RANS-based Aerodynamic Shape Optimization of a Blended-Wing-Body Aircraft

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106453/1/AIAA2013-2586.pd

Structure and electronic properties of the (3×3\sqrt{3}\times \sqrt{3})R30∘R30^{\circ} SnAu2_2/Au(111) surface alloy

We have investigated the atomic and electronic structure of the ($\sqrt{3}\times \sqrt{3}$)$R30^{\circ}$ SnAu$_2$/Au(111) surface alloy. Low energy electron diffraction and scanning tunneling microscopy measurements show that the native herringbone reconstruction of bare Au(111) surface remains intact after formation of a long range ordered ($\sqrt{3}\times \sqrt{3}$)$R30^{\circ}$ SnAu$_2$2/Au(111) surface alloy. Angle-resolved photoemission and two-photon photoemission spectroscopy techniques reveal Rashba-type spin-split bands in the occupied valence band with comparable momentum space splitting as observed for the Au(111) surface state, but with a hole-like parabolic dispersion. Our experimental findings are compared with density functional theory (DFT) calculation that fully support our experimental findings. Taking advantage of the good agreement between our DFT calculations and the experimental results, we are able to extract that the occupied Sn-Au hybrid band is of (s, d)-orbital character while the unoccupied Sn-Au hybrid bands are of (p, d)-orbital character. Hence, we can conclude that the Rashba-type spin splitting of the hole-like Sn-Au hybrid surface state is caused by the significant mixing of Au d- to Sn s-states in conjunction with the strong atomic spin-orbit coupling of Au, i.e., of the substrate.Comment: Copyright: https://journals.aps.org/authors/transfer-of-copyright-agreement; All copyrights by AP

Current status and developing recommendations of tailings dam failure

This is the final version of the article. Available from Hindawi Publishing Corporation via the DOI in this record.Tailings dam failure accidents with limited emergency response time and huge potential threats, can often lead to heavy casualties and serious financial losses. In recent years, the decreasing trend of tailings dam failure accidents evidences the development of modern technology and safety management. However, the frequency of major tailings dam failure accidents has increased, rather than decreased. The 2015 Samarco Accident in Brazil and the 2014 Mount Polley Accident in Canada, along with their disastrous consequences, once again sounded the alarm for the tailings ponds safety. China is now facing a complicated safety situation, with 8869 tailings ponds all over the country, including 1425 “Overhead Tailings Ponds” which represents the tailings ponds that located within 1 km upstream of residential area, workshops, schools or other important facilities. Based on a large amount of relevant research literatures, focusing on three main aspects of accident prevention and control which include safety monitoring, early-warning and emergency preparation, safety management codes and standards, the current status and frontier progress were reviewed in this paper. Furthermore, the relevant problems in China were discussed and several improvement recommendations were put forward, which could provide a reference for the tailings pond accident prevention theoretical research and technological innovation. The result shows: (1) the safety monitoring standards in China are relatively strict. However, the monitoring instruments are lack of the stability, reliability and practicability. Thus the development of specific devices and new technologies is urgently needed. (2) The current early-warning method is lack of diversity and reliability. And further interdisciplinary application of information technology is becoming the developing trend. (3) The emergency management and decision-making should be based on sufficient scientific proof. However the relevant research is limited by test methods and simulating algorithms. (4) China now has built a complete system of safety management codes and standards. But with shortcomings of safety level classification, life-cycle management, change management process, accident investigation and so on, there is still a long way to go

Tropical forest restoration: Fast resilience of plant biomass contrasts with slow recovery of stable soil C stocks

Due to intensifying human disturbance, over half of the world's tropical forests are reforested or afforested secondary forests or plantations. Understanding the resilience of carbon (C) stocks in these forests, and estimating the extent to which they can provide equivalent carbon (C) sequestration and stabilization to the old growth forest they replace, is critical for the global C balance. In this study, we combined estimates of biomass C stocks with a detailed assessment of soil C pools in bare land, Eucalyptus plantation, secondary forest and natural old-growth forest after over 50 years of forest restoration in a degraded tropical region of South China. We used isotope studies, density fractionation and physical fractionation to determine the age and stability of soil C pools at different soil depths. After 52 years, the secondary forests had equivalent biomass C stocks to natural forest, whereas soil C stocks were still much higher in natural forest (97.42 t/ha) than in secondary forest (58.75 t/ha) or Eucalyptus plantation (38.99 t/ha) and lowest in bare land (19.9 t/ha). Analysis of δ13C values revealed that most of the C in the soil surface horizons in the secondary forest was new C, with a limited increase of more recalcitrant old C, and limited accumulation of C in deeper soil horizons. However, occlusion of C in microaggregates in the surface soil layer was similar across forested sites, which suggests that there is great potential for additional soil C sequestration and stabilization in the secondary forest and Eucalyptus plantation. Collectively, our results demonstrate that reforestation on degraded tropical land can restore biomass C and surface soil C stocks within a few decades, but much longer recovery times are needed to restore recalcitrant C pools and C stocks at depth. Repeated harvesting and disturbance in rotation plantations had a substantial negative impact on the recovery of soil C stocks. We suggest that current calculations of soil C in secondary tropical forests (e.g. IPCC Guidelines for National Greenhouse Gas Inventories) could overestimate soil C sequestration and stabilization levels in secondary forests and plantations

Negative longitudinal magnetoresistance in GaAs quantum wells

Negative longitudinal magnetoresistances (NLMRs) have been recently observed in a variety of topological materials and often considered to be associated with Weyl fermions that have a defined chirality. Here we report NLMRs in non-Weyl GaAs quantum wells. In the absence of a magnetic field the quantum wells show a transition from semiconducting-like to metallic behaviour with decreasing temperature. We observed pronounced NLMRs up to 9 Tesla at temperatures above the transition and weak NLMRs in low magnetic fields at temperatures close to the transition and below 5 K. The observed NLMRs show various types of magnetic field behaviour resembling those reported in topological materials. We attribute them to microscopic disorder and use a phenomenological three-resistor model to account for their various features. Our results showcase a new contribution of microscopic disorder in the occurrence of novel phenomena. They may stimulate further work on tuning electronic properties via disorder/defect nano-engineering

Aerodynamic Shape Optimization Investigations of the Common Research Model Wing Benchmark

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140684/1/1.J053318.pd