KŪNQǓ IN PRACTICE: A CASE STUDY

Ph.D

Aquaporin-4-dependent K(+) and water transport modeled in brain extracellular space following neuroexcitation.

Potassium (K(+)) ions released into brain extracellular space (ECS) during neuroexcitation are efficiently taken up by astrocytes. Deletion of astrocyte water channel aquaporin-4 (AQP4) in mice alters neuroexcitation by reducing ECS [K(+)] accumulation and slowing K(+) reuptake. These effects could involve AQP4-dependent: (a) K(+) permeability, (b) resting ECS volume, (c) ECS contraction during K(+) reuptake, and (d) diffusion-limited water/K(+) transport coupling. To investigate the role of these mechanisms, we compared experimental data to predictions of a model of K(+) and water uptake into astrocytes after neuronal release of K(+) into the ECS. The model computed the kinetics of ECS [K(+)] and volume, with input parameters including initial ECS volume, astrocyte K(+) conductance and water permeability, and diffusion in astrocyte cytoplasm. Numerical methods were developed to compute transport and diffusion for a nonstationary astrocyte-ECS interface. The modeling showed that mechanisms b-d, together, can predict experimentally observed impairment in K(+) reuptake from the ECS in AQP4 deficiency, as well as altered K(+) accumulation in the ECS after neuroexcitation, provided that astrocyte water permeability is sufficiently reduced in AQP4 deficiency and that solute diffusion in astrocyte cytoplasm is sufficiently low. The modeling thus provides a potential explanation for AQP4-dependent K(+)/water coupling in the ECS without requiring AQP4-dependent astrocyte K(+) permeability. Our model links the physical and ion/water transport properties of brain cells with the dynamics of neuroexcitation, and supports the conclusion that reduced AQP4-dependent water transport is responsible for defective neuroexcitation in AQP4 deficiency

Automatic Objects Removal for Scene Completion

With the explosive growth of web-based cameras and mobile devices, billions of photographs are uploaded to the internet. We can trivially collect a huge number of photo streams for various goals, such as 3D scene reconstruction and other big data applications. However, this is not an easy task due to the fact the retrieved photos are neither aligned nor calibrated. Furthermore, with the occlusion of unexpected foreground objects like people, vehicles, it is even more challenging to find feature correspondences and reconstruct realistic scenes. In this paper, we propose a structure based image completion algorithm for object removal that produces visually plausible content with consistent structure and scene texture. We use an edge matching technique to infer the potential structure of the unknown region. Driven by the estimated structure, texture synthesis is performed automatically along the estimated curves. We evaluate the proposed method on different types of images: from highly structured indoor environment to the natural scenes. Our experimental results demonstrate satisfactory performance that can be potentially used for subsequent big data processing: 3D scene reconstruction and location recognition.Comment: 6 pages, IEEE International Conference on Computer Communications (INFOCOM 14), Workshop on Security and Privacy in Big Data, Toronto, Canada, 201

Ruddlesden–Popper perovskite sulfides A3B2S7: A new family of ferroelectric photovoltaic materials for the visible spectrum

Perovskite ferroelectric materials exhibit the novel ferroelectric photovoltaic effect, where photon-excited electron–hole pairs can be separated by ferroelectric polarization. Especially, semiconducting ferroelectric materials with small band gaps (E[subscript g]) have been extensively studied for applications in solar energy conversion. Traditional route for creating semiconducting ferroelectrics requires cation doping, where E[subscript g] of the insulating perovskite ferroelectric oxides are reduced via substitution of certain cations. But cation doping tends to reduce the carrier mobility due to the scattering, and usually lead to poor photovoltaic efficiency. In the present work, based on first-principles calculations, we propose and demonstrate a new strategy for designing stoichiometric semiconducting perovskite ferroelectric materials. Specifically, we choose the parent non-polar semiconducting perovskite sulfides AB S[subscript 3] with Pnma symmetry, and turn them into ferroelectric Ruddlesden–Popper A[subscript 3]B[subscript 2]S[subscript 7] perovskites with spontaneous polarizations. Our predicted Ruddlesden–Popper Ca[subscript 3]Zr[subscript 2]S[subscript 7] and other derived compounds exhibit the room-temperature stable ferroelectricity, small band gaps (E[subscript g] < 2.2 eV) suitable for the absorption of visible light, and large visible-light absorption exceeding that of Si.National Basic Research Program of China (973 Program) (Contract 2012CB619402)National Natural Science Foundation (China) (Contract 11574244)China. Ministry of Education (Program for Innovative Research Team in University. Contract IRT13034)National Science Foundation (U.S.) (Grant DMR-1410636