A structural strain method for low-cycle fatigue evaluation of welded components

Dong, P.,Pei, X.,Xing, S.,Kim, M.H. Applied Science Publishers ; Elsevier Science Ltd 2014 The International journal of pressure vessels and Vol.119 No.-

In this paper, a new structural strain method is presented to extend the early structural stress based master S-N curve method to low cycle fatigue regime in which plastic deformation can be significant while an elastic core is still present. The method is formulated by taking advantage of elastically calculated mesh-insensitive structural stresses based on nodal forces available from finite element solutions. The structural strain definition is consistent with classical plate and shell theory in which a linear through-thickness deformation field is assumed a priori in both elastic or elastic-plastic regimes. With considerations of both yield and equilibrium conditions, the resulting structural strains are analytically solved if assuming elastic and perfectly plastic material behavior. The formulation can be readily extended to strain-hardening materials for which structural strains can be numerically calculated with ease. The method is shown effective in correlating low-cycle fatigue test data of various sources documented in the literature into a single narrow scatter band which is remarkable consistent with the scatter band of the existing master S-N curve adopted ASME B&PV Code since 2007. With this new method, some of the inconsistencies of the pseudo-elastic structural stress procedure in 2007 ASME Div 2 Code can now be eliminated, such as its use of Neuber's rule in approximating structural strain beyond yield. More importantly, both low cycle and high cycle fatigue behaviors can now be treated in a unified manner. The earlier mesh-insensitive structural stress based master S-N curve method can now be viewed as an application of the structural strain method in high cycle regime, in which structural strains are linearly related to traction-based structural stresses according to Hooke's law. In low-cycle regime, the structural strain method characterizes fatigue damage directly in terms of structural strains that satisfy linear through-thickness deformation gradient assumption, material nonlinear behavior, and equilibrium conditions. The use of a pseudo-elastic structural stress definition is not fundamental, but merely a means to put low-cycle and high-cycle fatigue test data in a conventional stress-based S-N data representation which is typically preferred in engineering practice, than a strain-based representation.

Multi-Level Canonical Correlation Analysis for Standard-Dose PET Image Estimation

Le An,Pei Zhang,Adeli, Ehsan,Yan Wang,Guangkai Ma,Feng Shi,Lalush, David S.,Weili Lin,Dinggang Shen IEEE 2016 IEEE TRANSACTIONS ON IMAGE PROCESSING - Vol.25 No.7

<P>Positron emission tomography (PET) images are widely used in many clinical applications, such as tumor detection and brain disorder diagnosis. To obtain PET images of diagnostic quality, a sufficient amount of radioactive tracer has to be injected into a living body, which will inevitably increase the risk of radiation exposure. On the other hand, if the tracer dose is considerably reduced, the quality of the resulting images would be significantly degraded. It is of great interest to estimate a standard-dose PET (S-PET) image from a low-dose one in order to reduce the risk of radiation exposure and preserve image quality. This may be achieved through mapping both S-PET and low-dose PET data into a common space and then performing patch-based sparse representation. However, a one-size-fits-all common space built from all training patches is unlikely to be optimal for each target S-PET patch, which limits the estimation accuracy. In this paper, we propose a data-driven multi-level canonical correlation analysis scheme to solve this problem. In particular, a subset of training data that is most useful in estimating a target S-PET patch is identified in each level, and then used in the next level to update common space and improve estimation. In addition, we also use multi-modal magnetic resonance images to help improve the estimation with complementary information. Validations on phantom and real human brain data sets show that our method effectively estimates S-PET images and well preserves critical clinical quantification measures, such as standard uptake value.</P>

Semisupervised Tripled Dictionary Learning for Standard-Dose PET Image Prediction Using Low-Dose PET and Multimodal MRI

Wang, Yan,Shen, Dinggang,Ma, Guangkai,An, Le,Shi, Feng,Zhang, Pei,Lalush, David S.,Wu, Xi,Pu, Yifei,Zhou, Jiliu IEEE 2017 IEEE Transactions on Biomedical Engineering Vol.64 No.3

<P>Objective: To obtain high-quality positron emission tomography (PET) image with low-dose tracer injection, this study attempts to predict the standard-dose PET (S-PET) image from both its low-dose PET (L-PET) counterpart and corresponding magnetic resonance imaging (MRI). Methods: It was achieved by patch-based sparse representation (SR), using the training samples with a complete set of MRI, L-PET and S-PET modalities for dictionary construction. However, the number of training samples with complete modalities is often limited. In practice, many samples generally have incomplete modalities (i.e., with one or two missing modalities) that thus cannot be used in the prediction process. In light of this, we develop a semisupervised tripled dictionary learning (SSTDL) method for S-PET image prediction, which can utilize not only the samples with complete modalities (called complete samples) but also the samples with incomplete modalities (called incomplete samples), to take advantage of the large number of available training samples and thus further improve the prediction performance. Results: Validation was done on a real human brain dataset consisting of 18 subjects, and the results show that our method is superior to the SR and other baseline methods. Conclusion: This paper proposed a new S-PET prediction method, which can significantly improve the PET image quality with low-dose injection. Significance: The proposed method is favorable in clinical application since it can decrease the potential radiation risk for patients.</P>

Fabrication of 3D Cell-constructs Using Photocrosslinkable Hydrogel-coated Cells

S. J. Chae(채수정),H. Lee(이형진),J. Y. Lee(이재윤),Y. W. Koo(구영원),W. J. Kim(김원진),J. U. Lee(이지운),J. Y. Kim(김주연),D. Kim(김동윤),H. J. Hwangbo(황보한준),A. O. Mahmoudsalehi(아민 오라쉬 마하무트살레히),S. Y. Jo(조서율),M. H. Pei(배말한) Korean Society for Precision Engineering 2022 한국정밀공학회 학술발표대회 논문집 Vol.2022 No.5

Empirical evidence and stability analysis of the linear car-following model with gamma-distributed memory effect

Pei, X.,Pan, Y.,Wang, H.,Wong, S.C.,Choi, K. North-Holland Pub. Co 2016 PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIO Vol.449 No.-

<P>Car-following models, which describe the reactions of the driver of a following car to the changes of the leading car, are essential for the development of traffic flow theory. A car following model with a stochastic memory effect is considered to be more realistic in modeling drivers' behavior. Because a gamma-distributed memory function has been shown to outperform other forms according to empirical data, in this study, we thus focus on a car-following model with a gamma-distributed memory effect; analytical and numerical studies are then conducted for stability analysis. Accordingly, the general expression of undamped and stability points is achieved by analytical study. The numerical results show great agreement with the analytical results: introducing the effect of the driver's memory causes the stable regions to weaken slightly, but the metastable region is obviously enlarged. In addition, a numerical study is performed to further analyze the variation of the stable and unstable regions with respect to the different profiles of gamma distribution. (C) 2016 Elsevier B.V. All rights reserved.</P>

Ladder-like polysilsesquioxane dielectrics for organic field-effect transistor applications

Pei, M.,Lee, A.,Hwang, S.,Yang, H. Royal Society of Chemistry 2017 Journal of Materials Chemistry C Vol.5 No.42

<P>A series of trimethylsilyl-capped hybrid ladder-like polysilsesquioxane (LPSQ-TMS) derivatives were synthesized comprising an inorganic backbone functionalized with various organic side moieties and compositional ratios with application towards gate dielectrics or surface modifying materials. The surface energy (gamma) and roughness (R-q) values of the LPSQ-TMS coated SiO2 dielectrics were considerably affected by the side moieties of the polymer series; methyl, n-propyl, phenyl (P), naphthyl (N), methacryloxypropyl (MA), and fluorooctyl moieties. The gamma values varied from 17.0 to 42.0 mJ m(-2), while the R-q values also ranged from 0.34 to 1.10 nm. On polymer-treated SiO2 dielectrics possessing smooth and semiconductor-compatible surface properties, pentacene developed terrace-like crystallites formed through layer-by-island growth modes, a stark contrast to the three-dimensionally grown crystal islands formed on rough or extremely hydrophobic surfaces, which led to unfavorable conduction pathways. Depending on the order of conjugation and interconnections between the pentacene domains, the average mobility (mu(FET)) values of the resulting 50 nm thick pentacene organic field-effect transistors were varied by two orders of magnitude and reached 0.8 cm(2) V-1 s(-1), specifically, for both the P- and MA-substituted LPSQ-TMS treated SiO2 dielectrics (gamma = 37.0 mJ m(-2) and R-q = 0.40 nm). Moreover, we were able to demonstrate that a thermally cured 500 nm thick LPSQ-TMS layer on an Au gate-patterned flexible polyimide substrate could yield pentacene OFETs with mFET values as high as 0.60 cm(2) V-1 s(-1), comparable to that of the LPSQ-TMS treated SiO2 system. Also, the proper introduction of organic substituents to LPSQ improved the gate-bias stress stability for high performance OFETs.</P>

Identifying the social-balanced densest subgraph from signed social networks

Hao, F.,Park, D. S.,Pei, Z.,Lee, H.,Jeong, Y. S. Springer Science + Business Media 2016 The Journal of supercomputing Vol.72 No.7

<P>Identifying the dense subgraphs from large graphs is important and useful to various social media mining applications. Most of existing works focus on the densest subgraph problem in the unweighted and undirected represented social network which can maximize the average degree over all possible subgraphs. However, considering the frequent signed relationships occurred in real-life social network, this paper introduces the social-balanced densest subgraph problem in signed social network by incorporating the social balance theory. We obtain a novel problem formulation that is to identify the subset of vertices that can maximize the social-balanced density in signed social networks. Further, we propose an efficient approach for identifying the social-balanced densest subgraph based on formal concept analysis. The case study illustrates that our algorithm can efficiently identify the social-balanced densest subgraph for satisfying the specific application's requirements.</P>

GREEN BANK TELESCOPE OBSERVATIONS OF THE NH₃(3, 3) AND (6, 6) TRANSITIONS TOWARD SAGITTARIUS A MOLECULAR CLOUDS

Minh, Young Chol,Liu, Hauyu Baobab,Ho, Paul T. P.,Hsieh, Pei-Ying,Su, Yu-Nung,Kim, Sungsoo S.,Wright, Melvyn IOP Publishing 2013 The Astrophysical journal Vol.773 No.1

<P>Ammonia (3, 3) and (6, 6) transitions have been observed using the Green Bank Telescope toward the Sgr A region. The gas is mainly concentrated in 50 km s(-1) and 20 km s(-1) clouds located in a plane inclined to the galactic plane. These 'main' clouds appear to be virialized and influenced by the expansion of the supernova remnant Sgr A East. The observed emission shows very complicated features in the morphology and velocity structure. Gaussian multi-component fittings of the observed spectra revealed that various 'streaming' gas components exist all over the observed region. These components include those previously known as 'streamers' and 'ridges,' but most of these components appear not to be directly connected to the major gas condensations (the 50 km s(-1) and 20 km s(-1) clouds). They are apparently located out of the galactic plane, and they may have a different origin than the major gas condensations. Some of the streaming components are expected to be sources that feed the circumnuclear disk of our Galactic center directly and episodically. They may also evolve differently than major gas condensations under the influence of the activities of the Galactic center.</P>

The Fabrication of Highly Porous Cell-laden Gel-ma Structures

S. Y. Jo(조서율),J. U. Lee(이지운),W. J. Kim(김원진),Y. W. Koo(구영원),J. Y. Lee(이재윤),M. Pei(배말한),G. H. Kim(김근형) Korean Society for Precision Engineering 2022 한국정밀공학회 학술발표대회 논문집 Vol.2022 No.5

Shear localisation modelling of friction stir weld formation process

Pei, X. J.,Dong, P. S. Informa UK (Taylor Francis) 2014 Science and technology of welding and joining Vol.19 No.5