Fluorinated carbon materials (FCMs) have received significant attention, because of their exceptional stability, which is associated with the strong C‐F bonding, the strongest among carbon single ...bonds. However, the fluorination of carbon materials requires extremely toxic and moisture‐sensitive reagents, which makes it inapplicable for practical uses. Here, a straightforward and relatively safe method are reported for the scalable synthesis of FCMs, by mechanochemical depolymerization of polytetrafluoroethylene (PTFE) and fragmentation of graphite. The resultant FCMs are evaluated as anode materials for lithium‐ion batteries (LIBs). An optimized FCM delivered capacities as high as 951.6 and 329.3 mAh g −1 at 0.05 and 10 A g −1, respectively. It also demonstrated capacity retention as high as 76.6% even after 1000 cycles at 2.0 A g −1.
Fluorinated carbon materials (FCMs) w ere safely produced by a solid‐state reaction between PTFE and graphite using mechanochemical ball‐milling. The FCMs are tested as anode materials for lithium‐ion batteries and demonstrate a high lithium‐ion storage capacity with outstanding stability.
We examine whether equity-linked private securities offerings are used as a mechanism for tunneling among firms that belong to a Korean chaebol. We find that chaebol issuers involved in intragroup ...deals set the offering prices to benefit their controlling shareholders. We also find that chaebol issuers (member acquirers) realize an 8.8% (5.8%) higher (lower) announcement return than do other types of issuers (acquirers) if they sell private securities at a premium to other member firms, and if the controlling shareholders receive positive net gains from equity ownership in issuers and acquirers. These results are consistent with tunneling within business groups.
Finite-difference time domain (FDTD) has been widely used to analyze electromagnetic wave interaction with dispersive media. It is of great necessity to incorporate a dispersion model into FDTD ...formulation for electromagnetic wave analysis of dispersive media. Recently, it was reported that the modified Lorentz model can cover Debye, Drude, Lorentz, critical point, and quadratic complex rational function models. In this work, it is illustrated that the modified Lorentz model can also cover the complex-conjugate pole-residue model which is one of the most popular dispersion models. Modified Lorentz-based dispersive FDTD has not been thoroughly studied, especially for numerical aspects. In this work, we investigate auxiliary differential equation (ADE)-FDTD formulations for the modified Lorentz model based on electric flux density (D), current (J), or polarization (P). We perform a comprehensive study on memory requirement, the number of arithmetic operations, numerical stability, and numerical permittivity for the above three ADE-FDTD formulations. In addition, the bilinear transformation (BT) is incorporated into modified Lorentz-based FDTD formulations and it will be shown that the utilization of the BT can lead to better performance in terms of numerical stability and numerical accuracy. Numerical examples are used to demonstrate our work.
The complex-conjugate pole-residue (CCPR) model has been popularly adopted because CCPR-finite-difference time domain (FDTD) can reduce the memory requirement with the help of complex conjugate ...property of auxiliary variables. To fully utilize CCPR-FDTD, it is of great necessity to investigate its numerical stability since the FDTD method is conditionally stable. Nonetheless, the numerical stability conditions of CCPR-FDTD have not been studied because its derivation is not straightforward. In this communication, the numerical stability conditions of CCPR-FDTD are systematically derived by combining the von Neumann method with Routh-Hurwitz criterion. It is found that the numerical stability conditions of CCPR-FDTD are the same as those of the modified Lorentz-FDTD with bilinear transform. Moreover, the numerical accuracy of CCPR-FDTD is studied, and numerical examples are employed to validate this work.
For synthetic aperture radar (SAR) imaging, the irregular loss of received data and the non-uniformly under sampling yield the SAR azimuth ambiguity (SAA) resulting in the degradation in image ...quality. To address this issue, the incremental SAR imaging approach based on the estimation of sensing dictionary matrix in the pursuit of sparsity is presented in this paper. Several beneficial contributions are included in the proposed method. First, the SAA reduction achievable in the proposed method is considerably improved more than that of the conventional compressive sensing (CS) based approach in terms of the image quality and computational efficiency. Second, we established the signal parameterization scheme which is divided into coarse and fine search steps to estimate the sensing matrix for SAR image restoration via signal model reconstruction. Third, an incremental imaging approach is devised to overcome the drawback of the conventional CS-based approach which is not sufficiently good leading to limited SAA reduction performance under the non-sparse SAR image. These contributions are verified using numerical simulations and experimental results.
In synthetic aperture radar (SAR) imaging, perturbations in the motion of the moving platform induce an undesired phase error due to imprecise knowledge of the motion, which results in the ...significant degradations in the quality of SAR images. In this paper, we present an efficient compressive sensing (CS)-based SAR imaging integrated with autofocus technique. The novel approach is based on an estimation-theoretic l 1 -norm-based approach coupled with Tikhonov-type regularization which combines an observation model of the SAR image formation process with the CS reconstruction problem of the SAR image regarding the sparsity. The optimization problem derived by considering spatially variant phase errors along azimuth domain and the dataset sampled at low rates can be effectively addressed by an efficient iterative method, wherein each iteration both SAR image formation and phase error correction are simultaneously carried out. The simulations and experimental results are presented to validate the effectiveness of the proposed method in terms of reliable image recovery and efficient computational complexity.
Novel carbon‐based microporous nanoplates containing numerous heteroatoms (H‐CMNs) are fabricated from regenerated silk fibroin by the carbonization and activation of KOH. The H‐CMNs exhibit superior ...electrochemical performance, displaying a specific capacitance of 264 F/g in aqueous electrolytes, a specific energy of 133 Wh/kg, a specific power of 217 kW/kg, and a stable cycle life over 10000 cycles.
In the problem Mix(H) one is given a graph G and must decide if the Hom-graph Hom(G,H) is connected. We show that if H is a triangle-free reflexive graph with at least one cycle, Mix(H) is ...coNP-complete. The main part of this is a reduction to the problem NonFlat(H) for a simplicial complex H, in which one is given a simplicial complex G and must decide if there are any simplicial maps ϕ from G to H under which some 1-cycles of G maps to homologically nontrivial cycle of H. We show that for any reflexive graph H, if the clique complex H of H has a free, nontrivial homology group H1(H), then NonFlat(H) is NP-complete.
Chiral metamaterials comprise a promising platform for advanced optoelectronic and biomedical applications. However, conventional fabrication via lithography is limited by its complexity and high ...cost. Herein, the lithography‐free fabrication of terahertz chiral metamaterials and their enhancement for sensing the chirality of biocrystal enantiomers is presented. Chiral Au microstrip patterns (CHAMs) in a saw‐tooth shape are fabricated by combining two‐step buckling processes and glancing‐angle deposition. Non‐superimposable geometric chirality is achieved by controlling the tilt angle between the asymmetric and biaxial strain axes and the selective area deposition of the Au layers by using the shadow effect. The manufactured chiral metamaterials show mirror‐shaped terahertz circular dichroism (TCD) signals in the range of 0.2–2.5 THz. Coupling of the induced electric and magnetic dipoles to the chiral‐shaped Au surfaces results in effective optical chirality enhancement. Finite‐difference time‐domain computational simulations reveal the homogeneous distribution of optical chirality with an absolute maximum of 2.24 in the near field. Summing the TCD signals for enantiomeric cystine biocrystals onto the chiral metamaterials shows an ≈7‐fold amplification in magnitude. This enhancement can be attributed to the synergistic effects of superchiral field enhancement and the electromagnetic resonance between the CHAMs and biocrystals.
3D chiral Au microstrip patterns are fabricated by combining a two‐step buckling process and glancing‐angle deposition. Terahertz circular dichroism measurements with enantiomeric biocrystals show a significant increase in peak intensity sevenfold greater than the control. This is attributed to the synergistic effects of the superchiral field and electromagnetically induced resonances between the chiral metamaterials and biocrystals.
The half-bridge (HB) LLC converter is one of the most attractive dc-dc converters for medium power supplies due to its soft switching capability. However, its conversion efficiency is considerably ...degraded in wide-link-voltage applications because of a small magnetizing inductance and wide switching frequency variation for a high voltage gain. In this paper, a boost power factor correction (PFC) stage, which can also play an important role during the hold-up time, is proposed for a high-efficiency HB LLC converter. In the proposed PFC stage, the boost PFC converter can be effectively utilized as a HB converter by replacing a boost diode and inductor with a synchronous switch and transformer, respectively. After the ac line is lost, the proposed PFC stage can operate as the HB converter and regulate the output voltage instead of the HB LLC converter. Thus, it enables the HB LLC converter to be designed with a large magnetizing inductance and narrow switching frequency variation. As a result, the proposed PFC stage can enhance the overall efficiency of the PSU by improving the efficiency of the HB LLC converter. To confirm the validity of this paper, a prototype with 180-264-Vrms ac line, 250-400-V link voltage, and 48 V/480 W output is tested.
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