Laser sheet scattering and the cameras' positions in particle image velocimetry

Simulations of laser sheet scattering by microparticles, based on the generalized Lorenz-Mie theory for the case of numerous random spatial distributions of scattering particles, were done, using the novel computational time saving strategy. This type of scattering by particles immersed in a fluid flow and its recording on cameras, presents the essence of particle image velocimetry systems. The continuous and large change of the intensity of a scattered light failing on the camera causes the sequences of images of varying quality, which makes many of them useless. This paper shows how the problem could be alleviated by determining the angles of low relative standard deviation of scattered light intensity and using them for recording, as well as by avoiding the angles of high relative standard deviation of scattered light intensity

Laser doppler velocimetry and confined flows

Finding the mode, in which two component laser Doppler velocimetry can be applied to flows confined in cylindrical tubes or vessels, was the aim of this study. We have identified principle issues that influence the propagation of laser beams in laser Doppler velocimetry system, applied to flow confined in cylindrical tube. Among them, the most important are influences of fluid and wall refractive indices, wall thickness and internal radius ratio and beam intersection angle. In analysis of the degrees of these influences, we have applied mathematical model, based on geometrical optics. The separation of measurement volumes, that measure different velocity components, has been recognized as the main drawback. To overcome this, we propose a lens with dual focal length primary focal length for the measurement of one velocity component and secondary focal length for the measurement of the other velocity component. We present here the procedure for calculating the optimal value of secondary focal length, depending on experimental set-up parameters. The mathematical simulation of the application of the dual focal length lens, for chosen cases presented here, confirmed the accuracy of the proposed procedure

Influence of electromagnetic and nuclear radiation in medicine for therapy and diagnosis through processes, facts and statistical analysis

Contemporary medicine (biomedicine) cannot be imagined without diagnostics and therapeutic methods based on nuclear, laser, acoustical and other processes. The application of these methods is linked to common computer support, signal processing, measuring monitoring techniques, high degree of automatization, and image analyses. The paper analysed contemporary technical issues related to neonatology, ophthalmology, based on the influence of nuclear radiation and laser beams. Some statistical processing and presentations of results obtained in the IGA KCS Hospital, Belgrade, Serbia, in curing vision of prenatal type new-borns with a different degree of pathological state of retinopathy of prematurity are presented. The general conclusion is that, in spite of the good results, a multidisciplinary approach is needed for a deeper understanding of the role of lasers and laser techniques in medicine as well as possible couplings. Potential new applications of lasers important for the fields of neonatology and ophthalmology were also considered

Primena Husimijeve funkcije u vremensko-frekvencijskoj analizi signala

Husimi function originated in phase space formulation of quantum mechanics. This function appears naturally whenever simultaneous measurement of coordinate and impulse with maximal accuracy allowed by the Heisenberg uncertainty relation is performed on a given quantum state and it represents the probability distribution for simultaneous unsharp measurement of coordinate and impulse. Husimi function may analogously be defined for any pair of conjugated variables. In analysis of time varying signals these variables are time and frequency. In this paper we consider Husimi function in time-frequency space, we derive some properties of the function and give time-frequency analysis of some characteristic signals.U ovom radu razmotrena je Husimijeva funkcija na prostoru kanonski spregnutih promenljivih vreme-frekvencija. Izvedene su neke njene nove osobine koje su ilustrovane na nekoliko analitički zadatih signala. Pokazano je da se Husimijeva funkcija može koristiti pri vremensko-frekvencijskoj analizi signala

The possibilities of application of 3D digital models in cultural heritage objects' protection and revitalisation

Contemporary cultural heritage protection relies on precise technical documentation obtained by new technology accomplishments in the domain of 3D digital models. Both 3D models of the existing state of object and virtual ones are equally important in reconstruction and renewal processes. Accurate, textured and detailed 3D point cloud models of various objects, i.e. cultural heritage monuments, are outcomes of contemporary photogrammetric and laser scanning methods, aided by adequate software solutions. The authors presented procedures and results of terrestrial laser scanning and 3D modelling of a cultural heritage monument the monastery church of the complex Kastaljan, located in the mountain region Kosmaj in Serbia. The first part of presented research, concerning data acquisition, carried out using laser scanner and adequate software processing, resulted in 3D dense point cloud model and further 2D plan view along with characteristic cross sections. The possibilities of 3D model presentation, measurements and additional graphic operations were explored, through various software solutions aided by adequate technical support. The second part of research elaborated on the reconstruction of the entire 3D model of the church in the complex Kastaljan, dated back to the 13th century, according to its architectural style characteristics

The comparison of air flow LDA measurement in simple cylindrical and cylindrical tube with flat external wall

Primena 2D laser Dopler anemometarskih sistema je razmatrana za slučaj zatvorenog toka fluida u običnoj cilindričnoj i u cilindričnoj cevi sa ravnim spoljašnjim zidom. Zakoni geometrijske optike su primenjeni na centralne linije laserskih snopova. Izvedeni su izrazi za dislokacije mernih zapremina, uglove kalibracije i rastojanja centra merne zapremine od centra vidnog polja foto-detektora. Izrazi izvedeni u ovom radu su preimenjeni na određeni vrtložni tok u cevi. To je pokazalo nekoliko prednosti korišćenja obične cilindrične cevi u odnosu na danas omiljenije korišćenje cilindrične cevi sa ravnim spoljašnjim zidom. Ovi rezultati ukazuju na to da bi se sadašnje izbegavanje LDA merenja kod obične cilindrične cevi trebalo preispitati.The application of 2D laser Doppler anemometry systems is considered, in the case of fluid flow confined in simple cylindrical and in cylindrical tube with flat external surface of the wall. Geometric optics laws are applied to the central lines of laser beams. Measurement volume dislocations, calibration angles and distances of measurement volume centre from the photo-detector field of view centre are expressed. The expressions derived in this paper were applied to specific turbulent swirl flow in pipe. That revealed several advantages of use of a simple cylindrical tube over nowadays favored use of cylindrical tube with flat external surface. Those results suggest that current avoiding of laser Doppler anemometry measurements with simple cylindrical tubes should be reconsidered

3D modeling of material heating with the laser beam for cylindrical geometry

In this work an analytical approach for analyzing heating of material with a laser beam is presented. A thermal model of interaction for the case of cylindrical geometry of the material and asymmetric distribution of the laser beam intensity is used and an analytical procedure is developed to analyze the temporal and the spatial distribution of the temperature field inside the bulk of material. This kind of consideration is of practical interest in cases where the excitation by the laser beam is not symmetric in respect to its position or shape, e.g., multi-mode working regimes or asymmetrical distribution of the laser beam intensity. The heating effects were considered in the temperature range up to the melting point. The thermal and the optical parameters of the material were assumed to be independent of the temperature and were given constant values in the temperature range of interest. This approach makes use of the Laplace transform, in order to eliminate dependence on time. The Fourier method of variable separation was used to obtain the temperature field distribution in the Laplace transform domain. By using the pulse response and Duhamel's principle the 3D temperature field distribution in time domain is obtained. By using an appropriate set of orthogonal functions in r directions, the numerical procedure is made more effective, saving this way the CPU time. The general solutions for the temporal as well as spatial temperature field distributions are evaluated in a closed form in terms of the particular solutions of the governing partial differential equation (PDE). Because of linearity of the governing PDE, the superposition principle was used in the case of complex distributions of the laser beam intensity. The influence of different kinds of laser beam parameters to the temperature field distributions was considered

The effects of laser light interactions with materials of cultural heritage

The effects of laser light and material interaction during the process of testing, processing and conservations of cultural heritage objects are very important concerning of the material characteristics preservation. Ruby and Nd3YAG lasers are very often used as light sources in a variety of optical recording and testing methods of cultural heritage items (eg interferometry). Special emphasis is give on the undesirable effects that may occur in the tests due to local laser beam focusing and to energy density increasing, as well as on the application of the laser processing, corrosion cleaning and material sintering

Evaluation of laser beam interaction with carbon based material: Glassy carbon

U ovom radu se analizira interakcija laserskih snopova sa ugljeničnim materijalom (staklasti ugljenik). Korišćen je Nd3+:YAG lasera (1.06 μm, odnosno bliska IC oblast) u ms režimu rada sa snopovima različitih gustina energije. U svim eksperimentima, u primenjenom režimu rada, uočene su površinske povrede na uzorku. Povrede nastale dejstvom lasera su analizirane optičkim i SEM mikroskopima. Program Image J je korišćen za kvantitativnu analizu nastalih povreda na osnovu mikrografa dobijenih optičkom i SEM mikroskopijom. Temperaturna raspodela u izloženom uzorku je dobijena numeričkom simulacijom zasnovanom na programskom paketu COMSOL Multiphysics 3.5 u ograničenom opsegu energija.Laser beam interaction with carbon based material (glassy carbon) is analyzed in this paper. A Nd3+:YAG laser beam (1.06 μm, i.e., near infrared range (NIR)) in ms regime with various energy densities is used. In all experiments, provided in applied working regimes, surface damages have occurred. The results of laser damages are analyzed by light and scanning electron microscopy (SEM). Image J software is used for quantitative analysis of generated damages based on micrographs obtained by light and SEM microscopes. Temperature distribution in the exposed samples is evaluated by numerical simulations based on COMSOL Multiphysics 3.5 software in a limited energy range