Numerical simulation of fatigue crack growth in friction stir welded T joint made of Al 2024 T351 alloy

The Extended Finite Element Method (xFEM) has been applied to simulate fatigue crack growth in an AA2024-T351 T welded joint, 5 mm thick, made by friction stir welding. The ABAQUS and Morfeo software has been used. Tensile fatigue loading (mean stress 10 MPa, stress ratio R=0) is applied to Tjoints with a configuration suitable for reinforced panels where both skin and the web (reinforcement or stiffener) is made of a high strength AA2024-T351. Crack is introduced in one edge of the skin base material. The properties of materials in the areas of joints and geometry measures of Tjoint are adopted from available experiments. Following numerical results are obtained: crack front coordinates (x, y, z) and stress intensity factors (K-I, K-II, K-III and K-ef) distribution along the crack tip, as well as the fatigue life estimation for every crack propagation step. The main objective of this research is to better understand fatigue behaviour of friction stir welded T joint of AA2024-T351

Modeling and applications of Quantum Cascade in external magnetic field

The rapidly emerging field of nano-optoelectronics is based on the understanding and control of intersubband transitions in nano-dimensional systems. One of the most striking outcomes of intersubband transitions engineering is the quantum cascade laser (QCL) – an efficient and reliable unipolar semiconductor laser source [1], with the possibility to operate from the mid-infrared (MIR) to the THz range of frequencies. These powerful devices are particularly appreciated for such wide scope of operating wavelengths which can be achieved by using the same heterostructure combination, but changing the design of the active region, i.e. ‘tailoring’ the layers’ widths and composition. This renders QCLs suitable for numerous applications, including free-space communications, medical diagnostics and in particular, chemical sensing and monitoring [2]. In the MIR part of the spectrum, QCLs are of great interest for gas sensing and monitoring. We explore the possibilities of using advanced tools for global optimization, namely the genetic algorithm, to obtain structural parameters of gain-maximized QCL emitting at specified wavelengths, suitable for detection of pollutant gasses, such as SO2, HNO3, CH4 and NH3, in the ambient air. Then we introduce a strong external magnetic field perpendicular to the epitaxial layers, to fine tune the laser output properties [2]. This magnetic field alters the electron energy spectrum by splitting the continuous energy subbands into discrete Landau levels whose arrangement influences the magnitude of the optical gain. In addition, strong effects of band nonparabolicity result in subtle changes in the lasing wavelength at magnetic fields which maximize the gain, thus allowing us to explore the prospects of multi-wavelength emission of the given structure. THz frequencies belong to the quite under-utilized part of the electromagnetic spectrum, despite their significant application potential. This is mostly due to the lack of coherent solid-state THz sources. The so called „THz gap“ falls between two frequency ranges that have been well developed, the microwave and millimeter-wave frequency range. THz QCLs are great candidates to fill in this gap [3]. We have analyzed two structures lasing in this region (both of them reported in the literature, but not studied under the influence of an external magnetic field), the three- and four-well (per period) based structures that operate at 3.9THz and 1.9THz, respectively, implemented in GaAs/Al0.15Ga0.85As. Numerical results are presented for magnetic field values from 1.5 T up to 20 T, while the band nonparabolicity is carefully accounted for. Because of their high output gain, QCLs are suitable to be used as active media in metamaterial unit cells, thus enabling evasion of metallic inclusions present in conventional metamaterials [4]. We analyze a quantum cascade structure lasing at 4.6THz, placed under the influence of a strong magnetic field. We first solve the full system of rate equations for all the relevant Landau levels, and obtain the necessary information about the carrier distribution among the levels, after which we are able to evaluate the permittivity component along the growth direction of the structure, as well as the range of frequencies at which the structure exhibits negative refraction for a predefined total electron sheet density.V International School and Conference on Photonics and COST actions: MP1204, BM1205 and MP1205 and the Second international workshop "Control of light and matter waves propagation and localization in photonic lattices" : PHOTONICA2015 : book of abstracts; August 24-28, 2015; Belgrad

Primena modifikovanih tanina u antikorozionim alkidnim premazima

The study of the synthesis of anticorrosive inhibitors, based on chemically modified tannins, and their use in alkyd based coatings to improve anticorrosive properties is presented in this work. Two methods of tannin modification were applied: direct method using ammonium hydroxide, ammonium hydroxide/ammonium chloride buffer or diethylenetriamine (DETA); and a two-step method including tannin modification with epichlorohydrin (ECH) in first step to produce epoxy modified tannin, ET, and further modification with heteroaromatic amines or linseed oil fatty acids (LFA) in second step. The obtained anticorrosive additives were characterized using ATR-FTIR, 1H and 13C NMR spectroscopies and elemental analysis. Epoxy, amino, hydroxyl, acid and iodine values of the synthesized inhibitors were determined according to standard methods. The prepared alkyd coating with tannin inhibitors was tested according to standard SRPS EN ISO 4628 method. Anticorrosive coating containing modified tannin based additive showed increased anticorrosive properties, good adhesion and coverage comparing to the coating with zinc phosphate additive. The alkyd coating films based on ET-LFA and ET modified with 2-amino-5- mercapto-1,3,4-thiadiazole showed best anticorrosive results.U ovom radu prikazana je sinteza antikorozionih aditiva na bazi hemijski modifikovanog tanina i njihova primena u alkidnim premazima u cilju poboljšanja antikorozionih svojstava. Prikazane su dve metode modifikacije tanina: direktna modifikacija tanina primenom amonijum-hidroksida, amonijum-hidroksid/amonijum-hlorid pufera ili dietilentriamina (DETA); i dvostepena modifikacija tanina koja u prvom stupnju uključuje modifikaciju epihlorhidrinom sa ciljem da se dobije tannin sa epoksi terminiranim funkcionalnim grupama, ET, i modifikaciju ET tanina sa heteroaromatičnim aminima ili masnim kiselinama izolovanim iz lanenog ulja (LFA) u drugom stupnju. Sintetisani antikorozioni aditivi su okarakterisani primenom ATR-FTIR, 1H i 13C NMR spektroskopija, i elementalnom analizom. Sadržaj epoksi, amino, hidroksilnih i karboksilnih grupa i vrednost jodnog broja sintetisanih aditiva određen je prema standardnim metodama. Alkidni premazi koji sadrže antikorozione aditive na bazi modifikovanog tanina ispitani su prema standardnoj SRPS EN ISO 4628 metodi. Antikorozivni alkidni premazi na bazi modfikovanih tanina pokazali su poboljšane antikorozione karakteristike i adheziju u poređenju sa alkidnim premazom na bazi cink-fosfata. Alkidni premazi koji sadrže dvostepeno modifikovani tanin sa LFA i 2-amino-5-merkapto-1,3,4-tiadiazolom pokazali su najbolje antikorozione karakteristike

Synthesis and application of thiocarbamates obtained by oxidative treatment of waste xanthate

In this paper, the optimal treatment of industrial waste consisting from xanthate and oxidation product, i.e. diisobutyl and diethyl dixanthogenate, was developed for production of flotoreagents. Waste dixanthogenate was generated during production and storage of flotation agents, i.e. potassium isobutyl (KiBuX) and potassium ethyl xanthate (KEtX), respectively. The process of waste xanthate treatment is based on the reaction of the nucleophilic heterolysis of the persulfide bond in the diisobutyl dixanthogenates by alkylamines in presence of various oxidizing agents (sodium hypochlorite, hydrogen peroxide, potassium persulfate) to produce N-alkyl-, N,N-dialkyl- and N cycloalkyl-O-isobutyl thiocarbamate selective flotoreagents. Also, analogous methodology was applied for synthesis of N-alkyl and N,N-dialkyl-O-ethyl thiocarbamate from KetX using sodium hypochlorite at laboratory and semi-industrial level. The developed method provides the corresponding alkyl thiocarbamates in a high yield and purity. The flotation efficiency was analysed using the obtained thiocarbamate on a real sample of minerals in laboratory and industrial conditions

Quantum Cascade Laser Design for Tunable Output at Characteristic Wavelengths in the Mid-Infrared Spectral Range

We present a method for systematic optimization of quantum cascade laser active region, based on the use of the genetic algorithm. The method aims at obtaining a gain-maximized structure, designed to emit radiation at specified wavelengths suitable for direct absorption by pollutant gasses present in the ambient air. After the initial optimization stage, we introduce a strong external magnetic field to tune the laser output properties and to slightly modify the emission wavelength to match the absorption lines of additional compounds. The magnetic field is applied perpendicularly to the epitaxial layers, thus causing two dimensional continuous energy subbands to split into series of discrete Landau levels. This affects all the relevant relaxation processes in the structure and consequently the lifetime of carriers in the upper laser level. Furthermore, strong effects of band nonparabolicity result in subtle changes of the lasing wavelength at magnetic fields which maximize the gain, thus providing a path for fine tuning of the output radiation properties. Numerical results are presented for GaAs/Al(x)Ga(1-x)As based quantum cascade laser structures designed to emit at particular wavelengths in the mid infrared part of the spectrum.11th Annual Conference of the Materials-Research-Society-of-Serbia (YUCOMAT 2009), Aug 31-Sep 04, 2009, Herceg Novi, Montenegr

Long-period grating fiber-optic sensors of bending for applications in pulmonology

U ovom radu predstavili smo fiber-optički senzor krivine na bazi rešetke sa dugim periodom i njegovu primenu u praćenju disanja pri mehaničkoj ventilaciji pacijenata. Predložena šema merenja koristi monohromatski izvor svetlosti i fotodiodu kao detektor što je čini ekonomičnom i jednostavnom za upotrebu. Ovde smo demonstrirali primenu senzora u merenju disajnih zapremina koja se zasniva na korelaciji izmenu promene zapremine pluća i promene lokalne krivine torza. Poređenjem rezultata studije na skupu od 15 zdravih dobrovoljaca sa konkurentnim metodima zaključujemo da je predloženi neinvazivni metod pogodan za kliničku praksu.Here we present a fibre-optic sensor of bending and demonstrate its application in monitoring of assisted breathing. The sensor is based on a long-period fibre grating and uses a simple monochromatic interrogation scheme. Here, we first explain the working principle of the sensor and then present a method for the measurement of respiratory volumes. The measurement is based on the correlation between a change in lung volume and the corresponding change in a local torso curvature. We validate the method by applying a calibration-test measurement procedure on a set of 15 healthy volunteers. Results show good sensor accuracy in measurements of the tidal and minute respiratory volumes for clinically relevant types of breathing. Finally, we compare the proposed method with the current clinical standards and competing techniques

A long-period fibre grating sensor for respiratory monitoring

In the current clinical practice of non-invasive mechanical ventilation (NIV), continuous monitoring of respiratory volumes is based on the measurement of air flow through an oronasal mask or mouthpiece. Errors in respiratory-volumes monitoring and patientventilator asynchrony due to the inevitable air leaks from the mask may lead to insufficient ventilation and/or damage of the airway system. Therefore, clinician’s observations of the chest wall expansions are required, but they are subjective, time consuming and strongly dependent on clinician’s experience [1]. We present and validate a method for the measurement of respiratory volumes by a single long period fibre-grating (LPG) sensor of bending. This method is grounded on the hypothesis that the volume of the inhaled air can be correlated with the change in a local torso curvature in a ribs area with stiff underlying tissues. Here, we explain the working principle of the LPG sensors, a monochromatic interrogation scheme, a two-step calibration-test measurement procedure and present results that establish a linear correlation between the change in the local rib-cage curvature and the change in the lung volume. Results also show good sensor accuracy in measurements of tidal and minute respiratory volumes for all clinically relevant breathing volumes [2]. Additionally, we examine the possibility of using the rib-cage movement signal measured by a single LPG sensor as a new way to provide a trigger to the ventilator. Our preliminary results on healthy volunteers provide the statistical evidence of the 200 ms lag of the pneumotechometer with respect to the fibre-optic signal. The proposed single-sensor method is non-invasive, simple, low-cost and easy to implement. Moreover this method does not suffer from the flaws of air-flow measurements, it eliminates the need for chest movement observation by clinicians and can be implemented on both male and female patients. The preliminary results are promising and indicate that the method proposed here could be used in NIV.V International School and Conference on Photonics and COST actions: MP1204, BM1205 and MP1205 and the Second international workshop "Control of light and matter waves propagation and localization in photonic lattices" : PHOTONICA2015 : book of abstracts; August 24-28, 2015; Belgrad

Optimization of mid-infrared and terahertz quantum cascade lasers in strong magnetic field

Napredna oblast nano- i opto-elektronike se zasniva na razumevanju i kontroli unutarzonskih prelaza u sistemima nanometarskih dimenzija. Kvantno kaskadne strukture predstavljaju generalni koncept optoelektronskih uređaja baziranih na radijativnim prelazima između kvantizovanih energetskih nivoa u strukturama koje sačinjavaju višestruke kvantne jame. Danas, kvantni kaskadni laseri imaju mogućnost rada na frekvencijama srednjeg infracrvenog i terahercnog dela spektra, predstavljaju reprezentativne primere inţinjeringa unutarzonskih prelaza, i obezbeđuju moderni model struktura koji se koristi za proučavanje osnovnih osobina poluprovodničkih sistema. Ova disertacija se bavi formulisanjem detaljnog modela i odgovarajućim numeričkim simulacijama za proračun brzina rasejanja elektrona (usled rasejanja na neravninama površina, rasejanja elektrona sa longitudinalnim optičkim i akustičnim fononima), kao i optičkog pojačanja izračunatog za četiri različite strukture kvantnih kaskadnih lasera baziranih na GaAs, koje rade kako u srednjem infracrvenom, tako i u terahercnom opsegu, a sve pod dejstvom jakog spoljašnjeg magnetnog polja. Kada je magnetno polje primenjeno u pravcu paralelnom na ravan slojeva, svaka energetska podzona se cepa na serije diskretnih Landauovih nivoa, kojima se moţe manipulisati podešavanjem magnetnog polja, pa se na taj način moţe kontrolisati promena stepena inverzne populacije, a samim tim i optičko pojačanje. Simulacije su sprovedene uzimajući u obzir dizajn kvantnih kaskadnih lasera koje čine dve ili tri jame, i koji emituju svetlost na 4.6THz i 3.9THz, respektivno, a obe strukture su implementirane u GaAs/Al0.15Ga0.85As, dok primeri koji se tiču srednjeg infracrvenog opsega emituju na 7.3μm i 10.3μm, i implementirani su na GaAs/Al0.38Ga0.62As platformi. Predstavljeni su numerički rezultati za vrednosti spoljašnjeg polja od 1.5T do 20T u slučaju terahercnih struktura (20T do 60T u slučaju struktura srednje infracrvene oblasti), a zonska neparaboličnost je uzeta u obzir. Pokazano je koji su mehanizmi rasejanja nosilaca dominantni u kom tipu struktura (u zavisnosti od dela elektromagnetnog spektra za koji su namenjene). Takođe je istaknuto kako se magnetno polje moţe koristiti kao moćna spektroskopska alatka, jer se menjanjem jačine polja moţe uticati na poloţaje energetskih nivoa, time omogućujući rad lasera na određenoj talasnoj duţini, pogodnoj za detekciju štetnih gasova u vazduhuThe rapidly emerging field of nano-optoelectronics is based on the understanding and control of intersubband transitions in nanodimensional systems. A quantum cascade (QC) structure is a general concept of an optoelectronic device based on a cascade of radiative transitions between size-quantized energy levels in a multi-quantum-well structure. Today, Quantum Cascade Lasers (QCL), being able to operate from the mid-infrared (MIR) to the THz range of frequencies, represent one of the most striking outcomes of intersubband structure engineering, and provide a state-of-the-art model structure to study the basic properties of semiconductor systems. This dissertation concerns the formulation of a comprehensive model and corresponding numerical simulationsfor calculating the electron relaxation rates (due to interface roughness, electron – longitudinal optical phonon and electron-acoustic phonon scattering), as well as the optical gain of four different GaAs quantum cascade structures that operate in both MIR and THz spectral range placed in a strong external magnetic field. When the magnetic field is applied in the direction perpendicular to the plane of the layers, each energy subbandis split into series of discrete Landau levels, which are magnetically tunable and it is therefore possible to control the modulation of the population inversion, and consequently the optical gain. The simulations are performed on two- and three-well designsof quantum cascade lasers that operate at 4.6THz and 3.9THz, respectively, both implemented in GaAs/Al0.15Ga0.85As, while the structures concerning the MIR spectral range operate at 7.3μm and 10.3μm, and are implemented in GaAs/Al0.38Ga0.62As. Numerical results are presented for magnetic field values from 1.5T up to 20T for structures emitting in the THz range (20T up to 60T in the case of MIR structures), while the band nonparabolicity is taken into account. It has been shown which scattering mechanism can be considered dominant in different types of structures (according to the part of the electromagnetic spectrum they are designed for). It has alsobeen pointed out that external magnetic field can be used as powerful spectroscopic tool,because by changing the field value one can influence the positions of the split energy levels, therefore enabling the laser emission at specific wavelengths, suitable for detection of pollutant gases in the ambient air

Optimization of mid-infrared and terahertz quantum cascade lasers in strong magnetic field

Napredna oblast nano- i opto-elektronike se zasniva na razumevanju i kontroli unutarzonskih prelaza u sistemima nanometarskih dimenzija. Kvantno kaskadne strukture predstavljaju generalni koncept optoelektronskih uređaja baziranih na radijativnim prelazima između kvantizovanih energetskih nivoa u strukturama koje sačinjavaju višestruke kvantne jame. Danas, kvantni kaskadni laseri imaju mogućnost rada na frekvencijama srednjeg infracrvenog i terahercnog dela spektra, predstavljaju reprezentativne primere inţinjeringa unutarzonskih prelaza, i obezbeđuju moderni model struktura koji se koristi za proučavanje osnovnih osobina poluprovodničkih sistema. Ova disertacija se bavi formulisanjem detaljnog modela i odgovarajućim numeričkim simulacijama za proračun brzina rasejanja elektrona (usled rasejanja na neravninama površina, rasejanja elektrona sa longitudinalnim optičkim i akustičnim fononima), kao i optičkog pojačanja izračunatog za četiri različite strukture kvantnih kaskadnih lasera baziranih na GaAs, koje rade kako u srednjem infracrvenom, tako i u terahercnom opsegu, a sve pod dejstvom jakog spoljašnjeg magnetnog polja. Kada je magnetno polje primenjeno u pravcu paralelnom na ravan slojeva, svaka energetska podzona se cepa na serije diskretnih Landauovih nivoa, kojima se moţe manipulisati podešavanjem magnetnog polja, pa se na taj način moţe kontrolisati promena stepena inverzne populacije, a samim tim i optičko pojačanje. Simulacije su sprovedene uzimajući u obzir dizajn kvantnih kaskadnih lasera koje čine dve ili tri jame, i koji emituju svetlost na 4.6THz i 3.9THz, respektivno, a obe strukture su implementirane u GaAs/Al0.15Ga0.85As, dok primeri koji se tiču srednjeg infracrvenog opsega emituju na 7.3μm i 10.3μm, i implementirani su na GaAs/Al0.38Ga0.62As platformi. Predstavljeni su numerički rezultati za vrednosti spoljašnjeg polja od 1.5T do 20T u slučaju terahercnih struktura (20T do 60T u slučaju struktura srednje infracrvene oblasti), a zonska neparaboličnost je uzeta u obzir. Pokazano je koji su mehanizmi rasejanja nosilaca dominantni u kom tipu struktura (u zavisnosti od dela elektromagnetnog spektra za koji su namenjene). Takođe je istaknuto kako se magnetno polje moţe koristiti kao moćna spektroskopska alatka, jer se menjanjem jačine polja moţe uticati na poloţaje energetskih nivoa, time omogućujući rad lasera na određenoj talasnoj duţini, pogodnoj za detekciju štetnih gasova u vazduhuThe rapidly emerging field of nano-optoelectronics is based on the understanding and control of intersubband transitions in nanodimensional systems. A quantum cascade (QC) structure is a general concept of an optoelectronic device based on a cascade of radiative transitions between size-quantized energy levels in a multi-quantum-well structure. Today, Quantum Cascade Lasers (QCL), being able to operate from the mid-infrared (MIR) to the THz range of frequencies, represent one of the most striking outcomes of intersubband structure engineering, and provide a state-of-the-art model structure to study the basic properties of semiconductor systems. This dissertation concerns the formulation of a comprehensive model and corresponding numerical simulationsfor calculating the electron relaxation rates (due to interface roughness, electron – longitudinal optical phonon and electron-acoustic phonon scattering), as well as the optical gain of four different GaAs quantum cascade structures that operate in both MIR and THz spectral range placed in a strong external magnetic field. When the magnetic field is applied in the direction perpendicular to the plane of the layers, each energy subbandis split into series of discrete Landau levels, which are magnetically tunable and it is therefore possible to control the modulation of the population inversion, and consequently the optical gain. The simulations are performed on two- and three-well designsof quantum cascade lasers that operate at 4.6THz and 3.9THz, respectively, both implemented in GaAs/Al0.15Ga0.85As, while the structures concerning the MIR spectral range operate at 7.3μm and 10.3μm, and are implemented in GaAs/Al0.38Ga0.62As. Numerical results are presented for magnetic field values from 1.5T up to 20T for structures emitting in the THz range (20T up to 60T in the case of MIR structures), while the band nonparabolicity is taken into account. It has been shown which scattering mechanism can be considered dominant in different types of structures (according to the part of the electromagnetic spectrum they are designed for). It has alsobeen pointed out that external magnetic field can be used as powerful spectroscopic tool,because by changing the field value one can influence the positions of the split energy levels, therefore enabling the laser emission at specific wavelengths, suitable for detection of pollutant gases in the ambient air