Post density functional theoretical studies of highly polar semiconductive Pb(Ti1−x_{1-x}Nix_{x})O3−x_{3-x} solid solutions: The effects of cation arrangement on band gap

We use a combination of conventional density functional theory (DFT) and post-DFT methods, including the local density approximation plus Hubbard $U$ (LDA+$U$), PBE0, and self-consistent $GW$ to study the electronic properties of Ni-substituted PbTiO$_{3}$ (Ni-PTO) solid solutions. We find that LDA calculations yield unreasonable band structures, especially for Ni-PTO solid solutions that contain an uninterrupted NiO$_{2}$ layer. Accurate treatment of localized states in transition-metal oxides like Ni-PTO requires post-DFT methods. $B$-site Ni/Ti cation ordering is also investigated. The $B$-site cation arrangement alters the bonding between Ni and O, and therefore strongly affects the band gap ($E_{\rm g}$) of Ni-PTO. We predict that Ni-PTO solid solutions should have a direct band gap in the visible light energy range, with polarization similar to the parent PbTiO$_{3}$. This combination of properties make Ni-PTO solid solutions promising candidate materials for solar energy conversion devices.Comment: 19 pages, 6 figure

Spontaneous Crystallization of Skyrmions and Fractional Vortices in the Fast-rotating and Rapidly-quenched Spin-1 Bose-Einstein Condensates

We investigate the spontaneous generation of crystallized topological defects via the combining effects of fast rotation and rapid thermal quench on the spin-1 Bose-Einstein condensates. By solving the stochastic projected Gross-Pitaevskii equation, we show that, when the system reaches equilibrium, a hexagonal lattice of skyrmions, and a square lattice of half-quantized vortices can be formed in a ferromagnetic and antiferromagnetic spinor BEC, respetively, which can be imaged by using the polarization-dependent phase-contrast method

Transcritical flow of a stratified fluid over topography: analysis of the forced Gardner equation

Transcritical flow of a stratified fluid past a broad localised topographic obstacle is studied analytically in the framework of the forced extended Korteweg--de Vries (eKdV), or Gardner, equation. We consider both possible signs for the cubic nonlinear term in the Gardner equation corresponding to different fluid density stratification profiles. We identify the range of the input parameters: the oncoming flow speed (the Froude number) and the topographic amplitude, for which the obstacle supports a stationary localised hydraulic transition from the subcritical flow upstream to the supercritical flow downstream. Such a localised transcritical flow is resolved back into the equilibrium flow state away from the obstacle with the aid of unsteady coherent nonlinear wave structures propagating upstream and downstream. Along with the regular, cnoidal undular bores occurring in the analogous problem for the single-layer flow modeled by the forced KdV equation, the transcritical internal wave flows support a diverse family of upstream and downstream wave structures, including solibores, rarefaction waves, reversed and trigonometric undular bores, which we describe using the recent development of the nonlinear modulation theory for the (unforced) Gardner equation. The predictions of the developed analytic construction are confirmed by direct numerical simulations of the forced Gardner equation for a broad range of input parameters.Comment: 34 pages, 24 figure

Li isotopes in the middle Yellow River: seasonal variability, sources and fractionation

To evaluate the roles of climate and hydrology in continental-scale silicate weathering, we applied Li isotopes to the Yellow River and systematically investigated seasonal Li flux, Li isotopic compositions and potential sources. We collected samples from the middle reaches of the Yellow River weekly over the full hydrological year of 2013. We find that the dissolved Li is mainly derived from silicates and evaporites in the arid to semi-arid Yellow River basin. Silicate weathering of loess during the monsoonal season dominates the Li flux in the middle reaches of the Yellow River, with a positive relationship between dissolved Li flux and physical erosion rate. Evaporite contribution for riverine Li was relatively constant in the middle reaches of the Yellow River but slightly increased after the storm event, with an average proportion of ∼25%, which might represent the proportion of evaporite contribution to global oceans. Seasonal variations in the riverine Li isotopic compositions are dominantly controlled by temperature with a fractionation gradient as −0.182‰ per °C over the full year with deviations likely driven by re-dissolution of suspended particulate matter, extreme hydrological events, and groundwater contribution. Temperature dependent δ7Li value variation of river water inputted into oceans indicates that Cenozoic climate cooling itself may be able to explain ∼2‰ of the 9‰ rise of Cenozoic seawater δ7Li value (Misra and Froelich, 2012). The seasonal variation in riverine Li isotopes highlights that erosion and weathering of loess may provide valuable clues on secular chemical weathering and seawater δ7Li variation spanning a range of time scales

High-redshift star formation rate up to z~8.3 derived from gamma-ray bursts and influence of background cosmology

The high-redshift star formation rate (SFR) is difficult to measure directly even by modern approaches. Long-duration gamma-ray bursts (GRBs) can be detected to the edge of the visible universe because of their high luminorsities. The collapsar model of long gamma-ray bursts indicates that they may trace the star formation history. So long gamma-ray bursts may be a useful tool of measuring the high-redshift SFR. Observations show that long gamma-ray bursts prefer to form in a low-metallicity environment. We study the high-redshift SFR up to z~8.3 considering the Swift GRBs tracing the star formation history and the cosmic metallicity evolution in different background cosmological models including $\Lambda$CDM, quintessence, quintessence with a time-varying equation of state, and brane-world model. We use latest Swift GRBs including two highest-$z$ GRBs, GRB 080913 at $z=6.7$ and GRB 090423 at $z=8.3$. We find that the SFR at $z>4$ shows a steep decay with a slope of $\sim -5.0$ in $\Lambda$CDM. In the other three models, the high-redshift SFR is slightly different from $\Lambda$CDM model, and also shows a steep decay.Comment: 5 pages, 5 figures, 2 tables, two references adde

Cosmopolitan Risk Community and China's Climate Governance

Ulrich Beck asserts that global risks, such as climate change, generate a form of ‘compulsory cosmopolitanism’, which ‘glues’ various actors into collective action. Through an analysis of emerging ‘cosmopolitan risk communities’ in Chinese climate governance, this paper points out a ‘blind spot’ in the theorisation of cosmopolitan belonging and an associated inadequacy in explaining shifting power-relations. The paper addresses this problem by engaging with the intersectionality of the cosmopolitan space. It is argued that cosmopolitan belonging is a form of performative identity. Its key characteristic lies in a ‘liberating prerogative’, which enables individuals to participate in the solution of common problems creatively. It is this liberating prerogative that coerces the state out of political monopoly and marks the cosmopolitan moment

Transpolar arc observation after solar wind entry into the high-latitude magnetosphere

Recently, Cluster observations have revealed the presence of new regions of solar wind plasma entry at the high-latitude magnetospheric lobes tailward of the cusp region, mostly during periods of northward interplanetary magnetic field. In this study, observations from the Global Ultraviolet Imager (GUVI) experiment on board the TIMED spacecraft and Wideband Imaging Camera imager on board the IMAGE satellite are used to investigate a possible link between solar wind entry and the formation of transpolar arcs in the polar cap. We focus on a case when transpolar arc formation was observed twice right after the two solar wind entry events were detected by the Cluster spacecraft. In addition, GUVI and IMAGE observations show a simultaneous occurrence of auroral activity at low and high latitudes after the second entry event, possibly indicating a two-part structure of the continuous band of the transpolar arc

Fashion, Cooperation, and Social Interactions

Fashion plays such a crucial rule in the evolution of culture and society that it is regarded as a second nature to the human being. Also, its impact on economy is quite nontrivial. On what is fashionable, interestingly, there are two viewpoints that are both extremely widespread but almost opposite: conformists think that what is popular is fashionable, while rebels believe that being different is the essence. Fashion color is fashionable in the first sense, and Lady Gaga in the second. We investigate a model where the population consists of the afore-mentioned two groups of people that are located on social networks (a spatial cellular automata network and small-world networks). This model captures two fundamental kinds of social interactions (coordination and anti-coordination) simultaneously, and also has its own interest to game theory: it is a hybrid model of pure competition and pure cooperation. This is true because when a conformist meets a rebel, they play the zero sum matching pennies game, which is pure competition. When two conformists (rebels) meet, they play the (anti-) coordination game, which is pure cooperation. Simulation shows that simple social interactions greatly promote cooperation: in most cases people can reach an extraordinarily high level of cooperation, through a selfish, myopic, naive, and local interacting dynamic (the best response dynamic). We find that degree of synchronization also plays a critical role, but mostly on the negative side. Four indices, namely cooperation degree, average satisfaction degree, equilibrium ratio and complete ratio, are defined and applied to measure people's cooperation levels from various angles. Phase transition, as well as emergence of many interesting geographic patterns in the cellular automata network, is also observed.Comment: 21 pages, 12 figure

Spatial Symmetry of Superconducting Gap in YBa2Cu3O7-\delta Obtained from Femtosecond Spectroscopy

The polarized femtosecond spectroscopies obtained from well characterized (100) and (110) YBa2Cu3O7-\delta thin films are reported. This bulk-sensitive spectroscopy, combining with the well-textured samples, serves as an effective probe to quasiparticle relaxation dynamics in different crystalline orientations. The significant anisotropy in both the magnitude of the photoinduced transient reflectivity change and the characteristic relaxation time indicates that the nature of the relaxation channel is intrinsically different in various axes and planes. By the orientation-dependent analysis, d-wave symmetry of the bulk-superconducting gap in cuprate superconductors emerges naturally.Comment: 8 pages, 4 figures. To be published in Physical Review B, Rapid Communication