List of Publications

2021

  • A. Rahimzadeh, M. Rutsch, M. Kupnik, and R. von Klitzing “Visualization of Acoustic Energy Absorption in Confined Aqueous Solutions by PNIPAM Microgels: Effects of Bulk Viscosity” Langmuir, 37. Jg., Nr. 19, S. 5854-5863, 2021.
  • O. Ben Dali, H. von Seggern, G. Sessler, P. Pondrom, S. Zhukov, X. Zhang, M. Kupnik, “Ferroelectret energy harvesting with 3D‐printed air‐spaced cantilever design”. Nano Select, 2021.

2020

  • X. Ma, H. von Seggern, G. Sessler, S. Zhukov, O. Ben Dali, M. Kupnik, and X. Zhang, “High performance fluorinated polyethylene propylene ferroelectrets with an air-filled parallel-tunnel structure”, to appear in IOP Journal Smart Materials and Structures, pp. 1–16, 2020.
  • Y. Xue, X. Zhang, R. Chadda, G. M. Sessler, and M. Kupnik, “Ferroelectret-based flexible transducers A strategy for acoustic levitation and manipulation of particles”, The Journal of the Acoustical Society of America (JASA), vol. 147, no. 5, EL421–EL427, 2020.
  • C. E. Proulx, M. Beaulac, M. David, C. Deguire, C. Haché, F. Klug, M. Kupnik, J. Higgins, and D. H. Gagnon, “Review of the effects of soft robotic gloves for activity-based rehabilitation in individuals with reduced hand function and manual dexterity following a neurological event”, Journal of Rehabilitation and Assistive Technologies Engineering, vol. 7, pp. 1–18, 2020.
  • O. Ben Dali, P. Pondrom, G. M. Sessler, S. Zhukov, H. von Seggern, X. Zhang, and M. Kupnik, “Cantilever-based ferroelectret energy harvesting”, Applied Physics Letters, vol. 116, no. 24, p. 243 901, 2020.
  • S. Zhukov, X. Ma, H. von Seggern, G. M. Sessler, O. Ben Dali, M. Kupnik, and X. Zhang, “Biodegradable cellular polylactic acid ferroelectrets with strong longitudinal and transverse piezoelectricity”, Applied Physics Letters, vol. 117, no. 11, p. 112 901, 2020.
  • G. Allevato, J. Hinrichs, M. Rutsch, J. Adler, A. Jager, M. Pesavento, and M. Kupnik, “Real-time 3D imaging using an air-coupled ultrasonic phased-array”, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, pp. 1–11, 2020.
  • X. Zhang, H. von Seggern, G. M. Sessler, and M. Kupnik, “Mechanical energy harvesting with ferroelectrets”, IEEE Electrical Insulation Magazine, vol. 36, no. 6, pp. 47–58, 2020.
  • S. Zhukov, H. von Seggern, X. Zhang, Y. Xue, O. Ben Dali, P. Pondrom, G. M. Sessler, and M. Kupnik, “Microenergy harvesters based on fluorinated ethylene propylene piezotubes”, Advanced Engineering Materials, p. 1 901 399, 2020.
  • M. Kupnik, “Air-coupled transducer arrays: Imaging and other applications”, invited talk for IEEE International Ultrasonics Symposium (IUS), 2020.
  • G. Allevato, M. Rutsch, J. Hinrichs, M. Pesavento, and M. Kupnik, “Embedded air-coupled ultrasonic 3D sonar system with GPU acceleration”, accepted for Proc. IEEE Sensors Conference, pp. 1–4, 2020.
  • R. Chadda, J. Probst, C. Hartmann, M. Link, M. Hessinger, E. Abele, M. Weigold, and M. Kupnik, “Disruptive force sensor based on laser-based powder-bed-fusion”, in Proc. IEEE Sensors Conference, pp. 1–4, 2020.
  • F. Merbeler, S. Anzinger, C. Bretthauer, and M. Kupnik, “Ultra-compact clamp-on liquid level sensor based on a low-voltage CMUT”, accepted for Proc. IEEE Sensors, p. 4, 2020.
  • J. Hinrichs, Y. Bendel, M. Rutsch, G. Allevato, M. Sachsenweger, A. Jager, and M. Kupnik, “Schlieren photography of 40 kHz leaky Lamb waves in air”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 1396–1399, 2020.
  • M. Krenkel, N. Lange, S. G. Koch, and M. Kupnik, “Modeling and validation of CMUTs with mechanically coupled plate actuators”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 747–750, 2020.
  • M. Link, M. Weigold, J. Probst, R. Chadda, C. Hartmann, M. Hessinger, M. Kupnik, and E. Abele, “Investigation on structural integration of strain gauges using laser-based powder-bed-fusion (LPBF)”, in Proc. Production at the Leading Edge of Technology, pp. 387–395, 2020.
  • R. Müller, D. Schenck, G. Allevato, M. Rutsch, J. Hinrichs, M. Kupnik, and M. Pesavento, “Dictionarybased learning for 3D-imaging with air-coupled ultrasonic phased arrays”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 1536–1539, 2020.
  • G. Allevato, M. Rutsch, J. Hinrichs, E. Sarradj, M. Pesavento, and M. Kupnik, “Spiral air-coupled ultrasonic phased array for high resolution 3D imaging”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 737–740, 2020.
  • M. Rutsch, G. Allevato, J. Hinrichs, and M. Kupnik, “Protection layer for air-coupled waveguide ultrasonic phased arrays”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 743–746, 2020.
  • J. Seiler, N. Schäfer, B. Latsch, R. Chadda, M. Hessinger, P. Beckerle, and M. Kupnik, “Wearable vibrotactile interface using phantom tactile sensation for human – robot interaction”, in Proc. International Conference on Human Haptic Sensing and Touch Enabled Computer Applications EuroHaptics 2020, pp. 380–388, 2020.

2019

  • M. Krenkel, M. Stolz, S. G. Koch, and M. Kupnik, “CMUT with mechanically coupled plate actuators for low frequencies”, Journal of Micromechanics and Microengineering, vol. 29, no. 4, p. 044 001, 2019.
  • Y. Xue, J. Zhao, X. Zhang, G. M. Sessler, and M. Kupnik, “Acoustic energy harvesting with irradiated cross-linked polypropylene piezoelectret films”, Physica Scripta, vol. 94, no. 9, p. 095 002, 2019.
  • M. Gaal, R. Caldeira, J. Bartusch, F. Schadow, K. Vossing, and M. Kupnik, “Air-coupled ultrasonic ferroelectret receiver with additional bias voltage”, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 66, no. 10, pp. 1600–1605, 2019.
  • J. Fauser, S. Seelecke, R. Werthschutzky, M. Kupnik, A. Mukhopadhyay, R. Chadda, Y. Goergen, M. Hessinger, P. Motzki, I. Stenin, J. Kristin, T. Klenzner, and J. Schipper, “Planning for flexible surgical robots via Bézier spline translation”, IEEE Robotics and Automation Letters, vol. 4, no. 4, pp. 3270–3277, 2019.
  • R. Chadda, S. Wismath, M. Hessinger, N. Schafer, A. Schlaefer, and M. Kupnik, “Needle tip force sensor for medical applications”, in Proc. IEEE Sensors Conference, pp. 1–4, 2019.
  • G. Allevato, J. Hinrichs, D. Grosskurth, M. Rutsch, J. Adler, A. Jäger, M. Pesavento, and M. Kupnik, “3D imaging method for an air-coupled 40 kHz ultrasound phased-array”, in Proc. 23rd International Congress on Acoustics, pp. 1–8, 2019.
  • O. Ben Dali, S. Zhukov, R. Chadda, P. Pondrom, X. Zhang, G. Sessler, H. von Seggern, and M. Kupnik, “Modeling of piezoelectric coupling coefficients of soft ferroelectrets for energy harvesting”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 2454–2457, 2019.
  • Y. Goergen, R. Chadda, R. Britz, D. Scholtes, N. Koev, P. Motzki, R. Werthschützky, M. Kupnik, and S. Seelecke, “Shape memory alloys in continuum and soft robotic applications”, in Proc. ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, pp. 1–6, 2019.
  • F. Greiner, R. Chadda, J.-E. Adolf, S. Beck, and M. Kupnik, “Force sensor with increased local resolution for electronic contact normal force measurement in electrical connectors”, in Proc. IEEE Sensors Conference, pp. 1–4, 2019.
  • C. Haugwitz, A. Jager, G. Allevato, J. Hinrichs, A. Unger, S. Saul, J. Brotz, B. Matyschok, P. Pelz, and M. Kupnik, “Flow metering of gases using ultrasonic phased-arrays at high velocities”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 1–4, 2019.
  • A. Jager, W. M. D. Wright, M. Kupnik, J. Hinrichs, G. Allevato, M. Sachsenweger, S. Kadel, D. Stasevich, W. Gebhard, G. Hubschen, and T. Hahn-Jose, “Non-contact ultrasound with optimum electronic steering angle to excite Lamb waves in thin metal sheets for mechanical stress measurements”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 924–927, 2019.
  • F. Klug, M. Hessinger, T. Koka, P. Witulla, C. Will, T. Schlichting, C. Endl, A. Albenstetter, P.-O. Champagne, D. H. Gagnon, and M. Kupnik, “An anthropomorphic soft exosuit for hand rehabilitation”, in Proc. IEEE 16th International Conference on Rehabilitation Robotics (ICORR), pp. 1121–1126, 2019.
  • M. Krenkel, S. G. Koch, and M. Kupnik, “CMUT with mechanically coupled plate actuators – linearized electrostatic modeling”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 774–777, 2019.
  • M. Rutsch, O. B. Dali, A. Jager, G. Allevato, K. Beerstecher, J. Cardoletti, A. Radetinac, L. Alff, and M. Kupnik, “Air-coupled ultrasonic bending plate transducer with piezoelectric and electrostatic transduction element combination”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 147– 150, 2019.
  • M. Rutsch, A. Jager, A. Unger, T. Kaindl, and M. Kupnik, “Wave propagation in an acoustic waveguide for ultrasonic phased arrays”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 796–799, 2019.
  • I. Wygant, B. T. Khuri-Yakub, and M. Kupnik, “Performance parameters and frequency response of CMUTs in transmit, receive, and pulse-echo operation”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 766–769, 2019.

2018

  • C. Hatzfeld, S. Dorsch, C. Neupert and M. Kupnik, “Influence of surgical gloves on haptic perception thresholds”, The International Journal of Medical Robotics and Computer Assisted Surgery 14.1, e1852, 2018.
  • I. O. Wygant, M. Kupnik, and B. T. Khuri-Yakub, “An analytical model for capacitive pressure transducers with circular geometry”, IEEE Journal of Microelectromechanical Systems (JMEMS), vol. 27, no. 3, pp. 448–456, 2018.
  • M. Krenkel, M. Kircher, M. Kupnik and S. G. Koch, “CMUT with mechanically coupled plate actuators”, International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE). IEEE, 2018.
  • S. A. Wojcik, C. Neupert, J. Bilz, R. Werthschützky, M. Kupnik and C. Hatzfeld, “Pseudohaptic Feedback for Teleoperated Gripping Interactions”, International Conference on Human Haptic Sensing and Touch Enabled Computer Applications. Springer, Cham, 2018.
  • M. Hessinger, E. Christmann, R. Werthschutzky and M. Kupnik, “User interaction measurements of an exoskeleton using EMG and joint torque”, TM-TECHNISCHES MESSEN 85.7-8, 487-495, 2018.
  • M. Hessinger, E. Christmann, R. Werthschützky, and M. Kupnik, “Messung von nutzerinteraktion mit einem exoskelett durch EMG und gelenk-drehmomente”, tm – Technisches Messen, vol. 85, no. 7-8, pp. 487–495, 2018.
  • S. Park, I. Yoon, S. Lee, H. Kim, J.-W. Seo, Y. Chung, A. Unger, M. Kupnik, and H. J. Lee, “CMUTbased resonant gas sensor array for VOC detection with low operating voltage”, Sensors and Actuators B: Chemical, vol. 273, pp. 1556–1563, 2018.
  • S. A. Wojcik, C. Neupert, J. Bilz, R. Werthschützky, M. Kupnik, and C. Hatzfeld, “Pseudohaptic feedback for teleoperated gripping interactions”, in Proc. International Conference on Human Haptic Sensing and Touch Enabled Computer Applications EuroHaptics 2018, pp. 309–320, 2018.
  • M. Krenkel, M. Kircher, M. Kupnik, and S. G. Koch, “CMUT with mechanically coupled plate actuators”, in Proc. of 19th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE), pp. 1–8, 2018.

2017

  • C. Hatzfeld, S. Dorsch, C. Neupert, and M. Kupnik, “Influence of surgical gloves on haptic perception thresholds”, The International Journal of Medical Robotics and Computer Assisted Surgery, e1852–1–9, 2017.
  • C. Hatzfeld, M. Kühner, S. Söllner, T. Khanh, and M. Kupnik, “Human Perception Measures for Product Design and Development—A Tutorial to Measurement Methods and Analysis”, MDPI Journal of Multimodal Technologies and Interaction, vol. 1, no. 28, pp. 1–23, 2017.
  • I. O.Wygant, M. Kupnik, and B. T. Khuri-Yakub, “An Analytical Model for Capacitive Pressure Transducers with Circular Geometry”, Under review for IEEE Journal of Microelectromechanical Systems, 2017.
  • S. Matich, M. Hessinger, M. Kupnik, R. Werthschützky, and C. Hatzfeld, “Miniaturized multiaxial force/torque sensor with a rollable hexapod structure”, TM – Technisches Messen, vol. 84, no. s1, 2017.
  • H.-S. Yoon, S. Vaithilingam, K. K. Park, A. Nikoozadeh, K. Firouzi, J. W. Choe, R. D. Watkins, H. K. Oguz, M. Kupnik, K. B. Pauly, and P. Khuri-Yakub, “A 1-MHz 2-D CMUT array for HIFU thermal ablation”, in Proc. AIP Conference Proceedings 1821 from the 14th International Symposium on Therapeutic Ultrasound, pp. 050003–1–5, 2017.
  • M. Gaal, R. Caldeira, J. Bartusch, and M. Kupnik, “Air-Coupled Ultrasonic Ferroelectret Receiver with Additional DC Voltage”, in Proc. Eurosensors, vol. 1, no. 4, pp. 362–1–4, 2017.
  • A. Jäger, D. Großkurth, M. Rutsch, A. Unger, R. Golinske, H. Wang, S. Dixon, K. Hofmann, and M. Kupnik, “Air-coupled 40-KHZ ultrasonic 2d-phased array based on a 3d-printed waveguide structure”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 1–4, 2017.
  • A. Jäger, S. Johannesmann, L. Claes, M. Webersen, B. Henning, and M. Kupnik, “Evaluating the influence of 3d-printing parameters on acoustic material properties”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 1–4, 2017.
  • A. Jäger, A. Unger, H. Wang, Y. Arnaudov, L. Kang, R. Su, D. Lines, S. N. Ramadas, S. Dixon, and M. Kupnik, “Ultrasonic phased array for sound drift compensation in gas flow metering”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 1–4, 2017.
  • C. Hatzfeld, N. Stefanova, T. Opitz, T. Meiss, M. Degünther, J. Genzel, M. Kupnik, W. Voelker, and R. Werthschützky, “Measurement setup to evaluate haptic interaction in catheterization procedures for training purposes”, in Proc. IEEE World Haptics Conference (WHC), pp. 412–417, 2017.
  • C. Hatzfeld, C. Neupert, S. Matich, M. Braun, J. Bilz, J. Johannink, J. Miller, P. P. Pott, H. F. Schlaak, M. Kupnik, R. Werthschützky, and A. Kirschniak, “A teleoperated platform for transanal single-port surgery: Ergonomics and workspace aspects”, in Proc. IEEE World Haptics Conference (WHC), pp. 1–6, 2017.
  • L. Kang, A. Feeney, R. Su, D. Lines, A. Jäger, H. Wang, Y. Arnaudov, S. N. Ramadas, M. Kupnik, and S. Dixon, “Two-dimensional flexural ultrasonic phased array for flow measurement”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 1–4, 2017.
  • M. Hessinger, J. Krenzer, E. Christmann, J. Hielscher, M. Kupnik, and R.Werthschützky, “Structurally Integrated Joint Torque Sensors in an Assistive Upper Limb Exoskeleton”, in Proc. of 18th International Conference on Sensors and Measurement Technology, 2017.
  • M. Hessinger, M. Kniepkamp, J. Lotichius, C. Hatzfeld, R. Werthschützky, E. Abele, and M. Kupnik, “Strain Transmission Characteristics of Steel Substrates for Additive Sensor Manufacturing with Selective Laser Melting”, in Proc. of 18th International Conference on Sensors and Measurement Technology, 2017.

2016

  • C. Neupert, S. Matich, N. Scherping, M. Kupnik, R. Werthschützky, and C. Hatzfeld, “Pseudo-Haptic Feedback in Teleoperation”, IEEE Transactions on Haptics, vol. 9, no. 3, pp. 397–408, 2016.
  • C. Hatzfeld, S. Cao, M. Kupnik, and R. Werthschützky, “Vibrotactile Force Perception; Absolute and Differential Thresholds and External Influences”, IEEE Transactions on Haptics, vol. 9, no. 4, pp. 586–597, 2016.
  • C. Hatzfeld, V. Q. Hoang, and M. Kupnik, “It’s All About the Subject – Options to Improve Psychometric Procedure Performance”, Haptics: PERCEPTION, Devices, Control, and Applications, Lecture Notes in Computer Science, pp. 394–403, 2016.
  • C. Hatzfeld, J. Bilz, T. Fritzsche, and M. Kupnik, “A Reconfigurable Haptic Joystick Based on Magneto-Rheological Elastomers – System Design and First Evaluation”, in Proc. Eurohaptics: PERCEPTION, Devices, Control, and Applications, pp. 109–119, 2016.
  • T. Grosse-Puppendahl, X. Dellangnol, C. Hatzfeld, B. Fu, M. Kupnik, A. Kuijper, M. R. Hastall, J. Scott, and M. Gruteser, “Platypus: Indoor Localization and Identification through Sensing of Electric Potential Changes in Human Bodies”, in Proc. of 14th Annual International Conference on Mobile Systems, Applications, and Services, pp. 17–30, 2016.
  • I. O. Wygant, M. Kupnik, and B. T. Khuri-Yakub, “CMUT design equations for optimizing noise figure and source pressure”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 1–4, 2016.
  • F. Schiewer, H. Wang, A. Unger, N. Stefanova, and M. Kupnik, “Single-transducer acoustic levitator with equidistant vertical positioning capability”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 1–4, 2016.
  • S. E. Burrows, S. N. Ramadas, T. J. R. Eriksson, L. Kang, S. M. Dixon, A. Unger, and M. Kupnik, “High temperature flexural ultrasonic transducer for non-contact measurement applications”, in Proc. Joint IEEE International Symposium on the Applications of Ferroelectrics, European Conference on Application of Polar Dielectrics, and Piezoelectric Force Microscopy Workshop (ISAF/ECAPD/PFM), pp. 1–3, 2016.
  • L. Kang, T. Eriksson, S. N. Ramadas, R. Su, D. Lines, M. Kupnik, and S. Dixon, “Design of flexural ultrasonic phased array for fluid-coupled applications”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 1–4, 2016.

2015

  • M. Rutsch, E. Konetzke, A. Unger, M. Hoffmann, S. N. Ramadas, S. Dixon, and M. Kupnik, “Extending the receive performance of phased ultrasonic transducer arrays in air down to 40 kHz and below”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 1–4, 2015.
  • E. Konetzke, M. Rutsch, M. Hoffmann, A. Unger, R. Golinske, D. Killat, S. N. Ramadas, S. Dixon, and M. Kupnik, “Phased array transducer for emitting 40-kHz air-coupled ultrasound without grating lobes”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 1–4, 2015.
  • C. Hatzfeld, M. Kupnik, and R. Werthschützky, “Performance simulation of unforced choice paradigms in parametric psychometric procedures”, in Proc. IEEE World Haptics Conference (WHC), pp. 475–481, 2015.
  • A. Guseva, M. Hoffmann, A. Unger, S. Zulk, M. B. E. Amien, E. Sarradj, and M. Kupnik, “Ultrasonic transducer characterization in air based on an indirect acoustic radiation pressure measurement”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 1–4, 2015.
  • J. Lotichius, T. Singer, G. Brokmann, H. Übensee, T. Ortlepp, M. Kupnik, and R. Werthschützky, “A thermal network model for piezoresistive pressure sensors”, in Proc. IEEE SENSORS, pp. 1–4, 2015.
  • C. Neupert, S. Matich, C. Hatzfeld, M. Kupnik, and R. Werthschützky, “Investigation of the usability of pseudo-haptic feedback in teleoperation”, in Proc. IEEE World Haptics Conference (WHC), pp. 488–493, 2015.
  • R. Golinske, M. Hoffmann, E. Konetzke, A. Unger, M. Rutsch, and M. Kupnik, “Diffraction loss calculation based on boundary element method for an air-coupled phased array”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 1–4, 2015.
  • A. Unger, E. Konetzke, M. Rutsch, M. Hoffmann, S. N. Ramadas, S. Dixon, and M. Kupnik, “Versatile air-coupled phased array transducer for sensor applications”, in Proc. IEEE SENSORS, pp. 1–4, 2015.
  • T. J. R. Eriksson, S. N. Ramadas, A. Unger, M. Hoffman, M. Kupnik, and S. M. Dixon, “Flexural transducer arrays for industrial non-contact applications”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 1–4, 2015.
  • J. Lotichius, S. Wagner, M. Kupnik, and R. Werthschützky, “Measurement uncertainty of time-based and voltage-based wheatstone bridge readout circuits”, in Proc. IEEE SENSORS, pp. 1–4, 2015.
  • M.-C. Ho, M. Hoffmann, A. Unger, K. K. Park, M. Kupnik, and B. T. Khuri-Yakub, “CMUTs in permanent contact operation for high output pressure”, in Proc. International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems collocated with the ASME 2015 13th International Conference on Nanochannels, Microchannels, and Minichannels, pp. 1–6, 2015.
  • M. Hoffmann, A. Unger, A. Jäger, and M. Kupnik, “Effect of transducer port cavities in invasive ultrasonic transit-time gas flowmeters”, in Proc. IEEE International Ultrasonics Symposium (IUS), pp. 1–4, 2015.
  • C. Hatzfeld, C. Schröder, A. Unger, O. Morar, T. Klemm, M. Kupnik, and R. Werthschützky, “Flow sensor for field measurement of viscous liquid usage for consumer studies”, in Proc. IEEE SENSORS, pp. 1–4, 2015.