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₁¹H+ - and ₂⁴He+ - induced M-shell x-ray-production cross sections for selected elements in the rare-earth region
This article discusses ₁¹H+ - and ₂⁴He+ -induced M-shell x-ray production cross sections for selected elements in the rare-earth region. Abstract: The measurements of M-shell x-ray-production cross sections induced by ₁¹H+ and ₂⁴He+ ions are compared to the first-Born-approximation and ECPSSR (energy loss, Coulomb-deflection effects; perturbed-stationary-state approximation, with relativistic corrections) theories. Most of the reported experimental data were measured in the authors' laboratory and the other measurements were taken from the literature. The data from the authors' laboratory were for incident H+ and He+ ions in the energy range from 0.25 to 2.5 MeV. The M-shell x-ray-production cross sections were measured for the following thin targets: 59Pr, 60Nd, 63Eu, 64Gd, 66Dy, 67Ho, 68Er, 70Yb, and 72Hf. The data were for the following elements: 54Xe, 59Pr, 60Nd, 62Sm, 63Eu, 64Gd, 65Tb, 66Dy, 67Ho, 68Er, 70Yb, 72Hf, 73Ta, 74W, 78Pt, 79Au, 80Hg, 82Pb, 83Bi, and 92U. The first-born-approximation calculations of the ionization cross section were made using the plane-wave Born approximation for direct ionization and the Oppenheimer-Brinkman-Kramers approximation of Nikolaev for electron capture. The ECPSSR theory of Brandt and Lapicki [Phys. Rev. A 23, 1717 (1981)] goes beyond the first Born approximation and accounts for the energy loss, Coulomb deflection, and relativistic effects in the perturbed-stationary-state theory. The first Born approximation overpredicts all measurements. The ECPSSR theory predicts the M-shell production cross sections correctly for Z2 > 70 and energies per μ > 0.25 MeV/μ. In the rare-earth region the ECPSSR results lie above the data at higher projectile energies and fall off below the data at lower energies. digital.library.unt.edu/ark:/67531/metadc139491/
Absorption and Emission in the Non-Poissonian Case
This article discusses absorption and emission in the Non-Poissonian Case. Abstract: This Letter addresses the challenging problems posed to the Kubo-Anderson (KA) theory by the discovery of intermittent resonant fluorescence with a nonexponential distribution of waiting times. We show how to extend the KA theory from aged to aging systems, aging for a very extended time period or even forever, being a crucial consequence of non-Poisson statistics. digital.library.unt.edu/ark:/67531/metadc67641/
Activation of water on the TiO2 (110) surface: The case of Ti adatoms
This article discusses the activation of water on the TiO2 (110) surface. Abstract: Using first-principles calculations the authors have studied the reactions of water over Ti adatoms on the (110) surface of rutile TiO2. The authors' results provide fundamental insights into the microscopic mechanisms that drive this reaction at the atomic level and assess the possibility of using this system to activate the water dissociation reaction. In particular, the authors show that a single water molecule dissociates exothermically with a small energy barrier of 0.17 eV. After dissociation, both H⁺ and OH⁻ ions bind strongly to the Ti adatom, which serves as an effective reactive center on the TiO2 surface. Finally, clustering of Ti adatoms does not improve the redox activity of the system and results in a slightly higher energy barrier for water dissociation. digital.library.unt.edu/ark:/67531/metadc132989/
Aging and Rejuvenation with Fractional Derivatives
This article discusses aging rejuvenation with fractional derivatives. Abstract: We discuss a dynamic procedure that makes a fractional derivatives emerge in the time asymptotic limit of non-Poisson processes. We find that two-state fluctuations, with an inverse power-law distribution of waiting times, finite first moment, and divergent second moment, namely, with the power index μ in the interval 2<μ<3, yield a generalized master equation equivalent to the sum of an ordinary Markov contribution and a fractional derivative term. We show that the order of the fractional derivative depends on the age of the process under study. If the system is infinitely old, the order of the fractional derivative, o, is given by o=3-μ. A brand new system is characterized by the degree o=μ-2. If the system is prepared at time -tₐ<0 and the observation begins at time t=0, we derive the following scenario. For times 0<t«tₐ the system is satisfactorily described by the fractional derivative with o=3-μ. Upon time increase the system undergoes a rejuvenation process that in the time limit t⪢tₐ yields o=μ-2. The intermediate time regime is probably incompatible with a picture based on fractional derivatives, or, at least, with a mono-order fractional derivative. digital.library.unt.edu/ark:/67531/metadc67638/
Analytical solutions for a two-level system driven by a class of chirped pulses
In this article, the authors present analytical solutions for the problem of a two-level atom driven by a class of chirped pulses. The solutions are given in terms of Heun functions. By use of the appropriate chirping parameters, an enhancement of four orders of magnitude in the population transfer is obtained. digital.library.unt.edu/ark:/67531/metadc103257/
L- and M-shell x-ray production cross sections of Nd, Gd, Ho, Yb, Au, and Pb by 25-MeV carbon and 32-MeV oxygen ions
This article discusses L- and M-shell x-ray production. Abstract: L- and M-shell x-ray production cross sections have been measured for thin solid targets of neodymium, gadolinium, holmium, ytterbium, gold and lead by 25-MeV ₆¹²C(q)+ (q=4,5,6) and by 32-MeV ₈¹⁶O(q)+ (q=5,7,8). The cross sections were determined from measurements made with thin targets (less than 2.25 μg/cm2). For projectiles with one or two K-shell vacancies, the target x-ray production cross sections were found to be enhanced over those for projectiles without a K-shell vacancy. The sum of direct ionization to the continuum (DI) plus electron capture (EC) to the L,M,N,... shells and EC to the K shell of the projectile have been extracted from the data. The results are compared to the predictions of first Born theories, i.e., plane-wave Born approximation for DI and Oppenheimer-Brinkman-Kramers formula of Nikolaev for EC, and to the ECPSSR that accounts for energy loss and Coulomb deflection of the projectile as well as for relativistic and perturbed stationary states of inner-shell electrons. digital.library.unt.edu/ark:/67531/metadc139494/
Anomalous diffusion and ballistic peaks: A quantum perspective
This article discusses anomalous diffusion and ballistic peaks. Abstract: The quantum kicked rotor and the classical kicked rotor are both shown to have truncated Lévy distributions in momentum space, when the classical phase space has accelerator modes embedded in a chaotic sea. The survival probability for classical particles at the interface of an accelerator mode and the chaotic sea has an inverse power-law structure, whereas that for quantum particles has a periodically modulated inverse power law, with the period of oscillation being dependent on Planck's constant. These logarithmic oscillations are a renormalization group property that disappears as ħ → 0 in agreement with the correspondence principle. digital.library.unt.edu/ark:/67531/metadc75417/
Anomalous diffusion and environment-induced quantum decoherence
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. digital.library.unt.edu/ark:/67531/metadc139477/
Anomalous diffusion associated with nonlinear fractional derivative Fokker-Planck-like equation: Exact time-dependent solutions
This article discusses anomalous diffusion associated with nonlinear fractional derivative Fokker-Planck-like equation. Abstract: We consider the d=1 nonlinear Fokker-Planck-like equation with fractional derivatives (∂/∂t)P(x,t) = D(∂ƴ/∂xƴ)[P(x,t]v. Exact time-dependent solutions are found for v = (2 - y)/(1 + y)(-∞ < y ⩽ 2). By considering the long-distance asymptotic behavior of these solutions, a connection is established, namely, q = (y + 3)/(Y + 1)(0 < y ⩽ 2), with the solutions optimizing the nonextensive entropy characterized by index q. Interestingly enough, this relation coincides with the only already known for Lévy-like superdiffusion (i.e., v = 1 and 0 < y ⩽ 2). Finally, for (y,v) = (2,0) the authors obtain q=5/3, which differs from the value q = 2 corresponding to the y = 2 solutions available in the literature (v < 1 porous medium equation), thus exhibiting nonuniform convergence. digital.library.unt.edu/ark:/67531/metadc77162/
Atomic resolution ultrahigh vacuum scanning tunneling microscopy of epitaxial diamond (100) films
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. digital.library.unt.edu/ark:/67531/metadc84147/
Atomic structure of steps and defects on the clean diamond (100)-2 X 1 surface studied using ultrahigh vacuum scanning tunneling microscopy
In this article, the authors report ultrahigh vacuum scanning tunneling microscopy studies of the clean nonhydrogen-terminated diamond (100)-2 X 1 surface showing single- and double-layer steps that are rebonded. The main defects observed are single, multiple, and row dimer vacancies, and antiphase boundaries. Buckling of dimers is not observed, consistent with symmetric dimers. digital.library.unt.edu/ark:/67531/metadc83794/
Beyond the Death of Linear Response: 1/f Optimal Information Transport
This article discusses linear response and 1/f optimal information transport. Article: Nonergodic renewal processes have recently been shown by several authors to be insensitive to periodic perturbations, thereby apparently sanctioning the death of linear response, a building block of nonequilibrium statistical physics. The authors show that it is possible to go beyond the "death of linear response" and establish a permanent correlation between an external stimulus and the response of a complex network generating nonergodic renewal processes, by taking as stimulus a similar nonergodic process. The ideal condition of 1/f noise corresponds to a singularity that is expected to be relevant in several experimental conditions. digital.library.unt.edu/ark:/67531/metadc40407/
Bianucci, Mannella, and Grigolini Reply
This article is a reply to a comment by Massimo Falcioni and Angelo Vulpiani. In a previous letter, the authors have discussed the linear response theory (LRT) and shown that the breakdown of this theory occurring at intermediate times, observed in an earlier paper [2] as well as in [1], disappears upon an increase of the number of degrees of freedom. In a comment to [1] Falcioni and Vulpiani [3] claim that this breakdown is rather a consequence of the lack of mixing: according to them, regardless of the number of degrees of freedom, mixing is the key ingredient behind the LRT. digital.library.unt.edu/ark:/67531/metadc77166/
Brain, Music, and Non-Poisson Renewal Processes
This article discusses brain, music, and non-Poisson renewal processes. Abstract: In this paper we show that both music composition and brain function, as revealed by the electroencephalogram (EEG) analysis, are renewal non-Poisson processes living in the nonergodic dominion. To reach this important conclusion the authors process the data with the minimum spanning tree method, so as to detect significant events, thereby building a sequence of times, which is the time series to analyze. The the authors show that in both cases, EEG and music composition, these significant events are the signature of a non-Poisson renewal process. This conclusion is reached using a technique of statistical analysis recently developed by the authors' group, the aging experiment (AE). First, the authors find that in both cases the distances between two consecutive events are described by nonexponential histograms, thereby proving the non-Poisson nature of these processes. The corresponding survival probabilities ψ(t) are well fitted by stretched exponentials [ψ(t) ∝ exp (-(yt)a), with 0.5<a<1.] The second step rests on the adoption of AE, which shows that these are renewal processes. The authors show that the stretched exponential, due to its renewal character, is the emerging tip of an iceberg, whose underwater part has slow tails with an inverse power law structure with power index μ=1+ơ. Adopting the AE procedure, the authors find that both EEG and music composition yield μ<2. On the basis of the recently discovered complexity driving signal P with μp⩽μs, the authors conclude that the results of their analysis may explain the influence of music on the human brain. digital.library.unt.edu/ark:/67531/metadc40398/
Canonical and noncanonical equilibrium distribution
This article discusses canonical and noncanonical equilibrium distribution. Abstract: We address the problem of the dynamical foundation of noncanonical equilibrium. We consider, as a source of divergence from ordinary statistical mechanics, the breakdown of the condition of time scale separation between microscopic and macroscopic dynamics. We show that this breakdown has the effect of producing a significant deviation from the canonical prescription. We also show that, while the canonical equilibrium can be reached with no apparent dependence on dynamics, the specific form of noncanonical equilibrium is, in fact, determined by dynamics. We consider the special case where the thermal reservoir driving the system of interest to equilibrium is a generator of intermittent fluctuations. We assess the form of the noncanonical equilibrium reached by the system in this case. Using both theoretical and numerical arguments we demonstrate that Lévy statistics are the best description of the dynamics and that the Lévy distribution is the correct basin of attraction. We show that the correct path to noncanonical equilibrium by means of strictly thermodynamic arguments has not yet been found, and that further research has to be done to establish a connection between dynamics and thermodynamics. digital.library.unt.edu/ark:/67531/metadc77164/
Carbon K-shell x-ray and Auger-electron production in hydrocarbons and carbon oxides by 0.6-2.0-MeV protons
This article discusses carbon K-shell x-ray and Auger-electron production in hydrocarbons and carbon oxides by 0.6-2.0-MeV protons. Abstract: Carbon K-shell x-ray and Auger-electron-production cross sections are reported for 0.6-2.0-MeV protons incident on CH4 (methane), C2H2 (acetylene), n-C4H10 (normal butane), i-C4H10 (isobutane), C6H6 (benzene), CO, and CO2. A variable-geometry end-window proportional counter with an alternative procedure for the determination of its transmission was used in collection of the x-ray data. A constant-energy-mode π/4 parallel-plate electrostatic analyzer served in the detection of Auger electrons. K-shell Auger-electron-production cross sections are compared with the predictions of the first Born theory and the perturbed-stationary-state theory which accounts for energy-loss, Coulomb deflection, and relativistic effects (ECPSSR). These data show fair agreement with the ECPSSR theory when the chemical shifts, of the carbon K-shell binding energy in molecules, are included in the calculations. This agreement is even better after effects of intramolecular scattering are considered. Validity of the geometrical model by Matthews and Hopkins [Phys. Rev. Lett. 40, 1326(1978)] is established after a scrutiny of the inelastic cross sections for scattering of Auger-electrons within the molecule and their effective dislocation out of the detector's window. The x-ray cross sections show particularly strong variations with the target molecular species because of additional changes due to modifications in the fluorescence yields for molecular carbon. The correlation of these changes with the molecular character of carbon and a scaling procedure for the fluorescence yields in molecules will be discussed elsewhere. digital.library.unt.edu/ark:/67531/metadc139493/
Carrier-Envelope Phase Effect on Atomic Excitation by Few-Cycle rf Pulses
This article discusses carrier-envelope phase effect on atomic excitation by few-cycle rf pulses. Abstract: We present an experimental and theoretical study of the carrier-envelope phase effects on population transfer between two bound atomic states interacting with intense ultrashort pulses. Radio frequency pulses are used to transfer population among the ground state hyperfine levels in rubidium atoms. These pulses are only a few cycles in duration and have Rabi frequencies of the order of the carrier frequency. The phase difference between the carrier and the envelope of the pulses has a significant effect on the excitation of atomic coherence and population transfer. The authors provide a theoretical description of this phenomenon using density matrix equations. The authors discuss the implications and possible applications of their results. digital.library.unt.edu/ark:/67531/metadc103274/
Chaos and thermal conductivity
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. digital.library.unt.edu/ark:/67531/metadc139502/
Charge-state dependence of K-shell x-ray production in aluminum by 2-12-MeV carbon ions
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. digital.library.unt.edu/ark:/67531/metadc139497/
Charge-state dependence of M-shell x-ray production in 67Ho by 2-12-MeV carbon ions
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. digital.library.unt.edu/ark:/67531/metadc139496/
Charge transfer equilibria in ambient-exposed epitaxial graphene on (0001) 6 H-SiC
This article discusses charge transfer equilibria in ambient-exposed epitaxial graphene on (0001) 6 H-SiC. Abstract: The transport properties of electronic materials have been long interpreted independently from both the underlying bulk-like behavior of the substrate or the influence of ambient gases. This is no longer the case for ultra-thin graphene whose properties are dominated by the interfaces between the active material and its surroundings. Here, the authors show that the graphene interactions with its environments are critical for the electrostatic and electrochemical equilibrium of the active device layers and their transport properties. Based on the prototypical case of epitaxial graphene on (0001) 6 H-SiC and using a combination of 'in-situ' thermoelectric power and resistance measurements and simulations from first principles, the authors demonstrate that the cooperative occurrence of an electrochemically mediated charge transfer from the graphene to air, combined with the peculiar electronic structure of the graphene/SiC interface, explains the wide variation of measured conductivity and charge carrier type found in prior reports. digital.library.unt.edu/ark:/67531/metadc132974/
Coherent control of atomic excitation using off-resonant strong few-cycle pulses
This article discusses coherent control of atomic excitation using off-resonant strong few-cycle pulses. Abstract: We study the dynamics of a two-level system driven by an off-resonance few-cycle pulse which has a phase jump ø at t = t₀, in contrast to many-cycle pulses, under the nonrotating-wave approximation (NRWA). We give a closed form analytical solution for the evolution of the probability amplitude |Cₐ(t)| for the upper level. Using the appropriate pulse parameters like the phase jump ø, jump time t₀, pulse width Շ, frequency ν, and Rabi frequency Ώ₀ the population transfer after the pulse is gone can be optimized and, for the pulse considered here, an enhancement factor of 10⁶-10⁸ was obtained. digital.library.unt.edu/ark:/67531/metadc103266/
Coherent control of refractive index in far-detuned Λ systems
This article discusses the coherent control of refraction index in far-detuned Λ systems. Abstract: Enhancement and control of the index of refraction in a mixture of two three-level atomic species that form a pair of far-detuned Λ schemes under two-photon resonance and has been studied. We employ the density-matrix approach to properly take population relaxation into account and to describe the interaction of each Λ system with the electromagnetic fields. Both Λ systems are driven by a corresponding far-detuned coherent field at one atomic transition and are probed by the same weak field. In the dressed-state basis, it represents a superposition of effective two-level subsystems with the positions, widths, and amplitudes of the resonances controlled by the driving fields and allows for efficient control of the susceptibility of the total system; leading to refractive index (RI) enhancement with vanishing absorption in the absence of amplification. We analyze the experimental implementation of such a system in a cell of Rb atoms with a natural abundance of isotopes. An upper limit estimate of the RI enhancement is obtained. digital.library.unt.edu/ark:/67531/metadc103270/
Coherent excitation of a two-level atom driven by a far-off-resonant classical field: Analytical solutions
This article discusses the coherent excitation of a two-level atom driven by a far-off-resonant classical field. Abstract: We present an analytical treatment of coherent excitation of a two-level atom driven by a far-off-resonant classical field. A class of pulse envelope is obtained for which this problem is exactly solvable. The solutions are given in terms of the Heun function, which is a generalization of the hypergeometric function. Degeneracy of the Heun to a hypergeometric equation can give all the exactly solvable pulse shapes of Gauss hypergeometric form from the generalized pulse shape obtained here. We discuss the application of the results obtained to the generation of soft x-ray and ultraviolet radiations. digital.library.unt.edu/ark:/67531/metadc103262/
Comment on "Modification of graphene properties due to electron-beam irradiation"
This article is a comment on another article titled 'Modification of graphene properties due to electron-beam irradiation'. These articles discuss the modification of graphene properties due to electron-beam irradiation. digital.library.unt.edu/ark:/67531/metadc83795/
Complex Materials for Molecular Spintronics Applications: Cobalt Bis(dioxolene) Valence Tautomers, from Molecules to Polymers
This article discusses complex materials for molecular spintronics applications. Abstract: Using first principles calculations, the authors predict a complex multifunctional behavior in cobalt bis(dioxolene) valence tautomeric compounds. Molecular spin-state switching is shown to dramatically alter electronic properties and corresponding transport properties. This spin state dependence has been demonstrated for technologically relevant coordination polymers of valence tautomers as well as for novel conjugated polymers with valence tautomeric functionalization. As a result, these materials are proposed as promising candidates for spintronic devices that can couple magnetic bistability with novel electrical and spin conduction properties. The authors' findings pave the way to the fundamental understanding and future design of active multifunctional organic materials for spintronics applications. digital.library.unt.edu/ark:/67531/metadc132994/
Complexity and Synchronization
This article discusses complexity and synchronization. Abstract: We study a fully connected network (cluster) of interacting two-state units as a model of cooperative decision making. Each unit in isolation generates a Poisson process with rate g. We show that when the number of nodes is finite, the decision-making process becomes intermittent. The decision-time distribution density is characterized by inverse power-law behavior with index μ=1.5 and is exponentially truncated. We find that the condition of perfect consensus is recovered by means of a fat tail that becomes more and more extended with increasing numbers of nodes N. The intermittent dynamics of the global variable are described by the motion of a particle in a double well potential. The particle spends a portion of the total time τs at the top of the potential barrier. Using theoretical and numerical arguments it is proved that τs ∝ (1/g)1n(const X N). The second portion of its time, τk, is spent by the particle at the bottom of the potential well and it is given by τk=(1/g)exp(const X N). We show that the time τk is responsible for the Kramers fat tail. This generates a stronger ergodicity breakdown than that generated by the inverse power law without truncation. The authors establish that the condition of partial consensus can be transmitted from one cluster to another provided that both networks are in a cooperative condition. No significant information transmission is possible if one of the two networks is not yet self-organized. We find that partitioning a large network into a set of smaller interacting clusters has the effect of converting the fat Kramers tail into an inverse power law with μ=1.5. digital.library.unt.edu/ark:/67531/metadc40410/
Compression and Diffusion: A Joint Approach to Detect Complexity
This article discusses a joint approach to detect complexity. Abstract: The adoption of the Kolmogorov-Sinai (KS) entropy is becoming a popular research tool among physicists, especially when applied to a dynamical system fitting the conditions of validity of the Pesin theorem. The study of time series that are a manifestation of system dynamics whose rules are either unknown or too complex for a mathematical treatment, is still a challenge since the KS entropy is not computable, in general, in that case. Here the authors present a plan of action based on the joint action of two procedures, both related to the KS entropy, but compatible with computer implementation through fast and efficient programs. The former procedure, called Compression Algorithm Sensitive To Regularity (CASToRe), establishes the amount of order by the numerical evaluation of algorithmic compressibility. The latter, called Complex Analysis of Sequences via Scaling AND Randomness Assessment (CASSANDRA), establishes the complexity degree through the numerical evaluation of the strength of an anomalous effect. This is the departure, of the diffusion process generated by the observed fluctuations, from ordinary Brownian motion. The CASSANDRA algorithm shares with CASToRe a connection with the Kolmogorov complexity. This makes both algorithms especially suitable to study the transition from dynamics to thermodynamics, and the case of non-stationary time series as well. The benefit of the joint action of these two methods is proven by the analysis of artificial sequences with the same main properties as the real time series to which the joint use of these two methods will be applied in future research work. digital.library.unt.edu/ark:/67531/metadc139462/
Control of chaos in a CO2 laser
This article discusses the control of chaos in a CO2 laser. Abstract: We report the experimental control of chaos in an optically modulated CO2 laser. The CO2 laser was driven into chaos by injecting a feedback beam modulated by an electro-optical modulator. Control of chaos was achieved using a modified proportional feedback technique in which the control pulses were delayed by approximately one relaxation period. Using this technique, it was possible to control unstable periodic orbits up to period 6. digital.library.unt.edu/ark:/67531/metadc84149/
Controllable enhanced dragging of light in ultradispersive media
This article discusses controllable enhanced dragging of light in ultradispersive media. Abstract: We have theoretically demonstrated an enhanced Fizeau effect due to dragging the light that occurs when the group velocity of light is ultraslow. The proposed experiment can be done in a cell of atomic Rb vapor under conditions such that the group velocity of light is of the order of a few hundred meters per second. We show theoretically that higher-order dispersion can influence the Fizeau effect and can be observed experimentally. It has been shown that the change of phase is sensitive to the motion of the cell with the speed of the order of 10⁻³ cm/s and for possible displacements as small as 10 Å. The enhanced dragging effect can be applied for position control, detection of slow mechanical motion, and efficient modulators of light. digital.library.unt.edu/ark:/67531/metadc103255/
Controlled terahertz frequency response and transparency of Josephson chains and superconducting multilayers
This article discusses controlled terahertz frequency response and transparency of Josephson chains and superconducting multilayers. Abstract: A fundamental property of wave propagation is Anderson localization, which affects the transfer of information, energy, mass, and charge in disordered media. This localization can manifest itself via, e.g., the metal-insulator transition. We exactly map the behavior of a quantum particle moving in a potential with correlated disorder to teh sub-terahertz wave propagation in either Josephson chaines or superconducting multilayers. When the Josephson junction parameters vary randomly, the sub-THz electromagnetic waves cannot propagate through these Josephson structures due to localization. For parameter variations with long-range correlations, we predict sharp transitions from transparent to reflective frequency regions for Josephson plasma waves. With appropriate choices of the correlation function, frequency windows with targeted or designed transparencies for THz or sub-THz electromagnetic waves could be achieved. This could be useful for tailoring the electromagnetic wave spectrum of Josephson arrays within the THz frequency range, which is important for applications in physics, astronomy, chemistry, biology, and medicine. digital.library.unt.edu/ark:/67531/metadc103256/
Cooperation in neural systems: Bridging complexity and periodicity
This article discusses cooperation in neural systems. Abstract: Inverse power law distributions are generally interpreted as a manifestation of complexity, and waiting time distributions with power index μ < 2 reflect the occurrence of ergodicity-breaking renewal events. In this paper we show how to combine these properties with the apparently foreign clocklike nature of biological processes. We use a two-dimensional regular network of leaky integrate-and-fire neurons, each of which is linked to its four nearest neighbors, to show that both complexity and periodicity are generated by locality breakdown: Links of increasing strength have the effect of turning local interactions into long-range interactions, thereby generating time complexity followed by time periodicity. Increasing the density of neuron firings reduces the influence of periodicity, thus creating a cooperation-induced renewal condition that is distinctly non-Poissonian. digital.library.unt.edu/ark:/67531/metadc132986/
Cooperation-induced topological complexity: a promising road to fault tolerance and Hebbian learning
This article discusses cooperation-induced topological complexity. Abstract: According to an increasing number of researchers intelligence emerges from criticality as a consequence of locality breakdown and long-range correlation, well known properties of phase transition processes. The authors study a model of interacting units, as an idealization of real cooperative systems such as the brain or a flock of birds, for the purpose of discussing the emergence of long-range correlation from the coupling of any unit with its nearest neighbors. The authors focus on the critical condition that has been recently shown to maximize information transport and the authors study the topological structure of the network of dynamically linked nodes. Although the topology of this network depends on the arbitrary choice of correlation threshold, namely the correlation intensity selected to establish a link between two nodes; the numerical calculations of this paper afford some important indications on the dynamically induced topology. The first important property is the emergence of a perception length as large as the flock size, thanks to some nodes with a large number of links, thus playing the leadership role. All the units are equivalent and leadership moves in time from one to another set of nodes, thereby insuring fault tolerance. Then the authors focus on the correlation threshold generating a scale-free topology with power index v ≈ 1 and the authors find that if this topological structure is selected to establish consensus through the linked nodes, the control parameter necessary to generate criticality is close to the critical value corresponding to the all-to-all coupling condition. The authors find that criticality in this case generates also a third state, corresponding to a total lack of consensus. However, the authors make a numerical analysis of the dynamically induced network, and the authors find that it consists of two almost independent structures, each of which is equivalent to a network in the all-to-all coupling condition. This observation confirms that cooperation makes the system evolve toward favoring consensus topological structures. The authors argue that these results are compatible with both Hebbian learning and fault tolerance. digital.library.unt.edu/ark:/67531/metadc132972/
Correlation Function and Generalized Master Equation of Arbitrary Age
This article discusses correlation function and generalized master equation of arbitrary age. Abstract: We study a two-state statistical process with a non-Poisson distribution of sojourn times. In accordance with earlier work, we find that this process is characterized by aging and we study three different ways to define the correlation function of arbitrary age of the corresponding dichotomous fluctuation. These three methods yield exact expressions, thus coinciding with the recent result by Godrèche and Luck [J. Stat. Phys. 104, 489 (2001)]. Actually, non-Poisson statistics yields infinite memory at the probability level, thereby breaking any form of Markovian approximation, including the one adopted herein, to find an approximated analytical formula. For this reason, we check the accuracy of this approximated formula by comparing it with the numerical treatment of the second of the three exact expressions. We find that, although not exact, a simple analytical expression for the correlation function of arbitrary age is very accurate. We establish a connection between the correlation function and a generalized master equation of the same age. Thus this formalism, related to models used in glassy materials, allows us to illustrate an approach to the statistical treatment of blinking quantum dots, bypassing the limitations fo the conventional Liouville treatment. digital.library.unt.edu/ark:/67531/metadc40401/
Criticality and Transmission of Information in a Swarm of Cooperative Units
This article discusses criticality and transmission of information in a swarm of cooperative units. Abstract: We show that the intelligence of a swarm of cooperative units (birds) emerges at criticality, as an effect of the joint action of frequent organizational collapses and of spatial correlation as extended as the flock size. The organizational collapses make the birds become independent of one another, thereby allowing the flock to follow the direction of the lookout birds. Long-range correlation violates the principle of locality, making the lookout birds transmit information on either danger or resources with a time delay determined by the time distance between two consecutive collapses. digital.library.unt.edu/ark:/67531/metadc40392/
Diffusion Entropy and Waiting Time Statistics of Hard-X-Ray Solar Flares
This article discusses diffusion entropy and waiting time statistics of hard-x-ray solar flares. Abstract: We show at work a technique of scaling detection based on evaluating the Shannon entropy of the diffusion process obtained by converting the time series under study into trajectories. This method, called diffusion entropy, affords information that cannot be derived from the direct evaluation of waiting times. We apply this method to the analysis of the distribution of time distance τ between two nearest-neighbor solar flares. This traditional part of the analysis is based on the direct evaluation of the distribution function ψ(τ), or of the probability ψ(τ), that no time distance smaller than a given τ is found. We adopt the paradigm of the inverse power-law behavior, and the authors focus on the determination of the inverse power index μ, without ruling out different asymptotic properties that might be revealed, at larger scales, with the help of richer statistics. We then use the DE method, with three different walking rules, and the authors focus on the regime of transition to scaling. This regime of transition and the value of the scaling parameter itself, δ, depends on the walking rule adopted, a property of interest to shed light on the slow process of transition from dynamics to thermodynamics often occurring under anomalous statistical conditions. With the first two rules the transition regime occurs through-out a large time interval, and the information contained in the time series is transmitted, to a great extent, to it, as well as to the scaling regime. By using the third rule, on the contrary, the same information is essentially conveyed to the scaling regime, which, in fact, emerges very quickly after a fast transition process. We show that the DE method not only causes to emerge the long-range correlation with a given μ<3, and so a basin of attraction different from the ordinary Gaussian one, but it also reveals the presence of memory effects induced by the time dependence of the solar flare rate. When this memory is annihilated by shuffling, the scaling parameter δ is shown to fit the theoretically expected function of μ. All this leads us to the compelling conclusion that μ=2.138±0.01. digital.library.unt.edu/ark:/67531/metadc67629/
Direct evidence for the amorphous silicon phase in visible photoluminescent porous silicon
This article discusses direct evidence for the amorphous silicon phase in visible photoluminescent porous silicon. Abstract: We report on micro-Raman spectroscopy studies of porous silicon which show an amorphous silicon Raman line at 480 R cm-1 from regions that emit visible photoluminescence. A Raman line corresponding to microcrystalline silicon at 510 R cm-1 is also observed. X-ray photoelectron spectroscopy data is presented which shows a high silicon-dioxide content in porous silicon consistent with an amorphous silicon phase. digital.library.unt.edu/ark:/67531/metadc84327/
Direct ionization and electron capture in M-shell x-ray production by fluorine ions
This article discusses direct ionization and electron capture in M-shell x-ray production by fluorine ions. Abstract: Measurements of M-shell x-ray production cross sections are reported for thin solid targets of 79Au, 82Pb, 83Bi, and 92U. Fluorine ions of energies 25, 27, and 35 MeV and charge states of 4,5,6,8, and 9 were used. The microscopic cross sections were determined from measurements made with targets ranging in thickness from ~1 to ~300 μg/cm2. An enhancement in the target M-shell x-ray production cross section was observed for fluorine ions with one or two K-shell vacancies over those without a K-shell vacancy. The sums of cross sections for direct ionization to the target continuum and electron capture to the projectile's L,M,N,... shells are inferred from charge state q=4,5,6 data. The first Born calculations overpredict the cross-section data at all energies. Cross sections for electron capture from the target M shell to the projectile K shell for one (q = 8) and two (q = 9) K-shell vacancies in the projectile are also overpredicted by the first Born approximation for electron capture, i.e., the Oppenheimer-Brinkman-Kramers approximation of Nikolaev. The data are in good agreement with the ECPSSR theory of Brandt and Lapicki, which accounts for the energy-loss, Coulomb-deflection, and relativistic effects in the perturbed-stationary-state theory. digital.library.unt.edu/ark:/67531/metadc139488/
Dynamic Approach to the Thermodynamics of Superdiffusion
This article discusses dynamic approach to the thermodynamics of superdiffusion. Abstract: We address the problem of relating thermodynamics to mechanics in the case of microscopic dynamics without a finite time scale. The solution is obtained by expressing the Tsallis entropic index q as a function of the Lévy index α, and using dynamic rather than probabilistic arguments. digital.library.unt.edu/ark:/67531/metadc77167/
Dynamical approach to Lévy processes
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 can be given a spectroscopic significance, we also discuss the relevance of the results within this context. digital.library.unt.edu/ark:/67531/metadc139498/
Dynamical model for DNA sequences
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 especially focus on a method of regression to equilibrium, which they call the Onsager analysis. With these techniques the authors establish the statistical equivalence of the real DNA sequences with their CMM realizations. We show that long-range correlations are present in exons as well as in introns, but are difficult to detect, since the exon "dynamics" is shown to be determined by the entanglement of three distinct and independent CMM's. digital.library.unt.edu/ark:/67531/metadc139499/
Dynamical Origin of Memory and Renewal
This article discusses a dynamical origin of memory and renewal. Abstract: We show that the dynamic approach to fractional Brownian motion (FBM) establishes a link between a non-Poisson renewal process with abrupt jumps resetting to zero the system's memory and correlated dynamic processes, whose individual trajectories keep a nonvanishing memory of their past time evolution. It is well known that the recrossings of the origin by an ordinary one-dimensional diffusion trajectory generates a Lévy (and thus renewal) process of index θ=1/2. We prove with theoretical and numerical arguments that this is the special case of a more general condition, insofar as the recrossings produced by the dynamic FBM generates a Lévy process with 0<θ<1. This result is extended to produce a satisfactory model for the fluorescent signal of blinking quantum dots. digital.library.unt.edu/ark:/67531/metadc40399/
The Dynamics of EEG Entropy
This article discusses the dynamics of EEG entropy. Abstract: EEG time series are analyzed using the diffusion entropy method. The resulting EEG entropy manifests short-time scaling, asymptotic saturation and an attenuated alpha-rhythm modulation. These properties are faithfully modeled by a phenomenological Langevin equation interpreted within a neural network context. digital.library.unt.edu/ark:/67531/metadc132967/
Dynamics of Electroencephalogram Entropy and Pitfalls of Scaling Detection
This article discusses dynamics of electroencephalogram entropy and pitfalls of scaling detection. Abstract: In recent studies a number of research groups have determined that human electroencephalograms (EEG) have scaling properties. In particular, a crossover between two regions with different scaling exponents has been reported. Herein the authors study the time evolution of diffusion entropy to elucidate the scaling of EGG time series. For a cohort of 20 awake healthy volunteers with closed eyes, the authors find that the diffusion entropy of EEG increments (obtained from EEG waveforms by differencing) exhibits three features: short-time growth, an alpha wave related oscillation whose amplitude gradually decays in time, and asymptotic saturation which is achieved after approximately 1 s. This analysis suggests a linear, stochastic Ornstein-Uhlenbeck Langevin equation with a quasiperiodic forcing (whose frequency and/or amplitude may vary in time) as the model for the underlying dynamics. This model captures the salient properties of EEG dynamics. In particular, both the experimental and simulated EEG time series exhibit short-time scaling which is broken by a strong periodic component, such as alpha waves. The saturation of EEG diffusion entropy precludes the existence of asymptotic scaling. We find that the crossover between two scaling regions seen in detrended fluctuation analysis (DFA) of EEG increments does not originate from the underlying dynamics but is merely an artifact of the algorithm. This artifact is rooted in the failure of the "trend plus signal" paradigm of DFA. digital.library.unt.edu/ark:/67531/metadc40408/
Effective dielectric constants of photonic crystal of aligned anisotropic cylinders and the optical response of a periodic array of carbon nanotubes
This article discusses effective dielectric constants of photonic crystal of aligned anisotropic cylanders and the optical response of a periodic array of carbon nanotubes. Abstract: We calculate the static dielectric tensor of a periodic system of aligned anisotropic dielectric cylinders. Exact analytical formula for the effective dielectric constants for the H-eigenmodes is obtained for arbitrary 2D Bravais lattice and arbitrary cross section of anisotropic cylinders behaves like uniaxial or biaxial natural crystals. The developed theory of homogenization of anisotropic cylinders is applied for calculations of the dielectric properties of photonic crystals of carbon nanotubes. digital.library.unt.edu/ark:/67531/metadc103277/
Effects of Cs deposition on the field-emission properties of single-walled carbon-nanotube bundles
This article discusses the effects of Cs deposition on the field-emission properties of single-walled carbon-nanotube bundles. Abstract: We report the effects of Cs deposition on the field-emission (FE) properties of single-walled carbon-nanotube bundles. We observe that Cs deposition decreases the turn-on field for FE by a factor of 2.1-2.8 and increases the FE current by six orders of magnitude. After Cs deposition, the FE current versus voltage (I-V) curves show non-Fowler-Nordheim behavior at large currents, consistent with tunneling from adsorbate states. At lower currents, the ratio of the slope of the FE I-V curves before and after Cs deposition is approximately 2.1. Exposure to N2 does not decrease the FE current, while exposure to O2 decreases the FE current. digital.library.unt.edu/ark:/67531/metadc84148/
Effects of O2, Ar, and H2 gases on the field-emission properties of single-walled and multiwalled carbon nanotubes
In this article, the authors compare the effects of O2, Ar, and H2 gases on the field-emission (FE) properties of single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs). The authors find that H2 and Ar gases do not significantly affect the FE properties of SWNTs or MWNTs. O2 temporarily reduces the FE current and increases the turn-on voltages in an O2 environment cause a permanent decrease of the FE current and an increase in the turn-on field of MWNTs. The ratios of the slopes before and after O2 exposure are approximately 1.04 and 0.82 for SWNTs and MWNTs, respectively. digital.library.unt.edu/ark:/67531/metadc84150/
Effects of O2, H2, and N2 gases on the field emission properties of diamond-coated microtips
This article discusses the effects of O2, H2, and N2 gases on the field emission properties of diamond-coated microtips. Abstract: We report the effects of O2, H2, and N2 residual gases on the field emission properties of uncoated and diamond-coated individual Mo microtips. The microtips are made using electrochemical etching techniques and positioned 5 µm from the anode using a scanning tunneling microscopy system. The authors observe that the field emission (FE) current and turn-on voltage of diamond-coated microtips are significantly less degraded by O2 exposure that those of uncoated Mo microtips. H2 exposure enhances the FE properties of both uncoated and diamond-coated microtips, while N2 exposure does not have any significant effect. digital.library.unt.edu/ark:/67531/metadc84151/
Elastic and inelastic scattering of 1.5-MeV neutrons by the even-A isotopes of zirconium and molybdenum
This article discusses elastic and inelastic scattering of 1.5-MeV neutrons by the even-A isotopes of zirconium and molybdenum. Abstract: Differential elastic and inelastic cross sections were measured for 1.5-MeV neutrons scattered by the even-A isotopes of zirconium and molybdenum. The scattering samples were enriched isotopes of ⁹⁰Zr, ⁹²Zr, ⁹⁴Zr, ⁹²Mo, ⁹⁴Mo, ⁹⁶Mo, and ¹⁰⁰Mo. The cross sections were measured using a dynamically biased neutron time-of-flight spectrometer. The differential cross sections have root-mean-square relative and normalization uncertainties of 2 to 3.5% and 7 to 7.5%, respectively, for elastic scattering, and 6 to 13% and 9 to 15%, respectively, for inelastic scattering. Isotopes with similar level structures have almost identical elastic angular distributions. The entire set of data was theoretically fitted using the optical-statistical model with resonance-width-fluctuation corrections. The calculated elastic differential cross section was assumed to be an incoherent sum of shape-elastic and compound-elastic scattering. At the minima in the angular distributions the cross sections were dominated by compound-elastic scattering. digital.library.unt.edu/ark:/67531/metadc146595/
Electric Field Induced Phase Transitions in Polymers: A Novel Mechanism for High Speed Energy Storage
This article discusses electric field induced phase transitions in polymers. Abstract: Using first-principles simulations, the authors identify the microscopic origin of the nonlinear dielectric response and high energy density of polyvinylidene-fluoride-based polymers as a cooperative transition path that connects nonpolar and polar phases of the system. This path explores a complex torsional and rotational manifold and is thermodynamically and kinetically accessible at relatively low temperatures. Furthermore, the introduction of suitable copolymers significantly alters the energy barriers between phases providing tunability of both the energy density and the critical fields. digital.library.unt.edu/ark:/67531/metadc132987/
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