Wave Propagation Time Research Articles

Investigation of Backpressure Wave Propagation Properties during Gas Kicks in Managed Pressure Drilling

Summary It is often essential to provide backpressure to the wellbore by changing the opening size of the choke valve when a gas kick is detected during managed pressure drilling (MPD), which maintains the pressure in the bottom of the hole. In this study, a mathematical model was developed to explain how backpressure waves spread and weaken in a wellbore during MPD when there is a gas-liquid two-phase flow. The model is founded on a two-phase flow model, which thoroughly accounts for the gravity, shear force, and interphase interactions between the gas and liquid phases. The small perturbation theory was used to compute the backpressure wave’s propagation speed and attenuation coefficient. The outcome showed satisfactory agreement with other scholars’ experimental results. The model was used to study the impacts of the following variables on the backpressure wave propagation properties: void fraction, temperature, pressure, interphase resistance, shear force, density, invading gas composition, displacement of the drilling fluid, rate of intrusion of gas, gas-liquid surface tension, and drilling fluid viscosity. By using an example well, the laws of pressure wave propagation speed, attenuation coefficient, and propagation time with well depth were analyzed. Through evaluative methods in the field of economic management, the principal control variables governing the propagation of backpressure waves were determined. The conclusion is that, in terms of operational feasibility, lower drilling fluid density and reduced drilling fluid displacement are advantageous for a faster propagation of backpressure waves to the bottom of the well.

An approximation method to determine the travel time in total focusing imaging of carbon fiber-reinforced laminates

Abstract It is critical to accurately determine the propagation time in testing objects for ultrasonic array imaging using the Total Focusing Method (TFM). However, it poses challenges for the calculation of wave propagation time in carbon fiber reinforced polymer (CFRP) laminates because of the material anisotropy and inhomogeneity. This paper introduces a novel approach for computing ultrasonic wave travel time to enhance the TFM image of CFRP laminates. This method, termed the layer-by-layer acoustic travel time approximation (L-L TravelTimeAppro), considers the anisotropy within each monolayer and the heterogeneity of CFRP. It approximates the propagation path as straight throughout the material and computes the wave propagation duration utilizing the group velocity in each ply. The application of this method to TFM imaging is referred to as TravelTimeAppro-TFM. Experiments were conducted in a specially designed CFRP laminate. Subsequently, TFM imaging was processed by using propagation time calculated by isotropic, Dijkstra, and L-L TravelTimeAppro methods, respectively. The results indicate that TravelTimeAppro-TFM outperforms isotropic-TFM in terms of imaging amplitude gain with a maximum gain of 4.67 dB. Furthermore, it offers superior computational efficiency compared to Dijkstra-TFM.

Using Poisson’s ratio and acoustic anisotropy parameter to assess damage and accumulated plastic strain during fatigue loading of austenitic steel

The work investigated the effect of fatigue failure on the elastic characteristics of metastable austenitic steel AISI 321: Poisson’s ratio and acoustic anisotropy parameter. The elastic characteristics were calculated using ultrasonic measurements of the propagation time of longitudinal and shear elastic waves. The volume fraction of strain-induced martensite was determined by the eddy current method. Theoretical studies have shown that the main factors influencing Poisson’s ratio are the accumulation of microdamages and changes in phase composition. The change in the acoustic anisotropy parameter is associated with the influence of cyclic deformation on the crystallographic texture of the material matrix and the formation of oriented crystals of strain-induced martensite. Based on the analysis of experimental results, expressions were obtained for calculating damage and relative accumulated plastic deformation based on acoustic measurement data, which are widely used in engineering practice to determine the fatigue life of structural materials.

Evaluation of the Great Artery Mechanics with CarotidFemoral (Aortic) Pulse Wave Propagation Time in Patients with Rheumatoid Arthritis

Objectives: Rheumatoid arthritis (RA) is the most common chronic, systemic, rheumatic, autoimmune disease in adults, which has unknown etiology and targets primarily synovial tissue. Those patients have increased cardiovascular mortality based on inflammation and atherosclerosis. In our study, we evaluated great artery mechanics in newly diagnosed RA patients with inactive disease. Great artery mechanics, referred as arterial distensibility, elasticity, and compliance can be evaluated by pulse wave propagation time and pulse wave velocity. Methods: Our study included newly diagnosed and in inactive stage 25 RA patients ( mean age: 39.4±9.8 years, 21–63 years, 19 female, 6 male) and 29 healthy subjects (mean age: 36.9±9.9 years, 18–59 years, 13 female, 16 male). Aortic pulse wave propagation time and pulse wave velocitiy were determined using an automatic device, the Complior Colson (France), which allowed online recording and automatic calculation. Results: Height, waist circumference, and waist/hip ratio values were significantly higher in healthy objects. (p=0.006, p=0.030, p=0.004, respectively) pulse wave propagation time and pulse wave velocity were significantly lower and higher, respectively, in RA patients compared to healthy subjects (p=0.000, p=0.041, respectively). Conclusion: RA patients have decreased pulse wave propagation time and higher pulse wave velocity.

Arctic-Type Seismoacoustic Waveguide: Theoretical Foundations and Experimental Results

The results of theoretical analysis and practical implementation of seismoacoustic methods developed for monitoring ice-covered regions in the Arctic are presented and discussed. Special attention is paid to passive seismoacoustic tomography as a unique method of studying the deep structure of the lithosphere and hydrosphere without the use of powerful sources. One of the distinctive features of the considered approach is the use of receivers located on the ice surface to recover characteristics of Arctic-type seismoacoustic waveguide “lithosphere-hydrosphere-ice cover”. In passive monitoring, special attention is paid to reducing the noise signal accumulation time required to obtain seismoacoustic wave propagation times, as well as expanding the analyzed frequency bandwidth. The presented results can be used to develop technologies for seasonal and long-term monitoring of the currently observed variability of large areas of the Arctic region due to climatic changes.

Species-specific prediction model of wood moisture content based on electromagnetic wave propagation time

Laboratory and field experiments were performed to examine the feasibility of using Time Domain Reflectometry (TDR) to monitor moisture content (MC) of wood and standing trees. The TDR was used to detect the electromagnetic wave propagation time of four tree species (Betula platyphylla, Tilia tuan, Picea asperata, and Fraxinus mandshurica) at different MCs. During the TDR test, effects of probe insertion depths on MC predictive accuracy were considered. The best results were obtained at an insertion depth of 8 cm. At the selective 8 cm insertion depth, a species-specific MC prediction model (0.94 ≤ R2 ≤ 0.98), a generalized model for the four species (R2 = 0.65), and a hybrid model for the species with similar densities (0.80 ≤ R2 ≤ 0.96) were constructed, respectively. Overall, the species-specific MC prediction model showed good predictive ability for both tree and wood disc samples, including that TDR can be used to detect wood and standing tree MC. If possible, the hybrid model can be used for species with similar density.

Ice Thickness Assessment of Non-Freshwater Lakes in the Qinghai–Tibetan Plateau Based on Unmanned Aerial Vehicle-Borne Ice-Penetrating Radar: A Case Study of Qinghai Lake and Gahai Lake

Ice thickness has a significant effect on the physical and biogeochemical processes of a lake, and it is an integral focus of research in the field of ice engineering. The Qinghai–Tibetan Plateau, known as the Third Pole of the world, contains numerous lakes. Compared with some information, such as the area, water level, and ice phenology of its lakes, the ice thickness of these lakes remains poorly understood. In this study, we used an unmanned aerial vehicle (UAV) with a 400/900 MHz ice-penetrating radar to detect the ice thickness of Qinghai Lake and Gahai Lake. Two observation fields were established on the western side of Qinghai Lake and Gahai Lake in January 2019 and January 2021, respectively. Based on the in situ ice thickness and the propagation time of the radar, the accuracy of the ice thickness measurements of these two non-freshwater lakes was comprehensively assessed. The results indicate that pre-processed echo images from the UAV-borne ice-penetrating radar identified non-freshwater lake ice, and we were thus able to accurately calculate the propagation time of radar waves through the ice. The average dielectric constants of Qinghai Lake and Gahai Lake were 4.3 and 4.6, respectively. This means that the speed of the radar waves that propagated through the ice of the non-freshwater lake was lower than that of the radio waves that propagated through the freshwater lake. The antenna frequency of the radar also had an impact on the accuracy of ice thickness modeling. The RMSEs were 0.034 m using the 400 MHz radar and 0.010 m using the 900 MHz radar. The radar with a higher antenna frequency was shown to provide greater accuracy in ice thickness monitoring, but the control of the UAV’s altitude and speed should be addressed.

Evaluation of cardiac and vascular remodeling in patients with arterial hypertension in combination with atherosclerosis of the lower extremity arteries

Objective: to evaluate the features of cardiac and vascular remodeling in patients with arterial hypertension (AH) and atherosclerosis of the arteries of the lower extremities (LAA) of varying severity. Materials and methods: the study involved 120 patients with hypertension. Depending on the presence of AANC, all patients were divided into 3 groups: group 1 — 46 patients with hypertension and clinically manifested AANC, group 2 — 39 patients with hypertension and asymptomatic AANC, group 3 — 35 patients with hypertension without AANC. The characteristics of cardiac and vascular remodeling were assessed based on the results of 24-hour blood pressure monitoring (ABPM) using Vasotens technology, triplex ultrasound scanning (UTS) of the arteries of the lower extremities (LEA), and echocardiographic examination (EchoCG). Statistical data processing was carried out using Microsoft Office Excel 16 (2015, Microsoft, USA), Statistica 10.0 (StatSoft, USA) and IBM SPSS Statistica 26.0 (IBM, USA). Results: in the group of patients with severe circulatory disorders of the lower extremities, compared with patients with asymptomatic AANK, significantly lower values of the indicator — reflected wave propagation time (RWTT, ms) (p = 0.006) and significantly higher values of the indicator — augmentation index (AIX) were revealed) and augmentation index in the aorta (AIXao) (p<0.05). A direct statistically significant correlation of moderate strength was revealed between the degree of stenosis (%) of the ANC and the values of the AIX and AIXao indicators (r = 0.345, p = 0.001). Higher values of the dimensions of the walls of the left ventricle (LV) were determined: the thickness of the interventricular septum (IVS) and the posterior wall of the left ventricle (PLW) in patients of the 1st and 2nd groups in comparison with the indicators in patients of the 3rd group (p<0 .05). Patients of all three groups had thickening of the left ventricle and intraventricular septum (>11 mm) and an increase in LVMI. In patients with hypertension and severe AANC, the maximum values of LVMI were determined, which were significantly higher than the corresponding values in patients of the 2nd (p = 0.004) and 3rd (p = 0.0001) groups. LV systolic function in all patients included in the study was assessed as intact. However, the highest ejection fraction (EF) values were recorded in patients with hypertension without AANC, and were significantly higher than those in patients with hypertension and concomitant asymptomatic AANC (p = 0.02), as well as in patients with hypertension and clinically manifested AANC (p =0.001). Conclusions: the progression of AANK was associated with an increase in the stiffness of both peripheral and main arteries, which was accompanied by an increase in the load on the myocardium, which in 97.8% of cases led to more pronounced myocardial remodeling of the concentric hypertrophy type.

Variation in the Reflection Height of VLF/LF Transmitter Signals in the D‐Region Ionosphere and the Possible Source: A 2018 Meteoroid in Hokkaido, Japan

AbstractSeveral studies have examined ionospheric variation associated with meteorites, meteoroids, or meteors based on Global Satellite Navigation System total electron content observations. However, there have been few quantitative studies of the D‐region of the ionosphere (60–90 km), which is associated with meteoroids. We investigated variation in the D‐region during the passage of a meteoroid over northeastern Hokkaido, Japan, at 11:55:55 UT on 18 October 2018, using very low‐frequency (VLF, 3–30 kHz) and low‐frequency (LF, 30–300 kHz) signals observed by three transmitters [JJY (40 kHz), JJY (60 kHz), and JJI (22.2 kHz)], at Rikubetsu, Japan. Periodic variation of 100–200 s was observed in the VLF and LF amplitudes upon arrival of the acoustic wave. The vertical seismic velocity of Hi‐net and F‐net data also showed acoustic waves. Although the main period of the acoustic wave was 0.1–0.5 s in the seismic data, a longer period component (100–200 s) remained during propagation up to the D‐region ionosphere. The estimated velocity of the acoustic waves was ∼340 m/s on the ground according to the Hi‐net seismic data. The acoustic wave originated near the endpoint (25 km altitude) of the meteoroid trajectory. Based on the observed propagation time of the acoustic waves and ray tracing results, the acoustic waves propagated obliquely from near the endpoint of the meteoroid trajectory up to a D‐region height (about ∼90 km altitude), south of the Rikubetsu receiver.

Mixed Model and Gaussian Process to Investigate the External Influence on the Propagation Time of Ultrasonic Waves on Masonry Walls

The ultrasonic testing has been considered a promising method for diagnosing and characterizing masonry walls. As ultrasonic waves tend to travel faster in denser materials, their use is common in evaluating the conditions of various materials. Presence of internal voids, e.g., would alter the wave path, and this distinct behavior could be employed to identify unknown conditions within the material, allowing for the assessment of its condition. Therefore, we applied mixed models and Gaussian processes to analyze the behavior of ultrasonic waves on masonry walls and identify relevant factors impacting their propagation. We observed that the average propagation time behavior differs depending on the material for both models. Additionally, the condition of the wall influences the propagation time. Gaussian process and mixed model performances are compared, and we conclude that these models can be useful in a classification model to automatically identify anomalies within masonry walls.

The Mathematical Model of the Localization of Infrasonic Signal Propagation

This research paper proposes the construction of an mathematical model of infrasound signal propagation. The constructed model contains the following set of input data: standard deviation of measurement noise, infrasound wave propagation velocity, sensor coordinates, azimuth, and time of infrasound signal reception by sensors. The specified accuracy of the input data is discussed and justified. The main theoretical modeling methods are a combination of azimuth –based triangulated value averaging and Bayesian infrasound source localization. The result of the modeling is a Python software module with the ability to set input data and obtain a point with the coordinates of the location of the infrasound signal source, the distance of the sensors to it. Visualization of the results of mathematical modeling is provided for the purpose of verification of the obtained results, further studies of the influence of the accuracy of input data. The obtained modeling results are expected to be used to fill data samples for further research on infrasound signal localization using machine learning method sand tools; for iterative improvement of the current mathematical model.

Acoustic probe for temperature measurement suitable for operation with audio interfaces having random input/output delays

Measuring temperature distribution is an important technique in the fields of meteorology, agriculture, and architecture. The acoustic probe emits sound waves from a speaker and measures the time it takes for the waves to reach a microphone, enabling the measurement of the average temperature between the speaker and the microphone. Additionally, by placing multiple acoustic probes around the measurement area, it becomes possible to measure the temperature distribution using fewer sensors compared to point-type sensors. However, acoustic probes can have higher costs due to the requirement for externally controllable setups or interfaces with minimal audio input/output (I/O) delays. To address this issue, we propose an acoustic probe that achieves accurate measurements even with a low-cost audio interface featuring random I/O delays. The proposed acoustic probe measures the delay time from the recording start to the playback start. This design cancels the error of sound wave propagation time caused by random delays in the audio interface. Through temperature measurement experiments using the proposed acoustic probe, it was revealed that precise measurements (the error of the proposed probe was 0.34°C, while the error of the existing probe was 4.88°C) could be achieved by canceling the random delays in the audio interface.

Study on the evolution of transient flow field in WDS based on numerical and experimental methods

In order to reveal transient characteristics of flow field in WDS of HPs, theoretical analysis, numerical simulation and experiment are combined to investigate nine transitions. Detached eddy simulation is adopted to solve flow field and dynamic mesh technology is applied to achieve continuous movement of valves. The results show that numerical simulation is consistent with experiment, wherein the maximum difference is approximately 0.74% of HS(DT6, 1.3 m). HU has stronger influence on the flow stability in WDS, specifically analysed by pressure fluctuation range, the peaks of HS, TKE and wavelength etc. The pressure fluctuation phenomenon in load increasing processes is weaker than that in load rejection processes, wherein peaks and troughs of pressure are larger at the cases with more load change. In addition, the preconditions of unit before load rejection significantly affect swirling strength and TKE of transient flow in load rejection processes, but it is irrelevant to the maximum values of HS. The maximum values of HS under different conditions basically appear in the surge tank when the valves are about 20% closed. The round-trip time of wave propagation is far less than tV (Δt=1.254s<<10.32s), hence indirect water hammer also proves reasonable design. This study not only provides guidance to the operation of HPs, but also provides reference for design.

A method for detecting two‐dimensional plane stress distribution in basin‐type insulator based on critically refracted longitudinal wave

AbstractBasin‐type insulator often has small cracks due to stress concentration. The current method cannot accurately reflect the stress condition of the insulator to find the stress concentration areas. To solve these problems, a method for detecting two‐dimensional plane stress (δ1 and δ2) within different depth ranges in a basin‐type insulator is proposed based on critically refracted longitudinal (LCR) wave. First, the acoustoelastic equation characterising the relationship between the variation of LCR wave propagation time and the plane stress was derived. Next, the propagation characteristics of LCR wave in epoxy resin samples were investigated. Then, the stress distribution within different depth ranges of the insulator subjected to hydraulic load was measured using the proposed method, including direction (θ), δ1 and δ2. The results show that the magnitude of the stress alone cannot accurately characterise the stress state. Points with equal distances to the centre have similar stress magnitudes, but their directions are not the same. With increasing depth, θ remains essentially unchanged at the same location, while δ1 and δ2 decrease, and the rate of decrease varies at different locations. Comparing the measured and simulated data, the results showed that they were in good agreement, and the maximum errors of stress value and θ were 0.69 MPa and 2.97°, respectively, which confirmed the feasibility and accuracy of the stress detection in the proposed method.

Optimization of the Parameters of the Magnetizing Device of the Electromagnetic-Acoustic Transducer

Contactless electromagnetic-acoustic transducers have a set of significant advantages over contact transducers, but at the same time they have significant disadvantages that require the development of effective magnetizing devices. Compared to magnetizing devices that are using permanent magnets, electric current magnetization devices are easily removed from the object of testing and cleaned from contamination by metal particles. Unfortunately, such transducers have significant dimensions and weight.A transducer containing a magnetic circuit magnetized by an electric current coil and two independent electromagnetic inductors located in the gap between the central part of the magnetic circuit and the object of testing has been developed. Inductors are two flat coils, each of them has form like a butterfly. The inductor conductors located in the working area have mutually perpendicular directions; they allow exciting and receiving the transversely polarized acoustic waves without rearranging the transducer. In order to reduce the overall dimensions and mass of the transducer, the mass and dimensional parameters of the magnetizing device were optimized for operating conditions when the magnetization of the object of testing and measurement are performed during the active measurement phase. During the passive measurement phase, which is three times longer than the active phase in time, the magnetizing device cools down. The cyclic mode with alternating active and passive phases made it possible to reduce the weight of the transducer by more than 3 times. In the working area of the transducer with a size of 15×15 mm, with a gap of 1 mm between the magnetic field concentrator and the object of testing, a field with a normal component of 2.4 T is created. The transducer has protection of the magnetization device from overheating, and the cyclic mode of operation allows for continuous performance of up to 30 measurements per minute at an ambient temperature of 20 °C.The developed magnetizing device can be used in solving a number of problems of structuroscopy, thickness measurement, flaw detection by electromagnetic-acoustic methods based on accurate measurement of the propagation time of elastic waves in the object of testing.

Radio Frequency-Based Diagnostics for Superconducting Magnets

Operation of high-field superconducting magnets relies on diagnostic instrumentation for measuring strain, temperature, and magnetic field variations, detecting quenching, and identifying performance problems. Discrete sensor implementation is costly, requires multi-channel data acquisition systems, and sensor density is often insufficient to resolve problematic locations spatially. Distributed sensing is a viable alternative approach providing location-specific diagnostic information over single terminal output. In particular, it can be the key to quench protection of high-temperature superconductor (HTS)-based magnets where hot spots are known to form and persist before a quench. Fiber-optic technology offers distributed sensing solution for magnets but suffers from drawbacks such as fiber fragility, high costs of optical interrogators, and difficulty in differentiating between physical quantities such as temperature and strain. We propose an alternative, robust, and easily integrable way of implementing distributed sensing in magnets using radio-frequency (RF) technologies. RF Time Domain Reflectometry (TDR) technique has been around for nearly 60 years, and it is an essential diagnostic tool used in multiple areas of technology and applied research. We discuss operational principles and practical implementation of RF TDR sensors capable of detecting local variations of strain, temperature, and magnetic field through changes in RF impedance and wave propagation time. Results of cryogenic testing of our TDR sensors with HTS tape conductors are presented. The perspective of enabling a new diagnostics paradigm for high-energy physics and fusion energy applications based on distributed RF sensing is discussed.

Evaluation of glycerol speed of sound

The speed of sound in the liquid glycerol was calculated from the wave propagation time measurement in through transmission mode by using a designed acoustical cell. Measurements were carried out at atmospheric pressure and temperatures ranging from 298.47 K to 353.16 K. The proposed approach provided glycerol speed of sound values with experimental uncertainty of 1.9 m.s-1. The data were compared with the values from literature resulting in relative deviations around the range of 0.5%. The data were also used to develop an empirical equation for the calculation of the speed of sound covering the considered temperature range, with standard deviation  =2 m.s-1.

Sonic test singularities of granite stone masonries

For the non-destructive characterization of structures composed of granite stone masonry (heterogeneous materials), in this case of double sheet, one of the most suitable test options is the use of sonic tests. Through these sonic tests, it is possible to estimate the propagation velocities of the P, R and S waves. With these velocity values, it is possible to estimate the elastic parameters that characterize the material. Data acquisition requires special attention because during these tests there are factors that may significantly influence the signal, such as the possible recording of two momentary impacts of the hammer, bad coupling of the recording transducers and environmental noise, which can compromise the quality of the signals, and the literature this topic was not suficciently adressed. It is noteworthy that the estimation of the propagation time of waves and their propagation trajectories are not trivial, since it has great complexity in obtaining the value of the wave's arrival time being its automation a non-strait forward and not reliable process that should be carried out by an experienced user, especially for granite masonries. It is also necessary to identify which types of waves are being measured and represented by these signals, whether P, R or S. However, the identification of waves depends on the intrinsic characteristics of each one of them and on the type of test configuration to be performed. Thus, this work aims to present the advances obtained in the use of sonic tests, considering different configurations, in order to assist in the characterization of structures composed of granite stone masonry. In addition, to proposing new sonic data analysis and processing methodologies to improve the accuracy and reliability of the results obtained in this type of non-destructive test. For this, 8 samples of double sheet granite masonry walls were built in a controlled environment and sonic tests (direct, indirect and unconventional configuration) were performed to characterize these traditional masonries. The results of sonic tests are promising and novel, especially considering that the applicability of these tests on masonry walls is a research area that is not yet sufficiently consolidated, in addition to the difficulties inherent in the fact that the materials are not homogeneous and isotropic. The results showed great variations due to the heterogeneity of the panels. The velocity variation from for the first receiver was higher (1584 m/s) than the other receivers because the first trajectory has less interference from the vertical joints along the wave trajectory. For both tests (direct and indirect), a sensitivity study on the variation of these velocities as a function of the djdT ratio was presented to quantify the estimated velocity for these paths. As expected, the higher this relationship, the lower the velocity values, due to interference from wave attenuation in the horizontal joints. The non-conventional sonic tests proposed in this paper for adequate conditions to obtain the S waves by changing the position and orientation of the receivers and in the direction of impacts (with the aid of an 90° angle fixed to the structure) was adequated demonstrated: it is concluded that the waves interpreted as S reached mean velocity of 1500 m/s, without joint interference. To corroborate the results obtained by the sonic tests, ultrasonic tests were also carried out. The tests confirmed the wave propagation velocity values in the crossblock around 3700 m/s, and with the presence of a joint in the trajectory, the velocities are around 1000 m/s.

Adaptive Varying Contention Window MAC Protocol Based on Underwater Acoustic Propagation Delay

Underwater acoustic wave propagation time delay and fluctuations are much greater than radio waves. However, many of the protocols used for underwater acoustic networking and communication are designed according to the principles of terrestrial wireless communication networks, failing to give full consideration to utilizing the underwater acoustic propagation and its time delay variation. For this reason, this paper proposes an adaptive varying contention window MAC (AVCW-MAC) protocol based on propagation delay. The protocol uses AVCW random backoff mechanism to differently set up the contention window (CW) of each node based on the different propagation delays from each underwater sensor node to the cluster head node to improve the channel utilization. In addition, to avoid excessive difference in the CW of each node, the backoff factors <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> are introduced in the AVCW random backoff mechanism to improve the fairness of nodes’ accessing the channel. Simulation results show that for the same amount of sensor nodes, the AVCW-MAC protocol have significantly improved network throughput and decreased average end-to-end latency when compared to legacy CW-MAC protocols.

Influence of the presence of a nitrided layer on changes in the ultrasonic wave parameters

Abstract In this work, attempts are made to estimate the relationship between the ultrasonic wave parameters and the presence of the nitrided layer. Special samples were prepared, the surfaces of which were ground and then nitrided. The samples were evaluated by ultrasonic method before and after the nitriding. During the tests, three parameters of the ultrasonic wave were recorded i.e., time of wave propagation, dominant frequency of the spectrum and bandwidth. The measurements were repeated ten times. The obtained results indicate, in particular, a reduction in the wave propagation time in the samples after nitriding compared to the samples without the nitrided layer.