Spherical clustering of users navigating 360{\deg} content

In Virtual Reality (VR) applications, understanding how users explore the omnidirectional content is important to optimize content creation, to develop user-centric services, or even to detect disorders in medical applications. Clustering users based on their common navigation patterns is a first direction to understand users behaviour. However, classical clustering techniques fail in identifying these common paths, since they are usually focused on minimizing a simple distance metric. In this paper, we argue that minimizing the distance metric does not necessarily guarantee to identify users that experience similar navigation path in the VR domain. Therefore, we propose a graph-based method to identify clusters of users who are attending the same portion of the spherical content over time. The proposed solution takes into account the spherical geometry of the content and aims at clustering users based on the actual overlap of displayed content among users. Our method is tested on real VR user navigation patterns. Results show that our solution leads to clusters in which at least 85% of the content displayed by one user is shared among the other users belonging to the same cluster.Comment: 5 pages, conference (Published in: ICASSP 2019 - 2019 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)

Measuring user Quality of Experience in social VR systems

Virtual Reality (VR) is a computer-generated experience that can simulate physical presence in real or imagined environments [7]. A social VR system is an application that allows multiple users to join a collaborative Virtual Environment (VE), such as a computer-generated 3D scene or a 360-degree natural scene captured by an omnidirectional camera, and communicate with each other, usually by means of visual and audio cues. Each user is represented in the VE as a computer-generated avatar [3] or, in recently proposed systems, with a virtual representation based on live captures [1]. Depending on the system, the user’ virtual representation can also interact with the virtual environment, for example by manipulating virtual objects, controlling the appearance of the VE, or controlling the playout of additional media in the VE. The interest for social Virtual Reality (VR) systems dates back to the late 90s [4, 8] but has recently increased [2, 5, 6] due to the availability of affordable head-mounted displays on the consumer market and to the appearance of new applications, such as Facebook Spaces, YouTube VR, Hulu VR, which explicitly aim at including social features in existing VR platforms for multimedia delivery. In this talk, we will address the problem of measuring user Quality of Experience (QoE) in social VR systems. We will review the studies that have analysed how different features of a social VR system design, such as avatar appearance and behavioural realism, can affect user’s experience, and propose a comparison of the objective and subjective measures used in the literature to quantify user QoE in social VR. Finally, we will discuss the use case of watching movies together in VR and present the results of one of our recent studies focusing on this scenario, designed and performed in the framework of the European project VRTogether (http://vrtogether.eu). Particularly, we show an analysis of correlation between the objective and subjective measurements collected during our study, to provide guidelines toward the design of a unified methodology to monitor and quantify users’ QoE in social VR systems. The open questions to be addressed in the future in order to achieve such goal are also discussed

Direct and indirect noise generated by entropic and compositional inhomogeneities

Flow disturbances are generated inside a duct via pulsed injection of helium into a flow of air. This leads to the generation of an acoustic pulse (direct noise), as well as the production of entropic and compositional inhomogeneities which are convected with the mean flow. As these inhomogeneities are convected through a choked nozzle, they generate indirect noise. The resulting acoustic pressure fluctuations are measured experimentally using pressure transducers upstream of the nozzle. Insight obtained from theoretical models and a time-delay analysis can be used to isolate and extract the contributions of direct and indirect noise in the experimental signal. These results are directly compared to existing one-dimensional direct and indirect noise models. The experimental measurement of indirect noise is found to be in good agreement with the theoretical models for entropy noise and compositional noise for a compact one-dimensional isentropic nozzle

L1-regularization for multi-period portfolio selection

In this work we present a model for the solution of the multi-period portfolio selection problem. The model is based on a time consistent dynamic risk measure. We apply l1-regularization to stabilize the solution process and to obtain sparse solutions, which allow one to reduce holding costs. The core problem is a nonsmooth optimization one, with equality constraints. We present an iterative procedure based on a modified Bregman iteration, that adaptively sets the value of the regularization parameter in order to produce solutions with desired financial properties. We validate the approach showing results of tests performed on real data

Neuroimmune regulation of JCV by immune mediators in glial cells

2012 - 2013The human polyomavirus JC (JCV) is a small DNA virus responsible for the initiation of progressive multifocal leukoencephalopathy (PML), an often lethal disease of the brain characterized by lytic infection of oligodendrocytes in the central nervous system (CNS). Patients undergoing immune modulatory therapies for the treatment of autoimmune diseases such as multiple sclerosis, and individuals with an impaired-immune system, most notably AIDS patients, are in the high risk group of developing PML. Previous studies suggested that soluble immune mediators secreted from PBMCs inhibited viral genomic replication. However little is known regarding the molecular mechanism of this regulation. Here we investigated the impact of conditioned media (CM) from activated PBMCs on viral replication and gene expression by molecular virology techniques. Our data showed that viral gene expression as well as viral replication was suppressed by the CM. Further studies revealed that soluble immune mediators from PBMCs possessed a dual control on T-antigen expression at transcription and post-transcription level. These observations demonstrate a novel role of immune mediators in regulation of JCV gene expression, and provide a new avenue of research to understand molecular mechanism of viral reactivation in patients who are at risk of developing PML. [edited by author]XII n.s

Complexity measurement and characterization of 360-degree content

The appropriate characterization of the test material, used for subjective evaluation tests and for benchmarking image and video processing algorithms and quality metrics, can be crucial in order to perform comparative studies that provide useful insights. This paper focuses on the characterisation of 360-degree images. We discuss why it is important to take into account the geometry of the signal and the interactive nature of 360-degree content navigation, for a perceptual characterization of these signals. Particularly, we show that the computation of classical indicators of spatial complexity, commonly used for 2D images, might lead to different conclusions depending on the geometrical domain use

Complexity measurement and characterization of 360-degree content

The appropriate characterization of the test material, used for subjective evaluation tests and for benchmarking image and video processing algorithms and quality metrics, can be crucial in order to perform comparative studies that provide useful insights. This paper focuses on the characterisation of 360-degree images. We discuss why it is important to take into account the geometry of the signal and the interactive nature of 360-degree content navigation, for a perceptual characterization of these signals. Particularly, we show that the computation of classical indicators of spatial complexity, commonly used for 2D images, might lead to different conclusions depending on the geometrical domain use

Searching through photographic databases with QuickLook

G. Ciocca, C. Cusano, R. Schettini, S. Santini, A. de Polo, F. Tavanti, “Searching through photographic databases with QuickLook”. Proc. Multimedia on Mobile Devices 2012; and Multimedia Content Access: Algorithms and Systems VI. Ed- Reiner Creutzburg; David Akopian; Cees G. M. Snoek; Nicu Sebe; Lyndon Kennedy. 8304. 83040V-1 (2012). Copyright 2012 Society of Photo‑Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.We present here the results obtained by including a new image descriptor, that we called prosemantic feature vector, within the framework of QuickLook2 image retrieval system. By coupling the prosemantic features and the relevance feedback mechanism provided by QuickLook2, the user can move in a more rapid and precise way through the feature space toward the intended goal. The prosemantic features are obtained by a two-step feature extraction process. At the first step, low level features related to image structure and color distribution are extracted from the images. At the second step, these features are used as input to a bank of classifiers, each one trained to recognize a given semantic category, to produce score vectors. We evaluated the efficacy of the prosemantic features under search tasks on a dataset provided by Fratelli Alinari Photo Archive.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only