Multifunctional amorphous FeCoNiTixSi high-entropy alloys with excellent electromagnetic-wave absorption performances.

Amorphous high-entropy alloys (HEAs) as electromagnetic-wave absorbing materials have been rarely reported. In this work, amorphous FeCoNiTixSi HEAs were synthesized by introducing a high content of large-atom Ti using the high-energy ball-milling technique. This amorphous structure could improve the saturated magnetization and coercivity of HEAs, but slightly degraded the mechanical and oxidation resistance properties. In terms of electromagnetic properties, FeCoNiTi0.01Si and FeCoNiTiSi exhibit excellent electromagnetic-wave absorption performances, with significant absorptions of -68.4 dB at 6.14 GHz and -63.4 dB at 9.12 GHz, corresponding to bandwidths of 5.15 GHz (1.69 mm) and 3.64 GHz (1.43 mm), respectively. Overall, the prepared FeCoNiTixSi HEAs exhibited superior comprehensive performances compared to other HEA absorption materials. This work provided a novel strategy for the development of new electromagnetic-wave absorption materials with low weight, high absorption efficiency, and resistance to harsh environments.

Supramolecular Host-Guest Interaction-Driven Electrochemical Recognition for Pyrophosphate and Alkaline Phosphatase Analysis.

We report an electrochemical biosensor based on the supramolecular host-guest recognition between cucurbit[7]uril (CB[7]) and L-phenylalanine-Cu(II) complex for pyrophosphate (PPi) and alkaline phosphatase (ALP) analysis. First, L-Phe-Cu(II) complex is simply synthesized by the complexation of Cu(II) (metal node) with L-Phe (bioorganic ligand), which can be immobilized onto CB[7] modified electrode via host-guest interaction of CB[7] and L-Phe. In this process, the signal of the complex-triggered electro-catalytic reduction of H2 O2 can be captured. Next, due to the strong chelation between PPi and Cu(II), a biosensing system of the model "PPi and Cu(II) premixing, then adding L-Phe" was designed and the platform was applied to PPi analysis by hampering the formation of L-Phe-Cu(II) complex. Along with ALP introduction, PPi can be hydrolyzed to orthophosphate (Pi), where abundant Cu(II) ions are released to form L-Phe-Cu(II) complex, which gives rise to the catalytic reaction of complex to H2 O2 reduction. The quantitative analysis of H2 O2 , PPi and ALP activity was achieved successfully and the detection of limits are 0.067 µM, 0.42 µM and 0.09 mU/mL (S/N=3), respectively. With its high sensitivity and selectivity, cost-effectiveness, and simplicity, our analytical system has great potential to for use in diagnosis and treatment of ALP-related diseases.

Synthesis and Luminescence Properties of Ho3+ and Er3+-Doped CaWO4 Nanocrystalline Powders Prepared by Self-Propagating Combustion Method.

Nanocrystalline Er3+-doped CaWO4 (CaWO4:Er3+) and Ho3+-doped CaWO4 (CaWO4:Ho3+) powders were fabricated by a facile sol-gel self-propagating combustion method using glycin as reductant. The components, microstructure and luminescence properties of samples were studied in detail. The as-prepared CaWO4:Er3+ and CaWO4:Ho3+ samples presented meshy and porous structure, which can be attributed to the instantaneous releasing of a lot of gases during the combustion reaction. The emission spectra of CaWO4:Ho3+ presented two emission peaks around 415 and 542 nm, corresponding to the intrinsic emission of [WO4]2- complex and the characteristic emission of Ho3+ from excited state 5F4 to ground state 5I8 transition. For the CaWO4:Er3+ sample, three emission peaks centered at 420, 525 and 550 nm can be observed. The mechanism of emission process and energy transfer process in CaWO4:Er3+ and CaWO4:Ho3+ was explained in detail. This work shows that the multiple luminescence emission can be realized by doping a small amount of Er3+ or Ho3+ into CaWO4 host materials, which is significant for developing luminescent materials of tungstate systems.

A hybrid denoising approach for PPG signals utilizing variational mode decomposition and improved wavelet thresholding.

BACKGROUND: Photoplethysmography (PPG) signals are sensitive to motion-induced interference, leading to the emergence of motion artifacts (MA) and baseline drift, which significantly affect the accuracy of PPG measurements. OBJECTIVE: The objective of our study is to effectively eliminate baseline drift and high-frequency noise from PPG signals, ensuring that the signal's critical frequency components remain within the range of 1 ∼ 10 Hz. METHODS: This paper introduces a novel hybrid denoising method for PPG signals, integrating Variational Mode Decomposition (VMD) with an improved wavelet threshold function. The method initially employs VMD to decompose PPG signals into a set of narrowband intrinsic mode function (IMF) components, effectively removing low-frequency baseline drift. Subsequently, an improved wavelet thresholding algorithm is applied to eliminate high-frequency noise, resulting in denoised PPG signals. The effectiveness of the denoising method was rigorously assessed through a comprehensive validation process. It was tested on real-world PPG measurements, PPG signals generated by the Fluke ProSim™ 8 Vital Signs Simulator with synthesized noise, and extended to the MIMIC-III waveform database. RESULTS: The application of the improved threshold function let to a substantial 11.47% increase in signal-to-noise ratio (SNR) and an impressive 26.75% reduction in root mean square error (RMSE) compared to the soft threshold function. Furthermore, the hybrid denoising method improved SNR by 15.54% and reduced RMSE by 37.43% compared to the improved threshold function. CONCLUSION: This study proposes an effective PPG denoising algorithm based on VMD and an improved wavelet threshold function, capable of simultaneously eliminating low-frequency baseline drift and high-frequency noise in PPG signals while faithfully preserving their morphological characteristics. This advancement establishes the foundation for time-domain feature extraction and model development in the domain of PPG signal analysis.

Novel Sm3+-doped La3Ga5MO14 (M = Si or Ge) phosphors for indoor illumination: effects of M cations on photoluminescence.

A series of La3(1-x)Ga5MO14:xSm3+ (M = Si or Ge) orange-red phosphors with high color purity, low correlated color temperature, and good thermal stability were successfully synthesized via a high-temperature solid-phase technique. The phase structure and morphology of La3Ga5SiO14(LGSi):xSm3+ and La3Ga5GeO14(LGGe):xSm3+ were investigated. Sm3+-doped LGSi and LGGe phosphors emitted orange-red light under an excitation of 403 nm, and the optimal doping concentrations were 3 mol% and 2 mol% with excellent color purities of 98.46% and 98.25%, respectively. The concentration quenching mechanism of both the samples was dominated by dipole-dipole interaction, and the effect of Si4+ and Ge4+ on luminescence performance was discussed. The internal quantum efficiencies of LGSi:0.03Sm3+ and LGGe:0.02Sm3+ were calculated to be 27.14% and 56.07%, respectively. The CIE and CCT values indicated that the luminescence of the prepared phosphors was in the orange-red region. Additionally, a white light-emitting diode (w-LED) was fabricated with LGGe:0.02Sm3+ phosphors, which was capable of emitting bright and warm white light and exhibiting a high color rendering index (CRI) of 87.17 and an appropriate correlated color temperature (CCT) of 6108 K. These results indicated that the prepared phosphors with excellent luminescent performances have potential application in indoor illumination.

Efficient and Homogeneous Carbonitriding of High-Entropy Alloys by a Mechanochemical Process for Obtaining Coordinated Electromagnetic Matching.

Optimizing the impedance matching via electromagnetic adjustment is considered an effective strategy to accomplish exceptional electromagnetic wave absorption (EMA) performance. Here, we report an efficient and green process to obtain the carbonitriding FeCoNiCr high-entropy alloys (HEAs) with flake-shaped morphology by using organic cyanide (Dicyandiamide, C2H4N4) as nitrogen and carbon sources. The carbonitriding effects on the phase structure, magnetic properties, mechanical hardness, corrosion resistance, high-temperature oxidation resistance, and EMA performances were investigated systematically. The carbonitriding process optimized the impedance match by decreasing the dielectric constant via introducing the nonmetallic C and N. The #CN10 sample exhibited outstanding EMA performances with a minimum reflection loss of -32.3 dB at 7.89 GHz and a broad effective bandwidth of 4.46 GHz, which covered the majority of X-band. In addition, the carbonitriding FeCoNiCr HEAs had great mechanical properties, excellent corrosion resistance, and high-temperature oxidation resistance, indicating excellent adaptability to harsh environments as well as good EMA performances. This work provides a new idea for the preparation and design of carbonitriding EMA materials.

Pyroelectric catalytic performance of Sm3+-modified Pb(Mg1/3Nb2/3)O3-PbTiO3 for organic dyes: degradation efficiency, kinetics and pyroelectric catalytic mechanism.

The development of photocatalysis is hindered, in part, by the quick recombination of photogenerated carriers and the instability of light sources. In this study, the problem of too-fast electron-hole pair compounding in photocatalysis is effectively regulated by the polarization field of pyroelectric materials using the pyroelectric method. Self-polarized pyroelectric materials that depend on temperature variations can generate usable electrical energy and polarized charge carriers to degrade organic pollutants. Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) is a relaxor ferroelectric material with spontaneous polarization characteristics. The PMN-0.30PT:1 mol%Sm3+ catalyst was prepared by applying the high-temperature solid-state reaction method. Under the dark condition and nine cold-hot cycles of 23 °C-68 °C, using H2O2-assisted PMN-0.30PT:1 mol%Sm3+ as a catalyst, the degradation rate of rhodamine 6G (10 mg L-1) was 94.3 ± 2.5%. In addition, the degradation rates of 88.52% and 64.32% were obtained for rhodamine B (10 mg L-1) and methylene blue (10 mg L-1), respectively. This study provides a new approach to the pyroelectric catalytic degradation of organic pollutants.

Enhanced Electromagnetic-Wave Absorbing Performances and Corrosion Resistance via Tuning Ti Contents in FeCoNiCuTix High-Entropy Alloys.

Efficient and stable electromagnetic-wave (EMW) absorption materials have attracted great attention in the field of reducing microwave pollution. Herein, FeCoNiCuTix high-entropy alloys (HEAs) as electromagnetic-wave absorbing materials were prepared by a high-energy ball-milling method. The as-milled HEA powders presented a flaky shape with a high aspect ratio. Impedance matching was efficiently optimized by severe lattice distortion, which was caused by Ti incorporation. The introduced plentiful defects in FeCoNiCuTix HEAs provided abundant polarization sites for dielectric loss. By tuning Ti contents, FeCoNiCuTi0.2 HEAs delivered excellent EMW absorption performances. The maximal reflection loss (RLmax) values reached -47.8 dB at 10.86 GHz as thin as 2.16 mm, and the widest bandwidth was 4.76 GHz (5.97-10.73 GHz). Furthermore, the introduction of Ti enhanced corrosion resistance via increasing the charge transfer resistance of a passivated film. Those characteristics of FeCoNiCuTix HEAs made these materials a practical gigahertz-range EMW absorber. Additionally, our findings provided a facile and tunable strategy for designing EMW absorbing materials, which was aimed at lightweight, highly efficient absorption, and resistance to harsh environments.

Facile Synthesis and Microwave-Absorption Properties of Organic-Inorganic CoFe2O4/Polyaniline Nanocomposites with Embedded Structure.

Organic-inorganic CoFe2O4/polyaniline (CoFe2O4/PA) nanocomposites with embedded structures were synthesized by combining the sol-gel auto-combustion process and in-situ oxidative polymerization. The phases and morphologies of the prepared samples were identified. The pure CoFe2O4 samples exhibited inferior microwave-absorption properties in a frequency range of 2-18 GHz. Upon the incorporation of PA, the formed CoFe2O4/PA nanocomposites exhibited rather good absorption performances. When the sample thickness was 2.5 mm, the maximum reflection loss (RL) reached -22.3 dB, while the RL below -10 dB corresponded to the range of 11.0-17.1 GHz, which contains almost the entire Ku-band, making the structure promising for commercial and military applications. A physical model was employed to explain the effects of the embedded structure on the microwave-absorption performances. The excellent microwave-absorption performances could be attributed to the interfacial polarization and repeated reflection of the microwaves inside the CoFe2O4/PA composite.

Microwave-Absorption Properties of Three Kinds of Structured Cu/C Composites.

The microwave-absorption properties of three kinds of (core-shell, uniform-mixing and double-layer structured) Cu/C composites are investigated in the 2-18 GHz frequency range. The results show that the Cu/C composites with core-shell structure are favorable to obtain higher relative permittivity and better microwave-absorption properties in comparison with other Cu/C composites. The reflection loss (RL) values exceeding -10 dB are obtained in 13.0-17.2 GHz at the absorber thickness of 1.6 mm for the core-shell structured Cu/C nanoparticles, which cover most of Ku-band (12-18 GHz). The excellent microwave-absorption properties may result from synergetic effects induced by the tightly-connected core-shell interfaces. The synergetic effects are explained by a simulated physical model, wherein both the interfacial polarizations and interfacial multiple reflections are responsible to the excellent microwave-absorption performances.