Raccanelli, Alvise; Bertacca, Daniele; Jeong, Donghui; Neyrinck, Mark C.; Szalay, Alexander S.
2016-01-01
We study the parity-odd part (that we shall call Doppler term) of the linear galaxy two-point correlation function that arises from wide-angle, velocity, Doppler lensing and cosmic acceleration effects. As it is important at low redshift and at large angular separations, the Doppler term is usually neglected in the current generation of galaxy surveys. For future wide-angle galaxy surveys such as Euclid, SPHEREx and SKA, however, we show that the Doppler term must be included. The effect of t...
Two-point correlation functions in inhomogeneous and anisotropic cosmologies
Marcori, Oton H.; Pereira, Thiago S.
2017-02-01
Two-point correlation functions are ubiquitous tools of modern cosmology, appearing in disparate topics ranging from cosmological inflation to late-time astrophysics. When the background spacetime is maximally symmetric, invariance arguments can be used to fix the functional dependence of this function as the invariant distance between any two points. In this paper we introduce a novel formalism which fixes this functional dependence directly from the isometries of the background metric, thus allowing one to quickly assess the overall features of Gaussian correlators without resorting to the full machinery of perturbation theory. As an application we construct the CMB temperature correlation function in one inhomogeneous (namely, an off-center LTB model) and two spatially flat and anisotropic (Bianchi) universes, and derive their covariance matrices in the limit of almost Friedmannian symmetry. We show how the method can be extended to arbitrary N-point correlation functions and illustrate its use by constructing three-point correlation functions in some simple geometries.
Two-point Correlator Fits on HISQ Ensembles
Bazavov, A; Bouchard, C; DeTar, C; Du, D; El-Khadra, A X; Foley, J; Freeland, E D; Gamiz, E; Gottlieb, Steven; Heller, U M; Hetrick, J E; Kim, J; Kronfeld, A S; Laiho, J; Levkova, L; Lightman, M; Mackenzie, P B; Neil, E T; Oktay, M; Simone, J N; Sugar, R L; Toussaint, D; Van de Water, R S; Zhou, R
2012-01-01
We present our methods to fit the two point correlators for light, strange, and charmed pseudoscalar meson physics with the highly improved staggered quark (HISQ) action. We make use of the least-squares fit including the full covariance matrix of the correlators and including Gaussian constraints on some parameters. We fit the correlators on a variety of the HISQ ensembles. The lattice spacing ranges from 0.15 fm down to 0.06 fm. The light sea quark mass ranges from 0.2 times the strange quark mass down to the physical light quark mass. The HISQ ensembles also include lattices with different volumes and with unphysical values of the strange quark mass. We use the results from this work to obtain our preliminary results of $f_D$, $f_{D_s}$, $f_{D_s}/f_{D}$, and ratios of quark masses presented in another talk [1].
A rapid and accurate two-point ray tracing method in horizontally layered velocity model
Institute of Scientific and Technical Information of China (English)
TIAN Yue; CHEN Xiao-fei
2005-01-01
A rapid and accurate method for two-point ray tracing in horizontally layered velocity model is presented in this paper. Numerical experiments show that this method provides stable and rapid convergence with high accuracies, regardless of various 1-D velocity structures, takeoff angles and epicentral distances. This two-point ray tracing method is compared with the pseudobending technique and the method advanced by Kim and Baag (2002). It turns out that the method in this paper is much more efficient and accurate than the pseudobending technique, but is only applicable to 1-D velocity model. Kim(s method is equivalent to ours for cases without large takeoff angles, but it fails to work when the takeoff angle is close to 90o. On the other hand, the method presented in this paper is applicable to cases with any takeoff angles with rapid and accurate convergence. Therefore, this method is a good choice for two-point ray tracing problems in horizontally layered velocity model and is efficient enough to be applied to a wide range of seismic problems.
Characterization of mantle convection experiments using two-point correlation functions
Puster, Peter; Jordan, Thomas H.; Hager, Bradford H.
1995-04-01
Snapshots of the temperature T(r, phi, t), horizontal flow velocity u(r, phi, t), and radial flow velocity w(r, phi, t) obtained from numerical convection experiments of time-dependent flows in annular cylindrical geometry are taken to be samples of stationary, rotationally invariant random fields. For such a field f(r, phi, t), the spatio-temporal two-point correlation function, C(sub ff)(r, r-prime, delta, t(sub *)), is constructed by averaging over rotational transformations of this ensemble. To assess the structural differences among mantle convection experiments we construct three spartial subfunctions of C(sub ff)(r, r-prime, delta, t(sub *)): the rms variation, sigma(sub f)(r), the radial correlation function, R(sub f)(r, r-prime), and the angular correlation function, A(sub f)(r, delta). R(sub f)(r, r-prime) and A(sub f)(r, r-prime) are symmetric about the loci r = r-prime and delta = 0, respectively, where they achieve their maximum value of unity. The falloff of R(sub f) and A(sub f) away from their symmetry can be quantified by a correlation length rho(sub f)(r) and a correlation angle alpha(sub f)(r), which we define to be the half widths of the central peaks at the correlation level 0.75. The behavior of rho(sub f) is a diagnostic of radial structure, while alpha(sub f) measures average plume width. We have used two-point correlation functions of the temperature field (T-diagnostics) and flow velocity fields (V-diagnostics) to quantify some important aspects of mantle convection experiments. We explore the dependence of different correlation diagnostics on Rayleigh number, internal heating rate, and depth- and temperature-dependent viscosity. For isoviscous flows in an annulus, we show how radial averages of sigma(sub T), rho(sub T), and alpha(sub T) scale with Rayleigh number for various internal heating rates. A break in the power-law relationship at the transition from steady to time-dependent regimes is evident for rho(sub T) and alpha(sub T) but
Logarithmic two-Point Correlation Functions from a z = 2 Lifshitz Model
Zingg, T.
2013-01-01
The Einstein-Proca action is known to have asymptotically locally Lifshitz spacetimes as classical solutions. For dynamical exponent z=2, two-point correlation functions for fluctuations around such a geometry are derived analytically. It is found that the retarded correlators are stable in the sens
Gauge-fixing parameter dependence of two-point gauge variant correlation functions
Zhai, C
1996-01-01
The gauge-fixing parameter \\xi dependence of two-point gauge variant correlation functions is studied for QED and QCD. We show that, in three Euclidean dimensions, or for four-dimensional thermal gauge theories, the usual procedure of getting a general covariant gauge-fixing term by averaging over a class of covariant gauge-fixing conditions leads to a nontrivial gauge-fixing parameter dependence in gauge variant two-point correlation functions (e.g. fermion propagators). This nontrivial gauge-fixing parameter dependence modifies the large distance behavior of the two-point correlation functions by introducing additional exponentially decaying factors. These factors are the origin of the gauge dependence encountered in some perturbative evaluations of the damping rates and the static chromoelectric screening length in a general covariant gauge. To avoid this modification of the long distance behavior introduced by performing the average over a class of covariant gauge-fixing conditions, one can either choose ...
The real space clustering of galaxies in SDSS DR7: I. Two point correlation functions
Shi, Feng; Wang, Huiyuan; Zhang, Youcai; Mo, H J; Bosch, Frank C van den; Li, Shijie; Liu, Chengze; Lu, Yi; Tweed, Dylan; Yang, Lei
2016-01-01
Using a method to correct redshift space distortion (RSD) for individual galaxies, we present the measurements of real space two-point correlation functions (2PCFs) of galaxies in the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7). Galaxy groups selected from the SDSS are used as proxies of dark matter halos to correct the virial motions of galaxies in dark matter halos, and to reconstruct the large-scale velocity field. We use an ensemble of mock catalogs to demonstrate the reliability of our method. Over the range $0.2 < r < 20 h^{-1}{\\rm {Mpc}}$, the 2PCF measured directly in reconstructed real space is better than the measurement error due to cosmic variance, if the reconstruction uses the correct cosmology. Applying the method to the SDSS DR7, we construct a real space version of the main galaxy catalog, which contains 396,068 galaxies in the North Galactic Cap with redshifts in the range $0.01 \\leq z \\leq 0.12$. The Sloan Great Wall, the largest known structure in the nearby Universe, is not...
A Computationally Efficient Approach for Calculating Galaxy Two-Point Correlations
Demina, Regina; BenZvi, Segev; Hindrichs, Otto
2016-01-01
We develop a modification to the calculation of the two-point correlation function commonly used in the analysis of large scale structure in cosmology. An estimator of the two-point correlation function is constructed by contrasting the observed distribution of galaxies with that of a uniformly populated random catalog. Using the assumption that the distribution of random galaxies in redshift is independent of angular position allows us to replace pairwise combinatorics with fast integration over probability maps. The new method significantly reduces the computation time while simultaneously increasing the precision of the calculation.
Futures market efficiency diagnostics via temporal two-point correlations. Russian market case study
Mikhail Kopytin; Evgeniy Kazantsev
2013-01-01
Using a two-point correlation technique, we study emergence of market efficiency in the emergent Russian futures market by focusing on lagged correlations. The correlation strength of leader-follower effects in the lagged inter-market correlations on the hourly time frame is seen to be significant initially (2009-2011) but gradually goes down, as the erstwhile leader instruments -- crude oil, the USD/RUB exchange rate, and the Russian stock market index -- seem to lose the leader status. An i...
Meta-conformal invariance and the boundedness of two-point correlation functions
Henkel, Malte; Stoimenov, Stoimen
2016-11-01
The covariant two-point functions, derived from Ward identities in direct space, can be affected by consistency problems and can become unbounded for large time- or space-separations. This difficulty arises for several extensions of dynamical scaling, for example Schrödinger-invariance, conformal Galilei invariance or meta-conformal invariance, but not for standard ortho-conformal invariance. For meta-conformal invariance in (1+1) dimensions, which acts as a dynamical symmetry of a simple advection equation, these difficulties can be cured by going over to a dual space and an extension of these dynamical symmetries through the construction of a new generator in the Cartan sub-algebra. This provides a canonical interpretation of meta-conformally covariant two-point functions as correlators. Galilei-conformal correlators can be obtained from meta-conformal invariance through a simple contraction. In contrast, by an analogus construction, Schrödinger-covariant two-point functions are causal response functions. All these two-point functions are bounded at large separations, for sufficiently positive values of the scaling exponents.
Meta-conformal invariance and the boundedness of two-point correlation functions
Henkel, Malte
2016-01-01
The covariant two-point functions, derived from Ward identities in direct space, can be affected by consistency problems and can become unbounded for large time- or space-separations. This difficulty arises for several extensions of dynamical scaling, for example Schr\\"odinger-invariance, conformal Galilei invariance or meta-conformal invariance, but not for standard ortho-conformal invariance. For meta-conformal invariance in 1+1 dimensions, these difficulties can be cured by going over to a dual space and an extension of these dynamical symmetries through the construction of a new generator in the Cartan sub-algebra. This provides a canonical interpretation of meta-conformally covariant two-point functions as correlators. Galilei-conformal correlators can be obtained from meta-conformal invariance through a simple contraction. In contrast, by an analogus construction, Schr\\"odinger-covariant two-point functions are causal response functions. All these two-point functions are bounded at large separations, fo...
Equal-time two-point correlation functions in Coulomb gauge Yang-Mills theory
Campagnari, D; Reinhardt, H; Astorga, F; Schleifenbaum, W
2009-01-01
We apply a new functional perturbative approach to the calculation of the equal-time two-point correlation functions and the potential between static color charges to one-loop order in Coulomb gauge Yang-Mills theory. The functional approach proceeds through a solution of the Schroedinger equation for the vacuum wave functional to order g^2 and derives the equal-time correlation functions from a functional integral representation via new diagrammatic rules. We show that the results coincide with those obtained from the usual Lagrangian functional integral approach, extract the beta function and determine the anomalous dimensions of the equal-time gluon and ghost two-point functions and the static potential under the assumption of multiplicative renormalizability to all orders.
Usui, Kouta
2012-01-01
It will be proved that a model of lattice field theories which satisfies (A1) Hermiticity, (A2) translational invariance, (A3) reflection positivity, and (A4) polynomial boundedness of correlations, permits the Kallen-Lehmann representation of two point correlation functions with positive spectral density function. Then, we will also argue that positivity of spectral density functions is necessary for a lattice theory to satisfy conditions (A1) - (A4). As an example, a lattice overlap scalar boson model will be discussed. We will find that the overlap scalar boson violates the reflection positivity.
Banerjee, Supratik; Galtier, Sébastien
2013-01-01
Compressible isothermal magnetohydrodynamic turbulence is analyzed under the assumption of statistical homogeneity and in the asymptotic limit of large kinetic and magnetic Reynolds numbers. Following Kolmogorov we derive an exact relation for some two-point correlation functions which generalizes the expression recently found for hydrodynamics. We show that the magnetic field brings new source and flux terms into the dynamics which may act on the inertial range similarly as a source or a sink for the mean energy transfer rate. The introduction of a uniform magnetic field simplifies significantly the exact relation for which a simple phenomenology may be given. A prediction for axisymmetric energy spectra is eventually proposed.
Two-point correlators revisited: Fast and slow scales in multifield models of Inflation
Ghersi, José T Gálvez
2016-01-01
We study the structure of two-point correlators of the inflationary field fluctuations in order to improve the accuracy and efficiency of the existing spectral methods. We present a description motivated by the separation of the fast and slow evolving components of the spectrum. Our purpose is to rephrase all the relevant equations of motion in terms of slowly varying quantities. This is important in order to consider the contribution from high-frequency modes to the spectrum without affecting computational performance. The slow-roll approximation is not required to reproduce the main distinctive features in the power spectrum for each specific model of inflation.
Logarithmic two-point correlation functions from a z=2 Lifshitz model
Energy Technology Data Exchange (ETDEWEB)
Zingg, T. [Institute for Theoretical Physics and Spinoza Institute, Universiteit Utrecht,Leuvenlaan 4, 3584 CE Utrecht (Netherlands)
2014-01-21
The Einstein-Proca action is known to have asymptotically locally Lifshitz spacetimes as classical solutions. For dynamical exponent z=2, two-point correlation functions for fluctuations around such a geometry are derived analytically. It is found that the retarded correlators are stable in the sense that all quasinormal modes are situated in the lower half-plane of complex frequencies. Correlators in the longitudinal channel exhibit features that are reminiscent of a structure usually obtained in field theories that are logarithmic, i.e. contain an indecomposable but non-diagonalizable highest weight representation. This provides further evidence for conjecturing the model at hand as a candidate for a gravity dual of a logarithmic field theory with anisotropic scaling symmetry.
Measuring baryon acoustic oscillations with angular two-point correlation function
Alcaniz, Jailson S; Bernui, Armando; Carvalho, Joel C; Benetti, Micol
2016-01-01
The Baryon Acoustic Oscillations (BAO) imprinted a characteristic correlation length in the large-scale structure of the universe that can be used as a standard ruler for mapping out the cosmic expansion history. Here, we discuss the application of the angular two-point correlation function, $w(\\theta)$, to a sample of luminous red galaxies of the Sloan Digital Sky Survey (SDSS) and derive two new measurements of the BAO angular scale at $z = 0.235$ and $z = 0.365$. Since noise and systematics may hinder the identification of the BAO signature in the $w - \\theta$ plane, we also introduce a potential new method to localize the acoustic bump in a model-independent way. We use these new measurements along with previous data to constrain cosmological parameters of dark energy models and to derive a new estimate of the acoustic scale $r_s$.
Directory of Open Access Journals (Sweden)
Volodymyr V. Kindratenko
2009-01-01
Full Text Available We present a parallel implementation of an algorithm for calculating the two-point angular correlation function as applied in the field of computational cosmology. The algorithm has been specifically developed for a reconfigurable computer. Our implementation utilizes a microprocessor and two reconfigurable processors on a dual-MAP SRC-6 system. The two reconfigurable processors are used as two application-specific co-processors. Two independent computational kernels are simultaneously executed on the reconfigurable processors while data pre-fetching from disk and initial data pre-processing are executed on the microprocessor. The overall end-to-end algorithm execution speedup achieved by this implementation is over 90× as compared to a sequential implementation of the algorithm executed on a single 2.8 GHz Intel Xeon microprocessor.
The Two-Point Correlation Function of Gamma-ray Bursts
Li, Ming-Hua
2015-01-01
In this paper, we examine the spacial distribution of gamma-ray bursts (GRBs) using a sample of 373 objects. We subdivide the GRB data into two redshift intervals over the redshift range $0
Experimental Study of the Convergence of Two-Point Cross-Correlation Toward the Green's Function
Gouedard, P.; Roux, P.; Campillo, M.; Verdel, A.; Campman, X.
2007-12-01
It has been shown theoretically by several authors that cross-correlation of the seismic motion recorded at two points could yield the Green's Function (GF) between these points. Convergence of cross-correlations toward the GF depends on sources positions and/or the nature of the wavefield. Direct waves from an even distribution of sources can be used to retrieve the GF. On the other hand, in an inhomogeneous medium, recording the diffuse field (coda) is theoretically sufficient to retrieve the GF whatever the sources distribution is. Since none of these two conditions (even distribution of sources or a perfectly diffuse field) is satisfied in practice, the question of convergence toward the GF has to be investigated with real data. A 3D exploration survey with sources and receivers on a dense grid offers such an opportunity. We used a high- resolution survey recorded by Petroleum Development Oman in North Oman. The data have been obtained in a 1x1~km area covered with 1600 geophones located on a 25x25~m-cell grid. Records are 4-seconds long. A unique feature of this survey is that vibrators (working in the [8-120~Hz] frequency band), were located on a similar grid shifted with respect to the receiver grid by half a cell (12.5~m) in both directions. This allows us to compare estimated GF's with measured direct waves (GF's) between the geophones. The shallow subsurface is highly heterogeneous and records include seismic coda. From this dataset, we selected two receiver locations (Ra and Rb) distant from d=158~m. We used both different sets of source locations and time windows to compute the cross-correlation between these two receivers. Then we compared the derivatives of correlation functions with the actual GF measured in Rb (resp.~Ra) for a source close to Ra (resp.~Rb). By doing so, we show the actual influence of source locations and scattering (governed by the records' selected time window) on the Signal-to-Noise Ratio (SNR) of the reconstructed GF. When using
Spatiotemporal velocity-velocity correlation function in fully developed turbulence
Canet, Léonie; Wschebor, Nicolás; Balarac, Guillaume
2016-01-01
Turbulence is an ubiquitous phenomenon in natural and industrial flows. Since the celebrated work of Kolmogorov in 1941, understanding the statistical properties of fully developed turbulence has remained a major quest. In particular, deriving the properties of turbulent flows from a mesoscopic description, that is from Navier-Stokes equation, has eluded most theoretical attempts. Here, we provide a theoretical prediction for the {\\it space and time} dependent velocity-velocity correlation function of homogeneous and isotropic turbulence from the field theory associated to Navier-Stokes equation with stochastic forcing. This prediction is the analytical fixed-point solution of Non-Perturbative Renormalisation Group flow equations, which are exact in a certain large wave-number limit. This solution is compared to two-point two-times correlation functions computed in direct numerical simulations. We obtain a remarkable agreement both in the inertial and in the dissipative ranges.
Hosokawa, Iwao
2007-01-01
A decaying homogeneous isotropic turbulence is treated on the combined bases of the Kolmogorov hypothesis and the cross-independence hypothesis (for a closure of the Monin-Lundgren (ML) hierarchy of many-point velocity distributions) in turbulence. Similarity solutions for one- and two-point velocity distributions are obtained in the viscous, inertial and large-scale ranges of separation distance, from which we can give a reasonable picture of longitudinal and transverse velocity autocorrelation functions for any Reynolds number, even though they are distant from exact solutions of the infinite ML hierarchy. Possibility of non-similarity solutions with other reasonable and more realistic features is unveiled within the same theoretical framework. The cross-independence hypothesis is proved to be inconsistent with the Kolmogorov [1941b. Dissipation of energy in locally isotropic turbulence. Dokl. Akad. Nauk SSSR 32, 16-18.] theory in the inertial range. This is the main factor by which our special strategy (described in Introduction) is taken for solving this problem.
Two Point Correlation Functions for a Periodic Box-Ball System
Directory of Open Access Journals (Sweden)
Jun Mada
2011-03-01
Full Text Available We investigate correlation functions in a periodic box-ball system. For the second and the third nearest neighbor correlation functions, we give explicit formulae obtained by combinatorial methods. A recursion formula for a specific N-point functions is also presented.
Accuracy of two points correlation length measurement and its applications in H-1NF heliac
Kim, Jaewook; Michael, C. A.; Nam, Y. U.; Lampert, M.; Ghim, Y. C.
2016-10-01
Anomalous transport observed in fusion-grade plasmas is widely accepted to be correlated with spatial and temporal correlation characteristics of the turbulent eddies. While temporal and 2D spatial (radial and poloidal) correlation characteristics have been studied in detail, the lack of such information in the parallel direction, with respect to the background magnetic field, of hot core plasmas precludes us from full understanding and controlling plasma turbulence. KSTAR is equipped with a couple of 2D diagnostic systems measuring ion-scale density fluctuations, namely the BES and MIR systems, at two different toroidal locations. These systems provide a possibility to measure a parallel correlation length. As it is necessary to identify how reliably one can measure correlation length with only two spatial positions, there has been such a study [Jaewook Kim et al., Nucl. Fusion accepted] recently. Based on this recent study, we experimentally obtained 3D correlation functions from H-1NF heliac using the data from a set of Langmuir probes. One probe is spatially fixed, while the second one is scanned radially and poloidally at a different toroidal location. H1-NF heliac plasmas are highly reproducible, therefore we construct the 3D correlation functions with multi-discharges.
Two-Point Stress-Tensor Correlator in N=1 SYM(2+1)
Hiller, J R; Trittmann, U
2001-01-01
Recent advances in string theory have highlighted the need for reliable numerical methods to calculate correlators at strong coupling in supersymmetric theories. We present a calculation of the correlator in N=1 SYM theory in 2+1 dimensions. The numerical method we use is supersymmetric discrete light-cone quantization (SDLCQ), which preserves the supersymmetry at every order of the approximation and treats fermions and bosons on the same footing. This calculation is done at large $N_c$. For small and intermediate r the correlator converges rapidly for all couplings. At small r the correlator behaves like 1/r^6, as expected from conformal field theory. At large r the correlator is dominated by the BPS states of the theory. There is, however, a critical value of the coupling where the large-r correlator goes to zero, suggesting that the large-r correlator can only be trusted to some finite coupling which depends on the transverse resolution. We find that this critical coupling grows linearly with the square r...
Mapping Correlation of Two Point Sources in the Gamma-Ray Sky
Energy Technology Data Exchange (ETDEWEB)
Gibson, Alexander [SLAC National Accelerator Lab., Menlo Park, CA (United States)
2015-08-20
The Fermi Gamma-Ray Space Telescope has been taking data on high energy photons or γ rays since June 11th, 2008, and people have been cataloging and profiling point sources of these γ rays ever since. After roughly one year of being in operation over 1400 sources were cataloged. Now, in 2015 we have 3033 sources cataloged. With the increasing amount of sources it’s important to think about the limitations of likelihood analysis for highly correlated sources. In this paper I will present the problems of using likelihood analysis for sources that are highly correlated as well as show under what circumstances sources can be considered highly correlated. Dark matter over densities may show up as a point source, so it is a necessary step to learn how the two signals will interact to allow for a proper search for dark matter.
Energy Technology Data Exchange (ETDEWEB)
Li, Xue; Cao, Jia; Du, Dajun [Shanghai Univ. (China). Key Lab. of Power Station Automation Technology
2013-07-01
This paper is concerned with the probabilistic optimal power flow (POPF) calculation including wind farms with correlated parameters which contains nodal injections. The two-point estimate method (2PEM) is employed to solve the POPF. Moreover, the correlation samples between nodal injections and line parameters are generated by Cholesky Factorization method. Simulation results show that 2PEM is feasible and effective to solve the POPF including wind farms with correlated parameters, while the 2PEM has higher computation precision and consume less CPU time than Monte Carlo Simulation.
Keller, Jochen
2008-01-01
The thesis is considering aspects of SU(2) Yang-Mills thermodynamics in its deconfining high-temperature phase. We calculate the two-point correlation function of the energy density of the photon in a thermalized gas, at first in the conventional U(1) gauge theory, followed by a calculation, where the photon is identified with the massless gauge mode in deconfining SU(2) Yang-Mills thermodynamics. Apart from the fact, that this calculation is interesting from a technical point of view, we can consider several aspects of phenomenological relevance. Since we interpret the two-point correlator of energy density as a measure for the energy transfer, and thus for the electromagnetic interaction of microscopic objects, such as atoms immersed into a photon gas, we are able to give an explanation for the unexpected stability of cold, innergalactic clouds consisting of atomic hydrogen. Subsequently, we evaluate the spatial string tension in deconfining SU(2) Yang-Mills thermodynamics, which can be regarded as measure ...
Giuricin, G; Girardi, M; Mezzetti, M; Marinoni, C; Giuricin, Giuliano; Samurovic, Srdjan; Girardi, Marisa; Mezzetti, Marino; Marinoni, Christian
2001-01-01
We use the two-point correlation function in redshift space, $\\xi(s)$, to study the clustering of the galaxies and groups of the Nearby Optical Galaxy (NOG) sample, which is a nearly all-sky, complete, magnitude-limited sample of $\\sim$7000 bright and nearby optical galaxies. The correlation function of galaxies is well described by a power law, $\\xi(s)=(s/s_0)^{-\\gamma}$, with slope $\\gamma\\sim1.5$ and $s_0\\sim6.4 h^{-1}$Mpc (on scales $2.7 - 12 h^{-1}$Mpc), in agreement with previous results of several redshift surveys of optical galaxies. We confirm the existence of morphological segregation between early- and late-type galaxies and, in particular, we find a gradual decreasing of the strength of clustering from the S0 galaxies to the late-type spirals, on intermediate scales. Furthermore, luminous galaxies turn out to be more clustered than dim galaxies. The luminosity segregation, which is significant for both early- and late-type objects, starts to become appreciable only for galaxies brighter than $M_B\\...
Teichrieb, Claudio A.; Acevedo, Otávio C.; Degrazia, Gervásio A.; Moraes, Osvaldo L. L.; Roberti, Débora R.; Zimermann, Hans R.; Santos, Daniel M.; Alves, Rita C. M.
2013-03-01
The study presents an analysis of two-point correlations between time series of nocturnal atmospheric wind, obtained from two micrometeorological towers, 45 m horizontally apart, each equipped with two sonic anemometers, 2.5 m vertically apart. It focuses on the scale dependence of the two-point correlations obtained from sensors vertically and horizontally separated. In particular, the role of low-frequency non-turbulent processes in the correlations is assessed, and compared to that of the turbulent scales of motion. The vertical correlations of the streamwise and vertical wind components show little dependence on the turbulence intensity, but those of the spanwise component decrease appreciably as it gets more turbulent. Multiresolution decomposition shows that the two-point correlations become increasingly dominated by low-frequency scales as it gets less turbulent, and that such large-scale processes are largely reduced in fully turbulent conditions. It is also shown that the vertical correlations of the spanwise wind component is negative for very small time scales. Horizontal two-point correlations obtained at the 45 m separation distance between the towers are almost entirely dominated by low-frequency motions, regardless of the turbulence intensity, but the magnitude of such correlations decreases with increasing turbulence intensity for any wind components. A comparison between the horizontal two-point correlations and autocorrelations taken with a time lag given by the ratio of the horizontal separation to the mean wind component in the direction that connects the two towers leads to the conclusion that the statistical properties of turbulence are often preserved over the horizontal distance, despite the lack of turbulence correlations for that separation.
Esquivel, A; Pogosyan, D; Cho, J; Esquivel, Alejandro; Cho, Jungyeon
2003-01-01
In a previous work Lazarian and Pogosyan suggested a technique to extract velocity and density statistics, of interstellar turbulence, by means of analysing statistics of spectral line data cubes. In this paper we test that technique, by studying the effect of correlation between velocity and density fields, providing a systematic analysis of the noise, and exploring the effect of a linear shear. We make use of both compressible MHD simulations and synthetic data to emulate spectroscopic observations. With such synthetic spectroscopic data, we studied anisotropies of the two point statistics and related those anisotropies with the magnetic field direction. This presents a new technique for magnetic field studies. The results show that the velocity and density spectral indices measured are consistent with the analytical predictions. We identified the dominant source of error with the limited number of data points along a given line of sight. We argue that in real observations the number of emmiting elements is...
van Daalen, Marcel P; McCarthy, Ian G; Booth, C M; Vecchia, Claudio Dalla
2013-01-01
The observed clustering of galaxies and the cross-correlation of galaxies and mass (a measure of galaxy-galaxy lensing) provide important constraints on both cosmology and models of galaxy formation. Even though the dissipation, and more importantly the feedback processes associated with galaxy formation are thought to affect the distribution of matter, essentially all models used to predict clustering data are based on dark matter only simulations. Here, we use large hydrodynamical simulations to investigate how galaxy formation affects the autocorrelation functions of galaxies, subhaloes, as well as their cross-correlation with matter. We show that the changes due to the inclusion of baryons are not limited to small scales and are even present in samples selected by subhalo mass. Samples selected by subhalo mass cluster ~10% more strongly in a baryonic run on scales r ~ 1Mpc/h or larger, and this difference increases for smaller separations. While the inclusion of baryons boosts the clustering at fixed subh...
Contreras, Carlos; Poole, Gregory B; Marin, Felipe; Brough, Sarah; Colless, Matthew; Couch, Warrick; Croom, Scott; Croton, Darren; Davis, Tamara M; Drinkwater, Michael J; Forster, Karl; Gilbank, David; Gladders, Mike; Glazebrook, Karl; Jelliffe, Ben; Jurek, Russell J; Li, I-hui; Madore, Barry; Martin, D Christopher; Pimbblet, Kevin; Pracy, Michael; Sharp, Rob; Wisnioski, Emily; Woods, David; Wyder, Ted K; Yee, H K C; 10.1093/mnras/sts608
2013-01-01
The growth history of large-scale structure in the Universe is a powerful probe of the cosmological model, including the nature of dark energy. We study the growth rate of cosmic structure to redshift $z = 0.9$ using more than $162{,}000$ galaxy redshifts from the WiggleZ Dark Energy Survey. We divide the data into four redshift slices with effective redshifts $z = [0.2,0.4,0.6,0.76]$ and in each of the samples measure and model the 2-point galaxy correlation function in parallel and transverse directions to the line-of-sight. After simultaneously fitting for the galaxy bias factor we recover values for the cosmic growth rate which are consistent with our assumed $\\Lambda$CDM input cosmological model, with an accuracy of around 20% in each redshift slice. We investigate the sensitivity of our results to the details of the assumed model and the range of physical scales fitted, making close comparison with a set of N-body simulations for calibration. Our measurements are consistent with an independent power-spe...
Kim, Jaewook; Lampert, M; Ghim, Y -c
2016-01-01
A statistical method for the estimation of spatial correlation lengths of Gaussian-shaped fluctuating signals with two measurement points is examined to quantitatively evaluate its reliability (variance) and accuracy (bias error). The standard deviation of the correlation value is analytically derived for randomly distributed Gaussian shaped fluctuations satisfying stationarity and homogeneity, allowing us to evaluate, as a function of fluctuation-to-noise ratios, sizes of averaging time windows and ratios of the distance between the two measurement points to the true correlation length, the goodness of the two-point measurement for estimating the spatial correlation length. Analytic results are confirmed with numerically generated synthetic data and real experimental data obtained with the KSTAR beam emission spectroscopy diagnostic. Our results can be applied to Gaussian-shaped fluctuating signals where a correlation length must be measured with only two measurement points.
Kim, Jaewook; Nam, Y. U.; Lampert, M.; Ghim, Y.-C.
2016-10-01
A statistical method for the estimation of the spatial correlation lengths of Gaussian-shaped fluctuating signals with two measurement points is examined to quantitatively evaluate its reliability (variance) and accuracy (bias error). The standard deviation of the correlation value is analytically derived for randomly distributed Gaussian shaped fluctuations satisfying stationarity and homogeneity, allowing us to evaluate, as a function of fluctuation-to-noise ratios, the sizes of averaging time windows and the ratios of the distance between the two measurement points to the true correlation length, and the goodness of the two-point measurement for estimating the spatial correlation length. Analytic results are confirmed with numerically generated synthetic data and real experimental data obtained with the KSTAR beam emission spectroscopy diagnostic. Our results can be applied to Gaussian-shaped fluctuating signals where a correlation length must be measured with only two measurement points.
Space-time correlations of fluctuating velocities in turbulent shear flows.
Zhao, Xin; He, Guo-Wei
2009-04-01
Space-time correlations or Eulerian two-point two-time correlations of fluctuating velocities are analytically and numerically investigated in turbulent shear flows. An elliptic model for the space-time correlations in the inertial range is developed from the similarity assumptions on the isocorrelation contours: they share a uniform preference direction and a constant aspect ratio. The similarity assumptions are justified using the Kolmogorov similarity hypotheses and verified using the direct numerical simulation (DNS) of turbulent channel flows. The model relates the space-time correlations to the space correlations via the convection and sweeping characteristic velocities. The analytical expressions for the convection and sweeping velocities are derived from the Navier-Stokes equations for homogeneous turbulent shear flows, where the convection velocity is represented by the mean velocity and the sweeping velocity is the sum of the random sweeping velocity and the shear-induced velocity. This suggests that unlike Taylor's model where the convection velocity is dominating and Kraichnan and Tennekes' model where the random sweeping velocity is dominating, the decorrelation time scales of the space-time correlations in turbulent shear flows are determined by the convection velocity, the random sweeping velocity, and the shear-induced velocity. This model predicts a universal form of the space-time correlations with the two characteristic velocities. The DNS of turbulent channel flows supports the prediction: the correlation functions exhibit a fair good collapse, when plotted against the normalized space and time separations defined by the elliptic model.
Capri, M A L; Pereira, A D; Fiorentini, D; Guimaraes, M S; Mintz, B W; Palhares, L F; Sorella, S P
2016-01-01
In order to construct a gauge invariant two-point function in a Yang-Mills theory, we propose the use of the all-order gauge invariant transverse configurations A^h. Such configurations can be obtained through the minimization of the functional A^2_{min} along the gauge orbit within the BRST invariant formulation of the Gribov-Zwanziger framework recently put forward in [1,2] for the class of the linear covariant gauges. This correlator turns out to provide a characterization of non-perturbative aspects of the theory in a BRST invariant and gauge parameter independent way. In particular, it turns out that the poles of are the same as those of the transverse part of the gluon propagator, which are also formally shown to be independent of the gauge parameter entering the gauge condition through the Nielsen identities. The latter follow from the new exact BRST invariant formulation introduced before. Moreover, the correlator enables us to attach a BRST invariant meaning to the possible positivity violation of ...
Vector Velocity Imaging Using Cross-Correlation and Virtual Sources
DEFF Research Database (Denmark)
Holfort, Iben Kraglund; Kortbek, Jacob; Jensen, Jørgen Arendt
2006-01-01
Previous investigations have shown promising results in using the directional cross-correlation method to estimate velocity vectors. The velocity vector estimate provides information on both velocity direction and magnitude. The direction is estimated by beamforming signals along directions...
Mo, Jie-Xiong; Lin, Ze-Tao; Zeng, Xiao-Xiong
2016-01-01
To gain holographic insight into critical phenomena of $f(R)$ AdS black holes, we investigate their two point correlation function, which are dual to the geodesic length in the bulk. We solve the equation of motion constrained by the boundary condition numerically and probe both the effect of boundary region size and $f(R)$ gravity. Moreover, we introduce an analogous specific heat related to $\\delta L$. It is shown in the $T-\\delta L$ graph for the case $Q
Revisiting van der Waals like behavior of f(R AdS black holes via the two point correlation function
Directory of Open Access Journals (Sweden)
Jie-Xiong Mo
2017-05-01
Full Text Available Van der Waals like behavior of f(R AdS black holes is revisited via two point correlation function, which is dual to the geodesic length in the bulk. The equation of motion constrained by the boundary condition is solved numerically and both the effect of boundary region size and f(R gravity are probed. Moreover, an analogous specific heat related to δL is introduced. It is shown that the T−δL graphs of f(R AdS black holes exhibit reverse van der Waals like behavior just as the T−S graphs do. Free energy analysis is carried out to determine the first order phase transition temperature T⁎ and the unstable branch in T−δL curve is removed by a bar T=T⁎. It is shown that the first order phase transition temperature is the same at least to the order of 10−10 for different choices of the parameter b although the values of free energy vary with b. Our result further supports the former finding that charged f(R AdS black holes behave much like RN-AdS black holes. We also check the analogous equal area law numerically and find that the relative errors for both the cases θ0=0.1 and θ0=0.2 are small enough. The fitting functions between log|T−Tc| and log|δL−δLc| for both cases are also obtained. It is shown that the slope is around 3, implying that the critical exponent is about 2/3. This result is in accordance with those in former literatures of specific heat related to the thermal entropy or entanglement entropy.
Park, Dae Woo; Kruger, Grant H; Rubin, Jonathan M; Hamilton, James; Gottschalk, Paul; Dodde, Robert E; Shih, Albert J; Weitzel, William F
2013-10-01
This study investigated the use of ultrasound speckle decorrelation- and correlation-based lateral speckle-tracking methods for transverse and longitudinal blood velocity profile measurement, respectively. By studying the blood velocity gradient at the vessel wall, vascular wall shear stress, which is important in vascular physiology as well as the pathophysiologic mechanisms of vascular diseases, can be obtained. Decorrelation-based blood velocity profile measurement transverse to the flow direction is a novel approach, which provides advantages for vascular wall shear stress measurement over longitudinal blood velocity measurement methods. Blood flow velocity profiles are obtained from measurements of frame-to-frame decorrelation. In this research, both decorrelation and lateral speckle-tracking flow estimation methods were compared with Poiseuille theory over physiologic flows ranging from 50 to 1000 mm/s. The decorrelation flow velocity measurement method demonstrated more accurate prediction of the flow velocity gradient at the wall edge than the correlation-based lateral speckle-tracking method. The novelty of this study is that speckle decorrelation-based flow velocity measurements determine the blood velocity across a vessel. In addition, speckle decorrelation-based flow velocity measurements have higher axial spatial resolution than Doppler ultrasound measurements to enable more accurate measurement of blood velocity near a vessel wall and determine the physiologically important wall shear.
Correlative velocity fluctuations over a gravel river bed
Dinehart, R.L.
1999-01-01
Velocity fluctuations in a steep, coarse-bedded river were measured in flow depths ranging from 0.8 to 2.2 m, with mean velocities at middepth from 1.1 to 3.1 m s−1. Analyses of synchronous velocity records for two and three points in the vertical showed a broad range of high coherence for wave periods from 10 to 100 s, centering around 10–30 s. Streamwise correlations over distances of 9 and 14 m showed convection velocities near mean velocity for the same wave periods. The range of coherent wave periods was a small multiple of predicted “boil” periods. Correlative fluctuations in synchronous velocity records in the vertical direction suggested the blending of short pulses into longer wave periods. The highest spectral densities were measured beyond the range of coherent wave periods and were probably induced by migration of low-relief bed forms.
Correlation Between Particle Velocities and Conditions of Abrasive Waterjet Formation
Chen, Wei-Long
1990-01-01
The velocities of water and abrasive particles in abrasive waterjet(AWJ) were measured by the use of Laser Transit Anemometer(LTA). A setup for the velocity measurement was constructed and a statistical technique was used to improve the accuracy of the velocity determination. A comparison of the magnitude of velocities determined by LTA, Piezoelectric Force Transducer and Schlieren Photograph clearly indicates the feasibility of the use of LTA. The velocities of water and particles were measured for different diameters of water and slurry nozzles, abrasive mass flow rates and particle sizes. The performed experiments enabled us to evaluate the effects of conditions of jet formation on the particles velocities. An empirical equation for the prediction of particles velocities was constructed by the use of obtained results. The coefficient of correlation between experimental and computed results is equal to 0.93. The acquired information can be used to select the operational parameters in AWJ cutting. The obtained results also provide information on the acceleration mechanism of entrained particles, which may be used to improve the design of slurry nozzle.
Lagrangian Velocity Correlations and Absolute Dispersion in the Midlatitude Troposphere
Sukhatme, J
2004-01-01
Employing daily wind data from the ECMWF, we perform passive particle advection to estimate the Lagrangian velocity correlation functions (LVCF) associated with the midlatitude tropospheric flow. In particular we decompose the velocity field into time mean and transient (or eddy) components to better understand the nature of the LVCF's.A closely related quantity, the absolute dispersion (AD) is also examined. Given the anisotropy of the flow, meridional and zonal characteristics are considered separately. The zonal LVCF is seen to be non-exponential. In fact, for a broad set of intermediate timescales it is better described as a power law of the form $\\tau^{-\\alpha}$ with $ 0<\\alpha<1$. Indeed, the implied long time correlation in the zonal flow results in a superdiffusive zonal AD regime. On the other hand, the meridional LVCF decays rapidly to zero. Interestingly, before approaching to zero it shows a region of negative correlation. A physical argument based on the rotational inhibition of latitudinal...
Two-point optical coherency matrix tomography.
Abouraddy, Ayman F; Kagalwala, Kumel H; Saleh, Bahaa E A
2014-04-15
The two-point coherence of an electromagnetic field is represented completely by a 4×4 coherency matrix G that encodes the joint polarization-spatial-field correlations. Here, we describe a systematic sequence of cascaded spatial and polarization projective measurements that are sufficient to tomographically reconstruct G--a task that, to the best of our knowledge, has not yet been realized. Our approach benefits from the correspondence between this reconstruction problem in classical optics and that of quantum state tomography for two-photon states in quantum optics. Identifying G uniquely determines all the measurable correlation characteristics of the field and, thus, lifts ambiguities that arise from reliance on traditional scalar descriptors, especially when the field's degrees of freedom are correlated or classically entangled.
Tong, Jonathan; Mao, Oliver; Goldreich, Daniel
2013-01-01
Two-point discrimination is widely used to measure tactile spatial acuity. The validity of the two-point threshold as a spatial acuity measure rests on the assumption that two points can be distinguished from one only when the two points are sufficiently separated to evoke spatially distinguishable foci of neural activity. However, some previous research has challenged this view, suggesting instead that two-point task performance benefits from an unintended non-spatial cue, allowing spuriously good performance at small tip separations. We compared the traditional two-point task to an equally convenient alternative task in which participants attempt to discern the orientation (vertical or horizontal) of two points of contact. We used precision digital readout calipers to administer two-interval forced-choice versions of both tasks to 24 neurologically healthy adults, on the fingertip, finger base, palm, and forearm. We used Bayesian adaptive testing to estimate the participants' psychometric functions on the two tasks. Traditional two-point performance remained significantly above chance levels even at zero point separation. In contrast, two-point orientation discrimination approached chance as point separation approached zero, as expected for a valid measure of tactile spatial acuity. Traditional two-point performance was so inflated at small point separations that 75%-correct thresholds could be determined on all tested sites for fewer than half of participants. The 95%-correct thresholds on the two tasks were similar, and correlated with receptive field spacing. In keeping with previous critiques, we conclude that the traditional two-point task provides an unintended non-spatial cue, resulting in spuriously good performance at small spatial separations. Unlike two-point discrimination, two-point orientation discrimination rigorously measures tactile spatial acuity. We recommend the use of two-point orientation discrimination for neurological assessment.
Directory of Open Access Journals (Sweden)
Jonathan eTong
2013-09-01
Full Text Available Two-point discrimination is widely used to measure tactile spatial acuity. The validity of the two-point threshold as a spatial acuity measure rests on the assumption that two points can be distinguished from one only when the two points are sufficiently separated to evoke spatially distinguishable foci of neural activity. However, some previous research has challenged this view, suggesting instead that two-point task performance benefits from an unintended non-spatial cue, allowing spuriously good performance at small tip separations. We compared the traditional two-point task to an equally convenient alternative task in which participants attempt to discern the orientation (vertical or horizontal of two points of contact. We used precision digital readout calipers to administer two-interval forced-choice versions of both tasks to 24 neurologically healthy adults, on the fingertip, finger base, palm, and forearm. We used Bayesian adaptive testing to estimate the participants’ psychometric functions on the two tasks. Traditional two-point performance remained significantly above chance levels even at zero point separation. In contrast, two-point orientation discrimination approached chance as point separation approached zero, as expected for a valid measure of tactile spatial acuity. Traditional two-point performance was so inflated at small point separations that 75%-correct thresholds could be determined on all tested sites for fewer than half of participants. The 95%-correct thresholds on the two tasks were similar, and correlated with receptive field spacing. In keeping with previous critiques, we conclude that the traditional two-point task provides an unintended non-spatial cue, resulting in spuriously good performance at small spatial separations. Unlike two-point discrimination, two-point orientation discrimination rigorously measures tactile spatial acuity. We recommend the use of two-point orientation discrimination for neurological
A velocity parameter for the correlation of axial fan noise
Wright, T.
1982-08-01
An aerodynamic parameter that relates subsonic axial fan noise to the fundamental flow behavior in the blade row of a fan is proposed. The parameter is the peak or maximum blade surface velocity in the rotating reference frame and includes, either explicitly or implicitly, the influence of tip speed, volume flow rate, pressure rise, shaft horsepower and efficiency. Correlation of the noise associated with a very broad range of axial fans yields good agreement and collapse of data when compared to currently used correlation methods. Use of this parameter, rather than those based on overall performance, allows trade-off studies to be made within a given performance requirement so that a minimum noise configuration may be designed or selected.
Mattingly, S. W.; Berumen, J.; Chu, F.; Hood, R.; Skiff, F.
2013-11-01
A technique for probing velocity space correlations has been developed using laser-induced fluorescence. In this paper, a description of the experimental setup is given, with results to follow in a later publication. The experiment consists of a cylindrical plasma column 3 m long and radius ~ 0.25 cm, holding singly-charged argon ions (Ar II) with density n ~ 109 cm-3, Te ~ 5 eV, Ti,|| ~ .06 eV, and a 1 kG axial magnetic field. Two separate metastable lines are excited by single frequency lasers at 611 nm and 668 nm. These lasers may tune with a precision of .01 pm. The separate lasers are used to measure independent slices of the velocity distribution function. To confirm the velocity distribution and magnetic field, the Doppler-broadened, sigma-polarized Zeeman line for each transition is measured. With this, the absolute parallel component of ion velocity subject to LIF can be determined. The two separate lasers then give us a signal as a function of two separate parallel ion velocities. Two point correlation is used to reduce the noise floor on the plasma fluctuation. This fluctuation is then investigated as a function of the difference in velocity.
Velocity-vorticity correlation structures in compressible turbulent boundary layer
Chen, Jun; Li, Shi-Yao; She, Zhen-Su
2016-11-01
A velocity-vorticity correlation structure (VVCS) analysis is applied to analyze data of 3-dimensional (3-D) direct numerical simulations (DNS), to investigate the quantitative properties of the most correlated vortex structures in compressible turbulent boundary layer (CTBL) at Mach numbers, Ma = 2 . 25 and 6 . 0 . It is found that the geometry variation of the VVCS closely reflects the streamwise development of CTBL. In laminar region, the VVCS captures the instability wave number of the boundary layer. The transition region displays a distinct scaling change of the dimensions of VVCS. The developed turbulence region is characterized by a constant spatial extension of the VVCS. For various Mach numbers, the maximum correlation coefficient of the VVCS presents a clear multi-layer structure with the same scaling laws as a recent symmetry analysis proposed to quantifying the sublayer, the log-layer, and the wake flow. A surprising discovery is that the wall friction coefficient, Cf, holds a "-1"-power law of the wall normal distance of the VVCS, ys. This validates the speculation that the wall friction is determined by the near-wall coherent structure, which clarifies the correlation between statistical structures and the near-wall dynamics. Project 11452002 and 11172006 supported by National Natural Science Foundation of China.
Two-Point Fuzzy Ostrowski Type Inequalities
Directory of Open Access Journals (Sweden)
Muhammad Amer Latif
2013-08-01
Full Text Available Two-point fuzzy Ostrowski type inequalities are proved for fuzzy Hölder and fuzzy differentiable functions. The two-point fuzzy Ostrowski type inequality for M-lipshitzian mappings is also obtained. It is proved that only the two-point fuzzy Ostrowski type inequality for M-lipshitzian mappings is sharp and as a consequence generalize the two-point fuzzy Ostrowski type inequalities obtained for fuzzy differentiable functions.
Experimental investigation of transverse velocity estimation using cross-correlation
DEFF Research Database (Denmark)
Bjerngaard, Rasmus; Jensen, Jørgen Arendt
2001-01-01
A technique for estimating the full flow velocity vector has previously been presented by our group. Unlike conventional estimators, that only detect the axial component of the flow, this new method is capable of estimating the transverse velocity component. The method uses focusing along the flow....... A mean parabolic velocity profile was obtained for purely transverse flow with a mean bias to the true profile of -2.5% relative to the peak velocity and a standard deviation of 13.3% relative to the peak velocity. Twenty pulse-echo lines were used for each estimate and 18 profiles were obtained...
Spin-velocity correlations of optically pumped atoms
Marsland, R., III; McGuyer, B. H.; Olsen, B. A.; Happer, W.
2012-08-01
We present efficient theoretical tools for describing the optical pumping of atoms by light propagating at arbitrary directions with respect to an external magnetic field, at buffer-gas pressures that are small enough for velocity-selective optical pumping (VSOP) but large enough to cause substantial collisional relaxation of the velocities and the spin. These are the conditions for the sodium atoms at an altitude of about 100 km that are used as guidestars for adaptive optics in modern ground-based telescopes to correct for aberrations due to atmospheric turbulence. We use spin and velocity relaxation modes to describe the distribution of atoms in spin space (including both populations and coherences) and velocity space. Cusp kernels are used to describe velocity-changing collisions. Optical pumping operators are represented as a sum of poles in the complex velocity plane. Signals simulated with these methods are in excellent agreement with previous experiments and with preliminary experiments in our laboratory.
Holographic Two-Point Functions in Conformal Gravity
Ghodsi, Ahmad; Naseh, Ali
2014-01-01
In this paper we compute the holographic two-point functions of four dimensional conformal gravity. Precisely we calculate the two-point functions for Energy-Momentum (EM) and Partially Massless Response (PMR) operators that have been identified as two response functions for two independent sources in the dual CFT. The correlation function of EM with PMR tensors turns out to be zero which is expected according to the conformal symmetry. The two-point function of EM is that of a transverse and traceless tensor, and the two-point function of PMR which is a traceless operator contains two distinct parts, one for a transverse-traceless tensor operator and another one for a vector field, both of which fulfill criteria of a CFT. We also discuss about the unitarity of the theory.
A new maximum likelihood blood velocity estimator incorporating spatial and temporal correlation
DEFF Research Database (Denmark)
Schlaikjer, Malene; Jensen, Jørgen Arendt
2001-01-01
The blood flow in the human cardiovascular system obeys the laws of fluid mechanics. Investigation of the flow properties reveals that a correlation exists between the velocity in time and space. The possible changes in velocity are limited, since the blood velocity has a continuous profile in time...... of the observations gives a probability measure of the correlation between the velocities. Both the MLE and the STC-MLE have been evaluated on simulated and in-vivo RF-data obtained from the carotid artery. Using the MLE 4.1% of the estimates deviate significantly from the true velocities, when the performance...
Particle Velocity Fluctuations in Steady State Sedimentation: Stratification Controlled Correlations
Segrè, P N
2007-01-01
The structure and dynamics of steady state sedimentation of semi-concentrated ($\\phi=0.10$) monodisperse spheres are studied in liquid fluidized beds. Laser turbidity and particle imaging methods are used to measure the particle velocity fluctuations and the steady state concentration profiles. Using a wide range of particle and system sizes, we find that the measured gradients $\
Statistics of pressure and of pressure-velocity correlations in isotropic turbulence
Biferale, L.; Gualtieri, P.; Toschi, F.
2000-01-01
Some pressure and pressure-velocity correlations in a direct numerical simulations of a three-dimensional turbulent flow at moderate Reynolds numbers have been analyzed. We have identified a set of pressure-velocity correlations which possess a good scaling behavior. Such a class of
Two Point Pade Approximants and Duality
Banks, Tom
2013-01-01
We propose the use of two point Pade approximants to find expressions valid uniformly in coupling constant for theories with both weak and strong coupling expansions. In particular, one can use these approximants in models with a strong/weak duality, when the symmetries do not determine exact expressions for some quantity.
Effects of 3D random correlated velocity perturbations on predicted ground motions
Hartzell, S.; Harmsen, S.; Frankel, A.
2010-01-01
Three-dimensional, finite-difference simulations of a realistic finite-fault rupture on the southern Hayward fault are used to evaluate the effects of random, correlated velocity perturbations on predicted ground motions. Velocity perturbations are added to a three-dimensional (3D) regional seismic velocity model of the San Francisco Bay Area using a 3D von Karman random medium. Velocity correlation lengths of 5 and 10 km and standard deviations in the velocity of 5% and 10% are considered. The results show that significant deviations in predicted ground velocities are seen in the calculated frequency range (≤1 Hz) for standard deviations in velocity of 5% to 10%. These results have implications for the practical limits on the accuracy of scenario ground-motion calculations and on retrieval of source parameters using higher-frequency, strong-motion data.
Institute of Scientific and Technical Information of China (English)
ZHANG Xiao-Qiang; WANG Guang-Rui; CHEN Shi-Gang
2008-01-01
We propose a new approach to the old-standing problem of the anomaly of the scaling exponents of passive scalars of turbulence.Different to the original problem,the distribution function of the prescribed random velocity field is multi-dimensional normal and delta-correlated in time.Here,our random velocity field is spatially correlative.For comparison,we also give the result obtained by the Gaussian random velocity field without spatial correlation.The anomalous scaling exponents H (p) of passive scalar advected by two kinds of random velocity above are determined for structure function up to p= 15 by numerical simulations of the random shell model with Runge-Kutta methods to solve the stochastic differential equations.We observed that the H (p)'s obtained by the multi-dimensional normal distribution random velocity are more anomalous than those obtained by the independent Gaussian random velocity.
Efficient focusing scheme for transverse velocity estimation using cross-correlation
DEFF Research Database (Denmark)
Jensen, Jørgen Arendt
2001-01-01
The blood velocity can be estimated by cross-correlation of received RE signals, but only the velocity component along the beam direction is found. A previous paper showed that the complete velocity vector can be estimated, if received signals are focused along lines parallel to the direction...... simulations with Field II. A 64-elements, 5 MHz linear array was used. A parabolic velocity profile with a peak velocity of 0.5 m/s was considered for different angles between the flow and the ultrasound beam and for different emit foci. At 60 degrees the relative standard deviation was 0.58 % for a transmit...
Directory of Open Access Journals (Sweden)
Supriyono
2013-07-01
Full Text Available Conventional velocity analysis is usually done in a relatively spare grid, for instance every half kilometers, during the processing of seismic data. It is very laborious work and very subjective. To deliver an accurate velocity picking, processing geophysicists must have a good understanding of geological background of area being analyzed and experiences. Velocity errors often occur during picking. Proper quality control and checking are a must. A good and reliable velocity field is very important in seismic processing for achieving high-quality seismic images as well as for delivering an accurate depth conversion. The new method presented here, was developed to correct velocity errors automatically by means of residual velocity correction, and to produce an offset-dependent RMS velocity field at the same time. The method is data driven, based on the normal move out equation (NMO and measuring the local even correlation between adjacent traces. The stacking velocity is derived simply by averaging the velocity field. The proposed method was tested on synthetic and real data examples with good result. The velocity field has certain characteristics related to hydrocarbon presence. Supriyono (2011 and 2012 developed a new DHI method using velocity gradient attributes by cross-plotting the velocity versus offset (VVO. The velocity gradient exhibits high anomalous values in the presence of gas.
Study of Correlations Between Radio Jet Velocity and Supermassive Black Hole Mass in Active Galaxies
Directory of Open Access Journals (Sweden)
Timothy Pennucci
2006-01-01
Full Text Available Previous research has shown that numerous characteristics of many host galaxies, such as stellar velocity dispersion and bulge luminosity, are governed by the central supermassive black hole (SMBH. This same SMBH is also thought to be the origin of radio jets propagating outward from the nucleus of these galaxies. It was then hypothesized that the mass of a SMBH influences and correlates with the initial radio jet velocity in active galaxies. Mass and velocity data were collected for 48 radio galaxies but as a result from projection effects due to the nature of active galaxies, apparent transverse velocity replaced intrinsic velocity in this study as the dependent variable. From these transverse velocities, the minimum intrinsic velocities of the radio jets were calculated for further investigation. Three apparent transverse velocity groups arise in the results that may be weakly correlated to SMBH mass. The calculated minimum intrinsic velocity data supports this correlation. These results are qualitative in nature and need to be tested on additional samples. While no direct conclusion can be made, the positive trends produced in this research between SMBH mass and radio jet velocity may later aid in further studies and galactic evolutionary research.
Short-time evolution of Lagrangian velocity gradient correlations in isotropic turbulence
Fang, Le; Jin, G D
2015-01-01
We show by direct numerical simulation (DNS) that the Lagrangian cross correlation of velocity gradients in homogeneous isotropic turbulence increases at short times, whereas its auto-correlation decreases. Kinematic considerations allow to show that two invariants of the turbulent velocity field determine the short-time velocity gradient correlations. In order to get a more intuitive understanding of the dynamics for longer times, heuristic models are proposed involving the combined action of local shear and rotation. These models quantitatively reproduce the effects and disentangle the different physical mechanisms leading to the observations in the DNS.
Space-time ambiguity of two- and three-fragment reduced velocity correlation functions
Energy Technology Data Exchange (ETDEWEB)
Glasmacher, T.; Phair, L.; Bowman, D.R.; Gelbke, C.K.; Gong, W.G.; Kim, Y.D.; Lisa, M.A.; Lynch, W.G.; Peaslee, G.F.; de Souza, R.T.; Tsang, M.B.; Zhu, F. [National Superconducting Cyclotron Laboratory and Department of Physics Astronomy, Michigan State University, East Lansing, Michigan 48824 (United States)
1995-06-01
Reduced-velocity correlation functions between two and three intermediate mass fragments are compared for central {sup 36}Ar+{sup 197}Ar collisions at {ital E}/{ital A}=50 MeV. Previously published {ital N}-body Coulomb-trajectory calculations, capable of reproducing the measured two-fragment reduced velocity-correlation function, describe the measured three-fragment correlation function equally well. Moreover, ambiguities between source size and lifetime observed in the analysis of two-fragment correlations remain unresolved in the three-fragment correlation function.
Fractional Brownian motions: memory, diffusion velocity, and correlation functions
Fuliński, A.
2017-02-01
Fractional Brownian motions (FBMs) have been observed recently in the measured trajectories of individual molecules or small particles in the cytoplasm of living cells and in other dense composite systems, among others. Various types of FBMs differ in a number of ways, including the strength, range and type of damping of the memory encoded in their definitions, but share several basic characteristics: distributions, non-ergodic properties, and scaling of the second moment, which makes it difficult to determine which type of Brownian motion (fractional or normal) the measured trajectory belongs to. Here, we show, by introducing FBMs with regulated range and strength of memory, that it is the structure of memory which determines their physical properties, including mean velocity of diffusion; therefore, the course and kinetics of several processes (including coagulation and some chemical reactions). We also show that autocorrelation functions possess characteristic features which enable identification of an observed FBM, and of the type of memory governing its trajectory. In memoriam Marian Smoluchowski, on the 100th anniversary of the publication of his seminal papers on Brownian motion and diffusion-limited kinetics.
Hemodynamic Correlates of Late Systolic Flow Velocity Augmentation in the Carotid Artery
Heffernan, Kevin S.; Lefferts, Wesley K; Augustine, Jacqueline A.
2013-01-01
Background. The contour of the common carotid artery (CCA) blood flow velocity waveform changes with age; CCA flow velocity increases during late systole, and this may contribute to cerebrovascular disease. Late systolic flow velocity augmentation can be quantified using the flow augmentation index (FAIx). We examined hemodynamic correlates of FAIx to gain insight into determinants of CCA flow patterns. Methods. CCA Doppler ultrasound and wave intensity analysis (WIA) were used to assess regi...
Scambos, Theodore A.; Dutkiewicz, Melanie J.; Wison, Jeremy C.; Bindschadler, Robert A.
1992-01-01
A high-resolution map of the velocity field of the central portion of Ice Stream E in West Antarctica, generated by the displacement-measuring technique, is presented. The use of cross-correlation software is found to be a significant improvement over previous manually based photogrammetric methods for velocity measurement, and is far more cost-effective than in situ methods in remote polar areas. A hue-intensity-saturation image of Ice Stream E and its velocity field is shown.
Relative seismic velocity variations correlate with deformation at Kīlauea volcano.
Donaldson, Clare; Caudron, Corentin; Green, Robert G; Thelen, Weston A; White, Robert S
2017-06-01
Seismic noise interferometry allows the continuous and real-time measurement of relative seismic velocity through a volcanic edifice. Because seismic velocity is sensitive to the pressurization state of the system, this method is an exciting new monitoring tool at active volcanoes. Despite the potential of this tool, no studies have yet comprehensively compared velocity to other geophysical observables on a short-term time scale at a volcano over a significant length of time. We use volcanic tremor (~0.3 to 1.0 Hz) at Kīlauea as a passive source for interferometry to measure relative velocity changes with time. By cross-correlating the vertical component of day-long seismic records between ~230 station pairs, we extract coherent and temporally consistent coda wave signals with time lags of up to 120 s. Our resulting time series of relative velocity shows a remarkable correlation between relative velocity and the radial tilt record measured at Kīlauea summit, consistently correlating on a time scale of days to weeks for almost the entire study period (June 2011 to November 2015). As the summit continually deforms in deflation-inflation events, the velocity decreases and increases, respectively. Modeling of strain at Kīlauea suggests that, during inflation of the shallow magma reservoir (1 to 2 km below the surface), most of the edifice is dominated by compression-hence closing cracks and producing faster velocities-and vice versa. The excellent correlation between relative velocity and deformation in this study provides an opportunity to understand better the mechanisms causing seismic velocity changes at volcanoes, and therefore realize the potential of passive interferometry as a monitoring tool.
Theory and signal processing of acoustic correlation techniques for current velocity measurement
Institute of Scientific and Technical Information of China (English)
ZHU Weiqing; FENG Lei; WANG Changhong; WANG Yuling; QIU Wei
2008-01-01
A theoretical model and signal processing of acoustic correlation measurements to estimate current velocity are discussed. The sonar space-time correlation function of vol-ume reverberations within Fraunhofer zone is derived. The function, which is in exponential forms, is the theoretical model of acoustic correlation measurements. The characteristics of the correlation values around the maximum of the amplitude of the correlation function, where most information about current velocity is contained, are primarily analyzed. Localized Least Mean Squares (LLMS) criterion is put forward for velocity estimation. Sequential Quadratic Programming (SQP) method is adopted as the optimization method. So the systematic sig-nal processing method of acoustic correlation techniques for current velocity measurement is established. A prototype acoustic correlation current profiler (ACCP) underwent several sea trials, the results show that theoretical model approximately coincides with experimental re-sults. Current profiles including the speed and direction from ACCP are compared with those from acoustic Doppler current profiler (ADCP). The current profiles by both instruments agree reasonably well. Also, the standard deviation of velocity measurement by ACCP is statistically calculated and it is a little larger than predicted value.
Effects of correlated turbulent velocity fields on the formation of maser lines
Boeger, R; Hegmann, M
2003-01-01
The microturbulent approximation of turbulent motions is widely used in radiative transfer calculations. Mainly motivated by its simple computational application it is probably in many cases an oversimplified treatment of the dynamical processes involved. This aspect is in particular important in the analysis of maser lines, since the strong amplification of radiation leads to a sensitive dependence of the radiation field on the overall velocity structure. To demonstrate the influence of large scale motions on the formation of maser lines we present a simple stochastic model which takes velocity correlations into account. For a quantitative analysis of correlation effects, we generate in a Monte Carlo simulation individual realizations of a turbulent velocity field along a line of sight. Depending on the size of the velocity correlation length we find huge deviations between the resulting random profiles in respect of line shape, intensity and position of single spectral components. Finally, we simulate the e...
Artifacts in blood velocity estimation using ultrasound and cross-correlation
DEFF Research Database (Denmark)
Jensen, Jørgen Arendt
1994-01-01
Estimation of blood velocities using ultrasound and time-domain cross-correlation is investigated. The measurement principle is introduced, and the basic properties of the cross-correlation function are discussed. Expressions for the variance of the estimates of the peak location are given, showing...
Salvi, Paolo; Palombo, Carlo; Salvi, Giovanni Matteo; Labat, Carlos; Parati, Gianfranco; Benetos, Athanase
2013-12-01
Several studies showed a positive association between heart rate and pulse wave velocity, a sensitive marker of arterial stiffness. However, no study involving a large population has specifically addressed the dependence of pulse wave velocity on different components of the cardiac cycle. The aim of this study was to explore in subjects of different age the link between pulse wave velocity with heart period (the reciprocal of heart rate) and the temporal components of the cardiac cycle such as left ventricular ejection time and diastolic time. Carotid-femoral pulse wave velocity was assessed in 3,020 untreated subjects (1,107 men). Heart period, left ventricular ejection time, diastolic time, and early-systolic dP/dt were determined by carotid pulse wave analysis with high-fidelity applanation tonometry. An inverse association was found between pulse wave velocity and left ventricular ejection time at all ages (pulse wave velocity and heart period was also found, with the exception of the youngest subjects (P = 0.20). A significant positive correlation was also found between pulse wave velocity and dP/dt (P pulse wave velocity at all ages, whereas the contribution of heart period no longer became significant. Our data demonstrate that pulse wave velocity is more closely related to left ventricular systolic function than to heart period. This may have methodological and pathophysiological implications.
Estimation of blood velocity vectors using transverse ultrasound beam focusing and cross-correlation
DEFF Research Database (Denmark)
Jensen, Jørgen Arendt; Lacasa, Isabel Rodriguez
1999-01-01
Modern ultrasound scanners estimate the blood velocity by tracking the movement of the blood scatterers along the ultrasound beam. This is done by emitting pulsed ultrasound fields and finding the shift in position from pulse to pulse by correlating the received signals. Only the velocity component...... along the beam direction is found, and this is a serious limitation in the current scanners, since most blood vessels are parallel to the skin surface. A method to find the velocity across the vessel has been suggested by Bonnefous (1988). Here a number of parallel receive beams are measured and used...... or across it or in any direction to the beam. The focused lines, thus, follow the flow and a cross-correlation of lines from different pulses can find the movement of the blood particles between pulse emissions and, thus, the blood velocity. The new approach is investigated using the Field II simulation...
Machicoane, Nathanaël
2015-01-01
We investigate the response of large inertial particle to turbulent fluctuations in a inhomogeneous and anisotropic flow. We conduct a Lagrangian study using particles both heavier and lighter than the surrounding fluid, and whose diameters are comparable to the flow integral scale. Both velocity and acceleration correlation functions are analyzed to compute the Lagrangian integral time and the acceleration time scale of such particles. The knowledge of how size and density affect these time scales is crucial in understanding partical dynamics and may permit stochastic process modelization using two-time models (for instance Saw-ford's). As particles are tracked over long times in the quasi totality of a closed flow, the mean flow influences their behaviour and also biases the velocity time statistics, in particular the velocity correlation functions. By using a method that allows for the computation of turbulent velocity trajectories, we can obtain unbiased Lagrangian integral time. This is particularly usef...
Energy Technology Data Exchange (ETDEWEB)
Wilson, R.J.; Jones, B.G.; Roy, R.P.
1980-02-01
An experimental study of the fluctuating velocity field, the fluctuating static wall pressure and the in-stream fluctuating static pressure in an annular turbulent air flow system with a radius ratio of 4.314 has been conducted. The study included direct measurements of the mean velocity profile, turbulent velocity field; fluctuating static wall pressure and in-stream fluctuating static pressure from which the statistical values of the turbulent intensity levels, power spectral densities of the turbulent quantities, the cross-correlation between the fluctuating static wall pressure and the fluctuating static pressure in the core region of the flow and the cross-correlation between the fluctuating static wall pressure and the fluctuating velocity field in the core region of the flow were obtained.
Correlation of Spherical Thermistor for the Measurement of Low Velocity Air Flow
Institute of Scientific and Technical Information of China (English)
Xin－GangLiang; Ying－PingZhang; 等
1998-01-01
A spherical thermistor,an accurate temperature sensor is employed as an air velocity sensor in this work.The measuring principle is derived and the effects of the insulation layer,air temperature,netural convection and thermal radiation are discussed.Two different correlation relations for velocity measurements are proposed based on theoretical analyses and experimental calibrations,Experiments have shown that spherical thermistor is a good velocity sensor for speed between 0.1-2.5m/s at room temperature and the insulation layer hardly influences the accuracy of the thermistor used in the present work,Modification of correlation can even further imporve measurement accuracy.Since the thermistor is small and cheap,it is possible to apply this method to multi-Point velocity measurement with a low disturbance to the flow field.
Özkan, İlker; Yayla, Zeliha
2016-03-01
The aim of this study is to establish a correlation between physical properties and ultrasonic pulse velocity of clay samples fired at elevated temperatures. Brick-making clay and pottery clay were studied for this purpose. The physical properties of clay samples were assessed after firing pressed clay samples separately at temperatures of 850, 900, 950, 1000, 1050 and 1100 °C. A commercial ultrasonic testing instrument (Proceq Pundit Lab) was used to evaluate the ultrasonic pulse velocity measurements for each fired clay sample as a function of temperature. It was observed that there became a relationship between physical properties and ultrasonic pulse velocities of the samples. The results showed that in consequence of increasing densification of the samples, the differences between the ultrasonic pulse velocities were higher with increasing temperature. These findings may facilitate the use of ultrasonic pulse velocity for the estimation of physical properties of fired clay samples.
Determination of velocity vector angles using the directional cross-correlation method
DEFF Research Database (Denmark)
Kortbek, Jacob; Jensen, Jørgen Arendt
2005-01-01
with a normal transmission of a focused ultrasound field. The velocity profile estimates from simulations have relative mean standard deviations between 0 . 7% and 7 . 7% for flow between 45 ◦ and 90 ◦ . The angle estimation performance is highly dependent on the choice of the time k tprf · T prf ( correlation...
An On-Chip RBC Deformability Checker Significantly Improves Velocity-Deformation Correlation
Directory of Open Access Journals (Sweden)
Chia-Hung Dylan Tsai
2016-10-01
Full Text Available An on-chip deformability checker is proposed to improve the velocity–deformation correlation for red blood cell (RBC evaluation. RBC deformability has been found related to human diseases, and can be evaluated based on RBC velocity through a microfluidic constriction as in conventional approaches. The correlation between transit velocity and amount of deformation provides statistical information of RBC deformability. However, such correlations are usually only moderate, or even weak, in practical evaluations due to limited range of RBC deformation. To solve this issue, we implemented three constrictions of different width in the proposed checker, so that three different deformation regions can be applied to RBCs. By considering cell responses from the three regions as a whole, we practically extend the range of cell deformation in the evaluation, and could resolve the issue about the limited range of RBC deformation. RBCs from five volunteer subjects were tested using the proposed checker. The results show that the correlation between cell deformation and transit velocity is significantly improved by the proposed deformability checker. The absolute values of the correlation coefficients are increased from an average of 0.54 to 0.92. The effects of cell size, shape and orientation to the evaluation are discussed according to the experimental results. The proposed checker is expected to be useful for RBC evaluation in medical practices.
Offshore Southern California lithospheric velocity structure from noise cross-correlation functions
Bowden, D. C.; Kohler, M. D.; Tsai, V. C.; Weeraratne, D. S.
2016-05-01
A new shear wave velocity model offshore Southern California is presented that images plate boundary deformation including both thickening and thinning of the crustal and mantle lithosphere at the westernmost edge of the North American continent. The Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment (ALBACORE) ocean bottom seismometer array, together with 65 stations of the onshore Southern California Seismic Network, is used to measure ambient noise correlation functions and Rayleigh wave dispersion curves which are inverted for 3-D shear wave velocities. The resulting velocity model defines the transition from continental lithosphere to oceanic, illuminating the complex history and deformation in the region. A transition to the present-day strike-slip regime between the Pacific and North American Plates resulted in broad deformation and capture of the now >200 km wide continental shelf. Our velocity model suggests the persistence of the uppermost mantle volcanic processes associated with East Pacific Rise spreading adjacent to the Patton Escarpment, which marks the former subduction of Farallon Plate underneath North America. The most prominent of these seismic structures is a low-velocity anomaly underlying the San Juan Seamount, suggesting ponding of magma at the base of the crust, resulting in thickening and ongoing adjustment of the lithosphere due to the localized loading. The velocity model also provides a robust framework for future earthquake location determinations and ground-shaking simulations for risk estimates.
Nusser, Adi
2017-09-01
The peculiar velocity of a mass tracer is on average aligned with the dipole modulation of the surrounding mass density field. We present a first measurement of the correlation between radial peculiar velocities of objects in the cosmicflows-3 catalogue and the dipole moment of the 2MRS galaxy distribution in concentric spherical shells centred on these objects. Limiting the analysis to cosmicflows-3 objects with distances of 100h-1 Mpc, the correlation function is detected at a confidence level of ≳ 4σ. The measurement is found consistent with the standard ΛCDM model at the ≲ 1.7σ level. We formally derive the constraints 0.32 confidence level) or equivalently 0.34 type of correlations.
Velocity Distribution Measurement Using Pixel-Pixel Cross Correlation of Electrical Tomography
Institute of Scientific and Technical Information of China (English)
DENGXiang; PENGLihui; YAODanya; ZHANGBaofen
2004-01-01
Electrical tomography (ET) provides a novel means of visualizing the internal behavior of twophase flow in industrial process. Using a dual-sensingplane Electrical resistance tomography (ERT) or Electrical capacitance tomography (ECT) system, the raw data of two different section images can be acquired synchronously and the two images reflecting the inner medium distribution respectively can also be reconstructed by using imaging algorithm. Further, the analysis of pixel-pixel cross correlation is able to be setup and the measurement of velocity distribution of two-phase flow could be achieved. The principle is described in the paper. The FFT algorithm for gray value computation and cross correlation function calculation is also introduced. Some experimental results of velocity distribution measurement using pixelpixel cross correlation in vertical slug flow are presented.
Implementation of ultrasound time-domain cross-correlation blood velocity estimators
DEFF Research Database (Denmark)
Jensen, Jørgen Arendt
1993-01-01
are used in the algorithm, imposing a heavy burden on the signal processing hardware. The algorithm is analyzed with regard to the high sampling frequency, and a method for performing real-time high-speed-movement and cross-correlation is suggested. Implementation schemes based on using the sign......The implementation of real-time blood velocity estimators using time-domain cross-correlation is investigated. The basic algorithm for stationary echo canceling, cross-correlation estimation and subsequent velocity estimation is presented. Sampled data acquired at rates of approximately 20 MHz...... of the data as well as the full precision are proposed. From an analysis of the process it is concluded that the sign data implementation can attain real-time processing. This can also be obtained for the full precision data, but at the expense of using a number of dedicated signal processing chips. Both...
Lagrangian velocity auto-correlations in statistically-steady rotating turbulence
Del Castello, Lorenzo
2013-01-01
Lagrangian statistics of passive tracers in rotating turbulence is investigated by Particle Tracking Velocimetry. A confined and steadily-forced turbulent flow is subjected to five different rotation rates. The PDFs of the velocity components clearly reveal the anisotropy induced by background rotation. Although the statistical properties of the horizontal turbulent flow field are approximately isotropic, in agreement with previously reported results by van Bokhoven and coworkers [Phys. Fluids 21, 096601 (2009)], the velocity component parallel to the (vertical) rotation axis gets strongly reduced (compared to the horizontal ones) while the rotation is increased. The auto-correlation coefficients of all three components are progressively enhanced for increasing rotation rates, although the vertical one shows a tendency to decrease for slow rotation rates. The decorrelation is approximately exponential. Lagrangian data compare favourably with previously reported Eulerian data for horizontal velocity components...
Study of heat transfer in CI engine using heat transfer correlation based on intake jet velocity
Energy Technology Data Exchange (ETDEWEB)
Sharief, A. [Sri Siddharhta Inst. of Technology, Tumkur, Karnataka (India); Samaga, B.S.; Shrinivas Rao, B.R. [Nitte Mahalinga Adyantaya Institute of Technology, Karkala, Karnataka (India); JAntonyc, A. [Sahyadri Inst. of Technology, Mangalore, Karnataka (India)
2009-07-01
A reliable heat transfer formulation is needed to simulate reciprocating combustion engines. In order to reduce heat loss and improve thermal efficiency, it is necessary to calculate the rate of heat transfer from the working fluid to the combustion chamber walls. The thermal stresses in the engine components must also be determined. In this study, the author calculated heat transfer coefficient in a diesel engine using a heat transfer correlation based on intake jet velocity instead of mean piston speed. Experiments were conducted in a diesel engine with natural aspiration of hot air at 150 to 300 degrees C. Peak temperature was 1100 degrees C at various loads. The convective heat transfer coefficient and radiative heat transfer coefficient component was also determined separately at various loads. This model based on intake jet velocity instead of mean piston speed was found to be more realistic when considering the influence of gas velocities on the thermal boundary layer thickness. 11 refs., 12 figs.
Brunker, J.; Beard, P.
2013-03-01
Blood flow measurements have been demonstrated using the acoustic resolution mode of photoacoustic sensing. This is unlike previous flowmetry methods using the optical resolution mode, which limits the maximum penetration depth to approximately 1mm. Here we describe a pulsed time correlation photoacoustic Doppler technique that is inherently flexible, lending itself to both resolution modes. Doppler time shifts are quantified via cross-correlation of pairs of photoacoustic waveforms generated in moving absorbers using pairs of laser light pulses, and the photoacoustic waves detected using an ultrasound transducer. The acoustic resolution mode is employed by using the transducer focal width, rather than the large illuminated volume, to define the lateral spatial resolution. The use of short laser pulses allows depth-resolved measurements to be obtained with high spatial resolution, offering the prospect of mapping flow within microcirculation. Whilst our previous work has been limited to a non-fluid phantom, we now demonstrate measurements in more realistic blood-mimicking phantoms incorporating fluid suspensions of microspheres flowing along an optically transparent tube. Velocities up to 110 mm/s were measured with accuracies approaching 1% of the known velocities, and resolutions of a few mm/s. The velocity range and resolution are scalable with excitation pulse separation, but the maximum measurable velocity was considerably smaller than the value expected from the detector focal beam width. Measurements were also made for blood flowing at velocities up to 13.5 mm/s. This was for a sample reduced to 5% of the normal haematocrit; increasing the red blood cell concentration limited the maximum measurable velocity so that no results were obtained for concentrations greater than 20% of a physiologically realistic haematocrit. There are several possible causes for this limitation; these include the detector bandwidth and irregularities in the flow pattern. Better
Hemodynamic Correlates of Late Systolic Flow Velocity Augmentation in the Carotid Artery
Directory of Open Access Journals (Sweden)
Kevin S. Heffernan
2013-01-01
Full Text Available Background. The contour of the common carotid artery (CCA blood flow velocity waveform changes with age; CCA flow velocity increases during late systole, and this may contribute to cerebrovascular disease. Late systolic flow velocity augmentation can be quantified using the flow augmentation index (FAIx. We examined hemodynamic correlates of FAIx to gain insight into determinants of CCA flow patterns. Methods. CCA Doppler ultrasound and wave intensity analysis (WIA were used to assess regional hemodynamics in 18 young healthy men (age 22 ± 1 years. Forward waves ( and backward waves (negative area, NA were measured and used to calculate the reflection index (NA/ = RIx. Additional parameters included which is a forward travelling expansion/decompression wave of myocardial origin that produces suction, CCA single-point pulse wave velocity (PWV as a measure of arterial stiffness, and CCA pressure augmentation index (AIx. Results. Primary correlates of FAIx included , logRIx , and AIx . FAIx was not associated with CCA stiffness . Conclusions. FAIx is a complex ventricular-vascular coupling parameter that is associated with both increased expansion wave magnitude (increased suction from the left ventricle and increased pressure from wave reflections.
Hemodynamic correlates of late systolic flow velocity augmentation in the carotid artery.
Heffernan, Kevin S; Lefferts, Wesley K; Augustine, Jacqueline A
2013-01-01
Background. The contour of the common carotid artery (CCA) blood flow velocity waveform changes with age; CCA flow velocity increases during late systole, and this may contribute to cerebrovascular disease. Late systolic flow velocity augmentation can be quantified using the flow augmentation index (FAIx). We examined hemodynamic correlates of FAIx to gain insight into determinants of CCA flow patterns. Methods. CCA Doppler ultrasound and wave intensity analysis (WIA) were used to assess regional hemodynamics in 18 young healthy men (age 22 ± 1 years). Forward waves (W 1) and backward waves (negative area, NA) were measured and used to calculate the reflection index (NA/W 1 = RIx). Additional parameters included W 2 which is a forward travelling expansion/decompression wave of myocardial origin that produces suction, CCA single-point pulse wave velocity (PWV) as a measure of arterial stiffness, and CCA pressure augmentation index (AIx). Results. Primary correlates of FAIx included W 2 (r = - 0.52, P 0.05). Conclusions. FAIx is a complex ventricular-vascular coupling parameter that is associated with both increased expansion wave magnitude (increased suction from the left ventricle) and increased pressure from wave reflections.
Velocity Dispersion of Correlated Energy Spread Electron Beams in the Free Electron Laser
Campbell, L T
2016-01-01
The effects of a correlated linear energy/velocity chirp in the electron beam in the FEL, and how to compensate for its effects by using an appropriate taper (or reverse-taper) of the undulator magnetic field, is well known. The theory, as described thus far, ignores velocity dispersion from the chirp in the undulator, taking the limit of a `small' chirp. In the following, the physics of compensating for chirp in the beam is revisited, including the effects of velocity dispersion, or beam compression or decompression, in the undulator. It is found that the limit of negligible velocity dispersion in the undulator is different from that previously identified as the small chirp limit, and is more significant than previously considered. The velocity dispersion requires a taper which is non-linear to properly compensate for the effects of the detuning, and also results in a varying peak current (end thus a varying gain length) over the length of the undulator. The results may be especially significant for plasma d...
Pleasants, M.; Haritashya, U. K.
2013-12-01
Mountain glaciers make good indicators of even slight changes in climatic conditions because of their sensitivity to temperature and other environmental changes. Due to the inaccessibility of most mountain glaciers, field based measurements of glacier dynamics, especially ice velocities, has proved to be difficult and unrealistic. Because of this, evaluation of satellite imagery has become useful in the determination of glacial ice velocities and production of ice flow models. The calculation and comparison of ice velocities from three glaciated regions (the Southern Alps of New Zealand, the North-east Nepali Himalaya, and the south-eastern Chugach Mountains of Alaska) is presented here. This study was completed to establish the accuracy and global applicability of the method of precise orthorectification, co-registration, and correlation using the software COSI-Corr and in-house filtering techniques. We chose glaciers from different mountain ranges that present different dynamics to establish a specific ice velocity method. Advanced Spacebourne Thermal Emission and Reflection Radiometer (ASTER) L1A images were chosen as close to annual pairs as possible from the available data at the USGS Global Visualization Viewer (GloVis). This study focuses on the Tasman glacier in New Zealand, the Khumbu glacier in the Himalayas, the previously unstudied Scott glacier in Alaska, and the comparison of these ice velocities to climate data for each region compiled from numerous sources in an attempt to draw conclusions of the behavior of these glaciers in response to current climatic changes.
Velocity dispersion of correlated energy spread electron beams in the free electron laser
Campbell, L. T.; Maier, A. R.
2017-03-01
The effects of a correlated linear energy/velocity chirp in the electron beam in the free electron laser (FEL), and how to compensate for its effects by using an appropriate taper (or reverse-taper) of the undulator magnetic field, is well known. The theory, as described thus far, ignores velocity dispersion from the chirp in the undulator, taking the limit of a ‘small’ chirp. In the following, the physics of compensating for chirp in the beam is revisited, including the effects of velocity dispersion, or beam compression or decompression, in the undulator. It is found that the limit of negligible velocity dispersion in the undulator is different from that previously identified as the small chirp limit, and is more significant than previously considered. The velocity dispersion requires a taper which is nonlinear to properly compensate for the effects of the detuning, and also results in a varying peak current (end thus a varying gain length) over the length of the undulator. The results may be especially significant for plasma driven FELs and low energy linac driven FEL test facilities.
DEFF Research Database (Denmark)
Vattulainen, Ilpo Tapio; Hjelt, T.; Ala-Nissila, T.
2000-01-01
We study the diffusive dynamics of adparticles in two model systems with strong interactions by considering the decay of the single-particle velocity correlation function phi (t). In accordance with previous studies, we find phi (t) to decay nonexponentially and follow a power-law phi (t)similar ......We study the diffusive dynamics of adparticles in two model systems with strong interactions by considering the decay of the single-particle velocity correlation function phi (t). In accordance with previous studies, we find phi (t) to decay nonexponentially and follow a power-law phi (t...... be rationalized in terms of interaction effects. Namely, x is typically larger than two in cases where repulsive adparticle-adparticle interactions dominate, while attractive interactions lead to x...
The efficiency of lidar measurements of wind velocity by a correlation lidar
Energy Technology Data Exchange (ETDEWEB)
Astafurov, V.G.; Ignatova, E.Yu.; Matvienko, G.G. (Institute of Atmospheric Optics, Tomsk (Russian Federation))
1992-05-01
A suboptimal estimate of the wind velocity based on the spectral processing of lidar signals is constructed. The error of this estimate is calculated and its calculations are performed for different atmospheric conditions and instrumental parameters for the experimentally confirmed models of the correlation functions of lidar signals. Some recommendations are given on the choice of parameters of a two-path method of sounding with an account of evolution time of the aerosol inhomogeneities. 10 refs., 4 figs., 1 tab.
Porzycki, Jakub; WÄ s, Jarosław; Hedayatifar, Leila; Hassanibesheli, Forough; Kułakowski, Krzysztof
2017-08-01
The aim of the paper is an analysis of self-organization patterns observed in the unidirectional flow of pedestrians. On the basis of experimental data from Zhang et al. [J. Zhang et al., J. Stat. Mech. (2011) P06004, 10.1088/1742-5468/2011/06/P06004], we analyze the mutual positions and velocity correlations between pedestrians when walking along a corridor. The angular and spatial dependencies of the mutual positions reveal a spatial structure that remains stable during the crowd motion. This structure differs depending on the value of n , for the consecutive n th -nearest-neighbor position set. The preferred position for the first-nearest neighbor is on the side of the pedestrian, while for further neighbors, this preference shifts to the axis of movement. The velocity correlations vary with the angle formed by the pair of neighboring pedestrians and the direction of motion and with the time delay between pedestrians' movements. The delay dependence of the correlations shows characteristic oscillations, produced by the velocity oscillations when striding; however, a filtering of the main frequency of individual striding out reduces the oscillations only partially. We conclude that pedestrians select their path directions so as to evade the necessity of continuously adjusting their speed to their neighbors'. They try to keep a given distance, but follow the person in front of them, as well as accepting and observing pedestrians on their sides. Additionally, we show an empirical example that illustrates the shape of a pedestrian's personal space during movement.
Correlation of densities with shear wave velocities and SPT N values
Anbazhagan, P.; Uday, Anjali; Moustafa, Sayed S. R.; Al-Arifi, Nassir S. N.
2016-06-01
Site effects primarily depend on the shear modulus of subsurface layers, and this is generally estimated from the measured shear wave velocity (V s) and assumed density. Very rarely, densities are measured for amplification estimation because drilling and sampling processes are time consuming and expensive. In this study, an attempt has been made to derive the correlation between the density (dry and wet density) and V s/SPT (standard penetration test) N values using measured data. A total of 354 measured V s and density data sets and 364 SPT N value and density data sets from 23 boreholes have been used in the study. Separate relations have been developed for all soil types as well as fine-grained and coarse-grained soil types. The correlations developed for bulk density were compared with the available data and it was found that the proposed relation matched well with the existing data. A graphical comparison and validation based on the consistency ratio and cumulative frequency curves was performed and the newly developed relations were found to demonstrate good prediction performance. An attempt has also been made to propose a relation between the bulk density and shear wave velocity applicable for a wide range of soil and rock by considering data from this study as well as that of previous studies. These correlations will be useful for predicting the density (bulk and dry) of sites having measured the shear wave velocity and SPT N values.
Correlation Analysis between Spin, Velocity Shear, and Vorticity of Baryonic and Dark Matter Halos
Liu, L. L.
2016-05-01
Using cosmological hydrodynamic simulations, we investigate the alignments between velocity shear, vorticity, and the spin of dark matter halos, and study the correlation between baryonic and dark matter. We find that (1) mis-alignment between vorticity of baryonic and dark matter would develop on scales dark matter; (3) small/massive halos spinning parallel/perpendicular to the host filaments are sensitive to the identification of cosmic web, simulation box size, and resolution. These factors might complicate the connection between the spins of dark matter halos and galaxies, and affect the correlation signal of the alignments of galaxy spin with nearby large-scale structures.
Flow speed measurement using two-point collective light scattering
Energy Technology Data Exchange (ETDEWEB)
Heinemeier, N.P
1998-09-01
Measurements of turbulence in plasmas and fluids using the technique of collective light scattering have always been plagued by very poor spatial resolution. In 1994, a novel two-point collective light scattering system for the measurement of transport in a fusion plasma was proposed. This diagnostic method was design for a great improvement of the spatial resolution, without sacrificing accuracy in the velocity measurement. The system was installed at the W7-AS steallartor in Garching, Germany, in 1996, and has been operating since. This master thesis is an investigation of the possible application of this new method to the measurement of flow speeds in normal fluids, in particular air, although the results presented in this work have significance for the plasma measurements as well. The main goal of the project was the experimental verification of previous theoretical predictions. However, the theoretical considerations presented in the thesis show that the method can only be hoped to work for flows that are almost laminar and shearless, which makes it of very small practical interest. Furthermore, this result also implies that the diagnostic at W7-AS cannot be expected to give the results originally hoped for. (au) 1 tab., 51 ills., 29 refs.
Velocity Structure of the ISM as Seen by the Spectral Correlation Function
Ballesteros-Paredes, J; Goodman, A A; Ballesteros-Paredes, Javier; Vazquez-Semadeni, Enrique; Goodman, Alyssa A.
2002-01-01
(Abridged) We use the statistical tool known as the ``Spectral Correlation Function" [SCF] to intercompare simulations and observations of the atomic interstellar medium. The simulations considered mimic three distinct sets of physical conditions. One of them (run "ISM") is intended to represent a mixture of cool and warm atomic gas, and includes self-gravity and magnetic fields. For each simulation, H I spectral-line maps are synthesized and intercompared, both with each other, and with observations, using the SCF. We find that, when thermal broadening is large in comparison with fine-scale turbulent velocity structure, it masks sub-thermal velocity sub-structure in the synthesized spectra. The H I observations we use here for comparison are of the North Celestial Pole (NCP) Loop. None of the simulations match the NCP Loop data very well. The most realistic sets of line profiles and SCF statistics comes from artifically rescaling the velocity axis of run ISM. Without rescaling, almost all velocity structure ...
Kormendy, John; 10.1088/0004-637X/691/2/L142
2009-01-01
High-dynamic-range surface photometry in a companion paper makes possible accurate measurement of the stellar light deficits L_def and mass deficits M_def associated with the cores of elliptical galaxies. We show that L_def correlates with the velocity dispersion sigma of the host galaxy bulge averaged outside the central region that may be affected by a supermassive black hole (BH). We confirm that L_def correlates with BH mass MBH. Also, the fractional light deficit L_def/L correlates with MBH/M, the ratio of BH mass to the galaxy stellar mass. All three correlations have scatter similar to or smaller than the scatter in the well known correlation between MBH and sigma. The new correlations are remarkable in view of the dichotomy between ellipticals with cores and those with central extra light. Core light deficit correlates closely with MBH and sigma, but extra light does not. This supports the suggestion that extra light Es are made in wet mergers with starbursts whereas core Es are made in dry mergers. A...
Indian Academy of Sciences (India)
B. Ravindra; D. W. Longcope
2008-03-01
Time-dependent magneto-hydrodynamic simulations of active region coronal magnetic field require the underlying photospheric magnetic footpoint velocities. The minimum energy fit (MEF) is a new velocity inversion technique to infer the photospheric magnetic footpoint velocities using a pair of vector magnetograms, introduced by Longcope (2004). The MEF selects the smallest overall flow from several consistent flows by minimizing an energy functional. The inferred horizontal and vertical flow fields by the MEF can be further constrained by incorporating the partial or imperfect velocity information obtained through independent means. This hybrid method is expected to give a velocity close to the true magnetic footpoint velocity. Here, we demonstrate that a combination of the MEF, the local correlation tracking (LCT) and Doppler velocity is capable of inferring the velocity close to the photospheric flow.
Bradley, Derek
2013-01-01
The implosion technique has been used to extend measurements of turbulent burning velocities over greater ranges of fuels and pressures. Measurements have been made up to 3.5 MPa and at strain rate Markstein numbers as low as 23. The implosion technique, with spark ignition at two opposite wall positions within a fan-stirred spherical bomb is capable of measuring turbulent burning velocities, at higher pressures than is possible with central ignition. Pressure records and schlieren high speed photography define the rate of burning and the smoothed area of the flame front. The first aim of the study was to extend the previous measurements with ethanol and propane-air, with further measurements over wider ranges of fuels and equivalence ratios with mixtures of hydrogen, methane, 10% hydrogen-90% methane, toluene, and i-octane, with air. The second aim was to study further the low turbulence regime in which turbulent burning co-exists with laminar flame instabilities. Correlations are presented of turbulent burning velocity normalised by the effective rms turbulent velocity acting on the flame front, ut=u0k , with the Karlovitz stretch factor, K, for different strain rate Markstein numbers, a decrease in which increases ut=u0k . Experimental correlations are presented for the present measurements, combined with previous ones. Different burning regimes are also identified, extending from that of mixed turbulence/laminar instability at low values of K to that at high values of K, in which ut=u0k is gradually reduced due to increasing localised flame extinctions. © 2012 The Combustion Institute.
Finite-size scaling of two-point statistics and the turbulent energy cascade generators.
Cleve, Jochen; Dziekan, Thomas; Schmiegel, Jürgen; Barndorff-Nielsen, Ole E; Pearson, Bruce R; Sreenivasan, Katepalli R; Greiner, Martin
2005-02-01
Within the framework of random multiplicative energy cascade models of fully developed turbulence, finite-size-scaling expressions for two-point correlators and cumulants are derived, taking into account the observationally unavoidable conversion from an ultrametric to an Euclidean two-point distance. The comparison with two-point statistics of the surrogate energy dissipation, extracted from various wind tunnel and atmospheric boundary layer records, allows an accurate deduction of multiscaling exponents and cumulants, even at moderate Reynolds numbers for which simple power-law fits are not feasible. The extracted exponents serve as input for parametric estimates of the probabilistic cascade generator. Various cascade generators are evaluated.
Prediction of shear wave velocity using empirical correlations and artificial intelligence methods
Maleki, Shahoo; Moradzadeh, Ali; Riabi, Reza Ghavami; Gholami, Raoof; Sadeghzadeh, Farhad
2014-06-01
Good understanding of mechanical properties of rock formations is essential during the development and production phases of a hydrocarbon reservoir. Conventionally, these properties are estimated from the petrophysical logs with compression and shear sonic data being the main input to the correlations. This is while in many cases the shear sonic data are not acquired during well logging, which may be for cost saving purposes. In this case, shear wave velocity is estimated using available empirical correlations or artificial intelligent methods proposed during the last few decades. In this paper, petrophysical logs corresponding to a well drilled in southern part of Iran were used to estimate the shear wave velocity using empirical correlations as well as two robust artificial intelligence methods knows as Support Vector Regression (SVR) and Back-Propagation Neural Network (BPNN). Although the results obtained by SVR seem to be reliable, the estimated values are not very precise and considering the importance of shear sonic data as the input into different models, this study suggests acquiring shear sonic data during well logging. It is important to note that the benefits of having reliable shear sonic data for estimation of rock formation mechanical properties will compensate the possible additional costs for acquiring a shear log.
Prediction of shear wave velocity using empirical correlations and artificial intelligence methods
Directory of Open Access Journals (Sweden)
Shahoo Maleki
2014-06-01
Full Text Available Good understanding of mechanical properties of rock formations is essential during the development and production phases of a hydrocarbon reservoir. Conventionally, these properties are estimated from the petrophysical logs with compression and shear sonic data being the main input to the correlations. This is while in many cases the shear sonic data are not acquired during well logging, which may be for cost saving purposes. In this case, shear wave velocity is estimated using available empirical correlations or artificial intelligent methods proposed during the last few decades. In this paper, petrophysical logs corresponding to a well drilled in southern part of Iran were used to estimate the shear wave velocity using empirical correlations as well as two robust artificial intelligence methods knows as Support Vector Regression (SVR and Back-Propagation Neural Network (BPNN. Although the results obtained by SVR seem to be reliable, the estimated values are not very precise and considering the importance of shear sonic data as the input into different models, this study suggests acquiring shear sonic data during well logging. It is important to note that the benefits of having reliable shear sonic data for estimation of rock formation mechanical properties will compensate the possible additional costs for acquiring a shear log.
Djupsjöbacka, Mats; Domkin, Dmitry
2005-01-01
In order to plan and control movements the central nervous system (CNS) needs to continuously keep track of the state of the musculoskeletal system. Therefore the CNS constantly uses sensory input from mechanoreceptors in muscles, joints and skin to update information about body configuration on different levels of the CNS. On the conscious level, such representations constitute proprioception. Different tests for assessment of proprioceptive acuity have been described. However, it is unclear if the proprioceptive acuity measurements in these tests correlate within subjects. By using both uni- and multivariate analysis we compared proprioceptive acuity in different variants of ipsilateral active and passive limb position-matching and ipsilateral passive limb movement velocity-discrimination in a group of healthy subjects. The analysis of the position-matching data revealed a higher acuity of matching for active movements in comparison to passive ones. The acuity of matching was negatively correlated to movement extent. There was a lack of correlation between proprioceptive acuity measurements in position-matching and velocity-discrimination.
Approach to the origin of turbulence on the basis of two-point kinetic theory
Tsuge, S.
1974-01-01
Equations for the fluctuation correlation in an incompressible shear flow are derived on the basis of kinetic theory, utilizing the two-point distribution function which obeys the BBGKY hierarchy equation truncated with the hypothesis of 'ternary' molecular chaos. The step from the molecular to the hydrodynamic description is accomplished by a moment expansion which is a two-point version of the thirteen-moment method, and which leads to a series of correlation equations, viz., the two-point counterparts of the continuity equation, the Navier-Stokes equation, etc. For almost parallel shearing flows the two-point equation is separable and reduces to two Orr-Sommerfeld equations with different physical implications.
A clear age-velocity dispersion correlation in Andromeda's stellar disk
Dorman, Claire E.; Guhathakurta, Puragra; Seth, Anil C; Weisz, Daniel R.; Bell, Eric F.; Dalcanton, Julianne J.; Gilbert, Karoline M.; Hamren, Katherine M.; Lewis, Alexia R.; Skillman, Evan D.; Toloba, Elisa; Williams, Benjamin F.
2015-01-01
The stellar kinematics of galactic disks are key to constraining disk formation and evolution processes. In this paper, for the first time, we measure the stellar age-velocity dispersion correlation in the inner 20 kpc (3.5 disk scale lengths) of M31 and show that it is dramatically different from that in the Milky Way. We use optical Hubble Space Telescope/Advanced Camera for Surveys photometry of 5800 individual stars from the Panchromatic Hubble Andromeda Treasury (PHAT) survey and Keck/DE...
Yoon, Min; Ahn, Junsun; Hwang, Jinyul; Sung, Hyung Jin
2016-08-01
The relationship between the frictional drag and the velocity-vorticity correlations in wall-bounded turbulent flows is derived from the mean vorticity equation. A formula for the skin friction coefficient is proposed and evaluated with regards to three canonical wall-bounded flows: turbulent boundary layer, turbulent channel flow, and turbulent pipe flow. The frictional drag encompasses four terms: advective vorticity transport, vortex stretching, viscous, and inhomogeneous terms. Drag-reduced channel flow with the slip condition is used to test the reliability of the formula. The advective vorticity transport and vortex stretching terms are found to dominate the contributions to the frictional drag.
Institute of Scientific and Technical Information of China (English)
ZHOU Yan-guo; CHEN Yun-min; KE Han
2005-01-01
Recent studies using field case history data yielded new criteria for evaluating liquefaction potential in saturated granular deposits based on in situ, stress-corrected shear wave velocity. However, the conditions of relatively insufficient case histories and limited site conditions in this approach call for additional data to more reliably define liquefaction resistance as a function of shear wave velocity. In this study, a series of undrained cyclic triaxial tests were conducted on saturated sand with shear wave velocity Vs measured by bender element. By normalizing the data with respect to minimum void ratio, the test results, incorporated with previously published laboratory data, statistically revealed good correlation of cyclic shear strength with small-strain shear modulus for sandy soils, which is almost irrespective of soil types and confining pressures. The consequently determined cyclic resistance ratio, CRR, was found to be approximately proportional to Vs4. Liquefaction resistance boundary curves were established by applying this relationship and compared to liquefaction criteria derived from seismic field measurements. Although in the range of Vs1＞200 m/s the presented curves are moderately conservative, they are remarkably consistent with the published field performance criteria on the whole.
Peters, M. P.; Holbrook, W. S.; Flinchum, B. A.; Pasquet, S.
2016-12-01
Despite increasing scientific interest in the critical zone, the accurate determination of fracture density in the subsurface remains difficult as access and costs can prohibit ground-truthing through drilling. A more precise characterization of the fracturing process provides critical insight in to subsurface structures. This is particularly important in determining the point at which protolithic rock becomes fractured bedrock and then degrades to soil through the process of weathering. We studied outcrops in the Laramie Range of southeastern Wyoming were studied and fracture densities were correlated with seismic pressure (P) wave velocities. We used the Differential Effective Medium (DEM) rock physics model to validate our findings and provide a more robust characterization of the role of P-wave velocities acquired on outcrops play in critical zone science. This approach marks a significant departure from previous research, which has not applied P-wave fracture relationships in outcrops onto the critical zone for subsurface characterization. We compared our results with borehole data to establish a relationship between surface outcrops and subsurface rock structures. We found a clear, inverse relationship between a decrease in P-wave velocity and an increase in fracture density consistent with borehole data in the studied area. Our findings suggest that outcrops can be used to determine fracture density in the critical zone. We show that the use of seismic refraction surveys on outcrops provides a non-invasive, highly transferrable method through which we can predict fracturing densities in the subsurface.
A clear age-velocity dispersion correlation in Andromeda's stellar disk
Dorman, Claire E; Seth, Anil C; Weisz, Daniel R; Bell, Eric F; Dalcanton, Julianne J; Gilbert, Karoline M; Hamren, Katherine M; Lewis, Alexia R; Skillman, Evan D; Toloba, Elisa; Williams, Benjamin F
2015-01-01
The stellar kinematics of galactic disks are key to constraining disk formation and evolution processes. In this paper, for the first time, we measure the stellar age-velocity dispersion correlation in the inner 20 kpc (3.5 disk scale lengths) of M31 and show that it is dramatically different from that in the Milky Way. We use optical Hubble Space Telescope/Advanced Camera for Surveys photometry of 5800 individual stars from the Panchromatic Hubble Andromeda Treasury (PHAT) survey and Keck/DEIMOS radial velocity measurements of the same stars from the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo (SPLASH) survey. We show that the average line-of-sight velocity dispersion is a steadily increasing function of stellar age exterior to R=10 kpc, increasing from 30 km/s for the young upper main sequence stars to 90 km/s for the old red giant branch stars. This monotonic increase implies that a continuous or recurring process contributed to the evolution of the disk. Both the slope and normaliz...
Energy Technology Data Exchange (ETDEWEB)
Tal, Balazs; Bencze, Attila; Zoletnik, Sandor; Veres, Gabor [KFKI-Research Institute for Particle and Nuclear Physics, Association EURATOM, PO Box 49, H-1525 Budapest (Hungary); Por, Gabor [Department of Nuclear Techniques, Budapest University of Technology and Economics, Association EURATOM, Muegyetem rkp. 9., H-1111 Budapest (Hungary)
2011-12-15
Time delay estimation methods (TDE) are well-known techniques to investigate poloidal flows in hot magnetized plasmas through the propagation properties of turbulent structures in the medium. One of these methods is based on the estimation of the time lag at which the cross-correlation function (CCF) estimation reaches its maximum value. The uncertainty of the peak location refers to the smallest determinable flow velocity modulation, and therefore the standard deviation of the time delay imposes important limitation to the measurements. In this article, the relative standard deviation of the CCF estimation and the standard deviation of its peak location are calculated analytically using a simple model of turbulent signals. This model assumes independent (non interacting) overlapping events (coherent structures) with randomly distributed spatio-temporal origins moving with background flow. The result of our calculations is the derivation of a general formula for the CCF variance, which is valid not exclusively in the high event density limit, but also for arbitrary event densities. Our formula reproduces the well known expression for high event densities previously published in the literature. In this paper we also present a derivation of the variance of time delay estimation that turns out to be inversely proportional to the applied time window. The derived formulas were tested in real plasma measurements. The calculations are an extension of the earlier work of Bencze and Zoletnik [Phys. Plasmas 12, 052323 (2005)] where the autocorrelation-width technique was developed. Additionally, we show that velocities calculated by a TDE method possess a broadband noise which originates from this variance, its power spectral density cannot be decreased by worsening the time resolution and can be coherent with noises of other velocity measurements where the same turbulent structures are used. This noise should not be confused with the impact of zero mean frequency zonal flow
Honschoten, van J.W.; Druyvesteyn, W.F.; Kuipers, H.; Raangs, R.; Krijnen, G.J.M.
2004-01-01
In this paper a method is presented to reduce the noise level of a particle velocity sensor, a thermal two-wire sensor sensitive to acoustic particle velocities, which yields a reduction of the noise of 30 dB. The method is based on utilisation of cross- instead of auto-correlation spectra of two of
No evidence for activity correlations in the radial velocities of Kapteyn's star
Anglada-Escudé, Guillem; Arriagada, Pamela; Zechmeister, Mathias; Jenkins, James S; Ofir, Aviv; Dreizler, Stefan; Gerlach, Enrico; Marvin, Chistopher J; Reiners, Ansgar; Jeffers, Sandra V; Butler, Paul; Vogt, Steven S; Amado, Pedro J; Rodríguez-López, Cristina; Berdiñas, Zaira M; Morin, Julien; Crane, Jeffrey D; Shectman, Stephen A; Díaz, Matías; Sarmiento, Luis F; Jones, Hugh R A
2015-01-01
Stellar activity may induce Doppler variability at the level of a few m/s which can then be confused by the Doppler signal of an exoplanet orbiting the star. To first order, linear correlations between radial velocity measurements and activity indices have been proposed to account for any such correlation. The likely presence of two super-Earths orbiting Kapteyn's star was reported in Anglada et al. (2014, MNRAS 443L, 89A), but this claim was recently challenged by Robertson et al. (2015, ApJ 805L, 22R) arguing evidence of a rotation period (143 days) at three times the orbital period of one of the proposed planets (Kapteyn's b, P=48.6 days), and the existence of strong linear correlations between its Doppler signal and activity data. By re-analyzing the data using global optimization methods and model comparison, we show that such claim is incorrect given that; 1) the choice of a rotation period at 143 days is unjustified, and 2) the presence of linear correlations is not supported by the data. We conclude t...
Institute of Scientific and Technical Information of China (English)
Li-Xing Zhou; Yang Liu; Yi Xu
2011-01-01
In this paper the present authors measured the gas-particle two-phase velocity correlation in sudden expansion gas-particle flows with a phase Doppler particle anemometer(PDPA) and simulated the system behavior by using both a Reynolds-averaged Navier-Stokes(RANS)model and a large-eddy simulation(LES). The results of the measurements yield the axial and radial time-averaged velocities as well as the fluctuation velocities of gas and three particle-size groups(30μm,50μm,and 95μm) and the gasparticle velocity correlation for 30μm and 50μm particles.From the measurements,theoretical analysis,and simulation,it is found that the two-phase velocity correlation of sudden-expansion flows,like that of jet flows,is less than the gas and particle Reynolds stresses. What distinguishes the two-phase velocity correlations of sudden-expansion flow from those of jet and channel flows is the absence of a clear relationship between the two-phase velocity correlation and particle size in sudden-expansion flows. The measurements,theoretical analysis,and numerical simulation all lead to the above-stated conclusions. Quantitatively,the results of the LES are better than those of the RANS model.
Directory of Open Access Journals (Sweden)
V. S. Chok
2010-01-01
Full Text Available Problem statement: In Part I of this research, the main features of the fluidization behavior and characteristic velocities had been reported. Approach: In the present research, the mixtures characteristic velocity profiles for various sand sizes, palm shell sizes and weight percents were presented. It was recognized that there are instances where the characteristic values remain nearly unchanged from its pure sand values. This regime of constant values can be observed in both compartments and can be established depending on the bed properties. The term "Critical loading" is then selected to define the maximum palm shell content (size and weight percent that can be present in the mixtures where the characteristic velocities remain absolutely of pure sand values. Results: The critical loading increases with the increase of sand size but decreases with the increase of palm shell size. Moreover, it can be observed that the critical loading generally decreases with the increase in particle size ratio, although exception is sighted in the combustor for the mixture with the largest sand size. Overall, the largest sand size has the highest critical loading. Meanwhile, the selected correlations are able to describe the qualitative variation in the characteristic velocities. However, quantitatively, these correlations are unsatisfactory as they are either over-estimate or under-estimate. Conclusion/Recommendations: It is desirable to establish the regime of critical loading since the mixture characteristic velocities can be pre-determined using bed material properties made up from pure sand (inert values. Within this regime, a single operational velocity can be set for respective compartment that is independent from variation of palm shell size and weight percent in the mixtures (especially during combustion or gasification. Ultimately, the state of fluidization (e.g., bubbling or vigorously fluidized and mixing/segregation condition that depend on
Analysis of errors in the measurement of energy dissipation with two-point LDA
Energy Technology Data Exchange (ETDEWEB)
Ducci, A.; Yianneskis, M. [Department of Mechanical Engineering, King' s College London, Experimental and Computational Laboratory for the Analysis of Turbulence (ECLAT), London (United Kingdom)
2005-04-01
In the present study, an attempt has been made to identify and quantify, with a rigorous analytical approach, all possible sources of error involved in the estimation of the fluctuating velocity gradients ({partial_derivative}u{sub i}/{partial_derivative}x{sub j}){sup 2} when a two-point laser Doppler velocimetry (LDV) technique is employed. Measurements were carried out in a grid-generated turbulence flow where the local dissipation rate can be calculated from the decay of kinetic energy. An assessment of the cumulative error determined through the analysis has been made by comparing the values of the spatial gradients directly measured with the gradient estimated from the decay of kinetic energy. The main sources of error were found to be related to the length of the two control volumes and to the fitting range, as well as the function used to interpolate the correlation coefficient when the Taylor length scale (or({partial_derivative}u{sub i}/{partial_derivative}x{sub j}){sup 2}) are estimated. (orig.)
Voids and superstructures: correlations and induced large-scale velocity flows
Lares, Marcelo; Luparello, Heliana E.; Maldonado, Victoria; Ruiz, Andrés N.; Paz, Dante J.; Ceccarelli, Laura; Garcia Lambas, Diego
2017-09-01
The expanding complex pattern of filaments, walls and voids build the evolving cosmic web with material flowing from underdense on to high density regions. Here, we explore the dynamical behaviour of voids and galaxies in void shells relative to neighbouring overdense superstructures, using the Millenium simulation and the main galaxy catalogue in Sloan Digital Sky Survey data. We define a correlation measure to estimate the tendency of voids to be located at a given distance from a superstructure. We find voids-in-clouds (S-types) preferentially located closer to superstructures than voids-in-voids (R-types) although we obtain that voids within ∼40 h-1 Mpc of superstructures are infalling in a similar fashion independently of void type. Galaxies residing in void shells show infall towards the closest superstructure, along with the void global motion, with a differential velocity component depending on their relative position in the shell with respect to the direction to the superstructure. This effect is produced by void expansion and therefore is stronger for R-types. We also find that galaxies in void shells facing the superstructure flow towards the overdensities faster than galaxies elsewhere at the same relative distance to the superstructure. The results obtained for the simulation are also reproduced for the Sky Survey Data Release data with a linearized velocity field implementation.
Directory of Open Access Journals (Sweden)
Dulieu-Barton J.M.
2010-06-01
Full Text Available Characterisation of materials subject to high velocity deformation is necessary as many materials behave differently under such conditions. It is particularly important for accurate numerical simulation of high strain rate events. High velocity servo-hydraulic test machines have enabled material testing in the strain rate regime from 1 – 500 ε/s. The range is much lower than that experienced under ballistic, shock or impact loads, nevertheless it is a useful starting point for the application of optical techniques. The present study examines the possibility of using high speed cameras to capture images and then extracting deformation data using Digital Image Correlation (DIC from tensile testing in the intermediate strain rate regime available with the test machines. Three different materials, aluminium alloy 1050, S235 steel and glass fibre reinforced plastic (GFRP were tested at different nominal strain rates ranging from quasi static to 200 ε/s. In all cases DIC was able to analyse data collected up to fracture and in some cases post fracture. The use of highspeed DIC made it possible to capture phenomena such as multiple necking in the aluminium specimens and post compression failure in GFRP specimens.
Numerical simulation and CFD-Based Correlation of Erosion Threshold Gas Velocity in Pipe Bends
Directory of Open Access Journals (Sweden)
K A Ibrahim1
2010-04-01
Full Text Available
This paper presents numerical simulation of sand erosion phenomena in curved ducts. The Eulerian-Lagrangian approach is used to simulate the gas-solid two-phase flow while semi-empirical model is used to calculate the erosion rate. The effect of solid phase on the gas phase is included in the model. The model prediction is validated with the available experimental data and good agreement was obtained. Based on many predictions of the maximum penetration rate, a CFD based correlation is developed to calculate the penetration rate in bends. From this equation a model to predict the erosional velocity was developed. The present results showed that the flow velocity should be decreased as the mass loading ratio, particle size, pipe diameter increase in order to avoid failure.
Correlation-based correction of sound velocity inhomogeneities using delta-sigma modulators.
Li, P C; Huang, J J; O'Donnell, M
2000-10-01
Delta-sigma (deltasigma) modulator based beamformers have been proposed for high-quality ultrasonic imaging. Due to the high sampling rate and single bit data width, the cost and complexity of the receive beamformer can be significantly reduced. It was shown that with proper dynamic focusing controls, equivalent image quality could be achieved with an adequate signal-to-quantization noise ratio (SQNR). In this paper, deltasigma modulator based beamformers are used for correlation-based phase aberrations correction of sound velocity inhomogeneities in the body. It is shown that the correction can be efficiently implemented at a performance level similar to that of a conventional radio frequency (rf) beamformer. In addition, more than 6 dB contrast improvement is demonstrated. The different dynamic focusing techniques are also investigated in the context of phase aberration correction. It is shown that the single bit dynamic focusing approach does not affect the overall performance of phase aberration correction.
On a correlation among azimuthal velocities and the flyby anomaly sign
Acedo, L
2016-01-01
Data of six flybys, those of Galileo I, Galileo II, NEAR, Cassini, Rosetta and Messenger were reported by Anderson et al \\citep{Anderson}. Four of them: Galileo I, NEAR, Rosetta and Messenger gain Newtonian energy during the flyby transfer, while Galileo II and Cassini lose energy. This is, in both cases, a surprising anomaly since Newtonian forces derive from a potential and they are, therefore, conservative. We show here that the gravitational field of a rotating planet as derived from a new model introduces a non conservative force that gives a partial, but in our opinion satisfactory, explanation of these anomalies and suggests a correlation between the sign of the anomaly and the sign of the azimuthal velocity at perigee.
Hall, Alex
2016-01-01
We investigate the feasibility of measuring the effects of peculiar velocities in large-scale structure using the dipole of the redshift-space cross-correlation function. We combine number counts of galaxies with brightness-temperature fluctuations from 21cm intensity mapping, demonstrating that the dipole may be measured at modest significance ($\\lesssim 2\\sigma$) by combining the upcoming radio survey CHIME with the future redshift surveys of DESI and Euclid. More significant measurements ($\\lesssim~10\\sigma$) will be possible by combining intensity maps from the SKA with these of DESI or Euclid, and an even higher significance measurement ($\\lesssim 100\\sigma$) may be made by combining observables completely internally to the SKA. We account for effects such as contamination by wide-angle terms, interferometer noise and beams in the intensity maps, non-linear enhancements to the power spectrum, stacking multiple populations, sensitivity to the magnification slope, and the possibility that number counts and...
Serum Osteopontin Level Correlates with Carotid-Femoral Pulse Wave Velocity in Geriatric Persons
Directory of Open Access Journals (Sweden)
Chung-Jen Lee
2014-01-01
Full Text Available Osteopontin (OPN is involved in the regulation of vascular calcification processes. The aim of this study was to evaluate the relationship between fasting serum OPN concentration and carotid-femoral pulse wave velocity (cfPWV in geriatric persons. Fasting blood samples were obtained from 93 geriatric persons. cfPWV were performed by SphygmoCor system. Serum OPN levels were measured using a commercially available enzyme-linked immunosorbent assay. Geriatric adults who had diabetes (P=0.007 or dyslipidemia (P=0.029 had higher cfPWV levels than those without diabetes or dyslipidemia. The univariable linear regression analysis showed that age (P=0.002, waist circumference (P=0.048, body mass index (P=0.004, systolic blood pressure (P=0.001, diastolic blood pressure (P=0.036, pulse pressure (P=0.017, creatinine (P=0.002, and log-OPN level (P=0.001 were positively correlated with cfPWV levels, while the high-density lipoprotein cholesterol (HDL-cholesterol level (P=0.007 and glomerular filtration rate (P=0.001 were negatively correlated with cfPWV levels among the geriatric adults. Multivariable forward stepwise linear regression analysis of the significant variables also showed that log-OPN (β=0.233, R2=0.123, regression coefficient: 1.868, P=0.011 was still an independent predictor of cfPWV levels in geriatric persons.
Computational complexity for the two-point block method
See, Phang Pei; Majid, Zanariah Abdul
2014-12-01
In this paper, we discussed and compared the computational complexity for two-point block method and one-point method of Adams type. The computational complexity for both methods is determined based on the number of arithmetic operations performed and expressed in O(n). These two methods will be used to solve two-point second order boundary value problem directly and implemented using variable step size strategy adapted with the multiple shooting technique via three-step iterative method. Two numerical examples will be tested. The results show that the computational complexity of these methods is reliable to estimate the cost of these methods in term of the execution time. We conclude that the two-point block method has better computational performance compare to the one-point method as the total number of steps is larger.
Directory of Open Access Journals (Sweden)
Athikari ChandraSekhar
2014-02-01
Full Text Available Aims: To look for changes in nerve conduction velocity (NCV in newly diagnosed type II diabetic subjects. To compare the nerve conduction velocity studies of both sensory and motor nerves in upper and lower limb are correlated with height, weight, BMI, fasting and PPBS. Materials and Methods: The study comprises of 40 subjects, 25 subjects were male and 15 subjects were female aged between 38-62 years. All the patents are on oral hypoglycaemic agents. Random sampling techniques were applied for the criteria of sample selection. Results: The mean MCV was significantly lower in type II diabetics common peroneal nerve (38.37±9.43 m/s and posterior tibial nerve (9.78±9.39 m/s. The mean SNC in the type II diabetes median nerve 43.25±11.64, ulnar nerve 43.62±15.77 m/sec sural nerve 38.27±14.32 m/sec and posterior tibial nerve 33.51±20.39. The height mean 163.53±7.23 cm, weight mean 66.98±8.70 kg, BMI 25.10±3.29, FBS mean 158.70±56.58 mg/dl and PPBS mean 223.68±67.95 mg/dl. Abnormal MCV, SCV was found to be associated with FBS and PPBS. Conclusion: Hyperglycaemia is a well established risk factor in type 2 diabetic subjects. Other parameters correlated with Height, Weight, BMI, FBS, PPBS increases most recognized neurological complications. Predominately sensorimotor distal polyneuropathy is the most common of the diabetic neuropathy. Distal sensorimotor polyneuropathy. In our study conducted the changes of diabetic neuropathy affected sensorimotor nerves in both limbs. Nerve conduction studies not only used to diagnose the DM but also monitor the effects of treatment of DM by regular NCS good glycemic control, symptoms of diabetic neuropathy can be reversed and further complication like foot ulceration.
Institute of Scientific and Technical Information of China (English)
Jin Xing; Li Jun; Lin Shu; Zhou Zhengrong; Kang Lanchi; Ou Yiping
2008-01-01
This paper uses the 8 broad-band stations' microseism data recorded by the Seismic Monitoring Network of Fujian Province to calculate the vertical correlation coefficient between two stationsat intervals of 5 minutes. According to the time intervals technique we obtain the different coefficients and then add the correlative coefficients. Depending on this, we extract the group velocity of Rayleigh waves from the cross correlation of the ambient seismic noise between two seismic stations and figure out the group velocity' spatial distribution. The results show that the signal noise ratio (SNR) increases proportionally to the superposition times, but the results from different days are similar to one another. Synchronously, the arrival-time is also stable and there is no obvious change when coming across typhoons. It is found the velocity of the surface wave is 2.9～3. 1km/s in Fujian Province, which is close to the observationally attained value.
Two-point functions on deformed space-time
Trampetic, Josip
2014-01-01
We present a review of one-loop photon (\\Pi) and neutrino (\\Sigma) two-point functions in a covariant and deformed U(1) gauge-theory on d-dimensional noncommutative spaces, determined by a constant antisymmetric tensor \\theta, and by a parameter-space (\\kappa_f,\\kappa_g), respectively. For the general fermion-photon S_f(\\kappa_f) and photon self-interaction S_g(\\kappa_g) the closed form results reveal two-point functions with all kind of pathological terms: the UV divergence, the quadratic UV/IR mixing terms as well as a logarithmic IR divergent term of the type ln(\\mu^2(\\theta p)^2). In addition, the photon-loop produces new tensor structures satisfying transversality condition by themselves. We show that the photon two-point function in four-dimensional Euclidean spacetime can be reduced to two finite terms by imposing a specific full rank of \\theta and setting deformation parameters (\\kappa_f,\\kappa_g)=(0,3). In this case the neutrino two-point function vanishes. Thus for a specific point (0,3) in the para...
Similarity of solution branches for two-point semilinear problems
Directory of Open Access Journals (Sweden)
Philip Korman
2003-02-01
Full Text Available For semilinear autonomous two-point problems, we show that all Neumann branches and all Dirichlet branches with odd number of interior roots have the same shape. On the other hand, Dirichlet branches with even number of roots may look differently. While this result has been proved previously by Schaaf cite{S}, our approach appears to be simpler.
Decrease of muscle fiber conduction velocity correlates with strength loss after an endurance run.
Boccia, Gennaro; Dardanello, Davide; Tarperi, Cantor; Rosso, Valeria; Festa, Luca; La Torre, Antonio; Pellegrini, Barbara; Schena, Federico; Rainoldi, Alberto
2017-02-01
Monitoring surface electromyographic (EMG) signals can provide useful insights for characterizing muscle fatigue, which is defined as an exercise-induced strength loss. This experiment investigated the muscle fiber conduction velocity (CV) changes induced by an endurance run. The day before and immediately after a half-marathon run (21.097 km) 11 amateur runners performed maximum voluntary contractions (MVCs) of knee extensor muscles. During the MVC, multichannel EMG was recorded from the vastus lateralis and EMG amplitude and CV were calculated. After the run, knee extensors showed a decreased strength (-13 ± 9%, p = 0.001) together with a reduction in EMG amplitude (-13 ± 10%, p = 0.003) and in CV (-6 ± 8%, p = 0.032). Knee extensor strength loss positively correlated with vastus lateralis CV differences (r = 0.76, p = 0.006). Thus, the exercises-induced muscle fatigue was associated not only with a decrease in EMG amplitude, but also with a reduction in CV. This finding suggests that muscle fibers with higher CV (i.e. those with greater fiber size) were the most impaired during strength production after an endurance run.
A relation between velocity-vorticity correlations and skin friction in wall-bounded turbulent flows
Yoon, Min; Ahn, Junsun; Hwang, Jinyul; Sung, Hyung Jin
2016-11-01
The relationship between the skin friction and the velocity-vorticity correlations in wall-bounded turbulent flows is derived from the mean vorticity equation. A formula for the skin friction coefficient (Cf) is proposed and evaluated with regards to three canonical wall-bounded flows: turbulent boundary layer, turbulent channel flow, and turbulent pipe flow. The skin friction coefficient can be derived from the mean spanwise vorticity at the wall. Double integration with respect to the wall-normal direction (from 0 to y) is needed to derive Cf from the second derivative of the mean spanwise vorticity in the mean spanwise vorticity equation. One more integration is needed to find the contribution of each component to Cf from the wall to the boundary layer edge (from 0 to δ) . The present formula encompasses four terms: advective vorticity transport, vortex stretching, viscous, and inhomogeneous terms. Drag-reduced channel flow with the slip condition is used to test the reliability of the formula. The advective vorticity transport and vortex stretching terms are found to dominate the contributions to the frictional drag. This work was supported by the Creative Research Initiatives (No. 2016-004749) program of the National Research Foundation of Korea (MSIP).
Helgesson, J; Ekman, J; Helgesson, Johan; Ghetti, Roberta; Jorgen Ekman
2006-01-01
From velocity-gated small-angle correlation functions the emission chronology can be deduced for non-identical particles, if the emission is independent. This is not the case for non-identical particles that originate from two-body decay of fragments. Experimental results may contain contributions from both independent emission and two-body decay, so care is needed in interpreting the velocity-gated correlation functions. It is shown that in some special cases, it is still possible to deduce the emission chronology, even if there is a contribution from two-body decay.
Gayen, Bishakhdatta; Alam, Meheboob
2011-08-01
From particle simulations of a sheared frictional granular gas, we show that the Coulomb friction can have dramatic effects on orientational correlation as well as on both the translational and angular velocity distribution functions even in the Boltzmann (dilute) limit. The dependence of orientational correlation on friction coefficient (μ) is found to be nonmonotonic, and the Coulomb friction plays a dual role of enhancing or diminishing the orientational correlation, depending on the value of the tangential restitution coefficient (which characterizes the roughness of particles). From the sticking limit (i.e., with no sliding contact) of rough particles, decreasing the Coulomb friction is found to reduce the density and spatial velocity correlations which, together with diminished orientational correlation for small enough μ, are responsible for the transition from non-gaussian to gaussian distribution functions in the double limit of small friction (μ→0) and nearly elastic particles (e→1). This double limit in fact corresponds to perfectly smooth particles, and hence the maxwellian (gaussian) is indeed a solution of the Boltzmann equation for a frictional granular gas in the limit of elastic collisions and zero Coulomb friction at any roughness. The high-velocity tails of both distribution functions seem to follow stretched exponentials even in the presence of Coulomb friction, and the related velocity exponents deviate strongly from a gaussian with increasing friction.
Variyar, Jayasankar E.; Kivelson, Daniel; Lynden-Bell, R. M.
1992-12-01
We have carried out molecular-dynamics simulations over a range of densities in two and three dimensions for particles that interact through soft repulsive potentials. We have also carried out calculations of the corresponding systems in which all particles except a tagged particle and its neighbors within a certain distance are frozen. Velocity autocorrelation functions for a single particle, for clusters containing the particle, and for the velocity of the particle relative to an embedding cluster were obtained. The single-particle velocity autocorrelation function can be resolved into correlation functions describing the local rattling in a cage or a cluster, the motion of the cluster itself, and a small cross-correlation term; the function for the single particle is sensitive to the structure of the fluid over a much shorter time scale than are those of clusters, and the shape of the single-particle velocity autocorrelation function comes primarily from rattling motion within a cage. We show that the velocity autocorrelation functions of clusters are probably better probes than that for the single particle for investigating incipient glass formation since they can be used to establish a correlation length which increases when a liquid is cooled. The dynamics of clusters at a given state point depend upon their sizes, and the nature of their motions changes qualitatively from ``rattling'' for small to ``diffusional'' for large clusters, the ``critical'' size at which the change occurs increasing with decreasing temperature. A simple model for this cluster behavior is presented.
Vector velocity estimation using directional beam forming and cross-correlation
DEFF Research Database (Denmark)
2000-01-01
The two-dimensional velocity vector using a pulsed ultrasound field can be determined with the invention. The method uses a focused ultrasound field along the velocity direction for probing the moving medium under investigation. Several pulses are emitted and the focused received fields along...
Directory of Open Access Journals (Sweden)
Awang H.
2017-01-01
Full Text Available Seismic refraction survey is a non destructive method used in site investigation to identify the seismic velocity subsurface strata. Although it is widely known, the reliability of the result is still doubtable for some reason as well as due to an engineer’s ignorant, which insist on using conventional method rather than new advanced method causing the lack of usage in geophysical method for testing. This study aims to produce a correlation between P-wave velocity value and point load strength index value for shale. Both field and laboratory tests were carried out. In order to obtain the P-wave value, seismic refraction method was conducted as a field test at Precint 4, Putrajaya, Malaysia to achieve the Pwave velocity value of the shale bed. Ten samples of shale were collected from the field and laboratory tests were conducted. The tests are divided into three sections, namely non-destructive laboratory test, physical properties test and mechanical properties test. Ultrasonic Velocity Test via PUNDIT test was conducted as non-destructive laboratory test to acknowledge the P-wave velocity value in laboratory. Both field and laboratory P-wave velocity value were then compared and the result delivers are reliable due to it is within the range. For physical properties test, the rock density and porosity were acknowledged. Meanwhile, Point Load Test was conducted as mechanical properties. Correlation for both Pwave velocity value and point load strength value were achieved via producing an empirical relationship as the end result. Prediction of uniaxial compressive strength (UCS value was made via converting the point load strength value to UCS value using a correlation. By acknowledging this empirical relationship, it shows that geophysical methods are able to produce a reliable result. Hence more and widely used of geophysical method will be profound in the future.
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
The correlation, the spectrum and the turbu-lent scale between wall fluctuating pressure and fluctuating ve-locity, on the bed of plunging pool under the action of single and twin impinging jet, are investigated in the paper by using 2-D LDA and the dynamic pressure scanning system of multi-ple points. It is found that the cross correlation between the horizontal fluctuating velocity and the fluctuating pressure of twin jet is bigger than that of sinlge jet, and the spectrum be-tween horizontal fluctuating velocity and fluctuating pressure obviously has approximately dominant frequency. The rela-tionship between the fluctuation pressure coefficient on wall and the turbulent intensity near the wall can be described with logarithmic curve.
Total Ossiculoplasty: Advantages of Two-Point Stabilization Technique
Directory of Open Access Journals (Sweden)
Leonard Berenholz
2012-01-01
Full Text Available Objective. Evaluate a porous polyethylene prosthesis with two-point stabilization in total ossiculoplasty. This approach utilizes a lateral as well as a medial graft to stabilize a total ossicular prosthesis (TOP. Study Design. Retrospective cohort review of total ossiculoplasty. Methods. All patients who underwent total ossiculoplasty during the years 2004–2007 were included in the study group. Only five patients (10% had primary surgery whereas 45 (90% underwent revision surgery. Cartilage grafts covering the prosthesis (Sheehy, Xomed laterally were used in all patients with areolar tissue being used for medial stabilization at the stapes footplate. Follow-up examination and audiometrics were performed a mean of 8.1 months following surgery. Results. The percentage of patients closing their ABG to within 10 dB was 44% with 66% closing their ABG to within 20 dB. The mean four-frequency hearing gain was 15.7 dB. The mean postoperative ABG was 15.7 dB. Conclusion. Audiometric results following total ossiculoplasty surgery using two-point stabilization exceeded results from the otologic literature. Proper two-point fixation with areolar tissue and stabilization utilizing cartilage were the keys to achieving a relatively high percentage of success in chronic ear disease in this sample.
Strength and Power Correlates of Throwing Velocity on Subelite Male Cricket Players.
Freeston, Jonathan L; Carter, Thomas; Whitaker, Gary; Nicholls, Owen; Rooney, Kieron B
2016-06-01
Throwing velocity is an important aspect of fielding in cricket to affect run-outs and reduce the opponent's run-scoring opportunities. Although a relationship between strength and/or power and throwing velocity has been well established in baseball, water polo, and European handball, it has not been adequately explored in cricket. Consequently, this study aimed to determine the relationship between measures of strength and/or power and throwing velocity in cricket players. Seventeen male cricket players (mean ± SD; age, 21.1 ± 1.6 years; height, 1.79 ± 0.06 m; weight, 79.8 ± 6.4 kg) from an elite athlete program were tested for maximal throwing velocity from the stretch position and after a 3-meter shuffle. They were also assessed for strength and power using a range of different measures. Throwing velocity from the stretch position (30.5 ± 2.4 m·s) was significantly related to dominant leg lateral-to-medial jump (LMJ) distance (r = 0.71; p MB Rot) throw velocity and medicine ball chest pass (MB CP) distance (r = 0.67; p MB Rot and MB CP explained 66% of the variance. The results were similar for velocity after a shuffle step (31.8 ± 2.1 m·s); however, VJ height reached statistical significance (r = 0.51; p ≤ 0.05). The multiple regression was also similar with MB Rot and MB CP explaining 70% of the variance. The cricketers in this study threw with greater velocity than elite junior and subelite senior cricketers but with lower velocities than elite senior cricketers and collegiate level and professional baseball players. This is the first study to demonstrate a link between strength and/or power and throwing velocity in cricket players and highlight the importance of power development as it relates to throwing velocity. Exercises that more closely simulated the speed (body weight jumps and medicine ball throws) or movement pattern (shoulder IR) of overhead throwing were greater predictors of throwing velocity. Strength and conditioning staff should
Statistics of Centroids of Velocity
Esquivel, A
2009-01-01
We review the use of velocity centroids statistics to recover information of interstellar turbulence from observations. Velocity centroids have been used for a long time now to retrieve information about the scaling properties of the turbulent velocity field in the interstellar medium. We show that, while they are useful to study subsonic turbulence, they do not trace the statistics of velocity in supersonic turbulence, because they are highly influenced by fluctuations of density. We show also that for sub-Alfv\\'enic turbulence (both supersonic and subsonic) two-point statistics (e.g. correlation functions or power-spectra) are anisotropic. This anisotropy can be used to determine the direction of the mean magnetic field projected in the plane of the sky.
Simple correlation for predicting detonation velocity of ideal and non-ideal explosives.
Keshavarz, Mohammad Hossein
2009-07-30
This paper describes a simple method for prediction of detonation velocity of ideal and non-ideal explosives. A non-ideal aluminized and nitrated explosive can have Chapman-Jouguet detonation velocity significantly different from that expected from existing thermodynamic computer codes for equilibrium and steady-state calculations. Detonation velocity of explosives with general formula C(a)H(b)N(c)O(d)Al(e) can be predicted only from values of a, b, c, d, e and a specific structural parameter without using any assumed detonation products, heat of formation and experimental data. Predicted detonation velocities by this procedure for ideal and non-ideal explosives show good agreement with respect to experimental values as compared to computed results of BKWR and BKWS equations of state.
Institute of Scientific and Technical Information of China (English)
YIN XiangYu; SONG Hao; ZHOU HuiJun
2009-01-01
In this study, ultrasound grating was used to measure the sound velocity in solutions of ethylene glycol and polyethylene glycol with molecular weights of 200, 600, 2000, and 10000. We found Parthasarathy empirical rule, that is, sound velocity is higher in the solution of larger molecules, is invalid in the case of polyethylene glycol solution. We tried to provide a tentative explanation using the Flory-Krigbaum's chained block cloud model.
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
In this study,ultrasound grating was used to measure the sound velocity in solutions of ethylene glycol and polyethylene glycol with molecular weights of 200,600,2000,and 10000.We found Parthasarathy empirical rule,that is,sound velocity is higher in the solution of larger molecules,is invalid in the case of polyethylene glycol solution. We tried to provide a tentative explanation using the Flory-Krigbaum’s chained block cloud model.
Theory of resistor networks: the two-point resistance
Energy Technology Data Exchange (ETDEWEB)
Wu, F Y [Department of Physics, Northeastern University Boston, MA 02115 (United States)
2004-07-02
The resistance between two arbitrary nodes in a resistor network is obtained in terms of the eigenvalues and eigenfunctions of the Laplacian matrix associated with the network. Explicit formulae for two-point resistances are deduced for regular lattices in one, two and three dimensions under various boundary conditions including that of a Moebius strip and a Klein bottle. The emphasis is on lattices of finite sizes. We also deduce summation and product identities which can be used to analyse large-size expansions in two and higher dimensions.
Beyond Kaiser bias: mildly non-linear two-point statistics of densities in distant spheres
Uhlemann, C.; Codis, S.; Kim, J.; Pichon, C.; Bernardeau, F.; Pogosyan, D.; Park, C.; L'Huillier, B.
2017-04-01
We present simple parameter-free analytic bias functions for the two-point correlation of densities in spheres at large separation. These bias functions generalize the so-called Kaiser bias to the mildly non-linear regime for arbitrary density contrasts and grow as b(ρ) - b(1) ∝ (1 - ρ-13/21)ρ1 + n/3 with b(1) = -4/21 - n/3 for a power-law initial spectrum with index n. We carry out the derivation in the context of large-deviation statistics while relying on the spherical collapse model. We use a logarithmic transformation that provides a saddle-point approximation that is valid for the whole range of densities and show its accuracy against the 30 Gpc cube state-of-the-art Horizon Run 4 simulation. Special configurations of two concentric spheres that allow us to identify peaks are employed to obtain the conditional bias and a proxy for the BBKS extremum correlation functions. These analytic bias functions should be used jointly with extended perturbation theory to predict two-point clustering statistics as they capture the non-linear regime of structure formation at the per cent level down to scales of about 10 Mpc h-1 at redshift 0. Conversely, the joint statistics also provide us with optimal dark matter two-point correlation estimates that can be applied either universally to all spheres or to a restricted set of biased (over- or underdense) pairs. Based on a simple fiducial survey, we show that the variance of this estimator is reduced by five times relative to the traditional sample estimator for the two-point function. Extracting more information from correlations of different types of objects should prove essential in the context of upcoming surveys like Euclid, DESI and WFIRST.
Asano, Kimiyuki; Iwata, Tomotaka; Sekiguchi, Haruko; Somei, Kazuhiro; Miyakoshi, Ken; Aoi, Shin; Kunugi, Takashi
2017-08-01
Inter-station cross-correlation functions estimated using continuous ambient noise or microtremor records were used to extract the seismic wave propagation characteristics of the Osaka sedimentary basin, Japan. Temporary continuous observations were conducted at 15 sites in the Osaka basin between 2011 and 2013. The data were analyzed using seismic interferometry. The target period range was 2-8 s. Cross-correlations between all of the possible station pairs were calculated and stacked to produce a year-long data set, and Rayleigh wave signals in the vertical and radial components and Love wave signals in the transverse component were identified from the results. Simulation of inter-station Green's functions using the finite difference method was conducted to check the performance of the current three-dimensional velocity structure model. The measured time lag between the observed and theoretical Green's functions was less than 2 s for most station pairs, which is less than the wave period of interest in the target frequency range. Group velocity tomography was applied to group delay times estimated by means of multiple filter analysis. The estimated group velocities for longer periods of 5-8 s exhibited spatial variation within the basin, which is consistent with the bedrock depth distribution; however, the group velocities for shorter periods of 2-3 s were almost constant over the studied area. The waveform and group velocity information obtained by seismic interferometry analysis can be useful for future reconstruction of a three-dimensional velocity structure model in the Osaka basin.[Figure not available: see fulltext.
Point and planar LIF for velocity-concentration correlations in a jet in cross flow
DEFF Research Database (Denmark)
Meyer, Knud Erik; Özcan, Oktay; Larsen, Poul Scheel
2002-01-01
(LDA). The flow considered is the mixing of a jet in a fully developed cross flow in a square duct with a width of 10 jet diameters. Both a laminar flow case, Re=675, and a turbulent flow case, Re=33750, are presented . For both flows, the ratio jet-to-duct mean velocities was R=3.3. Result of mean...... velocities, mean concentration and Reynolds fluxes in the symmetry plane of the jet are presented for PIV and PLIF measurements. The LIF measurements performed with the LDA equipment was in general in good agreement with the PIV/PLIF measurements. The cross sections selected for comparison are challenging...
Soldati, Gaia; Zaccarelli, Lucia; Faenza, Licia; Michelini, Alberto
2015-07-01
The relative seismic velocity variations possibly associated to large earthquakes can be readily monitored via cross-correlation of seismic noise. In a recently published study, more than 2 yr of continuous seismic records have been analysed from three stations surrounding the epicentre of the 2009 April 6, Mw 6.1 L'Aquila earthquake, observing a clear decrease of seismic velocities likely corresponding to the co-seismic shaking. Here, we extend the analysis in space, including seismic stations within a radius of 60 km from the main shock epicentre, and in time, collecting 5 yr of data for the six stations within 40 km of it. Our aim is to investigate how far the crustal damage is visible through this technique, and to detect a potential post-seismic recovery of velocity variations. We find that the co-seismic drop in velocity variations extends up to 40 km from the epicentre, with spatial distribution (maximum around the fault and in the north-east direction from it) in agreement with the horizontal co-seismic displacement detected by global positioning system (GPS). In the first few months after L'Aquila earthquake, the crust's perturbation in terms of velocity variations displays a very unstable behaviour, followed by a slow linear recovery towards pre-earthquake conditions; by almost 4 yr after the event, the co-seismic drop of seismic velocity is not yet fully recovered. The strong oscillations of the velocity changes in the first months after the earthquake prevent to detect the fast exponential recovery seen by GPS data. A test of differently parametrized fitting curves demonstrate that the post-seismic recovery is best explained by a sum of a logarithmic and a linear term, suggesting that processes like viscoelastic relaxation, frictional afterlip and poroelastic rebound may be acting concurrently.
On measuring surface wave phase velocity from station–station cross-correlation of ambient signal
DEFF Research Database (Denmark)
Boschi, Lapo; Weemstra, Cornelis; Verbeke, Julie
2012-01-01
We apply two different algorithms to measure surface wave phase velocity, as a function of frequency, from seismic ambient noise recorded at pairs of stations from a large European network. The two methods are based on consistent theoretical formulations, but differ in the implementation: one met...
Energy Technology Data Exchange (ETDEWEB)
Fedorczak, N. [Center for Momentum Transport and Flow Organization, University of California at San Diego, San Diego, California 92093 (United States); CEA, IRFM, F-13108 Saint-Paul-Lez-Durance (France); Manz, P. [Center for Momentum Transport and Flow Organization, University of California at San Diego, San Diego, California 92093 (United States); Max-Planck-Institut feur Plasmaphysik, Association Euratom-IPP, 85748Garching (Germany); Thakur, S. C.; Xu, M.; Tynan, G. R. [Center for Momentum Transport and Flow Organization, University of California at San Diego, San Diego, California 92093 (United States); Xu, G. S.; Liu, S. C. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China)
2012-12-15
Time delay estimation (TDE) techniques are frequently used to estimate the flow velocity from fluctuating measurements. Tilted structures carried by the flow lead to misinterpretation of the time delays in terms of velocity direction and amplitude. It affects TDE measurements from probes, and is also intrinsically important for beam emission spectroscopy and gas puff imaging measurements. Local eddy shapes estimated from 2D fluctuating field are necessary to gain a more accurate flow estimate from TDE, as illustrated by Langmuir probe array measurements. A least square regression approach is proposed to estimate both flow field and shaping parameters. The technique is applied to a test case built from numerical simulation of interchange fluctuations. The local eddy shape does not only provide corrections for the velocity field but also quantitative information about the statistical interaction mechanisms between local eddies and E Multiplication-Sign B flow shear. The technique is then tested on gaz puff imaging data collected at the edge of EAST tokamak plasmas. It is shown that poloidal asymmetries of the fluctuation fields-velocity and eddy shape-are consistent at least qualitatively with a ballooning type of turbulence immersed in a radially sheared equilibrium flow.
Examination of Existing Shear Wave Velocity and Shear Modulus Correlations in Soils
1987-09-01
in Terms of Characteristic Indices of Soil," Butsuri- Tanko (Geophysical Exploration) (in Japanese), Vol 29, No. 4, pp 34-41. . 1978a. "Empirical Shear...34Physical Background of the Statistically Obtained S-Wave Velocity Equation in Terms of Soil Indexes," Butsuri- Tanko (Geophysical Explo- ration) (in Japanese
State feedback control of surge oscillations of two-point mooring system
Mitra, R. K.; Banik, A. K.; Chatterjee, S.
2017-01-01
Stability analysis of surge oscillations of two-point mooring system under state feedback control with time-delay is investigated. The two-point mooring system is harmonically excited and essentially represents a strongly nonlinear Duffing oscillator. In this paper, a frequency domain based method viz. incremental harmonic balance method along with arc-length continuation technique (IHBC) is first employed to identify the primary and higher order subharmonic responses which may be present in such system. The IHBC is then reformulated in a manner to treat two-point mooring system under state feedback control with time-delay and is applied to obtain control of responses in an efficient and systematic way. The stability of uncontrolled responses for primary and higher order subharmonic oscillations is obtained by Floquet's theory using Hsu' scheme; whereas the stability of controlled responses is obtained by applying semi-discretization method for delay differential equation. The study focussed on the controlling primary, higher order subharmonics and chaotic responses by considering appropriate feedback gains and delay by way of (i) appreciable reduction of primary, subharmonic responses, (ii) exclusion of all higher order subharmonics 2T, 3T, 5T and 9T (1/n subharmonics or period-n solutions), and (iii) reduction of the extent of domain of all instability phenomena represented by various type of bifurcation of solutions, jump phenomena, chaotic responses etc. In the study, negative velocity feedback is observed to be much effective than state feedback for better controlling of surge oscillation of two-point mooring system. Also, the effect of larger gain values is investigated by an extensive parametric study for vibration control with different delay values.
Two-point functions in (loop) quantum cosmology
Energy Technology Data Exchange (ETDEWEB)
Calcagni, Gianluca; Gielen, Steffen; Oriti, Daniele, E-mail: calcagni@aei.mpg.de, E-mail: gielen@aei.mpg.de, E-mail: doriti@aei.mpg.de [Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Am Muehlenberg 1, D-14476 Golm (Germany)
2011-06-21
The path-integral formulation of quantum cosmology with a massless scalar field as a sum-over-histories of volume transitions is discussed, with particular but non-exclusive reference to loop quantum cosmology. Exploiting the analogy with the relativistic particle, we give a complete overview of the possible two-point functions, pointing out the choices involved in their definitions, deriving their vertex expansions and the composition laws they satisfy. We clarify the origin and relations of different quantities previously defined in the literature, in particular the tie between definitions using a group averaging procedure and those in a deparametrized framework. Finally, we draw some conclusions about the physics of a single quantum universe (where there exist superselection rules on positive- and negative-frequency sectors and different choices of inner product are physically equivalent) and multiverse field theories where the role of these sectors and the inner product are reinterpreted.
Two-point functions in (loop) quantum cosmology
Energy Technology Data Exchange (ETDEWEB)
Calcagni, Gianluca; Oriti, Daniele [Max-Planck-Institute for Gravitational Physics (Albert Einstein Institute), Am Muehlenberg 1, D-14476 Golm (Germany); Gielen, Steffen [Max-Planck-Institute for Gravitational Physics (Albert Einstein Institute), Am Muehlenberg 1, D-14476 Golm (Germany); DAMTP, Centre for Mathematical Sciences, Wilberforce Road, Cambridge CB3 0WA (United Kingdom)
2011-07-01
We discuss the path-integral formulation of quantum cosmology with a massless scalar field as a sum-over-histories of volume transitions, with particular but non-exclusive reference to loop quantum cosmology (LQC). Exploiting the analogy with the relativistic particle, we give a complete overview of the possible two-point functions, pointing out the choices involved in their definitions, deriving their vertex expansions and the composition laws they satisfy. We clarify the origin and relations of different quantities previously defined in the literature, in particular the tie between definitions using a group averaging procedure and those in a deparametrized framework. Finally, we draw some conclusions about the physics of a single quantum universe (where there exist superselection rules on positive- and negative-frequency sectors and different choices of inner product are physically equivalent) and multiverse field theories where the role of these sectors and the inner product are reinterpreted.
Energy Technology Data Exchange (ETDEWEB)
Kaempfer, B. [Forschungszentrum Rossendorf e.V. (FZR), Dresden (Germany)]|[Technische Univ. Dresden (Germany). Inst. fuer Theoretische Physik; Kotte, R. [Forschungszentrum Rossendorf e.V. (FZR), Dresden (Germany); Moesner, J. [Forschungszentrum Rossendorf e.V. (FZR), Dresden (Germany); Neubert, W. [Forschungszentrum Rossendorf e.V. (FZR), Dresden (Germany); Wohlfarth, D. [Forschungszentrum Rossendorf e.V. (FZR), Dresden (Germany); Alard, J.P. [Clermont-Ferrand-2 Univ., 63 - Aubiere (France). Lab. de Physique Corpusculaire; Basrak, Z. [Institut Rudjer Boskovic, Zagreb (Croatia); Bastid, N. [Clermont-Ferrand-2 Univ., 63 - Aubiere (France). Lab. de Physique Corpusculaire; Belayev, I.M. [Institut Teoreticheskoj i Ehksperimental`noj Fiziki, Moscow (Russian Federation); Blaich, T. [Mainz Univ. (Germany); Buta, A. [Institutul Central de Fizica, Bucharest (Romania); Caplar, R. [Institut Rudjer Boskovic, Zagreb (Croatia); Cerruti, C. [Strasbourg-1 Univ., 67 (France). Centre de Recherches Nucleaires; Cindro, N. [Institut Rudjer Boskovic, Zagreb (Croatia); Coffin, J.P. [Strasbourg-1 Univ., 67 (France). Centre de Recherches Nucleaires; Dupieux, P. [Clermont-Ferrand-2 Univ., 63 - Aubiere (France). Lab. de Physique Corpusculaire; Eroe, J. [Institute for Physics and Nuclear Engineering, Budapest (Hungary); Fan, Z.G. [Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany); Fintz, P. [Strasbourg-1 Univ., 67 (France). Centre de Recherches Nucleaires; Fodor, Z. [Institute for Physics and Nuclear Engineering, Budapest (Hungary); Freifelder, R. [Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany); Fraysse, L. [Clermont-Ferrand-2 Univ., 63 - Aubiere (France). Lab. de Physique Corpusculaire; Frolov, S. [Institut Teoreticheskoj i Ehksperimental`noj Fiziki, Moscow (Russian Federation); Gobbi, A. [Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany); Grigorian, Y.; FOPI Collaboration
1993-05-01
Velocity correlations of intermediate mass fragments (IMFs), produced in central collisions of Au + Au at 150 A.MeV beam energy, are extracted from measurements with the FOPI (phase I) detector system at SIS in GSI Darmstadt. The IMF correlation function for semicentral events is found to be affected by the directed sideward flow. When rotating the events into a unique reaction plane an enhancement of correlations, resulting from event mixing effects, vanishes. Selecting violent collisions with a high degree of azimuthal symmetry the correlation function appears nearly independent of additional event or single particle gate conditions. The comparison of the data with a Coulomb dominated final-state interaction model points to time scales of {tau} {proportional_to} 25 fm/c or less for emitting IMFs from an expanding and multifragmenting source with radius R {proportional_to} 14 fm. (orig.)
Arroucau, Pierre; Kuponiyi, Ayodeji; Vlahovic, Gordana; Powell, Chris
2013-04-01
The Eastern Tennessee Seismic Zone (ETSZ) is an intraplate seismic region characterized by frequent but low magnitude earthquakes and is the second most active seismic area in the United States east of the Rocky Mountains. One key question in the ETSZ is the actual relationship between earthquake distribution and geological structure at depth. Seismicity is mostly confined in the Precambrian basement, below the Paleozoic cover of the southern Appalachian foreland fold-and-thrust belt and shows little to no correlation with surface geological features. Since the middle of the seventies, the Center for Earthquake Research and Information (CERI) has installed and maintained several seismic networks in central and eastern United States. In this work, we use Rayleigh wave group and phase velocity dispersion information obtained from cross-correlation of seismic ambient noise at 24 short-period stations located in the vicinity of the ETSZ. The 3D velocity structure is estimated in four steps. First, dispersion curves are obtained for simultaneously recording station pairs for periods ranging from 2 to 20 s. Then, 2D group and phase velocity maps are determined for each period. Those maps are further used to reconstruct dispersion curves at fixed, regularly spaced locations. For each of these locations, a 1D shear-wave velocity profile is finally inverted for, that takes velocity information from previous studies into account. By providing new information about the upper crustal structure of this region, this work is a contribution to the understanding of the seismic activity of the ETSZ, and -to a broader extent- of the structure and evolution of the North American lithosphere.
Leonard, Mary B.; Townsend, Raymond R.; Appel, Lawrence; Wolf, Myles; Budoff, Matt J.; Chen, Jing; Lustigova, Eva; Gadegbeku, Crystal A.; Glenn, Melanie; Hanish, Asaf; Raj, Dominic; Rosas, Sylvia E.; Seliger, Stephen L.; Weir, Matthew R.; Parekh, Rulan S.
2011-01-01
Summary Background and objectives Osteoprotegerin (OPG), a cytokine that regulates bone resorption, has been implicated in the process of vascular calcification and stiffness. Design, setting, participants, & measurements Serum OPG was measured in 351 participants with chronic kidney disease (CKD) from one site of the Chronic Renal Insufficiency Cohort Study. Cortical bone mineral content (BMC) was measured by quantitative computed tomography in the tibia. Multivariable linear regression was used to test the association between serum OPG and traditional cardiovascular risk factors, measures of abnormal bone and mineral metabolism, and pulse wave velocity. Results Higher serum OPG levels were associated with older age, female gender, greater systolic BP, lower estimated GFR, and lower serum albumin. OPG was not associated with measures of abnormal bone or mineral metabolism including serum phosphorus, albumin-corrected serum calcium, intact parathyroid hormone, bone-specific alkaline phosphatase, or cortical BMC. Among 226 participants with concurrent aortic pulse wave velocity measurements, increasing tertiles of serum OPG were associated with higher aortic pulse wave velocity after adjustment for demographics, traditional vascular risk factors, and nontraditional risk factors such as estimated GFR, albuminuria, serum phosphate, corrected serum calcium, presence of secondary hyperparathyroidism, serum albumin, and C-reactive protein or after additional adjustment for cortical BMC in a subset (n = 161). Conclusions These data support a strong relationship between serum OPG and arterial stiffness independent of many potential confounders including traditional cardiovascular risk factors, abnormal bone and mineral metabolism, and inflammation. PMID:21940840
Universal correlation for the rise velocity of long gas bubbles in round pipes
Viana, Flavia; Pardo, Raimundo; Yánez, Rodolfo; Trallero, José L.; Joseph, Daniel D.
2003-11-01
We collected all of the published data we could find on the rise velocity of long gas bubbles in stagnant fluids contained in circular tubes. Data from 255 experiments from the literature and seven new experiments at PDVSA Intevep for fluids with viscosities ranging from 1 mPa s up to 3900 mPa s were assembled on spread sheets and processed in log log plots of the normalized rise velocity, Fr {=} U/(gD)(1/2) Froude velocity vs. buoyancy Reynolds number, R {=} (D(3) g (rho_{l}-rho_{g}) rho_{l})(1/2) /mu for fixed ranges of the Eötvös number, Eo {=} grho_{l}D(2) /sigma where D is the pipe diameter, rho_{l}, rho_{g} and sigma are densities and surface tension. The plots give rise to power laws in Eo; the composition of these separate power laws emerge as bi-power laws for two separate flow regions for large and small buoyancy Reynolds. For large R (>200) we find [hboxFr = {0.34}/(1+3805/hboxEo^{3.06})^{0.58}.] For small R (PDVSA-Intevep on the rise of Taylor bubbles is presented.
Energy Technology Data Exchange (ETDEWEB)
Ofek, Eran O.; Arcavi, Iair; Tal, David; Gal-Yam, Avishay; Ben-Ami, Sagi; De Cia, Annalisa; Yaron, Ofer [Benoziyo Center for Astrophysics, Weizmann Institute of Science, 76100 Rehovot (Israel); Sullivan, Mark [School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ (United Kingdom); Kulkarni, Shrinivas R.; Cao, Yi [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States); Nugent, Peter E. [Computational Cosmology Center, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States); Bersier, David [Astrophysics Research Institute, Liverpool John Moores University, Liverpool L3 5RF (United Kingdom); Cenko, S. Bradley [Astrophysics Science Division, NASA Goddard Space Flight Center, Mail Code 661, Greenbelt, MD 20771 (United States); Filippenko, Alexei V. [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States); Fransson, Claes [Department of Astronomy, The Oskar Klein Centre, Stockholm University, AlbaNova University Centre, SE-106 91 Stockholm (Sweden); Kasliwal, Mansi M. [Observatories of the Carnegie Institution for Science, 813 Santa Barbara St, Pasadena, CA 91101 (United States); Laher, Russ; Surace, Jason [Spitzer Science Center, MS 314-6, California Institute of Technology, Pasadena, CA 91125 (United States); Quimby, Robert [Kavli IPMU (WPI), The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi, Chiba 277-8583 (Japan)
2014-06-20
Interaction of supernova (SN) ejecta with the optically thick circumstellar medium (CSM) of a progenitor star can result in a bright, long-lived shock-breakout event. Candidates for such SNe include Type IIn and superluminous SNe. If some of these SNe are powered by interaction, then there should be a specific relation between their peak luminosity, bolometric light-curve rise time, and shock-breakout velocity. Given that the shock velocity during shock breakout is not measured, we expect a correlation, with a significant spread, between the rise time and the peak luminosity of these SNe. Here, we present a sample of 15 SNe IIn for which we have good constraints on their rise time and peak luminosity from observations obtained using the Palomar Transient Factory. We report on a possible correlation between the R-band rise time and peak luminosity of these SNe, with a false-alarm probability of 3%. Assuming that these SNe are powered by interaction, combining these observables and theory allows us to deduce lower limits on the shock-breakout velocity. The lower limits on the shock velocity we find are consistent with what is expected for SNe (i.e., ∼10{sup 4} km s{sup –1}). This supports the suggestion that the early-time light curves of SNe IIn are caused by shock breakout in a dense CSM. We note that such a correlation can arise from other physical mechanisms. Performing such a test on other classes of SNe (e.g., superluminous SNe) can be used to rule out the interaction model for a class of events.
Zhang, Chun-Xiao; Wang, Fei; Li, Ning; Yan, Jian-Hua; Chi, Yong; Cen, Ke-Fa
2009-10-01
Simultaneous online measurement of gas concentration and velocity can be realized by tunable diode laser absorption spectroscopy (TDLAS) technique and optical signal cross-correlation method. The fundamental and relative factors of gas concentration and velocity measurement are described in the present paper. The spectral lines of NH3 used for gas sensing at communication band in near infrared range were selected and analyzed by the calculation based on the HITRAN database. In the verification experiment, NH3 and N2 were mixed by two mass flow meters and sent to flow through the quartz tube 0. 016 m in inner diameter and 1 m in length at normal temperature and pressure. The spectral line located at 6,548.7 cm(-1) was scanned at high frequency by the diode laser of 15 MHz linewidth and 1 cm' tunable range with no mode hoppings. The instantaneous NH3 absorbance was obtained using direct absorption method and the gas concentration was calculated. At the same time, the non-intrusive optical absorption signal cross-correlation method was utilized to obtain two concentration signals from two adjacent detectors mounted along the gas tube. The corresponding transit time of gas passing through the detectors was calculated by cross-correlation algorithm, and the average gas velocity was inferred according to the distance between the two detectors and the transit time. The relative errors were less than 7% for the gas concentration measurement, and less than 10% for the gas velocity measurement. Experimental results were proved to be of high precision and good repeatability in the lab. The feature of fast response and capacity immune to the in situ disturbance would lead to a potential in industry application for the real time measurement and control of gas pollutant emission in the future.
Zhou, Quan; Lu, Zhi-Ming; Liu, Yu-Lu
2010-01-01
We report an experimental investigation of the longitudinal space-time cross-correlation function of the velocity field, $C(r,\\tau)$, in a cylindrical turbulent Rayleigh-B\\'{e}nard convection cell using the particle image velocimetry (PIV) technique. We show that while the Taylor's frozen-flow hypothesis does not hold in turbulent thermal convection, the recent elliptic model advanced for turbulent shear flows [He & Zhang, \\emph{Phys. Rev. E} \\textbf{73}, 055303(R) (2006)] is valid for the present velocity field for all over the cell, i.e., the isocorrelation contours of the measured $C(r,\\tau)$ have a shape of elliptical curves and hence $C(r,\\tau)$ can be related to $C(r_E,0)$ via $r_E^2=(r-\\beta\\tau)^2+\\gamma^2\\tau^2$ with $\\beta$ and $\\gamma$ being two characteristic velocities. We further show that the fitted $\\beta$ is proportional to the mean velocity of the flow, but the values of $\\gamma$ are larger than the theoretical predictions. Specifically, we focus on two representative regions in the cell...
Energy Technology Data Exchange (ETDEWEB)
Lifshutz, N.; Pierce, M. [Hollingsworth & Vose Company, West Groton, MA (United States)
1997-08-01
The CertiTest 8160 is a Condensation Nucleus Counter (CNC) based filtration test stand which permits measurement of penetration as a function of particle size. The Model 8140 is also a CNC based filtration test stand which provides a single penetration measurement for a fixed particle distribution aerosol challenge. A study was carried out measuring DOP penetration on a broad range of flat filtration media at various face velocities to compare these two instruments. The tests done on the CertiTest 8160 incorporated a range of particle sizes which encompassed the most penetrating particle size (MPPS). In this paper we present a correlation between the MPPS penetration as measured by the CertiTest 8160 and the penetration values obtained on the Model 8140. We observed that at the lowest air face velocities of the study the Model 8140 tended to overpredict the MPPS penetration as measured by the CertiTest 8160. We also present a correlation of MPPS penetration with face velocity which may be of use for extrapolation purposes. 5 refs., 8 figs.
Stationary echo canceling in velocity estimation by time-domain cross-correlation
DEFF Research Database (Denmark)
Jensen, Jørgen Arendt
1993-01-01
that the filtration results in a velocity-dependent degradation of the signal-to-noise ratio. An analytic expression is given for the degradation for a realistic pulse. The probability of correct detection at low signal-to-noise ratios is influenced by signal-to-noise ratio, transducer bandwidth, center frequency......, number of samples in the range gate, and number of A-lines employed in the estimation. Quantitative results calculated by a simple simulation program are given for the variation in probability from these parameters. An index reflecting the reliability of the estimate at hand can be calculated from...
A multiscale two-point flux-approximation method
Møyner, Olav; Lie, Knut-Andreas
2014-10-01
A large number of multiscale finite-volume methods have been developed over the past decade to compute conservative approximations to multiphase flow problems in heterogeneous porous media. In particular, several iterative and algebraic multiscale frameworks that seek to reduce the fine-scale residual towards machine precision have been presented. Common for all such methods is that they rely on a compatible primal-dual coarse partition, which makes it challenging to extend them to stratigraphic and unstructured grids. Herein, we propose a general idea for how one can formulate multiscale finite-volume methods using only a primal coarse partition. To this end, we use two key ingredients that are computed numerically: (i) elementary functions that correspond to flow solutions used in transmissibility upscaling, and (ii) partition-of-unity functions used to combine elementary functions into basis functions. We exemplify the idea by deriving a multiscale two-point flux-approximation (MsTPFA) method, which is robust with regards to strong heterogeneities in the permeability field and can easily handle general grids with unstructured fine- and coarse-scale connections. The method can easily be adapted to arbitrary levels of coarsening, and can be used both as a standalone solver and as a preconditioner. Several numerical experiments are presented to demonstrate that the MsTPFA method can be used to solve elliptic pressure problems on a wide variety of geological models in a robust and efficient manner.
Prenatal prediction of pulmonary hypoplasia: clinical, biometric, and Doppler velocity correlates
J.A.M. Laudij (Jacqueline); D. Tibboel (Dick); S.G.F. Robben (Simon); R.R. de Krijger (Ronald); M.A.J. de Ridder (Maria); J.W. Wladimiroff (Juriy)
2002-01-01
textabstractOBJECTIVES: To determine the value of pulmonary artery Doppler velocimetry relative to fetal biometric indices and clinical correlates in the prenatal prediction of lethal lung hypoplasia (LH) in prolonged (>1 week) oligohydramnios. METHODS: Forty-two singleton pregnanc
Prenatal prediction of pulmonary hypoplasia: clinical, biometric, and Doppler velocity correlates
J.A.M. Laudij (Jacqueline); D. Tibboel (Dick); S.G.F. Robben (Simon); R.R. de Krijger (Ronald); M.A.J. de Ridder (Maria); J.W. Wladimiroff (Juriy)
2002-01-01
textabstractOBJECTIVES: To determine the value of pulmonary artery Doppler velocimetry relative to fetal biometric indices and clinical correlates in the prenatal prediction of lethal lung hypoplasia (LH) in prolonged (>1 week) oligohydramnios. METHODS: Forty-two singleton
Correlation between Shear Wave Velocity and Porosity in Porous Solids and Rocks
Directory of Open Access Journals (Sweden)
J. Kováčik
2013-01-01
Full Text Available The shear wave velocity dependence on porosity was modelled using percolation theory model for the shear modulus porosity dependence. The obtained model is not a power law dependence (no simple scaling with porosity, but a more complex equation. Control parameters of this equation are shear wave velocity of bulk solid, percolation threshold of the material and the characteristic power law exponent for shear modulus porosity dependence. This model is suitable for all porous materials, mortars and porous rocks filled with liquid or gas. In the case of pores filled with gas the model can be further simplified: The term for the ratio of the gas density to the density of solid material can be omitted in the denominator (the ratio is usually in the range of (10−4, 10−3 for all solids. This simplified equation was then tested on the experimental data set for porous ZnO filled with air. Due to lack of reasonable data the scientists are encouraged to test the validity of proposed model using their experimental data.
Velocity anti-correlation of diametrically opposed galaxy satellites in the low-redshift Universe.
Ibata, Neil G; Ibata, Rodrigo A; Famaey, Benoit; Lewis, Geraint F
2014-07-31
Recent work has shown that the Milky Way and the Andromeda galaxies both possess the unexpected property that their dwarf satellite galaxies are aligned in thin and kinematically coherent planar structures. It is interesting to evaluate the incidence of such planar structures in the larger galactic population, because the Local Group may not be a representative environment. Here we report measurements of the velocities of pairs of diametrically opposed satellite galaxies. In the local Universe (redshift z 7σ confidence). This may indicate that planes of co-rotating satellites, similar to those seen around the Andromeda galaxy, are ubiquitous, and their coherent motion suggests that they represent a substantial repository of angular momentum on scales of about 100 kiloparsecs.
Velocity anti-correlation of diametrically opposed galaxy satellites in the low redshift universe
Ibata, Neil G; Famaey, Benoit; Lewis, Geraint F
2014-01-01
Recent work has shown that both the Milky Way and the Andromeda galaxies possess the unexpected property that their dwarf satellite galaxies are aligned in thin and kinematically coherent planar structures. It is now important to evaluate the incidence of such planar structures in the larger galactic population, since the Local Group may not be a sufficiently representative environment. Here we report that the measurement of the velocity of pairs of diametrically opposed galaxy satellites provides a means to determine statistically the prevalence of kinematically coherent planar alignments. In the local universe (redshift $z7\\sigma$ confidence). Our finding may indicate that co-rotating planes of satellites, similar to that seen around the Andromeda galaxy, are ubiquitous in nature, while their coherent motion also suggests that they are a significant repository of angular momentum on $\\sim 100$ kpc scales.
Stanke, Monika; Palikot, Ewa; Adamowicz, Ludwik
2016-05-01
Algorithms for calculating the leading mass-velocity (MV) and Darwin (D) relativistic corrections are derived for electronic wave functions expanded in terms of n-electron explicitly correlated Gaussian functions with shifted centers and without pre-exponential angular factors. The algorithms are implemented and tested in calculations of MV and D corrections for several points on the ground-state potential energy curves of the H2 and LiH molecules. The algorithms are general and can be applied in calculations of systems with an arbitrary number of electrons.
Beijeren, H. van; Kehr, K.W.
1986-01-01
The correlation factor, defined as the ratio between the tracer diffusion coefficient in lattice gases and the diffusion coefficient for a corresponding uncorrelated random walk, is known to assume a very simple form under certain conditions. A simple derivation of this is given with the aid of
Prisiazhniuk, D.; Krämer-Flecken, A.; Conway, G. D.; Happel, T.; Lebschy, A.; Manz, P.; Nikolaeva, V.; Stroth, U.; the ASDEX Upgrade Team
2017-02-01
In fusion machines, turbulent eddies are expected to be aligned with the direction of the magnetic field lines and to propagate in the perpendicular direction. Time delay measurements of density fluctuations can be used to calculate the magnetic field pitch angle α and perpendicular velocity {{v}\\bot} profiles. The method is applied to poloidal correlation reflectometry installed at ASDEX Upgrade and TEXTOR, which measure density fluctuations from poloidally and toroidally separated antennas. Validation of the method is achieved by comparing the perpendicular velocity (composed of the E× B drift and the phase velocity of turbulence {{v}\\bot}={{v}E× B}+{{v}\\text{ph}} ) with Doppler reflectometry measurements and with neoclassical {{v}E× B} calculations. An important condition for the application of the method is the presence of turbulence with a sufficiently long decorrelation time. It is shown that at the shear layer the decorrelation time is reduced, limiting the application of the method. The magnetic field pitch angle measured by this method shows the expected dependence on the magnetic field, plasma current and radial position. The profile of the pitch angle reproduces the expected shape and values. However, comparison with the equilibrium reconstruction code cliste suggests an additional inclination of turbulent eddies at the pedestal position (2-3°). This additional angle decreases towards the core and at the edge.
DEFF Research Database (Denmark)
Artemieva, Irina; Vinnik, Lev
2016-01-01
across) lowdensity (down to 3.34 g/cm3) and high-density (up to 3.41 g/cm3) anomalies. High (3.40–3.42 g/cm3) mantle densities beneath the Eastern Cape Fold belt require the presence of a significant amount of eclogite in the mantle, such as associated with subducted oceanic slabs. We find a strong...... the composition and rheology of the lithospheric mantle to make it unfavorable for consequent kimberlite eruptions. (5) Density anomalies in the lithospheric mantle show inverse correlation with seismic Vp, Vs velocities at 100–150 km depth. However, this correlation is weaker than reported in experimental...
Ofek, E O; Tal, D; Sullivan, M; Gal-Yam, A; Kulkarni, S R; Nugent, P E; Ben-Ami, S; Bersier, D; Cao, Y; Cenko, S B; De Cia, A; Filippenko, A V; Fransson, C; Kasliwal, M M; Laher, R; Surace, J; Quimby, R; Yaron, O
2014-01-01
Interaction of supernova (SN) ejecta with the optically thick circumstellar medium (CSM) of a progenitor star can result in a bright, long-lived shock breakout event. Candidates for such SNe include Type IIn and superluminous SNe. If some of these SNe are powered by interaction, then there should be a relation between their peak luminosity, bolometric light-curve rise time, and shock-breakout velocity. Given that the shock velocity during shock breakout is not measured, we expect a correlation, with a significant spread, between the rise time and the peak luminosity of these SNe. Here, we present a sample of 15 SNe IIn for which we have good constraints on their rise time and peak luminosity from observations obtained using the Palomar Transient Factory. We report on a possible correlation between the R-band rise time and peak luminosity of these SNe, with a false-alarm probability of 3%. Assuming that these SNe are powered by interaction, combining these observables and theory allows us to deduce lower limit...
Directory of Open Access Journals (Sweden)
Siu H. Chan
2012-02-01
Full Text Available Vascular stiffness has been proposed as a simple method to assess arterial loading conditions of the heart which induce left ventricular hypertrophy (LVH. There is some controversy as to whether the relationship of vascular stiffness to LVH is independent of blood pressure, and which measurement of arterial stiffness, augmentation index (AI or pulse wave velocity (PWV is best. Carotid pulse wave contor and pulse wave velocity of patients (n=20 with hypertension whose blood pressure (BP was under control (<140/90 mmHg with antihypertensive drug treatment medications, and without valvular heart disease, were measured. Left ventricular mass, calculated from 2D echocardiogram, was adjusted for body size using two different methods: body surface area and height. There was a significant (P<0.05 linear correlation between LV mass index and pulse wave velocity. This was not explained by BP level or lower LV mass in women, as there was no significant difference in PWV according to gender (1140.1+67.8 vs 1110.6+57.7 cm/s. In contrast to PWV, there was no significant correlation between LV mass and AI. In summary, these data suggest that aortic vascular stiffness is an indicator of LV mass even when blood pressure is controlled to less than 140/90 mmHg in hypertensive patients. The data further suggest that PWV is a better proxy or surrogate marker for LV mass than AI and the measurement of PWV may be useful as a rapid and less expensive assessment of the presence of LVH in this patient population.
Beyond Kaiser bias: mildly non-linear two-point statistics of densities in distant spheres
Uhlemann, C; Kim, J; Pichon, C; Bernardeau, F; Pogosyan, D; Park, C; L'Huillier, B
2016-01-01
Simple parameter-free analytic bias functions for the two-point correlation of densities in spheres at large separation are presented. These bias functions generalize the so-called Kaiser bias to the mildly non-linear regime for arbitrary density contrasts. The derivation is carried out in the context of large deviation statistics while relying on the spherical collapse model. A logarithmic transformation provides a saddle approximation which is valid for the whole range of densities and shown to be accurate against the 30 Gpc cube state-of-the-art Horizon Run 4 simulation. Special configurations of two concentric spheres that allow to identify peaks are employed to obtain the conditional bias and a proxy to BBKS extrema correlation functions. These analytic bias functions should be used jointly with extended perturbation theory to predict two-point clustering statistics as they capture the non-linear regime of structure formation at the percent level down to scales of about 10 Mpc/h at redshift 0. Conversely...
THE CHERNOBYL ACCIDENT AND HEALTH (TWO POINTS OF VIEW
Directory of Open Access Journals (Sweden)
V. M. Shubik
2011-01-01
Full Text Available The article presents two alternative points of view on the relationship of health malfunctions after the Chernobyl accident with radiation effect or with the factors of non-radiation nature (social, stress, nutrition peculiarities, etc.. An analysis of literature data and results of author’s own research of radiosensitive indicators of immunity condition, having essential value for the immediate and long term consequences of radiation effect was done. Possible correlation between health malfunctions of the population living in the regions, contaminated by the radionuclides, and combined effect of radiation and factors of non-radiation nature is shown.
Asymptotic behaviour of two-point functions in multi-species models
Directory of Open Access Journals (Sweden)
Karol K. Kozlowski
2016-05-01
Full Text Available We extract the long-distance asymptotic behaviour of two-point correlation functions in massless quantum integrable models containing multi-species excitations. For such a purpose, we extend to these models the method of a large-distance regime re-summation of the form factor expansion of correlation functions. The key feature of our analysis is a technical hypothesis on the large-volume behaviour of the form factors of local operators in such models. We check the validity of this hypothesis on the example of the SU(3-invariant XXX magnet by means of the determinant representations for the form factors of local operators in this model. Our approach confirms the structure of the critical exponents obtained previously for numerous models solvable by the nested Bethe Ansatz.
Asymptotic behaviour of two-point functions in multi-species models
Kozlowski, Karol K.; Ragoucy, Eric
2016-05-01
We extract the long-distance asymptotic behaviour of two-point correlation functions in massless quantum integrable models containing multi-species excitations. For such a purpose, we extend to these models the method of a large-distance regime re-summation of the form factor expansion of correlation functions. The key feature of our analysis is a technical hypothesis on the large-volume behaviour of the form factors of local operators in such models. We check the validity of this hypothesis on the example of the SU (3)-invariant XXX magnet by means of the determinant representations for the form factors of local operators in this model. Our approach confirms the structure of the critical exponents obtained previously for numerous models solvable by the nested Bethe Ansatz.
Expansion schemes for gravitational clustering: computing two-point and three-point functions
Valageas, P
2007-01-01
We describe various expansion schemes that can be used to study gravitational clustering. Obtained from the equations of motion or their path-integral formulation, they provide several perturbative expansions that are organized in different fashion or involve different partial resummations. We focus on the two-point and three-point correlation functions, but these methods also apply to all higher-order correlation and response functions. We present the general formalism, which holds for the gravitational dynamics as well as for similar models, such as the Zeldovich dynamics, that obey similar hydrodynamical equations of motion with a quadratic nonlinearity. We give our explicit analytical results up to one-loop order for the simpler Zeldovich dynamics. For the gravitational dynamics, we compare our one-loop numerical results with numerical simulations. We check that the standard perturbation theory is recovered from the path integral by expanding over Feynman's diagrams. However, the latter expansion is organ...
Wei, Zhangrui; Zhang, Haibin; Su, Haili; Zhu, Ting; Zhu, Yongsheng; Zhang, Jun
2012-11-01
The purpose of this study was to investigate whether myocardial systolic dysfunction and perfusion impairment occur in diabetic rats, and to assess their relationship using velocity vector imaging (VVI) and myocardial contrast echocardiography (MCE). Forty-six rats were randomly divided into either control or the diabetes mellitus (DM) groups. DM was induced by intraperitoneal administration of streptozotocin. Twelve weeks later, 39 survival rats underwent VVI and MCE in short-axis view at the middle level of the left ventricle, both at rest and after dipyridamole stress. VVI-derived contractile parameters included peak systolic velocity (Vs ), circumferential strain (εc ), strain rate (SRc ), and their reserves. MCE-derived perfusion parameters consisted of myocardial blood flow (MBF) and myocardial flow reserve (MFR). At rest, SRc in the DM group was significantly lower than in the control group, Vs , εc , and MBF did not differ significantly between groups. After dipyridamole stress, all VVI parameters and their reserves in the DM group were significantly lower than those in the control group, MBF and MFR were substantially lower than those in the control group, too. Meanwhile, significant correlations between VVI parameter reserves and MFR were observed in the DM group. Both myocardial systolic function and perfusion were impaired in DM rats. Decreased MFR could be an important contributor to the reduction in myocardial contractile reserve.
Ahrens, Benedikt; Duda, Mandy; Renner, Jörg
2017-04-01
One of the key challenges in geophysics concerns the derivation of structure and state of rocks and rock formations from constraints on the spatial distribution of their physical properties, as gained from laboratory experiments, borehole logging, and surveys at the surface covering scales from centimeters to kilometers. The use of information from the propagation of elastic waves constitutes the most common approach to derive the structure and state of rocks, if direct information on in-situ properties is limited (e.g., through boreholes) or inaccessible. Furthermore, the determination of hydraulic rock properties serves the dual purpose of constraining structure and providing the basis for predictions of the behavior of a system of interest during continued fluid injection or production, as associated with, e.g., exploitation of hydrocarbon reservoirs, operation of subsurface liquid-waste repositories, or geothermal energy provision. In-situ, wave observations potentially provide better coverage of rock volumes (in space and time) than hydraulic investigations and thus constraints on correlations between elastic and hydraulic properties bear the potential to improve subsurface characterization. In our laboratory study, we continuously monitored hydraulic properties and elastic wave velocities of porous Wilkeson sandstone samples during conventional triaxial deformation. Confining pressures applied in the tests cover the range from below to above the critical pressure for crack closure to control the state of pre-existing cracks. Hydraulic properties were determined using the oscillatory pore-pressure method owing to its benefits regarding continuous and highly resolved monitoring of permeability and specific storage capacity during deformation and even imminent localized failure. The magnitude of the deformation-associated variations in the monitored physical properties strongly depends on initial microstructure and degree of hydrostatically induced crack closure
Turbulent correlation measurements in a two-stream mixing layer.
Jones, B. G.; Planchon, H. P.; Hammersley, R. J.
1973-01-01
Two point space-time measurements of the axial component of fluctuating velocity were made using linearized hot-wire anemometry. Space scales, convected frame correlations and time scales, and convection velocities in the shear layer were evaluated. Both filtered narrow and broad band convected frame autocorrelations were determined. Differences between axial broad band convection velocities and both mean turbulence and mean entrained fluid velocities were observed. Scaled broad band convection velocities for the mixing layer and simple round jets were found to collapse to a common curve. Axial narrow band convection velocities showed strong frequency and transverse position dependence.
Quantization of fluctuations in DSR: the two-point function and beyond
Gubitosi, Giulia; Magueijo, Joao
2015-01-01
We show that the two-point function of a quantum field theory with de Sitter momentum space (herein called DSR) can be expressed as the product of a standard delta function and an energy-dependent factor. This is a highly non-trivial technical result in any theory without a preferred frame. Applied to models exhibiting running of the dimensionality of space, this result is essential in proving that vacuum fluctuations are generally scale-invariant at high energies whenever there is running to two dimensions. This is equally true for theories with and without a preferred frame, with differences arising only as we consider higher order correlators. Specifically, the three-point function of DSR has a unique structure of "open triangles", as shown here.
Forecasts on neutrino mass constraints from the redshift-space two-point correlation function
Petracca, F.; Marulli, F.; Moscardini, L.; Cimatti, A.; Carbone, C.; Angulo, R. E.
2016-11-01
We provide constraints on the accuracy with which the neutrino mass fraction, fν, can be estimated when exploiting measurements of redshift-space distortions, describing in particular how the error on neutrino mass depends on three fundamental parameters of a characteristic galaxy redshift survey: density, halo bias and volume. In doing this, we make use of a series of dark matter halo catalogues extracted from the BASICC simulation. The mock data are analysed via a Markov Chain Monte Carlo likelihood analysis. We find a fitting function that well describes the dependence of the error on bias, density and volume, showing a decrease in the error as the bias and volume increase, and a decrease with density down to an almost constant value for high-density values. This fitting formula allows us to produce forecasts on the precision achievable with future surveys on measurements of the neutrino mass fraction. For example, a Euclid-like spectroscopic survey should be able to measure the neutrino mass fraction with an accuracy of δfν ≈ 3.1 × 10-3 (which is equivalent to δ∑mν ≈ 0.039eV), using redshift-space clustering once all the other cosmological parameters are kept fixed to the ΛCDM case.
Institute of Scientific and Technical Information of China (English)
Jie Yu; Jiang-Li Han; Li-Yun He; Xin-Heng Feng; Wei-Hong Li; Jie-Ming Mao; Wei Gao; Guang Wang
2013-01-01
Objectives To evaluate the association of coronary artery endothelial function and plasma levels of low density lipoprotein cholesterol (LDL-C) and high density lipoprotein cholesterol (HDL-C) in patients with Type 2 Diabetes Mellitus (DM). Methods We investigated 90 participants from our institution between October 2007 to March 2010: non-DM (n = 60) and DM (n = 30). As an indicator of coronary endothelial dysfunction, we used non-invasive Doppler echocardiography to quantify coronary flow velocity reserve (CFVR) in the distal part of the left descending artery after rest and after intravenous adenosine administration. Results Plasma level of LDL-C was significantly higher in patients with DM than in non-DM (3.21 0.64 vs. 2.86 0.72 mmo/L, P < 0.05), but HDL-C level did not differ between the groups (1.01 0.17 vs. 1.05 0.19 mmo/L). Furthermore, the CFVR value was lower in DM patients than non-diabetics (2.45±0.62 vs. 2.98±0.68, P < 0.001). Plasma levels of LDL-C were negatively correlated with CFVR in all subjects (r = 0.35, P < 0.001; 95% confidence interval (CI): 0.52 -C0.15) and in the non-DM (r = 0.29, P < 0.05; 95% CI: 0.51–0.05), with an even stronger negative correlation in the DM group (r = 0.42, P < 0.05; 95% CI: 0.68 –0.06). Age (β = 0.019, s = 0.007, sβ = 0.435, 95% CI: 0.033 –0.005, P = 0.008), LDL-C (β = 0.217, s = 0.105, sβ = 0.282, 95% CI: 0.428 –0.005, P = 0.045) remained independently correlated with CFVR in the DM group. However, we found no correlation between HDL-C level and CFVR in any group. Conclusions Diabetes may contribute to coronary artery disease (CAD) by inducing dysfunction of the coronary artery endothelium. Increased LDL-C level may adversely impair coronary endothelial function in DM. HDL-C may lose its endothelial-protective effects, in part as a result of pathological conditions, especially under abnormal glucose metabolism.
Goudfrooij, Paul; Kozhurina-Platais, Vera; Kalirai, Jason S; Platais, Imants; Puzia, Thomas H; Correnti, Matteo; Bressan, Alessandro; Chandar, Rupali; Kerber, Leandro; Marigo, Paola; Rubele, Stefano
2014-01-01
We present color-magnitude diagram analysis of deep Hubble Space Telescope imaging of a mass-limited sample of 18 intermediate-age (1 - 2 Gyr old) star clusters in the Magellanic Clouds, including 8 clusters for which new data was obtained. We find that ${\\it all}$ star clusters in our sample feature extended main sequence turnoff (eMSTO) regions that are wider than can be accounted for by a simple stellar population (including unresolved binary stars). FWHM widths of the MSTOs indicate age spreads of 200-550 Myr. We evaluate dynamical evolution of clusters with and without initial mass segregation. Our main results are: (1) the fraction of red clump (RC) stars in secondary RCs in eMSTO clusters scales with the fraction of MSTO stars having pseudo-ages $\\leq 1.35$ Gyr; (2) the width of the pseudo-age distributions of eMSTO clusters is correlated with their central escape velocity $v_{\\rm esc}$, both currently and at an age of 10 Myr. We find that these two results are unlikely to be reproduced by the effects ...
Hekker, S; Aerts, C; Quirrenbach, Andreas G; Reffert, S; Mitchell, D S
2008-01-01
Since 1999, we have been conducting a radial velocity survey of 179 K giants using the CAT at UCO/Lick observatory. At present ~20-100 measurements have been collected per star with a precision of 5 to 8 m/s. Of the stars monitored, 145 (80%) show radial velocity (RV) variations at a level >20 m/s, of which 43 exhibit significant periodicities. Our aim is to investigate possible mechanism(s) that cause these observed RV variations. We intend to test whether these variations are intrinsic in nature, or possibly induced by companions, or both. In addition, we aim to characterise the parameters of these companions. A relation between log g and the amplitude of the RV variations is investigated for all stars in the sample. Furthermore, the hypothesis that all periodic RV variations are caused by companions is investigated by comparing their inferred orbital statistics with the statistics of companions around main sequence stars. A strong relation is found between the amplitude of the RV variations and log g in K ...
Budi-Santoso, Agus; Lesage, Philippe
2016-07-01
We present a study of the seismic velocity variations that occurred in the structure before the large 2010 eruption of Merapi volcano. For the first time to our knowledge, the technique of coda wave interferometry is applied to both families of similar events (multiplets) and to correlation functions of seismic noise. About half of the seismic events recorded at the summit stations belong to one of the ten multiplets identified, including 120 similar events that occurred in the last 20 hr preceding the eruption onset. Daily noise cross-correlation functions (NCF) were calculated for the six pairs of short-period stations available. Using the stretching method, we estimate time-series of apparent velocity variation (AVV) for each multiplet and each pair of stations. No significant velocity change is detected until September 2010. From 10 October to the beginning of the eruption on 26 October, a complex pattern of AVV is observed with amplitude of up to ±1.5 per cent. Velocity decrease is first observed from families of deep events and then from shallow earthquakes. In the same period, AVV with different signs and chronologies are estimated from NCF calculated for various station pairs. The location in the horizontal plane of the velocity perturbations related with the AVV obtained from NCF is estimated by using an approach based on the radiative transfer approximation. Although their spatial resolution is limited, the resulting maps display velocity decrease in the upper part of the edifice in the period 12-25 October. After the eruption onset, the pattern of velocity perturbations is significantly modified with respect to the previous one. We interpret these velocity variations in the framework of a scenario of magmatic intrusion that integrates most observations. The perturbation of the stress field associated with the magma migration can induce both decrease and increase of the seismic velocity of rocks. Thus the detected AVVs can be considered as precursors of
Vandewalle, H; Peres, G; Heller, J; Panel, J; Monod, H
1987-01-01
The force-velocity relationship on a Monark ergometer and the vertical jump height have been studied in 152 subjects practicing different athletic activities (sprint and endurance running, cycling on track and/or road, soccer, rugby, tennis and hockey) at an average or an elite level. There was an approximately linear relationship between braking force and peak velocity for velocities between 100 and 200 rev.min-1. The highest indices of force P0, velocity V0 and maximal anaerobic power (Wmax) were observed in the power athletes. There was a significant relationship between vertical jump height and Wmax related to body mass.
Spica, Zack; Perton, Mathieu; Calò, Marco; Legrand, Denis; Córdoba-Montiel, Francisco; Iglesias, Arturo
2016-09-01
This work presents an innovative strategy to enhance the resolution of surface wave tomography obtained from ambient noise cross-correlation (C1) by bridging asynchronous seismic networks through the correlation of coda of correlations (C3). Rayleigh wave group dispersion curves show consistent results between synchronous and asynchronous stations. Rayleigh wave group traveltimes are inverted to construct velocity-period maps with unprecedented resolution for a region covering Mexico and the southern United States. The resulting period maps are then used to regionalize dispersion curves in order to obtain local 1-D shear velocity models (VS) of the crust and uppermost mantle in every cell of a grid of 0.4°. The 1-D structures are obtained by iteratively adding layers until reaching a given misfit, and a global tomography model is considered as an input for depths below 150 km. Finally, a high-resolution 3-D VS model is obtained from these inversions. The major structures observed in the 3-D model are in agreement with the tectonic-geodynamic features and with previous regional and local studies. It also offers new insights to understand the present and past tectonic evolution of the region.
Energy Technology Data Exchange (ETDEWEB)
Le Fevre, A. [Paris-7 Univ., 75 (France)
1997-05-14
This work is focused on the study of fragment and light particle production mechanisms in the multifragmentation process of hot nuclei, which are formed in the central collisions of Xe+Sn at 50 MeV/u. The experiment has been performed with the INDRA multidetector. The central collision events, selected via the flow angle variable, exhibit the presence of a heavy (Z=90) and highly excited (E{sup *}=12.5 MeV/u) isotropic emission source. The comparison of the data with a statistical multifragmentation model (MMMC) and a dynamical model (BNV) makes us conclude that the multifragmentation can only be explained in the frame of a relatively cold process, around 6 MeV/u of thermal excitation energy, preceded by a primary emission stage of the expanding source, during which nearly one third of the excitation energy is dissipated. In addition, it appears that the fragment energy spectra are not explained by a purely thermal process, and that one has to put forward an expansion collective motion, of 2 MeV/u of energy, following the compression of the compound system. In order to precise the existence of a two-step particle emission (primary and secondary), we have developed and applied an original method of reduced velocity correlations between particles and fragments. It has allowed us to underline two distinct origins for the particle production: one corresponding to secondary emissions, coming from the fragments, and the other one, associated with emissions which occur prior to the fragment production. At last, it has allowed us, also to bring out a hierarchy in the emission time in the decay process, with respect to the particle type. (author) 90 refs.
Park, Hyungkwon; Kim, Jinyoung; Lee, Sung Bo; Lee, Changhee
2016-12-01
Vacuum kinetic spraying (VKS) is a promising room-temperature process to fabricate dense ceramic films. However, unfortunately, the deposition mechanism is still not clearly understood. In this respect, the critical conditions for successful deposition were investigated. Based on simulation and microstructural analysis, it was found that as the particle velocity increased, fracture mode transition from tensile fracture to shear fracture occurred and particle did not bounce off anymore above a certain velocity. Simultaneously, particle underwent shock-induced plasticity and dynamic fragmentation. The plasticity assisted to prevent the fragments from rebounding by spending the excessive kinetic energy and fragmentation is essential for fragment bonding and film growth considering that the deposition rate increased as the fraction of fragmentation increased. Accordingly, plasticity and fragmentation take a crucial role for particle deposition. In this respect, the velocity that fracture mode transition occurs is newly defined as critical velocity. Consequently, for successful deposition, the particle should at least exceed the critical velocity and thus it is very crucial for film fabrication in VKS process at room temperature.
Zilevu, Kojo S.; Kammerman, Kelly L.; Nanzer, Jeffrey A.
2013-05-01
The design of a 29.5 GHz experimental active interferometer for the measurement of the angular velocity of moving humans is presented in this paper, as well as initial measurements of walking humans. Measurement of the angular motion of moving objects is a desirable function in remote security sensing applications. Doppler radar sensors are able to measure the signature of moving humans based on micro-Doppler analysis; however, a person moving with little to no radial velocity produces negligible Doppler returns. Measurement of the angular movement of humans can be done with traditional radar techniques however the process involves either continuous tracking with narrow beamwidth or angle-of arrival estimation algorithms. Recently, the authors presented a new method of measuring the angular velocity of moving objects using interferometry. The method measures the angular velocity of an object without tracking or complex processing. The frequency shift imparted on the signal response is proportional to the angular velocity of the object as it passes through the interferometer beam pattern. The experimental system consists of a transmitter and two separate receivers with two widely spaced antennas. The received signals in each of the two channels are downconverted and digitized, and post-processed offline. Initial results of a walking person passing through the interferometer beam pattern are presented, which verify the expected operation of the receiver derived from the initial theory.
Armstrong, W. H., Jr.; Anderson, R. S.; Moon, T. A.; Fahnestock, M. A.
2015-12-01
We investigate how glacier geometry and geographic setting govern a glacier's response to meltwater and precipitation inputs. Does the up-glacier limit of enhanced summer basal motion vary across glaciers? Do non-surge glaciers show consistent spatial patterns of basal motion from year to year? We investigate such questions by documenting the seasonal-to-annual evolution of surface velocity for over 25 surge- and non-surge type glaciers in the Wrangell-St Elias ranges of southeast Alaska, USA, during 2013-2015. We use the Python-implemented PYCORR image cross-correlation software to estimate ice surface velocity fields over ~35,000 km2 covered by four Landsat-8 (L8) scenes. PYCORR is an optimized version of IMCORR, and takes less than 5 minutes to process a full L8 scene. This computational efficiency allows us to calculate dozens of velocity fields for each scene to provide high temporal resolution. We automate the extraction of velocity profiles along longitudinal glacier profiles to document their temporal evolution over timespans ranging from 16 days to greater than one year at spatial resolution of several tens to several hundred meters. This method provides much greater spatial coverage than GPS-derived velocities, and succeeds in terrain of rough surface texture and significant temporal elevation change, both of which present substantial challenges for deriving InSAR velocities. Preliminary data on Kennicott Glacier (Figure 1) resolve the annual velocity cycle in which speeds are lowest over winter and highest in summer reflecting meltwater-induced basal motion. We find notable seasonal velocity fluctuations at distances of more than 30 km from the glacier terminus. While longitudinal stress gradient coupling may explain a portion of these velocity variations, local basal motion must contribute, as the relatively thin (~500 m) ice cannot transmit longitudinal stresses over such distances. Regions downstream of tributary junctions show consistently
Raangs, R.; Schlicke, Ted; Barham, Richard
2005-01-01
In this paper, a new method of calibrating an acoustic particle velocity sensor using laser Doppler anemometry (LDA) is discussed. The results were compared and were in good agreement with the results obtained by conventional methods, where the sensitivity of the microflown is obtained with the use
New two-point scleral-fixation technique for foldable intraocular lenses with four hollow haptics.
Liu, He-Ting; Jiang, Zheng-Xuan; Tao, Li-Ming
2016-01-01
The study was to report a new two-point scleral-fixation technique for foldable intraocular lenses with four haptics. Lenses were slid into the anterior chamber from a 2.8 mm corneal incision and fixed under two sclera flaps at two opposite points. The postoperative best-corrected visual acuities (BCVAs) of all patients were significantly better than their preoperative BCVA. The results demonstrate that two-point, scleral fixations of foldable, intraocular lenses might be practicable and effective.
Kotte, R.; Kämpfer, B.; Mösner, J.; Neubert, W.; Wohlfarth, D.; Alard, J. P.; Amouroux, V.; Basrak, Z.; Bastid, N.; Belayev, I. M.; Berger, L.; Blaich, Th.; Boussange, S.; Buta, A.; Čaplar, R.; Cerruti, C.; Cindro, N.; Coffin, J. P.; Donà, R.; Dupieux, P.; Erö, J.; Fan, Z. G.; Fintz, P.; Fodor, Z.; Fraysse, L.; Freifelder, R.; Frolov, S.; Gobbi, A.; Grigorian, Y.; Guillaume, G.; Herrmann, N.; Hildenbrand, K. D.; Hölbling, S.; Houari, O.; Ibnouzahir, M.; Jeong, S. C.; Jundt, F.; Kecskemeti, J.; Koncz, P.; Korchagin, Y.; Krämer, M.; Kuhn, C.; Legrand, I.; Lebedev, A.; Manko, V.; Matulewicz, T.; Mgebrishvili, G.; Moisa, D.; Montarou, G.; Montbel, I.; Pelte, D.; Petrovici, M.; Pras, P.; Rami, F.; Ramillien, V.; Reisdorf, W.; Sadchikov, A.; Schüll, D.; Seres, Z.; Sikora, B.; Simion, V.; Smolyankin, S.; Sodan, U.; Teh, K.; Tezkratt, R.; Trzaska, M.; Vasiliev, M. A.; Wagner, P.; Wessels, J. P.; Wienold, T.; Wilhelmi, Z.; Zhilin, A. V.
1995-05-01
Velocity correlations of intermediate mass fragments (IMF), produced in collisions of Au+Au at 100, 150, 250, and 400A MeV beam energy, are extracted from measurements with the 4π detector system (FOPI) in construction stage I at Schwerionen-Synchrotron (SIS) at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt. The IMF correlation functions of peripheral and semicentral events are found to be strongly affected by the collective sideward motion of nuclear matter. The sideflow causes an enhancement of correlations at small relative velocities. This enhancement results from the mixing of differently azimuthally oriented events; it vanishes if the events are rotated into a unique reaction plane. Selecting violent central collisions, the comparison of the data with a Coulomb dominated final-state interaction model points to a radius of the expanding and multifragmenting source of Rs~=13 fm for 100A MeV which appears shrinking by 20% when increasing the projectile energy to 400 MeV per nucleon. The deduced source radii are found to depend on the radial explosion energy used in the model. The inclusion of such a collective expansion is necessary for a reasonable description of the experimental single-particle spectra of the IMF. The unique Coulomb suppression of small relative IMF velocities, found for the given beam energy range, is attributed to rather constant averaged next-neighbor distances =8.6+/-0.2 fm of the IMF charge centers within the source at breakup time.
Energy Technology Data Exchange (ETDEWEB)
Kaempfer, B.; Kotte, R.; Moesner, J.; Neubert, W.; Wohlfarth, D.; Alard, J.P.; Basrak, Z.; Bastid, N.; Belayev, I.M.; Blaich, T.; Buta, A.; Caplar, R.; Cerruti, C.; Cindro, N.; Coffin, J.P.; Dupieux, P.; Eroe, J.; Fan, Z.G.; Fintz, P.; Fodor, Z.; Freifelder, R.; Fraysse, L.; Frolov, S.; Gobbi, A.; Grigorian, Y.; Guillaume, G.; Herrmann, N.; Hildenbrand, K.D.; Hoelbling, S.; Houari, O.; Jeong, S.C.; Jorio, M.; Jundt, F.; Kecskemeti, J.; Koncz, P.; Korchagin, Y.; Kraemer, M.; Kuhn, C.; Legrand, I.; Lebedev, A.; Maguire, C.; Manko, V.; Matulewicz, T.; Mgebrishvili, G.; Moisa, D.; Montaru, G.; Montbel, I.; Morel, P.; Pelte, D.; Petrovici, M.; Rami, F.; Reisdorf, W.; Sadchikov, A.; Schuell, D.; Seres, Z.; Sikora, B.; Simion, V.; Smolyankin, S.; Sodan, U.; Teh, K.; Tezkratt, R.; Trzaska, M.; Vasiliev, M.A.; Wagner, P.; Wessels, J.P.; Wienold, T.; Wilhelmi, Z.; Zhilin, A.L. (Forschungszentrum Rosendorf e.V., PF 51 01 19, 01314 Dresden (Germany) Institut fuer Theoretische Physik (KAI e.V.), T
1993-09-01
Velocity correlations of intermediate mass fragments (IMFs), produced in central collisions of Au+Au at 150 MeV beam energy, are extracted from measurements with the FOPI (phase I) detector system at SIS in GSI Darmstadt. The IMF correlation function for semicentral events is found to be affected by the directed sideward flow. When rotating the events into a unique reaction plane an enhancement of correlations, resulting from event mixing effects, vanishes. Selecting violent collisions with a high degree of azimuthal symmetry the correlation function appears nearly independent of additional event or single particle gate conditions. The comparison of the data with a Coulomb dominated final-state interaction model points to an expanding and multifragmenting soure with radius [ital R][similar to]14 fm.
Kämpfer, B.; Kotte, R.; Mösner, J.; Neubert, W.; Wohlfarth, D.; Alard, J. P.; Basrak, Z.; Bastid, N.; Belayev, I. M.; Blaich, Th.; Buta, A.; Čaplar, R.; Cerruti, C.; Cindro, N.; Coffin, J. P.; Dupieux, P.; Erö, J.; Fan, Z. G.; Fintz, P.; Fodor, Z.; Freifelder, R.; Fraysse, L.; Frolov, S.; Gobbi, A.; Grigorian, Y.; Guillaume, G.; Herrmann, N.; Hildenbrand, K. D.; Hölbling, S.; Houari, O.; Jeong, S. C.; Jorio, M.; Jundt, F.; Kecskemeti, J.; Koncz, P.; Korchagin, Y.; Krämer, M.; Kuhn, C.; Legrand, I.; Lebedev, A.; Maguire, C.; Manko, V.; Matulewicz, T.; Mgebrishvili, G.; Moisa, D.; Montaru, G.; Montbel, I.; Morel, P.; Pelte, D.; Petrovici, M.; Rami, F.; Reisdorf, W.; Sadchikov, A.; Schüll, D.; Seres, Z.; Sikora, B.; Simion, V.; Smolyankin, S.; Sodan, U.; Teh, K.; Tezkratt, R.; Trzaska, M.; Vasiliev, M. A.; Wagner, P.; Wessels, J. P.; Wienold, T.; Wilhelmi, Z.; Zhilin, A. L.
1993-09-01
Velocity correlations of intermediate mass fragments (IMFs), produced in central collisions of Au+Au at 150 MeV beam energy, are extracted from measurements with the FOPI (phase I) detector system at SIS in GSI Darmstadt. The IMF correlation function for semicentral events is found to be affected by the directed sideward flow. When rotating the events into a unique reaction plane an enhancement of correlations, resulting from event mixing effects, vanishes. Selecting violent collisions with a high degree of azimuthal symmetry the correlation function appears nearly independent of additional event or single particle gate conditions. The comparison of the data with a Coulomb dominated final-state interaction model points to an expanding and multifragmenting soure with radius R~14 fm.
A NEW METHOD TO CORRECT FOR FIBER COLLISIONS IN GALAXY TWO-POINT STATISTICS
Energy Technology Data Exchange (ETDEWEB)
Guo Hong; Zehavi, Idit [Department of Astronomy, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106 (United States); Zheng Zheng [Department of Physics and Astronomy, University of Utah, 115 South 1400 East, Salt Lake City, UT 84112 (United States)
2012-09-10
In fiber-fed galaxy redshift surveys, the finite size of the fiber plugs prevents two fibers from being placed too close to one another, limiting the ability to study galaxy clustering on all scales. We present a new method for correcting such fiber collision effects in galaxy clustering statistics based on spectroscopic observations. The target galaxy sample is divided into two distinct populations according to the targeting algorithm of fiber placement, one free of fiber collisions and the other consisting of collided galaxies. The clustering statistics are a combination of the contributions from these two populations. Our method makes use of observations in tile overlap regions to measure the contributions from the collided population, and to therefore recover the full clustering statistics. The method is rooted in solid theoretical ground and is tested extensively on mock galaxy catalogs. We demonstrate that our method can well recover the projected and the full three-dimensional (3D) redshift-space two-point correlation functions (2PCFs) on scales both below and above the fiber collision scale, superior to the commonly used nearest neighbor and angular correction methods. We discuss potential systematic effects in our method. The statistical correction accuracy of our method is only limited by sample variance, which scales down with (the square root of) the volume probed. For a sample similar to the final SDSS-III BOSS galaxy sample, the statistical correction error is expected to be at the level of 1% on scales {approx}0.1-30 h {sup -1} Mpc for the 2PCFs. The systematic error only occurs on small scales, caused by imperfect correction of collision multiplets, and its magnitude is expected to be smaller than 5%. Our correction method, which can be generalized to other clustering statistics as well, enables more accurate measurements of full 3D galaxy clustering on all scales with galaxy redshift surveys.
Mistakes and Pitfalls Associated with Two-Point Compression Ultrasound for Deep Vein Thrombosis
Directory of Open Access Journals (Sweden)
Tony Zitek, MD
2016-03-01
Full Text Available Introduction: Two-point compression ultrasound is purportedly a simple and accurate means to diagnose proximal lower extremity deep vein thrombosis (DVT, but the pitfalls of this technique have not been fully elucidated. The objective of this study is to determine the accuracy of emergency medicine resident-performed two-point compression ultrasound, and to determine what technical errors are commonly made by novice ultrasonographers using this technique. Methods: This was a prospective diagnostic test assessment of a convenience sample of adult emergency department (ED patients suspected of having a lower extremity DVT. After brief training on the technique, residents performed two-point compression ultrasounds on enrolled patients. Subsequently a radiology department ultrasound was performed and used as the gold standard. Residents were instructed to save videos of their ultrasounds for technical analysis. Results: Overall, 288 two-point compression ultrasound studies were performed. There were 28 cases that were deemed to be positive for DVT by radiology ultrasound. Among these 28, 16 were identified by the residents with two-point compression. Among the 260 cases deemed to be negative for DVT by radiology ultrasound, 10 were thought to be positive by the residents using two-point compression. This led to a sensitivity of 57.1% (95% CI [38.8-75.5] and a specificity of 96.1% (95% CI [93.8-98.5] for resident-performed two-point compression ultrasound. This corresponds to a positive predictive value of 61.5% (95% CI [42.8-80.2] and a negative predictive value of 95.4% (95% CI [92.9-98.0]. The positive likelihood ratio is 14.9 (95% CI [7.5-29.5] and the negative likelihood ratio is 0.45 (95% CI [0.29-0.68]. Video analysis revealed that in four cases the resident did not identify a DVT because the thrombus was isolated to the superior femoral vein (SFV, which is not evaluated by two-point compression. Moreover, the video analysis revealed that the
Holographic two-point functions for 4d log-gravity
Johansson, Niklas; Zojer, Thomas
2012-01-01
We compute holographic one- and two-point functions of critical higher curvature gravity in four dimensions. The two most important operators are the stress tensor and its logarithmic partner, sourced by ordinary massless and by logarithmic non-normalisable gravitons, respectively. In addition, the logarithmic gravitons source two ordinary operators, one with spin-one and one with spin-zero. The one-point function of the stress tensor vanishes for all Einstein solutions, but has a non-zero contribution from logarithmic gravitons. The two-point functions of all operators match the expectations from a three-dimensional logarithmic conformal field theory.
Numerical methods for stiff systems of two-point boundary value problems
Flaherty, J. E.; Omalley, R. E., Jr.
1983-01-01
Numerical procedures are developed for constructing asymptotic solutions of certain nonlinear singularly perturbed vector two-point boundary value problems having boundary layers at one or both endpoints. The asymptotic approximations are generated numerically and can either be used as is or to furnish a general purpose two-point boundary value code with an initial approximation and the nonuniform computational mesh needed for such problems. The procedures are applied to a model problem that has multiple solutions and to problems describing the deformation of thin nonlinear elastic beam that is resting on an elastic foundation.
Verified solutions of two-point boundary value problems for nonlinear oscillators
Bünger, Florian
Using techniques introduced by Nakao [4], Oishi [5, 6] and applied by Takayasu, Oishi, Kubo [11, 12] to certain nonlinear two-point boundary value problems (see also Rump [7], Chapter 15), we provide a numerical method for verifying the existence of weak solutions of two-point boundary value problems of the form -u″ = a(x, u) + b(x, u)u‧, 0 b are functions that fulfill some regularity properties. The numerical approximation is done by cubic spline interpolation. Finally, the method is applied to the Duffing, the van der Pol and the Toda oscillator. The rigorous numerical computations were done with INTLAB [8].
Adaptation of a two-point boundary value problem solver to a vector-multiprocessor environment
Energy Technology Data Exchange (ETDEWEB)
Wright, S.J. (Mathematics Dept., North Carolina State Univ., Raleigh, NC (US)); Pereyra, V. (Weidlinger Associates, Los Angeles, CA (US))
1990-05-01
Systems of linear equations arising from finite-difference discretization of two-point boundary value problems have coefficient matrices that are sparse, with most or all of the nonzeros clustered in blocks near the main diagonal. Some efficiently vectorizable algorithms for factorizing these types of matrices and solving the corresponding linear systems are described. The relative effectiveness of the different algorithms varies according to the distribution of initial, final, and coupled end conditions. The techniques described can be extended to handle linear systems arising from other methods for two-point boundary value problems, such as multiple shooting and collocation. An application to seismic ray tracing is discussed.
Wang, C. R.; Hingst, W. R.; Porro, A. R.
1991-01-01
The properties of 2-D shock wave/turbulent boundary layer interaction flows were calculated by using a compressible turbulent Navier-Stokes numerical computational code. Interaction flows caused by oblique shock wave impingement on the turbulent boundary layer flow were considered. The oblique shock waves were induced with shock generators at angles of attack less than 10 degs in supersonic flows. The surface temperatures were kept at near-adiabatic (ratio of wall static temperature to free stream total temperature) and cold wall (ratio of wall static temperature to free stream total temperature) conditions. The computational results were studied for the surface heat transfer, velocity temperature correlation, and turbulent shear stress in the interaction flow fields. Comparisons of the computational results with existing measurements indicated that (1) the surface heat transfer rates and surface pressures could be correlated with Holden's relationship, (2) the mean flow streamwise velocity components and static temperatures could be correlated with Crocco's relationship if flow separation did not occur, and (3) the Baldwin-Lomax turbulence model should be modified for turbulent shear stress computations in the interaction flows.
Intrinsic alignments of galaxies in the MassiveBlack-II simulation: analysis of two-point statistics
Tenneti, Ananth; Mandelbaum, Rachel; Di Matteo, Tiziana; Feng, Yu; Khandai, Nishikanta
2014-01-01
The intrinsic alignment of galaxies with the large-scale density field is an important astrophysical contaminant in upcoming weak lensing surveys whilst offering insights into galaxy formation and evolution. We present detailed measurements of the galaxy intrinsic alignments and associated ellipticity-direction (ED) and projected shape ($w_{g+}$) correlation functions for galaxies in the cosmological hydrodynamic MassiveBlack-II (MB-II) simulation. We carefully assess the effects on galaxy shapes, misalignments and two-point statistics of iterative weighted (by mass, luminosity, and color) definitions of the (reduced and unreduced) inertia tensor. We find that iterative procedures must be adopted for a reliable measurement of reduced tensor but that luminosity versus mass weighting has only negligible effects. Blue galaxies exhibit stronger misalignments and suppressed $w_{g+}$ amplitude. Both ED and $w_{g+}$ correlations increase in amplitude with subhalo mass (in the range of $10^{10} - 6.0\\times 10^{14}h^{...
Holographic two-point functions for 4d log-gravity
Johansson, Niklas; Naseh, Ali; Zojer, Thomas
2012-01-01
We compute holographic one- and two-point functions of critical higher-curvature gravity in four dimensions. The two most important operators are the stress tensor and its logarithmic partner, sourced by ordinary massless and by logarithmic non-normalisable gravitons, respectively. In addition, the
Solvability for a Class of Abstract Two-Point Boundary Value Problems Derived from Optimal Control
Directory of Open Access Journals (Sweden)
Wang Lianwen
2007-01-01
Full Text Available The solvability for a class of abstract two-point boundary value problems derived from optimal control is discussed. By homotopy technique existence and uniqueness results are established under some monotonic conditions. Several examples are given to illustrate the application of the obtained results.
Solvability for a Class of Abstract Two-Point Boundary Value Problems Derived from Optimal Control
Directory of Open Access Journals (Sweden)
Lianwen Wang
2008-01-01
Full Text Available The solvability for a class of abstract two-point boundary value problems derived from optimal control is discussed. By homotopy technique existence and uniqueness results are established under some monotonic conditions. Several examples are given to illustrate the application of the obtained results.
Modification of the Two-Point Touch Cane Technique: A Pilot Study.
Jacobson, William H.; Ehresman, Paul
1983-01-01
Four blind adults were observed to determine the extent of the natural movement of their centers of gravity in relation to arc height during the two-point touch technique for long cane travel. The Ss learned and practiced a modified technique using their center of gravity as much as possible. (Author)
Two-point discrimination of the upper extremities of healthy Koreans in their 20's.
Koo, Ja-Pung; Kim, Soon-Hee; An, Ho-Jung; Moon, Ok-Gon; Choi, Jung-Hyun; Yun, Young-Dae; Park, Joo-Hyun; Min, Kyoung-Ok
2016-03-01
[Purpose] The present study attempted to measure two-point discrimination in the upper extremities of healthy Koreans in their 20's. [Subjects and Methods] Using a three-point esthesiometer, we conducted an experiment with a group of 256 college students (128 male and 128 female), attending N University in Chonan, Republic of Korea. [Results] Females showed two-point discrimination at a shorter distance than males at the following points: (i) 5 cm above the elbow joint, the middle part, and 5 cm below the shoulder joint of the anterior upper arm; (ii) 5 cm above the elbow joint and 5 cm below the shoulder joint of the posterior upper arm; (iii) 5 cm above the front of the wrist joint of the forearm; 5 cm below the elbow joint, the palmar part of the distal interphalangeal joint of the thumb, the dorsal part of the distal interphalangeal joint of the middle and little fingers. It was also found that females showed greater two-point discrimination than males in distal regions rather than proximal regions. [Conclusion] The findings of this study will help establish normal values for two-point discrimination of upper extremities of young Koreans in their 20's.
Problem with two-point conditions for parabolic equation of second order on time
Directory of Open Access Journals (Sweden)
M. M. Symotyuk
2014-12-01
Full Text Available The correctness of a problem with two-point conditions ontime-variable and of Dirichlet-type conditions on spatialcoordinates for the linear parabolic equations with variablecoefficients are established. The metric theorem on estimationsfrom below of small denominators of the problem (the notions of Hausdorff measure is proved.
Adams, Caitlin; Blake, Chris
2017-10-01
We present the first simultaneous analysis of the galaxy overdensity and peculiar velocity fields by modelling their cross-covariance. We apply our new maximum-likelihood approach to data from the 6-degree Field Galaxy Survey (6dFGS), which has the largest single collection of peculiar velocities to date. We present a full derivation of the analytic expression for the cross-covariance between the galaxy overdensity and peculiar velocity fields and find direct evidence for a non-zero correlation between the fields on scales up to ∼50 h-1 Mpc. When utilizing the cross-covariance, our measurement of the normalized growth rate of structure is fσ _8(z=0) = 0.424^{+0.067}_{-0.064} (15 per cent precision), and our measurement of the redshift-space distortion parameter is β =0.341^{+0.062}_{-0.058} (18 per cent precision). Both measurements improve by ∼20 per cent compared to only using the autocovariance information. This is consistent with the literature on multiple-tracer approaches, as well as Fisher matrix forecasts and previous analyses of 6dFGS. Our measurement of fσ8 is consistent with the standard cosmological model, and we discuss how our approach can be extended to test alternative models of gravity.
Hamaus, Nico; Desjacques, Vincent
2011-01-01
One of the main signatures of primordial non-Gaussianity of the local type is a scale-dependent correction to the bias of large-scale structure tracers such as galaxies or clusters, whose amplitude depends on the bias of the tracers itself. The dominant source of noise in the power spectrum of the tracers is caused by sampling variance on large scales (where the non-Gaussian signal is strongest) and shot noise arising from their discrete nature. Recent work has argued that one can avoid sampling variance by comparing multiple tracers of different bias, and suppress shot noise by optimally weighting halos of different mass. Here we combine these ideas and investigate how well the signatures of non-Gaussian fluctuations in the primordial potential can be extracted from the two-point correlations of halos and dark matter. On the basis of large $N$-body simulations with local non-Gaussian initial conditions and their halo catalogs we perform a Fisher matrix analysis of the two-point statistics. Compared to the st...
Bowles, K. J.
1986-01-01
Summarized are basic studies that were conducted to correlate the impact resistance of graphite-fiber-reinforced composites with polymer matrix properties. Three crosslinked epoxy resins and a linear polysulfone were selected as composite matrices. As a group, these resins possess a significantly large range of mechanical properties. The mechanical properties of the resins and their respective composites were measured. Neat resin specimens and unidirectional and crossply composite specimens were impact tested with an instrumented dropweight tester. Impact resistances of the specimens were assessed on the basis of loading capability, energy absorption, and extent of damage.
NUMERICAL SIMULATION OF TWO-POINT CONTACT BETWEEN WHEEL AND RAIL
Institute of Scientific and Technical Information of China (English)
Jun Zhang; Shouguang Sun; Xuesong Jin
2009-01-01
The elastic-plastic contact problem with rolling friction of wheel-rail is solved using the FE parametric quadratic programming method. Thus, the complex elastic-plastic contact problem can be calculated with high accuracy and efficiency, while the Hertz's hypothesis and the elastic semi-space assumption are avoided. Based on the 'one-point' contact calculation of wheel-rail, the computational model of 'two-point' contact are established and calculated when the wheel flange is close to the rail. In the case of 'two-point' contact, the changing laws of wheelrail contact are introduced and contact forces in various load cases are carefully analyzed. The main reason of wheel flange wear and rail side wear is found. Lubrication computational model of the wheel flange is constructed. Comparing with the result without lubrication, the contact force between wheel flange and rail decreases, which is beneficial for reducing the wear of wheel-rail.
A NEW TWO-POINT ADAPTIVENONLINEAR APPROXIMATION METHOD FOR RELIABILITY ANALYSIS
Institute of Scientific and Technical Information of China (English)
LiuShutian
2004-01-01
A two-point adaptive nonlinear approximation (referred to as TANA4) suitable for reliability analysis is proposed. Transformed and normalized random variables in probabilistic analysis could become negative and pose a challenge to the earlier developed two-point approximations; thus a suitable method that can address this issue is needed. In the method proposed, the nonlinearity indices of intervening variables are limited to integers. Then, on the basis of the present method, an improved sequential approximation of the limit state surface for reliability analysis is presented. With the gradient projection method, the data points for the limit state surface approximation are selected on the original limit state surface, which effectively represents the nature of the original response function. On the basis of this new approximation, the reliability is estimated using a first-order second-moment method. Various examples, including both structural and non-structural ones, are presented to show the effectiveness of the method proposed.
Two-point functions of conformal primary operators in $\\mathcal{N}=1$ superconformal theories
Li, Daliang
2014-01-01
In $\\mathcal{N}=1$ superconformal theories in four dimensions the two-point function of superconformal multiplets is known up to an overall constant. A superconformal multiplet contains several conformal primary operators, whose two-point function coefficients can be determined in terms of the multiplet's quantum numbers. In this paper we work out these coefficients in full generality, i.e. for superconformal multiplets that belong to any irreducible representation of the Lorentz group with arbitrary scaling dimension and R-charge. From our results we recover the known unitarity bounds, and also find all shortening conditions, even for non-unitary theories. For the purposes of our computations we have developed a Mathematica package for the efficient handling of expansions in Grassmann variables.
Anggono, T.; Nishimura, T.; Sato, H.; Ueda, H.; Ukawa, M.
2008-12-01
Miyakejima Island, which is located about 170 km to the south of Tokyo, Japan, is an active volcano of basaltic magma. In 2000 volcanic activity started with magma ascent and migration northwestwardly on June 26 - 27. Then, the volcano formed a caldera on the summit in July, and large amount of volcanic gas emission continued from late August until now. We analyze the ambient seismic noise recorded at three NIED seismic stations (MKK, MKT, and MKS) in the island in order to study the volcano structure behavior associated with such significant volcanic activities. We apply cross correlation analyses to the continuous records of vertical component of short period seismometers (1 s). The data are sampled at a frequency of 100 Hz with an A/D resolution of 16-bit. We calculate cross correlation functions (CCFs) for time window of 60 s for each station pair. We stack the CCFs for each month and bandpass filter the stacked data at frequency band 0.4 - 0.8 Hz. The stacked CCFs, which may represent the Green function between two stations, at station pairs MKK - MKS (the distance is 1.8 km) and MKT - MKS (the distance is 3.9 km) show wave packets with large amplitudes at both sides (positive and negative time delays). The wave packets propagate at group velocities of about 0.8 - 1.0 km/s. The stacked CCFs for MKK - MKT (the distance is 3.1 km) is one sided (negative time delay). Such asymmetric might be due to the inhomogeneous distribution of propagation direction of ambient seismic noise, so we do not use the data for the following analyses. Comparing the CCFs obtained for periods from July 1999 to June 2000 with that of October 2002, we observe small phase difference of the main wave packet. Our results show that for station pair MKK - MKS, whose path crosses the northern part of the island, velocity increased about 1.6 % after the 2000 volcanic activity. For MKT - MKS, whose path closely crosses the newly formed caldera, we estimate the velocity decrease of about 1
Comparison of Optimization and Two-point Methods in Estimation of Soil Water Retention Curve
Ghanbarian-Alavijeh, B.; Liaghat, A. M.; Huang, G.
2009-04-01
Soil water retention curve (SWRC) is one of the soil hydraulic properties in which its direct measurement is time consuming and expensive. Since, its measurement is unavoidable in study of environmental sciences i.e. investigation of unsaturated hydraulic conductivity and solute transport, in this study the attempt is to predict soil water retention curve from two measured points. By using Cresswell and Paydar (1996) method (two-point method) and an optimization method developed in this study on the basis of two points of SWRC, parameters of Tyler and Wheatcraft (1990) model (fractal dimension and air entry value) were estimated and then water content at different matric potentials were estimated and compared with their measured values (n=180). For each method, we used both 3 and 1500 kPa (case 1) and 33 and 1500 kPa (case 2) as two points of SWRC. The calculated RMSE values showed that in the Creswell and Paydar (1996) method, there exists no significant difference between case 1 and case 2. However, the calculated RMSE value in case 2 (2.35) was slightly less than case 1 (2.37). The results also showed that the developed optimization method in this study had significantly less RMSE values for cases 1 (1.63) and 2 (1.33) rather than Cresswell and Paydar (1996) method.
Calculating two-point resistances in distance-regular resistor networks
Energy Technology Data Exchange (ETDEWEB)
Jafarizadeh, M A [Department of Theoretical Physics and Astrophysics, University of Tabriz, Tabriz 51664 (Iran, Islamic Republic of); Sufiani, R [Department of Theoretical Physics and Astrophysics, University of Tabriz, Tabriz 51664 (Iran, Islamic Republic of); Jafarizadeh, S [Department of Electrical and computer engineering, University of Tabriz, Tabriz 51664 (Iran, Islamic Republic of)
2007-05-11
An algorithm for the calculation of the resistance between two arbitrary nodes in an arbitrary distance-regular resistor network is provided, where the calculation is based on stratification introduced in Jafarizadeh and Salimi (2006 J. Phys. A: Math. Gen. 39 1-29) and the Stieltjes transform of the spectral distribution (Stieltjes function) associated with the network. It is shown that the resistances between a node {alpha} and all nodes {beta} belonging to the same stratum with respect to the {alpha} (R{sub {alpha}}{sub {beta}{sup (i)}}), {beta} belonging to the ith stratum with respect to the {alpha}) are the same. Also, the analytical formulae for two-point resistances R{sub {alpha}}{sub {beta}{sup (i)}}, i=1,2,3, are given in terms of the size of the network and corresponding intersection numbers. In particular, the two-point resistances in a strongly regular network are given in terms of its parameters (v, {kappa}, {lambda}, {mu}). Moreover, the lower and upper bounds for two-point resistances in strongly regular networks are discussed.
Energy Technology Data Exchange (ETDEWEB)
B. Gurau; P. Vassalo; K. Keller
2002-02-19
Local gas and liquid velocities are measured by cross-correlating signals from a double sensor hot-film anemometer probe in pure water flow and air water two-phase flow. The gas phase velocity measured in two-phase flow agrees with velocity data obtained using high-speed video to within +/-5%. A turbulent structure, present in the liquid phase, allows a correlation to be taken, which is consistent with the expected velocity profiles in pure liquid flow. This turbulent structure is also present in the liquid phase of a two-phase flow system. Therefore, a similar technique can be applied to measure the local liquid velocity in a two-phase system, when conditions permit.
Energy Technology Data Exchange (ETDEWEB)
Iliopoulos, Sokratis; Tsangouri, Eleni; Aggelis, Dimitrios G.; Pyl, Lincy [Vrije Univ., Brussels (Belgium). Dept. of Mechanics of Materials and Constructions; Vantomme, John [Vrije Univ., Brussels (Belgium). Dept. of Mechanics of Materials and Constructions; Royal Military Academy, Brussels (Belgium). Civil and Material Engineering Dept.; Marcke, Philippe van [ONDRAF/NIRAS (Belgium); Areias, Lou [EURIDICE GIE/SCK.CEN, Mol (Belgium); Vrije Univ., Brussels (Belgium). Dept. of Mechanics of Materials and Constructions
2014-11-01
The long term management of high-level and heat emitting radioactive waste is a worldwide concern, as it directly influences the environment and future generations. To address this issue, the Belgian Agency for Radioactive Waste and Enriched Fissile Materials has come up with the conceptual design of a massive concrete structure called Supercontainer. The feasibility to construct these structures is being evaluated through a number of scaled models that are tested using classical as well as state of the art measurement techniques. In the current paper, the results obtained from the simultaneous application of the Digital Image Correlation (DIC), the Acoustic Emission (AE) and the Ultrasonic Pulse Velocity (UPV) nondestructive testing techniques on the second scaled model for the detection and monitoring of cracks will be presented.
Covariant and infrared-free graviton two-point function in de Sitter spacetime. II.
Pejhan, Hamed; Rahbardehghan, Surena
2016-11-01
The solution to the linearized Einstein equation in de Sitter (dS) spacetime and the corresponding two-point function are explicitly written down in a gauge with two parameters "a " and "b ". The quantization procedure, independent of the choice of the coordinate system, is based on a rigorous group theoretical approach. Our result takes the form of a universal spin-two (transverse-traceless) sector and a gauge-dependent spin-zero (pure-trace) sector. Scalar equations are derived for the structure functions of each part. We show that the spin-two sector can be written as the resulting action of a second-order differential operator (the spin-two projector) on a massless minimally coupled scalar field (the spin-two structure function). The operator plays the role of a symmetric rank-2 polarization tensor and has a spacetime dependence. The calculated spin-two projector grows logarithmically with distance and also no dS-invariant solution for either structure functions exist. We show that the logarithmically growing part and the dS-breaking contribution to the spin-zero part can be dropped out, respectively, for suitable choices of parameters "a " and "b ". Considering the transverse-traceless graviton two-point function, however, shows that dS breaking is universal (cannot be gauged away). More exactly, if one wants to respect the covariance and positiveness conditions, the quantization of the dS graviton field (as for any gauge field) cannot be carried out directly in a Hilbert space and involves unphysical negative norm states. However, a suitable adaptation (Krein spaces) of the Gupta-Bleuler scheme for massless fields, based on the group theoretical approach, enables us to obtain the corresponding two-point function satisfying the conditions of locality, covariance, transversality, index symmetrizer, and tracelessness.
Covalent docking using autodock: Two-point attractor and flexible side chain methods.
Bianco, Giulia; Forli, Stefano; Goodsell, David S; Olson, Arthur J
2016-01-01
We describe two methods of automated covalent docking using Autodock4: the two-point attractor method and the flexible side chain method. Both methods were applied to a training set of 20 diverse protein-ligand covalent complexes, evaluating their reliability in predicting the crystallographic pose of the ligands. The flexible side chain method performed best, recovering the pose in 75% of cases, with failures for the largest inhibitors tested. Both methods are freely available at the AutoDock website (http://autodock.scripps.edu). © 2015 The Protein Society.
Two-point Functions at Two Loops in Three Flavour Chiral Perturbation Theory
Amorós, G; Talavera, P; Amoros, Gabriel; Bijnens, Johan; Talavera, Pere
2000-01-01
The vector and axial-vector two-point functions are calculated to next-to-next-to-leading order in Chiral Perturbation Theory for three light flavours. We also obtain expressions at the same order for the masses, $m_\\pi^2$, $m_K^2$ and $m_\\eta^2$, and the decay constants, $F_\\pi$, $F_K$ and $F_\\eta$. We present some numerical results after a simple resonance estimate of some of the new ${\\cal O}(p^6)$ constants.
Directory of Open Access Journals (Sweden)
Arvind
2014-12-01
Full Text Available OBJECTIVE : Approximately two thirds of patients with decompensated cirrhosis and one third of those with compensated cirrhosis have varices at the time of diagnosis. Therefore , it is essential to identify and treat those patients at highest risk because each episode of variceal hemorrhage carries a 20% to 30% risk of death , and 70% of patients not receiving treatment will die within 1 year of the initial bleeding episode . (1 METH OD S: For this study , patients with cirrhosis with or without the evidence of any upper Gastrointestinal bleed , admitted in the department of medicine , JA Group of Hospitals , GR Medical College were taken. The study was conducted between September 2011 and November 2012 and cases were evaluated on the basis of clinical , haematological , ultrasonographic and endoscopic findings. Total number of cases were 100. RESULT : The prevalence of esophageal varices was 75% in cirrhotic patients out of which 28% had bleeding. The prevalence of gastric varices was 1.33%. The portal vein diameter correlated with the presence of varices while portal vein velocity , congestion index and liver vascular index had no significant correlation with esophageal varices. The Portal vein diameter more than 1.4 cm can predict varices with sensitivity 76 % (p<0.05 and Portal vein diameter more than 1.5 cm can detect bleeding varices in cirrhotic patients with sensitivity 55.56% and specificity 80.70% . CONCLUSION : This study showed tha t duration of illness , spleen size and tense ascitis on ultrasonography and portal vein diameter correlated with the presence of esophageal varices. The duration of illness and portal vein diameter are also correlated with bleeding manifestation
Velocity selective optical pumping
Aminoff, C. G.; Pinard, M.
1982-01-01
We consider optical pumping with a quasi monochromatic tunable light beam, in the low intensity limit where a rate equation regime is obtained The velocity selective optical pumping (V.S.O.P.) introduces a correlation between atomic velocity and internal variables in the ground (or metastable) state. The aim of this article is to evaluate these atomic observables (orientation, alignment, population) as a function of velocity, using a phenomenological description of the relaxation effect of co...
Energy velocity and group velocity
Institute of Scientific and Technical Information of China (English)
陈宇
1995-01-01
A new Lagrangian method for studying the relationship between the energy velocity and the group velocity is described. It is proved that under the usual quasistatic electric field, the energy velocity is identical to the group velocity for acoustic waves in anisotropic piezoelectric (or non-piezoelectric) media.
Solving Directly Two Point Non Linear Boundary Value Problems Using Direct Adams Moulton Method
Directory of Open Access Journals (Sweden)
Zanariah A. Majid
2011-01-01
Full Text Available Problem statement: In this study, a direct method of Adams Moulton type was developed for solving non linear two point Boundary Value Problems (BVPs directly. Most of the existence researches involving BVPs will reduced the problem to a system of first order Ordinary Differential Equations (ODEs. This approach is very well established but it obviously will enlarge the systems of first order equations. However, the direct method in this research will solved the second order BVPs directly without reducing it to first order ODEs. Approach: Lagrange interpolation polynomial was applied in the derivation of the proposed method. The method was implemented using constant step size via shooting technique in order to determine the approximated solutions. The shooting technique will employ the Newtons method for checking the convergent of the guessing values for the next iteration. Results: Numerical results confirmed that the direct method gave better accuracy and converged faster compared to the existing method. Conclusion: The proposed direct method is suitable for solving two point non linear boundary value problems.
Statistics of the two-point cross-covariance function of solar oscillations
Nagashima, Kaori; Sekii, Takashi; Gizon, Laurent; Birch, Aaron C.
2016-09-01
Context. The cross-covariance of solar oscillations observed at pairs of points on the solar surface is a fundamental ingredient in time-distance helioseismology. Wave travel times are extracted from the cross-covariance function and are used to infer the physical conditions in the solar interior. Aims: Understanding the statistics of the two-point cross-covariance function is a necessary step towards optimizing the measurement of travel times. Methods: By modeling stochastic solar oscillations, we evaluate the variance of the cross-covariance function as function of time-lag and distance between the two points. Results: We show that the variance of the cross-covariance is independent of both time-lag and distance in the far field, that is, when they are large compared to the coherence scales of the solar oscillations. Conclusions: The constant noise level for the cross-covariance means that the signal-to-noise ratio for the cross-covariance is proportional to the amplitude of the expectation value of the cross-covariance. This observation is important for planning data analysis efforts.
McCarter, W. J.; Taha, H. M.; Suryanto, B.; Starrs, G.
2015-08-01
Ac impedance spectroscopy measurements are used to critically examine the end-to-end (two-point) testing technique employed in evaluating the bulk electrical resistivity of concrete. In particular, this paper focusses on the interfacial contact region between the electrode and specimen and the influence of contacting medium and measurement frequency on the impedance response. Two-point and four-point electrode configurations were compared and modelling of the impedance response was undertaken to identify and quantify the contribution of the electrode-specimen contact region on the measured impedance. Measurements are presented in both Bode and Nyquist formats to aid interpretation. Concretes mixes conforming to BSEN206-1 and BS8500-1 were investigated which included concretes containing the supplementary cementitious materials fly ash and ground granulated blast-furnace slag. A measurement protocol is presented for the end-to-end technique in terms of test frequency and electrode-specimen contacting medium in order to minimize electrode-specimen interfacial effect and ensure correct measurement of bulk resistivity.
Statistics of the two-point cross-covariance function of solar oscillations
Nagashima, Kaori; Gizon, Laurent; Birch, Aaron C
2016-01-01
Context: The cross-covariance of solar oscillations observed at pairs of points on the solar surface is a fundamental ingredient in time-distance helioseismology. Wave travel times are extracted from the cross-covariance function and are used to infer the physical conditions in the solar interior. Aims: Understanding the statistics of the two-point cross-covariance function is a necessary step towards optimizing the measurement of travel times. Methods: By modeling stochastic solar oscillations, we evaluate the variance of the cross-covariance function as function of time-lag and distance between the two points. Results: We show that the variance of the cross-covariance is independent of both time-lag and distance in the far field, i.e., when they are large compared to the coherence scales of the solar oscillations. Conclusions: The constant noise level for the cross-covariance means that the signal-to-noise ratio for the cross-covariance is proportional to the amplitude of the expectation value of the cross-...
Scott, Nicholas; Davies, Roger L; Kleijn, Gijs Verdoes; Bois, Maxime; Alatalo, Katherine; Blitz, Leo; Bournaud, Frederic; Bureau, Martin; Crocker, Alison; Davis, Timothy A; de Zeeuw, P T; Duc, Pierre-Alain; Emsellem, Eric; Khochfar, Sadegh; Krajnovic, Davor; Kuntschner, Harald; McDermid, Richard M; Morganti, Raffaella; Naab, Thorsten; Oosterloo, Tom; Sarzi, Marc; Serra, Paolo; Weijmans, Anne-Marie; Young, Lisa M
2012-01-01
We explore the connection between the local escape velocity, V_esc, and the stellar population properties in the ATLAS3D survey, a complete, volume-limited sample of nearby early-type galaxies. We make use of ugriz photometry to construct Multi-Gaussian Expansion models of the surface brightnesses of our galaxies. We are able to fit the full range of surface brightness profiles found in our sample, and in addition we reproduce the results of state-of-the-art photometry in the literature with residuals of 0.04 mags. We utilise these photometric models and SAURON integral-field spectroscopy, combined with Jeans dynamical modelling, to determine the local V_esc derived from the surface brightness. We find that the local V_esc is tightly correlated with the Mgb and Fe5015 linestrengths and optical colours, and anti-correlated with the Hbeta linestrength. In the case of the Mgb and Colour - V_esc relations we find that the relation within individual galaxies follows the global relation between different galaxies. ...
Understanding redshift space distortions in density-weighted peculiar velocity
Sugiyama, Naonori S; Spergel, David N
2015-01-01
Observations of the kinetic Sunyaev-Zel'dovich (kSZ) effect measure the density-weighted velocity field, a potentially powerful cosmological probe. This paper presents an analytical method to predict the power spectrum and two-point correlation function of the density-weighted velocity in redshift space, the direct observables in kSZ surveys. We show a simple relation between the density power spectrum and the density-weighted velocity power spectrum that holds for both dark matter and halos. Using this relation, we can then extend familiar perturbation expansion techniques to the kSZ power spectrum. One of the most important features of the density-weighted velocity is the change of the sign of infall velocity at small scales due to the nonlinear redshift space distortion. Our model can explain this characteristic feature without any free parameters. As a result, our results can precisely predict the non-linear behavior of the density-weighted velocity field in redshift space up to $\\sim10\\ h^{-1} {\\rm Mpc}$...
Hoessel, Peter; Riemann, Solveig; Knebl, Robert; Schroeder, Jens; Schuh, Gerd; Castillo, Catalina
2010-01-01
A new two-point bending stiffness method on flat hair strands was developed and validated after application of hair styling gels and hair styling sprays. A special mold was used to align single hair fibers after applying the formulations to the hair. The styling gels used contain different commercially available thickeners and styling polymers, e.g., carbomer, acrylates/beheneth-25 methacrylate copolymer, Polyquaternium-86, PVP, VP/VA copolymers, and VP/methacrylamide/vinylimidazole copolymer. Evaluation of hair sprays was performed after spray application on flat hair strands. Commercially available hair styling resins were used, e.g. acrylates/t-butylacrylamide copolymer, octylacrylamide/acrylates/butylaminoethyl methacrylate copolymer, and VP/VA copolymer (30:70). The new stiffness test method provided the best correlation with practically relevant sensory assessments on hair strands and a panel test in which styling gels were evaluated. However, we did not observe a correlation between the new stiffness method on flat hair strands and practical assessments in hair spray application. We postulate that different polymer/hair composites are responsible for these discrepancies. Hairs on model heads for half-side testing are spot-welded after spray application, while hairs are seam-welded in the stiffness test after alignment of single hair fibers. This alignment is necessary to achieve reproducible results.
Velocity measurements in jets with application to noise source modeling
Morris, Philip J.; Zaman, K. B. M. Q.
2010-02-01
This paper describes an experimental investigation of the statistical properties of turbulent velocity fluctuations in an axisymmetric jet. The focus is on those properties that are relevant to the prediction of noise. Measurements are performed using two single hot-wire anemometers as well as a two-component anemometer. Two-point cross correlations of the axial velocity fluctuations and of the fluctuations in the square of the axial velocity fluctuations are presented. Several reference locations in the jet are used including points on the jet lip and centerline. The scales of the turbulence and the convection velocity are determined, both in an overall sense as well as a function of frequency. The relationship between the second and fourth order correlations is developed and compared with the experimental data. The implications of the use of dimensional as well as non-dimensional correlations are considered. Finally, a comparison is made between the length scales deduced from the flow measurements and a RANS CFD calculation.
Fu, Liping; Erben, Thomas; Heymans, Catherine; Hildebrandt, Hendrik; Hoekstra, Henk; Kitching, Thomas D; Mellier, Yannick; Miller, Lance; Semboloni, Elisabetta; Simon, Patrick; Van Waerbeke, Ludovic; Coupon, Jean; Harnois-Déraps, Joachim; Hudson, Michael J; Kuijken, Konrad; Rowe, Barnaby; Schrabback, Tim; Vafaei, Sanaz; Velander, Malin
2014-01-01
Higher-order, non-Gaussian aspects of the large-scale structure carry valuable information on structure formation and cosmology, which is complementary to second-order statistics. In this work we measure second- and third-order weak-lensing aperture-mass moments from CFHTLenS and combine those with CMB anisotropy probes. The third moment is measured with a significance of $2\\sigma$. The combined constraint on $\\Sigma_8 = \\sigma_8 (\\Omega_{\\rm m}/0.27)^\\alpha$ is improved by 10%, in comparison to the second-order only, and the allowed ranges for $\\Omega_{\\rm m}$ and $\\sigma_8$ are substantially reduced. Including general triangles of the lensing bispectrum yields tighter constraints compared to probing mainly equilateral triangles. Second- and third-order CFHTLenS lensing measurements improve Planck CMB constraints on $\\Omega_{\\rm m}$ and $\\sigma_8$ by 26% for flat $\\Lambda$CDM. For a model with free curvature, the joint CFHTLenS-Planck result is $\\Omega_{\\rm m} = 0.28 \\pm 0.02$ (68% confidence), which is an i...
Inverted catenoid as a fluid membrane with two points pulled together.
Castro-Villarreal, Pavel; Guven, Jemal
2007-07-01
Under inversion in any (interior) point, a catenoid transforms into a deflated compact geometry which touches at two points (its poles). The catenoid is a minimal surface and, as such, is an equilibrium shape of a symmetric fluid membrane. The conformal symmetry of the Hamiltonian implies that inverted minimal surfaces are also equilibrium shapes. However, they will exhibit curvature singularities at their poles. Such singularities are the geometrical signature of the external forces required to pull the poles together. These forces will set up stresses in the inverted shapes. Tuning the force corresponds geometrically to the translation of the point of inversion. For any fixed surface area, there will be a maximum force. The associated shape is a symmetric discocyte. Lowering the external force will induce a transition from the discocyte to a cup-shaped stomatocyte.
Roul, Pradip
2016-06-01
This paper presents a new iterative technique for solving nonlinear singular two-point boundary value problems with Neumann and Robin boundary conditions. The method is based on the homotopy perturbation method and the integral equation formalism in which a recursive scheme is established for the components of the approximate series solution. This method does not involve solution of a sequence of nonlinear algebraic or transcendental equations for the unknown coefficients as in some other iterative techniques developed for singular boundary value problems. The convergence result for the proposed method is established in the paper. The method is illustrated by four numerical examples, two of which have physical significance: The first problem is an application of the reaction-diffusion process in a porous spherical catalyst and the second problem arises in the study of steady-state oxygen-diffusion in a spherical cell with Michaelis-Menten uptake kinetics.
A High Performance Spread Spectrum Clock Generator Using Two-Point Modulation Scheme
Kao, Yao-Huang; Hsieh, Yi-Bin
A new spread spectrum clock generator (SSCG) using two-point delta-sigma modulation is presented in this paper. Not only the divider is varied, but also the voltage controlled oscillator is modulated. This technique can enhance the modulation bandwidth so that the effect of EMI suppression is improved with lower order ΣΔ modulator and can simultaneously optimize the jitter and the modulation profile. In addition, the method of two-path is applied to the loop filter to reduce the capacitance value such that the total integration can be achieved. The proposed SSCG has been fabricated in a 0.35μm CMOS process. The clock of 400MHz with center spread ratios of 1.25% and 2.5% are verified. The peak EMI reduction is 19.73dB for the case of 2.5%. The size of chip area is 0.90×0.89mm2.
Two-point gauge invariant quark Green's functions with polygonal phase factor lines
Sazdjian, H
2013-01-01
Polygonal lines are used for the paths of the gluon field phase factors entering in the definition of gauge invariant quark Green's functions. This allows classification of the Green's functions according to the number of segments the polygonal lines contain. Functional relations are established between Green's functions with polygonal lines with different numbers of segments. An integrodifferential equation is obtained for the quark two-point Green's function with a path along a single straight line segment where the kernels are represented by a series of Wilson loop averages along polygonal contours. The equation is exactly and analytically solved in the case of two-dimensional QCD in the large-$N_c$ limit. The solution displays generation of an infinite number of dynamical quark masses accompanied with branch point singularities that are stronger than simple poles. An approximation scheme, based on the counting of functional derivatives of Wilson loops, is proposed for the resolution of the equation in fou...
Applying inversion to construct planar, rational spirals that satisfy two-point G(2) Hermite data
Kurnosenko, A
2010-01-01
A method of two-point G(2) Hermite interpolation with spirals is proposed. To construct a sought for curve, the inversion is applied to an arc of some other spiral. To illustrate the method, inversions of parabola are considered in detail. The resulting curve is 4th degree rational. The method allows the matching of a wide range of boundary conditions, including those which require an inflection. Although not all G(2) Hermite data can be matched with a spiral generated from a parabolic arc, introducing one intermediate G(2) data solves the problem. Expanding the method by involving other spirals arcs is also discussed. (C) 2009 Elsevier B.V. All rights reserved.
Two-point resistance of a resistor network embedded on a globe.
Tan, Zhi-Zhong; Essam, J W; Wu, F Y
2014-07-01
We consider the problem of two-point resistance in an (m-1) × n resistor network embedded on a globe, a geometry topologically equivalent to an m × n cobweb with its boundary collapsed into one single point. We deduce a concise formula for the resistance between any two nodes on the globe using a method of direct summation pioneered by one of us [Z.-Z. Tan, L. Zhou, and J. H. Yang, J. Phys. A: Math. Theor. 46, 195202 (2013)]. This method is contrasted with the Laplacian matrix approach formulated also by one of us [F. Y. Wu, J. Phys. A: Math. Gen. 37, 6653 (2004)], which is difficult to apply to the geometry of a globe. Our analysis gives the result in the form of a single summation.
Waheed, Umair bin
2013-09-01
On several simple models of isotropic and anisotropic media, we have studied the accuracy of the two-point paraxial traveltime formula designed for the approximate calculation of the traveltime between points S\\' and R\\' located in the vicinity of points S and R on a reference ray. The reference ray may be situated in a 3D inhomogeneous isotropic or anisotropic medium with or without smooth curved interfaces. The twopoint paraxial traveltime formula has the form of the Taylor expansion of the two-point traveltime with respect to spatial Cartesian coordinates up to quadratic terms at points S and R on the reference ray. The constant term and the coefficients of the linear and quadratic terms are determined from quantities obtained from ray tracing and linear dynamic ray tracing along the reference ray. The use of linear dynamic ray tracing allows the evaluation of the quadratic terms in arbitrarily inhomogeneous media and, as shown by examples, it extends the region of accurate results around the reference ray between S and R (and even outside this interval) obtained with the linear terms only. Although the formula may be used for very general 3D models, we concentrated on simple 2D models of smoothly inhomogeneous isotropic and anisotropic (~8% and ~20% anisotropy) media only. On tests, in which we estimated twopoint traveltimes between a shifted source and a system of shifted receivers, we found that the formula may yield more accurate results than the numerical solution of an eikonal-based differential equation. The tests also indicated that the accuracy of the formula depends primarily on the length and the curvature of the reference ray and only weakly depends on anisotropy. The greater is the curvature of the reference ray, the narrower its vicinity, in which the formula yields accurate results.
Csapo, Robert; Malis, Vadim; Sinha, Usha; Sinha, Shantanu
2015-09-01
The aim of this study was to assess the correlation between contraction-associated muscle kinematics as measured by velocity-encoded phase-contrast (VE-PC) magnetic resonance imaging (MRI) and activity recorded via electromyography (EMG), and to construct a detailed three-dimensional (3-D) map of the contractile behavior of the triceps surae complex from the MRI data. Ten axial-plane VE-PC MRI slices of the triceps surae and EMG data were acquired during submaximal isometric contractions in 10 subjects. MRI images were analyzed to yield the degree of contraction-associated muscle displacement on a voxel-by-voxel basis and determine the heterogeneity of muscle movement within and between slices. Correlational analyses were performed to determine the agreement between EMG data and displacements. Pearson's coefficients demonstrated good agreement (0.84 muscle revealed significant heterogeneity in displacement values both in-plane and along the cranio-caudal axis, with highest values in the mid-muscle regions. By contrast, no significant differences between muscle regions were found in the soleus muscle. Substantial differences among displacements were also observed within slices, with those in static areas being only 17-39% (maximum) of those in the most mobile muscle regions. The good agreement between EMG data and displacements suggests that VE-PC MRI may be used as a noninvasive, high-resolution technique for quantifying and modeling muscle activity over the entire 3-D volume of muscle groups. Application to the triceps surae complex revealed substantial heterogeneity of contraction-associated muscle motion both within slices and between different cranio-caudal positions.
Two-point L1 shortest path queries in the plane
Directory of Open Access Journals (Sweden)
Danny Z. Chen
2016-12-01
Full Text Available Let $P$ be a set of $h$ pairwise-disjoint polygonal obstacles with a total of $n$ vertices in the plane. We consider the problem of building a data structure that can quickly compute an $L_1$ shortest obstacle-avoiding path between any two query points $s$ and $t$. Previously, a data structure of size $O(n^2\\log n$ was constructed in $O(n^2\\log^2 n$ time that answers each two-point query in $O(\\log^2 n+k$ time, i.e., the shortest path length is reported in $O(\\log^2 n$ time and an actual path is reported in additional $O(k$ time, where $k$ is the number of edges of the output path. In this paper, we build a new data structure of size $O(n+h^2 \\log h 4^{\\sqrt{\\log h}}$ in $O(n+h^2 \\log^{2}h 4^{\\sqrt{\\log h}}$ time that answers each query in $O(\\log n+k$ time. (In contrast, for the Euclidean version of this two-point query problem, the best known algorithm uses $O(n^{11}$ space to achieve an $O(\\log n+k$ query time. Further, we extend our techniques to the weighted rectilinear version in which the ``obstacles" of $P$ are rectilinear regions with ``weights" and allow $L_1$ paths to travel through them with weighted costs. Previously, a data structure of size $O(n^2\\log^2 n$ was built in $O(n^2\\log^2 n$ time that answers each query in $O(\\log^2 n+k$ time. Our new algorithm answers each query in $O(\\log n+k$ time with a data structure of size $O(n^2 \\log n 4^{\\sqrt{\\log n}}$ that is built in $O(n^2 \\log^2 n 4^{\\sqrt{\\log n}}$ time.
An Attempt to Derive the epsilon Equation from a Two-Point Closure
Canuto, V. M.; Cheng, Y.; Howard, A. M.
2010-01-01
The goal of this paper is to derive the equation for the turbulence dissipation rate epsilon for a shear-driven flow. In 1961, Davydov used a one-point closure model to derive the epsilon equation from first principles but the final result contained undetermined terms and thus lacked predictive power. Both in 1987 and in 2001, attempts were made to derive the epsilon equation from first principles using a two-point closure, but their methods relied on a phenomenological assumption. The standard practice has thus been to employ a heuristic form of the equation that contains three empirical ingredients: two constants, c(sub 1 epsilon), and c(sub 2 epsilon), and a diffusion term D(sub epsilon) In this work, a two-point closure is employed, yielding the following results: 1) the empirical constants get replaced by c(sub 1), c(sub 2), which are now functions of Kappa and epsilon; 2) c(sub 1) and c(sub 2) are not independent because a general relation between the two that are valid for any Kappa and epsilon are derived; 3) c(sub 1), c(sub 2) become constant with values close to the empirical values c(sub 1 epsilon), c(sub epsilon 2), (i.e., homogenous flows); and 4) the empirical form of the diffusion term D(sub epsilon) is no longer needed because it gets substituted by the Kappa-epsilon dependence of c(sub 1), c(sub 2), which plays the role of the diffusion, together with the diffusion of the turbulent kinetic energy D(sub Kappa), which now enters the new equation (i.e., inhomogeneous flows). Thus, the three empirical ingredients c(sub 1 epsilon), c(sub epsilon 2), D (sub epsilon)are replaced by a single function c(sub 1)(Kappa, epsilon ) or c(sub 2)(Kappa, epsilon ), plus a D(sub Kappa)term. Three tests of the new equation for epsilon are presented: one concerning channel flow and two concerning the shear-driven planetary boundary layer (PBL).
Heinisch, Philip; Auster, Hans-Ulrich; Richter, Ingo; Hercik, David; Jurado, Eric; Garmier, Romain; Güttler, Carsten; Glassmeier, Karl-Heinz
2016-08-01
As part of the European Space Agency's ROSETTA Mission the Lander PHILAE touched down on comet 67P/Churyumov-Gerasimenko on November 12, 2014. The magnetic field has been measured onboard the orbiter and the lander. The orbiter's tri-axial fluxgate magnetometer RPC-MAG is one of five sensors of the ROSETTA Plasma Consortium. The lander is also equipped with a tri-axial fluxgate magnetometer as part of the ROSETTA Lander Magnetometer and Plasma-Monitor package (ROMAP). This unique setup makes a two point measurement between the two spacecrafts in a relatively small distance of less than 50 km possible. Both magnetometers were switched on during the entire descent, the initial touchdown, the bouncing between the touchdowns and after the final touchdown. We describe a method for attitude determination by correlating magnetic low-frequency waves, which was tested under different conditions and finally used to reconstruct PHILAE's attitude during descent and after landing. In these cases the attitude could be determined with an accuracy of better than ± 5 °. These results were essential not only for PHILAE operations planning but also for the analysis of the obtained scientific data, because nominal sources for this information, like solar panel currents and camera pictures could not provide sufficient information due to the unexpected landing position.
Covariant and infrared-free graviton two-point function in de Sitter spacetime II
Pejhan, Hamed
2016-01-01
The solution to the linearized Einstein equation in de Sitter (dS) spacetime and the corresponding two-point function are explicitly written down in a gauge with two parameters `$a$' and `$b$'. The quantization procedure, independent of the choice of the coordinate system, is based on a rigorous group theoretical approach. Our result takes the form of a universal spin-two (transverse-traceless) sector and a gauge-dependent spin-zero (pure-trace) sector. Scalar equations are derived for the structure functions of each part. We show that the spin-two sector can be written as the resulting action of a second-order differential operator (the spin-two projector) on a massless minimally coupled scalar field (the spin-two structure function). The operator plays the role of a symmetric rank-$2$ polarization tensor and has a spacetime dependence. The calculated spin-two projector grows logarithmically with distance and also no dS-invariant solution for either structure functions exist. We show that the logarithmically...
Directory of Open Access Journals (Sweden)
Andrius Gaizauskas
2014-01-01
Full Text Available Indication has led ureteroscopy to be a worldwide technique, with the expected appearance of multiple types of complications. Severe complications are possible including ureteral perforation or avulsion. Ureteral avulsion has been described as an upper urinary tract injury related to the action of blunt trauma, especially from traffic accidents, being the mechanism of injury, the result of an acute deceleration/acceleration movement. With the advent of endourology, that term is also applied to the extensive degloving injury resulting from a mechanism of stretching of the ureter that eventually breaks at the most weakened site, or ureteral avulsion is referred to as a discontinuation of the full thickness of the ureter. The paper presents a case report and literature review of the two-point or “scabbard” avulsion. The loss of long segment of the upper ureter, when end-to-end anastomosis is not technically feasible, presents a challenge to the urological surgeon. In the era of small calibre ureteroscopes these complications, due to growing incidence of renal stones will become more and more actual. Our message to other urologists is to know such a complication, to know the ways of treatment, and to analyse ureteroscopic signs, when to stop or pay attention.
Exteroceptive aspects of nociception: insights from graphesthesia and two-point discrimination.
Mørch, Carsten Dahl; Andersen, Ole K; Quevedo, Alexandre S; Arendt-Nielsen, Lars; Coghill, Robert C
2010-10-01
The exteroceptive capabilities of the nociceptive system have long been thought to be considerably more limited than those of the tactile system. However, most investigations of spatio-temporal aspects of the nociceptive system have largely focused on intensity coding as consequence of spatial or temporal summation. Graphesthesia, the identification of numbers "written" on the skin, and assessment of the two-point discrimination thresholds were used to compare the exteroceptive capabilities of the tactile and nociceptive systems. Numbers were "written" on the forearm and the abdomen by tactile stimulation and by painful non-contact infrared laser heat stimulation. Subjects performed both graphesthesia tasks better than chance. The tactile graphesthesia tasks were performed with 89% (82-97%) correct responses on the forearm and 86% (79-94%) correct responses on the abdomen. Tactile graphesthesia tasks were significantly better than painful heat graphesthesia tasks that were performed with 31% (23-40%) and 44% (37-51%) correct responses on the forearm and abdomen, respectively. These findings demonstrate that the central nervous system is capable of assembling complex spatio-temporal patterns of nociceptive information from the body surface into unified mental objects with sufficient accuracy to enable behavioral discrimination.
Assessing Performance of Multipurpose Reservoir System Using Two-Point Linear Hedging Rule
Sasireka, K.; Neelakantan, T. R.
2017-07-01
Reservoir operation is the one of the important filed of water resource management. Innovative techniques in water resource management are focussed at optimizing the available water and in decreasing the environmental impact of water utilization on the natural environment. In the operation of multi reservoir system, efficient regulation of the release to satisfy the demand for various purpose like domestic, irrigation and hydropower can lead to increase the benefit from the reservoir as well as significantly reduces the damage due to floods. Hedging rule is one of the emerging techniques in reservoir operation, which reduce the severity of drought by accepting number of smaller shortages. The key objective of this paper is to maximize the minimum power production and improve the reliability of water supply for municipal and irrigation purpose by using hedging rule. In this paper, Type II two-point linear hedging rule is attempted to improve the operation of Bargi reservoir in the Narmada basin in India. The results obtained from simulation of hedging rule is compared with results from Standard Operating Policy, the result shows that the application of hedging rule significantly improved the reliability of water supply and reliability of irrigation release and firm power production.
Suttorp, L.G.; Schoolderman, A.J.
1987-01-01
The long-time behaviour of the velocity autocorrelation function that describes the motion of a tagged particle through a one-component plasma in a uniform magnetic field has been determined with the use of mode-coupling theory. The long-time tail depends on the orientation of the velocity with resp
Mooney, Walter D.; Ritsema, Jeroen; Hwang, Yong Keun
2012-01-01
A joint analysis of global seismicity and seismic tomography indicates that the seismic potential of continental intraplate regions is correlated with the seismic properties of the lithosphere. Archean and Early Proterozoic cratons with cold, stable continental lithospheric roots have fewer crustal earthquakes and a lower maximum earthquake catalog moment magnitude (Mcmax). The geographic distribution of thick lithospheric roots is inferred from the global seismic model S40RTS that displays shear-velocity perturbations (δVS) relative to the Preliminary Reference Earth Model (PREM). We compare δVS at a depth of 175 km with the locations and moment magnitudes (Mw) of intraplate earthquakes in the crust (Schulte and Mooney, 2005). Many intraplate earthquakes concentrate around the pronounced lateral gradients in lithospheric thickness that surround the cratons and few earthquakes occur within cratonic interiors. Globally, 27% of stable continental lithosphere is underlain by δVS≥3.0%, yet only 6.5% of crustal earthquakes with Mw>4.5 occur above these regions with thick lithosphere. No earthquakes in our catalog with Mw>6 have occurred above mantle lithosphere with δVS>3.5%, although such lithosphere comprises 19% of stable continental regions. Thus, for cratonic interiors with seismically determined thick lithosphere (1) there is a significant decrease in the number of crustal earthquakes, and (2) the maximum moment magnitude found in the earthquake catalog is Mcmax=6.0. We attribute these observations to higher lithospheric strength beneath cratonic interiors due to lower temperatures and dehydration in both the lower crust and the highly depleted lithospheric root.
Expected properties of the Two-Point Autocorrelation Function of the IGM
Ursino, Eugenio; Galeazzi, Massimiliano; Marulli, Federico; Moscardini, Lauro; Piro, Luigi; Roncarelli, Mauro; Takei, Yoh
2010-01-01
Recent analyses of the fluctuations of the soft Diffuse X-ray Background (DXB) have provided indirect detection of a component consistent with the elusive Warm Hot Intergalactic Medium (WHIM). In this work we use theoretical predictions obtained from hydrodynamical simulations to investigate the angular correlation properties of the WHIM in emission and assess the possibility of indirect detection with next-generation X-ray missions. Our results indicate that the angular correlation signal of the WHIM is generally weak but dominates the angular correlation function of the DXB outside virialized regions. Its indirect detection is possible but requires rather long exposure times [0.1-1] Ms, large (~1{\\deg} x1{\\deg}) fields of view and accurate subtraction of isotropic fore/background contributions, mostly contributed by Galactic emission. The angular correlation function of the WHIM is positive for {\\theta} < 5' and provides limited information on its spatial distribution. A satisfactory characterization of ...
Andrea, Malizia; Rossi, Riccardo; Gaudio, Pasquale
2017-08-01
Dust explosions are dangerous events that still today represent a risk to all the industries that produce and/or handle combustible dust like the agro-alimentary, pharmaceutical and energy ones. When a dust cloud is dispersed in an oxidant gas, like air, it may reach the explosive concentration range. A model to predict the dust critical conditions, that can cause explosions, is a key factor for safety of operators and the security of the plants. The key point to predict this dust resuspension is to measure the velocity vectors of dust under the accidental conditions. In order to achieve this goal the authors have developed an experimental facility, STARDUST-U, which allow to obtain different conditions of temperature and pressurization rates characteristic of accidents in confined environment. The authors have developed also optical methods and software to analyse different dust resuspension phenomena under different conditions in confined environment. In this paper, the author will present how they measure the dust velocity vectors in different experimental conditions (and for different type of dusts) and how they have related the dust characteristics and positions inside STARDUST-U with the resuspension degree and the velocity values.
Slepian, Zachary; Blazek, Jonathan A; Brownstein, Joel R; Chuang, Chia-Hsun; Gil-Marín, Héctor; Ho, Shirley; Kitaura, Francisco-Shu; McEwen, Joseph E; Percival, Will J; Ross, Ashley J; Rossi, Graziano; Seo, Hee-Jong; Slosar, Anže; Vargas-Magaña, Mariana
2016-01-01
We search for a galaxy clustering bias due to a modulation of galaxy number with the baryon-dark matter relative velocity resulting from recombination-era physics. We find no detected signal and place the constraint $b_v < 0.01$ on the relative velocity bias for the CMASS galaxies. This bias is an important potential systematic of Baryon Acoustic Oscillation (BAO) method measurements of the cosmic distance scale using the 2-point clustering. Our limit on the relative velocity bias indicates a systematic shift of no more than $0.3\\%$ rms in the distance scale inferred from the BAO feature in the BOSS 2-point clustering, well below the $1\\%$ statistical error of this measurement. This constraint is the most stringent currently available and has important implications for the ability of upcoming large-scale structure surveys such as DESI to self-protect against the relative velocity as a possible systematic.
Energy Technology Data Exchange (ETDEWEB)
Henninger, B.; Rauch, S.; Schocke, M.; Jaschke, W.; Kremser, C. [Medical University of Innsbruck, Department of Radiology, Innsbruck (Austria); Zoller, H. [Medical University of Innsbruck, Department of Internal Medicine, Innsbruck (Austria); Kannengiesser, S. [Siemens AG, Healthcare Sector, MR Applications Development, Erlangen (Germany); Zhong, X. [Siemens Healthcare, MR R and D Collaborations, Atlanta, GA (United States); Reiter, G. [Siemens AG, Healthcare Sector, MR R and D Collaborations, Graz (Austria)
2015-05-01
To evaluate the automated two-point Dixon screening sequence for the detection and estimated quantification of hepatic iron and fat compared with standard sequences as a reference. One hundred and two patients with suspected diffuse liver disease were included in this prospective study. The following MRI protocol was used: 3D-T1-weighted opposed- and in-phase gradient echo with two-point Dixon reconstruction and dual-ratio signal discrimination algorithm (''screening'' sequence); fat-saturated, multi-gradient-echo sequence with 12 echoes; gradient-echo T1 FLASH opposed- and in-phase. Bland-Altman plots were generated and correlation coefficients were calculated to compare the sequences. The screening sequence diagnosed fat in 33, iron in 35 and a combination of both in 4 patients. Correlation between R2* values of the screening sequence and the standard relaxometry was excellent (r = 0.988). A slightly lower correlation (r = 0.978) was found between the fat fraction of the screening sequence and the standard sequence. Bland-Altman revealed systematically lower R2* values obtained from the screening sequence and higher fat fraction values obtained with the standard sequence with a rather high variability in agreement. The screening sequence is a promising method with fast diagnosis of the predominant liver disease. It is capable of estimating the amount of hepatic fat and iron comparable to standard methods. (orig.)
Wu, S. M.; Hung, S. H.
2015-12-01
Earthquake-induced temporal changes in seismic velocity of the earth's crust have been demonstrated to be monitored effectively by the time-lapse shifts of coda waves recently. Velocity drop during the coseismic rupture has been explicitly observed in proximity to the epicenters of large earthquakes with different styles of faulting. The origin of such sudden perturbation in crustal properties is closely related to the damage and/or volumetric strain change influenced by seismic slip distribution. In this study, we apply a coda wave interferometry method to investigate potential velocity change in both space and time related to the moderate-sized (Mw6.3) 2010 Jiasian earthquake, which nucleated deeply in the crust (~23 km), ruptured and terminated around the depth of 10 km along a previously unidentified blind thrust fault near the lithotectonic boundary of the southern Taiwan orogenic belt. To decipher the surface and crustal response to this relatively deep rupture, we first measure relative time-lapse changes of coda between different short-term time frames spanning one year covering the pre- and post-seismic stages by using the Moving Window Cross Spectral Method. Rather than determining temporal velocity variations based on a long-term reference stack, we conduct a Bayesian least-squares inversion to obtain the optimal estimates by minimizing the inconsistency between the relative time-lapse shifts of individual short-term stacks. The results show the statistically significant velocity reduction immediately after the mainshock, which is most pronounced at the pairs with the interstation paths traversing through the hanging-wall block of the ruptured fault. The sensitivity of surface wave coda arrivals mainly in the periods of 3-5 s to shear wave speed perturbation is confined within the depth of 10 km, where the crust mostly experienced extensional strain changes induced by the slip distribution from the finite-fault model. Compared with coseismic slip
Two-point discrimination of the upper extremities of healthy Koreans in their 20’s
Koo, Ja-Pung; Kim, Soon-Hee; An, Ho-Jung; Moon, Ok-Gon; Choi, Jung-Hyun; Yun, Young-Dae; Park, Joo-Hyun; Min, Kyoung-Ok
2016-01-01
[Purpose] The present study attempted to measure two-point discrimination in the upper extremities of healthy Koreans in their 20’s. [Subjects and Methods] Using a three-point esthesiometer, we conducted an experiment with a group of 256 college students (128 male and 128 female), attending N University in Chonan, Republic of Korea. [Results] Females showed two-point discrimination at a shorter distance than males at the following points: (i) 5 cm above the elbow joint, the middle part, and 5 cm below the shoulder joint of the anterior upper arm; (ii) 5 cm above the elbow joint and 5 cm below the shoulder joint of the posterior upper arm; (iii) 5 cm above the front of the wrist joint of the forearm; 5 cm below the elbow joint, the palmar part of the distal interphalangeal joint of the thumb, the dorsal part of the distal interphalangeal joint of the middle and little fingers. It was also found that females showed greater two-point discrimination than males in distal regions rather than proximal regions. [Conclusion] The findings of this study will help establish normal values for two-point discrimination of upper extremities of young Koreans in their 20’s. PMID:27134375
Energy Technology Data Exchange (ETDEWEB)
Kong Dexing [Department of Mathematics, Zhejiang University, Hangzhou 310027 (China); Sun Qingyou, E-mail: qysun@cms.zju.edu.cn [Center of Mathematical Sciences, Zhejiang University, Hangzhou 310027 (China)
2011-04-01
All articles must In this paper we introduce some new concepts for second-order hyperbolic equations: two-point boundary value problem, global exact controllability and exact controllability. For several kinds of important linear and nonlinear wave equations arising from physics and geometry, we prove the existence of smooth solutions of the two-point boundary value problems and show the global exact controllability of these wave equations. In particular, we investigate the two-point boundary value problem for one-dimensional wave equation defined on a closed curve and prove the existence of smooth solution which implies the exact controllability of this kind of wave equation. Furthermore, based on this, we study the two-point boundary value problems for the wave equation defined on a strip with Dirichlet or Neumann boundary conditions and show that the equation still possesses the exact controllability in these cases. Finally, as an application, we introduce the hyperbolic curvature flow and obtain a result analogous to the well-known theorem of Gage and Hamilton for the curvature flow of plane curves.
Van der Hofstad, R.; Hara, T.; Slade, G.
2003-01-01
We consider spread-out models of self-avoiding walk, bond percolation, lattice trees and bond lattice animals on ${\\mathbb{Z}^d}$, having long finite-range connections, above their upper critical dimensions $d=4$ (self-avoiding walk), $d=6$ (percolation) and $d=8$ (trees and animals). The two-point
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
In this paper, we consider a two-point boundary value problem for a system of second order ordinary differential equations. Under some conditions, we show the existence of positive solution to the system of second order ordinary differential equa-tions.
Institute of Scientific and Technical Information of China (English)
王同科
2002-01-01
In this paper, a high accuracy finite volume element method is presented for two-point boundary value problem of second order ordinary differential equation, which differs fromthe high order generalized difference methods. It is proved that the method has optimal order er-ror estimate O(h3) in H1 norm. Finally, two examples show that the method is effective.
Directory of Open Access Journals (Sweden)
Mary Hokazono
Full Text Available CONTEXT AND OBJECTIVE: Transcranial Doppler (TCD detects stroke risk among children with sickle cell anemia (SCA. Our aim was to evaluate TCD findings in patients with different sickle cell disease (SCD genotypes and correlate the time-averaged maximum mean (TAMM velocity with hematological characteristics. DESIGN AND SETTING: Cross-sectional analytical study in the Pediatric Hematology sector, Universidade Federal de São Paulo. METHODS: 85 SCD patients of both sexes, aged 2-18 years, were evaluated, divided into: group I (62 patients with SCA/Sß0 thalassemia; and group II (23 patients with SC hemoglobinopathy/Sß+ thalassemia. TCD was performed and reviewed by a single investigator using Doppler ultrasonography with a 2 MHz transducer, in accordance with the Stroke Prevention Trial in Sickle Cell Anemia (STOP protocol. The hematological parameters evaluated were: hematocrit, hemoglobin, reticulocytes, leukocytes, platelets and fetal hemoglobin. Univariate analysis was performed and Pearson's coefficient was calculated for hematological parameters and TAMM velocities (P < 0.05. RESULTS: TAMM velocities were 137 ± 28 and 103 ± 19 cm/s in groups I and II, respectively, and correlated negatively with hematocrit and hemoglobin in group I. There was one abnormal result (1.6% and five conditional results (8.1% in group I. All results were normal in group II. Middle cerebral arteries were the only vessels affected. CONCLUSION: There was a low prevalence of abnormal Doppler results in patients with sickle-cell disease. Time-average maximum mean velocity was significantly different between the genotypes and correlated with hematological characteristics.
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Andrei V. Obukhovskiĭ
2003-05-01
Full Text Available We consider second-order differential inclusions on a Riemannian manifold with lower semicontinuous right-hand sides. Several existence theorems for solutions of two-point boundary value problem are proved to be interpreted as controllability of special mechanical systems with control on nonlinear configuration spaces. As an application, a statement of controllability under extreme values of controlling force is obtained.
Vriens, J P M; van der Glas, H W
2009-11-01
The threshold value of a sensory test provides a numerical measure of the sensory function. In order to decide whether a threshold value from an affected site indicates 'abnormal' sensory function, it can be compared with normal values from a healthy control population. The aim of this study was to extend current information on normal values for static light touch and static two-point discrimination for facial sites. Using simple hand-held devices, 95% upper limits of confidence intervals of threshold values were determined for facial sites other than those studied previously and for a large sample of 100 healthy subjects. The MacKinnon-Dellon Disk-Criminator and the Aesthesiometer were used to measure novel normal values of two-point discrimination. As threshold values for two-point discrimination from the Aesthesiometer were similar to those obtained using the Disk-Criminator, the use of the Aesthesiometer might not be indicated. Apart from the Pressure Specified Sensory Device (a device with pressure control), Semmes-Weinstein nylon monofilaments and the Disk-Criminator are useful devices for studying sensory function, in particular under clinical test conditions in which easy and fast application are advantageous.
Rigid internal fixation of zygoma fractures: A comparison of two-point and three-point fixation
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Parashar Atul
2007-01-01
Full Text Available Background: Displaced fractures of the zygomatic bone can result in significant functional and aesthetic sequelae. Therefore the treatment must achieve adequate and stable reduction at fracture sites so as to restore the complex multidimensional relationship of the zygoma to the surrounding craniofacial skeleton. Many experimental biophysical studies have compared stability of zygoma after one, two and three-point fixation with mini plates. We conducted a prospective clinical study comparing functional and aesthetic results of two-point and three-point fixation with mini plates in patients with fractures of zygoma. Materials and Methods: Twenty-two patients with isolated zygomatic fractures over a period of one year were randomly assigned into two-point and three-point fixation groups. Results of fixation were analyzed after completion of three months. This included clinical, radiological and photographic evaluation. Results: The three-point fixation group maintained better stability at fracture sites resulting in decreased incidence of dystopia and enophthalmos. This group also had better malar projection and malar height as measured radiologically, when compared with the two-point fixation group. Conclusion: We recommend three-point rigid fixation of fractured zygoma after accurate reduction so as to maintain adequate stabilization against masticatory forces during fracture healing phase.
Visual control of walking velocity.
François, Matthieu; Morice, Antoine H P; Bootsma, Reinoud J; Montagne, Gilles
2011-06-01
Even if optical correlates of self-motion velocity have already been identified, their contribution to the control of displacement velocity remains to be established. In this study, we used a virtual reality set-up coupled to a treadmill to test the role of both Global Optic Flow Rate (GOFR) and Edge Rate (ER) in the regulation of walking velocity. Participants were required to walk at a constant velocity, corresponding to their preferred walking velocity, while eye height and texture density were manipulated. This manipulation perturbed the natural relationship between the actual walking velocity and its optical specification by GOFR and ER, respectively. Results revealed that both these sources of information are indeed used by participants to control walking speed, as demonstrated by a slowing down of actual walking velocity when the optical specification of velocity by either GOFR or ER gives rise to an overestimation of actual velocity, and vice versa. Gait analyses showed that these walking velocity adjustments result from simultaneous adaptations in both step length and step duration. The role of visual information in the control of self-motion velocity is discussed in relation with other factors.
Energy Technology Data Exchange (ETDEWEB)
Kotte, R.; Kaempfer, B.; Moesner, J.; Neubert, W.; Wohlfarth, D.; Alard, J.P.; Amouroux, V.; Basrak, Z.; Bastid, N.; Belayev, I.M.; Berger, L.; Blaich, T.; Boussange, S.; Buta, A.; Caplar, R.; Cerruti, C.; Cindro, N.; Coffin, J.P.; Dona, R.; Dupieux, P.; Eroe, J.; Fan, Z.G.; Fintz, P.; Fodor, Z.; Fraysse, L.; Freifelder, R.; Frolov, S.; Gobbi, A.; Grigorian, Y.; Guillaume, G.; Herrmann, N.; Hildenbrand, K.D.; Hoelbling, S.; Houari, O.; Ibnouzahir, M.; Jeong, S.C.; Jundt, F.; Kecskemeti, J.; Koncz, P.; Korchagin, Y.; Kraemer, M.; Kuhn, C.; Legrand, I.; Lebedev, A.; Manko, V.; Matulewicz, T.; Mgebrishvili, G.; Moisa, D.; Montarou, G.; Montbel, I.; Pelte, D.; Petrovici, M.; Pras, P.; Rami, F.; Ramillien, V.; Reisdorf, W.; Sadchikov, A.; Schuell, D.; Seres, Z.; Sikora, B.; Simion, V.; Smolyankin, S.; Sodan, U.; Teh, K.; Tezkratt, R.; Trzaska, M.; Vasiliev, M.A.; Wagner, P.; Wessels, J.P.; Wienold, T.; Wilhelmi, Z.; Zhilin, A.V. [Forschungszentrum Rossendorf, PF 510119, D-01314 Dresden (Germany)]|[Institut fuer Theoretische Physik, Technische Universitaet Dresden, Dresden (Germany)]|[Institute for Physics and Nuclear Engineering, Bucharest (Romania)]|[Central Research Insitute for Physics, Budapest (Hungary)]|[Laboratoire de Physique Corpusculaire, Universite Blaise Pascal, Clermont-Fd. (France)]|[Gesellschaft fuer Schwerionenforschung, Darmstadt (Germany)]|[Physikalisches Institut der Universitaet Heidelberg, Heidelberg (Germany)]|[Universitaet Mainz, Mainz (Germany)]|[Institute for Experimetnal Theoretical Physics, Moscow (Russian Federation)]|[Kurchatov Institute for Atomic Energy, Moscow (Russian Federation)]|[Centre de Recherches Nucleaires, Universite Louis Pasteur, Strasbourg (France)]|[Institute of Experimental Physics, Warsaw University, Warsaw (Poland)]|[Rudjer Boskovic Institute Zagreb, Zagreb (Croatia)]|[Istituto Nazionale di Fisica Nucleare, Legnaro (Italy); (FOPI Collaboration)
1995-05-01
Velocity correlations of intermediate mass fragments (IMF), produced in collisions of Au+Au at 100, 150, 250, and 400{ital A} MeV beam energy, are extracted from measurements with the 4{pi} detector system (FOPI) in construction stage I at Schwerionen-Synchrotron (SIS) at the Gesellschaft fuer Schwerionenforschung (GSI) in Darmstadt. The IMF correlation functions of peripheral and semicentral events are found to be strongly affected by the collective sideward motion of nuclear matter. The sideflow causes an enhancement of correlations at small relative velocities. This enhancement results from the mixing of differently azimuthally oriented events; it vanishes if the events are rotated into a unique reaction plane. Selecting violent central collisions, the comparison of the data with a Coulomb dominated final-state interaction model points to a radius of the expanding and multifragmenting source of {ital R}{sub {ital s}}{congruent}13 fm for 100{ital A} MeV which appears shrinking by 20% when increasing the projectile energy to 400 MeV per nucleon. The deduced source radii are found to depend on the radial explosion energy used in the model. The inclusion of such a collective expansion is necessary for a reasonable description of the experimental single-particle spectra of the IMF. The unique Coulomb suppression of small relative IMF velocities, found for the given beam energy range, is attributed to rather constant averaged next-neighbor distances {l_angle}{ital d}{sub IMF}{r_angle}=8.6{plus_minus}0.2 fm of the IMF charge centers within the source at breakup time.
Institute of Scientific and Technical Information of China (English)
顾婷; 姜博仁; 任荣亮; 陆颖理; 乔洁
2013-01-01
Objective To investigate the correlation between body composition and nerve conduction velocity in patients with type 2 diabetes mellitus.Methods One hundred and five patients with type 2 diabetes mellitus were enrolled,body composition related parameters including body mass index,body fat percent,body muscle percent and body water percent were measured by body composition analyzer,nerve conduction velocity related parameters including motor nerve conduction velocity,distal motor latency,amplitude of compound muscle action potential,sensory nerve conduction velocity,latency and amplitude of sensory nerve action potential were determined,and the correlation between body composition and nerve conduction velocity was explored.Results Body fat percent was positively correlated with nerve conduction velocity of motor-sensory ulnar nerve and motor peroneal nerve,and negatively correlated with distal latency of sensory ulnar nerve,sensory superficial peroneal nerve,motor peroneal nerve and motor amplitude of peroneal nerve.Body muscle percent was positively correlated with distal latency of sensory ulnar nerve,sensory superficial peroneal nerve,motor peroneal nerve and motor amplitude of peroneal nerve,and negatively correlated with nerve conduction velocity of motor-sensory ulnar nerve and motor peroneal nerve.Body water percent was positively correlated with distal latency of sensory ulnar nerve and sensory superficial peroneal nerve,and negatively correlated with nerve conduction velocity of sensory ulnar nerve.Body mass index and waist circumference were negatively correlated with sensory amplitude of median nerve and motor amplitude of tibial nerve.Conclusion Body mass index,waist circumference,body fat percent,body muscle percent and body water percent may be important influencing factors of nerve conduction velocity.%目的 分析2型糖尿病患者人体成分与神经传导速度的相关性.方法 选取105例2型糖尿病患者作为研究对象,使用身体
Energy Technology Data Exchange (ETDEWEB)
Kaempfer, B. (Research Center Rossendorf, Dresden (Germany). Inst. of Nuclear and Hadron Physics); Kotte, R. (Research Center Rossendorf, Dresden (Germany). Inst. of Nuclear and Hadron Physics); Moesner, J. (Research Center Rossendorf, Dresden (Germany). Inst. of Nuclear and Hadron Physics); Neubert, W. (Research Center Rossendorf, Dresden (Germany). Inst. of Nuclear and Hadron Physics); Wohlfarth, D. (Research Center Rossendorf, Dresden (Germany). Inst. of Nuclear and Hadron Physics)
1994-01-01
Velocity correlations of intermediate mass fragments (IMFs) with Z[>=]3, produced in central and semi-central collisions of Au+Au at 100, 150, 250 and 400 A.MeV beam energy, are extracted from measurements with the FOPI (phase I) detector system at SIS in GSI Darmstadt. The comparison of the data with a Coulomb dominated final-state interaction model points to time scale of [tau][approx]25 fm/c or less for emitting IMFs from a radially expanding and fast-multifragmenting source with radius R[approx]14 fm. (orig.)
Directory of Open Access Journals (Sweden)
Alfredo Tibúrcio Nunes Pires
2012-09-01
Full Text Available Introduction: Fiber-reinforced composite posts (FRC posts have been used for tooth reinforcement after endodontic treatment. The mechanical characteristics of FRC posts can influence the clinical prognostic. Objective: The aim of this study was to evaluate the flexural strength and fracture resistance of commercially available FRC posts Material and methods: Fourteen human single-rooted premolars with completely formed apices were selected and received endodontic treatment. The specimens were divided into two groups related to the post system: i Group A – cylindrical-conical fiber-reinforced post (White post DC, FGM, and ii group B – conical fiber-reinforced post (EXACTO, Angelus. The fracture resistance was evaluated and two point bending tests were carried out. The glass fiber characteristics and the tag penetration of the luting material into the radicular dentin structure were evaluated through scanning electronic microscopy in an illustrative way. One-way ANOVA and Tukey’s HSD test (α = 0.05 were applied. Results: The values obtained for fracture resistance and two point bending test were, respectively, 399.29 N and 109.5 N for group A, and 386.25 N and 119.5 N for group B. No significant differences in strength values among the groups were found. Conclusion: There were no significant statistical differences between the two post groups regarding to fracture strength and two point bending strength. It can be concluded that the posts selected for this study performed satisfactorily in terms of mechanical properties so that they can be used for tooth reinforcement after endodontic treatment.
Directory of Open Access Journals (Sweden)
Rana Majeed
2012-04-01
Full Text Available Abstract Background The zygoma plays an important role in the facial contour for both cosmetic and functional reasons; therefore zygomatic bone injuries should be properly diagnosed and adequately treated. Comparison of various surgical approaches and their complications can only be done objectively using outcome measurements which in turn require protocol management and long-term follow up. The preference for open reduction and internal fixation of zygomatic fractures at three points has continued to grow in response to observations of inadequate results from two point and one point fixation techniques. The objectives of this study were to compare the efficacy of zygomatic bone after treatment with ORIF using 2 point fixation and ORIF using 3 point fixation and compare the outcome of two procedures. Methods 100 patients were randomly divided equally into two groups. In group A, 50 patients were treated by ORIF using two point fixation by miniplates and in group B, 50 patients were treated by ORIF using three point fixation by miniplates. They were evaluated for their complications during and after surgery with their advantages and disadvantages and the difference between the two groups was observed. Results A total of 100 fractures were sustained. We found that postoperative complication like decreased malar height and vertical dystopia was more common in those patients who were treated by two point fixation than those who were treated with three point fixation. Conclusions Based on this study open reduction and internal fixation using three point fixation by miniplates is the best available method for the treatment zygomatic bone fractures.
Explicit Proof of Equivalence of Two-Point Functions in the Two Formalisms of Thermal Field Theory
Institute of Scientific and Technical Information of China (English)
ZHOU Bang-Rong
2002-01-01
We give an explicit proof of equivalence of the two-point function to one-loop order in the two formalisms of thermal λ3 theory based on the expressions in the real-time formalism and indicate that the key point of completing the proof is to separate carefully the imaginary part of the zero-temperature loop integralfrom relevant expressions and this fact will certainly be very useful for examination of the equivalent problem of two formalisms of thermal field theory in other theories, including the one of the propagators for scalar bound states in an NJL model.
Antar, B. N.
1976-01-01
A numerical technique is presented for locating the eigenvalues of two point linear differential eigenvalue problems. The technique is designed to search for complex eigenvalues belonging to complex operators. With this method, any domain of the complex eigenvalue plane could be scanned and the eigenvalues within it, if any, located. For an application of the method, the eigenvalues of the Orr-Sommerfeld equation of the plane Poiseuille flow are determined within a specified portion of the c-plane. The eigenvalues for alpha = 1 and R = 10,000 are tabulated and compared for accuracy with existing solutions.
Institute of Scientific and Technical Information of China (English)
Cheng Xiaoliang; Ying Weiting
2005-01-01
In this paper, we discuss the existence of solution of a nonlinear two-point boundary value problem with a positive parameter Q arising in the study of surfacetension-induced flows of a liquid metal or semiconductor. By applying the Schauder's fixed-point theorem, we prove that the problem admits a solution for 0 ≤ Q ≤ 14.306.It improves the result of 0 ≤ Q ＜ 1 in [2] and 0 ≤ Q ≤ 13.213 in [3].
Institute of Scientific and Technical Information of China (English)
MALLICK Mahendra; LA SCALA Barbara
2008-01-01
We consider the problem of initializing the tracking filter of a target moving with nearly constant velocity when positiononly (1D, 2D, or 3D) measurements are available. It is known that the Kalman filter is optimal for such a problem, provided it is correctly initialized. We compare a single-point and the well-known two-point difference track initialization algorithms. We analytically show that if the process noise approaches zero and the maximum speed of a target used to initialize the velocity variance approaches infinity, then the single-point algorithm reduces to the two-point difference algorithm. We present numerical results that show that the single-point algorithm performs consistently better than the two-point difference algorithm in the mean square error sense. We also present analytical results that support the conjecture that this is true in general.
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Priscila G. Franco
2015-08-01
Full Text Available Background: Changes in the proprioceptive system are associated with aging. Proprioception is important to maintaining and/or recovering balance and to reducing the risk of falls.Objective:To compare the performance of young and active elderly adults in three proprioceptive tests.Method:Twenty-one active elderly participants (66.9±5.5 years and 21 healthy young participants (24.6±3.9 years were evaluated in the following tests: perception of position of the ankle and hip joints, perceived force level of the ankle joint, and two-point discrimination of the sole of the foot.Results:No differences (p>0.05 were found between groups for the joint position and perceived force level. On the other hand, the elderly participants showed lower sensitivity in the two-point discrimination (higher threshold when compared to the young participants (p < 0.01.Conclusion:Except for the cutaneous plantar sensitivity, the active elderly participants had maintained proprioception. Their physical activity status may explain similarities between groups for the joint position sense and perceived force level, however it may not be sufficient to prevent sensory degeneration with aging.
Exact two-point resistance, and the simple random walk on the complete graph minus N edges
Energy Technology Data Exchange (ETDEWEB)
Chair, Noureddine, E-mail: n.chair@ju.edu.jo
2012-12-15
An analytical approach is developed to obtain the exact expressions for the two-point resistance and the total effective resistance of the complete graph minus N edges of the opposite vertices. These expressions are written in terms of certain numbers that we introduce, which we call the Bejaia and the Pisa numbers; these numbers are the natural generalizations of the bisected Fibonacci and Lucas numbers. The correspondence between random walks and the resistor networks is then used to obtain the exact expressions for the first passage and mean first passage times on this graph. - Highlights: Black-Right-Pointing-Pointer We obtain exact formulas for the two-point resistance of the complete graph minus N edges. Black-Right-Pointing-Pointer We obtain also the total effective resistance of this graph. Black-Right-Pointing-Pointer We modified Schwatt's formula on trigonometrical power sum to suit our computations. Black-Right-Pointing-Pointer We introduced the generalized bisected Fibonacci and Lucas numbers: the Bejaia and the Pisa numbers. Black-Right-Pointing-Pointer The first passage and mean first passage times of the random walks have exact expressions.
The covariant and infrared-free graviton two-point function in de Sitter space-time
Pejhan, Hamed
2015-01-01
In this paper, the two-point function of linearized gravitons on de Sitter (dS) space is presented. Technically, respecting the dS ambient space notation, the field equation is given by the coordinate-independent Casimir operators of the de Sitter group. Analogous to the quantization of the electromagnetic field in Minkowski space, the field equation admits gauge solutions. The notation allows to exhibit the formalism of Gupta-Bleuler triplets for the present field in exactly the same manner as it occurs for the electromagnetic field. In this regard, centering on the traceless part, the field solution is written as a product of a generalized polarization tensor and a minimally coupled massless scalar field. Then, admitting a de Sitter-invariant vacuum through the so-called "Krein Space Quantization", the de Sitter fully covariant two-point function is calculated. This function is interestingly free of pathological large distance behavior (infrared divergence). Moreover, the pure-trace part (conformal sector) ...
P-wave crustal tomography of Greece with use of an accurate two-point ray tracer
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G. N. Stavrakakis
1997-06-01
Full Text Available The three-dimensional velocity structure of the crust in the Aegean sea and the surrounding regions (34.0º-42.OºN, 19.0ºE-29.0ºE is investigated by inversion of about 10000 residuals of arrival times of P-wave from local events. The resulting velocity structure shows strong horizontal variations due to the complicated crustal structure and the variations of crustal thickness. The northern part of the region generally shows high velocities. In the inner part of the volcanic arc (Southern Aegean area, relatively low velocities are observed, suggesting a large-scale absorption of seismic energy as confirmed by the low seismicity of the region. A low velocity zone was observed along the subduction zone of the region, up to a depth of 4 km. The existence of such a zone could be due to granitic or other intrusions in the crust during the uplift of the region during Alpidic orogenesis.
Directory of Open Access Journals (Sweden)
Randhir Singh
2012-01-01
Full Text Available We propose two new modified recursive schemes for solving a class of doubly singular two-point boundary value problems. These schemes are based on Adomian decomposition method (ADM and new proposed integral operators. We use all the boundary conditions to derive an integral equation before establishing the recursive schemes for the solution components. Thus we develop recursive schemes without any undetermined coefficients while computing successive solution components, whereas several previous recursive schemes have done so. This modification also avoids solving a sequence of nonlinear algebraic or transcendental equations for the undetermined coefficients with multiple roots, which is required to complete calculation of the solution by several earlier modified recursion schemes using the ADM. The approximate solution is computed in the form of series with easily calculable components. The effectiveness of the proposed approach is tested by considering four examples and results are compared with previous known results.
Kaneko, Atsushi; Asai, Noriyoshi; Kanda, Tadashi
2005-01-01
The purpose of the present study was to determine the effect of age on digital pressure perception as measured by two-point discrimination (2PD) testing. The subjects were 177 normal volunteers ranging in age from 20 to 79 years. Perceptible pressure of static and moving 2PD was measured on the index finger and little finger, using the Pressure-specifying Sensory Device. The threshold of pressure perception increased significantly with advancing age in both static and moving 2PD tests. There was a marked increase in subjects older than 60 years. Pressure perception was significantly higher for static 2PD than for moving 2PD in subjects 70-79 years of age. The threshold of pressure perception for static and moving 2PD gradually increased with advancing age, and was markedly elevated in subjects older than 60 years.
Transforming activity of the c-Ha-ras oncogene having two point mutations in codons 12 and 61.
Sekiya, T; Prassolov, V S; Fushimi, M; Nishimura, S
1985-09-01
A recombinant plasmid carrying the human c-Ha-ras gene with two point mutations in codons 12 and 61 was constructed and its transforming activity on mouse NIH 3T3 cells was compared with those of genes with a single mutation in either codon 12 or 61. Quantitative analyses revealed that the gene with two mutations had essentially the same transforming activity as the genes with single mutations. These results indicate that a single mutation of the c-Ha-ras gene in either codon 12 or 61 is sufficient to activate the gene and that neither of the two mutation sites involved in activation of the gene needs to be intact for transforming activity.
Lucewicz, A; Fisher, K; Henry, A; Welsh, A W
2016-02-01
Twin anemia-polycythemia sequence (TAPS) is recognized increasingly antenatally by the demonstration of an anemic twin and a polycythemic cotwin using the middle cerebral artery peak systolic velocity (MCA-PSV). While the MCA-PSV has been shown to correlate well with anemia in singleton fetuses, the evidence to support its use to diagnose fetal polycythemia appears to be less clear-cut. We aimed to evaluate fetal, neonatal and adult literature used to support the use of MCA-PSV for the diagnosis of polycythemia. Comprehensive literature searches were performed for ultrasound evidence of polycythemia in the human fetus, neonate and adult using key search terms. Only manuscripts in the English language with an abstract were considered for the review, performed in June 2014. Fifteen manuscripts were found for the human fetus, including 38 cases of TAPS. Nine of these defined fetal polycythemia as MCA-PSV < 0.8 multiples of the median (MoM), five used < 1.0 MoM and one used 0.8-1.0 MoM. Only two studies, involving a total of 15 cases, proposed a diagnostic level, acknowledging false-positive and -negative cases, though neither reported sensitivities or specificities. Six neonatal studies (96 neonates) demonstrated evidence of decreased cerebral velocities in polycythemia and a consequent increase with hemodilution. In the adult, five studies (57 polycythemic adults) demonstrated increased flow or velocity with hemodilution. Neither neonatal nor adult studies conclusively defined levels for screening for polycythemia. Despite widespread adoption of a cut-off of < 0.8 MoM in the published literature for the polycythemic fetus in TAPS, this is based upon minimal evidence, with unknown sensitivity and specificity. We recommend caution in excluding TAPS based purely upon the absence of a reduced MCA-PSV.
Velocity kinematic relations in a turbulent flow past a grid
Liberzon, Alex; Gurka, Roi; Kopp, Gregory; Sarathi, Partha; Tsinober, Arkady
2009-11-01
We present velocity kinematic relations, involving average and difference of the longitudinal velocity component of the two points at distance r: u+= u(x+r) + u(x) and u-= u(x+r)-u(x), obtained using PIV measurements in a turbulent flow of water past a grid. The present study follows recent numerical and experimental studies, that demonstrated analytical and empirical evidence of the relations, their validity and it emphasizes the physical meaning of the relations. The relations that contain both the large (u+) and small (u-) scale quantities emphasize the non-local aspects of turbulent flows. For example, the pure kinematic relation of Hosokawa in conjunction with the the Kolmogorov 4/5 law leading to the = r/30 shows that the that the large and small scale quantities are correlated contrary to what is suggested by the commonly used sweeping decorrelation hypothesis. Some relations are purely kinematic and some are dynamic, i.e. involving , like the Kolmogorov 4/5 law. The most important aspect is that pure kinematic relations that emphasize the non-local effects, become dynamically significant. Furthermore, we suggest that many of these relations could be used for validation of experimental results.
Energy Technology Data Exchange (ETDEWEB)
Contreras Lopez, Enrique [Instituto de Investigaciones Electricas, Cuernavaca (Mexico)
1995-12-31
Departing from the analysis of a data base on the velocities of the compression waves (V{sub p}) and the transverse waves (V{sub s}) in a group of 97 specimens of sedimentary, igneous and metamorphic rocks, the existence of four types of empirical correlation very well entailed between the dynamic elastic constants and the velocities V{sub p} and V{sub s}. These correlation allow the estimation with a very close approximation the elastic dynamic constants without the need of having available of the complete set of data (V{sub p}, V{sub s} and total density) that is normally required for its determination. The identified correlation is mathematically expressed by means of adjustment equations that reproduce in all of the cases the experimental values with a standard error of estimation within 10%, for the universe of rocks studied and with much less error for different specific lithological groups. The application methodologies of the correlation found for different cases of practical interest, are described. [Espanol] A partir del analisis de una base de datos experimentales sobre la velocidad de las ondas compresionales (V{sub p}) y de las ondas transversales (V{sub s}) de un conjunto de 97 especimenes de rocas sedimentarias, igneas y metamorficas, se identifica la existencia de cuatro tipos de correlaciones empiricas muy bien comportadas entre las constantes elasticas dinamicas y las velocidades V{sub p} y V{sub s}. Estas correlaciones permiten estimar con muy buena aproximacion las constantes elasticas dinamicas de las rocas sin tener que disponer del conjunto completo de datos (V{sub p}, V{sub s} y densidad total) que normalmente se requieren para su determinacion. Las correlaciones identificadas se expresan matematicamente mediante ecuaciones de ajuste que reproducen en todos los casos los valores experimentales con un error estandar de estimacion dentro de 10% para el universo de las rocas estudiadas, y con mucho menor error para diferentes grupos litologicos
Institute of Scientific and Technical Information of China (English)
阚哲; 邵富群; 李庆华
2012-01-01
The probe shielding design provides a guarantee to measured signals, and this increases the similarity degree of the two measurement signals during the electrostatic sensor design. Meanwhile the choice of PVC tube can also effectively increase the sensitivity of the probe. The question of electrostatic shielding was focused on, and improving the shielding effect is to increase the similarity of the two measurement signals and improve velocity precision. With the shielding experiments it can explain the shielding design is very important to the probe making, and it obtains better measuring results. In the experiments the principle of cross-correlation noise immunity are probed, and the flow velocity was measured with same high at different radial position. Under the guidance of the cross - correlation theory, electrostatic theory and experiment, the experimental device has good repeatability and high measurement accuracy, and repeatability error is in + 2%. Within 2~7 m/s the flow velocity measuring experiment is done, and measurement results of the repeatability error are less than +2%.%在静电传感器电极设计中,电极屏蔽设计可有效获取被测信号的保障,并可以提高互相关速度测量中的两路测量信号的相似度.同时,PVC传送管的选择也可以有效提高电极的灵敏度.通过改进电极屏蔽效果来提高两路测量信号的相似度,进而提高相关测速精度.通过电极屏蔽实验,说明了屏蔽在电极设计中重要性,验证了互相关原理的抗噪声能力,并在同一高度测量得到传送管不同径向位置的流体速度.本实验装置具有较好的重复性和较高的测量精度,在2～7 m/s内进行了流速测量,测量结果的重复性误差在±2％以内.
Energy Technology Data Exchange (ETDEWEB)
Jirasek, A [Department of Physics and Astronomy, University of Victoria, Victoria BC V8W 3P6 (Canada); Matthews, Q [Department of Physics and Astronomy, University of Victoria, Victoria BC V8W 3P6 (Canada); Hilts, M [Medical Physics, BC Cancer Agency-Vancouver Island Centre, Victoria BC V8R 6V5 (Canada); Schulze, G [Michael Smith Laboratories, University of British Columbia, Vancouver BC V6T 1Z4 (Canada); Blades, M W [Department of Chemistry, University of British Columbia, Vancouver BC V6T 1Z1 (Canada); Turner, R F B [Michael Smith Laboratories, University of British Columbia, Vancouver BC V6T 1Z4 (Canada); Department of Chemistry, University of British Columbia, Vancouver BC V6T 1Z1 (Canada); Department of Electrical and Computer Engineering, University of British Columbia, Vancouver BC V6T 1Z4 (Canada)
2006-05-21
This study presents a new method of image signal-to-noise ratio (SNR) enhancement by utilizing a newly developed 2D two-point maximum entropy regularization method (TPMEM). When utilized as an image filter, it is shown that 2D TPMEM offers unsurpassed flexibility in its ability to balance the complementary requirements of image smoothness and fidelity. The technique is evaluated for use in the enhancement of x-ray computed tomography (CT) images of irradiated polymer gels used in radiation dosimetry. We utilize a range of statistical parameters (e.g. root-mean square error, correlation coefficient, error histograms, Fourier data) to characterize the performance of TPMEM applied to a series of synthetic images of varying initial SNR. These images are designed to mimic a range of dose intensity patterns that would occur in x-ray CT polymer gel radiation dosimetry. Analysis is extended to a CT image of a polymer gel dosimeter irradiated with a stereotactic radiation therapy dose distribution. Results indicate that TPMEM performs strikingly well on radiation dosimetry data, significantly enhancing the SNR of noise-corrupted images (SNR enhancement factors >15 are possible) while minimally distorting the original image detail (as shown by the error histograms and Fourier data). It is also noted that application of this new TPMEM filter is not restricted exclusively to x-ray CT polymer gel dosimetry image data but can in future be extended to a wide range of radiation dosimetry data.
Jirasek, A; Matthews, Q; Hilts, M; Schulze, G; Blades, M W; Turner, R F B
2006-05-21
This study presents a new method of image signal-to-noise ratio (SNR) enhancement by utilizing a newly developed 2D two-point maximum entropy regularization method (TPMEM). When utilized as an image filter, it is shown that 2D TPMEM offers unsurpassed flexibility in its ability to balance the complementary requirements of image smoothness and fidelity. The technique is evaluated for use in the enhancement of x-ray computed tomography (CT) images of irradiated polymer gels used in radiation dosimetry. We utilize a range of statistical parameters (e.g. root-mean square error, correlation coefficient, error histograms, Fourier data) to characterize the performance of TPMEM applied to a series of synthetic images of varying initial SNR. These images are designed to mimic a range of dose intensity patterns that would occur in x-ray CT polymer gel radiation dosimetry. Analysis is extended to a CT image of a polymer gel dosimeter irradiated with a stereotactic radiation therapy dose distribution. Results indicate that TPMEM performs strikingly well on radiation dosimetry data, significantly enhancing the SNR of noise-corrupted images (SNR enhancement factors >15 are possible) while minimally distorting the original image detail (as shown by the error histograms and Fourier data). It is also noted that application of this new TPMEM filter is not restricted exclusively to x-ray CT polymer gel dosimetry image data but can in future be extended to a wide range of radiation dosimetry data.
Institute of Scientific and Technical Information of China (English)
高永馨
2002-01-01
Studies the existence of solutions of nonlinear two point boundary value problems for nonlinear 4n-th-order differential equation y(4n)= f( t,y,y' ,y",… ,y(4n－1) ) (a) with the boundary conditions g2i(y(2i) (a) ,y(2i+1) (a)) = 0,h2i(y(2i) (c) ,y(2i+1) (c)) = 0, (I= 0,1,…,2n － 1 ) (b) where the functions f, gi and hi are continuous with certain monotone properties. For the boundary value problems of nonlinear nth order differential equation y(n) = f(t,y,y',y",… ,y(n－1)) many results have been given at the present time. But the existence of solutions of boundary value problem (a), (b) studied in this paper has not been covered by the above researches. Moreover, the corollary of the important theorem in this paper, I.e. Existence of solutions of the boundary value problem. Y(4n) = f(t,y,y',y",… ,y(4n－1) ) a2iy(2i) (at) + a2i+1y(2i+1) (a) = b2i ,c2iy(2O ( c ) + c2i+1y(2i+1) ( c ) = d2i, ( I = 0,1 ,…2n － 1) has not been dealt with in previous works.
Noh, Ji-Woong; Park, Byoung-Sun; Kim, Mee-Young; Lee, Lim-Kyu; Yang, Seung-Min; Lee, Won-Deok; Shin, Yong-Sub; Kang, Ji-Hye; Kim, Ju-Hyun; Lee, Jeong-Uk; Kwak, Taek-Yong; Lee, Tae-Hyun; Kim, Ju-Young; Kim, Junghwan
2015-06-01
[Purpose] This study investigated two-point discrimination (TPD) and the electrical sensory threshold of the blind to define the effect of using Braille on the tactile and electrical senses. [Subjects and Methods] Twenty-eight blind participants were divided equally into a text-reading and a Braille-reading group. We measured tactile sensory and electrical thresholds using the TPD method and a transcutaneous electrical nerve stimulator. [Results] The left palm TPD values were significantly different between the groups. The values of the electrical sensory threshold in the left hand, the electrical pain threshold in the left hand, and the electrical pain threshold in the right hand were significantly lower in the Braille group than in the text group. [Conclusion] These findings make it difficult to explain the difference in tactility between groups, excluding both palms. However, our data show that using Braille can enhance development of the sensory median nerve in the blind, particularly in terms of the electrical sensory and pain thresholds.
Institute of Scientific and Technical Information of China (English)
李国杰; 黄秀先; 梁树俊; 张红叶; 魏万林; 田国祥
2013-01-01
Objective To investigate the correlation between pulse wave velocity and cardiovascular diseases and their risk factors in elderly population. Methods Cluster sampling method was used to select 1701 people who were equal to or over 70 years old ( average age: 73.8 ) , and then they were given questionnaire survey, physical examination and laboratory tests. The level of carotid—femoral pulse wave velocity ( cfPWV ) was detected by applying French Complior SP, and the relationship between cfPWV and hypertension and their risk factors was observed. Results The level of cfPWV increased along with the increase of blood pressure, and was significantly higher in the patients with hypertension, brain stroke, myocardial infarction and diabetes than that in normal population with statistical difference. The results of multivariate regression analysis showed that age, male sex, mean arterial pressure, heart rate and insulin resistance index were correlated to cfPWV ( P<0.001 ) , and was negatively correlated to body mass index in whole population and the patients with brain stroke, myocardial infarction and diabetes. Conclusion The level of cfPWV is closely related to hypertension and risk factors of cardiovascular disease in elder population.%目的 探讨老年人群脉搏波速度(PWV)与心血管病及危险因素的相关性.方法 采用整群抽样方法纳入≥70岁人群1701例,进行问卷调查、体格检查和实验室检验,测量颈-股动脉脉搏波速度(cfPWV),观察cfPWV与高血压及相关危险因素的关系.结果 cfPWV 水平随血压水平升高而升高,在高血压、脑卒中、心肌梗死和糖尿病患者中cfPWV明显高于正常人群,差异有统计学意义.多元逐步回归分析显示在入选者和脑卒中、心肌梗死和糖尿病人群中,年龄、男性、平均动脉压、心率、胰岛素抵抗指数(Homa IR)与cfPWV呈正相关(P＜0.001),体重指数与cfPWV负相关.结论 在老年人群中,cfPWV与高血压及心血管病危险因素密切相关.
Directory of Open Access Journals (Sweden)
Tara L Alvarez
2014-06-01
Full Text Available Convergence insufficiency (CI is a prevalent binocular vision disorder with symptoms that include double/blurred vision, eyestrain, and headaches when engaged in reading or other near work. Randomized clinical trials support that Office-Based Vergence and Accommodative Therapy with home reinforcement leads to a sustained reduction in patient symptoms. However, the underlying neurophysiological basis for treatment is unknown. Functional activity and vergence eye movements were quantified from seven binocularly normal controls (BNC and four CI patients before and after 18 hours of vergence training. An fMRI conventional block design of sustained fixation versus vergence eye movements stimulated activity in the frontal eye fields (FEF, the posterior parietal cortex (PPC and the cerebellar vermis (CV. Comparing the CI patients’ baseline measurements to the post vergence training data sets with a paired t-test revealed the following: 1 the percent change in the BOLD signal in the FEF, PPC and CV significantly increased (p<0.02, 2 the peak velocity from 4° symmetrical convergence step responses increased (p<0.01 and 3 patient symptoms assessed using the CI Symptom Survey (CISS improved (p<0.05. CI patient measurements after vergence training were more similar to levels observed within BNC. A regression analysis revealed the peak velocity from BNC and CI subjects before and after vergence training was significantly correlated to the percent BOLD signal change within the FEF, PPC and CV (r=0.6;p<0.05. Results have clinical implications for understanding the behavioral and neurophysiological changes after vergence training in patients with CI, which may lead to the sustained reduction in visual symptoms.
Gait phase varies over velocities.
Liu, Yancheng; Lu, Kun; Yan, Songhua; Sun, Ming; Lester, D Kevin; Zhang, Kuan
2014-02-01
We sought to characterize the percent (PT) of the phases of a gait cycle (GC) as velocity changes to establish norms for pathological gait characteristics with higher resolution technology. Ninety five healthy subjects (49 males and 46 females with age 34.9 ± 11.8 yrs, body weight 64.0 ± 11.7 kg and BMI 23.5 ± 3.6) were enrolled and walked comfortably on a 10-m walkway at self-selected slower, normal, and faster velocities. Walking was recorded with a high speed camera (250 frames per second) and the eight phases of a GC were determined by examination of individual frames for each subject. The correlation coefficients between the mean PT of the phases of the three velocities gaits and PT defined by previous publications were all greater than 0.99. The correlation coefficient between velocity and PT of gait phases is -0.83 for loading response (LR), -0.75 for mid stance (MSt), and -0.84 for pre-swing (PSw). While the PT of the phases of three velocities from this study are highly correlated with PT described by Dr. Jacquenlin Perry decades ago, actual PT of each phase varied amongst these individuals with the largest coefficient variation of 24.31% for IC with slower velocity. From slower to faster walk, the mean PT of MSt diminished from 35.30% to 25.33%. High resolution recording revealed ambiguity of some gait phase definitions, and these data may benefit GC characterization of normal and pathological gait in clinical practice. The study results indicate that one should consider individual variations and walking velocity when evaluating gaits of subjects using standard gait phase classification.
Directory of Open Access Journals (Sweden)
Jiang Zhengxian
2009-01-01
Full Text Available This paper deals with a two-point boundary value problem of a class of Duffing-type systems with non-C1 perturbation term. Several existence and uniqueness theorems were presented.
Institute of Scientific and Technical Information of China (English)
石姗姗; 李保应; 于飞; 王茜; 张志勉; 高海青
2011-01-01
目的 研究颈-股脉搏波速度(CFPWV)、大动脉弹性指数(C1)、小动脉弹性指数(C2)和冠心病影响因素的相关性,并探讨CFFWV、C1、C2在冠心病早期诊断中的价值.方法 将131名受检者分为高血压组和高血压合并冠心病组,应用康普乐( Complior)动脉脉搏波速度测定仪(Artech,France)测定CFPWV,CV Profilor DO-2020型动脉弹性功能测定仪测定C1、C2.结果 ①与单纯高血压组相比,合并冠心病组的CFPWV、C1、C2均明显增高(P＜0.01)；②CFPWV与年龄、腔腹血糖(FPG)、甘油三酯(TG)、收缩压(SBP)、脉压(PP)呈正相关(r=0.475,0.186,0.183,0.360,0.455,P＜0.05),C1与年龄、SBP、PP呈负相关(r=-0.391,-0.247,-0.283,P＜0.01),C2与年龄、BMI、TG、SBP、PP、平均动脉压(MAP)呈负相关(r=-0.365,-0.126,-0.198,-0.340,-0.355,-0.210,P＜0.05).结论 CFPWV和C1、C2可作为早期预测冠心病的无创性敏感性指标.%Objective To analyze the relationship between pulse wave velocity, arterial elastic indexes and cardiovascular risk factors in patients with coronary heart disease, and to find the value of carotid-femoral pulse wave velocity(CF-PWV) , large arteria elastic indexes(Cl) and small arterial elastic indexes(C2) in early diagnosis of coronary heart disease. Methods 131 subjects were divided into two groups;the hypertension group and the hypertension with coronary heart disease group. CFPWV, Cl and C2 were measured by the pulse wave velocity measurement system (Complior) and the artery elasticity function measurement system(CV Profilor DO-2020). Results ① The CFPWV, Cl and C2 of the coronary heart disease group were significantly higher than those of the hypertension group (P < 0.01). ② In multiple regression analysis, CFPWV was correlated with age, fasting blood sugar(FPG) , triglycerides(TG) , systolic blood pressure( SBP) and pulse pressure( PP) (r = 0.475, 0.186, 0.183, 0.360, 0.455, P <0.05 ). Cl was negatively correlated with age, SBP and PP
Vector blood velocity estimation in medical ultrasound
DEFF Research Database (Denmark)
Jensen, Jørgen Arendt; Gran, Fredrik; Udesen, Jesper
2006-01-01
Two methods for making vector velocity estimation in medical ultrasound are presented. All of the techniques can find both the axial and transverse velocity in the image and can be used for displaying both the correct velocity magnitude and direction. The first method uses a transverse oscillation...... in the ultrasound field to find the transverse velocity. In-vivo examples from the carotid artery are shown, where complex turbulent flow is found in certain parts of the cardiac cycle. The second approach uses directional beam forming along the flow direction to estimate the velocity magnitude. Using a correlation...
Velocity anticipation in the optimal velocity model
Institute of Scientific and Technical Information of China (English)
DONG Li-yun; WENG Xu-dan; LI Qing-ding
2009-01-01
In this paper,the velocity anticipation in the optimal velocity model (OVM) is investigated.The driver adjusts the velocity of his vehicle by the desired headway,which depends on both instantaneous headway and relative velocity.The effect of relative velocity is measured by a sensitivity function.A specific form of the sensitivity function is supposed and the involved parameters are determined by the both numerical simulation and empirical data.It is shown that inclusion of velocity anticipation enhances the stability of traffic flow.Numerical simulations show a good agreement with empirical data.This model provides a better description of real traffic,including the acceleration process from standing states and the deceleration process approaching a stopped car.
Energy Technology Data Exchange (ETDEWEB)
Bourdon, A; Bonaventura, Z [Ecole Centrale Paris, EM2C Laboratory, UPR CNRS 288, Grande voie des vignes, 92295 Chatenay-Malabry Cedex (France); Celestin, S, E-mail: anne.bourdon@em2c.ecp.f [Communications and Space Sciences Laboratory, Department of Electrical Engineering, Pennsylvania State University, University Park, PA 16802 (United States)
2010-06-15
This paper presents simulations of positive and negative streamers propagating between two point electrodes in preheated air at atmospheric pressure. As many discharges have occurred before the simulated one, seed charges are taken into account in the interelectrode gap. First, for a pre-ionization background of 10{sup 9} cm{sup -3}, we have studied the influence of the data set used for transport parameters and reaction rates for air on the simulation results. We have compared results obtained in 1997 using input parameters from Morrow and Lowke and from Kulikovsky. Deviations as large as 20% of streamer characteristics (i.e. electric field in the streamer head and body, streamer velocity, streamer radius, streamer electron density) have been observed for this point-to-point configuration. Second, we have studied the influence of the pulsed voltage frequency on the discharge structure. For the studied discharge regime, a change in the applied voltage frequency corresponds to a change in the pre-ionization background. In this work, we have considered a wide range of pre-ionization values from 10{sup 4} and up to 10{sup 9} cm{sup -3}. We have noted that the value of the pre-ionization background has a small influence on the electron density, electric field and location of the negative streamer head. Conversely, it has a significant influence on the positive streamer characteristics. Finally, we have compared instantaneous and time-averaged optical emissions of the three band systems of N{sub 2} and N{sub 2}{sup +} (1PN{sub 2}, 2PN{sub 2} and 1NN{sub 2}{sup +}) during the discharge propagation. We have shown that the emission of the 2PN{sub 2} is the strongest of the three bands, in agreement with experimental observations. It is interesting to note that even with a short time averaging of a few nanoseconds, which corresponds to currently used instruments, the structure of the time-averaged emission of the 2PN{sub 2} is different from the instantaneous one and shows
Mattingly, Sean; Berumen, Jorge; Chu, Feng; Hood, Ryan; Skiff, Fred
2014-10-01
By using two independently tunable lasers, each with its own collection optics and Ar II LIF transition scheme, we are able to investigate plasma ion density fluctuations as a function of not only spatial scales but also as a function of ion velocities as sampled on different points of a single Doppler-broadened spectral emission line. We do this by measuring the two point correlation C (x , v ,x' ,v' , τ) = t . With the current system, the two carriages determine x and x', while the velocities selected by each laser determine v and v'. Using the two lasers to make two point correlations in phase space demonstrates effects that are not fully understood. In this experiment, we explore the striking difference in correlations when, in the past, the particle orbits overlap in space versus when they do not overlap. This is performed on a small cylindrical laboratory plasma with n ~109 cm-3 , Te ~ 5 eV, Ti ~ 0 . 06 , and a 1 kG axial magnetic field. LIF is performed on ions at two locations aligned with the magnetic field line with a viewing volume comparable to the size of the Larmor radius. Results and interpretations from these experiments are presented and discussed. DOE Grant DE-FG02-99ER54543.
Energy Technology Data Exchange (ETDEWEB)
Yoo, Hyun Suk; Lee, Jeong Min; Yoon, Jeong Hee; Lee, Dong Ho; Chang, Won; Han, Joon Koo [Seoul National University Hospital, Seoul (Korea, Republic of)
2016-09-15
To prospectively compare technical success rate and reliable measurements of virtual touch quantification (VTQ) elastography and elastography point quantification (ElastPQ), and to correlate liver stiffness (LS) measurements obtained by the two elastography techniques. Our study included 85 patients, 80 of whom were previously diagnosed with chronic liver disease. The technical success rate and reliable measurements of the two kinds of point shear wave elastography (pSWE) techniques were compared by χ{sup 2} analysis. LS values measured using the two techniques were compared and correlated via Wilcoxon signed-rank test, Spearman correlation coefficient, and 95% Bland-Altman limit of agreement. The intraobserver reproducibility of ElastPQ was determined by 95% Bland-Altman limit of agreement and intraclass correlation coefficient (ICC). The two pSWE techniques showed similar technical success rate (98.8% for VTQ vs. 95.3% for ElastPQ, p = 0.823) and reliable LS measurements (95.3% for VTQ vs. 90.6% for ElastPQ, p = 0.509). The mean LS measurements obtained by VTQ (1.71 ± 0.47 m/s) and ElastPQ (1.66 ± 0.41 m/s) were not significantly different (p = 0.209). The LS measurements obtained by the two techniques showed strong correlation (r = 0.820); in addition, the 95% limit of agreement of the two methods was 27.5% of the mean. Finally, the ICC of repeat ElastPQ measurements was 0.991. Virtual touch quantification and ElastPQ showed similar technical success rate and reliable measurements, with strongly correlated LS measurements. However, the two methods are not interchangeable due to the large limit of agreement.
Energy Technology Data Exchange (ETDEWEB)
McCoy, M.G.
1975-11-01
The problem of the numerical simulation of turbulent diffusion is studied. The two-dimensional velocity fields are assumed to be incompressible, homogeneous and stationary, and they are represented as stochastic processes. A technique is offered which creates velocity fields accurately representing the input statistics once a two point correlation function or an energy spectrum is given. Various complicated energy spectra may be represented utilizing this model. The program is then used to extract information concerning Gaussian diffusion processes. Various theories of other workers are tested including Taylor's classical representation of dispersion for times long compared with the Lagrangian correlation time. Also, a study is made of the relation between the Lagrangian and the Eulerian correlation function and a hypothesis is advanced and successfully tested. Questions concerning the relation between small eddies and the energy spectrum are considered. A criterion is advanced and successfully tested to decide whether small scale flow can be detected within the large eddies for any given spectrum. A method is developed to determine whether this small scale motion is in any sense periodic. Finally, the relation between two particle dispersion and the energy spectrum is studied anew and various theories are tested. (auth)
Wersal, C.; Ricci, P.; Loizu, J.
2017-04-01
A refined two-point model is derived from the drift-reduced Braginskii equations for the limited tokamak scrape-off layer (SOL) by balancing the parallel and perpendicular transport of plasma and heat and taking into account the plasma–neutral interaction. The model estimates the electron temperature drop along a field line, from a region far from the limiter to the limiter plates. Self-consistent first-principles turbulence simulations of the SOL plasma including its interaction with neutral atoms are performed with the GBS code and compared to the refined two-point model. The refined two-point model is shown to be in very good agreement with the turbulence simulation results.
Statistical Study of Turbulence: Spectral Functions and Correlation Coefficients
Frenkiel, Francois N.
1958-01-01
In reading the publications on turbulence of different authors, one often runs the risk of confusing the various correlation coefficients and turbulence spectra. We have made a point of defining, by appropriate concepts, the differences which exist between these functions. Besides, we introduce in the symbols a few new characteristics of turbulence. In the first chapter, we study some relations between the correlation coefficients and the different turbulence spectra. Certain relations are given by means of demonstrations which could be called intuitive rather than mathematical. In this way we demonstrate that the correlation coefficients between the simultaneous turbulent velocities at two points are identical, whether studied in Lagrange's or in Euler's systems. We then consider new spectra of turbulence, obtained by study of the simultaneous velocities along a straight line of given direction. We determine some relations between these spectra and the correlation coefficients. Examining the relation between the spectrum of the turbulence measured at a fixed point and the longitudinal-correlation curve given by G. I. Taylor, we find that this equation is exact only when the coefficient is very small.
Wakker, BP; vanWoerden, H
1997-01-01
High-velocity clouds (HVCs) consist of neutral hydrogen (HI) at velocities incompatible with a simple model of differential galactic rotation; in practice one uses \\v(LSR)\\ greater than or equal to 90 km/s to define HVCs. This review describes the main features of the sky and velocity distributions,
Transverse Spectral Velocity Estimation
DEFF Research Database (Denmark)
Jensen, Jørgen Arendt
2014-01-01
A transverse oscillation (TO)-based method for calculating the velocity spectrum for fully transverse flow is described. Current methods yield the mean velocity at one position, whereas the new method reveals the transverse velocity spectrum as a function of time at one spatial location. A convex...
Detection probabilities for time-domain velocity estimation
DEFF Research Database (Denmark)
Jensen, Jørgen Arendt
1991-01-01
Estimation of blood velocities by time-domain cross-correlation of successive high frequency sampled ultrasound signals is investigated. It is shown that any velocity can result from the estimator regardless of the true velocity due to the nonlinear technique employed. Using a simple simulation...... as a filter with a transfer function depending on the actual velocity. This influences the detection probability, which gets lower at certain velocities. An index directly reflecting the probability of detection can easily be calculated from the cross-correlation estimated. This makes it possible to assess...... the reliability of the velocity estimate in real time...
Energy Technology Data Exchange (ETDEWEB)
Ullrich, Peter [Institut fuer Informatik, TU Muenchen, Boltzmannstrasse 3, D-85748 Garching (Germany); Werner, Ernst [Institut fuer Physik, Universitaet Regensburg, Universitaetsstrasse 31, D-93040 Regensburg (Germany)
2006-05-19
We investigate the generally assumed inconsistency in light cone quantum field theory that the restriction of a massive, real scalar free field to the nullplane {sigma} = {l_brace}x{sup 0} + x{sup 3} = 0{r_brace} is independent of mass (Leutwyler, Klauder and Streit 1970 Nuovo Cimento A 66 536), but the restriction of the two-point function is mass dependent (see, e.g., Nakanishi and Yamawaki 1977 Nucl. Phys. B 122 15; Yamawaki K 1997 Proc. Int. Workshop New Nonperturbative Methods and Quantization on the Light Cone (Les Houches, France) Preprint hep-th/9707141). We resolve this inconsistency by showing that the two-point function has no canonical restriction to {sigma} in the sense of distribution theory. Only the so-called tame restriction of the two-point function, which we have introduced in (Ullrich P 2004 Uniqueness in the characteristic Cauchy problem of the Klein-Gordon equation and tame restrictions of generalized functions Preprint math-ph/0408022 (submitted)) exists. Furthermore, we show that this tame restriction is indeed independent of the mass. Hence the inconsistency is induced by the erroneous assumption that the two-point function has a (canonical) restriction to {sigma}.
Croce, Ronald V.; Jacobson, William H.
1986-01-01
Basic behavioral processes involved in motor control based on theories of motor control and learning are outlined using the teaching of two-point touch cane technique as an application of the theories. The authors assert the importance of repetition, practice, and sufficient learning time. (Author/CL)
Fröb, Markus B.; Higuchi, Atsushi; Lima, William C. C.
2016-06-01
We construct the graviton two-point function for a two-parameter family of linear covariant gauges in n -dimensional de Sitter space. The construction is performed via the mode-sum method in the Bunch-Davies vacuum in the Poincaré patch, and a Fierz-Pauli mass term is introduced to regularize the infrared (IR) divergences. The resulting two-point function is de Sitter invariant and free of IR divergences in the massless limit (for a certain range of parameters), although analytic continuation with respect to the mass for the pure-gauge sector of the two-point function is necessary for this result. This general result agrees with the propagator obtained by analytic continuation from the sphere [Phys. Rev. D 34, 3670 (1986); Classical Quantum Gravity 18, 4317 (2001)]. However, if one starts with strictly zero mass theory, the IR divergences are absent only for a specific value of one of the two parameters, with the other parameter left generic. These findings agree with recent calculations in the Landau (exact) gauge [J. Math. Phys. 53, 122502 (2012)], where IR divergences do appear in the spin-two (tensor) part of the two-point function. However, we find the strength (including the sign) of the IR divergence to be different from the one found in this reference.
Ultrasound systems for blood velocity estimation
DEFF Research Database (Denmark)
Jensen, Jørgen Arendt
1998-01-01
color image of velocity at up to 20 to 60 frames a second. Both measurements are performedby repeatedly pulsing in the same direction and then usethe correlation from pulse to pulse to determine the velocity.The paper gives a simple model for the interactionbetween the ultrasound and the moving blood......Medical ultrasound scanners can be used both for displayinggray-scale images of the anatomy and for visualizing theblood flow dynamically in the body.The systems can interrogate the flow at a single position in the bodyand there find the velocity distribution over time. They can also show adynamic....... The calculation of the velocity distribution is then explainedalong with the different physical effects influencing the estimation.The estimation of mean velocities using auto- andcross-correlation for color flow mapping is also described....
Khoo, B. C.; Chew, Y. T.; Teo, C. J.
This work continues the studies of Khoo et al. (Exp. Fluids 29: 448-460, 2001), where experiments were performed in turbulent-channel and flat-plate boundary-layer flows using near-wall hot-wire probes. The probability density function (pdf) of the wall-shear stress and streamwise velocity fluctuations in the viscous sublayer, buffer region and beyond were compared and analyzed. The convective velocity Uc of the streamwise velocity fluctuations in the very near-wall region was obtained using a two-point correlation technique. It was found that in the viscous sublayer, Uc is approximately constant at 13uτ and 15uτ, respectively, for the channel and boundary-layer flows. Spectra data for the viscous sublayer are presented for the first time, and the normalized spectral plots for different flow conditions collapse at high frequencies or wavenumbers, thus indicating the possible presence of small-scale universality at different Reynolds numbers. The integral time scale corresponding to the streamwise velocity fluctuations in the viscous sublayer is also presented.
Institute of Scientific and Technical Information of China (English)
沈玉萍; 尹立雪; 程重庆; 张丽娟
2013-01-01
Objective To investigate regional ventricular long-axis velocity and adjacent intraventricular flow velocity using dual-pulse wave(PW) Doppler echocardiography synchronously,and to analyze the coupling relationship between regional ventricular long-axis strain and adjacent intraventricular pressure gradients in normal cases using dual-PW Doppler echocardiography.Methods Eighty-six normal subjects aged 19～66 years [mean age (37.49 ± 11.97)years] underwent routine echocardiography and dualPW Doppler echocardiographic exam.Total 18 segments were sampled using dual-PW Doppler (PW/TDI mode) images at basal,mid and apical levels on three standard apical views,and electrocardiogram was recorded simultaneously.Peak early diastolic velocity (emax),peak late diastolic velocity (amax),peak early mitral diastolic inflow velocity (Emax),regional peak early diastolic velocity (Em),regional peak late diastolic velocity (Am) and regional peak early diastolic inflow velocity (E) were measured simultaneously in the same one cardiac cycle.Myocardial variations of left ventricular segments were observed.Em,Am and E of different levels from different ventricular wall were analyzed.The co-relationship between regional ventricular long-axis strain and adjacent intraventricular pressure gradients were calculated and analyzed.Results ①Regional myocardial velocity and regional peak early diastolic inflow velocity in normal subjects declined from basal to apical segments gradually at the same ventricular wall (P ＜ 0.01).② Emax was correlated with emax(r =0.418,P ＜0.001),and E was correlated with Em (posterior septum,r =0.610,P ＜0.001 ；anterior wall,r =0.499,P ＜0.001).③There was a medium correlation between normal longaxis strain in segments and adjacent intraventricular pressure gradients (the global,r =0.412,P ＜0.001 ；posterior septum,r =0.319,P ＜0.005).Conclusions The acquirement of E and Em by dual-PW Doppler showed downtrend of segmental wall movement and
Producing data-based sensitivity kernels from convolution and correlation in exploration geophysics.
Chmiel, M. J.; Roux, P.; Herrmann, P.; Rondeleux, B.
2016-12-01
Many studies have shown that seismic interferometry can be used to estimate surface wave arrivals by correlation of seismic signals recorded at a pair of locations. In the case of ambient noise sources, the convergence towards the surface wave Green's functions is obtained with the criterion of equipartitioned energy. However, seismic acquisition with active, controlled sources gives more possibilities when it comes to interferometry. The use of controlled sources makes it possible to recover the surface wave Green's function between two points using either correlation or convolution. We investigate the convolutional and correlational approaches using land active-seismic data from exploration geophysics. The data were recorded on 10,710 vertical receivers using 51,808 sources (seismic vibrator trucks). The sources spacing is the same in both X and Y directions (30 m) which is known as a "carpet shooting". The receivers are placed in parallel lines with a spacing 150 m in the X direction and 30 m in the Y direction. Invoking spatial reciprocity between sources and receivers, correlation and convolution functions can thus be constructed between either pairs of receivers or pairs of sources. Benefiting from the dense acquisition, we extract sensitivity kernels from correlation and convolution measurements of the seismic data. These sensitivity kernels are subsequently used to produce phase-velocity dispersion curves between two points and to separate the higher mode from the fundamental mode for surface waves. Potential application to surface wave cancellation is also envisaged.
Mohd Fauzi, Norizyan Izzati; Sulaiman, Jumat
2013-04-01
The aim of this paper is to describe the application of Quarter-Sweep Gauss-Seidel (QSGS) iterative method using quadratic spline scheme for solving fourth order two-point linear boundary value problems. In the line to derive approximation equations, firstly the fourth order problems need to be reduced onto a system of second-order two-point boundary value problems. Then two linear systems have been constructed via discretization process by using the corresponding quarter-sweep quadratic spline approximation equations. The generated linear systems have been solved using the proposed QSGS iterative method to show the superiority over Full-Sweep Gauss-Seidel (FSGS) and Half-Sweep Gauss-Seidel (HSGS) methods. Computational results are provided to illustrate that the effectiveness of the proposed QSGS method is more superior in terms of computational time and number of iterations as compared to other tested methods.
Belokogne, Andrei; Queva, Julien
2016-01-01
By considering Hadamard vacuum states, we first construct the two-point functions associated with Stueckelberg massive electromagnetism in de Sitter and anti-de Sitter spacetimes. Then, from the general formalism developed in [A. Belokogne and A. Folacci, Phys. Rev. D \\textbf{93}, 044063 (2016)], we obtain an exact analytical expression for the vacuum expectation value of the renormalized stress-energy tensor of the massive vector field propagating in these maximally symmetric spacetimes.
Dudok de Wit, T; Dunlop, M; Luehr, H
1999-01-01
A framework is described for estimating Linear growth rates and spectral energy transfers in turbulent wave-fields using two-point measurements. This approach, which is based on Volterra series, is applied to dual satellite data gathered in the vicinity of the Earth's bow shock, where Short Large Amplitude Magnetic Structures (SLAMS) supposedly play a leading role. The analysis attests the dynamic evolution of the SLAMS and reveals an energy cascade toward high-frequency waves.
Caixia Guo; Jianmin Guo; Ying Gao; Shugui Kang
2016-01-01
This paper is concerned with the two-point boundary value problems of nonlinear finite discrete fractional differential equations. On one hand, we discuss some new properties of the Green function. On the other hand, by using the main properties of Green function and the Krasnoselskii fixed point theorem on cones, some sufficient conditions for the existence of at least one or two positive solutions for the boundary value problem are established.
Fröb, Markus B; Lima, William C C
2016-01-01
We construct the graviton two-point function for a two-parameter family of linear covariant gauges in n-dimensional de Sitter space. The construction is performed via the mode-sum method in the Bunch-Davies vacuum in the Poincar\\'e patch, and a Fierz-Pauli mass term is introduced to regularize the infrared (IR) divergences. The resulting two-point function is de Sitter-invariant, and free of IR divergences in the massless limit (for a certain range of parameters) though analytic continuation with respect to the mass for the pure-gauge sector of the two-point function is necessary for this result. This general result agrees with the propagator obtained by analytic continuation from the sphere [Phys. Rev. D 34, 3670 (1986); Class. Quant. Grav. 18, 4317 (2001)]. However, if one starts with strictly zero mass theory, the IR divergences are absent only for a specific value of one of the two parameters, with the other parameter left generic. These findings agree with recent calculations in the Landau (exact) gauge ...
Puyguiraud, Alexandre; Dentz, Marco; Gouze, Philippe
2017-04-01
For the past several years a lot of attention has been given to pore-scale flow in order to understand and model transport, mixing and reaction in porous media. Nevertheless we believe that an accurate study of spatial and temporal evolution of velocities could bring important additional information for the upscaling from pore to higher scales. To gather these pieces of information, we perform Stokes flow simulations on pore-scale digitized images of a Berea sandstone core. First, micro-tomography (XRMT) imaging and segmentation processes allow us to obtain 3D black and white images of the sample [1]. Then we used an OpenFoam solver to perform the Stokes flow simulations mentioned above, which gives us the velocities at the interfaces of a cubic mesh. Subsequently, we use a particle streamline reconstruction technique which uses the Eulerian velocity field previously obtained. This technique, based on a modified Pollock algorithm [2], enables us to make particle tracking simulations on the digitized sample. In order to build a stochastic pore-scale transport model, we analyze the Lagrangian velocity series in two different ways. First we investigate the velocity evolution by sampling isochronically (t-Lagrangian), and by studying its statistical properties in terms of one- and two-points statistics. Intermittent patterns can be observed. These are due to the persistance of low velocities over a characteristic space length. Other results are investigated, such as correlation functions and velocity PDFs, which permit us to study more deeply this persistence in the velocities and to compute the correlation times. However, with the second approach, doing these same analysis in space by computing the velocities equidistantly, enables us to remove the intermittency shown in the temporal evolution and to model these velocity series as a Markov process. This renders the stochastic particle dynamics into a CTRW [3]. [1] Gjetvaj, F., A. Russian, P. Gouze, and M. Dentz (2015
DEFF Research Database (Denmark)
2000-01-01
Using a pulsed ultrasound field, the two-dimensional velocity vector can be determined with the invention. The method uses a transversally modulated ultrasound field for probing the moving medium under investigation. A modified autocorrelation approach is used in the velocity estimation. The new...
DEFF Research Database (Denmark)
2000-01-01
Using a pulsed ultrasound field, the two-dimensional velocity vector can be determined with the invention. The method uses a transversally modulated ultrasound field for probing the moving medium under investigation. A modified autocorrelation approach is used in the velocity estimation. The new...
代谢综合征各危险因素与不同节段脉搏波速度的相关性分析%The correlation of metabolic syndrome factors and pulse wave velocity
Institute of Scientific and Technical Information of China (English)
闵颖; 边素艳; 叶平; 骆雷鸣; 肖文凯; 吴红梅
2014-01-01
Objective A cross-sectional was conducted to investigate the correlation of pulse wave velocity (PWV)and metabolic syndrome (MS)factors.Methods All the adult participants in this cross-sectional investi-gation were recruited from 3 big communities during their annual physical examination.Regional arterial stiffness was assessed simultaneously by measuring PWV in three arterial segments,carotid -femoral (cfPWV),carotid -radial (crPWV)and carotid-ankle PWV (caPWV).Demographic characteristics and basal biochemical parameters inclu-ding height,weight,waist and hip circumference,blood pressure,and serum levels of glucose,lipid,uric acid and cre-atinine were collected.MS was identified according to the criteria from the International Diabetes Federation defini-tion.Results A total of 2439 citizens (aged 18 to 92 years)were enrolled into this study,which included 732 partic-ipants with MS (prevalence,30.01%).The subjects with MS were older[(53.25 ±13.73)vs.(50.03 ±15.73), P<0.01],and had a higher cfPWV,caPWV,crPWV(11.68 ±2.92)m/s vs.(10.24 ±2.43)m/s,(9.46 ±1.73) m/s vs.(8.76 ±2.23)m/s,(9.76 ±1.52)m/s vs.(9.42 ±1.45)m/s,P<0.01 for all],and an increased inci-dence of cardiovascular diseases (18.3% vs.9.1%,P<0.001).Partial correlation analysis after adjustment for age and sex showed that pulse pressure,LDL-C,uric acid and all component of MS were significantly correlated to the values of cfPWV and caPWV (P<0.05 for all).The results of multivariate stepwise linear regression analysis indicated that MS was an independent risk factor for the cfPWV,cfPWV and caPWV.Further analysis showed that increased sys-tolicblood pressure and hyperglycemia were the independent risk factors for cfPWV and caPWV ,and the diastolic blood pressure for crPWV.Central obesity was correlated with enhanced cfPWV,while no correlation was observed be-tween the level of serum triglyceride,high density lipoprotein and PWV.Conclusion MS is the independent risk fac-tor for the arteriosclerosis
Range/velocity limitations for time-domain blood velocity estimation
DEFF Research Database (Denmark)
Jensen, Jørgen Arendt
1993-01-01
The traditional range/velocity limitation for blood velocity estimation systems using ultrasound is elucidated. It is stated that the equation is a property of the estimator used, not the actual physical measurement situation, as higher velocities can be estimated by the time domain cross......-correlation approach. It is demonstrated that the time domain technique under certain measurement conditions will yield unsatisfactory results, when trying to estimate high velocities. Various methods to avoid these artifacts using temporal and spatial clustering techniques are suggested. The improvement...
The planar two point algorithm
O. Booij; Z. Zivkovic
2009-01-01
Vision-based localization, mapping and navigation is often performed by searching for corresponding image points and estimating the epipolar geometry. It is known that the possible relative poses of a camera mounted on a mobile robot that moves over a planar ground floor, has two degrees of freedom.
Spin Correlation in Binary Systems
Farbiash, N; Farbiash, Netzach; Steinitz, Raphael
2004-01-01
We examine the correlation of projected rotational velocities in binary systems. It is an extension of previous work (Steinitz and Pyper, 1970; Levato, 1974). An enlarged data basis and new tests enable us to conclude that there is indeed correlation between the projected rotational velocities of components of binaries. In fact we suggest that spins are already correlated.
Velocity Bias from the Small Scale Clustering of SDSS-III BOSS Galaxies
Guo, Hong; Zehavi, Idit; Dawson, Kyle; Skibba, Ramin A; Tinker, Jeremy L; Weinberg, David H; White, Martin; Schneider, Donald P
2014-01-01
We present the measurements and modelling of the projected and redshift-space clustering of CMASS galaxies in the Sloan Digital Sky Survey-III Baryon Oscillation Spectroscopic Survey Data Release 11. For a volume-limited luminous red galaxy sample in the redshift range of $0.48
Institute of Scientific and Technical Information of China (English)
周杨锐; 董明明; 吴海京; 王园君
2011-01-01
剪切波速是工程场地地震安全性评价最重要的参数之一.本文应用大量渤海浅层沉积物的剪切波速实测数据,利用最小二乘法通过三种模型探讨了不同土质类型的剪切波速与深度的关系,给出了不同土质类型的剪切波速与深度拟合最佳的统计公式.并与的推荐公式在某一海域工程场地的测试结果进行对比分析,结果表明:本文所建立的统计公式对剪切波速的预测效果明显好于规范所推荐的统计公式.因此本文所推荐的渤海不同土质类型的剪切波速与深度间的统计公式,可供无波速测试的渤海海洋工程场地借鉴使用.%The shear wave velocity of soils is one of the most important parameters in the field of geotechnical earthquake engineering. Based on the tested data of shear wave velocity of shallow sediments from lots of boreholes in Bohai Gulf, the best regression equations of shear wave velocity and depth for different types of soils are established by using three statistical models. The predicted shear wave velocity of soils with recommended equations are compared with the results of formula in the Chinese design code for earthquake resistance of special structures (GB50191-93) in a certain borehole. It is indicated that the fitting accuracy of recommended equations is better than that of formula in design code. Therefore, the recommended regression equations of shear wave velocity and depth of shallow sediments in Bohai Gulf can be used for marine sites of Bohai Gulf, whose shear wave velocities are not tested.
Suto, Y; Suto, Yasushi; Jing, Yi-Peng
1996-01-01
We discuss the effect of the finite size of galaxies on estimating small-scale relative pairwise peculiar velocity dispersions from the cosmic virial theorem (CVT). Specifically we evaluate the effect by incorporating the finite core radius $r_c$ in the two-point correlation function of mass, i.e. softening $r_s$ on small scales. We analytically obtain the lowest-order correction term for $\\gamma 2$. Compared with the idealistic point-mass approximation ($r_s=r_c=0$), the finite size effect can significantly reduce the small-scale velocity dispersions of galaxies at scales much larger than $r_s$ and $r_c$. Even without considering the finite size of galaxies, nonzero values for $r_c$ are generally expected, for instance, for cold dark matter (CDM) models with a scale-invariant primordial spectrum. For these CDM models, a reasonable force softening $r_s\\le 100 \\hikpc$ would have rather tiny effect. We present the CVT predictions for the small-scale pairwise velocity dispersion in the CDM models normalized by t...
Velocity spectrum for the Iranian plateau
Bastami, Morteza; Soghrat, M. R.
2017-09-01
Peak ground acceleration (PGA) and spectral acceleration values have been proposed in most building codes/guidelines, unlike spectral velocity (SV) and peak ground velocity (PGV). Recent studies have demonstrated the importance of spectral velocity and peak ground velocity in the design of long period structures (e.g., pipelines, tunnels, tanks, and high-rise buildings) and evaluation of seismic vulnerability in underground structures. The current study was undertaken to develop a velocity spectrum and for estimation of PGV. In order to determine these parameters, 398 three-component accelerograms recorded by the Building and Housing Research Center (BHRC) were used. The moment magnitude (Mw) in the selected database was 4.1 to 7.3, and the events occurred after 1977. In the database, the average shear-wave velocity at 0 to 30 m in depth (Vs30) was available for only 217 records; thus, the site class for the remaining was estimated using empirical methods. Because of the importance of the velocity spectrum at low frequencies, the signal-to-noise ratio of 2 was chosen for determination of the low and high frequency to include a wider range of frequency content. This value can produce conservative results. After estimation of the shape of the velocity design spectrum, the PGV was also estimated for the region under study by finding the correlation between PGV and spectral acceleration at the period of 1 s.
A new method of measuring the peculiar velocity power spectrum
Zhang, P; Juszkiewicz, R; Feldman, H A; Zhang, Pengjie; Stebbins, Albert; Juszkiewicz, Roman; Feldman, Hume
2004-01-01
We show that by directly correlating the cluster kinetic Sunyaev Zeldovich (KSZ) flux, the cluster peculiar velocity power spectrum can be measured to $\\sim 10%$ accuracy by future large sky coverage KSZ surveys. This method is almost free of systemics entangled in the usual velocity inversion method. The direct correlation brings extra information of density and velocity clustering. We utilize these information to construct two indicators of the Hubble constant and comoving angular distance and propose a novel method to constrain cosmology.
Two-point spin-1/2-spin-1/2 sl(2,bfC) conformal Kac-Moody blocks on the torus and their monodromies
Energy Technology Data Exchange (ETDEWEB)
Smyrnakis, J.M. [Columbia Univ., New York, NY (United States). Dept. of Mathematics
1995-10-02
Two issues of the SU(2) Wess-Zumino-Witten model are examined here, namely the computation of the untwisted conformal Kac-Moody blocks on the torus and their monodromy representations. Using the free field representation developed by Bernard and Felder, an integral representation of the twisted two point spin-1/2-spin-1/2 conformal Kac-Moody blocks on the torus is computed. From this, an integral representation of the untwisted blocks is computed after careful removal of infinities. Finally, the untwisted blocks are used to get a representation of the Braid Group on the torus on two strings, in terms of quantum group q-numbers. (orig.).
Superluminal Recession Velocities
Davis, T M; Davis, Tamara M.; Lineweaver, Charles H.
2000-01-01
Hubble's Law, v=HD (recession velocity is proportional to distance), is a theoretical result derived from the Friedmann-Robertson-Walker metric. v=HD applies at least as far as the particle horizon and in principle for all distances. Thus, galaxies with distances greater than D=c/H are receding from us with velocities greater than the speed of light and superluminal recession is a fundamental part of the general relativistic description of the expanding universe. This apparent contradiction of special relativity (SR) is often mistakenly remedied by converting redshift to velocity using SR. Here we show that galaxies with recession velocities faster than the speed of light are observable and that in all viable cosmological models, galaxies above a redshift of three are receding superluminally.
Perotti, Jose; Voska, Ned (Technical Monitor)
2002-01-01
This presentation provides an overview of the development of new hurricane wind sensor (Extreme Velocity Wind Sensor) for the Kennedy Space Center (KSC) which is designed to withstand winds of up to three hundred miles an hour. The proposed Extreme Velocity Wind Sensor contains no moveable components that would be exposed to extreme wind conditions. Topics covered include: need for new hurricane wind sensor, conceptual design, software applications, computational fluid dynamic simulations of design concept, preliminary performance tests, and project status.
Equilibrium Correlations in a Clustering Universe
Institute of Scientific and Technical Information of China (English)
张航; 黄霞; 李晓卿
2003-01-01
It is shown that the observed result of the two-point galaxy correlation function and the three-point correlation function in the Universe agrees with a quasi-equilibrium assumption of mass distribution.Utilizing the form of the three-point correlation,we find that the two-point correlation function can be obtained by solving an equation derived from maximizing entropy under some constraints in a self-gravitating particle model.A generalized non-extensive entropy is also introduced to improve our result.
Solutions of the Wheeler-Feynman equations with discontinuous velocities
de Souza, Daniel Câmara
2014-01-01
We generalize Wheeler-Feynman electrodynamics with a variational boundary-value problem having boundary conditions in past and future. The extended variational problem accepts trajectories with discontinuous velocities as critical points of the action functional. Critical-point trajectories must satisfy the Euler-Lagrange equations of the action functional, which are neutral-differential delay equations of motion. Moreover, at velocity discontinuity points critical-point orbits must satisfy the Weierstrass-Erdmann corner conditions of continuity of the partial momenta and partial energies. We study a special class of boundary data having the shortest time-separation between boundary segments, for which case the Wheeler-Feynman equations reduce to a two-point boundary problem for an ordinary differential equation. For this simple case we prove that solutions of the Wheeler-Feynman equations can have discontinuous velocities. We construct a numerical method to find critical-point orbits with a shooting method f...
Février, Pierre; Simonin, Olivier; Squires, Kyle D.
2005-06-01
The velocity distribution of dilute suspensions of heavy particles in gas-solid turbulent flows is investigated. A statistical approach - the mesoscopic Eulerian formalism (MEF) - is developed in which an average conditioned on a realization of the turbulent carrier flow is introduced and enables a decomposition of the instantaneous particle velocity into two contributions. The first is a contribution from an underlying continuous turbulent velocity field shared by all the particles - the mesoscopic Eulerian particle velocity field (MEPVF) - that accounts for all particle-particle and fluid-particle two-point correlations. The second contribution corresponds to a distribution - the quasi-Brownian velocity distribution (QBVD) - that represents a random velocity component satisfying the molecular chaos assumption that is not spatially correlated and identified with each particle of the system. The MEF is used to investigate properties of statistically stationary particle-laden isotropic turbulence. The carrier flow is computed using direct numerical simulation (DNS) or large-eddy simulation (LES) with discrete particle tracking employed for the dispersed phase. Particle material densities are much larger than that of the fluid and the force of the fluid on the particle is assumed to reduce to the drag contribution. Computations are performed in the dilute regime for which the influences of inter-particle collisions and fluid-turbulence modulation are neglected. The simulations show that increases in particle inertia increase the contribution of the quasi-Brownian component to the particle velocity. The particle velocity field is correlated at larger length scales than the fluid, with the integral length scales of the MEPVF also increasing with particle inertia. Consistent with the previous work of Abrahamson (1975), the MEF shows that in the limiting case of large inertia, particle motion becomes stochastically equivalent to a Brownian motion with a random spatial
Balasubramaniam, K. S.; Keil, S. L.; Smaldone, L. A.
1996-05-01
We investigate the three dimensional structure of solar pores and their surroundings using high spatial and spectral resolution data. We present evidence that surface velocities decrease around pores with a corresponding increase in the line-of-sight (LOS) velocities. LOS velocities in pores increase with the strength of the magnetic field. Surface velocities show convergence toward a weak downflow which appear to trace boundaries resembling meso-granular and super granular flows. The observed magnetic fields in the pores appear near these boundaries. We analyze the vertical velocity structure in pores and show that they generally have downflows decreasing exponentially with height, with a scale height of about 90 km. Evidence is also presented for the expanding nature of flux tubes. Finally we describe a phenomenological model for pores. This work was supported by AFOSR Task 2311G3. LAS was partially supported by the Progetto Nazionale Astrofisica e Fisica Cosmica of MURST and Scambi Internazionali of the Universita degli Studi di Napoli Frederico II. National Solar Observatory, NOAO, is operated for the National Science Foundation by AURA, Inc.
Quantitative velocity modulation spectroscopy
Hodges, James N.; McCall, Benjamin J.
2016-05-01
Velocity Modulation Spectroscopy (VMS) is arguably the most important development in the 20th century for spectroscopic study of molecular ions. For decades, interpretation of VMS lineshapes has presented challenges due to the intrinsic covariance of fit parameters including velocity modulation amplitude, linewidth, and intensity. This limitation has stifled the growth of this technique into the quantitative realm. In this work, we show that subtle changes in the lineshape can be used to help address this complexity. This allows for determination of the linewidth, intensity relative to other transitions, velocity modulation amplitude, and electric field strength in the positive column of a glow discharge. Additionally, we explain the large homogeneous component of the linewidth that has been previously described. Using this component, the ion mobility can be determined.
The Prescribed Velocity Method
DEFF Research Database (Denmark)
Nielsen, Peter Vilhelm
The- velocity level in a room ventilated by jet ventilation is strongly influenced by the supply conditions. The momentum flow in the supply jets controls the air movement in the room and, therefore, it is very important that the inlet conditions and the numerical method can generate a satisfactory...... description of this momentum flow. The Prescribed Velocity Method is a practical method for the description of an Air Terminal Device which will save grid points close to the opening and ensure the right level of the momentum flow....
Cirrus Crystal Terminal Velocities.
Heymsfield, Andrew J.; Iaquinta, Jean
2000-04-01
Cirrus crystal terminal velocities are of primary importance in determining the rate of transport of condensate from upper- to middle-tropospheric levels and profoundly influence the earth's radiation balance through their effect on the rate of buildup or decay of cirrus clouds. In this study, laboratory and field-based cirrus crystal drag coefficient data, as well as analytical descriptions of cirrus crystal shapes, are used to derive more physically based expressions for the velocities of cirrus crystals than have been available in the past.Polycrystals-often bullet rosettes-are shown to be the dominant crystal types in synoptically generated cirrus, with columns present in varying but relatively large percentages, depending on the cloud. The two critical parameters needed to calculate terminal velocity are the drag coefficient and the ratio of mass to cross-sectional area normal to their fall direction. Using measurements and calculations, it is shown that drag coefficients from theory and laboratory studies are applicable to crystals of the types found in cirrus. The ratio of the mass to area, which is shown to be relatively independent of the number of bullets in the rosette, is derived from an analytic model that represents bullet rosettes containing one to eight bullets in 19 primary geometric configurations. The ratio is also derived for columns. Using this information, a general set of equations is developed to calculate the terminal velocities and masses in terms of the aspect ratio (width divided by length), ice density, and rosette maximum dimension. Simple expressions for terminal velocity and mass as a function of bullet rosette maximum dimension are developed by incorporating new information on bullet aspect ratios.The general terminal velocity and mass relations are then applied to a case from the First International Satellite Cloud Climatology Project (ISCCP) Research Experiment (FIRE) 2, when size spectra from a balloon-borne ice crystal
Wang, Yuwen; Zhang, Yongyou; Zhang, Qingyun; Zou, Bingsuo; Schwingenschlogl, Udo
2016-01-01
We study the dynamics of an ultrafast single photon pulse in a one-dimensional waveguide two-point coupled with a Jaynes-Cummings system. We find that for any single photon input the transmissivity depends periodically on the separation between the two coupling points. For a pulse containing many plane wave components it is almost impossible to suppress transmission, especially when the width of the pulse is less than 20 times the period. In contrast to plane wave input, the waveform of the pulse can be modified by controlling the coupling between the waveguide and Jaynes-Cummings system. Tailoring of the waveform is important for single photon manipulation in quantum informatics. PMID:27653770
Kuzishchin, V. F.; Petrov, S. V.
2012-10-01
The problem of obtaining the mathematical model of a plant in the course of adaptively tuning the operating automatic closed-loop control systems is considered. A new method is proposed for calculating the parameters of a model with four free coefficients represented by two inertial sections with a time delay. The model parameters are calculated from the data of experiments on determining two points of a plant's complex frequency response. The results from checking the performance of the method in combination with obtaining information on the plant dynamics by applying the Fourier transform to the impulse transient response of the system are presented. The PID controller is tuned using a parameter scanning algorithm with directly checking the amplitude-frequency response of the closed-loop system, using which the stability margin can be calculated and different quality criteria can be applied.
Doha, E H; Abd-Elhameed, W M; Youssri, Y H
2015-09-01
Two families of certain nonsymmetric generalized Jacobi polynomials with negative integer indexes are employed for solving third- and fifth-order two point boundary value problems governed by homogeneous and nonhomogeneous boundary conditions using a dual Petrov-Galerkin method. The idea behind our method is to use trial functions satisfying the underlying boundary conditions of the differential equations and the test functions satisfying the dual boundary conditions. The resulting linear systems from the application of our method are specially structured and they can be efficiently inverted. The use of generalized Jacobi polynomials simplify the theoretical and numerical analysis of the method and also leads to accurate and efficient numerical algorithms. The presented numerical results indicate that the proposed numerical algorithms are reliable and very efficient.
Wang, Yuwen
2016-09-22
We study the dynamics of an ultrafast single photon pulse in a one-dimensional waveguide two-point coupled with a Jaynes-Cummings system. We find that for any single photon input the transmissivity depends periodically on the separation between the two coupling points. For a pulse containing many plane wave components it is almost impossible to suppress transmission, especially when the width of the pulse is less than 20 times the period. In contrast to plane wave input, the waveform of the pulse can be modified by controlling the coupling between the waveguide and Jaynes-Cummings system. Tailoring of the waveform is important for single photon manipulation in quantum informatics. © The Author(s) 2016.
Prediction of the Shear Wave Velocity from Compressional Wave Velocity for Gachsaran Formation
Directory of Open Access Journals (Sweden)
Parvizi Saeed
2015-10-01
Full Text Available Shear and compressional wave velocities, coupled with other petrophysical data, are very important for hydrocarbon reservoir characterization. In situ shear wave velocity (Vs is measured by some sonic logging tools. Shear velocity coupled with compressional velocity is vitally important in determining geomechanical parameters, identifying the lithology, mud weight design, hydraulic fracturing, geophysical studies such as VSP, etc. In this paper, a correlation between compressional and shear wave velocity is obtained for Gachsaran formation in Maroon oil field. Real data were used to examine the accuracy of the prediction equation. Moreover, the genetic algorithm was used to obtain the optimal value for constants of the suggested equation. Furthermore, artificial neural network was used to inspect the reliability of this method. These investigations verify the notion that the suggested equation could be considered as an efficient, fast, and cost-effective method for predicting Vs from Vp.
Design of correlation velocity measurement system based on virtual instrument%基于虚拟仪器的互相关流速测量系统设计
Institute of Scientific and Technical Information of China (English)
李文涛; 钱磊; 左鸿飞; 李忠虎
2014-01-01
This design combined computer simulation to experiment research, and established a cross-correlation measurement system based on the virtual instrument PXI platform through the research of the composition, working principle and mathematical models of the cross-correlation measurement system for two-phase flow. Based on the cross-correlation function module and auto-correlation function module provided by the LabVIEW signal computing section, two-phase flow measurement systems were designed respectively using cross-correlation function, polar cross-correlation function and differential autocorrela-tion function. The calculation results were compared through simulations to verify the accuracy of the sys-tems.%采用计算机模拟与实验相结合的方式，建立了基于虚拟仪器平台的互相关测量系统。系统采用LabVIEW函数选板中信号运算部分提供的互相关和自相关函数模块，设计了使用函数互相关、极性互相关和差动自相关3种算法实现互相关流速测量的程序。使用随机信号对上述3种算法进行验证，并对计算结果进行比较，验证结果表明互相关和差动自相关算法较为理想。
Ivashchenko, G.; Zhdanov, V. I.; Tugay, A. V.
2010-12-01
We analyse the quasar two-point correlation function (2pCF) within the redshift interval 0.8 10 h-1 Mpc, the parameter describing the large-scale infall to density inhomogeneities is β= 0.63 ± 0.10 with the linear bias b = 1.44 ± 0.22, which marginally (within 2σ) agrees with the linear theory of cosmological perturbations. We discuss possibilities to obtain a statistical estimate of the random component of quasar velocities (different from the large-scale infall). We note a slight dependence of the quasar velocity dispersion upon the 2pCF parameters in the region r < 2 Mpc.
Brand, Neal; Quintanilla, John A.
2013-01-01
Using a simultaneously falling softball as a stopwatch, the terminal velocity of a whiffle ball can be obtained to surprisingly high accuracy with only common household equipment. This classroom activity engages students in an apparently daunting task that nevertheless is tractable, using a simple model and mathematical techniques at their…
Wave propagation and group velocity
Brillouin, Léon
1960-01-01
Wave Propagation and Group Velocity contains papers on group velocity which were published during the First World War and are missing in many libraries. It introduces three different definitions of velocities: the group velocity of Lord Rayleigh, the signal velocity of Sommerfeld, and the velocity of energy transfer, which yields the rate of energy flow through a continuous wave and is strongly related to the characteristic impedance. These three velocities are identical for nonabsorbing media, but they differ considerably in an absorption band. Some examples are discussed in the last chapter
Polyakov Loop Correlations at Large N
Neuberger, Herbert
2014-01-01
I describe a study of the two-point single-eigenvalue distribution correlation function of Polyakov loops in the confined phase of four dimensional SU(N) YM theory at large N. The reasons for the interest in this correlation function are explained. Analytical and numerical results are presented. Brief conclusions are drawn.
Mean Velocity Estimation of Viscous Debris Flows
Institute of Scientific and Technical Information of China (English)
Hongjuan Yang; Fangqiang Wei; Kaiheng Hu
2014-01-01
The mean velocity estimation of debris flows, especially viscous debris flows, is an impor-tant part in the debris flow dynamics research and in the design of control structures. In this study, theoretical equations for computing debris flow velocity with the one-phase flow assumption were re-viewed and used to analyze field data of viscous debris flows. Results show that the viscous debris flow is difficult to be classified as a Newtonian laminar flow, a Newtonian turbulent flow, a Bingham fluid, or a dilatant fluid in the strict sense. However, we can establish empirical formulas to compute its mean velocity following equations for Newtonian turbulent flows, because most viscous debris flows are tur-bulent. Factors that potentially influence debris flow velocity were chosen according to two-phase flow theories. Through correlation analysis and data fitting, two empirical formulas were proposed. In the first one, velocity is expressed as a function of clay content, flow depth and channel slope. In the second one, a coefficient representing the grain size nonuniformity is used instead of clay content. Both formu-las can give reasonable estimate of the mean velocity of the viscous debris flow.
Institute of Scientific and Technical Information of China (English)
ZEMAN,V; ZEMAN,S
1999-01-01
The electric spark sensitivity of 12 nitramines was determined as the spark energy,EES, required for 50% initiation probability.A relationship between the EES and the square of detonation velocity of these substances was specified.The relationship was used to predict the EES values of nitramines not yet synthesised,particularly, the theoretically important compounds in the field of nitramine chemistry,such as 1-nitro-1-azaethylene,1,3-dinitro-1,3-diazacyclobutane and 1,3,5,7,9-pentanitro-1,3,5,7,9-pentaazacyclodecane.%通过测定12种硝胺50%发火概率下的静电火花能EES,建立了EES与爆速平方值(D2)的线性关系,以此可预估尚未合成的硝胺化合物,尤其是那些对硝胺化学有重要意义的化合物,如1-硝基-1-氮杂乙烯、1,3-二硝基-1,3-二氮杂环丁烷、1,3,5,7,9-五硝基-1,3,5,7,9-五氮杂环癸烷等的EES.
Roy, Arpita; Mahadevan, S.; Chakraborty, A.; Pathan, F. M.; Anandarao, B. G.
2010-01-01
The Physical Research Laboratory Advanced Radial-velocity All-sky Search (PARAS) is an efficient fiber-fed cross-dispersed high-resolution echelle spectrograph that will see first light in early 2010. This instrument is being built at the Physical Research laboratory (PRL) and will be attached to the 1.2m telescope at Gurushikhar Observatory at Mt. Abu, India. PARAS has a single-shot wavelength coverage of 370nm to 850nm at a spectral resolution of R 70000 and will be housed in a vacuum chamber (at 1x10-2 mbar pressure) in a highly temperature controlled environment. This renders the spectrograph extremely suitable for exoplanet searches with high velocity precision using the simultaneous Thorium-Argon wavelength calibration method. We are in the process of developing an automated data analysis pipeline for echelle data reduction and precise radial velocity extraction based on the REDUCE package of Piskunov & Valenti (2002), which is especially careful in dealing with CCD defects, extraneous noise, and cosmic ray spikes. Here we discuss the current status of the PARAS project and details and tests of the data analysis procedure, as well as results from ongoing PARAS commissioning activities.
Pulse Wave Velocity in the Carotid Artery
DEFF Research Database (Denmark)
Sørensen, Gertrud Laura; Jensen, Julie Brinck; Udesen, Jesper;
2008-01-01
The pulse wave velocity (PWV) in the carotid artery (CA) has been estimated based on ultrasound data collected by the experimental scanner RASMUS at DTU. Data is collected from one test subject using a frame rate (FR) of 4000 Hz. The influence of FRs is also investigated. The PWV is calculated from...... distension wave forms (DWF) estimated using cross-correlation. The obtained velocities give results in the area between 3-4 m/s, and the deviations between estimated PWV from two beats of a pulse are around 10%. The results indicate that the method presented is applicable for detecting the local PWV...
Sandage, Allan
1999-01-01
A distance-limited subset of the complete flux-limited sample of Sc galaxies in the Revised Shapley-Ames Catalog of Bright Galaxies is isolated by means of separate Spaenhauer diagrams for six individual van den Bergh luminosity class intervals from Sc I+I.2,.3 to Sc III-IV. The distribution functions of kinematic absolute B^0,i_T(220,50) magnitudes and 21 cm line widths, W_20, corrected to edge-on orientation, have been determined for the same six bins of luminosity class. The individual luminosity functions for each luminosity class are bounded on both the bright and faint ends, showing that the present sample includes no dwarf Sc spirals fainter than M(B_T)(220,50)=-18 belonging to luminosity classes I to III-IV, as defined by the regularity of the spiral pattern. Star-forming galaxies with spiral structures as regular as the ones found in these luminosity classes have absolute magnitudes brighter than M_B(H=50)=-18 and 21 cm line widths larger than W_20/sini=2v_rot(max)=165 km s^-1. Furthermore, the 21 cm line-width distributions move toward smaller rotational velocities as the luminosity classes change from I to III, showing that rotation is a principal parameter determining the regularity of the spiral pattern. Whether it is the only parameter awaits a similar investigation for spirals of all luminosity classes along the complete Hubble sequence. In particular, it has not yet been proved that all Im and Sm galaxies, where, by definition, the spiral arms are either lacking or are semichaotic, have absolute magnitudes that are fainter than M_B=-18 and whose 21 cm LWs are smaller than ~165 km s^-1, presumably because of smaller mass than the high-luminosity, regular spirals. The Teerikorpi ``cluster population incompleteness bias'' is demonstrated again. Here, however, as in Papers II-IV of this series, we use field galaxies to show that the slope and zero point of the Tully-Fisher (T-F) relation are systematically incorrect for flux-limited samples, the error
Institute of Scientific and Technical Information of China (English)
Eugene O'Riordan; Jeanne Stynes; Martin Stynes
2008-01-01
A system of m (≥ 2) linear convection-diffusion two-point boundary value problems is examined, where the diffusion term in each equation is multiplied by a small parameter e and the equations are coupled through their convective and reactive terms via matrices B and A respectively. This system is in general singularly perturbed. Unlike the case of a single equation, it does not satisfy a conventional maximum princi-ple. Certain hypotheses are placed on the coupling matrices B and A that ensure exis-tence and uniqueness of a solution to the system and also permit boundary layers in the components of this solution at only one endpoint of the domain; these hypotheses can be regarded as a strong form of diagonal dominance of B. This solution is decomposed into a sum of regular and layer components. Bounds are established on these compo-nents and their derivatives to show explicitly their dependence on the small parameterε. Finally, numerical methods consisting of upwinding on piecewise-uniform Shishkin meshes are proved to yield numerical solutions that are essentially first-order conver-gent, uniformly in ε, to the true solution in the discrete maximum norm. Numerical results on Shishkin meshes are presented to support these theoretical bounds.
Li, Cheng; Kauffmann, Guinevere; Boerner, Gerhard; Kang, Xi; Wang, Lan; 10.1111/j.1365-2966.2007.11518.x
2008-01-01
By comparing semi-analytic galaxy catalogues with data from the Sloan Digital Sky Survey (SDSS), we show that current galaxy formation models reproduce qualitatively the dependence of galaxy clustering and pairwise peculiar velocities on luminosity, but some subtle discrepancies with the data still remain. The comparisons are carried out by constructing a large set of mock galaxy redshift surveys that have the same selection function as the SDSS Data Release Four (DR4). The mock surveys are based on two sets of semi-analytic catalogues presented by Croton et al. and Kang et al. From the mock catalogues, we measure the redshift-space projected two-point correlation function, the power spectrum, and the pairwise velocity dispersion (PVD) in Fourier space and in configuration space, for galaxies in different luminosity intervals. We then compare these theoretical predictions with the measurements derived from the SDSS DR4. On large scales and for galaxies brighter than L*, both sets of mock catalogues agree well...
Solutions of the Wheeler-Feynman equations with discontinuous velocities.
de Souza, Daniel Câmara; De Luca, Jayme
2015-01-01
We generalize Wheeler-Feynman electrodynamics with a variational boundary value problem for continuous boundary segments that might include velocity discontinuity points. Critical-point orbits must satisfy the Euler-Lagrange equations of the action functional at most points, which are neutral differential delay equations (the Wheeler-Feynman equations of motion). At velocity discontinuity points, critical-point orbits must satisfy the Weierstrass-Erdmann continuity conditions for the partial momenta and the partial energies. We study a special setup having the shortest time-separation between the (infinite-dimensional) boundary segments, for which case the critical-point orbit can be found using a two-point boundary problem for an ordinary differential equation. For this simplest setup, we prove that orbits can have discontinuous velocities. We construct a numerical method to solve the Wheeler-Feynman equations together with the Weierstrass-Erdmann conditions and calculate some numerical orbits with discontinuous velocities. We also prove that the variational boundary value problem has a unique solution depending continuously on boundary data, if the continuous boundary segments have velocity discontinuities along a reduced local space.
Solutions of the Wheeler-Feynman equations with discontinuous velocities
de Souza, Daniel Câmara; De Luca, Jayme
2015-01-01
We generalize Wheeler-Feynman electrodynamics with a variational boundary value problem for continuous boundary segments that might include velocity discontinuity points. Critical-point orbits must satisfy the Euler-Lagrange equations of the action functional at most points, which are neutral differential delay equations (the Wheeler-Feynman equations of motion). At velocity discontinuity points, critical-point orbits must satisfy the Weierstrass-Erdmann continuity conditions for the partial momenta and the partial energies. We study a special setup having the shortest time-separation between the (infinite-dimensional) boundary segments, for which case the critical-point orbit can be found using a two-point boundary problem for an ordinary differential equation. For this simplest setup, we prove that orbits can have discontinuous velocities. We construct a numerical method to solve the Wheeler-Feynman equations together with the Weierstrass-Erdmann conditions and calculate some numerical orbits with discontinuous velocities. We also prove that the variational boundary value problem has a unique solution depending continuously on boundary data, if the continuous boundary segments have velocity discontinuities along a reduced local space.
Transverse velocity shifts in protostellar jets: rotation or velocity asymmetries?
De Colle, Fabio; Riera, Angels
2016-01-01
Observations of several protostellar jets show systematic differences in radial velocity transverse to the jet propagation direction, which have been interpreted as evidence of rotation in the jets. In this paper we discuss the origin of these velocity shifts, and show that they could be originated by rotation in the flow, or by side to side asymmetries in the shock velocity, which could be due to asymmetries in the jet ejection velocity/density or in the ambient medium. For typical poloidal jet velocities (~ 100-200 km/s), an asymmetry >~ 10% can produce velocity shifts comparable to those observed. We also present three dimensional numerical simulations of rotating, precessing and asymmetric jets, and show that, even though for a given jet there is a clear degeneracy between these effects, a statistical analysis of jets with different inclination angles can help to distinguish between the alternative origins of transverse velocity shifts. Our analysis indicate that side to side velocities asymmetries could ...
Maximum Likelihood Blood Velocity Estimator Incorporating Properties of Flow Physics
DEFF Research Database (Denmark)
Schlaikjer, Malene; Jensen, Jørgen Arendt
2004-01-01
The aspect of correlation among the blood velocities in time and space has not received much attention in previous blood velocity estimators. The theory of fluid mechanics predicts this property of the blood flow. Additionally, most estimators based on a cross-correlation analysis are limited...... of simulated and in vivo data from the carotid artery. The estimator is meant for two-dimensional (2-D) color flow imaging. The resulting mathematical relation for the estimator consists of two terms. The first term performs a cross-correlation analysis on the signal segment in the radio frequency (RF......)-data under investigation. The flow physic properties are exploited in the second term, as the range of velocity values investigated in the cross-correlation analysis are compared to the velocity estimates in the temporal and spatial neighborhood of the signal segment under investigation. The new estimator...
Richter, P; Fox, A J; Wakker, B P; Lehner, N; Bekhti, N Ben; Fechner, C; Wendt, M; Howk, J C; Muzahid, S; Ganguly, R; Charlton, J C
2016-01-01
To characterize the absorption properties of this circumgalactic medium (CGM) and its relation to the LG we present the so-far largest survey of metal absorption in Galactic high-velocity clouds (HVCs) using archival ultraviolet (UV) spectra of extragalactic background sources. The UV data are obtained with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope (HST) and are supplemented by 21 cm radio observations of neutral hydrogen. Along 262 sightlines we measure metal absorption in the lines of SiII, SiIII, CII, and CIV and associated HI 21 cm emission in HVCs in the velocity range |v_LSR|=100-500 km s^-1. With this unprecedented large HVC sample we were able to improve the statistics on HVC covering fractions, ionization conditions, small-scale structure, CGM mass, and inflow rate. For the first time, we determine robustly the angular two point correlation function of the high-velocity absorbers, systematically analyze antipodal sightlines on the celestial sphere, and compare the absor...
Dark Matter Velocity Spectroscopy.
Speckhard, Eric G; Ng, Kenny C Y; Beacom, John F; Laha, Ranjan
2016-01-22
Dark matter decays or annihilations that produce linelike spectra may be smoking-gun signals. However, even such distinctive signatures can be mimicked by astrophysical or instrumental causes. We show that velocity spectroscopy-the measurement of energy shifts induced by relative motion of source and observer-can separate these three causes with minimal theoretical uncertainties. The principal obstacle has been energy resolution, but upcoming experiments will have the precision needed. As an example, we show that the imminent Astro-H mission can use Milky Way observations to separate possible causes of the 3.5-keV line. We discuss other applications.
Minimum Length - Maximum Velocity
Panes, Boris
2011-01-01
We study a framework where the hypothesis of a minimum length in space-time is complemented with the notion of reference frame invariance. It turns out natural to interpret the action of the obtained reference frame transformations in the context of doubly special relativity. As a consequence of this formalism we find interesting connections between the minimum length properties and the modified velocity-energy relation for ultra-relativistic particles. For example we can predict the ratio between the minimum lengths in space and time using the results from OPERA about superluminal neutrinos.
Dark Matter Velocity Spectroscopy
Speckhard, Eric G; Beacom, John F; Laha, Ranjan
2016-01-01
Dark matter decays or annihilations that produce line-like spectra may be smoking-gun signals. However, even such distinctive signatures can be mimicked by astrophysical or instrumental causes. We show that velocity spectroscopy-the measurement of energy shifts induced by relative motion of source and observer-can separate these three causes with minimal theoretical uncertainties. The principal obstacle has been energy resolution, but upcoming and proposed experiments will make significant improvements. As an example, we show that the imminent Astro-H mission can use Milky Way observations to separate possible causes of the 3.5-keV line. We discuss other applications.
Advective surface velocity in the north west Pacific derived from NOAA AVHRR images
Digital Repository Service at National Institute of Oceanography (India)
Pankajakshan, T.; Akiyama, M.; Okada, Y.; Sugimori, Y.
Using sequential AVHRR images in November 1983, nearsurface advective velocities are derived in the region Kuroshio south of Japan. For deriving the velocities two methods are used. One is the Method of Cross Correlation (MCC), using image pair...
Video measurements of fluid velocities and water levels in breaking waves
CSIR Research Space (South Africa)
Govender, K
2002-01-01
Full Text Available The cost-effective measurement of the velocity flow fields in breaking water waves, using particle and correlation image velocimetry, is described. The fluid velocities are estimated by tracking the motion of neutrally buoyant particles and aeration...
Institute of Scientific and Technical Information of China (English)
韩笑纯; 黄靖正; 方晨; 曾贵华
2015-01-01
In the experiment presented in the paper, HBT (Hanbury-Brown and Twiss) interferometer is used to measure the second-order correlation function (G2) for two entangled photons, denoted as signal and idle ones, generated by the spontaneous parametric down-conversion process. When an extra optical fiber is inserted in the signal’s path, the arrival times of these two photons are different, so that the length of the fiber can be estimated by measuring the time offset in the G2 function. As the laser light we used is not monochromatic, the experimental result is affected by the group velocity dispersion (GVD). Light of different wavelength has different velocity and leads to different travelling time in the fiber. Through calculation, we find that the G2 function of each wavelength has the same shape but different center time offset. Thus, the final G2 function, as a superimposition of the functions with different wavelengths, is broadened in a long-distance measurement, which seriously reduces the estimation accuracy. We analyze this phenomenon in both theory and exper-iment, and the experimental results fit our theoretical simulations quite well. In the theoretical analysis, we find that the group velocity dispersion introduces an additional time offset to the final G2 function which is proportional to the total time offset. In our experiment, this additional time offset is about 1% of the total time offset. In particular, this effect results in a 63600 ps extra time offset, which can be compensated in post process, with a time accuracy of about 1 ps. This paper focuses on the G2 function affected by the group velocity dispersion, and also calculates the additional time offset produced by group velocity dispersion, and thus gives a method to compensate the additional time offset through calculation.%HBT干涉是量子测量中的一种重要手段，其通过计算光场的二阶关联函数而得到测量结果。在长距离测距中，光场的二阶关联函数
Velocity centroids as tracers of the turbulent velocity statistics
Lazarian, A E A
2004-01-01
We use the results of magnetohydrodynamic (MHD) simulations to emulate spectroscopic observations, and produce maps of variations of velocity centroids to study their scaling properties. We compare them with those of the underlying velocity field, and analytic predictions presented in a previous paper (Lazarian & Esquivel 2003). We tested, with success, a criteria for recovering velocity statistics from velocity centroids derived in our previous work. That is, if >> (where S is a 2D map of ``unnormalized'', v velocity, and I integrated intensity map -column density-), then the structure function of the centroids is dominated by the structure function of velocity. We show that it is possible to extract the velocity statistics using centroids for subsonic and mildly supersonic turbulence (e.g. Mach numbers ~2.5). While, towards higher Mach numbers other effects could affect significantly the statistics of centroids.
Statistics of Velocity from Spectral Data Modified Velocity Centroids
Lazarian, A
2003-01-01
We address the problem of studying interstellar (ISM) turbulence using spectral line data. We construct a measure that we term modified velocity centroids (MVCs) and derive an analytical solution that relates the 2D spectra of the modified centroids with the underlying 3D velocity spectrum. We test our results using synthetic maps constructed with data obtained through simulations of compressible MHD turbulence. We prove that the MVCs are able to restore the underlying spectrum of turbulent velocity. We show that the modified velocity centroids (MVCs) are complementary to the the Velocity Channel Analysis (VCA) technique that we introduced earlier. Employed together they make determining of the velocity spectral index more reliable. At the same time we show that MVCs allow to determine velocity spectra when the underlying statistics is not a power law and/or the turbulence is subsonic.
Institute of Scientific and Technical Information of China (English)
杨超; 黄达; 张永兴
2014-01-01
以锦屏I级水电站坝址大理岩岩体原位变形试验和勘察结果为例，在分析岩体变形模量Em、纵波波速Vp以及岩体质量指标Q值间的两两相关关系的基础上，利用Copula函数能够描述多变量相关性的优点，构造了拟合Em，Vp和Q值间关系的最优Copula函数，并在岩体变形模量估值中进行运用。研究结果表明，三维Clayton Copula函数是拟合岩体波速Vp，Q值和变形模量mE间相关关系最优Copula函数。利用构造的Em-Vp-Q间关系的最优Copula函数求条件概率，可在已知岩体Vp和Q值条件下计算其他方法对变形模量估值的保证率，或者计算具有一定保证率的岩体变形模量估值，得到具有最优拟合的变形模量估值。该方法建立多因素间的相关关系，使现场试验和勘察的数据得到充分利用，为建立岩体变形模量与岩体参数间相关关系及估值提供一种新的途径。%There are strong correlations between deformation modulus Em of rock mass and physico-mechanical parameters or rock mass quality indices. These correlations were usually used for the estimation of deformation modulus. However,most of these correlations are established between a single parameter and deformation modulus;the other related parameters obtained from the in-situ tests or engineering geology survey are underused. Based on the correlation investigation between deformation modulus and wave velocity( Vp),deformation modulus and Q system,wave velocity and Q system of marble rock mass in Jinping I hydropower station,taking the advantage of Copula functions that can describe the correlations of multivariate,the optimal fitting Copula function of Em- PV -Q is selected. Then it has been applied to the estimation of deformation modulus. The result m shows that Clayton Copula is the optimal fitting Copula function of Em-Vp-Q. The guaranteed rates of estimated by other methods can be obtained;and the estimation of mE can be
Minimal information in velocity space
Evrard, Guillaume
1995-01-01
Jaynes' transformation group principle is used to derive the objective prior for the velocity of a non-zero rest-mass particle. In the case of classical mechanics, invariance under the classical law of addition of velocities, leads to an improper constant prior over the unbounded velocity space of classical mechanics. The application of the relativistic law of addition of velocities leads to a less simple prior. It can however be rewritten as a uniform volumetric distribution if the relativistic velocity space is given a non-trivial metric.
Noworyta, Krzysztof; Marczak, Renata; Tylenda, Rafal; Sobczak, Janusz W; Chitta, Raghu; Kutner, Wlodzimierz; D'Souza, Francis
2007-02-27
The effect of "two-point" interactions of Zn(II) and Co(II) metalloporphyrins, bearing 15-crown-5 ether peripheral substituents, on their assembling in Langmuir and Langmuir-Blodgett (LB) films was investigated. That is, simultaneously, the central metal ion of the porphyrin was axially ligated by a nitrogen-containing ligand in the emerged part of the Langmuir film on one hand, and a suitably selected cation pertaining in the subphase solution was supramolecularly complexed by the crown ether moiety in the submerged part of the film on the other. The compression and polarity properties of the Langmuir films of the derivatized free-base 5,10,15-triphenyl-20-(benzo-15-crown-5)porphyrin, H2(TPMCP), and the corresponding cobalt(II) and zinc(II) metalloporphyrins, denoted as Co(TPMCP) and Zn(TPCMP), respectively, as well as inclusion complexes of the metalloporphyrins with selected cations were investigated. For the axial ligation of Zn(II) and Co(II), pyrazine (pyz) and 4,4'-bipyridnine (bpy) aromatic as well as piperazine (ppz) and 1,4-diazabicyclo[2.2.2]octane (DABCO) cyclic heteroaliphatic ligands were selected. The films were formed on the water subphase solution in the absence and presence of LiCl, NaCl, or NH4Cl. The Langmuir films were built of monolayer J-type aggregates of tilted porphyrin macrocycles. The porphyrins formed rather labile complexes with the cations in the subphase. Nevertheless, the XPS analysis revealed that these cations were LB transferred together with the porphyrins onto solid substrates. In the Co(TPMCP) Langmuir films formed on the water subphases, Co(II) was complexed by aromatic but not cyclic heteroaliphatic ligands, while, in these films formed on the NaCl subphase solutions, the metalloporphyrin was also complexed by DABCO. In Langmuir films spread on alkaline subphase solutions, both aromatic and heteroaliphatic ligands formed complexes with Co(TPMCP) of different stoichiometries. The X-ray reflectivity and GIXD measurements
Institute of Scientific and Technical Information of China (English)
Yi Yao; Jia-Hui Zhang; Xiao-Fang Tang; Chen He; Yuan-Liang Ma; Jing-Jing Xu; Ying Song
2016-01-01
Background:Platelet function tests are widely used in clinical practice to guide personalized antiplatelet therapy.In China,the thromboelastography (TEG) test has been well accepted in clinics,whereas VerifyNow,mainly used for scientific research,has not been used in routine clinical practice.The aim of the current study was to compare these two point-of-care platelet function tests and to analyze the consistency between the two tests for evaluating on-clopidogrel platelet reactivity in Chinese acute myocardial infarction patients undergoing percutaneous coronary intervention (PCI).Methods:A total of 184 patients admitted to Fuwai Hospital between August 2014 and May 2015 were enrolled in the study.On-clopidogrel platelet reactivity was assessed 3 days after PCI by TEG and VerifyNow using adenosine diphosphate as an agonist.Based on the previous reports,an inhibition of platelet aggregation (IPA) ＜30％ for TEG or a P2Y12 reaction unit (PRU) ＞230 for VerifyNow was defined as high on-clopidogrel platelet reactivity (HPR).An IPA ＞70％ or a PRU ＜178 was defined as low on-clopidogrel platelet reactivity (LPR).Correlation and agreement between the two methods were analyzed using the Spearman correlation coefficient (r) and kappa value (κ),respectively.Results:Our results showed that VerifyNow and TEG had a moderate but significant correlation in evaluating platelet reactivity (r =-0.511).A significant although poor agreement (κ =0.225) in identifying HPR and a significantly moderate agreement in identifying LPR (κ =0.412) were observed between TEG and VerifyNow.By using TEG as the reference for comparison,the cutoffvalues of VerifyNow for the Chinese patients in this study were identified as PRU ＞205 for HPR and PRU ＜169 for LPR.Conclusions:By comparing VerifyNow to TEG which has been widely used in clinics,VerifyNow could be an attractive alternative to TEG for monitoring on-clopidogrel platelet reactivity in Chinese patients.
Institute of Scientific and Technical Information of China (English)
苑云霞; 岳晓奎; 娄云峰
2011-01-01
The two-point boundary value problem (TPBVP) of a leader-follower spacecraft formation flying was studied. Aiming at unperturbed elliptical reference orbits, the state transfer matrix representing actual relative position and velocity was derived, and the first-order analytical solution of TPBVP is obtained, which can deal with the problems of the specified rendezvous time, fuel optimization and compromise between fuel and time, and is applicable to the periodic and non-periodic relative motion. The simulation results show that the normalized accuracy of this solution achieves 10~6 level. Furthermore, the fuel cost of relative transfer increases with eccentricity increasing, and decreases with semi-major axis increasing, and appears periodic change with initial true anomaly increasing, and decreases as the transfer time increasing.%针对无摄椭圆轨道,推导了表示真实相对位置速度的状态转移矩阵,进而推导出了相对运动两点边界值问题的一阶解析解.所得结果不仅可指定转移时间、还可在时间范围内进行全局的燃料优化或在时间和燃料两者间折中；对于周期和非周期的相对运动均适用.仿真结果表明此解的归一化精度达到10-6.进一步的仿真发现相对转移过程的燃料消耗会随目标轨道偏心率的增加而增加；随长半轴的增加而减少；随初始真近点角的增加呈现周期性变化；随着转移时间增加,燃料消耗的总趋势是减少的.
Topology dependent epidemic spreading velocity in weighted networks
Duan, Wei; Quax, Rick; Lees, Michael; Qiu, Xiaogang; Sloot, Peter M. A.
2014-12-01
Many diffusive processes occur on structured networks with weighted links, such as disease spread by airplane transport or information diffusion in social networks or blogs. Understanding the impact of weight-connectivity correlations on epidemic spreading in weighted networks is crucial to support decision-making on disease control and other diffusive processes. However, a real understanding of epidemic spreading velocity in weighted networks is still lacking. Here we conduct a numerical study of the velocity of a Reed-Frost epidemic spreading process in various weighted network topologies as a function of the correlations between edge weights and node degrees. We find that a positive weight-connectivity correlation leads to a faster epidemic spreading compared to an unweighted network. In contrast, we find that both uncorrelated and negatively correlated weight distributions lead to slower spreading processes. In the case of positive weight-connectivity correlations, the acceleration of spreading velocity is weak when the heterogeneity of weight distribution increases.
Cognitive regulation of saccadic velocity by reward prospect.
Chen, Lewis L; Hung, Leroy Y; Quinet, Julie; Kosek, Kevin
2013-08-01
It is known that expectation of reward speeds up saccades. Past studies have also shown the presence of a saccadic velocity bias in the orbit, resulting from a biomechanical regulation over varying eccentricities. Nevertheless, whether and how reward expectation interacts with the biomechanical regulation of saccadic velocities over varying eccentricities remains unknown. We addressed this question by conducting a visually guided double-step saccade task. The role of reward expectation was tested in monkeys performing two consecutive horizontal saccades, one associated with reward prospect and the other not. To adequately assess saccadic velocity and avoid adaptation, we systematically varied initial eye positions, saccadic directions and amplitudes. Our results confirmed the existence of a velocity bias in the orbit, i.e., saccadic peak velocity decreased linearly as the initial eye position deviated in the direction of the saccade. The slope of this bias increased as saccadic amplitudes increased. Nevertheless, reward prospect facilitated velocity to a greater extent for saccades away from than for saccades toward the orbital centre, rendering an overall reduction in the velocity bias. The rate (slope) and magnitude (intercept) of reward modulation over this velocity bias were linearly correlated with amplitudes, similar to the amplitude-modulated velocity bias without reward prospect, which presumably resulted from a biomechanical regulation. Small-amplitude (≤ 5°) saccades received little modulation. These findings together suggest that reward expectation modulated saccadic velocity not as an additive signal but as a facilitating mechanism that interacted with the biomechanical regulation.
Directory of Open Access Journals (Sweden)
Giovanni Corato
2014-10-01
Full Text Available Flow velocity measurements using point-velocity meters are normally obtained by sampling one, two or three velocity points per vertical profile. During high floods their use is inhibited due to the difficulty of sampling in lower portions of the flow area. Nevertheless, the application of standard methods allows estimation of a parameter, α, which depends on the energy slope and the Manning roughness coefficient. During high floods, monitoring of velocity can be accomplished by sampling the maximum velocity, umax, only, which can be used to estimate the mean flow velocity, um, by applying the linear entropy relationship depending on the parameter, M, estimated on the basis of historical observed pairs (um, umax. In this context, this work attempts to analyze if a correlation between α and M holds, so that the monitoring for high flows can be addressed by exploiting information from standard methods. A methodology is proposed to estimate M from α, by coupling the “historical” information derived by standard methods, and “new” information from the measurement of umax surmised at later times. Results from four gauged river sites of different hydraulic and geometric characteristics have shown the robust estimation of M based on α.
Geotail observations of FTE velocities
Directory of Open Access Journals (Sweden)
G. I. Korotova
2009-01-01
Full Text Available We discuss the plasma velocity signatures expected in association with flux transfer events (FTEs. Events moving faster than or opposite the ambient media should generate bipolar inward/outward (outward/inward flow perturbations normal to the nominal magnetopause in the magnetosphere (magnetosheath. Flow perturbations directly upstream and downstream from the events should be in the direction of event motion. Flows on the flanks should be in the direction opposite the motion of events moving at subsonic and subAlfvénic speeds relative to the ambient plasma. Events moving with the ambient flow should generate no flow perturbations in the ambient plasma. Alfvén waves propagating parallel (antiparallel to the axial magnetic field of FTEs may generate anticorrelated (correlated magnetic field and flow perturbations within the core region of FTEs. We present case studies illustrating many of these signatures. In the examples considered, Alfvén waves propagate along event axes away from the inferred reconnection site. A statistical study of FTEs observed by Geotail over a 3.5-year period reveals that FTEs within the magnetosphere invariably move faster than the ambient flow, while those in the magnetosheath move both faster and slower than the ambient flow.
Development of an optimal velocity selection method with velocity obstacle
Energy Technology Data Exchange (ETDEWEB)
Kim, Min Geuk; Oh, Jun Ho [KAIST, Daejeon (Korea, Republic of)
2015-08-15
The Velocity obstacle (VO) method is one of the most well-known methods for local path planning, allowing consideration of dynamic obstacles and unexpected obstacles. Typical VO methods separate a velocity map into a collision area and a collision-free area. A robot can avoid collisions by selecting its velocity from within the collision-free area. However, if there are numerous obstacles near a robot, the robot will have very few velocity candidates. In this paper, a method for choosing optimal velocity components using the concept of pass-time and vertical clearance is proposed for the efficient movement of a robot. The pass-time is the time required for a robot to pass by an obstacle. By generating a latticized available velocity map for a robot, each velocity component can be evaluated using a cost function that considers the pass-time and other aspects. From the output of the cost function, even a velocity component that will cause a collision in the future can be chosen as a final velocity if the pass-time is sufficiently long enough.
Velocity dependant splash behaviour
Hamlett, C. A. E.; Shirtcliffe, N. J.; McHale, G.; Ahn, S.; Doerr, S. H.; Bryant, R.; Newton, M. I.
2012-04-01
Extreme soil water repellency can occur in nature via condensation of volatile organic compounds released during wildfires and can lead to increased erosion rate. Such extreme water repellent soil can be classified as superhydrophobic and shares similar chemical and topographical features to specifically designed superhydrophobic surfaces. Previous studies using high speed videography to investigate single droplet impact behaviour on artificial superhydrophobic have revealed three distinct modes of splash behaviour (rebound, pinned and fragmentation) which are dependent on the impact velocity of the droplet. In our studies, using high-speed videography, we show that such splash behaviour can be replicated on fixed 'model' water repellent soils (hydrophobic glass beads/particles). We show that the type of splash behaviour is dependent on both the size and chemical nature of the fixed particles. The particle shape also influences the splash behaviour as shown by drop impact experiments on fixed sand samples. We have also studied soil samples, as collected from the field, which shows that the type of droplet splash behaviour can lead to enhanced soil particle transport.
Examples of Vector Velocity Imaging
DEFF Research Database (Denmark)
Hansen, Peter M.; Pedersen, Mads M.; Hansen, Kristoffer L.
2011-01-01
To measure blood flow velocity in vessels with conventional ultrasound, the velocity is estimated along the direction of the emitted ultrasound wave. It is therefore impossible to obtain accurate information on blood flow velocity and direction, when the angle between blood flow and ultrasound wa...... with a 90° angle on the vessel. Moreover secondary flow in the abdominal aorta is illustrated by scanning on the transversal axis....
Institute of Scientific and Technical Information of China (English)
赵盼盼; 陈九辉; Michel Campillo; 刘启元; 李昱; 李顺成; 郭飚; 王峻; 齐少华
2012-01-01
A temporal seismic array consisted of 297 broadband seismographs was deployed in Western Sichuan (100°~105°E, 26°~32°N) in 2006, and the observation covered the great 2008 Wenchuan earthquake. We used the continuous three-component ambient noise data from January, 2007 to October, 2008, recorded at the 137 stations north of 29°N, to study the crust seismic velocity changes before and after the earthquake. For every single station, three autocorrelation functions (ACF) and three cross correlation functions (CCF) are calculated and stacked in 10 days for three components of noise data respectively. Then we estimated the relative velocity changes by measuring travel time shifts between the 50-day-moving-average stacks and the reference empirical correlation functions. We obtained the characteristic of spatial distribution of relative velocity changes caused by Wenchuan earthquake. Our results indicate that ACF analysis can get similar coseismic velocity changes pattern with the CCF method, and the distribution of coseismic velocity changes is closely correlated with the volumetric strain changes during the Wenchuan earthquake. We also found an area of velocity increase in the region where the Longmenshan Fault zone adjoins the Xianshuihe Fault zone. This area is consistent with the faults that the Coulomb stress increased by the occurrence of the Wenchuan earthquake as predicted by the source mechanism and surface deformation. We also found that the crustal velocity increase lasted for about 2 months and then decreased with ubiquitous stress release in the studying region.%2006年中国地震局地质研究所地震动力学国家重点实验室在川西地区(100°E～105°E,26°N～32°N)布设了由297个宽频带地震台组成的密集流动地震观测台阵.本文利用川西流动地震台阵29°N以北地区的137个台站2007年1月至2008年10月的连续三分量地震环境噪声记录,研究了汶川地震震前震后地壳速度变化特征.借助
Radial velocities of southern visual multiple stars
Energy Technology Data Exchange (ETDEWEB)
Tokovinin, Andrei [Cerro Tololo Inter-American Observatory, Casilla 603, La Serena (Chile); Pribulla, Theodor [Astronomical Institute, Slovak Academy of Sciences, 059 60 Tatranská Lomnica (Slovakia); Fischer, Debra, E-mail: atokovinin@ctio.noao.edu, E-mail: pribulla@ta3.sk, E-mail: debra.fischer@gmail.com [Department of Astronomy, Yale University, New Haven, CT 06511 (United States)
2015-01-01
High-resolution spectra of visual multiple stars were taken in 2008–2009 to detect or confirm spectroscopic subsystems and to determine their orbits. Radial velocities of 93 late-type stars belonging to visual multiple systems were measured by numerical cross-correlation. We provide the individual velocities, the width, and the amplitude of the Gaussians that approximate the correlations. The new information on the multiple systems resulting from these data is discussed. We discovered double-lined binaries in HD 41742B, HD 56593C, and HD 122613AB, confirmed several other known subsystems, and constrained the existence of subsystems in some visual binaries where both components turned out to have similar velocities. The orbits of double-lined subsystems with periods of 148 and 13 days are computed for HD 104471 Aa,Ab and HD 210349 Aa,Ab, respectively. We estimate individual magnitudes and masses of the components in these triple systems and update the outer orbit of HD 104471 AB.
Advanced Ice Velocity Mapping Using Landsat 8
Klinger, M. J.; Scambos, T. A.; Fahnestock, M. A.; Haran, T. M.
2014-12-01
Improved image-to-image cross correlation software is applied to pairs of sequential Landsat 8 satellite imagery to accurately measure ice surface velocity over ice sheets and glaciers (±0.1 pixel displacement, 15 meter pixels). The high radiometric fidelity of Landsat 8's panchromatic band (12-bit), and exceptional geolocation accuracy (typically ±5 m) supports the generation of ice velocity fields over very short time intervals (e.g., 16-, 32-, or 48-day repeat images of the same scene location). The high radiometry supports velocity mapping in areas with very subtle topographic detail, including un-crevassed sastrugi regions on ice dome flanks or the ice sheet interior. New Python-based software presently under development (named PyCorr), takes two sequential Landsat 8 OLI scenes (or suitably processed ETM+ or TM scenes) and matches small sub-scenes ('chips') between the images based on similarity in their gray-scale value patterns, using an image correlation algorithm. Peak fitting in the region of maximum correlation for a chip pair yields sub-pixel fits to the feature offset vector. Vector editing after the image correlation runs seeks to eliminate spurious and cloud-impacted vectors, and correct residual geo-location error. This processing is based on plausible values of ice strain rates and known areas of near-zero ice flow (rock outcrops, ice dome areas, etc.). In preliminary processing, we have examined ~800 Landsat 8 image pairs having <20% cloud cover spanning the near-coastal Antarctic ice sheet during the 2013-14 summer season.
Sodium Velocity Maps on Mercury
Potter, A. E.; Killen, R. M.
2011-01-01
The objective of the current work was to measure two-dimensional maps of sodium velocities on the Mercury surface and examine the maps for evidence of sources or sinks of sodium on the surface. The McMath-Pierce Solar Telescope and the Stellar Spectrograph were used to measure Mercury spectra that were sampled at 7 milliAngstrom intervals. Observations were made each day during the period October 5-9, 2010. The dawn terminator was in view during that time. The velocity shift of the centroid of the Mercury emission line was measured relative to the solar sodium Fraunhofer line corrected for radial velocity of the Earth. The difference between the observed and calculated velocity shift was taken to be the velocity vector of the sodium relative to Earth. For each position of the spectrograph slit, a line of velocities across the planet was measured. Then, the spectrograph slit was stepped over the surface of Mercury at 1 arc second intervals. The position of Mercury was stabilized by an adaptive optics system. The collection of lines were assembled into an images of surface reflection, sodium emission intensities, and Earthward velocities over the surface of Mercury. The velocity map shows patches of higher velocity in the southern hemisphere, suggesting the existence of sodium sources there. The peak earthward velocity occurs in the equatorial region, and extends to the terminator. Since this was a dawn terminator, this might be an indication of dawn evaporation of sodium. Leblanc et al. (2008) have published a velocity map that is similar.
Institute of Scientific and Technical Information of China (English)
王嘉悦; 翁文国; 张小乐
2014-01-01
Study on the velocity characteristics of pedestrian behaviors can predict pedestrian movement trend dur -ing real mass events in crowded places .It is very important to warn the abnormal pedestrian behaviors and prevent the occurrence of excessive crowd or even stampede , thus ensure the large-scale mass activities successfully and safely .In this paper , empirical study was conducted on the large scale and high density of people ’ behaviors in the core area of a domestic major city , by a cross-correlation algorithm .The velocity of pedestrian movement was ex-tracted at different speeds .In addition, the average velocities of pedestrians were compared with four passages to the scenic spot , to investigate the motion characteristics of pedestrians .The results showed that the velocities on u-nidirectional path were large and the movement directions were nearly parallel to the boundaries .However , the ve-locities on two-way passage were changed due to the damping effect of the crowd .Some effective suggestions are thus proposed for the organization and the crowd evacuation of large-scale mass activities .The results can also pro-vide some theoretical information to risk prevention and control for stampede , make the emergency plan for stam-pede and the safety scheme for crowd activities .%研究人群密集场所的人群运动速度特征可以预测人群的运动趋势，在大型活动组织过程中可以对异常人群运动做出预警，避免过度的拥挤及踩踏事件的发生，保证大型群体性活动的安全顺利开展。利用国内某重要城市核心区公共场所人群运动的视频图像，通过互相关算法提取该场所人群的运动速度，并进一步比较通往景区的四条不同路径上人群运动速度的差异性，分析其人群运动特征。分析结果表明单向通道的人群运动速度较大且运动方向基本与通道的两侧边界平行，而双向通道中由于人群中阻尼效应的影响，人
Introduction to vector velocity imaging
DEFF Research Database (Denmark)
Jensen, Jørgen Arendt; Udesen, Jesper; Hansen, Kristoffer Lindskov;
Current ultrasound scanners can only estimate the velocity along the ultrasound beam and this gives rise to the cos() factor on all velocity estimates. This is a major limitation as most vessels are close to perpendicular to the beam. Also the angle varies as a function of space and time making...
Instantaneous Velocity Using Photogate Timers
Wolbeck, John
2010-01-01
Photogate timers are commonly used in physics laboratories to determine the velocity of a passing object. In this application a card attached to a moving object breaks the beam of the photogate timer providing the time for the card to pass. The length L of the passing card can then be divided by this time to yield the average velocity (or speed)…
Kriging Interpolating Cosmic Velocity Field
Yu, Yu; Jing, Yipeng; Zhang, Pengjie
2015-01-01
[abridge] Volume-weighted statistics of large scale peculiar velocity is preferred by peculiar velocity cosmology, since it is free of uncertainties of galaxy density bias entangled in mass-weighted statistics. However, measuring the volume-weighted velocity statistics from galaxy (halo/simulation particle) velocity data is challenging. For the first time, we apply the Kriging interpolation to obtain the volume-weighted velocity field. Kriging is a minimum variance estimator. It predicts the most likely velocity for each place based on the velocity at other places. We test the performance of Kriging quantified by the E-mode velocity power spectrum from simulations. Dependences on the variogram prior used in Kriging, the number $n_k$ of the nearby particles to interpolate and the density $n_P$ of the observed sample are investigated. (1) We find that Kriging induces $1\\%$ and $3\\%$ systematics at $k\\sim 0.1h{\\rm Mpc}^{-1}$ when $n_P\\sim 6\\times 10^{-2} ({\\rm Mpc}/h)^{-3}$ and $n_P\\sim 6\\times 10^{-3} ({\\rm Mpc...
A MAGNETIC CALIBRATION OF PHOTOSPHERIC DOPPLER VELOCITIES
Energy Technology Data Exchange (ETDEWEB)
Welsch, Brian T.; Fisher, George H. [Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450 (United States); Sun, Xudong [W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305 (United States)
2013-03-10
The zero point of measured photospheric Doppler shifts is uncertain for at least two reasons: instrumental variations (from, e.g., thermal drifts); and the convective blueshift, a known correlation between intensity and upflows. Accurate knowledge of the zero point is, however, useful for (1) improving estimates of the Poynting flux of magnetic energy across the photosphere, and (2) constraining processes underlying flux cancellation, the mutual apparent loss of magnetic flux in closely spaced, opposite-polarity magnetogram features. We present a method to absolutely calibrate line-of-sight (LOS) velocities in solar active regions (ARs) near disk center using three successive vector magnetograms and one Dopplergram coincident with the central magnetogram. It exploits the fact that Doppler shifts measured along polarity inversion lines (PILs) of the LOS magnetic field determine one component of the velocity perpendicular to the magnetic field, and optimizes consistency between changes in LOS flux near PILs and the transport of transverse magnetic flux by LOS velocities, assuming that ideal electric fields govern the magnetic evolution. Previous calibrations fitted the center-to-limb variation of Doppler velocities, but this approach cannot, by itself, account for residual convective shifts at the limb. We apply our method to vector magnetograms of AR 11158, observed by the Helioseismic and Magnetic Imager aboard the Solar Dynamics Observatory, and find clear evidence of offsets in the Doppler zero point in the range of 50-550 m s{sup -1}. In addition, we note that a simpler calibration can be determined from an LOS magnetogram and Dopplergram pair from the median Doppler velocity among all near-disk-center PIL pixels. We briefly discuss shortcomings in our initial implementation, and suggest ways to address these. In addition, as a step in our data reduction, we discuss the use of temporal continuity in the transverse magnetic field direction to correct apparently
Prediction of Minimum Spouting Velocity at Elevated Pressures and Temperatures
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
Minimum spouting velocity (Ums) is one of the most important flow characteristics for proper design and operation of spouted bed reactors. Many correlations for Ums have been published since spouted bed technology was initiated in 1955. In this paper, a new correlation is developed for Ums based on 767 published experimental data covering both high pressure and high temperature conditions. The calculated and the measured results of Ums are in better agreement than other published correlations.
Diffraction imaging and velocity analysis using oriented velocity continuation
Decker, Luke
2014-08-05
We perform seismic diffraction imaging and velocity analysis by separating diffractions from specular reflections and decomposing them into slope components. We image slope components using extrapolation in migration velocity in time-space-slope coordinates. The extrapolation is described by a convection-type partial differential equation and implemented efficiently in the Fourier domain. Synthetic and field data experiments show that the proposed algorithm is able to detect accurate time-migration velocities by automatically measuring the flatness of events in dip-angle gathers.
Apparatus and method for velocity estimation in synthetic aperture imaging
DEFF Research Database (Denmark)
2003-01-01
The invention relates to an apparatus for flow estimation using synthetic aperture imaging. The method uses a Synthetic Transmit Aperture, but unlike previous approaches a new frame is created after every pulse emission. In receive mode parallel beam forming is implemented. The beam formed RF data......). The update signals are used in the velocity estimation processor (8) to correlate the individual measurements to obtain the displacement between high-resolution images and thereby determine the velocity....
Institute of Scientific and Technical Information of China (English)
刘利利
2016-01-01
Using cosmological hydrodynamic simulations, we investigate the align-ments between velocity shear, vorticity, and the spin of dark matter halos, and study the correlation between baryonic and dark matter. We find that (1) mis-alignment between vorticity of baryonic and dark matter would develop on scales<0.2h−1 Mpc;(2) the vorticity of baryonic matter exhibits stronger alignment/anti-alignment with the eigenvectors of velocity shear than that of dark matter; (3) small/massive halos spinning parallel/perpendicular to the host filaments are sensitive to the identification of cosmic web, simulation box size, and resolution. These factors might complicate the connection between the spins of dark matter halos and galaxies, and affect the correlation signal of the alignments of galaxy spin with nearby large-scale structures.%在宇宙学流体力学模拟的基础上，通过对速度剪切场、涡量与暗物质晕自旋方向的相关性，以及重子与暗物质之间关系的研究，发现：(1)在小于0.2h−1 Mpc的尺度上，重子物质涡量与暗物质涡量的差异比较明显；(2)重子物质的涡量与速度剪切张量的相关性比暗物质要强；(3)小质量暗物质晕的自旋方向平行于其所在的纤维结构的方向，而大质量暗物质晕的自旋方向垂直于纤维结构的方向，并且这种相关性的强弱依赖于模拟盒子大小以及模拟精度.这些因素会使暗物质晕自旋与星系自旋之间的关系复杂化，也会对星系自旋方向与大尺度环境的相关性产生影响.
Laser Doppler anemometer measurements using nonorthogonal velocity components: error estimates.
Orloff, K L; Snyder, P K
1982-01-15
Laser Doppler anemometers (LDAs) that are arranged to measure nonorthogonal velocity components (from which orthogonal components are computed through transformation equations) are more susceptible to calibration and sampling errors than are systems with uncoupled channels. In this paper uncertainty methods and estimation theory are used to evaluate, respectively, the systematic and statistical errors that are present when such devices are applied to the measurement of mean velocities in turbulent flows. Statistical errors are estimated for two-channel LDA data that are either correlated or uncorrelated. For uncorrelated data the directional uncertainty of the measured velocity vector is considered for applications where mean streamline patterns are desired.
Gaseous versus Stellar Velocity Dispersion in Emission-Line Galaxies
Institute of Scientific and Technical Information of China (English)
Xiao-Yan Chen; Cai-Na Hao; Jing Wang
2008-01-01
We compare the ionized gas velocity dispersion σgas with the stellar velocity dis-persion σ* in star-forming galaxies, composite galaxies, Low Ionization Nuclear Emission-line Regions (LINERs) and Seyfert 2s, compiled from a cross-identification of Sloan Digital Sky Survey Fourth Data Release (SDSS DR4) and Point Source Catalogue Redshift Survey (PSCz). We measure σgas from the FWHMs of emission lines (Hα, [NII]λλ6548, 6583 and [SII] λλ6716, 6731). A significant correlation between the gas and stellar velocity dispersion exists, despite substantial scatter. The mean value of the gas to stellar velocity dispersion ratio is close to unity. This suggests that gas velocity dispersion can substitute for the stellar veloc-ity dispersion as a tracer of the gravitational potential well for all the four types of galaxies,but the involved uncertainties are different from type to type. We also studied σgas/σ* as a function of the redshift and the axial ratio to test the effects of aperture and galaxy inclina-tion, and found that both effects are weak. Finally we checked the trend of σgas/σ* with the infrared luminosity and found no significant correlation.
Streaming Velocities and the Baryon Acoustic Oscillation Scale.
Blazek, Jonathan A; McEwen, Joseph E; Hirata, Christopher M
2016-03-25
At the epoch of decoupling, cosmic baryons had supersonic velocities relative to the dark matter that were coherent on large scales. These velocities subsequently slow the growth of small-scale structure and, via feedback processes, can influence the formation of larger galaxies. We examine the effect of streaming velocities on the galaxy correlation function, including all leading-order contributions for the first time. We find that the impact on the baryon acoustic oscillation (BAO) peak is dramatically enhanced (by a factor of ∼5) over the results of previous investigations, with the primary new effect due to advection: if a galaxy retains memory of the primordial streaming velocity, it does so at its Lagrangian, rather than Eulerian, position. Since correlations in the streaming velocity change rapidly at the BAO scale, this advection term can cause a significant shift in the observed BAO position. If streaming velocities impact tracer density at the 1% level, compared to the linear bias, the recovered BAO scale is shifted by approximately 0.5%. This new effect, which is required to preserve Galilean invariance, greatly increases the importance of including streaming velocities in the analysis of upcoming BAO measurements and opens a new window to the astrophysics of galaxy formation.
Study of velocity centroids based on the theory of fluctuations in position-position-velocity space
Kandel, D.; Lazarian, A.; Pogosyan, D.
2017-01-01
We study the possibility of obtaining power spectrum of gas velocity in the turbulent interstellar medium from spatial correlation of velocity centroids (VCs) of optically thick emission lines. Combining this study with the earlier studies of centroids in Esquivel & Lazarian, we conclude that centroids are applicable for studies of subsonic/transonic turbulence for sufficiently small line-of-sight (LOS) separations at which self-absorption does not affect correlation scalings. At larger LOS separations where self-absorption becomes important, we find that there is a range of scales over which VC correlation demonstrates the universal scaling, similar to the effect found in the velocity channel analysis (VCA). In other words, for large absorptions the VCs lose their ability to reflect the spectra of turbulence. We develop analytical formalism that relates statistical properties of underlying magnetohydrodynamical (MHD) turbulence to observable scaling and anisotropy of VC correlations arising from Alfvén, slow and fast modes that constitute the compressible MHD modes, and show how the VC anisotropy can be used to find the media magnetization as well as to identify and separate the contributions from these MHD modes. Our study demonstrates that VCs are complementary to the VCA. In order to study turbulent volume with insufficient resolution of single-dish telescopes, we demonstrate how the studies of anisotropy can be performed using interferometers. We also suggest that restricted VC can be constructed for absorption lines by integrating LOS velocity weighted by the optical depth. We discuss the requirements for applicability of this approach.
Study of velocity centroids based on the theory of fluctuations in position-position-velocity space
Kandel, D.; Lazarian, A.; Pogosyan, D.
2016-10-01
We study the possibility of obtaining power spectrum of gas velocity in the turbulent interstellar medium from spatial correlation of velocity centroids (VC) of optically thick emission lines. Combining our present study with the earlier studies of centroids in Esquivel & Lazarian, we conclude that centroids are applicable for studies of subsonic/transsonic turbulence for sufficiently small line of sight (LOS) separations at which self-absorption does not affect correlation scalings. At larger LOS separations where self-absorption becomes important, we find that there is a range of scales over which VC correlation demonstrates the universal scaling, similar to the effect found in the velocity channel analysis (VCA). In other words, for large absorptions the VC lose their ability to reflect the spectra of turbulence. We develop analytical formalism the relates statistical properties of underlying magnetohydrodynamical turbulence to observable scaling and anisotropy of VC correlations arising from Alfvén, slow and fast modes that constitute the compressible MHD modes, and show how the VC anisotropy can be used to find the media magnetization as well as to identify and separate the contributions from these MHD modes. Our study demonstrates that VC are complementary to the VCA. In order to study turbulent volume with insufficient resolution of single dish telescopes, we demonstrate how the studies of anisotropy can be performed using interferometers. We also suggest that restricted VC can be constructed for absorption lines by integrating line-of-sight velocity weighted by the optical depth. We discuss the requirements for applicability of this approach.
Effects of running velocity on running kinetics and kinematics.
Brughelli, Matt; Cronin, John; Chaouachi, Anis
2011-04-01
Sixteen semiprofessional Australian football players performed running bouts at incremental velocities of 40, 60, 80, and 100% of their maximum velocity on a Woodway nonmotorized force treadmill. As running velocity increased from 40 to 60%, peak vertical and peak horizontal forces increased by 14.3% (effect size [ES] = 1.0) and 34.4% (ES = 4.2), respectively. The changes in peak vertical and peak horizontal forces from 60 to 80% were 1.0% (ES = 0.05) and 21.0% (ES = 2.9), respectively. Finally, the changes in peak vertical and peak horizontal forces from 80% to maximum were 2.0% (ES = 0.1) and 24.3% (ES = 3.4). In addition, both stride frequency and stride length significantly increased with each incremental velocity (p velocity (p velocity (r = 0.47). For the kinematic variables, only stride length was found to have a significant positive correlation with maximum running velocity (r = 0.66). It would seem that increasing maximal sprint velocity may be more dependent on horizontal force production as opposed to vertical force production.
Calibrating the Planck Cluster Mass Scale with Cluster Velocity Dispersions
Amodeo, Stefania; Mei, Simona; Stanford, Spencer A.; Bartlett, James G.; Melin, Jean-Baptiste; Lawrence, Charles R.; Chary, Ranga-Ram; Shim, Hyunjin; Marleau, Francine; Stern, Daniel
2017-08-01
We measure the Planck cluster mass bias using dynamical mass measurements based on velocity dispersions of a subsample of 17 Planck-detected clusters. The velocity dispersions were calculated using redshifts determined from spectra that were obtained at the Gemini observatory with the GMOS multi-object spectrograph. We correct our estimates for effects due to finite aperture, Eddington bias, and correlated scatter between velocity dispersion and the Planck mass proxy. The result for the mass bias parameter, (1-b), depends on the value of the galaxy velocity bias, {b}{{v}}, adopted from simulations: (1-b)=(0.51+/- 0.09){b}{{v}}3. Using a velocity bias of {b}{{v}}=1.08 from Munari et al., we obtain (1-b)=0.64+/- 0.11, i.e., an error of 17% on the mass bias measurement with 17 clusters. This mass bias value is consistent with most previous weak-lensing determinations. It lies within 1σ of the value that is needed to reconcile the Planck cluster counts with the Planck primary cosmic microwave background constraints. We emphasize that uncertainty in the velocity bias severely hampers the precision of the measurements of the mass bias using velocity dispersions. On the other hand, when we fix the Planck mass bias using the constraints from Penna-Lima et al., based on weak-lensing measurements, we obtain a positive velocity bias of {b}{{v}}≳ 0.9 at 3σ .
Mathews, Teresa J; Southworth, George; Peterson, Mark J; Roy, W Kelly; Ketelle, Richard H; Valentine, Charles; Gregory, Scott
2013-01-15
East Fork Poplar Creek (EF) and White Oak Creek (WC) are two mercury-contaminated streams located on the United States (U.S.) Department of Energy Oak Ridge Reservation in East Tennessee. East Fork Poplar Creek is the larger and more contaminated of the two, with average aqueous mercury (Hg) concentrations exceeding those in reference streams by several hundred-fold. Remedial actions over the past 20 years have decreased aqueous Hg concentrations in EF by 85% (from >1600 ng/L to Fish fillet concentrations, however, have not responded to this decrease in aqueous Hg and remain above the U.S. Environmental Protection Agency National Recommended Water Quality Criteria (NRWQC) of 0.3 mg/kg. The lack of correlation between aqueous and fish tissue Hg concentrations in this creek has led to questions regarding the usefulness of target aqueous Hg concentrations and strategies for future remediation efforts. White Oak Creek has a similar contamination history but aqueous Hg concentrations in WC are an order of magnitude lower than in EF. Despite the lower aqueous Hg concentrations (fish fillet concentrations in WC have also been above the NRWQC, making the aqueous Hg remediation goal of 200 ng/L in EF seem unlikely to result in an effective decrease in fillet Hg concentrations. Recent monitoring efforts in WC, however, suggest an aqueous total Hg threshold above which Hg bioaccumulation in fish may not respond. This new information could be useful in guiding remedial actions in EF and in other point-source contaminated streams.
Neutrino Velocity and Neutrino Oscillations
Minakata, H
2012-01-01
We study distances of propagation and the group velocities of the muon neutrinos in the presence of mixing and oscillations assuming that Lorentz invariance holds. Oscillations lead to distortion of the $\
Pairwise Velocity Statistics of Dark Halos
Institute of Scientific and Technical Information of China (English)
Hai-Yan Zhang; Yi-Peng Jing
2004-01-01
We have accurately evaluated the halo pairwise velocity dispersion and the halo mean streaming velocity in the LCDM model (the flat ω0 = 0.3 model)using a set of high-resolution N-body simulations. Based on the simulation results,we have developed a model for the pairwise velocity dispersion of halos. Our model agrees with the simulation results over all scales we studied. We have also tested the model of Sheth et al. for the mean streaming motion of halos derived from the pair-conservation equation. We found that their model reproduces the simulation data very well on large scale, but under-predicts the streaming motion on scales r ＜ 10 h-1 Mpc. We have introduced an empirical relation to improve their model.These improved models are useful for predicting the redshift correlation functions and the redshift power spectrum of galaxies if the halo occupation number model,e.g. the cluster weighted model, is given for the galaxies.
Kriging interpolating cosmic velocity field
Yu, Yu; Zhang, Jun; Jing, Yipeng; Zhang, Pengjie
2015-10-01
Volume-weighted statistics of large-scale peculiar velocity is preferred by peculiar velocity cosmology, since it is free of the uncertainties of galaxy density bias entangled in observed number density-weighted statistics. However, measuring the volume-weighted velocity statistics from galaxy (halo/simulation particle) velocity data is challenging. Therefore, the exploration of velocity assignment methods with well-controlled sampling artifacts is of great importance. For the first time, we apply the Kriging interpolation to obtain the volume-weighted velocity field. Kriging is a minimum variance estimator. It predicts the most likely velocity for each place based on the velocity at other places. We test the performance of Kriging quantified by the E-mode velocity power spectrum from simulations. Dependences on the variogram prior used in Kriging, the number nk of the nearby particles to interpolate, and the density nP of the observed sample are investigated. First, we find that Kriging induces 1% and 3% systematics at k ˜0.1 h Mpc-1 when nP˜6 ×1 0-2(h-1 Mpc )-3 and nP˜6 ×1 0-3(h-1 Mpc )-3 , respectively. The deviation increases for decreasing nP and increasing k . When nP≲6 ×1 0-4(h-1 Mpc )-3 , a smoothing effect dominates small scales, causing significant underestimation of the velocity power spectrum. Second, increasing nk helps to recover small-scale power. However, for nP≲6 ×1 0-4(h-1 Mpc )-3 cases, the recovery is limited. Finally, Kriging is more sensitive to the variogram prior for a lower sample density. The most straightforward application of Kriging on the cosmic velocity field does not show obvious advantages over the nearest-particle method [Y. Zheng, P. Zhang, Y. Jing, W. Lin, and J. Pan, Phys. Rev. D 88, 103510 (2013)] and could not be directly applied to cosmology so far. However, whether potential improvements may be achieved by more delicate versions of Kriging is worth further investigation.
Event Detection by Velocity Pyramid
2014-01-01
In this paper, we propose velocity pyramid for multimediaevent detection. Recently, spatial pyramid matching is proposed to in-troduce coarse geometric information into Bag of Features framework,and is eective for static image recognition and detection. In video, notonly spatial information but also temporal information, which repre-sents its dynamic nature, is important. In order to fully utilize it, wepropose velocity pyramid where video frames are divided into motionalsub-regions. Our meth...
Prestack migration velocity analysis based on simplifi ed two-parameter moveout equation
Institute of Scientific and Technical Information of China (English)
Chen Hai-Feng; Li Xiang-Yang; Qian Zhong-Ping; Song Jian-Jun; Zhao Gui-Ling
2016-01-01
Stacking velocityVC2, vertical velocity ratioγ0, effective velocity ratioγef, and anisotropic parameterχef are correlated in the PS-converted-wave (PS-wave) anisotropic prestack Kirchhoff time migration (PKTM) velocity model and are thus difficult to independently determine. We extended the simplified two-parameter (stacking velocity VC2 and anisotropic parameterkef) moveout equation from stacking velocity analysis to PKTM velocity model updating and formed a new four-parameter (stacking velocityVC2, vertical velocity ratioγ0, effective velocity ratioγef, and anisotropic parameterkef) PS-wave anisotropic PKTM velocity model updating and processfl ow based on the simplifi ed two-parameter moveout equation. In the proposed method, first, the PS-wave two-parameter stacking velocity is analyzed to obtain the anisotropic PKTM initial velocity and anisotropic parameters; then, the velocity and anisotropic parameters are corrected by analyzing the residual moveout on common imaging point gathers after prestack time migration. The vertical velocity ratioγ0 of the prestack time migration velocity model is obtained with an appropriate method utilizing the P- and PS-wave stacked sections after level calibration. The initial effective velocity ratioγef is calculated using the Thomsen (1999) equation in combination with the P-wave velocity analysis; ultimately, the final velocity model of the effective velocity ratioγef is obtained by percentage scanning migration. This method simplifi es the PS-wave parameter estimation in high-quality imaging, reduces the uncertainty of multiparameter estimations, and obtains good imaging results in practice.
Ikari, Yohei; Hirata, Shinnosuke; Hachiya, Hiroyuki
2015-07-01
Pulse compression using a maximum-length sequence (M-sequence) can improve the signal-to-noise ratio (SNR) of the reflected echo in the pulse-echo method. In the case of a moving object, however, the echo is modulated owing to the Doppler effect. The Doppler-shifted M-sequence-modulated signal cannot be correlated with the reference signal that corresponds to the transmitted M-sequence-modulated signal. Therefore, Doppler velocity estimation by spectrum-pattern analysis of a cyclic M-sequence-modulated signal and cross correlations with Doppler-shifted reference signals that correspond to the estimated Doppler velocities has been proposed. In this paper, measurements of the position and velocity of a moving object by the proposed method are described. First, Doppler velocities of the object are estimated using a microphone array. Secondly, the received signal from each microphone is correlated with each Doppler-shifted reference signal. Then, the position of the object is determined from the B-mode image formed from all cross-correlation functions. After that, the velocity of the object is calculated from velocity components estimated from the Doppler velocities and the position. Finally, the estimated Doppler velocities, determined positions, and calculated velocities are evaluated.
Institute of Scientific and Technical Information of China (English)
孔晓明; 谢新晖; 王晨; 孙艳; 王克永; 张许来; 张丽; 吴丽敏; 刘佳楠
2015-01-01
Objective To explore the eye tracking function of schizophrenia.Methods Visually guided saccade was checked on 27 schizophrenia patients who met the criterion of ICD-10 and 27 matched normal control participates.First,the peak velocity at duration index (PVADI) of each saccade was calculated; second,the relation of amplitude and PVADI (RPA) of every participate was also calculated; third,the RPA values of schizophrenia and normal control group were compared.Results Compared with normal control group,RPA values of schizophrenia group were significantly lower (RPA values of normal control group:0.42±0.17,RPA values of schizophrenia group:0.20±0.15,Mann-Whitney U test,Z=-4.282,P＜0.01).Conclusion The correlation of saccade velocity asymmetry and amplitude of schizophrenic patients is significant lower than that of normal controls.RPA is auxiliary diagnostic index for schizophrenia with great potential.%目的 探讨精神分裂症患者眼动追踪能力.方法 选取符合ICD-10诊断标准的精神分裂症患者27人,正常对照组27人,分别进行视觉引导眼跳范式,并计算每一次眼跳中眼动速度达到最高时刻所占整个眼跳时间的百分比指数(PVADI),并计算每一名被试的PVADI与眼跳幅度的相关系数RPA.然后比较两组间的RPA.结果 与对照组相比,精神分裂症组的RPA显著偏低[RPA在正常组为(0.42±0.17),在精神分裂症组为(0.20±0.15),Mann-Whitney U检验,Z=-4.282,P＜0.01)].结论 精神分裂症患者眼跳速度非对称性与眼跳幅度之间的相关性较正常人低.RPA是精神分裂症非常有潜力的辅助诊断指标.
The correlation function for density perturbations in an expanding universe. II - Nonlinear theory
Mcclelland, J.; Silk, J.
1977-01-01
A formalism is developed to find the two-point and higher-order correlation functions for a given distribution of sizes and shapes of perturbations which are randomly placed in three-dimensional space. The perturbations are described by two parameters such as central density and size, and the two-point correlation function is explicitly related to the luminosity function of groups and clusters of galaxies
Human skeletal muscle fibre types and force: velocity properties.
MacIntosh, B R; Herzog, W; Suter, E; Wiley, J P; Sokolosky, J
1993-01-01
It has been reported that there is a relationship between power output and fibre type distribution in mixed muscle. The strength of this relationship is greater in the range of 3-8 rad.s-1 during knee extension compared to slower or faster angular knee extensor speeds. A mathematical model of the force: velocity properties of muscle with various combinations of fast- and slow-twitch fibres may provide insight into why specific velocities may give better predictions of fibre type distribution. In this paper, a mathematical model of the force:velocity relationship for mixed muscle is presented. This model demonstrates that peak power and optimal velocity should be predictive of fibre distribution and that the greatest fibre type discrimination in human knee extensor muscles should occur with measurement of power output at an angular velocity just greater than 7 rad.s-1. Measurements of torque:angular velocity relationships for knee extension on an isokinetic dynamometer and fibre type distribution in biopsies of vastus lateralis muscles were made on 31 subjects. Peak power and optimal velocity were determined in three ways: (1) direct measurement, (2) linear regression, and (3) fitting to the Hill equation. Estimation of peak power and optimal velocity using the Hill equation gave the best correlation with fibre type distribution (r < 0.5 for peak power or optimal velocity and percentage of fast-twitch fibres). The results of this study confirm that prediction of fibre type distribution is facilitated by measurement of peak power at optimal velocity and that fitting of the data to the Hill equation is a suitable method for evaluation of these parameters.
Flux-Velocity Relation for H2 Outflows
Salas, Luis; Cruz-González, Irene
2002-06-01
We present an analysis of velocity-resolved near-IR molecular hydrogen observations of a variety of protostellar outflows with very different energetics, degrees of collimation, and morphologies. Observations in the 2.12 μm line of H2 were obtained using an IR Fabry-Pérot interferometer with a spectral resolution of 23 km s-1. The integrated flux-velocity diagrams for each outflow show a flat spectrum for low velocities followed by a decreasing power law dF/dv~vγ, with γ between -1.8 and -2.6, for velocities higher than a clearly defined break velocity at 2-17 km s-1. Contrary to shock model predictions, it is shown that the H2 intensity is constant with velocity. We argue that the flux-velocity relation can then be interpreted as a mass-velocity relation, in striking similarity to the power-law mass spectra observed in CO outflows. By comparing H2 and CO mass-velocity spectra, it is shown that there is a velocity regime in which both molecules coexist and produce similar γ-values. Evolution effects in outflows appear as a correlation between outflow length and γ as outflows age, the spectra becomes steeper. Our results support a common physical origin for both CO and H2 emission and a strong association between the molecular outflows traced in each molecule. Based on observations obtained at the Observatorio Astronómico Nacional at San Pedro Mártir, Mexico.
Robust seismic velocity change estimation using ambient noise recordings
Daskalakis, E.; Evangelidis, C. P.; Garnier, J.; Melis, N. S.; Papanicolaou, G.; Tsogka, C.
2016-06-01
We consider the problem of seismic velocity change estimation using ambient noise recordings. Motivated by Zhan et al., we study how the velocity change estimation is affected by seasonal fluctuations in the noise sources. More precisely, we consider a numerical model and introduce spatio-temporal seasonal fluctuations in the noise sources. We show that indeed, as pointed out by Zhan et al., the stretching method is affected by these fluctuations and produces misleading apparent velocity variations which reduce dramatically the signal to noise ratio of the method. We also show that these apparent velocity variations can be eliminated by an adequate normalization of the cross-correlation functions. Theoretically we expect our approach to work as long as the seasonal fluctuations in the noise sources are uniform, an assumption which holds for closely located seismic stations. We illustrate with numerical simulations in homogeneous and scattering media that the proposed normalization significantly improves the accuracy of the velocity change estimation. Similar behaviour is also observed with real data recorded in the Aegean volcanic arc. We study in particular the volcano of Santorini during the seismic unrest of 2011-2012 and observe a decrease in the velocity of seismic waves which is correlated with GPS measured elevation.
Directory of Open Access Journals (Sweden)
K. Ramachandran
2012-02-01
Full Text Available Spatial gradients of tomographic velocities are seldom used in interpretation of subsurface fault structures. This study shows that spatial velocity gradients can be used effectively in identifying subsurface discontinuities in the horizontal and vertical directions. Three-dimensional velocity models constructed through tomographic inversion of active source and/or earthquake traveltime data are generally built from an initial 1-D velocity model that varies only with depth. Regularized tomographic inversion algorithms impose constraints on the roughness of the model that help to stabilize the inversion process. Final velocity models obtained from regularized tomographic inversions have smooth three-dimensional structures that are required by the data. Final velocity models are usually analyzed and interpreted either as a perturbation velocity model or as an absolute velocity model. Compared to perturbation velocity model, absolute velocity models have an advantage of providing constraints on lithology. Both velocity models lack the ability to provide sharp constraints on subsurface faults. An interpretational approach utilizing spatial velocity gradients applied to northern Cascadia shows that subsurface faults that are not clearly interpretable from velocity model plots can be identified by sharp contrasts in velocity gradient plots. This interpretation resulted in inferring the locations of the Tacoma, Seattle, Southern Whidbey Island, and Darrington Devil's Mountain faults much more clearly. The Coast Range Boundary fault, previously hypothesized on the basis of sedimentological and tectonic observations, is inferred clearly from the gradient plots. Many of the fault locations imaged from gradient data correlate with earthquake hypocenters, indicating their seismogenic nature.
Velocity structure of uppermost mantle beneath North China from Pn tomography and its implications
Institute of Scientific and Technical Information of China (English)
汪素云; 许忠淮; 裴顺平
2003-01-01
20301 Pn arrival time data are collected from the seismological bulletins of both national and regional seismic networks. Pn travel time residuals are tomographically inverted for the Pn velocity structure of uppermost mantle beneath North China. The result indicates that the average Pn velocity in North China is 7.92 km/s, and the velocity varies laterally from ?0.21 to +0.29 km/s around the average. The approximately NNE trending high and low velocity regions arrange alternatively west-eastward. From west to east we can see high velocity in the middle Ordos region, the Shanxi graben low, the Jizhong depression high, the west Shandong uplift and Bohai Sea low, and the high velocity region to the east of the Tanlu fault. In the southern boundary zone of the North China block, except for the high velocity in the Qingling Mountains region, the velocity is generally lower than the average. Obvious velocity anisotropy is seen in the Datong Cenozoic volcanic region, with the fast velocity direction in NNE-SSW. Notable velocity anisotropy is also seen around the Bay of Bohai Sea, and the fast velocity directions seem to show a rotation pattern, possibly indicating a flow-like deformation in the uppermost mantle there. The Pn velocity variations show a reversed correlation with the Earth's heat flow. The low Pn velocity regions generally show high heat flow, e.g., the Shanxi graben and Bohai Sea region. While the high Pn velocity regions usually manifest low heat flow, e.g., the region of Jizhong depression. This indicates that the Pn velocity variation in the study region is mainly aroused by the regional temperature difference in the uppermost mantle. Strong earthquakes in the crust tend to occur in the region with the abnormal low Pn velocity, or in the transition zone between high and low Pn velocity regions. The earthquakes in the low velocity region are shallower, while that in the transition zone are deeper.
Interferometric measurement of the angular velocity of moving humans
Nanzer, Jeffrey A.
2012-06-01
This paper presents an analysis of the measurement of the angular velocity of walking humans using a millimeter-wave correlation interferometer. Measurement of the angular velocity of moving objects is a desirable function in remote sensing applications. Doppler radar sensors are able to measure the signature of moving humans based on micro-Doppler analysis; however, a person moving with little to no radial velocity produces negligible Doppler returns. Measurement of the angular movement of humans can be done with traditional radar techniques, however the process involves either continuous tracking with narrow beamwidth or angle-of-arrival estimation algorithms. A new method of measuring the angular velocity of moving objects using interferometry has recently been developed which measures the angular velocity of an object without tracking or complex processing. The frequency of the interferometer signal response is proportional to the angular velocity of the object as it passes through the interferometer beam pattern. In this paper, the theory of the interferometric measurement of angular velocity is covered and simulations of the response of a walking human are presented. Simulations are produced using a model of a walking human to show the significant features associated with the interferometer response, which may be used in classification algorithms.
Chalk porosity and sonic velocity versus burial depth
DEFF Research Database (Denmark)
Fabricius, Ida Lykke; Gommesen, Lars; Krogsbøll, Anette Susanne
2008-01-01
that porosity and sonic velocity follow the most consistent depth trends when fluid pressure and pore-volume compressibility are considered. Quartz content up to 10% has no marked effect, but more than 5% clay causes lower porosity and velocity. The mineralogical effect differs between P-wave and shear velocity...... for fluid pressure because the cementing ions originate from stylolites, which are mechanically similar to fractures. We find that cementation occurs over a relatively short depth interval.......Seventy chalk samples from four formations in the overpressured Danish central North Sea have been analyzed to investigate how correlations of porosity and sonic velocity with burial depth are affected by varying mineralogy, fluid pressure, and early introduction of petroleum. The results show...
Tuning Multiple Motor Travel Via Single Motor Velocity
Xu, Jing; Shu, Zhanyong; King, Stephen J.; Gross, Steven P.
2012-01-01
Microtubule-based molecular motors often work in small groups to transport cargos in cells. A key question in understanding transport (and its regulation in vivo) is to identify the sensitivity of multiple-motor-based motion to various single molecule properties. Whereas both single-motor travel distance and microtubule binding rate have been demonstrated to contribute to cargo travel, the role of single-motor velocity is yet to be explored. Here, we recast a previous theoretical study, and make explicit a potential contribution of velocity to cargo travel. We test this possibility experimentally, and demonstrate a strong negative correlation between single-motor velocity and cargo travel for transport driven by two motors. Our study thus discovers a previously unappreciated role of single-motor velocity in regulating multiple-motor transport. PMID:22672518
Velocity requirements for causality violation
Modanese, Giovanni
2013-01-01
It is known that the hypothetical existence of superluminal signals would imply the logical possibility of active causal violation: an observer in relative motion with respect to a primary source could in principle emit secondary superluminal signals (triggered by the primary ones) which go back in time and deactivate the primary source before the initial emission. This is a direct consequence of the structure of the Lorentz transformations, sometimes called "Regge-Tolman paradox". It is straightforward to find a formula for the velocity of the moving observer required to produce the causality violation. When applied to some recent claims of slight superluminal propagation, this formula yields a required velocity very close to the speed of light; this raises some doubts about the real physical observability of such violations. We re-compute this velocity requirement introducing a realistic delay between the reception of the primary signal and the emission of the secondary. It turns out that for -any- delay it...
Signal velocity in oscillator arrays
Cantos, C. E.; Veerman, J. J. P.; Hammond, D. K.
2016-09-01
We investigate a system of coupled oscillators on the circle, which arises from a simple model for behavior of large numbers of autonomous vehicles where the acceleration of each vehicle depends on the relative positions and velocities between itself and a set of local neighbors. After describing necessary and sufficient conditions for asymptotic stability, we derive expressions for the phase velocity of propagation of disturbances in velocity through this system. We show that the high frequencies exhibit damping, which implies existence of well-defined signal velocitiesc+ > 0 and c- < 0 such that low frequency disturbances travel through the flock as f+(x - c+t) in the direction of increasing agent numbers and f-(x - c-t) in the other.
Quantitative measurement of high flow velocities by a spin echo MR technique
Energy Technology Data Exchange (ETDEWEB)
Lin Yigun (First Military Medical Coll., Quangzhou, FJ (China)); Kojima, Akihiro; Shinzato, Jintetsu; Sakamoto, Yuji; Ueno, Sukeyoshi; Takahashi, Mutsumasa; Higashida, Yoshiharu
A new method of flow measurement using a spin echo (SE) technique has been developed on the basis of the flow effect that at high velocities signal intensity decreases linearly with increasing flow velocity. Flow velocity is calculated from the signal intensity ratio of the flowing material in two images with the same imaging parameters but different echo times. The linear relationship between the signal intensity and flow velocity was examined with a steady flow phantom. When assessed with steady flows in the phantom, flow velocities calculated by this method were in good agreement with velocities measured by a flow meter. This method was used with ECG gating to measure the blood flow of the right common carotid artery of a healthy volunteer. The measured peak flow velocity and the pattern of flow velocities during systole correlated well with the results obtained by Doppler ultrasound. (author).
Estimation of velocity vectors in synthetic aperture ultrasound imaging
DEFF Research Database (Denmark)
Jensen, Jørgen Arendt; Oddershede, Niels
2006-01-01
A method for determining both velocity magnitude and angle in a synthetic aperture ultrasound system is described. The approach uses directional beamforming along the flow direction and cross-correlation to determine velocity magnitude. The angle of the flow is determined from the maximum...... of the visually determined flow angle. The standard deviation of these estimates was below 2.7 deg. Full color flow maps from different parts of the cardiac cycle are presented, including vector arrows indicating both estimated flow direction and velocity magnitude....... normalized correlation calculated as a function of angle. This assumes the flow direction is within the imaging plane. Simulations of the angle estimation method show both biases and standard deviations of the flow angle estimates below 3 deg for flow angles from 20 deg to 90 deg (transverse flow...
Angle independent velocity spectrum determination
DEFF Research Database (Denmark)
2014-01-01
An ultrasound imaging system (100) includes a transducer array (102) that emits an ultrasound beam and produces at least one transverse pulse-echo field that oscillates in a direction transverse to the emitted ultrasound beam and that receive echoes produced in response thereto and a spectral vel...... velocity estimator (110) that determines a velocity spectrum for flowing structure, which flows at an angle of 90 degrees and flows at angles less than 90 degrees with respect to the emitted ultrasound beam, based on the received echoes....
Directory of Open Access Journals (Sweden)
Blaž Lešnik
2007-02-01
the help of a kinematic analysis, differences in the choice of a line of skiing between individual competitors were established based on a sample of top competitors in the World Cup in Kranjska Gora. We tried to establish whether the competitors achieved higher velocities with such a line of skiing, thus achieving faster sliding among the slalom gates and in the end a better time. In the first part of our research it was proven that none of the competitors had an extremely short line of skiing in the first two successive turns. It was also found out that the competitors who had the shortest lines of skiing in the first analysed turn had, as a rule, the longest lines of skiing in the second turn and vice versa. Based on these findings, it could be claimed that under present conditions, it is extremely difficult, possibly even impossible, to ski in such a way that the line of skiing would be very short in several successive turns. The second part of our research focussed on the establishment of the correlation between the trajectories of the skis and the velocity of skiing. The calculations of the correlations proved a statistically significant correlation between the average velocity of skiing and an average distance of the length of the line of skiing from the y-axis in the entire measured segment. It was established that the measured space was covered faster by the competitors whose line of skiing was shorter, which means more direct.
Boden, J.A.
1974-01-01
A survey is given of the most common types of coherent optical correlators, which are classified as spatial plane correlators, frequency plane correlators and special reference correlators. Only the spatial plane correlators are dealt with rather thoroughly. Basic principles, some special features,
Study on S wave velocity structure beneath part stations in Shanxi Province
Institute of Scientific and Technical Information of China (English)
张学民; 束沛镒; 刁桂苓
2003-01-01
Based on S wave records of deep teleseisms on Digital Seismic Network of Shanxi Province, shear wave velocity structures beneath 6 stations were obtained by means of S wave waveform fitting. The result shows that the crust is thick in the studied region, reaching 40 km in thickness under 4 stations. The crust all alternatives high velocity layer with low velocity one. There appear varied velocity structures for different stations, and the stations around the same tectonic region exhibit similar structure characteristics. Combined with dominant depth distribution of many small-moderate earthquakes, the correlation between seismogenic layers and crustal structures of high and low velocity layers has been discussed.
Time-Resolved PIV for Space-Time Correlations in Hot Jets
Wernet, Mark P.
2007-01-01
Temporally Resolved Particle Image Velocimetry (TR-PIV) is being used to characterize the decay of turbulence in jet flows a critical element for understanding the acoustic properties of the flow. A TR-PIV system, developed in-house at the NASA Glenn Research Center, is capable of acquiring planar PIV image frame pairs at up to 10 kHz. The data reported here were collected at Mach numbers of 0.5 and 0.9 and at temperature ratios of 0.89 and 1.76. The field of view of the TR-PIV system covered 6 nozzle diameters along the lip line of the 50.8 mm diameter jet. The cold flow data at Mach 0.5 were compared with hotwire anemometry measurements in order to validate the new TR-PIV technique. The axial turbulence profiles measured across the shear layer using TR-PIV were thinner than those measured using hotwire anemometry and remained centered along the nozzle lip line. The collected TR-PIV data illustrate the differences in the single point statistical flow properties of cold and hot jet flows. The planar, time-resolved velocity records were then used to compute two-point space-time correlations of the flow at the Mach 0.9 flow condition. The TR-PIV results show that there are differences in the convective velocity and growth rate of the turbulent structures between cold and hot flows at the same Mach number.
Rayleigh-Wave Group-Velocity Tomography of Saudi Arabia
Tang, Zheng; Mai, P. Martin; Chang, Sung-Joon; Zahran, Hani
2017-04-01
We use surface-wave tomography to investigate the lithospheric structure of the Arabian plate, which is traditionally divided into the Arabian shield in the west and the Arabian platform in the east. The Arabian shield is a complicated mélange of crustal material, composed of several Proterozoic terrains separated by ophiolite-bearing suture zones and dotted by outcropping Cenozoic volcanic rocks. The Arabian platform is primarily covered by very thick Paleozoic, Mesozoic and Cenozoic sediments. We develop high-resolution tomographic images from fundamental-mode Rayleigh-wave group-velocities across Saudi Arabia, utilizing the teleseismic data recorded by the permanent Saudi National Seismic Network (SNSN). Our study extends previous efforts on surface wave work by increasing ray path density and improving spatial resolution. Good quality dispersion measurements for roughly 3000 Rayleigh-wave paths have been obtained and utilized for the group-velocity tomography. We have applied the Fast Marching Surface Tomography (FMST) scheme of Rawlinson (2005) to obtain Rayleigh-wave group-velocity images for periods from 8 s to 40 s on a 0.8° 0.8° grid and at resolutions approaching 2.5° based on the checkerboard tests. Our results indicate that short-period group-velocity maps (8-15 s) correlate well with surface geology, with slow velocities delineating the main sedimentary features including the Arabian platform, the Persian Gulf and Mesopotamia. For longer periods (20-40 s), the velocity contrast is due to the differences in crustal thickness and subduction/collision zones. The lower velocities are sensitive to the thicker continental crust beneath the eastern Arabia and the subduction/collision zones between the Arabian and Eurasian plate, while the higher velocities in the west infer mantle velocity.
Tachoastrometry: astrometry with radial velocities
Pasquini, L; Lombardi, M; Monaco, L; Leão, I C; Delabre, B
2014-01-01
Spectra of composite systems (e.g., spectroscopic binaries) contain spatial information that can be retrieved by measuring the radial velocities (i.e., Doppler shifts) of the components in four observations with the slit rotated by 90 degrees in the sky. By using basic concepts of slit spectroscopy we show that the geometry of composite systems can be reliably retrieved by measuring only radial velocity differences taken with different slit angles. The spatial resolution is determined by the precision with which differential radial velocities can be measured. We use the UVES spectrograph at the VLT to observe the known spectroscopic binary star HD 188088 (HIP 97944), which has a maximum expected separation of 23 milli-arcseconds. We measure an astrometric signal in radial velocity of 276 \\ms, which corresponds to a separation between the two components at the time of the observations of 18 $\\pm2$ milli-arcseconds. The stars were aligned east-west. We describe a simple optical device to simultaneously record p...
The Weyl tensor correlator in cosmological spacetimes
Fröb, Markus B
2014-01-01
We give a general expression for the Weyl tensor two-point function in a general Friedmann-Lema\\^itre-Robertson-Walker spacetime. We work in reduced phase space for the perturbations, i.e., quantize only the dynamical degrees of freedom without adding any gauge-fixing term. The general formula is illustrated by a calculation in slow-roll single-field inflation to first order in the slow-roll parameters $\\epsilon$ and $\\delta$, and the result is shown to have the correct de Sitter limit as $\\epsilon, \\delta \\to 0$. Furthermore, it is seen that the Weyl tensor correlation function does not suffer from infrared divergences, unlike the two-point functions of the metric and scalar field perturbations. Lastly, we show how to recover the usual tensor power spectrum from the Weyl tensor correlation function.
EFFECT OF VELOCITY ON DUCTILITY UNDER HIGH VELOCITY FORMING
Institute of Scientific and Technical Information of China (English)
LI Zhong; LI Chunfeng
2007-01-01
The ring expansion procedures over various forming velocities are calculated with ANSYS software in order to show the effect of forming velocity on ductility of rate insensitive materials. Ring expansion procedures are simplified to one-dimensional tension by constraining the radial deformation, with element birth and death method, fracture problem of circular ring are considered. The calculated results show that for insensitive materials of 1060 aluminum and 3A21 aluminum alloy, fracture strain increases corresponding to the increase of forming velocity. This trend agrees well with experimental results, and indicates inertia is the key factor to affect ductility; With element birth and death methods, fracture problems can be solved effectively. Experimental studies on formability of tubular workpieces are also conducted, experimental results show that the formability of 1060 aluminum and 3A21 aluminum alloy under electromagnetic forming is higher than that under quasistatic forming, according to the characteristics of electromagnetic forming, the forming limit diagrams of the two materials tube are also built respectively, this is very important to promote the development of electromagnetic forming and guide the engineering practices.
Institute of Scientific and Technical Information of China (English)
刘厚通; 赵建新; 莫须涛; 韩玉峰
2013-01-01
对两点标定法求解气溶胶消光后向散射比Sa(z)的可行性进行了研究.讨论了利用两点标定法反演气溶胶消光后向散射比的精度和两标定点之间距离的关系:当两点之间的距离大于1 km时,利用两点标定法得到的气溶胶消光后向散射比是可靠的.对比分析了两标定点间的距离大小及两种不同的迭代方法对两标定点之间气溶胶消光后向散射比反演结果的影响.并对两点标定法用于气溶胶消光后向散射比反演时,预先对反演结果进行误差估计的可行性进行了探讨.实际反演结果表明,利用两点标定法进行气溶胶消光后向散射比的反演,当两标定点之间的距离大于1 km且标定点的气溶胶消光系数的误差为5％时,反演得到两标定点之间气溶胶消光后向散射比的误差一般不会超过6％.%Feasibility of using two-point calibration method to acquire aerosol extinction-to-backscattering ratio is explored. Two-point calibration method is one of the important methods for acquiring aerosol extinction-to-backscattering ratio. The relationship between the distance of the two calibration points and the accuracy of aerosol extinction-to-backscattering ratio acquired by using two-point calibration method is discussed. The aerosol extinction-to-backscattering ratio obtained by using two-point calibration method is reliable when the distance between the two points is greater than 1 km. The influence of the distance between the two calibration points on the inversion results of aerosol extinction-to-backscattering ratio from one calibration point to another one is analyzed. The influence to aerosol extinction-to-backscattering ratio inversion results of two different iterative methods is discussed. The feasibility of beforehand error estimation of inversion results when two-point calibration method is used for the inversion of aerosol extinction-to-backscattering ratio is investigated. The inversion
Structure of the velocity gradient tensor in turbulent shear flows
Pumir, Alain
2017-07-01
The expected universality of small-scale properties of turbulent flows implies isotropic properties of the velocity gradient tensor in the very large Reynolds number limit. Using direct numerical simulations, we determine the tensors formed by n =2 and 3 velocity gradients at a single point in turbulent homogeneous shear flows and in the log-layer of a turbulent channel flow, and we characterize the departure of these tensors from the corresponding isotropic prediction. Specifically, we separate the even components of the tensors, invariant under reflexion with respect to all axes, from the odd ones, which identically vanish in the absence of shear. Our results indicate that the largest deviation from isotropy comes from the odd component of the third velocity gradient correlation function, especially from the third moment of the derivative along the normal direction of the streamwise velocity component. At the Reynolds numbers considered (Reλ≈140 ), we observe that these second- and third-order correlation functions are significantly larger in turbulent channel flows than in homogeneous shear flow. Overall, our work demonstrates that a mean shear leads to relatively simple structure of the velocity gradient tensor. How isotropy is restored in the very large Reynolds limit remains to be understood.
High precision radial velocities with GIANO spectra
Carleo, I; Gratton, R; Benatti, S; Bonavita, M; Oliva, E; Origlia, L; Desidera, S; Claudi, R; Sissa, E
2016-01-01
Radial velocities (RV) measured from near-infrared (NIR) spectra are a potentially excellent tool to search for extrasolar planets around cool or active stars. High resolution infrared (IR) spectrographs now available are reaching the high precision of visible instruments, with a constant improvement over time. GIANO is an infrared echelle spectrograph at the Telescopio Nazionale Galileo (TNG) and it is a powerful tool to provide high resolution spectra for accurate RV measurements of exoplanets and for chemical and dynamical studies of stellar or extragalactic objects. No other high spectral resolution IR instrument has GIANO's capability to cover the entire NIR wavelength range (0.95-2.45 micron) in a single exposure. In this paper we describe the ensemble of procedures that we have developed to measure high precision RVs on GIANO spectra acquired during the Science Verification (SV) run, using the telluric lines as wavelength reference. We used the Cross Correlation Function (CCF) method to determine the v...
Fine structure of Pn velocity beneath Sichuan-Yunnan region
Institute of Scientific and Technical Information of China (English)
黄金莉; 宋晓东; 汪素云
2003-01-01
We use 23298 Pn arrival-time data from Chinese national and provincial earthquake bulletins to invert fine structure of Pn velocity and anisotropy at the top of the mantle beneath the Sichuan-Yunnan and its adjacent region. The results suggest that the Pn velocity in this region shows significant lateral variation; the Pn velocity varies from 7.7 to 8.3 km/s. The Pn-velocity variation correlates well with the tectonic activity and heat flow of the region. Low Pn velocity is observed in southwest Yunnan , Tengchong volcano area, and the Panxi tectonic area. These areas have very active seismicity and tectonic activity with high surface heat flow. On the other hand, high Pn velocity is observed in some stable regions, such as the central region of the Yangtze Platform; the most pronounced high velocity area is located in the Sichuan Basin, south of Chengdu. Pn anisotropy shows a complex pattern of regional deformation. The Pn fast direction shows a prominent clockwise rotation pattern from east of the Tibetan block to the Sichuan-Yunnan diamond block to southwest Yunnan, which may be related to southeastward escape of the Tibetan Plateau material due to the collision of the Indian Plate to the Eurasia Plate. Thus there appears to be strong correlation between the crustal deformation and the upper mantle structure in the region. The delay times of events and stations show that the crust thickness decreases from the Tibetan Plateau to eastern China, which is consistent with the results from deep seismic sounding.
A Vs30-derived Near-surface Seismic Velocity Model
Ely, G. P.; Jordan, T. H.; Small, P.; Maechling, P. J.
2010-12-01
Shallow material properties, S-wave velocity in particular, strongly influence ground motions, so must be accurately characterized for ground-motion simulations. Available near-surface velocity information generally exceeds that which is accommodated by crustal velocity models, such as current versions of the SCEC Community Velocity Model (CVM-S4) or the Harvard model (CVM-H6). The elevation-referenced CVM-H voxel model introduces rasterization artifacts in the near-surface due to course sample spacing, and sample depth dependence on local topographic elevation. To address these issues, we propose a method to supplement crustal velocity models, in the upper few hundred meters, with a model derived from available maps of Vs30 (the average S-wave velocity down to 30 meters). The method is universally applicable to regions without direct measures of Vs30 by using Vs30 estimates from topographic slope (Wald, et al. 2007). In our current implementation for Southern California, the geology-based Vs30 map of Wills and Clahan (2006) is used within California, and topography-estimated Vs30 is used outside of California. Various formulations for S-wave velocity depth dependence, such as linear spline and polynomial interpolation, are evaluated against the following priorities: (a) capability to represent a wide range of soil and rock velocity profile types; (b) smooth transition to the crustal velocity model; (c) ability to reasonably handle poor spatial correlation of Vs30 and crustal velocity data; (d) simplicity and minimal parameterization; and (e) computational efficiency. The favored model includes cubic and square-root depth dependence, with the model extending to a depth of 350 meters. Model parameters are fit to Boore and Joyner's (1997) generic rock profile as well as CVM-4 soil profiles for the NEHRP soil classification types. P-wave velocity and density are derived from S-wave velocity by the scaling laws of Brocher (2005). Preliminary assessment of the new model
Relationship between CME velocities and X-ray fluxes of associated flares
Institute of Scientific and Technical Information of China (English)
An-Qin Chen; Wei-Guo Zong
2009-01-01
Coronal mass ejection (CME) velocities have been studied over recent decades. We present a statistical analysis of the relationship between CME velocities and X-ray fluxes of the associated flares. We study two types of CMEs. One is the FL type associ- ated only with flares, while the other is the intermediate type associated with both filament eruptions and flares. It is found that the velocities of the FL type CMEs are strongly cor- related with both the peak and the time-integrated X-ray fluxes of the associated flares. However, the correlations between the intermediate type CME velocities and the corre- sponding two parameters are poor. It is also found that the correlation between the CME velocities and the peak X-ray fluxes is stronger than that between the CME velocities and the time-integrated X-ray fluxes of the associated flares.
Sensors for Using Times of Flight to Measure Flow Velocities
Fralick, Gutave; Wrbanek, John D.; Hwang, Danny; Turso, James
2006-01-01
Thin-film sensors for measuring flow velocities in terms of times of flight are undergoing development. These sensors are very small and can be mounted flush with surfaces of airfoils, ducts, and other objects along which one might need to measure flows. Alternatively or in addition, these sensors can be mounted on small struts protruding from such surfaces for acquiring velocity measurements at various distances from the surfaces for the purpose of obtaining boundary-layer flow-velocity profiles. These sensors are related to, but not the same as, hot-wire anemometers. Each sensor includes a thin-film, electrically conductive loop, along which an electric current is made to flow to heat the loop to a temperature above that of the surrounding fluid. Instantaneous voltage fluctuations in segments of the loop are measured by means of electrical taps placed at intervals along the loop. These voltage fluctuations are caused by local fluctuations in electrical resistance that are, in turn, caused by local temperature fluctuations that are, in turn, caused by fluctuations in flow-induced cooling and, hence, in flow velocity. The differential voltage as a function of time, measured at each pair of taps, is subjected to cross-correlation processing with the corresponding quantities measured at other pairs of taps at different locations on the loop. The cross-correlations yield the times taken by elements of fluid to travel between the pairs of taps. Then the component of velocity along the line between any two pairs of taps is calculated simply as the distance between the pairs of taps divided by the travel time. Unlike in the case of hot-wire anemometers, there is no need to obtain calibration data on voltage fluctuations versus velocity fluctuations because, at least in principle, the correlation times are independent of the calibration data.
Signal velocity for anomalous dispersive waves
Energy Technology Data Exchange (ETDEWEB)
Mainardi, F. (Bologna Univ. (Italy))
1983-03-11
The concept of signal velocity for dispersive waves is usually identified with that of group velocity. When the dispersion is anomalous, this interpretation is not correct since the group velocity can assume nonphysical values. In this note, by using the steepest descent method first introduced by Brillouin, the phase velocity is shown to be the signal velocity when the dispersion is anomalous in the full range of frequencies.
The integration of angular velocity
Boyle, Michael
2016-01-01
A common problem in physics and engineering is determination of the orientation of an object given its angular velocity. When the direction of the angular velocity changes in time, this is a nontrivial problem involving coupled differential equations. Several possible approaches are examined, along with various improvements over previous efforts. These are then evaluated numerically by comparison to a complicated but analytically known rotation that is motivated by the important astrophysical problem of precessing black-hole binaries. It is shown that a straightforward solution directly using quaternions is most efficient and accurate, and that the norm of the quaternion is irrelevant. Integration of the generator of the rotation can also be made roughly as efficient as integration of the rotation. Both methods will typically be twice as efficient naive vector- or matrix-based methods. Implementation by means of standard general-purpose numerical integrators is stable and efficient, so that such problems can ...
The Pulsar Kick Velocity Distribution
Hansen, B M S; Hansen, Brad M. S.
1997-01-01
We analyse the sample of pulsar proper motions, taking detailed account of the selection effects of the original surveys. We treat censored data using survival statistics. From a comparison of our results with Monte Carlo simulations, we find that the mean birth speed of a pulsar is 250-300 km/s, rather than the 450 km/s foundby Lyne & Lorimer (1994). The resultant distribution is consistent with a maxwellian with dispersion $ \\sigma_v = 190 km/s$. Despite the large birth velocities, we find that the pulsars with long characteristic ages show the asymmetric drift, indicating that they are dynamically old. These pulsars may result from the low velocity tail of the younger population, although modified by their origin in binaries and by evolution in the galactic potential.
Multilogarithmic velocity renormalization in graphene
Sharma, Anand; Kopietz, Peter
2016-06-01
We reexamine the effect of long-range Coulomb interactions on the quasiparticle velocity in graphene. Using a nonperturbative functional renormalization group approach with partial bosonization in the forward scattering channel and momentum transfer cutoff scheme, we calculate the quasiparticle velocity, v (k ) , and the quasiparticle residue, Z , with frequency-dependent polarization. One of our most striking results is that v (k ) ∝ln[Ck(α ) /k ] where the momentum- and interaction-dependent cutoff scale Ck(α ) vanishes logarithmically for k →0 . Here k is measured with respect to one of the charge neutrality (Dirac) points and α =2.2 is the strength of dimensionless bare interaction. Moreover, we also demonstrate that the so-obtained multilogarithmic singularity is reconcilable with the perturbative expansion of v (k ) in powers of the bare interaction.
Arm classification and velocity gradients in spiral galaxies
Energy Technology Data Exchange (ETDEWEB)
Biviano, A.; Girardi, M.; Giuricin, G.; Mardirossian, F.; Mezzetti, M. (Trieste Univ. (Italy) Scuola Internazionale Superiore di Studi Avanzati (Italy) Scuola Internazionale Superiore di Studi Avanzati, Trieste (Italy) Scuola Internazionale Superiore di Studi Avanzati (Italy) Centro Interuniversitario Regionale di Astrofisica e Cosmologia (Italy))
1991-08-01
On the basis of published rotation curves, velocity gradients are compiled for 94 galaxies. A significant correlation is found in this sample of galaxies between their gradients and arm classes (as given by Elmegreen and Elmegreen, 1982); galaxies with steeper curves tend to have a flocculent arm structure, and galaxies with flatter curves tend to have a grand design morphology. The correlation is true, since it is not induced by other correlations. The present result is in agreement with previous suggestions by Whitmore (1984) and with the recent result by Elmegreen and Elmegreen; it is also consistent with the predictions of density wave theory for the formation of the spiral structure. 89 refs.
The statistical properties of sea ice velocity fields
Agarwal, Sahil
2016-01-01
Thorndike (1982, 1986b) argued that the surface pressure field over the Arctic Ocean can be treated as an isotropic, stationary, homogeneous, Gaussian random field and thereby estimated a number of covariance functions from two years (1979 and 1980) of data. Given the active interest in changes of general circulation quantities and indices in the polar regions during the recent few decades, the spatial correlations in sea ice velocity fields are of particular interest. We ask how persistent are these correlations? To this end, we develop a stochastic model for Arctic sea ice velocity fields based on a multi-fractal analysis of observed sea ice velocity fields from satellites and buoys for the period 1978 - 2012. Having previously found that the Arctic Equivalent Ice Extent (EIE) has a white noise structure on annual to bi-annual time scales (Agarwal et al. 2012), we assess the connection between EIE and ice motion. We demonstrate the long-term stationarity of the spatial correlation structure of the velocity ...
Institute of Scientific and Technical Information of China (English)
孙江丽; 于海容
2012-01-01
[目的]探讨胎儿脐动脉舒张末期血流缺失(AEDV)与妊娠结局的关系.[方法]产前常规应用脉冲多普勒技术行胎儿脐动脉血流频谱检测,确诊为AEDV孕妇36例,分析AEDV与妊娠合并症、妊娠结局的关系.[结果]36例AEDV病例中,重度子痫前期69.4%(25/36),胎儿生长受限80.6%(29/36),羊水过少22.2%(8/36),妊娠期肝内胆管淤积症11.1%(4/36),妊娠期糖尿病8.3%(3/36);胎儿先天畸形发生率为16.7%(6 / 36),病死率55.6%(20 /36 ).[结论]脐动脉舒张末期血流缺失是脐动脉血流阻力增高的特有表现,表明胎儿-胎盘循环障碍,妊娠合并症增多,胎儿预后不良,临床应给予高度重视.%[Objective] To explore the relationship between absent end diastolic velocity (AEDV) in theumbilical artery and the pregnancy outcome. [Methods]Pulse Doppler was used to measure fetal umbilical ar tery flow. A total of 36 pregnant women were diagnosed as AEDV. The correlation of AEDV with pregnancy complications and pregnancy outcomes was analyzed. [Results] Among 36 AEDV cases, there were 25 cases of severe preeclampsia(69. 4%) , 29 cases of intrauterine growth retardation(IUGR) (80. 6%) , 8 cases of oli gohydramnios(22. 2%) , 4 cases of interahepatic cholestasis of pregnancy(ll. 1%) and 3 cases of gestational diabetes mellitus(8. 3%). The incident rate of fetal malformation was 16. 7% (6/36) and the mortality rate was 55. 6%(20/36). [Conclusion]AEDV in the umbilical artery is the unique performance of abnormally in creased resistance of blood flow in the umbilical artery, which suggests fetal placenta circulation barrier, more pregnancy complications and poor prognosis of fetus. Therefore AEDV should be paid attention.
Velocity-aligned Doppler spectroscopy
Energy Technology Data Exchange (ETDEWEB)
Xu, Z.; Koplitz, B.; Wittig, C.
1989-03-01
The technique of velocity-aligned Doppler spectrosocopy (VADS) is presented and discussed. For photolysis/probe experiments with pulsed initiation, VADS can yield Doppler profiles for nascent photofragments that allow detailed center-of-mass (c.m.) kinetic energy distributions to be extracted. When compared with traditional forms of Doppler spectroscopy, the improvement in kinetic energy resolution is dramatic. Changes in the measured profiles are a consequence of spatial discrimination (i.e., focused and overlapping photolysis and probe beams) and delayed observation. These factors result in the selective detection of species whose velocities are aligned with the wave vector of the probe radiation k/sub pr/, thus revealing the speed distribution along k/sub pr/ rather than the distribution of nascent velocity components projected upon this direction. Mathematical details of the procedure used to model VADS are given, and experimental illustrations for HI, H/sub 2/S, and NH/sub 3/ photodissociation are presented. In these examples, pulsed photodissociation produces H atoms that are detected by sequential two-photon, two-frequency ionization via Lyman-..cap alpha.. with a pulsed laser (121.6+364.7 nm), and measuring the Lyman-..cap alpha.. Doppler profile as a function of probe delay reveals both internal and c.m. kinetic energy distributions for the photofragments. Strengths and weaknesses of VADS as a tool for investigating photofragmentation phenomena are also discussed.
High velocity collisions of nanoparticles
Johnson, Donald F.; Mattson, William D.
2017-01-01
Nanoparticles (NPs) are a unique class of material with highly functionalizable surfaces and exciting applications. With a large surface-to-volume ratio and potentially high surface tension, shocked nanoparticles might display unique materials behavior. Using density functional theory, we have simulated high-velocity NP collisions under a variety of conditions. NPs composed of diamond-C, cubic-BN, and diamond-Si were considered with particle sizes up to 3.5 nm diameter. Additional simulations involved NPs that were destabilized by incorporating internal strain. The initial spherical NP structures were carved out of bulk crystals while the NPs with internal strain were constructed as a dense core (compressive strain) encompassed by a thin shell (tensile strain). Both on-axis and off-axis collisions were simulated at 10 km/s relative velocity. The amount of internal strain was artificially increased by creating a dense inner core with bond lengths compressed up to 8%. Collision dynamics, shock propagation, and fragmentation will be analyzed, but the simulation are ongoing and results are not finalized. The effect of material properties, internal strain, and collision velocity will be discussed.
Apparatus and method for velocity estimation in synthetic aperture imaging
DEFF Research Database (Denmark)
2003-01-01
by the object (4) and received by the elements of the transducer array (5). All of these signals are then combined in the beam processor (6) to focus all of the beams in the image in both transmit and receive mode and the simultaneously focused signals are used for updating the image in the processor (7......). The update signals are used in the velocity estimation processor (8) to correlate the individual measurements to obtain the displacement between high-resolution images and thereby determine the velocity....
Response of composite laminates on impact of high velocity projectiles
Energy Technology Data Exchange (ETDEWEB)
Siva Kumar, K.; Balakrishna Bhat, T. [Defence Metallurgical Research Lab., Hyderabad (India)
1998-05-01
Past work on damage of composites subjected to low velocity and hypervelocity impact has been briefly reviewed and some new results on the glass fibre reinforced plastic composite laminates impacted with high velocity projectiles are presented. The effect of thickness of the laminates and the angle of attack on the energy absorption by the composite laminates and the area of damage caused by impact are described. A correlation is made between the energy absorption and the area of damage. Also described is a new method called infiltration radiography useful for assessing the damage in laminated composites upon ballistic impact. (orig.) 28 refs.
Laser transit anemometer measurements of a JANNAF nozzle base velocity flow field
Hunter, William W., Jr.; Russ, C. E., Jr.; Clemmons, J. I., Jr.
1990-01-01
Velocity flow fields of a nozzle jet exhausting into a supersonic flow were surveyed. The measurements were obtained with a laser transit anemometer (LTA) system in the time domain with a correlation instrument. The LTA data is transformed into the velocity domain to remove the error that occurs when the data is analyzed in the time domain. The final data is shown in velocity vector plots for positions upstream, downstream, and in the exhaust plane of the jet nozzle.
Dense velocity reconstruction from tomographic PTV with material derivatives
Schneiders, Jan F. G.; Scarano, Fulvio
2016-09-01
A method is proposed to reconstruct the instantaneous velocity field from time-resolved volumetric particle tracking velocimetry (PTV, e.g., 3D-PTV, tomographic PTV and Shake-the-Box), employing both the instantaneous velocity and the velocity material derivative of the sparse tracer particles. The constraint to the measured temporal derivative of the PTV particle tracks improves the consistency of the reconstructed velocity field. The method is christened as pouring time into space, as it leverages temporal information to increase the spatial resolution of volumetric PTV measurements. This approach becomes relevant in cases where the spatial resolution is limited by the seeding concentration. The method solves an optimization problem to find the vorticity and velocity fields that minimize a cost function, which includes next to instantaneous velocity, also the velocity material derivative. The velocity and its material derivative are related through the vorticity transport equation, and the cost function is minimized using the limited-memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) algorithm. The procedure is assessed numerically with a simulated PTV experiment in a turbulent boundary layer from a direct numerical simulation (DNS). The experimental validation considers a tomographic particle image velocimetry (PIV) experiment in a similar turbulent boundary layer and the additional case of a jet flow. The proposed technique (`vortex-in-cell plus', VIC+) is compared to tomographic PIV analysis (3D iterative cross-correlation), PTV interpolation methods (linear and adaptive Gaussian windowing) and to vortex-in-cell (VIC) interpolation without the material derivative. A visible increase in resolved details in the turbulent structures is obtained with the VIC+ approach, both in numerical simulations and experiments. This results in a more accurate determination of the turbulent stresses distribution in turbulent boundary layer investigations. Data from a jet
UHF RiverSonde observations of water surface velocity at Threemile Slough, California
Teague, C.C.; Barrick, D.E.; Lilleboe, P.M.; Cheng, R.T.; Ruhl, C.A.
2005-01-01
A UHF RiverSonde system, operating near 350 MHz, has been in operation at Threemile Slough in central California, USA since September 2004. The water in the slough is dominated by tidal effects, with flow reversals four times a day and a peak velocity of about 0.8 m/s in each direction. Water level and water velocity are continually measured by the U. S. Geological Survey at the experiment site. The velocity is measured every 15 minutes by an ultrasonic velocity meter (UVM) which determines the water velocity from two-way acoustic propagation time-difference measurements made across the channel. The RiverSonde also measures surface velocity every 15 minutes using radar resonant backscatter techniques. Velocity and water level data are retrieved through a radio data link and a wideband internet connection. Over a period of several months, the radar-derived mean surface velocity has been very highly correlated with the UVM index velocity several meters below the surface, with a coefficient of determination R2 of 0.976 and an RMS difference of less than 10 cm/s. The wind has a small but measurable effect on the velocities measured by both instruments. In addition to the mean surface velocity across the channel, the RiverSonde system provides an estimate of the cross-channel variation of the surface velocity. ?? 2005 IEEE.
Shear velocity of the Rotokawa geothermal field using ambient noise
Civilini, F.; Savage, M. K.; Townend, J.
2014-12-01
Ambient noise correlation is an increasingly popular seismological technique that uses the ambient seismic noise recorded at two stations to construct an empirical Green's function. Applications of this technique include determining shear velocity structure and attenuation. An advantage of ambient noise is that it does not rely on external sources of seismic energy such as local or teleseismic earthquakes. This method has been used in the geothermal industry to determine the depths at which magmatic processes occur, to distinguish between production and non-production areas, and to observe seismic velocity perturbations associated with fluid extraction. We will present a velocity model for the Rotokawa geothermal field near Taupo, New Zealand, produced from ambient noise cross correlations. Production at Rotokawa is based on the "Rotokawa A" combined cycle power station established in 1997 and the "Nga Awa Purua" triple flash power plant established in 2010. Rotokawa Joint Venture, a partnership between Mighty River Power and Tauhara North No. 2 Trust currently operates 174 MW of generation at Rotokawa. An array of short period seismometers was installed in 2008 and occupies an area of roughly 5 square kilometers around the site. Although both cultural and natural noise sources are recorded at the stations, the instrument separation distance provides a unique challenge for analyzing cross correlations produced by both signal types. The inter-station spacing is on the order of a few kilometers, so waves from cultural sources generally are not coherent from one station to the other, while the wavelength produced by natural noise is greater than the station separation. Velocity models produced from these two source types will be compared to known geological models of the site. Depending on the amount of data needed to adequately construct cross-correlations, a time-dependent model of velocity will be established and compared with geothermal production processes.
Ku, Chin-Shang; Wu, Yih-Min; Huang, Bor-Shouh; Huang, Win-Gee; Liu, Chun-Chi
2016-04-01
A ML 6.4 earthquake occurred on 4 March 2010 in Kaohsiung, the southern part of Taiwan, this shallow earthquake is the largest one of that area in the past few years. Some damages occurred on buildings and bridges after the earthquake, obvious surface deformation up to few cm was observed and the transportation including road and train traffic was also affected near the source area. Some studies about monitoring the velocity change induced by the big earthquake were carried out recently, most of studies used cross-correlation of the ambient noise-based method and indicated velocity drop was observed immediately after the big earthquake. However, this method is not able to constrain the depth of velocity change, and need to assume a homogeneous seismic velocity change during the earthquake. In this study, we selected 25 broadband seismic stations in the southern Taiwan and time period is from 2009/03 to 2011/03. Then we explored the velocity change associated with the 2010 Kaohsiung earthquake by applying ambient noise tomography (ANT) method. ANT is a way of using interferometry to image subsurface seismic velocity variations by using surface wave dispersions extracted from the ambient noise cross-correlation of seismic station-pairs, then the 2-D group velocity map with different periods could be extracted. Compare to ambient noise-based cross-correlation analysis, we estimated sensitivity kernel of dispersion curves and converted 2-D group velocity map from "with the period" to "with the depth" to have more constraints on the depth of velocity change. By subtracting shear velocity between "before" and "after" the earthquake, we could explore velocity change associated with the earthquake. Our result shows velocity reduction about 5-10% around the focal depth after the 2010 Kaohsiung earthquake and the post-seismic velocity recovery was observed with time period increasing, which may suggest a healing process of damaged rocks.
Experimental analysis of turbulence effect in settling velocity of suspended sediments
Directory of Open Access Journals (Sweden)
H. Salinas–Tapia
2008-01-01
Full Text Available Settling velocities of sediment particles for different size ranges were measured in this work using PIV with the help of discriminatory filters. An experimental channel 10x15 cm cross section was used in order to obtain two set of turbulent characteristics corresponding with two different flow rates. The purpose was to analyze the effect of turbulence on the solids settling velocity. The technique allowed us to measure the individual settling velocity of the particles and the flow velocity field of the fluid. Capture and image analysis was performed with digital cameras (CCD using the software Sharp–provision PIV and the statistical cross correlation technique. Results showed that settling velocity of particles is affected by turbulence which enhances the fluid drag coefficient. Physical explanation of this phenomenon is related with the magnitude of the vertical fluctuating velocity of the fluid. However, more research is needed in order to define settling velocity formulas that takes into account this effect
Institute of Scientific and Technical Information of China (English)
2013-01-01
目的分析高血压患者肱踝动脉脉搏波传导速度(brachial-ankle pulse wave velocity，baPWV)与左心室肥厚的关系。方法入选2009年9月-2012年6月本院969例原发性高血压患者，按照左心室肥厚定义将其分为高血压伴左心室肥厚(n=380)、高血压不伴左心室肥厚(n=589)两组。应用全自动动脉硬化测定仪测定双侧baPWV，取双侧baPWV平均值。结果高血压伴左心室肥厚组baPWV水平明显高于高血压不伴左心室肥厚组(P＜0.05)。线性相关分析表明高血压患者baPWV水平与室间隔厚度(r=0.139，P＜0.01)、左心室后壁厚度(r=0.124，P＜0.01)以及左心室重量指数呈正相关(r=0.312，P＜0.01)。进一步应用多元线性回归分析调整了年龄、性别、体重指数、收缩压、舒张压、血糖、血清胆固醇、低密度脂蛋白胆固醇、高密度脂蛋白胆固醇、甘油三酯等心血管危险因素的影响后，baPWV与室间隔厚度(标化的相关系数β=0.125，P＜0.05)、左心室后壁厚度(标化的相关系数β=0.131，P＜0.05)以及左心室重量指数(标化的相关系数β=0.027，P＜0.01)仍然相关。结论高血压患者baPWV与左心室肥厚密切相关。%Objective To analyze the correlation between brachial-ankle pulse wave velocity (baPWV) and left ventricular hypertrophy (LVH) in hypertensive patients. Methods A total 969 primary hypertensive patients admitted to our hospital from September 2009 to June 2012 were divided into hypertension with LVH group (n=380) and hypertension without LVH group (n=589). Their bilateral baPWV was measured with automatic arteriosclerosis detector and its average value was calculated. Results The baPWV value was significantly higher in hypertension with LVH group than in hypertension without LVH group (P < 0.05). Linear correlation analysis showed that the baPW value was positively correlated with the interventricular septal thickness (r=0.139;P <0.01), LV posterior wall
Velocity Correction and Measurement Uncertainty Analysis of Light Screen Velocity Measuring Method
Institute of Scientific and Technical Information of China (English)
ZHENG Bin; ZUO Zhao-lu; HOU Wen
2012-01-01
Light screen velocity measuring method with unique advantages has been widely used in the velocity measurement of various moving bodies.For large air resistance and friction force which the big moving bodies are subjected to during the light screen velocity measuring,the principle of velocity correction was proposed and a velocity correction equation was derived.A light screen velocity measuring method was used to measure the velocity of big moving bodies which have complex velocity attenuation,and the better results were gained in practical tests.The measuring uncertainty after the velocity correction was calculated.
Berson, Arganthaël; Poignand, Gaelle; Jondeau, Emmanuel; Blanc-Benon, Philippe; Comte-Bellot, Geneviève
2012-01-01
International audience; This paper summarizes our recent work on the development of thermal anemometry to measure velocity and temperature fluctuations in oscillating flows. First, we demonstrate that velocity cannot be measured accurately by hot-wire anemometry in oscillating flows when the flow reverses its direction. Indeed, there is no unique and well-defined correlation between the flow velocity and heat transfer near flow reversal, which prevents the recovery of velocity fluctuations fr...
Correlation functions for a periodic box-ball system
Energy Technology Data Exchange (ETDEWEB)
Mada, Jun [College of Industrial Technology, Nihon University, 2-11-1 Shin-ei, Narashino, Chiba 275-8576 (Japan); Tokihiro, Tetsuji [Graduate School of Mathematical Sciences, University of Tokyo, 3-8-1 Komaba, Tokyo 153-8914 (Japan)
2010-04-02
We investigate correlation functions in a periodic box-ball system. For the two-point functions of short distance, we give explicit formulae obtained by combinatorial methods. We give expressions for general N-point functions in terms of ultradiscrete theta functions.
SLIP VELOCITY IN PULSED DISC AND DOUGHNUT EXTRACTION COLUMN
Directory of Open Access Journals (Sweden)
Mohammad Outokesh
2011-09-01
Full Text Available In the present work, slip velocity has been measured in a 76 mm diameter pulsed disc and doughnut extraction column for four different liquid-liquid systems. The effects of operating variables including pulsation intensity and dispersed and continuous phase flow rates on slip velocity have been investigated. The existence of three different operational regimes, namely mixersettler, transition, and emulsion regimes, was observed when the energy input was changed. Empirical correlations are derived for prediction of the slip velocity in terms of operating variables, physical properties of the liquid systems, and column geometry for different regimes. Good agreement between prediction and experiments was found for all operating conditions that were investigated.
Velocity measurement by coherent x-ray heterodyning
Energy Technology Data Exchange (ETDEWEB)
Lhermitte, Julien R. M.; Rogers, Michael C.; Manet, Sabine; Sutton, Mark
2017-01-01
We present a small-angle coherent x-ray scattering technique used for measuring flow velocities in slow moving materials. The technique is an extension of X-ray Photon Correlation Spectroscopy (XPCS): It involves mixing the scattering from moving tracer particles with a static reference that heterodynes the signal. This acts to elongate temporal effects caused by flow in homodyne measurements, allowing for a more robust measurement of flow properties. Using coherent x-ray heterodyning, velocities ranging from 0.1 to 10 μm/s were measured for a viscous fluid pushed through a rectangular channel. We describe experimental protocols and theory for making these Poiseuille flow profile measurements and also develop the relevant theory for using heterodyne XPCS to measure velocities in uniform and Couette flows.
A new settling velocity model to describe secondary sedimentation
DEFF Research Database (Denmark)
Ramin, Elham; Wágner, Dorottya Sarolta; Yde, Lars
2014-01-01
distribution in SSTs can be predicted using computational fluid dynamics (CFD) tools. Despite extensive studies on the compression settling behaviour of activated sludge and the development of advanced settling velocity models for use in SST simulations, these models are not often used, due to the challenges...... associated with their calibration. In this study, we developed a new settling velocity model, including hindered, transient and compression settling, and showed that it can be calibrated to data from a simple, novel settling column experimental set-up using the Bayesian optimization method DREAM......(ZS). In addition, correlations between the Herschel-Bulkley rheological model parameters and sludge concentration were identified with data from batch rheological experiments. A 2-D axisymmetric CFD model of a circular SST containing the new settling velocity and rheological model was validated with full...
Signal processing method for shear wave velocity measurement
Institute of Scientific and Technical Information of China (English)
Hou Xingmin; Qu Shuying; Shi Xiangdong
2007-01-01
Soil shear wave velocity (SWV) is an important parameter in geotechnical engineering. To measure the soil SWV, three methods are generally used in China, including the single-hole method, cross-hole method and the surface-wave technique. An optimized approach based on a correlation function for single-hole SWV measurement is presented in this paper. In this approach, inherent inconsistencies of the artificial methods such as negative velocities, and too-large and too-small velocities, are eliminated from the single-hole method, and the efficiency of data processing is improved. In addition, verification using the cross-hole method of upper measuring points shows that the proposed optimized approach yields high precision in signal processing.
Asymmetry of Coordinate and Velocity in Noisy Oscillator
Institute of Scientific and Technical Information of China (English)
SONG Yan-Li; BAO Jing-Dong; WANG Hai-Yan; JI Qing
2005-01-01
The velocity variable of a noise oscillator as an internal or external noise is proposed, the spectrum of which is quite different from that of the coordinate variable of the same noise oscillator. The former leads to ballistic diffusion for a free particle in long time limit and the asymptotical results of the system are sensitive to the initial condition. However, diffusion process induced by the coordinate of noise oscillator is a normal one and depends on the initial condition only in the transient time. This allows us to classify two kinds of non-Markovian processes: normal one and strong one, just like the processes induced by the coordinate and the velocity of noise oscillator, respectively.Applying to a correlation ratchet, we have found that the steady current of a particle subjected to the velocity of noise oscillator is opposite to that subjected to its coordinate, thus the former shows greenness and the latter redness.
A dissipative random velocity field for fully developed fluid turbulence
Pereira, Rodrigo M; Chevillard, Laurent
2015-01-01
We investigate the statistical properties, based on numerical simulations and analytical calculations, of a recently proposed stochastic model for the velocity field of an incompressible, homogeneous, isotropic and fully developed turbulent flow. A key step in the construction of this model is the introduction of some aspects of the vorticity stretching mechanism that governs the dynamics of fluid particles along their trajectory. An additional further phenomenological step aimed at including the long range correlated nature of turbulence makes this model depending on a single free parameter $\\gamma$ that can be estimated from experimental measurements. We confirm the realism of the model regarding the geometry of the velocity gradient tensor, the power-law behaviour of the moments of velocity increments (i.e. the structure functions), including the intermittent corrections, and the existence of energy transfers across scales. We quantify the dependence of these basic properties of turbulent flows on the free...
Velocity measurement by coherent x-ray heterodyning.
Lhermitte, Julien R M; Rogers, Michael C; Manet, Sabine; Sutton, Mark
2017-01-01
We present a small-angle coherent x-ray scattering technique used for measuring flow velocities in slow moving materials. The technique is an extension of X-ray Photon Correlation Spectroscopy (XPCS): It involves mixing the scattering from moving tracer particles with a static reference that heterodynes the signal. This acts to elongate temporal effects caused by flow in homodyne measurements, allowing for a more robust measurement of flow properties. Using coherent x-ray heterodyning, velocities ranging from 0.1 to 10 μm/s were measured for a viscous fluid pushed through a rectangular channel. We describe experimental protocols and theory for making these Poiseuille flow profile measurements and also develop the relevant theory for using heterodyne XPCS to measure velocities in uniform and Couette flows.
Peculiar velocities in dynamic spacetimes
Bini, Donato
2014-01-01
We investigate the asymptotic behavior of peculiar velocities in certain physically significant time-dependent gravitational fields. Previous studies of the motion of free test particles have focused on the \\emph{collapse scenario}, according to which a double-jet pattern with Lorentz factor $\\gamma \\to \\infty$ develops asymptotically along the direction of complete gravitational collapse. In the present work, we identify a second \\emph{wave scenario}, in which a single-jet pattern with Lorentz factor $\\gamma \\to \\infty$ develops asymptotically along the direction of wave propagation. The possibility of a connection between the two scenarios for the formation of cosmic jets is critically examined.
Minimum length-maximum velocity
Panes, Boris
2012-03-01
We study a framework where the hypothesis of a minimum length in space-time is complemented with the notion of reference frame invariance. It turns out natural to interpret the action of the obtained reference frame transformations in the context of doubly special relativity. As a consequence of this formalism we find interesting connections between the minimum length properties and the modified velocity-energy relation for ultra-relativistic particles. For example, we can predict the ratio between the minimum lengths in space and time using the results from OPERA on superluminal neutrinos.
Velocity condensation for magnetotactic bacteria
Rupprecht, Jean-Francois; Bocquet, Lydéric
2015-01-01
Magnetotactic swimmers tend to align along magnetic field lines against stochastic reorientations. We show that the swimming strategy, e.g. active Brownian motion versus run-and-tumble dynamics, strongly affects the orientation statistics. The latter can exhibit a velocity condensation whereby the alignment probability density diverges. As a consequence, we find that the swimming strategy affects the nature of the phase transition to collective motion, indicating that L\\'evy run-and-tumble walks can outperform active Brownian processes as strategies to trigger collective behavior.
Not a Copernican observer: biased peculiar velocity statistics in the local Universe
Hellwing, Wojciech A; Feix, Martin; Bilicki, Maciej
2016-01-01
We assess the effect of the local large scale structure on the estimation of two-point statistics of the observed radial peculiar velocities of galaxies. A large N-body simulation is used to examine these statistics from the perspective of random observers as well as "Local Group (LG)-like" observers conditioned to reside in an environment resembling the observed universe within 20 Mpc. The local environment systematically distorts the shape and amplitude of velocity statistics with respect to ensemble-averaged measurements made by a Copernican (random) observer. The Virgo cluster has the most significant impact, introducing large systematic deviations in all the statistics. For a simple "top-hat" selection function, an idealized survey extending to $\\sim 160h^{-1}\\,{\\rm Mpc}$ or deeper is needed to completely mitigate the effects of the local environment. Using shallower catalogues leads to systematic deviations of the order of $50$ to $200\\%$ depending on the scale considered. For a flat redshift distributi...
Guibout, Vincent M.
This dissertation has been motivated by the need for new methods to address complex problems that arise in spacecraft formation design. As a direct result of this motivation, a general methodology for solving two-point boundary value problems for Hamiltonian systems has been found. Using the Hamilton-Jacobi theory in conjunction with the canonical transformation induced by the phase flow, it is shown that generating functions solve two-point boundary value problems. Traditional techniques for addressing these problems are iterative and require an initial guess. The method presented in this dissertation solves boundary value problems at the cost of a single function evaluation, although it requires knowledge of at least one generating function. Properties of this method are presented. Specifically, we show that it includes perturbation theory and generalizes it to nonlinear systems. Most importantly, it predicts the existence of multiple solutions and allows one to recover all of these solutions. To demonstrate the efficiency of this approach, an algorithm for computing the generating functions is proposed and its convergence properties are studied. As the method developed in this work is based on the Hamiltonian structure of the problem, particular attention must be paid to the numerics of the algorithm. To address this, a general framework for studying the discretization of certain dynamical systems is developed. This framework generalizes earlier work on discretization of Lagrangian and Hamiltonian systems on tangent and cotangent bundles respectively. In addition, it provides new insights into some symplectic integrators and leads to a new discrete Hamilton-Jacobi theory. Most importantly, it allows one to discretize optimal control problems. In particular, a discrete maximum principle is presented. This dissertation also investigates applications of the proposed method to solve two-point boundary value problems. In particular, new techniques for designing
The relationship between trunk rotation, upper quarter dynamic stability and pitch velocity.
Bullock, Garrett S; Schmitt, Abigail C; Chasse, Patrick; Little, Barrett A; Diehl, Lee H; Butler, Robert J
2017-02-21
Understanding the relationship between upper quarter mobility, dynamic stability and pitching velocity may be beneficial in elucidating underlying factors that affect pitching performance. The purpose of this study was to investigate upper trunk rotation mobility and upper quarter dynamic stability and their correlation to pitch velocity in NCAA Division I collegiate pitchers. We hypothesized that collegiate pitchers with greater upper trunk rotation mobility and upper extremity dynamic stability would exhibit higher pitching velocity. Trunk rotation and the Upper Quarter Y-Balance Test (YBT-UQ) were measured utilizing standardized protocols. Collegiate pitchers (n=30) then proceeded to complete their team prescribed dynamic and throwing warm up followed by a pitching session from regulation distance at 100% effort. Each pitch was recorded for velocity and pitch type, only fastballs were utilized in analysis. The relationships between trunk rotation and fastball velocity, and YBT-UQ scores and fastball velocity were assessed using a series of two-tail Pearsons Correlations (p<.05). Throwing and non-throwing sides (69.6± 9.5 deg., 70.7± 9.4 deg.) had similar trunk rotation mobility. No statistically significant correlation between upper trunk rotation mobility and pitch velocity was found (throwing arm: r=.131, p<.491; non-throwing arm: r=.135, p<.478). There was also no correlation between the YBT-UQ and fastball velocity. In this study of Division I baseball pitchers, we found no relationship between trunk rotational mobility, upper quarter dynamic stability and pitching velocity. This suggests that increased upper extremity stability and trunk mobility are not directly related to fastball velocity. Understanding factors that associate to velocity may be helpful in predicting pitching performance.
Velocity of sound in hadron matter
Energy Technology Data Exchange (ETDEWEB)
Epele, L.N.; Fanchiotti, H.; Garcia Canal, C.A.; Roulet, E.
1987-09-01
The velocity of sound in hadron matter, in both the confined and deconfined phases, is studied. This velocity of sound appears to be an important tool to distinguish among different bag-model-based thermodynamical descriptions of hadronic matter.
Inexpensive Time-of-Flight Velocity Measurements.
Everett, Glen E.; Wild, R. L.
1979-01-01
Describes a circuit designed to measure time-of-flight velocity and shows how to use it to determine bullet velocity in connection with the ballistic pendulum demonstration of momentum conservation. (Author/GA)
The 2pt+: an enhanced 2 point correlation function
Ave, M; Cronin, J; Neto, J R T de Mello; Olinto, A V; Pavlidou, V; Privitera, P; Siffert, B B; Schmidt, F; Venters, T
2009-01-01
We introduce a new method for testing departure from isotropy of points on a sphere based on an enhanced form of the two-point correlation function that we named 2pt+. This method uses information from the two extra variables that define the vector between two points on a sphere. We show that this is a powerful method to test departure from isotropy of a distribution of points on a sphere especially when the number of events is small. We apply the method to a few examples in astronomy and discuss the relevance for limited datasets, such as the case of ultra-high energy cosmic rays.
Ishii, Takaoki; Watanabe, Ryo; Moriya, Toshimitsu; Ohmiya, Hirohisa; Mori, Seiji; Sawamura, Masaya
2013-09-27
Catalyst-substrate hydrogen bonds in artificial catalysts usually occur in aprotic solvents, but not in protic solvents, in contrast to enzymatic catalysis. We report a case in which ligand-substrate hydrogen-bonding interactions cooperate with a transition-metal center in alcoholic solvents for enantioselective catalysis. Copper(I) complexes with prolinol-based hydroxy amino phosphane chiral ligands catalytically promoted the direct alkynylation of aldehydes with terminal alkynes in alcoholic solvents to afford nonracemic secondary propargylic alcohols with high enantioselectivities. Quantum-mechanical calculations of enantiodiscriminating transition states show the occurrence of a nonclassical sp(3)-C-H···O hydrogen bond as a secondary interaction between the ligand and substrate, which results in highly directional catalyst-substrate two-point hydrogen bonding.
Spatiotemporal variations in the surface velocities of Antarctic Peninsula glaciers
Directory of Open Access Journals (Sweden)
J. Chen
2014-11-01
Full Text Available Velocity is an important parameter for the estimation of glacier mass balance, which directly signals the response of glaciers to climate change. Antarctic ice sheet movement and the associated spatiotemporal velocity variations are of great significance to global sea level rise. In this study, we estimate Antarctic Peninsula glacier velocities using the co-registration of optically sensed images and correlation (hereafter referred to as COSI-Corr based on moderate-resolution imaging spectroradiometer Level 1B data (hereafter referred to as MODIS L1B. The results show that the glaciers of Graham Land and the Larsen Ice Shelf have substantially different velocity features. The Graham Land glaciers primarily flow from the peninsula ridge towards the Weddell Sea and Bellingshausen Sea on the east and west sides, respectively. There are very large velocity variations among the different ice streams, with a minimum of −1 and a maximum of 1500 m a−1 (with an average of 100–150 m a−1. Over the period 2000–2012, the glaciers of Graham Land accelerated in the south but slowed down in the north. In contrast, the Larsen Ice Shelf flows in a relatively uniform direction, mainly towards the northeast into the Weddell Sea. Its average velocity is 750–800 m a−1 and the maximum is > 1500 m a−1. During the period 2000–2012, the Larsen Ice Shelf experienced significant acceleration. The use of COSI-Corr based on MODIS L1B data is suitable for glacier velocity monitoring on the Antarctic Peninsula over long time series and large spatial scales. This method is clearly advantageous for analysing macro-scale spatiotemporal variations in glacier movement.
Instantaneous velocity profile measurements in a turbulent boundary layer
Robinson, S. K.
1986-01-01
Instantaneous wall shear stress and streamwise velocities have been measured simultaneously in a flat-plate, turbulent boundary layer at moderate Reynolds number in an effort to provide experimental support for large eddy simulations. Data were obtained using a buried-wire, wall shear gage and a hot-wire rake positioned in the log region of the flow. Fluctuations of the instantaneous U(+) versus Y(+) profiles about a mean law of the wall are shown to be significant and complex. Peak cross-correlation values between wall shear stress and the velocities are high, and reflect the passage of a large structure inclined at a small angle to the wall. Estimates of this angle are consistent with those made by other investigators. Conditional sampling techniques were used to detect the passage of various sizes and types of flow disturbances (events), and to estimate their mean frequency of occurrence. Events characterized by large aand sudden streamwise accelerations were found to be highly coherent throughout the log region and were strongly correlated with large fluctuations in wall shear stress. Phase randomness between the near-wall quantities and the outer velocities was small. The results suggest that the flow events detected by conditional sampling applied to velocities in the log region may be related to the bursting process.
Velocity structure in long period variable star atmospheres
Pilachowski, C.; Wallerstein, G.; Willson, L. A.
1980-01-01
A regression analysis of the dependence of absorption line velocities on wavelength, line strength, excitation potential, and ionization potential is presented. The method determines the region of formation of the absorption lines for a given data and wavelength region. It is concluded that the scatter which is frequently found in velocity measurements of absorption lines in long period variables is probably the result of a shock of moderate amplitude located in or near the reversing layer and that the frequently observed correlation of velocity with excitation and ionization are a result of the velocity gradients produced by this shock in the atmosphere. A simple interpretation of the signs of the coefficients of the regression analysis is presented in terms of preshock, post shock, or across the shock, together with criteria for evaluating the validity of the fit. The amplitude of the reversing layer shock is estimated from an analysis of a series of plates for four long period variable stars along with the most probable stellar velocity for these stars.
Pairwise velocities in the Halo Model: Luminosity and Scale Dependence
Slosar, A; Tasitsiomi, A; Slosar, Anze; Seljak, Uros; Tasitsiomi, Argyro
2006-01-01
We investigate the properties of the pairwise velocity dispersion as a function of galaxy luminosity in the context of a halo model. We derive the distribution of velocities of pairs at a given separation taking into account both one-halo and two-halo contributions. We show that pairwise velocity distribution in real space is a complicated mixture of host-satellite, satellite-satellite and two-halo pairs. The peak value is reached at around 1 Mpc/h and does not reflect the velocity dispersion of a typical halo hosting these galaxies, but is instead dominated by the satellite-satellite pairs in high mass clusters. This is true even for cross-correlations between bins separated in luminosity. As a consequence the velocity dispersion at a given separation can decrease with luminosity, even if the underlying typical halo host mass is increasing, in agreement with some recent observations. We compare our findings to numerical simulations and find a good agreement. Numerical simulations also suggest a luminosity de...
Nozaki, Taiki; Tasaki, Atsushi; Horiuchi, Saya; Ochi, Junko; Starkey, Jay; Hara, Takeshi; Saida, Yukihisa; Yoshioka, Hiroshi
2016-08-01
Purpose To determine the degree of preoperative fatty degeneration within muscles, postoperative longitudinal changes in fatty degeneration, and differences in fatty degeneration between patients with full-thickness supraspinatus tears who do and those who do not experience a retear after surgery. Materials and Methods This prospective study had institutional review board approval and was conducted in accordance with the Committee for Human Research. Informed consent was obtained. Fifty patients with full-thickness supraspinatus tears (18 men, 32 women; mean age, 67.0 years ± 8.0; age range, 41-91 years) were recruited. The degrees of preoperative and postoperative fatty degeneration were quantified by using a two-point Dixon magnetic resonance (MR) imaging sequence; two radiologists measured the mean signal intensity on in-phase [S(In)] and fat [S(Fat)] images. Estimates of fatty degeneration were calculated with "fat fraction" values by using the formula S(Fat)/S(In) within the supraspinatus, infraspinatus, and subscapularis muscles at baseline preoperative and at postoperative 1-year follow-up MR imaging. Preoperative fat fractions in the failed-repair group and the intact-repair group were compared by using the Mann-Whitney U test. Results The preoperative fat fractions in the supraspinatus muscle were significantly higher in the failed-repair group than in the intact-repair group (37.0% vs 19.5%, P muscle tended to progress at 1 year postoperatively in only the failed-repair group. Conclusion MR imaging quantification of preoperative fat fractions by using a two-point Dixon sequence within the rotator cuff muscles may be a viable method for predicting postoperative retear. (©) RSNA, 2016.
Velocity Measurement Based on Laser Doppler Effect
Institute of Scientific and Technical Information of China (English)
ZHANG Yan-Yan; HUO Yu-Jing; HE Shu-Fang; GONG Ke
2010-01-01
@@ A novel method for velocity measurement is presented.In this scheme,a parallel-linear-polarization dualfrequency laser is incident on the target and senses the target velocity with both the frequencies,which can increase the maximum measurable velocity significantly.The theoretical analysis and verification experiment of the novel method are presented,which show that high-velocity measurement can be achieved with high precision using this method.
The circular velocity function of group galaxies
Energy Technology Data Exchange (ETDEWEB)
Abramson, Louis E. [Department of Astronomy and Astrophysics and Kavli Institute for Cosmological Physics, The University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Williams, Rik J.; Benson, Andrew J.; Kollmeier, Juna A.; Mulchaey, John S., E-mail: labramson@uchicago.edu [The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
2014-09-20
A robust prediction of ΛCDM cosmology is the halo circular velocity function (CVF), a dynamical cousin of the halo mass function. The correspondence between theoretical and observed CVFs is uncertain, however: cluster galaxies are reported to exhibit a power-law CVF consistent with N-body simulations, but that of the field is distinctly Schechter-like, flattened compared to ΛCDM expectations at circular velocities v {sub c} ≲ 200 km s{sup –1}. Groups offer a powerful probe of the role environment plays in this discrepancy as they bridge the field and clusters. Here, we construct the CVF for a large, mass- and multiplicity-complete sample of group galaxies from the Sloan Digital Sky Survey. Using independent photometric v {sub c} estimators, we find no transition from field to ΛCDM-shaped CVF above v {sub c} = 50 km s{sup –1} as a function of group halo mass. All groups with 12.4 ≲ log M {sub halo}/M {sub ☉} ≲ 15.1 (Local Group analogs to rich clusters) display similar Schechter-like CVFs marginally suppressed at low v {sub c} compared to that of the field. Conversely, some agreement with N-body results emerges for samples saturated with late-type galaxies, with isolated late-types displaying a CVF similar in shape to ΛCDM predictions. We conclude that the flattening of the low-v {sub c} slope in groups is due to their depressed late-type fractions—environment affecting the CVF only to the extent that it correlates with this quantity—and that previous cluster analyses may suffer from interloper contamination. These results serve as useful benchmarks for cosmological simulations of galaxy formation.
Discussion on origin of Pn velocity variation in China and adjacent region
Institute of Scientific and Technical Information of China (English)
裴顺平; 许忠淮; 汪素云
2004-01-01
Pn velocity lateral variation and anisotropy images were reconstructed by adding about 50 000 travel times from the regional seismic networks to the datum set of near 40 000 travel times from National Seismic Network of China used by WANG, et al. We discussed the relation of Pn velocity variation to Moho depth, Earth's heat flow, distribution of Cenozoic volcanic rock and the result of rock experiment under high pressure and high temperature. The result of quantitative analysis indicates that Pn velocity is positively correlated with the crust thickness and negatively correlated with the Earth's heat flow. Two linear regression equations, one between Pn velocity and crust thickness, and the other between Pn velocity and heat flow, were obtained. The rate of variation of Pn velocity vP with pressure P,()Vp/()P, estimated from the velocity variation with crust thickness()Vp/()His close to the result obtained from the rock experiment under high pressure and high temperature. If the effect of crust thickness on Pn velocity is deducted from the velocity variation, then the low Pn velocity beneath Qinghai-Xizang plateau is more notable. The low Pn velocity regions well agree with the Cenozoic volcanic rock. In the several regions with significant anisotropy, the direction of fast Pn velocity is consistent with the orientation of maximum principal crustal compressive stress, and also with the direction of present-day crustal movement. It indicates that the fast Pn velocity direction may be related to the deformation or flow of top mantle material along the direction of maximum pressure.
Improved accuracy in the estimation of blood velocity vectors using matched filtering
DEFF Research Database (Denmark)
Jensen, Jørgen Arendt; Gori, P.
2000-01-01
The blood velocity can be estimated by finding the shift in position of the blood scatterers between subsequent ultrasonic pulse emissions through cross-correlation of the received RF signals. Usually only the velocity component along the beam direction is found. It was shown in a previous paper...... that the complete velocity vector can be found, if the received signals are focused along lines parallel to the direction of the blood flow. A fairly broad beam is emitted in the approach, and this gives rise to a widening in the profiles of the estimated velocity. To reduce this effect, a focused ultrasound...
Dugave, Maxime; Kozlowski, Karol K; Suzuki, Junji
2016-01-01
We use the form factors of the quantum transfer matrix in the zero-temperature limit in order to study the two-point ground-state correlation functions of the XXZ chain in the antiferromagnetic massive regime. We obtain novel form factor series representations of the correlation functions which differ from those derived either from the q-vertex-operator approach or from the algebraic Bethe Ansatz approach to the usual transfer matrix. We advocate that our novel representations are numerically more efficient and allow for a straightforward calculation of the large-distance asymptotic behaviour of the two-point functions. Keeping control over the temperature corrections to the two-point functions we see that these are of order $T^\\infty$ in the whole antiferromagnetic massive regime. The isotropic limit of our result yields a novel form factor series representation for the two-point correlation functions of the XXX chain at zero magnetic field.
Weakly nonlinear density-velocity relation
Chodorowski, M J; Chodorowski, Michal J; Lokas, Ewa L
1996-01-01
We rigorously derive weakly nonlinear relation between cosmic density and velocity fields up to third order in perturbation theory. The density field is described by the mass density contrast, \\de. The velocity field is described by the variable \\te proportional to the velocity divergence, \\te = - f(\\Omega)^{-1} H_0^{-1} \
Balance velocities of the Greenland ice sheet
DEFF Research Database (Denmark)
Joughin, I.; Fahnestock, M.; Ekholm, Simon;
1997-01-01
We present a map of balance velocities for the Greenland ice sheet. The resolution of the underlying DEM, which was derived primarily from radar altimetery data, yields far greater detail than earlier balance velocity estimates for Greenland. The velocity contours reveal in striking detail......, the balance map is useful for ice-sheet modelling, mass balance studies, and field planning....
Application of Vectors to Relative Velocity
Tin-Lam, Toh
2004-01-01
The topic 'relative velocity' has recently been introduced into the Cambridge Ordinary Level Additional Mathematics syllabus under the application of Vectors. In this note, the results of relative velocity and the 'reduction to rest' technique of teaching relative velocity are derived mathematically from vector algebra, in the hope of providing…
Longitudinal and transverse velocity fields in parsec-scale jets
Mertens, Florent
2015-01-01
Radio-loud AGN typically manifest powerful relativistic jets extending up to millions of light years and often showing superluminal motions organised in a complex kinematic pattern. A number of physical models are still competing to explain the jet structure and kinematics revealed by radio images using the VLBI technique. Robust measurements of longitudinal and transverse velocity field in the jets would provide crucial information for these models. This is a difficult task, particularly for transversely resolved jets in objects like 3C 273 and M87. To address this task, we have developed a new technique for identifying significant structural patterns (SSP) of smooth, transversely resolved flows and obtaining a velocity field from cross-correlation of these regions in multi-epoch observations. Detection of individual SSP is performed using the wavelet decomposition and multiscale segmentation of the observed structure. The cross-correlation algorithm combines structural information on different scales of the...
Extending the unambiguous velocity range using multiple carrier frequencies
DEFF Research Database (Denmark)
Zhang, Z.; Jakobsson, A.; Nikolov, Svetoslav;
2005-01-01
Typically, velocity estimators based on the estimation of the Doppler shift will suffer from a limited unambiguous velocity range. Proposed are two novel multiple carrier based velocity estimators extending the velocity range above the Nyquist velocity limit. Numerical simulations indicate...