Assembly of micro/nanomaterials into complex, three-dimensional architectures by compressive buckling

Xu, Sheng,Yan, Zheng,Jang, Kyung-In,Huang, Wen,Fu, Haoran,Kim, Jeonghyun,Wei, Zijun,Flavin, Matthew,McCracken, Joselle,Wang, Renhan,Badea, Adina,Liu, Yuhao,Xiao, Dongqing,Zhou, Guoyan,Lee, Jungwoo,Chu American Association for the Advancement of Scienc 2015 Science Vol.347 No.6218

<P><B>Popping materials and devices from 2D into 3D</B></P><P>Curved, thin, flexible complex three-dimensional (3D) structures can be very hard to manufacture at small length scales. Xu <I>et al.</I> develop an ingenious design strategy for the microfabrication of complex geometric 3D mesostructures that derive from the out-of-plane buckling of an originally planar structural layout (see the Perspective by Ye and Tsukruk). Finite element analysis of the mechanics makes it possible to design the two 2D patterns, which is then attached to a previously strained substrate at a number of points. Relaxing of the substrate causes the patterned material to bend and buckle, leading to its 3D shape.</P><P><I>Science</I>, this issue p. 154; see also p. 130</P><P>Complex three-dimensional (3D) structures in biology (e.g., cytoskeletal webs, neural circuits, and vasculature networks) form naturally to provide essential functions in even the most basic forms of life. Compelling opportunities exist for analogous 3D architectures in human-made devices, but design options are constrained by existing capabilities in materials growth and assembly. We report routes to previously inaccessible classes of 3D constructs in advanced materials, including device-grade silicon. The schemes involve geometric transformation of 2D micro/nanostructures into extended 3D layouts by compressive buckling. Demonstrations include experimental and theoretical studies of more than 40 representative geometries, from single and multiple helices, toroids, and conical spirals to structures that resemble spherical baskets, cuboid cages, starbursts, flowers, scaffolds, fences, and frameworks, each with single- and/or multiple-level configurations.</P>

Boundary Lubrication in Transient Elliptical Contact: Part 1- Theoretical Formulation and Results

Di-Chu Xu,Qi Zhang,Jiu-Gen Wang 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.4

The transient elliptical contacts in boundary lubrication widely exist in modern mechanical systems with high durability. However, little attention has been paid to the squeeze effect of fluid film in this condition. A deterministic model which combines the contact mechanics with the pure squeeze lubrication model has been developed with the aim of understanding the squeeze effect of fluid film under the transient boundary lubrication. The leakage coefficient was introduced to capture the fluid leakage of rough surfaces. The squeeze effect of trapped fluid film was confirmed through comparing the fluid film stiffness in boundary lubrication with that of the elastohydrodynamic lubrication. Additionally, the effects of fluid film entrapment/leakage on the boundary lubrication performance were numerically analyzed during transients. The load capacity of the squeeze films is built up due to the trapped fluid film in the micro-valleys, which can be significantly affected by the interfacial shear coefficient of the boundary films. The simulation results show a good agreement with the experiments and justify the present numerical model is feasible in the boundary lubrication regime.

Separation dynamics of hydrogen isotope gas in mesoporous and microporous adsorbent beds at 77 K: SBA-15 and zeolites 5A, Y, 10X

Chu, X.Z.,Cheng, Z.P.,Xiang, X.X.,Xu, J.M.,Zhao, Y.J.,Zhang, W.G.,Lv, J.S.,Zhou, Y.P.,Zhou, L.,Moon, D.K.,Lee, C.H. Pergamon Press ; Elsevier Science Ltd 2014 International journal of hydrogen energy Vol.39 No.9

The separation of a hydrogen isotope mixture on porous materials was studied using equilibrium and breakthrough experiments. The adsorption equilibria of H<SUB>2</SUB> and D<SUB>2</SUB> on SBA-15 with mesopores and molecular sieves 5A, Y, and 10X with micropores were measured at 77 K using the volumetric method. The breakthrough experiments of a H<SUB>2</SUB> and D<SUB>2</SUB> mixture in each adsorbent bed were carried out at various conditions of flow rate and pressure. The equilibrium ratio of D<SUB>2</SUB> to H<SUB>2</SUB> on mesoporous molecular sieves was larger than the ratio on microporous molecular sieves (SBA-15 > 10X > Y > 5A), but the difference among the adsorbents decreased with increases in pressure. On the other hand, the order of breakthrough separation factor showed the opposite result (SBA-15 < 10X < Y < 5A). The breakthrough separation factors for zeolite 10X was approximately equal to the equilibrium ratio of D<SUB>2</SUB> to H<SUB>2</SUB> at the corresponding partial pressures, whereas zeolites 5A and Y showed higher breakthrough separation factors than their equilibrium ratios. In SBA-15, the separation factors from breakthrough results were even smaller than the corresponding equilibrium ratio. In the microporous adsorbent with a limited pore size (zeolite 5A in the study), the diffusion mechanism contributed to the separation of hydrogen isotope gases as one of key factors.

Hypoxia Mediates Runt-Related Transcription Factor 2 Expression via Induction of Vascular Endothelial Growth Factor in Periodontal Ligament Stem Cells

Xu, Qian,Liu, Zhihua,Guo, Ling,Liu, Rui,Li, Rulei,Chu, Xiang,Yang, Jiajia,Luo, Jia,Chen, Faming,Deng, Manjing Korean Society for Molecular and Cellular Biology 2019 Molecules and cells Vol.42 No.11

Periodontitis is characterized by the loss of periodontal tissues, especially alveolar bone. Common therapies cannot satisfactorily recover lost alveolar bone. Periodontal ligament stem cells (PDLSCs) possess the capacity of self-renewal and multilineage differentiation and are likely to recover lost alveolar bone. In addition, periodontitis is accompanied by hypoxia, and hypoxia-inducible $factor-1{\alpha}$ ($HIF-1{\alpha}$) is a master transcription factor in the response to hypoxia. Thus, we aimed to ascertain how hypoxia affects runt-related transcription factor 2 (RUNX2), a key osteogenic marker, in the osteogenesis of PDLSCs. In this study, we found that hypoxia enhanced the protein expression of $HIF-1{\alpha}$, vascular endothelial growth factor (VEGF), and RUNX2 ex vivo and in situ. VEGF is a target gene of $HIF-1{\alpha}$, and the increased expression of VEGF and RUNX2 proteins was enhanced by cobalt chloride ($CoCl_2$, $100{\mu}mol/L$), an agonist of $HIF-1{\alpha}$, and suppressed by 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1, $10{\mu}mol/L$), an antagonist of $HIF-1{\alpha}$. In addition, VEGF could regulate the expression of RUNX2, as RUNX2 expression was enhanced by human VEGF ($hVEGF_{165}$) and suppressed by VEGF siRNA. In addition, knocking down VEGF could decrease the expression of osteogenesis-related genes, i.e., RUNX2, alkaline phosphatase (ALP), and type I collagen (COL1), and hypoxia could enhance the expression of ALP, COL1, and osteocalcin (OCN) in the early stage of osteogenesis of PDLSCs. Taken together, our results showed that hypoxia could mediate the expression of RUNX2 in PDLSCs via $HIF-1{\alpha}$-induced VEGF and play a positive role in the early stage of osteogenesis of PDLSCs.

Seroprevalence of selected porcine respiratory pathogens in the pig herds in Chungcheong and Gyeongsang provinces in Korea

Chu, Jia-Qi,Hu, Xu-Min,Kim, Myung-Cheol,Park, Chang-Sik,Jun, Moo-Hyung The Korean Society of Veterinary Service 2009 韓國家畜衛生學會誌 Vol.32 No.1

We studied the seroprevalence of four respiratory pathogens in Korean swine farms located in Chungnam, Chungbuk, Gyeongnam and Gyeongbuk provinces during the period of spring of 2007 to winter of 2008. Serological tests were performed using commercial ELISA kits. A total of 530 serum samples were tested for the antibodies against porcine reproductive and respiratory syndrome virus (PRRSV), porcine circovirus type 2 (PCV2), Mycoplasma hyopneumoniae (M. hyo) and Actinobacillus pleuropneumoniae (APP). Seroprevalence for four respiratory pathogens were estimated by ELISA-positive rates of the submitted samples. The overall seropositive rates of PRRSV, APP, M. hyo and PCV2 were 32.6%, 10.6%, 38.4% and 88.5%, respectively. By production stage, the seropositive rate for PRRSV was highest in nursery pig populations (46.2%). In contrast, the highest seropositive rates of APP and M. hyo were observed in sow and growing pigs. However, the seroprevalence of PCV2 was ranged from 85.7% to 89.6%, showing no significant difference among the production stages. In the seroprevalence by season, PRRSV, APP and M. hyo infections revealed typical seasonal patterns that the peaks of the seropositive rates were observed between early winter and late spring. In case of PCV2, no particular seasonal patterns were noticed. The pig herds in Gyeongbuk province where PMWS was endemic during the period of survey showed the highest seropositive rates for PRRSV (44.6%), M. hyo (47.5%), and PCV2 (92.7%). Seropositive rates for APP of four provinces were approximately 10%. These results might be valuable for control and prevention of the respiratory diseases and helpful to define strategies related to vaccine applications.

The dilatancy and numerical simulation of failure behavior of granular materials based on Cosserat model

Chu, Xihua,Yu, Cun,Xu, Yuanjie Techno-Press 2012 Interaction and multiscale mechanics Vol.5 No.2

The dilatancy of granular materials has significant influence on its mechanical behaviors. The dilation angle is taken as a constant in conventional associated or non-associated flow rules based on Drucker-Prager yields theory. However, various experimental results show the dilatancy changes during progressive failure of granular materials. A non-associated flow rule with evolution of dilation angle is adopted in this study, and Cosserat continuum theory is used to describe the behaviors of granular materials for considering to some extent the its internal structure. Numerical examples focus on the bearing capacity and localization of granular materials, and results illustrate the capability and performance of the presented model in modeling the effect on failure behavior of granular materials.

Zero-Current-Switching in Full-Bridge DC-DC Converters Based on Activity Auxiliary Circuit

Chu, Enhui,Lu, Ping,Xu, Chang,Bao, Jianqun The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.2

To address the problem of circulating current loss in the traditional zero-current switching (ZCS) full-bridge (FB) DC/DC converter, a ZCS FB DC/DC converter topology and modulation strategy is proposed in this paper. The strategy can achieve ZCS turn on and zero-voltage and zero-current switching (ZVZCS) turn off for the primary switches and realize ZVZCS turn on and zero-voltage switching (ZVS) turn off for the auxiliary switches. Moreover, its resonant circuit power is small. Compared with the traditional phase shift full-bridge converter, the new converter decreases circulating current loss and does not increase the current stress of the primary switches and the voltage stress of the rectifier diodes. The diodes turn off naturally when the current decreases to zero. Thus, neither reverse recovery current nor loss on diodes occurs. In this paper, we analyzed the operating principle, steady-state characteristics and soft-switching conditions and range of the converter in detail. A 740 V/1 kW, 100 kHz experimental prototype was established, verifying the effectiveness of the converter through experimental results.

Morphology control of mesoporous Cu₂O by reductants and its photocatalytic activity

Chu, Xiao-Zhong,Cheng, Zhi-Peng,Zhao, Yi-Jiang,Xu, Ji-Ming,Li, Mei-Sheng,Hu, Lei,Zhou, Shou-Yong,Wu, Fei-Yue,Lee, Chang-Ha Elsevier 2017 CERAMICS INTERNATIONAL Vol.43 No.11

<P><B>Abstract</B></P> <P>Mesoporous Cu<SUB>2</SUB>O particles with different morphologies were synthesized via simple one-pot reactions. Effects of reducing agents, dispersant, template, and temperature on the <B>structure</B> of the prepared materials were investigated. Mesoporous flower-shaped Cu<SUB>2</SUB>O materials were obtained at 70℃ using glucose <B>as a reductant</B>. Different hollow microsphere shapes of Cu<SUB>2</SUB>O could be prepared at 40℃ using <B>another type of reductant, ascorbic acid</B>. The results indicated that the uniform morphology of synthesized Cu<SUB>2</SUB>O with mesopores presented a maximum specific surface area of 45.3m<SUP>2</SUP>/g. Furthermore, the as-prepared Cu<SUB>2</SUB>O particles showed good photodegradation efficiencies of methyl orange in the range of 86.0–93.7%, depending on their morphologies.</P>

Detection and genetic characterization of Lawsonia intracellularis from swine in Korea

Chu, Jia-Qi,Hu, Xu-Min,Kim, Myung-Cheol,Park, Chang-Sik,Jun, Moo-Hyung The Korean Society of Veterinary Service 2010 韓國家畜衛生學會誌 Vol.33 No.3

A total of 191 samples collected from the commercial swine farms located in Chungnam province were investigated by PCR to estimate the prevalence of Lawsonia (L.) intracellularis infection. In the group of the pigs with proliferative enteritis, 14 (93.3%) of 15 intestinal samples and 12 (80.0%) of 15 feces were positive in PCR. In contrast, a relatively low positive rate (18.0%, 29 of 161 samples) was determined in the group of normal healthy pigs. The group of pigs over 120 days showed the highest positive rates (26.8%, 15 of 56 samples). In the comparison of the sequences of 210bp for species specific fragments and 301bp for outer membrane protein, the isolates (L1. L2) showed almost 100% identity with the reference L. intracellularis (L08049, USA). For the sequences of partial 16s rDNA, the homologies among the 5 isolates (L1-L5) were 97.4% to 99.3%, and those of 5 sequences (L1-L5) versus 5 overseas reference strains of L. intracellularis ranged from 98.6% to 99.8%. In the comparison of the nucleotide sequences among 5 isolates and other species in Desulfovibrionales showed 82.4 to 99.5% identities. The 5 isolates shared relatively low identities (76.9% to 84.4%) with the species of alpha-proteobacteria. In phylogenetic analysis based on the 16s rDNA sequences, all of the 5 isolates (L1-L5) were located in the same branch with the strains of L. intracellularis that were previously isolated from the pigs in USA and China. Seven strains of Desulfovibrio sp. were clustered in the neighboring branches, whereas alpha and gamma Proteobacteria showed distant relationship with L. intracellularis strains. The present findings suggest that L. intracellularis infection is endemic in the swine farms in the regions, and that the domestic isolates maintained very limited genetic variation.

Simvastatin attenuates delayed encephalopathy induced by carbon monoxide poisoning in rats by regulating oxidative stress, inflammation and NF-κB pathway

Chu Zhe,Liu Zuolong,Li Wei,Xu Dahai,Pang Li 대한독성 유전단백체 학회 2021 Molecular & cellular toxicology Vol.17 No.2

Background Carbon monoxide (CO) poisoning is a leading cause of morbidity and mortality worldwide. The delayed encephalopathy occurs a period after poisoning in patients without effective treatment. Simvastatin (Sim), a lipid-lowering drug, was reported to exert endothelial protective effects and inhibit inflammatory response. This research focused on the effects of Sim on delayed encephalopathy caused by CO poisoning. Objective The acute CO poisoning model was established by exposing rats to 2500 ppm CO gas for 40 min, then 3000 ppm for 30 min or until they lost consciousness. Rats in the treatment group were given Sim (20 mg/kg/day, ig.). The behavioral tests included the Morris water maze test and shuttle box. The pathological changes were evaluated by H and E staining. The inflammatory mediators were analyzed by ELISA. The expression levels of eNOS, iNOS and the NF-κB-related proteins were analyzed by Western blot. Results The results showed that Sim could alleviate CO-induced behavioral disorders and the hippocampal nerve cells apoptosis. Sim administration reversed the effects of CO on oxidative stress-related molecules. Sim could also inhibit the production of the inflammatory mediators induced by CO. The level of eNOS was decreased after CO exposure, while iNOS was increased. Sim could significantly inhibit the effects of CO. Furthermore, Sim inhibited the phosphorylation of IκBα (an NF-κB inhibitory protein), i.e., the activation of NF-κB, which indicated that Simvastatin reduced the inflammatory response induced by CO poisoning partially through inhibiting the activation of NF-κB signaling pathway. Conclusion To sum up, our research indicated that Sim could attenuate the delayed encephalopathy induced by CO poisoning via regulating oxidative stress, inflammation and NF-κB pathway. Background Carbon monoxide (CO) poisoning is a leading cause of morbidity and mortality worldwide. The delayed encephalopathy occurs a period after poisoning in patients without effective treatment. Simvastatin (Sim), a lipid-lowering drug, was reported to exert endothelial protective effects and inhibit inflammatory response. This research focused on the effects of Sim on delayed encephalopathy caused by CO poisoning. Objective The acute CO poisoning model was established by exposing rats to 2500 ppm CO gas for 40 min, then 3000 ppm for 30 min or until they lost consciousness. Rats in the treatment group were given Sim (20 mg/kg/day, ig.). The behavioral tests included the Morris water maze test and shuttle box. The pathological changes were evaluated by H and E staining. The inflammatory mediators were analyzed by ELISA. The expression levels of eNOS, iNOS and the NF-κB-related proteins were analyzed by Western blot. Results The results showed that Sim could alleviate CO-induced behavioral disorders and the hippocampal nerve cells apoptosis. Sim administration reversed the effects of CO on oxidative stress-related molecules. Sim could also inhibit the production of the inflammatory mediators induced by CO. The level of eNOS was decreased after CO exposure, while iNOS was increased. Sim could significantly inhibit the effects of CO. Furthermore, Sim inhibited the phosphorylation of IκBα (an NF-κB inhibitory protein), i.e., the activation of NF-κB, which indicated that Simvastatin reduced the inflammatory response induced by CO poisoning partially through inhibiting the activation of NF-κB signaling pathway. Conclusion To sum up, our research indicated that Sim could attenuate the delayed encephalopathy induced by CO poisoning via regulating oxidative stress, inflammation and NF-κB pathway.