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255 results (View BibTeX file of all listed publications)

2007

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A Tutorial on Spectral Clustering

von Luxburg, U.

Statistics and Computing, 17(4):395-416, December 2007 (article)

Abstract
In recent years, spectral clustering has become one of the most popular modern clustering algorithms. It is simple to implement, can be solved efficiently by standard linear algebra software, and very often outperforms traditional clustering algorithms such as the k-means algorithm. On the first glance spectral clustering appears slightly mysterious, and it is not obvious to see why it works at all and what it really does. The goal of this tutorial is to give some intuition on those questions. We describe different graph Laplacians and their basic properties, present the most common spectral clustering algorithms, and derive those algorithms from scratch by several different approaches. Advantages and disadvantages of the different spectral clustering algorithms are discussed.

ei

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2007

ei von Luxburg, U. A Tutorial on Spectral Clustering Statistics and Computing, 17(4):395-416, December 2007 (article)

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A Tutorial on Kernel Methods for Categorization

Jäkel, F., Schölkopf, B., Wichmann, F.

Journal of Mathematical Psychology, 51(6):343-358, December 2007 (article)

Abstract
The abilities to learn and to categorize are fundamental for cognitive systems, be it animals or machines, and therefore have attracted attention from engineers and psychologists alike. Modern machine learning methods and psychological models of categorization are remarkably similar, partly because these two fields share a common history in artificial neural networks and reinforcement learning. However, machine learning is now an independent and mature field that has moved beyond psychologically or neurally inspired algorithms towards providing foundations for a theory of learning that is rooted in statistics and functional analysis. Much of this research is potentially interesting for psychological theories of learning and categorization but also hardly accessible for psychologists. Here, we provide a tutorial introduction to a popular class of machine learning tools, called kernel methods. These methods are closely related to perceptrons, radial-basis-function neural networks and exemplar theories of catego rization. Recent theoretical advances in machine learning are closely tied to the idea that the similarity of patterns can be encapsulated in a positive definite kernel. Such a positive definite kernel can define a reproducing kernel Hilbert space which allows one to use powerful tools from functional analysis for the analysis of learning algorithms. We give basic explanations of some key concepts—the so-called kernel trick, the representer theorem and regularization—which may open up the possibility that insights from machine learning can feed back into psychology.

ei

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ei Jäkel, F., Schölkopf, B., Wichmann, F. A Tutorial on Kernel Methods for Categorization Journal of Mathematical Psychology, 51(6):343-358, December 2007 (article)

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Accurate Splice site Prediction Using Support Vector Machines

Sonnenburg, S., Schweikert, G., Philips, P., Behr, J., Rätsch, G.

BMC Bioinformatics, 8(Supplement 10):1-16, December 2007 (article)

Abstract
Background: For splice site recognition, one has to solve two classification problems: discriminating true from decoy splice sites for both acceptor and donor sites. Gene finding systems typically rely on Markov Chains to solve these tasks. Results: In this work we consider Support Vector Machines for splice site recognition. We employ the so-called weighted degree kernel which turns out well suited for this task, as we will illustrate in several experiments where we compare its prediction accuracy with that of recently proposed systems. We apply our method to the genome-wide recognition of splice sites in Caenorhabditis elegans, Drosophila melanogaster, Arabidopsis thaliana, Danio rerio, and Homo sapiens. Our performance estimates indicate that splice sites can be recognized very accurately in these genomes and that our method outperforms many other methods including Markov Chains, GeneSplicer and SpliceMachine. We provide genome-wide predictions of splice sites and a stand-alone prediction tool ready to be used for incorporation in a gene finder. Availability: Data, splits, additional information on the model selection, the whole genome predictions, as well as the stand-alone prediction tool are available for download at http:// www.fml.mpg.de/raetsch/projects/splice.

ei

PDF DOI [BibTex]

ei Sonnenburg, S., Schweikert, G., Philips, P., Behr, J., Rätsch, G. Accurate Splice site Prediction Using Support Vector Machines BMC Bioinformatics, 8(Supplement 10):1-16, December 2007 (article)

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A unifying framework for robot control with redundant DOFs

Peters, J., Mistry, M., Udwadia, F., Nakanishi, J., Schaal, S.

Autonomous Robots, 24(1):1-12, October 2007 (article)

Abstract
Recently, Udwadia (Proc. R. Soc. Lond. A 2003:1783–1800, 2003) suggested to derive tracking controllers for mechanical systems with redundant degrees-of-freedom (DOFs) using a generalization of Gauss’ principle of least constraint. This method allows reformulating control problems as a special class of optimal controllers. In this paper, we take this line of reasoning one step further and demonstrate that several well-known and also novel nonlinear robot control laws can be derived from this generic methodology. We show experimental verifications on a Sarcos Master Arm robot for some of the derived controllers. The suggested approach offers a promising unification and simplification of nonlinear control law design for robots obeying rigid body dynamics equations, both with or without external constraints, with over-actuation or underactuation, as well as open-chain and closed-chain kinematics.

ei

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ei Peters, J., Mistry, M., Udwadia, F., Nakanishi, J., Schaal, S. A unifying framework for robot control with redundant DOFs Autonomous Robots, 24(1):1-12, October 2007 (article)

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The Need for Open Source Software in Machine Learning

Sonnenburg, S., Braun, M., Ong, C., Bengio, S., Bottou, L., Holmes, G., LeCun, Y., Müller, K., Pereira, F., Rasmussen, C., Rätsch, G., Schölkopf, B., Smola, A., Vincent, P., Weston, J., Williamson, R.

Journal of Machine Learning Research, 8, pages: 2443-2466, October 2007 (article)

Abstract
Open source tools have recently reached a level of maturity which makes them suitable for building large-scale real-world systems. At the same time, the field of machine learning has developed a large body of powerful learning algorithms for diverse applications. However, the true potential of these methods is not realized, since existing implementations are not openly shared, resulting in software with low usability, and weak interoperability. We argue that this situation can be significantly improved by increasing incentives for researchers to publish their software under an open source model. Additionally, we outline the problems authors are faced with when trying to publish algorithmic implementations of machine learning methods. We believe that a resource of peer reviewed software accompanied by short articles would be highly valuable to both the machine learning and the general scientific community.

ei

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ei Sonnenburg, S., Braun, M., Ong, C., Bengio, S., Bottou, L., Holmes, G., LeCun, Y., Müller, K., Pereira, F., Rasmussen, C., Rätsch, G., Schölkopf, B., Smola, A., Vincent, P., Weston, J., Williamson, R. The Need for Open Source Software in Machine Learning Journal of Machine Learning Research, 8, pages: 2443-2466, October 2007 (article)

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Some observations on the masking effects of Mach bands

Curnow, T., Cowie, DA., Henning, GB., Hill, NJ.

Journal of the Optical Society of America A, 24(10):3233-3241, October 2007 (article)

Abstract
There are 8 cycle / deg ripples or oscillations in performance as a function of location near Mach bands in experiments measuring Mach bands’ masking effects on random polarity signal bars. The oscillations with increments are 180 degrees out of phase with those for decrements. The oscillations, much larger than the measurement error, appear to relate to the weighting function of the spatial-frequency-tuned channel detecting the broad- band signals. The ripples disappear with step maskers and become much smaller at durations below 25 ms, implying either that the site of masking has changed or that the weighting function and hence spatial-frequency tuning is slow to develop.

ei

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ei Curnow, T., Cowie, DA., Henning, GB., Hill, NJ. Some observations on the masking effects of Mach bands Journal of the Optical Society of America A, 24(10):3233-3241, October 2007 (article)

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Mining complex genotypic features for predicting HIV-1 drug resistance

Saigo, H., Uno, T., Tsuda, K.

Bioinformatics, 23(18):2455-2462, September 2007 (article)

Abstract
Human immunodeficiency virus type 1 (HIV-1) evolves in human body, and its exposure to a drug often causes mutations that enhance the resistance against the drug. To design an effective pharmacotherapy for an individual patient, it is important to accurately predict the drug resistance based on genotype data. Notably, the resistance is not just the simple sum of the effects of all mutations. Structural biological studies suggest that the association of mutations is crucial: Even if mutations A or B alone do not affect the resistance, a significant change might happen when the two mutations occur together. Linear regression methods cannot take the associations into account, while decision tree methods can reveal only limited associations. Kernel methods and neural networks implicitly use all possible associations for prediction, but cannot select salient associations explicitly. Our method, itemset boosting, performs linear regression in the complete space of power sets of mutations. It implements a forward feature selection procedure where, in each iteration, one mutation combination is found by an efficient branch-and-bound search. This method uses all possible combinations, and salient associations are explicitly shown. In experiments, our method worked particularly well for predicting the resistance of nucleotide reverse transcriptase inhibitors (NRTIs). Furthermore, it successfully recovered many mutation associations known in biological literature.

ei

Web DOI [BibTex]

ei Saigo, H., Uno, T., Tsuda, K. Mining complex genotypic features for predicting HIV-1 drug resistance Bioinformatics, 23(18):2455-2462, September 2007 (article)

Web DOI [BibTex]

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Advances in Neural Information Processing Systems 19: Proceedings of the 2006 Conference

Schölkopf, B., Platt, J., Hofmann, T.

Proceedings of the Twentieth Annual Conference on Neural Information Processing Systems (NIPS 2006), pages: 1690, MIT Press, Cambridge, MA, USA, 20th Annual Conference on Neural Information Processing Systems (NIPS), September 2007 (proceedings)

Abstract
The annual Neural Information Processing Systems (NIPS) conference is the flagship meeting on neural computation and machine learning. It draws a diverse group of attendees--physicists, neuroscientists, mathematicians, statisticians, and computer scientists--interested in theoretical and applied aspects of modeling, simulating, and building neural-like or intelligent systems. The presentations are interdisciplinary, with contributions in algorithms, learning theory, cognitive science, neuroscience, brain imaging, vision, speech and signal processing, reinforcement learning, and applications. Only twenty-five percent of the papers submitted are accepted for presentation at NIPS, so the quality is exceptionally high. This volume contains the papers presented at the December 2006 meeting, held in Vancouver.

ei

Web [BibTex]

ei Schölkopf, B., Platt, J., Hofmann, T. Advances in Neural Information Processing Systems 19: Proceedings of the 2006 Conference Proceedings of the Twentieth Annual Conference on Neural Information Processing Systems (NIPS 2006), pages: 1690, MIT Press, Cambridge, MA, USA, 20th Annual Conference on Neural Information Processing Systems (NIPS), September 2007 (proceedings)

Web [BibTex]

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Real-Time Fetal Heart Monitoring in Biomagnetic Measurements Using Adaptive Real-Time ICA

Waldert, S., Bensch, M., Bogdan, M., Rosenstiel, W., Schölkopf, B., Lowery, C., Eswaran, H., Preissl, H.

IEEE Transactions on Biomedical Engineering, 54(10):1867-1874, September 2007 (article)

Abstract
Electrophysiological signals of the developing fetal brain and heart can be investigated by fetal magnetoencephalography (fMEG). During such investigations, the fetal heart activity and that of the mother should be monitored continuously to provide an important indication of current well-being. Due to physical constraints of an fMEG system, it is not possible to use clinically established heart monitors for this purpose. Considering this constraint, we developed a real-time heart monitoring system for biomagnetic measurements and showed its reliability and applicability in research and for clinical examinations. The developed system consists of real-time access to fMEG data, an algorithm based on Independent Component Analysis (ICA), and a graphical user interface (GUI). The algorithm extracts the current fetal and maternal heart signal from a noisy and artifact-contaminated data stream in real-time and is able to adapt automatically to continuously varying environmental parameters. This algorithm has been na med Adaptive Real-time ICA (ARICA) and is applicable to real-time artifact removal as well as to related blind signal separation problems.

ei

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ei Waldert, S., Bensch, M., Bogdan, M., Rosenstiel, W., Schölkopf, B., Lowery, C., Eswaran, H., Preissl, H. Real-Time Fetal Heart Monitoring in Biomagnetic Measurements Using Adaptive Real-Time ICA IEEE Transactions on Biomedical Engineering, 54(10):1867-1874, September 2007 (article)

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Feature Selection for Trouble Shooting in Complex Assembly Lines

Pfingsten, T., Herrmann, D., Schnitzler, T., Feustel, A., Schölkopf, B.

IEEE Transactions on Automation Science and Engineering, 4(3):465-469, July 2007 (article)

Abstract
The final properties of sophisticated products can be affected by many unapparent dependencies within the manufacturing process, and the products’ integrity can often only be checked in a final measurement. Troubleshooting can therefore be very tedious if not impossible in large assembly lines. In this paper we show that Feature Selection is an efficient tool for serial-grouped lines to reveal causes for irregularities in product attributes. We compare the performance of several methods for Feature Selection on real-world problems in mass-production of semiconductor devices. Note to Practitioners— We present a data based procedure to localize flaws in large production lines: using the results of final quality inspections and information about which machines processed which batches, we are able to identify machines which cause low yield.

ei

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ei Pfingsten, T., Herrmann, D., Schnitzler, T., Feustel, A., Schölkopf, B. Feature Selection for Trouble Shooting in Complex Assembly Lines IEEE Transactions on Automation Science and Engineering, 4(3):465-469, July 2007 (article)

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Gene selection via the BAHSIC family of algorithms

Song, L., Bedo, J., Borgwardt, K., Gretton, A., Smola, A.

Bioinformatics, 23(13: ISMB/ECCB 2007 Conference Proceedings):i490-i498, July 2007 (article)

Abstract
Motivation: Identifying significant genes among thousands of sequences on a microarray is a central challenge for cancer research in bioinformatics. The ultimate goal is to detect the genes that are involved in disease outbreak and progression. A multitude of methods have been proposed for this task of feature selection, yet the selected gene lists differ greatly between different methods. To accomplish biologically meaningful gene selection from microarray data, we have to understand the theoretical connections and the differences between these methods. In this article, we define a kernel-based framework for feature selection based on the Hilbert–Schmidt independence criterion and backward elimination, called BAHSIC. We show that several well-known feature selectors are instances of BAHSIC, thereby clarifying their relationship. Furthermore, by choosing a different kernel, BAHSIC allows us to easily define novel feature selection algorithms. As a further advantage, feature selection via BAHSIC works directly on multiclass problems. Results: In a broad experimental evaluation, the members of the BAHSIC family reach high levels of accuracy and robustness when compared to other feature selection techniques. Experiments show that features selected with a linear kernel provide the best classification performance in general, but if strong non-linearities are present in the data then non-linear kernels can be more suitable.

ei

Web DOI [BibTex]

ei Song, L., Bedo, J., Borgwardt, K., Gretton, A., Smola, A. Gene selection via the BAHSIC family of algorithms Bioinformatics, 23(13: ISMB/ECCB 2007 Conference Proceedings):i490-i498, July 2007 (article)

Web DOI [BibTex]

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Phenotyping of Chondrocytes In Vivo and In Vitro Using cDNA Array Technology

Zien, A., Gebhard, P., Fundel, K., Aigner, T.

Clinical Orthopaedics and Related Research, 460, pages: 226-233, July 2007 (article)

Abstract
The cDNA array technology is a powerful tool to analyze a high number of genes in parallel. We investigated whether large-scale gene expression analysis allows clustering and identification of cellular phenotypes of chondrocytes in different in vivo and in vitro conditions. In 100% of cases, clustering analysis distinguished between in vivo and in vitro samples, suggesting fundamental differences in chondrocytes in situ and in vitro regardless of the culture conditions or disease status. It also allowed us to differentiate between healthy and osteoarthritic cartilage. The clustering also revealed the relative importance of the investigated culturing conditions (stimulation agent, stimulation time, bead/monolayer). We augmented the cluster analysis with a statistical search for genes showing differential expression. The identified genes provided hints to the molecular basis of the differences between the sample classes. Our approach shows the power of modern bioinformatic algorithms for understanding and class ifying chondrocytic phenotypes in vivo and in vitro. Although it does not generate new experimental data per se, it provides valuable information regarding the biology of chondrocytes and may provide tools for diagnosing and staging the osteoarthritic disease process.

ei

DOI [BibTex]

ei Zien, A., Gebhard, P., Fundel, K., Aigner, T. Phenotyping of Chondrocytes In Vivo and In Vitro Using cDNA Array Technology Clinical Orthopaedics and Related Research, 460, pages: 226-233, July 2007 (article)

DOI [BibTex]

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Common Sequence Polymorphisms Shaping Genetic Diversity in Arabidopsis thaliana

Clark, R., Schweikert, G., Toomajian, C., Ossowski, S., Zeller, G., Shinn, P., Warthmann, N., Hu, T., Fu, G., Hinds, D., Chen, H., Frazer, K., Huson, D., Schölkopf, B., Nordborg, M., Rätsch, G., Ecker, J., Weigel, D.

Science, 317(5836):338-342, July 2007 (article)

Abstract
The genomes of individuals from the same species vary in sequence as a result of different evolutionary processes. To examine the patterns of, and the forces shaping, sequence variation in Arabidopsis thaliana, we performed high-density array resequencing of 20 diverse strains (accessions). More than 1 million nonredundant single-nucleotide polymorphisms (SNPs) were identified at moderate false discovery rates (FDRs), and ~4% of the genome was identified as being highly dissimilar or deleted relative to the reference genome sequence. Patterns of polymorphism are highly nonrandom among gene families, with genes mediating interaction with the biotic environment having exceptional polymorphism levels. At the chromosomal scale, regional variation in polymorphism was readily apparent. A scan for recent selective sweeps revealed several candidate regions, including a notable example in which almost all variation was removed in a 500-kilobase window. Analyzing the polymorphisms we describe in larger sets of accessions will enable a detailed understanding of forces shaping population-wide sequence variation in A. thaliana.

ei

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ei Clark, R., Schweikert, G., Toomajian, C., Ossowski, S., Zeller, G., Shinn, P., Warthmann, N., Hu, T., Fu, G., Hinds, D., Chen, H., Frazer, K., Huson, D., Schölkopf, B., Nordborg, M., Rätsch, G., Ecker, J., Weigel, D. Common Sequence Polymorphisms Shaping Genetic Diversity in Arabidopsis thaliana Science, 317(5836):338-342, July 2007 (article)

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Graph Laplacians and their Convergence on Random Neighborhood Graphs

Hein, M., Audibert, J., von Luxburg, U.

Journal of Machine Learning Research, 8, pages: 1325-1370, June 2007 (article)

Abstract
Given a sample from a probability measure with support on a submanifold in Euclidean space one can construct a neighborhood graph which can be seen as an approximation of the submanifold. The graph Laplacian of such a graph is used in several machine learning methods like semi-supervised learning, dimensionality reduction and clustering. In this paper we determine the pointwise limit of three different graph Laplacians used in the literature as the sample size increases and the neighborhood size approaches zero. We show that for a uniform measure on the submanifold all graph Laplacians have the same limit up to constants. However in the case of a non-uniform measure on the submanifold only the so called random walk graph Laplacian converges to the weighted Laplace-Beltrami operator.

ei

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ei Hein, M., Audibert, J., von Luxburg, U. Graph Laplacians and their Convergence on Random Neighborhood Graphs Journal of Machine Learning Research, 8, pages: 1325-1370, June 2007 (article)

PDF PDF [BibTex]

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Bayesian Reconstruction of the Density of States

Habeck, M.

Physical Review Letters, 98(20, 200601):1-4, May 2007 (article)

Abstract
A Bayesian framework is developed to reconstruct the density of states from multiple canonical simulations. The framework encompasses the histogram reweighting method of Ferrenberg and Swendsen. The new approach applies to nonparametric as well as parametric models and does not require simulation data to be discretized. It offers a means to assess the precision of the reconstructed density of states and of derived thermodynamic quantities.

ei

Web DOI [BibTex]

ei Habeck, M. Bayesian Reconstruction of the Density of States Physical Review Letters, 98(20, 200601):1-4, May 2007 (article)

Web DOI [BibTex]

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PALMA: mRNA to Genome Alignments using Large Margin Algorithms

Schulze, U., Hepp, B., Ong, C., Rätsch, G.

Bioinformatics, 23(15):1892-1900, May 2007 (article)

Abstract
Motivation: Despite many years of research on how to properly align sequences in the presence of sequencing errors, alternative splicing and micro-exons, the correct alignment of mRNA sequences to genomic DNA is still a challenging task. Results: We present a novel approach based on large margin learning that combines accurate plice site predictions with common sequence alignment techniques. By solving a convex optimization problem, our algorithm – called PALMA – tunes the parameters of the model such that true alignments score higher than other alignments. We study the accuracy of alignments of mRNAs containing artificially generated micro-exons to genomic DNA. In a carefully designed experiment, we show that our algorithm accurately identifies the intron boundaries as well as boundaries of the optimal local alignment. It outperforms all other methods: for 5702 artificially shortened EST sequences from C. elegans and human it correctly identifies the intron boundaries in all except two cases. The best other method is a recently proposed method called exalin which misaligns 37 of the sequences. Our method also demonstrates robustness to mutations, insertions and deletions, retaining accuracy even at high noise levels. Availability: Datasets for training, evaluation and testing, additional results and a stand-alone alignment tool implemented in C++ and python are available at http://www.fml.mpg.de/raetsch/projects/palma.

ei

Web DOI [BibTex]

ei Schulze, U., Hepp, B., Ong, C., Rätsch, G. PALMA: mRNA to Genome Alignments using Large Margin Algorithms Bioinformatics, 23(15):1892-1900, May 2007 (article)

Web DOI [BibTex]

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Training a Support Vector Machine in the Primal

Chapelle, O.

Neural Computation, 19(5):1155-1178, March 2007 (article)

Abstract
Most literature on Support Vector Machines (SVMs) concentrate on the dual optimization problem. In this paper, we would like to point out that the primal problem can also be solved efficiently, both for linear and non-linear SVMs, and that there is no reason for ignoring this possibilty. On the contrary, from the primal point of view new families of algorithms for large scale SVM training can be investigated.

ei

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ei Chapelle, O. Training a Support Vector Machine in the Primal Neural Computation, 19(5):1155-1178, March 2007 (article)

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Improving the Caenorhabditis elegans Genome Annotation Using Machine Learning

Rätsch, G., Sonnenburg, S., Srinivasan, J., Witte, H., Müller, K., Sommer, R., Schölkopf, B.

PLoS Computational Biology, 3(2, e20):0313-0322, February 2007 (article)

ei

PDF DOI [BibTex]

ei Rätsch, G., Sonnenburg, S., Srinivasan, J., Witte, H., Müller, K., Sommer, R., Schölkopf, B. Improving the Caenorhabditis elegans Genome Annotation Using Machine Learning PLoS Computational Biology, 3(2, e20):0313-0322, February 2007 (article)

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Statistical Consistency of Kernel Canonical Correlation Analysis

Fukumizu, K., Bach, F., Gretton, A.

Journal of Machine Learning Research, 8, pages: 361-383, February 2007 (article)

Abstract
While kernel canonical correlation analysis (CCA) has been applied in many contexts, the convergence of finite sample estimates of the associated functions to their population counterparts has not yet been established. This paper gives a mathematical proof of the statistical convergence of kernel CCA, providing a theoretical justification for the method. The proof uses covariance operators defined on reproducing kernel Hilbert spaces, and analyzes the convergence of their empirical estimates of finite rank to their population counterparts, which can have infinite rank. The result also gives a sufficient condition for convergence on the regularization coefficient involved in kernel CCA: this should decrease as n^{-1/3}, where n is the number of data.

ei

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ei Fukumizu, K., Bach, F., Gretton, A. Statistical Consistency of Kernel Canonical Correlation Analysis Journal of Machine Learning Research, 8, pages: 361-383, February 2007 (article)

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Some observations on the pedestal effect

Henning, G., Wichmann, F.

Journal of Vision, 7(1:3):1-15, January 2007 (article)

Abstract
The pedestal or dipper effect is the large improvement in the detectability of a sinusoidal grating observed when it is added to a masking or pedestal grating of the same spatial frequency, orientation, and phase. We measured the pedestal effect in both broadband and notched noiseVnoise from which a 1.5-octave band centered on the signal frequency had been removed. Although the pedestal effect persists in broadband noise, it almost disappears in the notched noise. Furthermore, the pedestal effect is substantial when either high- or low-pass masking noise is used. We conclude that the pedestal effect in the absence of notched noise results principally from the use of information derived from channels with peak sensitivities at spatial frequencies different from that of the signal and the pedestal. We speculate that the spatial-frequency components of the notched noise above and below the spatial frequency of the signal and the pedestal prevent ‘‘off-frequency looking,’’ that is, prevent the use of information about changes in contrast carried in channels tuned to spatial frequencies that are very much different from that of the signal and the pedestal. Thus, the pedestal or dipper effect measured without notched noise appears not to be a characteristic of individual spatial-frequency-tuned channels.

ei

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ei Henning, G., Wichmann, F. Some observations on the pedestal effect Journal of Vision, 7(1:3):1-15, January 2007 (article)

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Cue Combination and the Effect of Horizontal Disparity and Perspective on Stereoacuity

Zalevski, AM., Henning, GB., Hill, NJ.

Spatial Vision, 20(1):107-138, January 2007 (article)

Abstract
Relative depth judgments of vertical lines based on horizontal disparity deteriorate enormously when the lines form part of closed configurations (Westheimer, 1979). In studies showing this effect, perspective was not manipulated and thus produced inconsistency between horizontal disparity and perspective. We show that stereoacuity improves dramatically when perspective and horizontal disparity are made consistent. Observers appear to use unhelpful perspective cues in judging the relative depth of the vertical sides of rectangles in a way not incompatible with a form of cue weighting. However, 95% confidence intervals for the weights derived for cues usually exceed the a-priori [0-1] range.

ei

PDF PDF DOI [BibTex]

ei Zalevski, AM., Henning, GB., Hill, NJ. Cue Combination and the Effect of Horizontal Disparity and Perspective on Stereoacuity Spatial Vision, 20(1):107-138, January 2007 (article)

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Frequency-domain displacement sensing with a fiber ring-resonator containing a variable gap

Vollmer, F., Fischer, P.

SENSORS AND ACTUATORS A-PHYSICAL, 134(2):410-413, 2007 (article)

Abstract
Ring-resonators are in general not amenable to strain-free (non-contact) displacement measurements. We show that this limitation may be overcome if the ring-resonator, here a fiber-loop, is designed to contain a gap, such that the light traverses a free-space part between two aligned waveguide ends. Displacements are determined with nanometer sensitivity by measuring the associated changes in the resonance frequencies. Miniaturization should increase the sensitivity of the ring-resonator interferometer. Ring geometries that contain an optical circulator can be used to profile reflective samples. (c) 2006 Elsevier B.V. All rights reserved.

pf

DOI [BibTex]

pf Vollmer, F., Fischer, P. Frequency-domain displacement sensing with a fiber ring-resonator containing a variable gap SENSORS AND ACTUATORS A-PHYSICAL, 134(2):410-413, 2007 (article)

DOI [BibTex]

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Observation of the Faraday effect via beam deflection in a longitudinal magnetic field

Ghosh, A., Hill, W., Fischer, P.

PHYSICAL REVIEW A, 76(5), 2007 (article)

Abstract
We show that magnetic-field-induced circular differential deflection of light can be observed in reflection or refraction at a single interface. The difference in the reflection or refraction angles between the two circular polarization components is a function of the magnetic-field strength and the Verdet constant, and permits the observation of the Faraday effect not via polarization rotation in transmission, but via changes in the propagation direction. Deflection measurements do not suffer from n-pi ambiguities and are shown to be another means to map magnetic fields with high axial resolution, or to determine the sign and magnitude of magnetic-field pulses in a single measurement.

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DOI [BibTex]

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Circular differential double diffraction in chiral media

Ghosh, A., Fazal, F. M., Fischer, P.

OPTICS LETTERS, 32(13):1836-1838, 2007 (article)

Abstract
In an optically active liquid the diffraction angle depends on the circular polarization state of the incident light beam. We report the observation of circular differential diffraction in an isotropic chiral medium, and we demonstrate that double diffraction is an alternate means to determine the handedness (enantiomeric excess) of a solution. (c) 2007 Optical Society of America.

pf

DOI [BibTex]

pf Ghosh, A., Fazal, F. M., Fischer, P. Circular differential double diffraction in chiral media OPTICS LETTERS, 32(13):1836-1838, 2007 (article)

DOI [BibTex]

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Bacterial flagella-based propulsion and on/off motion control of microscale objects

Behkam, B., Sitti, M.

Applied Physics Letters, 90(2):023902, AIP, 2007 (article)

pi

[BibTex]

pi Behkam, B., Sitti, M. Bacterial flagella-based propulsion and on/off motion control of microscale objects Applied Physics Letters, 90(2):023902, AIP, 2007 (article)

[BibTex]

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Friction of partially embedded vertically aligned carbon nanofibers inside elastomers

Aksak, B., Sitti, M., Cassell, A., Li, J., Meyyappan, M., Callen, P.

Applied Physics Letters, 91(6):061906, AIP, 2007 (article)

pi

[BibTex]

pi Aksak, B., Sitti, M., Cassell, A., Li, J., Meyyappan, M., Callen, P. Friction of partially embedded vertically aligned carbon nanofibers inside elastomers Applied Physics Letters, 91(6):061906, AIP, 2007 (article)

[BibTex]

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Enhanced friction of elastomer microfiber adhesives with spatulate tips

Kim, S., Aksak, B., Sitti, M.

Applied Physics Letters, 91(22):221913, AIP, 2007 (article)

pi

Project Page [BibTex]

pi Kim, S., Aksak, B., Sitti, M. Enhanced friction of elastomer microfiber adhesives with spatulate tips Applied Physics Letters, 91(22):221913, AIP, 2007 (article)

Project Page [BibTex]

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The new robotics - towards human-centered machines

Schaal, S.

HFSP Journal Frontiers of Interdisciplinary Research in the Life Sciences, 1(2):115-126, 2007, clmc (article)

Abstract
Research in robotics has moved away from its primary focus on industrial applications. The New Robotics is a vision that has been developed in past years by our own university and many other national and international research instiutions and addresses how increasingly more human-like robots can live among us and take over tasks where our current society has shortcomings. Elder care, physical therapy, child education, search and rescue, and general assistance in daily life situations are some of the examples that will benefit from the New Robotics in the near future. With these goals in mind, research for the New Robotics has to embrace a broad interdisciplinary approach, ranging from traditional mathematical issues of robotics to novel issues in psychology, neuroscience, and ethics. This paper outlines some of the important research problems that will need to be resolved to make the New Robotics a reality.

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link (url) [BibTex]

am Schaal, S. The new robotics - towards human-centered machines HFSP Journal Frontiers of Interdisciplinary Research in the Life Sciences, 1(2):115-126, 2007, clmc (article)

link (url) [BibTex]

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Hydrogen storage in metal-organic frameworks

Hirscher, M., Panella, B.

{Scripta Materialia}, 56, pages: 809-812, 2007 (article)

mms

[BibTex]

mms Hirscher, M., Panella, B. Hydrogen storage in metal-organic frameworks {Scripta Materialia}, 56, pages: 809-812, 2007 (article)

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Substrate-induced current anisotropy in YBa2Cu3O7-δthin films

Djupmyr, M., Albrecht, J.

{Physica C}, 460-462, pages: 1190-1191, 2007 (article)

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DOI [BibTex]

mms Djupmyr, M., Albrecht, J. Substrate-induced current anisotropy in YBa2Cu3O7-δthin films {Physica C}, 460-462, pages: 1190-1191, 2007 (article)

DOI [BibTex]

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A micellar approach to magnetic ultrahigh-density data-storage media: extending the limits of current colloidal methods

Ethirajan, A., Wiedwald, U., Boyen, H.-G., Kern, B., Han, L., Klimmer, A., Weigl, F., Kästle, G., Ziemann, P., Fauth, K., Cai, J., Behm, J., Romanyuk, A., Oelhafen, P., Walther, P., Biskupek, J., Kaiser, U.

{Advanced Materials}, 19, pages: 406-410, 2007 (article)

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[BibTex]

mms Ethirajan, A., Wiedwald, U., Boyen, H.-G., Kern, B., Han, L., Klimmer, A., Weigl, F., Kästle, G., Ziemann, P., Fauth, K., Cai, J., Behm, J., Romanyuk, A., Oelhafen, P., Walther, P., Biskupek, J., Kaiser, U. A micellar approach to magnetic ultrahigh-density data-storage media: extending the limits of current colloidal methods {Advanced Materials}, 19, pages: 406-410, 2007 (article)

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Size dependence in the magnetization reversal of Fe/Gd multilayers on self-assembled arrays of nanospheres

Amaladass, E., Ludescher, B., Schütz, G., Tyliszczak, T., Eimüller, T.

{Applied Physics Letters}, 91, 2007 (article)

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DOI [BibTex]

mms Amaladass, E., Ludescher, B., Schütz, G., Tyliszczak, T., Eimüller, T. Size dependence in the magnetization reversal of Fe/Gd multilayers on self-assembled arrays of nanospheres {Applied Physics Letters}, 91, 2007 (article)

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Ma\ssgeschneiderte Wasserstoffspeicher

Hirscher, M., Panella, B.

{Nachrichten aus der Gdch-Energieinitiative}, (Sonderheft April 2007):12-13, 2007 (article)

mms

[BibTex]

mms Hirscher, M., Panella, B. Ma\ssgeschneiderte Wasserstoffspeicher {Nachrichten aus der Gdch-Energieinitiative}, (Sonderheft April 2007):12-13, 2007 (article)

[BibTex]

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Reconstruction of historical alloys for pipe organs brings true Baroque music back to life.

Baretzky, B., Friesel, M., Straumal, B.

{MRS Bulletin}, 32, pages: 249-255, 2007 (article)

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[BibTex]

mms Baretzky, B., Friesel, M., Straumal, B. Reconstruction of historical alloys for pipe organs brings true Baroque music back to life. {MRS Bulletin}, 32, pages: 249-255, 2007 (article)

[BibTex]

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Analysis of results from X-ray magnetic reflectometry for magnetic multilayer systems

Fähnle, M., Steiauf, D., Martosiswoyo, L., Goering, E., Brück, S., Schütz, G.

{Physical Review B}, 75, 2007 (article)

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[BibTex]

mms Fähnle, M., Steiauf, D., Martosiswoyo, L., Goering, E., Brück, S., Schütz, G. Analysis of results from X-ray magnetic reflectometry for magnetic multilayer systems {Physical Review B}, 75, 2007 (article)

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Dramatic role of critical current anisotropy on flux avalanches in MgB2 films

Albrecht, J., Matveev, A. T., Strempfer, J., Habermeier, H.-U., Shantsev, D. V., Galperin, Y. M., Johansen, T. H.

{Physical Review Letters}, 98, 2007 (article)

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[BibTex]

mms Albrecht, J., Matveev, A. T., Strempfer, J., Habermeier, H.-U., Shantsev, D. V., Galperin, Y. M., Johansen, T. H. Dramatic role of critical current anisotropy on flux avalanches in MgB2 films {Physical Review Letters}, 98, 2007 (article)

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Transport properties of LCMO/YBCO hybrid structures

Soltan, S., Albrecht, J., Habermeier, H.-U.

{Materials Science and Engineering B}, 144, pages: 15-18, 2007 (article)

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DOI [BibTex]

mms Soltan, S., Albrecht, J., Habermeier, H.-U. Transport properties of LCMO/YBCO hybrid structures {Materials Science and Engineering B}, 144, pages: 15-18, 2007 (article)

DOI [BibTex]

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Microscale and nanoscale robotics systems [grand challenges of robotics]

Sitti, M.

IEEE Robotics \& Automation Magazine, 14(1):53-60, IEEE, 2007 (article)

pi

[BibTex]

pi Sitti, M. Microscale and nanoscale robotics systems [grand challenges of robotics] IEEE Robotics \& Automation Magazine, 14(1):53-60, IEEE, 2007 (article)

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A new biomimetic adhesive for therapeutic capsule endoscope applications in the gastrointestinal tract

Glass, P., Sitti, M., Appasamy, R.

Gastrointestinal Endoscopy, 65(5):AB91, Mosby, 2007 (article)

pi

[BibTex]

pi Glass, P., Sitti, M., Appasamy, R. A new biomimetic adhesive for therapeutic capsule endoscope applications in the gastrointestinal tract Gastrointestinal Endoscopy, 65(5):AB91, Mosby, 2007 (article)

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Visual servoing-based autonomous 2-D manipulation of microparticles using a nanoprobe

Onal, C. D., Sitti, M.

IEEE Transactions on control systems technology, 15(5):842-852, IEEE, 2007 (article)

pi

[BibTex]

pi Onal, C. D., Sitti, M. Visual servoing-based autonomous 2-D manipulation of microparticles using a nanoprobe IEEE Transactions on control systems technology, 15(5):842-852, IEEE, 2007 (article)

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Cluster expansions in multicomponent systems: precise expansions from noisy databases

Diaz-Ortiz, A., Dosch, H., Drautz, R.

{Journal of Physics: Condensed Matter}, 19, 2007 (article)

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DOI [BibTex]

mms Diaz-Ortiz, A., Dosch, H., Drautz, R. Cluster expansions in multicomponent systems: precise expansions from noisy databases {Journal of Physics: Condensed Matter}, 19, 2007 (article)

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Unusual propagation of magnetic avalanches in gold covered MgB2

Albrecht, J., Matveev, A. T., Habermeier, H.-U.

{Physica C}, 460-462, pages: 1245-1246, 2007 (article)

mms

DOI [BibTex]

mms Albrecht, J., Matveev, A. T., Habermeier, H.-U. Unusual propagation of magnetic avalanches in gold covered MgB2 {Physica C}, 460-462, pages: 1245-1246, 2007 (article)

DOI [BibTex]

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Lowering of the L10 ordering temperature of FePt nanoparticles by He+ ion irradiation

Wiedwald, U., Klimmer, A., Kern, B., Han, L., Boyen, H.-G., Ziemann, P., Fauth, K.

{Applied Physics Letters}, 90, 2007 (article)

mms

[BibTex]

mms Wiedwald, U., Klimmer, A., Kern, B., Han, L., Boyen, H.-G., Ziemann, P., Fauth, K. Lowering of the L10 ordering temperature of FePt nanoparticles by He+ ion irradiation {Applied Physics Letters}, 90, 2007 (article)

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Magnetic core shell nanoparticles characterized by X-ray absorption and magnetic circular dichroism

Fauth, K.

{Modern Physics Letters B}, 21(18):1179-1187, 2007 (article)

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[BibTex]

mms Fauth, K. Magnetic core shell nanoparticles characterized by X-ray absorption and magnetic circular dichroism {Modern Physics Letters B}, 21(18):1179-1187, 2007 (article)

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