14,316 research outputs found

    Charge order and Mott insulating ground states in small-angle twisted bilayer graphene

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    In this work, we determine states of electronic order of small-angle twisted bilayer graphene. Ground states are determined for weak and strong couplings which are representatives for varying distances of the twist-angle from its magic value. In the weak-coupling regime, charge density waves emerge which break translational and C3C_{3}-rotational symmetry. In the strong coupling-regime, we find rotational and translational symmetry breaking Mott insulating states for all commensurate moir\'e band fillings. Depending on the local occupation of superlattice sites hosting up to four electrons, global spin-(ferromagnetic) and valley symmetries are also broken which may give rise to a reduced Landau level degeneracy as observed in experiments for commensurate band fillings. The formation of those particular electron orders is traced back to the important role of characteristic non-local interactions which connect all localized states belonging to one hexagon formed by the AB- and BA-stacked regions of the superlattice

    Meteorological effects on long-range outdoor sound propagation

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    Measurements of sound propagation over distances up to 1000 m were carried out with an impulse sound source offering reproducible, short time signals. Temperature and wind speed at several heights were monitored simultaneously; the meteorological data are used to determine the sound speed gradients according to the Monin-Obukhov similarity theory. The sound speed profile is compared to a corresponding prediction, gained through the measured travel time difference between direct and ground reflected pulse (which depends on the sound speed gradient). Positive sound speed gradients cause bending of the sound rays towards the ground yielding enhanced sound pressure levels. The measured meteorological effects on sound propagation are discussed and illustrated by ray tracing methods

    Replacing the Human Rights Act with a weaker British Bill of Rights would send a sign to the international community that we are no longer serious about human rights

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    The prime minister has made clear his intention to ‘repatriate’ human rights jurisdiction back from Europe to the UK. Helen Wildbore and Professor Francesca Klug survey the different currents which are driving the debate for a new UK bill of rights and argue that replacing the Human Rights Act with anything weaker would send a sign to the international community that the UK is not serious about human rights

    Role of the irr protein in the regulation of iron metabolism in Rhodobacter sphaeroides

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    In Rhizobia the Irr protein is an important regulator for iron-dependent gene expression. We studied the role of the Irr homolog RSP_3179 in the photosynthetic alpha-proteobacterium Rhodobacter sphaeroides. While Irr had little effect on growth under iron-limiting or non-limiting conditions its deletion resulted in increased resistance to hydrogen peroxide and singlet oxygen. This correlates with an elevated expression of katE for catalase in the Irr mutant compared to the wild type under non-stress conditions. Transcriptome studies revealed that Irr affects the expression of genes for iron metabolism, but also has some influence on genes involved in stress response, citric acid cycle, oxidative phosphorylation, transport, and photosynthesis. Most genes showed higher expression levels in the wild type than in the mutant under normal growth conditions indicating an activator function of Irr. Irr was however not required to activate genes of the iron metabolism in response to iron limitation, which showed even stronger induction in the absence of Irr. This was also true for genes mbfA and ccpA, which were verified as direct targets for Irr. Our results suggest that in R. sphaeroides Irr diminishes the strong induction of genes for iron metabolism under iron starvation

    Suez and Sterling, 1956

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    Daily data on spot and forward dollar/sterling exchange rates and on Britain's foreign exchange reserves are used to reassess the financial history of the 1956 Suez crisis. We find that support of sterling at its Bretton Woods lower bound lost credibility as early as July. Reserve losses also are consistent with an exchange rate crisis. We provide the first econometric study of foreign exchange market intervention in the pre-convertibility phase of the Bretton Woods system. The Bank of England's interventions reacted strongly both to official sterling and to the transferable sterling market in New York, which suggests that convertibility was a central goal of policy.Suez crisis, Bretton Woods system, foreign exchange market intervention

    Numerical calculation of three-point branched covers of the projective line

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    We exhibit a numerical method to compute three-point branched covers of the complex projective line. We develop algorithms for working explicitly with Fuchsian triangle groups and their finite index subgroups, and we use these algorithms to compute power series expansions of modular forms on these groups.Comment: 58 pages, 24 figures; referee's comments incorporate
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