Tone Generation Research Articles

Numerical prediction of mean flow and acoustic field of a supersonic impinging jet

The three-dimensional turbulent mean flow and acoustic field of a supersonic jet impinging on a solid plate is studied computationally using the general purpose CFD code Ansys Fluent. A pressure-based coupled solver formulation with the second order weighted central-upwind spatial discretization is applied to compute transient solutions. Cold and hot jet thermal conditions are considered. Mean flow characteristics are investigated by a steady-state modeling approach. Acoustic radiation of impingement tones is simulated using a transient time-domain formulation. The effects of turbulence in steady-state are modeled by the SST k-ω turbulence model. The Wall-Modeled Large-Eddy Simulation (WMLES) model is applied to compute transient solutions. The near-wall mesh on the impingement plate is fine enough to resolve the viscosity-affected near-wall region all the way to the laminar sublayer. Nozzle-to-plate distance is parameterized in the model for automatic re-generation of the mesh and results. Steady-state predictions of hover lift loss and mean jet velocity distributions are compared with experimental data, and favorable agreement is reported. The transient solution reproduces the mechanism of impingement tone generation by the interaction of large scale vortical structures with the impingement plate. The acoustic near-field is directly resolved by Computational Aeroacoustics (CAA) to accurately propagate impingement tone waves to near-field microphone locations. Calculated impingement tone frequencies and sound pressure levels agree with experimental values.

Acoustic stimulation of the human round window by laser-induced nonlinear optoacoustics.

The feasibility of low frequency pure tone generation in the inner ear by laser-induced nonlinear optoacoustic effect at the round window was demonstrated in three human cadaveric temporal bones (TB) using an integral pulse density modulation (IPDM). Nanosecond laser pulses with a wavelength in the near-infrared (NIR) region were delivered to the round window niche by an optical fiber with two spherical lenses glued to the end and a viscous gel at the site of the laser focus. Using IPDM, acoustic tones with frequencies between 20Hz and 1kHz were generated in the inner ear. The sound pressures in scala tympani and vestibuli were recorded and the intracochlear pressure difference (ICPD) was used to calculate the equivalent sound pressure level (eq. dB SPL) as an equivalent for perceived loudness. The results demonstrate that the optoacoustic effect produced sound pressure levels ranging from 140eq. dB SPL at low frequencies ≤ 200Hz to 90eq. dB SPL at 1kHz. Therefore, the produced sound pressure level is potentially sufficient for patients requiring acoustic low frequency stimulation. Hence, the presented method offers a potentially viable solution in the future to provide the acoustic stimulus component in combined electro-acoustic stimulation with a cochlear implant.

Sculpting harmonic comb states in terahertz quantum cascade lasers by controlled engineering

Optical frequency combs (OFCs), which establish a rigid phase-coherent link between the microwave and optical domains of the electromagnetic spectrum, are emerging as key high-precision tools for the development of quantum technology platforms. These include potential applications for communication, computation, information, sensing, and metrology and can extend from the near-infrared with micro-resonator combs, up to the technologically attractive terahertz (THz) frequency range, with powerful and miniaturized quantum cascade laser (QCL) FCs. The recently discovered ability of the QCLs to produce a harmonic frequency comb (HFC)—a FC with large intermodal spacings—has attracted new interest in these devices for both applications and fundamental physics, particularly for the generation of THz tones of high spectral purity for high data rate wireless communication networks, for radio frequency arbitrary waveform synthesis, and for the development of quantum key distributions. The controlled generation of harmonic states of a specific order remains, however, elusive in THz QCLs. Here, and by design, we devise a strategy to obtain broadband HFC emission of a pre-defined order in a QCL. By patterning n regularly spaced defects on the top surface of a double-metal Fabry–Perot QCL, we demonstrate harmonic comb emission with modes spaced by an (n+1) free spectral range and with an optical power/mode of ∼270µW.

Sounding saxophones like flutes

The saxophone can be modified with alternative non-single-reed tone generators, including double and free reeds and brass-instrument mouthpieces. It can also be played as a rim flute on the neck, which is a known extended technique for the saxophone. Flutes differ fundamentally from the other tone-generator types as they do not act like a valve, and their flutes are so-called open-open resonator instruments, while reeds and the lips in brass instruments effectively close one end of the resonator. As a practical consequence, all open-close hole key combinations result in fundamentally different pitches known from the regular saxophone. The fact that the saxophone is conically shaped, while the flute is typically cylindrical or inverse conical, further complicates the matter. Approaches to playing the saxophone as flute using alternative fingering combinations will be discussed along with measures of pitch accuracy, timbral, and level balance. While the achievable range aligns with many orchestral wind instruments, complex cross-fingerings make it difficult to play fast chromatic lines. The large bore of the saxophone gives the flute sound a dark character, more like a Native American flute or shakuhachi than a Western concert flute or recorder.

Astrocyte Regulation of Cerebral Blood Flow in Health and Disease.

Astrocytes play an important role in controlling microvascular diameter and regulating local cerebral blood flow (CBF) in several physiological and pathological scenarios. Neurotransmitters released from active neurons evoke Ca2+ increases in astrocytes, leading to the release of vasoactive metabolites of arachidonic acid (AA) from astrocyte endfeet. Synthesis of prostaglandin E2 (PGE2) and epoxyeicosatrienoic acids (EETs) dilate blood vessels while 20-hydroxyeicosatetraenoic acid (20-HETE) constricts vessels. The release of K+ from astrocyte endfeet also contributes to vasodilation or constriction in a concentration-dependent manner. Whether astrocytes exert a vasodilation or vasoconstriction depends on the local microenvironment, including the metabolic status, the concentration of Ca2+ reached in the endfoot, and the resting vascular tone. Astrocytes also contribute to the generation of steady-state vascular tone. Tonic release of both 20-HETE and ATP from astrocytes constricts vascular smooth muscle cells, generating vessel tone, whereas tone-dependent elevations in endfoot Ca2+ produce tonic prostaglandin dilators to limit the degree of constriction. Under pathological conditions, including Alzheimer's disease, epilepsy, stroke, and diabetes, disruption of normal astrocyte physiology can compromise the regulation of blood flow, with negative consequences for neurological function.

Viscosity effects and confined cochlea-like geometry in laser-induced cavitation dynamics

On the path to an optoacoustic hearing implant for stimulation of residual hearing, one possibility for tone generation in liquids is the concatenation of acoustic click events, which can be realized i. a. by the acoustic transients that accompany an optical breakdown. The application of a viscous gel is helpful in this context, as this results in an attenuation of the distortion of tone quality caused by higher harmonic components. To further understand the underlying cavitation bubble dynamics both in the viscous gel and in a confined volume that is dimensioned similarly to the human cochlea, a numerical model built in OpenFOAM was adapted and compared to additional experiments. Experimentally, the acoustic transients were generated by optical breakdown by nanosecond laser pulses with a pulse duration of 0.7 ns and a wavelength of 1064 nm. The pulses were focused on a viscous gel inside a water container. The pressure transients were measured by a needle hydrophone. The comparison of the bubble dynamics in different viscosities between the model and the experiment shows that, except for high viscosities, the experimental observations could be modeled by the simulation. We assume that the maximum size of the cavitation bubble strongly decreases with increasing viscosity, which can be used for high-frequency attenuation as reported in our previous research. In conclusion, this study aims at an application-oriented realization of the numerical cavitation bubble dynamics model to understand the experimental findings on the pathway to an optoacoustic hearing implant.

Analysis of the effect of turbulent inflow on the flow-field and noise of supersonic jet flow using large eddy simulation

The impact of inflow flow state on the flow-field and far-field noise of supersonic jet flow has been studied. A new turbulent inflow boundary condition based on the synthetic eddy method is implemented in an in-house LES code. The implementation was validated using a turbulent channel flow. Simulation results of an under-expanded supersonic jet with a converging nozzle have shown that turbulent inflow leads to thicker and turbulent initial shear layer with rich vortical structures. The thick initial shear layer hinders the growth of flow instability and break the acoustic feedback loop, which is vital to the generation of screech tone. The alternation of the flow-field by the turbulent inflow also leads to changes in the far-field noise radiation. The screech tone is eliminated, the noise in the downstream direction is considerably suppressed, and the noise radiates in the upstream direction is slightly amplified.

A new model for evaluating pressure-induced vascular tone in small cerebral arteries

The capacity of small cerebral arteries (SCAs) to adapt to pressure fluctuations has a fundamental physiological role and appears to be relevant in different pathological conditions. Here, we present a new computational model for quantifying the link, and its contributors, between luminal pressure and vascular tone generation in SCAs. This is assembled by combining a chemical sub-model, representing pressure-induced smooth muscle cell (SMC) signalling, with a mechanical sub-model for the tone generation and its transduction at tissue level. The devised model can accurately reproduce the impact of luminal pressure on different cytoplasmic components involved in myogenic signalling, both in the control case and when combined with some specific pharmacological interventions. Furthermore, the model is also able to capture and predict experimentally recorded pressure-outer diameter relationships obtained for vessels under control conditions, both in a Ca2+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{2+}$$\\end{document}-free bath and under drug inhibition. The modularity of the proposed framework allows the integration of new components for the study of a broad range of processes involved in the vascular function.

Generation of skin tone and pigmented region-modified images using a pigment discrimination model trained with an optical approach.

Skin tone and pigmented regions, associated with melanin and hemoglobin, are critical indicators of skin condition. While most prior research focuses on pigment analysis, the capability to simulate diverse pigmentation conditions could greatly broaden the range of applications. However, current methodologies have limitations in terms of numerical control and versatility. We introduce a hybrid technique that integrates optical methods with deep learning to produce skin tone and pigmented region-modified images with numerical control. The pigment discrimination model produces melanin, hemoglobin, and shading maps from skin images. The outputs are reconstructed into skin images using a forward problem-solving approach, with model training aimed at minimizing the discrepancy between the reconstructed and input images. By adjusting the melanin and hemoglobin maps, we create pigment-modified images, allowing precise control over changes in melanin and hemoglobin levels. Changes in pigmentation are quantified using the individual typology angle (ITA) for skin tone and melanin and erythema indices for pigmented regions, validating the intended modifications. The pigment discrimination model achieved correlation coefficients with clinical equipment of 0.915 for melanin and 0.931 for hemoglobin. The alterations in the melanin and hemoglobin maps exhibit a proportional correlation with the ITA and pigment indices in both quantitative and qualitative assessments. Additionally, regions overlaying melanin and hemoglobin are demonstrated to verify independent adjustments. The proposed method offers an approach to generate modified images of skin tone and pigmented regions. Potential applications include visualizing alterations for clinical assessments, simulating the effects of skincare products, and generating datasets for deep learning.

Aerodynamic-whistles-based ultrasonic tone generators for bat deterrence

Novel ultrasonic bat deterrents based on aerodynamic whistles are proposed and investigated experimentally and numerically for their ability to generate ultrasound. The baseline deterrent, a single-whistle design inspired by Beeken [“Fluid ultrasonic generator,” U.S. patent 3,432,804 (1969)], is examined first. It consists of two resonating cavities/chambers. The whistle is “powered” by a regulated high-pressure air supply, and the performance of the whistle is examined for a range of supply pressures. Far-field acoustic measurements in the 20 Hz–50 kHz frequency range are made in an anechoic chamber. The noise measurements are supplemented with two- and three-dimensional unsteady Reynolds-averaged Navier–Stokes (uRANS) simulations to investigate the mechanisms of ultrasound generation. The Ffowcs Williams–Hawkings acoustic analogy is used with the three-dimensional uRANS results to predict the far-field radiation. The far-field acoustic predictions are in good agreement with the measurements in the anechoic chamber. The peak frequency (fundamental) of the radiated ultrasound of the baseline deterrent is approximately 23 kHz. Harmonics and a sub-harmonic of the fundamental tone are also observed. The numerical simulations show that the two resonating chambers of the baseline deterrent operate out-of-phase and Helmholtz resonance determines the whistling frequency over the range of supply air pressure considered. A six-whistle deterrent targeting a broad spectral coverage in the 20–50 kHz frequency range is designed, fabricated, and tested in the anechoic chamber. Each whistle in the deterrent is obtained by geometrically scaling the baseline whistle. Measurements show that the six-whistle ultrasound deterrent generates ultrasound with six dominant peaks in the designed frequency range when the supply air pressure exceeds 5 psig. The proposed ultrasound devices can be used for a variety of purposes including bat deterrence at wind turbines.

Mach Number Dependence of Tone Generation by Impinging Round Jets

The Mach number dependence of tone generation by jets impinging on a plate is investigated using large-eddy simulations, for seven jets at Mach numbers between 0.6 and 1.3 and a nozzle-to-plate distance of 8 nozzle radii. For , the upstream sound radiation is broadband, whereas for , tones emerge in the near-nozzle spectra, highlighting the establishment of feedback loops. The tone frequencies are consistent with those for aeroacoustic feedback loops between the nozzle and the plate, and exhibit a staging behavior with the Mach number, staying inside or close to the ranges of the upstream-traveling free-stream guided jet waves predicted by a vortex-sheet model. The azimuthal and radial structures of the pressure fields at the tone frequencies agree with those of these waves closing the loops. The selection of the dominant tone and the staging behavior are discussed by evaluating the power gains of the shear-layer instability waves between the nozzle and the plate using linear stability. In most cases, the dominant tones emerge at the possible tone frequencies with the highest gain. For , the gain of the instability waves at the frequency of the guided jet waves most likely to close feedback mechanisms is lower than the gain peak values, possibly contributing to the absence of resonance.

Exploring Sound Generation and Processing in Mechatronic Systems through Digital Signal Processing: A MATLAB-Based Investigation

Digital signal processing (DSP) encompasses various applications such as convolution, censoring, and filtering. These techniques find relevance in diverse fields, including computer games consoles, tone generation for mobile cellular devices, and theatrical performances. For computer engineers facing limited memory budgets in their devices, generating new sounds by convolving with existing sounds or noises becomes a significant challenge. The objective of this paper is to elucidate and demonstrate the generation of sounds through sound and recorded sound processing. These operations form the foundation of DSP, particularly digital filtering. Sound processing involves modifying prerecorded sound clips using different types of digital filters and processors. The entire process, including sound recording and processing, will be implemented and tested using MATLAB, the widely adopted technical computing software. This project aims to provide valuable archival material that complements the learning and expertise of computer engineering students and specialists.

Muscle Activity during Passive and Active Movements in Preterm and Full-Term Infants.

Manifestation of muscle reactions at an early developmental stage may reflect the processes underlying the generation of appropriate muscle tone, which is also an integral part of all movements. In preterm infants, some aspects of muscular development may occur differently than in infants born at term. Here we evaluated early manifestations of muscle tone by measuring muscle responses to passive stretching (StR) and shortening (ShR) in both upper and lower limbs in preterm infants (at the corrected age from 0 weeks to 12 months), and compared them to those reported in our previous study on full-term infants. In a subgroup of participants, we also assessed spontaneous muscle activity during episodes of relatively large limb movements. The results showed very frequent StR and ShR, and also responses in muscles not being primarily stretched/shortened, in both preterm and full-term infants. A reduction of sensorimotor responses to muscle lengthening and shortening with age suggests a reduction in excitability and/or the acquisition of functionally appropriate muscle tone during the first year of life. The alterations of responses during passive and active movements in preterm infants were primarily seen in the early months, perhaps reflecting temporal changes in the excitability of the sensorimotor networks.

Pressure induced changes in endothelial cell morphology and Ca2+ signaling in ex vivo pressurized resistance arteries revealed using 4D diSPIM myography and AI deep-learning

The vascular endothelium is critical in promoting vasodilation of resistance-size arteries through Ca 2+ dependent pathways. Vascular endothelial cells (ECs) are exposed to mechanical stimulation through changing intravascular pressure and flow, yet it is unclear how these forces impact EC morphology and Ca 2+ signaling in pressurized arteries. Visualizing how the endothelium of an intact resistance-size vessel responds to changing physical forces requires isometric, sub-micron, resolution. Conventional confocal fluorescent microscope systems are limited by poor axial resolution. 4D dual inverted selective plane of illumination microscopy (diSPIM; 3i) uniquely provides isometric resolution at ~330 nm with high temporal resolution and minimal photobleaching or phototoxicity. We designed custom pressure myography chambers to allow simultaneous 4D diSPIM fluorescent imaging and vessel diameter tracking measurements via transmitted IR light (diSPIM Myography). We captured fluorescent images of ex vivo pressurized resistance-size mouse mesenteric arteries at 80, 60, 40, and 20 mm Hg before and after the generation of myogenic tone and in the absence of extracellular Ca 2+ . Representative images were annotated for ECs, nuclei, myoendothelial projections (MEPS), and Ca 2+ signals. Annotations were used as ground truth for CNN AI model generation and validation using Apeer (Zeiss). Arivis Vision4D (Zeiss) was used to run the AI model and quantify data. As static intravascular pressure is increased in arteries without tone (with or without Ca 2+ ), ECs increase in width as the vessel dilates. Myogenic tone minimizes pressure dilation and changes in EC width, however, ECs compress by up to 1 micron as pressure increases from 20 to 80 mm Hg. Additionally, increasing intravascular pressure in arteries with tone decreases local EC Ca 2+ signaling. The data demonstrate a relationship between intravascular pressure and EC shape and Ca 2+ signaling in intact resistance arteries under conditions of physiologic temperature, pressure, pH, and tone. diSPIM myography provides a method of studying the effects of physiologically relevant mechanical stimuli and the roles of various mechanosensitive mechanisms on vascular function. AI image annotation reduces analysis bias and increases the breadth of quantifiable microscopy data. DMC is supported by NIH R00HL133451 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Two distinct calcium signaling behaviors are present in interstitial cells of Cajal of the gastroesophageal junction

Background/Objectives: The lower esophageal sphincter (LES) is located within the gastroesophageal junction (GEJ) and generates tone to prevent gastric reflux into the esophagus. Previously, we demonstrated that the generation and maintenance of tone in the LES clasp muscle involves intramuscular interstitial cells of Cajal (ICC-IM) (Drumm et al., 2022; PMID: 35229888). The aim of the current study was to further characterize Ca2+ signaling in ICC-IM within the GEJ. We hypothesize that Ca2+ release from the endoplasmic reticulum (ER) activates Ca2+-activated Cl- channels (ANO1) in ICC leading to depolarization that is conducted to smooth muscle cells (SMCs) via gap junctions; this in turn leads to Ca2+ influx via L-type Ca2+ channels (CavL) and the development of tone. Methods: Confocal spinning disc microscopy was used to image Ca2+ transients in the LES and distal esophagus of mice expressing GCaMP6f in ICC (Kit-GCaMP6f). Muscles of the GEJ imaged with the submucosal surface upwards at 20x. Ani9 (3mM), nifedipine (1mM) and CPA (10mM) were used to inhibit ANO1, CavL and SERCA, respectively. Pinacidil (10mM) was used to activate KATP channels. Results: ICC-IM within the GEJ displayed two types of Ca2+ signaling behaviors. Ca2+ transients in ICC-IM of the LES clasp muscle were stochastic, arising from multiple firing sites within the same cell. These Ca2+ transients were not synchronized within the same cell or between adjacent cells. In contrast, two Ca2+ signaling patterns were observed in ICC-IM of the distal esophagus where smooth muscle transitions to skeletal muscle. One ICC-IM population (Type I) shared the Ca2+ signaling behaviors of ICC-IM in the LES clasp. Another ICC population (Type II) exhibited rhythmic whole-cell Ca2+ transients that were synchronized between adjacent Type II ICC. Whole cell Ca2+ transients in Type II ICC were abolished by Ani9, nifedipine or pinacidil, revealing underlying Ca2+ transients similar to those observed in Type I ICC. In contrast, Ca2+ transients in Type I ICC were resistant to Ani9, nifedipine and pinacidil. Ca2+ transients were abolished in both types of ICC by removal of extracellular Ca2+, however the activity in Type I ICC persisted longer than that of Type II ICC. Discussion/Conclusions: This study demonstrates two distinct Ca2+ signaling behaviors in ICC-IM of the GEJ with differing pharmacology. This is similar to what has been previously described within the internal anal sphincter (IAS) (Hannigan et al., 2020; PMID: 32587396). In the IAS, it has been suggested that Type II ICC-IM generate slow waves however their role in the GEJ remains unclear as slow waves have not been described within this region of the mouse. Thus, the functional role of ICC-IM in the GEJ, particularly Type II ICC, warrants further investigation. NIH DK129528 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Dual thick and thin filament linked regulation of stretch- and L-NAME-induced tone in young and senescent murine basilar artery.

Stretch-induced vascular tone is an important element of autoregulatory adaptation of cerebral vasculature to maintain cerebral flow constant despite changes in perfusion pressure. Little is known as to the regulation of tone in senescent basilar arteries. We tested the hypothesis, that thin filament mechanisms in addition to smooth muscle myosin-II regulatory-light-chain-(MLC20)-phosphorylation and non-muscle-myosin-II, contribute to regulation of stretch-induced tone. In young BAs (y-BAs) mechanical stretch does not lead to spontaneous tone generation. Stretch-induced tone in y-BAs appeared only after inhibition of NO-release by L-NAME and was fully prevented by treatment with 3μmol/L RhoA-kinase (ROK) inhibitor Y27632. L-NAME-induced tone was reduced in y-BAs from heterozygous mice carrying a point mutation of the targeting-subunit of the myosin phosphatase, MYPT1 at threonine696 (MYPT1-T696A/+). In y-BAs, MYPT1-T696A-mutation also blunted the ability of L-NAME to increase MLC20-phosphorylation. In contrast, senescent BAs (s-BAs; >24months) developed stable spontaneous stretch-induced tone and pharmacological inhibition of NO-release by L-NAME led to an additive effect. In s-BAs the MYPT1-T696A mutation also blunted MLC20-phosphorylation, but did not prevent development of stretch-induced tone. In s-BAs from both lines, Y27632 completely abolished stretch- and L-NAME-induced tone. In s-BAs phosphorylation of non-muscle-myosin-S1943 and PAK1-T423, shown to be down-stream effectors of ROK was also reduced by Y27632 treatment. Stretch- and L-NAME tone were inhibited by inhibition of non-muscle myosin (NM-myosin) by blebbistatin. We also tested whether the substrate of PAK1 the thin-filament associated protein, caldesmon is involved in the regulation of stretch-induced tone in advanced age. BAs obtained from heterozygotes Cald1+/- mice generated stretch-induced tone already at an age of 20-21months old BAs (o-BA). The magnitude of stretch-induced tone in Cald1+/- o-BAs was similar to that in s-BA. In addition, truncation of caldesmon myosin binding Exon2 (CaD-▵Ex2-/-) did not accelerate stretch-induced tone. Our study indicates that in senescent cerebral vessels, mechanisms distinct from MLC20 phosphorylation contribute to regulation of tone in the absence of a contractile agonist. While in y-and o-BA the canonical pathways, i.e., inhibition of MLCP by ROK and increase in pMLC20, predominate, tone regulation in senescence involves ROK regulated mechanisms, involving non-muscle-myosin and thin filament linked mechanisms involving caldesmon.

Hainbach and the Sound of Destruction

Hainbach is the stage name of the Berlin-based composer, lyricist, and live musician, Stefan Paul Goetsch, who is perhaps best known from his YouTube channel of the same name. Descriptions and classifications of Hainbach’s music invariably include references to the musician’s innovative and ‘experimental’ approach to music production and highlight his use of magnetic tape and obsolete tone generators, such as those used by the early proponents of electronic-based music. This article examines three of Hainbach’s recent electronic works: Tagwerk (2022), Landfill Totems (2019), and Destruction Loops (2019–2021), framing them as palimpsests of archived destruction that recall such wide-ranging works as the magnetic tape experiments of Alvin Lucier, the auto-destructive impulse and social engagement of German-born artist and activist Gustav Metzger, or even the ‘erasures’ of Robert Rauschenberg. In this article, I reveal the complex, seemingly contradictory, palimpsestuous structure of Hainbach’s works, where creation meets destruction, collage and décollage are co-planar, and the gestures of ‘play’—that creative act with destruction at its horizon—are ever present. Through play, Hainbach explores the creative potential of both sound and instrument, surveys their affordances, and courts creativity at the unpredictable intersection of serendipity and failure.

Optimization of the conversion efficiency and evaluation of the noise figure of an optical frequency converter based on a dual-pump fiber phase sensitive amplifier.

We propose a new architecture of phase sensitive optical frequency converter based on dual-pump phase sensitive amplification in a highly nonlinear fiber. This frequency converter allows generation of extra tones through nonlinear four-wave mixing between two strong pumps and an input tone. The frequency channel to which the input tone is converted can be chosen by adjusting the phase of the input signal. The conversion efficiency and extinction ratio of this frequency converter are predicted and optimized and its noise figure is calculated using a numerical approach based on the nonlinear Schrödinger equation. A semi-classical noise figure calculation for this approach was used and validated using an analytical fully quantum calculation based on the multi-wave model.

Постановка за Измерване Скоростта на Звука във Въздух

An experimental setup for measuring the speed of sound in air is described. The experiment can be reproduced with readily available tools, in any school. A smartphone was used, running tone generating apps available for free along with a digital oscilloscope. A sound frequency is assigned using the tone generator and is reproduced by the smartphone’s loudspeaker and is further observed using the digital oscilloscope. A pipe is used as a resonator, and by dipping one end in water the air column length is adjusted. Some of the systematic effects leading to error in results are researched and evaluated.

Recruitment and Differential Firing Patterns of Single Units During Conditioning to a Tone in a Mute Locked-In Human.

Single units that are not related to the desired task can become related to the task by conditioning their firing rates. We theorized that, during conditioning of firing rates to a tone, (a) unrelated single units would be recruited to the task; (b) the recruitment would depend on the phase of the task; (c) tones of different frequencies would produce different patterns of single unit recruitment. In our mute locked-in participant, we conditioned single units using tones of different frequencies emitted from a tone generator. The conditioning task had three phases: Listen to the tone for 20 s, then silently sing the tone for 10 s, with a prior control period of resting for 10 s. Twenty single units were recorded simultaneously while feedback of one of the twenty single units was made audible to the mute locked-in participant. The results indicate that (a) some of the non-audible single units were recruited during conditioning, (b) some were recruited differentially depending on the phase of the paradigm (listen, rest, or silent sing), and (c) single unit firing patterns were specific for different tone frequencies such that the tone could be recognized from the pattern of single unit firings. These data are important when conditioning single unit firings in brain-computer interfacing tasks because they provide evidence that increased numbers of previously unrelated single units can be incorporated into the task. This incorporation expands the bandwidth of the recorded single unit population and thus enhances the brain-computer interface. This is the first report of conditioning of single unit firings in a human participant with a brain to computer implant.