Guillermo Lara - Academia.edu (original) (raw)

Papers by Guillermo Lara

National Aut6noma de Mexico contain specimens of several species of amphibians and reptiles from ... more National Aut6noma de Mexico contain specimens of several species of amphibians and reptiles from Mexican states from which they have not hitherto been reported. The following records are from seven states, for which 22 taxa are newly reported, as fQllows: CHIAPAS-AgaZyahnis aaZZidryas; HIDALGO-Corytophanes hernandezi, EZaphe f. fZavirufa; JALISCO-Phrynohyas venuZosa, TomoaaatyZus nitidu8 OPariU8, TPiprion spatulatus ~eticutatu8, Coleony~ eZegans nemoPalis, EUmeaes paPVulus, Mbbuya brachypoda, Phryndsoma asio, Dipsas gaigeae, Loxoaemus bicolor, Micrurus distans oZiveri, PseudoZeptodeira Zatifasaiata, TFopidodipsas, oaaidentatis, T. philippi; PUEBLA-Coniophanes bipunatatus biseriatus, SpiZo,tes pUlZatu8 mezioonus, Tropidodipsas s. sartorii; SAN LUIS POTOSI-Chiropterotriton ahondPostega araaens; VERACRUZ-Siren intermedia; ZACATECAS-Rana montezumai. Information concerning the specimens reported herein, or any others in the herpetological collections of the Instituto de Biologla (IBH), m...

Cornell University - arXiv, Jul 7, 2022

We investigate neutron star solutions in scalar-tensor theories of gravity with first-order deriv... more We investigate neutron star solutions in scalar-tensor theories of gravity with first-order derivative self-interactions in the action and in the matter coupling. We assess the robustness of the kinetic screening mechanism present in these theories against general conformal couplings to matter. The latter include ones leading to the classical Damour-Esposito-Farèse scalarization, as well as ones depending on the kinetic term of the scalar field. We find that kinetic screening always prevails over scalarization, and that kinetic couplings with matter enhance the suppression of scalar gradients inside the star even more, without relying on the non-linear regime. Fine tuning the kinetic coupling with the derivative self-interactions in the action allows one to partially cancel the latter, resulting in a weakening of kinetic screening inside the star. This effect represents a novel way to break screening mechanisms inside matter sources, and provides new signatures that might be testable with astrophysical observations.

We point out that the initial-value (Cauchy) problem for self-interacting vector fields presents ... more We point out that the initial-value (Cauchy) problem for self-interacting vector fields presents the same well-posedness issues as for first-order derivative self-interacting scalar fields (often referred to as k-essence). For the latter, suitable strategies have been employed in the last few years to successfully evolve the Cauchy problem at the level of the infrared theory, without the need for an explicit ultraviolet completion. We argue that the very same techniques can also be applied to self-interacting vector fields, avoiding a number of issues and "pathologies" recently found in the literature.

2017 22nd International Conference on Digital Signal Processing (DSP)

Anthropogenic underwater sound is now recognized as a world-wide problem. Shipping, seismic surve... more Anthropogenic underwater sound is now recognized as a world-wide problem. Shipping, seismic surveys and pile driving, among some other human activities, have shown a broad range of negative effects in a variety of species. It is thus important to control, register and characterize these activities in order to establish policies that mitigate its effects. For this purpose, automatic detectors of the major anthropogenic sound categories (impulsive and tonal sounds) are needed. An efficient algorithm capable of detecting impulsive and tonal sound categories is proposed. The detection algorithm is based on the Pulsed to Tonal Ratio (PTR) and, in this work, we show not only its simplicity but also how well it performs in a variety of situations. In contrast to what happens with some other techniques, the proposed detector generally succeeds in detecting pulsed and tonal events with additive white and pink noise. This makes the PTR detector particularly appropriate for passive acoustic monitoring.

Journal of Marine Science and Engineering

Over the last decade, national authorities and European administrations have made great efforts t... more Over the last decade, national authorities and European administrations have made great efforts to establish methodological standards for the assessment of underwater continuous noise, especially under the requirements set by the Marine Strategy Framework Directive (MSFD). Through the MSFD implementation across EU Member States Marine Reporting Units (MRUs), it is intended to establish the Good Environmental Status (GES) whether it is achieved or not. The evaluation of the Sound Pressure Level (SPL) at the local or regional scale for 1/3 octave band of 63 Hz and 125 Hz and the identification of long temporary trends were considered to be a priority due to the valuable information they can offer in relation to continuous low-frequency noise. Nevertheless, the methodology to determine threshold values from which to evaluate the GES has become difficult to define, and new approaches and considerations are currently being discussed by groups of experts, such as the technical subgroup on...

Physical Review D

Scalar-tensor theories with first-derivative self interactions, known as k-essence, may provide i... more Scalar-tensor theories with first-derivative self interactions, known as k-essence, may provide interesting phenomenology on cosmological scales. On smaller scales, however, initial value evolutions (which are crucial for predicting the behavior of astrophysical systems, such as binaries of compact objects) may run into instabilities related to the Cauchy problem becoming potentially ill-posed. Moreover, on local scales the dynamics may enter in the nonlinear regime, which may lie beyond the range of validity of the infrared theory. Completions of k-essence in the ultraviolet, when they are known to exist, mitigate these problems, as they both render Cauchy evolutions well-posed at all times, and allow for checking the relation between nonlinearities and the low energy theory's range of validity. Here, we explore these issues explicitly by considering an ultraviolet completion to k-essence and performing vacuum 1+1 dynamical evolutions within it. The results are compared to those obtained with the low-energy theory, and with the low-energy theory suitably deformed with a phenomenological "fixing the equations" approach. We confirm that the ultraviolet completion does not incur in any breakdown of the Cauchy problem's well-posedness, and we find that evolutions agree with the results of the low-energy theory, when the system is within the regime of validity of the latter. However, we also find that the nonlinear behavior of k-essence lies (for the most part) outside this regime.

Sensors, 2020

Passive acoustic monitoring systems allow for non-invasive monitoring of underwater species and a... more Passive acoustic monitoring systems allow for non-invasive monitoring of underwater species and anthropogenic noise. One of these systems has been developed keeping in mind the need to create a user-friendly tool to obtain the ambient noise indicators, while at the same time providing a powerful tool for marine scientists and biologists to progress in studying the effect of human activities on species and ecosystems. The device is based on a low-power processor with ad-hoc electronics, ensuring that the system has efficient energy management, and that the storage capacity is large enough to allow deployments for long periods. An application is presented using data from an acoustic campaign done in 2018 at El Gorguel (Cartagena, Spain). The results show a good agreement between theoretical maps created using AIS data and the ambient noise level indicators measured in the frequency bands of 63 Hz and 125 Hz specified in the directive 11 of the EU Marine Strategy Framework Directive. U...

Physical Review D, 2021

The observation of the shadow of the supermassive black hole M87 * by the Event Horizon Telescope... more The observation of the shadow of the supermassive black hole M87 * by the Event Horizon Telescope (EHT) is sensitive to the spacetime geometry near the circular photon orbit and beyond, and it thus has the potential to test general relativity in the strong field regime. Obstacles to this program, however, include degeneracies between putative deviations from general relativity and both the description of the accretion flow and the uncertainties on "calibration parameters", such as e.g. the mass and spin of the black hole. In this work, we introduce a formalism, based on a principal component analysis, capable of reconstructing the black hole metric (i.e. the "signal") in an agnostic way, while subtracting the "foreground" due to the uncertainties in the calibration parameters and the modelling of the accretion flow. We apply our technique to simulated mock data for spherically symmetric black holes surrounded by a thick accretion disk. We show that separation of signal and foreground may be possible with next generation EHT-like experiments.

The design of directive loudspeakers is a challenge for traditional techniques because it implies... more The design of directive loudspeakers is a challenge for traditional techniques because it implies big speakers due to the sound wavelength. In this work, the design of a directive loudspeaker using PZT ultrasound transducers is presented. This technique uses lineal modulation between ultrasound carrier signal and acoustic message and takes advantage of non-lineal propagation effects. These non-lineal effects produce intermodulation phenomona between ultrasonic carrier frequency and transmitted signal demodulating and generating an audible and very narrow beam on the pointing direction of ultrasound loudspeaker.In this work, the theoretical aspects, the critical factors and a real implementation of this technique are presented.

2017 22nd International Conference on Digital Signal Processing (DSP), 2017

This work addresses the study of sounds produced by odontocetes using a brand-new approach based ... more This work addresses the study of sounds produced by odontocetes using a brand-new approach based on signal modality. Characterizing the mechanisms used in sound generation, as well as classifying the repertory of sounds, is a complicated task given the complexity of the marine environment and the huge number of different marine mammal species. Several works in the last years have been raised to clarify how these sounds are generated. Understanding the behaviour of the organs responsible for the production and the mechanisms used in the generation is essential for the proposal of new classification features related to the underlying physics. This complex panorama may gain leverage from the advances in signal processing to the design of new algorithms based on the nature of the signals. Reconstructing the phase space, obtaining Recurrence Plots (RPs) and quantifying the complexity of the resulting structures are processed used with the aim of discerning and characterizing the different sounds produced by the odontocetes. Specifically between sounds with strong (almost-)periodic components, where traditional algorithms of signal processing are unable to get information related to the corresponding underlying model.

Instrumentation viewpoint, 2011

Very little is known about the way cetaceans and particularly beluga whales communicate. However ... more Very little is known about the way cetaceans and particularly beluga whales communicate. However as scientists and biologists investigate it is observed the extraordinary adaptation of the cetacean communication system to the underwater medium and the surprising communication skills. The ultrasonic sound emitted by beluga whales can be identified in what some scientists call vocalizations and related to animal behavior. The signal processing group GTS (iTEAM) of the Universitat Polit`ecnica de Val`encia alongside with the Oceanogr`afic have developed an automatic system for continuously monitoring beluga whale sounds. This system is intended to establish new behaviour patterns and help biologists to obtain a better understanding of beluga whales. The present work is devoted to the comparison of the different Naive Bayes classifiers into the automatic monitoring system.

This paper reports the work carried out by iTEAM researchers in Passive Acoustic Monitoring (PAM)... more This paper reports the work carried out by iTEAM researchers in Passive Acoustic Monitoring (PAM) for underwater monitoring of cetaceans. It includes a description of novel signal processing algorithms for detection and classification of aquatic mammal species as well as a hardware system called SAMARUC specially designed in collaboration with marine biologists.

Physical Review D, 2021

Hořava gravity is a proposal for completing general relativity in the ultraviolet by interactions... more Hořava gravity is a proposal for completing general relativity in the ultraviolet by interactions that violate Lorentz invariance at very high energies. We focus on (2+1)-dimensional projectable Hořava gravity, a theory which is renormalizable and perturbatively ultraviolet-complete, enjoying an asymptotically free ultraviolet fixed point. Adding a small cosmological constant to regulate the long distance behavior of the metric, we search for all circularly symmetric stationary vacuum solutions with vanishing angular momentum and approaching the de Sitter metric with a possible angle deficit at infinity. We find a two-parameter family of such geometries. Apart from the cosmological de Sitter horizon, these solutions generally contain another Killing horizon and should therefore be interpreted as black holes from the viewpoint of the low-energy theory. Contrary to naive expectations, their central singularity is not resolved by the higher derivative terms present in the action. It is unknown at present if these solutions form as a result of gravitational collapse. The only solution regular everywhere is just the de Sitter metric devoid of any black hole horizon.

Ingeniería del agua, 2021

Se realizó una revisión de datos históricos del efluente de la PTAR de PDVSA en su filial de inve... more Se realizó una revisión de datos históricos del efluente de la PTAR de PDVSA en su filial de investigación y desarrollo en la Ciudad de Los Teques, Estado Miranda, durante el período 2003-2014. Se muestreo por seis semanas para calcular la eficiencia en la remoción de DQO, DBO5 y SST. La eficiencia para la DQO fue de 86.51 y 72.94% en DBO5. Se determinó la proporción de lodos biológicos y las aguas agrias tratadas con procesos de oxidación avanzada (POA), necesaria para la disminución de la DQO y la DBO5. El mejor resultado obtenido en él fue de 222 mg/L de DQO y DBO5 32.15 mg/L, satisfaciendo la norma nacional para descarga en cuerpos de agua naturales.

Marine Policy, 2021

International audienc

Sensors, 2021

Anthropogenic impulsive sound sources with high intensity are a threat to marine life and it is c... more Anthropogenic impulsive sound sources with high intensity are a threat to marine life and it is crucial to keep them under control to preserve the biodiversity of marine ecosystems. Underwater explosions are one of the representatives of these impulsive sound sources, and existing detection techniques are generally based on monitoring the pressure level as well as some frequency-related features. In this paper, we propose a complementary approach to the underwater explosion detection problem through assessing the arrow of time. The arrow of time of the pressure waves coming from underwater explosions conveys information about the complex characteristics of the nonlinear physical processes taking place as a consequence of the explosion to some extent. We present a thorough review of the characterization of arrows of time in time-series, and then provide specific details regarding their applications in passive acoustic monitoring. Visibility graph-based metrics, specifically the direc...

Proceedings of 6th International Electronic Conference on Sensors and Applications, 2019

A passive acoustic monitoring (PAM) device named SAMARUC has been developed to acquire underwater... more A passive acoustic monitoring (PAM) device named SAMARUC has been developed to acquire underwater sounds following the specifications of the Monitoring Guidance for Underwater Noise in European Seas: Monitoring Guidance Specifications. Based on a Texas Instruments processor, an ultra-low power ADC was programmed to work at a sampling rate of 192 kHz and adhoc electronics were designed allowing the processor's two microSD buses to be used, thereby increasing the storage capacity. Many other software and hardware enhancements were implemented, such as the new low latency file system, the construction of NITUFF anodized aluminium housing and ringed buoys. With the resulting application, data obtained by the SAMARUC at El Gorguel (Cartagena, Spain) in 2018 were compared to a theoretical underwater noise map created using AIS data. This was done following the Descriptor D11.2 by means of the ambient noise level indicators at two one-third-octave frequency bands (63 Hz and 125 Hz), mainly related to marine traffic and noise pollution. The conjunction between the acquisition of underwater acoustic data and the development of a numerical propagation model was found to be highly recommendable to estimate the ambient continuous noise level when validating the acquired data as well as when correcting the prediction provided by the model.

Applied Acoustics, 2019

Passive acoustic monitoring of underwater sounds is an emerging discipline that can be used to gu... more Passive acoustic monitoring of underwater sounds is an emerging discipline that can be used to guarantee that anthropogenic noise meets acceptable limits, to detect the presence of cetacean species, and to ensure sustainable exploitation of our oceans and seas. In this scenario, graphical representation techniques play a key role in helping to reveal seasonal structures of human made noises. Nevertheless, for very long temporal series, it might be challenging to find a graphic visualization technique that allows representing a time range that is long enough to capture these seasonal events, while at the same time preserving short isolated events. We propose a framework for the creation of such visualization techniques and analyze the different stages involved: data reduction, color encoding, and signal processing on graphs. All of this is applied to data from deployments in two marine protected areas in order to provide an acoustic panorama and identify seasonal events.

National Aut6noma de Mexico contain specimens of several species of amphibians and reptiles from ... more National Aut6noma de Mexico contain specimens of several species of amphibians and reptiles from Mexican states from which they have not hitherto been reported. The following records are from seven states, for which 22 taxa are newly reported, as fQllows: CHIAPAS-AgaZyahnis aaZZidryas; HIDALGO-Corytophanes hernandezi, EZaphe f. fZavirufa; JALISCO-Phrynohyas venuZosa, TomoaaatyZus nitidu8 OPariU8, TPiprion spatulatus ~eticutatu8, Coleony~ eZegans nemoPalis, EUmeaes paPVulus, Mbbuya brachypoda, Phryndsoma asio, Dipsas gaigeae, Loxoaemus bicolor, Micrurus distans oZiveri, PseudoZeptodeira Zatifasaiata, TFopidodipsas, oaaidentatis, T. philippi; PUEBLA-Coniophanes bipunatatus biseriatus, SpiZo,tes pUlZatu8 mezioonus, Tropidodipsas s. sartorii; SAN LUIS POTOSI-Chiropterotriton ahondPostega araaens; VERACRUZ-Siren intermedia; ZACATECAS-Rana montezumai. Information concerning the specimens reported herein, or any others in the herpetological collections of the Instituto de Biologla (IBH), m...

Cornell University - arXiv, Jul 7, 2022

We investigate neutron star solutions in scalar-tensor theories of gravity with first-order deriv... more We investigate neutron star solutions in scalar-tensor theories of gravity with first-order derivative self-interactions in the action and in the matter coupling. We assess the robustness of the kinetic screening mechanism present in these theories against general conformal couplings to matter. The latter include ones leading to the classical Damour-Esposito-Farèse scalarization, as well as ones depending on the kinetic term of the scalar field. We find that kinetic screening always prevails over scalarization, and that kinetic couplings with matter enhance the suppression of scalar gradients inside the star even more, without relying on the non-linear regime. Fine tuning the kinetic coupling with the derivative self-interactions in the action allows one to partially cancel the latter, resulting in a weakening of kinetic screening inside the star. This effect represents a novel way to break screening mechanisms inside matter sources, and provides new signatures that might be testable with astrophysical observations.

We point out that the initial-value (Cauchy) problem for self-interacting vector fields presents ... more We point out that the initial-value (Cauchy) problem for self-interacting vector fields presents the same well-posedness issues as for first-order derivative self-interacting scalar fields (often referred to as k-essence). For the latter, suitable strategies have been employed in the last few years to successfully evolve the Cauchy problem at the level of the infrared theory, without the need for an explicit ultraviolet completion. We argue that the very same techniques can also be applied to self-interacting vector fields, avoiding a number of issues and "pathologies" recently found in the literature.

2017 22nd International Conference on Digital Signal Processing (DSP)

Anthropogenic underwater sound is now recognized as a world-wide problem. Shipping, seismic surve... more Anthropogenic underwater sound is now recognized as a world-wide problem. Shipping, seismic surveys and pile driving, among some other human activities, have shown a broad range of negative effects in a variety of species. It is thus important to control, register and characterize these activities in order to establish policies that mitigate its effects. For this purpose, automatic detectors of the major anthropogenic sound categories (impulsive and tonal sounds) are needed. An efficient algorithm capable of detecting impulsive and tonal sound categories is proposed. The detection algorithm is based on the Pulsed to Tonal Ratio (PTR) and, in this work, we show not only its simplicity but also how well it performs in a variety of situations. In contrast to what happens with some other techniques, the proposed detector generally succeeds in detecting pulsed and tonal events with additive white and pink noise. This makes the PTR detector particularly appropriate for passive acoustic monitoring.

Journal of Marine Science and Engineering

Over the last decade, national authorities and European administrations have made great efforts t... more Over the last decade, national authorities and European administrations have made great efforts to establish methodological standards for the assessment of underwater continuous noise, especially under the requirements set by the Marine Strategy Framework Directive (MSFD). Through the MSFD implementation across EU Member States Marine Reporting Units (MRUs), it is intended to establish the Good Environmental Status (GES) whether it is achieved or not. The evaluation of the Sound Pressure Level (SPL) at the local or regional scale for 1/3 octave band of 63 Hz and 125 Hz and the identification of long temporary trends were considered to be a priority due to the valuable information they can offer in relation to continuous low-frequency noise. Nevertheless, the methodology to determine threshold values from which to evaluate the GES has become difficult to define, and new approaches and considerations are currently being discussed by groups of experts, such as the technical subgroup on...

Physical Review D

Scalar-tensor theories with first-derivative self interactions, known as k-essence, may provide i... more Scalar-tensor theories with first-derivative self interactions, known as k-essence, may provide interesting phenomenology on cosmological scales. On smaller scales, however, initial value evolutions (which are crucial for predicting the behavior of astrophysical systems, such as binaries of compact objects) may run into instabilities related to the Cauchy problem becoming potentially ill-posed. Moreover, on local scales the dynamics may enter in the nonlinear regime, which may lie beyond the range of validity of the infrared theory. Completions of k-essence in the ultraviolet, when they are known to exist, mitigate these problems, as they both render Cauchy evolutions well-posed at all times, and allow for checking the relation between nonlinearities and the low energy theory's range of validity. Here, we explore these issues explicitly by considering an ultraviolet completion to k-essence and performing vacuum 1+1 dynamical evolutions within it. The results are compared to those obtained with the low-energy theory, and with the low-energy theory suitably deformed with a phenomenological "fixing the equations" approach. We confirm that the ultraviolet completion does not incur in any breakdown of the Cauchy problem's well-posedness, and we find that evolutions agree with the results of the low-energy theory, when the system is within the regime of validity of the latter. However, we also find that the nonlinear behavior of k-essence lies (for the most part) outside this regime.

Sensors, 2020

Passive acoustic monitoring systems allow for non-invasive monitoring of underwater species and a... more Passive acoustic monitoring systems allow for non-invasive monitoring of underwater species and anthropogenic noise. One of these systems has been developed keeping in mind the need to create a user-friendly tool to obtain the ambient noise indicators, while at the same time providing a powerful tool for marine scientists and biologists to progress in studying the effect of human activities on species and ecosystems. The device is based on a low-power processor with ad-hoc electronics, ensuring that the system has efficient energy management, and that the storage capacity is large enough to allow deployments for long periods. An application is presented using data from an acoustic campaign done in 2018 at El Gorguel (Cartagena, Spain). The results show a good agreement between theoretical maps created using AIS data and the ambient noise level indicators measured in the frequency bands of 63 Hz and 125 Hz specified in the directive 11 of the EU Marine Strategy Framework Directive. U...

Physical Review D, 2021

The observation of the shadow of the supermassive black hole M87 * by the Event Horizon Telescope... more The observation of the shadow of the supermassive black hole M87 * by the Event Horizon Telescope (EHT) is sensitive to the spacetime geometry near the circular photon orbit and beyond, and it thus has the potential to test general relativity in the strong field regime. Obstacles to this program, however, include degeneracies between putative deviations from general relativity and both the description of the accretion flow and the uncertainties on "calibration parameters", such as e.g. the mass and spin of the black hole. In this work, we introduce a formalism, based on a principal component analysis, capable of reconstructing the black hole metric (i.e. the "signal") in an agnostic way, while subtracting the "foreground" due to the uncertainties in the calibration parameters and the modelling of the accretion flow. We apply our technique to simulated mock data for spherically symmetric black holes surrounded by a thick accretion disk. We show that separation of signal and foreground may be possible with next generation EHT-like experiments.

The design of directive loudspeakers is a challenge for traditional techniques because it implies... more The design of directive loudspeakers is a challenge for traditional techniques because it implies big speakers due to the sound wavelength. In this work, the design of a directive loudspeaker using PZT ultrasound transducers is presented. This technique uses lineal modulation between ultrasound carrier signal and acoustic message and takes advantage of non-lineal propagation effects. These non-lineal effects produce intermodulation phenomona between ultrasonic carrier frequency and transmitted signal demodulating and generating an audible and very narrow beam on the pointing direction of ultrasound loudspeaker.In this work, the theoretical aspects, the critical factors and a real implementation of this technique are presented.

2017 22nd International Conference on Digital Signal Processing (DSP), 2017

This work addresses the study of sounds produced by odontocetes using a brand-new approach based ... more This work addresses the study of sounds produced by odontocetes using a brand-new approach based on signal modality. Characterizing the mechanisms used in sound generation, as well as classifying the repertory of sounds, is a complicated task given the complexity of the marine environment and the huge number of different marine mammal species. Several works in the last years have been raised to clarify how these sounds are generated. Understanding the behaviour of the organs responsible for the production and the mechanisms used in the generation is essential for the proposal of new classification features related to the underlying physics. This complex panorama may gain leverage from the advances in signal processing to the design of new algorithms based on the nature of the signals. Reconstructing the phase space, obtaining Recurrence Plots (RPs) and quantifying the complexity of the resulting structures are processed used with the aim of discerning and characterizing the different sounds produced by the odontocetes. Specifically between sounds with strong (almost-)periodic components, where traditional algorithms of signal processing are unable to get information related to the corresponding underlying model.

Instrumentation viewpoint, 2011

Very little is known about the way cetaceans and particularly beluga whales communicate. However ... more Very little is known about the way cetaceans and particularly beluga whales communicate. However as scientists and biologists investigate it is observed the extraordinary adaptation of the cetacean communication system to the underwater medium and the surprising communication skills. The ultrasonic sound emitted by beluga whales can be identified in what some scientists call vocalizations and related to animal behavior. The signal processing group GTS (iTEAM) of the Universitat Polit`ecnica de Val`encia alongside with the Oceanogr`afic have developed an automatic system for continuously monitoring beluga whale sounds. This system is intended to establish new behaviour patterns and help biologists to obtain a better understanding of beluga whales. The present work is devoted to the comparison of the different Naive Bayes classifiers into the automatic monitoring system.

This paper reports the work carried out by iTEAM researchers in Passive Acoustic Monitoring (PAM)... more This paper reports the work carried out by iTEAM researchers in Passive Acoustic Monitoring (PAM) for underwater monitoring of cetaceans. It includes a description of novel signal processing algorithms for detection and classification of aquatic mammal species as well as a hardware system called SAMARUC specially designed in collaboration with marine biologists.

Physical Review D, 2021

Hořava gravity is a proposal for completing general relativity in the ultraviolet by interactions... more Hořava gravity is a proposal for completing general relativity in the ultraviolet by interactions that violate Lorentz invariance at very high energies. We focus on (2+1)-dimensional projectable Hořava gravity, a theory which is renormalizable and perturbatively ultraviolet-complete, enjoying an asymptotically free ultraviolet fixed point. Adding a small cosmological constant to regulate the long distance behavior of the metric, we search for all circularly symmetric stationary vacuum solutions with vanishing angular momentum and approaching the de Sitter metric with a possible angle deficit at infinity. We find a two-parameter family of such geometries. Apart from the cosmological de Sitter horizon, these solutions generally contain another Killing horizon and should therefore be interpreted as black holes from the viewpoint of the low-energy theory. Contrary to naive expectations, their central singularity is not resolved by the higher derivative terms present in the action. It is unknown at present if these solutions form as a result of gravitational collapse. The only solution regular everywhere is just the de Sitter metric devoid of any black hole horizon.

Ingeniería del agua, 2021

Se realizó una revisión de datos históricos del efluente de la PTAR de PDVSA en su filial de inve... more Se realizó una revisión de datos históricos del efluente de la PTAR de PDVSA en su filial de investigación y desarrollo en la Ciudad de Los Teques, Estado Miranda, durante el período 2003-2014. Se muestreo por seis semanas para calcular la eficiencia en la remoción de DQO, DBO5 y SST. La eficiencia para la DQO fue de 86.51 y 72.94% en DBO5. Se determinó la proporción de lodos biológicos y las aguas agrias tratadas con procesos de oxidación avanzada (POA), necesaria para la disminución de la DQO y la DBO5. El mejor resultado obtenido en él fue de 222 mg/L de DQO y DBO5 32.15 mg/L, satisfaciendo la norma nacional para descarga en cuerpos de agua naturales.

Marine Policy, 2021

International audienc

Sensors, 2021

Anthropogenic impulsive sound sources with high intensity are a threat to marine life and it is c... more Anthropogenic impulsive sound sources with high intensity are a threat to marine life and it is crucial to keep them under control to preserve the biodiversity of marine ecosystems. Underwater explosions are one of the representatives of these impulsive sound sources, and existing detection techniques are generally based on monitoring the pressure level as well as some frequency-related features. In this paper, we propose a complementary approach to the underwater explosion detection problem through assessing the arrow of time. The arrow of time of the pressure waves coming from underwater explosions conveys information about the complex characteristics of the nonlinear physical processes taking place as a consequence of the explosion to some extent. We present a thorough review of the characterization of arrows of time in time-series, and then provide specific details regarding their applications in passive acoustic monitoring. Visibility graph-based metrics, specifically the direc...

Proceedings of 6th International Electronic Conference on Sensors and Applications, 2019

A passive acoustic monitoring (PAM) device named SAMARUC has been developed to acquire underwater... more A passive acoustic monitoring (PAM) device named SAMARUC has been developed to acquire underwater sounds following the specifications of the Monitoring Guidance for Underwater Noise in European Seas: Monitoring Guidance Specifications. Based on a Texas Instruments processor, an ultra-low power ADC was programmed to work at a sampling rate of 192 kHz and adhoc electronics were designed allowing the processor's two microSD buses to be used, thereby increasing the storage capacity. Many other software and hardware enhancements were implemented, such as the new low latency file system, the construction of NITUFF anodized aluminium housing and ringed buoys. With the resulting application, data obtained by the SAMARUC at El Gorguel (Cartagena, Spain) in 2018 were compared to a theoretical underwater noise map created using AIS data. This was done following the Descriptor D11.2 by means of the ambient noise level indicators at two one-third-octave frequency bands (63 Hz and 125 Hz), mainly related to marine traffic and noise pollution. The conjunction between the acquisition of underwater acoustic data and the development of a numerical propagation model was found to be highly recommendable to estimate the ambient continuous noise level when validating the acquired data as well as when correcting the prediction provided by the model.

Applied Acoustics, 2019

Passive acoustic monitoring of underwater sounds is an emerging discipline that can be used to gu... more Passive acoustic monitoring of underwater sounds is an emerging discipline that can be used to guarantee that anthropogenic noise meets acceptable limits, to detect the presence of cetacean species, and to ensure sustainable exploitation of our oceans and seas. In this scenario, graphical representation techniques play a key role in helping to reveal seasonal structures of human made noises. Nevertheless, for very long temporal series, it might be challenging to find a graphic visualization technique that allows representing a time range that is long enough to capture these seasonal events, while at the same time preserving short isolated events. We propose a framework for the creation of such visualization techniques and analyze the different stages involved: data reduction, color encoding, and signal processing on graphs. All of this is applied to data from deployments in two marine protected areas in order to provide an acoustic panorama and identify seasonal events.