Momentum dependence in the dynamically assisted Sauter-Schwinger effect

Recently it has been found that the superposition of a strong and slow electric field with a weaker and faster pulse can significantly enhance the probability for non-perturbative electron-positron pair creation out of the vacuum -- the dynamically assisted Sauter-Schwinger effect. Via the WKB method, we estimate the momentum dependence of the pair creation probability and compare it to existing numerical results. Besides the theoretical interest, a better understanding of this pair creation mechanism should be helpful for the planned experiments aiming at its detection.Comment: 4 pages RevTeX, 1 figur

Working memory and cued recall

Previous research has found that individuals with high working memory have greater recall capabilities than those with low working memory (Unsworth, Spiller, & Brewers, 2012). Research did not test the extent to which cues affect one’s recall ability in relation to working memory. The present study will examine this issue. Participants completed a working memory measure. Then, they were provided with cued recall tasks whereby they recalled Facebook friends. The cues varied to be no cues, ambiguous cues high in imageability, and cues directly related to Facebook. The results showed that there was no difference between individual’s ability to recall their Facebook friends and their working memory scores. However, those in the ambiguous cue condition were able to recall significantly fewer Facebook friends than those in the Facebook cue or no cue condition. Thus, this research shows that ambiguous cues can interfere with recall. However, further research is needed to see the extent that working memory moderates this effect

Experimental simulation of long term weathering in alkaline bauxite residue tailings

Bauxite residue is an alkaline, saline tailings material generated as a byproduct of the Bayer process used for alumina refining. Developing effective plans for the long term management of potential environmental impacts associated with storage of these tailings is dependent on understanding how the chemical and mineralogical properties of the tailings will change during weathering and transformation into a soil-like material. Hydrothermal treatment of bauxite residue was used to compress geological weathering timescales and examine potential mineral transformations during weathering. Gibbsite was rapidly converted to boehmite; this transformation was examined with in situ synchrotron XRD. Goethite, hematite, and calcite all precipitated over longer weathering timeframes, while tricalcium aluminate dissolved. pH, total alkalinity, and salinity (electrical conductivity) all decreased during weathering despite these experiments being performed under “closed” conditions (i.e., no leaching). This indicates the potential for auto-attenuation of the high alkalinity and salinity that presents challenges for long term environmental management, and suggests that management requirements will decrease during weathering as a result of these mineral transformations

A VLBA survey of the core shift effect in AGN jets I. Evidence for dominating synchrotron opacity

The effect of a frequency dependent shift of the VLBI core position (known as the "core shift") was predicted more than three decades ago and has since been observed in a few sources, but often within a narrow frequency range. This effect has important astrophysical and astrometric applications. To achieve a broader understanding of the core shift effect and the physics behind it, we conducted a dedicated survey with NRAO's Very Long Baseline Array (VLBA). We used the VLBA to image 20 pre-selected sources simultaneously at nine frequencies in the 1.4-15.4 GHz range. The core position at each frequency was measured by referencing it to a bright, optically thin feature in the jet. A significant core shift has been successfully measured in each of the twenty sources observed. The median value of the core shift is found to be 1.21 mas if measured between 1.4 and 15.4 GHz, and 0.24 mas between 5.0 and 15.4 GHz. The core position, r, as a function of frequency, n, is found to be consistent with an r n^-1 law. This behavior is predicted by the Blandford & Koenigl model of a purely synchrotron self-absorbed conical jet in equipartition. No systematic deviation from unity of the power law index in the r(n) relation has been convincingly detected. We conclude that neither free-free absorption nor gradients in pressure and/or density in the jet itself and in the ambient medium surrounding the jet play a significant role in the sources observed within the 1.4-15.4 GHz frequency range. These results support the interpretation of the parsec-scale core as a continuous Blandford-Koenigl type jet with smooth gradients of physical properties along it.Comment: 31 pages, 6 figures, 5 tables; accepted to Astronomy & Astrophysic

Fly ash as a permeable cap for tailings management : pedogenesis in bauxite residue tailings

PURPOSE : Closure of tailings facilities typically involves either a ‘cap and store’ or ‘direct revegetation’ approach. Both have been used in the management of bauxite residue (alumina refining tailings), with mixed results. This study evaluated the merit of an intermediate approach, using a permeable cap, and examined the pedogenic trajectory of the Technosol. MATERIALS AND METHODS : Chemical, mineralogical and physical properties of samples from a Brazilian bauxite residue deposit, which had been capped with fly ash 14 years prior and supported a vegetation cover, were compared to evaluate soil formation and pedogenic trajectory of the developing Technosol according to the World Reference Base for Soil Resources. Samples were collected at three points along an elevation gradient, and from 0 to 150 cm below the surface. RESULTS AND DISCUSSION : Rainfall leaching was identified as the most important pedogenic process occurring in the tailings, lowering salinity and pH. The Technosol classification was poorly suited to describe the soil materials within the study site because two wastes (fly ash and bauxite residue) were co-disposed in discrete layers. CONCLUSIONS : The permeability of the fly ash cap is key to soil development in these tailings : it provides a suitable medium for plant growth whilst still allowing contact between the tailings and the surrounding environment. The introduction of a novel prefix qualifier,ordic, would enable more accurate description of layered Technosols. The Technosol at this site is likely to develop towards an Andosol or Ferralsol.Minerals and Energy Research Institute of Western Australia, Alcoa of Australia Ltd, and BHP Billiton Worsley Alumina Pty Ltd.http://link.springer.com/journal/11368hb2016Plant Production and Soil Scienc

The effect of landscape structure on dispersal distances of the Eurasian red squirrel

Landscape structure can affect dispersal and gene flow in a species. In urban areas, buildings, roads, and small habitat patches make the landscape highly fragmented and can inhibit movement and affect dispersal behavior. Similarly, in rural forested areas, large open areas, such as fields, may act as barriers to movement. We studied how landscape structure affects natal dispersal distances of Eurasian red squirrels (Sciurus vulgaris) in an urban area and a rural area in Finland, by monitoring juvenile red squirrels with radio telemetry. We observed extremely long dispersal distancesup to 16kmin the rural study area, but shorter distanceson average only half a kilometerin the urban study area. The landscape structure affected the eventual dispersal paths; in the rural landscape, dispersers favored spruce dominated areas and avoided fields along their dispersal route, although they occasionally even crossed wide fields. In the urban landscape, squirrels preferred areas with deciduous or coniferous trees. The movement steps made by dispersers were longer in the more hostile landscape compared to forested areas. Despite these effects on movement path, the landscape structure only had a minor effect on straight line dispersal distances moved from the natal nest. In other words, individuals moved longer distances and were likely to circumvent barriers in their path, but this did not affect how far they settled from their natal home. This result indicates that, although landscape structure has obvious effects on movement, it still may have only a small effect on other aspects of the population, for example, gene flow

HERRING Governance Report Herring network institutions and governance

The Governance Report presents the research about the governance framework in which the various aspects and sectors that are relevant for spawning ground management are embedded.https://commons.wmu.se/herring/1002/thumbnail.jp

Narrative skills in adolescents with a history of SLI in relation to non-verbal IQ scores

There is a debate about whether the language of children with primary language disorders and normal cognitive levels is qualitatively different from those with language impairments who have low or borderline non-verbal IQ (NVIQ). As children reach adolescence, this distinction may be even harder to ascertain, especially in naturalistic settings. Narrative may provide a useful, ecologically valid way in which to assess the language ability of adolescents with specific language impairment (SLI) who have intact or lowered NVIQ and to determine whether there is any discernable difference in every day language. Nineteen adolescents with a history of SLI completed two narrative tasks: a story telling condition and a conversational condition. Just under half the group (n = 8) had non-verbal IQs of 85. The remaining 11 had NVIQs in the normal range or above. Four areas of narrative (productivity, syntax, cohesion and performance) were assessed. There were no differences between the groups on standardized tests of language. However, the group with low NVIQ were poorer on most aspects of narrative, suggesting that cognitive level is important, even when language is the primary disorder. The groups showed similar patterns of differences between story telling and conversational narrative. It was concluded that adolescents with a history of SLI and poor cognitive levels have poorer narrative skills than those with normal range NVIQ even though these may not be detected by standardized assessment. Their difficulties present as qualitatively similar to those with normal range NVIQ and narratives appear impoverished rather than inaccurate