Fourier finite element modeling of light emission in waveguides: 2.5-dimensional FEM approach

We present a Fourier finite element modeling of light emission of dipolar emitters coupled to infinitely long waveguides. Due to the translational symmetry, the three-dimensional (3D) coupled waveguide-emitter system can be decomposed into a series of independent 2D problems (2.5D), which reduces the computational cost. Moreover, the reduced 2D problems can be extremely accurate, compared to its 3D counterpart. Our method can precisely quantify the total emission rates, as well as the fraction of emission rates into different modal channels for waveguides with arbitrary cross-sections. We compare our method with dyadic Green's function for the light emission in single mode metallic nanowire, which yields an excellent agreement. This method is applied in multi-mode waveguides, as well as multi-core waveguides. We further show that our method has the full capability of including dipole orientations, as illustrated via a rotating dipole, which leads to unidirectional excitation of guide modes. The 2.5D Finite Element Method (FEM) approach proposed here can be applied for various waveguides, thus it is useful to interface single-photon single-emitter in nano-structures, as well as for other scenarios involving coupled waveguide-emitters.Comment: 11 pages, 4 figures, Optics Express, 201

The Effects of Firm-Initiated Clawback Provisions on Earnings Quality and Auditor Behavior

While firm-initiated compensation recovery (or clawback) provisions are gaining popularity and the recently enacted Dodd-Frank Act seeks to make the clawback of erroneously awarded compensation mandatory for all listed companies, little is known about their effectiveness. We find that the incidence of accounting restatements declines after firms initiate such provisions. In addition, we show that investors and auditors view such provisions as associated with increased accounting quality and lower audit risk. Specifically, we find that firms' earnings response coefficients increase after the adoption of clawback provisions. Further, for firms that adopt clawbacks, auditors are less likely to report material internal control weaknesses, charge lower audit fees, and issue audit reports with a shorter lag

On the special oxidation mechanism of a Mg-Y-Al alloy contained LPSO phase at high temperatures

This work investigated the oxidation of Mg-11Y-1Al alloy in Ar-20%O2 at 500{\deg}through multiscale characterization. The results show that the network-like long-period stacking ordered(LPSO) phase decomposed into a needle-like LPSO phase and a polygonal Mg24Y5 phase. The needle-like LPSO phase resulted in the formation of a high-dense of needle-like oxide at the oxidation front of the area initially occupied by the network-like LPSO phase. The further inward oxygen would diffuse along the needle-like oxide-matrix interfaces and react with Y in the surrounding Mg matrix, resulting in the lateral growth of these needle-like oxides. Finally, the discrete needle-like oxides were interconnected to form a thicker and continuous oxide scale which could be more effective in hindering the elemental diffusion. Meanwhile, Al could partially enter the Y2O3 oxide scale and formed a strengthened (Y,Al)O oxide scale which could show a greater resistance to cracking and debonding

Self-patterning Gd nano-fibers in Mg-Gd alloys

Manipulating the shape and distribution of strengthening units, e.g. particles, fibers, and precipitates, in a bulk metal, has been a widely applied strategy of tailoring their mechanical properties. Here, we report self-assembled patterns of Gd nano-fibers in Mg-Gd alloys for the purpose of improving their strength and deformability. 1-nm Gd nano-fibers, with a 〈c〉-rod shape, are formed and hexagonally patterned in association with Gd segregations along dislocations that nucleated during hot extrusion. Such Gd-fiber patterns are able to regulate the relative activities of slips and twinning, as a result, overcome the inherent limitations in strength and ductility of Mg alloys. This nano-fiber patterning approach could be an effective method to engineer hexagonal metals

Ksak: A high-throughput tool for alignment-free phylogenetics

Phylogenetic tools are fundamental to the studies of evolutionary relationships. In this paper, we present Ksak, a novel high-throughput tool for alignment-free phylogenetic analysis. Ksak computes the pairwise distance matrix between molecular sequences, using seven widely accepted k-mer based distance measures. Based on the distance matrix, Ksak constructs the phylogenetic tree with standard algorithms. When benchmarked with a golden standard 16S rRNA dataset, Ksak was found to be the most accurate tool among all five tools compared and was 19% more accurate than ClustalW2, a high-accuracy multiple sequence aligner. Above all, Ksak was tens to hundreds of times faster than ClustalW2, which helps eliminate the computation limit currently encountered in large-scale multiple sequence alignment. Ksak is freely available at https://github.com/labxscut/ksak

SUPERball: Exploring Tensegrities for Planetary Probes

The Dynamic Tensegrity Robotics Lab (DTRL) at NASA Ames Research Center is developing a compliant and distributed tensegrity robotic platform for planetary exploration. Working in collaboration with Ghent University, the DTRL built an untethered prototype robot, the SUPERball. In this work, multiple issues with the current SUPERball design are addressed, when considering an example mission to Titan. Specifically, engineering requirements for the mission are empirically validated, and the current design is extended under these requirements to meet expanded goals.Survival of impact forces under entry, descent, and landing are verified with a physical experiment performed in collaboration with the University of Idaho. Then, concepts for a fully-actuated redesign of SUPERball are generated, compared, and validated against current engineering requirements. This exploratory work moves the SUPERball project toward an eventual flight-ready design.

Hardware Design and Testing of SUPERball, A Modular Tensegrity Robot

We are developing a system of modular, autonomous "tensegrity end-caps" to enable the rapid exploration of untethered tensegrity robot morphologies and functions. By adopting a self-contained modular approach, different end-caps with various capabilities (such as peak torques, or motor speeds), can be easily combined into new tensegrity robots composed of rods, cables, and actuators of different scale (such as in length, mass, peak loads, etc). As a first step in developing this concept, we are in the process of designing and testing the end-caps for SUPERball (Spherical Underactuated Planetary Exploration Robot), a project at the Dynamic Tensegrity Robotics Lab (DTRL) within NASA Ames's Intelligent Robotics Group. This work discusses the evolving design concepts and test results that have gone into the structural, mechanical, and sensing aspects of SUPERball. This representative tensegrity end-cap design supports robust and repeatable untethered mobility tests of the SUPERball, while providing high force, high displacement actuation, with a low-friction, compliant cabling system

Predictive Value of Blood Pressure, Heart Rate, and Blood Pressure/Heart Rate Ratio in a Chinese Subpopulation with Vasovagal Syncope

Objective: The head-up tilt test (HUTT) is widely used but is time-consuming and not cost-effective to evaluate patients with vasovagal syncope (VVS). The present study aims to verify the hypothesis that ambulatory blood pressure (BP) monitoring (ABPM) and the simplistic tilt test may be potential alternatives to the HUTT. Methods: The study consecutively enrolled 360 patients who underwent the HUTT to evaluate VVS. BP), heart rate (HR), and BP/HR ratios derived from ABPM and the simplistic tilt test were evaluated to predict the presence, pattern, and stage of syncope during the HUTT. Results: Mixed response was the commonest pattern, and syncope occurred frequently with infusion of isoproterenol at a rate of 3 μg/min. During the simplistic tilt test, the cardioinhibitory group had higher tilted BP/HR ratios than the vasodepressor group, while the vasodepressor group had a faster tilted HR and a larger HR difference than the cardioinhibitory group. The higher the BP/HR ratio in the tilted position, the higher the isoproterenol dosage needed to induce a positive response. During ABPM, BP/HR ratios were significantly higher in the cardioinhibitory group than in the vasodepressor group. The higher the ABPM-derived BP, the higher the dosage of isoproterenol needed to induce syncope. There were significant correlations in BP/HR ratios between ABPM and the supine position in the vasodepressor group, while significant correlation was found only for the diastolic BP/HR ratio between ABPM and the tilted position in the cardioinhibitory group. The mixed pattern shared correlative features of the other two patterns. Conclusion: ABPM and the simplistic tilt test might be used as promising alternatives to the HUTT in VVS evaluation in clinical settings

Multi‐model simulation of solar geoengineering indicates avoidable destabilization of the west Antarctic ice sheet

Heat transported in Circumpolar Deep Water is driving the break-up of ice shelves in the Amundsen Sea sector of Antarctica, that has been simulated to be unavoidable under all plausible greenhouse gas scenarios. However, Solar geoengineering scenarios remain largely unexplored. Solar geoengineering changes global thermal radiative balance, and atmospheric and oceanic transportation pathways. We simulate stratospheric aerosol injection (SAI) designed to reduce global mean temperatures from those under the unmitigated SSP5-8.5 scenario to those under the SSP2-4.5 scenario with six CMIP6-class Earth System Models. These consistently show intensified Antarctic polar vortex and sub-polar westerlies, which mitigates changes to easterly winds along the Amundsen Sea continental shelf compared with greenhouse gas scenarios. The models show significantly cooler Amundsen Sea waters and lower heat content at 300–600 m under SAI than with either solar dimming or the SSP5-8.5 unmitigated greenhouse gas scenarios. However, the heat content increases under all scenarios compared with present day suggesting that although vulnerable ice shelves would continue to thin, the rate would be lower for SAI even with SSP5-8.5 specified greenhouse gases, than for the moderate (SSP2-4.5) scenario. The simulations here use solar geoengineering designed to meet global temperature targets; interventions targeted at preserving the frozen high latitudes have also been proposed that might be expected to produce bigger local effects, but potentially deleterious impacts elsewhere. Considering the huge disruptions to society of ice sheet collapse, more research on avoiding them by intervention technology is a moral imperative