Search results for "Control and Systems Engineering"
showing 10 items of 994 documents
Kinetics of Photorefractive Light Scattering in LiNbO3:Cu and LiNbO3:Zn Single Crystals
2011
Results of studies of the kinetics of photorefractive light scattering (PRLS) in optically nonlinear congruent single crystals of lithium niobate (LiNbO3, Li/Nb = 0.946) containing multivalent cation admixtures of Cu [0.015 mass %] (“photorefractive”) and Zn [0.5 mass %] (“non-photorefractive”) are reported. The shape of the PRLS indicatrix is found to be different in case of Cu and Zn admixtures. However, the angular widening of the indicatrix in both cases reaches its stationary value faster at higher laser radiation intensities. The PRLS is found to depend on the site of the ingot from which the samples are cut – an evidence of non-uniform distribution of defects with localised electrons…
Growth of Lithium Niobate Single Crystals from Granulated Charge
2011
Comparative studies of different techniques and the synthesis of single-phase granulated mixtures of high density essentially improving technical and economical parameters of lithium niobate single crystal technology are reported. Efficiency of using granulated mixtures of high density in growing lithium niobate single crystals is discussed.
Modelling of Cluster Formation in Optically Nonlinear Lithium Niobate Crystal
2011
Modelling of qualitative processes at formation of energetically stable clusters of oxygen octahedrons in the ferroelectric phase of lithium niobate (LiNbO3) crystal is considered with respect to composition. The structure of clusters arranged along the direction of crystallographic axis Y is shown to be the most ordered. The least ordered structures occur in clusters arranged along Z axis in the direction of which the values of ratio R = Li/Nb are most scattered.
MICRO- AND NANO-STRUCTURES OF NOMINALLY PURE STOICHIOMETRIC LITHIUM NIOBATE SINGLE CRYSTAL IN RAMAN SPECTRA
2009
ABSTRACT The authors show that bandwidths in Raman spectra of ferroelectric photo-refractive single crystals may depend on wavelength of laser radiation exciting the spectrum. Raman bands of lithium niobate single crystals are broader if the spectrum is excited by laser radiation in visible as compared with the spectrum excited by infrared laser radiation. Local microscopic structural heterogeneities of altered index of refraction are shown to appear in parts of the crystal under laser irradiation. Under visible radiation the structural heterogeneities provide additional contribution to broadening of Raman bands. Similar microscopic heterogeneities are practically absent at laser irradiatio…
On the Possibility of Miniature Diamond-Based Magnetometers Using Waveguide Geometries
2018
Micromachines 9(6), 276 (2018). doi:10.3390/mi9060276
Mode I failure modeling of friction stir welding joints
2008
This paper analyzes mechanical response by finite element method up to the decohesion failure in fracture mode I for joints of friction stir welding (FSW) of an aluminum alloy. It first describes experimental investigations on specimens with FSW embedded, subjected to uniform traction and local punch tests used to characterize local elastic and plastic material parameters. The heterogeneity of the mechanical properties induced by the FSW process is taken into account for the elastic-plastic finite element simulation. The growing damage and the opening failure of the welding zone are described by the adoption of a cohesive interface model with specific mechanical properties.
Influence of mode stirrer and air renewal on controlled microwave drying of sliced zucchini
2017
An on-line temperature-controlled microwave (MW) system, based on infrared thermography, was developed for drying zucchini slices. Moreover, the effects of different configurations, including turntable rotation, mode stirrer and air renewal, alone or in combination, on drying kinetics and quality of dried product were evaluated. The combination of stirrer and air renewal reduced the drying time of zucchini slices by about 48% with respect to the basic configuration and by 22% with respect to air renewal only. The lowest oscillation of temperatures about the fixed level (65 °C) was found when operating with the stirrer mode, because of the improved uniformity of the MW distribution. The sa…
FERROELECTRIC LIQUID CRYSTAL GLASSES FOR AMBLYOPIA RESEARCH
2008
ABSTRACT Ferroelectric Liquid Crystal (FLC) filters offer the speed of electronic light shutters and the vibration free operation. These characteristics make them ideal for applications requiring short exposure times and minimal blur, offering switching times of 0.0002 of a second. FLC filters can be used as the optical shutters for machine vision purposes, also in vision research. On the basis of FLC filters we have developed ferroelectric glasses, allowing temporal separation of optical information for both eyes. In the case of amblyopia (“lazy eye”) the only way to oblige the “lazy” eye to work is to close the other better-seeing eye. We advice an appliance for dynamic visual system trai…
Donor/Acceptor Heterojunction Organic Solar Cells
2020
The operation and the design of organic solar cells with donor/acceptor heterojunction structure and exciton blocking layer is outlined and results of their initial development and assessment are reported. Under halogen lamp illumination with 100 mW/cm2 incident optical power density, the devices exhibits an open circuit voltage VOC = 0.45 V, a short circuit current density JSC between 2 and 2.5 mA/cm2 with a fill factor FF &asymp
FIRST-PRINCIPLES LCAO CALCULATIONS ON 5D TRANSITION METAL OXIDES: ELECTRONIC AND PHONON PROPERTIES
2009
ABSTRACT First-principles quantum chemistry calculations within the periodic linear combination of atomic orbitals (LCAO) formalism have been used to probe electronic and phonon properties of crystalline 5d transition metal oxides ReO3, ZnWO4 and CaWO4. The obtained equilibrium crystal structure is in good agreement with known crystallographic data. Rhenium trioxide is correctly predicted to be a metal, whereas both tungstates—a wide gap insulating compounds. The phonon frequencies, calculated by the frozen phonon method, agree rather well with those obtained by infrared and Raman spectroscopies.