A method of X-ray source spectrum estimation from transmission measurements based on compressed sensing

Liu Bin,Yang Hongrun,Lv Huanwen,Li Lan,Gao Xilong,Zhu Jianping,Jing Futing 한국원자력학회 2020 Nuclear Engineering and Technology Vol.52 No.7

A new method of X-ray source spectrum estimation based on compressed sensing is proposed in this paper. The algorithm K-SVD is applied for sparse representation. Nonnegative constraints are added by modifying the L1 reconstruction algorithm proposed by Rosset and Zhu. The estimation method is demonstrated on simulated spectra typical of mammography and CT. X-ray spectra are simulated with the Monte Carlo code Geant4. The proposed method is successfully applied to highly ill conditioned and under determined estimation problems with a good performance of suppressing noises. Results with acceptable accuracies (MSE < 5%) can be obtained with 10% Gaussian white noises added to the simulated experimental data. The biggest difference between the proposed method and the existing methods is that multiple prior knowledge of X-ray spectra can be included in one dictionary, which is meaningful for obtaining the true X-ray spectrum from the measurements.

Influence of Microstructure and Mechanical Properties on Formability in High Strain Rate Rolled AZ31 Magnesium Alloy Sheets

Fubao Liu,Xiao Liu,Biwu Zhu,Hui Yang,Gang Xiao,Mingyue Hu 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.6

High strain-rate rolling (≥ 10 s−1) has been successfully employed to produce AZ31 magnesium alloy sheets to a high reductionof 82% with a fine grain structure in a single pass. The rolled sheets inevitably undertake various forming processessuch as press and deep forming in the fabrication stage. To investigate the formability, the Erichsen tests were carried out onhigh strain rate rolled AZ31 magnesium alloy sheets at room temperature. The relationship among mechanical properties,microstructure and formability were investigated. The crack behavior during Erichsen tests was also studied. It was foundthat the formability was related to the lowest in-plane tensile strengthen and dislocation density of initial microstructure. The competitive relationship between micro-crack and twinning/shear bands would also influence the formability of highstrain rate rolled magnesium alloy sheets. Deformed shear band with substaintial twins prohibits the crack extension andenhances strengthen of materials in front of crack tip.

Green algae dominance quickly switches to cyanobacteria dominance after nutrient enrichment in greenhouse with high temperature

Xiaodong Wang,Xingguo Liu1,Boqiang Qin,Zhaojun Gu,Hao Xu,Hao Zhu,Guofeng Cheng,Huang Liu 한국생태학회 2015 Journal of Ecology and Environment Vol.38 No.3

In order to understand the mechanisms of conversion between different algal dominance, an experiment was performed in a greenhouse from 22 June to 10 July 2011. The experiment included a treatment group subjected to three instances of nutrient enrichment and a control with no nutrient enrichment. The initial water was dominated by Ankistrodesmus of Chlorophyta. The average water temperature at 08:30 h and 14:00 h during the experiment was 31.6°C and 34.6°C, respec¬tively. The results showed that the total nitrogen (TN), total phosphorus (TP), dissolved total nitrogen (DTN), dissolved total phosphorus (DTP), and soluble reactive phosphorus (SRP) concentrations in the treatment were significantly higher than in the control (P < 0.05). However, the TN/TP and DTN/DTP in the control was higher than in the treatment (P < 0.05). The dominant algae in the control did not change during the experiment, while the dominant algae in the treat¬ment switched to Planktothrix of Cyanophyta on day 9. The chlorophyll a (Chl-a), wet weight of all algae, wet weight of Cyanophyta, and percentage of Cyanophyta in the control were all significantly lower than in the treatment (P < 0.05). Amounts of zooplankton, especially rotifers, were present at the end of the experimental period. The density of rotifers between the control and treatment was not significantly different (P > 0.05), while the copepod density in the treatment was higher than in the control (P < 0.05). We conclude that green algae dominance quickly switches to cyanobacteria dominance after nutrient enrichment in a greenhouse with elevated temperature

Feasibility of a Clinical-Radiomics Model to Predict the Outcomes of Acute Ischemic Stroke

Zhou Yiran,Wu Di,Yan Su,Xie Yan,Zhang Shun,Lv Wenzhi,Qin Yuanyuan,Liu Yufei,Liu Chengxia,Lu Jun,Li Jia,Zhu Hongquan,Liu Weiyin Vivian,Liu Huan,Zhang Guiling,Zhu Wenzhen 대한영상의학회 2022 Korean Journal of Radiology Vol.23 No.8

Objective: To develop a model incorporating radiomic features and clinical factors to accurately predict acute ischemic stroke (AIS) outcomes. Materials and Methods: Data from 522 AIS patients (382 male [73.2%]; mean age ± standard deviation, 58.9 ± 11.5 years) were randomly divided into the training (n = 311) and validation cohorts (n = 211). According to the modified Rankin Scale (mRS) at 6 months after hospital discharge, prognosis was dichotomized into good (mRS ≤ 2) and poor (mRS > 2); 1310 radiomics features were extracted from diffusion-weighted imaging and apparent diffusion coefficient maps. The minimum redundancy maximum relevance algorithm and the least absolute shrinkage and selection operator logistic regression method were implemented to select the features and establish a radiomics model. Univariable and multivariable logistic regression analyses were performed to identify the clinical factors and construct a clinical model. Ultimately, a multivariable logistic regression analysis incorporating independent clinical factors and radiomics score was implemented to establish the final combined prediction model using a backward step-down selection procedure, and a clinical-radiomics nomogram was developed. The models were evaluated using calibration, receiver operating characteristic (ROC), and decision curve analyses. Results: Age, sex, stroke history, diabetes, baseline mRS, baseline National Institutes of Health Stroke Scale score, and radiomics score were independent predictors of AIS outcomes. The area under the ROC curve of the clinical-radiomics model was 0.868 (95% confidence interval, 0.825–0.910) in the training cohort and 0.890 (0.844–0.936) in the validation cohort, which was significantly larger than that of the clinical or radiomics models. The clinical radiomics nomogram was well calibrated (p > 0.05). The decision curve analysis indicated its clinical usefulness. Conclusion: The clinical-radiomics model outperformed individual clinical or radiomics models and achieved satisfactory performance in predicting AIS outcome

Anionic defect engineering of transition metal oxides for oxygen reduction and evolution reactions

Zhu, Yunmin,Liu, Xi,Jin, Shiguang,Chen, Huijun,Lee, Wonyoung,Liu, Meilin,Chen, Yan The Royal Society of Chemistry 2019 Journal of materials chemistry. A, Materials for e Vol.7 No.11

<P>The development of cost-effective catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial for enhancing the energy efficiency of many electrochemical energy conversion and storage devices. Owing to their low cost and high activity, transition metal oxides have attracted much attention as alternative electrocatalysts to replace the currently used noble metal-based catalysts. Anion defects (<I>e.g.</I>, oxygen vacancies, interstitials, and anion dopants) can significantly change the electronic structure of oxides or the stability of adsorbed intermediates, thus greatly enhancing the electrocatalytic activities of the oxide surface. Anionic defect engineering represents a potential new direction for rational design of high-performance electrocatalysts. In this review, recent progress in manipulating the anion defects in transition metal oxides for enhancing their activity and stability is summarized and the proposed mechanisms for enhanced performance are discussed in detail. Challenges and prospects are also discussed in the development of a new generation of highly efficient ORR and OER electrocatalysts.</P>

Effect of defect types in monolayer MoS2 on SO2 adsorption

Liu Ge,Liu Jianfei,Yan Jun,Chen Yunlin,Zhu Yabin,Tian Yahui 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.5

As a two-dimensional semiconductor material, molybdenum disulfde (MoS2) is extensively applied to sulfur dioxide (SO2) gas sensor. However, point defects will inevitably be produced in the preparation of MoS2, which signifcantly afect the adsorption properties of MoS2. Thus, understanding the properties of diferent point defects is essential for the successful application of MoS2. In this work, four types of point defects (VS-MoS2, VS2-MoS2, VMoS3-MoS2 and VMoS6-MoS2) of monolayers MoS2 were proposed, and the adsorption characteristics of SO2 on four typical defective MoS2 monolayers were investigated based on frst principles. The adsorption models were established to calculate the electronic properties and adsorption parameters of the adsorption systems. The results show that VMoS6-MoS2 defect has excellent adsorption properties for SO2 due to its largest adsorption energy, charge transfer and electrical response. The obtained results will contribute to the understanding of the efects on the MoS2 monolayers with diferent defects for SO2 sensing application.

Molecular engineering of indoline based organic sensitizers for highly efficient dye-sensitized solar cells

Liu, Bo,Liu, Qingbin,You, Dan,Li, Xiaoyan,Naruta, Yoshinori,Zhu, Weihong The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.26

<P>The increasing electron-donating ability of the donor part is focused to further optimize the light-harvesting capability. Our strategy is to introduce an additional donor group into the indoline unit in the donor part to form a donor–donor structure (D–D moiety). Three different units (carbazole, fluorene and 4-methylphenyl groups) with different degrees of electron-donating capability are incorporated, thus constructing the specific donor–donor–π–acceptor (D–D–π–A) system (C-CA, F-CA and I-3) and giving a systematic view of the absorption evolution. Through molecular engineering, their light-harvesting capabilities, energy levels and photovoltaic performances were studied. As expected, utilizing strong electron-donating carbazole unit as additional donor, the IPCE spectrum of DSSC based on C-CA is successfully broadened to NIR region on the premise of suitable LUMO level, with an extraordinarily high plateau in visible region till around 700 nm. In the system of C-CA and F-CA, the introduction of <I>n</I>-pentyl group in donor part of carbazole and fluorene unit has little effect on preventing the molecular π-aggregation due to the good co-planarity of π-linker (vinyl thiophene), suggesting that the most effective way to prevent π-aggregation is still the incorporation of long alkyl groups into planar π-linker segment. However, the introducing long alkyl group can effectively prevent the electron recombination between electrons in conduction band (CB) of TiO<SUB>2</SUB> and I<SUB>3</SUB><SUP>−</SUP> ions. Along with the preferable light-harvesting capability, C-CA presents excellent IPCE performance with a short-circuit photocurrent (<I>J</I><SUB>sc</SUB>) of 18.53 mA cm<SUP>−2</SUP>, an open-circuit photovoltage (<I>V</I><SUB>oc</SUB>) of 649 mV, a fill factor of 0.71, corresponding to a power conversion efficiency (<I>η</I>) of 8.49%. The internal relations between chemical structure and conversion efficiency provide a strategy for developing highly efficient organic sensitizers working in whole visible region with high photovoltaic performance.</P> <P>Graphic Abstract</P><P>Utilizing a carbazole unit as additional donor, the photoresponse of C-CA is broadened to the NIR region with a <I>η</I> of 8.49%. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm31704d'> </P>

ALMA Reveals Sequential High-mass Star Formation in the G9.62+0.19 Complex

Liu, Tie,Lacy, John,Li, Pak Shing,Wang, Ke,Qin, Sheng-Li,Zhang, Qizhou,Kim, Kee-Tae,Garay, Guido,Wu, Yuefang,Mardones, Diego,Zhu, Qingfeng,Tatematsu, Ken’ichi,Hirota, Tomoya,Ren, Zhiyuan,Liu, Sheng-Yu American Astronomical Society 2017 The Astrophysical journal Vol.849 No.1

<P>Stellar feedback from high-mass stars (e.g., H II regions) can strongly influence the surrounding interstellar medium and regulate star formation. Our new ALMA observations reveal sequential high-mass star formation taking place within one subvirial filamentary clump (the G9.62 clump) in the G9.62+0.19 complex. The 12 dense cores (MM1-MM12) detected by ALMA are at very different evolutionary stages, from the starless core phase to the UC H II region phase. Three dense cores (MM6, MM7/G, MM8/F) are associated with outflows. The mass-velocity diagrams of the outflows associated with MM7/G and MM8/F can be well-fit by broken power laws. The mass-velocity diagram of the SiO outflow associated with MM8/F breaks much earlier than other outflow tracers (e.g., CO, SO, CS, HCN), suggesting that SiO traces newly shocked gas, while the other molecular lines (e.g., CO, SO, CS, HCN) mainly trace the ambient gas continuously entrained by outflow jets. Five cores (MM1, MM3, MM5, MM9, MM10) are massive starless core candidates whose masses are estimated to be larger than 25 M-circle dot, assuming a dust temperature of <= 20 K. The shocks from the expanding H II regions ('B' and 'C') to the west may have a great impact on the G9.62 clump by compressing it into a filament and inducing core collapse successively, leading to sequential star formation. Our findings suggest that stellar feedback from H II regions may enhance the star formation efficiency and suppress low-mass star formation in adjacent pre-existing massive clumps.</P>

Research of the Mechanism of Low Frequency Oscillation Based on Dynamic Damping Effect

Liu, Wenying,Ge, Rundong,Zhu, Dandan,Wang, Weizhou,Zheng, Wei,Liu, Fuchao The Korean Institute of Electrical Engineers 2015 Journal of Electrical Engineering & Technology Vol.10 No.4

For now, there are some low frequency oscillations in the power system which feature low frequency oscillation with positive damping and cannot be explained by traditional low frequency oscillation mechanisms. Concerning this issue, the dynamic damping effect is put forward on the basis of the power-angle curve and the study of damping torque in this article. That is, in the process of oscillation, damping will dynamically change and will be less than that of the stable operating point especially when the angle of the stable operating point and the oscillation amplitude are large. In a situation with weak damping, the damping may turn negative when the oscillation amplitude increases to a certain extent, which may result in an amplitude-increasing oscillation. Finally, the simulation of the two-machine two-area system verifies the arguments in this paper which may provide new ideas for the analysis and control of some unclear low frequency phenomena.

Cloning and expression of a wild eggplant cytochrome P450 gene, StoCYP77A2, involved in plant resistance to Verticillium dahliae

Liu Yang,Ce Shi,Xiaoying Mu,Chao Liu,Ke Shi,Wen-jiao Zhu,Qing Yang 한국식물생명공학회 2015 Plant biotechnology reports Vol.9 No.4

Plant P450s play an important role in plant response to environmental stimuli, especially to pathogen challenge, besides leading to the biosynthesis of secondary metabolites. In this work, a Verticillium dahliae-induced cDNA sequence was cloned from wild eggplant Solanum torvum and designated StoCYP77A2. StoCYP77A2 encodes a 511-amino acid peptide that shows sequence homology to the plant CYP77 family. StoCYP77A2 is expressed in a tissue-specific manner with the highest expression level in stem. The expression level of StoCYP77A2 was increased in wild eggplants which were infected with Verticillium dahlia. We expressed StoCYP77A2 in V. dahliae-sensitive tobacco, and the transgenic tobacco plants were more resistant to V. dahliae infection than the wild type. Protein extraction of transgenic tobacco showed strong antifungal activity against V. dahliae, indicating that StoCYP77A2 may be involved in the synthesis of some antimicrobial compounds. These results suggest that StoCYP77A2 plays a role in plant defense to V. dahliae infection.