STATISTIQUES DE BRUITS AMBIANTS TRANSITOIRES DANS L'ARCTIQUE

Le bruit ambiant sous-marin dans l'Artique durant l'hiver est caractérisé par la présence de bruits transitoires, correspondant au craquement de la glace. Ces bruits transitoires rendent le bruit total non-stationnaire, et sa distribution non-normale. Leur effet dépend de leur contribution relativement à la durée et à la puissance du bruit ambiant total. Il est difficile d'accumuler des statistiques sur les bruits transitoires, puisque leur détection habituellement demande de l'assistance humaine, un procédé qui prend du temps. On a implémenté sur un ordinateur un algorithme non-paramétrique pour détecter automatiquement les bruits transitoires dans des enregistrements de bruit ambiants. L'algorithme cherche la distribution de probabilité des maxima locaux pour le niveau L au-dessus duquel une proportion arbitraire r des maxima se trouvent. Il calcule ensuite la probabilité p qu'un échantillon de longueur W contienne plus que N maxima dépassant L. Cette probabilité est simplement une somme de distributions binomiales. L'enregistrement est alors balayé avec une fenêtre de longueur W, et la probabilité p est calculée pour chaque position de la fenêtre. Quand p est plus petit qu'un seuil Po, la fenêtre est marquée comme contenant un bruit transitoire. On peut extraire la position précise du commencement et de la fin d'un bruit transitoire en cherchant à l'intérieur d'une fenêtre pour le premier maximum qui dépasse la valeur L. On a appliqué cet algorithme pour extraire les bruits transitoires d'une série d'échantillons de bruit ambiant, chacun d'une durée de cinq minutes, collectés sur la calotte polaire arctique durant le mois d'avril. On a filtré les échantillons avec des filtres passe-bande pour étudier le contenu transitoire pour plusieurs fréquences. On a trouvé que la fraction, en durée et en puissance, du contenu transitoire des échantillons varient grandement avec la fréquence. Le bruit transitoire ne tient compte que pour 5 - 25% de la puissance aux environs de 10 Hz, et 45 - 80% de la puissance entre 100 et 1000 Hz. D'un autre côté, pendant les périodes calmes, le bruit transitoire tient compte pour 35 - 45% de la puissance aux environs de 10 Hz, et 80 - 95% de la puissance entre 100 et 1000 Hz.Underwater ambient noise in the Arctic is characterized by the presence of transients, corresponding to ice cracking events. These transients cause the total signal to be non-Gaussian and non-stationary. The extent of their effect depends on their relative contribution to the total ambient noise field. Statistics on transients are difficult to accumulate, since their detection usually requires human assistance, and is a time-consuming process. A non-parametric transient detecting algorithm was implemented on a computer in order to extract the transients from ambient noise time series automatically. The algorithm searches the probability distribution of peaks for the level L above which a proportion r of the peaks lies. It then calculates the probability for a sample of length W to contain more than a certain number of peaks above L. This probability is simply a sum of binomial distributions. The time series is then scanned with a window of length W, and the probability p is calculated for each position of the window. When p is smaller than a threshold Po, the window is flagged as containing a transient. The beginning and end of the transient can be found precisely by scanning inside the window for the first peak which exceeds the value L. This transient-extracting algorithm was applied to a series of five-minute-long ambient noise samples taken under the Arctic pack ice during the month of April. The data were bandpass-filtered in order to study the transient content at different frequencies. It was found that the relative duration and power of transients within the time series varies greatly with frequency. Transients accounted for only 5 - 25% of the power around 10 Hz, and 45 - 80% of the power between 100 and 1000 Hz during noisy periods. On the other hand, during quiet periods, transients accounted for 35 - 45% of the power around 10 Hz, and 80 - 95% of the power between 100 and 1000 Hz

Interferon-γ drives macrophage reprogramming, cerebrovascular remodeling, and cognitive dysfunction in a zebrafish and a mouse model of ion imbalance and pressure overload

Dysregulated immune response contributes to inefficiency of treatment strategies to control hypertension and reduce the risk of end-organ damage. Uncovering the immune pathways driving the transition from the onset of hypertensive stimulus to the manifestation of multi-organ dysfunction are much-needed insights for immune targeted therapy.; To aid visualization of cellular events orchestrating multi-organ pathogenesis, we modeled hypertensive cardiovascular remodeling in zebrafish. Zebrafish larvae exposed to ion-poor environment exhibited rapid angiotensinogen upregulation, followed by manifestation of arterial hypertension and cardiac remodeling that recapitulates key characteristics of incipient Heart Failure with preserved Ejection Fraction. In the brain, time-lapse imaging revealed the occurrence of cerebrovascular regression through endothelial retraction and migration in response to the ion-poor treatment. This phenomenon is associated with macrophage/microglia-endothelial contacts and endothelial junctional retraction. Cytokine and transcriptomic profiling identified systemic upregulation of interferon-γ and interleukin 1β, and revealed altered macrophage/microglia transcriptional program characterized by suppression of innate immunity and vasculo/neuroprotective gene expression. Both zebrafish and a murine model of pressure overload-induced brain damage demonstrated that the brain pathology and macrophage/microglia phenotypic alteration are dependent on interferon-γ signaling. In zebrafish, interferon-γ receptor 1 mutation prevents cerebrovascular remodeling and dysregulation of macrophage/microglia transcriptomic profile. Supplementation of bone morphogenetic protein 5, identified from the transcriptomic approach as a downregulated gene in ion-poor-treated macrophages/microglia that is rescued by interferon-γ blockage, mitigated cerebral microvessel loss. In mice subjected to transverse aortic constriction-induced pressure overload, typically developing cerebrovascular injury, neuroinflammation and cognitive dysfunction, interferon-γ neutralization protected them from blood-brain-barrier disruption, cerebrovascular rarefaction, and cognitive decline.; These findings uncover cellular and molecular players of an immune pathway communicating hypertensive stimulus to structural and functional remodeling of the brain and identify anti-interferon-γ treatment as a promising intervention strategy capable of preventing pressure overload-induced damage of the cerebrovascular and nervous systems.; Hypertension is a major risk factor for damages of the vasculature, heart, and brain, and thereby a major healthcare burden. Inadequate cerebral blood supply due to altered cerebrovascular structure and vasoregulatory disruption upon hypertension render the brain highly susceptible to stroke and cognitive decline. We envision that the cellular and molecular mechanisms uncovered here linking immune dysregulation to cerebrovascular remodeling and functional impairment of the brain will inform future development of immunomodulatory therapeutic strategies for counteracting derangement of macrophage/microglia activation and their vasculo/neuroprotective function in response to systemic inflammation in hypertension

Perception of sound-source motion by the human brain

We assessed the human brain network for sound-motion processing using the same virtual stimulus in three independent functional imaging experiments. All experiments show a bilateral posterior network of activation, including planum temporale (PT) and parieto-temporal operculum (PTO). This was demonstrated in contrasts between sound movement and two control conditions: externalized stationary stimuli (in the midline or to the side of the head) and midline sounds within the head with similar spectro-temporal structure. We suggest specific computational mechanisms in PT for disambiguation of the intrinsic spectro-temporal features of a sound and the spectro-temporal effect of sound movement. The results support the existence of a posteriorly directed temporo-parietal pathway for obligatory perceptual processing of sound-source motion

Water footprint

The robust localization of speech sources is required for a wide range of applications, among them hearing aids and teleconferencing systems. This chapter focuses on binaural approaches to estimate the spatial position of multiple competing speakers in adverse acoustic scenarios by only exploiting the signals reaching both ears. A set of experiments is conducted to systematically evaluate the impact of reverberation and interfering noise on speaker-localization performance. In particular, the spatial distribution of the interfering noise has a considerable effect on speaker-localization performance, being most detrimental if the noise field contains strong directional components. In these conditions, interfering noise might be erroneously classified as a speaker position. This observation highlights the necessity to combine the localization stage with a decision about the underlying source type in order to enable a robust localization of speakers in noisy environments