back to 1760 agree with the reconstruction’s interannual variation, although a decoupling between (warmer) instrumental and (cooler) proxy data before ∼1840 is noted. This offset is larger than during any period of overlap with more recent high-elevation instrumental data, even though the proxy time series always contains some unexplained variance. The reconstruction indicates positive temperatures in the tenth and thirteenth century that resemble twentieth-century conditions, and are separated by a prolonged cooling from ∼1350 to 1700. Six of the 10 warmest decades over the 755–2004 period are recorded in the twentieth century. Maximum temperature amplitude over the past 1250 yr is estimated to be 3.1°C between the warmest (1940s) and coldest (1810s) decades. This estimate is, however, affected by the calibration with instrumental temperature data. Warm summers seem to coincide with periods of high solar activity, and cold summers vice versa. The record captures the full range of past European temperature variability, that is, the extreme years 1816 and 2003, warmth during medieval and recent times, and cold in between. Comparison with regional- and large-scale reconstructions reveals similar decadal to longer-term variability.
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Chevalier, M., R. Cheddadi, and B. M. Chase. "CREST (Climate REconstruction SofTware): a probability density function (PDF)-based quantitative climate reconstruction method." Climate of the Past 10, no. 6 (November 28, 2014): 2081–98. http://dx.doi.org/10.5194/cp-10-2081-2014.
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Abstract. Several methods currently exist to quantitatively reconstruct palaeoclimatic variables from fossil botanical data. Of these, probability density function (PDF)-based methods have proven valuable as they can be applied to a wide range of plant assemblages. Most commonly applied to fossil pollen data, their performance, however, can be limited by the taxonomic resolution of the pollen data, as many species may belong to a given pollen type. Consequently, the climate information associated with different species cannot always be precisely identified, resulting in less-accurate reconstructions. This can become particularly problematic in regions of high biodiversity. In this paper, we propose a novel PDF-based method that takes into account the different climatic requirements of each species constituting the broader pollen type. PDFs are fitted in two successive steps, with parametric PDFs fitted first for each species and then a combination of those individual species PDFs into a broader single PDF to represent the pollen type as a unit. A climate value for the pollen assemblage is estimated from the likelihood function obtained after the multiplication of the pollen-type PDFs, with each being weighted according to its pollen percentage. To test its performance, we have applied the method to southern Africa as a regional case study and reconstructed a suite of climatic variables (e.g. winter and summer temperature and precipitation, mean annual aridity, rainfall seasonality). The reconstructions are shown to be accurate for both temperature and precipitation. Predictable exceptions were areas that experience conditions at the extremes of the regional climatic spectra. Importantly, the accuracy of the reconstructed values is independent of the vegetation type where the method is applied or the number of species used. The method used in this study is publicly available in a software package entitled CREST (Climate REconstruction SofTware) and will provide the opportunity to reconstruct quantitative estimates of climatic variables even in areas with high geographical and botanical diversity.
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Petrovska, I., M. Jäger, D. Haitz, and B. Jutzi. "GEOMETRIC ACCURACY ANALYSIS BETWEEN NEURAL RADIANCE FIELDS (NERFS) AND TERRESTRIAL LASER SCANNING (TLS)." International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLVIII-1/W3-2023 (October 19, 2023): 153–59. http://dx.doi.org/10.5194/isprs-archives-xlviii-1-w3-2023-153-2023.
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Abstract. Neural Radiance Fields (NeRFs) use a set of camera poses with associated images to represent a scene through a position-dependent density and radiance at given spatial location. Generating a geometric representation in form of a point cloud is gained by ray tracing and sampling 3D points with density and color along the rays. In this contribution we evaluate object reconstruction by NeRFs in 3D metric space against Terrestrial Laser Scanning (TLS) using ground truth data in form of a Structured Light Imaging (SLI) mesh and investigate the influence of the density to the reconstruction’s accuracy. We extend the accuracy assessment from 2D to 3D space and perform high resolution investigations on NeRFs by using camera images with 36MP resolution as well as comparison among point clouds of more than 20 million points against a 0.1mm ground truth mesh. TLS achieves the highest geometric accuracy results with a standard deviation of 1.68mm, while NeRFδt=300 diverges 18.61mm from the ground truth. All NeRF reconstructions contain 3D points inside the object which have the highest displacements from the ground truth, thus contribute the most to the accuracy results. NeRFs accuracy improves with increasing the density threshold as a consequence of completeness, since beside noise and outliers the object points are also being removed.
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Ai, Mengchi, Zhixin Li, and Jie Shan. "Topologically Consistent Reconstruction for Complex Indoor Structures from Point Clouds." Remote Sensing 13, no. 19 (September 26, 2021): 3844. http://dx.doi.org/10.3390/rs13193844.
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Indoor structures are composed of ceilings, walls and floors that need to be modeled for a variety of applications. This paper proposes an approach to reconstructing models of indoor structures in complex environments. First, semantic pre-processing, including segmentation and occlusion construction, is applied to segment the input point clouds to generate semantic patches of structural primitives with uniform density. Then, a primitives extraction method with detected boundary is introduced to approximate both the mathematical surface and the boundary of the patches. Finally, a constraint-based model reconstruction is applied to achieve the final topologically consistent structural model. Under this framework, both the geometric and structural constraints are considered in a holistic manner to assure topologic regularity. Experiments were carried out with both synthetic and real-world datasets. The accuracy of the proposed method achieved an overall reconstruction quality of approximately 4.60 cm of root mean square error (RMSE) and 94.10% Intersection over Union (IoU) of the input point cloud. The development can be applied for structural reconstruction of various complex indoor environments.
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Bluemke, David A., Bridget Carragher, and Michael J. Potel. "Real-Space Reconstructions of Non-Ideal Helical Models." Proceedings, annual meeting, Electron Microscopy Society of America 43 (August 1985): 308–9. http://dx.doi.org/10.1017/s0424820100118412.
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We have studied the effects of variable pitch, particle flattening, particle curvature, imaging noise and variable negative stain on two dimensional (2D) real-space reconstructions using electron density models of the sickle cell hemoglobin (HbS) macrofiber. The HbS macrofiber, a 500 A diameter helical particle with a pitch of about 10,000 A, is formed in vitro at pH < 7.1. The Fourier transform of the particle is extremely complex due to disorder, large particle size, and variable pitch, making the indexing required for Fourier-Bessel reconstructions very difficult. However, real-space techniques require fewer assumptions about the particle order. Preliminary particle reconstructions have led us to consider the effect of non-ideal particle imaging on the reconstruction result.
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Verschoor, Adriana, Ronald Milligan, Suman Srivastava, and Joachim Frank. "Structural Studies on the Eukaryotic Ribosome." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 1 (August 12, 1990): 256–57. http://dx.doi.org/10.1017/s0424820100180033.
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We have studied the eukaryotic ribosome from two vertebrate species (rabbit reticulocyte and chick embryo ribosomes) in several different electron microscopic preparations (Fig. 1a-d), and we have applied image processing methods to two of the types of images. Reticulocyte ribosomes were examined in both negative stain (0.5% uranyl acetate, in a double-carbon preparation) and frozen hydrated preparation as single-particle specimens. In addition, chick embryo ribosomes in tetrameric and crystalline assemblies in frozen hydrated preparation have been examined. 2D averaging, multivariate statistical analysis, and classification methods have been applied to the negatively stained single-particle micrographs and the frozen hydrated tetramer micrographs to obtain statistically well defined projection images of the ribosome (Fig. 2a,c). 3D reconstruction methods, the random conical reconstruction scheme and weighted back projection, were applied to the negative-stain data, and several closely related reconstructions were obtained. The principal 3D reconstruction (Fig. 2b), which has a resolution of 3.7 nm according to the differential phase residual criterion, can be compared to the images of individual ribosomes in a 2D tetramer average (Fig. 2c) at a similar resolution, and a good agreement of the general morphology and of many of the characteristic features is seen.Both data sets show the ribosome in roughly the same ’view’ or orientation, with respect to the adsorptive surface in the electron microscopic preparation, as judged by the agreement in both the projected form and the distribution of characteristic density features. The negative-stain reconstruction reveals details of the ribosome morphology; the 2D frozen-hydrated average provides projection information on the native mass-density distribution within the structure. The 40S subunit appears to have an elongate core of higher density, while the 60S subunit shows a more complex pattern of dense features, comprising a rather globular core, locally extending close to the particle surface.
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Fegyveresi, J. M., R. B. Alley, M. K. Spencer, J. J. Fitzpatrick, E. J. Steig, J. W. C. White, J. R. McConnell, and K. C. Taylor. "Late-Holocene climate evolution at the WAIS Divide site, West Antarctica: bubble number-density estimates." Journal of Glaciology 57, no. 204 (2011): 629–38. http://dx.doi.org/10.3189/002214311797409677.
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AbstractA surface cooling of ∼1.7°C occurred over the ∼two millennia prior to ∼1700 CE at the West Antarctic ice sheet (WAIS) Divide site, based on trends in observed bubble number-density of samples from the WDC06A ice core, and on an independently constructed accumulation-rate history using annual-layer dating corrected for density variations and thinning from ice flow. Density increase and grain growth in polar firn are both controlled by temperature and accumulation rate, and the integrated effects are recorded in the number-density of bubbles as the firn changes to ice. Number-density is conserved in bubbly ice following pore close-off, allowing reconstruction of either paleotemperature or paleo-accumulation rate if the other is known. A quantitative late-Holocene paleoclimate reconstruction is presented for West Antarctica using data obtained from the WAIS Divide WDC06A ice core and a steady-state bubble number-density model. The resultant temperature history agrees closely with independent reconstructions based on stable-isotopic ratios of ice. The ∼1.7°C cooling trend observed is consistent with a decrease in Antarctic summer duration from changing orbital obliquity, although it remains possible that elevation change at the site contributed part of the signal. Accumulation rate and temperature dropped together, broadly consistent with control by saturation vapor pressure.
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Gürsoy, Doĝa, Tekin Biçer, Jonathan D. Almer, Raj Kettimuthu, Stuart R. Stock, and Francesco De Carlo. "Maximum a posteriori estimation of crystallographic phases in X-ray diffraction tomography." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 373, no. 2043 (June 13, 2015): 20140392. http://dx.doi.org/10.1098/rsta.2014.0392.
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A maximum a posteriori approach is proposed for X-ray diffraction tomography for reconstructing three-dimensional spatial distribution of crystallographic phases and orientations of polycrystalline materials. The approach maximizes the a posteriori density which includes a Poisson log-likelihood and an a priori term that reinforces expected solution properties such as smoothness or local continuity. The reconstruction method is validated with experimental data acquired from a section of the spinous process of a porcine vertebra collected at the 1-ID-C beamline of the Advanced Photon Source, at Argonne National Laboratory. The reconstruction results show significant improvement in the reduction of aliasing and streaking artefacts, and improved robustness to noise and undersampling compared to conventional analytical inversion approaches. The approach has the potential to reduce data acquisition times, and significantly improve beamtime efficiency.
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Viganò, Nicola, Laura Nervo, Lorenzo Valzania, Gaurav Singh, Michael Preuss, Kees Joost Batenburg, and Wolfgang Ludwig. "A feasibility study of full-field X-ray orientation microscopy at the onset of deformation twinning." Journal of Applied Crystallography 49, no. 2 (March 8, 2016): 544–55. http://dx.doi.org/10.1107/s1600576716002302.
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Three-dimensional X-ray orientation microscopy based on X-ray full-field imaging techniques such as diffraction contrast tomography is a challenging task when it comes to materials displaying non-negligible intragranular orientation spread and/or intricate grain microstructures as a result of plastic deformation and deformation twinning. As shown in this article, the optimization of the experimental conditions and a number of modifications of the data analysis routines enable detection and three-dimensional reconstruction of twin lamellae down to micrometre thickness, as well as more accurate three-dimensional reconstruction of grains displaying intragranular orientation spreads of up to a few degrees. The reconstruction of spatially resolved orientation maps becomes possible through the use of a recently introduced six-dimensional reconstruction framework, which has been further extended in order to enable simultaneous reconstruction of parent and twin orientations and to account for the finite impulse response of the X-ray imaging detector. The simultaneous reconstruction of disjoint orientation domains requires appropriate scaling of the scattering intensities based on structure and Lorentz factors and yields three-dimensional reconstructions with comparable density values for all the grains. This in turn enables the use of a global intensity-guided assembly procedure and avoids problems related to the single-grain thresholding procedure used previously. Last but not least, carrying out a systematic search over the list of known twin variants (forward modelling) for each of the indexed parent grains, it is possible to identify additional twins which have been left undetected at the previous stage of grain indexing based on diffraction spot peak positions. The enhanced procedure has been tested on a 1% deformed specimen made from a Ti–4% Al alloy and the result has been cross-validated against a two-dimensional electron backscatter diffraction orientation map acquired on one of the lateral sample surfaces.
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GUAN Yong-hong, 管永红, 景越峰 JING Yue-feng, and 肖智强 XIAO Zhi-qiang. "Density Reconstruction by Flash Radiography Using LEPM." ACTA PHOTONICA SINICA 39, no. 4 (2010): 719–22. http://dx.doi.org/10.3788/gzxb20103904.0719.
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Shoemaker, Michael A., Brendt Wohlberg, and Josef Koller. "Atmospheric Density Reconstruction Using Satellite Orbit Tomography." Journal of Guidance, Control, and Dynamics 38, no. 4 (April 2015): 685–98. http://dx.doi.org/10.2514/1.g000088.
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