The scalable preparation of two-dimensional hexagonal boron nitride (h-BN) is essential for practical applications. Despite intense research in this area, high-yield production of two-dimensional ...h-BN with large-size and high solubility remains a key challenge. In the present work, we propose a scalable exfoliation process for hydroxyl-functionalized BN nanoplatelets (OH-BNNPs) by a simple ball milling of BN powders in the presence of sodium hydroxide via the synergetic effect of chemical peeling and mechanical shear forces. The hydroxide-assisted ball milling process results in relatively large flakes with an average size of 1.5 μm with little damage to the in-plane structure of the OH-BNNP and high yields of 18%. The resultant OH-BNNP samples can be redispersed in various solvents and form stable dispersions that can be used for multiple purposes. The incorporation of the BNNPs into the polyethylene matrix effectively enhanced the barrier properties of the polyethylene due to increased tortuosity of the diffusion path of the gas molecules. Hydroxide-assisted ball milling process can thus provide simple and efficient approaches to scalable preparation of large-size and highly soluble BNNPs. Moreover, this exfoliation process is not only easily scalable but also applicable to other layered materials.
In this paper, we propose an angle- and polarization-insensitive metamaterial absorber. We design a metamaterial unit cell that is based on a split ring cross resonator (SRCR). We observe that the ...absorption frequency and absorption ratio are insensitive to incident angles when a via array surrounds the SRR. We demonstrate the effect of the via array using full-wave simulations by comparing the absorptivity of the SRCR with and without the via array. Because of the symmetric geometry, we also realize polarization insensitivity. We build the proposed absorber on a printed-circuit-board with 30 × 30 unit cells, and we demonstrate its performance experimentally in free space. Under normal incidence, the fabricated absorber shows 99.6% absorptivity at 11.3 GHz for all polarization angles, while for oblique incidence, the fabricated absorber maintains an absorptivity higher than 90% for incident angles up to 70° and 60° for transverse magnetic (TM) and transverse electric (TE) modes, respectively.
In this paper, a novel flexible tunable metasurface absorber is proposed for large-scale remote ethanol sensor applications. The proposed metasurface absorber consists of periodic split-ring-cross ...resonators (SRCRs) and microfluidic channels. The SRCR patterns are inkjet-printed on paper using silver nanoparticle inks. The microfluidic channels are laser-etched on polydimethylsiloxane (PDMS) material. The proposed absorber can detect changes in the effective permittivity for different liquids. Therefore, the absorber can be used for a remote chemical sensor by detecting changes in the resonant frequencies. The performance of the proposed absorber is demonstrated with full-wave simulation and measurement results. The experimental results show the resonant frequency increases from 8.9 GHz to 10.04 GHz when the concentration of ethanol is changed from 0% to 100%. In addition, the proposed absorber shows linear frequency shift from 20% to 80% of the different concentrations of ethanol.
In this study, the novel electronically switchable broadband metamaterial absorber, using a PIN diode, is proposed. The unit cell of the absorber was designed with a Jerusalem-cross resonator and an ...additive ring structure, based on the FR-4 dielectric substrate. Chip resistors and PIN diodes were used to provide both a broadband characteristic and a switching capability. To satisfy the polarization insensitivity, the unit cell was designed as a symmetrical structure, including the DC bias network, electronic devices, and conductor patterns. The performance of the proposed absorber was verified using full-wave simulation and measurements. When the PIN diode was in the ON state, the proposed absorber had a 90% absorption bandwidth from 8.45-9.3 GHz. Moreover, when the PIN diode was in the OFF state, the 90% absorption bandwidth was 9.2-10.45 GHz. Therefore, the absorption band was successfully switched between the low-frequency band and the high-frequency band as the PIN diode was switched between the ON and OFF states. Furthermore, the unit cell of the proposed absorber was designed as a symmetrical structure, and its performance showed insensitivity with respect to the polarization angle.
In this paper, an incident angle- and polarization-insensitive metamaterial absorber is proposed for X-band applications. A unit cell of the proposed absorber has a square patch at the centre and ...four circular sectors are rotated around the square patch. The vertically and horizontally symmetric structure of the unit cell enables polarization-insensitivity. The circular sector of the unit cell enables an angle-insensitivity. The performances of the proposed absorber are demonstrated with a full-wave simulation and measurements. The angular sensitivity is studied at different inner angles of the circular sector. When the inner angle of the circular sector is 90°, the simulated absorptivity is higher than 90%, and the frequency variation is less than 0.96% for incident angles up to 70°. The measured absorptivity at 10.44 GHz is close to 100% for all the polarization angles under normal incidence. When the incident angles are varied from 0°- 60°, the measured absorptivity is maintained above 90% for both the transverse electric (TE) and the transverse magnetic (TM) modes.
The Burkholderia cepacia complex (Bcc) consists of opportunistic pathogens known to cause pneumonia in immunocompromised individuals, especially those with cystic fibrosis. Treating Bcc pneumonia is ...challenging due to the pathogens' high multidrug resistance. Therefore, inhalation therapy with tobramycin powder, which can achieve high antibiotic concentrations in the lungs, is a promising treatment option. In this study, we investigated potential mechanisms that could compromise the effectiveness of tobramycin therapy. By selecting for B. cenocepacia survivors against tobramycin, we identified three spontaneous mutations that disrupt a gene encoding a key enzyme in the biosynthesis of cobalamin (Vitamin B12). This disruption may affect the production of succinyl-CoA by methylmalonyl-CoA mutase, which requires adenosylcobalamin as a cofactor. The depletion of cellular succinyl-CoA may impact the tricarboxylic acid (TCA) cycle, which becomes metabolically overloaded upon exposure to tobramycin. Consequently, the mutants exhibited significantly reduced reactive oxygen species (ROS) production. Both the wild-type and mutants showed tolerance to tobramycin and various other bactericidal antibiotics under microaerobic conditions. This suggests that compromised ROS-mediated killing, due to the impacted TCA cycle, underlies the mutants’ tolerance to bactericidal antibiotics. The importance of ROS-mediated killing and the potential emergence of mutants that evade it through the depletion of cobalamin (Vitamin B12) provide valuable insights for developing strategies to enhance antibiotic treatments of Bcc pneumonia. KCI Citation Count: 0
Increase in conductivity and mechanical properties of a carbon nanotube (CNT) fiber inspired by mussel‐adhesion chemistry is described. Infiltration of polydopamine into an as‐drawn CNT fiber ...followed by pyrolysis results in a direct insulation‐to‐conduction transformation of poly(dopamine) into pyrolyzed‐poly(dopamine) (py‐PDA), retaining the intrinsic adhesive function of catecholamine. The py‐PDA enhances both the electrical conductivity and the mechanical strength of the CNT fibers.
A stretchable metamaterial absorber is proposed in this study. The stretchability was achieved by liquid metal and polydimethylsiloxane (PDMS). To inject liquid metal, microfluidic channels were ...fabricated using PDMS powers and microfluidic-channel frames, which were built using a three-dimensional printer. A top conductive pattern and ground plane were designed after considering the easy injection of liquid metal. The proposed metamaterial absorber comprises three layers of PDMS substrate. The top layer is for the top conductive pattern, and the bottom layer is for the meandered ground plane. Flat PDMS layers were inserted between the top and bottom PDMS layers. The measured absorptivity of the fabricated absorber was 97.8% at 18.5 GHz, and the absorption frequency increased from 18.5 to 18.65 GHz as the absorber was stretched from its original length (5.2 cm) to 6.4 cm.
This paper presents a new type of flicker noise and mismatch up-converting active mixer with odd cascode switching pairs that require lower switching frequencies. This requirement relaxes the local ...oscillator (LO) switching speed, which mitigates the effect of flicker noise and IM2 due to parasitic capacitances. A frequency-scalable LO generator is designed to eliminate delay adjustments between the slave LO and master LO signals for multiband operations, and a high crossing master LO driving scheme is also presented for IIP3 improvement for low supply operations. Fabricated using a 0.11 μm CMOS process at a 1.2 V supply, the proposed mixer achieves <; 4 kHz flicker noise corner, 9.4 dBm IIP3 with a 7.2 dB conversion gain, and> 60 dBm IIP2 at an effective LO frequency of 1.8 GHz.
The influence of surface modifications on the mechanical properties of epoxy‐hexagonal boron nitride nanoflake (BNNF) nanocomposites is investigated. Homogeneous distributions of boron nitride ...nanoflakes in a polymer matrix, preserving intrinsic material properties of boron nitride nanoflakes, is the key to successful composite applications. Here, a method is suggested to obtain noncovalently functionalized BNNFs with 1‐pyrenebutyric acid (PBA) molecules and to synthesize epoxy–BNNF nanocomposites with enhanced mechanical properties. The incorporation of noncovalently functionalized BNNFs into epoxy resin yields an elastic modulus of 3.34 GPa, and 71.9 MPa ultimate tensile strength at 0.3 wt%. The toughening enhancement is as high as 107% compared to the value of neat epoxy. The creep strain and the creep compliance of the noncovalently functionalized BNNF nanocomposite is significantly less than the neat epoxy and the nonfunctionalized BNNF nanocomposite. Noncovalent functionalization of BNNFs is effective to increase mechanical properties by strong affinity between the fillers and the matrix.
The influence of surface modifications on the mechanical properties of epoxy‐hexagonal boron nitride nanoflake (BNNF) nanocomposites is investigated. The BNNFs chemically surface modified by noncovalent functionalization are prohibited from stacking and aggregation, resulted in homogeneous dispersions in the epoxy matrix with strong interfacial interactions. The incorporation of noncovalently functionalized BNNFs into epoxy resin yields outstanding strength and toughness at low BNNF loadings.
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