Linear systems with polynomials of filtered Poisson processes

Moment equations are calculated exactly for the response of linear systems subjected polynomials of filtered Poisson processes. The Itô formula for stochastic differential equations driven by Poisson white noise is applied to derive moment equations. It is shown that the set of moment equations is closed. The proposed method is used to calculate moments up to the fourth order for the response of two linear systems subjected to quadratic forms of filtered Poisson processes. Results by Monte Carlo simulations are also presented for comparison.     

On the spectral representation method in simulation

Two models X_n(t) and Y_n(t) are considered for generating samples of stationary band-limited Gaussian processes. The models are based on the spectral representation method and consist of a superposition of n harmonics. The harmonics of X_n(t) have random phase and amplitude while the harmonics of Y_n(t) only have random phase. It is shown that the two models are equal in the second-moment sense. However, Y_n(t) has stronger ergodic properties than X_n(t). On the other hand, X_n(t) is a Gaussian process for any value of n while Y_n(t) is asymptotically Gaussian as n approaches infinity. It is demonstrated that the rejection of X_n(t), because of its weak ergodic property, or of model Y_n(t), because of its nonGaussian distribution, it is not generally justified. One special case in which Y_n(t) should not be used is that of Gaussian processes with power concentrated at a few discrete frequencies.     

Frequency/temperature characteristics of Gunn devices

The variability and large magnitude of the frequency/temperature coefficient of Gunn oscillators has limited the application of these devices. The letter outlines a program of experiments and computer simulations aimed at achieving an understanding of the basic ?f/?T mechanism and thus producing a deep stable oscillator. Our simulations successfully predict observed trends in the ?f/?T behaviour of Gunn devices with both alloyed metal and n+ regrown contacts. The results of our study show that stable oscillators with a small loaded Q factor and near maximum power output are realisable.     

An algorithm of molasse formation

An algorithm is described for the simulation of the geological processes involved in the formation and evolution of a molasse basin. Variables include continuous subsidence, source-area denudation, formation of cyclothems, and fluviatile meandering     

Low-threshold 1.3 ?m GaInAsP/InP lasers grown by atmospheric-pressure MOVPE

Room-temperature pulsed operation has been achieved at and below 1.3 ?m for GaInAsP/InP lasers grown by atmospheric-pressure metalorganic vapour phase epitaxy. Thresholds as low as 1.0 kA/cm2 (for a cavity length of 1000 ?m) have been obtained.     

A Microfluidic Ion Sensor Array

A balanced concentration of ions is essential for biological processes to occur. For example, [H⁺] gradients power adenosine triphosphate synthesis, dynamic changes in [K⁺] and [Na⁺] create action potentials in neuronal communication, and [Cl^?] contributes to maintaining appropriate cell membrane voltage. Sensing ionic concentration is thus important for monitoring and regulating many biological processes. This work demonstrates an ion‐selective microelectrode array that simultaneously and independently senses [K⁺], [Na⁺], and [Cl^?] in electrolyte solutions. To obtain ion specificity, the required ion‐selective membranes are patterned using microfluidics. As a proof of concept, the change in ionic concentration is monitored during cell proliferation in a cell culture medium. This microelectrode array can easily be integrated in lab‐on‐a‐chip approaches to physiology and biological research and applications.     

Spectroscopic investigations on epoxy--multiwall carbon nanotubes composites

Room temperature electron spin resonance spectra of epoxy resins loaded with various concentrations of multiwalled carbon nanotubes of various lengths are analyzed. The resonance spectrum near the free electron line position is dominated by a single almost symmetric line assigned to delocalized electrons residing on multiwalled carbon nanotubes. The experimental research shown that: (1) The dependence of the g-factor on nanotubes length is controlled by the distortions of multiwalled carbon nanotubes. (2) The dependence of the g-factor on the concentration of multi-walled nanotubes reflects the interactions between electrons localized on different nanotubes. In insulating composites, the resonance line width broadens as the length and the concentration of multiwalled carbon nanotubes is increased. (3) For conducting composites, the dependence of the electron spin resonance line width on the length and concentration of multiwalled carbon nanotubes is controlled by Elliott contribution and exchange interactions, respectively. (4) The concentration of conduction electrons increases as the length and the concentration of multiwalled carbon nanotubes are increased.     

Synthesis and characterization of poly(butylene oxide) grafted carbon nanofibers

The grafting of polybutylene oxide onto purified and functionalized carbon nanofibers is reported. Grafting was possible after the insertion of 2-(formyloxy)ethyl 2-bromo-2-methylpropanoate onto the carbon nanofibers. The polymerization of tetrahydrofuran was mediated by copper(I) bromide and 1,1,4,7-pentamethyl diethylenetriamine. The polymer-grafted carbon nanofibers were characterized by Raman spectrsocopy, Transmission Electron Microscopy, and Thermogravimetric Analysis. TEM images of CNF-COOH (A), CNF-PBO (B), completely open tip of CNF-COOH, and coated tip of CNF-PBO (D) are shown in the left panel. The right panel depicts the distribution of bromine (blue), and carbon (red) atoms inside and in the vicinity of CNF-Br (as obtained by Electron Energy Loss Spectroscopy). The bottom shows the actual doped CNF. Preliminary data showed that these modified fibers have potential applications as smart (electrorheological) fluids.     

Nonlinear systems driven by polynomials of filtered Poisson processes

The perturbation method is applied to determine approximately the mean, variance, skewness and kurtosis of the transient and stationary response of nonlinear systems driven by polynomials of filtered Poisson processes. The analysis is based on the classical perturbation method, the Itô differentiation formula, and properties of the response of linear systems subjected to polynomials of filtered Poisson processes. Two examples are presented to demostrate the efficiency and accuracy of this approximate analysis.