Additional Noise Sources Research Articles

Multiplicative noise induced bistability and stochastic resonance

Abstract Stochastic resonance is a well established phenomenon, which proves relevant for a wide range of applications, of broad trans-disciplinary breath. Consider a one dimensional bistable stochastic system, characterized by a deterministic double well potential and shaken by an additive noise source. When subject to an external periodic drive, and for a proper choice of the noise strength, the system swings regularly between the two existing deterministic fixed points, with just one switch for each oscillation of the imposed forcing term. This resonant condition can be exploited to unravel weak periodic signals, otherwise inaccessible to conventional detectors. Here, we will set to revisit the stochastic resonance concept by operating in a modified framework where bistability is induced by the nonlinear nature of the multiplicative noise. A candidate model is in particular introduced which fulfils the above requirements while allowing for analytical progress to be made. Working with reference to this case study, we elaborate on the conditions for the onset of the generalized stochastic resonance mechanism. As a byproduct of the analysis, a novel resonant regime is also identified which displays no lower bound for the frequencies that can be resolved, at variance with the traditional setting.

Accurate Drift-Invariant Single-Molecule Force Calibration Using the Hadamard Variance.

Single-molecule force spectroscopy (SMFS) techniques play a pivotal role in unraveling the mechanics and conformational transitions of biological macromolecules under external forces. Among these techniques, multiplexed magnetic tweezers (MT) are particularly well suited to probe very small forces, ≤1 pN, critical for studying non-covalent interactions and regulatory conformational changes at the single-molecule level. However, to apply and measure such small forces, a reliable and accurate force calibration procedure is crucial. Here, we introduce a new approach to calibrate MT based on thermal motion using the Hadamard variance (HV). To test our method, we perform bead-tether Brownian dynamics simulations that mimic our experimental system and compare the performance of the HV method against two established techniques: power spectral density (PSD) and Allan variance (AV) analyses. Our analysis includes an assessment of each method's ability to mitigate common sources of additive noise, such as white and pink noise, as well as drift, which often complicate experimental data analysis. We find that the HV method exhibits overall similar or higher precision and accuracy, yielding lower force estimation errors across a wide range of signal-to-noise ratios (SNR) and drift speeds compared to the PSD and AV methods. Notably, the HV method remains robust against drift, maintaining consistent uncertainty levels across the entire studied SNR and drift speed spectrum. We also explore the HV method using experimental MT data, where we find overall smaller force estimation errors compared to PSD and AV approaches. Overall, the HV method offers a robust method for achieving sub-pN resolution and precision in multiplexed MT measurements. Its potential extends to other SMFS techniques, presenting exciting opportunities for advancing our understanding of mechano-sensitivity and force generation in biological systems. To make our methods widely accessible to the research community, we provide a well-documented Python implementation of the HV method as an extension to the Tweezepy package.

Optimal demodulation domain for microwave SQUID multiplexers in presence of readout system noise

The Microwave SQUID Multiplexer (μMUX) is the device of choice for the readout of a large number of low-temperature detectors in a wide variety of experiments within the fields of astronomy and particle physics. While it offers large multiplexing factors, the system noise performance is highly dependent on the cold- and warm-readout electronic systems used to read it out, as well as the demodulation domain and parameters chosen. In order to understand the impact of the readout systems in the overall detection system noise performance, first, we extended the available μMUX simulation frameworks, including additive and multiplicative noise sources in the probing tones (i.e., phase and amplitude noise), along with the capability of demodulating the scientific data, either in the resonator’s phase or the scattering amplitude. Then, considering the additive noise as a dominant noise source, the optimum readout parameters to achieve minimum system noise were found for both open-loop and flux-ramp demodulation schemes in the aforementioned domains. Later, we evaluated the system noise sensitivity to multiplicative noise sources under the optimum readout parameters. Finally, as a case study, we evaluated the optimal demodulation domain and the expected system noise level for a typical software-defined radio readout system. This work leads to an improved system performance prediction and noise engineering based on the available readout electronics and the selected demodulation domain.

The influence of jet on aerodynamic noise in the pantograph area at different sinking heights

The influence mechanism of jet on aerodynamic noise control in the pantograph region at different sinking heights was numerically studied using an Improved Delayed Detached Eddy Simulation (IDDES) model and the Ffowcs Williams-Hawkings (FW-H) equation. Active flow control was achieved by setting jet slots at the leading edge of the cavity to predict the noise generated by the jet itself. The results showed that in the pantograph region with a sinking height of 500 mm, the shear layer was lifted by the jet, which prevented high-speed turbulence caused by flow separation from entering the cavity. Therefore, the model with jet control device reduced the overall far-field noise on the side of the pantograph by 1.6 ∼ 3.9 dB. Through flow field analysis, for the pantograph region where flow separation occurs in the front of the cavity, the jet needs to lift the shear layer enough to cross the front of the pantograph and prevent flow separation, thereby reducing the aerodynamic noise. For the pantograph region without flow separation in the front of the cavity, the jet may introduce additional noise sources, deteriorating the aerodynamic noise in the pantograph region.

Effect of background noise characteristics on early warning indicators of thermoacoustic instability

In this work, we investigate the effects of background noise characteristics — specifically noise color (or correlation time) and intensity — arising from velocity-coupled and additive noise sources, on the early warning indicators (EWIs) of thermoacoustic instability. We employ a nonlinear reduced-order combustion dynamics model for our investigation. In the absence of noise, the nonlinear model undergoes a subcritical Hopf bifurcation, and our focus lies within the linearly stable region of the system (subthreshold region). The studied class of EWIs encompasses those derived from time series (variance), spectral analysis (coherence factor), Hurst exponent, and nonlinear methods (permutation entropy). We find that when the background noise is purely multiplicative, the trends in EWIs are primarily influenced by noise characteristics rather than the control parameter. Further, the EWIs cannot be estimated at low noise levels for large correlation times. In case of purely additive noise driven system, the coherence factor and variance are reliable EWIs across all range of investigated noise characteristics. The Hurst exponent can serve as effective EWI when the system features large noise correlation times, while permutation entropy is effective only when the system features small noise correlation time, i.e., where white noise assumption is acceptable. When the background noise includes contributions from both multiplicative and additive sources, coherence factor and variance emerges as the most reliable EWIs. These results provide insights for selecting appropriate EWIs to be employed in practical systems, considering potential variations in noise characteristics with simultaneous changes in combustor operating conditions.Novelty and significanceThis study conclusively shows that background noise (multiplicative and additive) characteristics – noise correlation time (color) and intensity – can significantly change the trends in early warning indicators (EWIs) for predicting the impending thermoacoustic oscillations. In gas turbine combustors, where thermoacoustic instability poses a critical challenge, inherent noise dynamics undergo variations with changing operating conditions and combustor designs. The development of effective EWIs to foresee the onset of thermoacoustic instability is crucial for preventing potential damage and ensuring the reliable operation of combustion systems. Previous works on stochastic dynamics of combustors simplify noise with the additive white noise assumption. Thus, our results demonstrated on a nonlinear combustion dynamics model advance the state-of-the-art with respect to the early prediction and control of thermoacoustic instability. The results provide valuable insights for selecting appropriate EWIs for engine monitoring in the absence of information on noise properties and their variation with operating conditions. This practical information is of direct relevance and interest to any gas turbine manufacturer/user.

Characterization of entanglement on superconducting quantum computers of up to 414 qubits

As quantum technology advances and the size of quantum computers grow, it becomes increasingly important to understand the extent of quality in the devices. As large-scale entanglement is a quantum resource crucial for achieving quantum advantage, the challenge in its generation makes it a valuable benchmark for measuring the performance of universal quantum devices. In this paper, we study entanglement in Greenberger-Horne-Zeilinger (GHZ) and graph states prepared on the range of IBM Quantum devices. We generate GHZ states and investigate their coherence times with respect to state size and dynamical decoupling techniques. A GHZ fidelity of 0.519±0.014 is measured on a 32-qubit GHZ state, certifying its genuine multipartite entanglement (GME). We show a substantial improvement in GHZ decoherence rates for a seven-qubit GHZ state after implementing dynamical decoupling, and observe a linear trend in the decoherence rate of α=(7.13N+5.54)×10−3µs−1 for up to N=15 qubits, confirming the absence of superdecoherence. Additionally, we prepare and characterize fully bipartite entangled native-graph states on 22 superconducting quantum devices with qubit counts as high as 414 qubits, all active qubits of the 433-qubit IBM Osprey device. Analysis of the decay of two-qubit entanglement within the prepared states shows suppression of coherent noise signals with the implementation of dynamical decoupling techniques. Additionally, we observe that the entanglement in some qubit pairs oscillates over time, which is likely caused by residual ZZ-interactions. Characterizing entanglement in native-graph states, along with detecting entanglement oscillations, can be an effective approach to low-level device benchmarking that encapsulates two-qubit error rates along with additional sources of noise, with possible applications to quantum circuit compilation. We develop several tools to automate the preparation and entanglement characterization of GHZ and graph states. In particular, a method to characterize graph state bipartite entanglement using just 36 circuits, constant with respect to the number of qubits. Published by the American Physical Society 2024

A Comparison of Denoising Approaches for Spoken Word Production Related Artefacts in Continuous Multiband fMRI Data

Abstract It is well-established from fMRI experiments employing gradient echo echo-planar imaging (EPI) sequences that overt speech production introduces signal artefacts compromising accurate detection of task-related responses. Both design and post-processing (denoising) techniques have been proposed and implemented over the years to mitigate the various noise sources. Recently, fMRI studies of speech production have begun to adopt multiband EPI sequences that offer better signal-to-noise ratio (SNR) and temporal resolution allowing adequate sampling of physiological noise sources (e.g., respiration, cardiovascular effects) and reduced scanner acoustic noise. However, these new sequences may also introduce additional noise sources. In this study, we demonstrate the impact of applying several noise-estimation and removal approaches to continuous multiband fMRI data acquired during a naming-to-definition task, including rigid body motion regression and outlier censoring, principal component analysis for removal of cerebrospinal fluid (CSF)/edge-related noise components, and global fMRI signal regression (using two different approaches) compared to a baseline of realignment and unwarping alone. Our results show the strongest and most spatially extensive sources of physiological noise are the global signal fluctuations arising from respiration and muscle action and CSF/edge-related noise components, with residual rigid body motion contributing relatively little variance. Interestingly, denoising approaches tended to reduce and enhance task-related BOLD signal increases and decreases, respectively. Global signal regression using a voxel-wise linear model of the global signal estimated from unmasked data resulted in dramatic improvements in temporal SNR. Overall, these findings show the benefits of combining continuous multiband EPI sequences and denoising approaches to investigate the neurobiology of speech production.

Influence of conspecifics and road noise on the properties ofthe advertisement call of Phyllodytes luteolus (Anura, Hylidae).

Acoustic communication in animals can be affected by multiple biotic (intra and interspecific) and abiotic (e.g., wind and rain) natural noises. In addition, human beings produce additional novel sources of noise, which can reduce or inhibit the reception of acoustic signals by conspecifics, leading to behavioral changes. In this study, we investigated whether sound of conspecifics and road noise additively affect the acoustic parameters of the advertisement call of males of a Yellow Heart-tongued Frog (Phyllodytes luteolus). We hypothesized that males that vocalize in choruses (males calling nearby) and in areas close to highways (anthropic noise) will increase their temporal and spectral acoustic parameters, respectively, to avoid acoustic signal masking. We recorded the vocalizations of 38 males in environments close (N = 18) to and distant (N = 20) from highways in different social contexts (many or few individuals calling nearby). Contrary to our expectation, the results indicated that males calling in areas close to highways had lower dominant frequency calls than those from natural areas (far from highways), and that the density of males in the chorus had no influence on the acoustic parameters. Furthermore, we found a positive relationship between body size and intensity, indicating that larger individuals can emit calls that can reach greater distances. The advertisement call of Phyllodytes luteolus has a high dominant frequency, with little overlap with the frequency of anthropic noises (roads), which may explain its presence and reproductive success of this species in bromeliads from urbanized areas.

Behind the mask: can HARMONI@ELT detect biosignatures in the reflected light of Proxima b?

ABSTRACT Proxima b is a rocky exoplanet in the habitable zone of the nearest star system and a key test case in the search for extraterrestrial life. Here, we investigate the characterization of a potential Earth-like atmosphere around Proxima b in reflected light via molecule mapping, combining high-resolution spectroscopy (HRS) and high contrast imaging, using the first-generation integral field spectrograph, High Angular Resolution Monolithic Optical and Near-infrared Integral field spectrograph (HARMONI), on the 39-m Extremely Large Telescope (ELT). We simulate comprehensive observations of Proxima b at an assumed 45° inclination using HARMONI’s High Contrast Adaptive Optics mode, with spatial resolution $\sim 8 \,\rm mas$ ($3.88 \,\rm mas$ spaxel−1) and spectral resolving power R ≃ 17 000 between 1.538–$1.678\,\mathrm{\mu }\mathrm{m}$, containing the spectral features of water, carbon dioxide, and methane. Tellurics, stellar features, and additional noise sources are included, and removed using established molecule mapping techniques. We find that HARMONI’s current focal plane mask (FPM) is too large and obscures the orbit of Proxima b and thus explore smaller and offset FPMs to yield a detection. An $\rm {S/N}=5$ detection of Proxima b’s reflected light, suitable for atmospheric characterization, is possible with such modifications, requiring a minimum of 20 h, but ideally at least 30 h of integration time. We highlight that such detections do not scale with the photon noise, hence suitably detailed simulations of future instruments for the ELTs are needed to fully understand their ability to perform HRS observations of exoplanet atmospheres. Alterations to the HARMONI FPM design are feasible at this stage, but must be considered in context of other science cases.

Cluster profiles from beyond-the-QE CMB lensing mass maps

Clusters of galaxies, being the largest collapsed structures in the universe, offer valuable insights into the nature of cosmic evolution. Precise calibration of the mass of clusters can be obtained by extracting their gravitational lensing signal on the Cosmic Microwave Background (CMB) fluctuations. We extend and test here the performance achieved on cluster scales by the parameter-free, maximum a posteriori (MAP) CMB lensing reconstruction method, which has been shown to be optimal in the broader context of CMB lensing mass map and power spectrum estimation. In the context of cluster lensing, the lensing signal of other large-scale structures acts as an additional source of noise. We show here that by delensing the CMB fluctuations around each and every cluster, this noise variance is reduced according to expectations. We also demonstrate that the well-known bias in the temperature quadratic estimator in this regime, sourced by the strong non-Gaussianity of the signal, is almost entirely mitigated without any scale cuts. Being statistically speaking an optimal and blind lensing mass map reconstruction, the MAP estimator is a promising tool for the calibration of the masses of clusters.

Sensitivity comparison of two-photon vs three-photon Rydberg electrometry

We investigate the sensitivity of co-linear three-photon electromagnetically induced transparency (EIT) in 133Cs Rydberg atoms to radio frequency electric fields and compare against the conventional two-photon system. Specifically, we model the 4-level and 5-level atomic systems and compare how the transmission of the probe changes with different laser powers and RF field strengths. In this model, we define a sensitivity metric that relates to the current best experimental implementation and assumes photon shot noise limited detection. We find that the three-photon system boasts much narrower linewidths compared to the conventional two-photon EIT. These narrow line features, however, do not align with the regions of the best sensitivity. In addition to this, we calculate the expected sensitivity for the two-photon Rydberg sensor and find that the best achievable sensitivity is over an order of magnitude better than the current measured values of 5 μVm−1Hz−1/2. However, by accounting for additional noise sources in the experiment and the quantum efficiency of the photo-detectors, the values are in good agreement.

Large Eddy Simulation of the ACAT1 fan stage for broadband noise prediction

A numerical study is carried out to assess the aerodynamic and noise radiation specific features of the ACAT1 fan stage, which was tested in the framework of the European project TurbonoiseBB. This study deals with the prediction of the broadband noise radiated by the fan stage at approach conditions, and particularly focuses on the rotor–stator interaction (RSI) noise, which results from the impact of the fan wakes onto the outlet guide vanes (OGV). To this end, two wall-modeled Large Eddy Simulations (LES) with different levels of mesh refinement have been performed on the full fan-OGV stage. The finer mesh significantly improved the aerodynamic predictions in terms of mean flow profiles, but also in terms of RMS profiles and velocity spectra, for which significant disparities are highlighted for the coarser LES. Only slight disparities regarding the turbulent content of the flow remain for the finer LES. The typical flow features at approach conditions are examined and the noise sources on both the stator and the rotor are analyzed, revealing the presence of additional broadband noise sources. Noise predictions are performed by using the free-field Ffowcs Williams and Hawkings (FW-H) analogy, and Goldstein’s in-duct acoustic analogy informed with the pressure fluctuations recorded on the stator and rotor surfaces. FW-H predictions of the stator noise, though well recovering the shape of the experimental spectra, overestimate the radiated noise especially upstream of the fan. Using the finer simulation data substantially reduces the gap with the measurements. Accounting for the duct effect on the sound propagation, further improves the predictions in terms of absolute levels, leading to a good agreement between the finer simulation and the noise measurements. The breakdown of the different stator noise source contributions, in conjunction with rotor broadband noise predictions made it possible to confirm the presence of additional significant broadband noise sources, questioning the common assumption considering the RSI sources as the only dominant fan noise mechanism at approach conditions.

Common pitfalls and potential solutions for crypto-currency mining facility noise

Crypto-currency mining facilities have become more and more common over the last few years, but there is no standard for construction or noise mitigation for these facilities. Many noise issues are encountered after the facilities are complete and operating. The facilities can contain thousands of "miners" which can be quite loud. Often, the manufacturers do not supply reliable sound data and the miners themselves are constantly evolving. The miners have extreme power and ventilation requirements which introduce additional noise sources and paths, as well as site requirements. I have examined the effectiveness of mitigation techniques for these facilities and addressed potential pitfalls for facilities based on similar issues observed across several projects.

Noise in the brain: Transcranial random noise stimulation and perceptual noise act on a stochastic resonance-like mechanism.

Stochastic resonance (SR) is a phenomenon in which a certain amount of random noise added to a weak subthreshold stimulus can enhance signal detectability. It is unknown how external noise interacts with neural noise in producing an SR-like phenomenon and whether this interaction results in a modulation of either network efficiency or the efficiency of single neurons. Using random dot motion stimuli and noninvasive brain stimulation, we attempted to unveil the specific mechanism of action of the SR-like phenomenon in motion perception, if present. We aimed to determine whether signal integration efficiency changes with external noise (random dot numerosity) and how electrical transcranial random noise stimulation (tRNS) can affect the peak performance. The participants performed a coherent motion detection task in which the random dot numerosity varied, whereas the signal-to-noise ratio (SNR) remained constant. We applied placebo or tRNS with an amplitude of either 1 or 2mA during task execution. We found peaks in participants' performance both in the case of placebo stimulation and in the case of 1-mA tRNS. In the latter case (i.e., with an additional noise source), the peak emerged at lower random dot numerosity levels than when no additional noise was added (placebo). No clear peak was observed with 2-mA tRNS. An equivalent noise (EN) analysis confirmed that SR arises from a modulation of the network efficiency underlying motion signal integration. These results indicate a joint contribution of external and neural noise (modulated by tRNS) in eliciting an SR-like phenomenon.

Numerical investigation of noise suppression and amplification in forced oscillations of single and tandem cylinders in high Reynolds number turbulent flows

The noise generated by a three-dimensional turbulent wake behind an oscillating single or tandem cylinder(s) is studied using detached eddy simulation and the Ffowcs Williams-Hawkings (FW-H) method. This hybrid methodology is validated using some experimental data of a turbulent flow past a single or tandem stationary cylinder(s) and some numerical data (obtained from a direct numerical simulation) of a laminar flow past tandem oscillating cylinders. For an oscillating cylinder at a fixed Reynolds number Re=120,000, the sound energy is suppressed compared to that of a stationary cylinder provided the value of oscillation frequency approaches 57% of the original vortex-shedding frequency of the stationary cylinder. This noise reduction arises from the structural oscillations suppressing the noise generated by the vortex shedding from the stationary cylinder—the additional source of noise stemming from the structural oscillations is too small to compensate for the mechanism responsible for the noise suppression. The noise generated by the cylinder motion includes contributions from the loading and thickness noise, whereas the noise generated by vortex shedding from the stationary cylinder only includes the loading noise. The flow past tandem stationary cylinders exhibits a larger number of spectral peaks in the sound pressure power spectrum and the peaks occur at a lower frequency compared to the flow past a single cylinder. The drag force fluctuations result in the propagation of the sound pressure in the in-line direction, whereas the lift force fluctuations result in the propagation of the sound pressure in the transverse direction. Five different scenarios of stationary and/or oscillating tandem cylinders are studied. The second and third invariants of the velocity gradient tensor are used to visualize the distinct vortex structures in the wake for the five different scenarios of tandem cylinders. A single cylinder oscillating in the transverse direction exhibits a larger sound pressure level (SPL) than the streamwise oscillation of the same cylinder. In contrast, the streamwise (in-line) oscillation of one or the other cylinder in a tandem array results in a larger SPL than the transverse oscillation of one or the other cylinder. Finally, the SPL is more sensitive to the oscillations of the rear (downstream) cylinder than the front (upstream) cylinder.

Logistic splicing correction for VNIR-SWIR reflectance imaging spectroscopy.

In the field of spectroscopy, a splicing correction is a process by which two spectra captured with different sensors in adjacent or overlapping electromagnetic spectrum ranges are smoothly connected. In our study, we extend this concept to the case of reflectance imaging spectroscopy in the visible-near-infrared (VNIR) and short-wave infrared (SWIR), accounting for additional sources of noise that arise at the pixel level. The proposed approach exploits the adaptive fitting of a logistic function to compute correcting coefficients that harmonize the two spectral sets. This short Letter addresses usage conditions and compares results against the existing state of the art.

Improving MDM–WDM optical network performance via optimized power allocation using Gaussian noise model

The few-mode fiber nonlinearity has been well modeled by an additive Gaussian Noise (GN) source. The available GN models in Mode Division Multiplexing–Wavelength Division Multiplexing (MDM–WDM) systems are incoherent and neglect the dispersion slope. The incoherent GN model assumes that the Nonlinear Interference (NLI) noise created at each span is summed up in power incoherently at the receiver and leads to underestimating the NLI noise power. In the first part of this paper, a coherent GN model is derived by taking into account the dispersion slope and verified through Split-Step Fourier Method (SSFM) simulations. In the second part of this paper, the total capacity maximization, as well as the minimum Signal to Noise Ratio (SNR) margin maximization problems are presented and solved based on the obtained GN model. MDM–WDM multi-node nonlinear network under different scenarios including Equal/Non-Equal Required SNR (ERS/NERS), and Flat/Non-Flat Amplifier Gain (FG/NFG) are considered in the numerical simulations. Considering 200 different sets of randomized traffic demands (random channel-mode distributions) the cumulative distribution function of minimum SNR margin improvement in optimized power allocation compared with the best flat power allocation is in 99% more than 1 dB, 1.2 dB, 2.4 dB, and 2.8 dB, for ERS-FG, ERS-NFG, NERS-FG, and NERS-NFG scenarios, respectively.

Improving Physical Layer Security in Vehicles and Pedestrians Networks With Ambient Backscatter Communication

Autonomous driving is considered one of the killer technologies in the intelligent era. The information transmission between autonomous vehicles and pedestrians (V2P) is very important to reduce the number of road accidents. Ambient backscatter communication (AmBC) technology can be used to increase the vehicle (or driver) awareness regarding the presence of pedestrians in a crosswalk to realize short-distance transmission of emergency messages. On the other hand, highly secure transmission in V2P networks is required to assure the broadcasting of emergency messages. However, the artificial noise scheme by an additional noise source to improve the physical layer security (PLS) is not suitable due to the dynamic vehicles. Therefore, in this paper, we propose a source-noise assisted AmBC transmission scheme in the V2P system, in which the noise is created by the ambient radio frequency (RF) source to improve the PLS performance. The closed-form expressions for the outage probability of the legitimate user and the intercept probability of eavesdropper are derived. Finally, the diversity gain performance of the system is studied by analyzing the asymptotic behaviors. The theoretical and simulation results show that the proposed scheme improves the system security performance at the expense of system reliability by utilizing the proposed source-noise aided scheme in the V2P network. Besides, the optimal reflection coefficient is related to the power allocation ratio for the signal of the reader and interference noise. The different reflection coefficient is required for achieving the best system performance under different power allocation ratios. Moreover, the results also show that there are error floors for the outage probability, depending on the reflection coefficient. Furthermore, the performance results show that the intercept probability will significantly decrease when the outage probability is fixed in the proposed scheme.

Jet noise sources for chevron nozzles in under-expanded condition

Imperfectly expanded jet flows are known to have additional noise sources known as Screech and broadband shock-associated noise. They are generated by the interaction between the instability waves that propagate from the lip of the nozzle and the shock cell structures. In this study, thorough experimental investigations were carried out on chevron nozzles to assess the importance of chevron parameters such as the chevron count and chevron penetration angle on the pressure field emitted by the jet. Data were acquired in the state-of-the-art aeroacoustic facility at the University of Bristol. Acoustic measurements such as pressure spectra, directivity and overall sound pressure levels along with near-field measurements were acquired for jet Mach numbers ranging from M = 1.1–1.4. Fourier-based and Wavelet-based analyses were used to highlight the different features of the various tested nozzles. Wavelet decomposition results highlight that the presence of the chevrons reduce the acoustic noise especially at a higher axial distance with increased levels of noise reduction achieved by chevron nozzle with deep penetration angle.

Extreme Vocals—A Retrospective Longitudinal study of Vocal Health in 20 Professional Singers Performing and Teaching Rough Vocal Effects

Rough vocal effects, extreme, or extended vocal techniques to sound intentionally hoarse or rough are an integral part of many genres and styles, and research has recently demonstrated the involvement of supraglottic narrowing and vibrations to produce such sounds. The vocal health of singing with rough vocal effects is poorly documented, especially in a longitudinal manner, while much vocal pedagogy continuously treats the sounds as harming to or dangerous for the vocal mechanism. To longitudinally investigate the vocal health of professional singers who perform the five rough-sounding vocal effects Distortion, Growl, Grunt, Rattle, and Creaking as part of their singing and teaching. Twenty singers underwent nasoendoscopic examination, filled in SVHI questionnaires, and were assessed by GRBAS with a 14-year interval in a retrospective longitudinal study (from 2007 to 2021). Endoscopic materials were assessed by Reflux Finding Score and a hybrid version of the Stroboscopy Rating Scale. Singers presented at initiation of study with an average SVHI of 9.2 (±9), which decreased at time of follow up 14 years later to an average of 5.12 (±6). Laryngeal assessments (RFS and SRS) revealed low averages at initiation of study as well as at conclusion of the study with only small fluctuations in averages, with findings mainly relating to arytenoid asymmetry. The participating singers perform and teach rough vocal effects continually and present with healthy laryngeal mechanisms and within-normal SVHI and GRBAS scores. The findings suggest that controlled supraglottic narrowing and techniques to allow for supraglottic structures to engage in vibration as an additional noise source can be performed sustainable and in a healthy manner if performed with correct vocal technique.