3,302 research outputs found

    Influence of warm SST anomalies formed in the eastern Pacific subduction zone on recent El Niño events

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    Anomalous April–June warm surface water in the eastern Pacific convergence zone (the Great Pacific Garbage Patch) subducts and depresses the thermocline as a single waveform. This waveform propagates toward the equator much more quickly (reaching the equator in 1.5–2.5 years) than the normal transit time (5–10 years) of the meridional overturning cell. The movements of the sea-surface temperature (SST) anomalies that occurred before the 1997 and 2009 El Niños can be clearly traced to the area south of 20°N using the altimeter sea-level signals. Upon arriving near the Pacific equator, these warm water anomalies can contribute to the formation of the El Niño by lowering the depth of the thermocline. The time required for a subducted SST anomaly to drift 3000 km to the equator depends upon its initial location and on the distribution of the SST anomalies near the western coast of North America. The subducted warm SST anomalies observed before the El Niños of 1982 and 1997 took 12 months to reach the equator. Longer drift times of 24 months were indicated for the 1972, 1986, 1993, 2003, 2006 and 2009 events. The thermocline depressions that drift toward the equator in the eastern Pacific are shown to be a major energy source for the onset of the El Niño in the central and eastern Pacific. This study presents a theory that could expand our understanding of the onset mechanism of the El Niño episode

    Half-Skyrmions and the Equation of State for Compact-Star Matter

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    The half-skyrmions that appear in dense baryonic matter when skyrmions are put on crystals modify drastically hadron properties in dense medium and affect strongly the nuclear tensor forces, thereby influencing the equation of state (EoS) of dense nuclear and asymmetric nuclear matter. The matter comprised of half skyrmions has vanishing quark condensate but non-vanishing pion decay constant and could be interpreted as a hadronic dual of strong-coupled quark matter. We infer from this observation combined with certain predictions of hidden local symmetry in low-energy hadronic interactionsa a set of new scaling laws -- called "new-BR" -- for the parameters in nuclear effective field theory controlled by renormalization-group flow. They are subjected to the EoS of symmetric and asymmetric nuclear matter, and are then applied to nuclear symmetry energies and properties of compact stars. The changeover from the skyrmion matter to a half-skyrmion matter that takes place after the cross-over density n1/2n_{1/2} provides a simple and natural field theoretic explanation for the change of the EoS from soft to stiff at a density above that of nuclear matter required for compact stars as massive as 2.4M\sim 2.4M_\odot. Cross-over density in the range 1.5n_0 \lsim n_{1/2} \lsim 2.0 n_0 has been employed, and the possible skyrmion half-skyrmion coexistence {or cross-over} near n1/2n_{1/2} is discussed. The novel structure of {the tensor forces and} the EoS obtained with the new-BR scaling is relevant for neutron-rich nuclei and compact star matter and could be studied in RIB (rare isotope beam) machines.Comment: 12 pages, 7 figures, slightly revised for PRC, in pres

    Synergistic multi-doping effects on the Li7La3Zr2O12 solid electrolyte for fast lithium ion conduction.

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    Here, we investigate the doping effects on the lithium ion transport behavior in garnet Li7La3Zr2O12 (LLZO) from the combined experimental and theoretical approach. The concentration of Li ion vacancy generated by the inclusion of aliovalent dopants such as Al(3+) plays a key role in stabilizing the cubic LLZO. However, it is found that the site preference of Al in 24d position hinders the three dimensionally connected Li ion movement when heavily doped according to the structural refinement and the DFT calculations. In this report, we demonstrate that the multi-doping using additional Ta dopants into the Al-doped LLZO shifts the most energetically favorable sites of Al in the crystal structure from 24d to 96 h Li site, thereby providing more open space for Li ion transport. As a result of these synergistic effects, the multi-doped LLZO shows about three times higher ionic conductivity of 6.14 × 10(-4) S cm(-1) than that of the singly-doped LLZO with a much less efforts in stabilizing cubic phases in the synthetic condition

    Metal-organic framework based on hinged cube tessellation as transformable mechanical metamaterial

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    Mechanical metamaterials exhibit unusual properties, such as negative Poisson???s ratio, which are difficult to achieve in conventional materials. Rational design of mechanical metamaterials at the microscale is becoming popular partly because of the advance in three-dimensional printing technologies. However, incorporating movable building blocks inside solids, thereby enabling us to manipulate mechanical movement at the molecular scale, has been a difficult task. Here, we report a metal-organic framework, self-assembled from a porphyrin linker and a new type of Zn-based secondary building unit, serving as a joint in a hinged cube tessellation. Detailed structural analysis and theoretical calculation show that this material is a mechanical metamaterial exhibiting auxetic behavior. This work demonstrates that the topology of the framework and flexible hinges inside the structure are intimately related to the mechanical properties of the material, providing a guideline for the rational design of mechanically responsive metal-organic frameworks