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2015


Scalable Robust Principal Component Analysis using {Grassmann} Averages
Scalable Robust Principal Component Analysis using Grassmann Averages

Hauberg, S., Feragen, A., Enficiaud, R., Black, M.

IEEE Trans. Pattern Analysis and Machine Intelligence (PAMI), December 2015 (article)

Abstract
In large datasets, manual data verification is impossible, and we must expect the number of outliers to increase with data size. While principal component analysis (PCA) can reduce data size, and scalable solutions exist, it is well-known that outliers can arbitrarily corrupt the results. Unfortunately, state-of-the-art approaches for robust PCA are not scalable. We note that in a zero-mean dataset, each observation spans a one-dimensional subspace, giving a point on the Grassmann manifold. We show that the average subspace corresponds to the leading principal component for Gaussian data. We provide a simple algorithm for computing this Grassmann Average (GA), and show that the subspace estimate is less sensitive to outliers than PCA for general distributions. Because averages can be efficiently computed, we immediately gain scalability. We exploit robust averaging to formulate the Robust Grassmann Average (RGA) as a form of robust PCA. The resulting Trimmed Grassmann Average (TGA) is appropriate for computer vision because it is robust to pixel outliers. The algorithm has linear computational complexity and minimal memory requirements. We demonstrate TGA for background modeling, video restoration, and shadow removal. We show scalability by performing robust PCA on the entire Star Wars IV movie; a task beyond any current method. Source code is available online.

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preprint pdf from publisher supplemental Project Page [BibTex]

2015


preprint pdf from publisher supplemental Project Page [BibTex]


{SMPL}: A Skinned Multi-Person Linear Model
SMPL: A Skinned Multi-Person Linear Model

Loper, M., Mahmood, N., Romero, J., Pons-Moll, G., Black, M. J.

ACM Trans. Graphics (Proc. SIGGRAPH Asia), 34(6):248:1-248:16, ACM, New York, NY, October 2015 (article)

Abstract
We present a learned model of human body shape and pose-dependent shape variation that is more accurate than previous models and is compatible with existing graphics pipelines. Our Skinned Multi-Person Linear model (SMPL) is a skinned vertex-based model that accurately represents a wide variety of body shapes in natural human poses. The parameters of the model are learned from data including the rest pose template, blend weights, pose-dependent blend shapes, identity-dependent blend shapes, and a regressor from vertices to joint locations. Unlike previous models, the pose-dependent blend shapes are a linear function of the elements of the pose rotation matrices. This simple formulation enables training the entire model from a relatively large number of aligned 3D meshes of different people in different poses. We quantitatively evaluate variants of SMPL using linear or dual-quaternion blend skinning and show that both are more accurate than a Blend-SCAPE model trained on the same data. We also extend SMPL to realistically model dynamic soft-tissue deformations. Because it is based on blend skinning, SMPL is compatible with existing rendering engines and we make it available for research purposes.

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pdf video code/model errata DOI Project Page Project Page [BibTex]

pdf video code/model errata DOI Project Page Project Page [BibTex]


Dyna: A Model of Dynamic Human Shape in Motion
Dyna: A Model of Dynamic Human Shape in Motion

Pons-Moll, G., Romero, J., Mahmood, N., Black, M. J.

ACM Transactions on Graphics, (Proc. SIGGRAPH), 34(4):120:1-120:14, ACM, August 2015 (article)

Abstract
To look human, digital full-body avatars need to have soft tissue deformations like those of real people. We learn a model of soft-tissue deformations from examples using a high-resolution 4D capture system and a method that accurately registers a template mesh to sequences of 3D scans. Using over 40,000 scans of ten subjects, we learn how soft tissue motion causes mesh triangles to deform relative to a base 3D body model. Our Dyna model uses a low-dimensional linear subspace to approximate soft-tissue deformation and relates the subspace coefficients to the changing pose of the body. Dyna uses a second-order auto-regressive model that predicts soft-tissue deformations based on previous deformations, the velocity and acceleration of the body, and the angular velocities and accelerations of the limbs. Dyna also models how deformations vary with a person’s body mass index (BMI), producing different deformations for people with different shapes. Dyna realistically represents the dynamics of soft tissue for previously unseen subjects and motions. We provide tools for animators to modify the deformations and apply them to new stylized characters.

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pdf preprint video data DOI Project Page Project Page [BibTex]

pdf preprint video data DOI Project Page Project Page [BibTex]


Linking Objects to Actions: Encoding of Target Object and Grasping Strategy in Primate Ventral Premotor Cortex
Linking Objects to Actions: Encoding of Target Object and Grasping Strategy in Primate Ventral Premotor Cortex

Vargas-Irwin, C. E., Franquemont, L., Black, M. J., Donoghue, J. P.

Journal of Neuroscience, 35(30):10888-10897, July 2015 (article)

Abstract
Neural activity in ventral premotor cortex (PMv) has been associated with the process of matching perceived objects with the motor commands needed to grasp them. It remains unclear how PMv networks can flexibly link percepts of objects affording multiple grasp options into a final desired hand action. Here, we use a relational encoding approach to track the functional state of PMv neuronal ensembles in macaque monkeys through the process of passive viewing, grip planning, and grasping movement execution. We used objects affording multiple possible grip strategies. The task included separate instructed delay periods for object presentation and grip instruction. This approach allowed us to distinguish responses elicited by the visual presentation of the objects from those associated with selecting a given motor plan for grasping. We show that PMv continuously incorporates information related to object shape and grip strategy as it becomes available, revealing a transition from a set of ensemble states initially most closely related to objects, to a new set of ensemble patterns reflecting unique object-grip combinations. These results suggest that PMv dynamically combines percepts, gradually navigating toward activity patterns associated with specific volitional actions, rather than directly mapping perceptual object properties onto categorical grip representations. Our results support the idea that PMv is part of a network that dynamically computes motor plans from perceptual information. Significance Statement: The present work demonstrates that the activity of groups of neurons in primate ventral premotor cortex reflects information related to visually presented objects, as well as the motor strategy used to grasp them, linking individual objects to multiple possible grips. PMv could provide useful control signals for neuroprosthetic assistive devices designed to interact with objects in a flexible way.

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publisher link DOI Project Page [BibTex]

publisher link DOI Project Page [BibTex]


Multi-view and 3D Deformable Part Models
Multi-view and 3D Deformable Part Models

Pepik, B., Stark, M., Gehler, P., Schiele, B.

Pattern Analysis and Machine Intelligence, 37(11):14, IEEE, March 2015 (article)

Abstract
As objects are inherently 3-dimensional, they have been modeled in 3D in the early days of computer vision. Due to the ambiguities arising from mapping 2D features to 3D models, 3D object representations have been neglected and 2D feature-based models are the predominant paradigm in object detection nowadays. While such models have achieved outstanding bounding box detection performance, they come with limited expressiveness, as they are clearly limited in their capability of reasoning about 3D shape or viewpoints. In this work, we bring the worlds of 3D and 2D object representations closer, by building an object detector which leverages the expressive power of 3D object representations while at the same time can be robustly matched to image evidence. To that end, we gradually extend the successful deformable part model [1] to include viewpoint information and part-level 3D geometry information, resulting in several different models with different level of expressiveness. We end up with a 3D object model, consisting of multiple object parts represented in 3D and a continuous appearance model. We experimentally verify that our models, while providing richer object hypotheses than the 2D object models, provide consistently better joint object localization and viewpoint estimation than the state-of-the-art multi-view and 3D object detectors on various benchmarks (KITTI [2], 3D object classes [3], Pascal3D+ [4], Pascal VOC 2007 [5], EPFL multi-view cars [6]).

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DOI Project Page [BibTex]

DOI Project Page [BibTex]


{Spike train SIMilarity Space} ({SSIMS}): A framework for single neuron and ensemble data analysis
Spike train SIMilarity Space (SSIMS): A framework for single neuron and ensemble data analysis

Vargas-Irwin, C. E., Brandman, D. M., Zimmermann, J. B., Donoghue, J. P., Black, M. J.

Neural Computation, 27(1):1-31, MIT Press, January 2015 (article)

Abstract
We present a method to evaluate the relative similarity of neural spiking patterns by combining spike train distance metrics with dimensionality reduction. Spike train distance metrics provide an estimate of similarity between activity patterns at multiple temporal resolutions. Vectors of pair-wise distances are used to represent the intrinsic relationships between multiple activity patterns at the level of single units or neuronal ensembles. Dimensionality reduction is then used to project the data into concise representations suitable for clustering analysis as well as exploratory visualization. Algorithm performance and robustness are evaluated using multielectrode ensemble activity data recorded in behaving primates. We demonstrate how Spike train SIMilarity Space (SSIMS) analysis captures the relationship between goal directions for an 8-directional reaching task and successfully segregates grasp types in a 3D grasping task in the absence of kinematic information. The algorithm enables exploration of virtually any type of neural spiking (time series) data, providing similarity-based clustering of neural activity states with minimal assumptions about potential information encoding models.

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pdf: publisher site pdf: author's proof DOI Project Page [BibTex]

pdf: publisher site pdf: author's proof DOI Project Page [BibTex]


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Structures of simple liquids in contact with nanosculptured surfaces

Singh, S. L., Schimmele, L., Dietrich, S.

Physical Review E, 91(3), American Physical Society, Melville, NY, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Line contribution to the critical Casimir force between a homogeneous and a chemically stepped surface

Parisen Toldin, F., Tröndle, M., Dietrich, S.

Journal of Physics: Condensed Matter, 27(21), IOP Publishing, Bristol, UK, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Self-propulsion of a catalytically active particle near a planar wall: from reflection to sliding and hovering

Uspal, W. E., Popescu, M. N., Dietrich, S., Tasinkevych, M.

Soft Matter, 11(3):434-438, Royal Society of Chemistry, Cambridge, UK, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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A size dependent evaluation of the cytotoxicity and uptake of nanographene oxide

Mendes, R. G., Koch, B., Bachmatiuk, A., Ma, X., Sanchez, S., Damm, C., Schmidt, O. G., Gemming, T., Eckert, J., Rümmeli, M. H.

Journal of Materials Chemistry B, 3(12):2522-2529, Royal Society of Chemistry, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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A bio-catalytically driven Janus mesoporous silica cluster motor with magnetic guidance

Ma, X., Sanchez, S.

Chemical Communications, 51(25):5467-5470, Royal Society of Chemistry, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Sperm Dynamics in Tubular Confinement

Magdanz, V., Koch, B., Sanchez, S., Schmidt, O. G.

Small, 11(7):781-785, Wiley Online Library, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Chromatic patchy particles: Effects of specific interactions on liquid structure

Vasilyev, O., Klumov, B. A., Tkachenko, A. V.

Physical Review E, 92(1), American Physical Society, Melville, NY, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Monte Carlo study of anisotropic scaling generated by disorder

Vasilyev, O., Berche, B., Dudka, M., Holovatch, Y.

Physical Review E, 92(4), American Physical Society, Melville, NY, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Fluctuations and diffusion in sheared athermal suspensions of deformable particles

Gross, M., Krüger, T., Varnik, F.

EPL, 108(6), IoPP, Bristol, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Enzyme-Powered Hollow Mesoporous Janus Nanomotors

Ma, Xing, Jannasch, Anita, Albrecht, Urban-Raphael, Hahn, Kersten, Miguel-Lopéz, Albert, Schäfer, Erik, Sanchez, Samuel

Nano Letters, 15(10):7043-7050, American Chemical Society, Washington, DC, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Interaction between colloidal particles on an oil\textendashwater interface in dilute and dense phases

Parolini, L., Cicuta, A. D. P., Law, A. D., Maestro, A., Buzza, M. A.

Journal of Physics: Condensed Matter, 27(19), IOP Publishing, Bristol, UK, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Anomalous Magnetotransport in Disordered Structures: Classical Edge-State Percolation

Schirmacher, Walter, Fuchs, Benedikt, Höfling, Felix, Franosch, Thomas

Physical Review Letters, 115, American Physical Society, Woodbury, N.Y., 2015 (article)

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DOI [BibTex]

DOI [BibTex]


Metric Regression Forests for Correspondence Estimation
Metric Regression Forests for Correspondence Estimation

Pons-Moll, G., Taylor, J., Shotton, J., Hertzmann, A., Fitzgibbon, A.

International Journal of Computer Vision, pages: 1-13, 2015 (article)

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springer PDF Project Page [BibTex]

springer PDF Project Page [BibTex]


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Precise Localization and Control of Catalytic Janus Micromotors using Weak Magnetic Fields

Khalil, I. S., Magdanz, V., Sanchez, S., Schmidt, O. G., Misra, S.

International Journal of Advanced Robotic Systems, 12, InTech, Rijeka, Croatia, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Nano-photocatalysts in microfluidics, energy conversion and environmental applications

Parmar, J., Jang, S., Soler, L., Kim, D., Sánchez, S.

Lab on a Chip, 15(11):2352-2356, Royal Society of Chemistry, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Static dielectric properties of dense ionic fluids

Zarubin, G., Bier, M.

The Journal of Chemical Physics, 142(18), American Institute of Physics, Woodbury, N.Y., 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Chemically Powered Micro-and Nanomotors

Sánchez, S., Soler, L., Katuri, J.

Angewandte Chemie, International Edition, 54(5):1414-1444, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, 2015 (article)

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[BibTex]

[BibTex]


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Convergence of large-deviation estimators

Rohwer, C. M., Angeletti, F., Touchette, H.

Physical Review E, 92(5), American Physical Society, Melville, NY, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Geometrically Tuned Channel Permeability

Malgaretti, P., Pagonabarraga, I., Rubi, J. M.

Macromolecular Symposia, 357(1):178-188, WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Critical Casimir forces between planar and crenellated surfaces

Troendle, M., Harnau, L., Dietrich, S.

Journal of Physics: Condensed Matter, 27(21), IOP Publishing, Bristol, UK, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Theory of rheology in confinement

Aerov, A. A., Krüger, M.

Physical Review E, 92(4), American Physical Society, Melville, NY, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Implications of interface conventions for morphometric thermodynamics

Reindl, A., Bier, M., Dietrich, S.

Physical Review E, 91(2), American Physical Society, Melville, NY, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Linked topological colloids in a nematic host

Martinez, A., Hermosillo, L., Tasinkevych, M., Smalyukh, I. I.

Proceedings of the National Academy of Sciences of the United States of America, 112(15):4546-4551, National Academy of Sciences, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Colloidal spirals in nematic liquid crystals

Senyuk, B., Pandey, M.B., Liu, Q., Tasinkevych, M., Smalyukh, I. I.

Soft Matter, 11, pages: 8758-8767, Royal Society of Chemistry, Cambridge, UK, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Rheotaxis of spherical active particles near a planar wall

Uspal, W. E., Popescu, M. N., Dietrich, S., Tasinkevych, M.

Soft Matter, 11(33):6613-6632, Royal Society of Chemistry, Cambridge, UK, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Applications of three-dimensional (3D) printing for microswimmers and bio-hybrid robotics

Stanton, M. M., Trichet-Paredes, C., Sanchez, S.

Lab on a Chip, 15(7):1634-1637, Royal Society of Chemistry, Cambridge, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Linear and nonlinear magnetic properties of ferrofluids

Szalai, I., Nagy, S., Dietrich, S.

Physical Review E, 92(4), American Physical Society, Melville, NY, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Microfluidic-Assisted Fabrication of Flexible and Location Traceable Organo-Motor

Seo, K. D., Kwak, B. K., Sanchez, S., Kim, D. S.

IEEE Transactions on Nanobioscience, 14(3):298-304, IEEE, New York, NY, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Tracer diffusion of hard-sphere binary mixtures under nano-confinement

Marconi, U., Malgaretti, P., Pagonabarraga, I.

The Journal of Chemical Physics, 143(18), American Institute of Physics, Woodbury, N.Y., 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Fluctuating multicomponent lattice Boltzmann model

Belardinelli, D., Sbragaglia, M., Biferale, L., Gross, M., Varnik, F.

Physical Review E, 91(2), American Physical Society, Melville, NY, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Phase diagram of fluid phases in He3\textminusHe4 mixtures

Farahmand Bafi, N., Maciolek, A., Dietrich, S.

Physical Review E, 91(2), American Physical Society, Melville, NY, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Three-body critical Casimir forces

Gomes de Mattos, T., Harnau, L., Dietrich, S.

Physical Review E, 91(4), American Physical Society, Melville, NY, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Thermal and structural properties of ionic fluids

Bartsch, H., Dannenmann, O., Bier, M.

Physical Review E, 91(4), American Physical Society, Melville, NY, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Micro- and Nanomachines
IEEE Transactions on Nanobioscience, 14, pages: 74, IEEE, New York, NY, 2015 (misc)

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[BibTex]

[BibTex]


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Frenetic aspects of second order response

Basu, U., Krüger, M., Lazarescu, A., Maes, C.

Physical Chemistry Chemical Physics, 17(9):6653-6666, Royal Society of Chemistry, Cambridge, England, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Critical Casimir forces in the presence of random surface fields

Maciolek, A., Vasilyev, O., Dotsenko, V., Dietrich, S.

Physical Review E, 91(3), American Physical Society, Melville, NY, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Lab-in-a-tube systems as ultra-compact devices

Sanchez, S.

Lab chip, (3):610-613, 2015 (article)

Abstract
{In this Focus article, I will give an overview on the current and future interests of our multidisciplinary research group. One of our main interests is to develop highly integrated on-chip components towards ultra-compact devices for biosensing technologies (lab-in-a-tube). Our other activities are focused in developing self-powered devices that can generate either motion of a fluid or autonomous propulsion. We are particularly interested in three-dimensional (3D) nanofabrication technologies and stimuli responsive soft materials.}

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DOI [BibTex]

DOI [BibTex]


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Catalytic Mesoporous Janus Nanomotors for Active Cargo Delivery

Ma, X., Hahn, K., Sanchez, S.

Journal of the American Chemical Society, 137(15):4976-4979, ACS Publications, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Guest Editorial: Special Issue: Micro- and Nanomachines

Paxton, W., Sanchez, S., Nitta, T.

IEEE Transactions on Nanobioscience, 14(3):258-259, IEEE, New York, NY, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Self-Assembly via Microfluidics

Wang, L., Sanchez, S.

Lab on a Chip, 15(23):4383-4386, Royal Society of Chemistry, Cambridge, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Nonequilibrium interfacial tension during relaxation

Bier, M.

Physical Review E, 92(4), American Physical Society, Melville, NY, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Operator Formalism for Topology-Conserving Crossing Dynamics in Planar Knot Diagrams

Rohwer, C. M., Müller-Nedebock, K. K.

Journal of Statistical Physics, 159(1):120-157, Kluwer Academic Publishers [etc.], New York, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Nano and micro architectures for self-propelled motors

Parmar, Jemish, Ma, X., Katuri, Jaideep, Simmchen, Juliane, Stanton, Morgan, Trichet-Paredes, Carolina, Soler, Llu\’\is, Sanchez, Samuel

Science and Technology of Advanced Materials, 16, IoPP, Bristol, 2015 (article)

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DOI [BibTex]

DOI [BibTex]


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Critical Casimir forces for a particle between two planar walls

Vasilyev, O., Maciolek, A.

Journal of Non-Crystalline Solids, 407, pages: 376-383, North-Holland, Amsterdam, 2015 (article)

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DOI [BibTex]

DOI [BibTex]