Response of duffing-type harvesters to band-limited noise

This paper aims to experimentally investigate the influence of stiffness-type nonlinearities on the transduction of vibratory energy harvesters (VEHs) under band-limited noise. For the purpose of the study, an energy harvester consisting of a clamped–clamped piezoelectric beam bi-morph is considered. The shape of the harvester's potential function is altered by applying a static compressive axial load at one end of the beam. The axial load permits the harvester to operate with different potential energy characteristics, namely, the mono-stable (pre-buckling) and bi-stable (post-buckling) configurations. The performance of the harvester in both the configurations is investigated and compared by tuning the harvester's oscillation frequencies around the static equilibria such that they have equal values in both scenarios. The harvester is then subjected to random base excitations of different levels, bandwidths, and center frequencies. The variance of the output voltage is measured across an arbitrary, purely resistive load and used for the purpose of performance comparison. Critical conclusions pertinent to the influence of the nonlinearity and relative performance in both configurations are presented and discussed.     

Synthesis and optical properties of basic fuchsin dye-doped PMMA polymeric films for laser applications: wide scale absorption band

Basic fuchsin dye-doped poly(methyl methacrylate) polymeric films were sensitized with various dye concentrations ranging from 0.0833 to 1.667 wt% of basic fuchsin. Their structure, linear absorption, and optical limiting properties were examined. The films were prepared using a simple and fast casting technique dissolved in chloroform for both the dye and the polymer. Structural characterizations were achieved by XRD, and the films showed an amorphous hump supporting the noncrystalline structure of studied polymeric composites. Spectrophotometer measurements were used to estimate the spectral absorption measurements of the films such as transmittance, absorbance with the calculations of absorption index (k), and optical energy band gap (E _g ) in the wavelength region from 190 to 2500 nm. Results show that the optical constants change with increasing the dye doping concentrations. It has been found that optical energy gap (E _g ) appearing that, both direct and indirect optical transitions are conceivable for these films. Optical limiting properties of the films with various dye concentrations were studied using a continuous wave He–Ne laser operating at 632.8 nm. The results appeared that the sample has an obvious optical limiting effect. The designed BF/PMMA composites can be applicable in wide-scale applications.     

Mid-infrared supercontinuum generation to 4.5 microm in ZBLAN fluoride fibers by nanosecond diode pumping

A mid-infrared supercontinuum (SC) is generated in ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF...) fluoride fibers from amplified nanosecond laser diode pulses with a continuous spectrum from approximately 0.8 microm to beyond 4.5 microm. The SC has an average power of approximately 23 mW, a pump-to-SC power conversion efficiency exceeding 50%, and a spectral power density of approximately -20 dBm/nm over a large fraction of the spectrum. The SC generation is initiated by the breakup of nanosecond laser diode pulses into femtosecond pulses through modulation instability, and the spectrum is then broadened primarily through fiber nonlinearities in approximately 2-7 m lengths of ZBLAN fiber. The SC long-wavelength edge is consistent with the intrinsic ZBLAN material absorption.     

Computer simulations of astronomical objects as seen by ground based optical telescopes

Computer simulations were carried out to investigate the limitations imposed by atmospheric turbulence on observing astronomical objects by 3·5 and 1·25 m optical telescopes. These limitations were studied in terms of the modulation transfer function of a reference star and the autocorrelation function of a binary star. Results demonstrate the quantitative comparative study between these telescopes in the presence of different seeing conditions for both short- and long-exposure recording.     

Linearization of vector fields and embedding of diffeomorphisms in flows via Nash–Moser theorem

In the first part of this paper we give suitable spectral properties of the adjoint operators induced by appropriate perturbations of some hyperbolic linear vector fields. These properties are useful to prove general facts based on the Nash–Moser inverse function theorem. In the second part of this work we study circumstances where a global linearization of a vector field X$X$ in a real numerical space is feasible and where some diffeomorphisms which are close to exp(X)$exp\left(X\right)$ can be embedded in a flow.     

The application of high frequency ultrasound waves to remove ammonia from simulated industrial wastewater

This article aims at applying the ultrasound technique in the field of clean technology to protect environment. The principle of ultrasound was conducted here to remove and recover ammonia from industrial wastewater. Three different concentrations of ammonia namely 5%, 15% and 25% (vol.%) were used to study the efficiency of removing ammonia from water. These concentrations are exactly similar to what may be found in wastewater resulting from strippers at petroleum refinery. High ultrasound frequency device with 2.4 and 1.7 MHz was conducted to study the effect of waves on the removal of ammonia. It was found that the ultrasound has the ability to remove ammonia with 5% concentration to meet the local standard of treated wastewater within less than 2 h for 0.080 L solution. It was also found that as the concentration of the ammonia increases the removing of ammonia within 2 h decreases, still the concentration of the ammonia meets the standard of the treated wastewater. The ability of the ultrasound to remove the ammonia failed to produce any mist when the height of the liquid solution increased, namely when the height reached (0.0337 m). This is equivalent to liquid volume of 0.150 L. It means that the device capacity to remove ammonia has certain limitations based on liquid heights. The best condition for ammonia removal was obtained at 5% concentration and 0.080 L liquid volume (equivalent to 0.0165 m).     

Bright‐Dark Rogue Waves

During the last two decades, revealing mechanisms of origin waves with anomalous amplitude (rogue waves) have been in the focus of researchers from different fields ranging from oceanography to laser physics. Mode‐locked lasers, as a test bed system, provide a unique opportunity to collect more data on rogue waves in the form of random pulses (soliton rain) and to clarify the mechanisms of rogue‐wave emergence caused by soliton–soliton and soliton–dispersive wave interactions. Here, for the first time, for an Er‐doped mode‐locked laser, a new type of vector rogue waves is demonstrated experimentally and theoretically, which is driven by desynchronization of the orthogonal linear states of polarization, so leading to output power oscillations in the form of anomalous spikes‐dips (bright‐dark rogue waves). The results can pave the way to unlocking the universal nature of the origin of rogue waves and thus can be of interest to the broad scientific community.     

Theoretical diagnostic and prediction of physical properties of quaternary InGaAsP compound using artificial neural networks optimized by the Levenberg Maquardt algorithm

The quaternaries \(In_{1 - x} Ga_{x} As_{y} P_{1 - y}\) are the main promising elements for the fabrication of optoelectronic devices. The adjustment of their physical parameters is assumed by the change of the molar fraction \(x\) and \(y\). These parameters can be affected by the variation of temperature and pressure. To make the theoretical diagnosis of these materials, it is fundamental to know the energy gap ‘\(\varvec{E}_{\varvec{g}}\)’ and the lattice parameter ‘\(a\)’, over a wide range of chemical compositions \(0 \le x \le 0.47\) and \(0 \le y \le 1\), at different temperatures and pressures. We show that by using the Artificial Neural Network method optimized by the Levenberg Maquardt algorithm ANN-LM, it is possible to obtain results very close to the experiment. The scatter plot and error calculation show that the ANN-LM model provides more accurate values of the lattice parameter than those calculated by Vegard’s law. On the other hand, the energy gap values \(Eg (x, y, T)\) estimated, using the ANN-LM model, proved to be close to the experimental values that those calculated by the empirical equations. In addition, the ANN-LM method allowed us to estimate with great accuracy the values of the energy gap at different temperatures and pressures \(Eg (P, T)\). Our work provides crucial information on the physical properties of the quaternary without the use of approximations, and without taking into account the hypothesis of a perfect agreement between \(InGaAsP\) and \(InP\) substrate.