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To understand steeply dipping events in seismic reflection interferometry (SRI), we derived an expression that describes the difference in travel time (Δτ) from a diffractor to two receivers in two dimensions. For a fixed receiver interval, the expression shows that Δτ is zero when the diffractor is at the midpoint of the paired receivers, increases with an apparent velocity of half the medium velocity as the diffractor moves toward either receiver, and remains constant for a diffractor located on the same side of both receivers. The horizontal portion of Δτ is slightly skewed during the normal moveout correction, yielding a maximum peak of the horizontally stacked trace at a slightly smaller time than Δτ. Accordingly, the diffracted waves have an apparent velocity slightly higher than half of the medium velocity in a horizontally stacked image. This conformed to virtual data for an elastic two-layer model with a vertical boundary. We then generalized the expression to three dimensions, in which listric travel time curves were predicted for an oblique edge diffractor, a vertex diffractor offline from the receiver pair, or a buried diffractor. Based on both two- and three-dimensional analyses of the edge diffractor, we tentatively interpreted the linear and listric dipping events observed in the passive SRI image across the Korean Peninsula to have been caused by diffractors near the intersection of the profile and geologic boundaries.

Misalignment angle will result in a considerable error for the integration of Doppler velocity log (DVL) and of Strapdown Inertial Navigation System (SINS). In this article, a robust initial alignment method for SINS/DVL is proposed to solve a practical applicable issue, which is that the outputs of DVL are often corrupted by the outliers. First, the alignment principle for SINS/DVL is summarized. Second, based on the principle of this alignment method, the apparent velocity model is investigated, and the parameters expression of the apparent velocity model are derived detailed. Using the apparent velocity model, the unknown parameters of the apparent velocity model are estimated by the developed robust Kalman filter, then the reconstructed observation vector, where the outliers are detected and isolated, is reconstructed by the estimated parameters. Based on the reconstructed observation vectors, the initial attitude is determined. Finally, the simulation and field tests are carried out to verify the performance of the proposed method. The test results are shown that the proposed method can detect and isolate the outliers effectively and get better performance than the previous work.

Seismic data are increasingly used to monitor subsurface velocity changes associated with tectonic and environmental processes that occur in different depth sections. To clarify the differences between effects associated with shallow and deep changes of properties, we conduct numerical experiments using simple layered models that include low velocities, low attenuation coefficients and stress-sensitivity of cracked rocks in the shallow crust. We find significant phase-velocity drops in the period range of 5–20 s when large structural changes occur in the top 1–3 km. The apparent velocity changes (δv/v) measured from the first part of the synthetic Rayleigh waves with a cross-correlation based technique show significant velocity drops in the period bands of 5–10 s and 10–20 s that are consistent with reported values of changes at seismogenic depth. The results highlight the importance of accounting for low velocities, attenuation coefficients and stress-sensitivity of parameters in the top 1–3 km in studies aiming to determine the source region of temporal changes. Analyses using different frequency ranges and calculations of apparent delay times over multiple period bands are essential for resolving the depth range of temporal changes of properties. For temporal changes occurring at seismogenic depths, the measured δv/v values at 5–10 s are significantly larger than those of 10–20 s, which are not observed for shallow changes.

Laser scanning microscopy is widely used to measure blood hemodynamics with line-scans. Analysis of red blood cell (RBC) velocity involves two types of algorithms. The algorithms of the first kind are the image-processing algorithms such as the shear [1], the LSPIV [2], the radon-transform [3] and the Fourier transform [4, 5] algorithms. Each of them provides the apparent velocity (VRBCapp) of RBCs in the image, which does not consider the scanning conditions. The algorithms of the second kind give the real RBC velocity from VRBC app and the scanning conditions [6]. Here we developed a predictive model that provide the accuracy of one image-processing algorithms. We find that the accuracy of the image-processing algorithm depends on several parameters such as the design of the scanned line, the scanning velocity and the velocity of RBCs. Last we validate our model by testing various types of artificial linescan images. The same strategy will be followed for various image-processing algorithms. Overall, our analysis will allow accurate comparisons of blood velocity from all vessel types in control and pathological animal models.

In contrast to the intuitive and traditional assumption of a centralized and universal neural clock, many recent studies have provided evidence against this idea. Here, we investigated whether subjective duration is estimated by a mechanism that tracks the trajectory of a moving object. Such a mechanism would integrate over the velocity and the spatial distance the object traveled to derive its duration. We exposed observers to a moving object that covered either a small or large spatial distance. We found that subjective duration decreased after this exposure when intervals were tested that were defined by stimuli covering a large, but not by stimuli covering a small, spatial distance. We compared the effects of our velocity exposure to previously used adaptation to a drifting grating and found a dependence of spatial distance only for velocity exposure. The finding that temporal estimations decrease after exposure to fast-moving stimuli selectively at large distances suggests that subjective duration is derived from measurements of velocity and space.

Motion estimation has become one of the most important techniques used in realtime computer vision application. There are several algorithms to estimate object motions. One of the most widespread techniques consists of calculating the apparent velocity field observed between two successive images of the same scene, known as the optical flow. However, the high accuracy of dense optical flow estimation is costly in run time. In this context, we designed an accurate motion estimation system based on the calculation of the optical flow of a moving object using the Lucas–Kanade algorithm. Our approach was applied on a local treatment region implemented into Raspberry Pi 4, with several improvements. The efficiency of our accurate realtime implementation was demonstrated by the experimental results, showing better performance than with the conventional calculation.

The tunnel seismic ahead prospecting method is usually used to estimate adverse geology ahead of a tunnel face. The observation system plays an important role in tunnel seismic ahead prospecting, which helps to obtain accurate imaging results. Optimizing the observation system is a key issue for seismic ahead prospecting. In this paper, observation layouts are evaluated and a new three-dimensional (3D) observation system is proposed by imaging results analysis. For linear and 3D layouts, imaging result analysis in this paper indicates that the mirror artifact caused by the linear layout (Which sets sources and geophones on a straight line) can be suppressed by the 3D layout, due to its energy concentration and convergence. Moreover, reflections using 3D layout identify real abnormal bodies better than the linear layout. Moreover, conventional observation layouts often use shot point on the tunnel face or front sidewall, which makes it difficult to filter interference waves from the back of the tunnel face. To solve this problem, typical numerical examples are conducted, and imaging results of observation layouts with shot point on front sidewall, tunnel face or back sidewall are studied. Results show shot point on the back sidewall helps to separate waves, suppress interference waves and extract effective waves (reflected P-waves by discontinuities) by apparent velocity filtering method, so shot point is designed on the back sidewall to get high-quality records. To balance record quality and application convenience, a new 3D observation system is proposed with 12 geophones and 10 shot points in a special arrangement. Compared with a linear layout, practical testing and application using the new 3D system indicate the main fractured zones are accurately identified and located, which proves the reliability and practicability of the new observation system.

Processing and interpretation of huge array of mine seismicity data obtained in mines of Norilsk Nickel Mining and Metallurgical Company has revealed the “pulsating” mode of seismic energy release on the background of an increase in the strata pressure and, based on the information on monthly migration of reduced centers of seismic energy release within the mine fields, enabled development of a rockburst hazard criterion for individual rock mass areas. The prognostic criterion of the limiting state of a rock mass area is developed based on the ratio of kinematic characteristics of seismic events, which are the velocity of a reduced center of seismic energy release and the apparent velocity of “migration” of individual seismic events closely timed within the ranges of stress concentration zones inside the mine fields. Verification of this criterion using an ample seismic data base accumulated for a number of years in a mine of Norilsk Nickel has displayed high sensitivity of the criterion towards the change in the stress state of rock mass areas under monitoring.

A semi-empirical model was developed to predict the apparent velocity of particles falling through foams. Different foams were generated from liquids with different viscosities and surface tensions ...

Special relativity (SR) holds that the velocity of light relative to any inertial system is the same velocity c in vacuum. Length contract effect, time dilation and mass-velocity relation derived from SR are not only inconsistent with human cognitive experience, but also logically form many paradoxes. Starting from the physical nature of light, this paper analyses the basic law of light movement, establishes the absolute space-time view of the universe based on the light trace reference system, and reveals the root causes of the errors in SR postulation of light speed invariance, the relativity of simultaneity and Lorentz transformation. In this paper, the law of movement of objects based on human observation is also discussed, and the relationship between apparent velocity and objective velocity of moving bodies is obtained. The reason why Newton classical mechanics is suitable for low-speed motion of objects and that the apparent velocity of objects deviates greatly from objective velocity under high-speed motion is explained. The effect of observer's position effect on apparent velocity of object motion is revealed. A new method for measuring the absolute speed of light is presented. The experimental results or observational phenomena of Michelson-Morley experiment, photonic clock, aberration of light, high-energy particle velocity, superluminal velocity, negative velocity, Doppler effect of light wave and symmetry breakage are also explained in this paper. Finally, the impact and development opportunities of "realism of movement" on modern physics and cosmology are discussed.

In this paper we propose a processing method with several linear subarrays for the joint estimation of the apparent velocity and the direction of propagation of a seismic wave. This method estimates the parallel velocities along the directions of the considered linear subarrays, followed by a geometrical based procedure to compute the apparent velocity and the direction of propagation of the wave. Examples, using synthetic as well as field data, are presented to verify the suggested method. The proposed method can be used to determine the properties and sources of the microseism and microtremor signals acquired by seismic array data.

The Betz theory of optimal circulation is developed in this chapter. The rigid helical wake model presented in Chap. 11 originated from the analysis of Betz. The expression of the kinematic boundary conditions on the rigid helical wake surface leads to Betz’s optimal circulation. The inclusion of drag to this theory is presented according to the work of Helmbold.

Interbed multiples, caused by ringing between strong reflectors deeper within the section, have been historically difficult to remove. Conventional separation methods, based on multiple periodicity or residual moveout, will typically fail. As an example, interbed multiples from limestone packages can actually have a faster apparent velocity than the real primaries. Different techniques have to be used in these situations. Two different interbed demultiple methods have been tried successfully on a recent 3D Ocean Bottom Cable (OBC) seismic survey (Tridacna survey) over the North Scott Reef offshore Australia. In these data, strong events in the upper section do produce interbed multiples below, -and with very little normal moveout discrimination. This paper will present a new (and old) development to resolve our imaging problem. Solution 1: Old method adapted to this: a horizon-based pattern-recognition algorithm is used pre-stack on migrated data. A robust algorithm. Assumptions, limitations, results, where-when will be discussed. Solution 2: New method with new methodology and tools: 3D Interbed removal by (deterministic) wavefield modelling. Adapting a 3D SRME (surface multiple) approach to interbeds. Originally this uses one-way WE to model interbeds between the reflectors situated under and over a horizon. We now run this many times over many windows to make all possible multiples, and adaptively subtract in 3D all models at once. We hit upon a new constraint, -the amplitude spectra, to stabilize even more. Runs per-migration. Successful results (may be a first here) -requiring no interpretation. The new algorithms and ideas will be described/shared. Discussion results, limitations, etc.

We present a non-linear study of the energy loss of heavy ions in solids, which is based on the transport cross section (TCS) and the extension of the Friedel sum rule (EFSR) for moving ions. We apply this approach to study the velocity dependence of the energy loss of heavy ions in the energy region below the stopping power maximum. With this formulation we are able to explain some striking effects in the energy loss of heavy ions which have been experimentally observed long time ago (Brown and Moak (1972) [14]), but have not been explained so far by the existing theoretical models: the deviations from the proportionality with ion velocity (predicted by alternative models in the low energy range), and the “apparent velocity threshold”.

[1] Forecasting the location of an eruption is of primary importance for risk management in volcanic regions. Locating the underground structural changes associated with a potential eruption is also a key issue to better understand the dynamics at work in a volcano. Using recent results in wave physics, we develop an imaging procedure that is based on the sensitivity of multiply scattered waves to weak changes in heterogeneous media. This procedure allows to locate changes in both mechanical and scattering properties of the studied medium. We study ambient seismic noise from 19 broadband stations at the active volcano Piton de la Fournaise on Reunion Island, recorded from June to December 2010. During this period, two volcanic eruptions occurred at two different locations. We calculate the noise cross correlations and study two types of changes in the coda: apparent velocity variations related to changes in the elastic properties of the medium; and, waveform decoherence associated with variations in the scattering, and thus the geological structures. We observe that the temporal variations of both of these parameters provide potential precursors of volcanic eruptions at Piton de la Fournaise. The locations determined from the preeruptive and coeruptive changes in both parameters are in good agreement with the actual eruptive activities. These data demonstrate that the coda of ambient noise correlations contains deterministic information on the locations of the eruptive processes in an active volcano. Our analysis offers an original and significant constraint for the localization of forthcoming volcanic eruptions.

Longitudinal seismic responses of CWR on bridges with high-piers and long-spans under uniform excitation and traveling wave effect were studied. Results are shown as follows: Under seismic action, rail longitudinal forces near beam joints increase greatly than rail expansion forces (due to beam expansion); Designing CWR on bridges with high-piers and long-spans needs to consider influences of traveling wave effect and wave spreading derection; With the increase of the apparent velocity of seismic waves, rail longitudinal force tends to decrease; We suggest that designing of CWR on bridges crossing high-intensity earthquake zone should consider impact of seismic action, and establish a reasonable check method.

The rotational seismic inputs for building design were discussed. The free ground rotations and the relation between free ground rotations and basement rotations were derived. The results show that the relation depends on the basement size, site and seismic frequency. For most building, the differences between the free ground rotations and the basement rotations are small. The suggestion is that for tall buildings the free ground rotations can be taken as the seismic input, but for low-rise building with large basement, the response spectra in short period region should be reduced.

Engineering seismic exploration aims at shallow imaging which is confused by statics if the surface is uneven. Direct pre-stack depth migration (DPDM) is based on accurate elevations of sources and receivers, by which static correction is completely abandoned before migration and surely the imaging quality is remarkably improved. To obtain some artificial shot gathers, high-order staggered-grid finite-difference (FD) method is adapted to model acoustic wave propagation. Since the shot gathers are always disturbed by regular interferences, the statics still must be applied to supporting the interference elimination by apparent velocity filtering method. Then all the shot gathers should be removed back to their original positions by reverse statics. Finally, they are migrated by pre-stack reverse-time depth migration and imaged. The numerical experiments show that the DPDM can ideally avoid the mistakes caused by statics and increase imaging precision.

In order to determine the calculational model of long span transmission tower structure under the multiple support excitation, tower-lines system are adopted. Seismic Performance of long span transmission tower lines system under Multiple Support Excitation were studied by time history analysis method. The seismic response difference of two kinds of excitation is analyzed from Dynamic Characteristics and the number of dangerous bar. It will offer the theory data for the seismic design of the kind of structure. Through analysis, the seismic response difference of the two kinds excitation is correlative to the apparent velocity; Therefore long span transmission tower structure should be considered the effect of multiple support excitation, otherwise the conclusion will be inclined to conservative or risk. Key words: tower lines system; seismic response; time history analysis,multiple support excitation

Direct observation of light in flight is enabled by recent avalanche photodiode arrays, which have the capability for time-correlated single photon counting. In contrast to classical imaging, imaging of light in flight depends on the relative sensor position, which is studied in detail by measurement and analysis of light pulses propagating at different angles. The time differences of arrival are analyzed to determine the propagation angle and distance of arbitrary light paths. Further analysis of the apparent velocity shows that light pulses can appear to travel at superluminal or subluminal apparent velocities.

Analysis of conventional wing dynamics exhibits limits imposed by physical laws which cannot be fully compensated by wing profile optimization nor by artificial flow lines modification. A different alternative is proposed by modifying drastically wing shape into a tubular one. It is shown here that such wings take advantage of their geometry allowing an enhanced new lifting effect produced by the apparent velocity due to the combination of their velocity with a rotation around their symmetry axis. At the same time this rotation generates a gyroscopic stabilization of the wing around its symmetry axis during its trajectory which can be more easily controlled for a large range value of angle of attack. In particular there results a much larger value of stall angle. These theoretical results have been verified by preliminary observations on a small size 3D printed model.

We present a method of separation of P- and S-wave components from three-component (3C) crosswell seismic data. Based on differences between P and S waves in polarization and apparent velocity, this method separates P and S waves in a common source gather without estimating emergence angles and by means of data processing techniques including band-pass filter for preprocessing, high-resolution τ–p transform for removing tube waves and separating up-going and down-going waves, and covariance polarization analysis for correcting the direction of geophone and separating polarization. To separate P- and S-wave data, this method requires only the input of original 3C crosswell data and the first arrivals of P waves. We verify and demonstrate effectiveness and practicability of this method using 2C modeling tests as well as real 3C crosswell data.

This paper presents that the cross-correlation method is used for estimating the direction of wavefront propagation and the apparent velocity for seismic signals in the small-size dense seismic array. The near earthquake signals samples adopted from US Geological Survey Parkfield Dense Seismograph Array (UPSAR array) of the U.S are used for analyzing. The results analyzed indicate that the wavefront propagation and the apparent velocity of near earthquake signals can be succinctly and accurately estimated by the method proposed in this paper.

Acoustic emission (AE) technique, as an effective method to monitor the crack characterization in concrete materials is investigated in this paper. An improved approach, based on the Akaike Information Criterion (AIC), is proposed to provide more reliable onset time determination of AE signals. The introduced parameters, quantification of the certainty degree and the apparent velocity in the improved method can help to eliminate the false or doubtful picked onset results automatically. The improved AIC method is successfully applied to the AE detection during a three-point bending test of a fiber reinforced concrete beam to analyze the crack pattern. It is shown that the proposed method is a reliable tool for automatic onset time determination and useful for the crack source location in concrete structures.

The effects that the two Kuril undersea earthquakes of November 15, 2006, and January 13, 2007, had on the ionosphere are considered on the basis of the results of measurements of variations in the ionosphere’s total electron content obtained from the network of Russian GPS stations. Owing to a favorable location of the stations, the ionosphere’s response to these earthquakes is studied in the vicinity of and far (up to distances on the order of 1000 km) from their epicenters. It is found that the apparent velocity of propagation of ionospheric disturbances (1–3 km/s) significantly exceeds the velocity of propagation of tsunami waves caused by earthquakes; this fact can be used in forecasting tsunamis. It is shown that, in parallel with the known type of ionospheric response to earthquakes in the form of an N-wave, there is also its response in the form of an inverted N-wave in the vicinity of and far from their epicenters. The causes of occurrence of the response in the form of an inverted N-wave are interpreted.

Risk assessment of snow avalanches is mostly related to weather conditions and snow cover. However, a robust risk validation requires avalanche activity data, in order to compare predictions to actual events. For this purpose in December 2009 we installed a temporary 4-element, small aperture (150 m), infrasound array in the northwestern Italian Alps. The array was installed south of Mt. Rosa, at an elevation of 2000 m a.s.l. in the valley of Gressoney, Italy, where natural avalanches are expected and avalanche control by explosives is regularly performed. A multi-channel correlation analysis is carried out on the continuous infrasound data set recorded by the array as a function of apparent velocity, back-azimuth and frequency of recorded infrasound. This allowed detectionof infrasonic signals propagating across the array from the background noise. During the 5-month-long experiment, 343 infrasonic events have been detected and characterized. These include sharp infrasonic transients (99 events) produced by explosions during avalanche control as well as longer lasting signals (244 events) possibly caused by avalanches. Although only few of these events were validated by direct avalanche observation, obtained results are promising and encouraging application of infrasound for long-term avalanche observation on wide areas, as the peak in avalanche activity in winter 2009–2010 was observed shortly after the infrasound events peaked as well.

The apparent velocity of the incident wave is an important parameter for simulating rotational ground motion with theoretical methods, but it is difficult to estimate effectively when there is only a single record. This paper discusses a P-SV ratio method based on elastodynamic theory in a multi-layer isotropic elastic half space. The apparent velocities of four earthquakes in the SMART1 array are calculated with this method. The result is close to a method that uses travel time analysis. Furthermore, the factors that impact the apparent velocity and equivalent incident angle are considered according to records from the Chi-Chi earthquake. There is no obvious relationship between the equivalent incident angle and epicenter distance. However, the equivalent incident angle is obviously dependent on the site conditions.

A practical method, based on the Akaike Information Criterion (AIC), is used to detect automatically the first P-wave arrival times during Acoustic Emissions (AE) monitoring. This method is used to increase the accuracy of detection procedure and to reject the data errors automatically. Two parameters, the quantification of the degree of certainty and the apparent velocity between observation sensors, were proposed to check the validity of AE events and to neglect errors. Both the original AIC-picker and improved AIC-picker algorithms are applied to AE signal processing. It can be shown that the improved AIC-picker is a reliable tool for automatic onset detection of AE signals.

The bottom tracking (BT) feature of the acoustic Doppler current profilers (ADCP) have emerged as a promising technique in evaluating the bed load. Strong statistical correlations are reported between the ADCP BT velocity and the transport rate obtained by physical sampling or dune tracking; however, these relations are strictly site-specific and a local calibration is necessary. The direct physical sampling is very labor intensive and it is prone to high instrument uncertainty. The aim of this work is to develop a methodology for evaluating the bed load transport using commercial ADCPs without calibration with physical samples. Relatively long stationary measurements were performed in a sand-bed and sand gravel rivers, using three different ADCPs working at 3MHz, 1.2MHz and 0.6MHz. Simultaneously, bed load samples were collected with physical samplers, and the riverbed was closely observed with digital cameras mounted on the samplers. It is demonstrated that the kinematic transport model can yield a relatively good estimate of the transport rate by directly using filtered apparent velocity, the knowledge of the hydraulic conditions and instrument-related calibration coefficients. Additionally, the ADCP data can help in qualitative assessment of the physical sampling. Future investigation of the backscattering echo and further confirmation of the BT apparent velocity should be performed in laboratory-controlled conditions. © The Authors, published by EDP Sciences, 2018. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (http://creativecommons.org/licenses/by/4.0/).

シールドトンネルなど地下構造物の縦断方向の耐震検討では，構造物に沿った地震波のみかけの伝播速度の評価が重要である．既往の研究では表面波の位相速度を利用することで安全側の評価を行う方法などが提案されているが，地盤の軸ひずみに関して実状に即した評価を行うことを目的とする場合に，みかけの伝播速度としてどの程度の値を用いるべきであるかについては，これまで十分な検討が行われてこなかった．そこで，本研究では，M5.3～M8.0の13の地震に対するシールドトンネルにおける地震観測結果，および，セグメントリング間の相対変位の計測結果に基づき，地震波の見かけの伝播速度に関する検討を行い，見かけ入射角依存性など，見かけの伝播速度に関するいくつかの特徴を明らかにした．

We use relative arrival times and locations for similar earthquake pairs that are found using a cross-correlation method to analyze the time dependence of P and S station terms in southern California from 1984 to 2002. We examine 494 similar event clusters recorded by Southern California Seismic Network (SCSN) stations and compute absolute arrival-time variations from the differential arrival-time resi- duals obtained following event relocation. We compute station terms from the robust means of the absolute arrival-time residuals from all events recorded by each station at 3-month intervals. We observe nine stations with abrupt offsets in timing of 20- 70 msec, which are likely caused by equipment changes during our study period. Taking these changes into account could improve the relative location accuracy for some of the event clusters. For other stations, we generally do not see systematic temporal variations greater than about 10 msec. Analysis of residuals along individual ray paths does not reveal any clear localized regions of apparent velocity changes at depth. These results limit large-scale, long-lasting temporal variations in P and S ve- locities across southern California during this time period to less than about � 0:2%. However, there is an increased fraction of individual travel-time residuals exceeding 20 msec immediately following major earthquakes from source regions near the main- shock rupture.

Detection of peristalsis in the human small intestine has been limited in the past by both the available measurement techniques and the complexity of this activity. Recent developments in ambulant recording have provided a means of monitoring the occurrence of intestinal contractions at multiple sites in the small bowel, but the problem of complexity remains. Using digital data recorded from an intra-luminal strain-gauge transducer in the proximal gut, an algorithm was implemented to identify and classify contractile events within the small bowel. By modelling propagated activity the effect of varying transducer spacing and the number of transducers used was assessed. The question of variability of apparent velocity of peristaltic contractions was examined using successive cross-correlation calculations to extract underlying phase differences between samples of 512 minutes of manometric recording over 150 mm of human small bowel. The effective velocity was found to have a median value of 14 mm sec-1 and an inter quartile range of 12–18 mm see-1). It is proposed that, in dynamically tracking variations in phase difference between adjacent recording sites, cross-correlation techniques should be used to control the parameters used for the recognition of propagated contractile events and thereby improve the specificity of this process.

Previous psychophysical experiments have demonstrated that various factors can exert a considerable influence on the apparent velocity of visual stimuli. Here, we investigated the effects of superimposing static luminance texture on the apparent speed of a drifting grating. In Experiment 1, we demonstrate that superimposing static luminance texture on a drifting luminance modulated grating can produce an increase in perceived speed. This supports the hypothesis that texture changes perceived speed by providing landmarks to assess relative motion. In Experiment 2, we showed that contrary to static luminance texture, dynamic luminance texture did not increase perceived speed. This demonstrates that texture must provide reliable spatial landmarks in order to generate an increase in perceived speed. The results of Experiment 3 demonstrate that perceived speed depends on the size of the area covered by texture. This suggests that luminance texture and the motion stimulus interacted with each other over a limited spatial scale and that these local responses are then pooled to determine the speed of the motion stimulus. In Experiment 4, we showed that static texture contrast could produce a greater effect than motion stimulus contrast on perceived speed and that these effects could still be observed at brief presentation times. We discuss these findings in the context of models proposed to account for phenomena in the perception of speed.

In this paper we have derived reflection and transmission coefficients of qP-waves at a corrugated interface between two different elastic half-spaces of monoclinic type. Using Rayleigh’s method, the expressions for reflection and transmission coefficients are derived in closed form for a specific interface and for the first order approximation of the corrugation. Numerical computations are performed for a specific model and the results obtained have been shown graphically. The variation of the modulus of reflection and transmission coefficients with the angle of incidence, frequency and corrugation of the interface are shown separately. These coefficients are found to be strongly influenced by the angle of incidence, frequency, elastic parameters and amplitude of the corrugation of the interface. It is found that (i) the modulus of reflection and transmission coefficients at the plane interface are independent of corrugation of the interface and that of frequency of the incident wave, (ii) the reflection and transmission coefficients of regularly reflected and transmitted waves are found to be greater than that of irregularly reflected and transmitted waves, (iii) the coefficients of irregularly reflected and transmitted waves are found to increase and decrease with increase of corrugation and frequency parameters respectively. The results of Singh and Khurana [Singh, S.J., Khurana, S., 2001. Reflection and transmission of P- and SV-waves at the interface two between monoclinic elastic half-spaces. Proc. Natl. Acad. Sci. India 71(A) (IV), 305–319] have been reduced from the present problem.

Avalanche risk management is strongly related to the ability to identify and timely report the occurrence of snow avalanches. Infrasound has been applied to avalanche research and monitoring for the last 20 years but it never turned into an operational tool to identify clear signals related to avalanches. We present here a method based on the analysis of infrasound signals recorded by a small aperture array in Ischgl (Austria), which provides a significant improvement to overcome this limit. The method is based on array-derived wave parameters, such as back azimuth and apparent velocity. The method defines threshold criteria for automatic avalanche identification by considering avalanches as a moving source of infrasound. We validate the efficiency of the automatic infrasound detection with continuous observations with Doppler radar and we show how the velocity of a snow avalanche in any given path around the array can be efficiently derived. Our results indicate that a proper infrasound array analysis allows a robust, real-time, remote detection of snow avalanches that is able to provide the number and the time of occurrence of snow avalanches occurring all around the array, which represent key information for a proper validation of avalanche forecast models and risk management in a given area.

Using a short-baseline seismic array (U.S. Geological Survey Parkfield Dense Seismograph Array [upsar]) about 12 km west of the rupture initiation of the 28 September 2004 M 6.0 Parkfield, California, earthquake, we have observed the movement of the rupture front of this earthquake on the San Andreas fault. The sources of high-frequency arrivals at upsar, which we use to identify the rupture front, are mapped onto the San Andreas fault using their apparent velocity and back azimuth. Measurements of apparent velocity and back azimuth are calibrated using aftershocks, which have a compact source and known location. Aftershock back azimuths show considerable lateral refraction, consistent with a high-velocity ridge on the southwest side of the fault. We infer that the initial mainshock rupture velocity was approximately the Rayleigh speed (with respect to slower side of the fault), and the rupture then slowed to about 0.66 β near the town of Parkfield after 2 sec. The last well-correlated pulse, 4 sec after S, is the largest at upsar, and its source is near the region of large accelerations recorded by strong-motion accelerographs and close to northern extent of continuous surface fractures on the southwest fracture zone. Coincidence of sources with preshock and aftershock distributions suggests fault material properties control rupture behavior. High-frequency sources approximately correlate with the edges of asperities identified as regions of high slip derived from inversion of strong-motion waveforms.

We analyze a long time–space series of Stromboli volcanic tremors. A very-low-frequency content in the range of 0.02–0.5 Hz has been found by using spectral analysis and independent component analysis. Independent component analysis is an entropy-based technique. We observe the occurrence of a component having a period of 30 sec. Polarization analysis shows that the wave field comes mainly from the crater area, well evidenced by seismometers located around the summit ring, whereas the radiation becomes increasingly scattered at stations located around the base of this volcano. Based on its apparent velocity, the 30-sec component appears to be a slow wave, related to inhomogeneities of the source and/or gas-pressure fluctuations inside the shallow plumbing system.

Seismological monitoring of the Comprehensive Test Ban Treaty (CTBT) requires detailed knowledge of travel-time characteristics of seismic phases across large areas. We use first-arrival travel times from several of Russian Deep Seismic Sounding (dss) profiles, primarily those from Peaceful Nuclear Explosions (pnes), to construct a 3D regional travel-time model of northern Eurasia. The method used, which can be viewed as a generalization of the existing regionalization techniques, is based on apparent-velocity-based spatial interpolation of the travel times picked from dss records. The resulting travel-time field is described in terms of an apparent velocity model in the 3D space of geographic coordinates and ray parameter. In the travel-time calibration, this model could be used to construct approximate source-specific station correction surfaces for any location within the region and also as a region-specific reference model to be used as a background for further calibration effort. This approach allows incremental refinement of the model as additional travel-time data become available. By converting the travel-time model into depth, a 3D regional velocity model is obtained, providing a description of the general features of the upper mantle in northern Eurasia.

The apparent velocity of a filmed person, walking in front of static or moving backgrounds, was estimated in 2 experiments by 18 observers. The camera either followed the walker or remained at the same position (= stabilized vs. mobile observer perspective). A factorial ANOVA was used with the estimate of the walker’s velocity (in km/h) as dependent variable. Based on the number of applicable motion cues and on the role of motion parallax, it was predicted that the mobile observer perspective should lead to a higher estimate of the walker’s velocity. In both experiments, the opposite of this prediction was observed: Stabilized observer perspective produced consistently higher velocity estimates as a main effect and in interaction with the background variables. No velocity increasing effect of motion parallax was found in stabilized observer perspective, presumably because of the ambiguity of motion cues with respect to background distance.

Neurons in the accessory optic system (AOS) and pretectum are involved in the analysis of optic flow and the generation of the optokinetic response. Previous studies found that neurons in the pretectum and AOS exhibit direction selectivity in response to large-field motion and are tuned in the spatiotemporal domain. Furthermore, it has been emphasized that pretectal and AOS neurons are tuned to a particular temporal frequency, consistent with the “correlation” model of motion detection. We examined the responses of neurons in the nucleus of the basal optic root (nBOR) of the AOS in pigeons to large-field drifting sine wave gratings of varying spatial (SF) and temporal frequencies (TF). nBOR neurons clustered into two categories: “Fast” neurons preferred low SFs and high TFs, and “Slow” neurons preferred high SFs and low TFs. The fast neurons were tuned for TF, but the slow nBOR neurons had spatiotemporally oriented peaks that suggested velocity tuning (TF/SF). However, the peak response was not independent of SF; thus we refer to the tuning as “apparent velocity tuning” or “velocity-like tuning.” Some neurons showed peaks in both the fast and slow regions. These neurons were TF-tuned at low SFs, and showed velocity-like tuning at high SFs. We used computer simulations of the response of an elaborated Reichardt detector to show that both the TF-tuning and velocity-like tuning shown by the fast and slow neurons, respectively, may be explained by modified versions of the correlation model of motion detection.

The interaction between domain walls and pinning centers in ferroelectrics is of great interest from both fundamental and practical points of view. In this work, we show that, counter to intuition, the apparent velocity of domain walls can increase as the defect density increases. However, when we closely investigate the propagating front of the domain wall, we find that it is not unified but can be rough, indicating the presence of multiple nucleated domains in advance of the primary wall. We therefore ascribe the increased apparent velocity with defect density to actually derive from nucleation-aided motion. To further investigate the effect of engineered pinning centers, we spatially confined the defect regions and then propagated domain walls in that direction. We found that, given a sufficiently high defect density, walls can be pinned indefinitely at sub-threshold voltages. Finally, we outline a method to create domain wall propagation channels in which the wall is confined to a low defect region bo...

Distribution of seismic events in rocks mass around a mineral deposit is studied, it is found that the distribution features conform with the local blasting operations and geology. Epicenters of concentration zones of seismic events are detected in the area of stoping and faulting between two ore locuses. Weakening planes generated under four chronologically ordered shocks are indentified. Occurrence of these planes is characterized, and the stress redistribution after blasting is analyzed. The authors apply an integrated approach to rockburst hazard prediction, including calculus of apparent velocity of migration of seismic events during the first ten minutes after a blast and the rockburst probability assessment.

We present three high resolution radio images of the Crab nebula, taken in 1998.6, 1998.8 and 2000.1 with the VLA. These are the best radio images of the Crab to date. We show that, near the pulsar, there are significant changes between our three observing epochs. These changes have an elliptical geometry very similar to that of the optical wisps. One radio wisp in particular can be unambiguously identified between two of our observing epochs, and moves outward with an apparent velocity of ~0.24. The similarity in both morphology and behavior of the present radio wisps to the optical wisps suggests that they are associated. This implies that the radio wisps, like the optical ones, are likely manifestations of the shock in the Crab pulsar's wind. This suggests that the radio emitting electrons are accelerated in the same region as the ones responsible for the optical to X-ray emission, contrary to most current models., Comment: 12 pages, 5 figures (6 figure files), LaTeX, accepted for publication in the Astrophysical Journal

Several types of electrical events occur in the small intestine but their spatial and temporal contributions to overall motility are not clear. In order to quantify local motility in greater detail, a new technique of recording and analysing movements at multiple sites was developed. Use was made of isolated segments of feline duodenum superfused in a tissue bath. Multiple marker dots (20-75) were placed on the serosal surface by applying fine spots of candle soot in rectangular arrays (1-2 mm dot separation). A digital video camera was used to record spontaneous movements of the dots for periods of 10-30 min. After each experiment, 4-6 periods (10-60 s each) of video frames were transferred to a computer (25 fps, 720 x 576 pixels) and the movements of the dots was tracked every 40 ms using custom-made software. Initial results (eight experiments) show that spontaneous motility is remarkably variable, both in space and time. Three types of movement could be discerned: (i) periodic, rolling or pendular movements, with a frequency of approximately 15 min-1 occurring predominantly in the longitudinal direction; (ii) twitches, wherein a subset of dots were suddenly displaced longitudinally; and (iii) drifts of most of the dots in a circular or oblique direction. All three types of movement occurred throughout every recording session although their relative magnitudes differed greatly from moment to moment. Occasionally, it was possible to detect propagated 'contractions' with an apparent velocity of 10 mm s(-1). Immobilizing the preparation at one point by inserting a needle through the middle of the array of markers had a negligible effect on the displacements, whereas application of verapamil (10(-5) mol L(-1)) reduced or abolished motility. In summary, we present a new technique to map in detail two-dimensional motility at the surface of the intestine. Initial results seem to suggest that motility at the serosal surface is not uniform and highly anisotropic.

We develop a real time monitoring system for evaluating both frequency of posture change and respiration rate without any contact to the subject. This system detects the optical flow (apparent velocity) using a temporal-spatial local optimization method to evaluate the subject motion on a bed. The system consists of a CCD video camera, a parallel image processing board and a PC. The parallel image processing board includes 256 CPUs that calculates the optical flow of the whole image (256 × 240 pixels) within 150ms. Healthy young volunteers were participated to evaluate the system. We propose a function that includes information of respiration and body movement from the detected optical flows on the blanket area of breast. The periodic fluctuation synchronizes with the volunteer's respiration. The large peaks occur during volunteer's posture change.

Through-air dryers are widely used for drying unbacked tufted carpets after dyeing- steaming-washing processes. Since the drying rate depends greatly on air velocity, carpet air permeability is a very important parameter affecting drying time. We study the effects of several carpet construction and process parameters on the air permeability of unbacked cut-pile nylon carpets with woven polypropylene primary backing using a modified Frazier air permeability tester and a laboratory through-air dryer. We then present a model predicting pressure drop over the carpets versus apparent velocity.

This paper presents a framework for predicting embryo survival in salmonid spawning gravels as a function of sediment deposition. This framework integrates three quantitative relationships modeling the variations of substrate permeability with sediment deposition, apparent velocity with substrate permeability, and embryo survival rate with apparent velocity. The model allows evaluation of the impacts of sediment deposition on embryo survival. The relative sensitivity of embryo survival to three selected environmental factors is investigated. The model results indicate that embryo survival is most sensitive to the composition of fine sediments (or sediment-gravel size ratio). The maximum influences of the hydraulic pressure head and the length of intragravel flow path are ;60 and 35% of the value influenced by size ratio. The proposed model is applied to determine the timing of flushing flows. The results suggest that the interval between flushing flows should be reduced when higher levels of embryo survival are prescribed or higher near-bed sediment concentrations are imposed.

We present here two epochs of Space VLBI Observations at 18 cm of the BL-Lac type object Mkn 501. Thanks to the high resolution of these new data we have found that the inner jet is centrally brightened at its beginning but becomes extended and limb brightened at ∼ 8 mas from the core. Moreover a comparison between the two epochs shows the presence of a proper motion with apparent velocity = 6.7c. Observational data have been used to constrain the jet velocity and orientation.