Hydrogen analysis in APT: methods to control adsorption and dissociation of H2.

Experimental factors that influence adsorption of hydrogen from the residual gas on a nickel-rich alloy during atom probe tomography are investigated. The rate of adsorption has a maximum value at field strengths between 24 and 26 V/nm. It is found that by selecting sufficiently high laser energies, or alternatively high DC fields, it is possible to significantly reduce adsorbed quantities. Some of the physical mechanisms for hydrogen supply to the analyzed area of the tip are discussed, and it is concluded that the dominating supply mechanism is most likely direct adsorption from the gas phase. Low hydrogen adsorption at high fields is attributed to autoionization, and a decline at low fields is explained by reduced field adsorption.

Spatial and temporal predictions of moose winter distribution.

Herbivores are usually distributed unevenly across the landscape often because of variation in resource availability. We used zero-inflated generalised additive models (to account for data with a high number of zeros) that include georeferences to predict winter distribution of a large herbivore (moose Alces alces). Moose distribution was analysed in relation to forage availability and distance to neighbouring sites. Our results showed that the ability to explain moose distribution indexed by pellet count data at a local scale increased when spatial information (longitude and latitude) was added to the model compared to the model only including food availability. By using the relationship between moose and forage distribution, and the spatial information, we predicted patch choice by moose reasonably well in 2 out of 4 years. However, the distribution of moose was also influenced by weather conditions, as it was most clumped in the year with most snow. In conclusion, our study lends support for a non-linear approach using georeferences for a comprehensive understanding of herbivore distribution at a small scale. This result also indicates that the use of a certain patch by moose not only depends on the selected patch itself but is also influenced by the neighbouring patch and factors at a larger spatial scale, such as moose management influencing the density above moose home range level. The relatively high proportion of unexplained variation suggests that the use of a certain patch is also influenced by other factors such as topography, predation, competition, weather conditions, and wildlife management strategies.

Quantitative APT analysis of Ti(C,N).

A specially produced Ti(C,N) standard material, with a known nominal composition, was investigated with laser assisted atom probe tomography. The occurrence of molecular ions and single/multiple events was found to be influenced by the laser pulse energy, and especially C related events were affected. Primarily two issues were considered when the composition of Ti(C,N) was determined. The first one is connected to detector efficiency, due to the detector dead-time. The second one is connected to peak overlap in the mass spectrum. A method is proposed for quantification of the C content in order to establish the C/N ratio. A correction was made to the major C peaks, C at 6 and 12 Da, with the (13)C isotopes, at 6.5 and 13 Da, according to the known natural abundance. In addition, a correction of the peak at 24 Da, where C and Ti overlap, is proposed based on the occurrence of single/multiple events for respective element. The results were compared to the results from other techniques such as electron energy loss spectroscopy, chemical analysis and X-ray diffraction. After applying the corrections, atom probe tomography results were satisfactory. Furthermore, the content of dissolved O in Ti(C,N) was successfully quantified.

A quantitative analysis of a multi-phase polycrystalline cubic boron nitride tool material using DualEELS.

This paper presents a quantitative analysis of a polycrystalline cubic boron nitride tool material by electron energy-loss spectroscopy spectrum imaging acquired in dual range mode. Having both the low-loss and core-loss regions acquired nearly simultaneously provides the advantage of accurate corrections for thickness effects and thus the possibility to perform quantification calculations. This has resulted in extracted bonding maps with areal (atoms/nm(2)) or volumetric (atoms/nm(3)) densities. Spectroscopic signatures in the low-loss and core-loss energy ranges, of the elements (Al, B, C, N, Ti and O) present in the existing phases, were studied and used when extracting the element specific bonding maps by the multiple linear least squares fitting procedure. Variations of elemental concentrations across the investigated area were determined, despite of phase overlap in the beam direction or energy overlaps in the EELS spectrum. Moreover, the surface oxidation of Ti(C,N) and AlN as well as the amorphisation of α-Al(2)O(3) is discussed.

Quantitative atom probe analysis of carbides.

Compared to atom probe analysis of metallic materials, the analysis of carbide phases results in an enhanced formation of molecular ions and multiple events. In addition, many multiple events appear to consist of two or more ions originating from adjacent sites in the material. Due to limitations of the ion detectors measurements generally underestimate the carbon concentration. Analyses using laser-pulsed atom probe tomography have been performed on SiC, WC, Ti(C,N) and Ti(2)AlC grains in different materials as well as on large M(23)C(6) precipitates in steel. Using standard evaluation methods, the obtained carbon concentration was 6-24% lower than expected from the known stoichiometry. The results improved remarkably by using only the (13)C isotope, and calculating the concentration of (12)C from the natural isotope abundance. This confirms that the main reason for obtaining a too low carbon concentration is the dead time of the detector, mainly affecting carbon since it is more frequently evaporated as multiple ions. In the case of Ti(C,N) and Ti(2)AlC an additional difficulty arises from the overlap between C(2)(+), C(4)(2+) and Ti(2+) at the mass-to-charge 24 Da.

Methods of quantitative matrix analysis of Zircaloy-2.

The zirconium-based alloy Zircaloy-2 contains small amounts of iron, chromium and nickel dissolved in the matrix. Several attempts to measure these amounts have been made in the past, but the results are conflicting and inconclusive. The advent of wide angle, laser pulsed atom probe tomography motivates a new attempt to analyze the matrix. Large datasets are now easily obtained using laser pulsing but quantification is not straightforward due to rather complex mass spectra. Zircaloy-2 contains about 1 wt% tin, 0.1 wt% oxygen and trace amounts of Si, C and Al. Severe overlaps make quantification of any Fe(+), Cr(+) and Ni(+) ions impossible. Quantification of Fe, Cr and Ni therefore requires that they appear as doubly charged ions only, and consequently the field must be kept high enough. In addition, adsorbed CO(+) may appear at the main peak of Fe(2+). In the paper a method is reported, which gives what we believe an accurate quantitative analysis of at least iron and chromium in the matrix.

Population density and sex do not influence fine-scale natal dispersal in roe deer.

It is commonly assumed that the propensity to disperse and the dispersal distance of mammals should increase with increasing density and be greater among males than among females. However, most empirical evidence, especially on large mammals, has focused on highly polygynous and dimorphic species displaying female-defence mating tactics. We tested these predictions on roe deer, a weakly polygynous species of large herbivore exhibiting a resource-defence mating tactic at a fine spatial scale. Using three long-term studies of populations that were subject to the experimental manipulation of size, we did not find any support for either prediction, whether in terms of dispersal probability or dispersal distance. Our findings of similar dispersal patterns in both sexes of roe deer suggest that the underlying cause of natal dispersal is not related to inbreeding avoidance in this species. The absence of positive density dependence in fine-scale dispersal behaviour suggests that roe deer natal dispersal is a pre-saturation process that is shaped by heterogeneities in habitat quality rather than by density per se.

Methods for atom probe analysis of microgradients in functionally graded cemented carbides.

Methods to prepare needle-shaped specimens for atom probe field ion microscopy from near surface regions have been developed. The material used was a cemented carbide with a composition gradient towards the surface, but the method is equally applicable for other materials. The preparation technique involves dimple grinding, electropolishing and focused ion beam (FIB) milling. The use of FIB milling allows for specimen preparation of materials which due to the preferential etching of different phases are difficult to electropolish. The technique also allows for preparation of specimens at well defined depth from the sample surface, selection of phase to be analysed, and to sharpen and re-use already analysed specimens. Atom probe analyses of the near surface zone region in a gradient sintered WC-Ti(C,N)-TaC-Co cemented carbide are presented.

Home range size and choice of management strategy for lynx in Scandinavia.

Annual and seasonal home ranges were calculated for 47 Eurasian lynx in four Scandinavian study sites (two in Sweden and two in Norway). The observed home ranges were the largest reported for the species, with study site averages ranging from 600 to 1,400 km2 for resident males and from 300 to 800 km2 for resident females. When home range sizes were compared to the size of protected areas (national parks and nature reserves) in Scandinavia, it was concluded that very few protected areas contained sufficient forest to provide space for more than a few individuals. As a direct consequence of this, most lynx need to be conserved in the multiuse semi-natural forest habitats that cover large areas in Scandinavia. This conservation strategy leads to a number of conflicts with some land uses (sheep and semidomestic reindeer herding, and roe deer hunters), but not all (forestry and moose harvest). Accordingly research must be aimed at understanding the ecology of these conflicts, and finding solutions.