Performance Analysis of Decode-and-Forward Relaying in Gamma-Gamma Fading Channels

Decode-and-forward (DF) cooperative communication based on free space optical (FSO) links is studied in this letter. We analyze performance of the DF protocol in the FSO links following the Gamma-Gamma distribution. The cumulative distribution function (CDF) and probability density function (PDF) of a random variable containing mixture of the Gamma- Gamma and Gaussian random variables is derived. By using the derived CDF and PDF, average bit error rate of the DF relaying is obtained.Comment: 3 pages, 1 figure, journa

Probability Density Function Modeling of Multi-Phase Flow in Porous Media with Density-Driven Gravity Currents

A probability density function (PDF) based approach is employed to model multi-phase flow with interfacial mass transfer (dissolution) in porous media. The joint flow statistics is represented by a mass density function (MDF), which is transported in the physical and probability spaces via Fokker-Planck equation. This MDF-equation requires Lagrangian evolutions of the random flow variables; these evolutions are stochastic processes honoring the micro-scale flow physics. To demonstrate the concept, we consider an example of immiscible two-phase flow with the non-equilibrium dissolution of single component from one phase into the other-a model for solubility trapping during CO2 storage in brine aquifer. Since CO2-rich brine is denser than pure brine, density-driven countercurrent flow is set up in the brine phase. The stochastic models mimicking the physics of countercurrent flow lead to a modeled MDF-equation, which is solved using our recently developed stochastic particle method for multi-phase flow (Tyagi etal. J Comput Phys 227:6696-6714, 2008). In addition, we derive Eulerian equations for stochastic moments (mean, variance, etc.) and show that unlike the MDF-equation the system of moment equations is not closed. In classical Darcy formulation, for example, the mean concentration equation is closed by neglecting variance. However, with several one- and two-dimensional simulations, it is demonstrated that the PDF and Darcy modeling approaches give significantly different results. While the PDF-approach properly accounts for the long correlation length scales and the concentration variance in density-driven countercurrent flow, the same phenomenon cannot be captured accurately with a standard Darcy mode

Impact of Channel Correlation on Different Performance Metrics of OSSK-Based FSO System

In this paper, we study the impact of correlation on the bit error rate (BER) and the channel capacity of a free-space optical (FSO) multiple-input-multiple-output (MIMO) system employing optical space shift keying (OSSK) over a fading channel. In order to study a practical correlated channel, we consider the effect of channel correlation due to both small-and large-scale eddies and show that the use of OSSK over correlated FSO channel can lead to an improved system performance with increasing correlation level of upto 0.9. In this work, we first develop an analytical framework for different performance metrics of the OSSK multiple-input single-output system with correlation and then extend our investigation by proposing an asymptotically accurate mathematical framework for MIMO. We also validate all the analytical results using MATLAB simulations. Finally, we develop an experimental setup of FSO with two correlated links to study the throughput and latency of the links at different turbulence levels

Show and Recall: Learning What Makes Videos Memorable

With the explosion of video content on the Internet, there is a need for research on methods for video analysis which take human cognition into account. One such cognitive measure is memorability, or the ability to recall visual content after watching it. Prior research has looked into image memorability and shown that it is intrinsic to visual content, but the problem of modeling video memorability has not been addressed sufficiently. In this work, we develop a prediction model for video memorability, including complexities of video content in it. Detailed feature analysis reveals that the proposed method correlates well with existing findings on memorability. We also describe a novel experiment of predicting video sub-shot memorability and show that our approach improves over current memorability methods in this task. Experiments on standard datasets demonstrate that the proposed metric can achieve results on par or better than the state-of-the art methods for video summarization.Comment: 10 pages, updated abstract, added few references, project page link and acknowledgements. Accepted at ICCV 2017 Workshop on Mutual Benefits of Cognitive and Computer Vision (MBCC

Toward the Establishment of an In-Vitro Model of Glaucoma Using Human Induced Pluripotent Stem Cells

poster abstractGlaucoma is a severe neurodegenerative disease of the retina, leading to eventual irreversible blindness. A crucial element in the pathophysiology of all forms of glaucoma is the death of retinal ganglion cells (RGCs), a population of CNS neurons with their soma in the inner retina and axons fasciculating together to form the optic nerve. Retinal astrocytes have also been associated with glaucomatous neurodegeneration, although the direct or indirect role for these cells in the disease process remains unclear. Human induced pluripotent stem cells (iPSCs) provide a promising approach to develop cellular models to study such neurodegenerative diseases in vitro. Directed differentiation of several somatic cell types from human iPSCs have been successfully achieved with great implications for disease modeling and cell replacement strategies. Using existing lines of iPSCs, efforts were undertaken to successfully differentiate and characterize RGCs and astrocytes, the affected cell types in glaucoma. Using a previously described protocol, these cells were directed to differentiate toward a retinal fate through a step-wise process that proceeds through all of the major stages of neuroretinal development. The differentiation of RGCs was observed within the first forty days of differentiation whereas astrocytes were observed only after at least 70 days of differentiation. Using techniques including immunocytochemistry and RT-PCR, the individually derived somatic cells types were characterized by the expression of developmentally associated transcription factors specific to each cell type. Further approaches were undertaken to characterize the morphological differences between RGCs and other neuroretinal cell types derived in the process. Overall, this study demonstrates a robust method to derive the complex cell types associated with glaucoma, with prospects for further investigations into the developmental progression of the disease

Enhancing The Specification Of Retinal Neurons From Human Induced Pluripotent Stem Cells

poster abstractA variety of retinal degenerative diseases, including retinitis pigmentosa and age-related macular degeneration, result in the loss of retinal neurons leading to a gradual loss of vision. An in vitro model to study the development of human retinal cells would provide a better understanding of the structure and functionality of the retina, eventually leading to new therapeutic approaches to blinding disorders that could involve replacing cells that had been lost to disease. Following previously established protocols, two types of populations of cells are observed early in the differentiation process, those that lead to retinal cells and those that lead to other anterior phenotypes of the central nervous system. These cells arise from a common progenitor population derived from induced pluripotent stem cells, yet the mechanism underlying the differentiation of these two different types of cells remains elusive. To further study the specification of retinal cells from this common progenitor population, a more efficient method to produce these cells needs to be developed. The purpose of this experiment is to test several candidate growth factors and observe their effect on the production of retinal cells. This study tests five different growth conditions using insulin-like growth factor-1, fibroblast growth factor-2, the sonic hedgehog agonist purmorphamine, retinoic acid and an untreated control. Treatment was carried out from Day 7 until Day 20, a period during which previous studies have demonstrated an ability to influence the decision of these cells to become retinal non-retinal. Immunocytochemistry (ICC) and RT-PCR analysis was used to monitor the expression of proteins characteristic of retinal and non-retinal cells. These results can be used to devise a more efficient protocol for retinal specification from human induced pluripotent stem cells and in turn, will further our understanding of the development of the retina