Role Of Fluctuations Research Articles

Statistical thermodynamics of soft surfaces

We review the continuum, statistical thermodynamics of surfaces and interfaces in soft matter where both the energy and entropy of the surface are comparable. These systems include complex fluids that are dominated by either surface tension or the interfacial curvature, such as: fluid and solid interfaces, colloidal dispersions, macromolecular solutions, membranes, and other self-assembling aggregates such as micelles, vesicles, and microemulsions. The primary focus is on the theoretical concepts, their universality, and the role of fluctuations and inhomogeneities with connections to relevant experimental systems.

Inventory investment and asymmetric adjustment: Some evidence for the UK

There is now a plethora of non-linear time-series models of output over the business cycle, and considerable empirical evidence that there are key non-linear, poorly understood mechanisms at work. Though they account for a small part of the total flow of national income, inventories play a disproportionately large role in fluctuations in output. It would seem natural to try to determine what role inventories play in the non-linear behaviour of the business cycle. The first question is, are there economic models of firm behaviour suggesting that the movement of inventories over the business cycle is non-linear? The second issue is whether we can detect such non-linearity in the data. In this paper we use data on the aggregate behaviour of UK manufacturing, but disaggregated according to the stage of fabrication. We find that the asymmetric adjustment of inventories varies with the stage of fabrication.

Phase diagram of polymer blends in confined geometry

Abstract Within self-consistent field theory we study the phase behavior of a symmetrical binary AB polymer blend confined into a thin film. The film surfaces interact with the monomers via short range potentials. One surface attracts the A component and the corresponding smei-infinite system exhibits a first order wetting transition. The surface interaction of the opposite surface is varied as to study the crossover from capillary condensation for symmetric surfaces fields to the interface localization/delocalization transition for antisymmetric surface fields. In the former case the phase diagram has a single critical point close to the bulk critical point. In the latter case the phase diagram exhibits two critical points which correspond to the prewetting critical points of the semi-infinite system. Only below a triple point there is a single two phase coexistence region. The crossover between these qualitatively different limiting behaviors occurs gradually, however, the critical temperature and the critical composition exhibit a non-monotonic dependence on the surface field. The dependence of the phase behavior for antisymmetric boundaries is studied as a function of the film thickness and the strength of the surface interactions. Upon reducing the film thickness or decreasing the strength of the surface interactions we can change the order of the interface localization/delocalization transition from first to second. The role of fluctuations is explored via Monte Carlo simulations of a coarse grained lattice model. Close to the (prewetting) critical points we observe 2D Ising critical behavior. At lower temperatures capillary waves of the AB interface lead to a pronounced dependence of the effective interface potential on the lateral system size.

PHASE EQUILIBRIA IN THIN POLYMER FILMS

Within self-consistent field theory and Monte Carlo simulations the phase behavior of a symmetrical binary AB polymer blend confined into a thin film is studied. The film surfaces interact with the monomers via short ranged potentials. One surface attracts the A component and the corresponding semi-infinite system exhibits a first order wetting transition. The surface interaction of the opposite surface is varied as to study the crossover from capillary condensation for symmetric surface fields to interface localization/delocalization transition for antisymmetric surface fields. In the former case the phase diagram has a single critical point close to the bulk critical point. In the latter case the phase diagram exhibits two critical points which correspond to the prewetting critical points of the semi-infinite system. Only below a triple point there is a single two-phase coexistence region. The crossover between these qualitatively different limiting behaviors occurs gradually, however, the critical temperature and the critical composition exhibit a non-monotonic dependence on the surface field. The dependence of the phase behavior for antisymmetric boundaries is studied as a function of the film thickness and the strength of the surface interactions. Upon reducing the film thickness or decreasing the strength of the surface interactions we can change the order of the interface localization/delocalization transition from first to second. The role of fluctuations is explored via Monte Carlo simulations of a coarse grained lattice model. Close to the (prewetting) critical points we observe 2D Ising critical behavior. Also, there is a rich crossover behavior between Ising critical, tricritical and mean field behavior. At lower temperatures capillary waves of the AB interface lead to a pronounced dependence of the effective interface potential on the lateral system size.

Physics of polymer melts.

We have mapped the physics of polymer melts onto a time-dependent Landau-Ginzburg |psi|(4) field theory using techniques of functional integration. Time in the theory is simply a label for the location of a given monomer along the extent of a flexible chain. With this model, one can show that the limit of infinitesimal concentration of a polymer melt corresponds to a dynamic critical phenomenon. The transition to the entangled state is also shown to be a critical point. For larger concentrations, when the role of fluctuations is reduced, a mean-field approximation is justifiably employed to show the existence of tubelike structures reminiscent of Edwards' model.

Anomalous electron mobility in a coaxial Hall discharge plasma.

A comprehensive analysis of measurements supporting the presence of anomalous cross-field electron mobility in Hall plasma accelerators is presented. Nonintrusive laser-induced fluorescence measurements of neutral xenon and ionized xenon velocities, and various electrostatic probe diagnostic measurements are used to locally determine the effective electron Hall parameter inside the accelerator channel. These values are then compared to the classical (collision-driven) Hall parameters expected for a quiescent magnetized plasma. The results indicate that in the vicinity of the anode, where there are fewer plasma instabilities, the electron-transport mechanism is likely elastic collisions with the background neutral xenon. However, we find that in the vicinity of the discharge channel exit, where the magnetic field is the strongest and where there are intense fluctuations in the plasma properties, the inferred Hall parameter departs from the classical value, and is close to the Bohm value of (omega(ce)tau)(eff) approximately 16. These results are used to support a simple model for the Hall parameter that is based on the scalar addition of the electron collision frequencies (elastic collision induced plus fluctuation induced), as proposed by Boeuf and Garrigues [J. Appl. Phys. 84, 3541 (1998)]. The results also draw attention to the possible role of fluctuations in enhancing electron transport in regions where the electrons are highly magnetized.

Layer-by-layer crystallization and the role of fluctuations in free standing smectic films.

Specular x-ray reflectivity has been used to study the changes in the thermal fluctuation behavior of eight layer freely suspended N-(4-n-butoxybenzilidene)-4-n-octylaniline (4O.8) films during the process of successive layer-by-layer crystallizations. Each of these steps is preceded by the formation of an intermediate layer structure with in-plane hexatic ordering. We find an unusually large reduction of the fluctuations after the emergence of only the first hexatic toplayer. The fluctuation profiles over the film are in all cases quenched at the surfaces though less so after each crystallization step. This behavior supports theoretical arguments that hexatic order is reduced by out-of-plane smectic layer fluctuations.

Vortices in superconductors

A personal view is given of important events in the research led by Joe Vinen on vortices in superconductors. The effect of electron-hole (`Andreev') scattering on transport processes, such as sound attenuation and thermal conductivity, in the mixed state is described. Theoretical work by Nozieres and Vinen on flux flow is shown still to be topical. The role of fluctuations in the transition to the normal state from the mixed state is described. These early experiments are reviewed in the light of evolving ideas about flux lattice melting which have been generated by high-Tc research. Finally, recent observations of flux lines, using neutron and muon techniques, are linked to the work inspired by Joe Vinen. An appreciation is given of his distinctive approach to physics.

Simulation of aging with an extended Penna model

We employed the Penna model for computer simulation of population evolution when it is controlled by (a) hunting out some of the population as well as (b) to find out the role of fluctuations in threshold T for the maximum number of bad mutations on population growth dynamics. Extinction of population may be caused by too many mutations inherited by offspring. Overhunting acts in the same way and may also result in vanishing of the whole population. When both factors are present, we get a critical line that defines a sharp transition between existence and non-existence of the population. A distribution of T around its average value with some width Δ may reflect some individual resistance to illnesses, or some non-inherited somatic mutations. Structural changes in the final population as a result of overhunting or threshold T fluctuations are observed.

Interfaces, boundaries and quantum device transport

Simulations with recursive Green's functions with damping are applied to the study of a variety of nanostructure configurations, including quantum point contacts, lateral resonant structures and symmetric and asymmetric open quantum dots. The roles of fluctuations and length dependence are introduced and a comparison with experiments on multiple-point contact systems is discussed.

Enhancement of fluctuation effects in superconductors with singularities near the Fermi surface. Paraconductivity

It is shown that the existence of certain topological features on the equipotential surfaces of seed charge carriers near the Fermi level in a superconductor can have an effect on the character of the temperature anomalies in the fluctuation corrections. An expression is obtained for the fluctuation correction to the conductivity in a superconductor model, in which high values of the transition temperature are caused by an increase in the density of states of seed charge carriers in the region near the Fermi surface, where the interaction constant is nonzero. An anomaly in the density of states leads to nonanalyticity of the frequency dependence of the Cooper-pair propagator and to alteration of the fluctuation relaxation time relative to the classical value in the BCS theory. This situation is responsible for enhancement of the role of fluctuations in raising the power of the singularity in the temperature corrections. Possible interpretations of the experimental data available in the literature are discussed from this point of view.

Time-resolved photoluminescence of heavily nitrogen-doped ZnSe: Role of fluctuations

Time-resolved photoluminescence of heavily nitrogen-doped ZnSe: Role of fluctuations

Time-resolved photoluminescence of heavily nitrogen-doped ZnSe: role of fluctuations

Results of time-resolved photoluminescence of several heavily nitrogen-doped ZnSe samples ([N] > 10 18 cm −3 are presented, with emphasis on the decay at relatively long times and at a particular wavelength of decay. Both these aspects are well explained by the presence of potential fluctuations in such materials, but not by earlier theories which neglected fluctuations. The observed decay as a function of N concentration is also well explained by our model. We obtain quantitative agreement, and obtain good values for the decay constant W 0 and for the net acceptor concentrations.

A Study on Role of Fluctuation in River Discharge in Forming River Environment

There are a number of clear reasons for researching the fluctuations in river discharge. Based on nationwide surveys, it is reported that because the seasonal fluctuations in stream-flow in some rivers have decreased, the bottom quality of the riverbeds has worsened and is exerting bad effects on the fish and other wildlife. In this paper, the purpose is to conduct research into the role of fluctuations in river discharge in maintaining and forming the river environment. First, we review the actual condition and the knowledge gained from existing research results concerning the influence exerted on the river's ecosystem by fluctuations in river discharge. Next, we present the concept of macro-habitat. We set up temporary working hypotheses concerning the influence of fluctuations in river discharge on the river environment and suggest an evaluation index for verifying them.

Algorithmic Complexity and Thermodynamics of Fractal Growth Processes

A statistical mechanical formalism is developed using the computer information concepts of algorithmic complexity and Kolmogorov universal probability. This formalism provides a thermodynamic description of microstates of a system. For an isolated classical system, the algorithmic complexity is equal to the thermodynamic entropy. This approach does not rely on probabilistic ensemble concepts and can be applied to non-ergodic systems. An H-function is developed from the Kolmogorov universal probability that satisfies the properties of an entropy function. Using this approach, the thermodynamics of irreversible growth processes far from equilibrium can be investigated. Entropy functions for fractal growth processes far from equilibrium are developed from the algorithmic complexity and are seen to be similar to Flory-type equilibrium functions. This development does not require energy minimization procedures associated with equilibrium arguments. Using this approach, constraints can be put on the types of mean field models that will yield fractal structures. The algorithmic complexity of a system can also be used to explore the role of fluctuations and criticality in highly ordered systems.

The role of fluctuations on the electrical resistivity and atomic volume for some liquid alloys with critical mixing

The electrical resistivity, ϱ, was measured by the dc four probe method for some liquid alloys with critical mixing, that is Bi-Ga, Cd-Ga and Hg-Ga alloys. The maximum of temperature coefficient of ϱ, dϱ/dT, was found at the critical composition, X c , on the isotherm for liquid Bi-Ga and Cd-Ga alloys. This tendency becomes far striking at the critical temperature T c . However, an opposite minimum behavior of dϱ/dT was found at X c for liquid Hg-Ga alloys. The atomic volume, V M , was also measured by a picnometer method for liquid Bi-Ga alloys. The obtained V M is a linear function of composition. The value of thermal expansion coefficient, α p, near X c is large and shows a strong temperature dependence. The critical exponent β for liquid Bi-Ga alloys is determined to be 0.365 ± 0.02 in the range, 5.6 × 10 −5 ≤ ε(= ¦T T c¦/T c) ≤ 7.5 × 10 −2 from the binodal curve determined by resistivity measurements on heating with mixing by agitations.

Cold-shock regulation of the Arabidopsis TCH genes and the effects of modulating intracellular calcium levels.

The Arabidopsis TCH genes, which encode calmodulin-related proteins and a xyloglucan endotransglycosylase, are shown to be up-regulated in expression following cold shock. We investigated a possible role of fluctuations in intracellular calcium ion concentrations ([Ca2+]) in the cold-shock-induced TCH gene expression. Transgenic plants harboring the apoaequorin gene were generated to monitor [Ca2+]) and to test the necessity of cold-induced [Ca2+] increases for TCH expression. Cold-shock-induced [Ca2+] increases can be blocked by La3+ and Gd3+, putative plasma membrane Ca2+ channel blockers, and 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, an extracellular Ca2+ chelator. Cold-shock-induced expression of the TCH genes is inhibited by levels of La3+, Gd3+, and 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, that have been shown to block [Ca2+] increases. These data support the hypotheses that (a) intracellular [Ca2+] increases following cold shock require extracellular Ca2+ and may derive from a Ca2+ influx mediated by plasmalemma Ca2+ channels, and (b) cold up-regulation of expression of at least a subset of the TCH genes requires an intracellular [Ca2+] increase. The inhibitors are also shown to have stimulus-independent effects on gene expression, providing strong evidence that these commonly used chemicals have more complex effects than generally reported.

Interface dynamics in a block copolymer melt and the effect of noise.

The role of fluctuations in the disorder-lamellar transition in a block copolymer melt is investigated using a cell dynamical system simulation by measuring the propagation velocity of the interface between ordered and disordered regions. Our results strongly suggest that near the transition temperature, in the absence of noise, the velocity increases with quench depth as $v\ensuremath{\sim}\sqrt{\ensuremath{\tau}}$ [$\ensuremath{\tau}=\frac{({T}_{c}\ensuremath{-}T)}{{T}_{c}}$ is the reduced temperature measured from the transition temperature ${T}_{c}$], while in the presence of noise, the velocity increases as $v\ensuremath{\sim}\ensuremath{\tau}$. These results lead us to conclude that the addition of noise causes the disorder-lamellar transition to change from second order to first order. This conclusion is consistent with the prediction of Brazovskii [Sov. Phys. JETP 41, 85 (1975)].

Electrostatic fluctuations and related transport in the edge and core plasma of the Keda Tokamak-5C

Using the swept double probe and triple probe technique, temperature, density and potential fluctuations have been measured in both the plasma edge and core of the Keda Tokamak-5C (KT-5C) [World Survey of Activities in Controlled Fusion Research, Nuclear Fusion Special Supplement (International Atomic Energy Agency, Vienna, 1991), p. 190]. The fluctuation-driven particle and energy fluxes were also estimated from the correlations of 〈ñeẼθ〉 and 〈T̃eẼθ〉. Evidence has been found that there exist substantial electron temperature fluctuations of T̃e/Te≂0.4ñe/ne in both regions. At the edge of KT-5C, many of the fluctuation features, such as the velocity shear stabilization of turbulence, the non-Boltzmann relation and the role of fluctuations in the edge confinement, are very similar to those obtained from other tokamaks. In the plasma interior, the fluctuations do obey the simple Boltzmann relationship and the profiles of the normalized fluctuating levels ñe/ne and φ̃p/Te vary roughly as ñe/ne∝ne−3/2 and φ̃p/Te∝ne−1/2Te−1, respectively. In addition, a spiky, radially intermittent structure in the particle and energy fluxes with large levels at the low-q resonances and lower levels in between was found. The experimental results provide some new evidence, particularly in the plasma core, for a better understanding of the basic mechanism of turbulence.

Elasticity of c*-Gels

A junction affine network model is solved for chains following a Redner-des Cloizeaux distribution In a gel at c* the network strands behave as isolated chains. In a good solvent their elastic properties cannot be obtained from Gaussian statistics as in the classical models of rubber elasticity. Instead the Redner-des Cloizeaux distribution is employed, which is known to be an excellent approximation to the end-to-end distance distribution of flexible polymer chains in a good solvent. The implications of using non-linear entropic springs, the role of fluctuations and the quality of the affine approxtmation are worked out for a Flory-Rehner model The applicability to swollen networks and the elasticity of two dimensional c*-gels are briefly discussed