Intensity Waveform Research Articles

A retinal imaging system for combined measurement of optic nerve head vascular pulsation and stimulated vasodilation in humans

Vascular pulsation at the optic nerve head (ONH) reflects vessel properties. Reduction in the stimulated retinal vasodilatory capacity has been reported in diabetes, but its relation with vascular pulsation is unknown. Here we report a new retinal imaging system for correlative assessment of ONH vascular pulsation and stimulated retinal vasodilation. Retinal reflectance images were acquired before and during light flicker stimulation to quantify arterial and venous vasodilation (DAR, DVR) in subjects with and without diabetic retinopathy (N = 25). ONH vascular pulsation amplitude and frequency (PA, PF), were quantified by curve fitting of periodic intensity waveforms acquired in retinal vasculature (RV) and ONH tissue (ONHT) regions. The relationships between pulsation metrics, heart rate (HR), intraocular pressure (IOP), and vasodilatory responses were evaluated. Pulsation metrics were not significantly different between regions (p ≥ 0.70). In RV, inter-image variabilities of PA and PF were 10% and 6%, whereas inter-observer variabilities were 7% and 2% respectively. In both regions, PF was correlated with HR (p ≤ 0.001). PA was associated with DAR in both regions (p ≤ 0.03), but only with DVR in RV (p ≤ 0.05). Overall, ONH vascular pulsation was associated with stimulated retinal vasodilation, suggesting diabetes may have concomitant effects on retinal vasculature compliance and neurovascular coupling.

Alterations in retinal pulse wave velocity under experimental ocular hypertension.

Impairments of blood flow and autoregulation have been implicated in diabetic retinopathy and glaucoma. Thus, identifying biomarkers of retinal vascular compliance and regulatory capacity is of potential value for understanding the pathophysiology and evaluating onset or progression of disease. Pulse wave velocity (PWV) represents the speed of the pulse-propagated pressure wave within blood vessels and has shown promise as a marker of vascular compliance. The purpose of the current study was to report a method for comprehensive assessment of retinal PWV based on spectral analysis of pulsatile intravascular intensity waveforms and determine alterations due to experimental ocular hypertension. Retinal PWV was linearly related to vessel diameter. Increased retinal PWV was associated with elevated intraocular pressure. Retinal PWV has the potential to serve as a vasoregulation biomarker for investigating vascular factors that contribute to the development of retinal diseases in animal models.

Deep Learning-Based Phase Retrieval Scheme for Minimum-Phase Signal Recovery

We propose a deep learning-based phase retrieval method to accurately reconstruct the optical field of a single-sideband minimum-phase signal from the directly detected intensity waveform. Our method relies on a fully convolutional Neural Network (NN) model to realize non-iterative and robust phase retrieval. The NN is trained so that it performs full-field reconstruction and jointly compensates for transmission impairments. Compared to the recently proposed Kramers-Kronig (KK) receiver, our method avoids the distortions introduced by the nonlinear operations involved in the KK phase-retrieval algorithm and hence does not require digital upsampling. We validate the proposed phase-retrieval method by means of extensive numerical simulations in relevant system settings, and we compare the performance of the proposed scheme with the conventional KK receiver operated with a 4-fold digital upsampling. The results show that the 7% hard-decision forward error correction (HD-FEC) threshold at BER 3.8e-3 can be achieved with up to 2.8 dB lower carrier-to-signal power ratio (CSPR) value and 1.8 dB better receiver sensitivity compared to the conventional 4-fold upsampled KK receiver. We also present a comparative analysis of the complexity of the proposed scheme with that of the KK receiver, showing that the proposed scheme can achieve the 7% HD-FEC threshold with 1.6 dB lower CSPR, 0.4 dB better receiver sensitivity, and 36% lower complexity.

Study on Output Characteristics of 20 kV/100 ns Nonlinear GaAs Photoconductive Semiconductor Switch

In this paper, the output electric pulse characteristics of gallium arsenide photoconductive semiconductor switch (GaAs PCSS) with bias voltage of 20 kV and pulse width of about 100 ns are studied. By designing the reflection and transmission optical paths, the absorption rate of the trigger optical of the GaAs PCSS at a wavelength of 1064 nm was measured to be 24.8%. When the bias voltage is 16 kV-20 kV, the avalanche multiplication rates of carriers are calculated respectively. The relationship between the output current waveform and the residual charge in the energy storage capacitor is analyzed when the bias voltage is 20 kV. And the trend of GaAs PCSS electric field intensity and current waveform change with time. This research will be helpful for the application design of GaAs PCSS under the nonlinear mode with special requirements, and has important significance for the application of frontier science.

Complete characterization of picosecond optical pulses by the offset frequency intensity modulation.

We present a method for characterizing the intensity waveform, spectrum, frequency chirp, and spectral phase of picosecond pulses at a moderate repetition rate of ∼100 MHz. The proposed method exploits the intensity modulation at ∼10 GHz, which is slightly offset from the integer multiple of the repetition rate of the pulses. The modulated pulses are split into two, and one is measured by an optical spectrum analyzer, whose output is detected by a lock-in amplifier, while the other is directly detected by a photodiode and its output is used as a reference signal of the lock-in amplifier. In the experiment, we demonstrate the measurement of picosecond Ti:sapphire laser pulses to investigate frequency chirp induced by self-phase modulation. We anticipate that the proposed method will be useful for the characterization of various types of picosecond pulses.

Structural optimization of disperser in polymer flooding distribution tank based on venturi pulse injection

ABSTRACT Polymer was carried by liquid in conventional polymer dispensing tank of polymer flooding in oilfield. Polymer particles often gather in the process of polymer blending, resulting in blockage of ground pipelines and formation. To reduce this phenomenon, finite element method was used. Optimization of polymer tank carrier based on venturi tube gas pulse injection. The polymer particles were carried into the liquid distribution tank by the injection method of pulse airflow to realize efficient carrying. Study on the effect of different pulse intensity and pulse waveform on cohesion. The results showed that the combined effect of strong pulse difference and pulse gap could make the airflow have strong carrying capacity for difficultly migrated polymer particles. Optimized the shortest pulse time and got the shortest time of triangle wave, sawtooth wave, square wave, and sine wave under simulated conditions. Time was 5.1 s, 6.3 s, 6.2 s, 6.2 s, respectively. The corresponding pulse frequencies were 20 times/s, 15 times/s, 10 times/s and 30 times/s, respectively. Properly increasing pulse intensity could enhance the carrying capacity of pulse airflow to polymer and reduced the carrying time of polymer. The optimal pulse parameters were triangular wave with pulse intensity of about 120 m/s and pulsed frequency of 20 times/s. Established the phenomenon and reason of indoor experiment. The viscosity of polymer solution after stirring was higher than that of liquid flow carried by gas phase pulse. This shows that the polymer system was more fully dissolved under the condition of gas phase pulse carrying. Pulsed airflow injection could effectively reduce polymer aggregation and shear action of agitator to protect polymer structure. Pulse airflow injection also plays an important role in safe operation of ground pipelines and stable seepage in porous media.

Combination of waveforms in modern spinal cord stimulation

BackgroundAfter the surge of burst stimulation, different waveforms were developed to optimize results in spinal cord stimulation. Studies have shown higher responder rates for multiwave therapy, but since the launch of such multiwave systems, little is known about the patients’ preference regarding waveforms in the long-term follow-up. No study connected particular waveforms to specific pain etiologies or required stimulation parameters so far.MethodThirty-four patients with refractory chronic neuropathic pain were treated with spinal cord stimulation systems providing multiwave therapy between September 2018 and October 2019. Patients with a follow-up of at least 6 months were selected; 10 subjects were excluded due to revision surgery, infection, and loss to follow-up. Data regarding pain intensity and preferred waveform for the trial, the implantation, 3-month and 6-month follow-up were recorded.ResultsDuring the trial phase, 10 patients (43.5%) achieved significant pain relief using tonic stimulation, 5 using burst (21.7%), 3 using microburst (13.0%), and 4 using a combination of tonic and microburst (17.4%). One single patient preferred Contour stimulation during the trial. After 3 months, 6 patients preferred microburst (25%), 6 preferred tonic (25%), 5 used a combination of tonic and microburst (20.8%), and 5 patients used burst (20.8%). After 6 months, similar results were obtained. Contour and Whisper were used in complex cases failing to other waveforms.ConclusionsTonic stimulation, isolated or in combination, remains an important component in spinal cord stimulation, being used by almost half of the patients. Over time, the usage of microburst increased considerably. Whisper and Contour, although battery-consuming, are good salvage options in complex cases.

Wave Intensity Analysis Combined With Machine Learning can Detect Impaired Stroke Volume in Simulations of Heart Failure.

Heart failure is treatable, but in the United Kingdom, the 1-, 5- and 10-year mortality rates are 24.1, 54.5 and 75.5%, respectively. The poor prognosis reflects, in part, the lack of specific, simple and affordable diagnostic techniques; the disease is often advanced by the time a diagnosis is made. Previous studies have demonstrated that certain metrics derived from pressure–velocity-based wave intensity analysis are significantly altered in the presence of impaired heart performance when averaged over groups, but to date, no study has examined the diagnostic potential of wave intensity on an individual basis, and, additionally, the pressure waveform can only be obtained accurately using invasive methods, which has inhibited clinical adoption. Here, we investigate whether a new form of wave intensity based on noninvasive measurements of arterial diameter and velocity can detect impaired heart performance in an individual. To do so, we have generated a virtual population of two-thousand elderly subjects, modelling half as healthy controls and half with an impaired stroke volume. All metrics derived from the diameter–velocity-based wave intensity waveforms in the carotid, brachial and radial arteries showed significant crossover between groups—no one metric in any artery could reliably indicate whether a subject’s stroke volume was normal or impaired. However, after applying machine learning to the metrics, we found that a support vector classifier could simultaneously achieve up to 99% recall and 95% precision. We conclude that noninvasive wave intensity analysis has significant potential to improve heart failure screening and diagnosis.

The Use of Maximum Entropy to Enhance Wave Intensity Analysis: An Application to Coronary Arteries in Hypertrophic Obstructive Cardiomyopathy.

Background: Wave intensity analysis is useful for analyzing coronary hemodynamics. Much of its clinical application involves the identification of waves indicated by peaks in the wave intensity and relating their presence or absence to different cardiovascular events. However, the analysis of wave intensity peaks can be problematic because of the associated noise in the measurements. This study shows how wave intensity analysis can be enhanced by using a Maximum Entropy Method (MEM).Methods: We introduce a MEM to differentiate between “peaks” and “background” in wave intensity waveforms. We apply the method to the wave intensity waveforms measured in the left anterior descending coronary artery from 10 Hypertrophic Obstructive Cardiomyopathy (HOCM) and 11 Controls with normal cardiac function. We propose a naming convention for the significant waves and compare them across the cohorts.Results: Using a MEM enhances wave intensity analysis by identifying twice as many significant waves as previous studies. The results are robust when MEM is applied to the log transformed wave intensity data and when all of the measured data are used. Comparing waves across cohorts, we suggest that the absence of a forward expansion wave in HOCM can be taken as an indication of HOCM. Our results also indicate that the backward compression waves in HOCM are significantly larger than in Controls; unlike the forward compression waves where the wave energy in Controls is significantly higher than in HOCM. Comparing the smaller secondary waves revealed by MEM, we find some waves that are present in the majority of Controls and absent in almost all HOCM, and other waves that are present in some HOCM patients but entirely absent in Controls. This suggests some diagnostic utility in the clinical measurement of these waves, which can be a positive sign of HOCM or a subgroup with a particular pathology.Conclusion: The MEM enhances wave intensity analysis by identifying many more significant waves. The method is novel and can be applied to wave intensity analysis in all arteries. As an example, we show how it can be useful in the clinical study of hemodynamics in the coronary arteries in HOCM.

Effective Stimulation Type and Waveform for Force Control of the Motor Unit System: Implications for Intraspinal Microstimulation.

The input–output properties of spinal motoneurons and muscle fibers comprising motor units are highly non-linear. The goal of this study was to investigate the stimulation type (continuous versus discrete) and waveform (linear versus non-linear) controlling force production at the motor unit level under intraspinal microstimulation. We constructed a physiological model of the motor unit with computer software enabling virtual experiments on single motor units under a wide range of input conditions, including intracellular and synaptic stimulation of the motoneuron and variation in the muscle length under neuromodulatory inputs originating from the brainstem. Continuous current intensity and impulse current frequency waveforms were inversely estimated such that the motor unit could linearly develop and relax the muscle force within a broad range of contraction speeds and levels during isometric contraction at various muscle lengths. Under both continuous and discrete stimulation, the stimulation waveform non-linearity increased with increasing speed and level of force production and with decreasing muscle length. Only discrete stimulation could control force relaxation at all muscle lengths. In contrast, continuous stimulation could not control force relaxation at high contraction levels in shorter-than-optimal muscles due to persistent inward current saturation on the motoneuron dendrites. These results indicate that non-linear adjustment of the stimulation waveform is more effective in regard to varying the force profile and muscle length and that the discrete stimulation protocol is a more robust approach for designing stimulation patterns aimed at neural interfaces for precise movement control under pathological conditions.

Cortical excitability measures from TMS‐EEG and TMS‐EMG – two sides of the same story?

Cortical excitability measures from TMS‐EEG and TMS‐EMG – two sides of the same story?

Estimation of plasma parameters in a pre-breakdown ionization wave at the glow discharge ignition in argon

The results of an experimental study of a pre-breakdown (slow) ionization wave (IW) in argon-filled discharge tubes of 15 mm i.d. and 80 and 100 cm length at a pressure of 1 and 4 Torr are presented. The breakdown and the IW were initiated by a positive voltage pulse with an amplitude of 2 and 4 kV. The IW was detected by the light emitted from its front. The IW emission spectrum consisted of the argon atomic and ion lines. The Ar(763.5 nm) and Ar+(488.0 nm) lines were used to retrieve the electric field strength value in the IW front. For this, the intensity ratio of these lines was measured. The upper levels for these lines are excited by electron impact, and, due to a large difference between their excitation energies, this ratio strongly depends on the reduced electric field strength E/N (E is the electric field strength, N is the atom number density). Theoretical modeling makes it possible to find a relation between the line intensity ratio and the E/N value. In the model, the axial profile of the IW electric field is approximated by a rectangle with a width determined from the measured emission intensity waveform and the wave velocity. As a result, the E/N magnitude in the IW front was found for various positions along the tube. Emission intensity of the DC discharge was also measured, which allowed us to estimate the emitting level population and electron number density in the IW front. The density of seed electrons ahead of the wave is also evaluated and processes responsible for the appearance of these electrons are discussed.

Study on pulse shape dependence of tungsten mass erosion under disruption-like heat load

We have studied pulse waveform dependence of tungsten mass erosion under disruption-like heat loads. In the experiment, tungsten samples were placed in a vacuum chamber and irradiated by a disruption-like heat load using a 1064 nm Nd: YAG laser. Mass erosion of tungsten samples by laser irradiation was measured by a microbalance. Laser intensity (up to 6.2 GW/m2), pulse duration (4 ms–5 ms), and pulsed laser waveform were changed as parameters. Five types of pulsed laser waveforms were used to investigate the mass erosion of tungsten; Positive Ramp, Symmetric Ramp, Negative Ramp, Half Amp Square, Half Width Square. Among these waveforms, the largest mass erosion was observed in Half Width Square under the same absorbed energy condition. Also, when the volume of the molten layer is sufficiently large, the mass erosion will be greater due to evaporation of tungsten and the release of droplets.

DeepClean: Self-Supervised Artefact Rejection for Intensive Care Waveform Data Using Deep Generative Learning.

Waveform physiological data are important in the treatment of critically ill patients in the intensive care unit. Such recordings are susceptible to artefacts, which must be removed before the data can be reused for alerting or reprocessed for other clinical or research purposes. Accurate removal of artefacts reduces bias and uncertainty in clinical assessment, as well as the false positive rate of ICU alarms, and is therefore a key component in providing optimal clinical care. In this work, we present DeepClean, a prototype self-supervised artefact detection system using a convolutional variational autoencoder deep neural network that avoids costly and painstaking manual annotation, requiring only easily obtained 'good' data for training. For a test case with invasive arterial blood pressure, we demonstrate that our algorithm can detect the presence of an artefact within a 10s sample of data with sensitivity and specificity around 90%. Furthermore, DeepClean was able to identify regions of artefacts within such samples with high accuracy, and we show that it significantly outperforms a baseline principal component analysis approach in both signal reconstruction and artefact detection. DeepClean learns a generative model and therefore may also be used for imputation of missing data.

Rapid declines in systolic blood pressure are associated with an increase in pulse transit time.

The correlation between pulse transit time and blood pressure has been proposed as a route to measure continuous non-invasive blood pressure. We investigated whether pulse transit time trends could model blood pressure trends during episodes of rapid declines in blood pressure. From the Medical Information Mart for Intensive Care waveform database we identified substantial blood pressure reductions. Pulse transit time was calculated from the R-peak of the electrocardiogram to the peak of the arterial pulse waveform. The time-series were processed with a moving average filter before comparison. Averaged, continuous heart rate was also analysed as a control. The intra-individual association between variables was assessed per subject using linear regression. In the 511 patients included we found a median correlation coefficient between blood pressure and pulse transit time of -0.93 (IQR -0.98 to -0.76) with regression slopes of -1.23 mmHg/ms (IQR -1.73 to -0.81). The median correlation coefficient between blood pressure and heart rate was 0.46 (IQR -0.16 to 0.83). In supplementary analysis, results did not differ substantially when widening inclusion criteria, but the results were not always consistent within subjects across episodes of hypotension. In a large cohort of critically ill patients experiencing episodes of rapid declines in systolic blood pressure, there was a moderate-strong intra-individual correlation between averaged systolic blood pressure and averaged pulse transit time. Our findings encourage further investigation into using the pulse transit time for non-invasive real-time detection of hypotension.

Transmission method of improved fiber nonlinearity tolerance for probabilistic amplitude shaping.

For probabilistic amplitude shaping (PAS), we propose a super-symbol transmission method that improves fiber nonlinearity tolerance. A simple fiber nonlinearity low-pass filtering model, as well as its interaction with the spectral dip of signal's intensity waveform, is provided to explain the origin of this nonlinear benefit. With 25-GHz-spaced, 26 × 22.5 GBaud dual-polarized PAS-64 quadrature amplitude modulation (QAM) signals transmitted over 12 spans of 80-km standard single mode fiber (SSMF), the proposed method is found to provide ∼0.15-dB gain over the previous finite-blocklength method with intra-DM pairing, ∼0.26-dB gain over finite-blocklength method with inter-DM pairing, and ∼0.44-dB benefit over the traditional method, all with a feasible blocklength at 200.

Spectral and Energy Efficient Fast-OFDM With Index Modulation for Optical Wireless Systems

This letter introduces fast-orthogonal frequency-division multiplexing (FOFDM) with index modulation (IM) based on discrete cosine transform (DCT) for optical wireless systems. For intensity-modulation and direct detection, the proposed approach realizes a real-valued intensity waveform by employing real-valued one-dimensional modulation formats and DCT; and brings about non-negativity via direct current bias. We shall establish that it attains up to 64% higher spectral efficiency (SE) with low order alphabets than conventional IM based approach on discrete Fourier transform and provides better flexibility to address energy efficiency/SE trade-off.

Reflection intensity waveform inversion

Traditional iteration-based full-waveform inversion (FWI) methods encounter serious challenges if the initial velocity model is far from the true model or if the observed data are lacking low-frequency content. As such, the optimization algorithm may be trapped in local minima and fail to go to a global optimal model. In addition, the traditional FWI method requires long-offset data to update the deep structure of a velocity model with diving waves. To overcome the disadvantages of traditional FWI under these circumstances, we have developed a reflection intensity waveform inversion method. This method aims to minimize the seismic intensity differences between the modeled reflection data and field data. Our method is less dependent on the starting model, and long-offset data are no longer required. The wave intensity, proportional to the square of the original data amplitude, can have a low-frequency band and a higher frequency band, even for waveforms without initial low-frequency content. Our multiscale intensity inversion starts from the low-frequency information in the intensity data, and it can largely avoid the cycle-skipping problem. Synthetic and field data examples demonstrate that our method is able to overcome cycle skipping in handling data with no low-frequency information.

Multibranch pulse synthesis and electro-optic detection of subcycle multi-terahertz electric fields.

We present a robust, compact pulse synthesis scheme generating intense phase-locked subcycle multi-terahertz waveforms. The ultrabroadband laser fundamental is split into two parallel branches driving optical rectification in crystals of GaSe and LiGaS2, each operated at the group velocity matching point. The coherent combination of the resulting pulses yields a continuous multi-terahertz spectrum covering 1.5 optical octaves. The corresponding 0.8-cycle electric field waveform is directly mapped out by electro-optic sampling, revealing peak fields of 15kV/cm at a repetition rate of 0.4MHz. The multiplexable and power scalable scheme opens the door to strong-field custom-tailored waveforms driving nonlinear optics and light wave electronics.

Modeling of Rotating Magnetic Properties of Electrical Steel Sheet Under DC-Biased Field

As the core material of an electrical device, the electrical steel sheet is often under ac and dc-biased magnetizing conditions due to the wide utilization of power electronics. For an accurate description of rotating magnetic properties of electrical steel sheet under the dc-biased field, an improved model considering magnetic hysteresis and nonlinear magnetization characteristics is established. The reluctivity coefficients and hysteresis coefficients of the improved model are calculated from magnetic flux density and magnetic field intensity waveforms measured by the feedback control system. The accuracy and reliability of the improved model are verified by the comparison of the measured and calculated hysteresis loops of electrical steel sheet under the dc-biased field.