Competing edge structures of Sb and Bi bilayers by trivial and nontrivial band topologies

One-dimensional (1D) edge states formed at the boundaries of 2D normal and topological insulators have shown intriguing quantum phases such as charge density wave and quantum spin Hall effect. Based on first-principles density-functional theory calculations including spin-orbit coupling (SOC), we show that the edge states of zigzag Sb(111) and Bi(111) nanoribbons drastically change the stability of their edge structures. For zigzag Sb(111) nanoribbon, the Peierls-distorted or reconstructed edge structure is stabilized by a band-gap opening. However, for zigzag Bi(111) nanoribbon, such two insulating structures are destabilized due to the presence of topologically protected gapless edge states, resulting in the stabilization of a metallic, shear-distorted edge structure. We also show that the edge states of the Bi(111) nanoribbon exhibit a larger Rashba-type spin splitting at the boundary of Brillouin zone, compared to those of the Sb(111) nanoribbon. Interestingly, the spin textures of edge states in the Peierls-distorted Sb edge structure and the shear-distorted Bi edge structure have all three spin components perpendicular and parallel to the edges, due to their broken mirror-plane symmetry. The present findings demonstrate that the topologically trivial and nontrivial edge states play crucial roles in determining the edge structures of normal and topological insulators.Comment: 7 pages, 8 figure

Characteristics of Cricopharyngeal Dysphagia After Ischemic Stroke

ObjectiveTo evaluate the characteristics of cricopharyngeal dysfunction (CPD), the frequency, and correlation with a brain lesion in patients with first-ever ischemic stroke, and to provide basic data for developing a therapeutic protocol for dysphagia management.MethodsWe retrospectively reviewed the medical records of a series of subjects post-stroke who underwent a videofluoroscopic swallowing study (VFSS) from January 2009 to December 2015. VFSS images were recorded on videotape and analyzed. CPD was defined as the retention of more than 25% of residue in the pyriform sinus after swallowing. The location of the brain lesion was assessed using magnetic resonance imaging.ResultsAmong the 262 dysphagic patients with first-ever ischemic stroke, 15 (5.7%) showed CPD on the VFSS. Patients with an infratentorial lesion had a significantly higher proportion of CPD than those with a supratentorial lesion (p=0.003), and lateral medullary infarction was identified as the single independent predictor of CPD (multivariable analysis: odds ratio=19.417; confidence interval, 5.560–67.804; p<0.0001). Compared to patients without CPD, those with CPD had a significantly prolonged pharyngeal transit time, lower laryngeal elevation, and a higher pharyngeal constriction ratio and functional dysphagia scale score.ConclusionOverall, the results support the notion that an impaired upper esopharyngeal opening is likely related to the specific locations of brain lesions. The association of CPD with lateral medullary infarction can be explained based on the regulation of the pharyngolaryngeal motor system by the motor neurons present in the dorsal nucleus ambiguus. Overall, the results reveal the relation between CPD and the problems in the pharyngeal phase as well as the severity of dysphagia

Additive Manufacturing of Metallic Materials: A Review

In this review article, the latest developments of the four most common additive manufacturing methods for metallic materials are reviewed, including powder bed fusion, direct energy deposition, binder jetting, and sheet lamination. In addition to the process principles, the microstructures and mechanical properties of AM-fabricated parts are comprehensively compared and evaluated. Finally, several future research directions are suggested

Design of the VISTA-ITL Test Facility for an Integral Type Reactor of SMART and a Post-Test Simulation of a SBLOCA Test

To validate the performance and safety of an integral type reactor of SMART, a thermal-hydraulic integral effect test facility, VISTA-ITL, is introduced with a discussion of its scientific design characteristics. The VISTA-ITL was used extensively to assess the safety and performance of the SMART design, especially for its passive safety system such as a passive residual heat removal system, and to validate various thermal-hydraulic analysis codes. The VISTA-ITL program includes several tests on the SBLOCA, CLOF, and PRHRS performances to support a verification of the SMART design and contribute to the SMART design licensing by providing proper test data for validating the system analysis codes. A typical scenario of SBLOCA was analyzed using the MARS-KS code to assess the thermal-hydraulic similarity between the SMART design and the VISTA-ITL facility, and a posttest simulation on a SBLOCA test for the shutdown cooling system line break has been performed with the MARS-KS code to assess its simulation capability for the SBLOCA scenario of the SMART design. The SBLOCA scenario in the SMART design was well reproduced using the VISTA-ITL facility, and the measured thermal-hydraulic data were properly simulated with the MARS-KS code

A Multi-Scale Multi-Physics Modeling Framework of Laser Powder Bed Fusion Additive Manufacturing Process

A longstanding challenge is to optimize additive manufacturing (AM) process in order to reduce AM component failure due to excessive distortion and cracking. To address this challenge, a multi-scale physics-based modeling framework is presented to understand the interrelationship between AM processing parameters and resulting properties. In particular, a multi-scale approach, spanning from atomic, particle, to component levels, is employed. The simulations of sintered material show that sintered particles have lower mechanical strengths than the bulk metal because of their porous structures. Higher heating rate leads to a higher mechanical strength due to accelerated sintering rates. The average temperature in the powder bed increases with higher laser power. The predicted distortion due to residual stress in the AM fabricated component is in good agreement with experimental measurements. In summary, the model framework provides a design tool to optimize the metal powder based additive manufacturing process

Electrical spin injection and detection in an InAs quantum well

We demonstrate fully electrical detection of spin injection in InAs quantum wells. A spin polarized current is injected from a NiFe thin film to a two-dimensional electron gas (2DEG) made of InAs based epitaxial multi-layers. Injected spins accumulate and diffuse out in the 2DEG, and the spins are electrically detected by a neighboring NiFe electrode. The observed spin diffusion length is 1.8 um at 20 K. The injected spin polarization across the NiFe/InAs interface is 1.9% at 20 K and remains at 1.4% even at room temperature. Our experimental results will contribute significantly to the realization of a practical spin field effect transistor

Temperature-Dependent Charpy Impact Property of 3D Printed 15-5 PH Stainless Steel

In this study, the impact property of 3D printed 15-5 PH stainless steel was investigated at low (77 K), room (298 K), and high temperatures (723 K) using integrated experimental and modelling studies. The finite element model was based on the Johnson-Cook phenomenological material model and fracture parameters. The experimentally measured impact energies are 0.01, 6.78 ± 4.07, and 50.84 ± 3.39 J cm−2, at the low, room, and high temperatures, respectively. The experimental and modelling predicted impact energies are in good agreement. The microstructures show that the steel exhibits a brittle behaviour at low and room temperatures as indicated by a transgranular fracture, but changes to a more ductile behaviour at high temperatures as illustrated by microvoid coalescence induced facture morphology