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Sample records for random fluctuations reveal

  1. Listening to the noise: random fluctuations reveal gene network parameters.

    PubMed

    Munsky, Brian; Trinh, Brooke; Khammash, Mustafa

    2009-01-01

    The cellular environment is abuzz with noise originating from the inherent random motion of reacting molecules in the living cell. In this noisy environment, clonal cell populations show cell-to-cell variability that can manifest significant phenotypic differences. Noise-induced stochastic fluctuations in cellular constituents can be measured and their statistics quantified. We show that these random fluctuations carry within them valuable information about the underlying genetic network. Far from being a nuisance, the ever-present cellular noise acts as a rich source of excitation that, when processed through a gene network, carries its distinctive fingerprint that encodes a wealth of information about that network. We show that in some cases the analysis of these random fluctuations enables the full identification of network parameters, including those that may otherwise be difficult to measure. This establishes a potentially powerful approach for the identification of gene networks and offers a new window into the workings of these networks.

  2. Listening to the Noise: Random Fluctuations Reveal Gene Network Parameters

    NASA Astrophysics Data System (ADS)

    Munsky, Brian; Trinh, Brooke; Khammash, Mustafa

    2010-03-01

    The cellular environment is abuzz with noise originating from the inherent random motion of reacting molecules in the living cell. In this noisy environment, clonal cell populations exhibit cell-to-cell variability that can manifest significant prototypical differences. Noise induced stochastic fluctuations in cellular constituents can be measured and their statistics quantified using flow cytometry, single molecule fluorescence in situ hybridization, time lapse fluorescence microscopy and other single cell and single molecule measurement techniques. We show that these random fluctuations carry within them valuable information about the underlying genetic network. Far from being a nuisance, the ever-present cellular noise acts as a rich source of excitation that, when processed through a gene network, carries its distinctive fingerprint that encodes a wealth of information about that network. We demonstrate that in some cases the analysis of these random fluctuations enables the full identification of network parameters, including those that may otherwise be difficult to measure. We use theoretical investigations to establish experimental guidelines for the identification of gene regulatory networks, and we apply these guideline to experimentally identify predictive models for different regulatory mechanisms in bacteria and yeast.

  3. Listening to the noise: random fluctuations reveal gene network parameters

    SciTech Connect

    Munsky, Brian; Khammash, Mustafa

    2009-01-01

    The cellular environment is abuzz with noise. The origin of this noise is attributed to the inherent random motion of reacting molecules that take part in gene expression and post expression interactions. In this noisy environment, clonal populations of cells exhibit cell-to-cell variability that frequently manifests as significant phenotypic differences within the cellular population. The stochastic fluctuations in cellular constituents induced by noise can be measured and their statistics quantified. We show that these random fluctuations carry within them valuable information about the underlying genetic network. Far from being a nuisance, the ever-present cellular noise acts as a rich source of excitation that, when processed through a gene network, carries its distinctive fingerprint that encodes a wealth of information about that network. We demonstrate that in some cases the analysis of these random fluctuations enables the full identification of network parameters, including those that may otherwise be difficult to measure. This establishes a potentially powerful approach for the identification of gene networks and offers a new window into the workings of these networks.

  4. Random numbers from vacuum fluctuations

    NASA Astrophysics Data System (ADS)

    Shi, Yicheng; Chng, Brenda; Kurtsiefer, Christian

    2016-07-01

    We implement a quantum random number generator based on a balanced homodyne measurement of vacuum fluctuations of the electromagnetic field. The digitized signal is directly processed with a fast randomness extraction scheme based on a linear feedback shift register. The random bit stream is continuously read in a computer at a rate of about 480 Mbit/s and passes an extended test suite for random numbers.

  5. Random numbers from vacuum fluctuations

    SciTech Connect

    Shi, Yicheng; Kurtsiefer, Christian; Chng, Brenda

    2016-07-25

    We implement a quantum random number generator based on a balanced homodyne measurement of vacuum fluctuations of the electromagnetic field. The digitized signal is directly processed with a fast randomness extraction scheme based on a linear feedback shift register. The random bit stream is continuously read in a computer at a rate of about 480 Mbit/s and passes an extended test suite for random numbers.

  6. Statistical regimes of random laser fluctuations

    SciTech Connect

    Lepri, Stefano; Cavalieri, Stefano; Oppo, Gian-Luca; Wiersma, Diederik S.

    2007-06-15

    Statistical fluctuations of the light emitted from amplifying random media are studied theoretically and numerically. The characteristic scales of the diffusive motion of light lead to Gaussian or power-law (Levy) distributed fluctuations depending on external control parameters. In the Levy regime, the output pulse is highly irregular leading to huge deviations from a mean-field description. Monte Carlo simulations of a simplified model which includes the population of the medium demonstrate the two statistical regimes and provide a comparison with dynamical rate equations. Different statistics of the fluctuations helps to explain recent experimental observations reported in the literature.

  7. Fluctuations of eigenvalues of patterned random matrices

    NASA Astrophysics Data System (ADS)

    Adhikari, Kartick; Saha, Koushik

    2017-06-01

    In this article, we study the fluctuations of linear statistics of eigenvalues of circulant, symmetric circulant, reverse circulant, and Hankel matrices. We show that the linear spectral statistics of these matrices converge to the Gaussian distribution in total variation norm when the matrices are constructed using independent copies of a standard normal random variable. We also calculate the limiting variance of the linear spectral statistics for circulant, symmetric circulant, and reverse circulant matrices.

  8. Cosmological fluctuations of a random field and radiation fluid

    SciTech Connect

    Bastero-Gil, Mar; Berera, Arjun; Moss, Ian G.; Ramos, Rudnei O. E-mail: ab@ph.ed.ac.uk E-mail: rudnei@uerj.br

    2014-05-01

    A generalization of the random fluid hydrodynamic fluctuation theory due to Landau and Lifshitz is applied to describe cosmological fluctuations in systems with radiation and scalar fields. The viscous pressures, parametrized in terms of the bulk and shear viscosity coefficients, and the respective random fluctuations in the radiation fluid are combined with the stochastic and dissipative scalar evolution equation. This results in a complete set of equations describing the perturbations in both scalar and radiation fluids. These derived equations are then studied, as an example, in the context of warm inflation. Similar treatments can be done for other cosmological early universe scenarios involving thermal or statistical fluctuations.

  9. Simulation of random wind fluctuations. [space shuttle ascent control

    NASA Technical Reports Server (NTRS)

    Perlmutter, M.

    1974-01-01

    A technique was developed for the simulation of random wind fluctuations for use in computer studies of the space shuttle ascent control. The simulated wind fluctuations were generated using the techniques of control theory that have statistical characteristics similar to the characteristics obtained from wind data at Kennedy Space Center.

  10. Phenomenological picture of fluctuations in branching random walks.

    PubMed

    Mueller, A H; Munier, S

    2014-10-01

    We propose a picture of the fluctuations in branching random walks, which leads to predictions for the distribution of a random variable that characterizes the position of the bulk of the particles. We also interpret the 1/sqrt[t] correction to the average position of the rightmost particle of a branching random walk for large times t≫1, computed by Ebert and Van Saarloos, as fluctuations on top of the mean-field approximation of this process with a Brunet-Derrida cutoff at the tip that simulates discreteness. Our analytical formulas successfully compare to numerical simulations of a particular model of a branching random walk.

  11. Phenomenological picture of fluctuations in branching random walks

    NASA Astrophysics Data System (ADS)

    Mueller, A. H.; Munier, S.

    2014-10-01

    We propose a picture of the fluctuations in branching random walks, which leads to predictions for the distribution of a random variable that characterizes the position of the bulk of the particles. We also interpret the 1 /√{t } correction to the average position of the rightmost particle of a branching random walk for large times t ≫1 , computed by Ebert and Van Saarloos, as fluctuations on top of the mean-field approximation of this process with a Brunet-Derrida cutoff at the tip that simulates discreteness. Our analytical formulas successfully compare to numerical simulations of a particular model of a branching random walk.

  12. Incompressibility, fluctuations, and elasticity in random solids

    NASA Astrophysics Data System (ADS)

    Xing, Xiangjun

    2007-03-01

    Rubbers and elastomers are usually characterized by two common properties: entropic elasticity and incompressibility. At short length-scales, these systems behave as incompressible liquids. Nevertheless, macroscopic shear deformations reduce the entropy of the polymer network, and therefore cost an elastic free energy that is proportional to temperature. In this talk I shall discuss the role of incompressibility in the elasticity of rubbery materials, and its interplay with the long wave-length fluctuations. Rubbers gain shear rigidity through the vulcanization transition, a second-order phase transition driven by cross-link density and closely related to percolation. The scaling of shear modulus as a critical phenomenon sensitively depends on the incompressibility. We have recently discovered that the vulcanization theory naturally exhibits two universality classes: phantom systems and incompressible systems. Each class exhibits distinct scaling exponent for the shear modulus near the transition. Incompressibility also crucially affects the nonlinear elasticity of rubbery materials. As we have shown recently, a subtle interplay between incompressibility and long wave-length fluctuations leads to a qualitative modification of the stress-strain relation predicted by the classical theory. To leading order, this mechanism provides a simple and generic explanation for the peak structure of Mooney-Rivlin stress-strain relation, and shows good agreement with experiments. It also leads to the prediction of a phonon correlation function that depends on the strain deformation. If time permits, I will also address incompressibility and fluctuations in liquid crystalline elastomers.

  13. A primer for structural response to random pressure fluctuations

    NASA Technical Reports Server (NTRS)

    Dowell, E. H.; Vaicaitis, R.

    1975-01-01

    A review was made of power spectral methods for determining linear response of structures to random pressure fluctuations. Various simplifying assumptions are made for the purpose of obtaining useful formula for structural response. The transmission of sound through a flexible structure into an interior cavity was also treated.

  14. Random paths and current fluctuations in nonequilibrium statistical mechanics

    SciTech Connect

    Gaspard, Pierre

    2014-07-15

    An overview is given of recent advances in nonequilibrium statistical mechanics about the statistics of random paths and current fluctuations. Although statistics is carried out in space for equilibrium statistical mechanics, statistics is considered in time or spacetime for nonequilibrium systems. In this approach, relationships have been established between nonequilibrium properties such as the transport coefficients, the thermodynamic entropy production, or the affinities, and quantities characterizing the microscopic Hamiltonian dynamics and the chaos or fluctuations it may generate. This overview presents results for classical systems in the escape-rate formalism, stochastic processes, and open quantum systems.

  15. Ultrafast quantum random number generation based on quantum phase fluctuations.

    PubMed

    Xu, Feihu; Qi, Bing; Ma, Xiongfeng; Xu, He; Zheng, Haoxuan; Lo, Hoi-Kwong

    2012-05-21

    A quantum random number generator (QRNG) can generate true randomness by exploiting the fundamental indeterminism of quantum mechanics. Most approaches to QRNG employ single-photon detection technologies and are limited in speed. Here, we experimentally demonstrate an ultrafast QRNG at a rate over 6 Gbits/s based on the quantum phase fluctuations of a laser operating near threshold. Moreover, we consider a potential adversary who has partial knowledge on the raw data and discuss how one can rigorously remove such partial knowledge with postprocessing. We quantify the quantum randomness through min-entropy by modeling our system and employ two randomness extractors--Trevisan's extractor and Toeplitz-hashing--to distill the randomness, which is information-theoretically provable. The simplicity and high-speed of our experimental setup show the feasibility of a robust, low-cost, high-speed QRNG.

  16. Bounded surfatron acceleration in the presence of random fluctuations

    NASA Astrophysics Data System (ADS)

    Ruiz Mora, Africa

    The mechanisms of acceleration and transport of collisionless plasma in the presence of electromagnetic turbulence (EMT) still remains not fully understood. The particle-EMT interaction can be modelled as the interaction of the particle with a particular wave in the presence of random noise. It has been shown that in such a model the acceleration of the charged particles can be almost free. This effect is known as resonance, which can be explained by the so-called "surfatron" mechanism. We have conducted several numerical simulations for the models with and without the presence of EMT. The turbulence has been modeled as small random fluctuations on the background magnetic field. Particles dynamics consist of two regimes of motion: (i) almost free (Larmor) rotation and (ii) captured (resonance) propagation, which are given by two different sets of invariants. We have determined the necessary conditions for capture and release from resonance for the model without fluctuations, as well as the intrinsic structure of the initial conditions domain for particles in order to be captured. We observed a difference in the orders of magnitude of the dispersion of adiabatic invariant due to the effects of the added fluctuations at the resonance. These results are important to describe the mixing of the different energy levels in the presence of EMT. To understand the impact of the EMT on the system dynamics, we have performed statistical analysis of the effects that different characteristics of the random fluctuations have on the system. The particles' energy gain can be viewed as a random walk over the energy levels, which can be described in terms of the diffusion partial differential equation for the probability distribution function. This problem can be reverse-engineered to understand the nature and structure of the EMT, knowing beforehand the energy distribution of a set of particles.

  17. Effect of random charge fluctuation on strongly coupled dusty Plasma

    SciTech Connect

    Issaad, M.; Rouiguia, L.; Djebli, M.

    2008-09-07

    Modeling the interaction between particles is an open issue in dusty plasma. We dealt with strongly coupled dust particles in two dimensional confined system. For small number of clusters, we investigate the effect of random charge fluctuation on background configuration. The study is conducted for a short rang as well as a long rang potential interaction. Numerical simulation is performed using Monte-Carlo simulation in the presence of parabolic confinement and at low temperature. We have studied the background configurations for a dust particles with constant charge and in the presence of random charge fluctuation due to the discrete nature of charge carriers. The latter is studied for a positively charged dust when the dominant charging process is due to photo-emission from the dust surface. It is found, for small classical cluster consisting of small number of particles, short rang potential gives the same result as long rang one. It is also found that the random charge fluctuation affect the background configurations.

  18. Fluctuation power spectra reveal dynamical heterogeneity of peptides

    NASA Astrophysics Data System (ADS)

    Khatri, Bhavin; Yew, Zu Thur; Krivov, Sergei; McLeish, Tom; Paci, Emanuele

    2010-07-01

    Characterizing the conformational properties and dynamics of biopolymers and their relation to biological activity and function is an ongoing challenge. Single molecule techniques have provided a rich experimental window on these properties, yet they have often relied on simple one-dimensional projections of a multidimensional free energy landscape for a practical interpretation of the results. Here, we study three short peptides with different structural propensity (α helical, β hairpin, and random coil) in the presence (or absence) of a force applied to their ends using Langevin dynamics simulation and an all-atom model with implicit solvation. Each peptide produces fluctuation power spectra with a characteristic dynamic fingerprint consistent with persistent structural motifs of helices, hairpins, and random coils. The spectra for helix formation shows two well-defined relaxation modes, corresponding to local relaxation and cooperative coil to uncoil interconversion. In contrast, both the hairpin and random coil are polymerlike, showing a broad and continuous range of relaxation modes giving characteristic power laws of ω-5/4 and ω-3/2, respectively; the -5/4 power law for hairpins is robust and has not been previously observed. Langevin dynamics simulations of diffusers on a potential of mean force derived from the atomistic simulations fail to reproduce the fingerprints of each peptide motif in the power spectral density, demonstrating explicitly that such information is lacking in such one-dimensional projections. Our results demonstrate the yet unexploited potential of single molecule fluctuation spectroscopy to probe more fine scaled properties of proteins and biological macromolecules and how low dimensional projections may cause the loss of relevant information.

  19. Impact of Random Dopant Fluctuation on Size-Dependence of Contact Resistance

    NASA Astrophysics Data System (ADS)

    Matsuzawa, Kazuya

    2011-12-01

    Reducing the size of semiconductor devices causes contact in deca-nano size. Substantial fluctuation of contact resistance is anticipated owing to the reduction of impurity atoms in the contact holes. In this study, the impact of the random dopant fluctuation on the contact resistance is revealed by three-dimensional device simulation with a Schottky contact model. The standard deviation of the contact resistance could become 50%, dominated by the number of impurity atoms in the depletion layer formed by the Schottky barrier. The average value of the contact resistance could increase as the impurity concentration decreases because of the reduction of the tunneling path.

  20. Fluctuations of Power Injection in Randomly Driven Granular Gases

    NASA Astrophysics Data System (ADS)

    Visco, Paolo; Puglisi, Andrea; Barrat, Alain; Trizac, Emmanuel; van Wijland, Frédéric

    2006-11-01

    We investigate the large deviation function π∞( w) for the fluctuations of the power W( t) = wt, integrated over a time t, injected by a homogeneous random driving into a granular gas, in the infinite time limit. Our analytical study starts from a generalized Liouville equation and exploits a Molecular Chaos-like assumption. We obtain an equation for the generating function of the cumulants μ(λ) which appears as a generalization of the inelastic Boltzmann equation and has a clear physical interpretation. Reasonable assumptions are used to obtain μ(λ) in a closed analytical form. A Legendre transform is sufficient to get the large deviation function π∞( w). Our main result, apart from an estimate of all the cumulants of W( t) at large times t, is that π∞ has no negative branch. This immediately results in the inapplicability of the Gallavotti-Cohen Fluctuation Relation (GCFR), that in previous studies had been suggested to be valid for injected power in driven granular gases. We also present numerical results, in order to discuss the finite time behavior of the fluctuations of W ( t) . We discover that their probability density function converges extremely slowly to its asymptotic scaling form: the third cumulant saturates after a characteristic time τ larger than ˜50 mean free times and the higher order cumulants evolve even slower. The asymptotic value is in good agreement with our theory. Remarkably, a numerical check of the GCFR is feasible only at small times (at most τ/10), since negative events disappear at larger times. At such small times this check leads to the misleading conclusion that GCFR is satisfied for π∞( w). We offer an explanation for this remarkable apparent verification. In the inelastic Maxwell model, where a better statistics can be achieved, we are able to numerically observe the "failure" of GCFR.

  1. Fluctuations of Power Injection in Randomly Driven Granular Gases

    NASA Astrophysics Data System (ADS)

    Visco, Paolo; Puglisi, Andrea; Barrat, Alain; Trizac, Emmanuel; van Wijland, Frédéric

    2006-11-01

    We investigate the large deviation function π∞( w) for the fluctuations of the power W( t) = wt, integrated over a time t, injected by a homogeneous random driving into a granular gas, in the infinite time limit. Our analytical study starts from a generalized Liouville equation and exploits a Molecular Chaos-like assumption. We obtain an equation for the generating function of the cumulants μ(λ) which appears as a generalization of the inelastic Boltzmann equation and has a clear physical interpretation. Reasonable assumptions are used to obtain μ(λ) in a closed analytical form. A Legendre transform is sufficient to get the large deviation function π∞( w). Our main result, apart from an estimate of all the cumulants of W( t) at large times t, is that π∞ has no negative branch. This immediately results in the inapplicability of the Gallavotti-Cohen Fluctuation Relation (GCFR), that in previous studies had been suggested to be valid for injected power in driven granular gases. We also present numerical results, in order to discuss the finite time behavior of the fluctuations of W ( t) . We discover that their probability density function converges extremely slowly to its asymptotic scaling form: the third cumulant saturates after a characteristic time τ larger than ˜50 mean free times and the higher order cumulants evolve even slower. The asymptotic value is in good agreement with our theory. Remarkably, a numerical check of the GCFR is feasible only at small times (at most τ/10), since negative events disappear at larger times. At such small times this check leads to the misleading conclusion that GCFR is satisfied for π∞( w). We offer an explanation for this remarkable apparent verification. In the inelastic Maxwell model, where a better statistics can be achieved, we are able to numerically observe the “failure” of GCFR.

  2. Two Dimensional Honeycomb Materials: Random Fields, Dissipation and Fluctuations

    NASA Astrophysics Data System (ADS)

    Frederico, T.; Oliveira, O.; de Paula, W.; Hussein, M. S.; Cardoso, T. R.

    2017-02-01

    In this paper, we propose a method to describe the many-body problem of electrons in honeycomb materials via the introduction of random fields which are coupled to the electrons and have a Gaussian distribution. From a one-body approach to the problem, after integrating exactly the contribution of the random fields, one builds a non-hermitian and dissipative effective Hamiltonian with two-body interactions. Our approach introduces besides the usual average over the electron field a second average over the random fields. The interplay of two averages enables the definition of various types of Green's functions which allow the investigation of fluctuation-dissipation characteristics of the interactions that are a manifestation of the many-body problem. In the current work, we study only the dissipative term, through the perturbative analysis of the dynamics associated the effective Hamiltonian generated by two different kinds of couplings. For the cases analyzed, the eigenstates of the effective Hamiltonian are complex and, therefore, some of the states have a finite life time. Moreover, we also investigate, in the mean field approximation, the most general parity conserving coupling to the random fields and compute the width of charge carriers Γ as a function of the Fermi energy E F . The theoretical prediction for Γ( E F ) is compared to the available experimental data for graphene. The good agreement between Γ t h e o and Γ e x p suggests that description of the many-body problem associated to the electrons in honeycomb materials can indeed be done via the introduction of random fields.

  3. Rupture of draining foam films due to random pressure fluctuations.

    PubMed

    Wang, Zebin; Narsimhan, Ganesan

    2007-02-27

    A generalized formalism for the rupture of a draining foam film due to imposed random pressure fluctuations, modeled as a Gaussian white noise, is presented in which the flow inside the film is decomposed into a flow due to film drainage and a flow due to imposed perturbation. The evolution of the amplitude of perturbation is described by a stochastic differential equation. The rupture time distribution is calculated from the sample paths of perturbation amplitude as the time for this amplitude to equal one-half the film thickness and is calculated for different amplitudes of imposed perturbations, film thicknesses, electrostatic interactions, viscosities, and interfacial mobilities. The probability of film rupture is high for thicker films, especially at smaller times, as a result of faster growth of perturbations in a thick film due to a smaller disjoining pressure gradient. Larger viscosity, larger surface viscosity, higher Marangoni number, and smaller imposed pressure fluctuation result in slower growth of perturbation of a draining film, thus leading to larger rupture time. It is shown that a composite rupture time distribution combining short time simulation results with equilibrium distribution is a good approximation.

  4. Electromagnetic fluctuation-induced interactions in randomly charged slabs.

    PubMed

    Rezvani, Vahid; Sarabadani, Jalal; Naji, Ali; Podgornik, Rudolf

    2012-09-21

    Randomly charged net-neutral dielectric slabs are shown to interact across a featureless dielectric continuum with long-range electrostatic forces that scale with the statistical variance of their quenched random charge distribution and inversely with the distance between their bounding surfaces. By accounting for the whole spectrum of electromagnetic field fluctuations, we show that this long-range disorder-generated interaction extends well into the retarded regime where higher order (non-zero) Matsubara frequencies contribute significantly. This occurs even for highly clean samples with only a trace amount of charge disorder and shows that disorder effects can be important down to the nanoscale. As a result, the previously predicted non-monotonic behavior for the total force between dissimilar slabs as a function of their separation distance is substantially modified by higher order contributions, and in almost all cases of interest, we find that the equilibrium inter-surface separation is shifted to substantially larger values compared to predictions based solely on the zero-frequency component. This suggests that the ensuing non-monotonic interaction is more easily amenable to experimental detection. The presence of charge disorder in the intervening dielectric medium between the two slabs is shown to lead to an additional force that can be repulsive or attractive depending on the system parameters and can, for instance, wash out the non-monotonic behavior of the total force when the intervening slab contains a sufficiently large amount of disorder charges.

  5. Electromagnetic fluctuation-induced interactions in randomly charged slabs

    NASA Astrophysics Data System (ADS)

    Rezvani, Vahid; Sarabadani, Jalal; Naji, Ali; Podgornik, Rudolf

    2012-09-01

    Randomly charged net-neutral dielectric slabs are shown to interact across a featureless dielectric continuum with long-range electrostatic forces that scale with the statistical variance of their quenched random charge distribution and inversely with the distance between their bounding surfaces. By accounting for the whole spectrum of electromagnetic field fluctuations, we show that this long-range disorder-generated interaction extends well into the retarded regime where higher order (non-zero) Matsubara frequencies contribute significantly. This occurs even for highly clean samples with only a trace amount of charge disorder and shows that disorder effects can be important down to the nanoscale. As a result, the previously predicted non-monotonic behavior for the total force between dissimilar slabs as a function of their separation distance is substantially modified by higher order contributions, and in almost all cases of interest, we find that the equilibrium inter-surface separation is shifted to substantially larger values compared to predictions based solely on the zero-frequency component. This suggests that the ensuing non-monotonic interaction is more easily amenable to experimental detection. The presence of charge disorder in the intervening dielectric medium between the two slabs is shown to lead to an additional force that can be repulsive or attractive depending on the system parameters and can, for instance, wash out the non-monotonic behavior of the total force when the intervening slab contains a sufficiently large amount of disorder charges.

  6. Revealing giant internal magnetic fields due to spin fluctuations in magnetically doped colloidal nanocrystals

    DOE PAGES

    Rice, William D.; Liu, Wenyong; Baker, Thomas A.; ...

    2015-11-23

    Strong quantum confinement in semiconductors can compress the wavefunctions of band electrons and holes to nanometre-scale volumes, significantly enhancing interactions between themselves and individual dopants. In magnetically doped semiconductors, where paramagnetic dopants (such as Mn2+, Co2+ and so on) couple to band carriers via strong sp–d spin exchange, giant magneto-optical effects can therefore be realized in confined geometries using few or even single impurity spins. Importantly, however, thermodynamic spin fluctuations become increasingly relevant in this few-spin limit. In nanoscale volumes, the statistical √N fluctuations of N spins are expected to generate giant effective magnetic fields Beff, which should dramatically impactmore » carrier spin dynamics, even in the absence of any applied field. In this paper, we directly and unambiguously reveal the large Beff that exist in Mn2+-doped CdSe colloidal nanocrystals using ultrafast optical spectroscopy. At zero applied magnetic field, extremely rapid (300–600 GHz) spin precession of photoinjected electrons is observed, indicating Beff ~ 15-30 T for electrons. Precession frequencies exceed 2 THz in applied magnetic fields. Finally, these signals arise from electron precession about the random fields due to statistically incomplete cancellation of the embedded Mn2+ moments, thereby revealing the initial coherent dynamics of magnetic polaron formation, and highlighting the importance of magnetization fluctuations on carrier spin dynamics in nanomaterials.« less

  7. Revealing giant internal magnetic fields due to spin fluctuations in magnetically doped colloidal nanocrystals

    SciTech Connect

    Rice, William D.; Liu, Wenyong; Baker, Thomas A.; Sinitsyn, Nikolai A.; Klimov, Victor Ivanovich; Crooker, Scott A.

    2015-11-23

    Strong quantum confinement in semiconductors can compress the wavefunctions of band electrons and holes to nanometre-scale volumes, significantly enhancing interactions between themselves and individual dopants. In magnetically doped semiconductors, where paramagnetic dopants (such as Mn2+, Co2+ and so on) couple to band carriers via strong sp–d spin exchange, giant magneto-optical effects can therefore be realized in confined geometries using few or even single impurity spins. Importantly, however, thermodynamic spin fluctuations become increasingly relevant in this few-spin limit. In nanoscale volumes, the statistical √N fluctuations of N spins are expected to generate giant effective magnetic fields Beff, which should dramatically impact carrier spin dynamics, even in the absence of any applied field. In this paper, we directly and unambiguously reveal the large Beff that exist in Mn2+-doped CdSe colloidal nanocrystals using ultrafast optical spectroscopy. At zero applied magnetic field, extremely rapid (300–600 GHz) spin precession of photoinjected electrons is observed, indicating Beff ~ 15-30 T for electrons. Precession frequencies exceed 2 THz in applied magnetic fields. Finally, these signals arise from electron precession about the random fields due to statistically incomplete cancellation of the embedded Mn2+ moments, thereby revealing the initial coherent dynamics of magnetic polaron formation, and highlighting the importance of magnetization fluctuations on carrier spin dynamics in nanomaterials.

  8. Revealing giant internal magnetic fields due to spin fluctuations in magnetically doped colloidal nanocrystals

    NASA Astrophysics Data System (ADS)

    Rice, William D.; Liu, Wenyong; Baker, Thomas A.; Sinitsyn, Nikolai A.; Klimov, Victor I.; Crooker, Scott A.

    2016-02-01

    Strong quantum confinement in semiconductors can compress the wavefunctions of band electrons and holes to nanometre-scale volumes, significantly enhancing interactions between themselves and individual dopants. In magnetically doped semiconductors, where paramagnetic dopants (such as Mn2+, Co2+ and so on) couple to band carriers via strong sp-d spin exchange, giant magneto-optical effects can therefore be realized in confined geometries using few or even single impurity spins. Importantly, however, thermodynamic spin fluctuations become increasingly relevant in this few-spin limit. In nanoscale volumes, the statistical fluctuations of N spins are expected to generate giant effective magnetic fields Beff, which should dramatically impact carrier spin dynamics, even in the absence of any applied field. Here we directly and unambiguously reveal the large Beff that exist in Mn2+-doped CdSe colloidal nanocrystals using ultrafast optical spectroscopy. At zero applied magnetic field, extremely rapid (300-600 GHz) spin precession of photoinjected electrons is observed, indicating Beff ˜ 15 -30 T for electrons. Precession frequencies exceed 2 THz in applied magnetic fields. These signals arise from electron precession about the random fields due to statistically incomplete cancellation of the embedded Mn2+ moments, thereby revealing the initial coherent dynamics of magnetic polaron formation, and highlighting the importance of magnetization fluctuations on carrier spin dynamics in nanomaterials.

  9. Fluctuating pancake vortices revealed by dissipation of Josephson vortex lattice.

    SciTech Connect

    Koshelev, A. E.; Buzdin, A. I.; Kakeya, I.; Yamamoto, T.; Kadowaki, K.

    2011-06-01

    In strongly anisotropic layered superconductors in tilted magnetic fields, the Josephson vortex lattice coexists with the lattice of pancake vortices. Due to the interaction between them, the dissipation of the Josephson vortex lattice is very sensitive to the presence of the pancake vortices. If the c-axis magnetic field is smaller than the corresponding lower critical field, the pancake stacks are not formed but the individual pancakes may exist in the fluctuational regime either near the surface in large-size samples or in the central region for small-size mesas. We calculate the contribution of such fluctuating pancake vortices to the c-axis conductivity of the Josephson vortex lattice and compare the theoretical results with measurements on small mesas fabricated out of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} crystals. A fingerprint of fluctuating pancakes is a characteristic exponential dependence of the c-axis conductivity observed experimentally. Our results provide strong evidence of the existence of the fluctuating pancakes and their influence on the Josephson vortex lattice dissipation.

  10. Random Strain Fluctuations as Dominant Disorder Source for High-Quality On-Substrate Graphene Devices

    NASA Astrophysics Data System (ADS)

    Couto, Nuno J. G.; Costanzo, Davide; Engels, Stephan; Ki, Dong-Keun; Watanabe, Kenji; Taniguchi, Takashi; Stampfer, Christoph; Guinea, Francisco; Morpurgo, Alberto F.

    2014-10-01

    We perform systematic investigations of transport through graphene on hexagonal boron nitride (hBN) substrates, together with confocal Raman measurements and a targeted theoretical analysis, to identify the dominant source of disorder in this system. Low-temperature transport measurements on many devices reveal a clear correlation between the carrier mobility μ and the width n* of the resistance peak around charge neutrality, demonstrating that charge scattering and density inhomogeneities originate from the same microscopic mechanism. The study of weak localization unambiguously shows that this mechanism is associated with a long-ranged disorder potential and provides clear indications that random pseudomagnetic fields due to strain are the dominant scattering source. Spatially resolved Raman spectroscopy measurements confirm the role of local strain fluctuations, since the linewidth of the Raman 2D peak—containing information of local strain fluctuations present in graphene—correlates with the value of maximum observed mobility. The importance of strain is corroborated by a theoretical analysis of the relation between μ and n* that shows how local strain fluctuations reproduce the experimental data at a quantitative level, with n* being determined by the scalar deformation potential and μ by the random pseudomagnetic field (consistently with the conclusion drawn from the analysis of weak localization). Throughout our study, we compare the behavior of devices on hBN substrates to that of devices on SiO2 and SrTiO3 , and find that all conclusions drawn for the case of hBN are compatible with the observations made on these other materials. These observations suggest that random strain fluctuations are the dominant source of disorder for high-quality graphene on many different substrates, and not only on hexagonal boron nitride.

  11. Random Matrix Approach to Fluctuations and Scaling in Complex Systems

    NASA Astrophysics Data System (ADS)

    Santhanam, M. S.

    The study of fluctuations, self-similarity and scaling in physical and socioeconomic sciences in the last several years has brought in new insights and new ideas for modelling them. For instance, one of the important empirical results of the market dynamics is that the probability distribution of price returns r in a typical market displays a power-law, i.e, (P|r| > x) ˜ r -α , where α ˜ 3.0 [1]. In fact, this "inverse cube law" is known to hold good for volume of stocks traded in stock exchanges, though the exponent in this case is α ˜ 1.5 [1]. Similar power laws appear for the cumulative frequency distribution of earth quake magnitudes, often called the Gutenberg-Richter relation [2]. Infect, anything from size distribution of cities and wealth distributions, display power law. These apparently universal power laws pertain to the distribution of actual values taken by some quantity of interest, say, a stock market index and these distributions reveal scaling with certain parameters.

  12. Social patterns revealed through random matrix theory

    NASA Astrophysics Data System (ADS)

    Sarkar, Camellia; Jalan, Sarika

    2014-11-01

    Despite the tremendous advancements in the field of network theory, very few studies have taken weights in the interactions into consideration that emerge naturally in all real-world systems. Using random matrix analysis of a weighted social network, we demonstrate the profound impact of weights in interactions on emerging structural properties. The analysis reveals that randomness existing in particular time frame affects the decisions of individuals rendering them more freedom of choice in situations of financial security. While the structural organization of networks remains the same throughout all datasets, random matrix theory provides insight into the interaction pattern of individuals of the society in situations of crisis. It has also been contemplated that individual accountability in terms of weighted interactions remains as a key to success unless segregation of tasks comes into play.

  13. ACCELERATION OF VERY SMALL DUST GRAINS DUE TO RANDOM CHARGE FLUCTUATIONS

    SciTech Connect

    Hoang, Thiem; Lazarian, A.

    2012-12-20

    We study the acceleration of very small dust grains including polycyclic aromatic hydrocarbons arising from electrostatic interactions of dust grains that have charge fluctuating randomly in time. Random charge fluctuations of very small grains due to discrete charging events (i.e., sticking collisions with electrons and ions in plasma, and emission of photoelectrons by UV photons) are simulated using the Monte Carlo (MC) method. The motion of dust grains in randomly fluctuating electric fields induced by surrounding charged grains is studied using MC simulations. We identify the acceleration induced by random charge fluctuations as a dominant acceleration mechanism for very small grains in the diffuse interstellar medium (ISM). We find that this acceleration mechanism is efficient for environments with a low degree of ionization (i.e., large Debye length), where charge fluctuations are slow but have a large amplitude. The implications of the present acceleration mechanism for grain coagulation and shattering in the diffuse ISM and dark clouds are also discussed.

  14. Statistics of velocity fluctuations arising from a random distribution of point vortices: the speed of fluctuations and the diffusion coefficient

    PubMed

    Chavanis; Sire

    2000-07-01

    This paper is devoted to a statistical analysis of the fluctuations of velocity and acceleration produced by a random distribution of point vortices in two-dimensional turbulence. We show that the velocity probability density function PDF behaves in a manner which is intermediate between Gaussian and Levy laws, while the distribution of accelerations is governed by a Cauchy law. Our study accounts properly for a spectrum of circulations among the vortices. In the case of real vortices (with a finite core), we show analytically that the distribution of accelerations makes a smooth transition from Cauchy (for small fluctuations) to Gaussian (for large fluctuations), probably passing through an exponential tail. We introduce a function T(V) which gives the typical duration of a velocity fluctuation V; we show that T(V) behaves like V and V-1 for weak and large velocities, respectively. These results have a simple physical interpretation in the nearest neighbor approximation, and in Smoluchowski theory concerning the persistence of fluctuations. We discuss the analogies with respect to the fluctuations of the gravitational field in stellar systems. As an application of these results, we determine an approximate expression for the diffusion coefficient of point vortices. When applied to the context of freely decaying two-dimensional turbulence, the diffusion becomes anomalous and we establish a relationship nu=1+(xi/2) between the exponent of anomalous diffusion nu and the exponent xi which characterizes the decay of the vortex density.

  15. Variance of phase fluctuations of waves propagating through a random medium

    NASA Technical Reports Server (NTRS)

    Chu, Nelson C.; Kong, Jin AU; Yueh, Simon H.; Nghiem, Son V.; Fleischman, Jack G.; Ayasli, Serpil; Shin, Robert T.

    1992-01-01

    As an electromagnetic wave propagates through a random scattering medium, such as a forest, its energy is attenuated and random phase fluctuations are induced. The magnitude of the random phase fluctuations induced is important in estimating how well a Synthetic Aperture Radar (SAR) can image objects within the scattering medium. The two-layer random medium model, consisting of a scattering layer between free space and ground, is used to calculate the variance of the phase fluctuations induced between a transmitter located above the random medium and a receiver located below the random medium. The scattering properties of the random medium are characterized by a correlation function of the random permittivity fluctuations. The effective permittivity of the random medium is first calculated using the strong fluctuation theory, which accounts for large permittivity fluctuations of the scatterers. The distorted Born approximation is used to calculate the first-order scattered field. A perturbation series for the phase of the received field in the Rytov approximation is then introduced and the variance of the phase fluctuations is also calculated assuming that the transmitter and receiver are in the paraxial limit of the random medium, which allows an analytic solution to be obtained. Results are compared using the paraxial approximation, scalar Green's function formulation, and dyadic Green's function formulation. The effects studied are the dependence of the variance of the phase fluctuations on receiver location in lossy and lossless regions, medium thickness, correlation length and fractional volume of scatterers, depolarization of the incident wave, ground layer permittivity, angle of incidence, and polarization.

  16. Random-matrix physics: spectrum and strength fluctuations

    SciTech Connect

    Brody, T.A.; Flores, J.; French, J.B.; Mello, P.A.; Pandey, A.; Wong, S.S.M.

    1981-07-01

    It now appears that the general nature of the deviations from uniformity in the spectrum of a complicated nucleus is essentially the same in all regions of the spectrum and over the entire Periodic Table. This behavior, moreover, is describable in terms of standard Hamiltonian ensembles which could be generated on the basis of simple information-theory concepts, and which give also a good account of fluctuation phenomena of other kinds and, apparently, in other many-body systems besides nuclei. The main departures from simple behavior are ascribable to the moderation of the level repulsion by effects due to symmetries and collectivities, for the description of which more complicated ensembles are called for. One purpose of this review is to give a self-contained account of the theory, using methods: sometimes approximate: which are consonant with the usual theory of stochastic processes. Another purpose is to give a proper foundation for the use of ensemble theory, to make clear the origin of the simplicities in the observable fluctuations, and to derive other general fluctuation results. In comparing theory and experiment, the authors give an analysis of much of the nuclear-energy-level data, as well as an extended discussion of observable effects in nuclear transitions and reactions and in the low-temperature thermodynamics of aggregates of small metallic particles.

  17. Fluctuation-induced interaction between randomly charged dielectrics.

    PubMed

    Naji, Ali; Dean, David S; Sarabadani, Jalal; Horgan, Ron R; Podgornik, Rudolf

    2010-02-12

    Monopolar charge disorder effects are studied in the context of fluctuation-induced interactions between neutral dielectric slabs. It is shown that quenched bulk charge disorder gives rise to an additive contribution to the net interaction force which decays as the inverse distance between the slabs and may thus completely mask the standard Casimir-van der Waals force at large separations. By contrast, annealed (bulk or surface) charge disorder leads to a net interaction force whose large-distance behavior agrees with the universal Casimir force between ideal conductors, which scales as the inverse cubic distance, and the dielectric properties enter only in the subleading corrections.

  18. The glassy random laser: replica symmetry breaking in the intensity fluctuations of emission spectra

    PubMed Central

    Antenucci, Fabrizio; Crisanti, Andrea; Leuzzi, Luca

    2015-01-01

    The behavior of a newly introduced overlap parameter, measuring the correlation between intensity fluctuations of waves in random media, is analyzed in different physical regimes, with varying amount of disorder and non-linearity. This order parameter allows to identify the laser transition in random media and describes its possible glassy nature in terms of emission spectra data, the only data so far accessible in random laser measurements. The theoretical analysis is performed in terms of the complex spherical spin-glass model, a statistical mechanical model describing the onset and the behavior of random lasers in open cavities. Replica Symmetry Breaking theory allows to discern different kinds of randomness in the high pumping regime, including the most complex and intriguing glassy randomness. The outcome of the theoretical study is, eventually, compared to recent intensity fluctuation overlap measurements demonstrating the validity of the theory and providing a straightforward interpretation of qualitatively different spectral behaviors in different random lasers. PMID:26616194

  19. Polysilicon Gate Enhancement of the Random Dopant Induced Threshold Voltage Fluctuations in Sub-100 nm MOSFET's with Ultrathin Gate Oxide

    NASA Technical Reports Server (NTRS)

    Asenov, Asen; Saini, Subhash

    2000-01-01

    In this paper, we investigate various aspects of the polysilicon gate influence on the random dopant induced threshold voltage fluctuations in sub-100 nm MOSFET's with ultrathin gate oxides. The study is done by using an efficient statistical three-dimensional (3-D) "atomistic" simulation technique described else-where. MOSFET's with uniform channel doping and with low doped epitaxial channels have been investigated. The simulations reveal that even in devices with a single crystal gate the gate depletion and the random dopants in it are responsible for a substantial fraction of the threshold voltage fluctuations when the gate oxide is scaled-in the range of 1-2 nm. Simulation experiments have been used in order to separate the enhancement in the threshold voltage fluctuations due to an effective increase in the oxide thickness associated with the gate depletion from the direct influence of the random dopants in the gate depletion layer. The results of the experiments show that the both factors contribute to the enhancement of the threshold voltage fluctuations, but the effective increase in the oxide-thickness has a dominant effect in the investigated range of devices. Simulations illustrating the effect or the polysilicon grain boundaries on the threshold voltage variation are also presented.

  20. Random-matrix-theory approach to mesoscopic fluctuations of heat current.

    PubMed

    Schmidt, Martin; Kottos, Tsampikos; Shapiro, Boris

    2013-08-01

    We consider an ensemble of fully connected networks of N oscillators coupled harmonically with random springs and show, using random-matrix-theory considerations, that both the average phonon heat current and its variance are scale invariant and take universal values in the large N limit. These anomalous mesoscopic fluctuations is the hallmark of strong correlations between normal modes.

  1. Random-matrix-theory approach to mesoscopic fluctuations of heat current

    NASA Astrophysics Data System (ADS)

    Schmidt, Martin; Kottos, Tsampikos; Shapiro, Boris

    2013-08-01

    We consider an ensemble of fully connected networks of N oscillators coupled harmonically with random springs and show, using random-matrix-theory considerations, that both the average phonon heat current and its variance are scale invariant and take universal values in the large N limit. These anomalous mesoscopic fluctuations is the hallmark of strong correlations between normal modes.

  2. Multichannel detrended fluctuation analysis reveals synchronized patterns of spontaneous spinal activity in anesthetized cats.

    PubMed

    Rodríguez, Erika E; Hernández-Lemus, Enrique; Itzá-Ortiz, Benjamín A; Jiménez, Ismael; Rudomín, Pablo

    2011-01-01

    The analysis of the interaction and synchronization of relatively large ensembles of neurons is fundamental for the understanding of complex functions of the nervous system. It is known that the temporal synchronization of neural ensembles is involved in the generation of specific motor, sensory or cognitive processes. Also, the intersegmental coherence of spinal spontaneous activity may indicate the existence of synaptic neural pathways between different pairs of lumbar segments. In this study we present a multichannel version of the detrended fluctuation analysis method (mDFA) to analyze the correlation dynamics of spontaneous spinal activity (SSA) from time series analysis. This method together with the classical detrended fluctuation analysis (DFA) were used to find out whether the SSA recorded in one or several segments in the spinal cord of the anesthetized cat occurs either in a random or in an organized manner. Our results are consistent with a non-random organization of the sets of neurons involved in the generation of spontaneous cord dorsum potentials (CDPs) recorded either from one lumbar segment (DFA-α mean = 1.04[Formula: see text]0.09) or simultaneously from several lumbar segments (mDFA-α mean = 1.01[Formula: see text]0.06), where α = 0.5 indicates randomness while α = 0.5 indicates long-term correlations. To test the sensitivity of the mDFA method we also examined the effects of small spinal lesions aimed to partially interrupt connectivity between neighboring lumbosacral segments. We found that the synchronization and correlation between the CDPs recorded from the L5 and L6 segments in both sides of the spinal cord were reduced when a lesion comprising the left dorsal quadrant was performed between the segments L5 and L6 (mDFA-[Formula: see text] = 0.992 as compared to initial conditions mDFA-α = 1.186). The synchronization and correlation were reduced even further after a similar additional right spinal lesion (mDFA-α = 0.924). In contrast

  3. Multichannel Detrended Fluctuation Analysis Reveals Synchronized Patterns of Spontaneous Spinal Activity in Anesthetized Cats

    PubMed Central

    Rodríguez, Erika E.; Hernández-Lemus, Enrique; Itzá-Ortiz, Benjamín A.; Jiménez, Ismael; Rudomín, Pablo

    2011-01-01

    The analysis of the interaction and synchronization of relatively large ensembles of neurons is fundamental for the understanding of complex functions of the nervous system. It is known that the temporal synchronization of neural ensembles is involved in the generation of specific motor, sensory or cognitive processes. Also, the intersegmental coherence of spinal spontaneous activity may indicate the existence of synaptic neural pathways between different pairs of lumbar segments. In this study we present a multichannel version of the detrended fluctuation analysis method (mDFA) to analyze the correlation dynamics of spontaneous spinal activity (SSA) from time series analysis. This method together with the classical detrended fluctuation analysis (DFA) were used to find out whether the SSA recorded in one or several segments in the spinal cord of the anesthetized cat occurs either in a random or in an organized manner. Our results are consistent with a non-random organization of the sets of neurons involved in the generation of spontaneous cord dorsum potentials (CDPs) recorded either from one lumbar segment (DFA- mean = 1.040.09) or simultaneously from several lumbar segments (mDFA- mean = 1.010.06), where  = 0.5 indicates randomness while 0.5 indicates long-term correlations. To test the sensitivity of the mDFA method we also examined the effects of small spinal lesions aimed to partially interrupt connectivity between neighboring lumbosacral segments. We found that the synchronization and correlation between the CDPs recorded from the L5 and L6 segments in both sides of the spinal cord were reduced when a lesion comprising the left dorsal quadrant was performed between the segments L5 and L6 (mDFA- = 0.992 as compared to initial conditions mDFA- = 1.186). The synchronization and correlation were reduced even further after a similar additional right spinal lesion (mDFA- = 0.924). In contrast to the classical methods, such as correlation

  4. Radiation Transport in Random Media With Large Fluctuations

    NASA Astrophysics Data System (ADS)

    Olson, Aaron; Prinja, Anil; Franke, Brian

    2017-09-01

    Neutral particle transport in media exhibiting large and complex material property spatial variation is modeled by representing cross sections as lognormal random functions of space and generated through a nonlinear memory-less transformation of a Gaussian process with covariance uniquely determined by the covariance of the cross section. A Karhunen-Loève decomposition of the Gaussian process is implemented to effciently generate realizations of the random cross sections and Woodcock Monte Carlo used to transport particles on each realization and generate benchmark solutions for the mean and variance of the particle flux as well as probability densities of the particle reflectance and transmittance. A computationally effcient stochastic collocation method is implemented to directly compute the statistical moments such as the mean and variance, while a polynomial chaos expansion in conjunction with stochastic collocation provides a convenient surrogate model that also produces probability densities of output quantities of interest. Extensive numerical testing demonstrates that use of stochastic reduced-order modeling provides an accurate and cost-effective alternative to random sampling for particle transport in random media.

  5. Continuous-variable quantum key distribution with random intensity fluctuation of the local oscillator

    NASA Astrophysics Data System (ADS)

    Gui, Ming; Huang, Ming-Qiu; Liang, Lin-Mei

    2016-10-01

    In practical continuous-variable quantum key distribution (CVQKD) systems, due to environmental disturbance or some intrinsic imperfections of devices, inevitably the local oscillator (LO) employed in a coherent detection always fluctuates arbitrarily over time, which compromises the security and performance of practical CVQKD systems. In this paper, we investigate the performance of practical CVQKD systems with LO fluctuating randomly. By revising the measurement result of balanced homodyne detection and embedding fluctuation parameters into security analysis, we find that in addition to the average LO intensity, the fluctuation variance also severely affects the secret key rate. No secret key can be obtained if fluctuation variance is relatively large. This indicates that in a practical CVQKD, LO intensity should be well monitored and stabilized. Our research can be directly applied to improve the robustness of a practical CVQKD system as well as be used to optimize CVQKD protocols.

  6. Cosmological models with the energy density of random fluctuations and the Hubble-constant problem

    NASA Astrophysics Data System (ADS)

    Tomita, Kenji

    2017-08-01

    The fluctuation energy is derived from adiabatic random fluctuations due to second-order perturbation theory, and the evolutionary relation for it is expressed in the form of ρ_f = ρ_f (ρ), where ρ and ρ_f are the densities of ordinary dust and the fluctuation energy, respectively. The pressureless matter as a constituent of the universe at the later stage is assumed to consist of ordinary dust and the fluctuation energy. Next, cosmological models including the fluctuation energy as a kind of dark matter are derived using the above relation, and it is found that the Hubble parameter and the other model parameters in the derived models can be consistent with the recent observational values. Moreover, the perturbations of ρ and ρ_f are studied.

  7. Random magnets and correlations of stock price fluctuations

    NASA Astrophysics Data System (ADS)

    Rosenow, Bernd; Gopikrishnan, Parameswaran; Plerou, Vasiliki; Stanley, H. Eugene

    2002-11-01

    Random magnets provide a paradigm for the study of competing interactions and frustration in physics. Here, we suggest that this paradigm is also useful for the study and explanation of correlations between stock price changes of different companies: it (i) provides for a mechanism to explain the origin of correlations, (ii) allows to understand the occurrence of power-law correlations in the time series of highly correlated eigenmodes, and (iii) is a useful framework for the analysis of optimal investment strategies where the knowledge of (anti-)correlations is an important prerequisite for the reduction of risk.

  8. Can fluctuations of classical random field produce quantum averages?

    NASA Astrophysics Data System (ADS)

    Khrennikov, Andrei

    2009-08-01

    Albert Einstein did not believe in completeness of QM. He dreamed of creation of prequantum classical statistical mechanics such that QM will be reproduced as its approximation. He also dreamed of total exclusion of corpuscules from the future model. Reality of Einstein's dream was pure fields' reality. Recently I made his dream come true in the form of so called prequantum classical statistical field theory (PCSFT). In this approach quantum systems are described by classical random fields, e.g., electromagnetic field (instead of photon), electron field or neutron field. In this paper we generalize PCSFT to composite quantum system. It is well known that in QM, unlike classical mechanics, the state of a composite system is described by the tensor product of state spaces for its subsystems. In PCSFT one can still use Cartesian product, but state spaces are spaces of classical fields (not particles). In particular, entanglement is nothing else than correlation of classical random fields, cf. again Einstein. Thus entanglement was finally demystified.

  9. Determination of scale invariance in random-matrix spectral fluctuations without unfolding

    NASA Astrophysics Data System (ADS)

    Torres-Vargas, G.; Fossion, R.; Tapia-Ignacio, C.; López-Vieyra, J. C.

    2017-07-01

    We apply the singular value decomposition (SVD) method, based on normal-mode analysis, to decompose the spectra of finite random matrices of standard Gaussian ensembles in trend and fluctuation modes. We use the fact that the fluctuation modes are scale invariant and follow a power law, to characterize the transition between the extreme regular and chaotic cases. Thereby, we quantify the quantum chaos in systems described by random matrix theory in a direct way, without performing any previous unfolding procedure, and therefore, avoiding possible artifacts.

  10. Appearance of a homochiral state of crystals induced by random fluctuation in grinding

    NASA Astrophysics Data System (ADS)

    Katsuno, Hiroyasu; Uwaha, Makio

    2012-11-01

    We study crystallization of chiral crystals from achiral molecules using a master equation based on a simple reaction model. Although there is no chiral symmetry breaking in the reaction model, random fluctuations drive the system to a homochiral state. The time necessary for the appearance of the homochiral state is proportional to the total number of molecules in the system. This behavior is described by a diffusion equation in a size space with a position-dependent diffusion coefficient. We also study the effect of chiral impurities, which affect the crystal growth. Depending on the type of impurities, the chiral symmetry breaking occurs either deterministically or with the help of random fluctuations.

  11. Effects of random path fluctuations on the accuracy of laser ranging systems.

    PubMed

    Gardner, C S

    1976-10-01

    The effects of turbulence induced pathlength fluctuations on the accuracy of single color and two color laser ranging systems are examined. Correlation and structure functions for the path deviations are derived using several proposed models for the variation of C(n)(2) with altitude. For single color systems, random pathlength fluctuations can limit the accuracy of a range measurement to a few centimeters when the turbulence is strong (C(n)(2) ~ 10(-13) m(-2/3)), and the effective propagation path is long (>10 km). Two color systems can partially correct for the random path fluctuations so that in most cases their accuracy is limited to a few millimeters. However, at low elevation angles for satellite ranging (<20 degrees ) and over long horizontal paths, two color systems can also have errors approaching a few centimeters.

  12. Random fluctuations and validity in measuring disease management effectiveness for small populations.

    PubMed

    Farah, J Ramsay; Kamali, Kyahn; Harner, Jeffrey; Duncan, Ian G; Messer, Thomas C

    2008-12-01

    One objective of a disease management (DM) program is the reduction of members' claims costs. A considerable amount of effort has been dedicated to standardizing the outcomes of DM measurement. An area that has not received as much attention is that of random fluctuations in measured outcomes and the related issue of the validity of outcomes subject to random fluctuation. From year to year, large random fluctuations in claims costs can increase or reduce actual savings from a DM program. Sponsors of DM programs want to know how large a group or sample is necessary to prevent the effect of random fluctuations from overwhelming the effect of claims reductions. In this paper, we measure the fluctuations in calculated DM savings in a large commercial population using an adjusted historical control methodology--the methodology that has become the industry standard and which is codified by DMAA's Guidelines. We then determine the sample size necessary to demonstrate DM program savings at different levels of confidence and model the effect on fluctuations in observed outcomes under different methods of choosing trend, different levels of truncation, and for different estimates of program savings. Some groups, particularly employers, will be smaller than the minimum size required for credible outcomes measurement. For groups smaller than this minimum size, we suggest a utilization-based outcomes measure that can be used as a proxy. For both claims- and utilization-based calculations, we provide confidence intervals to be placed around savings estimates. We do this for group sizes ranging from 1000 to 100,000 members.

  13. Quantum random bit generation using energy fluctuations in stimulated Raman scattering.

    PubMed

    Bustard, Philip J; England, Duncan G; Nunn, Josh; Moffatt, Doug; Spanner, Michael; Lausten, Rune; Sussman, Benjamin J

    2013-12-02

    Random number sequences are a critical resource in modern information processing systems, with applications in cryptography, numerical simulation, and data sampling. We introduce a quantum random number generator based on the measurement of pulse energy quantum fluctuations in Stokes light generated by spontaneously-initiated stimulated Raman scattering. Bright Stokes pulse energy fluctuations up to five times the mean energy are measured with fast photodiodes and converted to unbiased random binary strings. Since the pulse energy is a continuous variable, multiple bits can be extracted from a single measurement. Our approach can be generalized to a wide range of Raman active materials; here we demonstrate a prototype using the optical phonon line in bulk diamond.

  14. Random Field Sampling for a Simplified Model of Melt-Blowing Considering Turbulent Velocity Fluctuations

    NASA Astrophysics Data System (ADS)

    Hübsch, Florian; Marheineke, Nicole; Ritter, Klaus; Wegener, Raimund

    2013-03-01

    In melt-blowing very thin liquid fiber jets are spun due to high-velocity air streams. In literature there is a clear, unsolved discrepancy between the measured and computed jet attenuation (thinning). In this paper we will verify numerically that the turbulent velocity fluctuations causing a random aerodynamic drag on the fiber jets—that has been neglected so far—are the crucial effect to close this gap. For this purpose, we model the velocity fluctuations as vector Gaussian random fields on top of a k- ɛ turbulence description and develop an efficient sampling procedure. Taking advantage of the special covariance structure the effort of the sampling is linear in the discretization and makes the realization possible. Numerical results are discussed for a simplified melt-blowing model consisting of a system of random ordinary differential equations.

  15. Effects of cell-cycle-dependent expression on random fluctuations in protein levels

    PubMed Central

    Soltani, Mohammad

    2016-01-01

    Expression of many genes varies as a cell transitions through different cell-cycle stages. How coupling between stochastic expression and cell cycle impacts cell-to-cell variability (noise) in the level of protein is not well understood. We analyse a model where a stable protein is synthesized in random bursts, and the frequency with which bursts occur varies within the cell cycle. Formulae quantifying the extent of fluctuations in the protein copy number are derived and decomposed into components arising from the cell cycle and stochastic processes. The latter stochastic component represents contributions from bursty expression and errors incurred during partitioning of molecules between daughter cells. These formulae reveal an interesting trade-off: cell-cycle dependencies that amplify the noise contribution from bursty expression also attenuate the contribution from partitioning errors. We investigate the existence of optimum strategies for coupling expression to the cell cycle that minimize the stochastic component. Intriguingly, results show that a zero production rate throughout the cell cycle, with expression only occurring just before cell division, minimizes noise from bursty expression for a fixed mean protein level. By contrast, the optimal strategy in the case of partitioning errors is to make the protein just after cell division. We provide examples of regulatory proteins that are expressed only towards the end of the cell cycle, and argue that such strategies enhance robustness of cell-cycle decisions to the intrinsic stochasticity of gene expression. PMID:28083102

  16. Effects of cell-cycle-dependent expression on random fluctuations in protein levels.

    PubMed

    Soltani, Mohammad; Singh, Abhyudai

    2016-12-01

    Expression of many genes varies as a cell transitions through different cell-cycle stages. How coupling between stochastic expression and cell cycle impacts cell-to-cell variability (noise) in the level of protein is not well understood. We analyse a model where a stable protein is synthesized in random bursts, and the frequency with which bursts occur varies within the cell cycle. Formulae quantifying the extent of fluctuations in the protein copy number are derived and decomposed into components arising from the cell cycle and stochastic processes. The latter stochastic component represents contributions from bursty expression and errors incurred during partitioning of molecules between daughter cells. These formulae reveal an interesting trade-off: cell-cycle dependencies that amplify the noise contribution from bursty expression also attenuate the contribution from partitioning errors. We investigate the existence of optimum strategies for coupling expression to the cell cycle that minimize the stochastic component. Intriguingly, results show that a zero production rate throughout the cell cycle, with expression only occurring just before cell division, minimizes noise from bursty expression for a fixed mean protein level. By contrast, the optimal strategy in the case of partitioning errors is to make the protein just after cell division. We provide examples of regulatory proteins that are expressed only towards the end of the cell cycle, and argue that such strategies enhance robustness of cell-cycle decisions to the intrinsic stochasticity of gene expression.

  17. Control of the intensity fluctuations of random electromagnetic beams on propagation in weak atmospheric turbulence

    NASA Astrophysics Data System (ADS)

    Korotkova, O.

    2006-02-01

    The intensity fluctuations of random electromagnetic beams propagating in the atmosphere are studied. For such beams it is shown that when the atmospheric fluctuations are weak then the scintillation index (the normalized variance of intensity fluctuations) of the beam at any distance from the source depends not only on the state of coherence but also on the degree of polarization of the beam in the source plane. In particular, we found that for initially unpolarized beams the scintillation index generally takes on smaller values than that for completely polarized beams. The presented analysis might be useful in the applications (e.g. communications, laser radars) where atmospheric effects can be mitigated by adjusting the coherence properties and the polarization properties of the source.

  18. Phase fluctuations of radio waves experiencing total reflection from a randomly inhomogeneous plasma layer

    NASA Astrophysics Data System (ADS)

    Afanasiev, N. T.; Afanasiev, A. N.; Larunin, O. A.; Markov, V. P.

    2010-05-01

    We examine the problem of small-angle scattering of radio waves experiencing total reflection from a randomly inhomogeneous layer of plasma. We consider the waves to be normally incident on the layer. To take into account the scattering peculiarities in the neighborhood of the reflection point, we introduce an analytical transformation for the eikonal equation solution derived by the perturbation method. This transformation permits calculations of radio-wave phase fluctuations for any monotonous profile of the regular dielectric permittivity of the plasma in the layer. Using this approach, we have derived analytical formulas for the variance and two-dimensional spatial spectrum of phase fluctuations, depending on the three-dimensional power spectrum of plasma fluctuations. We have also estimated a contribution of reflection point fluctuations to the phase fluctuations and determined the limits of applicability of the derived formulas. The presented analytical transformation of the eikonal equation solution can be used to calculate other statistical moments of the radio wave phase in many problems of solar-terrestrial physics where scattering and reflection of radio waves by plasma formations are important.

  19. Probability density of strong intensity fluctuations of laser radiation in a weakly absorbing random medium

    SciTech Connect

    Almaev, R Kh; Suvorov, A A

    2010-01-31

    Based on the quasi-optic parabolic equation, we derived analytically an expression for the probability density of strong intensity fluctuations of radiation propagating in a random attenuating medium. This probability density is compared with that obtained experimentally. It is shown that the agreement between the theory and the experiment in the entire range of variations in the radiation intensity is achieved by the combined account for the effect of small random attenuation on the radiation propagation and the action of noises on the radiation receiver. (lasers)

  20. Fluctuations in sliding motion generated by independent and random actions of protein motors.

    PubMed

    Sekimoto, K; Tawada, K

    2001-01-31

    We consider theoretical fluctuations in the in vitro sliding movement of individual cytoskeletal filaments generated by an ensemble of protein motors whose actions are assumed to be statistically independent and random. We show that the mean square deviation of the sliding distances of a filament for a given period of time around their average is proportional to the inverse of the filament length. This result provides a basis for an experimental test of the general assumption on the independent and random actions of protein motors.

  1. Single-molecule spectroscopy reveals how calmodulin activates NO synthase by controlling its conformational fluctuation dynamics

    PubMed Central

    He, Yufan; Haque, Mohammad Mahfuzul; Stuehr, Dennis J.; Lu, H. Peter

    2015-01-01

    Mechanisms that regulate the nitric oxide synthase enzymes (NOS) are of interest in biology and medicine. Although NOS catalysis relies on domain motions, and is activated by calmodulin binding, the relationships are unclear. We used single-molecule fluorescence resonance energy transfer (FRET) spectroscopy to elucidate the conformational states distribution and associated conformational fluctuation dynamics of the two electron transfer domains in a FRET dye-labeled neuronal NOS reductase domain, and to understand how calmodulin affects the dynamics to regulate catalysis. We found that calmodulin alters NOS conformational behaviors in several ways: It changes the distance distribution between the NOS domains, shortens the lifetimes of the individual conformational states, and instills conformational discipline by greatly narrowing the distributions of the conformational states and fluctuation rates. This information was specifically obtainable only by single-molecule spectroscopic measurements, and reveals how calmodulin promotes catalysis by shaping the physical and temporal conformational behaviors of NOS. PMID:26311846

  2. The generation of 68 Gbps quantum random number by measuring laser phase fluctuations

    SciTech Connect

    Nie, You-Qi; Liu, Yang; Zhang, Jun Pan, Jian-Wei; Huang, Leilei; Payne, Frank

    2015-06-15

    The speed of a quantum random number generator is essential for practical applications, such as high-speed quantum key distribution systems. Here, we push the speed of a quantum random number generator to 68 Gbps by operating a laser around its threshold level. To achieve the rate, not only high-speed photodetector and high sampling rate are needed but also a very stable interferometer is required. A practical interferometer with active feedback instead of common temperature control is developed to meet the requirement of stability. Phase fluctuations of the laser are measured by the interferometer with a photodetector and then digitalized to raw random numbers with a rate of 80 Gbps. The min-entropy of the raw data is evaluated by modeling the system and is used to quantify the quantum randomness of the raw data. The bias of the raw data caused by other signals, such as classical and detection noises, can be removed by Toeplitz-matrix hashing randomness extraction. The final random numbers can pass through the standard randomness tests. Our demonstration shows that high-speed quantum random number generators are ready for practical usage.

  3. The generation of 68 Gbps quantum random number by measuring laser phase fluctuations.

    PubMed

    Nie, You-Qi; Huang, Leilei; Liu, Yang; Payne, Frank; Zhang, Jun; Pan, Jian-Wei

    2015-06-01

    The speed of a quantum random number generator is essential for practical applications, such as high-speed quantum key distribution systems. Here, we push the speed of a quantum random number generator to 68 Gbps by operating a laser around its threshold level. To achieve the rate, not only high-speed photodetector and high sampling rate are needed but also a very stable interferometer is required. A practical interferometer with active feedback instead of common temperature control is developed to meet the requirement of stability. Phase fluctuations of the laser are measured by the interferometer with a photodetector and then digitalized to raw random numbers with a rate of 80 Gbps. The min-entropy of the raw data is evaluated by modeling the system and is used to quantify the quantum randomness of the raw data. The bias of the raw data caused by other signals, such as classical and detection noises, can be removed by Toeplitz-matrix hashing randomness extraction. The final random numbers can pass through the standard randomness tests. Our demonstration shows that high-speed quantum random number generators are ready for practical usage.

  4. The generation of 68 Gbps quantum random number by measuring laser phase fluctuations

    NASA Astrophysics Data System (ADS)

    Nie, You-Qi; Huang, Leilei; Liu, Yang; Payne, Frank; Zhang, Jun; Pan, Jian-Wei

    2015-06-01

    The speed of a quantum random number generator is essential for practical applications, such as high-speed quantum key distribution systems. Here, we push the speed of a quantum random number generator to 68 Gbps by operating a laser around its threshold level. To achieve the rate, not only high-speed photodetector and high sampling rate are needed but also a very stable interferometer is required. A practical interferometer with active feedback instead of common temperature control is developed to meet the requirement of stability. Phase fluctuations of the laser are measured by the interferometer with a photodetector and then digitalized to raw random numbers with a rate of 80 Gbps. The min-entropy of the raw data is evaluated by modeling the system and is used to quantify the quantum randomness of the raw data. The bias of the raw data caused by other signals, such as classical and detection noises, can be removed by Toeplitz-matrix hashing randomness extraction. The final random numbers can pass through the standard randomness tests. Our demonstration shows that high-speed quantum random number generators are ready for practical usage.

  5. Fluctuations around equilibrium laws in ergodic continuous-time random walks.

    PubMed

    Schulz, Johannes H P; Barkai, Eli

    2015-06-01

    We study occupation time statistics in ergodic continuous-time random walks. Under thermal detailed balance conditions, the average occupation time is given by the Boltzmann-Gibbs canonical law. But close to the nonergodic phase, the finite-time fluctuations around this mean are large and nontrivial. They exhibit dual time scaling and distribution laws: the infinite density of large fluctuations complements the Lévy-stable density of bulk fluctuations. Neither of the two should be interpreted as a stand-alone limiting law, as each has its own deficiency: the infinite density has an infinite norm (despite particle conservation), while the stable distribution has an infinite variance (although occupation times are bounded). These unphysical divergences are remedied by consistent use and interpretation of both formulas. Interestingly, while the system's canonical equilibrium laws naturally determine the mean occupation time of the ergodic motion, they also control the infinite and Lévy-stable densities of fluctuations. The duality of stable and infinite densities is in fact ubiquitous for these dynamics, as it concerns the time averages of general physical observables.

  6. Simulations reveal increased fluctuations in estrogen receptor-alpha conformation upon antagonist binding.

    PubMed

    Ng, Ho Leung

    2016-09-01

    Molecular dynamics (MD) simulations have been used to model dynamic fluctuations in the structure of estrogen receptor-alpha (ER-α) upon binding to the natural agonist 17β-estradiol (E2) and to the active metabolite of the breast cancer drug and antagonist, 4-hydroxytamoxifen (OHT). We present the most extensive MD simulations to date of ER-α, with over 1μs of combined simulations for the monomer and dimer forms. Simulations reveal that the antagonist-bound complex includes significant fluctuations while the agonist-bound complex is tightly restrained. OHT increases dynamic disorder in the loops located to either side of the tail H12 helix; H12 has been associated with the activation status of ER-α. We also report that fluctuations near H12 lead to greater conformational variation in the binding mode of the ethylamine tail of OHT. Both the agonist and antagonist conformations are stable throughout the 240ns simulations, supporting the hypothesis that there are no transitions between these two states or into intermediate states. The stable position of H12 in the OHT-bound conformation suggests that OHT stabilizes a well-defined antagonist conformational ensemble rather than merely blocking the agonist-driven activation of ER-α. Simultaneously, the increased dynamic properties of the OHT-bound complex is a potential source of binding entropy.

  7. Lead-position dependent regular oscillations and random fluctuations of conductance in graphene quantum dots.

    PubMed

    Huang, Liang; Yang, Rui; Lai, Ying-Cheng; Ferry, David K

    2013-02-27

    Quantum interference causes a wavefunction to have sensitive spatial dependence, and this has a significant effect on quantum transport. For example, in a quantum-dot system, the conductance can depend on the lead positions. We investigate, for graphene quantum dots, the conductance variations with the lead positions. Since for graphene the types of boundaries, e.g., zigzag and armchair, can fundamentally affect the quantum transport characteristics, we focus on rectangular graphene quantum dots, for which the effects of boundaries can be systematically studied. For both zigzag and armchair horizontal boundaries, we find that changing the positions of the leads can induce significant conductance variations. Depending on the Fermi energy, the variations can be either regular oscillations or random conductance fluctuations. We develop a physical theory to elucidate the origin of the conductance oscillation/fluctuation patterns. In particular, quantum interference leads to standing-wave-like-patterns in the quantum dot which, in the absence of leads, are regulated by the energy-band structure of the corresponding vertical graphene ribbon. The observed 'coexistence' of regular oscillations and random fluctuations in the conductance can be exploited for the development of graphene-based nanodevices.

  8. Fluctuations of the partition function in the generalized random energy model with external field

    NASA Astrophysics Data System (ADS)

    Bovier, Anton; Klimovsky, Anton

    2008-12-01

    We study Derrida's generalized random energy model (GREM) in the presence of uniform external field. We compute the fluctuations of the ground state and of the partition function in the thermodynamic limit for all admissible values of parameters. We find that the fluctuations are described by a hierarchical structure which is obtained by a certain coarse graining of the initial hierarchical structure of the GREM with external field. We provide an explicit formula for the free energy of the model. We also derive some large deviation results providing an expression for the free energy in a class of models with Gaussian Hamiltonians and external field. Finally, we prove that the coarse-grained parts of the system emerging in the thermodynamic limit tend to have a certain optimal magnetization, as prescribed by the strength of the external field and by parameters of the GREM.

  9. Electronic consequences of random layer-thickness fluctuations in AlAs/GaAs superlattices

    SciTech Connect

    Maeder, K.A.; Wang, L.; Zunger, A.

    1995-12-01

    We study the effects of a few types of atomic disorder on the electronic and optical properties of AlAs/GaAs (001) and (111) superlattices: (i) atomic intermixing across the interfaces; (ii) replacing a single monolayer in a superlattice by one containing the opposite atomic type (isoelectronic {delta} doping); and (iii) random layer-thickness fluctuations in superlattices (SL). Type (i) is an example of lateral disorder, while types (ii) and (iii) are examples of vertical disorder. Using three-dimensional empirical pseudopotential theory and a plane-wave basis, we calculate the band gaps, electronic wave functions, and optical matrix elements for systems containing up to 2000 atoms in the computational unit cell. Spin-orbit interactions are omitted. Computationally much less costly effective-mass calculations are used to evaluate the density of states and eigenstates away from the band edges in vertically disordered SLs. Our main findings are: (i) Chemical intermixing across the interface can significantly shift the SL energy levels and even change the identity (e.g., symmetry) of the conduction-band minimum in AlAs/GaAs SLs; (ii) any amount of thickness fluctuations in SLs leads to band-edge wave-function localization; (iii) these fluctuation-induced bound states will emit photons at energies below the ``intrinsic`` absorption edge (red shift of photoluminescence); (iv) monolayer fluctuations in thick superlattices create a gap level whose energy is pinned at the value produced by a single {delta} layer with ``wrong`` thickness; (v) (001) AlAs/GaAs SLs with monolayer thickness fluctuations have a direct band gap, while the ideal (001) superlattices are indirect for {ital n}{lt}4; (vi) there is no mobility edge for vertical transport in a disordered superlattice, because all the states are localized; however, the density of states retains some of the features of the ordered-superlattice counterpart.

  10. Influence of the Polysilicon Gate on the Random Dopant Induced Threshold Voltage Fluctuations in Sub 100 nm MOSFETS with Thin Gate Oxides

    NASA Technical Reports Server (NTRS)

    Asenov, Asen; Saini, S.

    2000-01-01

    In this paper for the first time we study the influence of the polysilicon gate on the random dopant induced threshold voltage fluctuations in sub 100 nm MOSFETs with tunnelling gate oxides. This is done by using an efficient 3D 'atomistic' simulation technique described elsewhere. Devices with uniform channel doping and with low doped epitaxial channels have been investigated. The simulations reveale that the polysilicon gate is responsible for a substantial fraction of the threshold voltage fluctuations in both devices when the gate oxide is scaled to tunnelling thickness in the range of 1 - 2 nm.

  11. Analytical solution and scaling of fluctuations in complex networks traversed by damped, interacting random walkers

    NASA Astrophysics Data System (ADS)

    Hamaneh, Mehdi Bagheri; Haber, Jonah; Yu, Yi-Kuo

    2015-11-01

    A general model for random walks (RWs) on networks is proposed. It incorporates damping and time-dependent links, and it includes standard (undamped, noninteracting) RWs (SRWs), coalescing RWs, and coalescing-branching RWs as special cases. The exact, time-dependent solutions for the average numbers of visits (w ) to nodes and their fluctuations (σ2) are given, and the long-term σ -w relation is studied. Although σ ∝w1 /2 for SRWs, this power law can be fragile when coalescing-branching interaction is present. Damping, however, often strengthens it but with an exponent generally different from 1 /2 .

  12. Bach Is the Father of Harmony: Revealed by a 1/f Fluctuation Analysis across Musical Genres.

    PubMed

    Wu, Dan; Kendrick, Keith M; Levitin, Daniel J; Li, Chaoyi; Yao, Dezhong

    2015-01-01

    Harmony is a fundamental attribute of music. Close connections exist between music and mathematics since both pursue harmony and unity. In music, the consonance of notes played simultaneously partly determines our perception of harmony; associates with aesthetic responses; and influences the emotion expression. The consonance could be considered as a window to understand and analyze harmony. Here for the first time we used a 1/f fluctuation analysis to investigate whether the consonance fluctuation structure in music with a wide range of composers and genres followed the scale free pattern that has been found for pitch, melody, rhythm, human body movements, brain activity, natural images and geographical features. We then used a network graph approach to investigate which composers were the most influential both within and across genres. Our results showed that patterns of consonance in music did follow scale-free characteristics, suggesting that this feature is a universally evolved one in both music and the living world. Furthermore, our network analysis revealed that Bach's harmony patterns were having the most influence on those used by other composers, followed closely by Mozart.

  13. Bach Is the Father of Harmony: Revealed by a 1/f Fluctuation Analysis across Musical Genres

    PubMed Central

    Wu, Dan; Kendrick, Keith M.; Levitin, Daniel J.; Li, Chaoyi; Yao, Dezhong

    2015-01-01

    Harmony is a fundamental attribute of music. Close connections exist between music and mathematics since both pursue harmony and unity. In music, the consonance of notes played simultaneously partly determines our perception of harmony; associates with aesthetic responses; and influences the emotion expression. The consonance could be considered as a window to understand and analyze harmony. Here for the first time we used a 1/f fluctuation analysis to investigate whether the consonance fluctuation structure in music with a wide range of composers and genres followed the scale free pattern that has been found for pitch, melody, rhythm, human body movements, brain activity, natural images and geographical features. We then used a network graph approach to investigate which composers were the most influential both within and across genres. Our results showed that patterns of consonance in music did follow scale-free characteristics, suggesting that this feature is a universally evolved one in both music and the living world. Furthermore, our network analysis revealed that Bach’s harmony patterns were having the most influence on those used by other composers, followed closely by Mozart. PMID:26545104

  14. Efficient 3D 'Atomistic' Simulation Technique for Studying of Random Dopant Induced Threshold Voltage Lowering and Fluctuations in Decanano MOSFETs

    NASA Technical Reports Server (NTRS)

    Asenov, Asen

    1998-01-01

    A 3D 'atomistic' simulation technique to study random dopant induced threshold voltage lowering and fluctuations in sub 0.1 micron MOSFETs is presented. It allows statistical analysis of random impurity effects down to the individual impurity level. Efficient algorithms based on a single solution of Poisson's equation, followed by the solution of a simplified current continuity equation are used in the simulations.

  15. Electronic consequences of random layer-thickness fluctuations in AlAs/GaAs superlattices

    NASA Astrophysics Data System (ADS)

    Mäder, Kurt A.; Wang, Lin-Wang; Zunger, Alex

    1995-12-01

    We study the effects of a few types of atomic disorder on the electronic and optical properties of AlAs/GaAs (001) and (111) superlattices: (i) atomic intermixing across the interfaces; (ii) replacing a single monolayer in a superlattice by one containing the opposite atomic type (isoelectronic δ doping); and (iii) random layer-thickness fluctuations in superlattices (SL). Type (i) is an example of lateral disorder, while types (ii) and (iii) are examples of vertical disorder. Using three-dimensional empirical pseudopotential theory and a plane-wave basis, we calculate the band gaps, electronic wave functions, and optical matrix elements for systems containing up to 2000 atoms in the computational unit cell. Spin-orbit interactions are omitted. Computationally much less costly effective-mass calculations are used to evaluate the density of states and eigenstates away from the band edges in vertically disordered SLs. Our main findings are: (i) Chemical intermixing across the interface can significantly shift the SL energy levels and even change the identity (e.g., symmetry) of the conduction-band minimum in AlAs/GaAs SLs; (ii) any amount of thickness fluctuations in SLs leads to band-edge wave-function localization; (iii) these fluctuation-induced bound states will emit photons at energies below the ``intrinsic'' absorption edge (red shift of photoluminescence); (iv) monolayer fluctuations in thick superlattices create a gap level whose energy is pinned at the value produced by a single δ layer with ``wrong'' thickness; (v) (001) AlAs/GaAs SLs with monolayer thickness fluctuations have a direct band gap, while the ideal (001) superlattices are indirect for n<4; (vi) there is no mobility edge for vertical transport in a disordered superlattice, because all the states are localized; however, the density of states retains some of the features of the ordered-superlattice counterpart. We find quantitative agreement with experiments on intentionally disordered SLs [A

  16. Quantum Mechanical Enhancement of the Random Dopant Induced Threshold Voltage Fluctuations and Lowering in Sub 0.1 Micron MOSFETs

    NASA Technical Reports Server (NTRS)

    Asenov, Asen; Slavcheva, G.; Brown, A. R.; Davies, J. H.; Saini, Subhash

    1999-01-01

    A detailed study of the influence of quantum effects in the inversion layer on the random dopant induced threshold voltage fluctuations and lowering in sub 0.1 micron MOSFETs has been performed. This has been achieved using a full 3D implementation of the density gradient (DG) formalism incorporated in our previously published 3D 'atomistic' simulation approach. This results in a consistent, fully 3D, quantum mechanical picture which implies not only the vertical inversion layer quantisation but also the lateral confinement effects manifested by current filamentation in the 'valleys' of the random potential fluctuations. We have shown that the net result of including quantum mechanical effects, while considering statistical fluctuations, is an increase in both threshold voltage fluctuations and lowering.

  17. Exchange-correlation energy from pairing matrix fluctuation and the particle-particle random phase approximation.

    PubMed

    van Aggelen, Helen; Yang, Yang; Yang, Weitao

    2014-05-14

    Despite their unmatched success for many applications, commonly used local, semi-local, and hybrid density functionals still face challenges when it comes to describing long-range interactions, static correlation, and electron delocalization. Density functionals of both the occupied and virtual orbitals are able to address these problems. The particle-hole (ph-) Random Phase Approximation (RPA), a functional of occupied and virtual orbitals, has recently known a revival within the density functional theory community. Following up on an idea introduced in our recent communication [H. van Aggelen, Y. Yang, and W. Yang, Phys. Rev. A 88, 030501 (2013)], we formulate more general adiabatic connections for the correlation energy in terms of pairing matrix fluctuations described by the particle-particle (pp-) propagator. With numerical examples of the pp-RPA, the lowest-order approximation to the pp-propagator, we illustrate the potential of density functional approximations based on pairing matrix fluctuations. The pp-RPA is size-extensive, self-interaction free, fully anti-symmetric, describes the strong static correlation limit in H2, and eliminates delocalization errors in H2(+) and other single-bond systems. It gives surprisingly good non-bonded interaction energies--competitive with the ph-RPA--with the correct R(-6) asymptotic decay as a function of the separation R, which we argue is mainly attributable to its correct second-order energy term. While the pp-RPA tends to underestimate absolute correlation energies, it gives good relative energies: much better atomization energies than the ph-RPA, as it has no tendency to underbind, and reaction energies of similar quality. The adiabatic connection in terms of pairing matrix fluctuation paves the way for promising new density functional approximations.

  18. Exchange-correlation energy from pairing matrix fluctuation and the particle-particle random phase approximation

    SciTech Connect

    Aggelen, Helen van; Yang, Yang; Yang, Weitao

    2014-05-14

    Despite their unmatched success for many applications, commonly used local, semi-local, and hybrid density functionals still face challenges when it comes to describing long-range interactions, static correlation, and electron delocalization. Density functionals of both the occupied and virtual orbitals are able to address these problems. The particle-hole (ph-) Random Phase Approximation (RPA), a functional of occupied and virtual orbitals, has recently known a revival within the density functional theory community. Following up on an idea introduced in our recent communication [H. van Aggelen, Y. Yang, and W. Yang, Phys. Rev. A 88, 030501 (2013)], we formulate more general adiabatic connections for the correlation energy in terms of pairing matrix fluctuations described by the particle-particle (pp-) propagator. With numerical examples of the pp-RPA, the lowest-order approximation to the pp-propagator, we illustrate the potential of density functional approximations based on pairing matrix fluctuations. The pp-RPA is size-extensive, self-interaction free, fully anti-symmetric, describes the strong static correlation limit in H{sub 2}, and eliminates delocalization errors in H{sub 2}{sup +} and other single-bond systems. It gives surprisingly good non-bonded interaction energies – competitive with the ph-RPA – with the correct R{sup −6} asymptotic decay as a function of the separation R, which we argue is mainly attributable to its correct second-order energy term. While the pp-RPA tends to underestimate absolute correlation energies, it gives good relative energies: much better atomization energies than the ph-RPA, as it has no tendency to underbind, and reaction energies of similar quality. The adiabatic connection in terms of pairing matrix fluctuation paves the way for promising new density functional approximations.

  19. A stochastic model for leukocyte random motility and chemotaxis based on receptor binding fluctuations

    PubMed Central

    1988-01-01

    Two central features of polymorphonuclear leukocyte chemosensory movement behavior demand fundamental theoretical understanding. In uniform concentrations of chemoattractant, these cells exhibit a persistent random walk, with a characteristic "persistence time" between significant changes in direction. In chemoattractant concentration gradients, they demonstrate a biased random walk, with an "orientation bias" characterizing the fraction of cells moving up the gradient. A coherent picture of cell movement responses to chemoattractant requires that both the persistence time and the orientation bias be explained within a unifying framework. In this paper, we offer the possibility that "noise" in the cellular signal perception/response mechanism can simultaneously account for these two key phenomena. In particular, we develop a stochastic mathematical model for cell locomotion based on kinetic fluctuations in chemoattractant/receptor binding. This model can simulate cell paths similar to those observed experimentally, under conditions of uniform chemoattractant concentrations as well as chemoattractant concentration gradients. Furthermore, this model can quantitatively predict both cell persistence time and dependence of orientation bias on gradient size. Thus, the concept of signal "noise" can quantitatively unify the major characteristics of leukocyte random motility and chemotaxis. The same level of noise large enough to account for the observed frequency of turning in uniform environments is simultaneously small enough to allow for the observed degree of directional bias in gradients. PMID:3339093

  20. Dannie Heineman Prize for Mathematical Physics Talk: Shape fluctuations of growing droplets and random matrix theory

    NASA Astrophysics Data System (ADS)

    Spohn, Herbert

    2011-03-01

    In 1986 Kardar, Parisi, and Zhang (KPZ) proposed a stochastic evolution equation for growing interfaces, thereby triggering an intense study of growth processes with local growth rules. Specifically we have in mind the recent spectacular experiment of Takeuchi and Sano on droplet growth in a thin film of turbulent liquid crystal. Over the last ten years one has studied universal probability density functions on the basis of simplified lattice growth models. Surprisingly enough the one-point shape fluctuations are governed by the same statistical laws as the largest eigenvalue of a random matrix, Gaussian Unitary Ensemble (GUE) in case of a curved front and Gaussian Orthogonal Ensemble (GOE) for a flat front. Recently we obtained the first exact solution of the KPZ equation for initial conditions corresponding to droplet growth, thereby providing the probability density function for the height at any time. For long times we recover the universal statistical properties as computed from lattice growth models.

  1. When human walking becomes random walking: fractal analysis and modeling of gait rhythm fluctuations.

    PubMed

    Hausdorff, J M; Ashkenazy, Y; Peng, C K; Ivanov, P C; Stanley, H E; Goldberger, A L

    2001-12-15

    We present a random walk, fractal analysis of the stride-to-stride fluctuations in the human gait rhythm. The gait of healthy young adults is scale-free with long-range correlations extending over hundreds of strides. This fractal scaling changes characteristically with maturation in children and older adults and becomes almost completely uncorrelated with certain neurologic diseases. Stochastic modeling of the gait rhythm dynamics, based on transitions between different "neural centers", reproduces distinctive statistical properties of the gait pattern. By tuning one model parameter, the hopping (transition) range, the model can describe alterations in gait dynamics from childhood to adulthood including a decrease in the correlation and volatility exponents with maturation.

  2. Depinning transition and thermal fluctuations in the random-field Ising model.

    PubMed

    Roters, L; Hucht, A; Lübeck, S; Nowak, U; Usadel, K D

    1999-11-01

    We analyze the depinning transition of a driven interface in the three-dimensional (3D) random field Ising model (RFIM) with quenched disorder by means of Monte Carlo simulations. The interface initially built into the system is perpendicular to the [111] direction of a simple cubic lattice. We introduce an algorithm which is capable of simulating such an interface independent of the considered dimension and time scale. This algorithm is applied to the 3D RFIM to study both the depinning transition and the influence of thermal fluctuations on this transition. It turns out that in the RFIM characteristics of the depinning transition depend crucially on the existence of overhangs. Our analysis yields critical exponents of the interface velocity, the correlation length, and the thermal rounding of the transition. We find numerical evidence for a scaling relation for these exponents and the dimension d of the system.

  3. When human walking becomes random walking: fractal analysis and modeling of gait rhythm fluctuations

    NASA Astrophysics Data System (ADS)

    Hausdorff, Jeffrey M.; Ashkenazy, Yosef; Peng, Chang-K.; Ivanov, Plamen Ch.; Stanley, H. Eugene; Goldberger, Ary L.

    2001-12-01

    We present a random walk, fractal analysis of the stride-to-stride fluctuations in the human gait rhythm. The gait of healthy young adults is scale-free with long-range correlations extending over hundreds of strides. This fractal scaling changes characteristically with maturation in children and older adults and becomes almost completely uncorrelated with certain neurologic diseases. Stochastic modeling of the gait rhythm dynamics, based on transitions between different “neural centers”, reproduces distinctive statistical properties of the gait pattern. By tuning one model parameter, the hopping (transition) range, the model can describe alterations in gait dynamics from childhood to adulthood - including a decrease in the correlation and volatility exponents with maturation.

  4. The influence of random indium alloy fluctuations in indium gallium nitride quantum wells on the device behavior

    SciTech Connect

    Yang, Tsung-Jui; Wu, Yuh-Renn; Shivaraman, Ravi; Speck, James S.

    2014-09-21

    In this paper, we describe the influence of the intrinsic indium fluctuation in the InGaN quantum wells on the carrier transport, efficiency droop, and emission spectrum in GaN-based light emitting diodes (LEDs). Both real and randomly generated indium fluctuations were used in 3D simulations and compared to quantum wells with a uniform indium distribution. We found that without further hypothesis the simulations of electrical and optical properties in LEDs such as carrier transport, radiative and Auger recombination, and efficiency droop are greatly improved by considering natural nanoscale indium fluctuations.

  5. Isotopes reveal fluctuation in trophic levels of estuarine organisms, in space and time

    NASA Astrophysics Data System (ADS)

    Vinagre, C.; Salgado, J. P.; Mendonça, V.; Cabral, H.; Costa, M. J.

    2012-08-01

    The estimation of the trophic level (TL) occupied by organisms in estuarine food webs, based on isotopic analysis, is generally done only for one season or averaged among seasons and sites. This does not allow the observation of possible alterations of TL in time and space. As estuaries are highly dynamic environments, it is plausible that the TLs of many of its organisms are not static, like usually portrayed in food web diagrams, but fluctuate in space and time. The TLs of marine juvenile fish, resident fish, shrimp, polychaetes, bivalves and amphipods were determined isotopically, in the Tagus estuary. Sampling was carried out in two nursery areas at each season. Significant changes in TL were observed, in space and time, for the vast majority of the organisms. A drop in TL in summer was observed for various species. The high availability of microalgae and macroalgae in summer may be the cause for this drop, which mainly affects low TL omnivores. These omnivores may opportunistically increase the proportion of primary producers in their diet, thus lowering their mean TL. Such an effect seems to cascade to secondary consumers, like Solea senegalensis and Pomatoschistus microps, which also presented a drop in TL in summer. This study also revealed that organisms that have been considered to be mainly primary consumers, like Liza ramada, and Scrobicularia plana, can actually assume considerably higher TLs seasonally, placing them as secondary consumers.

  6. Characterization of maximally random jammed sphere packings. II. Correlation functions and density fluctuations.

    PubMed

    Klatt, Michael A; Torquato, Salvatore

    2016-08-01

    In the first paper of this series, we introduced Voronoi correlation functions to characterize the structure of maximally random jammed (MRJ) sphere packings across length scales. In the present paper, we determine a variety of different correlation functions that arise in rigorous expressions for the effective physical properties of MRJ sphere packings and compare them to the corresponding statistical descriptors for overlapping spheres and equilibrium hard-sphere systems. Such structural descriptors arise in rigorous bounds and formulas for effective transport properties, diffusion and reactions constants, elastic moduli, and electromagnetic characteristics. First, we calculate the two-point, surface-void, and surface-surface correlation functions, for which we derive explicit analytical formulas for finite hard-sphere packings. We show analytically how the contact Dirac delta function contribution to the pair correlation function g_{2}(r) for MRJ packings translates into distinct functional behaviors of these two-point correlation functions that do not arise in the other two models examined here. Then we show how the spectral density distinguishes the MRJ packings from the other disordered systems in that the spectral density vanishes in the limit of infinite wavelengths; i.e., these packings are hyperuniform, which means that density fluctuations on large length scales are anomalously suppressed. Moreover, for all model systems, we study and compute exclusion probabilities and pore size distributions, as well as local density fluctuations. We conjecture that for general disordered hard-sphere packings, a central limit theorem holds for the number of points within an spherical observation window. Our analysis links problems of interest in material science, chemistry, physics, and mathematics. In the third paper of this series, we will evaluate bounds and estimates of a host of different physical properties of the MRJ sphere packings that are based on the

  7. Characterization of maximally random jammed sphere packings. II. Correlation functions and density fluctuations

    NASA Astrophysics Data System (ADS)

    Klatt, Michael A.; Torquato, Salvatore

    2016-08-01

    In the first paper of this series, we introduced Voronoi correlation functions to characterize the structure of maximally random jammed (MRJ) sphere packings across length scales. In the present paper, we determine a variety of different correlation functions that arise in rigorous expressions for the effective physical properties of MRJ sphere packings and compare them to the corresponding statistical descriptors for overlapping spheres and equilibrium hard-sphere systems. Such structural descriptors arise in rigorous bounds and formulas for effective transport properties, diffusion and reactions constants, elastic moduli, and electromagnetic characteristics. First, we calculate the two-point, surface-void, and surface-surface correlation functions, for which we derive explicit analytical formulas for finite hard-sphere packings. We show analytically how the contact Dirac delta function contribution to the pair correlation function g2(r ) for MRJ packings translates into distinct functional behaviors of these two-point correlation functions that do not arise in the other two models examined here. Then we show how the spectral density distinguishes the MRJ packings from the other disordered systems in that the spectral density vanishes in the limit of infinite wavelengths; i.e., these packings are hyperuniform, which means that density fluctuations on large length scales are anomalously suppressed. Moreover, for all model systems, we study and compute exclusion probabilities and pore size distributions, as well as local density fluctuations. We conjecture that for general disordered hard-sphere packings, a central limit theorem holds for the number of points within an spherical observation window. Our analysis links problems of interest in material science, chemistry, physics, and mathematics. In the third paper of this series, we will evaluate bounds and estimates of a host of different physical properties of the MRJ sphere packings that are based on the

  8. Two-colour spin noise spectroscopy and fluctuation correlations reveal homogeneous linewidths within quantum-dot ensembles

    NASA Astrophysics Data System (ADS)

    Yang, Luyi; Glasenapp, P.; Greilich, A.; Reuter, D.; Wieck, A. D.; Yakovlev, D. R.; Bayer, M.; Crooker, S. A.

    2014-09-01

    ‘Spin noise spectroscopy’ is an optical technique for probing electron and hole spin dynamics that is based on detecting their intrinsic fluctuations while in thermal equilibrium. Here we show that fluctuation correlations can be further exploited in multi-probe noise studies to reveal information that in general cannot be accessed by conventional linear optical spectroscopy, such as the underlying homogeneous linewidths of individual constituents within inhomogeneously broadened systems. This is demonstrated in singly charged (In,Ga)As quantum-dot ensembles using two weak probe lasers: When the lasers have similar wavelengths, they probe the same quantum dots in the ensemble and show correlated spin fluctuations. In contrast, mutually detuned probe lasers measure different subsets of quantum dots, giving uncorrelated fluctuations. The noise correlation versus laser detuning directly reveals the quantum dot homogeneous linewidth even in the presence of a strong inhomogeneous broadening. Such noise-based correlation techniques are not limited to semiconductor spin systems, but are applicable to any system with measurable intrinsic fluctuations.

  9. Two-colour spin noise spectroscopy and fluctuation correlations reveal homogeneous linewidths within quantum-dot ensembles.

    PubMed

    Yang, Luyi; Glasenapp, P; Greilich, A; Reuter, D; Wieck, A D; Yakovlev, D R; Bayer, M; Crooker, S A

    2014-09-15

    'Spin noise spectroscopy' is an optical technique for probing electron and hole spin dynamics that is based on detecting their intrinsic fluctuations while in thermal equilibrium. Here we show that fluctuation correlations can be further exploited in multi-probe noise studies to reveal information that in general cannot be accessed by conventional linear optical spectroscopy, such as the underlying homogeneous linewidths of individual constituents within inhomogeneously broadened systems. This is demonstrated in singly charged (In,Ga)As quantum-dot ensembles using two weak probe lasers: When the lasers have similar wavelengths, they probe the same quantum dots in the ensemble and show correlated spin fluctuations. In contrast, mutually detuned probe lasers measure different subsets of quantum dots, giving uncorrelated fluctuations. The noise correlation versus laser detuning directly reveals the quantum dot homogeneous linewidth even in the presence of a strong inhomogeneous broadening. Such noise-based correlation techniques are not limited to semiconductor spin systems, but are applicable to any system with measurable intrinsic fluctuations.

  10. Random Dopant Threshold Voltage Fluctuations in 50 nm Epitaxial Channel MOSFETs: A 3D 'Atomoc' Simulation Study

    NASA Technical Reports Server (NTRS)

    Asenov, Asen

    2000-01-01

    3D 'atomistic' simulations are used to study random dopant related threshold voltage fluctuations in 50 nm MOSFETs. Comparisons are made between conventionally doped transistors and transistors with thin epitaxial silicon layers on heavily doped silicon. Issues related to both the optimum threshold voltage control and the suppression of the threshold voltage dispersion are addressed.

  11. Maps of random walks on complex networks reveal community structure.

    PubMed

    Rosvall, Martin; Bergstrom, Carl T

    2008-01-29

    To comprehend the multipartite organization of large-scale biological and social systems, we introduce an information theoretic approach that reveals community structure in weighted and directed networks. We use the probability flow of random walks on a network as a proxy for information flows in the real system and decompose the network into modules by compressing a description of the probability flow. The result is a map that both simplifies and highlights the regularities in the structure and their relationships. We illustrate the method by making a map of scientific communication as captured in the citation patterns of >6,000 journals. We discover a multicentric organization with fields that vary dramatically in size and degree of integration into the network of science. Along the backbone of the network-including physics, chemistry, molecular biology, and medicine-information flows bidirectionally, but the map reveals a directional pattern of citation from the applied fields to the basic sciences.

  12. Transverse eV ion heating by random electric field fluctuations in the plasmasphere

    NASA Astrophysics Data System (ADS)

    Artemyev, A. V.; Mourenas, D.; Agapitov, O. V.; Blum, L.

    2017-02-01

    Charged particle acceleration in the Earth inner magnetosphere is believed to be mainly due to the local resonant wave-particle interaction or particle transport processes. However, the Van Allen Probes have recently provided interesting evidence of a relatively slow transverse heating of eV ions at distances about 2-3 Earth radii during quiet times. Waves that are able to resonantly interact with such very cold ions are generally rare in this region of space, called the plasmasphere. Thus, non-resonant wave-particle interactions are expected to play an important role in the observed ion heating. We demonstrate that stochastic heating by random transverse electric field fluctuations of whistler (and possibly electromagnetic ion cyclotron) waves could explain this weak and slow transverse heating of H+ and O+ ions in the inner magnetosphere. The essential element of the proposed model of ion heating is the presence of trains of random whistler (hiss) wave packets, with significant amplitude modulations produced by strong wave damping, rapid wave growth, or a superposition of wave packets of different frequencies, phases, and amplitudes. Such characteristics correspond to measured characteristics of hiss waves in this region. Using test particle simulations with typical wave and plasma parameters, we demonstrate that the corresponding stochastic transverse ion heating reaches 0.07-0.2 eV/h for protons and 0.007-0.015 eV/h for O+ ions. This global temperature increase of the Maxwellian ion population from an initial Ti˜0.3 eV could potentially explain the observations.

  13. Transverse eV Ion Heating by Random Electric Field Fluctuations in the Plasmasphere

    NASA Technical Reports Server (NTRS)

    Artemyev, A. V.; Mourenas, D.; Agapitov, O. V.; Blum, L.

    2017-01-01

    Charged particle acceleration in the Earth inner magnetosphere is believed to be mainly due to the local resonant wave-particle interaction or particle transport processes. However, the Van Allen Probes have recently provided interesting evidence of a relatively slow transverse heating of eV ions at distances about 2-3 Earth radii during quiet times. Waves that are able to resonantly interact with such very cold ions are generally rare in this region of space, called the plasmasphere. Thus, non-resonant wave-particle interactions are expected to play an important role in the observed ion heating. We demonstrate that stochastic heating by random transverse electric field fluctuations of whistler (and possibly electromagnetic ion cyclotron) waves could explain this weak and slow transverse heating of H+ and O+ ions in the inner magnetosphere. The essential element of the proposed model of ion heating is the presence of trains of random whistler (hiss) wave packets, with significant amplitude modulations produced by strong wave damping, rapid wave growth, or a superposition of wave packets of different frequencies, phases, and amplitudes. Such characteristics correspond to measured characteristics of hiss waves in this region. Using test particle simulations with typical wave and plasma parameters, we demonstrate that the corresponding stochastic transverse ion heating reaches 0.07-0.2 eV/h for protons and 0.007-0.015 eV/h for O+ ions. This global temperature increase of the Maxwellian ion population from an initial Ti approx. 0.3 eV could potentially explain the observations.

  14. Targeting Temporomandibular Disorder Pain Treatment to Hormonal Fluctuations: A Randomized Clinical Trial

    PubMed Central

    Turner, Judith A.; Mancl, Lloyd; Huggins, Kimberly Hanson; Sherman, Jeffrey J.; Lentz, Gretchen; LeResche, Linda

    2011-01-01

    Mounting evidence supports the importance of hormonal fluctuations in temporomandibular disorder (TMD) pain among women. Stabilizing influential hormones or having a plan and skills for coping with hormonally-related increases in TMD pain therefore may be beneficial for women with TMD pain. This randomized clinical trial evaluated the short- and long-term efficacy of three interventions for women with TMD pain: (1) dental hygienist-delivered pain self-management training (SMT; n = 59); (2) the same dental hygienist-delivered pain self-management training, but with a focus on menstrual cycle-related changes in pain and other symptoms (targeted SMT, or TSMT; n = 55); and (3) continuous oral contraceptive therapy (6 month trial), aimed at stabilizing hormones believed to be influential in TMD pain (COCT; n = 57). Study participants completed outcome (pain, activity interference, depression) and process (pain beliefs, catastrophizing, coping effectiveness) measures before randomization, and 6 and 12 months later. Intent-to-treat analyses supported the benefits of the SMT and TSMT interventions relative to COCT. Targeting the self-management treatment to menstrual cycle-related symptoms did not increase the treatment’s efficacy. The benefits of the self-management interventions relative to COCT for pain and activity interference were statistically significant at 12 months, but not at 6 months, whereas the benefits for the process measures generally were apparent at both timepoints. COCT was associated with multiple adverse events (none serious). The study provides further support for long-term benefits of a safe, low intensity (two in-person sessions and six brief telephone contacts), dental hygienist-delivered self-management treatment for TMD pain. PMID:21680092

  15. Correlation and fluctuation in a random average process on an infinite line with a driven tracer

    NASA Astrophysics Data System (ADS)

    Cividini, J.; Kundu, A.; Majumdar, Satya N.; Mukamel, D.

    2016-05-01

    We study the effect of a single biased tracer particle in a bath of other particles performing the random average process (RAP) on an infinite line. We focus on the long time behavior of the mean and the fluctuations of the positions of the particles and also the correlations among them. In the long time t limit these quantities have well defined scaling forms and grow with time as \\sqrt{t} . A differential equation for the scaling function associated with the correlation function is obtained and solved perturbatively around the solution for a symmetric tracer. Interestingly, when the tracer is totally asymmetric, further progress is enabled by the fact that the particles behind the tracer do not affect the motion of the particles in front of it, which leads in particular to an exact expression for the variance of the position of the tracer. Finally, the variance and correlations of the gaps between successive particles are also studied. Numerical simulations support our analytical results.

  16. Can log-periodic power law structures arise from random fluctuations?

    NASA Astrophysics Data System (ADS)

    Wosnitza, Jan Henrik; Leker, Jens

    2014-05-01

    Recent research has established log-periodic power law (LPPL) patterns prior to the detonation of the German stock index (DAX) bubble in 1998. The purpose of this article is to explore whether a Langevin equation extracted from real world data can generate synthetic time series with comparable LPPL structures. To this end, we first estimate the stochastic process underlying the DAX log-returns during the period from mid-1997 until end-2003. The employed data set contains about 3.93ṡ106 intraday DAX quotes at a sampling rate of 15 s. Our results indicate that the DAX log-returns can be described as a Markov process. As a consequence, a Langevin equation is derived. Based on this model equation, we run extensive simulations in order to generate 100 synthetic DAX trajectories each covering 3000 trading days. We find LPPL behavior in ten artificial time series. Moreover, we can establish a link between LPPL patterns and ensuing bubble bursts in seven synthetic 600-week windows. However, the LPPL components in most synthetic trajectories differ fundamentally from those LPPL structures that have previously been detected in real financial time series. Summarized, this paper demonstrates that LPPL structures are not necessarily the signature of imitative behavior among investors but can also stem from noise, even though the likelihood of this is extremely low. Thus, our findings confirm with high statistical confidence that the LPPL structures in the DAX development are rooted deeper than only in the random fluctuations of the German stock market.

  17. The statistics of peaks of Gaussian random fields. [cosmological density fluctuations

    NASA Technical Reports Server (NTRS)

    Bardeen, J. M.; Bond, J. R.; Kaiser, N.; Szalay, A. S.

    1986-01-01

    A set of new mathematical results on the theory of Gaussian random fields is presented, and the application of such calculations in cosmology to treat questions of structure formation from small-amplitude initial density fluctuations is addressed. The point process equation is discussed, giving the general formula for the average number density of peaks. The problem of the proper conditional probability constraints appropriate to maxima are examined using a one-dimensional illustration. The average density of maxima of a general three-dimensional Gaussian field is calculated as a function of heights of the maxima, and the average density of 'upcrossing' points on density contour surfaces is computed. The number density of peaks subject to the constraint that the large-scale density field be fixed is determined and used to discuss the segregation of high peaks from the underlying mass distribution. The machinery to calculate n-point peak-peak correlation functions is determined, as are the shapes of the profiles about maxima.

  18. Anomalous fluctuations of currents in Sinai-type random chains with strongly correlated disorder.

    PubMed

    Oshanin, Gleb; Rosso, Alberto; Schehr, Grégory

    2013-03-08

    We study properties of a random walk in a generalized Sinai model, in which a quenched random potential is a trajectory of a fractional Brownian motion with arbitrary Hurst parameter H, 0random force field displays strong spatial correlations. In this case, the disorder-average mean-square displacement grows in proportion to log(2/H)(n), n being time. We prove that moments of arbitrary order k of the steady-state current J(L) through a finite segment of length L of such a chain decay as L(-(1-H)), independently of k, which suggests that despite a logarithmic confinement the average current is much higher than its Fickian counterpart in homogeneous systems. Our results reveal a paradoxical behavior such that, for fixed n and L, the mean-square displacement decreases when one varies H from 0 to 1, while the average current increases. This counterintuitive behavior is explained via an analysis of representative realizations of disorder.

  19. Mean and Fluctuating Force Distribution in a Random Array of Spheres

    NASA Astrophysics Data System (ADS)

    Akiki, Georges; Jackson, Thomas; Balachandar, Sivaramakrishnan

    2015-11-01

    This study presents a numerical study of the force distribution within a cluster of mono-disperse spherical particles. A direct forcing immersed boundary method is used to calculate the forces on individual particles for a volume fraction range of [0.1, 0.4] and a Reynolds number range of [10, 625]. The overall drag is compared to several drag laws found in the literature. As for the fluctuation of the hydrodynamic streamwise force among individual particles, it is shown to have a normal distribution with a standard deviation that varies with the volume fraction only. The standard deviation remains approximately 25% of the mean streamwise force on a single sphere. The force distribution shows a good correlation between the location of two to three nearest upstream and downstream neighbors and the magnitude of the forces. A detailed analysis of the pressure and shear forces contributions calculated on a ghost sphere in the vicinity of a single particle in a uniform flow reveals a mapping of those contributions. The combination of the mapping and number of nearest neighbors leads to a first order correction of the force distribution within a cluster which can be used in Lagrangian-Eulerian techniques. We also explore the possibility of a binary force model that systematically accounts for the effect of the nearest neighbors. This work was supported by the National Science Foundation (NSF OISE-0968313) under Partnership for International Research and Education (PIRE) in Multiphase Flows at the University of Florida.

  20. Random Dopant Induced Threshold Voltage Lowering and Fluctuations in Sub 50 nm MOSFETs: a Statistical 3D 'Atomistic' Simulation Study

    NASA Technical Reports Server (NTRS)

    Asenov, Asen

    1999-01-01

    A 3D 'atomistic' simulation study of random dopant induced threshold voltage fluctuations and lowering in sub 50 nm MOSFETs is presented. The attention is focused mainly on devices with 30 nm effective channel length which represent the expected level of scaling at the end of the Silicon Roadmap. An efficient algorithm, based on a single 3D ap solution of the Poisson equation and a simplified current continuity equation, is used in the simulations. Large samples of microscopically different devices (typically 200) arc used in order to obtain statistically reliable results. The influence of different aspects of the conventional MOSFET design on the threshold voltage fluctuations and lowering are investigated. Results for fluctuation resistant device architectures based on low-doped epitaxial channel MOSFETs are also presented.

  1. Homeostatic Plasticity Achieved by Incorporation of Random Fluctuations and Soft-Bounded Hebbian Plasticity in Excitatory Synapses

    PubMed Central

    Matsubara, Takashi; Uehara, Kuniaki

    2016-01-01

    Homeostatic plasticity is considered to maintain activity in neuronal circuits within a functional range. In the absence of homeostatic plasticity neuronal activity is prone to be destabilized because Hebbian plasticity mechanisms induce positive feedback change. Several studies on homeostatic plasticity assumed the existence of a process for monitoring neuronal activity on a time scale of hours and adjusting synaptic efficacy by scaling up and down. However, the underlying mechanism still remains unclear. Excitatory synaptic efficacy is associated with the size of the dendritic spine, and dendritic spine size fluctuates even after neuronal activity is silenced. These fluctuations could be a non-Hebbian form of synaptic plasticity that serves such a homeostatic function. This study proposed and analyzed a synaptic plasticity model incorporating random fluctuations and soft-bounded Hebbian plasticity at excitatory synapses, and found that the proposed model can prevent excessive changes in neuronal activity by scaling synaptic efficacy up and down. Soft-bounded Hebbian plasticity suppresses strong synapses, thereby scaling synapses down and preventing runaway excitation. Random fluctuations diffuse synaptic efficacy, thereby scaling synapses up and preventing neurons from falling silent. The proposed model acts as a form of homeostatic plasticity, regardless of neuronal activity monitoring. PMID:27313513

  2. Boundary Condition in Liquid Thin Films Revealed through the Thermal Fluctuations of Their Free Surfaces.

    PubMed

    Pottier, B; Frétigny, C; Talini, L

    2015-06-05

    We investigate the properties of nanometric liquid films with a new noninvasive technique. We measure the spontaneous thermal fluctuations of the free surfaces of liquids to probe their hydrodynamic boundary condition at a solid wall. The surface fluctuations of a silicon oil film could be described with a no-slip boundary condition for film thicknesses down to 20 nm. Oppositely, a 4 nm negative slip length had to be introduced to describe the behavior of n-hexadecane, consistently with previous surface force apparatus data on the same system. Our results demonstrate that at vanishing flow a nanometric solidlike layer close to the wall may exist according to the nature of the liquid.

  3. Competing magnetic fluctuations in iron pnictide superconductors: Role of ferromagnetic spin correlations revealed by NMR

    DOE PAGES

    Wiecki, P.; Roy, B.; Johnston, D. C.; ...

    2015-09-22

    In the iron pnictide superconductors, theoretical calculations have consistently shown enhancements of the static magnetic susceptibility at both the stripe-type antiferromagnetic and in-plane ferromagnetic (FM) wave vectors. However, the possible existence of FM fluctuations has not yet been examined from a microscopic point of view. Here, using 75As NMR data, we provide clear evidence for the existence of FM spin correlations in both the hole- and electron-doped BaFe2As2 families of iron-pnictide superconductors. Furthermore, these FM fluctuations appear to compete with superconductivity and are thus a crucial ingredient to understanding the variability of Tc and the shape of the superconducting domemore » in these and other iron-pnictide families.« less

  4. Competing magnetic fluctuations in iron pnictide superconductors: Role of ferromagnetic spin correlations revealed by NMR

    SciTech Connect

    Wiecki, P.; Roy, B.; Johnston, D. C.; Bud’ko, S. L.; Canfield, P. C.; Furukawa, Y.

    2015-09-22

    In the iron pnictide superconductors, theoretical calculations have consistently shown enhancements of the static magnetic susceptibility at both the stripe-type antiferromagnetic and in-plane ferromagnetic (FM) wave vectors. However, the possible existence of FM fluctuations has not yet been examined from a microscopic point of view. Here, using 75As NMR data, we provide clear evidence for the existence of FM spin correlations in both the hole- and electron-doped BaFe2As2 families of iron-pnictide superconductors. Furthermore, these FM fluctuations appear to compete with superconductivity and are thus a crucial ingredient to understanding the variability of Tc and the shape of the superconducting dome in these and other iron-pnictide families.

  5. Fluctuation Analysis of Centrosomes Reveals a Cortical Function of Kinesin-1

    PubMed Central

    Winkler, Franziska; Gummalla, Maheshwar; Künneke, Lutz; Lv, Zhiyi; Zippelius, Annette; Aspelmeier, Timo; Grosshans, Jörg

    2015-01-01

    The actin and microtubule networks form the dynamic cytoskeleton. Network dynamics is driven by molecular motors applying force onto the networks and the interactions between the networks. Here we assay the dynamics of centrosomes in the scale of seconds as a proxy for the movement of microtubule asters. With this assay we want to detect the role of specific motors and of network interaction. During interphase of syncytial embryos of Drosophila, cortical actin and the microtubule network depend on each other. Centrosomes induce cortical actin to form caps, whereas F-actin anchors microtubules to the cortex. In addition, lateral interactions between microtubule asters are assumed to be important for regular spatial organization of the syncytial embryo. The functional interaction between the microtubule asters and cortical actin has been largely analyzed in a static manner, so far. We recorded the movement of centrosomes at 1 Hz and analyzed their fluctuations for two processes—pair separation and individual movement. We found that F-actin is required for directional movements during initial centrosome pair separation, because separation proceeds in a diffusive manner in latrunculin-injected embryos. For assaying individual movement, we established a fluctuation parameter as the deviation from temporally and spatially slowly varying drift movements. By analysis of mutant and drug-injected embryos, we found that the fluctuations were suppressed by both cortical actin and microtubules. Surprisingly, the microtubule motor Kinesin-1 also suppressed fluctuations to a similar degree as F-actin. Kinesin-1 may mediate linkage of the microtubule (+)-ends to the actin cortex. Consistent with this model is our finding that Kinesin-1-GFP accumulates at the cortical actin caps. PMID:26331244

  6. A novel twelve class fluctuation test reveals higher than expected mutation rates for influenza A viruses

    PubMed Central

    Pauly, Matthew D; Procario, Megan C; Lauring, Adam S

    2017-01-01

    Influenza virus’ low replicative fidelity contributes to its capacity for rapid evolution. Clonal sequencing and fluctuation tests have suggested that the influenza virus mutation rate is 2.7 × 10–6 - 3.0 × 10–5 substitutions per nucleotide per strand copied (s/n/r). However, sequencing assays are biased toward mutations with minimal fitness impacts and fluctuation tests typically investigate only a subset of all possible single nucleotide mutations. We developed a fluctuation test based on reversion to fluorescence in a set of virally encoded mutant green fluorescent proteins, which allowed us to measure the rates of selectively neutral mutations representative of the twelve different mutation types. We measured an overall mutation rate of 1.8 × 10–4 s/n/r for PR8 (H1N1) and 2.5 × 10–4 s/n/r for Hong Kong 2014 (H3N2) and a transitional bias of 2.7–3.6. Our data suggest that each replicated genome will have an average of 2–3 mutations and highlight the importance of mutational load in influenza virus evolution. DOI: http://dx.doi.org/10.7554/eLife.26437.001 PMID:28598328

  7. Non-thermal fluctuations in living cells reveal nonlinear mechanical properties of the cytoskeleton

    NASA Astrophysics Data System (ADS)

    Ou-Yang, H. Daniel; Wei, Ming-Tzo; Vavylonis, Dimitris; Jedlicka, Sabrina

    2015-03-01

    Living cells are a non-equilibrium mechanical system, largely because intracellular molecular motors consume chemical energy to generate forces that reorganize and maintain cytoskeletal functions. Persistently under tension, the network of cytoskeletal proteins exhibits a nonlinear mechanical behavior where the network stiffness increases with intracellular tension. We examined the nonlinear mechanical properties of living cells by characterizing the differential stiffness of the cytoskeletal network for HeLa cells under different intracellular tensions. Combining active and passive microrheology methods, we measured non-thermal fluctuating forces and found them to be much larger than the thermal fluctuating force. From the variations of differential stiffness caused by the fluctuating non-thermal force for cells under different tension, we obtained a master curve describing the differential stiffness as a function of the intracellular tension. Varying the intracellular tension by treating cells with drugs that alter motor protein activities we found the differential stiffness follows the same master curve that describes intracellular stiffness as a function of intracellular tension. This observation suggests that cells can regulate their mechanical properties by adjusting intracellular tension. NSF DMR 0923299.

  8. A stochastic mechanism for signal propagation in the brain: Force of rapid random fluctuations in membrane potentials of individual neurons.

    PubMed

    Hong, Dawei; Man, Shushuang; Martin, Joseph V

    2016-01-21

    There are two functionally important factors in signal propagation in a brain structural network: the very first synaptic delay-a time delay about 1ms-from the moment when signals originate to the moment when observation on the signal propagation can begin; and rapid random fluctuations in membrane potentials of every individual neuron in the network at a timescale of microseconds. We provide a stochastic analysis of signal propagation in a general setting. The analysis shows that the two factors together result in a stochastic mechanism for the signal propagation as described below. A brain structural network is not a rigid circuit rather a very flexible framework that guides signals to propagate but does not guarantee success of the signal propagation. In such a framework, with the very first synaptic delay, rapid random fluctuations in every individual neuron in the network cause an "alter-and-concentrate effect" that almost surely forces signals to successfully propagate. By the stochastic mechanism we provide analytic evidence for the existence of a force behind signal propagation in a brain structural network caused by rapid random fluctuations in every individual neuron in the network at a timescale of microseconds with a time delay of 1ms. Published by Elsevier Ltd.

  9. Endpoint Force Fluctuations Reveal Flexible Rather Than Synergistic Patterns of Muscle Cooperation

    PubMed Central

    Kutch, Jason J.; Kuo, Arthur D.; Bloch, Anthony M.; Rymer, William Z.

    2008-01-01

    We developed a new approach to investigate how the nervous system activates multiple redundant muscles by studying the endpoint force fluctuations during isometric force generation at a multi-degree-of-freedom joint. We hypothesized that, due to signal-dependent muscle force noise, endpoint force fluctuations would depend on the target direction of index finger force and that this dependence could be used to distinguish flexible from synergistic activation of the musculature. We made high-gain measurements of isometric forces generated to different target magnitudes and directions, in the plane of index finger metacarpophalangeal joint abduction–adduction/flexion–extension. Force fluctuations from each target were used to calculate a covariance ellipse, the shape of which varied as a function of target direction. Directions with narrow ellipses were approximately aligned with the estimated mechanical actions of key muscles. For example, targets directed along the mechanical action of the first dorsal interosseous (FDI) yielded narrow ellipses, with 88% of the variance directed along those target directions. It follows the FDI is likely a prime mover in this target direction and that, at most, 12% of the force variance could be explained by synergistic coupling with other muscles. In contrast, other target directions exhibited broader covariance ellipses with as little as 30% of force variance directed along those target directions. This is the result of cooperation among multiple muscles, based on independent electromyographic recordings. However, the pattern of cooperation across target directions indicates that muscles are recruited flexibly in accordance with their mechanical action, rather than in fixed groupings. PMID:18799603

  10. 3D structural fluctuation of IgG1 antibody revealed by individual particle electron tomography

    DOE PAGES

    Zhang, Xing; Zhang, Lei; Tong, Huimin; ...

    2015-05-05

    Commonly used methods for determining protein structure, including X-ray crystallography and single-particle reconstruction, often provide a single and unique three-dimensional (3D) structure. However, in these methods, the protein dynamics and flexibility/fluctuation remain mostly unknown. Here, we utilized advances in electron tomography (ET) to study the antibody flexibility and fluctuation through structural determination of individual antibody particles rather than averaging multiple antibody particles together. Through individual-particle electron tomography (IPET) 3D reconstruction from negatively-stained ET images, we obtained 120 ab-initio 3D density maps at an intermediate resolution (~1–3 nm) from 120 individual IgG1 antibody particles. Using these maps as a constraint, wemore » derived 120 conformations of the antibody via structural flexible docking of the crystal structure to these maps by targeted molecular dynamics simulations. Statistical analysis of the various conformations disclosed the antibody 3D conformational flexibility through the distribution of its domain distances and orientations. This blueprint approach, if extended to other flexible proteins, may serve as a useful methodology towards understanding protein dynamics and functions.« less

  11. Cross-species gene-family fluctuations reveal the dynamics of horizontal transfers.

    PubMed

    Grilli, Jacopo; Romano, Mariacristina; Bassetti, Federico; Cosentino Lagomarsino, Marco

    2014-06-01

    Prokaryotes vary their protein repertoire mainly through horizontal transfer and gene loss. To elucidate the links between these processes and the cross-species gene-family statistics, we perform a large-scale data analysis of the cross-species variability of gene-family abundance (the number of members of the family found on a given genome). We find that abundance fluctuations are related to the rate of horizontal transfers. This is rationalized by a minimal theoretical model, which predicts this link. The families that are not captured by the model show abundance profiles that are markedly peaked around a mean value, possibly because of specific abundance selection. Based on these results, we define an abundance variability index that captures a family's evolutionary behavior (and thus some of its relevant functional properties) purely based on its cross-species abundance fluctuations. Analysis and model, combined, show a quantitative link between cross-species family abundance statistics and horizontal transfer dynamics, which can be used to analyze genome 'flux'. Groups of families with different values of the abundance variability index correspond to genome sub-parts having different plasticity in terms of the level of horizontal exchange allowed by natural selection. © The Author(s) 2014. Published by Oxford University Press on behalf of Nucleic Acids Research.

  12. Cross-species gene-family fluctuations reveal the dynamics of horizontal transfers

    PubMed Central

    Grilli, Jacopo; Romano, Mariacristina; Bassetti, Federico; Cosentino Lagomarsino, Marco

    2014-01-01

    Prokaryotes vary their protein repertoire mainly through horizontal transfer and gene loss. To elucidate the links between these processes and the cross-species gene-family statistics, we perform a large-scale data analysis of the cross-species variability of gene-family abundance (the number of members of the family found on a given genome). We find that abundance fluctuations are related to the rate of horizontal transfers. This is rationalized by a minimal theoretical model, which predicts this link. The families that are not captured by the model show abundance profiles that are markedly peaked around a mean value, possibly because of specific abundance selection. Based on these results, we define an abundance variability index that captures a family's evolutionary behavior (and thus some of its relevant functional properties) purely based on its cross-species abundance fluctuations. Analysis and model, combined, show a quantitative link between cross-species family abundance statistics and horizontal transfer dynamics, which can be used to analyze genome ‘flux’. Groups of families with different values of the abundance variability index correspond to genome sub-parts having different plasticity in terms of the level of horizontal exchange allowed by natural selection. PMID:24829449

  13. 3D Structural Fluctuation of IgG1 Antibody Revealed by Individual Particle Electron Tomography

    PubMed Central

    Zhang, Xing; Zhang, Lei; Tong, Huimin; Peng, Bo; Rames, Matthew J.; Zhang, Shengli; Ren, Gang

    2015-01-01

    Commonly used methods for determining protein structure, including X-ray crystallography and single-particle reconstruction, often provide a single and unique three-dimensional (3D) structure. However, in these methods, the protein dynamics and flexibility/fluctuation remain mostly unknown. Here, we utilized advances in electron tomography (ET) to study the antibody flexibility and fluctuation through structural determination of individual antibody particles rather than averaging multiple antibody particles together. Through individual-particle electron tomography (IPET) 3D reconstruction from negatively-stained ET images, we obtained 120 ab-initio 3D density maps at an intermediate resolution (~1–3 nm) from 120 individual IgG1 antibody particles. Using these maps as a constraint, we derived 120 conformations of the antibody via structural flexible docking of the crystal structure to these maps by targeted molecular dynamics simulations. Statistical analysis of the various conformations disclosed the antibody 3D conformational flexibility through the distribution of its domain distances and orientations. This blueprint approach, if extended to other flexible proteins, may serve as a useful methodology towards understanding protein dynamics and functions. PMID:25940394

  14. 3D structural fluctuation of IgG1 antibody revealed by individual particle electron tomography

    SciTech Connect

    Zhang, Xing; Zhang, Lei; Tong, Huimin; Peng, Bo; Rames, Matthew J.; Zhang, Shengli; Ren, Gang

    2015-05-05

    Commonly used methods for determining protein structure, including X-ray crystallography and single-particle reconstruction, often provide a single and unique three-dimensional (3D) structure. However, in these methods, the protein dynamics and flexibility/fluctuation remain mostly unknown. Here, we utilized advances in electron tomography (ET) to study the antibody flexibility and fluctuation through structural determination of individual antibody particles rather than averaging multiple antibody particles together. Through individual-particle electron tomography (IPET) 3D reconstruction from negatively-stained ET images, we obtained 120 ab-initio 3D density maps at an intermediate resolution (~1–3 nm) from 120 individual IgG1 antibody particles. Using these maps as a constraint, we derived 120 conformations of the antibody via structural flexible docking of the crystal structure to these maps by targeted molecular dynamics simulations. Statistical analysis of the various conformations disclosed the antibody 3D conformational flexibility through the distribution of its domain distances and orientations. This blueprint approach, if extended to other flexible proteins, may serve as a useful methodology towards understanding protein dynamics and functions.

  15. Intrinsic spin fluctuations reveal the dynamical response function of holes coupled to nuclear spin baths in (In,Ga)As quantum dots.

    PubMed

    Li, Yan; Sinitsyn, N; Smith, D L; Reuter, D; Wieck, A D; Yakovlev, D R; Bayer, M; Crooker, S A

    2012-05-04

    The problem of how single central spins interact with a nuclear spin bath is essential for understanding decoherence and relaxation in many quantum systems, yet is highly nontrivial owing to the many-body couplings involved. Different models yield widely varying time scales and dynamical responses (exponential, power-law, gaussian, etc.). Here we detect the small random fluctuations of central spins in thermal equilibrium [holes in singly charged (In,Ga)As quantum dots] to reveal the time scales and functional form of bath-induced spin relaxation. This spin noise indicates long (400 ns) spin correlation times at a zero magnetic field that increase to ∼5  μs as dominant hole-nuclear relaxation channels are suppressed with small (100 G) applied fields. Concomitantly, the noise line shape evolves from Lorentzian to power law, indicating a crossover from exponential to slow [∼1/log(t)] dynamics.

  16. Distinct role of hydration water in protein misfolding and aggregation revealed by fluctuating thermodynamics analysis.

    PubMed

    Chong, Song-Ho; Ham, Sihyun

    2015-04-21

    Protein aggregation in aqueous cellular environments is linked to diverse human diseases. Protein aggregation proceeds through a multistep process initiated by conformational transitions, called protein misfolding, of monomer species toward aggregation-prone structures. Various forms of aggregate species are generated through the association of misfolded monomers including soluble oligomers and amyloid fibrils. Elucidating the molecular mechanisms and driving forces involved in the misfolding and subsequent association has been a central issue for understanding and preventing protein aggregation diseases such as Alzheimer's, Parkinson's, and type II diabetes. In this Account, we provide a thermodynamic perspective of the misfolding and aggregation of the amyloid-beta (Aβ) protein implicated in Alzheimer's disease through the application of fluctuating thermodynamics. This approach "dissects" the conventional thermodynamic characterization of the end states into the one of the fluctuating processes connecting them, and enables one to analyze variations in the thermodynamic functions that occur during the course of protein conformational changes. The central quantity in this approach is the solvent-averaged effective energy, f = Eu + Gsolv, comprising the protein potential energy (Eu) and the solvation free energy (Gsolv), whose time variation reflects the protein dynamics on the free energy landscape. Protein configurational entropy is quantified by the magnitude of fluctuations in f. We find that misfolding of the Aβ monomer when released from a membrane environment to an aqueous phase is driven by favorable changes in protein potential energy and configurational entropy, but it is also accompanied by an unfavorable increase in solvation free energy. The subsequent dimerization of the misfolded Aβ monomers occurs in two steps. The first step, where two widely separated monomers come into contact distance, is driven by water-mediated attraction, that is, by a

  17. Correlated Fluctuations and Intraband Dynamics of J-Aggregates Revealed by Combination of 2DES Schemes

    PubMed Central

    2016-01-01

    The intraband exciton dynamics of molecular aggregates is a crucial initial step to determine the possibly coherent nature of energy transfer and its implications for the ensuing interband relaxation pathways in strongly coupled excitonic systems. In this work, we fully characterize the intraband dynamics in linear J-aggregates of porphyrins, good model systems for multichromophoric assemblies in biological antenna complexes. Using different 2D electronic spectroscopy schemes together with Raman spectroscopy and theoretical modeling, we provide a full characterization of the inner structure of the main one-exciton band of the porphyrin aggregates. We find that the redistribution of population within the band occurs with a characteristic time of 280 fs and dominates the modulation of an electronic coherence. While we do not find that the coupling to vibrations significantly affects the dynamics of excitonic coherence, our results suggest that exciton fluctuations are nevertheless highly correlated. PMID:27973862

  18. Long-tailed distribution of synaptic strength reveals origin and functional roles of ongoing fluctuation in cortical circuit

    NASA Astrophysics Data System (ADS)

    Teramae, Jun-nosuke

    2016-06-01

    Neurons in the cortical circuit continuous to generate irregular spike firing with extremely low firing rate (about 1-2 Hz) even when animals neither receive any external stimuli nor they do not show any significant motor movement. The ongoing activity is often called neuronal noise because measured spike trains are often highly irregular and also spike timings are highly asynchronous among neurons. Many experiments imply that neural networks themselves must generate the noisy activity as an intrinsic property of cortical circuit. However, how a network of neurons sustains the irregular spike firings with low firing rate remains unclear. Recently, by focusing on long-tailed distribution of amplitude of synaptic connections or EPSP (Excitatory Post-Synaptic Potential), we successfully revealed that due to coexistence of a few extremely strong synaptic connections and majority of weak synapses, nonlinear dynamics of population of spiking neurons can have a nontrivial stable state that corresponding to the intrinsic ongoing fluctuation of the cortical circuit. We also found that due to the fluctuation fidelity of spike transmission between neurons are optimized. Here, we report our recent findings of the ongoing fluctuation from viewpoints of mathematical and computational side.

  19. Double, Rydberg and Charge Transfer Excitations from Pairing Matrix Fluctuation and Particle-Particle Random Phase Approximation

    NASA Astrophysics Data System (ADS)

    Yang, Yang; van Aggelen, Helen; Yang, Weitao

    2014-03-01

    Double, Rydberg and charge transfer (CT) excitations have been great challenges for time-dependent density functional theory (TDDFT). Starting from an (N +/- 2) -electron single-determinant reference, we investigate excitations for the N-electron system through the pairing matrix fluctuation, which contains information on two-electron addition/removal processes. We adopt the particle-particle random phase approximation (pp-RPA) and the particle-particle Tamm-Dancoff approximation (pp-TDA) to approximate the pairing matrix fluctuation and then determine excitation energies by the differences of two-electron addition/removal energies. This approach captures all types of interesting excitations: single and double excitations are described accurately, Rydberg excitations are in good agreement with experimental data and CT excitations display correct 1/R dependence. Furthermore, the pp-RPA and the pp-TDA have a computational cost similar to TDDFT and consequently are promising for practical calculations.

  20. Double, Rydberg and charge transfer excitations from pairing matrix fluctuation and particle-particle random phase approximation

    NASA Astrophysics Data System (ADS)

    Yang, Yang; van Aggelen, Helen; Yang, Weitao

    2013-12-01

    Double, Rydberg, and charge transfer (CT) excitations have been great challenges for time-dependent density functional theory (TDDFT). Starting from an (N ± 2)-electron single-determinant reference, we investigate excitations for the N-electron system through the pairing matrix fluctuation, which contains information on two-electron addition/removal processes. We adopt the particle-particle random phase approximation (pp-RPA) and the particle-particle Tamm-Dancoff approximation (pp-TDA) to approximate the pairing matrix fluctuation and then determine excitation energies by the differences of two-electron addition/removal energies. This approach captures all types of interesting excitations: single and double excitations are described accurately, Rydberg excitations are in good agreement with experimental data and CT excitations display correct 1/R dependence. Furthermore, the pp-RPA and the pp-TDA have a computational cost similar to TDDFT and consequently are promising for practical calculations.

  1. Double, Rydberg and charge transfer excitations from pairing matrix fluctuation and particle-particle random phase approximation.

    PubMed

    Yang, Yang; van Aggelen, Helen; Yang, Weitao

    2013-12-14

    Double, Rydberg, and charge transfer (CT) excitations have been great challenges for time-dependent density functional theory (TDDFT). Starting from an (N ± 2)-electron single-determinant reference, we investigate excitations for the N-electron system through the pairing matrix fluctuation, which contains information on two-electron addition/removal processes. We adopt the particle-particle random phase approximation (pp-RPA) and the particle-particle Tamm-Dancoff approximation (pp-TDA) to approximate the pairing matrix fluctuation and then determine excitation energies by the differences of two-electron addition/removal energies. This approach captures all types of interesting excitations: single and double excitations are described accurately, Rydberg excitations are in good agreement with experimental data and CT excitations display correct 1/R dependence. Furthermore, the pp-RPA and the pp-TDA have a computational cost similar to TDDFT and consequently are promising for practical calculations.

  2. Double, Rydberg and charge transfer excitations from pairing matrix fluctuation and particle-particle random phase approximation

    SciTech Connect

    Yang, Yang; Aggelen, Helen van; Yang, Weitao

    2013-12-14

    Double, Rydberg, and charge transfer (CT) excitations have been great challenges for time-dependent density functional theory (TDDFT). Starting from an (N ± 2)-electron single-determinant reference, we investigate excitations for the N-electron system through the pairing matrix fluctuation, which contains information on two-electron addition/removal processes. We adopt the particle-particle random phase approximation (pp-RPA) and the particle-particle Tamm-Dancoff approximation (pp-TDA) to approximate the pairing matrix fluctuation and then determine excitation energies by the differences of two-electron addition/removal energies. This approach captures all types of interesting excitations: single and double excitations are described accurately, Rydberg excitations are in good agreement with experimental data and CT excitations display correct 1/R dependence. Furthermore, the pp-RPA and the pp-TDA have a computational cost similar to TDDFT and consequently are promising for practical calculations.

  3. Theoretical analysis of influence of random alloy fluctuations on the optoelectronic properties of site-controlled (111)-oriented InGaAs/GaAs quantum dots

    NASA Astrophysics Data System (ADS)

    Benchamekh, R.; Schulz, S.; O'Reilly, E. P.

    2016-09-01

    We use an s p3d5s* tight-binding model to investigate the electronic and optical properties of realistic site-controlled (111)-oriented InGaAs/GaAs quantum dots. Special attention is paid to the impact of random alloy fluctuations on several factors that determine the fine-structure splitting in these systems. Using a pure InAs/GaAs quantum dot as a reference system, we show that the combination of spin-orbit coupling and biaxial strain effects can lead to sizable spin-splitting effects in these systems. Then, a realistic alloyed InGaAs/GaAs quantum dot with 25% InAs content is studied. Our analysis reveals that the impact of random alloy fluctuations on the electronic and optical properties of (111)-oriented InGaAs/GaAs quantum dots reduces strongly as the lateral size of the dot increases and approaches realistic sizes. For instance the optical matrix element shows an almost vanishing anisotropy in the (111)-growth plane. Furthermore, conduction and valence band mixing effects in the system under consideration are strongly reduced compared to standard (100)-oriented InGaAs/GaAs systems. All these factors indicate a reduced fine-structure splitting in site-controlled (111)-oriented InGaAs/GaAs quantum dots. Thus, we conclude that quantum dots with realistic (50-80 nm) base length represent promising candidates for polarization-entangled-photon generation, consistent with recent experimental data.

  4. A study of the randomly fluctuating microbial counts in foods and water using the Expanded Fermi Solution as a model.

    PubMed

    Peleg, Micha; Normand, Mark D; Corradini, Maria G

    2012-01-01

    Randomly fluctuating industrial microbial count records, with and without zero counts, were simulated with a version of the Expanded Fermi Solution, originally developed for risk assessment. The basic assumption has been that each individual count is determined by the multiplicative effect of several random factors, which augment or suppress the microbial population size, and in the case of sporadic pathogens, determine the probability of their initial presence too. Records were generated by a series of Monte Carlo simulations in which the factors were specified by ranges and their values chosen randomly within them. The process has been automated and posted as a freely downloadable Wolfram Demonstration on the Internet. The program allows the user to enter and alter the series length, parameters' ranges, and count level deemed dangerous with sliders on the screen. The display includes the chosen factors' ranges, the corresponding generated count record and its histogram, and an estimate of the risk of surpassing the dangerous threshold. Where the record contains no zero counts, the histogram is accompanied by the lognormal distribution, which naturally emerges from the fluctuations' mathematical model. Once the factors are identified and their ranges specified, the method could be used as a tool to analyze, compare, and quantify microbial risks in foods and water.

  5. Surfing along Filopodia: A Particle Transport Revealed by Molecular-Scale Fluctuation Analyses.

    PubMed

    Kohler, Felix; Rohrbach, Alexander

    2015-05-05

    Filopodia perform cellular functions such as environmental sensing or cell motility, but they also grab for particles and withdraw them leading to an increased efficiency of phagocytic uptake. Remarkably, withdrawal of micron-sized particles is also possible without noticeable movements of the filopodia. Here, we demonstrate that polystyrene beads connected by optical tweezers to the ends of adherent filopodia of J774 macrophages, are transported discontinuously toward the cell body. After a typical resting time of 1-2 min, the cargo is moved with alternating velocities, force constants, and friction constants along the surface of the filopodia. This surfing-like behavior along the filopodium is recorded by feedback-controlled interferometric three-dimensional tracking of the bead motions at 10-100 kHz. We measured transport velocities of up to 120 nm/s and transport forces of ∼ 70 pN. Small changes in position, fluctuation width, and temporal correlation, which are invisible in conventional microscopy, indicate molecular reorganization of transport-relevant proteins in different phases of the entire transport process. A detailed analysis implicates a controlled particle transport with fingerprints of a nanoscale unbinding/binding behavior. The manipulation and analysis methods presented in our study may also be helpful in other fields of cellular biophysics.

  6. Surfing along Filopodia: A Particle Transport Revealed by Molecular-Scale Fluctuation Analyses

    PubMed Central

    Kohler, Felix; Rohrbach, Alexander

    2015-01-01

    Filopodia perform cellular functions such as environmental sensing or cell motility, but they also grab for particles and withdraw them leading to an increased efficiency of phagocytic uptake. Remarkably, withdrawal of micron-sized particles is also possible without noticeable movements of the filopodia. Here, we demonstrate that polystyrene beads connected by optical tweezers to the ends of adherent filopodia of J774 macrophages, are transported discontinuously toward the cell body. After a typical resting time of 1–2 min, the cargo is moved with alternating velocities, force constants, and friction constants along the surface of the filopodia. This surfing-like behavior along the filopodium is recorded by feedback-controlled interferometric three-dimensional tracking of the bead motions at 10–100 kHz. We measured transport velocities of up to 120 nm/s and transport forces of ∼70 pN. Small changes in position, fluctuation width, and temporal correlation, which are invisible in conventional microscopy, indicate molecular reorganization of transport-relevant proteins in different phases of the entire transport process. A detailed analysis implicates a controlled particle transport with fingerprints of a nanoscale unbinding/binding behavior. The manipulation and analysis methods presented in our study may also be helpful in other fields of cellular biophysics. PMID:25954870

  7. Dynamics of density fluctuations of a glass-forming epoxy resin revealed by Brillouin light scattering

    NASA Astrophysics Data System (ADS)

    Fioretto, D.; Comez, L.; Socino, G.; Verdini, L.; Corezzi, S.; Rolla, P. A.

    1999-02-01

    Brillouin light scattering is used for studying the spectrum of density fluctuations of the glass-forming epoxy resin diglycidyl ether of bisphenol-A. Spectra at different temperatures ranging from the glassy to the liquid phase are obtained from a direct subtraction of depolarized from polarized spectra. In addition to the structural relaxation, evidence is given of a fast secondary relaxation process, which affects Brillouin spectra also at temperatures lower than that of the glass transition Tg. For the elaboration of isotropic spectra, we exploit the possibility of using the same relaxation function gained from dielectric spectra taken from the same sample. The temperature behavior of the relaxation strength shows the existence of an onset for the structural relaxation, located at a temperature about 93 K higher than Tg, consistent with the results of previous dielectric spectroscopy and depolarized light scattering investigations. The role of secondary relaxations of intramolecular nature in the mode-coupling analysis of real glass formers is also discussed.

  8. Comment on "Nonlinear fluctuations and dissipation in matter revealed by quantum light"

    NASA Astrophysics Data System (ADS)

    Kira, M.; Koch, S. W.; Cundiff, S. T.

    2015-11-01

    In a recent paper [Phys. Rev. A 91, 053844 (2015), 10.1103/PhysRevA.91.053844], Mukamel and Dorfman compare spectroscopies performed with classical vs quantum light and conclude that nonlinear quantum-spectroscopy signals cannot be obtained from averaging their classical-spectroscopy counterparts over the Glauber-Sudarshan quasiprobability distribution of the quantum field. In this Comment, we show that this interpretation is correct only when classical spectroscopy is perceived as a theoretical description which neglects quantum fluctuations of light altogether. While such an assumption can be a good approximation and useful for comparing theoretical results, it is never realized exactly in laser-spectroscopy experiments that typically use coherent states. Even though coherent states represent the most classical form of light, their quantumness must be considered to fully understand laser-spectroscopy experiments and their connection to quantum spectroscopy, performed with true quantum sources, such as Schrödinger's cat states. Thus, instead of using a classical approximation, the connection between coherent states and true quantum states of light must be considered. We rigorously show that quantum spectroscopy can always be projected from the experimentally realized coherent-state spectroscopy regardless how nonlinear the system response is.

  9. Low Frequency Fluctuations Reveal Integrated and Segregated Processing among the Cerebral Hemispheres

    PubMed Central

    Gee, Dylan G.; Biswal, Bharat B.; Kelly, Clare; Stark, David E.; Margulies, Daniel S.; Shehzad, Zarrar; Uddin, Lucina Q.; Klein, Donald F.; Banich, Marie T.; Castellanos, F. Xavier; Milham, Michael P.

    2011-01-01

    Resting-state functional magnetic resonance imaging (fMRI) has provided a novel approach for examining interhemispheric interaction, demonstrating a high degree of functional connectivity between homotopic regions in opposite hemispheres. However, heterotopic resting state functional connectivity (RSFC) remains relatively uncharacterized. In the present study, we examine non-homotopic regions, characterizing heterotopic RSFC and comparing it to intrahemispheric RSFC, to examine the impact of hemispheric separation on the integration and segregation of processing in the brain. Resting-state fMRI scans were acquired from 59 healthy participants to examine interregional correlations in spontaneous low frequency fluctuations in BOLD signal. Using a probabilistic atlas, we correlated probability-weighted time series from 112 regions (56 per hemisphere) distributed throughout the entire cerebrum. We compared RSFC for pairings of non-homologous regions located in different hemispheres (heterotopic connectivity) to RSFC for the same pairings when located within hemisphere (intrahemispheric connectivity). For positive connections, connectivity strength was greater within each hemisphere, consistent with integrated intrahemispheric processing. However, for negative connections, RSFC strength was greater between the hemispheres, consistent with segregated interhemispheric processing. These patterns were particularly notable for connections involving frontal and heteromodal regions. The distribution of positive and negative connectivity was nearly identical within and between the hemispheres, though we demonstrated detailed regional variation in distribution. We discuss implications for leading models of interhemispheric interaction. The future application of our analyses may provide important insight into impaired interhemispheric processing in clinical and aging populations. PMID:20570737

  10. Fluorescence fluctuation microscopy to reveal 3D architecture and function in the cell nucleus.

    PubMed

    Lenser, Thorsten; Weisshart, Klaus; Ulbricht, Tobias; Klement, Karolin; Hemmerich, Peter

    2010-01-01

    The three-dimensional (3D) architecture of the cell nucleus is determined not only by the presence of subnuclear domains, such as the nuclear envelope, chromosome territories, and nuclear bodies, but also by smaller domains which form in response to specific functions, such as RNA transcription, DNA replication, and DNA repair. Since both stable and dynamic structures contribute to nuclear morphology, it is important to study the biophysical principles of the formation of macromolecular assemblies within the nucleus. For this purpose, a variety of fluorescence fluctuation microscopy techniques can be applied. Here, we summarize our current knowledge on the 3D architecture of the mammalian cell nucleus and describe in detail how the assembly of functional nuclear protein complexes can be analyzed in living cells using fluorescence bleaching techniques, fluorescence correlation spectroscopy, raster image correlation spectroscopy, and mathematical modeling. In conclusion, the application of all these techniques in combination is a powerful tool to assess the full spectrum of nuclear protein dynamics and to understand the biophysical principles underlying nuclear structure and function.

  11. Dopamine Receptor Signaling in MIN6 β-Cells Revealed by Fluorescence Fluctuation Spectroscopy.

    PubMed

    Caldwell, Brittany; Ustione, Alessandro; Piston, David W

    2016-08-09

    Insulin secretion defects are central to the development of type II diabetes mellitus. Glucose stimulation of insulin secretion has been extensively studied, but its regulation by other stimuli such as incretins and neurotransmitters is not as well understood. We investigated the mechanisms underlying the inhibition of insulin secretion by dopamine, which is synthesized in pancreatic β-cells from circulating L-dopa. Previous research has shown that this inhibition is mediated primarily by activation of the dopamine receptor D3 subtype (DRD3), even though both DRD2 and DRD3 are expressed in β-cells. To understand this dichotomy, we investigated the dynamic interactions between the dopamine receptor subtypes and their G-proteins using two-color fluorescence fluctuation spectroscopy (FFS) of mouse MIN6 β-cells. We show that proper membrane localization of exogenous G-proteins depends on both the Gβ and Gγ subunits being overexpressed in the cell. Triple transfections of the dopamine receptor subtype and Gβ and Gγ subunits, each labeled with a different-colored fluorescent protein (FP), yielded plasma membrane expression of all three FPs and permitted an FFS evaluation of interactions between the dopamine receptors and the Gβγ complex. Upon dopamine stimulation, we measured a significant decrease in interactions between DRD3 and the Gβγ complex, which is consistent with receptor activation. In contrast, dopamine stimulation did not cause significant changes in the interactions between DRD2 and the Gβγ complex. These results demonstrate that two-color FFS is a powerful tool for measuring dynamic protein interactions in living cells, and show that preferential DRD3 signaling in β-cells occurs at the level of G-protein release. Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  12. Band gaps and localization of surface water waves over large-scale sand waves with random fluctuations.

    PubMed

    Zhang, Yu; Li, Yan; Shao, Hao; Zhong, Yaozhao; Zhang, Sai; Zhao, Zongxi

    2012-06-01

    Band structure and wave localization are investigated for sea surface water waves over large-scale sand wave topography. Sand wave height, sand wave width, water depth, and water width between adjacent sand waves have significant impact on band gaps. Random fluctuations of sand wave height, sand wave width, and water depth induce water wave localization. However, random water width produces a perfect transmission tunnel of water waves at a certain frequency so that localization does not occur no matter how large a disorder level is applied. Together with theoretical results, the field experimental observations in the Taiwan Bank suggest band gap and wave localization as the physical mechanism of sea surface water wave propagating over natural large-scale sand waves.

  13. Increase in the Random Dopant Induced Threshold Fluctuations and Lowering in Sub 100 nm MOSFETs Due to Quantum Effects: A 3-D Density-Gradient Simulation Study

    NASA Technical Reports Server (NTRS)

    Asenov, Asen; Slavcheva, G.; Brown, A. R.; Davies, J. H.; Saini, S.

    2000-01-01

    In this paper we present a detailed simulation study of the influence of quantum mechanical effects in the inversion layer on random dopant induced threshold voltage fluctuations and lowering in sub 100 nm MOSFETs. The simulations have been performed using a 3-D implementation of the density gradient (DG) formalism incorporated in our established 3-D atomistic simulation approach. This results in a self-consistent 3-D quantum mechanical picture, which implies not only the vertical inversion layer quantisation but also the lateral confinement effects related to current filamentation in the 'valleys' of the random potential fluctuations. We have shown that the net result of including quantum mechanical effects, while considering statistical dopant fluctuations, is an increase in both threshold voltage fluctuations and lowering. At the same time, the random dopant induced threshold voltage lowering partially compensates for the quantum mechanical threshold voltage shift in aggressively scaled MOSFETs with ultrathin gate oxides.

  14. Revisiting the Stark Broadening by fluctuating electric fields using the Continuous Time Random Walk Theory

    NASA Astrophysics Data System (ADS)

    Capes, H.; Christova, M.; Boland, D.; Catoire, F.; Godbert-Mouret, L.; Koubiti, M.; Mekkaoui, A.; Rosato, J.; Marandet, Y.; Stamm, R.

    2010-10-01

    Stark broadening of atomic lines in plasmas is calculated by modelling the plasma stochastic electric field using the CTRW approach [1,2]. This allows retaining non Markovian terms in the Schrödinger equation averaged over the electric field fluctuations. As an application we consider a special case of a non separable CTRW process, the so called Kangaroo process [3]. An analytic expression for the line profile is presented for arbitrary waiting time distribution functions. A preliminary application to the hydrogen Lyman α line is discussed.

  15. Analysis of conformational motions and residue fluctuations for Escherichia coli ribose-binding protein revealed with elastic network models.

    PubMed

    Li, Hai Yan; Cao, Zan Xia; Zhao, Li Ling; Wang, Ji Hua

    2013-05-21

    The ribose-binding protein (RBP) is a sugar-binding bacterial periplasmic protein whose function is associated with a large allosteric conformational change from an open to a closed conformation upon binding to ribose. The open (ligand-free) and closed (ligand-bound) forms of RBP have been found. Here we investigate the conformational motions and residue fluctuations of the RBP by analyzing the modes of motion with two coarse-grained elastic network models, the Gaussian Network Model (GNM) and Anisotropic Network Model (ANM). The calculated B-factors in both the calculated models are in good agreement with the experimentally determined B-factors in X-ray crystal structures. The slowest mode analysis by GNM shows that both forms have the same motion hinge axes around residues Ser103, Gln235, Asp264 and the two domains of both structures have similar fluctuation range. The superposition of the first three dominant modes of ANM, consisting of the rotating, bending and twisting motions of the two forms, accounts for large rearrangement of domains from the ligand-free (open) to ligand-bound (closed) conformation and thus constitutes a critical component of the RBP's functions. By analyzing cross-correlations between residue fluctuation and the difference-distance plot, it is revealed that the conformational change can be described as a rigid rotation of the two domains with respect to each other, whereas the internal structure of the two domains remains largely intact. The results directly indicate that the dominant dynamic characteristics of protein structures can be captured from their static native state using coarse-grained models.

  16. A functional dissociation between language and multiple-demand systems revealed in patterns of BOLD signal fluctuations.

    PubMed

    Blank, Idan; Kanwisher, Nancy; Fedorenko, Evelina

    2014-09-01

    What is the relationship between language and other high-level cognitive functions? Neuroimaging studies have begun to illuminate this question, revealing that some brain regions are quite selectively engaged during language processing, whereas other "multiple-demand" (MD) regions are broadly engaged by diverse cognitive tasks. Nonetheless, the functional dissociation between the language and MD systems remains controversial. Here, we tackle this question with a synergistic combination of functional MRI methods: we first define candidate language-specific and MD regions in each subject individually (using functional localizers) and then measure blood oxygen level-dependent signal fluctuations in these regions during two naturalistic conditions ("rest" and story-comprehension). In both conditions, signal fluctuations strongly correlate among language regions as well as among MD regions, but correlations across systems are weak or negative. Moreover, data-driven clustering analyses based on these inter-region correlations consistently recover two clusters corresponding to the language and MD systems. Thus although each system forms an internally integrated whole, the two systems dissociate sharply from each other. This independent recruitment of the language and MD systems during cognitive processing is consistent with the hypothesis that these two systems support distinct cognitive functions. Copyright © 2014 the American Physiological Society.

  17. A functional dissociation between language and multiple-demand systems revealed in patterns of BOLD signal fluctuations

    PubMed Central

    Kanwisher, Nancy; Fedorenko, Evelina

    2014-01-01

    What is the relationship between language and other high-level cognitive functions? Neuroimaging studies have begun to illuminate this question, revealing that some brain regions are quite selectively engaged during language processing, whereas other “multiple-demand” (MD) regions are broadly engaged by diverse cognitive tasks. Nonetheless, the functional dissociation between the language and MD systems remains controversial. Here, we tackle this question with a synergistic combination of functional MRI methods: we first define candidate language-specific and MD regions in each subject individually (using functional localizers) and then measure blood oxygen level-dependent signal fluctuations in these regions during two naturalistic conditions (“rest” and story-comprehension). In both conditions, signal fluctuations strongly correlate among language regions as well as among MD regions, but correlations across systems are weak or negative. Moreover, data-driven clustering analyses based on these inter-region correlations consistently recover two clusters corresponding to the language and MD systems. Thus although each system forms an internally integrated whole, the two systems dissociate sharply from each other. This independent recruitment of the language and MD systems during cognitive processing is consistent with the hypothesis that these two systems support distinct cognitive functions. PMID:24872535

  18. Photodissociation in quantum chaotic systems: Random-matrix theory of cross-section fluctuations

    SciTech Connect

    Fyodorov, Y.V.; Alhassid, Y.

    1998-11-01

    Using the random matrix description of open quantum chaotic systems we calculate in closed form the universal autocorrelation function and the probability distribution of the total photodissociation cross section in the regime of quantum chaos. {copyright} {ital 1998} {ital The American Physical Society}

  19. The role of random fluctuations in the magnetosphere-ionosphere system: a dynamic stochastic model for AE-index variations

    NASA Astrophysics Data System (ADS)

    Pulkkinen, A.; Klimas, A.; Vassiliadis, D.; Uritsky, V.

    2005-12-01

    Understanding the evolution of bursts of activity in the magnetosphere-ionosphere system has been one of the central challenges in space physics since, and even prior to the introduction of the term "substorm". An extensive amount of work has been put to the characterization of the average near-space plasma environment behavior during substorms and several more or less deterministic models have been introduced to explain the observations. However, although most of substorms seem to have some common characteristics (otherwise any classification would be completely meaningless), like intensification of auroral electric currents, dipolarization of the magnetotail and injections of plasma sheet charged particles, each substorm has its distinct features in terms of strong fluctuations around the average "typical" behavior. This highly complex nature of individual substorms suggests that stochastic processes may play a role, even a central one in the evolution of substorms. In this work, we develop a simple stochastic model for the AE-index variations to investigate the role of random fluctuations in the substorm phenomenon. We show that by the introduction of a stochastic component, we are able to capture some fundamental features of the AE-index variations. More specifically, complex variations associated with individual bursts are a central part of the model. It will be demonstrated that by analyzing the structure of the constructed stochastic model some presently open questions about substorm-related bursts of the AE-index can be addressed quantitatively. First and foremost, it will be shown that the stochastic fluctuations are a fundamental part of the AE-index evolution and cannot be neglected even when the average properties of the index are of interest.

  20. Scattering of electromagnetic waves from random media with strong permittivity fluctuations. [with application to atmospheric turbulence effects on microwave remote sensing

    NASA Technical Reports Server (NTRS)

    Tsang, L.; Kong, J. A.

    1981-01-01

    By taking into account the singularity of the dyadic Green's function in the renormalization method, a theory is derived for vector electromagnetic wave propagation in a random medium with large permittivity fluctuations and with anisotropic correlation function. The strong fluctuation theory is then applied to a discrete scatterer problem in which the permittivity can assume only two values. The results are found to be consistent with those derived from discrete scatterer theory for all values of dielectric constants of the scatterers.

  1. Simple algorithm for the correction of MRI image artefacts due to random phase fluctuations.

    PubMed

    Broche, Lionel M; Ross, P James; Davies, Gareth R; Lurie, David J

    2017-07-24

    Fast Field-Cycling (FFC) MRI is a novel technology that allows varying the main magnetic field B0 during the pulse sequence, from the nominal field (usually hundreds of millitesla) down to Earth's field or below. This technique uses resistive magnets powered by fast amplifiers. One of the challenges with this method is to stabilise the magnetic field during the acquisition of the NMR signal. Indeed, a typical consequence of field instability is small, random phase variations between each line of k-space resulting in artefacts, similar to those which occur due to homogeneous motion but harder to correct as no assumption can be made about the phase error, which appears completely random. Here we propose an algorithm that can correct for the random phase variations induced by field instabilities without prior knowledge about the phase error. The algorithm exploits the fact that ghosts caused by field instability manifest in image regions which should be signal free. The algorithm minimises the signal in the background by finding an optimum phase correction for each line of k-space and repeats the operation until the result converges, leaving the background free of signal. We showed the conditions for which the algorithm is robust and successfully applied it on images acquired on FFC-MRI scanners. The same algorithm can be used for various applications other than Fast Field-Cycling MRI. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

  2. Ultrasonic thermometry simulation in a random fluctuating medium: Evidence of the acoustic signature of a one-percent temperature difference.

    PubMed

    Nagaso, M; Moysan, J; Benjeddou, S; Massacret, N; Ploix, M A; Komatitsch, D; Lhuillier, C

    2016-05-01

    We study the development potential of ultrasonic thermometry in a liquid fluctuating sodium environment similar to that present in a Sodium-cooled Fast Reactor, and thus investigate if and how ultrasonic thermometry could be used to monitor the sodium flow at the outlet of the reactor core. In particular we study if small temperature variations in the sodium flow of e.g. about 1% of the sodium temperature, i.e., about 5°C, can have a reliably-measurable acoustic signature. Since to our knowledge no experimental setups are available for such a study, and considering the practical difficulties of experimentation in sodium, we resort to a numerical technique for full wave propagation called the spectral-element method, which is a highly accurate finite-element method owing to the high-degree basis functions it uses. We obtain clear time-of-flight variations in the case of a small temperature difference of one percent in the case of a static temperature gradient as well as in the presence of a random fluctuation of the temperature field in the turbulent flow. The numerical simulations underline the potential of ultrasonic thermometry in such a context.

  3. Active control on high-order coherence and statistic characterization on random phase fluctuation of two classical point sources

    PubMed Central

    Hong, Peilong; Li, Liming; Liu, Jianji; Zhang, Guoquan

    2016-01-01

    Young’s double-slit or two-beam interference is of fundamental importance to understand various interference effects, in which the stationary phase difference between two beams plays the key role in the first-order coherence. Different from the case of first-order coherence, in the high-order optical coherence the statistic behavior of the optical phase will play the key role. In this article, by employing a fundamental interfering configuration with two classical point sources, we showed that the high- order optical coherence between two classical point sources can be actively designed by controlling the statistic behavior of the relative phase difference between two point sources. Synchronous position Nth-order subwavelength interference with an effective wavelength of λ/M was demonstrated, in which λ is the wavelength of point sources and M is an integer not larger than N. Interestingly, we found that the synchronous position Nth-order interference fringe fingerprints the statistic trace of random phase fluctuation of two classical point sources, therefore, it provides an effective way to characterize the statistic properties of phase fluctuation for incoherent light sources. PMID:27021589

  4. Analytical model for random dopant fluctuation in double-gate MOSFET in the subthreshold region using macroscopic modeling method

    NASA Astrophysics Data System (ADS)

    Shin, Yong Hyeon; Yun, Ilgu

    2016-12-01

    An analytical model is proposed for the random dopant fluctuation (RDF) in a symmetric double-gate metal-oxidesemiconductor field-effect-transistor (DG MOSFET) in the subthreshold region. Unintended impurity dopants cannot be absolutely prevented during the device fabrication; hence, it is important to analytically model the fluctuations in the electrical characteristics caused by these impurity dopants. Therefore, a macroscopic modeling method is applied to represent the impurity dopants in DG MOSFETs. With this method, the two-dimensional (2D) Poisson equation is separated into a basic analytical DG MOSFET model with channel doping concentration NA and an impurity-dopant-related term with local doping concentration NRD confined in a specific rectangular area. To solve the second term, the manually solvable 2D Green's function for DG MOSFETs is used. Through calculation of the channel potential (ϕ(x, y)), the variations in the drive current (IDS) and threshold voltage (Vth) are extracted from the analytical model. All results from the analytical model for an impurity dopant in a DG MOSFET are examined by comparisons with the commercially available 2D numerical simulation results, with respect to various oxide thicknesses (tox), channel lengths (L), and location of impurity dopants.

  5. Salmon Migration Patterns Revealed the Temporal and Spatial Fluctuations of the Radiocesium Levels in Terrestrial and Ocean Environments

    PubMed Central

    Arai, Takaomi

    2014-01-01

    The disabling of the Fukushima Daiichi Nuclear Power Plant (F1NPP) resulted in the release of radionuclides, including 134Cs and 137Cs, into the air and the ocean. The unpredicted nuclear accident is of global concern for human health and the ecosystem. Although investigations of radionuclides in environments were performed shortly after the accident started, the temporal and spatial impacts and fluctuations on the releasing radionuclides to natural environment remain unclear. I focused on salmon, which migrate from inland to the open ocean globally, to reveal the three-year (May 2011 to February 2014) fluctuations and accumulations of 134Cs and 137Cs from terrestrial to open ocean environments after the F1NPP accident. The 134Cs and 137Cs concentrations in six salmonids exhibited lower temporal variations for three years after the F1NPP accident, suggesting that these radionuclides are widely distributed and these radionuclides remain in the natural environment globally with less convergence. The accumulation patterns were significantly different among the different salmon species. Fluvial (freshwater residence) type salmons exhibited significantly higher accumulation in 134Cs (25.3–40.2 Bq kg−1 in mean) and 137Cs (41.4–51.7 Bq kg−1 in mean) than did the anadromous (sea-run) type salmons (0.64–8.03 Bq kg−1 in mean 134Cs and 0.42–10.2 Bq kg−1 in mean 137Cs) suggesting widespread contamination in terrestrial environments versus the coastal and open ocean environments. Salmonids are the most highly migratory animals and are characterised by their strong tendency to return home to their natal site for reproduction. Salmonids have a potential to be a good indicator as an effective monitoring animal. PMID:24964195

  6. Mitochondrial phylogeography of rock-dwelling cichlid fishes reveals evolutionary influence of historical lake level fluctuations of Lake Tanganyika, Africa.

    PubMed

    Verheyen, E; Rüber, L; Snoeks, J; Meyer, A

    1996-06-29

    The East African Lakes Tanganyika, Malawi and Victoria each harbour hundreds of endemic invertebrate and vertebrate species. Inferences about the ecological and evolutionary processes responsible for the origin of these species flocks will only be possible when they are made within historical and comparative frameworks. Specifically, the relative importance of intrinsic characteristics and extrinsic factors may offer information about the processes that drive diversification and speciation in these species. We investigated the sequence variation of a segment of the mitochondrial DNA control region of 32 populations representing all four nominal species in the three genera of eretmodine cichlids from Lake Tanganyika. Based on a phylogenetic analysis of these data we attempted to evaluate the importance of major lake level fluctuations on patterns of intralacustrine speciation. The geography of genetic variation reveals a high degree of within-lake endemism among genetically well-separated lineages distributed along the inferred shore lines of three historically intermittent lake basins. Seismic data indicate that extreme lowering of water levels in the Pleistocene caused the single Lake Tanganyika basin to split into three isolated ones. The strong phylogeographic structure of the Eretmodini, and the observation that some closely related populations occur on opposite shores of the lake, agree with this geological scenario. The three-clade-three-basin phylogeographic pattern was repeated twice within this tribe of cichlids. The phylogeographic pattern of eretmodine cichlids suggests that major fluctuations in the level of the lake have been important in shaping their adaptive radiation and speciation. The mitochondrially defined clades are in conflict with the current taxonomy of the group and suggest that there has been convergent evolution in trophic morphology, particularly in the shapes of oral teeth, taxonomically the most diagnostic characters of the three

  7. SSU Ribosomal DNA-Based Monitoring of Nematode Assemblages Reveals Distinct Seasonal Fluctuations within Evolutionary Heterogeneous Feeding Guilds

    PubMed Central

    Vervoort, Mariëtte T. W.; Vonk, J. Arie; Mooijman, Paul J. W.; Van den Elsen, Sven J. J.; Van Megen, Hanny H. B.; Veenhuizen, Peter; Landeweert, Renske; Bakker, Jaap; Mulder, Christian; Helder, Johannes

    2012-01-01

    Soils are among the most complex, diverse and competitive habitats on Earth and soil biota are responsible for ecosystem services such as nutrient cycling, carbon sequestration and remediation of freshwater. The extreme biodiversity prohibits the making of a full inventory of soil life. Hence, an appropriate indicator group should be selected to determine the biological condition of soil systems. Due to their ubiquity and the diverse responses to abiotic and biotic changes, nematodes are suitable indicators for environmental monitoring. However, the time-consuming microscopic analysis of nematode communities has limited the scale at which this indicator group is used. In an attempt to circumvent this problem, a quantitative PCR-based tool for the detection of a consistent part of the soil nematofauna was developed based on a phylum-wide molecular framework consisting of 2,400 full-length SSU rDNA sequences. Taxon-specific primers were designed and tested for specificity. Furthermore, relationships were determined between the quantitative PCR output and numbers of target nematodes. As a first field test for this DNA sequence signature-based approach, seasonal fluctuations of nematode assemblages under open canopy (one field) and closed canopy (one forest) were monitored. Fifteen taxa from four feeding guilds (covering ∼ 65% of the free-living nematode biodiversity at higher taxonomical level) were detected at two trophic levels. These four feeding guilds are composed of taxa that developed independently by parallel evolution and we detected ecologically interpretable patterns for free-living nematodes belonging to the lower trophic level of soil food webs. Our results show temporal fluctuations, which can be even opposite within taxa belonging to the same guild. This research on nematode assemblages revealed ecological information about the soil food web that had been partly overlooked. PMID:23112818

  8. SSU ribosomal DNA-based monitoring of nematode assemblages reveals distinct seasonal fluctuations within evolutionary heterogeneous feeding guilds.

    PubMed

    Vervoort, Mariëtte T W; Vonk, J Arie; Mooijman, Paul J W; Van den Elsen, Sven J J; Van Megen, Hanny H B; Veenhuizen, Peter; Landeweert, Renske; Bakker, Jaap; Mulder, Christian; Helder, Johannes

    2012-01-01

    Soils are among the most complex, diverse and competitive habitats on Earth and soil biota are responsible for ecosystem services such as nutrient cycling, carbon sequestration and remediation of freshwater. The extreme biodiversity prohibits the making of a full inventory of soil life. Hence, an appropriate indicator group should be selected to determine the biological condition of soil systems. Due to their ubiquity and the diverse responses to abiotic and biotic changes, nematodes are suitable indicators for environmental monitoring. However, the time-consuming microscopic analysis of nematode communities has limited the scale at which this indicator group is used. In an attempt to circumvent this problem, a quantitative PCR-based tool for the detection of a consistent part of the soil nematofauna was developed based on a phylum-wide molecular framework consisting of 2,400 full-length SSU rDNA sequences. Taxon-specific primers were designed and tested for specificity. Furthermore, relationships were determined between the quantitative PCR output and numbers of target nematodes. As a first field test for this DNA sequence signature-based approach, seasonal fluctuations of nematode assemblages under open canopy (one field) and closed canopy (one forest) were monitored. Fifteen taxa from four feeding guilds (covering ∼ 65% of the free-living nematode biodiversity at higher taxonomical level) were detected at two trophic levels. These four feeding guilds are composed of taxa that developed independently by parallel evolution and we detected ecologically interpretable patterns for free-living nematodes belonging to the lower trophic level of soil food webs. Our results show temporal fluctuations, which can be even opposite within taxa belonging to the same guild. This research on nematode assemblages revealed ecological information about the soil food web that had been partly overlooked.

  9. Salmon migration patterns revealed the temporal and spatial fluctuations of the radiocesium levels in terrestrial and ocean environments.

    PubMed

    Arai, Takaomi

    2014-01-01

    The disabling of the Fukushima Daiichi Nuclear Power Plant (F1NPP) resulted in the release of radionuclides, including 134Cs and 137Cs, into the air and the ocean. The unpredicted nuclear accident is of global concern for human health and the ecosystem. Although investigations of radionuclides in environments were performed shortly after the accident started, the temporal and spatial impacts and fluctuations on the releasing radionuclides to natural environment remain unclear. I focused on salmon, which migrate from inland to the open ocean globally, to reveal the three-year (May 2011 to February 2014) fluctuations and accumulations of 134Cs and 137Cs from terrestrial to open ocean environments after the F1NPP accident. The 134Cs and 137Cs concentrations in six salmonids exhibited lower temporal variations for three years after the F1NPP accident, suggesting that these radionuclides are widely distributed and these radionuclides remain in the natural environment globally with less convergence. The accumulation patterns were significantly different among the different salmon species. Fluvial (freshwater residence) type salmons exhibited significantly higher accumulation in 134Cs (25.3-40.2 Bq kg(-1) in mean) and 137Cs (41.4-51.7 Bq kg(-1) in mean) than did the anadromous (sea-run) type salmons (0.64-8.03 Bq kg(-1) in mean 134Cs and 0.42-10.2 Bq kg(-1) in mean 137Cs) suggesting widespread contamination in terrestrial environments versus the coastal and open ocean environments. Salmonids are the most highly migratory animals and are characterised by their strong tendency to return home to their natal site for reproduction. Salmonids have a potential to be a good indicator as an effective monitoring animal.

  10. Random sampling of skewed distributions implies Taylor’s power law of fluctuation scaling

    PubMed Central

    Cohen, Joel E.; Xu, Meng

    2015-01-01

    Taylor’s law (TL), a widely verified quantitative pattern in ecology and other sciences, describes the variance in a species’ population density (or other nonnegative quantity) as a power-law function of the mean density (or other nonnegative quantity): Approximately, variance = a(mean)b, a > 0. Multiple mechanisms have been proposed to explain and interpret TL. Here, we show analytically that observations randomly sampled in blocks from any skewed frequency distribution with four finite moments give rise to TL. We do not claim this is the only way TL arises. We give approximate formulae for the TL parameters and their uncertainty. In computer simulations and an empirical example using basal area densities of red oak trees from Black Rock Forest, our formulae agree with the estimates obtained by least-squares regression. Our results show that the correlated sampling variation of the mean and variance of skewed distributions is statistically sufficient to explain TL under random sampling, without the intervention of any biological or behavioral mechanisms. This finding connects TL with the underlying distribution of population density (or other nonnegative quantity) and provides a baseline against which more complex mechanisms of TL can be compared. PMID:25852144

  11. Highly sensitive optical interferometric technique reveals stress-dependent instantaneous nanometric growth fluctuations of Chinese chive leaf under heavy metal stress.

    PubMed

    Muthumali DeSilva, Kokge Thilini Kanchana; Rajagopalan, Uma Maheswari; Kadono, Hirofumi

    2017-03-01

    Plant growth apart from being a complex and highly dynamic is dependent on its immediate environment. Leaf expansion measurements using Statistical Interferometry Technique, a sensitive interferometric technique at nanometric accuracy and at sub-second levels revealed the presence of characteristic nanometric intrinsic fluctuations [Plant Biotechnology 31, 195 (2014)]. In this paper, we demonstrate that the nanometric intrinsic fluctuations are sensitive enough that they change under exposure of heavy metals, essential micronutrient zinc and non-essential element cadmium, at relatively low concentrations in the leaves of Chinese chive (Allium tuberosum). The nanometric intrinsic fluctuations of leaves were observed for 4h under three cadmium concentrations or two zinc concentrations. Results showed significant reduction of nanometric intrinsic fluctuations for all cadmium concentrations, and in contrast significant increase of nanometric intrinsic fluctuations for all zinc concentrations. There was significant reduction of nanometric intrinsic fluctuations for cadmium exposure of concentrations of 0.001mM for even an hour, and significant increment of nanometric intrinsic fluctuations under 0.75mM zinc from 1hr exposure. For comparison, antioxidative enzymes and metal uptake were also measured under 4hr exposure of cadmium or zinc. However, no significant changes could be seen in antioxidative enzymes within 4h under the smaller concentration of 0.001mM cadmium as seen for nanometric intrinsic fluctuations. The results imply that nanometric intrinsic fluctuations can be not only used as a measure for heavy metal stress but also it can be more sensitive to detect the toxic as well as positive effects of smaller amounts of heavy metal on plants at an early stage.

  12. Fluctuation of long-range order in Co-Pt alloy nanoparticles revealed by time-resolved electron microscopy

    NASA Astrophysics Data System (ADS)

    Sato, Kazuhisa; Yasuda, Hidehiro

    2017-04-01

    The development of long-range order in disordered Co-Pt alloy nanoparticles has been atomically resolved in situ with an ultra-high voltage electron microscope equipped with a direct electron detection camera. Electron-irradiation-enhanced ordering occurred at 573 K with 1 MeV electrons at a dose rate of 8.9 × 1024 e/m2s. High-speed (400 frames/s) imaging revealed fluctuations of the c-axis orientation of the L10-type ordered structure. Specifically, the c-axis orientation changes occurred at 2.5-ms intervals. Thus, the atomic ordering rate at 573 K is deduced to be 3 × 10-17 m2/s, which is 1013 times higher than that estimated for interdiffusion in a bulk Co-Pt alloy. The observed kinetic ordering temperature of 573 K is significantly lower than that reported previously (>800 K). The low-temperature ordering may be the result of enhanced atom migration via excess vacancies, 106 times higher than that at thermal equilibrium, introduced by the high-energy electron irradiation.

  13. Stable carbon and oxygen isotopes reveal Sahel drought events and ground water fluctuations in sub-Saharan Africa

    NASA Astrophysics Data System (ADS)

    Gebrekirstos, Aster

    2014-05-01

    Tree rings are important proxies for paleoclimate studies because they contain continuous historical records of inter-annual and intra-annual time resolutions, which range over hundreds of years. This study uses stable carbon and oxygen isotopes in tree rings to understand the drivers and impacts of climate change in sub-Saharan Africa and their ability to reconstruct past regional climate variability and climatic trends. Our approach considers large scale climate gradients and different temporal scales (inter-annual and intra-annual variations) and combines multi- parameter measurements (carbon and oxygen isotopes, whole wood and cellulose measurements). The study species are Faidherbia albida and Sclerocarya birrea from south and West Africa, respectively. Both are very important deciduous trees, and widely distributed in sub-Saharan Africa. Particularly, F. albida has a distinctive phenology; it bears leaves and flowers during the dry season and sheds its leaves during the rainy season. Stable carbon (δ13C) and oxygen (δ18O) mean values showed similar inter annual patterns. In general, both δ13C and δ18O show negative correlations with rainfall, humidity and PDSI. On the contrary, they are positively correlated with sunshine hours, maximum temperature and evaporation. The reverse phenology of Faidherbia and intra seasonal resolution measurements reveals seasonal ground water fluctuations. Both carbon and oxygen stable isotopes showed strong climatic signals including the long Sahel drought events and climatic recovery phases.

  14. Estimation of flow parameters of turbulent fluctuations and vortex motions based on randomly sampled velocity data in the near wake of a circular cylinder in a steady flow

    SciTech Connect

    Kong, D.

    1995-12-31

    Turbulent near wake flow is one of the key subjects for solving fluid dynamics-related problems in industrial practice, e.g. numerical simulation of gas explosions on offshore oil/gas production platforms. Flow velocities measured in the near-wake of bluff bodies contain information of mean flow, turbulent fluctuations and vortex motions. Flow parameters like RMS values of velocity fluctuations, Reynolds shear stresses, and auto-/spatial correlation of velocity fluctuations, derived by direct averaging of measured data, will include the total contributions of the periodic vortex motions and the random turbulent fluctuations. In the case of near-wake flows behind a cylinder at sub-critical Reynolds numbers, a vortex-street is formed in the wake and the vortex-shedding frequency is well defined. This offers a possibility for simplifying the decomposition of regular vortex motions and the random turbulent fluctuations. Velocity profiles and cross-stream spatial correlation of streamwise velocity were measured by positioning a TSI`s two-component LDA system in the region 2d to 4d downstream of a circular cylinder at Re = 35,000. The randomly sampled data were first interpolated linearly, and then re-sampled with a pertinent sampling frequency. The optimal FIR filters, designed using the Remez exchange algorithm, were applied to reject the digital signals in a narrow band around the vortex-shedding frequency. Various flow parameters associated with random turbulence were computed. The integration of the auto- and spatial correlation, obtained based on the filtered data gave a physically adequate estimation of the integral time and length scales of the turbulent fluctuations. Errors due to linear interpolation and filtering were discussed.

  15. Efficiency Drop in Green InGaN/GaN Light Emitting Diodes: The Role of Random Alloy Fluctuations.

    PubMed

    Auf der Maur, Matthias; Pecchia, Alessandro; Penazzi, Gabriele; Rodrigues, Walter; Di Carlo, Aldo

    2016-01-15

    White light emitting diodes (LEDs) based on III-nitride InGaN/GaN quantum wells currently offer the highest overall efficiency for solid state lighting applications. Although current phosphor-converted white LEDs have high electricity-to-light conversion efficiencies, it has been recently pointed out that the full potential of solid state lighting could be exploited only by color mixing approaches without employing phosphor-based wavelength conversion. Such an approach requires direct emitting LEDs of different colors, including, in particular, the green-yellow range of the visible spectrum. This range, however, suffers from a systematic drop in efficiency, known as the "green gap," whose physical origin has not been understood completely so far. In this work, we show by atomistic simulations that a consistent part of the green gap in c-plane InGaN/GaN-based light emitting diodes may be attributed to a decrease in the radiative recombination coefficient with increasing indium content due to random fluctuations of the indium concentration naturally present in any InGaN alloy.

  16. Anomalous magnetic fluctuations in superconducting Sr2RuO4 revealed by 101Ru nuclear spin-spin relaxation

    NASA Astrophysics Data System (ADS)

    Manago, Masahiro; Yamanaka, Takayoshi; Ishida, Kenji; Mao, Zhiqiang; Maeno, Yoshiteru

    2016-10-01

    We carried out 101Ru nuclear quadrupole resonance (NQR) measurement on superconducting (SC) Sr2RuO4 under zero magnetic field (H =0 ) and found that the nuclear spin-spin relaxation rate 1 /T2 is enhanced in the SC state. The 1 /T2 measurement in the SC state under H =0 is effective for detecting slow magnetic fluctuations parallel to the quantized axis of the nuclear spin. Our results indicate that low-energy magnetic fluctuations perpendicular to the RuO2 plane emerge when the superconductivity sets in, which is consistent with the previous 17O-NQR result that the nuclear spin-lattice relaxation rate 1 /T1 of the in-plane O site exhibits anomalous behavior in the SC state. The enhancement of the magnetic fluctuations in the SC state is unusual and suggests that the fluctuations are related to the unconventional SC pairing. We suggest that this phenomenon is a consequence of the spin degrees of freedom of the spin-triplet pairing.

  17. Fluctuation phenomena

    SciTech Connect

    Montroll, E.W.; Lebowitz, J.L.

    1986-01-01

    Fluctuation phenomena are the ''tip of the iceberg'' revealing the existence, behind even the most quiescent appearing macroscopic states, of an underlying world of agitated, ever-changing microscopic processes. While the presence of these fluctuations can be ignored in some cases, e.g. if one is satisfied with purely thermostatic description of systems in equilibrium, they are central to the understanding of other phenomena, e.g. the nucleation of a new phase following the quenching of a system into the co-existence region. This volume contains a collection of review articles, written by experts in the field, on the subject of fluctuation phenomena. Some of the articles are of a very general nature discussing the modern mathematical formulation of the problems involved, while other articles deal with specific topics such as kinetics of phase transitions and conductivity in solids. The juxtaposition of the variety of physical situations in which fluctuation phenomena play an important role is novel and should give the reader an insight into this subject.

  18. Fast, long-range, reversible conformational fluctuations in nucleosomes revealed by single-pair fluorescence resonance energy transfer

    NASA Astrophysics Data System (ADS)

    Tomschik, Miroslav; Zheng, Haocheng; van Holde, Ken; Zlatanova, Jordanka; Leuba, Sanford H.

    2005-03-01

    The nucleosome core particle, the basic repeated structure in chromatin fibers, consists of an octamer of eight core histone molecules, organized as dimers (H2A/H2B) and tetramers [(H3/H4)2] around which DNA wraps tightly in almost two left-handed turns. The nucleosome has to undergo certain conformational changes to allow processes that need access to the DNA template to occur. By single-pair fluorescence resonance energy transfer, we demonstrate fast, long-range, reversible conformational fluctuations in nucleosomes between two states: fully folded (closed), with the DNA wrapped around the histone core, or open, with the DNA significantly unraveled from the histone octamer. The brief excursions into an extended open state may create windows of opportunity for protein factors involved in DNA transactions to bind to or translocate along the DNA. conformational transitions | evanescent field fluorescence microscope | nucleosome dynamics | nucleosome opening

  19. Ferromagnetic Spin Fluctuation and Unconventional Superconductivity in Rb2Cr3As3 Revealed by 75As NMR and NQR

    NASA Astrophysics Data System (ADS)

    Yang, J.; Tang, Z. T.; Cao, G. H.; Zheng, Guo-qing

    2015-10-01

    We report 75As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) studies on the superconductor Rb2Cr3As3 with a quasi-one-dimensional crystal structure. Below T ˜100 K , the spin-lattice relaxation rate (1 /T1 ) divided by temperature, 1 /T1T , increases upon cooling down to Tc=4.8 K , showing a Curie-Weiss-like temperature dependence. The Knight shift also increases with decreasing temperature. These results suggest ferromagnetic spin fluctuation. In the superconducting state, 1 /T1 decreases rapidly below Tc without a Hebel-Slichter peak, and follows a T5 variation below T ˜3 K , which points to unconventional superconductivity with point nodes in the gap function.

  20. Ferromagnetic Spin Fluctuation and Unconventional Superconductivity in Rb2Cr3As3 Revealed by 75As NMR and NQR.

    PubMed

    Yang, J; Tang, Z T; Cao, G H; Zheng, Guo-Qing

    2015-10-02

    We report (75)As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) studies on the superconductor Rb(2)Cr(3)As(3) with a quasi-one-dimensional crystal structure. Below T∼100  K, the spin-lattice relaxation rate (1/T(1)) divided by temperature, 1/T(1)T, increases upon cooling down to T(c)=4.8  K, showing a Curie-Weiss-like temperature dependence. The Knight shift also increases with decreasing temperature. These results suggest ferromagnetic spin fluctuation. In the superconducting state, 1/T(1) decreases rapidly below T(c) without a Hebel-Slichter peak, and follows a T(5) variation below T∼3  K, which points to unconventional superconductivity with point nodes in the gap function.

  1. Alterations in task-induced activity and resting-state fluctuations in visual and DMN areas revealed in long-term meditators.

    PubMed

    Berkovich-Ohana, Aviva; Harel, Michal; Hahamy, Avital; Arieli, Amos; Malach, Rafael

    2016-07-15

    Recently we proposed that the information contained in spontaneously emerging (resting-state) fluctuations may reflect individually unique neuro-cognitive traits. One prediction of this conjecture, termed the "spontaneous trait reactivation" (STR) hypothesis, is that resting-state activity patterns could be diagnostic of unique personalities, talents and life-styles of individuals. Long-term meditators could provide a unique experimental group to test this hypothesis. Using fMRI we found that, during resting-state, the amplitude of spontaneous fluctuations in long-term mindfulness meditation (MM) practitioners was enhanced in the visual cortex and significantly reduced in the DMN compared to naïve controls. Importantly, during a visual recognition memory task, the MM group showed heightened visual cortex responsivity, concomitant with weaker negative responses in Default Mode Network (DMN) areas. This effect was also reflected in the behavioral performance, where MM practitioners performed significantly faster than the control group. Thus, our results uncover opposite changes in the visual and default mode systems in long-term meditators which are revealed during both rest and task. The results support the STR hypothesis and extend it to the domain of local changes in the magnitude of the spontaneous fluctuations.

  2. Spectroscopic microscopy can quantify the statistics of subdiffractional refractive-index fluctuations in media with random rough surfaces.

    PubMed

    Zhang, Di; Cherkezyan, Lusik; Capoglu, Ilker; Subramanian, Hariharan; Chandler, John; Thompson, Sebastian; Taflove, Allen; Backman, Vadim

    2015-11-01

    We previously established that spectroscopic microscopy can quantify subdiffraction-scale refractive index (RI) fluctuations in a label-free dielectric medium with a smooth surface. However, to study more realistic samples, such as biological cells, the effect of rough surface should be considered. In this Letter, we first report an analytical theory to synthesize microscopic images of a rough surface, validate this theory by finite-difference time-domain (FDTD) solutions of Maxwell's equations, and characterize the spectral properties of light reflected from a rough surface. Then, we report a technique to quantify the RI fluctuations beneath a rough surface and demonstrate its efficacy on FDTD-synthesized spectroscopic microscopy images, as well as experimental data obtained from biological cells.

  3. Spectroscopic microscopy can quantify the statistics of subdiffractional refractive-index fluctuations in media with random rough surfaces

    PubMed Central

    Zhang, Di; Cherkezyan, Lusik; Capoglu, Ilker; Subramanian, Hariharan; Chandler, John; Thompson, Sebastian; Taflove, Allen; Backman, Vadim

    2016-01-01

    We previously established that spectroscopic microscopy can quantify subdiffraction-scale refractive index (RI) fluctuations in a label-free dielectric medium with a smooth surface. However, to study more realistic samples, such as biological cells, the effect of rough surface should be considered. In this Letter, we first report an analytical theory to synthesize microscopic images of a rough surface, validate this theory by finite-difference time-domain (FDTD) solutions of Maxwell’s equations, and characterize the spectral properties of light reflected from a rough surface. Then, we report a technique to quantify the RI fluctuations beneath a rough surface and demonstrate its efficacy on FDTD-synthesized spectroscopic microscopy images, as well as experimental data obtained from biological cells. PMID:26512486

  4. Changes in low-frequency fluctuations in patients with antisocial personality disorder revealed by resting-state functional MRI.

    PubMed

    Liu, Huasheng; Liao, Jian; Jiang, Weixiong; Wang, Wei

    2014-01-01

    Antisocial Personality Disorder (APD) is a personality disorder that is most commonly associated with the legal and criminal justice systems. The study of the brain in APD has important implications in legal contexts and in helping ensure social stability. However, the neural contribution to the high prevalence of APD is still unclear. In this study, we used resting-state functional magnetic resonance imaging (fMRI) to investigate the underlying neural mechanisms of APD. Thirty-two healthy individuals and thirty-five patients with APD were recruited. The amplitude of low-frequency fluctuations (ALFF) was analyzed for the whole brain of all subjects. Our results showed that APD patients had a significant reduction in the ALFF in the right orbitofrontal cortex, the left temporal pole, the right inferior temporal gyrus, and the left cerebellum posterior lobe compared to normal controls. We observed that the right orbitofrontal cortex had a negative correlation between ALFF values and MMPI psychopathic deviate scores. Alterations in ALFF in these specific brain regions suggest that APD patients may be associated with abnormal activities in the fronto-temporal network. We propose that our results may contribute in a clinical and forensic context to a better understanding of APD.

  5. Signature of a Nonharmonic Potential as Revealed from a Consistent Shape and Fluctuation Analysis of an Adherent Membrane

    NASA Astrophysics Data System (ADS)

    Schmidt, Daniel; Monzel, Cornelia; Bihr, Timo; Merkel, Rudolf; Seifert, Udo; Sengupta, Kheya; Smith, Ana-Sunčana

    2014-04-01

    The interaction of fluid membranes with a scaffold, which can be a planar surface or a more complex structure, is intrinsic to a number of systems from artificial supported bilayers and vesicles to cellular membranes. In principle, these interactions can be either discrete and protein mediated, or continuous. In the latter case, they emerge from ubiquitous intrinsic surface interaction potentials as well as nature-designed steric contributions of the fluctuating membrane or from the polymers of the glycocalyx. Despite the fact that these nonspecific potentials are omnipresent, their description has been a major challenge from experimental and theoretical points of view. Here, we show that a full understanding of the implications of the continuous interactions can be achieved only by expanding the standard superposition models commonly used to treat these types of systems, beyond the usual harmonic level of description. Supported by this expanded theoretical framework, we present three independent, yet mutually consistent, experimental approaches to measure the interaction potential strength and the membrane tension. Upon explicitly taking into account the nature of shot noise as well as the nature of finite experimental resolution, excellent agreement with the augmented theory is obtained, which finally provides a coherent view of the behavior of the membrane in the vicinity of a scaffold.

  6. Changes in Low-Frequency Fluctuations in Patients with Antisocial Personality Disorder Revealed by Resting-State Functional MRI

    PubMed Central

    Jiang, Weixiong; Wang, Wei

    2014-01-01

    Antisocial Personality Disorder (APD) is a personality disorder that is most commonly associated with the legal and criminal justice systems. The study of the brain in APD has important implications in legal contexts and in helping ensure social stability. However, the neural contribution to the high prevalence of APD is still unclear. In this study, we used resting-state functional magnetic resonance imaging (fMRI) to investigate the underlying neural mechanisms of APD. Thirty-two healthy individuals and thirty-five patients with APD were recruited. The amplitude of low-frequency fluctuations (ALFF) was analyzed for the whole brain of all subjects. Our results showed that APD patients had a significant reduction in the ALFF in the right orbitofrontal cortex, the left temporal pole, the right inferior temporal gyrus, and the left cerebellum posterior lobe compared to normal controls. We observed that the right orbitofrontal cortex had a negative correlation between ALFF values and MMPI psychopathic deviate scores. Alterations in ALFF in these specific brain regions suggest that APD patients may be associated with abnormal activities in the fronto-temporal network. We propose that our results may contribute in a clinical and forensic context to a better understanding of APD. PMID:24598769

  7. Aberrant regional neural fluctuations and functional connectivity in generalized anxiety disorder revealed by resting-state functional magnetic resonance imaging.

    PubMed

    Wang, Wei; Hou, Jingming; Qian, Shaowen; Liu, Kai; Li, Bo; Li, Min; Peng, Zhaohui; Xin, Kuolin; Sun, Gang

    2016-06-15

    The purpose of this study was to investigate the neural activity and functional connectivity in generalized anxiety disorder (GAD) during resting state, and how these alterations correlate to patients' symptoms. Twenty-eight GAD patients and 28 matched healthy controls underwent resting-state functional magnetic resonance (fMRI) scans. Amplitude of low-frequency fluctuation (ALFF) and seed-based resting-state functional connectivity (RSFC) were computed to explore regional activity and functional integration, and were compared between the two groups using the voxel-based two-sample t test. Pearson's correlation analyses were performed to examine the neural relationships with demographics and clinical symptoms scores. Compared to controls, GAD patients showed functional abnormalities: higher ALFF in the bilateral dorsomedial prefrontal cortex, bilateral dorsolateral prefrontal cortex and left precuneus/posterior cingulate cortex; lower connectivity in prefrontal gyrus; lower in prefrontal-limbic and cingulate RSFC and higher prefrontal-hippocampus RSFC were correlated with clinical symptoms severity, but these associations were unable to withstand correction for multiple testing. These findings may help facilitate further understanding of the potential neural substrate of GAD.

  8. Analysis of Charge-spin-orbital Fluctuations by Ab Initio Calculation and Random Phase Approximation: Application to Non-coplanar Antiferromagnet Cd2Os2O7

    NASA Astrophysics Data System (ADS)

    Uehara, Amane; Shinaoka, Hiroshi; Motome, Yukitoshi

    We present a systematic analysis on the basis of ab initio calculations and many-body perturbation theory for clarifying the dominant fluctuation in complex charge-spin-orbital coupled systems. For a tight-binding multiband model obtained from the maximally-localized Wannier function analysis of the band structure by the local density approximation, we take into account electron correlations at the level of random phase approximation. To identify the dominant fluctuation, we carry out the eigenmode analysis of the generalized susceptibility that includes all the multiple degrees of freedom: charge, spin, and orbital. We apply this method to the paramagnetic metallic phase of a pyrochlore oxide Cd2Os2O7, which shows a metalinsulator transition accompanied by a peculiar noncoplanar antiferromagnetic order of all-in all-out type. We find that the corresponding spin fluctuation is dominantly enhanced by the on-site Coulomb repulsions in the presence of strong spin-orbit coupling and trigonal crystal field splitting. Our results indicate that the combined method offers an effective tool for the systematic analysis of potential instabilities in strongly correlated electron materials.

  9. Frequency spectra and vertical profiles of wind fluctuations in the summer Antarctic mesosphere revealed by MST radar observations

    NASA Astrophysics Data System (ADS)

    Sato, Kaoru; Kohma, Masashi; Tsutsumi, Masaki; Sato, Toru

    2017-01-01

    Continuous observations of polar mesosphere summer echoes at heights from 81-93 km were performed using the first Mesosphere-Stratosphere-Troposphere/Incoherent Scatter radar in the Antarctic over the three summer periods of 2013/2014, 2014/2015, and 2015/2016. Power spectra of horizontal and vertical wind fluctuations, and momentum flux spectra in a wide-frequency range from (8 min)-1 to (20 days) -1 were first estimated for the Antarctic summer mesosphere. The horizontal (vertical) wind power spectra obey a power law with an exponent of approximately -2 (-1) at frequencies higher than the inertial frequency of (13 h)-1 and have isolated peaks at about 1 day and a half day. In addition, an isolated peak of a quasi-2 day period is observed in the horizontal wind spectra but is absent from the vertical wind spectra, which is consistent with the characteristics of a normal-mode Rossby-gravity wave. Zonal (meridional) momentum flux spectra are mainly positive (negative), and large fluxes are observed in a relatively low-frequency range from (1 day)-1 to (1 h)-1. A case study was performed to investigate vertical profiles of momentum fluxes associated with gravity waves and time mean winds on and around 3 January 2015 when a minor stratospheric warming occurred in the Northern Hemisphere. A significant momentum flux convergence corresponding to an eastward acceleration of 200 m s-1 d-1 was observed before the warming and became stronger after the warming when mean zonal wind weakened. The strong wave forcing roughly accorded with the Coriolis force of mean meridional winds.

  10. Infrequent cavity-forming fluctuations in HPr from Staphylococcus carnosus revealed by pressure- and temperature-dependent tyrosine ring flips

    PubMed Central

    Hattori, Mineyuki; Li, Hua; Yamada, Hiroaki; Akasaka, Kazuyuki; Hengstenberg, Wolfgang; Gronwald, Wolfram; Kalbitzer, Hans Robert

    2004-01-01

    Infrequent structural fluctuations of a globular protein is seldom detected and studied in detail. One tyrosine ring of HPr from Staphylococcus carnosus, an 88-residue phosphocarrier protein with no disulfide bonds, undergoes a very slow ring flip, the pressure and temperature dependence of which is studied in detail using the on-line cell high-pressure nuclear magnetic resonance technique in the pressure range from 3 MPa to 200 MPa and in the temperature range from 257 K to 313 K. The ring of Tyr6 is buried sandwiched between a β-sheet and α-helices (the water-accessible area is less than 0.26 nm2), its hydroxyl proton being involved in an internal hydrogen bond. The ring flip rates101~105 s−1 were determined from the line shape analysis of Hδ1, δ2 and Hɛ1,ɛ2 of Tyr6, giving an activation volume ΔV‡ of 0.044 ± 0.008 nm3 (27 mL mol−1), an activation enthalpy ΔH‡ of 89 ± 10 kJ mol−1, and an activation entropy ΔS‡ of 16 ± 2 JK−1 mol−1. The ΔV‡ and ΔH‡ values for HPr found previously for Tyr and Phe ring flips of BPTI and cytochrome c fall within the range of ΔV‡ of 28 to 51 mL mol−1 and ΔH‡ of 71 to 155 kJ mol−1. The fairly common ΔV‡ and ΔH‡ values are considered to represent the extra space or cavity required for the ring flip and the extra energy required to create a cavity, respectively, in the core part of a globular protein. Nearly complete cold denaturation was found to take place at 200 MPa and 257 K independently from the ring reorientation process. PMID:15557257

  11. Revealing the mechanism of passive transport in lipid bilayers via phonon-mediated nanometre-scale density fluctuations

    DOE PAGES

    Zhernenkov, Mikhail; Bolmatov, Dima; Soloviov, Dmitry; ...

    2016-05-12

    We report the high resolution inelastic x-ray study of the in-plane phonon excitations in dipalmitoyl phosphatidylcholine (DPPC) above and below main transition temperature. In the Lβ' gel phase, we observe high frequency longitudinal phonon mode previously predicted by the molecular dynamics simulations and for the first time, we reveal low frequency weakly dispersive transverse acoustic mode which softens and exhibits a low-frequency phonon gap when the DPPC lipid transitions into the Lα fluid phase. The phonon softening of the high frequency longitudinal excitations and the transformation of the transverse excitations upon the phase transition from the Lβ' to Lα phasemore » is explained within the framework of the phonon theory of liquids. These findings illustrate the importance of the collective dynamics of biomembranes and reveal that hydrocarbon tails can act as an efficient mediator in controlling the passive transport across the bilayer plane.« less

  12. Revealing the mechanism of passive transport in lipid bilayers via phonon-mediated nanometre-scale density fluctuations

    SciTech Connect

    Zhernenkov, Mikhail; Bolmatov, Dima; Soloviov, Dmitry; Zhernenkov, Kirill; Toperverg, Boris P.; Cunsolo, Alessandro; Bosak, Alexey; Cai, Yong

    2016-05-12

    We report the high resolution inelastic x-ray study of the in-plane phonon excitations in dipalmitoyl phosphatidylcholine (DPPC) above and below main transition temperature. In the Lβ' gel phase, we observe high frequency longitudinal phonon mode previously predicted by the molecular dynamics simulations and for the first time, we reveal low frequency weakly dispersive transverse acoustic mode which softens and exhibits a low-frequency phonon gap when the DPPC lipid transitions into the Lα fluid phase. The phonon softening of the high frequency longitudinal excitations and the transformation of the transverse excitations upon the phase transition from the Lβ' to Lα phase is explained within the framework of the phonon theory of liquids. These findings illustrate the importance of the collective dynamics of biomembranes and reveal that hydrocarbon tails can act as an efficient mediator in controlling the passive transport across the bilayer plane.

  13. Temporal Fluctuation in North East Baltic Sea Region Cattle Population Revealed by Mitochondrial and Y-Chromosomal DNA Analyses

    PubMed Central

    Niemi, Marianna; Bläuer, Auli; Iso-Touru, Terhi; Harjula, Janne; Nyström Edmark, Veronica; Rannamäe, Eve; Lõugas, Lembi; Sajantila, Antti; Lidén, Kerstin; Taavitsainen, Jussi-Pekka

    2015-01-01

    Background Ancient DNA analysis offers a way to detect changes in populations over time. To date, most studies of ancient cattle have focused on their domestication in prehistory, while only a limited number of studies have analysed later periods. Conversely, the genetic structure of modern cattle populations is well known given the undertaking of several molecular and population genetic studies. Results Bones and teeth from ancient cattle populations from the North-East Baltic Sea region dated to the Prehistoric (Late Bronze and Iron Age, 5 samples), Medieval (14), and Post-Medieval (26) periods were investigated by sequencing 667 base pairs (bp) from the mitochondrial DNA (mtDNA) and 155 bp of intron 19 in the Y-chromosomal UTY gene. Comparison of maternal (mtDNA haplotypes) genetic diversity in ancient cattle (45 samples) with modern cattle populations in Europe and Asia (2094 samples) revealed 30 ancient mtDNA haplotypes, 24 of which were shared with modern breeds, while 6 were unique to the ancient samples. Of seven Y-chromosomal sequences determined from ancient samples, six were Y2 and one Y1 haplotype. Combined data including Swedish samples from the same periods (64 samples) was compared with the occurrence of Y-chromosomal haplotypes in modern cattle (1614 samples). Conclusions The diversity of haplogroups was highest in the Prehistoric samples, where many haplotypes were unique. The Medieval and Post-Medieval samples also show a high diversity with new haplotypes. Some of these haplotypes have become frequent in modern breeds in the Nordic Countries and North-Western Russia while other haplotypes have remained in only a few local breeds or seem to have been lost. A temporal shift in Y-chromosomal haplotypes from Y2 to Y1 was detected that corresponds with the appearance of new mtDNA haplotypes in the Medieval and Post-Medieval period. This suggests a replacement of the Prehistoric mtDNA and Y chromosomal haplotypes by new types of cattle. PMID:25992976

  14. Symmetry breaking induced by random fluctuations for Bose-Einstein condensates in a double-well trap

    SciTech Connect

    Garnier, J.; Abdullaev, F.Kh.

    2005-03-01

    This paper is devoted to the study of the dynamics of two weakly coupled Bose-Einstein condensates confined in a double-well trap and perturbed by random external forces. The energy diffusion due to random forcing is quantitatively analyzed. The energy distribution is shown to evolve to a stationary distribution which depends on the initial state of the condensate only through the total number of atoms. This loss of memory of the initial conditions allows a simple and complete description of the stationary dynamics of the condensate. In particular, when the number of atoms exceeds a threshold value, the condensate temporarily localizes into one of the wells and jumps into the other well according to a Markovian dynamics. This localization occurs even in the presence of dissipation.

  15. Phase fluctuations of a radio wave in the case of total internal reflection from a randomly inhomogeneous ionosphere

    NASA Astrophysics Data System (ADS)

    Afanasiev, N. T.; Laryunin, O. A.; Markov, V. P.

    2009-10-01

    Based on the geometrical-optics approximation, we propose a method for calculation of statistical moments of the radio-wave phase in the case of total internal reflection from a randomly inhomogeneous ionosphere with a monotonic height profile of regular dielectric permittivity. To take into account the radio-wave scattering at the reflection point in a correct way, we perform analytical transformation of the eikonal equation solution derived in a first approximation of the perturbation method.

  16. Sample-to-sample fluctuations of power spectrum of a random motion in a periodic Sinai model.

    PubMed

    Dean, David S; Iorio, Antonio; Marinari, Enzo; Oshanin, Gleb

    2016-09-01

    The Sinai model of a tracer diffusing in a quenched Brownian potential is a much-studied problem exhibiting a logarithmically slow anomalous diffusion due to the growth of energy barriers with the system size. However, if the potential is random but periodic, the regime of anomalous diffusion crosses over to one of normal diffusion once a tracer has diffused over a few periods of the system. Here we consider a system in which the potential is given by a Brownian bridge on a finite interval (0,L) and then periodically repeated over the whole real line and study the power spectrum S(f) of the diffusive process x(t) in such a potential. We show that for most of realizations of x(t) in a given realization of the potential, the low-frequency behavior is S(f)∼A/f^{2}, i.e., the same as for standard Brownian motion, and the amplitude A is a disorder-dependent random variable with a finite support. Focusing on the statistical properties of this random variable, we determine the moments of A of arbitrary, negative, or positive order k and demonstrate that they exhibit a multifractal dependence on k and a rather unusual dependence on the temperature and on the periodicity L, which are supported by atypical realizations of the periodic disorder. We finally show that the distribution of A has a log-normal left tail and exhibits an essential singularity close to the right edge of the support, which is related to the Lifshitz singularity. Our findings are based both on analytic results and on extensive numerical simulations of the process x(t).

  17. Optically trapped quasi-two-dimensional Bose gases in a random environment: Quantum fluctuations and superfluid density

    SciTech Connect

    Zhou Kezhao; Liang Zhaoxin; Zhang Zhidong; Hu Ying

    2010-10-15

    We investigate a dilute Bose gas confined in a tight one-dimensional (1D) optical lattice plus a superimposed random potential at zero temperature. Accordingly, the ground-state energy, quantum depletion, and superfluid density are calculated. The presence of the lattice introduces a crossover to the quasi-two-dimensional (2D) regime, where we analyze asymptotically the 2D behavior of the system, particularly the effects of disorder. We thereby offer an analytical expression for the ground-state energy of a purely 2D Bose gas in a random potential. The obtained disorder-induced normal fluid density n{sub n} and quantum depletion n{sub d} both exhibit a characteristic 1/ln(1/n{sub 2D}a{sub 2D}{sup 2}) dependence. Their ratio n{sub n}/n{sub d} increases to 2 compared to the familiar 4/3 in lattice-free three-dimensional (3D) geometry, signifying a more pronounced contrast between superfluidity and Bose-Einstein condensation in low dimensions. The conditions for possible experimental realization of our scenario are also proposed.

  18. Revisiting detrended fluctuation analysis

    PubMed Central

    Bryce, R. M.; Sprague, K. B.

    2012-01-01

    Half a century ago Hurst introduced Rescaled Range (R/S) Analysis to study fluctuations in time series. Thousands of works have investigated or applied the original methodology and similar techniques, with Detrended Fluctuation Analysis becoming preferred due to its purported ability to mitigate nonstationaries. We show Detrended Fluctuation Analysis introduces artifacts for nonlinear trends, in contrast to common expectation, and demonstrate that the empirically observed curvature induced is a serious finite-size effect which will always be present. Explicit detrending followed by measurement of the diffusional spread of a signals' associated random walk is preferable, a surprising conclusion given that Detrended Fluctuation Analysis was crafted specifically to replace this approach. The implications are simple yet sweeping: there is no compelling reason to apply Detrended Fluctuation Analysis as it 1) introduces uncontrolled bias; 2) is computationally more expensive than the unbiased estimator; and 3) cannot provide generic or useful protection against nonstationaries. PMID:22419991

  19. Functional Redundancy Patterns Reveal Non-Random Assembly Rules in a Species-Rich Marine Assemblage

    PubMed Central

    Guillemot, Nicolas; Kulbicki, Michel; Chabanet, Pascale; Vigliola, Laurent

    2011-01-01

    The relationship between species and the functional diversity of assemblages is fundamental in ecology because it contains key information on functional redundancy, and functionally redundant ecosystems are thought to be more resilient, resistant and stable. However, this relationship is poorly understood and undocumented for species-rich coastal marine ecosystems. Here, we used underwater visual censuses to examine the patterns of functional redundancy for one of the most diverse vertebrate assemblages, the coral reef fishes of New Caledonia, South Pacific. First, we found that the relationship between functional and species diversity displayed a non-asymptotic power-shaped curve, implying that rare functions and species mainly occur in highly diverse assemblages. Second, we showed that the distribution of species amongst possible functions was significantly different from a random distribution up to a threshold of ∼90 species/transect. Redundancy patterns for each function further revealed that some functions displayed fast rates of increase in redundancy at low species diversity, whereas others were only becoming redundant past a certain threshold. This suggested non-random assembly rules and the existence of some primordial functions that would need to be fulfilled in priority so that coral reef fish assemblages can gain a basic ecological structure. Last, we found little effect of habitat on the shape of the functional-species diversity relationship and on the redundancy of functions, although habitat is known to largely determine assemblage characteristics such as species composition, biomass, and abundance. Our study shows that low functional redundancy is characteristic of this highly diverse fish assemblage, and, therefore, that even species-rich ecosystems such as coral reefs may be vulnerable to the removal of a few keystone species. PMID:22039543

  20. The neural basis of trait self-esteem revealed by the amplitude of low-frequency fluctuations and resting state functional connectivity

    PubMed Central

    Pan, Weigang; Liu, Congcong; Yang, Qian; Gu, Yan; Yin, Shouhang

    2016-01-01

    Self-esteem is an affective, self-evaluation of oneself and has a significant effect on mental and behavioral health. Although research has focused on the neural substrates of self-esteem, little is known about the spontaneous brain activity that is associated with trait self-esteem (TSE) during the resting state. In this study, we used the resting-state functional magnetic resonance imaging (fMRI) signal of the amplitude of low-frequency fluctuations (ALFFs) and resting state functional connectivity (RSFC) to identify TSE-related regions and networks. We found that a higher level of TSE was associated with higher ALFFs in the left ventral medial prefrontal cortex (vmPFC) and lower ALFFs in the left cuneus/lingual gyrus and right lingual gyrus. RSFC analyses revealed that the strengths of functional connectivity between the left vmPFC and bilateral hippocampus were positively correlated with TSE; however, the connections between the left vmPFC and right inferior frontal gyrus and posterior superior temporal sulcus were negatively associated with TSE. Furthermore, the strengths of functional connectivity between the left cuneus/lingual gyrus and right dorsolateral prefrontal cortex and anterior cingulate cortex were positively related to TSE. These findings indicate that TSE is linked to core regions in the default mode network and social cognition network, which is involved in self-referential processing, autobiographical memory and social cognition. PMID:26400859

  1. The neural basis of trait self-esteem revealed by the amplitude of low-frequency fluctuations and resting state functional connectivity.

    PubMed

    Pan, Weigang; Liu, Congcong; Yang, Qian; Gu, Yan; Yin, Shouhang; Chen, Antao

    2016-03-01

    Self-esteem is an affective, self-evaluation of oneself and has a significant effect on mental and behavioral health. Although research has focused on the neural substrates of self-esteem, little is known about the spontaneous brain activity that is associated with trait self-esteem (TSE) during the resting state. In this study, we used the resting-state functional magnetic resonance imaging (fMRI) signal of the amplitude of low-frequency fluctuations (ALFFs) and resting state functional connectivity (RSFC) to identify TSE-related regions and networks. We found that a higher level of TSE was associated with higher ALFFs in the left ventral medial prefrontal cortex (vmPFC) and lower ALFFs in the left cuneus/lingual gyrus and right lingual gyrus. RSFC analyses revealed that the strengths of functional connectivity between the left vmPFC and bilateral hippocampus were positively correlated with TSE; however, the connections between the left vmPFC and right inferior frontal gyrus and posterior superior temporal sulcus were negatively associated with TSE. Furthermore, the strengths of functional connectivity between the left cuneus/lingual gyrus and right dorsolateral prefrontal cortex and anterior cingulate cortex were positively related to TSE. These findings indicate that TSE is linked to core regions in the default mode network and social cognition network, which is involved in self-referential processing, autobiographical memory and social cognition.

  2. Global and System-Specific Resting-State fMRI Fluctuations Are Uncorrelated: Principal Component Analysis Reveals Anti-Correlated Networks

    PubMed Central

    Carbonell, Felix; Bellec, Pierre

    2011-01-01

    Abstract The influence of the global average signal (GAS) on functional-magnetic resonance imaging (fMRI)–based resting-state functional connectivity is a matter of ongoing debate. The global average fluctuations increase the correlation between functional systems beyond the correlation that reflects their specific functional connectivity. Hence, removal of the GAS is a common practice for facilitating the observation of network-specific functional connectivity. This strategy relies on the implicit assumption of a linear-additive model according to which global fluctuations, irrespective of their origin, and network-specific fluctuations are super-positioned. However, removal of the GAS introduces spurious negative correlations between functional systems, bringing into question the validity of previous findings of negative correlations between fluctuations in the default-mode and the task-positive networks. Here we present an alternative method for estimating global fluctuations, immune to the complications associated with the GAS. Principal components analysis was applied to resting-state fMRI time-series. A global-signal effect estimator was defined as the principal component (PC) that correlated best with the GAS. The mean correlation coefficient between our proposed PC-based global effect estimator and the GAS was 0.97±0.05, demonstrating that our estimator successfully approximated the GAS. In 66 out of 68 runs, the PC that showed the highest correlation with the GAS was the first PC. Since PCs are orthogonal, our method provides an estimator of the global fluctuations, which is uncorrelated to the remaining, network-specific fluctuations. Moreover, unlike the regression of the GAS, the regression of the PC-based global effect estimator does not introduce spurious anti-correlations beyond the decrease in seed-based correlation values allowed by the assumed additive model. After regressing this PC-based estimator out of the original time-series, we observed

  3. A flash-drag effect in random motion reveals involvement of preattentive motion processing

    PubMed Central

    Fukiage, Taiki; Whitney, David; Murakami, Ikuya

    2013-01-01

    The flash-drag (FDE) effect refers to the phenomenon in which the position of a stationary flashed object in one location appears shifted in the direction of nearby motion. Over the past decade, it has been debated how bottom-up and top-down processes contribute to this illusion. In this study, we demonstrate that randomly phase-shifting gratings can produce the FDE. In the random motion sequence we used, the FDE inducer (a sinusoidal grating) jumped to a random phase every 125 ms and stood still until the next jump. Because this random sequence could not be tracked attentively, it was impossible for the observer to discern the jump direction at the time of the flash. By sorting the data based on the flash’s onset time relative to each jump time in the random motion sequence, we found that a large FDE with a broad temporal tuning occurred around 50 to 150 ms before the jump and that this effect was not correlated with any other jumps in the past or future. These results suggest that as few as two frames of unpredictable apparent motion can preattentively cause the FDE with a broad temporal tuning. PMID:22080448

  4. A flash-drag effect in random motion reveals involvement of preattentive motion processing.

    PubMed

    Fukiage, Taiki; Whitney, David; Murakami, Ikuya

    2011-11-11

    The flash-drag (FDE) effect refers to the phenomenon in which the position of a stationary flashed object in one location appears shifted in the direction of nearby motion. Over the past decade, it has been debated how bottom-up and top-down processes contribute to this illusion. In this study, we demonstrate that randomly phase-shifting gratings can produce the FDE. In the random motion sequence we used, the FDE inducer (a sinusoidal grating) jumped to a random phase every 125 ms and stood still until the next jump. Because this random sequence could not be tracked attentively, it was impossible for the observer to discern the jump direction at the time of the flash. By sorting the data based on the flash's onset time relative to each jump time in the random motion sequence, we found that a large FDE with a broad temporal tuning occurred around 50 to 150 ms before the jump and that this effect was not correlated with any other jumps in the past or future. These results suggest that as few as two frames of unpredictable apparent motion can preattentively cause the FDE with a broad temporal tuning.

  5. Charge fluctuations and nodeless superconductivity in quasi-one-dimensional Ta4Pd3Te16 revealed by 125Te-NMR and 181Ta-NQR

    NASA Astrophysics Data System (ADS)

    Li, Z.; Jiao, W. H.; Cao, G. H.; Zheng, Guo-qing

    2016-11-01

    We report 125Te nuclear magnetic resonance and 181Ta nuclear quadrupole resonance studies on single-crystal Ta4Pd3Te16 , which has a quasi-one-dimensional structure and superconducts below Tc=4.3 K. 181Ta with spin I =7 /2 is sensitive to quadrupole interactions, while 125Te with spin I =1 /2 can only relax by magnetic interactions. By comparing the spin-lattice relaxation rate (1 /T1 ) of 181Ta and 125Te, we found that electric-field-gradient (EFG) fluctuations develop below 80 K. The EFG fluctuations are enhanced with decreasing temperature due to the fluctuations of a charge density wave that sets in at TCDW=20 K, below which the spectra are broadened and 1 /T1T drops sharply. In the superconducting state, 1 /T1 shows a Hebel-Slichter coherence peak just below Tc for 125Te, indicating that Ta4Pd3Te16 is a full-gap superconductor without nodes in the gap function. The coherence peak is absent in the 1 /T1 of 181Ta due to the strong EFG fluctuations.

  6. Solution NMR of MPS-1 reveals a random coil cytosolic domain structure.

    PubMed

    Li, Pan; Shi, Pan; Lai, Chaohua; Li, Juan; Zheng, Yuanyuan; Xiong, Ying; Zhang, Longhua; Tian, Changlin

    2014-01-01

    Caenorhabditis elegans MPS1 is a single transmembrane helical auxiliary subunit that co-localizes with the voltage-gated potassium channel KVS1 in the nematode nervous system. MPS-1 shares high homology with KCNE (potassium voltage-gated channel subfamily E member) auxiliary subunits, and its cytosolic domain was reported to have a serine/threonine kinase activity that modulates KVS1 channel function via phosphorylation. In this study, NMR spectroscopy indicated that the full length and truncated MPS-1 cytosolic domain (134-256) in the presence or absence of n-dodecylphosphocholine detergent micelles adopted a highly flexible random coil secondary structure. In contrast, protein kinases usually adopt a stable folded conformation in order to implement substrate recognition and phosphoryl transfer. The highly flexible random coil secondary structure suggests that MPS-1 in the free state is unstructured but may require a substrate or binding partner to adopt stable structure required for serine/threonine kinase activity.

  7. Solution NMR of MPS-1 Reveals a Random Coil Cytosolic Domain Structure

    PubMed Central

    Lai, Chaohua; Li, Juan; Zheng, Yuanyuan; Xiong, Ying; Zhang, Longhua; Tian, Changlin

    2014-01-01

    Caenorhabditis elegans MPS1 is a single transmembrane helical auxiliary subunit that co-localizes with the voltage-gated potassium channel KVS1 in the nematode nervous system. MPS-1 shares high homology with KCNE (potassium voltage-gated channel subfamily E member) auxiliary subunits, and its cytosolic domain was reported to have a serine/threonine kinase activity that modulates KVS1 channel function via phosphorylation. In this study, NMR spectroscopy indicated that the full length and truncated MPS-1 cytosolic domain (134–256) in the presence or absence of n-dodecylphosphocholine detergent micelles adopted a highly flexible random coil secondary structure. In contrast, protein kinases usually adopt a stable folded conformation in order to implement substrate recognition and phosphoryl transfer. The highly flexible random coil secondary structure suggests that MPS-1 in the free state is unstructured but may require a substrate or binding partner to adopt stable structure required for serine/threonine kinase activity. PMID:25347290

  8. Single-cell RNA-seq reveals dynamic, random monoallelic gene expression in mammalian cells.

    PubMed

    Deng, Qiaolin; Ramsköld, Daniel; Reinius, Björn; Sandberg, Rickard

    2014-01-10

    Expression from both alleles is generally observed in analyses of diploid cell populations, but studies addressing allelic expression patterns genome-wide in single cells are lacking. Here, we present global analyses of allelic expression across individual cells of mouse preimplantation embryos of mixed background (CAST/EiJ × C57BL/6J). We discovered abundant (12 to 24%) monoallelic expression of autosomal genes and that expression of the two alleles occurs independently. The monoallelic expression appeared random and dynamic because there was considerable variation among closely related embryonic cells. Similar patterns of monoallelic expression were observed in mature cells. Our allelic expression analysis also demonstrates the de novo inactivation of the paternal X chromosome. We conclude that independent and stochastic allelic transcription generates abundant random monoallelic expression in the mammalian cell.

  9. A Numerical Study of the Regimes of Weak Fluctuation Theory for Ocean Acoustic Propagation through Random Internal Wave Sound Speed Fields

    DTIC Science & Technology

    2007-03-01

    wave spectrum and the adaptation of the Rytov method to the ocean by Munk and Zachariasen , the prediction of ocean acoustic fluctuations were on a...fluctuation spectrum had the GM (Garrett-Munk) form, they computed the intensity spectrum using the Rytov theory of Munk and Zachariasen (1976), and...1976), Kenneth M. Watson (1979), Fredrik Zachariasen (1976), B.J. Uscinski, T.E. Ewart (1998), John A. Colosi (2007), and many other researchers from

  10. Inverse-power-law behavior of cellular motility reveals stromal-epithelial cell interactions in 3D co-culture by OCT fluctuation spectroscopy.

    PubMed

    Oldenburg, Amy L; Yu, Xiao; Gilliss, Thomas; Alabi, Oluwafemi; Taylor, Russell M; Troester, Melissa A

    2015-10-20

    The progression of breast cancer is known to be affected by stromal cells within the local microenvironment. Here we study the effect of stromal fibroblasts on the in-place motions (motility) of mammary epithelial cells within organoids in 3D co-culture, inferred from the speckle fluctuation spectrum using optical coherence tomography (OCT). In contrast to Brownian motion, mammary cell motions exhibit an inverse power-law fluctuation spectrum. We introduce two complementary metrics for quantifying fluctuation spectra: the power-law exponent and a novel definition of the motility amplitude, both of which are signal- and position-independent. We find that the power-law exponent and motility amplitude are positively (p<0.001) and negatively (p<0.01) correlated with the density of stromal cells in 3D co-culture, respectively. We also show how the hyperspectral data can be visualized using these metrics to observe heterogeneity within organoids. This constitutes a simple and powerful tool for detecting and imaging cellular functional changes with OCT.

  11. Inverse-power-law behavior of cellular motility reveals stromal–epithelial cell interactions in 3D co-culture by OCT fluctuation spectroscopy

    PubMed Central

    Oldenburg, Amy L.; Yu, Xiao; Gilliss, Thomas; Alabi, Oluwafemi; Taylor, Russell M.; Troester, Melissa A.

    2015-01-01

    The progression of breast cancer is known to be affected by stromal cells within the local microenvironment. Here we study the effect of stromal fibroblasts on the in-place motions (motility) of mammary epithelial cells within organoids in 3D co-culture, inferred from the speckle fluctuation spectrum using optical coherence tomography (OCT). In contrast to Brownian motion, mammary cell motions exhibit an inverse power-law fluctuation spectrum. We introduce two complementary metrics for quantifying fluctuation spectra: the power-law exponent and a novel definition of the motility amplitude, both of which are signal- and position-independent. We find that the power-law exponent and motility amplitude are positively (p<0.001) and negatively (p<0.01) correlated with the density of stromal cells in 3D co-culture, respectively. We also show how the hyperspectral data can be visualized using these metrics to observe heterogeneity within organoids. This constitutes a simple and powerful tool for detecting and imaging cellular functional changes with OCT. PMID:26973862

  12. Molecular diversity in the genus Nicotiana as revealed by randomly amplified polymorphic DNA.

    PubMed

    Siva Raju, K; Sheshumadhav, M; Murthy, T G K

    2008-10-01

    The genus Nicotiana consists of 64 recognized species of which, only two species, tabacum and rustica are cultivated extensively. Wild Nicotiana species are storehouses of genes for several diseases and pests, besides genes for several important phytochemicals and quality traits, which are not present in cultivated varieties. Randomly amplified polymorphic DNA (RAPD) analysis was used to determine the degree of genetic variation in the genus Nicotiana and to develop species specific markers. Twenty two species and two interspecific hybrids were analyzed by using 18 random decamer primers. Genetic polymorphism abounds among the wild species of genus Nicotiana (99.5 %) as evidenced by the high degree of polymorphism in RAPD profiles. The pairwise similarity measures in the species of subgenus Rustica was 0.252 whereas in the subgenus Tabacum was 0.189, suggesting that there was significant diversity among the species of these subgenera. In the species of subgenus Petunioides, the range of pairwise similarity measures was 0.128 to 0.941. The clustering pattern coincided with the traditional classification of Nicotiana species. All the primers generated specific bands in the various species. Thirty six species-specific markers identified in the present study will be useful in interspecific breeding programs.

  13. Finding Order in Randomness: Single-Molecule Studies Reveal Stochastic RNA Processing | Center for Cancer Research

    Cancer.gov

    Producing a functional eukaryotic messenger RNA (mRNA) requires the coordinated activity of several large protein complexes to initiate transcription, elongate nascent transcripts, splice together exons, and cleave and polyadenylate the 3’ end. Kinetic competition between these various processes has been proposed to regulate mRNA maturation, but this model could lead to multiple, randomly determined, or stochastic, pathways or outcomes. Regulatory checkpoints have been suggested as a means of ensuring quality control. However, current methods have been unable to tease apart the contributions of these processes at a single gene or on a time scale that could provide mechanistic insight. To begin to investigate the kinetic relationship between transcription and splicing, Daniel Larson, Ph.D., of CCR’s Laboratory of Receptor Biology and Gene Expression, and his colleagues employed a single-molecule RNA imaging approach to monitor production and processing of a human β-globin reporter gene in living cells.

  14. Thermal Non-Equilibrium Revealed by Periodic Pulses of Random Amplitudes in Solar Coronal Loops

    NASA Astrophysics Data System (ADS)

    Auchère, Frédéric

    2016-10-01

    We recently detected variations in extreme ultraviolet intensity in coronal loops repeating with periods of several hours. Models of loops including stratified and quasi-steady heating predict the development of a state of thermal non-equilibrium (TNE): cycles of evaporative upflows at the footpoints followed by falling condensations at the apex. Based on Fourier and wavelet analysis, we demonstrate that the observed periodic signals are indeed not signatures of vibrational modes. Instead, superimposed on the power law expected from the stochastic background emission, the power spectra of the time series exhibit the discrete harmonics and continua expected from periodic trains of pulses of random amplitudes. These characteristics reinforce our earlier interpretation of these pulsations as being aborted TNE cycles.

  15. Thermal Non-equilibrium Revealed by Periodic Pulses of Random Amplitudes in Solar Coronal Loops

    NASA Astrophysics Data System (ADS)

    Auchère, F.; Froment, C.; Bocchialini, K.; Buchlin, E.; Solomon, J.

    2016-08-01

    We recently detected variations in extreme ultraviolet intensity in coronal loops repeating with periods of several hours. Models of loops including stratified and quasi-steady heating predict the development of a state of thermal non-equilibrium (TNE): cycles of evaporative upflows at the footpoints followed by falling condensations at the apex. Based on Fourier and wavelet analysis, we demonstrate that the observed periodic signals are indeed not signatures of vibrational modes. Instead, superimposed on the power law expected from the stochastic background emission, the power spectra of the time series exhibit the discrete harmonics and continua expected from periodic trains of pulses of random amplitudes. These characteristics reinforce our earlier interpretation of these pulsations as being aborted TNE cycles.

  16. Random transposon mutagenesis of the Saccharopolyspora erythraea genome reveals additional genes influencing erythromycin biosynthesis

    PubMed Central

    Fedashchin, Andrij; Cernota, William H.; Gonzalez, Melissa C.; Leach, Benjamin I.; Kwan, Noelle; Wesley, Roy K.; Weber, J. Mark

    2015-01-01

    A single cycle of strain improvement was performed in Saccharopolyspora erythraea mutB and 15 genotypes influencing erythromycin production were found. Genotypes generated by transposon mutagenesis appeared in the screen at a frequency of ∼3%. Mutations affecting central metabolism and regulatory genes were found, as well as hydrolases, peptidases, glycosyl transferases and unknown genes. Only one mutant retained high erythromycin production when scaled-up from micro-agar plug fermentations to shake flasks. This mutant had a knockout of the cwh1 gene (SACE_1598), encoding a cell-wall-associated hydrolase. The cwh1 knockout produced visible growth and morphological defects on solid medium. This study demonstrated that random transposon mutagenesis uncovers strain improvement-related genes potentially useful for strain engineering. PMID:26468041

  17. Fluctuating Selection in the Moran

    PubMed Central

    Dean, Antony M.; Lehman, Clarence; Yi, Xiao

    2017-01-01

    Contrary to classical population genetics theory, experiments demonstrate that fluctuating selection can protect a haploid polymorphism in the absence of frequency dependent effects on fitness. Using forward simulations with the Moran model, we confirm our analytical results showing that a fluctuating selection regime, with a mean selection coefficient of zero, promotes polymorphism. We find that increases in heterozygosity over neutral expectations are especially pronounced when fluctuations are rapid, mutation is weak, the population size is large, and the variance in selection is big. Lowering the frequency of fluctuations makes selection more directional, and so heterozygosity declines. We also show that fluctuating selection raises dn/ds ratios for polymorphism, not only by sweeping selected alleles into the population, but also by purging the neutral variants of selected alleles as they undergo repeated bottlenecks. Our analysis shows that randomly fluctuating selection increases the rate of evolution by increasing the probability of fixation. The impact is especially noticeable when the selection is strong and mutation is weak. Simulations show the increase in the rate of evolution declines as the rate of new mutations entering the population increases, an effect attributable to clonal interference. Intriguingly, fluctuating selection increases the dn/ds ratios for divergence more than for polymorphism, a pattern commonly seen in comparative genomics. Our model, which extends the classical neutral model of molecular evolution by incorporating random fluctuations in selection, accommodates a wide variety of observations, both neutral and selected, with economy. PMID:28108586

  18. Universal fluctuations of growing interfaces: evidence in turbulent liquid crystals.

    PubMed

    Takeuchi, Kazumasa A; Sano, Masaki

    2010-06-11

    We investigate growing interfaces of topological-defect turbulence in the electroconvection of nematic liquid crystals. The interfaces exhibit self-affine roughening characterized by both spatial and temporal scaling laws of the Kardar-Parisi-Zhang theory in 1+1 dimensions. Moreover, we reveal that the distribution and the two-point correlation of the interface fluctuations are universal ones governed by the largest eigenvalue of random matrices. This provides quantitative experimental evidence of the universality prescribing detailed information of scale-invariant fluctuations.

  19. Selection of DNA binding sites for zinc fingers using rationally randomized DNA reveals coded interactions.

    PubMed Central

    Choo, Y; Klug, A

    1994-01-01

    In the preceding paper [Choo, Y. & Klug, A. (1994) Proc. Natl. Acad. Sci. USA 91, 11163-11167], we showed how selections from a library of zinc fingers displayed on phage yielded fingers able to bind to a number of DNA triplets. Here, we describe a technique to deal efficiently with the converse problem--namely, the selection of a DNA binding site for a given zinc finger. This is done by screening against libraries of DNA triplet binding sites randomized in two positions but having one base fixed in the third position. The technique is applied here to determine the specificity of fingers previously selected by phage display. We find that some of these fingers are able to specify a unique base in each position of the cognate triplet. This is further illustrated by examples of fingers which can discriminate between closely related triplets as measured by their respective equilibrium dissociation constants. Comparing the amino acid sequences of fingers which specify a particular base in a triplet, we infer that in most instances, sequence-specific binding of zinc fingers to DNA can be achieved by using a small set of amino acid-nucleotide base contacts amenable to a code. Images PMID:7972028

  20. Magnetic fluctuations in n-type high-Tc superconductors reveal breakdown of fermiology:Experiments and Fermi-liquid/RPA calculations

    SciTech Connect

    Krueger, S.D.

    2010-03-02

    By combining experimental measurements of the quasiparticle and dynamical magnetic properties of optimally electron-doped Pr{sub 0.88}LaCe{sub 0.12}CuO{sub 4} with theoretical calculations, we demonstrate that the conventional fermiology approach cannot possibly account for the magnetic fluctuations in these materials. In particular, we perform tunneling experiments on the very same sample for which a dynamical magnetic resonance has been reported recently and use photoemission data by others on a similar sample to characterize the fermionic quasiparticle excitations in great detail. We subsequently use this information to calculate the magnetic response within the conventional fermiology framework as applied in a large body of work for the hole-doped superconductors to find a profound disagreement between the theoretical expectations and the measurements: this approach predicts a steplike feature rather than a sharp resonance peak, it underestimates the intensity of the resonance by an order of magnitude, it suggests an unreasonable temperature dependence of the resonance, and most severely, it predicts that most of the spectral weight resides in incommensurate wings which are a key feature of the hole-doped cuprates but have never been observed in the electron-doped counterparts. Our findings strongly suggest that the magnetic fluctuations reflect the quantum-mechanical competition between antiferromagnetic and superconducting orders.

  1. Fluctuation effects in grain growth

    NASA Astrophysics Data System (ADS)

    Kim, Seong Gyoon; Park, Yong Bum

    2016-08-01

    In this study, we attempted to clarify the roles of fluctuation effects in grain growth. To capture the persistent nature in both space and time of fluctuations due to variations in the local surroundings of individual grains, we developed a local mean-field model. The fluctuation strength in this model is arbitrarily controlled by employing an artificial number, n , of nearest neighbor grains. Large-scale numerical computations of the model for various n values and initial GSDs were carried out to follow transient behaviors and determine the steady states. This study reveals that, in the classical mean-field model with no fluctuation effects, the steady state is not unique but is strongly dependent upon the initial GSD. However, a small fluctuation drives the mean-field model to reach the Hillert solution, independent of the fluctuation strength and initial GSD, as long as the fluctuation strength is sufficiently small. On the other hand, when the fluctuation is sufficiently strong, the fluctuation pushes the steady state of the mean-field model out of the Hillert solution, and its strength determines a unique steady state independent of the initial GSD. The strong fluctuation makes the GSD more symmetric than the Hillert distribution. Computations designed to mimic actual 2 and 3D grain growth were carried out by taking the number of nearest neighbors of each grain as a function of the scaled grain size. The resultant GSDs in two and three dimensions were compared with the direct simulations of ideal grain growth.

  2. Directed random walks and constraint programming reveal active pathways in hepatocyte growth factor signaling.

    PubMed

    Kittas, Aristotelis; Delobelle, Aurélien; Schmitt, Sabrina; Breuhahn, Kai; Guziolowski, Carito; Grabe, Niels

    2016-01-01

    An effective means to analyze mRNA expression data is to take advantage of established knowledge from pathway databases, using methods such as pathway-enrichment analyses. However, pathway databases are not case-specific and expression data could be used to infer gene-regulation patterns in the context of specific pathways. In addition, canonical pathways may not always describe the signaling mechanisms properly, because interactions can frequently occur between genes in different pathways. Relatively few methods have been proposed to date for generating and analyzing such networks, preserving the causality between gene interactions and reasoning over the qualitative logic of regulatory effects. We present an algorithm (MCWalk) integrated with a logic programming approach, to discover subgraphs in large-scale signaling networks by random walks in a fully automated pipeline. As an exemplary application, we uncover the signal transduction mechanisms in a gene interaction network describing hepatocyte growth factor-stimulated cell migration and proliferation from gene-expression measured with microarray and RT-qPCR using in-house perturbation experiments in a keratinocyte-fibroblast co-culture. The resulting subgraphs illustrate possible associations of hepatocyte growth factor receptor c-Met nodes, differentially expressed genes and cellular states. Using perturbation experiments and Answer Set programming, we are able to select those which are more consistent with the experimental data. We discover key regulator nodes by measuring the frequency with which they are traversed when connecting signaling between receptors and significantly regulated genes and predict their expression-shift consistently with the measured data. The Java implementation of MCWalk is publicly available under the MIT license at: https://bitbucket.org/akittas/biosubg. © 2015 FEBS.

  3. Anisotropic phase diagram and spin fluctuations of the hyperkagome magnet Gd3Ga5O12 as revealed by sound velocity measurements

    NASA Astrophysics Data System (ADS)

    Rousseau, Alexandre; Parent, Jean-Michel; Quilliam, Jeffrey A.

    2017-08-01

    Sound velocity and attenuation measurements on the frustrated garnet material Gd3Ga5O12 (GGG) are presented as a function of field and temperature, with two different magnetic field orientations: [100 ] and [110 ] . We demonstrate that the phase diagram is highly anisotropic, with two distinct field-induced ordered phases for H ||[110 ] and only one for H ||[100 ] . Extensive lattice softening is found to occur at low fields, which can be associated with spin fluctuations. However, deep within the spin liquid phase a low-temperature stiffening of the lattice and reduced attenuation provide evidence for a spin gap which may be related to short-range antiferromagnetic correlations over minimal ten-spin loops.

  4. A model of gene expression based on random dynamical systems reveals modularity properties of gene regulatory networks.

    PubMed

    Antoneli, Fernando; Ferreira, Renata C; Briones, Marcelo R S

    2016-06-01

    Here we propose a new approach to modeling gene expression based on the theory of random dynamical systems (RDS) that provides a general coupling prescription between the nodes of any given regulatory network given the dynamics of each node is modeled by a RDS. The main virtues of this approach are the following: (i) it provides a natural way to obtain arbitrarily large networks by coupling together simple basic pieces, thus revealing the modularity of regulatory networks; (ii) the assumptions about the stochastic processes used in the modeling are fairly general, in the sense that the only requirement is stationarity; (iii) there is a well developed mathematical theory, which is a blend of smooth dynamical systems theory, ergodic theory and stochastic analysis that allows one to extract relevant dynamical and statistical information without solving the system; (iv) one may obtain the classical rate equations form the corresponding stochastic version by averaging the dynamic random variables (small noise limit). It is important to emphasize that unlike the deterministic case, where coupling two equations is a trivial matter, coupling two RDS is non-trivial, specially in our case, where the coupling is performed between a state variable of one gene and the switching stochastic process of another gene and, hence, it is not a priori true that the resulting coupled system will satisfy the definition of a random dynamical system. We shall provide the necessary arguments that ensure that our coupling prescription does indeed furnish a coupled regulatory network of random dynamical systems. Finally, the fact that classical rate equations are the small noise limit of our stochastic model ensures that any validation or prediction made on the basis of the classical theory is also a validation or prediction of our model. We illustrate our framework with some simple examples of single-gene system and network motifs.

  5. Proteomics Analysis with a Nano Random Forest Approach Reveals Novel Functional Interactions Regulated by SMC Complexes on Mitotic Chromosomes*

    PubMed Central

    Ohta, Shinya; Montaño-Gutierrez, Luis F.; de Lima Alves, Flavia; Ogawa, Hiromi; Toramoto, Iyo; Sato, Nobuko; Morrison, Ciaran G.; Takeda, Shunichi; Hudson, Damien F.; Earnshaw, William C.

    2016-01-01

    Packaging of DNA into condensed chromosomes during mitosis is essential for the faithful segregation of the genome into daughter nuclei. Although the structure and composition of mitotic chromosomes have been studied for over 30 years, these aspects are yet to be fully elucidated. Here, we used stable isotope labeling with amino acids in cell culture to compare the proteomes of mitotic chromosomes isolated from cell lines harboring conditional knockouts of members of the condensin (SMC2, CAP-H, CAP-D3), cohesin (Scc1/Rad21), and SMC5/6 (SMC5) complexes. Our analysis revealed that these complexes associate with chromosomes independently of each other, with the SMC5/6 complex showing no significant dependence on any other chromosomal proteins during mitosis. To identify subtle relationships between chromosomal proteins, we employed a nano Random Forest (nanoRF) approach to detect protein complexes and the relationships between them. Our nanoRF results suggested that as few as 113 of 5058 detected chromosomal proteins are functionally linked to chromosome structure and segregation. Furthermore, nanoRF data revealed 23 proteins that were not previously suspected to have functional interactions with complexes playing important roles in mitosis. Subsequent small-interfering-RNA-based validation and localization tracking by green fluorescent protein-tagging highlighted novel candidates that might play significant roles in mitotic progression. PMID:27231315

  6. Statistical interpretation of traveltime fluctuations

    NASA Astrophysics Data System (ADS)

    Roth, Michael

    1997-02-01

    A ray-theoretical relation between the autocorrelation functions of traveltime and slowness fluctuations is established for recording profiles with arbitrary angles to the propagation direction of a plane wave. From this relation follows that the variance of traveltime fluctuations is independent of the profile orientation and proportional to the variance, ɛ2, of slowness fluctuations, to the correlation distance, a, and to the propagation distance L. The halfwidth of the autocorrelation function of traveltime fluctuations is proportional to a and decreases with increasing profile angle. This relationship allows us to estimate the statistical parameters ɛ and a from observed traveltime fluctuations. Numerical experiments for spatial isotropic random media characterized by a Gaussian autocorrelation function show that the statistical parameters can be reproduced successfully if L/a ≤ 10 . For larger L/a the correlation distance is overestimated and the standard deviation is underestimated. However, the results of the numerical experiments provide empirical factors to correct for these effects. The theory is applied to observed traveltime fluctuations of the Pg phase on a profile of the BABEL project. For the upper crust east of Øland (Sweden) slowness fluctuations with standard deviation ɛ = 2.2-5% and correlation distance a = 330-600 m are found.

  7. The Effect of Pleistocene Climate Fluctuations on Distribution of European Abalone (Haliotis tuberculata), Revealed by Combined Mitochondrial and Nuclear Marker Analyses.

    PubMed

    Roussel, Valérie; Van Wormhoudt, Alain

    2017-04-01

    The genetic differentiation among the populations of the European abalone Haliotis tuberculata was investigated using different markers to better understand the evolutionary history and exchanges between populations. Three markers were used: mitochondrial cytochrome oxidase I (COI), the sperm lysin nuclear gene, and eight nuclear microsatellites. These markers present different characteristics concerning mutation rate and inheritance, which provided complementary information about abalone history and gene diversity. Genetic diversity and relationships among subspecies were calculated from a sample of approximately 500 individuals, collected from 17 different locations in the north-eastern Atlantic Ocean, Macaronesia, and Mediterranean Sea. COI marker was used to explore the phylogeny of the species with a network analysis and two phylogenetic methods. The analysis revealed 18 major haplotypes grouped into two distinct clades with a pairwise sequence divergence up to 3.5 %. These clades do not correspond to subspecies but revealed many contacts along Atlantic coast during the Pleistocene interglaciations. The sperm lysin gene analysis separated two different subtaxa: one associated to Macaronesian islands, and the other to all other populations. Moreover, a small population of the northern subtaxon was isolated in the Adriatic Sea-probably before the separation of the two lineages-and evolved independently. Microsatellites were analyzed by different genetics methods, including the Bayesian clustering method and migration patterns analysis. It revealed genetically distinct microsatellite patterns among populations from Mediterranean Sea, Brittany and Normandy, Morocco, and Canary and Balearic islands. Gene flow is asymmetric among the regions; the Azores and the Canary Islands are particularly isolated and have low effective population sizes. Our results support the hypothesis that climate changes since the Pleistocene glaciations have played a major role in the

  8. Random cascade model in the limit of infinite integral scale as the exponential of a nonstationary 1/f noise: Application to volatility fluctuations in stock markets

    NASA Astrophysics Data System (ADS)

    Muzy, Jean-François; Baïle, Rachel; Bacry, Emmanuel

    2013-04-01

    In this paper we propose a new model for volatility fluctuations in financial time series. This model relies on a nonstationary Gaussian process that exhibits aging behavior. It turns out that its properties, over any finite time interval, are very close to continuous cascade models. These latter models are indeed well known to reproduce faithfully the main stylized facts of financial time series. However, it involves a large-scale parameter (the so-called “integral scale” where the cascade is initiated) that is hard to interpret in finance. Moreover, the empirical value of the integral scale is in general deeply correlated to the overall length of the sample. This feature is precisely predicted by our model, which, as illustrated by various examples from daily stock index data, quantitatively reproduces the empirical observations.

  9. Fluctuations in polymer translocation

    NASA Astrophysics Data System (ADS)

    Krapivsky, P. L.; Mallick, K.

    2010-07-01

    We investigate a model of chaperone-assisted polymer translocation through a nanopore in a membrane. Translocation is driven by irreversible random sequential absorption of chaperone proteins that bind to the polymer on one side of the membrane. The proteins are larger than the pore and hence the backward motion of the polymer is inhibited. This mechanism rectifies Brownian fluctuations and results in an effective force that drags the polymer in a preferred direction. The translocated polymer undergoes an effective biased random walk and we compute the corresponding diffusion constant. Our methods allow us to determine the large deviation function which, in addition to velocity and diffusion constant, contains the entire statistics of the translocated length.

  10. Quantifying economic fluctuations

    NASA Astrophysics Data System (ADS)

    Stanley, H. Eugene; Nunes Amaral, Luis A.; Gabaix, Xavier; Gopikrishnan, Parameswaran; Plerou, Vasiliki

    2001-12-01

    This manuscript is a brief summary of a talk designed to address the question of whether two of the pillars of the field of phase transitions and critical phenomena-scale invariance and universality-can be useful in guiding research on interpreting empirical data on economic fluctuations. Using this conceptual framework as a guide, we empirically quantify the relation between trading activity-measured by the number of transactions N-and the price change G( t) for a given stock, over a time interval [ t, t+Δ t]. We relate the time-dependent standard deviation of price changes-volatility-to two microscopic quantities: the number of transactions N( t) in Δ t and the variance W2( t) of the price changes for all transactions in Δ t. We find that the long-ranged volatility correlations are largely due to those of N. We then argue that the tail-exponent of the distribution of N is insufficient to account for the tail-exponent of P{ G> x}. Since N and W display only weak inter-dependency, our results show that the fat tails of the distribution P{ G> x} arises from W. Finally, we review recent work on quantifying collective behavior among stocks by applying the conceptual framework of random matrix theory (RMT). RMT makes predictions for “universal” properties that do not depend on the interactions between the elements comprising the system, and deviations from RMT provide clues regarding system-specific properties. We compare the statistics of the cross-correlation matrix C-whose elements Cij are the correlation coefficients of price fluctuations of stock i and j-against a random matrix having the same symmetry properties. It is found that RMT methods can distinguish random and non-random parts of C. The non-random part of C which deviates from RMT results, provides information regarding genuine collective behavior among stocks. We also discuss results that are reminiscent of phase transitions in spin systems, where the divergent behavior of the response function at

  11. Random amplification of polymorphic DNA reveals serotype-specific clonal clusters among enterotoxigenic Escherichia coli strains isolated from humans.

    PubMed Central

    Pacheco, A B; Guth, B E; Soares, K C; Nishimura, L; de Almeida, D F; Ferreira, L C

    1997-01-01

    The genetic diversity of 47 enterotoxigenic Escherichia coli (ETEC) strains of serotypes O6:H16, O27:H7, O29:H21, O128ac:H12, and O153:H45, previously isolated from diarrheic patients in Brazil over a period of 15 years, was investigated by random amplification of polymorphic DNA (RAPD). Informative band arrays were obtained with three 10-mer primers with G+C contents of 50, 60, and 70%. Based on the combination of the band profiles generated by the three primers 22 RAPD types were detected, and 5 major clonal clusters, each one with at least 80% identical bands, were established. The clonal clusters corresponded to strains having the same serotype which, in most cases, also had the same virulence factors (colonization factors and toxin types) and outer membrane protein and lipopolysaccharide sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles. The results suggested a correlation between phenotypic properties and genetic relatedness of ETEC isolates of human origin and indicated that a reduced number of clonally related strains are found in areas of ETEC endemicity in Brazil. Moreover, the RAPD technique revealed intraserotype-specific variations, undetectable by the combination of several phenotypic typing methods, among the ETEC strains analyzed. These results show that RAPD typing represents a useful tool for population genetics as well as for epidemiological studies of ETEC. PMID:9163473

  12. Demographic and random amplified polymorphic DNA analyses reveal high levels of genetic diversity in a clonal violet.

    PubMed

    Auge, H; Neuffer, B; Erlinghagen, F; Grupe, R; Brandl, R

    2001-07-01

    We performed demographic and molecular investigations on woodland populations of the clonal herb Viola riviniana in central Germany. We investigated the pattern of seedling recruitment, the amount of genotypic (clonal) variation and the partitioning of genetic variation among and within populations. Our demographic study was carried out in six violet populations of different ages and habitat conditions. It revealed that repeated seedling recruitment takes place in all of these populations, and that clonal propagation is accompanied by high ramet mortality. Our molecular investigations were performed on a subset of three of these six violet populations. Random amplified polymorphic DNA analyses using six primers yielded 45 scorable bands that were used to identify multilocus genotypes, i.e. putative clones. Consistent with our demographic results and independent of population age, we found a large genotypic diversity with a mean proportion of distinguishable genotypes of 0.93 and a mean Simpson's diversity index of 0.99. Using AMOVA we found a strong genetic differentiation among these violet populations with a PhiST value of 0.41. We suggest that a high selfing rate, limited gene flow due to short seed dispersal distances and drift due to founder effects are responsible for this pattern. Although Viola riviniana is a clonal plant, traits associated with sexual reproduction rather than clonality per se are moulding the pattern of genetic variation in this species.

  13. Genetic analysis of Apuleia leiocarpa as revealed by random amplified polymorphic DNA markers: prospects for population genetic studies.

    PubMed

    Lencina, K H; Konzen, E R; Tsai, S M; Bisognin, D A

    2016-12-19

    Apuleia leiocarpa (Vogel) J.F. MacBride is a hardwood species native to South America, which is at serious risk of extinction. Therefore, it is of prime importance to examine the genetic diversity of this species, information required for developing conservation, sustainable management, and breeding strategies. Although scarcely used in recent years, random amplified polymorphic DNA markers are useful resources for the analysis of genetic diversity and structure of tree species. This study represents the first genetic analysis based on DNA markers in A. leiocarpa that aimed to investigate the levels of polymorphism and to select markers for the precise characterization of its genetic structure. We adapted the original DNA extraction protocol based on cetyltrimethyl ammonium bromide, and describe a simple procedure that can be used to obtain high-quality samples from leaf tissues of this tree. Eighteen primers were selected, revealing 92 bands, from which 75 were polymorphic and 61 were sufficient to represent the overall genetic structure of the population without compromising the precision of the analysis. Some fragments were conserved among individuals, which can be sequenced and used to analyze nucleotide diversity parameters through a wider set of A. leiocarpa individuals and populations. The individuals were separated into 11 distinct groups with variable levels of genetic diversity, which is important for selecting desirable genotypes and for the development of a conservation and sustainable management program. Our results are of prime importance for further investigations concerning the genetic characterization of this important, but vulnerable species.

  14. Light incoherence due to background space fluctuations

    NASA Astrophysics Data System (ADS)

    Maziashvili, Michael

    2016-12-01

    Working by analogy, we use the description of light fluctuations due to random collisions of the radiating atoms to figure out why the reduction of the coherence for light propagating a cosmological distance in the fluctuating background space is negligibly small to be observed by the stellar interferometry.

  15. The importance of fluctuations in fluid mixing

    PubMed Central

    Kadau, Kai; Rosenblatt, Charles; Barber, John L.; Germann, Timothy C.; Huang, Zhibin; Carlès, Pierre; Alder, Berni J.

    2007-01-01

    A ubiquitous example of fluid mixing is the Rayleigh–Taylor instability, in which a heavy fluid initially sits atop a light fluid in a gravitational field. The subsequent development of the unstable interface between the two fluids is marked by several stages. At first, each interface mode grows exponentially with time before transitioning to a nonlinear regime characterized by more complex hydrodynamic mixing. Unfortunately, traditional continuum modeling of this process has generally been in poor agreement with experiment. Here, we indicate that the natural, random fluctuations of the flow field present in any fluid, which are neglected in continuum models, can lead to qualitatively and quantitatively better agreement with experiment. We performed billion-particle atomistic simulations and magnetic levitation experiments with unprecedented control of initial interface conditions. A comparison between our simulations and experiments reveals good agreement in terms of the growth rate of the mixing front as well as the new observation of droplet breakup at later times. These results improve our understanding of many fluid processes, including interface phenomena that occur, for example, in supernovae, the detachment of droplets from a faucet, and ink jet printing. Such instabilities are also relevant to the possible energy source of inertial confinement fusion, in which a millimeter-sized capsule is imploded to initiate nuclear fusion reactions between deuterium and tritium. Our results suggest that the applicability of continuum models would be greatly enhanced by explicitly including the effects of random fluctuations. PMID:17470811

  16. Fluctuation theorem for partially masked nonequilibrium dynamics

    NASA Astrophysics Data System (ADS)

    Shiraishi, Naoto; Sagawa, Takahiro

    2015-01-01

    We establish a generalization of the fluctuation theorem for partially masked nonequilibrium dynamics. We introduce a partial entropy production with a subset of all possible transitions, and show that the partial entropy production satisfies the integral fluctuation theorem. Our result reveals the fundamental properties of a broad class of autonomous as well as nonautonomous nanomachines. In particular, our result gives a unified fluctuation theorem for both autonomous and nonautonomous Maxwell's demons, where mutual information plays a crucial role. Furthermore, we derive a fluctuation-dissipation theorem that relates nonequilibrium stationary current to two kinds of equilibrium fluctuations.

  17. Multiscale Fluctuation Analysis Revisited

    NASA Astrophysics Data System (ADS)

    Struzik, Zbigniew R.; Kiyono, Ken; Yamamoto, Yoshiharu

    2007-07-01

    Ubiquitous non-Gaussianity of the probability density of (time-series) fluctuations in many real world phenomena has been known and modelled extensively in recent years. Similarly, the analysis of (multi)scaling properties of (fluctuations in) complex systems has become a standard way of addressing unknown complexity. Yet the combined analysis and modelling of multiscale behaviour of probability density — multiscale PDF analysis — has only recently been proposed for the analysis of time series arising in complex systems, such as the cardiac neuro-regulatory system, financial markets or hydrodynamic turbulence. This relatively new technique has helped significantly to expand the previously obtained insights into the phenomena addressed. In particular, it has helped to identify a novel class of scale invariant behaviour of the multiscale PDF in healthy heart rate regulation during daily activity and in a market system undergoing crash dynamics. This kind of invariance reflects invariance of the system under renormalisation and resembles behaviour at criticality of a system undergoing continuous phase transition — indeed in both phenomena, such phase transition behaviour has been revealed. While the precise mechanism underlying invariance of the PDF under system renormalisation of both systems discussed is not to date understood, there is an intimate link between the non-Gaussian PDF characteristics and the persistent invariant correlation structure emerging between fluctuations across scale and time.

  18. Conductance fluctuations in nanostructures

    NASA Astrophysics Data System (ADS)

    Zhu, Ningjia

    1997-12-01

    In this Ph.D thesis the conductance fluctuations of different physical origins in semi-conductor nanostructures were studied using both diagrammatic analytical methods and large scale numerical techniques. In the "mixed" transport regime where both mesoscopic and ballistic features play a role, for the first time I have analytically calculated the non-universal conductance fluctuations. This mixed regime is reached when impurities are distributed near the walls of a quantum wire, leaving the center region ballistic. I have discovered that the existence of a ballistic region destroys the universal conductance fluctuations. The crossover behavior of the fluctuation amplitude from the usual quasi-1D situation to that of the mixed regime is clearly revealed, and the role of various length scales are identified. My analytical predictions were confirmed by a direct numerical simulation by evaluating the Landauer formula. In another direction, I have made several studies of conductance or resistance oscillations and fluctuations in systems with artificial impurities in the ballistic regime. My calculation gave explanations of all the experimental results concerning the classical focusing peaks of the resistance versus magnetic field, the weak localization peak in a Sinai billiard system, the formation of a chaotic billiard, and predicted certain transport features which were indeed found experimentally. I have further extended the calculation to study the Hall resistance in a four-terminal quantum dot in which there is an antidot array. From my numerical data I analyzed the classical paths of electron motion and its quantum oscillations. The results compare well with recent experimental studies on similar systems. Since these billiard systems could provide quantum chaotic dynamics, I have made a detailed study of the consequence of such dynamics. In particular I have investigated the resonant transmission of electrons in these chaotic systems, and found that the level

  19. Impact of Random Dopant Fluctuations on the Electronic Properties of In(x)Ga(1-x)N/GaN Axial Nanowire Heterostructures.

    PubMed

    Marquardt, Oliver; Geelhaar, Lutz; Brandt, Oliver

    2015-07-08

    We study the electronic properties of axial In(x)Ga(1-x)N/GaN nanowire heterostructures with randomly placed ionized donors. Our simulations are based on an eight-band k·p model and indicate large variations of both the ground state transition energy and the spatial distribution of the electron and hole charge density. We show that these variations are intrinsic to nanostructures containing ionized donors and that the presence of donors has important consequences for all nanowire-based light-emitting devices including single-photon emitters required for quantum computing and quantum cryptography.

  20. Metabolomics reveals the metabolic shifts following an intervention with rye bread in postmenopausal women- a randomized control trial

    PubMed Central

    2012-01-01

    Background Epidemiological studies have consistently shown that whole grain (WG) cereals can protect against the development of chronic diseases, but the underlying mechanism is not fully understood. Among WG products, WG rye is considered even more potent because of its unique discrepancy in postprandial insulin and glucose responses known as the rye factor. In this study, an NMR-based metabolomics approach was applied to study the metabolic effects of WG rye as a tool to determine the beneficial effects of WG rye on human health. Methods Thirty-three postmenopausal Finnish women with elevated serum total cholesterol (5.0-8.5 mmol/L) and BMI of 20–33 kg/m2 consumed a minimum of 20% of their daily energy intake as high fiber WG rye bread (RB) or refined wheat bread (WB) in a randomized, controlled, crossover design with two 8-wk intervention periods separated by an 8-wk washout period. At the end of each intervention period, fasting serum was collected for NMR-based metabolomics and the analysis of cholesterol fractions. Multilevel partial least squares discriminant analysis was used for paired comparisons of multivariate data. Results The metabolomics analysis of serum showed lower leucine and isoleucine and higher betaine and N,N-dimethylglycine levels after RB than WB intake. To further investigate the metabolic effects of RB, the serum cholesterol fractions were measured. Total- and LDL-cholesterol levels were higher after RB intake than after WB (p<0.05). Conclusions This study revealed favorable shifts in branched amino acid and single carbon metabolism and an unfavorable shift in serum cholesterol levels after RB intake in postmenopausal women, which should be considered for evaluating health beneficial effects of rye products. PMID:23088297

  1. Deep sequencing of the murine Igh repertoire reveals complex regulation of non-random V gene rearrangement frequencies

    PubMed Central

    Choi, Nancy M.; Loguercio, Salvatore; Verma-Gaur, Jiyoti; Degner, Stephanie C.; Torkamani, Ali; Su, Andrew I.; Oltz, Eugene M.; Artyomov, Maxim; Feeney, Ann J.

    2013-01-01

    A diverse antibody repertoire is formed through the rearrangement of V, D, and J segments at the immunoglobulin heavy chain (Igh) loci. The C57BL/6 murine Igh locus has over 100 functional VH gene segments that can recombine to a rearranged DJH. While the non-random usage of VH genes is well documented, it is not clear what elements determine recombination frequency. To answer this question we conducted deep sequencing of 5′-RACE products of the Igh repertoire in pro-B cells, amplified in an unbiased manner. ChIP-seq results for several histone modifications and RNA polymerase II binding, RNA-seq for sense and antisense non-coding germline transcripts, and proximity to CTCF and Rad21 sites were compared to the usage of individual V genes. Computational analyses assessed the relative importance of these various accessibility elements. These elements divide the Igh locus into four epigenetically and transcriptionally distinct domains, and our computational analyses reveal different regulatory mechanisms for each region. Proximal V genes are relatively devoid of active histone marks and non-coding RNA in general, but having a CTCF site near their RSS is critical, suggesting that being positioned near the base of the chromatin loops is important for rearrangement. In contrast, distal V genes have higher levels of histone marks and non-coding RNA, which may compensate for their poorer RSSs and for being distant from CTCF sites. Thus, the Igh locus has evolved a complex system for the regulation of V(D)J rearrangement that is different for each of the four domains that comprise this locus. PMID:23898036

  2. Fluctuations in percolation of sparse complex networks

    NASA Astrophysics Data System (ADS)

    Bianconi, Ginestra

    2017-07-01

    We study the role of fluctuations in percolation of sparse complex networks. To this end we consider two random correlated realizations of the initial damage of the nodes and we evaluate the fraction of nodes that are expected to remain in the giant component of the network in both cases or just in one case. Our framework includes a message-passing algorithm able to predict the fluctuations in a single network, and an analytic prediction of the expected fluctuations in ensembles of sparse networks. This approach is applied to real ecological and infrastructure networks and it is shown to characterize the expected fluctuations in their response to external damage.

  3. Quasilocal critical nature of cooperative paramagnetic fluctuations in CaRuO3 metal

    NASA Astrophysics Data System (ADS)

    Gunasekera, J.; Harriger, L.; Heitmann, T.; Dahal, A.; Knoll, H.; Singh, D. K.

    2015-06-01

    We report the observation of cooperative paramagnetic fluctuations of Ru4 + spins that coexist with the non-Fermi-liquid state in CaRuO3 perovskite below T ≃21 K. Detailed electrical, magnetic, and neutron scattering measurements reveal that the Ru4 + ions reside in magnetic-field-independent random domains with dynamic properties that are reminiscent of the cooperative paramagnetic fluctuations. The linear (E /T ) scaling of the dynamic susceptibilities and divergence of the mean relaxation time as T →0 K suggest a quasilocal critical nature of the spin fluctuations. We argue that the non-Fermi-liquid behavior arises due to the quantum critical nature of the cooperative paramagnetic fluctuations in CaRuO3.

  4. Research on the Voltage Fluctuation Rules of Power System Containing Wind Farms

    NASA Astrophysics Data System (ADS)

    Chen, Yixi; Xu, Guchao; Ma, Gang; Li, Feng; Ju, Rong

    2017-05-01

    The global energy shortage and environmental problems have contributed to the rapid development of wind power. However, due to the randomness and volatility of wind power, large-scale access may cause voltage fluctuation in power grid. Therefore, the reactive power control of power system containing wind farms has become a hot research topic in recent years, in which finding key nodes of voltage fluctuation is a foundation work. In this paper, the power model of wind farm is established first. Then, the influence on nodes voltage when wind farms access simple power system is analysed, and promoted to complex power systems in order to reveal the fluctuation rules of nodes voltage, and to summarize the distribution characteristics of key nodes of voltage fluctuation, which can provide the basis for reactive power optimization. At last, the conclusions are verified by IEEE 30-node system.

  5. Synchrony in broadband fluctuation and the 2008 financial crisis.

    PubMed

    Lin, Der Chyan

    2013-01-01

    We propose phase-like characteristics in scale-free broadband processes and consider fluctuation synchrony based on the temporal signature of significant amplitude fluctuation. Using wavelet transform, successful captures of similar fluctuation pattern between such broadband processes are demonstrated. The application to the financial data leading to the 2008 financial crisis reveals the transition towards a qualitatively different dynamical regime with many equity price in fluctuation synchrony. Further analysis suggests an underlying scale free "price fluctuation network" with large clustering coefficient.

  6. Instantaneous scale of fluctuation using Kalman-TFD and applications in machine tool monitoring

    NASA Astrophysics Data System (ADS)

    Madhavan, P. G.

    1997-10-01

    A new theory of random fields based on the concept of local averaging was developed in the 80s where the second-order properties of the random fields are characterized by the variance function. Certain asymptotic properties of the variance function lead to the definition of a scalar called the 'scale of fluctuation,' which has many interesting properties. A non- parametric method of estimating instantaneous scale of fluctuation is developed using the time-varying model-based time-frequency distribution. A wide range of random processes can be modeled by appropriate state-space models with white process noise. For properly defined state transition matrices and observation vectors, the states estimated using Kalman filtering or smoothing algorithms provide the estimated time-frequency distribution (Kalman-TFD). Using Kalman-TFD, the instantaneous scale of fluctuation is estimated. Performance of this estimator is compared to other instantaneous and block methods using the coefficient of variation of the estimators. The Kalman-TFD-based scale of fluctuation estimator has a coefficient of variation of 6% where as other methods yield coefficients of variation greater than 35%. The instantaneous scale of fluctuation quantifies the temporal variability of the underlying system and possible resultant limit- cycle oscillations. Tests with real vibration data from machine tools before and during chatter show that the estimated instantaneous scale of fluctuation may permit on-line prediction of chatter development many hundreds of milliseconds in advance. To explain the behavior of the estimated instantaneous scale of fluctuation during pre-chatter period, detailed simulations were undertaken which revealed that the random process during pre- chatter condition goes through an increase in 'degrees-of-freedom' or its unit standard deviation contour volume.

  7. Multiple Antiferromagnetic Spin Fluctuations and Novel Evolution of Tc in Iron-Based Superconductors LaFe(As1-xPx)(O1-yFy) Revealed by 31P-NMR Studies

    NASA Astrophysics Data System (ADS)

    Shiota, Takayoshi; Mukuda, Hidekazu; Uekubo, Masahiro; Engetsu, Fuko; Yashima, Mitsuharu; Kitaoka, Yoshio; Lai, Kwing To; Usui, Hidetomo; Kuroki, Kazuhiko; Miyasaka, Shigeki; Tajima, Setsuko

    2016-05-01

    We report on 31P-NMR studies of LaFe(As1-xPx)(O1-yFy) over wide compositions for 0 ≤ x ≤ 1 and 0 ≤ y ≤ 0.14, which provide clear evidence that antiferromagnetic spin fluctuations (AFMSFs) are one of the indispensable elements for enhancing Tc. Systematic 31P-NMR measurements revealed two types of AFMSFs in the temperature evolution, that is, one is the AFMSFs that develop rapidly down to Tc with low-energy characteristics, and the other, with relatively higher energy than the former, develops gradually upon cooling from high temperature. The low-energy AFMSFs in low y (electron doping) over a wide x (pnictogen height suppression) range are associated with the two orbitals of dxz/yz, whereas the higher-energy ones for a wide y region around low x originate from the three orbitals of dxy and dxz/yz. We remark that the nonmonotonic variation of Tc as a function of x and y in LaFe(As1-xPx)(O1-yFy) is attributed to these multiple AFMSFs originating from degenerated multiple 3d orbitals inherent to Fe-pnictide superconductors.

  8. Fluctuation Measurements in MRX

    NASA Astrophysics Data System (ADS)

    Carter, T.; Hsu, S.; Zaharia, S.; Ji, H.; Yamada, M.; Kulsrud, R.; Mazzucato, E.

    1998-11-01

    Recently, data(H. Ji, et al), Phys. Rev. Lett., 80, 3256 (1998) from the Magnetic Reconnection Experiment (MRX) have shown agreement with an MHD (Sweet-Parker) scaling modified to include, among other effects, an experimentally measured resistivity in collisionless current sheets for which η > η_Spitzer. Consistent with the observation of enhanced resistivity in these experiments was the measurement of current sheet widths on the order of ρ_i. Current sheet width scaling with ρi implies a drift parameter (v_d,i-v_d,e)/v_th,i which is constant with density. A potential explanation for these three observations is the existence of a current-driven instability in the current sheet of MRX which limits the relative drift speed, enhances the resistivity and widens the reconnection layer. Studies of fluctuations in the current sheet of MRX have begun, and preliminary fluctuation measurements using floating Langmuir and magnetic pick-up probes reveal frequency spectra with strong features near 30 MHz (≈ ω_LH). Theoretical studies of instabilities in the MRX current sheet and detailed measurements of frequency spectra using these diagnostics will be presented along with preliminary measurements using a new 35.6 cm-1 microwave scattering system.

  9. Chiral edge fluctuations of colloidal membranes

    NASA Astrophysics Data System (ADS)

    Jia, Leroy L.; Zakhary, Mark J.; Dogic, Zvonimir; Pelcovits, Robert A.; Powers, Thomas R.

    2017-06-01

    We study edge fluctuations of a flat colloidal membrane comprised of a monolayer of aligned filamentous viruses. Experiments reveal that a peak in the spectrum of the in-plane edge fluctuations arises for sufficiently strong virus chirality. Accounting for internal liquid crystalline degrees of freedom by the length, curvature, and geodesic torsion of the edge, we calculate the spectrum of the edge fluctuations. The theory quantitatively describes the experimental data, demonstrating that chirality couples in-plane and out-of-plane edge fluctuations to produce the peak.

  10. Fluctuational electrodynamics of hyperbolic metamaterials

    SciTech Connect

    Guo, Yu; Jacob, Zubin

    2014-06-21

    We give a detailed account of equilibrium and non-equilibrium fluctuational electrodynamics of hyperbolic metamaterials. We show the unifying aspects of two different approaches; one utilizes the second kind of fluctuation dissipation theorem and the other makes use of the scattering method. We analyze the near-field of hyperbolic media at finite temperatures and show that the lack of spatial coherence can be attributed to the multi-modal nature of super-Planckian thermal emission. We also adopt the analysis to phonon-polaritonic super-lattice metamaterials and describe the regimes suitable for experimental verification of our predicted effects. The results reveal that far-field thermal emission spectra are dominated by epsilon-near-zero and epsilon-near-pole responses as expected from Kirchoff's laws. Our work should aid both theorists and experimentalists to study complex media and engineer equilibrium and non-equilibrium fluctuations for applications in thermal photonics.

  11. Random Addition Concatenation Analysis: a novel approach to the exploration of phylogenomic signal reveals strong agreement between core and shell genomic partitions in the cyanobacteria.

    PubMed

    Narechania, Apurva; Baker, Richard H; Sit, Ryan; Kolokotronis, Sergios-Orestis; DeSalle, Rob; Planet, Paul J

    2012-01-01

    Recent whole-genome approaches to microbial phylogeny have emphasized partitioning genes into functional classes, often focusing on differences between a stable core of genes and a variable shell. To rigorously address the effects of partitioning and combining genes in genome-level analyses, we developed a novel technique called Random Addition Concatenation Analysis (RADICAL). RADICAL operates by sequentially concatenating randomly chosen gene partitions starting with a single-gene partition and ending with the entire genomic data set. A phylogenetic tree is built for every successive addition, and the entire process is repeated creating multiple random concatenation paths. The result is a library of trees representing a large variety of differently sized random gene partitions. This library can then be mined to identify unique topologies, assess overall agreement, and measure support for different trees. To evaluate RADICAL, we used 682 orthologous genes across 13 cyanobacterial genomes. Despite previous assertions of substantial differences between a core and a shell set of genes for this data set, RADICAL reveals the two partitions contain congruent phylogenetic signal. Substantial disagreement within the data set is limited to a few nodes and genes involved in metabolism, a functional group that is distributed evenly between the core and the shell partitions. We highlight numerous examples where RADICAL reveals aspects of phylogenetic behavior not evident by examining individual gene trees or a "'total evidence" tree. Our method also demonstrates that most emergent phylogenetic signal appears early in the concatenation process. The software is freely available at http://desalle.amnh.org.

  12. Elliptic Flow Fluctuations

    NASA Astrophysics Data System (ADS)

    Mrowczynski, Stanislaw; Shuryak, Edward V.

    2003-08-01

    We suggest to perform systematic measurements of the elliptic flow fluctuations which are sensitive to the early stage dynamics of heavy-ion collisions at high-energies. Significant flow fluctuations are shown to be generated due to the formation of topological clusters and development of the filamentation instability. The statistical noise and hydrodynamic fluctuations are also estimated.

  13. Genetic diversity among elite Sorghum lines revealed by restriction fragment length polymorphisms and random amplified polymorphic DNAs.

    PubMed

    Vierling, R A; Xiang, Z; Joshi, C P; Gilbert, M L; Nguyen, H T

    1994-02-01

    The genetic diversity of sorghum, as compared to corn, is less well characterized at the genetic and molecular levels despite its worldwide economic importance. The objectives of this study were to: (1) investigate genetic diversity for restriction fragment length polymorphism (RFLPs) and random amplified polymorphic DNAs (RAPDs) in elite sorghum lines, (2) compare similarities based on molecular markers with pedigree relationships, and (3) examine the potential of RFLPs and RAPDs for assigning sorghum lines to the A/B (sterile) and R (restorer) groups. Using four restriction enzymes, polymorphism was detected with 61% of the RFLP probes used, compared to 77% of the random primers. One hundred and sixteen (64%) probe-enzyme combinations yielded multiple-band profiles compared to 98% of the random primers. RFLP profiles generated 290 polymorphic bands compared to 177 polymorphic RAPDs. Pair-wise comparisons of polymorphic RFLPs and RAPDs were used to calculate Nei and Jaccard coefficients. These were employed to generate phenograms using UPGMA and neighborjoining clustering methods. Analysis of RFLP data with Jaccard's coefficient and neighbor-joining clustering produced the phenogram with the closest topology to the known pedigree.

  14. Non-equilibrium Majorana fluctuations

    NASA Astrophysics Data System (ADS)

    Smirnov, Sergey

    2017-06-01

    Non-equilibrium physics of random events, or fluctuations, is a unique fingerprint of a given system. Here we demonstrate that in non-interacting systems with dynamics driven essentially by Majorana states the effective charge {e}* , characterizing the electric current fluctuations, is fractional. This is in contrast to non-interacting Dirac systems with the trivial electronic charge {e}* =e. In the Majorana state, however, we predict two different fractional effective charges at low and high energies, {e}{{l}}* =e/2 and {e}{{h}}* =3e/2, accessible at low and high bias voltages, respectively. We show that while the low-energy effective charge {e}{{l}}* is sensitive to thermal fluctuations of the current, the high-energy effective charge {e}{{h}}* is robust against thermal noise. A unique fluctuation signature of Majorana fermions is therefore encoded in the high-voltage tails of the electric current noise easily accessible in experiments on strongly non-equilibrium systems even at high temperatures.

  15. Elastic Fluctuations and Rubber Elasticity

    NASA Astrophysics Data System (ADS)

    Xing, Xiangjun; Goldbart, Paul; Rradzihovsky, Leo

    2006-03-01

    A coarse-grained phenomenological model is constructed to describe both phonon fluctuations and elastic heterogeneities in rubbery materials. It is a nonlocal, spatially heterogeneous generalization of the classical model of rubber elasticity, and with a tunable repulsion interaction. This model can also be derived from the Vulcanization theory. The residual stress and the non-affine deformation field, as well as their correlations, are calculated perturbatively, to the leading order of quenched randomness. It is explicitly shown that the interplay between the repulsive interaction and quenched randomness induces non- affine deformation. The spatial correlations of the non- affine deformation field and residual stress exhibit power-law scaling, with no characteristic length scale. We also calculate the contributions to the elastic free energy from both thermal and quenched fluctuations for arbitrary deformation. We find that they naturally explain the universal features in the Mooney-Rivlin plot of the stress-strain curve for rubbery materials. The (disorder averaged) thermal fluctuation of monomers is shown to depend on deformation, and becomes anisotropic upon shear deformation, as long as the repulsive interaction is finite.

  16. Sensitivity of the Goldfish Motion Detection System Revealed by Incoherent Random Dot Stimuli: Comparison of Behavioural and Neuronal Data

    PubMed Central

    Masseck, Olivia Andrea; Förster, Sascha; Hoffmann, Klaus-Peter

    2010-01-01

    Background Global motion detection is one of the most important abilities in the animal kingdom to navigate through a 3-dimensional environment. In the visual system of teleost fish direction-selective neurons in the pretectal area (APT) are most important for global motion detection. As in all other vertebrates these neurons are involved in the control of slow phase eye movements during gaze stabilization. In contrast to mammals cortical pathways that might influence motion detection abilities of the optokinetic system are missing in teleost fish. Results To test global motion detection in goldfish we first measured the coherence threshold of random dot patterns to elicit horizontal slow phase eye movements. In addition, the coherence threshold of the optomotor response was determined by the same random dot patterns. In a second approach the coherence threshold to elicit a direction selective response in neurons of the APT was assessed from a neurometric function. Behavioural thresholds and neuronal thresholds to elicit slow phase eye movements were very similar, and ranged between 10% and 20% coherence. In contrast to these low thresholds for the optokinetic reaction and APT neurons the optomotor response could only be elicited by random dot patterns with coherences above 40%. Conclusion Our findings suggest a high sensitivity for global motion in the goldfish optokinetic system. Comparison of neuronal and behavioural thresholds implies a nearly one-to-one transformation of visual neuron performance to the visuo-motor output. In addition, we assume that the optomotor response is not mediated by the optokinetic system, but instead by other motion detection systems with higher coherence thresholds. PMID:20209165

  17. Genotoxicity of Thermopsis turcica on Allium cepa L. roots revealed by alkaline comet and random amplified polymorphic DNA assays.

    PubMed

    Ciğerci, İbrahim Hakkı; Cenkci, Süleyman; Kargıoğlu, Mustafa; Konuk, Muhsin

    2016-08-01

    This study was undertaken to evaluate genotoxic potential of Thermopsis turcica aqueous extracts on the roots of onion bulb (Allium cepa L.) by comet assay and random amplified polymorphic DNA technique. The Allium root growth inhibition test indicated that the EC50 and 2×EC50 values were 8 and 16 mg/ml concentrations of T. turcica aqueous extracts, respectively. The negative control (distilled water), positive control (methyl methane sulfonate, 10 mg/l) and 8 and 16 mg/ml concentrations of T. turcica extracts were introduced to the roots of onion bulbs for 24 and 96 h. The root growth, DNA damage in root cells and randomly amplified polymorphic DNA (RAPD) profiles of root tissue were used as endpoints of the genotoxicity. The comet assay clearly indicated that dose-dependent single strand DNA breaks in the root nuclei of onions were determined for the treatment concentrations of T. turcica extracts. In comparison to RAPD profile of negative control group, RAPD polymorphisms became evident as disappearance and/or appearance of RAPD bands in treated roots. The diagnostic and phenetic numerical analyses of RAPD profiles obviously indicated dose-dependent genotoxicity induced by Thermopsis extracts. In conclusion, the results clearly indicated that water extract of T. turcica has genotoxic potential on the roots of onion bulbs as shown by comet assay and RAPD technique.

  18. Reconstruction of Beam Shape Using Fluctuation Spectroscopy

    NASA Astrophysics Data System (ADS)

    Charman, A.; Catravas, P.; Wurtele, J. S.

    1999-11-01

    Information about a particle beam's shape and structure can be determined from noise in or produced by the beam. Fluctuations in the incoherent radiation emitted by a particle beam during interaction with external fields or in a medium are not ``totally random'' white noise, but encode certain information about the phase space structure of the beam, which can in principle be extracted by a careful statistical analysis of the spectral properties of the noise. The frequency scale at which correlations in the spectral noise decay is inversely related to the temporal duration of the beam, and more generally, structure in the spectral covariance matrix of the radiation encodes information about both the longitudinal and transverse shape of the beam, so that certain features of the beam can be reconstructed from these data. This technique of beam reconstruction by fluctuation spectroscopy was first suggested by M. Zolotorov and G. Stupakov(M.S. Zolotorov and G.V. Stupakov, SLAC-PUB-7132, 1996; in Proceedings of the 1997 Particle Accelerator Conference) (IEEE, Piscataway, NJ, 1998)., and a proof-of-principle experiment and data analysis have recently been performed by P. Catravas, et al.(P. Catravas, W.P. Leemans, J.S. Wurtele, M.S. Zolotorov, M. Babzien, I. Ben-Szi, Z. Segalov, X.-J. Wang, V. Yakimenko, Phys. Rev. Lett.), 82, 5261 (1999)., where the bunch length and emittance were estimated using shot-noise driven fluctuations in the spontaneous emission of a relativistic electron microbunch in a wiggler. Here we aim to improve the accuracy of the reconstructed beam morphology by developing a more elaborate statistical analysis. This technique shows promise as a diagnostic for particle beams which is non-destructive, can work either with single shots or with averages over many shots, can maintain accuracy even at short bunch lengths, and uses avaialble technology. Only the case of spontaneous emission of an electron beam in a wiggler has been studied in depth, but the

  19. Genomic Diversity within the Genus Pediococcus as Revealed by Randomly Amplified Polymorphic DNA PCR and Pulsed-Field Gel Electrophoresis

    PubMed Central

    Simpson, P. J.; Stanton, C.; Fitzgerald, G. F.; Ross, R. P.

    2002-01-01

    The genomic diversity of 33 previously assigned strains from six species within the genus Pediococcus was assessed by randomly amplified polymorphic DNA (RAPD) PCR and pulsed-field-gel electrophoresis (PFGE). The RAPD PCR patterns produced by two separate random primers, termed P1 (ACGCGCCCT) and P2 (ATGTAACGCC), were compared by the Pearson correlation coefficient and the unweighted pair group method with arithmetic averages clustering algorithm. Pattern variations between repeat samples set a strain discrimination threshold of less than 70% similarity. P1 and P2 primers alone and in combination produced 14, 21, and 28 distinct patterns, respectively. When each strain was assigned with a type strain with which it shared the highest level of similarity, both primers grouped 17 of the 27 strains to their proposed species. PFGE following genomic digestion with the restriction enzymes ApaI, NotI, and AscI produced 30, 32, and 28 distinct macrorestriction patterns, respectively. Specific DNA fragments within the NotI and AscI macrorestriction patterns for each strain were observed that allowed 27 of the 33 strains to be assigned to their proposed species. For example, following digestion with AscI, all Pediococcus parvulus strains were characterized by two DNA fragments, one of approximately 220 kb and another between 700 and 800 kb. The exceptions correlated with those observed with both RAPD PCR primers and included three P. damnosus and two P. pentosaceus strains that grew at temperatures regarded as nonpermissive for their proposed species but not for those with which they grouped. PMID:11823217

  20. Spacetime Conformal Fluctuations and Quantum Dephasing

    NASA Astrophysics Data System (ADS)

    Bonifacio, Paolo M.

    2009-06-01

    Any quantum system interacting with a complex environment undergoes decoherence. Empty space is filled with vacuum energy due to matter fields in their ground state and represents an underlying environment that any quantum particle has to cope with. In particular quantum gravity vacuum fluctuations should represent a universal source of decoherence. To study this problem we employ a stochastic approach that models spacetime fluctuations close to the Planck scale by means of a classical, randomly fluctuating metric (random gravity framework). We enrich the classical scheme for metric perturbations over a curved background by also including matter fields and metric conformal fluctuations. We show in general that a conformally modulated metric induces dephasing as a result of an effective nonlinear newtonian potential obtained in the appropriate nonrelativistic limit of a minimally coupled Klein-Gordon field. The special case of vacuum fluctuations is considered and a quantitative estimate of the expected effect deduced. Secondly we address the question of how conformal fluctuations could physically arise. By applying the random gravity framework we first show that standard GR seems to forbid spontaneous conformal metric modulations. Finally we argue that a different result follows within scalar-tensor theories of gravity such as e.g. Brans-Dicke theory. In this case a conformal modulation of the metric arises naturally as a result of the fluctuations in the Brans-Dicke field and quantum dephasing of a test particle is expected to occur. For large negative values of the coupling parameter the conformal fluctuations may also contribute to alleviate the well known problem of the large zero point energy due to quantum matter fields.

  1. Proteins, fluctuations and complexity

    SciTech Connect

    Frauenfelder, Hans; Chen, Guo; Fenimore, Paul W

    2008-01-01

    Glasses, supercooled liquids, and proteins share common properties, in particular the existence of two different types of fluctuations, {alpha} and {beta}. While the effect of the {alpha} fluctuations on proteins has been known for a few years, the effect of {beta} fluctuations has not been understood. By comparing neutron scattering data on the protein myoglobin with the {beta} fluctuations in the hydration shell measured by dielectric spectroscopy we show that the internal protein motions are slaved to these fluctuations. We also show that there is no 'dynamic transition' in proteins near 200 K. The rapid increase in the mean square displacement with temperature in many neutron scattering experiments is quantitatively predicted by the {beta} fluctuations in the hydration shell.

  2. Fluctuations in Cerebral Hemodynamics

    DTIC Science & Technology

    2003-12-01

    Determination of scaling properties Detrended Fluctuations Analysis (see (28) and references therein) is commonly used to determine scaling...pressure (averaged over a cardiac beat) of a healthy subject. First 1000 values of the time series are shown. (b) Detrended fluctuation analysis (DFA...1000 values of the time series are shown. (b) Detrended fluctuation analysis of the time series shown in (a). Fig . 3 Side-by-side boxplot for the

  3. Random Addition Concatenation Analysis: A Novel Approach to the Exploration of Phylogenomic Signal Reveals Strong Agreement between Core and Shell Genomic Partitions in the Cyanobacteria

    PubMed Central

    Narechania, Apurva; Baker, Richard H.; Sit, Ryan; Kolokotronis, Sergios-Orestis; DeSalle, Rob; Planet, Paul J.

    2012-01-01

    Recent whole-genome approaches to microbial phylogeny have emphasized partitioning genes into functional classes, often focusing on differences between a stable core of genes and a variable shell. To rigorously address the effects of partitioning and combining genes in genome-level analyses, we developed a novel technique called Random Addition Concatenation Analysis (RADICAL). RADICAL operates by sequentially concatenating randomly chosen gene partitions starting with a single-gene partition and ending with the entire genomic data set. A phylogenetic tree is built for every successive addition, and the entire process is repeated creating multiple random concatenation paths. The result is a library of trees representing a large variety of differently sized random gene partitions. This library can then be mined to identify unique topologies, assess overall agreement, and measure support for different trees. To evaluate RADICAL, we used 682 orthologous genes across 13 cyanobacterial genomes. Despite previous assertions of substantial differences between a core and a shell set of genes for this data set, RADICAL reveals the two partitions contain congruent phylogenetic signal. Substantial disagreement within the data set is limited to a few nodes and genes involved in metabolism, a functional group that is distributed evenly between the core and the shell partitions. We highlight numerous examples where RADICAL reveals aspects of phylogenetic behavior not evident by examining individual gene trees or a “‘total evidence” tree. Our method also demonstrates that most emergent phylogenetic signal appears early in the concatenation process. The software is freely available at http://desalle.amnh.org. PMID:22094860

  4. Fluctuation relations for spintronics.

    PubMed

    López, Rosa; Lim, Jong Soo; Sánchez, David

    2012-06-15

    Fluctuation relations are derived in systems where the spin degree of freedom and magnetic interactions play a crucial role. The form of the nonequilibrium fluctuation theorems relies on the assumption of a local balance condition. We demonstrate that in some cases the presence of magnetic interactions violates this condition. Nevertheless, fluctuation relations can be obtained from the microreversibility principle sustained only at equilibrium as a symmetry of the cumulant generating function for spin currents. We illustrate the spintronic fluctuation relations for a quantum dot coupled to partially polarized helical edge states.

  5. Moment method in the theory of cascade-process fluctuations

    SciTech Connect

    Vetoshkin, V.V.; Uchaikin, V.V.

    1987-09-01

    A method for calculating the fluctuations and correlations in cascade processes is outlined, on the basis of deriving random cascade curves from their spatial (longitudinal) moment. The method reduces the problem of calculating cascade fluctuations in a homogeneous medium to calculating the covariational matrix of random moments, depending only on the energy variable. The set of elements of this matrix allows the fluctuations and core correlations of any track characteristics of the cascade to be calculated. The method is intended for calculations of high-energy cascades, when the influence of fluctuations of high-order longitudinal moments (n greater than or equal to 5) may be neglected.

  6. Genetic diversity and phylogenetic relationship among Tunisian cactus species (Opuntia) as revealed by random amplified microsatellite polymorphism markers.

    PubMed

    Bendhifi Zarroug, M; Baraket, G; Zourgui, L; Souid, S; Salhi Hannachi, A

    2015-02-13

    Opuntia ficus indica is one of the most economically important species in the Cactaceae family. Increased interest in this crop stems from its potential contribution to agricultural diversification, application in the exploitation of marginal lands, and utility as additional income sources for farmers. In Tunisia, O. ficus indica has been affected by drastic genetic erosion resulting from biotic and abiotic stresses. Thus, it is imperative to identify and preserve this germplasm. In this study, we focused on the use of random amplified microsatellite polymorphisms to assess genetic diversity among 25 representatives of Tunisian Opuntia species maintained in the collection of the National Institute of Agronomic Research of Tunisia. Seventy-two DNA markers were screened to discriminate accessions using 16 successful primer combinations. The high percentage of polymorphic band (100%), the resolving power value (5.68), the polymorphic information content (0.94), and the marker index (7.2) demonstrated the efficiency of the primers tested. Therefore, appropriate cluster analysis used in this study illustrated a divergence among the cultivars studied and exhibited continuous variation that occurred independently of geographic origin. O. ficus indica accessions did not cluster separately from the other cactus pear species, indicating that their current taxonomical classifications are not well aligned with their genetic variability or locality of origin.

  7. Velocity fluctuations and population distribution in clusters of settling particles at low Reynolds number

    NASA Astrophysics Data System (ADS)

    Boschan, A.; Ocampo, B. L.; Annichini, M.; Gauthier, G.

    2016-06-01

    A study on the spatial organization and velocity fluctuations of non-Brownian spherical particles settling at low Reynolds number in a vertical Hele-Shaw cell is reported. The particle volume fraction ranged from 0.005 to 0.05, while the distance between cell plates ranged from 5 to 15 times the particle radius. Particle tracking revealed that particles were not uniformly distributed in space but assembled in transient settling clusters. The population distribution of these clusters followed an exponential law. The measured velocity fluctuations are in agreement with that predicted theoretically for spherical clusters, from the balance between the apparent weight and the drag force. This result suggests that particle clustering, more than a spatial distribution of particles derived from random and independent events, is at the origin of the velocity fluctuations.

  8. Localisation and universal fluctuations in ultraslow diffusion processes

    NASA Astrophysics Data System (ADS)

    Godec, Aljaž; Chechkin, Aleksei V.; Barkai, Eli; Kantz, Holger; Metzler, Ralf

    2014-12-01

    We study ultraslow diffusion processes with logarithmic mean squared displacement (MSD) < {{x}2}(t)> ≃ {{log }γ }t. Comparison of annealed (renewal) continuous time random walks (CTRWs) with logarithmic waiting time distribution \\psi (τ )≃ 1/(τ {{log }1+γ }τ ) and Sinai diffusion in quenched random landscapes reveals striking similarities, despite the great differences in their physical nature. In particular, they exhibit a weakly non-ergodic disparity of the time-averaged and ensemble-averaged MSDs. Remarkably, for the CTRW we observe that the fluctuations of time averages become universal, with an exponential suppression of mobile trajectories. We discuss the fundamental connection between the Golosov localization effect and non-ergodicity in the sense of the disparity between ensemble-averaged MSD and time-averaged MSD.

  9. Randomization and In Vivo Selection Reveal a GGRG Motif Essential for Packaging Human Immunodeficiency Virus Type 2 RNA ▿ †

    PubMed Central

    Baig, Tayyba T.; Lanchy, Jean-Marc; Lodmell, J. Stephen

    2009-01-01

    The packaging signal (ψ) of human immunodeficiency virus type 2 (HIV-2) is present in the 5′ noncoding region of RNA and contains a 10-nucleotide palindrome (pal; 5′-392-GGAGUGCUCC) located upstream of the dimerization signal stem-loop 1 (SL1). pal has been shown to be functionally important in vitro and in vivo. We previously showed that the 3′ side of pal (GCUCC-3′) is involved in base-pairing interactions with a sequence downstream of SL1 to make an extended SL1, which is important for replication in vivo and the regulation of dimerization in vitro. However, the role of the 5′ side of pal (5′-GGAGU) was less clear. Here, we characterized this role using an in vivo SELEX approach. We produced a population of HIV-2 DNA genomes with random sequences within the 5′ side of pal and transfected these into COS-7 cells. Viruses from COS-7 cells were used to infect C8166 permissive cells. After several weeks of serial passage in C8166 cells, surviving viruses were sequenced. On the 5′ side of pal there was a striking convergence toward a GGRGN consensus sequence. Individual clones with consensus and nonconsensus sequences were tested in infectivity and packaging assays. Analysis of individuals that diverged from the consensus sequence showed normal viral RNA and protein synthesis but had replication defects and impaired RNA packaging. These findings clearly indicate that the GGRG motif is essential for viral replication and genomic RNA packaging. PMID:18971263

  10. Theory of stress fluctuations

    PubMed

    Wallace

    2000-09-01

    The current status of the theory of stress fluctuations is marked by two circumstances: no currently available formulas are valid for a metallic system, and a series of contradictory formulas remains unresolved. Here we derive formulas for shear- and isotropic-stress energy fluctuations, in the primary statistical mechanics ensembles. These formulas are valid for a classical monatomic system representing a metal or nonmetal, in cubic crystal, amorphous solid, or liquid phases. Current contradictions in fluctuation formulas are resolved through the following observations. First, the expansion of a dynamical variable A in terms of the fluctuations explicit in a given ensemble distribution, for example deltaA=adeltaN+bdeltaH in the grand canonical ensemble, is correct if and only if deltaA is a function only of deltaN and deltaH. The common use of this expansion has produced incorrect fluctuation formulas. Second, the thermodynamic fluctuations of Landau and Lifshitz do not correspond to statistical mechanics fluctuations, and the two types of fluctuations have essentially different values.

  11. Fluctuations in Proteins

    NASA Astrophysics Data System (ADS)

    Frauenfelder, Hans

    2007-03-01

    Proteins are the machines of life. In order to perform their functions, they must move continuously. The motions correspond to equilibrium fluctuations and to non-equilibrium relaxations. At least three different fluctuation processes occur: α- and β-fluctuations and processes that occur even below one Kelvin. The α-fluctuations can be approximated by the Vogel-Tammann-Fulcher relation, while the β-fluctuations appear to follow a conventional Arrhenius law (but may in some cases be better characterized by a Ferry law). Both are usually nonexponential in time. These phenomena are similar in proteins and glasses, but there is a fundamental difference between fluctuations in glasses and proteins: In glasses, they are independent of the environment, in proteins the α-fluctuations are slaved to the α-fluctuations in the solvent surrounding the protein; they follow their rate coefficients but they are entropically slowed. The studies of the protein motions are actually still in their infancy, but we can expect that future work will not only help understanding protein functions, but will also feed back to the physics of glasses.

  12. Riemannian geometry of fluctuation theory: An introduction

    NASA Astrophysics Data System (ADS)

    Velazquez, Luisberis

    2016-05-01

    Fluctuation geometry was recently proposed as a counterpart approach of Riemannian geometry of inference theory (information geometry), which describes the geometric features of the statistical manifold M of random events that are described by a family of continuous distributions dpξ(x|θ). This theory states a connection among geometry notions and statistical properties: separation distance as a measure of relative probabilities, curvature as a measure about the existence of irreducible statistical correlations, among others. In statistical mechanics, fluctuation geometry arises as the mathematical apparatus of a Riemannian extension of Einstein fluctuation theory, which is also closely related to Ruppeiner geometry of thermodynamics. Moreover, the curvature tensor allows to express some asymptotic formulae that account for the system fluctuating behavior beyond the gaussian approximation, while curvature scalar appears as a second-order correction of Legendre transformation between thermodynamic potentials.

  13. Fluctuation-dissipation theory of input-output interindustrial relations

    NASA Astrophysics Data System (ADS)

    Iyetomi, Hiroshi; Nakayama, Yasuhiro; Aoyama, Hideaki; Fujiwara, Yoshi; Ikeda, Yuichi; Souma, Wataru

    2011-01-01

    In this study, the fluctuation-dissipation theory is invoked to shed light on input-output interindustrial relations at a macroscopic level by its application to indices of industrial production (IIP) data for Japan. Statistical noise arising from finiteness of the time series data is carefully removed by making use of the random matrix theory in an eigenvalue analysis of the correlation matrix; as a result, two dominant eigenmodes are detected. Our previous study successfully used these two modes to demonstrate the existence of intrinsic business cycles. Here a correlation matrix constructed from the two modes describes genuine interindustrial correlations in a statistically meaningful way. Furthermore, it enables us to quantitatively discuss the relationship between shipments of final demand goods and production of intermediate goods in a linear response framework. We also investigate distinctive external stimuli for the Japanese economy exerted by the current global economic crisis. These stimuli are derived from residuals of moving-average fluctuations of the IIP remaining after subtracting the long-period components arising from inherent business cycles. The observation reveals that the fluctuation-dissipation theory is applicable to an economic system that is supposed to be far from physical equilibrium.

  14. Probing Cu doped Ge0.3Se0.7 based resistance switching memory devices with random telegraph noise

    NASA Astrophysics Data System (ADS)

    Soni, R.; Meuffels, P.; Petraru, A.; Weides, M.; Kügeler, C.; Waser, R.; Kohlstedt, H.

    2010-01-01

    The ultimate sensitivity of any solid state device is limited by fluctuations. Fluctuations are manifestations of the thermal motion of matter and the discreteness of its structure which are also inherent ingredients during the resistive switching process of resistance random access memory (RRAM) devices. In quest for the role of fluctuations in different memory states and to develop resistive switching based nonvolatile memory devices, here we present our study on random telegraph noise (RTN) resistance fluctuations in Cu doped Ge0.3Se0.7 based RRAM cells. The influence of temperature and electric field on the RTN fluctuations is studied on different resistance states of the memory cells to reveal the dynamics of the underlying fluctuators. Our analysis indicates that the observed fluctuations could arise from thermally activated transpositions of Cu ions inside ionic or redox "double-site traps" triggering fluctuations in the current transport through a filamentary conducting path. Giant RTN fluctuations characterized by relative resistance variations of up to 50% in almost macroscopic samples clearly point to the existence of weak links with small effective cross-sectional areas along the conducting paths. Such large resistance fluctuations can be an important issue for the industrial applications of RRAM devices because they might lead to huge bit-error rates during reading cycles.

  15. Hadronic Correlations and Fluctuations

    SciTech Connect

    Koch, Volker

    2008-10-09

    We will provide a review of some of the physics which can be addressed by studying fluctuations and correlations in heavy ion collisions. We will discuss Lattice QCD results on fluctuations and correlations and will put them into context with observables which have been measured in heavy-ion collisions. Special attention will be given to the QCD critical point and the first order co-existence region, and we will discuss how the measurement of fluctuations and correlations can help in an experimental search for non-trivial structures in the QCD phase diagram.

  16. Spatial fluctuation theorem

    NASA Astrophysics Data System (ADS)

    Pérez-Espigares, Carlos; Redig, Frank; Giardinà, Cristian

    2015-08-01

    For non-equilibrium systems of interacting particles and for interacting diffusions in d-dimensions, a novel fluctuation relation is derived. The theorem establishes a quantitative relation between the probabilities of observing two current values in different spatial directions. The result is a consequence of spatial symmetries of the microscopic dynamics, generalizing in this way the Gallavotti-Cohen fluctuation theorem related to the time-reversal symmetry. This new perspective opens up the possibility of direct experimental measurements of fluctuation relations of vectorial observables.

  17. Continuous information flow fluctuations

    NASA Astrophysics Data System (ADS)

    Rosinberg, Martin Luc; Horowitz, Jordan M.

    2016-10-01

    Information plays a pivotal role in the thermodynamics of nonequilibrium processes with feedback. However, much remains to be learned about the nature of information fluctuations in small-scale devices and their relation with fluctuations in other thermodynamics quantities, like heat and work. Here we derive a series of fluctuation theorems for information flow and partial entropy production in a Brownian particle model of feedback cooling and extend them to arbitrary driven diffusion processes. We then analyze the long-time behavior of the feedback-cooling model in detail. Our results provide insights into the structure and origin of large deviations of information and thermodynamic quantities in autonomous Maxwell's demons.

  18. Work extraction from quantum systems with bounded fluctuations in work

    PubMed Central

    Richens, Jonathan G.; Masanes, Lluis

    2016-01-01

    In the standard framework of thermodynamics, work is a random variable whose average is bounded by the change in free energy of the system. This average work is calculated without regard for the size of its fluctuations. Here we show that for some processes, such as reversible cooling, the fluctuations in work diverge. Realistic thermal machines may be unable to cope with arbitrarily large fluctuations. Hence, it is important to understand how thermodynamic efficiency rates are modified by bounding fluctuations. We quantify the work content and work of formation of arbitrary finite dimensional quantum states when the fluctuations in work are bounded by a given amount c. By varying c we interpolate between the standard and minimum free energies. We derive fundamental trade-offs between the magnitude of work and its fluctuations. As one application of these results, we derive the corrected Carnot efficiency of a qubit heat engine with bounded fluctuations. PMID:27886177

  19. Work extraction from quantum systems with bounded fluctuations in work

    NASA Astrophysics Data System (ADS)

    Richens, Jonathan G.; Masanes, Lluis

    2016-11-01

    In the standard framework of thermodynamics, work is a random variable whose average is bounded by the change in free energy of the system. This average work is calculated without regard for the size of its fluctuations. Here we show that for some processes, such as reversible cooling, the fluctuations in work diverge. Realistic thermal machines may be unable to cope with arbitrarily large fluctuations. Hence, it is important to understand how thermodynamic efficiency rates are modified by bounding fluctuations. We quantify the work content and work of formation of arbitrary finite dimensional quantum states when the fluctuations in work are bounded by a given amount c. By varying c we interpolate between the standard and minimum free energies. We derive fundamental trade-offs between the magnitude of work and its fluctuations. As one application of these results, we derive the corrected Carnot efficiency of a qubit heat engine with bounded fluctuations.

  20. Work extraction from quantum systems with bounded fluctuations in work.

    PubMed

    Richens, Jonathan G; Masanes, Lluis

    2016-11-25

    In the standard framework of thermodynamics, work is a random variable whose average is bounded by the change in free energy of the system. This average work is calculated without regard for the size of its fluctuations. Here we show that for some processes, such as reversible cooling, the fluctuations in work diverge. Realistic thermal machines may be unable to cope with arbitrarily large fluctuations. Hence, it is important to understand how thermodynamic efficiency rates are modified by bounding fluctuations. We quantify the work content and work of formation of arbitrary finite dimensional quantum states when the fluctuations in work are bounded by a given amount c. By varying c we interpolate between the standard and minimum free energies. We derive fundamental trade-offs between the magnitude of work and its fluctuations. As one application of these results, we derive the corrected Carnot efficiency of a qubit heat engine with bounded fluctuations.

  1. Residue-specific millisecond to microsecond fluctuations in bacteriorhodopsin induced by disrupted or disorganized two-dimensional crystalline lattice, through modified lipid-helix and helix-helix interactions, as revealed by 13C NMR.

    PubMed

    Saitô, Hazime; Tsuchida, Takahiro; Ogawa, Keizi; Arakawa, Tadashi; Yamaguchi, Satoru; Tuzi, Satoru

    2002-09-20

    We have recorded 13C NMR spectra of [3-13C]-, [1-13C]Ala-, and [1-13C]Val-labeled bacteriorhodopsin (bR), W80L and W12L mutants and bacterio-opsin (bO) from retinal-deficient E1001 strain, in order to examine the possibility of their millisecond to microsecond local fluctuations with correlation time in the order of 10(-4) to 10(-5) s, induced or prevented by disruption or assembly of two-dimensional (2D) crystalline lattice, respectively, at ambient temperature. The presence of disrupted or disorganized 2D lattice for W12L, W80L and bO from E1001 strain was readily visualized by increased relative proportions of surrounding lipids per protein, together with their broadened 13C NMR signals of transmembrane alpha-helices and loops in [3-13C]Ala-labeled proteins, with reference to those of wild-type. In contrast, 13C CP-MAS NMR spectra of [1-13C]Ala- and Val-labeled these mutants were almost completely suppressed, owing to the presence of fluctuations with time scale of 10(-4) s interfered with magic angle spinning. In particular, 13C NMR signals of [1-13C]Ala-labeled transmembrane alpha-helices of wild-type were almost completely suppressed at the interface between the surface and inner part (up to 8.7 A deep from the surface) with reference to those of the similarly suppressed peaks by Mn(2+)-induced accelerated spin-spin relaxation rate. Such fluctuation-induced suppression of 13C NMR peaks from the interfacial regions, however, was less significant for [1-13C]Val-labeled proteins, because fluctuation motions in Val residues with bulky side-chains at the C(alpha) moiety were modified to those of longer correlation time (>10(-4) s), if any, by residue-specific manner. To support this view, we found that such suppressed 13C NMR signals of [1-13C]Ala-labeled peaks in the wild-type were recovered for D85N and bO in which correlation times of fluctuations were shifted to the order of 10(-5) s due to modified helix-helix interactions as previously pointed out

  2. Synchrony in Broadband Fluctuation and the 2008 Financial Crisis

    PubMed Central

    Lin, Der Chyan

    2013-01-01

    We propose phase-like characteristics in scale-free broadband processes and consider fluctuation synchrony based on the temporal signature of significant amplitude fluctuation. Using wavelet transform, successful captures of similar fluctuation pattern between such broadband processes are demonstrated. The application to the financial data leading to the 2008 financial crisis reveals the transition towards a qualitatively different dynamical regime with many equity price in fluctuation synchrony. Further analysis suggests an underlying scale free “price fluctuation network” with large clustering coefficient. PMID:24204782

  3. Heat fluctuations and initial ensembles.

    PubMed

    Kim, Kwangmoo; Kwon, Chulan; Park, Hyunggyu

    2014-09-01

    Time-integrated quantities such as work and heat increase incessantly in time during nonequilibrium processes near steady states. In the long-time limit, the average values of work and heat become asymptotically equivalent to each other, since they only differ by a finite energy change in average. However, the fluctuation theorem (FT) for the heat is found not to hold with the equilibrium initial ensemble, while the FT for the work holds. This reveals an intriguing effect of everlasting initial memory stored in rare events. We revisit the problem of a Brownian particle in a harmonic potential dragged with a constant velocity, which is in contact with a thermal reservoir. The heat and work fluctuations are investigated with initial Boltzmann ensembles at temperatures generally different from the reservoir temperature. We find that, in the infinite-time limit, the FT for the work is fully recovered for arbitrary initial temperatures, while the heat fluctuations significantly deviate from the FT characteristics except for the infinite initial-temperature limit (a uniform initial ensemble). Furthermore, we succeed in calculating finite-time corrections to the heat and work distributions analytically, using the modified saddle point integral method recently developed by us. Interestingly, we find noncommutativity between the infinite-time limit and the infinite-initial-temperature limit for the probability distribution function (PDF) of the heat.

  4. Scaling metabolic rate fluctuations

    PubMed Central

    Labra, Fabio A.; Marquet, Pablo A.; Bozinovic, Francisco

    2007-01-01

    Complex ecological and economic systems show fluctuations in macroscopic quantities such as exchange rates, size of companies or populations that follow non-Gaussian tent-shaped probability distributions of growth rates with power-law decay, which suggests that fluctuations in complex systems may be governed by universal mechanisms, independent of particular details and idiosyncrasies. We propose here that metabolic rate within individual organisms may be considered as an example of an emergent property of a complex system and test the hypothesis that the probability distribution of fluctuations in the metabolic rate of individuals has a “universal” form regardless of body size or taxonomic affiliation. We examined data from 71 individuals belonging to 25 vertebrate species (birds, mammals, and lizards). We report three main results. First, for all these individuals and species, the distribution of metabolic rate fluctuations follows a tent-shaped distribution with power-law decay. Second, the standard deviation of metabolic rate fluctuations decays as a power-law function of both average metabolic rate and body mass, with exponents −0.352 and −1/4 respectively. Finally, we find that the distributions of metabolic rate fluctuations for different organisms can all be rescaled to a single parent distribution, supporting the existence of general principles underlying the structure and functioning of individual organisms. PMID:17578913

  5. Fractal and nonlinear changes in the long-term baseline fluctuations of fetal heart rate.

    PubMed

    Echeverría, J C; Álvarez-Ramírez, J; Peña, M A; Rodríguez, E; Gaitán, M J; González-Camarena, R

    2012-05-01

    The interpretation of heart rate patterns obtained by fetal monitoring relies on the definition of a baseline, which is considered as the running average heart rate in the absence of external stimuli during periods of fetal rest. We present a study along gestation of the baseline's fluctuations, in relation to fractal and nonlinear properties, to assess these fluctuations according with time-varying attracting levels introduced by maturing regulatory mechanisms. A low-risk pregnancy was studied weekly from the 17th to 38th week of gestation during long-term recording sessions at night (>6 h). Fetal averaged pulse rate samples and corresponding baseline series were obtained from raw abdominal ECG ambulatory data. The fractal properties of these series were evaluated by applying detrended fluctuation analysis. The baseline series were also explored to evaluate nonlinear properties and time ordering by applying the scaling magnitude and sign analyses. Our main findings are that the baseline shows fractal and even nonlinear anticorrelated fluctuations. This condition was specially the case before mid-gestation, as revealed by α values near to unit, yet becoming significantly more complex after 30 weeks of gestation as indicated by α(mag) values >0.5. The structured (i.e. not random) fluctuations and particular nonlinear changes that we found thus suggest that the baseline provides on itself information concerning the functional integration of cardiac regulatory mechanisms. Copyright © 2011 IPEM. Published by Elsevier Ltd. All rights reserved.

  6. Stochastic and information-thermodynamic structures of population dynamics in a fluctuating environment

    NASA Astrophysics Data System (ADS)

    Kobayashi, Tetsuya J.; Sughiyama, Yuki

    2017-07-01

    Adaptation in a fluctuating environment is a process of fueling environmental information to gain fitness. Living systems have gradually developed strategies for adaptation from random and passive diversification of the phenotype to more proactive decision making, in which environmental information is sensed and exploited more actively and effectively. Understanding the fundamental relation between fitness and information is therefore crucial to clarify the limits and universal properties of adaptation. In this work, we elucidate the underlying stochastic and information-thermodynamic structure in this process, by deriving causal fluctuation relations (FRs) of fitness and information. Combined with a duality between phenotypic and environmental dynamics, the FRs reveal the limit of fitness gain, the relation of time reversibility with the achievability of the limit, and the possibility and condition for gaining excess fitness due to environmental fluctuation. The loss of fitness due to causal constraints and the limited capacity of real organisms is shown to be the difference between time-forward and time-backward path probabilities of phenotypic and environmental dynamics. Furthermore, the FRs generalize the concept of the evolutionary stable state (ESS) for fluctuating environment by giving the probability that the optimal strategy on average can be invaded by a suboptimal one owing to rare environmental fluctuation. These results clarify the information-thermodynamic structures in adaptation and evolution.

  7. Simulating Brownian suspensions with fluctuating hydrodynamics.

    PubMed

    Delmotte, Blaise; Keaveny, Eric E

    2015-12-28

    Fluctuating hydrodynamics has been successfully combined with several computational methods to rapidly compute the correlated random velocities of Brownian particles. In the overdamped limit where both particle and fluid inertia are ignored, one must also account for a Brownian drift term in order to successfully update the particle positions. In this paper, we present an efficient computational method for the dynamic simulation of Brownian suspensions with fluctuating hydrodynamics that handles both computations and provides a similar approximation as Stokesian Dynamics for dilute and semidilute suspensions. This advancement relies on combining the fluctuating force-coupling method (FCM) with a new midpoint time-integration scheme we refer to as the drifter-corrector (DC). The DC resolves the drift term for fluctuating hydrodynamics-based methods at a minimal computational cost when constraints are imposed on the fluid flow to obtain the stresslet corrections to the particle hydrodynamic interactions. With the DC, this constraint needs only to be imposed once per time step, reducing the simulation cost to nearly that of a completely deterministic simulation. By performing a series of simulations, we show that the DC with fluctuating FCM is an effective and versatile approach as it reproduces both the equilibrium distribution and the evolution of particulate suspensions in periodic as well as bounded domains. In addition, we demonstrate that fluctuating FCM coupled with the DC provides an efficient and accurate method for large-scale dynamic simulation of colloidal dispersions and the study of processes such as colloidal gelation.

  8. Fluctuating magnetic field induced resonant activation

    SciTech Connect

    Mondal, Shrabani; Das, Sudip; Baura, Alendu; Bag, Bidhan Chandra

    2014-12-14

    In this paper, we have studied the properties of a Brownian particle at stationary state in the presence of a fluctuating magnetic field. Time dependence of the field makes the system thermodynamically open. As a signature of that the steady state distribution function becomes function of damping strength, intensity of fluctuations and constant parts of the applied magnetic field. It also depends on the correlation time of the fluctuating magnetic field. Our another observation is that the random magnetic field can induce the resonant activation phenomenon. Here correlation time is increased under the fixed variance of the fluctuating field. But if the correlation time (τ) increases under the fixed field strength then the mean first passage time rapidly grows at low τ and it almost converges at other limit. This is sharp contrast to the usual colored noise driven open system case where the mean first passage time diverges exponentially. We have also observed that a giant enhancement of barrier crossing rate occurs particularly at large strength of constant parts of the applied magnetic field even for very weak fluctuating magnetic field. Finally, break down of the Arrhenius result and disappearance of the Kramers’ turn over phenomenon may occur in the presence of a fluctuating magnetic field.

  9. Application of scattering theory to P-wave amplitude fluctuations in the crust

    NASA Astrophysics Data System (ADS)

    Yoshimoto, Kazuo; Takemura, Shunsuke; Kobayashi, Manabu

    2015-12-01

    The amplitudes of high-frequency seismic waves generated by local and/or regional earthquakes vary from site to site, even at similar hypocentral distances. It had been suggested that, in addition to local site effects (e.g., variable attenuation and amplification in surficial layers), complex wave propagation in inhomogeneous crustal media is responsible for this observation. To quantitatively investigate this effect, we performed observational, theoretical, and numerical studies on the characteristics of seismic amplitude fluctuations in inhomogeneous crust. Our observations of P-wave amplitude for small to moderately sized crustal earthquakes revealed that fluctuations in P-wave amplitude increase with increasing frequency and hypocentral distance, with large fluctuations showing up to ten-times difference between the largest and the smallest P-wave amplitudes. Based on our theoretical investigation, we developed an equation to evaluate the amplitude fluctuations of time-harmonic waves that radiated isotropically from a point source and propagated spherically in acoustic von Kármán-type random media. Our equation predicted relationships between amplitude fluctuations and observational parameters (e.g., wave frequency and hypocentral distance). Our numerical investigation, which was based on the finite difference method, enabled us to investigate the characteristics of wave propagation in both acoustic and elastic random inhomogeneous media using a variety of source time functions. The numerical simulations indicate that amplitude fluctuation characteristics differ a little between medium types (i.e., acoustic or elastic) or source time function durations. These results confirm the applicability of our analytical equation to practical seismic data analysis.

  10. A Experimental Study of Fluctuating Pressure Loads Beneath Swept Shock Wave/boundary Layer Interactions

    NASA Astrophysics Data System (ADS)

    Garg, Sanjay

    An experimental research program providing basic knowledge and establishing a database on the fluctuating pressure loads produced on aerodynamic surfaces beneath three-dimensional shock wave/boundary layer interactions is described. Such loads constitute a fundamental problem of critical concern to future supersonic and hypersonic flight vehicles. A turbulent boundary layer on a flat plate is subjected to interactions with swept planar shock waves generated by sharp fins. Fin angles from 10 ^circ to 20^circ at freestream Mach numbers of 3 and 4 produce a variety of interaction strengths from weak to very strong. Miniature pressure transducers flush-mounted in the flat plate have been used to measure interaction-induced wall pressure fluctuations. The distributions of properties of the pressure fluctuations, such as their rms level, amplitude distribution and power spectra, are also determined. Measurements have been made for the first time in the aft regions of these interactions, revealing fluctuating pressure levels as high as 155 dB, which places them in the category of significant aeroacoustic load generators. The fluctuations near the foot of the fin are dominated by low frequency (0-5 kHz) components, and are caused by a previously unrecognized random motion of the primary attachment line. This phenomenon is probably intimately linked to the unsteadiness of the separation shock at the start of the interaction. The characteristics of the pressure fluctuations are explained in light of the features of the interaction flowfield. In particular, physical mechanisms responsible for the generation of high levels of surface pressure fluctuations are proposed based on the results of the study. The unsteadiness of the flowfield of the surface is also examined via a novel, non-intrusive optical technique. Results show that the entire shock structure generated by the interaction undergoes relatively low-frequency oscillations.

  11. In-office insertion of a miniaturized insertable cardiac monitor: Results from the Reveal LINQ In-Office 2 randomized study.

    PubMed

    Rogers, John D; Sanders, Prashanthan; Piorkowski, Christopher; Sohail, M Rizwan; Anand, Rishi; Crossen, Karl; Khairallah, Farhat S; Kaplon, Rachelle E; Stromberg, Kurt; Kowal, Robert C

    2017-02-01

    Recent miniaturization of an insertable cardiac monitor (ICM) may make it possible to move device insertion from a hospital to office setting. However, the safety of this strategy is unknown. The primary objective was to compare the safety of inserting the Reveal LINQ ICM in an office vs a hospital environment. Ancillary objectives included summarizing device- and procedure-related adverse events and responses to a physician questionnaire. Five hundred twenty-one patients indicated for an ICM were randomized (1:1 ratio) to undergo ICM insertion in a hospital or office environment at 26 centers in the United States in the Reveal LINQ In-Office 2 study (ClinicalTrials.gov identifier NCT02395536). Patients were followed for 90 days. ICM insertion was successful in all 482 attempted patients (office: 251; hospital: 231). The untoward event rate (composite of unsuccessful insertion and ICM- or insertion-related complications) was 0.8% (2 of 244) in the office and 0.9% (2 of 227) in the hospital (95% confidence interval, -3.0% to 2.9%; 5% noninferiority: P < .001). In addition, adverse events occurred during 2.5% (6 of 244) of office and 4.4% (10 of 227) of hospital insertions (95% confidence interval [office minus inhospital rates], -5.8% to 1.9%; 5% noninferiority: P < .001). Physicians indicated that for procedures performed in an office vs a hospital, there were fewer delays >15 minutes (16% vs 35%; P < .001) and patient response was more often "very positive." Physicians considered the office location "very convenient" more frequently than the hospital location (85% vs 27%; P < .001). The safety profile for the insertion of the Reveal LINQ ICM is excellent irrespective of insertion environment. These results may expand site of service options for LINQ insertion. Copyright © 2016 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.

  12. Fluctuating shells under pressure

    PubMed Central

    Paulose, Jayson; Vliegenthart, Gerard A.; Gompper, Gerhard; Nelson, David R.

    2012-01-01

    Thermal fluctuations strongly modify the large length-scale elastic behavior of cross-linked membranes, giving rise to scale-dependent elastic moduli. Whereas thermal effects in flat membranes are well understood, many natural and artificial microstructures are modeled as thin elastic shells. Shells are distinguished from flat membranes by their nonzero curvature, which provides a size-dependent coupling between the in-plane stretching modes and the out-of-plane undulations. In addition, a shell can support a pressure difference between its interior and its exterior. Little is known about the effect of thermal fluctuations on the elastic properties of shells. Here, we study the statistical mechanics of shape fluctuations in a pressurized spherical shell, using perturbation theory and Monte Carlo computer simulations, explicitly including the effects of curvature and an inward pressure. We predict novel properties of fluctuating thin shells under point indentations and pressure-induced deformations. The contribution due to thermal fluctuations increases with increasing ratio of shell radius to thickness and dominates the response when the product of this ratio and the thermal energy becomes large compared with the bending rigidity of the shell. Thermal effects are enhanced when a large uniform inward pressure acts on the shell and diverge as this pressure approaches the classical buckling transition of the shell. Our results are relevant for the elasticity and osmotic collapse of microcapsules. PMID:23150558

  13. Protrusion Fluctuations Direct Cell Motion

    PubMed Central

    Caballero, David; Voituriez, Raphaël; Riveline, Daniel

    2014-01-01

    Many physiological phenomena involve directional cell migration. It is usually attributed to chemical gradients in vivo. Recently, other cues have been shown to guide cells in vitro, including stiffness/adhesion gradients or micropatterned adhesive motifs. However, the cellular mechanism leading to these biased migrations remains unknown, and, often, even the direction of motion is unpredictable. In this study, we show the key role of fluctuating protrusions on ratchet-like structures in driving NIH3T3 cell migration. We identified the concept of efficient protrusion and an associated direction index. Our analysis of the protrusion statistics facilitated the quantitative prediction of cell trajectories in all investigated conditions. We varied the external cues by changing the adhesive patterns. We also modified the internal cues using drug treatments, which modified the protrusion activity. Stochasticity affects the short- and long-term steps. We developed a theoretical model showing that an asymmetry in the protrusion fluctuations is sufficient for predicting all measures associated with the long-term motion, which can be described as a biased persistent random walk. PMID:24988339

  14. Faraday polarization fluctuations of satellite beacon signals

    NASA Technical Reports Server (NTRS)

    Lee, M. C.; Klobuchar, J. A.

    1988-01-01

    The anisotropic effects of random density irregularities in causing Faraday polarization fluctuations of VHF radio signals are examined, taking both rod-like and sheet-like irregularities into consideration. It is found that the variance of Faraday polarization fluctuations depends on the ratio of perpendicular to parallel correlation lengths. The anisotropic effect of rod-like ionospheric irregularities are shown to be most appreciable for longitudinal propagation. The anisotropic effect of sheet-like ionospheric irregularities, however, is not strongly dependent on the radio propagation angle. During transionospheric propagation at large angles with respect to the geomagnetic field, sheet-like irregularities may cause greater Faraday polarization fluctuations than rod-like irregularities.

  15. Random Time-Scale Invariant Diffusion and Transport Coefficients

    NASA Astrophysics Data System (ADS)

    He, Y.; Burov, S.; Metzler, R.; Barkai, E.

    2008-08-01

    Single particle tracking of mRNA molecules and lipid granules in living cells shows that the time averaged mean squared displacement δ2¯ of individual particles remains a random variable while indicating that the particle motion is subdiffusive. We investigate this type of ergodicity breaking within the continuous time random walk model and show that δ2¯ differs from the corresponding ensemble average. In particular we derive the distribution for the fluctuations of the random variable δ2¯. Similarly we quantify the response to a constant external field, revealing a generalization of the Einstein relation. Consequences for the interpretation of single molecule tracking data are discussed.

  16. Fluctuations and interactions in microemulsions

    SciTech Connect

    Menes, R.; Safran, S.A.; Strey, R.

    1995-12-01

    We review the properties of microemulsions as described by an interfacial model which focuses upon the deformations of the surfactant monolayer separating mesoscopic water and oil domains. In some cases, the interfacial shape is well defined, resulting in a globular phase, while in others, the interface is strongly affected by thermal fluctuations, resulting in a random, sponge-like structure. In the globular phase, interactions between globules can result in phase coexistence comparable to those observed in polymeric systems. Recent experiments indicate that these interactions can result in closed-loop coexistence regions in the isothermal, concentration phase diagram. We propose a mechanism for this reentrant phase separation based on the combined effects of a shape transition and attractive interactions. Long cylindrical globules can phase separate at relatively low interglobular attractions. A transformation from elongated globules to compact spherical drops alters the balance between the entropy and the effective interglobule interactions, leading to the remixing of the globular system.

  17. Optimal information size in trial sequential analysis of time-to-event outcomes reveals potentially inconclusive results because of the risk of random error.

    PubMed

    Miladinovic, Branko; Mhaskar, Rahul; Hozo, Iztok; Kumar, Ambuj; Mahony, Helen; Djulbegovic, Benjamin

    2013-06-01

    The current approach for evaluating the risk of random error in meta-analyses (MAs) using trial sequential analysis (TSA) can accommodate binary and continuous data but not time-to-event data. We conducted a TSA for time-to-event outcomes and applied the method to determine the risk of random error in MAs for treatments of multiple myeloma. Literature search identified 11 systematic reviews consisting of 23 MAs. Of the 23 MAs, 13 had overall survival and 10 had progression-free survival as outcome; 48% (11 of 23) reported statistically significant treatment effects. We calculated the optimal a priori diversity-adjusted information size (APDIS) based on the relative risk reduction of 15% and 25%. We also calculated the optimal low-bias information size (LBIS) and low-bias diversity-adjusted information size (LBDIS). Overall, under APDIS15%, 48% (11 of 23) of MAs were false negative (FN) and 17% (4 of 23) of MAs were false positive. Under APDIS25%, 34% (8 of 23) of MAs were false negative and 4% (1 of 23) of MAs were false positive. LBIS identified 30% (7 of 23) as false negative MAs and 4% (1 of 23) as false positive MAs, whereas LBDIS identified 52% (12 of 23) as false negative MAs and 4% (1 of 23) as false positive MAs. The new method demonstrates the possibility of incorporating time-to-event outcomes into TSA and reveals that some MAs have potentially inconclusive results. Copyright © 2013 Elsevier Inc. All rights reserved.

  18. Turbulent magnetohydrodynamic density fluctuations

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.; Montgomery, David

    1988-01-01

    A spectral-method numerical code is used to compute mass-density fluctuation spectra in turbulent magnetofluids. The computations are used to test and extend the analytical theory of density variations in slightly compressible magnetofluids given by Montgomery, et al. (1987) and used to infer inertial-range density-fluctuation spectra for the nearby interstellar medium and solar wind. A local equation of state is assumed, relating density to pressure. Constant, scalar resistivities and viscosities are used. In the limit of low Mach numbers and high mechanical-to-magnetic pressure ratios, the fit of the computations to the analytical theory is seen to be close.

  19. Existence of orbital order and its fluctuation in superconducting Ba(Fe(1-x)Co(x))2As2 single crystals revealed by x-ray absorption spectroscopy.

    PubMed

    Kim, Y K; Jung, W S; Han, G R; Choi, K-Y; Chen, C-C; Devereaux, T P; Chainani, A; Miyawaki, J; Takata, Y; Tanaka, Y; Oura, M; Shin, S; Singh, A P; Lee, H G; Kim, J-Y; Kim, C

    2013-11-22

    We performed temperature dependent x-ray linear dichroism (XLD) experiments on an iron pnictide system, Ba(Fe(1-x)Co(x))2As2 with x=0.00, 0.05, 0.08, and 0.10 to experimentally verify the existence of orbital ordering (OO). Substantial XLD was observed in polarization dependent x-ray absorption spectra of Fe L edges. By exploiting the difference in the temperature dependent behaviors, OO, and structure contributions to XLD could be clearly separated. The observed OO signal indicates different occupation numbers for d(yz) and d(zx) orbitals and supports the existence of ferro-OO. The results are also consistent with the theoretical prediction. Moreover, we find substantial OO signal well above the structural and magnetic transition temperatures, which suggests the existence of strong OO fluctuations up to high temperatures.

  20. Resonance of plankton communities with temperature fluctuations.

    PubMed

    Benincà, Elisa; Dakos, Vasilis; Van Nes, Egbert H; Huisman, Jef; Scheffer, Marten

    2011-10-01

    The interplay between intrinsic population dynamics and environmental variation is still poorly understood. It is known, however, that even mild environmental noise may induce large fluctuations in population abundances. This is due to a resonance effect that occurs in communities on the edge of stability. Here, we use a simple predator-prey model to explore the sensitivity of plankton communities to stochastic environmental fluctuations. Our results show that the magnitude of resonance depends on the timescale of intrinsic population dynamics relative to the characteristic timescale of the environmental fluctuations. Predator-prey communities with an intrinsic tendency to oscillate at a period T are particularly responsive to red noise characterized by a timescale of τ = T/2π. We compare these theoretical predictions with the timescales of temperature fluctuations measured in lakes and oceans. This reveals that plankton communities will be highly sensitive to natural temperature fluctuations. More specifically, we demonstrate that the relatively fast temperature fluctuations in shallow lakes fall largely within the range to which rotifers and cladocerans are most sensitive, while marine copepods and krill will tend to resonate more strongly with the slower temperature variability of the open ocean.

  1. Entropic interaction between fluctuating twin boundaries

    NASA Astrophysics Data System (ADS)

    Chen, Dengke; Kulkarni, Yashashree

    2015-11-01

    Nanotwinned metals have opened up exciting avenues for the design of high-strength, high-ductility materials owing to the extraordinary properties of twin boundaries. The recent advances in the fabrication of nanostructured materials with twin lamella on the order of a mere few atomic layers call for a closer examination of the stability of these structural motifs, especially at high temperatures. This paper presents a study of the entropic interaction between fluctuating twin boundaries by way of atomistic simulations and statistical mechanics based analysis. The simulations reveal that fluctuations of twin boundaries are considerably enhanced in the presence of adjoining twin boundaries as their spacing, d, decreases. In addition, the theoretical analysis shows that fluctuating twin boundaries indeed exhibit an attractive entropic interaction which enhances their thermal fluctuations and that the entropic force decreases as 1 /d2. This finite temperature interaction between twin boundaries is fundamentally distinct from the well-known repulsive entropic interaction followed by fluctuating lipid membranes as well as many crystalline membranes and interfaces. This rather surprising attraction between fluctuating twin boundaries is attributed to their shear coupled normal motion.

  2. Mesoscale Temperature Fluctuations in the Southern Hemisphere Stratosphere

    NASA Technical Reports Server (NTRS)

    Gary, Bruce L.

    2008-01-01

    Isentrope surfaces in the Southern Hemisphere stratosphere reveal that air parcels undergo mesoscale temperature fluctuations that depend on latitude and season. The largest temperature fluctuations occur at high latitude winter, whereas the smallest fluctuations occur at high latitude summer. This is the same pattern found for the Northern Hemisphere stratosphere. However, the amplitude of the seasonal dependence in the Southern Hemisphere is only 37% of the Northern Hemisphere's seasonal amplitude.

  3. Mesoscale Temperature Fluctuations in the Southern Hemisphere Stratosphere

    NASA Technical Reports Server (NTRS)

    Gary, Bruce L.

    2008-01-01

    Isentrope surfaces in the Southern Hemisphere stratosphere reveal that air parcels undergo mesoscale temperature fluctuations that depend on latitude and season. The largest temperature fluctuations occur at high latitude winter, whereas the smallest fluctuations occur at high latitude summer. This is the same pattern found for the Northern Hemisphere stratosphere. However, the amplitude of the seasonal dependence in the Southern Hemisphere is only 37% of the Northern Hemisphere's seasonal amplitude.

  4. Cycles and Universality in Sunspot Number Fluctuations

    NASA Astrophysics Data System (ADS)

    Gonçalves, R.; Pinto, A. A.; Stollenwerk, N.

    2009-02-01

    We analyze the famous Wolf's sunspot numbers. Surprisingly, we discovered that the distribution of the sunspot number fluctuations for both the ascending and descending phases is close to the universal nonparametric Bramwell-Holdsworth-Pinton (BHP) distribution. Since the BHP probability density function appears in several other physical phenomena, our result reveals a universal feature of the Wolf's sunspot numbers.

  5. Stochastic isocurvature baryon fluctuations, baryon diffusion, and primordial nucleosynthesis

    SciTech Connect

    Kurki-Suonio, H.; Jedamzik, K.; Mathews, G.J.

    1997-04-01

    We examine effects on primordial nucleosynthesis from a truly random, one-dimensional spatial distribution in the baryon-to-photon ratio ({eta}). We generate stochastic fluctuation spectra characterized by different spectral indices and rms fluctuation amplitudes. For the first time we explicitly calculate the effects of baryon diffusion on the nucleosynthesis yields of such stochastic fluctuations. We also consider the collapse instability of large mass scale inhomogeneities. Our results are generally applicable to any primordial mechanism producing fluctuations in {eta} which can be characterized by a spectral index. In particular, these results apply to primordial isocurvature baryon fluctuation (PIB) models. The amplitudes of fluctuations that are scale-invariant in baryon fluctuation (PIB) models. The amplitudes of fluctuations that are scale-invariant in baryon density are found to be severely constrained by primordial nucleosynthesis. However, when the {eta} distribution is characterized by decreasing fluctuation amplitudes with increasing length scale, surprisingly large fluctuation amplitudes on the baryon diffusion scale are allowed. {copyright} {ital 1997} {ital The American Astronomical Society}

  6. GRADFLEX: Fluctuations in Microgravity

    NASA Technical Reports Server (NTRS)

    Vailati, A.; Cerbino, R.; Mazzoni, S.; Giglio, M.; Nikolaenko, G.; Cannell, D. S.; Meyer, W. V.; Smart, A. E.

    2004-01-01

    We present the results of experimental investigations of gradient driven fluctuations induced in a liquid mixture with a concentration gradient and in a single-component fluid with a temperature gradient. We also describe the experimental apparatus being developed to carry out similar measurement under microgravity conditions.

  7. Fluctuating transport in microstructures

    SciTech Connect

    Xie, X.

    1988-01-01

    In this dissertation, we study electronic transport properties of various kinds of quasi-one dimensional (Q1D) systems. The dissertation can be divided into the following categories: (1) Conductance fluctuations and phase coherence in microstructures. We study the conductance fluctuations for three different regimes of electronic transport: ballistic, diffusive and variable-range-hopping (VRH). Various numerical methods are used in the calculations. In the VRH problem, we also examine the possibility of observing the Aharonov-Bohm effect. We develop a technique based on the recursive Kubo formula to study the universal conductance fluctuations in the diffusive regime. Close comparison with relevant experiments is made and good agreement is found. (2) Drude transport properties of quasi-one dimensional systems. In this problem, we calculate the density of states and Drude conductivity for the screened impurity scattering using many body theory. The DOS and conductivity show strong oscillatory behavior as a function of the Fermi-energy. Self-consistency is included in our theory. Good agreement with experiment is found. (3) Transport in quasicrystals. In solving this problem we use the Landauer formula approach. We find that the electrical resistance of a finite 1D Fibonacci-sequence quasicrystal shows strong fluctuations as resonant tunneling occurs through the allowed energy states of the system. Power law localization and self-similarity can be seen in the transport properties. A possible experiment to observe this phenomenon is suggested.

  8. Nonequilibrium mesoscopic conductance fluctuations

    NASA Astrophysics Data System (ADS)

    Ludwig, T.; Blanter, Ya. M.; Mirlin, A. D.

    2004-12-01

    We investigate the amplitude of mesoscopic fluctuations of the differential conductance of a metallic wire at arbitrary bias voltage V . For noninteracting electrons, the variance ⟨δg2⟩ increases with V . The asymptotic large- V behavior is ⟨δg2⟩˜V/Vc (where eVc=D/L2 is the Thouless energy), in agreement with the earlier prediction by Larkin and Khmelnitskii. We find, however, that this asymptotics has a very small numerical prefactor and sets in at very large V/Vc only, which strongly complicates its experimental observation. This high-voltage behavior is preceded by a crossover regime, V/Vc≲30 , where the conductance variance increases by a factor ˜3 as compared to its value in the regime of universal conductance fluctuations (i.e., at V→0 ). We further analyze the effect of dephasing due to the electron-electron scattering on ⟨δg2⟩ at high voltages. With the Coulomb interaction taken into account, the amplitude of conductance fluctuations becomes a nonmonotonic function of V . Specifically, ⟨δg2⟩ drops as 1/V for voltages V≫gVc , where g is the dimensionless conductance. In this regime, the conductance fluctuations are dominated by quantum-coherent regions of the wire adjacent to the reservoirs.

  9. Active fluctuation symmetries

    NASA Astrophysics Data System (ADS)

    Maes, Christian; Salazar, Alberto

    2014-01-01

    In contrast with the understanding of fluctuation symmetries for entropy production, similar ideas applied to the time-symmetric fluctuation sector have been less explored. Here we give detailed derivations of time-symmetric fluctuation symmetries in boundary-driven particle systems such as the open Kawasaki lattice gas and the zero-range model. As a measure of time-symmetric dynamical activity over time T we count the difference (Nℓ - Nr)/T between the number of particle jumps in or out at the left edge and those at the right edge of the system. We show that this quantity satisfies a fluctuation symmetry from which we derive a new Green-Kubo-type relation. It will follow then that the system is more active at the edge connected to the particle reservoir with the largest chemical potential. We also apply these exact relations derived for stochastic particle models to a deterministic case, the spinning Lorentz gas, where the symmetry relation for the activity is checked numerically.

  10. Fluctuating Asymmetry and Intelligence

    ERIC Educational Resources Information Center

    Bates, Timothy C.

    2007-01-01

    The general factor of mental ability ("g") may reflect general biological fitness. If so, "g"-loaded measures such as Raven's progressive matrices should be related to morphological measures of fitness such as fluctuating asymmetry (FA: left-right asymmetry of a set of typically left-right symmetrical body traits such as finger…

  11. Ultrasonic beam fluctuation and flaw signal variance in inhomogeneous media

    NASA Astrophysics Data System (ADS)

    Ahmed, S.; Roberts, R.; Margetan, F.

    2000-05-01

    This paper examines the effect of forward scattering on ultrasonic beam propagation and flaw signal amplitude in inhomogeneous material microstructures. A beam propagating through a weakly-scattering, randomly inhomogeneous medium will display random fluctuations in amplitude and phase, attributable to forward scattering. Correspondingly, the signal received from a given flaw at a given position in the beam volume will fluctuate as the beam and flaw are simultaneously scanned throughout the volume of an inhomogeneous host medium. These effects have been prominently observed in the inspection of titanium. For example, maps of beam amplitude profiles after transmission through titanium reveal severe distortion of beam amplitude and phase. Similarly, signals from "identical" flat bottom holes (FBH) at equal depths but different lateral positions in titanium display a random variation in amplitude. Interestingly, it has been noted that this FBH signal variance varies inversely to the beam diameter, that is, signal variance normalized to the mean signal amplitude is a minimum when the flaw is in the focal zone of a focused bearn. As this observation has great significance to the inspection of titanium, a model, prediction of this phenomenon is being sought. In the work reported here, beam propagation is formulated as a volumetric integral equation employing the Green function for the homogeneous spatial mean of the medium. The integral equation is solved using iterative methods. Preliminary work considering scalar two-dimensional propagation in inhomogeneous media has predicted a flaw signal variance that displays an inverse relation to beam diameter, thus reproducing the qualitative behavior seen in experimental data in titanium. Current work is extending the preliminary two-dimensional scalar result to three-dimensional elasticity, representing propagation in an actual titanium microstructure. Progress on this effort will be reported.

  12. Statistical physics approaches to understanding physiological fluctuations

    NASA Astrophysics Data System (ADS)

    Hu, Kun

    This dissertation investigates the influences of the circadian pacemaker on the temporal structures of fluctuations in the human heartbeat and other related physiological signals. The scale-invariant properties of these physiological fluctuations are demonstrated to possess significant circadian rhythms. These findings are relevant in understanding the daily patterns of adverse cardiac events reported by epidemiological studies. Part I of this dissertation introduces the daily pattern in the onset of adverse cardiac events, the circadian pacemaker, and experimental methods of assessing the circadian influences. This part also reviews scale-invariant properties of physiological fluctuations, and scaling analyses that are used to access long-range correlations (an important scale-invariant property). Part II focuses on the effects of trends and nonstationarities---the mean value, standard deviation, and correlation function of signals are not invariant over time. In the case that trends and nonstationarities are unrelated to the underlying mechanism of a signal, simulations and analytic derivations are conducted to explore how to quantify accurately the correlations embedded in the noisy signals that have trends and nonstationarities. Part III investigates dynamics of human motor activity---a physiological function highly correlated with cardiac dynamics. Results demonstrate that apparently random forearm motion possesses previously unrecognized dynamic patterns. These are characterized by similar distribution forms, long-range correlations, and nonlinear Fourier phase interactions across separate individuals and measurements. Part IV reports circadian influences on the dynamic properties of heartbeat fluctuations and activity signals. Correlation properties of heartbeat fluctuations are found to exhibit a significant circadian rhythm that is independent of behavior-related factors including sleep/wake cycles, and random or scheduled events. This circadian rhythm is

  13. Random Sampling of Squamate Reptiles in Spanish Natural Reserves Reveals the Presence of Novel Adenoviruses in Lacertids (Family Lacertidae) and Worm Lizards (Amphisbaenia)

    PubMed Central

    Szirovicza, Leonóra; López, Pilar; Kopena, Renáta; Benkő, Mária; Martín, José; Pénzes, Judit J.

    2016-01-01

    Here, we report the results of a large-scale PCR survey on the prevalence and diversity of adenoviruses (AdVs) in samples collected randomly from free-living reptiles. On the territories of the Guadarrama Mountains National Park in Central Spain and of the Chafarinas Islands in North Africa, cloacal swabs were taken from 318 specimens of eight native species representing five squamate reptilian families. The healthy-looking animals had been captured temporarily for physiological and ethological examinations, after which they were released. We found 22 AdV-positive samples in representatives of three species, all from Central Spain. Sequence analysis of the PCR products revealed the existence of three hitherto unknown AdVs in 11 Carpetane rock lizards (Iberolacerta cyreni), nine Iberian worm lizards (Blanus cinereus), and two Iberian green lizards (Lacerta schreiberi), respectively. Phylogeny inference showed every novel putative virus to be a member of the genus Atadenovirus. This is the very first description of the occurrence of AdVs in amphisbaenian and lacertid hosts. Unlike all squamate atadenoviruses examined previously, two of the novel putative AdVs had A+T rich DNA, a feature generally deemed to mirror previous host switch events. Our results shed new light on the diversity and evolution of atadenoviruses. PMID:27399970

  14. High-Throughput Genotyping of Green Algal Mutants Reveals Random Distribution of Mutagenic Insertion Sites and Endonucleolytic Cleavage of Transforming DNA.

    PubMed

    Zhang, Ru; Patena, Weronika; Armbruster, Ute; Gang, Spencer S; Blum, Sean R; Jonikas, Martin C

    2014-04-01

    A high-throughput genetic screening platform in a single-celled photosynthetic eukaryote would be a transformative addition to the plant biology toolbox. Here, we present ChlaMmeSeq (Chlamydomonas MmeI-based insertion site Sequencing), a tool for simultaneous mapping of tens of thousands of mutagenic insertion sites in the eukaryotic unicellular green alga Chlamydomonas reinhardtii. We first validated ChlaMmeSeq by in-depth characterization of individual insertion sites. We then applied ChlaMmeSeq to a mutant pool and mapped 11,478 insertions, covering 39% of annotated protein coding genes. We observe that insertions are distributed in a manner largely indistinguishable from random, indicating that mutants in nearly all genes can be obtained efficiently. The data reveal that sequence-specific endonucleolytic activities cleave the transforming DNA and allow us to propose a simple model to explain the origin of the poorly understood exogenous sequences that sometimes surround insertion sites. ChlaMmeSeq is quantitatively reproducible, enabling its use for pooled enrichment screens and for the generation of indexed mutant libraries. Additionally, ChlaMmeSeq allows genotyping of hits from Chlamydomonas screens on an unprecedented scale, opening the door to comprehensive identification of genes with roles in photosynthesis, algal lipid metabolism, the algal carbon-concentrating mechanism, phototaxis, the biogenesis and function of cilia, and other processes for which C. reinhardtii is a leading model system.

  15. Genomic tagging reveals a random association of endogenous PtdIns5P 4-kinases IIα and IIβ and a partial nuclear localization of the IIα isoform

    PubMed Central

    Wang, Minchuan; Bond, Nicholas J.; Letcher, Andrew J.; Richardson, Jonathan P.; Lilley, Kathryn S.; Irvine, Robin F.; Clarke, Jonathan H.

    2010-01-01

    PtdIns5P 4-kinases IIα and IIβ are cytosolic and nuclear respectively when transfected into cells, including DT40 cells [Richardson, Wang, Clarke, Patel and Irvine (2007) Cell. Signalling 19, 1309–1314]. In the present study we have genomically tagged both type II PtdIns5P 4-kinase isoforms in DT40 cells. Immunoprecipitation of either isoform from tagged cells, followed by MS, revealed that they are associated directly with each other, probably by heterodimerization. We quantified the cellular levels of the type II PtdIns5P 4-kinase mRNAs by real-time quantitative PCR and the absolute amount of each isoform in immunoprecipitates by MS using selective reaction monitoring with 14N,13C-labelled internal standard peptides. The results suggest that the dimerization is complete and random, governed solely by the relative concentrations of the two isoforms. Whereas PtdIns5P 4-kinase IIβ is >95% nuclear, as expected, the distribution of PtdIns4P 4-kinase IIα is 60% cytoplasmic (all bound to membranes) and 40% nuclear. In vitro, PtdIns5P 4-kinase IIα was 2000-fold more active as a PtdIns5P 4-kinase than the IIβ isoform. Overall the results suggest a function of PtdIns5P 4-kinase IIβ may be to target the more active IIα isoform into the nucleus. PMID:20569199

  16. Terrestrial Gravity Fluctuations

    NASA Astrophysics Data System (ADS)

    Harms, Jan

    2015-12-01

    Different forms of fluctuations of the terrestrial gravity field are observed by gravity experiments. For example, atmospheric pressure fluctuations generate a gravity-noise foreground in measurements with super-conducting gravimeters. Gravity changes caused by high-magnitude earthquakes have been detected with the satellite gravity experiment GRACE, and we expect high-frequency terrestrial gravity fluctuations produced by ambient seismic fields to limit the sensitivity of ground-based gravitational-wave (GW) detectors. Accordingly, terrestrial gravity fluctuations are considered noise and signal depending on the experiment. Here, we will focus on ground-based gravimetry. This field is rapidly progressing through the development of GW detectors. The technology is pushed to its current limits in the advanced generation of the LIGO and Virgo detectors, targeting gravity strain sensitivities better than 10-23 Hz-1/2 above a few tens of a Hz. Alternative designs for GW detectors evolving from traditional gravity gradiometers such as torsion bars, atom interferometers, and superconducting gradiometers are currently being developed to extend the detection band to frequencies below 1 Hz. The goal of this article is to provide the analytical framework to describe terrestrial gravity perturbations in these experiments. Models of terrestrial gravity perturbations related to seismic fields, atmospheric disturbances, and vibrating, rotating or moving objects, are derived and analyzed. The models are then used to evaluate passive and active gravity noise mitigation strategies in GW detectors, or alternatively, to describe their potential use in geophysics. The article reviews the current state of the field, and also presents new analyses especially with respect to the impact of seismic scattering on gravity perturbations, active gravity noise cancellation, and time-domain models of gravity perturbations from atmospheric and seismic point sources. Our understanding of

  17. Terrestrial Gravity Fluctuations.

    PubMed

    Harms, Jan

    2015-01-01

    Different forms of fluctuations of the terrestrial gravity field are observed by gravity experiments. For example, atmospheric pressure fluctuations generate a gravity-noise foreground in measurements with super-conducting gravimeters. Gravity changes caused by high-magnitude earthquakes have been detected with the satellite gravity experiment GRACE, and we expect high-frequency terrestrial gravity fluctuations produced by ambient seismic fields to limit the sensitivity of ground-based gravitational-wave (GW) detectors. Accordingly, terrestrial gravity fluctuations are considered noise and signal depending on the experiment. Here, we will focus on ground-based gravimetry. This field is rapidly progressing through the development of GW detectors. The technology is pushed to its current limits in the advanced generation of the LIGO and Virgo detectors, targeting gravity strain sensitivities better than 10(-23) Hz(-1/2) above a few tens of a Hz. Alternative designs for GW detectors evolving from traditional gravity gradiometers such as torsion bars, atom interferometers, and superconducting gradiometers are currently being developed to extend the detection band to frequencies below 1 Hz. The goal of this article is to provide the analytical framework to describe terrestrial gravity perturbations in these experiments. Models of terrestrial gravity perturbations related to seismic fields, atmospheric disturbances, and vibrating, rotating or moving objects, are derived and analyzed. The models are then used to evaluate passive and active gravity noise mitigation strategies in GW detectors, or alternatively, to describe their potential use in geophysics. The article reviews the current state of the field, and also presents new analyses especially with respect to the impact of seismic scattering on gravity perturbations, active gravity noise cancellation, and time-domain models of gravity perturbations from atmospheric and seismic point sources. Our understanding of

  18. Spectroscopic investigation of electric field fluctuations in a steady plasma

    NASA Technical Reports Server (NTRS)

    Druetta, M. P.

    1971-01-01

    The electric fluctuations caused by plasma oscillations of a steady plasma were investigated. In order to observe this phenomenon electric field fluctuations are created in a helium plasma by an electron beam. Spectroscopic analysis reveals satellite lines disposed symmetrically in pairs about a forbidden atomic line and separated from it by the frequency of the electric field oscillations.

  19. Undoped high-Tc superconductivity in T'-La1.8Eu0.2CuO4+δ revealed by 63,65Cu and 139La NMR: Bulk superconductivity and antiferromagnetic fluctuations

    NASA Astrophysics Data System (ADS)

    Fukazawa, Hideto; Ishiyama, Seiya; Goto, Masato; Kanamaru, Shuhei; Ohashi, Kohki; Kawamata, Takayuki; Adachi, Tadashi; Hirata, Michihiro; Sasaki, Takahiko; Koike, Yoji; Kohori, Yoh

    2017-10-01

    We performed 63,65Cu and 139La NMR measurements of T'-La1.8Eu0.2CuO4+δ (T'-LECO) with the Nd2CuO4-type structure (so-called T'-structure). As a result, we detected the 63,65Cu NMR signal under finite magnetic fields and found superconductivity without antiferromagnetic (AF) order only in the reduced T'-LECO, where excess apical oxygen atoms are properly removed. This indicates that the intrinsic ground state of the ideal T'-LECO is a paramagnetic and superconducting (SC) state. Below Tc, the Knight shift was found to rapidly decrease, which indicates the emergence of bulk superconductivity due to spin-singlet Cooper pairs in the reduced T'-LECO. In the SC state of the reduced T'-LECO, moreover, a characteristic temperature dependence of the spin-lattice relaxation rate 1/T1 was observed, which implies the existence of nodal lines in the SC gap. These findings suggest that the superconductivity in the reduced T'-LECO probably has d-wave symmetry. In the normal state of the reduced T'-LECO, on the other hand, AF fluctuations were found to exist from the temperature dependence of 1/T1T, though no clear pseudogap behavior was observed. This suggests that the AF correlation plays a key role in the superconductivity of undoped high-Tc cuprate superconductors with the T'-structure.

  20. Relationship between magnetic fluctuations and superconductivity in Na x(H 3O) zCoO 2 · yH 2O revealed by a Co nuclear quadrupole resonance

    NASA Astrophysics Data System (ADS)

    Ishida, K.; Ihara, Y.; Takeya, H.; Michioka, C.; Yoshimura, K.; Takada, K.; Sasaki, T.; Sakurai, H.; Takayama-Muromachi, E.

    2007-09-01

    Nuclear quadrupole frequency (νQ) and spin-lattice relaxation rate 1/T1 of Co were measured on various bilayered hydrate (BLH) NaxCoO2 · yH2O (y ∼ 1.3) with different values of superconducting (SC) and magnetic-transition temperatures, Tc and TM, together with non-SC monolayered hydrate (MLH) NaxCoO2 · yH2O (y ∼ 0.7). In the temperature range above 70 K, 1/T1T in all samples follows the similar temperature dependence as each other. In the BLH compounds, 1/T1T is enhanced with decreasing temperature below 70 K, and the values of 1/T1T at Tc are larger in the higher-ν3 sample, where ν3 is the peak frequency of the NQR spectrum arising from ±5/2 ↔ ±7/2 transitions. The magnetic ordering is indicated from the prominent divergence of 1/T1T at TM and the presence of the internal field at the Co nuclear site in the samples with ν3 higher than 12.5 MHz. We analyze the temperature dependence of 1/T1T in all samples on the basis of identical formula, and discuss the relationship between magnetic fluctuations and superconductivity in the BLH cobaltate.

  1. Rapidly fluctuating anosmia: A clinical sign for unilateral smell impairment.

    PubMed

    Negoias, Simona; Friedrich, Hergen; Caversaccio, Marco D; Landis, Basile N

    2016-02-01

    Reports about fluctuating olfactory deficits are rare, as are reports of unilateral olfactory loss. We present a case of unilateral anosmia with contralateral normosmia, presenting as rapidly fluctuating anosmia. The olfactory fluctuation occurred in sync with the average nasal cycle duration. Examination after nasal decongestion, formal smell testing, and imaging revealed unilateral, left-sided anosmia of sinonasal cause, with right-sided normosmia. We hypothesize that the nasal cycle induced transient anosmia when blocking the normosmic side. Fluctuating olfactory deficits might hide a unilateral olfactory loss and require additional unilateral testing and thorough workup. © 2015 The American Laryngological, Rhinological and Otological Society, Inc.

  2. Traction force and tension fluctuations in growing axons.

    PubMed

    Polackwich, Robert J; Koch, Daniel; McAllister, Ryan; Geller, Herbert M; Urbach, Jeffrey S

    2015-01-01

    Actively generated mechanical forces play a central role in axon growth and guidance, but the mechanisms that underly force generation and regulation in growing axons remain poorly understood. We report measurements of the dynamics of traction stresses from growth cones of actively advancing axons from postnatal rat DRG neurons. By tracking the movement of the growth cone and analyzing the traction stress field from a reference frame that moves with it, we are able to show that there is a clear and consistent average stress field that underlies the complex spatial stresses present at any one time. The average stress field has strong maxima on the sides of the growth cone, directed inward toward the growth cone neck. This pattern represents a contractile stress contained within the growth cone, and a net force that is balanced by the axon tension. Using high time-resolution measurements of the growth cone traction stresses, we show that the stress field is composed of fluctuating local stress peaks, with a large number peaks that live for a short time, a population of peaks whose lifetime distribution follows an exponential decay, and a small number of very long-lived peaks. We show that the high time-resolution data also reveal that the tension appears to vary randomly over short time scales, roughly consistent with the lifetime of the stress peaks, suggesting that the tension fluctuations originate from stochastic adhesion dynamics.

  3. Reversible fluctuation rectifier

    NASA Astrophysics Data System (ADS)

    Sokolov, I. M.

    1999-10-01

    The analysis of a Feynman's ratchet system [J. M. R. Parrondo and P. Español, Am. J. Phys. 64, 1125 (1996)] and of its electrical counterpart, a diode engine [I. M. Sokolov, Europhys. Lett. 44, 278 (1998)] has shown that ``fluctuation rectifiers'' consisting of a nonlinear element (ratchet, diode) and a linear element (vane, resistor) kept at different temperatures always show efficiency smaller than the Carnot value, thus indicating the irreversible mode of operation. We show that this irreversibility is not intrinsic for a system in simultaneous contact with two heat baths at different temperatures and that a fluctuation rectifier can work reversibly. This is illustrated by a model with two diodes switched in opposite directions, where the Carnot efficiency is achieved when backward resistivity of the diodes tends to infinity.

  4. The cause and effect of power fluctuations near 250 kW

    SciTech Connect

    Church, L.B.

    1980-07-01

    In a 250kW Mark I TRIGA power fluctuations to an extent of 8% ({+-}4%) over a one-minute interval have been observed in three independent channels. These random and sudden changes are removed by the 'automatic' mode and are present only when the primary water system is on. Simultaneous electrical interference with the three channels from an external source (i.e., the primary pump) has been ruled out as a possible cause; so has the possible movement of the control rods, neutron chambers and lazy susan shafts by the primary water flow. A monitoring of water temperature above the core revealed changes by as much as 13 deg. C in about 10 seconds. It is thought (although not completely understood) that these temperature variations are the cause of the observed power fluctuations. (author)

  5. Fluctuating currents in stochastic thermodynamics. II. Energy conversion and nonequilibrium response in kinesin models

    NASA Astrophysics Data System (ADS)

    Altaner, Bernhard; Wachtel, Artur; Vollmer, Jürgen

    2015-10-01

    Unlike macroscopic engines, the molecular machinery of living cells is strongly affected by fluctuations. Stochastic thermodynamics uses Markovian jump processes to model the random transitions between the chemical and configurational states of these biological macromolecules. A recently developed theoretical framework [A. Wachtel, J. Vollmer, and B. Altaner, Phys. Rev. E 92, 042132 (2015), 10.1103/PhysRevE.92.042132] provides a simple algorithm for the determination of macroscopic currents and correlation integrals of arbitrary fluctuating currents. Here we use it to discuss energy conversion and nonequilibrium response in different models for the molecular motor kinesin. Methodologically, our results demonstrate the effectiveness of the algorithm in dealing with parameter-dependent stochastic models. For the concrete biophysical problem our results reveal two interesting features in experimentally accessible parameter regions: the validity of a nonequilibrium Green-Kubo relation at mechanical stalling as well as a negative differential mobility for superstalling forces.

  6. Universal fluctuations of the AEX index

    NASA Astrophysics Data System (ADS)

    Gonçalves, Rui; Ferreira, Helena; Stollenwerk, Nico; Pinto, Alberto Adrego

    2010-11-01

    We compute the analytic expression of the probability distributions F and F of the normalized positive and negative AEX (Netherlands) index daily returns r(t). Furthermore, we define the α re-scaled AEX daily index positive returns r( and negative returns (, which we call, after normalization, the α positive fluctuations and α negative fluctuations. We use the Kolmogorov-Smirnov statistical test as a method to find the values of α that optimize the data collapse of the histogram of the α fluctuations with the Bramwell-Holdsworth-Pinton (BHP) probability density function. The optimal parameters that we found are α+=0.46 and α-=0.43. Since the BHP probability density function appears in several other dissimilar phenomena, our result reveals a universal feature of stock exchange markets.

  7. Fractal Tempo Fluctuation and Pulse Prediction

    PubMed Central

    Rankin, Summer K.; Large, Edward W.; Fink, Philip W.

    2010-01-01

    WE INVESTIGATED PEOPLES’ ABILITY TO ADAPT TO THE fluctuating tempi of music performance. In Experiment 1, four pieces from different musical styles were chosen, and performances were recorded from a skilled pianist who was instructed to play with natural expression. Spectral and rescaled range analyses on interbeat interval time-series revealed long-range (1/f type) serial correlations and fractal scaling in each piece. Stimuli for Experiment 2 included two of the performances from Experiment 1, with mechanical versions serving as controls. Participants tapped the beat at ¼- and ⅛-note metrical levels, successfully adapting to large tempo fluctuations in both performances. Participants predicted the structured tempo fluctuations, with superior performance at the ¼-note level. Thus, listeners may exploit long-range correlations and fractal scaling to predict tempo changes in music. PMID:25190901

  8. Multicellular density fluctuations in epithelial monolayers

    NASA Astrophysics Data System (ADS)

    Zehnder, Steven M.; Wiatt, Marina K.; Uruena, Juan M.; Dunn, Alison C.; Sawyer, W. Gregory; Angelini, Thomas E.

    2015-09-01

    Changes in cell size often accompany multicellular motion in tissue, and cell number density is known to strongly influence collective migration in monolayers. Density fluctuations in other forms of active matter have been explored extensively, but not the potential role of density fluctuations in collective cell migration. Here we investigate collective motion in cell monolayers, focusing on the divergent component of the migration velocity field to probe density fluctuations. We find spatial patterns of diverging and converging cell groups throughout the monolayers, which oscillate in time with a period of approximately 3-4 h. Simultaneous fluorescence measurements of a cytosol dye within the cells show that fluid passes between groups of cells, facilitating these oscillations in cell density. Our findings reveal that cell-cell interactions in monolayers may be mediated by intercellular fluid flow.

  9. Chiral fluctuations in achiral systems

    NASA Astrophysics Data System (ADS)

    Harris, Robert A.

    2001-12-01

    "Chiral fluctuations" are defined, and their relation to "dynamic chirality" is discussed. Simple experiments to measure chiral fluctuations are proposed. The unique aspects of these measurements for systems such as atomic clusters and gases are outlined.

  10. Area-specific modulation of neural activation comparing escitalopram and citalopram revealed by pharmaco-fMRI: a randomized cross-over study.

    PubMed

    Windischberger, Christian; Lanzenberger, Rupert; Holik, Alexander; Spindelegger, Christoph; Stein, Patrycja; Moser, Ulrike; Gerstl, Florian; Fink, Martin; Moser, Ewald; Kasper, Siegfried

    2010-01-15

    Area-specific and stimulation-dependent changes of human brain activation by selective serotonin reuptake inhibitors (SSRI) are an important issue for improved understanding of treatment mechanisms, given the frequent prescription of these drugs in depression and anxiety disorders. The aim of this neuroimaging study was to investigate differences in BOLD-signal caused by administration of the SSRIs escitalopram and citalopram using pharmacological functional magnetic resonance imaging (pharmaco-fMRI). Eighteen healthy subjects participated in a placebo-controlled, randomized, double-blind study in cross-over repeated measures design. Each volunteer performed facial emotional discrimination and a sensorimotor control paradigm during three scanning sessions. Citalopram (20 mg/d), escitalopram (10 mg/d) and placebo were administered for 10 days each with a drug-free period of at least 21 days. Significant pharmacological effects on BOLD-signal were found in the amygdala, medial frontal gyrus, parahippocampal, fusiform and middle temporal gyri. Post-hoc t-tests revealed decreased BOLD-signal in the right amygdala and left parahippocampal gyrus in both pharmacological conditions, compared to placebo. Escitalopram, compared to citalopram, induced a decrease of BOLD-signal in the medial frontal gyrus and an increase in the right fusiform and left parahippocampal gyri. Drug effects were concentrated in brain regions with dense serotonergic projections. Both escitalopram and citalopram attenuated BOLD-signal in the amygdala and parahippocampal cortex to emotionally significant stimuli compared to control stimuli. We believe that reduced reactivity in the medial frontal gyrus found for escitalopram compared to citalopram administration might explain the response differences between study drugs as demonstrated in previous clinical trials.

  11. The Fluctuation Theorem

    NASA Astrophysics Data System (ADS)

    Evans, Denis J.; Searles, Debra J.

    2002-11-01

    The question of how reversible microscopic equations of motion can lead to irreversible macroscopic behaviour has been one of the central issues in statistical mechanics for more than a century. The basic issues were known to Gibbs. Boltzmann conducted a very public debate with Loschmidt and others without a satisfactory resolution. In recent decades there has been no real change in the situation. In 1993 we discovered a relation, subsequently known as the Fluctuation Theorem (FT), which gives an analytical expression for the probability of observing Second Law violating dynamical fluctuations in thermostatted dissipative non-equilibrium systems. The relation was derived heuristically and applied to the special case of dissipative non-equilibrium systems subject to constant energy 'thermostatting'. These restrictions meant that the full importance of the Theorem was not immediately apparent. Within a few years, derivations of the Theorem were improved but it has only been in the last few of years that the generality of the Theorem has been appreciated. We now know that the Second Law of Thermodynamics can be derived assuming ergodicity at equilibrium, and causality. We take the assumption of causality to be axiomatic. It is causality which ultimately is responsible for breaking time reversal symmetry and which leads to the possibility of irreversible macroscopic behaviour. The Fluctuation Theorem does much more than merely prove that in large systems observed for long periods of time, the Second Law is overwhelmingly likely to be valid. The Fluctuation Theorem quantifies the probability of observing Second Law violations in small systems observed for a short time. Unlike the Boltzmann equation, the FT is completely consistent with Loschmidt's observation that for time reversible dynamics, every dynamical phase space trajectory and its conjugate time reversed 'anti-trajectory', are both solutions of the underlying equations of motion. Indeed the standard proofs of

  12. Bed load fluctuations in a steep channel

    NASA Astrophysics Data System (ADS)

    Ghilardi, Tamara; Franca, Mário J.; Schleiss, Anton J.

    2014-08-01

    Bed load transport rate fluctuations have been observed over time in steep rivers and flumes with wide grain size distributions even under constant sediment feeding and water discharge. The observed bed load transport rate pulses are periodic and a consequence of grain sorting. Moreover, the presence of large, relatively immobile boulders, such as erratic stones, which are often present in mountain streams, has an impact on flow conditions. The detailed analysis of a 13 h laboratory experiment is presented in this paper. Boulders were randomly placed in a flume with a steep slope (6.7%), and water and sediment were constantly supplied to the flume. Along with the sediment transport and bulk mean flow velocity, the boulder protrusion, boulder surface, and number of hydraulic jumps, which are indicators of the channel morphology, were measured regularly during the experiment. Periodic bed load transport rate pulses are clearly visible in the data collected during this long-duration experiment, along with correlated fluctuations in the flow velocity and bed morphology. The links among the bulk velocity, the time evolution of the morphology variables, and the bed load transport rate are analyzed via correlational analysis, showing that the fluctuations are strongly related. A phase analysis of all observed variables is performed, and the average shapes of the time cycles of the fluctuations are shown. Observations indicate that the detected periodic fluctuations correspond to different bed states. Furthermore, the grain size distribution through the channel, which varies in time and space, clearly influences these bed load transport rate pulses. Finally, known bed load transport rate formulae are tested, showing that only the application of a drag shear stress allows a correct estimation of the time fluctuations.

  13. Hydrodynamic Fluctuations in Laminar Fluid Flow. II. Fluctuating Squire Equation

    NASA Astrophysics Data System (ADS)

    Ortiz de Zárate, José M.; Sengers, Jan V.

    2013-02-01

    We use fluctuating hydrodynamics to evaluate the enhancement of thermally excited fluctuations in laminar fluid flow using plane Couette flow as a representative example. In a previous publication (J. Stat. Phys. 144:774, 2011) we derived the energy amplification arising from thermally excited wall-normal fluctuations by solving a fluctuating Orr-Sommerfeld equation. In the present paper we derive the energy amplification arising from wall-normal vorticity fluctuation by solving a fluctuating Squire equation. The thermally excited wall-normal vorticity fluctuations turn out to yield the dominant contribution to the energy amplification. In addition, we show that thermally excited streaks, even in the absence of any externally imposed perturbations, are present in laminar fluid flow.

  14. Phase transition in spin systems with various types of fluctuations

    PubMed Central

    MIYASHITA, Seiji

    2010-01-01

    Various types ordering processes in systems with large fluctuation are overviewed. Generally, the so-called order–disorder phase transition takes place in competition between the interaction causing the system be ordered and the entropy causing a random disturbance. Nature of the phase transition strongly depends on the type of fluctuation which is determined by the structure of the order parameter of the system. As to the critical property of phase transitions, the concept “universality of the critical phenomena” is well established. However, we still find variety of features of ordering processes. In this article, we study effects of various mechanisms which bring large fluctuation in the system, e.g., continuous symmetry of the spin in low dimensions, contradictions among interactions (frustration), randomness of the lattice, quantum fluctuations, and a long range interaction in off-lattice systems. PMID:20689226

  15. The Nature and Perception of Fluctuations in Human Musical Rhythms

    PubMed Central

    Hennig, Holger; Fleischmann, Ragnar; Fredebohm, Anneke; Hagmayer, York; Nagler, Jan; Witt, Annette; Theis, Fabian J.; Geisel, Theo

    2011-01-01

    Although human musical performances represent one of the most valuable achievements of mankind, the best musicians perform imperfectly. Musical rhythms are not entirely accurate and thus inevitably deviate from the ideal beat pattern. Nevertheless, computer generated perfect beat patterns are frequently devalued by listeners due to a perceived lack of human touch. Professional audio editing software therefore offers a humanizing feature which artificially generates rhythmic fluctuations. However, the built-in humanizing units are essentially random number generators producing only simple uncorrelated fluctuations. Here, for the first time, we establish long-range fluctuations as an inevitable natural companion of both simple and complex human rhythmic performances. Moreover, we demonstrate that listeners strongly prefer long-range correlated fluctuations in musical rhythms. Thus, the favorable fluctuation type for humanizing interbeat intervals coincides with the one generically inherent in human musical performances. PMID:22046289

  16. Conformational Fluctuations of Chromosomal DNA in E. coli

    NASA Astrophysics Data System (ADS)

    Freeman, Clarissa; Meiners, Jens-Christian

    2012-02-01

    We measured the conformational fluctuations of the bacterial chromosome in E. Coli in vivo using fluorescence correlation spectroscopy (FCS). The chromosomal DNA was randomly decorated with a cell-permeable intercalating dye. Conformational fluctuations of the DNA move the fluorophores stochastically into the diffraction-limited excitation volume of a focused laser beam. The time correlation function of the fluorescence intensity reflects the underlying dynamics of the DNA on length scales down to ˜200 nm. A comparison between live cells and dead yet structurally intact cells shows identical fluctuation spectra for short time scales, yet substantial differences for frequencies below 100 Hz. Live cells show much stronger fluctuations in this regime. This observation points to the crucial importance of active molecular motor action, as opposed to passive thermal noise, in driving larger conformational fluctuations in the chromosomal DNA, in particular on length scales exceeding ˜500 nm.

  17. Synchronization of fluctuating delay-coupled chaotic networks

    NASA Astrophysics Data System (ADS)

    Jiménez-Martín, Manuel; Rodríguez-Laguna, Javier; D'Huys, Otti; de la Rubia, Javier; Korutcheva, Elka

    2017-05-01

    We study the synchronization of chaotic units connected through time-delayed fluctuating interactions. Focusing on small-world networks of Bernoulli and Logistic units with a fixed chiral backbone, we compare the synchronization properties of static and fluctuating networks in the regime of large delays. We find that random network switching may enhance the stability of synchronized states. Synchronization appears to be maximally stable when fluctuations are much faster than the time-delay, whereas it disappears for very slow fluctuations. For fluctuation time scales of the order of the time-delay, we report a resynchronizing effect in finite-size networks. Moreover, we observe characteristic oscillations in all regimes, with a periodicity related to the time-delay, as the system approaches or drifts away from the synchronized state.

  18. Ground state energy fluctuations in the nuclear shell model

    NASA Astrophysics Data System (ADS)

    Velázquez, Víctor; Hirsch, Jorge G.; Frank, Alejandro; Barea, José; Zuker, Andrés P.

    2005-05-01

    Statistical fluctuations of the nuclear ground state energies are estimated using shell model calculations in which particles in the valence shells interact through well-defined forces, and are coupled to an upper shell governed by random 2-body interactions. Induced ground-state energy fluctuations are found to be one order of magnitude smaller than those previously associated with chaotic components, in close agreement with independent perturbative estimates based on the spreading widths of excited states.

  19. Fluctuations, Intermittency and Predictivity

    NASA Astrophysics Data System (ADS)

    Charbonneau, Paul

    This chapter considers the various mechanisms capable of producing amplitude and duration variations in the various dynamo models introduced in Chap. 3 (10.1007/978-3-642-32093-4_3). After a survey of observed and inferred fluctuation patterns of the solar cycle, the effects on the basic cycle of stochastic forcing, dynamical nonlinearities and time delay are considered in turn. The occurrence of intermittency in a subset of these models is then investigated, with an eye on explaining Grand Minima observed in the solar activity record. The chapter closes with a brief discussion of solar cycle prediction schemes based on dynamo models.

  20. Large-scale structure of randomly jammed spheres

    NASA Astrophysics Data System (ADS)

    Ikeda, Atsushi; Berthier, Ludovic; Parisi, Giorgio

    2017-05-01

    We numerically analyze the density field of three-dimensional randomly jammed packings of monodisperse soft frictionless spherical particles, paying special attention to fluctuations occurring at large length scales. We study in detail the two-point static structure factor at low wave vectors in Fourier space. We also analyze the nature of the density field in real space by studying the large-distance behavior of the two-point pair correlation function, of density fluctuations in subsystems of increasing sizes, and of the direct correlation function. We show that such real space analysis can be greatly improved by introducing a coarse-grained density field to disentangle genuine large-scale correlations from purely local effects. Our results confirm that both Fourier and real space signatures of vanishing density fluctuations at large scale are absent, indicating that randomly jammed packings are not hyperuniform. In addition, we establish that the pair correlation function displays a surprisingly complex structure at large distances, which is however not compatible with the long-range negative correlation of hyperuniform systems but fully compatible with an analytic form for the structure factor. This implies that the direct correlation function is short ranged, as we also demonstrate directly. Our results reveal that density fluctuations in jammed packings do not follow the behavior expected for random hyperuniform materials, but display instead a more complex behavior.

  1. Fluctuation relations for anisotropic systems

    NASA Astrophysics Data System (ADS)

    Villavicencio-Sanchez, R.; Harris, R. J.; Touchette, H.

    2014-02-01

    Currents of particles or energy in driven non-equilibrium steady states are known to satisfy certain symmetries, referred to as fluctuation relations, determining the ratio of the probabilities of positive fluctuations to negative ones. A generalization of these fluctuation relations has been proposed recently for extended non-equilibrium systems of dimension greater than one, assuming, crucially, that they are isotropic (Hurtado P. I., Pérez-Espigares C., del Pozo J. J. and Garrido P. L., Proc. Natl. Acad. Sci. U.S.A., 108 (2011) 7704). Here we relax this assumption and derive a fluctuation relation for d-dimensional systems having anisotropic bulk driving rates. We test the validity of this anisotropic fluctuation relation by calculating the particle current fluctuations in the 2d anisotropic zero-range process, using both exact and fluctuating hydrodynamic approaches.

  2. Distribution of current fluctuations in a bistable conductor

    NASA Astrophysics Data System (ADS)

    Singh, S.; Peltonen, J. T.; Khaymovich, I. M.; Koski, J. V.; Flindt, C.; Pekola, J. P.

    2016-12-01

    We measure the full distribution of current fluctuations in a single-electron transistor with a controllable bistability. The conductance switches randomly between two levels due to the tunneling of single electrons in a separate single-electron box. The electrical fluctuations are detected over a wide range of time scales and excellent agreement with theoretical predictions is found. For long integration times, the distribution of the time-averaged current obeys the large-deviation principle. We formulate and verify a fluctuation relation for the bistable region of the current distribution.

  3. Microrheology, Stress Fluctuations, and Active Behavior of Living Cells

    NASA Astrophysics Data System (ADS)

    Lau, A. W.; Hoffman, B. D.; Davies, A.; Crocker, J. C.; Lubensky, T. C.

    2003-11-01

    We report the first measurements of the intrinsic strain fluctuations of living cells using a recently developed tracer correlation technique along with a theoretical framework for interpreting such data in heterogeneous media with nonthermal driving. The fluctuations' spatial and temporal correlations indicate that the cytoskeleton can be treated as a course-grained continuum with power-law rheology, driven by a spatially random stress tensor field. Combined with recent cell rheology results, our data imply that intracellular stress fluctuations have a nearly 1/ω2 power spectrum, as expected for a continuum with a slowly evolving internal prestress.

  4. Impact of magnetic fluctuations on lattice excitations in fcc nickel.

    PubMed

    Körmann, Fritz; Ma, Pui-Wai; Dudarev, Sergei L; Neugebauer, Jörg

    2016-02-24

    The spin-space averaging formalism is applied to compute atomic forces and phonon spectra for magnetically excited states of fcc nickel. Transverse and longitudinal magnetic fluctuations are taken into account by a combination of magnetic special quasi random structures and constrained spin-density-functional theory. It turns out that for fcc Ni interatomic force constants and phonon spectra are almost unaffected by both kinds of spin fluctuations. Given the computational expense to simulate coupled magnetic and atomic fluctuations, this insight facilitates computational modeling of magnetic alloys such as Ni-based superalloys.

  5. A multiscale hybrid algorithm for fluctuating hydrodynamics

    NASA Astrophysics Data System (ADS)

    Williams, Sarah Anne

    We develop an algorithmic hybrid for simulating multiscale fluid flow with microscopic fluctuations. Random fluctuations occur in fluids at microscopic scales, and these microscopic fluctuations can lead to macroscopic system effects. For example, in the Rayleigh-Taylor problem, where a relatively heavy gas sits on top of a relatively light gas, spontaneous microscopic fluctuation at the interface of the gases leads to turbulent mixing. Given near-term computational power, the physical and temporal domain on which these systems can be studied using traditional particle simulations is extremely limited. Therefore, we seek algorithmic solutions to increase the effective computing power available to study such problems. We develop an explicit numerical solver for the Landau-Lifshitz Navier-Stokes (LLNS) equations, which incorporate thermal fluctuations into macroscopic hydrodynamics via stochastic; fluxes. A major goal is to correctly preserve the influence of the microscopic fluctuations on the behavior of the system. We show that several classical approaches fail to accurately reproduce fluctuations in energy or density, and we introduce a customized conservative centered scheme with a third-order Runge-Kutta temporal integrator that is specficially designed to produce correct fluctuations in all conserved quantities. We then use the adaptive mesh and algorithm refinement (AMAR) paradigm to create a multiscale hybrid method by coupling our LLNS solver with the direct simulation Monte Carlo (DSMC) particle method. We present numerical tests of systems in and out of equilibrium, including time-dependent systems, and demonstrate dynamic adaptive refinement. Mean system behavior and second moment statistics of our simulations match theoretical values and benchmarks well. We find that particular attention should be paid to the spectrum of the flux at the interface between the particle and continuum methods, specifically at non-hydrodynamic time scales. As an extension of

  6. Fluctuation microscopy: a probe of medium range order

    NASA Astrophysics Data System (ADS)

    Treacy, M. M. J.; Gibson, J. M.; Fan, L.; Paterson, D. J.; McNulty, I.

    2005-12-01

    Fluctuation microscopy is a hybrid diffraction-imaging technique that detects medium range order in amorphous materials by examining spatial fluctuations in coherent scattering. These fluctuations appear as speckle in images and diffraction patterns. The volume of material contributing to the speckle is determined by the point-spread function (the resolution) of the imaging optics and the sample thickness. The spatial periodicities being probed are related to the diffraction vector. Statistical analysis of the speckle allows the random and non-random (ordered) contributions to be discriminated. The image resolution that gives the maximum speckle contrast, as determined by the normalized variance of the image intensity, is determined by the characteristic length scale of the ordering. Because medium range ordering length scales can extend out to about the tenth coordination shell, fluctuation microscopy tends to be a low image resolution technique. This review presents the kinematical scattering theory underpinning fluctuation microscopy and a description of fluctuation electron microscopy as it has been employed in the transmission electron microscope for studying amorphous materials. Recent results using soft x-rays for studying nanoscale materials are also presented. We summarize outstanding issues and point to possible future directions for fluctuation microscopy as a technique.

  7. Random walk with barriers

    PubMed Central

    Novikov, Dmitry S.; Fieremans, Els; Jensen, Jens H.; Helpern, Joseph A.

    2011-01-01

    Restrictions to molecular motion by barriers (membranes) are ubiquitous in porous media, composite materials and biological tissues. A major challenge is to characterize the microstructure of a material or an organism nondestructively using a bulk transport measurement. Here we demonstrate how the long-range structural correlations introduced by permeable membranes give rise to distinct features of transport. We consider Brownian motion restricted by randomly placed and oriented membranes (d − 1 dimensional planes in d dimensions) and focus on the disorder-averaged diffusion propagator using a scattering approach. The renormalization group solution reveals a scaling behavior of the diffusion coefficient for large times, with a characteristically slow inverse square root time dependence for any d. Its origin lies in the strong structural fluctuations introduced by the spatially extended random restrictions, representing a novel universality class of the structural disorder. Our results agree well with Monte Carlo simulations in two dimensions. They can be used to identify permeable barriers as restrictions to transport, and to quantify their permeability and surface area. PMID:21686083

  8. Gradient Driven Fluctuations

    NASA Technical Reports Server (NTRS)

    Cannell, David

    2005-01-01

    We have worked with our collaborators at the University of Milan (Professor Marzio Giglio and his group-supported by ASI) to define the science required to measure gradient driven fluctuations in the microgravity environment. Such a study would provide an accurate test of the extent to which the theory of fluctuating hydrodynamics can be used to predict the properties of fluids maintained in a stressed, non-equilibrium state. As mentioned above, the results should also provide direct visual insight into the behavior of a variety of fluid systems containing gradients or interfaces, when placed in the microgravity environment. With support from the current grant, we have identified three key systems for detailed investigation. These three systems are: 1) A single-component fluid to be studied in the presence of a temperature gradient; 2) A mixture of two organic liquids to be studied both in the presence of a temperature gradient, which induces a steady-state concentration gradient, and with the temperature gradient removed, but while the concentration gradient is dying by means of diffusion; 3) Various pairs of liquids undergoing free diffusion, including a proteidbuffer solution and pairs of mixtures having different concentrations, to allow us to vary the differences in fluid properties in a controlled manner.

  9. Generalized survival in step fluctuations

    NASA Astrophysics Data System (ADS)

    Tao, C. G.; Cullen, W. G.; Williams, E. D.; Dasgupta, C.

    2007-08-01

    The properties of the generalized survival probability, that is, the probability of not crossing an arbitrary location R during relaxation, have been investigated experimentally (via scanning tunneling microscope observations) and numerically. The results confirm that the generalized survival probability decays exponentially with a time constant τs(R) . The distance dependence of the time constant is shown to be τs(R)=τs0exp[-R/w(T)] , where w2(T) is the material-dependent mean-squared width of the step fluctuations. The result reveals the dependence on the physical parameters of the system inherent in the prior prediction of the time constant scaling with R/Lα , with L the system size and α the roughness exponent. The survival behavior is also analyzed using a contrasting concept, the generalized inside survival Sin(t,R) , which involves fluctuations to an arbitrary location R further from the average. Numerical simulations of the inside survival probability also show an exponential time dependence, and the extracted time constant empirically shows (R/w)λ behavior, with λ varying over 0.6 to 0.8 as the sampling conditions are changed. The experimental data show similar behavior, and can be well fit with λ=1.0 for T=300K , and 0.5<λ<1 for T=460K . Over this temperature range, the ratio of the fixed sampling time to the underlying physical time constant, and thus the true correlation time, increases by a factor of ˜103 . Preliminary analysis indicates that the scaling effect due to the true correlation time is relevant in the parameter space of the experimental observations.

  10. Persistence of singlet fluctuations in the coupled spin tetrahedra system Cu2Te2O5Br2 revealed by high-field magnetization, 79Br NQR, and 125Te NMR

    NASA Astrophysics Data System (ADS)

    Baek, S.-H.; Choi, K.-Y.; Berger, H.; Büchner, B.; Grafe, H.-J.

    2012-11-01

    We present high-field magnetization and 79Br nuclear quadrupole resonance (NQR) and 125Te nuclear magnetic resonance (NMR) studies in the weakly coupled Cu2+ (S=1/2) tetrahedral system Cu2Te2O5Br2. The field-induced level crossing effects were observed by the magnetization measurements in a long-ranged magnetically ordered state which was confirmed by a strong divergence of the spin-lattice relaxation rate T1-1 at T0=13.5 K. In the paramagnetic state, T1-1 reveals an effective singlet-triplet spin gap much larger than that observed by static bulk measurements. Our results imply that the inter- and the intratetrahedral interactions compete, but at the same time they cooperate strengthening effectively the local intratetrahedral exchange couplings. We discuss that the unusual feature originates from the frustrated intertetrahedral interactions.

  11. Vorticity Fluctuations in Plane Couette Flow

    NASA Astrophysics Data System (ADS)

    Ortiz de Zarate, Jose; Sengers, Jan V.

    2010-11-01

    In this presentation we evaluate the flow-induced amplification of the thermal noise in plane Couette configuration. The physical origin of the noise is the random nature of molecular collisions, that contribute with a stochastic component to the stress tensor (Landau's fluctuating hydrodynamics). This intrinsic stochastic forcing is then amplified by the mode- coupling mechanisms associated to shear flow. In a linear approximation, noise amplification can be studied by solving stochastic Orr-Sommerfeld and Squire equations. We compare the efficiency of the different mechanisms, being the most important the direct coupling between Squire and Orr-Sommerfed equations. The main effect is to amplify wall-normal vorticity fluctuations with an spanwise modulation at wave number around 1.5, a configuration that resembles the streaks that have been proposed as precursors of the flow instability.

  12. Hearing random matrices and random waves

    NASA Astrophysics Data System (ADS)

    Berry, M. V.; Shukla, Pragya

    2013-01-01

    The eigenangles of random matrices in the three standard circular ensembles are rendered as sounds in several different ways. The different fluctuation properties of these ensembles can be heard, and distinguished from the two extreme cases, of angles that are distributed uniformly round the unit circle and those that are random and uncorrelated. Similarly, in Gaussian random superpositions of monochromatic plane waves in one, two and three dimensions, the dimensions can be distinguished in sounds created from one-dimensional sections. This paper is dedicated to the memory of Richard E Crandall.

  13. The fluctuation test.

    PubMed

    Bridges, B A

    1980-11-01

    The fluctuation test is an assay for the detection of mutation induction in bacteria by chemicals, carried out in liquid medium, and scored by counting the number out of around 50 tubes or wells that turn yellow. It is suitable for the Ames Salmonella strains or for Escherichia coli WP2 trp and its derivatives. Calcium precipitated microsomes, S9 fraction or freshly prepared hepatocytes can be incorporated for metabolic activation. It is comparable to the Ames test in its ability to detect mutagens and carcinogens and generally shares the limitations of that test as regards extrapolation to animals and man. Its disadvantages are that it is marginally slower and slightly more labour intensive than the Ames protocol. For certain applications, however, these disadvantages may be offset by the advantages of somewhat greater sensitivity, ability to be automated, and facility for using hepatocytes for metabolic activation. The test is particularly suitable for the testing of aqueous samples containing low levels of mutagen.

  14. Nanoscale thermal fluctuation spectroscopy

    NASA Astrophysics Data System (ADS)

    Garrity, Patrick Louis

    The utilization of thermal fluctuations or Johnson/Nyquist noise as a spectroscopic method to determine transport properties in conductors or semiconductors is developed in this paper. The autocorrelation function is obtained from power spectral density measurements thus enabling electronic transport property calculation through the Green-Kubo formalism. This experimental approach is distinct from traditional numerical methods such as molecular dynamics simulations, which have been used to extract the autocorrelation function and directly related physics only. This work reports multi-transport property measurements consisting of the electronic relaxation time, resistivity, mobility, diffusion coefficient, electronic contribution to thermal conductivity and Lorenz number from experimental data. Double validation of the experiment was accomplished through the use of a standard reference material and a standard measurement method, i.e. four-probe collinear resistivity technique. The advantages to this new experimental technique include the elimination of any required thermal or potential gradients, multi-transport property measurements within one experiment, very low error and the ability to apply controlled boundary conditions while gathering data. This research has experimentally assessed the gas pressure and flow effects of helium and argon on 30 nm Au and Cu thin films. The results show a reduction in Au and Cu electronic thermal conductivity and electrical resistivity when subjected to helium and argon pressure and flow. The perturbed electronic transport coefficients, attributed to increased electron scattering at the surface, were so dominant that further data was collected through straight-forward resistance measurements. The resistance data confirmed the thermal noise measurements thus lending considerable evidence to the presence of thin film surface scattering due to elastic and inelastic gas particle scattering effects with the electron ensemble. Keywords

  15. Fluctuating multicomponent lattice Boltzmann model.

    PubMed

    Belardinelli, D; Sbragaglia, M; Biferale, L; Gross, M; Varnik, F

    2015-02-01

    Current implementations of fluctuating lattice Boltzmann equations (FLBEs) describe single component fluids. In this paper, a model based on the continuum kinetic Boltzmann equation for describing multicomponent fluids is extended to incorporate the effects of thermal fluctuations. The thus obtained fluctuating Boltzmann equation is first linearized to apply the theory of linear fluctuations, and expressions for the noise covariances are determined by invoking the fluctuation-dissipation theorem directly at the kinetic level. Crucial for our analysis is the projection of the Boltzmann equation onto the orthonormal Hermite basis. By integrating in space and time the fluctuating Boltzmann equation with a discrete number of velocities, the FLBE is obtained for both ideal and nonideal multicomponent fluids. Numerical simulations are specialized to the case where mean-field interactions are introduced on the lattice, indicating a proper thermalization of the system.

  16. Fluctuating Thermodynamics for Biological Processes

    NASA Astrophysics Data System (ADS)

    Ham, Sihyun

    Because biomolecular processes are largely under thermodynamic control, dynamic extension of thermodynamics is necessary to uncover the mechanisms and driving factors of fluctuating processes. The fluctuating thermodynamics technology presented in this talk offers a practical means for the thermodynamic characterization of conformational dynamics in biomolecules. The use of fluctuating thermodynamics has the potential to provide a comprehensive picture of fluctuating phenomena in diverse biological processes. Through the application of fluctuating thermodynamics, we provide a thermodynamic perspective on the misfolding and aggregation of the various proteins associated with human diseases. In this talk, I will present the detailed concepts and applications of the fluctuating thermodynamics technology for elucidating biological processes. This work was supported by Samsung Science and Technology Foundation under Project Number SSTF-BA1401-13.

  17. Transport generated by dichotomous fluctuations

    NASA Astrophysics Data System (ADS)

    Kula, J.; Czernik, T.; łuczka, J.

    1996-02-01

    Overdamped motion of Brownian particles in spatially periodic potentials and subjected to fluctuations modeled by asymmetric exponentially correlated two-state noise of zero mean value is considered. The probability current is presented in a closed form and analyzed in asymptotic regimes of very long and very short correlation times of the fluctuations. Explicit results are obtained for a piecewise linear potential. The role of correlations and temporal asymmetry of fluctuations is elucidated.

  18. Thermodynamic theory of equilibrium fluctuations

    SciTech Connect

    Mishin, Y.

    2015-12-15

    The postulational basis of classical thermodynamics has been expanded to incorporate equilibrium fluctuations. The main additional elements of the proposed thermodynamic theory are the concept of quasi-equilibrium states, a definition of non-equilibrium entropy, a fundamental equation of state in the entropy representation, and a fluctuation postulate describing the probability distribution of macroscopic parameters of an isolated system. Although these elements introduce a statistical component that does not exist in classical thermodynamics, the logical structure of the theory is different from that of statistical mechanics and represents an expanded version of thermodynamics. Based on this theory, we present a regular procedure for calculations of equilibrium fluctuations of extensive parameters, intensive parameters and densities in systems with any number of fluctuating parameters. The proposed fluctuation formalism is demonstrated by four applications: (1) derivation of the complete set of fluctuation relations for a simple fluid in three different ensembles; (2) fluctuations in finite-reservoir systems interpolating between the canonical and micro-canonical ensembles; (3) derivation of fluctuation relations for excess properties of grain boundaries in binary solid solutions, and (4) derivation of the grain boundary width distribution for pre-melted grain boundaries in alloys. The last two applications offer an efficient fluctuation-based approach to calculations of interface excess properties and extraction of the disjoining potential in pre-melted grain boundaries. Possible future extensions of the theory are outlined.

  19. Theory of slightly fluctuating ratchets

    NASA Astrophysics Data System (ADS)

    Rozenbaum, V. M.; Shapochkina, I. V.; Lin, S. H.; Trakhtenberg, L. I.

    2017-04-01

    We consider a Brownian particle moving in a slightly fluctuating potential. Using the perturbation theory on small potential fluctuations, we derive a general analytical expression for the average particle velocity valid for both flashing and rocking ratchets with arbitrary, stochastic or deterministic, time dependence of potential energy fluctuations. The result is determined by the Green's function for diffusion in the time-independent part of the potential and by the features of correlations in the fluctuating part of the potential. The generality of the result allows describing complex ratchet systems with competing characteristic times; these systems are exemplified by the model of a Brownian photomotor with relaxation processes of finite duration.

  20. Universality of flux-fluctuation law in complex dynamical systems

    NASA Astrophysics Data System (ADS)

    Zhou, Zhao; Huang, Zi-Gang; Huang, Liang; Lai, Ying-Cheng; Yang, Lei; Xue, De-Sheng

    2013-01-01

    Recent work has revealed a law governing flux fluctuation and the average flux in complex dynamical systems. We establish the universality of this flux-fluctuation law through the following steps: (i) We derive the law in a more general setting, showing that it depends on a single parameter characterizing the external driving; (ii) we conduct extensive numerical computations using distinct external driving, different network topologies, and multiple traffic routing strategies; and (iii) we analyze data from an actual vehicle traffic system in a major city in China to lend more credence to the universality of the flux-fluctuation law. Additional factors considered include flux fluctuation on links, window size effect, and hidden topological structures such as nodal degree correlation. Besides its fundamental importance in complex systems, the flux-fluctuation law can be used to infer certain intrinsic property of the system for potential applications such as control of complex systems for improved performance.

  1. When Human Walking is a Random Walk

    NASA Astrophysics Data System (ADS)

    Hausdorff, J. M.

    1998-03-01

    The complex, hierarchical locomotor system normally does a remarkable job of controlling an inherently unstable, multi-joint system. Nevertheless, the stride interval --- the duration of a gait cycle --- fluctuates from one stride to the next, even under stationary conditions. We used random walk analysis to study the dynamical properties of these fluctuations under normal conditions and how they change with disease and aging. Random walk analysis of the stride-to-stride fluctuations of healthy, young adult men surprisingly reveals a self-similar pattern: fluctuations at one time scale are statistically similar to those at multiple other time scales (Hausdorff et al, J Appl Phsyiol, 1995). To study the stability of this fractal property, we analyzed data obtained from healthy subjects who walked for 1 hour at their usual pace, as well as at slower and faster speeds. The stride interval fluctuations exhibited long-range correlations with power-law decay for up to a thousand strides at all three walking rates. In contrast, during metronomically-paced walking, these long-range correlations disappeared; variations in the stride interval were uncorrelated and non-fractal (Hausdorff et al, J Appl Phsyiol, 1996). To gain insight into the mechanism(s) responsible for this fractal property, we examined the effects of aging and neurological impairment. Using detrended fluctuation analysis (DFA), we computed α, a measure of the degree to which one stride interval is correlated with previous and subsequent intervals over different time scales. α was significantly lower in healthy elderly subjects compared to young adults (p < .003) and in subjects with Huntington's disease, a neuro-degenerative disorder of the central nervous system, compared to disease-free controls (p < 0.005) (Hausdorff et al, J Appl Phsyiol, 1997). α was also significantly related to degree of functional impairment in subjects with Huntington's disease (r=0.78). Recently, we have observed that just as

  2. Fluctuation dynamos and their Faraday rotation signatures

    NASA Astrophysics Data System (ADS)

    Bhat, Pallavi; Subramanian, Kandaswamy

    2013-03-01

    Turbulence is ubiquitous in many astrophysical systems like galaxies, galaxy clusters and possibly even the filaments in the intergalactic medium. We study fluctuation dynamo action in turbulent systems focusing on one observational signature, the random Faraday rotation measure (RM) from radio emission of background sources seen through the intermittent magnetic field generated by such a dynamo. We simulate the fluctuation dynamo in periodic boxes up to resolutions of 5123, with varying fluid and magnetic Reynolds numbers, and measure the resulting random RMs. We show that even though the magnetic field generated is intermittent, it still allows for contributions to the RM to be significant. When the dynamo saturates, the rms value of RM is of the order of 40-50 per cent of the value expected in a model where fields of strength Brms uniformly fill cells of the largest turbulent eddy but are randomly oriented from one cell to another. This level of RM dispersion is obtained across different values of magnetic Reynolds number and Prandtl number explored. We also use the random RMs to probe the structure of the generated fields to distinguish the contribution from intense and diffuse field regions. We find that the strong field regions (say with B > 2Brms) contribute only of the order of 15-20 per cent to the RM. Thus, rare structures do not dominate the RM; rather, the general `sea' of volume filling fluctuating fields are the dominant contributors. We also show that the magnetic integral scale, Lint, which is directly related to the RM dispersion, increases in all the runs, as Lorentz forces become important to saturate the dynamo. It appears that due to the ordering effect of the Lorentz forces, Lint of the saturated field tends to a modest fraction, 1/2-1/3 of the integral scale of the velocity field, for all our runs. These results are then applied to discuss the Faraday rotation signatures of fluctuation dynamo generated fields in young galaxies, galaxy

  3. Fluctuating mobility generation and transport in glasses.

    PubMed

    Wisitsorasak, Apiwat; Wolynes, Peter G

    2013-08-01

    In the context of the random first order transition theory we use an extended mode coupling theory of the glass transition that includes activated events to account for spatiotemporal structures in rejuvenating glasses. We numerically solve fluctuating dynamical equations for mobility and fictive temperature fields which capture both mobility generation through activated events and facilitation effects. Upon rejuvenating, a source of high mobility at a glass surface initiates a growth front of mobility which propagates into the unstable low mobility region. The speed of the front quantitatively agrees with experiments on the rejuvenation of ultrastable glasses, which "melt" from their surface.

  4. Faraday rotation echo spectroscopy and detection of quantum fluctuations.

    PubMed

    Chen, Shao-Wen; Liu, Ren-Bao

    2014-04-15

    Central spin decoherence is useful for detecting many-body physics in environments and moreover, the spin echo control can remove the effects of static thermal fluctuations so that the quantum fluctuations are revealed. The central spin decoherence approach, however, is feasible only in some special configurations and often requires uniform coupling between the central spin and individual spins in the baths, which are very challenging in experiments. Here, by making analogue between central spin decoherence and depolarization of photons, we propose a scheme of Faraday rotation echo spectroscopy (FRES) for studying quantum fluctuations in interacting spin systems. The echo control of the photon polarization is realized by flipping the polarization with a birefringence crystal. The FRES, similar to spin echo in magnetic resonance spectroscopy, can suppress the effects of the static magnetic fluctuations and therefore reveal dynamical magnetic fluctuations. We apply the scheme to a rare-earth compound LiHoF4 and calculate the echo signal, which is related to the quantum fluctuations of the system. We observe enhanced signals at the phase boundary. The FRES should be useful for studying quantum fluctuations in a broad range of spin systems, including cold atoms, quantum dots, solid-state impurities, and transparent magnetic materials.

  5. Chemical Applications of Fluctuation Spectroscopy.

    ERIC Educational Resources Information Center

    Green, Michael E.

    1984-01-01

    Examines some of the possibilities for applying the noise spectroscopic technique as well as the origin of noise (or fluctuations) which accompanies transport in physical systems. Indicates that fluctuation techniques are useful in studying liposome and micelle suspensions, liquid-liquid surfaces, semiconductors, and semiconductor devices. (JN)

  6. Fluctuation Relations for Molecular Motors

    NASA Astrophysics Data System (ADS)

    Lacoste, David; Mallick, Kirone

    This review is focused on the application of specific fluctuation relations, such as the Gallavotti-Cohen relation, to ratchet models of a molecular motor. A special emphasis is placed on two-state models such as the flashing ratchet model. We derive the Gallavotti-Cohen fluctuation relation for these models and we discuss some of its implications.

  7. Chemical Applications of Fluctuation Spectroscopy.

    ERIC Educational Resources Information Center

    Green, Michael E.

    1984-01-01

    Examines some of the possibilities for applying the noise spectroscopic technique as well as the origin of noise (or fluctuations) which accompanies transport in physical systems. Indicates that fluctuation techniques are useful in studying liposome and micelle suspensions, liquid-liquid surfaces, semiconductors, and semiconductor devices. (JN)

  8. Transition in fluctuation behaviour of normal liquids under high pressures

    NASA Astrophysics Data System (ADS)

    Postnikov, Eugene B.; Chorażewski, Mirosław

    2016-05-01

    We explore the behaviour of the inverse reduced density fluctuations and the isobaric expansion coefficient using α , ω-dibromoalkanes as an example. Two different states are revealed far from the critical point: the region of exponentially decaying fluctuations near the coexistence curve and the state with longer correlations under sufficiently high pressures. The crossing of the isotherms of the isobaric expansion coefficient occurs within the PVT range of the mentioned transition. We discuss the interplay of this crossing with the changes in molecular packing structure connected with the analysed function of the density, which represents inverse reduced volume fluctuations.

  9. Motion of Euglena gracilis: Active fluctuations and velocity distribution

    NASA Astrophysics Data System (ADS)

    Romanczuk, P.; Romensky, M.; Scholz, D.; Lobaskin, V.; Schimansky-Geier, L.

    2015-07-01

    We study the velocity distribution of unicellular swimming algae Euglena gracilis using optical microscopy and active Brownian particle theory. To characterize a peculiar feature of the experimentally observed distribution at small velocities we use the concept of active fluctuations, which was recently proposed for the description of stochastically self-propelled particles [Romanczuk, P. and Schimansky-Geier, L., Phys. Rev. Lett. 106, 230601 (2011)]. In this concept, the fluctuating forces arise due to internal random performance of the propulsive motor. The fluctuating forces are directed in parallel to the heading direction, in which the propulsion acts. In the theory, we introduce the active motion via the depot model [Schweitzer, et al., Phys. Rev. Lett. 80(23), 5044 (1998)]. We demonstrate that the theoretical predictions based on the depot model with active fluctuations are consistent with the experimentally observed velocity distributions. In addition to the model with additive active noise, we obtain theoretical results for a constant propulsion with multiplicative noise.

  10. Enhancement of thermal fluctuations in Plane Couette Flow

    NASA Astrophysics Data System (ADS)

    Ortiz de Zarate, Jose M.; Sengers, Jan V.

    2011-11-01

    Mode-coupling phenomena in systems outside equilibrium generically cause an enhancement of thermal fluctuations. These enhancements can be studied by Landau's fluctuating hydrodynamics. Here we present a detailed study for the case of plane Couette flow based on stochastically forced Orr-Sommerfeld and Squire equations. The forcing arises from random contributions to the stress tensor due to the stochastic nature of molecular collisions. This intrinsic stochastic forcing is then amplified by mode- coupling mechanisms associated with the shear flow. We discuss the different coupling mechanisms, the most important one being the direct coupling between fluctuations of the wall-normal velocity and vorticity. The most pronounced effect is amplification of wall-normal vorticity fluctuations with a spanwise modulation at dimensionless wave numbers q∥ around 1.5. Financial support: MICINN FIS2008/03801.

  11. On the composition fluctuations of reverse micelles.

    PubMed

    Tovstun, Sergey A; Razumov, Vladimir F

    2010-11-15

    The polydispersity of the reverse micelles is determined mainly by the fluctuations of their composition. The composition of the reverse micelle is a two-dimensional random variable whose components are the numbers of water (i) and surfactant (j) molecules. In this study the fluctuations of the composition of the reverse micelles are considered in the Gaussian approximation. It is shown that the standard deviation of the quantity w=i/j may be calculated from the dependence of the water vapor pressure above the microemulsion on the molar ratio W=[water]/[surfactant]. The estimation based on the literature data for microemulsion system sodium bis(2-ethylhexyl)sulfosuccinate/water/isooctane at 37°C in the range W=0-18 has shown that the relative standard deviation of the quantity w is about 10%. It is shown that the value of the composition fluctuations is related to the dependence of average composition on the concentration of reverse micelles at constant parameter W.

  12. Density fluctuations in vibrated granular materials

    SciTech Connect

    Nowak, E.R.; Knight, J.B.; Ben-Naim, E.; Jaeger, H.M.; Nagel, S.R.

    1998-02-01

    We report systematic measurements of the density of a vibrated granular material as a function of time. Monodisperse spherical beads were confined to a cylindrical container and shaken vertically. Under vibrations, the density of the pile slowly reaches a final steady-state value about which the density fluctuates. We have investigated the frequency dependence and amplitude of these fluctuations as a function of vibration intensity {Gamma}. The spectrum of density fluctuations around the steady state value provides a probe of the internal relaxation dynamics of the system and a link to recent thermodynamic theories for the settling of granular material. In particular, we propose a method to evaluate the compactivity of a powder, first put forth by Edwards and co-workers, that is the analog to temperature for a quasistatic powder. We also propose a stochastic model based on free volume considerations that captures the essential mechanism underlying the slow relaxation. We compare our experimental results with simulations of a one-dimensional model for random adsorption and desorption. {copyright} {ital 1998} {ital The American Physical Society}

  13. Population Fluctuation Promotes Cooperation in Networks

    PubMed Central

    Miller, Steve; Knowles, Joshua

    2015-01-01

    We consider the problem of explaining the emergence and evolution of cooperation in dynamic network-structured populations. Building on seminal work by Poncela et al., which shows how cooperation (in one-shot prisoner’s dilemma) is supported in growing populations by an evolutionary preferential attachment (EPA) model, we investigate the effect of fluctuations in the population size. We find that a fluctuating model – based on repeated population growth and truncation – is more robust than Poncela et al.’s in that cooperation flourishes for a wider variety of initial conditions. In terms of both the temptation to defect, and the types of strategies present in the founder network, the fluctuating population is found to lead more securely to cooperation. Further, we find that this model will also support the emergence of cooperation from pre-existing non-cooperative random networks. This model, like Poncela et al.’s, does not require agents to have memory, recognition of other agents, or other cognitive abilities, and so may suggest a more general explanation of the emergence of cooperation in early evolutionary transitions, than mechanisms such as kin selection, direct and indirect reciprocity. PMID:26061705

  14. Frequency fluctuations in silicon nanoresonators

    PubMed Central

    Sansa, Marc; Sage, Eric; Bullard, Elizabeth C.; Gély, Marc; Alava, Thomas; Colinet, Eric; Naik, Akshay K.; Villanueva, Luis Guillermo; Duraffourg, Laurent; Roukes, Michael L.; Jourdan, Guillaume; Hentz, Sébastien

    2016-01-01

    Frequency stability is key to performance of nanoresonators. This stability is thought to reach a limit with the resonator’s ability to resolve thermally-induced vibrations. Although measurements and predictions of resonator stability usually disregard fluctuations in the mechanical frequency response, these fluctuations have recently attracted considerable theoretical interest. However, their existence is very difficult to demonstrate experimentally. Here, through a literature review, we show that all studies of frequency stability report values several orders of magnitude larger than the limit imposed by thermomechanical noise. We studied a monocrystalline silicon nanoresonator at room temperature, and found a similar discrepancy. We propose a new method to show this was due to the presence of frequency fluctuations, of unexpected level. The fluctuations were not due to the instrumentation system, or to any other of the known sources investigated. These results challenge our current understanding of frequency fluctuations and call for a change in practices. PMID:26925826

  15. Thermally induced chronic developmental stress in coho salmon: Integrating measures of mortality, early growth and fluctuating asymmetry

    USGS Publications Warehouse

    Campbell, W.B.; Emlen, J.M.; Hershberger, W.K.

    1998-01-01

    Developmental stability, or homeostasis, facilitates the production of consistent phenotypes by buffering against stress. Fluctuating asymmetry is produced by developmental instability and is manifested as small random departures from bilateral symmetry. Increased fluctuating asymmetry is thought to parallel compromised fitness, in part, because stress promotes energy dissipation. Compensatory energy expenditures within the organism are required to complete development, thus promoting instability through reductions in homeostasis. Increased heterozygosity may enhance developmental stability by reducing energy dissipation from stress through increased metabolic efficiency, possibly by providing greater flexibility in metabolic pathways. Traditionally, fluctuating asymmetry has been used as a bioindicator of chronic stress, provided that selective mortality of less fit individuals did not reduce stress-mediated increases in fluctuating asymmetry to background levels produced by natural developmental error, or create data inconsistencies such as higher asymmetry in groups exposed to lower stress. Unfortunately, absence of selective mortality and its effects, while often assumed, can be difficult to substantiate. We integrated measures of early growth, mortality, fluctuating asymmetry (mandibular pores, pectoral finrays, pelvic finrays, and gillrakers on the upper and lower arms of the first branchial arch) and directional asymmetry (branchiostegal rays) to assess chronic thermal stress (fluctuating temperatures as opposed to ambient temperatures) in developing eggs from two different coho salmon (Oncorhynchus kisutch) stocks and their reciprocal hybrids. Hybridization provided insight on the capacity of heterozygosity to reduce stress during development. Although egg losses were consistently higher in crosses exposed to fluctuating temperatures, egg mortality was predominantly a function of maternal stock of origin. Post-hatch losses were higher in crosses exposed to

  16. Fluctuations and noise signatures of driven magnetic skyrmions

    NASA Astrophysics Data System (ADS)

    Díaz, Sebastián A.; Reichhardt, C. J. O.; Arovas, Daniel P.; Saxena, Avadh; Reichhardt, C.

    2017-08-01

    Magnetic skyrmions are particlelike objects with topologically protected stability which can be set into motion with an applied current. Using a particle-based model we simulate current-driven magnetic skyrmions interacting with random quenched disorder and examine the skyrmion velocity fluctuations parallel and perpendicular to the direction of motion as a function of increasing drive. We show that the Magnus force contribution to skyrmion dynamics combined with the random pinning produces an isotropic effective shaking temperature. As a result, the skyrmions form a moving crystal at large drives instead of the moving smectic state observed in systems with a negligible Magnus force where the effective shaking temperature is anisotropic. We demonstrate that spectral analysis of the velocity noise fluctuations can be used to identify dynamical phase transitions and to extract information about the different dynamic phases, and show how the velocity noise fluctuations are correlated with changes in the skyrmion Hall angle, transport features, and skyrmion lattice structure.

  17. Phase-dependent magnetoconductance fluctuations in a chaotic Josephson junction

    NASA Astrophysics Data System (ADS)

    Brouwer, P. W.; Beenakker, C. W. J.

    1996-11-01

    Motivated by recent experiments by Den Hartog et al., we present a random-matrix theory for the magnetoconductance fluctuations of a chaotic quantum dot that is coupled by point contacts to two superconductors and one or two normal metals. There are aperiodic conductance fluctuations as a function of the magnetic field through the quantum dot and 2π-periodic fluctuations as a function of the phase difference φ of the superconductors. If the coupling to the superconductors is weak compared to the coupling to the normal metals, the φ dependence of the conductance is harmonic, as observed in the experiment. In the opposite regime, the conductance becomes a random 2π-periodic function of φ, in agreement with the theory of Altshuler and Spivak. The theoretical method employs an extension of the circular ensemble which can describe the magnetic-field dependence of the scattering matrix.

  18. Cell surface fluctuations studied with defocusing microscopy

    NASA Astrophysics Data System (ADS)

    Agero, U.; Monken, C. H.; Ropert, C.; Gazzinelli, R. T.; Mesquita, O. N.

    2003-05-01

    Phase objects can become visible by slightly defocusing an optical microscope, a technique seldom used as a useful tool. We revisited the theory of defocusing and apply it to our optical microscope with optics corrected at infinity. In our approximation, we obtain that the image contrast is proportional to the two-dimensional (2D) Laplacian of the phase difference introduced by the phase object. If the index of refraction of the phase object is uniform the image obtained from defocusing microscopy is the image of curvature (Laplacian of the local thickness) of the phase object, while standard phase-contrast microscopy gives information about the thickness of the object. We made artificial phase objects and measured image contrasts with defocusing microscopy. Measured contrasts are in excellent agreement with our theoretical model. We use defocusing microscopy to study curvature fluctuations (ruffles) on the surface of macrophages (cell of the innate immune system), and try to correlate mechanical properties of macrophage surface and phagocytosis. We observe large coherent propagating structures: Their shape, speed, density are measured and curvature energy estimated. Inhomogeneities of cytoskeleton refractive index, curvature modulations due to thermal fluctuations and/or periodic changes in cytoskeleton-membrane interactions cause random fluctuations in image contrast. From the temporal and spatial contrast correlation functions, we obtain the decay time and correlation length of such fluctuations that are related to their size and the viscoelastic properties of the cytoskeleton. In order to associate the dynamics of cytoskeleton with the process of phagocytosis, we use an optical tweezers to grab a zymosan particle and put it into contact with the macrophage. We then measure the time for a single phagocytosis event. We add the drug cytochalasin D that depolymerizes the cytoskeleton F-actin network: It inhibits the large propagating coherent fluctuations on the

  19. Distributional behaviors of time-averaged observables in the Langevin equation with fluctuating diffusivity: Normal diffusion but anomalous fluctuations

    NASA Astrophysics Data System (ADS)

    Akimoto, Takuma; Yamamoto, Eiji

    2016-06-01

    We consider the Langevin equation with dichotomously fluctuating diffusivity, where the diffusion coefficient changes dichotomously over time, in order to study fluctuations of time-averaged observables in temporally heterogeneous diffusion processes. We find that the time-averaged mean-square displacement (TMSD) can be represented by the occupation time of a state in the asymptotic limit of the measurement time and hence occupation time statistics is a powerful tool for calculating the TMSD in the model. We show that the TMSD increases linearly with time (normal diffusion) but the time-averaged diffusion coefficients are intrinsically random when the mean sojourn time for one of the states diverges, i.e., intrinsic nonequilibrium processes. Thus, we find that temporally heterogeneous environments provide anomalous fluctuations of time-averaged diffusivity, which have relevance to large fluctuations of the diffusion coefficients obtained by single-particle-tracking trajectories in experiments.

  20. The origin of quantum fluctuations in microcanonical quantization

    NASA Astrophysics Data System (ADS)

    Kanenaga, Masahiko

    2004-04-01

    For the harmonic oscillator, we show that the important postulate of microcanonical quantization which yields quantum fluctuations can be derived from the random dynamics of stochastic electrodynamics, here chosen to be the ( D+1)-dimensional classical dynamics in the microcanonical quantization formalism.

  1. Revealing proton shape fluctuations with incoherent diffraction at high energy

    SciTech Connect

    Mantysaari, H.; Schenke, B.

    2016-08-30

    The di erential cross section of exclusive di ractive vector meson production in electron proton collisions carries important information on the geometric structure of the proton. More speci cally, the coherent cross section as a function of the transferred transverse momentum is sensitive to the size of the proton, while the incoherent, or proton dissociative cross section is sensitive to uctuations of the gluon distribution in coordinate space. We show that at high energies the experimentally measured coherent and incoherent cross sections for the production of J= mesons are very well reproduced within the color glass condensate framework when strong geometric uctuations of the gluon distribution in the proton are included. For meson production we also nd reasonable agreement. We study in detail the dependence of our results on various model parameters, including the average proton shape, analyze the e ect of saturation scale and color charge uctuations and constrain the degree of geometric uctuations.

  2. Revealing proton shape fluctuations with incoherent diffraction at high energy

    SciTech Connect

    Mantysaari, H.; Schenke, B.

    2016-08-30

    The di erential cross section of exclusive di ractive vector meson production in electron proton collisions carries important information on the geometric structure of the proton. More speci cally, the coherent cross section as a function of the transferred transverse momentum is sensitive to the size of the proton, while the incoherent, or proton dissociative cross section is sensitive to uctuations of the gluon distribution in coordinate space. We show that at high energies the experimentally measured coherent and incoherent cross sections for the production of J= mesons are very well reproduced within the color glass condensate framework when strong geometric uctuations of the gluon distribution in the proton are included. For meson production we also nd reasonable agreement. We study in detail the dependence of our results on various model parameters, including the average proton shape, analyze the e ect of saturation scale and color charge uctuations and constrain the degree of geometric uctuations.

  3. Revealing proton shape fluctuations with incoherent diffraction at high energy

    DOE PAGES

    Mantysaari, H.; Schenke, B.

    2016-08-30

    The di erential cross section of exclusive di ractive vector meson production in electron proton collisions carries important information on the geometric structure of the proton. More speci cally, the coherent cross section as a function of the transferred transverse momentum is sensitive to the size of the proton, while the incoherent, or proton dissociative cross section is sensitive to uctuations of the gluon distribution in coordinate space. We show that at high energies the experimentally measured coherent and incoherent cross sections for the production of J= mesons are very well reproduced within the color glass condensate framework when strongmore » geometric uctuations of the gluon distribution in the proton are included. For meson production we also nd reasonable agreement. We study in detail the dependence of our results on various model parameters, including the average proton shape, analyze the e ect of saturation scale and color charge uctuations and constrain the degree of geometric uctuations.« less

  4. Markov random fields reveal an N-terminal double beta-propeller motif as part of a bacterial hybrid two-component sensor system

    PubMed Central

    Menke, Matt; Berger, Bonnie; Cowen, Lenore

    2010-01-01

    The recent explosion in newly sequenced bacterial genomes is outpacing the capacity of researchers to try to assign functional annotation to all the new proteins. Hence, computational methods that can help predict structural motifs provide increasingly important clues in helping to determine how these proteins might function. We introduce a Markov Random Field approach tailored for recognizing proteins that fold into mainly β-structural motifs, and apply it to build recognizers for the β-propeller shapes. As an application, we identify a potential class of hybrid two-component sensor proteins, that we predict contain a double-propeller domain. PMID:20147619

  5. Chandler oscillations of the Earth's pole in the presence of fluctuational dissipative perturbations

    NASA Astrophysics Data System (ADS)

    Markov, Yu. G.; Perepelkin, V. V.; Rykhlova, L. V.; Filippova, A. S.

    2017-02-01

    Effects of fluctuational dissipative perturbations on the Earth's polar motion due to random components of the centrifugal potential are studied using a numerical-analytical approach. A combined model for the polar fluctuations is used to take into account stochastic components of the polar tides. Fluctuations excited at frequencies close to the Chandler frequency are analyzed using observations of sea level and the gravitional acceleration. Equations describing the correlation characteristics of the polar motions are presented.

  6. Fluctuation theorem: A critical review

    NASA Astrophysics Data System (ADS)

    Malek Mansour, M.; Baras, F.

    2017-10-01

    Fluctuation theorem for entropy production is revisited in the framework of stochastic processes. The applicability of the fluctuation theorem to physico-chemical systems and the resulting stochastic thermodynamics were analyzed. Some unexpected limitations are highlighted in the context of jump Markov processes. We have shown that these limitations handicap the ability of the resulting stochastic thermodynamics to correctly describe the state of non-equilibrium systems in terms of the thermodynamic properties of individual processes therein. Finally, we considered the case of diffusion processes and proved that the fluctuation theorem for entropy production becomes irrelevant at the stationary state in the case of one variable systems.

  7. Skewness of elliptic flow fluctuations

    NASA Astrophysics Data System (ADS)

    Giacalone, Giuliano; Yan, Li; Noronha-Hostler, Jacquelyn; Ollitrault, Jean-Yves

    2017-01-01

    Using event-by-event hydrodynamic calculations, we find that the fluctuations of the elliptic flow (v2) in the reaction plane have a negative skew. We compare the skewness of v2 fluctuations to that of initial eccentricity fluctuations. We show that skewness is the main effect lifting the degeneracy between higher-order cumulants, with negative skew corresponding to the hierarchy v2{4 } >v2{6 } observed in Pb+Pb collisions at the CERN Large Hadron Collider. We describe how the skewness can be measured experimentally and show that hydrodynamics naturally reproduces its magnitude and centrality dependence.

  8. O(n) model on a fluctuating planar lattice. Some exact results

    NASA Astrophysics Data System (ADS)

    Gaudin, M.; Kostov, I.

    1989-03-01

    The O(n) model on a planar random lattice with fluctuating geometry has been reformulated by one of us as a random matrix problem. Here we find the exact form of the spectral density of the random matrix along the critical line. Address after November 1988: Institute for Nuclear Research and Nuclear Energy, 72 Boulevard Lenin, 1784 Sofia, Bulgaria.

  9. Quantum entanglement and temperature fluctuations.

    PubMed

    Ourabah, Kamel; Tribeche, Mouloud

    2017-04-01

    In this paper, we consider entanglement in a system out of equilibrium, adopting the viewpoint given by the formalism of superstatistics. Such an approach yields a good effective description for a system in a slowly fluctuating environment within a weak interaction between the system and the environment. For this purpose, we introduce an alternative version of the formalism within a quantum mechanical picture and use it to study entanglement in the Heisenberg XY model, subject to temperature fluctuations. We consider both isotropic and anisotropic cases and explore the effect of different temperature fluctuations (χ^{2}, log-normal, and F distributions). Our results suggest that particular fluctuations may enhance entanglement and prevent it from vanishing at higher temperatures than those predicted for the same system at thermal equilibrium.

  10. Local fluctuations in solution mixtures

    PubMed Central

    Ploetz, Elizabeth A.; Smith, Paul E.

    2011-01-01

    An extension of the traditional Kirkwood-Buff (KB) theory of solutions is outlined which provides additional fluctuating quantities that can be used to characterize and probe the behavior of solution mixtures. Particle-energy and energy-energy fluctuations for local regions of any multicomponent solution are expressed in terms of experimentally obtainable quantities, thereby supplementing the usual particle-particle fluctuations provided by the established KB inversion approach. The expressions are then used to analyze experimental data for pure water over a range of temperatures and pressures, a variety of pure liquids, and three binary solution mixtures – methanol and water, benzene and methanol, and aqueous sodium chloride. In addition to providing information on local properties of solutions it is argued that the particle-energy and energy-energy fluctuations can also be used to test and refine solute and solvent force fields for use in computer simulation studies. PMID:21806137

  11. Nonequilibrium quantum fluctuations of work.

    PubMed

    Allahverdyan, A E

    2014-09-01

    The concept of work is basic for statistical thermodynamics. To gain a fuller understanding of work and its (quantum) features, it needs to be represented as an average of a fluctuating quantity. Here I focus on the work done between two moments of time for a thermally isolated quantum system driven by a time-dependent Hamiltonian. I formulate two natural conditions needed for the fluctuating work to be physically meaningful for a system that starts its evolution from a nonequilibrium state. The existing definitions do not satisfy these conditions due to issues that are traced back to noncommutativity. I propose a definition of fluctuating work that is free of previous drawbacks and that applies for a wide class of nonequilibrium initial states. It allows the deduction of a generalized work-fluctuation theorem that applies for an arbitrary (out-of-equilibrium) initial state.

  12. Fluctuation-Driven Neural Dynamics Reproduce Drosophila Locomotor Patterns

    PubMed Central

    Cruchet, Steeve; Gustafson, Kyle; Benton, Richard; Floreano, Dario

    2015-01-01

    The neural mechanisms determining the timing of even simple actions, such as when to walk or rest, are largely mysterious. One intriguing, but untested, hypothesis posits a role for ongoing activity fluctuations in neurons of central action selection circuits that drive animal behavior from moment to moment. To examine how fluctuating activity can contribute to action timing, we paired high-resolution measurements of freely walking Drosophila melanogaster with data-driven neural network modeling and dynamical systems analysis. We generated fluctuation-driven network models whose outputs—locomotor bouts—matched those measured from sensory-deprived Drosophila. From these models, we identified those that could also reproduce a second, unrelated dataset: the complex time-course of odor-evoked walking for genetically diverse Drosophila strains. Dynamical models that best reproduced both Drosophila basal and odor-evoked locomotor patterns exhibited specific characteristics. First, ongoing fluctuations were required. In a stochastic resonance-like manner, these fluctuations allowed neural activity to escape stable equilibria and to exceed a threshold for locomotion. Second, odor-induced shifts of equilibria in these models caused a depression in locomotor frequency following olfactory stimulation. Our models predict that activity fluctuations in action selection circuits cause behavioral output to more closely match sensory drive and may therefore enhance navigation in complex sensory environments. Together these data reveal how simple neural dynamics, when coupled with activity fluctuations, can give rise to complex patterns of animal behavior. PMID:26600381

  13. Medical management of motor fluctuations.

    PubMed

    Dewey, Richard B

    2008-08-01

    Given the magnitude of the problem of motor fluctuations in patients who have Parkinson's disease treated with levodopa, a significant effort has been expended by physicians, researchers, and pharmaceutical manufacturers over the years to find effective treatments. This article briefly reviews the medical options for managing motor fluctuations that are in common use in the United States or that are expected to be available soon.

  14. Principle of minimal work fluctuations

    NASA Astrophysics Data System (ADS)

    Xiao, Gaoyang; Gong, Jiangbin

    2015-08-01

    Understanding and manipulating work fluctuations in microscale and nanoscale systems are of both fundamental and practical interest. For example, in considering the Jarzynski equality =e-β Δ F , a change in the fluctuations of e-β W may impact how rapidly the statistical average of e-β W converges towards the theoretical value e-β Δ F, where W is the work, β is the inverse temperature, and Δ F is the free energy difference between two equilibrium states. Motivated by our previous study aiming at the suppression of work fluctuations, here we obtain a principle of minimal work fluctuations. In brief, adiabatic processes as treated in quantum and classical adiabatic theorems yield the minimal fluctuations in e-β W. In the quantum domain, if a system initially prepared at thermal equilibrium is subjected to a work protocol but isolated from a bath during the time evolution, then a quantum adiabatic process without energy level crossing (or an assisted adiabatic process reaching the same final states as in a conventional adiabatic process) yields the minimal fluctuations in e-β W, where W is the quantum work defined by two energy measurements at the beginning and at the end of the process. In the classical domain where the classical work protocol is realizable by an adiabatic process, then the classical adiabatic process also yields the minimal fluctuations in e-β W. Numerical experiments based on a Landau-Zener process confirm our theory in the quantum domain, and our theory in the classical domain explains our previous numerical findings regarding the suppression of classical work fluctuations [G. Y. Xiao and J. B. Gong, Phys. Rev. E 90, 052132 (2014), 10.1103/PhysRevE.90.052132].

  15. Principle of minimal work fluctuations.

    PubMed

    Xiao, Gaoyang; Gong, Jiangbin

    2015-08-01

    Understanding and manipulating work fluctuations in microscale and nanoscale systems are of both fundamental and practical interest. For example, in considering the Jarzynski equality 〈e-βW〉=e-βΔF, a change in the fluctuations of e-βW may impact how rapidly the statistical average of e-βW converges towards the theoretical value e-βΔF, where W is the work, β is the inverse temperature, and ΔF is the free energy difference between two equilibrium states. Motivated by our previous study aiming at the suppression of work fluctuations, here we obtain a principle of minimal work fluctuations. In brief, adiabatic processes as treated in quantum and classical adiabatic theorems yield the minimal fluctuations in e-βW. In the quantum domain, if a system initially prepared at thermal equilibrium is subjected to a work protocol but isolated from a bath during the time evolution, then a quantum adiabatic process without energy level crossing (or an assisted adiabatic process reaching the same final states as in a conventional adiabatic process) yields the minimal fluctuations in e-βW, where W is the quantum work defined by two energy measurements at the beginning and at the end of the process. In the classical domain where the classical work protocol is realizable by an adiabatic process, then the classical adiabatic process also yields the minimal fluctuations in e-βW. Numerical experiments based on a Landau-Zener process confirm our theory in the quantum domain, and our theory in the classical domain explains our previous numerical findings regarding the suppression of classical work fluctuations [G. Y. Xiao and J. B. Gong, Phys. Rev. E 90, 052132 (2014)].

  16. Fluctuation Probes of Quark Deconfinement

    SciTech Connect

    Asakawa, Masayuki; Heinz, Ulrich; Mueller, Berndt

    2000-09-04

    The size of the average fluctuations of net baryon number and electric charge in a finite volume of hadronic matter differs widely between the confined and deconfined phases. These differences may be exploited as indicators of the formation of a quark-gluon plasma in relativistic heavy-ion collisions, because fluctuations created in the initial state survive until freeze-out due to the rapid expansion of the hot fireball. (c) 2000 The American Physical Society.

  17. Fractal Dynamics of Heartbeat Interval Fluctuations in Health and Disease

    NASA Astrophysics Data System (ADS)

    Meyer, M.; Marconi, C.; Rahmel, A.; Grassi, B.; Ferretti, G.; Skinner, J. E.; Cerretelli, P.

    The dynamics of heartbeat interval time series were studied by a modified random walk analysis recently introduced as Detrended Fluctuation Analysis. In this analysis, the intrinsic fractal long-range power-law correlation properties of beat-to-beat fluctuations generated by the dynamical system (i.e. cardiac rhythm generator), after decomposition from extrinsic uncorrelated sources, can be quantified by the scaling exponent which, in healthy subjects, is about 1.0. The finding of a scaling coefficient of 1.0, indicating scale-invariant long-range power-law correlations (1/ƒnoise) of heartbeat fluctuations, would reflect a genuinely self-similar fractal process that typically generates fluctuations on a wide range of time scales. Lack of a characteristic time scale suggests that the neuroautonomic system underlying the control of heart rate dynamics helps prevent excessive mode-locking (error tolerance) that would restrict its functional responsiveness (plasticity) to environmental stimuli. The 1/ƒ dynamics of heartbeat interval fluctuations are unaffected by exposure to chronic hypoxia suggesting that the neuroautonomic cardiac control system is preadapted to hypoxia. Functional (hypothermia, cardiac disease) and/or structural (cardiac transplantation, early cardiac development) inactivation of neuroautonomic control is associated with the breakdown or absence of fractal complexity reflected by anticorrelated random walk-like dynamics, indicating that in these conditions the heart is unadapted to its environment.

  18. Fluctuations in classical sum rules

    NASA Astrophysics Data System (ADS)

    Elton, John R.; Lakshminarayan, Arul; Tomsovic, Steven

    2010-10-01

    Classical sum rules arise in a wide variety of physical contexts. Asymptotic expressions have been derived for many of these sum rules in the limit of long orbital period (or large action). Although sum-rule convergence may well be exponentially rapid for chaotic systems in a global phase-space sense with time, individual contributions to the sums may fluctuate with a width which diverges in time. Our interest is in the global convergence of sum rules as well as their local fluctuations. It turns out that a simple version of a lazy baker map gives an ideal system in which classical sum rules, their corrections, and their fluctuations can be worked out analytically. This is worked out in detail for the Hannay-Ozorio sum rule. In this particular case the rate of convergence of the sum rule is found to be governed by the Pollicott-Ruelle resonances, and both local and global boundaries for which the sum rule may converge are given. In addition, the width of the fluctuations is considered and worked out analytically, and it is shown to have an interesting dependence on the location of the region over which the sum rule is applied. It is also found that as the region of application is decreased in size the fluctuations grow. This suggests a way of controlling the length scale of the fluctuations by considering a time dependent phase-space volume, which for the lazy baker map decreases exponentially rapidly with time.

  19. Generalised tensor fluctuations and inflation

    SciTech Connect

    Cannone, Dario; Tasinato, Gianmassimo; Wands, David E-mail: g.tasinato@swansea.ac.uk

    2015-01-01

    Using an effective field theory approach to inflation, we examine novel properties of the spectrum of inflationary tensor fluctuations, that arise when breaking some of the symmetries or requirements usually imposed on the dynamics of perturbations. During single-clock inflation, time-reparameterization invariance is broken by a time-dependent cosmological background. In order to explore more general scenarios, we consider the possibility that spatial diffeomorphism invariance is also broken by effective mass terms or by derivative operators for the metric fluctuations in the Lagrangian. We investigate the cosmological consequences of the breaking of spatial diffeomorphisms, focussing on operators that affect the power spectrum of fluctuations. We identify the operators for tensor fluctuations that can provide a blue spectrum without violating the null energy condition, and operators for scalar fluctuations that lead to non-conservation of the comoving curvature perturbation on superhorizon scales even in single-clock inflation. In the last part of our work, we also examine the consequences of operators containing more than two spatial derivatives, discussing how they affect the sound speed of tensor fluctuations, and showing that they can mimic some of the interesting effects of symmetry breaking operators, even in scenarios that preserve spatial diffeomorphism invariance.

  20. Robustness of replica symmetry breaking phenomenology in random laser.

    PubMed

    Tommasi, Federico; Ignesti, Emilio; Lepri, Stefano; Cavalieri, Stefano

    2016-11-16

    Random lasers are optical sources where light is amplified by stimulated emission along random paths through an amplifying scattering medium. Connections between their physics and the one of quenched disordered nonlinear systems, notably spin glasses, have been recently suggested. Here we report a first experimental study of correlations of spectral fluctuations intensity in a random laser medium where the scatterers displacement significantly changes among consecutive shots. Remarkably, our results reveal that the replica symmetry breaking (RSB) phenomenology is robust with respect to an averaging over different realizations of the disorder. Moreover, besides opening new intriguing questions about the understanding of such a phenomenon, this work aims to clarify the connection between the RSB with the onset of the Lévy regime, i.e. the fluctuations regime that is a peculiar feature of the random lasing under critical conditions. Our results suggest that the former occurs independently of the latter and then the RSB phenomenology is a generic feature linked to the random laser threshold.

  1. Robustness of replica symmetry breaking phenomenology in random laser

    PubMed Central

    Tommasi, Federico; Ignesti, Emilio; Lepri, Stefano; Cavalieri, Stefano

    2016-01-01

    Random lasers are optical sources where light is amplified by stimulated emission along random paths through an amplifying scattering medium. Connections between their physics and the one of quenched disordered nonlinear systems, notably spin glasses, have been recently suggested. Here we report a first experimental study of correlations of spectral fluctuations intensity in a random laser medium where the scatterers displacement significantly changes among consecutive shots. Remarkably, our results reveal that the replica symmetry breaking (RSB) phenomenology is robust with respect to an averaging over different realizations of the disorder. Moreover, besides opening new intriguing questions about the understanding of such a phenomenon, this work aims to clarify the connection between the RSB with the onset of the Lévy regime, i.e. the fluctuations regime that is a peculiar feature of the random lasing under critical conditions. Our results suggest that the former occurs independently of the latter and then the RSB phenomenology is a generic feature linked to the random laser threshold. PMID:27849029

  2. Travel-time fluctuations along the TOR profile

    NASA Astrophysics Data System (ADS)

    Hock, S.; Korn, M.

    2003-04-01

    The interpretation of travel-time fluctuations is a possibility to obtain information about the statistical parameters of a random medium. There is a connection by ray theory between the autocorrelation function (ACF) of the travel-time fluctuations observed along a profile and the ACF of the slowness fluctuations. This method has been applied to travel-time observations of the P wave from the teleseismic tomography experiment TOR. The aim was to determine the small-scale random structure of the lithosphere below the receivers in terms of correlation length a and RMS-velocity fluctuation σ. The travel-time fluctuations show two different levels in relation to the IASP91 model according to the geological structure in the research area. Therefore, the data have been analysed separately in the two regions Baltic Shield and N-German Basin + Rhenohercynian Belt. Step by step improved deterministic reference models have been used to estimate the influence of these models on the scattering parameter determination. The determination of a and σ shows no systematics between reference model variation and determined scattering parameters. The parameter determination is not unaffected by the deterministic reference model. Both regions show a different behaviour for the different reference models. And they have different scattering parameters. For a tomography model we yield correlation lengths of 12-17 km and RMS-velocity fluctuations of 1.5-3 % in both regions. Because of the large distances between the receivers the ACF of the slowness fluctuations is only roughly sampled. Therefore, this method is not well suited to analyse teleseismic data.

  3. Intrinsically-generated fluctuating activity in excitatory-inhibitory networks.

    PubMed

    Mastrogiuseppe, Francesca; Ostojic, Srdjan

    2017-04-01

    Recurrent networks of non-linear units display a variety of dynamical regimes depending on the structure of their synaptic connectivity. A particularly remarkable phenomenon is the appearance of strongly fluctuating, chaotic activity in networks of deterministic, but randomly connected rate units. How this type of intrinsically generated fluctuations appears in more realistic networks of spiking neurons has been a long standing question. To ease the comparison between rate and spiking networks, recent works investigated the dynamical regimes of randomly-connected rate networks with segregated excitatory and inhibitory populations, and firing rates constrained to be positive. These works derived general dynamical mean field (DMF) equations describing the fluctuating dynamics, but solved these equations only in the case of purely inhibitory networks. Using a simplified excitatory-inhibitory architecture in which DMF equations are more easily tractable, here we show that the presence of excitation qualitatively modifies the fluctuating activity compared to purely inhibitory networks. In presence of excitation, intrinsically generated fluctuations induce a strong increase in mean firing rates, a phenomenon that is much weaker in purely inhibitory networks. Excitation moreover induces two different fluctuating regimes: for moderate overall coupling, recurrent inhibition is sufficient to stabilize fluctuations; for strong coupling, firing rates are stabilized solely by the upper bound imposed on activity, even if inhibition is stronger than excitation. These results extend to more general network architectures, and to rate networks receiving noisy inputs mimicking spiking activity. Finally, we show that signatures of the second dynamical regime appear in networks of integrate-and-fire neurons.

  4. Mesoscopic Conductance Fluctuations in Disordered Graphene

    NASA Astrophysics Data System (ADS)

    Bohra, Girish

    This thesis is focused on an experimental study of the fluctuations in the conductance of disordered graphene flakes. Conductance fluctuations (CF) are generated by varying either magnetic field (±8 T) or Fermi energy (via back-gate voltage) in both bilayer and single-layer graphene devices. A detailed comparative study of the conductance fluctuations at ultra-low temperatures (≤ 0.1 K), as a function of magnetic field and Fermi energy, is performed to address the question of whether mesoscopic transport in graphene is governed by similar theoretical principles as in regular dirty metals and semiconductors. This study reveals a dramatic deviation from ergodicity for the CF in graphene, according to which fluctuations generated by varying magnetic field are found to be much smaller than those obtained when sweeping Fermi energy. The CF also show a strongly anisotropic response to the symmetry-breaking effects of a magnetic field, applied perpendicular or parallel to the plane of the graphene sheet. An extensive study of the temperature dependence of CF is also performed (0.03 - 100 K), and further confirms the non-ergodic character of the CF in disordered graphene by showing two separate temperature cut-offs for magneto-CF and density-induced CF. The non-ergodic character and robust nature of density-induced CF suggests the complex and challenging nature of quantum interference in graphene, as compared to that in non-Dirac materials, emphasizing the need for development of more sophisticated theoretical models and a better understanding of substrate-induced disorder.

  5. Robustness of networks against fluctuation-induced cascading failures.

    PubMed

    Heide, Dominik; Schäfer, Mirko; Greiner, Martin

    2008-05-01

    Fluctuating fluxes on a complex network lead to load fluctuations at the vertices, which may cause them to become overloaded and to induce a cascading failure. A characterization of the one-point load fluctuations is presented, revealing their dependence on the nature of the flux fluctuations and on the underlying network structure. Based on these findings, an alternate robustness layout of the network is proposed. Taking load correlations between the vertices into account, an analytical prediction of the probability for the network to remain fully efficient is confirmed by simulations. Compared to previously proposed mean-flux layouts, the alternate layout comes with significantly less investment costs in the high-confidence limit.

  6. Ion antiport accelerates photosynthetic acclimation in fluctuating light environments

    PubMed Central

    Armbruster, Ute; Carrillo, L. Ruby; Venema, Kees; Pavlovic, Lazar; Schmidtmann, Elisabeth; Kornfeld, Ari; Jahns, Peter; Berry, Joseph A.; Kramer, David M.; Jonikas, Martin C.

    2014-01-01

    Many photosynthetic organisms globally, including crops, forests and algae, must grow in environments where the availability of light energy fluctuates dramatically. How photosynthesis maintains high efficiency despite such fluctuations in its energy source remains poorly understood. Here we show that Arabidopsis thaliana K+ efflux antiporter (KEA3) is critical for high photosynthetic efficiency under fluctuating light. On a shift from dark to low light, or high to low light, kea3 mutants show prolonged dissipation of absorbed light energy as heat. KEA3 localizes to the thylakoid membrane, and allows proton efflux from the thylakoid lumen by proton/potassium antiport. KEA3’s activity accelerates the downregulation of pH-dependent energy dissipation after transitions to low light, leading to faster recovery of high photosystem II quantum efficiency and increased CO2 assimilation. Our results reveal a mechanism that increases the efficiency of photosynthesis under fluctuating light. PMID:25451040

  7. Fluctuation Modes of a Twist-Bend Nematic Liquid Crystal

    NASA Astrophysics Data System (ADS)

    Parsouzi, Z.; Shamid, S. M.; Borshch, V.; Challa, P. K.; Baldwin, A. R.; Tamba, M. G.; Welch, C.; Mehl, G. H.; Gleeson, J. T.; Jakli, A.; Lavrentovich, O. D.; Allender, D. W.; Selinger, J. V.; Sprunt, S.

    2016-04-01

    We report a dynamic light-scattering study of the fluctuation modes in a thermotropic liquid crystalline mixture of monomer and dimer compounds that exhibits the twist-bend nematic (NTB ) phase. The results reveal a spectrum of overdamped fluctuations that includes two nonhydrodynamic modes and one hydrodynamic mode in the NTB phase, and a single nonhydrodynamic mode plus two hydrodynamic modes (the usual nematic optic axis or director fluctuations) in the higher temperature, uniaxial nematic phase. The properties of these fluctuations and the conditions for their observation are comprehensively explained by a Landau-de Gennes expansion of the free-energy density in terms of heliconical director and helical polarization fields that characterize the NTB structure, with the latter serving as the primary order parameter. A "coarse-graining" approximation simplifies the theoretical analysis and enables us to demonstrate quantitative agreement between the calculated and experimentally determined temperature dependence of the mode relaxation rates.

  8. Meta-analysis of randomized controlled trials reveals an improved clinical outcome of using genotype plus clinical algorithm for warfarin dosing.

    PubMed

    Liao, Zhenqi; Feng, Shaoguang; Ling, Peng; Zhang, Guoqing

    2015-02-01

    Previous studies have raised interest in using the genotyping of CYP2C9 and VKORC1 to guide warfarin dosing. However, there is lack of solid evidence to prove that genotype plus clinical algorithm provides improved clinical outcomes than the single clinical algorithm. The results of recent reported clinical trials are paradoxical and needs to be systematically evaluated. In this study, we aim to assess whether genotype plus clinical algorithm of warfarin is superior to the single clinical algorithm through a meta-analysis of randomized controlled trials (RCTs). All relevant studies from PubMed and reference lists from Jan 1, 1995 to Jan 13, 2014 were extracted and screened. Eligible studies included randomized trials that compared clinical plus pharmacogenetic algorithms group to single clinical algorithm group using adult (≥ 18 years) patients with disease conditions that require warfarin use. We further used fix-effect models to calculate the mean difference or the risk ratios (RRs) and 95% CIs to analyze the extracted data. The statistical heterogeneity was calculated using I(2). The percentage of time within the therapeutic INR range was considered to be the primary clinical outcome. The initial search strategy identified 50 citations and 7 trials were eligible. These seven trials included 1,910 participants, including 960 patients who received genotype plus clinical algorithm of warfarin dosing and 950 patients who received clinical algorithm only. We discovered that the percentage of time within the therapeutic INR range of the genotype-guided group was improved compared with the standard group in the RCTs when the initial standard dose was fixed (95% CI 0.09-0.40; I(2) = 47.8%). However, for the studies using non-fixed initial doses, the genotype-guided group failed to exhibit statistically significant outcome compared to the standard group. No significant difference was observed in the incidences of adverse events (RR 0.94, 95% CI 0.84-1.04; I(2) = 0%, p

  9. Evaluation of Overall Insolation Fluctuation Property Considering Insolation Fluctuation Independence among Various Points in Large Area

    NASA Astrophysics Data System (ADS)

    Kato, Takeyoshi; Inoue, Takato; Suzuoki, Yasuo

    Power output fluctuation of photovoltaic power generation systems (PVSs) of high penetration may cause negative impact on the load frequency control (LFC) of existing electric power utility. For the cost-effective mitigation, the proper evaluation of power output fluctuation of PVSs dispersed in large-area is very important. Based on the independence in insolation fluctuation among various points, this paper discusses the practical usability of the standard deviation (STD) of total power output fluctuation of PVSs simply calculated as 1/√N value of STD at the representative point. The statistical evaluation using the insolation observed at 5 points within 25km × 25km reveals that STD with simplified calculation would be useful to evaluate STD of ensemble average of insolation on average for a certain period. Besides, the probability density of STD with simplified calculation is almost the same with that of STD of ensemble average for the period with large STD. As a result, the simplified calculation of STD would be useful for the stochastic evaluation of STD of ensemble average insolation among area at least 25km × 25km.

  10. Screening of Random Peptide Library of Hemagglutinin from Pandemic 2009 A(H1N1) Influenza Virus Reveals Unexpected Antigenically Important Regions

    PubMed Central

    Xu, Wanghui; Han, Lu; Lin, Zhanglin

    2011-01-01

    The antigenic structure of the membrane protein hemagglutinin (HA) from the 2009 A(H1N1) influenza virus was dissected with a high-throughput screening method using complex antisera. The approach involves generating yeast cell libraries displaying a pool of random peptides of controllable lengths on the cell surface, followed by one round of fluorescence-activated cell sorting (FACS) against antisera from mouse, goat and human, respectively. The amino acid residue frequency appearing in the antigenic peptides at both the primary sequence and structural level was determined and used to identify “hot spots” or antigenically important regions. Unexpectedly, different antigenic structures were seen for different antisera. Moreover, five antigenic regions were identified, of which all but one are located in the conserved HA stem region that is responsible for membrane fusion. Our findings are corroborated by several recent studies on cross-neutralizing H1 subtype antibodies that recognize the HA stem region. The antigenic peptides identified may provide clues for creating peptide vaccines with better accessibility to memory B cells and better induction of cross-neutralizing antibodies than the whole HA protein. The scheme used in this study enables a direct mapping of the antigenic regions of viral proteins recognized by antisera, and may be useful for dissecting the antigenic structures of other viral proteins. PMID:21437206

  11. 1H-NMR analysis of CD3-epsilon reveals the presence of turn-helix structures around the ITAM motif in an otherwise random coil cytoplasmic tail.

    PubMed

    Borroto, A; Jiménez, M A; Alarcón, B; Rico, M

    1997-01-01

    The conformation adopted in solution by the cytoplasmic tail of CD3-epsilon has been analyzed by 1H-nmr. The cytoplasmic tail is mostly random coil expect for the amino acids conforming the immunoreceptor tyrosine-based activation motif (ITAM), YxxL/IxxxxxxxY xxL. Although the N-terminal Y xxL sequence of the motif is poorly folded, adopting 6-residue turn-like conformations with the Tyr side chain in two different orientations, the C-terminal Y xxL sequence is placed in a more complex structure involving a set of nonclassical alpha-helix turns and beta-turns that comprises 11 amino acids. This structure is not modified by phosphorylation of the tyrosine residue. The differences in the conformation adopted around the two tyrosines of the ITAM motif suggest that they may play different roles pertaining to either binding signal transducing proteins or, alternatively, proteins involved in other processes such as endoplasmic reticulum location.

  12. Deep Sequencing of Random Mutant Libraries Reveals the Active Site of the Narrow Specificity CphA Metallo-β-Lactamase is Fragile to Mutations

    PubMed Central

    Sun, Zhizeng; Mehta, Shrenik C.; Adamski, Carolyn J.; Gibbs, Richard A.; Palzkill, Timothy

    2016-01-01

    CphA is a Zn2+-dependent metallo-β-lactamase that efficiently hydrolyzes only carbapenem antibiotics. To understand the sequence requirements for CphA function, single codon random mutant libraries were constructed for residues in and near the active site and mutants were selected for E. coli growth on increasing concentrations of imipenem, a carbapenem antibiotic. At high concentrations of imipenem that select for phenotypically wild-type mutants, the active-site residues exhibit stringent sequence requirements in that nearly all residues in positions that contact zinc, the substrate, or the catalytic water do not tolerate amino acid substitutions. In addition, at high imipenem concentrations a number of residues that do not directly contact zinc or substrate are also essential and do not tolerate substitutions. Biochemical analysis confirmed that amino acid substitutions at essential positions decreased the stability or catalytic activity of the CphA enzyme. Therefore, the CphA active - site is fragile to substitutions, suggesting active-site residues are optimized for imipenem hydrolysis. These results also suggest that resistance to inhibitors targeted to the CphA active site would be slow to develop because of the strong sequence constraints on function. PMID:27616327

  13. Additivity, density fluctuations, and nonequilibrium thermodynamics for active Brownian particles

    NASA Astrophysics Data System (ADS)

    Chakraborti, Subhadip; Mishra, Shradha; Pradhan, Punyabrata

    2016-05-01

    Using an additivity property, we study particle-number fluctuations in a system of interacting self-propelled particles, called active Brownian particles (ABPs), which consists of repulsive disks with random self-propulsion velocities. From a fluctuation-response relation, a direct consequence of additivity, we formulate a thermodynamic theory which captures the previously observed features of nonequilibrium phase transition in the ABPs from a homogeneous fluid phase to an inhomogeneous phase of coexisting gas and liquid. We substantiate the predictions of additivity by analytically calculating the subsystem particle-number distributions in the homogeneous fluid phase away from criticality where analytically obtained distributions are compatible with simulations in the ABPs.

  14. Simulation of protonic fluctuations in hydrated protein powders

    NASA Astrophysics Data System (ADS)

    Careri, Giorgio; Milotti, Edoardo

    2003-05-01

    Protons migrating on the surface of weakly hydrated protein powders provide a percolating mesoscopic system which exhibits charge fluctuations near room temperature. In this paper, we describe a simple numerical model where the statistical redistribution of protons on a space distribution of identical side chains lying on a spherical protein surface is varied by random ionization-recombination process to investigate the noise power spectrum of the fluctuating dipole moment, the ergodicity of this system, and the occurrence of localized or extended proton distributions. The case of lysozyme is considered to this end.

  15. The MDF technique for the analysis of tokamak edge plasma fluctuations

    NASA Astrophysics Data System (ADS)

    Lafouti, M.; Ghoranneviss, M.; Meshkani, S.; Elahi, A. Salar; Elahi

    2014-02-01

    Tokamak edge plasma was analyzed by applying the multifractal detrend fluctuation analysis (MF-DFA) technique. This method has found wide application in the analysis of correlations and characterization of scaling behavior of the time-series data in physiology, finance, and natural sciences. The time evolution of the ion saturation current (Is ), the floating potential fluctuation (Vf ), the poloidal electric field (Ep ), and the radial particle flux (Γ r ) has been measured by using a set of Langmuir probes consisting of four tips on the probe head. The generalized Hurst exponents (h(q)), local fluctuation function (Fq(s)), the Rényi exponents (τ(q)) as well as the multifractal spectrum f(α h ) have been calculated by applying the MF-DFA method to Is , Vf , and the magnetohydrodynamic (MHD) fluctuation signal. Furthermore, we perform the shuffling and the phase randomization techniques to detect the sources of multifractality. The nonlinearity shape of τ(q) reveals a multifractal behavior of the time-series data. The results show that in the presence of biasing, Is , Vf , Ep , and Γ r reduce about 25%, 90%, 70%, and 50%, respectively, compared with the situation with no biasing. Also, they reduce about 15%, 90%, 35%, and 25%, respectively, after resonant helical magnetic field (RHF) application. In the presence of biasing or RHF, the amplitude of the power spectrum of Is , Vf , Γ r , and MHD activity reduce remarkably in all the ranges of frequency, while their h(q) increase. The values of h(q) have been restricted between 0.6 and 0.68. These results are evidence of the existence of long-range correlations in the plasma edge turbulence. They also show the self-similar nature of the plasma edge fluctuations. Biasing or RHF reduces the amount of Fq(s). The multifractal spectrum width of Is , Vf , and MHD fluctuation amplitude reduce about 60%, 70%, and 42%, respectively, by applying biasing. In the presence of RHF, their width reduces about 60%, 85%, and 75

  16. Improvement of Triglyceride Levels through the Intake of Enriched-β-Conglycinin Soybean (Nanahomare) Revealed in a Randomized, Double-Blind, Placebo-Controlled Study

    PubMed Central

    Nishimura, Mie; Ohkawara, Tatsuya; Sato, Yuji; Satoh, Hiroki; Takahashi, Yoko; Hajika, Makita; Nishihira, Jun

    2016-01-01

    Soybean is recognized as a beneficial food with various functional components, such as β-conglycinin, which improves lipid metabolism. We evaluated the effects of the β-conglycinin-rich soybean Nanahomare on triglyceride (TG) levels. In this randomized, double-blind, placebo-controlled study, we divided 134 adult subjects into test and placebo groups that consumed processed food containing enriched-β-conglycinin soybean or low-β-conglycinin soybean. Hematological tests and body composition measurements were performed at weeks 0 (baseline), 4, 8, and 12 of the study period. TG levels significantly decreased in the test group compared with the placebo group at weeks 4 (change from baseline to week 4, placebo: 0.27 ± 44.13 mg/dL, test: −20.31 ± 43.74 mg/dL, p = 0.035) and 12 (change from baseline to week 12, placebo: −0.14 ± 65.83 mg/dL, test: −21.30 ± 46.21 mg/dL, p = 0.041). In addition, among subjects whose baseline TG levels were ≥100 mg/dL, the levels significantly improved in the test group at weeks 4 (p = 0.010) and 12 (p = 0.030), whereas the levels were not different between the test and placebo groups among those whose baseline levels were <100 mg/dL. These results suggest that the ingestion of enriched-β-conglycinin soybean improves serum TG levels. PMID:27529274

  17. Randomly Amplified Polymorphic DNA Reveals Tight Links between Viruses and Microbes in the Bathypelagic Zone of the Northwestern Mediterranean Sea▿ †

    PubMed Central

    Winter, Christian; Weinbauer, Markus G.

    2010-01-01

    The study site located in the Mediterranean Sea was visited eight times in 2005 and 2006 to collect samples from the epipelagic (5 m), mesopelagic (200 m, 600 m), and bathypelagic (1,000 m, 2,000 m) zones. Randomly amplified polymorphic DNA PCR (RAPD-PCR) analysis was used to obtain fingerprints from microbial and viral size fractions using two different primers each. Depending on the primer used, the number of bands in the water column varied between 12 to 24 and 6 to 19 for the microbial size fraction and between 16 to 26 and 8 to 22 for the viral size fraction. The majority of sequences from the microbial fraction was related to Alphaproteobacteria, Cyanobacteria, Gammaproteobacteria, Firmicutes, and Eukaryota. Only 9% of sequences obtained from the viral fraction were of identifiable viral origin; however, 76% of sequences had no close relatives in the nr database of GenBank. Only 20.1% of complete phage genomes tested in silico resulted in potential RAPD-PCR products, and only 12% of these were targeted by both primers. Also, in silico analysis indicated that RAPD-PCR profiles obtained by the two different primers are largely representative of two different subsets of the viral community. Also, correlation analyses and Mantel tests indicate that the links between changes in the microbial and viral community were strongest in the bathypelagic. Thus, these results suggest a strong codevelopment of virus and host communities in deep waters. The data also indicate that virus communities in the bathypelagic zone can exhibit substantial temporal dynamics. PMID:20729320

  18. Quantum random number generator

    SciTech Connect

    Pooser, Raphael C.

    2016-05-10

    A quantum random number generator (QRNG) and a photon generator for a QRNG are provided. The photon generator may be operated in a spontaneous mode below a lasing threshold to emit photons. Photons emitted from the photon generator may have at least one random characteristic, which may be monitored by the QRNG to generate a random number. In one embodiment, the photon generator may include a photon emitter and an amplifier coupled to the photon emitter. The amplifier may enable the photon generator to be used in the QRNG without introducing significant bias in the random number and may enable multiplexing of multiple random numbers. The amplifier may also desensitize the photon generator to fluctuations in power supplied thereto while operating in the spontaneous mode. In one embodiment, the photon emitter and amplifier may be a tapered diode amplifier.

  19. NAC changes the course of cerebral small vessel disease in SHRSP and reveals new insights for the meaning of stases - a randomized controlled study.

    PubMed

    Bueche, Celine Zoe; Garz, Cornelia; Kropf, Siegfried; Bittner, Daniel; Li, Wenjie; Goertler, Michael; Heinze, Hans-Jochen; Reymann, Klaus; Braun, Holger; Schreiber, Stefanie

    2013-01-01

    N-Acetylcystein (NAC) reduces the reperfusion injury and infarct size in experimental macroangiopathic stroke. Here we now investigate the impact of NAC on the development of the histopathology of microangiopathic cerebrovascular disease including initial intravasal erythrocyte accumulations, blood-brain-barrier (BBB)-disturbances, microbleeds and infarcts. Spontaneously Hypertensive Stroke-Prone Rats (SHRSP) were treated with NAC (12 mg/kg body weight, daily oral application for three to 30 weeks) and compared to untreated SHRSP. In all rats the number of microbleeds, thromboses, infarcts and stases were quantified by HE-staining. Exemplary brains were stained against von Willebrand factor (vWF), IgG, Glutathione and GFAP. NAC animals exhibited significant more microbleeds, a greater number of vessels with BBB-disturbances, but also an elevation of Glutathione-levels in astrocytes surrounding small vessels. NAC-treatment reduced the numbers of thromboses, infarcts and arteriolar stases. NAC reduces the frequency of thromboses and infarcts to the expense of an increase of small microbleeds in a rat model of microangiopathic cerebrovascular disease. We suppose that NAC acts via an at least partial inactivation of vWF resulting in an insufficient sealing of initial endothelial injury leading to more small microbleeds. By elevating Glutathione-levels NAC most likely exerts a radical scavenger function and protects small vessels against extended ruptures and subsequent infarcts. Finally, it reveals that stases are mainly caused by endothelial injuries and restricted thromboses.

  20. Randomly detected genetically modified (GM) maize (Zea mays L.) near a transport route revealed a fragile 45S rDNA phenotype.

    PubMed

    Waminal, Nomar Espinosa; Ryu, Ki Hyun; Choi, Sun-Hee; Kim, Hyun Hee

    2013-01-01

    Monitoring of genetically modified (GM) crops has been emphasized to prevent their potential effects on the environment and human health. Monitoring of the inadvertent dispersal of transgenic maize in several fields and transport routes in Korea was carried out by qualitative multiplex PCR, and molecular analyses were conducted to identify the events of the collected GM maize. Cytogenetic investigations through fluorescence in situ hybridization (FISH) of the GM maize were performed to check for possible changes in the 45S rDNA cluster because this cluster was reported to be sensitive to replication and transcription stress. Three GM maize kernels were collected from a transport route near Incheon port, Korea, and each was found to contain NK603, stacked MON863 x NK603, and stacked NK603 x MON810 inserts, respectively. Cytogenetic analysis of the GM maize containing the stacked NK603 x MON810 insert revealed two normal compact 5S rDNA signals, but the 45S rDNA showed a fragile phenotype, demonstrating a "beads-on-a-string" fragmentation pattern, which seems to be a consequence of genetic modification. Implications of the 45S rDNA cluster fragility in GM maize are also discussed.

  1. Randomly Detected Genetically Modified (GM) Maize (Zea mays L.) near a Transport Route Revealed a Fragile 45S rDNA Phenotype

    PubMed Central

    Waminal, Nomar Espinosa; Ryu, Ki Hyun; Choi, Sun-Hee; Kim, Hyun Hee

    2013-01-01

    Monitoring of genetically modified (GM) crops has been emphasized to prevent their potential effects on the environment and human health. Monitoring of the inadvertent dispersal of transgenic maize in several fields and transport routes in Korea was carried out by qualitative multiplex PCR, and molecular analyses were conducted to identify the events of the collected GM maize. Cytogenetic investigations through fluorescence in situ hybridization (FISH) of the GM maize were performed to check for possible changes in the 45S rDNA cluster because this cluster was reported to be sensitive to replication and transcription stress. Three GM maize kernels were collected from a transport route near Incheon port, Korea, and each was found to contain NK603, stacked MON863 x NK603, and stacked NK603 x MON810 inserts, respectively. Cytogenetic analysis of the GM maize containing the stacked NK603 x MON810 insert revealed two normal compact 5S rDNA signals, but the 45S rDNA showed a fragile phenotype, demonstrating a “beads-on-a-string” fragmentation pattern, which seems to be a consequence of genetic modification. Implications of the 45S rDNA cluster fragility in GM maize are also discussed. PMID:24040165

  2. Fluctuation dynamo based on magnetic reconnections

    NASA Astrophysics Data System (ADS)

    Baggaley, A. W.; Shukurov, A.; Barenghi, C. F.; Subramanian, K.

    2010-01-01

    We develop a new model of the fluctuation dynamo in which the magnetic field is confined to thin flux ropes advected by a multi-scale flow which models turbulence. Magnetic dissipation occurs only via reconnections of flux ropes. The model is particularly suitable for rarefied plasma, such as the solar corona or galactic halos. We investigate the kinetic energy release into heat, mediated by dynamo action, both in our model and by solving the induction equation with the same flow. We find that the flux rope dynamo is more than an order of magnitude more efficient at converting mechanical energy into heat. The probability density of the magnetic energy released during reconnections has a power-law form with the slope -3, consistent with the solar corona heating by nanoflares. We also present a nonlinear extension of the model. This shows that a plausible saturation mechanism of the fluctuation dynamo is the suppression of turbulent magnetic diffusivity, due to suppression of random stretching at the location of the flux ropes. We confirm that the probability distribution function of the magnetic line curvature has a power-law form suggested by \\citet{Sheck:2002b}. We argue, however, using our results that this does not imply a persistent folded structure of magnetic field, at least in the nonlinear stage.

  3. Thermodynamic constraints on fluctuation phenomena.

    PubMed

    Maroney, O J E

    2009-12-01

    The relationships among reversible Carnot cycles, the absence of perpetual motion machines, and the existence of a nondecreasing globally unique entropy function form the starting point of many textbook presentations of the foundations of thermodynamics. However, the thermal fluctuation phenomena associated with statistical mechanics has been argued to restrict the domain of validity of this basis of the second law of thermodynamics. Here we demonstrate that fluctuation phenomena can be incorporated into the traditional presentation, extending rather than restricting the domain of validity of the phenomenologically motivated second law. Consistency conditions lead to constraints upon the possible spectrum of thermal fluctuations. In a special case this uniquely selects the Gibbs canonical distribution and more generally incorporates the Tsallis distributions. No particular model of microscopic dynamics need be assumed.

  4. Kerr black hole thermodynamical fluctuations

    NASA Astrophysics Data System (ADS)

    Pavon, D.; Rubi, J. M.

    1985-04-01

    The near-equilibrium thermodynamical (TD) fluctuations of a massive rotating uncharged Kerr black hole immersed in a uniformly corotating radiation bath at its temperature are investigated theoretically, generalizing Schwarzschild-black-hole analysis of Pavon and Rubi(1983), based on Einstein fluctuation theory. The correlations for the energy and angular moment fluctuations and the second moments of the other TD parameters are obtained, and the generalized second law of black-hole TD and the Bekenstein (1975) interpretation of black-hole entropy are seen as functioning well in this case. A local-stability criterion and relation for TD equilibrium between the Kerr hole and its own radiation in the flat-space-time limit are derived, and a restriction between C and Lambda is deduced.

  5. Spectrum of Wind Power Fluctuations

    NASA Astrophysics Data System (ADS)

    Bandi, M. M.

    2017-01-01

    Wind power fluctuations for an individual turbine and plant have been widely reported to follow the Kolmogorov spectrum of atmospheric turbulence; both vary with a fluctuation time scale τ as τ2 /3. Yet, this scaling has not been explained through turbulence theory. Using turbines as probes of turbulence, we show the τ2 /3 scaling results from a large scale influence of atmospheric turbulence. Owing to this long-range influence spanning 100s of kilometers, when power from geographically distributed wind plants is summed into aggregate power at the grid, fluctuations average (geographic smoothing) and their scaling steepens from τ2 /3→τ4 /3, beyond which further smoothing is not possible. Our analysis demonstrates grids have already reached this τ4 /3 spectral limit to geographic smoothing.

  6. Quantum fluctuations in mesoscopic systems

    NASA Astrophysics Data System (ADS)

    Benatti, F.; Carollo, F.; Floreanini, R.; Narnhofer, H.

    2017-10-01

    Recent experimental results point to the existence of coherent quantum phenomena in systems made of a large number of particles, despite the fact that for many-body systems the presence of decoherence is hardly negligible and emerging classicality is expected. This behaviour hinges on collective observables, named quantum fluctuations, that retain a quantum character even in the thermodynamic limit: they provide useful tools for studying properties of many-body systems at the mesoscopic level, in-between the quantum microscopic scale and the classical macroscopic one. We herein present the general theory of quantum fluctuations in mesoscopic systems, and study their dynamics in a quantum open system setting, taking into account the unavoidable effects of dissipation and noise induced by the external environment. As in the case of microscopic systems, decoherence is not always the only dominating effect at the mesoscopic scale: certain types of environment can provide means for entangling collective fluctuations through a purely noisy mechanism.

  7. Fluctuations in interbank network dynamics

    NASA Astrophysics Data System (ADS)

    Cajueiro, Daniel O.; Tabak, Benjamin M.; Andrade, Roberto F. S.

    2009-03-01

    This work investigates the scaling properties of fluctuations in the flux of individual agents with respect to their average flux in an interbank network. The analyzed data provide information on daily values of fiasset , the credit provided by bank i in the interbank network, and filiab , the credit received by bank i from the other banks of the network. The investigation focuses on the scaling properties of the fluctuations in the raw data fiasset , filiab , and fR,iext(t)=fiasset-filiab , as well as on similar properties internal and external fluctuations fiint and fiext , which are derived according to a recently proposed methodology [M. Argollo de Menezes and A. L. Barabasi, Phys. Rev. Lett. 93, 068701 (2004)]. Finally, a “rolling sampling” approach is introduced in order to deal with the nonstationarity of the fluxes. The results suggest that exponents are time varying, hinting that the considered interbank network is changing with time.

  8. Thermodynamic constraints on fluctuation phenomena

    NASA Astrophysics Data System (ADS)

    Maroney, O. J. E.

    2009-12-01

    The relationships among reversible Carnot cycles, the absence of perpetual motion machines, and the existence of a nondecreasing globally unique entropy function form the starting point of many textbook presentations of the foundations of thermodynamics. However, the thermal fluctuation phenomena associated with statistical mechanics has been argued to restrict the domain of validity of this basis of the second law of thermodynamics. Here we demonstrate that fluctuation phenomena can be incorporated into the traditional presentation, extending rather than restricting the domain of validity of the phenomenologically motivated second law. Consistency conditions lead to constraints upon the possible spectrum of thermal fluctuations. In a special case this uniquely selects the Gibbs canonical distribution and more generally incorporates the Tsallis distributions. No particular model of microscopic dynamics need be assumed.

  9. Fluctuation theorem in driven nonthermal systems with quenched disorder

    SciTech Connect

    Reichhardt, Charles; Reichhardt, C J; Drocco, J A

    2009-01-01

    We demonstrate that the fluctuation theorem of Evans and Searles can be used to characterize the class of dynamics that arises in nonthermal systems of collectively interacting particles driven over random quenched disorder. By observing the frequency of entropy-destroying trajectories, we show that there are specific dynamical regimes near depinning in which this theorem holds. Hence the fluctuation theorem can be used to characterize a significantly wider class of non-equilibrium systems than previously considered. We discuss how the fluctuation theorem could be tested in specific systems where noisy dynamics appear at the transition from a pinned to a moving phase such as in vortices in type-II superconductors, magnetic domain walls, and dislocation dynamics.

  10. Thermal fluctuations biased for directional motion in molecular motors.

    PubMed

    Ishii, Yoshiharu; Taniguchi, Yuichi; Iwaki, Mitsuhiro; Yanagida, Toshio

    2008-01-01

    Recently developed single molecule measurements have demonstrated that the mechanisms for numerous protein functions involve thermal fluctuation, or Brownian motion. Protein interactions bias the random thermal noise in a manner such that the protein can perform its given functions. This phenomenon has been observed in molecular motor unidirectional movement where Brownian motion is used to preferentially bind the motor heads in one direction causing directional motility. This is analogous to that used by proteins in which spontaneous structural fluctuations are used to switch function. Seeing that two very different systems implement similar mechanisms suggests there exists a general scheme applied by diverse proteins that exploits thermal fluctuations in order to achieve their respective functions.

  11. Ab-initio theory of spin fluctuations in magnets

    NASA Astrophysics Data System (ADS)

    Antropov, Vladimir; Ke, Liqin; van Schilfgaarde, Mark; Katsnelson, Mikhael

    2011-03-01

    We propose a framework for a true ab initio theory of magnetism, based on many-body perturbation theory (MPBT). It fits in naturally with methods based MPBT such as the GW approximation; but the approach can be implemented as an extension to any existing static method for electronic structure such as the local spin density approximation to density functional theory, to include spin fluctuations. Initially we calculated the spin fluctuation contributions using random phase approximation. The self consistency procedure similar to the one used in Moryia-Kawabata theory can be naturally implemented. The fluctuation dissipation theorem is used to calculate the reduction of the mean field magnetic moment in itinerant magnets. The applications of the technique includes traditional 3d ferromagnetic metals, their alloys and compounds and 5f systems.

  12. Merits and qualms of work fluctuations in classical fluctuation theorems

    NASA Astrophysics Data System (ADS)

    Deng, Jiawen; Tan, Alvis Mazon; Hänggi, Peter; Gong, Jiangbin

    2017-01-01

    Work is one of the most basic notions in statistical mechanics, with work fluctuation theorems being one central topic in nanoscale thermodynamics. With Hamiltonian chaos commonly thought to provide a foundation for classical statistical mechanics, here we present general salient results regarding how (classical) Hamiltonian chaos generically impacts on nonequilibrium work fluctuations. For isolated chaotic systems prepared with a microcanonical distribution, work fluctuations are minimized and vanish altogether in adiabatic work protocols. For isolated chaotic systems prepared at an initial canonical distribution at inverse temperature β , work fluctuations depicted by the variance of e-β W are also minimized by adiabatic work protocols. This general result indicates that, if the variance of e-β W diverges for an adiabatic work protocol, it diverges for all nonadiabatic work protocols sharing the same initial and final Hamiltonians. Such divergence is hence not an isolated event and thus greatly impacts on the efficiency of using Jarzynski's equality to simulate free-energy differences. Theoretical results are illustrated in a Sinai model. Our general insights shall boost studies in nanoscale thermodynamics and are of fundamental importance in designing useful work protocols.

  13. Merits and qualms of work fluctuations in classical fluctuation theorems.

    PubMed

    Deng, Jiawen; Tan, Alvis Mazon; Hänggi, Peter; Gong, Jiangbin

    2017-01-01

    Work is one of the most basic notions in statistical mechanics, with work fluctuation theorems being one central topic in nanoscale thermodynamics. With Hamiltonian chaos commonly thought to provide a foundation for classical statistical mechanics, here we present general salient results regarding how (classical) Hamiltonian chaos generically impacts on nonequilibrium work fluctuations. For isolated chaotic systems prepared with a microcanonical distribution, work fluctuations are minimized and vanish altogether in adiabatic work protocols. For isolated chaotic systems prepared at an initial canonical distribution at inverse temperature β, work fluctuations depicted by the variance of e^{-βW} are also minimized by adiabatic work protocols. This general result indicates that, if the variance of e^{-βW} diverges for an adiabatic work protocol, it diverges for all nonadiabatic work protocols sharing the same initial and final Hamiltonians. Such divergence is hence not an isolated event and thus greatly impacts on the efficiency of using Jarzynski's equality to simulate free-energy differences. Theoretical results are illustrated in a Sinai model. Our general insights shall boost studies in nanoscale thermodynamics and are of fundamental importance in designing useful work protocols.

  14. Visible imaging of edge fluctuations in TFTR

    SciTech Connect

    Zweben, S.J.; Medley, S.S.

    1989-03-01

    Images of the visible light emission from the inner wall region of TFTR have been made using a rapidly gated, intensified TV camera. Strong ''filamentation'' of the neutral deuterium D..cap alpha.. light is observed when the camera gating time is <100 ..mu..sec during neutral-beam-heated discharges. These turbulent filaments vary in position randomly vs. time and have a poloidal wavelength of approx.3-5 cm which is much shorter than their parallel wavelength of approx.100 cm. A second and new type of edge fluctuation phenomenon, which we call a ''merfe,'' is also described. Merfes are a regular poloidal pattern of toroidally symmetric, small-scale marfes which move away from the inner midplane during the current decay after neutral beam injection. Some tentative interpretations of these two phenomena are presented. 27 refs., 8 figs.

  15. Maximum entropy distribution of stock price fluctuations

    NASA Astrophysics Data System (ADS)

    Bartiromo, Rosario

    2013-04-01

    In this paper we propose to use the principle of absence of arbitrage opportunities in its entropic interpretation to obtain the distribution of stock price fluctuations by maximizing its information entropy. We show that this approach leads to a physical description of the underlying dynamics as a random walk characterized by a stochastic diffusion coefficient and constrained to a given value of the expected volatility, in this way taking into account the information provided by the existence of an option market. The model is validated by a comprehensive comparison with observed distributions of both price return and diffusion coefficient. Expected volatility is the only parameter in the model and can be obtained by analysing option prices. We give an analytic formulation of the probability density function for price returns which can be used to extract expected volatility from stock option data.

  16. Membranes with Fluctuating Topology: Monte Carlo Simulations

    NASA Astrophysics Data System (ADS)

    Gompper, G.; Kroll, D. M.

    1998-09-01

    Much of the phase behavior observed in self-assembling amphiphilic systems can be understood in the context of ensembles of random surfaces. In this article, it is shown that Monte Carlo simulations of dynamically triangulated surfaces of fluctuating topology can be used to determine the structure and thermal behavior of sponge phases, as well as the sponge-to-lamellar transition in these systems. The effect of the saddle-splay modulus, κ¯, on the phase behavior is studied systematically for the first time. Our data provide strong evidence for a positive logarithmic renormalization of κ¯ this result is consistent with the lamellar-to-sponge transition observed in experiments for decreasing amphiphile concentration.

  17. Einstein equations with fluctuating volume

    NASA Astrophysics Data System (ADS)

    Dzhunushaliev, Vladimir; Quevedo, Hernando

    2017-07-01

    We develop a simple model to study classical fields on the background of a fluctuating spacetime volume. It is applied to formulate the stochastic Einstein equations with a perfect-fluid source. We investigate the particular case of a stochastic Friedmann-Lema\\^itre-Robertson-Walker cosmology, and show that the resulting field equations can lead to solutions which avoid the initial big bang singularity. By interpreting the fluctuations as the result of the presence of a quantum spacetime, we conclude that classical singularities can be avoided even within a stochastic model that include quantum effects in a very simple manner.

  18. Thermal Fluctuations and Rubber Elasticity

    NASA Astrophysics Data System (ADS)

    Xing, Xiangjun; Goldbart, Paul M.; Radzihovsky, Leo

    2007-02-01

    The effects of thermal elastic fluctuations in rubbery materials are examined. It is shown that, due to their interplay with the incompressibility constraint, these fluctuations qualitatively modify the large-deformation stress-strain relation, compared to that of classical rubber elasticity. To leading order, this mechanism provides a simple and generic explanation for the peak structure of Mooney-Rivlin stress-strain relation and shows good agreement with experiments. It also leads to the prediction of a phonon correlation function that depends on the external deformation.

  19. Thermal fluctuations and rubber elasticity.

    PubMed

    Xing, Xiangjun; Goldbart, Paul M; Radzihovsky, Leo

    2007-02-16

    The effects of thermal elastic fluctuations in rubbery materials are examined. It is shown that, due to their interplay with the incompressibility constraint, these fluctuations qualitatively modify the large-deformation stress-strain relation, compared to that of classical rubber elasticity. To leading order, this mechanism provides a simple and generic explanation for the peak structure of Mooney-Rivlin stress-strain relation and shows good agreement with experiments. It also leads to the prediction of a phonon correlation function that depends on the external deformation.

  20. Density fluctuations from warm inflation

    SciTech Connect

    Graham, Chris; Moss, Ian G. E-mail: ian.moss@ncl.ac.uk

    2009-07-01

    Thermal fluctuations provide the main source of large scale density perturbations in warm inflationary models of the early universe. For the first time, general results are obtained for the power spectrum in the case when the friction coefficient in the inflaton equation of motion depends on temperature. A large increase in the amplitude of perturbations occurs when the friction coefficient increases with temperature. This has to be taken into account when constructing models of warm inflation. New results are also given for the thermal fluctuations in the weak regime of warm inflation when the friction coefficient is relatively small.

  1. Color Confinement from Fluctuating Topology

    NASA Astrophysics Data System (ADS)

    Kharzeev, Dmitri E.

    QCD possesses a compact gauge group, and this implies a non-trivial topological structure of the vacuum. In this contribution to the Gribov-85 Memorial volume, we first discuss the origin of Gribov copies and their interpretation in terms of fluctuating topology in the QCD vacuum. We then describe the recent work with E. Levin that links the confinement of gluons and color screening to the fluctuating topology, and discuss implications for spin physics, high energy scattering, and the physics of quark-gluon plasma.

  2. Color confinement from fluctuating topology

    NASA Astrophysics Data System (ADS)

    Kharzeev, Dmitri E.

    2016-10-01

    QCD possesses a compact gauge group, and this implies a non-trivial topological structure of the vacuum. In this contribution to the Gribov-85 Memorial volume, we first discuss the origin of Gribov copies and their interpretation in terms of fluctuating topology in the QCD vacuum. We then describe the recent work with E. Levin that links the confinement of gluons and color screening to the fluctuating topology, and discuss implications for spin physics, high energy scattering, and the physics of quark-gluon plasma.

  3. Color confinement from fluctuating topology

    DOE PAGES

    Kharzeev, Dmitri E.

    2016-10-19

    QCD possesses a compact gauge group, and this implies a non-trivial topological structure of the vacuum. In this contribution to the Gribov-85 Memorial volume, we first discuss the origin of Gribov copies and their interpretation in terms of fluctuating topology in the QCD vacuum. We then describe the recent work with E. Levin that links the confinement of gluons and color screening to the fluctuating topology, and discuss implications for spin physics, high energy scattering, and the physics of quark-gluon plasma.

  4. Origin of cosmological density fluctuations

    SciTech Connect

    Carr, B.J.

    1984-11-01

    The density fluctuations required to explain the large-scale cosmological structure may have arisen spontaneously as a result of a phase transition in the early Universe. There are several ways in which such fluctuations may have ben produced, and they could have a variety of spectra, so one should not necessarily expect all features of the large-scale structure to derive from a simple power law spectrum. Some features may even result from astrophysical amplification mechanisms rather than gravitational instability. 128 references.

  5. Fluctuation driven electroweak phase transition

    NASA Technical Reports Server (NTRS)

    Gleiser, Marcelo; Kolb, Edward W.

    1991-01-01

    We examine the dynamics of the electroweak phase transition in the early Universe. For Higgs masses in the range 46 less than or = M sub H less than or = 150 GeV and top quark masses less than 200 GeV, regions of symmetric and asymmetric vacuum coexist to below the critical temperature, with thermal equilibrium between the two phases maintained by fluctuations of both phases. We propose that the transition to the asymmetric vacuum is completed by percolation of these subcritical fluctuations. Our results are relevant to scenarios of baryogenesis that invoke a weakly first-order phase transition at the electroweak scale.

  6. On the origin of shape fluctuations of the cell nucleus.

    PubMed

    Chu, Fang-Yi; Haley, Shannon C; Zidovska, Alexandra

    2017-09-26

    The nuclear envelope (NE) presents a physical boundary between the cytoplasm and the nucleoplasm, sandwiched in between two highly active systems inside the cell: cytoskeleton and chromatin. NE defines the shape and size of the cell nucleus, which increases during the cell cycle, accommodating for chromosome decondensation followed by genome duplication. In this work, we study nuclear shape fluctuations at short time scales of seconds in human cells. Using spinning disk confocal microscopy, we observe fast fluctuations of the NE, visualized by fluorescently labeled lamin A, and of the chromatin globule surface (CGS) underneath the NE, visualized by fluorescently labeled histone H2B. Our findings reveal that fluctuation amplitudes of both CGS and NE monotonously decrease during the cell cycle, serving as a reliable cell cycle stage indicator. Remarkably, we find that, while CGS and NE typically fluctuate in phase, they do exhibit localized regions of out-of-phase motion, which lead to separation of NE and CGS. To explore the mechanism behind these shape fluctuations, we use biochemical perturbations. We find the shape fluctuations of CGS and NE to be both thermally and actively driven, the latter caused by forces from chromatin and cytoskeleton. Such undulations might affect gene regulation as well as contribute to the anomalously high rates of nuclear transport by, e.g., stirring of molecules next to NE, or increasing flux of molecules through the nuclear pores.

  7. Importance of Fluctuations in Light on Plant Photosynthetic Acclimation.

    PubMed

    Vialet-Chabrand, Silvere; Matthews, Jack S A; Simkin, Andrew J; Raines, Christine A; Lawson, Tracy

    2017-04-01

    The acclimation of plants to light has been studied extensively, yet little is known about the effect of dynamic fluctuations in light on plant phenotype and acclimatory responses. We mimicked natural fluctuations in light over a diurnal period to examine the effect on the photosynthetic processes and growth of Arabidopsis (Arabidopsis thaliana). High and low light intensities, delivered via a realistic dynamic fluctuating or square wave pattern, were used to grow and assess plants. Plants subjected to square wave light had thicker leaves and greater photosynthetic capacity compared with fluctuating light-grown plants. This, together with elevated levels of proteins associated with electron transport, indicates greater investment in leaf structural components and photosynthetic processes. In contrast, plants grown under fluctuating light had thinner leaves, lower leaf light absorption, but maintained similar photosynthetic rates per unit leaf area to square wave-grown plants. Despite high light use efficiency, plants grown under fluctuating light had a slow growth rate early in development, likely due to the fact that plants grown under fluctuating conditions were not able to fully utilize the light energy absorbed for carbon fixation. Diurnal leaf-level measurements revealed a negative feedback control of photosynthesis, resulting in a decrease in total diurnal carbon assimilated of at least 20%. These findings highlight that growing plants under square wave growth conditions ultimately fails to predict plant performance under realistic light regimes and stress the importance of considering fluctuations in incident light in future experiments that aim to infer plant productivity under natural conditions in the field.

  8. Stage fluctuations of Wisconsin lakes

    USGS Publications Warehouse

    House, Leo B.

    1985-01-01

    This report describes lake-stage fluctuations of 83 gaged lakes in Wisconsin and presents techniques for estimating stage fluctuation at ungaged lakes. Included are stage information at 83 lakes and stage-frequency data for 32 of these lakes that had sufficient record for analysis. Lakes are classified by a hydrologic-topographic lake classification scheme as ground-water flowthrough (GWF) lakes, surface-water drainage (SWD) lakes, and surface-water flow-through (SWF) lakes. Lakes within the same class were found to have similar water-level fluctuations. The lake-stage records indicate that most annual maximums occur during the months of May and June for all three classes. Annual minimum lake levels generally occur in September for surface-water drainage lakes, in March for surface-water flowthrough lakes, and in November for ground-water flow-through lakes. Data for each lake include location, period of water-level record, hydrologic classification, drainage area, surface area, lake volume, maximum depth, long-term mean stage and its standard deviation, maximum and minimum observed lake stage, and the average annual lake-stage fluctuation.

  9. Chaotic dynamics, fluctuations, nonequilibrium ensembles.

    PubMed

    Gallavotti, Giovanni

    1998-06-01

    The ideas and the conceptual steps leading from the ergodic hypothesis for equilibrium statistical mechanics to the chaotic hypothesis for equilibrium and nonequilibrium statistical mechanics are illustrated. The fluctuation theorem linear law and universal slope prediction for reversible systems is briefly derived. Applications to fluids are briefly alluded to. (c) 1998 American Institute of Physics.

  10. Fluctuating Hydrodynamics of Electrolytes Solutions

    NASA Astrophysics Data System (ADS)

    Peraud, Jean-Philippe; Nonaka, Andy; Chaudhri, Anuj; Bell, John B.; Donev, Aleksandar; Garcia, Alejandro L.

    2016-11-01

    In this work, we develop a numerical method for multicomponent solutions featuring electrolytes, in the context of fluctuating hydrodynamics as modeled by the Landau-Lifshitz Navier Stokes equations. Starting from a previously developed numerical scheme for multicomponent low Mach number fluctuating hydrodynamics, we study the effect of the additional forcing terms induced by charged species. We validate our numerical approach with additional theoretical considerations and with examples involving sodium-chloride solutions, with length scales close to Debye length. In particular, we show how charged species modify the structure factors of the fluctuations, both in equilibrium and non-equilibrium (giant fluctuations) systems, and show that the former is consistent with Debye-Huckel theory. We also discuss the consistency of this approach with the electroneutral approximation in regimes where characteristic length scales are significantly larger than the Debye length. Finally, we use this method to explore a type of electrokinetic instability. This work was supported by the U.S. Department of Energy, Office of Science, Office of Advanced Scientific Computing Research,.

  11. Fluctuation scaling in the visual cortex at threshold

    NASA Astrophysics Data System (ADS)

    Medina, José M.; Díaz, José A.

    2016-05-01

    Fluctuation scaling relates trial-to-trial variability to the average response by a power function in many physical processes. Here we address whether fluctuation scaling holds in sensory psychophysics and its functional role in visual processing. We report experimental evidence of fluctuation scaling in human color vision and form perception at threshold. Subjects detected thresholds in a psychophysical masking experiment that is considered a standard reference for studying suppression between neurons in the visual cortex. For all subjects, the analysis of threshold variability that results from the masking task indicates that fluctuation scaling is a global property that modulates detection thresholds with a scaling exponent that departs from 2, β =2.48 ±0.07 . We also examine a generalized version of fluctuation scaling between the sample kurtosis K and the sample skewness S of threshold distributions. We find that K and S are related and follow a unique quadratic form K =(1.19 ±0.04 ) S2+(2.68 ±0.06 ) that departs from the expected 4/3 power function regime. A random multiplicative process with weak additive noise is proposed based on a Langevin-type equation. The multiplicative process provides a unifying description of fluctuation scaling and the quadratic S -K relation and is related to on-off intermittency in sensory perception. Our findings provide an insight into how the human visual system interacts with the external environment. The theoretical methods open perspectives for investigating fluctuation scaling and intermittency effects in a wide variety of natural, economic, and cognitive phenomena.

  12. Fluctuation scaling in the visual cortex at threshold.

    PubMed

    Medina, José M; Díaz, José A

    2016-05-01

    Fluctuation scaling relates trial-to-trial variability to the average response by a power function in many physical processes. Here we address whether fluctuation scaling holds in sensory psychophysics and its functional role in visual processing. We report experimental evidence of fluctuation scaling in human color vision and form perception at threshold. Subjects detected thresholds in a psychophysical masking experiment that is considered a standard reference for studying suppression between neurons in the visual cortex. For all subjects, the analysis of threshold variability that results from the masking task indicates that fluctuation scaling is a global property that modulates detection thresholds with a scaling exponent that departs from 2, β=2.48±0.07. We also examine a generalized version of fluctuation scaling between the sample kurtosis K and the sample skewness S of threshold distributions. We find that K and S are related and follow a unique quadratic form K=(1.19±0.04)S^{2}+(2.68±0.06) that departs from the expected 4/3 power function regime. A random multiplicative process with weak additive noise is proposed based on a Langevin-type equation. The multiplicative process provides a unifying description of fluctuation scaling and the quadratic S-K relation and is related to on-off intermittency in sensory perception. Our findings provide an insight into how the human visual system interacts with the external environment. The theoretical methods open perspectives for investigating fluctuation scaling and intermittency effects in a wide variety of natural, economic, and cognitive phenomena.

  13. Fluctuation scaling in complex systems: Taylor's law and beyond

    NASA Astrophysics Data System (ADS)

    Eisler, Zoltán; Bartos, Imre; Kertész, János

    2008-01-01

    Complex systems consist of many interacting elements which participate in some dynamical process. The activity of various elements is often different and the fluctuation in the activity of an element grows monotonically with the average activity. This relationship is often of the form 'fluctuations ≈ constant × averageα', where the exponent α is predominantly in the range [1/2, 1]. This power law has been observed in a very wide range of disciplines, ranging from population dynamics through the Internet to the stock market and it is often treated under the names Taylor's law or fluctuation scaling. This review attempts to show how general the above scaling relationship is by surveying the literature, as well as by reporting some new empirical data and model calculations. We also show some basic principles that can underlie the generality of the phenomenon. This is followed by a mean-field framework based on sums of random variables. In this context the emergence of fluctuation scaling is equivalent to some corresponding limit theorems. In certain physical systems fluctuation scaling can be related to finite size scaling.

  14. Non-Gaussian microwave background fluctuations from nonlinear gravitational effects

    NASA Technical Reports Server (NTRS)

    Salopek, D. S.; Kunstatter, G. (Editor)

    1991-01-01

    Whether the statistics of primordial fluctuations for structure formation are Gaussian or otherwise may be determined if the Cosmic Background Explorer (COBE) Satellite makes a detection of the cosmic microwave-background temperature anisotropy delta T(sub CMB)/T(sub CMB). Non-Gaussian fluctuations may be generated in the chaotic inflationary model if two scalar fields interact nonlinearly with gravity. Theoretical contour maps are calculated for the resulting Sachs-Wolfe temperature fluctuations at large angular scales (greater than 3 degrees). In the long-wavelength approximation, one can confidently determine the nonlinear evolution of quantum noise with gravity during the inflationary epoch because: (1) different spatial points are no longer in causal contact; and (2) quantum gravity corrections are typically small-- it is sufficient to model the system using classical random fields. If the potential for two scalar fields V(phi sub 1, phi sub 2) possesses a sharp feature, then non-Gaussian fluctuations may arise. An explicit model is given where cold spots in delta T(sub CMB)/T(sub CMB) maps are suppressed as compared to the Gaussian case. The fluctuations are essentially scale-invariant.

  15. Random close packing of polydisperse jammed emulsions

    NASA Astrophysics Data System (ADS)

    Brujic, Jasna

    2010-03-01

    Packing problems are everywhere, ranging from oil extraction through porous rocks to grain storage in silos and the compaction of pharmaceutical powders into tablets. At a given density, particulate systems pack into a mechanically stable and amorphous jammed state. Theoretical frameworks have proposed a connection between this jammed state and the glass transition, a thermodynamics of jamming, as well as geometric modeling of random packings. Nevertheless, a simple underlying mechanism for the random assembly of athermal particles, analogous to crystalline ordering, remains unknown. Here we use 3D measurements of polydisperse packings of emulsion droplets to build a simple statistical model in which the complexity of the global packing is distilled into a local stochastic process. From the perspective of a single particle the packing problem is reduced to the random formation of nearest neighbors, followed by a choice of contacts among them. The two key parameters in the model, the available space around a particle and the ratio of contacts to neighbors, are directly obtained from experiments. Remarkably, we demonstrate that this ``granocentric'' view captures the properties of the polydisperse emulsion packing, ranging from the microscopic distributions of nearest neighbors and contacts to local density fluctuations and all the way to the global packing density. Further applications to monodisperse and bidisperse systems quantitatively agree with previously measured trends in global density. This model therefore reveals a general principle of organization for random packing and lays the foundations for a theory of jammed matter.

  16. Photoprotection of photosystems in fluctuating light intensities.

    PubMed

    Allahverdiyeva, Yagut; Suorsa, Marjaana; Tikkanen, Mikko; Aro, Eva-Mari

    2015-05-01

    Oxygenic photosynthetic organisms experience strong fluctuations in light intensity in their natural terrestrial and aquatic growth environments. Recent studies with both plants and cyanobacteria have revealed that Photosystem (PS) I is the potential target of damage upon abrupt changes in light intensity. Photosynthetic organisms have, however, developed powerful mechanisms in order to protect their photosynthetic apparatus against such potentially hazardous light conditions. Although the electron transfer chain has remained relatively unchanged in both plant chloroplasts and their cyanobacterial ancestors, the photoprotective and regulatory mechanisms of photosynthetic light reactions have experienced conspicuous evolutionary changes. In cyanobacteria, the specific flavodiiron proteins (Flv1 and Flv3) are responsible for safeguarding PSI under rapidly fluctuating light intensities, whilst the thylakoid located terminal oxidases are involved in the protection of PSII during 12h diurnal cycles involving abrupt, square-wave, changes from dark to high light. Higher plants such as Arabidopsis thaliana have evolved different protective mechanisms. In particular, the PGR5 protein controls electron flow during sudden changes in light intensity by allowing the regulation mostly via the Cytochrome b6f complex. Besides the function of PGR5, plants have also acquired other dynamic regulatory mechanisms, among them the STN7-related LHCII protein phosphorylation that is similarly responsible for protection against rapid changes in the light environment. The green alga Chlamydomonas reinhardtii, as an evolutionary intermediate between cyanobacteria and higher plants, probably possesses both protective mechanisms. In this review, evolutionarily different photoprotective mechanisms under fluctuating light conditions are described and their contributions to cyanobacterial and plant photosynthesis are discussed. © The Author 2014. Published by Oxford University Press on behalf of

  17. Theoretical estimation of static charge fluctuation in amorphous silicon

    NASA Astrophysics Data System (ADS)

    Kugler, Sándor; Surján, Péter R.; Náray-Szabó, Gábor

    1988-05-01

    A quantum-chemical method has been developed to determine charge fluctuations in finite aperiodic clusters of amorphous silicon. Calculated atomic net charges are in a close linear relationship to bond-angle distortions involving first and second neighbors. Applying this relationship to a continuous-random-network model of 216 silicon atoms proposed by Wooten et al., we obtained 0.021 electron units for the rms deviation from charge neutrality.

  18. Radiation-Induced Glass Transition and Structural Fluctuation in NiTi Metallic Glass System

    SciTech Connect

    Watanabe, Seiichi

    2006-05-05

    We report an evidence of fluctuation during amorphization in NiTi ordered intermetallic compounds under electron irradiation, using an in situ observation technique with a high resolution High Voltage Electron Microscope (HVEM). Molecular dynamics calculation, which is executed to simulate atomic-level electron micrographic images, also revealed the similar fluctuation trend.

  19. Spatially correlated fluctuations and coherence dynamics in photosynthesis.

    PubMed

    Yu, Z G; Berding, M A; Wang, Haobin

    2008-11-01

    Recent multicolor photon-echo experiments revealed a long-lasting quantum coherence between excitations on the donor and acceptor in photosynthetic systems. Identifying the origin of the quantum coherence is essential to fully understand photosynthesis. Here we present a generic model in which a strong intermolecular steric restoring force in densely packed pigment-protein complexes results in a spatial correlation in conformational (static) variations of chromophores, which in turn induces an effective coupling between high-frequency (dynamic) fluctuations in donor and acceptor. The spatially correlated static and dynamic fluctuations provide a favorable environment to maintain quantum coherence, which can consistently explain the photon-echo measurements.

  20. Overcoming recruitment barriers revealed high readiness to participate and low dropout rate among people with schizophrenia in a randomized controlled trial testing the effect of a Guided Self-Determination intervention

    PubMed Central

    2014-01-01

    Background Recruitment is one of the most serious challenges in performing randomized controlled trials. Often clinical trials with participants diagnosed with schizophrenia are terminated prematurely because of recruitment challenges resulting in a considerable waste of resources in the form of time, funding, and the participants’ efforts. Dropout rates in schizophrenia trials are also high. Recruitment challenges are often due to patients not wanting to participate in research but can also be due to clinicians’ concerns regarding individuals diagnosed with schizophrenia as participants in research. This paper reports how overcoming recruitment challenges not related to patients revealed high readiness to take part and low dropout rates in a one year long randomized controlled trial testing Guided Self-Determination (GSD) among outpatients with schizophrenia receiving treatment in Assertive Outreach Teams in the northern part of Denmark. Methods GSD is a shared decision-making and mutual problem-solving method using reflection sheets, which was developed in diabetes care and adjusted for this study and utilized by patients with schizophrenia. Descriptive data on strategies to overcome recruitment challenges were derived from notes and observations made during the randomized controlled trial testing of GSD in six outpatient teams. Results Three types of recruitment challenges not related to patients were identified and met during the trial: 1) organizational challenges, 2) challenges with finding eligible participants and 3) challenges with having professionals invite patients to participate. These challenges were overcome through: 1) extension of time, 2) expansion of the clinical recruitment area and 3) encouragement of professionals to invite patients to the study. Through overcoming these challenges, we identified a remarkably high patient-readiness to take part (101 of 120 asked accepted) and a low dropout rate (8%). Conclusion Distinction between

  1. Direct measurement of antiferromagnetic domain fluctuations.

    PubMed

    Shpyrko, O G; Isaacs, E D; Logan, J M; Feng, Yejun; Aeppli, G; Jaramillo, R; Kim, H C; Rosenbaum, T F; Zschack, P; Sprung, M; Narayanan, S; Sandy, A R

    2007-05-03

    Measurements of magnetic noise emanating from ferromagnets owing to domain motion were first carried out nearly 100 years ago, and have underpinned much science and technology. Antiferromagnets, which carry no net external magnetic dipole moment, yet have a periodic arrangement of the electron spins extending over macroscopic distances, should also display magnetic noise. However, this must be sampled at spatial wavelengths of the order of several interatomic spacings, rather than the macroscopic scales characteristic of ferromagnets. Here we present a direct measurement of the fluctuations in the nanometre-scale superstructure of spin- and charge-density waves associated with antiferromagnetism in elemental chromium. The technique used is X-ray photon correlation spectroscopy, where coherent X-ray diffraction produces a speckle pattern that serves as a 'fingerprint' of a particular magnetic domain configuration. The temporal evolution of the patterns corresponds to domain walls advancing and retreating over micrometre distances. This work demonstrates a useful measurement tool for antiferromagnetic domain wall engineering, but also reveals a fundamental finding about spin dynamics in the simplest antiferromagnet: although the domain wall motion is thermally activated at temperatures above 100 K, it is not so at lower temperatures, and indeed has a rate that saturates at a finite value-consistent with quantum fluctuations-on cooling below 40 K.

  2. Resonant population cycles in temporally fluctuating habitats.

    PubMed

    Costantino, R F; Cushing, J M; Dennis, B; Desharnais, R A; Henson, S M

    1998-03-01

    Experiments with the flour beetle Tribolium have revealed that animal numbers were larger in cultures grown in a periodically fluctuating volume of medium than in cultures grown in a constant volume of the same average size. In this paper we derive and analyze a discrete stage-structured mathematical model that explains this phenomenon as a kind of resonance effect. Habitat volume is incorporated into the model by the assumption that all rates of cannibalism (larvae on eggs, adults on eggs and pupae) are inversely proportional to the volume of the culture medium. We tested this modeling assumption by conducting and statistically analyzing laboratory experiments. For parameter estimates derived from experimental data, our model indeed predicts, under certain circumstances, a larger (cycle-average) total population abundance when the habitat volume periodically fluctuates than when the habitat volume is held constant at the average volume. The model also correctly predicts certain phase relationships and transient dynamics observed in data. The analyses involve a thorough integration of mathematics, statistical methods, biological details and experimental data.

  3. Enhanced hyperuniformity from random reorganization.

    PubMed

    Hexner, Daniel; Chaikin, Paul M; Levine, Dov

    2017-04-10

    Diffusion relaxes density fluctuations toward a uniform random state whose variance in regions of volume [Formula: see text] scales as [Formula: see text] Systems whose fluctuations decay faster, [Formula: see text] with [Formula: see text], are called hyperuniform. The larger [Formula: see text], the more uniform, with systems like crystals achieving the maximum value: [Formula: see text] Although finite temperature equilibrium dynamics will not yield hyperuniform states, driven, nonequilibrium dynamics may. Such is the case, for example, in a simple model where overlapping particles are each given a small random displacement. Above a critical particle density [Formula: see text], the system evolves forever, never finding a configuration where no particles overlap. Below [Formula: see text], however, it eventually finds such a state, and stops evolving. This "absorbing state" is hyperuniform up to a length scale [Formula: see text], which diverges at [Formula: see text] An important question is whether hyperuniformity survives noise and thermal fluctuations. We find that hyperuniformity of the absorbing state is not only robust against noise, diffusion, or activity, but that such perturbations reduce fluctuations toward their limiting behavior, [Formula: see text], a uniformity similar to random close packing and early universe fluctuations, but with arbitrary controllable density.

  4. Experimental studies of thermal fluctuations in electron plasmas

    NASA Astrophysics Data System (ADS)

    Shiga, Nobuyasu

    We have detected the thermally excited charge fluctuations in pure electron plasmas over a temperature range of 0.05 < kBT < 10eV. These fluctuation spectra have both a global mode component and a random particle fluctuation component. At low temperatures, the mtheta = 0, kz = 1, 2, 3,.... Trivelpiece-Gould modes are weakly damped and dominate, since the random particle component is suppressed by Debye-shielding. As the temperature increases, the broad random particle component increases in between the modes. We have developed 3 different non-perturbative methods to determine the plasma temperature. These 3 methods are valid in different regimes depending on the Debye length normalized by the plasma radius lDRp , and on the plasma length normalized by the plasma radius LpRp . The first method focuses on the near-Lorentzian spectrum of thermal fluctuations near a weakly damped mode. Each weakly damped mode has the same energy as the electron temperature. The measured emission spectrum together with a plasma-antenna impedance calibration uniquely determines the temperature of the plasma, using Nyquist theorem. Experimentally this method gives the correct temperature, agreeing with the standard "dump" temperature measurements when lDRp < 0.3. The second method utilizes the emission spectrum over a broad frequency range encompassing several modes and the non-resonant fluctuations between modes. The Nyquist theorem together with a kinetic theory calculation of the plasma-antenna impedance determines the temperature from the broad fluctuation spectrum. Kinetic theory implicitly assumes that Landau damping is the only damping mechanism, and also assumes an infinite length for the plasma. This method works if lDRp > 0.2 so that Landau damping is dominant, and if LpRp > 20 so that finite-length corrections to Landau damping are negligible. The third method utilizes the total (frequency-integrated) number delta N of the fluctuating image charges on the antenna, and

  5. Title: Spatial velocity fluctuations in flow through porous media

    NASA Astrophysics Data System (ADS)

    Aramideh, Soroush; Guo, Tianqi; Vlachos, Pavlos P.; Ardekani, Arezoo M.

    2016-11-01

    Understanding the flow in porous media is of great importance and has direct impact on many processes in chemical and oil industries, fuel cell design, and filtration. In this work, we use direct numerical simulations (DNS) to examine the flow through variety of sphere packings with different levels of complexity and heterogeneity. DNS results are validated with velocity fields obtained via volumetric particle tracking velocimetry at high resolution. We show that flow in random close packing of spheres has unique statistical properties while the medium is random itself. Furthermore, we quantify the relationship between pore geometry and velocity fluctuations.

  6. Audio watermarking method robust against time- and frequency-fluctuation

    NASA Astrophysics Data System (ADS)

    Tachibana, Ryuki; Shimizu, Shuichi; Nakamura, Taiga; Kobayashi, Seiji

    2001-08-01

    In this paper, we describe an audio watermarking algorithm that can embed a multiple-bit message which is robust against wow-and-flutter, cropping, noise-addition, pitch-shift, and audio compressions such as MP3. The algorithm calculates and manipulates the magnitudes of segmented areas in the time-frequency plane of the content using short-term DFTs. The detection algorithm correlates the magnitudes with a pseudo-random array that maps to a two-dimensional area in the time-frequency plane. The two-dimensional array makes the watermark robust because, even when some portions of the content are heavily degraded, other portions of the content can match the pseudo-random array and contribute to watermark detection. Another key idea is manipulation of magnitudes. Because magnitudes are less influenced than phases by fluctuations of the analysis windows caused by random cropping, the watermark resists degradation. When signal transformation causes pitch fluctuations in the content, the frequencies of the pseudo-random array embedded in the content shift, and that causes a decrease in the volume of the watermark signal that still correctly overlaps with the corresponding pseudo-random array. To keep the overlapping area wide enough for successful watermark detection, the widths of the frequency subbands used for the detection segments should increase logarithmically as frequency increases. We theoretically and experimentally analyze the robustness of proposed algorithm against a variety of signal degradations.

  7. Universal crossover of the charge carrier fluctuation mechanism in different polymer/carbon nanotubes composites

    SciTech Connect

    Barone, C. Mauro, C.; Pagano, S.; Landi, G.; Neitzert, H. C.

    2015-10-05

    Carbon nanotubes added to polymer and epoxy matrices are compounds of interest for applications in electronics and aerospace. The realization of high-performance devices based on these materials can profit from the investigation of their electric noise properties, as this gives a more detailed insight of the basic charge carriers transport mechanisms at work. The dc and electrical noise characteristics of different polymer/carbon nanotubes composites have been analyzed from 10 to 300 K. The results suggest that all these systems can be regarded as random resistive networks of tunnel junctions formed by adjacent carbon nanotubes. However, in the high-temperature regime, contributions deriving from other possible mechanisms cannot be separated using dc information alone. A transition from a fluctuation-induced tunneling process to a thermally activated regime is instead revealed by electric noise spectroscopy. In particular, a crossover is found from a two-level tunneling mechanism, operating at low temperatures, to resistance fluctuations of a percolative network, in the high-temperature region. The observed behavior of 1/f noise seems to be a general feature for highly conductive samples, independent on the type of polymer matrix and on the nanotube density.

  8. Velocity Fluctuations in Kinesin-1 Gliding Motility Assays Originate in Motor Attachment Geometry Variations.

    PubMed

    Palacci, Henri; Idan, Ofer; Armstrong, Megan J; Agarwal, Ashutosh; Nitta, Takahiro; Hess, Henry

    2016-08-09

    Motor proteins such as myosin and kinesin play a major role in cellular cargo transport, muscle contraction, cell division, and engineered nanodevices. Quantifying the collective behavior of coupled motors is critical to our understanding of these systems. An excellent model system is the gliding motility assay, where hundreds of surface-adhered motors propel one cytoskeletal filament such as an actin filament or a microtubule. The filament motion can be observed using fluorescence microscopy, revealing fluctuations in gliding velocity. These velocity fluctuations have been previously quantified by a motional diffusion coefficient, which Sekimoto and Tawada explained as arising from the addition and removal of motors from the linear array of motors propelling the filament as it advances, assuming that different motors are not equally efficient in their force generation. A computational model of kinesin head diffusion and binding to the microtubule allowed us to quantify the heterogeneity of motor efficiency arising from the combination of anharmonic tail stiffness and varying attachment geometries assuming random motor locations on the surface and an absence of coordination between motors. Knowledge of the heterogeneity allows the calculation of the proportionality constant between the motional diffusion coefficient and the motor density. The calculated value (0.3) is within a standard error of our measurements of the motional diffusion coefficient on surfaces with varying motor densities calibrated by landing rate experiments. This allowed us to quantify the loss in efficiency of coupled molecular motors arising from heterogeneity in the attachment geometry.

  9. Universal crossover of the charge carrier fluctuation mechanism in different polymer/carbon nanotubes composites

    NASA Astrophysics Data System (ADS)

    Barone, C.; Landi, G.; Mauro, C.; Neitzert, H. C.; Pagano, S.

    2015-10-01

    Carbon nanotubes added to polymer and epoxy matrices are compounds of interest for applications in electronics and aerospace. The realization of high-performance devices based on these materials can profit from the investigation of their electric noise properties, as this gives a more detailed insight of the basic charge carriers transport mechanisms at work. The dc and electrical noise characteristics of different polymer/carbon nanotubes composites have been analyzed from 10 to 300 K. The results suggest that all these systems can be regarded as random resistive networks of tunnel junctions formed by adjacent carbon nanotubes. However, in the high-temperature regime, contributions deriving from other possible mechanisms cannot be separated using dc information alone. A transition from a fluctuation-induced tunneling process to a thermally activated regime is instead revealed by electric noise spectroscopy. In particular, a crossover is found from a two-level tunneling mechanism, operating at low temperatures, to resistance fluctuations of a percolative network, in the high-temperature region. The observed behavior of 1/f noise seems to be a general feature for highly conductive samples, independent on the type of polymer matrix and on the nanotube density.

  10. Fluctuation energies in quantum cosmology

    NASA Astrophysics Data System (ADS)

    Bojowald, Martin

    2014-06-01

    Quantum fluctuations or other moments of a state contribute to energy expectation values and can imply interesting physical effects. In quantum cosmology, they turn out to be important for a discussion of density bounds and instabilities of initial-value problems in the presence of signature change in loop-quantized models. This paper provides an effective description of these issues, accompanied by a comparison with existing numerical results and an extension to squeezed states. The comparison confirms that canonical effective methods are well suited for computations of properties of physical states. As a side product, an example is found for a simple state in which quantum fluctuations can cancel holonomy modifications of loop quantum cosmology.

  11. Thermal fluctuations and bouncing cosmologies

    SciTech Connect

    Cai, Yi-Fu; Zhang, Xinmin; Xue, Wei; Brandenberger, Robert E-mail: xuewei@physics.mcgill.ca E-mail: xmzhang@ihep.ac.cn

    2009-06-01

    We study the conditions under which thermal fluctuations generated in the contracting phase of a non-singular bouncing cosmology can lead to a scale-invariant spectrum of cosmological fluctuations at late times in the expanding phase. We consider point particle gases, holographic gases and string gases. In the models thus identified, we also study the thermal non-Gaussianities of the resulting distribution of inhomogeneities. For regular point particle radiation, we find that the background must have an equation of state w = 7/3 in order to obtain a scale-invariant spectrum, and that the non-Gaussianities are suppressed on scales larger than the thermal wavelength. For Gibbons-Hawking radiation, we find that a matter-dominated background yields scale-invariance, and that the non-Gaussianities are large. String gases are also briefly considered.

  12. Algorithm refinement for fluctuating hydrodynamics

    SciTech Connect

    Williams, Sarah A.; Bell, John B.; Garcia, Alejandro L.

    2007-07-03

    This paper introduces an adaptive mesh and algorithmrefinement method for fluctuating hydrodynamics. This particle-continuumhybrid simulates the dynamics of a compressible fluid with thermalfluctuations. The particle algorithm is direct simulation Monte Carlo(DSMC), a molecular-level scheme based on the Boltzmann equation. Thecontinuum algorithm is based on the Landau-Lifshitz Navier-Stokes (LLNS)equations, which incorporate thermal fluctuations into macroscopichydrodynamics by using stochastic fluxes. It uses a recently-developedsolver for LLNS, based on third-order Runge-Kutta. We present numericaltests of systems in and out of equilibrium, including time-dependentsystems, and demonstrate dynamic adaptive refinement by the computationof a moving shock wave. Mean system behavior and second moment statisticsof our simulations match theoretical values and benchmarks well. We findthat particular attention should be paid to the spectrum of the flux atthe interface between the particle and continuum methods, specificallyfor the non-hydrodynamic (kinetic) time scales.

  13. Parity fluctuations in stellar dynamos

    NASA Astrophysics Data System (ADS)

    Moss, D. L.; Sokoloff, D. D.

    2017-10-01

    Observations of the solar butterfly diagram from sunspot records suggest persistent fluctuations in parity, away from the overall, approximately dipolar pattern. A simple mean-field dynamo model is used with a solar-like rotation law and perturbed α effect. The parity of the magnetic field relative to the rotational equator can demonstrate can be described as resonance behavior, while the magnetic energy behaves in a more or less expected way. Possible applications of this effect are discussed in the context of various deviations of the solar magnetic field from dipolar symmetry, as reported from analyses of archival sunspot data. The model produces fluctuations in field parity, and hence in the butterfly diagram, that are consistent with observed fluctuaions in solar behavior.

  14. Density Fluctuations in Liquid Water

    NASA Astrophysics Data System (ADS)

    English, Niall J.; Tse, John S.

    2011-01-01

    The density distributions and fluctuations in grids of varying size in liquid water at ambient pressure, both above the freezing point and in the supercooled state, are analyzed from the trajectories obtained from large-scale molecular dynamics simulations. It is found that the occurrence of low- and high-density regions (LDL and HDL) is transient and their respective residence times are dependent on the size of the simulated system. The spatial extent of density-density correlation is found to be within 7 Å or less. The temporal existence of LDL and HDL arises as a result of natural density fluctuations of an equilibrium system. The density of bulk water at ambient conditions is homogenous.

  15. Detecting temperature fluctuations at equilibrium.

    PubMed

    Dixit, Purushottam D

    2015-05-21

    The Gibbs and the Boltzmann definition of temperature agree only in the macroscopic limit. The ambiguity in identifying the equilibrium temperature of a finite-sized 'small' system exchanging energy with a bath is usually understood as a limitation of conventional statistical mechanics. We interpret this ambiguity as resulting from a stochastically fluctuating temperature coupled with the phase space variables giving rise to a broad temperature distribution. With this ansatz, we develop the equilibrium statistics and dynamics of small systems. Numerical evidence using an analytically tractable model shows that the effects of temperature fluctuations can be detected in the equilibrium and dynamical properties of the phase space of the small system. Our theory generalizes statistical mechanics to small systems relevant in biophysics and nanotechnology.

  16. Charge fluctuations in nanoscale capacitors.

    PubMed

    Limmer, David T; Merlet, Céline; Salanne, Mathieu; Chandler, David; Madden, Paul A; van Roij, René; Rotenberg, Benjamin

    2013-09-06

    The fluctuations of the charge on an electrode contain information on the microscopic correlations within the adjacent fluid and their effect on the electronic properties of the interface. We investigate these fluctuations using molecular dynamics simulations in a constant-potential ensemble with histogram reweighting techniques. This approach offers, in particular, an efficient, accurate, and physically insightful route to the differential capacitance that is broadly applicable. We demonstrate these methods with three different capacitors: pure water between platinum electrodes and a pure as well as a solvent-based organic electrolyte each between graphite electrodes. The total charge distributions with the pure solvent and solvent-based electrolytes are remarkably Gaussian, while in the pure ionic liquid the total charge distribution displays distinct non-Gaussian features, suggesting significant potential-driven changes in the organization of the interfacial fluid.

  17. Charge Fluctuations in Nanoscale Capacitors

    NASA Astrophysics Data System (ADS)

    Limmer, David T.; Merlet, Céline; Salanne, Mathieu; Chandler, David; Madden, Paul A.; van Roij, René; Rotenberg, Benjamin

    2013-09-01

    The fluctuations of the charge on an electrode contain information on the microscopic correlations within the adjacent fluid and their effect on the electronic properties of the interface. We investigate these fluctuations using molecular dynamics simulations in a constant-potential ensemble with histogram reweighting techniques. This approach offers, in particular, an efficient, accurate, and physically insightful route to the differential capacitance that is broadly applicable. We demonstrate these methods with three different capacitors: pure water between platinum electrodes and a pure as well as a solvent-based organic electrolyte each between graphite electrodes. The total charge distributions with the pure solvent and solvent-based electrolytes are remarkably Gaussian, while in the pure ionic liquid the total charge distribution displays distinct non-Gaussian features, suggesting significant potential-driven changes in the organization of the interfacial fluid.

  18. Fuel Temperature Fluctuations During Storage

    NASA Astrophysics Data System (ADS)

    Levitin, R. E.; Zemenkov, Yu D.

    2016-10-01

    When oil and petroleum products are stored, their temperature significantly impacts how their properties change. The paper covers the problem of determining temperature fluctuations of hydrocarbons during storage. It provides results of the authors’ investigations of the stored product temperature variations relative to the ambient temperature. Closeness and correlation coefficients between these values are given. Temperature variations equations for oil and petroleum products stored in tanks are deduced.

  19. Fluctuation relation for qubit calorimetry.

    PubMed

    Kupiainen, Antti; Muratore-Ginanneschi, Paolo; Pekola, Jukka; Schwieger, Kay

    2016-12-01

    Motivated by proposed thermometry measurement on an open quantum system, we present a simple model of an externally driven qubit interacting with a finite-sized fermion environment acting as a calorimeter. The derived dynamics is governed by a stochastic Schrödinger equation coupled to the temperature change of the calorimeter. We prove a fluctuation relation and deduce from it a notion of entropy production. Finally, we discuss the first and second law associated with the dynamics.

  20. Stochastic Fluctuations in Gene Regulation

    DTIC Science & Technology

    2005-04-01

    AFRL-IF- RS -TR-2005-126 Final Technical Report April 2005 STOCHASTIC FLUCTUATIONS IN GENE REGULATION Boston University...be releasable to the general public, including foreign nations. AFRL-IF- RS -TR-2005-126 has been reviewed and is approved for publication...AGENCY REPORT NUMBER AFRL-IF- RS -TR-2005-126 11. SUPPLEMENTARY NOTES AFRL Project Engineer: Peter J. Costianes/IFED/(315) 330-4030

  1. The fluctuation induced Hall effect

    SciTech Connect

    Shen, W.; Prager, S.C.

    1993-02-01

    The fluctuation induced Hall term, {le}{approximately}{ovr J} {times} {approximately}{ovr B}{ge}, has been measured in the MST reversed field pinch. The term is of interest as a possible source of current self-generation (dynamo). It is found to be non-negligible, but small in that it can account for less than 25% of the dynamo driven current.

  2. The fluctuation induced Hall effect

    SciTech Connect

    Shen, W.; Prager, S.C.

    1993-02-01

    The fluctuation induced Hall term, [le][approximately][ovr J] [times] [approximately][ovr B][ge], has been measured in the MST reversed field pinch. The term is of interest as a possible source of current self-generation (dynamo). It is found to be non-negligible, but small in that it can account for less than 25% of the dynamo driven current.

  3. Fluctuation relation for qubit calorimetry

    NASA Astrophysics Data System (ADS)

    Kupiainen, Antti; Muratore-Ginanneschi, Paolo; Pekola, Jukka; Schwieger, Kay

    2016-12-01

    Motivated by proposed thermometry measurement on an open quantum system, we present a simple model of an externally driven qubit interacting with a finite-sized fermion environment acting as a calorimeter. The derived dynamics is governed by a stochastic Schrödinger equation coupled to the temperature change of the calorimeter. We prove a fluctuation relation and deduce from it a notion of entropy production. Finally, we discuss the first and second law associated with the dynamics.

  4. Fluctuating hydrodynamics for ionic liquids

    NASA Astrophysics Data System (ADS)

    Lazaridis, Konstantinos; Wickham, Logan; Voulgarakis, Nikolaos

    2017-04-01

    We present a mean-field fluctuating hydrodynamics (FHD) method for studying the structural and transport properties of ionic liquids in bulk and near electrified surfaces. The free energy of the system consists of two competing terms: (1) a Landau-Lifshitz functional that models the spontaneous separation of the ionic groups, and (2) the standard mean-field electrostatic interaction between the ions in the liquid. The numerical approach used to solve the resulting FHD-Poisson equations is very efficient and models thermal fluctuations with remarkable accuracy. Such density fluctuations are sufficiently strong to excite the experimentally observed spontaneous formation of liquid nano-domains. Statistical analysis of our simulations provides quantitative information about the properties of ionic liquids, such as the mixing quality, stability, and the size of the nano-domains. Our model, thus, can be adequately parameterized by directly comparing our prediction with experimental measurements and all-atom simulations. Conclusively, this work can serve as a practical mathematical tool for testing various theories and designing more efficient mixtures of ionic liquids.

  5. Chemical Measurement and Fluctuation Scaling.

    PubMed

    Hanley, Quentin S

    2016-12-20

    Fluctuation scaling reports on all processes producing a data set. Some fluctuation scaling relationships, such as the Horwitz curve, follow exponential dispersion models which have useful properties. The mean-variance method applied to Poisson distributed data is a special case of these properties allowing the gain of a system to be measured. Here, a general method is described for investigating gain (G), dispersion (β), and process (α) in any system whose fluctuation scaling follows a simple exponential dispersion model, a segmented exponential dispersion model, or complex scaling following such a model locally. When gain and dispersion cannot be obtained directly, relative parameters, GR and βR, may be used. The method was demonstrated on data sets conforming to simple, segmented, and complex scaling. These included mass, fluorescence intensity, and absorbance measurements and specifications for classes of calibration weights. Changes in gain, dispersion, and process were observed in the scaling of these data sets in response to instrument parameters, photon fluxes, mathematical processing, and calibration weight class. The process parameter which limits the type of statistical process that can be invoked to explain a data set typically exhibited 0 < α < 1, with α > 4 possible. With two exceptions, calibration weight class definitions only affected β. Adjusting photomultiplier voltage while measuring fluorescence intensity changed all three parameters (0 < α < 0.8; 0 < βR < 3; 0 < GR < 4.1). The method provides a framework for calibrating and interpreting uncertainty in chemical measurement allowing robust comparison of specific instruments, conditions, and methods.

  6. Facing rim cavities fluctuation modes

    NASA Astrophysics Data System (ADS)

    Casalino, Damiano; Ribeiro, André F. P.; Fares, Ehab

    2014-06-01

    Cavity modes taking place in the rims of two opposite wheels are investigated through Lattice-Boltzmann CFD simulations. Based on previous observations carried out by the authors during the BANC-II/LAGOON landing gear aeroacoustic study, a resonance mode can take place in the volume between the wheels of a two-wheel landing gear, involving a coupling between shear-layer vortical fluctuations and acoustic modes resulting from the combination of round cavity modes and wheel-to-wheel transversal acoustic modes. As a result, side force fluctuations and tonal noise side radiation take place. A parametric study of the cavity mode properties is carried out in the present work by varying the distance between the wheels. Moreover, the effects due to the presence of the axle are investigated by removing the axle from the two-wheel assembly. The azimuthal properties of the modes are scrutinized by filtering the unsteady flow in narrow bands around the tonal frequencies and investigating the azimuthal structure of the filtered fluctuation modes. Estimation of the tone frequencies with an ad hoc proposed analytical formula confirms the observed modal properties of the filtered unsteady flow solutions. The present study constitutes a primary step in the description of facing rim cavity modes as a possible source of landing gear tonal noise.

  7. Consistency of detrended fluctuation analysis

    NASA Astrophysics Data System (ADS)

    Løvsletten, O.

    2017-07-01

    The scaling function F (s ) in detrended fluctuation analysis (DFA) scales as F (s ) ˜sH for stochastic processes with Hurst exponent H . This scaling law is proven for stationary stochastic processes with 0 fluctuation function in DFA is equal in expectation to (i) a weighted sum of the ACF and (ii) a weighted sum of the second-order structure function. These results enable us to compute the exact finite-size bias for signals that are scaling and to employ DFA in a meaningful sense for signals that do not exhibit power-law statistics. The usefulness is illustrated by examples where it is demonstrated that a previous suggested modified DFA will increase the bias for signals with Hurst exponents 1 fluctuation function F (s ) in the gap-free case.

  8. Fluctuation Analysis: Dissecting Transcriptional Kinetics with Signal Theory.

    PubMed

    Coulon, A; Larson, D R

    2016-01-01

    Recent live-cell microscopy techniques now allow the visualization in multiple colors of RNAs as they are transcribed on genes of interest. Following the number of nascent RNAs over time at a single locus reveals complex fluctuations originating from the underlying transcriptional kinetics. We present here a technique based on concepts from signal theory-called fluctuation analysis-to analyze and interpret multicolor transcriptional time traces and extract the temporal signatures of the underlying mechanisms. The principle is to generate, from the time traces, a set of functions called correlation functions. We explain how to compute these functions practically from a set of experimental traces and how to interpret them through different theoretical and computational means. We also present the major difficulties and pitfalls one might encounter with this technique. This approach is capable of extracting mechanistic information hidden in transcriptional fluctuations at multiple timescales and has broad applications for understanding transcriptional kinetics.

  9. Superconducting fluctuations in organic molecular metals enhanced by Mott criticality.

    PubMed

    Nam, Moon-Sun; Mézière, Cécile; Batail, Patrick; Zorina, Leokadiya; Simonov, Sergey; Ardavan, Arzhang

    2013-12-02

    Unconventional superconductivity typically occurs in materials in which a small change of a parameter such as bandwidth or doping leads to antiferromagnetic or Mott insulating phases. As such competing phases are approached, the properties of the superconductor often become increasingly exotic. For example, in organic superconductors and underdoped high-T(c) cuprate superconductors a fluctuating superconducting state persists to temperatures significantly above T(c). By studying alloys of quasi-two-dimensional organic molecular metals in the κ-(BEDT-TTF)₂X family, we reveal how the Nernst effect, a sensitive probe of superconducting phase fluctuations, evolves in the regime of extreme Mott criticality. We find strong evidence that, as the phase diagram is traversed through superconductivity towards the Mott state, the temperature scale for superconducting fluctuations increases dramatically, eventually approaching the temperature at which quasiparticles become identifiable at all.

  10. Order and Symmetry Breaking in the Fluctuations of Driven Systems

    NASA Astrophysics Data System (ADS)

    Tizón-Escamilla, N.; Pérez-Espigares, C.; Garrido, P. L.; Hurtado, P. I.

    2017-09-01

    Dynamical phase transitions (DPTs) in the space of trajectories are one of the most intriguing phenomena of nonequilibrium physics, but their nature in realistic high-dimensional systems remains puzzling. Here we observe for the first time a DPT in the current vector statistics of an archetypal two-dimensional (2D) driven diffusive system and characterize its properties using the macroscopic fluctuation theory. The complex interplay among the external field, anisotropy, and vector currents in 2D leads to a rich phase diagram, with different symmetry-broken fluctuation phases separated by lines of first- and second-order DPTs. Remarkably, different types of 1D order in the form of jammed density waves emerge to hinder transport for low-current fluctuations, revealing a connection between rare events and self-organized structures which enhance their probability.

  11. Fluctuation Theorem for Many-Body Pure Quantum States

    NASA Astrophysics Data System (ADS)

    Iyoda, Eiki; Kaneko, Kazuya; Sagawa, Takahiro

    2017-09-01

    We prove the second law of thermodynamics and the nonequilibrium fluctuation theorem for pure quantum states. The entire system obeys reversible unitary dynamics, where the initial state of the heat bath is not the canonical distribution but is a single energy eigenstate that satisfies the eigenstate-thermalization hypothesis. Our result is mathematically rigorous and based on the Lieb-Robinson bound, which gives the upper bound of the velocity of information propagation in many-body quantum systems. The entanglement entropy of a subsystem is shown connected to thermodynamic heat, highlighting the foundation of the information-thermodynamics link. We confirmed our theory by numerical simulation of hard-core bosons, and observed dynamical crossover from thermal fluctuations to bare quantum fluctuations. Our result reveals a universal scenario that the second law emerges from quantum mechanics, and can be experimentally tested by artificial isolated quantum systems such as ultracold atoms.

  12. Spatial mobility fluctuation induced giant linear magnetoresistance in multilayered graphene foam

    NASA Astrophysics Data System (ADS)

    Li, Peng; Zhang, Qiang; He, Xin; Ren, Wencai; Cheng, Hui-Ming; Zhang, Xi-xiang

    2016-07-01

    Giant, positive, and near-temperature-independent linear magnetoresistance (LMR), as large as 340%, was observed in graphene foam with a three-dimensional flexible network. Careful analysis of the magnetoresistance revealed that Shubnikov-de Haas (SdH) oscillations occurred at low temperatures and decayed with increasing temperature. The average classical mobility ranged from 300 (2 K) to 150 (300 K) c m2V-1s-1 , which is much smaller than that required by the observed SdH oscillations. To understand the mechanism behind the observation, we performed the same measurements on the microsized graphene sheets that constitute the graphene foam. Much more pronounced SdH oscillations superimposed on the LMR background were observed in these microscaled samples, which correspond to a quantum mobility as high as 26 ,500 c m2V-1s-1 . Moreover, the spatial mobility fluctuated significantly from 64 ,200 c m2V-1s-1 to 1370 c m2V-1s-1 , accompanied by a variation of magnetoresistance from near 20,000% to less than 20%. The presence of SdH oscillations actually excludes the possibility that the observed LMR originated from the extreme quantum limit, because this would demand all electrons to be in the first Landau level. Instead, we ascribe the large LMR to the second case of the classical Parish and Littlewood model, in which spatial mobility fluctuation dominates electrical transport. This is an experimental confirmation of the Parish and Littlewood model by measuring the local mobility randomly (by measuring the microsized graphene sheets) and finding the spatial mobility fluctuation.

  13. Dependence of velocity fluctuations on solar wind speeds: A simple analysis with IPS method

    NASA Technical Reports Server (NTRS)

    Misawa, H.; Kojima, M.

    1995-01-01

    A number of theoretical works have suggested that MHD plasma fluctuations in solar winds should play an important role particularly in the acceleration of high speed winds inside or near 0.1 AU from the sun. Since velocity fluctuations in solar winds are expected to be caused by the MHD plasma fluctuations, measurements of the velocity fluctuations give clues to reveal the acceleration process of solar winds. We made interplanetary scintillation (IPS) observations at the region out of 0.1 AU to investigate dependence of velocity fluctuations on flow speeds. For evaluating the velocity fluctuation of a flow, we selected the IPS data-set acquired at 2 separate antennas which located in the projected flow direction onto the baseline plane, and tried to compare skewness of the observed cross correlation function(CCF) with skewness of modeled CCFs in which velocity fluctuations were parametrized. The integration effect of IPS along a ray path was also taken into account in the estimation of modeled CCFs. Although this analysis method is significant to derive only parallel fluctuation components to the flow directions, preliminary analyses show following results: (1) High speed winds (Vsw greater than or equal to 500 km/s out of 0.3 AU) indicate enhancement of velocity fluctuations near 0.1 AU; and (2) Low speed winds (Vsw less than or equal to 400 Km/s out of 0.3 AU) indicate small velocity fluctuations at any distances.

  14. The study of RMB exchange rate complex networks based on fluctuation mode

    NASA Astrophysics Data System (ADS)

    Yao, Can-Zhong; Lin, Ji-Nan; Zheng, Xu-Zhou; Liu, Xiao-Feng

    2015-10-01

    In the paper, we research on the characteristics of RMB exchange rate time series fluctuation with methods of symbolization and coarse gaining. First, based on fluctuation features of RMB exchange rate, we define the first type of fluctuation mode as one specific foreign currency against RMB in four days' fluctuating situations, and the second type as four different foreign currencies against RMB in one day's fluctuating situation. With the transforming method, we construct the unique-currency and multi-currency complex networks. Further, through analyzing the topological features including out-degree, betweenness centrality and clustering coefficient of fluctuation-mode complex networks, we find that the out-degree distribution of both types of fluctuation mode basically follows power-law distributions with exponents between 1 and 2. The further analysis reveals that the out-degree and the clustering coefficient generally obey the approximated negative correlation. With this result, we confirm previous observations showing that the RMB exchange rate exhibits a characteristic of long-range memory. Finally, we analyze the most probable transmission route of fluctuation modes, and provide probability prediction matrix. The transmission route for RMB exchange rate fluctuation modes exhibits the characteristics of partially closed loop, repeat and reversibility, which lays a solid foundation for predicting RMB exchange rate fluctuation patterns with large volume of data.

  15. Dependence of velocity fluctuations on solar wind speeds: A simple analysis with IPS method

    NASA Technical Reports Server (NTRS)

    Misawa, H.; Kojima, M.

    1995-01-01

    A number of theoretical works have suggested that MHD plasma fluctuations in solar winds should play an important role particularly in the acceleration of high speed winds inside or near 0.1 AU from the sun. Since velocity fluctuations in solar winds are expected to be caused by the MHD plasma fluctuations, measurements of the velocity fluctuations give clues to reveal the acceleration process of solar winds. We made interplanetary scintillation (IPS) observations at the region out of 0.1 AU to investigate dependence of velocity fluctuations on flow speeds. For evaluating the velocity fluctuation of a flow, we selected the IPS data-set acquired at 2 separate antennas which located in the projected flow direction onto the baseline plane, and tried to compare skewness of the observed cross correlation function(CCF) with skewness of modeled CCFs in which velocity fluctuations were parametrized. The integration effect of IPS along a ray path was also taken into account in the estimation of modeled CCFs. Although this analysis method is significant to derive only parallel fluctuation components to the flow directions, preliminary analyses show following results: (1) High speed winds (Vsw greater than or equal to 500 km/s out of 0.3 AU) indicate enhancement of velocity fluctuations near 0.1 AU; and (2) Low speed winds (Vsw less than or equal to 400 Km/s out of 0.3 AU) indicate small velocity fluctuations at any distances.

  16. Correlation and fluctuations in relativistic nucleus-nucleus collisions

    NASA Astrophysics Data System (ADS)

    Mohsin Khan, M.; Ahmad, N.; Kamal, A.; Masoodi, A. A.; Irfan, M.

    2011-01-01

    Correlation and fluctuations are now well accepted analysis techniques in heavy-ion collisions at relativistic energies. At the current stage of RHIC exploration, matter in bulk and many of the physics questions about the final stage of collisions are addressed with the help of correlation techniques. In the present work after a general introduction to the underlying formalism to the exotic phenomena of correlation and fluctuations, discussion on various parameters disentangling dynamical fluctuations is presented. Analysis to investigate dynamical fluctuations and correlation is carried out in terms of F q - and G q -moments. A study of various other parameters involving multiplicity and pseudorapidity of relativistic charged particles produced in high energy nuclear interactions reveals the presence of correlation and fluctuations in particle production in these collisions. The experimental data on 14.5A GeV/c 28Si-nucleus interactions has been analyzed. A parallel analysis of correlation free data generated using MC-RAND Monte Carlo code, UrQMD data and for the HIJING generated events has also been carried out.

  17. Mechanistic constraints from the substrate concentration dependence of enzymatic fluctuations.

    PubMed

    Moffitt, Jeffrey R; Chemla, Yann R; Bustamante, Carlos

    2010-09-07

    The time it takes an enzyme to complete its reaction is a stochastic quantity governed by thermal fluctuations. With the advent of high-resolution methods of single-molecule manipulation and detection, it is now possible to observe directly this natural variation in the enzymatic cycle completion time and extract kinetic information from the statistics of its fluctuations. To this end, the inverse of the squared coefficient of variation, which we term n(min), is a useful measure of fluctuations because it places a strict lower limit on the number of kinetic states in the enzymatic mechanism. Here we show that there is a single general expression for the substrate dependence of n(min) for a wide range of kinetic models. This expression is governed by three kinetic parameters, which we term N(L), N(S), and alpha. These parameters have simple geometric interpretations and provide clear constraints on possible kinetic mechanisms. As a demonstration of this analysis, we fit the fluctuations in the dwell times of the packaging motor of the bacteriophage varphi29, revealing additional features of the nucleotide loading process in this motor. Because a diverse set of kinetic models display the same substrate dependence for their fluctuations, the expression for this general dependence may prove of use in the characterization and study of the dynamics of a wide range of enzymes.

  18. Casimir effect, quantum fluctuations and related topics

    NASA Astrophysics Data System (ADS)

    Hushwater, Velvel Shaia

    Casimir forces are the very long-range (retarded) forces between electrically neutral systems. Such forces may be thought of as arising from the quantum fluctuations of the electromagnetic field. Contrary to popular opinion such forces need not be attractive. After giving a foundation of the method of the change in the 'zero-point energy' we show how other methods to compute Casimir forces follow from it. We consider the repulsion between electric and magnetic dipoles induced by vacuum fluctuations of electromagnetic field. The calculation are made by the use of the Heisenberg picture operators and by the stochastic electrodynamics approach. We present a purely geometrical proof of the image method, and use it to discuss the Casimir interaction between an atom and a plate. We study the Casimir repulsion between a perfectly conducting and an infinitely permeable plate with the radiation pressure approach. This example illustrates how a repulsive force arises as a consequence of the redistribution of vacuum-field modes corresponding to specific boundary conditions. We show that result is independent of a cutoff function. Discussing the connection with perturbation theory, we prove the negativity of the leading order shift in the ground state. The Casimir effect supports the reality of the 'zero- point energy.' To clarify this we present a novel approach to quantum theory, based on the principle of the quantization of the ensemble-averaged action variable. This quantization leads to the probabilistic description of coordinates and momentum as random variables, which satisfy the uncertainty relation. Using such variables we show that the 'quantum momentum function' must satisfy the Riccati differential equation, which can be converted to the Schrodinger equation for the Ψ function. We derive also the form of basic operators and the rule for probabilities in quantum mechanics. We show that the approach leads to a simple interpretation of gauge invariance, and discuss

  19. Fluctuation and dissipation in liquid crystal electroconvection

    NASA Astrophysics Data System (ADS)

    Goldburg, Walter I.; Goldschmidt, Yadin Y.; Kellay, Hamid

    2002-11-01

    The power dissipation P( t) was measured in a liquid crystal (MBBA) driven by an ac voltage into the chaotic electroconvective state. In that state, the power fluctuates about its mean value < P>. The quantity measured, and compared with the fluctuation theorem of Gallavotti and Cohen, is the dimensionless standard deviation of the fluctuations, σP/< P>.

  20. Bimodality in the transverse fluctuations of a grafted semiflexible polymer and the diffusion-convection analogue: An effective-medium approach

    NASA Astrophysics Data System (ADS)

    Benetatos, P.; Munk, T.; Frey, E.

    2005-09-01

    Recent Monte Carlo simulations of a grafted semiflexible polymer in 1+1 dimensions have revealed a pronounced bimodal structure in the probability distribution of the transverse (bending) fluctuations of the free end, when the total contour length is of the order of the persistence length [G. Lattanzi , Phys. Rev E 69, 021801 (2004)]. In this paper, we show that the emergence of bimodality is related to a similar behavior observed when a random walker is driven in the transverse direction by a certain type of shear flow. We adapt an effective-medium argument, which was first introduced in the context of the sheared random-walk problem [E. Ben-Naim , Phys. Rev. A 45, 7207 (1992)], in order to obtain a simple analytic approximation of the probability distribution of the free-end fluctuations. We show that this approximation captures the bimodality and most of the qualitative features of the free-end fluctuations. We also predict that relaxing the local inextensibility constraint of the wormlike chain could lead to the disappearence of bimodality.

  1. Modeling of low- and high-frequency noise by slow and fast fluctuators

    NASA Astrophysics Data System (ADS)

    Nesterov, Alexander I.; Berman, Gennady P.

    2012-05-01

    We study the dynamics of dephasing in a quantum two-level system by modeling both 1/f and high-frequency noise by random telegraph processes. Our approach is based on a so-called spin-fluctuator model in which a noisy environment is modeled by a large number of fluctuators. In the continuous limit we obtain an effective random process (ERP) that is described by a distribution function of the fluctuators. In a simplified model, we reduce the ERP to the two (slow and fast) ensembles of fluctuators. Using this model, we study decoherence in a superconducting flux qubit and we compare our theoretical results with the available experimental data. We demonstrate good agreement of our theoretical predictions with the experiments. Our approach can be applied to many quantum systems, such as biological complexes, semiconductors, superconducting, and spin qubits, where the effects of interaction with the environment are essential.

  2. Fluctuations in the Weakly Asymmetric Exclusion Process with Open Boundary Conditions

    NASA Astrophysics Data System (ADS)

    Derrida, B.; Enaud, C.; Landim, C.; Olla, S.

    2005-03-01

    We investigate the fluctuations around the average density profile in the weakly asymmetric exclusion process with open boundaries in the steady state. We show that these fluctuations are given, in the macroscopic limit, by a centered Gaussian field and we compute explicitly its covariance function. We use two approaches. The first method is dynamical and based on fluctuations around the hydrodynamic limit. We prove that the density fluctuations evolve macroscopically according to an autonomous stochastic equation, and we search for the stationary distribution of this evolution. The second approach, which is based on a representation of the steady state as a sum over paths, allows one to write the density fluctuations in the steady state as a sum over two independent processes, one of which is the derivative of a Brownian motion, the other one being related to a random path in a potential.

  3. Effects of gas temperature fluctuations on the evolution of Nitrogenous species during coal devolatilization

    SciTech Connect

    Zhang, H.T.; Zhang, J.

    2009-02-15

    The effects of gas temperature fluctuations on the instantaneous evolution processes of nitrogenous species were investigated for pulverized coal particles undergoing devolatilization in a hot gas. The instantaneous mass variations of nitrogenous species released from the particles with diameters of 10-50 {mu} m were computed for different conditions. The instantaneous gas temperature was varied with time either in a simple harmonic way or in a random way. The calculated results showed that, under different time-average gas temperatures, the HCN evolution behaviors of particles with different diameters were all affected by the gas temperature fluctuations. The gas temperature fluctuations led to more rapid HCN release from the pulverized coal particles compared to the results obtained without gas temperature fluctuations. The effects were further enhanced by increasing the amplitude or intensity of the gas temperature fluctuations.

  4. Effects of stochastic population fluctuations in two models of biological macroevolution

    NASA Astrophysics Data System (ADS)

    Murase, Yohsuke; Shimada, Takashi; Ito, Nobuyasu; Rikvold, Per Arne

    Two mathematical models of macroevolution are studied. These models have population dynamics at the species level, and mutations and extinction of species are also included. The population dynamics are updated by difference equations with stochastic noise terms that characterize population fluctuations. The effects of the stochastic population fluctuations on diversity and total population sizes on evolutionary time scales are studied. In one model, species can make either predator-prey, mutualistic, or competitive interactions, while the other model allows only predator-prey interactions. When the noise in the population dynamics is strong enough, both models show intermittent behavior and their power spectral densities show approximate 1/f fluctuations. In the noiseless limit, the two models have different power spectral densities. For the predator-prey model, 1/f2 fluctuations appears, indicating random-walk like behavior, while the other model still shows 1/f noise. These results indicate that stochastic population fluctuations may significantly affect long-time evolutionary dynamics.

  5. Nonlinear random optical waves: Integrable turbulence, rogue waves and intermittency

    NASA Astrophysics Data System (ADS)

    Randoux, Stéphane; Walczak, Pierre; Onorato, Miguel; Suret, Pierre

    2016-10-01

    We examine the general question of statistical changes experienced by ensembles of nonlinear random waves propagating in systems ruled by integrable equations. In our study that enters within the framework of integrable turbulence, we specifically focus on optical fiber systems accurately described by the integrable one-dimensional nonlinear Schrödinger equation. We consider random complex fields having a Gaussian statistics and an infinite extension at initial stage. We use numerical simulations with periodic boundary conditions and optical fiber experiments to investigate spectral and statistical changes experienced by nonlinear waves in focusing and in defocusing propagation regimes. As a result of nonlinear propagation, the power spectrum of the random wave broadens and takes exponential wings both in focusing and in defocusing regimes. Heavy-tailed deviations from Gaussian statistics are observed in focusing regime while low-tailed deviations from Gaussian statistics are observed in defocusing regime. After some transient evolution, the wave system is found to exhibit a statistically stationary state in which neither the probability density function of the wave field nor the spectrum changes with the evolution variable. Separating fluctuations of small scale from fluctuations of large scale both in focusing and defocusing regimes, we reveal the phenomenon of intermittency; i.e., small scales are characterized by large heavy-tailed deviations from Gaussian statistics, while the large ones are almost Gaussian.

  6. Fluctuations in epidemic modeling - disease extinction and control

    NASA Astrophysics Data System (ADS)

    Schwartz, Ira

    2009-03-01

    The analysis of infectious disease fluctuations has recently seen an increasing rise in the use of new tools and models from stochastic dynamics and statistical physics. Examples arise in modeling fluctuations of multi-strain diseases, in modeling adaptive social behavior and its impact on disease fluctuations, and in the analysis of disease extinction in finite population models. Proper stochastic model reduction [1] allows one to predict unobserved fluctuations from observed data in multi-strain models [2]. Degree alteration and power law behavior is predicted in adaptive network epidemic models [3,4]. And extinction rates derived from large fluctuation theory exhibit scaling with respect to distance to the bifurcation point of disease onset with an unusual exponent [5]. In addition to outbreak prediction, another main goal of epidemic modeling is one of eliminating the disease to extinction through various control mechanisms, such as vaccine implementation or quarantine. In this talk, a description will be presented of the fluctuational behavior of several epidemic models and their extinction rates. A general framework and analysis of the effect of non-Gaussian control actuations which enhance the rate to disease extinction will be described. In particular, in it is shown that even in the presence of a small Poisson distributed vaccination program, there is an exponentially enhanced rate to disease extinction. These ideas may lead to improved methods of controlling disease where random vaccinations are prevalent. [4pt] Recent papers:[0pt] [1] E. Forgoston and I. B. Schwartz, ``Escape Rates in a Stochastic Environment with Multiple Scales,'' arXiv:0809.1345 2008.[0pt] [2] L. B. Shaw, L. Billings, I. B. Schwartz, ``Using dimension reduction to improve outbreak predictability of multi-strain diseases,'' J. Math. Bio. 55, 1 2007.[0pt] [3] L. B. Shaw and I. B. Schwartz, ``Fluctuating epidemics on adaptive networks,'' Physical Review E 77, 066101 2008.[0pt] [4] L. B

  7. Thermal fluctuations of an interface near a contact line.

    PubMed

    Belardinelli, D; Sbragaglia, M; Gross, M; Andreotti, B

    2016-11-01

    The effect of thermal fluctuations near a contact line of a liquid interface partially wetting an impenetrable substrate is studied analytically and numerically. Promoting both the interface profile and the contact line position to random variables, we explore the equilibrium properties of the corresponding fluctuating contact line problem based on an interfacial Hamiltonian involving a "contact" binding potential. To facilitate an analytical treatment, we consider the case of a one-dimensional interface. The effective boundary condition at the contact line is determined by a dimensionless parameter that encodes the relative importance of thermal energy and substrate energy at the microscopic scale. We find that this parameter controls the transition from a partial wetting to a pseudopartial wetting state, the latter being characterized by a thin prewetting film of fixed thickness. In the partial wetting regime, instead, the profile typically approaches the substrate via an exponentially thinning prewetting film. We show that, independently of the physics at the microscopic scale, Young's angle is recovered sufficiently far from the substrate. The fluctuations of the interface and of the contact line give rise to an effective disjoining pressure, exponentially decreasing with height. Fluctuations therefore provide a regularization of the singular contact forces occurring in the corresponding deterministic problem.

  8. Thermal fluctuations of an interface near a contact line

    NASA Astrophysics Data System (ADS)

    Belardinelli, D.; Sbragaglia, M.; Gross, M.; Andreotti, B.

    2016-11-01

    The effect of thermal fluctuations near a contact line of a liquid interface partially wetting an impenetrable substrate is studied analytically and numerically. Promoting both the interface profile and the contact line position to random variables, we explore the equilibrium properties of the corresponding fluctuating contact line problem based on an interfacial Hamiltonian involving a "contact" binding potential. To facilitate an analytical treatment, we consider the case of a one-dimensional interface. The effective boundary condition at the contact line is determined by a dimensionless parameter that encodes the relative importance of thermal energy and substrate energy at the microscopic scale. We find that this parameter controls the transition from a partial wetting to a pseudopartial wetting state, the latter being characterized by a thin prewetting film of fixed thickness. In the partial wetting regime, instead, the profile typically approaches the substrate via an exponentially thinning prewetting film. We show that, independently of the physics at the microscopic scale, Young's angle is recovered sufficiently far from the substrate. The fluctuations of the interface and of the contact line give rise to an effective disjoining pressure, exponentially decreasing with height. Fluctuations therefore provide a regularization of the singular contact forces occurring in the corresponding deterministic problem.

  9. Nonergodicity, fluctuations, and criticality in heterogeneous diffusion processes

    NASA Astrophysics Data System (ADS)

    Cherstvy, A. G.; Metzler, R.

    2014-07-01

    We study the stochastic behavior of heterogeneous diffusion processes with the power-law dependence D(x )˜|x|α of the generalized diffusion coefficient encompassing sub- and superdiffusive anomalous diffusion. Based on statistical measures such as the amplitude scatter of the time-averaged mean-squared displacement of individual realizations, the ergodicity breaking and non-Gaussianity parameters, as well as the probability density function P (x,t), we analyze the weakly nonergodic character of the heterogeneous diffusion process and, particularly, the degree of irreproducibility of individual realizations. As we show, the fluctuations between individual realizations increase with growing modulus |α| of the scaling exponent. The fluctuations appear to diverge when the critical value α =2 is approached, while for even larger α the fluctuations decrease, again. At criticality, the power-law behavior of the mean-squared displacement changes to an exponentially fast growth, and the fluctuations of the time-averaged mean-squared displacement do not converge for increasing number of realizations. From a systematic comparison we observe some striking similarities of the heterogeneous diffusion process with the familiar subdiffusive continuous time random walk process with power-law waiting time distribution and diverging characteristic waiting time.

  10. Nonergodicity, fluctuations, and criticality in heterogeneous diffusion processes.

    PubMed

    Cherstvy, A G; Metzler, R

    2014-07-01

    We study the stochastic behavior of heterogeneous diffusion processes with the power-law dependence D(x) ∼ |x|(α) of the generalized diffusion coefficient encompassing sub- and superdiffusive anomalous diffusion. Based on statistical measures such as the amplitude scatter of the time-averaged mean-squared displacement of individual realizations, the ergodicity breaking and non-Gaussianity parameters, as well as the probability density function P(x,t), we analyze the weakly nonergodic character of the heterogeneous diffusion process and, particularly, the degree of irreproducibility of individual realizations. As we show, the fluctuations between individual realizations increase with growing modulus |α| of the scaling exponent. The fluctuations appear to diverge when the critical value α = 2 is approached, while for even larger α the fluctuations decrease, again. At criticality, the power-law behavior of the mean-squared displacement changes to an exponentially fast growth, and the fluctuations of the time-averaged mean-squared displacement do not converge for increasing number of realizations. From a systematic comparison we observe some striking similarities of the heterogeneous diffusion process with the familiar subdiffusive continuous time random walk process with power-law waiting time distribution and diverging characteristic waiting time.

  11. Propagation of pulse fluctuations in single-mode fibers.

    PubMed

    Marcuse, D

    1980-06-01

    An earlier paper [Applied Optics 19, 1653 (1980)] dealt with the ensemble averages of pulses propagating in single-mode fibers. In this paper we discuss pulse fluctuations. The light pulses are generated by modulation of the power of a continuously operating light source consisting of N discrete sinusoidal frequencies randomly phased relative to each other. The fixed amplitudes of the sinusoidal frequency components of the source are adjusted to fit into a Gaussian envelope, and the modulating pulse has a Gaussian distribution in time. This mathematical model approximates a laser light source operating in several free-running longitudinal modes. We find that the fluctuations of the modulated light pulses can die out if the pulses travel a long distance in a dispersive fiber, provided the spacings between the sinusoidal frequency components of the light source are larger than the spectral width of the modulating signal. If the source frequency components are spaced more closely than the spectral width of the modulating pulse, fluctuations persist indefinitely independent of fiber length. However, in a practical system, whose input pulse is only about half as short as the output pulse, fluctuations are practically unaffected by transmission through a fiber.

  12. Mapping of dissipative particle dynamics in fluctuating hydrodynamics simulations

    NASA Astrophysics Data System (ADS)

    Qiao, R.; He, P.

    2008-03-01

    Dissipative particle dynamics (DPD) is a novel particle method for mesoscale modeling of complex fluids. DPD particles are often thought to represent packets of real atoms, and the physical scale probed in DPD models are determined by the mapping of DPD variables to the corresponding physical quantities. However, the nonuniqueness of such mapping has led to difficulties in setting up simulations to mimic real systems and in interpreting results. For modeling transport phenomena, where thermal fluctuations are important (e.g., fluctuating hydrodynamics), an area particularly suited for DPD method, we propose that DPD fluid particles should be viewed as only (1) to provide a medium in which the momentum and energy are transferred according to the hydrodynamic laws and (2) to provide objects immersed in the DPD fluids the proper random "kicks" such that these objects exhibit correct fluctuation behaviors at the macroscopic scale. We show that, in such a case, the choice of system temperature and mapping of DPD scales to physical scales are uniquely determined by the level of coarse graining and properties of DPD fluids. We also verified that DPD simulation can reproduce the macroscopic effects of thermal fluctuation in particulate suspension by showing that the Brownian diffusion of solid particles can be computed in DPD simulations with good accuracy.

  13. Measurement and discussion of potash alum crystal growth rate fluctuations and dispersion

    NASA Astrophysics Data System (ADS)

    Tulke, Arnd; Offerman, Hans

    1993-03-01

    The results of fluidized bed experiments for the two systems, potash alum/water and sodium chloride/water, can be described using the random fluctuation model. The growth rate fluctuations postulated by this model are confirmed in single crystal measurements for {111} faces of potash alum crystals. It is shown how the parameter DG ( = effective growth rate diffusivity) can be determined using the results of the single crystal experiments.

  14. Fluctuating asymmetry in grass goby Zosterisessor ophiocephalus Pallas, 1811 inhabiting polluted and unpolluted area in Tunisia.

    PubMed

    Mabrouk, Lotfi; Guarred, Taher; Hamza, Asma; Messaoudi, Imed; Hellal, Ahmed Noureddine

    2014-08-15

    Fluctuating asymmetry, a random deviation of bilateral traits, is assessed on grass goby Zosterisessor ophiocephalus Pallas, 1811 living in one disturbed site and in one unpolluted site Gulf of Gabes (Tunisia). Statistical analysis showed that assessed asymmetries are fluctuating. FA of orbital diameter, sub-orbital distance, pectoral fin and post-orbital length are higher in polluted site compared to control. Chemical pollution seems to be responsible for this high FA. Copyright © 2014 Elsevier Ltd. All rights reserved.

  15. The average shape of the closed trefoil knot fluctuating on a floppy rope.

    PubMed

    Modlinski, Marcin; Przybyl, Sylwester; Pieranski, Piotr

    2013-05-01

    The average shape of the trefoil knot tied on a floppy, hard rope subject to thermal fluctuations has been determined. The fluctuations of the shape of knots were performed by random bending. As a result of the changing shape procedure large sets of deformed conformations of the initial knot were obtained. Afterwards, these sets were subject to the shape-fitting procedure. It has been found that the conformation is different from the ideal conformation of the knot.

  16. Fluctuations of the Increment of the Argument for the Gaussian Entire Function

    NASA Astrophysics Data System (ADS)

    Buckley, Jeremiah; Sodin, Mikhail

    2017-07-01

    The Gaussian entire function is a random entire function, characterised by a certain invariance with respect to isometries of the plane. We study the fluctuations of the increment of the argument of the Gaussian entire function along planar curves. We introduce an inner product on finite formal linear combinations of curves (with real coefficients), that we call the signed length, which describes the limiting covariance of the increment. We also establish asymptotic normality of fluctuations.

  17. Chaotic fluctuations in mathematical economics

    NASA Astrophysics Data System (ADS)

    Yoshida, Hiroyuki

    2011-03-01

    In this paper we examine a Cournot duopoly model, which expresses the strategic interaction between two firms. We formulate the dynamic adjustment process and investigate the dynamic properties of the stationary point. By introducing a memory mechanism characterized by distributed lag functions, we presuppose that each firm makes production decisions in a cautious manner. This implies that we have to deal with the system of integro-differential equations. By means of numerical simulations we show the occurrence of chaotic fluctuations in the case of fixed delays.

  18. Critical swelling of fluctuating capsules

    NASA Astrophysics Data System (ADS)

    Diamant, Haim; Haleva, Emir

    2009-03-01

    In many natural transport processes the solute molecules to be transported are encapsulated in semipermeable, flexible membrane vesicles of micron size. We study the swelling of such fluctuating capsules, as the number of encapsulated particles is increased, or the concentration of the outer solution is decreased. The approach to the maximum volume-to-area ratio and the associated buildup of membrane tension involve a continuous phase transition and follow universal scaling laws. The criticality and its features are model-independent, arising solely from the interplay between volume and surface degrees of freedom.ootnotetextE. Haleva and H. Diamant, Phys. Rev. Lett. 101, 078104 (2008).

  19. Sexual hormone fluctuation in chinchillas.

    PubMed

    Celiberti, Simone; Gloria, Alessia; Contri, Alberto; Carluccio, Augusto; Peric, Tanja; Melillo, Alessandro; Robbe, Domenico

    2013-01-01

    The data about chinchilla (Chinchilla laniger) reproduction are limited and in some cases discordant. The aim of this study was to monitor the sexual hormone fluctuation by fecal progesterone level and colpocytology analysis by vaginal smears in order to evaluate the different phases of the oestrus cycle. Twenty-four non pregnant chinchillas aged from 1 to 4 years old and subdivided in three groups were monitored. In contrast with findings reported in other study, the high values of progesterone recorded in autumn suggested the presence of a ciclicity also in this period. The data indicate that chinchilla presents a continuous cycle.

  20. Fluctuations in tides and geomagnetic variations

    NASA Astrophysics Data System (ADS)

    Kohsiek, A.; Kiefer, M.; Meek, C. E.; Manson, A. H.

    Middle atmosphere tidal winds and the daily geomagnetic Sq-variation show a day-to-day variability, both with a local behaviour. Due to the main cause of the Sq-variation, the ionospheric dynamo effect, day-to-day fluctuation of Sq could be raised by fluctuations in tides. This coupling of fluctuations is investigated with radar wind data measured at Saskatoon at around 100 km height and with magnetic data from four observatories in the vicinity of the radar. We show that our definition of fluctuations exhibits properties of atmospheric tides in the winds and that the magnetic data can be assumed to represent a local behaviour. We find that there are some significant correlations between fluctuations in winds and magnetic variations. Apparently the local fluctuation of geomagnetic variations is weakly coupled not only to the fluctuations of the semidiurnal tides but also to those of the mean winds.