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A simple design of a broadband multifunctional polarization converter using an anisotropic metasurface for X-band application is proposed. The proposed polarization converter consists of a periodic array of the two-corner-cut square patch resonators based on the FR-4 substrate that achieves both cross-polarization and linear-to-circular polarization conversions. The simulated results show that the polarization converter displays the linear cross-polarization conversion in the frequency range from 8 to 12 GHz with the polarization conversion efficiency above 90%. The efficiency is kept higher than 80% with wide incident angle up to 45°. Moreover, the proposed design achieves the linear-to-circular polarization conversion at two frequency bands of 7.42–7.6 GHz and 13–13.56 GHz. A prototype of the proposed polarization converter is fabricated and measured, showing a good agreement between the measured and simulated results. The proposed polarization converter exhibits excellent performances such as simple structure, multifunctional property, and large cost-efficient bandwidth and wide incident angle insensitivity in the linear cross polarization conversion, which can be useful for X-band applications. Furthermore, this structure can be extended to design broadband polarization converters in other frequency bands.

Per- and polyfluoroalkyl substances (PFASs) are a group of concerned persistent toxic substances, especially for their application or unintentional formation in food contact materials (FCMs). However, information about the occurrence, sources, and fate of these pollutants in food packaging materials from Vietnam as well as Southeast Asian countries is probably still obscured. In this study, levels of 13 perfluoroalkyl carboxylic acids (PFCAs) and 4 sulfonates (PFSs) were determined in various types of food packaging samples collected from Vietnamese markets. Generally low concentrations of total 17 PFASs (median 0.341; max 624 ng/g) suggested that these compounds were mainly inadvertently produced rather than intentionally added to the packaging materials. A few mochi paper tray samples had relatively high PFAS levels (372–624 ng/g), which were dominated by long-chain (C 8 –C 12 ) PFCAs. A comprehensive and updated overview of PFASs in FCMs from different countries in the world was also provided. Current database could not provide conclusive trends of PFAS concentrations and profiles in FCMs between continents and countries. The highest levels up to ppm were reported for PFCAs (e.g., PFBA, PFHxA, PFOA, and PFDA) and several fluorotelomer alcohols and carboxylic acids, while PFSs were almost absent in FCMs. FPASs can emit from FCMs, migrate to food, and then contribute to dietary exposure in humans and animals. Additional investigations on the occurrence, sources, behavior and fate, and impacts of PFASs in FCMs are critically needed, especially in emerging and developing countries.

We report a facile design of an ultra-thin broadband metamaterial absorber (MA) for C-band applications by utilizing a single layer of a metal-dielectric-metal structure of FR-4 substrate. The absorption performances are characterized using a numerical method. The proposed MA exhibits the broadband absorption response over the entire C-band spectrum range from 4.0 GHz to 8.0 GHz with absorptivity above 90% and the high absorptivity is remained over 80% for a large incident angle up to 40° under both transverse electric (TE) and transverse magnetic (TM) polarizations over the band. The origin of absorption mechanism is explained by the electric and surface current distributions, which is also supported by the retrieved constitutive electromagnetic parameters, significantly affected by magnetic resonance. In addition, compared with the previous reports, the proposed MA presents a greater practical feasibility in term of low-profile and wide incident angle insensitivity, suggesting that the proposed absorber is a promising candidate for C-band applications.

Youths and adolescents are vulnerable to HIV/STIs from unprotected sex. Promotion of young population’s awareness about risky sexual behaviors is essential to develop contextualized interventions. A cross-sectional study was conducted in five Vietnamese provinces to document current attitudes and practices regarding sexual behaviors among youths. The information on sociodemographic characteristics, substance use, and sexual behaviors was collected via self-reported questionnaires. The factors associated with risky sexual behaviors were identified by the multivariate logistic regression. Among the 1200 participants, 73.5% reported having sex in their lifetime, and 48.1% used condoms at their latest sexual intercourse. Participants in urban areas were more likely not to intend to use condoms and had a higher unintended pregnancy rate than in rural areas. Older age was positively associated with not wanting to use and not using condoms. Substance-using participants were more likely to not use condoms. The participants taking alcohol or other stimulants before sex had a higher likelihood of unintended pregnancy. Respondents’ attitudes and practices regarding sexual behaviors were associated with gender and employment. This study indicated that young population’s awareness in Vietnam is high, however, risky sexual behaviors also remain common. Sex-related educational programs about the consequences of substance use, multiple sex partners, and unprotected sex should be developed.

This Article has been retracted. Please see the Retraction Note for more detail: https://doi.org/10.1038/s41598-021-81808-1 .

We report a facile design of an ultra-thin broadband metamaterial absorber (MA) for C-band applications by utilizing a single layer of a metal-dielectric-metal structure of FR-4 substrate. The absorption performances are characterized using a numerical method. The proposed MA exhibits the broadband absorption response over the entire C-band spectrum range from 4.0 GHz to 8.0 GHz with absorptivity above 90% and the high absorptivity is remained over 80% for a large incident angle up to 40° under both transverse electric (TE) and transverse magnetic (TM) polarizations over the band. The origin of absorption mechanism is explained by the electric and surface current distributions, which is also supported by the retrieved constitutive electromagnetic parameters, significantly affected by magnetic resonance. In addition, compared with the previous reports, the proposed MA presents a greater practical feasibility in term of low-profile and wide incident angle insensitivity, suggesting that the proposed absorber is a promising candidate for C-band applications.

Reconfigurable metasurfaces (RMSs) that enable the switching function of absorption and polarization conversion have attracted increasing attention. However, the design of RMSs to achieve wideband and high efficiency for both absorption and polarization conversion functions simultaneously remains a great challenge. Here, we propose the design of a RMS structure with a high-efficiency cross-polarization conversion and nearly perfect absorption. The reconfiguration between different functions of polarization conversion and absorption is obtained based on the reversible insulator-to-metal phase transition of Vanadium dioxide (VO 2 ). When the VO 2 is in insulator state, the RMS realizes the cross-polarization conversion function in the wideband of 1.04–3.75 THz with a relative bandwidth up to 113 % due to the multi-resonant modes of electric and magnetic resonances. Meanwhile, the nearly-perfect absorption is achieved in the range of 1.36–3.38 THz with the corresponding relative bandwidth up to 85 % for the VO 2 in metallic state. Specially, the wideband and high-efficiency performance of these functionalities is maintained for a wide angle incidence. The capability of bi-functional switch and integration with polarization conversion and absorption in a single metasurface structure endowed with both wideband and high-efficiency characteristics for a wide incident angle is very promising for emerging RMS devices in the terahertz region.

Concentrations and profiles of 17 perfluoroalkyl substances (PFAS) including 13 perfluorocarboxylic acids (PFA) and 4 perfluoroalkyl sulfonates (PFS) were determined in whole blood, muscle, and liver samples of four freshwater fish species in West Lake and Yen So Lake (Hanoi, Vietnam). Concentrations of total 17 PFAS in fish blood samples ranged from 5.2 to 29 (median 16) ng/mL. Total 17 PFAS levels in liver samples (4.5; 2.7–6.6 ng/g wet weight) were significantly higher than in muscle samples (1.0; 0.51–2.6 ng/g wet weight). More than 90% PFAS burdens in our fish samples were attributed to muscle and blood rather than liver, but contributions of individual compounds varied greatly. The most predominant substances were perfluorooctanesulfonate (PFOS) and PFA with chain lengths from C10 to C14 (i.e., PFDA, PFUnDA, PFDoDA, PFTrDA, and PFTeDA). There is no significant difference in PFAS concentrations between the studied species (i.e., bighead carp, common carp, rohu, and tilapia), but common carp showed specific PFAS profiles as compared to other species (e.g., higher proportions of PFOS and long-chain PFA such as PFTrDA, PFTeDA, and PFHxDA). Daily intake doses of PFOS and perfluorooctanoic acid (PFOA) through fish consumption were markedly lower than the US EPA reference dose of 20 ng/kg/day. Weekly intakes of the sum of PFHxS, PFOS, PFOA, and PFNA in our study were still lower than the EFSA tolerable weekly intake of 4.4 ng/kg/week.

We report a comparative study of room temperature ferromagnetism (RTFM) in undoped and Ni-doped TiO 2 nanowires synthesized by solvothermal method. Both undoped and Ni-doped TiO 2 nanowire samples showed the RTFM with coercive field of ~125 Oe due to intrinsic effect. Interestingly, compared to the doped TiO 2 nanowires, the undoped nanowires exhibited the higher saturation magnetization value, indicating surface defects such as Ti 3+ and oxygen vacancy play more important role in realizing RTFM than Ni doping. The origin of RTFM in the undoped nanowires can be attributed to the ferromagnetic coupling between Ti 3+ ions via F + center resulting from oxygen vacancy on the nanowire surface. Furthermore, saturation magnetization value of the doped nanowires is increased with increasing the doping concentration due to the enhanced ferromagnetic coupling between Ni 2+ ions via F + center.

The present study deals with the fabrication of activated carbon from longan peels (LPAC) using a phosphoric acid (H3PO4) activation method and an evaluation of LPAC’s capability for the adsorption of Reactive Black 5 (RB5) dye from aqueous solutions. The synthesized LPAC was characterized using XRD, SEM, FT-IR, and EDX, confirming a porous, carbon-rich structure with the dominant elemental composition of carbon (85.21%) and oxygen (12.43%), and a surface area of 1202.38 m2/g. Batch adsorption experiments revealed that optimal performance was achieved at pH 3.0, with equilibrium reached after 240 min. The experimental data were well fitted to the Elovich model p, suggesting a heterogeneous adsorption process with diffusion limitations. The intraparticle diffusion model further supported a multi-stage mechanism involving both film diffusion and intraparticle transport. Isotherm studies conducted at varying temperatures (293–323 K) showed a maximum adsorption capacity exceeding 370 mg/g. The adsorption data fit best with the Freundlich (R2 = 0.962) and Temkin (R2 = 0.970) models, indicating multilayer adsorption on a heterogeneous surface. Thermodynamic analysis revealed that the adsorption process was spontaneous and endothermic, with ΔG° values ranging from −23.15 to −26.88 kJ/mol, ΔH° = 14.23 kJ/mol, and ΔS° = 0.127 kJ/mol×K, consistent with physisorption as the dominant mechanism. Predictive modeling using an artificial neural network (ANN) achieved superior accuracy (R2 = 0.989 for RRE; R2 = 0.991 for q) compared to multiple linear regression (MLR). Calculation from ANN indicated that pH and contact time were the most influential factors for RB5 removal efficiency, while initial dye concentration and temperature were most critical for adsorption capacity. Furthermore, LPAC demonstrated excellent reusability, retaining over 83% removal efficiency after five adsorption–desorption cycles. These findings confirm that LPAC is an efficient and renewable adsorbent for the treatment of RB5 dye in wastewater treatment applications.