Effects Of Surface Fluctuations Research Articles

The dependence of the nuclear charge form factor on short range correlations and surface fluctuation effects

An investigation is carried out in order to study effects, originating from fluctuations of the nuclear surface, to the elastic charge form factor of light nuclei in which the two-body part of the short range correlation factor is also included through a Jastrow-type correlation function. It is found that if these effects are taken into account in the uncorrected (harmonic oscillator) part of such a form-factor for the 4He, l6O and 40Ca nuclei, the quality of the fitting is improved. In addition, they lead to a drastic change in the asymptotic behaviour of the point-proton form factor which now drops off for large values of the momentum transfer q quite slowly that is as const.•q^-4.

Investigation of Surface Fluctuation Effects on the Spectral Null of Rg Waves Generated by CLVD Source with Spectral Element Method Simulation

AbstractThe characteristics of the spectral null of Rg waves generated by CLVD source and the corresponding source depths are simulated numerically with Spectral Element Method under various ground surface fluctuation models. The results indicate that the spectral null of Rg waves exists under certain conditions, and the location of the spectral null reflects the signatures of the surface fluctuation near the source. However, the depth calculated according to the spectral null still has a certain bias compared with the theoretical value. The fluctuant surface far from the source has little effects on the spectral null.

Fermi surface fluctuations and breakdown of Fermi liquid behavior

Electron–electron interactions can induce Fermi surface deformations which break the point-group symmetry of the crystal structure of the system. In the vicinity of such a “Pomeranchuk instability” the Fermi surface is easily deformed by anisotropic perturbations, and exhibits enhanced collective fluctuations. We analyze Fermi surface fluctuation effects in a two-dimensional electron system on a square lattice in the vicinity of a Pomeranchuk instability with d-wave symmetry. At a quantum critical point d-wave density correlations and the dynamical forward scattering interaction diverge with a dynamical exponent z = 3. The singular forward scattering leads to large self-energy corrections, which destroy Fermi liquid behavior over the whole Fermi surface except near the Brillouin zone diagonal. The contribution from classical fluctuations to the self-energy spoils ω/ T scaling in the quantum critical regime. We discuss to what extent d-wave Fermi surface fluctuations may play a role in cuprate superconductors.

Simulations of Electron Acceleration at Collisionless Shocks: The Effects of Surface Fluctuations

Energetic electrons are a common feature of interplanetary shocks and planetary bow shocks, and they are invoked as a key component of models of nonthermal radio emission, such as solar radio bursts. A simulation study is carried out of electron acceleration for high Mach number, quasi-perpendicular shocks, typical of the shocks in the solar wind. Two dimensional self-consistent hybrid shock simulations provide the electric and magnetic fields in which test particle electrons are followed. A range of different shock types, shock normal angles, and injection energies are studied. When the Mach number is low, or the simulation configuration suppresses fluctuations along the magnetic field direction, the results agree with theory assuming magnetic moment conserving reflection (or Fast Fermi acceleration), with electron energy gains of a factor only 2 - 3. For high Mach number, with a realistic simulation configuration, the shock front has a dynamic rippled character. The corresponding electron energization is radically different: Energy spectra display: (1) considerably higher maximum energies than Fast Fermi acceleration; (2) a plateau, or shallow sloped region, at intermediate energies 2 - 5 times the injection energy; (3) power law fall off with increasing energy, for both upstream and downstream particles, with a slope decreasing as the shock normal angle approaches perpendicular; (4) sustained flux levels over a broader region of shock normal angle than for adiabatic reflection. All these features are in good qualitative agreement with observations, and show that dynamic structure in the shock surface at ion scales produces effective scattering and can be responsible for making high Mach number shocks effective sites for electron acceleration.

STUDY ON RELATIONSHIP BETWEEN TURBULENCE STRUCTURES AND WATER SURFACE FLUCTUATIONS IN WIND-DRIVEN OPEN-CHANNEL FLOWS

The present study describes an experimental relationship between turbulence structures in water layer and the water-surface fluctuations in wind-driven open-channel flows by using both a laser Doppler Anemometer (LDA) and a wave gauge simultaneously. The purpose of this study is to make clear the characteristics of surface fluctuations on water dynamics in air-sheared open-channel flows, and to evaluate the effects of surface fluctuations on vertical momentum transport in the water layer. As the results of experiments, it is shown by spectral analysis that the velocity fluctuations near the interface in both only open-channel flow and wind-driven open-channel flow are significantly affected by the water surface in every range of frequency, and that there exists a high correlation between turbulence near the air-water interface and the surface fluctuations in a predominant frequency due to high-sheared wind flow. Moreover, it is recognized by wavelet analysis that the turbulence structures in weak wind-driven open-channel flows are governed by both wall shear and wind-induced flows.

Depletion forces near a soft surface

We investigate excluded-volume effects in a bidisperse colloidal suspension near a flexible interface. Inspired by a recent experiment by Dinsmore et al. [Phys. Rev. Lett. 80, 409 (1998)], we study the adsorption of a mesoscopic bead on the surface and show that depletion forces could in principle lead to particle encapsulation. We then consider the effect of surface fluctuations on the depletion potential itself and construct the density profile of a polymer solution near a soft interface. Surprisingly we find that the chains accumulate at the wall, whereas the density displays a deficit of particles at distances larger than the surface roughness. This nonmonotonic behavior demonstrates that surface fluctuations can have major repercussions on the properties of a colloidal solution. On average, the additional contribution to the Gibbs adsorbance is negative. The amplitude of the depletion potential between a mesoscopic bead and the surface increases accordingly.

Surface-related phase noise in SAW resonators.

With the advent of nanotechnologies, electronic devices are shrinking in thickness and width to reduce mass and, thereby, increase frequency and spe Lithographic approaches are capable of creating metal connections with thickness and lateral dimensions down to about 20 nm, approaching the molecular scale. As a result, the dimensions of outer particles are comparable with, or even larger than, those of active or passive regions in electronics devices. Therefore, directing our attention toward the effect of surface fluctuations is of practical significance. In fact, electronic device surface-related phenomena have already received more and more attention as device size decreases. In connection with surface phase noise, selection of a suitable device with high surface sensitivity is important. In this paper, high Q-value surface acoustic wave resonators were employed because of their strong sensitivity to surface perturbation. Phase noise in SAW resonators related to surface particle motion has been examined both theoretically and experimentally. This kind of noise has been studied from the point of view of a stochastic process resulting from particle molecular adsorption and desorption. Experimental results suggest that some volatile vapors can change flicker noise 1/f and random walk noise 1/f2. An analysis has been made indicating that these effects are not associated with Q value variation, but are generated by the change in the dynamic rate of adsorption and desorption of surface particles. Research on particle motion above the device substrate might explain the differences observed from the model based only on the substrate itself. Results might lead to a better understanding of the phase noise mechanism in micro-electronic devices and help us to build oscillators with improved performance.

Effects of surface fluctuations in a two-dimensional emulsion

We investigate the role of geometrical shape fluctuations for the thermodynamic properties of a polydisperse ensemble of two-dimensional droplets. The energy of a droplet derives from the Hamiltonian for surface bending rigidity with spontaneous curvature. Interactions between individual droplets are omitted, but polydispersity in droplet size and arbitrarily large distortions of the droplet shape are incorporated fully. The physical property of self-avoidance is approximated by the less stringent topological requirement of unit winding number. This topological model shows that some physical observables are considerably more sensitive to the presence of shape fluctuations than others. The specific heat, in particular, is strongly affected by the presence of shape fluctuations. This observable is also very sensitive to approximate treatments of the shape fluctuations. The periodic Gaussian or Villain approximation is found to be reliable at all temperatures, whereas the Gaussian approximation fails except for very low temperatures.

Quark-hadron phase transition with surface fluctuations.

The effect of surface fluctuations on the observables of a quark-hadron phase transition is studied. The Ginzburg-Landau formalism is extended by the inclusion of an extra term in the free energy that depends on the vertical displacements from a flat surface. The probability that a bin has a particular net displacement is determined by lattice simulation, where the physics input is color confinement. The surface fluctuations from bin to bin are related to multiplicity fluctuations, which in turn are measured by the factorial moments. It is found that both the {ital F}-scaling behavior and the scaling exponent are essentially unaffected by the inclusion of surface fluctuations. {copyright} {ital 1996 The American Physical Society.}

The dependence of the nuclear charge form factor on short-range correlations and surface fluctuation effects

We investigate the effects of fluctuations of the nuclear surface on the harmonic oscillator elastic charge form factor of light nuclei, while simultaneously approximating the short-range correlations through a Jastrow correlation ~factor. Inclusion of surface-fluctuation effects within this description, by truncating the cluster expansion at the two-body part, is found to improve somewhat the fit to the elastic charge form-factor of $^{16}O$ and $^{40}Ca$. However, the convergence of the cluster expansion is expected to deteriorate. An additional finding is that the surface-fluctuation correlations produce a drastic change in the asymptotic behavior of the point-proton form factor, which now falls off quite slowly (i.e. as $const. \cdot q^{-4}$) at large values of the momentum transfer $q$.

Effect of surface fluctuations in the line shape of plasma resonances in small metal clusters.

The line shape of plasma resonances in small sodium clusters (8\ensuremath{\le}N\ensuremath{\le}20) is calculated taking into account quadrupole fluctuations of the cluster shape. At room temperatures, an average value of \ensuremath{\Gamma}/${\ensuremath{\omega}}_{M}$\ensuremath{\sim}0.1 for the damping factor is found. In the case of deformed clusters, these fluctuations are not able to wash out the multipeaked structure associated with the dipole resonance along the principal axes of the cluster.

Effect of surface fluctuations on the nuclear density.

Effect of surface fluctuations on the nuclear density.

Effect of surface fluctuations on the nuclear density.

Changes in the nuclear density arising from shape fluctuations are calculated in the case of the closed-shell nucleus /sup 40/Ca. The main contributions come from self-energy processes which renormalize the single-particle potential. Those due to ground-state correlations are much smaller. Processes involving the coupling to isoscalar vibrations are the most important, the role of isovector modes being small. Changes in the radius and in the diffusivity, of the order of 5% and 20%, respectively, are found.