Current-Voltage Characteristics of Weyl Semimetal Semiconducting Devices, Veselago Lenses and Hyperbolic Dirac Phase

The current-voltage characteristics of a new range of devices built around Weyl semimetals has been predicted using the Landauer formalism. The potential step and barrier have been reconsidered for a three-dimensional Weyl semimetals, with analogies to the two-dimensional material graphene and to optics. With the use of our results we also show how a Veselago lens can be made from Weyl semimetals, e.g. from NbAs and NbP. Such a lens may have many practical applications and can be used as a probing tip in a scanning tunneling microscope (STM). The ballistic character of Weyl fermion transport inside the semimetal tip, combined with the ideal focusing of the Weyl fermions (by Veselago lens) on the surface of the tip may create a very narrow electron beam from the tip to the surface of the studied material. With a Weyl semimetal probing tip the resolution of the present STMs can be improved significantly, and one may image not only individual atoms but also individual electron orbitals or chemical bonding and therewith to resolve the long-term issue of chemical and hydrogen bond formation. We show that applying a pressure to the Weyl semimental, having no centre of spacial inversion one may model matter at extreme conditions such as those arising in the vicinity of a black hole. As the materials Cd3As2 and Na3Bi show an asymmetry in their Dirac cones, a scaling factor was used to model this asymmetry. The scaling factor created additional regions of no propagation and condensed the appearance of resonances. We argue that under an external pressure there may arise a topological phase transition in Weyl semimetals, where the electron transport changes character and becomes anisotropic. There a hyperbolic Dirac phases occurs where there is a strong light absorption and photo-current generation

Movements of Walruses Radio-tagged in Bristol Bay, Alaska

Satellite radio-location data from 57 adult male Pacific walruses (Odobenus rosmarus divergens) were used to estimate haul-out fidelity, broadly describe seasonal foraging distributions, and determine the approximate timing of autumn migration from Bristol Bay, Alaska. Data were collected intermittently during 1987–91 and 1995–2000, primarily during the period from May to October. Transmitter longevity ranged from less than 1 day to 560 days (median 75 d). The four tagging sites were the only haul-outs that were commonly used in the bay from spring through autumn. Mean fidelity, defined as the chance that an animal will return to an area where it previously hauled out, was 0.56 (SE = 0.09). However, small sample sizes precluded comparisons of fidelity among years and among haul-outs by season. No tagged animals migrated out of the bay between spring and early autumn. Combined monthly locations suggest that foraging occurred primarily in the southern and eastern areas of the bay in spring and gradually shifted towards northwestern areas in late autumn and winter. Ninety-eight percent of the in-water locations were in waters under 60 m deep, which account for 76% of the study area. Some animals migrated out of the bay in late autumn and winter; others remained within the bay throughout the year. Those making long-range migrations departed the bay during November and December.On a utilisé des données de radiolocalisation satellitaire provenant de 57 morses du Pacifique (Odobenus rosmarus divergens) mâles afin d’évaluer la fidélité au site d’échouerie, de décrire sommairement la distribution saisonnière des aires d’alimentation et d’établir le moment approximatif de la migration automnale partant de la baie Bristol, en Alaska. Entre 1987 et 1991, puis entre 1995 et 2000, on a recueilli des données par intermittence, essentiellement durant la période allant de mai à octobre. La longévité des émetteurs allait de moins de 1 jour à 560 jours (médiane de 75 jours). Les quatre sites de marquage étaient les seules échoueries couramment utilisées dans la baie, du printemps à la fin de l’automne. La fidélité moyenne, définie comme la probabilité qu’un animal réutilise un site d’échouerie donné, était de 0,56 (erreur-type = 0,09). La petite taille des échantillons a cependant empêché une comparaison saisonnière de la fidélité d’une année à une autre et d’une échouerie à une autre. Aucun animal marqué n’a migré hors de la baie entre le printemps et le début de l’automne. Un regroupement mensuel des localisations suggère qu’au printemps, les aires d’alimentation se trouvaient surtout dans les zones méridionales et orientales de la baie, et qu’elles se déplaçaient graduellement vers des zones situées dans la partie nord-ouest à la fin de l’automne et en hiver. Quatrevingt- dix-huit p. cent des localisations au large se trouvaient dans des eaux d’une profondeur supérieure à 60 m, ce qui représente 76 % de la zone d’étude. Quelques animaux émigraient de la baie à la fin de l’automne et en hiver, tandis que d’autres restaient dans la baie tout au long de l’année. Ceux qui effectuaient des migrations sur une longue distance quittaient la baie durant les mois de novembre et décembre

Helmeted Muskox (Bootherium bombifrons) from Near Fort Saskatchewan, Alberta: Dating Evidence for Redeposition in Late Pleistocene Alluvium

Superimposition and intersection of preglacial and postglacial valley systems on the Canadian plains indicates that some of the recovered Quaternary vertebrate fossils may be redeposited. To test this proposition, an accelerator mass spectrometer (AMS) date was obtained on bone from a previously described helmeted muskox skull from near Fort Saskatchewan, Alberta. The specimen, identified as Bootherium bombifrons = Symbos cavifrons was previously thought to be Late Pleistocene (postglacial) in age but showed evidence of transport. A date of 30 570 ± 250 14C yrs BP indicates that it is of Middle Wisconsinan (pre-Last Glacial Maximum) age and therefore was ultimately derived from the Empress Formation (Saskatchewan Gravels and Sands) in the Edmonton area. Other vertebrate fossils must be assessed carefully in this light and direct dating is recommended wherever possible to facilitate both stratigraphic and paleontological studies.La surimposition et l’entrecroisement des réseaux fluviatiles pré- et postglaciaires dans les Prairies indiquent que certains fossiles de vertébrés du Quaternaire pourraient avoir fait l’objet d’un remaniement. Pour tester l’hypothèse, nous avons daté, à l'aide d'un accélérateur de particules (SMA), un os provenant d'un crâne d'ovibos casqué (antérieurement décrit) trouvé près de Fort Saskatchewan. Identifié comme un Bootherium bombifrons = Symbos cavifrons, le spécimen, qu'on avait daté du Pléistocène supérieur (postglaciaire), portait des traces de transport. La date de 30 570 ± 250 ans 14C BP obtenue par SMA, indique qu'il daterait plutôt du Wisconsinien moyen (avant le dernier maximum glaciaire) et qu'il proviendrait, par conséquent, de la Formation d’Empress (Graviers et Sables de la Saskatchewan), dans la région d'Edmonton. À la lumière de ce résultat, d'autres fossiles de vertébrés devraient être réétudiés et, dans la mesure du possible, faire l'objet d'une datation directe, afin de favoriser les études stratigraphiques et paléontologiques

Arctic Profiles: Second Series

In the June 1982 issue of Arctic, Richard Davis introduced "Arctic Profiles." At the time he said the purpose of the series was to cover "a more subjective and human element that has influenced the history of arctic development." He continued, "Should this series prove successful ..." more could follow. ... Because of the success of the Profiles, Arctic has decided to maintain the series and has asked us to see it through a second phase. ... The second series of profiles will be more contemporary but continue to recognize the contribution of those no longer active or alive. ..

A Hadrosaurid (Dinosauria: Ornithischia) from the Late Cretaceous (Campanian) Kanguk Formation of Axel Heiberg Island, Nunavut, Canada, and Its Ecological and Geographical Implications

A hadrosaurid vertebra was recovered during a palynological survey of the Upper Cretaceous Kanguk Formation in the eastern Canadian Arctic. This vertebra represents the farthest north record of any non-avian dinosaur to date. Although highly abraded, the fossil nonetheless represents an interesting biogeographic data point. During the Campanian, when this vertebra was deposited, the eastern Canadian Arctic was likely isolated both from western North America by the Western Interior Seaway and from more southern regions of eastern North America by the Hudson Seaway. This fossil suggests that large-bodied hadrosaurid dinosaurs may have inhabited a large polar insular landmass during the Late Cretaceous, where they would have lived year-round, unable to migrate to more southern regions during winters. It is possible that the resident herbivorous dinosaurs could have fed on non-deciduous conifers, as well as other woody twigs and stems, during the long, dark winter months when most deciduous plant species had lost their leaves.La vertèbre d’un hadrosauridé a été retrouvée pendant l’étude palynologique de la formation Kanguk remontant au Crétacé supérieur, dans l’est de l’Arctique canadien. Il s’agit de la vertèbre appartenant à un dinosaure non avien qui a été recueillie la plus au nord jusqu’à maintenant. Même si ce fossile est fortement abrasé, il n’en reste pas moins qu’il représente un point de donnée biogéographique intéressant. Pendant le Campanien, lorsque cette vertèbre a été déposée, l’est de l’Arctique canadien était vraisemblablement isolé de l’ouest de l’Amérique du Nord par la mer intérieure occidentale, et des régions plus au sud de l’est de l’Amérique du Nord par le bras de mer Hudson. Ce fossile suggère que de gros dinosaures hadrosauridés auraient pu habiter une grande masse terrestre insulaire polaire pendant le Crétacé tardif, où ils auraient évolué à l’année, étant incapables de migrer vers les régions plus au sud pendant l’hiver. Il est possible que les dinosaures herbivores résidents se soient nourris de conifères non décidus ainsi que d’autres tiges ou brindilles ligneuses pendant les longs mois sombres de l’hiver, lorsque la plupart des espèces végétales décidues avaient perdu leurs feuilles.

Dissipative dynamics of superfluid vortices at non-zero temperatures

We consider the evolution and dissipation of vortex rings in a condensate at non-zero temperature, in the context of the classical field approximation, based on the defocusing nonlinear Schr\"odinger equation. The temperature in such a system is fully determined by the total number density and the number density of the condensate. A vortex ring is introduced into a condensate in a state of thermal equilibrium, and interacts with non-condensed particles. These interactions lead to a gradual decrease in the vortex line density, until the vortex ring completely disappears. We show that the square of the vortex line length changes linearly with time, and obtain the corresponding universal decay law. We relate this to mutual friction coefficients in the fundamental equation of vortex motion in superfluids.Comment: 4 pages, 3 figure

Seismic Signature of a Swan Hills (Frasnian) Reef Reservoir, Snipe Lake, Alberta

Swan Hills formation (Frasnian stage) carbonate buildups of the Beaverhill Lake group are generally of low relief and considerable areal extent and are overlain by and encased within the relatively high-velocity shale of the Waterways formation, which thins but does not drape across the reefs. Consistent with this picture, prereef seismic events are not significantly pulled up beneath the reefs nor are postreef events draped across them. Indeed, the seismic images of these reefs are effectively masked by the high-amplitude reflections from the overlying top of the Beaverhill Lake group and underlying Gilwood member and cannot be distinguished from those of the basin fill. However, it is possible to identify the reefs indirectly on conventionally processed seismic sections because the image of the encompassing Beaverhill Lake/Gilwood interval varies significantly from onreef to offreef positions.One such Swan Hills formation field at Snipe Lake has an areal extent of about 90 km2 and typical reef relief of some 50 m above the platform facies. This reef is shown to be recognizable on three example seismic lines from interference phenomena that vary laterally in association with the lateral variations in thickness of the Swan Hills formation. These phenomena include an offreef peak that is one half-cycle below the Beaverhill Lake reflection trough and that dies out laterally going onreef, a tendency for the amplitude of the Gilwood event to decrease beneath the reef, and thinning of the order of 5 ms of the onreef section relative to the offreef section. Through seismic modeling, these seismic-image characteristics are seen to be predictable geophysical manifestations of the inherent geologic variations

An explanation for metallicity effects on X-ray Binary properties

We show that irradiation induced stellar winds can explain two important metallicity effects in X-ray binaries - the higher numbers and the softer spectra of the X-ray binaries in metal rich globular clusters compared to the metal poor ones. As has been previously noted by Iben, Tutukov and Fedorova, the winds should be stronger at lower metallicity due to less efficient line cooling. This will speed up the evolution of the LMXBs in metal poor clusters, hence reducing their numbers. These winds can also provide extra material near the accreting object which may create an intrinsic absorber to harden the X-ray spectra of the metal poor cluster systems relative to the metal rich ones, as suggested by observations. We outline some additional observational predictions of the model.Comment: 6 pages, no figures, accepted to Ap