Study of Heating Time of test model and Application in Low Density Wind Tunnel Using Infrared Thermography

Abstract The relation between the model heating time and constant heat transfer rate assumption is analyzed. The study indicates that the shorter is the model heating time, the better is constant heat transfer rate approximation. The typical test results obtained with infrared thermographic technique on the hypersonic winged vehicle as well as heating effect on the flat plate model caused by plume flow are presented

Reconstruction from limited-angle projections based on spectrum analysis

This paper proposes a sparse representation of an image using discrete δ-u functions. A δ-u function is defined as the product of a Kronecker delta function and a step function. Based on the sparse representation, we have developed a novel and effective method for reconstructing an image from limited-angle projections. The method first estimates the parameters of the sparse representation from the incomplete projection data, and then directly calculates the image to be reconstructed. Experiments have shown that the proposed method can effectively recover the missing data and reconstruct images more accurately than the total-variation (TV) regularized reconstruction method

Image reconstruction from limited-angle projections using sparsifying operators

Image reconstruction from limited-angle projections has been a challenging problem for which an effective solution is constantly sought. This paper presents a novel method based on the concept of sparsifying operators. The idea is to construct a sparse model of the to-be-reconstructed image using a sparsifying operator and to estimate the model parameters using l0-minimization approximation from the partial k-space data computed from the limited projections. Thus, the missing k-space data can be recovered using the model and image is reconstructed by inverse Fourier transform. Experiments have shown that the proposed method can effectively recover the missing data and reconstruct images more accurately than the zero-filling (ZF) method and the total-variation (TV) regularized reconstruction method

Removal of truncation artefacts in magnetic resonance images by recovering missing spectral data

Truncation artefacts are often present in many archived clinical magnetic resonance (MR) images due to the need of shortening the acquisition time by sampling a part of their k-space. This artificial information degrades the quality of the image and may hamper clinical diagnosis. In this paper, we propose a novel method to remove the artefacts by recovering the missing k-space or spectral data. The method consists of four steps: (a) estimating the truncated k-space from the images containing truncations artefacts, (b) computing the parameters of the sparse representation of the difference image of an image from the estimated truncated k-space, (c) recovering the missing spectral data using the parameters computed in (b), and (d) obtaining the artefact-removed image through inverse Fourier transform of the estimated and the recovered spectral data. Experiments on both simulated and real MR images have shown that the proposed method effectively removes truncation artefacts while preserving image quality and outperforms both the conventional Hamming window method and the popular TV method. (C) 2012 Elsevier Inc. All rights reserved

Image reconstruction from sparse projections using S-transform

Sparse projections are an effective way to reduce the exposure to radiation during X-ray CT imaging. However, reconstruction of images from sparse projection data is challenging. This paper introduces a new sparse transform, referred to as S-transform, and proposes an accurate image reconstruction method based on the transform. The S-transform effectively converts the ill-posed reconstruction problem into a well-defined one by representing the image using a small set of transform coefficients. An algorithm is proposed that efficiently estimates the S-transform coefficients from the sparse projections, thus allowing the image to be accurately reconstructed using the inverse S-transform. The experimental results on both simulated and real images have consistently shown that, compared to the popular total variation (TV) method, the proposed method achieves comparable results when the projections is sparse, and substantially improves the quality of the reconstructed image when the number of the projections is relatively high. Therefore, the use of the proposed reconstruction algorithm may permit reduction of the radiation exposure without trade-off in imaging performance

Study on the Simulation Method of the Ground Test in the Arc-Heated Wind Tunnel

To analyze the effectiveness of the thermal assessment test, the simulation method of the ground test in the arc-heated wind tunnel is studied. Based on the solution of the thermochemical nonequilibrium Navier-Stokes equations, the flowfield around the spherical cylinder is simulated in the flight and ground test conditions, and the difference in the high enthalpy flowfield between the flight and ground test conditions is investigated. The flight parameters and ground test conditions are selected according to the criterion that the total enthalpy and the stagnation point heat flux of the fully catalytic cold wall (calibrated heat flux) are similar. The flowfield for different temperature boundaries and different catalytic walls is solved under the same free stream conditions, and the stagnation point heat flux and oxygen atom mass fraction are compared and analyzed. It is found that the heat flux on the fully catalytic wall for the radiation balance temperature boundary in the ground test is lower than that in the corresponding flight condition, but the difference is not obvious on the noncatalytic wall. In addition, the oxygen atom mass fraction after the shock wave in the ground test is higher than that in the corresponding flight condition. To make the stagnation point heat flux and oxygen atom mass fraction after the shock wave similar to those of the flight, the simulation method of the arc-heated wind tunnel test needs to be adjusted

Arousal modulates valence effects on both early and late stages of affective picture processing in a passive viewing task

Valence and arousal are primary dimensions of affective stimuli. An interaction of these two factors on affective processing is largely unknown. In this study, the processing of affective pictures was investigated in an orthogonal valence (positive vs. negative) by arousal (high vs. low) task design. Participants were instructed to passively view each presented picture and did not need to make any responses. The valence by arousal interaction was observed on three event-related potential (ERP) components, including the P2 (160-190 ms), N2 (220-320 ms) and late positive potential (LPP) (400-700 ms). This interaction revealed that negative pictures evoked larger neural responses compared with positive pictures (i.e., negative bias) at the high-arousal level, whereas negative pictures evoked smaller neural responses than positive pictures (i.e., positive offset) at the low-arousal level. The current results suggest that the effect of emotional valence on affective picture perception is modulated by levels of arousal at both early and late stages of processing. Finally, the main effect of valence was evident in the P1 component (90-110 ms) and arousal effect in the N1 component (120-150 ms)

MRI reconstruction from 2D truncated k-space

Purpose: To shorten acquisition time by means of both partial scanning and partial echo acquisition and to reconstruct images from such 2D partial k-space acquisitions. Materials and Methods: We propose an approach to reconstructing magnetic resonance images from 2D truncated k-space in which the k-space is truncated in both phase- and frequency-encoding directions. Unlike conventional reconstruction techniques, the proposed approach is based on a newly developed 2D singularity function analysis (SFA) model and a sparse representation of an image whose parameters can be estimated from the 2D partial k-space data. Such a sparse representation leads to an accurate recovery of the missing k-space data and, hence, an accurate reconstruction of the image. Results: The proposed approach can reconstruct an image from as little as 20%–30% of the k-space data and the quality of the reconstructed image is comparable to the reference image that is reconstructed from the complete k-space data. Conclusion: Despite the high asymmetry of a 2D truncated k-space, the proposed approach allows for accurate reconstruction without the need of phase correction and, thus, overcomes the assumption of slow phase variations that is usually required by the existing reconstruction methods. It provides a new way of fast imaging for applications that require a significant reduction of the acquisition time

Improved Biohythane Production from Rice Straw in an Integrated Anaerobic Bioreactor under Thermophilic Conditions

This study evaluated the feasibility of continuous biohythane production from rice straw (RS) using an integrated anaerobic bioreactor (IABR) at thermophilic conditions. NaOH/Urea solution was employed as a pretreatment method to enhance and improve biohythane production. Results showed that the maximum specific biohythane yield was 612.5 mL/g VS, including 104.1 mL/g VS for H2 and 508.4 mL/g VS for CH4, which was 31.3% higher than the control RS operation stage. The maximum total chemical oxygen demand (COD) removal stabilized at about 86.8%. COD distribution results indicated that 2% of the total COD (in the feed) was converted into H2, 85.4% was converted to CH4, and 12.6% was retained in the effluent. Furthermore, carbon distribution analysis demonstrated that H2 production only diverted a small part of carbon, and most of the carbon flowed to the CH4 fermentation process. Upon further energy conversion analysis, the maximum value was 166.7%, 31.7 times and 12.8% higher than a single H2 and CH4 production process. This study provides a new perspective on lignocellulose-to-biofuel recovery