Littérature scientifique sur le sujet « UV photons »
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Articles de revues sur le sujet "UV photons"
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Kontos, Antonios, et Rainer Weiss. « Photon emission spectrum of ion pumps ». Review of Scientific Instruments 94, no 3 (1 mars 2023) : 034503. http://dx.doi.org/10.1063/5.0138917.
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As the sensitivity of gravitational-wave detectors increases, new sources of noise appear. A potential source of noise may arise from charge accumulating on the mirrors of the experiment, the origin of which can be related to UV photons from the surroundings. In order to test one hypothesis, we measured the photon emission spectrum from a type of ion pump that is used in the experiment, an Agilent VacIon Plus 2500 l/s. We found that there is significant emission of UV photons above 5 eV, capable of knocking electrons off mirrors or surrounding surfaces and charging them. Photon emission measurements were taken as a function of gas pressure, ion-pump voltage setting, and type of pumped gas. The overall emission and shape of the measured photon spectrum are consistent with bremsstrahlung as the mechanism for the production of the photons.
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Fraikin, G. Ya, N. S. Belenikina et A. B. Rubin. « Photochemical processes to cellular DNA damage by UV radiation of different wavelengths : biological consequences ». Молекулярная биология 58, no 1 (15 février 2024) : 3–21. http://dx.doi.org/10.31857/s0026898424010019.
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UV radiation of sunlight induces in cellular DNA of different organisms photochemical reactions, which may lead to the development of series biological responses to arising lesions, including apoptosis, mutagenesis, and carcinogenesis. The chemical nature and the amount of DNA lesions depend on the wavelength of UV radiation. Photons of UV radiation in the region B (UVB, 290–320 nm) cause the production of two main defects, namely, cyclobutane pyrimidine dimers and, with a less yield, pyrimidine (6-4) pyrimidone photoproducts; their formation is the result of the direct UVB photon absorption by DNA bases. Photons of UV radiation in the region A (UVA, 320–400 nm) induce only cyclobutane dimers that can be formed by triplet-triplet energy transfer from cellular chromophores, absorbing photons of this UV region, to DNA thymine bases. UVA is much more effective than UVB in the sensitized oxidatively lesion formation in DNA such as single strand breaks and oxidized bases; among those, 8-oxo-dihydroguanine is the most frequent since it can be produced from several oxidation processes. In recent years, multiple papers, reporting novel, more detailed information about molecular mechanisms of photochemical reactions underlying the formation of different lesions in DNA were published. The present review mainly aims at summarizing and analyzing data contained in these publications, particularly regarding oxidative reactions that are initiated by reactive oxygen species and radicals generated by potential endogenous photosensitizers such as pterins, riboflavin, protoporphyrin IX, NADH, and melanin. The role of specific DNA photoproducts in genotoxic processes induced in living systems by UV radiation of different wavelengths, including human skin carcinogenesis, is discussed.
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Kelvin Voon Yan Jie, Safizan Shaari, Mohd Fairus Ahmad, Nor Farhani Zakaria et Norhayati Sabani. « Photoluminescence Measurement of Triplet Sensitizer-Emitter Solution Using a Customized 3D-Printed Sample Holder ». International Journal of Nanoelectronics and Materials (IJNeaM) 17, June (12 juin 2024) : 187–93. http://dx.doi.org/10.58915/ijneam.v17ijune.854.
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This study explores the photoluminescence (PL) measurement of triplet sensitizer-emitter (TSE) solutions using a custom 3D-printed sample holder, within the context of triplet-triplet annihilation based molecular photon upconversion (TTA-UC) systems targeting the Vis-to-UV spectral region. TTA-UC converts low-energy visible photons to higher-energy ultraviolet (UV) photons, holding promise for solar energy harvesting and photonics applications. Two TSE couples, 4CzIPN/TP and 4CzIPN/QP, were investigated, and their upconverted fluorescence spectra showed peaks at 344 nm and 354 nm / 370 nm, respectively, confirming efficient upconversion capabilities. The 3D-printed sample holder facilitated reproducible PL measurements, enabling the calculation of quantum yields (ΦUC). The 4CzIPN/TP and 4CzIPN/QP couples exhibited low quantum yields (0.028% and 0.043%, respectively), suggesting the need for improved deoxygenation methods to enhance the triplet-triplet annihilation process and overall quantum efficiency. Despite modest yields, successful UV upconverted fluorescence observation underscores the feasibility of the Vis-to-UV TTA-UC system. This study provides insights into TTA-UC optimization and demonstrates the utility of the 3D-printed sample holder for affordable and precise PL measurements, paving the way for future advancements in photonics and solar energy applications.
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Cvetkovic, Dragan, Dejan Markovic, Dragana Cvetkovic et Blaga Radovanovic. « Effects of continuous UV-irradiation on the antioxidant activities of quercetin and rutin in solution in the presence of lecithin as the protective target ». Journal of the Serbian Chemical Society 76, no 7 (2011) : 973–85. http://dx.doi.org/10.2298/jsc101123089c.
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The stabilities and antioxidant action of two selected flavonoids, quercetin and rutin, dissolved in methanol and water, toward continuous UV-irradiation from three different sub-ranges (UV-A, UV-B and UV-C) were studied. The flavonoids underwent degradation (bleaching) following first-order kinetics. The bleaching rates were highly dependent on the energy input of the involved UV-photons. The antioxidant activities of the two flavonoids on UV-induced lecithin lipid peroxidation were studied by the TBA-MDA test, and appeared to be also affected by the continuous UV irradiation. The energy input of the incident UV-photons again played a major governing role, but an impact of the flavonoids structures cannot be neglected.
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Maté, Belén, Isabel Tanarro, Miguel A. Moreno, Miguel Jiménez-Redondo, Rafael Escribano et Víctor J. Herrero. « Stability of carbonaceous dust analogues and glycine under UV irradiation and electron bombardment ». Faraday Discuss. 168 (2014) : 267–85. http://dx.doi.org/10.1039/c3fd00132f.
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The effect of UV photon (120–200 nm) and electron (2 keV) irradiation of analogues of interstellar carbonaceous dust and of glycine were investigated by means of IR spectroscopy. Films of hydrogenated amorphous carbon (HAC), taken as dust analogues, were found to be stable under UV photon and electron bombardment. High fluences of photons and electrons, of the order of 1019cm−2, were needed for a film depletion of a few percent. UV photons were energetically more effective than electrons for depletion and led to a certain dehydrogenation of the HAC samples, whereas electrons led seemingly to a gradual erosion with no appreciable changes in the hydrocarbon structure. The rates of change observed may be relevant over the lifetime of a diffuse cloud, but cannot account for the rapid changes in hydrocarbon IR bands during the evolution of some proto-planetary nebulae. Glycine samples under the same photon and electron fluxes decay at a much faster rate, but tend usually to an equilibrium value different from zero, especially at low temperatures. Reversible reactions re-forming glycine, or the build-up of less transparent products, could explain this behavior. CO2and methylamine were identified as UV photoproducts. Electron irradiation led to a gradual disappearance of the glycine layers, also with formation of CO2. No other reaction products were clearly identified. The thicker glycine layers (a few hundred nm) were not wholly depleted, but a film of the order of the electron penetration depth (80 nm), was totally destroyed with an electron fluence of ∼1 × 1018cm−2. A 60 nm ice layer on top of glycine provided only partial shielding from the 2 keV electrons. From an energetic point of view, 2 keV electrons are less efficient than UV photons and, according to literature data, much less efficient than MeV protons for the destruction of glycine. The use of keV electrons to simulate effects of cosmic rays on analogues of interstellar grains should be taken with care, due to the low penetration depths of electrons in many samples of interest.
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Piston, David W., Brian D. Bennett et Guangtao Ying. « Imaging of Cellular Dynamics by Two-Photon Excitation Microscopy ». Microscopy and Microanalysis 1, no 1 (février 1995) : 25–34. http://dx.doi.org/10.1017/s1431927695110259.
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Two-photon excitation fluorescence microscopy provides attractive advantages over confocal microscopy for three-dimensionally resolved fluorescence imaging. Two-photon excitation arises from the simultaneous absorption of two photons in a single quantitized event whose probability is proportional to the square of the instantaneous intensity. For example, two red photons (∼700 nm) can cause the transition to an excited electronic state normally reached by absorption in the ultraviolet (∼350 nm). In the fluorescence experiments described here, the final excited state is the same singlet state that is populated during a conventional fluorescence experiment. Thus, the fluorophore exhibits the same emission properties (e.g., wavelength shifts, environmental sensitivity) used in typical biological microscopy studies. Three properties of two-photon excitation give this method its advantage over conventional optical sectioning microscopies: (1) the excitation is limited to the focal volume, thus providing inherent three-dimensional resolution and minimizing photobleaching and photodamage; (2) the two-photon technique allows imaging of UV fluorophores with only conventional visible light optics; (3) red light is far less damaging to most living cells and tissues than UV light and permits deeper sectioning, because both absorbance and scattering are reduced. Many cell biological applications of two-photon excitation microscopy have been successfully realized, demonstrating the wide ranging power of this technique.
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Carrascosa, H., G. A. Cruz-Díaz, G. M. Muñoz Caro, E. Dartois et Y.-J. Chen. « Photon-induced desorption of larger species in UV-irradiated methane ice ». Monthly Notices of the Royal Astronomical Society 493, no 1 (19 février 2020) : 821–29. http://dx.doi.org/10.1093/mnras/staa334.
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ABSTRACT At the low temperatures found in the interior of dense clouds and circumstellar regions, along with H2O and smaller amounts of species such as CO, CO2 or CH3OH, the infrared features of CH4 have been observed on icy dust grains. Ultraviolet (UV) photons induce different processes in ice mantles, affecting the molecular abundances detected in the gas phase. This work aims to understand the processes that occur in a pure CH4 ice mantle subjected to UV irradiation. We studied photon-induced processes for the different photoproducts arising in the ice upon UV irradiation. Experiments were carried out in ISAC, an ultra-high vacuum chamber equipped with a cryostat and an F-type UV lamp reproducing the secondary UV field induced by cosmic rays in dense clouds. Infrared spectroscopy and quadrupole mass spectrometry were used to monitor the solid and gas phases, respectively, during the formation, irradiation and warming-up of the ice. Direct photodesorption of pure CH4 was not observed. UV photons form CHx· and H· radicals, leading to photoproducts such as H2, C2H2, C2H6 and C3H8. Evidence for the photodesorption of C2H2 and photochemidesorption of C2H6 and C3H8 was found; the latter species is so far the largest molecule found to photochemidesorb. 13CH4 experiments were also carried out to confirm the reliability of these results.
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Elshan Aliyev, Marat Huseynov, et Hilal Tahirli Tarana Aghadiyeva. « IRRADIATION OF CARBON DIOXIDE WITH A VACUUM UV SOURCE AND OBTAINING OF STRATOSPHERIC OZONE ». ETM - Equipment, Technologies, Materials 13, no 01 (7 février 2023) : 150–55. http://dx.doi.org/10.36962/etm13012023-150.
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It has been known for more than 100 years that carbon dioxide absorbs photons in the ultraviolet and infrared ranges of radiation, creating a greenhouse effect. However, so far no one has answered the question: what is a photon? It is known that a photon has corpuscular and wave properties, has a certain pressure. An interesting experiment was carried out when a photon was dissected using Wilson chamber and it left traces of the opposite sign. The correct conclusion was made that one trace in the Wilson chamber was left by an electron, and the other - by a positron. There were other experiments, for example: birefringence of light in quartz crystals, Icelandic spar, etc., but there were no correct conclusions made about what a photon is. A photon is an electric dipole, consisting of an electron and a positron charges, without a spin charge-conjugate formation, which has a dipole magnetic field. Carbon dioxide, absorbing photons with a mass of 18.210-31 kg, being structured in the core, turns into triatomic oxygen, that is, into stratospheric ozone. A photon absorbs only a carbon atom that has an excess of spins. Photons absorbed by carbon dioxide (electric dipoles) having a magnetic field interact with the magnetic force lines of the dipole magnetic field of the Earth, and as a result of such interaction, triatomic oxygen-ozone moves into the stratosphere. Stratospheric ozone is not explosive in all aggregate states and at high pressures. In the atmosphere, it enters into a nuclear interaction with neutrons emanating from the sources of future earthquakes, forming water. So, naturally, the ozone layer of the Earth is depleted, replenishing the hydrosphere. Irradiation of CO2 and production of stratospheric ozone is a solution to the problem of climate warming. Stratospheric ozone can be widely used in the defense industry. An airship filled with stratospheric ozone will be much more efficient than airships filled with hydrogen or helium. The production of stratospheric ozone from carbon dioxide is a fundamental discovery in the field of photonuclear physics. Key words: electric dipole, photon, carbon dioxide, stratospheric ozone, photonuclear reaction.
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Salvio, Alberto. « Thermal production of massless dark photons ». Journal of Cosmology and Astroparticle Physics 2023, no 07 (1 juillet 2023) : 035. http://dx.doi.org/10.1088/1475-7516/2023/07/035.
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Abstract A dark photon is predicted by several well-motivated Standard Model extensions and UV completions. Here the most general effective field theory up to dimension-six operators describing the interactions of a massless dark photon with all Standard Model particles is considered. This captures the predictions of a generic model featuring this type of vector boson at sufficiently low energies. In such framework the thermal production rate of dark photons is computed at leading order, including the contributions of all SM particles. The corresponding cosmological yield of the dark photon and its contribution to the effective number of neutrinos are also calculated. These predictions satisfy the current observational bounds and will be tested by future measurements.
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Nakayama, Keiji, et Roman A. Nevshupa. « Characteristics and Pattern of Plasma Generated at Sliding Contact ». Journal of Tribology 125, no 4 (25 septembre 2003) : 780–87. http://dx.doi.org/10.1115/1.1540122.
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To verify the tribo-microplasma concept proposed by Nakayama, who suggested that a microplasma is generated in the gap of a sliding contact due to electrical discharge of the ambient gas in the electric field caused by tribo-charging, we challenged to observe directly the tribo-microplasma and to measure spectral characteristics of the emitted photons. In experiments to observe plasma image (with a diamond hemispherical pin sliding on a sapphire disk) it was found that the plasma was generated in the several micrometer gap of the sliding contact. The plasma had a shape of an ellipse with a tail, surrounding the contact and spread to the rear of the sliding contact. The plasma image observed through the UV transmittable filter (UV image) had a horseshoe pattern, while the IR image had a shape of a ring on the ellipse. The strongest UV emission was observed in the center of the horseshoe pattern outside the sliding contact, while the IR photon image showed that the most intense emission occurred at the sliding contact. The electrical discharge origin of the photon triboemission was proved by comparing spectra of tribophotons with spectra of photons emitted from plasma by electrical discharge in parallel electrodes in various gases. The results showed that the spectra of photons emitted from the sliding contact and those of gas-discharge completely coincided for all gases tested, i.e., dry air, N2,O2,H2, He, CH4,C2H4 and C3H8, except peaks originated from the excited atoms of the sliding surfaces. It was concluded that microplasma is produced by electrical breakdown of ambient gas at sliding contact. These results corroborate the tribomicroplasma concept.
Thèses sur le sujet "UV photons"
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Hunniford, C. A. « Ionization and fragmentation of biologically relevant molecules by low energy ions and UV photons ». Thesis, Queen's University Belfast, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.437413.
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Champion, Jason. « Photoevaporation des disques protoplanétaires par les photons UV d’étoiles massives proches : observation de proplyds et modélisation ». Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30392/document.
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Les disques protoplanétaires entourant les jeunes étoiles sont les embryons des systèmes planétaires. A différentes phases de leur évolution, ils peuvent subir d'importantes pertes de masse par photoévaporation : des photons énergétiques, issus de l'étoile centrale ou d'une étoile voisine, chauffe le disque qui perd en masse sous l'échappement des particules. Cependant, ce mécanisme et la physique sous-jacente n'ont que peu été contraints par les observations. Les objectifs de cette thèse sont d'étudier la photoévaporation dans le cas particulier où elle est due à des photons FUV, d'identifier les principaux paramètres physiques (densité, température) et processus (chauffage et refroidissement) impliqués, et d'estimer son impact sur l'évolution dynamique des disques. L'étude repose sur le couplage observations - modélisations des disques photoévaporés par les photons UV en provenance d'étoiles massives proches. Ces objets, appelés "proplyds", ont leur disque entouré d'une large enveloppe nourrie des flots de photoévaporation. A l'aide d'un modèle 1D d'une région de photodissociation, j'ai développé un modèle pour l'émission dans l'infrarouge lointain des proplyds. Ce modèle a été utilisé pour interpréter les observations, issues principalement de Herschel, pour quatre proplyds. Il apparait que les conditions physiques en surface de leur disque sont similaires: une densité de l'ordre de 10 6 par cm cube et une température d'environ 1000 K. Cette température est maintenue par un équilibre dynamique : si la surface se refroidit, la perte de masse diminue et l'enveloppe se réduit. L'atténuation UV produite par l'enveloppe diminue alors et le disque, recevant plus de photons UV, chauffe. La majorité du disque peut s'échapper sous forme de flots de photoévaporation avec des taux de perte de masse de quelques 10 -7 masse solaire par an ou plus, en accord avec les observations précédentes des traceurs du gaz ionisé. A la suite de ce travail, j'ai développé un modèle hydrodynamique 1D pour étudier l'évolution dynamique d'un disque en photoévaporation par un champ de rayonnement externe. [...]Protoplanetary disks are found around young stars, and represent the embryonic stage of planetary systems. At different phases of their evolution, disks may undergo substantial mass-loss by photoevaporation: energetic photons from the central or a nearby star heat the disk, hence particles can escape the gravitational potential and the disk loses mass. However, this mechanism, and the underlying physics regulating photoevaporation, have not been well constrained by observations so far. The aims of this thesis are to study photoevaporation, in the specific case when it is driven by far-UV photons, to identify the main physical parameters (density, temperature) and processes (gas heating and cooling mechanisms) that are involved, and to estimate its impact on the disk dynamical evolution. The study relies on coupling observations and models of disks being photoevaporated by UV photons coming from neighbouring massive star(s). Those objects, also known as "proplyds", appear as disks surrounded by a large cometary shaped envelope fed by the photoevaporation flows. Using a 1D code of the photodissociation region, I developed a model for the far-IR emission of proplyds. This model was used to interpret observations, mainly obtained with the Herschel Space Observatory, of four proplyds. We found similar physical conditions at their disk surface: a density of the order of 10 6 cm and a temperature about 1000 K. We found that this temperature is maintained by a dynamical equilibrium: if the disk surface cools, its mass-loss rate declines and the surrounding envelope is reduced. Consequently, the attenuation of the UV radiation field by the envelope decreases and the disk surface, receiving more UV photons, heats up. Most of the disk is thus able to escape through photoevaporation flows leading to mass-loss rates of the order of 10 -7 solar mass per year or more, in good agreement with earlier spectroscopic observations of ionised gas tracers. Following this work, I developed a 1D hydrodynamical code to study the dynamical evolution of an externally illuminated protoplanetary disk. [...]
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Lavigne, Claire. « Étude théorique et expérimentale de la propagation du rayonnement UV dans la basse atmosphère ». Rouen, 2001. http://www.theses.fr/2001ROUES042.
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Dans l'atmosphère, les sources ponctuelles sont entourées d'un halo dû à la diffusion par les particules et les molécules. Sous certaines conditions météorologiques, le champ de luminance provenant de ce halo peut devenir une part non négligeable du signal détecté par un instrument grand champ. Il apparaît donc nécessaire de le caractériser correctement. Dans ce cadre, nous avons développé un code de calcul basé sur une méthode Monte Carlo, permettant de modéliser la propagation du rayonnement UV issu d'une source ponctuelle. Une étude bibliographique sur les propriétés optiques et les statistiques de concentration des différentes espèces absorbant et diffusant dans le domaine spectral considéré a également été menée. Elle a permis de définir les données d'entrée du code. La validation du modèle mis au point a été effectuée par comparaison avec des expériences. En raison de la faiblesse des signaux à détecter, la technique de comptage de photons s'est avérée être la mieux adaptée. Afin de préparer la campagne de mesures de validation, un travail de caractérisation approfondi en laboratoire a été entrepris sur des photomultiplicateurs et un imageur à comptage de photons. Finalement, les résultats issus des expériences réalisées en extérieur et ceux provenant du code Monte Carlo ont été comparés et un très bon accord entre ces différentes données a pu être observé.
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Bouras, Karima. « Re-doped SnO2 oxides for efficient UV-Vis to infrared photon conversion : application to solar cells ». Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAD011/document.
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Ce travail a porté sur la synthèse et caractérisations structurales, optiques et électriques des films d’oxyde d'étain (SnOx) dopés avec des éléments de terres rares (RE: Néodyme, Praséodyme ou Ytterbium). L’objectif est de démontrer la conversion de photons UV voire Visible en photons rouges via ces films RE :SnOx, tout en conservant leurs propriétés d’oxydes transparents conducteurs. Les films ont été produits par des méthodes chimiques (sol-gel, précipitation) ou physiques (pulvérisation cathodique). Grâce à des analyses fines, nous avons pu corréler les propriétés structurales et de composition des couches RE :SnOx avec leurs propriétés d’émission de photons. Nous avons pu établir les conditions optimales de conversion photonique dans des systèmes à une seule ou double terre rare. Les mécanismes régissant le transfert dans ces films ont été avancés. Enfin, nous avons appliqué ces couches minces RE :SnOx optimisés sur des cellules solaires en silicium et en CIGS et nous avons montré une amélioration des paramètres photovoltaïques du dispositif ainsi qu’un net gain dans la réponse spectrale de la cellule dans l’UVSpectral conversion using lanthanide doped materials with excellent performances is a great challenging topic and of particular interest for photovoltaic. This work aims at functionalizing transparent conductive oxide materials with rare earth elements for photons conversion purpose without affecting transparency and transport properties of the TCO. The spectral conversion targeted in this thesis is of type “down”, in other words, we aim at converting high energy UV photons into low energy visible or NIR photons useful to solar cells. For this purpose we investigated the doping process of SnO2 as a host material with different rare earths such as Nd, Tb, Pr, and Yb. To understand the insertion process and the optical activation of the rare earth, RE-doped SnO2 nanoparticles (powders) have been synthesised by two chemical methods: co-precipitation and sol-gel. The results have shown an efficient insertion of the RE into the SnO2 structure with excellent emission properties. In view of application of RE-doped SnOx thin films to solar cells, studies concerning NIR emitting RE have been conducted (Nd, Yb, and co-doping with Yb and Nd) using sputtering. Several deposition parameters and post deposition treatments have been done in order to find the best chemical environment favourable to the RE emission. We have precisely identified the region of the UV light converted into NIR photons and proposed several energy transfer mechanisms occurring between the host SnOx and the REs. In case of co-doping, a second spectral conversion process has been identified; visible photons can be efficiently converted into NIR photons through energy transfer from Nd3+ to Yb3+ ions. Finally, application of these conversion layers to solar cells such as CIGS and Si based have shown an improvement of the cells characteristics, among others the Field factor, the cell efficiency and the increase of the spectral response of the cell in the UV region, thanks to the conversion of the UV photons into NIR photons. The good electrical properties of the RE-doped SnOx layers have been highlighted as well. We believe that these conversion layers will provide a step ahead towards better solar cells performances
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Torres, Díaz Daniela. « Non-thermal desorption from model molecular ices - towards quantitative astrochemical data ». Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASF068.
Texte intégralRésumé :
Cette thèse présente une étude expérimentale de la désorption non thermique de solides moléculaires physisorbés appelés glaces. La désorption non thermique est cruciale pour expliquer les abondances moléculaires en phase gaz observées dans divers environnements astrophysiques. Ce travail vise à mieux identifier les mécanismes directs et indirects de désorption induite par les photons UV et X et en contraindre les efficacités. Il implique donc l'étude de la désorption induite par les électrons. Sous irradiation UV, des électrons de basse énergie sont créés au sein de la glace par ionisation en couche de valence des systèmes. Sous irradiation X, des électrons plus énergétiques sont créés par la relaxation Auger des systèmes suite à leur excitation ou ionisation en couches de cœur. L'approche expérimentale vise à mieux comprendre le rôle des électrons secondaires dans la désorption en comparant quantitativement les désorptions induites par photons et par électrons.Les glaces moléculaires ont été condensées à des températures cryogéniques (15-100K) sous ultra-vide. Elles ont été irradiées pour induire la désorption à l'aide de photons UV ou X au synchrotron SOLEIL sur le dispositif expérimental SPICES (MONARIS), ou d'électrons sur le dispositif SOMO (ISMO). Les espèces neutres désorbées ont été analysées et quantifiées en temps réel par spectrométrie de masse. Les résidus irradiés ont été ensuite analysés, notamment par désorption thermique et par spectroscopies vibrationnelles. L'effet de plusieurs paramètres, tels que la morphologie de la glace, son épaisseur, l'énergie d'irradiation et la dose, a été étudié. Une intéressante complémentarité est obtenue entre des expériences exploratoires et flexibles sous irradiation d'électrons au laboratoire et celles menées au synchrotron.Deux systèmes modèles ont été étudiés en détail : l'acétonitrile et l'ammoniac. Pour l'acétonitrile, des expériences de désorption induite par électrons simulant les Auger de l'azote et du carbone ont permis d'observer la désorption de la molécule intacte, ainsi que divers produits d'irradiation, dont le méthane et le cyanure d'hydrogène. Les voies de formation possibles pour chaque produit sont discutées. Pour l'ammoniac, les expériences ont inclus des irradiations UV (5-12eV), par électrons de basse énergie (2-20eV), par rayons X au seuil de l'azote et par électrons de haute énergie (Auger de l'azote). Les rendements de désorption quantitatifs ont été déterminés pour l'ammoniac et l'azote moléculaire, principal produit observé dans tous les cas. Ces études reposent sur trois approches pour comprendre la désorption non thermique : i) la détermination des profondeurs pertinentes pour la désorption, ii) l'extraction de rendements quantitatifs et iii) la discussion des modèles cinétiques de désorption. Ces éléments permettent d'établir des comparaisons quantitatives entre les efficacités de désorption induite par photons et par électrons en molécules par particule incidente et en molécules par énergie déposée.Cette étude fournit des contraintes expérimentales pour les processus de désorption non thermique qui pourront alimenter les modèles chimiques des environnements astrophysiques. La détermination des rendements de désorption à différentes énergies de photons permet de calculer des rendements astrophysiques moyens pour un champ de rayonnement donné. L'identification et la quantification des produits d'irradiation contribuent à la compréhension de l'enrichissement chimique de la phase gazeuse. L'obtention par ce travail de valeurs en fonction de l'épaisseur montre l'existence de différents régimes où la désorption est dépendante ou non de l'épaisseur. Ces régimes varient en fonction du type et de l'énergie d'irradiation et doivent être intégrés dans les modèles. Des questions ouvertes subsistent concernant les contributions des processus de surface et de volume, ainsi que la dépendance des paramètres déterminés vis-à-vis de la composition de la glaceThis thesis presents an experimental investigation of non-thermal desorption from physisorbed molecular solids, also called ices. Non-thermal desorption processes are crucial in explaining the observed abundances of gaseous molecules in various astrophysical environments. This work aims to identify the direct and indirect desorption mechanisms and better constrain desorption efficiencies induced by UV and X-ray photons. Therefore, it also implies studying electron-induced desorption. Under UV irradiation, valence shell ionisation creates low-energy electrons in the ice. While under X-ray irradiation, more energetic electrons are produced by Auger relaxation of the systems following their core-shell excitation or ionisation. The experimental approach seeks to better understand the role of secondary electrons in desorption by quantitatively comparing photon- and electron-induced desorption yields.Molecular ices were grown at cryogenic temperatures (15-100 K) and under ultra-high vacuum conditions. The samples were irradiated to induce desorption with the monochromatic output of UV or X-ray synchrotron beamlines at the SOLEIL facility using the SPICES setup (MONARIS) or electrons in the SOMO setup (ISMO). The desorbing neutral species were analysed and quantified during irradiation using mass spectrometry. Various techniques were used to analyse the irradiated residues, including thermal desorption and vibrational spectroscopies. The effect of multiple parameters, such as ice morphology, thickness, irradiation energy, and dose, was studied. An interesting complementarity was obtained between the laboratory's exploratory and flexible electron irradiation experiments and those carried out at the synchrotron.Two model systems were studied in detail: acetonitrile and ammonia. For acetonitrile, electron-induced desorption experiments simulating nitrogen and carbon Auger electrons were performed. Desorption of the intact molecule was observed, as well as desorption of multiple irradiation products, including methane and hydrogen cyanide. The possible formation routes for each product are reviewed. For ammonia, experiments included UV (5-12 eV), low-energy electron (2-20 eV), X-ray (N 1s edge) and high-energy electron (nitrogen Auger) irradiation. Quantitative desorption yields were determined for ammonia and molecular nitrogen, the main product observed across all the irradiation conditions. These studies rely on three key aspects to understand non-thermal desorption: i) determining the desorption-relevant depths, ii) extracting quantitative yields, and iii) discussing kinetic models of desorption. These elements enable quantitative comparisons between photon- and electron-induced desorption efficiencies in terms of molecules per incident particle and molecules per deposited energy.This study provides experimental constraints for non-thermal desorption processes that can feed chemical models of astrophysical environments. The determination of desorption yields at different photon energies can be used to calculate average astrophysical yields according to the spectrum of a particular environment. Identifying and quantifying irradiation products is also essential for understanding gas-phase chemical enrichment. The thickness-dependent values obtained in this thesis show the existence of different regimes where desorption is dependent or independent of thickness. Said regimes depend on the irradiation type and energy considered and should be included in models. Open questions remain regarding the different contributions from surface and bulk processes and the dependence of the determined parameters on ice composition
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Helali, Sihem. « Application de la photocatalyse pour la dégradation des polluants chimiques et bactériologiques dans l'eau en utilisant des catalyseurs irradiés par des photons de lumière naturelle ou artificielle (UV‐A /UV‐B) ». Phd thesis, Université Claude Bernard - Lyon I, 2012. http://tel.archives-ouvertes.fr/tel-00876027.
Texte intégralRésumé :
La dégradation photocatalytique de deux amines, la méthylamine (MA) et la diméthylamine (DMA), a été étudiée en présence de TiO2 Degussa P25. Différents paramètres ont été étudiés: l'adsorption à l'obscurité et sous UV, la photolyse, les cinétiques de dégradation, l'effet du pH, l'effet de la nature et de l'intensité du flux photonique ainsi que les voies de dégradation de la MA et DMA.A l'obscurité, le taux de recouvrement des groupes OH est similaire pour la MA et DMA. Sous UV, ce taux devient deux fois plus élevé pour la MA. Les réactivités de MA et DMA sont directement corrélées à leur adsorption sous UV. Les atomes d'azote sont principalement décomposés en ammonium. Le nitrite a été également détecté, mais rapidement oxydé en nitrate. À pH basique, l'hydrolyse photo‐assisté et l'attaque de OH* sur l'atome N augmente. DMA est essentiellement transformé en MA. Les analyses du Carbone Organique Total (COT) montrent la présence de produits finaux contenant de l'azote difficilement minéralisables. Nous avons montré que, quelle que soit l'énergie des photons (UV‐A ou UV‐B), le rendement quantique reste constant et égal à 0,033.L'inactivation photocatalytique de E. coli en présence de la lumière solaire naturelle en absence (SODIS) et en présence de différents catalyseurs a été étudiée. L'effet de la température sur l'inactivation de E. coli a été aussi étudié. Les résultats ont montré que l'addition des différents types de catalyseurs accélère l'effet bactéricide du rayonnement solaire. Aucun phénomène de reviviscence bactérien n'a été observé après l'arrêt de l'exposition solaire durant au moins 72 heures. Seulement les ions ammonium et potassium ont été détectés au cours de l'inactivation de E. coli en accord avec la perforation de la membrane et l'oxydation des protéines.
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Helali, Sihem. « Application de la photocatalyse pour la dégradation des polluants chimiques et bactériologiques dans l’eau en utilisant des catalyseurs irradiés par des photons de lumière naturelle ou artificielle (UV‐A /UV‐B) ». Thesis, Lyon 1, 2012. http://www.theses.fr/2012LYO10316/document.
Texte intégralRésumé :
La dégradation photocatalytique de deux amines, la méthylamine (MA) et la diméthylamine (DMA), a été étudiée en présence de TiO2 Degussa P25. Différents paramètres ont été étudiés: l'adsorption à l’obscurité et sous UV, la photolyse, les cinétiques de dégradation, l'effet du pH, l'effet de la nature et de l'intensité du flux photonique ainsi que les voies de dégradation de la MA et DMA.A l’obscurité, le taux de recouvrement des groupes OH est similaire pour la MA et DMA. Sous UV, ce taux devient deux fois plus élevé pour la MA. Les réactivités de MA et DMA sont directement corrélées à leur adsorption sous UV. Les atomes d'azote sont principalement décomposés en ammonium. Le nitrite a été également détecté, mais rapidement oxydé en nitrate. À pH basique, l'hydrolyse photo‐assisté et l'attaque de OH• sur l’atome N augmente. DMA est essentiellement transformé en MA. Les analyses du Carbone Organique Total (COT) montrent la présence de produits finaux contenant de l’azote difficilement minéralisables. Nous avons montré que, quelle que soit l'énergie des photons (UV‐A ou UV‐B), le rendement quantique reste constant et égal à 0,033.L'inactivation photocatalytique de E. coli en présence de la lumière solaire naturelle en absence (SODIS) et en présence de différents catalyseurs a été étudiée. L'effet de la température sur l'inactivation de E. coli a été aussi étudié. Les résultats ont montré que l’addition des différents types de catalyseurs accélère l'effet bactéricide du rayonnement solaire. Aucun phénomène de reviviscence bactérien n’a été observé après l'arrêt de l'exposition solaire durant au moins 72 heures. Seulement les ions ammonium et potassium ont été détectés au cours de l'inactivation de E. coli en accord avec la perforation de la membrane et l’oxydation des protéinesThe photocatalytic degradation of two amino‐compounds, methylamine (MA) and dimethylamine (DMA) was investigated in the presence of UV‐irradiated TiO2 aqueous suspensions. Different parameters were studied: adsorption under dark and UV conditions, photolysis, kinetics of degradation, effect of pH, effect of the nature and intensities of photonic flux and finally the chemical pathway MA and DMA degradation.While, the percentage of covered OH in the dark was equal for MA and DMA, it becomes twice higher for MA under UV. The reactivity of MA and DMA is directly correlated with the adsorption under UV. The nitrogen atoms were decomposed mainly to ammonium. Nitrite was also formed but was rapidly oxidized to nitrate. At basic pH, photo assisted hydrolysis and the attack of OH• on N‐atom increase. DMA is mainly transformed to MA. Total Organic Carbon (TOC) analysis show the presence of final slightly mineralised intermediate compounds containing nitrogen atom. We shown that, whatever the energy of photons (UV‐A or UV‐B), the same quantum yield equal to 0.033 was obtained.The photocatalytic inactivation of E. coli under natural solar irradiation in the absence (SODIS) as well in the presence of different concentrations of varied photocatalysts has also been investigated. The effect of temperature on E. coli inactivation was studied. Results show that the additions of any types of catalyst to the water accelerate the bactericidal action of solar irradiation and leads to a total disinfection. No bacterial regrowth was observed during the subsequent dark period. Ammonium and potassium ions were formed during E. coli inactivation in agreement with the membrane perforation and the oxidation of proteins
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Bouvier, Stéphane. « Conception et mise au point d'un amplificateur integre rapide, a transimpedance, a faible bruit. Applicaiton a la detection de photons uv ». Université Louis Pasteur (Strasbourg) (1971-2008), 1993. http://www.theses.fr/1993STR13255.
Texte intégralRésumé :
Le travail accompli dans cette these porte sur la conception et la realisation d'un amplificateur a transimpedance associe a un detecteur de photo-electrons fonctionnant sur le principe de multiplication par avalanche. Les caracteristiques requises pour cette architecture sont les suivantes: mesures de courant, temps de montee inferieur a 15 nanosecondes, impedance d'entree de l'ordre de 100 ohms, gain de 100 millivolts par microampere, consommation inferieure a 100 milliwatts par canal et mise en forme du signal permettant la suppression de queue du signal ainsi que la compression de la dynamique. L'architecture globale comporte un preamplificateur faible bruit, a gain eleve, assurant la conversion courant tension, un etage de mise en forme, un etage tampon permettant la sortie differentielle sur 50 ohms et la compression dynamique. Un prototype a 4 voies, realise en technologie cmos, a confirme la validite de l'ensemble des concepts et des calculs developpes (fonctions de transfert, modeles de bruit)
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Denneval, Charline. « Design, synthèse et évaluation de contrastophores bimodaux pour l'imagerie par absorption à deux photons et par tomographie par émission de positons ». Thesis, Rouen, INSA, 2014. http://www.theses.fr/2014ISAM0012/document.
Texte intégralRésumé :
L’objectif de ce travail a porté sur l’élaboration d’une sonde bimodale ADP–TEP (absorption à deux photons–tomographie par emission de positons) pour des applications en imagerie médicale.Dans un premier temps, le projet a consisté en le design, la synthèse et l’évaluation des propriétés photophysiques d’une nouvelle série de chromophores diaziniques A–p–D (A : groupement électro-attracteur, p : lien conjugué, D : groupement électro-donneur). Des études de relation structure-propriétés photophysiques impliquant des modulations sur chacune des sous-structures (groupements A et D, lien p-conjugué) ont été réalisées puis étudiées en UV et en fluorescence. Suite à l’obtention de ces premiers résultats, des mesures d’absorption à deux photons ont été effectuées sur ces fluorophores.Dans un second temps, les fluorophores ont été modifiés afin de greffer des parties hydrophiles. Des propriétés photophysiques encourageantes ont été obtenues et des premiers tests en imagerie bi-photonique ont été réalisés.L’insertion du fluor radiomarqué est envisagée via l’insertion d’un groupement –BF2. Pour cela des structures chélatantes, « mimes de BODIPY », incorporant une pyrimidine ou un triazole ont été élaborées. Des premiers essais ont été conduits mais n’ont pas permis l’obtention des composés borés correspondantsThe purpose of this subject has been the synthesis of a bimodal probe using TPA–PET techniques for a potential application in biological imaging.In this context, we have synthesized a new range of A–π –D fluorophores incorporating diazine (p-deficient heterocycle) as electron-withdrawing moiety, N,N-dimethylaniline as electron-donating part and fluorene as p-conjugated linker. In order to increase the conjugation along the scaffold, ethynyl and/or triazole bridges have been introduced on both sides of the fluorene. The UV/Vis and photoluminescence properties have been measured. Further to those results two-photon absorption cross-section of our fluorophores (dTPA) has been obtained. Following these promising results, hydrophilic compounds using PEG groups have been prepared and photoluminescence properties have been carried out. In order to use the boron center as a site for radiofluorination, the synthesis of "BODIPY-like" probes has been considered. A new series of pyrimidine and triazole ligand have been synthesized but the corresponding boron complexes haven’t been obtained
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Tao, Zhi. « Photodétection dans une large gamme de longueur d’onde : phototransistor CdSe QDs/RGO sur des nanofils de ZnO dans la gamme UV-Vis, PbS QDs avec un transistor organique C60 de type N imprimé dans la gamme proche IR ». Thesis, Rennes 1, 2019. http://www.theses.fr/2019REN1S087.
Texte intégralRésumé :
La détection de lumière dans une large gamme de longueur d’onde allant de l’UV au proche infrarouge est réalisée avec une sensibilité importante en utilisant l’effet d’amplification amené par un transistor à effet de champ et la capacité de détection dans une grande gamme de longueur d’onde amenée par des nanoparticules de CdSe et de PbS de diamètres différents. Dans une première partie, un FET utilisant une couche active de nanofils de ZnO est fabriqué. La détection de lumière UV-Vis est assurée en enrobant ces nanofils par un mélange de nanoparticules de CdSe et d’oxyde de graphène. L’oxyde de graphène assure une bonne transition des électrons crées par la lumière dans le CdSe vers le ZnO. La photo-réponse obtenue, supérieure à 104 A/W à 350 nm, a été multipliée par un facteur 100 dans la gamme 200-500nm en utilisant l’oxyde de graphène. Dans une seconde partie, la détection de lumière infrarouge a été assurée par des nanoparticules de PbS incorporées dans un transistor organique de type N utilisant du C60 comme couche active. Les électrodes en argent de ce transistor et son isolant de grille en photorésine SU8 sont déposés par impression. Les nanoparticules sont déposées en solution à l’interface entre le semiconducteur et l’isolant de grille. Ce phototransistor incorporé dans un inverseur a montré l’apparition d’un signal de sortie de 2V dû à l’application d’une lumière de 1050 nm de longueur d’onde et de 250 µw/cm2 de puissanceDetection of light in large wavelength range, from the UV to NIR, is got with high sensitivity by using the amplification of a field effect transistor and the ability of light detection in large range by CdSe and PbS quantum dots with different diameters. In the first part, a FET with ZnO nanowires active layer is fabricated. The light detection in UV-Vis range is insured thanks to CdSe QDs/RGO (Reduced Graphene Oxide) fragments decorating the surface of the ZnO nanowires RGO insures good transfer of photo-electrons induced by the light into the CdSe QDs towards ZnO. The responsivity, higher than 104 A/W at 350 nm, has been improved by 100 in 200-500 nm range by using RGO. In the second part, IR light detection has been insured by using PbS QDs embedded in N-type Organic FET using C60 film as active layer. Silver electrodes of this transistor and its SU8 photoresist gate insulator have been printed. QDs have been deposited in solution at the interface between the semiconducting layer and the gate insulator. This phototransistor has been used in an inverter. The output voltage of the inverter change by 2V under lighting with 1050 nm wavelength and 250 µW/cm2 power
Livres sur le sujet "UV photons"
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Wright, A. G. The Photomultiplier Handbook. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780199565092.001.0001.
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This handbook is aimed at helping users of PMTs who are faced with the challenge of designing sensitive light detectors for scientific and industrial purposes. The raison d’être for photomultipliers (PMTs) stems from four intrinsic attributes: large detection area, high, and noiseless gain, and wide bandwidth. Detection involves a conversion process from photons to photoelectrons at the photocathode. Photoelectrons are subsequently collected and increased in number by the action of an incorporated electron multiplier. Photon detection, charge multiplication, and many PMT applications are statistical in nature. For this reason appropriate statistical treatments are provided and derived from first principles. PMTs are characterized by a range of photocathodes offering detection over UV to infra-red wavelengths, the sensitivities of which can be calibrated by National Laboratories. The optical interface between light sources and PMTs, particularly for diffuse or uncollimated light, is sparsely covered in the scientific literature. The theory of light guides, Winston cones, and other light concentrators points to means for optimizing light collection subject to the constraints of Liouville’s theorem (étandue). Certain PMTs can detect single photons but are restricted by the limitations of unwanted background ranging in magnitude from a fraction of a photoelectron equivalent to hundreds of photoelectrons. These sources, together with their correlated nature, are examined in detail. Photomultiplier biasing requires a voltage divider comprising a series of resistors or active components, such as FETs. Correct biasing provides the key to linear operation and so considerable attention is given to the treatment of this topic. Electronic circuits and modules that perform the functions of charge to voltage conversion, pulse shaping, and impedance matching are analysed in detail.
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Kawata, Satoshi, Gilles Lérondel et Yong-Hoon Cho. UV and Higher Energy Photonics : From Materials to Applications. SPIE, 2017.
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Kawata, Satoshi, Gilles Lérondel et Yong-Hoon Cho. UV and Higher Energy Photonics : From Materials to Applications 2017. SPIE, 2017.
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(Editor), I. I. Sobelman, et Vladimir A. Slemzin (Editor), dir. Current Russian Research in Optics & Photonics : New Methods & Instruments for Space & Earth Based Spectroscopy in Xuv, Uv, Ir< & Millimeter Waves (Proceedings ... Russian Research in Optics & Photonics). SPIE-International Society for Optical Engine, 1998.
Trouver le texte intégralChapitres de livres sur le sujet "UV photons"
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Yates, John T. « Photons (UV) ». Dans Experimental Innovations in Surface Science, 235–51. Cham : Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-17668-0_22.
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Schühle, Udo, et Jean-François Hochedez. « Solar-blind UV detectors based on wide band gap semiconductors ». Dans Observing Photons in Space, 467–77. New York, NY : Springer New York, 2013. http://dx.doi.org/10.1007/978-1-4614-7804-1_26.
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Parriani, Marco, Michele Alagia, Robert Richter, Stefano Stranges, Andrea Giustini, Simonetta Cavalli, Fernando Pirani et Franco Vecchiocattivi. « Fragmentation Dynamics of Astrochemical Molecules Induced by UV and EUV Photons ». Dans Computational Science and Its Applications – ICCSA 2023 Workshops, 693–704. Cham : Springer Nature Switzerland, 2023. http://dx.doi.org/10.1007/978-3-031-37108-0_44.
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Hoffmann, Michael R. « Possible Chemical Transformations in Snow and Ice Induced by Solar (UV PHOTONS) and Cosmic Irradiation (MUONS) ». Dans Chemical Exchange Between the Atmosphere and Polar Snow, 353–77. Berlin, Heidelberg : Springer Berlin Heidelberg, 1996. http://dx.doi.org/10.1007/978-3-642-61171-1_16.
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Li, Mo, Yuan Zhao et Jiansheng Yuan. « Relationship between Audible Noise and UV Photon Numbers ». Dans Lecture Notes in Electrical Engineering, 327–33. Berlin, Heidelberg : Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-26007-0_41.
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Iwayanagi, Takao, Takumi Ueno, Saburo Nonogaki, Hiroshi Ito et C. Grant Willson. « Materials and Processes for Deep-UV Lithography ». Dans Electronic and Photonic Applications of Polymers, 109–224. Washington, DC : American Chemical Society, 1988. http://dx.doi.org/10.1021/ba-1988-0218.ch003.
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Connerade, J. P. « Faraday Rotation in the UV/VUV and High Field Magneto-Optics ». Dans Polarized Electron/Polarized Photon Physics, 235–45. Boston, MA : Springer US, 1995. http://dx.doi.org/10.1007/978-1-4899-1418-7_18.
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Perkampus, H. H. « Photo-Akustik-Spektroskopie im UV-VIS-Spektralbereich ». Dans Analytiker-Taschenbuch, 93–134. Berlin, Heidelberg : Springer Berlin Heidelberg, 1985. http://dx.doi.org/10.1007/978-3-642-70026-2_4.
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Le, Hong Quang, et Soo Jin Chua. « Electrical Properties and UV Response of Single ZnO Nanorod ». Dans Semiconductor Photonics : Nano-Structured Materials and Devices, 192–95. Stafa : Trans Tech Publications Ltd., 2007. http://dx.doi.org/10.4028/0-87849-471-5.192.
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Mantelli, Andrea, Alessia Romani, Raffaella Suriano, Marinella Levi et Stefano Turri. « Additive Manufacturing of Recycled Composites ». Dans Systemic Circular Economy Solutions for Fiber Reinforced Composites, 141–66. Cham : Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-031-22352-5_8.
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AbstractAn additive remanufacturing process for mechanically recycled glass fibers and thermally recycled carbon fibers was developed. The main purpose was to demonstrate the feasibility of an additive remanufacturing process starting from recycled glass and carbon fibers to obtain a new photo- and thermally-curable composite. 3D printable and UV-curable inks were developed and characterized for new ad-hoc UV-assisted 3D printing apparatus. Rheological behavior was investigated and optimized considering the 3D printing process, the recyclate content, and the level of dispersion in the matrix. Some requirements for the new formulations were defined. Moreover, new printing apparatuses were designed and modified to improve the remanufacturing process. Different models and geometries were defined with different printable ink formulations to test material mechanical properties and overall process quality on the final pieces. To sum up, 3D printable inks with different percentages of recycled glass fiber and carbon fiber reinforced polymers were successfully 3D printed.
Actes de conférences sur le sujet "UV photons"
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Liu, Feng, James Farmer, Grahame Faulkner, Zhaoming Wang, Jianming Wang, Dominic O’Brien, Enyuan Xie et al. « 10 Mbit/s UV Solar-Blind OWC at 30 Photons per Bit ». Dans CLEO : Applications and Technology, JTu2A.85. Washington, D.C. : Optica Publishing Group, 2024. http://dx.doi.org/10.1364/cleo_at.2024.jtu2a.85.
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Goswami, Preetisha, Marta Gilaberte Basset, Jorge Fuenzalida, Markus Gräfe et Valerio Flavio Gili. « Non-degenerate correlated SPDC photon source for UV-A illumination ». Dans Quantum 2.0, QW3A.2. Washington, D.C. : Optica Publishing Group, 2024. http://dx.doi.org/10.1364/quantum.2024.qw3a.2.
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We present a correlated photon source consisting of a BBO nonlinear crystal that generates ultraviolet UV-A and infrared light via SPDC. Quantum imaging and sensing techniques can benefit from the correlations between the down-converted beams.
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Delmdahl, Ralph, et Rainer Paetzel. « Laser microprocessing powered by UV photons ». Dans ICALEO® 2010 : 29th International Congress on Laser Materials Processing, Laser Microprocessing and Nanomanufacturing. Laser Institute of America, 2010. http://dx.doi.org/10.2351/1.5061979.
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Haglund, Richard F., et Norman H. Tolk. « Laser-Synchrotron Studies of UV-Photon-Stimulated Desorption in Alkali Halide Crystals ». Dans Short Wavelength Coherent Radiation : Generation and Applications. Washington, D.C. : Optica Publishing Group, 1986. http://dx.doi.org/10.1364/swcr.1986.pd5.
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Desorption Induced by Electronic Transitions (DIET) is a primary mechanism through which energy deposited by electrons and photons in the surfaces of ionic insulators is dissipated.1 Studies of Photon-Stimulated Desorption (PSD) at ultraviolet wavelengths are important from a fundamental point of view because photons deposit energy but not free charge in dielectric materials. PSD also has practical consequences in problems as diverse as optical damage in high-power lasers, non-destructive surface analysis and uv photolithography.
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Nakayama, Keiji. « Triboplasma Generated Under Perfluoropolyether Oil Lubrication ». Dans ASME/STLE 2007 International Joint Tribology Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/ijtc2007-44467.
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In order to prove the triboplasma generation in the vicinity of the sliding contact under oil lubrication, two-dimensional images and energy spectra of the photons emitted from the sliding contact has been investigated under perfluoropolyether (PFPE) oil lubrication in a tribosystem of a diamond pin sliding on a sapphire disk in the atmospheric ambient air pressure and in vacuum. Two-dimensional image of the tribophoton clearly showed the plasma generation under PFPE oil lubrication. The UV photon energy spectrum and disappearance of the UV photon image in vacuum showed that the plasma is generated by air discharge even under oil lubrication.
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Weyl, Guy M. « Penetration of plasma radiation in tissue ». Dans OSA Annual Meeting. Washington, D.C. : Optica Publishing Group, 1988. http://dx.doi.org/10.1364/oam.1988.mr42.
Texte intégralRésumé :
Several applications of lasers in medicine, such as laser lithotripsy and plaque removal, involve formation of plasmas. These plasmas will radiate in the IR, visible, and UV. Possible deleterious effects of plasma radiation are tissue damage by heating and chemical changes induced by deposition of UV photons. Of particular concern is the possible mutagenic effects of UV photons that can penetrate the nucleus of cells and be absorbed there.
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Haglund, R. F., A. V. Barnes, N. Halas, M. H. Mendenhall et Norman H. Tolk. « Electronic transitions in photon-stimulated desorption ». Dans OSA Annual Meeting. Washington, D.C. : Optica Publishing Group, 1987. http://dx.doi.org/10.1364/oam.1987.thj3.
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The discovery that neutral excited-state atoms were desorbed by UV photons with orders of magnitude greater efficiency than ions from alkali-halide surfaces has wrought a fundamental change in our approach to the study of photon-surface interactions, both with synchrotron and laser light sources. In particular, laser-surface interactions in general and laser-induced material damage in particular—once considered primarily due to the absorption of thermal energy from the incident photons—now appear to be linked to electronic interactions both at the surface and in the near-surface bulk, even for photon energies below the bulk band gap. Thus it is appropriate to consider even laser-surface interactions as generically related to the process of desorption induced by electronic transitions (DIETs), a class of energy-surface interactions triggered in exemplary fashion by photons and electrons.
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Kung, Andrew H., E. Cromwell, T. Trickl et Y. T. Lee. « Ultrahigh resolution UV and VUV laser source ». Dans OSA Annual Meeting. Washington, D.C. : Optica Publishing Group, 1988. http://dx.doi.org/10.1364/oam.1988.mu2.
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Recent advances in high-power injection-seeded lasers, pulse amplified dye lasers, and four-wave mixing technologies make possible the development of high-power, broadly tunable, and ultranarrow sources in the UV, VUV, and XUV regions. By combining the latest technological advances in these areas we have developed a near-transform-limited laser source that tunes from 74 to 1000 nm with peak powers of >150 MW in the visible and >30 MW in the ultraviolet and has more than 1012 photons/s in the VUV-XUV region. The bandwidth in the XUV below 100 nm is mea sured to be 210 MHz. The spectral brightness of 1.5 × 1017 photons/s/0.1 % bandwidth of this tabletop laser source is several orders of magnitude higher than the best sources available today.
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Barulin, Aleksandr, Hyemi Park, Inki Kim et Byullee Park. « Simulation of metalens-based UV-visible photoacoustic imaging ». Dans Photons Plus Ultrasound : Imaging and Sensing 2024, sous la direction de Alexander A. Oraevsky et Lihong V. Wang. SPIE, 2024. http://dx.doi.org/10.1117/12.3001996.
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Bungay, Corey L., Thomas E. Tiwald et John A. Woollam. « Characterizing UV induced polymer degradation with spectroscopic ellipsometry ». Dans Optical Interference Coatings. Washington, D.C. : Optica Publishing Group, 1997. http://dx.doi.org/10.1364/oic.1998.tuf.5.
Texte intégralRésumé :
Polymers are susceptible to altered chemistry from UV radiation. The absorption of UV photons can promote breakage of important functional groups and structural bonds, such as C=C and C=O [1]. When an organic molecule absorbs UV radiation, it will be excited into higher energy states and possibly dissociate bonds. Dissociated radical species can then participate in additional reactions. Changes in chemistry may affect optical properties, which can have serious effects for polymers used in optical systems.
Rapports d'organisations sur le sujet "UV photons"
1
Asenath-Smith, Emily, Emma Ambrogi, Lee Moores, Stephen Newman et Jonathon Brame. Leveraging chemical actinometry and optical radiometry to reduce uncertainty in photochemical research. Engineer Research and Development Center (U.S.), septembre 2021. http://dx.doi.org/10.21079/11681/42080.
Texte intégralRésumé :
Subtle aspects of illumination sources and their characterization methods can introduce significant uncertainty into the data gathered from light-activated experiments, limiting their reproducibility and technology transition. Degradation kinetics of methyl orange (MO) and carbamazepine (CM) under illumination with TiO₂ were used as a case study for investigating the role of incident photon flux on photocatalytic degradation rates. Valerophenone and ferrioxalate actinometry were paired with optical radiometry in three different illumination systems: xenon arc (XE), tungsten halogen (W-H), and UV fluorescent (UV-F). Degradation rate constants for MO and CM varied similarly among the three light systems as k W-H < kiv-F < kXE, implying the same relative photon flux emission by each light. However, the apparent relative photon flux emitted by the different lights varied depending on the light characterization method. This discrepancy is shown to be caused by the spectral distribution present in light emission profiles, as well as absorption behavior of chemical actinometers and optical sensors. Data and calculations for the determination of photon flux from chemical and calibrated optical light characterization is presented, allowing us to interpret photo-degradation rate constants as a function of incident photon flux. This approach enabled the derivation of a calibrated ‘rate-flux’ metric for evaluating and translating data from photocatalysis studies.
2
Moores, Lee, Alan Kennedy, Lauren May, Shinita Jordan, Anthony Bednar, Stacy Jones, David Henderson, Luke Gurtowski et Kurt Gust. Identifying degradation products responsible for increased toxicity of UV-degraded insensitive munitions. Engineer Research and Development Center (U.S.), septembre 2021. http://dx.doi.org/10.21079/11681/42020.
Texte intégralRésumé :
Degradation of insensitive munitions (IMs) by ultraviolet (UV) light has become a concern following observations that some UV-degradation products have increased toxicity relative to parent compounds in aquatic organisms. This investigation focused on the Army's IM formulation, IMX-101, composed of three IM constituents: 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazol-5-one (NTO), and nitroguanidine (NQ). The IM constituents and IMX-101 were irradiated in a UV photo-reactor and then administered to Daphnia pulex in acute (48 h) exposures comparing toxicities relative to the parent materials. UV-degradation of DNAN had little effect on mortality whereas mortality for UV-degraded NTO and NQ increased by factors of 40.3 and 1240, making UV-degraded NQ the principle driver of toxicity when IMX-101 is UV-degraded. Toxicity investigations for specific products formed during UV-degradation of NQ, confirmed greater toxicity than the parent NQ for degradation products. Summation of the individual toxic units for the complete set of individually measured UV-degradation products identified for NQ only accounted for 25% of the overall toxicity measured in the exposures to the UV-degraded NQ product mixture. Given the underestimation of toxicity using the sum toxic units for the individually measured UV-degradation products of NQ, we conclude that: (1) other unidentified NQ degradation products contributed principally to toxicity and/or (2) synergistic toxicological interactions occurred among the NQ degradation product mixture that exacerbated toxicity.
3
Jiang, Hongxing, et Jingyu Lin. UV/Blue III-Nitride Micro-Cavity Photonic Devices. Fort Belvoir, VA : Defense Technical Information Center, mars 2002. http://dx.doi.org/10.21236/ada399578.
Texte intégral
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Jiang, Hongxing, et Jingyu Lin. UV/Blue III-Nitride Micro-Cavity Photonic Devices. Fort Belvoir, VA : Defense Technical Information Center, août 2001. http://dx.doi.org/10.21236/ada390015.
Texte intégral
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Jiang, Hongxing, et Jingyu Lin. UV/Blue III-Nitride Micro-Cavity Photonic Devices. Fort Belvoir, VA : Defense Technical Information Center, juillet 2001. http://dx.doi.org/10.21236/ada390174.
Texte intégral
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Becher, Julie, Samuel Beal, Susan Taylor, Katerina Dontsova et Dean Wilcox. Photo-transformation of aqueous nitroguanidine and 3-nitro-1,2,4-triazol-5-one : emerging munitions compounds. Engineer Research and Development Center (U.S.), août 2021. http://dx.doi.org/10.21079/11681/41743.
Texte intégralRésumé :
Two major components of insensitive munition formulations, nitroguanidine (NQ) and 3-nitro-1,2,4-triazol-5-one (NTO), are highly water soluble and therefore likely to photo-transform while in solution in the environment. The ecotoxicities of NQ and NTO solutions are known to increase with UV exposure, but a detailed accounting of aqueous degradation rates, products, and pathways under different exposure wavelengths is currently lacking. We irradiated aqueous solutions of NQ and NTO over a 32-h period at three ultraviolet wavelengths and analyzed their degradation rates and transformation products. NQ was completely degraded by 30 min at 254 nm and by 4 h at 300 nm, but it was only 10% degraded after 32 h at 350 nm. Mass recoveries of NQ and its transformation products were >80% for all three wavelengths. NTO degradation was greatest at 300 nm with 3% remaining after 32 h, followed by 254 nm (7% remaining) and 350 nm (20% remaining). Mass recoveries of NTO and its transformation products were high for the first 8 h but decreased to 22–48% by 32 h. Environmental half-lives of NQ and NTO in pure water were estimated as 4 and 6 days, respectively. We propose photo-degradation pathways for NQ and NTO supported by observed and quantified degradation products and changes in solution pH.
7
Christopher, David A., et Avihai Danon. Plant Adaptation to Light Stress : Genetic Regulatory Mechanisms. United States Department of Agriculture, mai 2004. http://dx.doi.org/10.32747/2004.7586534.bard.
Texte intégralRésumé :
Original Objectives: 1. Purify and biochemically characterize RB60 orthologs in higher plant chloroplasts; 2. Clone the gene(s) encoding plant RB60 orthologs and determine their structure and expression; 3. Manipulate the expression of RB60; 4. Assay the effects of altered RB60 expression on thylakoid biogenesis and photosynthetic function in plants exposed to different light conditions. In addition, we also examined the gene structure and expression of RB60 orthologs in the non-vascular plant, Physcomitrella patens and cloned the poly(A)-binding protein orthologue (43 kDa RB47-like protein). This protein is believed to a partner that interacts with RB60 to bind to the psbA5' UTR. Thus, to obtain a comprehensive view of RB60 function requires analysis of its biochemical partners such as RB43. Background & Achievements: High levels of sunlight reduce photosynthesis in plants by damaging the photo system II reaction center (PSII) subunits, such as D1 (encoded by the chloroplast tpsbAgene). When the rate of D1 synthesis is less than the rate of photo damage, photo inhibition occurs and plant growth is decreased. Plants use light-activated translation and enhanced psbAmRNA stability to maintain D1 synthesis and replace the photo damaged 01. Despite the importance to photosynthetic capacity, these mechanisms are poorly understood in plants. One intriguing model derived from the algal chloroplast system, Chlamydomonas, implicates the role of three proteins (RB60, RB47, RB38) that bind to the psbAmRNA 5' untranslated leader (5' UTR) in the light to activate translation or enhance mRNA stability. RB60 is the key enzyme, protein D1sulfide isomerase (Pill), that regulates the psbA-RN :Binding proteins (RB's) by way of light-mediated redox potentials generated by the photosystems. However, proteins with these functions have not been described from higher plants. We provided compelling evidence for the existence of RB60, RB47 and RB38 orthologs in the vascular plant, Arabidopsis. Using gel mobility shift, Rnase protection and UV-crosslinking assays, we have shown that a dithiol redox mechanism which resembles a Pill (RB60) activity regulates the interaction of 43- and 30-kDa proteins with a thermolabile stem-loop in the 5' UTR of the psbAmRNA from Arabidopsis. We discovered, in Arabidopsis, the PD1 gene family consists of II members that differ in polypeptide length from 361 to 566 amino acids, presence of signal peptides, KDEL motifs, and the number and positions of thioredoxin domains. PD1's catalyze the reversible formation an disomerization of disulfide bonds necessary for the proper folding, assembly, activity, and secretion of numerous enzymes and structural proteins. PD1's have also evolved novel cellular redox functions, as single enzymes and as subunits of protein complexes in organelles. We provide evidence that at least one Pill is localized to the chloroplast. We have used PDI-specific polyclonal and monoclonal antisera to characterize the PD1 (55 kDa) in the chloroplast that is unevenly distributed between the stroma and pellet (containing membranes, DNA, polysomes, starch), being three-fold more abundant in the pellet phase. PD1-55 levels increase with light intensity and it assembles into a high molecular weight complex of ~230 kDa as determined on native blue gels. In vitro translation of all 11 different Pill's followed by microsomal membrane processing reactions were used to differentiate among PD1's localized in the endoplasmic reticulum or other organelles. These results will provide.1e insights into redox regulatory mechanisms involved in adaptation of the photosynthetic apparatus to light stress. Elucidating the genetic mechanisms and factors regulating chloroplast photosynthetic genes is important for developing strategies to improve photosynthetic efficiency, crop productivity and adaptation to high light environments.