16,714 research outputs found
Emergence of quasi-one-dimensional physics in MoS(dmit), a nearly-isotropic three-dimensional molecular crystal
We report density functional theory calculations for MoS(dmit).
We derive an ab initio tight-binding model from overlaps of Wannier orbitals;
finding a layered model with interlayer hopping terms the size of the
in-plane terms. The in-plane Hamiltonian interpolates the kagom\'e and
honeycomb lattices. It supports states localized to dodecahedral rings within
the plane, which populate one-dimensional (1D) bands and lead to a quasi-1D
spin-one model on a layered honeycomb lattice once interactions are included.
Two lines of Dirac cones also cross the Fermi energy.Comment: 5 pages, 3 figure
Simulating the onset and spread of anoxic conditions during Cretaceous OAE2
A new model of the global atmosphere-ocean-continent-mantle system was set-up to investigate the triggering of the Oceanic Anoxic Event OAE2 through volcanic degassing processes at large igneous provinces (LIPs). The model simulates the changes in oceanic dissolved oxygen, phosphate, and carbon and the evolution of atmospheric
pCO2 values under mid-Cretaceous boundary conditions. It considers the effects of pCO2 on element ratios in marine plankton (C : P) and includes new parameterizations for phosphorus and carbon burial at the seafloor based on modern observations. Independent isotopic and chemical time-series of ocean and atmosphere change over OAE2 are applied to evaluate the model results. The model results support the hypothesis that OAE2 was triggered by massive CO2 emissions at LIPs. According to the model, the phosphorus weathering flux into the ocean and the C : P ratio in marine plankton were enhanced by the rise in surface temperature and atmosphere pCO2 caused by mantle degassing. Marine export production and oxygen consumption in intermediate and deep water masses increased in response to the expansion of the dissolved phosphate inventory of the ocean and the change in plankton element ratios. The spread of anoxic conditions in bottom waters -induced by enhanced carbon export and respiration- was further amplified by the oxygen-dependent burial of phosphorus in marine sediments in a positive feedback loop. The modeling implies that enhanced CO2 emissions favor the spread of low-oxygen conditions also in modern oceans
Dynamical effects of exchange symmetry breaking in mixtures of interacting bosons
In a double-well potential, a Bose-Einstein condensate exhibits Josephson
oscillations or self-trapping, depending on its initial preparation and on the
ratio of inter-particle interaction to inter-well tunneling. Here, we elucidate
the role of the exchange symmetry for the dynamics with a mixture of two
distinguishable species with identical physical properties, i.e. which are
governed by an isospecific interaction and external potential. In the
mean-field limit, the spatial population imbalance of the mixture can be
described by the dynamics of a single species in an effective potential with
modified properties or, equivalently, with an effective total particle number.
The oscillation behavior can be tuned by populating the second species while
maintaining the spatial population imbalance and all other parameters constant.
In the corresponding many-body approach, the single-species description
approximates the full counting statistics well also outside the realm of
spin-coherent states. The method is extended to general Bose-Hubbard systems
and to their classical mean-field limits, which suggests an effective
single-species description of multicomponent Bose gases with weakly
an-isospecific interactions.Comment: amended and expanded, accepted for Phys. Rev. A, 14 pages, 7 figure
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