Fluctuation and Noise Letters

This letter gives a concise and rigorous derivation of the power spectrum density function of fractional Gaussian noise (fGn).

In a forthcoming paper in IEE Proceedings Information Security, Feng Hao claims that temperature inaccuracies make the key exchange scheme based on Kirchhoff Loop with Johnson-like Noise insecure. First we point out that this claim is irrelevant for the security of the idealized/mathematical communicator because it violates basic assumptions. Furthermore, in general practical applications, as it has been pointed out in the very first paper, the use of thermal noise is disadvantageous therefore the issue of temperature and its accuracy is unimportant even for the security of common practical realizations. It is important to emphasize that any deviation from the idealized scheme can lead to a finite level of security. Thus, if the above-mentioned author had stressed the inaccuracy of the resistor values; his claim would have been practically valid. However the impact of such systematic errors can be kept under control. Here we cite our relevant analysis (Phys. Lett. A359, (2006) 741-744) of 1% voltage inaccuracy along the line due to wire resistance effects, which can be considered as a general result for inaccuracies of this order. The necessity to build a statistics to extract information during the properly chosen clock time leads to extremely poor eavesdropper statistics and this situation provides a good practical raw bit security that can be orders of magnitude beyond the raw bit security of idealized quantum communicators.

Signal detection in fluctuating background noise is a common problem in diverse fields of research and technology. It has been shown in hearing research that the detection of signals in noise that is correlated in amplitude across the frequency spectrum (comodulated) can be improved compared to uncorrelated background noise. We show that the mechanism leading to this effect is a general phenomenon which may be utilized in other areas where signal detection in comodulated noise needs to be done with a limited frequency resolution. Our model is based on neurophysiological experiments. The proposed signal detection scheme evaluates a fluctuating envelope, the statistics of which depend on the correlation structure across the spectrum of the noise. In our model, signal detection does not require a sophisticated neuronal network but can be accomplished through the encoding of the compressed stimulus envelope in the firing rate of neurons in the auditory system.

We studied the effect of additive and multiplicative noises on the growth of a tumor based on a logistic growth model. The steady-state probability distribution and the average population of the tumor cells were given to explain the important roles of correlated noises in the tumor growth. We explored that multiplicative noise induces a phase transition of the tumor growth from a uni-stable state to a bi-stable state; the relationship between the intensity of multiplicative noise and the population of the tumor cells shows a stochastic resonance-like characteristic. It was also confirmed that additive noise weakened rather than extinguish the tumor growth. Homologous noises, however, promote the growth of a tumor. We also discussed about the relationship between the tumor treatment and the model.

In this Letter, we propose and experimentally demonstrate a simple method to provide additional information on the electro-mechanical properties of soils by electrical conductivity measurements. The AC electrical conductance of the soil is measured while it is exposed to a periodic vibration. The vibration-induced density fluctuation implies a corresponding conductivity fluctuation that can be seen as combination frequency components, the sum and the difference of the mean AC frequency and the double of vibration frequency, in the current response. The method is demonstrated by measurements on clayey and sandy soils.

The noise circuit theory is used to analyze the asymmetry (skewnees) of thermal current fluctuations in the equilibrium nonlinear LR-circuit. We prove that the asymmetry of thermal current fluctuations at the inductor depends on the resistance nonlinearity and is independent of the inductance nonlinearity. A comparison between results of noise circuit theory and results of Gibbs statistical ensemble method shows that the Gibbs statistical ensemble method does not work when one is interested in calculating the nonlinear thermal fluctuations.

The multiple segmenting method (MSM) has been applied to investigate the scaling behaviour in the Earth's apparent resistivity time series, measured in a seismic area of southern Italy. The study of apparent resistivity represents one of the most important scientific challenges in the studies devoted to the geophysical monitoring. Our results show that apparent resistivity is characterized by a persistent scaling behaviour at all the periods considered, with the scaling exponent tending approximately to 0.5.

We study defect-line dynamics in a 2-D spiral-wave pair in the Rössler model for its underlying local dynamics in period-N and chaotic regimes with a single bifurcation parameter κ. We find that a spiral wave pair is always stable across the period-doubling cascade and in the chaotic regime. When N ≥ 2 defect lines appear spontaneously and a loop exchange occurs across the defect line. There exists a "critical point" κ_c below and above which the time-averaged total length of defect lines L converges to almost constant but different values L₁ and L₂. When κ > κ_c defect lines show large fluctuations due to creation and annihilation processes.

Bulk samples of double layered manganite La_1.4Ca_1.6Mn₂O₇ were prepared by solid-state reaction method. Study of magnetotransport properties revealed a metal to insulator transition at 160 K, a ferromagnetic transition at 164 K and appearance of two-dimensional short range ferromagnetic correlations around 235 K. The temperature dependence of conduction noise showed three peaks at 114 K, 165 K and 235 K which are attributed to excess noise generated due to setting up of three-dimensional out-of-plane ferromagnetic transition, two-dimensional out-of-plane ferromagnetic transition temperatures and appearance of two-dimensional short range ferromagnetic correlations respectively. In the temperature region ~ 160 K, excess noise was also generated due to the metal-insulator transition. In the paramagnetic region, conduction noise was found to remain unchanged with the applied magnetic field whereas in the ferromagnetic regions, the peaks at 114 K and 235 K got disappeared. The latter is attributed to the suppression of spin fluctuations.

The results of noise measurements in low frequency range for CNY 17 type optocouplers are presented. The research were carried out on devices with different values of Current Transfer Ratio (CTR). The methods for identification of Random Telegraph Signal (RTS) in noise signal of optocouplers were proposed. It was found that the Noise Scattering Pattern method (NSP method) enables to identify RTS noise as non-Gaussian component of noise signal of the optocoupler. The NSP method proves to be very fast and simple.

We present a theory which connects two-state and excitable versions of stochastic resonance. The latter appears as an extreme asymmetric limit of traditional two-state rate theory. To achieve this unified view we are led to a simple generalization of excitable stochastic resonance.

Arterial narrowing can cause an audible whirling in the blood flow. We propose diagnosing such narrowing by simply recording that sound and analyzing its spectrum. We show how the Navier-Stokes equation for flow through a narrowing can be turned into a Schrödinger type equation. The complex eigenvalues of the latter equation give the frequencies and decay rates of the vortices present in the whirling pattern. Our diagnosis is based on understanding the relation between features in the sound spectrum and the severity of the narrowing. Today the most commonly used method of diagnosis is duplex ultrasound. In a small clinical trial our method appears to be as good as duplex ultrasound.

In this work, we calculate, for the first time, the impact of carrier trapping at the gate polysilicon/oxide interface on the LF noise characteristics of polygate MOSFET's. After extending the channel LF noise analysis, based on carrier number and correlated mobility fluctuations approaches, to include charge variations at the polySi/oxide interface, we derive analytical expressions accounting for the impact of fluctuations of poly/oxide interfacial charge on the channel drain current and input gate voltage noise as a function of gate bias, polysilicon doping concentration and gate oxide thickness.

A gedanken model of an analog optical computer for general purpose Fourier transform tasks is built and studied assuming entangled or non-entangled photons appearing at the input. The performance of the entangled and non-entangled operation modes, regarding information content, power consumption, acquisition time, wavelength and bandwidth limitations are analyzed as function of qubit repetition rate and number of qubits in the entangled state, respectively, based on fundamental physical laws. The total number of input photons is assumed the same for the two operation modes. It is sown that the entangled mode outperforms the non-entangled one, but only above a certain number of qubits in the entangled state. It is argued that, for practical applications to general purpose computing, several limitations should be imposed regarding qubit repetition rate and number of qubits in the entangled state. In addition, it is pointed out that the conclusions that we present are equally valid for general purpose optical quantum computing and for quantum information processing, too.