Nanjing University

About: Nanjing University is a education organization based out in Nanjing, China. It is known for research contribution in the topics: Catalysis & Population. The organization has 85961 authors who have published 105504 publications receiving 2289036 citations. The organization is also known as: NJU & Nanking University.

Dryland climate change: Recent progress and challenges

Abstract: Drylands are home to more than 38% of the world's population and are one of the most sensitive areas to climate change and human activities. This review describes recent progress in dryland climate change research. Recent findings indicate that the long-term trend of the aridity index (AI) is mainly attributable to increased greenhouse gas emissions while anthropogenic aerosols exert small effects but alter its attributions. Atmosphere-land interactions determine the intensity of regional response. The largest warming during the last 100 years was observed over drylands and accounted for more than half of the continental warming. The global pattern and inter-decadal variability of aridity changes are modulated by oceanic oscillations. The different phases of those oceanic oscillations induce significant changes in land-sea and north-south thermal contrasts, which affect the intensity of the westerlies and planetary waves and the blocking frequency, thereby altering global changes in temperature and precipitation. During 1948-2008, the drylands in the Americas became wetter due to enhanced westerlies, whereas the drylands in the Eastern Hemisphere became drier because of the weakened East Asian summer monsoon. Drylands as defined by the AI have expanded over the last sixty years and are projected to expand in the 21st century. The largest expansion of drylands has occurred in semi-arid regions since the early 1960s. Dryland expansion will lead to reduced carbon sequestration and enhanced regional warming. The increasing aridity, enhanced warming and rapidly growing population will exacerbate the risk of land degradation and desertification in the near future in developing countries.

Broadband diffusion of terahertz waves by multi-bit coding metasurfaces

Abstract: The terahertz region is a special region of the electromagnetic spectrum that incorporates the advantages of both microwaves and infrared light waves. In the past decade, metamaterials with effective medium parameters or gradient phases have been studied to control terahertz waves and realize functional devices. Here, we present a new approach to manipulate terahertz waves by using coding metasurfaces that are composed of digital coding elements. We propose a general coding unit based on a Minkowski closed-loop particle that is capable of generating 1-bit coding (with two phase states of 0 and 180°), 2-bit coding (with four phase states of 0, 90°, 180°, and 270°), and multi-bit coding elements in the terahertz frequencies by using different geometric scales. We show that multi-bit coding metasurfaces have strong abilities to control terahertz waves by designing-specific coding sequences. As an application, we demonstrate a new scattering strategy of terahertz waves—broadband and wide-angle diffusion—using a 2-bit coding metasurface with a special coding design and verify it by both numerical simulations and experiments. The presented method opens a new route to reducing the scattering of terahertz waves. A team in China has demonstrated a new strategy for controlling terahertz waves by using ‘coding’ metasurfaces to attain broadband diffusion. Metamaterials have previously been used to control terahertz waves and develop functional devices. Now, Tie Jun Cui and co-workers have developed metasurfaces composed of one-, two- and three-bit digital coding elements based on Minkowski loops. They demonstrated their coding surfaces by showing that metasurfaces with appropriately designed coding sequences can be used to strongly manipulate terahertz waves. In particular, they realized broadband, wide-angle diffusion using a two-bit coding metasurface with a special design and obtained good agreement between the measured results and numerical simulations. The proposed method offers a new way to control scattering of terahertz waves and can be implemented using conventional lithography.

Topological cell clustering in the ATLAS calorimeters and its performance in LHC Run 1

Abstract: The reconstruction of the signal from hadrons and jets emerging from the proton–proton collisions at the Large Hadron Collider (LHC) and entering the ATLAS calorimeters is based on a three-dimensional topological clustering of individual calorimeter cell signals. The cluster formation follows cell signal-significance patterns generated by electromagnetic and hadronic showers. In this, the clustering algorithm implicitly performs a topological noise suppression by removing cells with insignificant signals which are not in close proximity to cells with significant signals. The resulting topological cell clusters have shape and location information, which is exploited to apply a local energy calibration and corrections depending on the nature of the cluster. Topological cell clustering is established as a well-performing calorimeter signal definition for jet and missing transverse momentum reconstruction in ATLAS.

Why does bulk boundary correspondence fail in some non-hermitian topological models

Abstract: The bulk-boundary correspondence is crucial to topological insulators. It associates the existence of boundary states (with zero energy and possessing chiral or helical properties) with the topological numbers defined in bulk. In recent years, topology has been extended to non-hermitian systems, opening a new research area called non-hermitian topological insulator. In this paper, however, we will illustrate that the bulk-boundary correspondence does not hold in these new models. This is because a prerequisite condition: 'the boundaries cannot alter most of the bulk states, so as to the topological numbers defined on them' does not hold any longer. This cuts out the correspondence between the topological numbers and the boundary states. We will illustrate that, as approaching the open boundary condition by eliminating the strength of the hopping between the two ends of a chain, a new series of exceptional points must be passed through and the topological structure of the spectrum in the complex plane has been changed. This makes the spectrum topology different for the chains with and without boundaries. We also discuss that such exotic behavior does not emerge when the open boundary is replaced by a domain-wall. So the index theorem can be applied to the systems with domain-walls but cannot be further used to those with open boundaries.

Verification of icephobic/anti-icing properties of a superhydrophobic surface.

Abstract: Four aluminum surfaces with wettability varied from superhydrophilic to superhydrophobic were prepared by combining an etching and a coating process. The surface wettability was checked in terms of water contact angle (CA) and sliding angle (SA) under different humidity at −10 °C. High-speed photography was applied to study water droplet impact dynamics on these surfaces. It was found that single and successive water droplets could rebound on the superhydrophobic surface and roll off at a tilt angle larger than 30° under an extremely condensing weather condition (−10 °C and relative humidity of 85–90%). In addition, the superhydrophobic surface showed a strong icephobic property, the ice adhesion on this surface was only 13% of that on the superhydrophilic surface, though they had a similar nano/microtopological structure. Moreover, this superhydrophobic surface displayed an excellent durability of the icephobic property. The ice adhesion only increased to 20% and 16% of that on the superhydrophobic surfa...