Magnetic defects promote ferromagnetism in Zn1-xCoxO

Experimental studies of Zn1-xCoxO as thin films or nanocrystals have found ferromagnetism and Curie temperatures above room temperature and that p- or n-type doping of Zn1-xCoxO can change its magnetic state. Bulk Zn1-xCoxO with a low defect density and x in the range used in experimental thin film studies exhibits ferromagnetism only at very low temperatures. Therefore defects in thin film samples or nanocrystals may play an important role in promoting magnetic interactions between Co ions in Zn1-xCoxO. The electronic structures of Co substituted for Zn in ZnO, Zn and O vacancies, substituted N and interstitial Zn in ZnO were calculated using the B3LYP hybrid density functional in a supercell. The B3LYP functional predicts a band gap of 3.34 eV for bulk ZnO, close to the experimental value of 3.47 eV. Occupied minority spin Co 3d levels are at the top of the valence band and unoccupied levels lie above the conduction band minimum. Majority spin Co 3d levels hybridize strongly with bulk ZnO states. The neutral O vacancy and interstitial Zn are deep and shallow donors, respectively. The Zn vacancy is a deep acceptor and the acceptor level for substituted N is at mid gap. The possibility that p- or n-type dopants promote exchange coupling of Co ions was investigated by computing total energies of magnetic states of ZnO supercells containing two Co ions and an oxygen vacancy, substituted N or interstitial Zn in various charge states. The neutral N defect and the singly-positively charged O vacancy are the only defects which strongly promote ferromagnetic exchange coupling of Co ions at intermediate range.Comment: 9 pages, 11 figure

Beached birds on the Flemish beaches

The history of collecting beached birds along the Flemish coast goes back to 1962. The study aims to determine the oil-rate (the proportion of oiled birds) of the beach washed birds, which is a good tool to determine trends in the chronic pollution of our coastal waters with oil. Since 1992, the Research Institute for Nature and Forest (INBO) is responsible for the Beached Bird Surveys (BBS) and organises systematic counts once a month during October - March.The numbers of beached birds fluctuated a lot over the previous decades, depending on the number of birds wintering along our coast, oil spills and weather conditions. During the winter 2006/2007, 447 beached birds were counted along the Flemish coast, being 0.99 birds km-1, close to the average number of 1.06 birds km-1 since the winter 1991/1992 (numbers of beached birds due to the Tricolor oil spill during the winter 2002/2003 are ignored in this analysis). The highest densities were encountered during February, a general tendency. Auks and gulls were the most numerous last winter, and that was always the case since the winter 1991/1992. A of Uria aalge and Razorbills) last winter will be remembered as the winter with the highest proportion of auks since the winter 1992.Guillemots and Razorbills are especially vulnerable for oil pollution because they spend most of their life swimming at beach were auks. During the first half of the winter, the oil-rate was relatively low, but the second half was characterised by a relatively high score. Recently, OSPAR (the commission for the Protection of Marine Environment of the North-East Atlantic) has recognised the oil-rate among Guillemots as EcoQ, an indicator to evaluate trends in chronic oil pollution of the marine environment. The EcoQ-objective is to force back the oil rate of Guillemots to 10% or less. When examining the changes in the oil-rate of Guillemots that washed ashore our beaches since 1962, three periods are noticeable. Between 1962 and 1990, the oil rate of beached Guillemots was very high (> 95% of all beached Guillemots were fouled). Since 1990, there was a remarkable decline with an average oil-rate of about 60%. Since 2004 the decline continued with an all time lowest score of an oil-rate of ‘only’ 17% last winter. On the other hand, there is no decline in the density of Guillemots found death along the Flemish coast, so possibly a problem in food viability is responsible for the death of many auks since 1990. Diet studies on collected auks will hopefully tell us something why auks wash ashore without any visible reason

Using bond-length dependent transferable force constants to predict vibrational entropies in Au-Cu, Au-Pd, and Cu-Pd alloys

A model is tested to rapidly evaluate the vibrational properties of alloys with site disorder. It is shown that length-dependent transferable force constants exist, and can be used to accurately predict the vibrational entropy of substitutionally ordered and disordered structures in Au-Cu, Au-Pd, and Cu-Pd. For each relevant force constant, a length- dependent function is determined and fitted to force constants obtained from first-principles pseudopotential calculations. We show that these transferable force constants can accurately predict vibrational entropies of L1$_{2}$-ordered and disordered phases in Cu$_{3}$Au, Au$_{3}$Pd, Pd$_{3}$Au, Cu$_{3}$Pd, and Pd$_{3}$Au. In addition, we calculate the vibrational entropy difference between L1$_{2}$-ordered and disordered phases of Au$_{3}$Cu and Cu$_{3}$Pt.Comment: 9 pages, 6 figures, 3 table

Atomic-scale structure of the SrTiO3(001)-c(6x2) reconstruction: Experiments and first-principles calculations

The c(6x2) is a reconstruction of the SrTiO3(001) surface that is formed between 1050-1100oC in oxidizing annealing conditions. This work proposes a model for the atomic structure for the c(6x2) obtained through a combination of results from transmission electron diffraction, surface x-ray diffraction, direct methods analysis, computational combinational screening, and density functional theory. As it is formed at high temperatures, the surface is complex and can be described as a short-range ordered phase featuring microscopic domains composed of four main structural motifs. Additionally, non-periodic TiO2 units are present on the surface. Simulated scanning tunneling microscopy images based on the electronic structure calculations are consistent with experimental images

Etiological diagnosis in limb reduction defects and the number of affected limbs:A population-based study in the Northern Netherlands

Limb reduction defects (LRDs) that affect multiple limbs are considered to be more often heritable, but only few studies have substantiated this. We aimed to investigate if an etiological diagnosis (genetic disorder or clinically recognizable disorder) is more likely to be made when multiple limbs are affected compared to when only one limb is affected. We used data from EUROCAT Northern Netherlands and included 391 fetuses and children with LRDs born in 1981-2017. Cases were classified as having a transverse, longitudinal (preaxial/postaxial/central/mixed), intercalary, or complex LRD of one or more limbs and as having an isolated LRD or multiple congenital anomalies (MCA). We calculated the probability of obtaining an etiological diagnosis in cases with multiple affected limbs versus one affected limb using relative risk (RR) scores and Fisher's exact test. We showed that an etiological diagnosis was made three times more often when an LRD occurred in multiple limbs compared to when it occurred in one limb (RR 2.9, 95% CI 2.2-3.8, p <0.001). No genetic disorders were found in isolated cases with only one affected limb, whereas a genetic disorder was identified in 16% of MCA cases with one affected limb. A clinically recognizable disorder was found in 47% of MCA cases with one affected limb. Genetic counseling rates were similar. We conclude that reduction defects of multiple limbs are indeed more often heritable. Genetic testing seems less useful in isolated cases with one affected limb, but is warranted in MCA cases with one affected limb