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2011


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BET specific surface area and pore structure of MOFs determined by hydrogen adsorption at 20 K

Streppel, B., Hirscher, M.

{Physical Chemistry Chemical Physics}, 13(8):3220-3222, 2011 (article)

mms

DOI [BibTex]

2011


DOI [BibTex]


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High contrast magnetic and nonmagnetic sample current microscopy for bulk and transparent samples using soft X-rays

Nolle, D., Weigand, M., Schütz, G., Goering, E.

{Microscopy and Microanalysis}, 17, pages: 834-842, 2011 (article)

mms

DOI [BibTex]

DOI [BibTex]


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Magnetic vortex core reversal by rotating magnetic fields generated on micrometer length scales

Curcic, M., Stoll, H., Weigand, M., Sackmann, V., Jüllig, P., Kammerer, M., Noske, M., Sproll, M., Van Waeyenberge, B., Vansteenkiste, A., Woltersdorf, G., Tyliszczak, T., Schütz, G.

{Physica Status Solidi B}, 248(10):2317-2322, 2011 (article)

mms

DOI [BibTex]

DOI [BibTex]


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Operational Space Control of Constrained and Underactuated Systems

Mistry, M., Righetti, L.

In Proceedings of Robotics: Science and Systems, Los Angeles, CA, USA, June 2011 (inproceedings)

Abstract
The operational space formulation (Khatib, 1987), applied to rigid-body manipulators, describes how to decouple task-space and null-space dynamics, and write control equations that correspond only to forces at the end-effector or, alternatively, only to motion within the null-space. We would like to apply this useful theory to modern humanoids and other legged systems, for manipulation or similar tasks, however these systems present additional challenges due to their underactuated floating bases and contact states that can dynamically change. In recent work, Sentis et al. derived controllers for such systems by implementing a task Jacobian projected into a space consistent with the supporting constraints and underactuation (the so called "support consistent reduced Jacobian"). Here, we take a new approach to derive operational space controllers for constrained underactuated systems, by first considering the operational space dynamics within "projected inverse-dynamics" (Aghili, 2005), and subsequently resolving underactuation through the addition of dynamically consistent control torques. Doing so results in a simplified control solution compared with previous results, and importantly yields several new insights into the underlying problem of operational space control in constrained environments: 1) Underactuated systems, such as humanoid robots, cannot in general completely decouple task and null-space dynamics. However, 2) there may exist an infinite number of control solutions to realize desired task-space dynamics, and 3) these solutions involve the addition of dynamically consistent null-space motion or constraint forces (or combinations of both). In light of these findings, we present several possible control solutions, with varying optimization criteria, and highlight some of their practical consequences.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


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Nanomechanics of AFM based nanomanipulation

Xie, H., Onal, C., Régnier, S., Sitti, M.

In Atomic Force Microscopy Based Nanorobotics, pages: 87-143, Springer Berlin Heidelberg, 2011 (incollection)

pi

[BibTex]

[BibTex]


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Under-actuated tank-like climbing robot with various transitioning capabilities

Seo, T., Sitti, M.

In Robotics and Automation (ICRA), 2011 IEEE International Conference on, pages: 777-782, 2011 (inproceedings)

pi

[BibTex]

[BibTex]


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Enhancing adhesion of biologically inspired polymer microfibers with a viscous oil coating

Cheung, E., Sitti, M.

The Journal of Adhesion, 87(6):547-557, Taylor & Francis Group, 2011 (article)

pi

Project Page [BibTex]

Project Page [BibTex]


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Rotating magnetic micro-robots for versatile non-contact fluidic manipulation of micro-objects

Diller, E., Ye, Z., Sitti, M.

In Intelligent Robots and Systems (IROS), 2011 IEEE/RSJ International Conference on, pages: 1291-1296, 2011 (inproceedings)

pi

Project Page [BibTex]

Project Page [BibTex]


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Formation of two amorphous phases in the Ni60Nb18Y22 alloy after high pressure torsion

Straumal, B. B., Mazilkin, A. A., Protasova, S. G., Goll, D., Baretzky, B., Bakai, A. S., Dobatkin, S. V.

{Kovove Materialy-Metallic Materials}, 49(1):17-22, 2011 (article)

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link (url) [BibTex]

link (url) [BibTex]


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Structure and properties of nanograined Fe-C alloys after severe plastic deformation

Straumal, B. B., Dobatkin, S. V., Rodin, A. O., Protasova, S. G., Mazilkin, A. A., Goll, D., Baretzky, B.

{Advanced Engineering Materials}, 13(6):463-469, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Increased flux pinning in YBa2Cu3O7-δthin-film devices through embedding of Au nano crystals

Katzer, C., Schmidt, M., Michalowski, P., Kuhwald, D., Schmidl, F., Grosse, V., Treiber, S., Stahl, C., Albrecht, J., Hübner, U., Undisz, A., Rettenmayr, M., Schütz, G., Seidel, P.

{Europhysics Letters}, 95(6), 2011 (article)

mms

DOI [BibTex]

DOI [BibTex]


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Signal transfer in a chain of stray-field coupled ferromagnetic squares

Vogel, A., Martens, M., Weigand, M., Meier, G.

{Applied Physics Letters}, 99, 2011 (article)

mms

DOI [BibTex]

DOI [BibTex]


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Transmission electron microscopy investigation of boundaries between amorphous "grains" in Ni50Nb20Y30 alloy

Mazilkin, A. A., Abrosimova, G. E., Protasova, S. G., Straumal, B. B., Schütz, G., Dobatkin, S. V., Bakai, A. S.

In 46, pages: 4336-4342, Mie, Japan, 2011 (inproceedings)

mms

DOI [BibTex]

DOI [BibTex]


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Electron theory of magnetoelectric effects in metallic ferromagnetic nanostructures

Subkow, S., Fähnle, M.

{Physical Review B}, 84, 2011 (article)

mms

DOI [BibTex]

DOI [BibTex]


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Magnetic antivortex-core reversal by rotating magnetic fields

Kamionka, T., Martens, M., Chou, K., Drews, A., Tyliszczak, T., Stoll, H., Van Waeyenberge, B., Meier, G.

{Physical Review B}, 83, 2011 (article)

mms

DOI [BibTex]

DOI [BibTex]


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Magnetic properties of exchange-spring composite films

Kronmüller, H., Goll, D.

{Physica Status Solidi B}, 248(10):2361-2367, 2011 (article)

mms

DOI [BibTex]

DOI [BibTex]


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Wetting transition of grain boundaries in the Sn-rich part of the Sn-Bi phase diagram

Yeh, C.-H., Chang, L.-S., Straumal, B. B.

{Journal of Materials Science}, 46(5):1557-1562, 2011 (article)

mms

DOI [BibTex]

DOI [BibTex]


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Online movement adaptation based on previous sensor experiences

Pastor, P., Righetti, L., Kalakrishnan, M., Schaal, S.

In 2011 IEEE/RSJ International Conference on Intelligent Robots and Systems, pages: 365-371, IEEE, San Francisco, USA, sep 2011 (inproceedings)

Abstract
Personal robots can only become widespread if they are capable of safely operating among humans. In uncertain and highly dynamic environments such as human households, robots need to be able to instantly adapt their behavior to unforseen events. In this paper, we propose a general framework to achieve very contact-reactive motions for robotic grasping and manipulation. Associating stereotypical movements to particular tasks enables our system to use previous sensor experiences as a predictive model for subsequent task executions. We use dynamical systems, named Dynamic Movement Primitives (DMPs), to learn goal-directed behaviors from demonstration. We exploit their dynamic properties by coupling them with the measured and predicted sensor traces. This feedback loop allows for online adaptation of the movement plan. Our system can create a rich set of possible motions that account for external perturbations and perception uncertainty to generate truly robust behaviors. As an example, we present an application to grasping with the WAM robot arm.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


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Learning to grasp under uncertainty

Stulp, F., Theodorou, E., Buchli, J., Schaal, S.

In Robotics and Automation (ICRA), 2011 IEEE International Conference on, Shanghai, China, May 9-13, 2011, clmc (inproceedings)

Abstract
We present an approach that enables robots to learn motion primitives that are robust towards state estimation uncertainties. During reaching and preshaping, the robot learns to use fine manipulation strategies to maneuver the object into a pose at which closing the hand to perform the grasp is more likely to succeed. In contrast, common assumptions in grasp planning and motion planning for reaching are that these tasks can be performed independently, and that the robot has perfect knowledge of the pose of the objects in the environment. We implement our approach using Dynamic Movement Primitives and the probabilistic model-free reinforcement learning algorithm Policy Improvement with Path Integrals (PI2 ). The cost function that PI2 optimizes is a simple boolean that penalizes failed grasps. The key to acquiring robust motion primitives is to sample the actual pose of the object from a distribution that represents the state estimation uncertainty. During learning, the robot will thus optimize the chance of grasping an object from this distribution, rather than at one specific pose. In our empirical evaluation, we demonstrate how the motion primitives become more robust when grasping simple cylindrical objects, as well as more complex, non-convex objects. We also investigate how well the learned motion primitives generalize towards new object positions and other state estimation uncertainty distributions.

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link (url) [BibTex]

link (url) [BibTex]


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Instrumentation Issues of an AFM Based Nanorobotic System

Xie, H., Onal, C., Régnier, S., Sitti, M.

In Atomic Force Microscopy Based Nanorobotics, pages: 31-86, Springer Berlin Heidelberg, 2011 (incollection)

pi

[BibTex]

[BibTex]


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Piezoelectric polymer fiber arrays for tactile sensing applications

Sümer, B., Aksak, B., Şsahin, K., Chuengsatiansup, K., Sitti, M.

Sensor Letters, 9(2):457-463, American Scientific Publishers, 2011 (article)

pi

Project Page [BibTex]

Project Page [BibTex]


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Assembly and disassembly of magnetic mobile micro-robots towards deterministic 2-D reconfigurable micro-systems

Pawashe, C., Diller, E., Floyd, S., Sitti, M.

In Robotics and Automation (ICRA), 2011 IEEE International Conference on, pages: 261-266, 2011 (inproceedings)

pi

[BibTex]

[BibTex]


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Stochastic dynamics of bacteria propelled spherical micro-robots

Arabagi, V., Behkam, B., Sitti, M.

In Intelligent Robots and Systems (IROS), 2011 IEEE/RSJ International Conference on, pages: 3937-3942, 2011 (inproceedings)

pi

[BibTex]

[BibTex]


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Control methodologies for a heterogeneous group of untethered magnetic micro-robots

Floyd, S., Diller, E., Pawashe, C., Sitti, M.

The International Journal of Robotics Research, 30(13):1553-1565, SAGE Publications, 2011 (article)

pi

[BibTex]

[BibTex]


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Projected Newton-type methods in machine learning

Schmidt, M., Kim, D., Sra, S.

In Optimization for Machine Learning, pages: 305-330, MIT Press, Cambridge, MA, USA, 2011 (incollection)

Abstract
{We consider projected Newton-type methods for solving large-scale optimization problems arising in machine learning and related fields. We first introduce an algorithmic framework for projected Newton-type methods by reviewing a canonical projected (quasi-)Newton method. This method, while conceptually pleasing, has a high computation cost per iteration. Thus, we discuss two variants that are more scalable, namely, two-metric projection and inexact projection methods. Finally, we show how to apply the Newton-type framework to handle non-smooth objectives. Examples are provided throughout the chapter to illustrate machine learning applications of our framework.}

mms

link (url) [BibTex]

link (url) [BibTex]


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Study of krypton/xenon storage and separation in microporous frameworks

Soleimani Dorcheh, A.

Universität Darmstadt, Darmstadt, 2011 (mastersthesis)

mms

[BibTex]

[BibTex]


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Influence of dot size and annealing on the magnetic properties of large-area L10-FePt nanopatterns

Bublat, T., Goll, D.

{Journal of Applied Physics}, 110(7), 2011 (article)

mms

DOI [BibTex]


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The temperature-dependent magnetization profile across an epitaxial bilayer of ferromagnetic La2/3Ca1/3MnO3 and superconducting YBa2Cu3O7-δ

Brück, S., Treiber, S., Macke, S., Audehm, P., Christiani, G., Soltan, S., Habermeier, H., Goering, E., Albrecht, J.

{New Journal of Physics}, 13(3), 2011 (article)

mms

DOI [BibTex]

DOI [BibTex]


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Spin interactions in bcc and fcc Fe beyond the Heisenberg model

Singer, R., Dietermann, F., Fähnle, M.

{Physical Review Letters}, 107, 2011 (article)

mms

DOI [BibTex]

DOI [BibTex]


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Route to a family of robust, non-interpenetrated metal-organic frameworks with pto-like topology

Klein, N., Senkovska, I., Baburin, I. A., Grünker, R., Stoeck, U., Schlichtenmayer, M., Streppel, B., Mueller, U., Leoni, S., Hirscher, M., Kaskel, S.

{Chemistry - A European Journal}, 17(46):13007-13016, 2011 (article)

mms

DOI [BibTex]

DOI [BibTex]


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Initial stages of growth of iron on silicon for spin injection through Schottky barrier

Dash, S. P., Carstanjen, H. D.

{Physica Status Solidi B}, 248(10):2300-2304, 2011 (article)

mms

DOI [BibTex]

DOI [BibTex]


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Fe3O4/ZnO: A high-quality magnetic oxide-semiconductor heterostructure by reactive deposition

Paul, M., Kufer, D., Müller, A., Brück, S., Goering, E., Kamp, M., Verbeeck, J., Tian, H., Van Tendeloo, G., Ingle, N. J. C., Sing, M., Claessen, R.

{Applied Physics Letters}, 98, 2011 (article)

mms

DOI [BibTex]

DOI [BibTex]


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Influence of texture on the ferromagnetic properties of nanograined ZnO films

Straumal, B., Mazilkin, A., Protasova, S., Myatiev, A., Straumal, P., Goering, E., Baretzky, B.

{Physica Status Solidi B}, 248(7):1581-1586, 2011 (article)

mms

DOI [BibTex]

DOI [BibTex]


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Control of spin configuration in half-metallic La0.7Sr0.3MnO3 nano-structures

Rhensius, J., Vaz, C. A. F., Bisig, A., Schweitzer, S., Heidler, J., Körner, H. S., Locatelli, A., Niño, M. A., Weigand, M., Méchin, L., Gaucher, F., Goering, E., Heyderman, L. J., Kläui, M.

{Applied Physics Letters}, 99(6), 2011 (article)

mms

DOI [BibTex]

DOI [BibTex]


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Comparison of various sol-gel derived metal oxide layers for inverted organic solar cells

Oh, H., Krantz, J., Litzov, I., Stubhan, T., Pinna, L., Brabec, C. J.

{Solar Energy Materials \& Solar Cells}, 95(8):2194-2199, 2011 (article)

mms

DOI [BibTex]

DOI [BibTex]

2008


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BCPy2000

Hill, N., Schreiner, T., Puzicha, C., Farquhar, J.

Workshop "Machine Learning Open-Source Software" at NIPS, December 2008 (talk)

ei

Web [BibTex]

2008


Web [BibTex]


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Stereo Matching for Calibrated Cameras without Correspondence

Helmke, U., Hüper, K., Vences, L.

In CDC 2008, pages: 2408-2413, IEEE Service Center, Piscataway, NJ, USA, 47th IEEE Conference on Decision and Control, December 2008 (inproceedings)

Abstract
We study the stereo matching problem for reconstruction of the location of 3D-points on an unknown surface patch from two calibrated identical cameras without using any a priori information about the pointwise correspondences. We assume that camera parameters and the pose between the cameras are known. Our approach follows earlier work for coplanar cameras where a gradient flow algorithm was proposed to match associated Gramians. Here we extend this method by allowing arbitrary poses for the cameras. We introduce an intrinsic Riemannian Newton algorithm that achieves local quadratic convergence rates. A closed form solution is presented, too. The efficiency of both algorithms is demonstrated by numerical experiments.

ei

PDF Web DOI [BibTex]

PDF Web DOI [BibTex]


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Joint Kernel Support Estimation for Structured Prediction

Lampert, C., Blaschko, M.

In Proceedings of the NIPS 2008 Workshop on "Structured Input - Structured Output" (NIPS SISO 2008), pages: 1-4, NIPS Workshop on "Structured Input - Structured Output" (NIPS SISO), December 2008 (inproceedings)

Abstract
We present a new technique for structured prediction that works in a hybrid generative/ discriminative way, using a one-class support vector machine to model the joint probability of (input, output)-pairs in a joint reproducing kernel Hilbert space. Compared to discriminative techniques, like conditional random elds or structured out- put SVMs, the proposed method has the advantage that its training time depends only on the number of training examples, not on the size of the label space. Due to its generative aspect, it is also very tolerant against ambiguous, incomplete or incorrect labels. Experiments on realistic data show that our method works eciently and robustly in situations for which discriminative techniques have computational or statistical problems.

ei

PDF Web [BibTex]

PDF Web [BibTex]


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Frequent Subgraph Retrieval in Geometric Graph Databases

Nowozin, S., Tsuda, K.

In ICDM 2008, pages: 953-958, (Editors: Giannotti, F. , D. Gunopulos, F. Turini, C. Zaniolo, N. Ramakrishnan, X. Wu), IEEE Computer Society, Los Alamitos, CA, USA, 8th IEEE International Conference on Data Mining, December 2008 (inproceedings)

Abstract
Discovery of knowledge from geometric graph databases is of particular importance in chemistry and biology, because chemical compounds and proteins are represented as graphs with 3D geometric coordinates. In such applications, scientists are not interested in the statistics of the whole database. Instead they need information about a novel drug candidate or protein at hand, represented as a query graph. We propose a polynomial-delay algorithm for geometric frequent subgraph retrieval. It enumerates all subgraphs of a single given query graph which are frequent geometric $epsilon$-subgraphs under the entire class of rigid geometric transformations in a database. By using geometric$epsilon$-subgraphs, we achieve tolerance against variations in geometry. We compare the proposed algorithm to gSpan on chemical compound data, and we show that for a given minimum support the total number of frequent patterns is substantially limited by requiring geometric matching. Although the computation time per pattern is lar ger than for non-geometric graph mining,the total time is within a reasonable level even for small minimum support.

ei

PDF Web DOI [BibTex]

PDF Web DOI [BibTex]


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Block Iterative Algorithms for Non-negative Matrix Approximation

Sra, S.

In ICDM 2008, pages: 1037-1042, (Editors: Giannotti, F. , D. Gunopulos, F. Turini, C. Zaniolo, N. Ramakrishnan, X. Wu), IEEE Service Center, Piscataway, NJ, USA, Eighth IEEE International Conference on Data Mining, December 2008 (inproceedings)

Abstract
In this paper we present new algorithms for non-negative matrix approximation (NMA), commonly known as the NMF problem. Our methods improve upon the well-known methods of Lee & Seung~cite{lee00} for both the Frobenius norm as well the Kullback-Leibler divergence versions of the problem. For the latter problem, our results are especially interesting because it seems to have witnessed much lesser algorithmic progress as compared to the Frobenius norm NMA problem. Our algorithms are based on a particular textbf {block-iterative} acceleration technique for EM, which preserves the multiplicative nature of the updates and also ensures monotonicity. Furthermore, our algorithms also naturally apply to the Bregman-divergence NMA algorithms of~cite{suv.nips}. Experimentally, we show that our algorithms outperform the traditional Lee/Seung approach most of the time.

ei

Web DOI [BibTex]

Web DOI [BibTex]


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A Bayesian Approach to Switching Linear Gaussian State-Space Models for Unsupervised Time-Series Segmentation

Chiappa, S.

In ICMLA 2008, pages: 3-9, (Editors: Wani, M. A., X.-W. Chen, D. Casasent, L. Kurgan, T. Hu, K. Hafeez), IEEE Computer Society, Los Alamitos, CA, USA, 7th International Conference on Machine Learning and Applications, December 2008 (inproceedings)

Abstract
Time-series segmentation in the fully unsupervised scenario in which the number of segment-types is a priori unknown is a fundamental problem in many applications. We propose a Bayesian approach to a segmentation model based on the switching linear Gaussian state-space model that enforces a sparse parametrization, such as to use only a small number of a priori available different dynamics to explain the data. This enables us to estimate the number of segment-types within the model, in contrast to previous non-Bayesian approaches where training and comparing several separate models was required. As the resulting model is computationally intractable, we introduce a variational approximation where a reformulation of the problem enables the use of efficient inference algorithms.

ei

PDF Web DOI [BibTex]

PDF Web DOI [BibTex]


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Logistic Regression for Graph Classification

Shervashidze, N., Tsuda, K.

NIPS Workshop on "Structured Input - Structured Output" (NIPS SISO), December 2008 (talk)

Abstract
In this paper we deal with graph classification. We propose a new algorithm for performing sparse logistic regression for graphs, which is comparable in accuracy with other methods of graph classification and produces probabilistic output in addition. Sparsity is required for the reason of interpretability, which is often necessary in domains such as bioinformatics or chemoinformatics.

ei

Web [BibTex]

Web [BibTex]


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New Projected Quasi-Newton Methods with Applications

Sra, S.

Microsoft Research Tech-talk, December 2008 (talk)

Abstract
Box-constrained convex optimization problems are central to several applications in a variety of fields such as statistics, psychometrics, signal processing, medical imaging, and machine learning. Two fundamental examples are the non-negative least squares (NNLS) problem and the non-negative Kullback-Leibler (NNKL) divergence minimization problem. The non-negativity constraints are usually based on an underlying physical restriction, for e.g., when dealing with applications in astronomy, tomography, statistical estimation, or image restoration, the underlying parameters represent physical quantities such as concentration, weight, intensity, or frequency counts and are therefore only interpretable with non-negative values. Several modern optimization methods can be inefficient for simple problems such as NNLS and NNKL as they are really designed to handle far more general and complex problems. In this work we develop two simple quasi-Newton methods for solving box-constrained (differentiable) convex optimization problems that utilize the well-known BFGS and limited memory BFGS updates. We position our method between projected gradient (Rosen, 1960) and projected Newton (Bertsekas, 1982) methods, and prove its convergence under a simple Armijo step-size rule. We illustrate our method by showing applications to: Image deblurring, Positron Emission Tomography (PET) image reconstruction, and Non-negative Matrix Approximation (NMA). On medium sized data we observe performance competitive to established procedures, while for larger data the results are even better.

ei

PDF [BibTex]

PDF [BibTex]


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Iterative Subgraph Mining for Principal Component Analysis

Saigo, H., Tsuda, K.

In ICDM 2008, pages: 1007-1012, (Editors: Giannotti, F. , D. Gunopulos, F. Turini, C. Zaniolo, N. Ramakrishnan, X. Wu), IEEE Computer Society, Los Alamitos, CA, USA, IEEE International Conference on Data Mining, December 2008 (inproceedings)

Abstract
Graph mining methods enumerate frequent subgraphs efficiently, but they are not necessarily good features for machine learning due to high correlation among features. Thus it makes sense to perform principal component analysis to reduce the dimensionality and create decorrelated features. We present a novel iterative mining algorithm that captures informative patterns corresponding to major entries of top principal components. It repeatedly calls weighted substructure mining where example weights are updated in each iteration. The Lanczos algorithm, a standard algorithm of eigendecomposition, is employed to update the weights. In experiments, our patterns are shown to approximate the principal components obtained by frequent mining.

ei

PDF Web DOI [BibTex]

PDF Web DOI [BibTex]