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Topanga is a kinetic ion code developed for simulating large-scale plasma phenomena in the Earth's ionosphere on magnetohydrodynamic timescales. It is a domain-decomposed parallel code that runs on high-performance computing platforms. Features of Topanga include spherical geometry for simplified boundary conditions and computational efficiency; a hybrid plasma model with inertia-less fluid electrons, kinetic ions, and an electric field specified via an Ohm's law; a Maxwell-FDTD (finite difference time domain) plasma model which retains the displacement current in Maxwell's equations and models electron currents in the ionosphere with a tensor conductivity; sponge-layer boundary conditions for absorption of electromagnetic and plasma waves incident on the domain boundaries; and a novel mixed-implicit algorithm for evolving the EM fields inside the Maxwell-FDTD region that is stable over many orders of magnitude in the electron–ion collision frequency. We verify the numerical methods used in Topanga on a pair of test problems. The first test involves modeling a three-dimensional collisionless shock using the hybrid set of equations. The second test involves modeling a spherical TEM mode in vacuum using the Maxwell-FDTD set of equations. Finally, we demonstrate how using the combined set of hybrid and Maxwell-FDTD equations to model the Starfish Prime high-altitude nuclear test recovers a "missing" EM signal on the ground that is not present when using only the hybrid set of equations. The magnitude of this signal in the simulation containing the Maxwell-FDTD region agrees well with the E3a portion of the magnetohydrodynamic electromagnetic pulse from Starfish Prime. [ABSTRACT FROM AUTHOR]

Abstract: Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests managed for timber in western Oregon frequently lack structure and diversity associated with old-growth forests. We examined thinning effects on overstory and understory [...]

The design of multiphase optical nanocomposites necessitates the understanding of coexisting phases' morphology and chemistry which have deterministic impacts on light–matter interaction. A prominent example is gradient refractive index (GRIN) materials proposed to realize an arbitrarily shaped, single optical component with minimal chromatic aberration. Ge‐As‐Pb‐Se materials are promising for GRIN due to their ability to exhibit spatially varying volume fraction of high‐index Pb‐rich phases in low index matrices. These materials are characterized to date, exclusively using transmission electron microscopy to reveal their phase separation and induced crystalline phase(s). It is found in the study that the intrinsic 2D perspective of the technique has hindered the identification of true morphology. To clarify this ambiguity, atom probe tomography (APT) is utilized to gain the first‐ever observation of the nanocomposites' microstructure and its evolution upon heat treatment in a 3D space. The APT‐quantified geometry and chemistry of coexisting phases are considered to predict the effective media's optical behaviors which closely match experimental data, enabling the establishment of the material's predictive and accurate process–structure–property relationship. Findings in the study demonstrate the robustness and advantage of the APT‐assisted characterization in the design and realization of GRIN materials. [ABSTRACT FROM AUTHOR]

Scolopostethus affinis, a species native to the Palearctic region, is reported from two localities in Montreal, Quebec. The species appears established and breeding in Quebec and is a new alien species in North America. A description of S. affinis is given, with illustrations, and details of the life cycle and diagnostic characters. [ABSTRACT FROM AUTHOR]

The Hemiptera superfamily Lygaeoidea is represented in the Canadian Prairie Provinces of Alberta, Saskatchewan and Manitoba by 76 species distributed among 10 families, namely: Artheneidae (1 species), Berytidae (2), Blissidae (3), Cymidae (4), Geocoridae (7 described plus 1 undescribed species), Lygaeidae (18) (Ischnorhynchinae (2), Lygaeinae (7), Orsillinae (9)), Oxycarenidae (3), Pachygronthidae (1), Piesmatidae (4) and Rhyparochromidae (31). Keys to families and species are presented and for each species we provide notes on distribution, recognition and ecology as well as a photograph of the dorsal habitus. The general ecology of lygaeoid bugs with special reference to those of the Canadian Prairies is discussed. Within the region, known lygaeoid fauna is most diverse in the Cypress Hills and adjacent dry prairie regions of southeastern Alberta and southwestern Saskatchewan. There the dominant transcontinental faunal element is enriched by western, eastern and southern species reaching their distribution limits. Few introduced species are present, and these are largely synanthropic or ecological specialists and appear to have had little effect on the native fauna. Humans, through disrupting natural ecosystems, generally enhance lygaeoid bug faunas for most species favour disturbed or early successional stage environments. However, modern prairie agriculture has probably greatly impacted the fauna by fragmenting and reducing habitat through the wide extent of cultivation, use of chemicals and intensive grazing. Most species of Lygaeoidea appear to be resilient to these impacts due to their rather general ecological requirements and there is no evidence that any species has been lost from the fauna although some are in surprisingly low densities or have small, very widely distributed populations. [ABSTRACT FROM AUTHOR]

One hundred twenty species of aleocharine beetles (Staphylinidae) are recognized in the province of Saskatchewan. Sixty-five new provincial records, including twelve new species and one new North American record, are presented. Oligota inflata (Mannerheim), a Palearctic species, is newly recorded for North America. The following twelve species are described as new to science: Acrotona pseudopygmaea Klimaszewski & Larson, sp. n., Agaricomorpha pulchra Klimaszewski & Larson, sp. n. (new genus record for Canadian fauna), Aleochara elisabethae Klimaszewski & Larson, sp. n., Atheta (Dimetrota) larsonae Klimaszewski & Larson, sp. n., Atheta (Microdota) pseudopittionii Klimaszewski & Larson, sp. n., Atheta (Microdota) spermathecorum Klimaszewski & Larson, sp. n., Atheta (sensu lato) richardsoni Klimaszewski & Larson, sp. n., Brachyusa saskatchewanae Klimaszewski & Larson, sp. n., Dochmonota langori Klimaszewski & Larson, sp. n., Dochmonota simulans Klimaszewski & Larson, sp. n., Dochmonota websteri Klimaszewski & Larson, sp. n., and Oxypoda domestica Klimaszewski & Larson, sp. n. Colour images of habitus and black and white images of the median lobe of the aedeagus, spermatheca, and tergite and sternite VIII are presented for all new species, Oligota inflata Mannerheim and Dochmonota rudiventris (Eppelsheim). A new synonymy is established: Tetralina filitarsus Casey, syn. n. = Tetralina helenae Casey, now placed in the genus Brachyusa Mulsant & Rey. [ABSTRACT FROM AUTHOR]

Atom-probe tomography (APT) and secondary ion mass spectrometry (SIMS) provide complementary in situ element and isotope data in minerals such as zircon. SIMS measures isotope ratios and trace elements from 1-20 µm spots with excellent accuracy and precision. APT identifies mass/ charge and three-dimensional position of individual atoms (±0.3 nm) in 100 nm-scale samples, volumes up to one million times smaller than SIMS. APT data provide unique information for understanding element and isotope distribution; crystallization and thermal history; and mechanisms of mineral reaction and exchange. This atomistic view enables evaluation of the fidelity of geochemical data for zircon because it provides new understanding of radiation damage, and can test for intracrystalline element mobility. Nano-geochronology is one application of APT in which Pb isotope ratios from sub-micrometer domains of zircon provide model ages of crystallization and identify later magmatic and metamorphic reheating. Based on SEM imaging and SIMS analysis, 11 needle-shaped specimens ~100 nm in diameter were sampled from one Archean and two Hadean zircons by focused ion-beam milling and analyzed with APT. The three-dimensional distribution of Pb and nominally incompatible elements (Y, REEs) differs at the atomic scale in each zircon. Zircon JH4.0 (4.007 Ga, Jack Hills, Western Australia) is homogeneous in Pb, Y, and REEs. In contrast, Pb and Y and REEs are clustered in sub-equant ~10 nm diameter domains, spaced 10-40 nm apart in zircons ARG2.5 (2.542 Ga, Grouse Creek Mountains, Utah) and JH4.4 (4.374 Ga, Jack Hills). Most clusters are flattened parallel to (100) or (010). U and Th are not collocated with Pb in clusters and appear to be homogeneously distributed in all three zircons. The analyzed domains experienced 4 to 8 x 1015 α-decay events/mg due to U and Th decay and yet all zircons yield U-Pb ages by SIMS that are better than 97% concordant, consistent with annealing of most radiation damage. The 207Pb/206Pb ratios for the 100 nm-scale specimens measured by APT average 0.17 for ARG2.5, 0.42 for the JH4.0, and 0.52 for JH4.4. These ratios are less precise (±10-18% 2σ) due to the ultra-small sample size, but in excellent agreement with values measured by SIMS (0.1684, 0.4269, and 0.5472, respectively) and the crystallization ages of the zircons. Thus Pb in these clusters is radiogenic, but unsupported, meaning that the Pb is not spatially associated with its parent isotopes of U and Th. For the domain outside of clusters in JH4.4, the 207Pb/206Pb ratio is 0.3, consistent with the SIMS value of 0.2867 for the zircon overgrowth rim and an age of 3.4 Ga. In ARG2.5, all Pb is concentrated in clusters and there is no detectable Pb remaining outside of the clusters. The Pb-Y-REE-rich clusters and lack of correlation with U in ARG2.5 and JH4.4 are best explained by diffusion of Pb and other elements into ~10 nm amorphous domains formed by α-recoil. Diffusion distances of ~20 nm for these elements in crystalline zircon are consistent with heating at temperatures of 800 °C for ~2 m.y. Such later reheating events are identified and dated by APT from 207Pb/206Pb model ages of clusters in JH4.4 and by the absence of detectable Pb outside of clusters in ARG2.5. SIMS dates for the zircon rims independently confirm reheating of ARG2.5 and JH4.4, which were xenocrysts in younger magmas when rims formed. It is proposed that most domains damaged by α-recoil were annealed at ambient temperatures above 200-300 °C before reheating and only a small number of domains were amorphous and available to concentrate Pb at the time of reheating. The size, shapes, and orientations of clusters were altered by annealing after formation. The absence of enriched clusters in JH4.0 shows that this zircon was not similarly reheated. Thus APT data provide thermochronologic information about crustal reworking even for zircons where no overgrowth is recognized. The clusters in JH4.4 document Pb mobility at the sub-50 nm scale, but show that the much larger 20 µm-scale domains analyzed by SIMS were closed systems. The reliability of oxygen isotope ratios and other geochemical data from zircon can be evaluated by these means. These results verify the age of this zircon and support previous proposals that differentiated crust existed by 4.4 Ga and that the surface of Earth was relatively cool with habitable oceans before 4.3 Ga. These analytical techniques are of general applicability to minerals of all ages and open many new research opportunities. [ABSTRACT FROM AUTHOR]

Atom-probe tomography ( APT) is currently the only analytical technique that, due to its spatial resolution and detection efficiency, has the potential to measure the carbon isotope ratios of individual nanodiamonds. We describe three different sample preparation protocols that we developed for the APT analysis of meteoritic nanodiamonds at sub-nm resolution and present carbon isotope peak ratios of meteoritic and synthetic nanodiamonds. The results demonstrate an instrumental bias associated with APT that needs to be quantified and corrected to obtain accurate isotope ratios. After this correction is applied, this technique should allow determination of the distribution of 12C/13C ratios in individual diamond grains, solving the decades-old question of the origin of meteoritic nanodiamonds: what fraction, if any, formed in the solar system and in presolar environments? Furthermore, APT could help us identify the stellar sources of any presolar nanodiamonds that are detected. [ABSTRACT FROM AUTHOR]

The ability to accurately reconstruct original spatial positions of field-evaporated ions emitted from a surface is fundamental to the success of atom probe tomography. As such, a clear understanding of the evolution of specimen shape and the resultant ions' trajectories during field evaporation plays an important role in improving reconstruction accuracy. To further this understanding, field-evaporation simulations of a bilayer specimen composed of two materials having an evaporation field difference of 20% were performed. The simulated field-evaporation patterns qualitatively compare favorably with experimental data, which provides confidence in the accuracy of specimen shapes predicted by the simulation. Correlations of known original atom positions with detector hit positions as a function of lateral detector position and evaporated depth were derived from the simulation. These correlations are contrasted with the current state-of-the-art reconstruction method thus outlining limitations of the current methodology. A pair of transformations are defined that take into account field-evaporated specimen shapes, and the resulting radial magnifications, to relate recorded ion positions in detector space to reconstructed atomic positions in specimen space. This novel process, when applied to simulated data, results in approximately a factor of 2 improvement in accuracy for reconstructions of interfaces with unequal fields (most general interfaces). This method is not constrained by the fundamental assumption of a hemispherical specimen shape. [ABSTRACT FROM PUBLISHER]

The development of laser-assisted atom probe tomography (APT) and specimen preparation techniques using a focused ion beam equipped with high-resolution scanning electron microscopy (SEM) has significantly advanced the characterization of semiconductor devices by APT. The capability of APT to map out elements in devices at the atomic scale with high sensitivity meets the characterization requirements of semiconductor devices such as the determination of elemental distributions for each device region. [ABSTRACT FROM PUBLISHER]

In the world of tomographic imaging, atom probe tomography (APT) occupies the high-spatial-resolution end of the spectrum. It is highly complementary to electron tomography and is applicable to a wide range of materials. The current state of APT is reviewed. Emphasis is placed on applications and data analysis as they apply to many fields of research and development including metals, semiconductors, ceramics, and organic materials. We also provide a brief review of the history and the instrumentation associated with APT and an assessment of the existing challenges in the field. [ABSTRACT FROM AUTHOR]

We demonstrate for the first time that multivariate statistical analysis techniques can be applied to atom probe tomography data to estimate the chemical composition of a sample at the full spatial resolution of the atom probe in three dimensions. Whereas the raw atom probe data provide the specific identity of an atom at a precise location, the multivariate results can be interpreted in terms of the probabilities that an atom representing a particular chemical phase is situated there. When aggregated to the size scale of a single atom (∼0.2 nm), atom probe spectral-image datasets are huge and extremely sparse. In fact, the average spectrum will have somewhat less than one total count per spectrum due to imperfect detection efficiency. These conditions, under which the variance in the data is completely dominated by counting noise, test the limits of multivariate analysis, and an extensive discussion of how to extract the chemical information is presented. Efficient numerical approaches to performing principal component analysis (PCA) on these datasets, which may number hundreds of millions of individual spectra, are put forward, and it is shown that PCA can be computed in a few seconds on a typical laptop computer. [ABSTRACT FROM PUBLISHER]

The state of application of atom probe tomography to electronic materials is assessed. The benefits and challenges of the technique are discussed with regard to its impact on this field of materials science. Specimen preparation in particular is emphasized as the key to success with modern atom probes. Electronic materials referenced in this paper include components of complementary metal/oxide/semiconductor (CMOS) structures, compound semi-conductors, and thin films for data storage and general applications. Many examples from recent work are provided as illustrations of the types of information that can be derived and the impact this information can have on the research, development, processing, and failure analysis of electronic materials. [ABSTRACT FROM AUTHOR]

The addition of a local electrode geometry has transformed the conventional atom probe into a high-speed, high sensitivity tool capable of mapping three-dimensional (3D) dopant atom distributions in nanoscale volumes of Si. Fields of view exceeding 100 nm in diameter and collection rates exceeding 18×106 at./h are possible with the local electrode geometry. The 3D evolution of dopants, specifically dopant clustering, grain-boundary segregation, shallow-doped B layers, Ni–Si layers, and preamorphization regions, was analyzed. A 200 eV 11B implant in Ge-amorphized Si was mapped. The native surface oxide, 8-nm-deep B-doped layer, and Ge distribution were simultaneously mapped in 3D space. A subsequent Ni silicide process was analyzed to show Ni penetration through the doped layer. In a heavily doped poly-Si sample, a cluster of dimensions 2×7×8 nm3 and containing 264 B atoms was identified at the intersection of three grains. This shows that annealing highly overdoped thin poly-Si layers does not facilitate uniformly doped and highly conductive gate contact layers for nanoscale complementary metal-oxide semiconductor transistors. [ABSTRACT FROM AUTHOR]

Abstract: Five conifers and two hardwoods native to the Pacific Northwest were planted under four overstory densities of 30-year-old plantations of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) in the Oregon Coast Range, USA. Stand treatments were unthinned (547 trees ha−1), narrow thin (252 trees ha−1), wide thin (138 trees ha−1), and very wide thin (72 trees ha−1). Conditions in the unthinned stands were lethal to both hardwoods and conifers. Eighth-year survival in thinned stands ranged from 87 to 94% for conifer species and 61 to 94% for hardwood species. Eighth-year mean heights of conifer species ranged from 2.6 to 5.4m. On the basis of size and damage incurred during the study, we ranked conifer species in decreasing order of suitability for underplanting as western hemlock (Tsuga heterophylla (Raf.) Sarg.), Sitka spruce (Picea sitchensis (Bong.) Carr.), Douglas-fir, grand fir (Abies grandis (Dougl. ex D. Don) Lindl.), and western redcedar (Thuja plicata Donn ex D. Don). Eighth-year mean height of red alder (Alnus rubra (Bong.)) was 7.7m in thinned stands. Heavy and repeated browse (mostly from elk, Cervus elaphus) on bigleaf maple (Acer macrophyllum Pursh) and to a lesser degree on western redcedar led us to conclude that these species may be unsuitable for underplanting unless they can be adequately protected. The other five conifer species and red alder suffered little damage during the study and are all viable choices for underplanting where diversity enhancement is an objective. Major findings from this study are (1) underplanting was successful (good survival and size) when the overstory canopy was thinned to wide or very wide spacings and available light was markedly increased; (2) fast growth of planted seedlings such as red alder, western hemlock, and Sitka spruce can enhance stand structure early in the development of thinned stands; (3) the level of thinning intensity affects light availability in the understory and will determine the vitality and longevity of underplanted seedlings; and (4) animal damage, mostly from elk browse and antler rubbing, varied by species and by size of seedlings but can be so serious as to limit the choice of seedlings. [Copyright &y& Elsevier]

The cabbage maggot, Delia radicum (L.), is a serious pest of cruciferous crops in temperate regions of North America and Europe. The effects of undersowing rutabaga, Brassica napus L. subsp, rapifera Metzg. (Brassicaceae), with white clover, Trifolium repens L. (Leguminosae), on second-generation cabbage maggot and its natural enemies were studied in Newfoundland in 1997 and 1998. In 1997, totals of 1311 and 724 eggs were recovered from bare and undersown plots, respectively. More eggs were present in bare plots than undersown plots on various specific dates. In 1997, rutabagas from bare plots weighed more than those from undersown plots, although damage ratings were similar, suggesting that competition, not cabbage maggot feeding, caused the yield differences. In 1998, there were few cabbage maggots present and little damage or yield reduction in either treatment. Similar numbers of cabbage maggot pupae were extracted and reared from each treatment in each year. In 1997, of the pupae reared from undersown plots, 48% produced cabbage maggot flies, 14% produced parasitic Hymenoptera, and 8% produced Aleochara bilineata Gyllenbal (Coleoptera: Staphylinidae); 19% of the pupae from bare plots produced cabbage maggot flies, 8% produced parasitic Hymenoptera, and 36% produced A. bilineata. More A. bilineata were captured in pitfall traps in bare plots than in undersown plots. The effect of clover on carabid beetles was species specific. There were more Bembidion lampros (Herbst) and Amara bifrons (Gyllenhal) in bare plots in 1997, and more Pterostichus melanarius (Illiger) in undersown plots in both years. Despite consistently lower egg numbers in undersown plots than in bare plots, the numbers of pupae in the two treatments were similar at the end of the season. We speculate that this may be due to differential, density-dependent mortality of immature stages of cabbage maggot caused by predators and parasitoids. [ABSTRACT FROM AUTHOR]