Development of an optical redox chemical sensor for nitrite determination

An optical chemical sensor for the determination of nitrite based on incorporating methyltrioctylammonium chloride as an anionic exchanger on the triacetylcellulose polymer has been reported. The response of the sensor is based on the redox reaction between nitrite in aqueous solution and iodide adsorbed on sensing membrane using anion exchange phenomena. The sensing membrane reversibly responses to nitrite ion over the range of 6.52×10-6 - 8.70×10-5 mol L-1 with a detection limit of 6.05×10-7 mol L-1 (0.03 µg mL-1) and response time of 6 min. The relative standard deviation for eight replicate measurements of 8.70×10-6 and 4.34×10-5 mol L-1 of nitrite was 4.4 and 2.5 %, respectively. The sensor was successfully applied for determination of nitrite in food, saliva and water samples.

Composição elementar do aerossol atmosférico na região central da Bacia Amazônica

The processes and sources that regulate the elemental composition of aerosol particles were investigated in both fine and coarse modes during the dry and wet seasons. One hundred and nine samples were collected from the biological reserve Cuieiras - Manaus from February to October 2008, and analyzed together with 668 samples that were previously collected at Balbina from 1998 to 2002. Particle induced X-ray emission technique was used to determine the elemental composition, while the concentration of black carbon was obtained from the measurement of optical reflectance. Absolute principal factor analysis and positive matrix factorization were performed for source apportionment, which was complemented with back trajectory analysis. A regional identity for the natural biogenic aerosol was found for the Central Amazon Basin and can be used in dynamical chemical region models.

An undergraduate level experiment on the synthesis of Au nanoparticles and their size-dependent optical and catalytic properties

The synthesis of gold nanoparticles (Au NPs) 15, 26, and 34 nm in diameter, followed by the investigation of their size-dependent optical and catalytic properties, is described herein as an undergraduate level experiment. The proposed experiment covers concepts on the synthesis, stabilization, and characterization of Au NPs, their size-dependent optical and catalytic properties at the nanoscale, chemical kinetics, and the role of a catalyst. The experiment should be performed by groups of two or three students in three lab sessions of 3 h each and organized as follows: i) synthesis of Au NPs of different sizes and investigation of their optical properties; ii) evaluation of their catalytic activity; and iii) data analysis and discussion. We believe that this activity enables students to integrate these multidisciplinary concepts in a single experiment as well as to become introduced/familiarized with an active research field and current literature in the areas of nanoparticle synthesis and catalysis.

Physical Realization of an Optical Automatic Target Recognition System

In the modern warfare there is an active development of a new trend connected with a robotic warfare. One of the critical elements of robotics warfare systems is an automatic target recognition system, allowing to recognize objects, based on the data received from sensors. This work considers aspects of optical realization of such a system by means of NIR target scanning at fixed wavelengths. An algorithm was designed, an experimental setup was built and samples of various modern gear and apparel materials were tested. For pattern testing the samples of actively arm engaged armies camouflages were chosen. Tests were performed both in clear atmosphere and in the artificial extremely humid and hot atmosphere to simulate field conditions.

Porous silicon optical filters in gas sensing applications

In this thesis, the gas sensing properties of porous silicon-based thin-film optical filters are explored. The effects of surface chemistry on the adsorption and desorption of various gases are studied in detail. Special emphasis is placed on investigating thermal carbonization as a stabilization method for optical sensing applications. Moreover, the possibility of utilizing the increased electrical conductivity of thermally carbonized porous silicon for implementing a multiparametric gas sensor, which would enable simultaneous monitoring of electrical and optical parameters, is investigated. In addition, different porous silicon-based optical filter-structures are prepared, and their properties in sensing applications are evaluated and compared. First and foremost, thermal carbonization is established as a viable method to stabilize porous silicon optical filters for chemical sensing applications. Furthermore, a multiparametric sensor, which can be used for increasing selectivity in gas sensing, is also demonstrated. Methods to improve spectral quality in multistopband mesoporous silicon rugate filters are studied, and structural effects to gas sorption kinetics are evaluated. Finally, the stability of thermally carbonized optical filters in basic environments is found to be superior in comparison to other surface chemistries currently available for porous silicon. The results presented in this thesis are of particular interest for developing novel reliable sensing systems based on porous silicon, e.g., label-free optical biosensors.

Fracture modes and acoustic emission characteristics of hydrogen-assisted cracking in high-strength low-alloy steel weldment

The aim of the present paper is to study the relationship between the fracture modes in hydrogen-assisted cracking (HAC) in microalloied steel and the emission of acoustic signals during the fracturing process. For this reason, a flux-cored arc weld (FCAW) was used in a high-strength low-alloy steel. The consumable used were the commercially available AWS E120T5-K4 and had a diameter of 1.6 mm. Two different shielding gases were used (CO2 and CO2+5% H2) to obtain complete phenomenon characterization. The implant test was applied with three levels of restriction stresses. An acoustic emission measurement system (AEMS) was coupled to the implant test apparatus. The output signal from the acoustic emission sensor was passed through an electronic amplifier and processed by a root mean square (RMS) voltage converter. Fracture surfaces were examined by scanning electron microscopy (SEM) and image analysis. Fracture modes were related with the intensity, the energy and the number of the peaks of the acoustic emission signal. The shielding gas CO2+5% H2 proved to be very useful in the experiments. Basically, three different fracture modes were identified in terms of fracture appearance: microvoid coalescence (MVC), intergranular (IG) and quasi-cleavage (QC). The results show that each mode of fracture presents a characteristic acoustic signal.

Linear prediction in optical spectroscopy

A linear prediction procedure is one of the approved numerical methods of signal processing. In the field of optical spectroscopy it is used mainly for extrapolation known parts of an optical signal in order to obtain a longer one or deduce missing signal samples. The first is needed particularly when narrowing spectral lines for the purpose of spectral information extraction. In the present paper the coherent anti-Stokes Raman scattering (CARS) spectra were under investigation. The spectra were significantly distorted by the presence of nonlinear nonresonant background. In addition, line shapes were far from Gaussian/Lorentz profiles. To overcome these disadvantages the maximum entropy method (MEM) for phase spectrum retrieval was used. The obtained broad MEM spectra were further underwent the linear prediction analysis in order to be narrowed.

Conventional and nonconventional Kramers-Kronig analysis in optical spectroscopy

This Master’s Thesis is dedicated to the investigation and testing conventional and nonconventional Kramers-Kronig relations on simulated and experimentally measured spectra. It is done for both linear and nonlinear optical spectral data. Big part of attention is paid to the new method of obtaining complex refractive index from a transmittance spectrum without direct information of the sample thickness. The latter method is coupled with terahertz tome-domain spectroscopy and Kramers-Kronig analysis applied for testing the validity of complex refractive index. In this research precision of data inversion is evaluated by root-mean square error. Testing of methods is made over different spectral range and implementation of this methods in future is considered.

Leaf optical properties of two liana species Canavalia parviflora Benth. and Gouania virgata Reissk in different light conditions

Lianas are plants that depend on support to reach some appreciable height, and they represent an important structural component of tropical forests. Although they predominate in clearings and gaps, some species survive in the understory. Changes in irradiance between these environments can affect leaf morphology and absorption of photosynthetic active radiation (PAR). We had examined the effects of different light regimes on leaf optical properties, chlorophyll content, specific leaf area, and leaf surface morphology in young seedlings of Canavalia parviflora Benth. (Fabaceae) and Gouania virgata Reissk (Rhamnaceae). The seedlings were distributed on workbenches covered by different layers of neutral shade netting, thus creating three levels of light intensity corresponding to about 40%, 10% and 1.5% of solar irradiance. Plants growing in full sun were used as a control. Both species exhibited an increase in reflectance in full sun and alterations in leaf morphology. Reduction in irradiance induced an increase in absorptance (decrease in reflectance and transmittance) in C. parviflora leaves in the green due to higher chlorophyll content. In G. virgata the spectral leaf changes were less observable. However, the efficiency of absorption was more pronounced in G. virgata than in C. parviflora leaves under 40%, 10% and 1.5% photon flux density (PFD). The greater efficiency of absorption in G. virgata was due to a larger specific leaf area (SLA) under these conditions. The adjustments in leaf optical properties can aid these species in overall carbon gain under limited light conditions.

Dispersal modes and fruiting periods in hyperseasonal and seasonal savannas, central Brazil

Seasonal savannas are characterized by an intense drought that influences their functioning. Hyperseasonal savannas experience additionally a waterlogging during the rainy season. In South America, the largest savanna environment is the Brazilian cerrado. To assess whether a particular dispersal mode or fruiting period is associated to the waterlogging, we examined dispersal and phenological groups in hyperseasonal and seasonal cerrado plant species. We compared the proportion of species and individuals in these groups with G-tests for independence in contingency tables. We did not find differences in the proportion of species; however, based on the proportion of individuals, the main dispersal strategy was anemochory in the hyperseasonal cerrado and zoochory in the seasonal cerrado. Phenological strategies of fruiting in safe periods of the year were differently selected in both cerrados. In the hyperseasonal cerrado, most individuals fruited in non-waterlogged periods, whereas in the seasonal cerrado, most individuals fruited in wetter periods. Thus, waterlogging may drive important modifications in the efficiency of the dispersal and phenological strategies of hyperseasonal savannas plants.

Early modes of exegesis : ideal figures in Malachi as a test case

Antikens judiska bibeltolkare hade ett annorlunda sätt att läsa Bibeln än den som moderna läsare är vana vid. Dessa tidiga exegeter tänkte att texten som nu finns i den hebreiska Bibeln, de kristnas Gamla Testamente, är helig ordagrant i den form som den fanns i under deras tid, att den inte innehåller några fel, och att Gud har en övergripande plan gällande helheten, så att man vid behov kan förklara ett Bibelställe med hjälp av ett annat. Dessa antaganden reflekteras i det sätt på vilket antikens exegeter läste och tolkade sin Bibel. Det här ser man då man läser deras texter, från 400-talet före vår tideräknings början till de första århundradena enligt vår tideräkning. Ett verktyg som antikens skrifttolkare ofta använde var den så kallade gezera shava -metoden, där de jämförde identiska ord och fraser i Bibeln för att skänka belysning åt oklara textställen. Hebreiskan, särskilt den ovokaliserade konsonanttexten, innehåller många homonyma ord, alltså ord som ser likadana ut men har olika betydelser. De tidiga exegeterna utnyttjade ofta de möjligheter till alternativa tolkningar som uppstår ur denna tvetydighet. Ibland kunde de dock tvärtom också dra paralleller ur kontextuella likheter, alltid efter behov. I denna avhandling står dessa tidiga anonyma bibeltolkare och deras tolkningar i fokus. Malakis bok, som härstammar från ca år 475 f.v.t., kan ses som ett viktigt tidigt exempel på denna tendens till nytolkning av traditioner. Boken själv har dock också blivit föremål till nytolkningar, redan i de tilläggsverser som finns i dess slut, men särskilt i senare judisk litteratur och i Nya Testamentet. I avhandlingen granskas de fem bibliska gestalter som nämns i Malaki: Jakob, Esau, Levi, Mose och Elia. Hur används de i boken och hur har senare traditioner som anknyter till dem influerats av Malaki? ------------------------------------------------ Antiikin juutalaiset raamatunselittäjät lukivat Raamattua eri tavoin kuin moderni lukija. Heidän näkemyksensä mukaan se teksti, joka nykyään löytyy heprealaisesta Raamatusta eli kristittyjen Vanhasta testamentista, oli pyhä juuri sellaisessa muodossa, jossa se oli heille välittynyt. Se oli virheetön, ja Jumalalla oli siitä kokonaisnäkemys, joka voisi selvitä myös tulkitsijalle, kun tämä vain tutkisi tekstiä riittävän tarkkaan. Nämä perusoletukset näkyvät tavassa, jolla antiikin eksegeetit lukivat ja tulkitsivat Raamattuaan. Se voidaan huomata heidän jälkeensä jättämistään teksteistä, alkaen noin 400-luvulta ennen ajanlaskumme alkua ja jatkuen ajanlaskumme ensimmäisiin vuosisatoihin. Antiikin raamatunselittäjät käyttivät yleisesti muun muassa metodia, joka rabbiinisessa kirjallisuudessa tunnetaan nimellä gezera shava. Raamatussa kahdessa tai useammassa kohtaa esiintyviä samoja sanoja ja ilmauksia verrattiin tällöin toisiinsa ja pyrittiin siten saamaan valaistusta epäselvinä pidettyihin tekstinkohtiin. Heprealle, etenkin sen vokalisoimattomassa muodossa, on tyypillistä homonyymisyys. Samannäköiset sanat voivat eri yhteyksissä tarkoittaa eri asioita. Varhaiset eksegeetit päätyivät usein tästä ilmiöstä nouseviin, keskenään vaihtoehtoisiin tulkintoihin. Toisaalta he saattoivat myös tarvittaessa selittää tekstinkohtaa toisella tekstinkohdalla ainoastaan näiden sisällöllisenkin yhtäläisyyden perusteella. Tässä väitöstutkimuksessa tarkastellaan näitä varhaisia, meille nimettömiksi jääneitä raamatunselittäjiä ja heidän tulkintojaan käyttämällä tutkimuksen lähtökohtana Malakian kirjaa. Malakiaa, joka on peräisin noin vuodelta 475 ennen ajanlaskumme alkua, voidaan pitää yhtenä tärkeimmistä ja varhaisimmista teksteistä, joissa traditioita yhdistellään ja kerrotaan uudelleen edellä mainittuihin perusajatuksiin nojaten ja niihin pohjautuvia menetelmiä käyttäen. Toisaalta Malakian kirjaa on myös tulkittu samojen periaatteiden mukaisesti jo sen myöhemmältä ajalta peräisin olevissa loppujakeissa, ja sittemmin muussa varhaisessa juutalaisessa kirjallisuudessa sekä Uudessa testamentissa. Väitöstutkimuksessa tarkastellaan erityisesti niitä viittä henkilöä, jotka mainitaan Malakian kirjassa: Jaakobia, Esauta, Leeviä, Moosesta ja Eliaa. Kirjoittaja tutkii, miten heidän hahmojaan on käytetty Malakian kirjassa, millaisiin heitä koskeviin traditioihin tämä käyttötapa perustuu, ja missä määrin Malakian kirjan vaikutus on havaittavissa myöhemmässä näihin henkilöihin liitetyssä perinteessä.

Entry Modes for Finnish Firms into the Zambian Renewable Energy Industry

The renewable energy industry in Zambia is poised for growth and offers many possibilities for Finnish firms willing to enter the market. The Zambian government’s deliberate policy measures aim at attracting foreign direct investment (FDI) into this sector. This study rationalises that this could be the pull factor for Finnish firms. The thesis gives an overview of the industry and investigates an appropriate mode of entry, basing its arguments on the comparison analysis of the two economies with the use of the world forum’s stages of economic development as a framework. The theoretical part of the study examines internationalisation theories, entry mode choice and factors influencing the choice. The multiple case study approach is implored, analysing four case companies from Finland with the use of extant literature on internationalisation relevant to the study. The research design involves the use of documentation, secondary data, interviews and observation. The results of the case analyses show that the Finnish firm’s most preferred entry mode initially is exporting because it is considered to be less risky. Additionally, the findings also reveal that the selection of a suitable mode of entry is dependent on the firms’ size, orientation and international experience and could therefore be considered to be subjective. Paramount is the act of gaining market knowledge. The study shows that only hydro-electrical, solar energies and biomass are by far the most used and known forms of renewable energy in Zambia, while other alternative sources still remain un-exploited thus highlighting a growth potential. However, policy formulation and the regulatory framework in the renewable energy sector were found to be wanting.

Defining the keyhole modes – the effects on the weld geometry and the molten pool behaviour in high power laser welding of stainless steels

Keyhole welding, meaning that the laser beam forms a vapour cavity inside the steel, is one of the two types of laser welding processes and currently it is used in few industrial applications. Modern high power solid state lasers are becoming more used generally, but not all process fundamentals and phenomena of the process are well known and understanding of these helps to improve quality of final products. This study concentrates on the process fundamentals and the behaviour of the keyhole welding process by the means of real time high speed x-ray videography. One of the problem areas in laser welding has been mixing of the filler wire into the weld; the phenomena are explained and also one possible solution for this problem is presented in this study. The argument of this thesis is that the keyhole laser welding process has three keyhole modes that behave differently. These modes are trap, cylinder and kaleidoscope. Two of these have sub-modes, in which the keyhole behaves similarly but the molten pool changes behaviour and geometry of the resulting weld is different. X-ray videography was used to visualize the actual keyhole side view profile during the welding process. Several methods were applied to analyse and compile high speed x-ray video data to achieve a clearer image of the keyhole side view. Averaging was used to measure the keyhole side view outline, which was used to reconstruct a 3D-model of the actual keyhole. This 3D-model was taken as basis for calculation of the vapour volume inside of the keyhole for each laser parameter combination and joint geometry. Four different joint geometries were tested, partial penetration bead on plate and I-butt joint and full penetration bead on plate and I-butt joint. The comparison was performed with selected pairs and also compared all combinations together.

Measuring higher order optical aberrations of the human eye: techniques and applications

In the present paper we discuss the development of "wave-front", an instrument for determining the lower and higher optical aberrations of the human eye. We also discuss the advantages that such instrumentation and techniques might bring to the ophthalmology professional of the 21st century. By shining a small light spot on the retina of subjects and observing the light that is reflected back from within the eye, we are able to quantitatively determine the amount of lower order aberrations (astigmatism, myopia, hyperopia) and higher order aberrations (coma, spherical aberration, etc.). We have measured artificial eyes with calibrated ametropia ranging from +5 to -5 D, with and without 2 D astigmatism with axis at 45º and 90º. We used a device known as the Hartmann-Shack (HS) sensor, originally developed for measuring the optical aberrations of optical instruments and general refracting surfaces in astronomical telescopes. The HS sensor sends information to a computer software for decomposition of wave-front aberrations into a set of Zernike polynomials. These polynomials have special mathematical properties and are more suitable in this case than the traditional Seidel polynomials. We have demonstrated that this technique is more precise than conventional autorefraction, with a root mean square error (RMSE) of less than 0.1 µm for a 4-mm diameter pupil. In terms of dioptric power this represents an RMSE error of less than 0.04 D and 5º for the axis. This precision is sufficient for customized corneal ablations, among other applications.

Optical spectroscopy of organic material based on C60

The structure and optical properties of thin films based on C60 materials are studied. Reproducible vacuum method of thin fullerene films production with Cd impurity on Si, glass and mica surfaces is developed. Surface morphology of the films are investigated by AFM and SEM methods. The ab initio quantum - chemical calculations of the geometry, total energy and excited energy states of complex fullerene- cadmium telluride supramolecules are performed. Photoluminescence spectra of composite thin films based on C60 before and after X-ray irradiation were measured. The intensity of additional peaks is defined as the charge composition due to the type of substrate. These results are interpreted as an appearance of the dipole-allowed transitions in the fullerene excited singlet states spectrum cause of an interference with cadmium telluride. X-ray irradiated films were investigated, and additional peaks in photoluminescence spectra were detected. These peaks appear as a result of molecular complexes formation from C60CdTe mixture and dimerization of the films. Density functional B3LYP quantum-chemical calculations for C60CdTe, molecular complexes, (C60)2 and C120O dimers were performed to elucidate some experimental results.