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Công bố mới năm 2019

09/03/2019 3:00 SA

A comprehensive review of flexible piezoelectirc generator based on organic-inorganic metal halide perovskites
Authors: Venkatraju Jella, Swathi Ippili, Ji-Ho Eom, S.V.N. Pammi, Hang-Soon Jung, Van-Dang Tran, Nguyen Van Hieu, Artavazd Kirakosyan, Deul Kim, Moon Ryul Sihn, Jihoon Choi, Yun-Jeong Kim, and Soon-Gil Yoon,
Journal: Nano Energy 57 (2019) 74-93. [Q1; ***IF2017: 13.61***]
Abstract: Organic-inorganic metal halide perovskites (OMHPs) have been extensively investigated over the past few years, not only because of their key features such as ease of solution-based processing, strong optical absorption, tunable bandgap, high carrier mobility, a long diffusion length, etc., and also because of their multi-faceted electronic applications with unprecedented power conversion efficiencies (PCE) in the field of photovoltaics. Apart from the impressive photovoltaic and optoelectronic applications, the applications for OMHPs have recently diverged towards mechanical energy harvesting applications owing to high levels of dielectric and piezoelectric properties that are relatively analogous to those of inorganic piezoelectric materials. Despite these assets, a fundamental understanding of physical behaviors such as ferroelectric and piezoelectric properties remains a key challenge that hampers the development of OMHP-based piezoelectric energy harvesters. This review updates the progress in nanogenerators for mechanical energy harvesting based on OMHPs and includes materials classifications and structural properties, as well as an overview of dielectric, ferroelectric, and piezoelectric properties based on the available literature. In addition, the numerous methods used to synthesize high-quality perovskite films and crystals are also addressed. In the overview of piezoelectric generators (PEGs), various approaches to PEGs based on OMHPs and flexible polymer composites are introduced. For flexible PEGs, fabrication, structural design, factors determining output, and applications are reviewed. Finally, some essential experimental features, perspectives, and issues in this exciting field are discussed and suggested.

Excellent detection of H2S gas at ppb concentration using ZnFe2O4 nanofibers loaded with reduced graphene oxide
Authors: Nguyen Van Hoang, Chu Manh Hung, Nguyen Duc Hoa, Nguyen Van Duy, Inkyu Park, Nguyen Van Hieu*
Journal: Sensors and Actuators B 282 (2019) 876-884. [Q1, ***IF2017: 5.66***]
Abstract: Cost-effective fabrication of sensors and detection of ultralow concentrations of toxic gases are important concerns for environmental monitoring. In this study, the reduced graphene oxide (RGO)-loaded ZnFe2O4 nanofibers (ZFO-NFs) were fabricated by facile on-chip electrospinning method and subsequent heat treatment. The multi-porous NFs with single-phase cubic spinel structure and typical spider-net morphology were directly assembled on Pt-interdigitated electrodes. The diameters of the RGO-loaded ZFO-NFs were approximately 50–100 nm with many nanograins. The responses to H2S gas showed a bell-shaped behaviour with respect to RGO contents and annealing temperatures. The optimal values of the RGO contents and the annealing temperatures were found to be about 1.0 wt% and 600 °C, respectively. The response of the RGO-loaded ZnFe2O4 NFs to 1 ppm H2S gas was as high as 147 at 350°C while their cross-gas responses to SO2 (10 ppm), NH3 (100 ppm), H2 (250 ppm), C3H6O (1000 ppm), and C2H5OH (1000 ppm) were rather low (1.8−5.6). The high sensor response was attributed to formation of a heterojunction between RGO and ZnFe2O4 and due to the fact that NFs consisted of many nanograins which resulted in multi-porous structure and formation of potential barriers at grain boundaries.

Magnetic iron oxide nanoparticles decorated graphene for gas sensing: The particle size effects
Authors: Tran Thanh Tung, Nguyen Viet Chien, Nguyen Van Duy, Nguyen Van Hieu*, J. Nine, C.J. Coghlan, Diana N.H. Tran, D. Losics*, "",
Journal: Journal of Colloid and Interface Science 539 (2019) 315-325. [Q1; ***IF2017: 5.09***].
Abstract: We report a synthesis of magnetic nanoparticles chemically immobilized onto reduced graphene oxide sheets (referred to as rGO-Fe3O4 NPs) as a gas and vapor sensing platform with precisely designed particle size of 5, 10 and 20 nm to explore their influence of particle size on sensing performance. The rGO-Fe3O4 NP sensors have been investigated their responses to different gases and volatile organic compounds (VOCs) at part-per-million (ppm) levels. Results show that the Fe3O4 NPs with smaller size (5 and 10 nm) on the rGO surface led to a lower sensitivity, while particles of a size of 20 nm have a significant enhancement of sensitivity compared to the bare rGO sensor. The rGO-Fe3O4 NP20 sensor can detect trace amounts of NO2 gas and ethanol vapor at the 1 ppm and is highly selective to the NO2 and ethanol among other tested gases and VOCs, respectively. The particle size causes different distribution behaviour of NPs over rGO surface and interspaced between them, which results in deceased or increased the surface interactions between gas and graphene. The NPs themselves contained different defects level and the charge depletion layer that affect their adsorption gas/vapor molecules, which are explained for different sensing responses.

An Eco-friendly flexible piezoelectric energy harverter that delivers high output performance is based on lead-free MASnI3Films and MASnI3-PVDF composite films
Authors: Swathi Ippili, Venkatraju Jella, Ji-Ho Eom, Jaegyu Kim, Seungbum Hong, Van-Dang Tran, Nguyen Van Hieu*, and Soon-Gil Yoon,
Journal: Nano Energy57 (2019) 911-923. [Q1;***IF2017: 13.61***]
Abstract: An environmentally-friendly lead-free methylammonium tin iodide (MASnI3) perovskite is successfully synthesized using a facile approach of an antisolvent-assisted collision technique (ACT) under room ambient conditions, which results stability within 24 h under ambient room conditions. The phase transition of MASnI3 from tetragonal to cubic is first observed at ~ 30°C. Polycrystalline MASnI3 films reveal a high dielectric constant of ~ 65 at 100 kHz, a low-leakage current density of 7 × 10−7 A cm−2 at 50 kV cm−1, well-developed P-E hysteresis loops, and a high piezoelectric coefficient (d33) of 20.8 pm V−1. The MASnI3 piezoelectric nanogenerator (PENG) shows an output voltage of ~ 3.8 V and an output current density of 0.35 μA cm−2. To enhance the piezoelectric output performance, the MASnI3 films are composited with an environmentally friendly PVDF polymer that had a porous structure. The PVDF-MASnI3 composite based-PENG reveals a maximum output voltage of ~ 12.0 V and current density of ~ 4.0 μA cm−2. A green light-emitting diode (LED) using the PVDF-MASnI3 PENGs is instantly lighted without need of a storage device, and long-term stability of the composite PENGs is validated for 90 days. This simple and cost-effective solution process is feasible for the fabrication of large-scale, high-performance, and environmental-friendly PENGs based on lead-free organic-inorganic perovskites to extensively implicate in medical and biomechanical applications.

Sex Differences and Psychological Factors Associated with General Health Examinations Participation: Results from a Vietnamese Cross-Section Dataset
Authors: Quan Hoang Vuong, Kien Cuong P.Nghiem, Viet Phuong La, Thu Trang Vuong, Hong Kong T.Nghiem, Manh Toan Ho, Kien Tran, Thu Hong Khuat and Manh Tung Ho
Abstract: This study focuses on the association of sex differences and psychological factors with periodic general health examination (GHE) behaviors. We conducted a survey in Hanoi and the surrounding areas, collecting 2068 valid observations; the cross-section dataset was then analyzed using the baseline category logit model. The study shows that most people are afraid of discovering diseases through general health examinations (76.64%), and the fear of illness detection appears to be stronger for females than for males (β1(male) = −0.409, p < 0.001). People whose friends/relatives have experienced prolonged treatment tend to show more hesitation in participating in physical check-ups (β2 = 0.221, p < 0.05). On the ideal frequency of GHEs, 90% of the participants agree on once or twice a year. The probability of considering a certain period of time as an appropriate frequency for GHEs changes in accordance with the last doctor visit (low probability of a health examination every 18 months) and one’s fear of potential health problems post-checkup (no fear raises probability of viewing a health examination every 6 months by 9–13 percentage points). The results add to the literature on periodic GHE in particular and on preventive health behaviors in general.

Online peer influences are associated with receptiveness of youths: The case of Shisha in Vietnam
Authors: Bach Xuan Tran, Long Hoang Nguyen, Giang Thu Vu, Huong Thi Le, Hinh Duc Nguyen, Vuogn Quan Hoang, Phuong Viet La, Duc Anh Hoang, Nhue Van Dam, Thu Trang Vuong, Huong Lan Thi Nguyen, Carl A.Latkin, Melvyn W.B.Zhang, Cyrus S.H.Ho, Roger C.M.Ho
Abstract: An explosion of Internet and social network sites (SNSs) among Vietnamese youths and adolescents increases the likelihood of being exposed or influenced by risky perceptions and beliefs from online peers, leading to the development of risk behaviors, especially new habits such as shisha smoking. However, evidence about the online peer influence on the occurrence of shisha smoking is limited. The objective of this study is to determine the associations between online peer influence and the shisha use among young Internet active users in Vietnam. An online cross-sectional study was conducted with 1041 young people, who were recruited by respondent-driven sampling method. The study found that 4.1% have had smoked shisha in the last 12 months. Among participants, 52.9% and 49.5% reported frequently visited places and engaged in activities recommended by online friends, respectively. People who were male (OR = 4.04; 95%CI = 1.94–8.41), of older age (OR = 1.27; 95%CI = 1.06–1.54) and having higher levels of “visiting places recommended by online friends” (OR = 3.05; 95%CI = 1.84–5.06) were more likely to smoke shisha. This study highlighted the influence of online peers on the occurrence of shisha smoking among youths and adolescents. Future interventions should educate young people to understand the harmful effects of shisha smoking as well as risky online presentations and online interactions.

Righting the Misperceptions of Men Having Sex with Men: A Pre-Requisite for Protecting and Understanding Gender Incongruence in Vietnam
Authors: Van Anh T. Nguyen, Ngoc Quynh H. Nguyen, Thu Hong Khuat, Phuong Thao T. Nguyen, Thu Trang Do, Xuan Thai Vu, Kien Tran, Manh Tung Ho, Hong Kong T.Nguyen, Thu Trang Vuong and Quan Hoang Vuong
Abstract: Protecting the rights of the lesbians, gays, bisexuals, transgender, intersex, and queers (LGBTIQ) population requires, first and foremost, a proper understanding of their sexual orientation and gender identity. This study highlights a severe misunderstanding and lack of knowledge among health professionals in Vietnam with regard to the men who have sex with men (MSM) and transgenders. This study uses (i) a survey based on the convenience sampling method among 150 health workers that covered 61 questions and (ii) 12 in-depth interviews in two metropolitan centres in Vietnam, Hanoi and Ho Chi Minh city. Three main topics are explored: (i) the general knowledge of healthcare workers about MSM and transgenders; (ii) their knowledge about the sexual reproductive health and human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) risks of MSM and transgenders; and (iii) their attitudes and behaviors towards MSM and transgenders. One of the notable findings is how prevalent the misperceptions are across the board, namely, in staff of both sexes, in both cities, at various kinds of medical facilities, at different work positions and educational levels. Half of the respondents consider transgenders to have a curable mental problem while 45% say MSM only have sex with males. Most remarkably, 12.7% state if they have any choice, they want nothing to do with MSM and transgenders. The study finds there is a considerable percentage of health professionals who lack knowledge about the diversity of sexual orientation, gender identity, and health issues related to the sexual minorities and gender non-conforming population. To improve the clinical process for serving these at-risk groups, the study suggests the continual education for the health workers needs to be added to their formal as well as in-job training.

HIV knowledge and risk behaviors among drug users in three Vietnamese mountainous provinces
AuthorsTam Minh Thi Nguyen, Bach Xuan Tran, Mercedes Fleming, Manh Duc Pham, Long Thanh Nguyen, Anh Lan Thi Nguyen, Huong Thi Le, Thang Huu Nguyen, Van Hai Hoang, Xuan Thanh Thi Le, Quan Hoang Vuong, Manh Tung Ho, Van Nhue Dam, Thu Trang Vuong, Vu Nguyen, Huong Lan Thi Nguyen, Huyen Phuc Do, Phuong Linh Doan, Hai Hong Nguyen, Carl A. Latkin, Cyrus S. H. Ho and Roger C. M. Ho
Globally, people who inject drugs are highly vulnerable to HIV transmission. Methadone maintenance treatment (MMT) programs are one of the most cost-effective mechanisms to substitute opioid use and improve the quality of life of patients. Since the coverage of MMT is still limited and even for those patients who are treated, improving their knowledge on HIV and maintaining healthy behaviors are key to maximizing the outcomes of HIV harm reduction programs. This study examined the knowledge on HIV, perceived risk and HIV testing among drug users accessing methadone maintenance services in three Vietnamese mountainous areas.

A cross-sectional study of 300 people enrolling for MMT services in three provinces in Vietnam was conducted. The factors associated with the knowledge, attitudes, and practices of respondents about HIV/AIDS were exploited using multivariable logistic model.
Of the 300-people surveyed, 99% knew of HIV and 60.6% were identified as having good knowledge. While 75.2% identified that injecting drugs was a risk factor for HIV, 52.2% thought they were not at risk of HIV mainly as they did not share needles. 92.6% had undergone HIV testing with 17.4% being positive, a number which was significantly lower than Vietnam’s national average for people who inject drugs. Age, ethnicity and education were associated with knowledge of HIV while ART treatment was linked to self-assessed HIV status.
This study sheds new light on the knowledge attitudes and practices of people who inject drugs, particularly males in mountainous areas of Vietnam regarding HIV prevention. Overall, knowledge was good with most conducting safe practices towards transmission. Enhanced education and targeting of minority groups could help in increasing the numbers receiving MMT and HIV services.

Flavor changing in the flipped trinification
Authors: D. N. Dinh, D. T. Huong, N. T. Duy, N. T. Nhuan, L. D. Thien, and Phung Van Dong
Abstract: The flipped trinification, a framework for unifying the 331 and left-right symmetries, has recently been proposed in order to solve profound questions, the weak parity violation and the number of families, besides the implication for neutrino mass generation and dark matter stability. In this work, we argue that this gauge completion naturally provides flavor-changing neutral currents in both quark and lepton sectors. The quark flavor changing happens at the tree level due to the nonuniversal couplings of ZL,R, while the lepton flavor changing l l γ  starts from the one-loop level, which is significantly contributed by the new charged currents of YL,R that couple ordinary leptons to exotic leptons. These effects disappear in the minimal left-right model but are present in the framework characterizing a flipped trinification symmetry.

Enhanced magneto-transport and thermoelectric properties of MnP nanorod thin films grown on Si (1 0 0)
Authors: Anh Tuan Duong, Thi Minh Hai Nguyen, Dinh Lam Nguyen, Raja Das, Huu Tuan Nguyen, Bach Thang Phan, Sunglae Cho
Abstract: The MnP thin films were grown on Si (1 0 0) substrates at 300 and 400 °C using molecular beam epitaxy (MBE). The films crystallize in an orthorhombic structure. FE-SEM images indicated that both films are composed of vertically aligned MnP nanorods. However, the density of the nanorods in the film grown at 400 °C is higher than that grown at 300 °C, leading to a considerable decrease of resistivity in this sample. Both films showed a ferromagnetic behavior, but the Curie temperature increased from 275 K for the film grown at 300 °C to 325 K for the film grown at 400 °C. Anomalous Hall effect (AHE) and negative magneto-resistance (MR) were observed in the films. While both films exhibited a metallic behavior, a higher thermoelectric power factor (PF) was achieved for the film grown at 400 °C.

Magnetically tunable iron oxide nanotubes for multifunctional biomedical applications
Authors: Raja, Jason A.Cardarelli, Manh Huong Phan, Hariharan Srikanth
Abstract: Design of a multifunctional magnetic bionanosystem has become increasingly important towards advancing the future of clinical medicine. While hollow iron oxide nanoparticles with enhanced surface areas allow for more drug molecules to be attached to the particles, their relatively low saturation magnetization (MS) hinders their practicality in medicinal applications such as drug delivery and hyperthermia therapy. We demonstrate that this limitation can be overcome by utilizing 1D magnetic nanotubes that possess both enhanced surface areas and high MS. In this study, highly crystalline, tunable aspect ratio Fe3O4 nanotubes have been successfully synthesized using a hydrothermal method. Magnetic measurements showed a clear Verwey transition (120 K) and high MS (75 emu/g) at 300 K, confirming the high quality of the synthesized Fe3O4nanotubes. Calorimetric experiments on randomly dispersed Fe3O4nanotubes in water with concentration of 1 mg/mL showed a large Specific Absorption Rate (SAR) value of 400 W/g for an AC magnetic field of 800 Oe, which increased to 500 W/g when the nanotubes were aligned parallel to the DC magnetic field and suspended in a 2% agar solution. Our study shows the possibility of using the Fe3O4 nanotubes as a highly effective multifunctional nanoscale tool for targeted hyperthermia and on-demand drug delivery.

Konjac glucomannan-templated synthesis of three-dimensional NiO nanostructures assembled from porous NiO nanoplates for gas sensors
Authors: Le Lam Son, Nguyen Duc Cuong*, Tran Thi Van Thi, Le Trung Hieu, Do Dang Trung, Nguyen Van Hieu*
Abstract: Biopolymer template synthesis has attracted extensive interest for fabricating highly porous metal oxide nanostructures. In this report, a green template-based approach for the synthesis of three-dimensional (3D) NiO nanostructures assembled from porous NiO nanoplates is introduced using a konjac glucomannan (KGM) template. The Ni–KGM composites, which were formed by the immersion of KGM nanofibrils in nickel nitrate solution, were annealed in air at 600 °C to obtain the highly porous NiO nanoplates. The KGM nanofibrils were used as a sacrificial template, which was combusted at a high temperature for the formation of the porous nanostructures. The gas sensor properties of the porous NiO architecture were systematically investigated with four reduced gases including hydrogen sulfide, ammonia, carbon monoxide and hydrogen. The results indicate that the porous NiO nanoplates show a good detection of hydrogen sulfide with a rapid response and recovery speed at low concentrations.

Fatigue lifetime prediction of arbitrarily-shaped MEMS structures made of polysilicon thin films
Authors: Vu Le Huy, Shoji Kamiya, Joao Gaspar, Oliver Paul
Abstract: This paper reports the results of fatigue lifetime prediction of polycrystalline silicon thin film structures on the basis of their static strength. The fatigue lifetime is formulated using Paris’ law as a crack extension process starting from initial cracks which represent the etching damage and thus determine the strength distribution described by Weibull distribution. The predictions were performed on three groups of specimens fabricated under different etching conditions. Specimens in each group were patterned with different types of shapes to have different stress distributions. The results showed that their fatigue lifetimes were predicted well despite the difference of stress distribution and the initial damage induced by etching process. This means that the damage accumulation under fatigue loading was independent of the fabrication conditions, the shapes and thus of the stress distributions of structures.