Barkhausen-type noise in the resistance of antiferromagnetic Cr thin films

We present an experimental study of the changes generated on the electrical resistance $R(T)$ of epitaxial Cr thin films by the transformation of quantized spin density wave domains as the temperature is changed. A characteristic resistance noise appears only within the same temperature region where a cooling-warming cycle in $R(T)$ displays hysteretic behavior. We propose an analysis based on an analogy with the Barkhausen noise seen in ferromagnets. There fluctuations in the magnetization $M(H)$ occur when the magnetic field $H$ is swept. By mapping $M \rightarrow \Psi_0$ and $H \rightarrow T$, where $\Psi_0$ corresponds to the order parameter of the spin density wave, we generalize the Preisach model in terms of a random distribution of {\it resistive hysterons} to explain our results. These hysterons are related to distributions of quantized spin density wave domains with different sizes, local energies and number of nodes.Comment: 5 pages, 3 figures. To be published in Europhysics Letter

Photometric and spectroscopic study of the intermediate age open cluster NGC 3960

We present CCD UBVI photometry and high-resolution spectroscopy of the intermediate age open cluster NGC 3960. The colour - magnitude diagrams (CMDs) derived from the photometric data and interpreted with the synthetic CMD method allow us to estimate the cluster parameters. We derive: age = 0.9 or 0.6 Gyr (depending on whether or not overshooting from convective regions is included in the adopted stellar models), distance (m-M)0 = 11.6 +/- 0.1, reddening E(B-V) = 0.29 +/- 0.02, differential reddening Delta E(B-V) = 0.05 and approximate metallicity between solar and half of solar. We obtained high resolution spectra of three clump stars, and derived an average [Fe/H] = -0.12 (rms 0.04 dex), in very good agreement with the photometric determination. We also obtained abundances of alpha-elements, Fe-peak elements, and of Ba. The reddenings toward individual stars derived from the spectroscopic temperatures and the Alonso et al. calibrations give further support to the existence of significative variations across the cluster.Comment: Accepted for publication on MNRAS; fig. 3, 4, 5, 6 at degraded resolutio

Ag and N acceptors in ZnO: ab initio study of acceptor pairing, doping efficiency, and the role of hydrogen

Efficiency of ZnO doping with Ag and N shallow acceptors, which substitute respectively cations and anions, was investigated. First principles calculations indicate a strong tendency towards formation of nearest neighbor Ag-N pairs and N-Ag-N triangles. Binding of acceptors stems from the formation of quasi-molecular bonds between dopants, and has a universal character in semiconductors. The pairing increases energy levels of impurities, and thus lowers doping efficiency. In the presence of donors, pairing is weaker or even forbidden. However, hydrogen has a tendency to form clusters with Ag and N, which favors the Ag-N aggregation and lowers the acceptor levels of such complexes.Comment: 10 pages, 4 figure

Radial velocities and membership of stars in the old, distant open cluster Berkeley 29

Multi slit spectroscopy at the Telescopio Nazionale Galileo was employed to measure radial velocities for 20 stars in the direction of the old open cluster Berkeley 29, the farthest known in our Galaxy. Membership information was derived for stars along all the red giant branch, in particular near its tip, and on the red clump. The sample of bona-fide cluster members was used to revise the cluster distance to about 15 kpc, on the basis of an empirical comparison with the red clump in open clusters with known distances. A metallicity [Fe/H] = -0.74 +/- 0.18 was also estimated using the colours of spectroscopically confirmed red giant stars.Comment: 7 pages, 5 figures (fig. 1 at low-res, but JPEG version included too), accepted for publication in A&

Intergenerational contacts and depressive symptoms among older parents in Eastern Europe

Objective: We investigate the association between parent-child contact frequency and changes in older parents’ depressive symptoms in Bulgaria, Georgia and Russia. These are countries in which societal transformations may mean that psychological feelings of security engendered by having children in close contact may have particularly important implications for the mental health of older parents. Methods: We analysed data from two waves of the Generation and Gender Surveys conducted three years apart and took account of relationships with more than one child. Analyses were performed using OLS regression models, adjusted for depressive symptoms at baseline. Results: Among mothers increases in depressive symptoms were greater for those who lacked at least weekly contact with any child than for those with frequent contact with at least one child (b = 0.64; p<0.01). Increases in depressive symptoms were associated with infrequent contacts with children, even after controlling for relationship quality (b = 0.55; p<0.05). Among unpartnered fathers, less than weekly meetings with children were associated with increases in depressive symptoms. Conclusions: Among mothers and unpartnered fathers changes in depressive symptoms varied by parent-child contact. The adverse effect of not having a partner on fathers’ mental health was reduced, but not eliminated, by having frequent contacts with adult children

Returns home by children and changes in parents’ well-being in Europe

Co-resident adult children may be a source of emotional and instrumental support for older parents, but also a source of conflict and stress. Results from previous research are far from conclusive and indicate that intergenerational co-residence may have both negative and positive effects on parents' depressive symptoms and physical health. We analyse longitudinal data from four waves of the Survey of Health, Ageing and Retirement in Europe (2007-2015) to examine whether returns to the parental home by adult children are associated with changes in the quality of life of parents aged 50-75. Results from fixed effects linear regression models show that returns to the parental home by adult children were associated with decreases in parents' quality of life and that this largely reflected declines associated with the return of a child to an ‘empty nest’ where no other children were still co-resident. In line with previous research which has indicated differing effects of co-residence on parents' depressive symptoms by cultural tradition, such moves were associated with decreases in parents' quality of life to a greater extent in a grouping of Nordic/social-democratic countries than in other parts of Europe. There were no associations between changes in parental quality of life and the returning child's characteristics, although unemployment of a child was negatively, and new partnership of a child, positively associated with changes in parental quality of life

The old anticentre open cluster Berkeley 32: membership and fundamental parameters

We have obtained medium-low resolution spectroscopy and BVI CCD imaging of Berkeley 32, an old open cluster which lies in the anticentre direction. From the radial velocities of 48 stars in the cluster direction we found that 31 of them, in crucial evolutionary phases, are probable cluster members, with an average radial velocity of +106.7 (sigma = 8.5) km/s. From isochrone fitting to the colour magnitude diagrams of Berkeley 32 we have obtained an age of 6.3 Gyr, (m-M)0 = 12.48 and E(B-V) = 0.10. The best fit is obtained with Z=0.008. A consistent distance, (m-M)0 ~= 12.6 +/- 0.1, has been derived from the mean magnitude of red clump stars with confirmed membership; we may assume (m-M)0 ~= 12.55 +/- 0.1. The colour magnitude diagram of the nearby field observed to check for field stars contamination looks intriguingly similar to that of the Canis Major overdensity.Comment: MNRAS, in press. Degraded resolution for Fig.

On the origin of the helium-rich population in the peculiar globular cluster Omega Centauri

In this contribution we discuss the origin of the extreme helium-rich stars which inhabit the blue main sequence (bMS) of the Galactic globular cluster Omega Centauri. In a scenario where the cluster is the surviving remnant of a dwarf galaxy ingested by the Milky Way many Gyr ago, the peculiar chemical composition of the bMS stars can be naturally explained by considering the effects of strong differential galactic winds, which develop owing to multiple supernova explosions in a shallow potential well.Comment: 2 pages, 1 figure, to appear in the Proceedings of IAU Symposium No. 268, Light Elements in the Universe (C. Charbonnel, M. Tosi, F. Primas, C. Chiappini, eds., Cambridge Univ. Press