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Underwater noise has been identified as a relevant pollution affecting marine ecosystems in different ways. Despite the numerous studies performed over the last few decades regarding the adverse effect of underwater noise on marine life, a lack of knowledge and methodological procedures still exists, and results are often tentative or qualitative. A monitoring methodology for the behavioral response of bluefin tuna (Thunnus thynnus) when exposed to ship and wind turbine operational noises was implemented and tested in a fixed commercial tuna feeding cage in the Mediterranean sea. Fish behavior was continuously monitored, combining synchronized echosounder and video recording systems. Automatic information extracted from acoustical echograms was used to describe tuna reaction to noise in terms of average depth and vertical dimensions of the school and the indicators of swimming speed and tilt direction. Video recordings allowed us to detect changes in swimming patterns. Different kinds of stimuli were considered during bluefin tuna cage monitoring, such as noise generated by feeding boats, wind farm operational noise, and other synthetic signals projected in the medium using a broadband underwater projector. The monitoring system design was revealed as a successful methodological approach to record and quantify reactions to noise. The obtained results suggested that the observed reactions presented a strong relationship with insonification pressure level and time. Behavioral changes associated with noise are difficult to observe, especially in semi-free conditions; thus, the presented approach offered the opportunity to link anthropogenic activity with possible effects on a given marine species, suggesting the possibility of achieving a more realistic framework to assess the impacts of underwater noise on marine animals., AZIMUT IEO, SI

[EN] The method of fundamental solutions has been applied to evaluate the influence of fish models geometrical features on the target strength (TS) directivity and TS frequency response of swimbladdered fish. Simplified models were considered for two fish species: gilt-head sea bream (Sparus aurata, Linnaeus 1758) and Atlantic salmon (Salmo salar, Linnaeus 1758), and different geometrical details of their morphology were studied, such as backbone presence, and its curvature or the inclusion of vertebrae modulation. Swimbladder shape and tilt, together with the inclusion of backbone (and its realistic curvature) for dorsal measurements were the most important features for proper estimation of mean TS. The estimation of mean TS is considered including the effect of fish tilt, the echosounder frequency, and the fish-to-transducer distance., This work received funding from ACUSTUNA project ref. CTM2015-70446-R (MINECO/ERDF, EU). LG acknowledges the support by FCT-Fundacao para a Ciencia e a Tecnologia, I.P., within the scope of the research unit "Institute for sustainability and innovation in structural engineering-ISISE" (UIDP/04029/2020) and of Regional Operational Programme CENTRO2020, within the scope of the project CENTRO-01-0145-FEDER000006 (SUSpENsE). IP-A and VE acknowledge the financial support of Generalitat Valenciana by grants BEST/2018/119 and BEST/2019/008.

[EN] Anthropogenic activities are causing increased noise levels in the marine environment. To date, few studies have been undertaken to investigate the effects of different noise frequencies on the behaviour of juvenile fish. In this study, the behavioural changes of juvenile gilthead seabream (Sparus aurata) are evaluated when exposed to white noise filtered in third-octave bands centred at 63, 125, 500, and 1000 Hz (sound pressure level, 140-150 dB re 1 mu& x3a1;a) for 7 h. The group dispersion, motility, and swimming height of the fish were analysed before and during the acoustic emission. Dispersion of the fish was found to reduce immediately upon application of low frequency sound (63 and 125 Hz) with a return to control condition after 2 h (indicative of habituation), whereas at 1 kHz, dispersion increased after 2 h without any habituation. The motility decreased significantly at 63 Hz throughout the 7 h of sound exposure. The swimming height decreased significantly for all frequencies other than 125 Hz. The results of this study highlight significant variations in the behavioural responses of juvenile fish that could have consequences on their fitness and survival., This study was conducted in the framework of the Ph.D. program in the Mediterranean Biodiversity XXXII cycle (International) of the University of Palermo. I.P.-A., M.B.-C. and V.E. acknowledge the financial support of the European Comission-Project No. 11.0661/2018794607/SUB/ENV.C2, risk-based approaches to good environmental status (RAGES). The other founding support comes from the Ph.D. Innovative with Industrial Characterization Programma Operativo Nazionale (PON) 2014-2020 and the projects bilateral Research laboratory on marine and maritime Science Italy-Argentina (CAIMAR) Joint Laboratory Italy-Argentina (Laboratori Congiunti Bilaterali Internazionali of the Italian National Reseach Council, 2017-2019). Document

[EN] This paper presents measures of target strength (TS; dB re 1 m(2)) and models of TS vs. fork length (L; cm), i.e. TS = 20log(L) + b(20), for skip-jack tuna associated with fish aggregating devices (FADs) in the Central Pacific Ocean. Measurements were made using 38-, 120-, and 200-kHz split-beam echosounders on a purse-seine workboat during fishing operations. To mitigate potential bias due to unresolved targets, TS measurements were rejected if they were not simultaneously detected with multiple echosounder frequencies in approximately the same location. The filtered TS and concomitantly sampled L data were used to estimate b(20) = -76, -71, and -70.5 dB for 38, 120, and 200 kHz, respectively, using the method of least squares. For comparison, quasi-independent estimates of TS and b(20) were calculated from acoustic echo-integration and catch data representing entire aggregations around the FADs. The results differed by, We thank the following organizations and people for their support of this work: the governments of Kiribati, Tuvalu, and Tokelau which permitted this research in their EEZs; Albacora for allowing this work aboard F/V ALBATUN TRES; Fishing Master Euken Mujika; the captain and crew; the scientists and divers J. Filmalter and F. Forget are thanked for invaluable insight about fish behaviour, vertical stratification and non-target species composition at FADs; Hector Pena for providing instruction on the sonar setup and analysis; Yolanda Lacalle for the illustration in Figure 2; and Andres Uriarte for advice concerning transmission of statistical errors. The research reported in the present document was funded by the International Seafood Sustainability Foundation (ISSF) and conducted independently by the authors. The report and its results, professional opinions and conclusions are solely the work of the authors. This paper is contribution 843 from AZTI (Marine or Food Research).

Underwater noise is mainly produced by anthropogenic activities and has increased in recent years. The Marine Strategy Framework Directive aims to monitor “continuous low frequency sound” trends in ambient noise in particular at 1/3rd octave bands centered at 63 and 125 Hz. The aim of this work is to evaluate the possibility of using the results of Sparus aurata juvenile’s behavior for parameterizing a numerical model of the fish behavior. The fishes were stressed with white noise filtered with a band pass filter at 1/3 octave band centered respectively at 63 Hz, 125 Hz, 500 Hz, and 1 kHz (SPL: 140-150 dB re 1µPa). We performed three test replicas for the control (without any sound emission) and for each of the four frequencies. Each trial lasted 7:15 hours in total and included the following three periods in which two video cameras recorded: 30 min before the acoustic emission; 60 min in which the acoustic stress was dispensed; 6 hours after the acoustic emission divided into 6 periods of 1 hour. To obtain the behavioral data (cohesion, motility, swimming height) the fishes were video monitored 15 min before the sound exposure, one hour during the sound exposure and the final 15 minutes of each hour after the sound exposure. The bottom of the tank was divided into squares. Cohesion was evaluated by counting the number of squares occupied by the group; motility by counting the number of squares crossed by each fish; swimming height by counting the fish presence in three zones (deepest, intermediate, and highest). Using Kruskal-Wallis tests and multiple comparisons post-hoc tests we assessed different behaviors of the fishes reacting to different acoustic frequencies. Here, we propose the use of part of these data (the first hour of acoustic emission) for the parameterization of a numerical model using an adaptation of the Boids method. In the model the cohesion, motility and the swimming height are analyzed in the same way as they are analyzed for in vivo video recordings. Preliminary results showed that it is possible to reproduce in the new model the same qualitative behavior of the in vivo recordings with fish. In this way, it will be possible to understand the behavioural responses of fish in laboratory experiments and contribute to the prediction of the impacts of other possible acoustic sounds emitted by human activities through the application of the created numerical model.

Human activities in the oceans, such as marine traffic and Deep Sea Mining (DSM), are increasing in the last years (Ross 2005; Calvo et al 2016). Underwater noise in the oceans, especially at lower frequencies, is mainly produced by marine traffic and DSM could increase this noise in the next future. Marine Strategy Framework Directive promotes the achievement of a good quality environmental status and aims to monitor “continuous low frequency sound” trend in the ambient noise level within the 1/3 octave bands centred at 63 and 125 Hz. The aim of this study is to evaluate the behavioural changes of Sparus aurata juveniles exposed to a four different acoustic signals in a tank. The emitted signal was white noise filtered at 1/3 octave band centred respectively at 63 Hz, 125 Hz, 500 Hz, and 1 kHz (SPL: 140-150 re 1μΡa). For each frequency we tested three independent groups of 6 specimens and video monitored them for a total of 7:30 hours (15 min before, one hour during and 6 hours after the sound exposition) using two cameras located above the tank and in the water column. Moreover, three control group (no acoustic emission) tests were performed (no sounds were dispensed). Behavioural data (cohesion, motility, swimming height) were collected from the 15 minutes of each hour except in during sound exposition, where we considered the entire hour. The bottom of the tank was divided into squares. Cohesion was evaluated counting the number of squares occupied by the group; motility counting the number of squares crossed by each fish; swimming height counting the fish presence in three zones (deepest, intermediate, and highest). Using Kruskal-Wallis tests and multiple comparisons post-hoc we assessed that the cohesion was significantly affected at 63,125 and 500 Hz. At 63 and 125 Hz, significant increase in cohesion was observed during and up to the third and sixth hour of exposition respectively; at 500 Hz cohesion increased only during the exposition. Significant increase in motility was observed during the 63 and 125Hz stimuli. For swimming height, all frequencies significantly increase the number of fish in the deepest zone and decrease in the intermediate zone. The juvenile of S. aurata exhibit different behaviours depending on the acoustic frequencies. This study evidences an impact at short and medium time on juvenile. This could determine an effect on budget energy and, consequently, a potential threat for their recruitment in a noise-polluted environment.

[EN] We propose the application of a numerical model based on the Method of Fundamental Solutions to the estimation of the target strength (TS) of single fish, a crucial parameter for evaluating fish abundance when using active acoustical techniques. We consider a realistic beam and the influence of the evolution of the scattered field with distance maintaining the target in the far field of the ultrasonic transducer. The cases of a fluid sphere and a prolate spheroid model for the swimbladder are used to verify the application of MFS against other analytical and numerical methods. Additionally, a model considering only the swimbladder and the fishbone is presented to evaluate the differences between dorsal and ventral aspect measurements, and to understand previous experimental works performed with Atlantic salmon (Salmo salar) in floating cages., I. Perez-Arjona and V. Espinosa acknowledge funding of ACUSTUNA project ref. CTM2015-70446-R (MINECO/FEDER, UE), and UPV grants of PAID-00-15 and GVA BEST/2015/270. L. Godinho acknowledges the funding by FEDER funds through the Competitivity Factors Operational Programme - COMPETE and by national funds through FCT - Foundation for Science and Technology within the scope of the project POCI-01-0145-FEDER-007633. The authors would like to thank Dr. Manuel Bou and Carlos Albino for the technical assistance with work-station procedures.

[EN] The possibility of detecting uneaten food pellets in aquaculture floating cages using a scientific single beam echosounder is demonstrated. The applied methodology is based in a basic scheme with the ultrasonic beam facing upwards the sea surface from the cage bottom. The target strength of single pellets is measured resulting in a linear relationship between target strength and pellet size. These results are the basis to quantify the uneaten food falling and to develop an automated feeding system based on demand. (C) 2017 Elsevier B.V. All rights reserved., This work was developed with the financial support of project ARM/1790/010 of the Tecnological Develoment Program of MAGRAMA, Spanish Government. E. Soliveres acknowledges support of Spanish Government grant AP2009-4459 FPU Subprogram. The authors would like to,acknowledge Prof. Helge Balk of the University of Oslo for his assistance with the software and license's access to Sonar 5 Pro, and the collaboration of Simrad Spain S.L. for lending the used EK15 echosounder.

The earth’ resources are running out, the population will increase and further sources will be needed. These, were found in the deep ocean. To date the mining activities (Deep Sea Mining, DSM) they have not started. One impact of DSM could be underwater noise. Considering the noise frequencies of anthropic activities in the ocean, and the European directive on underwater noise control, we stressed the animals with four acoustic 1/3 band noises around: 63 Hz, 125 Hz, 500 Hz, 1kHz. We study the effects on Sparus aurata juveniles, and on Mytilus galloprovincialis. We will analyse behavioural., molecular and biochemical responses Los recursos de la tierra se están agotando, la población aumentará y se necesitarán más fuentes. Esaos fueron encontradas en el océano profundo. Hasta ahora, las actividades mineras (Deep Sea Mining, DSM) no han empezado. Un impacto del DSM podría ser el ruido subacuático. Teniendo en cuenta las frecuencias de ruido de las actividades antrópicas en el océano, y la directiva europea sobre el control del ruido submarino, molestamos los animales con cuatro ruidos acústicos de 1/3 de banda alrededor: 63 Hz, 125 Hz, 500 Hz, 1kHz. Estudiamos los efectos en juveniles de Sparus aurata y en Mytilus galloprovincialis. Analizaremos respuestas comportamiental,moleculares y bioquímicas.

[EN] In this work, acoustic and computer vision techniques are combined to develop an automatic procedure for biomass estimation of tuna during transfers. A side scan sonar working at 200¿kHz and a stereo camera, positioned facing towards the surface to record the ventral aspect of fish, are set as acquisition equipment. Moreover, a floating structure has been devised to place the sensors between cages in transfers, creating a transfer canal that allows data acquisition while fish swim from donor to receiving cage. Biomass assessment is computed by counting transferred tuna and sizing a representative sample of the stock. The number of transferred tuna is automatically deduced from acoustic echograms by means of image processing techniques, whereas tuna size is computed from the stereo videos using our automatic computer vision procedure based on a deformable model of the fish ventral silhouette. The results show that the system achieves automatic tuna counting with error below 10%, achieving around 1% error in the best configuration, and automatic tuna sizing of more than 20% of the stock, with highly accurate Snout Fork Length estimation when compared to true data from harvests. These results fulfil the requirements imposed by International Commission for the Conservation of Atlantic Tunas for compliant transfer operations., This work was supported by funding from the BIACOP project, ES13/41, from the EU Fisheries Control Programme through the Secretaría General de Pesca, Ministerio de Agricultura, Alimentación y Medio Ambiente (MAGRAMA), and by ACUSTUNA project ref. CTM2015-70446-R (MINECO/ERDF, EU). The BIACOP project has been possible thanks to the collaboration of the Spanish company Grup Balfegó S.L. that also supplied boats and divers to acquire underwater video in the Mediterranean Sea. Special personal acknowledgements to Manuel Guijarro and Antonio López, and to David Baizán from IMA – Acuicultura Integrada Multitrófica S.L.U., for their assistance with the design and construction of the floating structures.

[EN] Horizontal hydroacoustics is a technique of remote fish detection that has proved to efficiently determine fish density and biomass in shallow or superficial waters. This non-intrusive technique could render better results than those obtained by conventional sampling when monitoring shallow waters. To apply this technique, we need equations that relate the amount of sound returned by fish, known as target strength (TS in dB), with their length (mm) or weight (g). This study presents horizontal conversion equations for the species gilt-head bream (Sparus aurata) and sea bass (Dicentrarchus labrax), two of the most important species bred in aquaculture. Moreover, this study presents a new formula to calculate a mixed equation adjusted to the percentage of distribution of those species in case of mixed populations. The results in this research have been obtained by applying a simple setup that allows for high-quality acoustic data. These new equations will enable the application of this technique in order to estimate these species' density and biomass in shallow aquatic systems such as aquaculture ponds with semi-intensive production densities., This study's authors would like to thank the Superintendent of Economy and Knowledge (Andalusian Government) for the funding provided as part of the project (PI_57052) developed in collaboration with CTAQUA. We would like to thank the researchers Carlos Orduna Marin and Juan Ramon Cid Quintero for their selfless work to obtain the field data and to the company PIMSA for generously allowing us to use their facilities and fish. We would also like to thank the veterinarian JR Rodriguez for being kind enough to perform X-rays on the studied fish and Cristina Ocana for her careful proofreading of the English text.

[EN] Fish anatomical vertical dimensions are extracted from a time-of-flight analysis of fish echo shape using narrow bandwidth echosounding of swimming individuals. These vertical dimensions fit a Gumbel distribution model and are successfully correlated with fish weight. The proposed method can be used to estimate the mean weight of fish in aquaculture cages as an alternative to target strength measurements. Full-waveform acquisition and signal correlation techniques permitted to increase the signal-to-noise ratio and to improve the performance against traditional envelope-based echosounding., This work was developed with the financial support of project ARM/1790/010 of the Tecnological Develoment Program of MAGRAMA, Spanish Government. E. Soliveres acknowledges support of Spanish Government grant AP2009-4459 FPU Subprogram.

In this paper the problem of parametric sound generation in an acoustic resonator filled with a fluid is considered, taking explicitly into account the influence of the nonlinearly generated second harmonic. A simple model is presented, and its stationary solutions were obtained. The main feature of these solutions is the appearance of bistable states of the fundamental field resulting from the coupling to the second harmonic. An experimental setup was designed to check the predictions of the theory. The results are consistent with the predicted values for the mode amplitudes and parametric thresholds. At higher driving values a self-modulation of the amplitudes is observed. This phenomenon is identified with a secondary instability previously reported in the frame of the theoretical model.

We show that any optical dissipative structure supported by degenerate optical parametric oscillators contains a special transverse mode that is free from quantum fluctuations when measured in a balanced homodyne detection experiment. The phenomenon is not critical as it is independent of the system parameters and, in particular, of the existence of bifurcations. This result is a consequence of the spatial symmetry breaking introduced by the dissipative structure. Effects that could degrade the squeezing level are considered., Comment: 4 pages and a half, 1 fugure. Version to appear in Europhysics Letters

Domain walls in type I degenerate optical parametric oscillators are numerically investigated. Both steady Ising and moving Bloch walls are found, bifurcating one into another through a nonequilibrium Ising--Bloch transition. Bloch walls are found that connect either homogeneous or roll planforms. Secondary bifurcations affecting Bloch wall movement are characterized that lead to a transition from a steady drift state to a temporal chaotic movement as the system is moved far from the primary, Ising--Bloch bifurcation. Two kinds of routes to chaos are found, both involving tori: a usual Ruelle-Takens and an intermittent scenarios., Comment: 12 figures

Instabilities in vectorial Kerr cavities can arise from two different bifurcations of scalar and vectorial character. We study the conditions that determine which of the instabilities is responsible for pattern formation. We find that a subcritical homogeneous polarization instability governs pattern formation when cavity anisotropy or injected field detuning is large. Under these conditions the system exhibits bright cavity solitons.

The propagation of nonlinear compressional waves in a one-dimensional granular chain driven at one end by a harmonic excitation is studied. The chain is described by a Fermi-Pasta-Ulam (FPU) lattice model with quadratic nonlinearity (alpha-FPU model), valid for strong initial compression of the chain by an external static force. A successive approximations method is used to obtain the analytical expressions for the amplitudes of the static displacement field and of the fundamental and second harmonics propagating through the lattice. Both propagating and evanescent second harmonics are shown to influence the nonlinear propagation characteristics of the fundamental frequency. The propagating regime is characterized by a periodic energy transfer between first and second harmonics, resulting from dispersion, which disappears when the second harmonic becomes evanescent., The work was financially supported by the MICINN of the Spanish Government, under Grant No. FIS2011-29734-C02-02 and by ANR Project Stabingram No. ANR-2010-BLAN-0927-03. V. S.-M. and I. P.-A. acknowledge financial support from Generalitat Valenciana, the Spanish Ministry of Science and Innovation, and Universitat Politecnica de Valencia. V. R.-G. is grateful for the support of "Programa de Contratos Post-Doctorales conMovilidad UPV del Campus de Eexcelencia Internacional (CEI-01-11)" and of Grant No. BEST2012 of the Generalitat Valenciana.

We report experimental evidences of spatial (angular) filtering of sound beams propagating through sonic crystals. We show that at specific frequencies of the incident wave the paraxial plane wave compo- nents of the beam can be efficiently transmitted through the crystal, whereas the components propagat- ing at large angles are strongly reflected or deflected (filtered out) by the crystal. The modification of the angular field distribution results in formation of sound beams of relatively high spatial quality., The work was financieall supported by Spanish Ministry of since and Innovation and European Union FEDER through projects FIS2011-29731-C02-01 and -02, Generalitat Valenciana through the procect GV/2011/2055 and the UPV through PAID-05-12.

[EN] A theoretical and experimental study of the propagation of sound beams in- and behind three-dimensional sonic crystals at frequencies close to the band edges is presented. An efficient collimation of the beam behind the crystal is predicted and experimentally demonstrated. This effect could allow the design of sources of high spatial quality sound beams. © 2012 American Institute of Physics., The work was financially supported by Spanish Ministry of Science and Innovation and by European Union FEDER through projects FIS2008-06024-C02-02, -03 and MAT2009-09438. V.R.G. is grateful for the support of post-doctoral contracts of the UPV CEI-01-11. K.S. acknowledges the grant of UPV PAID-02-01.

We propose and numerically demonstrate the feasibility of spatial filtering, i.e. a selective removal of the high spatial frequency components, of narrow acoustic beams during their propagation along a two- dimensional sonic crystal. The filtering effect occurs due to two different mechanisms, depending on the particular form of the dispersion surfaces of the propagation modes in sonic crystal. Reflection or deflection of undesired spatial frequency components occurs for these two mechanisms. It is shown that, as a consequence of spatial filtering, the angular spectrum of the beams is narrowed, and the noisy beams are efficiently cleaned., The work was financially supported by Generalitat Valenciana through GV/2011/055, Spanish Ministerio de Ciencia e Innovacion and by European Union FEDER trough Projects FIS 2008-06024-C02-02 and -03.

This work was financially supported by Spanish Ministerio de Ciencia e Innovacion, European Union FEDER (FIS2008-06024-C03-02).

The vibrational properties of out-of-plane elastic waves in hexagonal monolayer granular membranes were studied theoretically. The predicted propagation modes involve an out-of-plane displacement and two rotations with axes in the membrane plane. Shear and bending rigidities at the contact between beads were considered. Both the cases of freely suspended membranes and membranes coupled to a rigid substrate were analyzed. Dispersion relations and the existence of band gaps are presented and discussed for various contact properties. For freely suspended membranes with sufficient contact bending rigidity, it is shown that complete band gaps exist. The results obtained may be of interest for testing with acoustic waves the elasticity of recently developed granular membranes composed of nanoparticles (of interest because of their phoxonic properties) and more generally for the control of designing devices for membrane wave propagation., This work was supported by the STABINGRAM project (ANR-2010-BLAN-0927-03), by the MEC of the Spanish Government under project number FIS2008-06024-C03-03 and by the Jose Catillejo program. VT acknowledges the Universidad Politecnica de Valencia for support through a research visit fellowship.

We report the theoretical and experimental demonstration of pattern formation in acoustics. The system is an acoustic resonator containing a viscous fluid. When the system is driven by an external periodic force, the ultrasonic field inside the cavity experiences different pattern-forming instabilities leading to the emergence of periodic structures. The system is also shown to possess bistable regimes, in which localized states of the ultrasonic field develop. The thermal nonlinearity in the viscous fluid, together with the far-from-equilibrium conditions, are is the responsible of the observed effects.

[EN] In the last years we have proposed the use of the mechanism of spontaneous symmetry breaking with the purpose of generating perfect quadrature squeezing. Here we review previous work dealing with spatial (translational and rotational) symmetries, both on optical parametric oscillators and four-wave mixing cavities, as well as present new results. We then extend the phenomenon to the polarization state of the signal field, hence introducing spontaneous polarization symmetry breaking. Finally we propose a Jaynes-Cummings model in which the phenomenon can be investigated at the singlephoton-pair level in a non-dissipative case, with the purpose of understanding it from a most fundamental point of view., This work has been supported by the Spanish Ministerio de Educacion y Ciencia and the European Union FEDER through Project FIS2008-06024-C03-01. C.N.-B. acknowledges a grant from the FPU Programme of the Spanish Government.

A theoretical and experimental study of the propagation of sound beams in and behind two-dimensional sonic crystals at frequencies close to the band edges is presented. Beam focusing is predicted and discussed. We evaluate, by analytical numerical methods, the main focusing characteristics, such as the focal distance, the width of beam waist, and the beam quality at the waist. The field distribution is shown to depend strongly on the beam size and frequency. Experiments were performed on narrow sources radiating in ultrasound regime, although the results are extendable to arbitrary frequencies., This work was financially supported by the Spanish Ministerio de Ciencia e Innovacion and the European Union FEDER through Projects No. FIS2008-06024-C03 and No. FIS2008-06024-C02.

We demonstrate two alternative techniques for controlling and stabilizing domain walls (DW) in phase-sensitive, nonlinear optical resonators. The first of them uses input pumps with spatially modulated phase and can be applied also to dark-ring cavity solitons. An optical memory based on the latter is demonstrated. Here the physical mechanism of control relies on the advection caused to any feature by the phase gradients. The second technique uses a plane wave input pump with holes of null intensity across its transverse plane, which are able to capture DWs. Here the physical mechanism of control is of topological nature. When distributed as a regular array, these holes delimit spatial optical bits which constitute an optical memory. These techniques are illustrated in a degenerate optical parametric oscillator model, but can be applied to any phase-sensitive nonlinear optical cavity.

The model equations describing a large‐aspect acoustic resonator have been developed. A new type of robust localized structure, an ultrasonic cavity soliton, is exhibited by the system, both in the thermal and the pressure field. The existence of this structure has been proved by the numerical integration of the model equations. Previous experimental results show a good agreement with the theoretical predictions. A generalized Swift‐Hohenberg equation has been derived in a limit, relating the thermoacoustic resonator with a larger set of pattern forming systems.

In this work we present a theoretical description of parametric sound generation in a water‐filled interferometer, extending previous models of nonlinear acoustical resonators to include the coupling with the generated second harmonic. The stationary solutions both above and below the threshold are obtained and discussed. The solutions are compared with experimentally measured values, with an excellent agreement. The novel effects induced by the second harmonic (e.g. bistability or hysteresis) and its relation with complex temporal dynamics and extended pattern formation are discussed.

We show theoretically that a broad area bidirectional laser with slightly different cavity losses for the two counterpropagating fields sustains cavity solitons (CSs). These structures are complementary, i.e., there is a bright (dark) CS in the field with more (less) losses. Interestingly, the CSs can be written/erased by injecting suitable pulses in any of the two counterpropagating fields., 4 figures

We present an experimental demonstration of the subdiffractive propagation (self-collimation) of an ultrasound beam in a two-dimensional sonic crystal formed by a square array of steel cylinders inmersed in water. Measurements show that the diffractive spreading of a narrow beam is strongly reduced along the spatially modulated direction of the crystal. The effect of the finite crystal length is theoretically analyzed, resulting in a frequency shift of the subdiffractive point in good correspondence with the experimental results.

We theoretically study quadrature and polarization squeezing in dispersive optical bistability through a vectorial Kerr cavity model describing a nonlinear cavity filled with an isotropic chi(3) medium in which self-phase and cross-phase modulation, as well as four--wave mixing, occur. We derive expressions for the quantum fluctuations of the output field quadratures as a function of which we express the spectrum of fluctuations of the output field Stokes parameters. We pay particular attention to study how the bifurcations affecting the non-null linearly polarized output mode squeezes the orthogonally polarized vacuum mode, and show how this produces polarization squeezing., Comment: 10 text pages + 12 figures

We predict theoretically the nondiffractive propagation of sonic waves in periodic acoustic media (sonic crystals) by expansion into a set of plane waves (Bloch mode expansion) and by finite-difference time-domain calculations of finite beams. We also give analytical evaluations of the parameters for nondiffractive propagation, as well as the minimum size of the nondiffractively propagating acoustic beams.

We present a method for the study of quantum fluctuations of dissipative structures forming in nonlinear optical cavities, which we illustrate in the case of a degenerate, type I optical parametric oscillator. The method consists in (i) taking into account explicitly, through a collective variable description, the drift of the dissipative structure caused by the quantum noise, and (ii) expanding the remaining -internal- fluctuations in the biorthonormal basis associated to the linear operator governing the evolution of fluctuations in the linearized Langevin equations. We obtain general expressions for the squeezing and intensity fluctuations spectra. Then we theoretically study the squeezing properties of a special dissipative structure, namely, the bright cavity soliton. After reviewing our previous result that in the linear approximation there is a perfectly squeezed mode irrespectively of the values of the system parameters, we consider squeezing at the bifurcation points, and the squeezing detection with a plane--wave local oscillator field, taking also into account the effect of the detector size on the level of detectable squeezing., Comment: 10 figures

We report on a new type of localized structure, an ultrasonic cavity soliton, supported by large aspect-ratio acoustic resonators containing viscous media. These states of the acoustic and thermal fields are robust structures, existing whenever a spatially uniform solution and a periodic pattern coexist. Direct proof of their existence is given both through the numerical integration of the model and through the analysis and numerical integration of a generalized Swift-Hohenberg equation, derived from the microscopic equations under conditions close to nascent bistability. An analytical solution for the ultrasonic cavity soliton is given.

An anisotropic (dichroic) optical cavity containing a self-focusing Kerr medium is shown to display a bifurcation between static --Ising-- and moving --Bloch-- domain walls, the so-called nonequilibrium Ising-Bloch transition (NIB). Bloch walls can show regular or irregular temporal behaviour, in particular, bursting and spiking. These phenomena are interpreted in terms of the spatio-temporal dynamics of the extended patterns connected by the wall, which display complex dynamical behaviour as well. Domain wall interaction, including the formation of bound states is also addressed., 15 pages Tex file with 11 postscript figures. Resubmitted to Phys. Rev. E

This study shows methods of stabilisation and control of domain walls in degenerate optical parametric oscillators (DOPO). The first method involves stabilisation of two DWs from noise, with two phase maxima of injected field. The second method consists in introducing dark holes in the transverse profile of the injected pump by using a mask for example. In this way, an outer and an inner boundary limit the pumped region.

This paper investigates domain walls (DWs) in a degenerate optical parametric oscillator (DOPO) for positive pump and signal detunings. Here, two alternative methods are used for controlling and stabilising DWs.

It is well known that the squeezing spectrum of the field exiting a nonlinear cavity can be directly obtained from the fluctuation spectrum of normally ordered products of creation and annihilation operators of the cavity mode. In this article we show that the output field squeezing spectrum can be derived also by combining the fluctuation spectra of any pair of s-ordered products of creation and annihilation operators. The interesting result is that the spectrum obtained in this way from the linearized Langevin equations is exact, and this occurs in spite of the fact that no s-ordered quasiprobability distribution verifies a true Fokker-Planck equation, i.e., the Langevin equations used for deriving the squeezing spectrum are not exact. The (linearized) intracavity squeezing obtained from any s-ordered distribution is also exact. These results are exemplified in the problem of dispersive optical bistability., Comment: 15 pages, no figures, to be published in Journal of Modern Optics

Parametrically driven systems sustaining sech solitons are shown to support a new kind of localized state. These structures are walls connecting two regions oscillating in antiphase that form in the parameter domain where the sech soliton is unstable. Depending on the parameter set the oppositely phased domains can be either spatially uniform or patterned. Both chiral (Bloch) and nonchiral (Ising) walls are found, which bifurcate one into the other via an Ising-Bloch transition. While Ising walls are at rest Bloch walls move and may display secondary bifurcations leading to chaotic wall motion.

The phenomenon of pattern formation is ubiquitous in the dynamics of extended nonlinear systems. Patterns arise from the interplay of external forcing, dissipation, nonlinearity, and spatial coupling. These factors are also present in many acoustic systems. However, under usual conditions where the elastic nonlinearity dominates, the development of shock fronts in nonlinear regime strongly limits the possibility of a simple analysis. Viscous media, where thermal nonlinearity dominates over the elastic one and wave distortion is inhibited at short distances, are good candidates for acoustic systems presenting patterns with similar characteristics as those found in other fields, such as hydrodynamics or optics. A model describing the evolution of pressure and temperature variations in a resonator with plane walls containing a viscous medium is presented. The large aspect ratio of the resonator allows the transverse spatial coupling, mediated by sound diffraction and temperature diffusion. The homogeneous so...

Simultaneous self-collimation of sound beams with different frequencies, corresponding to fundamental wave and to its second harmonic, is proposed theoretically and demonstrated experimentally. The result is obtained when the isofrequency contours for each harmonics, corresponding to different propagation bands, develop flat segments along the same direction. The effect can be utilized for managing (enhancement and control) of nonlinear frequency mixing of narrow sound beams., The work was financially supported by Spanish Ministerio de Educacion y Ciencia and European Union FEDER through projects FIS2008-06024-C02-02 and -03. I. Perez-Arjona acknowledges Fundacion CajaMurcia postdoctoral program.