Correlation Function Of Sources Research Articles

Comparison of different source calculations in two-nucleon channel at large quark mass

We investigate a systematic error coming from higher excited state contributions in the energy shift of light nucleus in the two-nucleon channel by comparing two different source calculations with the exponential and wall sources. Since it is hard to obtain a clear signal of the wall source correlation function in a plateau region, we employ a large quark mass as the pion mass is 0.8 GeV in quenched QCD. We discuss the systematic error in the spin-triplet channel of the two-nucleon system, and the volume dependence of the energy shift.

Second-order statistics of a radially polarized cosine-Gaussian correlated Schell-model beam in anisotropic turbulence.

Recently, we introduced a new class of radially polarized cosine-Gaussian correlated Schell-model (CGCSM) beams of rectangular symmetry based on the partially coherent electromagnetic theory [Opt. Express23, 33099 (2015)]. In this paper, we extend the work to study the second-order statistics such as the average intensity, the spectral degree of coherence, the spectral degree of polarization and the state of polarization in anisotropic turbulence based on an extended von Karman power spectrum with a non-Kolmogorov power law α and an effective anisotropic parameter. Analytical formulas for the cross-spectral density matrix elements of a radially polarized CGCSM beam in anisotropic turbulence are derived. It is found that the second-order statistics are greatly affected by the source correlation function, and the change in the turbulent statistics induces relatively small effect. The significant effect of anisotropic turbulence on the beam parameters mainly appears nearα=3.1, and decreases with the increase of the anisotropic parameter. Furthermore, the polarization state exhibits self-splitting property and each beamlet evolves into a radially polarized structure in the far field. Our work enriches the classical coherence theory and may be important for free-space optical communications.

On the nature of an emergent symmetry in QCD with low-lying Dirac modes removed

Remarkable symmetry properties appear to arise in lattice calculations of correlation functions in which the lowest-lying eigenmodes of the Dirac operator in quark propagators are removed by hand. The Banks-Casher relation ties the chiral condensate to the density of low lying modes; thus, it is plausible that removal of such modes could lead to a regime where spontaneous chiral symmetry breaking does not occur. Surprising, a pattern of identical correlation functions was observed that is larger than can be explained by a restoration of chiral symmetry. This suggests that a larger symmetry---one that is not present in the QCD lagrangian---emerges when these modes are removed. Previously it was argued that this emergent symmetry was SU(4). However, when the low-lying modes are removed, the correlation functions of sources in the SU(4) 15-plet of spin-1 mesons appear to coincide with the correlation function of the SU(4) singlet. A natural explanation for this is an emergent symmetry larger than SU(4). In this work, it is shown that there exists no continuous symmetry whose generators in the field theory are spatial integrals of local operators that can account for the full pattern of identical correlation functions unless the apparent coincidence of the singlet channel with the 15-plet is accidental.

ALCOCK-PACZYŃSKI COSMOLOGICAL TEST

In order to test the expansion of the universe and its geometry, we carry out an Alcock & Paczynski cosmological test, that is, an evaluation of the ratio of observed angular size to radial/redshift size. The main advantage of this test is that it does not depend on the evolution of the galaxies, but only on the geometry of the universe. However, the redshift distortions produced by the peculiar velocities of the gravitational infall do also have an influence, which should be separated from the cosmological effect. We derive the anisotropic correlation function of sources in three surveys within the Sloan Digital Sky Survey (SDSS): galaxies from SDSS-III/Baryon Oscillation Spectroscopy Survey-Data Release 10 (BOSS-DR10), and QSOs from SDSS-II and SDSS-III/BOSS-DR10. From these, we are able to disentangle the dynamic and geometric distortions and thus derive the ratio of observed angular size to radial/redshift size at different redshifts. We also add some other values available in the literature. Then, we use the data to evaluate which cosmological model fits them. We used six different models: concordance Lambda-CDM, Einstein-de Sitter, open-Friedman Cosmology without dark energy, flat quasi-steady state cosmology, a static universe with a linear Hubble law, and a static universe with tired-light redshift. Only two of the six models above fit the data of the Alcock & Paczynski test: concordance Lambda-CDM and static universe with tired-light redshift; whereas the rest of them are excluded at a >95% confidence level. If we assume that Lambda-CDM is the correct one, the best fit with a free Omega_m is produced for Omega_m=0.24^{+0.10}_{-0.07}.

A measurement of the faint source correlation function in the GOODS and UDF surveys

We present a stable procedure for defining and measuring the two point angular autocorrelation function, w, of faint (25 < V < 29), barely resolved and unresolved sources in the HST GOODS and UDF datasets. We construct catalogs that include close pairs and faint detections. We show for the first time that on subarcsecond scales, the correlation function exceeds unity. This correlation function is well fit by a power law with index of 2.5 and a characteristic angular scale that decrease slowly with magnitude. This is very different from the purely gravitationalcorrelation function of brighter galaxies which has a index of 0.7 and a characteristic angular scale which decreases quickly with magnitude. This observed clustering probably reflects the presence of giant star-forming regions within galactic-scale potential wells. Its measurement enables a new approach to measuring the redshift distribution of the faintest sources in the sky.

Astrophysical and cosmological information from large-scale submillimetre surveys of extragalactic sources

We present a quantitative analysis of the astrophysical and cosmological information that can be extracted from the many important wide-area, shallow surveys that will be carried out in the next few years. Our calculations combine the predictions of the physical model by Granato et al. for the formation and evolution of spheroidal galaxies with up-to-date phenomenological models for the evolution of starburst and normal late-type galaxies and of radio sources. We compute the expected number counts and the redshift distributions of these source populations separately and then focus on protospheroidal galaxies. For the latter objects, we predict the counts and redshift distributions of strongly lensed sources at 250, 350, 500 and 850 μm, the angular correlation function of sources detected in the surveys considered, and the angular power spectra due to clustering of sources below the detection limit in Herschel and Planck surveys. An optimal survey for selecting strongly lensed protospheroidal galaxies is described, and it is shown how they can be easily distinguished from the other source populations. We also discuss the detectability of the imprints of the one-halo and two-halo regimes on angular correlation functions and clustering power spectra, as well as the constraints on cosmological parameters that can be obtained from the determinations of these quantities. The novel data relevant to derive the first submillimetre estimates of the local luminosity functions of starburst and late-type galaxies, and the constraints on the properties of rare source populations, such as blazars, are also briefly described.

Effects in the Solarp‐Mode Power Spectrum from Scattering on a Turbulent Background Flow with Stochastic Wave Sources

This work demonstrates how the scattered wave field, in combination with stochastic wave sources, influences the p-mode power spectrum. I adopt a zone with random fluctuations in sound speed and velocity (characterized by the respective correlation functions). I present a general formalism (for plane-parallel conditions) to calculate the expectation value of the p-mode power spectrum. The power due to the direct field from the sources dominates, and depends only on the source correlation function. Smaller, but significant, are due to scattered wave field components. These corrections depend in general on the correlation functions of the fluctuations in the medium. I adopt a simple waveguide for the purpose of clear demonstration, and show that the corrections generate three important effects: (1) the line profiles are shifted along the wavenumber (frequency) axis, with varying effects depending on which turbulent physical quantity we consider; (2) the shapes and widths of the line profiles are altered; and (3) the troughs between the line profiles are to some extent filled in, contributing to the solar background power. It is demonstrated that boundary zones can generate important contributions to the power spectrum.

Computation of supersonic jet mixing noise for an axisymmetric convergent-divergent nozzle

The turbulent mixing noise of a supersonic jet is calculated for an axisymmetric convergent-divergent nozzle at the design pressure ratio. Aerodynamic computations are performed using the PARC code with a k-e turbulence model. LighthiU's acoustic analogy is adopted. The acoustics solution is based upon the methodology followed in the MGB code. The source correlation function is expressed as a linear combination of second-order tensors (Ribner's assumption). Assuming separable second-order correlations and incorporating Batchelor's isotropic turbulence model, the source term was calculated from the kinetic energy of turbulence. A Gaussian distribution for the time-delay of correlation was introduced. The CFD solution was used to obtain the source strength as well as the characteristic time-delay of correlation. The effect of sound/flow interaction was incorporated using the high frequency asymptotic solution to Lilley's equation for axisymmetric geometries. Acoustic results include sound pressure level directivity and spectra at different polar angles. The aerodynamic and acoustic results demonstrate favorable agreement with experimental data.

Fourier-transform spectral imaging: retrieval of source information from three-dimensional spatial coherence

A method is described for efficiently obtaining the comprehensive information of a polychromatic radiator. Under certain conditions both the spatial and spectral details of the radiative object can be recovered simultaneously from the three-dimensional spatial coherence function in the diffraction region. The recovery of object information is based on a Fourier-transform relationship derived from the basic formula [ WolfE.CarterW. H., J. Opt. Soc. Am.68, 953– 964 ( 1978)] describing the field correlation function in terms of the source correlation function. A new type of interferometer is proposed for the efficient collection of the spatial coherence data. Experimental results of the spectral-image recovery are also presented.

Stationary response of a finite cable to a correlated moving turbulent force field

Following the method of Lyon [J. Acoust. Soc. Am. 28, 391–398 (1956)], the stationary response of a finite cable to a correlated moving turbulent force field is determined. The source correlation function assumed is not simply exponentially decaying (to reflect a loss of correlation) but harmonically varying, exponentially decaying [M. Yildiz, Univ. of New Hampshire (1974)]. The results obtained yield an expression for the mean-square response which, upon making proper limiting assumptions, reduces to results previously obtained by Lyon when the assumed harmonicity of the source correlation is omitted.

Coherence and radiant intensity in scalar wave fields generated by fluctuating primary planar sources

In the literature on coherence theory one almost invariably specifies any correlations that may exist in the source region by means of a correlation function of the field variable. However, when the source is a primary one, it seems more appropriate to specify the correlations by means of a correlation function of the source variable. In the present paper some basic formulas are derived, relating to coherence and radiant intensity in fields generated by primary sources in terms of a source correlation function. A number of results are obtained that exhibit the connection between the “field description” and the “source description.” Several illustrative examples are given relating to Gaussian-correlated sources and to Lambertian sources.

Jet Noise Source Distribution from Far-Field Cross Correlations

HIS paper contains the development of a technique to determine the relationship between the unknown source correlation function and the correlation of the far-field acoustic pressure. Based on LighthilPs equivalent source model, a Fredholm integral equation relating the unknown source-correlation function to the far-field pressure correlation is derived. Analytically, this is a statistically inverse radiation problem. It is assumed that the source is distributed over an axisymmetric region, that is, a cylindrical region in an axisymmetric jet. This technique was developed for an application in the study of the installation effects for static and moving jets, since the spatial and temporal distribution of the source relative to the jet were required.l In the literature, several techniques are available, for example, Refs. 2 through 5, which provide information of the spatial distribution only or suitable to reproduce far-field intensity without body effects. In addition, further information can be extracted from the source field if obtained from the far-field two-point correlation.6'7 Contents Consider the propagation of an acoustic wave generated by turbulence in the jet confined in a region D in space, Fig. 1; the sound pressure in the spectral or frequency domain satisfies