28 research outputs found
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Spatial patterns of climate change across the PaleoceneâEocene Thermal Maximum
This study was supported by HeisingâSimons Founda-tion Grants 2016-015 (to J.E.T.), 2016-011 (to M.L. and L.R.K.), 2016-013 (toA.R.), 2016-014 (to G.J.H.), and 2016-012 (to C.J.P.). R.D.M.W. and J.W.B.R. acknowledge funding from the European Research Council under the European Unionâs Horizon 2020 Research and Innovation Program Grant 805246. This material is based on work supported by the National Center for Atmospheric Research (NCAR), which is a major facility sponsored by NSF Cooperative Agreement 1852977. Computing and data storage resources, including the Cheyenne supercomputer (https://arc.ucar.edu/knowledgebase/70549542), were provided by the Computational and Information Systems Laboratory at NCAR.The PaleoceneâEocene Thermal Maximum (PETM; 56 Ma) is one of our best geological analogs for understanding climate dynamics in a âgreenhouseâ world. However, proxy data representing the event are only available from select marine and terrestrial sedimentary sequences that are unevenly distributed across Earthâs surface, limiting our view of the spatial patterns of climate change. Here, we use paleoclimate data assimilation (DA) to combine climate model and proxy information and create a spatially complete reconstruction of the PETM and the climate state that precedes it (âPETM-DAâ). Our data-constrained results support strong polar amplification, which in the absence of an extensive cryosphere, is related to temperature feedbacks and loss of seasonal snow on land. The response of the hydrological cycle to PETM warming consists of a narrowing of the Intertropical Convergence Zone, off-equatorial drying, and an intensification of seasonal monsoons and winter storm tracks. Many of these features are also seen in simulations of future climate change under increasing anthropogenic emissions. Since the PETM-DA yields a spatially complete estimate of surface air temperature, it yields a rigorous estimate of global mean temperature change (5.6 âC; 5.4 âC to 5.9 âC, 95% CI) that can be used to calculate equilibrium climate sensitivity (ECS). We find that PETM ECS was 6.5 âC (5.7 âC to 7.4 âC, 95% CI), which is much higher than the present-day range. This supports the view that climate sensitivity increases substantially when greenhouse gas concentrations are high.Publisher PDFPeer reviewe
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Room-temperature observation of near-intrinsic exciton linewidth in monolayer WS2
The homogeneous exciton linewidth, which captures the coherent quantum dynamics of an excitonic state, is a vital parameter in exploring light-matter interactions in two-dimensional transition metal dichalcogenides (TMDs). An efficient control of the exciton linewidth is of great significance, and in particular of its intrinsic linewidth, which determines the minimum timescale for the coherent manipulation of excitons. However, such a control has rarely been achieved in TMDs at room temperature (RT). While the intrinsic A exciton linewidth is down to 7 meV in monolayer WS2, the reported RT linewidth was typically a few tens of meV due to inevitable homogeneous and inhomogeneous broadening effects. Here, we show that a 7.18 meV near-intrinsic linewidth can be observed at RT when monolayer WS2 is coupled with a moderate-refractive-index hydrogenated silicon nanosphere in water. By boosting the dynamic competition between exciton and trion decay channels in WS2 through the nanosphere-supported Mie resonances, we have managed to tune the coherent linewidth from 35 down to 7.18 meV. Such modulation of exciton linewidth and its associated mechanism are robust even in presence of defects, easing the sample quality requirement and providing new opportunities for TMD-based nanophotonics and optoelectronics.J.F., K.Y., and
Y.Z. acknowledge the financial support of the National Aeronautics and Space Administration Early
Career Faculty Award (80NSSC17K0520), the National Science Foundation (NSF-ECCS-2001650),
and the National Institute of General Medical Sciences of the National Institutes of Health
(DP2GM128446). M.W. and A.A. acknowledge the financial support of the Air Force Office of
Scientific Research MURI program (FA9550-17-1-0002), the Vannevar Bush Faculty Fellowship, and
the Simons Foundation. T.Z. and M.T. acknowledge the financial support of the Air Force Office of
Scientific Research (FA9550-18-1-0072). T.J. and B.A.K. acknowledge the financial support of the
Robert A. Welch Foundation (F-1464), and the Center for Dynamics and Control of Materials
(CDCM), Materials Research Science and Engineering Center (MRSEC) (DMR-1720595).Center for Dynamics and Control of Material
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Sliding-layer laminates: a new robotic material enabling robust and adaptable undulatory locomotion
New robotic devices will benefit from new materials capable of controllable and variable material properties. In this thesis, we present a new composite laminated material with periodically arranged patterns of stiff and soft regions, laminated together in a multi-layer configuration with a central sliding layer, which is called sliding-layer laminates (SLLs). We first build a model based on Euler-Bernoulli beam theory and compute the stiffness variation as a function of layer alignment; we then explore the design principles, manipulating the stiffness patterning on the SLLs using computational and experimental methods. The comparison theory and experiment for two design principles exhibited strong agreement with differences only in the soft SLLs. In experiment, we demonstrate an up to 6-7 folds stiffness variation based on the fixed end cantilever beam test and an infinite stiffness variation is observed from the theoretical model. The effective bending stiffness under different sliding positions of the central laminate varies continuously with sufficiently many intermediate stiffness states available. To demonstrate the applicability of SLLs for robot locomotion, we implemented our SLL as a variable compliance wing structure in a wind tunnel and a robotic fish tail in a water tank to observe both the fluttering (air flow) and flapping motions (water flow) under actively tunable stiffness. The result shows great changes in amplitude (wing tip) and force (tail body) generations which indicates strong applications for multi-functional material to be exploited in mobile robots to achieve high performance under changing working conditions. In the future we envision, that SLL can be further extended into multiple areas, including innovative fabrication methods, multi-convertible properties, and high-dimensioned structures which will promote low-cost, easy controlled variable compliance solution into more unknown fields. Representative of a whole type of smart materials with tunable physical properties, the development of the SLL is still in its infancy, and the future applications of such an integrated multi-functionality system can be broadly extended in assisting the construction of bio-inspired Robotics
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Towards Reconfigurable and Adaptive Soft Robots via Hybrid Materials, Designs and Mechanisms
Inspired by biological systems, soft robotics has become a new research field that builds compliance and conformability into soft machines and devices. Soft robots are capable of functions that traditional rigid robots cannot achieve. The implementation of intrinsically soft materials allows for deformable robot bodies and adaptable robot kinematics, enabling applications such as flexible sensing technologies, robust grasping systems, and safe human-machine interactions. However, soft robots also face challenges associated with their compliance: lack of precision in kinematics, lack of reconfigurability, and lack of structural strength can all hinder soft robot capabilities. While significant research has focused on the control of actively tunable material properties and soft actuation methods for soft robots, in this work we focus on the design of soft reconfigurable robot architectures that utilize highly manipulatable soft materials and rigid components into hybrid soft/rigid building blocks. In this dissertation, the author provides new design paradigms for future reconfigurable and adaptive soft robots via the development of hybrid materials, designs, and mechanisms. This topic is addressed through three main design principles: a) Geometric reconfiguration of two-dimensional rigid and soft materials leading to variable stiffness change, and multifunctional robot laminates. b) Additive manufacturing combined with flexible laminates to achieve hybrid three-dimensional rigid and soft structures for on-demand stiffening and adaptive robot grasping and locomotion. c) Pinching of soft tubular structures enforced by rigid constraints to achieve on demand formation of reconfigurable virtual joints. Through these studies, the author seeks to present novel reconfigurable mechanisms that utilize combinations of passively compliant and rigid materials and simple activation approaches exploiting these materials. These same design paradigms can be extended to nonlinear programmable material properties enhancing robot performances in the future
Sliding-layer laminates: a new robotic material enabling robust and adaptable undulatory locomotion
New robotic devices will benefit from new materials capable of controllable and variable material properties. In this thesis, we present a new composite laminated material with periodically arranged patterns of stiff and soft regions, laminated together in a multi-layer configuration with a central sliding layer, which is called sliding-layer laminates (SLLs). We first build a model based on Euler-Bernoulli beam theory and compute the stiffness variation as a function of layer alignment; we then explore the design principles, manipulating the stiffness patterning on the SLLs using computational and experimental methods. The comparison theory and experiment for two design principles exhibited strong agreement with differences only in the soft SLLs. In experiment, we demonstrate an up to 6-7 folds stiffness variation based on the fixed end cantilever beam test and an infinite stiffness variation is observed from the theoretical model. The effective bending stiffness under different sliding positions of the central laminate varies continuously with sufficiently many intermediate stiffness states available. To demonstrate the applicability of SLLs for robot locomotion, we implemented our SLL as a variable compliance wing structure in a wind tunnel and a robotic fish tail in a water tank to observe both the fluttering (air flow) and flapping motions (water flow) under actively tunable stiffness. The result shows great changes in amplitude (wing tip) and force (tail body) generations which indicates strong applications for multi-functional material to be exploited in mobile robots to achieve high performance under changing working conditions. In the future we envision, that SLL can be further extended into multiple areas, including innovative fabrication methods, multi-convertible properties, and high-dimensioned structures which will promote low-cost, easy controlled variable compliance solution into more unknown fields. Representative of a whole type of smart materials with tunable physical properties, the development of the SLL is still in its infancy, and the future applications of such an integrated multi-functionality system can be broadly extended in assisting the construction of bio-inspired Robotics