Sensor Planning for Object Pose Estimation and Identification

This paper proposes a novel approach to sensor planning for simultaneous object identification and 3D pose estimation. We consider the problem of determining the next-best-view for a movable sensor (or an autonomous agent) to identify an unknown object from among a database of known object models. We use an information theoretic approach to define a metric (based on the difference between the current and expected model entropy) that guides the selection of the optimal control action. We present a generalized algorithm that can be used in sensor planning for object identification and pose estimation. Experimental results are also presented to validate the proposed algorithm

Dynamic sensor planning with stereo for model identification on a mobile platform

This paper presents an approach to sensor planning for simultaneous pose estimation and model identification of a moving object using a stereo camera sensor mounted on a mobile base. For a given database of object models, we consider the problem of identifying an object known to belong to the database and where to move next should the object not be easily identifiable from the initial viewpoint. No constraints on the motion of the object nor the robot itself are assumed, which is an improvement on previous methods. Sensor planning is based on the selection of the control action that optimizes a cost metric based on information gain. Experimental results from the implementation of the method on a two-wheeled nonholonomic robot are presented to illustrate and validate the method

Asymptotic properties of bridge estimators in sparse high-dimensional regression models

We study the asymptotic properties of bridge estimators in sparse, high-dimensional, linear regression models when the number of covariates may increase to infinity with the sample size. We are particularly interested in the use of bridge estimators to distinguish between covariates whose coefficients are zero and covariates whose coefficients are nonzero. We show that under appropriate conditions, bridge estimators correctly select covariates with nonzero coefficients with probability converging to one and that the estimators of nonzero coefficients have the same asymptotic distribution that they would have if the zero coefficients were known in advance. Thus, bridge estimators have an oracle property in the sense of Fan and Li [J. Amer. Statist. Assoc. 96 (2001) 1348--1360] and Fan and Peng [Ann. Statist. 32 (2004) 928--961]. In general, the oracle property holds only if the number of covariates is smaller than the sample size. However, under a partial orthogonality condition in which the covariates of the zero coefficients are uncorrelated or weakly correlated with the covariates of nonzero coefficients, we show that marginal bridge estimators can correctly distinguish between covariates with nonzero and zero coefficients with probability converging to one even when the number of covariates is greater than the sample size.Comment: Published in at http://dx.doi.org/10.1214/009053607000000875 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

A preliminary longitudinal study of white matter alteration in cocaine use disorder subjects

Background Previous diffusion tensor imaging (DTI) studies have consistently shown that subjects with cocaine use disorder (CocUD) had altered white matter microstructure in the corpus callosum. It is believed that these alterations are due to preexisting factors, chronic cocaine use, or both. However, there is no published longitudinal DTI study on human cocaine users yet which could shed light on the relationship between cocaine use and DTI findings. Methods This study used a longitudinal design and DTI to test if the white matter microstructure shows quicker alteration in CocUD subjects than controls. DTI data were acquired from eleven CocUD subjects who participated a treatment study and eleven non-drug-using controls at baseline (Scan 1) and after ten weeks (Scan 2). The baseline fractional anisotropy (FA), a general measure of white matter microstucture, and the change in FA (ΔFA, equals Scan 1 FA minus Scan 2 FA) were both compared between groups. Results The two groups did not show a difference in FA at baseline. The CocUD subjects had significantly greater ΔFA than the controls in the left splenium of the corpus callosum. In CocUD subjects, greater ΔFA in this region was associated with shorter lifetime cocaine use and greater number of positive cocaine urine samples collected during the treatment. Conclusion The finding in the left splenium is consistent with previous animal studies and provide indirect evidence about the effects of chronic cocaine use on white matter alterations. The subject sample size is small, therefore the results should be treated as preliminary

The Fates of Dendritic Cells and Antigen Regulate CD4+ T Cell Responses

The rapid activation of effector T cells by antigen-presenting dendritic cells (DCs) is necessary to contain and eradicate pathogens. Upon eradication of the pathogens by effector T cells, the immune response eventually resolves, and the clearance of residual antigen is necessary to prevent immune cell exhaustion or immunopathology. It has been proposed that the elimination of antigen-presenting DCs by CD8+ cytotoxic T cells (CTLs) limits the duration of antigen presentation, hence resolving ongoing immune responses. However, inter-DC antigen transfer spreads antigens for further antigen presentation and may reduce the effect of CTL-mediated DC killing. The aim of my thesis was to examine the impact of CTL-mediated DC killing and inter-DC antigen transfer on the induction and the quality of resulting T cell responses. Initial experiments established that CTLs eliminated antigen-bearing DCs mainly through the cytolytic molecule perforin, whereas FasL played a minor role. CTL-mediated DC killing prevented antigen-bearing DCs from stimulating naive CD4+ and CD8+ T cells in the draining lymph nodes. Thus, CTLs regulated the clonal expansion of naive T cells by controlling the survival of antigen-presenting DCs. The efficiency of CTL-mediated DC killing depended on the method of antigen loading onto DCs, and to a lesser extent, the method of generating CTLs. Surprisingly, efficient CTL-mediated DC killing that completely prevented the accumulation of injected DCs in the lymph nodes did not abolish T cell proliferation, indicating that other antigen presenting cells (APCs) were inducing the residual T cell proliferation when the antigen-bearing DCs were eliminated by CTLs. Further investigations revealed that the antigen from the injected DCs was transferred to host DCs. In the absence of direct antigen presentation by injected DCs, host DCs stimulated local T cell proliferation but did not induce a systemic effector T cell response. In contrast, in the presence of efficient CTL-mediated DC killing, inter-DC antigen transfer enabled the host DCs to stimulate T cell proliferation. These T cells then developed into iii functional effector T cells. In conclusion, in the absence of inter-DC antigen transfer, CTLmediated DC killing reduces the size of T cell responses. However, in the presence of inter- DC antigen transfer, the impact of CTL-mediated DC killing is reduced, hence influencing the size and quality of T cell responses. My findings shed light on how CTL-mediated DC killing and inter-DC antigen transfer regulate immune responses and how DC vaccine regimens for immunotherapy can be improved

Remote Sensing for Precision Agriculture: Sentinel-2 Improved Features and Applications

The use of satellites to monitor crops and support their management is gathering increasing attention. The improved temporal, spatial, and spectral resolution of the European Space Agency (ESA) launched Sentinel-2 A + B twin platform is paving the way to their popularization in precision agriculture. Besides the Sentinel-2 A + B constellation technical features the open-access nature of the information they generate, and the available support software are a significant improvement for agricultural monitoring. This paper was motivated by the challenges faced by researchers and agrarian institutions entering this field; it aims to frame remote sensing principles and Sentinel-2 applications in agriculture. Thus, we reviewed the features and uses of Sentinel-2 in precision agriculture, including abiotic and biotic stress detection, and agricultural management. We also compared the panoply of satellites currently in use for land remote sensing that are relevant for agriculture to the Sentinel-2 A + B constellation features. Contrasted with previous satellite image systems, the Sentinel-2 A + B twin platform has dramatically increased the capabilities for agricultural monitoring and crop management worldwide. Regarding crop stress monitoring, Sentinel-2 capacities for abiotic and biotic stresses detection represent a great step forward in many ways though not without its limitations; therefore, combinations of field data and different remote sensing techniques may still be needed. We conclude that Sentinel-2 has a wide range of useful applications in agriculture, yet still with room for further improvements. Current and future ways that Sentinel-2 can be utilized are also discussed.This research was funded by the Spanish projects AGL2016-76527-R and IRUEC PCIN-2017-063 from the Ministerio de Economía y Competividad (MINECO, Spain) and by the support of Catalan Institution for Research and Advanced Studies (ICREA, Generalitat de Catalunya, Spain), through the ICREA Academia Program

A probabilistic framework for stereo-vision based 3D object search with 6D pose estimation

This paper presents a method whereby an autonomous mobile robot can search for a 3-dimensional (3D) object using an on-board stereo camera sensor mounted on a pan-tilt head. Search efficiency is realized by the combination of a coarse-scale global search coupled with a fine-scale local search. A grid-based probability map is initially generated using the coarse search, which is based on the color histogram of the desired object. Peaks in the probability map are visited in sequence, where a local (refined) search method based on 3D SIFT features is applied to establish or reject the existence of the desired object, and to update the probability map using Bayesian recursion methods. Once found, the 6D object pose is also estimated. Obstacle avoidance during search can be naturally integrated into the method. Experimental results obtained from the use of this method on a mobile robot are presented to illustrate and validate the approach, confirming that the search strategy can be carried out with modest computation