Optimization of the eco-friendly synthesis of graphene oxide from graphite using Plackett–Burman and Box–Behnken models for industrial production orientation

Phuc Nguyen Thien,Giang Nguyen Thi Huong,An Vu Nguyen Thien Truong,Nam Nguyen Thanh Hoai,Anh Ly Duc,Nguyen Huynh Cam,An Hoang,Phong Mai Thanh,Hieu Nguyen Huu 한국탄소학회 2023 Carbon Letters Vol.33 No.2

In this study, graphene oxide (GO) was synthesized by the improved Hummers’ method. The degree of oxidation from graphite (Gi) to GO was determined through interlayer spacing calculated from X–ray diffraction. Besides, the effect of KMnO4:Gi ratios (X1), H2SO4 volume (X2), oxidation temperature (X3), oxidation time of stage 1 (X4), and oxidation time of stage 2 (X5) was screened by the Plackett–Burman model. The simultaneous impact of three factors that influenced the degree of oxidation (X1, X2, and X3) was studied by the Box–Behnken experimental model of response surface methodology to achieve suitable conditions for the GO synthesis process. The characterization of GO product was investigated via the modern analytical methods: X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, UV–Vis spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. In addition, the study was also carried out on a pilot scale for orientation in industrial application with the yield of 14 g/batch.

Customer Satisfaction in Hotel Services: A Case Study of Thanh Hoa Province, Vietnam

LE, Quang Hieu,NGUYEN, Thanh Xuan Thi,LE, Thanh Thuy Thi Korea Distribution Science Association 2020 The Journal of Asian Finance, Economics and Busine Vol.7 No.10

The study examines the influence of factors on customer satisfaction in hotel services in Thanh Hoa province of Vietnam. In terms of the tangible facilities of hotels, customers appreciate the availability and the full range of equipment and additional services, as the 3-to-5-star hotels in Thanh Hoa province are almost new, built in the last five years - 7 of 13 hotels were built in 2015. In the process of measuring the effect of factors on satisfaction in hotel services there, the researchers conducted exploratory factor analysis, reliability test, correlation and regression to confirm the relationships of factors. Based on a survey of 380 respondents, the test results showed that the proposed factors have positive impacts on consumer satisfaction; they are: perceived quality (including intangible and tangible elements), brand image, perceived value, and customer relationship management. In particular, intangible elements have the strongest influence on customer satisfaction, followed by tangible elements, brand image, perceived value, and finally, customer relationship management. In addition, the study found that foreigners and higher education customers tend to be more satisfied by the hotels than other groups, which helps to suggest important and appropriate solutions for hotel managers in Thanh Hoa province.

The Impact of Capital Structure on Firm Performance: Evidence from Vietnam

NGUYEN, Hieu Thanh,NGUYEN, Anh Huu Korea Distribution Science Association 2020 The Journal of Asian Finance, Economics and Busine Vol.7 No.4

This paper explores the impact of capital structure on firm performance in the context of Vietnam. The paper investigates the different effect of capital structure on firm performance in state-owned and non-state enterprises listed on the Vietnam stock market. The panel data of research sample includes 488 non-financial listed companies on the Vietnam stock market for a period of six years, from 2013 to 2018. The Generalized Least Square (GLS) is employed to address econometric issues and to improve the accuracy of the regression coefficients. In this research, firm performance is measured by return on equity (ROE), return on assets (ROA), and earnings per share (EPS). The ratios of short-term liabilities, long-term liabilities, and total liabilities to total assets are proxy for capital structure. Firm sizes, growth rate, liquidity, and ratio of fixed assets to total assets are control variables in the study. The empirical results show that capital structure has a statistically significant negative effect on the firm performance. The result also shows this effect is stronger in state-owned enterprises than non-state enterprises in Vietnam. These evidences provide a new insight to managers of both state-owned and non-state enterprises on how to improve the firm's performance with capital structure.

Advanced Magnetic Materials Produced by Using Rapid Quenching Technology

Nguyen Hoang Nghi,Nguyen Van Dung,Trinh Thi Thanh Nga,Bui Thi Khanh Nhung,Mai Thanh Tung,Nguyen Huu Tinh,Hoang Nhat Hieu,Bui Xuan Chien,Nguyen Thi Hong Tam 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.6

Amorphous alloys produced by using a rapid quenching technique are considered to be a precursor for producing nanosized and multiphase structures by precipitation (the top-down method). By using this technique, several new magnetic materials with different magnetic properties based on different physical mechanisms have been manufactured and investigated. Three new magnetic materials, a nanocrystalline soft magnetic material, a soft-hard permanent magnet and a Me-3d granular alloy with a GMR effect, what were prepared under local conditions, are presented and discussed in the experimental point of view. Amorphous alloys produced by using a rapid quenching technique are considered to be a precursor for producing nanosized and multiphase structures by precipitation (the top-down method). By using this technique, several new magnetic materials with different magnetic properties based on different physical mechanisms have been manufactured and investigated. Three new magnetic materials, a nanocrystalline soft magnetic material, a soft-hard permanent magnet and a Me-3d granular alloy with a GMR effect, what were prepared under local conditions, are presented and discussed in the experimental point of view.

Derivation and Analysis of the BER Closed Form in the OFDM Communication System with IQ Imbalance

Nguyen Thanh Hieu,Byung-Su Kang,Kwangchun Lee,Heung-Gyoon Ryu 한국전자파학회JEES 2006 Journal of Electromagnetic Engineering and Science Vol.6 No.3

Orthogonal frequency division multiplexing(OFDM) is very useful for the wireless communication system. However, OFDM is very sensitive to the radio frequency impairments. One of the most important major impairments is the IQ imbalance between in-phase(I) and quadrature(Q) branches in the up and down-conversion. IQ imbalance can be divided into phase and amplitude imbalances. These imbalances make constellation of signal to expand and rotate. The performance of system is severely degraded. In this paper, a closed-form for the bit error probability of the OFDM signal in IQ imbalance environment is derived in terms of the function of phase and amplitude imbalance parameters. So, it will be convenient and useful to evaluate the performance of OFDM communication system with IQ imbalance. It is confirmed that computer simulation results closely match with the results of the analytical derivation. When phase imbalance φ=20°, amplitude imbalance ε=0.1; 0.3; 0.4; 0.5, BER at 10?? is severely degraded by 1.8 ㏈, 3.12 ㏈, 4.72, and 8.44 ㏈, respectively.

Pynomial modeling for efficient predistortion of HPA

Hieu, Nguyen Thanh,Jianxue, Jin,Ryu, Heung-Gyoon 충북대학교 컴퓨터정보통신 연구소 2004 컴퓨터정보통신연구 Vol.12 No.3

High power amplifier (HPA) in transmitter of communication systems usually operates in near saturation point in order to achieve the maximum power efficiency. In this region, undesirable nonlinear distortions may be introduced. In this paper, we present a polynomial modeling method used for efficient predistortion to compensate for the nonlinear distortion. The polynomial models are derived from the electrical parameters in data sheets of actual amplifiers such as gain, the third order intercept point of output power and 1dB compression point. We can find the polynomial coefficients of predistorter from the HPA polynomial modeling. Then, it is simple and effective to suppress the nonlinear distortion. We also study the effects of predistortion on the SER performance of communication system with 16-QAM modulation format. From the simulation results, it can be shown that BER performance is improved by the proposed efficient predistortion.

The complete mitochondrial genome sequence of the indigenous I pig (Sus scrofa) in Vietnam

Hieu Duc Nguyen,Tuan Anh Bui,Phuong Thanh Nguyen,Oanh Thi Phuong Kim,Thuy Thi Bich Vo 아세아·태평양축산학회 2017 Animal Bioscience Vol.30 No.7

Objective: The I pig is a long nurtured longstanding breed in Vietnam, and contains excellent indigenous genetic resources. However, after 1970s, I pig breeds have become a small population because of decreasing farming areas and increasing pressure from foreign breeds with a high growth rate. Thus, there is now the risk of the disappearance of the I pigs breed. The aim of this study was to focus on classifying and identifying the I pig genetic origin and supplying molecular makers for conservation activities. Methods: This study sequenced the complete mitochondrial genome and used the sequencing result to analyze the phylogenetic relationship of I pig with Asian and European domestic pigs and wild boars. The full sequence was annotated and predicted the secondary tRNA. Results: The total length of I pig mitochondrial genome (accession number KX094894) was 16,731 base pairs, comprised two rRNA (12S and 16S), 22 tRNA and 13 mRNA genes. The annotation structures were not different from other pig breeds. Some component indexes as AT content, GC, and AT skew were counted, in which AT content (60.09%) was smaller than other pigs. We built the phylogenetic trees from full sequence and D loop sequence using Bayesian method. The result showed that I pig, Banna mini, wild boar (WB) Vietnam and WB Hainan or WB Korea, WB Japan were a cluster. They were a group within the Asian clade distinct from Chinese pigs and other Asian breeds in both phylogenetic trees (0.0004 and 0.0057, respectively). Conclusion: These results were similar to previous phylogenic study in Vietnamese pig and showed the genetic distinctness of I pig with other Asian domestic pigs.

A facile thermal evaporation route for large-area synthesis of tin oxide nanowires: Characterizations and their use for liquid petroleum gas sensor

Nguyen Van Hieu,Le Thi Ngoc Loan,Nguyen Duc Khoang,Nguyen Tuan Minh,Do Thanh Viet,Do Cong Minh,Tran Trung,Nguyen Duc Chien 한국물리학회 2010 Current Applied Physics Vol.10 No.2

In this paper, a very simple procedure was presented for the reproducible synthesis of large-area SnO2nanowires (NWs) on a silicon substrate by evaporating Sn powders at temperatures of 700, 750, and 800 ℃. As-obtained SnO2 NWs were characterized by field emission scanning electron microscopy (FESEM),transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. They revealed that the morphology of the NWs is affected by growth temperature and the SnO2 NWs are single-crystalline tetragonal. The band gap of the NWs is in the range of 4.2–4.3 eV as determined from UV/visible absorption. The NWs show stable photoluminescence with an emission peak centered at around 620 nm at room-temperature. The sensors fabricated from the SnO2 NWs synthesized at 700 ℃ exhibited good response to LPG (liquefied petroleum gas) at an operating temperature of 400 ℃.

Design, synthesis and evaluation of novel <i>N</i>-hydroxybenzamides/<i>N</i>-hydroxypropenamides incorporating quinazolin-4(3<i>H</i>)-ones as histone deacetylase inhibitors and antitumor agents

Hieu, Doan Thanh,Anh, Duong Tien,Tuan, Nguyen Minh,Hai, Pham-The,Huong, Le-Thi-Thu,Kim, Jisung,Kang, Jong Soon,Vu, Tran Khac,Dung, Phan Thi Phuong,Han, Sang-Bae,Nam, Nguyen-Hai,Hoa, Nguyen-Dang Elsevier 2018 Bioorganic chemistry Vol.76 No.-

<P><B>Abstract</B></P> <P>In our search for novel small molecules targeting histone deacetylases, we have designed and synthesized several series of novel <I>N</I>-hydroxybenzamides/<I>N</I>-hydroxypropenamides incorporating quinazolin-4(3<I>H</I>)-ones (<B>4a-h</B>, <B>8a-d, 10a-d)</B>. Biological evaluation showed that these hydroxamic acids were generally cytotoxic against three human cancer cell lines (SW620, colon; <I>PC</I>-3, prostate; NCI-H23, lung cancer). It was found that the <I>N</I>-hydroxypropenamides (<B>10a-d)</B> were the most potent, both in term of HDAC inhibition and cytotoxicity. Several compounds, e.g. <B>4e</B>, <B>8b-c</B>, and <B>10a-c</B>, displayed up to 4-fold more potent than SAHA (suberoylanilide hydroxamic acid, vorinostat) in term of cytotoxicity. These compounds also comparably inhibited HDACs with IC<SUB>50</SUB> values in sub-micromolar range. Docking experiments on HDAC2 isozyme revealed some important features contributing to the inhibitory activity of synthesized compounds, especially for propenamide analogues. Importantly, the free binding energy computed was found to have high quantitative correlation (<I>R</I> <SUP>2</SUP> ∼ 95%) with experimental results.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Novel quinazolin-4(3H)-one-based <I>N</I>-hydroxybenzamides/<I>N</I>-hydroxypropenamides were synthesized. </LI> <LI> The <I>N</I>-hydroxybenzamides/<I>N</I>-hydroxypropenamides exhibited potent HDAC inhibition. </LI> <LI> The <I>N</I>-hydroxybenzamides/<I>N</I>-hydroxypropenamides exhibited good cytotoxicity. </LI> <LI> Docking studies and ADMET estimation were carried out. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Two series of novel, simple <I>N</I>-hydroxybenzamides/<I>N</I>-hydroxypropenamides incorporating quinolin-4(3H)-one (<B>4a-h</B>, <B>8a-d, 10a-d</B>) were designed and synthesized. Biological evaluation showed that these benzamides/propenamides potently inhibited HDAC with IC<SUB>50</SUB> values in sub-micromolar range. A number of compounds also exhibited cytotoxicity up to 4-fold more potent than SAHA, a positive control.</P> <P>[DISPLAY OMISSION]</P>

Polynomial Modeling for Efficient Predistortion of HPA

Nguyen Thanh Hieu, Jin Jianxue, Heung-Gyoon Ryu 충북대학교 컴퓨터 정보통신 연구소 2004 컴퓨터정보통신연구 Vol.12 No.3

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