Kinetic Fluctuations Research Articles

An Energy Fluctuation Approach to Calculate Homogeneous Nucleation Rate in Superheated Liquids and Its Verification by Performing an LPG Rapid Discharge Experiment

To investigate conditions that are likely to produce a boiling-liquid-expanding-vapor explosion (BLEVE), the determination of homogeneous nucleation rates of superheated liquids is often crucial. A new approach to estimate nucleation rates of superheated liquids is proposed; the approach is based on the probability distribution of the energy fluctuation within the framework of statistical thermodynamic fluctuation theory. Formulae for calculating the homogeneous nucleation rate in Gibbs canonical ensembles are deduced and tested for some substances. The calculated rates are compared with those obtained by the commonly used kinetic method as well as with experimental values. Finally, the new approach is validated by analyzing pressure rebounds of rapid discharge of pressurized liquefied petroleum gas (LPG). From the pressure rebound conditions, estimates of homogeneous nucleation rates can be obtained with both the kinetic and energy fluctuation approaches. Comparison of calculated results reveals that the new energy fluctuation approach is reasonably effective and has practical relevance in BLEVE research.

GA-based Design Algorithms for the Robust Synthetic Genetic Oscillators with Prescribed Amplitude, Period and Phase

In the past decade, the development of synthetic gene networks has attracted much attention from many researchers. In particular, the genetic oscillator known as the repressilator has become a paradigm for how to design a gene network with a desired dynamic behaviour. Even though the repressilator can show oscillatory properties in its protein concentrations, their amplitudes, frequencies and phases are perturbed by the kinetic parametric fluctuations (intrinsic molecular perturbations) and external disturbances (extrinsic molecular noises) of the environment. Therefore, how to design a robust genetic oscillator with desired amplitude, frequency and phase under stochastic intrinsic and extrinsic molecular noises is an important topic for synthetic biology.In this study, based on periodic reference signals with arbitrary amplitudes, frequencies and phases, a robust synthetic gene oscillator is designed by tuning the kinetic parameters of repressilator via a genetic algorithm (GA) so that the protein concentrations can track the desired periodic reference signals under intrinsic and extrinsic molecular noises. GA is a stochastic optimization algorithm which was inspired by the mechanisms of natural selection and evolution genetics. By the proposed GA-based design algorithm, the repressilator can track the desired amplitude, frequency and phase of oscillation under intrinsic and extrinsic noises through the optimization of fitness function.The proposed GA-based design algorithm can mimic the natural selection in evolutionary process to select adequate kinetic parameters for robust genetic oscillators. The design method can be easily extended to any synthetic gene network design with prescribed behaviours.

Non-classical role of potential energy in adiabatic quantum annealing

Adiabatic quantum annealing is a paradigm of analog quantum computation, where a given computational job is converted to the task of finding the global minimum of some classical potential energy function and the search for the global potential minimum is performed by employing external kinetic quantum fluctuations and subsequent slow reduction (annealing) of them. In this method, the entire potential energy landscape (PEL) may be accessed simultaneously through a delocalized wave-function, in contrast to a classical search, where the searcher has to visit different points in the landscape (i.e., individual classical configurations) sequentially. Thus in such searches, the role of the potential energy might be significantly different in the two cases. Here we discuss this in the context of searching of a single isolated hole (potential minimum) in a golf-course type gradient free PEL. We show, that the quantum particle would be able to locate the hole faster if the hole is deeper, while the classical particle of course would have no scope to exploit the depth of the hole. We also discuss the effect of the underlying quantum phase transition on the adiabatic dynamics.

Reflections

Brain type II Ca2+/calmodulin-dependent protein kinase is a holoenzyme composed of several copies each of three subunits, alpha (50 kd), beta (60 kd), and beta' (58 kd), in varying proportions. The deduced amino acid sequences of alpha (reported here) and beta are highly similar but not identical. The major difference between them is the deletion from alpha of two short segments (residues 316-339 and 354-392 in beta). cDNAs that appear to encode beta' are identical to beta except for the deletion of a segment encoding residues 378-392. Thus, the structural differences among alpha, beta, and beta' arise primarily from deletions (or insertions) in a variable region lying immediately carboxyl to the protein kinase and calmodulin-binding domains. The alpha and beta subunits are encoded by distinct genes expressed primarily, if not exclusively, in brain. Rather than being encoded by a third gene, beta' may arise by alternative splicing of the beta gene transcript.

Nonhelical mean‐field dynamos in a sheared turbulence

AbstractMechanisms of nonhelical large‐scale dynamos (shear‐current dynamo and effect of homogeneous kinetic helicity fluctuations with zero mean) in a homogeneous turbulence with large‐scale shear are discussed. We have found that the shearcurrent dynamo can act even in random flows with small Reynolds numbers. However, in this case mean‐field dynamo requires small magnetic Prandtl numbers (i.e., when Pm < Pmcr < 1). The threshold in the magnetic Prandtl number, Pmcr = 0.24, is determined using second order correlation approximation (or first‐order smoothing approximation) for a background random flow with a scale‐dependent viscous correlation time τc = (νk 2)–1 (where ν is the kinematic viscosity of the fluid and k is the wave number). For turbulent flows with large Reynolds numbers shear‐current dynamo occurs for arbitrary magnetic Prandtl numbers. This dynamo effect represents a very generic mechanism for generating large‐scale magnetic fields in a broad class of astrophysical turbulent systems with large‐scale shear. On the other hand, mean‐field dynamo due to homogeneous kinetic helicity fluctuations alone in a sheared turbulence is not realistic for a broad class of astrophysical systems because it requires a very specific random forcing of kinetic helicity fluctuations that contains, e.g., low‐frequency oscillations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Coherent Structures in the Flow Field around a Circular Cylinder with Scour Hole

Large-eddy simulation (LES) and laboratory-flume visualizations were used to investigate coherent structures present in the flow field around a circular cylinder located in a scour hole. The bathymetry corresponds to equilibrium scour conditions and is fixed in LES. The flow parameters in the simulation correspond to the experimental conditions in which the approach flow is fully turbulent. Detailed consideration is given to the interaction of the horseshoe vortex (HV) system within the scour hole with the detached shear layers formed from the cylinder, and the near bed turbulence. It is found that the overall structure of the HV system varies considerably in space and time, though a large, relatively stable, primary necklace vortex is present at practically all times inside the scour hole. The simulation captures the presence of bimodal chaotic oscillations inside the HV system, as well as the sharp increase in the resolved turbulent kinetic energy levels and pressure fluctuations reported in prior experimental investigations. High levels of the mean bed shear stress are observed beneath the primary necklace vortex, especially over the region where the bimodal oscillations are strong, as well as beneath the small junction vortex at the base of the cylinder. It is also found that the detachment and advection of patches of vorticity from the downstream part of the legs of the necklace vortices can induce large instantaneous bed shear stress values. When the critical bed shear stress value for sediment entrainment on a flat surface is adjusted for bed slope effects, the LES simulation correctly predicts that the distribution of the mean bed shear stress is consistent with equilibrium scour conditions.

Mean-field dynamo in a turbulence with shear and kinetic helicity fluctuations

We study the effects of kinetic helicity fluctuations in a turbulence with large-scale shear using two different approaches: the spectral tau approximation and the second-order correlation approximation (or first-order smoothing approximation). These two approaches demonstrate that homogeneous kinetic helicity fluctuations alone with zero mean value in a sheared homogeneous turbulence cannot cause a large-scale dynamo. A mean-field dynamo is possible when the kinetic helicity fluctuations are inhomogeneous, which causes a nonzero mean alpha effect in a sheared turbulence. On the other hand, the shear-current effect can generate a large-scale magnetic field even in a homogeneous nonhelical turbulence with large-scale shear. This effect was investigated previously for large hydrodynamic and magnetic Reynolds numbers. In this study we examine the threshold required for the shear-current dynamo versus Reynolds number. We demonstrate that there is no need for a developed inertial range in order to maintain the shear-current dynamo (e.g., the threshold in the Reynolds number is of the order of 1).

Influence of an upper-hybrid pump on temperature relaxation processes in a magnetized plasma

AbstractBy means of kinetic fluctuation theory, the relaxation process between the electron and ion temperatures in a magnetized homogeneous plasma is considered. The cases when the external upper-hybrid pump wave excites modified convective cells and ion-acoustic waves are analysed. The inverse relaxation time in the regime where the turbulent fluctuations are developed is calculated for these cases and its dependence on the pump wave and plasma parameters is deduced.

Effects of ion temperature anisotropy on diffusion process in plasma with pump

On the basis of kinetic fluctuation theory, we consider the parametric interaction of lower and upper hybrid waves with ion-cyclotron oscillations in a plasma where the ion velocity distribution function is anisotropic. The turbulent diffusion coefficient is found to depend significantly on the ratio between the parallel and perpendicular ion temperatures. Our results can be of interest for the investigation of anomalous transport processes in space and laboratory plasma with ion temperature anisotropy.

Robust filtering circuit design for stochastic gene networks under intrinsic and extrinsic molecular noises

How to design a robust gene network to tolerate more intrinsic kinetic parameter variations and to attenuate more extrinsic environmental noises to achieve a desired filtering level will be an important topic for systems biology and synthetic biology. At present, there is no good systematic design method to achieve robust gene network design. In this study, a gene network suffering from intrinsic kinetic parameter fluctuations and extrinsic environmental noises is modeled as a Langevin equation with state-dependent stochastic noises. Based on the nonlinear stochastic filtering theory, a systematic gene circuit design method is proposed to make gene networks improve their robustness to tolerate more intrinsic noises and to attenuate extrinsic noises to a prescribed filtering level. The robust gene network design principles have not only yielded a comprehensive design theory of robust gene networks, but also gained valuable insights into the molecular noise filtering of gene networks from the systematic perspective.

Scaling laws and coherent structures in the solar wind

The interplanetary medium is characterized by a very high Reynolds number and is pervaded by fluctuations providing information on a wide range of scales, from fractions of second up to the solar rotation period. In the past decade or so, turbulence in the solar wind has been used as a large wind tunnel to investigate scaling laws of turbulent fluctuations and multifractal models. Moreover, new interesting insights in the theory of turbulence have been derived from the point of view which considers a turbulent flow as a complex system, a sort of benchmark for the theory of dynamical systems. Important finding like the lack of a strict self-similarity of the fluctuations with the consequent nonapplicability of strict scale invariance, the strong anisotropy of velocity and magnetic field fluctuations, the clear lack of equipartition between magnetic and kinetic fluctuations all contributed to suggest the idea that interplanetary fluctuations could possibly be due to a mixture of propagating waves and static structures convected by the wind. In this paper we further discuss this point and bring new evidence about the fact that the presence of a background magnetic field introduces not only a symmetry breaking in interplanetary space but also organizes fluctuations about its large scale orientation.

Numerical analysis of the unsteady character of “spoke pattern” in Bridgman top seeding geometry

Three-dimensional (3D) numerical simulations of spoke patterns were performed in a vertical cylinder (similar to the Bridgman top seeding method of single-crystal growth). Calculations were presented for Rayleigh numbers in the range between 10 5 and 10 7 (for the transient region from laminar to turbulent flow). The numerically simulated surface pattern shows unsteady flow behaviour. The spoke pattern was formed due to a buoyancy effect. All velocity components (radial, azimuthal and axial) show fluctuations. The region of the maximum fluctuations for the axial velocity component appears near the axis of symmetry. However the regions of maximum fluctuation for the radial and azimuthal velocity components are near the bottom of the crucible. The analysis of the numerical results shows that fluctuations in “spoke patterns” are driven by temperature fluctuations and by fluctuations of the azimuthal and axial velocity components. The calculated distributions of the kinetic fluctuation energy show that the height of the kinetic fluctuation energy profile depends on the Grashof number. As the Grashof number increases the flow structure becomes unstable and the vertical “cold jet” becomes dominant in the melt.

Radial transport of fluctuation energy in a two-field model of drift-wave turbulence

A theory of spatial propagation of turbulence, referred to as turbulence spreading, is developed for the two-field model of drift wave turbulence. Markovian closure expressions for the flux of kinetic and internal fluctuation energies are systematically derived. Simplified closure expressions are used to obtain two coupled reaction-diffusion equations for kinetic and internal energy. The efficacy of various nonlinear interaction mechanisms for spreading is analyzed systematically. Spreading of internal energy is predicted to “lead” that of kinetic energy. The important role of zonal flow damping in spreading is identified, but zonal flows are shown not to be the dominant agents of turbulence spreading.

Fluctuations and instability of a biological membrane induced by interaction with macromolecules

This paper studies the dynamics and fluctuations of a phospholipidic membrane in the presence of a diffusion field of foreign molecules, such as polymers, proteins, etc., which have the ability to adsorb on, and to desorb from, the membrane. We develop a model that includes, besides hydrodynamics, molecular diffusion in the surrounding fluid and lateral diffusion (i.e., diffusion along the membrane) as well as the kinetics of attachment and detachment to and from the membrane. This model is exploited here for the case of a free membrane which is globally at equilibrium while the nonequilibrium part will be presented in the future. We show that if the coupling between the membrane and the molecules is strong enough, the flat membrane can suffer a morphological instability. The numerical calculation in the nonlinear regime reveals budding, and an initial stage of spontaneous vesicle emission. When the condition of stability is satisfied we show how kinetic fluctuations lead to a rich variety of dynamical behaviors expressing the dominant dissipation mechanisms. We show that in the limit of well separated length scales related to the physical mechanisms that enter into play, the width of the membrane fluctuations exhibits various dynamical scalings with universal scaling exponents. It is shown that the usual behavior with time w approximately t(1/3) is altered in various time and length scales of interest. For example, we find that , w approximately t(1/4), w approximately t(1/2), and w approximately [t ln(t)](1/2), depending on which physical mechanism limits the membrane fluctuations on the time scale under consideration. The experimental study of the fluctuation spectrum can be viewed as a precious tool in order to have access to the underlying microscopic physical mechanisms.

Problem of the noise-noise correlation function in hot non-Abelian plasma

In this work on the basis of Kadomtsev’s kinetic fluctuation theory we present the more general expression for noise-noise correlation function in effective theory for ultrasoft field modes.Received 27 April 2005DOI:https://doi.org/10.1103/PhysRevD.71.117501©2005 American Physical Society

Evolution of Microscopic Cracks and Pores in Solids under Loading

Experimental data on the development and partial healing of microscopic cracks and pores in loaded crystalline materials are considered. An analysis of the data indicates that fracture development has a number of specific features depending on the state of the materials and the testing conditions and is a kinetic thermal fluctuation process occurring virtually throughout the entire time of loading.

Long-Term Rhinoflowmetry: A New Method for Functional Rhinologic Diagnostics

With current functional diagnostic tools in rhinology (rhinomanometry, rhinoresistometry, and acoustic rhinometry) long-term assessment of nasal function is difficult to acquire. Usually, only the situation at the time of examination is evaluated. Therefore, temporary nasal complaints of the nasal cycle are difficult to assess. It was the aim of this work to create a diagnostic tool to measure nasal flow over a long time period under physiological and everyday life conditions. We term the method long-term rhinoflowmetry (LRFM). A portable device recording nasal airflow over a time period up to 72 hours was developed. Kinetic pressure fluctuations during respiration as a measure for the flow were registered over time and relative airflow was calculated. A summary of diagnostic results is given in six exemplary patients. Classic nasal cycles could be recorded in detail with durations ranging from 90 minutes to 10 hours. The manifestation of nighttime nasal obstruction as well as a case of paradoxical nasal obstruction were objectified. LRFM enables the assessment of time, duration, and extent of temporary nasal obstruction. LRFM enables an assessment of temporary nasal obstruction as well as physiological and pathological fluctuations in the nasal cycle. Especially in cases in which traditional rhinological diagnostic tools are unsatisfying, the enhanced diagnostic quality of LRFM appears to be a promising supplement to the currently available rhinological monitoring methods.

Temperature dependence of rupture strength of the amorphous alloy Ni 82.1Cr 7.8Si 4.6Fe 3.1Mn 0.3Al 0.1Cu

Rupture strength of the amorphous alloy based on nickel (Ni >80) has been measured in the temperature region 293–650 K under loading with a rate of 25 MPa/s. The samples in the form of 60–70 μm bands were prepared by spinning and were stabilized by temperature and force treatments, the amorphous state being preserved. The observed linear decrease in the rupture strength with increasing test temperature was analyzed in the framework of the kinetic thermal fluctuation theory of fracture. The initial barrier for elementary events of fracture of the alloy (activation energy), coefficients of local overstresses in the samples, and the theoretical strength of the alloy has been found.

Stripes formation: Antiphase and in-phase domain walls

For stripes of hole rich lines in doped antiferromagnets, we investigate the competition between anti-phase and in-phase domain wall ground state configurations. We argue that a phase transition must occure as a function of the electron/hole filling fraction of the domain wall. Due to {\em transverse} kinetic hole fluctuations, empty domain walls are always anti-phase. At arbitrary electron filling fraction ($\delta $) of the domain wall (and in particular for $\delta \approx 1/4$ as in LaNdSrCuO), it is essential to account also for the transverse magnetic interactions of the electrons and their mobility {\em along} the domain wall. We find that the transition from anti-phase to in-phase stripe domain wall occurs at a critical filling fraction $0.28<\delta_{c}<0.30$, for any value of $\frac{J}{t}<{1/3}$. We further use our model to estimate the spin-wave velocity in a stripe system. Finally, relate the results of our microscopic model to previous Landau theory approach to stripes.

Effects of Material Properties on Granular Flow in a Silo Using DEM Simulation

In order to test the effect of material properties on flowability of particulate materials, discharge procedures of spherical particles within a flat-bottomed model silo with three sets of material properties, i.e., soft and hard without adhesion and adhesive hard, were simulated using the Discrete Element Method. For each system, three particles on the center line were selected and their instant vertical velocity components were traced. In addition, both discharge and the rate were recorded throughout the procedure. The predicted results show that, for both the systems without adhesion, though the soft has a material modulus only 1/1000 of the hard, there are no significant differences in f low pattern and discharge rate. This suggests that a soft system can be used to predict the behavior of a hard one to save CPU time in a gravity-driven granular flow. On the other hand, comparison between both hard systems shows that adhesion can significantly reduce the flowability in granular flow. By analyzing the velocity plot for the traced particles, free fall was clearly detected above the decompression zone, indicating the motion of a particle in a granular flow can be resolved as free fall together with the movement due to particle collision. In addition, select dynamic behavior related to the kinetic fluctuations affecting flow was observed. discrete element method silo granule flow particulate material