From all-electron fixed-spin-moment calculations we show that ferromagnetic and checkerboard antiferromagnetic ordering in LaFeAsO are not stable and the stripe antiferromagnetic configuration with ...M(Fe)=0.48 microB is the only stable ground state. The main exchange interactions between Fe ions are large, antiferromagnetic, and frustrated. The magnetic stripe phase breaks the tetragonal symmetry, removes the frustration, and causes a structural distortion. These results successfully explain the magnetic and structural phase transitions in LaFeAsO recently observed by neutron scattering. The presence of competing strong antiferromagnetic exchange interactions suggests that magnetism and superconductivity in doped LaFeAsO may be strongly coupled, much like in the high-T(c) cuprates.
From first-principles calculations, we unravel surprisingly strong interactions between arsenic ions in iron pnictides, the strength of which is controlled by the Fe-spin state. Reducing the ...Fe-magnetic moment weakens the Fe-As bonding, and in turn, increases As-As interactions, causing giant reduction in the c axis. For the CaFe2As2 system, this reduction is as large as 1.4 angstroms. Since the large c reduction has been recently observed only under high pressure, our results suggest that the iron magnetic moment should be present in Fe-pnictides at all times at ambient pressure. Finally, the conventional electron-phonon coupling in the collapsed phase of CaFe2As2 gives a maximum Tc of 0.6 K and cannot explain the approximately 12 K superconductivity observed in some experiments. Implications of these findings on the mechanism of superconductivity in iron pnictides are discussed.
That the COVID‐19 pandemic has affected the work conditions of large segments of society is in no doubt. A growing body of journalistic accounts raised the possibility that the lockdown caused by the ...pandemic has affected women and men in different ways, due mostly to the traditionally gendered division of labour in society. We attempt to test this oft‐cited argument by conducting an original survey with nearly 200 academics. Specifically, we explore the extent to which the effect of the lockdown on childcare, housework and home‐office environment varies across women and men. Our results show that a number of factors are associated with the effect of the lockdown on the work conditions of academics at home, including gender, having children, perceived threat from COVID‐19 and satisfaction with the work environment. We also show that having children disproportionately affects women in terms of the amount of housework during the lockdown.
We report a first-principles study, which demonstrates that a single Ti atom coated on a single-walled nanotube (SWNT) binds up to four hydrogen molecules. The first H2 adsorption is dissociative ...with no energy barrier while the other three adsorptions are molecular with significantly elongated H-H bonds. At high Ti coverage we show that a SWNT can strongly adsorb up to 8 wt % hydrogen. These results advance our fundamental understanding of dissociative adsorption of hydrogen in nanostructures and suggest new routes to better storage and catalyst materials.
The introduction of legislative television as a transparency initiative has been welcomed in an increasing number of democracies. The impact of television cameras on parliamentary behavior, however, ...has received scant attention in systems where personal vote‐earning attributes are thought to be of little importance (e.g., closed‐list proportional representation). Additionally, studies examining this relationship relied exclusively on over‐time variation in legislative behavior (i.e., before and after the introduction of television into parliament), which arguably has important deficiencies in demonstrating the true effect of legislative television. Capitalizing on a unique quasi‐experimental setting, the present study aims to close these gaps in the literature by analyzing parliamentary activities in Turkey, where the legislative television was restricted to 3 days per week (Tuesday, Wednesday, and Thursday) in 2011 after almost two decades of continuous 7‐day operation. Results based on original data sets of parliamentary activities from the pre‐ and postreform periods (2009–11 and 2011–13) indicate that the varying presence of television cameras exacerbated the effect of electoral and reputation‐building motivations on parliamentary behavior, encouraging electorally unsafe and junior MPs to shift their constituency focus to the televised proceedings. The results offer important implications for the study of legislative transparency and constituency representation in party‐list proportional representation systems.
From first-principles calculations, we predict that a single ethylene molecule can form a stable complex with two transition metals (TM) such as Ti. The resulting TM-ethylene complex then absorbs up ...to ten hydrogen molecules, reaching to gravimetric storage capacity of approximately 14 wt %. Dimerization, polymerizations, and incorporation of the TM-ethylene complexes in nanoporous carbon materials are also discussed. Our results are quite remarkable and open a new approach to high-capacity hydrogen-storage materials discovery.
Orthogonally linked BODIPY units show exceptional intersystem crossing efficiencies. We now report orthogonal BODIPY trimers with strong absorption in the visible region and high singlet oxygen ...generation capability. The X-ray diffraction structure confirms that the two peripheral BODIPY units are at a perpendicular angle to the core structure.
Despite the policy-relevant aspirations of military regimes, scholars have shown surprisingly little interest in exploring the agenda dynamics and policy processes in these regimes. We sought to ...close this gap by analysing the original datasets of over 13,000 legislative speeches, public budgets, and the background characteristics of 160 representatives who served in the Consultative Assembly of the military regime of Kenan Evren in Turkey (1980–1983). Empirical analyses indicate that the regime’s policy priorities did not differ significantly from those of democratic governments, and that while representatives with military backgrounds showed far more interest in the core functions of the government, the process through which they were selected (whether or not directly appointed by the National Security Council) appeared to have no explanatory power. Perhaps more importantly, there were more similarities than differences between the military regime of Kenan Evren and the coalition, minority and majority governments of the 1970s and 1980s. Our findings imply that the effect of institutions on policy agendas is overstated.
The hydrogen adsorption sites in MOF5 were determined using neutron powder diffraction along with first-principles calculations. The metal-oxide cluster is primarily responsible for the adsorption ...while the organic linker plays only a secondary role. Equally important, at low temperatures and high-concentration, molecules form unique interlinked high-symmetry nanoclusters with intermolecular distances as small as 3.0 Angstrom and H(2) uptake as high as 11 wt %. These results hold the key to optimizing metal-organic framework (MOF) materials for hydrogen storage applications and also suggest that MOFs can be used as templates to create artificial interlinked hydrogen nanocages with novel properties.
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