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UNT College of Arts and Sciences
Decade:
1990-1999
Year:
1995
Language:
English
Atomic resolution ultrahigh vacuum scanning tunneling microscopy of epitaxial diamond (100) films
Date: May 1, 1995
Creator: Stallcup, Richard E.; Aviles, A. F. & Pérez, José M.
Description: In this article, the authors report atomic resolution images of chemical vapor deposition grown epitaxial diamond (100) films obtained in ultrahigh vacuum (UHV) with a scanning tunneling microscope. A (2X1) dimer surface reconstruction and amorphous atomic regions are observed. The (2X1) unit cell is measured to be 0.51±0.01X0.25±0.01 nm2. The amorphous regions are identified as carbon. A radial structure 1.5 nm in diameter is observed on a plane at a 20° slope to the (2X1) surface. Tunneling current versus voltage spectra in UHV and Raman spectra are also obtained.
Contributing Partner: UNT College of Arts and Sciences
Permallink:digital.library.unt.edu/ark:/67531/metadc84147/
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/
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
Permallink:digital.library.unt.edu/ark:/67531/metadc139496/
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
Permallink:digital.library.unt.edu/ark:/67531/metadc139499/
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/
Z1 oscillations of the mean charge for isotachic ions in carbon foils
Date: April 1995
Creator: Arrale, A.M.; Jin, Jianyue; Zhao, Z.Y.; Weathers, Duncan L.; McDaniel, Floyd Del & Matteson, Samuel E.
Description: This article discusses Z1 oscillations of the mean charge for isotachic ions in carbon foils. Oscillations in the mean-charge state of swift ions as a function of the atomic number Z1 are reported for a wide range of ions of identical velocity (isotachic ions). A previously suggested mechanism for the enhancement of the mean charge for certain ion-charge combinations that involves closed shells is shown to be an inadequate explanation. Post-foil-Auger processes, however, are demonstrated to be a more plausible explanation for the observed behavior of the mean charge of the ions.
Contributing Partner: UNT College of Arts and Sciences
Permallink:digital.library.unt.edu/ark:/67531/metadc139492/