Change In Propagation Direction Research Articles

Propagation prediction of asymmetrically originated fractures by use of displacement discontinuity method

In existing fracture propagation simulation studies, the fracture propagation simulation is based on the assumption that the fracture originates symmetrically with respect to the wellbore. However, the drilling treatments can induce stress reorientation near the wellbore, resulting in asymmetrically originated fractures, which is different from the assumption of existing studies. In such cases, it can be difficult to predict the fracture geometries. In this work, the authors propose a fracture propagation model to simulate the propagation of asymmetrically originated fractures with the displacement discontinuity method. With the aid of the proposed model, the authors investigate the impact of the redistribution of stress field on the propagation of asymmetrically originated fractures and conduct a comprehensive study to investigate the effects of various geological and fluid parameters on the propagation of asymmetrically originated fractures. The results show that the redistribution of the stress field renders the newly generated fracture segments to deviate from the initial originations so that although the initial fracture origination is asymmetric, the asymmetrically originated fractures rapidly propagate along an approximately symmetrical path and propagate parallel to the direction of maximum principal stress as it goes away from the wellbore. The closer the two wings of the fracture are to the symmetric origin, the faster it is for the change of propagation direction to the direction of the maximum principal stress. A large principal stress difference tends to cause asymmetrically originated fractures to quickly deviate from the initial originations and propagate parallel to the direction of maximum principal stress. As the fluid power law index decreases, the fluid viscosity is significantly reduced due to the effect of shear thinning, causing the asymmetrically originated fractures to propagate parallel to the direction of maximum principal stress. The fluid leak-off coefficient only influences the fracture length and width, whereas its influence on the propagation trajectory can be slight.

Statistical Analysis of Low‐Latitude Boundary of Polar‐Type Medium‐Scale Traveling Ionospheric Disturbances Observed by a 630‐nm Airglow Imager at Nyrölä, Finland

AbstractMedium‐scale traveling ionospheric disturbances (MSTIDs) are one of the ionospheric plasma density structures and are observable through 630‐nm airglow images. Previous studies using airglow images at Tromsø (69.6°N, 19.2°E; magnetic latitude: 66.7°N), Norway, reported high‐latitude MSTIDs (here we call them as polar‐type MSTIDs) whose propagation direction changes associated with auroral brightening and magnetic field disturbances. However, there has been little statistical analysis on the connection of MSTIDs occurring at high and middle latitudes. In this study, we statistically analyzed the MSTIDs observed by an airglow imager at Nyrölä (62.3°N, 25.5°E; magnetic latitude: 59.4°N), Finland, which is located ∼7° south of Tromsø, corresponding to subauroral latitudes. The period analyzed was from 23 January 2017, to 30 September 2021. We found 11 cases of MSTIDs during this period. Eight cases were found to be the polar‐type MSTIDs whose motion changes associated with auroral brightening and magnetic field disturbances. We found that 9 cases of MSTID show the low‐latitude boundary at 61° ± 2°N for geographic latitude and 58° ± 2°N for magnetic latitude, indicating disconnection between high‐ and mid‐latitude MSTIDs. We also derived occurrence probability, velocity, wavelength, period, wave front direction, and propagation direction of these MSTIDs. The occurrence probability of MSTIDs at Nyrölä is 1.9%, which is much lower than those at high (Tromsoe, more than 50%) and middle (Japan, ∼30%) latitudes. We discuss these MSTID characteristics at subauroral latitudes based on possible difference of generation mechanisms of nighttime MSTIDs at high and middle latitudes.

Glycolytic Wave Patterns in a Simple Reaction‐diffusion System with Inhomogeneous Influx: Dynamic Transitions

An inhomogeneous profile of chemostatted species generates a rich variety of patterns in glycolytic waves depicted in a Selkov reaction-diffusion framework here. A key role played by diffusion amplitude and symmetry in the chemostatted species profile in dictating the fate of local spatial dynamics involving periodic, quasiperiodic, and chaotic patterns and transitions among them are investigated systematically. More importantly, various dynamic transitions, including wave propagation direction changes, are illustrated in interesting situations. Besides numerical results, our analytical formulation of the amplitude equation connecting complex Ginzburg-Landau and Lambda-omega representation shed light on the phase dynamics of the system. This systematic study of the glycolytic reaction-diffusion wave is in line with previous experimental results in open spatial reactor and will provide a knowledge about the dynamics that shape and control biological information processing and related phenomena.

Pore Structure Characteristics and Strength Variation of Red Sandstone under Freeze-Thaw Cycles.

To study pore structure characteristics and the strength of red sandstone under freeze–thaw cycles, the saturated red sandstone was studied by the combination of freeze–thaw cycle test, high-pressure mercury injection test, uniaxial compression test and theoretical analysis, and research shows that: with the increase of freeze–thaw cycles, the pores of red sandstone continue to expand and extend, macropore volume and the total pore volume increases gradually, and the pore size distribution curves become more continuous. Porosity of samples after 10, 30, 70 and 100 freeze–thaw cycles is 1.14 times, 1.17 times, 1.28 times and 1.44 times of that of 0 cycle, and the uniaxial compressive strength of samples is 0.68 times, 0.53 times, 0.26 times and 0.17 times of that of 0 cycle, respectively. With the increase of freeze–thaw cycles, freeze–thaw damage continues to accumulate, the crack propagation direction changes from axial through-through failure mode to transverse and axial simultaneous failure mode. Taken the change of porosity as a parameter, through the regression analysis of the test data, the functional relationship between uniaxial compressive strength and the change of porosity in red sandstone is established. The research results will provide a theoretical basis for stability research of slopes of railway subgrade in cold region.

Characterization of the laser-induced breakdown spectroscopy near the gas-liquid two-phase interface.

The characterization of laser-induced breakdown spectroscopy (LIBS) near the gas-liquid two-phase interface was investigated with the laser acting on the sample along the horizontal direction. Simulation of the laser beam focusing process and observation of laser beam spot images show that difference in focusing positions in the air and the solution results from refraction of the laser beam entering the solution from the air and the change of propagation direction on the container lateral. The peak power and mean irradiance of the focused laser beam spot increase with the distance away from the interface, which is attributed to the fact that the loss of laser energy due to the refraction and reflection of light at the interface decreases with the focusing position moving away from the interface. This variation trend of laser irradiance allows for the growth of the spectral line intensity and lifetime with increasing the distance from the interface. The plasma electron density and temperature decrease with the delay time but increase with the distance away from the interface at the same delay time. Our findings help us to gain more insight into the characteristics and evolution mechanisms of LIBS produced near the gas-liquid two-phase interface, which provides theoretical guidance for the correction of LIBS spectra especially in water pollution monitoring.

A criterion for a hydraulic fracture crossing a frictional interface considering T-stress

Hydraulic fracturing has been widely used to stimulate oil and gas production from low permeability reservoirs. However, the geologic discontinuities, such as natural fractures, joints, and bedding planes, can significantly affect the propagation direction of the hydraulic fracture. Considering the effect of the non-singular stress term of Williams’ series expression for stress field near the fracture tip (i.e., T-stress), an analytical criterion for a hydraulic fracture crossing a frictional interface (such as the natural fracture and bedding plane under compression-shearing) was proposed. The present criterion was validated by comparing it to the published experiments, and the effect of T-stress on the propagation of the hydraulic fracture crossing a frictional interface was analyzed by comparing the present criterion to the published criteria. The results show that the accuracy of the present criterion depends on the difference in geomechanical properties of the rock on either side of the interface. The effect of T-stress on the hydraulic fracture propagation can be divided into the facilitation and the inhibition, which depend on the intersection angle between the hydraulic fracture and the frictional interface. No matter what the intersection angle between the hydraulic fracture and the frictional interface is, the effect of T-stress can inhibit the change of propagation direction when the hydraulic fracture crosses the interface.

Dirac fermion metagratings in graphene

We theoretically demonstrate a Dirac fermion metagrating which is an artificially engineered material in graphene. Although its physics mechanism is different from that of optical metagrating, both of them can deliver waves to one desired diffraction order. Here we design the metagrating as a linear array of bias-tunable quantum dots to engineer electron beams to travel along the -1st-order transmission direction with unity efficiency. Equivalently, electron waves are deflected by an arbitrary large-angle ranging from 90° to 180° by controlling the bias. The propagation direction changes abruptly without the necessity of a large transition distance. This effect is irrelevant to complete band gaps and thus the advantages of graphene with high mobility are not destroyed. This can be attributed to the whispering-gallery modes, which evolve with the angle of incidence to completely suppress the other diffraction orders supported by the metagrating and produce unity-efficiency beam deflection by enhancing the -1st transmitted diffraction order. The concept of Dirac fermion metagratings opens up a new paradigm in electron beam steering and could be applied to achieve two-dimensional electronic holography.

Generation of a polarized optical field from a given scalar field for wide-viewing-angle holographic displays

Although the scalar wave theory does not fully describe the nature of the light, which is a vector wave field, it is common to characterize the optical field propagated from an object as a scalar wave in 3DTV research. A given scalar wave field is usually directly mapped to the transverse field components of a simply polarized optical field during the generation of the optical field by a holographic 3D display; this procedure gives accurate results in terms of the optical intensity if the field is paraxial. However, due to the nonnegligibly large longitudinal component of the vector field, this method fails in wide-angle fields. In order to generate a polarized optical field which has the same resultant effect as prescribed by a wide-angle scalar field, we extend this simple polarization approach to tilted and rotated planes. That is, we first put a constraint on the generated vector wave field such that each plane wave component has a simple polarization relation at its locally transverse plane. Then, we map the complex plane wave amplitudes of a given scalar field to the plane wave amplitudes of locally transverse field components of the polarization-constrained optical field. As a consequence of the developed mapping, for an observer which is located at a tilted and rotated plane and captures a locally paraxial segment of the incoming wave field, the intended scalar intensity results can also be obtained in wide-viewing-angle 3D holographic displays. The developed model is valid if the chosen local coordinate frames of the locally transverse planes of the propagating plane waves vary slowly as the propagation direction changes. For a 3DTV setup where the display is located at a z-plane and the observers are located away from the z-axis, an analytical representation for appropriate coordinate frames is developed. For the same setup, computer simulation results showed that the excessive amplification of the longitudinal component due to the conventional mapping does not arise in the proposed method and the desired scalar results are observed. Moreover, since the determined polarization state is preserved at each tilted and rotated plane, the new model can also be used in an optical setup where the polarization information is important. As a result, the proposed mapping enables the scalar wave theory to be used in wide-viewing angle holographic display applications under the given constraints.

Influence of a Magnetic Field on Wave Motions in Thermally Unstable Photodissociation Regions

The propagation of waves in a thermally unstable medium with a magnetic field is considered. The characteristic perturbation growth and wave breaking times have been found in the approximation of weak nonlinearity and small deviations from adiabaticity; the wave profiles at the breaking time are presented. We show that the development of instability is suppressed as the wave propagation direction changes from longitudinal to transverse relative to the magnetic field. Our studies have been carried out for the atomic zones of photodissociation regions, for which we have previously determined the conditions for the development of an isentropic thermal instability mode.

Dynamics of the Formation and Propagation of Nanobands with Elastic Lattice Distortion in Nickel Crystallites

The formation and propagation of localized nanobands with elastic lattice distortion in nickel crystallites have been studied within the molecular dynamics framework. Such nanobands are formed due to the presence of regions with tensile and compressive stresses on the free surface. The nanoband propagation region is characterized by a collective vortex motion of atoms. The effect of different-type grain boundaries on nanoband propagation was investigated. It was shown that grain boundaries do not significantly affect the reorientation angle in the nanoband, but the nanoband propagation direction changes after crossing a grain boundary in accordance with the different crystallographic orientation of grains.

A review and reassessment of diffraction, scattering, and shadows in electrodynamics

The concepts of diffraction and scattering are well known and considered fundamental in optics and other wave phenomena. For any type of wave, one way to define diffraction is the spreading of waves, i.e., no change in the average propagation direction, while scattering is the deflection of waves with a clear change of propagation direction. However, the terms “diffraction” and “scattering” are often used interchangeably, and hence, a clear distinction between the two is difficult to find. This review considers electromagnetic waves and retains the simple definition that diffraction is the spreading of waves but demonstrates that all diffraction patterns are the result of scattering. It is shown that for electromagnetic waves, the “diffracted” wave from an object is the Ewald–Oseen extinction wave in the far-field zone. The intensity distribution of this wave yields what is commonly called the diffraction pattern. Moreover, this is the same Ewald–Oseen wave that cancels the incident wave inside the object and thereafter continues to do so immediately behind the object to create a shadow. If the object is much wider than the beam but has a hole, e.g., a screen with an aperture, the Ewald–Oseen extinction wave creates the shadow behind the screen and the incident light that passes through the aperture creates the diffraction pattern. This point of view also illustrates Babinet's principle. Thus, it is the Ewald–Oseen extinction theorem that binds together diffraction, scattering, and shadows.

Temperature and Background Field Dependence of Thermal Stability in a Compact MgB2Solenoid Coil

A conduction-cooled compact react and wind MgB 2 solenoid magnet was tested for quench propagation and minimum quench energy (MQE) in a background field, which allows to an extent a decoupling of the peak field in the windings from the conductor field performance. MQE and propagation data were taken in self-field at 30 K, 30.5 K, and 31.5 K and at fields/temperatures of 1 T/25 K, 3 T/18 K, and 5 T/10 K where the power law $n$ -value characteristic was similar at $n \sim \text{30}$ . At all temperatures and at low $I/I_{c}$ , quench propagated first through the insulating layers, in a radial direction, and at high $I/I_{c}$ within the layer. The MQE values as a function of $I/I_{c}$ are shown to consistently have nonzero values as $I\rightarrow I_{c}$ , which is characteristic of an analytical quench model that includes the $n$ -value power law dissipation. At 30.5 K, a sharp drop in MQE occurs along with the change in propagation direction. The analytical model is then exploited as 1-D adiabatic, 3-D infinite solenoid, and 3-D with heat transfer at the boundary to explore the effect of dimensionality and conduction cooling on the propagation and MQE behavior.

Haustral boundary contractions in the proximal 3-taeniated rabbit colon.

The rabbit proximal colon is similar in structure to the human colon. Our objective was to study interactions of different rhythmic motor patterns focusing on haustral boundary contractions, which create the haustra, using spatiotemporal mapping of video recordings. Haustral boundary contractions were seen as highly rhythmic circumferential ring contractions that propagated slowly across the proximal colon, preferentially but not exclusively in the anal direction, at ∼0.5 cycles per minute; they were abolished by nerve conduction blockers. When multiple haustral boundary contractions propagated in the opposite direction, they annihilated each other upon encounter. Ripples, myogenic propagating ring contractions at ∼9 cycles per min, induced folding and unfolding of haustral muscle folds, creating an anarchic appearance of contractile activity, with different patterns in the three intertaenial regions. Two features of ripple activity were prominent: frequent changes in propagation direction and the occurrence of dislocations showing a frequency gradient with the highest intrinsic frequency in the distal colon. The haustral boundary contractions showed an on/off/on/off pattern at the ripple frequency, and the contraction amplitude at any point of the colon showed waxing and waning. The haustral boundary contractions are therefore shaped by interaction of two pacemaker activities hypothesized to occur through phase-amplitude coupling of pacemaker activities from interstitial cells of Cajal of the myenteric plexus and of the submuscular plexus. Video evidence shows the unique role haustral folds play in shaping contractile activity within the haustra. Muscarinic agents not only enhance the force of contraction, they can eliminate one and at the same time induce another neurally dependent motor pattern.

Ignition experiment with automotive spark on rotating detonation engine

An experimental study on rotating detonation engine with the slot-orifice impinging injection method was presented in this paper. Reactants were gaseous H2–Air mixtures and ignited by an automotive spark plug. The engine was initiated successfully and rotating detonation wave propagated continuously and steadily in the circumferential direction. Through the detailed analysis on the initiation and propagation process of rotating detonation wave, it was found that deflagration-to-detonation transition (DDT) was observed in the annular combustion chamber, and the DDT time exhibited an obvious randomness. For the operating conditions which the rotating detonation wave propagated stably, the fluctuation of the pressure spike of detonation wave was relatively small, and the detonation wave propagated continuously without interruption; for the operating conditions which the detonation wave was unstable, the fluctuation of pressure spike of detonation wave was relatively large, and the interruption occurred, which might result in the change of propagation direction of rotating detonation wave. And in some operating conditions, a new phenomenon that strong detonation and weak detonation occurred alternately was found. Besides, in order to obtain the success rate of rotating detonation wave initiation with automotive spark plug, repeatability experiments were carried out. The results show that the success rate was up to 94%.

Acoustic Kinematics of Helicopter BVI Noise

Helicopter blade-vortex interaction (BVI) noise is known as a critical source of noise annoyance from helicopters. A key feature of the noise is that the trace velocities of the sources generated by the BVI process are supersonic, and thus have high radiation efficiency. This further means that noise is generated selectively by only a limited part of the overall interaction. The consequences of this have been studied using a simple cycloidal shed wake model. This allows the whole process to be explicitly described mathematically. The trace velocity can be infinite for both forward and retreating blades. This will generate strong noise radiation in directions which can be simply defined as a function of advance ratio. Analysis shows that many features are functions of rotor disc position only, independent of the number of rotor blades. This offers a helpful simplification. Radiation generates a series of caustics which can be defined by the analysis. Simplified models of the blade-wake interaction show that both the advancing and retreating blade interactions can generate cusps in the noise. Under some conditions these cusps are predicted to continue to the far field in the rotor disc plane, due to a kinematic balance of the change in propagation direction of the basic source vector and the change in the Mach angle of the principal radiation. This gives a two-dimensional decay in sound levels and will give rise to locally intense BVI field. The model also shows areas of the stronger noise fields will be generated in the direction of motion of the interacting blade. A detailed analysis has been undertaken for a four blade rotor at an advance ratio of 0.2. Multiple caustics from successive blade interactions can be identified, some of which have cusps. The analysis shows that the BVI radiation field can have large levels locally and helps to explain why helicopters are often perceived to be noisier than a simple dBA level might suggest. Each part of the rotor disc noise radiation to the far field can be related back to specific positions on the blade and specific parts of the shed wake. This offers the prospect of providing local adjustments to minimize BVI sources under particular conditions. All these results are based on the two dimensional cycloidal model. However it is believed that these effects must be reflected in more complex computer models and in real helicopters.

Branching and path-deviation of positive streamers resulting from statistical photon transport

The branching and change in direction of propagation (path-deviation) of positive streamers in molecular gases such as air likely require a statistical process which perturbs the head of the streamer and produces an asymmetry in its space charge density. In this paper, the mechanisms for path-deviation and branching of atmospheric pressure positive streamer discharges in dry air are numerically investigated from the viewpoint of statistical photon transport and photoionization. A statistical photon transport model, based on randomly selected emitting angles and mean-free-path for absorption, was developed and embedded into a fluid-based plasma transport model. The hybrid model was applied to simulations of positive streamer coaxial discharges in dry air at atmospheric pressure. The results show that secondary streamers, often spatially isolated, are triggered by the random photoionization and interact with the thin space charge layer (SCL) of the primary streamer. This interaction may be partly responsible for path-deviation and streamer branching. The general process consists of random remote photo-electron production which initiates a back-traveling electron avalanche, collision of this secondary avalanche with the primary streamer and the subsequent perturbation to its SCL. When the SCL is deformed from a symmetric to an asymmetric shape, the streamer can experience an abrupt change in the direction of propagation. If the SCL is sufficiently perturbed and essentially broken, local maxima in the SCL can develop into new streamers, leading to streamer branching. During the propagation of positive streamers, this mechanism can take place repetitively in time and space, thus producing multi-level branching and more than two branches within one level.

Study of the Propagation Rules of Stress Wave in Bedding Rock Slope

After analyzing the propagation of stress wave at different angles of inclination, strength parameters and the group number of structural plane. The results of research are summarized as follows: Due to the change of propagation direction in structural planes with different angles of inclination, the original propagation rule of stress wave changes too, the peak velocity of the monitory point gets relatively flat as the strength parameters of structural plane turn greater. Stress wave repeatedly refracts and reflects in many groups of structural plane, then the appropriate dynamic characteristics of the wave no longer maintains as the number of group increases or decreases. By analyzing and verifying the slope instance, the test result provides a reference for studying dynamic response rules.

Propagation of ripple patterns on Si during ion bombardment

The lateral propagation of surface ripples on Si, generated by Xe ion irradiation with and without codeposition of Fe surfactant atoms, was investigated by scanning electron microscopy with the help of micron-sized marker structures prepared by focused ion beam milling. For 10-keV Xe ion irradiation of Si at oblique incidence between 62 and 70\ifmmode^\circ\else\textdegree\fi{}, we determine lateral ripple propagation velocities varying from \ensuremath{-}1.9 to $+$2.9 nm per 10${}^{15}$ Xe ions/cm${}^{2}$. The propagation direction changes from opposite to the projected direction of the incident ion beam to along the projected beam direction within a narrow angular regime. At 67\ifmmode^\circ\else\textdegree\fi{}, the pattern is almost static. The result is in good agreement with predictions from the theoretical model of Bradley and Harper. For perpendicular incident 5-keV Xe ions and oblique codeposition of Fe surfactant atoms, we find that ripple patterns propagate across the surface with a negative ripple propagation velocity of about \ensuremath{-}0.7 nm per 10${}^{15}$ Xe ions/cm${}^{2}$, i.e., opposite to the projected deposition direction of Fe surfactant atoms. The novel experimental method to determine the lateral ripple propagation based on markers set with a focused ion beam system does not require an in situ analysis and can therefore be applied in general to analyze the dynamics of ion beam-induced patterns.

SEM Study of High-Chromium Martensitic Steel LCF Fracture

Low cycle fatigue of high-chromium 13Х11Н2В2МФ stainless steel has been studied after cyclic tests at room temperature with the frequency of loading, 0.45Hz and amplitude, ± 1mm. The samples were v-notched with the dimensions x2x50, where =3mm. The peculiarities of fatigue crack propagation and influence of heat treatment, sizes of grains and laths, and disposition of microcrack and microstructure elements of the steel were studied. Next, the main effect on propagation direction is caused by the shape of grains and laths. It turned apparent that main microcrack is composed of individual micro-components with the lengths correlating with the dimensions of grains and martensitic laths. During growth crack propagation direction changes from lath to lath; however, general trend remains unchanged. The results of tests indicate that speed of fatigue failure rises when the frequency and amplitude of loading increases. The work includes x-ray characterization of the steel, statistical distribution curve for angles between the main direction of macrocrack propagation and micro-components, and explanation of micro- and macrocrack propagation alteration is given.

Migrating motor complex changes after side-to-side ileal bypass in mouse ileumex-vivo: mechanism underlying the blind loop syndrome?

PurposeThis study was intended to investigate the migrating motor complex (MMC) changes after ileal bypass in ex-vivo mouse models.MethodsPartial (side-to-side) and total bypass (occlusion of proximal part of bypassed loop) were performed on ileums of female Institute of Cancer Research mice. After 2 and 4 weeks, the bypassed segments were harvested and MMCs were recorded at 4 different sites ex-vivo. Amplitude, duration, interval, direction of propagation, and the area under the curve (AUC) of MMCs were measured and compared to those of the controls.ResultsIn control mice (n = 7), most MMCs propagated aborally (91.1%). After 2 weeks of partial bypass (n = 4), there was a significant decrease in both amplitude and AUC, and orally-propagating MMCs increased significantly (45%, P = 0.002). Bidirectional MMCs (originating in the bypassed loop and propagating in both directions) were also observed (10%). The amplitude of the MMCs remained decreased at 4 weeks after partial bypass (n = 4), and neither the AUC nor the direction of propagation showed significant changes compared to 2 weeks. Similarly, in the total bypass model, both the amplitude and AUC of the MMCs decreased significantly compared to controls. In contrast to partial bypass, 95% of the MMCs within the bypassed loop propagated aborally after 2 weeks (n = 6), which was similar to the control state. After 4 weeks (n = 5), however, MMCs either lost their temporal relationship or completely disappeared.ConclusionThe changes in propagation direction of the MMCs in the partially bypassed loop may contribute to stagnation of bowel contents and the development of blind loop syndrome.