Negative to Positive Crossover of Magnetoresistance in Layered WS2 with Ohmic Contact

The discovery of graphene has ignited intensive investigation on two dimensional (2D) materials. Among them, transition metal dichalcogenide (TMDC), a typical representative, attracts much attention due to the excellent performance in field effect transistor (FET) related measurements and applications. Particularly, when TMDC eventually reaches few-layer dimension, a wide range of electronic and optical properties, in striking contrast to bulk samples, are detected. In this Letter, we synthesized single crystalline WS2 nanoflakes by physical vapor deposition (PVD) method and carried out a series of transport measurements of contact resistance and magnetoresistance. Focused ion beam (FIB) technology was applied to deposit Pt electrodes on WS2 flakes. Different from the electron beam lithography (EBL) fabricated electrodes, FIB-deposited leads exhibited ohmic contact, resolving the dilemma of Schottky barrier. Furthermore, a temperature-modulated negative-to-positive transition of magnetoresistance (MR) associated with a crossover of carrier type at similar temperature was demonstrated. Our work offers a pathway to optimize the contact for TMDC and reveals the magnetoresistance characteristics of WS2 flakes, which may stimulate further studies on TMDC and corresponding potential electronic and optoelectronic applications

The Research on personalized Access Control Scheme Based on User Portrait

The arrival of the era of big data has made data become an important economic asset, and its security issues have gradually been valued by people. The big data platform usually face many users, traditional access control techniques cannot effectively evaluate whether users are in a trusted state, thus, this paper introduced the concept and method of user portrait and proposed a personalized access control scheme by analyzing the log of hadoop system, tracking user access behavior trajectory, which can protect data security by reasonable authorization

Symmetric Key Structural Residues in Symmetric Proteins with Beta-Trefoil Fold

To understand how symmetric structures of many proteins are formed from asymmetric sequences, the proteins with two repeated beta-trefoil domains in Plant Cytotoxin B-chain family and all presently known beta-trefoil proteins are analyzed by structure-based multi-sequence alignments. The results show that all these proteins have similar key structural residues that are distributed symmetrically in their structures. These symmetric key structural residues are further analyzed in terms of inter-residues interaction numbers and B-factors. It is found that they can be distinguished from other residues and have significant propensities for structural framework. This indicates that these key structural residues may conduct the formation of symmetric structures although the sequences are asymmetric

An Automatic Tool for Partial Discharge De-noising via Short Time Fourier Transform and Matrix Factorization

This paper develops a fully automatic tool for the denoising of partial discharge (PD) signals occurring in electrical power networks and recorded in on-site measurements. The proposed method is based on the spectral decomposition of the PD measured signal via the joint application of the short-time Fourier transform and the singular value decomposition. The estimated noiseless signal is reconstructed via a clever selection of the dominant contributions, which allows us to filter out the different spurious components, including the white noise and the discrete spectrum noise. The method offers a viable solution which can be easily integrated within the measurement apparatus, with unavoidable beneficial effects in the detection of important parameters of the signal for PD localization. The performance of the proposed tool is first demonstrated on a synthetic test signal and then it is applied to real measured data. A cross comparison of the proposed method and other state-of-the-art alternatives is included in the study

Writing and reading magnetization states via strain in Fe3GaTe2/h-BN/MnBi2Te4 junction

Writing and reading of magnetization states via mechanical strain are crucial for the development of ultralow-power spintronic devices. In this study, a van der Waals magnetic tunnel junction (vdW MTJ) of Fe3GaTe2/h-BN/MnBi2Te4 is constructed to explore the magnetization reversal under in-plane biaxial strains. Interestingly, the interlayer magnetic coupling of devices can be tuned to ferromagnetic and antiferromagnetic states by tensile and compressive strains, respectively. The various magnetic couplings on applied strains are analyzed using the superexchange theory. Importantly, the interlayer coupling nearly vanishes after removing external strains, ensuring the nonvolatility of magnetization reversal, resulting in the nonvolatile writing of magnetization states in the present vdW MTJ. Moreover, the tunneling magnetoresistance ratio of the device is up to −5745%, which remains −1478% even with −2% strain, showing great potential for reading the magnetization states. Therefore, this work provides an alternate avenue to write and read magnetization states in one vdW MTJ under biaxial strains

Uncertainty Quantification of Geo-Magnetically Induced Currents in UHV Power Grid

Geo-magnetically induced currents (GICs) have attracted more attention since many Ultra-High Voltage (UHV) transmission lines have been built, or are going to be built in the world. However, when calculating GICs based on the classical model, some input parameters, such as the earth conductivity and dc resistances of the grid, are uncertain or very hard to be determined in advance. Taking this into account, the uncertainty quantification (UQ) model of the geo-electric fields and GICs is proposed in this paper. The UQ of the maximums of the geo-electric fields and GICs during storms is carried out based on the polynomial chaos (PC) method. The results of the UHV grid, 1000 kV Sanhua Grid, were presented and compared to the Monte Carlo method. The total Sobol indices are calculated by using the PC expansion coefficients. The sensitivities of geo-electric fields and GICs to the input variables are analyzed based on the total Sobol indices. Results show that the GICs and geo-electric fields can be effectively simulated by the proposed model, which may offer a better understanding of the sensitivities to input uncertain variables and further give a reasonable evaluation of the geomagnetic threat to the grid