Intrinsic fluctuations in explosive reactions

A reaction is called explosive when the amount of a reactant becomes infinite in a finite time. When the intrinsic stochastic character of the reaction is taken into account, the explosion time is a random quantity. We compute its probability distribution, or at least its average and variance, for various kinds of reactions. If a reaction is unstable, so that a reactant can either explode or disappear, one first has to compute the probability for an explosion to occur at all, and then the average explosion time. Finally, the same ideas are applied to more general Markov processes.     

Bistability and intensity fluctuations in Zeeman lasers and amplifiers

It is shown that the fluctuation properties of certain Zeeman lasers and amplifiers are exhibit a sudden change when the coupling constant ξ is varied near ξ = 1. The possibility of a phase transition at ξ = 1 is discussed and fluctua properties both above and below this point are investigated using some previously derived equations for two-mode lasers.     

The future is noisy: the role of spatial fluctuations in genetic switching

A genetic switch may be realized by a certain operator sector on the DNA strand from which either genetic code, to the left or to the right of this operator sector, can be transcribed and the corresponding information processed. This switch is controlled by messenger molecules, i.e., they determine to which side the switch is flipped. Recently, it has been realized that noise plays an elementary role in genetic switching, and the effect of number fluctuations of the messenger molecules have been explored. Here we argue that the assumption of well stirredness taken in the previous models may not be sufficient to characterize the influence of noise: spatial fluctuations play a non-negligible part in cellular genetic switching processes.     

Bistability, hysteresis and fluctuations in adiabatic ensembles of nanoparticles

A presuppositionless thermodynamic analysis of the phase transformations of nanoparticles in an adiabatic enclosure leads to a series of predictions of the transformation behavior. These predictions are perfectly confirmed with experimental results, which have been difficult to be explained until now. The most important predicted and validated phenomena are: (i) a broad range of bistability or hysteresis in the vicinity of the transformation temperature, (ii) the width of this range increases with increasing particle size and with increasing temperature, and (iii) the transformation temperature may be higher than the one for bulk material. As in reality, an experiment can never be performed in an idealized isothermal or adiabatic environment; one always has a mixture of these conditions. This influences the results. The outcome of this analysis explains why different authors report, probably dependent on experimental conditions, widely scattering results. Within this article, upper case letters are referring to one mole of the material and lower case letters refer to one particle.     

Lagrangian tracers on a surface flow: the role of time correlations

Finite time correlations of the velocity in a surface flow are found to be important for the formation of clusters of Lagrangian tracers. The degree of clustering characterized by the Lyapunov spectrum of the flow is numerically shown to be in qualitative agreement with the predictions for the white-in-time compressible Kraichnan flow, but to deviate quantitatively. For intermediate values of compressibility the clustering is surprisingly weakened by time correlations.     

Statistical physics of bifurcation,spatial structures,and fluctuations of chemical reactions

Zeitschrift für Physik B Condensed Matter - We present a fully nonlinear stochastic theory of chemical reactions closely below, at and above instability points. As explicit example we treat...     

Magnitude and sign correlations in heartbeat fluctuations

We propose an approach for analyzing signals with long-range correlations by decomposing the signal increment series into magnitude and sign series and analyzing their scaling properties. We show that signals with identical long-range correlations can exhibit different time organization for the magnitude and sign. We find that the magnitude series relates to the nonlinear properties of the original time series, while the sign series relates to the linear properties. We apply our approach to the heartbeat interval series and find that the magnitude series is long-range correlated, while the sign series is anticorrelated and that both magnitude and sign series may have clinical applications.     

Atomic coherent states and reduced quantum fluctuations in optical transients

We show that the atomic coherent states (the Bloch states) commonly encountered in coherent transient phenomena exhibit squeezing. We illustrate this property calculating the degree of squeezing and the normalized correlation coefficient g⁽²⁾ for a system of N two-level atoms interacting with a cw laser electric field.     

The role of the nanoscale in surface reactions: CO2 on CdSe

Cd-rich CdSe nanocrystals below a critical size, under illumination, catalyze CO2 fixation, but bulk CdSe surfaces do not. We report first-principles calculations in which we determine the roles of faceting, deviations from stoichiometry, photoexcitation, and electron confinement, and the specific physics of the nanoscale. We further establish that catalysis does not occur at the nanocrystal surface; instead, neutral molecules adsorb, desorb negatively charged, and react elsewhere. Finally, we predict that n-type doped CdSe nanocrystals would be effective catalysts without photoexcitation.     

The effect of initial spatial correlations on late time kinetics of bimolecular irreversible reactions

We study anomalous kinetics associated with incomplete mixing for a bimolecular irreversible kinetic reaction where the underlying transport of reactants is governed by a fractional dispersion equation. As has been previously shown, we demonstrate that at late times incomplete mixing effects dominate and the decay of reactants follows a fundamentally different scaling comparing to the idealized well mixed case. We do so in a fully analytical manner using moment equations. In particular the novel aspect of this work is that we focus on the role that the initial correlation structure of the distribution of reactants plays on the late time scalings. We focus on short range and long (power law) range correlations and demonstrate how long range correlations can give rise to different late time scalings than one would expect purely from the underlying transport model. For the short range correlations the late time scalings deviate from the well mixed t⁻¹$t^{-1}$ and scale like t^−1/2α$t^{-1/2\alpha }$, where 1<α≤2$1<\alpha \le 2$ is the fractional dispersion exponent, in agreement with previous studies. For the long range correlation case it scales like t^−β/2α$t^{-\beta /2\alpha }$, where 0<β<1$0<\beta <1$ is the power law correlation exponent.     

Determination of surface state parameters from surface photovoltage transients: CdS

A method was developed for determining surface state parameters such as density, fractional occupancy and capture cross section for electrons and for photons from surface photovoltage transients. These transients were found to be associated with the photostimulated transition of electrons from surface states to the conduction band. Suitable analytical expressions were derived from basic semiconductor surface equations. The application of the method to CdS surfaces is presented.     

Thermal fluctuations and positional correlations in oriented lipid membranes

We have determined the positional correlation functions in aligned stacks of fully hydrated phospholipid bilayers from the thermal diffuse scattering measured by nonspecular x-ray reflectivity. While fair agreement can be obtained between experiment and linear smectic theory at length scales above 120 A, significant deviations occur at small r, which are tentatively attributed to collective protrusion modes.     

Near-field spatial correlations from partially coherent homogeneous planar sources: effects on surface wave excitation

We show that an increase of the coherence length of a statistically homogeneous planar source diminishes the contribution of surface waves to the spatial coherence of the near field, as well as producing changes in the enhancement of the near-field spectrum.     

Pairing correlations in finite systems: from the weak to the strong fluctuations regime

The Particle Number Projected Generator Coordinate Method is formulated for the pairing Hamiltonian in a detailed way in the projection after variation and the variation after projection methods. The dependence of the wave functions on the generator coordinate is analyzed performing numerical applications for the most relevant collective coordinates. The calculations reproduce the exact solution in the weak, crossover and strong pairing regimes. The physical insight of the ansatz and its numerical simplicity make this theory an excellent tool to study pairing correlations in complex situations and/or involved Hamiltonians.     

Measurements of stellar and explosive nuclear astrophysics reactions

This paper described the nuclear astrophysical studies using the unstable ion beam facility GIRAFFE in CIAE, by indirect measurements. We measured the angular distributions for some single proton or neutron transfer reactions, such as ⁷Be(d,n)⁸B, ¹¹C(d,n)¹²N, ⁸Li(d,p)⁹Li and ¹³N(d,n)¹⁴O in inverse kinematics, and derived the astrophysical S-factors or reaction rates of ⁷Be(p,γ)⁸B, ¹¹C(p,γ)¹²N, ⁸Li(n,γ)⁹Li, ¹³N(p,γ)¹⁴O by asymptotic normalization coefficient, spectroscopic factor, and R-matrix approach at astrophysically relevant energies. Some most recent progress of nuclear astrophyiscal work in CIAE are also summarized.