185 research outputs found

    Density-Matrix approach to a Strongly Coupled Two-Component Bose-Einstein Condensate

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    The time evolution equations for average values of population and relative phase of a strongly coupled two component BEC is derived analytically. The two components are two hyper-fine states coupled by an external laser that drives fast Rabi oscillations between these states. Specifically, this derivation incorporates the two-mode model proposed in [1] for the strongly coupled hyper-fine states of Rb. The fast Rabi cycle is averaged out and rate equations are derived that represents the slow dynamics of the system. These include the collapse and revival of Rabi oscillations and their subsequent dependence on detuning and trap displacement as reported in experiments of [1]. A proposal to create stable vortices is also given.Comment: 11 Latex pages, 2 figures (Figure 3 was removed and the text chnaged accordingly

    Stratification of a population of intracranial aneurysms using blood flow metrics.

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    Indices of the intra-aneurysm hemodynamic environment have been proposed as potentially indicative of their longitudinal outcome. To be useful, the indices need to be used to stratify large study populations and tested against known outcomes. The first objective was to compile the diverse hemodynamic indices reported in the literature. Furthermore, as morphology is often the only patient-specific information available in large population studies, the second objective was to assess how the ranking of aneurysms in a population is affected by the use of steady flow simulation as an approximation to pulsatile flow simulation, even though the former is clearly non-physiological. Sixteen indices of aneurysmal hemodynamics reported in the literature were compiled and refined where needed. It was noted that, in the literature, these global indices of flow were always time-averaged over the cardiac cycle. Steady and pulsatile flow simulations were performed on a population of 198 patient-specific and 30 idealised aneurysm models. All proposed hemodynamic indices were estimated and compared between the two simulations. It was found that steady and pulsatile flow simulations had a strong linear dependence (r ≥ 0.99 for 14 indices; r ≥ 0.97 for 2 others) and rank the aneurysms in an almost identical fashion (ρ ≥ 0.99 for 14 indices; ρ ≥ 0.96 for other 2). When geometry is the only measured piece of information available, stratification of aneurysms based on hemodynamic indices reduces to being a physically grounded substitute for stratification of aneurysms based on morphology. Under such circumstances, steady flow simulations may be just as effective as pulsatile flow simulation for estimating most key indices currently reported in the literature

    Landau Levels in the noncommutative AdS2AdS_2

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    We formulate the Landau problem in the context of the noncommutative analog of a surface of constant negative curvature, that is AdS2AdS_2 surface, and obtain the spectrum and contrast the same with the Landau levels one finds in the case of the commutative AdS2AdS_2 space.Comment: 19 pages, Latex, references and clarifications added including 2 figure

    Discussion on a possible neutrino detector located in India

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    We have identified some important and worthwhile physics opportunitites with a possible neutrino detector located in India. Particular emphasis is placed on the geographical advantage with a stress on the complimentary aspects with respect to other neutrino detectors already in operation.Comment: 9 pages; arXiv copy of published proceedings contributio

    Joint Goal and Strategy Inference across Heterogeneous Demonstrators via Reward Network Distillation

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    Reinforcement learning (RL) has achieved tremendous success as a general framework for learning how to make decisions. However, this success relies on the interactive hand-tuning of a reward function by RL experts. On the other hand, inverse reinforcement learning (IRL) seeks to learn a reward function from readily-obtained human demonstrations. Yet, IRL suffers from two major limitations: 1) reward ambiguity - there are an infinite number of possible reward functions that could explain an expert's demonstration and 2) heterogeneity - human experts adopt varying strategies and preferences, which makes learning from multiple demonstrators difficult due to the common assumption that demonstrators seeks to maximize the same reward. In this work, we propose a method to jointly infer a task goal and humans' strategic preferences via network distillation. This approach enables us to distill a robust task reward (addressing reward ambiguity) and to model each strategy's objective (handling heterogeneity). We demonstrate our algorithm can better recover task reward and strategy rewards and imitate the strategies in two simulated tasks and a real-world table tennis task.Comment: In Proceedings of the 2020 ACM/IEEE In-ternational Conference on Human-Robot Interaction (HRI '20), March 23 to 26, 2020, Cambridge, United Kingdom.ACM, New York, NY, USA, 10 page

    Embryogenesis in Sedum acre L.: structural and immunocytochemical aspects of suspensor development

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    The changes in the formation of both the actin and the microtubular cytoskeleton during the differentiation of the embryo-suspensor in Sedum acre were studied in comparison with the development of the embryo-proper. The presence and distribution of the cytoskeletal elements were examined ultrastructurally and with the light microscope using immunolabelling and rhodamine-phalloidin staining. At the globular stage of embryo development extensive array of actin filaments is present in the cytoplasm of basal cell, the microfilament bundles generally run parallel to the long axis of basal cell and pass in close to the nucleus. Microtubules form irregular bundles in the cytoplasm of the basal cell. A strongly fluorescent densely packed microtubules are present in the cytoplasmic layer adjacent to the wall separating the basal cell from the first layer of the chalazal suspensor cells. At the heart-stage of embryo development, in the basal cell, extremely dense arrays of actin materials are located near the micropylar and chalazal end of the cell. At this stage of basal cell formation, numerous actin filaments congregate around the nucleus. In the fully differentiated basal cell and micropylar haustorium, the tubulin cytoskeleton forms a dense prominent network composed of numerous cross-linked filaments. In the distal region of the basal cell, a distinct microtubular cytoskeleton with numerous microtubules is observed in the cytoplasmic layer adjacent to the wall, separating the basal cell from the first layer of the chalazal suspensor cells. The role of cytoskeleton during the development of the suspensor in S. acre is discussed
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