Interplay of antiferromagnetism, ferromagnetism and superconductivity in EuFe_2(As_1-xP_x)_2 single crystals

We report a systematic study on the influence of antiferromagnetic and ferromagnetic phases of Eu^2+ moments on the superconducting phase upon doping the As site by isovalent P, which acts as chemical pressure on EuFe_2As_2. Bulk superconductivity with transition temperatures of 22 K and 28 K are observed for x=0.16 and 0.20 samples respectively. The Eu ions order antiferromagnetically for x=0.22 whereupon the Eu ions order ferromagnetically. Density functional theory based calculations reproduce the observed experimental findings consistently. We discuss in detail the coexistence of superconductivity and magnetism in a tiny region of the phase space and comment on the competition of ferromagnetism and superconductivity in the title compound.Comment: 6 pages, 5 figures, 1 tabl

A Panel Data Study of Physicians’ Labor Supply: The Case of Norway

Physicians are key personnel in a sector which is important due to its size as well as the quality of service it provides. We estimate the labor supply of physicians employed at hospitals in Norway, using personnel register data merged with other public records. A dynamic labor supply equation is estimated using a sample of 1303 physicians observed over the period 1993-97. The methods of estimation are GMM and system GMM. We reject the static model in favor of a dynamic model and obtain a long-run wage elasticity of about 0.55. This is considerably higher than previously estimated for physicians, in particular for those who are not self-employed.physicians, labor supply, dynamic panel data

A panel data study of physicians’ labor supply: The case of Norway

Physicians are key personnel in a sector which is important due to its size as well as the quality of service it provides. We estimate the labor supply of physicians employed at hospitals in Norway, using personnel register data merged with other public records. A dynamic labor supply equation is estimated using a sample of 1303 physicians observed over the period 1993-97. The methods of estimation are GMM and system GMM. We reject the static model in favor of a dynamic model and obtain a long-run wage elasticity of about 0.55. This is considerably higher than previously estimated for physicians, in particular for those who are not self-employed.Physicians; labor supply; dynamic panel data.

Will Increased Wages Reduce Shortage of Nurses? A Panel Data Analysis of Nurses' Labor Supply

Shortage of nurses is a problem in several countries. It is an unsettled question whether increasing wages constitute a viable policy for extracting more labor supply from nurses. In this paper we use a unique matched panel data set of Norwegian nurses covering the period 1993-1997 to estimate wage elasticities. This data includes detailed information on 18,066 individuals over 5 years totaling 56,832 observations. The estimated elasticity when controlling for individual and time invariant fixed effects is significantly positive but not very high in magnitude. Individual and institutional features are significant and important for working hours. We have also access to information about contractual arrangements. It turns out that shift work is important for hours of work, and that omitting information about this common phenomenon will underestimate the wage effect.Nurses, labor supply, panel data, selection

Fatty acid synthesis in Escherichia coli and its applications towards the production of fatty acid based biofuels

The idea of renewable and regenerative resources has inspired research for more than a hundred years. Ideally, the only spent energy will replenish itself, like plant material, sunlight, thermal energy or wind. Biodiesel or ethanol are examples, since their production relies mainly on plant material. However, it has become apparent that crop derived biofuels will not be sufficient to satisfy future energy demands. Thus, especially in the last decade a lot of research has focused on the production of next generation biofuels. A major subject of these investigations has been the microbial fatty acid biosynthesis with the aim to produce fatty acids or derivatives for substitution of diesel. As an industrially important organism and with the best studied microbial fatty acid biosynthesis, Escherichia coli has been chosen as producer in many of these studies and several reviews have been published in the fields of E. coli fatty acid biosynthesis or biofuels. However, most reviews discuss only one of these topics in detail, despite the fact, that a profound understanding of the involved enzymes and their regulation is necessary for efficient genetic engineering of the entire pathway. The first part of this review aims at summarizing the knowledge about fatty acid biosynthesis of E. coli and its regulation, and it provides the connection towards the production of fatty acids and related biofuels. The second part gives an overview about the achievements by genetic engineering of the fatty acid biosynthesis towards the production of next generation biofuels. Finally, the actual importance and potential of fatty acid-based biofuels will be discussed

Extension of the spin-1/2 frustrated square lattice model: the case of layered vanadium phosphates

We study the influence of the spin lattice distortion on the properties of frustrated magnetic systems and consider the applicability of the spin-1/2 frustrated square lattice model to materials lacking tetragonal symmetry. We focus on the case of layered vanadium phosphates AA'VO(PO4)2 (AA' = Pb2, SrZn, BaZn, and BaCd). To provide a proper microscopic description of these compounds, we use extensive band structure calculations for real materials and model structures and supplement this analysis with simulations of thermodynamic properties, thus facilitating a direct comparison with the experimental data. Due to the reduced symmetry, the realistic spin model of layered vanadium phosphates AA'VO(PO4)2 includes four inequivalent exchange couplings: J1 and J1' between nearest-neighbors and J2 and J2' between next-nearest-neighbors. The estimates of individual exchange couplings suggest different regimes, from J1'/J1 and J2'/J2 close to 1 in BaCdVO(PO4)2, a nearly regular frustrated square lattice, to J1'/J1 ~ 0.7 and J2'/J2 ~ 0.4 in SrZnVO(PO4)2, a frustrated square lattice with sizable distortion. The underlying structural differences are analyzed, and the key factors causing the distortion of the spin lattice in layered vanadium compounds are discussed. We propose possible routes for finding new frustrated square lattice materials among complex vanadium oxides. Full diagonalization simulations of thermodynamic properties indicate the similarity of the extended model to the regular one with averaged couplings. In case of moderate frustration and moderate distortion, valid for all the AA'VO(PO4)2 compounds reported so far, the distorted spin lattice can be considered as a regular square lattice with the couplings (J1+J1')/2 between nearest-neighbors and (J2+J2')/2 between next-nearest-neighbors.Comment: 14 pages, 9 figures, 4 table