Collective modes of CP(3) Skyrmion crystals in quantum Hall ferromagnets

The two-dimensional electron gas in a bilayer quantum Hall system can sustain an interlayer coherence at filling factor nu=1 even in the absence of tunneling between the layers. This system has low-energy charged excitations which may carry textures in real spin or pseudospin. Away from filling factor nu =1 a finite density of these is present in the ground state of the 2DEG and forms a crystal. Depending on the relative size of the various energy scales, such as tunneling (Delta_SAS), Zeeman coupling (Delta_Z) or electrical bias (Delta_b), these textured crystal states can involve spin, pseudospin, or both intertwined. In this article, we present a comprehensive numerical study of the collective excitations of these textured crystals using the GRPA. For the pure spin case, at finite Zeeman coupling the state is a Skyrmion crystal with a gapless phonon mode, and a separate Goldstone mode that arises from a broken U(1) symmetry. At zero Zeeman coupling, we demonstrate that the constituent Skyrmions break up, and the resulting state is a meron crystal with 4 gapless modes. In contrast, a pure pseudospin Skyrme crystal at finite tunneling has only the phonon mode. For Delta_SAS=0, the state evolves into a meron crystal and supports an extra gapless U(1) mode in addition to the phonon. For a CP(3) Skyrmion crystal, we find a U(1) gapless mode in the presence of the symmetry-breaking fields. In addition, a second mode with a very small gap is present in the spectrum.Comment: 16 pages and 12 eps figure

Estimating Wind Stress at the Ocean Surface From Scatterometer Observations

Abstract—Wind stress is the most important ocean forcing for driving tropical surface currents. Stress can be estimated from scatterometer-reported wind measurements at 10 m that have been extrapolated to the surface, assuming a neutrally stable atmosphere and no surface current. Scatterometer calibration is designed to account for the assumption of neutral stability; however, the assumption of a particular sea state and negligible current often introduces an error in wind stress estimations. Since the fundamental scatterometer measurement is of the surface radar backscatter (sigma-0) which is related to surface roughness and, thus, stress, we develop a method to estimate wind stress directly from the scatterometer measurements of sigma-0 and their associated azimuth angle and incidence angle using a neural network approach. We compare the results with in situ estimations and observe that the wind stress estimations from this approach are more accurate compared with those obtained from the conventional estimations using 10-m-height wind measurements. Index Terms—Atmospheric stability, neutral stability, scatterometer, wind stress. I

Plot placement when using a passive tracking index to simultaneously monitor multiple species of animals

We evaluated a passive tracking index (PTI) when plots were placed on lightly used dirt roads versus placement on naturally occurring bare ground in natural habitat. PTIs were calculated before and after removal of coyotes and some non-target species during another study that evaluated capture devices. Six mammals were simultaneously monitored with the PTI: coyotes, raccoons, white-tailed deer, feral swine, javelina, and rabbits. PTIs from road plots were significantly higher than from off-road plots, except for deer and javelina, for which no differences were detected. After removal of coyotes, PTIs were significantly lower, both from on- and off-road plots. For coyotes and raccoons, the decline in index values primarily reflected population reductions. For animals hunted for sport (deer, swine, javelina), population reductions were minor compared with coyotes, and their declines in index values likely reflected conditioned responses to the activity and shooting that accompanied evaluations of the capture devices. We conclude that the PTI is sensitive to changes in population or changes in activity in response to an event for a variety of species, and it is most useful when placed on lightly used dirt roads

Effects of Forest Fire on Young-of-the-year Northern Pike, Esox lucius, in the Northwest Territories

In 1998, a forest fire burned 58% of the forested shoreline surrounding Tibbitt Lake, Northwest Territories, including riparian vegetation used by Northern Pike (Esox lucius) as spawning habitat. This presented an opportunity to investigate the effects that habitat disturbance from a natural forest fire had on young-of-the-year (Y-O-Y) Northern Pike. Pike fry were collected from three burned and three unburned sites around Tibbitt Lake in 1999 (the first post-fire spawning season) and again in 2001. Differences in size and relative abundance were evaluated between sites. Y-O-Y Northern Pike were significantly larger at the unburned sites (P<0.01) and the relative abundance of Y-O-Y Northern Pike increased significantly at burned sites (alpha=0.1; P<0.07) following re-vegetation two years post fire. These differences may be due to fire-induced changes in physical habitat or food availability. Forest fires decrease the density of riparian vegetation, which likely provides better spawning and rearing habitat for Northern Pike in the long-term.En 1998, un feu de forêt a brûlé 58% de la rive boisée entourant le lac Tibbitt, situé dans les Territoires du Nord-Ouest, y compris la végétation riveraine utilisé par le grand brochet (Esox lucius) comme habitat de fraie. Cet événement a présenté une occasion pour étudier les effets causés par un feu de foret sur l'habitat de jeunes de l'année du grand brochet. Les jeunes brochets ont été recueillis sur trois sites brûlées et trois sites non brûlés autour du lac Tibbitt en 1999 (la première année de fraie après le feu de forêt) et à nouveau en 2001. La différence de grandeur et l'abondance relative des poissons ont été analysés entre les différents sites. Les jeunes grands brochets aux sites non-atteints par le feu étaient considérablement plus grands (P < 0,01) que ceux aux sites brulés. Les sites brulés, subissant une rapide revégétation dans les deux années après le feu, ont augmenté en abondance relative de jeunes grands brochets (alpha = 0,1, P < 0,07). Ces différences peuvent être dues aux changements induits par le feu sur l'aspect physique de l'habitat ou sur la disponibilité de nourriture. Les incendies de forêt réduisent la densité de la végétation riveraine, qui fournit probablement de meilleure habitat de fraie et d'alevinage pour le grand brochet à long terme

Exposure to intimate partner violence : perceived links with other victimizations and the severity of violence by young adults in Québec

The objective of this qualitative study was to understand how young adults (18 - 25 years old) who were exposed to intimate partner violence (IPV) during childhood and adolescence explained the links between this violence and the other victimizations that they had experienced, as well as the perceived severity that they assigned to these victimizations. The participants (N = 45) were recruited in the Province of Quebec (Canada). Before the interview, they filled out an online questionnaire with the Adult Retrospective Version of the Juvenile Victimization Questionnaire as well as answering sociodemographic questions. They likewise noted the victimization to which they were subjected before they reached adulthood. These data helped us to better prepare the qualitative interviews, allowing us to explore the links the youth see or do not see between their exposure to IPV and other declared victimizations. Interviews lasted an average of two hours and were supported by a semi-structured interview guide and a life history calendar. The results show that many of the participants identified stronger links between exposure to IPV and child maltreatment, intimidation at school, and dating violence. Findings highlight the importance of considering youth’s viewpoints about the victimizations they suffer so as to develop intervention and prevention programs that are better adapted to these youth’s experiences and point of views