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The environmental neighborhoods of cities and their spatial extent 期刊论文
ENVIRONMENTAL RESEARCH LETTERS, 2020, 15 (7)
作者:  Llaguno-Munitxa, M.;  Bou-Zeid, E.
收藏  |  浏览/下载:7/0  |  提交时间:2020/08/18
urban environment  air quality  urban planning  sensor networks  spatial heterogeneity  
CMIP6 Models Predict Significant 21st Century Decline of the Atlantic Meridional Overturning Circulation 期刊论文
GEOPHYSICAL RESEARCH LETTERS, 2020, 47 (12)
作者:  Weijer, W.;  Cheng, W.;  Garuba, O. A.;  Hu, A.;  Nadiga, B. T.
收藏  |  浏览/下载:5/0  |  提交时间:2020/05/25
AMOC  CMIP6  
The Changing Relationship Between Rainfall and Surface Runoff on the Loess Plateau, China 期刊论文
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 2020, 125 (8)
作者:  Miao, Chiyuan;  Zheng, Haiyan;  Jiao, Juying;  Feng, Xiaoming;  Duan, Qingyun;  Mpofu, Ephraim
收藏  |  浏览/下载:8/0  |  提交时间:2020/07/02
rainfall  surface runoff  runoff coefficient  scaling  Loess Plateau  
Indirectly Measured Ambient Electric Fields for Lightning Initiation in Fast Breakdown Regions 期刊论文
GEOPHYSICAL RESEARCH LETTERS, 2020, 47 (4)
作者:  Cummer, Steven A.
收藏  |  浏览/下载:2/0  |  提交时间:2020/07/02
Near-Future Anthropogenic Aerosol Emission Scenarios and Their Direct Radiative Effects on the Present-Day Characteristics of the Indian Summer Monsoon 期刊论文
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 2020, 125 (4)
作者:  Das, Sushant;  Giorgi, Filippo;  Giuliani, Graziano;  Dey, Sagnik;  Coppola, Erika
收藏  |  浏览/下载:17/0  |  提交时间:2020/07/02
Climate change induced socio-economic tipping points: review and stakeholder consultation for policy relevant research 期刊论文
ENVIRONMENTAL RESEARCH LETTERS, 2020, 15 (2)
作者:  van Ginkel, Kees C. H.;  Botzen, W. J. Wouter;  Haasnoot, Marjolijn;  Bachner, Gabriel;  Steininger, Karl W.;  Hinkel, Jochen;  Watkiss, Paul;  Boere, Esther;  Jeuken, Ad;  de Murieta, Elisa Sainz;  Bosello, Francesco
收藏  |  浏览/下载:12/0  |  提交时间:2020/07/02
tipping points  climate change  systematic review  socio-economic  stakeholder consultation  
High-pressure strengthening in ultrafine-grained metals 期刊论文
NATURE, 2020
作者:  Yoshida, Kenichi;  Gowers, Kate H. C.;  Lee-Six, Henry;  Chandrasekharan, Deepak P.;  Coorens, Tim;  Maughan, Elizabeth F.;  Beal, Kathryn;  Menzies, Andrew;  Millar, Fraser R.;  Anderson, Elizabeth;  Clarke, Sarah E.;  Pennycuick, Adam;  Thakrar, Ricky M.;  Butler, Colin R.
收藏  |  浏览/下载:27/0  |  提交时间:2020/07/03

High-pressure diamond anvil cell experiments reveal that compression strengthening of nanocrystalline nickel increases as its grain sizes decrease to 3 nanometres, owing to dislocation hardening and suppression of grain boundary plasticity.


The Hall-Petch relationship, according to which the strength of a metal increases as the grain size decreases, has been reported to break down at a critical grain size of around 10 to 15 nanometres(1,2). As the grain size decreases beyond this point, the dominant mechanism of deformation switches from a dislocation-mediated process to grain boundary sliding, leading to material softening. In one previous approach, stabilization of grain boundaries through relaxation and molybdenum segregation was used to prevent this softening effect in nickel-molybdenum alloys with grain sizes below 10 nanometres(3). Here we track in situ the yield stress and deformation texturing of pure nickel samples of various average grain sizes using a diamond anvil cell coupled with radial X-ray diffraction. Our high-pressure experiments reveal continuous strengthening in samples with grain sizes from 200 nanometres down to 3 nanometres, with the strengthening enhanced (rather than reduced) at grain sizes smaller than 20 nanometres. We achieve a yield strength of approximately 4.2 gigapascals in our 3-nanometre-grain-size samples, ten times stronger than that of a commercial nickel material. A maximum flow stress of 10.2 gigapascals is obtained in nickel of grain size 3 nanometres for the pressure range studied here. We see similar patterns of compression strengthening in gold and palladium samples down to the smallest grain sizes. Simulations and transmission electron microscopy reveal that the high strength observed in nickel of grain size 3 nanometres is caused by the superposition of strengthening mechanisms: both partial and full dislocation hardening plus suppression of grain boundary plasticity. These insights contribute to the ongoing search for ultrastrong metals via materials engineering.


  
Dualities and non-Abelian mechanics 期刊论文
NATURE, 2020, 577 (7792) : 636-+
作者:  Song, Xinyang;  Sun, Ximei;  Oh, Sungwhan F.;  Wu, Meng;  Zhang, Yanbo;  Zheng, Wen;  Geva-Zatorsky, Naama;  Jupp, Ray;  Mathis, Diane;  Benoist, Christophe;  Kasper, Dennis L.
收藏  |  浏览/下载:13/0  |  提交时间:2020/07/03

Dualities-mathematical mappings between different systems-can act as hidden symmetries that enable materials design beyond that suggested by crystallographic space groups.


Dualities are mathematical mappings that reveal links between apparently unrelated systems in virtually every branch of physics(1-8). Systems mapped onto themselves by a duality transformation are called self-dual and exhibit remarkable properties, as exemplified by the scale invariance of an Ising magnet at the critical point. Here we show how dualities can enhance the symmetries of a dynamical matrix (or Hamiltonian), enabling the design of metamaterials with emergent properties that escape a standard group theory analysis. As an illustration, we consider twisted kagome lattices(9-15), reconfigurable mechanical structures that change shape by means of a collapse mechanism(9). We observe that pairs of distinct configurations along the mechanism exhibit the same vibrational spectrum and related elastic moduli. We show that these puzzling properties arise from a duality between pairs of configurations on either side of a mechanical critical point. The critical point corresponds to a self-dual structure with isotropic elasticity even in the absence of spatial symmetries and a twofold-degenerate spectrum over the entire Brillouin zone. The spectral degeneracy originates from a version of Kramers'  theorem(16,17) in which fermionic time-reversal invariance is replaced by a hidden symmetry emerging at the self-dual point. The normal modes of the self-dual systems exhibit non-Abelian geometric phases(18,19) that affect the semiclassical propagation of wavepackets(20), leading to non-commuting mechanical responses. Our results hold promise for holonomic computation(21) and mechanical spintronics by allowing on-the-fly manipulation of synthetic spins carried by phonons.


  
Signatures of self-organized criticality in an ultracold atomic gas 期刊论文
NATURE, 2020, 577 (7791) : 481-+
作者:  MacPherson, Laura;  Anokye, Juliana;  Yeung, Miriam M.;  Lam, Enid Y. N.;  Chan, Yih-Chih;  Weng, Chen-Fang;  Yeh, Paul;  Knezevic, Kathy;  Butler, Miriam S.;  Hoegl, Annabelle;  Chan, Kah-Lok;  Burr, Marian L.;  Gearing, Linden J.;  Willson, Tracy;  Liu, Joy;  Choi, Jarny;  Yang, Yuqing;  Bilardi, Rebecca A.;  Falk, Hendrik;  Nghi Nguyen;  Stupple, Paul A.;  Peat, Thomas S.;  Zhang, Ming;  De Silva, Melanie;  Carrasco-Pozo, Catalina;  Avery, Vicky M.;  Khoo, Sim;  Dolezal, Olan;  Dennis, Matthew L.;  Nuttall, Stewart;  Surjadi, Regina;  Newman, Janet;  Ren, Bin;  Leaver, David J.;  Sun, Yuxin;  Baell, Jonathan B.;  Dovey, Oliver;  Vassiliou, George S.;  Grebien, Florian;  Dawson, Sarah-Jane;  Street, Ian P.;  Monahan, Brendon J.;  Burns, Christopher J.;  Choudhary, Chunaram;  Blewitt, Marnie E.;  Voss, Anne K.;  Thomas, Tim;  Dawson, Mark A.
收藏  |  浏览/下载:24/0  |  提交时间:2020/07/03

Self-organized criticality is an elegant explanation of how complex structures emerge and persist throughout nature(1), and why such structures often exhibit similar scale-invariant properties(2-9). Although self-organized criticality is sometimes captured by simple models that feature a critical point as an attractor for the dynamics(10-15), the connection to real-world systems is exceptionally hard to test quantitatively(16-21). Here we observe three key signatures of self-organized criticality in the dynamics of a driven-dissipative gas of ultracold potassium atoms: self-organization to a stationary state that is largely independent of the initial conditions  scale-invariance of the final density characterized by a unique scaling function  and large fluctuations of the number of excited atoms (avalanches) obeying a characteristic power-law distribution. This work establishes a well-controlled platform for investigating self-organization phenomena and non-equilibrium criticality, with experimental access to the underlying microscopic details of the system.


A driven-dissipative gas of ultracold potassium atoms is used to demonstrate three key signatures of self-organized criticality, and provides a system in which the phenomenon can be experimentally tested.


  
A low climate threshold for south Greenland Ice Sheet demise during the Late Pleistocene 期刊论文
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 2020, 117 (1) : 190-195
作者:  Irvali, Nil;  Galaasen, Eirik V.;  Ninnemann, Ulysses S.;  Rosenthal, Yair;  Born, Andreas;  Kleiven, Helga (Kikki) F.
收藏  |  浏览/下载:8/0  |  提交时间:2020/05/13
Greenland Ice Sheet  Late Pleistocene interglacials  climate change  thresholds