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Whole-field measuring methods in ventilated rooms

HVAC&R RESEARCH 2007年第6期13卷 951-970页

作者： Sandberg, Mats Univ Gavle KTH Res Sch Dept Indoor Environm Gavle Sweden

The occupied zone of a ventilated room constitutes a large volume, and the temperature, velocity, and concentration cannot be mapped simultaneously over a whole field with standard point (local) measuring techniques. The situation is improving due to the introduction of whole-field measurement techniques. Whole-field techniques are relatively new and under development;therefore, this paper describes the principles behind the techniques and their pros and cons. All techniques are optical techniques in the sense that pictures are taken by an array of sensors responsive to different wavelengths of light depending on the application. The velocity components can be recorded with particle image velocimetry (PIV) or particle streak velocimetry (PSV). Both methods are based on adding tracer particles, which ideally follow the air motions;a digital camera records their displacement during a specified time interval. Recording the displacement corresponds to the Lagrangian formulation of fluid mechanics. With PIV, the displacement of groups of particles is recorded, in contrast to the PSV method, where the displacement of a single particle is recorded. PIV can provide high-resolution information over small regions, whereas the PSV method can cope with large areas. The two-dimensional concentration distributions of certain contaminants can be obtained by using tomography. The attenuation of light along a bundle of lines (rays) directed in a certain direction (view) and crossing the region with the contaminant is recorded. The measurements are repeated for several other angles. Based on the one-dimensional information in the form of attenuation of light along rays running in different directions, the two-dimensional concentration can be reconstructed by a reconstruction algorithm. The temperature distribution can be recorded and visualized with an infrared camera and a measuring screen that ideally attains the room air temperature. New development of the classical Schlieren tech

关键词： particle image velocimetry Time intervals velocity component air temperature wavelength of light Ventilation reconstruction algorithm Temperature distribution Atmospheric motion LIGHT ATTENUATION measuring method large volume Tracer particles Dislocated Workers Measurement techniques

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Experimental study on measurement of aspheric surface shape with complementary annular subaperture interferometric method

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OPTICS EXPRESS 2007年第20期15卷 12890-12899页

作者： Hou, Xi Wu, Fan Yang, Li Chen, Qiang Chinese Acad Sci Inst Opt & Elect Chengdu 610209 Peoples R China

Based on our previously reported annular subaperture reconstruction algorithm with Zernike annular polynomials and matrix method, we provide an experimental demonstration by testing a parabolic mirror with the complementary annular subaperture interferometric method. By comparing the results of annular subaperture method with that of the classical auto-collimation method, it is shown that the reconstruction results are in good agreement with the auto-collimation measurement. In addition, we discuss some limitations of characterizing annular subaperture measurement data with finite Zernike coefficients in our algorithm, and also show the possibility of characterizing higher spatial frequency information with adequate Zernike coefficients. It is believable that the reported method can be extended to test the surface shape of some large concave aspheric mirrors with acceptable accuracy. (c) 2007 Optical Society of America.

关键词： .characterizing interferograms aspheric surface shape reconstruction algorithm interferometric method annular subaperture method auto-collimation measurement subaperture measurement Zernike coefficients

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A series solution and a fast algorithm for the inversion of the spherical mean Radon transform

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INVERSE PROBLEMS 2007年第6期23卷 S11-S20页

作者： Kunyansky, Leonid A. Univ Arizona Dept Math Tucson AZ 85721 USA

An explicit series solution is proposed for the inversion of the spherical mean Radon transform. Such an inversion is required in problems of thermo- and photo-acoustic tomography. Closed-form inversion formulae are currently known only for the case when the centres of the integration spheres lie on a sphere surrounding the support of the unknown function, or on certain unbounded surfaces. Our approach results in an explicit series solution for any closed measuring surface surrounding a region for which the eigenfunctions of the Dirichlet Laplacian are explicitly known - such as, for example, cube, finite cylinder, half-sphere etc. In addition, we present a fast reconstruction algorithm applicable in the case when the detectors ( the centres of the integration spheres) lie on a surface of a cube. This algorithm reconstructs 3D images thousands times faster than backprojection-type methods.

关键词： .cube reconstruction algorithm Inverse Problems Radon transform series solution spherical mean inversion formulae integration spheres measuring surface Dirichlet Laplacian backprojection-type

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Digital Signal Processor-Based Electrical Impedance Image reconstruction

Digital Signal Processor-Based Electrical Impedance Image Re...

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作者： Fu-Chia Chiu National Cheng Kung University

学位级别：硕士

Electrical impedance tomography has the advantages of non-invasiveness, low cost, long-term use, and no radiation hazard. It attracts lots of attentions and is widely applied in the industry and medicine. Currently, there are many image reconstruction methods proposed and developed for EIT. Nevertheless, some of these methods may produce good image resolution, but may take long computation time. Some methods may be fast in image reconstruction, but may produce bad image quality. Therefore, the purpose of this study is to develop a stand alone image reconstructor that may have good image resolution as well as short computation time. A DSP (TI TMS320C6713) is employed as the kernel to realize the filtered backprojection based on the equi-potential lines using rotating sinusoidal current patterns. Firstly, the distribution of the equi-potential lines for sinusoidal current pattern of homogeneous phantom is computed using the finite element method. Secondly, the linear relationship between the inside region and electrode pair with the same equi-potential line is found and saved as the look-up-table. According to the measured voltage difference on the surface electrodes, the resistivity image can be reconstructed using the backprojection method. The distance between the pixel and electrode-pair is used the weight as the spatial filter. Both the sinusoidal current pattern and adjacent current pattern are applied to the phantom containing different size of targets and are added with 1% of Gaussian noise level. Using the finite element model for simulating the culture dish, their corresponding boundary voltage patterns may then computed for impedance image reconstruction. From the experimental results, it is shown that the smallest distinguishable centered targets are 0.0125 cm, and 0.0225 cm in diameter for sinusoidal current pattern and adjacent current pattern, respectively. For the centered target with 1% Gaussian noise added, the proposed image reconstructor still can

关键词： Electrical impedance tomography Current patterns Finite element method reconstruction algorithm

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X-CT imaging method for large objects using double offset scan mode

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NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 2007年第3期575卷 519-523页

作者： Fu, Jian Lu, Hongnian Li, Bing Zhang, Lei Sun, Jingjing Beijing Univ Aeronaut & Astronaut Sch Mech Engn & Automat Beijing 100083 Peoples R China

In X-ray computed tomography (X-CT) inspection, rotate-only scanner is commonly used because this configuration offers the highest imaging speed and best utilization of X-ray dose. But it requires that the imaging region of the scanned object must fit within the X-ray beam. Another configuration, transverse-rotate scanner, has a bigger field of view, but it is much more time consuming. In this paper, a two-dimensional X-CT imaging method for large objects is proposed to overcome the existing disadvantages. The scan principle of this method has been described and the reconstruction algorithm has been deduced. The results of the computer simulation and the experiments show the validity of the new method. Analysis shows that the scan field of view of this method is 1.8 times larger than that of rotate-only X-CT. The scan speed of this method is also much quicker than transverse-rotate X-CT. (c) 2007 Elsevier B.V. All rights reserved.

关键词： computed tomography scan mode reconstruction algorithm offset scan

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algorithms for reconstructing digital optical images distorted by pulse noise

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JOURNAL OF OPTICAL TECHNOLOGY 2007年第9期74卷 617-621页

作者： Samoilin, E. A. MI Nedelin Rostov Mil Inst Rocket Forces Rostov Na Donu Russia

This paper proposes algorithms that are invariant to the presence of pulse noise for reconstructing the signals of digital optical images. It shows the results of numerical studies of the proposed and known algorithms, and these results provide evidence of the advantages of the former. An example of the filtering of pulse noise on an image is presented, using the known algorithm and one of the proposed reconstruction algorithms. (C) 2007 Optical Society of America.

关键词： America Optical Imaging algorithms Filtration Invariant reconstruction algorithm

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The problem of reconstructing a Quasihomogeneous string from its part

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MATHEMATICAL NOTES 2007年第1-2期82卷 110-118页

作者： Sarkisyan, P. S. ZAO “OTsV”

We consider quasihomogeneous strings with piecewise constant density and derive the quasihomogeneity condition. For a small number of string components, we present explicit formulas for reconstructing a string from its part. For an arbitrary number of string components, we construct a theory of matrices of special form (that we call distinguished) and present an algorithm for string reconstruction from its part.

关键词： quasihomogeneous string polynomial equations rational mapping reconstruction algorithm

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Summarizing a posterior distribution of trees using agreement subtrees

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SYSTEMATIC BIOLOGY 2007年第4期56卷 578-590页

作者： Cranston, Karen A. Rannala, Bruce Univ Arizona Dept Ecol & Evolut Biol Tucson AZ 85721 USA Univ Calif Davis Genome Ctr Davis CA 95616 USA

Bayesian inference of phylogeny is unique among phylogenetic reconstruction methods in that it produces a posterior distribution of trees rather than a point estimate of the best tree. The most common way to summarize this distribution is to report the majority-rule consensus tree annotated with the marginal posterior probabilities of each partition. Reporting a single tree discards information contained in the full underlying distribution and reduces the Bayesian analysis to simply another method for finding a point estimate of the tree. Even when a point estimate of the phylogeny is desired, the majority- rule consensus tree is only one possible method, and there may be others that are more appropriate for the given data set and application. We present a method for summarizing the distribution of trees that is based on identifying agreement subtrees that are frequently present in the posterior distribution. This method provides fully resolved binary trees for subsets of taxa with high marginal posterior probability on the entire tree and includes additional information about the spread of the distribution.

关键词： reconstruction algorithm Posterior distribution Bayesian inference Bayes methods Dataset Binary trees Phylogeny

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Creation of a diagnostic complex for the characterization of cryogenic laser-fusion targets using the tomography method with probing irradiation in the visible spectrum

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JOURNAL OF RUSSIAN LASER RESEARCH 2007年第2期28卷 163-206页

作者： Koresheva, E. R. Osipov, I. E. Aleksandrova, I. V. Nikitenko, A. I. Tolokonnikov, S. M. Listratov, V. I. Timofeev, I. D. Kupriyashin, A. I. Leonov, V. N. Koshelev, E. L. Baranov, G. D. Usachev, G. S. Timasheva, T. P. Gromov, A. I. Russian Acad Sci PN Lebedev Phys Inst Moscow 119991 Russia Red Star State Enterprise Moscow 115230 Russia

We present our results on developing a diagnostic complex for high-precision characterization of the parameters of laser-fusion microobjects, such as microspheres and cryogenic targets (the microobject size is 1-2 mm). The complex operates based on the principle of tomography. The complex consists of (a) the scanning system providing a set of shadow projections of a microobject in the visible range of radiation and (b) specially developed software for 3D reconstruction of the microobject from the set of projections. The spatial resolution of the optical system is 1 mu m for a probing-radiation wavelength of 490 nm. The distinctive features of the diagnostic complex are (1) operation with both freestanding and mounted targets and (2) the possibility of scanning the targets from room to cryogenic temperatures. The operation of the complex was demonstrated in the reconstruction of polystyrene microspheres by a large set (80-90) of shadow projections at room and cryogenic temperatures.

关键词： tomograph scanning system imaging system image projection data bright band reconstruction algorithm inertial confinement fusion cryogenic target microshell

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Phylogenetic mixtures on a single tree can mimic a tree of another topology

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SYSTEMATIC BIOLOGY 2007年第5期56卷 767-775页

作者： Matsen, Frederick A. Steel, Mike Univ Canterbury Biomath Res Ctr Christchurch 1 New Zealand

Phylogenetic mixtures model the inhomogeneous molecular evolution commonly observed in data. The performance of phylogenetic reconstruction methods where the underlying data are generated by a mixture model has stimulated considerable recent debate. Much of the controversy stems from simulations of mixture model data on a given tree topology for which reconstruction algorithms output a tree of a different topology;these findings were held up to show the shortcomings of particular tree reconstruction methods. In so doing, the underlying assumption was that mixture model data on one topology can be distinguished from data evolved on an unmixed tree of another topology given enough data and the "correct" method. Here we show that this assumption can be false. For biologists, our results imply that, for example, the combined data from two genes whose phylogenetic trees differ only in terms of branch lengths can perfectly fit a tree of a different topology. [Mixture model;model identifiability;phylogenctics;sequence evolution.]

关键词： reconstruction algorithm topology Biologists False Mixture models mixtures Tree Topology

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