Using polarized optical and magneto-optical spectroscopy, we have demonstrated universal aspects of electrodynamics associated with Dirac nodal-lines. We investigated anisotropic electrodynamics of NbAs2 where the spin-orbit interaction triggers energy gaps along the nodal-lines, which manifest as sharp steps in the optical conductivity spectra. We show experimentally and theoretically that shifted 2D Dirac nodal-lines feature linear scaling σ1(ω) ∼ ω, similar to 3D nodal-points. Massive Dirac nature of the nodal-lines are confirmed by magneto-optical data, which may also be indicative of theoretically predicted surface states. Optical data also offer a natural explanation for the giant magneto-resistance in NbAs2. *
With the rapid growth in wearable electronics sensing devices, flexible sensing devices that monitor the human body have shown great promise in personalized healthcare. In the study, high-quality GaN pn junction microwire arrays with different aspect ratios and large-area uniformity are fabricated through an easy, repeatable fabrication process. The piezoelectric coefficient (d 33 ) of GaN pn junction microwire arrays increases from 7.23 to 14.46 pm V −1 with the increasing of the aspect ratio, which is several times higher than that of GaN bulk material. Furthermore, flexible ultrasensitive strain sensor based on GaN microwires with the highest d 33 is demonstrated to achieve the maximum open circuit voltage of 10.4 V, and presents excellent durability with stable output signals over 10 000 cycles with a response time of 50 ms. As a flexible and wearable sensor attached to the human skin, the GaN microwire pn junction arrays with such a high degree of uniformity can precisely monitor subtle human pulse and motions, which show great promise in future personalized healthcare.The piezoresistive strain sensors are unquestionably promising candidates for wearable and real-time human motiondetecting devices, [15,16] and they can be sensitive enough for even 10 nm vibration,  but the piezoelectric sensors are more prospective for self-powered devices owing to the piezoelectric effect of materials, defined as the occurrence of polarization when the material is subjected to external stress as a result of the separation of the positive and negative gravity centers of the molecules. Lead zirconate titanate (PZT) and polyvinylidene fluoride (PVDF) are the most commonly used piezoelectric mediums for piezoelectric sensors due to their high piezoelectric coefficients (d 33 ).  However, the toxic lead component in PZT and the high impedance of PVDF have limited their applications in wearable piezoelectric devices. [22,23] In this regard, semiconductor-based piezoelectric strain sensors represented by zinc oxide (ZnO) and GaN have been extensively studied as a result of their mechanical and chemical stability as well as environmental and biological compatibility.  In addition to the above advantages of the semiconductor, GaN exhibits merits of easy control of carrier concentration doping and higher stability compared to ZnO, while internal free carriers reduce the output of the device by screening the piezoelectric polarization, which is called free carriers screening. Suppressing the free carriers screening is undoubtedly an effective approach to improve the piezoelectric performance of the devices. [27,29,30] Another method is replacing the bulk or film materials with nanowires (NWs) considering the superior mechanical properties, large aspect ratio, and high energy conversion efficiency of NWs as compared to bulk materials.  For instance, Kacimi et al. fabricated a flexible strain sensor exhibiting 2 V peak outputs with vertically aligned ultra-long GaN wires,  ...
Experimental results show that 3D-SIFT-Flow is robust for segmenting the liver from CT images, which has large tissue deformation and blurry boundary, and 3D label transfer is effective and efficient for improving the registration accuracy.
We report a topological semimetal W2As3 with a space group C2/m. Based on the first-principles calculations, band crossings are partially gapped when spin-orbit coupling is included. The Z2 indices at the electron filling are [1;111], characterizing a strong topological insulator and topological surface states. From the magnetotransport measurements, nearly quadratic field dependence of magnetoresistance (MR) (B ) at 3 K indicates an electron-hole compensated compound whose longitudinal MR reaches 11500% at 3 K and 15 T. In addition, multiband features are detected from the high-magnetic-field Shubnikov-de Haas (SdH) oscillation, Hall resistivity, and band calculations. A nontrivial π Berry's phase is obtained, suggesting the topological feature of this material. A twoband model can fit well the conductivity and Hall coefficient. Our experiments manifest that the transport properties of W2As3 are in good agreement with the theoretical calculations.
Superconductivity in crystals without inversion symmetry has received extensive attention due to its unconventional pairing and possible nontrivial topological properties. Using first-principles calculations, we systemically study the electronic structure of noncentrosymmetric superconductors A 2 Cr 3 As 3 (A=Na, K, Rb and Cs). Topologically protected triply degenerate points connected by one-dimensional arcs appear along the C 3 axis, coexisting with strong ferromagnetic (FM) fluctuations in the non-superconducting state. Within random phase approximation, our calculations show that strong enhancements of spin fluctuations are present in K 2 Cr 3 As 3 and Rb 2 Cr 3 As 3 , and are substantially reduced in Na 2 Cr 3 As 3 and Cs 2 Cr 3 As 3 . Symmetry analysis of spin-orbit coupling g k suggests that the arc surface states might remain stable in the superconducting state, giving rise to possible nontrivial topological properties. *
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