THE STUDY ON OPTIMIZATION OF COPPER LEACHING FROM WASTE PCBs BY USING RESPONSE SURFACE METHODOLOGY

Recycling printed circuit boards (PCBs) is an important solution not only to treat hazardous waste but also to recover valuable materials. This research focus on optimizing the leaching copper process from waste PCBs to recycle. This process was performed in Fe2(SO4)3 solution at room temperature and using H2O2 as an oxidant. For optimization, response surface methodology was used to investigate the different parameters, including Fe2(SO4)3 concentration, volume of H2O2 addition and leaching time. Design Expert 10.0 software was applied to design the experiments and calculate the regression equation of the response function. As a result, a model was established which is compatible with the experimental data at the correlation coefficient (R2) of 0.99. The optimal conditions were identified as Fe2(SO4)3 concentration of 0.35 M, volume of H2O2 addition at 10 mL and leaching time of 10 h. Under this condition, leaching efficiency of 90.5 percent was achieved. After leaching, copper was recovered from extract solution by electrochemical technology with the efficiency of 85 percent. The results from this study hence proposed a very promising method for recycling copper in PCBs.

ANTIOXIDATIVE DEFENSE RESPONSE TO APHID-INDUCED OXIDATIVE STRESS IN Glycine max (L.) Merr. cv. “Nam Dan”

Infestation of cowpea aphid (Aphis craccivora Koch) induced oxidative stress in leaves of soybean (Glycine max (L.) Merr. cv. “Nam Dan”) with a burst in generation of reactive oxygen species (ROS) products such as superoxide anion radical (O2.-) and hydrogen peroxide (H2O2) recorded around 24 hours after aphid feeding. An increase in content of thiobarbituric acid reactive substances (TBARS) in lipid peroxidation and a defined percentage of injury in aphid-infested leaves were resulted from the cellular oxidative damage. The enhanced activity of the antioxidant enzymes such as superoxide dismutase (SOD, EC 1.15.1.1) and catalase (CAT, EC 1.11.1.6) in leaves of soybean “Nam Dan” functions as the antioxidative response that controlled both ROS-generation to be enough levels to play as defensive element and ROS-detoxifying to reduce aphid-induced oxidative damage. The enhancement of SOD and CAT also can improve the tolerance of soybean “Nam Dan” to impact from A. craccivora

The role of risk factors, partner compatibility, organizational creativity and co-creation value on firm performance: evidence from SMEs in Vietnam*

Ovo istraživanje analizira kako rizik i kompatibilnost partnera utječu na organizacijsku kreativnost, vrijednost zajedničkog stvaranja i na uspješnost tvrtke u gospodarstvu u razvoju. Metoda PLS-SEM korištena je za obradu i procjenu skupa podataka koji se sastoji od 454 važeća slučaja vlasnika nekretnina, izvršnih direktora, potpredsjednika, pomoćnika i voditelja odjela malih i srednjih poduzeća u Vijetnamu. Rezultati su potvrdili veze između varijabli rizika, kompatibilnosti partnera, organizacijske kreativnosti, vrijednosti zajedničkog stvaranja i uspješnosti tvrtke. Ova studija dodatno unapređuje dosadašnju bazu znanja u području odabira partnera i pruža vrijedne uvide koji se mogu primijeniti u menadžerskom kontekstu. Tvrtke moraju uzeti u obzir vanjske čimbenike poput rizika i kompatibilnosti partnera kako bi poboljšale organizacijsku kreativnost, vrijednost zajedničkog stvaranja i učinak tvrtke. Iako su faktori rizika, kompatibilnosti partnera, organizacijske kreativnosti, vrijednosti zajedničkog stvaranja i poslovne uspješnosti privukli značajnu pozornost u akademskim krugovima na globalnoj razini, postoji manjak studija koje istražuju međuodnose između ovih pet fenomena. Ovo je istraživanje jedno od početnih istraživanja koje predstavlja cjeloviti model koji pojašnjava međusobne veze između različitih kategorija.This research aims to analyze how risk and compatibility between partners affect organizational creativity, co-creation value, and firm performance in a developing economy. The PLS-SEM method was utilized to process and evaluate a dataset of 454 valid cases from property owners, chief executives, vice presidents, broad assistants, and department managers of SMEs in Vietnam. The results validated the connections between risk variables, partner compatibility, organizational creativity, co-creation value, and firm performance. This study further enhances the current knowledge base in the realm of partner selection and provides valuable insights that can be applied in managerial contexts. Companies must consider external factors like risk and partner compatibility to improve organizational creativity, co-creation value, and firm performance. While risk factors, partner compatibility, organizational creativity, co-creation value, and business performance have garnered significant attention in academic circles globally, there is a shortage of studies exploring the interrelationships among these five phenomena together. This research is one of the initial studies that presents a complete model elucidating the interconnections between different categories

CHARACTERIZATION AND MITIGATION OF VIETNAM COASTAL HAZARDS FOR SUSTAINABLE DEVELOPMENT

Joint Research on Environmental Science and Technology for the Eart

Research on microstructure and mechanical properties of Al-Zn-Mg-Cu alloy when modified by La, Ce and thermo-mechanical treatment

Influence of rare-earth (La, Ce) and thermo-mechanical treatment on microstructure and mechanical properties of Al-Zn-Mg-Cu alloy are presented in this article. After casting, the alloy which was modified by La, Ce, the grain size of samples obtained around 40–50 µm compared to that of without about 65 µm; and after homogeneous, the grain sizes is about 30 µm. After the cold deformation process, the distance between plates is 10 µm. By EDS after casting, the samples have tended to more La, Ce elements at the grain boundary, after homogeneous, the uniformation distribution of rare-earths was presented by mapping of EDS’s results. In addition, after rolling and heat treatment, the elements were found on the grain boundary and matrix. After recrystallization annealing, the grain size is around 10 µm with the modification sample. The grain size was reduced by two processes of modification as well as thermal-mechanical treatment is a condition for increasing the ductility of the studied alloy. Further, as a result of ability deformation from the tensile test, these results demonstrate that the tensile test obtained 140 % when adding La, Ce contents into the alloy combine with thermal-mechanical treatment. The combined used of La, Ce and thermal-mechanical treatment have increased the ductility of Al-Zn-Mg-Cu allo

Determinants of electronic word of mouth in the restaurant industry: An evidence from Vietnam

The food and beverage industry in Vietnam has developed dramatically, resulting in a highly competitive market. To win the competition, the restaurant managers not only strive to increase customer satisfaction but also create customers’ positive electronic Word-Of-Mouth (eWOM). This study aims to investigate the relationship between customer satisfaction, customer trust, customer loyalty, and eWOM. The quantitative method was implemented to examine the hypotheses in the research model. Data were collected from Ho Chi Minh City respondents using a convenient sampling method. Self-administrated questionnaires were delivered via the Internet for data collection. After data screening, 299 responses were qualified for analysis. Partial Least Squares Structural Equation Modeling (PLS-SEM) analysis was employed by SmartPLS software version 3.0. The measurement model test showed that one item of customer trust has a factor loading of less than 0.7 as a result, this item was removed from the research model. The structural model evaluation revealed the highly predictive accuracy of the model as all dependent variables have R2 values above 0.5. A bootstrapping test with 5,000 subsamples also showed that customer loyalty significantly influences eWOM, but customer trust does not. Customer satisfaction directly and significantly impacts customer trust and loyalty but has little influence on eWOM. However, the relationship between customer satisfaction and eWOM is significant without the presence of customer loyalty and trust. The indirect effect test also determines the full mediation role of customer loyalty in the relationship between customer satisfaction and eWOM

ANALYZING THE FACTORS AFFECTING FACIAL CLEANSER DEMAND AMONG YOUNG PEOPLE IN VIETNAM

The research analyzes the factors affecting the demand for made-in-Vietnam facial cleanseramong the Vietnamese youth. Based on the theory of commodity demand, the research team builds a survey form and collects responses from 415 students at high schools and universities in Vietnam on the factors affecting their demand for made-in-Vietnam facial cleansers. The synthesis and analysis of survey data show that the demand for face wash products among Vietnamese young people is influenced by many factors such as the price of the products, income, interests, prices of related goods, expectations of themarket, etc. Besides, the research team also considers the advantages of Vietnamese face wash products compared to imported products and young consumers' expectations for the products as well as their beliefs and supportfor made-in-Vietnam facial cleanser products in the future

Catalytic Dye Oxidation over CeO2 Nanoparticles Supported on Regenerated Cellulose Membrane

A novel regenerated cellulose (RC) membrane containing cerium oxide (CeO2) nanoparticles is described in detail. In this work, CeO2 nanoparticles with high surface area and mesoporosity were prepared by a modified template-assisted precipitation method. Successful synthesis was achieved using cerium nitrate as a precursor, adjusting the final pH solution to around 11 by ammonium hydroxide and ethylene diamine, and annealing at 550 °C for 3 hours under a protective gas flow. This resulted in a surface area of 55.55 m².g–1 for the nanoparticles. The regenerated cellulose membrane containing CeO2 particles was synthesized by the novel and environmentally friendly method. The catalyst CeO2 and cellulose/CeO2 membrane were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Electron paramagnetic resonance (EPR), and Brunauer-Emmett-Teller (BET) measurements. The g-value of 2.276 has confirmed the presence of the surface superoxide species of CeO2 nanoparticles in EPR. The photocatalytic activity of the catalyst and the membrane containing the catalyst was evaluated through the degradation of methylene blue under visible light irradiation by UV-VIS measurements. The cellulose/CeO2 membrane degraded 80% of the methylene blue solution in 120 minutes, showing a better photocatalytic activity than the CeO2 catalyst, which degraded approximately 62% in the same period. It has been proven that the RC membrane is not only a good transparent supporting material but also a good adsorption for high-performance of CeO2 catalyst. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

THỰC VẬT PHÙ DU VÙNG BIỂN VEN BỜ ĐÀ NẴNG

Phytoplankton, especially community characteristics, in coastal waters of Da Nang have not been well studied. This present study analyzed data of phytoplankton for diversity and abundance from surveys from 2002 to 2016 at 44 stations in the coastal Da Nang waters. A total of 316 taxa from 9 classes were identified: Dinophyceae (134 taxa), Mediophyceae (77 taxa), Coscinodiscophyceae (44 taxa), Bacillariophyceae (36 taxa), Cyanophyceae (3 taxa), Dictyochophyceae (2 taxa), Bacillariophyta classis incertae sedis (1 taxon), Conjugatophyceae (1 taxon) and Thecofilosea (1 taxon). A list of 36 species of potentially harmful microalgae was recorded in coastal waters of Da Nang. In which, Pseudo-nitzschia spp. often had higher cell densities in some locations during the northeast monsoon. Analyzing diversity indices in different locations showed that there were significance differences of Margalef and Shannon indices, low in estuarine area (CS) and higher in the south of Son Tra peninsula (NST). Meanwhile no strong differences of Pielou and Simpson indices were found among the locations. However, there were strong differences of Margalef, Simpson and Pielou indices, which were found over the three studied years (2004, 2005, and 2006), mainly in NST, the northeast of Son Tra peninsula (DBST) and Da Nang bay (VDN). Analysis of species accumulation curves indicated that only 56–95% of species  was found compared to maximal expected species richness in all studied locations. DMS analysis showed that there was year-based similarity among the years (ca. 50% of similarity) of phytoplankton communities. Among the studied years, average phytoplankton cell densities in Da Nang bay and the northeast of Son Tra were higher than those in other years and locations. This present study on species richness, expected species richness and variation in phytoplankton abundance suggested that there is a need of increasing sampling efforts, especially in riverine area and DBST for better understanding of characteristics of phytoplankton communities in coastal Da Nang waters.Thực vật phù du là đối tượng ít được nghiên cứu ở vùng biển ven bờ Đà Nẵng, nhất là những đặc trưng về thành phần loài và cấu trúc quần xã. Trong bài báo này, chúng tôi phân tích số liệu về đa dạng loài và sự phong phú của thực vật phù du thu thập được trong các chuyến khảo sát từ năm 2002 đến năm 2016 ở 44 trạm trong vùng biển ven bờ Đà Nẵng. Kết quả phân tích đã xác định được 316 loài và dưới loài thuộc 9 lớp tảo khác nhau. Trong các loài thực vật phù du ghi nhận được, có 36 loài tảo có khả năng gây hại, trong đó mật độ của Pseudo-nitzschia spp. cao hơn tại một số khu vực trong thời kỳ gió mùa Đông Bắc. Phân tích các chỉ số theo từng khu vực, có thể thấy chỉ số giàu có loài Margalef và chỉ số đa dạng Shannon khác nhau đáng kể giữa các khu vực, thấp ở cửa sông trong vịnh Đà Nẵng và cao ở nam bán đảo Sơn Trà. Trong khi các chỉ số cân bằng Pielou và đa dạng Simpson lại không khác biệt giữa các khu vực. Tuy nhiên, sự đa dạng và độ giàu có loài lại có sự khác biệt giữa các năm 2004, 2005 và 2016, chủ yếu ở nam bán đảo Sơn Trà, đông bắc bán đảo Sơn Trà và vịnh Đà Nẵng. Phân tích độ giàu có loài cho thấy hầu hết các khu vực đều chỉ ghi nhận được từ 56% đến 95% số loài mong đợi. Phân tích cấu trúc quần xã thực vật phù du thu thể hiện sự biến động giữa các năm nghiên cứu với mức độ tương đồng trong năm xấp xỉ 50%. So sánh trung bình mật độ thực vật phù du thu của từng khu vực cho thấy mật độ vào năm 2005 cao hơn hẳn so với các năm khác ở vịnh Đà Nẵng và đông bắc Sơn Trà. Các phân tích về độ giàu có loài, loài mong đợi và biến động mật độ thực vật phù du thu cho thấy dù vùng biển nghiên cứu được ghi nhận thành phần loài thực vật phù du thu cao, nhưng số lượng trạm và thời gian thu mẫu ở vùng biển Đà nẵng nhất là khu vực cửa sông cần được thu thập nhiều hơn, vẫn cần thu thập thêm vật mẫu ở tất cả các khu vực, nhất là vùng cửa sông trong vịnh Đà Nẵng và đông bắc bán đảo Sơn Trà