Jiaqi Zhang

Two collinear femtosecond laser pulses, one at wavelength of $800\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and the other at $400\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ (double frequency), simultaneously irradiated the surface of ZnSe crystal, which resulted in regular nanograting with period of $180\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ on the whole ablation area. We attribute the formation of the nanograting to be due to the interference between the surface scattered wave of $800\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ lasers and the $400\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ light. The period of the nanograting $\ensuremath{\Lambda}$ is about $\ensuremath{\lambda}∕2n$, where $n$ is refractive index of the sample, and $\ensuremath{\lambda}$, the laser wavelength. This mechanism is supported by observation of rotation of the nanograting with the polarization of $400\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ light, and by the dependence of $\ensuremath{\Lambda}\ensuremath{\sim}\ensuremath{\lambda}$ of the nanoripples on the surface of semiconductors and dielectrics.

In this report, a voltammetric sensor for simultaneous determination of hydroquinone (HQ) and catechol (CC) was developed at a glassy carbon electrode modified with graphene (GR/GCE). The separation of oxidation and reduction peak (ΔE) is decreased from 281 to 31 mV for HQ and from 250 to 26 mV for CC at GR/GCE, respectively. Separation of the oxidation peak potentials for HQ and CC was about 112 mV in 0.10 M acetate buffer solution (pH 4.5), and the anodic currents for the oxidation of both HQ and CC are greatly increased at GR/GCE, which makes it suitable for simultaneous determination of these compounds. Under the optimized condition, the anodic peak current of HQ is linear with the concentration of HQ from 1 × 10−6 to 5 × 10−5 M in the presence of 5 × 10−5 M CC. A detection limit of 1.5 × 10−8 M (S/N = 3) can be achieved. At the same time, the anodic current of CC is linear with the concentration of CC from 1 × 10−6 to 5 × 10−5 M with a detection limit of 1.0 × 10−8 M (S/N = 3) in the presence of 5 × 10−5 M HQ. The proposed sensor was successfully applied to the simultaneous determination of HQ and CC in tap water, and the results are satisfactory.

Abstract Disentangling the limitations of O-O bond activation and OH* site-blocking effects on Pt sites is key to improving the intrinsic activity and stability of low-Pt catalysts for the oxygen reduction reaction (ORR). Herein, we integrate of PtFe alloy nanocrystals on a single-atom Fe-N-C substrate (PtFe@Fe SAs -N-C) and further construct a ferromagnetic platform to investigate the regulation behavior of the spin occupancy state of the Pt d -orbital in the ORR. PtFe@Fe SAs -N-C delivers a mass activity of 0.75 A mg Pt −1 at 0.9 V and a peak power density of 1240 mW cm −2 in the fuel-cell, outperforming the commercial Pt/C catalyst, and a mass activity retention of 97%, with no noticeable current drop at 0.6 V for more than 220 h, is attained. Operando spectroelectrochemistry decodes the orbital interaction mechanism between the active center and reaction intermediates. The Pt dz 2 orbital occupation state is regulated to t 2g 6 e g 3 by spin-charge injection, suppressing the OH* site-blocking effect and effectively inhibiting H 2 O 2 production. This work provides valuable insights into designing high-performance and low-Pt catalysts via spintronics-level engineering.

Jamming and spoofing are the two main types of intentional interference for global navigation satellite system (GNSS) receivers. Due to the entirely different signal characteristics they have, a few techniques can deal with them simultaneously. This paper proposes a two-stage interference suppression scheme based on antenna arrays, which can detect and mitigate jamming and spoofing before the despreading of GNSS receivers. First, a subspace projection was adopted to eliminate the high-power jamming signals. The output signal is still a multi-dimensional vector so that the spatial processing technique can be used in the next stage. Then, the cyclostationarity of GNSS signals were fully excavated to reduce or even remove the noise component in the spatial correlation matrix. Thus, the signal subspace, including information of the power and the directions-of-arrival (DOAs) of the GNSS signals, can be obtained. Next, a novel cyclic correlation eigenvalue test (CCET) algorithm was proposed to detect the presence of a spoofing attack, and the cyclic music signal classification (Cyclic MUSIC) algorithm was employed to estimate the DOAs of all the navigation signals. Finally, this study employed a subspace projection again to eliminate the spoofing signals and provide a higher gain for authentic satellite signals through beamforming. All the operations were performed on the raw digital baseband signal so that they did not introduce additional computational complexity to the GNSS receiver. The simulation results show that the proposed scheme not only suppresses jamming and spoofing effectively but also maximizes the power of the authentic signals. Nonetheless, the estimated DOA of spoofing signals may be helpful for the interference source positioning in some applications.