Wave Curves Research Articles

Echo Monitoring Technology - The 'Smart Guardian' of the Dynamic Liquid Level in Oil and Gas Wells

The dynamic liquid level of oil and gas wells refers to the difference in liquid level between the wellhead and the pump barrel, which is related to the stable production and operational safety of oil and gas wells. The echo liquid level monitor is a professional tool for measuring the depth of dynamic liquid level in oil and gas wells. The principle of this instrument is to use sound to propagate longitudinally in gas, reflect when encountering a liquid surface, and then use electrical equipment and sensors to record the transmission time of sound waves to calculate the transmission distance and determine the depth of the liquid surface. So the page of the instrument displays a sound wave curve composed of one test point after another, but the sound wave will encounter various reflected waves such as downhole tools, perforation boreholes, couplings, irregular wellbore walls, and wellbore liquid levels in the well. The waveform of the curve will also have different manifestations according to different well conditions. This article summarizes the curve rules of shallow liquid level, middle liquid level, and deep liquid level extensively, establishes an oil and gas well wellbore liquid level curve model and analysis method, and successfully applies this method to guide the construction of Su 1-6 wells in Huabei Oilfield gas storage, achieving good results and providing a basis for accurate collection of oil and gas well liquid level data.

Global bifurcation for monotone fronts of elliptic equations

We present two results on global continuation of monotone front-type solutions to elliptic PDEs posed on infinite cylinders. This is done under quite general assumptions, and in particular applies even to fully nonlinear equations as well as quasilinear problems with transmission boundary conditions. Our approach is rooted in the analytic global bifurcation theory of Dancer (1973) and Buffoni–Toland (2003), but extending it to unbounded domains requires contending with new potential limiting behavior relating to loss of compactness. We obtain an exhaustive set of alternatives for the global behavior of the solution curve that is sharp, with each possibility having a direct analogue in the bifurcation theory of second-order ODEs.As a major application of the general theory, we construct global families of internal hydrodynamic bores. These are traveling front solutions of the full two-phase Euler equation in two dimensions. The fluids are confined to a channel that is bounded above and below by rigid walls, with incompressible and irrotational flow in each layer. Small-amplitude fronts for this system have been obtained by several authors. We give the first large-amplitude result in the form of continuous curves of elevation and depression bores. Following the elevation curve to its extreme, we find waves whose interfaces either overturn (develop a vertical tangent) or become exceptionally singular in that the flow in both layers degenerates at a single point on the boundary. For the curve of depression waves, we prove that either the interface overturns or it comes into contact with the upper wall.

Study on eccentric compressive performance of circular double skin concrete filled steel tube connected by thread through inside lining tube

Connection method of lengthening the steel tube of circular hollow sandwich concrete-filled steel tube by inside lining tube and thread is proposed. Twelve circular hollow sandwich concrete filled steel tubular beam-column connected by thread through inside lining tube are designed and fabricated using the length of the thread along the axial direction, the working height of the thread, and the position of the thread as parameters; In addition, one unconnected specimen and two welded specimens also are designed and fabricated to conduct controlled experimental research. The test phenomena and failure modes, axial compressive load-compression curve, axial compressive load-lateral deflection curve, and axial compressive load-strain in steel tube curve, as well as bearing capacity, strength reservation, deflection curve shape, lateral stiffness, ductility and plane section assumption are analyzed. The research results indicate that, within the parameter range studied, the thread connection through inside lining tube is reliable before tripping, and the experimental phenomenon of specimens connected by thread is basically consistent with that of the unconnected specimens. The axial compressive load-compression curve and axial compressive load-lateral deflection curve of all specimens can be approximately divided into elastic stage, elasto-plastic stage, and descending stage. The peak load of all specimens is relatively close, while although experiencing almost the same loading process, the strength reserve of the specimens connected by thread is insufficient. During the entire loading process, the shape of the deflection curve of all specimens is close to the sine half wave curve, and the distribution of longitudinal strain in the steel tube along the height of the middle cross-section basically conforms to the plane section assumption. Calculation method for bearing capacity of circular hollow sandwich concrete filled steel tubular beam-column connected by thread through inside lining tube is suggested.

Superstatistical functions of modified shifted Morse potential for diatomic molecules

The application of the molecular potential model to the study of different thermodynamic systems has been a focus of interest in recent time due to its importance in molecular and chemical physics. Hence, the asymptotic iteration method and the Laguerre polynomials are employed to obtain the eigensolutions of the Schrödinger equation with the modified shifted Morse potential model. Vibrational energy results for different diatomic molecules have been presented numerically, and these results are compared with experimental data and other results from available literature. The variation of normalised wave function and probability density of modified shifted Morse potential for some selected diatomic molecules at the ground- and first-excited states have been considered. Results obtained show that the equally spaced sinusoidal wave curves and varying nodes depend on the level of electron concentrations in the diatomic molecules considered. Partition function and other superstatistical function expressions of modified shifted Morse potential for some diatomic molecules within the modified Dirac delta distribution are obtained, using the Poisson summation formula. The superstatistical plots show a high level of dependence on the temperature parameter, maximum vibrational quantum number and deformation parameter. The superstatistical functions for a deformation parameter of zero correspond to the conventional thermodynamic functions.

Influence of post-weld rolling and artificial aging on microstructure and mechanical properties of friction stir welded 2195-T4 Al-Li alloy joints

Fiction stir welding (FSW) of a naturally aged (T4) 2195 Al-Li alloy was conducted to study the effect of post-weld artificial aging (AA) and rolling+artificial aging (R+AA) on microstructure and mechanical properties of the FSW joints. Grain features were analyzed by electron back scattered diffraction (EBSD) technology, and precipitates were characterized using transmission electron microscopy (TEM) along [011]Al and [001]Al zone axes. Mechanical properties of the joints were evaluated through micro-hardness and tensile testing. The results indicate that grain development, including grain orientation, grain boundary components and dislocation density, varies within different regions of the As-welded joints due to complicated thermal-mechanical history. The alloying elements mostly exist as Guinier-Preston zones in the base material (BM) with a few formations of δ'/β', and slightly precipitate into T1 in the heat affected zone (HAZ), form σ in the thermal-mechanical affected zone (TMAZ), as well as develop T1 and S' in the nugget zone (NZ) after FSW. The lowest hardness zone (LHZ) exhibits elevated precipitation levels, generating coarse T1 and grain boundary precipitates with evident σ and precipitate free zone. The overall precipitation level of the As-welded joints remains minor, resulting in a slight decrease in hardness at the LHZ. Post-weld AA promotes many T1 formations, enhancing the joint strength and hardness. As a result, the ultimate tensile strength (UTS) of the joints increases from 440 MPa to 506.5 MPa, while the elongation decreases from 13.5% to 3.4%. Furthermore, hardness profiles transform from a low-amplitude wave curve to a high-amplitude W-shaped curve, generating a significant LHZ due to the minimal precipitation of T1. Pre-rolling deformation can enhance dislocation density and low angle grain boundaries (LAGBs), promoting the nucleation of high-density, fine T1 during artificial aging, and especially improves precipitation ability of the LHZ, leading to an elevated hardness increment in the region after AA. Compared to the Joint-AA, both strength and elongation of the Joint-R+AA increase, obtaining 530.5 MPa and 3.9%, respectively.

Model of time-distance curve of electromagnetic waves diffracted on a local feature in the georadar study of permafrost zone rock layers

In GPR (georadar) studies, one of the most popular procedures for determining electromagnetic waves propagation velocity in a rock mass is the selection of theoretical hyperbolic time-distance curves and subsequent comparison with the time-distance curve obtained from a GPR measurement. This procedure is based on the model of homogeneous medium, but nowadays the subject of GPR study is often inhomogeneous media, such as horizontally layered media characteristic of loose permafrost zone sediments. The paper presents the findings of studying the formation of hyperbolic time-distance curves of georadar impulses in a horizontally layered medium without taking into account the dispersion and absorption of electromagnetic waves. On the basis of geometrical optics laws, formulas were derived to calculate the shape of the hyperbolic lineup of georadar impulses reflected from a local feature in a multilayer frozen rock mass. On the example of a permafrost zone rock mass containing a layer of unfrozen rocks, the effect of the thicknesses of rock layers and their relative dielectric permittivity on the apparent dielectric permittivity resulting from the calculation of the theoretical hyperbolic time-distance curve was shown. The conditions under which it is impossible to determine the presence of a layer of unfrozen rocks from a hyperbolic time-distance curve are also presented. The established regularities were tested on synthetic georadar radargrams calculated in the gprMax software program. The findings of the theoretical studies were confirmed by the comparison with the results of the analysis of the georadar measurements computer simulation data in the gprMax system (the relative error was less than 0.5%).

DISPERSION OF LAMB WAVES IN MULTILAYER STRUCTURES

Low cost, the possibility of online monitoring and high sensitivity distinguish the method of structural monitoring using Lamb waves from other available methods. Structural analysis based on Lamb waves in heterogeneous materials requires fundamental knowledge of the behavior of Lamb waves in such materials. This basic knowledge is critical for signal processing in determining possible damage that can be detected by the propagating wave. Recently, Lamb wave methods have been used to simultaneously survey large areas of composite structures. However, such methods are more complex than traditional ultrasonic testing because Lamb waves have dispersive characteristics, namely, the wave speed varies depending on the frequency, modes and thickness of the plates. Experimentally measured group velocities of Lamb waves in composite materials with anisotropic characteristics do not coincide with theoretical group velocities, which are calculated using the dispersion equation of Lamb waves. This discrepancy arises because in anisotropic materials there is an angle between the direction of the group velocity and the direction of the phase velocity. This work investigates the propagation characteristics of Lamb waves in composites, focusing on group velocity and characteristic wave curves. For symmetric laminates, a robust method is proposed by imposing boundary conditions on the mid-plane and top surface to separate symmetric and antisymmetric wave modes. The dispersive and anisotropic behavior of Lamb waves in two different types of symmetrical laminates is theoretically studied in detail. The dispersion of Lamb waves was studied for 10 symmetric and asymmetric modes. It is shown that only fundamental modes are not characterized by a cutoff frequency, which indicates the interaction of fundamental modes with composite layers in the low-frequency range. A high level of group velocity dispersion was discovered for the SH0 and S0 modes. It is concluded that in isotropic laminates, dispersion is characteristic of symmetric modes. It is shown that the frequency dependence of the group velocity of Lamb waves of laminar composites can be represented in polynomial form.

Flexible micro-strain graphene sensors enhanced by laser-induced cracks for health monitoring

In-situ fabrication of patterned laser-induced graphene (LIG) has unique advantages, holding broad application prospects in the preparation of flexible electronic devices. However, a facile strategy is still demanded to improve the sensitivity of LIG-based sensors in detecting micro-strains. Herein, we propose a flexible graphene strain sensor enhanced by laser-induced cracks, which is capable of detecting small deformations. When the scanning spacing was expanded from 100 μm to 140 μm, abundant micro-cracks formed between adjacent LIG stripes, providing more sensing units. The open and close of cracks lead to significant change of resistance, enhancing the sensitivity of LIG-based sensors. The average gauge factors of sensors were improved to 98 (0–2 % strain), increasing nearly 20 times. The strain sensors exhibit high performance response to subtle signals of the human body. High-quality seismocardiography (SCG), pulse wave and respiration curves were achieved by our sensors, providing a lot of useful information for screening chronic diseases. Overall, this research highlights an effective method for fabricating high performance flexible strain sensors for long-term health monitoring.

Research on new method of transformer winding deformation detection

As one of the most important electrical equipment in power system, the stable operation of transformer is the key factor to ensure the safety of power grid system. Winding deformation is the most common fault of transformer, which will seriously affect the reliable operation of the whole power system. Therefore, the detection of transformer winding deformation is of great significance to prevent transformer accidents. In order to further improve the reliability of transformer winding deformation detection, this paper proposes a transformer winding deformation detection method based on oscillation wave method. Firstly, the equivalent circuit model of transformer winding is established, and the transformer winding fault is simulated by changing the inductance and capacitance parameters in the model, and the law between the change of oscillation wave curve and the change of related performance indexes and equivalent parameters is obtained. Finally, the field test verification is carried out on a 10 kV transformer in the laboratory. The results show that the oscillation wave method can diagnose the transformer winding deformation and can be used for the actual transformer winding deformation detection.

Concentration and cavitation phenomena of Riemann solutions for the generalized Chaplygin gas equations under the flux approximation

In this paper, we investigate the concentration and cavitation phenomena of Riemann solutions for the generalized Chaplygin gas equations in the presence of flux approximation. The concentration and cavitation are fundamental and physical phenomena in fluid dynamics, which can be mathematically described by delta shock waves and vacuums (or constant density states), respectively. The main objective of this paper is to rigorously investigate the formation of delta shock waves and constant density states and observe the concentration and cavitation phenomena. First, the Riemann problem for the generalized Chaplygin gas equations under the flux approximation is solved constructively. Although the system is strictly hyperbolic and its two characteristic fields are genuinely nonlinear, the delta shock wave arises in Riemann solutions. The formation of mechanism for delta shock wave is analyzed, that is, the 1-shock wave curve and the 2-shock wave curve do not intersect each other in the phase plane. Second, it is rigorously proved that, as the pressure vanishes, the Riemann solutions for the generalized Chaplygin gas equations under the flux approximation tend to the two kinds of Riemann solutions to the transport equations in zero-pressure flow under the flux approximation, which include a delta shock wave formed by a weighted δ-measure and a constant density state.

Solder Defect Assessment Method for Power Electronic Devices Based on Mechanical Stress Wave Signals

The health of a power electronic device is closely related to the mechanical stress waves released at the moment when the device is turned on and off. Research has shown the potential of mechanical stress waves in power electronic device health monitoring. However, the correlation between power device defect severity and mechanical stress wave signal characteristics has not been fully established and an effective evaluation method is currently lacking. This article uses finite element simulation methods to explore the impact of void defects in the chip solder and base plate solder of insulated gate bipolar transistor (IGBT) devices on mechanical stress wave signals. By analyzing the mechanical stress wave curves of cavity defects of multiple sizes, a method for assessing the health status of power devices based on principal component analysis (PCA) is proposed. By calculating the projection of the mechanical stress wave signal on the principal component, the characteristic quantity representing the severity of the defect is obtained. Simulation results indicate that for chip soldering defects, as the severity of defects increases, the feature values gradually decrease. Therefore, this method exhibits good evaluation performance for defects throughout the entire lifecycle. In the case of plate solder defects, this approach can effectively identify mid-to-late-stage defects in devices and can also be utilized for reliability prediction before device failure.

Higher-order thin layer method as an efficient forward model for calculating dispersion curves of surface and Lamb waves in layered media

The thin layer method (TLM) is an effective semi-discrete numerical tool for analyzing wave motion in stratified media. The TLM can calculate the eigenvalues and eigenvectors for both propagating and decaying waves, which is essential to simulate waves near the source. The eigenvectors are particularly useful in various applications, such as estimating modal contributions, calculating synthetic seismograms, determining Green’s function, analyzing site response, and solving wave amplification problems in earthquake engineering, to name a few. In practice, most engineering applications use linear element-based TLM. However, the overall performance of TLM depends upon the type of element and the number of thin layers. The linear element TLM requires relatively thin sub-layers to obtain an accurate solution, making it computationally expensive and time-consuming. This study explores the potential of using non-linear higher-order TLM (HTLM) for forward modeling. The mathematical framework of TLM is used to formulate the generalized HTLM in determining the multimodal dispersion curve of Rayleigh, Love, and Lamb waves. The convergence and computational efficiency of different orders of HTLM have been investigated on a diverse set of published soil profiles and plate-like structures. Since non-linear interpolation functions better capture the change in displacement and stress between the layers, the findings reveal that the HTLM consistently outperforms the linear element TLM in terms of accuracy. Furthermore, the computational efficiency of different order HTLM is analyzed by comparing the total degrees of freedom and CPU time. Remarkably, higher-order HTLMs exhibit improved accuracy without increasing the computational burden, making them an attractive option for practical applications such as global search-based inversion and full spectrum inversions where fast and economical forward modeling is essential. Therefore, the HTLM will become helpful in seismic wavefield modeling, dynamic soil characterization, non-destructive evaluation methods, wave propagation analysis through waveguides, seismic site response analysis, etc.

County-Level Mandates Were Generally Effective At Slowing COVID-19 Transmission.

Throughout the COVID-19 pandemic in the US, counties adopted numerous nonpharmaceutical interventions, such as mask mandates and stay-at-home orders, to slow COVID-19 transmission and prevent hospitals from reaching full capacity. Early evidence has been mixed about whether these interventions are effective. However, most studies only covered the early waves of COVID-19 and did not account for county-level variation in the adoption and repeal of such policies. Using daily county-level data from the Centers for Disease Control and Prevention, we evaluated the joint impact of bans on large gatherings, stay-at-home orders, mask mandates, and bar and restaurant closures on slowing COVID-19 transmission during waves 1-4 of the pandemic in the US (March1, 2020-June30, 2021). Our survival analysis showed that these interventions were generally effective at slowing COVID-19 transmission during this period. The mitigating effect was particularly strong during waves 2 and 3 and less substantial during waves 1 and 4. We also found strong evidence of the overall protective effect of mask mandates and, to a lesser degree, anticongregation policies. These study findings provide crucial evidence for public health officials to reference for support when using nonpharmaceutical interventions to flatten the curve of future waves of COVID-19 or other infectious disease outbreaks.

Preventive Detection of Driver Drowsiness from EEG Signals using Fuzzy Expert Systems

Currently, the percentage of traffic accidents has increased, and according to statistics, this percentage will continue to increase every year, so it is necessary to develop new technologies to prevent this kind of accidents. This paper presents a drowsiness detection system based on electroencephalogram (EEG) signals using a pair of channels (Fp1 and Fp2) applied to drivers before entering their vehicles. First, this model detects the relationship between the area under the curve (AUC) of alpha brain waves, an effective parameter for detecting drowsiness. Then, the extracted information is passed to a fuzzy expert system (FES) that classifies the subject's state as "alert" or "sleepy"; the criterion used was a threshold and training with subjective levels. The proposed system was compared with neural network models, such as support vector machine (SVM), K nearest neighbors (KNN), and random forest (RF). Measurements of one hundred and twenty minutes were performed on each of the ten drivers for two days to test the system. The tests confirm that this system is suitable for preventive measures and that the fuzzy system is superior to traditional neural network methods.

Complex Modal Characteristic Analysis of a Tensegrity Robotic Fish's Body Waves.

A bionic robotic fish based on compliant structure can excite the natural modes of vibration, thereby mimicking the body waves of real fish to generate thrust and realize undulate propulsion. The fish body wave is a result of the fish body's mechanical characteristics interacting with the surrounding fluid. Thoroughly analyzing the complex modal characteristics in such robotic fish contributes to a better understanding of the locomotion behavior, consequently enhancing the swimming performance. Therefore, the complex orthogonal decomposition (COD) method is used in this article. The traveling index is used to quantitatively describe the difference between the real and imaginary modes of the fish body wave. It is defined as the reciprocal of the condition number between the real and imaginary components. After introducing the BCF (body and/or caudal fin) the fish's body wave curves and the COD method, the structural design and parameter configuration of the tensegrity robotic fish are introduced. The complex modal characteristics of the tensegrity robotic fish and real fish are analyzed. The results show that their traveling indexes are close, with two similar complex mode shapes. Subsequently, the relationship between the traveling index and swimming performance is expressed using indicators reflecting linear correlation (correlation coefficient (Rc) and p value). Based on this correlation, a preliminary optimization strategy for the traveling index is proposed, with the potential to improve the swimming performance of the robotic fish.

The analytical solutions of the Riemann problem to 1-D non-ideal flow of dusty gas with external force

This work focuses on the analytical solution to the Riemann problem (RP) for a 1-D non-ideal flow of dusty gas with external force. Here it is presumed that external force is a continuous function of time. We explicitly obtain the elementary wave curves to 1-D non-ideal flow of dusty gas with external force and determine these wave curves in form of characteristics. Exhaustive calculations were performed for the elementary wave solutions, such as the rarefaction wave, shock wave, and contact discontinuity. We examine the influence of dust particles on density, velocity of flow, and shock speed and their implications on the solution of RP. Also, the implication of addition of external force is that all solutions are not self similar.

Exact Riemann solver for non-convex relativistic hydrodynamics

We present the general analytical solution of the Riemann problem (decay of a jump discontinuity) for non-convex relativistic hydrodynamics. In convex dynamics, an elementary nonlinear wave, i.e. a rarefaction or a shock, originates at the discontinuity and travels towards one of the initial states. Between the left and right waves, an equilibrium state appears represented by a contact discontinuity. The exact solution to the Riemann problem in convex relativistic hydrodynamics was first addressed by Martí & Müller (J. Fluid Mech., vol. 258, 1994, pp. 317–333). In non-convex dynamics, two sequences of elementary nonlinear waves move towards the left and right initial states. Solving the Riemann problem involves determining the types of wave developing and the equilibrium state where they coincide. The procedure consists of constructing the wave curves associated with the nonlinear waves in the pressure–velocity phase space, where the intersection of the wave curves indicates the equilibrium state. We describe the relation between the wave curves, the explicit formulas for their calculation, and the outline of the process for a correct derivation and representation of the waves in the spatial domain. We present examples of the exact solution of a Riemann problem that illustrate the complex phenomena of non-convex dynamics by using the phenomenological non-convex equation of state proposed by Ibáñez et al. (Mon. Not. R. Astron. Soc., vol. 476, 2017, pp. 1100–1110).

Frictional slip wave solutions for dynamic sliding between a layer and a half-space

Interfacial waves propagate along the interface between two elastic solids, and are the subject of basic interest to diverse scientific fields, like, seismology, geophysics, material science and composite structures. The focus of the present work is to analyse the interfacial waves arising due to frictional slipping between an elastic layer and an elastic half-space having dissimilar elastic properties, wherein the deformations are confined to the plane of the solids. The interfacial friction is modelled by employing a slip-dependent friction law. The elastodynamic relations between the displacement discontinuities across the fractured interface and the associated traction components of stress for pure slip events (no crack opening along the interface) are obtained. This allows us to derive a secular dispersion relation governing the interfacial wave solutions. The dispersion relation relating the phase velocity and wavenumber is analysed numerically. A family of solutions are shown to exist depending on the critical slip distance, δc, a parameter governing the interfacial friction law, and on the contrast in material properties. We demonstrate the existence of a number of wave modes, all being dispersive in nature. The fundamental wave mode with the lowest phase velocity exists over the largest range of wavenumbers, while other wave modes exist only at sufficiently high non-dimensional wavenumber. The dispersion curves for the frictional slip waves are found to lie between the dispersion curves for the cases of the smooth and the bonded interface. As a case study, the present model is used to study the dispersion of slip waves propagating in Earth's crust-mantle geophysical model. The field observations of surface wave dispersion appear to be in good agreement with that of the frictional slip waves studied here. Based on our results, we suggest an alternative explanation for the observed surface wave dispersion at the regional and global scales. It is suggested that frictional slip waves at the crust-mantle interface could propagate with phase velocities similar to the Rayleigh and Love surface waves.

A New Method for Selecting the Phase and Group Velocity Dispersion Curves of Rayleigh and Love Surface Waves: Real Data Case of Central Anatolia, Turkey (Türkiye)

We propose a new method to select the dispersion curve of Rayleigh and Love surface waves obtained from local and regional earthquakes. This method is efficient for the crustal tomography studies and the Central Anatolia is chosen to test it. The single-station method utilizing both seismograms and accelerograms is used for the group velocities from local earthquakes while the two-station approach utilizing the cross correlograms is employed for the group and phase velocities using both local and regional earthquakes. The proposed method is made of two stages. The first stage based on the multiple filter technique – MFT is designed for an automatic selection of the desired dispersion curve. In case of the single-station approach, the MFT diagrams are computed for both Rayleigh and Love seismograms or accelerograms. An algorithm based on several selection criteria is employed to extract the corresponding group velocity dispersion curve from the MFT diagram. In case of the two-station method, the MFT diagrams are computed for both Rayleigh and Love cross correlograms. The latter algorithm developed for the MFT diagram is again applied to the cross correlogram to select the respective two-station group velocity dispersion curve. To select the corresponding two-station phase velocity dispersion curve, another algorithm is developed where the joint inversion of phase and group velocities is employed. The RMS value quantifying the misfit between the selected and inverted dispersion curves is found minimum when the selected phase velocity curve is compatible with the group velocity curve extracted via the MFT. The selection procedures defined up until this point constitute the first stage. In the second stage, phase and group velocity gathering around base pathways is performed. This way it is possible to compute the averages and standard deviations for the observed pathways traversing the similar geology. The outliers determined by using the averages and standard deviations are eliminated from the data set and this elimination is performed for phase and group velocities, separately.

Does ghrelin regulate intestinal motility in rabbits? An in vitro study using isolated duodenal strips

Rabbit duodenum has been used for examining the ability of motilin to cause muscle contraction in vitro. A motilin-related peptide, ghrelin, is known to be involved in the regulation of gastrointestinal (GI) motility in various animals, but its ability to cause rabbit GI contraction have not been well examined. The aim of this study is to clarify the action of rat ghrelin and its interaction with motilin in the rabbit duodenum. The mRNA expression of ghrelin and motilin receptors was also examined using RT-PCR. Rat ghrelin (10−9–10−6 M) did not change the contractile activity of the duodenum measured by the mean muscle tonus and area under the curve of contraction waves. In agreement with this result, the distribution of ghrelin receptor mRNA in the rabbit GI tract varied depending on the GI region from which the samples were taken; the expression level in the duodenum was negligible, but that in the esophagus or stomach was significant. On the other hand, motilin (10−10–10−6 M) caused a concentration-dependent contraction by means of increased mean muscle tonus, and consistently, motilin receptor mRNA was expressed heterogeneously depending on the GI region (esophagus = stomach = colon = rectum < duodenum = jejunum = ileum < cecum). Expression level of motilin receptor was comparable to that of ghrelin receptor in the esophagus and stomach. Pretreatment with ghrelin (10−6 M) prior to motilin did not affect the contractile activity of motilin in the duodenum. In conclusion, ghrelin does not affect muscle contractility or motilin-induced contraction in the rabbit duodenum, which is due to the lack of ghrelin receptors. The present in vitro results suggest that ghrelin might not be a regulator of intestinal motility in rabbits.