Four-Mode Programmable Metamaterial Using Ternary Foldable Origami

Le, Dinh Hai,Lim, Sungjoon American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.31

<P>Designing a multifunctional metamaterial with programmable feature has become a new trend in mechanical, acoustic, and electromagnetic research fields due to the controllability of their structural behaviors and functionalities. The codable or reconfigurable structures have shown more remarkable characteristics than the traditional and conventional metamaterials to implement functional programmability. However, structural complexity and hi-tech requirement are the biggest constraints to their practical applications. This paper numerically and experimentally investigates a programmable metamaterial based on ternary foldable origami in the gigahertz-frequency regime. The proposed metamaterial provides four transformable modes corresponding to four different functions of electromagnetic reflector and frequency-selectable absorbers by programming unique ternary foldable origami coded as “0”, “1”, and “2” for different folding levels. Interestingly, the proposed foldable origami consists of a simple dielectric paper and a bottom conductor, while there is no conductive pattern on the top. Therefore, the proposed programmable metamaterial is extremely robust and can be extended to a multiresonance mode and origami computing.</P> [FIG OMISSION]</BR>

Dual-band isotropic metamaterial absorber based on near-field interaction in the Ku band

The Linh Pham,Hong Tiep Dinh,Dinh Hai Le,Xuan Khuyen Bui,Son Tung Bui,Hong Luu Dang,Anh Duc Phan,Dac Tuyen Le,Dinh-Lam Vu 한국물리학회 2020 Current Applied Physics Vol.20 No.2

We numerically and experimentally investigate single-band and dual-band isotropic metamaterial absorbers (IMAs) based on metallic disks. By optimizing the diameter of the metallic disks and the thickness of the dielectric substrate, the single-band IMA is observed at 16.2 GHz with absorptivity of 97%. When adding one diskpair to the structure, the dual-band IMA is obtained at 12.8 and 15.5 GHz due to the symmetry breaking. The physical mechanics is explained by near-field coupling effect and equivalent LC circuit model. The measurement results performed in the range 12–18 GHz show a good agreement with simulation and theoretical analysis. Our findings demonstrate a new approach to achieve dual-band and multi-band IMAs.

Potential to mitigate ammonia emission from slurry by increasing dietary fermentable fiber through inclusion of tropical byproducts in practical diets for growing pigs

Quan Hai Nguyen,Phung Dinh Le,Channy Chim,Ngoan Duc Le,Veerle Fievez 아세아·태평양축산학회 2019 Animal Bioscience Vol.32 No.4

Objective: Research was conducted to test the effect of including fiber-rich feedstuffs in practical pig diets on nutrient digestibility, nitrogen balance and ammonia emissions from slurry. Methods: Three Vietnamese fiber sources were screened, namely cassava leaf meal (CL), cassava root residue (CR), and tofu by-product (TF). Accordingly, a control diet (Con) with 10% of dietary non-starch polysaccharides (NSP) and three test diets including one of the three fiber-rich feedstuffs to reach 15% of NSP were formulated. All formulated diets had the same level of crude protein (CP), in vitro ileal protein digestible and metabolisable energy, whereas the in vitro hindgut volatile fatty acid (VFA) production of the test diets was 12% to 20% higher than the control diet. Forty growing barrows with initial body weight at 28.6±1.93 kg (mean±standard deviation) were allocated to the four treatments. When pigs reached about 50 kg of body weight, four pigs from each treatment were used for a nitrogen balance trial and ammonia emission assessment, the remaining six pigs continued the second period of the feeding trial. Results: The TF treatment increased fecal VFA by 33% as compared with the control treatment (p = 0.07), suggesting stimulation of the hindgut fermentation. However, urinary N was not significantly reduced or shifted to fecal N, nor was slurry pH decreased. Accordingly, ammonia emissions were not mitigated. CR and CL treatments failed to enhance in vivo hindgut fermentation, as assessed by fecal VFA and purine bases. On the contrary, the reduction of CP digestibility in the CL treatment enhanced ammonia emissions from slurry. Conclusion: Dietary inclusion of cassava and tofu byproducts through an increase of dietary NSP from 10% to 15% might stimulate fecal VFA excretion but this does not guarantee a reduction in ammonia emissions from slurry, while its interaction with protein digestibility even might enhance enhanced ammonia emission.

Critical properties around the ferromagnetic-paramagnetic phase transition in La_0.7Ca_0.3-xA_xMnO₃ compounds (A = Sr, Ba and <i>x</i> = 0, 0.15, 0.3)

Linh, Dinh Chi,Thanh, Tran Dang,Anh, Le Hai,Dao, Van Duong,Piao, Hong-Guang,Yu, Seong-Cho Elsevier 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.725 No.-

<P><B>Abstract</B></P> <P>Influence of alkaline earth element doping in the A-site on the structure, magnetic and magnetocaloric properties of La<SUB>0.7</SUB>Ca<SUB>0.3-x</SUB>A<SUB>x</SUB>MnO<SUB>3</SUB> (A = Sr and Ba; <I>x</I> = 0, 0.15 and 0.3) perovskite manganites have been investigated. X-ray diffraction data indicates that samples <I>x</I> = 0 and 0.15 crystallize in the orthorhombic structure (space group <I>Pnma</I>), whereas samples <I>x</I> = 0.3 belong to the rhombohedral structure (space group <I>R</I>-3<I>c</I>). Substitution of Sr or Ba for Ca plays an important role in the increase of Curie temperature (<I>T</I> <SUB>C</SUB>) and modification the nature of the magnetic phase transition in materials. Sample <I>x</I> = 0 exhibits the first-order phase transition (FOPT) with a large magnetic entropy change (Δ<I>S</I> <SUB>m</SUB>), whereas samples <I>x</I> = 0.15 and 0.3 exhibit the second-order phase transition (SOPT) characterizations and the moderate values of Δ<I>S</I> <SUB>m</SUB>. Using the modified Arrott plots method, the critical behaviors around <I>T</I> <SUB>C</SUB> for SOPT samples have been investigated through the values of critical parameters (<I>T</I> <SUB>C</SUB>, <I>β</I>, <I>γ</I>, and <I>δ</I>). We pointed out that Ba-doping favors establishing long-range ferromagnetic order, contrary to the case of Sr-doping.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Sr or Ba-doped La<SUB>0.7</SUB>Ca<SUB>0.3</SUB>MnO<SUB>3</SUB> leads to modify the nature of the phase transition. </LI> <LI> Ba-doping favors establishing long-range FM order, contrast with Sr-doping. </LI> <LI> The effective exponents vary non-monotonically in the asymptotic region. </LI> </UL> </P>

A bayesian network analysis of reforestation decisions by rural mountain communities in Vietnam

Thi Mai Anh Tran,고동욱,박찬열,Hai Dinh Le 한국산림과학회 2019 Forest Science And Technology Vol.15 No.2

Reforestation is a primary factor in protecting upland forests providing economic sustenance for livelihood and keeping watersheds intact. In this study, we evaluated the importance of several direct and indirect drivers that can influence people’s decision for reforestation. Acquiring data from Cao Phong district of Vietnam, we utilized Bayesian Network (BN) to analyze how household characteristics, socio-economic status, biophysical environment, institutional support, and farm characteristics influenced reforestation decisions of local people. BN allowed us to identify 1) the main drivers that affect landholders ‘planted forest area, 2) how the key drivers affect among themselves, and 3) what causes constraints in tree planting. We surveyed 100 households for potential drivers, identified significant drivers by using bivariate analysis and stepwise linear regression, and created a BN to predict scenarios with different household’s perception regarding the planted forest area. The results revealed five direct drivers (attitude of household to tree planting, sources of investment capital for planting practice, land area, distance from household to market, experience of participating in forestry program) and seven indirect drivers (information about forestry program, incentives supported for tree planters, land tenure, accessibility to plantation forest, rotation length of planting trees, forest area, household income) that significantly influenced farmers’ reforestation decisions. Constraints in planting trees were due to the difficulties in protecting property from mortality and unreliable profit. Our results can assist design efficient forestry programs in Vietnam and in other comparable areas.

Understanding the COVID-19 Infodemic: Analyzing User-Generated Online Information During a COVID-19 Outbreak in Vietnam

Ha-Linh Quach,Thai Quang Pham,Ngoc-Anh Hoang,Dinh Cong Phung,Viet-Cuong Nguyen,Son Hong Le,Thanh Cong Le,Dang Hai Le,Anh Duc Dang,Duong Nhu Tran,Nghia Duy Ngu,Florian Vogt,Cong-Khanh Nguyen 대한의료정보학회 2022 Healthcare Informatics Research Vol.28 No.4

Objectives: Online misinformation has reached unprecedented levels during the coronavirus disease 2019 (COVID-19) pandemic. This study analyzed the magnitude and sentiment dynamics of misinformation and unverified information about public health interventions during a COVID-19 outbreak in Da Nang, Vietnam, between July and September 2020. Methods: We analyzed user-generated online information about five public health interventions during the Da Nang outbreak. We compared the volume, source, sentiment polarity, and engagements of online posts before, during, and after the outbreak using negative binomial and logistic regression, and assessed the content validity of the 500 most influential posts. Results: Most of the 54,528 online posts included were generated during the outbreak (n = 46,035; 84.42%) and by online newspapers (n = 32,034; 58.75%). Among the 500 most influential posts, 316 (63.20%) contained genuine information, 10 (2.00%) contained misinformation, 152 (30.40%) were non-factual opinions, and 22 (4.40%) contained unverifiable information. All misinformation posts were made during the outbreak, mostly on social media, and were predominantly negative. Higher levels of engagement were observed for information that was unverifiable (incidence relative risk [IRR] = 2.83; 95% confidence interval [CI], 1.33–0.62), posted during the outbreak (before: IRR = 0.15; 95% CI, 0.07–0.35; after: IRR = 0.46; 95% CI, 0.34-0.63), and with negative sentiment (IRR = 1.84; 95% CI, 1.23–2.75). Negatively toned posts were more likely to be misinformation (odds ratio [OR] = 9.59; 95% CI, 1.20–76.70) or unverified (OR = 5.03; 95% CI, 1.66–15.24). Conclusions: Misinformation and unverified information during the outbreak showed clustering, with social media being particularly affected. This indepth assessment demonstrates the value of analyzing online “infodemics” to inform public health responses.