Enriching the Learning Experience: A CALM Approach.

This paper outlines and evaluates a new learning strategy implemented in the Faculty of Economics and Commerce at the University of Melbourne. The strategy is an Internet based assignment delivery and assessment system designed to (i) equip students to make link between macroeconomic theory and important real-world issues, (ii) develop positive attitudes to the subject (iii) develop deep approaches to learning (iv) develop a facility for critical analysis and problem solving and (v) develop effective study habits. Using a multi-dimensional evaluation strategy, the indications are that the new approach has succeeded in its aims.MACROECONOMICS ; TECHNOLOGY ; NETWORK ANALYSIS

NMR Determination of an Incommensurate Helical Antiferromagnetic Structure in EuCo2As2

We report $^{153}$Eu, $^{75}$As and $^{59}$Co nuclear magnetic resonance (NMR) results on EuCo$_2$As$_2$ single crystal. Observations of $^{153}$Eu and $^{75}$As NMR spectra in zero magnetic field at 4.3 K below an antiferromagnetic (AFM) ordering temperature $T_{\rm N}$ = 45 K and its external magnetic field dependence clearly evidence an incommensurate helical AFM structure in EuCo$_2$As$_2$. Furthermore, based on $^{59}$Co NMR data in both the paramagnetic and the incommensurate AFM states, we have determined the model-independent value of the AFM propagation vector ${\bf k}$ = (0, 0, 0.73 $\pm$ 0.07)2$\pi$/$c$ where $c$ is the $c$ lattice parameter. Thus the incommensurate helical AFM state was characterized by only NMR data with model-independent analyses, showing NMR to be a unique tool for determination of the spin structure in incommensurate helical AFMs.Comment: 6 pages, 4 figures, accepted for publication in Phys.Rev.

A Radio--Optical Reference Frame VIII. CCD observations from KPNO and CTIO: internal calibration and first results

In this pilot investigation, precise optical positions in the FK5 system are presented for a set of 16 compact extragalactic radio sources, which will be part of the future radio--optical reference frame. The 0.9 m KPNO and CTIO telescopes equipped with 2K CCD's have been used for this project. The astrometric properties of these instruments are investigated in detail. New techniques of using wide field CCD observations for astrometry in general are developed. An internal precision of 5 to 31 mas in position per single exposure is found, depending on the brightness of the object. The tie to the primary optical reference system is established by photographic astrometry using dedicated astrographs on both hemispheres. An accuracy of $\approx 30$ mas per source is estimated for the multi--step reduction procedure when based on the future Hipparcos catalog, while the FK5--based positions suffer from system errors of 100 to 200 mas as compared to the radio positions. This work provides a contribution to the international effort to link the Hipparcos instrumental coordinate system to the quasi--inertial VLBI radio reference frame. Precise radio and optical astrometry of a large sample of compact extragalactic sources will also contribute to the astrophysics of these objects by comparing the respective centers of emission at the optical and radio wavelengths.Comment: AAS v.4 LaTeX, 2 parts on 1 file (main text + deluxetable), accepted by AJ, Dec.95, fig. with reprint

EuCo2P2: A Model Molecular-Field Helical Heisenberg Antiferromagnet

The metallic compound EuCo2P2 with the body-centered tetragonal ThCr2Si2 structure containing Eu spins 7/2 was previously shown from single-crystal neutron diffraction measurements to exhibit a helical antiferromagnetic (AFM) structure below TN = 66.5 K with the helix axis along the c axis and with the ordered moments aligned within the ab-plane. Here we report crystallography, electrical resistivity, heat capacity, magnetization and magnetic susceptibility measurements on single crystals of this compound. We demonstrate that EuCo2P2 is a model molecular-field helical Heisenberg antiferromagnet from comparisons of the anisotropic magnetic susceptibility chi, high-field magnetization and magnetic heat capacity of EuCo2P2 single crystals at temperature T < TN with the predictions of our recent formulation of molecular field theory. Values of the Heisenberg exchange interactions between the Eu spins are derived from the data. The low-T magnetic heat capacity ~ T^3 arising from spin-wave excitations with no anisotropy gap is calculated and found to be comparable to the lattice heat capacity. The density of states at the Fermi energy of EuCo2P2 and the related compound BaCo2P2 are found from the heat capacity data to be large, 10 and 16 states/eV per formula unit for EuCo2P2 and BaCo2P2, respectively. These values are enhanced by a factor of ~2.5 above those found from DFT electronic structure calculations for the two compounds. The calculations also find ferromagnetic Eu-Eu exchange interactions within the ab-plane and AFM interactions between nearest- and next-nearest planes, in agreement with the MFT analysis of chi{ab}(T < TN).Comment: 20 pages, 17 figures, 3 tables, 46 references. This is an extended replacement of arXiv:1512.02958 with an additional coautho

Experimental and theoretical electronic structure of EuRh2As2

The Fermi surfaces (FS's) and band dispersions of EuRh2As2 have been investigated using angle-resolved photoemission spectroscopy. The results in the high-temperature paramagnetic state are in good agreement with the full potential linearized augmented plane wave calculations, especially in the context of the shape of the two-dimensional FS's and band dispersion around the Gamma (0,0) and X (pi,pi) points. Interesting changes in band folding are predicted by the theoretical calculations below the magnetic transition temperature Tn=47K. However, by comparing the FS's measured at 60K and 40K, we did not observe any signature of this transition at the Fermi energy indicating a very weak coupling of the electrons to the ordered magnetic moments or strong fluctuations. Furthermore, the FS does not change across the temperature (~ 25K) where changes are observed in the Hall coefficient. Notably, the Fermi surface deviates drastically from the usual FS of the superconducting iron-based AFe2As2 parent compounds, including the absence of nesting between the Gamma and X FS pockets.Comment: 4 pages, 4 figure