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Partner: UNT College of Arts and Sciences
Department: Physics
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Ab initio transport properties of nanostructures from maximally localized Wannier functions
Article on ab initio transport properties of nanostructures from maximally localized Wannier functions. Abstract: We present a comprehensive first-principles study of the ballistic transport properties of low-dimensional nanostructures such as linear chains of atoms (Al, C) and carbon nanotubes in the presence of defects. An approach is introduced where quantum conductance is computed from the combination of accurate plane-wave electronic structure calculations, the evaluation of the corresponding maximally localized Wannier functions, and the calculation of transport properties by a real-space Green's function method based on the Landauer formalism. This approach is computationally very efficient, can be straightforwardly implemented as a post-processing step in a standard electronic-structure calculation, and allows us to directly link the electronic transport properties of a device to the nature of the chemical bonds, providing insight onto the mechanisms that govern electron flow at the nanoscale. digital.library.unt.edu/ark:/67531/metadc234911/
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/
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/
Aging and Rejuvenation with Fractional Derivatives
Paper discussing aging and rejuvenation with fractional derivatives. Abstract: We discuss a dynamic procedure that makes the fractional derivative 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, yields a generalized master equation equivalent to the sum of an ordinary Markov contribution and of 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, ord = 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 ord = 3 - μ. Upon time increase the system undergoes a rejuvenation process that in the time limit t >> tₐ yields ord = 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/metadc174699/
Aging in financial market
Article discussing aging in the financial market. Abstract: We analyze the data of the Italian and U.S. futures on the stock markets and we test the validity of the Continuous Time Random Walk assumption for the survival probability of the returns time series via a renewal aging experiment. We also study the survival probability of returns sign and apply a coarse graining procedure to reveal the renewal aspects of the process underlying its dynamics. digital.library.unt.edu/ark:/67531/metadc174703/
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 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/
Brain, Music, and Non-Poisson Renewal Processes
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/
Cognitive Scale-Free Networks as a Model for Intermittency in Human Natural Language
Paper discussing cognitive scale-free networks as a model for intermittency in human natural language. Abstract: We model certain features of human language complexity by means of advanced concepts borrowed from statistical mechanics. Using a time series approach, the diffusion entropy method (DE), we compute the complexity of an Italian corpus of newspapers and magazines. We find that the anomalous scaling index is compatible with a simple dynamical model, a random walk on a complex scale-free network, which is linguistically related to Saussurre's paradigms. The model yields the famous Zipf's law in terms of the generalized central limit theorem. digital.library.unt.edu/ark:/67531/metadc174698/
Collective polarization effects in β-polyvinylidene fluoride and its copolymers with tri- and tetrafluoroethylene
Article on collective polarization effects in β-polyvinylidene fluoride and its copolymers with tri- and tetrafluoroethylene. Abstract: The polar properties of the β phase of polyvinylidene fluoride (PVDF) and its copolymers with tri- and tetrafluoroethylene are investigated theoretically at different VDF-to-copolymer ratios. The calculations show that polarization in such polymers is described by cooperative, quantum-mechanical interactions between polymer chains, which cannot be viewed as a superposition of rigid dipoles. For β-PVDF, the monomer dipole moment is increased by 50% (from 2 to 3 D) as the isolated chains are brought together to form a crystal. In PVDF crystals containing copolymers, we observe a weakly parabolic dependence of monomer dipole moments on copolymer concentration. digital.library.unt.edu/ark:/67531/metadc234928/
Comment on "Modification of graphene properties due to electron-beam irradiation"
Complexity and Synchronization
Compression and Diffusion: A Joint Approach to Detect Complexity
Article discussing a joint approach to detect complexity by combining the Compression Algorithm Sensitive To Regularity (CASToRe) and Complex Analysis of Sequences via Scaling AND Randomness Assessment (CASSANDRA) procedures. digital.library.unt.edu/ark:/67531/metadc139462/
Conflict between trajectories and density description: the statistical source of disagreement
Paper discussing the statistical source of disagreement between trajectories and density description. Abstract: We study an idealized version of intermittent process leading the fluctuations of a stochastic dichotomous variable. It consists of an overdamped and symmetric potential well with a cusp-like minimum. The right-hand and left-hand portions of the potential corresponds to = W and = W, respectively. When the particle reaches this minimum is injected back to a different and randomly chosen position, still within the potential well. We build up the corresponding Frobenius-Perron equation and we evaluate the correlation function of the stochastic variable, called (t). We assign the potential well a form yielding (t) = (T = (t=T)), with > 0. Thanks to the symmetry of potential, there are no biases, and we limit ourselves to considering correlation functions with an even number of times, indicated for concision, by h12i, h1234i, and more, in general, by h1:::2ni. The adoption of a formal treatment, based on density, and thus of the operator driving the density time evolution, establishes a prescription for the evaluation of the correlation functions, yielding h1::2ni - h12i:::h(2n 1)2ni. We study the same dynamic problem using trajectories, and we establish that the resulting two-time correlation function coincides with that ordered by the density picture, as it should. We then study the four-times correlation function and we prove that in the non-Poisson case it departs from the density prescription, namely, from h1234i=h12ih34i. We conclude that this is the main reason why the two pictures yield two different diffusion processes, as noticed in an earlier work. [M. Bologna, P. Grigolini, B. J. West, Chem. Phys. 284, (1-2) 115-128 (2002)]. digital.library.unt.edu/ark:/67531/metadc174689/
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/
Correlation Function and Generalized Master Equation of Arbitrary Age
This article discusses correlation function and generalized master equation of arbitrary age using non-Poisson, Markovian, and Liouville methods. digital.library.unt.edu/ark:/67531/metadc40401/
Decoherence, wave function collapses and non-ordinary statistical mechanics
Article discussing decoherence, wave function collapses, and non-ordinary statistical mechanics. Abstract: We consider a toy model of pointer interacting with a 1/2-spin system, whose $\sigma_{x}$ variable is \emph{measured} by the environment, according to the prescription of decoherence theory. If the environment measuring the variable $\sigma_{x}$ yields ordinary statistical mechanics, the pointer sensitive to the 1/2-spin system undergoes the same, exponential, relaxation regardless of whether real collapses or an entanglement with the environment, mimicking the effect of real collapses, occur. In the case of non-ordinary statistical mechanics the occurrence of real collapses make the pointer still relax exponentially in time, while the equivalent picture in terms of reduced density matrix generates an inverse power law relaxation. digital.library.unt.edu/ark:/67531/metadc174684/
Detection of invisible and crucial events: from seismic fluctuations to the war against terrorism
Paper discussing the detection of invisible and crucial events. Abstract: We argue that the recent discovery of the non-Poissonian statistics of the seismic main-shocks is a special case of a more general approach to the detection of the distribution of the time increments between one crucial but invisible event and the next. We make the conjecture that the proposed approach can be applied to the analysis of terrorist network with significant benefits for the Intelligence Community. digital.library.unt.edu/ark:/67531/metadc174695/
Diffusion Entropy and Waiting Time Statistics of Hard-X-Ray Solar Flares
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 EEG Entropy: beyond signal plus noise
Paper discussing 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. Detrended fluctuation analysis of the EEG data is compared with diffusion entropy analysis and is found to suppress certain important properties of the EEG time series. digital.library.unt.edu/ark:/67531/metadc174706/
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/
Electromagnetically induced transparency controlled by a microwave field
This article discusses electromagnetically induced transparency controlled by a microwave field. Abstract: We have experimentally studied the propagation of two optical fields in a dense rubidium (Rb) gas in the case when an additional microwave field is coupled to the hyperfine levels of Rb atoms. The Rb energy levels form a close-Λ three-level system coupled to the optical fields and the microwave field. It has been found that the maximum transmission of the probe field depends on the relative phase between the optical and the microwave fields. We have observed both constructive and destructive interferences in electromagnetically induced transparency. A simple theoretical model and a numerical simulation have been developed to explain the observed experimental results. digital.library.unt.edu/ark:/67531/metadc103259/
Electron localization in a two-channel tight-binding model with correlated disorder
This article discusses electron localization in a two-channel tight-binding model with correlated disorder. Abstract: We calculate the localization length in a two-channel tight-binding model for correlated disordered site potential. Both intra- and interchannel correlations are taken into account. The localization length is obtained in quadratic approximation by expanding the two-channel conductance over weak disorder. The result is applied to a simple two-stranded model of DNA molecule and it is shown that a strong pair coupling between the basic nucleotides in the strands is not sufficient to delocalize electronic states. digital.library.unt.edu/ark:/67531/metadc103276/
Electronic and field emission properties of boron nitride/carbon nanotube superlattices
Article on electronic and field emission properties of boron nitride/carbon nanotube superlattices. Abstract: BN/C nanotube superlattices are quasi one-dimensional heterostructures that show unique physical properties derived from their pecular geometry. Using state-of-the-art ab initio calculations, we show that BN/C systems can be used for effective band-offset nanodevice engineering, polarization-based devices, and robust field emitters with an efficiency enhanced by up to two orders of magnitude over carbon nanotube systems. digital.library.unt.edu/ark:/67531/metadc226889/
Enhanced UV Light emission from Silicon nanoparticles induced by Au ion implantation
Paper discussing a study of light emitting silicon fabricated by ion implantation. digital.library.unt.edu/ark:/67531/metadc174705/
Enhancement of Localization in One-Dimensional Random Potentials with Long-Range Correlations
This article discusses the enhancement of localization in one-dimensional random potentials with long-range correlations. Abstract: We experimentally study the effect of enhancement of localization in weak one-dimensional random potentials. Our experimental setup is a single-mode waveguide with 100 tunable scatterers periodically inserted into the waveguide. By measuring the amplitudes of transmitted and reflected waves in the spacing between each pair of scatterers, we observe a strong decrease of the localization length when white-noise scatterers are replaced by a correlated arrangement of scatterers. digital.library.unt.edu/ark:/67531/metadc103275/
Equivalence of dipole correction and Coulomb cutoff techniques in supercell calculations
Article on the equivalence of dipole correction and Coulomb cutoff techniques in supercell calculations. In this work, the authors compare the dipole correction and Coulomb cutoff methods under the same conditions in the framework of plane-wave based density-functional theory. digital.library.unt.edu/ark:/67531/metadc234924/
Event-Driven Power-Law Relaxation in Weak Turbulence
This article discusses event-driven power-law relaxation in weak turbulence. Abstract: We characterize the spectral properties of weak turbulence in a liquid crystal sample driven by an external electric field, as a function of the applied voltage, and we find a 1/f noise spectrum S(f) ∝ 1/fn within the whole range 0< ɳ <2. We theoretically explore the hypothesis that the system complexity is driven by non-Poisson events resetting the system through creation and annihilation of coherent structures, retaining no memory of previous history (crucial events). The authors study the time asymptotic regime by means of the density ψ(τ) of the time distances between two crucial events, yielding ɳ = 3 - μ, where μ is defined through the long-time form ψ(τ) ∝ 1/τµ, with 1 < µ < 3. The system regression to equilibrium after an abrupt voltage change experimentally confirms the theory, proving violations of the ordinary linear response theory for both ɳ > 1 and ɳ < 1. digital.library.unt.edu/ark:/67531/metadc40395/
Experimental Quenching of Harmonic Stimuli: Universality of Linear Response Theory
This article discusses experimental quenching of harmonic stimuli. Abstract: We show that liquid crystals in the weak turbulence electroconvective regime respond to harmonic perturbations with oscillations whose intensity decay with an inverse power law of time. We use the results of this experiment to prove that this effect is the manifestation of a form of linear response theory (LRT) valid in the out-of-equilibrium case, as well as at thermodynamic equilibrium where it reduces to the ordinary LRT. We argue that this theory is a universal property, which is not confined to physical processes such as turbulent or excitable media, and that it holds true in all possible conditions, and for all possible systems, including a complex networks, thereby establishing a bridge between statistical physics and all the fields of research in complexity. digital.library.unt.edu/ark:/67531/metadc40394/
First-principles analysis of lattice thermal conductivity in monolayer and bilayer graphene
Article on first-principles analysis of lattice thermal conductivity in monolayer and bilayer graphene. Abstract: Using calculations from first principles, we investigate the lattice thermal conductivity of ideal monolayer and bilayer graphenes. Our result estimates that the intrinsic thermal conductivity of both materials is around 2200 W m⁻¹ K⁻¹ at 300 K, a value close to the one observed theoretically and experimentally in graphite along the basal plane. It also illustrates the expected T⁻¹ dependence at higher temperatures. The little variation between monolayer and bilayer thermal conductivities suggests that the number of layers may not affect significantly the in-plane thermal properties of these systems. The intrinsic thermal conductivity also appears to be nearly isotropic for graphene. digital.library.unt.edu/ark:/67531/metadc234913/
First-principles investigations of the dielectric properties of polypropylene/metal-oxide interfaces
Article on first-principles investigations of the dielectric properties of polypropylene/metal-oxide interfaces. Nanoscale-resolved dielectric properties of polypropylene/metal-oxide (alumina, PbTiO₃) interfaces and of the corresponding surfaces are investigated via first-principles calculations. digital.library.unt.edu/ark:/67531/metadc234923/
First principles theory of artificial metal chains on NiAl(110) surface
Article on the first principles theory of artificial metal chains on NiAl(110) surface. Abstract: Using first-principle calculations we have studied the stable phases of metal-atom chains on the (110) surface of NiAl. Our investigation is mainly focused on the technologically relevant case of Au chains, but the results will be analyzed in the broader framework of a family of metallic systems. We demonstrate that the nature of the adatom (Au, Mn, Ni, Cu, Al, H, C, Na, K, and Ca) is responsible for different levels of interaction with the substrate and gives rise to a variety of electronic behaviors. With some transition metals (such as Au, Mn, Ni, and Cu) the NiAl surface acts as a simple structural template for the formation of the artificial one-dimensional system and does not affect the electronic properties of the chains. With other atomic species (H, C, Na, K, and Ca) we observe substantially different couplings and stronger interactions. We demonstrate that the different electronic properties of the various adatoms are responsible for different couplings with the substrate and compare our findings with the existing experimental results. Finally, in the case of Au chains we have investigated the role of adatom-adatom interactions in the formation of such one-dimensional structures. digital.library.unt.edu/ark:/67531/metadc234916/
First-principles theory of metal-alkaline earth oxide interfaces
Article on the first-principles theory of metal-alkaline earth oxide interfaces. Abstract: Using calculations from first principles, we discuss the interplay between structure and functionality at metal-insulator interfaces using the paradigmatic example of the junctions between various metals (Ag, Pd, Pt, Ni, Cu, Al) and binary alkaline earth crystalline oxides (BaO, CaO, and SrO). Our results demonstrate that it is possible to tune the Schottky barrier height in a very broad range of values by manipulating the metal at the interface, and elucidate the role of the relative overlap in the density of states of the different components in determining the band alignment. We conclude by stating a "modified Schottky-Mott rule" for this class of metal-insulator heterojunctions. digital.library.unt.edu/ark:/67531/metadc234922/
A fluctuating environment as a source of periodic modulation
Article discussing a fluctuating environment as a source of periodic modulation. Abstract: We study the intermittent fluorescence of a single molecule, jumping from the "light on" to the "light off" state, as a Poisson process modulated by a fluctuating environment. We show that the quasi-periodic and quasi-deterministic environmental fluctuations make the distribution of the times of sojourn in the "light off" state depart from the exponential form, and that their succession in time mirrors environmental dynamics. As an illustration, we discuss some recent experimental results, where the environmental fluctuations depend on enzymatic activity. digital.library.unt.edu/ark:/67531/metadc132981/
Fluctuation-dissipation process without a time scale
This article discusses fluctuation-dissipation process without a time scale. Abstract: We study the influence of a dissipation process on diffusion dynamics triggered by fluctuations with long-range correlations. We make the assumption that the perturbation process involved is of the same kind as those recently studied numerically and theoretically, with a good agreement between theory and numerical treatment. As a result of this assumption the equilibrium distribution departs from the ordinary canonical distribution. The distribution tails are truncated, the distribution border is signaled by sharp peaks, and, in the weak dissipation limit, the central distribution body becomes identical to a truncated Lévy distribution. digital.library.unt.edu/ark:/67531/metadc77161/
Fluctuation-Dissipation Theorem for Event-Dominated Processes
This article discusses fluctuation-dissipation theorem for event-dominated processes. Abstract: We study a system whose dynamics are driven by non-Poisson, renewal, and nonergodic events. We show that external perturbations influencing the times at which these events occur violate the standard fluctuation-dissipation prescription due to renewal aging. The fluctuation-dissipation relation of this Letter is shown to be the linear response limit of an exact expression that has been recently proposed to account for the luminescence decay in a Gibbs ensemble of semiconductor nanocrystals, with intermittent fluorescence. digital.library.unt.edu/ark:/67531/metadc40397/
Fluorescence intermittency in blinking quantum dots: renewal or slow modulation?
Article discussing fluorescence intermittency in blinking quantum dots. Abstract: We study time series produced by the blinking quantum dots, by means of an aging experiment, and we examine the results of this experiment in the light of two distinct approaches to complexity, renewal, and slow modulation. We find that the renewal approach fits the result of the aging experiment, while the slow modulation perspective does not. We make also an attempt at establishing the existence of an intermediate condition. digital.library.unt.edu/ark:/67531/metadc174701/
From Knowledge, Knowability and the Search for Objective Randomness to a New Vision of Complexity
Paper discussing knowledge, knowability, and the search for objective randomness to a new vision of complexity. Abstract: Herein we consider various concepts of entropy as measure of the complexity of phenomena and in so doing encounter a fundamental problem in physics that affects how we understand the nature of reality. In essence the difficulty has to do with our understanding of randomness, irreversibility and unpredictability using physical theory, and these in turn undermine our certainty regarding what we can and what we cannot know about complex phenomena in general. The sources of complexity examined herein appear to be channels for the amplification of naturally occurring randomness in the physical world. Our analysis suggests that when the conditions for the renormalization group apply, this spontaneous randomness, which is not a reflection of our limited knowledge, but a genuine property of nature, does not realize the conventional thermodynamic state, and a new condition, intermediate between the dynamic and the thermodynamic state, emerges. We argue that with this vision of complexity, life, which with ordinary statistical mechanics seems to be foreign to physics, becomes a natural consequence of dynamical processes. digital.library.unt.edu/ark:/67531/metadc174694/
From power law intermittence to macroscopic coherent regime
This article offers discussions from power law intermittence to macroscopic coherent regime. The authors address the problem of establishing which is the proper form of quantum master equation generating a survival probability identical to that corresponding to the nonergodic sequence of "light on" and "light off" fluorescence fluctuations in blinking quantum dots. digital.library.unt.edu/ark:/67531/metadc132992/
Fullerene Coalescence in Nanopeapods: A Path to Novel Tubular Carbon
Article on fullerene coalescence in nanopeapods. Abstract: A fascinating structural transformation occurring inside single-walled carbon nanotubes (SWNTs) is the fullerene coalescence, which is responsible for forming stable zeppelinlike carbon molecules. We report in situ transmission electron microscope (TEM) observations revealing sequences of fullerene coalescence induced by electron irradiation on pristine nanotube peapods, together with extensive theoretical investigations of the microscopic mechanism underlying this process. TEM images indicate that the merging of fullerenes results in stable but corrugated tubules (5 to 7 Å in diameter) confined within SWNTs. These observations have been confirmed using a combination of theoretical approaches based on molecular dynamics, empirical potentials, tight-binding methods, Monte Carlo techniques, and first principles calculations. We have fully elucidated the coalescence mechanism of fullerenes inside SWNTs under electron irradiation and thermal annealing. The process occurs via the polymerization of C₆₀ molecules followed by surface reconstruction, which can be triggered either by the formation of vacancies (created under electron irradiation) or by surface-energy minimization activated by thermal annealing. These novel tubular forms of carbon contain hexagons, pentagons, heptagons, and octagons. The stability, electronic properties, and electron conductance of the novel tubules are strongly affected by the final geometry of the coalesced fullerene complex. The possibility of forming highly conducting and semiconducting tubular structures suggests new avenues in designing carbon nanowires with specific electronic characteristics. digital.library.unt.edu/ark:/67531/metadc228304/
Generalized Master Equation Via Aging Continuous-Time Random Walks
This article discusses the problem of the equivalence between continuous-time random walk (CTRW) and generalized master equation (GME). digital.library.unt.edu/ark:/67531/metadc67635/
Generation of correlated binary sequences from white noise
This article discusses the generation of correlated binary sequences from white noise. Abstract: We suggest a method for generation of random binary sequences of elements 0 and 1, with prescribed correlation properties. It is based on a modification of the widely used convolution method of constructing continuous random processes. Using this method, a binary sequence with a power-law decaying pair correlator can be easily generated. digital.library.unt.edu/ark:/67531/metadc103260/
High sensitivity measurement of implanted As in the presence of Ge in Ge(x)Si(1-x)/Si layered alloys using trace element accelerator mass spectrometry
This article discusses high sensitivity measurement of implanted As in the presence of Ge in Ge(x)Si(1-x)/Si layered alloys using trace element accelerator mass spectrometry. Abstract: Various devices can be realized on strained GeSi/Si substrates by doping the substrate with different impurities such as As. As is an n-type dopant in both Ge and Si. As cross contamination can also arise during germanium preamorphization implantation due to inadequate mass resolution in the implanter. Thus, it is important to be able to accurately measure low-level As concentrations in the presence of Ge. Secondary ion mass spectrometry (SIMS) is the standard technique for these types of measurements but is constrained by mass interferences from molecular ions (⁷⁴GeH, ²⁹Si³⁰Si¹⁶O). The trace element accelerator mass accelerator technique allows the breakup of interfering molecules. As is measured in a GeSi matrix with sensitivity significantly better than SIMS. digital.library.unt.edu/ark:/67531/metadc146576/
Homogenization of Magnetodielectric Photonic Crystals
This article discusses homogenization of magnetodielectric photonic crystals. Abstract: We calculate the low-frequency index of refraction of a medium which is homogeneous along axis z and possesses a periodic dependence of the permittivity ɛ(r) and permeability μ(r) in the x-y plane (2D magnetodielectric photonic crystal). Exact analytical formulas for the effective index of refraction for two eigenmodes with vector E or H polarized along axis z are obtained. We show that, unlike nonmagnetic photonic crystals where the E mode is ordinary and the H mode is extraordinary, now both modes exhibit extraordinary behavior. Because of this distinction, the magnetodielectric photonic crystals exhibit optical properties that do not exist for natural crystals. We also discuss the limiting case of perfectly conducting cylinders and clarify the so-called problem of noncommuting limits, ω → 0 and ɛ → ∞. digital.library.unt.edu/ark:/67531/metadc107768/
In the search for the low-complexity sequences in prokaryotic and eukaryotic genomes: how to derive a coherent picture from global and local entropy measures
Paper discussing the search for the low-complexity sequences in prokaryotic and eukaryotic genomes and how to derive a coherent picture from global and local entropy measures. Abstract: We investigate on a possible way to connect the presence of Low-Complexity Sequences (LCS) in DNA genomes and the nonstationary properties of base correlations. Under the hypothesis that these variations signal a change in the DNA function, we use a new technique, called Non-Stationarity Entropic Index (NSEI) method, and we prove that this technique is an efficient way to detect functional changes with respect to a random baseline. The remarkable aspect is that NSEI does not imply any training data or fitting parameter, the only arbitrarity being the choice of a marker in the sequence. We make this choice on the basis of biological information about LCS distributions in genomes. We show that there exists a correlation between changing the amount in LCS and the ration of long-to short-range correlation. digital.library.unt.edu/ark:/67531/metadc174697/
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