Search results for "Ultra"
showing 10 items of 4451 documents
Boreal fishes and ultraviolet radiation : actions of UVR at molecular and individual levels
2005
Eeva-Riikka Vehniäinen on väitöskirjatyössään tutkinut UV-säteilyn vaikutuksia siian, hauen ja muikun poikasissa. Ihmisen aiheuttama otsonikerroksen ohentuminen on lisännyt maan pinnalle saapuvan ultravioletti-B-säteilyn (UVB) määrää viime vuosikymmenten aikana, ja lisääntymisen odotetaan jatkuvan vielä noin 2050-luvulle saakka. UVB-säteily on haitallista eliöille, koska se aiheuttaa vaurioita solun keskeisissä rakenteissa: DNA:ssa, proteiineissa ja lipideissä.Vehniäinen arvioi lisääntyvän UVB-säteilyn aiheuttamaa riskiä taloudellisesti ja ekologisesti tärkeille makeanveden kalalajeillemme, siialle, muikulle ja hauelle, niiden herkimmässä elämänvaiheessa välittömästi kuoriutumisen jälkeen. …
Tunable chirp in Bragg gratings written in tapered core fibers
2002
In this paper we present a technique to control the chirp of a fiber grating capable to produce positive or negative chirp in a single grating. The device is based on a uniform period grating written in a tapered core fiber, this grating has a positive chirp that can be reduced and removed by subjecting the fiber to mechanical stress, after some stress level the grating chirps to negative values. A chirp range of ±4 nm with respect to a central wavelength of 1546 nm has been experimentally achieved.
<title>Tunable chirp in Bragg gratings written in tapered core fibers</title>
2001
In this paper we present a technique to control the chirp of a fiber grating capable to produce positive or negative chirp in a single grating. The device is based ona uniform period grating written in a tapered core fiber, this grating has a positive chirp that can be reduced and removed by subjecting the fiber to mechanical stress, after some stress level the grating chirps to negative values. A chirp range of +/- 4 nm with respect to a central wavelength of 1546 nm has been experimentally achieved.
Effective length of short Fabry-Perot cavity formed by uniform fiber Bragg gratings
2009
In this paper, we describe the properties of Fabry-Perot fiber cavity formed by two fiber Bragg gratings in terms of the grating effective length. We show that the grating effective length is determined by the group delay of the grating, which depends on its diffraction efficiency and physical length. We present a simple analytical formula for calculation of the effective length of the uniform fiber Bragg grating and the frequency separation between consecutive resonances of a Fabry-Perot cavity. Experimental results on the cavity transmission spectra for different values of the gratings' reflectivity support the presented theory.
In-fiber Fabry-Perot refractometer assisted by a long-period grating
2010
We present an optical fiber refractometer based on a Fabry-Perot interferometer defined by two fiber Bragg gratings and an intracavity long-period grating that makes the light confined in the resonator interact with the surrounding medium. The external refractive index is monitored by the resonant frequencies of the Fabry-Perot interferometer, which can be measured either in transmission or in reflection. In this first experiment, wavelength shifts measured with a resolution of 0.1 pm have allowed one to establish a refractive index detection limit of 2.1x10(-5).
Sulfurēta poli(ēterēterketona) un cirkonija nanodaļiņu kompozītmembrānu sintēze un to fizikālķīmisko īpašību analīze
2016
Sulfurēta poli(ēterēterketona) un cirkonija hidrogēnfosfāta nanodaļiņu kompozītmembrānu sintēze un to fizikālķīmisko īpašību analīze. Markus M., zinātniskais vadītājs Dr.ķīm. Guntars Vaivars, konsultants Dr. h. ķīm., prof. Andris Zicmanis. Maģistra darbs, 57 lappuses, 94 attēli, 9 tabulas, 51 literatūras avots, 3 pielikumi. Latviešu valodā. Darbā sintezētas modificēta poli(ēterēterketona) membrānas un to kompozītmembrānas ar cirkonija hidrogēnfosfāta daļiņām, ko paredzēts izmantot degšūnās. Īpaša uzmanība veltīta tādas kompozītmateriāla koncentrāciju attiecību atrašanai, kas nodrošina kvalitatīvu membrānu iegūšanu ar uzlabotām īpašībām tālākas izmantošanas iespējām, kā arī pētīta ultraskaņa…
Effect of high power ultrasound on physical–chemical properties of polypropylene films aimed for food packaging: structure and surface features
2019
International audience; Biaxially oriented polypropylene (BOPP) coated with acrylic/polyvinylidene chloride (BOPPAcPVDC) and biaxially oriented coextruded polypropylene (BOPPcoex) films have been treated with high power ultrasound (HPUS) while submerged in water. Polymer structure and the surface morphology changes were noticed, and obtained results were correlated with the physical properties of tested materials. In anticipation of sonochemically enhanced reactions, physical–chemical profile of film samples was determined using thermogravimetric analysis, differential scanning calorimetry, Fourier-transform infrared spectroscopy, UV spectrophotometry and environmental scanning electron mic…
What Ingredients are Essential for the Recipe of a Study?
2019
In this investigation [1], the authors evaluated among other objectives, the analgesic efficacy and the duration of analgesia from a cohort of 60 patients for arthroscopic shoulder surgery. The gro...
Gilding and pigments of Renaissance marble of Abatellis Palace: non-invasive investigation by XRF spectrometry
2012
Most of the artworks constituting the collection of Renaissance statuary of Abatellis Palace in Palermo (Sicily) show evidence of colour layers and fragments of gold foil that probably once covered the whole marble surface. The restoration of some of these statues has allowed to carry out archaeometric studies about the painting technique and to highlight the original materials and inclusion present on the precious marbles by two famous Italian sculptors of the Renaissance, Francesco Laurana and Antonello Gagini. The measurements have been performed in situ through the integrated use of two non-invasive techniques: visible fluorescence stimulated by ultraviolet light and X-ray fluorescence.…
B-mode versus A-mode ultrasonographic measurements of mucosal thickness in vivo
2002
Abstract Objective: The objective of this study was to compare the measurement accuracy of A-mode and B-mode ultrasonographic assessments of palatal masticatory mucosal thickness in vivo. Study Design: Thickness of palatal masticatory mucosa in the molar region of 50 volunteers was measured once with a B-mode ultrasound device (10 MHz) combined with a standoff for intraoral applications. At identical reading points thickness was also assessed with an A-mode device (5 replicates) and by needle probing for determination of true thickness. Results: On average true thickness ranged between 2.9 and 3.3 mm (95% confidence intervals; median, 3.1 mm). B-mode ultrasonography overestimated truth by 0…