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Kontos, Antonios, i Rainer Weiss. "Photon emission spectrum of ion pumps". Review of Scientific Instruments 94, nr 3 (1.03.2023): 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 i A. B. Rubin. "Photochemical processes to cellular DNA damage by UV radiation of different wavelengths: biological consequences". Молекулярная биология 58, nr 1 (15.02.2024): 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 i 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 (12.06.2024): 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 i 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, nr 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 i 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 i Guangtao Ying. "Imaging of Cellular Dynamics by Two-Photon Excitation Microscopy". Microscopy and Microanalysis 1, nr 1 (luty 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 i Y.-J. Chen. "Photon-induced desorption of larger species in UV-irradiated methane ice". Monthly Notices of the Royal Astronomical Society 493, nr 1 (19.02.2020): 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, i Hilal Tahirli Tarana Aghadiyeva. "IRRADIATION OF CARBON DIOXIDE WITH A VACUUM UV SOURCE AND OBTAINING OF STRATOSPHERIC OZONE". ETM - Equipment, Technologies, Materials 13, nr 01 (7.02.2023): 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, nr 07 (1.07.2023): 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, i Roman A. Nevshupa. "Characteristics and Pattern of Plasma Generated at Sliding Contact". Journal of Tribology 125, nr 4 (25.09.2003): 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.
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Rai, Neha, Luis Orlando Morales i Pedro José Aphalo. "Perception of solar UV radiation by plants: photoreceptors and mechanisms". Plant Physiology 186, nr 3 (7.04.2021): 1382–96. http://dx.doi.org/10.1093/plphys/kiab162.
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Abstract About 95% of the ultraviolet (UV) photons reaching the Earth’s surface are UV-A (315–400 nm) photons. Plant responses to UV-A radiation have been less frequently studied than those to UV-B (280–315 nm) radiation. Most previous studies on UV-A radiation have used an unrealistic balance between UV-A, UV-B, and photosynthetically active radiation (PAR). Consequently, results from these studies are difficult to interpret from an ecological perspective, leaving an important gap in our understanding of the perception of solar UV radiation by plants. Previously, it was assumed UV-A/blue photoreceptors, cryptochromes and phototropins mediated photomorphogenic responses to UV-A radiation and “UV-B photoreceptor” UV RESISTANCE LOCUS 8 (UVR8) to UV-B radiation. However, our understanding of how UV-A radiation is perceived by plants has recently improved. Experiments using a realistic balance between UV-B, UV-A, and PAR have demonstrated that UVR8 can play a major role in the perception of both UV-B and short-wavelength UV-A (UV-Asw, 315 to ∼350 nm) radiation. These experiments also showed that UVR8 and cryptochromes jointly regulate gene expression through interactions that alter the relative sensitivity to UV-B, UV-A, and blue wavelengths. Negative feedback loops on the action of these photoreceptors can arise from gene expression, signaling crosstalk, and absorption of UV photons by phenolic metabolites. These interactions explain why exposure to blue light modulates photomorphogenic responses to UV-B and UV-Asw radiation. Future studies will need to distinguish between short and long wavelengths of UV-A radiation and to consider UVR8’s role as a UV-B/UV-Asw photoreceptor in sunlight.
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Nanayakkara, Themiya. "A VLT/MUSE analysis of HeIIλ1640 emitters at z = 2 – 4". Proceedings of the International Astronomical Union 15, S352 (czerwiec 2019): 78. http://dx.doi.org/10.1017/s1743921320001143.
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AbstractIn the quest to study early star-formation physics in the universe, one of the most sought after tracers is HeIIλ1640, with its presence in the lack of other metal emission/absorption lines generally being interpreted as evidence for metal-poor stellar populations. HeII ionizing photons are produced via sources of hard ionizing radiation and requires photons with energies ⩾ 54.4eV, however, traditional stellar population models lack sufficient ionising photons to match with current observations. Our analysis of z = 2 – 4 HeIIλ1640 emitters from deep 10-30h pointings from MUSE has shown that ISM properties inferred from multiple rest-UV diagnostics are not compatible with requirements necessary to reproduce HeIIλ1640 equivalent-widths. Thus, we have used latest generation of single, rotational, and binary stellar population models with realistic dust physics to explore rest-UV emission line diagnostics and link with H and He+ ionisation photon production efficiencies (ξion (H,He+)) in a variety of stellar/gas metallicities and star-formation histories. I will discus our latest results and show that including ‘exotic’ stellar phenomena such as extreme low-metallicity binary stars, X-ray binaries, and dust dissociation physics may be necessary to lessen the tension between models and observations.
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Henningsen, F., N. Braam i M. Danninger. "Picosecond and high-power UV/Vis light pulsing using gallium nitride field-effect transistors: implementation and design evaluation". Journal of Instrumentation 18, nr 10 (1.10.2023): P10010. http://dx.doi.org/10.1088/1748-0221/18/10/p10010.
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Abstract This paper discusses the development of cost-effective and high-performance picosecond and high-power light pulsers. The use of innovative gallium nitride field-effect transistor technology, in combination with meticulous electronic design and careful selection of light-emitting diodes or laser diodes for ultraviolet and visible spectral ranges, has resulted in superior characteristics compared to commonly used designs. The sub-ns design achieves pulse widths as low as 300 ps, with photon outputs ranging between 104-109 photons per pulse, over a wavelength range of 235-470 nm. Meanwhile, the high-power design achieves pulse widths as low as 1.8 ns, with photon outputs ranging between 107-1011 photons per pulse, and a wavelength range of 375-525 nm. The two designs complement each other in photon outputs, covering a dynamic range of almost ten orders of magnitude. This paper provides an evaluation of the electrical design and emitter selection of both pulsers, as well as their electrical and optical performance.
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Zeng, Si-Qi, K. C. Chuang, Ashish Kumar i Wen-Hsi Lee. "Influence of Plasma Ultraviolet/Vacuum Ultraviolet Irradiation Damage on Silicon Metal-Oxide-Semiconductor Capacitor During Etching". Journal of Nanoscience and Nanotechnology 21, nr 4 (1.04.2021): 2163–73. http://dx.doi.org/10.1166/jnn.2021.19067.
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In this study, we evaluate the defects and charges caused by the ultraviolet (UV)/vacuum ultraviolet (VUV) irradiation in the high-k/metal gate stack structure, especially in HfO2 layer and at Si/HfO2 interface. First, we measured the photons irradiating to the surface in the neutral beam etching (NBE) system and in the conventional inductively coupled plasma (ICP) system through optical emission spectroscopy (OES), respectively. By using this method, we evaluate the ability of reducing UV/VUV irradiation damage in the NBE system. As a result, photon intensity detected in the ICP system shows larger magnitude as compared to the NBE system, which indicates the UV/VUV irradiation is more severe in the ICP system. Moreover, in order to understand the twisting of electrical characteristics caused by UV/VUV irradiation, we set the prefabricated metal-oxide-semiconductor (MOS) capacitors in both systems to absorb the irradiation of UV/VUV photons respectively. The electrical characteristics of the etched MOS capacitors and its related plasma-induced damage model are discussed. The result of the devices exposed in the ICP system reveals a greater electrical characteristics shift compared to the devices in NBE such as the interface trap density (Dit) in case of NBE is 3.55621×1012 cm-2eV-1 and in case of ICP is higher i.e., 4.19961×1012 cm-2eV-1.
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Moisan, Michel, Jean Barbeau, Marie-Charlotte Crevier, Jacques Pelletier, Nicolas Philip i Bachir Saoudi. "Plasma sterilization. Methods and mechanisms". Pure and Applied Chemistry 74, nr 3 (1.01.2002): 349–58. http://dx.doi.org/10.1351/pac200274030349.
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Utilizing a plasma to achieve sterilization is a possible alternative to conventional sterilization means as far as sterilization of heat-sensitive materials and innocuity of sterilizing agents are concerned. A major issue of plasma sterilization is the respective roles of ultraviolet (UV) photons and reactive species such as atomic and molecular radicals. At reduced gas pressure (£10 torr) and in mixtures containing oxygen, the UV photons dominate the inactivation process, with a significant contribution of oxygen atoms as an erosion agent. Actually, as erosion of the spore progresses, the number of UV photons successfully interacting with the genetic material increases. The different physicochemical processes at play during plasma sterilization are identified and analyzed, based on the specific characteristics of the spore survival curves.
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Liu, Jiaxin, Shalong Wang, Kai Liu, Liqun Ming, Yousheng Zou, Zhengfeng Zhu, Yuhang Dong i in. "Highly sensitive detection and imaging of ultraviolet-B light for precisely controlling vitamin D generation in the human body". Journal of Materials Chemistry C 7, nr 15 (2019): 4503–8. http://dx.doi.org/10.1039/c9tc00479c.
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A highly sensitive photodetector with selective response to UV-B photons in air is firstly demonstrated in this work. The quite low noise current of ∼2 × 10−14 A Hz−1/2 allows an accurate detection of UV-B photons of 31.8 nW cm−2 intensity with detectivity of >4 × 1014 Jones. All the figures of merit in our PDs show promising potential in quantitative detection of UV-B for precisely controlling vitamin D generation.
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Ershov, K. S., S. V. Valiulin i A. P. Pyryaeva. "Inglet oxygen generaion via silver nanoparticles UV-photoexcitation". Химическая физика 43, nr 2 (15.02.2024): 103–11. http://dx.doi.org/10.31857/s0207401x24020114.
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The NIR-luminescence of suspension of silver nanoparticles stabilized in distilled water has been investigated by photoexcitation of surface plasmon resonance (SPR). The observed short-living luminescence with the spectral maximum at 1300 nm is attributed to the singlet oxugen molecules luminescence. The singlet oxygen generation is assumed to pass in two stages as a result of three-photon process. First the one-photon SPR excitation of silver nanoparticle is occurred and leads to superoxide oxygen generation on the nanoparticle surface. Next the superoxide anion absorbs two more photons of the same laser pulse resulting in electron photodetachment with singlet oxygen formation. During a long period of UV-irradiation the studying suspension ceases to be photostable and sedimentation occurs. The sedimentation may be related to disturbance of nanoparticles steric stability resulting in more efficient superoxide anion adsorption on nanoparticles surface with silver oxide formation.
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Michaelian, Karo. "The Pigment World: Life’s Origins as Photon-Dissipating Pigments". Life 14, nr 7 (22.07.2024): 912. http://dx.doi.org/10.3390/life14070912.
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Many of the fundamental molecules of life share extraordinary pigment-like optical properties in the long-wavelength UV-C spectral region. These include strong photon absorption and rapid (sub-pico-second) dissipation of the induced electronic excitation energy into heat through peaked conical intersections. These properties have been attributed to a “natural selection” of molecules resistant to the dangerous UV-C light incident on Earth’s surface during the Archean. In contrast, the “thermodynamic dissipation theory for the origin of life” argues that, far from being detrimental, UV-C light was, in fact, the thermodynamic potential driving the dissipative structuring of life at its origin. The optical properties were thus the thermodynamic “design goals” of microscopic dissipative structuring of organic UV-C pigments, today known as the “fundamental molecules of life”, from common precursors under this light. This “UV-C Pigment World” evolved towards greater solar photon dissipation through more complex dissipative structuring pathways, eventually producing visible pigments to dissipate less energetic, but higher intensity, visible photons up to wavelengths of the “red edge”. The propagation and dispersal of organic pigments, catalyzed by animals, and their coupling with abiotic dissipative processes, such as the water cycle, culminated in the apex photon dissipative structure, today’s biosphere.
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Bulak, M., D. M. Paardekooper, G. Fedoseev i H. Linnartz. "Novel approach to distinguish between vacuum UV-induced ice photodesorption and photoconversion". Astronomy & Astrophysics 636 (kwiecień 2020): A32. http://dx.doi.org/10.1051/0004-6361/201937298.
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Context. In cold regions of the interstellar medium with intense ultraviolet radiation fields, photodesorption has been suggested as a nonthermal desorption mechanism promoting the transition of molecules from the solid state to the gas phase. Laboratory experiments measuring photodesorption rates are crucial in attempting to explain high molecular gas phase abundances of species that are expected to form in the solid state, such as methane, methanol, and acetonitrile, and to aid astrochemical modeling. Due to the convoluted competition between photodesorption and photoconversion, it is far from trivial to derive accurate photodesorption rates. Aims. The aim of this study is to apply a new methodology to discriminate between the two processes. The method has been validated using the well-studied case of CO and extended to CH4, CH3OH, and CH3CN. Methods. Vacuum ultraviolet (VUV; photon energy of 7–10.2 eV) irradiated ices at 20 K are studied, first as a pure CH4, CH3OH, or CH3CN ice and subsequently with an Ar coating on top. The latter is transparent to the VUV photons (wavelength below 200 nm), but it quenches the photodesorption process. Comparing the laser desorption post ionization time-of-flight mass spectrometry of the ices with and without the Ar coating provides information on the different interactions of the VUV photons with the ice. Results. The newly developed experimental technique allowed for a derivation of photodesorption rates for ices at 20 K of: CO (3.1 ± 0.3)×10−3 mol. photon−1, CH4 (3.1 ± 0.5)×10−2 mol. photon−1, and upper limits for CH3OH (< 6 × 10−5 mol. photon−1) and CH3CN (< 7.4 × 10−4 mol. photon−1); in the latter case, no literature values have been reported yet. The newly introduced approach provides more insight into the photodesorption process, in particular, for commonly observed complex organic molecules (COMs). Photoconversion cross sections are presented in the 7–10.2 eV range. The possible role of photodesorption and photoconversion in the formation of interstellar COMs is discussed.
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Liu, Pujun, Jie Liu, Xiao Zheng, Hongde Luo, Xiaoqing Li, Zhiling Yao, Xibin Yu, Xiumeng Shi, Binghu Hou i Yusheng Xia. "An efficient light converter YAB:Cr3+,Yb3+/Nd3+ with broadband excitation and strong NIR emission for harvesting c-Si-based solar cells". J. Mater. Chem. C 2, nr 29 (2014): 5769–77. http://dx.doi.org/10.1039/c4tc00482e.
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The Cr3+–Yb3+ co-doped YAB could convert almost high-energy UV-Vis photons into low-energy NIR photons efficiently, which benefits the enhancement of silicon solar photovoltaic conversion efficiency.
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Rodriguez Pinilla, Omar, i Wilmar Hernández. "Generation of UV Photons Produced by Lightning in Vacuum Conditions:". European Journal of Engineering Research and Science 4, nr 9 (16.09.2019): 78–80. http://dx.doi.org/10.24018/ejers.2019.4.9.1400.
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In the following work, a theoretical proposal is presented on the mechanism of generation UV photons produced by lightning in vacuum conditions under anisotropic medium (gas) using the quantum model of near field electrodynamics through paths integrals. The aim is calculate and sensing the number of photons that can generate a lightning discharge under a voltage of 2000 volts AC in t seconds
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Rodriguez Pinilla, Omar, i Wilmar Hernández. "Generation of UV Photons Produced by Lightning in Vacuum Conditions:". European Journal of Engineering and Technology Research 4, nr 9 (16.09.2019): 78–80. http://dx.doi.org/10.24018/ejeng.2019.4.9.1400.
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In the following work, a theoretical proposal is presented on the mechanism of generation UV photons produced by lightning in vacuum conditions under anisotropic medium (gas) using the quantum model of near field electrodynamics through paths integrals. The aim is calculate and sensing the number of photons that can generate a lightning discharge under a voltage of 2000 volts AC in t seconds
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Ning, Yuanhang, Zheng Cai, Linhua Jiang, Xiaojing Lin, Shuqi Fu i Daniele Spinoso. "An Hα Impression of Lyα Galaxies at z ≃ 6 with Deep JWST/NIRCam Imaging". Astrophysical Journal Letters 944, nr 1 (1.02.2023): L1. http://dx.doi.org/10.3847/2041-8213/acb26b.
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Abstract We present a study of seven spectroscopically confirmed (Lyα-emitting) galaxies at redshift z ≃ 6 using the JWST/NIRCam imaging data. These galaxies, with a wide range of Lyα luminosities, were recently observed in a series of NIRCam broad and medium bands. We constrain the rest-frame UV/optical continua and measure the Hα line emission of the galaxies using the combination of JWST/NIRCam and archival HST/WFC3 infrared photometry. We further estimate the escape fractions of their Lyα photons ( f esc Ly α ) and the production efficiency of ionizing photons (ξ ion). Among the sample, six out of seven galaxies have Lyα escape fractions of ≲10%, which might be the status for most of the star-forming galaxies at z ≃ 6. One UV-faint Lyα galaxy with an extremely blue UV slope has a large value of f esc Ly α reaching ≃50%. These galaxies have a broad range of ξ ion over log10 ξ ion,0 (Hz erg−1) ∼ 25.0–26.5. We find that UV-fainter galaxies with bluer UV-continuum slopes likely have higher escape fractions of Lyα photons. We also find that galaxies with higher Lyα line emission tend to produce ionizing photons more efficiently. The most Lyα-luminous galaxy in the sample has a very high ξ ion,0 of log10 ξ ion,0 (Hz erg−1) > 26. Our results support the scenario that Lyα galaxies may have served as an important contributor to cosmic reionization. Blue and bright Lyα galaxies are excellent targets for JWST follow-up spectroscopic observations.
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Boukhicha, Mohamed, Thomas Y. Tsang, Gabriele Giacomini, Amir M. Dabiran i Luca Cultrera. "UV hybrid photon detector based on GaN photocathodes and Si low gain avalanche diode". Journal of Instrumentation 19, nr 07 (1.07.2024): P07020. http://dx.doi.org/10.1088/1748-0221/19/07/p07020.
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Abstract Photon detectors featuring single-photon sensitivity play a crucial role in various scientific domains, including high-energy physics, astronomy, and quantum optics. Fast response time, high quantum efficiency, and minimal dark counts are the characteristics that render them ideal candidates for detecting individual photons with exceptional signal-to-noise ratios, at frequencies in the range of hundreds of MHz. Here, we report on our first design and operational results on a Hybrid Photon Detector (HPD) that combines the high quantum efficiency of a Gallium Nitride (GaN) photocathode and the low noise characteristics of a Si-based Low-Gain Avalanche Diode (LGAD). This hybrid detection scheme has the potential to reach single-photon detection sensitivity with high quantum efficiency, low noise levels and capable of operating at hundreds of MHz repetition rates.
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Jimenéz-Vivanco, María R., Godofredo García, Jesús Carrillo, Francisco Morales-Morales, Antonio Coyopol, Miguel Gracia, Rafael Doti, Jocelyn Faubert i J. Eduardo Lugo. "Porous Si-SiO2 UV Microcavities to Modulate the Responsivity of a Broadband Photodetector". Nanomaterials 10, nr 2 (28.01.2020): 222. http://dx.doi.org/10.3390/nano10020222.
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Porous Si-SiO2 UV microcavities are used to modulate a broad responsivity photodetector (GVGR-T10GD) with a detection range from 300 to 510 nm. The UV microcavity filters modified the responsivity at short wavelengths, while in the visible range the filters only attenuated the responsivity. All microcavities had a localized mode close to 360 nm in the UV-A range, and this meant that porous Si-SiO2 filters cut off the photodetection range of the photodetector from 300 to 350 nm, where microcavities showed low transmission. In the short-wavelength range, the photons were absorbed and did not contribute to the photocurrent. Therefore, the density of recombination centers was very high, and the photodetector sensitivity with a filter was lower than the photodetector without a filter. The maximum transmission measured at the localized mode (between 356 and 364 nm) was dominant in the UV-A range and enabled the flow of high energy photons. Moreover, the filters favored light transmission with a wavelength from 390 nm to 510 nm, where photons contributed to the photocurrent. Our filters made the photodetector more selective inside the specific UV range of wavelengths. This was a novel result to the best of our knowledge.
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Kalita, B. I., L. M. Karatayeva i M. O. Melnyk. "Detection the wave processes in atmosphere on the basis of ultraviolet supervision". Information extraction and processing 2017, nr 45 (26.12.2017): 77–82. http://dx.doi.org/10.15407/vidbir2017.45.077.
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It is proved that the electromagnetic ultraviolet radiation, penetrating through an atmosphere, can be recorded by the analysis of the direction, spatial form and the period of change of acoustogravitational waves. An ultraviolet radiation is partly dissipated into acousto-gravitational waves and its intensity acquires a time profile that coincides with the form of acousto-gravitational waves. The ultraviolet radiation fluxes are sensitive to the dynamics of wave processes in the atmosphere. Based on supervision the ultraviolet using the multichannel concentrator allow one to set the direction, spatial form and period of change of acousto-gravitational waves. Based on the supervision of the ultraviolet (UV) using the multichannel concentrator one can set the direction, spatial form and period of change of acousto-gravitational waves. The purpose of the research is to investigate the relation between UV photons in the range from 200 to 400 nm, solar activity, and processes in the atmosphere. Experiments showed that maximum daily variations of UV photons values in the range from 200 to 400 nm are out of phase with solar activity. One can suppose that a part of UV photons are the result of interaction of the galactic cosmic rays with atmosphere.
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Royon, Maxime, Francis Vocanson, Damien Jamon, Emmanuel Marin, Adriana Morana, Aziz Boukenter, Sylvain Girard, Youcef Ouerdane, François Royer i Yves Jourlin. "Comparison between the UV and X-ray Photosensitivities of Hybrid TiO2-SiO2 Thin Layers". Materials 13, nr 17 (24.08.2020): 3730. http://dx.doi.org/10.3390/ma13173730.
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The photo-induced effects on sol–gel-based organo TiO2-SiO2 thin layers deposited by the dip-coating technique have been investigated using two very different light sources: A light-emitting diode (LED) emitting in the UV (at 365 nm, 3.4 eV) and an X-ray tube producing 40 keV mean-energy photons. The impact of adding a photo-initiator (2,2-dimethoxy-2-phenylacetophenone-DMPA) on the sol–gel photosensitivity is characterized namely in terms of the photo-induced refractive index measured through M-line spectroscopy. Results show that both silica-titania sol–gel films with or without the photo-initiator are photosensitive to both photon sources. The induced refractive index values reveal several features where slightly higher refractive indexes are obtained for the sol–gel containing the photo-initiator. UV and X-ray-induced polymerization degrees are discussed using Fourier-transform infrared (FTIR) spectroscopy where the densification of hybrid TiO2-SiO2 layers is related to the consumption of the CH=C groups and to the decomposition of Si-OH and Si-O-CH3 bonds. X-rays are more efficient at densifying the TiO2-SiO2 inorganic and organic network with respect to the UV photons. Hard X-ray photolithography, where no cracks or damages are observed after intense exposition, can be a promising technique to design submicronic-structure patterns on TiO2-SiO2 thin layers for the building of optical sensors.
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Plis, Elena A., Daniel P. Engelhart, Russell Cooper, W. Robert Johnston, Dale Ferguson i Ryan Hoffmann. "Review of Radiation-Induced Effects in Polyimide". Applied Sciences 9, nr 10 (16.05.2019): 1999. http://dx.doi.org/10.3390/app9101999.
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Polyimide (PI, Kapton-H®) films are widely utilized in the spacecraft industry for their insulating properties, mechanical durability, light weight, and chemical resistance to radiation. Still PI materials remain exposed to a combination of high-energy electrons, protons, and ultraviolet (UV) photons, particles primarily responsible for radiation-induced damage in geosynchronous Earth orbit (GEO), which drastically change PI’s properties. This work reviews the effect of electron, proton, and UV photon irradiation on the material properties (morphology, absorption, mechanical properties, and charge transport) of PI. The different damaging mechanisms and chemical consequences that drive changes in the material properties of PI caused by each individual kind of irradiation will be discussed in detail.
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Pahl, Anthony J., Alice Shapley, Andreas L. Faisst, Peter L. Capak, Xinnan Du, Naveen A. Reddy, Peter Laursen i Michael W. Topping. "The redshift evolution of rest-UV spectroscopic properties to z ∼ 5". Monthly Notices of the Royal Astronomical Society 493, nr 3 (10.02.2020): 3194–211. http://dx.doi.org/10.1093/mnras/staa355.
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ABSTRACT We perform a comprehensive analysis of the redshift evolution of the rest-UV spectra of star-forming galaxies out to z ∼ 5. We combine new z ∼ 5 measurements of H i Ly α and low- and high-ionization interstellar metal absorption features with comparable measurements at z ∼ 2–4. We measure the equivalent widths of interstellar absorption features using stacked spectra in bins of Ly α equivalent width, performing corrections to Ly α strengths based on a model for the transmission of the intergalactic medium. We find a strong correlation between decreasing low-ionization absorption strength and increasing Ly α emission strength over the redshift range z ∼ 2–5, suggesting that both of these quantities are fundamentally linked to neutral gas covering fraction. At the highest Ly α equivalent widths, we observe evolution at z ∼ 5 towards greater Ly α emission strength at fixed low-ionization absorption strength. If we interpret the non-evolving relationship of Ly α emission strength and low-ionization line strength at z ∼ 2−4 as primarily reflecting the radiative transfer of Ly α photons, this evolution at z ∼ 5 suggests a higher intrinsic production rate of Ly α photons than at lower redshift. Our conclusion is supported by the joint evolution of the relationships among Ly α emission strength, interstellar absorption strength, and dust reddening. We perform additional analysis in bins of stellar mass, star formation rate, UV luminosity, and age, examining how the relationships between galaxy properties and Ly α emission evolve towards higher redshift. We conclude that increasing intrinsic Ly α photon production and strong detection of nebular C iv emission (signalling lower metallicity) at z ∼ 5 indicate an elevated ionized photon production efficiency (ξion).
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GEORGANOPOULOS, MARKOS, AMANDA DOTSON, DEMOSTHENES KAZANAS i ERIC PERLMAN. "LOCATING THE BLAZAR EMISSION SITE WITH FERMI VARIABILITY". International Journal of Modern Physics: Conference Series 08 (styczeń 2012): 37–42. http://dx.doi.org/10.1142/s2010194512004394.
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This work presents a method for settling the following ongoing debate: is the GeV emission of powerful blazars produced inside the sub-pc size broad line region (BLR) or further out at scales of ~ 10 pc where the IR photon field of the dusty molecular torus dominates over that the UV field of the BLR? In the first case the GeV emission is most probably external Compton (EC) scattering of the ~ 10 eV BLR photons21, while in the second the seed photons for the EC GeV emission are the ~ 0.1 eV photons of the dust9 in the molecular torus8. The issue of the energy dissipation location is connected to the jet formation and collimation process25 and, as we argue here, can be resolved with Fermi spectral variability observations.
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Lehmann, A., B. Godard, G. Pineau des Forêts i E. Falgarone. "Self-generated ultraviolet radiation in molecular shock waves". Astronomy & Astrophysics 643 (listopad 2020): A101. http://dx.doi.org/10.1051/0004-6361/202038644.
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Context. Shocks are ubiquitous in the interstellar and intergalactic media, where their chemical and radiative signatures reveal the physical conditions in which they arise. Detailed astrochemical models of shocks at all velocities are necessary to understand the physics of many environments including protostellar outflows, supernova remnants, and galactic outflows. Aims. We present an accurate treatment of the self-generated ultraviolet (UV) radiation in models of intermediate velocity (VS = 25–60 km s−1), stationary, weakly magnetised, J-type, molecular shocks. We show how these UV photons modify the structure and chemical properties of shocks and quantify how the initial mechanical energy is reprocessed into line emission. Methods. We develop an iterative scheme to calculate the self-consistent UV radiation field produced by molecular shocks. The shock solutions computed with the Paris–Durham shock code are post-processed using a multi-level accelerated Λ-iteration radiative transfer algorithm to compute Lyman α, Lyman β, and two-photon continuum emission. The subsequent impacts of these photons on the ionisation and dissociation of key atomic and molecular species as well as on the heating by the photoelectric effect are calculated by taking the wavelength dependent interaction cross-sections and the fluid velocity profile into account. This leads to an accurate description of the propagation of photons and the thermochemical properties of the gas in both the postshock region and in the material ahead of the shock called the radiative precursor. With this new treatment, we analyse a grid of shock models with velocities in the range VS = 25–60 km s−1, propagating in dense (nH ≥ 104 cm−3) and shielded gas. Results. Self-absorption traps Lyα photons in a small region in the shock, though a large fraction of this emission escapes by scattering into the line wings. We find a critical velocity VS ~ 30 km s−1 above which shocks generate Lyα emission with a photon flux exceeding the flux of the standard interstellar radiation field. The escaping photons generate a warm slab of gas (T ~ 100 K) ahead of the shock front as well as pre-ionising C and S. Intermediate velocity molecular shocks are traced by bright emission of many atomic fine structure (e.g. O and S) and metastable (e.g. O and C) lines, substantive molecular emission (e.g. H2, OH, and CO), enhanced column densities of several species including CH+ and HCO+, as well as a severe destruction of H2O. As much as 13–21% of the initial kinetic energy of the shock escapes in Lyα and Lyβ photons if the dust opacity in the radiative precursor allows it. Conclusions. A rich molecular emission is produced by interstellar shocks regardless of the input mechanical energy. Atomic and molecular lines reprocess the quasi totality of the kinetic energy, allowing for the connection of observable emission to the driving source for that emission.
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Lackmann, Jan-Wilm, Simon Schneider, Eugen Edengeiser, Fabian Jarzina, Steffen Brinckmann, Elena Steinborn, Martina Havenith, Jan Benedikt i Julia E. Bandow. "Photons and particles emitted from cold atmospheric-pressure plasma inactivate bacteria and biomolecules independently and synergistically". Journal of The Royal Society Interface 10, nr 89 (6.12.2013): 20130591. http://dx.doi.org/10.1098/rsif.2013.0591.
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Cold atmospheric-pressure plasmas are currently in use in medicine as surgical tools and are being evaluated for new applications, including wound treatment and cosmetic care. The disinfecting properties of plasmas are of particular interest, given the threat of antibiotic resistance to modern medicine. Plasma effluents comprise (V)UV photons and various reactive particles, such as accelerated ions and radicals, that modify biomolecules; however, a full understanding of the molecular mechanisms that underlie plasma-based disinfection has been lacking. Here, we investigate the antibacterial mechanisms of plasma, including the separate, additive and synergistic effects of plasma-generated (V)UV photons and particles at the cellular and molecular levels. Using scanning electron microscopy, we show that plasma-emitted particles cause physical damage to the cell envelope, whereas UV radiation does not. The lethal effects of the plasma effluent exceed the zone of physical damage. We demonstrate that both plasma-generated particles and (V)UV photons modify DNA nucleobases. The particles also induce breaks in the DNA backbone. The plasma effluent, and particularly the plasma-generated particles, also rapidly inactivate proteins in the cellular milieu. Thus, in addition to physical damage to the cellular envelope, modifications to DNA and proteins contribute to the bactericidal properties of cold atmospheric-pressure plasma.
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Wielopolski, Mateusz, Katharine E. Linton, Magdalena Marszałek, Murat Gulcur, Martin R. Bryce i Jacques E. Moser. "Harvesting UV photons for solar energy conversion applications". Phys. Chem. Chem. Phys. 16, nr 5 (2014): 2090–99. http://dx.doi.org/10.1039/c3cp54914c.
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August, Robert, Lawrence Forsley i Robert Whitlock. "Observing sonoluminescent UV photons below the water cutoff". Journal of the Acoustical Society of America 113, nr 4 (kwiecień 2003): 2222. http://dx.doi.org/10.1121/1.4780287.
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Biagi, S. F., T. J. V. Bowcock, D. Duxbury i E. Gabathuler. "Observation of UV photons with a microdot chamber". Nuclear Physics B - Proceedings Supplements 61, nr 3 (luty 1998): 311–14. http://dx.doi.org/10.1016/s0920-5632(97)00579-3.
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Zvezdanovic, Jelena, Jelena Stanojevic, Dejan Markovic i Dragan Cvetkovic. "Irreversible UV-induced quercetin and rutin degradation in solution, studied by UV-spectrophotometry and HPLC chromatography". Journal of the Serbian Chemical Society 77, nr 3 (2012): 297–312. http://dx.doi.org/10.2298/jsc110618180z.
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Irreversible degradation of quercetin and rutin, dissolved in methanol and water, induced by continuous UV-irradiation from two different sub-ranges (UV-B and UV-C) has been studied in this work. The degradation of both flavonoids is related to formation of UV-induced degradation products: both processes follow first-order kinetics. The degradation and products formation rate constants are both dependent on the involved UV-photons energy input in both solvents.
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Goponenko, Darya, Kamila Zhumanova, Sabina Shamarova, Zhuldyz Yelzhanova, Annie Ng i Timur Sh Atabaev. "Hydrophobic and Luminescent Polydimethylsiloxane PDMS-Y2O3:Eu3+ Coating for Power Enhancement and UV Protection of Si Solar Cells". Nanomaterials 14, nr 8 (12.04.2024): 674. http://dx.doi.org/10.3390/nano14080674.
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Solar cells have been developed as a highly efficient source of alternative energy, collecting photons from sunlight and turning them into electricity. On the other hand, ultraviolet (UV) radiation has a substantial impact on solar cells by damaging their active layers and, as a result, lowering their efficiency. Potential solutions include the blocking of UV light (which can reduce the power output of solar cells) or converting UV photons into visible light using down-conversion optical materials. In this work, we propose a novel hydrophobic coating based on a polydimethylsiloxane (PDMS) layer with embedded red emitting Y2O3:Eu3+ (quantum yield = 78.3%) particles for UV radiation screening and conversion purposes. The favorable features of the PDMS-Y2O3:Eu3+ coating were examined using commercially available polycrystalline silicon solar cells, resulting in a notable increase in the power conversion efficiency (PCE) by ~9.23%. The chemical and UV stability of the developed coatings were assessed by exposing them to various chemical conditions and UV irradiation. It was found that the developed coating can endure tough environmental conditions, making it potentially useful as a UV-protective, water-repellent, and efficiency-enhancing coating for solar cells.
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Prevenslik, Thomas V. "ISM spectrum by cosmic dust?" Proceedings of the International Astronomical Union 4, S251 (luty 2008): 263–64. http://dx.doi.org/10.1017/s1743921308021716.
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AbstractThe interstellar medium (ISM) spectrum is usually explained by the response of dust particles (DPs) to the absorption of ultraviolet (UV) and visible (VIS) photons from nearby stars. With regard to the unidentified infrared (UIR) bands, the DPs are thought heated by UV and VIS photons to about 100 K thereby exciting the polycyclic aromatic hydrocarbons (PAHs). However, the UIR bands may be explained with the DPs at 2.7 K. To wit, the UIR bands form by the direct excitation of PAHs by infrared (IR) radiation induced from the absorption of cosmic microwave background (CMB) radiation in DPs by quantum electrodynamics (QED).
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Du, Fei, Wenzhi Chang, Jiangang Bi, Shuai Yuan, Xinghui Zhang i Yanpeng Gong. "Evolution mechanism of ultraviolet and electrical phenomena induced by protrusion discharge in GIS". Journal of Electrical Engineering 71, nr 4 (1.08.2020): 268–73. http://dx.doi.org/10.2478/jee-2020-0036.
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AbstractTo improve the sensitive and reliability of condition monitoring in gas insulated switchgear (GIS), discharge perception system applied to GIS insulators protrusion discharge based on single ultraviolet photon is built. Step method is used to inspire the discharges of different severity, based on which, the regression relationship of ultraviolet (UV) signal and electrical signal are studied, and the perception mechanism of UV signal in different severity of discharges is analyzed. The study indicates that, the development of protrusion discharge in GIS can be divided into four stages, and there is no positive correlation between the number of ultraviolet photons caused by discharge radiation and insulation deterioration level, but related to the diffusion, migration and recombination of charged particles, then UV optical method for quantitative monitoring of discharge in each stage is provided, which provide a new method for quantitative measurement of GIS insulator discharge.
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Cadena, Danielle M., Xinyi Wu, Maryan Baraazandeh, Honghao Wang, Kefu Wang, R. Peyton Cline, Joseph Schwan i in. "(Invited) Reshaping Light with Hybrid Quantum Dot: Molecule Systems". ECS Meeting Abstracts MA2024-01, nr 23 (9.08.2024): 1371. http://dx.doi.org/10.1149/ma2024-01231371mtgabs.
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Photon upconversion is an energy conversion process wherein a material absorbs two or more low-energy photons and uses their energy to generate high-energy photons. Upconversion systems that convert near-infrared light into the visible range can address current challenges in solar energy capture and near-infrared sensor design while materials that operate at higher energy, producing UV photons from visible light, can enable applications in photocatalysis and light-based 3D printing. Due to their high extinction coefficients and size-tunable optical properties, quantum dots have emerged as ideal photosensitizers for photon upconversion systems. In these systems, light absorbed by a quantum dot is passed to a molecule at its surface, placing the molecule into a spin-triplet state. Upconversion is achieved when two molecules in their triplet state encounter one another and undergo triplet fusion, a process that deexcites one molecule and promotes the other to a high-energy, emissive spin-singlet state. In this presentation, I will present spectroscopic measurements and electronic structure calculations that identify energy transfer rates and key intermediates involved in two quantum dot systems that respectively demonstrate red-to-blue and blue-to-UV photon upconversion. In the first system, which consists of silicon quantum dots functionalized with anthracene ligands, we find that by controlling the chemical structure of molecular tethers that covalently link anthracene to silicon, we can produce strongly coupled states wherein excited charge carriers are shared between silicon and anthracene. By controlling the energy of these states, we can optimize the system’s performance, achieving an upconversion quantum yield of 17.2%. In the second system, we use CsPbBr3 perovskite quantum dots to drive triplet energy transfer to naphthalene ligands. This energy transfer process is found to be highly sensitive to the structure of the chemical linker that binds naphthalene to CsPbBr3, which we attribute to modulation of the degree of wavefunction overlap between the states of the quantum dot energy donor and naphthalene energy acceptor.
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Mainali, Ramesh, Jane R. Rigby, John Chisholm, Matthew Bayliss, Rongmon Bordoloi, Michael D. Gladders, T. Emil Rivera-Thorsen i in. "The Connection Between Galactic Outflows and the Escape of Ionizing Photons". Astrophysical Journal 940, nr 2 (1.12.2022): 160. http://dx.doi.org/10.3847/1538-4357/ac9cd6.
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Abstract We analyze spectra of a gravitationally lensed galaxy, known as the Sunburst Arc, that is leaking ionizing photons, also known as the Lyman continuum (LyC). Magnification from gravitational lensing permits the galaxy to be spatially resolved into one region that leaks ionizing photons and several that do not. Rest-frame UV and optical spectra from Magellan target 10 different regions along the lensed Arc, including six multiple images of the LyC leaking region and four regions that do not show LyC emission. The rest-frame optical spectra of the ionizing photon emitting regions reveal a blueshifted (ΔV = 27 km s−1) broad emission component (FWHM = 327 km s−1), comprising 55% of the total [O iii] line flux, in addition to a narrow component (FWHM = 112 km s−1), suggesting the presence of strong highly ionized gas outflows. This is consistent with the high-velocity ionized outflow inferred from the rest-frame UV spectra. In contrast, the broad emission component is less prominent in the nonleaking regions, comprising ∼26% of total [O iii] line flux. The high-ionization absorption lines are prominent in both the leaker and the nonleaker, but the low-ionization absorption lines are very weak in the leaker, suggesting that the line-of-sight gas is highly ionized in the leaker. Analyses of stellar wind features reveal that the stellar population of the LyC leaking regions is considerably younger (∼3 Myr) than that of the nonleaking regions (∼12 Myr), emphasizing that stellar feedback from young stars may play an important role in ionizing photon escape.
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Nogueira, Juan J., Felix Plasser i Leticia González. "Electronic delocalization, charge transfer and hypochromism in the UV absorption spectrum of polyadenine unravelled by multiscale computations and quantitative wavefunction analysis". Chemical Science 8, nr 8 (2017): 5682–91. http://dx.doi.org/10.1039/c7sc01600j.
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Liu, Peiai, Qingbo Ma, Yunkun Han i Rongxin Luo. "A Quantification of the Effects Using Different Stellar-population Synthesis Models for Epoch of Reionization". Astrophysical Journal 968, nr 1 (1.06.2024): 13. http://dx.doi.org/10.3847/1538-4357/ad41e1.
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Abstract The luminosity and spectral energy distribution of high-z galaxies are sensitive to the stellar-population synthesis (SPS) models. In this paper, we study the effects of different SPS models on the measurements of high-z galaxies and the budget of ionizing photons during the epoch of reionization by employing each of them in the semianalytical galaxy formation model L-Galaxies 2020. We find that the different SPS models lead to ≲0.5 dex differences on the amplitudes of UV luminosity functions, while two modes of the same SPS model with and without the inclusion of binary stars lead to similar UV luminosity functions at z ≥ 6. Instead, the binary stars produce ∼40% more ionizing photons than the single stars, while such differences are smaller than those caused by different SPS models; for example, the BPASS model produces ∼100% more ionizing photons than other models.
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Dumur, Frédéric. "Recent Advances on Furan-Based Visible Light Photoinitiators of Polymerization". Catalysts 13, nr 3 (28.02.2023): 493. http://dx.doi.org/10.3390/catal13030493.
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Photopolymerization is an active research field enabling to polymerize in greener conditions than that performed with traditional thermal polymerization. At present, a great deal of effort is devoted to developing visible light photoinitiating systems. Indeed, the traditional UV photoinitiating systems are currently the focus of numerous safety concerns so alternatives to UV light are being actively researched. However, visible light photons are less energetic than UV photons so the reactivity of the photoinitiating systems should be improved to address this issue. In this field, furane constitutes an interesting candidate for the design of photocatalysts of polymerization due to its low cost and its easy chemical modification. In this review, an overview concerning the design of furane-based photoinitiators is provided. Comparisons with reference systems are also established to demonstrate evidence of the interest of these photoinitiators in innovative structures.
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Ragazzoni, R., L. Buson, M. Turatto, A. Bianchini, E. Cappellaro, M. Cecconi, F. La Franca i in. "Mouse: A Mini Observatory for UV Space Exploration of the Galactic Poles and Equator". Symposium - International Astronomical Union 161 (1994): 52–54. http://dx.doi.org/10.1017/s0074180900047033.
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The small orbiting observatory MOUSE is described in its essential features. Insights in the optical solution (a 2 mirrors 3 reflections telescope using pure hyperbolical surfaces, no aspherics) are given which fit such type of optical layout to scientific requirements. An in-flight recentering of the photons collected by a solar-blind photon counter device will allow for an equivalent angular resolution of 2–3 arcsec over a field-of-view exceeding one square degree. The capabilities of the proposed satellite (imaging, low resolution grisms, polarizers) are described. The choice of the selected sky areas (the two Galactic Poles, the galactic equator and some Bulge Windows) is justified in terms of forefront astrophysical scientific objectives requiring imaging in UV over large fields. The science comprises UV analysis of a complete sample of QSOs, stellar population in galaxies, White Dwarfs, Globular and Open Clusters and OB Associations. In addition a plan for the early UV detection of Supernova events is described.
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Herburger, Andreas, Christian van der Linde i Martin K. Beyer. "Photodissociation spectroscopy of protonated leucine enkephalin". Physical Chemistry Chemical Physics 19, nr 17 (2017): 10786–95. http://dx.doi.org/10.1039/c6cp08436b.
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Zheng, W. "Emission Lines in the Far-UV and Extreme-UV Region". International Astronomical Union Colloquium 159 (1997): 108–15. http://dx.doi.org/10.1017/s0252921100039750.
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AbstractRecent observations with HST and HUT have been made of the spectral region shortward of Lyα in AGN. Emission lines in this region, such as O VIλ1035 and Ne VIIIλ774, are mainly produced by collisional excitation. Their strengths and the lack of other significant emission lines of higher excitation energy indicate a temperature of ~ 6 × 104 K for the highly ionized gas in line-emitting clouds. Model calculations suggest that the strength of O VI and Ne vIII emission is correlated to the intensity of the high-energy photons above 100 eV. Therefore, these lines are useful diagnostics of the continuum shape in the soft X-ray range. The luminosity dependence of emission-line equivalent widths is more prominent for lines of higher ionization level, suggesting that the UV bump in AGN spectra may be weaker at higher luminosities.
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Ade, H., W. Yang, S. L. English, J. Hartman, R. F. Davis, R. J. Nemanich, V. N. Litvinenko, I. V. Pinayev, Y. Wu i J. M. J. Madey. "A Free Electron Laser–Photoemission Electron Microscope System (FEL–PEEM)". Surface Review and Letters 05, nr 06 (grudzień 1998): 1257–68. http://dx.doi.org/10.1142/s0218625x98001596.
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We report first results from our effort to couple a high resolution photoemission electron microscope (PEEM) to the OK-4 ultraviolet free electron laser at Duke University (OK-4/Duke UV FEL). The OK-4/Duke UV FEL is a high intensity source of tunable monochromatic photons in the 3–10 eV energy range. This tunability is unique and allows us to operate near the photoemission threshold of any samples and thus maximize sample contrast while keeping chromatic berrations in the PEEM minimal. We have recorded first images from a variety of samples using spontaneous radiation from the OK-4/ Duke UV FEL in the photon energy range of 4.0–6.5 eV. Due to different photothreshold emission from different sample areas, emission from these areas could be turned on (or off) selectively. We have also observed relative intensity reversal with changes in photon energy which are interpreted as density-of-state contrast. Usable image quality has been achieved, even though the output power of the FEL in spontaneous emission mode was several orders of magnitude lower than the anticipated full laser power. The PEEM has achieved a spatial resolution of 12 nm.
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Kume, Naoto, Hidehiko Kuroda i Yukio Yoshimura. "ICONE23-1087 REMOTE DETECTION OF ALPHA RADIATION USING UV PHOTONS EMITTED BY NITROGEN". Proceedings of the International Conference on Nuclear Engineering (ICONE) 2015.23 (2015): _ICONE23–1—_ICONE23–1. http://dx.doi.org/10.1299/jsmeicone.2015.23._icone23-1_44.
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Bernstein, L. S., F. O. Clark i D. K. Lynch. "Dirty H2 Molecular Clusters as the DIB Sources: Spectroscopic and Physical Properties". Proceedings of the International Astronomical Union 9, S297 (maj 2013): 378–80. http://dx.doi.org/10.1017/s1743921313016165.
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AbstractWe propose that the diffuse interstellar bands (DIBs) arise from absorption lines of electronic transitions in molecular clusters primarily composed of a single molecule, atom, or ion (“seed”), embedded in a single-layer shell of H2 molecules (Bernstein et al. 2013). Less abundant variants of the cluster, including two seed molecules and/or a two-layer shell of H2 molecules may also occur. The lines are broadened, blended, and wavelength-shifted by interactions between the seed and surrounding H2 shell. We refer to these clusters as CHCs (Contaminated H2 Clusters). CHC spectroscopy matches the diversity of observed DIB spectral profiles, and provides good fits to several DIB profiles based on a rotational temperature of 10 K. CHCs arise from ~cm-sized, dirty H2 ice balls, called CHIMPs (Contaminated H2 Ice Macro-Particles), formed in cold, dense, Giant Molecular Clouds (GMCs), and later released into the interstellar medium (ISM) upon GMC disruption. Attractive interactions, arising from Van der Waals and ion-induced dipole potentials, between the seeds and H2 molecules enable CHIMPs to attain cm-sized dimensions. When an ultraviolet (UV) photon is absorbed in the outer layer of a CHIMP, it heats the icy matrix and expels CHCs into the ISM. While CHCs are quickly destroyed by absorbing UV photons, they are replenished by the slowly eroding CHIMPs. Since CHCs require UV photons for their release, they are most abundant at, but not limited to, the edges of UV-opaque molecular clouds, consistent with the observed, preferred location of DIBs. An inherent property of CHCs, which can be characterized as nanometer size, spinning, dipolar dust grains, is that they emit in the radio-frequency region. Thus, CHCs offer a natural explanation to the anomalous microwave emission (AME) feature in the ~10-100 GHz spectral region.