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Positive definiteness of real quadratic forms resulting from the variable-step L1-type approximations of convolution operators

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Science China Mathematics 2024年第2期67卷 237-252页

作者： hong-Lin liao tao Tang tao Zhou School of Mathematics Nanjing University of Aeronautics and AstronauticsNanjing 211106China Division of Science and Technology BNU-HKBU United International CollegeZhuhai 519087China SUSTech International Center for Mathematics Shenzhen 518055China NCMIS&LSEC Institute of Computational Mathematics and Scientific/Engineering ComputingAcademy of Mathematics and Systems ScienceChinese Academy of SciencesBeijing 100190China

The positive definiteness of real quadratic forms with convolution structures plays an important rolein stability analysis for time-stepping schemes for nonlocal operators. In this work, we present a novel analysistool to handle discrete convolution kernels resulting from variable-step approximations for convolution operators.More precisely, for a class of discrete convolution kernels relevant to variable-step L1-type time discretizations, weshow that the associated quadratic form is positive definite under some easy-to-check algebraic conditions. Ourproof is based on an elementary constructing strategy by using the properties of discrete orthogonal convolutionkernels and discrete complementary convolution kernels. To our knowledge, this is the first general result onsimple algebraic conditions for the positive definiteness of variable-step discrete convolution kernels. Using theunified theory, we obtain the stability for some simple nonuniform time-stepping schemes straightforwardly.

关键词： discrete convolution kernels positive definiteness variable time-stepping orthogonal convolution kernels complementary convolution kernels

Analysis of the second-order BDF scheme with variable steps for the molecular beam epitaxial model without slope selection

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Science China Mathematics 2021年第5期64卷 887-902页

作者： hong-Lin liao Xuehua Song tao Tang tao Zhou Department of Mathematics Nanjing University of Aeronautics and AstronauticsNanjing 211101China Department of Mathematics and International Center for Mathematics Southern University of Science and TechnologyShenzhen 518055China Division of Science and Technology BNU-HKBU United International CollegeZhuhai 519087China NCMIS&LSEC Institute of Computational Mathematics and Scientific Engineering ComputingAcademy of Mathematics and Systems ScienceChinese Academy of SciencesBeijing 100190China

In this work,we are concerned with the stability and convergence analysis of the second-order backward difference formula(BDF2)with variable steps for the molecular beam epitaxial model without slope selection.We first show that the variable-step BDF2 scheme is convex and uniquely solvable under a weak time-step constraint.Then we show that it preserves an energy dissipation law if the adjacent time-step ratios satisfy r_(k):=τ_(k)/τ_(k-1)<3.561.Moreover,with a novel discrete orthogonal convolution kernels argument and some new estimates on the corresponding positive definite quadratic forms,the L^(2)norm stability and rigorous error estimates are established,under the same step-ratio constraint that ensures the energy stability,i.e.,0

关键词： molecular beam epitaxial growth variable-step BDF2 scheme discrete orthogonal convolution kernels energy stability convergence analysis

Development and validation of a new oxide fuel rod performance analysis code for the liquid metal fast reactor

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Nuclear Science and Techniques 2022年第5期33卷 167-177页

作者： Guang-Liang Yang Hai-Long liao tao Ding hong-Li Chen School of Nuclear Science and Technology University of Science and Technology of ChinaHefei230026China

The integrity and reliability of fuel rods under both normal and accidental operating conditions are of great importance for nuclear reactors.In this study,considering various irradiation behaviors,a fuel rod performance analysis code,named KMC-Fueltra,was developed to evaluate the thermal–mechanical performance of oxide fuel rods under both normal and transient conditions in the LMFR.The accuracy and reliability of the KMC-Fueltra were validated by analytical solutions,as well as the results obtained from codes and experiments.The results indicated that KMC-Fueltra can predict the performance of oxide fuel rods under both normal and transient conditions in the LMFR.

关键词： Fuel rod analysis code Thermal-mechanical performance Irradiation behaviors Pellet-cladding mechanical interaction Liquid metal fast reactor

Off-grid DOA estimation via a deep learning framework

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Science China(Information Sciences) 2023年第12期66卷 222-237页

作者： Yan HUANG Yanjun ZHANG Jun tao Cai WEN Guisheng liao Wei hong State Key Lab of Millimeter Waves Southeast University Key Laboratory of Underwater Acoustic Signal Processing of Ministry of Education Southeast University School of Information Science and Technology Northwest University National Key Lab of Radar Signal Processing Xidian University

Direction-of-arrival(DOA) estimation problem is one of the most important tasks for array signal processing. Conventional methods are limited by either the computational complexity or the resolution. In this paper, a novel deep learning(DL) framework for super-resolution DOA estimation is developed, where the grid mismatch problem is fully considered into the DL DOA estimation and the offset between the real DOA and the discrete sampling grid is thereby trained as a part of the network output. Specifically, we first model the DOA estimation problem as a multi-classification task and obtain the on-grid estimation result with a resolution of 1° as the first output. Then we designed another regression module to estimate the offset between target angles and the corresponding grids. By combining both on-grid and offset estimation results, the accurate off-grid estimation is achieved. In addition, the method of fusing low-level features and high-level features by skip connection is adopted between the on-grid estimation module and the offset estimation module. The high-level features in the first part of the network are combined with the original input to improve the training speed and the estimation accuracy. Herein, our training dataset contains a large number of off-grid signal data, which is close to the practical application. Also, the utilization of the off-grid part information improves DOA estimation performance compared to existing DL-based methods,achieving more accurate DOA estimations. Numerous simulation results have demonstrated the superiority of the proposed method in DOA estimation precision, and a good performance advantage maintains even when using a limited number of snapshots. Further, we test the proposed method on the real millimeter-wave radar system, and it outperforms the other state-of-the-art methods, especially for two adjacent targets in the same range and Doppler bin.

关键词： direction-of-arrival (DOA) estimation deep learning (DL) off-grid array signal processing

Microstructure and mechanical property of NbTaTiV refractory high-entropy alloy with different Y_(2)O_(3) contents

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Rare Metals 2022年第10期41卷 3504-3514页

作者： tao liao Yuan-Kui Cao Wen-Min Guo Qi-hong Fang Jia Li Bin Liu State Key Laboratory of Powder Metallurgy Central South UniversityChangsha410083China State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body Hunan UniversityChangsha410082China

In this study,NbTaTiV refractory high-entropy alloys(RHEAs) reinforced with dispersed oxides were successfully designed and fabricated by mechanical alloying and subsequent spark plasma sintering(SPS).The effects of Y_(2)O_(3) content on the microstructure and mechanical properties have been systematically studied.The results show that the oxide dispersion strengthening(ODS) RHEAs are mainly composed of body centered cubic(BCC) matrix and multiscale oxides,including submicron Ti-(N,O) particles,nano-sized Y-Ti-O particles and nano-sized Y_(2)O_(3) particles.The ODS-RHEAs have excellent mechanical properties due to the multisc ale oxides.With the content of Y_(2)O_(3) increasing from 1 wt% to 3 wt% Y_(2)O_(3),the compressive yield strength of the ODSRHEAs significantly increases from 1528 to 1866 MPa,while the fracture strain slightly reduces from 22% to 16%.The enhancement of the mechanical property is mainly attributed to the increased amount of multisc ale oxide particles and the refined grain structure.

关键词： Refractory high-entropy alloy Oxide dispersion strengthening Spark plasma sintering(SPS) Mechanical property Strengthening mechanism

Left atrial enlargement and non-paroxysmal atrial fibrillation as risk factors for left atrial thrombus/spontaneous Echo contrast in patients with atrial fibrillation and low CHA2DS2-VASc score

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Journal of Geriatric Cardiology 2020年第3期17卷 155-159页

作者： Wei-Dong LIN Yu-Mei XUE Fang-Zhou LIU Xian-hong FANG Xian-Zhang ZHAN Hong-Tao LIAO Gary Tse Shu-Lin WU Guangdong Cardiovascular Institute Guangdong General HospitalGuangzhouChina Department of Medicine and Therapeutics Faculty of MedicineChinese University of Hong KongHong KongChina Li Ka Shing Institute of Health Sciences Faculty of MedicineChinese University of Hong KongHong KongChina

Objective To determine the risk factors for thromboembolism in lower risk patients with non-valvular atrial fibrillation(AF)and low CHA2DS2-VASc scores,which remain undefined.Methods We retrospectively analyzed the baseline clinical characteristics,routine laboratory parameters,and echocardiographic measurements of 705 patients(71.1%male;mean age:52.10±9.64 years)with low CHA2DS2-VASc score(0 or 1;1 point for female sex)out of 1346 consecutive patients with non-valvular AF who underwent transesophageal echocardiography(TEE)at Guangdong Cardiovascular Institute between January 2013 and December 2015.Results Patients with left atrial thrombus(LAT)or spontaneous echo contrast(SEC)on TEE(24/705,4%)showed a higher incidence rate of vascular disease(54.2%vs.32.9%,P=0.045)and non-paroxysmal AF(79.2%vs.29.4%,P<0.001),larger left atrial diameter(43.08±4.59 vs.36.02±5.53 mm,P<0.001),and lower left ventricular ejection fraction(58.23±8.82%vs.64.15±7.14%,P<0.001)than those without.Multivariate logistic regression analysis identified left atrial diameter[odds ratio(OR)=1.171,95%confidence interval(CI):1.084–1.265,P<0.001]and non-paroxysmal AF(OR=3.766,95%CI:1.282–11.061,P=0.016)as independent risk factors for LAT/SEC.In ROC curve analysis,a left atrial dimeter cutoff of 37.5 mm yielded 95.0%sensitivity and 62.7%specificity(AUC:0.847,P<0.0001,95%CI:0.793–0.914).Conclusion In patients with non-valvular AF with low CHA2DS2-VASc score,the presence of LAT or SEC was associated with left atrial enlargement,which had moderate predictive value,and non-paroxysmal AF.

关键词： Atrial fibrillation Left atrial diameter Left atrial spontaneous echo contrast Left atrial thrombus

Clinical, sonographic characteristics and long-term prognosis of valvular heart disease in elderly patients

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Journal of Geriatric Cardiology 2019年第1期16卷 33-41页

作者： Feier SONG Fang-Zhou LIU Yuan-Feng LIANG Gary Tse Xin LI Hong-Tao LIAO Ji-Yan CHEN Department of Cardiology Guangdong Cardiovascular InstituteGuangdong Provincial Key Laboratory of Coronary Heart Disease PreventionGuangdong Provincial People's HospitalGuangdong Academy of Medical SciencesGuangzhouChina Department of Cardiology Guangdong Cardiovascular InstituteGuangdong Provincial People's HospitalGuangdong Academy of Medical SciencesGuangzhouChina Guangdong Geriatric Institute Guangdong Provincial People s Hospital and Guangdong Academy of Medical SciencesGuangzhouChina Department of Medicine and Therapeutics Faculty of MedicineChinese University of Hong KongHong KongChina Iinstitute of Health Sciences Faculty of MedicineChinese University of Hong KongHong KongChina

Background Valvular heart disease(VHD)is expected to become more prevail as the population ages and disproportionately affects older adults.However,direct comparison of clinical characteristics,sonographic diagnosis,and outcomes in VHD patients aged over 65 years is scarce.The objective of this study was to evaluate the differences in clinical characteristics and prognosis in two age-groups of geriatric patients with VHD.Methods We retrospectively enrolled consecutive individuals aged>65 years from Guangdong Provincial Peopled Hospital and screened for VHD using transthoracic echocardiography(TTE)or transesophageal echocardiography(TEE).Finally,260(48.9%)patients were in the 65-74 years group,and 272(51.1%)were in the>75-year group.Factors that affected long-term survival was explored.A multivariable Cox hazards regression was performed to identify the predictors of major adverse cardiac events(MACEs)in each group.Results In our population,the older group were more likely to have chronic obstructive pulmonary disease(COPD),degenerative VHD,but with less rheumatic VHD,aortic stenosis(AS)and mitral stenosis(MS).Compared with those aged 65-74 years,the older group had a higher incidence of all-cause death(10.0%vs.16.5%,P=0.027),ischemic stroke(13.5%vs.20.2%,P=0.038)and MACEs(37.3%vs.48.2%,P=0.011)at long-term follow-up.In multivariable Cox regression analysis,mitral regurgitation,a history of COPD,chronic kidney disease,diabetes,hypertension,atrial fibrillation and New York Heart Association(NYHA)functional class were identified as independent predictors of MACEs in the older group.Conclusion Advanced age profoundly affect prognosis and different predictors were associated with MACEs in geriatric patients with VHD.

关键词： Echocardiography Geriatrics Mortality Prognosis The aged Valvular heart disease

Transplantation of bone marrow stromal cells overexpressing humanvascular endothelial growth factor 165 enhances tissue repair in a ratmodel of radiation-induced injury

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Chinese Medical Journal 2014年第6期127卷 1093-1099页

作者： Wang tao liao Tian'an Wang hong Deng Wei Yu Dahai China 570311 China 530021

Background The multilineage differentiation potential ability of bone marrow stromal cells(BMSCs) showed great potential in tissue engineering, while vascular endothelial growth factor 165(VEGF165) promotes vasculogenesis and further promotes tissue regeneration. This study aimed to assess the ability of rat BMSCs expressing human VEGF A165(hVEGF165) to promote tissue repair in rat model of radiation-induced injury.Methods Rat BMSCs were isolated from the tibia. Plasmid DNA expressing hVEGF165 was stably transfected into BMSCs using liposomes. The right hindlimb muscle of 40 rats was irradiated using a 60 Co γ source(total dose 30 Gy). The animals were divided into four groups(n=10): not injected with BMSCs(control; group 1) or intramuscularly injected two times(once in 2 weeks) with pcDNATM3.1-transfected BMSCs(group 2), untransfected BMSCs(group 3), or hVEGF165-transfected BMSCs(group 4). Angiography was performed 1 week after the last injection of BMSCs; samples of the hindlimb muscle were subjected to transmission electron microscopy, ultrastructural analysis, reverse transcription-PCR(RT-PCR), Western blotting, and immunohistochemistry.Results Rat BMSCs with multipotent differentiation capacity were isolated. hVEGF165-transfected BMSCs overexpressed hVEGF165 mRNA and protein. Injection of BMSCs(groups 2–4) increased the average vessel number, density, diameter, and cross-sectional area; mRNA expression of the myogenic markers including myoblast determination protein, myogenin, and α-smooth muscle actin; and CD31 protein expression; and promoted the repair of blood vessels and myofibers after radiation-induced injury compared to group 1; each of these parameters and hVEGF165 mRNA or protein expression were markedly improved in rats injected with hVEGF165-transfected BMSCs compared to groups 2 and 3.Conclusions BMSCs expressing hVEGF165 enhanced the repair of radiation-induced tissue injury by promoting vasculogenesis and muscle fiber regeneration. BMSCs expressing hVEGF165 may have potential clinical applicat

关键词： bone marrow stromal cell vascular endothelial growth factor radiation-induced tissue injury

Screening of natural compounds with neuronal differentiation promoting effects in a cell-based model

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Chinese Journal of Natural Medicines 2015年第8期13卷 602-608页

作者： CHEN tao WANG Juan LIU Mei ZHANG Lu-Yong liao hong National Center for Drug Screening China Pharmaceutical University

The purpose of this study was to establish a drug screening method for small molecules extracted from traditional Chinese medicines(TCM) that have neuronal differentiation promoting effects, using P19 embryonic carcinoma cell as a cell-based model. First, the constructed plasmid(p Tα1-Luc) was transfected into P19 cells to establish a screening model. Second, several TCMs were screened using the established model and all-trans-retinoic acid as a positive control. Finally, the underlying molecular mechanism was explored using immunofluorescence staining, q T-PCR, and Western blot analysis. Our results indicated that the drug screen model was established successfully and that both honokiol and hyperoside induced P19 differentiation into neurons, with the possible molecular mechanism being modulating the Wnt signaling pathway. In conclusion, the drug screening model developed in the present study provides a rapid, cell-based screening platform for identifying natural compounds with neuronal differentiation effects.

关键词： Drug screening model Neuronal differentiation P19 embryonic carcinoma cells Wnt signaling pathway Traditional Chinese Medicine