Oscillation Threshold Research Articles

The effect of blowing pressure, lip force and tonguing on transients: A study using a clarinet-playing machine

Wind instrument players control the initial and final transients of notes using breath, lips, and tonguing. This paper uses a clarinet-playing machine and high-speed camera to investigate how blowing pressure, lip force, and tonguing parameters affect transients. After tongue release, the reed quickly comes to rest, losing its mechanical energy. However, the changing aperture past the reed rapidly changes the airflow. For pressure above the oscillation threshold, successive interactions between reflections of this pulse of airflow and the reed produce an exponential increase in the sound. The rates r of exponential increase in the fundamental of the sound range from several tens to several hundreds of dB s(-1), as functions of blowing pressure and lip force. Because the reed's initial mechanical energy is lost, tongue force and acceleration have little effect on r. However, larger tongue force and acceleration produce more rapid changes in flow, which start notes sooner after tongue release. Further, large tongue force increases the third harmonic during the transient. There is a hysteresis region on the (pressure, lip force) plane where regenerative oscillation is not produced spontaneously by increasing blowing pressure only. Here, tongue action can initiate sustained notes at low pressure.

Some examples of photorefractive oscillators

The photorefractive effect presents a periodical change of the refractive index of an optical environment under the influence of a coherent light. An interesting phenomenon which occurs at this effect is optical phase conjugation (PC). Photorefractive oscillators, that is photorefractive mirrors present important decides in photorefractive optics and their function is based on photorefractive effect. In these oscillators, a phase-conjugated light beam occurs. The basic characteristics of photorefractive oscillators, such as reflectivity, the existance of the oscillation threshold and the threshold of the coupling strength are explained by the so-called grating-action method. This is analysed on a ring oscillator, semilinear mirror and linear mirror.

Terahertz emission from SiC natural superlattices in strong electrical field

Results are reported from a study of the terahertz electroluminescence from 8H-, 6H-, and 4H-SiC natural superlattices under the action of an electrical field applied along the natural superlattice axis. It is shown that the single, relatively narrow emission lines (L1-lines) dominate in the electroluminescence spectrum at moderate bias voltages and follow the increase of the width of the first mini-band of the superlattice in accordance with the criterion for Bloch oscillations. At bias voltages well above the Bloch oscillation threshold, the structure of the terahertz emission spectra undergoes considerable changes, which occur due to the appearance of a new intense, broader emission line (L2-line) with a maximum at about 12–13 meV. Tentatively, this latter emission is attributed to optical transitions between Wannier-Stark ladders formed from degenerate states in a side minimum of the SiC conduction band under strong electric field conditions.

Theoretical analysis of an optoelectronic oscillator based on a directly modulated semiconductor laser

We numerically simulated the performance of an optoelectronic oscillator (OEO) based on a directly modulated (DM) semiconductor laser. The standard coupled rate equations were used to describe the DM-OEO modulation process. A rate-equation-based analysis is a means of analyzing OEO performance that is a variation of the method used to assess standard OEOs that employ external modulators. We modeled an OEO with an open-loop response and calculated the oscillation threshold gain and amplitude of the DM-OEO as functions of the DC bias current. By using this method, we were able to optimize OEO operation conditions for a given laser DC bias level in both gain- and amplitude-limited operating environments.

Controlled nanoparticle release from stable magnetic microbubble oscillations

Magnetic microbubbles (MMBs) are microbubbles (MBs) coated with magnetic nanoparticles (NPs). MMBs not only maintain the acoustic properties of MBs, but also serve as an important contrast agent for magnetic resonance imaging. Such dual-modality functionality makes MMBs particularly useful for a wide range of biomedical applications, such as localized drug/gene delivery. This article reports the ability of MMBs to release their particle cargo on demand under stable oscillation. When stimulated by ultrasound at resonant frequencies, MMBs of 450 nm to 200 μm oscillate in volume and surface modes. Above an oscillation threshold, NPs are released from the MMB shell and can travel hundreds of micrometers from the surface of the bubble. The migration of NPs from MMBs can be described with a force balance model. With this technology, we deliver doxorubicin-containing poly(lactic-co-glycolic acid) particles across a physiological barrier both in vitro and in vivo, with a 18-fold and 5-fold increase in NP delivery to the heart tissue of zebrafish and tumor tissue of mouse, respectively. The penetration of released NPs in tissues is also improved. The ability to remotely control the release of NPs from MMBs suggests opportunities for targeted drug delivery through/into tissues that are not easily diffused through or penetrated. Microsized gas bubbles containing magnetic nanoparticles and drug nanoparticles (nanodrugs) can eject nanodrugs across biobarriers in cell, tissue and animals. Drug-delivery technologies use triggers such as enzymes, shear stress or magnetic fields to deposit medicinal payloads directly to afflicted tissues and organs. Chenjie Xu at Nanyang Technological University reports non-invasive drug delivery can be realized by using ultrasonic triggers to ‘magnetic microbubbles’ — spherical complexes of iron oxide nanoparticles and nanodrugs. The team loaded magnetic microbubbles with doxorubicin-containing polymer nanoparticles and used ultrasound irradiation to make the microspheres shrink and expand at their resonant frequencies. The constant oscillation caused the doxorubicin–nanoparticle complexes to be expelled hundreds of micrometres from the bubbles. The on-demand delivery proved powerful enough to cross tricky physiological barriers such as zebrafish heart/brain tissue and the vasculature of solid tumor in mouse. Drug-encapsulated nanoparticles (NPs) are emerging as therapeutic agents to deliver DNA\drugs into cells. However, clinical applications demand a technique to concentrate NPs at the diseased cells that are beneath other tissues. We report a strategy to achieve this goal with magnetic- and therapeutic NP-coated microbubbles as carriers. Although external magnetic field concentrates them at the targeted tissue, moderate ultrasound irradiation at their resonance frequency drives stable oscillation and microstreaming flow. Consequently, the NP armor detaches, penetrates into tissues and is later internalized by the cells. This technique would greatly improve the on-target delivery of nanomedicine, thereby reduces cost and side effects.

Frequency tuning of single photons from a whispering-gallery mode resonator to MHz-wide transitions

Quantum repeaters rely on interfacing flying qubits with quantum memories. The most common implementations include a narrowband single photon matched in bandwidth and central frequency to an atomic system. Previously, we demonstrated the compatibility of our versatile source of heralded single photons, which is based on parametric down-conversion in a triply resonant whispering-gallery mode resonator, with alkaline transitions [Schunk et al., Optica 2015, 2, 773]. In this paper, we analyse our source in terms of phase matching, available wavelength-tuning mechanisms and applications to narrowband atomic systems. We resonantly address the D1 transitions of caesium and rubidium with this optical parametric oscillator pumped above its oscillation threshold. Below threshold, the efficient coupling of single photons to atomic transitions heralded by single telecom-band photons is demonstrated. Finally, we present an accurate analytical description of our observations. Providing the demonstrated flexibility in connecting various atomic transitions with telecom wavelengths, we show a promising approach to realize an essential building block for quantum repeaters.

Control of the oscillation threshold with asymmetric gain in operational amplifiers

We have observed the quench of the lasing at the exceptional point in the electronic circuit system by applying asymmetric gain in the coupled oscillator. Since there is the analogy between oscillation in laser and oscilation in the operational amplifier, when the system hits the exceptional point, oscillation stops. This phenomenon is also theoretically investigated.

Critical behavior of coherence and correlation of counterpropagating twin beams

This work analyzes the temporal coherence and correlation of twin beams generated in a quasi-phase-matched nonlinear crystal in a counterpropagating configuration, ranging from the low-gain regime, where counterpropagating photon pairs are generated spontaneously, to the regime of stimulated pair production, close to the mirrorless optical parametric oscillator threshold. Here, we show a critical divergence of the correlation time and slowing down of quantum fluctuations originating from the feedback mechanism responsible for the MOPO threshold.

Chronic Glucose Exposure Systematically Shifts the Oscillatory Threshold of Mouse Islets: Experimental Evidence for an Early Intrinsic Mechanism of Compensation for Hyperglycemia.

Mouse islets exhibit glucose-dependent oscillations in electrical activity, intracellular Ca(2+) and insulin secretion. We developed a mathematical model in which a left shift in glucose threshold helps compensate for insulin resistance. To test this experimentally, we exposed isolated mouse islets to varying glucose concentrations overnight and monitored their glucose sensitivity the next day by measuring intracellular Ca(2+), electrical activity, and insulin secretion. Glucose sensitivity of all oscillation modes was increased when overnight glucose was greater than 2.8mM. To determine whether threshold shifts were a direct effect of glucose or involved secreted insulin, the KATP opener diazoxide (Dz) was coapplied with glucose to inhibit insulin secretion. The addition of Dz or the insulin receptor antagonist s961 increased islet glucose sensitivity, whereas the KATP blocker tolbutamide tended to reduce it. This suggests insulin and glucose have opposing actions on the islet glucose threshold. To test the hypothesis that the threshold shifts were due to changes in plasma membrane KATP channels, we measured cell KATP conductance, which was confirmed to be reduced by high glucose pretreatment and further reduced by Dz. Finally, treatment of INS-1 cells with glucose and Dz overnight reduced high affinity sulfonylurea receptor (SUR1) trafficking to the plasma membrane vs glucose alone, consistent with insulin increasing KATP conductance by altering channel number. The results support a role for metabolically regulated KATP channels in the maintenance of glucose homeostasis.

Tunable, continuous-wave single-resonant optical parametric oscillator with output coupling for resonant wave**Project supported by the National Natural Science Foundation of China (Grant Nos. 61308056, 11204044, 11232015, and 11072271), the Research Fund for the Doctoral Program of Higher Education of China (Grant Nos. 20120171110005 and 20130171130003), the Fundamental Research Funds for the Central Universities of China (Grant No. 14lgpy07), and the

We present a continuous-wave singly-resonant optical parametric oscillator with 1.5% output coupling of the resonant signal wave, based on an angle-polished MgO-doped periodically poled lithium niobate (MgO:PPLN), pumped by a commercial Nd:YVO4 laser at 1064 nm. The output-coupled optical parametric oscillator delivers a maximum total output power of 4.19 W with 42.8% extraction efficiency, across a tuning range of 1717 nm in the near- and mid-infrared region. This indicates improvements of 1.87 W in output power, 19.1% in extraction efficiency and 213 nm in tuning range extension in comparison with the optical parametric oscillator with no output coupling, while at the expense of increasing the oscillation threshold by a factor of ∼ 2. Moreover, it is confirmed that the finite output coupling also contributes to the reduction of the thermal effects in crystal.

Dynamics and coherence resonance of tri-stable energy harvesting system

To improve the efficiency of energy harvesting, this paper presents a tri-stable energy harvesting device, which can realize inter-well oscillation at low-frequency base excitation and obtain a high harvesting efficiency by tri-stable coherence resonance. First, the model of a magnetic coupling tri-stable piezoelectric energy harvester is established and the corresponding equations are derived. The formula for the magnetic repulsion force between three magnets is given. Then, the dynamic responses of a system subject to harmonic excitation and Gaussian white noise excitation are explored by a numerical method and validated by experiments. Compared with a bi-stable energy harvester, the threshold for inter-well oscillation to occur can be moved forward to the low frequency, and the tri-stable device can create a dense high output voltage and power at the low intensity of stochastic excitation. Results show that for a definite deterministic or stochastic excitation, the system can be optimally designed such that it increases the frequency bandwidth and achieves a high energy harvesting efficiency at coherence resonance.

Abstract 14619: Ultrasound-stimulated Microbubbles for Drug/gene Delivery: Microbubble-generated Shear Stress Induces Pores in Cellular Membranes

Background: Ultrasound (US)-stimulated microbubbles (MBs) are emerging as novel target-specific non-viral gene/drug delivery vectors for treatment of vascular disease, e.g. to deliver VEGF plasmid DNA to promote arteriogenesis. The nature of the MB-target cell interactions that facilitate nucleic acid delivery across cell membranes, and hence strategies to optimize the efficiency of this platform, are poorly understood. The objective of this study was to gain mechanistic insight into MB-mediated increases in cell membrane permeability. Methods: Phospholipid coated MBs were allowed to lay adjacent to cultured human umbilical vein endothelial cells (HUVEC) at 37C. Propidium iodide (PI) was put into the media before US exposure to assess membrane permeability (sonoporation). Individual MB-cell pairs (n=351) were exposed to a single US pulse at 0.5, 1, or 2 MHz, with a duration of 4, 8 or 16 μs and pressures 0.1-0.8 MPa. Ultrafast microscopy recorded MB oscillations (Fig. 1a); a second camera simultaneously recorded fluorescence (PI uptake, Fig. 1b). US-induced MB radius change (excursion) was measured and used to calculate shear stress. HUVEC membranes were fluorescently labeled to visualize pore features. Results: Absolute MB excursion distance and associated shear stress were strong threshold indicators of sonoporation (PI uptake). For an 8 μs pulse, the oscillation (shear stress) threshold above which HUVECs porate was 3.9, 2.6, and 1.4 μm (7.8, 14.5, 22.7 kPa) at 0.5, 1 and 2 MHz respectively. At a given US frequency, increases in pulse duration decreased the required excursion and shear stress. Cell membrane imaging showed that MBs can induce apical and basal pores (sub-μm to μm sizes) that reseal (Fig. 1c). Conclusions: Sonoporation is related to absolute MB excursion distance and its associated shear stress and can occur with various US parameters and MB sizes. This data has implications on intelligent US-MB design for their use as payload delivery vehicles.

Predicting playing frequencies for clarinets: A comparison between numerical simulations and simplified analytical formulas.

When designing a wind instrument such as a clarinet, it can be useful to be able to predict the playing frequencies. This paper presents an analytical method to deduce these playing frequencies using the input impedance curve. Specifically there are two control parameters that have a significant influence on the playing frequency, the blowing pressure and reed opening. Four effects are known to alter the playing frequency and are examined separately: the flow rate due to the reed motion, the reed dynamics, the inharmonicity of the resonator, and the temperature gradient within the clarinet. The resulting playing frequencies for the first register of a particular professional level clarinet are found using the analytical formulas presented in this paper. The analytical predictions are then compared to numerically simulated results to validate the prediction accuracy. The main conclusion is that in general the playing frequency decreases above the oscillation threshold because of inharmonicity, then increases above the beating reed regime threshold because of the decrease of the flow rate effect.

Quantum correlation in degenerate optical parametric oscillators with mutual injections

We theoretically and numerically study the quantum dynamics of two degenerate optical parametric oscillators with mutual injections. The cavity mode in the optical coupling path between the two oscillator facets is explicitly considered. Stochastic equations for the oscillators and mutual injection path based on the positive $P$ representation are derived. The system of two gradually pumped oscillators with out-of-phase mutual injections is simulated, and its quantum state is investigated. When the incoherent loss of the oscillators other than the mutual injections is small, the squeezed quadratic amplitudes $\hat{p}$ in the oscillators are positively correlated near the oscillation threshold. It indicates finite quantum correlation, estimated via Gaussian quantum discord, and the entanglement between the intracavity subharmonic fields. When the loss in the injection path is low, each oscillator around the phase transition point forms macroscopic superposition even under a small pump noise. It suggests that the squeezed field stored in the low-loss injection path weakens the decoherence in the oscillators.

Analytical Determination of the Attack Transient in a Clarinet With Time-Varying Blowing Pressure

This article uses a basic model of a reed instrument , known as the lossless Raman model, to determine analytically the envelope of the sound produced by the clarinet when the mouth pressure is increased gradually to start a note from silence. Using results from dynamic bifur-cation theory, a prediction of the amplitude of the sound as a function of time is given based on a few parameters quantifying the time evolution of mouth pressure. As in previous uses of this model, the predictions are expected to be qualitatively consistent with simulations using the Raman model, and observations of real instruments. Model simulations for slowly variable parameters require very high precisions of computation. Similarly, any real system, even if close to the model would be affected by noise. In order to describe the influence of noise, a modified model is developed that includes a stochastic variation of the parameters. Both ideal and stochastic models are shown to attain a minimal amplitude at the static oscillation threshold. Beyond this point, the amplitude of the oscillations increases exponentially, although some time is required before the oscillations can be observed at the '' dynamic oscillation threshold ''. The effect of a sudden interruption of the growth of the mouth pressure is also studied, showing that it usually triggers a faster growth of the oscillations.

Quantum limits for cascaded nondegenerate optical parametric oscillators

The continuous variable multicolor entangled state of optical modes is one of the essential quantum resources for constructing quantum information networks composed of many nodes and channels. It has been well proved that the cascaded nondegenerate optical parametric oscillators (CNOPOs) are the most successful devices to produce bright entangled optical beams with different wavelengths. Here, we discuss the dependence of the possibly obtained largest-size multicolor entangled state and the entanglement degree on optical parameters of CNOPOs. Each NOPO in the cascaded system is operated above its oscillation threshold. One of two output optical beams produced by a NOPO is used for the pump light of the subsequent one, and the remained another beam serves as a submode of the multicolor entangled state. The obtainable maximal number of entangled submodes and the multicolor entanglement degree are numerically calculated under experimentally accessible conditions. The calculated results provide direct references for the design of generation systems of multicolor entangled optical beams.

Co-precipitation synthesis and vacuum sintering of Nd:YAG powders for transparent ceramics

The Nd:YAG nanopowders were synthesized at 800–1300°C via a modified co-precipitation method. Nd:YAG transparent ceramics were fabricated by vacuum sintering at 1770–1790°C for 20h with heating rates 1–10°C/min. The effects of calcining temperatures of highly sinterable Nd:YAG nanopowders, sintering temperature and heating rate on microstructure and transmittance of Nd:YAG ceramics have been investigated. After calcination at 1250°C for 4h, Nd:YAG nanopowders with primary particle size of about 106nm and low agglomeration were obtained. Using as prepared powders, high optical quality Nd:YAG ceramics prepared at 1780°C with dwell time of 20h and heating rate at 1°C/min have been obtained and shows the in-line transmittance reached 83.9% (1064nm). With 17.6W of maximum absorbed pump power, laser output of 4.5W has been obtained with an oscillation threshold and a slope efficiency of 0.5W and 25.6%.

Time-resolved phase-space tomography of an optomechanical cavity

We experimentally study the phase space distribution (PSD) of a mechanical resonator that is simultaneously coupled to two electromagnetic cavities. The first one, operating in the microwave band, is employed for inducing either cooling or self-excited oscillation, whereas the second one, operating in the optical band, is used for displacement detection. A tomography technique is employed for extracting the PSD from the signal reflected by the optical cavity. Measurements of PSD are performed in steady state near the threshold of self-excited oscillation while sweeping the microwave cavity detuning. In addition, we monitor the time evolution of the transitions from an optomechanically cooled state to a state of self excited oscillation. This transition is induced by abruptly switching the microwave driving frequency from the red-detuned region to the blue-detuned one. The experimental results are compared with theoretical predictions that are obtained by solving the Fokker-Planck equation. The feasibility of generating quantum superposition states in the system under study is briefly discussed.

Radiation-pressure-driven mechanical oscillations in silica microdisk resonators on chip

We demonstrate radiation-pressure-driven mechanical oscillations from high optical quality factor silica microdisk resonators on chip. Mechanical quality factors of 3520 in air and 12540 in vacuum for the fundamental radial breathing modes are obtained from 73 μm-diameter silica microdisks with mechanical frequencies of ∼51 MHz. The measured mechanical oscillation threshold powers for the input light are determined to be 62.5 μW in air and down to 26.6 μW in vacuum.

Miniature multioctave light source based on a monolithic microcavity

Optical microresonators are ideal tools for the reduction of the threshold of optical parametric oscillation based on four-wave mixing. Usually, the efficiency and bandwidth of the resonant process are interdependent due to stringent phase matching requirements leading to limitation of the bandwidth of the spectrum generated for a given pump power. We demonstrate a continuous-wave low-threshold resonant optical parametric oscillator with optical spectral span ranging from 0.36 to 1.6 μm. Harmonic generation is observed when a MgF2 microresonator characterized by quality factor approaching 1010 is pumped either at 780 nm, with a standard distributed-feedback semiconductor laser, or at 698 nm, with a reflective amplifier. Pump power does not exceed 25 mW. The nonlinear process is phase matched due to χ(3)-facilitated interaction of different mode families of the resonator. The optical harmonics generated can be used to seed high-power visible lasers, generate correlated photon pairs, and perform spectroscopy measurements.