Conference Papers

Hide and code: Session anonymity in wireless line networks with coded packets

Sousa-Pinto H., Lucani D.E., Barros J.

2012 Information Theory and Applications Workshop, ITA 2012 - Conference Proceedings

2012

Abstract:

The broadcast nature of the communication channel enables a malicious eavesdropper to gain information about connectivity and active sessions in a multi-hop wireless network. This can be achieved simply by overhearing the transmitted signals over the ether and analyzing their timings. Focusing on techniques that can meet information-theoretic criteria for session anonymity under traffic analysis attacks, we rely on a judicious choice of transmission schedules to conceal multicast or bidirectional unicast sessions from a global eavesdropper at any given point in time. A systematic approach for constructing the aforementioned transmission schedules for arbitrary network topologies is derived from an equivalent coloring problem in an auxiliary conflict graph. Although this type of anonymity requires various nodes to send dummy transmissions to confuse the eavesdropper, our results show that the additional cost in terms of energy, delay and throughput can be alleviated using network coding. The key intuition is that dummy transmissions can be replaced by coded transmissions, which carry useful information. For the case of a line network with N nodes supporting coded flows, we derive closed-form expressions, which show that anonymity comes at no cost in terms of throughput if at least one of the destinations is two hops away. The average per packet delay is shown to increase by at most 50%.

Higher-order processes, functions, and sessions: A monadic integration

Toninho B., Caires L., Pfenning F.

Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)

2013

Abstract:

In prior research we have developed a Curry-Howard interpretation of linear sequent calculus as session-typed processes. In this paper we uniformly integrate this computational interpretation in a functional language via a linear contextual monad that isolates session-based concurrency. Monadic values are open process expressions and are first class objects in the language, thus providing a logical foundation for higher-order session typed processes. We illustrate how the combined use of the monad and recursive types allows us to cleanly write a rich variety of concurrent programs, including higher-order programs that communicate processes. We show the standard metatheoretic result of type preservation, as well as a global progress theorem, which to the best of our knowledge, is new in the higher-order session typed setting.

Hot tiles: A heat diffusion based descriptor for automatic tile panel assembly

Brandao S., Marques M.

Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)

2016

Abstract:

We revisit the problem of forming a coherent image by assembling independent pieces, also known as the jigsaw puzzle. Namely, we are interested in assembling tile panels, a relevant task for art historians, currently facing many disassembled panels. Existing jigsaw solving algorithms rely strongly on texture alignment to locally decide if two pieces belong together and build the complete jigsaw from local decisions. However, pieces in tile panels are handmade, independently painted, with poorly aligned patterns. In this scenario, existing algorithms suffer from severe degradation. We here introduce a new heat diffusion based affinity measure to mitigate the misalignment between two abutting pieces. We also introduce a global optimization approach to minimize the impact of wrong local decisions. We present experiments on Portuguese tile panels, where our affinity measure performs considerably better that state of the art and we can assemble large parts of a panel.

Hourly traffic prediction of news stories

Marujo L., Bugalho M., Neto J.P., Gershman A., Carbonell J.

CEUR Workshop Proceedings

2011

Abstract:

In this paper we develop a dynamic continuous solution to the clustering problem of data characterized by a mixture of K distributions, where K is given a priori. The proposed solution resorts to game theory tools, in particular mean field games and can be interpreted as the continuous version of a generalized Expectation-Maximization (GEM) algorithm. The main contributions of this paper are twofold: first, we prove that the proposed solution is a GEM algorithm; second, we derive closed-form solution for a Gaussian mixture model and show that the proposed algorithm converges exponentially fast to a maximum of the log-likelihood function, improving significantly over the state of the art. We conclude the paper by presenting simulation results for the Gaussian case that indicate better performance of the proposed algorithm in term of speed of convergence and with respect to the overlap problem

How can I choose an explainer? An Application-grounded Evaluation of Post-hoc Explanations

Jesus S., Belém C., Balayan V., Bento J., Saleiro P., Bizarro P., Gama J.

ACM FAccT’2021

2021

Abstract:

There have been several research works proposing new Explainable AI (XAI) methods designed to generate model explanations having specific properties, or desiderata, such as fidelity, robustness, or human-interpretability. However, explanations are seldom evaluated based on their true practical impact on decision-making tasks. Without that assessment, explanations might be chosen that, in fact, hurt the overall performance of the combined system of ML model + end-users. This study aims to bridge this gap by proposing XAI Test, an application-grounded evaluation methodology tailored to isolate the impact of providing the end-user with different levels of information. We conducted an experiment following XAI Test to evaluate three popular post-hoc explanation methods — LIME, SHAP, and TreeInterpreter — on a real-world fraud detection task, with real data, a deployed ML model, and fraud analysts. During the experiment, we gradually increased the information provided to the fraud analysts in three stages: Data Only, i.e., just transaction data without access to model score nor explanations, Data + ML Model Score, and Data + ML Model Score + Explanations. Using strong statistical analysis, we show that, in general, these popular explainers have a worse impact than desired. Some of the conclusion highlights include: i) showing Data Only results in the highest decision accuracy and the slowest decision time among all variants tested, ii) all the explainers improve accuracy over the Data + ML Model Score variant but still result in lower accuracy when compared with Data Only; iii) LIME was the least preferred by users, probably due to its substantially lower variability of explanations from case to case.

How does technological regime affect performance of technology development projects?

Song M., Hooshangi S., Zhao Y.L., Halman J.I.M.

Journal of Product Innovation Management

2014

Abstract:

In this study, we examine how technological regime affects the performance of technology development projects (i.e., project quality, sales, and profit). Technological regime is defined as the set of attributes of a technological environment where the innovative activities of firms take place. Technological opportunity, appropriability of innovations, cumulativeness of knowledge and capabilities, and closeness of knowledge base to basic sciences (versus applied sciences) are attributes of technological regime. Using data from 381 firms across five industries, we show that high levels of technological opportunity, appropriability, and closeness of knowledge base to basic sciences are associated with higher project performance. Cumulativeness is associated with higher project quality, but not higher sales and profit. We also show that the effect of technological opportunity on project performance is moderated by two other determinants of technological regime: cumulativeness and nature of knowledge base. We find that cumulativeness has a negative moderating effect on the positive relationship between technological opportunity and project performance, while closeness of knowledge base to basic sciences positively moderates the effect of technological opportunity on project performance. We discuss the implications of our findings for new product development research and practice.

How feasible is network coding in current satellite systems?

Vieira F., Shintre S., Barros J.

ASMS/SPSC 2010: 2010 5th Advanced Satellite Multimedia Systems Conference and the 11th Signal Processing for Space Communications Workshop

2010

Abstract:

The benefits of network coding in terms of throughput, security and robustness are well understood for a large class of networks, such as wireless mesh networks and peer-to-peer systems. We ask if similar performance enhancements can be attained in satellite based communications. Our feasibility study focuses on GEO satellite communication systems including regenerative payloads and multi spot-beam satellites. In addition, we consider LEO satellite constellations with multi-path scenarios. Our analysis reveals that several network coding techniques are worthy of consideration for new generation satellite systems with highly dynamic and unpredictable behavior.

Human identification based on ECG signals from wearable health monitoring devices

Ye C., Kumar B.V.K.V., Coimbra M.T.

ACM International Conference Proceeding Series

2011

Abstract:

Wearable health monitoring devices have been widely explored to enable continuous monitoring of physiological vital signals, such as electrocardiogram (ECG). In this work, we investigate the applicability of ECG signals from such wearable devices in human identification. In the 5-subject study we undertook, the proposed method exhibits near-100% recognition rates based on single heartbeats, even with a six-month interval between the training and testing data. This indicates that ECG signals can be used as robust biometrics and as an automatic login solution for such wearable health monitoring devices.

Hydroprinted Electronics: Ultrathin Stretchable Ag–In–Ga E-Skin for Bioelectronics and Human–Machine Interaction

Lopes P.A., Paisana H., Almeida A.T., Majidi C., Tavakoli M.

Applied Materials and Interfaces

2018

Abstract:

We introduce a soft ultrathin and stretchable electronic skin with surface-mounted components that can be transferred and wrapped around any three-dimensional (3D) surface or self-adhere to the human skin. The ∼5 μm thick circuit is fabricated by printing the pattern over a temporary tattoo paper using a desktop laser printer, which is then coated with a silver ink and eutectic gallium–indium (EGaIn) liquid metal alloy. The resulting “Ag–In–Ga” traces are highly conductive and maintain low electrical resistivity as the circuit is stretched to conform to nondevelopable 3D surfaces. We also address integration of surface-mounted microelectronic chips by introducing a novel z-axis conductive interface composed of magnetically aligned EGaIn-coated Ag–Ni microparticles embedded in polyvinyl alcohol (PVA). This “zPVA conductive glue” allows for robust electrical contacts with microchips that have pins with dimensions as small as 300 μm. If printed on the temporary tattoo transfer paper, the populated circuit can be attached to a 3D surface using hydrographic transfer. Both printing and interfacing processes can be performed at the room temperature. We demonstrate examples of applications, including an electronic tattoo over the human epidermis for electromyography signal acquisition, an interactive circuit with touch buttons, and light-emitting diodes transferred over the 3D printed shell of a robotic prosthetic hand, and a proximity measurement skin transferred over a 3D surface. Keywords: anisotropic conductor; EGaIn; electronic tattoo; hydroprinted electronics; liquid metal; printed electronics; silver lnks; stretchable electronics