Nonlinear Compression Research Articles

The Effects of Nonlinear Frequency Compression and Digital Noise Reduction on Word Recognition and Satisfaction Ratings in Noise in Adult Hearing Aid Users.

Nonlinear frequency compression (NLFC) and digital noise reduction (DNR) are hearing aid features often used simultaneously in the adult population with hearing loss. Although each feature has been studied extensively in isolation, the effects of using them in combination are unclear. The effects of NLFC and DNR in noise on word recognition and satisfaction ratings in noise in adult hearing aid users were evaluated. A repeated measures design was used. Two females and 13 males between the ages of 55 and 83 yr who were experienced hearing aid users participated. Thirteen were experienced with NLFC and all were experienced with DNR. Each participant was fit with Phonak Bolero Q90-P hearing instruments using their specific audiometric data and the Desired Sensation Level v5.0 (adult) fitting strategy. Fittings were verified with probe microphone measurements using speech at 65-dB sound pressure level (SPL). NLFC verification was performed using the Protocol for the Provision of Amplification, Version 2014.01. All testing was conducted in a double-walled sound booth. Four hearing aid conditions were used for all testing: Baseline (NLFC off, DNR off), NLFC only, DNR only, and Combination (NLFC on, DNR on). A modified version of the Pascoe's High-Frequency Word List was presented at 65-dB SPL with speech spectrum noise at 6-dB signal-to-noise ratio (SNR) and 1-dB SNR for each hearing aid condition. Listener satisfaction ratings were obtained after each listening condition in terms of word comfort, word clarity, and average satisfaction. Two-way repeated measures analyses of variance were conducted to assess listener performance. Pairwise comparisons were then completed for significant main effects. Word recognition results indicated a significant SNR effect only (6 dB SNR > 1 dB SNR). Satisfaction ratings results indicated a significant SNR and hearing aid condition effect for clarity, comfort, and average satisfaction. Clarity ratings were significantly higher for DNR and Combination than NLFC. Comfort ratings were significantly higher for DNR than NLFC. Average satisfaction was significantly higher for DNR and Combination than for NLFC. Also, average ratings were significantly higher for Combination than Baseline. Activating NLFC or DNR in isolation or in combination did not significantly impact word recognition in noise. Activating NLFC in isolation reduced satisfaction ratings relative to the DNR or Combination conditions. The isolated use of DNR significantly improved all satisfaction ratings when compared with the isolated use of NLFC. These findings suggest NLFC should not be used in isolation and should be coupled with DNR for best results. Future research should include a field trial as this was a limitation of the study.

Loss models for on and off-design performance of radial inflow turbomachinery

It is critical to accurately predict the performance of radial inflow turbomachinery in the preliminary design stages. Preliminary design of radial inflow turbomachinery uses basic geometry information and does not have access to detailed blade design. Experimentally derived models using an optimised geometry are widely used to develop a correlation between real world performance and basic design parameters of the turbine. Yet, these correlation models are primarily based on ideal working fluids. Modern turbomachinery systems operate with new complex fluids such as CO2 and R143a which have non-linear compressibility and non-ideal viscosity. Additionally, modern turbomachinery systems are expected to run with reliable performance at off-design conditions.This paper develops a new loss model configuration suitable for the analysis of turbomachinery operating with CO2 and R143a working fluids where off-design performance estimation is critical and temperature fluctuation may be expected. The paper systematically analyses over 1.5 million loss model configurations developed through the enumeration of analytical models for each loss mechanism from within literature. Each loss model configuration is compared against computational simulations of a turbine running at a wide range of off-design conditions. Primary findings of the paper are that loss model configurations must capture the appropriate physics. A loss model configuration must account for slip, as well as interaction between the turbine and immediate downstream components. Furthermore, models that were directly derived from experimental data showed better predictive performance. Specifically, due to the inclusion of appropriate physics and models directly derived from experiments, the proposed loss model within this work showed high accuracy, with a maximum error between the model and CFD of less than 2%. Many performance analysis methods focussed on the on-design performance of turbomachinery alone; the present work extends the application to incorporate more in-depth analysis of the off-design performance of turbomachinery. The paper provides a loss model configuration that is immediately useful for the development of radial inflow turbomachinery operating with CO2 and R143a and can be easily adopted to the early cycle design phase to ensure that performance is consistently high.

Influence of matric suction on nonlinear time-dependent compression behavior of a granular fill material

The site formation for the construction of a new airport in a mountainous region is typically performed by cutting and filling a hill section. The fill materials are subjected to seasonal changes and large variations in water content. The water content change renders the fill material to be characterized as unsaturated or saturated. This study aims to investigate the influence of matric suction on the time-dependent compression behavior of one local soil as a fill material for the construction of a new runway of an airport in Chongqing city, a mountainous region in China. A series of unsaturated drained triaxial tests were conducted on this coarse-grained soil to obtain the relationship between the effective stress parameter, χ, and the matric suction. Subsequently, multistaged compression tests were performed on this soil using a newly designed suction-controlled oedometer apparatus. The influence of suction on the time-dependent compression behavior of the fill material is emphasized. The results indicate that the matric suction can increase the compression stiffness, and that the unloading–reloading index varies nonlinearly with suction. A linear relationship between the time-dependent compression coefficient and normalized effective vertical loading is established. The linear relationship is subsequently used to predict the time-dependent compression coefficient to describe the time-dependent behavior of the fill under unsaturated conditions. Further, a nonlinear function based on the work of Yin (Geotechnique 49(5):699–707, 1999) is adopted to describe the development of time-dependent compression. The results indicate that the prediction obtained from the two newly proposed methods are promising, and can predict the nonlinear time-dependent compression behavior of this coarse-grained soil.

High-power two-cycle ultrafast source based on hybrid nonlinear compression.

We demonstrate a hybrid dual-stage nonlinear compression scheme, which allows the temporal compression of 330 fs-pulses down to 6.8 fs-pulses, with an overall transmission of 61%. This high transmission is obtained by using a first compression stage based on a gas-filled multipass cell, and a second stage based on a large-core gas-filled capillary. The source output is fully characterized in terms of spectral, temporal, spatial, and short- and long-term stability properties. The system's compactness, stability, and high average power makes it ideally suited to drive high photon flux XUV sources through high harmonic generation.

High-energy femtosecond pulse shaping, compression, and contrast enhancement using multicore fiber

Nonlinear spatiotemporal dynamics of femtosecond pulses in a hexagonal seven-core silica fiber pumped by a sub-μJ 370fs Er:fiber chirped pulse amplification (CPA) system were studied. Nonlinear pulse shaping and compression in the central core and pedestal coupling to the outer cores were directly measured by frequency-resolved optical gating. Further compression of the pulses spectrally broadened in the multicore fiber down to 53fs was demonstrated. Two orders of magnitude contrast enhancement of the pulses after compression was observed.

One-dimensional nonlinear consolidation behavior of structured soft clay under time-dependent loading

This research investigated the nonlinear compressibility, permeability, the yielding due to structural degradation and their effects on consolidation behavior of structured soft soils. Based on oedometer and hydraulic conductivity test results of natural and reconstituted soft clays, linear log (1+e) ~ log sigma\'v and log (1+e) ~ log kv relationships were developed to capture the variations in compressibility and permeability, and the yield stress ratio (YSR) was introduced to characterize the soil structure of natural soft clay. Semi-analytical solutions for one-dimensional consolidation of soft clay under time-dependent loading incorporating the effects of soil nonlinearity and soil structure were proposed. The semi-analytical solutions were verified against field measurements of a well-documented test embankment and they can give better accuracy in prediction of excess pore pressure compared to the predictions using the existing analytical solutions. Additionally, parametric studies were conducted to analyze the effects of YSR, compression index (lambda_r and lambda_c), and permeability index (eta_k) on the consolidation behavior of structured soft clays. The magnitude of the difference between degree of consolidation based on excess pore pressure (Up) and that based on strain (Us) depends on YSR. The parameter lamda_c/eta_k plays a significant role in predicting consolidation behavior.

Research on Nonlinear Frequency Compression Method of Hearing Aid with Adaptive Compression Ratio

Research on Nonlinear Frequency Compression Method of Hearing Aid with Adaptive Compression Ratio

Generation of few-cycle laser pulses by coherent synthesis based on a femtosecond Yb-doped fiber laser amplification system

We demonstrate a coherent synthesis system based on femtosecond Yb-doped fiber laser technology. The output pulse of the amplification system is divided into two replicas and seeded into photonic crystal fibers of two parallel branches for nonlinear pulse compression. Because of the different nonlinear dynamics in the photonic crystal fibers, the compressed pulses show different spectra, which can be spliced to form a broad coherent spectrum. The integrated timing jitter between the pulses of two branches is less than one tenth of an optical cycle. By coherently synthesizing pulses from these two branches, 8 fs few-cycle pulses are produced.

Hollow-core fiber compression of a commercial Yb:KGW laser amplifier

High-repetition-rate high-harmonic sources are desired for novel attosecond and time-resolved spectroscopies. One route to generating these sources is the nonlinear compression of high-average power Yb fiber and solid-state amplifiers, which can achieve >100 fs pulse duration with microjoule to millijoule pulse energy. Here, we demonstrate compression of 280 fs, 400 μJ pulses from a moderately high power (20 W) Yb:KGW laser amplifier to 15 fs. Few-cycle pulses (<5 cycles) with an energy of up to 200 μJ are obtained with a relatively simple scheme utilizing a xenon-filled hollow-core fiber and chirped mirror compressor and are used to generate XUV harmonics.

Superstrong light (achievements and prospects)

A review of the production of extreme-power supershort laser pulses and their applications for the interaction of superstrong light fields with matter is presented. The main issues with, and the possibility of, creating pulses with multipetawatt peak power using linear and nonlinear compression are considered. A prediction is made regarding the future use of such laser systems.

The Gain Game: Using the Four Principal Amplifier Gain Metrics

In the ongoing quest to improve energy efficiency for power amplifiers (PAs), it is necessary to operate the amplifier transistors in both the cutoff and nonlinear compression operating regions [1], [2]. In these operation modes, the usual measures of amplifier gain can no longer be used indiscriminately [3]. Earlier work with the amplifier voltage transfer function shows how the slope and ratiometric gains of any amplifier diverge as nonlinear amplifier operation increases [4]. Here, the extended gain metrics, which also include the power transfer function [5], bring the total number of important gain metrics up to four. While many of these points may seem elementary, it is well documented that concepts regarding gain are actually not clearly understood. It is worthwhile to clarify these important differences because designs using intentional amplifier compression are becoming more common. We can then evaluate their relative effectiveness in support of design tasks such as PA linearizers.

A Fully Configurable Non-Linear Mixed-Signal Interface for Multi-Sensor Analytics

This paper presents a highly configurable non-linear compression scheme and its implementation as a configurable, compressive successive approximation register analog-to-digital converter (ADC). The non-linear ADC takes advantage of the input signal amplitude statistics and application sensitivity to maximize the information content of the digitized signal. This allows for potential power savings in the ADC conversion and the digital post-processing that follows it. This paper is the first mixed-signal interface that is fully configurable in terms of its non-linear quantization approach, supporting a wide variety of quantization functions. A 90-nm CMOS proof-of-concept chip operating at 33 kS/s is presented. The versatility and broad applicability of this proposal are further demonstrated with various case studies.

Self-similar pulse compression by defective core photonic crystal fiber with cubic–quintic nonlinearities

We propose a class of photonic crystal fiber called as defective core photonic crystal fiber which can fulfill the self-similar condition for pulse compression in a relatively simple means, without the necessity for a complex approach of changing the size of air holes in the cladding. The proposed model obeys exponential decrease (increase) in dispersion (nonlinearity) along the fiber length and hence compresses the pulse under self-similar technique. We also study the effect of system parameters such as initial dispersion, nonlinearity and chirping in the self-similar compression and compared with adiabatic compression. Using extended nonlinear Schrödinger equation, we have taken into account the effect of quintic nonlinearity on the pulse compression. In the proposed configuration, the quintic nonlinearity shows only a weaker effect in the compression as compared to the cubic nonlinearity. In the present system, we show that the self-similar technique is superior with high degree of compression than the adiabatic route of compressing the pulse. The effect of fiber loss is also taken into account and the critical fiber loss coefficient for compression is estimated.

Ins, Outs of Frequency-lowering Processing

Ins, Outs of Frequency-lowering Processing

High-power OPCPA generating 1.7 cycle pulses at 2.5 µm.

We present a high-power mid-infrared (mid-IR) optical parametric chirped-pulse amplifier (OPCPA) generating 14.4 fs pulses centered at 2.5 µm with an average power of 12.6 W and a repetition rate of 100 kHz. The short pulses are obtained without nonlinear pulse compression. This is in contrast to most few-cycle systems operating in the mid-IR. In our case, the ultrashort pulse duration is enabled by a careful design of the gain profile of each amplification stage as well as a precise control of the signal dispersion throughout the system. A pulse shaper is used in the seed beam to adjust the spectral phase at the output of the OPCPA system. This approach allows for a clean temporal profile leading to a high peak power of 6.3 GW.

Femtosecond laser pulse generation with self-similar amplification of picosecond laser pulses.

Compressing picosecond laser pulses to the femtosecond level is an attractive shortcut for obtaining femtosecond laser pulses. However, dechirped pulses generated by nonlinear compression with self-phase modulation (SPM) show obvious pedestals, which are induced by nonlinear chirp accumulation in spectral broadening process and cannot be easily suppressed. Here, we report systematic numerical simulations and experimental studies on self-similar amplification of picosecond pulses in a short gain fiber for obtaining ~100-fs laser pulses with nearly transform-limited (TL) temporal quality. It is demonstrated that self-similar amplification with picosecond seed pulses is only sensitive to pulse duration and pulse energy. Based on this optimization guideline, we built a compact self-similar amplification fiber system with a picosecond fiber laser as the seed source. This system outputs 66-fs pulses with 6.1-W average power at a repetition rate of 30 MHz. Due to the linear chirp produced in self-similar evolution process, compressed pulses show nearly TL temporal quality. It promises an efficient way of obtaining high-quality femtosecond laser pulses from a picosecond laser source.

Generation of few-cycle radially-polarized infrared pulses in a gas-filled hollow-core fiber**Project supported by the National Natural Science Foundation of China (Grant No. 61521093), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB16), the International S & T Cooperation Program of China (Grant No. 2016YFE0119300), and the Program of Shanghai Academic/Technology Research Leader, China (Grant No.

We perform a numerical study for temporally compressing radially-polarized (RP) infrared pulses in a gas-filled hollow-core fiber (HCF). The dynamic transmission and nonlinear compression of RP pulses centered at wavelengths of 0.8 μm, 1.8 μm, 3.1 μm, and 5.0 μm in HCFs are simulated. By comparing the propagation of pulses with the same optical cycles and intensity, we find that under proper conditions these pulses can be compressed down to 2–3 cycles. In the transverse direction, the spatiotemporal beam profile ameliorates from 0.8-μm to 1.8-μm and 3.1-μm pulses before the appearance of high-order dispersion. These results show an alternative method of scaling generation for delivering RP infrared pulses in gas-filled HCFs, which can obtain energetic few-cycle pulses, and will be beneficial for relevant researches in the infrared scope.

Compressible turbulent flame speeds of highly turbulent standing flames

In this paper we present the first measurement of turbulent burning velocities of a highly turbulent compressible standing flame induced by shock-driven turbulence in a Turbulent Shock Tube. High-speed schlieren, chemiluminescence, PIV, and dynamic pressure measurements are made to quantify flame–turbulence interaction for high levels of turbulence at elevated temperatures and pressure. Distributions of turbulent velocities, vorticity and turbulent strain are provided for regions ahead and behind the standing flame. The turbulent flame speed is directly measured for the high-Mach standing turbulent flame. From measurements of the flame turbulent speed and turbulent Mach number, transition into a non-linear compressibility regime at turbulent Mach numbers above 0.4 is confirmed, and a possible mechanism for flame generated turbulence and deflagration-to-detonation transition is established.

Nonlinear Compression of Ultrashort-Pulse Laser to 36 fs With 556-MW Peak Power

The setup of nonlinear pulse compression with hollow-core photonic crystal fiber (HC-PCF) is demonstrated. In our experiment, the HC-PCF is just put in the air with no extra gas fill. The spectrum is effectively broadened to more than 60 nm by delivering the ultrashort laser in the HC-PCF and compressing the pulse with Gires–Tournois interferometer-type dispersion mirrors. The initial pulse duration of 279 fs has been shortened to 36 fs with $20\mu \text{J}$ of pulse energy, which corresponds to a peak power of about 556 MW. To our best knowledge, it is the highest peak power obtained from the solid-state laser at the wavelength around $1~\mu \text{m}$ by using Kagome-type HC-PCF without extra gas fill. With precise dispersion compensation and higher input pulse energy, even shorter pulse width and higher peak power can be obtained.

Active, artificial hair cells for biomimetic sound detection based on active cantilever technology.

We aim at building and studying artificial hair cells (AHC) based on MEMS technology to understand the extraordinary sound perception of the human ear and build a sensor system with similar properties. These perception properties, i.e. detecting six orders of sound pressure level and simultaneously frequency differences of only 3-5 Hz, are obtained mainly due to the sophisticated biological sensors in the inner ear, called hair cells, which convert the acoustic waves into electric signals. They amplify weak inputs and compress larger ones, known as compressive nonlinearity, thus enabling this impressive dynamic range, typically not captured by current engineering solutions. We tackle this demand by building artificial hair cells on the basis of smart, self-actuated and self-sensing mechanical resonator beams with suitable actuation feedback. Thereby, we take advantage of the fact that the compressive nonlinearity arises naturally in dynamical systems tuned to a bifurcation point. This tuning is achieved by an appropriate feedback loop inspired by physiological models. Initial results on the detection properties of a single AHC will be shown demonstrating amplification and a decreased width of the resonance peak.