Charge-state dependence of M-shell x-ray production in 67Ho by 2-12-MeV carbon ions
Date: November 1995
Creator: Yu, Y. C.; Sun, H. L.; Duggan, Jerome L.; McDaniel, Floyd Del. (Floyd Delbert), 1942-; Yin, J. Y. & Lapicki, G.
Description: This article discusses charge-state dependence of M-shell x-ray production in 67Ho by 2-12-MeV carbon ions. Abstract: Charge-state dependence of M-shell x-ray production cross sections of 67Ho bombarded by 2-12-MeV carbon ions, with and without K-shell vacancies, were measured using a windowless Si(Li) x-ray detector with a full-width-at-half-maximum resolution of 135 eV at 5.9 keV. Carbon ions of different charge states were produced using a postacceleration, nitrogen gas stripping cell. The carbon ions were then magnetically analyzed to select the desired charge state and energy before entering the target chamber. The total M-shell and Mζ, Mα,β, and Mγ x-ray cross sections were measured. The electron-capture (EC) contributions as well as the direct-ionization (DI) contributions can be determined by making a comprehensive study of the projectile-charge-state dependence of the target x-ray production cross sections for targets in which the single-collision realm is maintained. In this paper, both EC and DI contributions and the total M-shell x-ray production cross sections are compared to both the first Born theory and to the perturbed-stationary-state theory with energy-loss, Coulomb-deflection, and relativistic corrections.
Contributing Partner: UNT College of Arts and Sciences
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Dynamical model for DNA sequences
Date: November 1995
Creator: Allegrini, Paolo; Barbi, M.; Grigolini, Paolo & West, Bruce J.
Description: This article discusses a dynamical model for DNA sequences. Abstract: We address the problem of DNA sequences, developing a "dynamical" method based on the assumption that the statistical properties of DNA paths are determined by the joint action of two processes, one deterministic with long-range correlations and the other random and δ-function correlated. The generator of the deterministic evolution is a nonlinear map belonging to a class of maps recently tailored to mimic the processes of weak chaos responsible for the birth of anomalous diffusion. It is assumed that the deterministic process corresponds to unknown biological rules that determine the DNA path, whereas the noise mimics the influence of an infinite-dimensional environment on the biological process under study. We prove that the resulting diffusion process, if the effect of the random process is determined by the joint action of the deterministic and the random process, the correlation effects of the "deterministic dynamics" are canceled on the short-range scale, but show up in the long-range one. We denote their prescription to generate statistical sequences as the copying mistake map (CMM). We carry out their analysis of several DNA sequences and their CMM realizations with a variety of techniques and the authors ...
Contributing Partner: UNT College of Arts and Sciences
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Chaos and thermal conductivity
Date: December 1995
Creator: Corezzi, Silvia; Bianucci, Marco & Grigolini, Paolo
Description: This article discusses chaos and thermal conductivity. Abstract: We argue that the condition of local thermal equilibrium realized several years ago by Rich and Visscher [Phys. Rev. B 11, 2164 (1975)] through a process of mathematical convergence can be obtained dynamically by adopting the prescription of a recent paper [M. Bianucci, R. Mannella, B.J. West, and P. Grigolini, Phys. Rev. E 51, 3002 (1995)]. This should contribute to shedding light on the still unsolved problem fo the microscopic derivation of the heat Fourier law.
Contributing Partner: UNT College of Arts and Sciences
Permallink:digital.library.unt.edu/ark:/67531/metadc139502/
Noise-induced transition from anomalous to ordinary diffusion: The crossover time as a function of noise intensity
Date: December 1995
Creator: Floriani, Elena; Mannella, Riccardo & Grigolini, Paolo
Description: In this article, the authors study the interplay between a deterministic process of weak chaos, responsible for the anomalous diffusion of a variable x, and a white noise of intensity ≡. The deterministic process of anomalous diffusion results from the correlated fluctuations of a statistical variable ξ between two distinct values +1 and -1, each of them characterized by the same waiting time distribution ψ(t), given by ψ(t)≃ t(-μ) with 2 < μ < 3, in the long-time limit. The authors prove that under the influence of a weak white noise of intensity ≡, the process of anomalous diffusion becomes normal at a time t(c) given by t(c) ~ 1/≡(β)(μ). Here β(μ) is a function of μ which depends on the dynamical generator of the waiting-time distribution ψ(t). The authors derive an explicit expression for β(μ) in the case of two dynamical systems, a one-dimensional superdiffusive map and the standard map in the accelerating state. The theoretical prediction is supported by numerical calculations.
Contributing Partner: UNT College of Arts and Sciences
Permallink:digital.library.unt.edu/ark:/67531/metadc139501/
Historic Archaeology of the Johnson and Jones Farmsteads in the Ray Roberts Lake Area: 1850-1950
Date: 1996
Creator: University of North Texas. Institute of Applied Sciences.
Description: This study represents the findings of research done on the Jones and Johnson farms, "situated in Johnson Branch Park in the north-central portion of the Ray Roberts Lake area." The purpose of the study was to offset future disturbances and damages to these farmsteads, and it includes "archival investigations, architectural documentation, oral-history interviews of long-time area residents and family members, farm equipment and artifact analyses, archaeological excavations, stabilization measures, and the development of interpretative exhibits for area schools, museums, and the general public" (p. i).
Contributing Partner: UNT College of Arts and Sciences
Permallink:digital.library.unt.edu/ark:/67531/metadc29393/
Charge-state dependence of K-shell x-ray production in aluminum by 2-12-MeV carbon ions
Date: June 1996
Creator: Sun, H. L.; Yu, Y. C.; Lin, E. K.; Wang, C. W.; Duggan, Jerome L.; Azordegan, A. R. et al
Description: This article discusses charge-state dependence of K-shell x-ray production in aluminum by 2-12-MeV carbon ions. Abstract: Charge-state dependence for K-shell x-ray production cross sections in 13Al bombarded by 2-12-MeV 6C ions with charge states from 2+ to 6+ was measured using a Si(Li) detector. A thin Al target was used to ensure single collision conditions. Contributions of the electron capture as well as direct ionization to the inner-shell ionization were determined by an analysis of the charge-state dependence of the target x-ray production. The measurements are compared with the prediction of the ECPSSR theory using a single-hole fluorescence yield. The ECPSSR theory is based on the perturbed stationary state (PSS) formalism and relativistic efforts (R) for the target electrons, and energy loss (E) and Coulomb deflection (C) of the projectile. In general, this theory gives reasonable agreement with the data for carbon ions without K vacancies while it overpredicts the data for carbon ions with K vacancies. The significant underprediction of the data at the lowest energy is likely associated with the molecular-orbital effect that is not accounted for in the ECPSSR theory.
Contributing Partner: UNT College of Arts and Sciences
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Anomalous diffusion and environment-induced quantum decoherence
Date: July 1996
Creator: Bonci, Luca; Grigolini, Paolo & Laux, Adam
Description: This article discusses anomalous diffusion and environment-induced quantum decoherence. Abstract: We study the anomalous diffusion resulting from the standard map in the so-called accelerating state, and we observe that it is determined by unusually large times of sojourn of the classical trajectories in the fractal region at the border between the chaotic sea and the acceleration island. The quantum-mechanical breakdown of this property implies a coherence among so slightly different values of momentum as to become much more robust against environment fluctuations than the quantum localization corresponding to normal diffusion.
Contributing Partner: UNT College of Arts and Sciences
Permallink:digital.library.unt.edu/ark:/67531/metadc139477/
Linear Response of Hamiltonian Chaotic Systems as a Function of the Number of Degrees of Freedom
Date: August 12, 1996
Creator: Bianucci, Marco; Mannella, Riccardo & Grigolini, Paolo
Description: This article discusses the linear response of Hamiltonian chaotic systems as a function of the number of degrees of freedom. Abstract: Using numerical simulations we show that the response to weak perturbations of a variable of Hamiltonian chaotic systems depend on the number of degrees of freedom: When this is small (≈2) the response is not linear, in agreement with the well known objections to the Kubo linear response theory, while, for a larger number of degrees of freedom, the response becomes linear. This is due to the fact that increasing the number of degrees of freedom the shape of the distribution function, projected onto the subspace of the variable of interest, becomes fairly "regular."
Contributing Partner: UNT College of Arts and Sciences
Permallink:digital.library.unt.edu/ark:/67531/metadc139479/
Dynamical approach to Lévy processes
Date: November 1996
Creator: Allegrini, Paolo; Grigolini, Paolo & West, Bruce J.
Description: This article discusses a dynamical approach to Lévy processes.Abstract: We derive the diffusion process generated by a correlated dichotomous fluctuating variable y starting from a Liouville-like equation by means of a projection procedure. This approach makes it possible to derive all statistical properties of the diffusion process from the correlation function of the dichotomous fluctuating variable Φy(t). Of special interest is that the distribution of the times of sojourn in the two states of the fluctuating process is proportional to d²Φy(t)/dt². Furthermore, in the special case where Φy(t) has an inverse power law, with the index β ranging from 0 to 1, thus making it nonintegrable, the authors show analytically that the statistics of the diffusing variable approximate in the long-time limit the α-stable Lévy distributions. The departure of the diffusion process of dynamical origin from the ideal condition of the Lévy statistics is established by means of a simple analytical expression. We note, first of all, that the characteristic function of a genuine Lévy process should be an exponential in time. We evaluate the correction to this exponential and show it to be expressed by a harmonic time oscillation modulated by the correlation function Φy(t). Since the characteristic function ...
Contributing Partner: UNT College of Arts and Sciences
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Site correlation, anomalous diffusion, and enhancement of the localization length
Date: November 1, 1996
Creator: Allegrini, Paolo; Bonci, Luca; Grigolini, Paolo & West, Bruce J.
Description: This article discusses site correlation, anomalous diffusion, and enhancement of localization length. Herein the authors study the effects on Anderson localizations of correlations in the energy distribution of the sites of a tight-binding Hamiltonian. The lattice correlations are introduced are introduced by means of classical maps generating anomalous diffusion, that have recently been found to account for the correlated disorder of "biological" lattices. The authors show that the enhancement of localization length takes place on a much wider band of energies than in the case of the random-dimer model if the random walk on the site energies of the tight-binding Hamiltonian is determined by the joint action of short- and long-range correlations.
Contributing Partner: UNT College of Arts and Sciences
Permallink:digital.library.unt.edu/ark:/67531/metadc139487/