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Institute Talks

How to make your agent gesture in a natural way?

Talk
  • 19 September 2019 • 11:00 12:00
  • Taras Kucherenko
  • PS-Aquarium

Conversational agents in the form of virtual agents or social robots are rapidly becoming wide-spread. Humans use non-verbal behaviors to signal their intent, emotions and attitudes in human-human interactions. Conversational agents therefore need this ability as well in order to make an interaction pleasant and efficient. An important part of non-verbal communication is gesticulation: gestures communicate a large share of non-verbal content. Previous systems for gesture production were typically rule-based and could not represent the range of human gestures. Recently the gesture generation field has shifted to data-driven approaches. We follow this line of research by extending the state-of-the-art deep-learning based model. Our model leverages representation learning to enhance speech-gesture mapping. We provide analysis of different representations for the input (speech) and the output (motion) of the network by both objective and subjective evaluations. We also analyze the importance of smoothing of the produced motion and emphasize how challenging it is to evaluate gesture quality. In the future we plan to enrich input signal by taking semantic context (text transcription) as well, make the model probabilistic and evaluate our system on the social robot NAO.

Organizers: Mohamed Hassan Soubhik Sanyal

A Dynamical Systems Perspective on Optimization with Momentum

Talk
  • 19 September 2019 • 14:00 15:00
  • Dr. Michael Muehlebach
  • MPI-IS Stuttgart, Heisenbergstr. 3, seminar room 2P4

My talk will be divided into two parts. In the first part, I will analyze Nesterov's accelerated gradient method from a dynamical systems point of view. More precisely, I will derive the accelerated gradient method by discretizing an ordinary differential equation with a semi-implicit Euler integration scheme. I will analyze both the ordinary differential equation and the discretization for obtaining insights into the phenomenon of acceleration. In particular, geometric properties of the dynamics, such as asymptotic stability, time-reversibility, and phase-space volume contraction are shown to be preserved through the discretization. In the second part, I will show that these geometric properties are enough for characterizing the convergence rate. The results therefore provide criteria that are easily verifiable for the accelerated convergence of any momentum-based optimization algorithm. The results also yield guidance for the design of new optimization algorithms. The talk will focus on unconstrained optimization problems with smooth and strongly-convex objective functions, even though the analysis potentially generalizes to non-convex or non-Euclidean settings, or when the decision variables are constrained to a smooth manifold.

Organizers: Sebastian Trimpe

From Fingertip Skin Mechanics to Dexterous Object Manipulation

IS Colloquium
  • 25 September 2019 • 13:00 14:00
  • Jean-Louis Thonnard
  • MPI-IS Stuttgart, Heisenbergstr. 3, Room 2P4

Fingertip skin friction plays a critical role during object manipulation. We will describe a simple and reliable method to estimate the fingertip static coefficient of friction (CF) continuously and quickly during object manipulation, and we will describe a global expression of the CF as a function of the normal force and fingertip moisture. Then we will show how skin hydration modifies the skin deformation dynamics during grip-like contacts. Certain motor behaviours observed during object manipulation could be explained by the effects of skin hydration. Then the biomechanics of the partial slip phenomenon will be described, and we will examine how this partial slip phenomenon is related to the subjective perception of fingertip slip.

Organizers: Katherine J. Kuchenbecker David Gueorguiev

Soft Aerial Robotics for Infrastructure Manufacturing

Talk
  • 26 September 2019 • 14:00 15:00
  • Mirko Kovac
  • 2R04

Future cities and infrastructure systems will evolve into complex conglomerates where autonomous aerial, aquatic and ground-based robots will coexist with people and cooperate in symbiosis. To create this human-robot ecosystem, robots will need to respond more flexibly, robustly and efficiently than they do today. They will need to be designed with the ability to move across terrain boundaries and physically interact with infrastructure elements to perform sensing and intervention tasks. Taking inspiration from nature, aerial robotic systems can integrate multi-functional morphology, new materials, energy-efficient locomotion principles and advanced perception abilities that will allow them to successfully operate and cooperate in complex and dynamic environments. This talk will describe the scientific fundamentals, design principles and technologies for the development of biologically inspired flying robots with adaptive morphology that can perform monitoring and manufacturing tasks for future infrastructure and building systems. Examples will include flying robots with perching capabilities and origami-based landing systems, drones for aerial construction and repair, and combustion-based jet thrusters for aerial-aquatic vehicles.

Organizers: Metin Sitti

  • Stan Sclaroff

In the first part of the talk, I will describe methods that learn a single family of detectors for object classes that exhibit large within-class variation. One common solution is to use a divide-and-conquer strategy, where the space of possible within-class variations is partitioned, and different detectors are trained for different partitions.

However, these discrete partitions tend to be arbitrary in continuous spaces, and the classifiers have limited power when there are too few training samples in each subclass. To address this shortcoming, explicit feature sharing has been proposed, but it also makes training more expensive. We show that foreground-background classification (detection) and within-class classification of the foreground class (pose estimation) can be jointly solved in a multiplicative form of two kernel functions. One kernel measures similarity for foreground-background classification. The other kernel accounts for latent factors that control within-class variation and implicitly enables feature sharing among foreground training samples. The multiplicative kernel formulation enables feature sharing implicitly; the solution for the optimal sharing is a byproduct of SVM learning.

The resulting detector family is tuned to specific variations in the foreground. The effectiveness of this framework is demonstrated in experiments that involve detection, tracking, and pose estimation of human hands, faces, and vehicles in video.


Dino Sejdinovic - TBA

IS Colloquium
  • Dino Sejdinovic



  • Tim Sullivan

Beginning with a seminal paper of Diaconis (1988), the aim of so-called "probabilistic numerics" is to compute probabilistic solutions to deterministic problems arising in numerical analysis by casting them as statistical inference problems. For example, numerical integration of a deterministic function can be seen as the integration of an unknown/random function, with evaluations of the integrand at the integration nodes proving partial information about the integrand. Advantages offered by this viewpoint include: access to the Bayesian representation of prior and posterior uncertainties; better propagation of uncertainty through hierarchical systems than simple worst-case error bounds; and appropriate accounting for numerical truncation and round-off error in inverse problems, so that the replicability of deterministic simulations is not confused with their accuracy, thereby yielding an inappropriately concentrated Bayesian posterior. This talk will describe recent work on probabilistic numerical solvers for ordinary and partial differential equations, including their theoretical construction, convergence rates, and applications to forward and inverse problems. Joint work with Andrew Stuart (Warwick).

Organizers: Philipp Hennig