Source: https://www.institut-langevin.espci.fr/journal_articles_2009?lang=fr
Timestamp: 2019-04-20 06:12:15+00:00

Document:
In vivo performance evaluation of bi-directional ultrasonic axial transmission for cortical bone assessment.
Talmant, M., Kolta. S, C. Roux, D. Haguenauer, I. Vedel, B. Cassou, E. Bossy, and P. Laugier.
Ultrasound in Medicine and Biology 35, no. 6 (2009): 912–919.
Résumé: Our objective was to assess a new quantitative ultrasound device suitable for the measurement of speed of sound in radius. The so-called “bidirectional” technique allows an accurate estimation of velocity based on a compensation for soft tissue effects implemented directly inside the probe. Velocity measurements at 1 MHz of the first arriving signal were performed at the one third distal radius in 358 enrolled women. The average velocity by age decade increases to a peak velocity of 4043 m/s in the class 30–39 y (n = 19) and decreases thereafter. Fracture discrimination was investigated on the subset of the population for which dual-energy x-ray absorptiometry measurement was available, in addition to first arriving signal velocity measurements. The study group consisted of 122 postmenopausal women without history of fracture (group NF) and 44 postmenopausal patients (group F) with osteoporotic fractures (hip, spine, Colles fracture). When adjusted for age and bone mass index, the odds ratio (OR) for fracture prediction by ultrasound velocity, was 1.81 (1.21; 2.70) and OR associated to neck femur BMD was 2.07 (1.31–3.29). For the full model including age and body mass index as cofactors, the area under the receiver operating characteristic curve was 0.77, either for ultrasound velocity or neck femur bone mineral density. Despite the small population and the variety of fractures in the fracture group, our data indicate that the velocity of the first arriving signal measured by bidirectional technique discriminates patients with osteoporotic fracture from controls.
Detection and discrimination of optical absorption and shear stiffness at depth in tissue-mimicking phantoms by transient optoelastography.
Daoudi, K., A. - C. Boccara, and E. Bossy.
Applied Physics Letters 94, no. 15 (2009): 154103.
Résumé: This work investigates the ability of transient optoelastography to detect both shear stiffness contrasts and optical absorption contrasts embedded deep in tissuelike media. The technique consists of a camera-based optical detection scheme designed to detect selectively the transient shear motion created at depth by the acoustic radiation force in optically turbid media. It is demonstrated on tissue-mimicking phantoms that transient optoelastography is not only sensitive to both optical absorption and shear stiffness contrasts, but also provides discrimination between these two types of contrasts. © 2009 American Institute of Physics.
Photoacoustic guidance of high intensity focused ultrasound with selective optical contrasts and time-reversal.
Funke, A. R., J. - F. Aubry, M. Fink, A. - C. Boccara, and E. Bossy.
Applied Physics Letters 94, no. 5 (2009): 054102.
Résumé: The authors present a method of focusing high intensity ultrasound by time-reversing the photoacoustic response of an optically selective target in a nonselective background. The target's photoacoustic response was isolated from the background by subtracting the photoacoustic waveforms obtained at different optical wavelengths and convolved with a continuous signal. It was found that the focus produced was comparable in quality to that obtained by delay-law beam-forming. The method holds the promise of allowing precise targeting of high intensity focused ultrasound on nonechogenic targets, in moving environments, independently of the presence of aberrating layers. © 2009 American Institute of Physics.
Fringe-free holographic measurements of large-amplitude vibrations.
Joud, F., F. Verpillat, F. Laloë, M. Atlan, J. Hare, and M. Gross.
Optics Letters 34, no. 23 (2009): 3698–3700.
Résumé: In the measurement of the amplitude of vibration of objects, holographic imaging techniques usually involve fringe counting; because of the limited resolution of the images, measurements of large amplitudes are not accessible. We demonstrate a technique that suppresses the necessity of fringe counting-frequency sideband imaging-where the order of the sideband is considered a marker of the amplitude. The measurement is completely local: no comparison with another reference point on the object is necessary. It involves a sharp variation of a signal, which makes it robust against perturbations. The method is demonstrated in an experiment made with a vibrating clarinet reed; phase modulations as large as 1000 rad have been measured. © 2009 Optical Society of America.
High-resolution quantitative imaging of cornea elasticity using supersonic shear imaging.
Tanter, M., D. Touboul, J. - L. Gennisson, J. Bercoff, and M. Fink.
IEEE Transactions on Medical Imaging 28, no. 12 (2009): 1881–1893.
Résumé: The noninvasive estimation of in vivo mechanical properties of cornea is envisioned to find several applications in ophthalmology. Such high-resolution measurements of local cornea stiffness could lead to a better anticipation and understanding of corneal pathologies such as Keratoconus. It could also provide a quantitative evaluation of corneal biomechanical response after corneal refractive surgeries and a tool for evaluating the efficacy of new cornea treatments such as cornea transplant using femtosecond laser or therapy based on Riboflavin/UltraViolet-A Corneal Cross Linking (UVA CXL). In the very important issue of glaucoma diagnosis and management, the fine tuning corneal elasticity measurement could also succeed to strongly correlate the applanation tonometry with the true intra-ocular pressure (IOP). This initial investigation evaluates the ability of ultrafast and high-resolution ultrasonic systems to provide a real-time and quantitative mapping of corneal viscoelasticity. Quantitative elasticity maps were acquired ex vivo on porcine cornea using the supersonic shear imaging (SSI) technique. A conventional 15 MHz linear probe was used to perform conventional ultrasonic imaging of the cornea. A dedicated ultrasonic sequence combines the generation of a remote palpation in the cornea and ultrafast (20000 frames/s) ultrasonic imaging of the resulting corneal displacements that evolve into a shear wave propagation whose local speed was directly linked to local elasticity. A quantitative high-resolution map (150 mum resolution) of local corneal elasticity can be provided by this dedicated sequence of ultrasonic insonifications. Quantitative maps of corneal elasticity were obtained on ex vivo freshly enucleated porcine corneas. In the cornea, a quite homogenous stiffness map was found with a 190 kPa +/-32 kPa mean elasticity. The influence of photodynamic Riboflavin/UVA induced CXL was measured. A significant Young's modulus increase was obtained with a mean 890 kPa +/-250 kPsa posttreatment Young's modulus (460% increase), located in the anterior part of the cornea. Simulations based on 3-D time domain finite differences simulation were also performed and found to be in good agreement with ex vivo experiments. The SSI technique can perform real-time, noninvasive, high-resolution, and quantitative maps of the whole corneal elasticity. This technique could be real time and straightforward adapted for a very wide field of in vivo investigations. © 2006 IEEE.
1-D elasticity assessment in soft solids from shear wave correlation: The time-reversal approach.
Benech, N., S. Catheline, J. Brum, T. Gallot, and C. A. Negreira.
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 56, no. 11 (2009): 2400–2410.
Résumé: One-channel time-reversal (TR) experiments allow focalization of waves in reverberant cavities. According to the Rayleigh criterion, the focal spot width is directly related to the wavelength and therefore depends on the mechanical properties of the medium. Thus, the general idea of this work is to extract quantitative estimations of these mechanical properties using a time-reversal approach based on cross-correlations of the wave field. An external source creates mechanical waves in the audible frequency range. One component of the vectorial field is measured along a line as function of time with signal processing developed in the field of 1-D elastography. The shear wavelength information is deduced from these mechanical waves using spatiotemporal correlations and interpreted in the frame of the time-reversal symmetry. The impact of wave attenuation in soft solids is reduced using a spatial average of the correlation field. The result is shown to be suitable for global elasticity estimation. The advantage is that the technique is almost independent of the source kind, shape, and time excitation function. This robustness as regard to shear wave source allows translation of this technique to applications in the medical field, including deep or moving organs. © 2009 IEEE.
Decomposition theorems and fine estimates for electrical fields in the presence of closely located circular inclusions.
Ammari, H., H. Kang, H. Lee, M. Lim, and H. Zribi.
Journal of Differential Equations 247, no. 11 (2009): 2897–2912.
Résumé: When two inclusions get closer and their conductivities degenerate to zero or infinity, the gradient of the solution to the conductivity equation blows up in general. In this paper, we show that the solution to the conductivity equation can be decomposed into two parts in an explicit form: one of them has a bounded gradient and the gradient of the other part blows up. Using the decomposition, we derive the best possible estimates for the blow-up of the gradient. We then consider the case when the inclusions have positive permittivities. We show quantitatively that in this case the size of the blow-up is reduced. © 2009 Elsevier Inc. All rights reserved.
Reflection and transmission at low concentration by a depth-varying random distribution of cylinders in a fluid slab-like region.
Conoir, J. M., S. Robert, A. El Mouhtadi, and F. Luppé.
Wave Motion 46, no. 8 (2009): 522–538.
Résumé: This paper deals with multiple scattering by a random arrangement of parallel circular elastic cylinders immersed in a fluid. The cylinders are distributed in a region called “slab” that is located between two parallel planes orthogonal to a given x-direction. The disorder inside the slab depends on the x-variable. The goal is to calculate the reflection and transmission coefficients by this space-varying slab. For low concentrations of cylinders, two methods are developed from Twersky's theory on the propagation of coherent waves in an effective medium. The first method is based upon the discretization of the properties of the space-varying slab. The second one is based on the WKB method. They are successfully compared in the case of a smooth space-varying slab in which the random distribution of cylinders varies slowly along the x-direction. An effective mass density is defined, which allows the derivation of the mean acoustic displacement from the mean pressure field. The continuity of both pressure and normal displacement is thus shown at the interface between two different effective media as well as at the interface between the space-varying slab and a homogeneous fluid. © 2009 Elsevier B.V. All rights reserved.
Enhanced resolution in structured media.
Ammari, H., E. Bonnetier, and Y. Capdeboscq.
SIAM Journal on Applied Mathematics 70, no. 5 (2009): 1428–1452.
Résumé: The aim of this paper is to prove that we can achieve a resolution enhancement in detecting a target inclusion if it is surrounded by an appropriate structured medium. The physical notions of resolution and focal spot are revisited. Indeed, the resolution enhancement is estimated in terms of the material parameters of the structured medium. © by SIAM.
Incidence dependence of negative index in asymmetric cut wire pairs metamaterials.
Burokur, S. N., T. Lepetit, and A. D. Lustrac.
Applied Physics Letters 95, no. 19 (2009).
Résumé: Metamaterials made of asymmetric cut wire pairs have experimentally demonstrated a negative refractive index at microwave frequencies. In this letter, we begin by presenting the analogy between asymmetric cut wire pairs and S-shaped metamaterials by a simple unifying approach. Then, using simulations and experiments in the microwave domain, we investigate the dependence of resonances and retrieved effective index on the incident angle in asymmetric cut wire pairs. While it is found that resonances shift in frequency with increasing oblique incidence in the E-plane, it is shown that the structure is angle-independent in the H-plane. © 2009 American Institute of Physics.
Non-invasive transcranial ultrasound therapy based on a 3D CT scan: Protocol validation and in vitro results.
Marquet, F., M. Pernot, J. - F. Aubry, G. Montaldo, L. Marsac, M. Tanter, and M. Fink.
Physics in Medicine and Biology 54, no. 9 (2009): 2597–2613.
Résumé: A non-invasive protocol for transcranial brain tissue ablation with ultrasound is studied and validated in vitro. The skull induces strong aberrations both in phase and in amplitude, resulting in a severe degradation of the beam shape. Adaptive corrections of the distortions induced by the skull bone are performed using a previous 3D computational tomography scan acquisition (CT) of the skull bone structure. These CT scan data are used as entry parameters in a FDTD (finite differences time domain) simulation of the full wave propagation equation. A numerical computation is used to deduce the impulse response relating the targeted location and the ultrasound therapeutic array, thus providing a virtual time-reversal mirror. This impulse response is then time-reversed and transmitted experimentally by a therapeutic array positioned exactly in the same referential frame as the one used during CT scan acquisitions. In vitro experiments are conducted on monkey and human skull specimens using an array of 300 transmit elements working at a central frequency of 1 MHz. These experiments show a precise refocusing of the ultrasonic beam at the targeted location with a positioning error lower than 0.7 mm. The complete validation of this transcranial adaptive focusing procedure paves the way to in vivo animal and human transcranial HIFU investigations. © 2009 Institute of Physics and Engineering in Medicine.
Space-time resolved wave turbulence in a vibrating plate.
Cobelli, P., P. Petitjeans, A. Maurel, V. Pagneux, and N. Mordant.
Physical Review Letters 103, no. 20 (2009).
Résumé: Wave turbulence in a thin elastic plate is experimentally investigated. By using a Fourier transform profilometry technique, the deformation field of the plate surface is measured simultaneously in time and space. This enables us to compute the wave-vector-frequency (k, ω) Fourier spectrum of the full space-time deformation velocity. In the 3D (k, ω) space, we show that the energy of the motion is concentrated on a 2D surface that represents a nonlinear dispersion relation. This nonlinear dispersion relation is close to the linear dispersion relation. This validates the usual wave-number-frequency change of variables used in many experimental studies of wave turbulence. The deviation from the linear dispersion, which increases with the input power of the forcing, is attributed to weak nonlinear effects. Our technique opens the way for many new extensive quantitative comparisons between theory and experiments of wave turbulence. © 2009 The American Physical Society.
Application of DENSE-MR-elastography to the human heart.
Robert, B., R. Sinkus, J. - L. Gennisson, and M. Fink.
Magnetic Resonance in Medicine 62, no. 5 (2009): 1155–1163.
Résumé: Typically, MR-elastography (MRE) encodes the propagation of monochromatic acoustic waves in the MR-phase images via sinusoidal gradients characterized by a detection frequency equal to the frequency of the mechanical vibration. Therefore, the echo time of a conventional MRE sequence is typically longer than the vibration period which is critical for heart tissue exhibiting a short T 2. Thus, fast acquisition techniques like the so-called fractional encoding of harmonic motions were developed for cardiac applications. However, fractional encoding of harmonic motions is limited since it is two orders of magnitude less sensitive to motion than conventional MRE sequences for low-frequency vibrations. Here, a new sequence is derived from the so-called displacement encoding with stimulated echoes (DENSE) sequence. This sequence is more sensitive to displacement than fractional encoding of harmonic motions, and its spectral specificity is equivalent to conventional MRE sequences. The theoretical spectral properties of this new motion-encoding technique are validated in a phantom and excised pork heart specimen. An excellent agreement is found for the measured displacement fields using classic MRE and displacement encoding with stimulated echoes MRE (8% maximum difference). In addition, initial in vivo results on a healthy volunteer clearly show propagating shear waves at 50 Hz. Thus, displacement encoding with stimulated echoes MRE is a promising technique for motion encoding within short T 2* materials. © 2009 Wiley-Liss, Inc.
Ultrafast Imaging of Ultrasound Contrast Agents.
Couture, O., S. Bannouf, G. Montaldo, J. - F. Aubry, M. Fink, and M. Tanter.
Ultrasound in Medicine and Biology 35, no. 11 (2009): 1908–1916.
Résumé: The disappearance of ultrasound contrast agents after disruption can provide useful information on their environment. However, in vivo acoustical imaging of this transient phenomenon, which has a duration on the order of milliseconds, requires high frame rates that are unattainable by conventional ultrasound scanners. In this article, ultrafast imaging is applied to microbubble tracking using a 128-element linear array and an elastography scanner. Contrast agents flowing in a wall-less tissue phantom are insonified with a high-intensity disruption pulse followed by a series of plane waves emitted at a 5 kHz PRF. A collection of compounded images depicting the evolution of microbubbles is obtained after the echoes are beamformed in silico. The backscattering of the microbubbles appears to increase in the first image after disruption (4 ms) and decrease following an exponential decay in the next hundred milliseconds. This microbubble dynamic depends on the length and amplitude of the high-intensity pulse. Furthermore, confined microbubbles are found to differ significantly from their free-flowing counterparts in their dissolution curves. The high temporal resolution provided by ultrafast imaging could help distinguish targeted microbubbles during molecular imaging. (E-mail: ). © 2009 World Federation for Ultrasound in Medicine & Biology.
Metamaterial-based phased array for directional beam steering.
Ourir, A., and A. De Lustrac.
Microwave and Optical Technology Letters 51, no. 11 (2009): 2653–2656.
Résumé: Ultracompact metamaterial-based cavity (thickness X/15) is proposed to realize a low secondary lobes level and highly directive phased array antenna. The cavity is fed by an array of four patch antennas designed to operate at around 9.5 GHz. The radiation patterns of the phased arrays are compared with those of their respective metamaterial-based cavity antennas. The latter structures have lower secondary lobes and provide higher gain and directivity. Moreover, the cavities enhance the beam steering of the phased arrays. © 2009 Wiley Periodicals, Inc.
Energy-based adaptive focusing of waves: application to noninvasive aberration correction of ultrasonic wavefields.
Herbert, E., M. Pernot, G. Montaldo, M. Fink, and M. Tanter.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control 56, no. 11 (2009): 2388–2399.
Résumé: An aberration correction method based on the maximization of the wave intensity at the focus of an emitting array is presented. The potential of this new adaptive focusing technique is investigated for ultrasonic focusing in biological tissues. The acoustic intensity is maximized noninvasively through direct measurement or indirect estimation of the beam energy at the focus for a series of spatially coded emissions. For ultrasonic waves, the acoustic energy at the desired focus can be indirectly estimated from the local displacements induced in tissues by the ultrasonic radiation force of the beam. Based on the measurement of these displacements, this method allows determination of the precise estimation of the phase and amplitude aberrations, and consequently the correction of aberrations along the beam travel path. The proof of concept is first performed experimentally using a large therapeutic array with strong electronic phase aberrations (up to 2pi). Displacements induced by the ultrasonic radiation force at the desired focus are indirectly estimated using the time shift of backscattered echoes recorded on the array. The phase estimation is deduced accurately using a direct inversion algorithm which reduces the standard deviation of the phase distribution from sigma = 1.89 radian before correction to sigma = 0.53 radian following correction. The corrected beam focusing quality is verified using a needle hydrophone. The peak intensity obtained through the aberrator is found to be -7.69 dB below the reference intensity obtained without any aberration. Using the phase correction, a sharp focus is restored through the aberrator with a relative peak intensity of -0.89 dB. The technique is tested experimentally using a linear transmit/receive array through a real aberrating layer. The array is used to automatically correct its beam quality, as it both generates the radiation force with coded excitations and indirectly estimates the acoustic intensity at the focus with speckle tracking. This technique could have important implications in the field of high-intensity focused ultrasound even in complex configurations such as transcranial, transcostal, or deep seated organs.
Archimedean lattices in the bound states of wave interacting particles.
Eddi, A., A. Decelle, E. Fort, and Y. Couder.
EPL 87, no. 5 (2009).
Résumé: The possible periodic arrangements of droplets bouncing on the surface of a vibrated liquid are investigated. Because of the nature of the interaction through waves, the possible distance of binding of nearest neighbors is multi-valued. For large amplitude of the forcing, the bouncing becomes sub-harmonic and the droplets can have two different phases. This effect increases the possible distances of binding and the formation of various polygonal clusters is observed. From these elements it is possible to assemble crystalline structures related to the Archimedean tilings of the plane, the periodic tesselations which tile uniformly the 2D plane with convex polygons. Eight of the eleven possible configurations are observed. They are stabilized by the coupling of two sub-lattices of droplets of different phase, both contributing to sustain a common wave field. © 2009 Europhysics Letters Association.
Reply to “comment on 'Interaction of a surface wave with a dislocation'”.
Physical Review B – Condensed Matter and Materials Physics 80, no. 13 (2009).
Résumé: A subsurface moving dislocation in an elastic half space generates vertical displacements at the free surface. We compare this displacement for two different values of the dislocation viscous drag coefficient. The different resulting surface patterns suggest the free surface plays a decisive dynamical effect. We thus compare this displacement, using the dynamic Green function for an elastic half space, with the result of the calculation using the static Green function for an infinite space, as in the work of Zolotoyabko and Shilo [preceding paper, Phys. Rev. B 80, 136101 (2009), and Shilo and Zolotoyabko, Phys. Rev. Lett. 91, 115506 (2003)] when the dislocation dynamics is the same. Considering the static Green function of an infinite space instead of the correct dynamic Green function of the half space leads to an underestimation of the resulting displacement at the free surface by a factor up to 50 for dislocation depths smaller than one Rayleigh wavelength λR. We also discuss the constraints that recent ultrasound attenuation and resonant ultrasound spectroscopy experiments place on dislocation parameters, such as density and viscous drag coefficient. © 2009 The American Physical Society.
Experimental observation of trapped modes in a water wave channel.
Cobelli, P. J., V. Pagneux, A. Maurel, and P. Petitjeans.
Europhysics Letters 88, no. 2 (2009).
Résumé: The fluid around a free surface piercing circular cylinder in a long narrow wave tank can exhibit a local oscillation that does not propagate down the channel but is confined to the vicinity of the cylinder. This is a manifestation of the so-called trapped modes, bound states in the continuum occurring in many situations in physics. In this letter, using Fourier Transform Profilometry, fully space time resolved measurements for the free surface deformation are obtained. The scattering characteristics of the cylinder and consequently the behavior of the trapped-mode frequency are determined. Copyright © EPLA, 2009.
Acousto-optical coherence tomography using random phase jumps on ultrasound and light.
Lesaffre, M., S. Farahi, M. Gross, P. Delaye, A. C. Boccara, and F. Ramaz.
Optics Express 17, no. 20 (2009): 18211–18218.
Résumé: Imaging objects embedded within highly scattering media by coupling light and ultrasounds (US) is a challenging approach. In deed, US enable direct access to the spatial localization, though resolution can be poor along their axis (cm). Up to now, several configurations have been studied, giving a millimetric axial resolution by applying to the US a microsecond pulse regime, as is the case with conventional echography. We introduce a new approach called Acousto-Optical Coherence Tomography (AOCT), enabling us to get a millimetric resolution with continuous US and light beams by applying random phase jumps on US and light. An experimental demonstration is performed with a self-adaptive holographic setup containing a photorefractive GaAs bulk crystal and a single large area photodetector. © 2009 Optical Society of America.
Interaction between elastic waves and prismatic dislocation loops.
Rodríguez, N., A. Maurel, V. Pagneux, F. Barra, and F. Lund.
Journal of Applied Physics 106, no. 5 (2009).
Résumé: The properties of prismatic dislocation loops, generated by radiation in metals, have remained elusive for decades, and recent advances in computational capabilities as well as transmission electron microscopy have renewed interest in their study. Acoustic and elastic waves could become an interesting, nonintrusive, probe to this end, as they have for other dislocation configurations. What then are the characteristics of elastic wave scattering that would be sensitive to a prismatic loop signature? In this paper, we report the scattering cross section for an elastic wave by a prismatic dislocation loop. It differs in significant ways from the analog quantity in the case of pinned dislocation segments, the most significant being the polarization of the scattered wave. The properties of a coherent wave traveling through an elastic medium filled with randomly placed and randomly oriented such loops are also reported. At long wavelengths, the effective wave velocity and attenuation coefficients resemble those for a similar case with pinned dislocation segments. © 2009 American Institute of Physics.
Angle resolved Mueller polarimetry with a high numerical aperture and characterization of transparent biaxial samples.
Ibrahim, B. H., S. B. Hatit, and A. De Martino.
Applied Optics 48, no. 27 (2009): 5025–5034.
Résumé: We present a polarimetric instrument suitable for the simultaneous measurement of angle resolved normalized Mueller matrices for polar angles ranging from 0° to 60° and all azimuths. The polarimetric modulation and analysis are performed by means of an optimized polarization state generator and analyzer based on nematic liquid crystals. A high numerical aperture (0.95) microscope objective is used in double pass to illuminate the sample, with its rear focal plane imaged on a low noise CCD. This polarimeter can be used either in reflection, with the sample set in the objective front focal plane, or in transmission, for thin transparent samples. This latter configuration, which involves an additional spherical mirror with its center of curvature at the objective front focus, is described in detail. This instrument was used to accurately determine the directions of the optic axes and the angular dependence of the retardation of a biaxial polyethylene terephthalate (PET) plastic substrate in spite of the strong depolarization essentially due to the source 10nm spectral width or the limitation in angular resolution due to the pixels distribution of the CCD combined with the sample large retardation. © 2009 OpticalSociety of America.
Metallic films and nanostructures for molecular fluorescence enhancement.
Le Moal, E., E. Fort, and S. Lévêque-Fort.
Actualite Chimique, no. 332 (2009): 36–44.
Résumé: Molecule fluorescence is subject to the influence of its direct electromagnetic environment. Excitation and emission processes can be modified by the presence of a metallic structure, due to interference phenomena and coupling to surface plasmon modes. Metallic films ranging in morphology from nanoparticles to percolated, continuous, plane and rough films were designed and characterized. Their influence on the optical behaviour of the fluorophores was investigated by experiments and a theoretical model, as a function of fluorophore-to-metal distance and molecular orientation. The detected signal is found to be amplified by one to two orders of magnitude. Moreover, fluorophore photostabilization and the modification of intermolecular energy transfer processes are reported. This paper demonstrates the interest in this technology for sensitivity improvement of DNA chip and for applications in cell and tissue imaging.
Ultrasound as a probe of plasticity? the interaction of elastic waves with dislocations.
International Journal of Bifurcation and Chaos 19, no. 8 (2009): 2765–2781.
Résumé: An overview of recent work on the interaction of elastic waves with dislocations is given. The perspective is provided by the wish to develop nonintrusive tools to probe plastic behavior in materials. For simplicity, ideas and methods are first worked out in two dimensions, and the results in three dimensions are then described. These results explain a number of recent, hitherto unexplained, experimental findings. The latter include the frequency dependence of ultrasound attenuation in copper, the visualization of the scattering of surface elastic waves by isolated dislocations in LiNbO 3, and the ratio of longitudinal to transverse wave attenuation in a number of materials. Specific results reviewed include the scattering amplitude for the scattering of an elastic wave by a screw, as well as an edge, dislocation in two dimensions, the scattering amplitudes for an elastic wave by a pinned dislocation segment in an infinite elastic medium, and the wave scattering by a sub-surface dislocation in a semi-infinite medium. Also, using a multiple scattering formalism, expressions are given for the attenuation coefficient and the effective speed for coherent wave propagation in the cases of anti-plane waves propagating in a medium filled with many, randomly placed screw dislocations; in-plane waves in a medium similarly filled with randomly placed edge dislocations with randomly oriented Burgers vectors; elastic waves in a three-dimensional medium filled with randomly placed and oriented dislocation line segments, also with randomly oriented Burgers vectors; and elastic waves in a model three-dimensional polycrystal, with only low angle grain boundaries modeled as arrays of dislocation line segments. © 2009 World Scientific Publishing Company.
Magnetic resonance elastography in the liver at 3 Tesla using a second harmonic approach.
Herzka, D. A., M. S. Kotys, R. Sinkus, R. I. Pettigrew, and A. M. Gharib.
Magnetic Resonance in Medicine 62, no. 2 (2009): 284–291.
Résumé: Magnetic resonance elastography (MRE) using mechanical stimulation has demonstrated diagnostic value and clinical promise in breast, liver, and kidney at 1.5 Tesla (T). However, MRE at 1.5T suffers from long imaging times and would benefit from greater signal-to-noise for more robust postprocessing. We present an MRE sequence modified for liver imaging at 3.0T. To avoid artifacts in the phase images, the sequence maintains a short TE by using a second harmonic approach, including stronger motion encoding gradients, shorter radio frequency pulses and an echo-planar readout. Scan time was decreased by a factor of ∼2 relative to 1.5T by using an EPI readout and a higher density sampling of the phase waveform was used to calculate shear stiffness and viscosity. Localized (small region of interest) and global (whole-liver region of interest) measurements in normal healthy subjects compared very favorably with previously published results at 1.5T. There was no significant difference between global and localized measures. © 2009 Wiley-Liss, Inc.
Nanoroughened plasmonic films for enhanced biosensing detection.
Le Moal, E., S. Leveque-Fort, M. - C. Potier, and E. Fort.
Nanotechnology 20, no. 22 (2009).
Résumé: Although fluorescence is the prevailing labeling technique in biosensing applications, sensitivity improvement is still a striving challenge. We show that coating standard microscope slides with nanoroughened silver films provides a high fluorescence signal enhancement due to plasmonic interactions. As a proof of concept, we applied these films with tailored plasmonic properties to DNA microarrays. Using common optical scanning devices, we achieved signal amplifications of more than 40-fold. © 2009 IOP Publishing Ltd.
Unpredictable tunneling of a classical wave-particle association.
Eddi, A., E. Fort, F. Moisy, and Y. Couder.
Physical Review Letters 102, no. 24 (2009).
Résumé: A droplet bouncing on a vibrated bath becomes a “walker” moving at constant velocity on the interface when it couples to the surface wave it generates. Here the motion of a walker is investigated when it collides with barriers of various thicknesses. Surprisingly, it undergoes a form of tunneling: the reflection or transmission of a given incident walker is unpredictable. However, the crossing probability decreases exponentially with increasing barrier width. This shows that this wave-particle association has a nonlocality sufficient to generate a quantumlike tunneling at a macroscopic scale. © 2009 The American Physical Society.
Exact space symmetry of electron states in lattices under a magnetic field.
Physica Status Solidi (B) Basic Research 246, no. 6 (2009): 1248–1251.
Résumé: We previously established the transformations (including the gauge transformations) induced within the electron Hamiltonian by the point- and space-symmetry operations of three-and low-periodic lattices under a uniform magnetic field [P. Tronc and V. P. Smirnov, Phys. Status Solidi B 244, 2010 (2007)]. We also determined the full symmetry group of electron eigenfunctions by taking into account the electron confinement in tubes whose axes are parallel to the magnetic field direction. The confinement is known from experiments with semiconductors. From the symmetry point of view, the confinement implies a lack of translational symmetry in the directions that are not parallel to the field. A theoretical proof is given here for the lack of translational symmetry in any lattice and the relation between the electron-Hamiltonian symmetry group and the eigenfunction symmetry group is provided. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Mathematical models and reconstruction methods in magneto-acoustic imaging.
Ammari, H., Y. Capdeboscq, H. Kang, and A. Kozhemyak.
European Journal of Applied Mathematics 20, no. 3 (2009): 303–317.
Résumé: In this paper, we provide the mathematical basis for three different magneto-acoustic imaging approaches (vibration potential tomography, magneto-acoustic tomography with magnetic induction and magneto-acoustic current imaging) and propose new algorithms for solving the inverse problem for each of them. © 2009 Copyright University Press.
Assessment of muscle hardness changes induced by a submaximal fatiguing isometric contraction.
Nordez, A., A. Guével, P. Casari, S. Catheline, and C. Cornu.
Journal of Electromyography and Kinesiology 19, no. 3 (2009): 484–491.
Résumé: Transient elastography consists of measuring the transverse local shear elastic modulus defined as local muscle hardness (LMH). It has previously been shown that LMH is correlated to muscle activity level during non-fatiguing contractions. The aim of this study was to describe how LMH and muscle activity level change during a submaximal fatiguing constant-torque protocol. Changes in gastrocnemius medialis LMH and in surface electromyographic activities (sEMG) of plantar flexors induced by a submaximal isometric plantar flexion (40% of the maximal isometric torque) until exhaustion were quantified. During the contraction, sEMG of each muscle increased (P < 0.001) whereas LMH remained constant (P > 0.05). Active LMH assessed during the contraction did not parallel muscle activity level changes during this type of submaximal fatigue protocol. Interestingly, LMH at rest assessed in passive conditions was higher prior to the fatiguing effort (P < 0.05), rather than that assessed immediately after. Muscle and tendon viscous behaviors could imply a creep phenomenon during a prolonged isometric contraction, and our results in LMH at rest could indicate that this phenomenon induces changes in muscle intrinsic mechanical properties. Further studies are needed to examine whether it could have an influence on muscle activity levels during the contraction. © 2007 Elsevier Ltd. All rights reserved.
Global measurement of water waves by Fourier transform profilometry.
Cobelli, P. J., A. Maurel, V. Pagneux, and P. Petitjeans.
Experiments in Fluids 46, no. 6 (2009): 1037–1047.
Résumé: In this paper, we present an optical profilometric technique that allows for single-shot global measurement of free-surface deformations. This system consists of a high-resolution system composed of a videoprojector and a digital camera. A fringe pattern of known characteristics is projected onto the free surface and its image is registered by the camera. The deformed fringe pattern arising from the surface deformations is later compared to the undeformed (reference) one, leading to a phase map from which the free surface can be reconstructed. Particularly, we are able to project wavelength-controlled sinusoidal fringe patterns, which considerably increase the overall performance of the technique and the quality of the reconstruction compared to that obtained with a Ronchi grating. In comparison to other profilometric techniques, it allows for single-shot non-intrusive measurement of surface deformations over large areas. In particular, our measurement system and analysis technique is able to measure free surface deformations with sharp slopes up to 10 with a 0.2 mm vertical resolution over an interrogation window of size 450 × 300 mm2 sampled on approximately 6.1 × 106 measurement points. Some illustrative examples of the application of this measuring system to fluid dynamics problems are presented. © 2009 Springer-Verlag.
Charge redistribution in electrochemically actuated mechanical sensors.
Amiot, F., F. Kanoufi, F. Hild, and J. P. Roger.
Sensors and Actuators, A: Physical 152, no. 1 (2009): 88–95.
Résumé: Many proofs of concept studies have established the mechanical sensitivity of functionalized microcantilevers to a large spectrum of target molecules. However, moving to real-life applications also requires the monitored mechanical effect to be highly specific. Moving towards more specificity in cantilever-based sensing, monitoring the mechanical response of electrochemically actuated microcantilevers is then thought to provide a fast, reliable and complementary experimental information to the long-time cantilever bending measurement for the detection of target molecules. Full-field measurements are therefore used to investigate the way the electro-elastic coupling is altered when a microcantilever undergoes decane-thiol adsorption. The proposed technique reveals that the latter results in a charge density redistribution along the cantilever in addition to the local surface passivation. Focusing on the cantilever tip displacement under electrochemical actuation, this redistribution partially compensates the electro-elastic coupling alteration due to the surface passivation, therefore possibly yielding an ambiguous detection result. This effect should be taken into account for the optimal design of specific electrochemically actuated mechanical sensors. © 2009 Elsevier B.V. All rights reserved.
Vibration testing for anomaly detection.
Amman, H., H. Kang, E. Kim, and H. Lee.
Mathematical Methods in the Applied Sciences 32, no. 7 (2009): 863–874.
Résumé: In this paper we propose an efficient method to reconstruct a small inclusion buried inside a body using the perturbation of modal parameters measured on the boundary of the body. We design a reconstruction algorithm based on the asymptotic expansions of the eigenvalue perturbations obtained by Ammari and Moskow (Math. Meth. Appl. Sci. 2003; 26:67-75). We then implement this algorithm and demonstrate its viability and limitations. © 2008 John Wiley.
Defocus test and defocus correction in full-field optical coherence tomography.
Labiau, S., G. David, S. Gigan, and A. C. Boccara.
Optics Letters 34, no. 10 (2009): 1576–1578.
Résumé: We report experimental evidence and correction of defocus in full-field optical coherence tomography of biological samples owing to mismatch of the refractive index of biological tissues and water. Via a metric based on the image quality, we demonstrate that we are able to compensate this index-induced defocus and to recover a sharp image in depth. © 2009 Optical Society of America.
Time-reversal focusing of therapeutic ultrasound on targeted microbubbles.
Couture, O., J. - F. Aubry, M. Tanter, and M. Fink.
Applied Physics Letters 94, no. 17 (2009).
Résumé: Targeted microbubbles bind specifically to molecular markers of diseases and their unique acoustic signature is used to image cellular processes in vivo. The ability of time-reversal processing to focus waves through heterogeneities on such targeted microbubbles is demonstrated. For this purpose, microbubbles were deposited on a gelatin phantom and their specific signal was recorded by a high intensity ultrasonic array. The amplified time-reversed signal was re-emitted and shown to focus back in the region where the bound microbubbles were present. This proof of concept emphasizes that molecular-time-reversal focusing could guide energy deposition on early, diffuse, or metastatic disease. © 2009 American Institute of Physics.
Subwavelength dynamic focusing in plasmonic nanostructures using time reversal.
Bartal, G., G. Lerosey, and X. Zhang.
Physical Review B – Condensed Matter and Materials Physics 79, no. 20 (2009).
Résumé: We employ time reversal for deep subwavelength focusing in plasmonic periodic nanostructures. The strong anisotropy enables propagating modes with very large transverse wave vector and moderate propagation constant, facilitating transformation of diffraction-limited plane waves to high- K Bloch waves in the plasmonic nanostructure. Time reversal is used to excite the waves in the nanostructure at the exact amplitude and phase to focus the incident light to dimensions well below the diffraction limit at any point in the structure, exemplifying a true subdiffractional confinement and resolution. © 2009 The American Physical Society.
Near-offset effects on Rayleigh-wave dispersion measurements: Physical modeling.
Bodet, L., O. Abraham, and D. Clorennec.
Journal of Applied Geophysics 68, no. 1 (2009): 95–103.
Résumé: Surface-wave profiling techniques using active sources and linear arrays are often performed with short source-receiver distances, compared to the involved wavelengths. Dispersion measurements however are usually performed by assuming body-wave amplitudes to be negligible and the recorded wave-field to be dominated by plane Rayleigh-waves. The estimated dispersion curves may then be corrupted by near-field effects. In this instance, both numerical and physical modeling has helped illustrate such effects, which are typically identified as a systematic underestimation of measured phase velocity at low frequencies. A normalized representation, based on theoretical phase velocities and spread length, has shown the apparent invariability of near-offset effects: the underestimation occurred as soon as the measured wavelength exceeded 50% of the spread length; homogeneous and normally-dispersive media provide the same limitation, regardless of the spread length value. © 2009 Elsevier B.V. All rights reserved.
Full-field OCT approaches clinical application.
Laser Focus World 45, no. 4 (2009): 69–71.
Résumé: The introduction of the newly developed full-field Cell optical coherence tomography (OCT) has enabled researchers to image breast-cancer tissue with similar results to histology. The technique offers several advantages, including fast tissue imaging at the cellular level. It has enabled biomedical researchers to slice ablated breast tumors and lymph nodes with 1 μm isotropic resolution and produce images that compare favorably with histology sections of the same tissues. These results confirm the potential of this approach for histopathology that implies reduced trauma for patients and lower costs for health-care providers. Full-face Cell OCT acquires tomographic images in the en face or transverse orientation and uses an interferometer to move the focal plane at different depths below the surface to produce 3-D tomographs. En face capture enables high lateral resolution using medium- or large-aperture microscope objectives.
Gene expression signature of cerebellar hypoplasia in a mouse model of Down syndrome during postnatal development.
Laffaire, J., I. Rivals, L. Dauphinot, F. Pasteau, R. Wehrle, B. Larrat, T. Vitalis, R. X. Moldrich, J. Rossier, R. Sinkus et al.
Résumé: Background: Down syndrome is a chromosomal disorder caused by the presence of three copies of chromosome 21. The mechanisms by which this aneuploidy produces the complex and variable phenotype observed in people with Down syndrome are still under discussion. Recent studies have demonstrated an increased transcript level of the three-copy genes with some dosage compensation or amplification for a subset of them. The impact of this gene dosage effect on the whole transcriptome is still debated and longitudinal studies assessing the variability among samples, tissues and developmental stages are needed. Results: We thus designed a large scale gene expression study in mice (the Ts1Cje Down syndrome mouse model) in which we could measure the effects of trisomy 21 on a large number of samples (74 in total) in a tissue that is affected in Down syndrome (the cerebellum) and where we could quantify the defect during postnatal development in order to correlate gene expression changes to the phenotype observed. Statistical analysis of microarray data revealed a major gene dosage effect: for the three-copy genes as well as for a 2 Mb segment from mouse chromosome 12 that we show for the first time as being deleted in the Ts1Cje mice. This gene dosage effect impacts moderately on the expression of euploid genes (2.4 to 7.5% differentially expressed). Only 13 genes were significantly dysregulated in Ts1Cje mice at all four postnatal development stages studied from birth to 10 days after birth, and among them are 6 three-copy genes. The decrease in granule cell proliferation demonstrated in newborn Ts1Cje cerebellum was correlated with a major gene dosage effect on the transcriptome in dissected cerebellar external granule cell layer. Conclusion: High throughput gene expression analysis in the cerebellum of a large number of samples of Ts1Cje and euploid mice has revealed a prevailing gene dosage effect on triplicated genes. Moreover using an enriched cell population that is thought responsible for the cerebellar hypoplasia in Down syndrome, a global destabilization of gene expression was not detected. Altogether these results strongly suggest that the three-copy genes are directly responsible for the phenotype present in cerebellum. We provide here a short list of candidate genes. © 2009 Laffaire et al; licensee BioMed Central Ltd.
Coherent plane-wave compounding for very high frame rate ultrasonography and transient elastography.
Montaldo, G., M. Tanter, J. Bercoff, N. Benech, and M. Fink.
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 56, no. 3 (2009): 489–506.
Résumé: The emergence of ultrafast frame rates in ultrasonic imaging has been recently made possible by the development of new imaging modalities such as transient elastography. Data acquisition rates reaching more than thousands of images per second enable the real-time visualization of shear mechanical waves propagating in biological tissues, which convey information about local viscoelastic properties of tissues. The first proposed approach for reaching such ultrafast frame rates consists of transmitting plane waves into the medium. However, because the beamforming process is then restricted to the receive mode, the echographic images obtained in the ultrafast mode suffer from a low quality in terms of resolution and contrast and affect the robustness of the transient elastography mode. It is here proposed to improve the beamforming process by using a coherent recombination of compounded plane-wave transmissions to recover high-quality echographic images without degrading the high frame rate capabilities. A theoretical model is derived for the comparison between the proposed method and the conventional B-mode imaging in terms of contrast, signal-to-noise ratio, and resolution. Our model predicts that a significantly smaller number of insonifications, 10 times lower, is sufficient to reach an image quality comparable to conventional B-mode. Theoretical predictions are confirmed by in vitro experiments performed in tissue-mimicking phantoms. Such results raise the appeal of coherent compounds for use with standard imaging modes such as B-mode or color flow. Moreover, in the context of transient elastography, ultrafast frame rates can be preserved while increasing the image quality compared with flat insonifications. Improvements on the transient elastography mode are presented and discussed. © 2006 IEEE.
Shear elasticity estimation from surface wave: The time reversal approach.
Brum, J., S. Catheline, N. Benech, and C. Negreira.
Journal of the Acoustical Society of America 124, no. 6 (2009): 3377–3380.
Résumé: In this work the shear elasticity of soft solids is measured from the surface wave speed estimation. An external source creates mechanical waves which are detected using acoustic sensors. The surface wave speed estimation is extracted from the complex reverberated elastic field through a time-reversal analysis. Measurements in a hard and a soft gelatin-based phantom are validated by independent transient elastography estimations. In contrast with other elasticity assessment methods, one advantage of the present approach is its low sound technology cost. Experiments performed in cheese and soft phantoms allows one to envision applications in the food industry and medicine. © 2008 Acoustical Society of America.
The time-reversal operator with virtual transducers: Application to far-field aberration correction.
Journal of the Acoustical Society of America 124, no. 6 (2009): 3659–3668.
Résumé: The decomposition of the time-reversal operator (DORT) is a detection and focusing technique using an array of transmit receive transducers. It can extract Green's functions of scatterers in a medium. A variant consists in transmitting focused beams (FDORT). It is shown here that the FDORT method can be interpreted as the decomposition of a time-reversal operator between an array of virtual transducers located at the transmit beams' foci and the physical array. The receive singular vectors correspond to scatterers' Green's functions expressed in the physical array while the transmit singular vectors correspond to Green's functions expressed in the virtual array. The position of the virtual array can be changed by varying the position of the foci, thus offering different points of view. Parameters and performance of some transmit schemes are discussed. Appropriately positioning the virtual transducers can simplify some problems. One application is measuring and correcting aberration in the case of a far-field phase screen model. Placing the virtual transducers near the phase screen transforms the problem in a simpler near-field phase screen problem. © 2008 Acoustical Society of America.
Quantitative Viscoelasticity Mapping of Human Liver Using Supersonic Shear Imaging: Preliminary In Vivo Feasability Study.
Muller, M., J. - L. Gennisson, T. Deffieux, M. Tanter, and M. Fink.
Ultrasound in Medicine and Biology 35, no. 2 (2009): 219–229.
Résumé: This paper demonstrates the feasibility of in vivo quantitative mapping of liver viscoelasticity using the concept of supersonic shear wave imaging. This technique is based on the combination of a radiation force induced in tissues by focused ultrasonic beams and a very high frame rate ultrasound imaging sequence capable of catching in real time the transient propagation of resulting shear waves. The local shear wave velocity is recovered using a dedicated time-of-flight estimation technique and enables the 2-D quantitative mapping of shear elasticity. This imaging modality is performed using a conventional ultrasound probe during a standard intercostal ultrasonographic examination. Three supersonic shear imaging (SSI) sequences are applied successively in the left, middle and right parts of the 2-D ultrasonographic image. Resulting shear elasticity images in the three regions are concatenated to provide the final image covering the entire region-of-interest. The ability of the SSI technique to provide a quantitative and local estimation of liver shear modulus with a millimetric resolution is proven in vivo on 15 healthy volunteers. Liver moduli extracted from in vivo data from healthy volunteers are consistent with those reported in the literature (Young's modulus ranging from 4 to 7.5 kPa). Moreover, liver stiffness estimation using the SSI mode is shown to be fast (less than one second), repeatable (5.7% standard deviation) and reproducible (6.7% standard deviation). This technique, used as a complementary tool for B-mode ultrasound, could complement morphologic information both for fibrosis staging and hepatic lesions imaging (E-mail: ). © 2009 World Federation for Ultrasound in Medicine & Biology.
The prolate spheroidal wave functions as invariants of the time reversal operator for an extended scatterer in the Fraunhofer approximation.
Journal of the Acoustical Society of America 125, no. 1 (2009): 218–226.
Résumé: The decomposition of the time reversal operator, known by the French acronym DORT, is widely used to detect, locate, and focus on scatterers in various domains such as underwater acoustics, medical ultrasound, and nondestructive evaluation. In the case of point-scatterers, the theory is well understood: The number of nonzero eigenvalues is equal to the number of scatterers, and the eigenvectors correspond to the scatterers Green's function. In the case of extended objects, however, the formalism is not as simple. It is shown here that, in the Fraunhofer approximation, analytical solutions can be found and that the solutions are functions called prolate spheroidal wave-functions. These functions have been studied in information theory as a basis of band-limited and time-limited signals. They also arise in optics. The theoretical solutions are compared to simulation results. Most importantly, the intuition that for an extended objects, the number of nonzero eigenvalues is proportional to the number of resolution cell in the object is justified. The case of three-dimensional objects imaged by a two-dimensional array is also dealt with. Comparison with previous solutions is made, and an application to super-resolution of scatterers is presented. © 2009 Acoustical Society of America.
Experimental and theoretical inspection of the phase-to-height relation in fourier transform profilometry.
Maurel, A., P. Cobelli, V. Pagneux, and P. Petitjeans.
Applied Optics 48, no. 2 (2009): 380–392.
Résumé: The measurement of an object's shape using projected fringe patterns needs a relation between the measured phase and the object's height. Among various methods, the Fourier transform profilometry proposed by Takeda and Mutoh [Appl. Opt. 22, 3977-3982 (1983)] is widely used in the literature. Rajoub et al. have shown that the reference relation given by Takeda is erroneous [J. Opt. A. Pure Appl. Opt. 9, 66-75 (2007)]. This paper follows from Rajoub's study. Our results for the phase agree with Rajoub's results for both paralleland crossed-optícal-axes geometries and for either collimated or noncollimated projection. Our two main results are: (i) we show experimental evidence of the error in Takeda's formula and (ii) we explain the error in Takeda's derivation and we show that Rajoub's argument concerning Takeda's error is not correct. © 2009 Optical Society of America.
Vibration analysis for detecting internal corrosion.
Ammari, H., H. Kang, E. Kim, H. Lee, and K. Louati.
Studies in Applied Mathematics 122, no. 1 (2009): 85–104.
Résumé: The vibration behavior of structures can be characterized in terms of resonance frequencies and mode shapes, which describe properties of the tested object in a global way but do not, in general, provide information about structural details. Following an asymptotic formalism, in much the same spirit as the work in  and recent text , we develop an efficient method to address the inverse problem of identifying an internal corrosive part of small Hausdorff measure in a two-dimensional structure by vibration analysis. The viability of our reconstruction method is documented by a variety of numerical results from synthetic, noiseless and noisy data. © 2009 by the Massachusetts Institute of Technology.
Controlling the phase and amplitude of plasmon sources at a subwavelength scale.
Lerosey, G., D. F. P. Pile, P. Mathieu, G. Bartel, and X. Zheng.
Nano Letters 9, no. 1 (2009): 327–331.
Résumé: We present a new class of nanoscale plasmonίc sources based on subwavelength dielectric cavities embedded in a metal siab. Exploiting the streng dispersion near the Fabry-Perot resonance in such a resonator, we control the phase and the amplitude of the generated plasmons at the subwavelength scale. As an example, we present a subwavelength unidirectional plasmonic antenna utilizing interference between two plasmonic cavίty sources wίth matched phase and amplitude.© 2009 American Chemcal Society.

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