Self-localization of composite spin-lattice polarons

Self-localization of holes in the Holstein t-J model is studied in the adiabatic limit using exact diagonalization and the retraceable path approximation. It is shown that the critical electron-phonon coupling \lambda_c decreases with increasing J and that this behavior is determined mainly by the incoherent rather than by the coherent motion of the hole. The obtained spin correlation functions in the localized region can be understood within a percolation picture where antiferromagnetic order can persist up to a substantial hole doping. These results restrict the possibility of self-localization of holes in lightly doped cuprates.Comment: 4 pages, 5 figure

Pairs of Languages Closed under Shuffle Projection

Shuffle projection is motivated by the verification of safety properties of special parameterized systems. Basic definitions and properties, especially related to alphabetic homomorphisms, are presented. The relation between iterated shuffle products and shuffle projections is shown. A special class of multi-counter automata is introduced, to formulate shuffle projection in terms of computations of these automata represented by transductions. This reformulation of shuffle projection leads to construction principles for pairs of languages closed under shuffle projection. Additionally, it is shown that under certain conditions these transductions are rational, which implies decidability of closure against shuffle projection. Decidability of these conditions is proven for regular languages. Finally, without additional conditions, decidability of the question, whether a pair of regular languages is closed under shuffle projection, is shown. In an appendix the relation between shuffle projection and the shuffle product of two languages is discussed. Additionally, a kind of shuffle product for computations in S-automata is defined

Incomplete pure dephasing of N-qubit entangled W states

We consider qubits in a linear arrangement coupled to a bosonic field which acts as a quantum heat bath and causes decoherence. By taking the spatial separation of the qubits explicitly into account, the reduced qubit dynamics acquires an additional non-Markovian element. We investigate the time evolution of an entangled many-qubit W state, which for vanishing qubit separation remains robust under pure dephasing. For finite separation, by contrast, the dynamics is no longer decoherence-free. On the other hand, spatial noise correlations may prevent a complete dephasing. While a standard Bloch-Redfield master equation fails to describe this behavior even qualitatively, we propose instead a widely applicable causal master equation. Here we employ it to identify and characterize decoherence-poor subspaces. Consequences for quantum error correction are discussed.Comment: 14 pages, 6 figures, revised version, to appear in Phys. Rev.

DEMAND FOR PLANT NUTRIENTS IN TENNESSEE DISAGGREGATED BY MIXED FERTILIZERS AND DIRECT APPLICATION MATERIALS

When obtaining nitrogen (N), phosphate (P) and potash (K), purchasing decisions concerning the quantity and the form of each plant nutrient must be made. Logit models are estimated for the choice-of-form decision by considering those variables influencing the probability that plant nutrients will be purchased in Tennessee as part of a mixed fertilizer or as direct application materials. Parameter and elasticity estimates can be used by fertilizer manufacturers and distributors to anticipate changes in the composition of demand for plant nutrients in Tennessee.Crop Production/Industries,

Tax reform and labour-market performance in the euro area: a simulation-based analysis using the New Area-Wide Model

In this paper, we employ a calibrated two-country version of the New Area-Wide Model (NAWM) currently under development at the European Central Bank to examine the potential benefits and spillovers of reducing labour-market distortions caused by euro area tax structures. Our analysis shows that lowering tax distortions to levels prevailing in the United States would result in an increase in hours worked and output by more than 10 percent. At the same time, tax reductions would have positive spillovers to the euro area’s trade partners, bolstering the case for tax reforms from a global perspective. Finally, we illustrate that, in the presence of heterogeneous households, distributional effects may be of importance when gauging the impact of tax reforms. JEL Classification: E32, E62DSGE modelling, euro area, Fiscal Policy, limited asset-market participation, tax reform

CHOICE OF TECHNOLOGY: THE CASE OF GRASS FED VERSUS GRAIN FED CATTLE IN HAWAII

A model describing the choice of technology is developed from theoretical considerations. It is shown that the model can be approximated using a logit function. Estimates of short-run elasticities are easily obtained. The model is then applied to the decision to place feeder cattle in confined feeding situations or on range. With one possible exception, the results are consistent with theoretical expectations and with previous studies.Livestock Production/Industries,