Mantle flow underneath the South China Sea revealed by seismic anisotropy.

It has long been established that plastic flow in the asthenosphere interacts constantly with the overlying lithosphere and plays a pivotal role in controlling the occurrence of geohazards such as earthquakes and volcanic eruptions. Unfortunately, accurately characterizing the direction and lateral extents of the mantle flow field is notoriously difficult, especially in oceanic areas where deployment of ocean bottom seismometers (OBSs) is expensive and thus rare. In this study, by applying shear wave splitting analyses to a dataset recorded by an OBS array that we deployed between mid-2019 and mid-2020 in the South China Sea (SCS), we show that the dominant mantle flow field has a NNW-SSE orientation, which can be attributed to mantle flow extruded from the Tibetan Plateau by the ongoing Indian-Eurasian collision. In addition, the results suggest that E-W oriented flow fields observed in South China and the Indochina Peninsula do not extend to the central SCS.

A Finite-Time Sliding-Mode Controller Based on the Disturbance Observer and Neural Network for Hysteretic Systems with Application in Piezoelectric Actuators.

Piezoelectric actuators (PEAs) have the benefits of a high-resolution and high-frequency response and are widely applied in the field of micro-/nano-high-precision positioning. However, PEAs undergo nonlinear hysteresis between input voltage and output displacement, owing to the properties of materials. In addition, the input frequency can also influence the hysteresis response of PEAs. Research on tracking the control of PEAs by using various adaptive controllers has been a hot topic. This paper presents a finite-time sliding-mode controller (SMC) based on the disturbance observer (DOB) and a radial basis function (RBF) neural network (NN) (RBF-NN). RBF-NN is used to replace the hysteresis model of the dynamic system, and a novel finite-time adaptive DOB is proposed to estimate the disturbances of the system. By using RBF-NN, it is no longer necessary to establish the hysteresis model. The proposed DOB does not rely on any priori knowledge of disturbances and has a simple structure. All the solutions of closed-loop systems are practical finite-time-stable, and tracking errors can converge to a small neighborhood of zero in a finite time. The proposed control method was compiled in C language in the VC++ environment. A series of comparative experiments were conducted on a platform of a commercial PEA to validate the method. According to the experimental results of the sinusoidal and triangular trajectories under the frequencies of 1, 50, 100, and 200 Hz, the proposed control method is feasible and effective in improving the tracking control accuracy of the PEA platform.

Luminescence properties and energy transfer investigations of Ce3+ and Tb3+ co-doped NaCaGaSi2O7 phosphors.

The NaCaGaSi2O7:Ce3+、NaCaGaSi2O7:Tb3+ and NaCaGaSi2O7:Ce3+/Tb3+ phosphors were synthesized under a weak reducing atmosphere by the traditional high temperature solid state reaction method. The synthesized phosphors were characterized by X-ray diffraction (XRD), fluorescent decay times, photoluminescence (PL) emission and excitation spectra including temperature-dependent PL properties. The effects of Ce3+ singly doped and Ce3+/Tb3+ co-doped concentrations on the structure, luminescence properties and energy transfer of NaCaGaSi2O7 phosphors were studied in detail. The results indicated that the energy transfers between Ce3+ and Tb3+ in the host occurred mainly via a dipole-dipole mechanism, and the critical distances of the ion pairs (Rc) were calculated by the quenching concentration method and spectral overlap method. The Ce3+ emission intensity and decay lifetimes decrease with the raise of Tb3+ concentration in NaCaGaSi2O7:Ce3+/Tb3+ samples. The above results indicate that NaCaGaSi2O7:Ce3+/Tb3+ can be a candidate as a host material for solid-state lighting and display fields.

Early biomarkers for post-stroke cognitive impairment.

The aim of this study was to investigate whether some biomarkers could predict cognitive impairment after stroke. One hundred fifty-two first-ever stroke patients were recruited within 6-72 h after the onset of symptoms. Blood was drawn within 1 h after admission for determining biomarkers. Cognitive function was assayed 2 weeks after stroke. The patients were divided into four groups: stroke, vascular cognitive impairment with no dementia (VCIND), vascular dementia (VaD), and mixed dementia (MD). Forty healthy subjects were used as controls. The results indicated that lower soluble receptor levels for advanced glycation end products (sRAGE) and higher ß-secretase enzyme (BACE1) and neprilysin (NEP) levels were found in the VCIND, VaD, and MD groups. In addition, the percentages of ε3/ε4 genotypes and ε4 alleles in the VCIND, VaD, and MD groups were higher than in the stroke group. Correlation analysis determined that sRAGE, BACE1, and NEP were significantly related to the results of neuropsychological assessments. Logistic regression analysis, however, suggested that only sRAGE and BACE1 changed ahead of cognitive impairment after stroke. In conclusion, only BACE1 and sRAGE, not NEP or APOE genotypes, may be biomarkers diagnosing post-stroke cognitive impairment.