Tunneling spectroscopy for probing orbital anisotropy in iron pnictides

Using realistic multi-orbital tight-binding Hamiltonians and the T-matrix formalism, we explore the effects of a non-magnetic impurity on the local density of states in Fe-based compounds. We show that scanning tunneling spectroscopy (STS) has very specific anisotropic signatures that track the evolution of orbital splitting (OS) and antiferromagnetic gaps. Both anisotropies exhibit two patterns that split in energy with decreasing temperature, but for OS these two patterns map onto each other under 90 degree rotation. STS experiments that observe these signatures should expose the underlying magnetic and orbital order as a function of temperature across various phase transitions.Comment: 12 pages, 9 figures, replacement with minor changes suggested by referee

Cost-benefit Analysis of a Genetic Marker on Cow-calf Operations Differentiated by Pasture and Breed

Genetic sequencing in beef cattle (Bos taurus L.) is expected to aid producers with selecting breeding stock. Using data from experimental trials conducted with Angus, Brahman, and their reciprocal cross, the single nucleotide polymorphism (SNP) P450 C994G marker expression was investigated for use in selecting genetics suited to grazing endophyte-infected tall fescue (Festuca arundinacea Schreb. L.) compared to bermudagrass (Cynodon dactylon L.) pasture. The study is unique in the sense that actual cow-calf breeding failure rates (open cows were not culled) were tracked from 1991 to 1997 on herds that were bred to calf in spring and were either exposed to fungal endophyte-infected (Acremonium coenophialum L.) tall fescue grazing and hay or not. The study used the Forage and Cattle Analysis and Planning (FORCAP) decision support software to assess economic performance driven by birth weight, weaning weight, and breeding failure rate differences across treatment. Results suggest that for reciprocal cross herds primarily grazing bermudagrass pastures, the P450 C994C genotype (CC) was most favorable; whereas, the P450 G994C genotype (GC) was more profitable with tall fescue. Adding genetic market information when selecting a production strategy led to approximately $15/head in added profitability. In comparison to the prorated cost of$2.40/head over the life of a dam, the collection, interpretation, and management of genetic information under the conditions observed in this study may be worthwhile

Spin fluctuations and superconductivity in a 3D tight-binding model for BaFe2As2

Despite the wealth of experimental data on the Fe-pnictide compounds of the KFe2As2-type, K = Ba, Ca, or Sr, the main theoretical work based on multiorbital tight-binding models has been restricted so far to the study of the related 1111 compounds. This can be ascribed to the more three dimensional electronic structure found by ab initio calculations for the 122 materials, making this system less amenable to model development. In addition, the more complicated Brillouin zone (BZ) of the body-centered tetragonal symmetry does not allow a straightforward unfolding of the electronic band structure into an effective 1Fe/unit cell BZ. Here we present an effective 5-orbital tight-binding fit of the full DFT band structure for BaFeAs including the kz dispersions. We compare the 5-orbital spin fluctuation model to one previously studied for LaOFeAs and calculate the RPA enhanced susceptibility. Using the fluctuation exchange approximation to determine the leading pairing instability, we then examine the differences between a strictly two dimensional model calculation over a single kz cut of the BZ and a completely three dimensional approach. We find pairing states quite similar to the 1111 materials, with generic quasi-isotropic pairing on the hole sheets and nodal states on the electron sheets at kz = 0 which however are gapped as the system is hole doped. On the other hand, a substantial kz dependence of the order parameter remains, with most of the pairing strength deriving from processes near kz = pi. These states exhibit a tendency for an enhanced anisotropy on the hole sheets and a reduced anisotropy on the electron sheets near the top of the BZ.Comment: 12 pages, 15 figure

Running to Stand Still: Challenges Economists Face with Imperfect Data

Some suggest that land application of phosphorus rich poultry litter has negatively affected area waters' recreational value. However, key data are unavailable to conduct thorough economic analysis to aid in policy development. This paper examines the challenges associated with using limited economic analyses to construct policy to address this situation.Research Methods/ Statistical Methods,