Preparation, Structure and Spectroscopic Properties of NH 4 [Ln(S 2 CNH 2 ) 4 ] ⋅ H 2 O (Ln=La, Eu)

The title compounds were prepared under mild ambient conditions by a facile co-precipitation route. NH4[Eu(S2CNH2)4] ⋅ H2O (a) and NH4[La(S2CNH2)4] ⋅ H2O (b) crystallize isotypically in the monoclinic space group P21/c with a=8.4461(3), b=13.6367(3), c=16.2945(5) Å, β=103.759(2)° (for (a)), and a=8.50484(9), b=13.84476(16), c=16.20816(17) Å, β=103.7644(11)° for (b), respectively. The spectroscopic data reveal the presence of a ligand-to-metal charge transfer (LMCT) process of low energy in a and in the solid solutions NH4[La1−xEux(S2CNH2)4] ⋅ H2O (x=0.016 and 0.05). Despite of the consequent efficient luminescent quenching, it was possible to recorded excitation and emission spectra at room temperature. These spectra are characterized by narrow bands due to intraconfigurational-4f transitions of the Eu3+ ion. However, broad bands associated to the LMCT state were also observed, mainly for the solid solutions NH4[La1−xEux(S2CNH2)4] ⋅ H2O (x=0.016 and 0.05). Consequently, an intramolecular energy transfer mechanism is proposed, taking into account the role of the LMCT on the spectroscopic properties of dithiocarbamate complexes

Single-hole dynamics in dimerized and frustrated spin-chains

We present a unified account for the coupled single-hole- and spin-dynamics in the spin-gap phase of dimerized and frustrated spin-chains and two-leg spin ladders. Based on the strong dimer-limit of a one-dimensional $t_123$-$J_123$-model a diagrammatic approach is presented which employs a mapping of the spin-Hamiltonian onto a pseudo-fermion bond-boson model. Results for the single-hole spectrum are detailed. A finite quasi-particle weight is observed and studied for a variety of system parameters. A comparison with existing exact diagonalization data is performed and good agreement is found.Comment: 10 pages, 12 figure

Power theories in political ecology

Power plays a key role in definitions of political ecology. Likewise, empirical studies within this field tend to provide detailed presentations of various uses of power, involving corporate and conservation interventions influencing access to land and natural resources. The results include struggle and conflict. Yet, there is a lack of theoretical elaboration showing how power may be understood in political ecology. In this article, we start to fill this gap by reviewing the different theoretical perspectives on power that have dominated this field. There are combinations of influences, two of them being actor-oriented and neo-Marxist approaches used from the 1980s. Typically, case studies are presented of environmental interventions by a broad range of actors at various scales from the local to the global. The focus has been on processes involving actors behind these interventions, as well as the outcomes for different social groups. Over the last two decades, in political ecology we have increasingly seen a move in power perspectives towards poststructuralist thinking about "discursive power", inspired by Foucault. Today, the three approaches (actor-oriented, neo-Marxist and Foucauldian) and their combinations form a synergy of power perspectives that provide a set of rich and nuanced insights into how power is manifested in environmental conflicts and governance. We argue that combining power perspectives is one of political ecology's strengths, which should be nurtured through a continuous examination of a broad spectrum of social science theories on power

A Hot Saturn Orbiting an Oscillating Late Subgiant Discovered by TESS

© 2019. The American Astronomical Society. All rights reserved.. We present the discovery of HD 221416 b, the first transiting planet identified by the Transiting Exoplanet Survey Satellite (TESS) for which asteroseismology of the host star is possible. HD 221416 b (HIP 116158, TOI-197) is a bright (V = 8.2 mag), spectroscopically classified subgiant that oscillates with an average frequency of about 430 μHz and displays a clear signature of mixed modes. The oscillation amplitude confirms that the redder TESS bandpass compared to Kepler has a small effect on the oscillations, supporting the expected yield of thousands of solar-like oscillators with TESS 2 minute cadence observations. Asteroseismic modeling yields a robust determination of the host star radius (R∗ = 2.943 ± 0.064 Ro), mass (M∗ = 1.212 ± 0.074 Mo), and age (4.9 ± 1.1 Gyr), and demonstrates that it has just started ascending the red-giant branch. Combining asteroseismology with transit modeling and radial-velocity observations, we show that the planet is a "hot Saturn" (Rp = 9.17 ± 0.33 R⊕) with an orbital period of ∼14.3 days, irradiance of F = 343 ± 24 F⊕, and moderate mass (Mp = 60.5 ± 5.7 M⊕) and density (ρp = 0.431 ± 0.062 g cm-3). The properties of HD 221416 b show that the host-star metallicity-planet mass correlation found in sub-Saturns (4-8 R⊕) does not extend to larger radii, indicating that planets in the transition between sub-Saturns and Jupiters follow a relatively narrow range of densities. With a density measured to ∼15%, HD 221416 b is one of the best characterized Saturn-size planets to date, augmenting the small number of known transiting planets around evolved stars and demonstrating the power of TESS to characterize exoplanets and their host stars using asteroseismology