Fluctuation and Noise Letters

In the case of the need of extraordinary security, Kirchhoff-loop-Johnson-(like)-noise ciphers can easily be integrated on existing types of digital chips in order to provide secure data communication between hardware processors, memory chips, hard disks and other units within a computer or other data processor system. The secure key exchange can take place at the very first run and the system can renew the key later at random times with an authenticated fashion to prohibit man-in-the-middle attack. The key can be stored in flash memories within the communicating chip units at hidden random addresses among other random bits that are continuously generated by the secure line but are never actually used. Thus, even if the system is disassembled, and the eavesdropper can have direct access to the communication lines between the units, or even if she is trying to use a man-in-the-middle attack, no information can be extracted. The only way to break the code is to learn the chip structure, to understand the machine code program and to read out the information during running by accessing the proper internal ports of the working chips. However such an attack needs extraordinary resources and even that can be prohibited by a password lockout. The unconditional security of commercial algorithms against piracy can be provided in a similar way.

A specific model for the low frequency (LF) noise in SiO₂/HfO₂ metal-oxide-semiconductor devices on fully depleted silicon-on-insulator (FD-SOI) is proposed based on a proper spatial and energy slow trap profile. This model relates the spatial position of the probed traps with the applied vertical electric field in the gate dielectric via their energy distribution and thereby enables to explain the behaviour of LF noise regarding the front and back gate voltages. The dependence of the trap profile and thus the noise level on the interfacial layer thickness is also analysed by the model.

We analyze a simple model of a scalar optical wave with partial coherence. The model is devised to describe the influence on the coherence of the wave, of the statistical properties of its random phase, including both the second-order statistics (phase correlation) — which is classic, but also the first-order statistics (phase distribution) — which is nonclassic. Expectedly, upon increasing the disorder of the fluctuating phase through a reduction of its correlation duration, the model shows that the coherence of the wave is always reduced. By contrast, upon increasing the disorder of the fluctuating phase through an increase of its dispersion, the model reveals that the coherence of the wave can sometimes be enhanced. This beneficial consequence of an increase in disorder is related to the phenomenon of stochastic resonance or improvement by noise in signal processing.

First we present and theoretically analyze the phenomenological physical picture behind Vibration-Induced Conductivity Fluctuations. We identify the relevant tensors characterizing the electromechanical response against the vibrations for both longitudinal and transversal responses. We analyze the conductivity response with acceleration type vibrations and a new scheme, measurements with more advantageous compression type vibrations that are first introduced here. Compression vibrations provide sideband spectral lines shifted by the frequency of the vibration instead of its second harmonics; moreover the application of this method is less problematic with loose electrodes. Concerning geometry and electrodes, the large measurement errors in earlier experiment indicated electrode effects which justify using four-electrode type measurements. We propose and analyze new arrangements for the longitudinal and transversal measurements with both compression vibration and acceleration vibration for laboratory and field conditions.

Within the Relativistic Theory of Gravitation it is shown that the equation of state p = ρ holds near the center of a black hole. For the stiff equation of state p = ρ − ρ_c the interior metric is solved exactly. It is matched with the Schwarzschild metric, which is deformed in a narrow range beyond the horizon. The solution is regular everywhere, with a specific shape at the origin. The gravitational redshift at the horizon remains finite but is large, z ~ 10²³ M_⊙/M. Time keeps its standard role also in the interior. The energy of the Schwarzschild metric, shown to be minus infinity in the General Theory of Relativity, is regularized in this setup, resulting in E = Mc².

In this paper we present a systematic and rigorous method for calculating the diffusion tensor for a Brownian particle moving in a periodic potential which is valid in arbitrary dimensions and for all values of the dissipation. We use this method to obtain an explicit formula for the diffusion coefficient in one dimension which is valid in the underdamped limit, and we also obtain higher order corrections to the Lifson-Jackson formula for the diffusion coefficient in the overdamped limit. A numerical method for calculating the diffusion coefficient is also developed and is shown to perform extremely well for all values of the dissipation.

Time regimes in fire data recorded from 1992 to 2007 in a fire vulnerable area of Patagonia (Argentina) were revealed by using the Allan Factor statistics. The obtained results show the presence of seasonal periodicities, superimposed to three time-scaling regimes, which characterize the point process of the fire sequence as a fractal time process with a rather high degree of time-clusterization of the events.

We study noise influence on universal properties of period-doubling cascade in a well-defined model of periodically kicked nonlinear dissipative oscillator. Two approaches of noise adding are considered: (i) modulation of kick's amplitude and (ii) modulation of the interval between kicks. We then derive corresponding stochastic discrete one- and two-dimensional maps and provide a detailed study of the noise scaling properties of the Feigenbaum scenario and of the non-Feigenbaum tricritical case. Illustrations of bifurcations trees and Lyapunov exponent charts are given.

Small flagellated bacteria cannot swim in a straight course due to rotational Brownian motion. By using Langevin equation and rotational diffusion equation we develop a model for the flagellated bacterial motion; thus, the model includes the rotational Brownian motion. Our model shows that the rotational Brownian motion is more significant at smaller turn angle during a tumble. It is also compared with experiment data.

Intentionally designed silicon microplasmas with breakdown voltage 10.4–10.8 V have been investigated. Avalanche pulse rate time dependence and Fano factor were measured to evidence the presence of time-clustering in the series of pulses. The two-level fluctuations of avalanche pulse rate were observed for diodes containing two charge multiplication regions. Probabilistic model for pulse rate fluctuations was introduced.

The associated relaxation time T_c and the normalized correlation function C(s) are investigated in the logistic growth system, which is used to describe a tumor cell growth process, driven by two Gaussian white noise sources and the correlation between the additive and multiplicative noise. The expression of T_c and C(s), which is the function of noise parameters (additive noise intensity α, multiplicative noise intensity D, correlation intensity λ and correlation time τ), is obtained by using the projection operator method. After introducing noise intensity ratio, a dimensionless parameter R = α/D, and performing the numerical computations, the two case are analyzed: (1) In the growth case, λ and τ play opposite roles on the T_c and the C(s). It must emphasize that there is a minimal evolution velocity to appear and the tumor cell numbers is hard to evolve from an arbitrary initial condition to the maximum. (2) In the decay case, λ and τ play same roles on the T_c and the C(s). There is a maximal evolution velocity to appear. The noises induce different responses of tumor cells between the growth and decay case.

Recently, it was reported that some saturation nonlinearities could effectively act as noise-aided signal-noise-ratio amplifiers. In the letter we consider the signal detection performance of saturation nonlinearities driven by a sinusoidal signal buried in Gaussian white noise. It is showed that the signal detection statistics still undergo a nonmonotonic evolution as noise is raised. We also particularly show that an improvement of the SNR in terms of the first harmonic does not imply the possibility to improve the signal detection performance through stochastic resonance. The study might also complement other reports about stochastic resonance in saturation nonlinearities.