Browse Articles

CFD simulation of impeller shape effect on the solid cloud volume in the solid and liquid stirred vessel

Phase transition induced inherent superhydrophobicity on Al alloys surface via femtosecond laser multi-scanning process

Fabrication of biomimetic superhydrophobic metals has attracted considerable interest because of their exceptional surface wettability. Conventional methods for achieving this property often rely on additional organic coatings to lower the surface energy; however, they are very prone to chemical decomposition and even flaking during practical usages. Here, we demonstrated that the laser-induced phase transition in hierarchical structures of metal surface can act as an effective approach to directly produce the superhydrophobic effect without any organic decorations. Through gradual increasing numbers of the femtosecond laser processing, we transfer the surface structures from the initial polycrystalline material into the super-nanometer-sized dual-phase and three-phase material that consists of nano and para-crystallinity embedded in amorphous substance, both of which contribute to lowering the surface energy. Meanwhile, the geometrical profiles of the surface structures become richer and more complicated for improving the stability of air pockets. Remarkably, it is found that both the mechanical and chemical durability of such superhydrophobic surfaces are enhanced significantly for the three-phase based material. This study describes the great value of the metal phase transition in achieving the inherent superhydrophobic properties, which provides a different route to develop high-performance coating-free superhydrophobic surfaces.

Association between METS-IR index and obstructive sleep apnea: evidence from NHANES

Plasmonic properties of gold nanoparticle arrays fabricated using a sequential dewetting process

A scalable, cost-effective technique to fabricate ordered gold nanoparticle arrays with fine control over nanoparticle size and interparticle distance is presented. The array is grown in the pores of an anodic aluminum oxide membrane by the solid-state dewetting process. Control over the nanoparticle size and spacing between particles was achieved by sequential metal deposition and annealing processes, yielding nanoparticles with diameters (D) ranging from 50 to 70 nm and corresponding interparticle distances ranging from 12 to 30 nm. The advantage of this technique is that the nanoparticle size, spherical shape, and hexagonal close-packed ordering of the array can be precisely controlled, allowing for fine tuning of the plasmonic absorption properties. The important parameters that determine the size, shape, and distribution of nanoparticles in the array are the template morphology (dimple geometry) and the thickness of the evaporated metal layer. Above a certain critical film thickness, the nanoparticles coalesce to form nano-islands. The significance of this work is that it provides a reliable technique to assemble metal nanoparticles into high density arrays, with good control over particle shape and distribution. Such arrays can be used to generate highly concentrated electromagnetic fields for plasmonic sensor applications.

Simultaneous screening of 211 pesticide residues in date fruits in Iran and health risk assessments based on Mont Carlo simulation

Boosting low-pressure reversible barocaloric effect in plastic crystal KPF6 through controlled particle size

Plastic crystals have large entropy change during first-order phase transitions due to strong molecular orientation disorder and volume changes. This feature has revived interest in plastic crystals, as they have great potential in solid-state refrigeration applications induced by external pressure. However, the reversible barocaloric effect in most plastic crystals does not compare favorably with their isothermal entropy change. Here, we demonstrate that controlling the particle size of the plastic crystal KPF6 can help achieve a compromise between the phase transition resistance at grain boundaries and the phase transition correlation within grains and induce a giant reversible barocaloric effect at low pressure. In particular, the 75–150 μm plastic crystal KPF6 displays the lowest thermal hysteresis, with a giant reversible barocaloric entropy change of 50.0 J · kg−1 · K−1 under a pressure change of 40 MPa. The reversible barocaloric effect can be more than doubled by simply optimizing the microstructures of the plastic crystal KPF6. Our work provides an effective way to enhance the reversible barocaloric effect in plastic crystal materials. We also give insight into the physical mechanism that enhances the reversible barocaloric effect through transmission electron microscopy analysis.

The intelligent fault identification method based on multi-source information fusion and deep learning

Active rheology of soft solids performed with acoustical tweezers

Single-beam acoustical tweezers are used to manipulate individual microbubbles and provide quantitative measurements of the local shear modulus of soft hydrogels. The microbubbles are directly generated by electrolysis of the hydrogel, and their displacement is detected using optical microscopy in the focal plane of a focused vortex beam. Microbubbles displaced off-axis can be pulled by a restoring radial force component that forms a stable two-dimensional trap. We also observe an off-axis tangential microbubble motion that is due to the transfer of the beam's angular momentum flux. A simple elastic model for the hydrogel deformation combined with radiation force calculations finally provides local values of the medium's shear modulus, which are found to be in good agreement with standard bulk measurements performed with a rheometer. Our results suggest that acoustical tweezers are relevant tools to characterize the local mechanical properties of complex soft materials, opening opportunities in the field of active rheology.

Cyclically symmetric radially self-similar phononic pseudocrystal isolator for broadband, ultrasonic vibration bandstop filtering

A 2D phononic pseudocrystal isolator exhibiting cyclic symmetry and radial self-similarity is measured and demonstrated to block a wide range of ultrasonic vibration. Measurements of longitudinal and shear wave blocking effects are made and compared with computational results. The use of the bandgap edge ratio is recommended for quantifying suppression in very-wide-bandgap materials. The upper-to-lower suppression edge frequency ratios of 3–4 are remarkably large for shear waves and even larger for longitudinal waves upper-to-lower suppression ratio (13 at 5 dB), such that 92.5% of frequencies in that range experience ≥ 5 dB of suppression.

Circularly polarized cavity mode emission from quantum dots in a semiconductor three-dimensional chiral photonic crystal

We experimentally demonstrated a circularly polarized cavity mode in a GaAs-based chiral photonic crystal (PhC) containing a planar defect. Low-temperature photoluminescence measurements of InAs quantum dots (QDs) embedded in the planar defect revealed a polarization bandgap for left-handed circularly polarized light in the near-infrared spectrum. Within this bandgap, where the QDs preferably emitted right-handed circularly polarized light, we observed a distinct cavity mode peak characterized by left-handed circular polarization (CP). This observation indicates that the chiral PhC modifies the optical density of states for left-handed circular polarization to be suppressed in the polarization bandgap and be largely enhanced at the cavity mode. The results obtained may not only provide photonic devices such as compact circularly polarized light sources but also promote strong coupling between circularly polarized photons and excitons in solid states or molecules, paving the way for advancements in polaritonics, spintronics, and quantum information technology.

Polarization selectivity in single-mode photonic molecule lasers

An efficient approach to achieve single-polarization selectivity in single-mode double microring lasers (photonic molecule lasers) is presented in this study. The fabricated microring lasers achieved polarization extinction ratios of 11.3 dB for TM polarization and −12.8 dB for TE polarization. The fabrication process was conducted by direct laser writing on SU-8 photoresist doped with Rhodamine B dye. In order to obtain an optimum single-mode operation with a specified polarization capability, the study employs Vernier effect double microring lasers and investigates the effects of geometric characteristics, surface scattering loss, and coupling efficiency on polarization performance. The finite-difference time-domain method was utilized to conduct simulations, and the results were verified experimentally. The proposed single-polarized microring lasers provide open possibilities for advanced integrated photonic systems with potential applications in quantum photonics, nonlinear optics, and optical sensors.

A multi-degree-of-freedom model-based method for Young's modulus determination of soft tissue by resonance spectroscopy

Elastic properties of soft tissues are important indicators for disease progression. Previous studies have utilized mechanical resonance spectroscopy to infer elastic properties of soft tissues by extracting their resonance frequencies. However, the method to accurately obtain the elastic modulus from the resonance frequencies remains inconclusive. In this study, we report a method based on a multi-degree-of-freedom (MDOF) model to determine the Young's modulus of soft tissue samples from the measured resonance spectroscopy. Resonance frequencies of agar tissue phantoms with different elastic properties were obtained, and Young's modulus was calculated using the MDOF-based method. The result was validated by mechanical compression tests and finite element method simulations. The results show that the multi-degree-of-freedom (MDOF)-based method is capable of determining Young's modulus of soft tissue samples with various elasticities and dimensions. This study provides an opportunity to accurately assess the elastic properties of small-sized soft tissue samples.

Polymer-integrated optical fiber Fabry–Pérot interferometer with Vernier effect for the detection of myoglobin

Acute myocardial infarction (AMI) is the most severe manifestation of coronary artery disease and one of the leading causes of morbidity and mortality worldwide. The concentration of myoglobin (Mb) in serum has been regarded as an essential indicator for the early diagnosis of AMI. Developing a rapid, sensitive, and accurate Mb detection method is very important for the early diagnosis of AMI. This study reports a fiber optic biosensor based on polymer and Vernier effect composite sensitization for real-time detection of serum Mb concentration. The sensor is made of a Fabry–Pérot interferometer cascade tapered microfiber filled with photothermal material polydimethylsiloxane. Two interference structures with similar but unequal free spectral range are combined, and the superposition spectrum produces periodic interference fringes, forming a fiber sensor with a Vernier effect. By detecting the photothermal signal generated by the absorption of light by Mb, marker-free, specific detection can be achieved. The sensing device attained a sensitivity of 5.235 nm/(mg/L) in the 0.0001–10 mg/L concentration range. The linearity reached 0.9978, with a limit of detection of 3.82 ng/ml, which meets the sensitivity requirements for detecting Mb concentration in serum, and the detection time was less than 40 s, which has potential in the early diagnosis of related diseases.

Preparation and simulation of high-frequency lead-free NBBT/epoxy 1–3 piezoelectric composites with high electromechanical coupling characteristics

In this article, we design and fabricate (1 − x)Na0.5Bi0.5TiO3-xBaTiO3 single-crystal/epoxy 1–3 piezoelectric composites (NBBT 1–3 composites) with high coefficients of electromechanical coupling and demonstrate their considerable potential for use in high-frequency ultrasonic devices. We conducted finite element simulations on samples of the NBBT 1–3 composite to optimize their dimensional parameters. We used the cut-and-fill method to prepare an array of the NBBT-based 1–3 composite with a spacing of 20 μm between elements. It exhibited an exceptionally high coefficient of electromechanical coupling kt of 80.8%, with measured resonant and antiresonant frequencies of 11.6 and 18.5 MHz, respectively. Lead-free NBBT 1–3 composites that can deliver excellent performance are highly promising for use in medical applications of high-frequency ultrasound, especially for the brain–computer interface and intravascular ultrasound imaging.

Gradient-based optimization of spintronic devices

The optimization of physical parameters serves various purposes in device development, including in system identification and efficiency. Spin-torque oscillators have been experimentally and theoretically applied to neuromorphic computing, but their physical parameters are usually optimized via grid search procedures. In this paper, we propose a scheme to optimize the dynamics parameters of macrospin-type spin-torque oscillators using the gradient descent method with automatic differentiation. First, we numerically create dynamic data for teaching and tune the parameters to reproduce the dynamics. This approach can be applied to determine the correspondence between spin-torque oscillator simulations and experiments. Next, we solve an image recognition task with high accuracy by connecting a coupled system of spin-torque oscillators to the input and output layers and training all of them through gradient descent. Combining this approach with experimentation makes it possible to design an experimental setup and physical system to solve a task with high precision using a spin-torque oscillator.

Strain-induced Kramers–Weyl phase in III–V zinc blende systems

We present theoretical observations on the topological nature of strained III–V semiconductors. By k·p perturbation, it can be shown that the strain-engineered conduction band hosts a Kramers–Weyl node at the Γ point. It is theoretically shown that a curated strain can create and then tune the sign of the topological charge. Furthermore, we outline experimental methods for both the realization and detection of strain-induced topological phase transitions.

A highly integrated three-axis vector diamond quantum magnetometer with a compact electrical package

Diamond nitrogen-vacancy (NV) center has been widely studied as a high-sensitivity solid-state quantum sensor with a wide range of applications, including magnetometry, thermometry manometry, and chemical sensing. However, its application in practical scenarios remains challenging due to difficulties of component manufacturing, miniaturization, and integration for NV control and readout. Here, we demonstrate an all-electric driving diamond sensor fabricated using standard microfabrication processes and micro-assembly, achieving integration of five key components—laser diode, diamond, microwave antenna, long pass filter, and photodiode in a hermetically sealed package case, with dimensions of 2.72 cm3. The integrated diamond magnetometer achieved a magnetic sensitivity of 2.25 nT · Hz−1/2. Additionally, the inherent crystallographic axes of the diamond are used to simultaneously detect vector magnetic field signals. The design and fabrication process allows for wafer-level assembly, enabling low-cost mass-production and easy integration with peripheral circuits.

High-frequency magnetic properties of modified Cu–Ni 18H ferrites with low magnetic loss up to 6 GHz for 5G communications

Rapidly developing fifth-generation (5G) communications urgently require a ferrite material with high permeability and low magnetic loss in frequency bands up to 6 GHz. However, none of the present magnetic materials are capable of meeting the requirements of 5G communications because their magnetic properties deteriorate drastically when approaching GHz frequencies. Herein, we report the high-frequency magnetic properties of the modified Ba5Cu2-xNixTi3Fe12O31 (Cu–Ni 18H) ferrites, achieving a relatively high permeability of 1.6 and a low magnetic loss of 0.05 at 6 GHz, which is much better than previous reports. Such excellent performance is attributed to the expanded mono-domain critical size and reduced damping of magnetic moment precession. Moreover, deploying Cu–Ni 18H ferrites as a substrate on a patch antenna working at 6 GHz can reduce the antenna dimensions to 35% of traditional commercial materials. The present work provides a proven and promising candidate material for 5G communications and expands the research landscape for the high-frequency magnetic properties of microwave ferrites.

Retainable large magnetoelectric coupling in BiFeO3@CoFe2O4 core-shell nanoparticle embedded P(VDF-TrFE) matrix

Flexible magnetoelectric composite devices have exceptional features and potential in peculiar scenes. However, maintaining the magnetoelectric response under extreme bending conditions remains a challenge. Polyvinylidene fluoride-based polymers, possessing favorable piezoelectric properties and high flexibility, provide a viable solution for magnetoelectric composites. This work constructed multiferroic core-shell nanoparticle-embedded flexible membranes and achieved a retainable high magnetoelectric (ME) coupling coefficient in the curved composite materials. A maximum ME coefficient of 74 mV cm−1 Oe−1 was obtained, far higher than the 0–3 ME nanocomposites reported thus far. The ME coefficient can be maintained above 40 mV cm−1 Oe−1 when the bending angle is less than 90° and expresses high sensitivity within the Hdc range of 100–2400 Oe. Based on crystal structure analysis and phase-field simulation, the synergy magnetoelectric effects accounting for the multiferroic core-shell nanoparticles, copolymer matrix, and magnetic cores contribute to the promoted ME coefficient in the flexible composites. This work provides a feasible pathway for next-generation flexible devices in the wearable and portable fields.

Realizing sub-6-nm-channel high-performance spin field-effect transistors in lateral Sc2CHO/Sc2CHF/Sc2CHO heterojunctions

In this work, nanoscale spin field-effect transistors (spin-FETs) based on lateral heterojunctions composed of two-dimensional (2D) ferromagnetic half-metallic Sc2CHO electrodes and nonmagnetic semiconductor Sc2CHF channel are theoretically designed. The channel lengths (Lc) for investigated nanoscale spin-FETs are shorter than 6 nm. The spin transport properties of these nanoscale spin-FETs are subsequently studied by using the nonequilibrium Green's function method in combination with density functional theory. Due to the strong electronic coupling at the interfaces between electrodes and channel, p-type Ohmic contacts are obtained for spin down. Calculations reveal that at very-low temperature, the spin injection efficiency can reach 100%, and the magnetoresistance ratio (MR) is generally larger than 109% for these nanoscale spin-FETs. Very-low subthreshold swing (SS) values below 60 mV/dec are found for spin-FETs with Lc≥ 4.05 nm, and the lowest SS value is 39 mV/dec for the spin-FET with Lc=5.75 nm. At room temperature, the values of MR exceed 106%, and the corresponding SS values are below 92 mV/dec with a minimum SS of 82 mV/dec, still demonstrating high performance for designed nanoscale spin-FETs. Our study provides valuable insights into the design of high-performance nanoscale spin-FET devices based on 2D MXenes.