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Using Monte Carlo ray tracing simulations to model the quantum harmonic oscillator modes observed in uranium nitride

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Physical Review B 2014年第14期89卷 144302-144302页

作者： J. Y. Y. Lin A. A. Aczel D. L. Abernathy S. E. Nagler W. J. L. Buyers G. E. Granroth Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA

Recently an extended series of equally spaced vibrational modes was observed in uranium nitride (UN) by performing neutron spectroscopy measurements using the ARCS and SEQUOIA time-of-flight chopper spectrometers [A. A. Aczel et al., Nat. Commun. 3, 1124 (2012)]. These modes are well described by three-dimensional isotropic quantum harmonic oscillator (QHO) behavior of the nitrogen atoms, but there are additional contributions to the scattering that complicate the measured response. In an effort to better characterize the observed neutron scattering spectrum of UN, we have performed Monte Carlo ray tracing simulations of the ARCS and SEQUOIA experiments with various sample kernels, accounting for nitrogen QHO scattering, contributions that arise from the acoustic portion of the partial phonon density of states, and multiple scattering. These simulations demonstrate that the U and N motions can be treated independently, and show that multiple scattering contributes an approximate Q-independent background to the spectrum at the oscillator mode positions. Temperature-dependent studies of the lowest few oscillator modes have also been made with SEQUOIA, and our simulations indicate that the T dependence of the scattering from these modes is strongly influenced by the uranium lattice.

关键词： URANIUM MONTE Carlo method NITRIDES ray tracing algorithms HARMONIC oscillators

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ray tracing and beyond : phase space methods in plasma wave theory /

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2014年

作者： E.R. Tracy ... [et al.].

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Framework for Simulating Aircraft Flyover Noise Through Nonstandard Atmospheres

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JOURNAL OF AIRCRAFT 2014年第3期51卷 956-966页

作者： Arntzen, Michael Rizzi, Stephen A. Visser, Hendrikus G. Simon, Dick G. Natl Aerosp Lab NL-1059 CM Amsterdam Netherlands NASA Langley Res Ctr Struct Acoust Branch MS 463 Hampton VA 23681 USA Delft Univ Technol NL-2600 AA Delft Netherlands

This paper describes a new framework for the synthesis of aircraft flyover noise through a nonstandard atmosphere. Central to the framework is a ray-tracing algorithm that defines multiple curved propagation paths, if the atmosphere allows, between the moving source and listener. Because each path has a different emission angle, synthesis of the sound at the source must be performed independently for each path. The time delay, spreading loss, and absorption (ground and atmosphere) are integrated along each path and applied to each synthesized aircraft noise source to simulate a flyover. A final step assigns each resulting signal to its corresponding receiver angle for the simulation of a flyover in a virtual reality environment. Spectrograms of the results from a straight path and a curved path modeling assumption are shown. When the aircraft is at close range, the straight path results are valid. Differences appear especially when the source is relatively far away at shallow elevation angles. These differences, however, are not significant in common sound metrics. Although the framework used in this work performs off-line processing, it is conducive to real-time implementation.

关键词： AIRPLANES -- Noise AERODYNAMIC noise RESEARCH AIRPLANE sounds ray tracing algorithms VIRTUAL reality

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Sparsely Precomputing The Light Transport Matrix for Real-Time Rendering

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COMPUTER GRAPHICS FORUM 2010年第4期29卷 1335-1345页

作者： Huang, Fu-Chung Ramamoorthi, Ravi Univ Calif Berkeley Berkeley CA 94720 USA

Precomputation-based methods have enabled real-time rendering with natural illumination, all-frequency shadows, and global illumination. However, a major bottleneck is the precomputation time, that can take hours to days. While the final real-time data structures are typically heavily compressed with clustered principal component analysis and/or wavelets, a full light transport matrix still needs to be precomputed for a synthetic scene, often by exhaustive sampling and raytracing. This is expensive and makes rapid prototyping of new scenes prohibitive. In this paper, we show that the precomputation can be made much more efficient by adaptive and sparse sampling of light transport. We first select a small subset of "dense vertices", where we sample the angular dimensions more completely (but still adaptively). The remaining "sparse vertices" require only a few angular samples, isolating features of the light transport. They can then be interpolated from nearby dense vertices using locally low rank approximations. We demonstrate sparse sampling and precomputation 5x faster than previous methods.

关键词： REAL-time rendering (Computer graphics) INTERACTIVE computer graphics PRINCIPAL components analysis WAVELETS (Mathematics) ray tracing algorithms RAPID prototyping TRANSMISSION of light INTERPOLATION

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An extension of the light meshes method for three-dimensional scenes with semitransparent surfaces

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PROGRAMMING AND COMPUTER SOFTWARE 2008年第5期34卷 271-278页

作者： Debelov, V. A. Smirnova, G. G. Vasilyeva, L. F. Russian Acad Sci Siberian Branch Inst Computat Math & Math Geophys Novosibirsk 600090 Russia Novosibirsk State Univ Novosibirsk 630090 Russia

The light meshes method (a modification of the Whitted backwards recursive ray tracing) was justified and studied for scenes consisting of opaque surfaces. Its main difference from the basic method is that the rendered image may include soft shadows (i.e., point sources are simulated by area sources). This study makes a further step in the development of this method: it is extended for rendering scenes containing semitransparent surfaces. A few computational schemes are considered and, for each of them, the difference between the image calculated by the standard scheme and obtained by the application of the light meshes method is shown.

关键词： DIGITAL image processing THREE-dimensional imaging ray tracing algorithms OPACITY (Optics) INFORMATION processing SHADES & shadows COMPUTER simulation

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Monte Carlo simulation study of scanning Auger electron images

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JOURNAL OF APPLIED PHYSICS 2009年第2期106卷 024316-024316-11页

作者： Li, Y. G. Ding, Z. J. Zhang, Z. M. Univ Sci & Technol China Dept Phys Hefei 230026 Anhui Peoples R China Univ Sci & Technol China Hefei Natl Lab Phys Sci Microscale Hefei 230026 Anhui Peoples R China Univ Sci & Technol China Dept Astron & Appl Phys Hefei 230026 Anhui Peoples R China

Simulation of contrast formation in Auger electron imaging of surfaces is helpful for analyzing scanning Auger microscopy/microanalysis (SAM) images. In this work, we have extended our previous Monte Carlo model and the simulation method for calculation of scanning electron microscopy (SEM) images to SAM images of complex structures. The essentials of the simulation method are as follows. (1) We use a constructive solid geometry modeling for a sample geometry, which is complex in elemental distribution, as well as in topographical configuration and a ray-tracing technique in the calculation procedure of electron flight steps that across the different element zones. The combination of the basic objects filled with elements, alloys, or compounds enables the simulation to a variety of sample geometries. (2) Sampled Auger signal electrons with a characteristic energy are generated in the simulation following an inner-shell ionization event, whose description is based on the Castani's inner-shell ionization cross section. This paper discusses in detail the features of simulated SAM images and of line scans for structured samples, i.e., the objects embedded in a matrix, under various experimental conditions (object size, location depth, beam energy, and the incident angle). Several effects are predicted and explained, such as the contrast reversion for nanoparticles in sizes of 10-60 nm, the contrast enhancement for particles made of different elements and wholly embedded in a matrix, and the artifact contrast due to nearby objects containing different elements. The simulated SAM images are also compared with the simulated SEM images of secondary electrons and of backscattered electrons. The results indicate that the Monte Carlo simulation can play an important role in quantitative SAM mapping. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3183936]

关键词： SCANNING Auger electron microscopy MONTE Carlo method ray tracing algorithms INNER-shell ionization NANOPARTICLES BACKSCATTERING AUGER effect

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Interactive ray Casting of Geodesic Grids

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COMPUTER GRAPHICS FORUM 2013年第3期32卷 481-490页

作者： Xie, Jinrong Yu, Hongfeng Ma, Kwan-Liu Univ Calif Davis Davis CA 95616 USA Univ Nebraska Lincoln NE USA

Geodesic grids are commonly used to model the surface of a sphere and are widely applied in numerical simulations of geoscience applications. These applications range from biodiversity, to climate change and to ocean circulation. Direct volume rendering of scalar fields defined on a geodesic grid facilitates scientists in visually understanding their large scale data. Previous solutions requiring to first transform the geodesic grid into another grid structure (e.g., hexahedral or tetrahedral grid) for using graphics hardware are not acceptable for large data, because such approaches incur significant computing and storage overhead. In this paper, we present a new method for efficient ray casting of geodesic girds by leveraging the power of Graphics Processing Units (GPUs). A geodesic grid can be directly fetched from storage or streamed from simulations to the rendering stage without the need of any intermediate grid transformation. We have designed and implemented a new analytic scheme to efficiently perform value interpolation for ray integration and gradient calculations for lighting. This scheme offers a more cost-effective rendering solution over the existing direct rendering approach. We demonstrate the effectiveness of our rendering solution using real-world geoscience data.

关键词： GRAPHICS processing units (Computers) ray tracing algorithms GEODESICS (Mathematics) OCEAN circulation EARTH sciences SIMULATION methods & models PERFORMANCE evaluation

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Visual Realism Enhances Realistic Response in an Immersive Virtual Environment

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IEEE COMPUTER GRAPHICS AND APPLICATIONS 2009年第3期29卷 76-84页

作者： Slater, Mel Khanna, Pankaj Mortensen, Jesper Yu, Insu UCL London WC1E 6BT England Univ Barcelona ICREA E-08007 Barcelona Spain

A study comparing real-time recursive ray tracing with ray casting in an immersive visual environment shows how greater visual realism induces greater participant presence.

关键词： RESEARCH ray tracing algorithms VIRTUAL reality RENDERING (Computer graphics) COMPUTER graphics PERCEPTION testing SOFTWARE visualization

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Modeling and observations of an elevated, moving infrasonic source: Eigenray methods

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JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2017年第4期141卷 2681-2692页

作者： Blom, Philip Waxler, Roger Los Alamos Natl Lab Los Alamos NM 87545 USA Univ Mississippi NCPA University MS 38655 USA

The acoustic ray tracing relations are extended by the inclusion of auxiliary parameters describing variations in the spatial ray coordinates and eikonal vector due to changes in the initial conditions. Computation of these parameters allows one to define the geometric spreading factor along individual ray paths and assists in identification of caustic surfaces so that phase shifts can be easily identified. A method is developed leveraging the auxiliary parameters to identify propagation paths connecting specific source-receiver geometries, termed eigenrays. The newly introduced method is found to be highly efficient in cases where propagation is non-planar due to horizontal variations in the propagation medium or the presence of cross winds. The eigenray method is utilized in analysis of infrasonic signals produced by a multi-stage sounding rocket launch with promising results for applications of tracking aeroacoustic sources in the atmosphere and specifically to analysis of motor performance during dynamic tests. (C) 2017 Acoustical Society of America.

关键词： INFRASONIC waves EIKONAL equation ray tracing algorithms ACOUSTICS (Physical sciences)

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Two Methods for Fast ray-Cast Ambient Occlusion

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COMPUTER GRAPHICS FORUM 2010年第4期29卷 1325-1333页

作者： Laine, Samuli Karras, Tero NVIDIA Research

Ambient occlusion has proven to be a useful tool for producing realistic images, both in offline rendering and interactive applications. In production rendering, ambient occlusion is typically computed by casting a large number of short shadow rays from each visible point, yielding unparalleled quality but long rendering times. Interactive applications typically use screen-space approximations which are fast but suffer from systematic errors due to missing information behind the nearest depth layer. In this paper, we present two efficient methods for calculating ambient occlusion so that the results match those produced by a ray tracer. The first method is targeted for rasterization-based engines, and it leverages the GPU graphics pipeline for finding occlusion relations between scene triangles and the visible points. The second method is a drop-in replacement for ambient occlusion computation in offline renderers, allowing the querying of ambient occlusion for any point in the scene. Both methods are based on the principle of simultaneously computing the result of all shadow rays for a single receiver point.

关键词： RENDERING (Computer graphics) INTERACTIVE computer graphics DIGITAL image processing SHADES & shadows ERRORS ray tracing algorithms

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