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Simulation of Hubbard model physics in WSe2/WS2 moire superlattices 期刊论文
NATURE, 2020, 579 (7799) : 353-+
作者:  Stein, Reed M.;  Kang, Hye Jin;  McCorvy, John D.;  Glatfelter, Grant C.;  Jones, Anthony J.;  Che, Tao;  Slocum, Samuel;  Huang, Xi-Ping;  Savych, Olena;  Moroz, Yurii S.;  Stauch, Benjamin;  Johansson, Linda C.;  Cherezov, Vadim;  Kenakin, Terry;  Irwin, John J.;  Shoichet, Brian K.;  Roth, Bryan L.;  Dubocovich, Margarita L.
收藏  |  浏览/下载:27/0  |  提交时间:2020/07/03

Study of WSe2/WS2 moire superlattices reveals the phase diagram of the triangular-lattice Hubbard model, including a Mott insulating state at half-filling and a possible magnetic quantum phase transition near 0.6 filling.


The Hubbard model, formulated by physicist John Hubbard in the 1960s(1), is a simple theoretical model of interacting quantum particles in a lattice. The model is thought to capture the essential physics of high-temperature superconductors, magnetic insulators and other complex quantum many-body ground states(2,3). Although the Hubbard model provides a greatly simplified representation of most real materials, it is nevertheless difficult to solve accurately except in the one-dimensional case(2,3). Therefore, the physical realization of the Hubbard model in two or three dimensions, which can act as an analogue quantum simulator (that is, it can mimic the model and simulate its phase diagram and dynamics(4,5)), has a vital role in solving the strong-correlation puzzle, namely, revealing the physics of a large number of strongly interacting quantum particles. Here we obtain the phase diagram of the two-dimensional triangular-lattice Hubbard model by studying angle-aligned WSe2/WS2 bilayers, which form moire superlattices(6) because of the difference between the lattice constants of the two materials. We probe the charge and magnetic properties of the system by measuring the dependence of its optical response on an out-of-plane magnetic field and on the gate-tuned carrier density. At half-filling of the first hole moire superlattice band, we observe a Mott insulating state with antiferromagnetic Curie-Weiss behaviour, as expected for a Hubbard model in the strong-interaction regime(2,3,7-9). Above half-filling, our experiment suggests a possible quantum phase transition from an antiferromagnetic to a weak ferromagnetic state at filling factors near 0.6. Our results establish a new solid-state platform based on moire superlattices that can be used to simulate problems in strong-correlation physics that are described by triangular-lattice Hubbard models.


  
Loopy Levy flights enhance tracer diffusion in active suspensions 期刊论文
NATURE, 2020, 579 (7799) : 364-+
作者:  Hu, Bo;  Jin, Chengcheng;  Zeng, Xing;  Resch, Jon M.;  Jedrychowski, Mark P.;  Yang, Zongfang;  Desai, Bhavna N.;  Banks, Alexander S.;  Lowell, Bradford B.;  Mathis, Diane;  Spiegelman, Bruce M.
收藏  |  浏览/下载:24/0  |  提交时间:2020/07/03

A theoretical framework describing the hydrodynamic interactions between a passive particle and an active medium in out-of-equilibrium systems predicts long-range Levy flights for the diffusing particle driven by the density of the active component.


Brownian motion is widely used as a model of diffusion in equilibrium media throughout the physical, chemical and biological sciences. However, many real-world systems are intrinsically out of equilibrium owing to energy-dissipating active processes underlying their mechanical and dynamical features(1). The diffusion process followed by a passive tracer in prototypical active media, such as suspensions of active colloids or swimming microorganisms(2), differs considerably from Brownian motion, as revealed by a greatly enhanced diffusion coefficient(3-10) and non-Gaussian statistics of the tracer displacements(6,9,10). Although these characteristic features have been extensively observed experimentally, there is so far no comprehensive theory explaining how they emerge from the microscopic dynamics of the system. Here we develop a theoretical framework to model the hydrodynamic interactions between the tracer and the active swimmers, which shows that the tracer follows a non-Markovian coloured Poisson process that accounts for all empirical observations. The theory predicts a long-lived Levy flight regime(11) of the loopy tracer motion with a non-monotonic crossover between two different power-law exponents. The duration of this regime can be tuned by the swimmer density, suggesting that the optimal foraging strategy of swimming microorganisms might depend crucially on their density in order to exploit the Levy flights of nutrients(12). Our framework can be applied to address important theoretical questions, such as the thermodynamics of active systems(13), and practical ones, such as the interaction of swimming microorganisms with nutrients and other small particles(14) (for example, degraded plastic) and the design of artificial nanoscale machines(15).


  
Single-cell and spatial transcriptomics reveal somitogenesis in gastruloids 期刊论文
NATURE, 2020
作者:  Nixon, Christopher C.;  Mavigner, Maud;  Sampey, Gavin C.;  Brooks, Alyssa D.;  Spagnuolo, Rae Ann;  Irlbeck, David M.;  Mattingly, Cameron;  Ho, Phong T.;  Schoof, Nils;  Cammon, Corinne G.;  Tharp, Greg K.;  Kanke, Matthew;  Wang, Zhang;  Cleary, Rachel A.;  Upadhyay, Amit A.;  De, Chandrav;  Wills, Saintedym R.;  Falcinelli, Shane D.;  Galardi, Cristin;  Walum, Hasse;  Schramm, Nathaniel J.;  Deutsch, Jennifer;  Lifson, Jeffrey D.;  Fennessey, Christine M.;  Keele, Brandon F.;  Jean, Sherrie;  Maguire, Sean;  Liao, Baolin;  Browne, Edward P.;  Ferris, Robert G.;  Brehm, Jessica H.;  Favre, David;  Vanderford, Thomas H.;  Bosinger, Steven E.;  Jones, Corbin D.;  Routy, Jean-Pierre;  Archin, Nancie M.;  Margolis, David M.;  Wahl, Angela;  Dunham, Richard M.;  Silvestri, Guido;  Chahroudi, Ann;  Garcia, J. Victor
收藏  |  浏览/下载:53/0  |  提交时间:2020/07/03

Single-cell RNA sequencing and spatial transcriptomics reveal that the somitogenesis clock is active in mouse gastruloids, which can be induced to generate somites with the correct rostral-caudal patterning.


Gastruloids are three-dimensional aggregates of embryonic stem cells that display key features of mammalian development after implantation, including germ-layer specification and axial organization(1-3). To date, the expression pattern of only a small number of genes in gastruloids has been explored with microscopy, and the extent to which genome-wide expression patterns in gastruloids mimic those in embryos is unclear. Here we compare mouse gastruloids with mouse embryos using single-cell RNA sequencing and spatial transcriptomics. We identify various embryonic cell types that were not previously known to be present in gastruloids, and show that key regulators of somitogenesis are expressed similarly between embryos and gastruloids. Using live imaging, we show that the somitogenesis clock is active in gastruloids and has dynamics that resemble those in vivo. Because gastruloids can be grown in large quantities, we performed a small screen that revealed how reduced FGF signalling induces a short-tail phenotype in embryos. Finally, we demonstrate that embedding in Matrigel induces gastruloids to generate somites with the correct rostral-caudal patterning, which appear sequentially in an anterior-to-posterior direction over time. This study thus shows the power of gastruloids as a model system for exploring development and somitogenesis in vitro in a high-throughput manner.


  
Long-term cyclic persistence in an experimental predator-prey system 期刊论文
NATURE, 2020, 577 (7789) : 226-+
作者:  Blasius, Bernd;  Rudolf, Lars;  Weithoff, Guntram;  Gaedke, Ursula;  Fussmann, Gregor F.
收藏  |  浏览/下载:27/0  |  提交时间:2020/04/16

Predator-prey cycles rank among the most fundamental concepts in ecology, are predicted by the simplest ecological models and enable, theoretically, the indefinite persistence of predator and prey(1-4). However, it remains an open question for how long cyclic dynamics can be self-sustained in real communities. Field observations have been restricted to a few cycle periods(5-8) and experimental studies indicate that oscillations may be short-lived without external stabilizing factors(9-19). Here we performed microcosm experiments with a planktonic predator-prey system and repeatedly observed oscillatory time series of unprecedented length that persisted for up to around 50 cycles or approximately 300 predator generations. The dominant type of dynamics was characterized by regular, coherent oscillations with a nearly constant predator-prey phase difference. Despite constant experimental conditions, we also observed shorter episodes of irregular, non-coherent oscillations without any significant phase relationship. However, the predator-prey system showed a strong tendency to return to the dominant dynamical regime with a defined phase relationship. A mathematical model suggests that stochasticity is probably responsible for the reversible shift from coherent to non-coherent oscillations, a notion that was supported by experiments with external forcing by pulsed nutrient supply. Our findings empirically demonstrate the potential for infinite persistence of predator and prey populations in a cyclic dynamic regime that shows resilience in the presence of stochastic events.


  
Climate Responses to the Splitting of a Supercontinent: Implications for the Breakup of Pangea 期刊论文
GEOPHYSICAL RESEARCH LETTERS, 2019, 46 (11) : 6059-6068
作者:  Tabor, Clay R.;  Feng, Ran;  Otto-Bliesner, Bette L.
收藏  |  浏览/下载:15/0  |  提交时间:2019/11/26
paleoclimate  climate dynamics  proxy records  Earth system model  Walker circulation  Hadley circulations  
Exploring the development of electric vehicles under policy incentives: A scenario-based system dynamics model 期刊论文
ENERGY POLICY, 2018, 120: 8-23
作者:  Liu, Dunnan;  Xiao, Bowen
收藏  |  浏览/下载:13/0  |  提交时间:2019/04/09
Electric vehicle  System dynamics model  Financial support  Emission trade scheme  Scenario analysis  
Assessing the Dynamic Versus Thermodynamic Origin of Climate Model Biases 期刊论文
GEOPHYSICAL RESEARCH LETTERS, 2018, 45 (16) : 8471-8479
作者:  Wehrli, Kathrin;  Guillod, Benoit P.;  Hauser, Mathias;  Leclair, Matthieu;  Seneviratne, Sonia I.
收藏  |  浏览/下载:24/0  |  提交时间:2019/04/09
climate model biases  Earth system models  atmospheric nudging  dynamics versus thermodynamics  global climate models  systematic biases  
Exploring synergies between transit investment and dense redevelopment: A scenario analysis in a rapidly urbanizing landscape 期刊论文
LANDSCAPE AND URBAN PLANNING, 2017, 167
作者:  Cox, L.;  Bassi, A.;  Kolling, J.;  Procter, A.;  Flanders, N.;  Tanners, N.;  Araujo, R.
收藏  |  浏览/下载:17/0  |  提交时间:2019/04/09
Land use model  Urban sustainability  Light rail  Transit-oriented development  System dynamics  Redevelopment  
Impact of seasonal forecast use on agricultural income in a system with varying crop costs and returns: an empirically-grounded simulation 期刊论文
ENVIRONMENTAL RESEARCH LETTERS, 2017, 12 (3)
作者:  Gunda, T.;  Bazuin, J. T.;  Nay, J.;  Yeung, K. L.
收藏  |  浏览/下载:16/0  |  提交时间:2019/04/09
weather forecasts  coupled natural and human systems  system dynamics model  laboratory in the field games  farmers  climate change adaptation  agriculture systems