Excitation Backprop for RNNs

Deep models are state-of-the-art for many vision tasks including video action recognition and video captioning. Models are trained to caption or classify activity in videos, but little is known about the evidence used to make such decisions. Grounding decisions made by deep networks has been studied in spatial visual content, giving more insight into model predictions for images. However, such studies are relatively lacking for models of spatiotemporal visual content - videos. In this work, we devise a formulation that simultaneously grounds evidence in space and time, in a single pass, using top-down saliency. We visualize the spatiotemporal cues that contribute to a deep model's classification/captioning output using the model's internal representation. Based on these spatiotemporal cues, we are able to localize segments within a video that correspond with a specific action, or phrase from a caption, without explicitly optimizing/training for these tasks.Comment: CVPR 2018 Camera Ready Versio

Agents, Bookmarks and Clicks: A topical model of Web traffic

Analysis of aggregate and individual Web traffic has shown that PageRank is a poor model of how people navigate the Web. Using the empirical traffic patterns generated by a thousand users, we characterize several properties of Web traffic that cannot be reproduced by Markovian models. We examine both aggregate statistics capturing collective behavior, such as page and link traffic, and individual statistics, such as entropy and session size. No model currently explains all of these empirical observations simultaneously. We show that all of these traffic patterns can be explained by an agent-based model that takes into account several realistic browsing behaviors. First, agents maintain individual lists of bookmarks (a non-Markovian memory mechanism) that are used as teleportation targets. Second, agents can retreat along visited links, a branching mechanism that also allows us to reproduce behaviors such as the use of a back button and tabbed browsing. Finally, agents are sustained by visiting novel pages of topical interest, with adjacent pages being more topically related to each other than distant ones. This modulates the probability that an agent continues to browse or starts a new session, allowing us to recreate heterogeneous session lengths. The resulting model is capable of reproducing the collective and individual behaviors we observe in the empirical data, reconciling the narrowly focused browsing patterns of individual users with the extreme heterogeneity of aggregate traffic measurements. This result allows us to identify a few salient features that are necessary and sufficient to interpret the browsing patterns observed in our data. In addition to the descriptive and explanatory power of such a model, our results may lead the way to more sophisticated, realistic, and effective ranking and crawling algorithms.Comment: 10 pages, 16 figures, 1 table - Long version of paper to appear in Proceedings of the 21th ACM conference on Hypertext and Hypermedi

Analysis of floating marine garbage in Barcelona using representation tools in Python language

Microplastics on coastal waters around the world are every day a bigger concern to the popu- lation. This project studies the litter concentration on Barcelona coastal waters by using repre- sentations tools in Python language, with calculation libraries written in C++. This project is based on a previous study called LOCATE, that uses the Lagrangian simulator Parcels, which is capable of predicting the movement and accumulation of floating debris in coastal waters, by combining wave and current data with simulations of the movement of rubbish particles. The objectives of the project are to understand how the LOCATE model works, implement and analyse the data of the project Surfing for Science, as well as improve the simulation by working the Stokes drift. In order to carry out the objectives, it is explained how the Lagrangian simulation (Parcels) works, and it is put to practice. The project starts by improving the numerical simulation, work- ing on the Stokes drift. Then, it implements the microplastic data collected by the project Surfing for Science, and numerically simulates it. The model predicts the movement of virtual particles and provides the potential fate and origin of the microplastics. Once the numerical simulation has been run, it is seen that beaches act as microplastics reser- voirs, since 80, 13% of microplastics have their potential origin on the different beaches, and 83, 56% have their potential fate on the same locations. In this thesis, the effect of beaching mod- els and a possible anti-diffusion component in order to better find the origin of the microplastics are discussed. To conclude, the project has a positive environmental impact, since it allows finding and erad- icating the potential microplastics’ origin, opening other lines of future investigation and im- provement to make the simulation more accurate.Objectius de Desenvolupament Sostenible::6 - Aigua Neta i Sanejamen

Towards Usable End-user Authentication

Authentication is the process of validating the identity of an entity, e.g., a person, a machine, etc.; the entity usually provides a proof of identity in order to be authenticated. When the entity - to be authenticated - is a human, the authentication process is called end-user authentication. Making an end-user authentication usable entails making it easy for a human to obtain, manage, and input the proof of identity in a secure manner. In machine-to-machine authentication, both ends have comparable memory and computational power to securely carry out the authentication process using cryptographic primitives and protocols. On the contrary, as a human has limited memory and computational power, in end-user authentication, cryptography is of little use. Although password based end-user authentication has many well-known security and usability problems, it is the de facto standard. Almost half a century of research effort has produced a multitude of end-user authentication methods more sophisticated than passwords; yet, none has come close to replacing passwords. In this dissertation, taking advantage of the built-in sensing capability of smartphones, we propose an end-user authentication framework for smartphones - called ePet - which does not require any active participation from the user most of the times; thus the proposed framework is highly usable. Using data collected from subjects, we validate a part of the authentication framework for the Android platform. For web authentication, in this dissertation, we propose a novel password creation interface, which helps a user remember a newly created password with more confidence - by allowing her to perform various memory tasks built upon her new password. Declarative and motor memory help the user remember and efficiently input a password. From a within-subjects study we show that declarative memory is sufficient for passwords; motor memory mostly facilitate the input process and thus the memory tasks have been designed to help cement the declarative memory for a newly created password. This dissertation concludes with an evaluation of the increased usability of the proposed interface through a between-subjects study

Isometric versus Elastic Surfboard Interfaces for 3D Travel in Virtual Reality

Three dimensional travel in immersive virtual environments (IVE) has been a difficult problem since the beginning of virtual reality (VR), basically due to the difficulty of designing an intuitive, efficient, and precise three degrees of freedom (DOF) interface which can map the user\u27s finite local movements in the real world to a potentially infinite virtual space. Inspired by the Silver Surfer Sci-Fi movie and the popularity of the Nintendo Wii Balance Board interface, a surfboard interface appears to be a good solution to this problem. Based on this idea, I designed and developed a VR Silver Surfer system which allows a user to surf in the sky of an infinite virtual environment, using either an isometric balance board or an elastic tilt board. Although the balance board is the industrial standard of board interface, the tilt board seems to provide the user more intuitive, realistic and enjoyable experiences, without any sacrifice of efficiency or precision. To validate this hypothesis we designed and conducted a user study that compared the two board interfaces in three independent experiments that break the travel procedure into separate DOFs. The results showed that in all experiments, the tilt board was not only as efficient and precise as the balance board, but also more intuitive, realistic and fun. In addition, despite the popularity of the balance board in the game industry, most subjects in the study preferred the tilt board in general, and in fact complained that the balance board could have been the cause of possible motion sickness

Extending the Touchscreen Pattern Lock Mechanism with Duplicated and Temporal Codes

We investigate improvements to authentication on mobile touchscreen phones and present a novel extension to the widely used touchscreen pattern lock mechanism. Our solution allows including nodes in the grid multiple times, which enhances the resilience to smudge and other forms of attack. For example, for a smudge pattern covering 7 nodes, our approach increases the amount of possible lock patterns by a factor of 15 times. Our concept was implemented and evaluated in a laboratory user test (n = 36). The test participants found the usability of the proposed concept to be equal to that of the baseline pattern lock mechanism but considered it more secure. Our solution is fully backwards-compatible with the current baseline pattern lock mechanism, hence enabling easy adoption whilst providing higher security at a comparable level of usability

The Role of (Dis)satisfaction in the Effectiveness of E-Mail usage at Work

This paper focuses on e-mail related activities in the workplace, in particular emails that are sent during work hours, and demonstrates the great extent of waste involved in their daily use, not just for private purposes, but also for purposes of work. The survey includes a thorough statistical analysis referring to 15 different service organizations operating in Israel. In the research, influences parameters were reviewed, among which quantity of "net connections", and "existence of organization culture/policy, satisfaction at work and demographic parameters. the research explores interruptions at work, resulting from (dis)satisfaction at work and the extent to, which the e-mail tool contribute to interruptions and diminish our ability to focus on important tasks. The findings show that increasing e-mail usage in the workplace and spending large amounts of time on private emails may be an indicator for dissatisfaction at work, in service organizations. Moreover, it emphasizes the importance of introducing greater control, supervision, training and e-mail boxes separation.dissatisfaction at work, effects of e-mail at work, service organization, organization culture/policy, efficiency.

Life at the front of an expanding population

Recent microbial experiments suggest that enhanced genetic drift at the frontier of a two-dimensional range expansion can cause genetic sectoring patterns with fractal domain boundaries. Here, we propose and analyze a simple model of asexual biological evolution at expanding frontiers to explain these neutral patterns and predict the effect of natural selection. Our model attributes the observed gradual decrease in the number of sectors at the leading edge to an unbiased random walk of sector boundaries. Natural selection introduces a deterministic bias in the wandering of domain boundaries that renders beneficial mutations more likely to escape genetic drift and become established in a sector. We find that the opening angle of those sectors and the rate at which they become established depend sensitively on the selective advantage of the mutants. Deleterious mutations, on the other hand, are not able to establish a sector permanently. They can, however, temporarily "surf" on the population front, and thereby reach unusual high frequencies. As a consequence, expanding frontiers are susceptible to deleterious mutations as revealed by the high fraction of mutants at mutation-selection balance. Numerically, we also determine the condition at which the wild type is lost in favor of deleterious mutants (genetic meltdown) at a growing front. Our prediction for this error threshold differs qualitatively from existing well-mixed theories, and sets tight constraints on sustainable mutation rates for populations that undergo frequent range expansions.Comment: Updat