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1
Deconto-Machado, A., R. A. Riffel, G. S. Ilha, S. B. Rembold, T. Storchi-Bergmann, R. Riffel, J. S. Schimoia, et al. "Ionised gas kinematics in MaNGA AGN." Astronomy & Astrophysics 659 (March 2022): A131. http://dx.doi.org/10.1051/0004-6361/202140613.
Повний текст джерелаАнотація:
Context. Feedback from active galactic nuclei (AGNs) in general seems to play an important role in the evolution of galaxies, although the impact of AGN winds on their host galaxies is still unknown in the absence of a detailed analysis. Aims. We aim to analyse the kinematics of a sample of 170 AGN host galaxies as compared to those of a matched control sample of non-active galaxies from the MaNGA survey in order to characterise and estimate the extents of the narrow-line region (NLR) and of the kinematically disturbed region (KDR) by the AGN. Methods. We defined the observed NLR radius (rNLR, o) as the farthest distance from the nucleus within which both [O III]/Hβ and [N II]/Hα ratios fall in the AGN region of the BPT diagram, and the Hα equivalent width was required to be larger than 3.0 Å. The extent of the KDR (rKDR, o) is defined as the distance from the nucleus within which the AGN host galaxies show a more disturbed gas kinematics than the control galaxies. Results. The AGN [O III]λ5007 luminosity ranges from 1039 to 1041 erg s−1, and the kinematics derived from the [O III] line profiles reveal that, on average, the most luminous AGNs (L[O III] > 3.8 × 1040 erg s−1) possess higher residual differences between the gaseous and stellar velocities and velocitie dispersions than their control galaxies in all the radial bins. Spatially resolved NLRs and KDRs were found in 55 and 46 AGN host galaxies, with corrected radii 0.2 < rKDR, c < 2.3 kpc and 0.4 < rNLR, c < 10.1 kpc and a relation between the two given by log rKDR, c = (0.53 ± 0.12) log rNLR, c + (1.07 ± 0.22), respectively. On average, the extension of the KDR corresponds to about 30% of that of the NLR. Assuming that the KDR is due to an AGN outflow, we have estimated ionised gas mass outflow rates that range between 10−5 and ∼1 M⊙ yr−1, and kinetic powers that range from 1034 to 1040 erg s−1. Conclusions. Comparing the power of the AGN ionised outflows with the AGN luminosities, they are always below the 0.05 LAGN model threshold for having an important feedback effect on their respective host galaxies. The mass outflow rates (and power) of our AGN sample correlate with their luminosities, populating the lowest AGN luminosity range of the correlations previously found for more powerful sources.
2
Walker, G. A. H., J. Amor, S. Yang, and B. Campbell. "Precise Radial Velocities and Radial Velocity Standards." Symposium - International Astronomical Union 111 (1985): 587–89. http://dx.doi.org/10.1017/s0074180900079547.
Повний текст джерелаАнотація:
By imposing absorption lines of HF in stellar spectra we can measure changes in r.v. with a precision of ~10m/s from a single spectrum, provided stellar line profiles are not distorted by atmospheric motions. The precision of absolute radial velocities is currently limited to ~100m/s by knowledge of rest wavelengths. Representative results are presented from our three, active PRV programs: velocity variations of δ Scuti stars; a search for unseen companions to late-type stars; and routine observations of certain IAU velocity ‘standards’.
3
Ehlen, Georg J., Hai Feng Wang, and Dieter M. Herlach. "Concentration Dependent Growth Velocities in Undercooled Al-Rich Al-Ni Alloy Systems." Materials Science Forum 790-791 (May 2014): 485–90. http://dx.doi.org/10.4028/www.scientific.net/msf.790-791.485.
Повний текст джерелаАнотація:
Dendrite growth velocity V as a function of undercooling on the Al-rich side of the Al-Ni system has recently been measured by electromagnetic levitation. The results have shown an anomalous behaviour, which so far cannot be theoretically described. The present work uses two simplified qualitative models of sharp interface theory, one of them treating the forming AlNi (B2) phase as a solid-solution, one treating it as an intermetallic phase, to investigate the influence of the phase diagram on the growth velocities. The results imply that the concentration dependent growth behaviour is a superposition of at least two effects: 1) A strong decrease of the total growth velocitiy level for increasing Al concentrations. 2) An increase of growth velocities with increase of Al concentration at medium and low undercoolings. The present work is able to explain the first effect, namely the concentration dependent reduction of velocities. Results are compared to experimental data. In both models the properties of the phase diagram lead to an increase of the constitutional undercooling ΔTc when the Al content increases. This reduces the fraction left for kinetic undercooling ΔTk, which is responsible for interface migration and which determines the growth velocity. Neither of the models can reproduce the second effect.
4
Maybank, SJ. "Rigid velocities compatible with five image velocity vectors." Image and Vision Computing 8, no. 1 (February 1990): 18–23. http://dx.doi.org/10.1016/0262-8856(90)90051-6.
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Toldi, John L. "Velocity analysis without picking." GEOPHYSICS 54, no. 2 (February 1989): 191–99. http://dx.doi.org/10.1190/1.1442643.
Повний текст джерелаАнотація:
Conventionally, interval velocities are derived from picked stacking velocities. The velocity‐analysis algorithm proposed in this paper is also based on stacking velocities; however, it eliminates the conventional picking stage by always considering stacking velocities from the point of view of an interval‐velocity model. This view leads to a model‐based, automatic velocity‐analysis algorithm. The algorithm seeks to find an interval‐velocity model such that the stacking velocities calculated from that model give the most powerful stack. An additional penalty is incurred for models that differ in smoothness from an initial interval‐velocity model. The search for the best model is conducted by means of a conjugate‐gradient method. The connection between the interval‐velocity model and the stacking velocities plays an important role in the algorithm proposed in this paper. In the simplest case, stacking velocity is assumed to be equal to rms velocity. For the more general case, a linear theory is developed, connecting interval velocity and stacking velocity through the intermediary of traveltime. When applied to a field data set, the method produces an interval‐velocity model that explains the lateral variation in both stacking velocity and traveltime.
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Wendt, Anke S., Monzurul Alam, and Joao Paulo Castagnoli. "Sand injectite mapping using a resistivity-velocity transform function." Leading Edge 40, no. 3 (March 2021): 202–7. http://dx.doi.org/10.1190/tle40030202.1.
Повний текст джерелаАнотація:
Lack of resolution in the distribution of sand injectites in hydrocarbon fields is common and makes it difficult to predict drilling challenges and plan for optimum production. A practical workflow was developed that enables the distinction of shale and sand bodies by using a combination of low-resolution seismic data and high-resolution resistivity log data. Measured resistivity logs were used to predict synthetic velocity logs, which accurately match shale velocities and over- or underestimate velocities of other rock types. The synthetic velocity logs were spatially distributed in a 3D cube in order to predict synthetic velocities in between and away from the well locations. The 3D cube was representative of a field. It covered the interval from the seabed to below the reservoir. The spatial distribution was based on a geostatistical approach guided by measured seismic interval velocities. A residual velocity cube was calculated from the measured and synthetic velocities. The residual velocity cube produced near-zero velocities for shaly materials and velocity over- or underestimates for other rock types. Interpretation of the residual velocity cube required the identification of strong stratigraphic markers. The markers were removed from the residual cube by setting their specific layer velocities to 0 m/s. The final information stored in the residual velocity cube was then related to the over- or underestimated velocities in sand bodies.
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Du, Xue Jing, and Jin Peng Li. "Simulation of Pedestrian Colliding with Microbus Windshield." Key Engineering Materials 572 (September 2013): 574–77. http://dx.doi.org/10.4028/www.scientific.net/kem.572.574.
Повний текст джерелаАнотація:
In order to research the injury of pedestrian collided with microbus windshield, the finite element model of pedestrian and windshield are established based on the characteristics of pedestrian collision with microbus windshield in traffic accident to simulate the collision process by ANSYS/LS-DYNA. In the condition of different impact velocities, HIC, TTI and stress intensity of pedestrian are studied in simulation test. The results illustrate that with the impact velocitys increasing the original impact energy, stress intensity, acceleration, HIC, and TTI increase. Also, the collision time is prolonged. Collision in head, the head of pedestrian would suffer serious injury with more than 29 km/h impact velocity. The chest would suffer serious injury with more than 25 km/h impact velocity in condition of colliding on chest.
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Herman, Przemyslaw, and Krzysztof Kozlowski. "Velocity tracking control algorithm in terms of quasi-velocities." IFAC Proceedings Volumes 42, no. 13 (2009): 599–604. http://dx.doi.org/10.3182/20090819-3-pl-3002.00104.
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Cox, B. E., P. L. A. Winthaegen, D. J. Verschuur, and K. Roy-Chowdhury. "Common focus point velocity estimation for laterally varying velocities." First Break 19, no. 2 (February 2001): 75–83. http://dx.doi.org/10.1046/j.0263-5046.2001.00140.x.
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Blias, Emil. "Stacking velocities in the presence of overburden velocity anomalies." Geophysical Prospecting 57, no. 3 (May 2009): 323–41. http://dx.doi.org/10.1111/j.1365-2478.2008.00750.x.
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Kumaran, V., and Donald L. Koch. "Properties of a bidisperse particle–gas suspension Part 2. Viscous relaxation time small compared with collision time." Journal of Fluid Mechanics 247 (February 1993): 643–60. http://dx.doi.org/10.1017/s0022112093000606.
Повний текст джерелаАнотація:
The properties of a dilute bidisperse particle–gas suspension under low Reynolds number, high Stokes number conditions are studied in the limit τv [Lt ] τc, where τc is the time between successive collisions of a particle, and τv is the viscous relaxation time. In this limit, the particles relax close to their terminal velocity between successive collisions, and we use a perturbation analysis in the small parameter ε, which is proportional to τv/τc, about a base state in which all the particles settle at their terminal velocities. The mean velocities of the two species are O(ε) different from their terminal velocities, and the mean-square velocities are O(ε) smaller than the square of the terminal velocity. The distribution functions for the two species, which incorporate the first effects of collisions between particles settling at their terminal velocities, are derived. The velocity distribution is highly anisotropic in this limit, and the mean-square velocity in the vertical direction is twice that in the horizontal plane. The distribution function for each species is singular at its terminal velocity, and the distributions are non-zero in a finite region in velocity space between the two terminal velocities.
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Molyneux, Joseph B., and Douglas R. Schmitt. "Compressional‐wave velocities in attenuating media: A laboratory physical model study." GEOPHYSICS 65, no. 4 (July 2000): 1162–67. http://dx.doi.org/10.1190/1.1444809.
Повний текст джерелаАнотація:
Elastic‐wave velocities are often determined by picking the time of a certain feature of a propagating pulse, such as the first amplitude maximum. However, attenuation and dispersion conspire to change the shape of a propagating wave, making determination of a physically meaningful velocity problematic. As a consequence, the velocities so determined are not necessarily representative of the material’s intrinsic wave phase and group velocities. These phase and group velocities are found experimentally in a highly attenuating medium consisting of glycerol‐saturated, unconsolidated, random packs of glass beads and quartz sand. Our results show that the quality factor Q varies between 2 and 6 over the useful frequency band in these experiments from ∼200 to 600 kHz. The fundamental velocities are compared to more common and simple velocity estimates. In general, the simpler methods estimate the group velocity at the predominant frequency with a 3% discrepancy but are in poor agreement with the corresponding phase velocity. Wave velocities determined from the time at which the pulse is first detected (signal velocity) differ from the predominant group velocity by up to 12%. At best, the onset wave velocity arguably provides a lower bound for the high‐frequency limit of the phase velocity in a material where wave velocity increases with frequency. Each method of time picking, however, is self‐consistent, as indicated by the high quality of linear regressions of observed arrival times versus propagation distance.
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Comas-Rodríguez, Isis, Alonso Hernández-Guerra, and Elaine L. McDonagh. "Referencing geostrophic velocities using ADCP data Referencing geostrophic velocities using ADCP data." Scientia Marina 74, no. 2 (March 16, 2010): 331–38. http://dx.doi.org/10.3989/scimar.2010.74n2331.
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Zhu, Jinming, Larry Lines, and Sam Gray. "Smiles and frowns in migration/velocity analysis." GEOPHYSICS 63, no. 4 (July 1998): 1200–1209. http://dx.doi.org/10.1190/1.1444420.
Повний текст джерелаАнотація:
Reliable seismic depth migrations require an accurate input velocity model. Inaccurate velocity estimates will distort point diffractors into smiles or frowns on a depth section. For both poststack and prestack migrated sections, high velocities cause deep smiles while low velocities cause shallow frowns on migrated gathers. However, for prestack images in the offset domain, high velocities cause deep frowns while low velocities cause shallow smiles. If the velocity is correct, there will be no variation in the depth migration as a function of offset and no smiles or frowns in the offset domain. We explain migration responses both mathematically and graphically and thereby provide the basis for depth migration velocity analysis.
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Bajewski, Łukasz, Aleksander Wilk, and Andrzej Urbaniec. "Porównanie modeli prędkości obliczonych z wykorzystaniem różnych wariantów prędkości i algorytmów na profilu sejsmicznym 2D na potrzeby migracji czasowej po składaniu." Nafta-Gaz 77, no. 7 (July 2021): 419–28. http://dx.doi.org/10.18668/ng.2021.07.01.
Повний текст джерелаАнотація:
This article presents a construction method of the velocity field for poststack time migration for 2D seismic calculated on the basis of interval velocities in boreholes and structural interpretation, as well as the results of poststack time migration based on this solution. Three velocity field models have been developed. The models used differ in the way of spatial interpolation and extrapolation in the adopted calculation grid in the depth domain, which was created on the basis of a structural interpretation of 2D seismic profiles. Three methods of interpolation and extrapolation were used: Gaussian distribution, kriging and moving average. The spatial distribution of the interval velocities in the boreholes was made using the Petrel software by Schlumberger. The interval velocities along the analyzed seismic profile were extracted from the computed spatial interval velocity models, and after conversion from the depth to the time domain, they were used for the poststack time migration. For comparison, poststack time migration was calculated for the same seismic profile based on the stacking velocities obtained in the seismic processing data as a result of velocity analyzes. The velocity field calculated on the basis of interval velocities and structural interpretation was used for the poststack time migration procedure performed with the Implicit FD Time Migration algorithm (finite difference), while the stacking velocities were used for the poststack time migration procedure performed with the Stolt and Kirchhoff algorithms in accordance with the technical conditions of correct operation of these algorithms. The selected percentage ranges of 60%, 100%, and 140% have been used for all velocity fields. Application of the element of directional velocity variation resulting from the spatial distribution of interval velocities in the boreholes to the velocity field for the poststack time migration allowed to obtain a better seismic image in relation to the one obtained as a result of applying the stacking velocities. The most reliable seismic image after poststack time migration was obtained for the velocity field calculated on the basis of the interval velocities with Gaussian distribution, using the finite difference algorithm with 60 percent value of the velocity field.
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Bamber, J. L., R. J. Hardy, and I. Joughin. "An analysis of balance velocities over the Greenland ice sheet and comparison with synthetic aperture radar interferometry." Journal of Glaciology 46, no. 152 (2000): 67–74. http://dx.doi.org/10.3189/172756500781833412.
Повний текст джерелаАнотація:
AbstractBalance velocities for the Greenland ice sheet have been calculated from a new digital elevation model (DEM), accumulation rates and an existing ice-thickness grid, using a fully two-dimensional finite-difference scheme. The pattern of velocities is compared with velocities derived from synthetic-aperture radar (SAR) interferometry for three different regions of the ice sheet. Differences between the two estimates of velocity highlight the respective strengths and weaknesses of the datasets and techniques used. A comparison with ten global positioning system-derived velocities indicates that the balance-velocity scheme and input datasets used here provide a remarkably good representation of the velocity distribution inland from the margins. These balance-velocity data, therefore, could help constrain numerical ice-sheet models. The balance velocities were found to be unreliable close to the ice-sheet margins due to larger errors in ice thickness, surface slope and ablation rate in this region. Comparison of the balance velocities with SAR interferometry in the region of the “Northeast Greenland Ice Stream” indicates the importance of the smoothing distance that must be applied to the DEM before calculating balance velocities. A smoothing distance of 20 times the ice thickness gave good agreement between the two measures of velocity.
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Wang, Hua, Mike Fehler, Guo Tao, and Zhoutuo Wei. "Investigation of collar properties on data-acquisition scheme for acoustic logging-while-drilling." GEOPHYSICS 81, no. 6 (November 2016): D611—D624. http://dx.doi.org/10.1190/geo2016-0016.1.
Повний текст джерелаАнотація:
We have used the wavenumber integration, velocity-time semblance, and dispersion methods to investigate the influence of collar properties including velocities, density, and attenuation on acoustic logging-while-drilling wavefields. We have found that when the velocities of the collar wave and the P-wave of the formation are similar, they interfere. However, the interference disappears when the velocity difference increases. Having a collar with large velocities (especial large shear velocity) and density makes the direct P-velocity determination possible in a fast formation even without isolators. For a slow formation, the interference of the collar flexural wave with the formation flexural and leaky P-waves is slight for a dipole tool when collar velocities are large. For this case, the S velocity can be determined by the flexural formation wave at low frequency (approximately 2 kHz). Based on these observations, we propose that the measurement of the P- and S-velocities can be easier if the collar is made of an advanced composite material that has high compressional and shear velocities as well as density. This is a direct and easy change to implement and a new idea for an acoustic logging-while-drilling tool design.
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Iqbal, Ibrar, Xiong Bin, Gang Tian, Honghua Wang, Peng Sanxi, Yang Yang, Zahid Masood, and Sun Hanwu. "Near Surface Velocity Estimation Using GPR Data: Investigations by Numerical Simulation, and Experimental Approach with AVO Response." Remote Sensing 13, no. 14 (July 17, 2021): 2814. http://dx.doi.org/10.3390/rs13142814.
Повний текст джерелаАнотація:
The velocity of near-surface materials is one of the most important for Ground-Penetrating Radar (GPR). In the study, we evaluate the options for determining the GPR velocity to measure the accuracy of velocity approximations from the acquired GPR data at an experimental site in Hangzhou, China. A vertical profile of interval velocities can be estimated from each common mid-point (CMP) gather using velocity spectrum analysis. Firstly, GPR data are acquired and analyzed using the popular method of hyperbola fitting which generated surprisingly high subsurface signal velocity estimates while, for the same profile, the Amplitude variation with offset (AVO) analysis of the GPR data (using the same hyperbola fitting method) generate a more reasonable subsurface signal velocity estimate. Several necessary processing steps are applied both for CMP and AVO analysis. Furthermore, experimental analysis is conducted on the same test site to get velocities of samples based on dielectric constant measurement during the drilling process. Synthetic velocities generated by AVO analysis are validated by the experimental velocities which confirmed the suitability of velocity interpretations.
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Chakraborty, Nilanjan, and Andrei N. Lipatnikov. "Statistics of Conditional Fluid Velocity in the Corrugated Flamelets Regime of Turbulent Premixed Combustion: A Direct Numerical Simulation Study." Journal of Combustion 2011 (2011): 1–13. http://dx.doi.org/10.1155/2011/628208.
Повний текст джерелаАнотація:
The statistics of mean fluid velocity components conditional in unburned reactants and fully burned products in the context of Reynolds Averaged Navier Stokes (RANS) simulations have been studied using a Direct Numerical Simulation database of statistically planar turbulent premixed flame representing the corrugated flamelets regime combustion. Expressions for conditional mean velocity and conditional velocity correlations which are derived based on a presumed bimodal probability density function of reaction progress variable for unity Lewis number flames are assessed in this study with respect to the corresponding quantities extracted from DNS data. In particular, conditional surface averaged velocities(ui)¯Rsand the velocity correlations(uiu)j¯Rsin the unburned reactants are demonstrated to be effectively modelled by the unconditional velocities(ui)¯Rand velocity correlations(uiuj)¯R, respectively, for the major part of turbulent flame brush with the exception of the leading edge. By contrast, conditional surface averaged velocities(ui)¯Psand the velocity correlations(uiu)j¯Psin fully burned products are shown to be markedly different from the unconditional velocities(ui)¯Pand velocity correlations(uiuj)¯P, respectively.
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Reiter, Michael A., and Robert E. Carlson. "Current Velocity in Streams and the Composition of Benthic Algal Mats." Canadian Journal of Fisheries and Aquatic Sciences 43, no. 6 (June 1, 1986): 1156–62. http://dx.doi.org/10.1139/f86-144.
Повний текст джерелаАнотація:
Water velocity is commonly accepted as a factor in the development of benthic algal mats in streams. Within a stream, two different zones of velocity are observed: the free-water velocity of the open water and the local velocity near the stream substrate. A closed laboratory flume system was used to observe the taxonomic composition of benthic algal mats and corresponding changes in the local velocities under different free-water velocities. As the algal mat developed under each experimental velocity, local velocities diminished and eventually became equal in all sections, while free-water velocities remained different. After a period of maximum taxonomic diversity during the first 2 wk of mat development, taxonomic composition, relative abundance of the taxa, and dry weight biomass became increasingly similar in the three velocity regimes, although the mats appeared different upon casual observation. Differences in composition and morphology in natural algal mats may not result from differences in current velocity, and the idea of a "closed monolayer" algal mat may not be appropriate in all situations.
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Yu, Bo, Jinfeng Wang, Jing Xie, Bingjun Wang, Fei Wang, and Meng Deng. "Bubble Sliding Characteristics and Dynamics of R134a during Subcooled Boiling Flow in a Narrow Gap." Mathematics 11, no. 9 (May 6, 2023): 2197. http://dx.doi.org/10.3390/math11092197.
Повний текст джерелаАнотація:
The numerical method was used to study bubble sliding characteristics and dynamics of R134a during subcooled flow boiling in a narrow gap. In the numerical method, the volume of fraction (VOF) model, level set method, Lee phase change model and the SST k − ω turbulent model were adopted for the construction of the subcooled flow boiling model. In order to explore bubble sliding dynamics during subcooled flow boiling, the bubble sliding model was introduced. The bubble velocity, bubble departure diameter, sliding distance and bubble sliding dynamics were investigated at 0.2 to 5 m/s inlet velocities. The simulation results showed that the bubble velocity at the flow direction was the most important contribution to bubble velocity. Additionally, the bubble velocity of 12 bubbles mostly oscillated with time during the sliding process at 0.2 to 0.6 m/s inlet velocities, while the bubble velocity increased during the sliding process due to the bubble having had a certain inertia at 2 to 5 m/s inlet velocities. It was also found that the average bubble velocity in flow direction accounted for about 80% of the mainstream velocities at 0.2 to 5 m/s. In the investigation of bubble sliding distance and departure diameter, it was concluded that the ratio of the maximum sliding distance to the minimum sliding distance was close to two at inlet velocities of 0.3 to 5 m/s. Moreover, with increasing inlet velocity, the average sliding distance increased significantly. The average bubble departure diameter obviously increased from 0.2 to 0.5 m/s inlet velocity and greatly reduced after 0.6 m/s. Finally, the investigations of the bubble sliding dynamics showed that the surface tension dominated the bubble sliding process at 0.2 to 0.6 m/s inlet velocities. However, the drag force dominated the bubble sliding process at 2 to 5 m/s inlet velocities.
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Lee, Myung W. "A simple method of predicting S-wave velocity." GEOPHYSICS 71, no. 6 (November 2006): F161—F164. http://dx.doi.org/10.1190/1.2357833.
Повний текст джерелаАнотація:
Prediction of shear-wave velocity plays an important role in seismic modeling, amplitude analysis with offset, and other exploration applications. This paper presents a method for predicting S-wave velocity from the P-wave velocity on the basis of the moduli of dry rock. Elastic velocities of water-saturated sediments at low frequencies can be predicted from the moduli of dry rock by using Gassmann’s equation; hence, if the moduli of dry rock can be estimated from P-wave velocities, then S-wave velocities easily can be predicted from the moduli. Dry rock bulk modulus can be related to the shear modulus through a compaction constant. The numerical results indicate that the predicted S-wave velocities for consolidated and unconsolidated sediments agree well with measured velocities if differential pressure is greater than approximately [Formula: see text]. An advantage of this method is that there are no adjustable parameters to be chosen, such as the pore-aspect ratios required in some other methods. The predicted S-wave velocity depends only on the measured P-wave velocity and porosity.
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Ramachandran, Kumar, Gilles Bellefleur, Tom Brent, Michael Riedel, and Scott Dallimore. "Imaging permafrost velocity structure using high resolution 3D seismic tomography." GEOPHYSICS 76, no. 5 (September 2011): B187—B198. http://dx.doi.org/10.1190/geo2010-0353.1.
Повний текст джерелаАнотація:
A 3D seismic survey (Mallik 3D), covering [Formula: see text] in the Mackenzie Delta area of Canada’s north, was conducted by industry in 2002. Numerous lakes and marine inundation create a complex near-surface structure in the permafrost terrain. Much of the near subsurface remains frozen but significant melt zones exist particularly from perennially unfrozen water bodies. This results in an irregular distribution of permafrost ice creating a complex pattern of low and high frequency near-surface velocity variations which induce significant traveltime distortions in surface seismic data. A high resolution 3D traveltime tomography study was employed to map the permafrost velocity structure utilizing first-arrival traveltimes picked from 3D seismic shot records. Approximately 900,000 traveltime picks from 3167 shots were used in the inversion. Tomographic inversion of the first-arrival traveltimes resulted in a smooth velocity model for the upper 200 m of the subsurface. Ray coverage in the model is excellent down to 200 m providing effective control for estimating velocities through tomographic inversion. Resolution tests conducted through horizontal and vertical checkerboard tests confirm the robustness of the velocity model in detailing small scale velocity variations. Well velocities were used to validate tomographic velocities. The tomographic velocities do not show systematic correlation with well velocities. The velocity model clearly images the permafrost velocity structure in lateral and vertical directions. It is inferred from the velocity model that the permafrost structure in the near subsurface is discontinuous. Extensions of surface water bodies in depth, characterized by low P-wave velocities, are well imaged by the velocity model. Deep lakes with unfrozen water, inferred from the tomographic velocity model, correlate with areas of strong amplitude blanking and frequency attenuation observed in processed reflection seismic stack sections.
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Agarwal, Anju, Nikhil Agrawal, Neetu Sharma, Durgesh Shukla, and Ajit Singh Rajput. "Discriminative Ability of Electrophysiological Tests Such as Nerve Conduction Velocities for The Classification of Malnourished Children from Normal Children." National Journal of Community Medicine 14, no. 07 (July 1, 2023): 418–23. http://dx.doi.org/10.55489/njcm.140720233052.
Повний текст джерелаАнотація:
Background: Nerve Conduction Velocities (NCVs) measures electrical changes and speed in the nerve. Objectives of this study were: to compare mean velocities, to find rank of importance of different velocities and to frame equation to classify severely acute malnourished (SAM) children with normal children. Material & Methods: Present case- control study was conducted on 50 SAM children and 50 normal children aged 6 months to 59 months. Independent t test and Discriminant analysis was performed. Standardized discriminant coefficient, canonical correlation and Wilks’ Lambda was calculated and p value was judges at 5% level of significance. Results: NCVs were observed significantly lower among the cases as compared with the controls. Sural Sensory Nerve Velocity holds first position followed by Sensory Nerve Velocity. So, in final discriminant model 3 variables i.e., Sural Sensory Nerve Velocity; Median Sensory Nerve Velocity; Tibial Motor Nerve Velocity were used and 42.1 % of the total variance in the discriminant scores not explained by differences among the groups by the three-variable model. Model is able to classify 82.5% cases correctly. Conclusion: Sural Sensory Nerve Velocity; Median Sensory Nerve Velocity; Tibial Motor Nerve Velocity were found as most important nerve conduction velocities with a good classification ability.
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Duysens, J., G. A. Orban, and J. Cremieux. "Velocity selectivity in the cat visual system. II. Independence from interactions between different loci." Journal of Neurophysiology 54, no. 4 (October 1, 1985): 1050–67. http://dx.doi.org/10.1152/jn.1985.54.4.1050.
Повний текст джерелаАнотація:
To investigate the dependence of velocity characteristics on spatiotemporal interactions the velocity selectivity of 15 geniculate and 72 cortical cells (areas 17 and 18) was examined with light and dark bars before and after masking all but the most sensitive part of the receptive field. The use of a 0.3 degree window proved effective in eliminating enough spatiotemporal interactions to abolish cortical direction selectivity. The same window improved the responsiveness at high velocities in only 26% of the cortical cells preferring low velocities and having a receptive field with nonoverlapping ON and OFF subregions. The remaining 74% showed various degrees of velocity-independent decrease in response amplitude. The only two geniculate cells that had a velocity upper cutoff lost this cutoff when tested with the mask. Cortical units preferring high velocities lost their responsiveness at high velocities in the mask condition, provided that their receptive fields contained nonoverlapping ON and OFF subregions. Cortical units, which responded best at intermediate velocities and which had receptive fields with nonoverlapping subregions, lost their sharp velocity tuning when tested with a mask. We conclude that inhibitory spatiotemporal interactions can account for the preference for low velocities in at most a quarter of the cells with nonoverlapping subregions. In contrast, facilitatory interactions seem to be important for cortical cells preferring high or intermediate velocities and having receptive fields with nonoverlapping subregions.
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Cook, C. S., and M. J. McDonagh. "Force responses to constant-velocity shortening of electrically stimulated human muscle-tendon complex." Journal of Applied Physiology 81, no. 1 (July 1, 1996): 384–92. http://dx.doi.org/10.1152/jappl.1996.81.1.384.
Повний текст джерелаАнотація:
Force-velocity curves in human muscle often have unexpectedly high forces at high velocities. If series elasticity is the cause, it should have less effect at lower activation levels and larger shortening amplitudes. The first dorsal interosseus muscle-tendon complex was shortened at different levels of activation and by different amplitudes. Force-velocity curves had high force well maintained at high velocities. With an actuator release of 4.21 mm at 80% of maximal activation, force was > 45% of isometric force (Po) for all actuator velocities > 200 mm/s (1.49 muscle lengths/s). At 30% activation, the force was > 25% of Po at these velocities. The smaller 2.46-mm releases produced higher forces than the 4.21-mm releases at these velocities. At 80% activation, force was > 65% of Po, and at 30% activation, it was > 50% of Po at these velocities. Corrections of these data for elasticity produced classic Hill-type force-velocity curves. A model incorporating the Hill force-velocity equation and a spring in series accounts for the results.
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Jung, Jae-Sang, and Changhoon Lee. "Development of Analytical Solutions on Velocities of Regular Waves Generated by Bottom Wave Makers in a Flume." Journal of Korean Society of Coastal and Ocean Engineers 34, no. 3 (June 30, 2022): 58–71. http://dx.doi.org/10.9765/kscoe.2022.34.3.58.
Повний текст джерелаАнотація:
Analytical solutions for two-dimensional velocities of regular waves generated by bottom wave makers in a flume were derived in this study. Triangular and rectangular bottom wave makers were adopted. The velocity potential was derived based on the linear wave theory with the bottom moving boundary condition, kinematic and dynamic free surface boundary conditions. Then, analytical solutions of two-dimensional particle velocities were derived from the velocity potential. The velocity potential and two-dimensional particle velocities which were derived as complex integral equations were numerically calculated. The solutions showed physically valid results as velocities of regular waves generated by bottom wave makers in a flume.
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Jiao, Junru, Paul L. Stoffa, Mrinal K. Sen, and Roustam K. Seifoullaev. "Residual migration‐velocity analysis in the plane‐wave domain." GEOPHYSICS 67, no. 4 (July 2002): 1258–69. http://dx.doi.org/10.1190/1.1500388.
Повний текст джерелаАнотація:
Over the last few years, migration‐velocity analysis methods have been developed for 2‐D and 3‐D models by extending the assumptions and approximations used for rms velocity models. Computational requirements for these analyses have increased dramatically because top‐down layer‐stripping migration is needed to derive interval velocities directly instead of using rms velocities and then converting into interval velocities. We establish exact equations for 1‐D and 2‐D residual velocity analysis in the depth‐plane‐wave domain and use these in an iterative and interactive migration velocity analysis program. The new method updates interval velocities directly in a top‐down residual‐difference correction for all layers after prestack depth migration instead of top‐down layer‐stripping migration followed by residual analysis. This makes the new method a suitable tool for migration velocity analysis, especially for 3‐D surveys. We test the method on synthetic and field data. The field data results show that a reasonable velocity model is obtained and most common image gathers are correctly imaged using no more than four iterations.
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Medvedev, Andrey V., Konstantin G. Ratovsky, Maxim V. Tolstikov, Roman V. Vasilyev, and Maxim F. Artamonov. "Method for Determining Neutral Wind Velocity Vectors Using Measurements of Internal Gravity Wave Group and Phase Velocities." Atmosphere 10, no. 9 (September 13, 2019): 546. http://dx.doi.org/10.3390/atmos10090546.
Повний текст джерелаАнотація:
This study presents a new method for determining a neutral wind velocity vector. The basis of the method is measurement of the group velocities of internal gravity waves. Using the case of the Boussinesq dispersion relation, we demonstrated the ability to measure a neutral wind velocity vector using the group velocity and wave vector data. An algorithm for obtaining the group velocity vector from the wave vector spectrum is proposed. The new method was tested by comparing the obtained winter wind pattern with wind data from other sources. Testing the new method showed that it is in quantitative agreement with the Fabry–Pérot interferometer wind measurements for zonal and vertical wind velocities. The differences in meridional wind velocities are also discussed here. Of particular interest were the results related to the measurement of vertical wind velocities. We demonstrated that two independent methods gave the presence of vertical wind velocities with amplitude of ~20 m/s. Estimation of vertical wind contribution to plasma drift velocity indicated the importance of vertical wind measurements and the need to take them into account in physical and empirical models of the ionosphere and thermosphere.
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Jiang, Guanghui, Jianping Zuo, Teng Ma, and Xu Wei. "Experimental Investigation of Wave Velocity-Permeability Model for Granite Subjected to Different Temperature Processing." Geofluids 2017 (2017): 1–10. http://dx.doi.org/10.1155/2017/6586438.
Повний текст джерелаАнотація:
Understanding the change of permeability of rocks before and after heating is of great significance for exploitation of hydrocarbon resources and disposal of nuclear waste. The rock permeability under high temperature cannot be measured with most of the existing methods. In this paper, quality, wave velocity, and permeability of granite specimen from Maluanshan tunnel are measured after high temperature processing. Quality and wave velocity of granite decrease and permeability of granite increases with increasing temperature. Using porosity as the medium, a new wave velocity-permeability model is established with modified wave velocity-porosity formula and Kozeny-Carman formula. Under some given wave velocities and corresponding permeabilities through experiment, the permeabilities at different temperatures and wave velocities can be obtained. By comparing the experimental and the theoretical results, the proposed formulas are verified. In addition, a sensitivity analysis is performed to examine the effect of particle size, wave velocities in rock matrix, and pore fluid on permeability: permeability increases with increasing particle size, wave velocities in rock matrix, and pore fluid; the higher the rock wave velocity, the lower the effect of wave velocities in rock matrix and pore fluid on permeability.
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Winkler, Kenneth W. "Acoustic evidence of mechanical damage surrounding stressed boreholes." GEOPHYSICS 62, no. 1 (January 1997): 16–22. http://dx.doi.org/10.1190/1.1444116.
Повний текст джерелаАнотація:
Laboratory experiments demonstrate that acoustic waveforms recorded in a borehole provide evidence of stress‐induced mechanical damage in surrounding rock. In the experiments, external uniaxial stress was applied perpendicular to the borehole. Stress concentrations near the borehole wall caused velocities of refracted compressional‐wave to vary with azimuth. Low velocities occurred in zones of tensile stress, and high velocities occurred in zones of compressive stress. Velocity variations are on the order of 10%. At high values of externally applied uniaxial stress, rock exceede its yield strength and permanent damage developed. This damage decreased the measured velocities by approximately 10%, especially in the zones of compressive stress concentration. The heterogenous nature of the velocities surrounding the borehole resulted in low‐velocity channels parallel to the borehole wall, caused either by tensile stress concentrations or by mechanical damage. These low‐velocity channels may be responsible for high‐amplitude “bright‐spots” that appear on variable density plots of azimuthal waveform scans. The amplitude increases can be on the order of 500% and are associated with low‐velocity zones, not with decreased attenuation. The hypothezised mechanism is acoustic focusing, whereby velocity gradients refract acoustic waves back towards the borehole.
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Pappas, P. T., T. P. Pappas, and L. P. Pappas. "Noninertial frames, velocity of light not constant, and absolute velocities." Physics Essays 29, no. 3 (September 27, 2016): 418–22. http://dx.doi.org/10.4006/0836-1398-29.3.418.
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Tamburrino, Aldo, and Francisco Sandoval. "Probability density functions of free-surface velocities and velocity gradients." Mechanics Research Communications 25, no. 6 (November 1998): 605–12. http://dx.doi.org/10.1016/s0093-6413(98)00078-0.
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Doi, Takao, C. R. O'Dell, and Patrick Hartigan. "Internal Velocities in the Orion Nebula: Large Radial Velocity Features." Astronomical Journal 127, no. 6 (June 2004): 3456–78. http://dx.doi.org/10.1086/386351.
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Brown, Michael E., and Hyron Spinrad. "The Velocity Distribution of Cometary Hydrogen: Evidence for High Velocities?" Icarus 104, no. 2 (August 1993): 197–205. http://dx.doi.org/10.1006/icar.1993.1095.
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Le, Hong Quan, Dong Tran, Van Tien Nguyen, and Dac The Nguyen. "A machine learning approach for calibrating seismic interval velocity in 3D velocity model." Petrovietnam Journal 10 (November 1, 2022): 12–18. http://dx.doi.org/10.47800/pvj.2022.10-02.
Повний текст джерелаАнотація:
Velocity model technique is routinely used to convert data from the time-to-depth domain to support prospect evaluation, reservoir modelling, well engineering, and further drilling operation. In Vietnam, the conventional velocity model building workflow oversimplifies the interval velocities as only well interval velocities are populated into 2D grids for depth conversion or oversimplified calibration interval velocities by applying a single scaling factor function. This study explores the 3D velocity model workflow to obtain accurate and high-resolution interval velocities using a machine learning approach for both fields A and B in Cuu Long basin, offshore Vietnam.
To design an effective approach to depth conversion, the anisotropy factor analysis was performed to understand the differences between the seismic and well interval velocities in geological layer in the 3D structural model. The seismic interval velocity was multiplied by the anisotropy factor to achieve the scaling seismic interval velocity. The scaling seismic interval velocity, elastic attributes, geometric attributes, structural and stratigraphic attributes were used as training features (variables) for predicting interval velocity using the supervised learning algorithm in the machine learning model. Supervised learning offers an opportunity to develop an expert-knowledge-based automated system, which incorporates both domain knowledge and quantitative data mining [1]. The random forest regression algorithms were selected for predicting interval velocity after evaluating several machine learning algorithms. To provide insight into the uncertainty of final interval velocity, a depth uncertainty analysis was conducted using a blind well test for 24 wells and 7 horizons.
The comprehensive 3D velocity model using machine learning approach was built for the first time in Cuu Long basin, offshore Vietnam. The result showed the machine learning algorithm can address the disadvantages of conventional velocity calibration to create highly accurate depth representations of the subsurface including a measure of the uncertainty.
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Homayounfar, Farzin, and Babak Khorsandi. "Evaluating acoustic Doppler velocimetry pulse-pair spacing/velocity range setting for turbulent flow measurements." Physics of Fluids 34, no. 3 (March 2022): 035116. http://dx.doi.org/10.1063/5.0086303.
Повний текст джерелаАнотація:
The velocity range, which is inversely proportional to acoustic pulse-pair spacing, is one of the most important user-set parameters of acoustic Doppler velocimeters (ADVs) and is expected to influence their flow measurements. An experimental study of the effect of the ADV velocity range on the mean and turbulence statistics measured in stagnant water, a turbulent channel flow, and a turbulent jet was undertaken. The results show that as long as the instantaneous velocities are within the user-set velocity range, increasing the velocity range does not noticeably influence the mean velocities, whereas it increases the velocity variances due to the increased noise variance. If the instantaneous velocities exceed the velocity range, phase wrapping occurs, resulting in underestimated mean velocities and overestimated velocity variances. The rate of increase in noise variance with the velocity range increases drastically as the turbulence level rises. From this, it can be inferred that in turbulence measurements, the contribution to the total noise made by Doppler noise is much more substantial than that of the sampling error. Furthermore, it is observed that for highly turbulent flows the ADV correlation significantly drops and signal quality reduces. Increasing the velocity range solves this problem at the expense of higher Doppler noise. Post-processing of the data effectively improves the statistics, even when the velocity range was set to overly high values. Finally, Doppler noise is found to be linearly related to velocity variances (at a constant velocity range), while it is nonlinearly proportional to the velocity range in measurements of turbulent flows.
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John, J., and T. Schobeiri. "A Simple and Accurate Method of Calibrating X-Probes." Journal of Fluids Engineering 115, no. 1 (March 1, 1993): 148–52. http://dx.doi.org/10.1115/1.2910098.
Повний текст джерелаАнотація:
This paper presents an improved method of calibrating hot-film X-probes in incompressible flow. The yaw response of a hot-film X-probe was investigated for different velocities and found to be strongly velocity dependent at low velocities. A simple relation was developed to correct for the variation of yaw response at low velocities. The method using the yaw correction is compared with the single-velocity yaw calibration method. The correction to the yaw response considerably improves accuracy at low velocities.
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Ayabakan, Canan, and Süheyla Özkutlu. "Left ventricular myocardial velocities in healthy children: quantitative assessment by tissue Doppler echocardiography and relation to the characteristics of filling of the left ventricle." Cardiology in the Young 14, no. 2 (April 2004): 156–63. http://dx.doi.org/10.1017/s1047951104002070.
Повний текст джерелаАнотація:
Aim:To assess the myocardial velocities of the mitral annulus, left ventricular lateral wall, and midseptum in healthy children, and to compare these parameters with transmitral and pulmonary venous velocities.Methods and results:We examined 72 children, half being male, who had no systemic or cardiac pathologies. Their mean age was 6.73 ± 5.10 years, with a range from 0.1 to 17.75 years, and a median age of 6.71 years. Each parameter was measured twice, at end inspiration and end expiration. The tissue velocities are similar in males and females (p > 0.05). The longitudinal velocity of the heart in early diastole has a positive correlation with age (p < 0.05; midseptum velocity r = 0.57, left ventricular lateral wall velocity r = 0.56, mitral annulus velocity r = 0.56), and the tissue velocities are not influenced by respiration (p > 0.05). The myocardial velocities of different segments of the left ventricle are not correlated with the transmitral or pulmonary venous flows (p < 0.05). When age is controlled for heart rate, age mainly affects the systolic velocity of the mitral annulus and the early diastolic velocity of the midseptum in longitudinal axis, as well as the early diastolic velocity of the midseptum in transverse axis (p > 0.05 for all, r = 0.34, 0.29, 0.30 respectively).Conclusion:This study, which has determined reference values for tissue velocities in a large healthy group of children, will now set the scene for further studies in children with heart disease.
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Neidell, Norman S., and Neal Berry. "Documenting the sand/shale crossover." GEOPHYSICS 54, no. 11 (November 1989): 1430–34. http://dx.doi.org/10.1190/1.1442606.
Повний текст джерелаАнотація:
All types of velocity data, i.e., surface seismic and well log or sonic log data, indicate that velocity in shallow, unconsolidated sands is lower than in associated shales, while velocity in older sands in more consolidated rock sequences is higher than in their associated shales. As the low‐velocity sands compact to become the high‐velocity member in the sand‐shale sequence, sand and shale velocities must become equal or crossover at some age and depth of burial. If the same type of velocity data is used consistently, this crossover occurs at the same depth and age of rocks in the geologic sequence as would be indicated by other types of velocity data, even though the different kinds of velocities would not agree elsewhere. If all rocks in the province are older and compacted, this crossover of sand and shale velocities may not be observed or, if observed, may be very near the surface.
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Kikuyama, Koji, Mitsukiyo Murakami, Shin-ichi Oda, and Ken-ichi Gomi. "Pressure Recovery of Rotating Diffuser With Distorted Inflows." Journal of Fluids Engineering 109, no. 2 (June 1, 1987): 114–20. http://dx.doi.org/10.1115/1.3242630.
Повний текст джерелаАнотація:
The pressure recovery and velocity distributions in a two-dimensional rotating curved diffuser have been studied experimentally when even and uneven flows, respectively, were introduced to the diffuser. Two types of uneven flow were adopted; one has a linear velocity gradient on the surface of revolution and the other a linear velocity gradient in the meridian plane. The pressure recovery in the diffuser is improved by the unformalizing process of the uneven inlet velocities in the downstream sections if larger velocities are in the suction side region, but it is deteriorated if larger velocities are introduced in the pressure side region. When an uneven flow with a velocity gradient in the meridian plane is introduced to the diffuser, increased rotation speed and the gradient of the inlet velocity profile deteriorate the pressure recovery.
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Carter, M. D. "Depth conversion using a normalized velocity ? lithology correlation." Exploration Geophysics 20, no. 2 (1989): 243. http://dx.doi.org/10.1071/eg989243.
Повний текст джерелаАнотація:
In areas where the exploration objectives require a reliable depth conversion algorithm, two methods are commonly used. In the best of the average velocity techniques, the values of average velocity are derived from the seismic velocities. For the "layer cake" method, the values of interval velocity are from either well velocity surveys, seismic times and well depths or seismic velocities. In both methods, the success of the depth conversion is dependent upon the correlation between the interval velocity and the geology of the layer.
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Dubose, John B. "A technique for stabilizing interval velocities from the Dix equation." GEOPHYSICS 53, no. 9 (September 1988): 1241–43. http://dx.doi.org/10.1190/1.1442565.
Повний текст джерелаАнотація:
Interval velocities, the velocities at which sounds travel in the earth, can be computed from stacking or root‐mean‐square (rms) velocities by applying the Dix equation (Dix, 1955): [Formula: see text] where [Formula: see text] are the stacking velocity picks, [Formula: see text] are the associated times, and [Formula: see text] is the average interval velocity between [Formula: see text] and [Formula: see text].
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Zhen, Bin, Wei Luo, and Jian Xu. "Analysis of Critical Velocities for an Infinite Timoshenko Beam Resting on an Elastic Foundation Subjected to a Harmonic Moving Load." Shock and Vibration 2014 (2014): 1–9. http://dx.doi.org/10.1155/2014/848536.
Повний текст джерелаАнотація:
Critical velocities are investigated for an infinite Timoshenko beam resting on a Winkler-type elastic foundation subjected to a harmonic moving load. The determination of critical velocities ultimately comes down to discrimination of the existence of multiple real roots of an algebraic equation with real coefficients of the 4th degree, which can be solved by employing Descartes sign method and complete discrimination system for polynomials. Numerical calculations for the European high-speed rail show that there are at most four critical velocities for an infinite Timoshenko beam, which is very different from those gained by others. Furthermore, the shear wave velocity must be the critical velocity, but the longitudinal wave velocity is not possible under certain conditions. Further numerical simulations indicate that all critical velocities are limited to be less than the longitudinal wave velocity no matter how large the foundation stiffness is or how high the loading frequency is. Additionally, our study suggests that the maximum value of one group velocity of waves in Timoshenko beam should be one “dangerous” velocity for the moving load in launching process, which has never been referred to in previous work.
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Lu, Ye, and Junbao Li. "Shock and Spallation Behavior of a Compositionally Complex High-Strength Low-Alloy Steel under Different Impact Stresses." Applied Sciences 13, no. 6 (March 7, 2023): 3375. http://dx.doi.org/10.3390/app13063375.
Повний текст джерелаАнотація:
The shock and spalling behavior of a compositionally complex high strength low-alloy steel (HSLA) was studied using plate impact testing. The free surface velocity of the specimen in the range of 194~938 m/s was measured by a displacement interferometer system for any reflector (DISAR). The Hugoniot elastic limit (HEL), spallation fracture and microstructural evolution of the HSLA under an impact stress of 3.04~18.66 GPa were analyzed. Shock Hugoniots were obtained from the measured particle velocities and calculated shock velocities. The velocity curves show clear signs of HEL and velocity fallback, indicating a transition from elastic to plastic and spalling behavior. When the impact velocity exceeds 757 m/s, the particle velocity rises to the peak and then increases again, indicating that an α→ε phase transition occurred, with a threshold of 13.51 GPa. It was found that the impact velocity is linearly related to the particle velocity of the HSLA. As the impact stress increased, the HEL remained within the range of 1.32~1.50 GPa, while the spalling strength presented an upward trend with the increasing impact stresses. Metallographic analysis shows that the impact failure is dominated by brittle fracture at lower velocities, while more ductile fracture occurs at higher velocities.
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Fontaine, A. A., H. L. Petrie, and T. A. Brungart. "Velocity profile statistics in a turbulent boundary layer with slot-injected polymer." Journal of Fluid Mechanics 238 (May 1992): 435–66. http://dx.doi.org/10.1017/s0022112092001770.
Повний текст джерелаАнотація:
The modification of a flat-plate turbulent boundary layer resulting from the injection of drag-reducing polymer solutions through a narrow inclined slot into the near-wall region of the flow has been studied. Two-component coincident laser-Doppler velocity profile measurements were taken with a free-stream velocity of 4.5 m/s with polymer injection, water injection, and no injection. Polyethylene oxide solutions at concentrations of 500 and 1025 w.p.p.m. were injected. These data are complemented by polymer concentration profile measurements that were taken using a laser-induced-fluorescence technique. Also, integrated skin friction measurements were made with a drag balance for a range of polymer injection conditions and free-stream velocities. The immediate effects of polymer injection are a deceleration of the flow near the wall, a dramatic decrease of the vertical r.m.s. velocit}’ fluctuation levels and the Reynolds shear stress levels, and a mean velocity profile approaching Virk's asymptotic condition. These effects relax substantially with increasing stream wise distance from the injection slot and become similar to the effects observed for dilute homogeneous polymer flows.
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Loturco, Irineu, Timothy Suchomel, Chris Bishop, Ronaldo Kobal, Lucas A. Pereira, and Michael R. McGuigan. "Determining the Optimum Bar Velocity in the Barbell Hip Thrust Exercise." International Journal of Sports Physiology and Performance 15, no. 4 (April 1, 2020): 585–89. http://dx.doi.org/10.1123/ijspp.2019-0228.
Повний текст джерелаАнотація:
Purpose: To identify the bar velocities that optimize power output in the barbell hip thrust exercise. Methods: A total of 40 athletes from 2 sports disciplines (30 track-and-field sprinters and jumpers and 10 rugby union players) participated in this study. Maximum bar-power outputs and their respective bar velocities were assessed in the barbell hip thrust exercise. Athletes were divided, using a median split analysis, into 2 groups according to their bar-power outputs in the barbell hip thrust exercise (“higher” and “lower” power groups). The magnitude-based inferences method was used to analyze the differences between groups in the power and velocity outcomes. To assess the precision of the bar velocities for determining the maximum power values, the coefficient of variation (CV%) was also calculated. Results: Athletes achieved the maximum power outputs at a mean velocity, mean propulsive velocity, and peak velocity of 0.92 (0.04) m·s−1 (CV: 4.1%), 1.02 (0.05) m·s−1 (CV: 4.4%), and 1.72 (0.14) m·s−1 (CV: 8.4%), respectively. No meaningful differences were observed in the optimum bar velocities between higher and lower power groups. Conclusions: Independent of the athletes’ power output and bar-velocity variable, the optimum power loads frequently occur at very close bar velocities.
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Quintana, Hernán, Dominique Proust, Rolando Dünner, Eleazar R. Carrasco, and Andreas Reisenegger. "A redshift database towards the Shapley supercluster region." Astronomy & Astrophysics 638 (June 2020): A27. http://dx.doi.org/10.1051/0004-6361/202037726.
Повний текст джерелаАнотація:
We present a database and catalogue of radial velocities of galaxies towards the region of the Shapley Supercluster (SSC) based on 18 129 measured velocities for 10 702 galaxies in the approximately 300 square degree area between 12h43m00s < RA < 14h17m00s and −23° 30′00″ > Dec > − 38° 30′00″. The database contains velocity measurements that have been reported in the literature up until 2015. It also includes 5084 velocities, corresponding to 4617 galaxies, observed by us at Las Campanas Observatory and Cerro Tololo Inter-American Observatory, which had not been reported individually until now. Of the latter, 2585 correspond to galaxies with no other previously published velocity measurement before 2015. Every galaxy in the velocity database has been identified with a galaxy extracted from the SuperCOSMOS photometric catalogues. We also provide a combined average velocity catalogue for all 10 702 galaxies with measured velocities, adopting the SuperCOSMOS positions as a homogeneous base. A general magnitude cut-off at R2 = 18.0 mag was adopted (with exceptions only for some of the new reported velocities). In general terms, we confirm the overall structure of the SSC as reported in earlier papers. However, the more extensive velocity data show finer structures, which is to be discussed in a future publication.
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Dhobi, Saddam Husain, Arjun Panthi, Subash Panthi, and Roshan Subedi. "Development of Mathematical Model to Study the Variation Temperature due to the Collision of." European Journal of Applied Physics 3, no. 3 (May 6, 2021): 1–5. http://dx.doi.org/10.24018/ejphysics.2021.3.3.70.
Повний текст джерелаАнотація:
To study the variation of temperature with the collision of the air molecules, with aircraft the authors consider the random velocities of the air molecules or aerosol and aircraft. After this, the authors start to develop and extend the old relation of gases, collision, velocities, and temperature. On combining, the authors derived a new equation and relation among these parameters. The derivation for this work assumes some suitable and considerable, assumptions based on collision theory. The relation shows, on collision between the aircraft and air molecules the velocity of the aircraft does not change while the velocity of the air molecules goes on change, which is our goal.
The change in velocity of gases is used to develop and study the variation of temperature of the atmosphere, the variation of temperature takes place because the speed of aircraft and air molecules are exchangeable in some cases. Therefore, two relations are developed (24) and (25), finally, which depend upon the initial velocities of aircraft and air molecules. On considering the case for initial velocities of aircraft is greater than initial velocities of air molecules, after the collision, the velocities of gases go on the increase, and hence the temperature increase and vice-versa in case of initial velocities of aircraft is less than the initial velocity of air molecules.
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Yuan, Yue, Ping Wang, Di Wang, and Junzhi Shi. "A Velocity Dealiasing Scheme Based on Minimization of Velocity Differences between Regions." Advances in Meteorology 2020 (February 20, 2020): 1–12. http://dx.doi.org/10.1155/2020/6157636.
Повний текст джерелаАнотація:
The velocity dealiasing is an essential work of automatic weather phenomenon identification, nowcasting, and disaster monitoring based on radial velocity data. The noise data, strong wind shear, and isolated echo region in the Doppler radar radial velocity data severely interfere with the velocity dealiasing algorithm. This paper proposes a two-step velocity dealiasing algorithm based on the minimization of velocity differences between regions to solve this problem. The first step is to correct aliased velocities by minimizing the sum of gradients in every region to eliminate abnormal velocity gradients between points. The interference of noise data and strong wind shear can be reduced by minimizing the whole gradients in a region. The second step is to dealiase velocities by the velocity differences between different isolated regions. The velocity of an unknown isolated region is determined by the velocities of all known regions. This step improves the dealiasing results of isolated regions. In this paper, 604 volume scan samples, including typhoons, squall lines, and heavy precipitation, were used to test the algorithm. The statistical results and analysis show that the proposed algorithm can dealiase the velocity field with a high probability of detection and a low false alarm rate.