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2012


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Evaluation of Tactile Feedback Methods for Wrist Rotation Guidance

Stanley, A. A., Kuchenbecker, K. J.

IEEE Transactions on Haptics, 5(3):240-251, July 2012 (article)

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[BibTex]

2012


[BibTex]


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Creating realistic virtual textures from contact acceleration data

Romano, J. M., Kuchenbecker, K. J.

IEEE Transactions on Haptics, 5(2):109-119, April 2012, Cover article (article)

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[BibTex]

[BibTex]


Estimation of MIMO Closed-Loop Poles using Transfer Function Data
Estimation of MIMO Closed-Loop Poles using Transfer Function Data

Vardar, Y.

Eindhoven University of Technology, the Netherlands, 2012 (mastersthesis)

Abstract
For the development of high-tech systems such as lithographic positioning systems, throughput and accuracy are the main requirements. Nowadays, the trend to reach demanded accuracy and throughput levels is designing lightweight and consequently more flexible systems. To control these systems with a more effective and less conservative way, control design should go beyond the traditional rigid control and cope with the flexibilities that limit achievable bandwidth and performance. Therefore, conventional loop shaping methods are not sufficient to reach the performance criterions. Since obtaining an accurate parametric model is very complex and time-consuming for these high-tech systems, using well-developed model-based controller synthesis methods is also not a superior option. To achieve desired performance criterions, one solution can be implemented is reducing the gap between model-based and data-based control synthesis methods. In previous research, a method was developed to define the dynamic behavior of the system without a need for a parametric model. By this method transfer function data (TFD), which provides the information on the whole s-plane can be obtained from frequency response data (FRD) of the system. This innovation was a very important step to use data-based techniques for model-based controller synthesis methods. In this thesis firstly the standard technique to obtain TFD defined in [2] is extended. This standard technique to obtain TFD is not compatible with systems with pure integrators. To extend the methodology also for those systems, two techniques, which are altering the contour and filtering the system, are proposed. Then, the accuracy of TFD is investigated in detail. It is shown that the accuracy of TFD depends on the quality of FRD obtained and the computation techniques used to calculate TFD. Then, a technique which enables to determine the closed-loop poles of a MIMO system using TFD is discussed. The validity of the technique is proven with the help of complex function theory and calculus. Also, the factors that prevent determination of the closed-loop poles are discussed. In addition, it is observed that the accuracy of the closed-loop determination method depends on the quality of obtained TFD and the computation techniques. The proposed theory to obtain TFD and determination of closed-loop poles is validated with experiments conducted to a prototype lightweight system. Also, using experimental frequency response data of NXT-A7 test rig, the success of the proposed methodology is validated also for complex systems. Through these experimental results, it can be concluded that this new technique could be very advantageous in terms of ease of use and accuracy to determine the closed-loop poles of a MIMO lightly damped system.

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[BibTex]

[BibTex]


Fourier-transform photocurrent spectroscopy using a supercontinuum light source
Fourier-transform photocurrent spectroscopy using a supercontinuum light source

Petermann, C., Beigang, R., Fischer, P.

APPLIED PHYSICS LETTERS, 100(6), 2012 (article)

Abstract
We demonstrate an implementation of frequency-encoded photocurrent spectroscopy using a super-continuum light source. The spectrally broad light is spatially dispersed and modulated with a special mechanical chopper design that permits a continuous wavelength-dependent modulation. After recombination, the light beam contains a frequency encoded spectrum which enables us to map the spectral response of a given sample in 60 ms and with a lateral resolution of 10 mu m. (C) 2012 American Institute of Physics.

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DOI [BibTex]

DOI [BibTex]


Eine neue Form von Cavity Enhanced Absorption Spectroscopy
Eine neue Form von Cavity Enhanced Absorption Spectroscopy

Petermann, C., Fischer, P.

DE Gruyter, 79(1), 2012, Best paper award OPTO 2011 (article)

Abstract
Wir stellen eine Kopplungsmethode für resonatorgestützte Absorptionsmessungen vor, bei der Licht durch einen im Resonator platzierten akustooptischen Modulator aktiv ein- und ausgekoppelt wird. Dies ermöglicht es Cavity-Ring-Down-Spektroskopie (CRDS) mit breitbandigen und zeitlich inkohärenten Lichtquellen niedriger spektraler Leistungsdichte durchzuführen. Das Verfahren wird zum ersten Mal mit einer breitbandigen Superkontinuum-Quelle demonstriert.

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A new coupling scheme for cavity enhanced absorption spectroscopy makes use of an intracavity acousto-optical modulator to actively switch light into (and out of) a resonator. This allows cavity ringdown spectroscopy (CRDS) to be implemented with broadband temporally incoherent light sources with low spectral power densities. The method is demonstrated for the first time using a broadband supercontinuum source. Best paper award OPTO 2011.

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link (url) [BibTex]

link (url) [BibTex]


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Construct Validity of Instrument Vibrations as a Measure of Robotic Surgical Skill

Gomez, E. D., Bark, K., Rivera, C., McMahan, W., Remington, A., Lee, D. I., Williams, N., Murayama, K., Dumon, K., Kuchenbecker, K. J.

Journal of the American College of Surgeons, 215(3):S119-120, Chicago, Illinois, USA, 2012, Oral presentation given by Gomez at the {\em American College of Surgeons (ACS) Clinical Congress} (article)

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[BibTex]

[BibTex]

2009


Full phase and amplitude control in computer-generated holography
Full phase and amplitude control in computer-generated holography

Fratz, M., Fischer, P., Giel, D. M.

OPTICS LETTERS, 34(23):3659-3661, 2009 (article)

Abstract
We report what we believe to be the first realization of a computer-generated complex-valued hologram recorded in a single film of photoactive polymer. Complex-valued holograms give rise to a diffracted optical field with control over its amplitude and phase. The holograms are generated by a one-step direct laser writing process in which a spatial light modulator (SLM) is imaged onto a polymer film. Temporal modulation of the SLM during exposure controls both the strength of the induced birefringence and the orientation of the fast axis. We demonstrate that complex holograms can be used to impart arbitrary amplitude and phase profiles onto a beam and thereby open new possibilities in the control of optical beams. (C) 2009 Optical Society of America

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[BibTex]

2009


[BibTex]


Digital polarization holograms with defined magnitude and orientation of each pixel's birefringence
Digital polarization holograms with defined magnitude and orientation of each pixel’s birefringence

Fratz, M., Giel, D. M., Fischer, P.

OPTICS LETTERS, 34(8):1270-1272, 2009 (article)

Abstract
A new form of digital polarization holography is demonstrated that permits both the amplitude and the phase of a diffracted beam to be independently controlled. This permits two independent intensity images to be stored in the same hologram. To fabricate the holograms, a birefringence with defined retardance and orientation of the fast axis is recorded into a photopolymer film. The holograms are selectively read out by choosing the polarization state of the read beam. Polarization holograms of this kind increase the data density in holographic data storage and allow higher quality diffractive optical elements to be written. (C) 2009 Optical Society of America

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[BibTex]


Controlled Propulsion of Artificial Magnetic Nanostructured Propellers
Controlled Propulsion of Artificial Magnetic Nanostructured Propellers

Ghosh, A., Fischer, P.

NANO LETTERS, 9(6):2243-2245, 2009, Featured highlight ‘Nanotechnology: The helix that delivers’ Nature 459, 13 (2009). (article)

Abstract
For biomedical applications, such as targeted drug delivery and microsurgery, it is essential to develop a system of swimmers that can be propelled wirelessly in fluidic environments with good control. Here, we report the construction and operation of chiral colloidal propellers that can be navigated in water with micrometer-level precision using homogeneous magnetic fields. The propellers are made via nanostructured surfaces and can be produced in large numbers. The nanopropellers can carry chemicals, push loads, and act as local probes in rheological measurements.

Featured highlight ‘Nanotechnology: The helix that delivers’ Nature 459, 13 (2009).

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Video - Nanospropellers DOI [BibTex]

Video - Nanospropellers DOI [BibTex]


Absolute Asymmetric Reduction Based on the Relative Orientation of Achiral Reactants
Absolute Asymmetric Reduction Based on the Relative Orientation of Achiral Reactants

Kuhn, A., Fischer, P.

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 48(37):6857-6860, 2009 (article)

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DOI [BibTex]

DOI [BibTex]

2000


Phenomenological damping in optical response tensors
Phenomenological damping in optical response tensors

Buckingham, A., Fischer, P.

PHYSICAL REVIEW A, 61(3), 2000 (article)

Abstract
Although perturbation theory applied to the optical response of a molecule or material system is only strictly valid far from resonances, it is often applied to ``near-resonance{''} conditions by means of complex energies incorporating damping. Inconsistent signs of the damping in optical response tensors have appeared in the recent literature, as have errors in the treatment of the perturbation by a static held. The ``equal-sign{''} convention used in a recent publication yields an unphysical material response, and Koroteev's intimation that linear electro-optical circular dichroism may exist in an optically active liquid under resonance conditions is also flawed. We show that the isotropic part of the Pockels tensor vanishes.

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DOI [BibTex]

2000


DOI [BibTex]


Ab initio investigation of the sum-frequency hyperpolarizability of small chiral molecules
Ab initio investigation of the sum-frequency hyperpolarizability of small chiral molecules

Champagne, B., Fischer, P., Buckingham, A.

CHEMICAL PHYSICS LETTERS, 331(1):83-88, 2000 (article)

Abstract
Using a sum-over-states procedure based on configuration interaction singles /6-311++G{*}{*}, we have computed the sum-frequency hyperpolarizability beta (ijk)(-3 omega; 2 omega, omega) Of two small chiral molecules, R-monofluoro-oxirane and R-(+)-propylene oxide. Excitation energies were scaled to fit experimental UV-absorption data and checked with ab initio values from time-dependent density functional theory. The isotropic part of the computed hyperpolarizabilities, beta(-3 omega; 2 omega, omega), is much smaller than that reported previously from sum-frequency generation experiments on aqueous solutions of arabinose. Comparison is made with a single-centre chiral model. (C) 2000 Elsevier Science B.V. All rights reserved.

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DOI [BibTex]

DOI [BibTex]


Three-wave mixing in chiral liquids
Three-wave mixing in chiral liquids

Fischer, P., Wiersma, D., Righini, R., Champagne, B., Buckingham, A.

PHYSICAL REVIEW LETTERS, 85(20):4253-4256, 2000 (article)

Abstract
Second-order nonlinear optical frequency conversion in isotropic systems is only dipole allowed for sum- and difference-frequency generation in chiral media. We develop a single-center chiral model of the three-wave mixing (sum:frequency generation) nonlinearity and estimate its magnitude. We also report results from ab initio calculations and from three- and four-wave mixing experiments in support of the theoretical estimates. We show that the second-order susceptibility in chiral liquids is much smaller than previously thought.

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DOI [BibTex]

DOI [BibTex]