Deterministic creation, pinning, and manipulation of quantized vortices in a Bose-Einstein condensate

We experimentally and numerically demonstrate deterministic creation and manipulation of a pair of oppositely charged singly quantized vortices in a highly oblate Bose-Einstein condensate (BEC). Two identical blue-detuned, focused Gaussian laser beams that pierce the BEC serve as repulsive obstacles for the superfluid atomic gas; by controlling the positions of the beams within the plane of the BEC, superfluid flow is deterministically established around each beam such that two vortices of opposite circulation are generated by the motion of the beams, with each vortex pinned to the \emph{in situ} position of a laser beam. We study the vortex creation process, and show that the vortices can be moved about within the BEC by translating the positions of the laser beams. This technique can serve as a building block in future experimental techniques to create, on-demand, deterministic arrangements of few or many vortices within a BEC for precise studies of vortex dynamics and vortex interactions.Comment: 9 pages, 7 figure

Self-consistent wave-particle interactions in dispersive scale long-period field-line-resonances

Using 1D Vlasov drift-kinetic computer simulations, it is shown that electron trapping in long period standing shear Alfven waves (SAWs) provides an efficient energy sink for wave energy that is much more effective than Landau damping. It is also suggested that the plasma environment of low altitude auroral-zone geomagnetic field lines is more suited to electron acceleration by inertial or kinetic scale Alfven waves. This is due to the self-consistent response of the electron distribution function to SAWs, which must accommodate the low altitude large-scale current system in standing waves. We characterize these effects in terms of the relative magnitude of the wave phase and electron thermal velocities. While particle trapping is shown to be significant across a wide range of plasma temperatures and wave frequencies, we find that electron beam formation in long period waves is more effective in relatively cold plasma

Corporate Social Responsibility as a Critical Tool in achieving Harmony with Host Communities: The Case of SEPLAT

Sustainability is not just important for people and the planet but also for business success. Business experts will cite everything from strong loyalty programme to a personalised, mobile friendly shopping experience as keys to business success. These offerings are certainly important, but one thing that may tilt the scale in your favour is using your profits to do good in the world. This is where Corporate Social Responsibility (CSR) comes in. CSR refers to a business practice that involves participating in initiatives that benefit society. This study therefore appraises the use of cooperate social responsibility in achieving harmonious coexistence with host communities with its ripple effect on the economy and corporate image of an organisation. The study adopts the qualitative analytical technique in evaluating the very essence of corporate social responsibility practice by corporate organisations as an off-shoot of public relations practice vis-à-vis its salient contributions to the health of any organisation. It goes without saying that CSR determines to a large extent the existence, profitability and sustainability of an organisation. The foregoing underscores the particular mention of SEPLAT Petroleum Development Company Plc and its CSR model as an acme of good corporate citizen. The study concludes among others that without CSR, an organisation may find it difficult to operate in a safe environment and may even go into extinction. It recommends among others that organisations operating in Nigeria should take a cue from SEPLAT Petroleum Company Plc in developing a CSR model in tandem with the needs and aspirations of their host communities with an aim to promoting mutual and harmonious relationship with them. Keywords: Corporate Social Responsibility, Critical tool, Harmony, Host Communities, SEPLAT Plc

The Informal Sector Tax Revenue Potential: A Case of Zimbabwe

In this paper we sought to analyse the performance of informal sector tax revenue and to establish whether economic resources should be channelled to this sector in a bid to tax it. The study employed literature review method.  The evidence suggests that the informal sector play an important role in the Zimbabwean economy such as creating jobs, poverty eradication and also as a test bed from which willing taxpayers can graduate into mainstream however their contribution to the national tax revenue is insignificant despite Government efforts. We established that Zimbabwe has no effective mechanism to collect revenue from the informal sector. The study recommends that more resources be channelled to the informal sector due to high revenue potentials. Keywords: Informal sector, presumptive tax, Tax revenu

Modelling groundwater-dependent vegetation patterns using ensemble learning

International audienceVegetation patterns arise from the interplay between intraspecific and interspecific biotic interactions and from different abiotic constraints and interacting driving forces and distributions. In this study, we constructed an ensemble learning model that, based on spatially distributed environmental variables, could model vegetation patterns at the local scale. The study site was an alluvial floodplain with marked hydrologic gradients on which different vegetation types developed. The model was evaluated on accuracy, and could be concluded to perform well. However, model accuracy was remarkably lower for boundary areas between two distinct vegetation types. Subsequent application of the model on a spatially independent data set showed a poor performance that could be linked with the niche concept to conclude that an empirical distribution model, which has been constructed on local observations, is incapable to be applied beyond these boundaries

Observation of vortex dipoles in an oblate Bose-Einstein condensate

We report experimental observations and numerical simulations of the formation, dynamics, and lifetimes of single and multiply charged quantized vortex dipoles in highly oblate dilute-gas Bose-Einstein condensates (BECs). We nucleate pairs of vortices of opposite charge (vortex dipoles) by forcing superfluid flow around a repulsive gaussian obstacle within the BEC. By controlling the flow velocity we determine the critical velocity for the nucleation of a single vortex dipole, with excellent agreement between experimental and numerical results. We present measurements of vortex dipole dynamics, finding that the vortex cores of opposite charge can exist for many seconds and that annihilation is inhibited in our highly oblate trap geometry. For sufficiently rapid flow velocities we find that clusters of like-charge vortices aggregate into long-lived dipolar flow structures.Comment: 4 pages, 4 figures, 1 EPAPS fil

Examining Classroom Contexts in Support of Culturally Diverse Learners’ Engagement: An Integration of Self-Regulated Learning and Culturally Responsive Pedagogical Practices.

Research shows that culturally diverse students are often disengaged in multicultural classrooms. To address this challenge, literatures on self-regulated learning (SRL) and culturally responsive teaching (CRT) both document practices that foster engagement, although from different perspectives. This study examined how classroom teachers at schools that enrol students from diverse cultural communities on the West Coast of Canada built on a Culturally Responsive Self-Regulated Learning Framework to design complex tasks that integrated SRL pedagogical practices (SLPPs) and culturally-responsive pedagogical practices (CRPPs) to support student engagement. Two elementary school teachers and their 43 students (i.e., grades 4 and 5) participated in this study. We used a multiple, parallel case study design that embedded mixed methods approaches to examine how the teachers integrated SRLPPs and CRPPs into complex tasks; how culturally diverse students engaged in each teacher’s task; and how students’ experiences of engagement were related to their teachers' practices. We generated evidence through video-taped classroom observations, records of classroom practices, students’ work samples, a student self-report, and teacher interviews. Overall findings showed: (1) that teachers were able to build on the CR-SRL framework to guide their design of an CR-SRL complex task; (2) benefits to students’ engagement when those practices were present; and (3) dynamic learner-context interactions in that student engagement was situated in features of the complex task that were present on a given day. We close by highlighting implications of these findings, limitations, and future directions.   &nbsp