Propagation Velocity Of Wave Front Research Articles

Study on Hydraulic Characteristic of Unsteady Flow at Huangchigou Water Distribution Hub by Observing Instantaneous Water Level Based on Single-Camera and Fixed-Scale Compensation Method

The Huangchigou Water Distribution Hub is the core water distribution structure in the Hanjiang-to-Weihe Valley Water Diversion Project. It plays a decisive role in ensuring the safety of downstream water transport, allocating water reasonably and reducing the waste of abandoned water. The study on its unsteady-flow hydraulic characteristics is of key significance in the formulation for the opening and closing rules of the hub gates. The shape of the instantaneous water surface profile is an important factor for the hydraulic characteristics of the unsteady flow in the hub. The effect of the traditional instantaneous water level measurement method is not ideal. A single-camera and fixed-scale compensation method is proposed for an instantaneous water level observation. The proposed method meets the requirement of measurement accuracy and reduces the observation cost of the model test. The unsteady-flow test of the hydraulic model in the Southern Main Tunnel of the Huangchigou Water Distribution Hub was carried out under two operating conditions when the model flow is 0.0246 m3/s. Precise data such as wave front propagation velocity and hydraulic oscillation recovery time of unsteady flows in the Southern Main Tunnel was obtained. It has an important reference value for the research and design of water transfer dispatching and gate-opening and gate-closing rules for the Huangchigou Water Distribution Hub.

Thermally coupled SHS processes in (Ni + Al)/(Co + Ti)/(Ni + Al) layered system: experimental and theoretical study

The paper focuses on the theoretical and experimental study of the mechanisms of reaction mixture combustion in the ≪chemical oven≫ mode in a three-layer Ni–Al/Ti–Co/Ni–Al sample. Experimental studies were carried out in a reactor in an argon atmosphere at atmospheric pressure and an ambient temperature of 298 K on rectangular samples pressed from Ni–Al and Ti–Co powder mixtures in the form of a three-layer package. The Ti–Co acceptor layer was in the middle of the sample, and the Ni–Al donor layer was outside. The acceptor layer thickness was varied from 4.3 to 13 mm, while the donor layer thickness (4.7 mm) remained constant. It was found that as the acceptor layer thickness increases, the combustion wave front propagation velocity and reaction initiation temperature decrease, and the maximum temperature in the front remains constant and equal to the melting point of the final product. The time of acceptor layer heating before the reaction increases. The acceptor mixture reaction proceeds in the thermal explosion mode when the thickness of the acceptor layer exceeds that of the donor one. Maximum temperature in this case is higher than the melting point of the final product. The inner layer synthesis modes change with an increase in the acceptor layer thickness: stationary – pulsating – extinction. The mathematical model of the three-layer sample high-temperature synthesis in dimensional variables is constructed taking into account heat transfer with the environment. As a result of experimental studies and numerical calculations, the critical thickness of the inner layer was found to be 15 mm, at which the inner layer combustion becomes impossible at fixed sizes of donor layers. Critical conditions for the combustion wave propagation along the acceptor layer are weakly dependent on the external heating source. The experimental technique and mathematical model of the layered system combustion can be used to assess the critical conditions for the metal composite synthesis in the frontal combustion mode.

Prolonged Right Ventricular Outflow Tract Endocardial Activation Duration and Presence of Deceleration Zones in Patients With Idiopathic Premature Ventricular Contractions. Association With Low Voltage Areas.

Background and AimsThe wavefront propagation velocity in the myocardium with fibrosis is characterized by the presence of deceleration zones and late activated zones, that are absent in the normal myocardium. Our aim was to study the right ventricular outflow tract (RVOT) endocardial activation duration in sinus rhythm, and assess the presence of deceleration zones, in patients with premature ventricular contractions (PVCs) and in controls.MethodsWe studied 29 patients with idiopathic PVCs from the outflow tract, subjected to catheter ablation that had an activation and voltage map of the RVOT in sinus rhythm. A control group of 15 patients without PVCs that underwent ablation of supraventricular arrhythmias was also studied. RVOT endocardial activation duration and number of 10 ms isochrones across the RVOT were assessed. Propagation speed was calculated at the zone with the higher number of isochrones per cm radius. Deceleration zones were defined as zones with >3 isochrones within 1 cm radius. Low voltage areas were defined as areas with local electrogram with amplitude <1.5 mV.ResultsThe two groups did not differ in relation to age, gender or number of points in the map. RVOT endocardial activation duration and number of 10 ms isochrones were higher in the PVC group; 56 (41–66) ms vs. 39 (35–41) ms, p = 0.001 and 5 (4–8) vs. 4 (4–5), p = 0.001. Presence of deceleration zones and low voltage areas were more frequent in the PVC group; 20 (69%) vs. 0 (0%), p < 0.0001 and 21 (72%) vs. 0 (0%), p < 0.0001. The wavefront propagation speed was significantly lower in patients with PVCs than in the control group, 0.35 (0.27–0.40) vs. 0.63 (0.56–0.66) m/s, p < 0.0001. Patients with low voltage areas had longer activation duration 60 (52–67) vs. 36 (32–40) ms, p < 0.0001, more deceleration zones, 20 (95%) vs. 0 (0%), p < 0.0001, and lower wavefront propagation speed, 0.30 (0.26–0.36) vs. 0.54 (0.36–0.66) m/s, p = 0.002, than patients without low voltage areas.ConclusionRight ventricular outflow tract endocardial activation duration was longer, propagation speed was lower and deceleration zones were more frequent in patients with PVCs than in controls and were associated with the presence of low voltage areas.

A technique for measuring anisotropy in atrial conduction to estimate conduction velocity and atrial fibre direction

BackgroundCardiac conduction properties exhibit large variability, and affect patient-specific arrhythmia mechanisms. However, it is challenging to clinically measure conduction velocity (CV), anisotropy and fibre direction. Our aim is to develop a technique to estimate conduction anisotropy and fibre direction from clinically available electrical recordings. MethodsWe developed and validated automated algorithms for estimating cardiac CV anisotropy, from any distribution of recording locations on the atrial surface. The first algorithm is for elliptical wavefront fitting to a single activation map (method 1), which works well close to the pacing location, but decreases in accuracy further from the pacing location (due to spatial heterogeneity in the conductivity and fibre fields). As such, we developed a second methodology for measuring local conduction anisotropy, using data from two or three activation maps (method 2: ellipse fitting to wavefront propagation velocity vectors from multiple activation maps). ResultsEllipse fitting to CV vectors from two activation maps (method 2) leads to an improved estimation of longitudinal and transverse CV compared to method 1, but fibre direction estimation is still relatively poor. Using three activation maps with method 2 provides accurate estimation, with approximately 70% of atrial fibres estimated within 20∘. We applied the technique to clinical activation maps to demonstrate the presence of heterogeneous conduction anisotropy, and then tested the effects of this conduction anisotropy on predicted arrhythmia dynamics using computational simulation. ConclusionsWe have developed novel algorithms for calculating CV and measuring the direction dependency of atrial activation to estimate atrial fibre direction, without the need for specialised pacing protocols, using clinically available electrical recordings.

Fine wave dynamics in umbral flash sources

Context. Umbral flashes (UFs) are most common phenomenon of wave processes in sunspots. Studying the relationship between wave time dynamics and the origin of UFs requires further investigation of their fine spatial and height structure. Aims. We investigated the association between a short time increase in the variations of 3-min extreme ultraviolet (EUV) emission at footpoints of coronal magnetic loops and the UF emergence in sunspot umbra. The spatial structure of magnetic field lines and their inclination determine the cut-off frequency and visibility of sunspot waves. Methods. We applied the pixelized wavelet filtering (PWF) technique to analyse a cube of the images obtained by SDO/AIA at 1600 Å, 304 Å, and 171 Å to study the spatio-temporal oscillation power distribution in individual magnetic loops. Time–distance plots were used to obtain the wave front propagation velocity. Results. For the first time, we obtained the 2D images of the fine wave processes in magnetic structures of different spatial scales related to the UFs in sunspot. We revealed two types of the UFs as background and local. The background UFs associated with random increasing of separate parts of wave fronts. These UFs are seen as weak and diffuse details that ride the wave fronts without stable shapes and localization in space. The local UFs sources mainly localize near to the footpoint of magnetic loops, anchored in an umbra, along which the propagation of 3-min waves was observed. The time dynamics of flash evolution shows an increase in 3-min oscillations before the UFs peak value within one low-frequency wave train. It is shown that the maxima of 3-min oscillation trains coincide with the peak intensity of UFs. During the UFs evolution, a fine wave spatial and temporal dynamics in UFs local sources was observed. Conclusions. The sunspot 3-min wave dynamics showed a relation between the localization of oscillations power peak at the coronal magnetic loop footpoints and the UFs origin. The spatial structure of the UFs sources, their power, and lifetime are determined by the cut-off frequency of the waves for the detected waveguides. We concluded that UFs are a global process of short-time increase of the wave activity.

평탄지형 제내지에서의 제방붕괴속도에 따른 범람홍수파 선단 거동에 관한 연구

본 연구에서는 평탄지형의 제내지에서 제방붕괴속도에 따른 범람홍수파 선단의 전파 특성을 규명하기 위하여 제내지와 하도로 이루어진 실험수조에서 실험을 수행하여 전파 거리를 산정하였다. 실험에 의해 측정된 전파거리를 시간에 대한 상관식으로 나타내기 위하여 댐붕괴에 의한 수로에서의 홍수파의 1차원 흐름 해석해인 Ritter의 해에 3차원 거동특성을 반영할 수 있는 상수 k와 m을 도입한 일반식에 실험결과를 적용하여 실험식을 도출하였다. 기존 연구에서 하도내의 초기수위가 범람홍수파의 전파속도에 지배적인 영향을 준다는 사실은 알려져 있으나, 본 실험연구를 통해 제방붕괴속도도 범람홍수파의 전파속도에 영향을 주며, k와 m이 상수가 아닌 제방붕괴속도와 선형관계를 갖는 변수임을 밝혔다. 실험결과를 이용하여 범람홍수파 선단의 전파거리를 산정할 수 실험식을 제시했으며, 범람홍수파의 전파속도 산정시 하도내의 초기수위뿐만 아니라 제방붕괴속도도 고려해야 함을 본 연구를 통해 확인할 수 있었다. 본 연구에서는 대규모 제내지 범람실험을 수행하여 범람양상을 관찰하고 수리학적 관점에서 해석하였으며, 실험결과를 토대로 제방붕괴속도에 대한 홍수파 전파속도의 상관관계도 제시하였다. 본 연구결과는 홍수위험지도 작성이나 긴급대피계획 수립시 기본적인 판단 자료로 사용할 수 있으며, 2차원 범람 수치모형 검증시 유용한 자료로 이용될 수 있을 것으로 기대된다. An experimental study was carried out to investigate the characteristics of the propagation distance of a flood wave considering the levee failure speed in a flat inundation area. The Ritter solution for one dimensional flow was considered to formulate the experimental results and a representative form with coefficients of k and m, which consider the three dimensional flow characteristics, was applied. The experiments showed that the propagation velocity of the wave front in the inundation area was influenced by the levee breach speed as well as the initial water level, which is a significant variable representing the flood wave behavior. In addition, coefficients k and m are not constants, but variables that vary with levee breach speed. An empirical formula was also suggested using the experimental results in the form of the relationships between k and m. In this study, a large-scale experiment for flood inundation was carried out to examine the behavior of flooding in the inundated area and the relationships between the levee breach speed and wave-front propagation velocity were suggested based on the experimental results. These research results are expected to be used as the baseline data to draw a flow inundation map, establish an emergency action plan, and verify the two-dimensional numerical model.

Sunspot waves and flare energy release

We address a possibility of the flare process initiation and further maintenance of its energy release due to a transformation of sunspot longitudinal waves into transverse magnetic loop oscillations with initiation of reconnection. This leads to heating maintaining after the energy release peak and formation of a flat stage on the X-ray profile. We applied the time-distance plots and pixel wavelet filtration (PWF) methods to obtain spatio-temporal distribution of wave power variations in SDO/AIA data. To find magnetic waveguides, we used magnetic field extrapolation of SDO/HMI magnetograms. The propagation velocity of wave fronts was measured from their spatial locations at specific times. In correlation curves of the 17 GHz (NoRH) radio emission we found a monotonous energy amplification of 3-min waves in the sunspot umbra before the 2012 June 7 flare. This dynamics agrees with an increase in the wave-train length in coronal loops (SDO/AIA, 171 {\AA}) reaching the maximum 30 minutes prior to the flare onset. A peculiarity of this flare time profile in soft X-rays (RHESSI, 3-25 keV) is maintaining the constant level of the flare emission for 10 minutes after the short impulse phase, which indicates at the energy release continuation. Throughout this time, we found 30-sec period transverse oscillations of the flare loop in the radio-frequency range (NoRH, 17 GHz). This periodicity is apparently related to the transformation of propagating longitudinal 3-min waves from the sunspot into the loop transverse oscillations. The magnetic field extrapolation showed the existence of the magnetic waveguide (loop) connecting the sunspot with the energy release region. A flare loop heating can be caused by the interaction (reconnections) of this transversally oscillating waveguide with the underlying twisted loops.

Electrophysiological Abnormalities Occur Prior to the Development of Clinical Episodes of Atrial Fibrillation: Observations from Human Epicardial Mapping

Atrial fibrillation (AF) is characterized by irregular atrial activation maintained by an arrhythmogenic substrate. We addressed the hypothesis that the substrate of human AF includes changes in atrial conduction properties. Patients in sinus rhythm (SR) and permanent AF undergoing cardiac surgery underwent right atrial epicardial mapping. AF was induced by burst pacing in patients in SR and was defined as sustained at >30 seconds. Epicardial maps were analyzed to determine conduction properties, AF activation patterns, and refractoriness. Patients in SR underwent postoperative Holter monitoring. Thirty-seven subjects were recruited. (27 in SR and 10 in permanent AF). Sustained AF was induced in 17 patients in SR. Only patients with sustained AF developed any episodes of postoperative AF (P < 0.05), indicating the preexistence of an arrhythmogenic substrate, which was characterized by prolonged unipolar electrograms (37.0 +/- 9.4 ms vs 27.5 +/- 6.4 ms, P = 0.03), particularly in the region of the crista terminalis (41.2 ms +/- 12.1 vs 26.7 ms +/- 5.8, P = 0.004) compared with the nonsustaining group. However, these differences in electrogram characteristics were not associated with changes in wavefront propagation velocity (WPV) during SR or pacing. Activation mapping of acutely induced AF was compared with permanent AF and although there were shorter mean fibrillation intervals in permanent AF (171 +/- 16 ms vs 229 +/- 51 ms, P < 0.001), there was no difference in fibrillatory activation pattern (complexity scores: 2.21 +/- 0.52 vs 2.02 +/- 0.61) or WPV (46.9 +/- 15.4 cm/s vs 53.5 +/- 17.6 cm/s, P = 0.37). Fibrillatory activation pattern was associated with both WPV (P = 0.03) and wavelength (P = 0.03) in both pacing-induced and permanent AF. Patients in SR capable of sustaining pacing-induced AF have differences in electrogram duration, which are apparent before clinical episodes of AF. Although patients with permanent AF had shortening of refractoriness, there was no evidence of further changes in fibrillatory activation pattern or macroscopic wavefront propagation velocity in permanent AF. These results imply that changes occur before the onset of AF and indicate the presence of a substrate capable of maintaining AF with only alterations in refractoriness required for the development of permanent AF.

The Effects of Carbenoxolone on Human Myocardial Conduction: A Tool to Investigate the Role of Gap Junctional Uncoupling in Human Arrhythmogenesis

This study assessed the effects of carbenoxolone on human myocardial conduction and refractoriness. Carbenoxolone, an antipeptic ulcer drug, has been shown to reduce gap junctional coupling without affecting cellular ion channels. Gap junctions (GJ) are considered to be determinants of cardiac action potential propagation. The effects of GJ uncoupling in the human heart are unknown. Right atrial (RA) and ventricular (RV) activation mapping (Carto, Biosense Webster Inc., Diamond Bar, California) was performed during sinus rhythm. Right atrial and RV wavefront propagation velocity (WPV), specifically in the direction of propagation, was determined from these maps using a triangulation method. Refractoriness at multiple RA and RV sites, sinus rhythm cycle length, and AH, PR, QRS, and QT intervals were measured. The protocol was repeated 1 h after oral administration of 100 mg of carbenoxolone. In 11 patients, WPV was reduced from 79.6 +/- 13.3 cm/s to 57.2 +/- 9.1 cm/s (-27.1 +/- 12.8%, p < 0.001) in RA and from 98.7 +/- 19.8 cm/s to 76.5 +/- 21.7 cm/s (-22.7 +/- 14.1%, p < 0.01) in RV after carbenoxolone. Conduction slowing was more marked in 6 older patients with ischemic heart disease compared with younger subjects with normal hearts (RA -35.1 +/- 5.5% vs. -17.5 +/- 12.7%, p = 0.03; RV -33.8 +/- 5.1% vs. -9.3 +/- 7.7%, p < 0.001). Refractoriness and electrocardiogram parameters remained unchanged. Carbenoxolone causes a 27% reduction in human RA WPV and 23% in the RV without affecting refractoriness. The slowing of myocardial conduction by carbenoxolone demonstrates the significance of GJ in regulating human myocardial conduction and provides a tool for investigating the effects of GJ uncoupling on human arrhythmogenesis.

Role of biatrial wavefront propagation velocities in remodelling of paroxysmal and persistent AF

Background: Slowing of myocardial conduction is considered to be important in the development of atrial fibrillation (AF) on the basis of non-specific, surrogate markers of conduction. Wavefront propagation velocity (WPV) can only be calculated if the direction of activation as well as distances and activation times can be measured. We used 3D activation mapping to test the hypothesis that slowing of atrial WPV occurs in patients with AF and that there are differences in the substrate of paroxysmal and persistent AF.

Evolution of activation patterns during long-duration ventricular fibrillation in dogs.

Although resuscitation for sudden cardiac arrest attempts are frequently not instituted for several minutes after the onset of ventricular fibrillation (VF), previous mapping studies have examined only the first 40 s of VF or have involved isolated perfused hearts that did not become ischemic during VF. We applied quantitative pattern analysis to mapping data throughout the first 10 min of VF acquired from a 21 x 24 unipolar electrode array located on the ventricular epicardium of six open-chest dogs. The following twelve descriptors were continuously quantified: 1) number of wavefronts, 2) incidence of reentry, 3) wavefront propagation velocity, 4) incidence of breakthrough/focus, 5) incidence of block, 6) mean area activated by the wavefronts, 7) wavefront fractionations, 8) wavefront collisions, 9) multiplicity index, 10) repeatability, 11) negative peak rate of voltage change, and 12) peak frequency of activation. Cluster analysis of these descriptors divided VF into five stages (stages i-v). The values of most descriptors (except block and breakthrough incidence) increased during stage i (1-11 s after VF induction) and maintained high values with rapid dynamic fluctuations during stage ii (12-62 s). Descriptors changed quickly to values indicating greater organization during stage iii (63-86 s), decreased steadily during stage iv (87-310 s), and approached zero during stage v (311-600 s). There was a high incidence of reentry just before, during, and after stage iii. In conclusion, during the first 10 min, VF can be divided into five stages according to the evolution of electrophysiological characteristics. All of the parameters show a rapid deterioration during VF, except for a temporary reversal approximately 1 min after induction when activation briefly became more organized. Thus a quantitative description of activation does not uniformly decrease as VF progresses, but undergo rapid changes and exhibit a brief interval of increased organization after approximately 1 min of VF. Further studies are warranted to determine whether these changes, particularly the increased organization of stage iii, have clinical consequences, such as an alteration in defibrillation efficacy.

Effects of feed composition of coke oven gas on a layered bed H(2)PSA process

The effects of feed composition on the adsorption dynamics and the optimal process design were studied from the experimental and simulated results in the H2 layered bed PSA with activated carbon and zeolite 5A. The breakthrough results using the “base composition” (56.4 vol% H2; 26.6 vol% CH4; 8.4 vol% CO; 5.5 vol% N2; and 3.1 vol% CO2) in various layered beds were compared with those using the “higher nitrogen composition” and the “no nitrogen composition”. In the breakthrough dynamics, the propagation velocity of wave front of each component was closely related to the slope of isotherm estimated at its concentration in the feed. Breakthrough behavior at each layered bed in the “higher nitrogen composition” showed similar trends as that in the “base composition”. However, the “no nitrogen composition” showed different breakthrough behavior from the other groups. In this feed composition, it was observed that the order of CO and CH4 breakthrough times was reversed with a change in the carbon-to-zeolite ratio. Based on the adsorption dynamics and breakthrough behavior of each feed composition group in various layered beds, the effect of feed composition on a seven-step two-bed PSA process for the H2 recovery from coke oven gas was investigated numerically to develop a well-designed H2 PSA process under various operating conditions. As expected from the breakthrough results, the trends of the PSA performance in the “higher nitrogen composition” were similar to those in the “base composition” except for the slight decrease in the optimal carbon-to-zeolite ratio. However, in case of the “no nitrogen composition”, high purity product was obtained from the activated carbon-rich layered bed PSA because the adsorption capacity of the activated carbon for impurities was superior to that of zeolite. As a result, the optimum carbon-to-zeolite ratio at each operating condition was slightly changed depending on the propagation velocity of each component on each layer.

Evolution of the organization of epicardial activation patterns during ventricular fibrillation.

This study quantified how the organization of epicardial activation changes during the first 40 seconds of ventricular fibrillation (VF). Unipolar potentials were mapped from a 504 (24 x 21) electrode array (2-mm interelectrode spacing) on the anterior right ventricle (RV) and left ventricle (LV) epicardium. The array covered approximately 20% of the epicardial surface. In each of seven pigs, six episodes of VF were induced by premature stimulation. One-half second epochs of VF were analyzed, starting 0, 10, 20, 30, and 40 seconds post induction and using novel pattern analysis algorithms. Eight parameters were quantified: (1) the number of wavefronts; (2) the epicardial area activated by wavefronts; (3) the fraction of wavefronts arising from epicardial breakthrough or from a focus; (4) the fraction of wavefronts terminated by conduction block; (5) the multiplicity index (number of distinct activation pathways in the rhythm); (6) the repeatability index (number of times activation pathways are traversed); (7) the activation rate; and (8) the wavefront propagation velocity. The results showed that VF patterns were less organized at 10 than at 0 seconds, with more, smaller wavefronts traversing a larger variety of pathways for fewer repetitions. VF activation patterns then gradually reorganized up to 40 seconds, but by a different mechanism: the spatial size of subpatterns grew, but the dynamics otherwise appeared unchanged. During both transitions, both activation rate and propagation velocity slowed monotonically. Thus, changes in organization during VF can occur by multiple mechanisms.

SHS-process in external electric fields

The possibility of controlling the SHS-process by means of supplementary Joule heat release in gasless combustion systems is considered theoretically. The cases of longitudinal and transverse electric fields with respect to the direction of wave propagation are considered. The advantages for different SHS-systems are pointed out. The influence of electric current on the thickness of the zone determining the wave-front propagation velocity is investigated. A general stability analysis shows the possibility of wave propagation being controlled when the reagent is completely exhausted in a quasi-stationary front. Instability of the combustion regime at a definite moment of time or, conversely, establishment of steady-wave propagation during some time interval, may be caused by choosing initial substance and product parameters (thermal diffusivity, electric conductivity and its temperature dependence, etc.) from a definite region of values and passing a corresponding value of electric current through the system. On the other hand, the instability of a gasless combustion wave with phase transition in the front depends only on the development of distortions and is controlled by the differential coefficient of reagent exhaustion. This coefficient depends on the kinetics of chemical reaction, but is independent of the external electric field influence in practice.

Lorentz-covariant lagrangians and causality

A class of Lorentz-covariant Lagrangians is described which seem to violate causality in the sense that the propagation velocity of wave fronts and particles can be larger than the velocity of light. As a simple model of a Lagrangian of this type we consider a point particle coupled to a massless rank-two tensor field. While it seems kinematically possible to accelerate a particle through the Minkowski light-cone, it turns out that dynamical reasons prevent this. The reaction force due to the radiation emitted by the particle diverges when the particle approaches the Minkowski light-cone. This simple model seems to indicate that Lorentz covariance is indeed sufficient to guarantee causality and no restrictions concerning the type of couplings which may be contained in the Lagrangian are necessary.