Damage on HfO2/SiO2 high-reflecting coatings under single and multiple Nd:YAG laser pulse irradiation

The single- and multi-shot damage behaviors of HfO2/SiO2 high-reflecting (HR) coatings under Nd:YAG laser exposure were investigated. Fundamental aspects of multi-shot laser damage, such as the instability due to pulse-to-pulse accumulation of absorption defect and structural defect effect, and the mechanism of laser induced defect generation, are considered. It was found in multi-shot damage, the main factors influencing laser-induced damage threshold (LIDT) are accumulation of irreversible changes of structural defects and thermal stress that induced by thermal density fluctuations.     

Spatial persistence of angular correlations in amyloid fibrils

Using atomic force microscopy height maps, we resolve and quantify torsional fluctuations in one-dimensional amyloid fibril aggregates self-assembled from three different representative polypeptide systems. Furthermore, we show that angular correlation in these nanoscale structures is maintained over several microns, corresponding to many thousands of molecules along the fibril axis. We model disorder in the fibril in respect of both thermal fluctuations and structural defects, and determine quantitative values for the defect density, as well as the energy scales involved in the fundamental interactions stabilizing these generic structures.     

Experimental test of the fluctuation theorem for a driven two-level system with time-dependent rates

A single defect center in diamond periodically excited by a laser is shown to provide a simple realization for a system obeying a fluctuation theorem for nonthermal noise. The distribution of these fluctuations is distinctly non-Gaussian, which has also been verified by numerical calculation. For driving protocols symmetric under time reversal a more restricted form of the theorem holds, which is also known from entropy fluctuations caused by thermal noise.     

Low-Temperature Thermal Conductance in Superlattice Nanowire with Structural Defect

Using the scattering-matrix cascading method, we investigate the effect of structural defect on the acoustic phonon transmission and thermal conductance in the superlattice nanowire at low temperatures. In the present system, the phonon transmissions exhibit quite complex oscillatory behaviour. It is found that a lateral defect in an otherwise periodic structure significantly decrease the thermal conductance and completely washes away the transmission quantization. However, the appreciable transmission quantization survives in the presence of a longitudinal defect whereas a good quantization plateau of thermal conductance emerges below the universal level in a wide temperature range with the lateral defect.     

Thermal 1/ω fluctuations of a quantum oscillator under a parametric effect of a random field

It is shown that the effect of a time-correlated Gaussian random field of sufficiently high intensity on the elasticity coefficient of a quantum oscillator manifests itself in the generation of thermal fluctuations with a 1/ω spectrum in the oscillator. It is also shown that, in any physical system described by the equation of an anharmonic oscillator, fluctuations with a 1/ω spectrum arise at an above-critical temperature.     

Infrared spectroscopy and ultrasonic velocimetry as a tool for probing conformational flexibility of proteins

Abstract

Because of the crucial importance of structural fluctuations for function and stability of proteins, there is a strong interest for the relationships between structural fluctuations, the parameters of protein denaturation and the kinetics of H/D-exchange. Structural fluctuations can be described by volume and entropy fluctuations and these quantities are accessible via the isothermal compressibility, the thermal expansion and the isobaric heat capacity.

Our aim is to present the principal problem concerning the experimental procedures to answer those questions using lysozyme and α-lactalbumin. Whereas the transition parameters and the kinetics of the H/D-exchange were obtained using FTIR spectroscopy, the adiabatic compressibility was obtained by a combination of ultrasonic velocimetry and densitometry. It could be shown that the stability of the investigated proteins is correlated with reduced volume fluctuations. The expected direct correlation between H/D exchange rates and structural fluctuations could not be seen and it is assumed that the interactions are more complex than from the intuitive point of view.     

Statistical fluctuations in hot rotating nuclei

Thermal fluctuations in angular momentum due to excitation is investigated. Shape changes or structural rearrangement are observed as a consequence of fluctuation in second moment of spin. The uncertainty in angular momentum is considerably enhanced due to thermal fluctuation and is strongly dependent on spin and structural changes.     

Local melting and drag for a particle driven through a colloidal crystal

We numerically investigate a colloidal particle driven through a colloidal crystal as a function of temperature. When the charge of the driven particle is larger or comparable to that of the colloids comprising the crystal, a local melting can occur, characterized by defect generation in the lattice surrounding the driven particle. The generation of the defects is accompanied by an increase in the drag force on the driven particle, as well as large noise fluctuations. We discuss the similarities of these results to the peak effect phenomena observed for vortices in superconductors.     

Time-resolved measurements of thermodynamic fluctuations of the particle number in a nondegenerate Fermi gas

We report on time-resolved measurements of thermodynamic fluctuations in the number of particles in a nondegenerate Fermi gas. The gas is comprised of thermal quasiparticles, confined in a superconducting Al box by large-gap Ta leads. The average number of quasiparticles is about 10(5). This number fluctuates due to quasiparticle generation and recombination. The number is measured from the tunneling current through a barrier that bisects the box. The recombination time is independently measured by single-photon excitation and agrees with the frequency dependence of the fluctuations.     

Induced quantum numbers of a magnetic vortex at non-zero temperature

The phenomenon of the finite-temperature induced quantum numbers in fermionic systems with topological defects is analyzed. We consider an ideal gas of two-dimensional relativistic massive electrons in the background of a defect in the form of a pointlike magnetic vortex with arbitrary flux. This system is found to acquire, in addition to fermion number, also orbital angular momentum, spin, and induced magnetic flux, and we determine the functional dependence of the appropriate thermal averages and correlations on the temperature, the vortex flux, and the continuous parameter of the boundary condition at the location of the defect. We find that non-negativeness of thermal quadratic fluctuations imposes a restriction on the admissible range of values of the boundary parameter. The long-standing problem of the adequate definition of total angular momentum for the system considered is resolved.     

Fluctuation-induced couplings between defect lines or particle chains

One-dimensional structures such as defect lines or chains of dipolar particles are generally subject to strong Landau-Peierls thermal fluctuations. Coupling between these fluctuations in parallel lines may lead to an attractive force, analogous to the London force, or to a repulsive force of entropic origin. We analyze these forces for chains of electric dipoles and for flux lines in isotropic superconductors. In the first case the force is attractive, and can significantly change the Hamaker constant, which governs the attraction between colloidal particles. In the second case, over much of the magnetic field-temperature phase diagram the force is repulsive, and dominates over the direct repulsive interaction between flux lines.     

Characteristics of gas heating in a transverse discharge in air flow

The thermal instability of discharge plasma in air is analyzed. The contributions of specific mechanisms of instability are examined, including VT relaxation, the increase in the fractional energy dissipation via rapid heating due to an increase in reduced field strength, and ionization thermal instability. The effects of acoustic wave generation caused by heating and of charged particle motion relative to the neutral gas on both the length scale and the growth rate of unstable fluctuations are taken into account.     

The influence of boundary conditions on thermal conductance in semiconductor quantum wire with structural defect

Using the scattering-matrix method, we investigate the influences of boundary conditions on thermal conductance in quantum wire with structural defect. A comparison between the thermal conductances is made when stress-free, hard-wall, and mixed boundary conditions are applied for acoustic transport leads. The results show that the quantized thermal conductance plateau at very low temperature can be observed only in transport lead with stress-free boundary condition. For hard-wall or mixed boundary conditions, qualitatively different thermal conductance characteristics are found. Moreover, we find that the behavior of the thermal conductance sensitively depend on the geometric parameters and the position of the defect in quantum wire.     

Thermodynamics of superstrings

We study the thermal properties and the thermodynamical equilibrium fluctuations of a gas of massive heterotic string excitations at Planck energy scales. The behavior of this system parallels in several ways that of massive Schwarzschild black holes. We briefly comment on its possible influence on primeval entropy generation.     

Toward Quantum Paraelectric,Paraelastic, and Paramagnetic 2D Materials

Quantum fluctuations are known to affect the finite-temperature properties of materials made out of light elements such as hydrogen and helium. More recently, it has also been realized that quantum effects may play a role on structural transformations of ferroic materials containing heavier atoms, provided the energy barrier separating two different phases is small when compared to thermal fluctuations. Herein, 2D ferroelectric and ferroelastic materials are showcased as potential candidates to experience quantum effects on their structural conformation at liquid helium temperatures. A brief literature overview of the path integral molecular dynamics approach, which could be useful for the discovery of quantum paraelectric, paraelastic, and paramagnetic behavior in 2D materials, is also provided.     

High pyroelectric power generation of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 single crystal

We report the pyroelectric power generation of a relaxor ferroelectric 0.7Pb(Mg_1/3Nb_2/3)O₃–0.3PbTiO₃ (PMN–PT) single crystal. For a temperature variation rate of 0.5 K/s, the PMN–PT generated a closed-circuit current of 10 nA and an open-circuit voltage of 1.1 V at room temperature. The pyroelectric current and voltage of the PMN–PT single crystal were proportional to the temperature variation rate and were sharply enhanced near the structural phase-transition temperature. Additionally, the PMN–PT pyroelectric generator produced stable power for excessive thermal cycling and was highly sensitive to random thermal fluctuations. Our results indicate the potential importance of PMN–PT for high-power pyroelectric generator applications.     

Transport damping by fluctuations and cluster-type expansions in kinetics

A mechanism of transport damping by fluctuations is proposed and analyzed in detail for the thermal diffusivity of a one-dimensional gas in the case when the externally induced temperature gradient is weaker than fluctuating gradients. Thermal diffusivity is calculated as a function of parameters of a one-dimensional gas characterized by a homogeneous potential of interaction between particles: for the potential V(x)=Q/|x|^k, thermal diffusivity is χ ∼ (Qn ^k/T)^1/(k−1)ν_T/n. The nonanalytic form of thermal diffusivity as a function of concentration is elucidated. The nonanalytic behavior of thermal diffusivity as a function of concentration is explained by a nontrivial symmetry of the problem under analysis at long times, after the initial fluctuations have dissipated. It is shown that spontaneous generation of macroscopic structures developing through selective growth of fluctuations of a certain type in a medium with an externally induced temperature gradient controls the transport properties of the medium when k≈1.     

Silver-island films probed by hyper-Rayleigh scattering and atomic force microscopy

Incoherent second-harmonic generation, or hyper-Rayleigh scattering (HRS), and atomic force microscopy (AFM) are proposed as a combined probe of nonlinear optical and structural properties of silver-island films. HRS and linear (Rayleigh) scattering indicatrices are measured. The correlation function, deduced from the HRS indicatrices and characterising spatial fluctuations of the total polarisation at second-harmonic frequency, has a length scale significantly larger than that of the correlation functions that are obtained from the AFM data and characterise spatial fluctuations of quadratic optical susceptibilities of the dipole and quadrupole types. This difference is interpreted as indicating that the HRS indicatrix shape is determined by the long-range fluctuations of the local-field factors. Received: 16 October 2001 / Revised version: 16 April 2002 / Published online: 6 June 2002     

Constructive role of noise: Fast fluctuation asymptotics of transport in stochastic ratchets

The constructive role of random fluctuations is studied in the context of transport in stochastic ratchets. We discuss the interplay of independent white (thermal) and discrete (external) noises and their generation of transport in anisotropic potentials. The constructive cooperation of such fluctuations is most apparent in the asymptotic limit of fast discrete-valued noise, a limit which presents some interesting mathematical features. We describe the asymptotic analysis of the current in the limit of fast external noise, pointing out the strong qualitative dependence of the current on the interplay of the independent noise sources and its surprising sensitivity to the regularity of the underlying anisotropic ratchet potential. (c) 1998 American Institute of Physics.     

Optical breakdown threshold in the electron-thermal model of defect generation

An investigation is made of the conditions for the nucleation of optical breakdown in transparent material when recombination-stimulated defect-formation reactions occur in it. It is shown that a positive feedback between the conduction electron concentration and point defects activates defect formation even if the medium is not heated. Under real conditions, where heating of the medium by the light is important, lowering of the activation barrier by thermal defect generation aided by conduction electrons results in optical breakdown of the medium at light intensities much lower than predicted in the classical “semiconductor” or “thermochemical” models of thermal breakdown. The analysis confirms that optical breakdown of transparent condensed media is due to electron-aided defect formation reactions over a broad range of illumination conditions. Zh. Tekh. Fiz. 67, 48–53 (May 1997)