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Water mist spray is considered a potential and effective method for controlling or mitigating the risk of natural gas (NG) leakage. In order to address the lack of understanding of the dynamical behaviours and interacting mechanisms between water mist spray and high-velocity leakage gas jets, a series of small-scale experiments were conducted by means of a 2D particle image velocimetry technique. For safety reasons, nitrogen was tested instead of NG. The results demonstrate that the two-phase flow field could be divided into gas- or spray-dominant flow for different gas-spray momentum ratios. The exponential correlation model based on the effective gas-spray momentum ratio Φ Eff could predict the vertical gas-spray interaction interface position more effectively. The gas-spray momentum ratio and relative gas-spray opening angle values are important factors affecting the gas-spray interaction. An effective gas-spray momentum ratio of Φ Eff 1 is necessary for practical applications. A counter-rotating vortex pair is formed due to the entrainment effect of the high-velocity gas flow, which may enhance the mitigation efficiency by means of effective gas-droplet mixing. The comparison of Nozzle A with Nozzle B indicates that the water mist spray with larger coverage relative to the gas plume should exhibit superior performance in terms of controlling or mitigation effects.

Generalized-barrier parameters are studied theoretically for rectangular and trapezoidal single-barriers as well as parallel-plane ones, which are basic units for double-barrier and multiple-barrier structures. Analytical expressions for these parameters are derived by taking into account the position-dependent effective-mass effect. Furthermore, the expressions for the generalized-barrier parameters of optical single-layer thin film structures are considered and permit direct application of previous results to thin film interference filters also. The heights of resonant peaks and the resonance widths in asymmetrical double-barrier structures are studied as functions of the generalized-barrier parameters.

The resonance condition for triple-barrier structures with arbitrary potential is studied systematically. The quasisymmetrical triple-barrier (QST) resonance mode and the quasi-asymmetrical double-barrier (QAD) resonance mode may both exist in asymmetric triple-barrier structures. The QST consists of two submodes: a normal mode (doublet) and a degenerate mode (singlet). The critical condition for distinguishing the two modes is examined. It is confirmed that there are both unity resonant transmission and below-unit resonant transmission in the asymmetrical triple-barrier structure. Furthermore, the wavefunctions of an electron at resonance level are calculated and the confining phenomenon is studied.

Resonant tunneling in multiple-barrier structures with arbitrary potential profile is studied theoretically. Analytical expressions of the transmission coefficient and the resonance condition are derived by taking into account the mass difference between well and barrier layers. The basic barrier unit in the periodic multiple-barrier structure may be a compound-barrier structure, and the simplest compound-barrier unit is the double-barrier unit. Two independent resonance conditions exist in the multiple-barrier structures with compound-barrier unit and both the subband gap energy and the energy value at the center of the subband gap may be determined analytically and independently for the multiple-barrier structure with double-barrier unit.

Resonant tunneling is studied theoretically in asymmetrical double-barrier structures with arbitrary potential profile. Analytical expressions of the transmission coefficient and resonance condition are derived by taking into account the mass difference between the well and barrier layers. It is confirmed that resonant tunneling with unity resonant transmission or under-unity resonant transmission may occur in asymmetrical double-barrier structures. Two independent conditions are required for unity resonant transmission: one is the Phase Difference Condition for Resonance (PDCR) and the other is the Maximum Condition for the Peak Value (MCPV). The under-unity resonant transmission occurs when only PDCR holds. Furthermore, wave functions of an electron at resonance level are calculated and the confining phenomenon is studied.

Patient anatomy has complicated effects on cardiac SPECT images. The authors investigated reconstruction methods which substantially reduced these effects for improved image quality. A 3D mathematical cardiac-torso (MCAT) phantom which models the anatomical structures in the thorax region were used in the study. The phantom was modified to simulate variations in patient anatomy including regions of natural thinning along the myocardium, body size, diaphragmatic shape, gender, and size and shape of breasts for female patients. Distributions of attenuation coefficients and Tl-201 uptake in different organs in a normal patient were also simulated. Emission projection data were generated from the phantoms including effects of attenuation and detector response. The authors have observed the attenuation-induced artifacts caused by patient anatomy in the conventional FBP reconstructed images. Accurate attenuation compensation using iterative reconstruction algorithms and attenuation maps substantially reduced the image artifacts and improved quantitative accuracy. The authors conclude that reconstruction methods which accurately compensate for nonuniform attenuation can substantially reduce image degradation caused by variations in patient anatomy in cardiac SPECT. >

The goal of the authors' investigation was to study the effectiveness of the corrective reconstruction methods in cardiac SPECT using a realistic phantom and to qualitatively and quantitatively evaluate the reconstructed images using bull's-eye plots. A 3D mathematical phantom which realistically models the anatomical structures of the cardiac-torso region of patients was used. The phantom allows simulation of both the attenuation distribution and the uptake of radiopharmaceuticals in different organs. Also, the phantom can be easily modified to simulate different genders and variations in patient anatomy. Two-dimensional projection data were generated from the phantom and included the effects of attenuation and detector response blurring. The reconstruction methods used in the study included the conventional filtered backprojection (FBP) with no attenuation compensation, and the first-order Chang algorithm, an iterative filtered backprojection algorithm (IFBP), the weighted least square conjugate gradient algorithm and the ML-EM algorithm with non-uniform attenuation compensation. The transaxial reconstructed images were rearranged into short-axis slices from which bull's-eye plots of the count density distribution in the myocardium were generated. The FBP reconstructed images clearly demonstrated the effects of attenuation on the myocardial distribution caused by anatomical structures and the inadequacy of the algorithm to provide accurate quantitative reconstructions. The images reconstructed using the Chang, IFBP, and ML-EM methods with attenuation compensation showed substantial improvement in terms of reduction in artifacts and improvement in quantitative accuracy. The results also demonstrate that the ML-EM method is the most robust in attenuation compensation for a wide range of anatomical variations when compared to the Chang and IFBP methods. The combination of the 3D mathematical phantoms and bull's-eye plots provides an effective tool for evaluation of corrective reconstruction methods for quantitative cardiac SPECT. >

Summary form only given. The authors investigate the practical implementation of iterative reconstruction methods to improve the quality and quantitative accuracy of cardiac single photon emission computed tomography (SPECT) images over the filtered backpropagation (FB) algorithm. A cardiac-chest phantom based on a patient CT scan and Tl-201 uptake data was used in the study. Projection data were generated which included the effects of nonuniform attenuation detector response, scatter and noise. Use was made of the iterative Chang algorithm with nonuniform attenuation compensation only, the iterative maximum likelihood-expectation maximization (ML-EM) and WLS-CG methods, and variations of the WLS-CG methods, including the use of the FB or Chang reconstructed image as initial estimate and filtering to suppress noise amplifications at high iteration number. The mean-square-error over the region of the heart and the normalized standard deviation over a background region were used to evaluate the different reconstruction methods. It was found that, using the Chang reconstructed image as the initial estimate in the WLS-CG method together with filtering between iterations, cardiac SPECT images with good quality and quantitative accuracy can be obtained in a few iterations. >

Although quantitative single-photon emission computed tomography (SPECT) has been the goal of much research effort for a number of years, only recently has it received wide interest, especially for clinical applications. It has been increasingly recognized that the achievement of quantitative SPECT will increase the accuracy of measurements, such as dimensions of specific regions of interest, absolute amount of radioactivity, and dosimetry calculations, and substantially reduce reconstruction image artifacts and distortions, thus, greatly improving clinical diagnosis. This article provides a review of the definition of terms, major factors affecting SPECT quantitation and their degrading effects on SPECT image quality, and methods to compensate for these effects. Compensation methods include those that make certain approximations for ease of implementation and those that provide more accurate compensation by modeling the imaging process more exactly, usually at the cost of increased complexity and computational requirements. Different reconstruction and compensation methods may be compared through the use of phantom cardiac and brain SPECT studies. The clinical efficacy of the methods may be demonstrated by applying them to a clinical thallium-201 myocardial perfusion SPECT study. The results clearly demonstrate that, by modeling the imaging process and/or image degrading factors three-dimensionally, quantitative reconstruction and compensation methods provide the best image quality and quantitative accuracy. Important research efforts and developmental work being conducted currently to bring quantitative SPECT into routine clinical use are also discussed.

The paper describes the model of a permanent magnet synchronous motor with non-salient rotor, which is used for simulation the effect of asymmetrical phase parameters on the quasi-steady state torque waveform. An example of phase asymmetry has been studied in (i) the open-loop operating mode, i.e. without position-feedback phase commutation, and (ii) the vector-control mode.

The properties of the maximum likelihood with expectation maximization (ML-EM) and the weighted least squares with conjugate gradient (WLS-CG) algorithms for use in compensation for attenuation and detector response in cardiac SPECT imaging were studied. A realistic phantom, derived from a patient X-ray CT study to simulate /sup 201/Tl SPECT data, was used in the investigation. In general, the convergence rate of the WLS-CG algorithm is about ten times that of the ML-EM algorithm. Also, the WLS-CG exhibits a faster increase in image noise at large iteration numbers than the ML-EM algorithm. >

In the recent decade, considerable numerical models have been built up to simulate the thermal spray process. However, much less work has focused on the prediction of thermo-physical properties of the thermal spray coating, in particular the heat insulation properties. In this paper, a microstructure integrated finite element model is developed to investigate the heat insulation behavior of the thermal spray coating. A two-layer model is used to calculate thermal conductivity of the coating, where one layer stands for the coating by a unit cell, while another one for a standard material with known thermal conductivity. In the proposed unit cell model, pores and unmelted particles are assumed spherical and randomly distributed, and the interface between the coating and the unmelted particles is perfectly debonding. Based on the predictions, the effect of the pores, unmelted particles, cracks and their respective distributions on the heat insulation behavior of the coating has been further discussed in the paper.

The integral control via state and output feedback for continuous-time switched linear systems is studied with the use of a linear matrix inequality (LMI) approach. LMI-based quadratic stability conditions are established for both a state feedback case and an observer-based output feedback case. And as at that a similar separation property to the counterpart on observer design in the linear system theory are obtained.

Summary We report the case of a 42-year-old man with a 13-year history of bilateral faciocervical infiltrative erythema, which had been misdiagnosed as tuberculoderma and which had failed to respond to treatment with adrenal corticosteroids and antituberculotics. On admission to the department, Scedosporium apiospermum was identified on lesion biopsies and fungus cultures as the causative agent and a diagnosis of cutaneous infection by S. apiospermum was made. This is the first report of chronic skin granuloma caused by S. apiospermum in China. Treatment with oral itraconazole (100–400mg/day) led to clinical cure within 4 months.

We studied the properties of two iterative reconstruction algorithms, namely the ML-EM and the WLSCG algorithms, for use in compensation for attenuation and detector response in cardiac SPECT. A realistic phantom, derived from a patient X-ray CT image to simulate 201T1 SPECT data, was used in the study. Both algorithms are effective in compensating for the non-uniform attenuation distribution in the thorax region and the spatially variant detector response function of the imaging system. At low iteration numbers, additional compensation for detector response provides improvement in both spatial resolution and image noise when compared with attenuation compensation alone. However, at higher iteration numbers, there is a more rapid increase in image noise when detector response compensation is included, and the increase is more dramatic for WLS-CG algorithm. In general, the initial convergence rate of the WLS-CG algorithm is about ten times that of the ML-EM algorithm. Also, the WLS-CG exhibits a faster increase in image noise at large iteration numbers than the ML-EM algorithm. The investigation provides valuable information about the choice of iterative algorithms and optimum iteration number for improved cardiac SPECT image reconstruction.

This preliminary study is to improve /sup 67/Ga planar and SPECT images by compensating for the response function of a medium energy (ME) collimator. The point response functions (PRFs) of a GE ME collimator for the 93, 185 and 300 keV photons of /sup 67/Ga at 5, 10, 15 and 20 cm from the collimator face were experimentally determined. For small pixel sizes, the PRFs for all distances showed hole pattern effects. Images from the higher energy photopeaks showed increased penetration fractions. For a specified source distance, a Butterworth filter can be designed to eliminate the collimator hole pattern with minimal degradation of the spatial resolution. Compensation for the distance-dependent collimator-detector response was accomplished using iterative reconstruction methods. To evaluate the compensation methods, planar images and SPECT projection data were acquired from a phantom consisting of 3 hot spheres with diameters of 1, 1.3 and 1.6 cm inside a cylindrical phantom. The iterative reconstruction-based compensation method provided improved resolution and fewer artifacts than in images reconstructed with filtered backprojection. The authors conclude that degradation caused by ME collimator in /sup 67/Ga imaging can be effectively compensated for using these techniques.

The purpose of the study is to investigate the imaging characteristics of scintimammography (SM) using parallel-hole (PR) and pinhole (PN) collimators in a clinical setting. Experimental data were acquired from a phantom that models the breast with small lesions using a low energy high resolution (LEHR) PR and a PN collimator. At close distances, the PN collimator provides better spatial resolution and higher detection efficiency than the PR collimator, at the expense of a smaller field-of-view (FOV). Detection of small breast lesions can be further enhanced by noise smoothing, field uniformity correction, scatter subtraction and resolution recovery filtering. Monte Carlo (MC) simulation data were generated from a realistic 3D MCAT phantom that models the Tc-99m sestamibi uptake and attenuation distributions in an average female patient. The scatter to primary ratio (S/P) decreases from the base to the tip of the breast. For PR collimation, S/P is higher in the left than right breast due to scatter of photons from the heart. For PN collimation, S/P is highest at the base and lowest at the tip of the breast as compared to PR collimation. It is higher in the right than left breast due to contributions from organ uptakes in the body. Results from the study add to understanding of the imaging characteristics of SM using PR and PN collimators and assist in the design of data acquisition and image processing methods to enhance the detection of breast lesions using SM.

The goal of the study is to evaluate collimator-detector response (CDR) compensation methods that apply to tumor SPECT imaging using medium-energy (ME) and high-energy (HE) collimators. The compensation method involves accurate models of the geometric, penetration and scatter components of ME and HE collimators based on Monte Carlo simulations verified by experimental measurements. The models were used in iterative OS-EM reconstruction methods for CDR compensation. In experimental studies, a cylindrical phantom consisting of spheres with different sizes and filled with Ga-67, In-111 or I-131 was used. Projection data were acquired using ME and HE collimators designed for use with the radionuclides. Patient data included those from Ga-67 citrate, In-111 octreotide, and I-131 tumor studies. The FBP without compensation and the iterative OS-EM with different models of the CDR were used in image reconstruction. Results from phantom studies showed asymptotic decrease of the reconstructed sphere sizes as a function of iteration number. The full CDR model that included the geometric, penetration and scatter components provided the best results. Drastic improvements in clinical image quality were found using the full CDR model. It is concluded that full CDR compensation provides substantial improvements in image quality and quantitative accuracy in tumor SPECT.

We investigated the characteristics of the reconstructed point response in SPECT images obtained with and without compensation of the spatially variant collimator-detector response in 3D. The 3D compensation was achieved by modeling the 3D collimatordetector response function in the projector/backprojector pair of a WLS-CG iterative reconstruction algorithm. Using two 3D numerical phantoms, we studied the effects of collimation and data sampling. Total resolution recovery can be achieved when the reconstruction voxel size is small compared with that of the object. Recovery for smaller objects is limited by the spatial resolution of the collimator and the voxel size used in image reconstruction and requires more number of iterations than larger objects. The reconstructed 3D point response is asymmetric with the best resolution in the longitudinal direction and worst in the radial direction.

The purpose of this study was to investigate the importance of 2D versus 3D compensation methods in SPECT. The compensation methods included in the study addressed two important degrading factors, namely attenuating and collimator-detector response in SPET. They can be divided into two general categories. The conventional methods are based on the filtered backprojection algorithm, the Chang algorithm for attenuation compensation and the Metz filter for detector response compensation. These methods, which were computationally efficient, could only achieve approximate compensation due to the assumptions made. The quantitative compensation methods provide accurate compensation by modelling the degrading effects at the expense of large computational requirements. Both types of compensation methods were implemented in 2D and 3D reconstructions. The 2D and 3D reconstruction/compensation methods were evaluated using data from simulation of brain and heart, and patient thallium SPECT studies. Our results demonstrate the importance of compensation methods in improving the quality and quantitative accuracy of SPECT images and the relative effectiveness of the different 2D and 3D reconstruction/compensation methods. We concluded that 3D implementation of the quantitative compensation methods provides the best SPECT image in terms of quantitative accuracy, spatial resolution, and noise at a cost of high computational requirements.