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- 저자 : ( Da Huang Chen ) (검색결과 24 건)
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Graphitization of graphene oxide films under pressure
Chen, Xianjue,Deng, Xiaomei,Kim, Na Yeon,Wang, Yu,Huang, Yuan,Peng, Li,Huang, Ming,Zhang, Xu,Chen, Xiong,Luo, Da,Wang, Bin,Wu, Xiaozhong,Ma, Yufei,Lee, Zonghoon,Ruoff, Rodney S. Elsevier 2018 Carbon Vol.132 No.-
<P><B>Abstract</B></P> <P>Lightweight, flexible graphite foils that are chemically inert, high-temperature resistant, and highly electrically and thermally conductive can be used as component materials in numerous applications. “Graphenic” foils can be prepared by thermally transforming graphene oxide films. For this transformation, it is desirable to maintain a densely packed film structure at high heating rates as well as to lower the graphitizing temperatures. In this work, we discuss the pressure-assisted thermal decomposition of graphene oxide films by hot pressing at different temperatures (<I>i.e.</I>, 300 °C, 1000 °C, or 2000 °C). The films pressed at 1000 °C or 2000 °C were subsequently heated at 2750 °C to achieve a higher degree of graphitization. The combination of heating and pressing promotes the simultaneous thermal decomposition and graphitic transformation of G-O films. Films pressed at 2000 °C as well as films further graphitized at 2750 °C show high chemical purity, uniformity, and retain their flexibility. For films pressed at 2000 °C and then further heated at 2750 °C, the mechanical performances outperform the reported values of the “graphite” foils prepared by calendering exfoliated graphite flakes; the electrical conductivity is ∼3.1 × 10<SUP>5</SUP> S/m and the in-plane thermal conductivity is ∼1.2 × 10<SUP>3</SUP> W/(m·K).</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Controlling the Thickness of Thermally Expanded Films of Graphene Oxide
Chen, Xianjue,Li, Wei,Luo, Da,Huang, Ming,Wu, Xiaozhong,Huang, Yuan,Lee, Sun Hwa,Chen, Xiong,Ruoff, Rodney S. American Chemical Society 2017 ACS NANO Vol.11 No.1
<P>'Paper-like' film material made from stacked and overlapping graphene oxide sheets can be exfoliated (expanded) through rapid heating, and this has until now been done with no control of the final geometry of the expanded graphene oxide material, i.e., the expansion has been physically unconstrained. (As a consequence of the heating and exfoliation, the graphene oxide is 'reduced', i.e., the graphene oxide platelets are deoxygenated to a degree.) We have used a confined space to constrain the expanding films to a controllable and uniform thickness. By changing the gap above the film, the final thickness of expanded films prepared from, e.g., a 10 mu m-thick graphene oxide film, could be controlled to values such as 20, 30, 50, or 100 mu m. When the expansion of the films was unconstrained, the final film was broken into pieces or had many cracks. In contrast, when the expansion was constrained, it never cracked or broke. Hot pressing the expanded reduced graphene oxide films at 1000 degrees C yielded a highly compact structure and promoted graphitization. Such thickness-controlled expansion of graphene oxide films up to tens or hundreds of times the original film thickness was used to emboss patterns on the films to produce areas with different thicknesses that remain connected 'in plane'. In another set of experiments, we treated the original graphene oxide film with NaOH before its controlled expansion resulted in a different structure featuring uniformly distributed pores and interconnected layers as well as simultaneous activation of the carbon.</P>
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( Da Wei Chen ),( Zhen Quan Yang ),( Xia Chen ),( Yu Jun Huang ),( Bo Xing Yin ),( Fei Xiang Guo ),( Hai Qing Zhao ),( Jia Di Huang ),( Yun Wu ),( Rui Xia Gu ) 한국미생물 · 생명공학회 2015 Journal of microbiology and biotechnology Vol.25 No.5
Accumulating evidence indicates that lactic acid bacteria could improve host physiology and lipid metabolism. To investigate the effect of the gut microbiota on host lipid metabolism, a hyperlipidemic rat model was established by feeding rats a high-fat diet for 28 days, and the gut microbiota of the rats was analyzed using real-time PCR before and after administration of Lactobacillus rhamnosus hsryfm 1301 and its fermented milk for 28 days. The findings showed that the Lactobacillus spp., Bifidobacterium spp., Bacteroides spp., and Enterococcus spp. content in the hyperlipidemic rats gut was increased significantly (p < 0.05), while the Clostridium leptum and Enterobacter spp. content was decreased significantly after intervening with L. rhamnosus hrsyfm 1301 and its fermented milk for 28 days (p < 0.05). Furthermore, the lipid levels of the serum and the liver were decreased significantly (p < 0.05) and the fecal water content was increased significantly (p < 0.05) in the hyperlipidemic rats after the intervention, and hepatocyte fatty degeneration of liver tissues was also prevented. A positive correlation was observed between the Clostridium leptum content and the level of serum cholesterol, triglycerides, low-density lipoprotein, and high-density lipoprotein, and a negative correlation was observed between the Enterobacter spp. content and the Lactobacillus spp. and Bifidobacterium spp. content in the hyperlipidemic rats gut. These results suggest that the gut microbiota and lipid metabolism of hyperlipidemic rats could be improved by supplementation with L. rhamnosus hsryfm 1301 and its fermented milk.
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Tzu-Chau Chen,Chao-Tsai Huang,Yan-Chen Chiu,Wei-Da Wang,Cheng-Li Hsu,Chen-Yang Lin,Lung-Wen Kao 한국정밀공학회 2013 International Journal of Precision Engineering and Vol. No.
Runner system plays a very important role in injection molding process. A quality runner design is helpful in improving product qualities and saving material. However, traditional cold runner systems have certain inherent issues. Moreover, poor product cosmetics are commonly seen with the use of traditional cold runners. As a result, hot runner technology has been widely applied. On the other hand, It has been one of the green molding solutions for material/energy saving and clean environments. But the mechanism behind the hot runner system is too complicated to be fully understood. There exist some critical issues currently. As a result, the simulation technolgy is highly needed to examine hot runner designs before the real manufacturing. Through simulation analyses, designers and manufafctuers are able to catch the potential issues on their hot runner systems and revise their designs. Hot runner simulation technology helps with the investigations into the behavior in hot runner system. In this paper, a true 3D numerical method is proposed and applied to investigate the temperature behavior in a real hot runner system for PC material. The experiment is conducted and the simulating result is compared with that from the experiment for the validation purpose.
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Risk Factors for Anxiety in Major Depressive Disorder Patients
Li-Min Xin,Lin Chen,Zhen-Peng Ji,Suo-Yuan Zhang,Jun Wang,Yan-Hong Liu,Da-Fang Chen,Fu-De Yang,Gang Wang,Yi-Ru Fang,Zheng Lu,Hai-Chen Yang,Jian Hu,Zhi-Yu Chen,Yi Huang,Jing Sun,Xiao-Ping Wang,Hui-Chun 대한정신약물학회 2015 CLINICAL PSYCHOPHARMACOLOGY AND NEUROSCIENCE Vol.13 No.3
Objective: To analyze the sociodemographic and clinical factors related to anxiety in patients with major depressive disorder (MDD). Methods: This study involved a secondary analysis of data obtained from the Diagnostic Assessment Service for People with Bipolar Disorders in China (DASP), which was initiated by the Chinese Society of Psychiatry (CSP) and conducted from September 1, 2010 to February 28, 2011. Based on the presence or absence of anxiety-related characteristics, 1,178 MDD patients were classified as suffering from anxious depression (n=915) or non-anxious depression (n=263), respectively. Results: Compared with the non-anxious group, the anxious-depression group had an older age at onset (t=−4.39, p<0.001), were older (t=−4.69, p<0.001), reported more lifetime depressive episodes (z=−3.24, p=0.001), were more likely to experience seasonal depressive episodes (χ2=6.896, p=0.009) and depressive episodes following stressful life events (χ2=59.350, p <0.001), and were more likely to have a family history of psychiatric disorders (χ2=6.091, p=0.014). Their positive and total scores on the Mood Disorder Questionnaire (MDQ) and the 32-item Hypomania Checklist (HCL-32) (p<0.05) were also lower. The logistic regression analysis indicated that age (odds ratio [OR]=1.03, p<0.001), a lower total MDQ score (OR=0.94, p=0.011), depressive episodes following stressful life events (OR=3.04, p<0.001), and seasonal depressive episodes (OR=1.75, p=0.039) were significantly associated with anxious depression. Conclusion: These findings indicate that older age, fewer subclinical bipolar features, an increased number of depressive episodes following stressful life events, and seasonal depressive episodes may be risk factors for anxiety-related characteristics in patients with MDD.
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Chen, Yao-Sheng,Xu, Song-Xin,Ding, Yan-Bing,Huang, Xin-En,Deng, Bin,Gao, Xue-Feng,Wu, Da-Cheng Asian Pacific Journal of Cancer Prevention 2013 Asian Pacific journal of cancer prevention Vol.14 No.11
To investigate the cognition of medical professionals when following screening guidelines for colorectal cancer (CRC) and barriers to CRC screening. Between February 2012 and December 2012, an anonymous survey with 19-questions based on several CRC screening guidelines was randomly administered to gastroenterologists, oncologists, general surgeons, and general practitioners in Jiangsu, a developed area in China where the incidence of CRC is relatively high. The average cognitive score was 26.4% among 924 respondents. Gastroenterologists and oncologists had higher scores compared with others (p<0.01 and p<0.01, respectively); doctor of medicine (M.D.) with or without doctor of philosophy (Ph.D.) or holders with bachelor of medical science (BMS) achieved higher scores than other lower degree holders (P<0.05). More importantly, doctors who finished CRC related education in the past year achieved higher scores than the others (p<0.001). The most commonly listed barriers to referring high-risk patients for CRC screening were "anxiety about colonoscopy without anesthesia", "lack of awareness of the current guidelines" and "lack of insurance reimbursement". Lack of cognition was detected among doctors when following CRC screening guidelines for high-risk populations. Educational programs should be recommended to improve their cognition and reduce barriers to CRC screening.
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( Huang Xiao Mei ),( Jin Xia Fan ),( Qian Yang ),( Xiu Ling Chen ),( Zhi Hua Liu ),( Yun Wang ),( Da Qing Wang ) 한국미생물 · 생명공학회 2012 Journal of microbiology and biotechnology Vol.22 No.3
Endoglucanase gene egIV was cloned from Trichoderma viride AS 3.3711, an important cellulose-producing fungus, by using an RT-PCR protocol. The egIV cDNA is 1,297 bp in length and contains a 1,035 bp open reading frame encoding a 344 amino acid protein with an estimated molecular mass of 35.5 kDa and isoelectronic point (pI) of 5.29. The expression of gene egIV in T. viride AS 3.3711 could be induced by sucrose, corn straw, carboxymethylcellulose (CMC), or microcrystalline cellulose, but especially by CMC. The transcripts of egIV were regulated under these substrates, but the expression level of the egIV gene could be inhibited by glucose and fructose. Three recombinant vectors, pYES2-xegIV, pYES2Mα-egIV, and pYES2Mα-xegIV, were constructed to express the egIV gene in Saccharomyces cerevisiae H158. The CMCase activity of yeast transformants IpYES2Mα-xegIV was higher than that of transformant IpYES2-xegIV or IpYES2Mα-egIV, with the highest activity of 0.13 U/ml at induction for 48 h, illustrating that the modified egIV gene could enhance CMCase activity and that MFα signal peptide from S. cerevisiae could regulate exogenous gene expression more effectively in S. cerevisiae. The recombinant EGIV enzyme was stable at pH 3.5 to 7.5 and temperature of 35oC to 65oC. The optimal reaction condition for EGIV enzyme activity was at the temperature of 55oC, pH of 5.0, 0.75 mM Ba2+, and using CMC as substrate. Under these conditions, the highest activity of EGIV enzyme in transformant IpYES2Mα-xegIV was 0.18 U/ml. These properties would provide technical parameters for utilizing cellulose in industrial bioethanol production.
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Role of Graphene in Water-Assisted Oxidation of Copper in Relation to Dry Transfer of Graphene
Luo, Da,You, Xueqiu,Li, Bao-Wen,Chen, Xianjue,Park, Hyo Ju,Jung, Minbok,Ko, Taeg Yeoung,Wong, Kester,Yousaf, Masood,Chen, Xiong,Huang, Ming,Lee, Sun Hwa,Lee, Zonghoon,Shin, Hyung-Joon,Ryu, Sunmin,Kwak American Chemical Society 2017 Chemistry of materials Vol.29 No.10
<P>The process of oxidation of a copper surface coated by a layer of graphene in water-saturated air at 50 degrees C was studied where it was observed that oxidation started at the graphene edge and was complete after 24 h. Isotope labeling of the oxygen gas and water showed that the oxygen in the formed copper oxides originated from water and not from the oxygen in air for both Cu and graphene-coated Cu, and this has interesting potential implications for graphene as a protective coating for Cu in dry air conditions. We propose a reaction pathway where surface hydroxyl groups formed at graphene edges and defects induce the oxidation of Cu. DFT simulation shows that the binding energy between graphene and the oxidized Cu substrate is smaller than that for the bare Cu substrate, which facilitates delamination of the graphene. Using this process, dry transfer is demonstrated using poly(bisphenol A carbonate) (PC) as the support layer. The high quality of the transferred graphene is demonstrated from Raman maps, XPS, STM, TEM, and sheet resistance measurements. The copper foil substrate was reused without substantial weight loss to grow graphene (up to 3 cycles) of equal quality to the first growth after each cycle. It was found that dry transfer yielded graphene with less Cu impurities as compared to methods using etching of the Cu substrate. Using PC yielded graphene with less polymeric residue after transfer than the use of poly(methyl methacrylate) (PMMA) as the supporting layer. Hence, this dry and clean delamination technique for CVD graphene grown on copper substrates is highly advantageous for the cost-effective large-scale production of graphene, where the Cu substrate can be reused after each growth.</P>
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