Correlation of signals of thermal acoustic radiation

The spatial correlation function is measured for the pressure of thermal acoustic radiation from a source (a narrow plasticine plate) whose temperature is made both higher and lower than the temperature of the receiver. The spatial correlation function of the pressure of thermal acoustic radiation is found to be oscillatory in character. The oscillation amplitude is determined not by the absolute temperature of the source but by the temperature difference between the source and the receiver. The correlation function changes its sign when a source heated with respect to the receiver is replaced by a cooled one.     

Study of the time correlation function of scattered light in bounded strongly inhomogeneous media

The time correlation function of the multiply scattered light by a medium comprised of finite-size scatterers is studied theoretically and experimentally. A solution of the Bethe-Salpeter equation for the time correlation function is sought in the P ₂-approximation in the form of a series of terms of the Legendre polynomials. With allowance for the boundedness of the medium, the problem is reduced to a generalized Milne equation, which is solved by the Wiener-Hopf method. The time dependence of the correlation function is studied experimentally in a concentrated latex suspension for particles of different sizes. The results of numerical calculations are in qualitative agreement with the measured dependence of the time correlation function on the scatterer size.     

(β, γ)-Richtungskorrelationen im Zerfall des Tm170

Measurements of the beta-gamma directional correlation in the decay of Tm¹⁷⁰ were performed as a function of the time delay inserted in the fast coincidence circuit. Various chemical compounds of Thulium were used to study the influences of the crystal fields and the chemical bonds on the directional correlation. Attenuations up to 40% were observed. The largest anisotropy was found with a liquid source of a Ga-Tm alloy. Also the intensity and directional correlation of the internal brems-strahlung was measured. Since there is a pronounced angular dependence of the internal bremsstrahlung relative to the direction of the emitted beta-particle, the directional correlation measurement can be disturbed seriously even if the intensity of the internal bremsstrahlung is weak.     

Bose-Einstein correlations of light hadrons and the stochastic scale of particle emitter source

Based on quantum field theory at finite temperature, we obtained new results for two-particle Bose-Einstein correlation (BEC) function C ₂(Q) in case of light hadrons. The important parameters of BEC function related to the size of emitting source, mean multiplicity, stochastic forces range and correlation radius with the particle energy and the mass dependence, and the temperature of the source are obtained in analytical form for the first time. Not only is the correlation between identical bosons explored but also the off-correlation between non-identical particles is proposed. The article is published in the original.     

Characterization of nuclear sources via two-neutron intensity interferometry

The neutron energy spectrum and the two-neutron correlation function have been measured for the E/A=45 MeV Ni + Al reaction in order to assess the space-time characteristics of the neutron emitting source. When comparing the data to a statistical model, the kinetic energy spectra, the integrated correlation function as well as the longitudinal correlation function are reproduced by one single source. However, only the inclusion of a short-lived pre-equilibrium component can account for the stronger correlation exhibited by neutron pairs emitted with high total momentum. The correlation function from events defined as peripheral by constraints on the highest charge of the projectile-like fragment does show a significantly weaker correlation than the minimum bias sample.     

Measurement of roughness of two interfaces of a dielectric film by scattering ellipsometry

The polarization of light scattered by oxide films thermally grown on photolithographically generated microrough silicon surfaces was measured as functions of scattering angle. Using the predictions of first-order vector perturbation theory for scattering from interfacial roughness to interpret the results, the roughness of each interface and the correlation function between the two interfaces can be determined. The results show the spatial frequency dependence of the SiO (2)/Si interface smoothening.     

Search for lifetime effects of an evaporative source using two-proton correlations

The directional dependence of the measured correlationfunction of two particles emitted from an evaporative source is shown to offer a weak sensitivity to the source lifetime. From the agreement with evaporative calculations, one cannot rule out a sequential emission.     

Centrality and energy dependence of rapidity correlation patterns in relativistic heavy ion collisions

The centrality and energy dependence of rapidity correlation patterns are studied in Au+Au collisions by using AMPT with string melting,RQMD and UrQMD models.The behaviors of the shortrange correlation(SRC)and the long-range correlation(LRC)are presented clearly by two spatial-position dependent correlation patterns.For centrality dependence.UrQMD and RQMD give similar results as those in AMPT,i.,e., in most central collisions,the correlation structure is flatter and the correlation range is larger,which indicates a long range rapidity correlation.A long range rapidity correlation showing up in RQMD and UrQMD implies that patton interaction is not the only source of long range rapidity correlations.For energy dependence,AMPT with string melting and RQMD show quite different results.The correlation patterns in RQMD at low collision energies and those in AMPT at high collision energies have similar structures,i.e.aconvex curve.while the correlation patterns in RQMD at high collision energies and those in AMPT at low collision energies show fiat structures,having no position dependence.Long range rapidity correlation presents itself at high energy and disappears at low energy in RQMD,which also indicates that long range rapidity correlations may come from some trivial effects,rather than the parton interactions.     

Two-photon fluorescence measurements in a hexagonal CdS crystal

Measurements of two-photon fluorescence (TPF) in a CdS crystal using a dye laser pumped by a Q-switched ruby laser are reported. The TPF is measured as a function of source intensity and wavelength. The total fluorescence shows linear and non-linear dependence on the source intensity; from these measurements the TPF part is determined. The measured transition of the crystal's fundamental gap is 2.5 ± 0.02 eV and another forbidden one-photon but allowed two-photon transition is found at 3.24 ± 0.02 eV.     

New approach to imaging of two-proton source functions

The influence of protons emitted from both fast and slow emission mechanisms in 2-proton correlations measured in heavy ion collisions at intermediate energies is discussed. The size of the fast emitting source is found to be determined mainly by the width of the correlation peak at 20 MeV/c, rather than by its magnitude. To illustrate the new analysis technique, the total momentum dependence of p-p correlations measured in ¹⁴N+¹⁹⁷Au reactions at E/A=75 MeV is studied with an imaging analysis. The extracted results and the basic ideas behind the proposed analysis technique provide new tools for using particle-partcile correlation measurements as a probe of nuclear reactions.     

Statistical properties of trading volume of Chinese stocks

The cumulative distribution of trading volume is investigated for Chinese stocks. Different from the power-law scaling of mature markets, the distribution is well fitted by a stretched exponential function . With the autocorrelation function and the detrended fluctuation analysis, the long-range autocorrelation of trading volume is revealed. The conditional dependence of volume on volatility and the volume-volatility cross-correlation are studied, and a positive long-range correlation between volume and volatility is observed.     

Fine-tuning two-particle interferometry I: Effects from temperature gradients in the source

A comprehensive model study of Bose-Einstein correlation radii in heavy ion collisions is presented. The starting point is a longitudinally and transversally expanding fireball, represented at freeze-out by an azimuthally symmetric emission function. The freeze-out temperature is allowed to feature transverse and temporal gradients. Their effects on the correlation radii are studied. In particular, we evaluate numerically their dependence on the transverse mass of the particle pairs and check a recent suggestion, based on analytical approximations, that for certain reasonable source parameters all three correlation radii satisfy simultaneously a scaling. Received: 2 July 1997 / Revised version: 25 September 1997 / Published online: 23 February 1998     

On the possibility of using acoustic reverberation for remote sensing of ocean dynamics

The two-point correlation function of diffuse noise fields produced by distributed random sound sources carries useful information on the medium of sound propagation. Such information can be used for performing passive acoustic tomography of the ocean. In a number of cases that are important for practice, the noise field in the ocean is predominated by contributions of individual point sources. Here, a theoretical study is presented on the possibility of determining the sound speed and current velocity in the water column by the correlation processing of reverberation signals measured by two vertical receiving arrays. In other words, we study the possibility of replacing the diffuse noise produced by a great number of delta-correlated sources by waves generated by a localized source and scattered at the rough surface and bottom of the ocean for sensing the medium. The correlation function of scattered waves is calculated by using the method of small perturbations. It is shown that the correlation processing of the scattered waves offers an opportunity of measuring the acoustic nonreciprocity and reconstructing the field of sound speed in the fluid, without using any acoustiLc transceivers.     

An ensemble source spectra model for merchant ship-radiated noise

This paper presents an evaluation of the classical model for determining an ensemble of the broadband source spectra of the sound generated by individual ships and proposes an alternate model to overcome the deficiencies in the classical model. The classical model, proposed by Ross [Mechanics of Underwater Noise (Pergamon, New York, 1976)] postulates that the source spectrum for an individual ship is proportional to a baseline spectrum with the constant of proportionality determined by a power-law relationship on the ship speed and length. The model evaluation, conducted on an ensemble of 54 source spectra over a 30-1200-Hz to 1200-Hz frequency band, shows that this assumption yields large rms errors in the broadband source level for the individual ships and significantly overestimates the variability in the source level across the ensemble of source spectra. These deficiencies are a consequence of the negligible correlation between the source level and the ship speed and the source level and the ship length. The alternate model proposed here represents the individual ship spectra by a modified rational spectrum where the poles and zeros are restricted to the real axis and the exponents of the terms are not restricted to integer values. An evaluation of this model on the source spectra ensemble indicates that the rms errors are significantly less than those obtained with any model where the frequency dependence is represented by a single baseline spectrum. Furthermore, at high frequencies (400 to 1200 Hz), a single-term rational spectrum model is sufficient to describe the frequency dependence and, at the low frequencies (30 to 400 Hz), there is only a modest reduction in the rms error for a higher order model. Finally, a joint probability density on the two parameters of the single term model based on the measured histograms of these parameters is proposed. This probability density provides a mechanism for generating an ensemble of ship spectra.     

Measurement of the sizes of a source of α particles from the collisions of relativistic 22Ne and 24Mg nuclei with photoemulsion nuclei

The correlation of two α particles has been measured. In the case of a one-dimensional parameterization of the correlation function, the size of the source of the α particles is R(α) = 2.84 ± 0.28_stat ± 0.23_sist fm. This result is compared to similar measurements for protons and deuterons.     

On the viscosity and thermal conductivity of dense gases

The modified Enskog theory (MET) of transport in dense gases can be used to predict the density dependence of transport coefficients provided the function y, which is a product of a dimensionless density and a pair correlation function, is known as a function of density. In this communication we consider the inverse problem, extracting information on the y function from measured transport property data, both to resolve some peculiarities found by others, and to provide the basis for improved MET predictions.     

氟化锂偏振器紫外-真空紫外偏振特性的研究

介绍了一种研究偏振元件偏振特性的方法,利用这一方法研究了氟化锂偏振器紫外-真空紫外偏振特征.一组氟化锂偏振器由对称放置的氟化锂晶片组成,各氟化锂片的入射角为60°.利用真空紫外空心阴极光源和Seya-Namioka型紫外-真空紫外单色仪提供单色辐射,测得两片组、四片组和八片组氟化锂偏振器的消光比,与用菲涅尔公式计算的氟化锂偏振器的偏振度在误差范围内一致.利用氟化锂偏振器产生的偏振辐射,初步研究了铝+氟化镁膜反射率以及全息光栅绝对效率在真空紫外波段的偏振特征.     

Study of the applicability conditions of the correlation function of a wideband multipath signal for estimating source coordinates

Using theoretical analysis and mathematical modeling, we study the dependence of the number of maxima in the correlation function of a wideband signal, whose parameters are related to the source coordinates, on the hydroacoustic conditions, the parameters of the receiver, and the signal/noise ratio.     

An E.S.R. study of some alkyl substituted benzene anion radicals : an experimental evaluation of the extent of vibronic interaction

E.S.R. studies of the proton hyperfine splitting in the anion radicals of benzene, toluene, ethylbenzene, iso-propylbenzene, t-butylbenzene, and p-xylene show that it is strongly dependent upon temperature. In the case of the monoalkylbenzenides there are two contributions to this observed temperature dependence. First, there is a rapid thermal averaging over two near-degenerate states which have different spin-density distributions. The energy separations between these two near-degenerate states have been measured for the above series of monoalkylbenzenides and are reported here. It is also possible to measure experimentally the spin-density distributions for the two states between which the averaging takes place. With this information one can obtain an experimental estimate of the extent of vibronic interaction which occurs in these systems. Such estimates are presented here and compared with those obtained theoretically. The second source of the strong temperature dependence of the proton hfs lies in the temperature dependence of the sigma-pi interaction parameter, Q _H. The sigma-pi interaction parameter has been studied as a function of temperature for all members of the above series and the results reported. Finally, restricted rotation of the iso-propyl group in the anion radical of iso-propylbenzenide was observed and the barrier to rotation has been measured.     

Self assembly modulated by interactions of two heterogeneously charged surfaces

Recent experiments have measured attractive interactions between two surfaces that each bear two molecular species with opposite charge. Such surfaces form charged domains of finite size. We present a theoretical model that predicts the dependence of the domain size, phase behavior and the interlayer forces as a function of spacing and salt concentration for two such interacting surfaces. A strong correlation between two length scales, the screening length and the surface separation, at the spinodal is shown. Remarkably, the first-order phase transition to infinite sized domains depends logarithmically on the ratio of the domain size to the molecular size. Finally, we fit the predicted pressure with experiments.