Active attenuation of propeller blade passage noise

Acoustic measurements are presented to show that active cancellation can be used to achieve significant reduction of blade passage noise in a turboprop cabin. Simultaneous suppression of all blade passage frequencies was attained. The spatial volume over which cancellation occurred, however, is limited. Acoustic intensity maps are presented to show that the acoustic input to the fuselage was sufficiently non-localized so as to require more judicious selection of cancellation speaker location

Features of the alkynyl ruthenium chromophore with modified anionic subsystem UV absorption

Theoretical simulation of UV–vis absorption for a new series of alkynyl ruthenium chromophores spectra and investigations the influence of anionic substituence on a spectral shift of UV absorption was presented. The MM+ molecular force field method was used for total energy minimization and for building of the molecular optimized geometry [S.J. Weiner, P.A. Kollman, D.A. Case, U.C. Ghio, G. Alagona, J.S. Profeta, P. Weiner, J. Am. Chem. Soc. 106 (1984) 765; S.J. Weiner, P.A. Kollman, D.T. Nguyen, D.A. Case, J. Comput. Chem. 7 (1986) 230]. All quantum chemical calculations were performed by semi-empirical ZINDO/1 method within a framework of the restricted Hartree–Fock approach and convergence limit up to 10−6 eV after 500 iterations was achieved. Good agreement between the theoretically calculated and experimentally measured spectra was observed. The largest spectral shift in position of absorption peaks was observed for compound containing the anionic (Cl), substituent. The theoretically calculated absorption maximum is blue shifted with respect to the experimental spectra for all compounds what is connected with the changes of the charge transfer determining the corresponding state dipole moments. Analysis of the theoretical spectra shows a substantial sensitivity to the backside groups

Picosecond nonlinear optical features of ferroelectric A(6)M(2)M(8)O-30 large sized nanocrystallites

Second and third order nonlinear optical susceptibilities of A(6)M(2)M(8)O-30 ferroelectric crystallites 100 nm powders were studied. The measurements were carried out for powders and thin films of guest-host composites made of Poly(methyl methacrylate) (PMMA) matrix. The studies were carried out by Kurtz Perry method using a Q-switch 16 ps picosecond Nd:YAG laser with peak pulse power 25 MW operating at 1064 nm fundamental wavelength. We have established that Ba6Ti2Nb8O30 ferroelectric crystallites achieve the highest (among the studied materials) second order optical susceptibilities equal to about 8.12 pm/V. The use of picosecond laser pulses and of the crystallites with high monodispersion allow to obtain an information concerning the second order optical susceptibilities with the avoiding of the local thermoheating which may change the output susceptibilities

Nonlinear optical characterization of functionalized organometallic complexes using THG and Z-scan techniques

We report the measurements of third-order nonlinear optical (NLO) properties in picosecond regim of functionalized organometallic complexes using third harmonic generation (THG) and Z-scan techniques. We show the results obtained for solutions dissolved in dichloromethane with different concentrations. For each chromophore, we give the values of: the nonlinear absorption coefficient β, the nonlinear refractive index n2, the third-order nonlinear susceptibility χ 3 and the second-order nonlinear hyperpolarisability γ of individual molecules. This approach allowed us to determine also the electronic and rotational contributions of χ 3 by using a picosecond laser Nd:YAG at the fundamental wavelength 1064 nm

Multimodal Vibration Damping of a Smart Beam Structure using Modal SSDI-Max Technique

Advanced materials such as carbon fiber, composite materials et al. are more and more used in modern industry. They make the structures lighter and Stiffer. However, they bring vibration problems. Researchers studied numerous methods to eliminate the undesirable vibrations. These treatments are expected to be a compact, light, intellectual and modular system. Recently, nonlinear techniques which are known as Synchronized Switch Damping (SSD) technique was proposed. These techniques synchronously switched when structure got to its displacement extremes that leading to a nonlinear voltage on the piezoelectric elements. This paper presents a performance analysis of an improved modal SSDI approach called "SSDI Max". The particularity of this new approach is to maximize the self generated voltage amplitude by a proper definition of the switch instants according to the chosen targeted mode. This paper presents simulations performed on a model representative of a smart beam. Damping results are given in the case of multimodal excitations. The paper analyses the control time window influence on the damping performance of the system. Results show that substantial damping increase can be obtained with very slight modification of the control architecture and the same control energy

Experimental and theoretical studies of NLO properties of organic–inorganic materials base on p-nitroaniline

Third order nonlinear optical properties of a serie of chromophores were investigated using nonlinear transmission (NLT), degenerate four waves mixing (DFWM) and third harmonic generation (THG) experiments. The investigations are completed by theoritical studies performed using quantum chemical semi empirical calculations. Theoretical calculation of UV–VIS spectra and second order molecular hyperpolarisabillity for organic–inorganic hybrid materials base on p-nitroalinine was presented. Third order nonlinear optical susceptibility of the studied compounds was evaluated using third harmonic generation (THG) set up at 1064 nm. The measurements were performed on thin films, deposited on a thick glass substrate

Theoretical and experimental investigations on the nonlinear optical properties of gold(III) dithiolene complexes

International audienceThe synthesis by following green approaches of a new material based on benzodifuran and bithiophene units connected by azomethine junctions is described. X-ray structure analysis revealed a strong π–π stacking of the molecules in the solid state. The electronic properties were investigated by using UV–vis spectroscopy and cyclic voltammetry. This environmentally friendly material has been evaluated as a donor material in basic bilayer heterojunction solar cells by using C60 as the acceptor material to afford a power conversion efficiency superior to 1%