Jean-Michel Geffrin

Documents

Publications

	Imaging of the internal structure of an asteroid analogue from quasi-monostatic microwave measurement data I. The frequency domain approach A. Dufaure , C. Eyraud , L.-I. Sorsa , Y.O. Yusuf , S. Pursiainen Astronomy and Astrophysics - A&A, 2023, 674, pp.A72. ⟨10.1051/0004-6361/202244777⟩ Article dans une revue hal-04251357v1
	Imaging of the internal structure of an asteroid analogue from quasi-monostatic microwave measurement data II. The time domain approach Liisa-Ida Sorsa , Yusuf Oluwatoki Yusuf , Astrid Dufaure , Jean-Michel Geffrin , Christelle Eyraud Astronomy and Astrophysics - A&A, 2023, 674, pp.A73. ⟨10.1051/0004-6361/202244778⟩ Article dans une revue hal-04251383v1
	Scattering properties of protoplanetary dust analogs with microwave analogy: Aggregates of fractal dimensions from 1.5 to 2.8 Vanesa Tobon Valencia , Jean-Michel Geffrin , François Ménard , Julien Milli , Jean-Baptiste Renard Astronomy and Astrophysics - A&A, 2022, 666, pp.A68. ⟨10.1051/0004-6361/202142656⟩ Article dans une revue hal-03837453v1
	High‐Q Transparency Band in All‐Dielectric Metasurfaces Induced by a Quasi Bound State in the Continuum Diego Abujetas , Ángela Barreda , Fernando Moreno , Amelie Litman , Jean-Michel Geffrin Laser and Photonics Reviews, 2021, 15 (1), pp.2000263. ⟨10.1002/lpor.202000263⟩ Article dans une revue hal-02989980v1
	Complex-structured 3D-printed wireframes as asteroid analogues for tomographic microwave radar measurements Liisa-Ida Sorsa , Christelle Eyraud , Alain Hérique , Mika Takala , Sampsa Pursiainen Materials & Design, 2021, 198, pp.109364. ⟨10.1016/j.matdes.2020.109364⟩ Article dans une revue hal-03054178v1
	Full wavefield simulation versus measurement of microwave scattering by a complex 3D-printed asteroid analogue★ Christelle Eyraud , L.-I. Sorsa , Jean-Michel Geffrin , M. Takala , G. Henry Astronomy and Astrophysics - A&A, 2020, 643, pp.A68. ⟨10.1051/0004-6361/202038510⟩ Article dans une revue hal-02960004v1
	Counting and Phase Function Measurements with the LONSCAPE Instrument to Determine Physical Properties of Aerosols in Ice Giant Planet Atmospheres Jean-Baptiste Renard , Olivier Mousis , Pascal Rannou , Anny Chantal Levasseur-Regourd , Gwenaël Berthet Space Science Reviews, 2020, 216 (2), pp.Article number 28. ⟨10.1007/s11214-020-00653-2⟩ Article dans une revue insu-02492388v1
	Influence of the description of the scattering matrix on permittivity reconstruction with a quantitative imaging procedure: polarization effects Christelle Eyraud , Hassan Saleh , Jean-Michel Geffrin Journal of the Optical Society of America. A, Optics and image science, 2019, 36 (2), pp.234-244. ⟨10.1364/josaa.36.000234⟩ Article dans une revue hal-01986569v1
	Brewster quasi bound states in the continuum in all-dielectric metasurfaces from single magnetic-dipole resonance meta-atoms Diego Abujetas , Angela ´ Barreda , Fernando Moreno , Juan Sáenz , Amelie Litman Scientific Reports, 2019, 9 (1), ⟨10.1038/s41598-019-52223-4⟩ Article dans une revue hal-02374991v1
	Experimental demonstration of spectrally broadband Huygens sources using low-index spheres Mohamed Ismail Abdelrahman , Hassan Saleh , Ivan Fernandez-Corbaton , Boris Gralak , Jean-Michel Geffrin APL Photonics, 2019, 4 (2), pp.020802. ⟨10.1063/1.5080980⟩ Article dans une revue hal-02056744v1
	Mesure de surface équivalente radar (SER) - Aspect expérimental Fabrice Comblet , Franck Daout , Christelle Eyraud , Jean-Michel Geffrin , Pierre Massaloux Techniques de l'Ingénieur, 2018 Article dans une revue hal-02008418v1
	Imaging the interior of a comet from bistatic microwave measurements: case of a scale comet model Christelle Eyraud , Alain Hérique , Jean-Michel Geffrin , Wlodek W. Kofman Advances in Space Research, 2018, 62 (8), pp.1977-1986. ⟨10.1016/j.asr.2017.10.012⟩ Article dans une revue hal-01626737v1
	On the scattering directionality of a dielectric particle dimer of High Refractive Index Angela ´ Barreda , Hassan Saleh , Amelie Litman , Francisco González , Jean-Michel Geffrin Scientific Reports, 2018, 8 (1), ⟨10.1038/s41598-018-26359-8⟩ Article dans une revue hal-01803030v1
	Electromagnetic polarization-controlled perfect switching effect with high-refractive-index dimers and the beam-splitter configuration Angela ´ Barreda , Hassan Saleh , Amelie Litman , Francisco González , Jean-Michel Geffrin Nature Communications, 2017, 8, pp.13910. ⟨10.1038/ncomms13910⟩ Article dans une revue hal-01430138v1
	Microwave analog experiments on optically soft spheroidal scatterers with weak electromagnetic signature Hassan Saleh , Julien Charon , Jérémi Dauchet , Hervé Tortel , Jean-Michel Geffrin Journal of Quantitative Spectroscopy and Radiative Transfer, 2017, 196, pp.1 - 9. ⟨10.1016/j.jqsrt.2017.03.024⟩ Article dans une revue hal-01579249v1
	Directional Fano resonances in light scattering by a high refractive index dielectric sphere Michael I. Tribelsky , Jean-Michel Geffrin , Amelie Litman , Christelle Eyraud , Fernando Moreno Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2016, 94 (12), pp.121110. ⟨10.1103/PhysRevB.94.121110⟩ Article dans une revue hal-01365811v1
	Molding acoustic, electromagnetic and water waves with a single cloak Jun Xu , Xu Jiang , Nicholas Fang , Elodie Georget , Redha Abdeddaim Scientific Reports, 2015, 5, pp.10678. ⟨10.1038/srep10678⟩ Article dans une revue hal-01283608v1
	Small Dielectric Spheres with High Refractive Index as New Multifunctional Elements for Optical Devices Michael I. Tribelsky , Jean-Michel Geffrin , Amelie Litman , Christelle Eyraud , Fernando Moreno Scientific Reports, 2015, pp.1-7. ⟨10.1038/srep12288⟩ Article dans une revue hal-01199730v1
	Complex Permittivity Determination From Far-Field Scattering Patterns Christelle Eyraud , Jean-Michel Geffrin , Amelie Litman , Hervé Tortel IEEE Antennas and Wireless Propagation Letters, 2015, 14, pp.309 - 312. ⟨10.1109/LAWP.2014.2362995⟩ Article dans une revue hal-01279554v1
	3-D Imaging of a Microwave Absorber Sample From Microwave Scattered Field Measurements Jean-Michel Geffrin , Christelle Eyraud , Amelie Litman IEEE Microwave and Wireless Components Letters, 2015, 25 (7), pp.472 - 474. ⟨10.1109/LMWC.2015.2427577⟩ Article dans une revue hal-01279547v1
	Evanescent wave scattering by particles on a surface: validation of the discrete dipole approximation with surface interaction against microwave analog experiments M. Short , Jean-Michel Geffrin , Rodolphe Vaillon , Hervé Tortel , B. Lacroix Journal of Quantitative Spectroscopy and Radiative Transfer, 2014, 146, pp.452-458. ⟨10.1016/j.jqsrt.2013.12.007⟩ Article dans une revue hal-01018895v1
	Recent advances in microwave analog to light scattering experiments Rodolphe Vaillon , Jean-Michel Geffrin Journal of Quantitative Spectroscopy and Radiative Transfer, 2014, 146, pp.100-105. ⟨10.1016/j.jqsrt.2014.02.031⟩ Article dans une revue hal-01018897v1
	Controllable emission of a dipolar source coupled with a magneto-dielectric resonant subwavelength scatterer Brice Rolly , Jean-Michel Geffrin , Redha Abdeddaim , Brian Stout , Nicolas Bonod Scientific Reports, 2013, 3, pp.3063. ⟨10.1038/srep03063(2013)⟩ Article dans une revue hal-00878472v1
	Polarization effects in 3D vectorial induced current reconstructions Christelle Eyraud , Rodolphe Vaillon , Amelie Litman , Jean-Michel Geffrin , Olivier Merchiers Journal of the Optical Society of America. A Optics, Image Science, and Vision, 2013, 30 (10), pp.1967-1974. ⟨10.1364/JOSAA.30.001967⟩ Article dans une revue hal-01811746v1
	Les métamatériaux : une solution pour l'ingénierie d'indice complexe Redha Abdeddaim , Abdelwaheb Ourir , Jean-Michel Geffrin , Julien de Rosny , Gérard Tayeb La Revue de l'électricité et de l'électronique, 2013, 4, pp.59-62 Article dans une revue hal-00945386v1
	An extended-DORT method and its application in a cavity configuration Xiaoyun Zhang , Hervé Tortel , Amelie Litman , Jean-Michel Geffrin Inverse Problems, 2012, 28 (11), pp.115008. ⟨10.1088/0266-5611/28/11/115008⟩ Article dans une revue hal-00944610v1
	A large 3D target with small inner details : A difficult cocktail for imaging purposes without a-priori knowledge on the scatterers geometry, Christelle Eyraud , Jean-Michel Geffrin , Amelie Litman , Jean Pierre Spinelli Radio Science, 2012, 47, pp.RS0E23 Article dans une revue hal-01910294v1
	A large 3D target with small inner details : A diffi cult cocktail for imaging purposes without a-priori knowledge on the scatterers geometry, Christelle Eyraud , Jean-Michel Geffrin , Amelie Litman , Jean Pierre Spinelli Radio Science, 2012, 47, pp.RS0E23 Article dans une revue hal-00938974v1
	Magnetic and electric coherence in forward- and back-scattered electromagnetic waves by a single dielectric subwavelength sphere Jean-Michel Geffrin , B. García-Cámara , R. Gómez-Medina , P. Albella , L.S. Froufe-Pérez Nature Communications, 2012, 3 (1171), pp.3:1171. ⟨10.1038/ncomms2167⟩ Article dans une revue hal-00939074v1
	3D-Aggregate Quantitative Imaging: Experimental Results and Polarization Effects Christelle Eyraud , Jean-Michel Geffrin , Amelie Litman IEEE Transactions on Antennas and Propagation, 2011, 59 (4), pp.1237 - 1244. ⟨10.1109/TAP.2011.2109353⟩ Article dans une revue hal-01910338v1
	A rigorous forest scattering model validation through comparison with indoor bistatic scattering measurements Sami Bellez , Hélène Roussel , Cyril Dahon , Jean-Michel Geffrin Progress In Electromagnetics Research B, 2011, 33, pp.1 - 19. ⟨10.2528/PIERB11063009⟩ Article dans une revue hal-00628199v1
	3D-Aggregate Quantitative Imaging: Experimental Results and Polarization Effects Christelle Eyraud , Jean-Michel Geffrin , Amelie Litman IEEE Transactions on Antennas and Propagation, 2011, 59 (4), pp.1237 - 1244. ⟨10.1109/TAP.2011.2109353⟩ Article dans une revue hal-00583626v1
	Combining spatial support information and shape-based method for tomographic imaging inside a microwave cylindrical scanner Amelie Litman , R. Lencrerot , Jean-Michel Geffrin Inverse Problems in Science and Engineering, 2010, 18 (1), pp.19-34. ⟨10.1080/17415970903233580⟩ Article dans une revue hal-00453662v1
	On the calibration of a multistatic scattering matrix measured by a fixed circular array of antennas Amelie Litman , Jean-Michel Geffrin , Hervé Tortel Progress In Electromagnetics Research (PIER), 2010, 110, pp.1-21. ⟨10.2528/PIER10090302⟩ Article dans une revue hal-00581585v1
	Aperture Antenna Modeling by a Finite Number of Elemental Dipoles From Spherical Field Measurements Mohammed Serhir , Jean-Michel Geffrin , Amelie Litman , Philippe Besnier IEEE Transactions on Antennas and Propagation, 2010, 58 (4), pp.1260-1268. ⟨10.1109/TAP.2010.2041157⟩ Article dans une revue hal-00474447v1
	Microwave measurements of the full amplitude scattering matrix of a complex aggregate: a database for the assessment of light scattering codes Olivier Merchiers , Christelle Eyraud , Jean-Michel Geffrin , Rodolphe Vaillon , Brian Stout Optics Express, 2010, 18 (3), pp.2056-2075. ⟨10.1364/OE.18.002056⟩ Article dans une revue hal-00453661v1
	Imposing Zernike representation for imaging two-dimensional targets R. Lencrerot , Amelie Litman , Hervé Tortel , Jean-Michel Geffrin Inverse Problems, 2009, 25 (3), pp.035012 Article dans une revue hal-00438246v1
	Microwave analog to light scattering measurements on a fully characterized complex aggregate Olivier Merchiers , Jean-Michel Geffrin , Rodolphe Vaillon , Pierre Sabouroux , Bernard Lacroix Applied Physics Letters, 2009, 94 (18), pp.181107 Article dans une revue hal-00437589v1
	Target localization and measured scattered field pre-processing using spectral bandwidth minimization for shallowly buried target problems Christelle Eyraud , Jean-Michel Geffrin , Peter Lewyllie , Ann Franchois , Anthony Dubois Microwave and Optical Technology Letters, 2009, 52 (1), pp.147 - 151. ⟨10.1002/mop.24855⟩ Article dans une revue hal-00438257v1
	A New Value Picking Regularization Strategy-Application to the 3-D Electromagnetic Inverse Scattering Problem Jürgen de Zaeytijd , Ann Franchois , Jean-Michel Geffrin IEEE Transactions on Antennas and Propagation, 2009, 57 (2) (4), pp.1133-1149. ⟨10.1109/TAP.2009.2015823⟩ Article dans une revue hal-00437881v1
	Measurement strategies for a confined microwave circular scanner R. Lencrerot , Amelie Litman , Hervé Tortel , Jean-Michel Geffrin Inverse Problems in Science and Engineering, 2009, 17 (6), pp.787 - 802. ⟨10.1080/17415970802577012⟩ Article dans une revue hal-00438249v1
	Optimization of a Bistatic Microwave Scattering Measurement Setup: From High to Low Scattering Targets Jean-Michel Geffrin , Christelle C. E. Eyraud , Amélie Litman , Pierre Sabouroux Radio Science, 2009, 44 (RS2007), pp.RS2007. ⟨10.1029/2008RS003837⟩ Article dans une revue hal-00355811v1
	Continuing with the Fresnel database: experimental setup and improvements in 3D scattering measurements Jean Michel Jm G Geffrin , Pierre Sabouroux Inverse Problems, 2009, 25 (2), pp.035012. ⟨10.1088/0266-5611/25/2/024001⟩ Article dans une revue hal-00367473v1
	Electromagnetic three-dimensional reconstruction of targets from free space experimental data Jean Michel Jm G Geffrin , Patrick C. Chaumet , Christelle C. E. Eyraud , Kamal Belkebir , Pierre Sabouroux Applied Physics Letters, 2008, 92 (19), pp.194103. ⟨10.1063/1.2924303⟩ Article dans une revue hal-00358300v1
	A single-view imaging strategy for transient scattered fields Ilaria Catapano , Kamal Belkebir , Jean-Michel Geffrin Inverse Problems, 2008, 24 (1), pp.015008 Article dans une revue hal-00438197v1
	Validation of a 3D bistatic microwave scattering measurement setup Christelle C. E. Eyraud , Jean Michel Jm G Geffrin , Pierre Sabouroux , Patrick C. Chaumet , Hervé Tortel Radio Science, 2008, 43, pp.RS4018. ⟨10.1029/2008RS003836⟩ Article dans une revue hal-00348506v1
	The reconstruction of inhomogeneous targets from single view transient data Kamal Belkebir , Ilaria Catapano , Jean-Michel Geffrin Near Surface Geophysics, 2008, 6 (6), pp.381-390 Article dans une revue hal-00437893v1
	Plane Wave and Gaussian Beam Scattering by Long Dielectric Cylinders: 2.5D Simulations versus Measurements Sara van den Bulcke , L. Zhang , Ann Franchois , Jean-Michel Geffrin , J. Steins International Journal of Infrared and Millimeter Waves, 2008, 29 (11), pp.1038-1047. ⟨10.1007/s10762-008-9399-9⟩ Article dans une revue hal-00438200v1
	Full-Wave Three-Dimensional Microwave Imaging With a Regularized Gauss-Newton Method-- Theory and Experiment Jürgen de Zaeytijd , Ann Franchois , Christelle Eyraud , Jean-Michel Geffrin IEEE Transactions on Antennas and Propagation, 2007, 55 (2), pp.3279-3292 Article dans une revue hal-00438194v1
	Amplitude and phase of light scattered by micro-scale aggregates of dielectric spheres: Comparison between theory and microwave analogy experiments Pierre Sabouroux , Brian Stout , Jean-Michel Geffrin , Christelle Eyraud , I. Ayranci Journal of Quantitative Spectroscopy and Radiative Transfer, 2007, 103 (1), pp.156-167. ⟨10.1016/j.jqsrt.2006.06.001⟩ Article dans une revue hal-00453659v1
	Imaging of dielectric cylinders from experimental stepped-frequency data Anthony Dubois , Jean Michel Jm G Geffrin , Kamal Belkebir Applied Physics Letters, 2006, 88, pp 164104-1-3 Article dans une revue hal-00083976v1
	Drift correction for scattering measurements Christelle C. E. Eyraud , Jean Michel Jm G Geffrin , Amélie Litman , Pierre Sabouroux , Hugues Giovannini Applied Physics Letters, 2006, 89, pp.244104. ⟨10.1063/1.2404978⟩ Article dans une revue hal-00120448v1
	free space experimental scattering database continuation: experimental set-up and measurement precision Jean Michel Jm G Geffrin , Pierre Sabouroux , Christelle C. E. Eyraud Inverse Problems, 2005, Vol 21, N 6, pp S117-S130 Article dans une revue hal-00082489v1
	Newton-Kantorovich and modified gradient-inversion algorithms applied to Ipswich data Kamal Belkebir , Jean-Manuel Elissalt , Jean-Michel Geffrin , Christian Pichot IEEE Antennas and Propagation Magazine, 1996, 38 (3), pp. 41-44 Article dans une revue hal-00438193v1

	Gradient and Newton-Kantorovich methods for microwave tomography Christian Pichot , Pierre Lobel , Laure Blanc-Féraud , Michel Barlaud , Kamal Belkebir H.W. Engl, A.K. Louis, W. Rundell. Inverse Problems in Medical Imaging and Nondestructive Testing, Springer-Verlag Publisher (Wien New York), pp.168-187, 1997 Chapitre d'ouvrage hal-00438266v1

	Device for near field and far field imaging in the microwave range Rodolphe Vaillon , Bernard Lacroix , Jean-Michel Geffrin , Mathieu Francoeur United States, Patent n° : US9797847B2. 2017 Brevet hal-01832260v1
	Dispositif d'imagerie en champ proche et lointain dans le domaine des micro-ondes Rodolphe Vaillon , B. Lacroix , Jean-Michel Geffrin , M. Francoeur France, N° de brevet: demande No. 1352803. 2013 Brevet hal-01021881v1

	Analyse expérimentale de la diffusion électromagnétique par des particules complexes via l'analogie micro-ondes Rodolphe Vaillon , Jean-Michel Geffrin , Christelle Eyraud , Olivier Merchiers , Pierre Sabouroux 2011 Autre publication scientifique hal-01023427v1

Jean-Michel Geffrin

Publications

Imaging of the internal structure of an asteroid analogue from quasi-monostatic microwave measurement data I. The frequency domain approach

Imaging of the internal structure of an asteroid analogue from quasi-monostatic microwave measurement data II. The time domain approach

Scattering properties of protoplanetary dust analogs with microwave analogy: Aggregates of fractal dimensions from 1.5 to 2.8

High‐Q Transparency Band in All‐Dielectric Metasurfaces Induced by a Quasi Bound State in the Continuum

Complex-structured 3D-printed wireframes as asteroid analogues for tomographic microwave radar measurements

Full wavefield simulation versus measurement of microwave scattering by a complex 3D-printed asteroid analogue★

Counting and Phase Function Measurements with the LONSCAPE Instrument to Determine Physical Properties of Aerosols in Ice Giant Planet Atmospheres

Influence of the description of the scattering matrix on permittivity reconstruction with a quantitative imaging procedure: polarization effects

Brewster quasi bound states in the continuum in all-dielectric metasurfaces from single magnetic-dipole resonance meta-atoms

Experimental demonstration of spectrally broadband Huygens sources using low-index spheres

Mesure de surface équivalente radar (SER) - Aspect expérimental

Imaging the interior of a comet from bistatic microwave measurements: case of a scale comet model

On the scattering directionality of a dielectric particle dimer of High Refractive Index

Electromagnetic polarization-controlled perfect switching effect with high-refractive-index dimers and the beam-splitter configuration

Microwave analog experiments on optically soft spheroidal scatterers with weak electromagnetic signature

Directional Fano resonances in light scattering by a high refractive index dielectric sphere

Molding acoustic, electromagnetic and water waves with a single cloak

Small Dielectric Spheres with High Refractive Index as New Multifunctional Elements for Optical Devices

Complex Permittivity Determination From Far-Field Scattering Patterns

3-D Imaging of a Microwave Absorber Sample From Microwave Scattered Field Measurements

Evanescent wave scattering by particles on a surface: validation of the discrete dipole approximation with surface interaction against microwave analog experiments

Recent advances in microwave analog to light scattering experiments

Controllable emission of a dipolar source coupled with a magneto-dielectric resonant subwavelength scatterer

Polarization effects in 3D vectorial induced current reconstructions

Les métamatériaux : une solution pour l'ingénierie d'indice complexe

An extended-DORT method and its application in a cavity configuration

A large 3D target with small inner details : A difficult cocktail for imaging purposes without a-priori knowledge on the scatterers geometry,

A large 3D target with small inner details : A diffi cult cocktail for imaging purposes without a-priori knowledge on the scatterers geometry,

Magnetic and electric coherence in forward- and back-scattered electromagnetic waves by a single dielectric subwavelength sphere

3D-Aggregate Quantitative Imaging: Experimental Results and Polarization Effects

A rigorous forest scattering model validation through comparison with indoor bistatic scattering measurements

3D-Aggregate Quantitative Imaging: Experimental Results and Polarization Effects

Combining spatial support information and shape-based method for tomographic imaging inside a microwave cylindrical scanner

On the calibration of a multistatic scattering matrix measured by a fixed circular array of antennas

Aperture Antenna Modeling by a Finite Number of Elemental Dipoles From Spherical Field Measurements

Microwave measurements of the full amplitude scattering matrix of a complex aggregate: a database for the assessment of light scattering codes

Imposing Zernike representation for imaging two-dimensional targets

Microwave analog to light scattering measurements on a fully characterized complex aggregate

Target localization and measured scattered field pre-processing using spectral bandwidth minimization for shallowly buried target problems

A New Value Picking Regularization Strategy-Application to the 3-D Electromagnetic Inverse Scattering Problem

Measurement strategies for a confined microwave circular scanner

Optimization of a Bistatic Microwave Scattering Measurement Setup: From High to Low Scattering Targets

Continuing with the Fresnel database: experimental setup and improvements in 3D scattering measurements

Electromagnetic three-dimensional reconstruction of targets from free space experimental data

A single-view imaging strategy for transient scattered fields

Validation of a 3D bistatic microwave scattering measurement setup

The reconstruction of inhomogeneous targets from single view transient data

Plane Wave and Gaussian Beam Scattering by Long Dielectric Cylinders: 2.5D Simulations versus Measurements

Full-Wave Three-Dimensional Microwave Imaging With a Regularized Gauss-Newton Method-- Theory and Experiment

Amplitude and phase of light scattered by micro-scale aggregates of dielectric spheres: Comparison between theory and microwave analogy experiments

Imaging of dielectric cylinders from experimental stepped-frequency data

Drift correction for scattering measurements

free space experimental scattering database continuation: experimental set-up and measurement precision

Newton-Kantorovich and modified gradient-inversion algorithms applied to Ipswich data

Gradient and Newton-Kantorovich methods for microwave tomography

Device for near field and far field imaging in the microwave range

Dispositif d'imagerie en champ proche et lointain dans le domaine des micro-ondes

Analyse expérimentale de la diffusion électromagnétique par des particules complexes via l'analogie micro-ondes