762 research outputs found

    Non-Adiabatic Electronic and Vibrational Ring-Opening Dynamics resolved with Attosecond Core-Level Spectroscopy

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    Non-adiabatic dynamics and conical intersections play a central role in the chemistry of most polyatomic molecules, ranging from isomerization to heterocyclic ring opening and avoided photo-damage of DNA. Studying the underpinning correlated dynamics of electronic and nuclear wave packets is a major challenge in real-time and, many times involves optically dark transient states. We show that attosecond core-level spectroscopy reveals the pathway dynamics of neutral furan across its conical intersections and dark states. Our method measures electronic-nuclear correlations to detect the dephasing of electronic coherence due to nuclear motion and identifies the ring-opened isomer as the dominant product. These results demonstrate the efficacy of attosecond core level spectroscopy as a potent method to investigate the real-time dynamics of photochemical reaction pathways in complex molecular systems

    Two-Dimensional Helioseismic Power, Phase, and Coherence Spectra of {\it Solar Dynamics Observatory} Photospheric and Chromospheric Observables

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    While the {\it Helioseismic and Magnetic Imager} (HMI) onboard the {\it Solar Dynamics Observatory} (SDO) provides Doppler velocity [VV], continuum intensity [ICI_C], and line-depth [LdLd] observations, each of which is sensitive to the five-minute acoustic spectrum, the {\it Atmospheric Imaging Array} (AIA) also observes at wavelengths -- specifically the 1600 and 1700 Angstrom bands -- that are partly formed in the upper photosphere and have good sensitivity to acoustic modes. In this article we consider the characteristics of the spatio--temporal Fourier spectra in AIA and HMI observables for a 15-degree region around NOAA Active Region 11072. We map the spatio--temporal-power distribution for the different observables and the HMI Line Core [ILI_L], or Continuum minus Line Depth, and the phase and coherence functions for selected observable pairs, as a function of position and frequency. Five-minute oscillation power in all observables is suppressed in the sunspot and also in plage areas. Above the acoustic cut-off frequency, the behaviour is more complicated: power in HMI ICI_C is still suppressed in the presence of surface magnetic fields, while power in HMI ILI_L and the AIA bands is suppressed in areas of surface field but enhanced in an extended area around the active region, and power in HMI VV is enhanced in a narrow zone around strong-field concentrations and suppressed in a wider surrounding area. The relative phase of the observables, and their cross-coherence functions, are also altered around the active region. These effects may help us to understand the interaction of waves and magnetic fields in the different layers of the photosphere, and will need to be taken into account in multi-wavelength local helioseismic analysis of active regions.Comment: 18 pages, 15 figures, to be published in Solar Physic

    Stellar Iron Abundances: non-LTE Effects

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    We report new statistical equilibrium calculations for Fe I and Fe II in the atmosphere of Late-Type stars. We used atomic models for Fe I and Fe II having respectively 256 and 190 levels, as well as 2117 and 3443 radiative transitions. Photoionization cross-sections are from the Iron Project. These atomic models were used to investigate non-LTE effects in iron abundances of Late-Type stars with different atmospheric parameters. We found that most Fe I lines in metal-poor stars are formed in conditions far from LTE. We derived metallicity corrections of about 0.3 dex with respect to LTE values, for the case of stars with [Fe/H] ~ -3.0. Fe II is found not to be affected by significant non-LTE effects. The main non-LTE effect invoked in the case of Fe I is overionization by ultraviolet radiation, thus classical ionization equilibrium is far to be satisfied. An important consequence is that surface gravities derived by LTE analysis are in error and should be corrected before final abundances corrections. This apparently solves the observed discrepancy between spectroscopic surface gravities derived by LTE analyses and those derived from Hipparcos parallaxes. A table of non-LTE [Fe/H] and log g values for a sample of metal-poor late-type stars is given.Comment: 22 pages, 9 figures, 1 table, ApJ style, accepte

    O conhecimento local e o potencial de coleta de lianas produtoras de fibras nos municípios de Pedra Branca do Amapari e Porto Grande/AP, com ênfase ao cipó-tititca (Heteropsis spp - Araceae).

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    O cipó é a matéria prima mais utilizada pelos artesãos na fabricação de móveis e artesanato, tanto no Amapá, como em outros estados brasileiros. O Objetivo foi verificar a freqüência de planta da família Araceae com potencial de produção de fibras e entrevistas com artesãos, agroextratores, extratores, comunitários e estudante sobre o nível de conhecimento da comunidade envolvida sobre o manejo de cipós naquela região. Verificou-se que existem 7 espécies que os coletores denominam popularmente de cipó-titica, a saber: Heteropsis steyermarkii, H. salicifolia, H. tenuispadix, spruceana, H. mellinonii, H. linearis e H. flexuosa, sendo esta, a espécie com o maior índice de ocorrência no levantamento. Das 984 plantas da família Araceae inventariadas, 32.24% eram de plantas produtoras de fibras denominadas de cipó-titica. Em relação à quantidade de cipó coletado, 71.42% dos entrevistados afirmaram que chegam a coletar mais de 50 kg/dia, e 222% afirmaram que essa coleta, feita durante todo ano. É necessário observar a época de corte da liana, para se pensar na viabilidade do manejo. para a manutenção de indivíduos jovens, garantindo assim, a recuperação das espécies no período em que ocorre o déficit hídrico

    Encapsulation of active pharmaceutical ingredients in lipid micro/nanoparticles for oral administration by spray-cooling

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    Nanoencapsulation via spray cooling (also known as spray chilling and spray congealing) has been used with the aim to improve the functionality, solubility, and protection of drugs; as well as to reduce hygroscopicity; to modify taste and odor to enable oral administration; and many times to achieve a controlled release profile. It is a relatively simple technology, it does not require the use of low-cost solvents (mostly associated to toxicological risk), and it can be applied for lipid raw materials as excipients of oral pharmaceutical formulations. The objective of this work was to revise and discuss the advances of spray cooling technology, with a greater emphasis on the development of lipid micro/nanoparticles to the load of active pharmaceutical ingredients for oral administration.This research was funded by the Portuguese Science and Technology Foundation (FCT/MCT) and European Funds (PRODER/COMPETE), under the project reference UIDB/04469/2020 (strategic fund), co-financed by FEDER, under the Partnership Agreement PT2020, granted to Eliana B. Souto. This work was also supported by the National Science Centre within the MINIATURA 4 for a single research activity carried out by Aleksandra Zieli ´nska (grant no: 2020/04/X/ST5/00789), and by the Institute of Human Genetics, Polish Academy of Sciences by the internal grant for the implementation of a single scientific activity.info:eu-repo/semantics/publishedVersio
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