Measurement Of Pulsations Research Articles

Printed soft skin electrodes for seamless bio-impedance measurements

Bio-impedance measurements are widely used to assess various physiological parameters. Contemporary skin electrodes for bio-impedance measurements are cumbersome and novel electrode designs are needed to allow fast and easy placement, long-term stability and user comfort. This investigation introduces dry, printed, bio-compatible electrode arrays, made of screen-printed carbon and inkjet-printed PEDOT:PSS that measure bio-impedance non-invasively and stably. Two contact impedance measurements yield the lowest normalized values of soft electrodes reported to date. Four contact bio-impedance measurements from the radial, ulnar, common carotid and superficial temporal arteries were performed, demonstrating the ability to capture blood pulsation in different areas with small form factor. Owing to the unique properties of the printed electrodes reported here, we were able to demonstrate for the first time blood pulsation in the face, continuous blood pulsation measurement during simultaneous muscle activation and signal stability over many hours.

The application of integrated MRI CSF flowmetry in the diagnosis and treatment of CSF dynamic changes in hydrocephalus patients: a systematic review

Background: CSF has contributed to the growth of brain development during the time of evolution and later protects against external trauma. Idiopathic normal pressure hydrocephalus (iNPH) is known as an aberration of intracranial hydrodynamics resulting in the accumulation of CSF endo-ventricular. The use of phase-contrast (PC) MRI is proven effective in assessing the communication of arachnoid cyst and subarachnoid CSF spaces. The CSF flow MRI has been found to show efficacy in differentiation between the communicating and non-communicating hydrocephalus for localizing obstruction levels in obstructive hydrocephalus and later providing important information concerning the preoperative evaluation of NPH, along with the differential diagnosis and the prediction of the related advantages from surgery and post-operative follow-up. Hence, the present study aimed for analyzing the role of MRI CSF flowmetry in the evaluation of patients with suspected hydrocephalus. Method: The role of MRI CSF flowmetry in the evaluation of patients with suspected hydrocephalus was undertaken by conducting a systematic literature review. The current review was reported as required reporting features for systematic reviews and meta-analysis statements (PRISMA). The systematic literature review included a total of 22 studies that analyzed the various applications of MRI CSF flowmetry in the medical field, mainly focusing on the use of MRI CSF flowmetry in the evaluation of patients with suspected hydrocephalus. Results: The result mainly included the identification of the CSF flow by integrating the PC MRI technique and the aqueduct-CSF flow rate was detected accurately showing as statistically significant in diagnosis of NPH. Evaluating the peak velocities and aqueductal stroke volume (ASV) showed a significant increase among hydrocephalus patients. Conclusion: The condition of hydrocephalus makes the ventricular size increase and eventually puts pressure on the brain due to excess accumulation of fluid while blocking the CSF flow after it exits ventricles. Currently, many imaging techniques are available for the detection of hydrocephalus that study the CSF flow dynamics and its related parameters. Among them, the MRI technique is the most reliable, rapid, and most importantly, a non-invasive method for the quantitative measurement of CSF flow rate and intracranial pulsations. Keywords: Intracranial pressure, Magnetic resonance imaging (MRI), MRI CSF Flowmetry, Neurological disorder, CSF dynamics

In vivo measurement of anterior chamber pulsation in healthy subjects using full-range complex spectral domain optical coherence tomography

A pulsation measurement algorithm was presented in this study, by using the phase-based method to visualize ocular pulse in the anterior chamber of healthy eyes. The algorithm mainly tracks the relative displacement between the cornea and lens by extracting the phase difference between adjacent images separated by 5 ms time intervals. The anterior chamber structural image in vivo is achieved by full-range, complex spectral domain, optical coherence tomography (FRC SD-OCT). Phase tracking was performed on a total of 1000 images within 5 s. In order to eliminate the noise phase caused by human motion during the acquisition process, the high-order phase compensation algorithm was used to eliminate the phase motion of large tissues. The frequency of the phase change in the relative motion after the noise subtraction was 1.2 Hz. Comparing with the heart beat measured by a finger pulse oximeter at the same time, the frequency of the phase change was consistent with the heart beat frequency. This measurement technique can be used to evaluate the biomechanical properties of ocular tissue and has a positive effect on the pathological studies of glaucoma.

Inner Damping of Water in Conduit of Hydraulic Power Plant

The operation of any hydraulic power plant is accompanied by pressure pulsations that are caused by vortex rope under the runner, rotor–stator interaction and various transitions during changes in operating conditions or start-ups and shut-downs. Water in the conduit undergoes volumetric changes due to these pulsations. Compression and expansion of the water are among the mechanisms by which energy is dissipated in the system, and this corresponds to the second viscosity of water. The better our knowledge of energy dissipation, the greater the possibility of a safer and more economic operation of the hydraulic power plant. This paper focuses on the determination of the second viscosity of water in a conduit. The mathematical apparatus, which is described in the article, is applied to data obtained during commissioning tests in a water storage power plant. The second viscosity is determined using measurements of pressure pulsations in the conduit induced with a ball valve. The result shows a dependency of second viscosity on the frequency of pulsations.

The "Brain Stethoscope": A Non-Invasive Method for Detecting Elevated Intracranial Pressure.

IntroductionMinimally invasive intracranial pressure (ICP) screening has long been desired by neurosurgeons. A novel approach deriving ICP from tympanic membrane (TM) pulsation may offer the solution. The ICP waveform appears to be transmitted to the TM by the cochlear aqueduct. The resulting TM infrasonic pulsations can be measured by certain sensors. Elevated ICP alters brain compliance, which appears to yield slower rise times of the TM pulsation waveform. Measurement of this change may be useful in screening for elevated ICP. This paper investigates one such technique.MethodsA stethoscope was modified for airtight external ear canal fit; the dome was exchanged for a magnetic reluctance pressure sensor, allowing measurement of TM pulsations. Analog TM pulsations were analyzed by measuring the pulsation's slope ratio between the waveform’s downslope and upslope. Seventeen normal subjects (ages 18-32 years) underwent hyperventilation and tilt table testing to induce ICP changes. An algorithm processed this data and predicted the subject's ICP status.ResultsThe slope ratio method showed consistent and stable changes with the expected alterations in ICP from the tilt test and hyperventilation maneuvers. The classification algorithm correctly identified subjects with elevated ICP in 60 of 60 independent recordings on 17 subjects.ConclusionThis paper has four conclusions. First, the "brain stethoscope" can detect increased ICP from the TM pulsation waveform in healthy subjects. Second, analysis of the TM waveform using slope ratio calculations is capable of distinguishing normal versus elevated ICP. Third, the tilt and hyperventilation maneuvers showed the expected physiologic trends. Last, further studies are needed on patients with pathological ICP before the brain stethoscope can be implemented into clinical practice.

Pressure measurements in detonation engines

The influence of waveguide tubes on the signals received by remote pressure sensors measuring pressure histories in pulsed detonation engines (PDEs) and rotating detonation engines (RDEs) is studied computationally. Two types of pressure sensors are considered: low-frequency static pressure sensors and high-frequency sensors of pressure pulsations. Three approaches to solving the problem are used: based on Euler (inviscid flow), Navier–Stokes (laminar flow), and unsteady Reynolds-averaged Navier–Stokes (turbulent flow) equations. The approaches based on the inviscid and laminar flow models are shown to provide the best predictive capability. The laminar flow model is applied to analyzing the readings of pressure sensors installed remotely in the waveguide tubes attached to the hydrogen-fueled PDE, RDE, and detonation ramjet (DR). It is shown that the measurements of static pressure and pressure pulsations by remote pressure sensors do not correspond to the time-averaged mean and local instantaneous values of pressure in the combustors. The pressure time histories can be recovered based on the measurements and computational fluid dynamics calculations of the operation process. The latter is demonstrated by analyzing the results of test fires with a dual-duct DR model.

A review on imaging techniques and quantitative measurements for dynamic imaging of cerebral aneurysm pulsations

Measurement of intracranial aneurysm wall motion may refine the current rupture risk estimation. A golden standard for measuring aneurysm pulsation is lacking. The aim is to evaluate magnitudes of aneurysm pulsation as published in current literature. Embase and PubMed were searched for publications containing quantitative measures of cardiac-cycle related cerebral aneurysm pulsation (no date or language restrictions). Eleven studies were included, covering 197 unruptured and untreated cerebral aneurysms. Quantitative pulsation measurements were extracted from the studies. Characteristics of the study population and aneurysms were taken into account, as well as the imaging modality, scanning technique and data processing methods used. A meta-analysis was performed of studies with similar methodologies and individual IA measures and locations. The magnitude of the absolute volume pulsations varied between 14 ± 9 mm3 and 106 ± 123 mm3 and the mean relative volume change varied between 5 and 36%. The meta-analysis revealed a positive correlation between size and absolute volume change. The relative volume change in Basilar artery aneurysms seems smaller. No authors were contacted for original study data and articles only describing visual pulsations were excluded. The variation in methodologies impedes an accurate estimation of the magnitude of IA pulsations. Validation of aneurysm pulsation measurement is crucial prior to clinical studies evaluating IA pulsatility in relation to IA rupture risk. Prerequisite is a reliable and robust imaging method with high spatial and temporal resolution and standardization of the image analysis methods.

One-Minute Finger Pulsation Measurement for Diabetes Rapid Screening with 1.3% to 13% False-Negative Prediction Rate

Previous non-invasive Diabetes Mellitus (DM) prediction methods for rapid screening suffered from the trade-off between speed and accuracy. The accurate results of questionnaires rely on long and detailed questions thus sacrifice speed, meanwhile, photoplethysmography (PPG) offers convenient and fast testing but lacking accuracy. In this work, we developed a 5-grade model to accurately screen out non-DM subjects (low prediction grades) via one-minute PPG measurement. This efficient and effective rapid screening will practically reduce the loading for further invasive verification on the remaining DM-grade subjects. A total of 2538 subjects are recruited (DM: 1310, non-DM: 1228) with two 1-minute PPG samples taken from each subject. The model includes 8 features: 3 autonomic- and 3 vascular-related PPG features, heart rate, and waist circumference. All 8 features monotonically alter with increased DM prediction grade. The model provides users 5 DM risk grades. While defined grade 1 and grade 2 as non-DM grades, the prediction result shows a low false-negative rate of 13%. If only considering grade 1 as non-DM, the false-negative rate will be significantly reduced to 1.3%. Thus subjects predicted as grades 1 and 2 are substantially away from DM. The remaining subjects with higher DM risk grades such as grades 3, 4, and 5 (or unlikely grade 2) are recommended to take clinical-standard invasive DM test for corresponding therapeutic treatment. A table for assessing the risk index for each feature is also compiled. We have experimentally demonstrated a 1-minute pulsation measurement with PPG-based device (SpO ₂ oximeter, smartphone, or wearable device) can be an efficient/effective DM rapid screening technique to filter out non-DM subjects. The resulted high-risk feature indexes also pose as warning signs of the degradation of either autonomic or vascular functions for personal healthcare management. The fast and convenient execution and useful results suggest that our approach is very simple and informative for quick DM risk assessment.

Signature Investigation of Typical Faults on Francis Turbines

Hydropower is facing new operational strategies as the increasingly competitive power market demands for higher flexibility. Consequently, turbines are forced to handle tougher operation and are prone to more frequent degradation. By implementing a real-time monitoring system, a better understanding of the behavior of components may contribute to detect faults at an earlier stage, reducing potential downtime. This paper will present the work done in the preliminary work of the author’s master thesis. The focus has been to characterize the normal behaviour of a Francis turbine through amplitude and frequency analysis. Steady-state measurements of pressure pulsations have been conducted on the Francis test-rig at the Waterpower laboratory at NTNU. Different hydraulic phenomena and respective frequencies were identified. In addition, the results revealed several unexpected frequencies and suspicious observations, and potential sources of these are discussed. Possible fault detection schemes based on peak-peak and frequency analysis are suggested. Alarm should be raised in case of mismatches in sensor relations, magnitude variations or if new harmonics or frequencies appears.

Dynamic measurements on unsteady pressure pulsations and flow distributions in a nuclear reactor coolant pump

The operational stability of the nuclear reactor coolant pump (RCP) will directly affect the safety of the nuclear power plants (NPPs). A comprehensive analysis of the dynamic characteristics of the internal flow structure in the RCP is extremely important to assess its operational stability. Because the unsteady pressure characteristics of the spherical casing wall of the RCP and the dynamic flow field inside the RCP are complicated, it is highly demanding to be accurately measured by a reliable approach. Dynamic pressure pulsation and Laser Doppler Velocimetry (LDV) measurements have been carried out on the spherical casing wall and internal flow of the RCP under different operating conditions. Based on the pressure pulsation measurement, it is convinced that different unsteadiness flow structures directly affect the pressure pulsation characteristics, which will generate various excitation signals. The intercoupling between rotor-stator interaction (RSI) and the collision of the fluid discharged from the diffuser with the circulating flow to the casing bottom is the main reason for leading to strong pressure pulsations. Dynamic LDV measurement result shows that there is a significant counterclockwise periodic vortex shedding from the diffuser blade trailing edge, especially under high flow rate (1.2QN), which is also the main reason of strong velocity pulsations. The core of this paper is to comprehensively elaborate the dynamic flow characteristics in such a complex hydraulic machinery through combining multiple dynamic measurement methods. Moreover, an exhaustive understanding of dynamic flow characteristics is the basis for optimizing the RCP. The experimental results can provide ideas and basis for the optimization of the RCP with stable operation characteristics.

Numerical and Experimental Investigation of External Characteristics and Pressure Fluctuation of a Submersible Tubular Pumping System

This paper presents an investigation of external flow characteristics and pressure fluctuation of a submersible tubular pumping system by using a combination of numerical simulation and experimental methods. The steady numerical simulation is used to predicted the hydraulic performance of the pumping system, and the unsteady calculation is adopted to simulate the pressure fluctuation in different components of a submersible tubular pumping system. A test bench for a model test and pressure pulsation measurement is built to validate the numerical simulation. The results show that the performance curves of the calculation and experiment are in agreement with each other, especially in the high efficiency area, and the deviation is minor under small discharge and large discharge conditions. The pressure pulsation distributions of different flow components, such as the impeller outlet, middle of the guide vane, and guide vane outlet and bulb unit, are basically the same as the measurement data. For the monitoring points on the impeller and the wall of the guide vane especially, the main frequency and its amplitude matching degree are higher, while the pressure pulsation values on the wall of the bulb unit are quite different. The blade passing frequency and its multiples are important parameters for analysis of pressure pulsation; the strongest pressure fluctuation intensity appears in the impeller outlet, which is mainly caused by the rotor–stator interaction. The farther the measuring point from the impeller, the less the pressure pulsation is affected by the blade frequency. The frequency amplitudes decrease from the impeller exit to the bulb unit.

Turbulent spots in the flame of a diffusion torch

Jet flame in modes of manageable instability development inside the source of jet formation is one of the methods for controlling the space-time and thermodynamic parameters of the torch. When a system of vortices flows into a free atmosphere, their interaction with the mixing layer and the flame front is accompanied by the appearance of a number of effects. The introduction of artificial perturbations into the flow allowed initiating the onset of a laminarturbulent transition in the tube, which led to the formation of vortex structures in the jet stream. Hot-wire anemometric measurements of the velocity pulsations in the isothermal flow has shown that the disturbance introduced by the controlled valve is an acoustic precursor and a large-scale vortex formation. In this work, we investigated the effect of a system of turbulent spots on a laminar diffusion plume. Based on the two-point space-time temperature correlation dependences, data characterizing the rate of propagation of thermal perturbations during burning of H2/CO2 and C3H8/CO2 fuel mixtures were obtained.

About improvement of the scheme of correction of frequency characteristics of probes for measurement of pulsations of pressure in gte

It is known that pressure pulsations affect the performance of power plants, including a gas turbine engine, reducing the reserve of gas-dynamic stability of the compressor, creating conditions for oscillatory combustion in the combustion chamber. When fine-tuning the engine in the context of the pressure pulsations there is need for measuring means working at extreme temperatures and vibrations. The most acceptable of these means is a probe consisting of a supply waveguide, a pressure pulsation sensor and a corrective element in the form of a long line. However, in the low frequency region there is an uneven amplitude-frequency characteristic of the probe, due to the influence of the reflected pressure waves from the closed end of the long line. It is proposed to install an acoustic RC-filter with resistance equal to the wave resistance of the long line at the output of a long line. The paper theoretically shows that such an improvement of the probe allows to expand the frequency range of measurement of pressure pulsations. The material of the article will be useful for specialists who develop and use tools for measuring pressure fluctuations in extreme conditions, for example, when developing gas turbine engines.

Onboard measurements of pressure pulsations in a low specific speed Francis model runner

Over the last years, there have been several incidents with cracks in high head Francis turbines. These cracks are understood to be related to pressure pulsations, vibration modulus and the combination of these. In this paper, a setup for the investigation of pressure pulsations in a low specific speed model turbine is presented with the use of onboard pressure sensors. Earlier onboard measurements have mainly utilized blade-mounted sensors. In this paper, a setup with hub-mounted pressure sensors are described. In addition, a position sensor is utilized to analyse the pressure data relative to the angular position of the runner. The setup is considered as a good reference for computational fluid dynamics validation and is considered less extensive for evaluating the onboard pressure pulsations compared to blade-mounted sensors.

Analysis of schemes of correction of dynamic characteristics of acoustic probes for measuring pressure pulsations in a gas turbine engine

Gas pressure pulsations are one of the main parameters taken into account in gas turbine engine development. Therefore, special attention is paid to the accuracy of measuring pressure fluctuations. A high temperature of gas flow, sensors size limitations in many cases do not allow it to be installed directly at the measurement point. There is a need to connect the sensor to the process using a waveguide channel (waveguide). It is known that resonant oscillations occur in the waveguide, leading to an additional dynamic error of the measuring channel. To improve the accuracy of measuring pressure fluctuations, corrective elements are used. A device consisting of a pressure pulsation sensor, a waveguide connected to the process, and a correction element is called a pressure pulsation probe in technical literature. In foreign and domestic literature there is a large amount of information on probes, but because of the variety of schemes of probe correction selecting those that would provide the required accuracy of measurement of pressure pulsations always poses a challenge. Therefore, taking into account the constant increase in the energy intensity of modern engines, and, accordingly, the increase in the temperature of working media, the authors analyzed the effectiveness of corrective elements on the basis of available patents, articles, and monographs. The article considers hardware and software schemes of correction of dynamic characteristics of acoustic probes based on corrective elements with distributed and lumped parameters. The advantages and disadvantages of the schemes are pointed out. Information on methods of calculating frequency characteristics of probes and their digital correction in the processing of experimental data is presented. The article will be of interest to developers of pressure pulsation probes and engineering and technical workers involved in GTE refinement.

The Importance of Posture and Skin-Site Selection on Remote Measurements of Neck Pulsations: An Ultrasonographic Study.

Laser Doppler vibrometry (LDV) and camerabased vibrocardiography imaging (cVCGI) systems can sense cardiac-related displacements of the skin. This allows that carotid artery (CA) or jugular vein (JV) wall movements are acquired, non-obtrusively, at the neck and used for assessing cardiovascular health. However, skin-neck measurements are invalid if the CA and JV pulsations overlap. The concern is plausible since these vessels are anatomically close to one another until the carotid sinus. In this paper, we build on ultrasonographic (US) insights to verify whether trunk posture and skin-site variability within the neck influence cVCGI outcomes. Using ultrasound (US), we recorded the wall movements of the CA and JV in 4 subjects (ages, 28-41 yrs) in the supine, recumbent and seated positions at sites in the vicinity of the common CA. Skin-displacement waveforms were subsequently recorded by cVCGI and compared with US recordings. Our results show that CA displacements are dominant at the upper neck in the seated-to-recumbent positions whereas JV pulsations are best probed in recumbent-to-supine positions at the lower neck. These insights help to recognize the possible value of cVCGI in early-stage diagnosis or ambulatory monitoring.

Pressure Pulsation in a High Head Francis Turbine Operating at Variable Speed

This paper presents the preliminary work of the master thesis of the author, written at the Norwegian University of Science and Technology. Today, many Francis turbines experience formations of cracks in the runner due to pressure pulsations. This can eventually cause failure. One way to reduce this effect is to change the operation point of the turbine, by utilizing variable speed technology. This work presents the results from measurements of the Francis turbine at the Waterpower Laboratory at NTNU. Measurements of pressure pulsations and efficiency were done for the whole operating range of a high head Francis model turbine. The results will be presented in a similar diagram as the Hill Chart, but instead of constant efficiency curves there will be curves of constant peak-peak values. This way, it is possible to find an optimal operation point for the same power production, were the pressure pulsations are at its lowest. Six points were chosen for further analysis to instigate the effect of changing the speed by ±50 rpm. The analysis shows best results for operation below BEP when the speed was reduced. The change in speed also introduced the possibility to have other frequencies in the system. It is therefore important avoid runner speeds that can cause resonance in the system.

Beneficial effects of a Fermented Papaya Preparation for the treatment of electrohypersensitivity self-reporting patients: results of a phase I-II clinical trial with special reference to cerebral pulsation measurement and oxidative stress analysis

Background: Electromagnetic Field Intolerance Syndrome (EMFIS), also termed Idiopathic Environmental Intolerance (IEI) attributed to Electromagnetic Fields (IEI-EMF) by WHO, is a newly identified pathological disorder occurring in electrohypersensitivity (EHS) self-reporting patients. To date, there has been no recognized treatment of this disorder. We have shown that EHS self-reporting patients experience some degree of oxidative stress, inflammation, and autoimmune response. Additionally, Fermented Papaya Preparation (FPP) has some antioxidant, anti-inflammation, and immuno-modulating properties. The objective of this phase I-II clinical trial was thus to test whether FPP treatment is well tolerated, can improve clinical outcomes, and normalize biological abnormalities. Methods: 32 EMFIS-bearing patients were serially included in this trial, among which 26 and 16 of them were evaluable after 3 and 6 months of FPP treatment, respectively. Clinical assessment was conducted during a specific face to face interview by using a validated pre-established questionnaire. Biological assessment consisted of measuring intracerebral tissue pulsometric index (PI) in the temporal lobes with ultrasonic cerebral tomosphygmography (UCTS), in addition to oxidative stress and inflammation with a battery of oxidative stress and inflammation-related peripheral blood tests.Results: Overall clinical improvement was obtained in 50-60% of the cases, among which 20-35% presented major improvement that mainly consisted of the regression of cognitive symptoms such as loss of short term memory, concentration, attention deficiencies, insomnia, and fatigue. This clinical improvement was objectively supported by a statistically significant normal recovery of mean PI in the temporal lobes and by a FPP-related antioxidative effect evidenced by a statistically significant decrease in malondialdehyde levels in the plasma (p<0.0001) and increase in the Glutathione peroxidase activity in red blood cells (p<0.01) in patients experiencing oxidative stress. Moreover, this trial evidenced some degree of FPP-related anti-inflammatory effects by demonstrating a statistically significant decrease in histamine (p=0.049) and HSP27/HSP70 chaperone proteins (p=0.007) in the peripheral blood of patients with initial increased values of these inflammation-related biomarkers.Conclusion: The results suggest a beneficial clinical and biological therapeutic effect of FPP in EHS self-reporting patients. However, the precise underlying mechanism has not yet been elucidated.

Troitskaya-Bolshakova effect as a manifestation of the solar wind wave turbulence

The impact of changes in the direction of the interplanetary magnetic field (IMF) on the amplitude of geomagnetic Pc3 pulsations (the Troitskaya-Bolshakova effect) is demonstrated using observations of several pulsation events. We show that the source of changes in the IMF cone angle is sometimes Alfvén waves propagating in the solar wind. For the analysis, measurements of geomagnetic pulsations at the mid-latitude Uzur magneto-telluric observatory and on three spacecraft outside the bow shock wave were used. The results show that the influence is exerted only by waves with a period of more than 40–60 min in a coordinate system fixed relative to the Earth. The Alfvén turbulence of a higher frequency is incoherent; the oscillations are of a chaotic nature, not coordinated in amplitude and phase either between satellites or with variations in the amplitude of Pc3. In some cases, the modulation of the pulsation amplitude is associated with the passage of the IMF sector boundary. An evaluation of the direction of propagation of Alfvén waves showed that they predominantly propagate from the Sun, but the normal of the wave fronts can deviate from the Sun-Earth line. This is quite consistent with earlier published results. The statistics of the basic properties of the oscillatory structures in the interplanetary medium, which we observed during the observation period, are given.

Experimental study of shock-wave structure of supersonic underexpanded microjets

The structure of supersonic underexpanded room temperature air microjets is experimentaly studied. Microjets escaping from the nozzles with characteristic heights of 22.3 and 83.3 μm and widths of 2410 and 3900 μm respactacly with the Reynolds numbers of 640 and 2390. At these Reynolds numbers hot-wire anemometer measurements of mass flow pulsations are performed. It is shown that low value of the mass flow pulsations are corresponding with the high supersonic core length.