Improved light extraction in the bioluminescent lantern of a Photuris firefly (Lampyridae)

A common problem of light sources emitting from an homogeneous high-refractive index medium into air is the loss of photons by total internal reflection. Bioluminescent organisms, as well as artificial devices, have to face this problem. It is expected that life, with its mechanisms for evolution, would have selected appropriate optical structures to get around this problem, at least partially. The morphology of the lantern of a specific firefly in the genus Photuris has been examined. The optical properties of the different parts of this lantern have been modeled, in order to determine their positive or adverse effect with regard to the global light extraction. We conclude that the most efficient pieces of the lantern structure are the misfit of the external scales (which produce abrupt roughness in air) and the lowering of the refractive index at the level of the cluster of photocytes, where the bioluminescent production takes place.Comment: 13 pages, 11 figures, published in Optics Expres

Hoitoonohjauksen ideologiasta

Summary : The ideology of referral to treatment

Flame generated magnetic iron oxide nanoparticles

Työssä tuotettiin rautaoksidinanohiukkasia nesteliekkiruiskulla. Prekursoreina käytettiin rauta(III)nitraattia ja ferroseeniä. Tuotettua aerosolia tutkittiin aerosolimittalaitteilla ja kerättiin talteen sähkösuodattimella sekä kaskadi-impaktorilla nanojauheena, jota tutkittiin edelleen röntgendiffraktiolla, Raman-spektroskopialla, läpäisyelektronimikroskoopilla ja ominaispinta-ala –mittauksella kiderakenteen ja koostumuksen selvittämiseksi. Myös prekursorin väkevyyden ja syöttönopeuden vaikutusta hiukkasten koostumukseen tutkittiin. Hiukkaset olivat primäärikooltaan 5-20 nm ja kiderakenteeltaan magnetiittia, maghemiittia ja hematiittia kun prekursorina oli rauta(III)nitraatti, sekä magnetiittia ja maghemiittia kun prekursorina oli ferroseeni.Iron oxide nanoparticles were generated by liquid flame spray. The precursor solutions were iron(III)nitrate and ferrocene. Size distribution and number concentration of the produced aerosol was measured, and also an electrostatic precipitator and a cascade-impactor was used to collect nanopowder, which was analyzed with X-ray diffaktion, Raman spectroscopy, transmission electron microscope and specific surface area measurement to identify the crystal structure and morphology of the particles. Also the effect of varying the concentration and feed rate of the precursor solution was studied. The primary size of the particles were 5-20 nm and the oxide was hematite, maghemite and magnetite when the precursor was iron(III) nitrate, and maghemite and magnetite when the precursor was ferrocene

Sironta ja taittuminen kontrastimekanismeina röntgenkuvantamisessa

Differentiation of various types of soft tissues is of high importance in medical imaging, because changes in soft tissue structure are often associated with pathologies, such as cancer. However, the densities of different soft tissues may be very similar, making it difficult to distinguish them in absorption images. This is especially true when the consideration of patient dose limits the available signal-to-noise ratio. Refraction is more sensitive than absorption to changes in the density, and small angle x-ray scattering on the other hand contains information about the macromolecular structure of the tissues. Both of these can be used as potential sources of contrast when soft tissues are imaged, but little is known about the visibility of the signals in realistic imaging situations. In this work the visibility of small-angle scattering and refraction in the context of medical imaging has been studied using computational methods. The work focuses on the study of analyzer based imaging, where the information about the sample is recorded in the rocking curve of the analyzer crystal. Computational phantoms based on simple geometrical shapes with differing material properties are used. The objects have realistic dimensions and attenuation properties that could be encountered in real imaging situations. The scattering properties mimic various features of measured small-angle scattering curves. Ray-tracing methods are used to calculate the refraction and attenuation of the beam, and a scattering halo is accumulated, including the effect of multiple scattering. The changes in the shape of the rocking curve are analyzed with different methods, including diffraction enhanced imaging (DEI), extended DEI (E-DEI) and multiple image radiography (MIR). A wide angle DEI, called W-DEI, is introduced and its performance is compared with that of the established methods. The results indicate that the differences in scattered intensities from healthy and malignant breast tissues are distinguishable to some extent with reasonable dose. Especially the fraction of total scattering has large enough differences that it can serve as a useful source of contrast. The peaks related to the macromolecular structure come to angles that are rather large, and have intensities that are only a small fraction of the total scattered intensity. It is found that such peaks seem to have only limited usefulness in medical imaging. It is also found that W-DEI performs rather well when most of the intensity remains in the direct beam, indicating that dark field imaging methods may produce the best results when scattering is weak. Altogether, it is found that the analysis of scattered intensity is a viable option even in medical imaging where the patient dose is the limiting factor.Lääketieteellisessä kuvantamisessa on usein tarve erottaa toisistaan tiheydeltään hyvin samankaltaisia kudoksia, erityisesti pehmytkudoksista tehtävien tutkimusten yhteydessä, kuten mammografiassa. Tavallinen röntgensäteiden vaimenemiseen perustuva kuvantaminen ei kykene erottelemaan tiheydeltään samankaltaisia kudoksia toisistaan erityisen hyvin. Aiemmin on havaittu röntgensäteiden taittumisen olevan paljon herkempi kudosten välisille tiheyseroille kuin vaimenemisen. Myös röntgensäteiden sirontakuviot, jotka johtuvat säteiden suunnan hajautumisesta, riippuvat kudostyypistä. Sirontaa kudoksista on tutkittu pääasiassa ohuilla kudosnäytteillä, käyttämällä hyvin voimakasta röntgensäteilyä. Todellisissa lääketieteellisissä kuvantamisessa kohteet ovat selvästi paksumpia kuin ohuet kudosnäytteet, ja röntgensäteen voimakkuutta on rajoitettava potilaaseen kohdistuvan säteilyannoksen takia. Tässä työssä tutkittiin sirontakuvioiden näkymistä kun nämä käytännön tilanteissa rajoittavat tekijät otetaan huomioon. Kudokset sirottavat ja taittavat röntgensäteitä hyvin pienelle kulma-alueelle, joten havaintojen tekemiseen tarvitaan erityisen herkkiä laitteita. Eräs tapa havaita nämä pienet suunnanmuutokset säteiden kulussa on käyttää kidehilaa heijastamaan tiettyyn kulmaan tulevat röntgensäteet. Tällaista hilaa kutsutaa analysaattorikiteeksi, ja sen asentoa muuttamalla saadaan mitattua eri kulmissa tulevien röntgensäteiden voimakkuuksia. Analysaattoriin perustuva kuvantaminen (engl. analyzer based imaging, ABI) mahdollistaa säteen kulkusuunnassa tapahtuneiden muutosten mittaamisen mikroradiaania paremmalla tarkkuudella. Tässä tutkimuksessa mallinnettiin tietokoneella ABI-kuvausmenetelmää, ja tutkittiin laskennallisesti eri tyyppisistä näytteistä tulevan sironnan näkymistä. Erityisesti kiinnitettiin huomiota siihen, kuinka suuri potilaaseen kohdistuva säteilyannos tarvitaan sironnan luotettavan näkymisen mahdollistamiseksi. Sironnan kokonaisvoimakkuuden muutosten havaittiin näkyvän melko selkeästi. Sirontakuvion yksityiskohtien, kuten esimerkiksi sirontapiikkien paikkojen ja leveyksien, havaittiin puolestaan näkyvän huonosti. Tulokset osoittavat, että sironnan kokonaismäärässä tapahtuvat muutokset voivat olla hyvä kontrastin lähde lääketieteellisen kuvantamisen kannalta, mahdollistaen sellaisten kudosten erottamisen toisistaan, jotka eivät tavallisessa vaimenemiseen perustuvassa kuvantamisessa erotu

Inspection of gas bubbles in frozen Betula pendula xylem with micro-CT: Conduit size, water status and bark permeability affect bubble characteristics

Abstract Bubbles of gas trapped in the xylem during freezing are a major cause of damage for trees growing at high altitudes or latitudes, as the bubbles may cause embolism during thawing. Yet the factors controlling bubble formation upon freeze-thaw cycles remain poorly understood. Especially the size of the bubbles formed in the ice is crucial for winter embolism formation. We used high-resolution X-ray microtomography combined with freezing experiments to investigate the size and shape of 68 343 gas bubbles in frozen conduits in branches of Betula pendula. We also studied how conduit size, tree water status (-0.2 MPa vs -0.6 MPa) and bark permeability to gases (decreased by Vaseline-coating) affect the gas bubbles characteristics. High-resolution X-ray images allowed us to detect gas bubbles down to 1.0 ?m in diameter and revealed that not only small spherical gas bubbles but gaseous volumes of various shapes and sizes were found from the frozen xylem indicating that gas bubbles may have started to grow already during the freezing propagation. Most of the gas bubbles were found in fibers, but the rare gas bubbles found in the vessels were larger than those in the fibers. Bubble volume increased with conduit volume in both fibers and vessels, but conduit size alone could not explain gas bubble volume. Low water potential and restriction of gas escape from the branch seem to cause more, larger, and less spherical bubbles and thus increase the risk of embolism formation. These findings open new research avenues for further studies of winter embolism formation. This article is protected by copyright. All rights reserved.Peer reviewe

Identifying Late Iron Age textile plant fibre materials with microscopy and X-ray methods — a study on finds from Ravattula Ristimäki (Kaarina, Finland)

In Finland, the earliest remains of a Christian church and cemetery date to the Late Iron Age (800-1150/1300 AD) and have been excavated in Ravattula Ristimaki, in Kaarina, southwestern Finland. In this study, seven assumingly plant fibre textile samples from individual inhumation graves were analysed to identify their materials. The aim of the study was to investigate the possibilities of identifying archaeological plant fibre samples using a three-stage procedure by observing the surface characteristics, microfibrillar orientation and cross section of the fibres via transmitted light microscopy (TLM). The identification process was based on such a TLM characterisation. Additionally, parts of the samples were studied with X-ray microtomography (micro-CT) and wide-angle X-ray scattering (WAXS) to test the possibilities of using the X-ray methods in research and to identify bast fibre textiles. Both flax and nettle were found in the samples, indicating a preference for these two fibre plants in Late Iron Age Finland.Peer reviewe

Laser-induced spallation of minerals common on asteroids

The ability to deflect dangerous small bodies in the Solar System or redirect profitable ones is a necessary and worthwhile challenge. One well-studied method to accomplish this is laser ablation, where solid surface material sublimates, and the escaping gas creates a momentum exchange. Alternatively, laser-induced spallation and sputtering could be a more efficient means of deflection, yet little research has studied these processes in detail. We used a 15-kW Ytterbium fiber laser on samples of olivine, pyroxene, and serpentine (minerals commonly found on asteroids) to induce spallation. We observed the process with a high-speed camera and illumination laser, and used X-ray micro-tomography to measure the size of the holes produced by the laser to determine material removal efficiency. We found that pyroxene will spallate at power densities between 1.5 and 6.0 kW cm(-2), serpentine will also spallate at 13.7 kW cm(-2), but olivine does not spallate at 1.5 kW cm(-2) and higher power densities melt the sample. Laser-induced spallation of pyroxene and serpentine can be two- to three-times more energy efficient (volume removed per unit of absorbed energy) than laser-induced spattering, and over 40x more efficient than laser ablation.Peer reviewe

The role of living bark in Betula pendula ability to refill embolised xylem

Non peer reviewe

Laser processing of minerals common on asteroids

Asteroid mining and redirection are two trends that both can utilize lasers, one to drill and cut, the other to ablate and move. Yet little is known about what happens when a laser is used to process the types of materials we typically expect to find on most asteroids. To shed light on laser processing of asteroid material, we used a 300-W, pulsed Ytterbium fiber laser on samples of olivine, pyroxene, and serpentine, and studied the process with a high-speed camera and illumination laser at 10 000 frames per second. We also measure the sizes of the resulting holes using X-ray micro-tomography to find the pulse parameters which remove the largest amount of material using the least amount of energy. We find that at these power densities, all three minerals will melt and chaotically throw off spatter. Short, low-power pulses can efficiently produce thin, deep holes, and long, high-power pulses are more energy efficient at removing the most amount of material.Peer reviewe