We study dynamical systems which have bounded complexity with respect to three kinds metrics: the Bowen metric d n , the max-mean metricd n and the mean metric d n , both in topological dynamics and ergodic theory.It is shown that a topological dynamical system (X, T ) has bounded complexity with respect to d n (resp.d n ) if and only if it is equicontinuous (resp. equicontinuous in the mean). However, we construct minimal systems which have bounded complexity with respect tod n but not equicontinuous in the mean.It turns out that an invariant measure µ on (X, T ) has bounded complexity with respect to d n if and only if (X, T ) is µ-equicontinuous. Meanwhile, it is shown that µ has bounded complexity with respect tod n if and only if µ has bounded complexity with respect tod n if and only if (X, T ) is µ-mean equicontinuous if and only if it has discrete spectrum.
Emerging two-dimensional (2D) noble-metal dichalcogenides (NMDCs) PdX2 (X = S and Se) crystallize in an unusual orthorhombic structure (2O phase) with unique pentagons and PdX4 planar squares as building blocks,...
Li–CO2 batteries have attracted worldwide attention
because of their dual characteristics of high energy density and effective
CO2 capture. However, the basic electrochemistry mechanism
involved has been unclear, which is mainly confused by the complicated
decomposition of organic electrolytes. Herein, water-in-salt (WIS,
LiTFSI/H2O 21.0 mol/1 kg) has been explored as a suitable
electrolyte for the first time to investigate the reaction mechanism
of Li–CO2 batteries with different cathodes (carbon
nanotube (CNT) and Mo2C/CNT, respectively). An Mo2C-based Li–CO2 battery with WIS delivers a higher
energy efficiency of 83% and a superior cyclability, compared to those
of the CNT-based counterpart cell. Through various ex/in situ qualitative/quantitative
characterizations, the Mo2C-based Li–CO2 battery with WIS can operate on the reversible conversion of CO2-to-Li2C2O4 ((e–/CO2)ideal = 1) at lower discharge/charge overpotentials,
while the CNT-based counterpart cell is based on the formation/decomposition
of Li2CO3 ((e–/CO2)ideal ≈ 1.33) at high overpotentials. Such a difference
in CO2 reduction products stems from the stronger interaction
between Mo2C(101) and Li2C2O4 than that of the CNT and Li2C2O4 based on the density functional theory calculations, resulting
in the selective stabilization of the intermediate product Li2C2O4 on the Mo2C surface.
Abstract. We consider positive entropy G-systems for certain countable, discrete, infinite left-orderable amenable groups G. By undertaking local analysis, the existence of asymptotic pairs and chaotic sets will be studied in connecting with the stable sets. Examples are given for the case of integer lattice groups, the Heisenberg group, and the groups of integral unipotent upper triangular matrices.
Quantifying variation in animals’ paleodiet from the fossil record is difficult as a continuous record of their remains is difficult to obtain. Here we assess dietary change in seabirds from Guangjin Island, Xisha Archipelago, South China Sea, by using stable nitrogen isotopes in seabird bones and prey remains collected from a coral sand ornithogenic sediment profile. δ15N of seabird bone collagen varied from 11.7‰ to 14.1‰ (averaging 12.8‰ ± 0.4‰), but that of fish bones and scales showed minor variations. Flying fish and squid are two favorite foods of tropical seabirds, and the average values of muscle δ15N in typical flying fish and squid samples were 9.2‰ and 10.2‰, respectively. Based on nitrogen isotope mass balance calculation, we conclude that flying fish accounts for 80% ± 40% of seabird diet averaged over the past 1200 years, but this prey accounted for only about 37% ± 30% during the ‘Little Ice Age’ (AD 1400–1850). Flying fish averaged up to 88% ± 2% during the ‘Medieval Warm Period’ (AD 850–1200), close to modern observed value of 89.6%. Thus, it appears that seabirds on Guangjin Island mainly preyed on flying fish during warm periods, and shift to squid during cooler periods. Our results suggest that recent global warming and human activities have likely caused a rapid decrease in tropical seabird population and dietary shift.
Based on three ornithogenic sediment profiles and seabird subfossils therein from the Xisha Islands, South China Sea, the relative population size of seabirds over the past 1000 years was reconstructed using reflectance spectrum. Here we present an apparent increase and subsequent decline of seabirds on these islands in the South China Sea. Seabird populations peaked during the Little Ice Age (LIA, 1400–1850 AD), implying that the cool climate during the LIA appears to have been more favorable to seabirds on the Xisha Islands in the South China Sea. Climate change partly explains the recent decrease in seabird populations over the past 150 years, but the significant decline and almost complete disappearance thereof on most of the Xisha Islands is probably attributable to human disturbance. Our study reveals the increasing impact of anthropogenic activities on seabird population in recent times.
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