Multibin long-range correlations

A new method to study the long-range correlations in multiparticle production is developed. It is proposed to measure the joint factorial moments or cumulants of multiplicity distribution in several (more than two) bins. It is shown that this step dramatically increases the discriminative power of data.     

Detection of material property errors in handbooks and databases using artificial neural networks with hidden correlations

The authors have discovered a systematic, intelligent and potentially automatic method to detect errors in handbooks and stop their transmission using unrecognised relationships between materials properties. The scientific community relies on the veracity of scientific data in handbooks and databases, some of which have a long pedigree covering several decades. Although various outlier-detection procedures are employed to detect and, where appropriate, remove contaminated data, errors, which had not been discovered by established methods, were easily detected by our artificial neural network in tables of properties of the elements. We started using neural networks to discover unrecognised relationships between materials properties and quickly found that they were very good at finding inconsistencies in groups of data. They reveal variations from 10 to 900% in tables of property data for the elements and point out those that are most probably correct. Compared with the statistical method adopted by Ashby and co-workers [Proc. R. Soc. Lond. Ser. A 454 (1998) p. 1301, 1323], this method locates more inconsistencies and could be embedded in database software for automatic self-checking. We anticipate that our suggestion will be a starting point to deal with this basic problem that affects researchers in every field. The authors believe it may eventually moderate the current expectation that data field error rates will persist at between 1 and 5%.     

Local normalization: Uncovering correlations in non-stationary financial time series

The measurement of correlations between financial time series is of vital importance for risk management. In this paper we address an estimation error that stems from the non-stationarity of the time series. We put forward a method to rid the time series of local trends and variable volatility, while preserving cross-correlations. We test this method in a Monte Carlo simulation, and apply it to empirical data for the S&P 500 stocks.     

Complete Analysis of the 1H and 13C NMR Spectra of 5-Isopropylsulfonyl-2-Norbornenes Through the Application of Two-Dimensional NMR Techniques

Total assignment of ¹³C and ¹H NMR spectra of the 5-isopropylsulfonyl-2-norbornenes 2 was achieved using the concerted application of two-dimensional homonuclear and heteronuclear chemical shift correlations. The stereochemistry of both the diastereoisomers endo 2a and exo 2b have been established using the magnitude of the proton coupling constants.     

Concentration polarization in a reverse osmosis/nanofiltration plate-and-frame membrane module

The flow structure and solute concentration distribution in a nanofiltration/reverse osmosis plate-and-frame module with radial thin feed channels that have considerable entrance and outlet effects was determined by computational fluid dynamics (CFD). Simulations were performed for binary aqueous solutions, Reynolds (Re) numbers in the range of 64–570 (based on the channel height) and Schmidt (Sc) numbers between 450 and 8900.     

Effect of changing microstructure of Y-Ba-Cu-O superconductors on the vortex motion under non-equilibrium thermal conditions

Repetition of cooling and heating of high-T_c superconductors is detected to be able to result in some change of their microstructure. A non-equilibrium experimental technique provides direct measurement of the velocity of vortex motion in high-T_c Y-Ba-Cu-O superconductors. Its value falls in the interval of mm/s depending on the number of the cooling or heating cycles, to which the samples are submitted. The thermal cycling created homogenization of the specimen's microstructure, and is presumed to cause this phenomenon, decreasing the number and strength of pinning centers. This supposition is proved by X-ray diffractography and transmission electron microscopy. A simple irreversible thermodynamic theory is elaborated to describe the reason, direction and dissipative character of the vortex motion. Received: 17 December 1997 / Accepted: 28 January 1998     

Statistics of close visits to the indifferent fixed point of an interval map

We study a dynamical system defined by a map of the interval [0, 1] which has 0 as an indifferent fixed point but is otherwise expanding. We prove that the sequence of successive entrance times in a small neighborhood [0,a] converges in law when suitably normalized to a homogeneous Poisson point process.     

Initial state dependence of nonlinear kinetic equations: The classical electron gas

The method of nonequilibrium cluster expansion is used to stydy the decay to equilibrium of a weakly coupled inhomogeneous electron gas prepared in a local equilibrium state at the initial time,t=0. A nonlinear kinetic equation describing the long time behavior of the one-particle distribution function is obtained. For consistency, initial correlations have to be taken into account. The resulting kinetic equation-differs from that obtained when the initial state of the system is assumed to be factorized in a product of one-particle functions. The question of to what extent correlations in the initial state play an essential role in determining the form of the kinetic equation at long times is discussed. To that end, the present calculations are compared with results obtained before for hard sphere gases and in general gases with strong short-range forces. A partial answer is proposed and some open questions are indicated.     

Long-range boundary effects in simple fluids

We discuss long-range boundary effects in simple two- or three-dimensional fluids. These boundary effects are due to the existence of long-range correlations in nonequilibrium fluids and can be computed either by means of kinetic theory or phenomenological mode-coupling theories. In particular, we use kinetic theory to compute the stress tensor and heat flux vector for a fluid in a nonequilibrium steady state in a finite geometry and show that both the effective shear viscosity and effective heat conductivity have contributions due to the walls of the container that influence the behavior of the system far into the fluid. We also show that the mechanocaloric effect is present in the bulk of a three-dimensional fluid and that there are normal stresses in a fluid whenever the temperature gradient is nonzero.Work performed under National Science Foundation grant No. CHE 77-16308.     

Renormalized equilibria of a Schlögl model lattice gas

A lattice gas model for Schlögl's second chemical reaction is described and analyzed. Because the lattice gas does not obey a semi-detailed-balance condition, the equilibria are non-Gibbsian. In spite of this, a self-consistent set of equations for the exact homogeneous equilibria are described, using a generalized cluster-expansion scheme. These equations are solved in the two-particle BBGKY approximation, and the results are compared to numerical experiment. It is found that this approximation describes the equilibria far more accurately than the Boltzmann approximation. It is also found, however, that it can give rise to spurious solutions to the equilibrium equations.