Fluctuation and Noise Letters

Optimization design of the structures and thicknesses of the sound packages is performed for automotive interior acoustic performance and lightweight characteristics. A SEA model of the car was created, and its interior noise of the automobile was predicted and validated at speed of 120 km/h. The contributions of some major subsystems to interior noise were calculated at 120 km/h. Both of major characteristic indices including interior SPL and total weight of sound packages are selected to evaluate automotive interior acoustic performance and lightweight characteristics, and four selected optimization parameters are structures and thicknesses of the sound package of firewall and front floor. The problem of multiple performance indices is simplified into single performance index by using grey relational grade. The optimal combination of sound package parameters is determined by employing grey relational analysis method. Furthermore, the validation tests show that the values of interior SPL and overall weight of sound packages decrease by 1.31% and 60.36%, respectively. Also, the comparison of the overall SPL for automotive interior noise experiments between original and optimized structures and thicknesses of the sound packages shows that automotive interior acoustic performance is obviously improved from 200 Hz to 10,000 Hz. Therefore, it is demonstrated that it is an effective way to deal with optimization problems by using the presented approach in this research.

We introduce the complex noise-bit as information carrier, which requires noise signals in two parallel wires instead of the single-wire representations of noise-based logic discussed so far. The immediate advantage of this new scheme is that, when we use random telegraph waves as noise carrier, the superposition of the first 2^N integer numbers (obtained by the Achilles heel operation) yields nonzero values. We introduce basic instantaneous operations, with O(2⁰) time and hardware complexity, including bit-value measurements in product states, single-bit and two-bit noise-gates (universality exists) that can instantaneously operate over large superpositions with full parallelism. We envision the possibility of implementing instantaneously running quantum algorithms on classical computers while using similar number of classical bits as the number of quantum bits emulated without the necessity of error corrections. Mathematical analysis and proofs are given.

We propose theoretically a method for the control of the frequency of the nonlinear optical response of a model nonlinear medium driven by an electric field and suggest an experimental realization on the basis of isotropic LiF, or NaCl crystals and pulsed Nd glass laser. The theoretical background of the proposed optical control is the nonlinear resonance and the resonance overlapping which is typical for nonlinear systems. It is shown that by a proper choice of the parameters of the applied pulses a diffusive growth of the oscillation amplitude can be achieved resulting in a controlled switching of the system's frequency. The maximum frequency of the nonlinear response is identified to be proportional to the intensity of the applied noise. An experimental suggestion for particular materials is proposed.

This paper considers a hybrid risky asset price model given by a constant elasticity of variance multiplied by a stochastic volatility factor. A multiscale analysis leads to an asymptotic pricing formula for both European vanilla option and a Barrier option near the zero elasticity of variance. The accuracy of the approximation is provided in a rigorous manner. A numerical experiment for implied volatilities shows that the hybrid model improves some of the well-known models in view of fitting the data for different maturities.

We demonstrate a new instance of useful-noise effect or stochastic resonance, occurring in magnetic resonance imaging (MRI). Based on the physics of signal–noise coupling specific to MRI, we establish the possibility of regimes where nonlinear post-processing can benefit from an increase in the level of the noise present in the MRI apparatus. The validation is obtained by both theoretical analysis and experimental observations. We especially show that the beneficial tuning of the noise can be practically achieved by controlling the bandwidth of the sampling receiver of the MRI apparatus. These results constitute a nontrivial extension of stochastic resonance in the domain of images, arising here with a signal–noise coupling in MRI which is distinct from the purely additive or multiplicative couplings previously investigated in the framework of useful-noise effect.

Measurement devices always add noise to the signal of interest and it is necessary to evaluate the variance of the results. This article focuses on stationary random processes whose power spectrum density is a power law of frequency. For flicker noise, behaving as 1/f and which is present in many different phenomena, the usual way to compute the variance leads to infinite values. This article proposes an alternative definition of the variance which takes into account the fact that measurement devises need to be calibrated. This new variance, which depends on the calibration duration, the measurement duration and the duration between the calibration and the measurement, allows avoiding infinite values when computing the variance of a measurement.

Spectra estimation in the field of low frequency noise measurements (LFNMs) is almost always performed by resorting to Discrete Fourier Transform (DFT) based spectrum analyzers. In this approach, the input signal is sampled at a proper frequency f_s and the power spectrum of sequences of N samples at a time are calculated and averaged in order to obtain an estimate of the spectrum at discrete frequency values f_k = kΔf, where the integer k is the frequency index and Δf = f_s/N is the frequency resolution. As the number of average increases, the statistical error, which is inversely proportional to the resolution bandwidth, can be made very small. However, if the spectrum of the signal is not a slowly changing function of the frequency, as in the case of 1/f^γ processes, spectra estimation by means of the DFT also results in systematic errors. In this paper we discuss the dependence of these errors on spectral parameters (the spectrum amplitude, the frequency f, the spectral exponent γ and the DC power) and on measurement parameters (the spectral window, the resolution bandwidth Δf and the instrumentation AC cutoff frequency). Quantitative expressions for the systematic errors are obtained that, besides helping in the interpretation of the results of actual LFNMs, can be used as a guideline for the optimization of the measurement parameters and/or for the estimation of the maximum accuracy that can be obtained in given experimental conditions. This quantitative analysis is particularly important since while we find that, in general, the systematic error at a given frequency f_k = kΔf can be made small if k is made large, which implies that Δf must be much smaller than f_k, possibly in contrast with the need for a Δf as large as possible in order to reduce the measurement time, the magnitude of the error depends on the selected spectral window. The role of the instrumentation AC cutoff frequency f_AC on the systematic error is also investigated and quantified and it is demonstrated that the error increases as f_AC reduces. This last result is very important since, often, f_AC is chosen much lower than the frequencies of interest and this choice may result in an increase of the systematic error.

In order to determine the origin of 1/f noise in devices made on the basis of GaAs the structure and spatial multistability mechanism of complexes of defects originated by donor–acceptor pairs are researched. Examples of complexes, which potentially exist in n-GaAs:Si, are such pairs as Si_AsSi_Ga, V_GaSi_Ga, V_GaV_As, V_AsSi_As and V_GaI_Si. For instance, V_GaSi_Ga complex contains a gallium vacancy (V_Ga) and an atom of silicon (Si_Ga), which substitutes the nearest atom of gallium in the crystal lattice. The mechanism of spatial multistability of the entire complex of defects is linked with the influence of the Jahn–Teller effect on the complex or one of its elements. The ability of V_GaSi_Ga complex to be one of the sources of 1/f noise is analyzed. It is assumed that 1/f noise may be generated by defects influenced by the Jahn–Teller effect.